[EVALUATION OF DIFFERENT TIMINGS OF EARLY CARDIAC REHABILITATION AFTER MYOCARDIAL INFARCTION AND EXAMINATION OF DRUG THERAPY BASED ON THE SYNTHESIZED PEPTIDE TO BALANCE THE MITOCHONDRIAL DYNAMICS PROCESSES]

INTRODUCTION

Cardiovascular diseases are the main cause of mortality in the world. Their most common expression is ischemic heart disease (IHD) such as myocardial infarction (MI). Physical rehabilitation is a common practice for IHD patients. Yet, there is no definition of when is the most effective time to start physical rehabilitation. However, it is recommended to start it as soon as possible. There is a growing interest in understanding the relationship between IHD and cardiomyocytes mitochondrial dynamics processes. Mitochondrial imbalance after MI accelerates cardiac damage. Peptide-based drugs are an effective and safe treatment option.

AIMS

To examine rehabilitation and peptide intervention post-MI to assess optimal time to start a physical activity and mitochondrial function post-MI.

BACKGROUND

Early training as well as peptide treatment will protect the cardiac muscle post-MI from accelerated damage.

METHODS

Sixty rats will be divided into 6 groups: Six groups will undergo ischemia-reperfusion (I/R) surgery, by a 30 minute occlusion of their left anterior descending artery (LAD) followed by reperfusion. Three groups will start moderate-intensity exercise training for 8 weeks at different time-points post-MI (3, 7, or 21 days). Another group will be injected with synthetic peptide 5' pre-reperfusion. A sedentary group and a sham group will be used as controls. Results will be assessed by a mitochondrial function test, echocardiography, blood inflammatory and biochemical markers, pressure/volume loops, an exercise test and histology.

RESULTS

Improvement of cardiac physiology following exercise training, and mitochondrial treatment will shed light on the preferred timing of cardiac rehabilitation and the mitochondrial damage post-MI.

The Role of Extracellular Signal-Regulated Kinase Pathways in Different Models of Cardiac Hypertrophy in Rats

Cardiac hypertrophy develops following different triggers of pressure or volume overload. In several previous studies, different hypertrophy types were demonstrated following alterations in extracellular signal-regulated kinase (ERK) pathway activation. In the current study, we studied two types of cardiac hypertrophy models in rats: eccentric and concentric hypertrophy. For the eccentric hypertrophy model, iron deficiency anemia caused by a low-iron diet was implemented, while surgical aortic constriction was used to induce aortic stenosis (AS) and concentric cardiac hypertrophy. The hearts were evaluated using echocardiography, histological sections, and scanning electron microscopy. The expression of ERK1/2 was analyzed using Western blot. During the study period, anemic rats developed eccentric hypertrophy characterized by an enlarged left ventricle (LV) cavity cross-sectional area (CSA) (59.9 ± 5.1 mm2 vs. 47 ± 8.1 mm2, p = 0.002), thinner septum (2.1 ± 0.3 mm vs. 2.5 ± 0.2 mm, p < 0.05), and reduced left ventricular ejection fraction (LVEF) (52.6% + 4.7 vs. 60.3% + 2.8, p < 0.05). Rats with AS developed concentric hypertrophy with a thicker septum (2.8 ± 0.6 vs. 2.4 ± 0.1 p < 0.05), increased LV muscle cross-sectional area (79.5 ± 9.33 mm2 vs. 57.9 ± 5.0 mm2, p < 0.001), and increased LVEF (70.3% + 2.8 vs. 60.0% + 2.1, p < 0.05). ERK1/2 expression decreased in the anemic rats and increased in the rats with AS. Nevertheless, the p-ERK and the p-MEK did not change significantly in all the examined models. We concluded that ERK1/2 expression was altered by the type of hypertrophy and the change in LVEF.

Resolving the conflicts around Par2 opposing roles in regeneration by comparing immune-mediated and toxic-induced injuries

BACKGROUND

Different factors may lead to hepatitis. Among which are liver inflammation and poisoning. We chose two hepatitis models, typical for these two underlying causes. Thus, we aimed to characterize the role of protease-activated receptor 2 (Par2) in liver regeneration and inflammation to reconcile Par2 conflicting role in many damage models, which sometimes aggravates the induced damage and sometimes alleviates it.

METHODS

WT and knockout (Par2KO) mice were injected with concanavalin A (ConA) to induce immune-mediated hepatitis or with carbon tetrachloride (CCl₄) to elicit direct hepatic damage. To distinguish the immune component from the liver regenerative response, we conducted bone marrow (BM) replacements of WT and Par2KO mice and repeated the damage models.

RESULTS

ConA injection caused limited damage in Par2KO mice livers, while in the WT mice severe damage followed by leukocyte infiltration was evident. Reciprocal BM replacement of WT and Par2KO showed that WT BM-reconstituted Par2KO mice displayed marked liver damage, while in Par2KO BM-reconstituted WT mice, the tissue was generally protected. In the CCl₄ direct damage model, hepatocytes regenerated in WT mice, whereas Par2KO mice failed to recover. Reciprocal BM replacement did not show significant differences in hepatic regeneration. In Par2KO mice, hepatitis was more apparent, while WT recovered regardless of the BM origin.

CONCLUSIONS

We conclude that Par2 activation in the immune system aggravates hepatitis and that Par2 activation in the damaged tissue promotes liver regeneration. When we incorporate this finding and revisit the literature reports, we reconciled the conflicts surrounding Par2's role in injury, recovery, and inflammation.

