Renal elimination of beta-2-microglobulin and myoglobin in patients with normal and impaired renal function

Since the demonstration that beta 2-microglobulin (beta 2M) is an amyloidogenic protein in man, the excretion of this low-molecular-weight protein under conditions with normal and reduced renal function has received increased interest. The renal arteriovenous extraction of beta 2M, polyfructosan (an inulin analogue), and a second low-molecular-weight protein, myoglobin, was measured in vivo in 16 human kidneys with normal renal function/gross morphology and in 22 kidneys with reduced function. In kidneys with normal function, the extraction of beta 2M significantly exceeded that of polyfructosan (0.198 +/- 0.037 vs. 0.182 +/- 0.05; p = 0.04), while that of myoglobin (0.177 +/- 0.068) was not different from that of polyfructosan. In kidneys with reduced function, the extraction of polyfructosan or myoglobin was not significantly altered. In contrast, the beta 2M extraction decreased to 0.110 +/- 0.060 (p less than 0.01 vs. extraction of polyfructosan or myoglobin). This decrease was significantly correlated with the decrease of the endogenous creatinine clearance or the total or unilateral 131I-hippuran clearance. These results indicate that in normal renal function the glomerular filtration of beta 2M may be supplemented by a peritubular mode of removal. The mechanism(s) underlying the selective decrease of beta 2M extraction in kidneys with reduced function remain speculative. However, this decrease will lead to a further augmentation of the retention of beta 2M in renal failure.