Adrenal Mitochondrial Cytochrome P-450 and Cholesterol Side Chain Cleavage Activity

Binding domain-driven intracellular trafficking of sterols for synthesis of steroid hormones, bile acids and oxysterols

Steroid hormones, bioactive oxysterols and bile acids are all derived from the biological metabolism of lipid cholesterol. The enzymatic pathways generating these compounds have been an area of intense research for almost a century, as cholesterol and its metabolites have substantial impacts on human health. Owing to its high degree of hydrophobicity and the chemical properties that it confers to biological membranes, the distribution of cholesterol in cells is tightly controlled, with subcellular organelles exhibiting highly divergent levels of cholesterol. The manners in which cells maintain such sterol distributions are of great interest in the study of steroid and bile acid synthesis, as limiting cholesterol substrate to the enzymatic pathways is the principal mechanism by which production of steroids and bile acids is regulated. The mechanisms by which cholesterol moves within cells, however, remain poorly understood. In this review, we examine the subcellular machinery involved in cholesterol metabolism to steroid hormones and bile acid, relating it to both lipid- and protein-based mechanisms facilitating intracellular and intraorganellar cholesterol movement and delivery to these pathways. In particular, we examine evidence for the involvement of specific protein domains involved in cholesterol binding, which impact cholesterol movement and metabolism in steroidogenesis and bile acid synthesis. A better understanding of the physical mechanisms by which these protein- and lipid-based systems function is of fundamental importance to understanding physiological homeostasis and its perturbation.

Stress adaptation in athletes: relation of lipoprotein levels to hormonal response

Increased physical stress is produced in acute exercise conditions before and during a physical trial. The effects of the physical stress on lipid and lipoprotein parameters as well as on testosterone and cortisol levels were examined in male elite athletes. In a sample of 22 measured athletes, 11 showed increases and 11 showed decreases in testosterone levels. Subsequently these subjects were treated as two separate groups for statistical purposes in order to characterise the source of individual differences in response to a stressor. Group 1 showed a 16.1% significant increase in testosterone levels, 13.3% in total cholesterol and low density lipoproteins, and a 105% increase in testosterone/cortisol ratio immediately after an acute bout of physical stress of 30 s. Group 2 showed a -25.8% significant decline in testosterone levels and no significant change in either total cholesterol or lipoprotein concentrations, followed by a significant correlation of all lipid and hormonal parameters to psychophysiological factors, such as skin temperature. A measurement of testosterone/cortisol and total cholesterol and high density lipoprotein (HDL-C) levels after a bout of acute physical stress may give a picture of the ability to "respond quickly" to stress, which will be useful in assessing the performance of the elite athlete.

Cold swimming stress: effects on serum lipids, lipoproteins and LCAT activity in male and female rats

Effects of consistent cold swimming stress on lipid and lipoprotein metabolism parameters were studied using male and female rats over a period of 60 and 20 days respectively. At the end of treatment serum total cholesterol, high density lipoproteins (HDL-C) and lecithin:cholesterol acetyltransferase (LCAT) activity declined in both male and female rats. TC/HDL-C ratio declined in 20 days in females, while in males it did not change. Free fatty acids increased, while triglycerides remained unchanged in both sexes. %Lipoprotein distribution in male animals did not show any phenotype alteration except in the group of 40 days where %VLDL declined and %LDL-C increased. Body weights did not change, except in males in 60 days. Consistent cold swimming stress by lowering HDL-C and LCAT activity seems to influence lipoprotein metabolism.

Effects of cold stress on serum lipids, lipoproteins, and the activity of lecithin:cholesterol acyltransferase in rabbits

Effects of prolonged stress on lipid metabolism factors were studied for 9 weeks using four groups of young New Zealand rabbits. Two groups (A,B) were rendered atherosclerotic by administering 1% (w/w) cholesterol. One group (C) was subjected to cold stress together with one of the atherosclerotic groups (B); one group was used as control (N). At the end of treatment serum total cholesterol and total lipids of A and B increased significantly, while in stress group (C) a significant decrease was observed. HDL-C levels were reduced in all experimental groups. Triglycerides did not change in A, while they were reduced in both stress groups (C,B). Serum lecithin:cholesterol acyltransferase (LCAT) activity levels of B and C were decreased. Lipoprotein electrophoresis patterns showed a significant redistribution of percentage values in all experimental groups: %LDL-C increased and %VLDL-C decreased in all groups, %HDL-C declined in A and B and did not change in C. The combination of stress and atherosclerosis in rabbits elicits far greater alterations in lipid and lipoprotein profiles than stress or atherosclerosis alone. A stress and atherosclerotic diet combination may be a hazardous one in relation to CHD and atherosclerosis.

