Peroxisome proliferation and beta-oxidation in Fao and MH1C1 rat hepatoma cells, HepG2 human hepatoblastoma cells and cultured human hepatocytes: effect of ciprofibrate

Human HepG2, rat Fao and MH1C1 hepatoma cell lines have been examined for their response to ciprofibrate, a potent peroxisome proliferator. Changes in the morphological characteristics of peroxisomes, the inductibility of their proliferation and of their beta-oxidation enzymes, palmitoyl-CoA oxidase and bifunctional enzyme, were studied in control and treated cells. In Fao cells, peroxisomes are less numerous and smaller than in rat liver, but they increase in size and number under the effect of ciprofibrate, similarly to those of treated rat liver. The high peroxisome proliferation is accompanied by a strong induction of beta-oxidation enzymes as in vivo. In MH1C1 cells, peroxisomes are seen in irregular clusters in the cytoplasm, small with rounded to tubular forms, suggesting rapid peroxisomal growth. A striking observation is the particularly elongated, worm-like form of many of the peroxisomes. Under the effect of ciprofibrate, the proliferation is low, as is the induction of beta-oxidation enzymes. HepG2 cells contain few, small peroxisomes with a heterogeneity of forms, from spherical to elongated. The only peroxisomal response to ciprofibrate in these cells seemed to be a morphological reorganization. There is little or no induction of beta-oxidation enzymes by ciprofibrate in HepG2 cells, as in cultured human hepatocytes. Therefore, on the one hand, Fao and MH1C1 cells are complementary tools in the investigation of the regulation of the hepatic response to peroxisome proliferators in the rat, on the other hand, HepG2 and Fao cells are useful in the study of the species specificity of the response.

Aldosterone synthase activity in the Y-1 adrenal cell line

The Y-1 adrenal cell line was shown to produce 20 alpha-dihydroaldosterone from deoxycorticosterone. This compound was identified by GC-MS by comparison with the previously synthesized reference compound. Two other 18-hydroxylated metabolites were identified as 11 beta,18-dihydroxy-20 alpha-dihydroprogesterone from endogenous cholesterol and 18-hydroxy-20 alpha-dihydro-11-dehydrocorticosterone from DOC. The conditions necessary for the synthesis of these compounds are culturing in 20% serum-supplemented medium and repeated incubations with the substrate. The production of 11 beta-hydroxylated steroids and that of 18-oxygenated steroids is stimulated differently by ACTH and angiotensin II suggesting the expression of two different enzymes, cytochrome P-450(11)beta and cytochrome P-450aldo. The Y-1 cell line can secrete either 11 beta-hydroxylated steroids characteristic of the glucocorticoid pathway or 18-oxygenated steroids characteristic of the mineralocorticoid pathway, which in vivo are generally produced in two different zones of the adrenal cortex. This cell line should be an interesting model for the study of the molecular mechanisms regulating the expression of these two enzymes involved in the final steps of the steroidogenic pathways.

Stimulation of peroxisomal palmitoyl-CoA oxidase activity by ciprofibrate in hepatic cell lines: comparative studies in Fao, MH1C1 and HepG2 cells

The response of two rat cell lines, Fao and MH1C1, and one human cell line, HepG2, to the peroxisome proliferator ciprofibrate, was studied. Using a fluorometric assay for palmitoyl-CoA oxidase, the dose- and time-dependent increase of this enzymatic activity was determined. From the lowest concentration (100 microM) stimulation is evident in the two rat cell lines. In the Fao line, the activity was stimulated reaching a seven-fold increase over the control level at 250 microM after 72 h of treatment. In the MH1C1 line, the maximum stimulation, four- to five-fold, was obtained at 250 and 500 microM after 72 h. In the HepG2 cell line, activity increased two-fold at 250 microM after 72 h reaching a three-fold increase at 1000 microM after 48 h. Ciprofibrate was more toxic to Fao cells than to MH1C1 and HepG2 cells which is also the order of the acyl-CoA oxidase stimulation by ciprofibrate. These preliminary results suggest that the two rat cell lines are appropriate for investigating the induction of peroxisomal beta-oxidation enzymes and the expression of their genes. The HepG2 cell line is a complementary model for the study of interspecies differences in the response to peroxisomal proliferators and of the peroxisomal functions implied in the lipid metabolism of human liver.

