Search Results (14)

The enzyme γ-glutamyl transpeptidase (GGT), located on the surface of cellular membranes, hydrolyzes extracellular glutathione (GSH) to guarantee the recycling of cysteine and maintain intracellular redox homeostasis. High expression levels of GGT on tumor cells are associated with increased cell proliferation and resistance against chemotherapy. Therefore, GGT inhibitors have potential as adjuvants in treating GGT-positive tumors; however, most have been abandoned during clinical trials due to toxicity. Recent studies indicate marine-derived ovothiols as more potent non-competitive GGT inhibitors, inducing a mixed cell-death phenotype of apoptosis and autophagy in GGT-overexpressing cell lines, such as the chronic B leukemic cell HG-3, while displaying no toxicity towards non-proliferative cells. In this work, we characterize the activity of two synthetic ovothiol analogs, L-5-sulfanylhistidine and iso-ovothiol A, in GGT-positive cells, such as HG-3 and HL-60 cells derived from acute promyelocytic leukemia. The two compounds inhibit the activity of membrane-bound GGT, without altering cell vitality nor inducing cytotoxic autophagy in HG-3 cells. We provide evidence that a portion of L-5-sulfanylhistidine enters HG-3 cells and acts as a redox regulator, contributing to the increase in intracellular GSH. On the other hand, ovothiol A, which is mostly sequestered by external membrane-bound GGT, induces intracellular ROS increase and the consequent autophagic pathways. These findings provide the basis for developing ovothiol derivatives as adjuvants in treating GGT-positive tumors’ chemoresistance. Full article

Using sunscreens is one of the most widespread measures to protect human skin from sun ultraviolet radiation (UVR) damage. However, several studies have highlighted the toxicity of certain inorganic and organic UV filters used in sunscreens for the marine environment and human health. An alternative strategy may involve the use of natural products of marine origin to counteract UVR-mediated damage. Ovothiols are sulfur-containing amino acids produced by marine invertebrates, microalgae, and bacteria, endowed with unique antioxidant and UV-absorption properties. This study aimed to evaluate the protective effect of synthetic L-5-sulfanyl histidine derivatives, inspired by natural ovothiols, on human dermal fibroblasts (HDFs) upon UVA exposure. By using a custom-made experimental set-up to assess the UV screening ability, we measured the levels of cytosolic and mitochondrial reactive oxygen species (ROS), as well as cell viability and apoptosis in HDFs, in the presence of tested compounds, after UVA exposure, using flow cytometry assays with specific fluorescent probes. The results show that L-5-sulfanyl histidine derivatives display a UV screening capacity and prevent loss in cell viability, the production of cytosolic and mitochondrial ROS induced by UVA exposure in HDFs, and subsequent apoptosis. Overall, this study sheds light on the potential applications of marine-inspired sulfur-containing amino acids in developing alternative eco-safe sunscreens for UVR skin protection. Full article

One of the major threats to skin aging and the risk of developing skin cancer is excessive exposure to the sun’s ultraviolet radiation (UVR). The use of sunscreens containing different synthetic, organic, and inorganic UVR filters is one of the most widespread defensive measures. However, increasing evidence suggests that some of these compounds are potentially eco-toxic, causing subtle damage to the environment and to marine ecosystems. Resorting to natural products produced in a wide range of marine species to counteract UVR-mediated damage could be an alternative strategy. The present work investigates marine-inspired thiol compounds, derivatives of ovothiol A, isolated from marine invertebrates and known to exhibit unique antioxidant properties. However, their potential use as photoprotective molecules for biocompatible sunscreens and anti-photo aging formulations has not yet been investigated. Here, we report on the UVR absorption properties, photostability, and in vitro UVA shielding activities of two synthetic ovothiol derivatives, 5-thiohistidine and iso-ovothiol A, by spectrophotometric and fluorimetric analysis. We found that the UVA properties of these compounds increase upon exposure to UVA and that their absorption activity is able to screen UVA rays, thus reducing the oxidative damage induced to proteins and lipids. The results of this work demonstrate that these novel marine-inspired compounds could represent an alternative eco-friendly approach for UVR skin protection. Full article

