Epiandrosterone, a metabolite of testosterone precursor, blocks L-type calcium channels of ventricular myocytes and inhibits myocardial contractility

Impact of estradiol, testosterone and their ratio on left and right auricular myofilament function in male and female patients undergoing coronary artery bypass grafting

BACKGROUND

The impact of sex hormones on right and left auricular contractile apparatus function is largely unknown. We evaluated the impact of sex hormones on left and right heart contractility at the level of myocardial filaments harvested from left and right auricles during elective coronary artery bypass surgery.

METHODS

150 patients (132 male; 18 female) were enrolled. Preoperative testosterone and estradiol levels were measured with Immunoassay. Calcium induced force measurements were performed with left- and right auricular myofilaments in a skinned fiber model. Correlation analysis was used for comparison of force values and levels of sex hormones and their ratio.

RESULTS

Low testosterone was associated with higher top force values in right-sided myofilaments but not in left-sided myofilaments for both sexes (p = 0.000 in males, p = 0.001 in females). Low estradiol levels were associated with higher top force values in right-sided myofilaments (p 0.000) in females and only borderline significantly associated with higher top force values in males (p 0.056). In females, low estradiol levels correlated with higher top force values in left sided myofilaments (p 0.000). In males, higher Estradiol/Testosterone ratio (E/T ratio) was only associated with higher top force values from right auricular myofilaments (p 0.04) In contrast, in females higher E/T ratio was associated with lower right auricular myofilament top force values (p 0.03) and higher top force values in left-sided myofilaments (p 0.000).

CONCLUSIONS

This study shows that patients' comorbidities influence left and right sided contractility and may blur results concerning influence of sex hormones if not eliminated. A sex hormone dependent influence is obvious with different effects on the left and right ventricle. The E/T ratio and its impact on myofilament top force showed divergent results between genders, and may partially explain gender differences in patients with cardiovascular disease.

A Patent Review on SARS Coronavirus Papain-Like Protease (PLpro ) Inhibitors

The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic is an unprecedented global health emergency causing more than 6.6 million fatalities by 31 December 2022. So far, only three antiviral drugs have been granted emergency use authorisation or approved by the FDA. The SARS-CoV-2 papain-like protease (PLpro ) is deemed an attractive drug target as it plays an essential role in viral polyprotein processing and pathogenesis although no inhibitors have yet been approved. This patent review discusses coronavirus PLpro inhibitors reported in patents published between 1 January 2003 to 2 March 2023, giving an overview on the inhibitors that have generated commercial interest, especially amongst drug companies.

Visible-Light Photocatalysis of Eosin Y: HAT and Complementing MS-CPET Strategy to Trifluoromethylation of β-Ketodithioesters with Langlois' Reagent

A metal- and oxidant-free photoinduced strategy for thioxo sulfur-selective trifluoromethylation of β-ketodithioesters at room temperature is reported. Excellent Z/E-stereoselectivity has been achieved with cheap and viable Langlois' reagent (CF₃SO₂Na, sodium triflinate) in the presence of eosin Y, which acts as a hydrogen atom transfer (HAT) catalyst. The reaction proceeds via disulfide intermediate disulfanediylbis(3-(alkylthio)-1-phenylprop-2-en-1-one) (a dimer of β-ketodithioester) followed by complementing proton-coupled electron transfer-mediated reverse HAT cycle of eosin Y. This operationally simple and efficient protocol allows direct access to triflinated α-oxoketene dithioacetals in good to excellent yields bearing diverse synthetically useful functional groups of different electronic and steric nature.

Dehydroepiandrosterone inhibits ICa,L and its window current in voltage-dependent and -independent mechanisms in arterial smooth muscle cells

