Effects of Nitrate Intake on Myocardial Ischemia-Reperfusion Injury in Diabetic Rats

Effect of long-term inorganic nitrate administration on myocardial ischemia-reperfusion injury in ovariectomized rats

Introduction: Menopause is associated with reduced nitric oxide (NO) bioavailability and lower tolerance against myocardial ischemia-reperfusion (IR) injury. This study investigated whether long-term nitrate administration provides resistance against myocardial IR injury in ovariectomized (OVX) rats. Method: After ovariectomy, female rats were assigned to the OVX and the OVX + nitrate groups (n = 14/group); the latter group consumed nitrate (100 mg/L) for 9 months. At month 9, each group was divided into two subgroups (n = 7/subgroup), of which one subgroup was exposed to myocardial IR (IR+ hearts) and the other was not exposed (IR- hearts). The hearts of rats were isolated, and NO metabolite (NOx), oxidative stress indices, and mRNA expressions of endothelial (eNOS), inducible (iNOS), and neuronal (nNOS) NO synthases, as well as markers of apoptosis, were measured in the IR- and IR+ hearts. In the IR+ hearts, cardiac function indices (CFI) and the infarct size were also measured. Results: Nitrate increased catalase activity (97%) and eNOS expression (2.94-fold) in the IR- hearts. In the IR+ hearts, nitrate reduced left ventricular (LV) end-diastolic pressure (11.6%) and infarct size (26.2%) and increased recovery of LV developed pressure (44.0%) and peak rate of positive (28.9%) and negative (15.4%) changes in LV pressure. In addition, in the IR+ hearts, nitrate increased eNOS and B-cell lymphoma-2 (Bcl-2) as well as decreased iNOS, Bcl-2 associated X protein (Bax), caspase-3, caspase-8, caspase-9, and tumor necrosis factor-α (TNF-α) expression. Nitrate increased total antioxidant capacity (TAC) and catalase (CAT) activity and decreased malondialdehyde (MDA) levels at month nine in serum and IR+ hearts. Conclusion: The favorable effects of nitrate against IR injury were associated with higher eNOS and Bcl-2 expression, CAT activity, TAC, and lower iNOS, Bax, caspase-3, caspase-8, caspase-9 and TNF-α expression, and MDA in the heart tissue. Nitrate preconditioning alleviated IR-induced myocardial injury in OVX rats; this effect was associated with eNOS upregulation before IR and the blunting of OVX-induced eNOS downregulation, iNOS upregulation, apoptosis, and oxidative stress in heart tissue after IR.

Myocardial infarct size is reduced by nitrite and nitrate administration: a systematic review and meta-analysis of animal studies

Ischemic heart disease (IHD) is the leading cause of mortality worldwide and can be complicated by myocardial infarction (MI), leading to cardiac failure. Inorganic nitrite and nitrate, which release nitric oxide (NO), can protect the heart against myocardial injury. This animal systematic review and meta-analysis aims to assess whether the administration of nitrite/nitrate decreases myocardial infarct size. We systematically searched PubMed, Scopus, and Web of Science databases until October 2023; 15 eligible animal studies (35 study arms for in-vivo and 10 for in-vitro studies) published between 1989 and 2023 were included. In-vivo studies were conducted on rats, mice, cats, and dogs, and in-vitro studies on rats and mice with an overall exposure of 0.03 to 12713 mg/kg to nitrate/nitrite administrated before, after, or during ischemia mainly by intravenous single bolus or by oral over 270 days. All in-vitro studies used nitrite/nitrate before ischemia, with the concentration ranging between 0.34 to 201 μM. MI was induced by occlusion of the left anterior diagonal or left circumflex arteries in in-vitro studies and by isoproterenol in in-vivo studies. Infarct size was measured by direct staining of the sliced heart sections. In in-vivo studies, nitrite (overall effect size (ES)=-17.0 %, 95 % confidence interval (CI)=-21.3, -12.8, P<0.001) and nitrate (overall ES= -9.6 %, 95 % CI=-15.7, -3.4, P=0.002) reduced myocardial infarct size. In in-vitro studies, nitrite (overall ES=-15.8 %, 95 % CI=-25.5, -6.2, P=0.001) reduced the infarct size. Sensitivity analysis showed that the overall effect of nitrite on myocardial infarct size was unaffected by doses or health conditions in in-vivo and in-vitro studies. In conclusion, our meta-analysis showed that nitrite/nitrate administration can effectively reduce myocardial infarct size. However, these results should be approached with caution because of the limitations of animal studies and the existing high heterogeneity.

