Differential susceptibilities of the prosthetic heme of hemoglobin-based red cell substitutes. Implications in the design of safer agents

One approach to the development of an effective red cell substitute has been chemical modification of human hemoglobin to optimize oxygen transport and plasma half-life. Human hemoglobin A0 and two of these modified hemoglobins, one prepared from the cross-linking of the alpha-chains at lysine residue 99 by bis(3,5-dibromosalicyl)fumarate (Hb-DBBF) and the other by acylation of lysine residue 82 of the beta-chain by mono-(3,5-dibromosalicyl)fumarate (Hb-FMDA), were tested by HPLC for their susceptibility to oxidative damage caused by H2O2. Such oxidative insult may occur during ischemia and reperfusion of tissues after transfusion of red cell substitutes to patients with hypovolemic shock and trauma. Hb-DBBF was extremely susceptible to damage of its heme and protein moieties with stoichiometric amounts of H2O2, whereas Hb-FMDA was highly resistant, even at 10-fold molar excess and at an acidic pH of 4.7. Hemoglobin A0 was of intermediate susceptibility, exhibiting alteration of heme and protein moieties at acidic but not neutral pH. Since the degradation of heme can release the potentially toxic agent iron, Hb-FMDA may be a more promising candidate than Hb-DBBF for development as a red cell substitute. A similar approach may be used to assess the susceptibility of other hemoglobin-based red cell substitutes to oxidative damage in order to determine the molecular basis of heme and protein alteration.

Immunolocalization of steroidogenic enzymes, P450scc, 3 beta-HSD, P450c17, and P450arom in the Hokkaido brown bear (Ursus arctos yesoensis) testis

Hokkaido brown bears (Ursus arctos yesoensis) are seasonal breeders and the profile of their serum testosterone concentrations undergoes annual changes. However, precise sites of steroidogenesis in the bear testis have not been identified. Therefore, our objective was to localize steroidogenic enzymes by immunocytochemistry using polyclonal antibodies generated against steroidogenic enzymes of mammalian origin. The steroidogenic enzymes localized were cholesterol side-chain cleavage cytochrome P450 (P450scc), 3 beta-hydroxysteroid dehydrogenase (3 beta-HSD), 17 alpha-hydroxylase cytochrome P450 (P450c17), and aromatase cytochrome P450 (P450arom) as biosynthetic sites of pregnenolone, progesterone or androstenedione, androgens, and estrogens, respectively. Testes were collected from three adult bears prior to the mating season (April, Hokkaido, Japan) and prepared for immunostaining with primary antibodies, followed by an avidin-biotin-peroxidase method. P450scc was localized in Leydig cells and spermatids. 3 beta-HSD was found only in Leydig cells. P450c17 was identified in Leydig cells and spermatids. Finally, P450arom was found in Leydig cells and in spermatids that stained very intensely. Therefore, Leydig cells appear to be a site of progestin (both delta 4 and delta 5 C21 steroids), androgen, and estrogen production, whereas spermatids appear to be a site of pregnenolone, androgen, and estrogen production. Immunolocalization of steroidogenic enzymes suggests that steroidogenesis may occur not only in Leydig cells, but also in spermatids of the Hokkaido brown bear testis prior to the mating season. We also suggest that Leydig cells and spermatids are the predominant sites of androgen and estrogen synthesis, respectively, in the Hokkaido brown bear testis.

Immunohistochemical localization of 17 alpha-hydroxylase/C17-20 lyase and aromatase cytochrome P-450 in polycystic human ovaries

Immunohistochemical localization of 17 alpha-hydroxylase/C17-20 lyase (P-450(17 alpha,lyase)) and aromatase cytochrome P-450 (P-450arom) in polycystic ovary (PCO) syndrome was studied using specific polyclonal antibodies which had been raised against the corresponding enzymes. In the majority of follicles that were atretic and smaller than 7 mm in diameter, theca interna cells showed high P-450(17 alpha,lyase) immunoreaction, while small numbers of granulosa cells showed little P-450arom immunoreaction. In some atretic follicles that were larger than 11 mm in diameter, the hyperplastic theca interna cell layer showed high immunoreaction to P-450(17 alpha,lyase), while the poorly proliferated granulosa cell layer showed a mixture of weak and negative immunoreaction to P-450arom. No immunoreaction to P-450(17 alpha,lyase) or P-450arom was recognized in PCO stroma. These findings suggest that the theca interna cells and the granulosa cells from PCOs show abnormal steroidogenic function, while the localization of P-450(17 alpha,lyase) and P-450arom in PCOs was essentially identical to that in the normal ovary. Theca interna cells in PCO atretic follicles are the main site of excess androgen production.

