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Article

Polysaccharides from Brown Seaweeds (Padina boergesenii and Sargassum euryphyllum) as Promising Inhibitors of SARS-CoV-2: Characterization, Mechanisms, and Therapeutic Potential

by
Saly Gheda
1,*,
Ali M. Karkour
1,
Shimaa El Shafay
1,
Mohamed GabAllah
2,
João Cotas
3 and
Leonel Pereira
3,4,*
1
Botany and Microbiology Department, Faculty of Science, Tanta University, Tanta 31527, Egypt
2
Center of Scientific Excellence for Influenza Viruses, National Research Centre, Dokki, Cairo 12622, Egypt
3
CFE—Centre for Functional Ecology: Science for People & Planet, Marine Resources, Conservation and Technology—Marine Algae Lab, Department of Life Sciences, University of Coimbra, 3000-456 Coimbra, Portugal
4
IATV—Instituto do Ambiente, Tecnologia e Vida, 3030-790 Coimbra, Portugal
*
Authors to whom correspondence should be addressed.
Macromol 2025, 5(2), 18; https://doi.org/10.3390/macromol5020018
Submission received: 19 February 2025 / Revised: 2 April 2025 / Accepted: 3 April 2025 / Published: 10 April 2025
(This article belongs to the Special Issue Recent Trends in Carbohydrate-Based Therapeutics)
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Abstract

:
Unexpected mutations in SARS-CoV-2 produce unique variations. While numerous vaccines and antiviral medications are available for SARS-CoV-2, their use in controlling and preventing COVID-19 is restricted in some areas and countries due to accessibility and cost issues. This study investigated polysaccharides produced from two brown seaweed (Padina boergesenii and Sargassum euryphyllum) for their capacity to inhibit SARS-CoV-2. The seaweed polysaccharides were characterized and identified using ultraviolet and visible (UV/VIS) and Fourier transform infrared attenuated total reflectance (FTIR-ATR) spectra. The polysaccharides inhibited SARS-CoV-2 propagation with inhibitory concentration 50% (IC50) values ranging from 24.2 to 29.3 µg/mL and cytotoxicity concentration 50% (CC50) values for Vero-E6 cells ranging from 587.7 to 396.4 µg/mL for P. boergesenii and S. euryphyllum, respectively. P. boergesenii polysaccharide had a more substantial antiviral potential than S. euryphyllum against SARS-CoV-2 and appeared more promising. At a concentration of 575 µL/mL of P. boergesenii polysaccharide, the virucidal mechanism was found to be the most effective, followed by viral adsorption and replication, with viral inhibition percentages of 68.6% ± 0.8, 57.1% ± 1.4, and 37.2 ± 3, respectively, compared to remdesivir as an antiviral drug. Thus, we concluded that brown seaweed alginate polysaccharides efficiently inhibit SARS-CoV-2 from spreading by preventing viral entry. Finally, P. boergesenii polysaccharide looked promising as a potential therapeutic candidate for the treatment of COVID-19.

1. Introduction

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) outbreak was initially reported in December 2019 in Wuhan, China. Since then, it has rapidly spread throughout the world. The coronavirus disease 2019 (COVID-19) has infected ~770 million confirmed cases to date, with about 1% of patients dying from it [1]. The SARS-CoV-2 pandemic has put a significant strain on the current healthcare system and has had a negative social and economic impact. Several recently produced vaccinations have shown remarkable defensive effects against SARS-CoV-2 [2]. However, due to the challenges in commercial accessibility and economic constraints in some locations and areas, the current COVID-19 vaccination programs have not been successfully implemented [3], leading to ongoing viral transmission and outbreaks of variant viruses. Therefore, the creation of a novel antiviral therapy is essential. A safe and effective medicine often takes much time and effort to produce. “Drug repurposing” is regarded as a viable tactic for dealing with the crisis of the SARS-CoV-2 pandemic. Remdesivir, a medication that has a clinically established anti-Ebola virus disease (EVD) action, has been tested on COVID-19, and the results have been promising [4]. In addition, researchers have investigated the effectiveness of chloroquine and its derivatives, which are used to treat malaria, to treat various illnesses like COVID-19, tissue sicknesses, and several cancers like colon, breast, prostate, and bladder [5]. Numerous investigations have assessed how employing immunomodulators can improve the health of severe COVID-19 patients. Consequently, applying naturally occurring bioactive substances and nutraceuticals that include not only immunomodulatory but also antimicrobial and non-toxic effects seems to be a promising cure.
Because of their adaptability, seaweed (marine macroalgae) can be utilized in food and medicine due to their biochemical compositions [6]. Numerous studies have shown that the significant biological and chemical diversity of macroalgae has attracted interest in recent years due to a diversity of active compounds derived from them, including polysaccharides, polyunsaturated fatty acids, pigments, peptides, carbohydrates, vitamins, and polyphenols [7]. These compounds have a variety of properties, including antimicrobial [8], antioxidant [9,10], anti-inflammatory, and immunomodulatory capabilities [11]. They have antiviral properties against a variation of enveloped viral infections, including hepatitis virus [12], human immunodeficiency virus (HIV) [13], herpes simplex virus (HSV) [14], and most recently, SARS-CoV-2 virus [15,16,17,18]. They can also be used as immune boosters [7]. They also help the human gut microbiota by controlling the immune system and metabolism [19,20]. For these reasons, they are called nutritional foods or prebiotics [21]. Worldwide, much research has been performed to identify molecules that can stop the spread, replication, and infection of SARS-CoV-2 using marine bioactive components, such as polyphenolics, carotenoids, and polysaccharides [22,23]. Polysaccharides have received much attention in marine compounds for the development of COVID-19 prevention and therapies.
According to reports, lambda-carrageenan has antiviral properties against SARS-CoV-2 in vitro [24]. Furthermore, healthcare professionals caring for patients with COVID-19 disease showed a 79.8% relative risk decrease in preventing SARS-CoV-2 with an iota-carrageenan nasal spray [25]. Moreover, by obstructing the spike protein’s ability to connect with the host cell’s ACE2 receptor in vitro, several marine sulfated polysaccharides and sulfated galactofucan from Saccharina japonica (formerly Laminaria japonica) (Phaeophyceae) efficiently prevented SARS-CoV-2 entry [26]. According to a recent study by Song et al. [27], the sulfated polysaccharides fucoidan and carrageenan demonstrated noteworthy antiviral properties against SARS-CoV-2 at concentrations ranging from 3.90 to 500 μg/mL.
Fucoidan powders extracted from marine brown seaweed Sargassum spp. may have antiviral properties against SARS-CoV-2 infection in vitro. When DMSO was used as a solvent, fucoidan powder’s antiviral activity increased to 100% protection against SARS-CoV-2 infection [28]. It was determined whether crude polysaccharides made from two seaweed species, Sargassum horneri and Sargassum fusiforme (formerly Hizikia fusiformis), could stop the spread of SARS-CoV-2. These unrefined polysaccharides effectively stopped the spread of SARS-CoV-2, as demonstrated by plaque titration, which showed IC50 values ranging from 0.35 to 4.37 g/mL. With an IC50 of 0.35 g/mL, the crude polysaccharide of S. fusiforme exhibited the most potent antiviral effect. Treatment of Vero-E6 cells with these crude polysaccharides either prior to or following viral infection significantly reduced the number of SARS-CoV-2 spikes, nucleocapsid proteins, and RNA copies of RNA-dependent RNA-polymerase and nucleocapsid that were expressed. According to Kang et al. [16], these findings demonstrate how these crude marine polysaccharides successfully prevent SARS-CoV-2 from spreading by obstructing the virus’s entrance.
According to Binsuwaidan et al. [18], through virucidal activity, inhibition of viral replication, and interference with viral adsorption (% inhibitions of 64%, 33.3%, and 31.1%, respectively), Ulva lactuca, a green macroalgae, showed potent anti-SARS-CoV-2 activity in its aqueous extract. Therefore, ulvan may be a promising compound for preclinical research in the drug development process to combat SARS-CoV-2.
Brown seaweed polysaccharides were reported to have antiviral properties in earlier studies. However, research on the antiviral effect of marine brown seaweeds collected from the coast of Egypt against SARS-CoV-2 is scant or lacking. To the best of our knowledge, none of the seaweed species examined here were shown to have any protective effects against SARS-CoV-2. In this regard, the study’s objectives are to assess the safety of extracted polysaccharides in the treatment of COVID-19 illness and investigate the antiviral activity of polysaccharides (alginate) from two brown seaweed species, Padina boergesenii, and Sargassum euryphyllum, against the SARS-CoV-2 virus. Previous work reported that P. boergesenii was already used for foodstuff, and extracts exhibited hepatoprotective, antidiabetic, and antioxidant activity [15].

