Many factors influence the outcome of islet transplantation. As islets in the early posttransplant setting are supplied with oxygen by diffusion only and are in a hypoxic state in the portal system, we tested whether small human islets are superior to large islets both in vitro and in vivo. We assessed insulin secretion of large and small islets and quantified cell death during hypoxic conditions simulating the intraportal transplant environment. In the clinical setting, we analyzed the influence of transplanted islet size on insulin production in patients with type 1 diabetes. Our results provide evidence that small islets are superior to large islets with regard to in vitro insulin secretion and show a higher survival rate during both normoxic and hypoxic culture. Islet volume after 48 h of hypoxic culture decreased to 25% compared with normoxic culture at 24 h due to a preferential loss of large islets. In human islet transplantation, the isolation index (islet volume as expressed in islet equivalents/islet number), or more simply the islet number, proved to be more reliable to predict stimulated C-peptide response compared with islet volume. Thus, islet size seems to be a key factor determining human islet transplantation outcome. Diabetes 56:594 -603, 2007

Dystrophin is selectively localized in the postsynaptic density of neurons in cerebral cortex, hippocampus and cerebellum. Here, we show by double-immunofluorescence staining that dystrophin is extensively colocalized with GABAA receptor subunit clusters in these brain regions. To determine the relevance of this observation, we investigated in mdx mice, which provide a model of Duchenne muscular dystrophy, whether the absence of dystrophin affects the synaptic clustering of GABAA receptors. A marked reduction in the number of clusters immunoreactive for the alpha1 and alpha2 subunits was observed in, respectively, cerebellum and hippocampus of mdx mice, but not in striatum, which is normally devoid of dystrophin. Furthermore, these alterations were not accompanied by a change in gephyrin staining, although gephyrin is colocalized with the majority of GABAA receptor clusters in these regions. These results indicate that dystrophin may play an important role in the clustering or stabilization of GABAA receptors in a subset of central inhibitory synapses. These deficits may underlie the cognitive impairment seen in Duchenne patients.

Loss of beta-cell mass and function raises a concern regarding the application of sulfonylureas for the treatment of type 2 diabetes because previous studies have shown that agents that cause closure of inwardly rectifying K(+) sulfonylurea receptor subtype of ATP-sensitive potassium channels, such as tolbutamide and glibenclamide, induce apoptosis in beta-cell lines and rodent islets. Therefore, we investigated the effect of the new insulin secretagogues, repaglinide and nateglinide, and the sulfonylurea, glibenclamide, on beta-cell apoptosis in human islets. Human islets from six organ donors were cultured onto extracellular matrix-coated plates and exposed to glibenclamide, repaglinide, or nateglinide. The doses of the three compounds were chosen according to detected maximal effects, i.e. efficacy. Exposure of human islets for 4 h to 0.1 and 10 microm glibenclamide induced a 2.09- and 2.46-fold increase in beta-cell apoptosis, respectively, whereas repaglinide (0.01 and 1 microm) did not change the number of apoptotic beta-cells. At low concentration (10 microm), nateglinide did not induce beta-cell apoptosis. However, at high concentration of 1000 microm, it induced a 1.49-fold increase in the number of apoptotic beta-cells. Prolonged exposure for 4 d of the islets to the secretagogues induced beta-cell apoptosis. The increase was of 3.71- and 4.4-fold at 0.1 and 10 microm glibenclamide, 2.37- and 3.8-fold at 0.01 and 1 microm repaglinide, and of 3.2- and 4.6-fold at 10 and 1000 microm nateglinide, respectively. Glibenclamide at 0.1-10 nm (doses that were less efficient on insulin secretion) did not induce beta-cell apoptosis after 4 h incubation as well as 0.1 nm after 4 d incubation. However, 1 and 10 nm glibenclamide for 4 d induced a 2.24- and 2.53-fold increase in beta-cell apoptosis, respectively. Taken together, closure of the inwardly rectifying K(+) sulfonylurea receptor subtype of ATP-sensitive potassium channels induces beta-cell apoptosis in human islets and may precipitate the decrease in beta-cell mass observed in patients with type 2 diabetes.

Duchenne muscular dystrophy is a severe X chromosome-linked, muscle-wasting disease caused by lack of the protein dystrophin. The exact function of dystrophin rem to be determined. However, analysis of its interaction with a large oligomeric protein complex at the sarcolemma and the identicaton of a structurally related protein, utrophin, is leading to the characterization ofcandidate genes for other neuromusular disorders.Duchenne muscular dystrophy (DMD) is the most common muscular dystrophy, affecting 1 in 3,300 boys. It

Increasing evidence indicates that a progressive decrease in the functional ␤-cell mass is the hallmark of both type 1 and type 2 diabetes. The underlying causes, ␤-cell apoptosis and impaired secretory function, seem to be partly mediated by macrophage production of interleukin (IL)-1␤ and/or high-glucose-induced ␤-cell production of IL-1␤. Treatment of type 1 and type 2 diabetic patients with the potassium channel opener diazoxide partially restores insulin secretion. Therefore, we studied the effect of diazoxide and of the novel potassium channel opener NN414, selective for the ␤-cell potassium channel SUR1/Kir6.2, on glucose-and IL-1␤-induced apoptosis and impaired function in human ␤-cells. Exposure of human islets for 4 days to 11.1 and 33.3 mmol/l glucose, 2 ng/ml IL-1␤, or 10 and 100 mol/l of the sulfonylurea tolbutamide induced ␤-cell apoptosis and impaired glucose-stimulated insulin secretion. The deleterious effects of glucose and IL-1␤ were blocked by 200 mol/l diazoxide as well as by 3 and 30 mol/l NN414. By Western blotting with phosphospecific antibodies, glucose and IL-1␤ were shown to activate the extracellular signal-regulated kinase (ERK) 1/2, an effect that was abrogated by 3 mol/l NN414. Similarly, 1 mol/l of the mitogen-activated protein kinase/ERK kinase 1/2 inhibitor PD098059 or 1 mol/l of the L-type Ca 2؉ channel blocker nimodipine prevented glucose-and IL-1␤-induced ERK activation, ␤-cell apoptosis, and impaired function. Finally, islet release of IL-1␤ in response to high glucose could be abrogated by nimodipine, NN414, or PD098059. Thus, in human islets, glucose-and IL-1␤-induced ␤-cell secretory dysfunction and apoptosis are Ca 2؉ influx and ERK dependent and can be prevented by the ␤-cell selective potassium channel opener NN414. Diabetes 53