A Comparison of the Fatty Acid Esters of Estradiol and Corticosterone Synthesized by tIssues of the Rat

Retention of Flunisolide in Rat Lungs after Single Inhalation

Flunisolide (6α-fluorine 11β, 16α, 17α, 21-tetrahydroxypregna-1, 4-diene-3.20-dione 16.17 acetonide) is a potent inhaled corticosteroid, as demonstrated by its anti-inflammatory activities. Clinical data have widely demonstrated that inhaled flunisolide administered twice daily is effective for the treatment of bronchial asthma. However, pharmacokinetic studies suggest that the high solubility rate of flunisolde in bronchial fluid reduces the residence time of the drug in the lungs to a few minutes. The aim of this study is to determine the concentration of flunisolide in lung tissue of rats after administration by inhalation at varying time periods. Male Wistar rats weighing approximately 300 g were divided into four groups and administered a single dose of 1 mg flunisolide via inhalation. Rats were sacrificed with the exposure to CO2 either immediately or 3,6,12 hours after inhalation. The whole lung was then surgically removed and analysed for flunisolide concentration using gas chromatography. The mean concentration (2 standard deviation) of flunisolide detected in the lung tissue at 0, 3, 6 hours after inhalation were 66.4 (11.9), 48.6 (5.9), 42.7 (8.1) ng/mg of proteins, respectively. No flunisolide was detected after 12 hours in lung tissue. We conclude that flunisolide is retained for long duration (more than 6 hours) in lung tissue. This finding partially explains the mechanisms of action of the drug.

Fatty acid esters of steroids: synthesis and metabolism in lipoproteins and adipose tissue

At the end of the last century ideas concerning the physiological role of the steroid fatty acid ester family were emerging. Estrogens, fatty acylated at C-17 hydroxyl group and incorporated in lipoproteins were proposed to provide antioxidative protection to these particles. A large number of studies involving non-estrogenic adrenal steroids, and their fatty acylated forms, demonstrated their lipoprotein-mediated transport into cells and subsequent intracellular activation, suggesting a novel transport mechanism for lipophilic steroid derivatives. After these important advances the main focus of interest has shifted away from C-19 and C-21 steroids to fatty acylated estrogens. However, interest in their lipoprotein-mediated transport has decreased because only minute amounts of these derivatives were detected in circulating lipoproteins, and their antioxidative activity remained unconfirmed under physiological circumstances. It now appears that the overwhelming majority of estradiol in postmenopausal women resides in adipose tissue, most of it in esterified form. This is poorly reflected in plasma levels which are very low. Recent data suggest that estrogen fatty acid esters probably represent a storage form. The future focus of investigation is likely to be on firstly, the enzymatic mechanisms regulating the esterification and de-esterification of estradiol and other steroids residing in adipose tissue and secondly, on the role of insulin and other hormones in the regulation of these enzymatic mechanisms. Thirdly, as a large proportion of fatty acid esterified C-19 and C-21 non-estrogenic steroids is transported in lipoproteins and as they are important precursors of androgens and estrogens, this field should be investigated further.

Sexual dimorphism in esterified steroid levels in the gastropod Marisa cornuarietis: the effect of xenoandrogenic compounds

Molluscs can conjugate a variety of steroids to form fatty acid esters. In this work, the freshwater ramshorn snail Marisa cornuarietis was used to investigate sex differences in endogenous levels of esterified steroids. Testosterone and estradiol were mainly found in the esterified form in the digestive gland/gonad complex of M. cornuarietis, and males had higher levels of esterified steroids than females (4-10-fold). Additionally, the ability of several xenobiotics, namely tributyltin (TBT), methyltestosterone (MT) and fenarimol (FEN) to interfere with the esterification of testosterone and estradiol was investigated. All three compounds induced imposex - appearance of male sexual characteristics in females. Exposure to TBT led to a decrease in both esterified testosterone (60-85%) and estradiol (16-53%) in females after 100 days exposure, but had no effect on males. Exposure to FEN and MT did not alter levels of esterified steroids in males or in females, although exposed females developed imposex after 150 days exposure. The decrease in esterified steroids by TBT could not be directly linked with a decrease in microsomal acyl-CoA:testosterone acyltransferase (ATAT) activity, which catalyzes the esterification of steroids. In fact, ATAT activity was marginally induced in organisms exposed to TBT for 50 days (1.3-fold), and significantly induced in males and females exposed to MT for 50 days (1.8- and 1.5-fold, respectively), whereas no effect on ATAT activity was observed after 150 days exposure.

