Background: The build-up of excess ammonia has been implicated in environmental conditions such as autism and may contribute to physiological effects of others as well. In recent days, we have discussed how homocysteinemia may impair the urea cycle which may lead to excess ammonia levels and that some common treatments used for environmental illness also are used as treatments to reduce physiological ammonia levels. Exogenous environmental factors may also lead to elevations in ammonia. Interestingly, in fish, exposure to ammonia leads to symptoms one may conclude typical of sickness syndrome which includes loss of appetite. While it is difficult to extrapolate behavior in these animals to similar behaviors in humans, we have mentioned previously that sickness syndrome is not exclusive to the human organism and has been observed in other animals (ie domesticated dogs). In the recent study of fish, ammonia activates the stress regulator corticotropin releasing factor and other stress systems including the one that controls dopamine and leads to elevations in this stress hormone also. The activation of this system has also been implicated in psychological effects associated with PTSD in humans and addictive behaviors such as alcohol abuse.
Taken these studies into account, one would suggest that ammonia which also contributes to mitochondrial dysfunction may contribute to a number of environmental illnesses by activating different systems during the stress response and may exacerbate the complications associated with injury or down-regulation in function from toxic exposures to the liver. In addition, there are several negative psychological and physical effects in environmental illnesses that can be attributed to abherrant signaling by GSK-3b which is modulated through the Wnt pathway. As Burke writes, "The liver contains two systems for the removal of ammonia - the urea cycle and the enzyme glutamine synthetase. These systems are expressed in a complementary fashion in two distinct populations of hepatocytes, referred to as periportal and perivenous cells. One of the unresolved problems in hepatology has been to elucidate the molecular mechanisms responsible for induction and maintenance of the cellular heterogeneity for ammonia detoxification. There is now a potential molecular explanation for the zonation of the urea cycle and glutamine synthetase based on the Wnt/-c:atenin pathway[]." Experts admit there is a lot to learn about this relatively unexplored molecular pathway. However, the most recent evidence suggests it is an important pathway that interacts with other pathways in inflammation and acts as a crucial regulator of functions of different biological systems. Recent studies associate Wnt signaling in inflammation in adipocytes which is the major site for bioaccumulation of toxicants in the body. This fact elevates the significance of this pathway in environmental health studies. Of course, further research is needed to identify the level of the role it plays on the physical and mental effects of exposures from environmental contaminants.
The Wnt/β-catenin pathway: master regulator of liver zonation?. Zoë D. Burke. 2006; BioEssays - Wiley InterScience
Ortega, V. A., Renner, K. J., and Bernier, N. J. (2005). Appetite-suppressing effects of ammonia exposure in rainbow trout associated with regional and temporal activation of brain monoaminergic and crf systems. J Exp Biol, 208(10):1855-1866. http://www.citeulike.org/user/HEIRS/article/6594636
Castelo-Branco, G., Rawal, N., and Arenas, E. (2004). Gsk-3beta inhibition/beta-catenin stabilization in ventral midbrain precursors increases differentiation into dopamine neurons. J Cell Sci, 117(24):5731-5737. http://www.citeulike.org/user/HEIRS/article/6582306
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