Animals, diets and experimental design

The experiment was conducted on 40 adult male Sprague Dawley (SD) rats, supplied by the Vital River Laboratory Animal Ltd. (Beijing, China). The rats, body weight of 200 ± 20 g, were housed at a constant temperature (23 ± 2 °C) and humidity (55 ± 5%) with a 12 h light/dark cycle (7:00 a.m. to 7:00 p.m.). Food and water were supplied ad libitum. Rats were individually housed in cages and assigned into two different dietary groups. After 1-week adaptive period on a basal diet, the 40 rats were randomly selected and assigned to four groups of 10 rats each, viz. (I) control group (CT), (II) high-fat diet fed group (HF/model group), (III) high-fat diet fed + low-dose sodium selenite (Se content: 0.05 mg/kg·bw) and low-dose magnesium gluconate (Mg²⁺ content: 5.83 mg/kg·bw) supplemented (HF + LSe + LMg), (IV) HFD fed + high-dose sodium selenite (Se content: 0.10 mg/kg·bw) and high-dose magnesium gluconate (Mg content: 58.33 mg/kg·bw) supplemented (HF + HSe + HMg). Sodium selenite was purchased from Sigma Aldrich Ltd. Magnesium gluconate was supplied by Beijing Huikangyuan Biotechnology Co., Ltd. (Beijing, China). On 0 to 4 weeks of experiment period, rats in CT group were given basal diet, and the other groups of animals was fed on a high-fat diet (63.6% standard diet, 20% sucrose, 15% lard, 1.2% cholesterol and 0.2% cholic acid sodium) to generate a diet-induced hyperlipidemia model as previously reported [13]. Composition (%) of basal and high-fat chow is shown in Table 1. After 4 weeks, rats were given sodium selenite and magnesium gluconate solution by oral gavage for 8 weeks. CT and HF groups had no selenium or magnesium supplementation but an equivalent amount of distilled water by the same route. The rats were fed for 12 weeks. Throughout the 8-weeks intervention period, body weight was obtained weekly and at the time of culling. Food consumption (energy intake) of the animals was measured weekly. On day 0, 20, 40 and 60 of the Se/Mg intervention, whole blood was collected from the eye canthus in each animal under general anesthesia and serum for the determination of total cholesterol (TC), triglyceride (TG), low density lipoprotein cholesterol (LDL-C) and high density lipoprotein cholesterol (HDL-C) concentrations. At the end of the experiment, rats in all four groups were fasted for 12 h and blood samples were taken from the abdominal aorta under anesthesia. The livers were rapidly dissected, frozen in liquid nitrogen, and stored at − 80 °C until analysis.

General composition of the experimental diets

All diet were prepared by HFK BIOSCIENCE Co., Ltd.(Beijing, China)

^AControl diet provided to CT (ad libitum), HF, HF + LSe + LMg and HF + HSe + HMg groups during the acclimatization period. ^B High-fat diet provided to HF, HF + LSe + LMg and HF + HSe + HMg groups