Impact of reversible trapping of tracer and the presence of blood metabolites on measurements of myocardial glucose utilization performed by PET and 18F-fluorodeoxyglucose using the Patlak method

Effects of the Novel Long-Acting GLP-1 Agonist, Albiglutide, on Cardiac Function, Cardiac Metabolism, and Exercise Capacity in Patients With Chronic Heart Failure and Reduced Ejection Fraction

OBJECTIVES

This study sought to determine if glucagon-like peptide (GLP)-1 ameliorates myocardial metabolic abnormalities in chronic heart failure.

BACKGROUND

Albiglutide (GSK716155) is a GLP-1 agonist indicated for type 2 diabetes.

METHODS

We performed a randomized, placebo-controlled study evaluating 12 weeks of albiglutide in New York Heart Association II or III subjects with ejection fraction <40%. Subjects received weekly placebo (n = 30) or albiglutide 3.75 mg (n = 12), 15 mg (n = 13), or 30 mg (n = 27). The primary comparison was between albiglutide 30 mg and placebo. Assessments included echocardiography, 6-minute-walk test, and peak oxygen consumption. In a subgroup of patients, myocardial glucose and oxygen use were assessed. Endpoints are reported as change from baseline ± SE.

RESULTS

Albiglutide 30 mg compared with placebo did not improve change from baseline in left ventricular ejection fraction (2.4% [1.1%] vs. 4.4% [1.1%]; p = 0.22), 6-min walk test (18 [12] m vs. 9 [11] m; p = 0.58), myocardial glucose use (p = 0.59), or oxygen use (p = 0.25). In contrast, albiglutide 30 mg versus placebo improved change from baseline in peak oxygen consumption (0.9 [0.5] ml/kg/min vs. -0.6 [0.5] ml/kg/min; p = 0.02). Albiglutide was well tolerated.

CONCLUSIONS

Although there was no detectable effect of albiglutide on cardiac function or myocardial glucose use, there was a modest increase in peak oxygen consumption, which could have been mediated by noncardiac effects. (A Multi-center, Placebo-controlled Study to Evaluate the Safety of GSK716155 and Its Effects on Myocardial Metabolism, Myocardial Function, and Exercise Capacity in Patients With NYHA Class II/III Congestive Heart Failure; NCT01357850).

Repeatable noninvasive measurement of mouse myocardial glucose uptake with 18F-FDG: evaluation of tracer kinetics in a type 1 diabetes model

A noninvasive and repeatable method for assessing mouse myocardial glucose uptake with (18)F-FDG PET and Patlak kinetic analysis was systematically assessed using the vena cava image-derived blood input function (IDIF).

METHODS

Contrast CT and computer modeling was used to determine the vena cava recovery coefficient. Vena cava IDIF (n = 7) was compared with the left ventricular cavity IDIF, with blood and liver activity measured ex vivo at 60 min. The test-retest repeatability (n = 9) of Patlak influx constant K(i) at 10-40 min was assessed quantitatively using Bland-Altman analysis. Myocardial glucose uptake rates (rMGU) using the vena cava IDIF were calculated at baseline (n = 8), after induction of type 1 diabetes (streptozotocin [50 mg/kg] intraperitoneally, 5 d), and after acute insulin stimulation (0.08 mU/kg of body weight intraperitoneally). These changes were analyzed with a standardized uptake value calculation at 20 and 40 min after injection to correlate to the Patlak time interval.

RESULTS

The proximal mouse vena cava diameter was 2.54 ± 0.30 mm. The estimated recovery coefficient, calculated using nonlinear image reconstruction, decreased from 0.76 initially (time 0 to peak activity) to 0.61 for the duration of the scan. There was a 17% difference in the image-derived vena cava blood activity at 60 min, compared with the ex vivo blood activity measured in the γ-counter. The coefficient of variability for Patlak K(i) values between mice was found to be 23% with the proposed method, compared with 51% when using the left ventricular cavity IDIF (P < 0.05). No significant bias in K(i) was found between repeated scans with a coefficient of repeatability of 0.16 mL/min/g. Calculated rMGU values were reduced by 60% in type 1 diabetic mice from baseline scans (P < 0.03, ANOVA), with a subsequent increase of 40% to a level not significantly different from baseline after acute insulin treatment. These results were confirmed with a standardized uptake value measured at 20 and 40 min.

CONCLUSION

The mouse vena cava IDIF provides repeatable assessment of the blood time-activity curve for Patlak kinetic modeling of rMGU. An expected significant reduction in myocardial glucose uptake was demonstrated in a type 1 diabetic mouse model, with significant recovery after acute insulin treatment, using a mouse vena cava IDIF approach.

An abbreviated hyperinsulinemic-euglycemic clamp results in similar myocardial glucose utilization in both diabetic and non-diabetic patients with ischemic cardiomyopathy

BACKGROUND

Positron emission tomography (PET) with insulin-stimulated (18)F-2-deoxyglucose (FDG) uptake is the gold standard for myocardial viability. However, insulin stimulation is infrequently performed due to time and inconvenience. We therefore assessed the clinical applicability of an abbreviated hyperinsulinemic-euglycemic clamp.

METHODS AND RESULTS

Dynamic FDG PET was performed in 50 patients with ischemic cardiomyopathy (ejection fraction: .30 +/- .10) using an abbreviated hyperinsulinemic-euglycemic clamp with separate Non-Diabetic (n = 26) and Diabetic (n = 24) protocols (American Society of Nuclear Cardiology guidelines), and supplemental potassium. In regions with normal resting perfusion ((13)N-ammonia uptake >or=80% maximal segment), there were no differences in either maximal (Non-Diabetic: .60 +/- .20 vs Diabetic: .60 +/- .17 micromol/min/g, P = .93) or mean rates of myocardial glucose uptake (MGU) (Non-Diabetic: .52 +/- .18 vs Diabetic: .52 +/- .14 micromol/min/g, P = .63) between the protocols. Multivariate analysis showed that diastolic blood pressure alone (maximal MGU, r (2) = .20, P = .001) or with NYHA Heart Failure Class (mean MGU, r (2) = .25, P = .003) could account for some of the variability in normal-region MGU. Potassium supplementation safely attenuated the decline in plasma levels.

CONCLUSIONS

This abbreviated hyperinsulinemic-euglycemic clamp produced similar MGU values in normal resting myocardium in non-diabetic and diabetic subjects, which are no different than published rates with a standard insulin clamp. Thus, this abbreviated approach is sufficient to overcome myocardial insulin resistance.