Cardiac dysfunction in rats with dietary-induced insulin resistance associated with pharmacologically-induced dyslipidemia

Metabolic disorders such as insulin resistance (IR) and dyslipidemia (DL) might contribute to the induction of diabetic cardiomyopathy (DCM). However, few relevant animal models are currently available for studying the time-course of DCM and evaluating experimental therapeutics. The present study proposes a rodent model of dietary-induced IR combined or not with DL in order to investigate the impact of chronic IR and DL on in vivo myocardial function. Male rats were fed a western-type diet (65% fat; 15% fructose; WD). DL was induced by combining the western diet with i.p. injections of a nonionic surface-active agent (P-407; 0.2 mg/kg, 3 times/wk; P-407). A chow diet was used as control. At 11 and 14 weeks, cardiac function was assessed by echocardiography. Fasting blood glucose increased in WD group while plasma lipids markedly accumulated in P-407 treated rats. Echocardiographic data showed no significant difference in cardiac geometry under basal conditions. Diastolic dysfunction was evidenced at 14 weeks by a significant decrease in E/A ratio in the P-407 group. Moreover, fractional shortening was significantly depressed under dobutamine stress in WD group at 14 weeks whereas systolic dysfunction appeared as early as 11 weeks and worsened at 14 weeks in P-407 animals. Finally, myocardial TNF-alpha tissue content increased in P-407 group. In conclusion, DL exacerbated cardiac lipotoxicity and functional complications associated with IR. This experimental model of combined IR and DL closely mimics the main clinical manifestations of DCM and might therefore constitute a useful tool for the evaluation of pharmacological treatments.

Analysis of the occupational, consumer and environmental exposure to engineered nanomaterials used in 10 technology sectors

Humans and the environment can come into contact with nanomaterials through a wide range of applications during all stages of the life cycle of nanoproducts. The aim of this commentary is to present an assessment of the potential for exposure and thus identify possible environmental, health and safety (EHS) issues for nanomaterials used in 10 technology sectors. We analysed all life cycle stages with regard to potential for exposure of workers, consumers/patients, and the environment. A wide variety of nanomaterials are used of which many have negligible potential for exposure, while others have medium or even high potential for exposure. Based on the likelihood of exposure, it appears that in general most attention should be paid to the agrifood, chemistry/materials, textiles and health sectors; and less to the information and communication technology (ICT), security and energy sectors. Toxicity and exposure are both important; however, the EHS impact of nanomaterials is always dependent on their particular use.

Inhibition of cardiac leptin expression after infarction reduces subsequent dysfunction

Leptin is known to exert cardiodepressive effects and to induce left ventricular (LV) remodelling. Nevertheless, the autocrine and/or paracrine activities of this adipokine in the context of post-infarct dysfunction and remodelling have not yet been elucidated. Therefore, we have investigated the evolution of myocardial leptin expression following myocardial infarction (MI) and evaluated the consequences of specific cardiac leptin inhibition on subsequent LV dysfunction. Anaesthetized rats were subjected to temporary coronary occlusion. An antisense oligodesoxynucleotide (AS ODN) directed against leptin mRNA was injected intramyocardially along the border of the infarct 5 days after surgery. Cardiac morphometry and function were monitored by echocardiography over 11 weeks following MI. Production of myocardial leptin and pro-inflammatory cytokines interleukin (IL)-1β and IL-6 were assessed by ELISA. Our results show that (1) cardiac leptin level peaks 7 days after reperfused MI; (2) intramyocardial injection of leptin-AS ODN reduces early IL-1β and IL-6 overexpression and markedly protects contractile function. In conclusion, our findings demonstrate that cardiac leptin expression after MI could contribute to the evolution towards heart failure through autocrine and/or paracrine actions. The detrimental effect of leptin could be mediated by pro-inflammatory cytokines such as IL-1β and IL-6. Our data could constitute the basis of new therapeutic approaches aimed to improve post-MI outcome.

Dietary flavonoids increase plasma very long-chain (n-3) fatty acids in rats

Flavonoids probably contribute to the health benefits associated with the consumption of fruit and vegetables. However, the mechanisms by which they exert their effects are not fully elucidated. PUFA of the (n-3) series also have health benefits. Epidemiological and clinical studies have suggested that wine flavonoids may interact with the metabolism of (n-3) PUFA and increase their blood and cell levels. The present studies in rats were designed to assess whether flavonoids actually increase plasma levels of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA), the main very long-chain (n-3) PUFA. Rats were fed a corn-derived anthocyanin (ACN)-rich (ACN-rich) or ACN-free diet with constant intakes of plant and marine (n-3) PUFA for 8 wk (Expt. 1). Plasma fatty acids were measured by GC. The ACN-rich diet contained ~0.24 ± 0.01 mg of ACN/g pellets. There were no significant differences between groups in the main saturated, monounsaturated, and (n-6) fatty acids. In contrast, plasma EPA and DHA were greater in the ACN-rich diet group than in the ACN-free diet group (P < 0.05). We obtained similar results in 2 subsequent experiments in which rats were administered palm oil (80 μL/d) and consumed the ACN-rich or ACN-free diet (Expt. 2) or were supplemented with fish oil (60 mg/d, providing 35 mg DHA and 12 mg EPA) and consumed the ACN-rich or ACN-free diet (Expt. 3). In both experiments, plasma EPA and DHA were significantly greater in the ACN-rich diet group. These studies demonstrate that the consumption of flavonoids increases plasma very long-chain (n-3) PUFA levels. These data confirm previous clinical and epidemiological studies and provide new insights into the health benefits of flavonoids.