Phencyclidine, a psychotomimetic agent and drug of abuse, is a suicide inhibitor of brain nitric oxide synthase

Phencyclidine, 1-(1-phenylcyclohexyl)piperidine, was shown in this study to be an effective irreversible inhibitor of brain nitric oxide synthase, the enzyme responsible for the conversion of L-arginine to nitric oxide. The inactivation of nitric oxide synthase was time- and concentration-dependent and required reduced nicotinamide adenine dinucleotide phosphate, a necessary cofactor for nitric oxide synthesis. These results indicate that phencyclidine is metabolized by nitric oxide synthase to reactive intermediates that irreversibly inactivate the enzyme. The inactivation of nitric oxide synthase by xenobiotics, such as phencyclidine, may be pharmacologically and toxicologically important due to the role of nitric oxide in a variety of physiological processes.

Cigarette smoking during pregnancy lowers aromatase cytochrome P-450 in the human placenta

To clarify whether cigarette smoking during pregnancy causes an organic alteration in placental estrogen producing ability, we determined the catalytic activity of aromatase by the tritiated water assay, and tissue level of aromatase cytochrome P-450 (P-450arom) by the specific enzyme-linked immunosorbent assay, in placental samples from nonsmokers and smokers. As pregnancy progressed, both aromatase activity and P-450arom concentration increased in placentas from nonsmokers and smokers. However, the gradient of the increase was significantly less in heavy smokers (> or = 20 cigarettes a day) than in normal and moderate smokers (< 20 cigarettes a day). At term, the mean aromatase activity and P-450arom concentration in placentas from heavy smokers were significantly lower than in nonsmokers and moderate smokers, while aromatase activity per P-450arom (turnover rate) and the mean placental weight were comparable among the three groups. In contrast, the ratio of aryl hydrocarbon hydroxylase activity to aromatase activity was higher in placentas from heavy smokers. Immunohistochemical studies showed that P-450arom was localized in the cytoplasm of syncytiotrophoblasts of chorionic villi in placentas from both nonsmokers and smokers. These results suggest that the induction of placental P-450arom during gestation is suppressed by maternal smoking, resulting in a reduction in estrogen producing ability, while placental xenobiotic P-450 is induced.

Catalytic efficiency of expressed aromatase following site-directed mutagenesis

Mutant aromatase cytochrome P-450s, expressed in CHO cells after transfection with cDNAs, have been characterized in terms of their catalytic efficiencies. After solubilization from microsomes, specific aromatase P-450 content of wild-type and mutants Pro308Phe, Asp309Asn, Asp309Ala and Phe406Arg was quantitated by a sandwich enzyme-linked immunosorbent assay (ELISA). Microsomal aromatase activity was determined by the 3H-water method using [1 beta-3H]androstenedione as substrate. Estimations of the actual turnover rate (catalytic efficiency) were derived from the combined data. The P-450 content in the mutants varied but was always less than that in the wild type. Hence, the decreases in the Vmax observed in the mutant enzymes did not correlate completely with reductions in catalytic effectiveness. In recent studies on the structure-function relationship of aromatase cytochrome P-450, the observed reduction of enzyme activity in terms of Vmax following site-directed mutagenesis led to the assumption that there was a corresponding loss of catalytic effectiveness. The present study reveals that a lower P-450 content can contribute significantly to decreasing catalytic activity in the mutants. In fact, in mutant Phe406Arg which exhibited virtually no catalytically active aromatase, the specific P-450 content was below the detectable level. Because of its location, the result of this latter mutation could be a major structural perturbation of the heme-binding property. Thus, interpretation of losses and reductions in aromatase activity resulting from single amino-acid replacement should take into account changes in the specific content of aromatase cytochrome P-450.

