Aldosterone impairs vascular reactivity by decreasing glucose-6-phosphate dehydrogenase activity

Elevated pulmonary arterial and systemic plasma aldosterone levels associate with impaired cardiac reserve capacity during exercise in left ventricular systolic heart failure patients: A pilot study

BACKGROUND

Elevated levels of aldosterone are a modifiable contributor to clinical worsening in heart failure with reduced ejection fraction (HFrEF). Endothelin-1 (ET-1), which is increased in HFrEF, induces pulmonary endothelial aldosterone synthesis in vitro. However, whether transpulmonary aldosterone release occurs in humans or aldosterone relates to functional capacity in HFrEF is not known. Therefore, we aimed to characterize ET-1 and transpulmonary aldosterone levels in HFrEF and determine if aldosterone levels relate to peak volume of oxygen uptake (pVO2).

METHODS

Data from 42 consecutive HFrEF patients and 18 controls referred for invasive cardiopulmonary exercise testing were analyzed retrospectively.

RESULTS

Radial ET-1 levels (median [interquartile range]) were higher in HFrEF patients compared with controls (17.5 [11.5-31.4] vs 11.5 [4.4-19.0] pg/ml, p = 0.04). A significant ET-1 transpulmonary gradient (pulmonary arterial [PA] - radial arterial levels) was present in HFrEF (p < 0.001) but not in controls (p = 0.24). Compared with controls, aldosterone levels (median [interquartile range]) were increased in HFrEF patients in the PA (364 [250-489] vs 581 [400-914] ng/dl, p < 0.01) and radial compartments (366 [273-466] vs 702 [443-1223] ng/dl, p < 0.001). Akin to ET-1, a transpulmonary increase (median [interquartile range]) in aldosterone concentration was also observed between controls and HFrEF patients at rest (7.5 [-54 to 40] vs 61.6 [-13.6 to 165] ng/dl, p = 0.01) and peak exercise (-20.7 [-39.6 to 79.1] vs 25.8 [-29.2 to 109.3] ng/dl, p = 0.02). The adjusted pVO2 correlated inversely with aldosterone levels at peak activity in the PA (r = -0.31, p = 0.01) and radial artery (r = -0.32, p = 0.01).

CONCLUSIONS

These data provide preliminary evidence in support of increased transpulmonary aldosterone levels in HFrEF and suggest an inverse relationship between circulating aldosterone and pVO2. Future prospective studies are needed to characterize the functional effects of transpulmonary and circulating aldosterone on cardiac reserve capacity in HFrEF.

Sulfenic Acid Modification of Endothelin B Receptor is Responsible for the Benefit of a Nonsteroidal Mineralocorticoid Receptor Antagonist in Renal Ischemia

AKI is associated with high mortality rates and the development of CKD. Ischemia/reperfusion (IR) is an important cause of AKI. Unfortunately, there is no available pharmacologic approach to prevent or limit renal IR injury in common clinical practice. Renal IR is characterized by diminished nitric oxide bioavailability and reduced renal blood flow; however, the mechanisms leading to these alterations are poorly understood. In a rat model of renal IR, we investigated whether the administration of the novel nonsteroidal mineralocorticoid receptor (MR) antagonist BR-4628 can prevent or treat the renal dysfunction and tubular injury induced by IR. Renal injury induced by ischemia was associated with increased oxidant damage, which led to a cysteine sulfenic acid modification in endothelin B receptor and consequently decreased endothelial nitric oxide synthase activation. These modifications were efficiently prevented by nonsteroidal MR antagonism. Furthermore, we demonstrated that the protective effect of BR-4628 against IR was lost when a selective endothelin B receptor antagonist was coadministered. These data describe a new mechanism for reduced endothelial nitric oxide synthase activation during renal IR that can be blocked by MR antagonism with BR-4628.

Gender-specific association between urinary sodium excretion and body composition: Analysis of the 2008-2010 Korean National Health and Nutrition Examination Surveys

OBJECTIVE

Few studies have reported the relationship between sarcopenia and the estimated amount of sodium excreted in 24 h, as measured by the spot urine test (E24UNA), in a community-dwelling cohort. We investigated the gender specific association between E24UNA values and body composition indices.

MATERIALS AND METHODS

Data from a total of 7162 participants (3545 men and 3617 postmenopausal women) aged 45 years or older were obtained from multiple Korea National Health and Nutrition Examination Surveys (2008-2010) and analyzed. The total amount of sodium excreted in the urine in a 24-h period was estimated with spot urine specimens. Sarcopenia was defined as an appendicular skeletal muscle mass divided by body weight (ASM/Wt) that was less than 1 standard deviation below the sex-specific mean for young adults.

RESULTS

E24UNA values were positively correlated with body mass index, waist circumference, total fat mass, and blood pressure; in contrast, E24UNA values were negatively correlated with ASM/Wt in both sexes. Compared with those in the lowest E24UNA tertile, participants in the highest E24UNA tertile were at higher risk for sarcopenia (men: odds ratio (OR)=1.3 [95% confidence interval (CI)=1.07-1.59]; women: OR=1.41 [95% CI=1.16-1.73]). Further classification of subjects with sarcopenia into sarcopenic obese and sarcopenic nonobese groups revealed that the highest E24UNA values were found in the sarcopenic obese group; this difference was statistically significant. The next highest levels were found in the sarcopenic nonobese group, followed by the nonsarcopenic group. This trend was observed in both sexes.

CONCLUSION

High E24UNA values were independently associated with both sarcopenia and obesity in Korean individuals older than 45 years. These results suggest that high salt intake may have a deleterious effect on body composition.

PGC-1α overexpression suppresses blood pressure elevation in DOCA-salt hypertensive mice

Increasing evidences have accumulated that endothelial dysfunction is involved in the pathogenesis of hypertension. Peroxisome proliferator-activated receptor γ (PPARγ) coactivator-1α (PGC-1α) has been identified as an essential factor that protects against endothelial dysfunction in vascular pathologies. However, the functional role of PGC-1α in hypertension is not well understood. Using an adenovirus infection model, we tested the hypothesis that PGC-1α overexpression retards the progression of hypertension in deoxycorticosterone acetate (DOCA)-salt mice model through preservation of the function of endothelium. We first demonstrated that PGC-1α expression not only in conductance and resistance arteries but also in endothelial cells was decreased after DOCA-salt treatment. In PGC-1α adenovirus-infected mice, the elevation of blood pressure in DOCA-salt mice was attenuated, as determined using tail-cuff measurement. Furthermore, PGC-1α overexpression inhibited the decrease in nitric oxide (NO) generation and the increase in superoxide anion (O2 (-)) production in DOCA-salt-treated mice, in parallel with improved endothelium-dependent relaxation. Rather than affecting endothelial NO synthase (eNOS) total expression and phosphorylation, PGC-1α significantly inhibited eNOS uncoupling, as evidenced by increased eNOS homodimerization, BH4 levels, GTP-cyclohydrolase 1 (GTPCH1) and dihydrofolate reductase (DHFR) expression and heat-shock protein (Hsp)90-eNOS interaction. Our findings demonstrate that PGC-1α overexpression preserves eNOS coupling, enhances NO generation, improves endothelium-dependent relaxation and thus lowers blood pressure, suggesting that up-regulation of PGC-1α may be a novel strategy to prevent and treat hypertension.

