Effect of vitamin D supplementation on rats' liver
In order to understand the molecular mechanism responsible for the therapeutic potential of vitamin D, we conducted an analysis of the liver transcriptome – a central place of metabolic changes. The experiment was carried out on adult female rats (about one year old), n=18, divided into three experimental subjects, receiving different doses of vitamin D for three months: group I - 0, group II - 1000 U/Kg, group III - 5000 U/Kg. After the experiment, the biochemical and haematological parameters of the blood were evaluated. RNA-seq was used to analyze the changes in the liver transcriptome, and Gene Set Enrichment Analysis (GSEA) was used to identify enrichments in gene expression profiles of experimental groups. qPCR was employed to evaluate the expression of several genes connected to cholesterol biosynthesis, metallothioneins, vitamin D metabolism and others. At the end of the experiment, 25(OH) vitamin D concentrations were as follows: group I: 29 ng/ml, group II 43: ng/ml, group III: 70 ng/mL. Considering blood parameters, we observed a lower platelet count (p<0,008) and significantly higher (p<0.02) number of WBC in rats supplemented with 1000 U/Kg than in rats from group III (5000 U/Kg), but no difference between rats from group I and III were detected in these parameters.  Moreover,  we noted a trend (p<0.06 ) in total cholesterol concentration, suggesting a linear decrease with increasing doses of vitamin D. RNA-seq analysis did not identify any differentially expressed genes with FDR<0.05 in any of the three comparisons. However, GSEA revealed significant activation of the number of processes and pathways. In the I vs III comparison, the most enriched were the genes from the “metallothionein, and TspO/MBR family” (Enrichment Score=8,170, FDR= 0.00006), the genes associated with “glyceraldehyde-3-phosphate dehydrogenase (NAD+) (phosphorylating) activity” (Enrichment Score=5.13, FDR<00049) and the genes associated with  “Negative regulation of tumour necrosis factor production” (Enrichment score=1.26, FDR0.0064. qPCR analysis identified significant upregulation of  Mt1, Mt2 and Orm1 genes in animals receiving high doses of vitamin D (p<0.025, p<0.025, p<0009, respectively). Moreover, significant downregulation of Srebp2 and Insig2 was observed in both experimental groups when compared to the control group (p<0.003, p<0.036, respectively). Our results support the potential of vitamin D supplementation in ameliorating oxidative stress, inflammation and high blood cholesterol and underlie the need for further studies aimed at identifying optimal vitamin D doses with therapeutic effects. Overall design: The experiment was carried out on adult female rats (about one year old), n=18, divided into three experimental groups, receiving different doses of vitamin D for three months: group I - 0, group II - 1000 U/Kg, group III - 5000 U/Kg. After the experiment, the biochemical and haematological parameters of the blood were evaluated. RNA-seq was used to analyze the changes in the liver transcriptome