Pharmaceutical Prospects of Bee Products: Special Focus on Anticancer, Antibacterial, Antiviral, and Antiparasitic Properties

Bee products have long been used in traditional healing practices to treat many types of disorders, including cancer and microbial-related diseases. Indeed, several chemical compounds found in bee products have been demonstrated to display anticancer, antibacterial, antiviral, and antiparasitic properties. With the improvement of research tools and in view of recent advances related to bee products, this review aims to provide broad yet detailed insight into the pharmaceutical prospects of bee products such as honey, propolis, bee pollen, royal jelly, bee bread, beeswax, and bee venom, in the domain of cancer and infectious disease management. Available literature confirms the efficacy of these bee products in the alleviation of cancer progression, inhibition of bacterial and viral proliferation, and mitigation of parasitic-related symptoms. With such potentials, bioactive components isolated from the bee products can be used as an alternative approach in the long-run effort to improve humans’ health at a personal and community level.


Introduction
Biologically active bee products are being popular in the current world due to their promising health benefits. The use of honey for nutritional and medicinal purposes dates back nearly 5500 years [1]. Hand collecting honeybees was a significant traditional practice in ancient populations as it was the individual method to get honey, which is still being practiced currently by some people in forest areas [2]. To date, several honeybee products such as honey, bee pollen, royal jelly, propolis, beeswax, bee bread, and bee venom have been identified as prospective sources of compounds with therapeutical potentials in the management of cancer and infections by different types of bacteria, viruses, and parasites [3].
Cancer is one of the major maladies affecting humankind and remains one of the leading causes of death worldwide [4]. Honey, pollen, bee venom, royal jelly, and propolis are commonly used in apitherapy to treat various cancers. Several research studies have reported that bee products are promising candidates for cancer treatment [5][6][7]. Studies have confirmed that honey is an oxidizing agent with pro-apoptotic, anti-proliferative, anti-metastatic, immune-modulatory, and anti-inflammatory properties [6]. Bee venom is a biotoxin or apitoxin synthesized and secreted by a gland in the bee's abdominal cavity. It appears to be effective in the management of cancer, including the induction of cytotoxicity, In addition to their anticancer, antibacterial, and antiviral activities, bee products have been shown to exert antiprotozoal activity against the nematode model Caenorhabditis elegans and the intestinal parasite Giardia lamblia [3,28,29]. Studies showed that propolis yielded anti-malarial activities against Plasmodium vivax, P. ovale, P. malariae, and P. falciparum [28]. Honey and propolis were also used in ancient times for embalming bodies, and honey in traditional medicine was used for treating wounds and pain relief [8]. Royal jelly, another type of bee product, appears to have significant antimicrobial activity, as reported in several studies [27]. Beeswax, a lipid-based complex organic compound secreted by the younger worker bees in liquid form, forms in solidifies and scales when exposed to air [27,30]. In recent years, the crude extract of beeswax has been reported effective against pathogenic bacteria, viruses, and fungi [31]. Bee pollen is obtained from plants and transferred to hive as pollen loads. Load formation includes hydrating pollen with honey or nectar. In winter, pollen stored in honeycomb cells during winter fermentation undergoes lactic fermentation and produces bee bread. The bacteriostatic and bactericidal properties of bee bread and pollen are also well known [3].
Notwithstanding the immense application of bee products in the medical and pharmaceutical sectors [3], bee products also possess a substantial economic value. Bee products are primarily used in the food and cosmetics industries [8]. Honey is a great sweetener [32], and bee pollen is high in protein, fatty acids, and vitamins [33], suggesting their excellent dietary properties. Royal jelly can improve brain function and general wellbeing [34], while bee propolis and bee venom can be tapped as potential sources of anticancer [35,36] and antiviral [37,38] drug candidates. On the other hand, beeswax has antibiotic and skin softening properties; thus, this particular bee product has been extensively used in the cosmetics industry. This review discusses the importance of bee products in the medical-pharmaceutical fields as well as the potential use and prospective implication of bee products against cancer and different types of microbial pathogens and parasites.

Honey
Honey is a natural food substance generated by honeybees from deposits of plant and floral nectar, which are then coalesced with specific substances of honeybee, processed and stored in honeycombs to ripen [39]. The chemical components of honey depend on several factors including the species of honey-collecting bee, its plant source, climatic conditions, geographical region, and storage condition [40]. Honey consists of enzymes (acid phosphatase, amylase, catalase, diastase, glucose oxidase, invertase, and sucrose diastase) and amino acid monomers (alanine, asparagine, glutamine, glycine, and proline) [1]. Various phenolic acid such as caffeic-, cinnamic-, ferulic-, etc. ( Figure 2) and several organic acids, mainly as gluconic and citric acid, followed by acetic acid, formic acid, and others in small amounts ( Figure 3) are present in honey. These acids are responsible for the acidic pH of honey ranging from pH 3.4 to 6.1 [41]. Flavonoids ( Figure 4) such as quercetin, kaempferol, chrysin, apigenin, hesperetin, galangin, catechin, luteolin, myricetin, and naringenin have also been reported in honey. The total phenolic content (TPC) and the total flavonoid content (TFC) of the honey samples varied from 4.2 ± 0.6 to 1.9 ± 0.1 mg QE/100 g and 31.5 ± 2.1 to 126.6 ± 2.7 mg GAE/100 g, respectively [42].

