[Composition of proteinuria in primary glomerulonephritides: association with tubolo-interstitial damage, outcome and response to therapy].
Experimental and clinical studies show that proteinuria is an independent risk factor for the progression of chronic glomerular diseases and is associated with the extent of tubulo-interstitial damage. The accumulation of proteins in tubular cells induces the increased expression of a variety of inflammatory and fibrogenic cytokines, with the consequent development of interstitial inflammation, a proliferation of fibroblasts, the increased production of extracellular matrix, and the formation of interstitial fibrosis. Laboratory methods, such as immunonephelometry, can easily evaluate the glomerular component of proteinuria, due to the alteration of the structural integrity of the glomerular capillary wall. This alteration allows the tubular lumen to pass proteins of high and middle molecular weight (HMW and MMW proteins: IgM, alpha2-macroglobulin, IgG, transferrin, albumin). Using the same method and SDS-PAGE, it is possible to evaluate those tubular components of proteinuria that are composed of low molecular weight (LMW) proteins, such as alpha1-microglobulin (alpha1m) and beta2-microglobulin (beta2m), whose reabsorption by tubular cells-almost complete in physiological conditions-is impaired in pathological conditions. Recent studies clarified some aspects of the relationships between the components of proteinuria, histological lesions, prediction of outcome, and response to therapy. The extent of tubulo-interstitial damage is correlated with selectivity of proteinuria and IgG excretion, suggesting a possible tubulo-toxic role for IgG or for some other protein of similar molecular weight. The tubulo-interstitial lesions are also correlated with the excretion of LMW proteins, due to their impaired reabsorption. The remission of nephrotic syndrome, not predicted by the amount of proteinuria, is highly predicted by the selectivity index or IgG excretion in membranous glomerulonephritis (MGN) and focal segmental glomerulosclerosis (FSGS). Progression to chronic renal failure is better predicted both by the glomerular component (selectivity index, IgG excretion) and by the tubular component of proteinuria (alpha1m, beta1m, LMW proteins), than by 24-hour proteinuria. The response to therapy in MGN and FSGS is dependent on the excretion of IgG and alpha1m. In conclusion the composition of proteinuria can easily be assessed using automated methods, and it is useful to evaluate the relationship of proteinuria with histological lesions to predict the functional outcome and response to therapy in primary glomerulonephritis.
Bazzi
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U.O. Nefrologia e Dialisi, Azienda Ospedaliera, Ospedale San Carlo Borromeo, Milano, Italy. daniela@oscb.sined.net
D004591:Electrophoresis, Polyacrylamide Gel; D005921:Glomerulonephritis / Q000150:complications* / Q000378:metabolism / Q000503:physiopathology / Q000628:therapy; D006801:Humans; D007684:Kidney Tubules; D011379:Prognosis; D011506:Proteins / Q000378:metabolism; D011507:Proteinuria / Q000209:etiology* / Q000378:metabolism / Q000503:physiopathology / Q000628:therapy
D011506:Proteins