Nephrocalcinosis In Female Rats Research Articles

Diet-Induced Nephrocalcinosis in Female Rats

Diet-Induced Nephrocalcinosis in Female Rats

Diet-Induced Nephrocalcinosis in Female Rats: A Response to L'Abbé et al.

Diet-Induced Nephrocalcinosis in Female Rats: A Response to L'Abbé et al.

Different Dietary Sources of Omega‐3 Polyunsaturated Fatty Acids Influences Renal Fatty Acid Composition, Gene Expression, and Risk of Nephrocalcinosis in Female Rats

Nephrocalcinosis, the accumulation of calcium (Ca) in the kidneys, is associated with multiple renal disorders including renal stones. Populations with low risk of renal stones have been shown to have a diet high in fish oil, a rich source of omega‐3 polyunsaturated fatty acids (n‐3 PUFAs). However, sources of n‐3 PUFAs differ in the amount, type, and structure. The study objective was to determine the effect of feeding different sources of n‐3 PUFAs on the development of nephrocalcinosis. Young (age 28 day) female Sprague‐Dawley rats were fed a casein diet supplemented with corn oil or omega‐3 rich oils consisting of flaxseed, krill, menhaden, salmon, or tuna oil for 12 wks. Gas chromatography showed that renal fatty acid composition reflected the fatty acid profile of the dietary oils. RT‐qPCR showed that rats fed fish oils had reduced inflammation as indicated by lower (P<0.05) COX‐2 and TGF‐β. Furthermore, rats fed salmon or tuna oil had increased (P<0.05) osteopontin (SPP1) gene expression, indicating antagonist action to renal Ca crystallization. Rats fed fish oils had lower (P<0.05) renal NFκB and prostaglandin E2 activity as determined by enzyme immunoassay. However, krill oil induced nephrocalcinosis due to the high phosphorous (P) content associated with phospholipids. Different sources of n‐3 PUFAs mitigated the effects of nephrocalcinosis, but failed to prevent nephrocalcinosis due to Ca:P imbalance.

Nephrocalcinosis in Female Rats Fed Diets Containing Either Pectin or Cellulose

Problem statement: There is evidence that the type of fiber influences the development of nephrocalcinosis in rats, but the effect of pectin was unknown. Approach: The effects of dietary pectin and cellulose on kidney calcification were studied in female rats. The diets used contained either 0.4-0.6% phosphorus and either cellulose (10%, w/w) or pectin. The purified diets used were balanced for residual calcium, magnesium and phosphorus in the fiber preparations. Results: Increasing the phosphorus concentration of the diet from 0.4-0.6% caused massive nephrocalcinosis in rats fed the cellulose diets. Pectin (10%, w/w) versus cellulose in diets containing 0.4% phosphorus significantly increased calcium and phosphorus concentrations in kidney. When compared with cellulose, pectin did not influence the apparent absorption of calcium, phosphorus and magnesium. Urinary concentrations of calcium and magnesium were not affected by pectin feeding, but those of phosphorus were increased. When pectin was given with the diet containing 0.6% phosphorus, its nephrocalcinogenic action as compared with cellulose was not observed. Conclusion: Pectin instead of cellulose in diets containing 0.4% phosphorus induced nephrocalcinosis in female rats. The effect of pectin may be explained by an increase in urinary phosphorus concentration. The lack of nephrocalcinogenic action of pectin in a diet with 0.6% phosphorus indicates that the nephrocalcinosis-inducing effect of high phosphorus intake had overruled any effect of fiber type.

The Concentrations and Ratio of Dietary Calcium and Phosphorus Influence Development of Nephrocalcinosis in Female Rats

Nephrocalcinosis (NC) in female rats can complicate the interpretation of nutritional or toxicological studies involving the kidney. Recent reformulations of standardized rodent diets such as AIN-93G and NTP-2000 sought to optimize the dietary Ca:P ratio, an important etiologic factor in NC. The effect of increasing intakes of Ca and P together at their optimal molar ratio has not been systematically studied. Weanling female and male Sprague-Dawley rats were fed modified AIN-93G diets containing Ca and P at AIN-93G diet concentrations (5 g Ca + 3 g P/kg diet), with multiples of Ca and P at the same ratio (1.5x = 7.5 g Ca + 4.5 g P, 2.5x = 12.5 g Ca + 7.5 g P, 4.0x = 20.0 g Ca + 12.0 g P/kg diet), or Ca and P at concentrations found in the AIN-76A diet (5 g Ca + 5 g P/kg diet), for 16 wk. Incidence and severity of NC and kidney Ca concentration in female rats increased with dietary Ca and P, although not to levels in female rats fed at the AIN-76A Ca:P ratio. Male rats showed limited evidence of kidney Ca accumulation or NC. The concentrations of dietary Ca and P, as well as the ratio of these two elements, affected development of NC in female rats.