Long-term inorganic nitrate administration protects against myocardial ischemia-reperfusion injury in female rats

BACKGROUND

The favorable effects of nitrate against myocardial ischemia-reperfusion injury (MIRI) have primarily focused on male rats and in short term. Here we determine the impact of long-term nitrate intervention on baseline cardiac function and the resistance to MIRI in female rats.

METHODS

Female Wistar rats were randomly divided into untreated and nitrate-treated (100 mg/L sodium nitrate in drinking water for 9 months) groups (n = 14/group). At intervention end, levels of serum progesterone, nitric oxide metabolites (NOx), heart NOx concentration, and mRNA expressions of NO synthase isoforms (NOS), i.e., endothelial (eNOS), neuronal (nNOS), and inducible (iNOS), were measured. Isolated hearts were exposed to ischemia, and cardiac function indices (CFI) recorded. When the ischemia-reperfusion (IR) period ended, infarct size, NO metabolites, eNOS, nNOS, and iNOS expression were measured.

RESULTS

Nitrate-treated rats had higher serum progesterone (29.8%, P = 0.013), NOx (31.6%, P = 0.035), and higher heart NOx (60.2%, P = 0.067), nitrite (131%, P = 0.018), and eNOS expression (200%, P = 0.005). Nitrate had no significant effects on baseline CFI but it increased recovery of left ventricular developed pressure (LVDP, 19%, P = 0.020), peak rate of positive (+ dp/dt, 16%, P = 0.006) and negative (-dp/dt, 14%, P = 0.014) changes in left ventricular pressure and decreased left ventricular end-diastolic pressure (LVEDP, 17%, P < 0.001) and infarct size (34%, P < 0.001). After the IR, the two groups had significantly different heart nitrite, nitrate, NOx, and eNOS and iNOS mRNA expressions.

CONCLUSIONS

Long-term nitrate intervention increased the resistance to MIRI in female rats; this was associated with increased heart eNOS expression and circulating progesterone before ischemia and blunting ischemia-induced increased iNOS and decreased eNOS after MIRI.

The effect of dapagliflozin on myocardial ischemia-reperfusion injury in diabetic rats

The incidence of ischemic heart disease is 2-3 times higher in diabetic patients. However, the effect of dapagliflozin on ischemia-reperfusion myocardial injury in diabetic rats has not been studied. We examined the effects of dapagliflozin on myocardial IR injury in streptozotocin-nicotinamide-induced diabetic rats. Rats were divided into four groups (n = 7 in each group): control, control-dapagliflozin, diabetes, and diabetes-dapagliflozin. Dapagliflozin (1.5 mg/kg/day) was administered concomitantly in drinking water for 2 months. The hearts were perfused in a Langendorff's apparatus at 2 months and assessed before (baseline) and after myocardial IR for the following parameters: left ventricular developed pressure (LVDP), minimum and maximum rates of pressure change in the left ventricle (±dP/dt), endothelial nitric oxide (NO) synthase (eNOS) and inducible NO synthase (iNOS) mRNA expressions, creatine kinase MB (CK-MB) and troponin imyocardial enzyme extravasation, and lactate dehydrogenase. The recovery of LVDP and ±dP/dt in diabetic rats was lower than that in controls but near normal after dapagliflozin treatment. Diabetic rats had decreased eNOS expression and increased iNOS expression at baseline and after IR, whereas dapagliflozin normalized these parameters after IR. Compared with controls, cardiac NOx levels were initially lower in diabetic patients but higher after IR. Baseline MDA levels were higher in diabetic rats after IR, whereas cardiac NOx levels decreased after treatment with dapagliflozin. Dapagliflozin protects the diabetic rat heart from ischemia-reperfusion myocardial injury by regulating the expression of eNOS and iNOS and inhibiting cardiac lipid peroxidation.