18-hydroxylation in the Y-1 adrenal cell line: response to ACTH and to culture conditions

The 18-hydroxylation of deoxycorticosterone in the Y-1 adrenal cell line was studied under various incubation and cell culture conditions and compared to 11 beta-hydroxylation. Repeated incubation of the substrate increased both 18- and 11 beta-hydroxylation in the Y-1 cells. Furthermore, both 18- and 11 beta-hydroxylation were increased with increased serum concentration and prolonged incubation time. While the increase in 11 beta-hydroxylation seemed to be independent of the type of serum, 18-hydroxylation was much more important in cells cultured in fetal or newborn calf serum supplemented medium than in those cultured in horse serum supplemented medium. As expected, ACTH treatment increased 11 beta-hydroxylation; however, it decreased 18-hydroxylation. The different regulation of these two hydroxylating pathways by ACTH, point to a heterogeneity of the cytochrome P-450(11) beta of the Y-1 cell line.

Chromatographic and mass spectrometric characteristics of 20-dihydroaldosterone

The 20 alpha-reduced derivative of aldosterone, 20 alpha-dihydroaldosterone, was needed as reference compound in order to continue the studies on 18-hydroxylation in the Y-1 adrenal cell line. It was obtained by reduction of aldosterone with sodium borohydride. Analysis of the products of the reaction as methoxime trimethylsilyl (MO-TMS) derivatives by gas chromatography (GC) and GC-mass spectrometry (GC-MS) showed three possible forms of the compound. Their identification was confirmed by comparison with the products obtained by stereospecific reduction of aldosterone using 3 alpha,20 beta-hydroxysteroid dehydrogenase. Chromatographic behavior and mass spectra are given for the three forms of 20 alpha-dihydroaldosterone as the MO-TMS derivatives; that is, the 18-aldehyde, the 18,11 beta-hemiacetal, and the 11 beta:18,18:20 alpha-acetal. The possible origin of these different forms is discussed as a function of these results and of the results obtained by complementary analysis on high-performance liquid chromatography.

19-Hydroxylated steroids, new metabolites produced by the Y1 adrenal cell line

The expression of 19-hydroxylase activity in the Y1 adrenal cell line is reported here for the first time. Two new metabolites from the incubation of deoxycorticosterone (DOC) with these cells, 19-hydroxy-20 alpha-dihydroDOC and 19-hydroxy-20 alpha-dihydrocorticosterone, have been identified. The most important of the two is the 11 beta,19-dihydroxylated metabolite, which is produced in smaller amounts than 18-hydroxy-20 alpha-dihydrocorticosterone. A third 19-hydroxylated metabolite was identified as 19-hydroxy-20 alpha-dihydroprogesterone, produced from the cholesterol in the serum supplemented medium. These results show that the cytochrome P-450(11)beta of this cell line expresses 19-hydroxylase activity in addition to 11 beta- and 18-hydroxylase activities, as do those of other species.

Evidence of formation of isomeric methoximes from 20-oxosteroids

The formation and gas chromatographic behavior of syn- and anti-isomers in position 20 of the methoxime-trimethylsilyl (MO-TMS) derivatives of many 20-oxo and 3,20-dioxo-21-hydroxysteroids is reported. The existence of such isomers was established from the gas chromatographic (GC) and mass spectrometric analysis of the MO-TMS derivatives of 3 alpha,21-dihydroxy-5 beta-pregnan-20-one and its 17 alpha-epimer. The degree of separation during GC analysis of the syn- and anti-isomers in position 20, as well as those in position 3, is associated to the position of additional hydroxyl groups on the steroid ring. These data are very important for the location of oxygenated substituents such as 2 alpha/2 beta, 6 alpha/6 beta, 11 beta, 16 alpha, 17 alpha, 18, 19 or 21-hydroxyl groups during structural studies of 20-oxo and 3,20-dioxosteroids.

