Proof of the hepatic synthesis of a sex-dependent protein in the rat

Evaluation of the 52-week chronic toxicity of a novel phthalate-free plasticizer, Eco-DEHCH (bis(2-ethylhexyl) cyclohexane-1,4-dicarboxylate), in Han Wistar rats

Phthalate esters (PEs) are the most widely used class of plasticizers. Several PEs, however, were found to have adverse effects on the health of animals. A new phthalate-free plasticizer, Eco-DEHCH (bis(2-ethylhexyl) cyclohexane-1,4-dicarboxylate), was recently developed as an ecofriendly replacement for phthalate plasticizers and to be less harmful to organisms. The present study evaluated the long-term toxicity of Eco-DEHCH in Wistar Han rats to explore adverse effects and predict hazardous potential to humans. Forty male and forty female Wistar Han rats were exposed to Eco-DEHCH in dietary feed for 52 weeks, and their hematologic, coagulation, and serum biochemical parameters were monitored. The rats were subjected to close clinical, ophthalmic, and histopathologic examinations and urinalysis throughout the consumption of Eco-DEHCH. The effects of this plasticizer on food consumption and organ weight were also determined. Chronic exposure to Eco-DEHCH was generally safe, although it also resulted in α_2u-globulin accumulation, a parameter with no human relevance. In conclusion, Eco-DEHCH can serve as a safe and promising alternative plasticizer.

Two predominant MUPs, OBP3 and MUP13, are male pheromones in rats

BACKGROUND

In rats, urine-borne male pheromones comprise organic volatile compounds and major urinary proteins (MUPs). A number of volatile pheromones have been reported, but no MUP pheromones have been identified in rat urine.

RESULTS

We used sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE), isoelectric focusing electrophoresis (IEF), nano-liquid chromatography-tandem mass spectrometry (nLC-MS/MS) after in gel digestion of the proteins and quantitative real-time PCR (qRT-PCR) and showed that the levels of two MUPs, odorant-binding protein 3 (OBP3) (i.e. PGCL4) and MUP13 (i.e. PGCL1), in urine and their mRNAs in liver were higher in males than in females and were suppressed by orchidectomy and restored by testosterone treatment (T treatment). We then generated recombinant MUPs (rMUPs) and found that the sexual attractiveness of urine from castrated males to females significantly increased after the addition of either recombinant OBP3 (rOBP3) or recombinant MUP13 (rMUP13). Using c-Fos immunohistochemistry, we further examined neuronal activation in the brains of female rats after they sniffed rOBP3 or rMUP13. Both rOBP3 and rMUP13 activated the accessory olfactory bulb (AOB), medial preoptic area (MPA), bed nucleus of the stria terminalis (BST), medial amygdala (MeA), posteromedial cortical amygdala (PMCo) and ventromedial nucleus of the hypothalamus (VMH), which participate in the neural circuits responsible for pheromone-induced sexual behaviours. In particular, more c-Fos-immunopositive (c-Fos-ir) cells were observed in the posterior AOB than in the anterior AOB.

CONCLUSIONS

The expression of OBP3 and MUP13 was male-biased and androgen-dependent. They attracted females and activated brain areas related to sexual behaviours in female rats, suggesting that both OBP3 and MUP13 are male pheromones in rats. Particularly, an OBP excreted into urine was exemplified to be a chemical signal.

Sex differences in the excretion levels of traditional and novel urinary biomarkers of nephrotoxicity in rats

Urinary biomarkers have been used widely in preclinical toxicity studies to detect dysfunctions and injuries of the kidney caused by drugs under development. While they have been well studied for evaluating nephrotoxicity, knowledge of sex differences in excretion levels of urinary biomarkers remains inadequate. We conducted experiments focused on effects of endogenous sex hormones on urinary biomarkers using intact and castrated male and female rats. Comparisons of the urinary biomarker excretion levels between intact male and female rats at 5, 7, 9 and 12 weeks of age revealed higher excretion levels of leucine aminopeptidase (LAP), γ-glutamyl transpeptidase (γGTP), total protein, liver-type fatty acid-binding protein (L-FABP), cystatin C (Cys-C) and β2-microglobulin (β2-MG), and lower excretion level of kidney injury molecule 1 (Kim-1), in male rats as compared to female rats. Orchidectomized male rats showed lower urinary excretion levels of alkaline phosphatase (ALP), LAP, γGTP, N-acetyl-β-D-glucosaminidase (NAG), glucose, total protein, L-FABP, Cys-C, β2-MG and neutrophil gelatinase-associated lipocalin (NGAL), and higher urinary excretion levels of clusterin (CLU) and Kim-1, than sham-operated male rats. On the other hand, no significant differences in the urinary biomarker excretion levels excluding ALP were observed between ovariectomized and sham-operated female rats. In the present study, we demonstrated the existence of sex differences in excretion levels of urinary biomarkers that are universally used in preclinical toxicity studies, and also that these differences, especially in relation to the urinary excretions of ALP, LAP, γGTP, total protein, L-FABP, Cys-C, and β2-MG, may closely relate to the endogenous testosterone.

The major urinary protein system in the rat

The genomes of rats and mice both contain a cluster of multiple genes that encode small (18–20 kDa) eight-stranded β-barrel lipocalins that are expressed in multiple secretory tissues, some of which enter urine via hepatic biosynthesis. These proteins have been given different names, but are mostly generically referred to as MUPs (major urinary proteins). The mouse MUP cluster is increasingly well understood, and, in particular, a number of roles for MUPs in chemical communication between conspecifics have been established. By contrast, the literature on the rat orthologues is much less well developed and is fragmented. In the present review, we summarize current knowledge on the MUPs from the Norway (or brown) rat, Rattus norvegicus.

Changes in male rat urinary protein profile during puberty: a pilot study

Background

Androgen-dependent proteins (lipocalins) circulate in blood of male rats and mice and, being small (~ 18 kDa), pass freely into glomerular filtrate. Some are salvaged in proximal nephrons but some escape in urine. Several organic molecules can bind to these proteins causing, where salvage occurs, nephropathy including malignancy in renal cortex. In urine, both free lipocalins and ligands contribute to an increasingly-recognised vital biological role in social communication between adults, especially in the dark where reliance is on smell and taste. Crystal structure of the first-characterised lipocalin of male rats, α2u-globulin, has been determined and peptide sequences for others are available, but no study of occurrence during early puberty has been made. We have followed temporal occurrence in urine of juveniles (n = 3) for non-invasive pilot study by high resolution gradient mini-gel electrophoresis, tryptic digest of excised protein bands, and LC-MS/MS of digest to identify peptide fragments and assign to specific lipocalins. Study objective refers directly to external availability for social communication but also indirectly to indicate kinetics of circulating lipocalins to which some xenobiotics may bind and constitute determinants of renal disease.

Results

Mini-gels revealed greater lipocalin complexity than hitherto recognised, possibly reflecting post-translational modifications. Earliest patterns comprised rat urinary protein 1, already evident in Sprague-Dawley and Wistar strains at 36 and 52 days, respectively. By 44 and 57 days major rat protein (α2u-globulin) occurred as the progressively more dominant protein, though as two forms with different electrophoretic mobility, characterised by seven peptide sequences. No significant change in urinary testosterone had occurred in Wistars when major rat protein became evident, but testosterone surged by 107 days concomitant with the marked abundance of excreted lipocalins.