Dehydroepiandrosterone (DHEA) is an adrenal steroid hormone, which has the highest serum concentration among steroid hormones with DHEA sulfate (DHEAS). DHEA possesses an inhibitory action on glucose-6-phosphate dehydrogenase (G6PD), the first pentose-phosphate pathway enzyme that reduces NADP⁺ to NADPH. DHEA induced relaxation of high K⁺-induced contraction in rat arterial strips, whereas DHEAS barely induced it. We studied the effects of DHEA on L-type Ca²⁺ current ( I_Ca,L) of A7r5 arterial smooth muscle cells and compared the mechanism of inhibition with that produced by the 6-aminonicotinamide (6-AN) competitive inhibitor of G6PD. DHEA moderately inhibited I_Ca,L that was elicited from a holding potential (HP) of -80 mV [voltage-independent inhibition (VIDI)] and accelerated decay of I_Ca,L during the depolarization pulse [voltage-dependent inhibition (VDI)]. DHEA-induced VDI decreased peak I_Ca,L at depolarized HPs. By applying repetitive depolarization pulses from multiple HPs, novel HP-dependent steady-state inactivation curves ( f_∞-HP) were constructed. DHEA shifted f_∞-HP to the left and inhibited the window current, which was recorded at depolarized HPs and obtained as a product of current-voltage relationship and f_∞-HP. The IC₅₀ value of I_Ca,L inhibition was much higher than serum concentration. DHEA-induced VDI was downregulated by the dialysis of guanosine 5'- O-(2-thiodiphosphate), which shifted f_∞-voltage to the right before the application of DHEA. 6-AN gradually and irreversibly inhibited I_Ca,L by VIDI, suggesting that the inhibition of G6PD is involved in DHEA-induced VIDI. In 6-AN-pretreated cells, DHEA induced additional inhibition by increasing VIDI and generating VDI. The inhibition of G6PD underlies DHEA-induced VIDI, and DHEA additionally induces VDI as described for Ca²⁺ channel blockers. NEW & NOTEWORTHY Dehydroepiandrosterone, the most abundantly released adrenal steroid hormone with dehydroepiandrosterone sulfate, inhibited L-type Ca²⁺ current and its window current in aortic smooth muscle cells. The IC₅₀ value of inhibition decreased with the depolarization of holding potential to 15 µM at -20 mV. The inhibition occurred in a voltage-dependent manner as described for Ca²⁺ channel blockers and in a voltage-independent manner because of the inhibition of glucose-6-phosphate dehydrogenase.

In vivo and in vitro evidences of dehydroepiandrosterone protective role on the cardiovascular system

CONTEXT

Dehydroepiandrosterone (DHEA) and its sulfate ester, Dehydroepiandrosterone Sulfate (DHEA-S) have been considered as putative anti-aging hormones for many years. Indeed, while DHEAS is the most abundant circulating hormone, its concentration is markedly decreased upon aging and early epidemiologic trials have revealed a strong inverse correlation between the hormone concentrations and the occurrence of several dysfunctions frequently encountered in the elderly. Naturally, hormonal supplementation has been rapidly suggested to prevent DHEA (S) deficiency and therefore, age-related development of these pathologies, using the same strategy as estrogen replacement therapy proposed in postmenopausal women.

EVIDENCE ACQUISITION

All references were searched using PubMed and the following strategy: our initial selection included all articles in English and we sorted them with the following keywords: "DHEA or DHEA-S" and "heart or vascular or endothelium or cardiovascular disease". The search was limited to neither the publication date nor specific journals. The final selection was made according to the relevance of the article content with the aims of the review. According to these criteria, fewer than 10% of the articles retrieved at the first step were discarded.

RESULTS

In this short review, we have focused on the cardiovascular action of DHEA. We started by analyzing evidences in favor of a strong inverse association between DHEA (S) levels and the cardiovascular risk as demonstrated in multiple observational epidemiologic studies for several decades. Then we discussed the different trials aimed at supplementing DHEA (S), both in animals and human, for preventing cardiovascular diseases and we analyzed the possible reasons for the discrepancy observed among the results of some studies. Finally, we presented putative molecular mechanisms of action for DHEA (S), demonstrated in vitro in different models of vascular and cardiac cells, highlighting the complexity of the involved signaling pathways.

CONCLUSIONS

The identification of the beneficial cardiovascular effects of DHEA (S) and a better understanding of the involved mechanisms should be helpful to develop new strategies or pharmacologic approaches for many lethal diseases in Western countries.

Dehydroepiandrosterone, its metabolites and ion channels

This review is focused on the physiological and pathophysiological relevance of steroids influencing the activities of the central and peripheral nervous systems with regard to their concentrations in body fluids and tissues in various stages of human life like the fetal development or pregnancy. The data summarized in this review shows that DHEA and its unconjugated and sulfated metabolites are physiologically and pathophysiologically relevant in modulating numerous ion channels and participate in vital functions of the human organism. DHEA and its unconjugated and sulfated metabolites including 5α/β-reduced androstane steroids participate in various physiological and pathophysiological processes like the management of GnRH cyclic release, regulation of glandular and neurotransmitter secretions, maintenance of glucose homeostasis on one hand and insulin insensitivity on the other hand, control of skeletal muscle and smooth muscle activities including vasoregulation, promotion of tolerance to ischemia and other neuroprotective effects. In respect of prevalence of steroid sulfates over unconjugated steroids in the periphery and the opposite situation in the CNS, the sulfated androgens and androgen metabolites reach relevance in peripheral organs. The unconjugated androgens and estrogens are relevant in periphery and so much the more in the CNS due to higher concentrations of most unconjugated steroids in the CNS tissues than in circulation and peripheral organs. This article is part of a Special Issue entitled "Essential role of DHEA".

