In vitro enzyme inhibitory effects of green and brown Australian seaweeds and potential impact on metabolic syndrome

Hypertension, type-2-diabetes (T2D) and obesity are contributory risk factors for the development of metabolic syndrome. Peptides, polyphenols and polysaccharides may inhibit enzymes involved in the disease pathways of this disorder. Peptide hydrolysates (PEP), polyphenol (PP) and polysaccharide (PS) extracts generated from the Australian seaweeds Phyllospora comosa (Labillardiere) C. Agardh, Ecklonia radiata (C. Agardh) J. Agardh, and Ulva ohnoi M. Hiraoka & S. Shimada were screened in vitro for their potential to inhibit enzymes important in the control of diseases associated with metabolic syndrome. These enzymes include angiotensin-I-converting enzyme (ACE-1; EC 3.4.15.1) which affects the development of hypertension in mammals, alpha-amylase (EC 3.2.1.1) and lipase (EC 3.1.1.3) which play a role in the development of T2D and dietary lipid absorption, respectively. The inhibitory activity of each seaweed extract was determined using established in vitro colorimetric methods with mammalian-derived enzymes and their respective substrates. The ACE-1 half-maximal inhibitory (IC50) concentrations of generated bioactive extracts ranged from 167.52 +/- 3.17 mu g mL(-1) (U. ohnoi PEP) to 713.84 +/- 12.45 mu g mL(-1) (E. radiata PS). None of the extracts screened displayed IC50 values comparable to the positive control drug Captopril (8.87 +/- 0.04 mu g mL(-1)). IC50 values determined for extracts that inhibited alpha-amylase ranged from 58.31 +/- 1.41 mu g mL(-1) (P. comosa PP) to 515.24 +/- 10.53 mu g mL(-1) (E. radiata PEP). All PS and PP had significantly lower IC50 values than the alpha-amylase inhibitor control, Acarbose (89.90 +/- 0.15 mu g mL(-1)). Lipase IC50 values determined for extracts ranged from 52.14 +/- 2.77 mu g mL(-1) (P. comosa PP) to 876.30 +/- 34.92 mu g mL(-1) (E. radiata PEP). All PP had significantly lower IC50 values than the lipase inhibitory drug Orlistat (70.83 +/- 0.07 mu g mL(-1)). To the authors' knowledge there are no published values for the inhibitory potential of P. comosa, E. radiata or U. ohnoi extracts against the enzymes ACE-1, alpha-amylase, or lipase. These findings demonstrate the functional food potential of P. comosa, E. radiata and U. ohnoi polyphenols, polysaccharides and peptides.