Mineralocorticoid exposure and receptor activity modulate microvascular endothelial function in African Americans with and without hypertension

Prior work suggests blood pressure in African Americans is more sensitive to the effects of aldosterone than in Caucasians. This mechanism may relate to a negative response of the vascular endothelium to aldosterone, including reduced glucose-6-phosphate dehydrogenase (G6PD) activity. Thirty-three African Americans (11 hypertensives, 22 controls) without evidence of diabetes or metabolic syndrome completed the protocol. The protocol included measurement of in vivo microvascular endothelial function by digital pulse arterial tonometry and ex vivo measurement of endothelial function by videomicroscopy of arterioles obtained from these same subjects with and without exposure to aldosterone or spironolactone. Systemic and arteriolar G6PD activities were also measured. In vivo and ex vivo microvascular endothelial function were impaired in African Americans with hypertension. One-hour exposure with aldosterone impaired endothelium-dependent vasodilation in arterioles from normotensive subjects, while 1 hour of spironolactone exposure reversed endothelial dysfunction in arterioles from hypertensive subjects. G6PD activity was impaired in hypertensive arterioles. Aldosterone-related endothelial dysfunction may be responsible for at least a portion of the greater blood pressure sensitivity to aldosterone in African Americans. This may be in part related to vascular suppression of G6PD activity.

Inhibition of FHL1 inhibits cigarette smoke extract-induced proliferation in pulmonary arterial smooth muscle cells

Cigarette smoke can induce pulmonary vascular remodeling, which involves pulmonary artery smooth muscle cell (PASMC) proliferation, resulting in pulmonary hypertension in chronic obstructive pulmonary disease. FHL1 is a member of the FHL subfamily, characterized by an N‑terminal half LIM domain, followed by four complete LIM domains, and has been suggested to be critical in cell proliferation. However, the effects of FHL1 on cigarette smoke‑induced PASMC proliferation and the precise molecular mechanism remain to be elucidated. The present study demonstrated that the protein expression of FHL1 correlated with cigarette smoke extract (CSE)‑induced PASMC proliferation. Knockdown of the expression of FHL1 using siRNA significantly suppressed cell proliferation and inhibited the cell cycle transition between the G1 and S phase by regulating the cyclin‑dependent kinase pathway at the basal level and following CSE stimulation. By contrast, overexpressing FHL1 using an adenovirus increased cell proliferation and promoted the cell cycle transition between the G1 and S phase. Furthermore, CSE significantly increased the protein expression of FHL1, however, exerted no effect on the mRNA expression levels. This alteration was due to the prolonged FHL1 half‑life, leading to the antagonizing of protein degradation. Collectively, these data suggested that FHL1 may be involved in excessive cell proliferation and may represent a potential therapeutic target for pulmonary hypertension.

Healing the orphaned heart: heart failure in a patient with glucose-6-phosphate dehydrogenase deficiency

Patients with glucose-6-phosphate dehydrogenase (G6PD) deficiency are not represented in clinical trials for heart failure. Moreover, many of the recommended medications can cause haemolysis in this group of patients. We present the case of a 71-year-old woman with G6PD deficiency admitted for acute non-ischemic heart failure with reduced ejection fraction. Our experience showed that a combination of ethacrynic acid and spironolactone is safe and effective for relief of volume overload in this group of patients. Studies are needed to determine whether the morbidity and mortality benefits of established heart failure regimens extend to patients with G6PD deficiency.

Tanshinone IIA Prevents Rat Basilar Artery Smooth Muscle Cells Proliferation by Inactivation of PDK1 During the Development of Hypertension

Basilar vascular smooth muscle cells (BASMCs) hyperplasia is a prominent feature of cerebrovascular remodeling and stroke during the development of hypertension. Tanshinone IIA (Tan) has been reported to exhibit a protective effect against the pathological features of hypertension. Previous studies have shown that phosphoinostitide-3 kinase (PI3K)/3'-phosphoinostitide dependent kinase (PDK1)/AKT pathway is involved in the regulation of proliferation of various cell types. Therefore, there may be a crosstalk between Tan antihypertension processes and PI3K/PDK1/AKT proliferative effect in BASMCs. To test this hypothesis, we used a 2-kidney, 2-clip hypertension model to examine the effect of Tan on PI3K/PDK1/AKT pathway by cellular, molecular, and biochemical approaches. Our results revealed that the abundance of PDK1 in plasma was paralleled with an increase in blood pressure and the cross-sectional area of basilar artery in hypertensive rats. Tan decreased blood pressure and hypertension-induced PDK1 phosphorylation but produced no effect on the phosphorylation of PI3K. Moreover, Tan attenuated endothelin 1 induced the activation of PDK1/AKT pathway in rat BASMCs. Tan could inhibit cell cycle transition by regulating the expression of cyclin D1 and p27, in turn, prevent proliferation of BASMCs. Our study provides a novel mechanism by which Tan prevents cerebrovascular cell proliferation during hypertension, and thus Tan may be a potential therapeutic agent for cerebrovascular remodeling and stroke.

Mineralocorticoid receptor antagonism treats obesity-associated cardiac diastolic dysfunction

Patients with obesity and diabetes mellitus exhibit a high prevalence of cardiac diastolic dysfunction (DD), an independent predictor of cardiovascular events for which no evidence-based treatment exists. In light of renin-angiotensin-aldosterone system activation in obesity and the cardioprotective action of mineralocorticoid receptor (MR) antagonists in systolic heart failure, we examined the hypothesis that MR blockade with a blood pressure-independent low-dose spironolactone (LSp) would treat obesity-associated DD in the Zucker obese (ZO) rat. Treatment of ZO rats exhibiting established DD with LSp normalized cardiac diastolic function, assessed by echocardiography. This was associated with reduced cardiac fibrosis, but not reduced hypertrophy, and restoration of endothelium-dependent vasodilation of isolated coronary arterioles via a nitric oxide-independent mechanism. Further mechanistic studies revealed that LSp reduced cardiac oxidative stress and improved endothelial insulin signaling, with no change in arteriolar stiffness. Infusion of Sprague-Dawley rats with the MR agonist aldosterone reproduced the DD noted in ZO rats. In addition, improved cardiac function in ZO-LSp rats was associated with attenuated systemic and adipose inflammation and an anti-inflammatory shift in cardiac immune cell mRNAs. Specifically, LSp increased cardiac markers of alternatively activated macrophages and regulatory T cells. ZO-LSp rats had unchanged blood pressure, serum potassium, systemic insulin sensitivity, or obesity-associated kidney injury, assessed by proteinuria. Taken together, these data demonstrate that MR antagonism effectively treats established obesity-related DD via blood pressure-independent mechanisms. These findings help identify a particular population with DD that might benefit from MR antagonist therapy, specifically patients with obesity and insulin resistance.

