Background. In patients with type 1 diabetes, some consider microalbuminuria to be a predictor of diabetic nephropathy while others believe it is an early feature of diabetic nephropathy. Methods. Levels of mRNAs that are of pathogenetic relevance in diabetic nephropathy were compared in glomeruli isolated from microalbuminuric and overtly proteinuric subjects and in control normoalbuminuric diabetic subjects and living renal transplant donors. Results. In subjects with microalbuminuria and overt proteinuria, glomerular mRNAs were virtually identical and approximately twofold higher for connective tissue growth factor (CTGF; P < 0.01) and collagen α2(IV) (P < 0.03) compared to living renal donors and normoalbuminuric patients. Glomerular glyceraldehyde-3-phosphate dehydrogenase (GAPDH) levels were not significantly different among the groups (P = 0.4). Weak but statistically significant correlations were noted between CTGF mRNA and albuminuria (assessed by rank), fractional mesangial surface area, and a composite renal biopsy index. Glomerular CTGF mRNA correlated inversely with creatinine clearance. Glomerular collagen α2(IV) mRNA levels correlated with albuminuria (by rank) and less strongly with fractional mesangial area. Conclusion. To our knowledge, these data provide the first biochemical evidence demonstrating that the glomeruli of microalbuminuric patients and those with overt proteinuria do not differ significantly. The data support the concept that microalbuminuria is not "predictive" of diabetic nephropathy, but rather is an earlier point in the spectrum of diabetic nephropathy.
Bibliographical noteFunding Information:
This work was supported by the American Diabetes Association (SA), the Juvenile Diabetes Foundation, International (SA), and the National Institutes of Health grant to the Harbor-UCLA Medical Center General Clinical Research Center (M01RR00425). It was presented in part in abstract form at the meeting of the American Society of Nephrology in Toronto, October 2000. The authors thank Dr. Jacob Rajfer for performing intraoperative biopsies on renal allografts.
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