Diabetes, perioperative ischaemia and volatile anaesthetics: consequences of derangements in myocardial substrate metabolism

Association between non-alcoholic fatty liver disease and myocardial glucose uptake measured by 18F-fluorodeoxyglucose positron emission tomography

BACKGROUND

Non-alcoholic fatty liver disease (NAFLD) has emerged as an independent risk factor for cardiovascular diseases. However, there were few studies evaluating the condition of myocardial glucose metabolism in patients with NAFLD. Therefore, the aim of this study was to investigate the association between NAFLD and myocardial glucose uptake assessed by using 18F-fluorodeoxyglucose (18F-FDG) positron emission tomography (PET) and whether or not alteration of myocardial glucose uptake could be an indicator linking to cardiac dysfunction in NAFLD individuals.

METHODS AND RESULTS

A total of 743 asymptomatic subjects (201 with NAFLD, 542 without NAFLD) were retrospectively studied. The ratio of maximum myocardium FDG uptake to the mean standardized uptake value of liver (SUVratio) was calculated to estimate myocardial glucose uptake by using 18F-FDG PET. The diagnosis of fatty liver and fatty liver grading was confirmed by unenhanced CT according to diagnostic criterion of previous studies. The myocardial geometric and functional data were obtained by echocardiogram. Myocardial glucose uptake was significantly lower in individuals with NAFLD compared with those without fatty liver (P < .001). When analysis of association trend was performed, SUVratio quartiles showed correlated inversely and strongly with liver steatosis (P < .001). NAFLD patients with lower myocardial glucose uptake were more likely to have higher proportion of increased LV filling pressure (P < .05). A significant relationship between myocardial SUVratio and E/e' ratio was presented in the trend analysis (P < .05). Moreover, multivariate regression analysis showed that myocardial glucose uptake was independently associated with NAFLD after adjusting for clinical important factors (all P < .001).

CONCLUSIONS

The presence of NAFLD in otherwise healthy subjects is closely associated with decreased myocardial glucose uptake assessing by 18F-FDG PET imaging. Furthermore, the NAFLD individuals with lower myocardial glucose uptake are more likely to have high risk of having impaired diastolic heart function.

Early Imaging Biomarker of Myocardial Glucose Adaptations in High-Fat-Diet-Induced Insulin Resistance Model by Using 18F-FDG PET and [U-13C]glucose Nuclear Magnetic Resonance Tracer

Background

High-fat diet (HFD) induces systemic insulin resistance leading to myocardial dysfunction. We aim to characterize the early adaptations of myocardial glucose utility to HFD-induced insulin resistance.

Methods

Male Sprague–Dawley rats were assigned into two groups, fed a regular chow diet or HFD ad libitum for 10 weeks. We used in vivo imaging of cardiac magnetic resonance (CMR), ¹⁸F-FDG PET, and ex vivo nuclear magnetic resonance (NMR) metabolomic analysis for the carbon-13-labeled glucose ([U-¹³C]Glc) perfused myocardium.

Results

As compared with controls, HFD rats had a higher ejection fraction and a smaller left ventricular end-systolic volume (P < 0.05), with SUV_max of myocardium on ¹⁸F-FDG PET significantly increased in 4 weeks (P < 0.005). The [U-¹³C]Glc probed the increased glucose uptake being metabolized into pyruvate and acetyl-CoA, undergoing oxidative phosphorylation via the tricarboxylic acid (TCA) cycle, and then synthesized into glutamic acid and glutamine, associated with overexpressed LC3B (P < 0.05).

Conclusions

HFD-induced IR associated with increased glucose utility undergoing oxidative phosphorylation via the TCA cycle in the myocardium is supported by overexpression of glucose transporter, acetyl-CoA synthase. Noninvasive imaging biomarker has potentials in detecting the metabolic perturbations prior to the decline of the left ventricular function.

Immune Modulation by Volatile Anesthetics

Volatile general anesthetics continue to be an important part of clinical anesthesia worldwide. The impact of volatile anesthetics on the immune system has been investigated at both mechanistic and clinical levels, but previous studies have returned conflicting findings due to varied protocols, experimental environments, and subject species. While many of these studies have focused on the immunosuppressive effects of volatile anesthetics, compelling evidence also exists for immunoactivation. Depending on the clinical conditions, immunosuppression and activation due to volatile anesthetics can be either detrimental or beneficial. This review provides a balanced perspective on the anesthetic modulation of innate and adaptive immune responses as well as indirect effectors of immunity. Potential mechanisms of immunomodulation by volatile anesthetics are also discussed. A clearer understanding of these issues will pave the way for clinical guidelines that better account for the impact of volatile anesthetics on the immune system, with the ultimate goal of improving perioperative management.

