糙薏仁的活性區分物對倉鼠脂質代謝之研究

Abstract

本研究係選用國產台中選育四號品系糙薏仁為原料，進行糙薏仁的活性區分物對倉鼠脂質代謝的相關研究。首先，在探討糙薏仁攝取量對倉鼠降血脂作用的影響，結果顯示以20及40%的糙薏仁取代高脂飼料 (10% corn oil + 1.0% cholesterol)餵食倉鼠，四週後可降低倉鼠血漿脂質濃度，而八週後除可降低倉鼠血漿脂質外，亦會減少肝臟TC與TG含量並促進糞便脂質的排出。 再者，在探討糙薏仁的活性區分物對倉鼠脂質代謝的影響，結果顯示(ㄧ)糙薏仁經100℃、30 分鐘的熱水萃取區分，在20及40%的糙薏仁熱水萃取物(ABW)與20及50%的糙薏仁熱水萃渣(ABR)取代高脂飼料(10% corn oil + 0.25% cholesterol)，均對倉鼠具有降血脂作用，故無法藉由熱水萃取區分方式區分出糙薏仁降血脂作用的活性成分所在。(二)糙薏仁以甲醇萃取並再以正己烷、乙酸乙酯及正丁醇等不同極性溶劑進行分配區分，甲醇萃取物(AM)的萃取率多寡會影響其抑制膽固醇酯轉移蛋白(cholesteryl ester transfer protein, CETP)活性的能力與降血脂作用的效果。在體外及動物試驗同時顯示乙酸乙酯層及正丁醇層區分物的抑制CETP活性較甲醇萃取物為強，其IC50分別為55μg /mL及65μg /mL。另，正己烷層區分物（AM-H）或水層區分物（AM-W）或其甲醇萃取渣的水萃物（AMR-W）等三種區分物亦具有降血脂作用，就此推知糙薏仁降血脂作用是因多種不同極性活性成分作用所致。(三)糙薏仁的富含水溶性膳食纖維區分物(ACF)具有降血脂的作用且呈現劑量關係，而其40%酒精次區分之不可溶及可溶區分物(ACF-EI和ACF-ES)亦具降血脂作用但會受理化性質的差異而有所不同。ACF、ACF-EI和ACF-ES 的分子量分別為12.4、14.5和8.7 x 104 Daltons。另外，糙薏仁的75%酒精可溶性區分物（ACE）可提高血漿HDL-C濃度，其作用機制可能為抑制CETP活性，惟其組成分仍有待進一步研究。正己烷萃取區分物(AH)亦具有降血脂的生理機能性。糙薏仁中所含的Campesterol、Stigmasterol及Sitosterol三種植物固醇含量分別為65±10，34±7及445±36 mg/100g。 綜合言之，糙薏仁對倉鼠脂質代謝的活性區分物有其富含水溶性膳食纖維、甲醇、正己烷與75%酒精之可溶性區分物。

In this study, we used the Taichung select No.4 dehulled adlay (Coix lachryma-jobi L. var. ma-yuen Stapf) as our experimental material to investigate the dehulled adlay active fractions on the lipid metabolism in hamsters. First, we examined the hypolipidemic effect in hamsters fed high fat diets (10% corn oil + 1.0% cholesterol) that was substituted with different percents of dehulled adlay for 4 or 8 weeks. The results showed that after 4 weeks feeding period, 20 and 40% dehulled adlay substituted high fat diets could lower serum lipids concentration in hamsters. After 8 weeks, we found that 20 and 40% diet groups lowering levels of serum lipids and hepatic TC, TG and also showed increaseing fecal lipids excretion in hamsters. Second, we investigated the dehulled adlay active fractions on the lipid metabolism in hamsters. The results showed that (1) the dehulled adlay extracted by 100℃ water for 30 min to obtain hot water-soluble fraction (ABW) and hot water-insoluble fraction (ABR). As hamsters fed with high fat diets (10% corn oil + 0.25% cholesterol) that were substituted 20, 40% ABW and 20, 50% ABR, showed hypolipidemic effect. So we could not isolate the hypolipidemic active components by means of fractionating dehulled adlay with boiling water extraction. (2) The dehulled adlay extracted by methanol and fractionated by n-hexane, ethyl acetate, 1-butanol and water. The methanol extract (AM) had lipid-lowering effect and reduced the plasma cholesteryl ester transfer protein (CEPT) activity, and that might be related with the ratio of extraction. As compared with AM, the AM-EA and AM-B fractions significantly inhibited the CETP activity in vitro and in vivo. Their IC50 were 55μg /mL and 65μg /mL. Moreover, 3 groups of hamsters were fed with AM-H, AM-W and AMR-W and the results showed different hypolipidemic effects. Therefore, our results demonstrated that the hypolipidemic effect of dehulled adlay was due to various active components. (3) The water-soluble dietary fiber enriched fraction of dehulled adlay (ACF) showed a hypolipidemic effect in hamsters and which was positively correlated with the amount of ACF. The insoluble and soluble fractions (ACF-EI and ACF-ES, respectively) of ACF that prepared by 40% ethanol concentration fractionation also showed hypolipidemic effects and which was influenced with their physicochemical properties. The apparent molecular-weights of ACF-EI and ACF-ES were 14.5 and 8.7 x 104 Daltons, respectively. Furthermore, the adlay 75% alcohol soluble fraction (ACE) could elevated plasma HDL cholesterol concentraction, and the possible hypolipidemic mechanism was due to its inhibitory CETP activity and further investigation about its active composition is needed. The hexane fraction (AH) of dehulled adlay also showed a hypolipidemic effect. The contents of 3 phytosterols, i.e. campesterol, stigmasterol and sitosterol in the dehulled adlay were 65±10, 34±7, 445±36 mg/100g, respectively. In conclusion, we demonstrated that the dehulled adlay active fractions on the lipid metabolism in hamsters were their water-soluble dietary fiber enriched, and methanol, n-hexane and 75％ alcohol soluble fractions.