The Molecular Effects of SGLT2i Empagliflozin on the Autophagy Pathway in Diabetes Mellitus Type 2 and Its Complications

BACKGROUND

Type 2 diabetes mellitus (T2DM), especially hyperglycemia, is associated with increased glucose cell toxicity and oxidative stress that can lead to irreversible damage in the kidney such as diabetic nephropathy (DN). Autophagy plays a key role in the degradation of damaged intracellular proteins in order to maintain intracellular homeostasis and cell integrity. The disturbance of autophagy is involved in the pathogenesis of diabetic nephropathy. We aim to investigate the molecular effect of sodium-glucose transporter 2 inhibitor (SGLT2i) on the expression of ATG5 and its downstream collaborator LC3-II in diabetic nice model. Material and Methods. We used eight weeks old male mice: twenty C57BL/6 wild type (C57BL/6), twenty BTBR ob/ob (DM), and twenty BTBR ob/ob that were treated with empagliflozin (DM+EMPA), FDA approved SGLT2i. Lysate from murine renal cortex was analyzed by Western blot and immunohistochemistry. ATG5, LC3B, and fibronectin expression were analyzed in murine kidney tissues. All mice were sacrificed 13 weeks after the beginning of the experiment.

RESULTS

Histological and Western blot analyses reveal decrease ATG5, LC3-II, and fibronectin levels at renal specimens taken from DM mice. EMPA treatment reduced T2DM mice body weight and blood glucose and increased urine glucose. Further, it upregulated all of the abovementioned proteins.

CONCLUSIONS

Hyperglycemia reduces LC3-II and ATG5 protein levels which contribute to deficiencies in the autophagy process, with development and progression of DN. SGLT2i significantly reduces progression of DN and onset of end-stage renal disease in T2DM patients, probably through its effect on autophagy.

Comparison of Speckle Tracking Echocardiography During Different Pacing Modalities for Cardiac Resynchronization Therapy Response Prediction

Background: The aim of this study was to evaluate left ventricular mechanical activation pattern by speckle tracking echocardiography (STE) as a predictor of response to cardiac resynchronization therapy (CRT) in patients with heart failure. Methods: Echocardiography was performed during no pacing, right ventricular pacing (RVP), biventricular pacing (BVP) and multipolar pacing (MPP) immediately after CRT implantation in 16 patients at a single centre. Seven patients were diagnosed as responders and 9 patients as non-responders after 6 months of standard CRT pacing. All had adequate short axis views, and 1 CRT responder and 2 CRT non-responders had limited longitudinal views. Results: Longitudinal and circumferential global strain (GS) and global strain rate (GSR) or their change analysis, did not yield any CRT response prediction. However, the longitudinal BVP/RVP GS ratio was significantly higher in the responder group (1.32 ± 0.2%, 2.0 ± 0.4% and 1.9 ± 0.4%), compared with the non-responder group (1.06 ± 0.2%, 1.1 ± 0.4% and 1.2 ± 0.4%) in the apical two-chamber, APLAX and four-chamber views, respectively. Similarly, the longitudinal BVP/RVP GSR at active systolic phase (GSRs) was significantly higher in the responder group (1.9 ± 0.9% and 1.7 ± 0.4%) compared with the non-responder group (1.0 ± 0.4% and 1.1 ± 0.2%) in the apical APLAX and four-chamber views, respectively. Measurements of the strain delay index showed predictive power regarding CRT response in non-paced patients. Conclusion: Post implantation, longitudinal BVP/RVP GS and GSRs ratios of 1.4% and above may be useful as a CRT response prediction tool. Furthermore, our findings support the usefulness of strain delay index prior to CRT implantation in non-paced patients.

Vasodilation and blood pressure-lowering effect mediated by 5,6-EEQ lactone in 5/6 nephrectomy hypertensive rats

Microvascular dysfunction is a key contributor to vascular hypertension, one of the most common chronic diseases in the world. Microvascular dysfunction leads to the loss of nitric oxide-mediated endothelial dilation and the subsequent compensatory function of endothelium-derived hyperpolarizing (EDH) factors in the regulation of vascular tone. Previously, we showed that lactone metabolite derived from arachidonic acid induces endothelial-dependent vasodilation in isolated human microvessels. Based on structural similarities, we hypothesize that additional lactone metabolites formed from eicosapentaenoic fatty acid (EPA) may bear EDH properties.

AIM

To elucidate the vasodilatory and blood pressure (BP)-reducing characteristics of the 5,6-EEQ (5,6-epoxyeicosatetraenoic acids) lactone (EPA-L) in hypertensive 5/6 nephrectomy (5/6Nx) rats.

METHODS

5/6Nx hypertensive rats intravenously administrated with EPA-L for five days. BP, blood and urine chemistry, and kidney function were detected and analyzed. Vascular dilation was detected using a pressure myograph with or without Ca²⁺ - activated K⁺ (K_Ca) endothelial channel inhibitors. KCNN3 and KCNN4 gene expression (mRNA) detected in mesenteric arteries from 5/6Nx and NT rats.

RESULTS

EPA-L administration to 5/6Nx rats significantly (p < 0.05) reduced BP and heart rate without affecting kidney function. 5/6Nx rat mesenteric arterioles exhibited a lower dilation response to acetylcholine (10^-7 mol/l) than normotensive (NT) vessels, while EPA-L administration restored the vessel relaxation response. The EPA-L-driven relaxation of mesenteric arteries was significantly reduced by pretreatment with TRAM-34 and apamin. However, K_Ca channel expression did not significantly differ between 5/6Nx and NT mesenteric arteries.

CONCLUSION

EPA-L reduces BP by improving microvessel dilation involving calcium-dependent potassium endothelial channels.

The impact of empagliflozin on cardiac physiology and fibrosis early after myocardial infarction in non-diabetic rats

BACKGROUND

Myocardial fibrosis is a multistep process, which results in collagen deposition in the injured muscle. Empagliflozin, a sodium-glucose cotransporter 2 inhibitor (SGLT2i), decreases cardiovascular events risk. Little is known on the effects of empagliflozin in non-diabetic patients early post myocardial infarction.

METHODS

Fourteen non-diabetic rats underwent myocardial infarction induction, and treated or not (control)immediately after myocardial infarction by daily empagliflozin (30 mg/kg/day). We evaluated cardiac function at baseline, 2 and 4 weeks after myocardial infarction by echocardiography, and prior to sacrifice by Millar pressure-volume system. We performed histological and biochemical evaluation of fibrosis and humoral factors promoting fibrosis.

