Carbon monoxide exposure enhances arrhythmia after cardiac stress: involvement of oxidative stress

Effects and possible mechanisms of combined exposure to noise and carbon monoxide on male reproductive system in rats

Environmental hazards are an increasing concern due to the rapid pace of industrialization. Among these hazards, noise and carbon monoxide (CO) are common risk factors and have been shown to cause serious health problems. However, existing studies focused on the individual effects of noise and CO exposure and the combined effects of these two factors remain poorly understood. Our study aimed to examine the combined effects of noise and CO exposure on testicular function by constructing individual and combined exposure models. Our findings indicated that combined exposure to noise and CO was associated with a higher risk of testicular damage and male reproductive damage when compared to exposure alone. This was evidenced by poorer semen quality and more severe pathological damage to the testis. This combined exposure led to higher levels of oxidative stress and apoptosis in the testes, with bioinformatics analyses suggesting the signaling pathways involved in these responses. Specifically, activation of the P53 signaling pathway was found to contribute to the testicular damage caused by the combined exposure. Encouragingly, pterostilbene (PTE), a novel phytochemical, alleviated combined exposure-induced testicular damage by reducing oxidative stress and germ cell apoptosis. Overall, we identified joint reproductive toxicity resulting from the exposure to noise and CO, and found that PTE is a promising potential treatment for injuries caused by these factors. The cover image is based on the Research Article Effects and possible mechanisms of combined exposure to noise and carbon monoxide on male reproductive system in rats by Yingqing Li et al., https://doi.org/10.1002/tox.23927.

Association between ambient carbon monoxide levels and hospitalization costs of patients with myocardial infarction: Potential effect modification by ABO blood group

Previous researches have reported the association between air pollution and various diseases. However, few researches have investigated whether air pollutants are associated with the economic loss resulting from patients' hospitalization, especially the economic loss of hospitalization due to acute cardiovascular events. The purpose of our research was to explore the association between the levels of carbon monoxide (CO), taken as an index of pollution, and the hospitalization costs of myocardial infarction (MI), and the potential effect modification by the ABO blood group. A total of 3237 MI inpatients were included in this study. A multiple linear regression model was used to evaluate the association between ambient CO levels and hospitalization costs of MI patients. Moreover, we performed stratified analyses by age, gender, body mass index (BMI), season, hypertension, and ABO blood types. There was a positive association between the levels of CO in the air and the costs of hospitalization caused by MI. Furthermore, such association was stronger in males, BMI ≥25, <65 years, with hypertension, and non-O blood group. Interestingly, we found the association was particularly significant in patients with blood group B. Overall, our study first found that ambient CO levels could have an impact on the hospitalization costs for MI patients, and those with blood group B can be more sensitive.

An integral perspective of canonical cigarette and e-cigarette-related cardiovascular toxicity based on the adverse outcome pathway framework

BACKGROUND

Nowadays, cigarette smoking remains the leading cause of chronic disease and premature death, especially cardiovascular disease. As an emerging tobacco product, e-cigarettes have been advocated as alternatives to canonical cigarettes, and thus may be an aid to promote smoking cessation. However, recent studies indicated that e-cigarettes should not be completely harmless to the cardiovascular system.

AIM OF REVIEW

This review aimed to build up an integral perspective of cigarettes and e-cigarettes-related cardiovascular toxicity.

KEY SCIENTIFIC CONCEPTS OF REVIEW

This review adopted the adverse outcome pathway (AOP) framework as a pivotal tool and aimed to elucidate the association between the molecular initiating events (MIEs) induced by cigarette and e-cigarette exposure to the cardiovascular adverse outcome. Since the excessive generation of reactive oxygen species (ROS) has been widely approved to play a critical role in cigarette smoke-related CVD and may also be involved in e-cigarette-induced toxic effects, the ROS overproduction and subsequent oxidative stress are regarded as essential parts of this framework. As far as we know, this should be the first AOP framework focusing on cigarette and e-cigarette-related cardiovascular toxicity, and we hope our work to be a guide in exploring the biomarkers and novel therapies for cardiovascular injury.