Chronic Toxicity and Carcinogenicity Study of Erythritol in Rats

The potential toxicity and carcinogenicity of erythritol, a low-calorie sugar substitute, were examined in Wistar Crl:(WI) WU BR rats. Groups of 50 rats of each sex consumed diets with 0, 2, 5, or 10% erythritol, or 10% mannitol, for a period of 104–107 weeks. To each of these main groups, two satellite groups of 20 males each were attached for interim kills after 52 and 78 weeks of treatment. At start of the study, the rats were 5–6 weeks old. The average intakes of erythritol in the 2, 5, and 10% groups were 0.9, 2.2, and 4.6 g/kg body wt/day for males and 1.0, 2.6, and 5.4 g/kg body wt/day for females, respectively. Mannitol intakes were 4.4 and 5.2 g/kg body wt/day in males and females, respectively. All treatments were well tolerated without diarrhea or other side effects. Body weights were significantly below control levels during most of the study in males of the 5% erythritol group and in males and females of the 10% erythritol and 10% mannitol groups. Survival of the animals was not adversely affected by the treatments. Hematological and clinicochemical examinations did not reveal noticeable changes which could be attributed to treatment. Analysis of urine samples collected during five 48-hr periods, from rats of the satellite groups in Weeks 26, 42, 50, and 78 and from rats of the main groups in Week 102, showed that about 60% of ingested erythritol was excreted unchanged. The urine volumes increased with increasing dietary erythritol levels. In line with previous observations on other polyols, erythritol and mannitol ingestion led to an increased excretion of urinary calcium and citrate. The urinary excretions of sodium, potassium, phosphate,N-acetylglucosaminidase (NAG), γ-glutamyltransferase (GGT), low-molecular-weight protein (LMP), and total protein (TP) were slightly elevated in the 10% erythritol group. Increased GGT and NAG excretions also were seen occasionally at the 5% dose. Significantly increased relative cecum weights were seen in rats of either sex in the 10% mannitol and, somewhat less pronounced, 10% erythritol groups. Some cecal enlargement also was seen in the 5% erythritol group. The relative weight of the kidneys was highest in the 10% erythritol group, the difference from controls reaching statistical significance at interim kills (males) and termination (females). Except for more frequent pelvic nephrocalcinosis in female rats of all erythritol dose groups, the histopathological examinations did not reveal any nonneoplastic, preneoplastic, or neoplastic changes that could be attributed to the ingestion of erythritol. In male and female rats of the 10% mannitol group, pelvic nephrocalcinosis, which in females was associated occasionally with pelvic hyperplasia, was the only remarkable finding. The incidence and progression of nephrosis, which is commonly seen in aging rats of this strain, were not influenced by the treatments. In the absence of morphological alterations in the kidneys or other signs of nephrotoxicity, the increased excretions of NAG, GGT, LMP, and TP are regarded as innocuous, functional sequelae of the renal elimination of erythritol. In conclusion, the toxicological profile of erythritol in rats resembles that of other polyols in several respects. Except for nephrocalcinosis, which is commonly seen in polyol-fed rats, no other treatment-related, morphological changes were observed in the kidneys. Evidence for a tumor-inducing or tumor-promoting effect of erythritol was not seen.

Diet-induced nephrocalcinosis in female rats is irreversible and is induced primarily before the completion of adolescence.