Roles of oxidative stress and the mineralocorticoid receptor in cardiac pathology in a rat model of metabolic syndrome

Oxidative stress and the mineralocorticoid receptor (MR) are implicated in the pathogenesis of salt-induced left ventricular (LV) diastolic dysfunction associated with metabolic syndrome (MetS). We recently characterized DahlS.Z-Lepr(fa) /Lepr(fa) (DS/obese) rats, derived from a cross between Dahl salt-sensitive and Zucker rats, as a new animal model of MetS. We investigated the pathophysiological roles of increased oxidative stress and MR activation in cardiac injury with this model. DS/obese rats were treated with the antioxidant tempol (1 mmol/L in drinking water) or the selective MR antagonist eplerenone (15 mg/kg per day, per os) for 5 weeks beginning at 10 weeks of age. The increased systolic blood pressure and LV hypertrophy that develop in untreated DS/obese rats were substantially ameliorated by eplerenone but not by tempol. Eplerenone also attenuated LV fibrosis and diastolic dysfunction more effectively than did tempol in DS/obese rats, whereas cardiac oxidative stress and inflammation were reduced similarly by both drugs. Both the ratio of plasma aldosterone concentration to plasma renin activity and cardiac expression of the MR and serum/glucocorticoid-regulated kinase 1 genes were decreased to a greater extent by eplerenone than by tempol. Our results indicate that both increased oxidative stress and MR activation in the heart may contribute to the development of LV remodeling and diastolic dysfunction in DS/obese rats. The superior cardioprotective action of eplerenone is likely attributable to its greater antihypertensive effect, which is likely related to its greater inhibition of aldosterone-MR activity in the cardiovascular system.

Hypoxia-induced glucose-6-phosphate dehydrogenase overexpression and -activation in pulmonary artery smooth muscle cells: implication in pulmonary hypertension

Severe pulmonary hypertension is a debilitating disease with an alarmingly low 5-yr life expectancy. Hypoxia, one of the causes of pulmonary hypertension, elicits constriction and remodeling of the pulmonary arteries. We now know that pulmonary arterial remodeling is a consequence of hyperplasia and hypertrophy of pulmonary artery smooth muscle (PASM), endothelial, myofibroblast, and stem cells. However, our knowledge about the mechanisms that cause these cells to proliferate and hypertrophy in response to hypoxic stimuli is still incomplete, and, hence, the treatment for severe pulmonary arterial hypertension is inadequate. Here we demonstrate that the activity and expression of glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the pentose phosphate pathway, are increased in hypoxic PASM cells and in lungs of chronic hypoxic rats. G6PD overexpression and -activation is stimulated by H2O2. Increased G6PD activity contributes to PASM cell proliferation by increasing Sp1 and hypoxia-inducible factor 1α (HIF-1α), which directs the cells to synthesize less contractile (myocardin and SM22α) and more proliferative (cyclin A and phospho-histone H3) proteins. G6PD inhibition with dehydroepiandrosterone increased myocardin expression in remodeled pulmonary arteries of moderate and severe pulmonary hypertensive rats. These observations suggest that altered glucose metabolism and G6PD overactivation play a key role in switching the PASM cells from the contractile to synthetic phenotype by increasing Sp1 and HIF-1α, which suppresses myocardin, a key cofactor that maintains smooth muscle cell in contractile state, and increasing hypoxia-induced PASM cell growth, and hence contribute to pulmonary arterial remodeling and pathogenesis of pulmonary hypertension.

Mineralocorticoid receptor blockade improves coronary microvascular function in individuals with type 2 diabetes

Reduced coronary flow reserve (CFR), an indicator of coronary microvascular dysfunction, is seen in type 2 diabetes mellitus (T2DM) and predicts cardiac mortality. Since aldosterone plays a key role in vascular injury, the aim of this study was to determine whether mineralocorticoid receptor (MR) blockade improves CFR in individuals with T2DM. Sixty-four men and women with well-controlled diabetes on chronic ACE inhibition (enalapril 20 mg/day) were randomized to add-on therapy of spironolactone 25 mg, hydrochlorothiazide (HCTZ) 12.5 mg, or placebo for 6 months. CFR was assessed by cardiac positron emission tomography at baseline and at the end of treatment. There were significant and similar decreases in systolic blood pressure with spironolactone and HCTZ but not with placebo. CFR improved with treatment in the spironolactone group as compared with the HCTZ group and with the combined HCTZ and placebo groups. The increase in CFR with spironolactone remained significant after controlling for baseline CFR, change in BMI, race, and statin use. Treatment with spironolactone improved coronary microvascular function, raising the possibility that MR blockade could have beneficial effects in preventing cardiovascular disease in patients with T2DM.

Mineralocorticoid Receptors in the Pathophysiology of Vascular Inflammation and Atherosclerosis

Atherosclerosis is a chronic inflammatory disease of the vasculature that causes significant morbidity and mortality from myocardial infarction, stroke, and peripheral vascular disease. Landmark clinical trials revealed that mineralocorticoid receptor (MR) antagonists improve outcomes in cardiovascular patients. Conversely, enhanced MR activation by the hormone aldosterone is associated with increased risk of MI, stroke, and cardiovascular death. This review summarizes recent advances in our understanding of the role of aldosterone and the MR in the pathogenesis of vascular inflammation and atherosclerosis as it proceeds from risk factor-induced endothelial dysfunction and inflammation to plaque formation, progression, and ultimately rupture with thrombosis, the cause of acute ischemia. The role of the MR in converting cardiac risk factors into endothelial dysfunction, in enhancing leukocyte adhesion and infiltration into the vasculature, in promoting systemic inflammation and vascular oxidative stress, and in plaque destabilization and thrombosis are discussed. A greater understanding of the mechanisms by which the MR promotes atherosclerosis has substantial potential to identify novel treatment targets to improve cardiovascular health and decrease mortality.

Transcription factor cAMP response element modulator (Crem) restrains Pdgf-dependent proliferation of vascular smooth muscle cells in mice

Transcription factors of the cAMP response element-binding protein (Creb)/cAMP response element modulator (Crem) family were linked to the switch from a contractile to a proliferating phenotype in vascular smooth muscle cells (VSMCs). Here, we analyzed the vascular function of Crem in mice with a global inactivation of Crem (Crem(-/-)). CRE-mediated transcriptional activity was enhanced in primary Crem(-/-) VSMCs under nonstimulated conditions and under stimulation with Forskolin and platelet-derived growth factor (Pdgf) whereas stimulation with nitric oxide or cGMP showed no effect. This elevated CRE-mediated transcriptional activity as a result of Crem inactivation did not alter aortic contractility or fractions of proliferating or apoptotic aortic VSMCs in situ, and no impact of Crem inactivation on the development of atherosclerotic plaques was observed. Crem(-/-) mice exhibited an increased neointima formation after carotid ligation associated with an increased proliferation of VSMCs in the carotid media. Pdgf-stimulated proliferation of primary aortic Crem(-/-) VSMCs was increased along with an upregulation of messenger RNA (mRNA) levels of Pdgf receptor, alpha polypeptide (Pdgfra), cyclophilin A (Ppia), the regulator of G-protein signaling 5 (Rgs5), and Rho GTPase-activating protein 12 (Arhgap12). Taken together, our data reveal the inhibition of Pdgf-stimulated proliferation of VSMCs by repressing the Pdgf-stimulated CRE-mediated transcriptional activation as the predominant function of Crem in mouse vasculature suggesting an important role of Crem in vasculoproliferative diseases.

