Four weeks SGLT2 inhibition improves beta cell function and glucose tolerance without affecting muscle free fatty acid or glucose uptake in subjects with type 2 diabetes

AIMS

Sodium glucose co-transporter-2 (SGLT2) inhibition lowers glucose levels independently of insulin, leading to reduced insulin secretion and increased lipolysis, resulting in elevated circulating free fatty acids (FFAs). While SGLT2 inhibition improves tissue insulin sensitivity, the increase in circulating FFAs could reduce insulin sensitivity in skeletal muscle and the liver. We aimed to investigate the effects of SGLT2 inhibition on substrate utilization in skeletal muscle and the liver and to measure beta-cell function and glucose tolerance.

METHODS

Thirteen metformin-treated individuals with type 2 diabetes were randomized to once-daily empagliflozin 25 mg or placebo for 4 weeks in a crossover design. Skeletal muscle glucose and FFA uptake together with hepatic tissue FFA uptake were measured using [18F]FDG positron emission tomography/computed tomography (PET/CT) and [11C]palmitate PET/CT. Insulin secretion and action were estimated using the oral minimal model.

RESULTS

Empagliflozin did not affect glucose (0.73 ± 0.30 vs. 1.16 ± 0.64, μmol/g/min p = 0.11) or FFA (0.60 ± 0.30 vs. 0.56 ± 0.3, μmol/g/min p = 0.54) uptake in skeletal muscle. FFA uptake in the liver (21.2 ± 10.1 vs. 19 ± 8.8, μmol/100 ml/min p = 0.32) was unaffected. Empagliflozin increased total beta-cell responsivity (20 ± 8 vs. 14 ± 9, 10-9 min-1, p < 0.01) and glucose effectiveness (2.6 × 10-2 ± 0.3 × 10-2 vs. 2.4 × 10-2 ± 0.3 × 10-2, dL/kg/min, p = 0.02).

CONCLUSIONS

Despite improved beta-cell function and glucose tolerance, empagliflozin does not appear to affect skeletal muscle FFA or glucose uptake.

Effects of exogenous lactate on lipid, protein, and glucose metabolism-a randomized crossover trial in healthy males

Lactate may inhibit lipolysis and thus enhance insulin sensitivity, but there is a lack of metabolic human studies. This study aimed to determine how hyperlactatemia affects lipolysis, glucose- and protein metabolism, and insulin sensitivity in healthy men. In a single-blind, randomized, crossover design, eight healthy men were studied after an overnight fast on two occasions: 1) during a sodium-lactate infusion (LAC) and 2) during a sodium-matched NaCl infusion (CTR). Both days consisted of a 3-h postabsorptive period followed by a 3-h hyperinsulinemic-euglycemic clamp (HEC). Lipolysis rate, endogenous glucose production (EGP), and delta glucose rate of disappearance (ΔRdglu) were evaluated using [9,10-3H]palmitate and [3-3H]glucose tracers. In addition, whole body- and forearm protein metabolism was assessed using [15N]phenylalanine, [2H4]tyrosine, [15N]tyrosine, and [13C]urea tracers. In the postabsorptive period, plasma lactate increased to 2.7 ± 0.5 mmol/L during LAC vs. 0.6 ± 0.3 mmol/L during CTR (P < 0.001). In the postabsorptive period, palmitate flux was 30% lower during LAC compared with CTR (84 ± 32 µmol/min vs. 120 ± 35 µmol/min, P = 0.003). During the HEC, palmitate flux was suppressed similarly during both interventions (P = 0.7). EGP, ΔRdglu, and M value were similar during LAC and CTR. During HEC, LAC increased whole body phenylalanine flux (P = 0.02) and protein synthesis (P = 0.03) compared with CTR; LAC did not affect forearm protein metabolism compared with CTR. Lactate infusion inhibited lipolysis by 30% under postabsorptive conditions but did not affect glucose metabolism or improve insulin sensitivity. In addition, whole body phenylalanine flux was increased. Clinical trial registrations: NCT04710875.NEW & NOTEWORTHY Lactate is a decisive intermediary metabolite, serving as an energy substrate and a signaling molecule. The present study examines the effects of lactate on substrate metabolism and insulin sensitivity in healthy males. Hyperlactatemia reduces lipolysis by 30% without affecting insulin sensitivity and glucose metabolism. In addition, hyperlactatemia increases whole body amino acid turnover rate.

The impact of CHOP versus bendamustine on bone mineral density in patients with indolent lymphoma enrolled in the GALLIUM study

Standard CHOP treatment includes a high cumulative dose of prednisone, and studies have shown increased fracture risk following CHOP. It is unclear whether reductions in bone mineral density (BMD) are caused by glucocorticoids or by the combination with chemotherapy. Our objective was to determine the effect of obinutuzumab (G)/rituximab (R)-bendamustine versus G/R-CHOP on BMD in follicular lymphoma patients. Patients in this GALLIUM post hoc study were ≥60 years old and in complete remission at induction treatment completion (ITC), following treatment with G or R in combination with bendamustine or CHOP. To assess BMD, Hounsfield units (HU) were measured in lumbar vertebra L1 on annual computed tomography. Furthermore, vertebral compression fractures were recorded. Of 173 patients included, 59 (34%) received CHOP and 114 (66%) received bendamustine. At baseline, there was no difference in HU between groups. The mean HU decrease from baseline to ITC was 27.8 after CHOP and 17.3 after bendamustine, corresponding to a difference of 10.4 (95% CI: 3.2-17.6). Vertebral fractures were recorded in 5/59 patients receiving CHOP and in 2/114 receiving bendamustine. CHOP was associated with a significant greater decrease in BMD and more frequent fractures. These results suggest that prophylaxis against BMD loss should be considered.

Increased lesion detectability in patients with locally advanced breast cancer-A pilot study using dynamic whole-body [18F]FDG PET/CT

BACKGROUND

Accurate diagnosis of axillary lymph node (ALN) metastases is essential for prognosis and treatment planning in breast cancer. Evaluation of ALN is done by ultrasound, which is limited by inter-operator variability, and by sentinel lymph node biopsy and/or ALN dissection, none of which are without risks and/or long-term complications. It is known that conventional 2-deoxy-2-[18F]fluoro-D-glucose ([18F]FDG) positron emission tomography/computed tomography (PET/CT) has limited sensitivity for ALN metastases. However, a recently developed dynamic whole-body (D-WB) [18F]FDG PET/CT scanning protocol, allowing for imaging of tissue [18F]FDG metabolic rate (MRFDG), has been shown to have the potential to increase lesion detectability. The study purpose was to examine detectability of malignant lesions in D-WB [18F]FDG PET/CT compared to conventional [18F]FDG PET/CT.

RESULTS

This study prospectively included ten women with locally advanced breast cancer who were referred for an [18F]FDG PET/CT as part of their diagnostic work-up. They all underwent D-WB [18F]FDG PET/CT, consisting of a 6 min single bed dynamic scan over the chest region started at the time of tracer injection, a 64 min dynamic WB PET scan consisting of 16 continuous bed motion passes, and finally a contrast-enhanced CT scan, with generation of MRFDG parametric images. Lesion visibility was assessed by tumor-to-background and contrast-to-noise ratios using volumes of interest isocontouring tumors with a set limit of 50% of SUVmax and background volumes placed in the vicinity of tumors. Lesion visibility was best in the MRFDG images, with target-to-background values 2.28 (95% CI: 2.04-2.54) times higher than target-to-background values in SUV images, and contrast-to-noise values 1.23 (95% CI: 1.12-1.35) times higher than contrast-to-noise values in SUV images. Furthermore, five imaging experts visually assessed the images and three additional suspicious lesions were found in the MRFDG images compared to SUV images; one suspicious ALN, one suspicious parasternal lymph node, and one suspicious lesion located in the pelvic bone.

CONCLUSIONS

D-WB [18F]FDG PET/CT with MRFDG images show potential for improved lesion detectability compared to conventional SUV images in locally advanced breast cancer. Further validation in larger cohorts is needed.

CLINICAL TRIAL REGISTRATION

The trial is registered in clinicaltrials.gov, NCT05110443, https://www.

