Subchronic Immunotoxicity Assessment of Genetically Modified Virus-Resistant Papaya in Rats.

Papaya is an important fruit that provides a variety of vitamins with nutritional value and also holds some pharmacological properties, including immunomodulation. Genetically modified (GM) papaya plants resistant to Papaya ringspot virus (PRSV) infection have been generated by cloning the coat protein gene of the PRSV which can be used as a valuable strategy to fight PRSV infection and to increase papaya production. In order to assess the safety of GM papaya as a food, this subchronic study was conducted to assess the immunomodulatory responses of the GM papaya line 823-2210, when compared with its parent plant of non-GM papaya, Tainung-2 (TN-2), in Sprague-Dawley (SD) rats. Both non-GM and GM 823-2210 papaya fruits at low (1 g/kg bw) and high (2 g/kg bw) dosages were administered via daily oral gavage to male and female rats consecutively for 90 days. Immunophenotyping, mitogen-induced splenic cell proliferation, antigen-specific antibody response, and histopathology of the spleen and thymus were evaluated at the end of the experiment. Results of immunotoxicity assays revealed no consistent difference between rats fed for 90 days with GM 823-2210 papaya fruits, as opposed to those fed non-GM TN-2 papaya fruits, suggesting that with regard to immunomodulatory responses, GM 823-2210 papaya fruits maintain substantial equivalence to fruits of their non-GM TN-2 parent.

Repeated Dose 90-Day Feeding Study of Whole Fruits of Genetically Modified Papaya Resistant to Papaya Ringspot Virus in Rats.

Genetically modified (GM) papaya plants resistant to infection by Papaya ringspot virus (PRSV) have been successfully generated by cloning the coat protein (CP) gene of PRSV to increase fruit production. In this study, the GM papaya line 823-2210 was used to conduct a 90-day feeding toxicity study and compared to its parent plant of non-GM papaya, Tainung-2 (TN-2) based on the experimental guidance reported by the European Food Safety Authority.1 Ten male and 10 female Sprague-Dawley albino rats were gavaged at low (1 g/kg bw) and high (2 g/kg bw) doses of non-GM and GM lyophilized papaya fruits for 90 days. Hematology, coagulation, biochemistry, urinalysis, and pathology were examined in all animals. Although some differences were found in feed consumption, hematology, and serum chemistry examinations between non-GM and GM papaya, the results were within historical control values and not considered biologically significant in rats. In addition, there were no treatment-related gross or microscopic lesions in male or female rats attributable to the non-GM or GM papaya fruit. This 90-day feeding study of GM papaya fruit did not reveal adverse effects in rats and indicates that GM papaya fruits may be substantially equivalent to their non-GM parent plants.

Kidney stone distribution caused by melamine and cyanuric acid in rats.

BACKGROUND: Melamine (M), which is composed of multi-amine, has been used as a food additive to falsely increase protein contents. Furthermore, cyanuric acid (CA) is a derivative of melamine. It is known that these mixtures can cause renal toxicity. METHODS: The objective of this study was to investigate the possible target cells during acute renal toxicity of melamine and cyanuric acid (MCA) mixture crystals in vivo. Rats were provided with a lethal dose of MCA (1:1; 400mg/kg) and observed after 0.5, 1, 3, 12, 24, and 48-h intervals. RESULTS: MCA caused degeneration/necrosis in the proximal tubules starting at 12h and increased at 24 and 48 h. A small number of yellow-green crystals were observed in the dilated distal renal tubules at 48 h post-treatment. Ultrastructurally, pyknosis, mitochondrial vesicles, and cellular swelling were found in the proximal tubular cells at 0.5h. Small needle-like crystals in the cytoplasm and large crystals in the lumen of tubules indicated physical damage to the renal cells. CONCLUSION: These results clearly reveal that in the MCA-induced renal toxicity model, crystals are distributed to both the proximal and distal tubules in rats. The proximal tubular cells may be initially injured and subsequently block the distal tubules with MCA crystals during early acute intoxication.

Toxicity assessment of transgenic papaya ringspot virus of 823-2210 line papaya fruits.

The transgenic papaya is a valuable strategy for creating plants resistant to papaya ringspot virus (PRSV) infection and increasing production. This study was further performed to evaluate the comparative toxicity effects of the newly developed transgenic line of the fruits of two backcross transgenic papaya lines (2210 and 823) and one hybrid line (823-2210) and compare to their parent non-transgenic (TN-2) counterparts. The stability analysis of coat protein (CP) of PRSV was investigated using the digestion stability assays in simulated gastric fluid (SGF), simulated intestinal fluid (SIF), and bile salts to detect the CP fragments. Results revealed that the CP fragments were rapidly hydrolyzed in SGF and were undetectable in organs and gastrointestinal contents in rats. For the genotoxicity, three in vitro assays were conducted and exhibited that non-transgenic and backcross transgenic papaya fruits were negative. Moreover, a repeated animal feeding study was conducted by feeding 2 g/kg of body weight (bw) of non-transgenic and backcross transgenic papaya fruits for 28 days in rats. There were no biological or toxicological significances between non-transgenic and backcross transgenic papaya fruits in rats. The results demonstrated that the backcross transgenic papaya fruit can be recognized as an equivalent substitution for traditional papaya in food safety.

Evaluation of subchronic toxicity of pet food contaminated with melamine and cyanuric acid in rats.

Outbreaks of food-associated renal failure in pets occurred in Asia and the United States of America in 2004 and 2007. They were related to the combined intoxication of cyanuric acid and melamine. Our aims were to investigate cyanuric acid and melamine contamination of pet food and to examine subchronic toxicity in rats. Levels of 10%, 20%, 50%, and 50%-100% (w/w) of contaminated pet food were fed to rats for three months. Analytical results revealed that the tainted food contained significant levels of cyanuric acid and melamine in a ratio of 1:6.8. Rats fed the diet of 50%-100% for three months exhibited elevated serum blood urea nitrogen and creatinine, as well as dose-dependent melamine/cyanuric acid crystal-induced nephrotoxicity. The melamine/cyanuric acid crystals of various sizes were mixed with necrotic cell debris and inflammatory cells, accompanied by tubular dilation and interstitial fibrosis. The immunohistochemistry index of proliferative cellular nuclear antigen and osteopontin in the kidney of the 50%-100% group were elevated, indicating regeneration of renal cells and the formation of crystals. In conclusion, the combination ratio of cyanuric acid to melamine and the acidic urine content were two factors that, upon repeated exposure, determined the severity of the nephrotoxicity.