Foodborne Toxicants

Epipolythiodioxopiperazines (ETPs) are toxic secondary metabolites made only by fungi. The best-known ETP is gliotoxin, which appears to be a virulence factor associated with invasive aspergillosis of immunocompromised patients. The toxicity of ETPs is due to the presence of a disulphide bridge, which can inactivate proteins via reaction with thiol groups, and to the generation of reactive oxygen species by redox cycling. With the availability of complete fungal genome sequences and efficient gene-disruption techniques for fungi, approaches are now feasible to delineate biosynthetic pathways for ETPs and to gain insights into the evolution of such gene clusters.

We tested the brain tissues of the Chamorro people of Guam who died of amyotrophic lateral sclerosis/Parkinsonism dimentia complex (ALS/PDC) for the neurotoxin beta-methylamino-l-alanine (BMAA). We used validated high-pressure liquid chromatography and liquid chromatography-mass spectrometry analyses to test well-characterized archival tissues of the superior frontal gyrus from eight Chamorros from Guam and a comparison group of 15 Canadians. BMAA was found as a free amino acid in 83% of Chamorro ALS/PDC patients (3-10 microg/g) as a protein-associated amino acid in 100% of the Chamorro individuals (149-1190 microg/g). Both forms of BMAA were also found at comparable levels in two Canadians who died of progressive neurodegenerative disease. BMAA, which is produced by cyanobacteria, may be associated with some cases of neurodegenerative disease.

Lectins are carbohydrate binding (glyco)proteins which are ubiquitous in nature. In plants, they are distributed in various families and hence ingested daily in appreciable amounts by both humans and animals. One of the most nutritionally important features of plant lectins is their ability to survive digestion by the gastrointestinal tract of consumers. This allows the lectins to bind to membrane glycosyl groups of the cells lining the digestive tract. As a result of this interaction a series of harmful local and systemic reactions are triggered placing this class of molecules as antinutritive and/or toxic substances. Locally, they can affect the turnover and loss of gut epithelial cells, damage the luminal membranes of the epithelium, interfere with nutrient digestion and absorption, stimulate shifts in the bacterial flora and modulate the immune state of the digestive tract. Systemically, they can disrupt lipid, carbohydrate and protein metabolism, promote enlargement and/or atrophy of key internal organs and tissues and alter the hormonal and immunological status. At high intakes, lectins can seriously threaten the growth and health of consuming animals. They are also detrimental to numerous insect pests of crop plants although less is presently known about their insecticidal mechanisms of action. This current review surveys the recent knowledge on the antinutritional/toxic effects of plant lectins on higher animals and insects.