Cutaneous estradiol permeation, penetration and metabolism in pig and man.

AIM AND METHODS: Drug development in dermatotherapy and also development of transdermal therapeutic systems (TTS) demand high-predictive in vitro models to estimate drug levels in skin and systemic uptake. Here we compare three ready-to-use models, reconstructed human epidermis, split porcine skin and the perfused porcine forelimb. 17beta-Estradiol (E(2)), which is highly metabolized by skin cells, serves as model drug since E(2) application is of high relevance in hormone replacement therapy while topical E(2) may promote wound healing. E(2) TTS, gel and an ethanolic solution were investigated for cutaneous penetration, permeation and metabolism. RESULTS: E(2) TTS enabled an E(2) uptake of 42.9% of the applied dose accompanied by a high percentage of E(2) metabolism (30% of the penetrated dose) in the perfused porcine forelimb. In Franz cell experiments with reconstructed human epidermis and split porcine skin, the gel allowed an E(2) uptake of 41.7 and 22.9% of the applied dose accompanied by a high E(2) metabolism (42.6 and 28.6% of the penetrated dose). Due to toxic effects of the vehicle, this was not true with an ethanolic solution, then E(2) permeation and metabolism were clearly diminished. Most importantly, the in vitro models proved to be predictive with respect to the E(2)/estrone ratio in female plasma under transdermal hormone replacement therapy. CONCLUSION: In vitro tests should reduce the need for both animal and human studies for cutaneous uptake and metabolism in the future.

Transient experimental anemia in cholesterol-fed rabbits induces systemic overexpression of the reticulocyte-type 15-lipoxygenase and protects from aortic lipid deposition.

Oxidative modification of low-density lipoprotein has been implicated in atherogenesis and the lipid peroxidizing enzyme 12/15-lipoxygenase (12/15-LOX) was suggested to be involved. For this study, we induced a strong and long-lasting systemic overexpression of the 15-LOX, in female New Zealand White rabbits by transient experimental anemia. After the hematopoietic parameters had returned to normal, these animals and age-matched controls were fed a lipid-rich Western-type diet for 10 weeks. Analyzing the lipid deposition in the aortic wall, we found that the 15-LOX overexpressing rabbits deposited significantly (P<0.01) less cholesteryl linoleate in the thoracic aorta than the corresponding controls. Similar results were obtained when free cholesterol and cholesteryl oleate were quantified. However, in the aortic arch where lipid deposition was much more severe a similar trend was observed, but the effects were not significant any more. Comparative determination (lipoxygenase overexpressing vs. control animals) of various plasma parameters as well as histological inspections of major organs did not reveal any indications for major organ malfunction. These data suggest that transient experimental anemia, which is accompanied by a long-lasting overexpression of the reticulocyte-type 15-LOX protects cholesterol-fed rabbits from lipid deposition in the aortic wall.

Oxidation of LDL by rabbit and human 15-lipoxygenase: prevalence of nonenzymatic reactions.

15-Lipoxygenase (15-LO)-induced oxidation of lipids in human LDL may be pro-atherogenic. However, the extent to which 15-LO promotes enzymatic oxidation of esterified (i.e., major) lipids in LDL may depend on various factors. Here, we show that overall, LDL lipid oxidation was favored with high activity of human 15-LO, that phospholipids were the preferred esterified substrate, and that low temperature maintained a higher proportion of enzymatic product. However, under all conditions, 15-LO induced alpha-tocopherol consumption and the accumulation of nonenzymatic products that predominated with increasing time of incubation and inactivation of the enzyme. Lysates prepared from cells overexpressing human 15-LO oxidized linoleic acid readily and in an almost exclusive enzymatic manner. In sharp contrast, such lysates failed to oxidize LDL lipids unless linoleic acid was added, in which case nonenzymatic oxidation of LDL lipids occurred. We conclude that although purified 15-LO can oxidize isolated LDL lipids in vitro, such oxygenation always includes nonenzymatic reactions that likely play a major role in the more extensive oxidation of LDL by cell-derived 15-LO.

Regulation of cellular 15-lipoxygenase activity on pretranslational, translational, and posttranslational levels.