RESULTS

Baseline ejection fractions were 69.9 ± 5.3% and 76.4 ± 5.4%, and dropped to final values of 40.1 ± 5.8% and 39.4 ± 5.4% in the control and empagliflozin groups, respectively (P < 0.001 vs. baseline, P > 0.05 between groups). Collagen deposition, measured as collagen volume fraction, was higher in both the scar and the remote cardiac areas of the control group 79.1 ± 6.2% and 4.6 ± 2.5% for control, and 53.8 ± 5.4% and 2.5 ± 1.3% for empagliflozin group, respectively (P < 0.05 for each). Remote cardiac muscle collagen, measured by hydroxyproline, was 4.1 ± 0.4 μg/μl and 3.6 ± 0.2 μg/μl (P = 0.07). TGF-β1 and Smad3 expression decreased by empagliflozin-18.73 ± 16.32%, 9.16 ± 5.69% and 16.32 ± 5.4%, 7.00 ± 5.28% in the control and empagliflozin groups, respectively (P < 0.05).

CONCLUSION/INTERPRETATION

Empagliflozin administered early after myocardial infarction reduce myocardial fibrosis and inhibit the TGF-β1/Smad3 fibrotic pathway, probably prior to exerting any hemodynamic or physiological effect.

Local Delivery of Mometasone Furoate from an Eluting Endotracheal Tube Reduces Airway Morbidity Following Long-Term Animal Intubation

BACKGROUND

upper airway complications are common sequelae of endotracheal tube (ETT) intubation, and systemic corticosteroids are considered a mainstay treatment for this problem. Drug-eluting ETT may present an attractive option for topical steroid delivery while avoiding systemic side effects and improving the therapeutic outcome. The objective of the present study is to evaluate the reduction of tube-related tracheal morbidity via a self-designed steroid-eluting ETT with controlled sustained release properties in an animal model.

METHODS

steroid-eluting ETTs were coated by poly(lactic-co-glycolic acid) -electrospun nanofibers loaded with mometasone furoate (MF) as a model drug. Animals were randomly assigned into three equal groups: non-intubated, blank-ETT, and loaded-ETT. The intubation interval was 1 week. Specimens were analyzed by histology, specific fibrosis staining, and scanning electron microscopy (SEM).

RESULTS

the blank-ETT group exhibited a significant increase in tracheal mucosal thickness compared to the loaded-ETT and control groups. Average tracheal mucosal thickness was 112 ± 34, 242 ± 49, and 113 ± 43 μm in the control, blank-ETT, and loaded-ETT groups, respectively. The blank-ETT group exhibited a significant increase in tracheal fibrosis compared to the loaded-ETT and control groups. Relative fibrosis values were 0.07 ± 0.05, 0.154 ± 0.1, and 0.0984 ± 0.084% for the control, blank-ETT, and loaded-ETT groups, respectively. While SEM imaging showed normal surface structures in the control group, intubated blank-ETT rats showed severe surface structural damage, whereas only mild damage was observed in the loaded-ETT group.

CONCLUSIONS

local sustained release of MF via a self-designed drug-eluting ETT is a potential therapeutic approach which may significantly reduce tube-related upper airway morbidity.

Localized Antileptin Therapy Prevents Aortic Root Dilatation and Preserves Left Ventricular Systolic Function in a Murine Model of Marfan Syndrome

Background Marfan syndrome (MFS) is a genetically transmitted connective tissue disorder characterized by aortic root dilatation, dissection, and rupture. Molecularly, MFS pathological features have been shown to be driven by increased angiotensin II in the aortic wall. Using an angiotensin II-driven aneurysm mouse model, we have recently demonstrated that local inhibition of leptin activity restricts aneurysm formation in the ascending and abdominal aorta. As we observed de novo leptin synthesis in the ascending aortic aneurysm wall of patients with MFS, we hypothesized that local counteracting of leptin activity in MFS may also prevent aortic cardiovascular complications in this context. Methods and Results Fbn1^C1039G/+ mice underwent periaortic application of low-dose leptin antagonist at the aortic root. Treatment abolished medial degeneration and prevented increase in aortic root diameter (P<0.001). High levels of leptin, transforming growth factor β1, Phosphorylated Small mothers against decapentaplegic 2, and angiotensin-converting enzyme 1 observed in saline-treated MFS mice were downregulated in leptin antagonist-treated animals (P<0.01, P<0.05, P<0.001, and P<0.001, respectively). Leptin and angiotensin-converting enzyme 1 expression levels in left ventricular cardiomyocytes were also decreased (P<0.001) and coincided with prevention of left ventricular hypertrophy and aortic and mitral valve leaflet thickening (P<0.01 and P<0.05, respectively) and systolic function preservation. Conclusions Local, periaortic application of leptin antagonist prevented aortic root dilatation and left ventricular valve remodeling, preserving left ventricular systolic function in an MFS mouse model. Our results suggest that local inhibition of leptin may constitute a novel, stand-alone approach to prevent MFS aortic root aneurysms and potentially other similar angiotensin II-driven aortic pathological features.

A novel rat model for tracheal mucosal damage assessment of following long term intubation

OBJECTIVE

Tracheal mucosal damage is a well-known complication of endo-tracheal intubation and animal models are essential for studying the underlying cellular injury cascade. The novel rat model described here is based on retrograde intubation via tracheotomy and suture fixation of the tube. It aims to simulate the common clinical scenario of tube-related airway damage due to long term intubation.

STUDY DESIGN

Prospective randomized control pilot study.

METHODS

Male Sprague-Dawley were randomly assigned into two groups: control (no intubation, n = 10), one week of intubation (n = 13). The animals were then euthanized and the trachea was sent for histological analysis. Epithelial damage, mucosal thickness, mucosal gland hypertrophy and fibrosis were reviewed.