2. Materials and Methods

2.1. Collection of Seaweed Samples

Two brown seaweed species were harvested in the summer of 2021 from the seashore in Hurghada, Egypt. The collected seaweed was given to the phycology lab in plastic bags with seawater (Botany Department, Faculty of Science, Tanta University). Seaweeds were cleansed with tap water and then refined water to remove any debris and attached epiphytes. For taxonomical identification, some samples were stored in saltwater containing formalin (0.4%), while the remaining samples were air-dried at 25–30 °C. After being dried and processed into a powder using an electronic mill, the samples were kept at −20 °C until needed. In accordance with Aleem [29], Jha et al. [30], and Guiry and Guiry [31], the seaweed samples were identified as Padina boergesenii Alender and Kraft (Phaeophyceae, Dictyotales, Dictyotaceae) and Sargassum euryphyllum Grunow Tseng and Lu Baoren (Phaeophyceae, Fucales, Sargassaceae).

2.2. Extraction of the Crude Seaweed Polysaccharides

The seaweed powder was boiled in distilled water (1:5 w/v) at 100 °C for 2 h using a reflux condenser under reduced pressure. The hot extract was filtered with a nylon mesh bag (pore size 24 μm), sequentially filtered with 0.45 μM Millipore filters, and then subjected to drying [32].

2.3. Characterization and Identification of Seaweed Polysaccharides

Identification of polysaccharides was carried out using ultraviolet (UV/VIS) spectra and vibrational spectroscopy Fourier transform infrared attenuated total reflectance (FTIR-ATR) at the Marine Algae Lab, Department of Life Sciences, University of Coimbra, Portugal.

2.3.1. Alginate Extraction

Cotas et al. [33] outlined the process as the foundation for sodium alginate extraction. A commercial grinder (TitanMill 300 DuoClean, Cecotec, Valencia, Spain) was used to grind the dried seaweed (3 g) to a particle size of less than 1 cm. The resulting solution of hydrochloric acid (José Manuel Gomes dos Santos, Portugal) was mixed at a ratio of 1.23% (1:30 v:v) (3 mL of hydrochloric acid: 87 mL of distilled water per 3 g of dried seaweed). The mixture was then kept at room temperature (23 °C) for 24 h. The solution was filtered using a Gooch funnel (porosity: G2) under vacuum (Laborport N820, Lisbon, Portugal), and it was then repeated two or three times with distilled water washing. After 24 h at room temperature (23 °C), the residue was alkali extracted in 90 mL of 2% sodium carbonate (Fisher Chemicals, Portugal) (1:30 m:v for the initial weight of the dried biomass). To remove the leftovers from the alginate solution, the extract was once again vacuum-filtered through a cloth filter using a Gooch funnel (porosity: G2). The alginic acid was then precipitated by adding 37% hydrochloric acid (José Manuel Gomes dos Santos, Portugal) to the filtrate (2 mL of 37% hydrochloric acid per 30 mL of the final solution). After being cleaned with ethanol 96% (José Manuel Gomes dos Santos, Portugal) at a 1:3 v:v ratio, the alginate was left in the cold. After discarding the liquid solution, the precipitate was dried for 48 h at 60 °C in an air-force oven (Raypa DAF-135, R. Espinar S.L., Barcelona, Spain).

2.3.2. Physiochemical Properties of Alginate (Viscosity, pH, EC, and TDS)

Alginate solutions (1% m/v) were prepared by dissolving the polysaccharide in distilled water using temperature and magnetic stirring. Then, the solutions were cooled to a temperature of 25 °C. Later, viscosity measurement was carried out using spindles SP2 and SP3 in an IKA Rotavisc Viscometer at a speed of 100 rpm at room temperature for 1 min. A pH/conductivity/TDS meter (Combo HI98129, HANNA instruments, Woonsocket, RI, USA) was used to measure the pH and TDS values of the alginate solutions [34].

2.3.3. UV/VIS Spectrophotometric Profiles of Alginate Solutions

Alginate solutions (1% m/v) prepared for the viscosity analyses were diluted in distilled water (1:2), and UV/VIS absorption spectra were measured in the range of 200–800 nm using a UV-3100PC, UV/VIS Scanning Spectrophotometer (VWR® Radnor, PA, USA) with 1 cm quartz cuvettes [34].

2.3.4. FTIR-ATR Analysis

Fourier transform infrared (FT-IR) attenuated total reflectance (ATR) spectroscopy was employed to characterize the structure of dried extracted alginate [34]. The IR spectra (24 scans) were obtained at room temperature (referenced against air) in the wavenumber range of 400–4000 cm−1 (resolution of 4 cm−1) using a Bruker Alpha II (Bruker, Ettlingen, Germany). Spectra were analyzed with OPUS 7.2 software (Bruker, Ettlingen, Germany).

2.4. SARS-CoV-2 Virus Isolation and Propagation

Utilizing a specimen from an oropharyngeal swab obtained on 18 March 2020 from an Egyptian woman aged 34, Vero-E6 cells (ATCC No. CRL-1586) were used in this study to isolate the highly pathogenic SARS-CoV-2 strain hCoV-19/Egypt/NRC-03/2020. It was isolated from infected humans in Egypt in 2020, characterized as previously described by Kandeil et al. [35] (GISAID accession number: EPI_ISL_430819). All virus experiments were carried out at the Center of Scientific Excellence for Influenza Viruses (CSEIV), Vaccine Development and Virological Tests Unit, National Research Center (NRC), Giza, Egypt.

2.4.1. Cell Line

The African green monkey kidney epithelial (Vero-E6) cells were kindly provided by Dr. Richard Webby, St. Jude Children’s Research Hospital, Department of Virology and Molecular Biology, USA. The cells were cultivated as a confluent sheet in 75 cm2 tissue culture flasks in the DMEM medium, supplemented with 10% fetal bovine serum (FBS) and 2% penicillin/streptomycin.

2.4.2. Detection of Antiviral Activity and Cytotoxicity of Seaweed Polysaccharide Virus Titration by TCID50

Vero-E6 cells were used to prepare a 96-well plate in growth media with 10% FBS and 2% antibiotic/antimycotic and incubated overnight at 37 °C with 5% CO2. Following confluence, 1 log serial dilution of the virus stock was prepared and used in infecting cell monolayers. The virus inoculum was then removed within 1 h of infection, replaced with 160 µL of infection media in each well, and incubated for 72 h. The TCID50 value was calculated using the Reed and Mensch method by observing and counting the cytopathic effect in each well [36].

