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 urine excretion of the renal osmolyte, glycine betaine, was compared to known markers of glycemic control, renal dysfunction and to the excretion of related betaines, including trigonelline, proline betaine, carnitine and acetyl-carnitine. Of the 85 subjects, 20 patients had urine glycine betaine concentrations above the reference range for normal subjects. Plasma glycine betaine concentrations were within reference ranges for normal subjects. Patients with elevated glycine betaine excretion tended to have lower plasma glycine betaine concentrations, but this did not reach statistical significance. One way analysis of variance found excretion is independent of treatment, duration of diagnosed diabetes, blood pressure and body mass index (BMI). An association between glycine betaine excretion and glycemic control was 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 proline 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 concentrations (r = 0.30, P < 0.01). Increased urine retinol binding protein concentrations (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 increase in urine glycine betaine, carnitine, acetyl-carnitine and RBP excretion in diabetic patients. However, <50% of the observed increase in glycine betaine excretion has been accounted for by the variables measured, suggesting other unidentified processes may also be involved. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.