Effects of marine 2-polyprenyl-1,4-hydroquinones on phospholipase A2 activity and some inflammatory responses

Regulation of mitochondrial function by hydroquinone derivatives as prevention of platelet activation

Platelet activation plays an essential role in the pathogenesis of thrombotic events in different diseases (e.g., cancer, type 2 diabetes, Alzheimer's, and cardiovascular diseases, and even in patients diagnosed with coronavirus disease 2019). Therefore, antiplatelet therapy is essential to reduce thrombus formation. However, the utility of current antiplatelet drugs is limited. Therefore, identifying novel antiplatelet compounds is very important in developing new drugs. In this context, the involvement of mitochondrial function as an efficient energy source required for platelet activation is currently accepted; however, its contribution as an antiplatelet target still has little been exploited. Regarding this, the intramolecular hydrogen bonding of hydroquinone derivatives has been described as a structural motif that allows the reach of small molecules at mitochondria, which can exert antiplatelet activity, among others. In this review, we describe the role of mitochondrial function in platelet activation and how hydroquinone derivatives exert antiplatelet activity through mitochondrial regulation.

Pharmacological Activities of Extracts and Compounds Isolated from Mediterranean Sponge Sources

Marine pharmacology is an exciting and growing discipline that blends blue biotechnology and natural compound pharmacology together. Several sea-derived compounds that are approved on the pharmaceutical market were discovered in sponges, marine organisms that are particularly rich in bioactive metabolites. This paper was specifically aimed at reviewing the pharmacological activities of extracts or purified compounds from marine sponges that were collected in the Mediterranean Sea, one of the most biodiverse marine habitats, filling the gap in the literature about the research of natural products from this geographical area. Findings regarding different Mediterranean sponge species were individuated, reporting consistent evidence of efficacy mainly against cancer, infections, inflammatory, and neurological disorders. The sustainable exploitation of Mediterranean sponges as pharmaceutical sources is strongly encouraged to discover new compounds.

Cytotoxic Compounds of Two Demosponges (Aplysina aerophoba and Spongia sp.) from the Aegean Sea

The class of demosponges is the biggest and most diverse of all described sponge species and it is reported to produce a plethora of chemically different metabolites with interesting biological activities. The focus of the present study was to investigate the chemical composition of two Mediterranean demosponges, targeting their brominated compounds and prenylated hydroquinones, compounds with interesting cytotoxic and anti-microbial properties. In order to gain a deeper insight into the chemical diversity of their metabolites and their activities, 20 pure secondary metabolites including new natural products were isolated from two different species (Aplysina aerophoba and Spongia sp.) using various chromatographic techniques. Their structures were confirmed by NMR and HRMS, revealing molecules with various chemical scaffolds, mainly prenylated hydroquinones from Spongia sp. and halogenated compounds from Aplysina aerophoba, including 5 novel natural products. The isolated compounds were investigated for their cytotoxic properties using 9 different cell lines, and especially one compound, 2,6-dibromo-4-hydroxy-4-methoxycarbonylmethylcyclohexa-2,5-dien-1-one showed good activities in all tested models.

A new prenylated benzoquinone from Cyathocalyx pruniferus abrogates LPS-induced inflammatory responses associated with PGE2, COX-2 and cytokines biosynthesis in human plasma

In our previous laboratory findings, Cyathocalyx pruniferus extracts exhibited platelet-activating factor inhibition, suggesting their anti-inflammatory potential. Hence, this study was designed with the aim to isolate phyto-constituents from C. pruniferus with potent anti-inflammatory activities. Column and volume liquid chromatography were used for isolation of phyto-constituents. The structure elucidation was carried out using spectroscopic analysis (HRESI-MS, ¹H and ¹³C-NMR) and compared with published literature. For cytotoxicity analysis, 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium-bromide assay was performed on peripheral blood mononuclear cells. Anti-inflammatory activities were evaluated against the levels of inflammatory cytokines (IL-1β and IL-6), prostaglandin-E₂ (PGE₂) and cyclooxegenase-2 (COX-2), in lipopolysaccharide (LPS)-induced human plasma using ELISA and radioimmunoassay (RIA). The chromatographic purification of methanol leaves extract afforded 13 (1-13) secondary metabolites. Additionally, cytotoxicity analysis suggested that isolates were non-cytotoxic at 100 μM. In anti-inflammatory evaluation, 2-octaprenyl-1, 4-benzoquinone (5) produced strong (≥ 70%) inhibition of PGE₂, COX-2, IL-1β and IL-6 at 50 µM. Moreover, 2-octaprenyl-1,4-benzoquinone (5) exhibited concentration-dependent inhibition with IC₅₀ values (µM) of 11.21, 6.61, 2.20 and 3.56 as compared to controls; indomethacin for PGE₂ (11.84) and dexamethasone in COX-2 (5.19), IL-1β (1.83) and IL-6 (3.76) analysis, respectively. In conclusion, two new compounds including 2-octaprenyl-1, 4-benzoquinone (5) and 14-methyloctadec-1-ene (6) are reported for the first time from plant species. Additionally, 2-octaprenyl-1, 4-benzoquinone (5) dose-dependently suppressed the production of pro-inflammatory mediators involved in acute and chronic inflammation at non-cytotoxic concentrations.