18-Hydroxylase activity in the Y1 adrenal cell line

18-Hydroxylase activity, reported here for the first time in the mouse adrenal tumor cell line (Y1), was expressed in the metabolism of 11-deoxycorticosterone (DOC) and corticosterone (B). Detected after 24 h of incubation, it was more evident after 48 h and produced mostly 18-hydroxy-20 alpha-DHB from these exogenous substrates. However, 18-hydroxylation was quantitatively less significant than the metabolism of 20 alpha-reduction and 11 beta-hydroxylation (of DOC). The latter is also the predominant metabolism of progesterone in this cell line, during the conversion of cholesterol from the serum-supplemented culture media. The cytochrome P-450 11 beta activity of the Y1 cells is similar to that of the mouse in vivo which catalyzes the production of an 11 beta 18-dihydroxylated metabolite as the principal 18-hydroxylated steroid. It is different from that of other species, such as the rat and the bovine, both in terms of the ratio of 11 beta- to 18-hydroxylated metabolites and of the structure of these metabolites.

Alternate hydroxylating activities in newborn rat adrenal cells in primary culture

During the course of a study to produce reference compounds, the metabolism of tetrahydrogenated derivatives (ring A reduced) of progesterone, 6 alpha-hydroxyprogesterone, 11-deoxycorticosterone and corticosterone in newborn rat adrenal cells in primary culture was studied. Analysis of the metabolites was made by gas chromatography-mass spectrometry. Most products resulted from the enzymatic reactions of 11 beta-, 18- and 21-hydroxylation, reduction of the 20-oxo group and oxidoreduction of the 3-hydroxyl group. However, unexpected metabolites were produced from the incubation of 3 beta, 5 alpha-tetrahydroprogesterone and 6 alpha-hydroxy-3 alpha, 5 beta-tetrahydroprogesterone. They resulted from the 16 alpha-hydroxylation of the precursors and probably from the 15 alpha-, 16 beta- and 17 alpha-hydroxylation of 6 alpha-hydroxy-3 alpha, 5 beta-tetrahydroprogesterone. These hydroxylating activities are weak and were not detected from the endogenous steroidogenesis. They were not detected either from the incubation of exogenous steroids with a 3-oxo-4-ene structure or from steroids with a 21-hydroxyl substituent. They result only from substrates showing diminished or no affinity towards the 11 beta/18- and 21-steroid hydroxylase systems. These unusual hydroxylations could be catalyzed by monooxygenase systems in the endoplasmic reticulum similar to those present in the liver or by the monooxygenase systems specific to steroidogenesis. In particular, the reaction specificity of cytochrome P-450(11) beta could be altered by the presence of a 6 alpha-hydroxyl group in a tetrahydrogenated steroid.

Synthesis and gas chromatographic-mass spectrometric analysis of reduced compounds derived from 6 alpha- and 6 beta-hydroxy-11-deoxycorticosterone

A series of thirty two 6-hydroxylated steroids were synthesized by selective reduction of the 4-5 double bond, the 3-oxo group, and/or the 20-oxo group of 6 alpha- and 6 beta-hydroxyDOC. The different reactions leading to the production of specific isomers are discussed. The gas chromatographic and spectrometric characteristics of the methoxime-trimethylsilyl (MO-TMS) or trimethylsilyl (TMS) derivatives of the isomers obtained are given. The gas chromatographic separation of the syn- and anti-isomers of the methoxime in position 3 was found to be characteristic of the configuration of the hydroxyl in position 6. The difference between methylene unit values of syn- and anti- isomers is much larger for the 6 alpha-series than for the 6 beta-series. The mass spectral analysis showed that many ions are specific of the MO-TMS derivatives of steroids with 3,6-dihydroxy-4-ene or 3-oxo-6-hydroxy-4-ene structure. In the case of steroids with a saturated ring A no significant ions characteristic of the presence of a 6-trimethylsilyloxy substituent were found. This work provides previously unavailable reference data on 6-hydroxylated steroids which should facilitate the study of corticosteroid metabolism.

