Richard L. Guerrant, MD
Recognition, Diagnosis, Pathogenesis, Impact, Treatment and Prevention of Enteric Infections; Global Health and Tropical Infectious Diseases
Building on a background of work defining the unique, prolonged activation of adenylate cyclase by cholera toxin and E. coli LT (1971-1972), the development of the CHO cell assay for cholera toxin and E. coli LT (1974-1976), and the discovery that particulate guanylate cyclase is activated by E. coli ST (1978-1981) and on field work defining the magnitude of diarrheal diseases and their nutritional impact in rural and urban communities in Northeast Brazil (1978-present), Guerrant's laboratory is focused on the recognition, diagnosis, pathogenesis, impact, treatment and prevention of enteric infections. This work includes active studies of the roles of PLA2, PAF, enteric cytokines and neutrophils and the neutrophil marker lactoferrin in pathogenesis and diagnosis as well as of glutamine derivatives in the repair of disrupted intestinal barrier function. Guerrant's research on the leading cause of hospital-acquired diarrhea, Clostridium difficile, shows a key role for PLA2, PAF and COX-2 in the secretory and inflammatory effects of C. difficile toxin A. Guerrant's laboratory also finds PAF to be a key mediator of cholera toxin-induced secretion as well. Current work involves animal, tissue culture, Using chamber, and clinical studies of the roles of these mediators in inflammatory, parasitic (Cryptosporidium) and microbial adhesion or toxin-induced (ex. enteroaggregative E. coli, C. difficile, cholera) diarrheas. Work with colleagues at the Federal University of Ceara in Fortaleza, Brazil, supported by a current NIH International Collaboration for Infectious Diseases Research (ICIDR) award in its 16th year, shows three new and emerging pathogens to be leading causes of persistent diarrhea: enteroaggregative E. coli, Cryptosporidium and toroviruses. In addition, Cryptosporidium and other persistent diarrheas disrupt intestinal barrier function (as determined by lactulose:mannitol permeability) and lead to substantial increased diarrhea burdens for extended periods thereafter in young children. Having recently shown an apparent role for leukocytes (with fecal lactoferrin) in cryptosporidial and enteroaggregative E. coli persistent diarrheas, current work includes studies of the roles of cytokines in intestinal barrier disruption and secretion in bacterial and parasitic diarrheas. Most important, with colleagues in Brazil, Guerrant has shown that early childhood diarrhea and enteric infections have a lasting impact on growth and cognitive development, more than doubling the global diarrhea DALYs (disability-adjusted life years lost). Current work involves in-vitro, animal model and field studies of mechanisms, genetics (including APOE polymorphisms) and micronutrient interventions to ameliorate these effects. Having also recently demonstrated in collaborative studies that glutamine (the major bowel enterocyte energy source) and its new stable derivatives enhance intestinal sodium absorption at least as well if not better than glucose, current studies are addressing the roles of these compounds and micronutrients in speeding the repair of intestinal barrier functions oral rehydration and nutrition therapy (ORNT) and hence improving child development and also absorption of antiretroviral drugs in collaborative studies at Virginia, Haiti, South Africa and in Brazil. This work also involves collaborations to address HIV drug malabsorption and resistance genotyping and, with Michael Timko, to engineer Arg-Gln derivatives into edible plants.