Propolis
Propolis or bee glue is a resinous substance that honeybees produce by mixing their salivary gland excretions with exudate accumulated from different parts of plants, mainly branches, bark, flower buds, leaves, and stems. Propolis comes from two Greek words: pro (defense) and polis (city or community) [48]. The color of propolis is varied, ranging from green to brown and reddish. Propolis possesses a sweet or pleasant odor, and becomes soft and sticky upon heating [49]. Typically, raw propolis consists of resins and balms (50-60%), fatty acids and waxes (30-40%), essential oils (5-10%), and other components (5%) such as enzymes (acid phosphatase, adenosine triphosphatase, glucose-6-phosphatase, and succinic dehydrogenase), vitamins (B1, B2, B6, C, and E), minerals (Mg, Cu, F, Ca, K, Na, Mn, and Zn) [50,51]. Propolis must be purified and dewaxed via solvent extraction to remove inert materials and preserve the phenolic fractions for commercialization [52].

Propolis
Propolis or bee glue is a resinous substance that honeybees produce by mixing their salivary gland excretions with exudate accumulated from different parts of plants, mainly branches, bark, flower buds, leaves, and stems. Propolis comes from two Greek words: pro (defense) and polis (city or community) [48]. The color of propolis is varied, ranging from green to brown and reddish. Propolis possesses a sweet or pleasant odor, and becomes soft and sticky upon heating [49]. Typically, raw propolis consists of resins and balms (50-60%), fatty acids and waxes (30-40%), essential oils (5-10%), and other components (5%) such as enzymes (acid phosphatase, adenosine triphosphatase, glucose-6-phosphatase, and succinic dehydrogenase), vitamins (B1, B2, B6, C, and E), minerals (Mg, Cu, F, Ca, K, Na, Mn, and Zn) [50,51]. Propolis must be purified and dewaxed via solvent extraction to remove inert materials and preserve the phenolic fractions for commercialization [52].

Bee Pollen
One of the bee products, namely bee pollen, is produced by worker honeybees as the staple food for developing larvae [57,58]. This product results from the mixture of floral nectar, flower pollen, and enzymes with honeybee salivary substances [58]. The chemical compound of bee pollen depends on plant species, bee activities, and weather conditions [59]. The color of bee pollen is diverse, ranging from bright yellow to black and their

Bee Pollen
One of the bee products, namely bee pollen, is produced by worker honeybees as the staple food for developing larvae [57,58]. This product results from the mixture of floral nectar, flower pollen, and enzymes with honeybee salivary substances [58]. The chemical compound of bee pollen depends on plant species, bee activities, and weather conditions [59]. The color of bee pollen is diverse, ranging from bright yellow to black and their shapes are also wide ranging: bell-shaped, cylindrical, thorny, or triangular. Bee pollen consist of single grains which are sometimes joined with two or more other grains [60].

Royal Jelly
Royal jelly (bee's milk) is a viscous whitish to yellow jelly-like substance secreted by the mandibular and hypopharyngeal glands of worker honeybees [72,73]. It is slightly soluble in water with a strong smell and sour or sweet flavor and a pH of 3.1-3.9 [74]. Royal jelly plays an important role in honeybee larvae diet. It is fed exclusively to young larvae of workers and drones in their maturation process, and is provided to queen honeybees during their entire life cycle [75]. Generally, royal jelly contains water (50-70%), carbohydrates (30%), proteins (27-41%), and lipids (3-19%) [48,76]. The major sugars present in royal jelly include fructose and glucose. Moreover, sucrose and other oligosaccharides like erlose, gentobiose, isomaltose, maltose, melezitose, raffinose, and trehalose are present in very small concentrations [76,77]. A unique group of nine soluble major royal jelly proteins (MRJPs 1-9) functions as the specific factors responsible for development of queen honeybees. The peptides of royal jelly including apisimin, jelleines, and royalisin, have been shown to yield antibacterial activity [3].

Bee Bread
Bee bread (ambrosia) is a mixture of honey, pollen, and honeybee salivary secretion, which is then stored in the beehive and enclosed with honey and wax [84]. Bee bread is also called "fermented bee pollen" due to during the preservation, as the content is subjected to lactic fermentation in the beehive environment [85]. Therefore, the color of bee bread is caramel with a pungent flavor. Bee bread is the main food for larvae and the young worker bees that produce royal jelly [84].

Beeswax
Beeswax is a liquid substance secreted by the wax glands of younger worker honeybees that is used in the construction of the honeycombs. The color of beeswax turns from white to yellowish-brown after contact with honey and bee pollen. It dissolves completely in chloroform and partially in boiling alcohol [31]. Generally, beeswax consists of more than 300 components, including hydrocarbons (12-16%, Figure 9), mainly heptacosane, nonacosane, hentriacontane, pentacosane and tricosane; free fatty acids (12-14%) such as 15-hydroxypalmitic acid, oleic acid, and palmitic acid; linear wax monoesters and hydroxy monoesters (35-45%), complex wax esters (15-27%) containing 15-hydroxypalmitic acid or diols. Vitamins (A, B1, B4, B6 and P) and minerals (Ca, Cu, Fe, K, Mn, Na, P, and Zn) are also present in beeswax. Beeswax is used in the food, pharmaceutical, and cosmetic industries as an additive [31,52]. In addition, beeswax exhibits antimicrobial activities against Staphylococcus aureus, Salmonella enterica, Candida albicans and Aspergillus niger [31].