Upregulation of CREM/ICER suppresses wound endothelial CRE-HIF-1α-VEGF-dependent signaling and impairs angiogenesis in type 2 diabetes

Impaired angiogenesis and endothelial dysfunction in type 2 diabetes constitute dominant risk factors for non-healing wounds and most forms of cardiovascular disease. We propose that diabetes shifts the ‘angiogenic balance’ in favor of an excessive anti-angiogenic phenotype. Herein, we report that diabetes impairs in vivo sponge angiogenic capacity by decreasing VEGF expression and fibrovascular invasion, and reciprocally enhances the formation of angiostatic molecules, such as thrombospondins, NFκB and FasL. Defective in vivo angiogenesis prompted cellular studies in cultured endothelial cells derived from subcutaneous sponge implants (SIECs) of control and Goto-Kakizaki rats. Ensuing data from diabetic SIECs demonstrated a marked upregulation in cAMP-PKA-CREB signaling, possibly stemming from increased expression of adenylyl cyclase isoforms 3 and 8, and decreased expression of PDE3. Mechanistically, we found that oxidative stress and PKA activation in diabetes enhanced CREM/ICER expression. This reduces IRS2 cellular content by inhibiting cAMP response element (CRE) transcriptional activity. Consequently, a decrease in the activity of Akt-mTOR ensued with a concomitant reduction in the total and nuclear protein levels of HIF-1α. Limiting HIF-1α availability for the specific hypoxia response elements in diabetic SIECs elicited a marked reduction in VEGF expression, both at the mRNA and protein levels. These molecular abnormalities were illustrated functionally by a defect in various pro-angiogenic properties, including cell proliferation, migration and tube formation. A genetic-based strategy in diabetic SIECs using siRNAs against CREM/ICER significantly augmented the PKA-dependent VEGF expression. To this end, the current data identify the importance of CREM/ICER as a negative regulator of endothelial function and establish a link between CREM/ICER overexpression and impaired angiogenesis during the course of diabetes. Moreover, it could also point to CREM/ICER as a potential therapeutic target in the treatment of pathological angiogenesis.

Endothelial cell metabolism: parallels and divergences with cancer cell metabolism

The stromal vasculature in tumors is a vital conduit of nutrients and oxygen for cancer cells. To date, the vast majority of studies have focused on unraveling the genetic basis of vessel sprouting (also termed angiogenesis). In contrast to the widely studied changes in cancer cell metabolism, insight in the metabolic regulation of angiogenesis is only just emerging. These studies show that metabolic pathways in endothelial cells (ECs) importantly regulate angiogenesis in conjunction with genetic signals. In this review, we will highlight these emerging insights in EC metabolism and discuss them in perspective of cancer cell metabolism. While it is generally assumed that cancer cells have unique metabolic adaptations, not shared by healthy non-transformed cells, we will discuss parallels and highlight differences between endothelial and cancer cell metabolism and consider possible novel therapeutic opportunities arising from targeting both cancer and endothelial cells.

Mineralocorticoid receptor: a critical player in vascular remodeling

Vascular remodeling is a pathological condition with structural changes of blood vessels. Both inside-out and outside-in hypothesis have been put forward to describe mechanisms of vascular remodeling. An integrated model of these two hypotheses emphasizes the importance of immune cells such as monocytes/macrophages, T cells, and dendritic cells. These immune cells are at the center stage to orchestrate cellular proliferation, migration, and interactions of themselves and other vascular cells including endothelial cells (ECs), vascular smooth muscle cells (VSMCs), and fibroblasts. These changes on vascular wall lead to inflammation and oxidative stress that are largely responsible for vascular remodeling. Mineralocorticoid receptor (MR) is a classic nuclear receptor. MR agonist promotes inflammation and oxidative stress and therefore exacerbates vascular remodeling. Conversely, MR antagonists have the opposite effects. MR has direct roles on vascular cells through non-genomic or genomic actions to modulate inflammation and oxidative stress. Recent studies using genetic mouse models have revealed that MR in myeloid cells, VSMCs and ECs all contribute to vascular remodeling. In conclusion, data in the past years have demonstrated that MR is a critical control point in modulating vascular remodeling. Studies will continue to provide evidence with more detailed mechanisms to support this notion.

Direct contribution of vascular mineralocorticoid receptors to blood pressure regulation

Hypertension is an extremely prevalent cardiovascular risk factor and current antihypertensive therapies do not adequately treat hypertension in many affected individuals. Thus, a better understanding of mechanisms of hypertension could lead to novel therapies. Mineralocorticoid receptors (MR) are known to regulate blood pressure by responding to aldosterone in the kidney to regulate sodium retention. Recent evidence supports a direct contribution of the vasculature to control of BP and suggests the possibility that MR antagonists may also lower blood pressure by acting on extrarenal MR. This review summarizes existing research considering the role of the vascular MR in regulating vasoreactivity and blood pressure. Multiple studies indicate a role for vascular MR in modulating vasoconstriction and vasorelaxation. Activation of MR in vascular endothelial and smooth muscle cells leads to increased reactive oxygen species production and decreased availability of nitric oxide, important regulators of vascular reactivity. Transgenic mouse models, including an endothelial MR overexpressing mouse and a smooth muscle cell-specific MR-knockout mouse, support a direct role for vascular MR in control of blood pressure. This new evidence demonstrating that vascular MR directly contribute to control of vasoreactivity and blood pressure supports vascular MR and the pathways they control as novel therapeutic targets to treat hypertension.

The pentose phosphate pathway and cancer

The pentose phosphate pathway (PPP), which branches from glycolysis at the first committed step of glucose metabolism, is required for the synthesis of ribonucleotides and is a major source of NADPH. NADPH is required for and consumed during fatty acid synthesis and the scavenging of reactive oxygen species (ROS). Therefore, the PPP plays a pivotal role in helping glycolytic cancer cells to meet their anabolic demands and combat oxidative stress. Recently, several neoplastic lesions were shown to have evolved to facilitate the flux of glucose into the PPP. This review summarizes the fundamental functions of the PPP, its regulation in cancer cells, and its importance in cancer cell metabolism and survival.

Regulation of the pentose phosphate pathway in cancer

Energy metabolism is significantly reprogrammed in many human cancers, and these alterations confer many advantages to cancer cells, including the promotion of biosynthesis, ATP generation, detoxification and support of rapid proliferation. The pentose phosphate pathway (PPP) is a major pathway for glucose catabolism. The PPP directs glucose flux to its oxidative branch and produces a reduced form of nicotinamide adenine dinucleotide phosphate (NADPH), an essential reductant in anabolic processes. It has become clear that the PPP plays a critical role in regulating cancer cell growth by supplying cells with not only ribose-5-phosphate but also NADPH for detoxification of intracellular reactive oxygen species, reductive biosynthesis and ribose biogenesis. Thus, alteration of the PPP contributes directly to cell proliferation, survival and senescence. Furthermore, recent studies have shown that the PPP is regulated oncogenically and/or metabolically by numerous factors, including tumor suppressors, oncoproteins and intracellular metabolites. Dysregulation of PPP flux dramatically impacts cancer growth and survival. Therefore, a better understanding of how the PPP is reprogrammed and the mechanism underlying the balance between glycolysis and PPP flux in cancer will be valuable in developing therapeutic strategies targeting this pathway.

