Nephrotoxicity of Bence Jones proteins in the rat: Importance of protein isoelectric point

Abstract

Bence Jones proteins (BJP) were isolated from the urine of 12 patients with multiple myeloma and various degrees of renal dysfunction. Proteins were characterized as to type (six type lambda and five type kappa), isoelectric point (pI), and secondary structure by circular dichroism (CD). Clinical renal function was more impaired with type-lambda proteins and with proteins of pI greater than 5.7. CD studies distinguished kappa from lambda proteins in most cases but did not correlate with nephrotoxicity. Protein dimer preparations were tested for nephrotoxicity in aciduric, hydropenic, female, Sprague Dawley rats by following renal function and morphology over 6 hours after injection i.p. of 300 mg of protein. Twelve rats of urine pH less than 5.5 injected with four BJP of pI less than 5.7 showed a mean rise in SUN of 5.3 mg/dl and in creatinine of 0.06 mg/dl, compared with a mean rise of 28.0 mg/dl (SUN) and 0.75 mg/dl (creatinine) in 21 rats injected with seven BJP of pI greater than 5.7 (P less than 0.01). Seven sodium-bicarbonate-fed rats of urine pH greater than 8 injected with a BJP of pI 6.2 showed mean rise in SUN of 1.8 mg/dl and in creatinine of 0.01 mg/dl, compared with 19.3 mg/dl (SUN) and 0.55 mg/dl (creatinine) in 7 aciduric rats injected with the same BJP (P = 0.009). Morphologic and immunohistologic studies showed distal cast formation in 9 rats with acute deterioration in renal function. It is concluded that BJP of pI greater than urine pH are acutely nephrotoxic in the rat by a mechanism that may involve a charge interaction in the distal nephron.

Bence Jones proteins bind to a common peptide segment of Tamm-Horsfall glycoprotein to promote heterotypic aggregation.

“…In the competition study with BJPs, different BJPs replaced each other despite having different isotypes (K or X). Other investigators showed that both K and X BJPs deposited as casts in mouse and rat kidneys (13)(14)(15)(16)(17)(18)(19)29). The difference in the binding affinity in the current study was also not related directly to the isoelectric point of BJPs (Table III).…”

“…These intraluminal casts are composed of Bence Jones protein (BJP)' and Tamm-Horsfall glycoprotein (THP) (8), a protein that is synthesized by cells of the thick ascending limb of the loop of Henle (9,10) and is the major constituent ofurinary casts ( 11 ). As shown originally by Koss et al ( 12) and confirmed by others (13)(14)(15)(16)(17)(18)(19), cast nephropathy can be reproduced in mice and rats by parenteral injection of purified human Bence Jones protein. We have demonstrated that cast-forming human Bence Jones proteins coaggregate with Tamm-Horsfall glycoprotein to obstruct the distal nephron (14)(15)(16).…”

Differential nephrotoxicity of low molecular weight proteins including Bence Jones proteins in the perfused rat nephron in vivo.

“…This observation contradicts Clyne and associates (10), who suggested a correlation between nephrotoxicity of BJPs and higher pl. One difference between their study and ours was the route ofadministration ofthe protein.…”

“…Previous studies have demonstrated that LMWPs, such as BJPs (3,4,6,7,(10)(11)(12)(13)(14)(15)(16)(17), MYG (7,(18)(19)(20)(21), lysozyme (22), and BLG (6, 7), can cause renal damage in humans and animals. Although most ofthese studies have shown a tubulointerstitial lesion (3, 4, 6, 10-12, 13-18, 20-23), other abnormalities including alterations in intrarenal hemodynamics (19,21) and glomerular damage (19,22) may also participate in the pathogenesis of renal failure from these proteins.…”

“…While some authors have suggested that the pI ofthe protein is an important nephrotoxic property in humans (20,24) and in animal models of cast nephropathy (10) and cell toxicity (25), others have not been able to reproduce these results (6,16,17,26,27). A reason for this confusion is that, as we have demonstrated, LMWPs can produce two distinct tubular lesions, PT injury and intrarenal obstruction, and these lesions were not considered separately by most of these investigators.…”