Bioconversion of 16 alpha-hydroxyprogesterone to 16 alpha-hydroxylated corticosteroids by newborn rat adrenal cells in primary culture

Using newborn rat adrenal cells in primary culture, 16 alpha-hydroxyprogesterone was bioconverted into numerous 16 alpha-hydroxylated steroids. The method of analysis of these steroids comprised the association of column and thin-layer chromatography to gas chromatography-mass spectrometry in order to obtain the mass spectra of pure compounds. The identified compounds resulted principally from the enzymatic reactions of 21-hydroxylation 11 beta-hydroxylation and reduction of the 20-oxo and 3-oxo-4-ene groups. Minor metabolites resulted from 18-hydroxylation and 6 beta-hydroxylation of the substrate. The metabolism of 16 alpha-hydroxyprogesterone is similar to that of progesterone in the same cell-culture system; however, there are two exceptions. The 21-hydroxylation of 16 alpha-hydroxyprogesterone occurs at a rate similar to that of its 11 beta-hydroxylation, whereas the 21-hydroxylation of progesterone is faster than its 11 beta-hydroxylation. The ratio of 11 beta- to 18-hydroxylation of 16 alpha-hydroxyprogesterone is about 3, whereas the ratio of 11 beta- to 18-hydroxylation of progesterone, 20 alpha-dihydroxyprogesterone and DOC is between 1./ and 2. It is most likely the rate of 18-hydroxylation which is decreased by the hydroxyl group at C-16. The use of adrenal cell cultures is a practical, simple method for the preparation of a variety of 16 alpha-hydroxylated steroids from a single substrate. Its adaptation to the production of important amounts of 16 alpha-hydroxylated corticosteroids will permit the study of their biological activity.

Bioconversion of 2 alpha-hydroxyprogesterone to 2-hydroxylated corticosteroids by newborn rat adrenal cells in primary culture

The bioconversion of 2 alpha-hydroxyprogesterone into 2-hydroxylated steroids was accomplished using newborn rat adrenal cells in primary culture. The products were purified using column and thin-layer chromatography, and identified by GC-MS. They resulted principally from the enzymatic reactions of 21-hydroxylation, 11 beta-hydroxylation, reduction of 20-oxo and 3-oxo groups, and epimerization of the substrate. In addition, minor metabolites resulted from 18-hydroxylation, 6 beta-hydroxylation and reduction of the 3-oxo-4-ene group. The identification of these compounds allowed us to conclude that the metabolism of 2 alpha-hydroxyprogesterone is similar to that of progesterone in this cellular system. Assuming that the 2 beta-epimers of the different metabolites arose principally from the transformation of 2 beta-hydroxyprogesterone, the specificity of the various enzyme systems seems to be similar for both epimers except in the case of the 11 beta-hydroxylation where the reaction appears stereospecific for the 2 beta-epimer. The 2 alpha-hydroxyl group on ring A seems to favor the reduction of the 3-oxo group and it does this stereospecifically to the 3 beta-structure. The epimerization of the substrate, which is most likely enzymatically induced, is the first example of steroid epimerization reported in the adrenal. This is a practical preparative method for synthesizing a variety of steroids hydroxylated at C-2 from a single substrate and could be adjusted to the production of important quantities of 2-hydroxylated metabolites of corticosteroids.

The role of ACTH in determining the metabolic pathways of deoxycorticosterone by newborn rat adrenal cells in primary culture