Aldosterone's rapid, nongenomic effects are mediated by striatin: a modulator of aldosterone's effect on estrogen action

The cellular responses to steroids are mediated by 2 general mechanisms: genomic and rapid/nongenomic effects. Identification of the mechanisms underlying aldosterone (ALDO)'s rapid vs their genomic actions is difficult to study, and these mechanisms are not clearly understood. Recent data suggest that striatin is a mediator of nongenomic effects of estrogen. We explored the hypothesis that striatin is an intermediary of the rapid/nongenomic effects of ALDO and that striatin serves as a novel link between the actions of the mineralocorticoid and estrogen receptors. In human and mouse endothelial cells, ALDO promoted an increase in phosphorylated extracellular signal-regulated protein kinases 1/2 (pERK) that peaked at 15 minutes. In addition, we found that striatin is a critical intermediary in this process, because reducing striatin levels with small interfering RNA (siRNA) technology prevented the rise in pERK levels. In contrast, reducing striatin did not significantly affect 2 well-characterized genomic responses to ALDO. Down-regulation of striatin with siRNA produced similar effects on estrogen's actions, reducing nongenomic, but not some genomic, actions. ALDO, but not estrogen, increased striatin levels. When endothelial cells were pretreated with ALDO, the rapid/nongenomic response to estrogen on phosphorylated endothelial nitric oxide synthase (peNOS) was enhanced and accelerated significantly. Importantly, pretreatment with estrogen did not enhance ALDO's nongenomic response on pERK. In conclusion, our results indicate that striatin is a novel mediator for both ALDO's and estrogen's rapid and nongenomic mechanisms of action on pERK and phosphorylated eNOS, respectively, thereby suggesting a unique level of interactions between the mineralocorticoid receptor and the estrogen receptor in the cardiovascular system.

7-Ketocholesterol inhibits isocitrate dehydrogenase 2 expression and impairs endothelial function via microRNA-144

Oxysterol is associated with the induction of endothelial oxidative stress and impaired endothelial function. Mitochondria play a central role in oxidative energy metabolism and the maintenance of proper redox status. The purpose of this study was to determine the effects and mechanisms of 7-ketocholesterol (7-KC) on isocitrate dehydrogenase 2 (IDH2) and its impact on endothelial function in both human aortic endothelial cells (HAECs) and C57BL/6J mice. HAECs treated with 7-KC showed significant reductions of IDH2 mRNA and protein levels and enzyme activity, leading to decreased NADPH concentration and an increased ratio of reduced-to-oxidized glutathione in the mitochondria. 7-KC induced the expression of a specific microRNA, miR-144, which in turn targets and downregulates IDH2. In silico analysis predicted that miR-144 could bind to the 3'-untranslated region of IDH2 mRNA. Overexpression of miR-144 decreased the expression of IDH2 and the levels of NADPH. A complementary finding is that a miR-144 inhibitor increased the mRNA and protein expression levels of IDH2. Furthermore, miR-144 level was elevated in HAECs in response to 7-KC. Anti-Ago1/2 immunoprecipitation coupled with a real-time polymerase chain reaction assay revealed that 7-KC increased the functional targeting of miR-144/IDH2 mRNA in HAECs. Infusion of 7-KC in vivo decreased vascular IDH2 expression and impaired vascular reactivity via miR-144. 7-KC controls miR-144 expression, which in turn decreases IDH2 expression and attenuates NO bioavailability to impair endothelial homeostasis. The newly identified 7-KC-miR-144-IDH2 pathway may contribute to atherosclerosis progression and provides new insight into 7-KC function and microRNA biology in cardiovascular disease.

The role of the renin-angiotensin-aldosterone system in the pathobiology of pulmonary arterial hypertension (2013 Grover Conference series)

Pulmonary arterial hypertension (PAH) is associated with aberrant pulmonary vascular remodeling that leads to increased pulmonary artery pressure, pulmonary vascular resistance, and right ventricular dysfunction. There is now accumulating evidence that the renin-angiotensin-aldosterone system is activated and contributes to cardiopulmonary remodeling that occurs in PAH. Increased plasma and lung tissue levels of angiotensin and aldosterone have been detected in experimental models of PAH and shown to correlate with cardiopulmonary hemodynamics and pulmonary vascular remodeling. These processes are abrogated by treatment with angiotensin receptor or mineralocorticoid receptor antagonists. At a cellular level, angiotensin and aldosterone activate oxidant stress signaling pathways that decrease levels of bioavailable nitric oxide, increase inflammation, and promote cell proliferation, migration, extracellular matrix remodeling, and fibrosis. Clinically, enhanced renin-angiotensin activity and elevated levels of aldosterone have been detected in patients with PAH, which suggests a role for angiotensin and mineralocorticoid receptor antagonists in the treatment of PAH. This review will examine the current evidence linking renin-angiotensin-aldosterone system activation to PAH with an emphasis on the cellular and molecular mechanisms that are modulated by aldosterone and may be of importance for the pathobiology of PAH.

Upregulation of steroidogenic acute regulatory protein by hypoxia stimulates aldosterone synthesis in pulmonary artery endothelial cells to promote pulmonary vascular fibrosis

BACKGROUND

The molecular mechanism(s) regulating hypoxia-induced vascular fibrosis are unresolved. Hyperaldosteronism correlates positively with vascular remodeling in pulmonary arterial hypertension, suggesting that aldosterone may contribute to the pulmonary vasculopathy of hypoxia. The hypoxia-sensitive transcription factors c-Fos/c-Jun regulate steroidogenic acute regulatory protein (StAR), which facilitates the rate-limiting step of aldosterone steroidogenesis. We hypothesized that c-Fos/c-Jun upregulation by hypoxia activates StAR-dependent aldosterone synthesis in human pulmonary artery endothelial cells (HPAECs) to promote vascular fibrosis in pulmonary arterial hypertension.

METHODS AND RESULTS

Patients with pulmonary arterial hypertension, rats with Sugen/hypoxia-pulmonary arterial hypertension, and mice exposed to chronic hypoxia expressed increased StAR in remodeled pulmonary arterioles, providing a basis for investigating hypoxia-StAR signaling in HPAECs. Hypoxia (2.0% FiO2) increased aldosterone levels selectively in HPAECs, which was confirmed by liquid chromatography-mass spectrometry. Increased aldosterone by hypoxia resulted from enhanced c-Fos/c-Jun binding to the proximal activator protein-1 site of the StAR promoter in HPAECs, which increased StAR expression and activity. In HPAECs transfected with StAR-small interfering RNA or treated with the activator protein-1 inhibitor SR-11302 [3-methyl-7-(4-methylphenyl)-9-(2,6,6-trimethylcyclohexen-1-yl)nona-2,4,6,8-tetraenoic acid], hypoxia failed to increase aldosterone, confirming that aldosterone biosynthesis required StAR activation by c-Fos/c-Jun. The functional consequences of aldosterone were confirmed by pharmacological inhibition of the mineralocorticoid receptor with spironolactone or eplerenone, which attenuated hypoxia-induced upregulation of the fibrogenic protein connective tissue growth factor and collagen III in vitro and decreased pulmonary vascular fibrosis to improve pulmonary hypertension in vivo.

CONCLUSION

Our findings identify autonomous aldosterone synthesis in HPAECs attributable to hypoxia-mediated upregulation of StAR as a novel molecular mechanism that promotes pulmonary vascular remodeling and fibrosis.