In mammalian cells, enzymatic lipid peroxidation catalyzed by 12/15-lipoxygenases is regulated by pretranslational, translational, and posttranslational processes. In rabbits, rats, and mice induction of experimental anemia leads to a systemic up-regulation of 12/15-lipoxygenases expression. In addition, interleukins-4 and -13 were identified as strong up-regulators of this enzyme in human and murine monocyte/macrophages and in the lung carcinoma cell line A549, and the interleukin-4(13) cell surface receptor as well as the signal transducer and activator of transcription 6 (STATG) appears to be involved in the signal transduction cascade. On the level of translation, 15-lipoxygenase synthesis is blocked by the binding of regulatory proteins to a characteristic guanine-cytosine-rich repetitive element in the 3'-untranslated region of the rabbit 15-lipoxygenase mRNA, and the formation of such 15-lipoxygenase mRNA/protein complexes was identified as molecular reason for the translational inactivity of the 15-lipoxygenase mRNA in immature red blood cells. However, proteolytic breakdown of the regulatory proteins which were recently identified as hnRNP K and hnRNP E1 overcomes translational inhibition during later stages of reticulocyte maturation. For maximal intracellular activity, 12/15-lipoxygenases require a rise in cytosolic calcium concentration inducing a translocation of the enzyme from the cytosol to cellular membranes as well as small amounts of preformed hydroperoxides which act as essential activators of the enzymes. 12/15-Lipoxygenases undergo irreversible suicide inactivation during fatty acid oxygenation, and this process may be considered an element of down-regulation of enzyme activity. Suicide inactivation and proteolytic breakdown may contribute to the disappearance of functional 12/15-lipoxygenase at later stages of erythropoiesis.

Interleukin-4 and -13 induce upregulation of the murine macrophage 12/15-lipoxygenase activity: evidence for the involvement of transcription factor STAT6.

When human monocytes or alveolar macrophages are cultured in the presence of interleukin (IL)-4 or IL-13, the expression of the reticulocyte-type 15-lipoxygenase is induced. In mice a 15-lipoxygenase is not expressed, but a leukocyte-type 12-lipoxygenase is present in peritoneal macrophages. To investigate whether both lipoxygenase isoforms exhibit a similar regulatory response toward cytokine stimulation, we studied the regulation of the leukocyte-type 12-lipoxygenase of murine peritoneal macrophages by interleukins and found that the activity of this enzyme is upregulated in a dose-dependent manner when the cells were cultured in the presence of the IL-4 or IL-13 but not by IL-10. When peripheral murine monocytes that do not express the lipoxygenase were treated with IL-4 expression of 12/15-lipoxygenase mRNA was induced, suggesting pretranslational control mechanisms. In contrast, no upregulation of the lipoxygenase activity was observed when the macrophages were prepared from homozygous STAT6-deficient mice. Peritoneal macrophages of transgenic mice that systemically overexpress IL-4 exhibited a threefold to fourfold higher 12-lipoxygenase activity than cells prepared from control animals. A similar upregulation of 12-lipoxygenase activity was detected in heart, spleen, and lung of the transgenic animals. Moreover, a strong induction of the enzyme was observed in red cells during experimental anemia in mice. The data presented here indicate that (1) the 12-lipoxygenase activity of murine macrophages is upregulated in vitro and in vivo by IL-4 and/or IL-13, (2) this upregulation requires expression of the transcription factor STAT6, and (3) the constitutive expression of the enzyme appears to be STAT6 independent. The cytokine-dependent upregulation of the murine macrophage 12-lipoxygenase and its induction during experimental anemia suggests its close relatedness with the human reticulocyte-type 15-lipoxygenase despite their differences in the positional specificity of arachidonic acid oxygenation.

Membrane translocation of 15-lipoxygenase in hematopoietic cells is calcium-dependent and activates the oxygenase activity of the enzyme.

Mammalian 15-lipoxygenases, which have been implicated in the differentiation of hematopoietic cells are commonly regarded as cytosolic enzymes. Studying the interaction of the purified rabbit reticulocyte 15-lipoxygenase with various types of biomembranes, we found that the enzyme binds to biomembranes when calcium is present in the incubation mixture. Under these conditions, an oxidation of the membrane lipids was observed. The membrane binding was reversible and led to an increase in the fatty acid oxygenase activity of the enzyme. To find out whether such a membrane binding also occurs in vivo, we investigated the intracellular localization of the enzyme in stimulated and resting hematopoietic cells by immunoelectron microscopy, cell fractionation studies and activity assays. In rabbit reticulocytes, the 15-lipoxygenase was localized in the cytosol, but also bound to intracellular membranes. This membrane binding was also reversible and the detection of specific lipoxygenase products in the membrane lipids indicated the in vivo activity of the enzyme on endogenous substrates. Immunoelectron microscopy showed that in interleukin-4 -treated monocytes, the 15-lipoxygenase was localized in the cytosol, but also at the inner side of the plasma membrane and at the cytosolic side of intracellular vesicles. Here again, cell fractionation studies confirmed the in vivo membrane binding of the enzyme. In human eosinophils, which constitutively express the 15-lipoxygenase, the membrane bound share of the enzyme was augmented when the cells were stimulated with calcium ionophore. Only under these conditions, specific lipoxygenase products were detected in the membrane lipids. These data suggest that in hematopoietic cells the cytosolic 15-lipoxygenase translocates reversibly to the cellular membranes. This translocation, which increases the fatty acid oxygenase activity of the enzyme, is calcium-dependent, but may not require a special docking protein.