Systematic review and meta-analysis of studies between short-term exposure to ambient carbon monoxide and non-accidental, cardiovascular, and respiratory mortality in China

Although a growing number of original epidemiological studies imply a link between ambient pollution exposure and mortality risk, the findings associated with carbon monoxide (CO) exposure are inconsistent. Thus, we conducted a systematic review and meta-analysis of epidemiological studies to evaluate the correlations between ambient CO and non-accidental, cardiovascular, and respiratory mortality in China. Eight databases were searched from inception to 15 May 2021. A random-effect model was used to calculate the pooled relative risks (RRs) and 95% confidence intervals (CIs). Subgroup analyses as well as sensitivity analyses were performed. The I square value (I²) was used to assess heterogeneity among different studies. The assessment of publication bias on included studies was examined by funnel plot and Egger's test. The influence of a potential publication bias on findings was explored by using the trim-and-fill procedure. Ultimately, a total of 19 studies were included in our analysis. The pooled relative risk for each 1 mg/m³ increase of ambient carbon monoxide was 1.0220 (95%CI: 1.0102-1.0339) for non-accidental mortality, 1.0304 (95%CI:1.0154-1.0457) for cardiovascular mortality, and 1.0318 (95%CI:1.0132-1.0506) for respiratory mortality. None of subgroup analyses could explain the source of heterogeneity. Exclusion of any single study did not materially alter the pooled effect estimates. Although it was suggestive of publication bias, findings were generally similar with principal findings when we explored the influence of a potential publication bias using the trim-and-fill method. Our meta-analysis demonstrated that exposure to ambient CO was positive with risk of deaths from all non-accidental causes, total cardiovascular, and respiratory diseases. Based on these findings, tougher intervention policies and initiatives to reduce the health effects of CO exposure should be established.

Carbon monoxide releasing molecule-2 suppresses stretch-activated atrial natriuretic peptide secretion by activating large-conductance calcium-activated potassium channels

Carbon monoxide (CO) is a known gaseous bioactive substance found across a wide array of body systems. The administration of low concentrations of CO has been found to exert an anti-inflammatory, anti-apoptotic, anti-hypertensive, and vaso-dilatory effect. To date, however, it has remained unknown whether CO influences atrial natriuretic peptide (ANP) secretion. This study explores the effect of CO on ANP secretion and its associated signaling pathway using isolated beating rat atria. Atrial perfusate was collected for 10 min for use as a control, after which high atrial stretch was induced by increasing the height of the outflow catheter. Carbon monoxide releasing molecule-2 (CORM-2; 10, 50, 100 µM) and hemin (HO-1 inducer; 0.1, 1, 50 µM), but not CORM-3 (10, 50, 100 µM), decreased high stretch-induced ANP secretion. However, zinc porphyrin (HO-1 inhibitor) did not affect ANP secretion. The order of potency for the suppression of ANP secretion was found to be hemin > CORM-2 >> CORM-3. The suppression of ANP secretion by CORM-2 was attenuated by pretreatment with 5-hydroxydecanoic acid, paxilline, and 1H-[1,2,4] oxadiazolo [4,3-a] quinoxalin-1-one, but not by diltiazem, wortmannin, LY-294002, or NG-nitro-L-arginine methyl ester. Hypoxic conditions attenuated the suppressive effect of CORM-2 on ANP secretion. In sum, these results suggest that CORM-2 suppresses ANP secretion via mitochondrial K_ATP channels and large conductance Ca²⁺-activated K⁺ channels.

