Friday, August 12, 2011

Taurine Mimics Effects of Insulin, Annihilates Appetite and Quadruples Hypothalamic mTOR Activity in Rodent Study.

Image 1: Bought in bulk, taurine is one of
the cheapest amino acids on the market.
If you listened to the third installment of the Amino Acids for Super Humans Series on Carl Lenore's Super Human Radio, you will know that I am a firm a believer in the power of the non-essential sulfur-amino acid taurine. You would have heard me talk about it's beneficial effects on diabetes, hepatic health, weight management and more.... a recent study (Solon. 2011) published in the influential journal Amino Acids does not only confirm all the beneficial effects, we already knew about, it also expands our current knowledge about taurine to its effects on the hypothalamic Akt/FOXO1, JAK2/STAT3 and mTOR/AMPK/ACC signaling cascades and the satiety signal neuropeptide Y (NPY).

Carina S. Solon and her colleagues from the University of Campinas in Brazil hypothesized that "some of the activity of taurine in the control of body fat would be exerted through direct action in the hypothalamus". To verify their hypothesis, the scientists injected an acute dose of taurine (1.0, 3.0 and 5.0mM) and/or insulin intracerebroventricularly into a cannula that had been placed in the lateral ventricle of the animals more than a week before. What they found was
that the intracerebroventricular injection of an acute dose of taurine reduces food intake and locomotor activity, and activates signal transduction through the Akt/FOXO1, JAK2/STAT3 and mTOR/AMPK/ACC signaling pathways. These effects are accompanied by the modulation of expression of NPY. In addition, taurine can enhance the anorexigenic action of insulin.
Even administered on its own (without insulin) the anorexic effect of taurine had a "similar magnitude to the effect produced by either insulin or leptin" that cannot be ascribed to the reduction in locomotor activity alone. Rather, the scientists argue that the latter is probably a direct result of the "increased primary satiety produced by taurine", which suppresses the well-known food-seeking behavior food-deprived rodents (and interestingly also anorexic human beings) display.
Figure 1: Changes in Akt, mTOR & AMPK expression after intracerebroventricular injection of insulin, taurine or a combination of both (calculated based on Solon. 2011)
At the hypthalamic level, taurine did in fact act similarly to insulin and activated the "Akt/FOXO1 and JAK2/STAT3 signaling pathways, while inhibiting the AMPK signaling pathway" without modulating systemic glucose or insulin levels. By selective inhibition of the JAK2 pathway and upregulation of the AMPK signaling cascade by AICAR infusion, the scientists were able to show that the upregulation of JAK2 and not the downregulation of AMPK were responsible for the appetite-suppressant effects of taurine.
Figure 2: Relative changes in food intake in rats vs. control after intracerebroventricular injection of taurine, AICAR or a combination of both (calculated based on Solon. 2011)
Taken together, these results suggest that the effects of taurine go well beyond its insulin-sensitizing effects on peripheral tissues (Wu. 2010). And while the exact mechanism by which taurine acts on the complex signaling cascade in the hypothalamus, as well as the respective downstream effects at the tissue level (eg. muscle, liver, pancreas, etc.) still have to be elucidated, it becomes increasingly evident that an amino acid, of which many people still believe that it was a somewhat esoteric, horse-sperm derived ingredient of energy drinks, could become a cornerstone in the ongoing battle against obesity.