In Vitro Growth Inhibitory Activities of Natural Products from Irciniid Sponges against Cancer Cells: A Comparative Study

Marine sponges of the Irciniidae family contain both bioactive furanosesterterpene tetronic acids (FTAs) and prenylated hydroquinones (PHQs). Both classes of compounds are known for their anti-inflammatory, antioxidant, and antimicrobial properties and known to display growth inhibitory effects against various human tumor cell lines. However, the different experimental conditions of the reported in vitro bioassays, carried out on different cancer cell lines within separate studies, prevent realistic actual discrimination between the two classes of compounds from being carried out in terms of growth inhibitory effects. In the present work, a chemical investigation of irciniid sponges from Tunisian coasts led to the purification of three known FTAs and three known PHQs. The in vitro growth inhibitory properties of the six purified compounds have been evaluated in the same experiment in a panel of five human and one murine cancer cell lines displaying various levels of sensitivity to proapoptotic stimuli. Surprisingly, FTAs and PHQs elicited distinct profiles of growth inhibitory-responses, differing by one to two orders of magnitude in favor of the PHQs in all cell lines. The obtained comparative results are discussed in the light of a better selection of drug candidates from natural sources.

The Algal Meroterpene 11-Hydroxy-1'-O-Methylamentadione Ameloriates Dextran Sulfate Sodium-Induced Colitis in Mice

Inflammatory bowel disease (IBD) is a complex class of immune disorders. Unfortunately, a treatment for total remission has not yet been found, while the use of natural product-based therapies has emerged as a promising intervention. The present study was aimed to investigate the anti-inflammatory effects of the algal meroterpene 11-hydroxy-1'-O-methylamentadione (AMT-E) in a murine model of dextran sodium sulphate (DSS)-induced colitis. AMT-E was orally administered daily (1, 10, and 20 mg/kg animal) to DSS treated mice (3% w/v) for 7 days. AMT-E prevented body weight loss and colon shortening and effectively attenuated the extent of the colonic damage. Similarly, AMT-E increased mucus production and reduced myeloperoxidase activity (marker for anti-inflammatory activity). Moreover, the algal meroterpene decreased the tumor necrosis factor (TNF)-α, interleukin (IL)-1β, and IL-10 levels, and caused a significant reduction of the expression of inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2). Our results demonstrate the protective effects of AMT-E on experimental colitis, provide an insight of the underlying mechanisms of this compound, and suggest that this class of marine natural products might be an interesting candidate for further studies on the prevention/treatment of IBD.

Marine Natural Product Inhibitors of Neutrophil-Associated Inflammation

Neutrophils are widely recognized to play an important role in acute inflammatory responses, and recent evidence has expanded their role to modulating chronic inflammatory and autoimmune diseases. Reactive oxygen species (ROS) and microbicidal compounds released from neutrophils that are recruited to the site of inflammation contribute to the pathogenesis of multiple inflammation-associated diseases such as chronic obstructive pulmonary disease, atherosclerosis, and hepatitis. Marine organisms are a valuable source of bioactive compounds with potential for industrial and pharmaceutical application. Marine natural products that inhibit neutrophil activation could be used as drugs for the treatment of inflammatory diseases. Numerous studies investigating marine natural products have reported novel anti-inflammatory agents. Nevertheless, the detailed mechanisms underlying their actions, which could facilitate our understanding of the molecular events occurring in neutrophils, have not been reported in most of the associated research studies. Therefore, in this review, we will present marine products that inhibit neutrophil-associated inflammation. Furthermore, we will be limiting the detailed discussion to agents with well-investigated molecular targets.

