Publications

OBJECTIVE

To evaluate the effects of diarrhea on appetite among Peruvian children age 12 to 71 months and to assess whether elevated plasma levels of peptide YY, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-1beta contribute to anorexia in this population.

STUDY DESIGN

A total of 46 Peruvian children with diarrhea and 46 healthy controls underwent an observed feeding trial that was repeated when cases were healthy. Blood samples were obtained from 30 cases and 30 controls at the first trial and from 30 cases at the second trial and assayed for peptide YY, TNF-alpha, and IL-1beta.

RESULTS

In the cases, mean consumption was less when sick than when healthy. The mean plasma level of peptide YY was higher for cases than controls and higher for cases when sick than when healthy. TNF-alpha levels were higher in cases than controls at visit 1 and also higher in cases when sick than when healthy. There were no differences in IL-1beta levels between cases and controls or between cases when sick and healthy. Peptide YY levels in children with diarrhea correlated with the likelihood of them eating less when sick than when healthy.

CONCLUSIONS

Elevated serum peptide YY may be a mechanism for anorexia in children with diarrhea.

Inflammation produces marked changes in lipid metabolism, including increased serum fatty acids (FAs) and triglycerides (TGs), increased hepatic TG production and VLDL secretion, increased adipose tissue lipolysis, and decreased FA oxidation in liver and heart. Lipopolysaccharide (LPS) also increases TG and cholesteryl ester levels in kidneys. Here we confirm these findings and define potential mechanisms. LPS decreases renal FA oxidation by 40% and the expression of key proteins required for oxidation of FAs, including FA transport protein-2, fatty acyl-CoA synthase, carnitine palmitoyltransferase-1, medium-chain acyl-CoA dehydrogenase, and acyl-CoA oxidase. Similar decreases were observed in peroxisome proliferator-activated receptor alpha (PPARalpha)-deficient mice. LPS also caused a reduction in renal mRNA levels of PPARalpha (75% decrease), thyroid hormone receptor alpha (TRalpha) (92% decrease), and TRbeta (84% decrease), whereas PPARbeta/delta and gamma were not altered. Expression of PGC1 alpha and beta, coactivators required for PPARs and TR, was also decreased in kidneys of LPS-treated mice, as were mitochondrial genes regulated by PGC1 (Atp5g1, COX5a, Idh3a, and Ndufs8). Decreased renal FA oxidation could be a by-product of the systemic coordinated host response to increase FAs and TGs available for host defense and/or tissue repair. However, the kidney requires energy to support its transport functions, and the inability to generate energy via FA oxidation might contribute to the renal failure seen in severe sepsis.

Structural studies of caspase-1 reveal that the dimeric thiol protease can exist in two states: in an on-state, when the active site is occupied, or in an off-state, when the active site is empty or when the enzyme is bound by a synthetic allosteric ligand at the dimer interface approximately 15 A from the active site. A network of 21 hydrogen bonds from nine side chains connecting the active and allosteric sites change partners when going between the on-state and the off-state. Alanine-scanning mutagenesis of these nine side chains shows that only two of them-Arg286 and Glu390, which form a salt bridge-have major effects, causing 100- to 200-fold reductions in catalytic efficiency (k(cat)/K(m)). Two neighbors, Ser332 and Ser339, have minor effects, causing 4- to 7-fold reductions. A more detailed mutational analysis reveals that the enzyme is especially sensitive to substitutions of the salt bridge: even a homologous R286K substitution causes a 150-fold reduction in k(cat)/K(m). X-ray crystal structures of these variants suggest the importance of both the salt bridge interaction and the coordination of solvent water molecules near the allosteric binding pocket. Thus, only a small subset of side chains from the larger hydrogen bonding network is critical for activity. These form a contiguous set of interactions that run from one active site through the allosteric site at the dimer interface and onto the second active site. This subset constitutes a functional allosteric circuit or "hot wire" that promotes site-to-site coupling.

A key goal of pharmacogenetics--the use of genetic variation to elucidate inter-individual variation in drug treatment response--is to aid the development of predictive genetic tests that could maximize drug efficacy and minimize drug toxicity. The completion of the Human Genome Project and the associated HapMap Project, together with advances in technologies for investigating genetic variation, have greatly advanced the potential to develop such tests; however, many challenges remain. With the aim of helping to address some of these challenges, this article discusses the steps that are involved in the development of predictive tests for drug treatment response based on genetic variation, and factors that influence the development and performance of these tests.