Reducing Caloric Intake Prevents Ischemic Injury and Myocardial Dysfunction and Affects Anesthetic Cardioprotection in Type 2 Diabetic Rats

Background. Type 2 diabetes mellitus (T2DM) increases the risk of myocardial ischemia, followed by increased perioperative risk of cardiovascular morbidity. We investigated whether reducing caloric intake reduces ischemic injury and myocardial dysfunction and affects the protective effects of the volatile anesthetic sevoflurane in diet-induced T2DM rats. Methods. Rats received a western (WD) or control diet (CD). Caloric intake was reduced by reversing WD-fed rats to CD. Myocardial function was determined with echocardiography. After 8 weeks of diet feeding, myocardial infarction was induced and the effect of sevoflurane was studied on myocardial function and ischemia/reperfusion injury. Results. WD-feeding resulted in a mild T2DM phenotype and myocardial dysfunction. Sevoflurane further impaired systolic function in WD-fed rats. Unexpectedly, WD-feeding reduced infarct size compared to CD-feeding. Sevoflurane reduced infarct size in CD-fed rats; however it enlarged infarct size in WD-fed rats. Caloric reduction restored myocardial dysfunction and the protective effect of sevoflurane against ischemia compared to WD-fed rats, whereas the protective effects of WD-feeding persisted. Conclusion. Caloric reduction restored the T2DM phenotype and myocardial function, while the cardioprotective properties of WD-feeding or sevoflurane persisted. Our data suggest that reducing caloric intake in T2DM might be a possible intervention to reduce perioperative risk of cardiovascular morbidity.

Peri-operative cardiac protection for non-cardiac surgery

Cardiovascular complications are an important cause of morbidity and mortality after non-cardiac surgery. Pre-operative identification of high-risk individuals and appropriate peri-operative management can reduce cardiovascular risk. It is important to continue chronic beta-blocker and statin therapy. Statins are relatively safe and peri-operative initiation may be beneficial in high-risk patients and those scheduled for vascular surgery. The pre-operative introduction of beta-blockers reduces myocardial injury but increases rates of stroke and mortality, possibly due to hypotension. They should only be considered in high-risk patients and the dose should be titrated to heart rate. Alpha-2 agonists may also contribute to hypotension. Aspirin continuation can increase the risk of major bleeding and offset the benefit of reduced myocardial risk. Contrary to the initial ENIGMA study, nitrous oxide does not seem to increase the risk of myocardial injury. Volatile anaesthetic agents and opioids have been shown to be cardioprotective in animal laboratory studies but these effects have, so far, not been conclusively reproduced clinically.

Long-term insulin treatment restores cardioprotection induced by sufentanil postconditioning in diabetic rat heart

Sufentanil, a commonly used opioid analgesic, could mimic ischemia postconditioning to attenuate ischemia reperfusion injury, but this effect might be hindered in diabetic animals by inhibition of glycogen synthase kinase-3β phosphorylation. Also, diabetes can abrogate the cardioprotection of sevoflurane (an inhaled anesthetic) against ischemia reperfusion injury, and short-term insulin treatment does not restore protection by sevoflurane postconditioning. We hypothesized that long-term insulin treatment might restore the cardioprotective effect of sufentanil postconditioning in diabetic rats via phosphorylation of glycogen synthase kinase-3β. Streptozotocin (55 mg/kg)-induced diabetic rats received insulin (Novolin N, 6-8 u/d) for two days or two weeks, then were exposed to 30-min ischemia and 120-min reperfusion. Sufentanil postconditioning was performed 5 min before the onset of reperfusion. Controls included non-diabetic rats, sham surgery for ischemia/reperfusion, and sufentanil vehicle. Infarct size, cardiac troponin I, and phosphorylated glycogen synthase kinase-3β were examined. Sufentanil postconditioning reduced infarct size by 46% in non-diabetic rats (P < 0.001), but diabetes prevented this protective effect. Two-day insulin treatment was not effective, but two-week treatment reduced infarct size by 45% (P < 0.001), reduced cardiac troponin I by 33% (P < 0.001), and increased phosphorylated glycogen synthase kinase-3β levels (P < 0.001) in the diabetic sufentanil postconditioning group. In conclusion, sufentanil-induced cardioprotection was restored by long-term insulin treatment. The underlying mechanism may be increased phosphorylation of glycogen synthase kinase-3β.