DHEA prevents mineralo- and glucocorticoid receptor-induced chronotropic and hypertrophic actions in isolated rat cardiomyocytes

Corticosteroids have been involved in the genesis of ventricular arrhythmias associated with pathological heart hypertrophy, although molecular mechanisms responsible for these effects have not been completely explained. Because mineralocorticoid receptor (MR) antagonists have been demonstrated to be beneficial on the cardiac function, much attention has been given to the action of aldosterone on the heart. However, we have previously shown that both aldosterone and corticosterone in vitro induce a marked acceleration of the spontaneous contractions, as well as a significant cell hypertrophy in isolated neonate rat ventricular cardiomyocytes. Moreover, a beneficial role of the steroid hormone dehydroepiandrosterone (DHEA) has been also proposed, but the mechanism of its putative cardioprotective function is not known. We found that DHEA reduces both the chronotropic and the hypertrophic responses of cardiomyocytes upon stimulation of MR and glucocorticoid receptor (GR) in vitro. DHEA inhibitory effects were accompanied by a decrease of T-type calcium channel expression and activity, as assessed by quantitative PCR and the patch-clamp technique. Prevention of cell hypertrophy by DHEA was also revealed by measuring the expression of A-type natriuretic peptide and BNP. The kinetics of the negative chronotropic effect of DHEA, and its sensitivity to actinomycin D, pointed out the presence of both genomic and nongenomic mechanisms of action. Although the genomic action of DHEA was effective mostly upon MR activation, its rapid, nongenomic response appeared related to DHEA antioxidant properties. On the whole, these results suggest new mechanisms for a putative cardioprotective role of DHEA in corticosteroid-associated heart diseases.

Sex and gender aspects in antiarrhythmic therapy

Although cardiac arrhythmia had long been considered a predominantly male syndrome, it is now clear that arrhythmia is also a primary cause of mortality in women. Notably, the manifestation of specific arrhythmia syndromes appears to be gender specific. In particular, female sex is an independent risk factor for development of torsade de pointes (TdP) arrhythmias not only in congenital long QT syndromes but also in acquired long QT syndromes which occur as adverse effects of existing drugs. Males, on the other hand, are more likely to develop Brugada syndrome. Recent clinical and experimental studies suggest that these differences may stem from intrinsic sex differences in cardiac tissue. These include fundamental electrical differences resulting from variable ion channel expression and diverse sex hormonal regulation via long-term genomic and acute nongenomic pathways, and sex differences in drug responses and metabolisms. Undoubtedly, determining the effect of gender on cardiac function will be difficult and require sophisticated methodologies. However, gender differences underlying predilection to distinct arrhythmia syndromes must be revealed so that new therapeutic strategies that take gender into account can be applied to at-risk patients.

Glucose-6-phosphate dehydrogenase and NADPH redox regulates cardiac myocyte L-type calcium channel activity and myocardial contractile function

We recently demonstrated that a 17-ketosteroid, epiandrosterone, attenuates L-type Ca²⁺ currents (I_Ca-L) in cardiac myocytes and inhibits myocardial contractility. Because 17-ketosteroids are known to inhibit glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme in the pentose phosphate pathway, and to reduce intracellular NADPH levels, we hypothesized that inhibition of G6PD could be a novel signaling mechanism which inhibit I_Ca-L and, therefore, cardiac contractile function. We tested this idea by examining myocardial function in isolated hearts and Ca²⁺ channel activity in isolated cardiac myocytes. Myocardial function was tested in Langendorff perfused hearts and I_Ca-L were recorded in the whole-cell patch configuration by applying double pulses from a holding potential of −80 mV and then normalized to the peak amplitudes of control currents. 6-Aminonicotinamide, a competitive inhibitor of G6PD, increased pCO₂ and decreased pH. Additionally, 6-aminonicotinamide inhibited G6PD activity, reduced NADPH levels, attenuated peak I_Ca-L amplitudes, and decreased left ventricular developed pressure and ±dp/dt. Finally, dialyzing NADPH into cells from the patch pipette solution attenuated the suppression of I_Ca-L by 6-aminonicotinamide. Likewise, in G6PD-deficient mice, G6PD insufficiency in the heart decreased GSH-to-GSSG ratio, superoxide, cholesterol and acetyl CoA. In these mice, M-mode echocardiographic findings showed increased diastolic volume and end-diastolic diameter without changes in the fraction shortening. Taken together, these findings suggest that inhibiting G6PD activity and reducing NADPH levels alters metabolism and leads to inhibition of L-type Ca²⁺ channel activity. Notably, this pathway may be involved in modulating myocardial contractility under physiological and pathophysiological conditions during which the pentose phosphate pathway-derived NADPH redox is modulated (e.g., ischemia-reperfusion and heart failure).

Dehydroepiandrosterone (DHEA) inhibits voltage-gated T-type calcium channels

BACKGROUND AND PURPOSE

Dehydroepiandrosterone (DHEA) and its sulfated form, DHEAS, are the most abundant steroid hormones in the mammalian blood flow. DHEA may have beneficial effects in various pathophysiological conditions such as cardiovascular diseases or deterioration of the sense of well-being. However to date, the cellular mechanism underlying DHEA action remains elusive and may involve ion channel modulation. In this study, we have characterized the effect of DHEA on T-type voltage-activated calcium channels (T-channels), which are involved in several cardiovascular and neuronal diseases.