Beeswax
Beeswax is a liquid substance secreted by the wax glands of younger worker honeybees that is used in the construction of the honeycombs. The color of beeswax turns from white to yellowish-brown after contact with honey and bee pollen. It dissolves completely in chloroform and partially in boiling alcohol [31]. Generally, beeswax consists of more than 300 components, including hydrocarbons (12-16%, Figure 9), mainly heptacosane, nonacosane, hentriacontane, pentacosane and tricosane; free fatty acids (12-14%) such as 15-hydroxypalmitic acid, oleic acid, and palmitic acid; linear wax monoesters and hydroxy monoesters (35-45%), complex wax esters (15-27%) containing 15-hydroxypalmitic acid or diols. Vitamins (A, B1, B4, B6 and P) and minerals (Ca, Cu, Fe, K, Mn, Na, P, and Zn) are also present in beeswax. Beeswax is used in the food, pharmaceutical, and cosmetic industries as an additive [31,52]. In addition, beeswax exhibits antimicrobial activities against Staphylococcus aureus, Salmonella enterica, Candida albicans and Aspergillus niger [31]. Antibiotics 2021, 10, x FOR PEER REVIEW 11 of 37 Figure 9. Chemical structures of hydrocarbons found in beeswax.

Bee Venom
Bee venom or apitoxin is a clear liquid secreted by the venom gland of honeybee located in the abdominal cavity. It is injected into victims by a stringer, causing an immunological response, mainly inflammation [3]. Bee venom is soluble in water with a pH 5-5.5. Bee venom is highly hydrophilic due to the fact more than 80% of BV is water. Bee venom constituents include enzymes, predominantly two allergenic peptides: phospholipase A2 and hyaluronidase (Api m2), followed by icarapin, two serine proteases: Api SI and Api SII, and acid phosphatase or Api m3 [92,93]. Minerals such as Ca, Mg, and P are present in measurable concentrations. Volatile compounds are detected in bee venom such as isopentyl acetate, n-butyl acetate, isopentanol, n-hexyl acetate, n-octyl acetate, 2nonanol, n-decyl acetate, benzyl acetate, benzyl alcohol, and (Z)-11-eicosen-1-ol ( Figure  10) [36]. Furthermore, bee venom is composed of a very complex mixture that contains more than 18 active components, including peptides ( Figure 11), proteins, enzymes, sugars, amines, phospholipids, pheromones, and volatile compounds [94]. The major amphipathic polycationic peptides, mellitin and apamin, which are a unique component of bee venom. Other peptides such as mast-cell degranulating (MCD) peptide, adolapin, tertiapin, secapin, and cardiopep also present in bee venom [94,95].

Bee Venom
Bee venom or apitoxin is a clear liquid secreted by the venom gland of honeybee located in the abdominal cavity. It is injected into victims by a stringer, causing an immunological response, mainly inflammation [3]. Bee venom is soluble in water with a pH 5-5.5. Bee venom is highly hydrophilic due to the fact more than 80% of BV is water. Bee venom constituents include enzymes, predominantly two allergenic peptides: phospholipase A2 and hyaluronidase (Api m2), followed by icarapin, two serine proteases: Api SI and Api SII, and acid phosphatase or Api m3 [92,93]. Minerals such as Ca, Mg, and P are present in measurable concentrations. Volatile compounds are detected in bee venom such as isopentyl acetate, n-butyl acetate, isopentanol, n-hexyl acetate, n-octyl acetate, 2-nonanol, n-decyl acetate, benzyl acetate, benzyl alcohol, and (Z)-11-eicosen-1-ol ( Figure 10) [36].

Bee Venom
Bee venom or apitoxin is a clear liquid secreted by the venom gland of honeybee located in the abdominal cavity. It is injected into victims by a stringer, causing an immunological response, mainly inflammation [3]. Bee venom is soluble in water with a pH 5-5.5. Bee venom is highly hydrophilic due to the fact more than 80% of BV is water. Bee venom constituents include enzymes, predominantly two allergenic peptides: phospholipase A2 and hyaluronidase (Api m2), followed by icarapin, two serine proteases: Api SI and Api SII, and acid phosphatase or Api m3 [92,93]. Minerals such as Ca, Mg, and P are present in measurable concentrations. Volatile compounds are detected in bee venom such as isopentyl acetate, n-butyl acetate, isopentanol, n-hexyl acetate, n-octyl acetate, 2nonanol, n-decyl acetate, benzyl acetate, benzyl alcohol, and (Z)-11-eicosen-1-ol ( Figure  10) [36]. Furthermore, bee venom is composed of a very complex mixture that contains more than 18 active components, including peptides ( Figure 11), proteins, enzymes, sugars, amines, phospholipids, pheromones, and volatile compounds [94]. The major amphipathic polycationic peptides, mellitin and apamin, which are a unique component of bee venom. Other peptides such as mast-cell degranulating (MCD) peptide, adolapin, tertiapin, secapin, and cardiopep also present in bee venom [94,95].

Drone Brood
Drone brood or apilarnil is a little-known bee product acquired by the collection of drone larvae from drone cells (3-11 days after hatching) [98]. Drone brood is a milky, sweet substance with a slightly acidic taste. The odor of drone brood is similar to that of royal jelly. Drone brood is a tenacious substance of creamy consistency with a yellowish gray color [98].