Carbon monoxide activation of delayed rectifier potassium currents of human cardiac fibroblasts through diverse pathways

To identify the effect and mechanism of carbon monoxide (CO) on delayed rectifier K⁺ currents (I_K) of human cardiac fibroblasts (HCFs), we used the wholecell mode patch-clamp technique. Application of CO delivered by carbon monoxidereleasing molecule-3 (CORM3) increased the amplitude of outward K⁺ currents, and diphenyl phosphine oxide-1 (a specific I_K blocker) inhibited the currents. CORM3- induced augmentation was blocked by pretreatment with nitric oxide synthase blockers (L-NG-monomethyl arginine citrate and L-NG-nitro arginine methyl ester). Pretreatment with KT5823 (a protein kinas G blocker), 1H-[1,-2,-4] oxadiazolo-[4,-3-a] quinoxalin-1-on (ODQ, a soluble guanylate cyclase blocker), KT5720 (a protein kinase A blocker), and SQ22536 (an adenylate cyclase blocker) blocked the CORM3 stimulating effect on I_K. In addition, pretreatment with SB239063 (a p38 mitogen-activated protein kinase [MAPK] blocker) and PD98059 (a p44/42 MAPK blocker) also blocked the CORM3's effect on the currents. When testing the involvement of S-nitrosylation, pretreatment of N-ethylmaleimide (a thiol-alkylating reagent) blocked CO-induced I_K activation and DL-dithiothreitol (a reducing agent) reversed this effect. Pretreatment with 5,10,15,20-tetrakis(1-methylpyridinium-4-yl)-21H,23H porphyrin manganese (III) pentachloride and manganese (III) tetrakis (4-benzoic acid) porphyrin chloride (superoxide dismutase mimetics), diphenyleneiodonium chloride (an NADPH oxidase blocker), or allopurinol (a xanthine oxidase blocker) also inhibited CO-induced I_K activation. These results suggest that CO enhances I_K in HCFs through the nitric oxide, phosphorylation by protein kinase G, protein kinase A, and MAPK, S-nitrosylation and reduction/oxidation (redox) signaling pathways.

Carbon monoxide activates large-conductance calcium-activated potassium channels of human cardiac fibroblasts through various mechanisms

Carbon monoxide (CO) is a cardioprotectant and potential cardiovascular therapeutic agent. Human cardiac fibroblasts (HCFs) are important determinants of myocardial structure and function. Large-conductance Ca²⁺-activated K⁺ (BK) channel is a potential therapeutic target for cardiovascular disease. We investigated whether CO modulates BK channels and the signaling pathways in HCFs using whole-cell mode patch-clamp recordings. CO-releasing molecules (CORMs; CORM-2 and CORM-3) significantly increased the amplitudes of BK currents (IBK). The CO-induced stimulating effects on IBK were blocked by pre-treatment with specific nitric oxide synthase (NOS) blockers (L-N^G-monomethyl arginine citrate and L-N^G-nitroarginine methyl ester). 8-bromo-cyclic GMP increased IBK. KT5823 (inhibits PKG) or ODQ (inhibits soluble guanylate cyclase) blocked the CO-stimulating effect on IBK. Moreover, 8-bromo-cyclic AMP also increased IBK, and pre-treatment with KT5720 (inhibits PKA) or SQ22536 (inhibits adenylate cyclase) blocked the CO effect. Pre-treatment with N-ethylmaleimide (a thiol-alkylating reagent) also blocked the CO effect on IBK, and DL-dithiothreitol (a reducing agent) reversed the CO effect. These data suggest that CO activates IBK through NO via the NOS and through the PKG, PKA, and S-nitrosylation pathways.

Interplay of pro-inflammatory cytokines, pro-inflammatory microparticles and oxidative stress and recurrent ventricular arrhythmias in elderly patients after coronary stent implantations

BACKGROUND

The roles of pro-inflammatory microparticles, pro-inflammatory cytokines and oxidative stress were unknown in elderly patients with recurrent ventricular arrhythmias (VA). We evaluated whether cross talk between oxidative stress, pro-inflammatory microparticles, and pro-inflammatory cytokines play the roles in elderly patients with recurrent VA after coronary stenting. This research sought to investigate the effects of oxidative stress, pro-inflammatory microparticles, and pro-inflammatory cytokines on recurrent VA in elderly patients after coronary stenting.

