Fishing for Targets of Alien Metabolites: A Novel Peroxisome Proliferator-Activated Receptor (PPAR) Agonist from a Marine Pest

Marine Compounds and Age-Related Diseases: The Path from Pre-Clinical Research to Approved Drugs for the Treatment of Cardiovascular Diseases and Diabetes

Ageing represents a main risk factor for several pathologies. Among them, cardiovascular diseases (CVD) and type 2 diabetes mellitus (T2DM) are predominant in the elderly population and often require prolonged use of multiple drugs due to their chronic nature and the high proportion of co-morbidities. Hence, research is constantly looking for novel, effective molecules to treat CVD and T2DM with minimal side effects. Marine active compounds, holding a great diversity of chemical structures and biological properties, represent interesting therapeutic candidates to treat these age-related diseases. This review summarizes the current state of research on marine compounds for the treatment of CVD and T2DM, from pre-clinical studies to clinical investigations and approved drugs, highlighting the potential of marine compounds in the development of new therapies, together with the limitations in translating pre-clinical results into human application.

Exploring toxicological interactions in a changing sea: The case of the alkaloids caffeine and caulerpin

The bisindolic alkaloid caulerpin (CAU) is a bioactive compound isolated from green algae of the genus Caulerpa that are highly invasive in the Mediterranean Sea. On the other side, the purine alkaloid caffeine (CAF) is one of the most globally consumed psychoactive substances and a widespread anthropogenic water pollutant. Both compounds display a large panel of biological properties and are well known to accumulate in the tissues of aquatic organisms and, in certain circumstances, co-occur in the human diet. On this premise, the present study aimed to investigate possible synergistic interactions between CAU and CAF by using the bivalve Mytilus galloprovincialis as a model organism. Mussels were exposed to CAF via medium while they were fed with food enriched with CAU. After treatments, biochemical analysis confirmed the toxic potential of CAF, with increased AChE activity and lipid peroxidation. Also, histopathological alterations were observed in the gills and digestive tubules. The NMR-based metabolomics analysis detected higher levels of free amino acids under CAF treatments. Conversely, the food administration of CAU did not affect the above toxicological biomarkers. In addition, we did not observe any cumulative effect between CAF and CAU toward increased cellular damage and neurotoxicity. On the other hand, a possible action of CAU in decreasing CAF toxicity could be hypothesized based on our results. This hypothesis is supported by the activity of CAU as an agonist of peroxisome proliferator-activated receptors (PPARs). PPARs mediate xenobiotic detoxification via cytochromes P450, which is involved in CAF metabolism. Overall, the results obtained not only rule out any cumulative adverse effects of CAF and CAU but also encourage further research to evaluate the possible use of CAU, a compound easily obtained through the valorization of biomass from invasive species, as a food additive to improve the clearance of xenobiotics.

Early life stage mechanisms of an active fish species to cope with ocean warming and hypoxia as interacting stressors

Ocean's characteristics are rapidly changing, modifying environmental suitability for early life stages of fish. We assessed whether the chronic effects of warming (24 °C) and hypoxia (<2-2.5 mg L-1) will be amplified by the combination of these stressors on mortality, growth, behaviour, metabolism and oxidative stress of early stages of the white seabream Diplodus sargus. Combined warming and hypoxia synergistically increased larval mortality by >51%. Warming induced faster growth in length and slower gains in weight when compared to other treatments. Boldness and exploration were not directly affected, but swimming activity increased under all test treatments. Under the combination of warming and hypoxia, routine metabolic rate (RMR) significantly decreases when compared to other treatments and shows a negative thermal dependence. Superoxide dismutase and catalase activities increased under warming and were maintained similar to control levels under hypoxia or under combined stressors. Under hypoxia, the enzymatic activities were not enough to prevent oxidative damages as lipid peroxidation and DNA damage increased above control levels. Hypoxia reduced electron transport system activity (cellular respiration) and isocitrate dehydrogenase activity (aerobic metabolism) below control levels. However, lactate dehydrogenase activity (anaerobic metabolism) did not differ among treatments. A Redundancy Analysis showed that ∼99% of the variability in mortality, growth, behaviour and RMR among treatments can be explained by molecular responses. Mortality and growth are highly influenced by oxidative stress and energy metabolism, exhibiting a positive relationship with reactive oxygen species and a negative relationship with aerobic metabolism, regardless of treatment. Under hypoxic condition, RMR, boldness and swimming activity have a positive relationship with anaerobic metabolism regardless of temperature. Thus, seabreams may use anaerobic reliance to counterbalance the effects of the stressors on RMR, activity and growth. The outcomes suggests that early life stages of white seabream overcame the single and combined effects of hypoxia and warming.