Vitexin Mitigates Myocardial Ischemia/Reperfusion Injury in Rats by Regulating Mitochondrial Dysfunction via Epac1-Rap1 Signaling

Revascularization is an effective therapy for rescuing myocardial tissue after ischemic events. However, the process of reperfusion can lead to more severe cardiomyocyte damage, called myocardial ischemia-reperfusion (I/R) injury (MIRI). We have previously shown that vitexin (VT) (a flavonoid compound derived from natural products) protects against MIRI; however, the exact mechanisms underpinning this effect require further elucidation. This study is aimed at elucidating the protective mechanism of VT in inhibiting ischemic myocardial mitochondrial dysfunction and reducing cardiomyocyte apoptosis by regulating Epac1-Rap1 signaling. Isolated rat hearts were subjected to MIRI in a Langendorff perfusion system, and H9c2 cells were subjected to hypoxia/reoxygenation (H/R) in vitro. Our analyses show that during I/R, Epac1 expression was upregulated, left ventricular dysfunction deteriorated, mitochondrial dynamics were disrupted, and both myocardial cells and tissues exhibited apoptosis. Furthermore, administration of 8-CPT (an Epac agonist) exacerbated cardiomyocyte injury and mitochondrial dysfunction. Interestingly, suppressing the function of Epac1 through VT or ESI-09 (an Epac inhibitor) treatment during I/R reduced the myocardial infarct size, cardiomyocyte apoptosis, and reactive oxygen species production; alleviated mitochondrial dysfunction by increasing mitochondrial membrane potential; elevated MFN2 expression; and inhibited Drp1 expression. To our knowledge, our results reveal, for the first time, the mechanisms underlying the protective effect of VT in the myocardium of rats with MIRI. Moreover, we provide a new target and theoretical basis for VT in the treatment of ischemic heart disease.

The Efficacy and Safety of Nicorandil for Periprocedural Myocardial Injury in Patients Undergoing PCI: A Meta-Analysis

Purpose

To evaluate the efficacy and safety of nicorandil for periprocedural myocardial injury in patients undergoing PCI through meta-analysis of randomized controlled trials.

Methods

We analyzed the clinical data of patients including the incidence of periprocedural myocardial injury (PMI) and major adverse cardiovascular events (MACE) from selected articles. RCTs were retrieved from medical literature databases. RR and 95% confidence intervals (CI) were calculated to compare the endpoints.

Results

In total, 15 articles (16 trial comparisons) were retrieved which contained 2221 patients. In general, 1130 patients (50.9%) were randomized to the experimental group, whereas 1091 patients (49.1%) were randomized to the control group. The result showed that nicorandil significantly reduced the incidence of PMI and MACE after PCI compared to the control group.

Conclusions

Overall, early use of nicorandil in patients undergoing percutaneous coronary intervention (PCI) was associated with a significant reduction of PMI and MACE.

Evaluation of ameliorative effect of sodium nitrate in experimental model of streptozotocin-induced diabetic neuropathy in male rats

OBJECTIVE

Diabetes induces sensory symptoms of neuropathy as positive (hyperalgesia), negative (hypoalgesia), or both.

METHODS

In the present study, fifty male Wistar rats were allocated to five groups: control, control+nitrate, diabetes, diabetes+insulin, and diabetes+nitrate. Thirty days after diabetes confirmation, insulin (2-4 U/day) was injected subcutaneously in diabetes+insulin group and nitrate (100 mg/l) was added into drinking water of the control+nitrate and diabetes+nitrate groups for a period of 2 months. In order to assess the mechanical and thermal algesia, tail immersion, hot plate, and von Frey tests were performed. The serum insulin levels were determined with insulin ELISA Kit. Serum level of NOx was determined by the Griess method.