Competitive product inhibition of aromatase by natural estrogens

In order to better understand the function of aromatase, we carried out kinetic analyses to assess the ability of natural estrogens, estrone (E1), estradiol (E2), 16 alpha-OHE1, and estriol (E3), to inhibit aromatization. Human placental microsomes (50 micrograms protein) were incubated for 5 min at 37 degrees C with [1 beta-3H]testosterone (1.24 x 10(3) dpm 3H/ng, 35-150 nM) or [1 beta-3H,4-14C]androstenedione (3.05 x 10(3) dpm 3H/ng, 3H/14C = 19.3, 7-65 nM) as substrate in the presence of NADPH, with and without natural estrogens as putative inhibitors. Aromatase activity was assessed by tritium released to water from the 1 beta-position of the substrates. Natural estrogens showed competitive product inhibition against androgen aromatization. The Ki of E1, E2, 16 alpha-OHE1, and E3 for testosterone aromatization was 1.5, 2.2, 95, and 162 microM, respectively, where the Km of aromatase was 61.8 +/- 2.0 nM (n = 5) for testosterone. The Ki of E1, E2, 16 alpha-OHE1, and E3 for androstenedione aromatization was 10.6, 5.5, 252, and 1182 microM, respectively, where the Km of aromatase was 35.4 +/- 4.1 nM (n = 4) for androstenedione. These results show that estrogen inhibit the process of androgen aromatization and indicate that natural estrogens regulate their own synthesis by the product inhibition mechanism in vivo. Since natural estrogen binds to the active site of human placental aromatase P-450 complex as competitive inhibitors, natural estrogens might be further metabolized by aromatase. This suggests that human placental estrogen 2-hydroxylase activity is catalyzed by the active site of aromatase cytochrome P-450 and also agrees with the fact that the level of catecholestrogens in maternal plasma increases during pregnancy. The relative affinities and concentration of androgens and estrogens would control estrogen and catecholestrogen biosynthesis by aromatase.

Structure-function studies of human aromatase

Site-directed mutagenesis experiments have been carried out to determine the structure-function relationship of human aromatase. By sequence comparison, the region in aromatase that corresponds to the distal helix of cytochrome P-450cam has been identified to be Gln-298 to Val-313. Eight aromatase mutants with changes in this region, i.e. C299A, E302L, P308F, D309N, D309A, T310S, T310C, and S312C, have been generated using a mammalian cell stable-expression system. The results from site-directed mutagenesis studies indicate that the region containing Gln-298 to Val-313 is indeed a very important part of the active site of aromatase. The catalytic properties of P308F, D309N, and D309A have been examined in detail and are discussed. Active site-directed labeling is also an important approach to investigate the structure-function relationship of aromatase. HPLC-linked electrospray mass spectrometry is indicated as a useful technique for the characterization of active site-directed probe-modified enzyme. The mass spectral analysis of aromatase suggests that aromatase is glycosylated.

Studies on the mechanism of aromatase and other cytochrome P450 mediated deformylation reactions

Aromatase is a microsomal cytochrome P450 that converts androgens to estrogens by three sequential oxidations. The isolation of the 19-hydroxy and 19-oxo androgens suggests that the first two oxidations occur at the C19 carbon. However, the mechanism of the third oxidation, which results in C10--C19 bond cleavage, has not been determined. Two proposed mechanisms which remain viable involve either initial 1 beta-hydrogen atom abstraction or addition of the ferric peroxy anion from aromatase to the C19 aldehyde. Semiempirical molecular orbital calculations (AM1) were used to study potential reaction mechanisms initiated by initial 1 beta-hydrogen atom abstraction. Initially, the energetics of carbon--carbon bond cleavage of the keto and enol forms of C1-radicals were studied and were found to be energetically similar. A mechanism was proposed in which the 19-oxo intermediate is subject to initial nucleophilic attack by the protein. The geometry of the A-ring in the androgens is between that for the 1-radicals and estrogen, suggesting that some transition state stabilization for the homolytic cleavage reaction can occur. More recently, studies on liver microsomal cytochrome P450 mediated deformylation of xenobiotic aldehydes supports mechanisms involving an alkyl peroxy intermediate formed by addition of the ferric peroxy anion from aromatase to the C19 aldehyde. Although this intermediate could proceed through several different concerted or non-concerted pathways, one non-concerted pathway involves the heterolytic cleavage of the dioxygen bond resulting in an active oxygenating species (iron-oxene) and a diol. The diol could then undergo hydrogen atom abstraction followed by homolytic carbon--carbon bond cleavage as in the mechanisms modeled previously. When this cleavage was modeled for seven aldehydes, a good correlation with reported experimental aldehyde turnover numbers was obtained. However, when dialkoxy derivatives of the aldehydes are subject to microsomal metabolism, the rates of carbon-carbon cleavage products do not approach the rates of deformylation of the aldehyde analog.

