Biochemical and histopathological changes in nephrectomized mice

Renal regenerative capacity related to stem cell reserve in nephrectomized rats

PURPOSE

On the new era of stem cell therapy, the present experimental study was conducted to investigate renal regenerative capacity related to kidney stem cell reserve in different nephrectomy (Nx) models.

METHODS

Three- and eight-week-old rats (n = 168) were randomly divided into four groups to include control and three Nx subgroups (1/6 Nx, 1/2 Nx, and 5/6 Nx) (Fig. 1). On post-Nx days 15, 30 and 60, kidney specimens were obtained to determine renal regenerative capacity. The specimens were examined with immunofluorescence. CD90/CD105 and Ki-67 expressions were determined as stem cell and cellular proliferation markers, respectively. Fig. 1 Intraoperative photographs showing three different types of nephrectomies (unilateral total Nx has not been shown in 5/6 Nx group) RESULTS: CD90 and CD105 expressions were stronger in glomeruli, but Ki-67 expressions were present only in tubuli. When all Nx types and post-Nx days were considered, both 3- and 8-week-old rats undergone 5/6 Nx had the highest glomerular CD90 and CD105 double expressions. While the expressions gradually increased toward the day 60 in 3-weeks old rats, 8-week-old rats had almost stable double expressions. The strongest tubular Ki-67 expressions were seen in 5/6 Nx groups of both in 3- and 8-week-old rats. The expressions were strongest on day 15 and then gradually decreased. Ipsilateral 1/6 Nx groups had stronger Ki-67 expression than contralateral ones in both age groups.

CONCLUSIONS

Kidneys may pose a regenerative response to tissue/volume loss through its own CD90- and CD105-related stem cell reserve which mainly takes place in glomeruli and seems to have some interactions with Ki-67-related tubular proliferative process. This response supports that kidney stem cells may have a potential to overcome tissue/volume loss-related damage.

A new low-nephron CKD model with hypertension, progressive decline of renal function, and enhanced inflammation in C57BL/6 mice

Chronic kidney disease (CKD) is a major health issue in the US. The typical five-sixths nephrectomy (typical 5/6 NX) is a widely used experimental CKD model. However, the typical 5/6 NX model is hypertensive in rats but strain dependent in mice. In particular, C57BL/6 mice with the typical 5/6 NX exhibits normal blood pressure and well-preserved renal function. The goal of the present study was to create a new hypertensive CKD model in C57BL/6 mice. We first characterized the vascular architecture originated from each renal artery branch by confocal laser-scanning microscopy with fluorescent lectin. Then, a novel 5/6 NX-BL model was generated by uninephrectomy combined with 2/3 renal infarction via a ligation of upper renal artery branch on the contralateral kidney. Compared with 5/6 NX-C, the 5/6 NX-BL model exhibited elevated mean arterial pressure (137.6 ± 13.9 vs. 104.7 ± 8.2 mmHg), decreased glomerular filtration rate (82.9 ± 19.2 vs. 125.0 ± 13.9 µl/min) with a reciprocal increase in plasma creatinine (0.31 ± 0.03 vs. 0.19 ± 0.04 mg/dl), and significant renal injury as assessed by proteinuria, histology with light, and transmission electron microscopy. In addition, inflammatory status, as indicated by the level of proinflammatory cytokine TNFα and the leukocyte counts, was significantly upregulated in 5/6 NX-BL compared with the 5/6 NX-C. In summary, we developed a new hypertensive CKD model in C57BL/6 mice with 5/6 renal mass reduction by uninephrectomy and upper renal artery branch ligation on the contralateral kidney. This 5/6 NX-BL model exhibits an infarction zone-dependent hypertension and progressive deterioration of the renal function accompanied by enhanced inflammatory response.