KEY RESULTS

Using the whole-cell patch-clamp technique, we demonstrate that DHEA inhibits the three recombinant T-channels (Ca(V)3.1, Ca(V)3.2 and Ca(V)3.3) expressed in NG108-15 cell line, as well as native T-channels in pulmonary artery smooth muscle cells. This effect of DHEA is both concentration (IC(50) between 2 and 7μM) and voltage-dependent and results in a significant shift of the steady-state inactivation curves toward hyperpolarized potentials. Consequently, DHEA reduces window T-current and inhibits membrane potential oscillations induced by Ca(V)3 channels. DHEA inhibition is not dependent on the activation of nuclear androgen or estrogen receptors and implicates a PTX-sensitive Gi protein pathway. Functionally, DHEA and the T-type inhibitor NNC 55-0396 inhibited KCl-induced contraction of pulmonary artery rings and their effect was not cumulative.

CONCLUSIONS

Altogether, the present data demonstrate that DHEA inhibits T-channels by a Gi protein dependent pathway. DHEA-induced alteration in T-channel activity could thus account for its therapeutic action and/or physiological effects.

Glucose-6-phosphate dehydrogenase is a regulator of vascular smooth muscle contraction

Glucose-6-phosphate dehydrogenase (G6PD) is the rate-limiting enzyme in the pentose phosphate pathway and a major source of nicotinamide adenine dinucleotide phosphate reduced (NADPH), which regulates numerous enzymatic (including glutathione reductase and NADPH oxidase that, respectively, generates reduced glutathione and reactive oxygen species) reactions involved in various cellular actions, yet its physiological function is seldom investigated. We, however, recently showed that inhibiting G6PD causes precontracted coronary artery (CA) to relax in an endothelium-derived relaxing factor- and second messenger-independent manner. Here we assessed the role of G6PD in regulating CA contractility. Treating bovine CAs for 20 min with potassium chloride (KCl; 30 mM), amphotericin B (50 μM), or U46619 (100 nM) significantly (p < 0.05) increased both G6PD activity and glucose flux through the pentose phosphate pathway. The effect was Ca(2+) independent, and there was a corresponding increase in protein kinase C (PKC) activity. Activation of G6PD by KCl was blocked by the PKCδ inhibitor rottlerin (10 μM) or by knocking down PKCδ expression using siRNA. Phorbol 12, 13-dibutyrate (10 μM), a PKC activator, significantly increased G6PD phosphorylation and activity, whereas single (S210A, T266A) and double (S210A/T266A) mutations at sites flanking the G6PD active site significantly inhibited phosphorylation, shifted the isoelectric point, and reduced enzyme activity. Knocking down G6PD decreased NADPH and reactive oxygen species generation, and reduced KCl-evoked increases in [Ca(2+)](i) and myosin light chain phosphorylation, thereby reducing CA contractility. Similarly, aortas from G6PD-deficient mice developed less KCl/phorbol 12, 13-dibutyrate-evoked force than those from their wild-type littermates. Conversely, overexpression of G6PD augmented KCl-evoked increases in [Ca(2+)](i), thereby augmenting CA contraction. Our findings demonstrate that G6PD activity and NADPH is increased in activated CA in a PKCδ-dependent manner and that G6PD modulates Ca(2+) entry and CA contractions evoked by membrane depolarization.

Effects of hypoxia on testosterone release in rat Leydig cells

The aim of this study was to explore the effect and action mechanisms of intermittent hypoxia on the production of testosterone both in vivo and in vitro. Male rats were housed in a hypoxic chamber (12% O(2) + 88% N(2), 1.5 l/ml) 8 h/day for 4 days. Normoxic rats were used as control. In an in vivo experiment, hypoxic and normoxic rats were euthanized and the blood samples collected. In the in vitro experiment, the enzymatically dispersed rat Leydig cells were prepared and challenged with forskolin (an adenylyl cyclase activator, 10(-4) M), 8-Br-cAMP (a membrane-permeable analog of cAMP, 10(-4) M), hCG (0.05 IU), the precursors of the biosynthesis testosterone, including 25-OH-C (10(-5) M), pregnenolone (10(-7) M), progesterone (10(-7) M), 17-OH-progesterone (10(-7) M), and androstendione (10(-7)-10(-5) M), nifedipine (L-type Ca(2+) channel blocker, 10(-6)-10(-4) M), nimodipine (L-type Ca(2+) channel blocker, 10(-5) M), tetrandrine (L-type Ca(2+) channel blocker, 10(-5) M), and NAADP (calcium-signaling messenger causing release of calcium from intracellular stores, 10(-6)-10(-4) M). The concentrations of testosterone in plasma and medium were measured by radioimmunoassay. The level of plasma testosterone in hypoxic rats was higher than that in normoxic rats. Enhanced testosterone production was observed in rat Leydig cells treated with hCG, 8-Br-cAMP, or forskolin in both normoxic and hypoxic conditions. Intermittent hypoxia resulted in a further increase of testosterone production in response to the testosterone precursors. The activity of 17β-hydroxysteroid dehydrogenase was stimulated by the treatment of intermittent hypoxia in vitro. The intermittent hypoxia-induced higher production of testosterone was accompanied with the influx of calcium via L-type calcium channel and the increase of intracellular calcium via the mechanism of calcium mobilization. These results suggested that the intermittent hypoxia stimulated the secretion of testosterone at least in part via stimulatory actions on the activities of adenylyl cyclase, cAMP, L-type calcium channel, and steroidogenic enzymes.

