Salacia reticulata and its polyphenolic constituents with lipase inhibitory and lipolytic activities have mild antiobesity effects in rats

Salacia (S.) reticulata, a Hippocrateaceae plant distributed in Sri Lankan and Indian forests, has been used as a supplementary food in Japan to prevent obesity and diabetes. We examined the antiobesity effects of the hot water-soluble extract (SRHW) from the roots of S. reticulata using obese rat models and an in vitro study. Body weight (P = 0.07) and periuterine fat storage (P = 0.10) in female Zucker fatty rats (8-9 wk old) tended to be suppressed by oral administration of SRHW (125 mg/kg) for 27 d. Male rats fed a high fat diet were not affected by SRHW. Furthermore, SRHW inhibited porcine pancreatic iipase (PL), rat adipose tissue-derived lipoprotein lipase (LPL) and glycerophosphate dehydrogenase (GPDH) activities with 50% inhibitory concentrations (IC50) of 264 (95% confidence limits: 203-393) mg/L, 15 (12-18) mg/L and 54 (35-85) mg/L, respectively, but did not inhibit hormone-sensitive lipase activity in rat adipose tissue. Next, we examined the effects of polyphenols, di- and triterpenes and salacinol isolated from the roots of S. reticulata on lipid metabolizing enzymes and lipolysis. (-)-Epigallocatechin and (-)-epicatechin-(4beta-->8)-(-)-O-methylepigallocatechin inhibited PL activity with IC50 of 88 (not calculated) and 68 (26-122) mg/L, respectively. (-)-Epicatechin, 3beta,22beta-dihydroxyolean-12-en-29-oic acid and the tannin fraction inhibited LPL activity with IC50 of 81 (54-214), 89 (62-214) and 35 (24-62) mg/L. Only the tannin fraction inhibited GPDH activity with an IC50 of 6.8 (3.4-10.9) mg/L. These constituents may be involved in the lipase and GPDH inhibitory activities of SRHW. On the other hand, SRHW at 100 mg/L tended to enhance lipolysis in rat adipocytes (P = 0.06). Significant lipolytic effects were exerted by mangiferin, (-)-4'-O-methylepigallocatechin and maytenfolic acid at 100 mg/L (P < 0.01). In conclusion, polyphenolic compounds may be involved in the antiobesity effects of SRHW in rats through inhibition of fat metabolizing enzymes (PL, LPL and GPDH) and enhanced lipolysis.