Isolation of Hydroxyoctaprenyl-1′,4′-hydroquinone, a new Octaprenylhydroquinone from the Marine Sponge Sarcotragus spinosulus and Evaluation of its Pharmacological Activity on Acetylcholine and Glutamate Release in the Rat Central Nervous System

Three polyprenyl-1′,4′-hydroquinone derivatives, heptaprenyl-1′,4′-hydroquinone (1), octaprenyl-1′,4′-hydroquinone (2), and hydroxyoctaprenyl-1′,4′-hydroquinone (3) were isolated from the marine sponge Sarcotragus spinosulus collected at Baia di Porto Conte, Alghero (Italy). Our findings indicate that the compounds isolated from S. spinosulus can significantly modulate the release of glutamate and acetylcholine in the rat hippocampus and cortex and might, therefore, represent the prototype of a new class of drugs regulating glutamatergic and cholinergic transmission in the mammalian central nervous system.

A new hydroxylated nonaprenylhydroquinone from the Mediterranean marine sponge Sarcotragus spinosulus

Chemical investigation of the Mediterranean sponge Sarcotragus spinosulus led to the isolation of a new hydroxylated nonaprenylhydroquinone, along with two known metabolites, hepta- and octaprenylhydroquinones. The structure of the new metabolite was assigned by extensive 1D and 2D NMR analyses and MS studies. The antileukemic effect of the three compounds towards the chronic myelogenous leukemia (CML) cells line K562 was also evaluated.

The molecular mechanism of human group IIA phospholipase A2 inactivation by bolinaquinone

The molecular basis of the human group IIA secretory phospholipase A(2) inactivation by bolinaquinone (BLQ), a hydroxyquinone marine terpenoid, has been investigated for the comprehension of its relevant antiinflammatory properties, through the combination of spectroscopic techniques, biosensors analysis, mass spectrometry (MS) and molecular docking. Indeed, sPLA(2)s are well known to be implicated in the pathogenesis of inflammation such as rheumatoid arthritis, septic shock, psoriasis and asthma. Our results suggest a mechanism of competitive inhibition guided by a non-covalent molecular recognition event, disclosing the key role of the BLQ hydroxyl-quinone moiety in the chelation of the catalytic Ca(2+) ion inside the enzyme active site.The understanding of the sPLA(2)-IIA inactivation mechanism by BLQ could be useful for the development of a new chemical class of PLA(2) inhibitors, able to specifically target the enzyme active site.

Hexa-, hepta- and nonaprenylhydroquinones isolated from marine sponges Sarcotragus muscarum and Ircinia fasciculata inhibit NF-k B signalling in H4IIE cells

Objectives

Marine organisms have proven to be a rich source of potent pharmacologically active compounds. Three polyprenyl-1,4-hydroquinone derivates (hexaprenyl-1,4-hydroquinone, heptaprenyl-1,4-hydroquinone and nonaprenyl-1,4-hydroquinone) were isolated from the Zoobenthos-inhabiting sponges Sarcotragus muscarum and Ircinia fasciculata from the Eastern Mediterranean Sea (phylum: Porifera; class: Demospongiae).

Methods

Hexa-, hepta- and nonaprenylhydroquinone were identified by 1H-NMR, H,H-COSY, heteronuclear multiple bond correlation, FAB-MS and UV spectroscopy. The effects of the compounds on cell viability was determined using the MTT assay; anti-oxidative potential was measured using the Trolox equivalent antioxidative capacity assay. Inhibition of nuclear factor-k B activity was detected by secreted alkaline phosphatase assay. Activity against an array of protein kinases was determined in 96-well FlashPlates.

Key findings

All compounds had prominent antioxidative activity, comparable to that of the synthetic vitamin E derivate Trolox. Hexaprenylhydroquinone showed the greatest cytotoxicity in H4IIE hepatoma cells (EC50 2.5 μM). All three compounds inhibited NF-k B signalling in this cell line, with heptaprenylhydroquinone being the most active. Screening of 23 kinases involved in signal transduction pathways (cell proliferation, survival, angiogenesis and metastasis) showed that hexaprenylhydroquinone and heptaprenylhydroquinone inhibited the activity of the epidermal growth factor receptor (IC50 1.6 and 1.4 μg/ml, respectively), and heptaprenylhydroquinone also inhibited the activity of other kinases (Src tyrosine kinase, vascular endothelial growth factor receptor 3 and insulin-like growth factor 1 receptor).

