Health Implications of Bt Cotton Seeds in Animals and Man

Abstract

Cotton (Gossypium spp.) is an arborous plant from the Malvaceae family. Cottonseed meal is a by-product of cotton that is used for animal feeding because it is rich in oil and proteins. However, gossypol toxicity limits cottonseed use in animal feed. Gossypol is a phenolic compound produced by pigment glands in cotton stems, leaves, seeds and flower buds. Cotton is a long duration crop and is attacked by a number of insect pests. Earlier, insecticide quantity applied on cotton was highest but with the advent of Bt cotton, there is a great reduction in insecticide and pesticide usage as majority of the bollworms are controlled by it. Bt cotton refers to transgenic cotton which contains endotoxin protein inducing gene from soil bacterium Bacillus thuringiensis. It was discovered by a Japanese scientist Ishiwata in 1901. B.thuringiensis strains produces 3 types of insecticidal toxins that are Crystal toxins (Cry), Cytolytic toxins (Cyt) and vegetatively expressed insecticidal proteins (vip). Bt-delta-endotoxins which functions as oral toxins are ingested by insect and protoxins are proteolytically activated to trypsin-resistant active core δ- endotoxin in alkaline mid-gut. The active toxin binds to cadherin receptors present on the brush border membrane of the insect midgut. Cadherins process the toxins to form homo-oligomers, bind to specific receptors like alkaline phosphatases and aminopeptidases before causing pores in the epithelial membrane, resulting in osmotic lysis of the cells which results in cessation of feeding and finally mortality of the insect. Cry toxins have not been reported to be toxic to higher animals such as goats, sheep and cattle in any part of the world as scientific evidences indicate that the Cry toxins do not get activated under the acidic conditions of non-target animals such as goat, sheep and cattle. In one study of acute oral toxicity study in rats, Bt cotton seed material did not induce any treatment related observable toxic effects when compared with Non-Bt cottonseeds. Histological studies in another study revealed that there were no difference in cellular architecture in liver, heart, kidney and intestine of Bt and non-Bt diet fed rats. The Cry toxins Cry1Ac, Cry1Ab, Cry2Ab, Cry1F and Cry1C are considered to be safe to human beings. The stomach of humans, being the first organ of digestion which the Bt protein encounters, is acidic and contains proteases like pepsin which degrade the Bt protein. Thus, the alkaline conditions needed for pro-toxin solubilization and protease action required for toxin activation are absent in the stomach. More importantly, the human intestine lacks the specific receptors to which the activated Bt protein binds and initiates the physiological effect. However, there are several reports that Bt genes cause some serious problems to human health. Cry1Ac toxin at higher concentration have lethal cytotoxic and genotoxic effects on the human lymphocytes. The present review is an attempt to provide details from the available literature regarding uses of Bt cotton and its implications on animal and human health.