The thiamine analogue and advanced glycation endproducts crosslink breaker ALT-711 does not interfere with transketolase activity

The enzyme transketolase (sedoheptulose-7-phosphate:D-glyceraldehyde-3-phosphate glycolaldehydetransferase, EC 2.2.1.1) is involved in the pentose phosphate pathway (PPP) and catalyses the transfer of a 2-carbon fragment from a 5-carbon keto sugar (xylulose-5-P) to a 5-carbon aldo sugar (ribose-5-P) to form a 7-carbon keto sugar (sedoheptulose- 7-P) and a 3-carbon aldo sugar (glyceraldehyde-3-P). Transketolase requires thiamine pyrophosphate as a co-factor. Advanced glycation endproducts (AGEs) are implicated in the complications of diabetes and aging, primarily via adventitious and crosslinking of tissue proteins. ALT-711 is an AGE crosslink breaker and has been tested as an intervention therapy in established complications of diabetes. It has been noticed that it has a similar structure to that of thiamine and it was hypothesized that it might inhibit transketolase by replacing the active co-factor rendering the enzyme inactive. In this study, we have established a novel microtiter plate format transketolase assay which determines the concentration of NADH by measuring its fluorescence. Using this assay, it was found that ALT-711 does not inhibit the activity of transketolase up to concentration of 5 mM. We conclude that ALT-711 does not interfere with transketolase activity at clinically relevant concentrations.