Conclusions

The prenylated hydroquinones isolated from the marine sponges S. muscarum and I. fasciculata showed cytotoxic and antioxidative activities and inhibited NF-k B signalling in H4IIE hepatoma cells and protein kinases. These findings may result in the generation of new lead substances in cancer therapy.

Constitutive COX-2 activity in cardiomyocytes confers permanent cardioprotection Constitutive COX-2 expression and cardioprotection

Different lines of evidence suggest that inhibition of COX-2 activity exacerbates reperfusion injury, but direct data showing beneficial effects of increased COX-2 activity are lacking. The aim of this study was to determine the effect of constitutive expression of COX-2 on cardiomyocyte tolerance to ischemia-reperfusion injury. We generated a transgenic mouse (B6D2-Tg (MHC-PTGS2)17Upme) that constitutively expresses functional human COX-2 in cardiomyocytes under the control of alpha-myosin heavy chain promoter. COX-2 expression was confirmed by immunoblotting and by increased levels of PGE(2) and PGI(2) in myocardium. Histological and echocardiographic analysis revealed no differences in the phenotype of transgenic mice (TgCOX-2) with respect to wild type (Wt) mice. Tolerance to ischemia-reperfusion injury was analysed in a Langendorff system. Reperfused TgCOX-2 hearts after 40 min of ischemia improved functional recovery (32.9+/-6.2% vs. 9.45+/-4.4%, P=0.004) and reduced cell death assessed by LDH release (43% of reduction, P<0.001) and triphenyltetrazolium staining (41% of reduction, P=0.002). Cardioprotection was not further increased by ischemic preconditioning. Pretreatment of mice with the COX-2 inhibitor DFU attenuated cardioprotection with a correlation between myocardial PGE(2) levels and the extent of cell death. NMR spectroscopy showed a marked reduction in arachidonic acid (AA) content in TgCOX-2 hearts. Both, DFU pretreatment and perfusion of TgCOX-2 hearts with AA increased myocardial AA to values similar to those measured in Wt hearts and reversed cardioprotection. We conclude that constitutive expression of COX-2 in cardiomyocytes confers a permanent cardioprotective state against reperfusion injury. Increased PGE(2) synthesis and reduced AA content could explain this effect.

Marine polyprenylated hydroquinones, quinones, and chromenols with inhibitory effects on leukotriene formation

A series of polyprenylated hydroquinones, quinones, and chromenols were isolated from the extracts of the marine sponge Ircinia spinosula and the brown alga Taonia atomaria, which gave rise to the constituents 1-4 and 5-8, respectively. Compounds 1, 2, 6, and 7 are new natural products, which were fully characterized. Their anti-inflammatory activities in terms of leukotriene formation were evaluated in an in vitro assay with pork leukocytes. The new hydroxylated compound, 2'-[28-hydroxy]heptaprenyl-1',4'-hydroquinone (= 2-[(2E,6E,10E,14E,18Z,22E)-19-(hydroxymethyl)-3,7,11,15,23,27-hexamethyloctacosa-2,6,10,14,18,22,26-heptaen-1-yl]benzene-1,4-diol; 1), the known tetraprenyl benzoquinone sargaquinone (5), and the known polyprenyl chromenols 3 and 4 exhibited the highest anti-inflammatory activities, with IC50 values of 1.9-9.4 microM (Table 3). Potential structure-activity relationships (SAR) are discussed.

The Molecular Mechanism of Bee Venom Phospholipase A2 Inactivation by Bolinaquinone

The molecular basis of the inactivation of bee venom PLA2 by the marine natural product bolinaquinone (BLQ) was studied by several spectral techniques (CD, fluorescence, and NMR spectroscopy, mass spectrometry), biomimetic reactions, and molecular modeling. Our data suggest competitive inhibition based on a BLQ-PLA2 noncovalent molecular recognition. However, BLQ is also able to react selectively with Lys133 through conjugate addition followed by a beta elimination. The biological implications of both the covalent and noncovalent molecular events are discussed.

