Neuroprotective effect of seaweeds inhabiting South Indian coastal area (Hare Island, Gulf of Mannar Marine Biosphere Reserve): Cholinesterase inhibitory effect of Hypnea valentiae and Ulva reticulata

Alzheimer's disease (AD) is the most common form of dementia, which is one of the four leading causes of death in developed nations. Until date the only symptomatic treatment for this disease is based on the “cholinergic hypothesis” where the drugs enhance acetylcholine levels in the brain by inhibiting acetylcholinesterase (AChE). In the course for screening cholinesterase inhibitors about eight seaweeds, with wide pharmaceutical applications, were collected from Hare Island, Gulf of Mannar, Marine Biosphere Reserve, Tamil Nadu, India. Inhibitory effect of methanol extract of the seaweeds was studied in vitro by incubating various concentration of the extract with AChE or butyryl cholinesterase (BuChE) and assessing their activities by Ellman's colorimetric method. Kinetic parameters like IC50, Ki and Vmax were also analyzed. The results showed that of the eight seaweeds screened Hypnea valentiae, Padina gymnospora, Ulva reticulata and Gracilaria edulis exhibited inhibitory activity to AChE with IC50 value of 2.6, 3.5, 10 and 3 mg/ml respectively, while H. valentiae, Enteromorpha intestinalis, Dictyota dichotoma and U. reticulata showed 50% inhibition to BuChE at concentration 3.9, 7, 6.5 and 10 mg/ml respectively. The inhibitory activities of the seaweed extracts were comparable to the standard drug donepezil. Enzyme kinetic analysis showed that algal extracts exhibited mixed type inhibition (partial noncompetitive inhibition).