alpha 2u-globulin nephropathy and renal tumors in national toxicology program studies

Chemically induced renal neoplasms in male rats, developed coincident with alpha(2u)-globulin nephropathy, are not considered predictive of risk to humans by the International Agency for Research on Cancer (IARC) and the U.S. Environmental Protection Agency. Criteria have been defined to establish the role of alpha(2u)-globulin nephropathy in renal carcinogenesis, based on a proposed mode of action involving sustained tubular cell proliferation resulting from alpha(2u)-induced nephropathy, with consequent development of neoplastic lesions. Recent NTP studies demonstrated inconsistencies with this proposed mechanism, including in some cases, far weaker kidney tumor responses than expected based on the extent of alpha(2u)-globulin nephropathy. NTP studies with decalin, propylene glycol mono-t-butyl ether and Stoddard solvent IIC included extended evaluations of alpha(2u)-related nephropathy, and were thus used in assessing the linkage between key events in 90-day studies with renal tumors in 2-year studies. This review revealed no or at best weak associations of tumor responses with renal alpha(2u)-globulin concentrations, indices of cell turnover, or microscopic evidence of alpha(2u)-associated nephropathy in prechronic studies. While tumor responses corresponded somewhat with a measure of cumulative alpha(2u)-associated nephropathy (linear mineralization of the papilla) at the end of the 2-year studies, the severity of chronic nephropathy was generally in best agreement with the pattern of tumor response. These results suggest that while alpha(2u)-globulin nephropathy may contribute to the renal tumor response, the critical component(s) of the nephropathy most closely associated with the development of tumors could not be clearly identified in this review.

2-sec-butyl-4,5-dihydrothiazole is a ligand for mouse urinary protein and rat alpha 2u-globulin: physiological and toxicological relevance

Mouse urinary protein (MUP) and alpha 2u-globulin are structurally homologous proteins that belong to a superfamily of ligand-binding proteins and represent the major urinary proteins excreted by adult male mice and rats, respectively. Although a variety of xenobiotics bind to alpha 2u-globulin and produce a male rat-specific hyaline droplet nephropathy, no endogenous ligand for this protein has been identified. Despite extensive sequence homology. MUP does not bind to hyaline droplet-inducing agents. While performing experiments with purified MUP, we observed that it presented with a strong, distinctive odor reminiscent of mouse urine. To determine whether this odor was the result of contamination or degradation or was attributed to an endogenous ligand bound to the protein, the protein was subjected to thermal desorption and any released volatile compounds were detected with a gas chromatograph equipped with an external sniff port and mass spectrometer. With this approach, two odorous compounds were detected at the sniff port by a human observer, but only one was present in sufficient mass to allow identification. This compound, which presented with the characteristic odor, was subsequently identified as 2-sec butyl-4,5-dihydrothiazole (DHT) by GC/MS/matrix isolation IR and NMR analyses. The identification of DHT was confirmed by comparing the chromatographic and spectral properties to those of the synthesized authentic compound. In direct contrast, purified urinary alpha 2u-globulin did not present with an obvious odor, and no volatile ligands were detected on this protein. Although DHT is a major endogenous ligand for MUP, it was also found to competitively inhibit the binding of [14C]d-limonene-1,2-epoxide to alpha 2u-globulin with relatively high affinity (Ki = 2.3 microM). When dosed orally to F344 rats, DHT (1 mmol/kg for 3 days) caused the characteristic exacerbation of hyaline droplets in male rat kidneys and increased renal levels of immunoreactive alpha 2u-globulin about threefold over control levels. These results indicate that despite structural homology, MUP and alpha 2u-globulin are distinguished by the presence of a volatile endogenous ligand only on the former, a distinction that may reflect differences in the physiological functions of the two proteins. Furthermore, although DHT can bind to both MUP and alpha 2u-globulin, renal toxicity was only observed in rats, thereby emphasizing the unique toxicological properties of alpha 2u-globulin in the development of hyaline droplet nephropathy.

