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

1. Analysis of urine by 1 H-nuclear magnetic resonance (NMR) spectroscopy is used to detect biochemical disturbances predictive of toxicological changes. Recent studies, using 1 H-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 1 H-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.