In Vivo Metabolism of Topically Applied Benzo[a]pyrene-4,5-oxide in Neonatal Rat Skin

The metabolism of benzo[a]pyrene (BP)-4,5-oxide in the skin and liver of neonatal rats was studied after topical application of the arene oxide in vivo. The metabolism of BP-4,5-oxide was time-dependent and showed a 2-h maximum for BP-4,5-dihydrodiol formation in both skin and liver. Product formation was also dose-dependent. Inhibitors of epoxide hydrolase such as clotrimazole, 1,1,1,-trichloropropene oxide, and cyclohexene oxide largely abolished the formation of BP-4,5-dihydrodiol. The rapid biotransformation of arene oxides such as BP-4,5-oxide in the skin emphasizes the potential importance of epoxide hydrolase in the activation and inactivation of polycyclic aromatic hydrocarbons. Furthermore, the topically applied arene oxide also penetrated the skin and was rapidly metabolized in the liver as well

The Effect of Psoralens on Hepatic and Cutaneous Drug Metabolizing Enzymes and Cytochrome P-450

Psoralens are tricyclic furocoumarins with potent photosensitizing properties in the skin and are now widely used in the treatment of several dermatologic diseases. In this study the effect of 3 different psoralens 8-methoxypsoralen (8-MOP), 4,5',8-trimethylpsoralen (TMP) and isopsoralen on hepatic microsomal drug-metabolizing enzymes and cytochrome P-450 has been assessed in mice and rats. 8-MOP administered orally to CD-1 mice daily for 6days caused 2–3 fold increases in hepatic aryl hydrocarbon hydroxylase (AHH), ethylmorphine N-demethylase and cytochrome P-450. The absorbance maximum of the induced cytochrome was at 450nm. Aniline hydroxylase activity was unchanged. Chronic administration of 8-MOP, to hairless mice caused significant enhancement of hepatic ethylmorphine N-demethylase and cytochrome P-450 but had no effect on AHH; whereas chronically administered TMP had no significant effect on any of these parameters. Isopsoralen and TMP administered orally to CD-1 mice daily for 6days had no effect on any of these liver enzymes or on hepatic drug-metabolizing enzymes and cytochrome P-450 to a lesser extent than do the barbituaes and suggest that this drug could influence the rate of biotransformation of concomitantly administered drugs in patients undergoing PUVA therapy

STUDIES IN PORPHYRIA

Porphyrin biosynthesis in mammalian skin and in skin obtained from patients with selected types of porphyria has been studied. Cutaneous porphyrinogenesis required the precursor δ-aminolevulinic acid (ALA) which, when added to murine, rat, and human skin in vitro, was rapidly converted to porphyrins. Total porphyrin content was quantitated by fluorescence assay, and spectral studies indicated that more than 80% of the porphyrin produced was protoporphyrin. The majority of skin porphyrinogenesis occurred in epidermis or in epidermal derivatives such as hair roots. Known inducers of hepatic δ-aminolevulinic acid synthetase (ALAS), the rate-limiting enzyme for heme biosynthesis, were not inducers when added to skin in vitro.Skin from patients with acute intermittent porphyria demonstrated a 43% decrease in cutaneous porphyrin production as compared to unaffected normals. This is consistent with the known deficiency of uroporphyrinogen synthetase that has been previously demonstrated in the liver and red blood cells of these patients. Porphyrinogenesis in skin of patients with porphyria cutanea tarda was not different from controls.These studies demonstrate that skin has the enzymatic capacity to synthesize porphyrins from added ALA and that cutaneous porphyrinogenesis from ALA is deficient in patients with acute intermittent porphyria

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) units in normal epidermis and 24.8 ± 2.1 units in epidermis from patients with psoriasis (NS). Following addition of BA (100μM), 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 the AHH reaction was linear up to 60 min and to 50 μg protein, had a pH optimum of 7.4, and the Km for BP was 0.62 MM. 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

Multiple Cytochrome P450 Isozymes in Murine Skin: Induction of P450 1A, 2B, 2E, and 3A by Dexamethasone