Chronic dietary intake of plant-derived anthocyanins protects the rat heart against ischemia-reperfusion injury

Consumption of flavonoid-rich foods and beverages is thought to reduce the risk of cardiovascular diseases. Whereas the biological activities of flavonoids have been characterized in vitro, there are no clear experimental data demonstrating that chronic dietary intake and intestinal absorption of flavonoids actually protects the heart against ischemia-reperfusion injury. We tested whether long-term consumption of specific flavonoids (anthocyanins) included in normal food could render the heart of rats more resistant to myocardial infarction. Maize kernels that differed specifically in their accumulation of anthocyanins were used to prepare rodent food in which anthocyanins were either present or absent. Male Wistar rats were fed the anthocyanin-rich (ACN-rich) or the anthocyanin-free (ACN-free) diet for a period of 8 wk. Anthocyanins were significantly absorbed and detected in the blood and urine of only rats fed the ACN-rich diet. In Langendorff preparations, the hearts of rats fed the ACN-rich diet were more resistant to regional ischemia and reperfusion insult. Moreover, on an in vivo model of coronary occlusion and reperfusion, infarct size was reduced in rats that ate the ACN-rich diet than in those that consumed the ACN-free diet (P < 0.01). Cardioprotection was associated with increased myocardial glutathione levels, suggesting that dietary anthocyanins might modulate cardiac antioxidant defenses. Our findings suggest important potential health benefits of foods rich in anthocyanins and emphasize the need to develop anthocyanin-rich functional foods with protective activities for promoting human health.

Delayed expression of cytokines after reperfused myocardial infarction: possible trigger for cardiac dysfunction and ventricular remodeling

Previous studies have shown that 1 wk after permanent coronary artery ligation in rats, some cellular mechanisms involving TNF-alpha occur and contribute to the development of cardiac dysfunction and subsequent heart failure. The aim of the present study was to determine whether similar phenomena also occur after ischemia-reperfusion and whether cytokines other than TNF-alpha can also be involved. Anesthetized male Wistar rats were subjected to 1 h coronary occlusion followed by reperfusion. Cardiac geometry and function were assessed by echocardiography at days 5, 7, 8, and 10 postligation. Before death, heart function was assessed in vivo under basal conditions, as well as after volume overload. Finally, hearts were frozen for histoenzymologic assessment of infarct size and remodeling. The profile of cardiac cytokines was determined by ELISA and ChemiArray on heart tissue extracts. As expected, ischemia-reperfusion induced a progressive remodeling of the heart, characterized by left ventricular free-wall thinning and cavity dilation. Heart function was also decreased in ischemic rats during the first week after surgery. Interestingly, a transient and marked increase in TNF-alpha, IL-1beta, IL-6, cytokine-induced neutrophil chemoattractant (CINC) 2, CINC3, and macrophage inflammatory protein-3alpha was also observed in the myocardium of myocardial ischemia (MI) animals at day 8, whereas the expression of anti-inflammatory interleukins IL-4 and IL-10 remained unchanged. These results suggest that overexpression of proinflammatory cytokines occurring during the first week after ischemia-reperfusion may play a role in the adaptative process in the myocardium and contribute to early dysfunction and remodeling.

Does nitric oxide contribute to progressive cardiac tissue damage and dysfunction after infarction?

Myocardial infarction induces contractile dysfunction and remodeling that can lead to heart failure. Nitric oxide has been proposed as one of the major actors of this pathophysiologic process. We note that N (G)-nitro-L-arginine methyl ester (L-NAME) administration from day 2 to day 7 after myocardial infarction in rats improves stroke volume, preserves cardiac compliance, and reduces infarct expansion. Our observations lead to the hypothesis that the mechanisms by which cytokines contribute to myocardial remodeling and dysfunction in the days after infarction might involve *NO signalling pathways.