Deregulated Renal Calcium and Phosphate Transport during Experimental Kidney Failure

Impaired mineral homeostasis and inflammation are hallmarks of chronic kidney disease (CKD), yet the underlying mechanisms of electrolyte regulation during CKD are still unclear. Here, we applied two different murine models, partial nephrectomy and adenine-enriched dietary intervention, to induce kidney failure and to investigate the subsequent impact on systemic and local renal factors involved in Ca(2+) and Pi regulation. Our results demonstrated that both experimental models induce features of CKD, as reflected by uremia, and elevated renal neutrophil gelatinase-associated lipocalin (NGAL) expression. In our model kidney failure was associated with polyuria, hypercalcemia and elevated urinary Ca(2+) excretion. In accordance, CKD augmented systemic PTH and affected the FGF23-αklotho-vitamin-D axis by elevating circulatory FGF23 levels and reducing renal αklotho expression. Interestingly, renal FGF23 expression was also induced by inflammatory stimuli directly. Renal expression of Cyp27b1, but not Cyp24a1, and blood levels of 1,25-dihydroxy vitamin D3 were significantly elevated in both models. Furthermore, kidney failure was characterized by enhanced renal expression of the transient receptor potential cation channel subfamily V member 5 (TRPV5), calbindin-D28k, and sodium-dependent Pi transporter type 2b (NaPi2b), whereas the renal expression of sodium-dependent Pi transporter type 2a (NaPi2a) and type 3 (PIT2) were reduced. Together, our data indicates two different models of experimental kidney failure comparably associate with disturbed FGF23-αklotho-vitamin-D signalling and a deregulated electrolyte homeostasis. Moreover, this study identifies local tubular, possibly inflammation- or PTH- and/or FGF23-associated, adaptive mechanisms, impacting on Ca(2+)/Pi homeostasis, hence enabling new opportunities to target electrolyte disturbances that emerge as a consequence of CKD development.

Angiotensin II overcomes strain-dependent resistance of rapid CKD progression in a new remnant kidney mouse model

The remnant kidney model in C57BL/6 mice does not develop progressive chronic kidney disease (CKD). In this study we modified the model to mimic features of human CKD and to define accelerants of disease progression using three strains of mice. Following the procedure, there was a progressive increase in albuminuria, progressive loss in renal function, severe glomerulosclerosis and interstitial fibrosis, hypertension, cardiac fibrosis, and anemia by 4 weeks in CD-1 mice and by 12 weeks in 129S3 mice. In contrast, even after 16 weeks, the C57BL/6 mice with a remnant kidney had modestly increased albuminuria without increased blood pressure and without developing CKD or cardiac fibrosis. The baseline blood pressure, determined by radiotelemetry in conscious animals, correlated with CKD progression rates in each strain. Administering angiotensin II overcame the resistance of C57BL/6 mice to CKD following renal mass reduction, displaying high blood pressure and albuminuria, severe glomerulosclerosis, and loss of renal function by 4 weeks. Decreasing blood pressure with olmesartan, but not hydralazine, in CD-1 mice with a remnant kidney reduced CKD progression and cardiac fibrosis. C57BL/6 mice with a remnant kidney and DOCA-salt hypertension developed modest CKD. Each strain had similar degrees of interstitial fibrosis in three different normotensive models of renal fibrosis. Thus, reducing renal mass in CD-1 or 129S3 mice mimics many features of human CKD. Angiotensin II can convert the C57BL/6 strain from CKD resistant to susceptible in this disease model.

Accumulation of methylguanidine and changes in guanidino compound levels in plasma, urine, and kidneys of furosemide-treated rats

Antidiuresis and renal diseases alter the levels of guanidino compounds (GCs) in various tissues. Therefore, we hypothesized that diuresis could also disturb GC metabolism, storage, and elimination. In this study, rats were made diuretic to analyze GC levels in plasma, urine, and kidneys. Furosemide was chosen because of its wide use in various human pathologies. Rats were injected intraperitoneally 5 or 10 mg furosemide spread over a 24-hour cycle. Urine was collected over a period of 24 hours before and during furosemide treatment. Plasma was obtained from arterial blood. Renal zones were dissected. The GCs were determined by liquid chromatography. Five milligrams of furosemide provoked a significant increase in plasma and urine levels of GCs compared with those of the controls. The renal distribution and content of GCs were weakly modified by furosemide except for methylguanidine (MG). The level of MG was enhanced by 10 to 16 times in all renal zones. The MG level was 60% higher in renal zones of rats treated with 10 rather than 5 mg furosemide. The fractional excretion of MG was decreased by furosemide. Our data suggest that MG accumulation in kidney and plasma was caused by furosemide, which might induce MG synthesis, and that MG washout from tissue cells into urine by furosemide through the kidney may cause an increase in MG in the kidney.