2.4.3. Determination of Inhibitory Concentration 50% (IC50)

Vero-E6 cells (2.4 × 104) were seeded into each well of 96-well tissue culture plates, and the plates were incubated for the entire night at 37 °C in a humidified environment with 5% CO2. After giving the cell monolayers one wash with 1× PBS, they were exposed to viral adsorption for 1 h at room temperature (RT) using hCoV-19/Egypt/NRC-03/2020 (accession number on GSAID: EPI_ISL_430820). The test compounds were added to the cell monolayers at different concentrations using 100 μL of DMEM. After incubation for 72 h at 37 °C in an incubator with 5% CO2, the cells were fixed for 4 h with 50 μL of 10% formaldehyde and stained for 15 min at room temperature with 0.1% crystal violet in distilled water. After dissolving the crystal violet dye with 100 μL of absolute methanol in each well, the Anthos Zenyth 200 rt plate reader (Anthos Labtec Instruments, Heerhugowaard, The Netherlands) was used to measure the optical density of the color at 570 nm. According to Mostafa et al. [37], the compound’s half-life (IC50) is the amount needed to decrease the virus-induced cytopathic effect (CPE) by 50% in comparison to the virus control.

2.4.4. Viral Plaque Titration Assay

As previously mentioned, the plaque titration method was used to count the number of plaque-forming units in each viral passage [38]. In short, Vero-E6 cells (105 cells/well) were seeded into tissue culture plates with 6 wells. The cells underwent two PBS washes 2–3 days after seeding, or at 90–100% confluence. The viruses were diluted ten times in DMEM, with 100 μL of the undiluted virus mixed with 400 μL of DMEM before being inoculated into Vero-E6 cells. The plates were incubated for 1 h at 37 °C.
The remaining inoculum was then aspirated out of the wells. Then, 3 mL of DMEM overlay medium containing 2% agarose type 1 (Lonza, Basel, Switzerland), 2% antibiotic–antimycotic mixture, and 1 µg/mL TPCK-treated trypsin was immediately added to each well. Afterward, the plates were incubated for three days at 37 °C with 5% CO2. Every day, the plaques were examined under a microscope. One milliliter of 10% formaldehyde was added to each well and left for six hours after clear plaques were visible. For virus inactivation and cell fixation, cells were incubated at room temperature. After discarding the formaldehyde, the plates were cleaned with water and allowed to dry. In 1 mL of the staining solution, a mixture of 1% crystal violet and 20% methanol in distilled water was added to each well to visualize the plaques. The wells were then allowed to incubate for five minutes at room temperature, after which the dye was disposed of, and the wells were cleaned with water and dried. Afterward, the number of viral plaques was determined, and the virus titer was calculated using the formula below:
Plaque-forming unit (PFU)/mL = Number of plaques × Reciprocal virus dilution × Multiplicand number to bring the inoculum volume to 1 mL.

2.4.5. Mode of Action of Virus Inhibition

At three distinct phases of the virus propagation cycle, the potential mechanisms of action of the polysaccharides of the chosen seaweeds’ ability to inhibit viruses were investigated. These mechanisms were based on three primary theories: (i) the prevention of viral replication and budding; (ii) each extract’s capacity to prevent the virus from adhering to infected cells, a process known as membrane fusion that blocks viral entry and is referred to as “viral adsorption”; and (iii) each polysaccharide extract’s direct ability to render the virus inactive (virucidal activity). Furthermore, the antiviral activities that were observed may be explained by the aforementioned mechanism of action alone or in combination to establish how the chosen seaweed polysaccharide interacts with the virus.

Viral Adsorption

For the viral adsorption test, Vero-E6 cells were grown in a 6-well plate with 105 cells/mL for 24 h at 37 °C using the Zhang et al. method [39]. Different concentrations of seaweed polysaccharide were added to a 200 µL medium without any supplements, and the cells were co-incubated for 2 h at 4 °C. After washing the cells three times with free-medium supplements to remove the unabsorbed polysaccharide extract, the virus was diluted and co-incubated with the pretreated cells for one hour. Finally, three milliliters of DMEM supplemented with 2% agarose was added. After allowing the plates to solidify, they were incubated at 37 °C to facilitate the formation of viral plaques. These were then fixed and stained, as previously mentioned, to determine the percentage reduction in the formation of viral plaques compared to control wells where the virus was directly infected into untreated Vero-E6 cells.

Viral Replication

The viral replication assay was conducted in accordance with Kuo et al. [40]. In a 6-well plate, Vero-E6 cells were grown at 37 °C for 24 h (105 cells/mL). After being directly applied to the cells and diluted to 103 PFU/well, the virus was incubated for 1 h at 37 °C. Viral particles that were not absorbed were eliminated by repeatedly washing cells with free-medium supplements three times. After applying the extract at varying concentrations for 1 h, the cell monolayer was supplemented with 3 mL of 2× DMEM medium containing 2% agarose. After allowing the plates to solidify, they were incubated at 37 °C until viral plaques started to appear. After six hours of fixing in a 10% formalin solution, cell monolayers were stained with crystal violet. The control wells contained Vero-E6 cells infected with the virus but not exposed to the extract. Following the counting of plaques, the percentage drop in plaque formation compared to control wells was recorded.

Virucidal Mechanism

Before performing the virucidal assay, Vero-E6 cells (105 cells/mL) were grown for 24 h at 37 °C in a 6-well plate [41]. Serum-free DMEM (200 µL) containing the virus was added to the extracted concentration under test. After one hour of incubation, the mixture was diluted three times with serum-free medium, resulting in a ten-fold dilution increase. This resulted in nearly no extract being left behind, allowing the viral particles to continue growing on Vero-E6 cells. The Vero-E6 cell monolayer was then filled with 100 µL of each dilution. The cell monolayer received a DMEM overlayer after a 1 h contact period. To determine the percentage reduction in the formation of viral plaques in comparison to control wells containing infected cells that were not pretreated with the tested polysaccharide extract, the plates were allowed to solidify before being incubated at 37 °C to allow the formation of viral plaques. The plates were then fixed and stained, as previously mentioned.

2.5. Statistical Analyses

Every experiment was run through three biological replications. For statistical analysis and graphical data visualization, GraphPad Prism 8.01 was utilized. The average of the means of three replicates plus the standard deviation were used to present the data. The obtained data’s non-linear fit was represented by the CC50 and IC50 curves, whose values were determined as the “best-fit value” using GraphPad Prism.

3. Results

3.1. Physicochemical Characterization of Seaweed Polysaccharides (Alginate)

The physicochemical parameters measured are summarized in Table 1. The 1% alginate solutions demonstrated low pH, electrical conductivity, and viscosity.

3.2. UV/VIS Spectra

The spectra do not show any evidence of absorbance peaks in the visible zone (400–700 nm). This can be observed in the spectra below; therefore, it is verified that the samples do not contain pigments like contaminants (Figure 1 and Figure 2). These spectra present even more evidence that the samples are not chemically cleaned. This is because they present absorption in the UV zone, in this case at about 225 and 250 nm. An absorption peak at this wavelength is characteristic of carbonyl and sulfated groups’ absorbance. Absorption in the 210 nm region suggests a strong presence of polysaccharides, while the alginate from S. euryphyllum, owing to its brownish color, exhibits greater absorbance of these compounds compared to P. boergesenii.