Visceral adiposity is associated with altered myocardial glucose uptake measured by (18)FDG-PET in 346 subjects with normal glucose tolerance, prediabetes, and type 2 diabetes

Background

The heart requires constant sources of energy mostly from free fatty acids (FFA) and glucose. The alteration in myocardial substrate metabolism occurs in the heart of diabetic patients, but its specific association with other metabolic variables remains unclear. We aimed to evaluate glucose uptake in hearts of subjects with normal glucose tolerance (NGT), prediabetes, and type 2 diabetes mellitus (T2DM) using [¹⁸F]-fluorodeoxyglucose-positron emission tomography (¹⁸FDG-PET) in association with visceral and subcutaneous adiposity, and metabolic laboratory parameters.

Methods

A total of 346 individuals (NGT, n = 76; prediabetes, n = 208; T2DM, n = 62) in a health promotion center of a tertiary hospital were enrolled. The fasting myocardial glucose uptake, and visceral and subcutaneous fat areas were evaluated using ¹⁸FDG-PET and abdominal computed tomography, respectively.

Results

Myocardial glucose uptake was significantly decreased in subjects with T2DM compared to the NGT or prediabetes groups (p for trend = 0.001). Multivariate linear regression analyses revealed that visceral fat area (β = −0.22, p = 0.018), fasting FFA (β = −0.39, p < 0.001), and uric acid levels (β = −0.21, p = 0.007) were independent determinants of myocardial glucose uptake. Multiple logistic analyses demonstrated that decreased myocardial glucose uptake (OR 2.32; 95 % CI 1.02–5.29, p = 0.045) and visceral fat area (OR 1.02, 95 % CI 1.01–1.03, p = 0.018) were associated with T2DM.

Conclusions

Our findings indicate visceral adiposity is strongly associated with the alteration of myocardial glucose uptake evaluated by ¹⁸FDG-PET, and its association further relates to T2DM.

Roles of obese-insulin resistance and anti-diabetic drugs on the heart with ischemia-reperfusion injury

The incidence of obesity with insulin resistance is increasing worldwide. This condition is also known as a risk factor of coronary artery disease and associated with increased arrhythmias, impaired left ventricular function, and increased infarct size during cardiac ischemia-reperfusion (I/R) injury. The proposed mechanisms are due to impaired glucose utilization and pro-survival signaling molecules, and increased inflammatory cytokines, which have been demonstrated in the I/R hearts in various models of obese-insulin resistance. However, the cardiac effects of diets in the I/R heart are still unsettled since several studies reported that high-caloric diet consumption might protect the heart from I/R injury. Although several therapeutic strategies such as anti-diabetic drugs, natural compounds as well as treadmill exercise have been proposed to exert cardioprotection in the I/R heart in obese-insulin resistant animals, some interventions including ischemic post-conditioning failed to protect the heart from I/R injury. In this comprehensive review, reports from both genetic deletion and dietary-induced obese-insulin resistant animal models regarding the effects of obese-insulin resistance on metabolic parameters, cardiac function, infarct size, and molecular mechanisms under I/R injury are summarized. Moreover, the effects of anti-diabetic drugs and other pharmacological interventions on these parameters in an obese-insulin resistant model under I/R injury are also comprehensively summarized and discussed.

Anaesthetics as cardioprotectants: translatability and mechanism

The pharmacological conditioning of the heart with anaesthetics, such as volatile anaesthetics or opioids, is a phenomenon whereby a transient exposure to an anaesthetic agent protects the heart from the harmful consequences of myocardial ischaemia and reperfusion injury. The cellular and molecular mechanisms of anaesthetic conditioning appear largely to mimic those of ischaemic pre- and post-conditioning. Progress has been made on the understanding of the underlying mechanisms although the order of events and the specific targets of anaesthetics that trigger protection are not always clear. In the laboratory, the protection afforded by certain anaesthetics against cardiac ischaemia and reperfusion injury is powerful and reproducible but this has not necessarily translated into similarly robust clinical benefits. Indeed, clinical studies and meta-analyses delivered variable results when comparing in the laboratory setting protective and non-protective anaesthetics. Reasons for this include underlying conditions such as age, obesity and diabetes. Animal models for disease or ageing, human cardiomyocytes derived from stem cells of patients and further clinical studies are employed to better understand the underlying causes that prevent a more robust protection in patients.

