Aryl hydrocarbon hydroxylase activity in cultured lymphocytes of psoriatic patients

The metabolism of 2,5-diphenyloxazole (PPO) in human lymphocytes and rat liver microsomes

The oxidative metabolism of 2,5-diphenyloxazole (PPO) is associated with 3-methylcholanthrene inducible cytochrome P-450. The major metabolite formed has m/z of 237, corresponding to hydroxylated PPO. All the possible hydroxylated metabolites of PPO were synthesized and characterized, enabling the assignment of a structure for the major metabolite and two minor metabolites. The metabolites are easily extracted and their fluorescence is quantifiable in alkaline medium with a sample fluorescence to blank fluorescence ratio of 400:1. A sensitive HPLC assay of PPO metabolism was also developed. PPO metabolism is readily catalyzed by 3-methylcholanthrene-induced rat liver microsomes and strongly inhibited by alpha-naphthoflavone, but poorly inhibited by metyrapone or SKF 525A, indicating the involvement of cytochrome P-448 or P1-450 in the metabolism of PPO. With human lymphocytes the method has proven to be a good indicator of "aryl hydrocarbon hydroxylase" (AHH) activity, correlating well with AHH assays using benzo(alpha)pyrene (BP) as a substrate. Both the induced BP and PPO metabolism by human lymphocytes is inhibited by alpha-naphthoflavone, but not by metyrapone.

Aryl hydrocarbon hydroxylase in lymphocytes and lung tissue from lung cancer patients and controls

The inducibility of aryl hydrocarbon hydroxylase (AHH) activity in peripheral mitogen-treated lymphocytes, and of AHH and other monoxygenase activities in lung samples, was studied in 41 patients--34 with pulmonary carcinoma, 4 with a benign lung tumour and 3 with chronic obstructive pulmonary disease. Lymphocyte AHH induction alone was studied in 43 non-smoking and 37 smoking surgical patients. Absolute induced and non-induced AHH activities were at about the same level in the lymphocytes from the lung cancer patients as in those from the non-smoking controls, whereas the activities in smoking controls were about 100% higher. The mean inducibility ratios were very similar in all groups, ranging from 4.4 in the benign tumour patients to 5.4 in both control groups. Thymidine incorporation was on average about 40% lower in the lymphocytes from the lung cancer patients. AHH activity was detectable in all the peripheral lung samples, both normal or tumorous tissue, and its inter-individual variation was more than 67-fold. ECDE activity was also detectable in all the samples studied and its correlation with AHH activity was statistically significant (r = 0.888), suggesting that the same enzyme metabolizes both substrates. ERDE was detectable only in the samples with the highest AHH and ECDE activities. There was no correlation between basal or induced lymphocyte AHH activities and lung tissue AHH activity, but there were statistically significant correlations between lung AHH activity and the inducibility ratio with (r = 0.618) or without correction by thymidine incorporation (r = 0.442). These correlations suggest that there are common regulatory factors for AHH inducibility in different tissues. No significant difference in any drug metabolism parameter measured was observed between the lung cancer patients and the controls.

Aryl hydrocarbon hydroxylase, epoxide hydrolase, and benzo[a]-pyrene metabolism in human epidermis: comparative studies in normal subjects and patients with psoriasis

Prior studies have shown that human skin possesses a cytochrome P-450-dependent microsomal enzyme that is capable of metabolizing drugs and polycyclic aromatic hydrocarbon (PAH) carcinogens. This study characterized benzo[a]pyrene (BP) metabolism in human epidermis of normal and psoriatic individuals. The basal level of the cytochrome P-450-dependent microsomal enzyme aryl hydrocarbon hydroxylase (AHH) and epoxide hydrolase (EH) were measured in freshly keratomed epidermis from 12 normal individuals and from uninvolved skin sites of 12 patients with psoriasis. The induction response of AHH following the in vitro addition of the PAH benz[a]anthracene (BA) was also assessed. The basal activity (mean +/- SE) of AHH in normal epidermis was 62.1 +/- 5.6 units (fmol 3-hydroxybenzo[a]pyrene, 3-OH-BP/min/mg protein) whereas the activity in uninvolved skin of psoriatic individuals was 62.9 +/- 5.1 units (NS), Epoxide hydrolase activity was 25.1 +/- 1.1 (pmol BP 4,5-diol/min/mg protein) unites in normal epidermis and 24.8 +/- 2.1 units in epidermis from patients with psoriasis (NS). Following addition of BA (100 microM), in vitro, AHH activity in normal epidermis increased by a mean value of 165% whereas activity in nonlesional epidermis of psoriatic individuals increased 320%. Kinetic studies in normal epidermis revealed that AHH reaction was linear up to 60 min and to 50 micrograms protein, had a pH optimum of 7.4, and the Km for BP was 0.62 microM. High-performance liquid chromatography (HPLC) confirmed that the pattern of metabolism of BP was quite similar in epidermal microsomes prepared from normal and psoriatic individuals, insofar as the formation of diols, phenols, and quinones was concerned. These studies indicate that human epidermis is capable of metabolizing BP and that there is no significant difference between normal individuals and patients with psoriasis insofar as basal AHH activity or total BP metabolism is concerned. Furthermore, the epidermal enzyme system in patients with psoriasis has a greater responsiveness to environmental PAH than does that of normal individuals.

Alterations in leukocyte aryl hydrocarbon hydroxylase activity associated with treatment and age in psoriasis patients and healthy individuals

We have examined the relationship between topical psoriasis treatment and the activity of the mixed function oxidase, aryl hydrocarbon hydroxylase (AHH), in peripheral blood monocytes and lymphocytes from 20 patients with psoriasis. These data were compared to monocyte and lymphocyte AHH activity measured in 20 normal subjects. AHH activity was determined in cells induced with benzanthracene and in uninduced control cells. Monocyte and lymphocyte AHH activity in six untreated psoriasis patients was similar to that in the healthy controls. AHH activity in either uninduced or induced monocytes showed an increase with age in both the healthy and the untreated psoriatic subjects. Lymphocytes from the healthy subjects showed an age-related decline in enzyme activity. Fourteen patients with psoriasis receiving topical tar and/or topical corticosteroid therapy had significantly higher (P less than 0.05) levels of basal and induced monocyte and lymphocyte AHH activity than the healthy controls. AHH activity is age-related and appears to be controlled differently in monocytes and in lymphocytes. AHH activity in circulating monocytes and lymphocytes may be stimulated by topical tar and/or steroid therapy of psoriasis.

Blood monocyte aryl hydrocarbon hydroxylase activity in psoriasis

The activity of aryl hydrocarbon hydroxylase (AHH) in monocytes from 13 healthy control subjects and in 16 patients with discoid psoriasis was measured. The mean basal monocyte AHH activities of the control and psoriatic groups were 3.4 +/- 0.47 and 4.46 +/- 0.55 respectively (pmol 3-OHBP h-1 10(-6) cells). This difference was not significant. The mean induced monocyte AHH activities in the control and psoriatic groups were 56.4 +/- 10.8 and 77.8 +/- 16.0 pmol 3-OHBP h-1 10(-6) cells respectively but this difference was not significant. The mean induction ratios in the control and psoriatic groups were 16.5 +/- 1.8 and 20.4 +/- 3.6 respectively. Again, this difference was not significant. We conclude therefore, that monocyte aryl hydrocarbon hydroxylase activity is not reduced in psoriasis.