RESULTS

Intubation procedure survival rate was 84.6% (11/13) and 100% in the control (10/10). The damaged ciliary mechanism was a common finding in the intubated group compared to the preserved normal ciliary architecture in almost all control rats. Average tracheal mucosal thickness was 119.0 ± 21.8 μm for the control group and 254.6 ± 22.8 μm for the intubated group, (p < 0.001). The ciliary damage score was 1.00 ± 0.02 in the intubated group, and 0 ± 0.02 in the control group. (p < 0.001). The (objective) average total tracheal mucosal gland area was 19,530 ± 24,606 in the intubated group and 10,031 ± 23,461 in the control group (p < 0,05). Collagen deposition seems higher in the intubated trachea compared to the control.

CONCLUSIONS

We describe a novel rat-based animal model for simulating tracheal mucosal damage following long term intubation. This animal model is easy to carry out, reproducible and involves containable animal mortality rates.

LEVEL OF EVIDENCE

I.

A novel rat model for assessment of laryngotracheal injury following transoral intubation

OBJECTIVE

Laryngotracheal damage is a well-described complication of endotracheal intubation and animal models are essential for studying the underlying cellular injury cascade. This novel rat model is based on transoral intubation and aims to simulate the common clinical scenario of tube-related airway damage.

METHODS

Prospective randomized control pilot study. 28 male Sprague-Dawley were randomly assigned into three groups: control, 3-h' intubation and 6-h' intubation. The animals were then euthanized and their laryngotracheal complexes sent for histological analysis. Epithelial damage, mucosal thickness and mucosal gland hypertrophy were reviewed.

RESULTS

Total of 13 control animals and 15 intubated animals. 10 intubated animals survived the study protocol. Loss of epithelial surface architecture including damage to the microscopic ciliary mechanism was a common feature amongst all intubated animals. Average mucosal thickness of the larynx (including vocal cords and subglottic area) was 143 ± 88 μm for control rats, 315 ± 101 μm for rats intubated 3 h and 574 ± 174 μm for rats intubated 6 h .This was a statistically significant difference. Average mucosal gland hypertrophy in the laryngeal subsite was 0.41 ± 0.5 in control rats, 1.4 ± 0.5 in rats intubated 3 h and 2.0 ± 0.0 for rats intubated 6 h (statistically significant difference). There was a clear difference between three and 6 h of intubation with poorer mucosal injury parameters for longer intubation.

CONCLUSIONS

We describe a novel rat-based animal model for simulating airway mucosal damage following transoral intubation. This animal model is easy to carry out, reproducible and involves containable animal mortality rates.

Local delivery of mometasone furoate from an eluting endotracheal tube

Laryngeal and tracheal morbidity is a common complication of endotracheal tube (ETT)-based airway management, and manifests as local irritation, inflammation, and edema. Systemic corticosteroids are commonly administered to manage these conditions; however, their efficacy is inadequate and limited by potential severe side effects. In the present study, a steroid delivery system for local therapy was developed to generate relatively high local drug concentrations and to improve drug efficacy. ETTs were coated with electrospun poly (lactic-co-glycolic acid) (PLGA) nanofibers loaded with mometasone furoate (MF), creating a microscale thick layer. MF exhibited sustained release from coated ETTs over 14days in vitro. An in vivo efficacy study in rats demonstrated the therapeutic benefit of MF-coated ETTs over bare ETTs, as measured by reduced laryngeal mucosal thickness and submucosal laryngeal edema. The fiber coating remained intact during tube intubation and extubation, demonstrating good adhesion to the tubes even after 24h in aqueous solution at 37°C. These findings demonstrate the potential of drug-loaded ETTs to revolutionize the standard of care for endotracheal intubation.

High-Intensity Training Improves Global and Segmental Strains in Severe Congestive Heart Failure

BACKGROUND

High-intensity training (HIT) is superior to moderate aerobic training (MAT) for improving quality of life in congestive heart failure (CHF) patients. Speckle-tracking echocardiography (STE) has recently been suggested for estimation of left ventricle global and regional function. We evaluated the utility of STE for characterizing differences in cardiac function following MAT or HIT in a CHF rat model.

METHODS AND RESULTS

After baseline physiologic assessment, CHF was induced by means of coronary artery ligation in Sprague-Dawley rats. Repeated measurements confirmed the presence of CHF (ejection fraction 52 ± 10%, global circumferential strain (GCS) 10.5 ± 4, and maximal oxygen uptake (V˙O_2max) 71 ± 11 mL⋅min^-1⋅kg^-1; P < .001 vs baseline for all). Subsequently, rats were divided into training protocols: sedentary (SED), MAT, or HIT. After the training period, rats underwent the same measurements and were killed. Training intensity improved V˙O_2max (73 ± 13 mL⋅min^-1⋅kg^-1 in MAT [P < .01 vs baseline] and 82 ± 6 mL⋅min^-1⋅kg^-1 in HIT [P < .05 vs baseline or SED] and ejection fraction (50 ± 21% in MAT [P < .001 vs baseline] and 66 ± 7% in HIT [P > .05 vs baseline]). In addition, strains of specific segments adjacent to the infarct zone regained basal values (P > .05 vs baseline), whereas global cardiac functional parameters as assessed with the use of 2-dimensional echocardiography did not improve.

CONCLUSIONS

High-intensity exercise training improved function in myocardial segments remote from the scar, which resulted in compensatory cardiac remodeling. This effect is prominent, yet it could be detected only with the use of STE.

