A minimally invasive tracer protocol is effective for assessing the response of leucine kinetics and oxidation to vaccination in chronically energy-deficient adult males and children

Abstract

In disadvantaged populations, recurrent infections lead to a loss of body nitrogen and worsen nutritional status. The resulting malnutrition, in its turn, produces a greater susceptibility to infection. This study aimed to examine the ability of a new minimally invasive tracer protocol to measure leucine oxidation, and then to use it to quantify the effect of vaccination on leucine kinetics and oxidation. Undernourished men (n = 5; body mass index 16.3 ± 0.9 kg/m2) and children (n = 9; age 4.1 ± 0.6 y; weight-for-age Z- score -2.3 ± 0.7) underwent metabolic studies 6 d before and 1 d after vaccination with diphtheria, pertussis and tetanus (DPT). The tracer protocol was performed in the fed state and involved two 3-h sequential periods of frequent (20 min) oral doses of NaH13CO3 or [1-13C] leucine. Frequent breath samples and urine collections were made. Blood samples were obtained from the men and used for the determination of the isotopic enrichment of α- ketoisocaproic acid. The prevaccination oxidation of leucine (percentage of dose ± SD) was 18.1 ± 2.3 (men) and 16.7 ± 3.8 (children). One day after vaccination, these values had risen to 19.9 ± 1.9 (P < 0.05) in the men and to 19.5 ± 4.6 (P < 0.01) in the children. In the adults, vaccination was associated with a rise in whole-body protein breakdown [mg protein/(kg.h)] from 200 ± 40 to 240 ± 10 (P < 0.05). A minor simulated infection increases leucine catabolism in undernourished humans and this new, minimally invasive protocol is sufficiently sensitive to measure these changes.