Anticancer Properties of Bee Products
There is currently growing interest in bee products particularly in terms of their potential anticancer activities. It has been previously reported that some bee products can interfere with the development of cancer cells. In this review, we highlight several studies regarding the most recent anticancer activities of bee products (summarized in Table 1). In addition, we also discuss the potency of each presented bee product and the possible mechanisms by which the products or their constituents act in inhibiting the cancer cell growth.
As one of the most utilized bee products, honey has been an undoubtedly an important bee product not only because of its nutritional values but also its medicinal properties. In terms of anticancer activities, honey exerts cytotoxicity against several cancer cell lines. For instance, in an MTT assay, honey samples obtained from Morocco decreased the cell viability of human colorectal cancer (HCT-1) cell cultures [100]. Further investigation to identify the constituents in the active honey samples revealed that phenolic compounds such as rosmarinic acid, tannic acid, caffeic acid, coumaric acid, gallic acid, ferulic acid, syringic acid, catechin, and pyrogallol were present [100]. Meanwhile, manuka honey is reported to actively inhibit the proliferation of MCF-7 at various concentrations [101][102][103][104]. Acacia honey also exhibited anticancer activity against MCF-7 at a concentration of 5.5% v/v [105]. Beside HCT-1 and MCF-7, honey (0.5 to 1 mg/mL) was also reported to inhibit the growth of PC-3, a prostate cancer cell model [106].
These anticancer activities are suggested to be influenced by the substances that are present in honey and hence, correlate to its mechanisms in inhibiting the growth of cancer cells [107]. In general, honey consists of inverted sugar like glucose and fructose at a relatively high concentration but some compounds such as flavonoids, polyphenols, amino acids, carotenoids, vitamins and minerals may also be found [107,108]. Other phytochemicals such as simple polyphenols and flavonoids (chrysin, apigenin, caffeic acid, chrysin, galangin, kaemfereol, pinocembrin, pinobanksin and quercetin) can also be found [109,110]. In the evaluation of the anticancer activity of chestnut honey, a quinoline alkaloid was shown to be responsible for the apoptosis mechanism against castration-resistant prostate cancer (CRPC) cells [111]. Other mechanisms by which honey and its constituents interfere with the development of cancer cells are prevention of cellular damage by free radicals by the antioxidant constituents in honey, induction of apoptosis via cellular signalling pathways and immunomodulation activity, and estrogenic effects [102,107,111,112].
The antiproliferative potencies of propolis have also been studied extensively in recent years. Unlike honey, propolis is not usually tested in a form of a raw product, but rather, it is extracted using methanol, ethanol or other organic solvents before the pharmacological activities are evaluated because of its resinous consistency. Cytotoxic tests against A549 cells, a model of human lung cancer cell, revealed that propolis extract obtained from Turkey indicated inhibition of cell growth [113]. The ethyl acetate fraction of propolis from Saudi Arabia is reported to inhibit Jurkat cells (a T-lymphocyte leukemia model), as well as human liver carcinoma cells (HEP-62) and squamous carcinoma (SW-756) cell lines [114]. Similarly, propolis from Lebanon was also reported to suppress the growth of Jurkat cells [115]. Interestingly, when tested in other carcinoma cell models such as U251 (glioblastoma) and MDA-MB-231 (breast adenocarcinoma), the hexane fraction is the only fraction to show inhibition against these cell models compared to the aqueous and dichloromethane fraction [115]. These results suggest that less polar substances in the propolis may be responsible for the anticancer activities.
Simple polyphenol compounds such as caffeic acid, chrysin, p-coumaric acid, galangin, ferulic acid, and pinocembrin are among the most reported phytochemicals to be found in propolis. These compounds have also been suggested to play significant roles in the suppression of cancer cell growth. Czyewska compared the anticancer activity of extracted propolis to the mixture of polyphenols containing chrysin, galangin and p-coumaric acid using CAL-27 cells, a human tongue squamous cancer model. Although the results also showed that the mixture of polyphenolic compounds exhibited higher cytotoxicity than the propolis extract [116], it is important to note that the mixture was tested at higher concentration of polyphenols instead of mimicking the relative concentration each substance found in the tested propolis. One possible mechanism in which propolis may interfere with the development of cancer is by the enhancement of the immune system. As an example, propolis samples from northern Morocco which are reported to be cytotoxic against MCF-7, HCT and THP-1 are shown to enhance production of interleukin-10 (IL-10) and decrease TNF-α and IL-6 production [117], suggesting an immunomodulatory activity of this propolis as a possible mechanism to combat the tested cancer cells. The other mechanisms underlying the anticancer activities of propolis are predicted to be related to its ability to interact with microtubules and induction of tubulin depolymerisation [114], activation of apoptosis via caspase-3, -8 and -9 [116], and reduction of proline in cancer cells via proline dehydrogenase/proline oxidase activity [118].
Bee pollen is another bee product that has been examined for its anticancer properties. Compared to other bee products, bee pollen seems to yield a relatively weaker anticancer potency. In an in vitro assay of anticancer activities using mouse B16 melanoma cells, up to 100 µg/mL of bee pollen was not able to reduce the cultured cell viability [119]. However, it inhibits intracellular tyrosinase (TYR) and interfere with the expression of mRNA corresponding to TYR and tyrosinase receptor, TRP-1 and TRP-2 [119]. Bee pollens collected from different places in South Korea were tested against human prostate adenocarcinoma (PC-3), human lung carcinoma (NCI-H727), human lung carcinoma (A549), MCF-7, and AGS, resulting in IC 50 values between 0.9 to >25 mg/mL [120]. Stronger anticancer properties were shown by enzymatically cleaved bee pollen proteins, also known as the hydrolysates. It was reported that the hydrolysate peptides lower than 65 kDa in molecular weight were able to inhibit ChaGo-K1 cells, a human bronchogenic carcinoma model, at an IC 50 of 1.37 µg/mL [121]. From the above data, it is known that higher concentrations of bee pollen are required to inhibit certain cancer cell lines. However, it should also be seen as a sign that bee pollen may be less toxic to normal cells although we did not describe its toxicity profiles in this review.
Bee venoms have also been reported to exhibit anticancer properties [122,123]. One of the most notable components in bee venom is melittin, a major protein substituent found in most venoms of bee species under the Apis genus. Melittin from Apis florea and Apis mellifera have been shown to exhibit a relatively strong anticancer activity (IC 50 = 3.38 and 4.97 µg/mL, respectively) when challenged against A375 (human malignant melanoma), comparable to that of doxorubicin [124]. A cytotoxicity examination of melittin against HeLa, WiDr and Vero cell lines was also reported, showing anticancer activities with IC 50 values of 2.54, 2.68 and 3.53 µg/mL, respectively [125]. Melittin also exerts cytotoxic activity against MDA-MDB-231, a human breast cancer cell line, with an IC 50 of 6.25 µg/mL [126]. At a concentration of 0.5 µg/mL, melittin is able to reduce the viability of cultured AGS cells, a gastric cancer model [127]. The anticancer mechanism of melittin is possibly related to its ability to activate the apoptotic pathway via cytochrome-c discharge and therefore activates caspase-9 which leads to the activation of caspase-3 [124]. In relation to this, further investigation was carried out which indicated that melittin prevents the invasion and migration of melanoma cells in a metastatic cell model, mainly though interference with F-actin reorganization and epidermal growth factor receptor (EGFR) activation [124]. Although it is encouraging that melittin seems to be a promising anticancer agent, there is a growing concern that this protein may also be active against normal cells. Besides, bee venom in general is also highlighted for its adverse cytolytic effects. Therefore, measures to avoid or minimize the disadvantages of bee venom administration in cancer therapy have been attempted. Some of the solutions to this problem are the application of specialized drug delivery systems, i.e., nanoparticles, to carry the toxin protein [128,129], and conjugation of the toxin to specific cancer-targeting biomolecules [7,130,131].
The anticancer potential of other bee products such as royal jelly and bee bread was also reported. Royal jelly's effect on mammary cancer has been examined using 4T1 cells inoculated in mice. The results revealed that the tumor weight was significantly reduced and further evaluation of the mechanisms revealed changes in interleukin (IL)-2, IL-10 and interferon (INF)-α concentrations in mice plasma [132]. In a recent review regarding the anticancer activity of royal jelly, it was highlighted that the main compound in royal jelly that is thought to be responsible for its anticancer activity is called 10-hydroxydecenoic acid (10-HDA), since it is exclusively found in royal jelly (among the other bee products) at relatively high concentration [133]. However, in another study, it was reported that royal jelly or 10-HDA alone were not effective in inhibiting the growth of human colorectal carcinoma (Caco-2) cells but a mixture of royal jelly and human IFN-α3N at a ratio of 2:1 significantly reduced the cell viability [134]. Miyata et al. expanded the research further to test the anticancer potency of royal jelly in a randomized double-blinded clinical trial. Although the anticancer activity of royal jelly was found to be insignificant, there was a reduction on the adverse events frequencies among patients receiving royal jelly as adjuvant for tyrosine kinase inhibitors [135,136]. In contrast, Osama et al. reported that although a certain potency of royal jelly in protecting the renal functions of patients is observed, it was found to be insignificant in anticancer therapy of cisplatin [137]. Apart from that, the investigation on the mechanisms in the activity of royal jelly as anticancer revealed that it may enhance production of cytokine from mononuclear cells to suppress the growth of U937, a leukemia cell model [138]. Meanwhile, bee bread, a bee product that is closely related to royal jelly, was also shown to have antiproliferative activities against Caco-2 and PC-3 cell lines [139]. Bee bread has also been tested against MCF-7, HeLa, HepG-2 and non-small cell lung cancer (NCI-H460), although the potency was relatively low to moderate (GI 25 > 400 to 68 µg/mL) [89]. It consists mainly of polyunsaturated and monounsaturated fatty acids [139], but the substances that are thought to be responsible for the anticancer potency are its flavonoids and polyphenolic constituents including isorhamnetin-O-glycoside, quercetin-O-glycoside, herbacetin glycosides, kaempferol, and myricetin [89].
In general, the anticancer activities of bee products presented in this review reveal that bee products are potential sources of anticancer agents with a wide range of cytotoxic mechanisms. We are aware that anticancer activities of the bee products were mostly assessed using in vitro MTT assays. Hence, a detailed evaluation on these products against cancer-bearing animal models is required to obtain a deeper insight on the influence of different factors on the potencies of these natural products. Additionally, the toxicity profiles of each bee products against normal cells should be evaluated since many anticancer agents are not only toxic to cancer cells but also to normal tissues.