Safety of inhaled corticosteroids: room for improvement

Inhaled corticosteroids (ICS) are the standard of care in asthma and are widely used in the treatment of patients with chronic obstructive pulmonary disease. High-dose regimens and long-term use of ICS in predisposed individuals may be associated with a variety of side effects, similar to those observed with systemic corticosteroid therapy. Side effects associated with long-term ICS use include reduction in growth velocity, cataracts, glaucoma, osteoporosis, and fractures. Fear of unwanted complications may be of concern in all patients using ICS, particularly in age- and gender-specific populations that are more prone to develop side effects or to reduce treatment adherence because of physical, behavioral, or psychological problems. In addition to concerns about ICS safety, dosing regimens that are difficult to follow may further reduce a patient's ability to comply with treatment. Ciclesonide, a new-generation ICS with unique pharmacokinetic properties, was developed to provide effective anti-inflammatory control for asthma with once-daily administration to improve patient adherence and a high safety profile to reduce the occurrence of local and systemic side effects.

Formation of fatty acid conjugates of ciclesonide active metabolite in the rat lung after 4-week inhalation of ciclesonide

Ciclesonide, an inhaled corticosteroid (ICS) with prolonged anti-inflammatory activity, is being developed for the treatment of asthma. Fatty acid conjugation of ICS is thought to be related to prolonged ICS activity. In vitro studies demonstrated that ciclesonide is converted to an active metabolite, desisobutyryl-ciclesonide (des-CIC), which undergoes reversible fatty acid conjugation. We tested the in vivo metabolism of ciclesonide in the lung by exposing rats to inhaled ciclesonide (0.16 mg/kg/day) for 1h daily over 4 weeks. Lungs (n=6 per time point) were extracted with ethanol 2, 5, and approximately 27 h after the final treatment. Ciclesonide and des-CIC concentrations were determined using solid-phase extraction and reverse-phase high-performance liquid chromatography with tandem mass spectrometry (LC/MS/MS). Concentrations of fatty acid ester conjugates were indirectly assessed using enzymatic de-esterification before LC/MS/MS. At 2 and 5 h, fatty acid conjugates of des-CIC were the major metabolites (61 and 55%, respectively). Ciclesonide, des-CIC, and fatty acid conjugates of des-CIC were clearly present in lung samples the day after the last inhalation. This in vivo study confirmed ciclesonide activation to des-CIC and formation of fatty acid conjugates. The presence of des-CIC fatty acid conjugates at >24 h after dosing suggests that ciclesonide is appropriate for once-daily dosing.

The role of intracellular esterification in budesonide once-daily dosing and airway selectivity

BACKGROUND

Since their introduction in the 1970s, inhaled corticosteroids (ICSs) have been used to control airway inflammation associated with asthma. Budesonide is one of the ICSs recommended as first-line therapy for mild to moderate persistent asthma.

OBJECTIVE

This article describes the esterification of budesonide and how it results in prolonged, location-specific retention of drug in the airways, allowing once-daily dosing.

RESULTS

Studies conducted over the past decade have shown that budesonide forms reversible fatty acid esters within the cells of airway tissue, resulting in the formation of an intracellular depot pool of inactive drug. As the intracellular concentration of free budesonide decreases, these budesonide esters are hydrolyzed back to their active state. This process increases budesonide's retention in the airways, prolongs its duration of action, and lowers the risk of systemic effects.