Levels of adrenodoxin, NADPH-cytochrome P-450 reductase and cytochromes P-45011 beta, P-45021, P-450scc, in adrenal zona fasciculata-reticularis tissue from androgen-treated rats

Treatment of rats with methylandrostenediol (MAD), an anabolic androgen, caused a profound reduction (65%) in the level of cytochrome P-450 11 beta in rat adrenocortical mitochondria as measured by immunoblots using a specific antibody. The decreases in mitochondrial cytochrome P-450scc (15%) and adrenodoxin (20%) were much less than that observed for cytochrome P-45011 beta. A 35% decrease in adrenal microsomal cytochrome P-450 21 and NADPH-cytochrome P-450 reductase levels was brought about by the treatment with MAD. The data establish that the preferential decrease in adrenal steroid 11 beta-hydroxylase activity associated with androgen treatment results from a decrease in cytochrome P-450 11 beta. This is consistent with the role of 11-deoxycorticosterone in the pathogenesis of androgen-induced hypertension in rats.

The adrenal gland of stranded whales (Kogia breviceps and Mesoplodon europaeus): in vitro modulation of mitochondrial steroid enzyme activities

The effects of adrenocorticotropic hormone (ACTH), cyclic AMP (cAMP), NADPH, Krebs cycle intermediates (KCl), and metyrapone on the two key mitochondrial reactions in the biosynthesis of glucocorticoids--11 beta-hydroxylation and cholesterol cleavage--were studied in preparations from the adrenal glands of stranded whales (Kogia breviceps and Mesoplodon europaeus) and some terrestrial mammals. ACTH (30 pM) and cAMP (1.0 mM) enhanced the 11 beta-hydroxylation of [11-3H]deoxycorticosterone ([3H]DOC) in monolayer cultures of whale adrenal cells during a 4-hr incubation period. Mitochondria from whale and beef adrenals responded in a similar dose-related fashion to NADPH generated by the addition of increasing amounts of NADP (0-0.6 mM) to the in vitro system: at each level of NADPH, 11 beta-hydroxylation of [14C]DOC was several-fold greater than the cleavage of [14C]cholesterol. Metyrapone interfered in a dose-related manner with both the 11 beta-hydroxylation of [14C]DOC and the cleavage of [14C]cholesterol by mitochondria from whale and beef adrenals; inhibition of 11 beta-hydroxylation exceeded 60% at 0.1 mM metyrapone and was virtually complete at 1.0 mM in both species, while inhibition of [14C]cholesterol cleavage averaged 25% at 0.1 mM metyrapone and 50% at 1.0 mM. The effect of exogenous NADPH in supporting the 11 beta-hydroxylation of [14C]DOC could be maintained in beef and rat adrenal mitochondria to the extent of 70-100% by substitution with any of the KCl. This phenomenon was not found in similar whale studies where the KCl were all ineffective.(ABSTRACT TRUNCATED AT 250 WORDS)

Gamma 3-melanotropin promotes mitochondrial cholesterol accumulation in the rat adrenal cortex

Gamma 3-melanotropin (gamma 3-MSH) facilitates a rapid, dose-dependent, and cycloheximide-insensitive increase in the concentration of mitochondrial free cholesterol in the adrenals of hypophysectomized rats. Physiological concentrations of various synthetic and native preparations of gamma 3-MSH are potent, while gamma-MSH is not. This cholesterol accumulation coincides with the activation of cholesteryl ester hydrolysis by gamma 3-MSH, while the rates of cholesterol esterification and of mitochondrial cholesterol side-chain cleavage are unaffected. Conversely, ACTH inhibits cholesterol ester esterification. Therefore, gamma 3-MSH and ACTH together may coordinate a substantial shift in the set-point of cholesteryl ester in equilibrium cholesterol cycling toward the right. Because ACTH also activates cholesterol side-chain cleavage, this coordinate effect on the flux of cholesterol substrate is manifest as a potentiation of corticosteroidogenesis by gamma 3-MSH. These data extend our previous studies demonstrating that pro-gamma-MSH polypeptides have an endocrine influence on the rat adrenal cortex.