The cardioprotective efficacy of TVP1022 against ischemia/reperfusion injury and cardiac remodeling in rats

Following acute myocardial infarction (MI), early and successful reperfusion is the most effective strategy for reducing infarct size and improving the clinical outcome. However, immediate restoration of blood flow to the ischemic zone results in myocardial damage, defined as “reperfusion‐injury”. Whereas we previously reported that TVP1022 (the S‐isomer of rasagiline, FDA‐approved anti‐Parkinson drug) decreased infarct size 24 h post ischemia reperfusion (I/R) in rats, in this study we investigated the chronic cardioprotective efficacy of TVP1022 14 days post‐I/R. To simulate the clinical settings of acute MI followed by reperfusion therapy, we employed a rat model of left anterior descending artery occlusion for 30 min followed by reperfusion and a follow‐up for 14 days. TVP1022 was initially administered postocclusion–prereperfusion, followed by chronic daily administrations. Cardiac performance and remodeling were evaluated using customary and advanced echocardiographic methods, hemodynamic measurements by Millar Mikro‐Tip^® catheter, and histopathological techniques. TVP1022 administration markedly decreased the remodeling process as illustrated by attenuation of left ventricular enlargement and cardiac hypertrophy (both at the whole heart and the cellular level). Furthermore, TVP1022 inhibited cardiac fibrosis and reduced ventricular BNP levels. Functionally, TVP1022 treatment preserved cardiac wall motion. Specifically, the echocardiographic and most of the direct hemodynamic measures were pronouncedly improved by TVP1022. Collectively, these findings indicate that TVP1022 provides prominent cardioprotection against I/R injury and post‐MI remodeling in this I/R model.

Detection of small subendocardial infarction using speckle tracking echocardiography in a rat model

BACKGROUND

It is challenging to detect small nontransmural infarcts visually or automatically. As it is important to detect myocardial infarction (MI) at early stages, we tested the hypothesis that small nontransmural MI can be detected using speckle tracking echocardiography (STE) at the acute stage.

METHODS

Minimal nontransmural infarcts were induced in 18 rats by causing recurrent ischemia-reperfusion of the left anterior descending (LAD) coronary artery, followed by a 30-min ligation and by reperfusion. A week later, the scar size was measured by histological analysis. Each rat underwent three echocardiography measurements: at baseline, 1 day post-MI, and 1 week post-MI. To measure the peak circumferential strain (CS), peak systolic CS, radial strain (RS), and time-to-peak (TTP) of the CS, short-axis view of the apex was analyzed by a STE program. The TTP was normalized by the duration of the heart cycle to create percent change of heart cycle.

RESULTS

Histological analysis after 1 week showed scar size of 4±6% at the anterior wall. At 24 h post-MI, the peak CS, peak systolic CS, and RS were reduced compared to baseline at the anterior wall due to the MI, and at the adjacent segments-the anterior septum and lateral wall, due to stunning (P<.05). However, only the anterior wall, the genuine damaged segment, showed prolonged TTP vs baseline (baseline 36%, 24 h 48%, P<.05).

CONCLUSION

The TTP of the CS can distinguish between regions adjacent to MI (stunned or tethered) and MI, even in small nontransmural infarcts.

Strain Analysis in the Detection of Myocardial Infarction at the Acute and Chronic Stages

BACKGROUND

Myocardial ischemia causes contractile dysfunction in ischemic, stunned, and tethered regions with larger infarcted zones having a negative prognostic impact on patients' outcomes. To distinguish the infarcted myocardium from the other regions, we investigated the diagnostic potential of circumferential strain (CS) and radial strain (RS) during the acute and chronic stages of myocardial infarction.

METHODS

Ten pigs underwent 90-minute occlusion of the left anterior descending artery, followed by reperfusion. Echocardiography was performed at baseline, after 90-minute occlusion, and at 2 hours, 30, and 60 days postreperfusion. CS and RS were measured using speckle tracking echocardiography. Subsequently, the pigs were sacrificed, and histological analysis for infarct size was performed.

RESULTS

After 90-minute occlusion, reduced strains were detected for all segments (infarcted anterior wall - baseline: CS: -17.6 ± 5.7%, RS: 54.4 ± 16.9%; 90 min: CS: -10.3 ± 3.0%, RS: 23.3 ± 7.0%; tethered posterior wall - baseline: CS: -18.4 ± 3.5%, RS: 68.7 ± 21.1%; 90 min: CS: -10.7 ± 6.4%, RS: 34.5 ± 14.7%, P < 0.001). However, postsystolic shortening was detected only in the infarcted segments, and the time-to-peak CS was 25% longer (P < 0.05). At 30 and 60 days postreperfusion, time-to-peak CS could only detect large scars in the anterior and anterior-septum walls (P < 0.05), while peak CS also detected smaller scars in the lateral wall (P < 0.05). RS failed to distinguish between normal, stunned/tethered, and infarcted myocardium.

CONCLUSIONS

During occlusion and 2 hours postreperfusion, time-to-peak CS could distinguish between infarcted and stunned/tethered myocardial segments, while at 30 and 60 days postreperfusion, peak CS was the best detector of infarction.

Layer-specific strain analysis: investigation of regional deformations in a rat model of acute versus chronic myocardial infarction

Myocardial infarction (MI) injury extends from the endocardium toward the epicardium. This phenomenon should be taken into consideration in the detection of MI. To study the extent of damage at different stages of MI, we hypothesized that measurement of layer-specific strain will allow better delineation of the MI extent than total wall thickness strain at acute stages but not at chronic stages, when fibrosis and remodeling have already occurred. After baseline echocardiography scans had been obtained, 24 rats underwent occlusion of the left anterior descending coronary artery for 30 min followed by reperfusion. Thirteen rats were rescanned at 24 h post-MI and eleven rats at 2 wk post-MI. Next, rats were euthanized, and histological analysis for MI size was performed. Echocardiographic scans were postprocessed by a layer-specific speckle tracking program to measure the peak circumferential strain (S(C)(peak)) at the endocardium, midlayer, and epicardium as well as total wall thickness S(C)(peak). Linear regression for MI size versus S(C)(peak) showed that the slope was steeper for the endocardium compared with the other layers (P < 0.001), meaning that the endocardium was more sensitive to MI size than the other layers. Moreover, receiver operating characteristics analysis yielded better sensitivity and specificity in the detection of MI using endocardial S(C)(peak) instead of total wall thickness S(C)(peak) at 24 h post-MI (P < 0.05) but not 2 wk later. In conclusion, at acute stages of MI, before collagen deposition, scar tissue formation, and remodeling have occurred, damage may be nontransmural, and thus the use of endocardial S(C)(peak) is advantageous over total wall thickness S(C)(peak).