Bee Products as Prospective Sources of Antibacterial and Antiviral Agents
Bacterial and viral infections are two of the top causes of deaths worldwide. An increasing number of reports describing the development of bacterial and viral resistance, including in the form of polymicrobial infections, against currently available antibiotics and antivirals has urged the use of alternative products with potential activities against those two types of pathogens [141][142][143][144]. One of the commodities equipped with such activities are bee products [3,[145][146][147][148][149]. Bee products such as honey, propolis, bee pollen, royal jelly, beebread, and bee venom have been broadly used in the traditional healing practices, including in the management of infectious diseases [49,147,150,151]. A selected list of bee products with antibacterial properties can be seen in Table 2. With their enormous medical and pharmaceutical potentials, bee products shall be considered as one of best prospective sources to discover novel antibacterial and antiviral drugs.
Honey is comprised of more than 150 different substances, including nutrients such as carbohydrates, proteins, vitamins, minerals, water, and different types of polyphenolic compounds [149,150]. Geographical setting and climate condition have been suggested to play a decisive role in determining the composition and concentration of active compounds in the nectar [151], thus the quality and, subsequently, the antimicrobial and antiviral activities of the blossom honey can vary from one to another.
Honey exerts broad spectrum antimicrobial efficacy against different types of pathogenic bacteria [152] and viruses [153]. The antibacterial activities of honey are influenced by numerous physical and chemical properties such as high sugar content (high osmolality), low pH, glucose oxidase activation that leads to hydrogen peroxide production, and in addition to that, the biological action of chemical compounds present in honey such as bacteriocins, bee defensin, methylglyoxal, 3-phenyllactic acid (PLA), and the so-called Major Royal Jelly Proteins (MRJPs) [154]. Honey has been shown to yield exceptional antibacterial activities against both Gram-positive (including methicillin-resistant S. aureus (MRSA)), and Gram-negative bacteria, which are frequently linked to skin infections [155]. Manuka honey, a type of honey derived from Leptospermum scoparium, has been reported to have a strong antibacterial activity against S. aureus, S. epidermidis, Enterobacter aerogenes, Salmonella enterica serovar Typhimurium, Klebsiella pneumoniae, and Escherichia coli [156].
Honey has been reported to yield biological effects not only against bacterial pathogens but also against human pathogenic viruses, including the latest threat of SARS-CoV-2 [157].
Overall reports indicate that honey is a prospective sources of antiviral compounds with excellent in vitro efficacy against varicella zoster virus (VZV) [158] and rubella virus [159]. Honey, either in a single use or in a combination with other products, has also been reported to demonstrate antiviral activity against influenza virus [13], herpes simplex virus (HSV)-1 [160], and respiratory syncytial virus (RSV) [14]. In addition, honey can improve the life of patients infected with human immunodeficiency virus (HIV) by promoting the proliferation of lymphocytes and by maintaining the hematological and biochemical parameters at optimal conditions [160,161].
The antibacterial activity of other types of bee products such as propolis, bee pollen, royal jelly, bee bread, and bee venom have also been reported [3,145,148,162]. Propolis exerts its antibacterial potential using two distinct mechanisms: either by promoting the activation of host immune responses (indirect action) or via direct interaction of its component(s) with certain parts of bacteria, for example by disruption of cell wall synthesis and alteration of membrane potential [148,163]. Research carried out by a Brazilian group demonstrated the antibacterial activity of propolis against MRSA [164], most likely due to the presence of artepillin C. Separate studies by Japanese and Chilean groups confirmed the effectiveness of propolis against Porphyromonas gingivalis [165] and Streptococcus mutans [166], respectively, suggesting the potential use of propolis in the management of periodontal diseases. In addition, the high content of kaempferide, artepillin C, drupanin and p-coumaric acid present in the ethanolic extract of propolis has been shown to positively correlate with its excellent antioxidant and antimicrobial activity against diverse types of pathogenic bacteria, including S. aureus, S. saprophyticus, Listeria monocytogenes, and E. faecalis [167]. In addition to its antibacterial effect, propolis has also been reported to exert antiviral activity against many human pathogenic viruses, including human herpesviruses [15], influenza virus [16][17][18], HIV [19], human T-cell leukemia-lymphoma virus type 1 (HLTV-1) [20], Newcastle disease virus (NDV) [21], RSV [22], poliovirus (PV)-type 1 [23], and dengue virus (DENV) [24]. Recently, flavonoids of propolis and honey such as rutin, naringin, and quercetin, have been suggested as candidates for potential adjuvant treatment against SARS-CoV-2 [168].
Bee-collected pollen, simply called bee pollen, and bee bread are two bee products commonly known for their dietary value [145]. Based on the published literature, bee pollen and bee bread demonstrate good antimicrobial activities against several human bacterial and viral pathogens [145]. However, like honey and propolis, the antimicrobial activities of bee pollen and bee bread are varied, and largely dependent on the geographical source of the collected samples and the solvents used in the extraction process [145]. Chilean bee pollen extracts inhibited the growth of Streptococcus pyogenes I.S.P. 364-00 but did not show any biological activities against S. aureus ATCC 25923, P. aeruginosa ATCC 27853, and E. coli ATCC 25922 [169]. Interestingly, Slovakian bee pollen extract demonstrated good antibacterial features against a clinical isolate of E. coli CCM 3988 [170]. Nonetheless, a general observation in several studies is that the antibacterial action of bee pollen is much higher towards Gram-positive bacteria than their Gram-negative counterparts [169,[171][172][173] with some exceptions [174,175]. It is important to note, however, that almost all the antibacterial data were generated in vitro, so it is urgent to confirm the antibacterial efficacy of bee products using currently available vertebrate [176][177][178][179] or invertebrate [180][181][182][183][184][185] in vivo model systems.
In addition to their antibacterial efficacies, bee pollen and bee bread have been reported to display antiviral activities. For example, bee pollen of date palm was found to be active against HSV-1 and HSV-2 [25] and bee pollen extracts of Korean Papaver rhoeas was fairly effective against influenza viruses (strains of H1N1, H3N2, and H5N1) [26]. The antiviral activity of bee pollen was most likely due to the action of flavonoids such as luteolin, galangin, kaempferol, and quercetin. Luteolin has been shown as one of the most potent inhibitors of the neuraminidase of influenza virus [26], thus is a prospective anti-influenza drug candidate (as a class of neuraminidase inhibitor). In addition, quercetin was shown to interact with the HA2 subunit of hemagglutinin and inhibit the entry of influenza virus into the host cells [186]. Quercetin-mediated inhibition of hemagglutinin might play a determinant role in the prevention of the hemagglutinin-sialic acid interaction that is required in influenza virus entry. With an increasing rate of viral resistance against the available anti-influenza drugs, such a mechanism shall play a future role in the pharmacological treatment of influenza virus infections.
The emergence of SARS-CoV-2, the causative agent of coronavirus disease (COVID)-19, in late 2019 has increased researchers' interest in the medical and pharmaceutical potentials of bee products. Several published literatures have encouraged the use of bee products such as honey, propolis, bee pollen, bee bread, and even bee venom, in the management of COVID-19. Lima et al., for example, argued that apitherapy is one of alternative ways that can be tapped to prevent and/or to manage some of the COVID-19-associated symptoms [27]. Indeed, honey and other bee products contain a number of compounds that have been shown effective as antivirals, thus potentially promising against SARS-CoV-2 [27,157,187]. On the basis of such argument, several randomized clinical trials are now carried out to investigate whether the use of honey and propolis in the management COVID-19 are truly effective [27]. All honey samples demonstrated good antibacterial activity against all tested pathogens with S. aureus and P. aeruginosa were the most sensitive ones. It seems that the origins and the color of honey, but not acidity, play a role in the antibacterial activity of honey [193] Apis mellifera ligustica propolis (extracted using methanol)