Quantitation of alpha(2)-microglobulin after administration of structurally divergent chemical compounds

alpha(2)-Microglobulin-induced nephropathy is a phenomenon which is exclusively found in adult male rats. Various chemicals are able to bind to alpha(2)-microglobulin thus inhibiting its proteolytic degradation in lysosomes of the P2 segment of the rat nephron. The accumulation of this protein in 'protein droplets' or 'hyaline droplets' leads to necrosis, followed by regeneration which possibly later results in the formation of tumours. Here we report the development of a monoclonal antibody which is specific for alpha(2)-microglobulin. It was utilized to measure alpha(2)-microglobulin concentrations in plasma and tissues, and to stain alpha(2)-microglobulin in fixed tissue slides. In two studies we administered to adult male Wistar rats two groups of compounds: (1) one group of structurally diverse compounds, which give an overview of chemical entities capable of inducing the accumulation of alpha(2)-microglobulin; and (2) another group of structurally closely related compounds (i.e. substituted benzene derivatives) for the purpose of elucidating possible structure-activity relationships. The degree of alpha(2)-microglobulin-induced nephropathy was determined by immunohistochemical staining of kidney sections. In addition, liver and kidney tissue and plasma concentrations of alpha(2)-microglobulin were not found to be elevated whereas kidney tissue concentrations were higher than the controls. The increase over control values ranged from 154% (1,4-dichloromethyl-benzene) to 321% [alpha-methyl-4-(1-methylethyl)-cyclohexanemethanol]. Comparing structurally related benzene derivatives, the hyaline droplet accumulating (HDA) potential was found to depend both on the type of substituent and its position at the aromatic ring. In general HDA activity increased in the order benzene approximately equal to phenol approximately equal to alkylated phenols < halogenated phenols < halogenated benzenes. Further QSAR studies are needed to provide a theoretical base for these observations.

Preparation and properties of a therapeutic inter-alpha-trypsin inhibitor concentrate from human plasma

Inter-alpha-trypsin inhibitor (ITI) is a serine protease inhibitor found in human plasma. Its antiprotease activity is due to bikunin which is effective in various types of experimental shock and pancreatitis. Therefore ITI, which releases bikunin by proteolytic cleavage, could be of therapeutic interest. A method for the large-scale isolation of ITI from human plasma is described. ITI was purified from the prothrombin complex concentrate (PCC) by diethylaminoethyl-Sepharose fast-flow chromatography followed by a chromatographic step on immobilized heparin designed to remove C4, factor X and protein C. With this procedure, which was performed under mild conditions, a homogeneous preparation of native ITI was obtained, as demonstrated by electrophoretic and chromatographic analyses. ITI maintained its biological activity, as exhibited by its specific antitryptic activity of 420 +/- 65 IU/g. In order to decrease or eliminate the risk of transmission of viral disease due to lipid-enveloped viruses, the process incorporated a solvent-detergent treatment. Animal studies on the final product revealed no adverse side-effects in terms of toxicity, thrombogenicity or hypotension. This preparation appears suitable for therapeutic evaluation in animal experimental models.

Antitumor activity of normal human globulin: effects on murine and human erythroleukemic cells

The effect of the antitumor fraction isolated from the alpha 2-globulin region of normal human serum (NHG-I) upon murine (FELC) and human (K562) erythroleukemic cells in vitro was determined. NHG-I inhibited the growth of both actively growing FELC and K562 cells in a dose-dependent manner. However, it has no effect upon mitomycin C treated FELC which were unable to divide nor upon dimethylsulfoxide-induced FELC in stationary phase. These results indicate that NHG-I has a cytostatic effect upon cell growth and suggests that its action may be dependent upon DNA synthesis. This is in marked contrast to TNF, the alpha 2-globulin factor obtained from murine serum which is also not species-specific but whose action upon these cell lines is cytotoxic.