Topoisomerase Inhibition Accelerates Gene Expression after Adeno-associated Virus-mediated Gene Transfer to the Mammalian Heart

Utility of adeno-associated virus 2 (AAV2) vectors for cardiac gene therapy is limited by the prolonged lag phase before maximal gene expression. Topoisomerase inhibition can induce AAV2-mediated gene expression in vivo, but with variable success in different tissues. In this study, we demonstrate that topoisomerase inhibition can accelerate AAV2-mediated gene expression in the mouse heart. We used an AAV2 vector expressing firefly luciferase and monitored expression kinetics using non-invasive bioluminescence imaging. In the group receiving vector alone, cardiac luciferase activity was evident from week 2 onward and increased progressively to reach a steady plateau by 9 weeks postinjection. In the group receiving vector and camptothecine (CPT), luciferase expression was evident from days 2 to 4 onward and increased rapidly to reach a steady plateau by 3-4 weeks postinjection, nearly three times faster than in the absence of CPT (P<0.05). Southern blot analysis of AAV2 genomes in cardiac tissue showed rapid conversion of the AAV2 genome from its single-stranded to double-stranded form in CPT-treated mice. Non-invasive determinations of luciferase expression correlated well with in vitro luciferase assays. Direct injection of the AAV2 vector and long-term luciferase gene expression had no detectable effects on normal cardiac function as assessed by magnetic resonance imaging.

Myocardial infarct-sparing effect of adenosine A2A receptor activation is due to its action on CD4+ T lymphocytes

BACKGROUND

We previously used adenosine A2A receptor (A2AR) knockout (KO) mice and bone marrow transplantation to show that the infarct-sparing effect of A2AR activation at reperfusion is primarily due to effects on bone marrow-derived cells. In this study we show that CD4+ but not CD8+ T lymphocytes contribute to myocardial ischemia/reperfusion injury.

METHOD AND RESULTS

After a 45-minute occlusion of the left anterior descending coronary artery and reperfusion, T cells accumulate in the infarct zone within 2 minutes. Addition of 10 microg/kg of the A2AR agonist ATL146e 5 minutes before reperfusion produces a significant reduction in T-cell accumulation and a significant reduction in infarct size (percentage of risk area) measured at 24 hours. In Rag1 KO mice lacking mature lymphocytes, infarct size is significantly smaller than in C57BL/6 mice. Infarct size in Rag1 KO mice is increased to the level of B6 mice by adoptive transfer of 50 million CD4+ T lymphocytes derived from C57BL/6 or A2AR KO but not interferon-gamma KO mice. ATL146e completely blocked the increase in infarct size in Rag1 KO mice reconstituted with B6 but not A2AR KO CD4+ T cells. The number of neutrophils in the reperfused heart at 24 hours after infarction correlated well with the number of lymphocytes and infarct size.

CONCLUSIONS

These results strongly suggest that the infarct-sparing effect of A2AR activation is primarily due to inhibition of CD4+ T-cell accumulation and activation in the reperfused heart.

Assessment of non-reperfused and reperfused myocardial infarction using diffusible or deposited radiolabelled perfusion imaging agents

PURPOSE

Incomplete microvascular reperfusion is often observed in patients undergoing thrombolytic therapy or angioplasty for acute myocardial infarction and has important prognostic implications. We compared the myocardial uptake of diffusible ((201)Tl) and deposited ((99m)TcN-NOET) perfusion imaging agents in the setting of experimental infarction.

METHODS

Rats were subjected to permanent coronary occlusion (OCC, n=10) or to 45-min occlusion and reperfusion (REP, n=17). Seven days later, the tracers were co-injected and the animals were euthanised 15 min (all ten rats in the OCC group and 12 rats in the REP group) or 120 min (five rats from the REP group, euthanised at this time point to evaluate any redistribution of the tracers: REP-RED group) afterwards. Infarct size determination and (99m)TcN-NOET/(201)Tl ex vivo imaging were performed. Regional flow and tissue oedema were quantified using radioactive microspheres and (99m)Tc-DTPA, respectively.

RESULTS

(99m)TcN-NOET and (201)Tl defect magnitudes were similar in OCC animals (0.11+/-0.01 vs 0.13+/-0.01). In REP animals, (201)Tl defect magnitude (0.25+/-0.02) was significantly lower than the magnitude of (99m)TcN-NOET and flow defects (0.14+/-0.03 and 0.17+/-0.01, respectively; p<0.05), despite the lack of (201)Tl redistribution (REP-RED animals). (99m)Tc-DTPA indicated the presence of oedema in the reperfused area. Blood distribution studies showed that, unlike (99m)TcN-NOET, (201)Tl plasma activity was mostly unbound to plasma proteins.

CONCLUSION

(99m)TcN-NOET and (201)Tl delineated the non-viable area in chronic non-reperfused and reperfused myocardial infarction. The significantly decreased (201)Tl defect in reperfused infarction was likely due to partial diffusion of the tracer from the plasma into the oedema present in the infarcted area. Deposited perfusion tracers might be better suited than diffusible agents for the assessment of regional flow following reperfusion of myocardial infarction.