S. aureus (ATCC 25923) and
Klebsiella pneumoniae (ATCC 13883) In vitro (agar diffusion and broth dilution assays) The examined Australian propolis demonstrated antibacterial effect against S. aureus (bactericidal) but did not yield any effect on the K. pneumoniae [194] Brazilian brown and green propolis (extracted either using ethanol, hexane, or dicholometane) The Brazilian propolis demonstrated antibacterial effect against all tested microorganisms but mainly active against Gram-positive bacteria [196] Antibiotics 2021, 10, 822 20 of 37 In vitro (micro-dilution assay) Both ethanol and water propolis extracts demonstrated good antimicrobial activity against most of Gram-positive bacteria (range of MICs: 0.08-5 mg/mL), with the Irish propolis yielded the highest bactericidal effect followed by Czech and German. All propolis extracts demonstrated moderate antibacterial against MRSA and VRE and also against β-lactamase positive H. influenzae, and S. pneumoniae. Propolis ethanol extract, but not water extract, yielded moderate antibacterial activity against Gtam-negative pathogens tested in the study (MICs: 0.6-5 mg/mL) [200] Propolis and bud poplar resins (extracted using ethanol) Italy P. aeruginosa PAO1 (ATCC 15692) and transgenic P. aeruginosa (P1242) with the luciferase gene and luciferin substrate (under the control of a constitutive P1 integron promoter) In vitro (micro-dilution assay) Both ethanol extracts (propolis and bud poplar resins) demonstrated good antibacterial activity against P. aeruginosa biofilm and negatively affected the swimming and swarming motility properties of P. aeruginosa    The resazurin microtiter assay (REMA) Apitoxin and melittin yielded antibacterial activity against MRSA (MIC: 7.2 µg/mL, and 6.7 µg/mL, respectively). Apitoxin and melittin had no effect on the production of enterotoxin and/or its release. [212] Apis mellifera venom (commercial, freeze-dried) n/a