Modulation of neurotransmitter systems by dehydroepiandrosterone and dehydroepiandrosterone sulfate: mechanism of action and relevance to psychiatric disorders

Dehydroepiandrosterone (DHEA) is synthesized in the brain and several studies have shown that this steroid is a modulator of synaptic transmission. The effect of DHEA, and its sulfate ester DHEAS, on glutamate and GABA neurotransmission has been extensively studied but some effects on other neurotransmitter systems, such as dopamine, serotonin and nitric oxide, have also been reported. This review summarizes studies showing the effect of DHEA and DHEAS on neurotransmitter systems at different levels (metabolism, release, reuptake, receptor activation), as well as the activation of voltage-gated ion channels and calcium homeostasis, showing the variety of effects that these steroids exert on those systems, allowing the discussion of its mechanisms of action and its relevance to psychiatric disorders.

Oxidant and redox signaling in vascular oxygen sensing: implications for systemic and pulmonary hypertension

It has been well known for >100 years that systemic blood vessels dilate in response to decreases in oxygen tension (hypoxia; low PO2), and this response appears to be critical to supply blood to the stressed organ. Conversely, pulmonary vessels constrict to a decrease in alveolar PO2 to maintain a balance in the ventilation-to-perfusion ratio. Currently, although little question exists that the PO2 affects vascular reactivity and vascular smooth muscle cells (VSMCs) act as oxygen sensors, the molecular mechanisms involved in modulating the vascular reactivity are still not clearly understood. Many laboratories, including ours, have suggested that the intracellular calcium concentration ([Ca2+]i), which regulates vasomotor function, is controlled by free radicals and redox signaling, including NAD(P)H and glutathione (GSH) redox. In this review article, therefore, we discuss the implications of redox and oxidant alterations seen in pulmonary and systemic hypertension, and how key targets that control [Ca2+]i, such as ion channels, Ca2+ release from internal stores and uptake by the sarcoplasmic reticulum, and the Ca2+ sensitivity to the myofilaments, are regulated by changes in intracellular redox and oxidants associated with vascular PO2sensing in physiologic or pathophysiologic conditions.

Rapid actions of androgens

The biological activity of androgens is thought to occur predominantly through binding to intracellular androgen-receptors, a member of the nuclear receptor family, that interact with specific nucleotide sequences to alter gene expression. This genomic-androgen effect typically takes at least more than half an hour. In contrast, the rapid or non-genomic actions of androgens are manifested within in seconds to few minutes. This rapid effect of androgens are manifold, ranging from activation of G-protein coupled membrane androgen-receptors or sex hormone-binding globulin receptors, stimulation of different protein kinases, to direct modulation of voltage- and ligand gated ion-channels and transporters. The physiological relevance of these non-genomic androgen actions has not yet been determined in detail. However, it may contribute to modulate several second messenger systems or transcription factors, which suggests a cross-talk between the fast non-genomic and the slow genomic pathway of androgens. This review will focus on the rapid effects of androgens on cell surface and cytoplasmic level.

Upregulation of glucose-6-phosphate dehydrogenase and NAD(P)H oxidase activity increases oxidative stress in failing human heart

BACKGROUND

We previously found that higher NADPH levels produced by glucose-6-phosphate dehydrogenase (G6PD) can enhance myocardial superoxide generation by NAD(P)H oxidase in a dog model of dilated cardiomyopathy. Therefore, we tested whether G6PD activity is elevated and enhances NADPH level and increases NAD(P)H oxidase-derived superoxide production in the myocardium from patients with heart failure from ischemic cardiomyopathy.