3.3. FTIR-ATR

FTIR-ATR was used to analyze the polysaccharides that were extracted (Figure 3 and Figure 4). This spectroscopic method required little material and enabled quick, non-destructive polysaccharide characterization. The acquired spectra were examined and supported by references. FTIR-ATR spectra showed the characteristic absorption bands of alginate (Table 2). Only the extracted alginate spectra showed bands between 1730 and 1710 cm−1, which were proposed to represent the carboxylic acid ester form (C=O). The spectra’s peaks at 1428 cm−1 and 1400 cm−1 were attributed to the symmetric stretching vibrations of alginate carboxyl groups (COOH). The 1280–1230 cm−1 range is associated with fucoidan and other sulfated polysaccharides. The range from 1280 cm−1 to 1230 cm−1 is associated with fucoidan and other sulfated polysaccharides, mainly corresponding to fucoidan, representing peaks with some mild intensity, as shown in Table 2 symbols (+, ++, +++, +++++) to indicate the peaks relative intensity).
The highest peak in both spectra was found in the bands 1030 cm−1 and 1025 cm−1, which correspond to the characteristic alginic acid. The derived alginate spectra’s strong band at 1027 cm−1 may indicate the sample’s high guluronic acid content. Uronic acid residues’ C-O stretching vibration is typically associated with bands that are centered between 950 and 930 cm−1. The carbohydrate anomeric regions ranged from 806 cm−1 to 788 cm−1, with mannuronic acid and guluronic acid residues responsible for each. The main difference between the two samples is the 1082 cm−1 peak in the Padina boergesenii alginate, corresponding to –CO groups. Thus, the UV/VIS and FTIR-ATR spectra support the idea that the extracts are composed mainly of alginate but contain fucoidan and other sulfated polysaccharides.

3.4. Antiviral Activity of Seaweed Polysaccharides Against SARS-CoV-2

Table 3 presents the cytotoxicity concentration 50% (CC50), inhibitory concentration 50% (IC50), and selectivity index (SI) for seaweed polysaccharides on Vero-E6 cells and SARS-CoV-2 virus using the crystal violet assay.
Seaweed polysaccharides’ cytotoxicity concentration 50% (CC50) varied between 587.7 µg/mL for P. boergesenii and 396.4 µg/mL for S. euryphyllum in Vero-E6 cells. The inhibitory concentration 50% (IC50) ranged from 24.2 µg/mL to 29.3 µg/mL for P. boergesenii and S. euryphyllum, respectively, against the SARS-CoV-2 virus. This was also indicated by the selectivity index (CC50)/(IC50), which was 24.3 and 13.5 for P. boergesenii and S. euryphyllum, respectively (Table 3).
P. boergesenii demonstrated potent antiviral activity against SARS-CoV-2 and was therefore more promising than S. euryphyllum, as evidenced by the results, which showed that its polysaccharide had a higher selectivity index than that of S. euryphyllum’s polysaccharide (Figure 5). To confirm P. boergesenii polysaccharide’s efficacy as an anti-SARS-CoV-2 virus agent, further research was conducted to determine its mechanism of action.
Three modes of action of the P. boergesenii polysaccharide were examined (Table 4 and Figure 6 and Figure 7). The results showed that at a concentration of 575 µg/mL of the polysaccharide, the virucidal mechanism was the most effective, followed by viral adsorption, and finally, viral replication, with viral inhibition percentages 68.6% ± 0.8, 57.1% ± 1.4, and 37.2 ± 3, respectively, compared with remdesivir as an antiviral drug (Table 5).

4. Discussion

Human respiratory diseases caused by coronaviruses are responsible for a considerable portion of morbidity and mortality rates worldwide. The ability of the novel coronavirus SARS-CoV-2 to spread from person to person has raised concerns in the wake of its discovery. The public are aware of this severe issue [28]. Antiviral drugs to fight the SARS-CoV-2 virus could be another defense against the new pandemic. This would help contain the infection until sufficient vaccines are produced in sufficient numbers. It is now crucial to find new alternative anti-SARS medications in order to combat the latest strains.
It is believed that algae are rich in bioactive compounds. The use of these bioactive substances in treating various human illnesses is well supported by the available evidence. Furthermore, studies have demonstrated the immunomodulatory and antiviral qualities of sulfated polysaccharides, including ulvan, carrageenan, galactan, alginate, fucan and fucoidan, laminaran, calcium spirulan, and nostaflan. Alginate and carrageenan may open up new possibilities for developing cutting-edge treatment approaches for SARS-CoV-2 and other viral diseases, as numerous studies employing bioinformatic techniques have shown [42,43,44].
Hepatitis C, HIV, herpes simplex, influenza, and most recently, the coronavirus, were all shown to be susceptible to the virucidal effects of sulfated polysaccharides. Worldwide, scientists are investigating and creating vaccines to stop the spread of COVID-19 and SARS-CoV-2 infection. Natural polymers with antiviral qualities, non-toxicity, and biocompatibility, such as chitosan, alginate, gums, and so on, have a good chance of being developed into safe and novel vaccines to stop the spread of infectious diseases, including the COVID-19 disease [45,46].
The present study’s FTIR-ATR and UV/VIS spectra revealed the distinctive absorption bands of alginate containing mannuronic and guluronic acid residues and also the presence of fucoidan and other sulfated polysaccharides (also lowering the viscosity rate of alginate). The C-O stretching vibration of uronic acid residues is generally linked to bands and sulfated esters in the tested brown seaweeds that may have anti-SARS-CoV-2 properties. Sulfated polysaccharides (such as fucoidan) were reported to have a structure similar to heparan sulfates or human glycosaminoglycans due to the presence of uronic acid and sulphate moieties. By attaching itself to viral glycoproteins, this molecular mimicry blocks the entry of the virus [47].
The results of the current study regarding anti-SARS-CoV-2 activity indicated that P. boergesenii and S. euryphyllum exhibited selectivity indices of 24.3 and 13.5, respectively, based on the ratio of CC50 to IC50. This suggests that the polysaccharides from P. boergesenii show a higher level of inhibition against SARS-CoV-2 and present a more promising option than S. euryphyllum (Table 3 and Figure 5).
The polysaccharides from P. boergesenii displayed a distinct mode of action against the hCoV-19/Egypt/NRC-03/2020 strain. Among the three mechanisms tested, the virucidal mechanism demonstrated the highest level of viral inhibition, reducing the viral count from 3.5 × 105 (control) to 1.1 × 105 (after treatment), with an inhibition percentage of 68.6% ± 0.8. This was followed by the viral adsorption mechanism, which achieved an inhibition percentage of 57.1% ± 1.4. Lastly, the viral replication mechanism recorded an inhibition percentage of 37.2% ± 3.0 at the highest tested concentration of 575 µg/mL (Table 4 and Figure 6).
The results supported previous studies that demonstrated the ability of seaweed and abalone viscera’s crude polysaccharides to halt SARS-CoV-2 transmission both before and after infection. Furthermore, by preventing viral entry in vitro, it has been shown that these polysaccharides can stop replication [16]. Additionally, the study’s findings agree with those of Binsuwaidan et al. [18], who discovered that the polysaccharide from Ulva lactuca (ulvan), a green seaweed, exhibited intense anti-SARS-CoV-2 activity through interference with viral adsorption, inhibition of viral replication, and virucidal activity (26, 33, and 31 percent inhibition, respectively). Therefore, ulvan might be a helpful material for preclinical studies searching for a drug to treat SARS-CoV-2.
According to earlier research—an in silico analysis—the main protease complex with laminarin showed the most stable RMSD over a 150 ns MD simulation time. According to Mohammed et al. [48], they might have an inhibitory effect on SARS-CoV-2.
Algae-derived polysaccharides inhibit dengue virus (DENV) replication through the inhibition of cell internalization [49]. Elizondo-Gonzalez [50] discovered that fucoidan, a polysaccharide, inhibited the early stages of Newcastle disease virus infection, in line with this study. Fucoidan may also prevent the internalization of the virus, which would stop SARS-CoV-2 infection. Moreover, PBMCs from COVID-19 recovered patients have demonstrated that fucoidan can support mitochondrial membrane potential recovery. This implies that fucoidan might be a valuable medication that decreases the long-term consequences of the illness [28]. Additionally, our results supported the findings of Yang et al. [51], who found that alginate derivatives, such as Polymannuronate Monophosphate (PMPD), were similar to previously reported heparin analogs and an effective way to block the interaction of spike protein with ACE2. The aforementioned findings show that PMPD has enormous potential for use in preventing SARS-CoV-2 infection.
According to a different study, the seaweed Ecklonia cava subsp. kurome (formerly Ecklonia kurome) crude polysaccharide derivatives 37501, 37502 (alginate), and 37503 have intense anti-SARS-CoV-2 infection activity in cells and can inhibit 3CL protease’s enzymatic activity. The study also demonstrated that alginate disrupted spike protein binding to the ACE2 receptor and could obstruct SARS-CoV-2 replication. Researchers are investigating whether these polysaccharides could prevent SARS-CoV-2 replication in response to the above results [52].
A prior investigation revealed anti-SARS-CoV-2 activity in crude polysaccharides derived from Sargassum horneri and Sargassum fusiforme (Phaeophyceae). Counting the number of plaques following crystal violet staining revealed that crude polysaccharides (CPs; 500 µg/mL) decreased plaque formation by over 98% compared to the virus alone (without CPs). Before SARS-CoV-2 infection, Vero-E6 cells treated with 0.8 µg/mL CP concentrations showed more than 60% reduction in plaque formation [16].
The present work points to possible impacts on viral replication, adsorption, and significant virucidal activity. Numerous studies indicate that these negatively charged substances interfere with the enveloped virus’s early stages of the proliferation cycle, thereby preventing viral infection [53]. According to other studies, sulfated polysaccharides may prevent the production of viral proteins or stop the life cycle at specific points [54]. According to Sepúlveda-Crespo et al. [55], the sulphate residues obstruct the positively charged viral glycoprotein domain and stop the virus from interacting with cells at first. According to Lopes et al. [56], specific sulfated polysaccharides from green macroalgae also stop viral replication, consistent with our findings. Thus, bioactive substances from certain brown algae with antiviral properties may offer a cheap, easily obtainable natural supplement, particularly for managing illnesses brought on by recent or re-emerging viruses. Our research indicates that polysaccharides from certain brown algae may be a unique option for creating easily accessible, reasonably priced antiviral medications and prophylactics.