Antiparasitic Potential of Bee Products
Parasitic diseases are still among the most challenging public health issues in the countries with subtropical, tropical, and temperate climates [215][216][217]. One factor contributing to the spread of these infections is the lack of an effective and safe therapy. The current pharmacotherapy options are reported to have significant shortcomings such as being suboptimally active, especially towards the specific form of the parasites, have varying rates of efficacy, have burdensome side effects, need long treatment/administration terms, and the resistance to their action of some parasites [218][219][220]. Considering this scenario, there is a substantial need to find and promote new potent antiparasitic treatments which are affordable and have minimal adverse reactions.
In recent decades, there has been a keen interest in screening the pharmacological and chemical characteristics of bee-related products, a promising source of natural bioactive substances, as an alternative antiparasitic therapy [221]. Since classical times, bee related products have been popularly used traditionally as herbal remedies for treating some infectious diseases in many communities around the world [222]. In this review, we found that there are four bee-related products i.e., propolis, bee venom, bee pollen and honey that have been extensively studied to uncover their antiparasitic activities against protozoa and worms as the commonest classes of parasites infecting humans. Diverse studies have indicated that bee products are shown to be scientifically effective, via in vitro and/or in vivo tests, in treating a wide variety of infectious diseases such as schistosomiasis, trypanosomiasis (chagas disease), leishmaniasis, toxocariasis, plasmodiasis, toxoplasmosis, blastocystis infection, amebiasis, giardiasis, cryptosporidiosis, and echinococcosis ( Table 3).
The curative properties of bee products have been directly associated to their chemical components. However, the chemical constituents of bee products are complex and differ according to their botanical source and geographical origins as indicated by the regional variations in the antiparasitic activities of the bee products [223][224][225]. Other factors reported to influence the dissimilarity of the physicochemical characteristics of the bee products are the vegetation surrounding the beehive, collection time, soil diversity, geoclimatic conditions or seasons in the collection area, the bee species, and particular flora living at the harvesting location [226][227][228]. Variations in the concentration of effective bee products are also predominantly affected by the type and origins of parasites used in the experiments as well as the preparation method [198,229,230]. There is a wide range of the extraction method applied to obtain, for example, propolis extracts ranging from conventional separation technique using organic solvent such as ethanol to a more sophisticated one such as a supercritical fluid extraction method [231]. The extraction methods can influence the amount of active substances in the extract and therefore, might change the biological activities of the extracts [231]. Lastly, the type of bee products also determines the magnitude of biological properties. Some studies indicated that different varieties of Brazilian propolis such as red, green, and brown have distinct chemical compounds and therefore, have a different potency against parasites parasitizing humans [198,232].