Novel Synthesis of Prenylated Phenols and Their Antioxidant Properties

A novel method for the prenylation of phenols has been developed using 2-methyl-but-3-ene-2-ol as the prenylating agent in the presence of Amberlyst 15. The prenylated catechols and quinols showed better antioxidant activity than the corresponding non-prenylated compounds in the in vitro DPPH and lipid peroxidation assay. The resorcinol derivatives did not show significant antioxidant activity.

Reactivity and biological activity of the marine sesquiterpene hydroquinone avarol and related compounds from sponges of the order Dictyoceratida

A review of results of bioactivity and reactivity examinations of marine sesquiterpene (hydro)quinones is presented. The article is focused mostly on friedo- rearranged drimane structural types, isolated from sponges of the order Dictyoceratida. Examples of structural correlations are outlined. Available results on the mechanism of redox processes and examinations of chemo- and regioselectivity in addition reactions are presented and, where possible, analyzed in relation to established bioactivities. Most of the bioactivity examinations are concerned with antitumor activities and the mechanism thereof, such as DNA damage, arylation of nucleophiles, tubulin assembly inhibition, protein kinase inhibition, inhibition of the arachidonic cascade, etc. Perspectives on marine drug development are discussed with respect to biotechnological methods and synthesis. Examples of the recognition of validated core structures and synthesis of structurally simplified compounds retaining modes of activity are analyzed.

Polyprenyl-hydroquinones and -furans from three marine sponges inhibit the cell cycle regulating phosphatase CDC25A

The CDC25 phosphatases regulate the cell division cycle by controlling the activity of cyclin-dependent kinases. While screening for inhibitors of phosphatases among natural products we repeatedly found that some polyprenyl-hydroquinones and polyprenyl-furans (furanoterpenoids) (furospongins, furospinosulins) were potent CDC25 phosphatase inhibitors. These compounds were extracted, isolated and identified independently from three sponge species (Spongia officinalis, Ircinia spinulosa, Ircinia muscarum), collected at different locations in the Mediterranean Sea. The compounds were inactive on the Ser/Thr phosphatase PP2C-alpha and on three kinases (CDK1, CDK5, GSK-3), suggesting that some potent and selective CDC25 phosphatase might be designed from these initial structures.

Antioxidant potential of natural and synthesised polyprenylated hydroquinones

The metabolites 2-octaprenyl-1,4-hydroquinone (1) and 2-(24-hydroxy)-octaprenyl-1,4-hydroquinone (2), isolated from the sponge Ircinia spinosula, along with a series of synthetic derivatives, were evaluated for their antioxidant capacity, in order to establish a potential relationship between structural characteristics and antioxidant activity. The antioxidant potential of both natural and synthesised compounds was evaluated in vitro by their ability: (1) to interact with the stable free 1,1-diphenyl-2-picrylhydrazyl radical (DPPH) and (2) to inhibit the peroxidation, induced by the Fe(++)/ascorbate system, of heat inactivated hepatic microsomal membrane lipids. Metabolite 1 presented a strong interaction with DPPH and had a moderate effect on lipid peroxidation, while metabolite 2 interacted extensively with DPPH and exhibited a significant effect against lipid peroxidation. All derivatives retaining the free 1,4-hydroquinone system maintained fully or partly the free radical scavenging capacity.

Anti-inflammatory activity in mice of extracts from Mediterranean marine invertebrates

The effects of dichloromethane and methanol extracts from the marine invertebrates Leptogorgia ceratophyta, Holothuria tubulosa, Coscinasterias tenuispina and Phallusia fumigata on carrageenan-induced paw oedema in mice were investigated. The dichloromethane extract of Coscinasterias tenuispina and the methanol extract of Holothuria tubulosa administered p.o. at 50, 100 and 150 mg/kg, inhibited oedema in a dose-dependent manner 3 h after administration of carrageenan. Both extracts partially decreased elastase activity and PGE2 levels measured in homogenates from inflamed paws, without affecting the levels of this prostanoid present in stomach homogenates. As observed with the selective inhibitor NS398, both extracts can decrease cyclo-oxygenase activity in inflamed tissues but do not modify the constitutive cyclo-oxygenase enzyme. Therefore, these extracts represent new marine resources for the isolation of novel agents active on inflammatory conditions.