Reduced Na+/K+ ATPase transport activity, resting membrane potential, and bradykinin-stimulated phosphatidylinositol synthesis by polyol accumulation in cultured neuroblastoma cells

1-methylnicotinamide (MNA) in prevention of diabetes-associated brain disorders

The present study has been designed to establish the potential benefits from 1-methylnicotinamide (MNA) treatment on brain disorders associated with type 1 diabetes. All experiments were carried out after 6 weeks of streptozotocin-induced diabetes (60 mg/kg of body weight, i.p.) in male Wistar rats treated for 5 weeks with or without MNA (100 mg/kg of body weight, per os in drinking water) after 1 week of diabetes induction. Diabetes was shown to reduce monoamine neurotransmitter serotonin transporters activity, as assessed by significant inhibition of [2-(14)C]serotonin uptake, that was accompanied by elevation of spontaneous mediator release in rat brain synaptosomes. Treatment with MNA slightly attenuated diabetes-induced changes in brain serotoninergic system. The precise mechanism underlying MNA action on central serotonin neurotransmission is not known, but appears to be linked to metabolic and signalling pathways involved in controlling synaptic function rather than being associated with direct modulation of serotonin transporters. In particular, MNA action was associated with its partial normalizing effects on such biochemical indices of neuropathy development as decrease in synaptosomal Na(+),K(+)-ATPase activity and plasma membrane depolarization of synaptic endings. Elevated sorbitol formation in brain and NAD(+) deficits resulted from diabetes as major metabolic imbalances were remarkably countered by MNA treatment. However, diabetes-induced decrease in cytosolic NAD(+) to NADH ratio in brain remained unchanged. Notably, MNA supplementation to diabetic rats caused a slight lowering effect on blood glucose level. Accordingly, our findings indicate that neuroprotective properties of MNA are linked to modulation of synaptic activity through multiple mechanisms. In conclusion, we suggest that 1-methylnicotinamide might be a useful agent for treating brain failures related to diabetes.

Temporal gene expression profile in hippocampus of mice treated with D-galactose

(1) Rodent chronically treated with D-galactose (D-gal) is increasingly used in pharmacological studies on aging; however, its mechanism remains unclear. The present study investigated the alterations of gene expression in the hippocampus of D-gal-treated mice. (2) C57 mice were subcutaneously injected with D-gal for 2, 4, and 8 weeks or vehicle, and then were subjected to behavioral tests. Gene expression profiles in hippocampus of each group were finally examined with cDNA microarray. (3) Both 4- and 8-week D-gal treatment led to a decrease of discrimination index in object recognition test, and 8-week D-gal-treated mice showed significant spatial learning & memory impairment in Morris water maze test. In comparison with the vehicle control group, the 2-, 4-, and 8-week D-gal treatment repressed the expression of 10, 13, and 30 genes by 2-fold or more, respectively. The early pattern was mainly characterized by down regulation of genes involved in ion transport. The delayed pattern included genes involved in protein biosynthesis, transport and signal transduction, which were highly related to synaptic functions. (4) These findings will contribute to the understanding of the mechanism of learning and memory impairment in mice treated with D-galactose.

The differential osmoregulation and localization of taurine transporter mRNA and Na+/myo-inositol cotransporter mRNA in rat eyes

We studied the cellular localization and osmotic regulation of taurine transporter (TauT) mRNA in the rat eyes using in situ hybridization. TauT mRNA signals were expressed in the ciliary body, and the outer part of the inner nuclear layer (INL), the outer nuclear layer (ONL) and the inner segment (IS) of the adult rat retina. Chronic hypernatrema, induced by gavaging with 1 ml/100 g body weight of 5% NaCl every other day for 7 days, markedly increased in TauT mRNA in the retina compared with control rats. However, there was little change in TauT mRNA in the eyes in acute hypernatremic state that is induced by single injection of high concentration of NaCl. On the contrary, acute hypernatremic rats displayed markedly elevated Na+/myo-inositol cotransporter (SMIT) mRNA in the retina and the iris-ciliary body and the lens epithelium. Under chronic hypernatremic conditions, there was no significant increase in SMIT mRNA in rat eyes. These findings suggest that TauT mRNA is osmotically regulated in vivo to protect retinal neuronal function, especially against chronic hypernatremic conditions, in contrast to rapid up-regulation of SMIT mRNA in acute hypernatremic rats.

Effect of an aldose reductase inhibitor on type IV collagen production by human endothelial cells cultured in high glucose

Diabetic microangiopathy is characterized by a thickening of capillary basement membranes associated with type IV collagen accumulation. An increase in type IV collagen content of the aortic wall is also observed in macroangiopathy. In order to analyse the importance of the polyol pathway in the development of the collagen metabolism alterations seen in diabetic angiopathy and their prevention by aldose reductase inhibitors, we have studied the effects of sorbinil on the high glucose-induced stimulation of type IV collagen biosynthesis in human umbilical vein endothelial cells. Primary cultures were exposed to high glucose (16.7 mmol/l), with and without 0.11 mmol/l sorbinil, for 3 or 6 days after beginning of confluence. We measured the soluble type IV collagen secreted into the culture medium and the insoluble type IV collagen accumulated in the extracellular matrix and cells, by ELISA. We also studied [14C]proline incorporation into the newly synthesized collagenous and total proteins in the culture supernatant and in the extracellular matrix and cell fraction. High glucose decreased the number of cells and increased the amount of type IV collagen in the culture supernatant and in the extracellular matrix and cell fraction. It also increased proline incorporation into the newly synthesized collagenous and total proteins in the culture supernatant and in the extracellular matrix and cell fraction. Sorbinil corrected all these high glucose-induced alterations. The corrective effects of sorbinil on the proliferation and on type IV collagen metabolism of endothelial cells cultured in high glucose may be attributed to prevention of polyol pathway dysregulation.

Expression of Na+/myo-inositol cotransporter mRNA in normal and hypertonic stress rat eyes

We studied the localization of Na+/myo-inositol cotransporter (SMIT) mRNA in normal and hypertonic stress rat eyes by in situ hybridization histochemistry using cRNA probes. SMIT mRNA signals were observed in the iris-ciliary body, the lens epithelial cells, and the ganglion cell layer and the inner nuclear layer of the retina. There was a rapid increase on SMIT mRNA in the retina of hypertonic stress rats compared with control rats. These findings suggest that Na+/myo-inositol cotransporter gene expression is osmotically regulated in vivo to protect retinal neuronal function against hypertonic stress.