5. Conclusions

Researchers are motivated to find a more effective solution to this pandemic in light of the limited availability, financial concerns, and poor control and prevention of COVID-19 with these therapies for SARS-CoV-2. Marine seaweeds have potential medical applications because of their diverse biochemical compositions, including polysaccharides, polyunsaturated fatty acids, pigments, peptides, carbohydrates, vitamins, and polyphenols. These substances exhibit antiviral characteristics against various enveloped viral infections, such as the hepatitis virus, the human immunodeficiency virus (HIV), herpes simplex virus (HSV), and more recently, the SARS-CoV-2 virus. The characteristic absorption bands of alginate that exhibited the anti-SARS-CoV-2 effect were visible in UV/VIS and FTIR-ATR spectra. Our findings showed that alginate and fucoidan from P. boergesenii had a more significant antiviral activity against SARS-CoV-2, and these sulfated polysaccharides were a more promising option than the polysaccharides from S. euryphyllum. The distinct modes of action of the P. boergesenii polysaccharide against the SARS-CoV-2 virus demonstrated that, at a concentration of 575 µg/mL, the virucidal mechanism was the most effective of the three mechanisms employed for virus inhibition, followed by the adsorption mechanism, and finally, viral replication. The above findings showed that certain sulfated polysaccharides, such as alginates and fucoidan from brown algae, can be used in the prevention/treatment of SARS-CoV-2 infection. More future research is needed to screen and investigate different metabolites from different seaweed species against the SARS-CoV-2 virus.

Author Contributions

Conceptualization, S.G. and S.E.S.; methodology, S.E.S., M.G. and A.M.K.; software, S.G.; validation, S.G.; formal analysis, S.G., A.M.K. and L.P.; investigation, S.G., M.G., J.C. and S.G.; resources, S.G.; writing—original draft preparation, S.G., A.M.K., S.E.S. and M.G.; writing—review and editing, S.G., J.C. and L.P.; visualization, L.P.; supervision, S.G. All authors have read and agreed to the published version of the manuscript.

Funding

The Academy of Scientific Research and Technology, Egypt, is acknowledged by the authors of this work for providing financial support for research projects. This work was supported by FCT—Fundação para a Ciência e Tecnologia, I.P., in the framework of the Project UIDB/04004/2025—Centre for Functional Ecology—Science for the People & the Planet.