In vitro
The extract displays antitrypanosomal activity against the wild type of T. brucei and the multi-drug resistant clone [257] 6. Bee Product-Derived Nanoparticles as Potential Therapeutic Agents Green chemistry principles have recently received much attention for their use in creating biocompatible nanomaterials. Due to the presence of phytoconstituents as stabilizing ligands on their surfaces, nanoparticles prepared by the application of natural product extracts have frequently demonstrated promising bioactivity. Honey bee products such as honey, royal jelly, bee venom, pollen, and beeswax are thought to be promising sources of products to avoid nanoparticle aggregation thus improving the biocompatibility, stability, and biological application. It is possible to functionalize these nanomaterial biomolecules. Metal nanoparticles such as platinum, gold, silver, zinc and others are commonly used nanoparticles in the biomedicine sector. The bactericidal and inhibitory properties of Ag NPs-based nanoparticles against various microbes are quite impressive, along with their high efficiency, strong biocompatibility, easy availability, and low cost which, made them gain significant consideration to scientists and technologists [258].
Al-Yousef et al. prepared Ag NPs (AgNPs-G) using bee pollen aqueous extract as a bioreductant during the experiments and found that they demonstrated excellent antioxidant properties and worked against different Gram-positive and negative bacteria. They even successfully exerted an anti-proliferative effect against cancer cell lines, including MCF-7 and HepG2 [259]. Magnetite nanoparticles are another type of nanoparticle with antimicrobial properties. According to El-Guendouz et al. magnetite nanoparticles twinned with propolis shows antimicrobial activities against methicillin-resistant strains of S. aureus [260]. Honey is another bee product that has antimicrobial, anti-inflammatory, and antioxidant properties. Chen et al. reported a new bioactive component-vesicle-like nanoparticles (H-VLNs) in honey that shows anti-inflammatory activities [261]. H-VLNs can disrupt a crucial inflammatory signaling platform in the innate immune system by restraining the formation and activation of the nucleotide-binding domain and pyrin domain-containing 3 (NLRP3) inflammasome. In mice, these nanoparticles reduced inflammation and liver damage in an experimentally induced acute liver injury model [261].
Like metal nanoparticles, polymeric nanoparticles and liposomes are other types of nanoparticles that are a popular choice as drug delivery vehicles for therapeutic applications in the pharmaceutical area and are safe. A study conducted by Iadnut et al. concluded that ethanolic extract of propolis loaded with polymeric nanoparticles pro-foundly inhibited the growth of Candida albicans [262]. They found that the ethanolic extract of propolis-loaded poly(lactic-co-glycolic acid) nanoparticles can reduce gene-encoding virulence-associated hyphal adhesion proteins of C. albicans, which further attenuates the fungal virulence [262]. In another study, do Nascimento et al. investigated the immunosuppressive activity of "multiple-constituent extract in the co-delivery system" against leishmaniasis by loading using Brazilian red propolis extract into polymeric nanoparticles [263]. Various dosage forms of red propolis extract loaded with nanoparticles were tested and discovered to be a potential intermediate product for the preparation of various drugs for diseases like leishmaniasis.
Bee venom is gaining popularity for its antipathogenic, anticancer, anti-tumor activities. Alalawy et al. prepared fungal chitosan nanoparticles loaded with bee venom and demonstrated that such bee-venom nanoparticle preparation was significantly potent as a natural anti-proliferative agent against cervical cancer [28]. In addition to that, Saber et al. used bee venom loaded with chitosan to successfully treat amoebiasis in mice [264], indicating that, bee venom possesses antiparasitic properties in addition to its anticancer properties.

Concluding Remarks and Future Directions
Bee products such as honey, propolis, bee pollen, royal jelly, beebread, beeswax, and bee venom have been broadly used in traditional healing practices. With their potential medical and pharmaceutical properties, increasing interest in bee products has been seen in the last century. With the advancements in research tools and our great progress in the understanding of biological processes, the main active component(s) responsible for the anticancer, antibacterial, antiviral as well as antiparasitic properties of bee products need to be clearly elucidated in a standardized way in order to improve the application of bee products in disease management. The issue of standardization has also been hampering the use of bee products not only in pharmaceuticals but also in cosmetics and food industries. Furthermore, there is also a need to determine the optimal dose of bee products and how to use the products to treat cancer as well as infections. This information is substantial in order to bridge the experimental results from the bench to the bedside.

Conflicts of Interest:
The authors declare no conflict of interest.