Metabolic potential of the adipose tissue of rats during hyper- and hypovitaminosis A

The Roles of Vitamin A in the Regulation of Carbohydrate, Lipid, and Protein Metabolism

Currently, two-thirds of American adults are overweight or obese. This high prevalence of overweight/obesity negatively affects the health of the population, as obese individuals tend to develop several chronic diseases, such as type 2 diabetes and cardiovascular diseases. Due to obesity's impact on health, medical costs, and longevity, the rise in the number of obese people has become a public health concern. Both genetic and environmental/dietary factors play a role in the development of metabolic diseases. Intuitively, it seems to be obvious to link over-nutrition to the development of obesity and other metabolic diseases. However, the underlying mechanisms are still unclear. Dietary nutrients not only provide energy derived from macronutrients, but also factors such as micronutrients with regulatory roles. How micronutrients, such as vitamin A (VA; retinol), regulate macronutrient homeostasis is still an ongoing research topic. As an essential micronutrient, VA plays a key role in the general health of an individual. This review summarizes recent research progress regarding VA's role in carbohydrate, lipid, and protein metabolism. Due to the large amount of information regarding VA functions, this review focusses on metabolism in metabolic active organs and tissues. Additionally, some perspectives for future studies will be provided.

Global effects of vitamin A deficiency on gene expression in rat liver: evidence for hypoandrogenism

Vitamin A (retinol) metabolites are ligands for transcription factors that regulate many genes. The liver is the main storage depot for retinol and plays a role in vitamin A homeostasis. To better understand the effects of vitamin A deficiency on liver gene expression, we produced retinol deficiency in male rats by feeding a diet low in retinol for 53 days after weaning and examined the effects on gene expression in liver using Affymetrix oligonucleotide microarrays. We detected expression of 41% of the 8799 probe sets represented on the RGU-34A GeneChips. Vitamin A deficiency resulted in major changes in liver gene expression: 805 genes (22% of all genes detected) differed at P<or=.05 (false discovery rate <0.143). Genes involved in fatty acid metabolism, peroxisomal function, glycolysis, glutamate metabolism and the urea cycle were altered. The expression of many sexually dimorphic genes was altered toward a feminized or senescent pattern of gene expression in the liver. Retinol deficiency also produces a shift toward increased protein and fat catabolism and decreased fatty acid synthesis.

Estimation of the dietary vitamin A requirement of juvenile grass shrimp, Penaeus monodon

Two growth experiments were conducted to estimate the minimal dietary vitamin A requirement for juvenile grass shrimp, Penaeus monodon. In expt. 1, purified diets containing 0, 1,500, 3,000, 15, 000, 30,000, 45,000 and 60,000 retinol equivalent (RE)/kg (i.e., 0, 5,000, 10,000, 50,000, 100,000, 150,000, 200,000 IU/kg) of supplemental vitamin A (retinyl acetate) were fed to P. monodon (mean initial weight 0.97 +/- 0.01 g) for 8 wk. In expt. 2, diets with 0, 600, 1,200, 1,800, 2,400, 3,000, 3,600, and 4,500 RE/kg (i.e. , 0, 2,000, 4,000, 6,000, 8,000, 10,000, 12,000, 15,000 IU/kg) of supplemental vitamin A were fed to the shrimp (mean weight 0.68 +/- 0.01 g) for 6 wk. The basal unsupplemented diet contained 54 RE vitamin A/kg, and supplemental levels were confirmed by analysis. Each diet was fed to three replicate groups of shrimp. In expt. 1, shrimp fed diets supplemented with 300 RE vitamin A/kg had significantly greater weight gain (P < 0.05) than those fed the unsupplemented control diet and diets supplemented with >===" BORDER="0">30,000 RE vitamin A/kg. Survival rate was higher in shrimp fed diets supplemented with 1,500-30,000 RE vitamin A/kg than shrimp fed the control diet. Highest blood triglyceride concentration and body lipid concentration were in shrimp fed diets supplemented with 45,000 and 60,000 RE vitamin A/kg, respectively. Eye vitamin A concentration and hepatopancreatic total lipid concentration in shrimp generally increased as dietary vitamin A supplementation increased. In expt. 2, feed efficiency was highest in shrimp fed diets supplemented with 2,400, 3,000, 3,600 and 4,500 RE vitamin A/kg, followed by shrimp fed diets with 600 and 1,200 RE vitamin A/kg and finally the unsupplemented control group. Shrimp fed diets supplemented with vitamin A had significantly higher survival percentages than those fed the unsupplemented control diet. Weight gain percentage of the shrimp analyzed by broken-line regression indicated that the minimal dietary vitamin A concentration in growing P. monodon is 2,511 RE/kg ( approximately 8, 400 IU/kg).