Marine Natural and Nature-Inspired Compounds Targeting Peroxisome Proliferator Activated Receptors (PPARs)

Peroxisome proliferator-activated receptors α, γ and β/δ (PPARα, PPARγ, and PPARβ/δ) are a family of ligand-activated transcriptional factors belonging to the superfamily of nuclear receptors regulating the expression of genes involved in lipid and carbohydrate metabolism, energy homeostasis, inflammation, and the immune response. For this reason, they represent attractive targets for the treatment of a variety of metabolic diseases and, more recently, for neurodegenerative disorders due to their emerging neuroprotective effects. The degree of activation, from partial to full, along with the selectivity toward the different isoforms, greatly affect the therapeutic efficacy and the safety profile of PPAR agonists. Thus, there is a high interest toward novel scaffolds with proper combinations of activity and selectivity. This review intends to provide an overview of the discovery, optimization, and structure-activity relationship studies on PPAR modulators from marine sources, along with the structural and computational studies that led to their identification and/or elucidation, and rationalization of their mechanisms of action.

In-silico molecular interactions among the secondary metabolites of Caulerpa spp. and colorectal cancer targets

Caulerpa spp. secrete more than thirty different bioactive chemicals which have already been used in cancer treatment research since they play a pivotal role in cancer metabolism. Colorectal cancer is one of the most common cancer types, thus using novel and effective chemicals for colorectal cancer treatment is crucial. In the cheminformatics pipeline of this study, ADME-Tox and drug-likeness tests were performed for filtering the secondary metabolites of Caulerpa spp. The ligands which were selected from the ADME test were used for in silico molecular docking studies against the enzymes of the oxidative branch of the pentose phosphate pathway (glucose-6-phosphate dehydrogenase and 6-phosphoglutarate dehydrogenase), which is of great importance for colorectal cancer, by using AutoDock Vina. Pharmacophore modeling was carried out to align the molecules. Molecular dynamic simulations were performed for each target to validate the molecular docking studies and binding free energies were calculated. According to the ADME test results, 13 different secondary metabolites were selected as potential ligands. Molecular docking studies revealed that vina scores of caulerpin and monomethyl caulerpinate for G6PDH were found as -10.6 kcal mol-1, -10.5 kcal mol-1, respectively. Also, the vina score of caulersin for 6PGD was found as -10.7 kcal mol-1. The highest and the lowest binding free energies were calculated for monomethyl caulerpinate and caulersin, respectively. This in silico study showed that caulerpin, monomethyl caulerpinate, and caulersin could be evaluated as promising marine phytochemicals against pentose phosphate pathway enzymes and further studies are recommended to investigate the detailed activity of these secondary metabolites on these targets.

An Efficient and Quick Analytical Method for the Quantification of an Algal Alkaloid Caulerpin Showed In-Vitro Anticancer Activity against Colorectal Cancer

Biological invasion is the successful spread and establishment of a species in a novel environment that adversely affects the biodiversity, ecology, and economy. Both invasive and non-invasive species of the Caulerpa genus secrete more than thirty different secondary metabolites. Caulerpin is one of the most common secondary metabolites in genus Caulerpa. In this study, caulerpin found in invasive Caulerpa cylindracea and non-invasive Caulerpa lentillifera extracts were analyzed, quantified, and compared using high-performance thin layer chromatography (HPTLC) for the first time. The anticancer activities of caulerpin against HCT-116 and HT-29 colorectal cancer (CRC) cell lines were also tested. Caulerpin levels were found higher in the invasive form (108.83 ± 5.07 µg mL^-1 and 96.49 ± 4.54 µg mL^-1). Furthermore, caulerpin isolated from invasive Caulerpa decreased cell viability in a concentration-dependent manner (IC50 values were found between 119 and 179 µM), inhibited invasion-migration, and induced apoptosis in CRC cells. In comparison, no cytotoxic effects on the normal cell lines (HDF and NIH-3T3) were observed. In conclusion, HPTLC is a quick and novel method to investigate the caulerpin levels found in Caulerpa extracts, and this paper proposes an alternative utilization method for invasive C. cylindracea due to significant caulerpin content compared to non-invasive C. lentillifera.

