Purpose and Methods In this study, the analgesic activity of the crude alcohol (acetone-methanol) and aqueous (in PBS, pH 7.2) extracts of the marine molluscs, Pachymelania aurita and Tympanotonus fuscatus, has been evaluated using the formalin test (for chronic antinociceptive) and the tail-flick (acute antinociceptive) pain models in male swiss albino mice. Results The results show that the extracts of P. aurita and T. fuscatus demonstrated high safety margins as single doses of up to 2000 mg/kg bwt proved to be well tolerated and non-lethal, although the alcohol extract of P. aurita caused necrosis in the liver and kidney when administered at a dose level of 2000 mg/kg bwt. In the formalin test, treatment with the aqueous extracts of P. aurita and T. fuscatus as well as the alcohol extract of T. fuscatus 30 min before the subcutaneous injection of 5% formalin to the paw of the mice resulted in a significant time- and dose-dependent reduction in total and phase 2a pain-related behavior and thus nociception. The extracts had no analgesic effect in tail-flick test up to the highest dose tested. Conclusion Hence, the results from both models indicate that the site of their analgesic action is probably peripheral.

Marine organisms make up approximately half of the total global biodiversity, with the Mollusca containing the second largest number of species, including snails and bivalves. The marine environment is highly competitive, hostile and aggressive, which has led to the production of specific and potent bioactive compounds by the mollusca and their associated microorganisms, in a bid to protect themselves and ensure their survival. A diverse array of bioactive compounds can be isolated from the extracts of marine molluscs of which linear, cyclic, and conjugated peptides and depsipeptides form some of the most important bioactive compounds that have been well characterized and some of have already reached clinical trials or been approved for use as therapeutic agents and supplements. This review highlights some of the bioactive peptides that have been obtained from marine molluscs as well the challenges facing bioprospecting of valuable peptides from marine mollusc sources.

Low molecular weight peptides are among the most active bioactive components that have been isolated from marine molluscs. Currently, peptides isolated from molluscs as well as their synthetic structural analogues are in clinical trials as anticancer compounds and have been approved for use in pain management. These Bioactive peptides have also been demonstrated to exhibit antioxidant activities. This study aimed at isolating and profiling the low molecular weight peptide fractions from extracts of two common marine molluscs; P. aurita and T. fuscatus obtained from the Niger-Delta region of Nigeria. This study also investigated the free radical scavenging activity of the isolated fraction. Fourier Transform Infrared Spectroscopy analysis was carried out to determine the chemical entities and common functional groups found in the extracts. The Low molecular weight peptides were isolated using Molecular sieve chromatography, while the peptide profiles were established using SDS-PAGE and Thin Layer Chromatography (TLC). The free radical scavenging potential of the peptides was also assessed qualitatively using TLC, with DPPH as stain. The results show the presence of several low molecular weight peptides in the extracts of both P. aurita and T. fuscatus. Yellow spot on a purple background, indicating antioxidant activity was observed in the TLC plates sprayed before the chromatographic run. This activity was lost on further separation, indicating a synergistic effect. Further studies to effectively separate these fractions into individual peptides, investigate the synergistic effect observed as well as further explorations of possible bioactivity of these peptides is required.

Context: Multifunctional food protein-derived peptides attract a great deal of research interest due to their health-promoting benefits. Particularly, peptides that have both antihypertensive and antioxidant properties are desired, since both effects can be synergistic in prevention of cardiovascular diseases. Aim: The aim of this study was to investigate the angiotensin-I-converting enzyme (ACE) inhibitory and 2,2 ′ -diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities of two species of the Nigerian periwinkles: Pachymelania aurita and Tympanotonus fuscatus . Methods: The ACE inhibitory and 2,2 ′ -diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities of simulated gastrointestinal digestion (SGID) hydrolysates and ultrafiltered (UF) fractions of T. fuscatus var. radula and P. aurita were determined. Human SGID of the protein extracts of T. fuscatus and P. aurita was carried out using pepsin, trypsin, and chymotrypsin, and the hydrolysates were fractionated into two by centrifugal ultrafiltration. The ACE inhibitory and DPPH radical scavenging activities of the crude hydrolysates and UF fractions were tested. The UF permeates were observed to have relatively higher activities and was subjected to gel filtration chromatography on Sephadex G-50. The chromatographic fractions showed absorbance at 215, 225, and 280 nm and were assayed for DPPH radical scavenging activity. Results: The inhibitory effect of the fractions on ACE activity was reported as the minimum concentration of extract that caused 50% of the inhibition (IC 50 ), where the IC 50 values of P. aurita UF permeate and P. aurita UF retentate were 65.2 ± 6.4 and 301.9 ± 59.1 μg/ml, respectively, and that of T. fuscatus UF permeate (TFUFP) and T. fuscatus UF retentate were 54.93 ± 2.83 and 291.7 ± 8.6 μg/ml, respectively. Conclusion: This study suggests the potential health benefits of consuming T. fuscatus var. radula and P. aurita in health maintenance.