Prolonged latency to CNS-O2 toxicity induced by heat acclimation in rats is associated with increased antioxidative defenses and metabolic energy preservation

We have previously shown that heat acclimation provides protection against central nervous system oxygen toxicity (CNS-OT). This was well correlated with increased levels of heat shock protein 72 (HSP72). We now examine other antioxidative defenses against CNS-OT that are correlated with heat acclimation. Two groups of male Sprague-Dawley rats were used. The heat-acclimated group (HA) was exposed for 4 wk to 32°C, and the control group (C) was maintained at 24°C. At the end of the acclimation period, rats were exposed to oxygen at 608 kPa. EEG was recorded continuously until appearance of the first electrical discharge. Brain samples were taken from each group after exposure to pressure. Levels of the antioxidant enzymes CuZnSOD, MnSOD, catalase, and glutathione peroxidase, as well as levels of HSP72, were quantified by Western blot. Comparative proteome analysis of the brains of HA and C rats was carried out using two-dimensional electrophoresis and mass spectrometry to define protein spot alterations. Levels of HSP72 and CuZnSOD were higher in HA rats. Levels of the other antioxidant enzymes were not affected significantly by heat acclimation. Differences in the levels of four protein spots identified as α-synuclein, valosin-containing protein, adenylate kinase 1 (AK1), and the mitochondrial H+-ATP synthase α subunit were found between HA and C rats. We conclude that elevation of HSP72, CuZnSOD, AK1, and the mitochondrial H+-ATP synthase α subunit and possible phosphorylation of α-synuclein--all proteins involved in oxidative stress or energy conservation--might contribute to the prolongation of latency to CNS-OT induced by heat acclimation.

The cardioprotective efficacy of TVP1022 in a rat model of ischaemia/reperfusion

BACKGROUND AND PURPOSE

Because myocardial infarction is a major cause of morbidity and mortality worldwide, protecting the heart from the ischaemia and reperfusion (I/R) damage is the focus of intense research. Based on our in vitro findings showing that TVP1022 (the S-enantiomer of rasagiline, an anti-Parkinsonian drug) possesses cardioprotective effects, in the present study we investigated the hypothesis that TVP1022 can attenuate myocardial damage in an I/R model in rats.

EXPERIMENTAL APPROACH

The model consisted of 30-min occlusion of the left anterior descending artery followed by 4 or 24 h reperfusion. In addition, we investigated the possible mechanisms of cardioprotection in H9c2 cells and neonatal rat ventricular myocytes (NRVM) exposed to oxidative stress induced by H(2) O(2) .

KEY RESULTS

TVP1022 (20 and 40 mg·kg(-1) ) administered 5 min before reperfusion followed by an additional dose 4 h after reperfusion reduced the infarct size and attenuated the decline in ventricular function. TVP1022 also attenuated I/R-induced deterioration in cardiac mitochondrial integrity evaluated by mitochondrial swelling capacity. In vitro, using H9c2 cells and NRVM, TVP1022 attenuated both serum free- and H(2) O(2) -induced damage, preserved mitochondrial membrane potential and Bcl-2 levels, inhibited mitochondrial cytochrome c release and the increase in cleaved caspase 9 and 3 levels, and enhanced the phosphorylation of protein kinase C and glycogen synthase kinase-3β.

CONCLUSIONS AND IMPLICATIONS

TVP1022 provided cardioprotection in a model of myocardial infarction, and therefore should be considered as a novel adjunctive therapy for attenuating myocardial damage resulting from I/R injuries.

Energetic efficiency in trained and sedentary rats after exposure to normobaric and hyperbaric oxygen

INTRODUCTION

Contradictory results have been obtained regarding the beneficial effect of hyperbaric oxygen (HBO) on exercise performance. The purpose of this study was to investigate the effect of different combinations of pressure and time in hyperoxia on the energetic efficiency of trained and sedentary rats.

METHODS

At the end of the training period, rats were exposed to one of three protocols: 1) 100% normobaric oxygen for 24 h; 2) HBO at 2 ATA for 4 h; 3) HBO at 2.5 ATA for 6 h. After the hyperoxic exposures, V(O2max) was evaluated and compared with preexposure values.

RESULTS

The slope of the linear section of the oxygen consumption-velocity curve in the trained rats was significantly steeper after exposure to either 100% normobaric oxygen for 24 h or HBO at 2 ATA for 4 h than before the exposure. The opposite was found for the sedentary rats. After exposure to HBO at 2.5 ATA for 6 h, the slope of the oxygen consumption-velocity curve in the trained rats did not differ from the pre-exposure slope. However, the highest velocity these rats reached was lower than their maximum velocity before this exposure. In the sedentary rats, the slope of the oxygen consumption-velocity curve was found to be steeper after the 2.5 ATA exposure compared with the preexposure slope.

CONCLUSIONS

Our results suggest that exposure to 100% normobaric oxygen for 24 h and HBO at 2 ATA for 4 h induces a reduction in the energetic efficiency of trained rats, but improves energetic efficiency in sedentary rats.

Layer-specific strain analysis by speckle tracking echocardiography reveals differences in left ventricular function between rats and humans

The rat heart is commonly used as an experimental model of the human heart in both health and disease states, assuming that heart function of rats and humans is alike. When studying a rat model, echocardiography is usually performed on sedated rats, whereas standard echocardiography on adult humans does not require any sedation. Since echocardiography results of sedated rats are usually inferred to alert humans, in the present study, we tested the hypothesis that differences in left ventricular (LV) function may be present between rats sedated by a low dose of ketamine-xylazine and alert humans. Echocardiography was applied to 110 healthy sedated rats and 120 healthy alert humans. Strain parameters were calculated from the scans using a layer-specific speckle tracking echocardiography program. The results showed that layer longitudinal strain is equal in rats and humans, whereas segmental strain is heterogeneous ( P < 0.05) in a different way in rats and humans ( P < 0.05). Furthermore, layer circumferential strain is larger in humans ( P < 0.001), and the segmental results showed different segmental heterogeneity in rats and humans ( P < 0.05). Radial strain was found to be homogeneous at the apex and papillary muscle levels in humans and heterogeneous in rats ( P < 0.001). Additionally, whereas LV twist was equal in rats and humans, in rats the rotation was larger at the apex ( P < 0.01) and smaller at the base ( P < 0.001). The torsion-to-shortening ratio parameter, which indicates the transmural distribution of contractile myofibers, was found to be equal in rats and humans. Thus, when evaluating LV function of sedated rats under ketamine-xylazine, it is recommended to measure the global longitudinal strain, LV twist, and torsion-to-shortening ratio, since no scaling is required when converting these parameters and inferring them to humans.