Metabolomics in monitoring kidney transplants

PURPOSE OF REVIEW

The success of any given kidney transplant is closely tied to the ability to monitor patients and responsively change their medications. Transplant monitoring is still, however, dependent on relatively old technologies: serum creatinine levels, urine output, blood pressure, blood glucose and histopathology of biopsy samples. These older technologies do not offer sufficient specificity, sensitivity, or accuracy to allow appropriate and timely interventions. Using the tools of genomics, proteomics and metabolomics new biomarkers are being found that may greatly improve transplant monitoring and significantly enhance graft survival. This review describes the basic principles of metabolomics and summarizes a number of recent developments in the use of metabolite biomarkers and metabolomics to monitor kidney transplants.

RECENT FINDINGS

Changes in the concentration profiles of a number of small molecule metabolites found in either blood or urine can be used to localize organ damage, identify organs at risk of rejection, assess organs suffering from ischemia-repurfusion injury or identify organs that have been damaged by immunosuppressive drugs.

SUMMARY

The application of metabolomics to kidney transplant monitoring is still very much in its infancy. Nevertheless, there are a number of easily measured metabolites in both urine and serum that can provide reliable indications of organ function, organ injury, and immunosuppressive drug toxicity. As the field matures, metabolomics may eventually lead to the development of rapid, inexpensive and noninvasive approaches to assist clinicians in monitoring kidney transplants.

Biochemical validation of a rat model for polycystic kidney disease: Comparison of guanidino compound profile with the human condition

Polycystic kidney disease (PKD) accounts for 7-10% of all dialyzed renal insufficient patients. Accumulation of specific guanidino compounds (GCs) has been related to neurological, cardiovascular, hematological, and immunological complications of renal failure. In this study, we investigate whether the PKD/Mhm rat model can be used as a biochemical model for human PKD. For the validation of the rat model, we performed the first detailed evaluation of the concentrations of GCs in serum and urine of patients with PKD in addition to the GC patterns in the plasma, urine, and tissues of the PKD/Mhm rat model. The GCs were determined after separation on a cation exchange resin and fluorescence detection. The GC levels and changes observed in blood and urine of patients with PKD are comparable with those found in patients with renal insufficiency due to different etiologies. The PKD/Mhm rat model can be used as a biochemical model for human PKD as the obvious increases of urea, guanidinosuccinic acid, creatinine, guanidine, methylguanidine, and N(G)N(G)-dimethylarginine (symmetrical dimethylarginine) seen in blood of oldest heterozygous and younger homozygous PKD rats were largely within the same range as those found in the studied human PKD population, especially in patients with a glomerular filtration rate below 60 ml/min/1.73 m(2). The decreased levels of plasma guanidinoacetic acid seen at end-stage renal disease in homozygous and oldest heterozygous rats were also observed in serum of patients with a glomerular filtration rate below 20 ml/min/1.73 m(2). The PKD/Mhm rat model has, besides similar disease characteristics with human PKD, comparable GC alterations.

Metabolomics: the principles and potential applications to transplantation

This review provides a summary of the applications and potential applications of metabolite profiling (i.e. metabolomics) in monitoring organ transplants. While the concept of metabolomics is relatively new to organ transplantation, the idea of measuring metabolites as a quick, noninvasive probe of organ function is not. Indeed, metabolite measurements of serum creatinine have long been used to assess pre- and post-operative organ function. Over the past 10 years, a number of lesser-known, organ-specific metabolites have also been shown to be good diagnostic indicators of both organ function and viability. In general, metabolomics offers a complementary picture to what can be revealed via techniques based on genomics, proteomics or histology. Because metabolic changes typically happen within seconds or minutes after an 'event', whereas some transcript, protein abundance or tissue changes may take place over days or weeks, metabolomic measurements may offer a particularly useful and inexpensive diagnostic tool to monitor donor organ viability or to detect organ rejection. The excitement associated with metabolomics, however, must be tempered by the fact that the technology for rapid metabolite identification is still in its infancy, and that metabolites are but one part of a very complex picture pertaining to organ function.

