Additional Evidence That Transaldolase Exchange, Isotope Discrimination during the Triose-Isomerase Reaction or Both Occurs in Humans: Effects of Type 2 Diabetes

Abstract

Objective- We sought to determine whether deuterium enrichment on C5 and C3 in plasma glucose is influenced by processes other than gluconeogenesis and if so, are these processes altered by type 2 diabetes.

Research Design and Methods- Ten obese diabetic and ten obese non-diabetic subjects were infused intravenously with [3,5-²H₂] galactose enriched at a C5/C3 ratio of 1.0, and the enrichment of deuterium on C5 and C3 of plasma glucose measured with NMR using the acetaminophen glucuronide method.

Results- The ratio of deuterium enrichment on C5/C3 of glucose was less than one (p<0.001) in all of the diabetic and non-diabetic subjects resulting in a mean C5/C3 ratio that did not differ between groups (0.81 ± 0.01 vs. 0.79 ± 0.01).

Conclusions- The fact that the C5/C3 glucose ratio is less than one indicates that transaldolase exchange, selective retention of deuterium at the level of the triose- isomerase reaction, or a combination of both occurs in humans. They also indicate that the net effect of these processes on the C5/C3 ratio is the same in people with and without type 2 diabetes. The possible effects of transaldolase exchange and/or selective retention of deuterium (or tritium) at the level of the triose-isomerase reaction on tracee labeling and tracer metabolism should be borne in mind when the deuterated water method is used to measure gluconeogenesis or [3-³H] glucose is used to measure glucose turnover in humans.