CLINICALTRIALS

gov/study/NCT05110443?term=NCT05110443&rank=1 .

Dynamic whole-body [18F]FES PET/CT increases lesion visibility in patients with metastatic breast cancer

BACKGROUND

Correct classification of estrogen receptor (ER) status is essential for prognosis and treatment planning in patients with breast cancer (BC). Therefore, it is recommended to sample tumor tissue from an accessible metastasis. However, ER expression can show intra- and intertumoral heterogeneity. 16α-[18F]fluoroestradiol ([18F]FES) Positron Emission Tomography/Computed Tomography (PET/CT) allows noninvasive whole-body (WB) identification of ER distribution and is usually performed as a single static image 60 min after radiotracer injection. Using dynamic whole-body (D-WB) PET imaging, we examine [18F]FES kinetics and explore whether Patlak parametric images ( K i ) are quantitative and improve lesion visibility.

RESULTS

This prospective study included eight patients with metastatic ER-positive BC scanned using a D-WB PET acquisition protocol. The kinetics of [18F]FES were best characterized by the irreversible two-tissue compartment model in tumor lesions and in the majority of organ tissues. K i values from Patlak parametric images correlated with K i values from the full kinetic analysis, r2 = 0.77, and with the semiquantitative mean standardized uptake value (SUVmean), r2 = 0.91. Furthermore, parametric K i images had the highest target-to-background ratio (TBR) in 162/164 metastatic lesions and the highest contrast-to-noise ratio (CNR) in 99/164 lesions compared to conventional SUV images. TBR was 2.45 (95% confidence interval (CI): 2.25-2.68) and CNR 1.17 (95% CI: 1.08-1.26) times higher in K i images compared to SUV images. These quantitative differences were seen as reduced background activity in the K i images.

CONCLUSION

[18F]FES uptake is best described by an irreversible two-tissue compartment model. D-WB [18F]FES PET/CT scans can be used for direct reconstruction of parametric K i images, with superior lesion visibility and K i values comparable to K i values found from full kinetic analyses. This may aid correct ER classification and treatment decisions. Trial registration ClinicalTrials.gov: NCT04150731, https://clinicaltrials.gov/study/NCT04150731.

Guiding early revascularization using [15O]H2O PET myocardial perfusion imaging - Impact of atrial fibrillation

AIMS

Myocardial perfusion imaging (MPI) using [15O]H2O positron emission tomography (PET) is used to guide the selection of patients with angina for invasive angiography and possible revascularization. Our study evaluated whether atrial fibrillation (AF): 1) reduces global hyperemic myocardial blood flow (MBF) and 2) whether [15O]H2O PET MPI effectively guides revascularization procedures for patients with ongoing AF.

METHODS AND RESULTS

We prospectively recruited 346 patients with angina and persistent or paroxysmal AF referred for baseline/hyperemic [15O]H2O PET MPI. The primary outcome was revascularization within 3 months of MPI. In the analyses, patients were divided into four groups based on whether they had ongoing AF or sinus rhythm (SR) and whether they had previously documented coronary artery disease (CAD) or not. Thus, four groups were compared: SR-noCAD, AF-noCAD, SR-CAD and AF-CAD. Hyperemic MBF was affected by both ongoing AF and prior CAD [MBF (mL/min/g): 2.82 (SR-noCAD) vs. 2.12 (AF-noCAD) vs. 2.22 (SR-CAD) vs. 1.80 (AF-CAD), two-way ANOVA p<0.0001]. In multiple linear regression ongoing AF was independently associated with reduced hyperemic MBF. Every 0.1 mL/min/g decrease in hyperemic MBF was associated with a 23% increase in odds of early revascularization. ROC-analysis of vessel specific hyperemic MBF to predict early revascularization yielded the following areas under the ROC curve (AUC): SR-noCAD: 0.95 (p<0.0001); AF-noCAD: 0.79 (p<0.0001); SR-CAD: 0.78 (p<0.0001); AF-CAD: 0.88 (p<0.0001).

CONCLUSION

Ongoing AF is associated with 19-25 % reduced global hyperemic MBF as measured by [15O]H2O MPI PET. Regardless, vessel specific hyperemic MBF still predicts early revascularization in patients with AF.

Quantitative and qualitative comparison of Rubidium-82 and Oxygen-15 water cardiac PET

BACKGROUND

Differences in tracer characteristics may influence the interpretation of positron emission tomography myocardial perfusion imaging (MPI). We compare the reading of MPIs with a low-extraction retention tracer (82Rb) and a high-extraction non-retention tracer (15O-water) in a selected cohort of patients with known coronary artery disease (CAD).

METHODS

Thirty-nine patients with known CAD referred to 82Rb MPI due to angina underwent rest and stress imaging with both tracers and experienced MPI readers provided blinded consensus reads of all studies. In addition, a comparison of regional and global quantitative measures of perfusion was performed.

RESULTS

The results showed 74 % agreement in the reading of 82Rb and 15O-water MPI for regional reversible ischemia and global disease, and 82 % agreement for regional irreversible ischemia. The 15O-water MPI identified more cases of global disease (n = 12 (15O-water) vs n = 4 (82Rb), p = 0.03), whereas differences in reversible ischemia (n = 22 vs n = 16, p = 0.11) and, irreversible ischemia (n = 8 vs n = 11, p = 0.45) were not significant. The correlation between myocardial blood flow measured using the two tracers was similar to previous studies (R2 = 0.78) with wide limits of agreement (-0.93 to 0.84 ml/g/min).

CONCLUSIONS

Agreement between consensus readings of 82Rb and 15O-water MPI was good in patients with known CAD. In this limited size study, no significant differences in the identification of reversible and irreversible ischemia found, whereas 15O-water MPI had a higher positive rate for suspected global disease.

Rationale and design of the RAPID-WATER-FLOW trial: Radiolabeled perfusion to identify coronary artery disease using water to evaluate responses of myocardial FLOW

OBJECTIVES

The objective of this study was to determine the diagnostic performance of 15O-water positron emission tomography (PET) myocardial perfusion imaging to detect coronary artery disease (CAD) using the truth-standard of invasive coronary angiography (ICA) with fractional flow reserve (FFR) or instantaneous wave-Free Ratio (iFR) or coronary computed tomography angiogram (CCTA).

BACKGROUND

15O-water has a very high first-pass extraction that allows accurate quantification of myocardial blood flow and detection of flow-limiting CAD. However, the need for an on-site cyclotron and lack of automated production at the point of care and relatively complex image analysis protocol has limited its clinical use to date.

METHODS

The RAPID WATER FLOW study is an open-label, multicenter, prospective investigation of the accuracy of 15O-water PET to detect obstructive angiographic and physiologically significant stenosis in patients with suspected CAD. The study will include the use of an automated system for producing, dosing, and injecting 15O-water and enrolling approximately 215 individuals with suspected CAD at approximately 10 study sites in North America and Europe. The primary endpoint of the study is the diagnostic sensitivity and specificity of the 15O-water PET study using the truth-standard of ICA with FFR or iFR to determine flow-limiting stenosis, or CCTA to rule out CAD and incorporating a quantitative analytic platform developed for the 15O-water PET acquisitions. Sensitivity and specificity are to be considered positive if the lower bound of the 95% confidence interval is superior to the threshold of 60% for both, consistent with prior registration studies. Subgroup analyses include assessments of diagnostic sensitivity, specificity, and accuracy in female, obese, and diabetic individuals, as well as in those with multivessel disease. All enrolled individuals will be followed for adverse and serious adverse events for up to 32 hours after the index PET scan. The study will have >90% power (one-sided test, α = 0.025) to test the hypothesis that sensitivity and specificity of 15O-water PET are both >60%.

CONCLUSIONS

The RAPID WATER FLOW study is a prospective, multicenter study to determine the diagnostic sensitivity and specificity of 15O-water PET as compared to ICA with FFR/iFR or CCTA. This study will introduce several novel aspects to imaging registration studies, including a more relevant truth standard incorporating invasive physiologic indexes, coronary CTA to qualify normal individuals for eligibility, and a more quantitative approach to image analysis than has been done in prior pivotal studies.