GSA: behavioral, histological, electrophysiological and neurochemical effects

Renal insufficient patients suffer from a variety of complications as direct and indirect consequence of accumulation of retention solutes. Guanidinosuccinic acid (GSA) is an important probable uremic toxin, increased in plasma, urine, cerebrospinal fluid and brain of patients with uremia and supposed to play a role in the pathogenesis of some neurological symptoms. GSA, an NMDA-receptor agonist and GABA-receptor antagonist, is suggested to act as an excitotoxin and shown to be convulsive. The effect of hippocampal (i.h.) GSA injection on behavior and hippocampal volume in mice is presented here. In addition, hippocampal cGMP concentration after systemic injection of GSA was measured. The effect of co-application of NMDA-receptor antagonist CGP37849 with GSA was tested, in vivo, after hippocampal GSA injection and, in vitro, on GSA evoked currents in spinal cord neurons. A significant dose-dependent effect of i.h. injection of GSA on cognitive performance, activity and social exploratory behavior was observed. There was a protective effect of CGP37849 on GSA induced behavioral alterations. Volume of hippocampal cornu ammonis region decreased significantly and dose-dependently after GSA injection. Systemic GSA injection increased cGMP concentration in hippocampal formation. It can be concluded that GSA is an important neurotoxin. As GSA is increased in patients with uremia, it probably contributes to their neurological symptoms. Knowledge of neurotoxic effects and mechanisms of action of GSA and other uremic retention solutes could help in the development of more efficient treatment of uremic patients. Animal models like the 'GSA mouse model' are useful tools for research in this context.

Model of robust induction of glomerulosclerosis in mice: importance of genetic background

BACKGROUND

Increasing evidence suggests that genetic background plays an important role in the development of progressive glomerulosclerosis. The remnant kidney model (RKM) of progressive renal disease has been used extensively in rats. However, C57BL/6 mice are resistant to glomerulosclerosis with RKM induced by either pole amputation or renal artery ligation. A pole resection protocol, applied in 129/Sv mice, induced only mild glomerulosclerosis. We present here a highly reproducible, modified RKM approach to successfully establish a glomerulosclerosis model in mice.

METHODS

Male C57BL/6 (N = 17), 129/Sv (N = 20) and Swiss-Webster (N = 3) mice underwent RKM as follows: the lower branch of the left renal artery was ligated to produce about one third infarct; the upper pole of the left kidney (about one third kidney size) was removed by cautery and the right kidney was nephrectomized to induce a total 5/6 nephrectomy (Nx). In some C57BL/6 mice, 7/8 nephrectomy was induced by removing additional renal mass from the upper pole of the left kidney by cautery. Systolic blood pressure (BP) was measured in conscious mice using a tail-cuff blood pressure monitor and animals were sacrificed at 9, 12, 18, and 24 weeks after nephrectomy. Kidneys were harvested for morphologic analysis.

RESULTS

BP in C57BL/6 mice increased slightly after 5/6 nephrectomy over time without significant difference compared to baseline blood pressure except at 8 weeks (blood pressure at week 0, 98 +/- 1 mm Hg; week 4, 105 +/- 2 mm Hg; week 8, 113 +/- 4 mm Hg; and week 12, 110 +/- 3 mm Hg). Blood presssure remained normal in C57BL/6 mice at 18 weeks after 7/8 nephrectomy (103 +/- 2 mm Hg). Blood pressure in 129/Sv mice increased significantly after 5/6 nephrectomy from 4 to 12 weeks (week 0, 112 +/- 3 mm Hg; week 4, 161 +/- 9 mm Hg; week 8, 166 +/- 5 mm Hg; and week 12, 176 +/- 5 mm Hg; P < 0.01 weeks 4, 8, and 12 vs. week 0 blood pressure). Urine protein excretion in C57BL/6 mice increased only at 4 weeks after 5/6 nephrectomy, and was back to normal at 8 and 12 weeks (week 0, 13.2 +/- 1.4 mg/24 hours; week 4, 20.5 +/- 1.8 mg/24 hours; week 8, 18.8 +/- 1.6 mg/24 hours; and week 12, 17.2 +/- 1.2 mg/24 hours, P < 0.05 week 4 vs. week 0). 129/Sv mice developed significant proteinuria 12 weeks after 5/6 nephrectomy compared to their baseline and to levels achieved in C57BL/6 mice (week 0, 17.2 +/- 1 mg/24 hours; week 4, 14.9 +/- 1.8 mg/24 hours; week 8, 23.8 +/- 6.7 mg/24 hours; and week 12, 36.3 +/- 6.6 mg/24 hours, P < 0.01 week 12 vs. week 0; P < 0.01 129/Sv vs. C57BL/6 at week 12). Mortality varied in response to nephrectomy injury in the different strains. Ten percent of C57BL/6 and 43% of 129/Sv died within 12 weeks after 5/6 nephrectomy. Although 50% of C57BL/6 mice died by 12 weeks after 7/8 nephrectomy, there was only mild glomerulosclerosis (<5%) in C57BL/6 mice even at 24 weeks after 5/6 nephrectomy or 18 weeks after 7/8 nephrectomy. In contrast, glomerulosclerosis was marked in both 129/Sv mice and Swiss-Webster mice as early as 9 weeks after 5/6 nephrectomy: 42% of glomeruli showed sclerosis in 129/Sv mice [average sclerosis index (SI), 0 to 4+ scale, 1.08] vs. 24% in Swiss-Webster mice (average SI, 0.57). Tubulointerstitial fibrosis developed in parallel with glomerulosclerosis in both 129/Sv and Swiss-Webster mice.