Regulation of G6PD acetylation by SIRT2 and KAT9 modulates NADPH homeostasis and cell survival during oxidative stress

Glucose-6-phosphate dehydrogenase (G6PD) is a key enzyme in the pentose phosphate pathway (PPP) and plays an essential role in the oxidative stress response by producing NADPH, the main intracellular reductant. G6PD deficiency is the most common human enzyme defect, affecting more than 400 million people worldwide. Here, we show that G6PD is negatively regulated by acetylation on lysine 403 (K403), an evolutionarily conserved residue. The K403 acetylated G6PD is incapable of forming active dimers and displays a complete loss of activity. Knockdown of G6PD sensitizes cells to oxidative stress, and re-expression of wild-type G6PD, but not the K403 acetylation mimetic mutant, rescues cells from oxidative injury. Moreover, we show that cells sense extracellular oxidative stimuli to decrease G6PD acetylation in a SIRT2-dependent manner. The SIRT2-mediated deacetylation and activation of G6PD stimulates PPP to supply cytosolic NADPH to counteract oxidative damage and protect mouse erythrocytes. We also identified KAT9/ELP3 as a potential acetyltransferase of G6PD. Our study uncovers a previously unknown mechanism by which acetylation negatively regulates G6PD activity to maintain cellular NADPH homeostasis during oxidative stress.

Deletion of the angiotensin II type 1 receptor-associated protein enhances renal sodium reabsorption and exacerbates angiotensin II-mediated hypertension

Angiotensin II type 1 receptor (AT1R)–associated protein (ATRAP) promotes AT1R internalization along with suppression of pathological activation of tissue AT1R signaling. However, the functional significance of ATRAP in renal sodium handling and blood pressure regulation under pathological stimuli is not fully resolved. Here we show the blood pressure of mice with a gene-targeted disruption of ATRAP was comparable to that of wild-type mice at baseline. However, in ATRAP-knockout mice, angiotensin II–induced hypertension was exacerbated and the extent of positive sodium balance was increased by angiotensin II. Renal expression of the sodium-proton antiporter 3, a major sodium transporter in the proximal tubules, urinary pH, renal angiotensinogen production, and angiotensin II content was unaffected. Stimulation of the renal expression and activity of the epithelial sodium channel (ENaC), a major sodium transporter in the distal tubules, was significantly enhanced by chronic angiotensin II infusion. The circulating and urinary aldosterone levels were comparable. The blood pressure response and renal ENaC expression by aldosterone were not affected. Thus, ATRAP deficiency exacerbated angiotensin II–mediated hypertension by pathological activation of renal tubular AT1R by angiotensin II. This directly stimulates ENaC in the distal tubules and enhances sodium retention in an aldosterone-independent manner.

The cooperative roles of inflammation and oxidative stress in the pathogenesis of hypertension

SIGNIFICANCE

Innate and adaptive immunity play fundamental roles in the development of hypertension and its complications. As effectors of the cell-mediated immune response, myeloid cells and T lymphocytes protect the host organism from infection by attacking foreign intruders with bursts of reactive oxygen species (ROS).

RECENT ADVANCES

While these ROS may help to preserve the vascular tone and thereby protect against circulatory collapse in the face of overwhelming infection, aberrant elaboration of ROS triggered by immune cells in the absence of a hemodynamic insult can lead to pathologic increases in blood pressure. Conversely, misdirected oxidative stress in cardiovascular control organs, including the vasculature, the kidney, and the nervous system potentiates inflammatory responses, augmenting blood pressure elevation and inciting target organ damage.

CRITICAL ISSUES

Inflammation and oxidative stress thereby act as cooperative and synergistic partners in the pathogenesis of hypertension.

FUTURE DIRECTIONS

Pharmacologic interventions for hypertensive patients will need to exploit this robust bidirectional relationship between ROS generation and immune activation in cardiovascular control organs to maximize therapeutic benefit, while limiting off-target side effects.

A critical role of glucose-6-phosphate dehydrogenase in TAp73-mediated cell proliferation

The pentose phosphate pathway (PPP) provides ribose and NADPH that support biosynthesis and antioxidant defense. Our recent findings suggest that the p53-related protein TAp73 enhances the PPP flux. TAp73 stimulates the expression of glucose-6-phophate dehydrogenase (G6PD), the rate-limiting enzymes of the PPP. Through this regulation, TAp73 promotes the accumulation of macromolecules and increases cellular capability to withstand oxidative stresses. TAp73 also regulates other metabolic enzymes, and the relative importance of these targets in TAp73-mediated cell growth is not well understood. Here we show that, like in other cell lines, TAp73 is required for supporting proliferation and maintaining the expression of G6PD in the human lung cancer H1299 cells. Restoration of G6PD expression almost fully rescues the defects in cell growth caused by TAp73 knockdown, suggesting that G6PD is the major proliferative target of TAp73 in these cells. G6PD expression is elevated in various tumors, correlating with the upregulation of TAp73. These results indicate that TAp73 may function as an oncogene, and that G6PD is likely a focal point of regulation in oncogenic growth.

Systems analysis of oxidant stress in the vasculature

Systems biology and network analysis are emerging as valuable tools for the discovery of novel relationships, the identification of key regulatory factors, and the prediction of phenotypic changes in complex biological systems. Redox homeostasis in the vasculature is maintained by an intricate balance between oxidant-generating and antioxidant systems. When these systems are perturbed, conditions are permissive for oxidant stress, which, in turn, promotes vascular dysfunction and structural remodeling. Owing to the number of elements involved in redox regulation and the different vascular pathophenotypes associated with oxidant stress, vascular oxidant stress represents an ideal system to study by network analysis. Networks offer a method to organize experimentally derived factors, including proteins, metabolites, and DNA, that are represented as nodes into an unbiased comprehensive platform for study. Through analysis of the network, it is possible to determine essential or regulatory nodes, identify previously unknown connections between nodes, and locate modules, which are groups of nodes located within the same neighborhood that function together and have implications for phenotype. Investigators have only recently begun to construct oxidant stress-related networks to examine vascular structure and function; however, these early studies have provided mechanistic insight to further our understanding of this complicated biological system.

Role of endothelial cell metabolism in vessel sprouting

Endothelial cells (ECs) are quiescent for years but can plastically switch to angiogenesis. Vascular sprouting relies on the coordinated activity of migrating tip cells at the forefront and proliferating stalk cells that elongate the sprout. Past studies have identified genetic signals that control vascular branching. Prominent are VEGF, activating tip cells, and Notch, which stimulates stalk cells. After the branch is formed and perfused, ECs become quiescent phalanx cells. Now, emerging evidence has accumulated indicating that ECs not only adapt their metabolism when switching from quiescence to sprouting but also that metabolism regulates vascular sprouting in parallel to the control by genetic signals.

Mineralocorticoid receptor phosphorylation regulates ligand binding and renal response to volume depletion and hyperkalemia

Nuclear receptors are transcription factors that regulate diverse cellular processes. In canonical activation, ligand availability is sufficient to produce receptor binding, entraining downstream signaling. The mineralocorticoid receptor (MR) is normally activated by aldosterone, which is produced in both volume depletion and hyperkalemia, states that require different homeostatic responses. We report phosphorylation at S843 in the MR ligand-binding domain that prevents ligand binding and activation. In kidney, MR(S843-P) is found exclusively in intercalated cells of the distal nephron. In volume depletion, angiotensin II and WNK4 signaling decrease MR(S843-P) levels, whereas hyperkalemia increases MR(S843-P). Dephosphorylation of MR(S843-P) results in aldosterone-dependent increases of the intercalated cell apical proton pump and Cl(-)/HCO3(-) exchangers, increasing Cl(-) reabsorption and promoting increased plasma volume while inhibiting K(+) secretion. These findings reveal a mechanism regulating nuclear hormone receptor activity and implicate selective MR activation in intercalated cells in the distinct adaptive responses to volume depletion and hyperkalemia.

