Xenohormesis

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    Xenohormesis is a hypothesis that posits that certain compounds known as xenohormetic compounds, such as plant polyphenols, which indicate stress in the plants, can have benefits of another organism (heterotrophs) which consumes it. Or in simpler terms, xenohormesis is interspecies hormesis. The expected benefits include improve lifespan and fitness, by activating the animal's cellular stress response.[1]

    The term xenohormesis was first coined by Kondrad T. Howitz and David A. Sinclair, in the 2004 paper "Small molecules that regulate lifespan: evidence for xenohormesis".[2] Xeno comes from greek, meaning foreign, and hormesis is the adaptive response of organisms and cells to stress.[1]

    This may be useful to evolve, as it gives possible cues about the state of the environment. If the plants an animal is eating have increased polyphenol content, it means the plant is under stress and may signal famines. Using the chemical cues the heterotophs could preemptively prepare and defend itself before conditions worsen. A possible example may be resveratrol, which is famously found in red wine, which modulates over two dozen receptors and enzymes in mammals.[1]

    Xenohormesis could also explain several phenomena seen in the ethno-pharmaceutical (traditional medicine) side of things. Such as in the case of cinnamon, which in several studies have shown to help treat type 2 diabetes, but hasn't been confirmed in meta analysis. This can be caused by the cinnamon used in one study differing from the other in xenohormic properties.[3]

    Some explanations as to why this works is:

    1. It could be a coincidence. Especially for cases which partially venomous products, cause a positive stress in the organism.
    2. It is a shared evolutionary attribute, as both animals and plants share a huge amount of homology between their pathways.
    3. There is evolutionary pressure to evolve to better respond to the molecules.[3]

    There also might be the problem that our focus on maximizing the crop output, may be losing many of the xenohormetic advantages. Although the ideal conditions will cause the plant to increase its crop output it can also be argued it is loosing stress and therefore the hormesis. The honeybee colony collapse syndrome may be caused by lack of consumption of stressed nutrients.[3]

    See Also[edit | edit source]

    References[edit | edit source]

    1. 1.0 1.1 1.2 Howitz KT & Sinclair DA: Xenohormesis: sensing the chemical cues of other species. Cell 2008. (PMID 18455976) [PubMed] [DOI] [Full text] Many plant molecules interact with and modulate key regulators of mammalian physiology in ways that are beneficial to health, but why? We propose that heterotrophs (animals and fungi) are able to sense chemical cues synthesized by plants and other autotrophs in response to stress. These cues provide advance warning about deteriorating environmental conditions, allowing the heterotrophs to prepare for adversity while conditions are still favorable.
    2. Lamming DW et al.: Small molecules that regulate lifespan: evidence for xenohormesis. Mol Microbiol 2004. (PMID 15306006) [PubMed] [DOI] Barring genetic manipulation, the diet known as calorie restriction (CR) is currently the only way to slow down ageing in mammals. The fact that CR works on most species, even microorganisms, implies a conserved underlying mechanism. Recent findings in the yeast Saccharomyces cerevisiae indicate that CR extends lifespan because it is a mild biological stressor that activates Sir2, a key component of yeast longevity and the founding member of the sirtuin family of deacetylases. The sirtuin family appears to have first arisen in primordial eukaryotes, possibly to help them cope with adverse conditions. Today they are found in plants, yeast, and animals and may underlie the remarkable health benefits of CR. Interestingly, a class of polyphenolic molecules produced by plants in response to stress can activate the sirtuins from yeast and metazoans. At least in the case of yeast, these molecules greatly extend lifespan by mimicking CR. One explanation for this surprising observation is the 'xenohormesis hypothesis', the idea that organisms have evolved to respond to stress signalling molecules produced by other species in their environment. In this way, organisms can prepare in advance for a deteriorating environment and/or loss of food supply.
    3. 3.0 3.1 3.2 Hooper PL et al.: Xenohormesis: health benefits from an eon of plant stress response evolution. Cell Stress Chaperones 2010. (PMID 20524162) [PubMed] [DOI] [Full text] Xenohormesis is a biological principle that explains how environmentally stressed plants produce bioactive compounds that can confer stress resistance and survival benefits to animals that consume them. Animals can piggyback off products of plants' sophisticated stress response which has evolved as a result of their stationary lifestyle. Factors eliciting the plant stress response can judiciously be employed to maximize yield of health-promoting plant compounds. The xenohormetic plant compounds can, when ingested, improve longevity and fitness by activating the animal's cellular stress response and can be applied in drug discovery, drug production, and nutritional enhancement of diet.