CONCLUSIONS

By extending budesonide's local anti-inflammatory effect and increasing its airway selectivity, the esterification process appears to contribute to the drug's efficacy, particularly during once-daily administration. Reducing the number of required daily inhalations may increase patient compliance with asthma therapy, although this remains to be evaluated.

Budesonide fatty-acid esterification: a novel mechanism prolonging binding to airway tissue. Review of available data

AIMS

Evidence is accumulating that budesonide (BUD) forms intracellular esters in airways. which may affect both duration of action and therapeutic ratio of this drug. The aim of the present paper is to review the preclinical and human experimental evidence supporting the esterification of BUD, and to discuss the clinical implications this may have on asthma and rhinitis treatment.

RESULTS

After inhalation, intact BUD binds primarily to available steroid receptors, and mainly excess (unbound) BUD is esterified. Esterification of BUD is a rapid process: within 20 minutes of inhalation in the rat of radiolabeled BUD, approximately 80% of radioactivity within the trachea and main bronchi was associated with BUD esters, primarily BUD oleate. After 4 hours, the proportion of BUD esters/total cellular BUD was typically 40 to 50% for lung, 70 to 90% for trachea, and only 10 to 15% for peripheral muscle. Comparative in vitro and in vivo studies have shown that esterification prolongs BUD's anti-inflammatory activity longer than that of corticosteroids that can not form esters. Clinical studies have confirmed the prolonged presence of BUD esters, as well as intact BUD, in human airway tissues: 6 hours postdosing, nasal biopsy concentrations of intact BUD were >10-fold greater than those of fluticasone propionate and at 24 hours BUD was detectable in threefold more biopsies than fluticasone propionate. The impact of esterification on airway selectivity of BUD has also been demonstrated in vivo and using pharmacokinetic/pharmacodynamic models.

CONCLUSIONS

BUD is retained in airways as esters, a novel kinetic mechanism for synthetic glucocorticoids. In preclinical studies this esterification is correlated to a prolonged local tissue binding and efficacy, which is not found when the esterification is inhibited by an esterification blocker. Because less esters are formed in the systemic compartment than in airways/lung, the local benefit:systemic risk ratio may also be improved by this mechanism. BUD possesses favorable clinical properties, including its approved once-daily efficacy in asthma, which is probably in part attributable to esterification. However, a direct proof of the latter in patients requires effective and safe inhibitors of the esterification, which are not yet available. Therefore, evidence to support the therapeutic impact of esterification is still circumstantial.

Effect of clofibrate administration on the esterification and deesterification of steroid hormones by liver and extrahepatic tissues in rats

Treatment of rats with clofibrate markedly stimulated the liver microsomal esterification of estradiol, testosterone, pregnenolone, dehydroepiandrosterone, and corticosterone by acyl-CoA:steroid acyltransferase. This enzyme catalyzes the esterification of estradiol with long-chain fatty acids in both liver and extrahepatic tissues. In untreated control rats, brain had the highest acyltransferase activity per milligram of microsomal protein for estradiol esterification (3- to 4-fold higher than in the liver). Although, treatment of rats with clofibrate stimulated the esterification of estradiol by 9- to 14-fold in the liver, estradiol esterification in kidney, lung, brain, uterus, fat, and mammary glands was not increased, indicating that liver may be uniquely sensitive to induction of acyl-CoA:estradiol acyltransferase by clofibrate. In additional studies, esterase activity for hydrolysis of the oleoyl ester of estradiol was determined in control and clofibrate-treated rats. Clofibrate administration increased esterase activity by an average of 107% in fat and 70% in liver. The results indicate that treatment of rats with clofibrate stimulates the hepatic formation of highly lipophilic fatty acid esters that can be hydrolyzed in the liver and in extrahepatic tissues to the parent steroid hormone by a clofibrate-inducible esterase.

