Urinary excretion of the carboxy terminal domain of type IV collagen is associated with kidney size and function in IDDM

Urinary transforming growth factor-beta(1), collagen IV and the effect of insulin in children at diagnosis of diabetes mellitus

OBJECTIVE

This study investigated whether metabolic derangement at diagnosis of diabetes mellitus affects the function of the basement membrane and the excretion of several components and whether insulin treatment can normalize this. It was designed to evaluate urinary excretion rates of transforming growth factor-beta(1) (TGF-beta(1)), the carboxy-terminal domain of collagen IV (NC1) and albumin in children during the first 20 days of treatment after diagnosis of type 1 diabetes.

MATERIAL AND METHODS

Thirty-four newly diagnosed diabetic children between 4 and 16 years of age and 26 healthy children of matching age were studied with timed overnight urine collections. Urine was collected during the first 20 days of treatment.

RESULTS

Urinary excretion of albumin and TGF-beta(1) in diabetic children were significantly increased at entry but normalized during 20 days of treatment with insulin compared with control children. In contrast, the non-significant high NC1 excretion at diagnosis did not change but became significantly increased after 20 days of insulin treatment. Overall, the kidney size was within normal limits and unaffected by treatment. The largest kidneys had less NC1 excretion (R= - 0.67, p<0.05, n=13) and a lower glomerular filtration rate (R= - 0.77, p<0.01, n=10) than the smallest kidneys. After 20 days of treatment TGF-beta(1) excretion had decreased in children with kidney size > 8.5 cm.

CONCLUSION

Correction of the metabolic derangement with insulin decreased excretion of albumin and TGF-beta(1), but had no effect on kidney size and urine NC1 excretion, presumably because the observation period was too short.

Urinary excretion rate of NC1 and Tamm-Horsfall protein in the microalbuminuric type I diabetic patient

Fifty-six type I diabetic patients with microalbuminuria (albumin excretion rate 20-200 micrograms/min) were characterized as to sex, age, duration of diabetes, smoking habits, blood pressure, glomerular filtration rate, urinary NC1 (the carboxy-terminal domain of collagen IV), and Tamm-Horsfall protein excretion rate. Albumin excretion rate was considered a sign of glomerular damage, NC1 excretion rate a measure of renal basement membrane turnover, and Tamm-Horsfall protein excretion rate a marker for distal tubular function. There were no differences between males and females and between smokers and nonsmokers with respect to blood pressure, body-mass index, albumin excretion rate, glomerular filtration rate, excretion rate of NC1, and Tamm-Horsfall protein. As a group, the patients with microalbuminuria had normal glomerular filtration rate, excretion rate of NC1, and Tamm-Horsfall protein. The latter was influenced by glycosylated hemoglobin (HbA1c) levels, especially so in patients with an albumin excretion rate less than the median value of 53.0 micrograms/min (r = -0.61, p < 0.01). Furthermore, both excretion rate of NC1 and Tamm-Horsfall protein were increased in patients with high glomerular filtration rate > or = 130 mL min-1 1.73 m-2). There was no association between glomerular filtration rate and HbA1c levels. As glomerular filtration rate is related to kidney size, these observations suggest that patients with a high glomerular filtration rate have an increased mass and turnover of tubular basement membrane.(ABSTRACT TRUNCATED AT 250 WORDS)

Type I diabetic nephropathy: clinical characteristics and economic impact

Approximately one-third of type I diabetic patients develop diabetic nephropathy with confounding pathogenesis--frequently manifested as heavy persistent proteinuria, fall in glomerular filtration rate, and increased arterial hypertension. There is increasing incidence and prevalence of type I diabetes, particularly in northern Europe and the United States. Increased morbidity and mortality occur in type I diabetic patients with renal disease. Among type I patients with persistent proteinuria, death occurs on the average within 5-10 years. The economic impact of endstage renal disease due to diabetic nephropathy is overwhelming, and the cost is increasing at an alarming rate.