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The Renal Handling of Low Molecular Weight Proteins: II The renal handling of low molecular weight proteins: II. Disorders of serum protein catabolism in patients with tubular proteinuria, the nephrotic syndrome, or uremia Thomas A. Waldmann, … , Warren Strober, R. Peter Mogielnicki J Clin Invest. 1972;51(8):2162-2174. https://doi.org/10.1172/JCI107023. The present study was directed toward determining the role of the kidney in the metabolism of various classes of serum proteins and to define the urinary protein excretion patterns and the pathogenesis of disorders of protein metabolism in patients with proteinuria. To this end, the metabolic fates of a small protein, λ-L chain (mol wt 44,000), and a protein of intermediate size, IgG (mol wt 160,000), were studied in controls and patients with renal disease. Controls metabolized 0.28%/hr of circulating IgG and 22.3%/hr of circulating λ-L chain. All the IgG and 99% of the λ-L chain was catabolized with the remaining λ-L chain lost intact into the urine. The kidney was shown to be the major site of catabolism for small serum proteins. Three distinct disorders of protein metabolism were noted in patients with renal tubular disease and tubular proteinuria, glomerular disease (the nephrotic syndrome), and disease involving the entire nephrons (uremia), respectively. Patients with renal tubular disease had a 50-fold increase in the daily urinary excretion of 15-40,000 molecular weight proteins such as lysozyme and λ-L chains. Serum IgG and λ-L chain survivals were normal; however, the fraction of the over-all λ-L chain metabolism accounted for by proteinuria was increased 40-fold whereas endogenous catabolism was correspondingly decreased. Thus, tubular proteinuria results from a failure of proximal tubular uptake and […] Find the latest version: https://jci.me/107023/pdf The Renal Handling of Low Molecular Weight Proteins II. DISORDERS OF SERUM PROTEIN CATABOLISM IN PATIENTS WITH TUBULAR PROTEINURIA, THE NEPHROTIC SYNDROME, OR UREMIA THOMAS A. WALDMANN, WARREN STROBER, and R. PETER MOGIELNICKI From the Immunophysiology Section of the Metabolism Branch, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20014 A B S T R A C T The present study was directed toward markedly increased. Here, abnormal glomerular perme- determining the role of the kidney in the metabolism of ability to proteins of intermediate size is the basic ab- various classes of serum proteins and to define the uri- normality. Patients with uremia had a normal IgG nary protein excretion patterns and the pathogenesis of survival but a four to 10-fold prolongation of X-L chain disorders of protein metabolism in patients with pro- survival due to loss of entire nephrons, the major site of teinuria. To this end, the metabolic fates of a small pro- metabolism of these proteins. This results in an increase tein, X-L chain (mol wt 44,000), and a protein of (up to 10-fold) in the serum concentration of X-L chain, intermediate size, IgG (mol wt 160,000), were studied lysozyme, and other small biologically active proteins, a in controls and patients with renal disease. Controls phenomenon that may be of importance in causing some metabolized 0.28%/hr of circulating IgG and 22.3%/hr of the manifestations of the uremic syndrome. of circulating X-L chain. All the IgG and 99% of the X-L chain was catabolized with the remaining X-L chain lost intact into the urine. The kidney was shown to be INTRODUCTION the major site of catabolism for small serum proteins. The relationship of normal renal function to the metab- Three distinct disorders of protein metabolism were olism of serum proteins is reflected in the fact that pro- noted in patients with renal tubular disease and tubular teinuria and abnormalities of serum protein concentration proteinuria, glomerular disease (the nephrotic syndrome), accompany most forms of renal disease. In recent years and disease involving the entire nephrons (uremia), re- this role of the kidney in protein metabolism has been spectively. Patients with renal tubular disease had a 50- clarified with the use of analytical techniques for the fold increase in the daily urinary excretion of 1540,000 quantitation of proteins in biological fluids. Such tech- molecular weight proteins such as lysozyme and X-L niques have led to the concept that there are two main chains. Serum IgG and X-L chain survivals were normal; forms of proteinuria, one associated with glomerular however, the fraction of the over-all X-L chain metab- damage, glomerular proteinuria, and the other associ- olism accounted for by proteinuria was increased 40-fold ated with disorders of the convoluted tubule of the kidney, whereas endogenous catabolism was correspondingly de- tubular proteinuria. In glomerular proteinuria large creased. Thus, tubular proteinuria results from a failure quantities of proteins of intermediate molecular size such of proximal tubular uptake and catabolism of small pro- as albumin (mol wt 68,000), transferrin (mol wt 90,000), teins that are normally filtered through the glomerulus. and, to a lesser extent, IgG (mol wt 160,000) appear in Patients with the nephrotic syndrome had a slight in- the urine. In tubular proteinuria the total urinary pro- crease in X-L chain survival whereas IgG survival was tein loss is usually much less than in glomerular protein- decreased and the fraction of IgG lost in the urine was uria and the proteins present in greatest abundance in the urine are a heterogeneous group of proteins with An abstract of this work appeared in J. Clin. Invest. 