Modulatory Effects of the Functional Gut Microbiome in Relation to Cassava Associated Motor and Neurocognitive Deficits

Abstract: Cassava (Manihot esculenta Crantz) serves as a staple crop for more than 600 million people in
tropical regions of the world. Two types of cassava are traditionally grown across the globe, the “sweet” and
“bitter” varieties, the latter being an environmentally tolerant plant, harboring extremely high to lethal doses of
toxic cyanogenic compounds. Chronic dietary reliance on toxic cassava is associated with cyanide
neurotoxicity, causing an irreversible, non-progressive motor neuron disease known as konzo and possibly,
deficits in neurocognition. Within prone regions of sub-Saharan Africa, there are a disproportionate number of
children affected for reasons and mechanisms that have yet to be fully elucidated. While nearly most subjects
in konzo-affected villages rely heavily on cyanogenic cassava as a staple food, only about 5 to 10% present
with a visible spastic paraparesis. This suggests that exposure levels, nutrition, and environmental components
such as the detoxification capabilities of the gut microbiome are likely contributing factors in disease
susceptibility. We have shown that the gut flora profiles are significantly different between adolescents who rely
on cassava with low-high levels of toxicity in the DRC. Even within a region of the DRC that is highly
susceptible to outbreaks of disease, there are marked differences in bacterial composition between unaffected
individuals depending on whether they reside in villages with historically high or low konzo prevalence, again
adding to the likelihood of disease modulation through the gut microbiome. Based on insight from our
preliminary and published data, we will investigate if there are functional differences in the gut-flora between
sex-matched sibling pairs who are discordant for disease, by utilizing metagenomic and transcriptomic
sequencing approaches on stool specimens (Aim 1). Using the same study population, we will also determine
if metabolic biomarkers are identifiable that indicate a disease state or susceptibility using state-of-the-art
metabolic applications, such as ultra-high performance liquid chromatography coupled with mass spectrometry
(UHPLC-MS/MS) (Aim 2). The data generated from both approaches will enable us to not only assess the
profiles and functionality of the gut microbiome in relation to disease status, but will provide the power to
determine the host-microbiome interaction in regards to downstream metabolic processes. Given that the
World Health Organization estimates that the burden and deaths resulting from non-communicable diseases
(NCDs) will surpass those from malaria and HIV combined, in the coming years, we have embedded a
comprehensive advanced training plan to expand knowledge on pertinent topics relating to NCDs, such as
nutrition, toxicology, neuroepidemiology and other relevant disciplines. Collectively, this proposal and training
plan will significantly expand our understanding of disease modulators associated with cassava neurotoxicity
that can be potentially used for monitoring and prevention strategies, while providing adequate academic and
research-based training for an independent global health scientific career.

Grant Number: 5K01TW011772-05
NIH Institute/Center: NIH
Principal Investigator: Matthew Bramble