An Alkaloid from a Highly Invasive Seaweed Increases the Voracity and Reproductive Output of a Model Fish Species

The invasive macroalga Caulerpa cylindracea has spread widely in the Mediterranean Sea, becoming a favorite food item for native fish for reasons yet unknown. By using a combination of behavioral, morphological, and molecular approaches, herein we provide evidence that the bisindole alkaloid caulerpin, a major secondary metabolite of C. cylindracea, significantly increases food intake in the model fish Danio rerio, influencing the regulation of genes involved in the orexigenic pathway. In addition, we found that the compound improves fish reproductive performance by affecting the hypothalamus-pituitary-gonadal axis. The obtained results pave the way for the possible valorization of C. cylindracea as a sustainable source of a functional feed additive of interest to face critical challenges both in aquaculture and in human nutrition.

Chasing Chances in a Changing Sea

Bioactive marine natural products (BMNPs) of interest for applications as drugs, antimicrobials, cosmetics, nutraceuticals, or antifoulants, are often present in traces in producer organisms and often occur in threatened or endangered species, or in organisms playing key ecological roles [...]

Caulerpin Mitigates Helicobacter pylori-Induced Inflammation via Formyl Peptide Receptors

The identification of novel strategies to control Helicobacter pylori (Hp)-associated chronic inflammation is, at present, a considerable challenge. Here, we attempt to combat this issue by modulating the innate immune response, targeting formyl peptide receptors (FPRs), G-protein coupled receptors that play key roles in both the regulation and the resolution of the innate inflammatory response. Specifically, we investigated, in vitro, whether Caulerpin—a bis-indole alkaloid isolated from algae of the genus Caulerpa—could act as a molecular antagonist scaffold of FPRs. We showed that Caulerpin significantly reduces the immune response against Hp culture filtrate, by reverting the FPR2-related signaling cascade and thus counteracting the inflammatory reaction triggered by Hp peptide Hp(2–20). Our study suggests Caulerpin to be a promising therapeutic or adjuvant agent for the attenuation of inflammation triggered by Hp infection, as well as its related adverse clinical outcomes.

Fishery reforms for the management of non-indigenous species

Marine ecosystems are undergoing major transformations due to the establishment and spread of Non-Indigenous Species (NIS). Some of these organisms have adverse effects, for example by reducing biodiversity and causing ecosystem shifts. Others have upsides, such as benefits to fisheries or replacing lost ecological functions and strengthening biogenic complexity. Stopping the spread of NIS is virtually impossible and so the societal challenge is how to limit the socioeconomic, health, and ecological risks, and sustainably exploit the benefits provided by these organisms. We propose a move away from the notion that NIS have only negative effects, and suggest a turn towards an Ecosystem-Based Fishery Management approach for NIS (EBFM-NIS) in the Mediterranean Sea, the world's most invaded marine region. A structured, iterative, and adaptive framework that considers the range of costs and benefits to ecosystems, ecosystem services, and fisheries is set out to determine whether NIS stocks should be managed using sustainable or unsustainable exploitation. We propose fishery reforms such as multiannual plans, annual catch limits, technical measures for sustainable exploitation, and legitimization of unlimited fishing of selected NIS and introduction of a radical new license for NIS fishing for unsustainable exploitation. Depending on local conditions, investment strategies can be included within the EBFM-NIS framework to protect/enhance natural assets to improve ecosystem resilience against NIS, as well as fishery assets to improve the performance of NIS fisheries. Examples of the former include the enhancement of Marine Protected Areas, harvesting of invasive NIS within MPAs, and protection of overfished predators and key species. Examples of the latter include market promotion and valorisation of NIS products, development of novel NIS products, and innovative/alternative NIS fishing such as fishery-related tourism ('pescatourism'). The application of the suggested EBFM-NIS would create jobs, protect and enhance ecosystem services, and help to meet the United Nations Sustainable Development Goal 14: Conserve and sustainably use the oceans, seas, and marine resources for sustainable development.

Species vulnerability under climate change: Study of two sea urchins at their distribution margin

In order to develop powerful predictions on the impact of climate change on marine organisms, it is critical to understand how abiotic drivers such as temperature can directly and indirectly affect marine organisms. Here, we evaluated and compared the physiological vulnerability of the leading-edge populations of two species of sea urchins Loxechinus albus and Pseudechinus magellanicus in response to predicted ocean warming and food limitation. After exposing sea urchins to a 60-day experimental period to contrasting temperature (1 °C, 7 °C and 14 °C corresponding respectively to the actual average summer temperature in Antarctica, the control treatment temperature and the predicted future temperature in the Strait of Magellan) and diet levels (ad libitum or food limitation), sea urchin stress tolerance was assessed. Sea urchins' physiology was measured at the organismal and sub-cellular level by studying the organisms energy balance (behavior, growth, gonad index, ingestion rate, O₂ uptake, energy reserves) and the expression of genes associated with aerobic metabolism. Our results showed that at their distribution edge, and despite their distinct geographical repartition, both species might be resilient to ocean warming. However, the combination of ocean warming and food limitation reduced the stress tolerance of sea urchins. In a warming ocean, another strategy could be to migrate toward the pole to a cooler environment but incubation at 1 °C resulted in a diminution of both species' aerobic scope. Overall, if these engineer species are unable to acclimate to food limitation under future climate, population fitness could be affected with ecological and economic consequences.

