Insulin sensitivity is inversely related to cellular energy status, as revealed by biotin deprivation.

We have reported an early decrease in glycemia in rats fed a biotin-deficient diet with reduced cellular ATP levels, suggesting increased insulin sensitivity. Here, we show that biotin-deprived rats are more tolerant of glucose, as shown by both oral and intraperitoneal glucose tolerance tests, during which insulin plasma levels were significantly diminished in deficient rats compared with controls. Biotin-deficient rats had lower blood glucose concentrations during intraperitoneal insulin sensitivity tests than controls. Furthermore, more glucose was infused to maintain euglycemia in the biotin-deficient rats during hyperinsulinemic euglycemic clamp studies. These results demonstrate augmented sensitivity to insulin in biotin-deprived rats. They are most likely the consequence of an insulin-independent effect of AMPK activation on GLUT4 membrane translocation with increased glucose uptake. In biotin-deficient cultured L6 muscle cells, there was increased phosphorylation of the energy sensor AMPK. We have now confirmed the augmented AMPK activation in both biotin-deprived in vivo muscle and cultured muscle cells. In these cells, glucose uptake is increased by AMPK activation by AICAR and diminished by its knockdown by the specific siRNAs directed against its α1- and α2-catalytic subunits, with all of these effects being largely independent of the activity of the insulin-signaling pathway that was inhibited with wortmannin. The enhanced insulin sensitivity in biotin deficiency likely has adaptive value for organisms due to the hormone promotion of uptake and utilization of not only glucose but other nutrients such as branched-chain amino acids, whose deficiency has been reported to increase insulin tolerance.

Temporal development of genetic and metabolic effects of biotin deprivation. A search for the optimum time to study a vitamin deficiency.

Biotin deficiency (Bt-D) is usually studied at the point at which the animal model exhibits the signs of full-blown deficiency symptoms; in rats, this typically occurs at 6-8 weeks of feeding a deficient diet. To differentiate specific deficiency effects from those of undernutrition, biotin sufficient and deficient rats were studied at 2, 3, 4, and 5 weeks on the deficiency diet, before the onset of weight loss and deficiency signs. The deficiency state was confirmed by biochemical and molecular analyses. Blood and liver metabolites were determined and western blots of signaling proteins, and qRT-PCR gene expression studies. The main effects of Bt-D were already well established by the fourth week on the diet; thus, we consider the fourth week as the optimum time to study the consequences of biotin depletion. Early effects, which were already apparent at week 2, included cellular energy deficit (as assessed by increased AMP/ATP ratio), activation of the AMPK energy sensor, and changes of carbon metabolism gene transcripts (e.g., phosphoenolpyruvate carboxykinase, carnitine palmitoyl transferase 1, liver glucokinase and fatty acid synthetase). Reduced post-prandial blood concentrations of glucose were also observed early; we speculate that these are attributable to augmented sensitivity to insulin and increased glucose utilization, a likely effect of AMPK induction of translocation of glucose transporter GLUT4 to the cell membranes and increased hexokinase expression. Other late-onset changes (week 4) included increased serum concentrations of lactate and free fatty acids and decreased liver glycogen and serum concentrations of triglycerides and total cholesterol. The identification of the early specific molecular and metabolic disturbances of biotin deficiency might be useful in identifying individuals with marginal deficiency of this vitamin, which appears to be common in normal human pregnancy. The study of time-course of other vitamin deficiencies, such as this one, might help to better understand and cope with their effects.

Thiamine Deprivation Produces a Liver ATP Deficit and Metabolic and Genomic Effects in Mice: Findings Are Parallel to Those of Biotin Deficiency and Have Implications for Energy Disorders.

Thiamine is one of several essential cofactors for ATP generation. Its deficiency, like in beriberi and in the Wernicke-Korsakoff syndrome, has been studied for many decades. However, its mechanism of action is still not completely understood at the cellular and molecular levels. Since it acts as a coenzyme for dehydrogenases of pyruvate, branched-chain keto acids, and ketoglutarate, its nutritional privation is partly a phenocopy of inborn errors of metabolism, among them maple syrup urine disease. In the present paper, we report metabolic and genomic findings in mice deprived of thiamine. They are similar to the ones we have previously found in biotin deficiency, another ATP generation cofactor. Here we show that thiamine deficiency substantially reduced the energy state in the liver and activated the energy sensor AMP-activated kinase. With this vitamin deficiency, several metabolic parameters changed: blood glucose was diminished and serum lactate was increased, but insulin, triglycerides, and cholesterol, as well as liver glycogen, were reduced. These results indicate a severe change in the energy status of the whole organism. Our findings were associated with modified hepatic levels of the mRNAs of several carbon metabolism genes: a reduction of transcripts for liver glucokinase and fatty acid synthase and augmentation of those for carnitine palmitoyl transferase 1 and phosphoenolpyruvate carboxykinase as markers for glycolysis, fatty acid synthesis, beta-oxidation, and gluconeogenesis, respectively. Glucose tolerance was initially increased, suggesting augmented insulin sensitivity, as we had found in biotin deficiency; however, in the case of thiamine, it was diminished from the 3rd week on, when the deficient animals became undernourished, and paralleled the changes in AKT and mTOR, 2 main proteins in the insulin signaling pathway. Since many of the metabolic and gene expression effects on mice deprived of thiamine are similar to those in biotin deficiency, it may be that they result from a more general impairment of oxidative phosphorylation due to a shortage of ATP generation cofactors. These findings may be relevant to energy-related disorders, among them several inborn errors of metabolism, as well as common energy disorders like obesity, diabetes, and neurodegenerative illnesses.