Stimulation of A2A-adenosine receptors after myocardial infarction suppresses inflammatory activation and attenuates contractile dysfunction in the remote left ventricle

Following myocardial infarction (MI), contractile dysfunction develops not only in the infarct zone but also in noninfarcted regions of the left ventricle remote from the infarct zone. Inflammatory activation secondary to MI stimulates inducible nitric oxide synthase (iNOS) induction with excess production of nitric oxide. We hypothesized that the anti-inflammatory effects of selective A2A-adenosine receptor (A2AAR) stimulation would suppress inflammation and preserve cardiac function in the remote zone early after MI. A total of 53 mice underwent 60 min of coronary occlusion followed by 24 h of reperfusion. The A2AAR agonist (ATL146e, 2.4 μg/kg) was administered intraperitoneally 1, 3, and 6 h postreperfusion. Because of the 1-h delay in treatment after MI, ATL146e had no effect on infarct size, as demonstrated by contrast-enhanced cardiac MRI ( n = 18) performed 24 h post-MI. ATL146e did however preserve global cardiac function at that time by limiting contractile dysfunction in remote regions [left ventricle wall thickening: 51 ± 4% in treated ( n = 9) vs. 29 ± 3% in nontreated groups ( n = 9), P < 0.01]. RT-PCR, immunohistochemistry, and Western blot analysis indicated that iNOS mRNA and protein expression were significantly reduced by ATL146e treatment in both infarcted and noninfarcted zones. Similarly, elevations in plasma nitrate-nitrite after MI were substantially blunted by ATL146e ( P < 0.01). Finally, treatment with ATL146e reduced NF-κB activation in the myocardium by over 50%, not only in the infarct zone but also in noninfarcted regions ( P < 0.05). In conclusion, A2AAR stimulation after MI suppresses inflammatory activation and preserves cardiac function, suggesting the potential utility of A2AAR agonists against acute heart failure in the immediate post-MI period.

Early pre-diabetic state alters adaptation of myocardial glucose metabolism during ischemia in rats

Pre-diabetic subjects with high insulin secretory capacity have double risk of cardiovascular disease compared with subjects who do not develop insulin-resistance. It is well established that the ability of the myocardium to increase its glycolytic ATP production plays a crucial role in determining cell survival under conditions of ischemia. Up to now, whether the pre-diabetic state reduces the tolerance of the heart to ischemia by affecting its ability to increase its energy production through glycolysis remains unknown. The aim of the present study was to assess whether insulin resistance affects the ability of the myocardium to increase glycolysis under ischemic conditions. Male Wistar rats were fed for 8 weeks a fructose-enriched (33%) diet to induce a pre-diabetic state. Hearts were isolated and subjected to ex-vivo low-flow (2%) ischemia for 30 min. The fructose diet increased sarcolemmal GLUT4 localisation in myocardial cells under basal conditions compared with controls. This effect was not accompanied by increased glucose utilisation. Ischemia induced the translocation of GLUT4 to the plasma membrane in controls but did not significantly modify the distribution of these transporters in pre-diabetic hearts. Glycolytic flux under ischemic conditions was significantly lower in fructose-fed rat hearts compared with controls. The reduction of glycolytic flux during ischemia in fructose-fed rat hearts was not due to metabolic inhibition downstream hexokinase II since no cardiac accumulation of glucose-6-phosphate was detected. In conclusion, our results suggest that the pre-diabetic state reduces the tolerance of the myocardium to ischemia by decreasing glycolytic flux adaptation.

Activated platelets contribute importantly to myocardial reperfusion injury

Platelets become activated during myocardial infarction (MI), but the direct contribution of activated platelets to myocardial reperfusion injury in vivo has yet to be reported. We tested the hypothesis that activated platelets contribute importantly to reperfusion injury during MI in mice. After 30 min of ischemia and 60 min of reperfusion, P-selectin knockout mice had a significantly smaller infarct size than that of wild-type mice (P < 0.05). Platelets were detected by P-selectin antibody in the previously ischemic region of wild-type mice as early as 2 min postreperfusion after 45 min, but not 20 min, of ischemia. The appearance of neutrophils in the heart was delayed when compared with platelets. Flow cytometry showed that the number of activated platelets more than doubled after 45 min of ischemia when compared with 20 min of ischemia or sham treatment (P < 0.05). Platelet-rich or platelet-poor plasma was then transfused from either sham-operated or infarcted mice after 45 and 10 min of ischemia-reperfusion to mice undergoing 20 and 60 min of ischemia-reperfusion. Infarct size was increased by threefold and platelet accumulation was remarkably enhanced in mice treated with wild-type, MI-activated platelet-rich plasma but not in mice receiving either platelet-poor plasma from wild types or MI-activated platelet-rich plasma from P-selectin knockout mice. In conclusion, circulating platelets become activated early during reperfusion and their activation depends on the duration of the preceding coronary occlusion and is proportional to the extent of myocardial injury. Activated platelets play an important role in the process of myocardial ischemia-reperfusion injury, and platelet-derived P-selectin is a critical mediator.