Peptic ulcer is a widespread disease, with a lifetime frequency of 5–10% among the general population and an annual incidence of 0.1–0.3%. Ovothiol A is naturally produced from sea urchin eggs with special antioxidant activity. Gastric ulcers were induced in rats by a single ethanol dose (5 mL/kg). The rats were divided into control, ulcer, and ulcer with 250 and 500 mg/kg ovothiol A doses. Molecular docking studies were used to examine the interactions between ovothiol A and the H+/K+ ATPase active site residues. Ovothiol A led to a significant decline (p < 0.05) in gastric juice volume, ulcer index, MDA, IL-6, and cytochrome c, while levels of gastric juice pH, GSH, CAT, GST, SOD, and NO increased. Histopathological investigation of stomach sections revealed architecture preservation of the gastric mucosa after ovothiol A administration. The anti-ulcerogenic activity of ovothiol A includes scavenging free radicals, inhibition of inflammation, regulation of apoptosis, and stabilization of fibroblast growth factors to promote gastric ulcers healing. Full article

Ovothiols are histidine-derived thiols produced by a variety of marine invertebrates, protists and bacteria. These compounds, which are among the strongest natural antioxidants, are involved in controlling the cellular redox balance due to their redox exchange with glutathione. Although ovothiols were initially reported as protective agents against environmental stressors, new evidence suggests that they can also act as pheromones and participate in fundamental biological processes such as embryogenesis. To get further insight into the biological roles of ovothiols, we compared ovothiol biosynthesis in the sea urchin Paracentrotus lividus and in the mussel Mytilus galloprovincialis, the two species that represent the richest sources of these compounds among marine invertebrates. Ovothiol content was measured in different tissues and in the immune cells from both species and the expression levels of ovoA, the gene responsible for ovothiol biosynthesis, was inferred from publicly available transcriptomes. A comparative analysis of ovothiol biosynthesis in the two species allowed the identification of the tissues and cells synthesizing the metabolite and highlighted analogies and differences between sea urchins and mussels. By improving our knowledge on the biological roles of ovothiols and pointing out the existence of sustainable natural sources for their isolation, this study provides the basis for future biotechnological investigations on these valuable compounds. Full article

Ovothiol is one of the most powerful antioxidants acting in marine organisms as a defense against oxidative stress during development and in response to environmental cues. The gene involved in the ovothiol biosynthesis, OvoA, is found in almost all metazoans, but open questions existed on its presence among arthropods. Here, using an in silico workflow, we report a single OvoA gene in marine arthropods including copepods, decapods, and amphipods. Phylogenetic analyses indicated that OvoA from marine arthropods separated from the other marine phyla (e.g., Porifera, Mollusca) and divided into two separate branches, suggesting a possible divergence through evolution. In the copepod Calanus finmarchicus, we suggest that OvoA has a defense role in oxidative stress as shown by its high expression in response to a toxic diet and during the copepodite stage, a developmental stage that includes significant morphological changes. Overall, the results of our study open possibilities for the use of OvoA as a biomarker of stress in copepods and possibly also for other marine holozooplankters. The finding of OvoA in copepods is also promising for the drug discovery field, suggesting the possibility of using copepods as a new source of bioactive compounds to be tested in the marine biotechnological sector. Full article