METHODS

In this study, we included 613 consecutive elderly patients with recurrent ventricular arrhythmias induced by coronary reocclusions after coronary stenting. We measured CD31⁺ endothelial microparticle (CD31⁺EMP), CD62E⁺ endothelial microparticle (CD62E⁺EMP), high-sensitivity C-reactive protein (hs-CRP), aldosterone (ALD), malondialdehyde (MDA), tumor necrosis factor-α (TNF-α), soluble tumor necrosis factor receptor-1 (sTNFR-1) and soluble tumor necrosis factor receptor-2 (sTNFR-2) in elderly patients with recurrent VA and assessed impacts of pro-inflammatory microparticles, pro-inflammatory cytokines and oxidative stress on recurrent VA in elderly patients after coronary stenting.

RESULTS

The levels of CD31⁺EMP, CD62E⁺EMP, hs-CRP, ALD, MDA, TNF-α, sTNFR-1 and sTNFR-2 were increased in recurrent malignant ventricular arrhythmia, sustained ventricular tachycardia, multiple ventricular premature beat and left and right ventricular bundle branch block groups (P < 0.001) in elderly patients with coronary reocclusions after coronary stent implantation. Upregulation of pro-inflammatory microparticles, pro-inflammatory cytokines and oxidative stress markers induced recurrent VA in elderly patients after coronary stenting.

CONCLUSIONS

High levels of pro-inflammatory microparticles, pro-inflammatory cytokines and oxidative stress markers were associated with recurrent VA in elderly patients after coronary stenting. Our results suggested that the pro-inflammatory microparticles, pro-inflammatory cytokines and oxidative stress may simultaneously induce and aggravate recurrent VA in elderly patients after coronary stenting.

Role of oxidative stress in cardiovascular disease outcomes following exposure to ambient air pollution

Exposure to ambient air pollution is associated with adverse cardiovascular outcomes. These are manifested through several, likely overlapping, pathways including at the functional level, endothelial dysfunction, atherosclerosis, pro-coagulation and alterations in autonomic nervous system balance and blood pressure. At numerous points within each of these pathways, there is potential for cellular oxidative imbalances to occur. The current review examines epidemiological, occupational and controlled exposure studies and research employing healthy and diseased animal models, isolated organs and cell cultures in assessing the importance of the pro-oxidant potential of air pollution in the development of cardiovascular disease outcomes. The collective body of data provides evidence that oxidative stress (OS) is not only central to eliciting specific cardiac endpoints, but is also implicated in modulating the risk of succumbing to cardiovascular disease, sensitivity to ischemia/reperfusion injury and the onset and progression of metabolic disease following ambient pollution exposure. To add to this large research effort conducted to date, further work is required to provide greater insight into areas such as (a) whether an oxidative imbalance triggers and/or worsens the effect and/or is representative of the consequence of disease progression, (b) OS pathways and cardiac outcomes caused by individual pollutants within air pollution mixtures, or as a consequence of inter-pollutant interactions and (c) potential protection provided by nutritional supplements and/or pharmacological agents with antioxidant properties, in susceptible populations residing in polluted urban cities.

Carbon monoxide pollution aggravates ischemic heart failure through oxidative stress pathway

Risk of hospital readmission and cardiac mortality increases with atmospheric pollution for patients with heart failure. The underlying mechanisms are unclear. Carbon monoxide (CO) a ubiquitous environmental pollutant could be involved. We explored the effect of daily exposure of CO relevant to urban pollution on post-myocardial infarcted animals. Rats with ischemic heart failure were exposed 4 weeks to daily peaks of CO mimicking urban exposure or to standard filtered air. CO exposure worsened cardiac contractile dysfunction evaluated by echocardiography and at the cardiomyocyte level. In line with clinical reports, the animals exposed to CO also exhibited a severe arrhythmogenic phenotype with numerous sustained ventricular tachycardias as monitored by surface telemetric electrocardiograms. CO did not affect cardiac β-adrenergic responsiveness. Instead, mitochondrial dysfunction was exacerbated leading to additional oxidative stress and Ca²⁺ cycling alterations. This was reversed following acute antioxidant treatment of cardiomyocytes with N-acetylcysteine confirming involvement of CO-induced oxidative stress. Exposure to daily peaks of CO pollution aggravated cardiac dysfunction in rats with ischemic heart failure by specifically targeting mitochondria and generating ROS-dependent alterations. This pathway may contribute to the high sensibility and vulnerability of individuals with cardiac disease to environmental outdoor air quality.

