Hypoxanthine, uric acid and allantoin as indicators of in vivo free radical reactions. Description of a HPLC method and human brain microdialysis data.

A practical one-step high performance liquid chromatography (HPLC) method was developed for the simultaneous determination of hypoxanthine, uric acid and allantoin in small (4 microL) microdialysis samples. The rationale for this work was the current interest in hypoxanthine as a marker for energy perturbation in hypoxia/ ischemia, in uric acid as an endogenous antioxidant, and in allantoin as a marker for in vivo formation of reactive oxygen species (ROS). The method is based on ion pairing reversed phase chromatography and UV detection. The coefficient of variance for within and between run imprecision was generally below 5%, somewhat higher for concentrations close to the detection limit (0.4-1.0 pmoles). Recoveries ranged from 89 to 102% and linearity was observed in the concentration range from 0.25 to 25.0 mmol/L. There was an excellent correlation between the present method and available reference methods. The method was applied to cerebral microdialysis samples from a patient with severe subarachnoid haemorrhage complicated by secondary ischemia leading to cerebral infarction. The secondary ischemia was associated with an increase of hypoxanthine followed by increasing allantoin and uric acid levels. We submit that this pattern of chemical changes indicates increased ROS formation produced by secondary ischemia. The HPLC method appears to be a useful tool for studying changes of hypoxanthine, uric acid and allantoin levels in microdialysis samples.