Data Availability Statement

Data are available from the authors.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. World Health Organization. Weekly Epidemiological Update on COVID-19—16 March 2023; World Health Organization: Geneva, Switzerland, 2023.
  2. Krammer, F. SARS-CoV-2 vaccines in development. Nature 2020, 586, 516–527. [Google Scholar] [CrossRef] [PubMed]
  3. Grubaugh, N.D.; Hodcroft, E.B.; Fauver, J.R.; Phelan, A.L.; Cevik, M. Public health actions to control new SARS-CoV-2 variants. Cell 2021, 184, 1127–1132. [Google Scholar] [CrossRef] [PubMed]
  4. Cohen, J.; Kupferschmidt, K. A very, very bad look’for remdesivir. Science 2020, 370, 642–643. [Google Scholar] [CrossRef]
  5. Cortegiani, A.; Ingoglia, G.; Ippolito, M.; Giarratano, A.; Einav, S. A systematic review on the efficacy and safety of chloroquine for the treatment of COVID-19. J. Crit. Care 2020, 57, 279–283. [Google Scholar] [CrossRef]
  6. Holdt, S.L.; Kraan, S. Bioactive compounds in seaweed: Functional food applications and legislation. J. Appl. Phycol. 2011, 23, 543–597. [Google Scholar] [CrossRef]
  7. Bhatt, A.; Arora, P.; Prajapati, S.K. Can Algal Derived Bioactive Metabolites Serve as Potential Therapeutics for the Treatment of SARS-CoV-2 Like Viral Infection? Front. Microbiol. 2020, 11, 596374. [Google Scholar] [CrossRef]
  8. Abotaleb, S.; Gheda, S.; Alam, N.; ELMehalawy, A.; Saeed, A. In vitro Assessment of Antimicrobial, Antioxidant and Anticancer Activities of Some Marine Macroalgae. Egypt. J. Bot. 2019, 60, 81–96. [Google Scholar] [CrossRef]
  9. Ismail, G.A.; Gheda, S.F.; Abo-Shady, A.M.; Abdel-Karim, O.H. In vitro potential activity of some seaweeds as antioxidants and inhibitors of diabetic enzymes. Food Sci. Technol. 2020, 40, 681–691. [Google Scholar] [CrossRef]
  10. Gheda, S.; Hamouda, R.A.; Naby, M.A.; Mohamed, T.M.; Al-Shaikh, T.M.; Khamis, A. Potent Effect of Phlorotannins Derived from Sargassum linifolium as Antioxidant and Antidiabetic in a Streptozotocin-Induced Diabetic Rats Model. Appl. Sci. 2023, 13, 4711. [Google Scholar] [CrossRef]
  11. Riccio, G.; Lauritano, C. Microalgae with Immunomodulatory Activities. Mar. Drugs 2019, 18, 2. [Google Scholar] [CrossRef]
  12. Gheda, S.F.; El-Adawi, H.I.; El-Deeb, N.M. Antiviral Profile of Brown and Red Seaweed Polysaccharides Against Hepatitis C Virus. Iran. J. Pharm. Res. 2016, 15, 483–491. [Google Scholar]
  13. Mori, T.; O’Keefe, B.R.; Sowder, R.C.; Bringans, S.; Gardella, R.; Berg, S.; Cochran, P.; Turpin, J.A.; Buckheit, R.W.; McMahon, J.B.; et al. Isolation and Characterization of Griffithsin, a Novel HIV-inactivating Protein, from the Red Alga Griffithsia sp. J. Biol. Chem. 2005, 280, 9345–9353. [Google Scholar] [CrossRef] [PubMed]
  14. Lee, J.-B.; Hayashi, K.; Maeda, M.; Hayashi, T. Antiherpetic Activities of Sulfated Polysaccharides from Green Algae. Planta Med. 2004, 70, 813–817. [Google Scholar] [CrossRef] [PubMed]
  15. Pereira, L.; Critchley, A.T. The COVID 19 novel coronavirus pandemic 2020: Seaweeds to the rescue? Why does substantial, supporting research about the antiviral properties of seaweed polysaccharides seem to go unrecognized by the pharmaceutical community in these desperate times? J. Appl. Phycol. 2020, 32, 1875–1877. [Google Scholar] [CrossRef] [PubMed]
  16. Kang, S.-M.; Tark, D.; Song, B.-M.; Lee, G.-H.; Yang, J.-H.; Han, H.-J.; Yim, S.K. Evaluation of Antiviral Effect against SARS-CoV-2 Propagation by Crude Polysaccharides from Seaweed and Abalone Viscera In Vitro. Mar. Drugs 2022, 20, 296. [Google Scholar] [CrossRef]
  17. Ziyaei, K.; Ataie, Z.; Mokhtari, M.; Adrah, K.; Daneshmehr, M.A. An insight to the therapeutic potential of algae-derived sulfated polysaccharides and polyunsaturated fatty acids: Focusing on the COVID-19. Int. J. Biol. Macromol. 2022, 209, 244–257. [Google Scholar] [CrossRef]
  18. Binsuwaidan, R.; El-Masry, T.A.; El-Sheekh, M.; Seadawy, M.G.; Makhlof, M.E.M.; Aboukhatwa, S.M.; El-Shitany, N.A.; Elmorshedy, K.E.; El-Nagar, M.M.F.; El-Bouseary, M.M. Prospective Antiviral Effect of Ulva lactuca Aqueous Extract against COVID-19 Infection. Mar. Drugs 2024, 22, 30. [Google Scholar] [CrossRef]
  19. You, L.; Gong, Y.; Li, L.; Hu, X.; Brennan, C.; Kulikouskaya, V. Beneficial effects of three brown seaweed polysaccharides on gut microbiota and their structural characteristics: An overview. Int. J. Food Sci. Technol. 2020, 55, 1199–1206. [Google Scholar] [CrossRef]
  20. Nova, P.; Pimenta-Martins, A.; Laranjeira Silva, J.; Silva, A.M.; Gomes, A.M.; Freitas, A.C. Health benefits and bioavailability of marine resources components that contribute to health—what’s new? Crit. Rev. Food Sci. Nutr. 2020, 60, 3680–3692. [Google Scholar] [CrossRef]
  21. Lopez-Santamarina, A.; Miranda, J.M.; Mondragon, A.d.C.; Lamas, A.; Cardelle-Cobas, A.; Franco, C.M.; Cepeda, A. Potential Use of Marine Seaweeds as Prebiotics: A Review. Molecules 2020, 25, 1004. [Google Scholar] [CrossRef]
  22. Aatif, M.; Muteeb, G.; Alsultan, A.; Alshoaibi, A.; Khelif, B.Y. Dieckol and Its Derivatives as Potential Inhibitors of SARS-CoV-2 Spike Protein (UK Strain: VUI 202012/01): A Computational Study. Mar. Drugs 2021, 19, 242. [Google Scholar] [CrossRef] [PubMed]
  23. Iravani, S.; Varma, R.S. Important Roles of Oligo- and Polysaccharides against SARS-CoV-2: Recent Advances. Appl. Sci. 2021, 11, 3512. [Google Scholar] [CrossRef]
  24. Jang, Y.; Shin, H.; Lee, M.K.; Kwon, O.S.; Shin, J.S.; Kim, Y.-I.; Kim, C.W.; Lee, H.-R. Antiviral activity of lambda-carrageenan against influenza viruses and severe acute respiratory syndrome coronavirus 2. Sci. Rep. 2021, 11, 821. [Google Scholar] [CrossRef]
  25. Figueroa, J.M.; Lombardo, M.E.; Dogliotti, A.; Flynn, L.P.; Giugliano, R.; Simonelli, G.; Valentini, R.; Ramos, A.; Romano, P.; Marcote, M.; et al. Efficacy of a Nasal Spray Containing Iota-Carrageenan in the Postexposure Prophylaxis of COVID-19 in Hospital Personnel Dedicated to Patients Care with COVID-19 Disease. Int. J. Gen. Med. 2021, 14, 6277–6286. [Google Scholar] [CrossRef] [PubMed]
  26. Jin, W.; Zhang, W.; Mitra, D.; McCandless, M.G.; Sharma, P.; Tandon, R.; Zhang, F.; Linhardt, R.J. The structure-activity relationship of the interactions of SARS-CoV-2 spike glycoproteins with glucuronomannan and sulfated galactofucan from Saccharina japonica. Int. J. Biol. Macromol. 2020, 163, 1649–1658. [Google Scholar] [CrossRef]
  27. Song, S.; Peng, H.; Wang, Q.; Liu, Z.; Dong, X.; Wen, C.; Ai, C.; Zhang, Y.; Wang, Z.; Zhu, B. Inhibitory activities of marine sulfated polysaccharides against SARS-CoV-2. Food Funct. 2020, 11, 7415–7420. [Google Scholar] [CrossRef]
  28. Garcia-Ruiz, D.; Villalobos-Sánchez, E.; Alam-Escamilla, D.; Elizondo-Quiroga, D. In vitro inhibition of SARS-CoV-2 Infection by dry algae powders. Sci. Rep. 2022, 12, 17101. [Google Scholar] [CrossRef]
  29. Aleem, A.A. The Marine Algae of Alexandria; Faculty of Science, University of Alexandria: Alexandria, Egypt, 1993. [Google Scholar]
  30. Jha, B.; Reddy, C.R.K.; Thakur, M.C.; Rao, M.U. Seaweeds of India; Springer: Dordrecht, The Netherlands, 2009. [Google Scholar] [CrossRef]
  31. Guiry, M.D.; Guiry, G.M. AlgaeBase. World-Wide Electronic Publication. 2023. Available online: http://www.algaebase.org (accessed on 16 October 2024).
  32. Sakugawa, K.; Ikeda, A.; Takemura, A.; Ono, H. Simplified method for estimation of composition of alginates by FTIR. J. Appl. Polym. Sci. 2004, 93, 1372–1377. [Google Scholar] [CrossRef]
  33. Cotas, J.; Pacheco, D.; Araujo, G.S.; Valado, A.; Critchley, A.T.; Pereira, L. On the Health Benefits vs. Risks of Seaweeds and Their Constituents: The Curious Case of the Polymer Paradigm. Mar. Drugs 2021, 19, 164. [Google Scholar] [CrossRef]
  34. Mamede, M.; Cotas, J.; Bahcevandziev, K.; Pereira, L. Seaweed polysaccharides on seed germination of Brassica napus L. Algal Res. 2023, 76, 103288. [Google Scholar] [CrossRef]
  35. Kandeil, A.; Mostafa, A.; El-Shesheny, R.; Shehata, M.; Roshdy, W.H.; Ahmed, S.S.; Gomaa, M.; El Taweel, A.; Kayed, A.E.; Mahmoud, S.H.; et al. Coding-Complete Genome Sequences of Two SARS-CoV-2 Isolates from Egypt. Microbiol. Resour. Announc. 2020, 9, 10–1128. [Google Scholar] [CrossRef] [PubMed]
  36. Feoktistova, M.; Geserick, P.; Leverkus, M. Crystal Violet Assay for Determining Viability of Cultured Cells. Cold Spring Harb. Protoc. 2016, 2016, pdb.prot087379. [Google Scholar] [CrossRef]
  37. Mostafa, A.; Kandeil, A.; A. M. M. Elshaier, Y.; Kutkat, O.; Moatasim, Y.; Rashad, A.A.; Shehata, M.; Gomaa, M.R.; Mahrous, N.; Mahmoud, S.H.; et al. FDA-Approved Drugs with Potent In Vitro Antiviral Activity against Severe Acute Respiratory Syndrome Coronavirus 2. Pharmaceuticals 2020, 13, 443. [Google Scholar] [CrossRef]
  38. Tobita, K. Permanent canine kidney (MDCK) cells for isolation and plaque assay of influenza B viruses. Med. Microbiol. Immunol. 1975, 162, 23–27. [Google Scholar] [CrossRef] [PubMed]
  39. Zhang, J.; Zhan, B.; Yao, X.; Gao, Y.; Shong, J. Antiviral activity of tannin from the pericarp of Punica granatum L. against genital Herpes virus in vitro. Zhongguo Zhong Yao Za Zhi 1995, 20, 556–558, 576. [Google Scholar]
  40. Kuo, Y.-C.; Lin, L.-C.; Tsai, W.-J.; Chou, C.-J.; Kung, S.-H.; Ho, Y.-H. Samarangenin B from Limonium sinense Suppresses Herpes simplex Virus Type 1 Replication in Vero Cells by Regulation of Viral Macromolecular Synthesis. Antimicrob. Agents Chemother. 2002, 46, 2854–2864. [Google Scholar] [CrossRef]