Magnetic resonance study of the structure and functions of cytochrome P450

Cytochrome P450 is a membrane-bound enzyme providing oxidation of numerous organic compounds in organisms. The objective of this review is to show the wide possibilities that are provided by Electron Spin Resonance (ESR) and Nuclear Magnetic Resonance (NMR) techniques to the study of the structure and functions of this unique enzyme. High sensitivity of ESR spectra of cytochrome P450 to its functional state and interaction with substrates and inhibitors is illustrated. NMR and proton relaxation make it possible to obtain unique information about the structure of the active center of cytochrome P450 under physiological conditions. ESR and NMR methods allow one to obtain structural data on location of substrates, inhibitors, and their spin-labeled analogs with respect to Fe3+ ions in the enzyme-active center. Of special interest seems to be coupling of ESR with the affinity modification method. For this purpose, the spin-labeled analogs of cytochrome P450 substrates containing alkylating groups were used. As a result, an important datum has been obtained on the structure of active centers of cytochrome P450 in microsomes and in a highly purified state. In conclusion, the problems of the structure and functions of cytochrome P450, which can be most efficiently resolved with the use of magnetic resonance methods, are discussed.

Purification and analysis of phospholipids in the inner mitochondrial membrane fraction of bovine corpus luteum, and properties of cytochrome P-450scc incorporated into vesicles prepared from these phospholipids

Cytochrome P-450scc, which catalyses the conversion of cholesterol to pregnenolone in steroidogenic tissues, can be incorporated into artificial phospholipid vesicles and cholesterol binding to the cytochrome is affected by the composition of the vesicles. We have purified the phospholipids from the inner mitochondrial membrane fraction of the bovine corpus luteum where the cytochrome is located. The composition in mol % was 49% phosphatidylcholine, 34% phosphatidylethanolamine, 8.7% cardiolipin, 6.4% lysophosphatidylethanolamine and 1.5% phosphatidylinositol. The ratio of cholesterol to phospholipid (mol/mol) in the inner membrane fraction was 0.14 to 1. The Km for cholesterol of purified luteal cytochrome P-450scc incorporated into vesicles prepared from the total inner mitochondrial membrane phospholipids was 0.063 mol of cholesterol per mol of phospholipid. Removal of the cardiolipin component of the inner mitochondrial membrane phospholipids prior to preparation of vesicles caused a four fold increase in the Kd of cytochrome P-450 for cholesterol and a two fold increase in Km. The data suggests that in the inner mitochondrial membrane of the bovine corpus luteum the cholesterol concentration is less than saturating for cytochrome P-450scc.

Turnover of newly synthesized cytochromes P-450scc and P-45011 beta and adrenodoxin in bovine adrenocortical cells in monolayer culture: effect of adrenocorticotropin

The turnover of newly synthesized cytochromes P-450scc and P-45011 beta, and adrenodoxin was investigated in bovine adrenocortical cells in primary monolayer cultures. Cells were pulse-radiolabeled with [35S]methionine, and specific newly synthesized enzymes were immunoisolated at various times following labeling and quantitated. Adrenocorticotropin (ACTH) treatment did not alter the average turnover rate of total cellular proteins or that of total mitochondrial proteins. The half-life of total cellular proteins of control and ACTH-treated cells was determined to be 20.5 and 23 h, respectively. The half-life of mitochondrial proteins of control and ACTH-treated cells was determined to be 42.5 and 44 h, respectively. The turnover rate of newly synthesized cytochrome P-450scc was approximately the same as total mitochondrial protein (t1/2 = 38 h), and was unchanged by ACTH treatment (t1/2 = 42 h). ACTH treatment did not greatly alter the turnover rate of adrenodoxin. The half-life of adrenodoxin from control and ACTH-treated cells was determined to be 20 and 17 h, respectively. However, ACTH treatment appeared to increase the half-life of cytochrome P-45011 beta from 16 h in control cells to 24 h in treated cells. The differential rate of turnover of mitochondrial proteins studied here supports the contention that mitochondria are subject to heterogeneous degradation. It appears that chronic treatment of bovine adrenocortical cells in culture with ACTH leads to increased steroidogenic capacity, primarily as a result of increased synthesis of steroidogenic enzymes, although, as shown for cytochrome P-45011 beta, ACTH action might also increase steroidogenic capacity by increasing the half-life of this steroid hydroxylase.

Induction of synthesis of bovine adrenocortical cytochromes P-450scc, P-45011 beta, P-450C21, and adrenodoxin by prostaglandins E2 and F2 alpha and cholera toxin

To further elucidate the mechanisms by which ACTH (adrenocorticotropin) exerts its long-term action to maintain normal levels of adrenocortical cytochromes P-450 and related enzymes, the abilities of cholera toxin and prostaglandins E2 and F2 alpha to induce the synthesis of cytochromes P-450scc, P-45011 beta, and P-450C21 and adrenodoxin have been examined. These effectors stimulate the production of cyclic AMP and thus steroidogenesis in the adrenal cortex. Using bovine adrenocortical cells in primary monolayer culture, we have shown that treatment with cholera toxin results in increased synthesis of cytochromes P-450scc and P-45011 beta and adrenodoxin, similar to the effect observed upon ACTH treatment. Prostaglandins E2 and F2 alpha are less effective at inducing the synthesis of the mitochondrial cytochromes P-450, and do not seem to induce the synthesis of adrenodoxin. Furthermore, cholera toxin was found to be less effective at inducing the synthesis of microsomal cytochrome P-450C21 than ACTH, and no more effective than the prostaglandins. Thus, while it appears that elevation of cyclic AMP levels is a necessary step leading to increased synthesis of adrenocortical forms of cytochrome P-450, the detailed mechanism of this induction will be found to be different for each of the different enzymes.