Aural barotrauma in submarine escape: is mastoid pneumatization of significance?

OBJECTIVE

Submarine escape training is carried out by preselected, healthy young men under strictly controlled conditions regarding exposure to pressure and the rate of pressure change. This provides a unique opportunity to investigate the relations between middle ear characteristics and susceptibility to barotrauma while avoiding possible confounding parameters. We examined a possible association between mastoid pneumatization and middle ear barotrauma (MEB) in submarine escape trainees.

STUDY DESIGN

Cross-sectional, parallel-group design.

METHODS

Sixty-six subjects aged 19 to 28 participated in the study. The escape simulation included pressurization to 30 or 60 feet followed by a buoyant ascent to the surface. Subjects were evaluated for MEB after each ascent. A Schuller's mastoid radiograph was taken for the evaluation of mastoid pneumatization.

RESULTS

Fifteen (23%) of the subjects suffered from MEB, and 6 (40%) of them had bilateral involvement. Repeated impedance audiometry after the completion of a successful ascent revealed a significant increase in middle ear compliance. Schuller's radiographs were obtained from 49 (74%) of the subjects. Of these radiographs, 16 (16%) were of ears that had suffered MEB. Mastoid pneumatization for all ears approached a normal Gaussian distribution, with a mean area of 9.58 cm. The mastoid areas and the proportion of ears with mastoid pneumatization at the extremes of the study population did not differ between barotrauma and no-barotrauma ears.

CONCLUSION

In a population with no history of recurrent or chronic otitis media and normal tympanic membrane morphology and compliance, the amount of mastoid pneumatization probably represents merely the normal distribution of variation in organ size and is not related to the ability to equalize pressure in the middle ear.

Optimal oxygen pressure and time for reduced bubble formation in theN2-saturated decompressed prawn

Bubbles that grow during decompression are believed to originate from preexisting gas micronuclei. We showed that pretreatment of prawns with 203 kPa oxygen before nitrogen loading reduced the number of bubbles that evolved on decompression, presumably owing to the alteration or elimination of gas micronuclei (Arieli Y, Arieli R, and Marx A. J Appl Physiol 92: 2596–2599, 2002). The present study examines the optimal pretreatment for this assumed crushing of gas micronuclei. Transparent prawns were subjected to various exposure times (0, 5, 10, 15, and 20 min) at an oxygen pressure of 203 kPa and to 5 min at different oxygen pressures (Po2 values of 101, 151, 203, 405, 608, and 810 kPa), before nitrogen loading at 203 kPa followed by explosive decompression. After the decompression, bubble density and total gas volume were measured with a light microscope equipped with a video camera. Five minutes at a Po2 of 405 kPa yielded maximal reduction of bubble density and total gas volume by 52 and 71%, respectively. It has been reported that 2–3 h of hyperbaric oxygen at bottom pressure was required to protect saturation divers decompressed on oxygen against decompression sickness. If there is a shorter pretreatment that is applicable to humans, this will be of great advantage in diving and escape from submarines.

Effects of nitrogen and helium on CNS oxygen toxicity in the rat

The contribution of inert gases to the risk of central nervous system (CNS) oxygen toxicity is a matter of controversy. Therefore, diving regulations apply strict rules regarding permissible oxygen pressures (Po(2)). We studied the effects of nitrogen and helium (0, 15, 25, 40, 50, and 60%) and different levels of Po(2) (507, 557, 608, and 658 kPa) on the latency to the first electrical discharge (FED) in the EEG in rats, with repeated measurements in each animal. Latency as a function of the nitrogen pressure was not homogeneous for each rat. The prolongation of latency observed in some rats at certain nitrogen pressures, mostly in the range 100 to 500 kPa, was superimposed on the general trend for a reduction in latency as nitrogen pressure increased. This pattern was an individual trait. In contrast with nitrogen, no prolongation of latency to CNS oxygen toxicity was observed with helium, where an increase in helium pressure caused a reduction in latency. This bimodal response and the variation in the response between rats, together with a possible effect of ambient temperature on metabolic rate, may explain the conflicting findings reported in the literature. The difference between the two inert gases may be related to the difference in the narcotic effect of nitrogen. Proof through further research of a correlation between individual sensitivity to nitrogen narcosis and protection by N(2) against CNS oxygen toxicity in rat may lead to a personal O(2) limit in mixed-gas diving based on the diver sensitivity to N(2) narcosis.

PCO(2) threshold for CNS oxygen toxicity in rats in the low range of hyperbaric PO(2)

Central nervous system (CNS) oxygen toxicity, as manifested by the first electrical discharge (FED) in the electroencephalogram, can occur as convulsions and loss of consciousness. CO(2) potentiates this risk by vasodilation and pH reduction. We suggest that CO(2) can produce CNS oxygen toxicity at a PO(2) that does not on its own ultimately cause FED. We searched for the CO(2) threshold that will result in the appearance of FED at a PO(2) between 507 and 253 kPa. Rats were exposed to a PO(2) and an inspired PCO(2) in 1-kPa steps to define the threshold for FED. The results confirmed our assumption that each rat has its own PCO(2) threshold, any PCO(2) above which will cause FED but below which no FED will occur. As PO(2) decreased from 507 to 456, 405, and 355 kPa, the percentage of rats that exhibited FED without the addition of CO(2) (F(0)) dropped from 91 to 62, to 8 and 0%, respectively. The percentage of rats (F) having FED as a function of PCO(2) was sigmoid in shape and displaced toward high PCO(2) with the reduction in PO(2). The following formula is suggested to express risk as a function of PCO(2) and PO(2) [abstract: see text] where P(50) is the PCO(2)for the half response and N is power. A small increase in PCO(2) at a PO(2) that does not cause CNS oxygen toxicity may shift an entire population into the risk zone. Closed-circuit divers who are CO(2)retainers or divers who have elevated inspired CO(2)are at increased risk of CNS oxygen toxicity.

