POTENT INTERACTION OF HISTAMINE AND POLYAMINES AT MICROSOMAL CYTOCHROME-P450, NUCLEI, AND CHROMATIN FROM RAT HEPATOCYTES

Histamine and polyamines have been implicated ir the mediation of cell proliferation. Our previous work linked the growth-modulatory effects of histamine with its binding to intracellular sites in microsomes an d nuclei of various tissues. In this study, we identify cytochrome P45 0 enzymes as a major component of microsomal intracellular sites in he patocytes and demonstrate that polyamines compete with high affinity f or histamine binding to them. Spectral measurement of histamine bindin g to P450 in liver microsomes resolved high and intermediate affinity binding sites (K-s1 = 2.4 +/- 1.6 mu M; K-s2 = 90 +/- 17 mu M) that co rresponded to microsomal binding sites (K-d1 = 1.0 +/- 0.9 mu M; K-d2 = 57 +/- 13 mu M) resolved by H-3-histamine binding; additional low af finity (K-d3 similar to 3 mM), and probably physiologically irrelevant , sites were resolved only by H-3-histamine radioligand studies. As de termined spectrally, treatment of microsomes with NADPH/carbon monoxid e decreased histamine binding to P450 by about 90% and, as determined by H-3-histamine binding, abolished the high affinity sites and reduce d by 85% the number of intermediate sites. Spermine competed potently for H-3-histamine binding: in microsomes, K-i = 9.8 +/- 5.8 mu M; in n uclei, K-i = 13.7 +/- 3.1 mu M; in chromatin, K-i = 46 +/- 33 nM. Poly amines inhibited the P450/histamine absorbance complex with the rank o rder of potency: spermine > spermidine much greater than putrescine. I n contrast, histamine did not compete for H-3-spermidine binding in nu clei or microsomes, suggesting that polyamines modulate histamine bind ing allosterically. We propose that certain P450 isozymes that modulat e gene function by controlling the level of oxygenated lipids, represe nt at least one common intracellular target of growth-regulatory endog enous bioamines and, as shown previously, of exogenous growth-modulato ry drugs including antiestrogens, antiandrogens, and certain antidepre ssants and antihistamines. (C) 1998 Wiley-Liss, Inc.