Conclusions

Qualitative temporal changes in the composition of excreted lipocalins early in puberty, and apparent increase in major urinary protein as two resolvable forms, should catalyse systematic non-invasive study of urinary lipocalin and testosterone dynamics from early age, to illuminate this aspect of laboratory rodent social physiology. It could also define the potential temporal onset of nephrotoxic ligand risk, applicable to young animals used as toxicological models.

Renal biomarker changes associated with hyaline droplet nephropathy in rats are time and potentially compound dependent

Alpha 2u-globulin mediated hyaline droplet nephropathy (HDN) is a male rat specific lesion induced when a compound or metabolite binds to alpha 2u-globulin. The objective of this study was to investigate if the newer and more sensitive renal biomarkers would be altered with HDN as well as be able to distinguish between HDN and oxidative stress-induced kidney injury. Rats were dosed orally for 7 days to determine (1) if HDN (induced by 2-propanol or D-limonene) altered the newer renal biomarkers and not BUN or creatinine, (2) if renal biomarkers could distinguish between HDN and oxidative stress-induced kidney injury (induced by potassium bromate), (3) sensitivity of HDN-induced renal biomarker changes relative to D-limonene dose, and (4) reversibility of HDN and renal biomarkers, using vehicle or 300 mg/kg/day D-limonene with 7 days of dosing and necropsies scheduled over the period of Days 8-85. HDN-induced renal biomarker changes in male rats were potentially compound specific: (1) 2-propanol induced mild HDN without increased renal biomarkers, (2) potassium bromate induced moderate HDN with increased clusterin, and (3) D-limonene induced marked HDN with increased αGST, μGST and albumin. Administration of potassium bromate did not result in oxidative stress-induced kidney injury, based on histopathology and renal biomarkers creatinine and BUN. The compound D-limonene induced a dose dependent increase in HDN severity and renal biomarker changes without altering BUN, creatinine or NAG: (1) minimal induction of HDN and no altered biomarkers at 10 mg/kg/day, (2) mild induction of HDN with increased αGST and μGST at 50 mg/kg/day and (3) marked induction of HDN with increased αGST, μGST and albumin at 300 mg/kg/day. HDN induced by D-limonene was reversible, but with a variable renal biomarker pattern over time: Day 8 there was increased αGST, μGST and albumin; on Day 15 increased clusterin, albumin and Kim-1. In summary, HDN altered the newer and more sensitive renal biomarkers in a time and possibly compound dependent manner.

Urinary protein profiles in a rat model for diabetic complications

Diabetes mellitus is estimated to affect approximately 24 million people in the United States and more than 150 million people worldwide. There are numerous end organ complications of diabetes, the onset of which can be delayed by early diagnosis and treatment. Although assays for diabetes are well founded, tests for its complications lack sufficient specificity and sensitivity to adequately guide these treatment options. In our study, we employed a streptozotocin-induced rat model of diabetes to determine changes in urinary protein profiles that occur during the initial response to the attendant hyperglycemia (e.g. the first two months) with the goal of developing a reliable and reproducible method of analyzing multiple urine samples as well as providing clues to early markers of disease progression. After filtration and buffer exchange, urinary proteins were digested with a specific protease, and the relative amounts of several thousand peptides were compared across rat urine samples representing various times after administration of drug or sham control. Extensive data analysis, including imputation of missing values and normalization of all data was followed by ANOVA analysis to discover peptides that were significantly changing as a function of time, treatment and interaction of the two variables. The data demonstrated significant differences in protein abundance in urine before observable pathophysiological changes occur in this animal model and as function of the measured variables. These included decreases in relative abundance of major urinary protein precursor and increases in pro-alpha collagen, the expression of which is known to be regulated by circulating levels of insulin and/or glucose. Peptides from these proteins represent potential biomarkers, which can be used to stage urogenital complications from diabetes. The expression changes of a pro-alpha 1 collagen peptide was also confirmed via selected reaction monitoring.

Species specificity in major urinary proteins by parallel evolution

Species-specific chemosignals, pheromones, regulate social behaviors such as aggression, mating, pup-suckling, territory establishment, and dominance. The identity of these cues remains mostly undetermined and few mammalian pheromones have been identified. Genetically-encoded pheromones are expected to exhibit several different mechanisms for coding 1) diversity, to enable the signaling of multiple behaviors, 2) dynamic regulation, to indicate age and dominance, and 3) species-specificity. Recently, the major urinary proteins (Mups) have been shown to function themselves as genetically-encoded pheromones to regulate species-specific behavior. Mups are multiple highly related proteins expressed in combinatorial patterns that differ between individuals, gender, and age; which are sufficient to fulfill the first two criteria. We have now characterized and fully annotated the mouse Mup gene content in detail. This has enabled us to further analyze the extent of Mup coding diversity and determine their potential to encode species-specific cues.

Our results show that the mouse Mup gene cluster is composed of two subgroups: an older, more divergent class of genes and pseudogenes, and a second class with high sequence identity formed by recent sequential duplications of a single gene/pseudogene pair. Previous work suggests that truncated Mup pseudogenes may encode a family of functional hexapeptides with the potential for pheromone activity. Sequence comparison, however, reveals that they have limited coding potential. Similar analyses of nine other completed genomes find Mup gene expansions in divergent lineages, including those of rat, horse and grey mouse lemur, occurring independently from a single ancestral Mup present in other placental mammals. Our findings illustrate that increasing genomic complexity of the Mup gene family is not evolutionarily isolated, but is instead a recurring mechanism of generating coding diversity consistent with a species-specific function in mammals.

Studies of the FABP family: a retrospective

Following my research on the role played by soluble proteins in their function as hydrophobic ligand carriers acting through squalene epoxidase, Dr Odani and I started to work together on low molecular lipid binding proteins. As a result of this collaboration, in 1982 we managed to determine the complete primary structure of Z-protein in rat liver. This was the first report ever to give the complete amino acid sequence of a fatty acid binding protein (FABP). This gave momentum to further such research, and now extensive exploration has been carried out on a whole family of homologous intracellular hydrophobic ligand binding proteins, the product of the expression of an ancient gene family in numerous organisms. Takahashi et al. have determined the primary structures of mammalian FABP family protein in liver, intestine, heart, kidney, and skin through amino acid sequencing as well as through determination of the cDNA sequence. Out of all my research on the FABP family, I believe, my initial study on FABP in liver, my work on kidney FABP, heart type FABP and my discovery of an I-15P (BAPB) and I-FABP application as a diagnostic marker stand out in particular.