CLINICAL TRIAL REGISTRATION INFORMATION

Clinical-Trials.gov (#NCT05134012).

Detection and correction of patient motion in dynamic 15O-water PET MPI

BACKGROUND

Patient motion constitutes a limitation to 15O-water cardiac PET imaging. We examined the ability of image readers to detect and correct patient motion using simulated motion data and clinical patient scans.

METHODS

Simulated data consisting of 16 motions applied to 10 motion-free scans were motion corrected using two approaches, pre-analysis and post-analysis for motion identification. Both approaches employed a manual frame-by-frame correction method. In addition, a clinical cohort was analyzed for assessment of prevalence and effect of motion and motion correction.

RESULTS

Motion correction was performed on 94% (pre-analysis) and 64% (post-analysis) of the scans. Large motion artifacts were corrected in 91% (pre-analysis) and 74% (post-analysis) of scans. Artifacts in MBF were reduced in 56% (pre-analysis) and 58% (post-analysis) of the scans. The prevalence of motion in the clinical patient cohort (n = 762) was 10%. Motion correction altered exam interpretation in only 10 (1.3%) clinical patient exams.

CONCLUSION

Frame-by-frame motion correction after visual inspection is useful in reducing motion artifacts in cardiac 15O-water PET. Reviewing the initial results (parametric images and polar maps) as part of the motion correction process, reduced erroneous corrections in motion-free scans. In a large clinical cohort, the impact of motion correction was limited to few patients.

Single time point quantitation of cerebral glucose metabolism by FDG-PET without arterial sampling

BACKGROUND

Until recently, quantitation of the net influx of 2-[18F]fluorodeoxyglucose (FDG) to brain (Ki) and the cerebrometabolic rate for glucose (CMRglc) required serial arterial blood sampling in conjunction with dynamic positron emission tomography (PET) recordings. Recent technical innovations enable the identification of an image-derived input function (IDIF) from vascular structures, but are frequently still encumbered by the need for interrupted sequences or prolonged recordings that are seldom available outside of a research setting. In this study, we tested simplified methods for quantitation of FDG-Ki by linear graphic analysis relative to the descending aorta IDIF in oncology patients examined using a Biograph Vision 600 PET/CT with continuous bed motion (Aarhus) or using a recently installed Biograph Vision Quadra long-axial field-of-view (FOV) scanner (Bern).

RESULTS

Correlation analysis of the coefficients of a tri-exponential decomposition of the IDIFs measured during 67 min revealed strong relationships among the total area under the curve (AUC), the terminal normalized arterial integral (theta(52-67 min)), and the terminal image-derived arterial FDG concentration (Ca(52-67 min)). These relationships enabled estimation of the missing AUC from late recordings of the IDIF, from which we then calculated FDG-Ki in brain by two-point linear graphic analysis using a population mean ordinate intercept and the single late frame. Furthermore, certain aspects of the IDIF data from Aarhus showed a marked age-dependence, which was not hitherto reported for the case of FDG pharmacokinetics.

CONCLUSIONS

The observed interrelationships between pharmacokinetic parameters in the IDIF measured during the PET recording support quantitation of FDG-Ki in brain using a single averaged frame from the interval 52-67 min post-injection, with minimal error relative to calculation from the complete dynamic sequences.

Coronary Artery Stenosis Evaluation by Angiography-Derived FFR: Validation by Positron Emission Tomography and Invasive Thermodilution

BACKGROUND

Fractional flow reserve (FFR) derived from invasive coronary angiography (QFR) is promising for evaluation of intermediate coronary artery stenosis.

OBJECTIVES

The authors aimed to compare the diagnostic performance of QFR and the guideline-recommended invasive FFR using 82Rubidium positron emission tomography (82Rb-PET) myocardial perfusion imaging as reference standard.

METHODS

This is a prospective, observational study of symptomatic patients with suspected obstructive coronary artery disease on coronary computed tomography angiography (≥50% diameter stenosis in ≥1 vessel). All patients were referred to 82Rb-PET and invasive coronary angiography with FFR and QFR assessment of all intermediate (30%-90% diameter stenosis) stenoses. Main analyses included a comparison of the ability of QFR and FFR to identify reduced myocardial blood flow (<2 mL/g/min) during vasodilation and/or relative perfusion abnormalities (summed stress score ≥4 in ≥2 adjacent segments).

RESULTS

A total of 250 patients (320 vessels) with indication for invasive physiological assessment were included. The continuous relationship of 82Rb-PET stress myocardial blood flow per 0.10 increase in FFR was +0.14 mL/g/min (95% CI: 0.07-0.21 mL/g/min) and +0.08 mL/g/min (95% CI: 0.02-0.14 mL/g/min) per 0.10 QFR increase. Using 82Rb-PET as reference, QFR and FFR had similar diagnostic performance on both a per-patient level (accuracy: 73%; 95% CI: 67%-79%; vs accuracy: 71%; 95% CI: 64%-78%) and per-vessel level (accuracy: 70%; 95% CI: 64%-75%; vs accuracy: 68%; 95% CI: 62%-73%). The per-vessel feasibility was 84% (95% CI: 80%-88%) for QFR and 88% (95% CI: 85%-92%) for FFR by intention-to-diagnose analysis.

CONCLUSIONS

With 82Rb-PET as reference modality, the wire-free QFR solution showed similar diagnostic accuracy as invasive FFR in evaluation of intermediate coronary stenosis. (DAN-NICAD - Danish Study of Non-Invasive Diagnostic Testing in Coronary Artery Disease; NCT02264717).

Ultrasonography in the assessment of disease activity in cranial and large-vessel giant cell arteritis: a prospective follow-up study

OBJECTIVES

We evaluated sensitivity to change and discriminative abilities of vascular US scores in disease monitoring in the follow-up of a prospective cohort of new-onset cranial and large-vessel (LV) GCA patients.

METHODS

Baseline and follow-up (8 weeks, 24 weeks and 15 months) US of temporal arteries (TA), carotid and axillary arteries (LV) included assessment of halo and measurement of the intima media complex (IMC). Max IMC, max halo IMC, sum IMC, sum halo IMC, mean IMC, halo count and the Southend halo score were calculated. The provisional OMERACT US score, OGUS, was obtained, taking the average of temporal arteries and axillary arteries IMCs divided by their normal cut-off values.

RESULTS

Baseline US was positive in 44/47 patients (72% TA, 72% LV). Sensitivity to change of all composite US scores containing TAs was evident by week 8 onward. LVs responded poorly and new axillary US lesions emerged in six patients despite clinical remission. The OGUS showed a large magnitude of change and is considered the score least prone to potential bias. All TA-based US scores showed moderate-strong correlation with disease activity markers. OGUS, TA halo count, Southend TA halo score, TA sum IMC and TA mean IMC showed potential to discriminate remission and relapse with area under the curve ≥0.8.

CONCLUSIONS

The OGUS is suggested as an outcome measurement for the assessment of treatment response in clinical trials. The abilities of US scores to discriminate remission and relapse are encouraging and should be further explored.

Multiparametric dynamic whole-body PSMA PET/CT using [68Ga]Ga-PSMA-11 and [18F]PSMA-1007

BACKGROUND

Routine prostate-specific membrane antigen (PSMA) positron emission tomography (PET) performed for primary staging or restaging of prostate cancer patients is usually done as a single static image acquisition 60 min after tracer administration. In this study, we employ dynamic whole-body (D-WB) PET imaging to compare the pharmacokinetics of [⁶⁸Ga]Ga-PSMA-11 and [¹⁸F]PSMA-1007 in various tissues and lesions, and to assess whether Patlak parametric images are quantitative and improve lesion detection and image readability.

METHODS

Twenty male patients with prostate cancer were examined using a D-WB PSMA PET protocol. Ten patients were scanned with [⁶⁸Ga]Ga-PSMA-11 and ten with [¹⁸F]PSMA-1007. Kinetic analyses were made using time-activity curves (TACs) extracted from organs (liver, spleen, bone, and muscle) and lesions. For each patient, three images were produced: SUV + Patlak parametric images (K_i and DV). All images were reviewed visually to compare lesion detection, image readability was quantified using target-to-background ratios (TBR), and Ki and DV values were compared.

