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H Merk

Publications and source records attributed to H Merk.

At least 91 records · Page 5Linked to original sources
PubMed1985

[Current immunological aspects of allergic contact dermatitis].

We give a review of the function of Langerhans' cells and ETAF as well as the influence of UVB irradiation on the presentation of antigens. We than discuss some evidences for the possible involvement of cytochrome P-450 in the processing of antigens (parallelism between carcinogenesis and immunogenicity induced by aromatic hydrocarbons, high inducibility of cytochrome P-450 dependent enzyme activity in human monocytes, significance of compounds with quinone structure as allergens and carcinogenic agents.

Animals↗
PubMed1985

Influence of chloroquine on the porphyrin metabolism.

Rats were treated with the well-known porphyrogen hexachlorobenzene (HCB) to induce experimental porphyria. At the same time another group of rats was treated with chloroquine in addition to HCB. The HCB-induced increase of the urinary excretion of porphyrin precursors could thereby be reduced to normal levels and the porphyrin excretion rates were decreased significantly in comparison to those of the other group. The delta-aminolevulinate synthase in the liver of the animals was slightly increased by exclusive treatment with chloroquine, which in the HCB-treated rats chloroquine led to a dramatic decrease in the key enzyme of the porphyrin (heme)-biosynthesis. The influence of chloroquine on the HCB-induced increase of the cytochrome P-450 content and the dependent enzymatic activities were different. The 7-ethoxycumarin deethylase and the arylhydrocarbon hydroxylase activities were not influenced, whereas the increased aminopyrine-N-demethylase activity was reduced to nearly normal levels. Our findings indicate that chloroquine acts by reduction of the delta-aminolevulinate synthase activity, probably by influencing the regulation of the key enzyme of the heme biosynthesis, which is enhanced in human porphyria cutanea tarda, as well as in the HCB-induced porphyria of the rats.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1985

Influence of (+)-propoxyphene on the hexachlorobenzene-induced porphyria of rats.

The increased urinary porphyrin excretion after hexachlorobenzene (HCB) could be reduced by simultaneous application of (+)-4-(dimethylamino)-3-methyl-1,2-diphenyl-2-butanol propionate ((+)-propoxyphene) to female Wistar rats over a period of 60 days. Total porphyrin excretion and predominantly the higher carboxylated porphyrins, such as uroporphyrin were reduced under the influence of (+)-propoxyphene. (+)-Propoxyphene led to an increase of hepatic cytochrome P-450 content and the cytochrome P-450 dependent enzymes arylhydrocarbon-hydroxylase- and aminopyrine-N-demethylase activities, whereas the 7-ethoxycoumarine-deethylase activity was not changed. The simultaneous treatment of rats with HCB and (+)-propoxyphene decreased the HCB induced cytochrome P-450 content and the aminopyrine-N-demethylase activity. The arylhydrocarbon-hydroxylase activity, however, was increased, whereas no influence on the 7-ethoxycoumarine-deethylase activity could be demonstrated by (+)-propoxyphene treatment of HCB exposed rats. It is under discussion that a reduction of aminopyrine-N-demethylase activity by the drug in the liver alters the HCB metabolism resulting in a reduced production of a probable ultimative porphyrogenic agent.

7-Alkoxycoumarin O-Dealkylase↗
PubMed1985

[Porphyria cutanea tarda (PCT)].

Porphyria cutanea tarda (PCT) can be divided into two genetically determined (hereditary) forms and one acquired type. Hereditary PCT is due to an inborn deficiency of the uroporphyrinogen decarboxylase activity in all tissues. The homozygote defect (porphyria hepatoerythropoetica) involves reduced enzyme activity down to nearly 5%, whereas the hemizygote form causes reduction of the porphyrinogen decarboxylase activity of about 50%, which means that the remaining enzyme activity is still sufficient for normal heme or porphyrin biosynthesis. Only an overload of heme or porphyrin biosynthesis leads to decompensation of the uroporphyrinogen decarboxylase. Substances able to act in this way are: ethanol, lipophilic drugs, xenobiotics, steroid hormones, and iron. Sporadic (acquired) PCT is associated with reduction of the uroporphyrinogen decarboxylase activity in the liver exclusively induced by the above cited chemicals. From these types of PCT, pseudo-PCT (or PCT-like syndrome) must be differentiated. Pseudo-PCT is observed in patients with terminal renal insufficiency under hemodialysis therapy as well as after application of certain drugs. Pseudo-PCT can be separated from PCT by means of porphyrin analysis and histopathological findings.

Chemical and Drug Induced Liver Injury↗
PubMed1985

[Tar treatment of psoriasis].

