Characterization of a mouse model of chronic uremia

Sexual dysfunction and sudden death in epileptic male EL mice: inheritance and prevention with the ketogenic diet

PURPOSE

The EL mouse is an animal model for multifactorial idiopathic epilepsy. Although EL mice have been studied extensively for >45 years, the etiology of male sudden death and its relation to seizures have not been defined. Here we investigated the cause of EL male sudden death and its relation to epilepsy.

METHODS

For histopathologic analysis, the terminally ill EL mice (n = 15) were killed, and the tissues were fixed. Blood chemical composition was compared between the terminally ill EL (n = 9) and the healthy age-matched EL (n = 17) and DDY (n = 11) males. To determine the effect of the ketogenic diet (KD) on sudden male death, young male EL mice (P30) were randomly separated into two groups that were fed ad libitum with either Agway lab chow (control n = 38) or with the KD (treated, n = 39) for 5 months. The genetic predisposition to sudden death was analyzed in the backcross generation (n = 106) of a cross between EL and the nonepileptic ABP strains.

RESULTS

Sudden death coincided with the onset of seizures (70-80 days) and affected 94% of male EL mice by age 300 days. Urethral plugs were observed histologically in 13 of 15 longitudinally sectioned penises. Concentrations of blood urea nitrogen, creatinine, phosphorus, and calcium in the terminally ill mice were significantly elevated when compared with those of healthy animals. None of the mice treated with the KD experienced sudden death, whereas 15 (39%) of the untreated control mice died by age 5 months. The sudden death in male EL mice was inherited as an autosomal recessive sex-limited lethal trait.

CONCLUSIONS

The cause of sudden death in male EL mice arises from abnormal ejaculation, which produces a urethral plug with consequent urinary retention and acute severe uremia. The coincident onset of seizures and sudden death in EL males suggests that a sexual dysfunction is associated with epilepsy in this model.

Treatment of a murine model of high-turnover renal osteodystrophy by exogenous BMP-7

BACKGROUND

The secondary hyperparathyroidism of chronic kidney disease (CKD) produces a high turnover osteodystrophy that is associated with peritrabecular fibrosis. The nature of the cells involved in the development of peritrabecular fibrosis may represent osteoprogenitors expressing a fibroblastic phenotype that are retarded from progressing through osteoblast differentiation.

METHODS

To test the hypothesis that osteoblast differentiation is retarded in secondary hyperparathyroidism due to CKD producing bone marrow fibrosis, we administered bone morphogenetic protein 7 (BMP-7), a physiologic regulator of osteoblast regulation, to C57BL6 mice that had CKD produced by electrocautery of one kidney followed by contralateral nephrectomy two weeks later. Following the second surgical procedure, a subgroup of mice received daily intraperitoneal injections of BMP-7 (10 microg/kg). Three to six weeks later, the animals were sacrificed, blood was obtained for measurements of blood urea nitrogen (BUN) and parathyroid hormone (PTH) levels, and the femora and tibiae were processed for histomorphometric analysis.

RESULTS

The animals had significant renal insufficiency with BUN values of 77.79 +/- 22.68 mg/dL, and the level of renal impairment between the CKD untreated mice and the CKD mice treated with BMP-7 was the same in the two groups. PTH levels averaged 81.13 +/- 51.36 and 75.4 +/- 43.61 pg/mL in the CKD and BMP-7 treated groups, respectively. The animals with CKD developed significant peritrabecular fibrosis. In addition, there was an increase in osteoblast surface and osteoid accumulation as well as increased activation frequency and increased osteoclast surface consistent with high turnover renal osteodystrophy. Treatment with BMP-7 eliminated peritrabecular fibrosis, increased osteoblast number, osteoblast surface, mineralizing surface and single labeled surface. There was also a significant decrease in the eroded surface induced by treatment with BMP-7.

