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

Optimised Fermentation Production of Radiolabelled Ochratoxin A by Aspergillus ochraceus with Maximum 14C in the Pentaketide Moiety for Exploring Its Rat Renal Toxicology

In the context of the mysterious Balkan endemic nephropathy of the 1900s, and the discovery in the 1960s of the potent mycotoxin ochratoxin A, experimental research projects sought to explore any inter-relationship. Experimental lifetime administration of the toxin to male rats had revealed renal DNA adducts with the toxin, correlated with renal tumours, confirmation of which required molecular evidence. Consequently, production of 14C-ochratoxin A of a high specific radioactivity was required, practical biosynthetic detail of which had not previously been published. A fermentation study of Aspergillus ochraceous was carried out during 2002 for a European project, to select for the production of high-quality 14C-ochratoxin A, necessarily exploring for the maximum diversion of 14C-sodium acetate into the pentaketide portion of mycotoxin. Experimentation necessarily had to optimise the competitive context of fungal growth dynamics and addition of the biosynthetic precursor in the early days of shaken-flask fermentation before adding the radiolabelled precursor. From optimal fermentation, 50 mg of the 14C ochratoxin A was supplied within a European project for DNA adduct experimentation, but that proved negative as subsequently published. Experimental description of the radiolabelled ochratoxin A production was later made in a doctoral thesis, but is first publicised here. Further review of the literature reveals an explanation for the published failure to confirm rat DNA/ochratoxin A adduct formation, for which further experimentation is now recommended.

Rat Tumour Histopathology Associated with Experimental Chronic Dietary Exposure to Ochratoxin A in Prediction of the Mycotoxin's Risk for Human Cancers

Mammalian animal toxicity of ochratoxin A (OTA) has focused largely in the past half-century on pigs because of initial recognition of it as a principal cause of intermittent growth suppression and renal disease caused by mouldy feed. Subsequent classical toxicology has used laboratory rodents because renal pathology in pigs raised questions concerning possible involvement in the human idiopathic bilateral renal atrophy of Balkan endemic nephropathy for which OTA was a focus of attention for human nephropathy through 1980s and into 2000s. Emphasis on human nephropathy has more recently concerned the plant metabolite aristolochic acid. Recognition that agricultural management can often minimise food and feed-stuff spoilage by OTA-producing Aspergilli and Penicillia has moderated some of the risks for animals. Legislation for human food safety combined with sophisticated analysis generally provides safety in the developed world. Chronic experimental exposure of male rats, in the absence of clinical dis-ease, specifically causes renal cancer. The possibility of this as a unique model for the human has generated considerable experimental evidence which may be more directly relevant for carcinogenesis in the complex kidney than that obtained from biochemical toxicities in vitro. Nevertheless, there does not appear to be any case of human renal or urinary tract cancer for which there is verified etiological proof for causation by OTA, contrary to much claim in the literature. To contribute to such debate, histopathology review of OTA/rat renal cancers, augmented where appropriate by immune profiles, has been completed for all remaining tumours in our research archive. Overall consistency of positivity for vimentin, is matched with occasional positives either for CD10 or the cytokeratin MNF 116. The current situation is discussed. Suggestion that OTA could cause human testicular cancer has also been challenged as unsupported by any experimental findings in rats, where the Leydig cell tumour immune profile does not match that of human germ cell neoplasms.

A Review of Specific Biomarkers of Chronic Renal Injury and Their Potential Application in Nonclinical Safety Assessment Studies

A host of novel renal biomarkers have been developed over the past few decades which have enhanced monitoring of renal disease and drug-induced kidney injury in both preclinical studies and in humans. Since chronic kidney disease (CKD) and acute kidney injury (AKI) share similar underlying mechanisms and the tubulointerstitial compartment has a functional role in the progression of CKD, urinary biomarkers of AKI may provide predictive information in chronic renal disease. Numerous studies have explored whether the recent AKI biomarkers could improve upon the standard clinical biomarkers, estimated glomerular filtration rate (eGFR), and urinary albumin to creatinine ratio, for predicting outcomes in CKD patients. This review is an introduction to alternative assays that can be utilized in chronic (>3 months duration) nonclinical safety studies to provide information on renal dysfunction and to demonstrate specific situations where these assays could be utilized in nonclinical drug development. Novel biomarkers such as symmetrical dimethyl arginine, dickkopf homolog 3, and cystatin C predict chronic renal injury in animals, act as surrogates for GFR, and may predict changes in GFR in patients over time, ultimately providing a bridge from preclinical to clinical renal monitoring.