1970. relatively low molecular weights (mol wt 10-50,000) in- 49: 99a. (Abstr.) Received for publication 28 December 1971 and in revised cluding serum enzymes, immunoglobulin light chains, and form 13 March 1972. small protein hormones (1-8). As the name implies, 2162 The Journal of Clinical Investigation Volume 51 August 1972 tubular proteinuria is observed in a number of conditions The serum and urine of additional patients were ob- showing acquired or hereditary abnormalities of renal tained for studies of protein excretion patterns and serum tubular function. Examples include cadmium lysozyme concentrations. This group included eight patients poisoning with proximal renal tubular disease, six patients with the (9), Wilson's disease (10), hypokalemic nephropathy nephrotic syndrome, and 21 patients with uremia and end- (11), acute tubular necrosis (12), renal allograft rejec- stage kidney disease. tion (13), and the Fanconi syndrome (1). Mode of collection and concentration of the urine. In A second technique that has been applied to the study order to determine the pattern of urinary protein excre- of the role of the kidney in tion and the 24-hr excretion rate of various specific proteins, protein homeostasis is the urine was collected in 24-hr lots without addition of pre- use of radiolabeled proteins in metabolic turnover studies. servatives and stored at -20'C until used. Before analysis Such studies provide a quantitative description of the urine was first clarified by centrifugation for 10 min at various pathways of metabolism and excretion for indi- 3000 rpm at 40C. The urine was then- concentrated to a vidual protein components. They have been used to de- volume of 30-40 ml by ultrafiltration using a Diaflo ultra- filtration apparatus 1 (containing a 1000 mol wt cut-off, termine the role of the kidney in albumin metabolism in UM-2, ultrafilter). In a final concentration step the urine both normal individuals and those with glomerular dis- was reduced to a volume of 2-4 ml by placing the urine ease (14-18). In addition, metabolic turnover studies in an 8/32 Visking dialysis tube and then immersing the have been used to show that the kidney is a major site latter in dry, cross-linked dextran (Sephadex G-200). The exact concentration of catabolism of low molecular serum degree of achieved by these procedures weight proteins was determined by adding a known quantity of 'I labeled (19-24). X-type Bence Jones protein to the urine at the start of the In the present study analytical techniques and turnover manipulations and then determining the extent to which studies with radiolabeled proteins were used in concert the labeled material was concentrated by comparing counts milliliter in to shed additional light on the pathogenesis of abnormali- per pre- and postconcentration samples of urine. Determination of urine protein excretion patterns. (a) ties of serum and urinary protein levels in patients with Urinary electrophoresis. The concentrated urine specimens different forms of renal disease. To this end the metabolic were subjected to analytical polyacrylamide disc gel electro- fates of a small serum protein, X-L chain (mol wt 44,000) phoresis using a 7.5% alkaline polyacrylamide gel according and a protein of intermediate size, IgG (mol wt 160,000), to the method of Davis (25). In addition, polyacrylamide were studied in control individuals as well as in pa- gel electrophoresis was also performed in the presence of the anionic detergent sodium dodecyl sulfate (SDS)2 ac- tients with glomerular damage and the nephrotic syn- cording to the method of Shapiro, Vinuela, and Maizel (26). drome, patients with renal tubular disease, and patients (b) 24-hr excretion rates of various proteins. The con- with nephron loss and uremia. centration of total protein and specific protein components were determined in concentrated urine specimens and con- METHODS verted to 24-hr excretion rates using the 24 hr urine volume and the degree of concentration determined as discussed Patient material. 45 turnover studies were performed above. The total protein concentration of the urine was with purified lambda (X) L chain dimers (mol wt 44,000) determined by the Biuret technique of Gornall, Bardawill, or IgG (mol wt 160,000) in patients with proximal renal and David (27).
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