RESULTS

The two PSMA tracers exhibited markedly different pharmacokinetics in organs: reversible for [⁶⁸Ga]Ga-PSMA-11 and irreversible for [¹⁸F]PSMA-1007. For both tracers, lesions kinetics were best described by an irreversible model. All parametric images were of good visual quality using both radiotracers. In general, Ki images were characterized by reduced vascular signal and increased lesion TBR compared with SUV images. No additional malignant lesions were identified on the parametric images.

CONCLUSION

D-WB PET/CT is feasible for both PSMA tracers allowing for direct reconstruction of parametric Ki images. The use of multiparametric PSMA images increased TBR but did not lead to the detection of more lesions. For quantitative whole-body Ki imaging, [¹⁸F]PSMA-1007 should be preferred over [⁶⁸Ga]Ga-PSMA-11 due to its irreversible kinetics in organs and lesions.

Exercise increases myocardial free fatty acid oxidation in subjects with metabolic dysfunction-associated fatty liver disease

BACKGROUND AND AIMS

Metabolic dysfunction-associated fatty liver disease (MAFLD) is associated with dyslipidemia and may promote cardiac lipotoxicity. Myocardial free fatty acids (FFA) oxidation (MO_FFA) is normal in pre-diabetes, but reduced in heart failure. We hypothesized that during exercise MO_FFA, very low-density lipoprotein triglycerides (VLDL-TG) secretion, hepatic FFA utilization, and lactate production differ among obese subjects with and without MAFLD.

METHODS

Nine obese subjects with MAFLD and 8 matched subjects without MAFLD (Control) without a history of heart failure and cardiovascular disease were compared before and after 90-min exercise at 50% Peak oxygen consumption. Basal and exercise induced cardiac and hepatic FFA oxidation, uptake and re-esterification and VLDL-TG secretion were measured using [¹¹C]palmitate positron-emission tomography and [1-¹⁴C]VLDL-TG.

RESULTS

In the heart, increased MO_FFA was observed after exercise in MAFLD, whereas MO_FFA decreased in Control (basal vs exercise, MAFLD: 4.1 (0.8) vs 4.8 (0.8) μmol·100 ml^-1 min^-1; Control: 4.9 (1.8) vs 4.0 (1.1); μmol·100 ml^-1 min^-1, mean (SD), p < 0.048). Hepatic FFA fluxes were significantly lower in MAFLD than Control and increased ≈ two-fold in both groups. VLDL-TG secretion was 50% greater in MAFLD at rest and similarly suppressed during exercise. Plasma lactate increased significantly less in MAFLD than Control during exercise.

CONCLUSIONS

Using robust tracer-techniques we found that obese subjects with MAFLD do not downregulate MO_FFA during exercise compared to Control, possibly due to diminished lactate supply. Hepatic FFA fluxes are significantly lower in MAFLD than Control, but increase similarly with exercise. VLDL-TG export remains greater in MAFLD compared to Control. Basal and post-exercise myocardial and hepatic FFA, VLDL-TG and lactate metabolism is abnormal in subjects with MAFLD compared to Control.

Inclusion of Metabolic Tumor Volume in Prognostic Models of Bone and Soft Tissue Sarcoma Increases the Prognostic Value

Sarcomas are rare and have a high mortality rate. Further prognostic classification, with readily available parameters, is warranted, and several studies have examined circulating biomarkers and PET parameters separately. This single-site, retrospective study aimed to examine the prognostic values of several scoring systems in combination with PET parameters. We included 148 patients with sarcoma, who were treated and scanned at Aarhus University Hospital from 1 January 2016 to 31 December 2019. The Akaike information criterion and Harrell's concordance index were used to evaluate whether the PET parameters added prognostic information to existing prognostic models using circulating biomarkers. Of the PET parameters, metabolic tumor volume (MTV) performed best, and when combined with the existing prognostic models, the prognostic value improved in all models. Backward stepwise selection was used to create a new model, SBSpib, which included albumin, lymphocytes, and one PET parameter, MTV. It has scores ranging from zero to three and increasing hazard ratios; HR = 4.83 (1.02-22.75) for group one, HR = 7.40 (1.6-33.42) for group two, and HR = 17.32 (3.45-86.93) for group three. Consequently, implementing PET parameters in prognostic models improved the prognostic value. SBSpib is a new prognostic model that includes both circulating biomarkers and PET parameters; however, validation in another sarcoma cohort is warranted.

Comparison of second-line on-site computed quantitative flow ratio from coronary computed tomography angiography to PET perfusion imaging for detecting obstructive coronary artery disease

Introduction

In patients with suspected obstructive coronary artery disease (CAD) on coronary computed tomography (CTA), guidelines endorse second-line selective testing for hemodynamic evaluation of suspected CAD. A variety of non-invasive modalities are available, and myocardial perfusion imaging with Rubidium-82 positron emission tomography (PET) is an established method with high diagnostic performance. Recently, an on-site method estimating computed tomography-derived quantitative flow ratio (CT-QFR) showed promising results for discriminating obstructive CAD. However, no study has compared the diagnostic performances of PET and CT-QFR.

Purpose

To assess a possible non-inferiority of CT-QFR compared to PET in patients with suspected obstructive CAD at CTA using invasive coronary angiography (ICA) with fractional flow reserve (FFR) as reference.

Methods

Patients (n=1732, 57% males, age 59±9.5) referred on a clinical indication with symptoms suggestive of obstructive CAD underwent routine CTA. Patients with ≥50% diameter stenosis (DS) on CTA were referred for PET and subsequent ICA with FFR. CT-QFR was analyzed post-hoc blinded to PET and ICA results.

Abnormal CT-QFR was defined as CT-QFR ≤0.80 in any vessel with a diameter ≥1.5mm. An independent core-lab evaluated PET scans as abnormal/normal with optional analyst-dependent application of pre-specified criteria; summed stress score of ≥4 in ≥2 contiguous segments, vessel-specific myocardial blood flow (MBF) &lt;2.00 ml/g/min, global myocardial blood flow reserve ≤1.8, and/or transient ischemic dilatation ratio &gt;1.13. Obstructive CAD was defined as ICA with FFR ≤0.80 or high-grade stenosis (≥90% DS).

Results

In total, 445/1732 patients (25%) had suspected obstructive CAD on CTA of whom 400/445 patients (90%) underwent subsequent PET and ICA. CT-QFR was successfully analysed in 383/400 (96%) patients classifying 174/383 (45%) patients as having disease. In comparison, PET classified 130/383 (34%) patients as having disease. In total, obstructive CAD by ICA with FFR was identified in 162 (42%) patients.

There was no significant difference in area under the receiver-operating characteristic curves for CT-QFR compared to the best performing PET metric (lowest vessel-specific MBF); 0.84 (95% CI 0.80–0.89) vs. 0.81 (0.77–0.85), p=0.19)) (Fig. 1). Overall diagnostic accuracy of CT-QFR versus PET was similar (78% (95% CI 74–82) vs. 77% (72–81), p=0.70. Sensitivities for CT-QFR and PET were 78% (71–84) and 63% (55–70), p&lt;0.01, respectively, and specificities 78% (72–84) and 87% (82–91), p=0.01, respectively (Fig. 2). Three-vessel or left main disease on ICA was correctly identified in 30/31 patients by both CT-QFR and PET.

Conclusion

In patients with suspected obstructive CAD by CTA, second-line CT-QFR was non-inferior to PET for discriminating obstructive CAD by invasive FFR; Although diagnostic accuracy was similar, CT-QFR demonstrated higher sensitivity while PET showed higher specificity

Funding Acknowledgement

Type of funding sources: Public Institution(s). Main funding source(s): Aarhus University PhD fellowshipRegion Mid Health Research Foundation

Clinical validation of a population-based input function for 20-min dynamic whole-body 18F-FDG multiparametric PET imaging

Purpose

Contemporary PET/CT scanners can use 70-min dynamic whole-body (D-WB) PET to generate more quantitative information about FDG uptake than just the SUV by generating parametric images of FDG metabolic rate (MR_FDG). The analysis requires the late (50–70 min) D-WB tissue data combined with the full (0–70 min) arterial input function (AIF). Our aim was to assess whether the use of a scaled population-based input function (sPBIF) obviates the need for the early D-WB PET acquisition and allows for a clinically feasible 20-min D-WB PET examination.