Neuroprotective Potentials of Marine Algae and Their Bioactive Metabolites: Pharmacological Insights and Therapeutic Advances

Beyond their significant contribution to the dietary and industrial supplies, marine algae are considered to be a potential source of some unique metabolites with diverse health benefits. The pharmacological properties, such as antioxidant, anti-inflammatory, cholesterol homeostasis, protein clearance and anti-amyloidogenic potentials of algal metabolites endorse their protective efficacy against oxidative stress, neuroinflammation, mitochondrial dysfunction, and impaired proteostasis which are known to be implicated in the pathophysiology of neurodegenerative disorders and the associated complications after cerebral ischemia and brain injuries. As was evident in various preclinical studies, algal compounds conferred neuroprotection against a wide range of neurotoxic stressors, such as oxygen/glucose deprivation, hydrogen peroxide, glutamate, amyloid β, or 1-methyl-4-phenylpyridinium (MPP+) and, therefore, hold therapeutic promise for brain disorders. While a significant number of algal compounds with promising neuroprotective capacity have been identified over the last decades, a few of them have had access to clinical trials. However, the recent approval of an algal oligosaccharide, sodium oligomannate, for the treatment of Alzheimer's disease enlightened the future of marine algae-based drug discovery. In this review, we briefly outline the pathophysiology of neurodegenerative diseases and brain injuries for identifying the targets of pharmacological intervention, and then review the literature on the neuroprotective potentials of algal compounds along with the underlying pharmacological mechanism, and present an appraisal on the recent therapeutic advances. We also propose a rational strategy to facilitate algal metabolites-based drug development.

Identification and Characterization of Cannabimovone, a Cannabinoid from Cannabis sativa, as a Novel PPARγ Agonist via a Combined Computational and Functional Study

Phytocannabinoids (pCBs) are a large family of meroterpenoids isolated from the plant Cannabis sativa. Δ⁹-Tetrahydrocannabinol (THC) and cannabidiol (CBD) are the best investigated phytocannabinoids due to their relative abundance and interesting bioactivity profiles. In addition to various targets, THC and CBD are also well-known agonists of peroxisome proliferator-activated receptor gamma (PPARγ), a nuclear receptor involved in energy homeostasis and lipid metabolism. In the search of new pCBs potentially acting as PPARγ agonists, we identified cannabimovone (CBM), a structurally unique abeo-menthane pCB, as a novel PPARγ modulator via a combined computational and experimental approach. The ability of CBM to act as dual PPARγ/α agonist was also evaluated. Computational studies suggested a different binding mode toward the two isoforms, with the compound able to recapitulate the pattern of H-bonds of a canonical agonist only in the case of PPARγ. Luciferase assays confirmed the computational results, showing a selective activation of PPARγ by CBM in the low micromolar range. CBM promoted the expression of PPARγ target genes regulating the adipocyte differentiation and prevented palmitate-induced insulin signaling impairment. Altogether, these results candidate CBM as a novel bioactive compound potentially useful for the treatment of insulin resistance-related disorders.

Biological Effects of the Azaspiracid-Producing Dinoflagellate Azadinium dexteroporum in Mytilus galloprovincialis from the Mediterranean Sea

Azaspiracids (AZAs) are marine biotoxins including a variety of analogues. Recently, novel AZAs produced by the Mediterranean dinoflagellate Azadinium dexteroporum were discovered (AZA-54, AZA-55, 3-epi-AZA-7, AZA-56, AZA-57 and AZA-58) and their biological effects have not been investigated yet. This study aimed to identify the biological responses (biomarkers) induced in mussels Mytilus galloprovincialis after the bioaccumulation of AZAs from A. dexteroporum. Organisms were fed with A. dexteroporum for 21 days and subsequently subjected to a recovery period (normal diet) of 21 days. Exposed organisms accumulated AZA-54, 3-epi-AZA-7 and AZA-55, predominantly in the digestive gland. Mussels' haemocytes showed inhibition of phagocytosis activity, modulation of the composition of haemocytic subpopulation and damage to lysosomal membranes; the digestive tissue displayed thinned tubule walls, consumption of storage lipids and accumulation of lipofuscin. Slight genotoxic damage was also observed. No clear occurrence of oxidative stress and alteration of nervous activity was detected in AZA-accumulating mussels. Most of the altered parameters returned to control levels after the recovery phase. The toxic effects detected in M. galloprovincialis demonstrate a clear biological impact of the AZAs produced by A. dexteroporum, and could be used as early indicators of contamination associated with the ingestion of seafood.

