Characterization and bioactive potentials of secondary metabolites from mollusks Crassostrea madrasensis and Amphioctopus marginatus

Sulphated glycosaminoglycan isolated from the edible slipper oyster Magallana bilineata (Röding, 1798) attenuates inflammatory cytokines on lipopolysaccharide-prompted macrophages

The slipper oyster Magallana bilineata (Ostreidae) is considered as culinary delicacy among marine bivalves, and a sulphated glycosaminoglycan, 4,6-O-SO3-β-(1→3)-GalNAcp (unit A) and β-(1→4)-GlcAp (unit B) as principle structural motif containing laterally branched 4-O-SO3-β-glucopyranose (unit C) (MBP-3) was isolated from this species. Nuclear magnetic resonance (NMR), Fourier transform infra-red (FTIR), and mass spectroscopy techniques were used to characterise MBP-3. MBP-3 exhibited anti-inflammatory activities against inflammatory 5-lipoxygenase (IC50 0.11 mg mL-1) and cyclooxygenase-2 (IC50 0.12 mg mL-1) enzymes. MBP-3 (at 100 μg mL-1) showed effective downregulation against pro-inflammatory cytokines generation, namely interleukins-6, 1β, (IL-6, 1β) (1-1.7 pg mL-1) and tumour necrosis factor-α (TNF-α) (4 pg mL-1) along with substantial downregulation of ROS production in lipopolysaccharide (LPS)-inflamed cells. MBP-3 blocked the mRNA of NF-κB, cyclooxygenase-2 (COX-2), and other cytokines, in lipopolysaccharide-induced macrophages. The potential to constrain inflammatory cytokine production revealed its application to develop functional food to attenuate inflammation-associated disorders.

Anti-hyperglycemic Δ5 steroids, marginoids A-C from marine veined octopus Amphioctopus marginatus (Octopodidae): Prospective natural leads inhibit serineexopeptidase dipeptidyl peptidase-4

Three Δ⁵ steroid analogues, marginoids A-C were purified from the organic extract of marine veined octopus Amphioctopus marginatus (Taki, 1964) (family Octopodidae) distributed on the Asian and Mediterranean coasts. Their structures were elucidated as (5Z)-3β-acetoxy-cholesta-5-en-25-ethylene-22β-hydroxy-23,26-lactone (marginoid A), (5Z, 25Z)-3β-yl-(1'-(E)-3'-hydroxy-4'-methyl-hex-5'-enoate)-22-oxo-26-furanyl-cholesta-5,25-diene (marginoid B), and (5Z)-3β-yl-(7'-methoxypropan-8'-yl)-tetrahydro-2H-pyran-2-one-cholesta-5,24-dien (marginoid C) based on extensive spectroscopic experiments. Marginoid B with hydroxyl-methyl-hexanoate at the C-3 position in conjunction with the heterocyclic furanyl ring displayed superior anti-hyperglycemic properties as acknowledged by its promising serine protease dipeptidyl peptidase-4 attenuation potential (IC₅₀ 3.49 µM) displaying comparable activity with the standard DPP-4 inhibitor (DPP-4i) diprotin A (IC₅₀ 4.53 µM). The anti-hyperglycemic properties were corroborated by the promising antioxidant activities (IC₅₀ ∼ 0.8-1.0 mM) of these Δ⁵ steroids, marginoids A-C. Sizeably greater electronic properties, balanced hydrophobic-lipophilic properties (log P_OW 6.4-8.3), and comparatively lower steric factors were directly proportional to their bioactive properties. Molecular simulation studies in the binding sites of DPP-4 and lesser binding energy (-12.17 kcal/mol) and inhibition constant (Ki 1.20 nM) of marginoid B could be correlated with anti-hyperglycemic properties. Promising bioactivities of marginoid B isolated from A. marginatus are anticipated for nutraceutical applications against hyperglycemia.

Cistobislactone, an undescribed variant of 14-membered bislactonic macrodiolide, from old-lady octopus Cistopus indicus (family Octopodidae) attenuates inflammatory lipoxygenase

Chemical evaluation of specialised metabolites from the old-lady marine octopus Cistopus indicus (family Octopodidae) led to the isolation of an undescribed 14-membered bislactonic macrodiolide cistobislactone, which was characterized as 12-(4'-ethyl-6'-methoxy-3'-methyl-hex-1-enyl)-5,11-dihydroxy-6-methyl-1,7-dioxacyclotetradeca-3,9-diene-2,8-dione. Cistobislactone exhibited noticeably greater inhibitory potential against 5-lipoxygenase (IC₅₀ 2.06 mM) compared to standard anti-inflammatory agent ibuprofen (IC₅₀ 4.61 mM, p < 0.05). Superior antioxidant properties of cistobislactone against the oxidants (IC₅₀ ∼1.8 mM) also reinforced its promising anti-inflammatory activity. Higher electronic properties (topological polar surface area of 102.3) and balanced hydrophobicity (logarithm of octanol-water coefficient ∼3) could recognize its higher interaction at the enzyme active site resulting in an effective attenuation of 5-lipoxygenase and efficient inter-membrane permeability. Comparatively lesser binding energy (-6.5 kcal mol^-1) and docking score (-7.5 kcal mol^-1) of cistobislactone with the aminoacyl residues of 5-lipoxygenase could further recognize its anti-inflammatory potential.

Marine natural products

This review covers the literature published in 2019 for marine natural products (MNPs), with 719 citations (701 for the period January to December 2019) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1490 in 440 papers for 2019), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. Methods used to study marine fungi and their chemical diversity have also been discussed.