Methods

A PBIF was calculated based on AIFs from 20 patients that were D-WB PET scanned for 120 min with simultaneous arterial blood sampling. MR_FDG imaging using PBIF requires that the area under the curve (AUC) of the sPBIF is equal to the AUC of the individual patient’s input function because sPBIF AUC bias translates into MR_FDG bias. Special patient characteristics could affect the shape of their AIF. Thus, we validated the use of PBIF in 171 patients that were divided into 12 subgroups according to the following characteristics: diabetes, cardiac ejection fraction, blood pressure, weight, eGFR and age. For each patient, the PBIF was scaled to the aorta image-derived input function (IDIF) to calculate a sPBIF, and the AUC bias was calculated.

Results

We found excellent agreement between the AIF and IDIF at all times. For the clinical validation, the use of sPBIF led to an acceptable AUC bias of 1–5% in most subgroups except for patients with diabetes or patients with low eGFR, where the biases were marginally higher at 7%. Multiparametric MR_FDG images based on a short 20-min D-WB PET and sPBIF were visually indistinguishable from images produced by the full 70-min D-WB PET and individual IDIF.

Conclusions

A short 20-min D-WB PET examination using PBIF can be used for multiparametric imaging without compromising the image quality or precision of MR_FDG. The D-WB PET examination may therefore be used in clinical routine for a wide range of patients, potentially allowing for more precise quantification in e.g. treatment response imaging.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40658-022-00490-y.

SGLT2 inhibition reduces myocardial oxygen consumption

Aims/hypothesis

SGLT2 inhibition is associated with a reduced risk of cardiac disease that is still largely unexplained. According to one hypothesis, improved myocardial energetics may explain the cardioprotective effects of SGLT2i. However, recent mechanistic studies that have addressed this question have lacked the power to detect discrete but still clinically significant effects.

Methods

We pooled data from two recent randomized clinical trials and performed a meta-analysis to determine the effect of SGLT2 inhibition on myocardial oxygen consumption and myocardial external efficiency measured by positron emission tomography.

Results

SGLT2 inhibition reduced myocardial oxygen consumption (−1.06 [95%CI: 0.22–1.89] mL/100 g/min (n = 59, p = 0.01)), but did not affect myocardial external efficiency (2.22 [95%CI: 0.66-5.11] % (n = 59, p = 0.13))

Conclusions

/interpretation: SGLT2 inhibition reduces myocardial oxygen consumption at rest, which may contribute to the drugs’ cardioprotective effects.

The role of PET/CT in large vessel vasculitis and related disorders: diagnosis, extent evaluation and assessment of therapy response

Large vessel vasculitides (LVV) are defined as chronic inflammatory disorders that affect the arteries with two major variants being distinguished: giant cell arteritis (GCA) and Takayasu's arteritis (TAK). These often present with nonspecific constitutional symptoms which makes an accurate diagnosis often challenging. Nevertheless, timely diagnosis is of utmost importance to initiate treatment and to avoid potential life-threatening complications. [¹⁸F]FDG-PET/CT is nowadays widely accepted as useful tool to aid in the diagnosis of large vessel vasculitis. However, its role to monitor disease activity and to predict disease relapse during follow-up is less obvious since vascular [¹⁸F]FDG uptake can be detected in the absence of clinical or biochemical signs of disease activity. In addition to the two major variants, [¹⁸F]FDG-PET/CT has shown promise in (peri-)aortitis and related disorders. This article aims to provide an update on the current knowledge and limitations of [¹⁸F]FDG-PET/CT for the diagnosis and assessment of treatment response in LVV. Furthermore, other radiopharmaceuticals targeting key components of the vascular immune system are being discussed which could provide an interesting alternative to image vascular inflammation in LVV.

The pathophysiology of Wilson's disease visualized: A human 64 Cu PET study

BACKGROUND AND AIMS

Wilson's disease (WD) is a genetic disease with systemic accumulation of copper that leads to symptoms from the liver and brain. However, the underlying defects in copper transport kinetics are only partly understood. We sought to quantify hepatic copper turnover in patients with WD compared with heterozygote and control subjects using PET with copper-64 (64 Cu) as a tracer. Furthermore, we assessed the diagnostic potential of the method.

APPROACH AND RESULTS

Nine patients with WD, 5 healthy heterozygote subjects, and 8 healthy controls were injected with an i.v. bolus of 64 Cu followed by a 90-min dynamic PET scan of the liver and static whole-body PET/CT scans after 1.5, 6, and 20 h. Blood 64 Cu concentrations were measured in parallel. Hepatic copper retention and redistribution were evaluated by standardized uptake values (SUVs). At 90 min, hepatic SUVs were similar in the three groups. In contrast, at 20 h postinjection, the SUV in WD patients (mean ± SEM, 31 ± 4) was higher than in heterozygotes (24 ± 3) and controls (21 ± 4; p < 0.001). An SUV-ratio of hepatic 64 Cu concentration at 20 and 1.5 h completely discriminated between WD patients and control groups (p < 0.0001; ANOVA). By Patlak analysis of the initial 90 min of the PET scan, the steady-state hepatic clearance of 64 Cu was estimated to be slightly lower in patients with WD than in controls (p = 0.04).

CONCLUSIONS

64 Cu PET imaging enables visualization and quantification of the hepatic copper retention characteristic for WD patients. This method represents a valuable tool for future studies of WD pathophysiology, and may assist the development of therapies, and accurate diagnosis.

Effects of SGLT2 inhibition on lipid transport in adipose tissue in type 2 diabetes

SGLT2 inhibition induces an insulin-independent reduction in plasma glucose causing increased lipolysis and subsequent lipid oxidation by energy-consuming tissues. However, it is unknown whether SGLT2 inhibition also affects lipid storage in adipose tissue. Therefore, we aimed to determine the effects of SGLT2 inhibition on lipid storage and lipolysis in adipose tissue. We performed a randomized, double-blinded, placebo-controlled crossover design of 4 weeks of empagliflozin 25 mg and placebo once-daily in 13 individuals with type 2 diabetes treated with metformin. Adipose tissue fatty acid uptake, lipolysis rate and clearance were measured by 11C-palmitate PET/CT. Adipose tissue glucose uptake was measured by 18F-FDG PET/CT. Protein and gene expression of pathways involved in lipid storage and lipolysis were measured in biopsies of abdominal s.c. adipose tissue. Subjects were weight stable, which allowed us to quantify the weight loss-independent effects of SGLT2 inhibition. We found that SGLT2 inhibition did not affect free fatty acids (FFA) uptake in abdominal s.c. adipose tissue but increased FFA uptake in visceral adipose tissue by 27% (P < 0.05). In addition, SGLT2 inhibition reduced GLUT4 protein (P = 0.03) and mRNA content (P = 0.01) in abdominal s.c. adipose tissue but without affecting glucose uptake. In addition, SGLT2 inhibition decreased the expression of genes involved in insulin signaling in adipose tissue. We conclude that SGLT2 inhibition reduces GLUT4 gene and protein expression in abdominal s.c. adipose tissue, which could indicate a rebalancing of substrate utilization away from glucose oxidation and lipid storage capacity through reduced glycerol formation.

Clinical feasibility and impact of data-driven respiratory motion compensation studied in 200 whole-body 18F-FDG PET/CT scans

Background

This study examines the clinical feasibility and impact of implementing a fully automated whole-body PET protocol with data-driven respiratory gating in patients with a broad range of oncological and non-oncological pathologies 592 FDG PET/CT patients were prospectively included. 200 patients with lesions in the torso were selected for further analysis, and ungated (UG), belt gated (BG) and data-driven gating (DDG) images were reconstructed. All images were reconstructed using the same data and without prolonged acquisition time for gated images. Images were quantitatively analysed for lesion uptake and metabolic volume, complemented by a qualitative analysis of visual lesion detection. In addition, the impact of gating on treatment response evaluation was evaluated in 23 patients with malignant lymphoma.

