Apolipoproteins play a central role in transport and metabolism of lipids in animals. We investigated the regulatory mechanisms responsible for expression of apolipoproteins in the small intestine. Animal experiments using surgical procedures suggested that the biliary component is a luminal factor regulating apolipoprotein A-IV expression in the intestine. In addition, peptide YY stimulated the apolipoprotein A-IV expression in Caco-2 intestinal cells in a dose- and time-dependent manner, suggesting that peptide YY is a humoral factor regulating the expression of apolipoprotein A-IV. Furthermore, intravenous infusion of hexamethonium and atropine, but not propranolol, diminished apolipoprotein A-IV mRNA levels in the rat ileum, suggesting the presence of basal cholinergic stimulatory expression of the apolipoprotein A-IV gene in the ileum. In conclusion, we propose that expression of apolipoprotein A-IV in the intestine is regulated by luminal, humoral, and neural factors. We also discuss the relationship between the hypocholesterolemic action of dietary beet fiber and hepatic expression of the apolipoprotein A-I gene in rats.
Although buckwheat protein has high biological value, its digestibility is relatively low. We have found that this low digestibility is closely associated with its hypocholesterolemic activity in cholesterol-fed rats. This prompted us to investigate the possibility that buckwheat protein has dietary fiber-like effects, including anti-constipation, anti-obesity, and anti-tumor effects. The results we obtained supported this possibility. The silk protein, sericin, is also resistant to several proteases, and has a number of physiological functions such as strong water-holding capacity and antioxidant activity. These properties suggest that it would exert protective effects against constipation and colon carcinogenesis. In view of these facts, we postulated that low digestibility of dietary protein might improve the functions of the intestine and be beneficial for human health. By drawing an analogy with resistant starch, we propose that buckwheat protein and sericin might be “resistant proteins”, and discuss their physiological significance.
The procedures for preparing a food material with antihypertensive efficacy from sardine muscle have been reviewed. Hydrolysis of sardine muscle by pepsin yielded angiotensin I-converting enzyme (ACE)-inhibitory peptides. Further studies aimed at preparing a hydrolyzate with potent ACE-inhibitory activity as well as having good flavor were carried out using Bacillus licheniformis alkaline protease. After 17h of hydrolysis of 0.3wt% sardine protein, the 10wt% ethanol fraction obtained with ODS resin showed some excellent properties, including strong ACE-inhibitory activity (IC50=0.015mg protein/mL), high digestive resistance, no bitterness, and no antigenicity. In addition, this fraction was confirmed to have a significant in vivo depressor effect in mildly hypertensive volunteers (n=29), who showed a 9.3mmHg reduction in systolic blood pressure and 5.2mmHg reduction in diastolic blood pressure after 4 weeks of oral administration of this peptide drink (4g of the ODS fraction/200mL/day).
The intake of dietary fiber necessary for amelioration of hypercholesterolemia and prevention of ischemic heart disease and diabetes mellitus was tentatively assessed by searching articles from databases on the Internet such as Medline, Chemical Abstracts, etc. The values obtained were much higher than those in the Recommended Dietary Allowances for the Japanese, Sixth Revision, in which 20-25g/day (10g/1, 000kcal) is set as the adequate dietary intake level for adults. In view of the average intake of dietary fiber among Japanese people, which is assumed to be about 16g/day, efforts should be made to attain at least the recommended level. In addition, as the amelioration and prevention of the above disorders are accomplished by water-soluble dietary fiber, the intake of this type of fiber, as well as total dietary fiber, should be increased.