Precision-Cut Tissue Slices (PCTS) from the digestive gland of the Mediterranean mussel Mytilus galloprovincialis: An ex vivo approach for molecular and cellular responses in marine invertebrates

The precision-cut tissue slices (PCTS) represent a largely used biological model in mammalian research. This ex vivo approach offers the main advantages of in vitro systems, while maintaining the natural architecture of the tissue. The use of PCTS in toxicological research has been proposed for investigating the cellular effects of xenobiotics or bioactive compounds mostly in mammalian models. Their application is increasing also in marine organisms, but still limited to fish. This work validates the use of PCTS in an invertebrate species, the Mediterranean mussel Mytilus galloprovincialis. Intact tissue slices of different thicknesses (300, 350 and 400 μm) were successfully obtained from the digestive gland. The slices maintained the histological integrity and the viability after 6 h and 24 h incubation in culture medium, with some differences depending on the thickness. The enzymatic activities and mRNA levels of catalase and glutathione S-transferase, chosen as model biological endpoints, were measured until 24 h incubation, revealing the functionality of such systems. This work demonstrates the suitability of mussel PCTS for investigating molecular and cellular responses in ecotoxicological research.

Astaxanthin as a Peroxisome Proliferator-Activated Receptor (PPAR) Modulator: Its Therapeutic Implications

Peroxisome proliferator-activated receptors (PPARs) are part of the nuclear hormone receptors superfamily that plays a pivotal role in functions such as glucose and lipid homeostasis. Astaxanthin (ASX) is a lipid-soluble xanthophyll carotenoid synthesized by many microorganisms and various types of marine life that is known to possess antioxidant, anti-inflammatory, antidiabetic, anti-atherosclerotic, and anticancer activities. As such, it is a promising nutraceutical resource. ASX-mediated modulation of PPARs and its therapeutic implications in various pathophysiological conditions are described in this review. ASX primarily enhances the action of PPARα and suppresses that of PPARβ/δ and PPARγ, but it has also been confirmed that ASX displays the opposite effects on PPARs, depending on the cell context. Anti-inflammatory effects of ASX are mediated by PPARγ activation, which induces the expression of pro-inflammatory cytokines in macrophages and gastric epithelial cells. The PPARγ-agonistic effect of ASX treatment results in the inhibition of cellular growth and apoptosis in tumor cells. Simultaneous and differential regulation of PPARα and PPARγ activity by ASX has demonstrated a hepatoprotective effect, maintaining hepatic lipid homeostasis and preventing related hepatic problems. Considering additional therapeutic benefits of ASX such as anti-gastric, cardioprotective, immuno-modulatory, neuroprotective, retinoprotective, and osteogenic effects, more studies on the association between ASX-mediated PPAR regulation and its therapeutic outcomes in various pathophysiological conditions are needed to further elucidate the role of ASX as a novel nutraceutical PPAR modulator.

In Silico Identification and Experimental Validation of (-)-Muqubilin A, a Marine Norterpene Peroxide, as PPARα/γ-RXRα Agonist and RARα Positive Allosteric Modulator

The nuclear receptors (NRs) RARα, RXRα, PPARα, and PPARγ represent promising pharmacological targets for the treatment of neurodegenerative diseases. In the search for molecules able to simultaneously target all the above-mentioned NRs, we screened an in-house developed molecular database using a ligand-based approach, identifying (−)-Muqubilin (Muq), a cyclic peroxide norterpene from a marine sponge, as a potential hit. The ability of this compound to stably and effectively bind these NRs was assessed by molecular docking and molecular dynamics simulations. Muq recapitulated all the main interactions of a canonical full agonist for RXRα and both PPARα and PPARγ, whereas the binding mode toward RARα showed peculiar features potentially impairing its activity as full agonist. Luciferase assays confirmed that Muq acts as a full agonist for RXRα, PPARα, and PPARγ with an activity in the low- to sub-micromolar range. On the other hand, in the case of RAR, a very weak agonist activity was observed in the micromolar range. Quite surprisingly, we found that Muq is a positive allosteric modulator for RARα, as both luciferase assays and in vivo analysis using a zebrafish transgenic retinoic acid (RA) reporter line showed that co-administration of Muq with RA produced a potent synergistic enhancement of RARα activation and RA signaling.