The effect of altering the dietary Ca:P ratio during critical points of growth (based on reproductive and skeletal age) on kidney calcification in female rats was investigated. Groups of weanling animals were fed one of three nutritionally complete but calcium-altered diets (0.25, 0.5 or 1.0 g Ca/100 g diet) from 4 to 12 wk of age (Phase 1). Phosphorus concentration remained constant at 0.4 g/100 g diet resulting in Ca:P molar ratios of 0.48, 0.96 and 1.92, respectively. During Phase 2, the same animals within each diet group were then rerandomized into one of the above diets and fed for an additional 25 wk. Each group contained five rats. The data from the nine treatment groups were analyzed statistically using a two-way ANOVA (Phase 1 dietary Ca level by Phase 2 dietary Ca level). The level of dietary Ca during Phase 1 only exerted a significant influence on kidney Ca accumulation. Rats fed the two lower dietary Ca levels, and hence lower dietary Ca:P molar ratios, during Phase 1 had two- to threefold greater kidney Ca concentration and kidney ash Ca concentration than rats fed the diet with the highest dietary Ca level (1.92 Ca:P molar ratio) during Phase 1, regardless of the Ca intake during Phase 2. In contrast, the dietary Ca:P molar ratio during Phase 2 had little effect either positively or negatively on the kidney Ca concentration that had been established during Phase 1. The results indicate that dietary-induced nephrocalcinosis in female rats is irreversible and is induced primarily before the completion of adolescence (approximately 12 wk of age) in Sprague-Dawley female rats.

Development and Testing of the AIN-93 Purified Diets for Rodents: Results on Growth, Kidney Calcification and Bone Mineralization in Rats and Mice

Because of nutritional and technical problems the AIN-76A rodent diet was revised. One of the new formulations was designated AIN-93G and was suggested for use during growth, pregnancy and lactation studies. Some major differences in this new formulation compared with the AIN-76A diet are as follows: 7 g soybean oil was substituted for 5 g corn oil/100 g diet to increase the amount of linolenic acid; the amounts of vitamins E and K were increased; cornstarch was substituted for most of the sucrose; the amount of phosphorus was reduced to eliminate the problem of nephrocalcinosis in female rats; L-cystine was substituted for DL-methionine; and the manganese concentration was reduced. Various developmental modifications of the AIN-93G diet were fed to weanling rats and mice to determine effects on growth and tissue mineralization. After rats were fed the developmental version of AIN-93G for 16 wk, body weights in both male and female rats were not different from those of rats fed a cereal-based nonpurified diet. After 13 wk, male mice fed this diet weighed 13% more than those fed the nonpurified diet. Body weights of female mice were not affected. The new diet formulation prevented kidney calcification in female rats and mice during 16 wk of feeding.

Long-Term Phosphorus Restriction Prevents Corticomedullary Nephrocalcinosis and Sustains Reproductive Performance but Delays Bone Mineralization in Rats

In a long-term experiment with three successive generations of rats, the influence of dietary phosphorus restriction (2 instead of 4 g phosphorus/kg diet) on nephrocalcinosis, reproduction and bone mineralization was studied. Nephrocalcinosis in female rats, as based on kidney calcium concentration and histological examination, was prevented by phosphorus restriction. The low phosphorus diet caused reduced femur concentrations of magnesium, calcium and phosphorus in rats of the first and second generation aged 4 to 12 wk. The low phosphorus diet resulted in lower plasma phosphorus concentrations. In the kidneys of female rats, immediately after lactation, a higher degree of tubular hyperplasia was seen after the low phosphorus diet was fed. Reproductive performance was not affected by phosphorus restriction. We conclude that 0.2% phosphorus in the diet prevents nephrocalcinosis in female rats while it sustains reproduction but delays bone mineralization.

Increasing Intake of Soybean Protein or Casein, but Not Cod Meal, Reduces Nephrocalcinosis in Female Rats

Female weanling rats were fed diets with soybean protein, casein or cod meal at 171, 342 or 513 mmol nitrogen/100 g for 3 wk. The diets were isonitrogenous and balanced for fat, cholesterol, calcium, magnesium and phosphorus. Cod meal feeding at 171 and 342 mmol nitrogen/100 g diet produced lower kidney calcium concentrations than the feeding of either soybean protein or casein. Increasing protein intakes were associated with reduced kidney calcium concentrations in the rats fed either soybean protein or casein but not in those fed cod meal. The anti-nephrocalcinogenic effect of increasing intakes of soybean protein may relate to the lowering of urinary phosphorus concentration. Increasing intakes of casein probably inhibited nephrocalcinogenesis by lowering urinary pH and raising urinary magnesium concentration. Increasing cod meal concentrations in the diet lowered urinary pH and raised urinary magnesium and calcium concentrations, but the effects on nephrocalcinogenesis of these changes probably counteracted each other.

