Safety assessment of cystatins used to control pests in transgenic bananas in Uganda.
In this study the safety of the maize and papaya cystatins used to controls nematodes and banana weevil borer was assessed by determining the allergenicity and toxicity of the proteins using both in vitro as well as the in vivo method of oral gavage using albino rats. The maize and papaya cystatins were expressed in Esherechia coli strain M15 since this organism is easily cultured. Determination of in vitro digestive assays for both cystatins as well oral feeding of the animals with the cystatins in various concentrations of 10mg, 100mg and 1000mg/kg body weight was carried out followed by sacrificing the animals on the seventh day for clinical and histopathological examination of the blood and animal organs. The results indicate that the maize and papaya cystatins were fully expressed in the E.coli M15 and E.coli M15 culture grew well to produce enough protein. The two proteins rapidly degraded in the simulated gastric fluid taking less than 2 minutes to degrade in the pepsin. The maize and papaya cystatins had amino acid sequence similarity with Actinidia deliciosa a kiwi fruit of 48.3% and 40.4% respectively over their full length, suggesting that both cystatins are not potential allergens. The results of the amino acid sequence homology comparison with the known toxins in the database did not indicate any relatives, suggesting that these cystatins are not potential toxins. The feed intake data showed that the maize and papaya cystatins did not affect feed intake of the animals. The results of urinalysis, haematology, serum chemistry and organ weights showed that feeding the rats with acute doses of maize and papaya cystatins did not affect the liver and kidneys which play a big role in various metabolic processes. This study shows that the maize and papaya cystatins used to control pests in transgenic bananas in Uganda do not have allergenic and toxic effects. These cystatins may therefore be safely used in transgenic bananas to resist nematodes and weevils.