Chronic hyperaldosteronism in cryptochrome-null mice induces high-salt- and blood pressure-independent kidney damage in mice

Although aldosterone has an essential role in controlling electrolyte and body fluid homeostasis, aldosterone also exerts certain pathological effects on the kidney. Several previous studies have attempted to examine these deleterious effects. However, the majority of these studies were performed using various injury models, including high-salt treatment and/or mineralocorticoid administration, by which the kidney changes observed were not only due to aldosterone but also due to prior injury caused by salt and hypertension. In the present study, we investigated aldosterone's pathological effect on the kidney using a mouse model with a high level of endogenous aldosterone. We used cryptochrome-null (Cry 1, 2 DKO) mice characterized by high aldosterone levels and low plasma renin activity and observed that even under normal salt exposure conditions, these mice showed increased albumin excretion and kidney tubular injury, decreased nephrin expression and increased reactive oxygen species production in the absence of hypertension. Exposure to high salt levels exacerbated the kidney damage observed in these mice. Moreover, we noted that decreasing blood pressure without blocking aldosterone action did not provide beneficial effects to the kidney in high-salt-treated Cry 1, 2 DKO mice. Thus, our findings support the hypothesis that aldosterone has deleterious effects on the kidney independent of high-salt exposure and high blood pressure.

Effect of NR3C2 genetic polymorphisms on the blood pressure response to enalapril treatment

AIM

The mineralocorticoid receptor (MR; also known as NR3C2) plays important roles in the modulation of blood pressure. The effect of NR3C2 polymorphisms on antihypertensive response to enalapril was investigated.

PATIENTS & METHODS

Two hundred and seventy nine essential hypertension patients treated with enalapril were genotyped for two NR3C2 tagSNPs, rs5522 and rs2070950, by Sequenom MassArray™ technology.

RESULTS

The reductions in diastolic blood pressure (DBP) were significantly greater in AA homozygotes compared with AG+GG genotype carriers for the rs5522 polymorphism (p = 0.009), and the reductions in DBP were greater in GG homozygotes compared with GC+CC genotype carriers for the rs2070950 polymorphism, with marginal significance (p = 0.065). Stepwise multiple regression analysis indicated that significant predictors of DBP reduction were baseline DBP (p < 0.001), waist:hip ratio (p = 0.001) and rs5522 genotype (p = 0.003).

CONCLUSION

NR3C2 rs5522 affects blood pressure response to enalapril treatment and may serve as a useful pharmacogenomic marker of antihypertensive response to enalapril in essential hypertension patients.

Long-term effects of addition of mineralocorticoid receptor antagonist to angiotensin II receptor blocker in patients with diabetic nephropathy: a randomized clinical trial

BACKGROUND

Addition of spironolactone (SPR) to angiotensin-converting enzyme (ACE) inhibitors or angiotensin II receptor blockers (ARBs) might provide antiproteinuric effects beyond what is gained by either medication alone. This study was designed to assess the long-term efficacy of SPR/ARB combination in comparison with the standard ACE/ARB regimen in diabetic nephropathy.

METHODS

In an open-label, parallel-group, single-center, randomized clinical trial (NCT01667614), 136 patients with diabetes and proteinuria, already treated with enalapril and losartan, were included. In 74 patients, ACE inhibitors were discontinued. After a wash-out period of 2 weeks, 25 mg SPR daily was initiated. The remainder of the patients (n = 62) received ACE inhibitors and ARBs as before. Patients were followed every 3 months for 18 months. During each visit, systolic and diastolic blood pressure (BP), urinary albumin excretion (UAE), serum creatinine, estimated glomerular filtration rate (eGFR) and serum potassium concentrations were determined.

RESULTS

After 18 months, three patients in the SPR/ARB group developed asymptomatic hyperkalemia. SPR/ARB significantly reduced both systolic and diastolic BP (P < 0.001 and 0.001, respectively). SPR/ARB decreased UAE by 46, 72 and 59% after 3, 12 and 18 months, respectively. Compared with the continuation regimen, SPR/ARB was superior in UAE reduction (P = 0.017 after 18 months), independent of BP change. In both groups, eGFR declined significantly over the trial course and the decline rate did not differ significantly between the two groups.

CONCLUSIONS

Addition of SPR to ARB provides added benefits with respect to BP control and proteinuria diminution. These antiproteinuric effects are not accompanied by prevention of eGFR loss compared with conventional therapy with ACE/ARB.

The role of the renin-angiotensin-aldosterone system in obesity-related renal diseases

Obesity is an independent risk factor for the development and progression of chronic kidney disease and one of the emerging reasons for end-stage renal disease owing to its dramatic increase worldwide. Among the potential underlying pathophysiologic mechanisms, activation of the renin-angiotensin-aldosterone-system (RAAS) plays a central role. Increased angiotensin II (AngII) levels also are central in hypertension, dyslipidemia, and insulin resistance, which, taken together with obesity, represent the metabolic syndrome. Increased AngII levels contribute to hyperfiltration, glomerulomegaly, and subsequent focal glomerulosclerosis by altering renal hemodynamics via afferent arteriolar dilation, together with efferent renal arteriolar vasoconstriction as well as by its endocrine and paracrine properties linking the intrarenal and the systemic RAAS, adipose tissue dysfunction, as well as insulin resistance and hypertension. The imbalance between increased AngII levels and the angiotensin converting enzyme 2/Ang (1-7)/Mas receptor axis additionally contributes to renal injury in obesity and its concomitant metabolic disturbances. As shown in several large trials and experimental studies, treatment of obesity by weight loss is associated with an improvement of kidney disease because it also is beneficial in dyslipidemia, hypertension, and diabetes. The most promising data have been seen by RAAS blockade, pointing to the central position of RAAS within obesity, kidney disease, and the metabolic syndrome.

Aldosterone affects blood flow and vascular tone regulated by endothelium-derived NO: therapeutic implications

Aldosterone, in doses inappropriate to the salt status, plays an important role in the development of cardiovascular injury, including endothelial dysfunction, independent of its hypertensive effects. Acute non-genomic effects of aldosterone acting on mineralocorticoid receptors are inconsistent in healthy humans: vasoconstriction or forearm blood flow decrease via endothelial dysfunction, vasodilatation mediated by increased NO actions, or no effects. However, in studies with experimental animals, aldosterone mostly enhances vasodilatation mediated by endothelium-derived NO. Chronic exposure to aldosterone, which induces genomic responses, results in impairments of endothelial function through decreased NO synthesis and action in healthy individuals, experimental animals and isolated endothelial cells. Chronic aldosterone reduces NO release from isolated human endothelial cells only when extracellular sodium is raised. Oxidative stress is involved in the impairment of endothelial function by promoting NO degradation. Aldosterone liberates endothelin-1 (ET-1) from endothelial cells, which elicits ET(A) receptor-mediated vasoconstriction by inhibiting endothelial NO synthesis and action and through its own direct vasoconstrictor action. Ca(2+) flux through T-type Ca(2+) channels activates aldosterone synthesis and thus enhances unwanted effects of aldosterone on the endothelium. Mineralocorticoid receptor inhibitors, ET(A) receptor antagonists and T-type Ca(2) + channel blockers appear to diminish the pathophysiological participation of aldosterone in cardiovascular disease and exert beneficial actions on bioavailability of endothelium-derived NO, particularly in resistant hypertension and aldosteronism.