Ovothiol A (OSH) is one of the strongest natural antioxidants. So far, its presence was found in tissues of marine invertebrates, algae and fish. Due to very low pKa value of the SH group, under physiological conditions, this compound is almost entirely present in chemically active thiolate form and reacts with ROS and radicals significantly faster than other natural thiols. In biological systems, OSH acts in tandem with glutathione GSH, with OSH neutralizing oxidants and GSH maintaining ovothiol in the reduced state. In the present work, we report the rate constants of OSH oxidation by H₂O₂ and of reduction of oxidized ovothiol OSSO by GSH and we estimate the Arrhenius parameters for these rate constants. The absorption spectra of reaction intermediates, adduct OSSG and sulfenic acid OSOH, were obtained. We also found that OSH effectively quenches the triplet state of kynurenic acid with an almost diffusion-controlled rate constant. This finding indicates that OSH may serve as a good photoprotector to inhibit the deleterious effect of solar UV irradiation; this assumption explains the high concentrations of OSH in the fish lens. The unique antioxidant and photoprotecting properties of OSH open promising perspectives for its use in the treatment of human diseases. Full article

Diatoms are one of the most widespread groups of microalgae on Earth. They possess extraordinary metabolic capabilities, including a great ability to adapt to different light conditions. Recently, we have discovered that the diatom Skeletonema marinoi produces the natural antioxidant ovothiol B, until then identified only in clams. In this study, we investigated the light-dependent modulation of ovothiol biosynthesis in S. marinoi. Diatoms were exposed to different light conditions, ranging from prolonged darkness to low or high light, also differing in the velocity of intensity increase (sinusoidal versus square-wave distribution). The expression of the gene encoding the key ovothiol biosynthetic enzyme, ovoA, was upregulated by high sinusoidal light mimicking natural conditions. Under this situation higher levels of reactive oxygen species and nitric oxide as well as ovothiol and glutathione increase were detected. No ovoA modulation was observed under prolonged darkness nor low sinusoidal light. Unnatural conditions such as continuous square-wave light induced a very high oxidative stress leading to a drop in cell growth, without enhancing ovoA gene expression. Only one of the inducible forms of nitric oxide synthase, nos2, was upregulated by light with consequent production of NO under sinusoidal light and darkness conditions. Our data suggest that ovothiol biosynthesis is triggered by a combined light stress caused by natural distribution and increased photon flux density, with no influence from the daily light dose. These results open new perspectives for the biotechnological production of ovothiols, which are receiving a great interest for their biological activities in human model systems. Full article

Reactive oxygen species present a challenge for marine organisms releasing gametes into the water. Thiol-containing molecules protect cells against oxidative stress, and ovothiol (OSH), an antioxidant-reducing mercaptohistidine, has been described as especially relevant in the oocytes of marine invertebrates. Ovothiol synthase (ovoA), in charge of the first step in OSH synthesis, was sequenced in mussels, Mytilus galloprovincialis. Transcription levels of ovoA in mantle did not significantly change along the reproductive cycle. No alterations of ovoA transcription were observed after a laboratory copper (10 µg/L) exposure or in mussels captured in a highly polluted site. Conversely, the metabolomic analysis of the hydrophilic metabolite content in mantle clearly classified mussels according to their site of origin, especially at the most advanced stages of oogenesis. Quantification of OSH-A and -B and glutathione (GSH), revealed stable levels in mantle at early gametogenesis in the unpolluted sampling site, but a strong increase in female mantle previous to spawning in the polluted site. These increased concentrations under pollution suggest that OSH-A accumulates along oogenesis, independent of gene transcription regulation. The concerted accumulation of OSH-A and GSH suggests the building of a balanced cellular redox-system to scavenge ROS produced in the oocyte before and during fertilization. Full article

