Pyrrolizidine alkaloid toxicity in livestock: a paradigm for human poisoning?

Livestock poisoning, primarily liver damage, caused by consumption of plants containing 1,2-dehydropyrrolizidine ester alkaloids (dehydroPAs), and the corresponding N-oxides, is a relatively common occurrence worldwide. Because of the economic impact, extensive investigations of such episodes have been performed, particularly in Australia, South Africa the United States and, more recently, South America. Plant species most commonly involved are members of the families Boraginaceae, Asteraceae and Leguminosae. These may be native species that periodically flourish under particular climatic conditions or introduced species that thrive in the absence of natural control factors such as herbivory and competition. Contamination of grain crops with dehydroPA-producing plants has resulted in large-scale incidents of food poisoning in humans, with high morbidity and mortality, especially in Africa and in central and south Asia, with recent episodes in Afghanistan and possibly Ethiopia. Attention has recently focused on the potential for low levels of dehydroPAs to contaminate many food products in developed countries, possibly leading to progressive, chronic diseases that may not include overt hepatotoxicity. This overview examines the potential for better control of exposure and means of monitoring dehydroPA intake by extrapolation of knowledge gained from animal studies to the human situation.