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Nutrient Interactions and Toxicity
Research Communication

Prima Facie Evidence That a Phytocystatin for Transgenic Plant Resistance to Nematodes Is Not a Toxic Risk in the Human Diet¹

Centre for Plant Sciences, University of Leeds, Leeds, LS2 9JT, UK and ^* BIBRA International, Carshalton, Surrey, SM5 4DS, UK

²To whom correspondence should be addressed. E-mail: h.j.atkinson{at}leeds.ac.uk.

A protein-engineered rice cystatin (OcID86) provides transgenic, partial crop resistance to plant nematodes. This study determined whether its oral uptake has adverse effects on male Sprague-Dawley rats when they are administered by oral gavage 0.1–10 mg OcID86/kg body weight daily for 28 d. Body weight and water and food intakes were unaltered for most of the study. The only significant changes in fresh weight of nine organs were for the liver (4% decrease; P < 0.05) and the empty cecum (14% increase; P < 0.05) at the two lowest doses and the highest dose of OcID86, respectively. No abnormalities in either organ were detected by histochemistry. There were no changes in the urine or in hematological variables measured, and blood serum revealed no dose-dependent responses for any of 17 variables measured. OcID86 was degraded by boiling with a 50% loss of its inhibition of papain after 9.2 ± 8.0 min. It also showed >95% loss of such inhibition after 15 s in simulated gastric fluid. The results suggest that the no effect level (NOEL) for OcID86 is >10 mg/(kg · d). This provides a range of dietary exposure >200–2000 fold depending upon the promoter used to control its expression in potato.

KEY WORDS: • toxicity • cystatin • OcID86 • anti-nematode • biopesticide