The metabolism of deoxycorticosterone (DOC) by newborn rat adrenal cells in primary culture at various times after culture, with and without ACTH, was studied. After 5 days in culture before addition of ACTH, the main products of the metabolism of DOC were corticosterone and 18-hydroxy-11-deoxycorticosterone in a 2:1 ratio. Smaller amounts of 20 alpha-dihydrocorticosterone and 18-hydroxycorticosterone were also found. No reduced metabolites of DOC were detected. Without ACTH the conversion of DOC to corticosterone and 18-hydroxyDOC declined rapidly. After 13 days in culture, this conversion accounted for only half the metabolites. The reductive metabolism of DOC which yields products reduced at 20 alpha and/or 3 alpha/beta and 5 alpha accounted for the other half. When ACTH (22 mU/ml) was added to the culture daily for several weeks, the primary metabolism of DOC remained that of 11 beta- and 18-hydroxylation yielding corticosterone and 18-hydroxyDOC. A minor reductive metabolism was found. Both cultures produced 6 beta-hydroxyDOC. These results demonstrate that ACTH is needed to maintain the efficiency of the 11 beta/18-hydroxylating system. They also show that ACTH controls the type of metabolism predominant in the rat adrenal cell and may be responsible for the balance between the biosynthesis of glucocorticoids and their reductive catabolism in the fasciculata zone of the adrenal gland.

Partial characterization of unusual polar steroids in the urine of a child with low renin hypertension

Analysis of urinary steroids excreted by a 7-year old girl with low renin hypertension following ACTH treatment revealed several unknown steroids, which have been analysed by gas chromatography-mass spectrometry. It is proposed that these steroids are monohydroxylated derivatives of cortisol, cortisone, either or both tetrahydro and allo-tetrahydrocortisol and either or both tetrahydro and allo-tetrahydro-11-deoxycortisol. Further analysis indicated that there are two likely positions for the additional hydroxyl group, either on the A or B ring.

Separation and characterization of the reduced metabolites of the 18-hydroxydeoxycorticosterone hormone by gas-liquid chromatography-mass spectrometry. Occurrence of stereoisomeric forms in rat adrenals and liver

In order to study the metabolism of 18-OH-11-deoxycorticosterone, the mineralocorticoid hormone responsible for hypertension in rats and humans, we have synthesized the following dihydrogenated and tetrahydrogenated reference derivatives: 18,21-dihydroxy-5alpha-pregnane-3,20-dione, 18,21-dihydroxy-5beta-pregnane-3,20-dione, 3alpha,18,21-trihydroxy-5alpha-pregnan-20-one (I), 3beta,18,21-trihydroxy-5alpha-pregnan-20-one (II), 3alpha,18,21-trihydroxy-5beta-pregnan-20-one (III) and 3beta,18,21-trihydroxy-5beta-pregnan-20-one (IV). A complete separation of these compounds from each other and from tetrahydrocorticosterone isomers has been realized only by the association of thin-layer chromatography and gas-liquid chromatography on high-efficiency glass capillary columns. Characterization by gas-liquid chromatography-mas spectrometry is described. The stereoisomer distribution in rats is: adrenals of adult males and females (compounds I and II in the ratio 4:1); adrenals of 23-day-old males and females (compounds I, II and III, 11:11:3); liver of females (compound I and traces of III); and the liver of adult male (compounds II, III and IV, 4.5:4.5:1).

Adrenal and liver metabolites of 18-hydroxy-11-deoxycorticosterone in the rat. Identification of reduced compounds (18-OH-TH-DOC)

The presence of reduced metabolites of 18-hydroxy-11-deoxycorticosterone has been investigated in the adrenals of 23 day-old and adult rats and in the liver of adult rats. By thin-layer chromatography a fraction of the adrenal steroid extract migrating like tetrahydrocorticosterone has been isolated. By gas chromatography-mass spectrometry several isomers of 3,18,21-trihydroxy-pregnan-20-one (18-OH-TH-DOC) have been separated in this fraction and identified by comparison with authentic samples which have been chemically and enzymatically synthesized. The major tetrahydrogenated metabolite in the adult and prepuberal rat adrenals is 3beta,18,21-trihydroxy-5alpha-pregnan-20-one (18-OH-TH-DOC II). The 3alpha,18,21-trihydroxy-5beta-pregnan-20-one has been found only in the prepuberal rat adrenal. A third tetrahydrogenated isomer has been tentatively indentified as 3alpha,18,21-trihydroxy-5alpha-pregnan-20-one. Quantitative measurements by mass fragmentography show that adrenal reductase activity on 18-hydroxy-11-deoxycorticosterone is higher than on corticosterone. The 18-OH-TH-DOC II has been identified in the liver of adult male rat.