Dietary fluoride, unlike bromide or iodide, counteracts phosphorus-induced nephrocalcinosis in female rats

Supplemental dietary F has been shown to counteract P-induced nephrocalcinosis in female rats. In order to obtain information as to the specificity of this F effect, the effect of other halogens, namely Br and I, on P-induced nephrocalcinosis was studied in weanling female rats. Supplemental dietary Br (5.24 mmol/kg of diet) and I (1.43 mmol/kg of diet) did not influence P-induced nephrocalcinosis, whereas F at equimolar dietary concentrations had marked antinephrocalcinogenic activity. The halogens were added to the diets in the form of KBr, KI, and NaF; the diets were balanced for the kations with Cl salts. The addition of KI to the diet to a concentration of 5.24 mmol/kg caused pronounced growth retardation, decreased feed intake, hepatomegaly, and signs of lethargy. It is concluded that the protective effect of dietary F against P-induced nephrocalcinosis does not extend to other halogens.

In-vivomonitoring of corticomedullary nephrocalcinosis in rats using computerized tomography

An in-vivo method, computerized tomography (CT), was used to monitor nephrocalcinosis in female rats. CT density data correlated well with renal Ca content measured by atomic absorption spectrophotometry. In-vivo CT measurements revealed that the severity of nephrocalcinosis may change spontaneously with time. Manifest calcifications may exhibit spontaneous regression and are probably affected positively by high dietary Mg, in contrast to increased Ca. It is concluded that CT is a suitable and reliable non-invasive in vivo method to follow up time-dependent alterations in kidney calcifications in rats.

Phosphorus-induced nephrocalcinosis in female rats: a study on regression and clinical abnormalities

The question addressed was whether preestablished phosphorus (P)-induced nephrocalcinosis would regress after dietary P restriction. Female rats were fed purified diets containing either 0.2% (w/w) P (low P) or 0.6% P (high P). After 29 days, the high-P diet had caused massive nephrocalcinosis as demonstrated chemically (by the analysis of calcium in kidney) and histologically (by inspection of kidney sections stained for calcium phosphate deposits). Switching rats from the high P to the low P diet did not result in a decrease in the degree of nephrocalcinosis within 91 days. Thus, P-induced nephrocalcinosis may not regress upon subsequent P restriction. Rats that had been fed either the 0.2 or 0.6% P diet for 56 days were examined clinically with respect to 14 selected variables. None of the variables discriminated between rats with or without nephrocalcinosis. This might imply that P-induced nephrocalcinosis in female rats does not cause significant discomfort.

Dietary fluoride prevents phosphorus-induced nephrocalcinosis in female rats

The effect of dietary fluoride (F) on nephrocalcinosis was studied in young, female rats. Nephrocalcinosis was induced by a diet rich in phosphorus (P). F in the diet effectively counteracted P-induced nephrocalcinosis in a dose-dependent fashion. The feeding of increasing amounts of F caused decreasing calcium (Ca) and F concentrations in kidney. This suggests that the amount of Ca in kidney determines F accumulation in this organ, rather than F intake. Increasing amounts of F in the diet caused increasing rates of urinary and fecal excretion and whole-body retention of F. Dietary F did not influence urinary and fecal excretion and plasma concentrations of Ca, magnesium (Mg), and P. The metabolic basis for the protective effect of F against the development of nephrocalcinosis remains to be established.

Diet-induced nephrocalcinosis and urinary excretion of albumin in female rats

This study was carried out to test the hypothesis that diet-induced nephrocalcinosis causes enhanced loss of albumin in urine, irrespective of the composition of the nephrocalcinogenic diet. Female rats were fed various purified diets for 28 days. There was a control diet (0.5% Ca, 0.04% Mg, 0.4% P, 15.1% protein, wt/wt), a low Mg (0.01% Mg), a high protein (30.2% protein) and a high P diet (0.6% P). The low Mg and high P diet induced nephrocalcinosis as demonstrated histologically and by markedly increased concentrations of kidney Ca. In rats fed the high protein diet, nephrocalcinosis was essentially absent. Group mean values of urinary excretion of albumin and plasma concentrations of urea were increased in rats fed either the low Mg or high P diet. The high protein diet did not affect urinary albumin but caused lysozymuria which was not seen in the other groups. Plasma urea was increased in rats fed the high protein diet. In individual rats, the concentration of Ca in kidney and urinary albumin excretion were positively correlated. It is suggested that nephrocalcinosis in female rats induced by either low Mg or high P intake causes kidney damage which in turn leads to increased concentrations of albumin in urine and urea in plasma.