RESULTS

Both thermal and mechanical nociceptive thresholds showed a significant decrease (p<0.05) which was followed by a significant increase (p<0.01) in the thermal nociceptive threshold in the diabetes group. Chronic nitrate or insulin treatment led to a significant decrease (p<0.01) in blood glucose levels, as well as a significant (p<0.05) increase in the body weight and serum NOx. Moreover, nitrate treatment significantly increased serum insulin levels (p<0.001) compared to the other groups.

CONCLUSION

Chronic nitrate treatment modified the thermal and mechanical sensitivities in diabetic animals.

Dietary Nitrate Protects Against Skin Flap Ischemia-Reperfusion Injury in Rats via Modulation of Antioxidative Action and Reduction of Inflammatory Responses

Dietary nitrate, found abundant in green vegetables, can be absorbed into the blood and be converted to nitric oxide (NO) in the body. Dietary nitrate has been proved to have many positive physiological functions in the body. Here, we evaluated the therapeutic effects of dietary nitrate on skin flap recovery following ischemia reperfusion (IR). Wistar rats were pretreated with nitrate from one week prior to ischemia to the end of reperfusion. It was found that oral administration of nitrate increased serum nitrate and nitrite levels, protected cells from apoptosis, and attenuated flap tissue edema. In the meantime, the oxidative stress marker malondialdehyde was reduced, while the activities of antioxidant enzymes were restored after nitrate treatment. Moreover, the macrophage and neutrophil infiltration in the flap was significantly attenuated by nitrate supplementation, as were the pro-inflammatory cytokines. In sum, we found that oral administration of nitrate can attenuate skin flap IR injury through the regulation of oxidative stress and inflammatory response.

Regulation of carbohydrate metabolism by nitric oxide and hydrogen sulfide: Implications in diabetes

Nitric oxide (NO) and hydrogen sulfide (H₂S) are two gasotransmitters that are produced in the human body and have a key role in many of the physiological activities of the various organ systems. Decreased NO bioavailability and deficiency of H₂S are involved in the pathophysiology of type 2 diabetes and its complications. Restoration of NO levels have favorable metabolic effects in diabetes. The role of H₂S in pathophysiology of diabetes is however controversial; H₂S production is decreased during development of obesity, diabetes, and its complications, suggesting the potential therapeutic effects of H₂S. On the other hand, increased H₂S levels disturb the pancreatic β-cell function and decrease insulin secretion. In addition, there appear to be important interactions between NO and H₂S at the levels of both biosynthesis and signaling pathways, yet clear an insight into this relationship is lacking. H₂S potentiates the effects of NO in the cardiovascular system as well as NO release from its storage pools. Likewise, NO increases the activity and the expression of H₂S-generating enzymes. Inhibition of NO production leads to elimination/attenuation of the cardioprotective effects of H₂S. Regarding the increasing interest in the therapeutic applications of NO or H₂S-releasing molecules in a variety of diseases, particularly in the cardiovascular disorders, much is to be learned about their function in glucose/insulin metabolism, especially in diabetes. The aim of this review is to provide a better understanding of the individual and the interactive roles of NO and H₂S in carbohydrate metabolism.

