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Like obese humans, Zucker diabetic fatty (ZDF) rats exhibit early [Beta] cell compensation for insulin resistance (4-fold [Beta] cell hyperplasia) followed by decompensation (> 50% loss of [Beta] cells). In prediabetic and diabetic ZDF islets, apoptosis measured by DNA laddering is increased 3- and >7-fold, respectively, compared with lean ZDF controls. Ceramide, a fatty acid-containing messenger in cytokine-induced apoptosis, was significantly increased (P < 0.01) in prediabetic and diabetic islets. Free fatty acids (FFAs) in plasma are high (>1 mM) in prediabetic and diabetic ZDF rats; therefore, we cultured prediabetic islets in 1 mM FFA. DNA laddering rose to 19.6% vs. 4.6% in lean control islets, preceded by an 82% increase in ceramide. [C.sub.2]-Ceramide without FFA induced DNA laddering, but fumonisin [B.sub.1], a ceramide synthetase inhibitor, completely blocked FFA-induced DNA laddering in cultured ZDF islets. [3H] Palmitate incorporation in [3H] ceramide in ZDF islets was twice that of controls, but [3H] paimitate oxidation was 77% less. Triacsin C, an inhibitor of fatty acyl-CoA synthetase, and troglitazone, an enhancer of FFA oxidation in ZDF islets, both blocked DNA laddering. These agents also reduced inducible nitric oxide (NO) synthase mRNA and NO production, which are involved in FFA-induced apoptosis. In ZDF obesity, [Beta] cell apoptosis is induced by increased FFA via de novo ceramide formation and increased NO production.

As shown earlier, raft-like domains resembling those thought to be present in natural cell membranes can be formed in supported planar lipid monolayers. These liquid-ordered domains coexist with a liquid-disordered phase and form in monolayers prepared both from synthetic lipid mixtures and lipid extracts of the brush border membrane of mouse kidney cells. The domains are detergent-resistant and are highly enriched in the glycosphingolipid GM1. In this work, the properties of these raft-like domains are further explored and compared with properties thought to be central to raft function in plasma membranes. First, it is shown that domain formation and disruption critically depends on the cholesterol density and can be controlled reversibly by treating the monolayers with the cholesterol-sequestering reagent methyl-[Beta]-cyclodextrin. Second, the glycosylphosphatidylinositol-anchored cell-surface protein Thy-1 significantly partitions into the raft-like domains. The extent of this partitioning is reduced when the monolayers contain GM1, indicating that different molecules can compete for domain occupation. Third, the partitioning of a saturated phospholipid analog into the raft phase is dramatically increased (15% to 65%) after cross-linking with antibodies, whereas the distribution of a doubly unsaturated phospholipid analog is not significantly affected by cross-linking ([approximately equals] 10%). This result demonstrates that cross-linking, a process known to be important for certain cell-signaling processes, can selectively translocate molecules to liquid-ordered domains. membrane domains | receptor cross-linking | cholesterol | glycosylphosphatidylinositol-anchored proteins | signal transduction

Presents a study on fatty acid-induced beta apoptosis. Methodology used to conduct the study; Findings of the study.