Selenium, which is present in foods such as Brazil nuts and in smaller amounts in wheat flour and beef, can reduce cholesterol, a fatty substance in the blood that heightens the risk of cardiovascular disease if its levels are excessive.
Researchers affiliated with the University of São Paulo’s School of Animal Science and Food Engineering (FZEA-USP) at Pirassununga, Brazil, have discovered that supplementing the diet of beef cattle with varying amounts of selenium from different sources reduces the production of an enzyme that regulates cholesterol synthesis in blood and tissue.
The study, which resulted from a project supported by FAPESP and the doctoral research of Janaína Silveira da Silva at FZEA-USP, was presented during the 26th Brazilian Food Science and Technology Conference (CBCTA), held on August 13-16, 2018, at Belém, Pará State.
“There were no reports in the scientific literature of the direct effect of selenium on the cholesterol enzyme, HMG-CoA reductase, in animals. In humans, only indirect effects had been observed, such as the enzyme’s activity and gene expression. Our study furnishes the first proof that selenium can reduce the production of this enzyme,” said Marcus Antonio Zanetti, a professor at FZEA-USP and principal investigator for the study, in an interview given to Agência FAPESP.
The research group at FZEA-USP led by Zanetti has conducted studies designed to assess the effect of supplementing beef cattle feed with selenium on blood and meat cholesterol levels.
A 2014 study showed that supplementing the diet of Nelore cattle with a high dose of organic selenium for a three-month beef finishing period reduced blood and tissue cholesterol in the animals and in a group of people who consumed their meat.
Laboratory and statistical analysis of liver samples from the cattle indicated that selenium supplementation led to increased levels of oxidized glutathione (GSSG) and lower levels of reduced glutathione (GSH). These alterations in the levels of both glutathiones, which inhibit the action of HMG-CoA reductase, caused a reduction in cholesterol synthesis (read more at agencia.fapesp.br/18613).
“Despite our finding in the previous study that selenium reduced cholesterol in beef cattle, hitherto we hadn’t been able to gauge the effects of different levels and sources of selenium on cholesterol and concomitantly on GSSG, GSH, glutathione peroxidase and HMG-CoA reductase,” Zanetti said.
“Moreover, in the previous experiments, we used only high doses of selenium and wanted to find out whether lower doses would also serve to reduce cholesterol.”
The researchers supplemented the diet of 63 Nelore calves confined for 84 days in individual feedlots with organic selenium derived from sodium selenite and Alkosel 3000, an inactivated yeast containing elevated levels of organic selenium.
The animals were divided into seven groups of nine for each treatment. Three groups were fed a diet of silage, corn grain and soymeal supplemented with organic selenium at 0.3 milligrams per kilo of the diet (mg/kg), 0.9 mg/kg and 2.7 mg/kg, respectively. Three were given the same diet supplemented with the same doses of inorganic selenium, and the seventh group received the diet without selenium supplementation.
The analysis of blood samples taken monthly throughout the 84-day finishing period, after which the animals were slaughtered, showed that all levels of supplementation with both organic and inorganic selenium reduced the amount of HMG-CoA by up to 32.7% compared with the no-selenium diet, as well as increasing levels of glutathione peroxidase and GSSG.
The higher the dose of selenium, the greater the effect on cholesterol levels.
“All the selenium supplement doses we used [0.3 mg/kg, 0.9 mg/kg and 2.7 mg/kg] were less than the recommended maximum level of supplementation for Nelore cattle,” Zanetti said.
Alternative to statins
According to Zanetti, until this study, one of the widely accepted explanations for the reduction of cholesterol by selenium was that the mineral lowers the level of GSH, a substrate for HMG-CoA reductase, and raises the level of GSSG, which inhibits the action of HMG-CoA reductase.
Another explanation was that selenium plays a key role in the synthesis of thyroid hormones, which, among other functions, regulate the levels of LDL receptors in the blood. LDL is often called “bad cholesterol”.
“Our analysis of HMG-CoA reductase showed that selenium supplementation can lower levels of this cholesterol-synthesizing enzyme, reducing the amount of cholesterol in the blood and meat of beef cattle,” Zanetti said.
The results of the study, he added, indicate that selenium supplementation could be an alternative to statins, which are currently used to treat hypercholesterolemia (high blood cholesterol) by inhibiting HMG-CoA reductase.
Because selenium reduces cholesterol by a different mechanism (reducing the production of HMG-CoA reductase), selenium supplementation could serve at least as a partial substitute for statins, which have a number of adverse side effects.
“However, we don’t know whether the effect observed in animals also occurs in humans, although the metabolic pathway for cholesterol is the same in both,” Zanetti said.
Source : By Elton Alisson | Agência FAPESP