Changes of serum alpha 2u-globulin in the subacute oral toxicity study of ethynyl estradiol and bisphenol A based on the draft protocol for the 'Enhanced OECD Test Guideline No. 407'

To investigate the usefulness of serum alpha 2u-globulin changes as a new parameter for detecting endocrine-mediated effects, we performed a 28-day repeated-dose toxicity study using the administration of bisphenol A (BPA) or ethynyl estradiol (EE) in male rats, based on the draft protocol of the 'Enhanced OECD Test Guideline 407 (enhanced TG 407)'. BPA at doses of 0, 40, 200 and 1000 mg/kg per day or EE at doses of 0, 15, 75 and 375 microg/kg per day were orally administered to SD rats. The highest dose of BPA was reduced to 600 mg/kg per day from the second week of the study onwards because a male rat given 1000 mg/kg per day of BPA died within the first week, showing toxic clinical signs. In the assay using BPA, a reduction in the level of alpha 2u-globulin was detected in the group receiving a dose of 600 mg/kg per day. Reductions in the absolute and relative ventral prostate weights were only observed in the 600 mg/kg per day group. In the assay using EE, the alpha 2u-globulin level decreased significantly in the 375 microg/kg per day group. A reduction in the absolute and relative dorsolateral prostate weights was also observed in the 75 and 375 microg/kg per day groups, morphologically abnormal sperm were observed in the 375 microg/kg per day group. Furthermore, atrophic changes in the prostate and seminal vesicle and degenerative changes in the testis were observed in the 375 microg/kg per day group. Although the alpha 2u-globulin level was reduced in this assay using BPA and EE, further studies are necessary before this assay becomes a useful method for detecting endocrine-mediated effects.

Initial induction and subsequent reduction of alpha(2u)-globulin in urine and serum of mature male rats after repeated intraperitoneal injections of (anti)estrogen

The influence of sex (anti)hormones on expression of alpha(2u)-globulin (a2uG) is complex and has not been sufficiently detailed. In order to assess the specificity of sex (anti)hormone action on a2uG expression and the utility of this approach as a sensitive screening method, mature male rats were given daily intraperitoneal injections of 17beta-estradiol (E2), dihydrotestosterone (DHT), tamoxifen (TX) and flutamide (FL) for 5 consecutive days. They were employed as representatives of estrogen, androgen, antiestrogen and antiandrogen categories, respectively. Urinary a2uG was specifically altered with E2 (1 microg/kg/day) and TX (50 mg/kg/day), but not by DHT (1 mg/kg/day) or FL (50 mg/kg/day). E2 and TX temporarily increased urinary a2uG on days 1 or 2, and days 2-4, respectively, followed by a return to the control level, and then a decrease with E2. The reduction in urinary a2uG on day 6 was more pronounced than the drop in serum a2uG. Serum hormone levels, and liver and testis weights were not remarkably altered with any treatment. Another strong xenoestrogen, diethylstilbestrol, also significantly reduced urinary and serum a2uG at 1 mg/kg/day on day 6. However, the other xenoestrogens (100 mg/kg/day of bisphenol A, nonylphenol, and dichlorodiphenyltrichloroethane, and 10 mg/kg/day of dieldrin) and phytoestrogens (10 mg/kg/day of genistein and daidzein) were without any appreciable influence. The results indicate that urinary a2uG is a sensitive indicator of estrogen action in mature male rats, with two different responses, initial induction and subsequent reduction.

Three subsets of genes whose tissue specific expression is sex and age-dependent can be identified within the rat alpha 2u-globulin family

The rat alpha 2u-globulins are encoded by a multigene family whose 20-25 members are subjected to multihormonal regulation that is dependent upon the sex of the animal, the developmental stage and the tissue being examined. Using RT-PCR and diagnostic restriction analysis of the products, we have examined the specificity of the expression of different members of the gene family. All family members can be classified into three subsets, depending on how the amplified cDNA responds to digestion with ApaLI, SstI and VspI. Subset A contains the restriction sites for both ApaLI and SstI but not VspI and typifies the genes expressed in the salivary glands of both mature and juvenile animals of both sexes, where it is the only subset expressed. This subset of genes also accounts for all the transcripts observed in the kidneys and mammary glands of juvenile males. Although subset A was represented in the transcript populations of all the other tissues examined, its proportion relative to the total varied greatly. The two other subsets were subset V, which contains only the restriction site for VspI, and subset N, which lacks all three restriction sites. In all the other tissues examined, two or all three of the subsets were expressed, usually in a manner that was unique to the sex and age of the tissue in question. The proportion of each of the three alpha 2u-globulin subsets in the alpha 2u-globulin gene family was determined by quantitation of the restriction products of amplified genomic DNA. Interestingly, the most prevalent subset in the genome (N) has the most limited tissue expression pattern, but is found in liver and preputial glands, the tissues expressing the most substantial quantities of alpha 2u-globulin. These results indicate the complexity of the regulation of the alpha 2u-globulins and point to the necessity for gene specific analyses if the expression of the family is to be understood in molecular terms.

Molecular evidence of complex tissue- and sex-specific mRNA expression of the rat alpha(2u)-globulin multigene family

alpha(2u)-Globulin is well known to be a rat protein encoded by a highly homologous multigene family with more than twenty members. We report here the cloning and identification of major alpha(2u)-globulin mRNA species expressed in various tissues. Initially, eight individual clones (PGCL1-8) were obtained from a male preputial gland cDNA library. Data base analysis with BLAST demonstrated six mRNAs to be novel, all clones being characterized by highly conserved sequence motifs as lipocalins. All cDNAs contained an open reading frame of 543 nucleotides and encode 181 amino acid proteins showing 92.5-98.7% and 87.3-98.3% nucleic and amino acid identity, respectively. Denaturing gradient gel electrophoresis (DGGE) with sequence analysis showed that PGCL4 is a major member in the female mammary gland, and in the submaxillary and lachrymal glands of both sexes, while the counterpart in male liver and the coagulate glands was found to be PGCL1. Numbers of cDNA species including PGCL1 and PGCL4 were found in preputial glands, no sex-related difference being observed. These results directly demonstrate complex tissue- and sex-specific expression of alpha(2u)-globulins in terms of mRNA species, providing useful information for understanding regulation of the alpha(2u)-globulin multigene family.

Direct lysosomal uptake of alpha 2-microglobulin contributes to chemically induced nephropathy

BACKGROUND

An abnormal accumulation of alpha 2-microglobulin (alpha 2 mu) in kidney lysosomes of male rats has been described in the nephropathy resulting from exposure to a variety of chemicals. The increment in lysosomal levels of alpha 2 mu cannot be explained by a decrease in its proteolytic susceptibility. Because a portion of alpha 2 mu resides in the cytosol of kidney cells, we decided to analyze whether this cytosolic form also contributes to the abnormal lysosomal accumulation of alpha 2 mu after exposure to chemicals.

METHODS

Intact kidney lysosomes were isolated from untreated or 2,2,4-trimethylpentane (TMP) treated rats, and their ability to take up alpha 2 mu was compared.

RESULTS

alpha 2 mu can be directly transported into isolated lysosomes in the presence of the heat shock cognate protein of 73 kDa (hsc73). alpha 2 mu specifically binds to a lysosomal membrane glycoprotein of 96 kDa, previously identified as the receptor for the hsc73-mediated lysosomal pathway of protein degradation. In rats exposed to TMP, the specific lysosomal transport of alpha 2 mu increases, as well as the ability of lysosomes to directly transport other substrates for this pathway. The increased lysosomal transport is mainly due to an increase in the levels of the receptor protein in the lysosomal membrane.

