M.A. Rivoira

Ursodeoxycholic and deoxycholic acids: A good and a bad bile acid for intestinal calcium absorption

The aim of this study was to investigate the effect of ursodeoxycholic acid (UDCA) on intestinal Ca(2+) absorption and to find out whether the inhibition of this process caused by NaDOC could be prevented by UDCA. Chicks were employed and divided into four groups: (a) controls, (b) treated with 10mM NaDOC, (c) treated with 60 μg UDCA/100g of b.w., and (d) treated with 10mM NaDOC and 60 μg UDCA/100g of b.w. UDCA enhanced intestinal Ca(2+) absorption, which was time and dose-dependent. UDCA avoided the inhibition of intestinal Ca(2+) absorption caused by NaDOC. Both bile acids altered protein and gene expression of molecules involved in the transcellular pathway of intestinal Ca(2+) absorption, but in the opposite way. UDCA aborted the oxidative stress produced by NaDOC in the intestine. UDCA and UDCA plus NaDOC increased vitamin D receptor protein expression. In conclusion, UDCA is a beneficial bile acid for intestinal Ca(2+) absorption. Contrarily, NaDOC inhibits the intestinal cation absorption through triggering oxidative stress. The use of UDCA in patients with cholestasis would be benefited because of the protective effect on the intestinal Ca(2+) absorption, avoiding the inhibition caused by hydrophobic bile acids and neutralizing the oxidative stress.

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.

Time dependent changes in the intestinal Ca2 + absorption in rats with type I diabetes mellitus are associated with alterations in the intestinal redox state

The aim was to determine the intestinal Ca²⁺ absorption in type I diabetic rats after different times of STZ induction, as well as the gene and protein expression of molecules involved in both the transcellular and paracellular Ca²⁺ pathways. The redox state and the antioxidant enzymes of the enterocytes were also evaluated in duodenum from either diabetic or insulin-treated diabetic rats as compared to control rats. Male Wistar rats (150-200 g) were divided into two groups: 1) controls and 2) STZ-induced diabetic rats (60 mg/kg b.w.). A group of diabetic rats received insulin for five days. The insulin was adjusted daily to maintain a normal blood glucose level. Five 5 d after STZ injection, there was a reduction in the intestinal Ca²⁺ absorption, which was maintained for 30 d and disappeared at 60 d. Similar changes occurred in the GSH and (˙)O(2)(-) levels. The protein expression of molecules involved in the transcellular pathway increased at 5 and 30 d returning to control values at 60 d. Their mRNA levels declined considerably at 60 d. The gene and protein expression of claudin 2 was upregulated at 30 d. Catalase activity increased at 5 and 30 d normalizing at 60 d. To conclude, type I D.m. inhibits the intestinal Ca²⁺ absorption, which is transient leading to a time dependent adaptation and returning the absorptive process to normal values. The inhibition is accompanied by oxidative stress. When insulin is administered, the duodenal redox state returns to control values and the intestinal Ca²⁺ absorption normalizes.

Ursodeoxycholic and deoxycholic acids: Differential effects on intestinal Ca2+ uptake, apoptosis and autophagy of rat intestine

The aim of this work was to study the effect of sodium deoxycholate (NaDOC) and ursodeoxycholic acid (UDCA) on Ca(2+) uptake by enterocytes and the underlying mechanisms. Rats were divided into four groups: a) controls, b) treated with NaDOC, c) treated with UDCA d) treated with NaDOC and UDCA. Ca(2+) uptake was studied in enterocytes with different degrees of maturation. Apoptosis, autophagy and NO content and iNOS protein expression were evaluated. NaDOC decreased and UDCA increased Ca(2+) uptake only in mature enterocytes. The enhancement of protein expression of Fas, FasL, caspase-8 and caspase-3 activity by NaDOC indicates triggering of the apoptotic extrinsic pathway, which was blocked by UDCA. NO content and iNOS protein expression were enhanced by NaDOC, and avoided by UDCA. The increment of acidic vesicular organelles and LC3 II produced by NaDOC was also prevented by UDCA. In conclusion, the inhibitory effects of NaDOC on intestinal Ca(2+) absorption occur by decreasing the Ca(2+) uptake by mature enterocytes. NaDOC triggers apoptosis and autophagy, in part as a result of nitrosative stress. In contrast, UDCA increases the Ca(2+) uptake by mature enterocytes, and in combination with NaDOC acts as an antiapoptotic and antiautophagic agent normalizing the transcellular Ca(2+) pathway.

Past, Present, and Future of Melatonin’s Clinical Uses

Melatonin (MEL) is a pleiotropic hormone which exerts its action through different mechanisms, either by binding to its receptors or by acting as an antioxidant molecule and ROS scavenger. Its mechanisms of action together with the wide distribution of MT1 and MT2 receptors have provoked an ever-increasing number of clinical trials in the last two decades. These studies have evaluated the exogenous administration of MEL in different doses and formulations to prevent or to treat many health disorders. The predominant field of research has been the treatment of insomnia and other circadian rhythm disorders due to the confirmed resynchronizing properties of this indolamine. However, in the last decade, a profound interest has arisen concerning its potential therapeutic value in different conditions such as cancer, cardiovascular diseases, gastrointestinal problems, and inflammatory states, among others. The relatively low toxicity of MEL over a wide range of doses has made the research even more promising. However, new multicenter clinical trials could shed light on different aspects of MEL’s clinical uses contributing thus to clarify the conditions in which MEL might be considered as a first-line therapeutical strategy and to identify when the combination of MEL with other drugs is necessary. In this chapter, we revise the milestones in the field of MEL research from its discovery to the present time and analyze the future perspectives of its clinical uses.