In vivo action of 15-lipoxygenase in early stages of human atherogenesis.

Oxidative modification of low density lipoprotein has been suggested as patho-physiologically relevant process in atherogenesis and the lipid peroxidizing enzyme 15-lipoxygenase may be involved. For experimental evidence on the in vivo action of this enzyme in the time course of plaque formation we analyzed the lipid extracts of lesional areas representing various stages of human atherogenesis for the occurrence of specific 15-lipoxygenase products. In advanced human lesions the degree of oxygenation of the lesion lipids measured as hydroxy linoleic acid/linoleic acid ratio varied between 0.2 and 3.2%. Here an unspecific pattern of oxygenated lipids that did not differ from the pattern formed during copper-catalyzed LDL oxidation was detected. In both cases an enantiomer ratio (S/R-ratio) of 13-hydroxy-9Z,11E-octadecadienoic acid (13-HODE) of approximately 1:1 was found. In young human lesions which were obtained from the collection of the pathological determinants of atherosclerosis in youth (PDAY) program the hydroxy linoleic acid/linoleic acid ratio was much smaller (variation between 0.05 and 0.6%), and a significant share of specific 15-lipoxygenase products was detected (S/R-ratio of 13-hydroxy linoleic acid of 54 +/- 3.1/46 +/- 3.1 [mean +/- SD]). These data suggest that the 15-lipoxygenase is enzymatically active on endogenous substrates in young human lesions and thus, may be of patho-physiological importance for early atherogenesis. In advanced human plaques the 15-lipoxygenase may be functionally silent and specific lipoxygenase products formed in earlier stages may be decomposed or superimposed by large amounts of nonenzymatic lipid peroxidation products.

Regulation of 15-lipoxygenase expression in lung epithelial cells by interleukin-4.

We have studied the expression of the 15-lipoxygenase gene in various permanent mammalian cell lines in response to interleukins-4 and -13, and found that none of the cell lines tested expressed 5-, 12- or 15-lipoxygenase when cultured under standard conditions. However, when the lung carcinoma cell line A549 was maintained in the presence of either interleukin for 24 h or more, we observed a major induction of 15-lipoxygenase, as indicated by quantification of 15-lipoxygenase mRNA, by immunohistochemistry, by immunoblot analysis and by enzyme activity assays. This effect was 15-lipoxygenases-specific, since expression of 5- and 12-lipoxygenases remained undetectable. The time course of interleukin-4 treatment indicated maximal accumulation of both 15-lipoxygenase mRNA and functional protein after 48 h. Binding studies revealed that A549 cells express about 2100 high-affinity interleukin-4 binding sites per cell. The interleukin-4 mutant Y124D, which is capable of binding to the interleukin-4 receptor but is unable to trigger receptor activation, counteracted the effect of the wild-type cytokine. Other cell lines, including several epithelial cells and various monocytic cell lines expressing comparable numbers of interleukin-4 receptors, did not express 15-lipoxygenase when stimulated with interleukin-4. These data indicate that A549 cells selectively express 15-lipoxygenase when stimulated with interleukins-4 and -13. The activation of the interleukin-4/13 receptor(s) appears to be mandatory, but not sufficient, for 15-lipoxygenase gene expression.

Prenatal hypoxia alters the postnatal development of beta-adrenoceptors in the rat myocardium.

The effect of prenatal hypoxia on the development of the beta-adrenoceptor during the ontogenesis of rats was investigated. It was shown that the offspring from hypoxic dams, in comparison with normoxic control animals, exhibited alterations of the density (Bmax) of the myocardial beta-receptors and of the catecholamine levels in heart tissue during development. The results suggest that the beta-adrenoceptor changes might be involved in the phenomenon of enhanced sensitivity of prenatal hypoxic animals to catecholamines in adult age.

The catecholamine sensitivity of adult rats is enhanced after prenatal hypoxia.