Gamma-glutamyl transpeptidase (GGT) is a cell surface enzyme involved in glutathione metabolism and maintenance of redox homeostasis. High expression of GGT on tumor cells is associated with an increase of cell proliferation and resistance against chemotherapy. GGT inhibitors that have been evaluated in clinical trials are too toxic for human use. We have previously identified ovothiols, 5(Nπ)-methyl-thiohistidines of marine origin, as non-competitive-like inhibitors of GGT that are more potent than the known GGT inhibitor, 6-diazo-5-oxo-l-norleucine (DON), and are not toxic for human embryonic cells. We extended these studies to the desmethylated form of ovothiol, 5-thiohistidine, and confirmed that this ovothiol derivative also acts as a non-competitive-like GGT inhibitor, with a potency comparable to ovothiol. We also found that both 5-thiohistidine derivatives act as reversible GGT inhibitors compared to the irreversible DON. Finally, we probed the interactions of 5-thiohistidines with GGT by docking analysis and compared them with the 2-thiohistidine ergothioneine, the physiological substrate glutathione, and the DON inhibitor. Overall, our results provide new insight for further development of 5-thiohistidine derivatives as therapeutics for GGT-positive tumors. Full article

Liver fibrosis is a pathophysiologic process involving the accumulation of extracellular matrix proteins as collagen deposition. Advanced liver fibrosis can evolve in cirrhosis, portal hypertension and often requires liver transplantation. At the cellular level, hepatic fibrosis involves the activation of hepatic stellate cells and their transdifferentiation into myofibroblasts. Numerous pro-fibrogenic mediators including the transforming growth factor-β1, the platelet-derived growth factor, endothelin-1, toll-like receptor 4, and reactive oxygen species are key players in this process. Knowledge of the cellular and molecular mechanisms underlying hepatic fibrosis development need to be extended to find novel therapeutic strategies. Antifibrotic therapies aim to inhibit the accumulation of fibrogenic cells and/or prevent the deposition of extracellular matrix proteins. Natural products from terrestrial and marine sources, including sulfur-containing compounds, exhibit promising activities for the treatment of fibrotic pathology. Although many therapeutic interventions are effective in experimental models of liver fibrosis, their efficacy and safety in humans are largely unknown. This review aims to provide a reference collection on experimentally tested natural anti-fibrotic compounds, with particular attention on sulfur-containing molecules. Their chemical structure, sources, mode of action, molecular targets, and pharmacological activity in the treatment of liver disease will be discussed. Full article

Tissue protection from oxidative stress by antioxidants is of vital importance for cellular metabolism. The lens mostly consists of fiber cells lacking nuclei and organelles, having minimal metabolic activity; therefore, the defense of the lens tissue from the oxidative stress strongly relies on metabolites. Protein-free extracts from lenses and gills of freshwater fish, Sander lucioperca and Rutilus rutilus lacustris, were subjected to analysis using high-field ¹H NMR spectroscopy and HPLC with optical and high-resolution mass spectrometric detection. It was found that the eye lenses of freshwater fish contain high concentrations of ovothiol A (OSH), i.e., one of the most powerful antioxidants exciting in nature. OSH was identified and quantified in millimolar concentrations. The concentration of OSH in the lens and gills depends on the fish genus and on the season. A possible mechanism of the reactive oxygen species deactivation in fish lenses is discussed. This work is the first to report on the presence of OSH in vertebrates. The presence of ovothiol in the fish tissue implies that it may be a significantly more common antioxidant in freshwater and marine animals than was previously thought. Full article

Ovothiols are histidine-derived thiols isolated from sea urchin eggs, where they play a key role in the protection of cells toward the oxidative burst associated with fertilization by controlling the cellular redox balance and recycling oxidized glutathione. In this study, we show that treatment of a human liver carcinoma cell line, Hep-G2, with ovothiol A, isolated from Paracentrotus lividus oocytes, results in a decrease of cell proliferation in a dose-dependent manner. The activation of an autophagic process is revealed by phase contrast and fluorescence microscopy, together with the expression of the specific autophagic molecular markers, LC3 II and Beclin-1. The effect of ovothiol is not due to its antioxidant capacity or to hydrogen peroxide generation. The concentration of ovothiol A in the culture media, as monitored by HPLC analysis, decreased by about 24% within 30 min from treatment. The proliferation of normal human embryonic lung cells is not affected by ovothiol A. These results hint at ovothiol as a promising bioactive molecule from marine organisms able to inhibit cell proliferation in cancer cells. Full article