Sodium deoxycholate inhibits chick duodenal calcium absorption through oxidative stress and apoptosis.

High concentrations of sodium deoxycholate (NaDOC) produce toxic effects. This study explores the effect of a single high concentration of NaDOC on the intestinal Ca(2+) absorption and the underlying mechanisms. Chicks were divided into two groups: 1) controls and 2) treated with different concentrations of NaDOC in the duodenal loop for variable times. Intestinal Ca(2+) absorption was measured as well as the gene and protein expressions of molecules involved in the Ca(2+) transcellular pathway. NaDOC inhibited the intestinal Ca(2+) absorption, which was concentration dependent. Ca(2+)-ATPase mRNA decreased by the bile salt and the same occurred with the protein expression of Ca(2+)-ATPase, calbindin D(28k) and Na(+)/Ca(2+) exchanger. NaDOC produced oxidative stress as judged by ROS generation, mitochondrial swelling and glutathione depletion. Furthermore, the antioxidant quercetin blocked the inhibitory effect of NaDOC on the intestinal Ca(2+) absorption. Apoptosis was also triggered by the bile salt, as indicated by the TUNEL staining and the cytochrome c release from the mitochondria. As a compensatory mechanism, enzyme activities of the antioxidant system were all increased. In conclusion, a single high concentration of NaDOC inhibits intestinal Ca(2+) absorption through downregulation of proteins involved in the transcellular pathway, as a consequence of oxidative stress and mitochondria mediated apoptosis.

Chronic Exposure to Fluoride During Gestation and Lactation Increases Mandibular Bone Volume of Suckling Rats.

We aimed to investigate the effect of maternal exposure to NaF on mandibular bone microarchitecture and phosphocalcic plasma parameters of the offspring. For this purpose, 10-, 15-, and 21-day-old pups (n = 6-8 per group) from two groups of mothers, control and NaF 50mg/L treated dams, were used. Plasma calcium (Ca) and phosphorus (P) levels and alkaline phosphatase activity (ALP) were measured. Fluoride concentration (F-) in bone and in stomach content was measured using potentiometry after isothermal distillation. Morphometric, histological, and histomorphometric analyses of the jaw bones were performed. Plasma Ca and P levels and ALP activity increased in 10-day and decreased in 21-day-old pups from NaF-treated mothers. Fluoride concentration in stomach content samples of 15- and 21-day-old nursing pups from mothers exposed to NaF in their drinking water was higher compared to that observed in control dam offspring. Mandibular F- content was higher in 21-day-old pups born to F--exposed dams compared to those observed in age-matched control pups. Mandibular area increased in 21-day-old pups born to treated mothers as compared to controls. Mandibular bone volume BV/TV (%) was higher in offspring from NaF-exposed dams than in controls at all the studied times. The increase in bone volume after exposure to F- was concomitant with the increase in trabecular thickness and the decrease in trabecular separation. Altogether, our results showed that exposure to NaF during gestation and lactation increased mandibular area and bone volume of pups, with concomitant changes in phosphocalcic parameters associated with the bone modeling process.

Effects of a single dose of menadione on the intestinal calcium absorption and associated variables.

The effect of a single large dose of menadione on intestinal calcium absorption and associated variables was investigated in chicks fed a normal diet. The data show that 2.5 micro mol of menadione/kg of b.w. causes inhibition of calcium transfer from lumen-to-blood within 30 min. This effect seems to be related to oxidative stress provoked by menadione as judged by glutathione depletion and an increment in the total carbonyl group content produced at the same time. Two enzymes presumably involved in calcium transcellular movement, such as alkaline phosphatase, located in the brush border membrane, and Ca(2+)- pump ATPase, which sits in the basolateral membrane, were also inhibited. The enzyme inhibition could be due to alterations caused by the appearance of free hydroxyl groups, which are triggered by glutathione depletion. Addition of glutathione monoester to the duodenal loop caused reversion of the menadione effect on both intestinal calcium absorption and alkaline phosphatase activity. In conclusion, menadione shifts the balance of oxidative and reductive processes in the enterocyte towards oxidation causing deleterious effects on intestinal Ca(2+) absorption and associated variables, which could be prevented by administration of oral glutathione monoester.

Molecular mechanisms involved in the enhancement of mitochondrial malate dehydrogenase activity by calcitriol in chick intestine.

Mitochondrial malate dehydrogenase (mMDH) from the intestine is the NAD-linked oxidoreductase of the tricarboxylic acid cycle with the highest activity and response to vitamin D treatment in vitamin D-deficient chicks (-D). The aim of this study was to elucidate potential molecular mechanisms by which cholecalciferol or calcitriol enhances the activity of this enzyme. One group of animals used was composed of -D and -D treated with cholecalciferol or with calcitriol. A second group consisted of -D and -D supplemented with high Ca(2+) diet. A third group included chicks receiving either a normal or a low Ca(2+) diet. In some experiments, animals were injected with cycloheximide. Data showed that either vitamin D (cholecalciferol or calcitriol) or a low Ca(2+) diet increases mMDH activity. High Ca(2+) diet did not modify the intestinal mMDH activity from -D. The mMDH activity from -D remained unaltered when duodenal cells were exposed to 10(-8) mol/L calcitriol for 15 min. The enhancement of mMDH activity by calcitriol was completely abolished by simultaneous cycloheximide injection to -D. mMDH mRNA levels, detected by RT-PCR, indicate that calcitriol did not affect gene expression. In contrast, Western blots show that calcitriol enhanced the protein expression. In conclusion, calcitriol stimulates intestinal mMDH activity by increasing protein synthesis. No response of mMDH activity by rapid effects of calcitriol or activation through increment of serum Ca(2+) was demonstrated. Consequently, ATP production would be increased, facilitating the Ca(2+) exit from the enterocytes via the Ca(2+)-ATPase and Na(+)/Ca(2+) exchanger, which participate in the intestinal Ca(2+) absorption.

Dietary calcium deficiency increases Ca2+ uptake and Ca2+ extrusion mechanisms in chick enterocytes.

Ca2+ uptake and Ca2+ extrusion mechanisms were studied in enterocytes with different degree of differentiation from chicks adapted to a low Ca2+ diet as compared to animals fed a normal diet. Chicks adapted to a low Ca2+ diet presented hypocalcemia, hypophosphatemia and increased serum 1,25(OH)2D3 and Ca2+ absorption. Low Ca2+ diet increased the alkaline phosphatase (AP) activity, independently of the cellular maturation, but it did not alter gamma-glutamyl-transpeptidase activity. Ca2+ uptake, Ca2+-ATPase and Na(+)/Ca2+ exchanger activities and expressions were increased by the mineral-deficient diet either in mature or immature enterocytes. Western blots analysis shows that vitamin D receptor (VDR) expression was much higher in crypt cells than in mature cells. Low Ca2+ diet decreased the number of vitamin D receptor units in both kinds of cells. In conclusion, changes in Ca2+ uptake and Ca2+ extrusion mechanisms in the enterocytes by a low Ca2+ diet appear to be a result of enhanced serum levels of 1,25(OH)2D3, which would promote cellular differentiation producing cells more efficient to express vitamin D dependent genes required for Ca2+ absorption.