CONCLUSIONS

The hsc73-mediated lysosomal pathway contributes to the normal degradation of alpha 2 mu in rat kidney and liver, and the activity of this pathway is increased after exposure to TMP. Our results suggest that the chemically induced accumulation of cytosolic alpha 2 mu in lysosomes is mediated by an increased rate of direct uptake into lysosomes.

Effect of continual light deprivation and alpha-2u-globulin replacement therapy on serum concentration of gonadotropins and testicular activity in rats

Prolonged darkness caused a fall in testicular 17 beta-hydroxysteroid dehydrogenase (17 beta-HSD) activity and diminished spermatogenesis, serum levels of gonadotropins, testosterone and alpha 2u-globulin. Administration of alpha 2u-globulin at a dose of 1.5 mg rat-1 per day for 7 days after 68 days of light deprivation, reversed the 17 beta-HSD activity and serum levels of gonadotropins, testosterone and alpha 2u-globulin, while spermatogenesis was restored to normal. The animals kept in prolonged darkness for 68 days and then received saline (7 days in light-dark cycle, 14 L: 10 D), showed no significant changes of testicular activity, serum levels of gonadotropins, testosterone and alpha 2u-globulin, when compared with dark-exposed animals (68 days) receiving rabbit serum (7 days in light-dark cycle, 14 L: 10 D). These results suggest that alpha 2u-globulin plays an important role in testicular function in dark-exposed rats by inducing gonadotropins and testosterone secretion.

The lipocalin protein family: structure and function

The lipocalin protein family is a large group of small extracellular proteins. The family demonstrates great diversity at the sequence level; however, most lipocalins share three characteristic conserved sequence motifs, the kernel lipocalins, while a group of more divergent family members, the outlier lipocalins, share only one. Belying this sequence dissimilarity, lipocalin crystal structures are highly conserved and comprise a single eight-stranded continuously hydrogen-bonded antiparallel beta-barrel, which encloses an internal ligand-binding site. Together with two other families of ligand-binding proteins, the fatty-acid-binding proteins (FABPs) and the avidins, the lipocalins form part of an overall structural superfamily: the calycins. Members of the lipocalin family are characterized by several common molecular-recognition properties: the ability to bind a range of small hydrophobic molecules, binding to specific cell-surface receptors and the formation of complexes with soluble macromolecules. The varied biological functions of the lipocalins are mediated by one or more of these properties. In the past, the lipocalins have been classified as transport proteins; however, it is now clear that the lipocalins exhibit great functional diversity, with roles in retinol transport, invertebrate cryptic coloration, olfaction and pheromone transport, and prostaglandin synthesis. The lipocalins have also been implicated in the regulation of cell homoeostasis and the modulation of the immune response, and, as carrier proteins, to act in the general clearance of endogenous and exogenous compounds.

Effects of passive immunization against alpha-2u-globulin and supplementation with alpha-2u-globulin on serum gonadotrophins and testicular activity

The purpose of the present study was to evaluate the effects of anti-alpha-2U-globulin on pituitary-gonadal functions in male rats. Adult male rats were given injections of anti-alpha-2u-globulin (1 mg/day) for 14 days, when they were killed 7 days after the last injection, serum levels of gonadotrophins and testosterone measured by radioimmunoassays, were less, testicular delta 3 beta- and 17 beta-hydroxy-steroid dehydrogenase (3 beta- and 17 beta-HSD) activities were suppressed, spermatogenesis was inhibited and serum level of alpha-2u-globulin was decreased in anti-alpha-2u-globulin treated rats. Administration of alpha-2u-globulin (1.5 mg/day) for 7 days to anti-alpha-2u-globulin treated rats reversed the 3beta-HSD and 17beta-HSD activities and serum levels of gonadotrophins, testosterone and alpha-2u-globulin, while spermatogenesis was restored to normal. The results indicate that changes in testicular steroidogenesis and spermatogenesis in rats after passive immunization against alpha-2u-globulin may be due to decrease in availability of endogenous alpha-2u-globulin.

Acute nephrotoxicity of a carcinogenic iron chelate. Selective inhibition of a proteolytic conversion of alpha 2U-globulin to the kidney fatty acid-binding protein

The mechanism of acute nephrotoxicity of an iron chelate in vivo has been investigated. Administration of a renal carcinogen ferric nitrilotriacetate (Fe-NTA) (15 mg Fe/kg body weight, intraperitoneally) led to selective loss of a renal protein with an apparent molecular mass of 17 kDa. Analysis of the 17 kDa protein by NH2-terminal sequence demonstrated its identity over 16 NH2-terminal residues as a kidney fatty acid-binding protein (k-FABP) that is a proteolytically modified form of alpha 2U-globulin, a major urinary protein of adult male rats. An immunochemical study using anti-alpha 2U-globulin polyclonal antibodies confirmed that a single injection of Fe-NTA led to a decrease in k-FABP levels. However, a 19-kDa protein identical to the alpha 2U-globulin progressively appeared in the kidney, suggesting that the proteolytic processing of alpha 2U-globulin in the renal proximal tubules was suppressed by the treatment with Fe-NTA. By monitoring k-FABP and its precursor alpha 2U-globulin, it was determined that repeated exposure to Fe-NTA caused suppression of both proteolytic and endocytotic activity of the kidney. The implications of these data in relation to the nephrotoxicity of Fe-NTA are discussed.

A comparison of European High Test gasoline and PS-6 unleaded gasoline in their abilities to induce alpha 2u-globulin nephropathy and renal cell proliferation

Male Fischer-344 rats were administered European High Test gasoline (EHT) (50-500 mg/kg), PS-6 unleaded gasoline (UG) (16-500 mg/kg) or 2,2,4-trimethylpentane (TMP) (0.95-30 mg/kg) by gavage for ten consecutive days. To measure cell replication, rats were exposed to [3H]thymidine continuously over the last 7 days of the exposure period. Twenty-four hours after the final dose, protein droplet (PD) accumulation, alpha 2u-globulin (alpha 2u) concentration and the nuclear labeling index (LI), as a measure of cell replication, were measured in the kidneys of control and treated rats. Dose-related increases in PD, alpha 2u and cell replication were detected in the kidneys of rats treated with either gasoline mixture or TMP. The accumulation of PD and the increase in alpha 2u was greater in the kidneys of UG- and TMP-treated rats than in the kidneys of rats treated with EHT. These differences were attributed to the higher composition of branched hydrocarbons in UG, which have been shown to be the biologically active components for these endpoints. The extent of renal cell proliferation was similar in both EHT-, UG- and TMP-treated rats. This suggests that other components besides the branched hydrocarbons are responsible for the increased renal cell replication in EHT-treated rats.

The role of lysosomes in hyaline droplet nephropathy induced by a variety of pharmacological agents in the male rat

The male rat is prone to hyaline droplet formation in renal proximal tubular cells. Several unrelated pharmaceutical agents exacerbate the formation and accumulation of these droplets. Where the loading of the proximal tubular cells is marked it gives rise to increased cell turnover and a hyaline droplet nephropathy develops. Cytochemical procedures, have confirmed that this accumulation of hyaline droplets represents an increase in the size and number of secondary lysosomes involved in protein uptake and metabolism. This predisposition of the male rat to develop hyaline droplet nephropathy relates to (1) the large amounts of the low-molecular-weight protein alpha 2U globulin in the glomerular filtrate, (2) the resistance of the globulin to proteolysis, and (3) the low protease activity in the proximal tubule lysosomes. The current data would suggest that the pharmacological agents, which cause the nephropathy, exert their effect by reducing the proteolytic breakdown of alpha 2U globulin in the proximal tubule lysosomes. This results in the overloading of a system which is already operating near maximal load. Female rats, and all other species excrete only small amounts of alpha 2U globulin or similar proteins, which are more easily hydrolyzed. Thus it is argued that the type of hyaline droplet nephropathy induced by these pharmacological agents is unique to the male rat and of little relevance to man.