Urotensin-#receptor antagonist SB-706375 protected isolated rat heart from ischaemia-reperfusion injury by attenuating myocardial necrosis via RhoA/ROCK/RIP3 signalling pathway

SB-706375 is a selective receptor antagonist of human urotensin-II (hU-II), which can block the aorta contraction induced by hU-II in rats. The effect of SB-706375 on myocardial ischaemia-reperfusion (I/R) injury is unclear. The major objective of this study was to investigate whether SB-706375 has a protective effect on myocardial I/R injury in rats and explore its possible mechanisms. Isolated hearts of Adult Sprague-Dawley were perfused in a Langendorff apparatus, and haemodynamic parameters, lactate dehydrogenase (LDH), creatine phosphokinase-MB (CK-MB), cardiac troponin I (cTnI), RhoA, and the protein expressions of U-II receptor (UTR), receptor-interacting protein 3 (RIP3), Rho-associated coiled-coil-containing protein kinase 1 (ROCK1) and Rho-associated coiled-coil-containing protein kinase 2 (ROCK2) were assessed. We found that SB-706375 (1 × 10-6 and 1 × 10-5 mol/L) significantly inhibited the changes of haemodynamic parameters and reduced LDH and CK-MB activities and also cTnI level in the coronary effluents in the heart subjected to myocardial I/R injury. Further experiments studies showed that SB-706375 obviously prevented myocardial I/R increased RhoA activity and UTR, RIP3, ROCK1, and ROCK2 protein expressions. ROCK inhibition abolished the improving effect of SB-706375 on myocardial I/R-induced haemodynamic change in the isolated perfused rat heart. These findings suggested that SB-706375 provides cardio-protection against I/R injury in isolated rats by blocking UTR-RhoA/ROCK-RIP3 pathway.

Mid-dose losartan mitigates diabetes-induced hepatic damage by regulating iNOS, eNOS, VEGF, and NF-κB expressions

Background/aim

Losartan, an antihypertensive drug, is highly preferred in patients with diabetes mellitus (DM) and hypertension because of its retarding effect on diabetic nephropathy. In this study, we investigated the potential therapeutic effect of different doses of losartan on hepatic damage in a streptozotocin (STZ, 50 mg/kg)-induced DM model in rats.

Materials and methods

In this study, five different groups were formed: control, DM, low-dose losartan (5 mg/kg), mid-dose losartan (20 mg/kg), and high-dose losartan (80 mg/kg). Liver tissues of experimental groups were evaluated immunohistochemically for TUNEL, iNOS, eNOS, VEGF, and NF-κB pathways. In addition to immunohistochemical analysis, analyses of SOD and MDA, which are oxidative stress markers, were also performed and the results were evaluated together.

Results

When biochemical and immunohistochemical findings were evaluated together, it was found that the results obtained from the mid-dose losartan group were closer to those of the control than the other groups.

Conclusion

This study indicated that mid-dose losartan administration may have a therapeutic effect by inhibiting apoptosis and regulating iNOS, eNOS, VEGF, and NF-κB protein expressions in DM-induced hepatic damage.

Polydatin Protects Diabetic Heart against Ischemia-Reperfusion Injury via Notch1/Hes1-Mediated Activation of Pten/Akt Signaling

Diabetes exacerbates oxidative/nitrative stress during myocardial ischemia-reperfusion (MI/R) injury. Recent studies highlighted the cardioprotective actions of polydatin. However, its effect on diabetic MI/R injury and the underlying mechanisms remain unknown. This work was undertaken to evaluate the effect of polydatin on diabetic MI/R injury with a focus on Notch1/Hes1 signaling and myocardial oxidative/nitrative stress. Streptozotocin- (STZ-) induced diabetic rats were administered with polydatin (20 mg/kg/d) in the absence or presence of DAPT (a γ-secretase inhibitor) or LY294002 (a PI3K/Akt inhibitor) and then subjected to MI/R injury. Polydatin administration preserved cardiac function and reduced myocardial infarct size. Moreover, polydatin ameliorated myocardial oxidative/nitrative stress damage as evidenced by decreased myocardial superoxide generation, malondialdehyde, gp91^phox expression, iNOS expression, NO metabolite level, and nitrotyrosine content and increased eNOS phosphorylation. However, these effects were blocked by DAPT administration. DAPT also inhibited the stimulatory effect of polydatin on the Notch1/Hes1-Pten/Akt signaling pathway in a diabetic myocardium. Additionally, LY294002 not only abolished polydatin's antiapoptotic effect but also reversed its inhibitory effect on myocardial oxidative/nitrative stress. Polydatin effectively reduced MI/R injury and improved left ventricular functional recovery under diabetic condition by ameliorating oxidative/nitrative stress damage. Importantly, Notch1/Hes1-mediated activation of Pten/Akt signaling played a crucial role in this process.