Quantitative Determination of Estradiol Fatty Acid Esters in Human Pregnancy Serum and Ovarian Follicular Fluid

Background: Lipophilic estradiol derivatives carried by lipoprotein particles in blood may mediate antioxidant or endocrine effects. We developed a new quantitative method to determine the concentration of circulating lipophilic estradiol fatty acid esters in human early- and late-pregnancy serum and in ovarian follicular fluid.

Methods: After extraction from serum or follicular fluid, estradiol fatty acid esters were separated from nonesterified estradiol by Sephadex LH-20 column chromatography. The estradiol ester fraction was hydrolyzed by saponification and further purified by several chromatographic steps. The hydrolyzed estradiol esters were measured by time-resolved fluoroimmunoassay.

Results: The average estradiol fatty acid ester concentration in serum increased 10-fold during pregnancy, from 40.4 pmol/L (expressed as pmol/L estradiol; range, 25.0–64.2 pmol/L) in early pregnancy (n = 8) to 404 pmol/L (196–731 pmol/L) in late pregnancy (n = 10). The ratio of estradiol ester to nonesterified estradiol remained relatively constant during pregnancy, at 0.4–0.6%. In 10 follicular fluid samples, the mean estradiol ester concentration was 106 nmol/L (56.9–262 nmol/L). Compared with serum, a greater proportion of estradiol in follicular fluid (3.0–10%) was in the esterified form.

Conclusion: The new method provides a means to measure circulating estradiol fatty acid ester concentrations in human pregnancy serum.

Isolation and characterization of novel endogenous digitalis-like factors in the ovary of the giant toad, Bufo marinus

We have previously described the structures of four novel unconjugated bufadienolides in the ovary of the toad, Bufo marinus. In this study, we report the separation and characterization of three novel bufadienolide conjugates. These compounds were purified by HPLC, and their structures were determined to be 11alpha, 19-dihydroxytelocinobufagin-3-(12-hydroxydodecanoic acid) ester, 11alpha,19-dihydroxytelocinobufagin-3-(14-hydroxy-7-tetra decenoic acid) ester, and 11alpha, 19-dihydroxytelocinobufagin-3-(14-hydroxytetradecanoic acid) ester on the basis of NMR and MS data. Numerous dicarboxylic acid esters of bufadienolides have previously been described, but the three bufadienolide conjugates described in this report differ from previously described esters in that they contain hydroxylated monocarboxylic acids. The function of these three conjugates is not known but they are, like bufotoxins, potent inhibitors of Na+, K+-ATPase and may play a developmental role in the differentiation of toad oocytes.

Aromatase and testosterone fatty acid esters: the search for a cryptic biosynthetic pathway to estradiol esters

The estradiol fatty acid esters (lipoidal derivatives, LE2) are extremely potent estrogens that accumulate in fat, including fat of menopausal women. These steroidal esters are protected from metabolism and are converted to the free, biologically active steroid through the action of esterases. Previous studies have shown that biosynthetic pathways in the adrenal gland exist in which steroid fatty acid esters are substrates. This led us to determine whether a cryptic aromatase pathway exists in which testosterone esters could be converted directly into LE2. We tested a representative fatty acid ester, testosterone stearate, both as an inhibitor and as a substrate for the aromatase enzyme from human placental microsomes. This ester had neither activity. In addition, we tested [1 beta-3H]testosterone acetate as a substrate for this enzyme complex, measuring the production of 3H2O as evidence of aromatization. Although the rate of reaction was considerably slower than that of testosterone, 3H2O was produced. However, when [2, 4, 6, 7-3H]testosterone acetate was incubated and the steroidal products isolated, we found that hydrolysis of the substrate had occurred. Both [3H]-labeled testosterone and estradiol were found, and very little if any [3H]estradiol acetate was formed. Thus, we conclude that an aromatase pathway involving testosterone esters does not exist and that the sole source of LE2 is through direct esterification of estradiol.

