Differential metabolic response in AIDS‐related chronic protozoal diarrhoea

Objective As the pro-inflammatory cytokine tumour necrosis factor-alpha is greater in microsporidiosis than cryptosporidiosis, there may be a distinct metabolic response between the two organisms. Design Male HIV seropositive subjects with an untreated AIDS-defining diagnosis of microsporidiosis or cryptosporidiosis had measurement of oxygen consumption and carbon dioxide production by indirect calorimetry and body composition analysis to express resting energy expenditure (REE) and substrate oxidation per kilogram of metabolically active tissue. Methods Resting energy expenditure (REE), non-protein respiratory quotient (NPRQ), fat and carbohydrate oxidation were calculated from respiratory gas analysis. Fat, fat-free and appendicular muscle masses were measured by dual-energy X-ray absorptiometry. Subjects with protozoal diarrhoea were compared to other newly diagnosed, active opportunistic infections. Controls were asymptomatic HIV-seropositive men matched by peripheral CD4 count. Results Seven subjects with microsporidiosis and six with cryptosporidiosis were compared with 24 subjects with other AIDS-defining diagnosis (Pneumocystis carinii pneumonia, cytomegalovirus enteritis and Mycobacterium avium-intracellulare) and 10 controls free from secondary infection. Subjects with cryptosporidiosis had a decreased REE, a significantly increased NPRQ (P< 0.05), decreased fat oxidation (P < 0.05) and increased carbohydrate oxidation compared to microsporidiosis. Subjects with other AIDS diagnoses had an increased REE (P < 0.01) and fat oxidation and decreased carbohydrate oxidation compared to cryptosporidiosis, and a similar metabolic response to microsporidiosis. Conclusions The metabolic response to cryptosporidiosis differs from microsporidiosis and associated weight loss may be mediated by different mechanisms. Metabolism in other AIDS diagnoses, including microsporidiosis, is compatible with a cachectic response.