Fecal Amino Acid Analysis Can Discriminate De Novo Treatment-Naïve Pediatric Inflammatory Bowel Disease From Controls.

OBJECTIVES: Endoscopy remains mandatory in the diagnostic work-up of inflammatory bowel disease (IBD), but is a costly and invasive procedure. Identification of novel, noninvasive, diagnostic biomarkers remains a priority. The aim of the present study was to explore the potential of fecal amino acid composition as diagnostic biomarker for pediatric IBD. METHODS: In this case-control study, treatment-naïve, de novo pediatric patients with IBD from two tertiary centers were included. Endoscopic severity of ulcerative colitis (UC) and Crohn's disease (CD) was based on physician global assessment scores, substantiated by levels of fecal calprotectin and C-reactive protein at study inclusion. Patients were instructed to collect a fecal sample prior to bowel cleansing. Healthy controls (HCs) were recruited from primary schools in the same region. Dedicated amino acid analysis was performed on all samples. RESULTS: Significant differences between 30 IBD patients (15 UC, 15 CD) and 15 age and sex-matched HCs were found in six amino acids (histidine, tryptophan, phenylalanine, leucine, tyrosine, and valine; all area under the curve >0.75 and P < 0.005), displaying higher levels in IBD. When distributing the patients according to type of IBD, a similar spectrum of amino acids differed between UC and HC (histidine, tryptophan, phenylalanine, leucine, valine, and serine), whereas three amino acids were different between CD and HC (histidine, tryptophan, and phenylalanine). CONCLUSIONS: Significantly increased levels of six different fecal amino acids were found in patients with IBD compared to controls. Whether these differences reflect decreased absorption or increased loss by inflamed intestines needs to be elucidated.

Relevance of allosteric conformations and homocarnosine concentration on carnosinase activity.

Activity of carnosinase (CN1), the only dipeptidase with substrate specificity for carnosine or homocarnosine, varies greatly between individuals but increases clearly and significantly with age. Surprisingly, the lower CN1 activity in children is not reflected by differences in CN1 protein concentrations. CN1 is present in different allosteric conformations in children and adults since all sera obtained from children but not from adults were positive in ELISA and addition of DTT to the latter sera increased OD450 values. There was no quantitative difference in the amount of monomeric CN1 between children and adults. Further, CN1 activity was dose dependently inhibited by homocarnosine. Addition of 80 microM homocarnosine lowered V (max) for carnosine from 440 to 356 pmol/min/microg and increased K (m) from 175 to 210 microM. The estimated K (i) for homocarnosine was higher (240 microM). Homocarnosine inhibits carnosine degradation and high homocarnosine concentrations in cerebrospinal fluid (CSF) may explain the lower carnosine degradation in CSF compared to serum. Because CN1 is implicated in the susceptibility for diabetic nephropathy (DN), our findings may have clinical implications for the treatment of diabetic patients with a high risk to develop DN. Homocarnosine treatment can be expected to reduce CN1 activity toward carnosine, resulting in higher carnosine levels.