Infarct-sparing effect of A2A-adenosine receptor activation is due primarily to its action on lymphocytes

BACKGROUND

A2A-adenosine receptor (A2AAR) activation on reperfusion after ischemia reduces the size of myocardial infarction, but the mechanism of action has not been fully defined.

METHODS AND RESULTS

We created chimeric mice by bone marrow transplantation from A2AAR-knockout or green fluorescent donor mice to irradiated congenic C57BL/6 (B6) recipients. In the GFP chimeras, we were unable to detect green fluorescent-producing cells in the vascular endothelium, indicating that bone marrow-derived cells were not recruited to endothelium at appreciable levels after bone marrow transplantation and/or acute myocardial infarction. Injection of 5 or 10 microg/kg of a potent and selective agonist of A2AAR, ATL146e, had no effect on hemodynamic parameters but reduced infarct size in B6 mice after 45 minutes of left anterior descending artery occlusion followed by 24 hours of reperfusion to 42.5+/-3.0% and 39.3+/-4.7% of risk region, respectively, compared with 61.0+/-2.3% in vehicle-treated B6 mice (P<0.05). Myocardial myeloperoxidase activity in the risk region measured at 4 hours after reperfusion was significantly reduced by ATL146e. The salutary effects of ATL146e were absent in A2AAR-knockout mice or in mice treated with a selective A2AAR antagonist, ZM241385. ATL146e also reduced infarct size and myeloperoxidase in B6/B6 (donor/recipient) chimeras (P<0.05) but not in A2AAR-knockout/B6 chimeras. In immunocompromised Rag-1-KO mice, infarct size was significantly reduced compared with B6 mice but was not further reduced by ATL146e.

CONCLUSIONS

The results indicate that A2AAR activation on bone marrow-derived cells, specifically T or B lymphocytes, is responsible for the infarct-sparing and antiinflammatory effects of ATL146e administered at the time of reperfusion after coronary occlusion.

Selenium status as determinant of connexin-43 dephosphorylation in ex vivo ischemic/reperfused rat myocardium

Recent studies have demonstrated that electrical uncoupling at gap junctions during ischemia is associated with cardiac Connexin-43 (Cx43) dephosphorylation. Whether oxidative stress is involved in this phenomenon still remains unclear. In the present study, we examined the influence of selenium intake on reperfusion-induced Cx43 dephosphorylation. Male Wistar rats were fed a diet containing either 0.05 mg/kg (Low-Se, n = 13) or 1.5 mg/kg (High-Se, n = 11) selenium for 8 weeks. At the end of this diet, hearts were isolated and subjected to 10 min regional ischemia followed by 10 min reperfusion. The level of dephosphorylated Cx43 was determined in tissue samples from ischemic/reperfused and non-ischemic regions of the hearts. At the end of the experiemental diet, the activity of the antioxidant enzyme glutathione peroxidase (GSH-Px) was increased in high-Se hearts compared with low-Se hearts (+ 13%; p < 0.05). After ischemia/reperfusion, in low-Se hearts, Cx43 dephosphorylation appeared significantly increased in the left ventricle compared to the non-ischemic right ventricle (+ 149%; p < 0.05). The high-Se diet significantly reduced Cx43 dephosphorylation in the left ventricle (p < 0.05 vs. low-Se diet). In conclusion, our results suggest that oxidative stress may be involved in Cx43 dephosphorylation during myocardial ischemia/reperfusion, thereby contributing to arrhythmogenesis.

Preischemic selenium status as a major determinant of myocardial infarct size in vivo in rats

Prospective epidemiological studies have shown that the incidence of numerous cardiovascular pathologies is correlated with body selenium status. However, it remains unclear whether selenium status also influences the outcome of myocardial infarction. The aim of the present study was to test whether dietary selenium intake affects myocardial necrosis induced by transient regional ischemia in vivo in rats. For this purpose, male Wistar rats received either a high-selenium (High-Se: 1.5 mg of Se/kg) or a low-selenium (Low-Se: 0.05 mg of Se/kg) diet for 10 weeks. Animals were subjected to 30 min of myocardial ischemia induced by coronary artery ligation followed by 60 min of reperfusion. Pre- and postischemic blood samples were collected for glutathione (GSH and GSSG) determination and for glutathione peroxidase (GSH-Px) assessment. Our results show that high-selenium intake reduces myocardial infarct size (High-Se: 25.16 +/- 1.19% versus Low-Se: 36.51 +/- 4.14%, p < 0.05), preserves postischemic GSH/GSSG ratio (High-Se: 1.37 +/- 0.37 versus Low-Se: 0.47 +/- 0.10, p < 0.05), increases plasma GSH-Px activity, and improves postischemic mean arterial pressure. In conclusion, preischemic body selenium status is a major determinant of the outcome of myocardial ischemia in vivo in rats probably because it influences the cellular redox status.