  41. Schuhmacher, A.; Reichling, J.; Schnitzler, P. Virucidal effect of peppermint oil on the enveloped viruses Herpes simplex virus type 1 and type 2 in vitro. Phytomedicine 2003, 10, 504–510. [Google Scholar] [CrossRef] [PubMed]
  42. Morokutti-Kurz, M.; Fröba, M.; Graf, P.; Große, M.; Grassauer, A.; Auth, J.; Schubert, U.; Prieschl-Grassauer, E. Iota-carrageenan neutralizes SARS-CoV-2 and inhibits viral replication in vitro. PLoS ONE 2021, 16, e0237480. [Google Scholar] [CrossRef]
  43. Song, Y.; He, P.; Rodrigues, A.L.; Datta, P.; Tandon, R.; Bates, J.T.; Bierdeman, M.A.; Chen, C.; Dordick, J.; Zhang, F.; et al. Anti-SARS-CoV-2 Activity of Rhamnan Sulfate from Monostroma nitidum. Mar. Drugs 2021, 19, 685. [Google Scholar] [CrossRef]
  44. Rohilla, D.; Srivastava, A.K.; Singh, R.P.; Yadav, P.; Singh, S.K.; Kumar, D.; Bhardwaj, N.; Kesawat, M.S.; Pandey, K.D.; Kumar, A. Algae Polysaccharides (Carrageenan and Alginate)—A Treasure-Trove of Antiviral Compounds: An In Silico Approach to Identify Potential Candidates for Inhibition of S1-RBD Spike Protein of SARS-CoV2. Stresses 2023, 3, 555–569. [Google Scholar] [CrossRef]
  45. Mallakpour, S.; Azadi, E.; Hussain, C.M. Chitosan, alginate, hyaluronic acid, gums, and β-glucan as potent adjuvants and vaccine delivery systems for viral threats including SARS-CoV-2: A review. Int. J. Biol. Macromol. 2021, 182, 1931–1940. [Google Scholar] [CrossRef] [PubMed]
  46. Bataglioli, R.A.; Rocha Neto, J.B.M.; Calais, G.B.; Lopes, L.M.; Tsukamoto, J.; de Moraes, A.P.; Arns, C.W.; Beppu, M.M. Hybrid alginate–copper sulfate textile coating for coronavirus inactivation. J. Am. Ceram. Soc. 2022, 105, 1748–1752. [Google Scholar] [CrossRef]
  47. Sangtani, R.; Ghosh, A.; Jha, H.C.; Parmar, H.S.; Bala, K. Potential of algal metabolites for the development of broad-spectrum antiviral therapeutics: Possible implications in COVID-19 therapy. Phytother. Res. 2021, 35, 2296–2316. [Google Scholar] [CrossRef]
  48. Mohammed Ali, H.S.H.; Altayb, H.N.; Bayoumi, A.A.M.; El Omri, A.; Firoz, A.; Chaieb, K. In silico screening of the effectiveness of natural compounds from algae as SARS-CoV-2 inhibitors: Molecular docking, ADMT profile and molecular dynamic studies. J. Biomol. Struct. Dyn. 2023, 41, 3129–3144. [Google Scholar] [CrossRef]
  49. Hidari, K.I.P.J.; Takahashi, N.; Arihara, M.; Nagaoka, M.; Morita, K.; Suzuki, T. Structure and anti-dengue virus activity of sulfated polysaccharide from a marine alga. Biochem. Biophys. Res. Commun. 2008, 376, 91–95. [Google Scholar] [CrossRef]
  50. Elizondo-Gonzalez, R.; Cruz-Suarez, L.E.; Ricque-Marie, D.; Mendoza-Gamboa, E.; Rodriguez-Padilla, C.; Trejo-Avila, L.M. In vitro characterization of the antiviral activity of fucoidan from Cladosiphon okamuranus against Newcastle Disease Virus. Virol. J. 2012, 9, 307. [Google Scholar] [CrossRef]
  51. Yang, C.; Li, D.; Wang, S.; Xu, M.; Wang, D.; Li, X.; Xu, X.; Li, C. Inhibitory activities of alginate phosphate and sulfate derivatives against SARS-CoV-2 in vitro. Int. J. Biol. Macromol. 2023, 227, 316–328. [Google Scholar] [CrossRef] [PubMed]
  52. Zhang, S.; Pei, R.; Li, M.; Su, H.; Sun, H.; Ding, Y.; Su, M.; Huang, C.; Chen, X.; Du, Z.; et al. Cocktail polysaccharides isolated from Ecklonia kurome against the SARS-CoV-2 infection. Carbohydr. Polym. 2022, 275, 118779. [Google Scholar] [CrossRef]
  53. Wang, H.; Ooi, E.V.; Ang, P.O. Antiviral activities of extracts from Hong Kong seaweeds. J. Zhejiang Univ. Sci. B 2008, 9, 969–976. [Google Scholar] [CrossRef]
  54. Huleihel, M.; Ishanu, V.; Tal, J.; Arad, S. Antiviral effect of red microalgal polysaccharides on Herpes simplex and Varicella zoster viruses. J. Appl. Phycol. 2001, 13, 127–134. [Google Scholar] [CrossRef]
  55. Sepúlveda-Crespo, D.; Ceña-Díez, R.; Jiménez, J.L.; Ángeles Muñoz-Fernández, M. Mechanistic Studies of Viral Entry: An Overview of Dendrimer-Based Microbicides as Entry Inhibitors Against Both HIV and HSV-2 Overlapped Infections. Med. Res. Rev. 2017, 37, 149–179. [Google Scholar] [CrossRef] [PubMed]
  56. Lopes, N.; Ray, S.; Espada, S.F.; Bomfim, W.A.; Ray, B.; Faccin-Galhardi, L.C.; Linhares, R.E.C.; Nozawa, C. Green seaweed Enteromorpha compressa (Chlorophyta, Ulvaceae) derived sulfated polysaccharides inhibit herpes simplex virus. Int. J. Biol. Macromol. 2017, 102, 605–612. [Google Scholar] [CrossRef] [PubMed]
Macromol 05 00018 g001
Figure 1. UV spectra of the Padina boergesenii polysaccharide.
Figure 1. UV spectra of the Padina boergesenii polysaccharide.
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Figure 2. UV spectra of the Sargassum euryphyllum polysaccharide.
Figure 2. UV spectra of the Sargassum euryphyllum polysaccharide.
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Figure 3. FTIR-ATR spectra of the Padina boergesenii polysaccharides.
Figure 3. FTIR-ATR spectra of the Padina boergesenii polysaccharides.
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Figure 4. FTIR-ATR spectra of the Sargassum euryphyllum polysaccharides.
Figure 4. FTIR-ATR spectra of the Sargassum euryphyllum polysaccharides.
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Figure 5. Cytotoxicity concentration 50% (CC50), inhibition concentration 50% (IC50), and selectivity index (SI) for the two seaweed polysaccharides and remdesivir as a control drug.
Figure 5. Cytotoxicity concentration 50% (CC50), inhibition concentration 50% (IC50), and selectivity index (SI) for the two seaweed polysaccharides and remdesivir as a control drug.
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Figure 6. The mode of action of Padina boergesenii polysaccharide (A) and remdesivir control drug (B) against SARS-CoV-2 virus according to virucidal, adsorption, and replication effects.
Figure 6. The mode of action of Padina boergesenii polysaccharide (A) and remdesivir control drug (B) against SARS-CoV-2 virus according to virucidal, adsorption, and replication effects.
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Figure 7. Mode of action of Padina boergesenii polysaccharide against SARS-CoV-2 virus. (1) Viral adsorption, (2) Viral replication, and (3) Virucidal mechanisms.
Figure 7. Mode of action of Padina boergesenii polysaccharide against SARS-CoV-2 virus. (1) Viral adsorption, (2) Viral replication, and (3) Virucidal mechanisms.
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Table 1. Physicochemical characterization of seaweed polysaccharides.
Table 1. Physicochemical characterization of seaweed polysaccharides.
SeaweedpHECTDSViscosity (cP)
Padina boergesenii4.21118463.9
Sargassum euryphyllum3.812001083.6
Table 2. FTIR-ATR band identification and characterization of the brown seaweed polysaccharide.
Table 2. FTIR-ATR band identification and characterization of the brown seaweed polysaccharide.
Reference Wave Number (cm−1)BoundWave Number Observed (cm−1)
Padina BoergeseniiSargassum Euryphyllum
1730–1710Carboxylic acid ester (C=O)++++++
1610–1600Asymmetric stretching vibration of carboxyl groups (COOH)++
1428–1400Symmetric stretching vibration of carboxyl groups (COOH)++
1280–1230Sulfated esters (S=O)++++++
1030–1025Alginic acid (C-O group)++++++++++
950–930C-O stretching vibration of uronic acids++++
806Guluronic acid residues++
788Mannuronic acid residues++++
+—intensity.
Table 3. Cytotoxicity concentration 50% (CC50) and inhibition concentration 50% (IC50) for the two seaweed polysaccharides and standard drugs using crystal violet assay.
Table 3. Cytotoxicity concentration 50% (CC50) and inhibition concentration 50% (IC50) for the two seaweed polysaccharides and standard drugs using crystal violet assay.
Antiviral CompoundCC50
µg/mL		IC50
µg/mL		Selectivity Index (SI)
(CC50/IC50)
Padina boergesenii polysaccharide587.724.224.3
Sargassum euryphyllum polysaccharide396.429.313.5
Standard antiviral drug
(Remdesivir)		351.82.34 5150
Table 4. The different mechanisms of action of Padina boergesenii polysaccharide against SARS-CoV-2 virus.
Table 4. The different mechanisms of action of Padina boergesenii polysaccharide against SARS-CoV-2 virus.
MechanismConc. µg/mLVirus Control (PFU/mL)Viral Count Following
Treatment (PFU/mL)		Viral Inhibition
%
Viral adsorption5753.5 × 1051.50 × 10557.1% ± 1.4
5501.60 × 10554.3% ± 1.3
5001.75 × 10550.0% ± 0.6
Viral replication5753.5 × 1052.20 × 10537.2% ± 3.0
5502.30 × 10534.3% ± 1.7
5002.40 × 10531.5% ± 6.7
Virucidal5753.5 × 1051.10 × 10568.6% ± 0.8
5501.25 × 10564.3% ± 0.7
5001.45 × 10558.6% ± 0.8
Table 5. The different mechanisms of action of remdesivir against SARS-CoV-2 virus.
Table 5. The different mechanisms of action of remdesivir against SARS-CoV-2 virus.
MechanismConc. µg/mLVirus Control (PFU/mL)Viral Count Following Treatment (PFU/mL)Viral Inhibition %
Viral adsorption3503.5 × 1053.15 × 10527.1% ± 1.40
3002.80 × 10520.0% ± 2.10
2502.55 × 10510.0% ± 1.10
Viral replication3503.5 × 1050.45 × 10587.1% ± 0.87
3000.65 × 10581.4% ± 0.73
2500.87 × 10575.1% ± 0.95
Virucidal3503.5 × 1052.85 × 10542.9% ± 1.90
3002.50 × 10533.3% ± 1.20
2502.00 × 10518.6% ± 2.30
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Gheda, S.; Karkour, A.M.; Shafay, S.E.; GabAllah, M.; Cotas, J.; Pereira, L. Polysaccharides from Brown Seaweeds (Padina boergesenii and Sargassum euryphyllum) as Promising Inhibitors of SARS-CoV-2: Characterization, Mechanisms, and Therapeutic Potential. Macromol 2025, 5, 18. https://doi.org/10.3390/macromol5020018