An aromatase-associated cytoplasmic inclusion, the "stigmoid body," in the rat brain: II. Ultrastructure (with a review of its history and nomenclature)

The ultrastructure of aromatase-associated "stigmoid (dot-like) structures," which were detected in a previous study using light-microscopic immunohistochemistry (Shinoda et al.: J. Comp. Neurol. 322:360-376, '92), were examined in the rat medial preoptic region, bed nucleus of the stria terminalis, medial amygdaloid nucleus, and arcuate nucleus by pre- and post-embedding marking with a polyclonal antibody against human placental antigen X-P2 (hPAX-P2) for immuno-electron microscopic analysis. The immunoreactive stigmoid structure was identified as a distinct, non-membrane-bounded cytoplasmic inclusion (approximately 1-3 microns in diameter), which has a granulo-fuzzy texture with moderate-to-low electron density in non-immunostained preparations. It consists of at least four distinct granular and three distinct fibrillo-tubular elements forming a granulo-fibrillar conglomerate. This type of inclusions was formally termed the "stigmoid body" under the electron microscope. The stigmoid body is composed of the outer granulo-fibrillar and inner hyaloplasmic compartments. The immunoreactivity for hPAX-P2 is mainly localized to the former, especially to the low density granulo-fuzzy materials associated with the fibrillo-tubular elements. Identification of the ultrastructure of stigmoid body clarified their prevalence not only in the limbic and hypothalamic regions, but also in sex-steroid-sensitive peripheral tissues (e.g., peripheral sensory ganglia, ovary, testis) by consulting earlier electron-microscopic studies. Reviewing the history and nomenclature of this inclusion body, we reorganized the terminology of related neuronal cytoplasmic inclusions, the terms of which have often been confused, and discussed its functional significance on the basis of the present and previously accumulated data. In conclusion, we emphasized the importance of the stigmoid bodies in the sex-steroid-sensitive neural system because of their large size, high frequency, specific distribution in brains and peripheral tissues, effects of sex-steroids, and immunological and histochemical characteristics of the antibody marking the inclusion. The stigmoid bodies may provide a subcellular site for sex-steroid metabolism in their target tissues and play a critical role in cytosolic modulation of their actions (e.g., by aromatization) prior to their receptor binding.

Germ cells of the mouse testis express P450 aromatase

Estrogen production within the testis has been a subject of considerable controversy for many years. Several studies have shown that both Sertoli and Leydig cells produce estrogen during different stages of development. Therefore, we have conducted experiments to localize aromatase, a cytochrome P450 enzyme that converts androgen to estrogen, within the testis. First, P450 aromatase (P450arom) was localized in germ cells of the adult mouse testis by immunocytochemistry, using an antiserum generated against purified human placental cytochrome P450arom. In the germinal epithelium, P450arom was located primarily in the Golgi region of round spermatids, throughout the cytoplasm of elongating spermatids, and along the flagella of late spermatids. Second, localization of P450arom within the germinal epithelium was supported by Western blot analysis of isolated germ cells. Third, Northern blot analysis using a mouse P450arom cDNA probe indicated that the mRNA for the mouse P450arom was present in testicular germ cells. Fourth, P450arom activity was measured in germ cells by the 3H2O water assay. Based upon these observations, we conclude that germ cells are a site of estrogen synthesis in the adult mouse testis.