METHODS AND RESULTS

Surgical discards of left ventricle were collected from 8 congestive heart failure patients undergoing surgical ventricular restoration procedures, whereas control left ventricle tissue was obtained from 5 normal donor hearts deemed not suitable for transplantation. Biochemical assays were performed in tissue homogenates. We found that superoxide and hydrogen peroxide were elevated, respectively, by 9- and 3-fold in failing versus normal hearts (P < .05). The NAD(P)H oxidase inhibitors gp91(ds-tat), apocynin, and diphenyleneiodonium, significantly inhibited superoxide generation by approximately 75%, 89%, and 91%, respectively. Superoxide production by NAD(P)H oxidase increased 10- and 3-fold by adding NADPH (100 micromol/L) and NADH (100 micromol/L), respectively, in a DPI- and gp91(ds-tat)-inhibitable manner. Interestingly, chelerythrine, a PKC inhibitor, and PP2, a Src kinase family inhibitor, reduced G6PD activity (0.29 +/- 0.04 nM x min x mg protein) by 50% and 51% and these inhibitors also decreased myocardial superoxide by 99% and 79%, respectively. Furthermore, 6-aminonicotinamide, a G6PD inhibitor, decreased myocardial superoxide production by 71%.

CONCLUSIONS

These data suggest that high NAD(P)H oxidase, fueled by G6PD-derived NADPH, generates most of the superoxide in failing hearts of patients with ischemic cardiomyopathy. In addition, PKC-Src kinase signaling pathways seem to coordinate the activation of both G6PD and NAD(P)H oxidase in human cardiac muscle.

Molecular requirements for L-type Ca2+ channel blockade by testosterone

Despite being generally perceived as detrimental to the cardiovascular system, testosterone has marked beneficial vascular effects; most notably it acutely and directly causes vasodilatation. Indeed, men with hypotestosteronaemia can present with myocardial ischemia and angina which can be rapidly alleviated by infusion of testosterone. To date, however, in vitro studies have failed to provide a convincing mechanism to account for this clinically important effect. Here, using whole-cell patch-clamp recordings to measure current flow through recombinant human L-type Ca2+ channel alpha(1C) subunits (Ca(v)1.2), we demonstrate that testosterone inhibits such currents in a concentration-dependent manner. Importantly, this occurs over the physiological range of testosterone concentrations (IC50 34 nM), and is not mimicked by the metabolite 5alpha-androstan-17beta-ol-3-one (DHT), nor by progesterone or estradiol, even at high (10 microM) concentration. L-type Ca2+ channels in the vasculature are also important clinical targets for vasodilatory dihydropyridines. A single point mutation (T1007Y) almost completely abolishes nifedipine sensitivity in our recombinant expression system. Crucially, the same mutation renders the channels insensitive to testosterone. Our data strongly suggest, for the first time, the molecular requirements for testosterone binding to L-type Ca2+ channels, thereby supporting its beneficial role as an endogenous Ca2+ channel antagonist in the treatment of cardiovascular disease.

Regulation of cardiac ion channels via non-genomic action of sex steroid hormones: implication for the gender difference in cardiac arrhythmias

Long QT syndrome (LQTS) is a disorder associated with prolonged electrocardiographic QT intervals and the development of ventricular arrhythmias. LQTS occurs as a congenital form in an autosomal-dominant or an autosomal-recessive manner, and as an acquired form occurred in various cardiac disorders and induced by drug side actions. Accumulating clinical information indicates the presence of gender difference in LQTS. Rate-corrected QT interval (QT(c) interval) is longer in females than in males, and female gender itself is an independent risk factor for development of arrhythmias in both congenital and acquired forms of LQTS. Gender differences in QT(c) interval and arrhythmic event in LQTS are not observed before puberty, while they become suddenly notable upon the onset of puberty. In females, QT(c) interval and risk of arrhythmic events in LQTS patients fluctuates during the menstrual cycle, and is affected by hormone replacement therapy. These clinical data suggest a critical role of sex steroid hormones on QT(c) interval and gender difference in LQTS risk. Sex steroid hormones have been traditionally considered as transactivation factors regulating the expression of target genes. However, accumulating evidences indicate the presence of novel non-transcriptional mechanisms of signal transduction through steroid hormone receptors. Sex steroid hormones rapidly regulate cardiac ion channel activity without transcription processes, which involves nitric oxides produced via the PI3-kinase/Akt/eNOS signaling cascade. In addition to transcriptional regulation, non-transcriptional regulation of cardiac ion channels is in part responsible for the gender difference in LQTS risk and its fluctuation during the menstrual cycle in females.