Anaesthetics as cardioprotectants: translatability and mechanism

The pharmacological conditioning of the heart with anaesthetics, such as volatile anaesthetics or opioids, is a phenomenon whereby a transient exposure to an anaesthetic agent protects the heart from the harmful consequences of myocardial ischaemia and reperfusion injury. The cellular and molecular mechanisms of anaesthetic conditioning appear largely to mimic those of ischaemic pre- and post-conditioning. Progress has been made on the understanding of the underlying mechanisms although the order of events and the specific targets of anaesthetics that trigger protection are not always clear. In the laboratory, the protection afforded by certain anaesthetics against cardiac ischaemia and reperfusion injury is powerful and reproducible but this has not necessarily translated into similarly robust clinical benefits. Indeed, clinical studies and meta-analyses delivered variable results when comparing in the laboratory setting protective and non-protective anaesthetics. Reasons for this include underlying conditions such as age, obesity and diabetes. Animal models for disease or ageing, human cardiomyocytes derived from stem cells of patients and further clinical studies are employed to better understand the underlying causes that prevent a more robust protection in patients.

Increased haemodynamic adrenergic load with isoflurane anaesthesia in type 2 diabetic and obese rats in vivo

Background

Increasing numbers of type 2 diabetic and obese patients with enhanced rates of cardiovascular complications require surgical interventions, however they have a higher incidence of perioperative haemodynamic complications, which has been linked to adrenergic dysfunction. Therefore, we aimed to determine how α- and β-adrenoceptor (AR)-mediated haemodynamic responses are affected by isoflurane anaesthesia in experimental type 2 diabetes and obesity in vivo.

Methods

Sixteen-week old male Zucker type 2 Diabetic Fatty (ZDF) rats, Zucker Obese rats and their lean counterparts (n = 7-9 per group) were instrumented with radio telemeters to record blood pressure and heart rate and with vascular access ports for non-invasive intravenous drug delivery in vivo. Haemodynamic effects of α-AR (phenylephrine; 1-100 μg.kg⁻¹) or β-AR (dobutamine; 2-120 μg.kg⁻¹) stimulation were assessed under conscious and anaesthetised (isoflurane; 2%) conditions.

Results

Vascular α-AR sensitivity was increased in both diabetic (non-diabetic 80 ± 3 vs. diabetic 95 ± 4 ΔmmHg at 100 μg.kg⁻¹; p < 0.05) and obese (lean 65 ± 6 vs. obese 84 ± 6 ΔmmHg at 20 μg.kg⁻¹; p < 0.05) conscious rats. Interestingly, anaesthesia exacerbated and prolonged the increased α-AR function in both diabetic and obese animals (non-diabetic 51 ± 1 vs. diabetic 68 ± 4 ΔmmHg, lean 61 ± 5 vs. obese 84 ± 2 ΔmmHg at 20 μg.kg⁻¹; p < 0.05). Meanwhile, β-AR chronotropic sensitivity was reduced in conscious diabetic and obese rats (non-diabetic 58 ± 7 vs. diabetic 27 ± 8 Δbpm, lean 103 ± 12 vs. obese 61 ± 9 Δbpm at 15 μg.kg⁻¹; p < 0.05). Anaesthesia normalised chronotropic β-AR responses, via either a limited reduction in obese (lean 51 ± 3 vs. obese 66 ± 5 Δbpm; NS at 15 μg.kg⁻¹) or increased responses in diabetic animals (non-diabetic 49 ± 8 vs. diabetic 63 ± 8 Δbpm, at 15 μg.kg⁻¹; NS at 15 μg.kg⁻¹).

Conclusions

Long term metabolic stress, such as during type 2 diabetes and obesity, alters α- and β-AR function, its dynamics and the interaction with isoflurane anaesthesia. During anaesthesia, enhanced α-AR sensitivity and normalised β-AR function may impair cardiovascular function in experimental type 2 diabetes and obesity.

Myocardial blood flow under general anaesthesia with sevoflurane in type 2 diabetic patients: a pilot study

Background

In type 2 diabetic patients, cardiac events in the perioperative period may be associated with diminished myocardial vasomotor function and endothelial dysfunction. The influence of sevoflurane anaesthesia on myocardial endothelial dysfunction in type 2 diabetic mellitus is investigated in this pilot study.

Methods

Six males with type 2 diabetes mellitus and eight healthy controls were included. Using myocardial contrast echocardiography, myocardial blood flow (MBF) was measured at rest, during adenosine-induced hyperaemia (endothelium-independent vasodilation) and after sympathetic stimulation by the cold pressor test (endothelium-dependent vasodilation). Measurements were performed before and after induction of sevoflurane anaesthesia.

Results

Sevoflurane anaesthesia decreased resting MBF in diabetics but not in controls (P = 0.03), while baseline MBF did not differ between diabetics and controls. Without anaesthesia, adenosine-induced hyperaemia increased MBF in both groups compared to resting values. Adenosine combined with sevoflurane resulted in a lower hyperaemic MBF in both groups compared to no anaesthesia. Differences in MBF in response to adenosine before and after sevoflurane administration were larger in diabetic patients, however not statistically significant in this pilot group (P = 0.08). Myocardial blood flow parameters after the cold pressor test were not different between groups.