Parity Conditions the Risk for Low Birth Weight after Maternal Exposure to Air Pollution

Multiparous mothers have greater umbilical blood flow and thus more efficient transport of pollutants than primiparous mothers. We tested a hypothesis that multiparous mothers are more prone to have an infant with low birth weight (LBW) after prenatal exposure to air pollution. A study was conducted on a representative group of more than 74,000 singleton, live, full-term infants. Birth data were obtained from the birth registry, while pollution data were from an environmental monitoring system (Poland). Multiple comparisons were controlled by the false discovery rate procedure (FDR). After standardization, the harmful effect of carbon monoxide (CO) on the odds ratio (OR) for LBW was seen among the multiparous mothers (OR = 1.28; 95% CI 1.06-1.54), while in primiparous mothers it was nonsignificant. The effect of CO on the OR for LBW differed according to parity, which was confirmed by the test for interaction (FDR-adjusted p = 0.03). The interaction between parity and sulfur dioxide (SO₂) was statistically nonsignificant (FDR-adjusted p = 0.08). Multiparous mothers may be more vulnerable to CO than primiparous mothers. Parity may be the modifier of the association between pollutants and the risk of LBW.

Mitochondria and carbon monoxide: cytoprotection and control of cell metabolism - a role for Ca(2+) ?

Carbon monoxide (CO) is an endogenously produced gasotransmitter with important biological functions: anti-inflammation, anti-apoptosis, vasomodulation and cell metabolism modulation. The most recognized cellular target for CO is the mitochondria. Physiological concentrations of CO generate mitochondrial reactive oxygen species (ROS), which are signalling molecules for CO-induced pathways. Indeed, small amounts of ROS promote cytoprotection by a preconditioning effect. Furthermore, CO prevents cell death by limiting mitochondrial membrane permeabilization, which inhibits the release of pro-apoptotic factors into the cytosol; both events are ROS dependent. CO also increases the ability of mitochondria to take up Ca(2+) . Mitochondrial metabolism is modulated by CO, namely by increasing TCA cycle rate, oxidative phosphorylation and mitochondrial biogenesis, which, in turn, increases ATP production. CO's modulation of metabolism might be important for cellular response to diseases, namely cancer and ischaemic diseases. Finally, another cytoprotective role of CO involves the control of Ca(2+) channels. By limiting the activity of T-type and L-type Ca(2+) channels, CO prevents excitotoxicity-induced cell death and modulates cell proliferation. Several questions concerning Ca(2+) signalling, mitochondria and CO can be asked, for instance whether CO modulation of cell metabolism would be dependent on the mitochondrial Ca(2+) uptake capacity, since small amounts of Ca(2+) can increase mitochondrial metabolism. Whether CO controls Ca(2+) communication between mitochondria and endoplasmic reticulum is another open field of research. In summary, CO emerges as a key gasotransmitter in the control of several cellular functions of mitochondria: metabolism, cell death and Ca(2+) signalling.

Risk of Peripheral Artery Disease in Patients With Carbon Monoxide Poisoning: A Population-Based Retrospective Cohort Study

Carbon monoxide (CO) poisoning can cause several life-threatening complications, particularly in cardiovascular and neurological systems. However, no studies have been performed to investigate the association between peripheral artery disease (PAD) and CO poisoning. We constructed a population-based retrospective cohort study to clarify the risks between PAD and CO poisoning. This population-based cohort study involved analyzing data from 1998 to 2010 obtained from the Taiwanese National Health Insurance Research Database, with a follow-up period extending to the end of 2011. We identified patients with CO poisoning and selected a comparison cohort that was frequency matched according to age, sex, and year of diagnosis of CO poisoning at a ratio of 1 patient to 4 control patients. We analyzed the risks for patients with CO poisoning and PAD by using Cox proportional hazards regression models. In this study, 9046 patients with CO poisoning and 36,183 controls were included. The overall risks for developing PAD were 1.85-fold in the patients with CO poisoning compared with the comparison cohort after adjusting for age, sex, and comorbidities. Our long-term cohort study results showed a higher risk for PAD development among patients with CO poisoning.