Simultaneous evaluation of infarct size and cardiac function in intact mice by contrast-enhanced cardiac magnetic resonance imaging reveals contractile dysfunction in noninfarcted regions early after myocardial infarction

BACKGROUND

The objective of this study was to noninvasively determine the effects of reperfused myocardial infarction (MI) on regional and global left-ventricular (LV) function 24 hours after MI in intact mice with contrast-enhanced cardiac MRI and a single, gradient-echo pulse sequence.

METHODS AND RESULTS

Twenty-three mice received baseline MRI scans followed by either 60 minutes of coronary occlusion (MI group, n=15) or thoracotomy without occlusion (sham group, n=8). Gadolinium-DTPA-enhanced magnetic resonance (MR) images were acquired 24 hours after surgery. Hearts were then excised for conventional infarct size determination via 2,3,5-triphenyl tetrazolium chloride (TTC) staining. In addition to infarct size, analysis of the MR images yielded left ventricular (LV) mass, LV end-systolic volume (LVESV), LV end-diastolic volume (LVEDV), LV ejection fraction (LVEF), cardiac output, and percent LV wall thickening (%WTh). Twenty-four hours after surgery, infarct size was 28.1+/-1.8% of LV mass by MRI and 27.5+/-1.7% by TTC (P=NS). Bland-Altman analysis revealed close agreement between the results obtained by the 2 methods. MI had little effect on LVEDV but caused a 98% increase in LVESV (from 11.3 to 22.4 microL, P<0.05), which resulted in a significant reduction in LVEF (from 70% to 37%, P<0.05). Compared with LV regional function at baseline, %WTh 24 hours after MI was significantly depressed, not only in infarcted myocardium but also in regions remote from the infarct zone. In contrast, sham-operated mice showed a small but significant increase in %WTh 24 hours after surgery (P<0.05).

CONCLUSIONS

MRI can accurately assess both infarct size and cardiac function in intact mice early after large, reperfused MI, revealing the existence of contractile dysfunction in noninfarcted regions of the heart.

Effects of increased lipid concentration and hyperemic blood flow on the intrinsic myocardial washout kinetics of (99m)TcN-NOET

Bis(N-ethoxy,N-ethyldithiocarbamato)nitrido technetium (V) ((99m)Tc) ((99m)TcN-NOET) is a myocardial perfusion imaging agent demonstrating significant redistribution and currently in phase III clinical trials. Previous studies have suggested that (99m)TcN-NOET is bound intravascularly. Therefore, we sought to determine whether modifications in the vascular compartment would provide further insights into the mechanisms of (99m)TcN-NOET myocardial washout and redistribution.

METHODS

(99m)TcN-NOET cardiac washout was studied ex vivo in 15 isolated perfused rat hearts after bolus injection (1.5 MBq) in the absence (n = 6) or presence of bovine serum albumin ([BSA] 0.03%) with (n = 5) or without (n = 4) bound lipids. The intrinsic myocardial washout of the tracer was also studied in vivo in 6 dogs after intracoronary bolus injection of the tracer (0.75 MBq) before and after hyperlipidemia induced by intravenous administration of 300 mL of 20% intralipids (n = 3) or hyperemia induced by intravenous infusion of the adenosine A(2A) receptor agonist ATL-146e (0.3 micro g/kg/min; n = 6).

RESULTS

On isolated hearts, there was no significant myocardial washout of (99m)TcN-NOET with Krebs-Henseleit buffer. Addition of BSA without bound lipids resulted in a significant cardiac washout of the tracer (P < 0.001 by repeated measures ANOVA). The presence of lipids bound to BSA further accelerated the washout rate of (99m)TcN-NOET (half-life [t(1/2)], 431.5 +/- 23.2 min vs. 242.9 +/- 63.2 min; P < 0.05). In vivo in dogs, intralipid administration significantly increased the intrinsic washout rate of (99m)TcN-NOET (t(1/2), 108.0 +/- 23.9 min vs. 51.8 +/- 11.8 min; P < 0.05). In addition, vasodilatation with ATL-146e resulted in a 4.9-fold increase in coronary flow (P < 0.05 vs. baseline) and a significantly faster intrinsic (99m)TcN-NOET myocardial washout (t(1/2), 81.1 +/- 12.1 min vs. 40.7 +/- 7.3 min; P < 0.05).

CONCLUSION

The myocardial washout kinetics of (99m)TcN-NOET are affected by a variety of intravascular factors, supporting the hypothesis that the tracer is most likely localized on the vascular endothelium. The potential impact of variations in circulating lipid levels among patients on clinical imaging with (99m)TcN-NOET requires further investigation.

