Insulin-stimulated release of D-chiro-inositol-containing inositolphosphoglycan mediator correlates with insulin sensitivity in women with polycystic ovary syndrome.

Some actions of insulin are mediated by inositolphosphoglycan (IPG) mediators. Deficient release of a putative D-chiro-inositol-containing (DCI) IPG mediator may contribute to insulin resistance in women with polycystic ovary syndrome (PCOS). Previously, we demonstrated that oral DCI supplementation improved ovulation and metabolic parameters in women with PCOS. However, whether oral DCI mediates an increase in the release of the DCI-IPG mediator and an improvement in insulin sensitivity in women with PCOS is unknown. We conducted a randomized controlled trial of DCI supplementation vs placebo in 11 women with PCOS who were assessed at 2 time points 6 weeks apart. Plasma DCI, DCI-IPG release during oral glucose tolerance test (AUC(DCI-IPG)), and insulin sensitivity (S(i)) by frequently sampled intravenous glucose tolerance test were assessed at baseline and end of study. The study was terminated early because of a sudden unavailability of the study drug. However, in all subjects without regard to treatment assignment, there was a positive correlation between the change in AUC(DCI-IPG)/AUC(insulin) ratio and the change in S(i) during the 6-week period (r = 0.69, P = .02), which remained significant after adjustment for body mass index (P = .022) and after further adjustment for body mass index and treatment allocation (P = .0261). This suggests that, in women with PCOS, increased glucose-stimulated DCI-IPG release is significantly correlated with improved insulin sensitivity. The significant relationship between DCI-IPG release and insulin sensitivity suggests that the DCI-IPG mediator may be a target for therapeutic interventions in PCOS.

ADP-mimicking platelet aggregation caused by rugosin E, an ellagitannin isolated from Rosa rugosa Thunb.

Among the nine ellagitannins, rugosin E was the most potent platelet aggregating agent with an EC50 of 1.5 +/- 0.1 microM in rabbit platelets and 3.2 +/- 0.1 microM in human platelets. The aggregations caused by rugosin E and ADP were inhibited by EGTA, PGE1, mepacrine, sodium nitroprusside and neomycin, but not by indomethacin, verapamil, TMB-8, BN52021 and GR32191B. Rugosin E-induced thromboxane formation was suppressed by indomethacin, EGTA, PGE1, verapamil, mepacrine, TMB-8 and neomycin. ADP-scavenging agents, such as CP/CPK and apyrase inhibited concentration-dependently ADP (20 microM)-, but not rugosin E (5 microM)-induced platelet aggregation. In thrombin (0.1 U/ml)-treated and degranulated platelets, rugosin E and ADP still caused 63.5 +/- 3.0% and 61.2 +/- 3.5% of platelet aggregation, respectively. Selective ADP receptor antagonists, ATP and FSBA inhibited rugosin E- and ADP-induced platelet aggregations in a concentration-dependent manner. Both rugosin E and ADP did not induce platelet aggregation in ADP (1 mM)-desensitized platelets. In contrast to ADP, rugosin E did not decrease cAMP formation in washed rabbit platelets. Both rugosin E and ADP did not cause phosphoinositide breakdown in [3H]myo-inositol-labeled rabbit platelets. In fura-2/AM-load platelets, both rugosin E and ADP induced increase in intracellular calcium concentration and these responses were inhibited by ATP and PGE1. All these data suggest that rugosin E may be an ADP receptor agonist in rabbit platelets.

Does verapamil act as an immunomodulatory drug in vivo?

Based on in vitro data, previous investigators have hypothesized that Ca2+ entry blockers might affect lymphocyte activation, proliferation and effector function. We have tested this hypothesis by comparing the in vitro and in vivo effects of the Ca2+ entry blocker verapamil on human lymphocytes. In vitro high concentrations of verapamil (100 microM) inhibited mitogen-stimulated Ca2+ influx, inositol phosphate generation, and proliferation; similar effects were observed with diltiazem and nifedipine. In vivo treatment of healthy volunteers with verapamil (2-4 times 240 mg per day for 7 days) did not affect the number of circulating lymphocytes or their subset distribution. Moreover, we did not observe any effect of in vivo treatment with verapamil on mitogen-stimulated lymphocyte proliferation or expression of interleukin-2 receptors in vitro. We conclude that the inhibitory effects of verapamil on lymphocyte activation in vitro are unlikely to be of therapeutic relevance and may not be related to the Ca2+ entry blocking effects of this drug.

Membrane-associated 41-kDa GTP-binding protein in collagen-induced platelet activation.

Initially we established that the binding of collagen to human blood platelets stimulates both the rapid loss of PIP2 and the generation of inositol-4,5-bisphosphate (IP2) and inositol-1,4,5-triphosphate (IP3). These results indicate that the binding of collagen stimulates inositol phospholipid-specific phospholipase C during platelet activation. The fact that GTP or GTP-gamma-S augments, and pertussis toxin inhibits, collagen-induced IP3 formation suggests that a GTP-binding protein (or (or proteins) may be directly involved in the regulation of phospholipase C-mediated phosphoinositide turnover in human platelets. We have used several complementary techniques to isolate and characterize a platelet 41-kDa polypeptide (or polypeptides) that has a number of structural and functional similarities to the regulatory alpha i subunit of the GTP-binding proteins isolated from bovine brain. This 41-kDa polypeptide (or polypeptides) is found to be closely associated with at least four membrane glycoproteins (e.g., gp180, gp110, gp95, and gp75) in a 330-kDa complex that can be dissociated by treatment with high salt plus urea. Most important, we have demonstrated that antilymphoma 41-kDa (alpha i subunit of GTP-binding proteins) antibody cross-reacts with the platelet 41-kDa protein (or proteins) and the alpha i subunit of bovine brain Gi alpha proteins, and blocks GTP/collagen-induced IP3 formation. These data provide strong evidence that the 41-kDa platelet GTP-binding protein (or proteins) is directly involved in collagen-induced signal transduction during platelet activation.

Diets rich in n-9, n-6 and n-3 fatty acids differentially affect the generation of inositol phosphates and of thromboxane by stimulated platelets, in the rabbit.

We have studied the effects of semi-synthetic diets rich in either n-9 (olive oil, OO) or n-6 (corn oil, CO), or n-3 (fish oil, FO, as MaxEPA) fatty acids on the levels of major PUFA in platelet lipids, on the generation of inositol phosphates by [3H]inositol labelled platelets after stimulation with thrombin and of thromboxane B2 (TxB2) by platelet rich plasma (PRP) after stimulation with collagen. The predicted elevations of oleic (OA), linoleic (LA) and eicosapentaenoic (EPA) and docosahexaenoic (DHA) acids were observed in platelet lipids of each animal group, but in the MaxEPA fed group accumulation of EPA was associated with depletion of linoleic acid (LA) rather than of arachidonic acid (AA). Basal levels of inositol-tris-phosphate (IP3) in platelets were lowest in the OO group and highest in the CO group, whereas the increment after thrombin stimulation (1 unit/ml NIH) was maximal in the OO group and minimal in the FO group. Instead, when generation of TxB2 by stimulated platelets was evaluated, no appreciable difference among the various groups could be detected, in accordance with the limited modifications of platelet AA content induced by the diets. The overall data indicate that dietary fatty acids modulate the pathway of inositol phosphate generation in rabbit platelets, independently of modifications of TxB2 production.