Physicochemical properties of heme iron products in the Korean market.

Since absorption efficacy of heme iron (HI) is critically dependent on its solubility in aqueous solution, we investigated the physicochemical properties of two HI products available in the Korean market. The two HI products did not differ in ingredients and color. However, HI polypeptide (HIP), produced in Korea, was fairly soluble over a wide pH range in water-based solutions, whereas HI imported from Japan was insoluble except in strong acid and base solutions. Analysis using an ultraviolet-visible spectrophotometer showed that the chromophore of HIP was shifted to the red compared with that of HI. Fourier transform-infrared analysis revealed that HIP contained mainly amide (NH) groups, while HI largely contained amine (NH(2)) groups. With regard to constituents, between HIP and HI, their major components were different from each other according to their ratio of fronts obtained by thin-layer chromatography. These results suggest that determination of solubility should be included in the quality control process of HI products.

Antidiabetic effect of a prodrug of cysteine, L-2-oxothiazolidine-4-carboxylic acid, through CD38 dimerization and internalization.

CD38 is a bifunctional enzyme synthesizing (ADP-ribosyl cyclase) and degrading (cyclic ADP-ribose (cADPR) hydrolase) cADPR, a potent Ca(2+) mobilizer from intracellular pools. CD38 internalization has been proposed as a mechanism by which the ectoenzyme produced intracellular cADPR, and thiol compounds have been shown to induce the internalization of CD38. Here, we show that the disulfide bond between Cys-119 and Cys-201 in CD38 may be involved in CD38 dimerization and internalization. We tested the effect of a reducing agent, l-2-oxothiazolidine-4-carboxylic acid (OTC), a prodrug of cysteine, on CD38 internalization in pancreatic islets. OTC enhanced insulin release from isolated islets as well as CD38 internalization and cytoplasmic Ca(2+) level. Furthermore, islet cells treated with antisense CD38 oligonucleotide showed inhibition of OTC-induced insulin secretion. Intake of OTC in db/db mice ameliorated glucose tolerance, insulin secretion, and morphology of islets when compared with control mice. These data indicate that OTC improves glucose tolerance by enhancing insulin secretion via CD38/cADPR/Ca(2+) signaling machinery. Thus, OTC may represent a novel class of antidiabetic drug.