A methylsulphonyl metabolite of a polychlorinated biphenyl can serve as a ligand for alpha 2mu-globulin in rat and major-urinary-protein in mice

1. Kidneys from rats given an intraperitoneal dose of 4,4'-bis[( 3H]methylsulphonyl)-2,2',5,5'- tetrachlorobiphenyl[(CT3SO2)2TCB)] contained (CT3SO2)2TCB associated with a protein which has been isolated and characterized by SDS-polyacrylamide gel electrophoresis (SDS-PAGE), immunoblot and immunodiffusion analysis to be alpha 2 mu-globulin (alpha 2 mu). 2. The same radioactive alpha 2 mu-globulin complex was isolated from urine of rats given an i.p. dose of (CT3SO2)2TCB. This complex represented 12.3% (0.27% dose) and 9.3% (0.06% dose) of the radioactivity excreted in 0-24 h and 24-48 h urine, respectively. 3. The radioactivity was extractable from alpha 2 mu and characterized by t.l.c. (co-chromatography in two solvent systems) to be (CT3SO2)2TCB. 4. A radioactive-protein complex was isolated from urine of mice given an i.p. dose of (CT3SO2)2 TCB. The radioactive-protein complex was characterized to be mouse major urinary protein (MUP) by SDS-PAGE, immunoblot and immunodiffusion analysis. This complex was not detected in mouse kidney. 5. Urinary excretion of radioactive-MUP complex represented 51.7% (2.3% dose) and 28% (1.3% dose) of the radioactivity excreted in 0-24 h and 24-48 h urine, respectively.

Relationships between structure and induction of hyaline droplet accumulation in the renal cortex of male rats by aliphatic and alicyclic hydrocarbons

A rapidly growing list of hydrocarbons has been reported to induce morphological changes in the kidney of adult male rats, beginning with hyaline droplet accumulation (HDA) followed by the development of granular casts, later on chronic nephrosis as sequela, and finally renal adenomas and carcinomas. The present study focuses on identifying structure-based properties common to HDA-inducing aliphatics and cycloaliphatics. On the basis of rank-ordered activities reported in the literature, a calculated n-octanol-water partition coefficient above 3.5 and the presence of an isopentyl structural moiety appear to be associated with HDA-inducing activity in aliphatics. A binding site model for highly active aliphatics has been derived by superimposing their minimum energy conformations along the common isopentyl substructure and calculating the union volume of their respective van der Waal (VDW) volumes. Generalization of this model to include cycloaliphatics has been achieved by maximizing the steric overlap of the VDW volumes of the compounds with their binding site union volume. HDA-inducing cycloaliphatics are correctly identified on the basis of their negligible excess volume. This approach has been used to predict the HDA-inducing activity of previously untested compounds. Eighteen aliphatic/cycloaliphatic hydrocarbons were screened in a study on adult male Wistar rats treated with 250 mg/kg per day for 5 days. Azan-stained kidney sections were semiquantitatively evaluated for the presence of HDA. The predicted and observed HDA activities were in very good agreement.

A comparison of male rat and human urinary proteins: implications for human resistance to hyaline droplet nephropathy

alpha 2u-Globulin (alpha G), the major urinary protein of sexually mature male rats, is a key determinant of susceptibility to hyaline droplet nephropathy (HDN) induced by a variety of hydrocarbons in male rats. Arguments against extrapolating renal toxicity and carcinogenicity data for HDN-inducing toxicants from male rats to risk assessment for humans rely on the observation that humans do not express alpha G. Yet, human serum and urine are known to contain proteins coded for by the same gene family that also controls alpha G synthesis in the rat. Therefore, to understand some of the quantitative and qualitative differences between proteins of human and male rat urine which confer apparent resistance to HDN in humans, urinary proteins of male F344 rats (ca. 3 months old) and normal human males were compared by cation exchange, gel filtration, SDS-PAGE, and partially identified by Western blotting. We observed that (1) the protein content of human urine is only 1% that of male rat urine; (2) human urinary proteins, recovered by (NH4)2SO4 precipitation followed by dialysis, are primarily of high (greater than or equal to 75 kDa) molecular weight (MW) with minor components of 12-66 kDa; (3) male rat urine has little high-MW protein, but is rich in alpha G (18.5 kDa); (4) at pH 5, the most cationic fraction of human urinary protein constituted only about 4% of the total while the analogous fraction of rat urine, containing alpha G, contained 26% of total urinary protein; and (5) cationic (at pH 5.0) human urinary proteins included small amounts of proteins, e.g., alpha 1-acid glycoprotein, and alpha 1-microglobulin, which are products of the gene family coding for alpha G in rat. Thus, although humans excrete trace amounts of proteins similar to alpha G, the very low protein content of human urine, the relatively small proportion of cationic to total proteins, and the high MW of the most abundant human urinary proteins form a biological basis for suggesting that humans are not at risk for the type of fuel and solvent hydrocarbon-induced nephropathy, and the sequelae of such nephropathy, observed in male rats.

Methylsulphone metabolites of m-dichlorobenzene as ligands for alpha 2u-globulin in rat kidney and urine

1. Kidneys from rats given oral doses of either 3,5- or 2,4- dichlorophenyl[14C]methylsulphide contained the corresponding sulphones that were associated with a protein which has been isolated and characterized by SDS-polyacrylamide gel electrophoresis and immunoblot analysis to be alpha 2u-globulin. 2. The same methylsulphone-alpha 2u-globulin complex was isolated from the urine from rats doses with 3,5-dichlorophenyl[14C]methylsulphide (0.3-1.0% of dose, 8.5% of 14C in urine. 3. The stoichiometry of binding of the isolated methylsulphone-alpha 2u-globulin complex was shown to be 0.54-0.78 nmol/nmol protein. This binding was not covalent.

Effects of a major androgen-dependent urinary protein, alpha 2u-globulin on the pituitary-gonadal axis and hypothalamic monoamines in adult male mice

The purpose of the present study was to evaluate the effects of alpha-2u-globulin, a sex-dependent male rat urinary protein on pituitary-gonadal functions and hypothalamic monoamine contents in male mice. Adult male mice, maintained under standardized laboratory conditions (L:D, 14:10) were injected subcutaneously with alpha-2u-globulin at a dose of 1 mg/animal/day or with vehicle daily for 14 days and killed 16 h after the last injection. Plasma levels of luteinizing hormone (LH), follicle-stimulating hormone (FSH), testosterone (T) and testicular levels of T were measured by radioimmunoassays. The concentrations of norepinephrine (NE), dopamine (DA) and serotonin (5-HT) in medial basal hypothalamus (MBH) and anterior hypothalamus (AH) were measured by high performance liquid chromatography. Administration of alpha-2u-globulin led to a significant increase in plasma FSH and LH levels (P less than 0.05) as well as in plasma and testicular T levels (P less than 0.025). In the MBH of alpha-2u-globulin treated mice, there were significant elevations of NE (P less than 0.025), DA (P less than 0.01) and 5-HT (P less than 0.025) contents. In the AH, both DA (P less than 0.025) and 5-HT (P less than 0.01) contents were decreased while NE content remained unaltered. These results indicate that administration of alpha-2u-globulin can lead to a significant stimulation of pituitary-testicular axis and that this effect may be mediated through alteration of hypothalamic monoamines.