Administration of pregnenolone and dehydroepiandrosterone to guinea pigs and rats causes the accumulation of fatty acid esters of pregnenolone and dehydroepiandrosterone in plasma lipoproteins

Steroids were administered continuously to guinea pigs and rats using subcutaneously applied silastic tubing implants, and the effects on circulating steroid and steroid conjugate levels were monitored. Using implants filled with pregnenolone, we observed that pregnenolone had a marked effect on increasing the levels of its fatty acid-esterified derivative, while dehydroepiandrosterone-releasing implants produced a rise in circulating nonconjugated dehydroepiandrosterone, androst-5-ene-3 beta,17 beta-diol, androstenedione, testosterone, and lipoidal derivatives of both dehydroepiandrosterone and androst-5-ene-3 beta,17 beta-diol. Implants filled with androstenedione produced a 20-fold increase in plasma androstenedione levels relative to untreated controls and a corresponding five-fold increase over control testosterone levels. No fatty acid-esterified derivative of testosterone could be detected within the plasma. Lipoproteins were isolated from both rats and guinea pigs treated with implants filled with pregnenolone or dehydroepiandrosterone. The steroid and steroid fatty acid esters present in each fraction were analyzed, revealing that approximately 75% of all the fatty acid esters of pregnenolone recovered in the lipoproteins was localized within the high-density lipoprotein (HDL) fraction of both guinea pig and rat plasma. Similarly, lipoidal dehydroepiandrosterone was found associated predominantly with the low-density lipoprotein and HDL fractions in the guinea pig, while in the rat this steroid conjugate was exclusively within the HDL fraction. High-density lipoprotein-incorporated tritiated pregnenolone fatty acid esters and dehydroepiandrosterone fatty acid esters were injected into castrated male guinea pigs to study the fate of these complexes.(ABSTRACT TRUNCATED AT 250 WORDS)

Delta 5-3 beta-hydroxysteroid acyl transferase activity in the rat brain

Pregnenolone and dehydroepiandrosterone accumulate in brain as sulfate and fatty acid esters and unconjugated steroids. The steroid fatty acid ester-synthesizing activity was investigated in rat brain microsomes. Endogenous fatty acids in the microsomal fraction were used for the esterification of steroids. The enzyme system had a pH optimum of 4.5 in acetate buffer with [3H]dehydroepiandrosterone as substrate. The apparent Km was 9.2 +/- 3.1 x 10(-5) M and Vmax was 18.6 +/- 3.4 nmol/h/mg protein (mean +/- SEM). The inhibition constants of pregnenolone and testosterone were 123 and 64 microM, respectively. Results were compatible with a competitive type of inhibition. A high level of synthetic activity was found in the brain of 1- to 3-week-old male rats, which rapidly decreased with aging. Saponification of purified [3H]pregnenolone esters yielded pregnenolone and a mixture of palmitate, oleate, linoleate, stearate, and myristate as the predominant fatty acids. Contrasting with the high rates of esterification of several radioactive delta 5-3 beta-hydroxysteroids or 17 beta-hydroxysteroids, no fatty acid esters of either cholesterol, epitestosterone (with a hydroxyl group at position C-17 alpha), or corticosterone (with hydroxyl groups at C-21 and C-11 beta) were formed in the same incubation conditions.