AMA Style

Gheda S, Karkour AM, Shafay SE, GabAllah M, Cotas J, Pereira L. Polysaccharides from Brown Seaweeds (Padina boergesenii and Sargassum euryphyllum) as Promising Inhibitors of SARS-CoV-2: Characterization, Mechanisms, and Therapeutic Potential. Macromol. 2025; 5(2):18. https://doi.org/10.3390/macromol5020018

Chicago/Turabian Style

Gheda, Saly, Ali M. Karkour, Shimaa El Shafay, Mohamed GabAllah, João Cotas, and Leonel Pereira. 2025. "Polysaccharides from Brown Seaweeds (Padina boergesenii and Sargassum euryphyllum) as Promising Inhibitors of SARS-CoV-2: Characterization, Mechanisms, and Therapeutic Potential" Macromol 5, no. 2: 18. https://doi.org/10.3390/macromol5020018

APA Style

Gheda, S., Karkour, A. M., Shafay, S. E., GabAllah, M., Cotas, J., & Pereira, L. (2025). Polysaccharides from Brown Seaweeds (Padina boergesenii and Sargassum euryphyllum) as Promising Inhibitors of SARS-CoV-2: Characterization, Mechanisms, and Therapeutic Potential. Macromol, 5(2), 18. https://doi.org/10.3390/macromol5020018

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