Multiple functions of aromatase and the active site structure; aromatase is the placental estrogen 2-hydroxylase

Androgen aromatase was found to also be estrogen 2-hydroxylase. The substrate specificity among androgens and estrogens and multiplicity of aromatase reactions were further studied. Through purification of human placental microsomal cytochrome P-450 by monoclonal antibody-based immunoaffinity chromatography and gradient elution on hydroxyapatite, aromatase and estradiol 2-hydroxylase activities were co-purified into a single band cytochrome P-450 with approx. 600-fold increase of both specific activities, while other cytochrome P-450 enzyme activities found in the microsomes were completely eliminated. The purified P-450 showed M(r) of 55 kDa, specific heme content of 12.9 +/- 2.6 nmol.mg-1 (+/- SD, n = 4), reconstituted aromatase activity of 111 +/- 19 nmol.min-1.mg-1 and estradiol 2-hydroxylase activity of 5.85 +/- 1.23 nmol.min-1.mg-1. We found no evidence for the existence of catechol estrogen synthetase without concomitant aromatase activity. The identity of the P-450 for the two different hormone synthetases was further confirmed by analysis of the two activities in the stable expression system in Chinese hamster ovarian cells transfected with human placental aromatase cDNA, pH beta-Aro. Kinetic analysis of estradiol 2-hydroxylation by the purified and reconstituted aromatase P-450 in 0.1 M phosphate buffer (pH 7.6) showed Km of 1.58 microM and Vmax of 8.9 nmol.min-1.mg-1. A significant shift of the optimum pH and Vmax, but not the Km, for placental estrogen 2-hydroxylase was observed between microsomal and purified preparations. Testosterone and androstenedione competitively inhibited estradiol 2-hydroxylation, and estrone and estradiol competitively inhibited aromatization of both testosterone and androstenedione. Estrone and estradiol showed Ki of 4.8 and 7.3 microM, respectively, for testosterone aromatization, and 5.0 and 8.1 microM, respectively, for androstenedione aromatization. Androstenedione and testosterone showed Ki of 0.32 and 0.61 microM, respectively, for estradiol 2-hydroxylation. Our studies showed that aromatase P-450 functions as estrogen 2-hydroxylase as well as androgen 19-, 1 beta-, and 2 beta-hydroxylase and aromatase. The results indicate that placental aromatase is responsible for the highly elevated levels of the catechol estrogen and 19-hydroxyandrogen during pregnancy. These results also indicate that the active site structure holds the steroid substrates to face their beta-side of the A-ring to the heme, tilted in such a way as to make the 2-position of estrogens and 19-, 1-, and 2-positions of androgens available for monooxygenation.

Metabolism-based transformation of myoglobin to an oxidase by BrCCl3 and molecular modeling of the oxidase form

The stoichiometric reductive debromination of BrCCl3 to a trichloromethyl radical by myoglobin caused the prosthetic heme to become covalently cross-linked to the protein moiety and transformed myoglobin from an oxygen storage protein to an oxidase. This was shown in experiments in which oxygen consumption was measured during redox cycling of the altered myoglobin in the presence of ascorbate or an enzymatic reducing system containing diaphorase and NADH. Redox cycling eventually led to loss of the protein-bound heme adduct and oxidase activity of myoglobin. We have used molecular modeling and the known structure of the protein-bound heme adduct to identify probable mechanisms for transformation of myoglobin to an oxidase. Based on these modeling studies, the most likely structure of the experimentally observed adduct involves ligation to the heme iron of the epsilon-nitrogen atom of histidine 97 and/or that of histidine 64. The model structures revealed access of solvent to the heme active site, which could facilitate oxygen reduction. The transformation of myoglobins and perhaps other hemoproteins to oxidases may have toxicological importance in causing the tissue damage resulting from exposure to various xenobiotics and endogenous chemicals as well as explaining how hemoproteins are inactivated during catalysis.

Inhibition of cytochromes P450 by nitric oxide and a nitric oxide-releasing agent