Naringin prevents the inhibition of intestinal Ca 2+ absorption induced by a fructose rich diet

This study tries to elucidate the mechanisms by which fructose rich diets (FRD) inhibit the rat intestinal Ca2+ absorption, and determine if any or all underlying alterations are prevented by naringin (NAR). Male rats were divided into: 1) controls, 2) treated with FRD, 3) treated with FRD and NAR. The intestinal Ca2+ absorption and proteins of the transcellular and paracellular Ca2+ pathways were measured. Oxidative/nitrosative stress and inflammation parameters were evaluated. FRD rats showed inhibition of the intestinal Ca2+ absorption and decrease in the protein expression of molecules of both Ca2+ pathways, which were blocked by NAR. FRD rats showed an increase in the superoxide anion, a decrease in the glutathione and in the enzymatic activities of the antioxidant system, as well as an increase in the NO content and in the nitrotyrosine content of proteins. They also exhibited an increase in both IL-6 and nuclear NF-κB. All these changes were prevented by NAR. In conclusion, FRD inhibit both pathways of the intestinal Ca2+ absorption due to the oxidative/nitrosative stress and inflammation. Since NAR prevents the oxidative/nitrosative stress and inflammation, it might be a drug to avoid alteration in the intestinal Ca2+ absorption caused by FRD.

Melatonin: Basic and Clinical Aspects

Melatonin (MEL), the “hormone of darkness,” is an indolamine mainly secreted at night by the pineal gland. It is also synthesized by other tissues, being the enterochromaffin cells the most important extrapineal sites. The ubiquity, pleiotropy, and complexity are the three terms that summarize the properties and actions of MEL. Two well-characterized enzymes participate in its synthesis: N-acetyltransferase, the first-rate limiting enzyme in MEL production, which converts serotonin to N-acetylserotonin (NAS), and hydroxyindole-O-methyltransferase, which converts NAS to MEL. Most of the MEL’s actions are mediated by membrane (MT1 and MT2) and nuclear (ROR/RZR) receptors. However, some MEL effects seem to be independent of the involvement of receptors or related to Ca2+-binding proteins. The signal transduction pathways triggered by MEL involve the AC/cAMP/PKA/CREB, phospholipase C (PLC)-β and PLC-η, and Rafs/MEK1/2/ERK1/2 cascades. MEL participates in the circadian rhythms, the modulation of season changes, in reproduction, as well as an antioxidant, antiapoptotic, anti-inflammatory, oncostatic, and anticonvulsant drug. Exogenous MEL is employed in a number of physiopathological conditions, mainly for the treatment of sleep disorders and jet lag. The antioxidant properties of MEL have been proven to be beneficial to patients with rheumatoid arthritis, females with infertility, elderly patients with primary essential hypertension, and multiple sclerosis patients. The spectrum of the uses of MEL seems to be wide, although more investigation is needed in order to know better the molecular mechanisms and the possible side effects.

Sodium deoxycholate alters the transcellular pathway of intestinal calcium absorption

Diabetes mellitus (DM) type I is a disorder characterized by hyperglycemia due to a deficient insulin secretion. Alterations in different organs have been observed in DM. The aim of this work was to study intestinal calcium absorption, alkaline phosphatase (AP) activity and the expression of some genes involved in calcium transport in an experimental diabetes model. Two-month old male Wistar rats were divided into two groups: control (n=5) and treated rats (n=5). Diabetes was induced by intraperitoneal injection of streptozotocin (STZ) (60 mg/kg) after fasting for 12-hours. Control rats were injected with the vehicle. Serum and urine glucose were determined before and 5 days after STZ induction. Rats with glycemia over 250 mg/dL were considered diabetic. Intestinal calcium absorption was measured and AP activity from duodenal mucosa was assayed. Ca-ATPase pump and calbindin D28K gene expressions were analyzed by RT-PCR. The weight of the STZ-injected rats decreased after 5 days of the induction and the glucose levels were significantly higher than those of the control group (406±13 mg/dL vs 142±17 mg/dL, p<0.001). Diabetic rats had polyuria and glycosuria. Calcium absorption was lower in diabetic rats than in controls (0.26±0.01 nmol Ca/mL plasma vs 0.65±0.05 nmol Ca/mL plasma, p<0.001). AP activity was significantly lower in diabetic rats than in controls (0.31±0.06 IU/mg protein vs 0.59±0.10 IU/mg protein, p<0.05). Preliminary determinations show that the expression of the studied genes would be similar in both groups. To conclude, the metabolic alteration in DM would alter intestinal calcium absorption and AP activity. The molecular mechanisms responsible of these effects are under investigation. This article is part of a Special Issue entitled AAOMM 2010 Abstracts.