Inhibitory effect of aluminium on calcium absorption in small intestine of rats with different thyroid hormone status

Intestinal Calcium Absorption

In this article, we focus on mammalian calcium absorption across the intestinal epithelium in normal physiology. Intestinal calcium transport is essential for supplying calcium for metabolism and bone mineralization. Dietary calcium is transported across the mucosal epithelia via saturable transcellular and nonsaturable paracellular pathways, both of which are under the regulation of 1,25-dihydroxyvitamin D₃ and several other endocrine and paracrine factors, such as parathyroid hormone, prolactin, 17β-estradiol, calcitonin, and fibroblast growth factor-23. Calcium absorption occurs in several segments of the small and large intestine with varying rates and capacities. Segmental heterogeneity also includes differential expression of calcium transporters/carriers (e.g., transient receptor potential cation channel and calbindin-D_9k ) and the presence of favorable factors (e.g., pH, luminal contents, and gut motility). Other proteins and transporters (e.g., plasma membrane vitamin D receptor and voltage-dependent calcium channels), as well as vesicular calcium transport that probably contributes to intestinal calcium absorption, are also discussed. © 2021 American Physiological Society. Compr Physiol 11:1-27, 2021.

Lactobacillus plantarum CCFM639 Alleviate Trace Element Imbalance-Related Oxidative Stress in Liver and Kidney of Chronic Aluminum Exposure Mice

Aluminum (Al) has various adverse effects on health of humans and animals. The aim of present study was to demonstrate that Lactobacillus plantarum CCFM639 can alleviate the adverse effects on liver and kidney of mice caused by chronic Al exposure. Animals were assigned into control, CCFM639 only, Al only, Al plus CCFM639, and Al plus deferiprone groups. The strain was given by oral gavage for 14 weeks, and Al was introduced via drinking water for the first 8 weeks. Analyses of Al and trace elements levels in feces, blood, and tissues were performed. The biochemical markers (GSH, GPx, SOD, CAT, and MDA) of oxidative stress in livers and kidneys, as well as the levels of ALT, AST, BUN, and CRE in blood, were determined. Our results showed that L. plantarum CCFM639 can significantly reduce Al accumulation in tissues, regulate imbalance of trace elements, and thereby alleviate oxidative stress and pathological changes in hepatic and renal tissues. Therefore, L. plantarum CCFM639 could alleviate Al-induced hepatic and renal injuries, and the possible mechanisms may involve in regulating the imbalance of trace elements.

Dietary and pharmacological compounds altering intestinal calcium absorption in humans and animals

The intestine is the only gate for the entry of Ca to the body in humans and mammals. The entrance of Ca occurs via paracellular and intracellular pathways. All steps of the latter pathway are regulated by calcitriol and by other hormones. Dietary and pharmacological compounds also modulate the intestinal Ca absorption process. Among them, dietary Ca and P are known to alter the lipid and protein composition of the brush-border and basolateral membranes and, consequently, Ca transport. Ca intakes are below the requirements recommended by health professionals in most countries, triggering important health problems. Chronic low Ca intake has been related to illness conditions such as osteoporosis, hypertension, renal lithiasis and incidences of human cancer. Carbohydrates, mainly lactose, and prebiotics have been described as positive modulators of intestinal Ca absorption. Apparently, high meat proteins increase intestinal Ca absorption while the effect of dietary lipids remains unclear. Pharmacological compounds such as menadione, dl-butionine-S,R-sulfoximine and ursodeoxycholic acid also modify intestinal Ca absorption as a consequence of altering the redox state of the epithelial cells. The paracellular pathway of intestinal Ca absorption is poorly known and is under present study in some laboratories. Another field that needs to be explored more intensively is the influence of the gene × diet interaction on intestinal Ca absorption. Health professionals should be aware of this knowledge in order to develop nutritional or medical strategies to stimulate the efficiency of intestinal Ca absorption and to prevent diseases.

Molecular aspects of intestinal calcium absorption

Intestinal Ca²⁺ absorption is a crucial physiological process for maintaining bone mineralization and Ca²⁺ homeostasis. It occurs through the transcellular and paracellular pathways. The first route comprises 3 steps: the entrance of Ca²⁺ across the brush border membranes (BBM) of enterocytes through epithelial Ca²⁺ channels TRPV6, TRPV5, and Ca_v1.3; Ca²⁺ movement from the BBM to the basolateral membranes by binding proteins with high Ca²⁺ affinity (such as CB_9k); and Ca²⁺ extrusion into the blood. Plasma membrane Ca²⁺ ATPase (PMCA1b) and sodium calcium exchanger (NCX1) are mainly involved in the exit of Ca²⁺ from enterocytes. A novel molecule, the 4.1R protein, seems to be a partner of PMCA1b, since both molecules co-localize and interact. The paracellular pathway consists of Ca²⁺ transport through transmembrane proteins of tight junction structures, such as claudins 2, 12, and 15. There is evidence of crosstalk between the transcellular and paracellular pathways in intestinal Ca²⁺ transport. When intestinal oxidative stress is triggered, there is a decrease in the expression of several molecules of both pathways that inhibit intestinal Ca²⁺ absorption. Normalization of redox status in the intestine with drugs such as quercetin, ursodeoxycholic acid, or melatonin return intestinal Ca²⁺ transport to control values. Calcitriol [1,25(OH)₂D₃] is the major controlling hormone of intestinal Ca²⁺ transport. It increases the gene and protein expression of most of the molecules involved in both pathways. PTH, thyroid hormones, estrogens, prolactin, growth hormone, and glucocorticoids apparently also regulate Ca²⁺ transport by direct action, indirect mechanism mediated by the increase of renal 1,25(OH)₂D₃ production, or both. Different physiological conditions, such as growth, pregnancy, lactation, and aging, adjust intestinal Ca²⁺ absorption according to Ca²⁺ demands. Better knowledge of the molecular details of intestinal Ca²⁺ absorption could lead to the development of nutritional and medical strategies for optimizing the efficiency of intestinal Ca²⁺ absorption and preventing osteoporosis and other pathologies related to Ca²⁺ metabolism.