Stigmasterol- an Acetylcholinesterase Inhibitor from Phormidium retzii with relevance to Alzheimer's disease Therapy.

This study observed in vitro screening, purification and identification of cholinesterase inhibitors from the microalgae Phormidium retzii. Mixed microalgal culture was screened from freshwater samples for Phormidium sp. Single colony was purified and authenticated as P. retzii. Acetylcholinesterase (AChE) enzyme was purified from hRBC ghost. Sequential extraction of P. retzii was performed using organic solvents. Cholinesterase enzyme activity and its inhibition by various extracts were then tested. The active fractions were then subjected to partial purification and characterization. Petroleum ether extract of P. retzii showed maximum inhibition of 68.6 % against AChE while other solvent extracts showed no inhibition. Seven fractions were obtained from the active extract using thin layer chromatography. Among which fraction no. 5 showed maximum inhibition of 86.37 % towards AChE. Fraction no. 5 when subjected to GC-MS led to determination of the active principle as stigmasterol. The maximum inhibition of stigmasterol (0.45µM) was 81.2±0.08% with IC50 value of 0.214. Stigmasterol from P. retzii inhibited AChE projecting itself as safer drug for Alzheimer's disease with minimal side effects.