Variation in human platelet glycoprotein VI content modulates glycoprotein VI-specific prothrombinase activity.

- Glycoprotein VI (GPVI) is a platelet-specific receptor for collagen that figures prominently in signal transduction. An addition to binding to type I and III collagens, GPVI is also bound specifically by collagen-related peptide and convulxin (CVX), a snake venom protein. We developed a quantitative assay of platelet GPVI in which biotin-conjugated CVX binds selectively to GPVI in separated total platelet proteins by a ligand blot procedure. Using this approach, we have documented a 5-fold range in platelet GPVI content among 23 normal healthy subjects. In addition, we have determined that CVX-induced or collagen-related peptide-induced prothrombinase activity is directly proportional to the platelet content of GPVI. A statistically significant correlation was observed at 2 CVX concentrations: 14.7 ng/mL (R(2)=0.854 and P<0.001, n=11) and 22 ng/mL (R(2)=0.776 and P<0.001, n=12). In previous studies, we established a similar range of expression of the integrin collagen receptor alpha(2)beta(1) on platelets of normal subjects. Among 15 donors, there is a direct correlation between platelet alpha(2)beta(1) density and GPVI content (R(2)=0.475 and P=0.004). In view of the well-documented association of GPVI with platelet procoagulant activity, this study suggests that the variation in GPVI content is a potential risk factor that may predispose individuals to hemorrhagic or thromboembolic disorders.

Identification of a taurine transport inhibitory substance in sesame seeds.

An ethanol extract from sesame seeds inhibited the taurine uptake in human intestinal epithelial Caco-2 cells. The uptake of such alpha-amino acids as leucine and glutamic acid was not inhibited by the extract, indicating that this inhibition is specific to the taurine uptake. The unknown inhibitor in the sesame extract was purifled by reversed-phase HPLC by monitoring the inhibitory effect on taurine uptake. The isolated substance was identified as lysophosphatidylcholine, linoleoyl (Lyso-PC), by NMR and MS analysis. Lyso-PC inhibited the taurine uptake in a dose-dependent manner with an IC50 value of approximately 200 microM. Although Lyso-PC is known to be a surface active and cell lytic compound, neither damage nor loss of integrity of the Caco2 cell monolayer was apparent after treating with 200 microM Lyso-PC. Inhibition was observed by incubating cells with Lyso-PC for only 1 min prior to the uptake experiments. These results suggest the direct effect of Lyso-PC on the cell membrane to be the main mechanism for this inhibition. Lyso-PC may play a role in the regulation of certain intestinal transporters.

Inhibitory effect of 220-oxa-1,25-dihydroxyvitamin D3 on the proliferation of pancreatic cancer cell lines.

BACKGROUND & AIMS: Effective chemotherapy for pancreatic cancer is urgently needed. The aim of this study was to compare the anti-proliferative activity of a new vitamin D3 analogue, 22-oxa-1,25-dihydroxyvitamin D3 (22-oxa-calcitriol), on pancreatic cancer cells lines with that of 1,25-dihydroxyvitamin D3 (calcitriol) with analysis of vitamin D receptor status. METHODS: Antiproliferative effects of both agents were compared using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide method and by measuring the tumor size of xenograft inoculated into athymic mice. Vitamin D receptor contents by Scatchard analysis and mutational analysis of receptor complementary DNA were performed. RESULTS: In vitro, 22-oxa-calcitriol and calcitriol markedly inhibited the proliferation (3 of 9 cell lines) and caused a G1 phase cell cycle arrest by appearance of numerous domes. In vivo, 22-oxa-calcitriol inhibited the growth of BxPC-3 xenografts more significantly than calcitriol without including hypercalcemia. Hs 766T, showing no response to either agent, had the second highest receptor contents with no abnormalities in its primary structure deduced by receptor complementary DNA. CONCLUSIONS: 22-oxa-calcitriol may provide a more useful tool for the chemotherapy of pancreatic cancer than calcitriol. Also, the susceptibility of the cell lines to both agents is not well determined by evaluating either the contents or the mutation of vitamin D receptor.

A mutation in the ceruloplasmin gene is associated with systemic hemosiderosis in humans.

We identified a mutation in the ceruloplasmin (Cp) gene in a Japanese family with aceruloplasminemia, some of whose members showed extrapyramidal disorders, cerebellar ataxia, and diabetes mellitus. A post-mortem study of the proband revealed excessive iron deposition mainly in the brain, liver and pancreas. The G to A transition at the splice acceptor site introduces a premature termination codon at the amino acid position 991 by defective splicing, thereby truncating the carboxyl terminus of Cp in affected individuals. We conclude that the mutation in the Cp gene is associated with systemic hemosiderosis in humans.