Protein kinase B/Akt signalling is required for palmitate-induced beta-cell lipotoxicity.

AIM: This study was conducted to clarify cell death and survival signals in pancreatic beta-cell lipotoxicity. METHODS: Rat insulinoma INS-1 cells, with or without expression of dominant-negative mutant of Akt (K179M), were cultured with palmitate (C16:0) or oleate (C18:1) and cell numbers were determined by 0.2% eosin dye exclusion assay. The Akt activity was determined by anti-3'-phospho-inositide-dependent protein kinase (Akt)/protein kinase B (PKB) or anti-phospho-Akt (Serine 473) immunoblotting, and nuclear protein nuclear factor-kB (NF-kappaB)-binding activity was by supershift analysis. RESULTS: Twenty-four hours treatment with palmitate increased the INS-1 cell number at 0.1-0.2 mM but decreased the cell number at 0.5-1 mM. Oleate did not affect cell number at 0.1-1.0 mM. Palmitate dose-dependently increased phosphorylation of 473th serine in Akt/PKB. The K179M form of Akt/PKB abolished palmitate-induced cell proliferation at the low dose and death at the high dose. Nuclear protein NF-kappaB binding was enhanced at 0.2 and 0.5 mM of palmitate but decreased at 1.0 mM. CONCLUSION: Results suggest that Akt/PKB signalling is involved in palmitate-induced cell death and survival of pancreatic beta cell.

Antioxidant and hepatoprotective actions of the medicinal herb Artemisia campestris from the Okinawa Islands.

The antioxidant action of Artemisia campestris was examined in vitro and in vivo. A water extract of A. campestris showed a strong scavenging action of 1,1-diphenyl-2-picrylhydrazyl (DPPH), hydroxyl and superoxide anion radicals. When the extract was given intraperitoneally to mice prior to carbon tetrachloride (CCl4) treatment, CCl4-induced liver toxicity, as seen by an elevation of serum aspartate aminotransferase and alanine aminotransferase activities, was significantly reduced. Depression of the elevation of serum enzyme levels after CCl4-treatment was also observed by oral administration of the extract. In that case, CCl4-derived lipid peroxidation in the liver was decreased by the extract treatment. These results suggest that the extract of A. campestris scavenges radicals formed by CCl4 treatment resulting in protection against CCl4-induced liver toxicity.

Long-term nifedipine treatment reduces calcium overload in isolated reperfused hearts of diabetic rats.

1. Streptozotocin-induced diabetic rats showed poor post-ischemic recovery in isolated working rat hearts. 2. Diabetic rats showed myocardial Na+ accumulation after ischemia, and Ca2+ level and water content elevation after reperfusion. 3. A 6-wk nifedipine treatment improved post-ischemic recovery of cardiac parameters and prevented myocardial Na+ accumulation after ischemia and myocardial Ca2+ level and water content elevation after reperfusion of diabetic rats. 4. Results suggest that nifedipine treatment improves cardiac dysfunction in the reperfused ischemic hearts of diabetic rats through normalization of the Na+-Ca2+ imbalance and water content.

Impaired mechanical response to calcium of diabetic rat hearts: reversal by nifedipine treatment.

Streptozotocin-induced diabetic and age-matched control rats were treated with 0.03% nifedipine-containing chow for 6 weeks, and mechanical response to Ca2+ was studied using isolated working hearts. At 14 weeks of age, 7 weeks after a streptozotocin injection, diabetic rats had a lower body weight and heart weight than controls, and an increase in heart weight-to-body weight ratio. Nifedipine treatment did not alter these parameters of controls, but decreased the heart weight and heart weight-to-body weight ratio of diabetic rats without affecting the body weight. In diabetic rats, systolic blood pressure was decreased compared to controls (124 +/- 5 vs. 137 +/- 6 mm Hg, p < 0.01), and reduced more by nifedipine treatment (111 +/- 4 mm Hg, p < 0.01). In control rats, LV developed pressure, LV +/- dP/dt, and cardiac work were unchanged regardless of the increment in preload at 1.25, 1.88, and 2.50 mM Ca2+. However, the responses of diabetic rats were decreased with an increment in preload at 2.5 mM Ca2+. Nifedipine treatment produced a partial recovery of all four parameters at 2.5 mM Ca2+ in diabetic rats. The myocardial Ca2+ content and sarcolemmal lipid peroxidation were similar in hearts from control and diabetic rats at all Ca2+ concentrations and nifedipine treatment did not affect these values. Results suggest that chronic nifedipine treatment improve the contractility of diabetic rat hearts under high Ca2+ conditions.