Long-term and immediate effect of testosterone on single T-type calcium channel in neonatal rat cardiomyocytes

In the cardiovascular system, T-type calcium channels play an important role for the intracellular calcium homeostasis and spontaneous pacemaker activity and are involved in the progression of structural heart diseases. Androgens influence the cardiovascular physiology and pathophysiology. However, their effect on native T-type calcium currents (I(Ca,T)) remains unclear. To test the chronic effect of testosterone on the cardiac I(Ca,T), cultured neonatal rat ventricular cardiomyocytes were treated with testosterone (1 nM-10 microM) for 24-30 h. Current measurements were performed after testosterone washout to exclude any acute testosterone effects. Testosterone (100 nm) pretreatment significantly increased whole-cell I(Ca,T) density from 1.26 +/- 0.48 pA/pF (n = 8) to 5.06 +/- 1.75 pA/pF (n = 7; P < 0.05) and accelerated beating rate. This was attributed to both increased expression levels of the pore-forming subunits Ca(v)3.1 and Ca(v)3.2 and increased T-type single-channel activity. On single-channel level, the increase of the ensemble average current by testosterone vs. time-matched controls was due to an increased availability (58.1 +/- 4.2 vs. 21.5 +/- 4.0%, P < 0.01) and open probability (2.78 +/- 0.29 vs. 0.85 +/- 0.23%, P < 0.01). Cotreatment with the selective testosterone receptor antagonist flutamide (10 mum) prevented these chronic testosterone-induced effects. Conversely, acute application of testosterone (10 microM) decreased T-type single-channel activity in testosterone pretreated cells by reducing the open probability (0.78 +/- 0.13 vs. 2.91 +/- 0.38%, P < 0.01), availability (23.6 +/- 3.3 vs. 57.6 +/- 4.5%, P < 0.01), and peak current (-20 +/- 4 vs. -58 +/- 4 fA, P < 0.01). Flutamide (10 microM) did not abolish the testosterone-induced acute block of T-type calcium channels. Our results indicate that long-term testosterone treatment increases, whereas acute testosterone decreases neonatal rat T-type calcium currents. These effects seem to be mediated by a genomic chronic stimulation and a nongenomic acute inhibitory action.

Glucose-6-phosphate dehydrogenase-derived NADPH fuels superoxide production in the failing heart

In the failing heart, NADPH oxidase and uncoupled NO synthase utilize cytosolic NADPH to form superoxide. NADPH is supplied principally by the pentose phosphate pathway, whose rate-limiting enzyme is glucose 6-phosphate dehydrogenase (G6PD). Therefore, we hypothesized that cardiac G6PD activation drives part of the excessive superoxide production implicated in the pathogenesis of heart failure. Pacing-induced heart failure was performed in eight chronically instrumented dogs. Seven normal dogs served as control. End-stage failure occurred after 28 +/- 1 days of pacing, when left ventricular end-diastolic pressure reached 25 mm Hg. In left ventricular tissue homogenates, spontaneous superoxide generation measured by lucigenin (5 microM) chemiluminescence was markedly increased in heart failure (1338 +/- 419 vs. 419 +/- 102 AU/mg protein, P < 0.05), as were NADPH levels (15.4 +/- 1.5 vs. 7.5 +/- 1.5 micromol/gww, P < 0.05). Superoxide production was further stimulated by the addition of NADPH. The NADPH oxidase inhibitor gp91(ds-tat) (50 microM) and the NO synthase inhibitor L-NAME (1 mM) both significantly lowered superoxide generation in failing heart homogenates by 80% and 76%, respectively. G6PD was upregulated and its activity higher in heart failure compared to control (0.61 +/- 0.10 vs. 0.24 +/- 0.03 nmol/min/mg protein, P < 0.05), while superoxide production decreased to normal levels in the presence of the G6PD inhibitor 6-aminonicotinamide. We conclude that the activation of myocardial G6PD is a novel mechanism that enhances NADPH availability and fuels superoxide-generating enzymes in heart failure.

Role of pentose phosphate pathway-derived NADPH in hypoxic pulmonary vasoconstriction

We have previously shown that pentose phosphate pathway (PPP) inhibitors, 6-aminonicotinamide (6-AN) and epiandrosterone (EPI), markedly reduce hypoxic pulmonary vasoconstriction (HPV). Although it has been suggested that changes in the NADPH/NADP+ ratio and redox status are involved in the mechanism of HPV, the role of PPP-derived NADPH in this phenomenon is not known. The aim of this study, therefore, was to investigate the role of PPP-derived NADPH in HPV using isolated rat pulmonary arteries (PA) and perfused rat lungs. The NADPH/NADP+ ratio and NADPH levels in PA and lungs exposed to hypoxia increased 2-fold and 7-fold, respectively, compared to time-matched normoxic controls. Both hypoxia-induced increases in lung NADPH levels and lung perfusion pressure were inhibited by 6-AN (500 microM) or EPI (300 microM). The chemical inhibitors of PPP and hypoxia similarly decreased lung tissue NOx levels by approximately 50%. In contrast, hypoxia increased the lung soluble guanylate cyclase (sGC) activity (from 22.9+/-6.3 to 57.1+/-7.6 pmol/min/g), which was prevented by PPP inhibitors. ODQ, a sGC inhibitor, potentiated HPV. These results suggest that while PPP-derived NADPH may play a significant role in HPV, it may also moderate the magnitude of HPV through activation of the NO-sGC-cGMP vasodilation pathway.

