Elevated glycine betaine excretion in diabetes mellitus patients is associated with proximal tubular dysfunction and hyperglycemia

In an ambulatory population of diabetic subjects (Type 1 and Type 2), the u rine excretion of the renal osmolyte, glycine betaine, was compared to know n markers of glycemic control, renal dysfunction and to the excretion of re lated betaines, including trigonelline, proline betaine, carnitine and acet yl-carnitine. Of the 85 subjects, 20 patients had urine glycine betaine con centrations above the reference range for normal subjects. Plasma glycine b etaine concentrations were within reference ranges for normal subjects. Pat ients with elevated glycine betaine excretion tended to have lower plasma g lycine betaine concentrations, but this did not reach statistical significa nce. One way analysis of variance found excretion is independent of treatme nt, duration of diagnosed diabetes, blood pressure and body mass index (BMI ). An association between glycine betaine excretion and glycemic control wa s observed with statistically significant correlations occurring with both plasma glucose (r = 0.43, P < 0.001) and glycated haemoglobin (HbA(1c)) (r = 0.35, P < 0.005). The excretion of carnitine, acetyl-carnitine and prolin e betaine were related to glycine betaine excretion (r = 0.49, P < 0.001; r = 0.40, P < 0.001; r = 0.27, P < 0.05, respectively). Urine carnitine and acetyl-carnitine concentrations were also related to plasma glucose concent rations (r = 0.30, P < 0.01). Increased urine retinol binding protein conce ntrations (RBP), a marker of proximal tubular dysfunction, correlated with elevated urine glycine betaine excretion and plasma HbA(1c) (r = 0.28, P < 0.01). These results suggest poor glycemic control is associated with the i ncrease in urine glycine betaine, carnitine, acetyl-carnitine and RBP excre tion in diabetic patients. However, <50% of the observed increase in glycin e betaine excretion has been accounted for by the variables measured, sugge sting other unidentified processes may also be involved. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.