Conclusion

These pilot data in type 2 diabetic patients show that sevoflurane anaesthesia decreases resting myocardial blood flow compared to healthy controls. Further, we observed a trend towards a lower endothelium-independent vasodilation capacity in diabetic patients under sevoflurane anaesthesia. Endothelium-dependent vasodilation was not affected by sevoflurane in diabetic patients. These data provide preliminary insight into myocardial responses in type 2 diabetic patients under general anaesthesia.

Trial registration

http://www.clinicialtrials.gov, NCT00866801

Influence of GLP-1 on myocardial glucose metabolism in healthy men during normo- or hypoglycemia

Background and Aims

Glucagon-like peptide-1 (GLP-1) may provide beneficial cardiovascular effects, possibly due to enhanced myocardial energetic efficiency by increasing myocardial glucose uptake (MGU). We assessed the effects of GLP-1 on MGU in healthy subjects during normo- and hypoglycemia.

Materials and Methods

We included eighteen healthy men in two randomized, double-blinded, placebo-controlled cross-over studies. MGU was assessed with GLP-1 or saline infusion during pituitary-pancreatic normo- (plasma glucose (PG): 4.5 mM, n = 10) and hypoglycemic clamps (PG: 3.0 mM, n = 8) by positron emission tomography with ¹⁸fluoro-deoxy-glucose (¹⁸F-FDG) as tracer.

Results

In the normoglycemia study mean (± SD) age was 25±3 years, and BMI was 22.6±0.6 kg/m² and in the hypoglycemia study the mean age was 23±2 years with a mean body mass index of 23±2 kg/m². GLP-1 did not change MGU during normoglycemia (mean (+/− SD) 0.15+/−0.04 and 0.16+/−0.03 µmol/g/min, P = 0.46) or during hypoglycemia (0.16+/−0.03 and 0.13+/−0.04 µmol/g/min, P = 0.14). However, the effect of GLP-1 on MGU was negatively correlated to baseline MGU both during normo- and hypoglycemia, (P = 0.006, r² = 0.64 and P = 0.018, r² = 0.64, respectively) and changes in MGU correlated positively with the level of insulin resistance (HOMA 2IR) during hypoglycemia, P = 0.04, r² = 0.54. GLP-1 mediated an increase in circulating glucagon levels at PG levels below 3.5 mM and increased glucose infusion rates during the hypoglycemia study. No differences in other circulating hormones or metabolites were found.

Conclusions

While GLP-1 does not affect overall MGU, GLP-1 induces changes in MGU dependent on baseline MGU such that GLP-1 increases MGU in subjects with low baseline MGU and decreases MGU in subjects with high baseline MGU. GLP-1 preserves MGU during hypoglycemia in insulin resistant subjects.

ClinicalTrials.gov registration numbers: NCT00418288: (hypoglycemia) and NCT00256256: (normoglycemia).

The heart is better protected against myocardial infarction in the fed state compared to the fasted state

OBJECTIVE

A variety of calorie restriction diets and fasting regimens are popular among overweight people. However, starvation could result in unexpected cardiovascular effects. Therefore, it is necessary to evaluate the short-term effects of diets on cardiovascular function, energy metabolism and potential risk of heart damage in case of myocardial infarction. The objective of the present study was to investigate whether the increased level of glucose oxidation or reduction of fatty acid (FA) load in the fed state provides the basis for protection against myocardial infarction in an experimental rat model of ischemia-reperfusion.

MATERIALS/METHODS

We tested the effects of the availability of energy substrates and their metabolites on the heart functionality and energy metabolism under normoxic and ischemia-reperfusion conditions.

RESULTS

In a fasted state, the heart draws energy exclusively from FAs, whereas in a fed state, higher concentration of circulating insulin ensures a partial switch to glucose oxidation, while the load of FA on heart and mitochondria is reduced. Herein, we demonstrate that ischemic damage in hearts isolated from Wistar rats and diabetic Goto-Kakizaki rats is significantly lower in the fed state compared to the fasted state.

CONCLUSIONS

Present findings indicate that postprandial or fed-state physiology, which is characterised by insulin-activated glucose and lactate utilisation, is protective against myocardial infarction. Energy metabolism pattern in the heart is determined by insulin signalling and the availability of FAs. Overall, our study suggests that even overnight fasting could provoke and aggravate cardiovascular events and high-risk cardiovascular patients should avoid prolonged fasting periods.