Dietary selenium intake affects cardiac susceptibility to ischaemia/reperfusion in male senescent rats

BACKGROUND

cardiovascular ageing is associated with an increase in cardiac susceptibility to ischaemia and reperfusion. This has been suggested to be partly related to an increased sensitivity of the myocardium to the reactive oxygen species that are produced during post-ischaemic reperfusion. The aim of the present study was therefore to determine whether increasing cardiac glutathione peroxidase activity by a selenium-enriched diet could afford some protection against ischaemia and reperfusion to senescent rat hearts.

METHODS

22 months old male Wistar rats received either a high-selenium (1.5 mg Se/kg diet) or a low-selenium (0.05 mg Se/kg diet) diet for 10 weeks. At the end of the diet, hearts were submitted to ischaemia and reperfusion ex vivo and either fixed for semi-quantitative analysis of ultrastructural damage by electron microscopy or used for glutathione peroxidase activity assessment.

RESULTS

high-selenium supply increased cardiac total, mitochondrial and cytosolic glutathione peroxidase activities. Moreover, this diet induced a significant improvement of cardiac post-ischaemic functional recovery. Finally, this preservation of cardiac function was associated with a significant limitation of ultrastructural alterations of sarcomeres and mitochondria.

CONCLUSION

our high-selenium diet considerably limits the sensitivity of senescent rat hearts to ischaemia and reperfusion. This finding suggests that peroxides might play a key role in the increase in cardiac sensitivity to ischaemia and reperfusion during ageing. Together with the observation that selenium status decreases with age in humans, our results indicate that reinforcing selenium supply could improve the prognosis of cardiovascular diseases in old patients.

Involvement of reactive oxygen species in cardiac preconditioning in rats

To date, the involvement of reactive oxygen species in ischemic preconditioning in vivo in rats is not clearly demonstrated. The aim of the present study was to determine whether N-(2-mercaptopropionyl)glycine (MPG), a cell-diffusible hydroxyl radical scavenger, and carnosine, a potent singlet oxygen quencher, could block protection afforded by a single cycle of ischemic preconditioning in vivo in the rat. An ESR study was first performed to validate in vitro the specific antioxidant properties of carnosine and MPG. In a second set of experiments, open-chest rats were subjected to 30 min of left coronary occlusion followed by 60 min of reperfusion. Preconditioning was elicited by 5 min of ischemia and 5 min of reperfusion. Neither MPG (1-h infusion, 20 mg/kg) nor carnosine injection (bolus, 25 micro mol/rat) affected infarct size. The infarct size-limiting effect of preconditioning was completely blunted by MPG, whereas carnosine did not alter the cardioprotection. It is concluded that free radicals and especially hydroxyl radicals could be involved in the adaptive mechanisms induced by a single cycle of preconditioning in vivo in rats.

Cardiac toxicity of singlet oxygen: implication in reperfusion injury

Oxygen-derived free radicals (O2.-, H2O2, and .OH) that are produced during postischemic reperfusion are currently suspected to be involved in the pathogenesis of tissue injury. Another reactive oxygen species, the electronically excited molecular oxygen (1O2), is of increasing interest in the area of experimental research in cardiology. In this review are discussed the main potential sources of singlet oxygen in the organism, particularly in the myocardium, the various cardiovascular cytotoxic effects induced by this reactive oxygen intermediate, and the growing evidence of its involvement in ischemia/reperfusion injury.

Role of reactive oxygen species in cardiac preconditioning: study with photoactivated Rose Bengal in isolated rat hearts

Oxygen radical scavengers have been shown to prevent the development of ischemic preconditioning, suggesting that reactive oxygen species (ROS) might be involved in this phenomenon. In the present study, we have investigated whether direct exposure to ROS produced by photoactivated Rose Bengal (RB) could mimic the protective effects of ischemic preconditioning.

METHODS

In vitro generation of ROS from photoactivated RB in a physiological buffer was first characterised by ESR spectroscopy in the presence of 2,2,6,6-tetramethyl-1-piperidone (oxoTEMP) or 5,5-dimethyl-1-pyrroline-N-oxide (DMPO). In a second part of the study, isolated rat hearts were exposed for 2.5 min to photoactivated RB. After 5 min washout, hearts underwent 30 min no-flow normothermic ischemia followed by 30 min of reperfusion.

