The aim of the present study was to evaluate renal and liver distribution of two monoclonal immunoglobulin light chains. The chains were purified individually from the urine of patients with multiple myeloma and characterized as lambda light chains with a molecular mass of 28 kDa. They were named BJg (high amount of galactose residues exposed) and BJs (sialic acid residues exposed) on the basis of carbohydrate content. A scintigraphic study was performed on male Wistar rats weighing 250 g for 60 min after iv administration of 1 mg of each protein (7.4 MBq), as the intact proteins and also after carbohydrate oxidation. Images were obtained with a Siemens gamma camera with a high-resolution collimator and processed with a MicroDelta system. Hepatic and renal distribution were established and are reported as percent of injected dose. Liver uptake of BJg was significantly higher than liver uptake of BJs (94.3 vs 81.4%) (P<0.05). This contributed to its greater removal from the intravascular compartment, and consequently lower kidney accumulation of BJg in comparison to BJs (5.7 vs 18.6%) (P<0.05). After carbohydrate oxidation, there was a decrease in hepatic accumulation of both proteins and consequently a higher renal overload. The tissue distribution of periodate-treated BJg was similar to that of native BJs: 82.7 vs 81.4% in the liver and 17.3 vs 18.6% in the kidneys. These observations indicate the important role of sugar residues of Bence Jones proteins for their recognition by specific membrane receptors, which leads to differential tissue accumulation and possible toxicity.

Proximal tubule handling of two human Bence Jones proteins (neutral and acidic BJP) was evaluated using protein A-gold labelling. After 30 min of acute light-chain infusion into 6 rats (alone or in combination with dinitrophenyl-aminopropyl-methylamine [DAMP]), kidney biopsies were processed for immunoelectron microscopy. Antibodies directed at monoclonal lambda light chains, mannose-6-phosphate cation-independent receptor (MPR) and DAMP were used.Labelling density (number of pA-gold particles/µm²), expressed as median (25–75 percentiles), differed (p < 0.05) between the two BJP, being 94.5 (32.9–212.5) vs. 19.4 (3.7–45.6) pA-gold/µm² in endocytic vacuoles, and 297.3 (207.1–382.1) vs. 83.2 (16.6–197.0) pA-gold/µm² in non-vacuolar electrondense endosome-lysosome structures. Labelling density for MPR was 47.7 (22.2–84.6) vs. 4.0 (2.7–6.3) pA-gold/µm². The area of MPR-labelled structures was also different, i.e.: 0.2 (0.1–0.4) vs. 0.9 (0.5–1.8) µm². The endosome-lysosome pH distribution range differed significantly: 6.8 (6.4–7.0) vs. 6.3 (5.8–7.0). There was a significant accumulation of neutral BJP in endocytic structures, an acidification deficit of pre-lysosomes/lysosomes and MPR retention, suggestive of defective receptor recycling with this BJP. Interference with the physiological process of lysosomal acidification may be an important mechanism of higher nephrotoxicity in some BJP.

The aim of the present study was to evaluate the acidification of the endosome-lysosome system of renal epithelial cells after endocytosis of two human immunoglobulin lambda light chains (Bence-Jones proteins, BJP) obtained from patients with multiple myeloma. Renal epithelial cell handling of two BJP (neutral and acidic BJP) was evaluated by rhodamine fluorescence. Renal cells (MDCK) were maintained in culture and, when confluent, were incubated with rhodamine-labeled BJP for different periods of time. Photos were obtained with a fluorescence microscope (Axiolab-Zeiss). Labeling density was determined on slides with a densitometer (Shimadzu Dual-Wavelength Flying-Spot Scanner CS9000). Endocytosis of neutral and acidic BJP was correlated with acidic intracellular compartment distribution using acridine orange labeling. We compared the pattern of distribution after incubation of native neutral and acidic BJP and after complete deglycosylation of BJP by periodate oxidation. The subsequent alteration of pI converted neutral BJP to acidic BJP. There was a significant accumulation of neutral BJP in endocytic structures, reduced lysosomal acidification, and a diffuse pattern of acidification. This pattern was reversed after total deglycosylation and subsequent alteration of the pI to an acidic BJP. We conclude that the physicochemical characteristics of BJP interfere with intracellular acidification, possibly explaining the strong nephrotoxicity of neutral BJP. Lysosomal acidification is fundamental for adequate protein processing and catabolism.

The aim of this investigation was to evaluate the endocytosis of two Bence-Jones proteins by renal cells in order to