CONCLUSION

We conclude that genetic background is one of the important factors determining the susceptibility to the development of glomerulosclerosis in mice. We speculate that the superior effects of renal artery ligation plus cautery to produce glomerulosclerosis may result from higher blood pressure responses due to local ischemia activating the renin-angiotensin system.

Overexpression of arginase alters circulating and tissue amino acids and guanidino compounds and affects neuromotor behavior in mice

Arginine is an intermediate of the ornithine cycle and serves as a precursor for the synthesis of nitric oxide, creatine, agmatine and proteins. It is considered to be a conditionally essential amino acid because endogenous synthesis only barely meets daily requirements. In rapidly growing suckling neonates, endogenous arginine biosynthesis is crucial to compensate for the insufficient supply of arginine via the milk. Evidence is accumulating that the intestine rather than the kidney plays a major role in arginine synthesis in this period. Accordingly, ectopic expression of hepatic arginase in murine enterocytes by genetic modification induces a selective arginine deficiency. The ensuing phenotype, whose severity correlates with the level of transgene expression in the enterocytes, could be reversed with arginine supplementation. We analyzed the effect of arginine deficiency on guanidine metabolism and neuromotor behavior. Arginine-deficient transgenic mice continued to suffer from an arginine deficiency after the arginine biosynthetic enzymes had disappeared from the enterocytes. Postweaning catch-up growth in arginine-deficient mice was characterized by increased levels of all measured amino acids except arginine. Furthermore, plasma total amino acid concentration, including arginine, was significantly lower in adult male than in adult female transgenic mice. Decreases in the concentration of plasma and tissue arginine led to significant decreases in most metabolites of arginine. However, the accumulation of the toxic guanidino compounds, guanidinosuccinic acid and methylguanidine, corresponded inversely with circulating arginine concentration, possibly reflecting a higher oxidative stress under hypoargininemic conditions. In addition, hypoargininemia was associated with disturbed neuromotor behavior, although brain levels of toxic guanidino compounds and ammonia were normal.

Creatine and creatinine metabolism

The goal of this review is to present a comprehensive survey of the many intriguing facets of creatine (Cr) and creatinine metabolism, encompassing the pathways and regulation of Cr biosynthesis and degradation, species and tissue distribution of the enzymes and metabolites involved, and of the inherent implications for physiology and human pathology. Very recently, a series of new discoveries have been made that are bound to have distinguished implications for bioenergetics, physiology, human pathology, and clinical diagnosis and that suggest that deregulation of the creatine kinase (CK) system is associated with a variety of diseases. Disturbances of the CK system have been observed in muscle, brain, cardiac, and renal diseases as well as in cancer. On the other hand, Cr and Cr analogs such as cyclocreatine were found to have antitumor, antiviral, and antidiabetic effects and to protect tissues from hypoxic, ischemic, neurodegenerative, or muscle damage. Oral Cr ingestion is used in sports as an ergogenic aid, and some data suggest that Cr and creatinine may be precursors of food mutagens and uremic toxins. These findings are discussed in depth, the interrelationships are outlined, and all is put into a broader context to provide a more detailed understanding of the biological functions of Cr and of the CK system.

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.

The course of the remnant kidney model in mice

The remnant kidney model was produced in mice by unilateral nephrectomy and partial infarction of the remaining kidney. Control mice underwent laparotomy only. The mice were studied for up to 44 weeks. No quantitative differences were noted in systolic arterial pressure, proteinuria, or histopathology between control mice and those with a remnant kidney. Glomerular enlargement occurred in the remnant kidney.