Acute and subchronic nephrotoxicity of d-limonene in Fischer 344 rats

In the studies described here, we have examined the sex-specific sensitivity of rat kidney to d-limonene. At 24 hr after an acute dose of 200 mg d-limonene/kg body weight administered to adult male and female Fischer 344 rats by oral gavage, an increase in the incidence and severity of hyaline droplets was observed in the kidneys of males only. This histological change was accompanied by a treatment-related increase in alpha 2u-globulin in males only and a greater accumulation of radioactivity in renal cortex of the male rat compared with that in the females dosed with [14C]d-limonene. In a separate subchronic study, groups of 5-wk-old male rats were administered d-limonene in a corn oil vehicle at 0 (control), 2, 5, 10, 30, or 75 mg/kg body weight by single daily gavage (5 days/wk) for 13 wk. Rats from selected dose groups received interim necropsies from days 8-29, while all groups were necropsied at the end of the study. Linear regression analyses indicated a dose-related trend in the increased relative weights of the kidney and liver at 30 and 75 mg d-limonene/kg body weight. Histological examination of kidney tissue confirmed that d-limonene induced changes characterized by hyaline droplets, granular casts at the corticomedullary junction and multiple cortical changes collectively classified as chronic nephrosis. The no-observable-effect level for these effects was 5 mg d-limonene/kg body weight. At the earliest necropsy, 8 days after the start of the treatment, it was evident that d-limonene exacerbated the hyaline droplets at the 10 mg/kg body weight dose. It is concluded that treatment with d-limonene caused an increase in the formation of hyaline droplets in male rats only, that this increase was associated with an accumulation of alpha 2u-globulin, that d-limonene (or its metabolite) accumulated significantly in male rat kidney compared with that in females and that subchronic dosing produced a triad of morphological changes in the male rat kidney. These observations suggest that d-limonene caused nephrotoxicity specific to the male rat and that this toxicity may not be predictive of a similar response in humans.

Kidney fatty acid-binding protein: identification as alpha 2U-globulin

A fatty acid-binding protein was purified from male rat kidney by the method of Fujii et al. [(1987) Arch. Biochem. Biophys. 254, 552-558]. Based on the close similarity of amino acid composition and the identity of the amino acid sequence in the amino-terminal region, the fatty acid-binding protein was identified as alpha 2U-globulin, which is the major male-specific protein in rat urine. The amino-terminal residue of the isolated kidney protein corresponds to residue 10 of alpha 2U-globulin, suggesting that the protein has been proteolytically processed in the kidney. This fatty acid-binding protein could not be immunologically detected in female rat kidney.

T antigen expression and tumorigenesis in transgenic mice containing a mouse major urinary protein/SV40 T antigen hybrid gene

A hybrid mouse major urinary protein (MUP)/SV40 T antigen gene was microinjected into fertilized mouse embryos and the resulting transgenic mice analyzed for the regulated expression of the transgene. Available evidence indicates that the MUP gene used for the hybrid gene construct is expressed in both male and female liver and possibly mammary gland. Three different transgenic lines exhibited a consistent pattern of tissue specific expression of the transgene. As a consequence of transgene expression and T antigen synthesis in the liver, both male and female transgenic animals developed liver hyperplasia and tumors. Transgene expression and liver hyperplasia commenced at approximately 2-4 weeks of age, the same time that MUP gene expression is first detected in the liver. The expression of the transgene resulted in an immediate strong suppression of liver MUP mRNA levels but had relatively little effect on other liver specific mRNAs. From 4 to 8 weeks, the liver increased several fold in size, relative to non-transgenic littermates. Definitive tumor nodules were not apparent until 8-10 weeks. The transgene was also consistently found to be expressed in the skin sebaceous glands and the preputial gland, a modified sebaceous gland. The expression of the transgene in the skin sebaceous glands is consistent with the presence of MUP mRNA in the skin and a putative role for MUPs in the transport and excretion of small molecules. Occasional expression of the transgene in other tissues (kidney and mammary connective tissues) was also noted.(ABSTRACT TRUNCATED AT 250 WORDS)

Hydrocarbon-induced hyaline droplet nephropathy in male rats during senescence

Male rats administered unleaded gasoline rapidly develop nephropathy characterized by accumulation of hyaline droplets in cells of the proximal convoluted tubules (PCT). This acute response is implicated in development of renal carcinoma in male rats exposed chronically to wholly volatilized gasoline. A major constituent of hyaline droplets is alpha 2 mu-globulin, a protein of hepatic origin for which the rate of synthesis declines during aging. Little information, however, is presently available on possible age-dependent susceptibility of male rats to hydrocarbon-induced nephropathy. In kidneys of untreated male Fischer 344 rats the number of constitutive hyaline droplets declined progressively with increasing age. Electrophoresis of renal cortical homogenates revealed a protein with Mr about 18 X 10(3), probably alpha 2 mu-globulin, in young (3.5 months old) male rats and total absence of this protein in aged (26 months old) males. RIA confirmed that constitutive levels of renal and hepatic alpha 2 mu-globulin in old rats were less than 1.5% of those in young adults. Unleaded gasoline (0.4 ml/kg/day, po, 5 days) caused accumulation of hyaline droplets in renal PCT of 3.5-month-old males accompanied by a marked increase (about twofold) in the renal content of alpha 2 mu-globulin, whereas the same treatment was without effect in 26-month-old rats. Finally, in the renal cortex of young rats the activities of the lysosomal proteases cathepsin B and D were increased following gasoline administration, presumably in response to protein accumulation. However, in 26-month-old rats cathepsin B activity was unaffected, while cathepsin D was increased by gasoline administration. Thus, we conclude that animal age is an important determinant in the development of hydrocarbon-induced nephropathy and only rats which produce large amounts of alpha 2 mu-globulin are susceptible to development of this pathology.

The role of alpha-2u-globulin in corticosteroidogenesis in male rats

Administration of estradiol-17 beta for 7 days to the adult male rat results in adrenal hyperplasia, decreased serum corticosterone along with elevation in serum ACTH and inhibition of adrenal 5-ene-3 beta-hydroxysteroid dehydrogenase activity (5-ene-3 beta-HSD). Treatment with alpha 2u-globulin for following 14 days of estrogen-treated rats reversed the effects of estrogen while in normal rats alpha 2u-globulin treatment increased adrenal 5-ene-3 beta-HSD activity and serum corticosterone level while causing a fall in serum ACTH. It is concluded that alpha 2u-globulin may play a role in ACTH secretion by inducing corticosterone synthesis.