Cytochrome P450s (P450s) are a supergene family of enzymes responsible for the metabolism of a wide range of endogenous and foreign compounds. P450 isozymes possess overlapping substrate specificity. Systemic administration of dexamethasone, a widely used topical agent in dermatologic practice, to animals is known to result in the induction of multiple P450 isozymes in liver. In this study the effect of topical application of dexamethasone to mice on P450-dependent monooxygenase activities, expression of P450 isozymes, and P450 mRNA levels in skin was assessed. The treatment of mice with dexamethasone resulted in significant induction of 7-ethoxyresorufin O-deethylase (2.3 times), 7-pentoxyresorufin O-depentylase (19.2 times), para-nitrophenol hydroxylase (7.5 times), and erythromycin N-demethylase (2.2 times) activities; the monooxygenases catalyzed preferentially by P450 isozymes 1A1, 2B1, 2E1, and 3A, respectively. Immunoblot analysis of cutaneous microsomes, employing antibodies directed against purified P450s 1A1/2, 2B1/2, 2E1, and 3A, showed that dexamethasone treatment results in an increased immunoreactivity (1.8 – 13.9 times). In immunohistochemical staining of skin with antibody against P4502B1/2, topical application of dexamethasone resulted in an increased reactivity towards microsomal protein in the suprabasal layer of the epidermis and with the cells of the hair follicles. Whereas constitutive expression of mRNAs for CYP1A1 and CYP2E1 was evident in murine skin, any change in the levels of these mRNAs following treatment with dexamethasone was not apparent. The results of our study indicate that the application of dexamethasone to murine skin results in the induction of several families of P450 isozymes, suggesting that murine skin contains multiple inducible P450 isozymes capable of participating in the metabolism of a wide range of xenobiotics and endogenous compounds

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) units in normal epidermis and 24.8 ± 2.1 units in epidermis from patients with psoriasis (NS). Following addition of BA (100μM), 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 the AHH reaction was linear up to 60 min and to 50 μg protein, had a pH optimum of 7.4, and the Km for BP was 0.62 MM. 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

Immunoprevention of Basal Cell Carcinomas with Recombinant Hedgehog-interacting Protein

Basal cell carcinomas (BCCs) are driven by abnormal hedgehog signaling and highly overexpress several hedgehog target genes. We report here our use of one of these target genes, hedgehog-interacting protein (Hip1), as a tumor-associated antigen for immunoprevention of BCCs in Ptch1+/− mice treated with ionizing radiation. Hip1 mRNA is expressed in adult mouse tissues at levels considerably lower than those in BCCs. Immunization with either of two large recombinant Hip1 polypeptides was well tolerated in Ptch1+/− mice, induced B and T cell responses detectable by enzyme-linked immunosorbent assay, Western blot, delayed type hypersensitivity, and enzyme-linked immunospot assay, and reduced the number of BCCs by 42% (P < 0.001) and 32% (P < 0.01), respectively. We conclude that immunization with proteins specifically up-regulated by hedgehog signaling may hold promise as a preventive option for patients such as those with the basal cell nevus syndrome who are destined to develop large numbers of BCCs

On the physical nature of photon and the modeling of its wave function of free propagation in space and time

In the framework of quantum mechanics the physical nature of the photon is discussed. It is substantiated that a photon is a quantum quasiparticle, the free propagation of which must be considered taking into account the processes in a physical vacuum at Planck distances. For practical purposes on a macroscopic scale, the photon propagation can be modeled using the wave function (wave packet) normalized to the unit probability in the coordinate representation

Kondo time scales for quantum dots - response to pulsed bias potentials

The response of a quantum dot in the Kondo regime to rectangular pulsed bias potentials of various strengths and durations is studied theoretically. It is found that the rise time is faster than the fall time, and also faster than time scales normally associated with the Kondo problem. For larger values of the pulsed bias, one can induce dramatic oscillations in the induced current with a frequency approximating the splitting between the Kondo peaks that would be present in steady state. The effect persists in the total charge transported per pulse, which should facilitate the experimental observation of the phenomenon.Comment: 5 pages with 4 encapsulated figures which come in separate postscript files: latex file: text.tex figures: fig1.eps, fig2.eps, fig3.eps, fig4.ep