23 enero 2013

La extinción de especies es un desastre para la salud humana / Species extinction is a disaster for human health

Species extinction is a disaster for human health

A species faced with extinction is more than a potential tragedy for the species concerned. Human wellbeing and economy depend on the world's biodiversity and ecosystem services, but human actions are damaging the environment and threatening the existence of countless organisms that have, or could provide, humankind with valuable medicines, according to a recent publication.

One such group of threatened organisms is cone snails. Cone snails are marine molluscs that live mostly in coral reefs and mangroves. Of the 700 or so estimated cone snail species, seven new ones were identified in 2004. Although only four cone snail species are classified as 'vulnerable' on the 2006 IUCN Red List of Threatened Species, a systematic assessment of the status of cone snails has never been carried out, so there are no reliable estimates. In reality, a large number of cone snail species are likely to be threatened because of the rapid degradation and loss of their habitats around the world.

Climate change acts as an additional major threat on coral reefs already weakened through overexploitation and invasive species. Sea water that becomes more acidic from absorbed carbon dioxide emissions makes the development of the calcium skeletons of the coral difficult and, finally, if the trend cannot be reversed, the corals will crumble and will no longer be able to provide their adaptation function protecting coastline against storm surges and waves. Rising sea surface temperatures can bleach corals (as they tend to lose the symbiotic algae on which they depend for oxygen and nutrients), leaving them susceptible to infectious diseases and eventual death. Mangrove systems are equally under threat - it is estimated that around 50% of mangroves have already been destroyed worldwide. In Southeast Asia, where more than half of cone snail species live, around 90% of coral reefs are threatened. It should be noted that cone snail species often have a narrow geographical range, making them even more vulnerable to habitat destruction.

Cone snails have venoms that they use to paralyse their prey. These venoms contain complex mixtures of toxic, small protein molecules (peptides), many of which have already been found to be useful for human medicine.

For example, one of the toxins isolated from the cone snail C. magus has been synthetically produced, as a drug called ziconotide. It is a highly potent pain-relieving drug, around 1000 times more potent than morphine, but acts without addiction or the build-up of a patient's tolerance. Long-term management of pain for conditions, including cancer and AIDS, has traditionally relied on opiates, such as morphine, but over time, tolerance to opiates can develop, requiring higher and higher doses to be given. Because of the development of tolerance, opiates often lose their effectiveness.

Another cone snail toxin is being investigated to prevent brain cell death when blood flow is restricted, such as when people suffer head injuries or strokes. Still others have shown potential in the treatment of Alzheimer's and Parkinson's disease, epilepsy, and heart attacks.

Each cone snail species has a total of around 100 to 200 different and distinct peptides, so there may be as many as 70,000 to 140,000 toxic peptides, many of which could become medicines for human use. Cone snails may contain the largest number of medicines to treat human diseases and to relieve human suffering as compared to any other group of organisms on Earth. Yet only about 100 of its toxins have been characterised so far.

Source: Chivian E.S., Bernstein, A.S. (2008). Threatened groups of organisms valuable to medicine. In: Chivian, E.S, Bernstein A.S, ed. 2008. Sustaining life: how human health depends on biodiversity. New York: Oxford University Press. Ch. 5.

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