Nontranscriptional Regulation of Cardiac Repolarization Currents by Testosterone

BACKGROUND

Women have longer QTc intervals than men and are at greater risk for arrhythmias associated with long QTc intervals, such as drug-induced torsade de pointes. Recent clinical and experimental data suggest an important role of testosterone in sex-related differences in ventricular repolarization. However, studies on effects of testosterone on ionic currents in cardiac myocytes are limited.

METHODS AND RESULTS

We examined effects of testosterone on action potential duration (APD) and membrane currents in isolated guinea pig ventricular myocytes using patch-clamp techniques. Testosterone rapidly shortened APD, with an EC50 of 2.1 to 8.7 nmol/L, which is within the limits of physiological testosterone levels in men. APD shortening by testosterone was mainly due to enhancement of slowly activating delayed rectifier K+ currents (IKs) and suppression of L-type Ca2+ currents (I(Ca,L)), because testosterone failed to shorten APD in the presence of an IKs inhibitor, chromanol 293B, and an I(Ca,L) inhibitor, nisoldipine. A nitric oxide (NO) scavenger and an inhibitor of NO synthase 3 (NOS3) reversed the effects of testosterone on APD, which suggests that NO released from NOS3 is responsible for the electrophysiological effects of testosterone. Electrophysiological effects of testosterone were reversed by a blocker of testosterone receptors, a c-Src inhibitor, a phosphatidylinositol 3-kinase inhibitor, and an Akt inhibitor. Immunoblot analysis revealed that testosterone induced phosphorylation of Akt and NOS3.

CONCLUSIONS

The nontranscriptional regulation of IKs and I(Ca,L) by testosterone is a novel regulatory mechanism of cardiac repolarization that can potentially contribute to the control of QTc intervals by androgen.

Testosterone enhances calcium reabsorption by the kidney

The kidney is a target tissue for androgens, but the role of these hormones in the regulation of calcium (Ca2+) reabsorption remains unclear. The present study examines the effects of testosterone on Ca2+ transport by the luminal membranes of proximal and distal nephrons of the rabbit kidney. Tubule suspensions were pre-incubated in the presence or absence of the hormone, and 45C2+ uptake by the luminal membranes was measured using the rapid filtration technique. In the proximal tubules, testosterone did not influence Ca2+ uptake. In the distal tubules, a 5 min incubation with the hormone increased this uptake with a maximal response at 10(-10)M. Ca2+ transport by the distal membranes shows a dual kinetics. Testosterone enhanced the Vmax value of the low affinity component. In an attempt to identify the underlying mechanisms involved in this action, several messenger inhibitors were introduced in the tubule suspension. PD 98059 and U0 126 as well as AG 99 and genistein interfered with the hormone action suggesting the implication of a MEK kinase and a tyrosine kinase. To determine the type of the channels involved in this effect, Ca2+ uptake was measured in the presence of diltiazem, omega-conotoxin MVIIC and mibefradil, i.e. selective inhibitors of the L-type, P/Q type and T-type channels. An inhibition of Ca2+ transport was observed exclusively with mibefradil. These results indicate that testosterone enhances Ca2+ transport by opening a T-type Ca2+ channel in the distal luminal membrane, via MEK kinase and tyrosine kinase dependent mechanisms.

Pentose phosphate pathway coordinates multiple redox-controlled relaxing mechanisms in bovine coronary arteries

Pentose phosphate pathway (PPP) inhibitors, 6-aminonicotinamide (6-AN) and epiandrosterone (Epi), were employed to examine whether changes in NADP(H) redox regulates contractile force in endothelium-removed bovine coronary arteries (BCAs). 6-AN (0.01-5 mM) or Epi (1-500 microM) elicited dose-dependent relaxation in BCAs contracted with 30 mM KCl, 0.1 microM U-44619, and endothelin-1 but not with phorbol 12,13-dibutyrate, a protein kinase C activator that causes Ca2+-independent contraction. Relaxation to PPP inhibition was associated with oxidation of NADPH and glutathione (GSH). Relaxation to 6-AN was not mediated by H2O2, because it was not altered by hypoxia or the peroxide scavenger ebselen (100 microM). The thiol reductant DTT (3 mM) attenuated the relaxation to 6-AN and Epi by 30-40%. Inhibition of glycolysis or mitochondrial electron transport did not elicit relaxation in BCAs contracted with 30 mM KCl, suggesting these pathways may not be involved in relaxation elicited by PPP inhibition. High doses of K+ channel blockers [e.g., TEA (10 mM) and 4-aminopyridine (10 mM)] only partially inhibited the relaxation to 6-AN. On the basis of changes in the fura-2 fluorescence ratio, 6-AN and Epi appeared to markedly reduce intracellular Ca2+. Thus PPP inhibition oxidizes NADPH and GSH and appears to activate a novel coordination of redox-controlled relaxing mechanisms in BCAs mediated primarily through decreasing intracellular Ca2+.