Results

Placement of the belt needed for BG was associated with problems in 27% of the BG scans, whereas no issues were reported using DDG imaging. For lesion quantification, DDG and BG images had significantly greater SUV values and smaller volumes than UG. The physicians reported notable image blurring in 44% of the UG images that was problematic for clinical evaluation in 4.5% of cases.

Conclusion

Respiratory motion compensation using DDG is readily integrated into clinical routine and produce images with more accurate and significantly greater SUV values and smaller metabolic volumes. In our broad cohort of patients, the physicians overwhelmingly preferred gated over ungated images, with a slight preference for DDG images. However, even in patients with malignant disease in the torso, no additional diagnostic information was obtained by the gated images that could not be derived from the ungated images.

Pre-treatment total metabolic tumour volumes in lymphoma: Does quantity matter?

Positron emission tomography/computed tomography (PET/CT) is used for the staging of lymphomas. Clinical information, such as Ann Arbor stage and number of involved sites, is derived from baseline staging and correlates with tumour volume. With modern imaging software, exact measures of total metabolic tumour volumes (tMTV) can be determined, in a semi- or fully-automated manner. Several technical factors, such as tumour segmentation and PET/CT technology influence tMTV and there is no consensus on a standardized uptake value (SUV) thresholding method, or how to include the volumes in the bone marrow and spleen. In diffuse large B-cell lymphoma, follicular lymphoma, peripheral T-cell lymphoma, and Hodgkin lymphoma, tMTV has been shown to predict progression-free survival and/or overall survival, after adjustments for clinical risk scores. However, most studies have used receiver operating curves to determine the optimal cut-off for tMTV and many studies did not include a training-validation approach, which led to the risk of overestimation of the independent prognostic value of tMTV. The identified cut-off values are heterogeneous, even when the same SUV thresholding method is used. Future studies should focus on testing tMTV in homogeneously-treated cohorts and seek to validate identified cut-off values externally so that a prognostic value can be documented, over and above currently used clinical surrogates for tumour volume.

Human skeletal muscle CD90+ fibro-adipogenic progenitors are associated with muscle degeneration in type 2 diabetic patients

Type 2 diabetes mellitus (T2DM) is associated with impaired skeletal muscle function and degeneration of the skeletal muscles. However, the mechanisms underlying the degeneration are not well described in human skeletal muscle. Here we show that skeletal muscle of T2DM patients exhibit degenerative remodeling of the extracellular matrix that is associated with a selective increase of a subpopulation of fibro-adipogenic progenitors (FAPs) marked by expression of THY1 (CD90)-the FAP^CD90+. We identify platelet-derived growth factor (PDGF) as a key FAP regulator, as it promotes proliferation and collagen production at the expense of adipogenesis. FAPs^CD90+ display a PDGF-mimetic phenotype, with high proliferative activity, clonogenicity, and production of extracellular matrix. FAP^CD90+ proliferation was reduced by in vitro treatment with metformin. Furthermore, metformin treatment reduced FAP content in T2DM patients. These data identify a PDGF-driven conversion of a subpopulation of FAPs as a key event in the fibrosis development in T2DM muscle.

Mechanoenergetic coupling in heart failure with preserved, mid-range and reduced left ventricular ejection fraction

Background

Heart failure (HF) classification based on left ventricular ejection fraction (LVEF) can vary because of changes in filling pressures, afterload, and contractile function. 11C-acetate positron emission tomography (PET) provides a load-independent measure of myocardial external efficiency (MEE) by simultaneous assessment of myocardial oxygen consumption (MVO2), cardiac work, left ventricular mass (LVM), end-systolic wall stress (ESWS), and myocardial blood flow (MBF).

Purpose

We aimed to characterize mechanoenergetic derangements in patients with HF and to study its interrelation with age, sex and obesity.

Methods

MEE was measured in 121 participants with 11C-acetate PET, and LVEF was acquired with echocardiography. We investigated healthy controls (n=20) and patients with HF and reduced LVEF &lt;40% (HFrEF; n=25), mid-range LVEF 40–49% (HFmrEF; n=23), as well as patients with asymptomatic aortic valve stenosis (AS) and LVEF ≥50% (AS-asymp; n=38), and symptomatic AS and LVEF ≥50% (defined as HF with preserved LVEF (HFpEF); n=15).

Results

MEE declined in tandem with reduced LVEF from HFpEF and HFmrEF to HFrEF (p=0.041, p&lt;0.001, and p&lt;0.001 versus control, respectively; Figure 1). Impaired MEE was aggravated with increasing LVM (p=0.001) due to a disproportionate increase in overall left ventricular MVO2. In a multivariate analysis, female sex (p&lt;0.001), a lower body mass index (p&lt;0.001), and advanced age (p=0.01) were associated with a lower MEE (Figure 2). HFpEF, HFmrEF, and HFrEF patients had distinct energetic profiles involving MEE, MVO2, MBF, ESWS, and LVM (Figure 2).

Conclusions

Mechanoenergetic uncoupling was evident in every clinical state within the HF syndrome and associated with left ventricular hypertrophy and progressive systolic dysfunction. Sex, age, and obesity impacted myocardial energetics. To date, the present study is the largest investigation of mechanoenergetic coupling across several categories of patients with heart failure. 11C-acetate PET extends our pathophysiological comprehension of the HF syndrome beyond LVEF.

Funding Acknowledgement

Type of funding sources: Foundation. Main funding source(s): The Danish Heart FoundationThe Lundbeck Foundation Relationship between LVEF and MEEMyocardial energetics in heart failure

Routine clinical use of 15O-water cardiac PET: Initial experience with a novel automated solution

Funding Acknowledgements

Type of funding sources: None.

Introduction

 While considered the gold standard for cardiac perfusion imaging and myocardial blood flow quantitation, the use of 15O-water has been largely restricted to research purposes. The practical hurdles associated with the ultra-short half-life of the tracer and the lack of dedicated software have hampered the routine clinical use of 15O-water and novel solutions have been sought to obviate the issues limiting its use. An innovative bedside 15O-water generator designed for simple push button operation and high patient through-put has been developed and recently installed at our institution and utilized clinically under a magistral exception. The system also includes an infusion device and a dedicated display and analysis software. We report the initial experience utilizing such solution for routine clinical use of 15O-water.

Methods

 The first routine human myocardial perfusion imaging tests with PET 15O-water were conducted at our institution in December 2020. The 15O-water was produced and infused using the bed-side water generator. The activity per scan was 400 MBq in 20-35 mL of saline infused at a speed of 1-2 mL/s. Each exam consisted of a low-dose CT followed by a 4 min rest dynamic PET scan and, finally, a 4 min stress dynamic PET scan. Pharmacological stress was induced using a 6 min infusion of adenosine (0.14 mg/kg/min) starting 2 min prior to the stress PET scan. The exam time (time from initiation of the low dose CT to the end of the stress PET scan) was monitored. Images were analyzed using the dedicated software.

Results

 Since its implementation on December 7, 2020 and as of February 23, 2021, all patients referred to the hospital for cardiac perfusion imaging have been studied with this approach. Over this period of time, a total of 295 patients have been imaged with an average of 6 patients per day (a total of 50 scan days, 3-8 patients per day). The median total exam time was 22 min (85% of the exams were within 25 min and 95% below 30 min).

Conclusion

  Routine clinical use of 15O-water PET has been practically implemented utilizing a novel bedside generator and infusion solution. The system has proven to be reliable and efficient. This initial experience suggests that a very high patient throughput is achievable with improved resource utilization. The expected high diagnostic accuracy of the test is being evaluated with the dedicated imaging software.

