Studies on the protective effect of dietary fish oil on uranyl-nitrate-induced nephrotoxicity and oxidative damage in rat kidney.

Human and animal exposure demonstrates that uranium is nephrotoxic. However, attempts to reduce it were not found suitable for clinical use. Dietary fish oil (FO) enriched in omega-3 fatty acids reduces the severity of cardiovascular and renal diseases. Present study investigates the protective effect of FO on uranyl nitrate (UN)-induced renal damage. Rats prefed with experimental diets for 15 days, given single nephrotoxic dose of UN (0.5mg/kg body weight) intraperitoneally. After 5d of UN treatment, serum/urine parameters, enzymes of carbohydrate metabolism, brush border membrane (BBM), oxidative stress and phosphate transport were analyzed in rat kidney. UN nephrotoxicity was characterized by increased serum creatinine and blood urea nitrogen. UN increased the activity of lactate dehydrogenase and NADP-malic enzyme whereas decreased malate, isocitrate and glucose-6-phophate dehydrogenases; glucose-6-phophatase, fructose-1, 6-bisphosphatase and BBM enzyme activities. UN caused oxidant/antioxidant imbalances as reflected by increased lipid peroxidation, activities of superoxide dismutase, glutathione peroxidase and decreased catalase activity. Feeding FO alone increased activities of enzymes of glucose metabolism, BBM, oxidative stress and Pi transport. UN-elicited alterations were prevented by FO feeding. However, corn oil had no such effects and was not similarly effective. In conclusion, FO appears to protect against UN-induced nephrotoxicity by improving energy metabolism and antioxidant defense mechanism.

Effects of water restriction on gene expression in mouse renal medulla: identification of 3betaHSD4 as a collecting duct protein.

To identify novel gene targets of vasopressin regulation in the renal medulla, we performed a cDNA microarray study on the inner medullary tissue of mice following a 48-h water restriction protocol. In this study, 4,625 genes of the possible approximately 12,000 genes on the array were included in the analysis, and of these 157 transcripts were increased and 63 transcripts were decreased by 1.5-fold or more. Quantitative, real-time PCR measurements confirmed the increases seen for 12 selected transcripts, and the decreases were confirmed for 7 transcripts. In addition, we measured transcript abundance for many renal collecting duct proteins that were not represented on the array; aquaporin-2 (AQP2), AQP3, Pax-8, and alpha- and beta-Na-K-ATPase subunits were all significantly increased in abundance; the beta- and gamma-subunits of ENaC and the vasopressin type 1A receptor were significantly decreased. To correlate changes in mRNA expression with changes in protein expression, we carried out quantitative immunoblotting. For most of the genes examined, changes in mRNA abundances were not associated with concomitant protein abundance changes; however, AQP2 transcript abundance and protein abundance did correlate. Surprisingly, aldolase B transcript abundance was increased but protein abundance was decreased following 48 h of water restriction. Several transcripts identified by microarray were novel with respect to their expression in mouse renal medullary tissues. The steroid hormone enzyme 3beta-hydroxysteroid dehydrogenase 4 (3betaHSD4) was identified as a novel target of vasopressin regulation, and via dual labeling immunofluorescence we colocalized the expression of this protein to AQP2-expressing collecting ducts of the kidney. These studies have identified several transcripts whose abundances are regulated in mouse inner medulla in response to an increase in endogenous vasopressin levels and could play roles in the regulation of salt and water excretion.

Inhibitory effects of female sex hormones on urinary stone formation in rats.

BACKGROUND: The effects of female sex hormones on urinary stone formation are not known. This study was conducted to investigate the effects of these hormones on stone formation by using an ethylene glycol (EG) and vitamin D-induced rat urolithiasis model. METHODS: Adult female Wistar rats were fed the same diet for four weeks and were then divided into four groups (N = 10 each). One group was administered 0.5 ml of olive oil three times per week for four weeks as a control. The other three groups were administered 0. 5 microg of vitamin D3 and 0.5 ml of 5% EG three times per week for four weeks. The rats in two of these three groups were oophorectomized, and the rats of the remaining group underwent a sham operation on the day before the start of the four-week treatment period. One of the two oophorectomized groups was then administered a supplementation of female sex hormones (0.1 mg of estrogen and 2.5 mg of progesterone 3 times per week for 4 weeks). On the first day of the fifth week of the experimental period, the degree of crystal deposition was determined histologically, and the calcium content in renal tissue was measured. We also investigated the level of osteopontin (OPN) mRNA in renal tissues by Northern blot analysis. OPN is a matrix protein thought to be a promoter of stone formation. RESULTS: The urinary oxalate excretion, crystal deposition and calcium content in renal tissue and the expression of OPN-mRNA were greater in the oophorectomized rats compared with the controls, and the same parameters were inhibited by the female sex hormone supplementation. CONCLUSIONS: These results suggest that female sex hormones can inhibit renal crystal deposition in EG-treated rats by suppressing the urinary oxalate excretion and the expression of OPN.

