Recently, an improved analytical procedure for pheomelanin analysis in pigmented tissues based on alkaline H2O2 degradation has led to the identification, besides BTCA, of a new product, 7-(2-amino-2-carboxy ethyl)-2-carboxy-4-hydroxybenzothiazole (BTCA-2), generated from 2-S-cysteinyldopa (2SCD) derived units. Simultaneous determination of BTCA and BTCA-2 in segments of red hair locks taken at variable distances from the scalp in a group of 19 individuals indicated an abrupt drop of BTCA yields on passing from the root to the tip, whereas BTCA-2 values remained constant throughout hair length. Analysis of 4-amino-3-hydroxyphenylalanine (AHP) and 3-aminotyrosine (AT) showed a closely similar trend, whereas yields of thiazole-2,4,5-tricarboxylic acid (TTCA) increased with increasing distance from the scalp. Prolonged exposure of hair locks to sun light caused a significant decrease in BTCA- but not BTCA-2-yielding elements. Model studies showed a substantial degradation of 5SCD-, but not 2SCD-derived units during pheomelanin synthesis in vitro. It is concluded that red hair pheomelanin consists of a degradable 5SCD-derived bulk component associated to stable 2SCD-derived units. Structural degradation occurs during hair growth probably as a result of oxidative processes related at least in part to sun exposure.
Red Hair Photochemistry: Differential Behaviour of Structural Components to (Photo)degradation
M. d'Ischia
2009
Abstract
Recently, an improved analytical procedure for pheomelanin analysis in pigmented tissues based on alkaline H2O2 degradation has led to the identification, besides BTCA, of a new product, 7-(2-amino-2-carboxy ethyl)-2-carboxy-4-hydroxybenzothiazole (BTCA-2), generated from 2-S-cysteinyldopa (2SCD) derived units. Simultaneous determination of BTCA and BTCA-2 in segments of red hair locks taken at variable distances from the scalp in a group of 19 individuals indicated an abrupt drop of BTCA yields on passing from the root to the tip, whereas BTCA-2 values remained constant throughout hair length. Analysis of 4-amino-3-hydroxyphenylalanine (AHP) and 3-aminotyrosine (AT) showed a closely similar trend, whereas yields of thiazole-2,4,5-tricarboxylic acid (TTCA) increased with increasing distance from the scalp. Prolonged exposure of hair locks to sun light caused a significant decrease in BTCA- but not BTCA-2-yielding elements. Model studies showed a substantial degradation of 5SCD-, but not 2SCD-derived units during pheomelanin synthesis in vitro. It is concluded that red hair pheomelanin consists of a degradable 5SCD-derived bulk component associated to stable 2SCD-derived units. Structural degradation occurs during hair growth probably as a result of oxidative processes related at least in part to sun exposure.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
