Effect of intestinal microflora on the urinary metabolic profile of rats:: a 1H-nuclear magnetic resonance spectroscopy study

1. Analysis of urine by H-1-nuclear magnetic resonance (NMR) spectroscopy is used to detect biochemical disturbances predictive of toxicological changes. Recent studies, using H-1-NMR spectroscopy have suggested that Alderley Park rats can be classified as hippuric acid (HA) or m-(hydroxyphenyl)propionic acid (m- HPPA) excretors. Evidence exists for the role of intestinal microflora in the excretion of aromatic phenolic compounds including HA and m- HPPA. 2. We sought to investigate whether intestinal microflora contribute to the difference in excretion. Urinary HA and m- HPPA levels were monitored to characterize excretion over time. The effect of intestinal microflora on the H-1-NMR spectrum was also investigated using antibiotics to sterilize the intestine. Finally, the levels of m- HPPA and phenylpropionic acid (a precursor for HA) were analysed in the caecum and colon (entire tissue, including contents). 3. Characterization confirmed the presence of HA and m- HPPA excretors; enquiries revealed that the rats were obtained from two floors within a barriered breeding unit. Housing the rats from the two floors together for 21 days resulted in comparable levels of HA and m- HPPA excretion demonstrating that the profiles are not stable. 4. Following antibiotic treatment, HA and m- HPPA excretion decreased, indicating that intestinal microflora contribute to the excretion of these compounds. Finally, m-HPPA levels were higher in the colon of rats that excreted m- HPPA whilst PPA was increased in the caecum and colon of rats that excreted HA. 5. These results demonstrate that the observed difference in HA/m-HPPA excretion is due to differences in the intestinal microflora.