Cytochrome P450 1A1 (CYP1A1) in blood lymphocytes - Evidence for catalyticactivity and mRNA expression

Studies initiated to characterise the catalytic activity and expression of CYP1A1 in rat blood lymphocytes revealed significant activity of 7-ethoxyre sorufin-O-deethylase (EROD) in rat blood lymphocytes. Pretreatment with 3-m ethylcholanthrene (MC) and beta -naphthoflavone (NF) resulted in significan t induction in the activity of lymphocyte EROD suggesting that like the liv er enzyme, EROD activity in lymphocytes is inducible and is mediated by the MC inducible isoenzymes of P450. The increase in the activity of EROD was associated with a significant increase in the apparent V-max and affinity o f the substrate towards EROD. That this increase in the activity of EROD co uld be primarily due to the increase in the expression of CYP1A1 isoenzymes was demonstrated by RT-PCR and western immunoblotting studies indicating a n increase in the expression of CYP1A1 in blood lymphocytes after MC pretre atment. Significant inhibition in the EROD activity of MC induced lymphocyt e by anti-CYP1A1/1A2 and alpha -naphthoflavone further provided evidence th at the CYP1A1/1A2 isoenzymes are involved in the activity of EROD in blood lymphocytes. The data indicating similarities in the regulation of CYP1A1 i n blood lymphocytes with the liver isoenzyme suggests that factors which ma y affect expression of CYP1A1 in liver may also affect expression in blood lymphocytes and that blood lymphocytes could be used as a surrogates for st udying hepatic expression of the xenobiotic metabolising enzymes. (C) 2001 Elsevier Science Inc. All rights reserved.