Limitations and Pitfalls of FDG-PET/CT in Infection and Inflammation

White blood cells activated by either a pathogen or as part of a systemic inflammatory disease are characterized by high energy consumption and are therefore taking up the glucose analogue PET tracer FDG avidly. It is therefore not surprising that a steadily growing body of research and clinical reports now supports the use of FDG PET/CT to diagnose a wide range of patients with non-oncological diseases. However, using FDG PET/CT in patients with infectious or inflammatory diseases has some limitations and potential pitfalls that are not necessarily as pronounced in oncology FDG PET/CT. Some of these limitations are of a general nature and related to the laborious acquisition of PET images in patients that are often acutely ill, whereas others are more disease-specific and related to the particular metabolism in some of the organs most commonly affected by infections or inflammatory disease. Both inflammatory and infectious diseases are characterized by a more diffuse and less pathognomonic pattern of FDG uptake than oncology FDG PET/CT and the affected organs also typically have some physiological FDG uptake. In addition, patients referred to PET/CT with suspected infection or inflammation are rarely treatment naïve and may have received varying doses of antibiotics, corticosteroids or other immune-modulating drugs at the time of their examination. Combined, this results in a higher rate of false positive FDG findings and also in some cases a lower sensitivity to detect active disease. In this review, we therefore discuss the limitations and pitfalls of FDG PET/CT to diagnose infections and inflammation taking these issues into consideration. Our review encompasses the most commonly encountered inflammatory and infectious diseases in head and neck, in the cardiovascular system, in the abdominal organs and in the musculoskeletal system. Finally, new developments in the field of PET/CT that may help overcome some of these limitations are briefly highlighted.

SGLT2 Inhibition Does Not Affect Myocardial Fatty Acid Oxidation or Uptake, but Reduces Myocardial Glucose Uptake and Blood Flow in Individuals With Type 2 Diabetes: A Randomized Double-Blind, Placebo-Controlled Crossover Trial

Sodium-glucose cotransporter 2 (SGLT2) inhibition reduces cardiovascular morbidity and mortality in individuals with type 2 diabetes. Beneficial effects have been attributed to increased ketogenesis, reduced cardiac fatty acid oxidation, and diminished cardiac oxygen consumption. We therefore studied whether SGLT2 inhibition altered cardiac oxidative substrate consumption, efficiency, and perfusion. Thirteen individuals with type 2 diabetes were studied after 4 weeks' treatment with empagliflozin and placebo in a randomized, double-blind, placebo-controlled crossover study. Myocardial palmitate and glucose uptake were measured with ¹¹C-palmitate and ¹⁸F-fluorodeoxyglucose positron emission tomography (PET)/computed tomography (CT). Oxygen consumption and myocardial external efficiency (MEE) were measured with ¹¹C-acetate PET/CT. Resting and adenosine stress myocardial blood flow (MBF) and myocardial flow reserve (MFR) were measured using ¹⁵O-H₂O PET/CT. Empagliflozin did not affect myocardial free fatty acids (FFAs) uptake but reduced myocardial glucose uptake by 57% (P < 0.001). Empagliflozin did not change myocardial oxygen consumption or MEE. Empagliflozin reduced resting MBF by 13% (P < 0.01), but did not significantly affect stress MBF or MFR. In conclusion, SGLT2 inhibition did not affect myocardial FFA uptake, but channeled myocardial substrate utilization from glucose toward other sources and reduced resting MBF. However, the observed metabolic and hemodynamic changes were modest and most likely contribute only partially to the cardioprotective effect of SGLT2 inhibition.

Metformin Biodistribution: A Key to Mechanisms of Action?

Metformin has undisputed glucose-lowering effects in diabetes and an impressive safety record. It has also shown promising effects beyond diabetes, and several hundred clinical trials involving metformin are currently planned or active. Metformin targets intracellular effectors, but exactly which remain to be established, and in an era of precision medicine, an incomplete understanding of mechanisms of action may limit the use of metformin. Distribution of metformin depends on specific organic cation transporter proteins that are organ- and species-specific. Therefore, target tissues of metformin can be identified by cellular uptake of the drug, and exploring the biodistribution of the drug in humans becomes an attractive strategy to assist the many investigations into the mechanisms of action of metformin performed in animals. In this review, we combine the emerging evidence from the use of 11C-labeled metformin in humans to discuss metformin action in liver, intestines, and kidney, which are the organs with the most avid uptake of the drug.

Successful Prediction of Positron Emission Tomography-Imaged Metformin Hepatic Uptake Clearance in Humans Using the Quantitative Proteomics-Informed Relative Expression Factor Approach

Predicting transporter-mediated in vivo hepatic drug clearance (CL) from in vitro data (IVIVE) is important in drug development to estimate first-in-human dose and the impact of drug interactions and pharmacogenetics on hepatic drug CL. For IVIVE, one can use human hepatocytes and the traditional milligrams of protein content per gram of liver tissue (MGPGL) approach. However, this approach has been found to consistently underpredict the observed in vivo hepatic drug CL. Therefore, we hypothesized that using transporter-expressing cells and the relative expression factor (REF), determined using targeted quantitative proteomics, will accurately predict in vivo hepatic CL of drugs. We have successfully tested this hypothesis in rats with rosuvastatin, which is transported by hepatic Organic anion transporting polypeptides (OATPs). Here, we tested this hypothesis for another drug and another transporter; namely, organic cation transporter (OCT)1-mediated hepatic distributional CL of metformin. First, we estimated the in vivo metformin hepatic sinusoidal uptake CL (CL_h,s,in) of metformin by reanalysis of previously published human positron emission tomography imaging data. Next, using the REF approach, we predicted the in vivo metformin CL_h,s,in using OCT1-transporter-expressing HEK293 cells or plated human hepatocytes. Finally, we compared this REF-based prediction with that using the MGPGL approach. The REF approach accurately predicted the in vivo metformin hepatic CL_h,s,in, whereas the MGPGL approach considerably underpredicted the in vivo metformin CL_h,s,in Based on these and previously published data, the REF approach appears to be superior to the MGPGL approach for a diverse set of drugs transported by different transporters. SIGNIFICANCE STATEMENT: This study is the first to use organic cation transporter 1-expressing cells and plated hepatocytes to compare proteomics-informed REF approach with the traditional MGPGL approach to predict hepatic uptake CL of metformin in humans. The proteomics-informed REF approach, which corrected for plasma membrane abundance, accurately predicted the positron emission tomography-imaged metformin hepatic uptake CL, whereas the MGPGL approach consistently underpredicted this CL.

Acute Hyperketonemia Does Not Affect Glucose or Palmitate Uptake in Abdominal Organs or Skeletal Muscle

CONTEXT

It has recently been hypothesized that ketone bodies may have independent cardioprotective effects due to increased myocardial efficiency and that this may explain the improved survival of individuals with type 2 diabetes treated with mildly ketogenic sodium-glucose cotransporter-2 inhibitors.

OBJECTIVE

To determine whether ketone bodies are selectively utilized in tissues critical for preservation of conscience and circulation. We investigated the effect of acute hyperketonemia on substrate metabolism in less prioritized tissues such as abdominal organs, adipose tissue, and skeletal muscle.

DESIGN

Acute, randomized, single-blinded, crossover design.

SETTING

Ambulatory care.

PARTICIPANTS

Eight healthy participants completed the study. Two additional participants withdrew because of claustrophobia during the scans.

INTERVENTION

Infusions of saline and ketone bodies during a hyperinsulinemic-euglycemic clamp.

MAIN OUTCOME MEASURES

Organ-specific glucose and palmitate uptake was determined by dynamic positron emission tomography/computed tomography (PET/CT) scans with 18F-fluorodeoxyglucose (18F-FDG) and 11C-palmitate. Blood flow to abdominal organs was measured with O-15-labeled water (15O-H2O) perfusion PET. The study was performed as a post hoc analysis.

RESULTS

We found that ketone body infusion did not affect glucose uptake, palmitate uptake, or blood flow to abdominal organs and skeletal muscles.

CONCLUSION

Acute hyperketonemia does not affect glucose or palmitate uptake in skeletal muscle or abdominal tissues, supporting the notion that ketone bodies are selectively used by critical organs such as the heart and brain.

Metformin is distributed to tumor tissue in breast cancer patients in vivo: A 11C-metformin PET/CT study

PURPOSE

Epidemiological studies and randomized clinical trials suggest that the antidiabetic drug, metformin, may have anti-neoplastic effects. The mechanism that mediates these beneficial effects has been suggested to involve direct action on cancer cells, but this will require distribution of metformin in tumor tissue. The present study was designed to investigate metformin distribution in vivo in breast and liver tissue in breast cancer patients.

