Toshiaki Ichimura

Angiotensin I-converting enzyme inhibitory activity and insulin secretion stimulative activity of fermented fish sauce

Angiotensin I-converting enzyme (ACE) inhibitory peptides, Ala-Pro, Lys-Pro, and Arg-Pro, were isolated from fermented fish sauce. Five other proline-containing dipeptides having weak ACE inhibitory activity were also isolated from the fermented fish sauce. Orally administered Lys-Pro showed a tendency to lower the blood pressure of spontaneously hypertensive rats. As fermented anchovy sauce also stimulated insulin secretion by cultured RINm5F insulinoma cells, the sauce may be useful as a source of biologically active substances.

Antihypertensive Effect of an Extract of Passiflora edulis Rind in Spontaneously Hypertensive Rats

Orally administered methanol extract of Passiflora edulis rind (10 mg/kg or 50 mg/kg) or luteolin (50 mg/kg), which is one of consistent polyphenols of the extract, significantly lowered systolic blood pressure in spontaneously hypertensive rats (SHRs). Quantitative analysis by liquid chromatography tandem mass spectrometry (LC-MS/MS) showed that the extract contained 20 μg/g dry weight of luteolin and 41 μg/g dry weight of luteolin-6-C-glucoside. It also contained γ-aminobutyric acid (GABA, 2.4 mg/g dry weight by LC-MS/MS or 4.4 mg/g dry weight by amino acid analysis) which has been reported to be an antihypertensive material. Since the extract contained a relatively high concentration of GABA, the antihypertensive effect of the extract in SHRs might be due mostly to the GABA-induced antihypertensive effect and partially to the vasodilatory effect of polyphenols including luteolin.

Antihypertensive effect of enzymatic hydrolysate of collagen and Gly-Pro in spontaneously hypertensive rats

Continuous oral feeding of enzymatic hydrolysate of porcine skin collagen showed an antihypertensive effect in spontaneously hypertensive rats (SHRs). We isolated an angiotensin I-converting enzyme (ACE) inhibitory peptide, Gly-Phe-Hyp-Gly-Pro (IC50=91 μM), from the hydrolysate, but the ACE inhibitory activities of the other peptides isolated were weak. Although the ACE inhibitory activity of Gly-Pro (IC50=360 μM) was not potent, Gly-Pro exists in collagen as a large number of repeated sequences. We then examined the antihypertensive effect of Gly-Pro. Orally administered Gly-Pro at 500 mg/kg significantly decreased the blood pressure of SHRs, and at 50 mg/kg it also showed a tendency to lower the blood pressure. Oral administration of Gly-Phe-Hyp-Gly-Pro (10 or 30 mg/kg) also decreased the blood pressure of SHRs.

Luteolin Inhibits Endothelin-1 Secretion in Cultured Endothelial Cells

We discovered that luteolin, a typical flavonoid contained in various kinds of plants, inhibits the secretion and gene expression of endothelin-1 (ET-1), a potent vasoconstrictor regulating blood pressure, in porcine aortic endothelial cells. Its ED50 was about 10 μM. In addition, the inhibition of ET-1 by a glycoside compound of luteolin (luteolin-6-C-glucoside) was weak.

A synthetic polymer, poly(2-methacryloyloxyethyl phosphorylcholine-co-n-stearyl methacrylate), stimulates insulin release from RINm5F insulinoma cells

A water-soluble phospholipid-like polymer, poly(2-methacryloyloxyethyl phosphorylcholine-co-n-stearyl methacrylate) (PMC18, average molecular weight = 4.3×104), at a concentration (0.5–5 mg/ml) showing no inhibition of cell proliferation, stimulated insulin release from RINm5F rat insulinoma cells in a concentration- and time-related manner. But poly(2-methacryloyloxyethyl phosphorylcholine) and other synthetic phospholipid-like polymers failed to stimulate insulin release.

Effects of Poly (amino acid) s on Photophosphorylation in a Cyanobacterial Thylakoid

National Chemical Laboratory for Industry, 1-1 Higashi, Tsukuba-shi 305, Japan Poly-L-glutamic acid accelerated by about 25% the cyclic photophosphorylation in the thylakoid a thermophilic cyanobacterium. A mixture of poly-L-glutamic acid and poly-L ornithine of a ratio 2/1 (w/w) also enhanced by 20-30% the photophosphorylation. The acceleration behaviors by poly-L-glutamic acid alone are different from those by the mixture of acidic and basic poly (amino acid) s.

Effects of basic poly(amino acid)s on a photosynthetic membrane system of a cyanobacterium.

Effects of basic poly (amino acid) s on the photosynthetic activities of the thylakoid membranes of thermophilic cyanobacterium Synechococcus sp. were examined. Poly-L-ornithine, poly-L-arginine, poly-L-lysine and poly-D-lysine uncouple the thylakoid membranes, dissipating ΔpH generated across the membranes and inhibiting cyclic photophosphorylation mediated by phenazine methosulfate. Contrary to the previous reports with some algae, poly-L-ornithine, poly-L-lysine and poly-D-lysine inhibit photosystem 1-dependent electron flow from tetramethyl-p-hydroquinone to methylviologen, presumably by affecting the function of soluble acidic protein cytochrome c-553. Poly-L-histidine gives no effect on photochemical activities of the cyanobacterial thylakoid membranes.