Nutrition and kidney calcification in rats

Nephrocalcinosis is a 'spontaneous' disorder in rats which refers to the deposition of calcium salts in the kidney, preferably in the cortico-medullary region. Studies using defined, semi-purified diets have shown that low dietary concentrations of magnesium, high concentrations of calcium, high concentrations of phosphorus and low calcium: phosphorus ratios induce kidney calcification. Dietary phosphorus induced nephrocalcinosis in female rats is associated with increased kidney size and weight, tubular hyperplasia, fibrosis and increased excretion of albumin in urine. This suggests that nephrocalcinosis may impair kidney function. In rats fed different commercial diets the incidence of nephrocalcinosis can vary considerably. Differences in the degree of nephrocalcinosis in different experiments may negatively influence the comparability of experimental outcome, especially when this is affected by kidney function and structure. Experimental data are needed so that diets can be formulated that do not produce nephrocalcinosis without inducing other disorders.

Influence of Dietary Calcium:Phosphorus Ratio on Mineral Excretion and Nephrocalcinosis in Female Rats

The effects of dietary calcium (Ca) concentration and calcium: phosphorus (Ca:P) ratio on mineral balance and nephrocalcinosis were studied in female rats. In the first experiment there were two dietary Ca concentrations (0.25 and 0.50%, wt/wt) at two different Ca:P ratios (0.6 and 1.3). In the second experiment the diets were formulated to contain 0.40% P and either 0.13, 0.25, 0.50 or 0.75% Ca. The diets contained 0.03% magnesium (Mg). The fecal outputs of Ca, P and Mg were lower (P less than 0.01) after feeding low Ca diets than after feeding high Ca diets. Urinary excretion of P decreased with increasing dietary Ca and increased with increasing P intake. In rats fed the 0.25% Ca diets whole-body retentions of Ca and P were lower than in the rats fed 0.50% Ca. Both increases in dietary Ca from 0.13 to 0.50% and P from 0.20 to 0.40% elevated Ca and P content of kidneys as well as the degree of nephrocalcinosis. However, after feeding the highest Ca concentration (0.75%) nephrocalcinosis was essentially absent while kidney concentrations of Ca and P were relatively low. When compared with 0.50% Ca in the diet, 0.75% Ca increased group mean whole-body retention of Ca but lowered that of P. In individual rats the degree of nephrocalcinosis and the concentrations of minerals in kidney were positively correlated.

The pathogenesis and effect on renal function of nephrocalcinosis induced by different diets in female rats

The ability of three diets to produce nephrocalcinosis in female rats has been compared after 30, 60 and 90 days of feeding. Severe nephrocalcinosis with associated tubular damage was induced with a standard laboratory maintenance low-protein diet and with a diet containing a single-cell protein (Pruteen) but not with a casein-containing diet. Both the Pruteen and casein diets were high-protein diets. The development of the lesion was equally rapid following feeding of either the laboratory maintenance diet or the Pruteen diet. Nephrocalcinosis was present, with body kidneys similarly affected, at each 30-day interval with either diet. A severe degree of nephrocalcinosis was associated with widespread renal damage although signs of tubular regeneration and repair were evident at 30 days. Nephrocalcinosis induced by the Pruteen diet was accompanied by enlargement of the kidney. Renal function was assessed at each time by the measurement of urine volume, specific gravity and protein content, inulin clearance, and the excretion of the urinary enzymes N-acetyl-β-glucosaminidase and alkaline phosphatase. Despite extensive calcification and some tubular damage, renal function was unimpaired, reflecting the capacity of the functional reserve of the kidney.

Dietary protein, fat, and minerals in nephrocalcinosis in female rats

Young female rats fed semipurified diets containing casein or a soy protein isolate had extensive nephrocalcinosis at the junction between the outer and inner stripe of the outer medullary zone after 5 wk on the diets, whereas rats fed a diet containing a lactalbumin concentrate did not. Although the percentages of actual protein and of total ash were similar in all three diets, the concentrations of individual minerals were not, owing to methods used in isolating the proteins. Comparison of the individual mineral contents of these diets with those in other laboratories as compiled from the literature suggested that factors other than minerals, including protein, are also implicated. Dietary fat appeared to be another such factor in a series of experiments in which saturated medium-chain triglycerides and corn oil were included in diets containing soy protein isolate. Although these diets had identical mineral compositions, the rats fed medium-chain triglycerides had less severe lesions.