Suppression of the accumulation of triosephosphates and increased formation of methylglyoxal in human red blood cells during hyperglycaemia by thiamine in vitro

The accumulation of triosephosphates and the increased formation of the pot ent glycating agent methylglyoxal in intracellular hyperglycaemia are impli cated in the development of diabetic complications. A strategy to counter t his is to stimulate the anaerobic pentosephosphate pathway of glycolysis by maximizing transketolase activity by thiamine supplementation, with the co nsequent consumption of glyceraldehyde-3-phosphate and increased formation of ribose-6-phosphate, To assess the effect of thiamine supplementation on the accumulation of triosephosphates and methylglyoxal formation in cellula r hyperglycaemia, we incubated human red blood cell suspensions (50% v/v) i n short-term culture with 5 mM glucose and 50 mM glucose in Krebs-Ringer ph osphate buffer at 37 degreesC as models of cellular metabolism under normog lycaemic and hyperglycaemic conditions. In hyperglycaemia, there is a chara cteristic increase in the concentration of the triosephosphate pool of glyc olytic intermediates and a consequent increase in the concentration and met abolic flux of the formation of methylglyoxal, The addition of thiamine (50 -500 muM) increased the activity of transketolase, decreased the concentrat ion of the triosephosphate pool, decreased the concentration and metabolic flux of the formation of methylglyoxal, and increased the concentration of total sedoheptulose7-phosphate and ribose-5-phosphate. Biochemical changes implicated in the development of diabetic complications were thereby preven ted. This provides a biochemical basis for high dose thiamine therapy for t he prevention of diabetic complications.