Role of inducible nitric oxide synthase in myocardial ischemia-reperfusion injury in sleep-deprived rats

INTRODUCTION

REM sleep deprivation (SD) decreases tolerance of the rat heart to ischemia-reperfusion (IR) injury; the underlying mechanisms, however, are unknown. This study aimed at determining whether changes in iNOS, Bax, and Bcl-2 gene expression are involved in this detrimental effect.

METHOD

SD was induced by flowerpot technique for a period of 4 days. This method is simple and able to induce sleep fragmentation which occurs as one of the sleep disorder symptoms in clinical conditions. The hearts of control and SD rats were perfused in Langendorff apparatus and subjected to 30 min ischemia, followed by 90 min reperfusion. The hemodynamic parameters (left ventricular developed pressure (LVDP), and ± dp/dt), NOx (nitrite + nitrate) level, infarct size, and mRNA expression of iNOS, Bax, and Bcl-2 were measured after IR.

RESULTS

SD rats had lower recovery of post-ischemic LVDP (32.8 ± 2.5 vs. 51.5 ± 2.1 mmHg; P < 0.05), + dp/dt (1555 ± 66 vs. 1119.5 ± 87 mmHg/s; P < 0.05) and - dp/dt (1437 ± 65 vs. 888 ± 162 mmHg/s; P < 0.05). SD rats also had higher NOx levels (41.4 ± 3.1 vs. 22.4 ± 3.6 μmol/L; P < 0.05) and infarct size (64.3 ± 2.3 vs. 38.3 ± 1.6%; P < 0.05) after IR, which along with LVDP, ± dp/dt restored to near normal status in the presence of aminoguanidine, a selective iNOS inhibitor. Following IR, expression of iNOS and Bax increased and Bcl-2 decreased (502, 372, and 54%, respectively) in SD rats; whereas in the presence of aminoguanidine, expression of iNOS and Bax significantly decreased and Bcl-2 increased (165, 168, and 19%, respectively).

CONCLUSION

Higher expression of iNOS and subsequent increase in apoptosis in the hearts after IR may contribute to less tolerance to myocardial IR injury in SD rats.

Hypoxia in Obesity and Diabetes: Potential Therapeutic Effects of Hyperoxia and Nitrate

The prevalence of obesity and diabetes is increasing worldwide. Obesity and diabetes are associated with oxidative stress, inflammation, endothelial dysfunction, insulin resistance, and glucose intolerance. Obesity, a chronic hypoxic state that is associated with decreased nitric oxide (NO) bioavailability, is one of the main causes of type 2 diabetes. The hypoxia-inducible factor-1α (HIF-1α) is involved in the regulation of several genes of the metabolic pathways including proinflammatory adipokines, endothelial NO synthase (eNOS), and insulin signaling components. It seems that adipose tissue hypoxia and NO-dependent vascular and cellular dysfunctions are responsible for other consequences linked to obesity-related disorders. Although hyperoxia could reverse hypoxic-related disorders, it increases the production of reactive oxygen species (ROS) and decreases the production of NO. Nitrate can restore NO depletion and has antioxidant properties, and recent data support the beneficial effects of nitrate therapy in obesity and diabetes. Although it seems reasonable to combine hyperoxia and nitrate treatments for managing obesity/diabetes, the combined effects have not been investigated yet. This review discusses some aspects of tissue oxygenation and the potential effects of hyperoxia and nitrate interventions on obesity/diabetes management. It can be proposed that concomitant use of hyperoxia and nitrate is justified for managing obesity and diabetes.