Lipoproteins and the regulation of adrenal steroidogenesis

ACTH has both short-term (acute) and long-term (chronic) effects to regulate steroid hormone biosynthesis in the adrenal cortex. The acute action of ACTH involves the mobilization of cholesterol and its binding to cytochrome P-450scc. The long-term action of ACTH involves the regulation of synthesis of the various enzymes involved in steroidogenesis. Evidence is presented that cholesterol may have a role to play in this regulatory process as it does in the short-term action of ACTH, consistent with the concept that substrates of specific forms of cytochrome P-450 are frequently able to regulate the synthesis of these specific forms.

ACTH-mediated induction of synthesis and activity of cytochrome P-450s and related enzymes in cultured bovine adrenocortical cells

1. Cytochromes P-450sec and P-450(11) beta, adrenodoxin and adrenodoxin reductase, mitochondrial components of the adrenocortical steroid hydroxylase pathway, are synthesized as higher molecular weight precursors; cytochrome P-450C-21, a microsomal component of this pathway, is synthesized as the mature form. 2. Synthesis of the above mitochondrial components is induced by ACTH in a co-ordinated fashion. Synthesis of cytochrome P-450C-21 and NADPH-cytochrome P-450 reductase is also induced by ACTH, however, the induction of these microsomal components is not co-ordinated with that of the mitochondrial components. 3. Following treatment of cultured cells with ACTH, the pattern of glucocorticoid output changes from approximately equal amounts of cortisol and corticosterone to predominately cortisol within 24 h. This change results from a large induction of cytochrome P-450(17) alpha activity in response to ACTH. 4. Bovine adrenocortical cells in culture become refractory to continued treatment with ACTH. This refractoriness is manifested in terms of steroid output; synthesis of cytochromes P-450scc, P-450(11) beta and P-450C-21, adrenodoxin and adrenodoxin reductase; and activities of cholesterol side-chain cleavage, 11 beta-hydroxylase and 17 alpha-hydroxylase.

Pro-adrenocorticotropin/endorphin-derived peptides: coordinate action on adrenal steroidogenesis

A synthetic peptide, representing a portion of the 16K (16,000 dalton)-fragment sequence within the pro-adrenocorticotropin/endorphin precursor molecule, potentiates the steroidogenic action of the 1 to 24 portion of adrenocorticotropin [ACTH(1-24)] on the rat adrenal cortex. The peptide has 27 amino acid residues and consists of gamma-melanotropin with a carboxyl terminal extension. It affects both the inner and outer adrenocortical zones of hypophysectomized animals, as evidenced by a synergistic augmentation of corticosterone and aldosterone production, respectively. The peptide can be distinguished from adrenocorticotropin by its activation of cholesterol ester hydrolase and its failure to stimulate cholesterol side-chain cleavage.

Electron paramagnetic resonance studies of the purified cytochrome P-450scc and P-45011beta from bovine adrenocortical mitochondria

Electron paramagnetic resonance studies have been carried out on two species of cytochrome P-450 (P-450scc and P-45011beta) purified from bovine adrenocortical mitochondria. The g values of the steroid-bound cytochromes in the high spin form were determined at 4.2 degrees K to be 8.07, 3.60 and 1.70 for P-450scc and 8.00, 3.65 and 1.71 for P-45011beta. The E/D values were estimated to be 0.103 for P-450scc and 0.099 for P-45011beta. Either high spin P-450 was converted into the low spin form by the treatment with an NADPH dependent electron donating system and subsequent gel filtration in order to remove the steroid. The g values of the low spin ferric cytochromes were 2.423, 2.247 and 1.914 for P-450scc and 2.430, 2.251 and 1.919 for P-45011beta at 77 degrees K. The values for magnitude of delta/gamma, magnitude of V/gamma and k were 5.69, 5.21 and 1.11 for P-450scc and 5.94, 5.38 and 1.16 for P-45011beta. These studies indicate that there are some differences in the ferric heme environment between P-450scc and P-45011beta.