CONCLUSIONS

These findings indicate that BMP-7 treatment in the setting of high turnover renal osteodystrophy prevents the development of peritrabecular fibrosis, affects the osteoblast phenotype and mineralizing surfaces, and decreases bone resorption. This is compatible with a role of osteoblast differentiation in the pathophysiology of osteitis fibrosa.

Behavioural deficits during the acute phase of mild renal failure in mice

Partially nephrectomized (NX) and sham-operated mice were biochemically and behaviourally compared, 10 days, 1 month and 1 year post-surgery. Plasma urea and creatinine concentrations were mildly increased in all NX groups, but creatinine clearance was significantly decreased, 10 days post-surgery only. NX mice showed lower body weights and reduced growth. Wire suspension and rotarod indicated unaffected motor functions, but NX mice did show reduced ambulation and swimming velocity, 10 days post-surgery. Hidden-platform water maze indicated a spatial learning impairment in NX mice, 10 days post-surgery, which could not be entirely reduced to motor incapacity. The acute behavioural deficits in these mildly uremic mice may relate to analogous symptoms in uraemic encephalopathy, a poorly understood brain syndrome occurring in uraemic patients.

Rat hypoplastic kidney (hpk/hpk) induces renal anemia, hyperparathyroidism, and osteodystrophy at the end stage of renal failure

In rats with genetically hypoplastic kidneys (hpk/hpk) and associated hypogonadism (hgn/hgn), their kidneys contain only one-quarter the number of nephrons that are found in those of normal rats [26]. Not surprisingly, therefore, renal excretive function has been shown to be depressed in hpk/hpk rats [26]. In the study presented here, we have examined the process of the progression of renal failure and the development of renal secondary disease in hpk/hpk rats. The plasma concentrations of urea-nitrogen and creatinine were significantly higher in adult hpk/hpk rats than in normal rats. These values elevated gradually and the degree of renal histological damage also progressed with advancing age in the hpk/hpk rats. In addition, renal anemia appeared at 140 days of age or later in these rats, and hyperplasia of the parathyroid glands was visible macroscopically at 280 days of age. In the hpk/hpk rats plasma levels of calcium and phosphorus were significantly lower and higher than in normal rats, respectively, at 280 days of age. Pathologically, the left femora of hpk/hpk rats exhibited fibrous osteodystrophy at 280 days of age and the calcium content of the right femora (as a percentage of the dry weight of bone) was significantly lower than in normal rats at both 210 and 280 days of age. These results indicate that the reduced nephrogenesis of the hpk/hpk rats causes progressive renal failure, secondarily inducing anemia, hyperparathyroidism, and osteodystrophy.

Biochemical and histopathological changes in nephrectomized mice

Renal failure is characterized by the retention of nitrogenous metabolites such as urea, creatinine (CTN) and other guanidino compounds (GCs), uric acid, and hippuric acid, which could be related to the clinical syndrome associated with renal insufficiency. A model of renal failure has been developed in male C57BL x Swiss-Webster mice using nephrectomy (NX) and/or arterial ligation. A sham group (group A) and two nephrectomized groups, group B (one kidney removed) and group C (one kidney removed and ligation of the contralateral anterior artery branch), were studied. Ten days postsurgery, morphological and functional indices of renal failure were investigated. Nephrectomized mice manifested features of renal failure like polyuria and wasting. CTN clearance (CTN[Cl]) decreased by +/-26% in group B and +/-33% in group C as compared with the control values. Marked increases in the plasma concentration of guanidinosuccinic acid ([GSA] fourfold) and guanidine ([G] twofold) were observed in the experimental animals. CTN and alpha-keto-delta-guanidinovaleric acid (alpha-keto-delta-GVA) reached levels of, respectively, 1.5-fold and twofold those of controls. Urinary GSA excretion increased and guanidinoacetic acid (GAA) excretion decreased about twofold in group C. GSA increases (2.6-fold) were also observed in the brain in group C, in addition to a significant increase of G (2.5-fold) and gamma-guanidinobutyric acid ([GBA] 1.5-fold). Finally, the extent of NX was found to be 45.2% in group B and 71.4% in group C. Light microscopy revealed an expansion and increase in cellularity of the mesangium of the glomeruli, particularly in group C. A significant correlation (r = .574, P < .0001) was found between CTN(Cl) and the degree of NX as calculated from the remaining functional area. These data suggest that the model can be used as a tool for further pathophysiological and/or behavioral investigations of renal failure.

