Influence of various forms of calcium in the diet on the micro- and macroelement profiles of organs and tissues in rats

The problems of the body’'s calcium supply have several etiologies. Firstly, calcium in the diet should have a high biological availability which requires the selection of forms of calcium-containing substances that meet this criterion. Secondly, feed producers tend to over-saturate diets with calcium or it is added to improve physical properties during the processing of certain types of waste from the grain processing industry, e.g., soybean meal, but such inclusions are often ignored. Despite the widespread scientific study of the issue, the search for the most accessible form of calcium for the animal body is still relevant. In this work, the elemental profile of target organs in Wistar rats with an excess of various forms of calcium was established for the first time. The metabolic relationships of macro- and microelements, including calcium-conjugated ones, have been revealed, depending on the organ and the form of the injected substances. The aim of the work was studing the concentration of macro-, micro- and toxic elements in the liver, kidneys, femur and blood serum of Wistar rats with the additional use of various sources of calcium in the diet: chloride, citrate and carbonate. The work was performed in the vivarium of the Federal Research Center for Biological Systems and Agrotechnologies RAS (Orenburg) in 2024 on male Wistar rats aged 6 months. The duration of the experimental reference period was 21 days. After the preparatory period (10 days), 20 rats were randomly divided into four groups ( n = 5): a control group and three experimental groups. In addition to the basic diet, 45% of the daily calcium requirement was administered to the animals of the experimental groups in the form of CaCl2 for group I, Ca3(C6H5O7)2 for group II, and CaCO3 for group III. The amount of feed consumed, according to the daily requirement for this type of animal, was 30 g/individual. The starting material for the preparation of various forms of calcium was limestone flour (CaCO3) (Akkerman Cement LLC, Russia). For the synthesis of CaCl2, the method of transferring Ca2+ ions into solution by reaction with hydrochloric acid was used. The citrate form of Ca3(C6H5O7)2 was obtained by reacting a solution of citric acid in one water (concentration less than 10 %) with limestone flour. Biomaterial (blood, liver, kidneys, femur) for the study was obtained after decapitation of rats under inhalation anesthesia 21 days after the start of the experiment. The elemental analysis of the substrates was performed by mass spectrometry on a single quadrupole mass spectrometer with inductively coupled plasma Agilent 7900 ICP-MS (Agilent, USA). Thermo-oxidative degradation of the organic matrix was carried out in a microwave TOPEX+ sample preparation system (PREEKEM, China). The content of Cr, Fe, Zn, and As was analyzed in the helium regime using a collision cell. The concentration of certain elements (Ca, P, Mg, Fe) in blood serum was determined using an automatic biochemical analyzer CS-T240 (DIRUI Industrial Co., Ltd., China). Analyzing the elemental profile of rat organs and tissues when various forms of calcium were added to the diet, we found that they accumulated toxic and conditionally toxic elements (Pb, Ba, Al) to a greater extent with dietary Ca chloride and carbonate, and to a lesser extent (Bi) when using the citrate form in the diet. The body lost toxic and conditionally toxic elements upon the use of Ca3(C6H5O7)2 (five elements, V, Al, Ba, Sr, Sn), CaCl2 (four elements, Cd, Al, Ba, Sn), CaCO3 (one element, Sn). In turn, the forms of calcium-containing substances did not affect the concentration of calcium-dependent elements. The experiment did not establish a critical decrease in their number. A tendency to a decrease in the content of iron and nickel in the femur was revealed with the accumulation of selenium and barium in the liver, and nickel and chromium in the kidneys in all groups. Calcium accumulated only in the liver after administration of CaCl2. There was a tendency to decrease the content of copper, iron, zinc, magnesium, and manganese in the blood serum when using all forms of calcium. The results obtained made it possible to evaluate the metabolism of calcium, its synergists and antagonists under the influence of the studied factor, which in practice can ensure the optimization of dietary rationing and the prioritization of a particular form of calcium, especially at the risk of its overdose.