Glucose-6-phosphate dehydrogenase deficiency in transfusion medicine: the unknown risks

The hallmark of glucose-6-phosphate dehydrogenase (G6PD) deficiency is red blood cell (RBC) destruction in response to oxidative stress. Patients requiring RBC transfusions may simultaneously receive oxidative medications or have concurrent infections, both of which can induce haemolysis in G6PD-deficient RBCs. Although it is not routine practice to screen healthy blood donors for G6PD deficiency, case reports identified transfusion of G6PD-deficient RBCs as causing haemolysis and other adverse events. In addition, some patient populations may be more at risk for complications associated with transfusions of G6PD-deficient RBCs because they receive RBCs from donors who are more likely to have G6PD deficiency. This review discusses G6PD deficiency, its importance in transfusion medicine, changes in the RBC antioxidant system (of which G6PD is essential) during refrigerated storage and mechanisms of haemolysis. In addition, as yet unanswered questions that could be addressed by translational and clinical studies are identified and discussed.

Glutathione (GSH) and the GSH synthesis gene Gclm modulate plasma redox and vascular responses to acute diesel exhaust inhalation in mice

CONTEXT

Inhalation of fine particulate matter (PM₂.₅) is associated with acute pulmonary inflammation and impairments in cardiovascular function. In many regions, PM₂.₅ is largely derived from diesel exhaust (DE), and these pathophysiological effects may be due in part to oxidative stress resulting from DE inhalation. The antioxidant glutathione (GSH) is important in limiting oxidative stress-induced vascular dysfunction. The rate-limiting enzyme in GSH synthesis is glutamate cysteine ligase and polymorphisms in its catalytic and modifier subunits (GCLC and GCLM) have been shown to influence vascular function and risk of myocardial infarction in humans.

OBJECTIVE

We hypothesized that compromised de novo synthesis of GSH in Gclm⁻/⁺ mice would result in increased sensitivity to DE-induced lung inflammation and vascular effects.

MATERIALS AND METHODS

WT and Gclm⁻/⁺ mice were exposed to DE via inhalation (300 μg/m³) for 6 h. Neutrophil influx into the lungs, plasma GSH redox potential, vascular reactivity of aortic rings and aortic nitric oxide (NO•) were measured.

RESULTS

DE inhalation resulted in mild bronchoalveolar neutrophil influx in both genotypes. DE-induced effects on plasma GSH oxidation and acetylcholine (ACh)-relaxation of aortic rings were only observed in Gclm⁻/⁺ mice. Contrary to our hypothesis, DE exposure enhanced ACh-induced relaxation of aortic rings in Gclm⁻/⁺ mice.

DISCUSSION AND CONCLUSION

THESE data support the hypothesis that genetic determinants of antioxidant capacity influence the biological effects of acute inhalation of DE. However, the acute effects of DE on the vasculature may be dependent on the location and types of vessels involved. Polymorphisms in GSH synthesis genes are common in humans and further investigations into these potential gene-environment interactions are warranted.

TAp73 enhances the pentose phosphate pathway and supports cell proliferation

TAp73 is a structural homologue of the pre-eminent tumor suppressor p53. However, unlike p53, TAp73 is rarely mutated, and instead is frequently over-expressed in human tumors. It remains unclear whether TAp73 affords an advantage to tumor cells and if so, what is the underlying mechanism. Here we show that TAp73 supports the proliferation of human and mouse tumor cells. TAp73 activates the expression of the glucose-6-phosphate dehydrogenase (G6PD), the rate-limiting enzyme of the pentose phosphate pathway (PPP). By stimulating G6PD, TAp73 increases PPP flux and directs glucose to the production of NADPH and ribose, for the synthesis of macromolecules and detoxification of reactive oxygen species (ROS). The growth defect of TAp73-deficient cells can be rescued by either enforced G6PD expression or the presence of nucleosides plus an ROS scavenger. These findings establish a critical role for TAp73 in regulating metabolism, and connect TAp73 and the PPP to oncogenic cell growth.

Contribution of aldosterone to cardiovascular and renal inflammation and fibrosis

The steroid hormone aldosterone regulates sodium and potassium homeostasis. Aldosterone and activation of the mineralocorticoid receptor also causes inflammation and fibrosis of the heart, fibrosis and remodelling of blood vessels and tubulointerstitial fibrosis and glomerular injury in the kidney. Aldosterone and mineralocorticoid-receptor activation initiate an inflammatory response by increasing the generation of reactive oxygen species by nicotinamide adenine dinucleotide phosphate (NADPH) oxidase and mitochondria. High salt intake potentiates these effects, in part by activating the Rho family member Rac1, a regulatory subunit of reduced NADPH oxidase that activates the mineralocorticoid receptor. Studies in mice in which the mineralocorticoid receptor has been deleted from specific cell types suggest a key role for macrophages in promoting inflammation and fibrosis. Aldosterone can exert mineralocorticoid-receptor-independent effects via the angiotensin II receptor and via G-protein-coupled receptor 30. Mineralocorticoid-receptor antagonists are associated with decreased mortality in patients with heart disease and show promise in patients with kidney injury, but can elevate serum potassium concentration. Studies in rodents genetically deficient in aldosterone synthase or treated with a pharmacological aldosterone-synthase inhibitor are providing insight into the relative contribution of aldosterone compared with the contribution of mineralocorticoid-receptor activation in inflammation, fibrosis, and injury. Aldosterone-synthase inhibitors are under development in humans.

The role of mineralocorticoid receptor antagonists (MRAs) in very old patients with heart failure

Mineralocorticoid receptor antagonists (MRAs) have been effective in reducing total mortality in patients with heart failure (HF) and a reduced left ventricular ejection fraction. Due to the finding that aldosterone levels decrease with age, one might question the effectiveness of MRAs in very old patients (≥80 years of age), those at the greatest risk for developing HF with a preserved left ventricular ejection fraction (PEF). However, while aldosterone levels decrease with age, there is also a decrease in the enzyme 11 beta HSD2 levels with age, thereby allowing cortisol to stimulate the mineralocorticoid receptor (MR), which in younger patients with higher levels of 11 beta HSD 2 levels is converted to cortisone which cannot activate the MR. There is also an increase in the expression of the MR in the vascular wall with age. Thus, there is reason to believe that MRAs might be effective in reducing cardiovascular mortality and the incidence of hospitalizations for HF in very old patients with HFPEF. There is also reason to believe that MRAs might favorably affect many of the comorbid conditions associated with HFPEF in very old patients. The safety and efficacy of this hypothesis is currently under investigation in the NHLBI sponsored TOPCAT trial.

Pharmacology of Aldosterone and the Effects of Mineralocorticoid Receptor Blockade on Cardiovascular Systems

It is well-known that aldosterone plays an important role in reabsorption of sodium and fluid, and in potassium excretion in kidneys via epithelial mineralocorticoid receptor (MR) activation. Recent studies have shown that aldosterone causes cardiovascular remodeling not only in a blood pressure-dependent manner, but also in a blood pressure-independent manner by decreasing nitric oxide bioavailability and modulating oxidative stress, leading to vascular inflammation. In addition, MR blockade does provide beneficial effects associated with cardiovascular protection, resulting in a reduction of cardiovascular morbidity and mortality. A growing body of evidence suggests that MR blockade is a promising therapeutic target to help prevent cardiovascular events.

KEY WORDS

Aldosterone; Mineralocorticoid receptor; Nitrix oxide; Renin-angiotensin-aldosterone system.