Motor neuron disease is an umbrella term frequently used to designate diseases, especially neurodegenerative conditions that prominently strike the motor system in a fashion that has remained enigmatic. The existence of high incidence foci of motor neuron diseases among human populations (e.g. the Guam amyotrophic lateral sclerosis, konzo, and/or lathyrism) suggests that environmental factors e.g. exposure to certain neurotoxins cause the motor system to degenerate. The identification of such neurotoxins is highly relevant as they can be used as experimental tools to probe molecular mechanisms underlying this type of neuropathology. In our previous research, we have extensively characterized the lesion in konzo, a highly prevalent but neglected motor neuron disease occurring in sub-Saharan Africa. We have shown that konzo is a pure, permanent and irreversible disease that prominently targets the pyramidal motor tracts among populations in which the diet is almost restricted to poorly detoxified cyanogenic (linamarin)-containing cassava. In addition, affected subjects have a low intake in sulfur amino acids (SAA) needed to detoxify endogenously produced cyanide (CN). Under these conditions, oxidative metabolism of CN is favored and there is increased production of cyanate (OCN), a protein-carbamoylating agent. OCN induces myeloneuropathy in primates through mechanisms that are not understood but possibly associated with protein misfolding. SAA deficiency by itself is known to alter the activities of cystein-dependent enzymes (e.g. rodhanese) but its relationship to konzo is unkown. It is possible that SAA deficiency also alters the expression/activity of protein disulfide isomerase (PDI), an enzyme that modulates proper folding of proteins by catalyzing thiol/disulfide exchange reactions and hence, impairs the """"""""repair"""""""" capabilities of the enzyme. We have used neuroproteomics to study mechanisms by which neurotoxic protein-reactants induce axonopathy. In this R21 project, we will use a similar approach to elucidate biomarkers of OCN/linamarin neurotoxicity and test the hypothesis that linamarin (cassava) motor neuron disease is mediated by OCN and/or SAA deficiency-sustained protein misfolding. Accordingly, we will identify (neuro)protein targets of OCN, quantify OCN adducts, characterize the neuropathology, and assess changes in selected indicators of protein misfolding in brain/spinal cord tissues of young Wistar rats kept on SAA-deficient diets and treated with linamarin, NaOCN (positive control) or equivalent amount of 5% glucose in aqueous solution (negative control) for up to 8 weeks. This line of research fits well with FIC/NIH objectives in that it addresses an issue of public health concern in the developing world while providing a neuroscience-focused framework for training and research capacity building in the Democratic Republic of Congo, a country that is currently the most affected by konzo.
Cassava (manioc) contains toxic compounds e.g. linamarin that are incriminated in the paralysis of legs (disease is called konzo) and other diseases of the nervous system across the lifespan. We seek funds from the Fogarty International Center/National Institutes of Health to clarify mechanisms by which it (cassava) induces neurotoxicity and to train scientists from the Democratic Republic of Congo (seriously affected by konzo) to conduct toxicological research. This project has a global heath relevance because the crop (cassava) is a staple for more than 400 million people dwelling under the tropics and it is increasingly exported worldwide for snack production and animal feed.