A specific sorting signal is not required for the polarized secretion of newly synthesized proteins from cultured intestinal epithelial cells

Caco-2 cells, derived from human colon, have the morphological, functional, and biochemical properties of small intestinal epithelial cells. After infection with enveloped viruses, influenza virions assembled at the apical plasma membrane while vesicular stomatitis virus (VSV) particles appeared exclusively at the basolateral membrane, similar to the pattern observed in virus-infected Madin-Darby canine kidney (MDCK). When grown in Millicell filter chamber devices and labeled with [35S]methionine, Caco-2 monolayers released all of their radiolabeled secretory products preferentially into the basal chamber. Among the proteins identified were apolipoproteins AI and E, transferrin, and alpha-fetoprotein. No proteins were observed to be secreted preferentially from the apical cell surface. The lysosomal enzyme beta-hexosaminidase was also secreted primarily from the basolateral surface of the cells in the presence or absence of lysosomotropic drugs or tunicamycin, which inhibit the targetting of lysosomal enzymes to lysosomes. Neither of these drug treatments significantly affected the polarized secretion of other nonlysosomal proteins. In addition, growth hormone (GH), which is released in a nonpolar fashion from MDCK cells, was secreted exclusively from the basolateral membrane after transfection of Caco-2 cells with GH cDNA in a pSV2-based expression vector. Similar results were obtained in transient expression experiments and after selection of permanently transformed Caco-2 cells expressing GH. Since both beta-hexosaminidase and GH would be expected to lack sorting signals for polarized exocytosis in epithelial cells, these results indicate that in intestinal cells, proteins transported via the basolateral secretory pathway need not have specific sorting signals.

Leupeptin-mediated alteration of renal phagolysosomes: similarity to hyaline droplet nephropathy of male rats exposed to unleaded gasoline

alpha 2u-Globulin, a protein of hepatic origin found in the urine of male rats, is accumulated in the kidney cortex during exposure to unleaded gasoline and has been implicated in the development of fuel hydrocarbon-induced nephropathy and renal neoplasia. The principal morphological feature of gasoline-induced nephropathy is accumulation of hyaline droplets (enlarged secondary lysosomes or phagolysosomes) in epithelial cells of the proximal convoluted tubule S1 and S2 segments. Inhibition of cathepsin B (a major lysosomal peptidase) by treatment of male rats with leupeptin causes rapid accumulation of phagolysosomes and alpha 2u-globulin in the kidney very similar to gasoline exposure. Further, the renal cortical subcellular distribution of alpha 2u-globulin, determined with an electron microscopic immunochemical method, is almost totally confined to phagolysosomes following administration of either gasoline or leupeptin. These results, taken together, indicate that the mechanism of nephrotoxicity of gasoline involves inhibition of renal phagolysosomal proteolysis.

Increased hepatic androgen receptor expression in female rats during diethylnitrosamine liver carcinogenesis. A possible correlation with liver tumor development

This study investigated the relationship between liver tumor development and androgen-receptor expression in diethylnitrosamine hepatocarcinogenesis in Wistar rats (SUAH substrain). Random liver samples were assayed by an isoelectric focusing method, with [3H]mibolerone as androgenic radioligand. After 16 wk of oral diethylnitrosamine treatment there was a greater than 20-fold increase in hepatic androgen receptor concentration in female rats (control group 0.3 +/- 0.07 fmol/mg cytosol protein; test group 8.36 +/- 0.96 fmol/mg cytosol protein; p less than 0.001, unpaired Student's t-test). This coincided with, and may be related to, an accelerated development of neoplastic nodules or hepatocellular carcinoma, or both. Male rats showed slower tumor development and no change in androgen receptor concentrations. This model is the first to demonstrate significantly increased androgen sensitivity in experimental hepatic carcinogenesis analogous to increased androgen receptor expression in human hepatocellular carcinoma. It may provide insight into steroid hormone sensitivity in developing tumors, and a means of testing potential therapeutic use of hormonal manipulation in human liver cancer.

Hyalin droplet nephrosis in male Fischer-344 rats following inhalation of diisobutyl ketone

Four groups, each consisting of 10 male and 10 female Fischer-344 rats, were exposed 6 h/day, 5 days/week, for 9 days to diisobutyl ketone (DIBK) vapor at concentrations of 905, 300, 98, or 0 (control) ppm. An additional 10 rats/sex were assigned to the 905 and 0 ppm groups and allowed two weeks recovery prior to sacrifice. Rats exposed to 905 ppm had mild ocular irritation (lacrimation) and evidence of kidney toxicity, manifested as: 1) an increase in absolute and relative (as a percentage of body weight) kidney weights, 2) an increase in urine volume (and water intake) with a concomitant decrease in urine osmolality (males only), and 3) an increase in severity of hyalin droplet nephrosis in the proximal tubules (males only). Absolute and relative liver weights were also increased in both male and female rats of the 905 and 300 ppm groups. These effects either disappeared or lessened in severity following the 2-week recovery period. Male rats exposed to 300 ppm had similar renal alterations to the males of the 905 ppm group, although the alterations were fewer in number and smaller in magnitude. Kidney weights and renal histology of the males of the 98 ppm group were similar to the control male rats, although an increase in urine volume with a decrease in urine osmolality was observed. The kidney findings in this study were not surprising because of the chemical relationship of DIBK with other aliphatic ketones (e.g., methyl isobutyl ketone, methyl isoamyl ketone) which, after repeated inhalation exposure, cause hyalin droplet nephropathy in male rats. The significance of this male rat nephrosis with regard to human exposure is unknown.

2,2,4-Trimethylpentane-induced nephrotoxicity. I. Metabolic disposition of TMP in male and female Fischer 344 rats

2,2,4-Trimethylpentane (TMP), a component of unleaded gasoline, causes nephrotoxicity in male, but not in female, rats. In the present study, male and female Fischer 344 rats were treated with a single oral dose of [14C]TMP (4.4 mmol/kg; 2 microCi/mmol). Radiolabeled material in kidney, liver, and plasma was determined at 4, 8, 12, 24, and 48 hr after dosing. Maximum concentration of TMP-derived radioactivity in kidney, liver, and plasma of male rats was found after 12 hr (1252, 1000, and 403 nmol eq/g, respectively), whereas those measured in females were found after 8 hr (577, 1163, and 317 nmol eq/g, respectively). A selective retention of the TMP-derived radiolabel in the kidneys of male rats was noted when peak tissue concentration was expressed as a percentage of administered dose. Kidney concentrations of TMP-derived radiolabel increased in a nonlinear, but dose-dependent, manner; the kidney to plasma ratio was greater at low doses than at higher doses. Increased retention of radiolabel material in the kidney was associated with a significant increase in renal concentration of the male-rat-specific protein, alpha 2u-globulin, 24 and 48 hr after TMP administration. Total radioactivity collected in urine 48 hr after TMP administration was similar in males and females (32 and 31% of dose). Identification and quantitation of the urinary metabolites of TMP showed that both male and female rats metabolize TMP via the same pathway and at a similar rate. Female rats, however, excreted more conjugates of 2,4,4-trimethyl-2-pentanol in urine than males. 2,4,4-Trimethyl-2-pentanol was the major metabolite present in the male rat kidney, but was absent in the female rat kidney. The renal retention of 2,4,4-trimethyl-2-pentanol appears to account for the delayed clearance observed in the disposition of [14C]TMP-derived radiolabel. Based on the concomitant accumulations in renal alpha 2u-globulin concentration and renal 2,4,4-trimethyl-2-pentanol concentration, an association is speculated between these two components. The male-rat-specific accumulation of 2,4,4-trimethyl-2-pentanol may therefore reflect the accumulation of a "metabolite-alpha 2u-globulin" complex. This may be relevant to the male-rat-specific nephrotoxicity produced by TMP.