Calbindin localization in African giant rat kidney (Cricetomys gambianus).

Cricetomys gambianus are rodents living in savanna and follow area. They can live with restricted drinking water eating fresh food. Therefore their kidney may have some adaptive mechanisms for ion/water homeostasis compared to usual laboratory rats. In this study we have looked for calbindin, an intracellular calcium binding protein previously found in distal convoluted tubules from all mammalian species that have been studied and able to increase, in vitro, Ca2+ reabsorption. We have shown by using in situ hybridization, immunoblotting and immunohistochemistry that calbindin was expressed in three different portions of the distal nephron of the African giant rat. Calbindin was found in distal convoluted tubules, in cortical collecting tubules and in outer medullary collecting ducts. By contrast, in laboratory rat, calbindin was only found in distal convoluted tubules and undetectable in medullary collecting ducts. Thick ascending limb of Henle's loop were calbindin negative as shown by double immunolabelling using anti-uromucoid (Tamm-Horsfall protein). As previously shown in laboratory rat and rabbit, transcellular Ca2+ movement seems to be facilitated by calbindin in renal tubules segments predominantly actively transporting Ca2+, it may be suggested that in African giant rat, outer medullary collecting ducts may also actively transport Ca2+. As calretinin, another intracellular calcium binding protein highly homologous to calbindin but whose function is still conjectural has been suspected to be expressed in kidney, we have looked and not found any calretinin in both adult rat species.

Immunocytochemical localization of stanniocalcin cells in the rat kidney.

Stanniocalcin (STC) is a polypeptide hormone that was first discovered in fishes, where it functions as a regulator of calcium and phosphate homoeostasis. Recently, complementary DNAs encoding human STC (hSTC) have been characterized, and recombinant hSTC has been synthesized in a bacterial expression system. In preliminary studies, STC-immunoreactive cells have already been identified in human kidney tubules with antibodies to recombinant hSTC. The purpose of this study was to map the overall spatial distribution of STC cells in mammalian kidney, using the rat as a model system. Immunocytochemistry was performed on fixed sections of rat kidney tissue using hSTC antiserum in conjunction with fluorescein isothiocyanate-conjugated second antibodies. STC-immunoreactive cells were found in cortical thick ascending limb, in macula densa, in distal convoluted tubules, and in the cortical and medullary collecting ducts. All cortical thick ascending limb cells contained immunoreactive STC. Most distal convoluted tubules cells contained STC, and these were identified as principal cells. The distribution of STC cells in cortical and medullary collecting ducts also corresponded closely to the known frequently of principle cells in these segments, suggesting that principal cells are the site of STC storage and/or synthesis in both distal convoluted tubules and collecting ducts. Some collecting duct intercalated cells contained STC as well, and these were tentatively identified as alpha-type intercalated cells. As all tubular segments containing STC are known to be involved in regulated ion transport, renally derived STC may be acting in an autocrine, paracrine and/or endocrine fashion to regulate one or more of these transport processes.

Hypercalcemia reduces renal medullary content of organic osmolytes.

Hypercalcemia is often associated with a urinary concentration defect. During antidiuresis, organic osmolytes [sorbitol, myo-inositol, taurine, and glycerophosphorylcholine (GPC)] accumulate in the renal inner medulla and are essential for urinary concentration. To clarify the relationship between organic osmolytes and urinary concentration defect in hypercalcemia, examination was made of the effects of hypercalcemia on renal medullary osmolytes content. Rats were put in a state of hypercalcemia by a calcium-rich diet supplemented with CaCO3 (2.5%/wt) and daily s.c. injection of 1.25(OH)2VitD3 (1.6 micrograms/kg). They were killed on days 7 and 14. Hypercalcemia induced a urinary concentration defect. Myo-inositol, sorbitol, and GPC contents in the renal medulla were significantly reduced. Aldose reductase activity decreased significantly. Hypercalcemia would thus appear to directly affect renal medullary content of organic osmolytes, thereby modifying renal concentration ability.