PTCA determination in human hair: reliability and analytical aspects.

BACKGROUND: In this study we analysed the reliability of HPLC determination of 2.3.5-pyrroletricarboxylic acid (PTCA). This product derives from oxidation of melanin in human hair, and is a good candidate as a risk marker for skin tumors. MATERIAL/METHODS: We determined PTCA in 100 melanoma cases and 100 controls, 21 replicates from six different reference hairs, two trace elements, and one reference sample (brown hair). RESULTS: Work-up procedures showed an almost perfect reproducibility with an Intraclass Correlation Coefficient (ICC) of 0.990. We noticed a low, detectable, but not statistically significant decrease in reproducibility proportional to the amount of PTCA. Agreement between determination following injection of the same solution in HPLC column was also high, with an overall ICC of 0.986. Simultaneous analysis of reproducibility showed a partial ICC for work-up (0.986), for injection (0.987), and an overall standardised ICC (0.975). The analysis of the two reference tracers in successive tests showed a weak, not statistically significant, decreasing linear drift, possibly due to various factors, such as aging of chemical solutions and HPLC columns. CONCLUSIONS: PTCA extracted from human hair through oxidation and determined with HPLC can be considered a reliable marker as a candidate for identifying persons at high risk for melanoma.

Near infrared spectroscopy as a tool for the determination of eumelanin in human hair.

Eumelanins are brown-black pigments present in the hair and in the epidermis which are acknowledged as protection factors against cell damage caused by ultraviolet radiation. The quantity of eumelanin present in hair has recently been put forward as a means of identifying subjects with a higher risk of skin tumours. For epidemiological studies, chromatographic methods of determining pyrrole-2,3,5-tricarboxylic acid (PTCA; the principal marker of eumelanin) are long, laborious and unsuitable for screening large populations. We suggest near infrared (NIR) spectroscopy as an alternative method of analysing eumelanin in hair samples. PCTA was determined on 93 samples of hair by means of oxidizing with hydrogen peroxide in a basic environment followed by chromatographic separation. The same 93 samples were then subjected to NIR spectrophotometric analysis. The spectra were obtained in reflectance mode on hair samples which had not undergone any preliminary treatment, but had simply been pressed and placed on the measuring window of the spectrophotometer. The PTCA values obtained by means of HPLC were correlated with the near infrared spectrum of the respective samples. A correlation between the PTCA values obtained by means of HPLC and the PTCA values obtained from an analysis of the spectra was obtained using the principal component regression (PCR) algorithm. The correlation obtained has a coefficient of regression (R(2)) of 0.89 and a standard error of prediction (SEP) of 13.8 for a mean value of 108.6 ng PTCA/mg hair. Some considerations about the accuracy of the obtained correlation and the main sources of error are made and some validation results are shown.