Carbon monoxide increases inducible NOS expression that mediates CO-induced myocardial damage during ischemia-reperfusion

We investigated the role of inducible nitric oxide (NO) synthase (iNOS) on ischemic myocardial damage in rats exposed to daily low nontoxic levels of carbon monoxide (CO). CO is a ubiquitous environmental pollutant that impacts on mortality and morbidity from cardiovascular diseases. We have previously shown that CO exposure aggravates myocardial ischemia-reperfusion (I/R) injury partly because of increased oxidative stress. Nevertheless, cellular mechanisms underlying cardiac CO toxicity remain hypothetical. Wistar rats were exposed to simulated urban CO pollution for 4 wk. First, the effects of CO exposure on NO production and NO synthase (NOS) expression were evaluated. Myocardial I/R was performed on isolated perfused hearts in the presence or absence of S-methyl-isothiourea (1 μM), a NOS inhibitor highly specific for iNOS. Finally, Ca(2+) handling was evaluated in isolated myocytes before and after an anoxia-reoxygenation performed with or without S-methyl-isothiourea or N-acetylcystein (20 μM), a nonspecific antioxidant. Our main results revealed that 1) CO exposure altered the pattern of NOS expression, which is characterized by increased neuronal NOS and iNOS expression; 2) cardiac NO production increased in CO rats because of its overexpression of iNOS; and 3) the use of a specific inhibitor of iNOS reduced myocardial hypersensitivity to I/R (infarct size, 29 vs. 51% of risk zone) in CO rat hearts. These last results are explained by the deleterious effects of NO and reactive oxygen species overproduction by iNOS on diastolic Ca(2+) overload and myofilaments Ca(2+) sensitivity. In conclusion, this study highlights the involvement of iNOS overexpression in the pathogenesis of simulated urban CO air pollution exposure.

The effects of B0, B20, and B100 soy biodiesel exhaust on aconitine-induced cardiac arrhythmia in spontaneously hypertensive rats

CONTEXT

Diesel exhaust (DE) has been shown to increase the risk of cardiac arrhythmias. Although biodiesel has been proposed as a "safer" alternative to diesel, it is still uncertain whether it actually poses less threat.

OBJECTIVE

We hypothesized that exposure to pure or 20% soy biodiesel exhaust (BDE) would cause less sensitivity to aconitine-induced arrhythmia than DE in rats.

METHODS

Spontaneously hypertensive (SH) rats implanted with radiotelemeters were exposed once or for 5 d (4 h) to either 50 mg/m(3) (low), 150 mg/m(3) (medium), or 500 mg/m(3) (high) of DE (B0), 20% (B20) or 100% (B100) soy biodiesel exhaust. Arrhythmogenesis was assessed 24 h later by continuous infusion of aconitine, an arrhythmogenic drug, while heart rate (HR), and electrocardiogram (ECG) were monitored.

RESULTS

Rats exposed once or for 5 d to low, medium, or high B0 developed arrhythmia at significantly lower doses of aconitine than controls, whereas rats exposed to B20 were only consistently sensitive after 5 d of the high concentration. B100 caused mild arrhythmia sensitivity at the low concentration, only after 5 d of exposure at the medium concentration and after either a single or 5 d at the high concentration.

DISCUSSION AND CONCLUSIONS

These data demonstrate that exposure to B20 causes less sensitivity to arrhythmia than B0 and B100. This diminished effect may be due to lower irritant components such as acrolein and nitrogen oxides. Thus, in terms of cardiac health, B20 may be a safer option than both of the pure forms.