Subtherapeutic erythropoietin and insulin-like growth factor-1 correct the anemia of chronic renal failure in the mouse

Chronic renal failure (CRF) is associated with a hyporegenerative anemia, which is caused primarily by inadequate production of erythropoietin (EPO) by the diseased kidneys and is responsive to exogenous EPO administration. Little is known about compensatory mechanisms that might supervene in anemia with low levels of EPO. Multiple investigations in vitro suggest an important role for insulin-like growth factor-1 (IGF-1) as well as EPO in erythropoiesis. Recently, both EPO and IGF-1 in vitro have been found to stimulate erythroid colony forming units in the mouse. However, no studies have examined the effect of IGF-1, singly and in combination with EPO, in CRF in vivo. This study examined mice with surgically-induced renal failure of six weeks duration that were treated for three weeks with the combination of subtherapeutic doses of both EPO and IGF-1. The single administration of each cytokine caused no significant change in hemoglobin in all CRF mice. In marked contrast the combined administration of the two cytokines produced a striking rise in hemoglobin, resulting in anemia correction in the majority of animals. The response to the combination therapy was comparable to the maximal response obtained with a single EPO dose (10 U) in a dose-finding study. Although the data are limited to utilizing one dose of each cytokine and one preparation of IGF-1, the large increase in hemoglobin observed with the combination therapy indicates that these two cytokines work in concert to stimulate erythroid precursors in CRF. In addition, untreated CRF mice showed markedly increased serum levels of low molecular weight binding proteins for IGF-1, potentially reducing the bioavailability of IGF-1. These findings taken together suggest that the anemia of CRF may represent both an EPO and a functional IGF-1 deficient state.

Response of chronic renal failure mice to peritoneal Staphylococcus epidermidis challenge: impact of repeated peritoneal instillation of dialysis solution

The effect of repeated instillation of peritoneal dialysis (PD) solution on the peritoneal clearance of a Staphylococcus epidermidis challenge was investigated in a mouse model of surgically induced chronic renal failure. For periods of up to 2 weeks, mice bearing peritoneal catheter implants underwent daily (3 mL) or twice daily (1.5 mL) peritoneal instillation of PD solution (4.25% dextrose) by transcutaneous injection into the catheter lumen. Peritoneal instillation of PD solution did not have a significant influence on the microbiological status of peritoneal structures of renal failure or sham-operated mice following experimental intracatheter S epidermidis inoculation with 10(6) colony-forming units (CFU) (assessment 48 hours after inoculation) or 10(8) CFU (assessment 1 week after inoculation). Microbiological and scanning electron microscopy (SEM) assessments of recovered peritoneal catheters demonstrated that S epidermidis remained associated with the catheter site after other peritoneal structures had become culture negative. SEM of the parietal peritoneum revealed striking morphologic alterations of the mesothelial surface as a consequence of daily PD solution infusion. In the absence of S epidermidis inoculation, repeated instillation of PD solution caused a marked acute peritoneal inflammation without evidence of a concomitant systemic inflammatory response. Furthermore, peritoneal inflammatory response to S epidermidis challenge was augmented by the infusion procedure. Concurrent assessments of inflammatory response and microbiological status revealed that, in spite of heightened peritoneal inflammatory response with peritoneal infusion, bacterial clearance from the catheter site was not improved. Although the animal preparation was limited to peritoneal infusion without drainage, the influence of repeated peritoneal instillation of hyperosmolar, acidic PD solution on the response of mice to S epidermidis challenge was successfully addressed.