Use of a mass spectrometer for direct respiratory gas sampling from the hyperbaric chamber

BACKGROUND

When conducting respiratory gas measurements during hyperbaric chamber research, it is preferable to carry out gas concentration analysis by mass spectrometry. Gas samples for the mass spectrometer are normally taken from a bypass flow exiting the high pressure chamber to the ambient atmosphere. Under these conditions, mixing in the sampling line smoothes the concentration profile, and much of the advantage of low sampling flow is lost. We propose to use a direct sampling method by mass spectrometer that overcomes these deficiencies.

METHODS

In the present study, the original high resistance capillary of a QP 9000 mass spectrometer was inserted through the wall of a hyperbaric chamber. Series A: Air and pure nitrogen flowed alternately (1 s each) via the sampling tip of the mass spectrometer. Series B: End expired CO2 from 15 immersed, professional divers exercising at 405 kPa was measured in a screening test for CO2 retention for nitrox diving.

RESULTS

There was no difference in the recorded rise time, fall time and plateau reached in the concentration of oxygen at pressures of 101, 202, 303, 405 and 506 kPa. The new sampling method functioned correctly throughout the full-scale experiment, and the recording of end tidal CO2 was more precise than in the conventional method. CONCLUSIONS. Direct sampling of gases from a hyperbaric chamber by the QP 9000 mass spectrometer has many advantages over sampling of the same gases once they are outside the chamber.

Latency to CNS oxygen toxicity in rats as a function of PCO(2) and PO(2)

Central nervous system (CNS) oxygen toxicity can occur as convulsions and loss of consciousness, without any premonitory symptoms. We have made a quantitative study of the effect of inspired carbon dioxide on sensitivity to oxygen toxicity in the rat. Rats were exposed to four oxygen pressures (PO(2); 456, 507, 608 and 709 kPa) and an inspired partial pressure of carbon dioxide (PCO(2)) in the range 0-12 kPa until the appearance of the electroencephalograph first electrical discharge (FED) that precedes the clinical convulsions. Exposures were conducted at a thermoneutral temperature of 27 degrees C. Latency to the FED decreased linearly with the increase in PCO(2) at all four PO(2) values studied. This decrease, which is probably related to the cerebral vasodilatory effect of carbon dioxide, reached a minimal value that remained constant on further elevation of PCO(2). The slopes (absolute value) and intercepts of latency to the FED as a function of carbon dioxide decreased with the increase in PO(2). This log-linear relationship made possible the derivation of equations that describe latency to the FED as a function of both PO(2) and PCO(2) in the PCO(2) - dependent range: Latency (min) = e((5.19-0.0040)(P)(O(2)))-e((2.77-0.0034)(P)(O(2))) x PCO(2) (kPa), and in the PCO(2)-independent range: Latency(min) = e((2.44-0. 0009)(P)(O(2))). A PCO(2) as low as 1 kPa significantly reduced the latency to the FED. It is suggested that in closed-circuit oxygen diving, any accumulation of carbon dioxide should be avoided in order to minimize the risk of CNS oxygen toxicity.

Infrared CO2 analyzer error: an effect of background gas (N2 and O2)

Three infrared CO2 analyzers were tested for the effect of background gases: the Ametek CD-3A (Ametek, Thermox Instruments Division, Pittsburgh, PA), the Dräger Multiwarn P CO2 (Dräger, L ubeck, Germany), and the Servomex 1440 (Servomex, Crowborough, East Sussex, UK). Various CO2 concentrations were prepared with Wösthoff precision pumps (H. Wösthoff, Bochum, Germany). Calibration with a different background gas (O2 or N2) caused a similar but systematic error in the CO2 readings of all three analyzers. When the CO2 analyzers were calibrated with N2 as the background gas, the CO2 reading in an O2-enriched atmosphere was 8% lower than the true value. Conversely, calibration with O2 as the background gas resulted in a 10% overestimation of CO2 levels when N2 was the background gas. This error may be important in a few fields of respiratory physiology.

Effect of the anti-motion-sickness medication cinnarizine on central nervous system oxygen toxicity

Severe seasickness could pose a serious problem in diving, and anti-seasickness medication should therefore be prescribed for the seasickness-susceptible diver. Cinnarizine may be used as a medication if it does not increase the risk of central nervous system (CNS) oxygen toxicity when diving with closed-circuit oxygen or O2-enriched gas mixtures. Twenty-six male, white Sprague-Dawley rats were exposed to high O2 pressures (507 and 608 kPa) before and after cinnarizine ingestion (3.3 mg.kg-1), until the appearance of the first electrical discharge (FED) in the electroencephalogram (EEG) which precedes the clinical convulsions. Each rat was tested on five exposure protocols (control and cinnarizine at 507 kPa O2, control, cinnarizine, and 15 h starvation as a control for cinnarizine at 608 kPa O2) at intervals of at least 2 days or until the EEG connector became detached (a mean of 3.1 exposures per rat). Latency to the FED increased after cinnarizine ingestion in 16 of the 17 pairs of measurements at 507 kPa O2 (by more than 61%, P < 0.002) and in 17 of the 19 pairs of measurements at 608 kPa O2 (by 36%, P < 0.002). There was no significant effect of 15 h starvation. Cinnarizine can be further considered for use in seasickness-susceptible divers as it does not increase the risk of CNS O2 toxicity.