In vitro effects of exogenous carbon monoxide on oxidative stress and lipid metabolism in macrophages

Carbon monoxide (CO) is a major constituent of traffic-related air pollution and is also produced endogenously under conditions of oxygen-mediated stress. It has been shown to affect both oxidative stress and inflammation. However, its role in lipid metabolism has been neglected. Using short exposure times, the effect of CO on J774A.1 macrophage atherogenic functions was investigated up to 16 h after exposure. Exposure of macrophages was found to be pro-atherogenic as it significantly increased triglyceride mass, up to 60%, and decreased high-density lipoprotein-mediated cholesterol efflux, up to 27%. In contrast, paraoxonase 2 lactonase activity was increased, up to 65%, and cellular oxidative stress was attenuated by 29%, compared with the control cells. The above results on lipid metabolism may lead to arterial macrophage foam cell formation, the hallmark of early atherogenesis.

Air pollution exposure as a risk factor for cardiovascular disease morbidity and mortality

There is growing evidence of an association between increasing exposure to air pollutants (both short-term and long-term exposures) and elevated risk of mortality and incidence of cardiovascular diseases in certain high-risk populations and throughout different geographic regions. The pathophysiologic mechanisms of air pollutant-induced cardiovascular morbidity and mortality are actively being studied, with autonomic system dysregulation and inflammatory pathway activation believed to be among the key culprits. Policy changes at the local and global levels are addressing the need for more stringent air pollution standards. These initiatives are projected to lower costs and improve health outcomes. In this review, we examine some major studies of the cardiovascular health impacts of air pollution.

Biphasic response of mitochondrial biogenesis to oxidative stress in visceral fat of diet-induced obesity mice

AIMS

Studies in skeletal muscle demonstrate a strong association of mitochondrial dysfunction with insulin resistance (IR). However, there is still a paucity of knowledge regarding the alteration of mitochondria in adipose tissue (AT) in the pathogenesis of IR in obesity. We investigated the mitochondrial biogenesis in visceral fat (VF) and subcutaneous fat (SF) in C57BL/6J mice fed a high-fat high-sucrose diet for 12 months.

RESULTS

Impairment of glucose tolerance and insulin sensitivity developed after 1 month of the diet and was associated with a prompt increase of VF. The VF adipocytes were larger than those in the SF and had increased expressions of HIF-1α and p-NFκB p65. However, the alteration of mitochondrial biogenesis did not occur in the early stage when increased intracellular reactive oxygen species (ROS), mitochondrial oxygen consumption rate, and mitochondrial ROS emerged at the 1st, 2nd and 2nd month, respectively. Until the 6th month, the VF had markedly increased mitochondrial DNA content and expression of PGC-1α, Tfam, ATP5A, and MnSOD. This increase of mitochondrial biogenesis was followed by a generalized decrease at the 12th month and the mitochondrial morphology altered markedly. In the late stage, although mitochondrial ROS decreased, the increased expression of 8-OHdG in VF continued.

INNOVATION AND CONCLUSION

These data suggest that IR and ROS production occur before the biphasic changes of mitochondrial biogenesis in AT, and the VF plays a more crucial role.

Exercise-induced cardioprotection: a role for eNOS uncoupling and NO metabolites

Exercise is an efficient strategy for myocardial protection against ischemia-reperfusion (IR) injury. Although endothelial nitric oxide synthase (eNOS) is phosphorylated and activated during exercise, its role in exercise-induced cardioprotection remains unknown. This study investigated whether modulation of eNOS activation during IR could participate in the exercise-induced cardioprotection against IR injury. Hearts isolated from sedentary or exercised rats (5 weeks training) were perfused with a Langendorff apparatus and IR performed in the presence or absence of NOS inhibitors [N-nitro-L-arginine methyl ester, L-NAME or N5-(1-iminoethyl)-L-ornithine, L-NIO] or tetrahydrobiopterin (BH₄). Exercise training protected hearts against IR injury and this effect was abolished by L-NAME or by L-NIO treatment, indicating that exercise-induced cardioprotection is eNOS dependent. However, a strong reduction of eNOS phosphorylation at Ser1177 (eNOS-PSer1177) and of eNOS coupling during early reperfusion was observed in hearts from exercised rats (which showed higher eNOS-PSer1177 and eNOS dimerization at baseline) in comparison to sedentary rats. Despite eNOS uncoupling, exercised hearts had more S-nitrosylated proteins after early reperfusion and also less nitro-oxidative stress, indexed by lower malondialdehyde content and protein nitrotyrosination compared to sedentary hearts. Moreover, in exercised hearts, stabilization of eNOS dimers by BH4 treatment increased nitro-oxidative stress and then abolished the exercise-induced cardioprotection, indicating that eNOS uncoupling during IR is required for exercise-induced myocardial cardioprotection. Based on these results, we hypothesize that in the hearts of exercised animals, eNOS uncoupling associated with the improved myocardial antioxidant capacity prevents excessive NO synthesis and limits the reaction between NO and O₂·- to form peroxynitrite (ONOO⁻), which is cytotoxic.