Molluscan Compounds Provide Drug Leads for the Treatment and Prevention of Respiratory Disease

Respiratory diseases place an immense burden on global health and there is a compelling need for the discovery of new compounds for therapeutic development. Here, we identify research priorities by critically reviewing pre-clinical and clinical studies using extracts and compounds derived from molluscs, as well as traditional molluscan medicines, used in the treatment of respiratory diseases. We reviewed 97 biomedical articles demonstrating the anti-inflammatory, antimicrobial, anticancer, and immunomodulatory properties of >320 molluscan extracts/compounds with direct relevance to respiratory disease, in addition to others with promising bioactivities yet to be tested in the respiratory context. Of pertinent interest are compounds demonstrating biofilm inhibition/disruption and antiviral activity, as well as synergism with approved antimicrobial and chemotherapeutic agents. At least 100 traditional medicines, incorporating over 300 different mollusc species, have been used to treat respiratory-related illness in cultures worldwide for thousands of years. These medicines provide useful clues for the discovery of bioactive components that likely underpin their continued use. There is particular incentive for investigations into anti-inflammatory compounds, given the extensive application of molluscan traditional medicines for symptoms of inflammation, and shells, which are the principal molluscan product used in these preparations. Overall, there is a need to target research toward specific respiratory disease-related hypotheses, purify bioactive compounds and elucidate their chemical structures, and develop an evidence base for the integration of quality-controlled traditional medicines.

High-value compounds from the molluscs of marine and estuarine ecosystems as prospective functional food ingredients: An overview

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Reviewed enthnomedical, nutritive and pharmacological profiles of molluscs.

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Gastropods and bivalves are potential sources of functional food.

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More than 1334 bioactive metabolites were reported from total of about 1287 publications.

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Molluscan derived metabolites were mostly belonged to terpenoids and sterols.

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Number of patents were increased to more than 30% during 2016–2019.

Extensive biodiversity and availability of marine and estuarine molluscs, along with their their wide-range of utilities as food and nutraceutical resources developed keen attention of the food technologists and dieticians, particularly during the recent years. The current review comprehensively summarized the nutritional qualities, functional food attributes, and bioactive properties of these organisms. Among the phylum mollusca, Cephalopoda, Bivalvia, and Gastropoda were mostly reported for their nutraceutical applications and bioactive properties. The online search tools, like Scifinder/Science Direct/PubMed/Google Scholar/MarinLit database and marine natural product reports (1984–2019) were used to comprehend the information about the molluscs. More than 1334 secondary metabolites were reported from marine molluscs between the periods from 1984 to 2019. Among various classes of specialized metabolites, terpenes were occupied by 55% in gastropods, whereas sterols occupied 41% in bivalves. The marketed nutraceuticals, such as Cadalmin^TM green mussel extract (Perna viridis) and Lyprinol® (Perna canaliculus) were endowed with potential anti-inflammatory activities, and were used against arthritis. Molluscan-derived therapeutics, for example, ziconotide was used as an analgesic, and elisidepsin was used in the treatment of cancer. Greater numbers of granted patents (30%) during 2016–2019 recognized the increasing importance of bioactive compounds from molluscs. Consumption of molluscs as daily diets could be helpful in the enhancement of immunity, and reduce the risk of several ailments. The present review comprehended the high value compounds and functional food ingredients from marine and estuarine molluscs.

Polygalactan from bivalve Crassostrea madrasensis attenuates nuclear factor-κB activation and cytokine production in lipopolysaccharide-activated macrophage

A polygalactosamino-glucopyranosyl fucopyranose →4)-β-GlcAp{(3→1)-α-Fucp}-β-GalNAcp-(4,6-SO₃^-)-(1→ isolated from the bivalve Crassostrea madrasensis exhibited prospective anti-inflammatory activity against cyclooxygenase-2 and 5-lipoxygenase (IC₅₀ < 50 μg mL^-1) on lipopolysaccharide-induced macrophages. The polygalactan attenuated inducible nitric oxide synthase (IC₅₀ 65.7 μg mL^-1) in lipopolysaccharide-prompted inflammation leading to the reduction of pro-inflammatory cytokine nitric oxide (236.2 μg mL^-1 lysate), nuclear factor-κB, tumor necrosis factor-α, and interleukins (0.19-0.22 units mg^-1 protein at 100 μg mL^-1) by inhibiting cyclooxygenase-2. The polygalacatan suppressed the mRNA of nuclear factor-κB and cyclooxygenase-2 in lipopolysaccharide-induced macrophages. Western blot experiment revealed that the polygalactan attenuated the migration of nuclear factor-κB-p⁶⁵ to the nucleus from cytoplasm, and suppressed the phosphorylation of α-subunit of κB inhibitor. Greater selectivity index of sulfated polygalactan (3.93) towards inducible cyclooxygenase-2 as compared with the anti-inflammatory agent ibuprofen (1.11), and the potential to inhibit nuclear factor-κB cascade to generate chemokine production manifested its utilization in the development of functional food attenuating inflammation-related disorders.

A new bis-γ-pyrone polypropionate of onchidiol family from marine pulmonate mollusk Onchidium sp

A new bis-γ-pyrone polypropionate, 4,16-di-epi-onchidiol (1), along with three known related compounds (2-4) were isolated from the marine pulmonate mollusk Onchidium sp. The structure of compound 1 was elucidated by extensive spectroscopic analysis and by comparison the NMR data with its stereoisomers 2-4, whereas its absolute configuration was determined by the combination of X-ray diffraction analysis and TDDFT-ECD calculation. In bioassay, the isolated compounds exhibited broad cytotoxicity against several cancer cell lines with IC₅₀ values ranging from 24.6 to 88.5μM.