Effect of dehydroepiandrosterone on insulin sensitivity in Otsuka Long-Evans Tokushima-fatty rats.

In order to clarify the effect of dehydroepiandrosterone (DHEA) on improvement of insulin resistance, we examined the effects of overexpression of wild-type protein kinase C-zeta (wt-PKCzeta)/3-phosphoinositide-dependent protein kinase-1 (wt-PDK1) and kinase-inactive PKCzeta/PDK1 (DeltaPKCzeta/DeltaPDK1) on DHEA-induced [(3)H]2-deoxyglucose (DOG) uptake using the electroporation method in rat adipocytes. Overexpression of wt-PKCzeta and wt-PDK1 significantly increased in DHEA-induced [(3)H]2-DOG uptake. Wortmannin completely suppressed DHEA-induced [(3)H]2-DOG uptake in wt-PKCzeta- and wt-PDK1-transfected adipocytes.

Platelet aggregation in obese and diabetic subjects: association with leptin level.

To clarify the relationship between serum leptin concentration and platelet aggregation mechanism, we investigated serum leptin concentration and agonist-induced platelet aggregation in eight obese subjects and eight non-obese and non-diabetic controls. In addition we also measured them in 15 type 2 diabetic subjects and 17 control subjects. Maximum platelets aggregation rate (MPAR) in control and diabetic subjects by adenosine diphosphate (ADP), collagen and thrombin were measured by aggregometer after pretreatment with 100 ng/ml leptin for 60 min.

TNFalpha reduces the expression of peroxisome proliferator-activated receptor gamma (PPARgamma) via the production of ceramide and activation of atypical PKC.

Although tumor necrosis factor alpha (TNFalpha) decreases the expression of peroxisome proliferator-activated receptor gamma (PPARgamma), its mechanism is not understood. We evaluated the effect of ceramide, the second messenger of TNFalpha, on the expression of PPARgamma in primary cultured adipocytes. PPARgamma mRNA and aP2 mRNA levels were measured with real-time PCR.

Protein kinase C (PKC) beta modulates serine phosphorylation of insulin receptor substrate-1 (IRS-1)--effect of overexpression of PKCbeta on insulin signal transduction.

In vitro phosphorylation of 180-kDa protein, obtained by immunoprecipitation of adipocyte homogenate with anti-IRS-1 antibody was increased with the addition of conventional PKC in the presence of Ca2+, phosphatidylserine (PS) and diolein (DL). Human purified IRS-1 was phosphorylated by purified conventional PKC (cPKC) in the presence of Ca2+/PS/DL. These results suggest that PKC may have a role in the serine phosphorylation of IRS-1.

Depressive state and paresthesia dramatically improved by intravenous MgSO4 in Gitelman's syndrome.

A 69-year-old woman was referred to our department for evaluation of hypokalemia, which had been treated by oral potassium for more than ten years. She complained of headache, knee joint pain, sleeplessness and paresthesia in extremities and, most prominently, depression. Laboratory data suggested Gitelman's syndrome, which is caused by mutations in the gene encoding the thiazide-sensitive Na-Cl cotransporter.

Dominant negative protein kinase Cbeta improves 1alpha, 25-dihydroxy vitamin D3-induced insulin resistance.

1alpha,25-Dihydroxy vitamin D3 (1,25D3) activates conventional PKC and may subsequently lead to insulin resistance. Previous studies from our laboratory have shown that pretreatment with 10 nM-10 microM 1,25D3 dose-responsively suppressed insulin-induced glucose. To assess PKC(beta)-mediated inhibition of insulin-induced glucose uptake in rat adipocytes, we preincubated with Go6976 and LY379196, conventional PKC inhibitors, and found they abolished the 1,25D3-mediated inhibitory effect on insulin-induced 2-deoxyglucose (DOG) uptake.

Inhibition of PKCbeta improves glucocorticoid-induced insulin resistance in rat adipocytes.

Pretreatment with glucocorticoids for 60 min depressed insulin-stimulated uptake of 2-[3H] deoxyglucose (2-DOG), an effect that neither cycloheximide, an inhibitor of protein synthesis, nor RU38486, a glucocorticoid receptor antagonist, could restore. Preincubation with conventional PKC inhibitors restored dexamethasone-induced insulin resistance. We also examined the dexamethasone-mediated inhibitory effect on insulin-induced 2-DOG uptake in adipocytes overexpressed with wild-type and dominant negative forms of PKCbeta.

Inhibitory effect of ceramide on insulin-induced protein kinase Czeta translocation in rat adipocytes.

Ceramide has been confirmed to be a signal mediator of apoptosis that is induced by tumor necrosis factor-alpha (TNF-alpha). It has also been reported that ceramide may induce insulin resistance as well as TNF-alpha. We investigated the effect of ceramide on insulin signaling pathways, such as insulin receptor (IR) beta-subunit, insulin receptor substrate 1 (IRS-1), phosphatidylinositol 3-kinase (PI3K), and protein kinase Czeta (PKCzeta) in rat adipocytes.

Dehydroepiandrosterone down-regulates the expression of peroxisome proliferator-activated receptor gamma in adipocytes.

Dehydroepiandrosterone (DHEA) is expected to have a weight-reducing effect. In this study, we evaluated the effect of DHEA on genetically obese Otsuka Long Evans Fatty rats (OLETF) compared with Long-Evans Tokushima rats (LETO) as control. Feeding with 0.

Effect of 1 alpha,25-dihydroxy vitamin D3 and vitamin E on insulin-induced glucose uptake in rat adipocytes.

Vitamin E, an antioxidant, improves insulin sensitivity through the suppression of conventional PKC in vascular smooth muscle cells. It has been reported that vitamin E reduces platelet aggregation through the suppression of PKC alpha and beta (Diabetes 47 (1998) 1494). On the other hand, 1 alpha,25-dihydroxy vitamin D3 (1,25D3) activates conventional PKC and may subsequently cause insulin resistance.