2,2,4-Trimethylpentane-induced nephrotoxicity. II. The reversible binding of a TMP metabolite to a renal protein fraction containing alpha 2u-globulin

Trimethylpentane (TMP) produces nephrotoxicity in male but not in female rats. The toxicity is characterized by an increase in protein droplets in proximal convoluted tubular cells and an increase in the renal concentration of the male-rat-specific protein alpha 2u-globulin. Subcellular fractionation of the kidneys from male rats 24 hr after [3H]TMP administration showed that about 60% of the radiolabeled material was localized in the 116,000g supernatant. Column chromatography of this supernatant resolved the radioactivity into two components; one, which contained about 26% of the radiolabel, coeluted with alpha 2u-globulin and cross-reacted with an antibody specific for alpha 2u-globulin. The remaining component eluted in the low-molecular-weight range (less than 1000 Da) and was assumed to be TMP metabolites. Radiolabel from [3H]TMP in male rat urine also resolved into two components with about 0.1% of the radiolabel in urine coeluting with the alpha 2u-globulin-containing fraction. Radiolabel from TMP in male rat liver 116,000g supernatant and plasma and in female rat kidney 116,000g supernatant eluted as a single component in the low-molecular-weight range. Dialysis (1000-Da cutoff) of male kidney 116,000g supernatant led to a loss of the low-molecular-weight components, but nondialyzable radiolabel (about 20%) still coeluted with the alpha 2u-globulin after gel chromatography. Dialysis against 0.1% sodium dodecyl sulfate led to a loss of both the low- and high-molecular-weight radioactive material. These results suggested that the high-molecular-weight radioactive material was formed by the reversible binding of a radioactive component of TMP to a male-rat-specific protein. Gas chromatography-mass spectrometry of an ethyl acetate extract of the alpha 2u-globulin-containing fractions of TMP-treated male rat kidney 116,000g supernatant identified 2,4,4-trimethyl-2-pentanol as the only bound metabolite to alpha 2u-globulin. These studies provide the first evidence for a reversible binding between a metabolite of TMP and a male-rat-specific protein in the kidney and thus provide important insight delineating a potential mechanism of hydrocarbon-induced hyaline-droplet nephropathy.

Comparison of the 5' upstream putative regulatory sequences of three members of the alpha 2u-globulin gene family

We have isolated and characterized seven members of the alpha 2u-globulin gene family from a rat genomic library. The 5' upstream region (up to 1250 base pairs starting from the EcoRI site in exon 2) of three clones was sequenced. The major transcriptional start points were located 25 base pairs downstream from the 'TATA' box. A very high degree of homology was observed over the entire studied region. Two of the examined genes displayed structural features which suggest that their expression may be impeded. A high degree of homology was observed between the promotor regions of alpha 2u-globulin and those of the major urinary protein (MUP) multigene family of the mouse. A remarkable feature is the variable length of an A-rich region between the putative 'CAAT' and the 'TATA' consensus sequences. The size of this region differs markedly between MUP and alpha 2u-globulin and between different members of the alpha 2u-globulin gene family. Comparison of the alpha 2u-globulin promotor with the corresponding region of other androgen-dependent genes (the C1, C2 and C3 subunits of prostatic steroid binding protein) reveals the presence of an A-rich region of homology located approximately 378 base pairs upstream from the cap site in the alpha 2u-globulin genes. This region compares well with a sequence of putative enhancer function previously demonstrated in the alpha-fetoprotein promotor and in the immunoglobulin heavy chain promoter.

Assessment of the covalent binding potential of 2,2,4-trimethylpentane to rat alpha 2u-globulin

Subchronic exposure of male rats to the nephrotoxin 2,2,4-trimethylpentane (TMP) causes an accumulation of protein droplets in the epithelial cells of the renal cortex. Experimental evidence suggests that these droplets contain alpha 2u-globulin, a low-molecular-weight protein found specifically in the urine of male rats. It has been proposed that aldehyde metabolites of TMP form Schiff base adducts with the lysine groups of alpha 2u-globulin and thereby inhibit renal lysosomal processing of the protein. Accordingly, the ability of TMP and its metabolites to covalently bind to alpha 2u-globulin was examined. As a model, a [14C] formaldehyde-alpha 2u-globulin Schiff base was formed. This protein adduct was stabilized by reduction with cyanoborohydride and could be identified by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Protein analysis by SDS-PAGE demonstrated that hepatocytes isolated from male Fischer-344 rats produced significant quantities of alpha 2u-globulin in culture, whereas hepatocytes from female rats did not. A 15-hr exposure of metabolically competent, primary cultures of male rat hepatocytes to [14C] TMP (0.1 and 0.5%, v/v), followed by reduction with cyanoborohydride, dialysis, and analysis with SDS-PAGE, revealed no evidence of radiolabeled alpha 2u-globulin. When [14C]TMP was administered to an adult male Fischer-344 rat (300 mg/kg, ig) 22, 16, and 10 hr before sacrifice, 16% of the administered radioactivity was eliminated in the urine as TMP metabolites. Analysis as above showed no TMP-derived radioactivity in fractions containing alpha 2u-globulin from liver, blood, kidney cortex, or urine. The absence of a detectable covalent interaction between TMP and alpha 2u-globulin following in vitro or in vivo exposure suggests that a TMP-alpha 2u-globulin adduct is not responsible for the excessive formation of protein droplets in the renal cortex of exposed male rats.

Tissue-specific expression of the rat alpha 2u globulin gene family

The rat alpha 2u globulin gene family encodes approximately 20 low-molecular-weight (20,000) proteins with pIs ranging from 4.5 to 7.9. alpha 2u globulin protein isoforms were detected in the liver and in the submaxillary, lachrymal, preputial, and mammary glands of Sprague-Dawley rats. The hormonal and developmental regulation of alpha 2u globulin synthesis in each of these tissues was unique, and it appears that different alpha 2u gene sets were transcribed in the various tissues.

The complete amino acid sequence of human serum retinol-binding protein

The complete amino acid sequence of human serum Retinol-binding protein (RBP) including the distribution of its three disulfide bridges, has been determined. The protein consists of 182 amino acid residues, the order of which was determined following the isolation of five CNBr-fragments. Direct amino acid sequence analysis in an automatic liquid phase sequencer provided almost the entire sequences of the five CNBr-fragments. Several sets of enzymatically derived peptides of RBP were also used to elucidate the primary structure. RBP displays significant homology to bovine beta-lactoglobulin, human alpha 1-microglobulin and rat alpha 1-microglobulin. RBP contains an internal homology. Thus, residues 36 to 83 display statistically significant homology with residues 96 to 141.