The effect of nitric oxide (NO) on cytochrome P450-mediated benzyloxyresorufin and ethoxyresorufin O-dealkylase activity of rat hepatic postmitochondrial (S-9) or microsomal subfractions, or purified rat liver CYP2B1, was examined. Two distinct inhibitory phases were observed regardless of whether the NO was added prior to initiation of the reactions with NADPH or during the course of substrate turnover. The first was a reversible inhibition characterized by complete cessation of catalytic activity, the duration of which was NO concentration-dependent with an IC50 in the range of 8-60 microM. This phase was followed by a second, irreversible, inhibitory phase characterized by a varying extent of recovery of activity, with inhibition ranging from < 1 to approximately 100%. The extent of this diminution in substrate conversion rate was also NO concentration-dependent, with an IC50 in the range of 13-72 microM, and could be partially abrogated by the inclusion of bovine serum albumin in the reaction mixture. Lower IC50 values for both inhibitory phases were obtained in the case of benzyloxyresorufin O-dealkylase activity than in the case of ethoxyresorufin O-dealkylase activity, suggesting a differential susceptibility to inhibition by NO for the two O-dealkylase activities. A nitric oxide-releasing compound ([Et2NN(O)NO]Na,DEA/NO) caused qualitatively similar inhibitory effects on benzyloxyresorufin O-dealkylase activity when added prior to the initiation of the reactions with NADPH, or during the course of substrate turnover. Based upon these results, it is possible that NO may play a role in the regulation of P450 activity in vivo.

Kinetic properties of aromatase mutants Pro308Phe, Asp309Asn, and Asp309Ala and their interactions with aromatase inhibitors

Mutant forms of aromatase cytochrome P-450 bearing modifications of amino acid residues Pro308 and Asp309 and expressed in transfected Chinese hamster ovary cells were subjected to kinetic analysis and inhibition studies. The Km for androstenedione for expressed wild type (11.0 +/- 0.3 nM SEM, n = 3) increased 4-, 25- and 31-fold for mutants Pro308Phe, Asp309Asn and Asp309Ala, respectively. There were significant differences in sensitivity among wild type and mutants to highly selective inhibitors of estrogen biosynthesis. 4-Hydroxyandrostenedione (4-OHA) a strong inhibitor of wild type aromatase activity (IC50 = 21 nM and Ki = 10 nM), was even more effective against mutant Pro308Phe (IC50 = 13 nM and Ki = 2.8 nM), but inhibition of mutants Asp309Asn and Asp309Ala was considerably less (IC50 = 345 and 330 nM and Ki = 55 and 79 nM, respectively). Expressed wild type aromatase and Pro308Phe aromatase were strongly inhibited by CGS 16949A (IC50 = 4.0 and 4.6 nM, respectively) whereas mutants Asp309Asn and Asp309Ala were markedly less sensitive (IC50 = 140 and 150 nM, respectively). CGS 18320B produced similar inhibition. Kinetic analyses produced Ki = 0.4 nM for CGS 16949A inhibition of wild type versus 1.1, 37 and 58 nM, respectively, against Pro308Phe, Asp309Asn and Asp309Ala. The results demonstrate significant changes in function resulting from single amino acid modifications of the aromatase enzyme. Our data indicate that mutation in Asp309 creates a major distortion in the substrate binding site, rendering the enzyme much less efficient for androstenedione aromatization. The substitution of Pro308 with Phe produces weaker affinity for androstenedione in the substrate pocket, but this alteration favors 4-OHA binding. Similarly, mutant Pro308Phe exhibits a slightly greater sensitivity to inhibition by CGS 18320B than does the wild type. These results indicate that residues Pro308 and Asp309 play critical roles in determining substrate specificity and catalytic capability in aromatase.

Immunohistochemical localization of 17 alpha-hydroxylase/C17-20 lyase and aromatase cytochrome P-450 in the human ovary during the menstrual cycle

Immunohistochemical localization of 17 alpha-hydroxylase/C17-20 lyase (P-450(17 alpha,lyase)) and aromatase cytochrome P-450 (P-450arom) in normal human ovaries during the menstrual cycle was studied using specific polyclonal antibodies which were raised against corresponding enzymes. In the follicular phase of matured follicles, P-450(17 alpha,lyase) was localized in theca interna cells and P-450arom in granulosa cells. P-450(17 alpha,lyase) was expressed in theca interna cells before P-450arom was expressed in granulosa cells. The corpus luteum showed immunoreactivity to both enzymes and, after menstruation, immunoreactivity decreased gradually until it could not be detected in the corpus albicans. In corpus luteum graviditatis the immunoreactivity continued to be expressed strongly. In some atretic follicles, P-450(17 alpha,lyase) and/or P-450arom continued to be expressed. In the stromal layer, P-450(17 alpha,lyase was detected in secondary interstitial cells, which originated from the theca interna of atretic follicles, and P-450arom was detected in hilar cells. Immunoreactivity to both enzymes was also detected in oocytes of developing follicles. These results are consistent with the two cell theory in the human ovary. They also suggest that androgens and oestrogens are produced not only by follicles and corpora lutea but also by stroma and oocytes.