Molecular complexity of the major urinary protein system of the Norway rat, Rattus norvegicus

Major urinary proteins (MUP) are the major component of the urinary protein fraction in house mice (Mus spp.) and rats (Rattus spp.). The structure, polymorphism and functions of these lipocalins have been well described in the western European house mouse (Mus musculus domesticus), clarifying their role in semiochemical communication. The complexity of these roles in the mouse raises the question of similar functions in other rodents, including the Norway rat, Rattus norvegicus. Norway rats express MUPs in urine but information about specific MUP isoform sequences and functions is limited. In this study, we present a detailed molecular characterization of the MUP proteoforms expressed in the urine of two laboratory strains, Wistar Han and Brown Norway, and wild caught animals, using a combination of manual gene annotation, intact protein mass spectrometry and bottom-up mass spectrometry-based proteomic approaches. Cluster analysis shows the existence of only 10 predicted mup genes. Further, detailed sequencing of the urinary MUP isoforms reveals a less complex pattern of primary sequence polymorphism in the rat than the mouse. However, unlike the mouse, rat MUPs exhibit added complexity in the form of post-translational modifications, including the phosphorylation of Ser4 in some isoforms, and exoproteolytic trimming of specific isoforms. Our results raise the possibility that urinary MUPs may have different roles in rat chemical communication than those they play in the house mouse. Shotgun proteomics data are available via ProteomExchange with identifier PXD013986.

Proteinuria in relation to age-dependent changes in the plasma and urine concentrations of some electrolytes and hematological indices in Wistar rats

The study was carried out to determine the influence of proteinuria on plasma and urine concentrations of electrolytes and hematological indices in Wistar rats of different age groups. Eighty Wistar rats of both sexes were used for this study. Groups 1 and 2 each consisted of 8 one month old male and female rats; 3 and 4 had 8 three month old rats; 5 and 6 had 8 six month old rats; 7 and 8 had 8 nine month old rats; 9 and 10 had 8 twelve month old rats. The plasma sodium, potassium and calcium concentrations of 3 month old rats were significantly lower when compared with 1, 6, 9 and 12 months of age. Similarly, rats aged 3 months had significantly lower urine concentrations of sodium, potassium and calcium than rats of other age groups. A strong correlation was observed between the urine protein and urine sodium of the female rats at ages 3, 9 and 12 months but it was only significant at age 12 months (p = 0.105 and p = 0.021, respectively). Also, the female rats aged 3 and 12 months had a strong correlation between their urine protein and urine calcium (p = 0.002 and p = 0.131, respectively). The red blood cells, lymphocyte and monocyte counts of the rats increased gradually and peaked at age 9 months with a subsequent decline at 12 months of age. It was concluded that the influence of proteinuria on electrolytes was least observed in the rats aged 3 months, since they had reduced and consistent plasma and urine concentrations of electrolytes measured when compared with other age groups. This implies that long-term renal studies involving the use of rats must be carefully interpreted because of the changes in plasma and urine concentrations of electrolytes as the rats age.

Age-related changes in urinary protein excretion in relation to indices of renal function in Wistar rats

BACKGROUND

The study determined the fractions of proteins in the urine and plasma of rats at different ages, measured the plasma and urine concentrations of markers of renal function, with a view to determining the influence of proteinuria on renal function.

METHODS

Eighty Wistar rats were used for this study. Groups 1 and 2 each consisted of eight 1-month-old male and female rats; 3 and 4 had eight 3-month-old male and female rats; 5 and 6 had eight 6-month-old male and female rats; 7 and 8 had eight 9-month old male and female rats; and 9 and 10 had eight 12-month-old male and female rats.

RESULTS

A fraction of the molecular weight of protein in the urine of rats aged 1, 9 and 12 months was higher than that of 3 and 6 months. The total protein concentration in the urine of male and female rats aged 9 and 12 months was significantly higher than that of rats aged 1 and 3 months. The urine creatinine concentrations of male and female rats aged 9 months were significantly higher when compared with that of 1, 3, 6 and 12 months.

CONCLUSION

Our results suggest that the 3-month-old rats seem less affected by proteinuria, because they had the least urine protein, and consistent and reduced plasma and urine concentrations of markers of renal function. The results of this study may provide a foundation for future mechanistic inquiries as to why this age group was the least affected by proteinuria.

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.

Contribution of organ vasculature in rat renal analysis for ochratoxin a: relevance to toxicology of nephrotoxins

Assumptions surrounding the kidney as a target for accumulation of ochratoxin A (OTA) are addressed because the contribution of the toxin in blood seems invariably to have been ignored. Adult rats were maintained for several weeks on toxin-contaminated feed. Using standard perfusion techniques, animals were anaesthetised, a blood sample was taken, one kidney was ligated, and the other kidney perfused with physiological saline in situ under normal blood pressure. Comparative analysis of OTA in pairs of kidneys showed marked reduction in the perfused organ in the range 37%-98% (mean 75%), demonstrating the general efficiency of perfusion supported also by histology, and implying a major role of blood in the total OTA content of kidney. Translation of OTA values in plasma to whole blood, and its predicted contribution as a 25% vascular compartment in kidney gave values similar to those in non-perfused kidneys. Thus, apparent 'accumulation' of OTA in kidney is due to binding to plasma proteins and long half-life in plasma. Attention should be re-focused on whole animal pharmacokinetics during chronic OTA exposure. Similar principles may be applied to DNA-OTA adducts which are now recognised as occurring in blood; application could also extend to other nephrotoxins such as aristolochic acid. Thus, at least, quantitative reassessment in urological tissues seems necessary in attributing adducts specifically as markers of potentially-tumourigenic exposure.