Subendocardial increase in reactive oxygen species production affects regional contractile function in ischemic heart failure

AIMS

Heart failure (HF) is characterized by regionalized contractile alterations resulting in loss of the transmural contractile gradient across the left ventricular free wall. We tested whether a regional alteration in mitochondrial oxidative metabolism during HF could affect myofilament function through protein kinase A (PKA) signaling.

RESULTS

Twelve weeks after permanent left coronary artery ligation that induced myocardial infarction (MI), subendocardial (Endo) cardiomyocytes had decreased activity of complex I and IV of the mitochondrial electron transport chain and produced twice more superoxide anions than sham Endo and subepicardial cells. This effect was associated with a reduced antioxidant activity of superoxide dismutase and Catalase only in MI Endo cells. The myofilament contractile properties (Ca(2+) sensitivity and maximal tension), evaluated in skinned cardiomyocytes, were also reduced only in MI Endo myocytes. Conversely, in MI rats treated with the antioxidant N-acetylcysteine (NAC) for 4 weeks, the generation of superoxide anions in Endo cardiomyocytes was normalized and the contractile properties of skinned cardiomyocytes restored. This effect was accompanied by improved in vivo contractility. The beneficial effects of NAC were mediated, at least, in part, through reduction of the PKA activity, which was higher in MI myofilaments, particularly, the PKA-mediated hyperphosphorylation of cardiac Troponin I.

INNOVATION

The Transmural gradient in the mitochondrial content/activity is lost during HF and mediates reactive oxygen species-dependent contractile dysfunction.

CONCLUSIONS

Regionalized alterations in redox signaling affect the contractile machinery of sub-Endo myocytes through a PKA-dependent pathway that contributes to the loss of the transmural contractile gradient and impairs global contractility.

Hypoxia stress test reveals exaggerated cardiovascular effects in hypertensive rats after exposure to the air pollutant acrolein

Exposure to air pollution increases the risk of cardiovascular morbidity and mortality, especially in susceptible populations. Despite increased risk, adverse responses are often delayed and require additional stress tests to reveal latent effects of exposure. The goal of this study was to use an episode of "transient hypoxia" as an extrinsic stressor to uncover latent susceptibility to environmental pollutants in a rodent model of hypertension. We hypothesized that exposure to acrolein, an unsaturated aldehyde and mucosal irritant found in cigarette smoke, diesel exhaust, and power plant emissions, would increase cardiopulmonary sensitivity to hypoxia, particularly in hypertensive rats. Spontaneously hypertensive and Wistar Kyoto (normotensive) rats, implanted with radiotelemeters, were exposed once for 3h to 3 ppm acrolein gas or filtered air in whole-body plethysmograph chambers and challenged with a 10% oxygen atmosphere (10min) 24h later. Acrolein exposure increased heart rate, blood pressure, breathing frequency, and minute volume in hypertensive rats and also increased the heart rate variability parameter LF, suggesting a potential role for increased sympathetic tone. Normotensive rats only had increased blood pressure during acrolein exposure. The hypoxia stress test after acrolein exposure revealed increased diastolic blood pressure only in hypertensive rats and increased minute volume and expiratory time only in normotensive rats. These results suggest that hypertension confers exaggerated sensitivity to air pollution and that the hypoxia stress test is a novel tool to reveal the potential latent effects of air pollution exposure.