Tar is generated by dry distillation of coal or wood. Crude coal tar, tar extracts or refined tar products are used for therapy. Tar exerts an antipsoriatic effect by reducing cell proliferation. This effect is enhanced when tar is applied in combination with UV irradiation. The phototoxic reactions induced by several tar components in combination with UV-A cannot be employed for therapeutic purposes, since the painful smarting reaction prevents the application of the large UV-A doses required for therapy. Tar applied together with anthralin has recently been found to decrease the irritative qualities of anthralin. Due to the potential carcinogenic properties of tar, uncontrolled applications are to be avoided.

Anthralin↗
PubMed1985

[Metabolism of foreign substances in human skin and hair follicles].

Human skin has an inducible aryl hydrocarbon hydroxylase (AHH) activity which is dependent on cytochrome P-450. The cutaneous AHH-activity is inhibited by 7,8 benzoflavone but not by metapyrone, whereas recently published data showed that AHH-activity in human liver is enhanced by 7,8 benzoflavone and inhibited by metapyrone. These results suggest that AHH activity of human skin depends on different isoenzymes compared with those in human liver.

Aryl Hydrocarbon Hydroxylases↗
PubMed1985

Influence of N-acetylcysteine on the hexachlorobenzene induced porphyria in rats.

The course of hexachlorobenzene (HCB) induced porphyria was not influenced by the concomitant administration of N-acetylcysteine (NAC) to the animals: urinary excretion of total porphyrins and porphyrin precursors as well as the hepatic aminolevulinate synthase activities were not influenced by NAC treatment. In addition, no differences could be shown between the HCB and the HCB/NAC combination group concerning the hepatic cytochrome P-450 contents or the P-450 dependent enzyme activities.

5-Aminolevulinate Synthetase↗
PubMed1985

[Interactions between theophylline and drug metabolizing liver enzymes in the rat].

Theophylline induces increase of hepatic cytochrome P-450 contents and P-450 dependent polysubstrate monooxygenases (e.g. p-nitroanisol-demethylase, 7-ethoxycoumarin-deethylase) in rats and other animals and in man. The purpose of this study is to investigate the long-term effect of theophylline on hepatic cytochrome P-450 and P-450 dependent enzyme activities in rats. P-450 content is enhanced after 6 days treatment with theophylline (150 mg/kg/d orally), but reaches the initial level after 28 days treatment. However, the P-450 dependent enzyme activities (7-ethoxycoumarin-deethylase, p-nitroanisol-demethylase) remain elevated. The in vitro inhibition of 7-ethoxycoumarin-deethylase by alpha-naphthoflavone and metyrapone suggests a mixed type induction by theophylline. Treatment of the animals with phenobarbital and theophylline or with benzo(alpha)pyrene and theophylline does not lead to an enhancement of P-450 content compared with a treatment solely by phenobarbital or benzo(alpha)pyrene. However, the simultaneous application of theophylline and phenobarbital increases the 7-ethoxycoumarin-deethylase and p-nitroanisol-demethylase activities compared with an exclusive phenobarbital treatment, whereas the benzo(alpha)pyrene effect is not enhanced by theophylline.

Animals↗
PubMed1984

[Hair analysis].

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Diabetes Mellitus↗
PubMed1984

Inducibility of arylhydrocarbon-hydroxylase activity in human hair follicles by topical application of liquor carbonis detergens (coal tar).

Arylhydrocarbon-hydroxylase (AHH) is a cytochrome P-450-dependent polysubstrate mono-oxygenase which plays an important role in converting some compounds (e.g. benzo[a]pyrene) to highly reactive carcinogenic species. A simple AHH assay is described, using [3H]benzo[a]-pyrene as substrate. 7,8-Benzoflavone (10(-4)M) inhibits 92% of the measured enzyme activity. Liquor carbonis detergens (which contains coal tar) induces AHH activity in human hair follicles in vivo. We suggest that using this simple assay, hair follicles would be a very suitable tissue to test whether the AHH-controlling gene is of significance in producing cancer.

Aryl Hydrocarbon Hydroxylases↗
PubMed1984

Influence of 13-cis retinoic acid and of arotinoid on the cytochrome P-450 system in rat liver.

Female Wistar rats were treated with either 13-cis retinoic acid or arotinoidethyl ester in a dose comparable to those used in humans over different periods up to 28 days. In the liver of the animals the following parameters were estimated: microsomal protein content, cytochrome P-450 content, and cytochrome P-450-dependent activities of enzymes such as aminopyrine-N-demethylase, arylhydrocarbon hydroxylase, and 7-ethoxycoumarin deethylase. Only a transitory increase of the aminopyrine-N-demethylase after 3 days of treatment could be demonstrated. From this animal study, there is no evidence of interactions between retinoids and drug-metabolizing monooxygenases, e.g., the metabolism of contraceptive active steroids.

7-Alkoxycoumarin O-Dealkylase↗