RESULTS AND CONCLUSIONS

The production of singlet oxygen (1O2) by photoactivated RB in the perfusion medium was evidenced by the ESR detection of the nitroxyl radical oxoTEMPO. Histidine completely inhibited oxoTEMPO formation. In addition, the use of DMPO has indicated that (i) superoxide anions (O2*-) are produced directly and (ii) hydroxyl radicals (HO*) are formed indirectly from the successive O2*- dismutation and the Fenton reaction. In the perfusion experiments, myocardial post-ischemic recovery was dramatically impaired in hearts previously exposed to the ROS produced by RB photoactivation (1O2, O2*-, H2O2 and HO*) as well as when 1O2 was removed by histidine (50 mM) addition. However, functional recovery was significantly improved when hearts were exposed to photoactivated RB in presence of superoxide dismutase (10(5) IU/L) and catalase (10(6) IU/L). Further studies are now required to determine whether the cardioprotective effects of Rose Bengal in presence of O2*- and H2O2 scavengers are due to singlet oxygen or to other species produced by Rose Bengal degradation.

Effects of selenium deficiency on the response of cardiac tissue to ischemia and reperfusion

Over a 10-week period, female Wistar rats received a diet containing a low level of selenium, cofactor of the antioxidant enzyme glutathione peroxidase (GPx) in order to examine the influence of deficiency of this trace element (i) on tissue antioxidant enzyme defence systems, and (ii) on the susceptibility of the myocardium to ischemia-reperfusion injury. At the end of the dietary treatment, hearts were perfused at constant flow (11 ml/min) before being subjected to 15 min of global normothermic ischemia, followed by 30 min of reperfusion. The effects of selenium deficiency were estimated by studying functional recovery of various cardiac parameters (left ventricular developed pressure LVDevP, heart rate HR, and the product HR x LVDevP), as well as ultrastructural tissue characteristics. Furthermore, superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities were measured at the end of the reperfusion period. Results suggest that: (a) the activity of GPx is decreased by selenium deficiency while SOD activity remains unchanged, (b) the recovery of cardiac function and myocardial ventricular ultrastructure during reperfusion are altered in the selenium-deficient group compared to controls. These results illustrate the crucial role that selenium, the co-factor of one of the major antioxidant enzymes of the myocardium, plays in determining the vulnerability of the heart to ischemia and reperfusion.

Effects of fasting and exogenous glucose delivery on cardiac tolerance to low-flow ischemia in adult and senescent rats

Metabolic disorders due to changes in cytosolic glucose utilisation are suspected to be involved in the increased sensitivity of the aged myocardium to ischemia. This study presents the first direct measurement of glucose utilisation in hearts from senescent rats during low-flow ischemia under different conditions of substrate delivery and glycogen stores. Isolated hearts from young adult (4-months-old) and senescent (24-months-old) rats were subjected to 30 min coronary flow restriction (residual flow rate=2% of control flows). Experiments were performed using glucose-free or glucose-enriched (11 mmol/L) perfusion media. The effects of increased glycogen stores were assessed after 24-h fasting in both age groups. Ischemic contracture was measured via a left-ventricular balloon. Ageing increased ischemic contracture under both conditions of substrate delivery in fed rat hearts. The increase in ischemic tolerance induced by fasting in senescent rat hearts was less than that seen in young rat hearts. Moreover, fasting decreased glucose utilisation in hearts from young rats, an effect which was not found in hearts from old rats. Furthermore, myocardial glycogen utilisation was increased in all groups of aged rats compared with that of young adults, particularly under fasting conditions. It is concluded that fasting is less detrimental to the aged myocardium during low-flow ischemia than to the young myocardium because it does not further reduce exogenous glucose utilisation, and it stimulates glycogen consumption. Moreover, a reduction in exogenous glucose utilisation, which is only partly compensated for by increased glycogenolytic flux could be, at least in part, responsible for the increased ischemic contracture in hearts from old fed rats. Finally, our glucose-free experiments suggest that residual oxidative phosphorylation during low-flow ischemia might be less relevant in hearts from senescent rats than in those from young adults.

Aging exacerbates hydrogen peroxide-induced alteration of vascular reactivity in rats

Reactive oxygen species (ROS) such as superoxide anion (O2-*) and hydrogen peroxide (H2O2) can be produced by vascular endothelium and smooth muscle cells under diverse physiological and pathophysiological situations. These species are known to exert various deleterious effects by which they might induce changes in vascular reactivity. The aim of the present study was to evaluate the evolution of vascular susceptibility to H2O2 during aging in rats. Catalase activity was assessed in aortas from young adult (4 months) and aged (24 months) Wistar rats. In parallel experiments, isolated rings from both age groups were exposed to increasing doses of H2O2 (0, 0.1, 1, 5, or 10 mM) for 20 min and the residual vascular response to phenylephrine (PE = 10(-6) M) and acetylcholine (ACh = 10(-6) M) was evaluated. Our results indicate that aging increases aortic catalase activity (4 months: 0.20 +/- 0.02 IU/mg prot versus 24 months: 0.46 +/- 0.06 IU/mg prot, p < 0.001) while it exacerbates vascular sensitivity to H2O2. These results suggest that the observed increased H2O2-induced alterations of vascular reactivity during aging in rats might be due to increased sensitivity of the vasculature to ROS rather than to a decrease in the defense systems against these species.