Synthesis of deuterium-labeled 16 alpha,19-dihydroxy C19 steroids as internal standards for gas chromatography-mass spectrometry

[2 beta,7,7,16 beta-2H4]16 alpha,19-Dihydroxyandrost-4-ene-3,17-dione (14) and [7,7,16 beta-2H3]3 beta,16 alpha,19-trihydroxyandrost-5-en-17-one (16), with high isotopic purity, respectively, were synthesized from unlabeled 3 beta-(tert-butyldimethylsiloxy)-androst-5-ene-17 beta-yl acetate (1). The deuterium introduction at C-7 was carried out by reductive deoxygenation of the 7-keto compound 3 with dichloroaluminum deuteride and that at C-2 beta and/or C-16 beta by controlled alkaline hydrolysis of 16-bromo-17-ketone 11 or 12 with NaOD in D2O and pyridine. [7,7-2H2]3 beta-Hydroxyandrost-5-en-17-one (6), obtained from compound 1 by a five-step sequence, was converted to compound 14 or 16 by an eight-step or seven-step sequence, respectively. The labeled steroids 14 and 16 are useful as internal standards for gas chromatography-mass spectrometry analysis of the endogenous levels.

The use of stable isotopes to identify reactive metabolites and target macromolecules associated with toxicities of halogenated hydrocarbon compounds

1. Halogenated compounds, such as the inhalation anaesthetics, halothane and enflurane, and the chemicals chloroform, carbon tetrachloride, and bromotrichloromethane can cause hepatotoxicity, nephrotoxicity, and inactivation of cytochromes P-450. Each of these toxicities is mediated by reactive metabolites. 2. Stable isotopes of hydrogen, carbon, chlorine and oxygen have been used in conjunction with mass spectrometry and n.m.r. spectrometry to identify the structures of these metabolites, to elucidate the mechanisms of their formation, and to characterize the structures of their macromolecular adducts. 3. In a number of cases, oxidative pathways of metabolism to toxic metabolites have been defined by kinetic deuterium isotope effects. 4. Recently, we have found that the trichloromethyl radical metabolite of bromotrichloromethane can activate myoglobin by causing the covalent cross-linking of haem to protein. The structure of a haem-myoglobin adduct has been defined by the use of stable isotope studies.

An aromatase-associated cytoplasmic inclusion, the "stigmoid body," in the rat brain: I. Distribution in the forebrain

An aromatase-containing neural system was examined in the rat forebrain, using a polyclonal antibody against aromatase-associated human placental antigen X-P2 (hPAX-P2). Numerous dot-like structures, which we have called stigmoid bodies, were immunostained in the preoptico-hypothalamic region, the bed nucleus of the stria terminalis, the medial amygdala, the arcuate nucleus, the subfornical organ, and the area extending from the hypothalamic area to the central gray through the medial forebrain bundle and the periventricular fiber system of the posterior diencephalon. The stigmoid bodies were always found as inclusions in the neuronal cytoplasm. Their diameter was usually 1-3 microns, but exceptionally large forms, over 3 microns, were found in some brain regions, including the area extending from the median preoptic nucleus surrounding the organosum vasculosum laminae terminalis to the anterior medial preoptic nucleus, the periventricular nucleus of the preoptic area, and some parts of the medial preoptic nucleus. Most of these nuclei show sexual dimorphism. The distribution pattern of the hPAX-P2 immunoreactive stigmoid bodies agreed well with that of aromatase activity previously reported in many biochemical studies. Brain regions where the stigmoid bodies were prominent largely coincide with steroid binding locations common to both androgen and estrogen, or regions where both sex steroid receptors are present. Although it still remains to be determined whether aromatase is localized within these stigmoid bodies, it appears likely that they are closely associated with the function of sex steroids at their target sites in the brain.

