High glucose concentrations impair the replication of cultured human umbilical vein (HUVEC) [1][2][3] and bovine retinal endothelial cells (BREC) [4] and this may be secondary to enhanced glycolytic flux. Altered concentrations of intermediate phosphorylated metabolites could play a role in determining cell damage. In particular, increased availability of glyceraldehyde 3-phosphate (G3P), which is much more active than glucose in promoting protein glycation and AGE formation [5], might be one of the mechanism(s) involved.Thiamine (vitamin B 1 ) acts as a coenzyme for transketolase [6], pyruvate-dehydrogenase [7] and a -ketoglutarate-dehydrogenase [8]. The former shifts G3P from glycolysis to the pentose phosphate shunt, the second transforms pyruvate in acetyl-coenzyme A, which then enters the Krebs cycle, and the third catalyses the oxidation of ketoglutaric acid to succinyl-CoA within the Krebs cycle.The aim of this study was to ascertain whether thiamine would modify glycolysis, AGE production and replication in HUVEC and BREC cultured in high glucose concentrations. Diabetologia (1996) Summary This study aimed at verifying whether thiamine, a co-enzyme which decreases intracellular glycolysis metabolites by allowing pyruvate and glyceraldheyde 3-phosphate to enter the Krebs cycle and the pentose-phosphate shunt, respectively, corrects delayed replication caused by high glucose concentrations in cultured human umbilical vein (HU-VEC) and bovine retinal endothelial cells (BREC). After incubation in physiological (5.6 mmol/l) or high (28.0 mmol/l) glucose with or without 150 m mol/l thiamine, cells were counted and proliferation assessed by mitochondrial dehydrogenase activity. Lactate was measured in both cell types as an index of glycolytic activity and fluorescent advanced glycosylation end-products (AGE) concentration was determined in the HUVEC lysate. Both cell counts and proliferation assays in either of the cell types confirmed the impairment to cell replication induced by high glucose. When thiamine was added to cells kept under high glucose conditions, the number of surviving cells was significantly increased and the reduced cell proliferation appeared to be corrected. Lactate assays confirmed the increased production of this metabolite by BREC and HUVEC in high glucose, which was reduced by thiamine. Fluorescent AGE determination showed that thiamine may prevent non-enzymatic glycation in HUVEC. Thiamine restores cell replication, decreases the glycolytic flux and prevents fluorescent AGE formation in endothelial cells cultured in high glucose, suggesting that abnormal levels of glycolytic metabolite(s) may damage cells.

Pericyte loss is an early feature of diabetic retinopathy and represents a key step in the progression of this disease. This study aimed to evaluate the effect of dehydroepiandrosterone (DHEA) on glucose toxicity in retinal capillary pericytes. Bovine retinal pericytes (BRP) were cultured in a high glucose concentration, with or without DHEA. After 4 days of incubation the number of BRP was significantly reduced by the high glucose concentration. The addition of DHEA to the medium reversed the adverse effect of high glucose: BRP proliferation partially recovered in the presence of 10 nmol/l DHEA, and completely recovered in the presence of DHEA at concentrations equal to or greater than 100 nmol/l. At physiological glucose concentrations, DHEA had no effect on BRP growth. Data show that DHEA, at concentrations similar to those found in human plasma, protects BRP against glucose toxicity. This effect seems specific for DHEA, since its metabolites, 5-en-androstene-3 ,17 -diol, dihydrotestosterone and estradiol did not alter BRP growth in normal or high glucose media. Various pieces of evidence link the antioxidant properties of DHEA to its protective effect on glucose-induced toxicity in BRP.

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We suggest that alendronate mainly acts on mature bone resorbing osteoclasts in the short term, whereas, its long-term administration diminishes their formation by reducing their precursors and serum RANKL.

There is evidence indicating that the cholinergic system positively modulates GH release probably by inhibiting somatostatinergic tone. In the present study, the effects of cholinergic enhancement by pyridostigmine, (PD), a cholinesterases inhibitor, on GH release in normal adults (n = 14) (NA) and in both normal (n = 5) (NC) and short children (n = 19) (SC) with familial short stature (n = 7) or constitutional growth delay (n = 12) were studied. In SC the insulin hypoglycaemia (IH)-induced GH increase was also studied. In both NC and SC 60 mg orally PD induced a significant GH increase with mean peak at 90 min (mean +/- SEM 11.0 +/- 2.2 ng/ml in NC and 11.2 +/- 2.3 ng/ml in SC). The GH areas under response curve (AUC) were 379.3 +/- 76.6 and 327.8 +/- 43.2 ng/ml/h in NC and SC respectively. In NA 120 mg orally PD induced a significant GH increase with mean peak at 120 min (5.1 +/- 1.1 ng/ml) which was significantly lower (P less than 0.05) than that observed in both NC and SC. This statistical difference was strengthened by evaluating AUC (NA:205.6 +/- 33.7 ng/ml/h, P less than 0.05 vs NC and SC). The correlation of drug dosage with body area ruled out that this difference could be related to the different PD dose in adults and children. In SC, IH induced a GH increase significantly lower than that observed after PD (GH peak 7.8 +/- 0.6 vs 16.4 +/- 1.9 ng/ml P less than 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)