Neurosteroids: biosynthesis, metabolism and function of pregnenolone and dehydroepiandrosterone in the brain

Pregnenolone (P) and dehydroepiandrosterone (D) accumulate in the brain as unconjugated steroids and their sulfate (S) and fatty acid (L) esters. The microsomal acyl-transferase activity is highest in immature (1-3 weeks old) male rats. The immunocytochemical and biochemical evidence for P biosynthesis by differentiated oligodendrocytes is reviewed. The importance of P synthesis for its brain accumulation is assessed by the intracysternal injection of the inhibitor aminoglutethimide. Primary glial cell cultures convert P to 20-OH-P, PL, progesterone, 5 alpha-pregnane-3,20-dione and 3 alpha-hydroxy-5 alpha-pregnane-20-one (Polone). Astroglial cell cultures also produce these metabolites, whereas neurons from 17-day mouse embryos only form 20-OH-P. P and D are converted to the corresponding 7 alpha-hydroxylated metabolites by a very active P-450 enzyme from rat brain microsomes. Several functions of neurosteroids are documented. P decreases in olfactory bulb of intact male rats exposed to the scent of estrous females. D inhibits the aggressive behavior of castrated male mice towards lactating female intruders. The D analog 3 beta-methyl-androst-5-en-17-one, which cannot be metabolized into sex steroids and is not demonstrably androgenic or estrogenic is at least as efficient as D. Both compounds elicit a marked decrease of PS in rat brain. The Cl- conductance of gamma-aminobutyric (GABAA) receptor is stimulated by GABA agonists, an effect which is enhanced by Polone and antagonized by PS. Thus, P metabolites in brain as well as steroids of extraencephalic sources may be involved physiologically in GABAA receptor function. The neurosteroids accumulated in brain may be precursors of sex steroid hormones and progesterone receptors have been localized in glial cells. P and D do not bind to any known intracellular receptor. A heat stable P binding protein has been found in brain cytosol with distinct ligand specificity. A binding component specific for steroids sulfates, including Polone S, DS and PS, in the order of decreasing affinity is localized in adult rat brain synaptosomal membranes. Its relationship to the GABAA receptor is under current investigation.

Steroidal fatty acid esters

Several years ago we discovered an unexpected family of steroidal metabolites, steroidal fatty acid esters. We found that fatty acid esters of 5-ene-3 beta-hydroxysteroids, pregnenolone and dehydroisoandrosterone are present in the adrenal. Subsequently, others have shown the existence of these non-polar 5-ene-3 beta-hydroxysteroidal esters in blood, brain and ovaries. Currently, almost every family of steroid hormone is known to occur in esterified form. We have studied the esters of the estrogens and glucocorticoids in some detail, and have found that these two steroidal families are esterified by separate enzymes. In a biosynthetic experiment performed simultaneously with estradiol and corticosterone, we established that the fatty acid composition of the steroidal esters is quite different. The corticoid is composed predominantly of one fatty acid, oleate, while the estradiol esters are extremely heterogeneous. Our studies have demonstrated that the estrogens are extremely long-lived hormones, that they are protected by the fatty acid from metabolism. They are extremely potent estrogens, with prolonged activity. Esterification appears to be the only form of metabolism that does not deactivate the biological effects of estradiol. We have demonstrated the biosynthesis of fatty acid esters of estriol, monoesters at both C-16 alpha and C-17 beta. They too are very potent estrogens. These fatty acid esters of the estrogens are the endogenous analogs of estrogen esters, like benzoate, cypionate, etc., which have been used for decades, pharmacologically because of their prolonged therapeutic potency. We have found that the estradiol esters are located predominantly in hydrophobic tissues, such as fat. Sequestered in these tissues, they are an obvious reservoir of estrogenic reserve, requiring only an esterase for activation. To the contrary the biological activity of the fatty acid esters of the glucocorticoid, corticosterone, is not different from that of its free parent steroid. We have shown that the rapid kinetics of its induction of gluconeogenic responses is caused by its labile C-21 ester which is rapidly hydrolyzed by esterase enzymes. While it appears that the physiological role of the estrogen esters may be related to their long-lived hormonal activity, the role of the other families of steroidal esters is not yet apparent. They, and perhaps the estrogen esters as well, must serve other purposes. Indeed they may serve important biological functions beyond those which we ordinarily associate with steroid hormones.