[Studies on changes in low esophageal sphincter function after esophageal transection or esophago-esophagostomy in children]

An aim of the present study is to clarify the changes of esophageal function after surgical treatments of the esophageal varices or the congenital esophageal stenosis in children. Esophageal manometric studies were performed in sixteen children undergoing the esophageal transection with paraesophageal devascularization or the esophago-esophagostomy with partial esophagectomy before, within 1 month and over 7 months after the operation. The pressure of lower esophageal sphincter (LES), the length of LES, the LES relaxation test and the gastroesophageal reflux (GER) inducing test were measured. 1) Esophageal transection; The pressure dropped within 1 month and returned to the preoperative level over 11 months after the operation. Temporal deterioration of LES function was observed during the early postoperative days. However, return to the preoperative state was gained over 1 year. 2) Esophago-esophagostomy; The pressure and the length of LES were not changed after the operation. The LES function was disturbed preoperatively and moreover long postoperatively, in the case when congenital stenosis closely existed to the esophago-gastric junction. Degree of the postoperative disturbance of the LES function may be influenced by the distance to the part of the transection or the partial esophagectomy from the E-C junction.

Covalent alteration of the prosthetic heme of human hemoglobin by BrCCl3. Cross-linking of heme to cysteine residue 93

Recent studies have shown that a protein-bound heme adduct formed from the reaction of BrCCl3 with myoglobin was due to bonding of the proximal histidine residue through the ring I vinyl of a heme-CCl2 moiety. The present study reveals that BrCCl3 also reacts with the heme of reduced human hemoglobin to form two protein-bound heme adducts. Edman degradation and mass spectrometry provided evidence that these protein-bound heme adducts were addition products in which heme-CCL2 or heme-CCl3 were bound to cysteine residue 93 of the beta-chain of hemoglobin. It appeared that the cysteine residue was bonded regiospecifically to the ring I vinyl group of the altered heme moiety, because the nonprotein-bound products of the reaction included the beta-carboxyvinyl and alpha-hydroxy-beta-trichloromethylethyl derivatives of the ring I vinyl moiety of heme. The absorption spectra of the protein-bound adducts in both the oxidized and reduced states were highly similar to those described for hemichromes, which are thought to be involved in the formation of Heinz bodies and subsequent red cell lysis.

Role of nitric oxide in NMDA-evoked release of [3H]-dopamine from striatal slices

Evidence that excitatory amino acids act via N-methyl-D-aspartate (NMDA) receptors to evoke the release of catecholamines from axonal terminals and synaptosomes has been used to argue for the presence of pre-synaptic NMDA receptors. NMDA receptor agonists also generate nitric oxide (NO) which rapidly diffuses through neural tissue. We find that exogenously applied NO evokes [3H]-dopamine release from cultured neurons. This release is not blocked by the NMDA antagonist MK-801 nor by tetrodotoxin. Both NG-nitroarginine which inhibits NO synthesis, and hemoglobin which binds extracellular NO, block NMDA-evoked [3H]-dopamine release from striatal slices. A major role of endogenously-synthesized NO may be to evoke neurotransmitter release in local volumes of neural tissue.

Increasing aromatase cytochrome P-450 level in human placenta during pregnancy: studied by immunohistochemistry and enzyme-linked immunosorbent assay

We investigated the immunohistochemical localization of aromatase cytochrome P-450 (P-450arom) using a specific polyclonal antiserum (PAb R-8-2). We compared catalytic activity, as detected by the tritiated water assay, and tissue levels of P-450arom, as detected by the specific enzyme-linked immunosorbent assay, in placental samples from early pregnancy to term. Immunostaining and subsequent detection by light and electron microscopy demonstrated that P-450arom is localized in the microvilli and endoplasmic reticulum of the syncytiotrophoblasts of the chorionic villi, but is not present in the mitochondria, nuclei, or cytotrophoblasts at any time during gestation. The P-450arom concentration and aromatase activity were greater in the microsomal fraction than in the mitochondrial fraction or total homogenate at each gestational stage and increased linearly as pregnancy progressed. However, the specific activity of P-450arom was comparable among subcellular fractions in each gestational period. These results suggest that the nature and localization of P-450arom are unchangeable, and the P-450arom concentration increases during pregnancy. It appears that the aromatase detected in the mitochondrial fraction is a contamination of microsomal aromatase, and the increase in aromatase activity can be attributed to an increase in the number of P-450arom molecules rather than an increase in the catalytic ability of each molecule.