In this study, the effect of prenatal hypoxia on the catecholamine sensitivity of the offspring of pregnant rats was investigated. The offspring from hypoxic animals showed after treatment with isoproterenol in adult age a distinctly more pronounced decrease of protein content and enzyme activities in heart tissue as well as a significantly higher elevation of enzyme activities in blood plasma as compared with the offspring from normoxic rats. These results suggest a long-lasting enhancement of catecholamine sensitivity after prenatal oxygen deficiency.

Arachidonic acid metabolism in cultured adult myocardial cells under short-time hypoxic conditions.

The present study utilized a cultured adult myocardial cell model to examine the arachidonic acid metabolism under different cell-damaging and normoxic conditions. Cell injury was caused by short-time hypoxia, calcium ionophore A 23187-triggered cell-damage under hypoxia and cell disruption by freezing and thawing. The current study demonstrates that under the cell-damaging conditions cultured adult heart myocytes resemble myocardial cells under normoxic conditions in metabolizing arachidonic acid into triacylglycerols and phospholipids as the major route (a), in formation of ETYA-inhibitable indomethacin-resistant lipid metabolites in minor amounts (b) and in being independent of calcium overload in the metabolic pathways of arachidonic acid metabolism (c). The ETYA-inhibitable components were resolved by HPLC. There was no evidence in formation of lipoxygenase products. The results were supported by negative hybridisation experiments of the total mRNA isolated from adult myocardial cells with a cDNA probe of a red-cell-specific lipoxygenase mRNA. We conclude from these observations that cell injury does not result in expression of lipoxygenase activities in heart myocytes.

On the reaction of wheat lipoxygenase with arachidonic acid and its oxygenated derivatives.

Lipoxygenase was purified from wheat kernels by means of ammonium sulfate precipitation, gel chromatography on Sephadex G-200 and anion exchange chromatography on DEAE-Sephadex A-50. Arachidonic acid was mainly converted by the wheat lipoxygenase to 5D-hydroperoxy-6E,8Z,11Z,14Z-eicosatetraenoic acid (5D8-HPETE) with other HPETE isomers including 8-HPETE being minor products. At higher concentrations of lipoxygenase, multiple oxygenation products such as 5,15-dihydroxyeicosatetraenoic acid (5,15-diHETE) and, to a lower extent, 8,15-diHETE and lipoxin isomers were detected after reduction of the hydroperoxy derivatives primarily formed. Similar results were obtained with 5D8- or 15L8-hydroxyeicosatetraenoic acid as substrate. Moreover, evidence was obtained for leukotriene A4 synthase activity of the wheat lipoxygenase.

On the mechanistic reasons for the dual positional specificity of the reticulocyte lipoxygenase.

A set of octadecadienoic acid isomers and selected eicosatrienoic acids were tested as substrates for the lipoxygenases from soybeans and reticulocytes. Among the dienoic fatty acids, 8Z,11Z-octadecadienoic acid containing a n - 9 doubly allylic methylene group turned out to be the best substrate for the reticulocyte enzyme. This substrate was converted to its corresponding n - 7 hydroperoxy derivative. The soybean lipoxygenase, in contrast, prefers the 9Z,12Z-octadecadienoic acid (linoleic acid) which is oxygenated to its n - 6 hydroperoxy derivative. In both cases a strong preference for the LS-isomer has been observed. Analysis of the oxygenation products formed from various eicosatrienoic acids indicated that 8Z,11Z,14Z-eicosatrienoic acid was converted by the reticulocyte enzyme to its 12S- and 15S-hydroperoxy derivative in a ratio of about 1:7 (dual positional specificity), whereas the 7Z,10Z,13Z-isomer was oxygenated predominantly (greater than 97%) to its 14S-hydroperoxy derivative (singular positional specificity). 9Z,12Z,15Z-eicosatrienoic acid was oxygenated with a dual positional specificity to the corresponding 13- and 16-hydroperoxy compounds in a ratio of about 7:1. The soybean lipoxygenase converts the 8Z,11Z,14Z-isomer with a singular positional specificity to the corresponding 15S-hydroperoxy derivatives. The 9Z,12Z,15Z-eicosatrienoic acid, however, was oxygenated with a dual positional specificity to its 13S-hydroperoxy and 16S-hydroperoxy derivative in a ratio of about 1:4.

Improved procedure for the detection of activity of lipoxygenases on electropherograms.

Several procedures for activity staining of lipoxygenases were compared. The best results were obtained with the o-dianisidine method of De Lumen and Kazeniac which had to be modified, however, with respect to the conditions of electrophoretic separation, treatment of the gel after separation, incubation conditions and staining solution, to achieve satisfactory detection of the lipoxygenases from wheat grains, pea seeds, soybeans and rabbit reticulocytes.