METHODS

Seven patients recently diagnosed with ductal carcinoma were recruited. Using PET/CT, tissue distribution of metformin was determined in vivo for 90 min after injection of a carbon-11-labeled metformin tracer. After surgery, tumor tissue was investigated for gene expression levels of metformin transporter proteins.

RESULTS

Tumor tissue displayed a distinct uptake of metformin compared to normal breast tissue AUC_0-90 min (75.4 ± 5.5 vs 42.3 ± 6.3) g/ml*min (p = 0.01). Maximal concentration in tumor was at 1 min where it reached approximately 30% of the activity in the liver. The metformin transporter protein with the highest gene expression in tumor tissue was multidrug and toxin extrusion 1 (MATE 1) followed by plasma membrane monoamine transporter (PMAT).

CONCLUSION

This study confirms that metformin is transported into tumor tissue in women with breast cancer. This finding support that metformin may have direct anti-neoplastic effects on tumor cells in breast cancer patients. However, distribution of metformin in tumor tissue is markedly lower than in liver, an established metformin target tissue.

Myocardial Viability Testing by Positron Emission Tomography: Basic Concepts, Mini-Review of the Literature and Experience From a Tertiary PET Center

Ischemic heart disease ranges in severity from slightly reduced myocardial perfusion with preserved contractile function to chronic occlusion of coronary arteries with myocardial cells replaced by acontractile scar tissue-ischemic heart failure (iHF). Progression towards scar tissue is thought to involve a period in which the myocardial cells are acontractile but still viable despite severely reduced perfusion. This state of reduced myocardial function that can be reversed by revascularization is termed "hibernation." The concept of hibernating myocardium in iHF has prompted an increasing amount of requests for preoperative patient workup, but while the concept of viability is widely agreed upon, no consensus on clinical testing of hibernation has been established. Therefore, a variety of imaging methods have been used to assess hibernation including morphology based (MRI and ultrasound), perfusion based (MRI, SPECT, or PET) and/or methods to assess myocardial metabolism (PET). Regrettably, the heterogeneous body of literature on the subject has resulted in few robust prospective clinical trials designed to assess the impact of preoperative viability testing prior to revascularization. However, the PARR-2 trial and sub-studies has indicated that >5% hibernating myocardium favors revascularization over optimized medical therapy. In this paper, we review the basic concepts and current evidence for using PET to assess myocardial hibernation and discuss the various methodologies used to process the perfusion/metabolism PET images. Finally, we present our experience in conducting PET viability testing in a tertiary referral center.

Cardiovascular Effects of Treatment With the Ketone Body 3-Hydroxybutyrate in Chronic Heart Failure Patients

Supplemental Digital Content is available in the text.

Background:

Myocardial utilization of 3-hydroxybutyrate (3-OHB) is increased in patients with heart failure and reduced ejection fraction (HFrEF). However, the cardiovascular effects of increased circulating plasma-3-OHB levels in these patients are unknown. Consequently, the authors’ aim was to modulate circulating 3-OHB levels in HFrEF patients and evaluate: (1) changes in cardiac output (CO); (2) a potential dose-response relationship between 3-OHB levels and CO; (3) the impact on myocardial external energy efficiency (MEE) and oxygen consumption (MVO₂); and (4) whether the cardiovascular response differed between HFrEF patients and age-matched volunteers.

Methods:

Study 1: 16 chronic HFrEF patients (left ventricular ejection fraction: 37±3%) were randomized in a crossover design to 3-hour of 3-OHB or placebo infusion. Patients were monitored invasively with a Swan-Ganz catheter and with echocardiography. Study 2: In a dose-response study, 8 HFrEF patients were examined at increasing 3-OHB infusion rates. Study 3 to 4: 10 HFrEF patients and 10 age-matched volunteers were randomized in a crossover design to 3-hour 3-OHB or placebo infusion. MEE and MVO₂ were evaluated using 11C-acetate positron emission tomography.

Results:

3-OHB infusion increased circulating levels of plasma 3-OHB from 0.4±0.3 to 3.3±0.4 mM (P<0.001). CO rose by 2.0±0.2 L/min (P<0.001) because of an increase in stroke volume of 20±2 mL (P<0.001) and heart rate of 7±2 beats per minute (bpm) (P<0.001). Left ventricular ejection fraction increased 8±1% (P<0.001) numerically. There was a dose-response relationship with a significant CO increase of 0.3 L/min already at plasma-3-OHB levels of 0.7 mM (P<0.001). 3-OHB increased MVO₂ without altering MEE. The response to 3-OHB infusion in terms of MEE and CO did not differ between HFrEF patents and age-matched volunteers.

Conclusions:

3-OHB has beneficial hemodynamic effects in HFrEF patients without impairing MEE. These beneficial effects are detectable in the physiological concentration range of circulating 3-OHB levels. The hemodynamic effects of 3-OHB were observed in both HFrEF patients and age-matched volunteers. 3-OHB may potentially constitute a novel treatment principle in HFrEF patients.

Metformin increases endogenous glucose production in non-diabetic individuals and individuals with recent-onset type 2 diabetes

AIMS/HYPOTHESIS

Metformin is the endorsed first-line glucose-lowering drug for treating patients with type 2 diabetes but despite more than 50 years of use, no consensus has been reached on its mechanisms of action. In this study, we investigated the glucose-lowering effects of metformin in individuals with type 2 diabetes and non-diabetic individuals.

METHODS

We performed a randomised, placebo-controlled trial in 24 individuals with recent-onset type 2 diabetes (diabetes duration 50 [48] months) who had good glycaemic control (HbA_1c 48 mmol/mmol [6.5%]). The studies were conducted at Aarhus University Hospital between 2013 and 2016. Participants were randomised to receive either metformin (2000 mg/day, n = 12, MET group) or placebo (n = 12, PLA group) for 90 days, using block randomisation set up by an unblinded pharmacist. Two participants withdrew from the study prior to completion and were replaced with two new participants receiving the same treatment. In addition, we recruited a group of non-diabetic individuals with similar age and BMI (n = 12, CONT group), who were all treated with 2000 mg metformin daily. Before and after treatment all individuals underwent studies of whole-body glucose metabolism by non-steady-state [3-³H]glucose kinetics, hyperinsulinaemic-euglycaemic clamping, indirect calorimetry, metabolomics, dual x-ray absorptiometry and muscle biopsies. The primary study endpoint was the effect of metformin treatment on lipid kinetics as well as glucose rate of disappearance (R_d) and endogenous glucose production (EGP).

RESULTS

One participant from the CONT group withdrew due to intolerable gastrointestinal side-effects and was excluded from analysis. As expected, metformin treatment lowered fasting plasma glucose (FPG) in the MET group (~1.5 mmol/l, p < 0.01), whereas no effect was observed in the PLA and CONT groups. Body weight and composition did not change in any of the groups. In both of the metformin-treated groups (MET and CONT), basal glucose R_d, EGP and glucagon levels increased by ~30% (p < 0.05) whereas this was not the case in the PLA group.

CONCLUSIONS/INTERPRETATION

Ninety days of metformin treatment resulted in similar increases in EGP and glucose R_d in individuals with recent-onset type 2 diabetes and in non-diabetic control individuals. These results challenge the existing paradigm that metformin primarily acts in the liver by inhibiting EGP, at least in individuals with type 2 diabetes of short duration and who have discretely affected glycaemic status. Whether metformin increases basal glucose R_d by facilitating glucose uptake in other tissues such as the intestines remains to be further clarified.

TRIAL REGISTRATION

ClinicalTrials.gov NCT01729156 FUNDING: This study was supported by grants from The Danish Council for Independent Research | Medical Sciences, Aase Danielsen Fund, the Novo Nordisk Foundation, the Danish Diabetes Association and the Danish Diabetes Academy supported by the Novo Nordisk Foundation.

Focal skeletal FDG uptake indicates poor prognosis in cHL regardless of extent and first-line chemotherapy

¹⁸ F-fluoro-2-deoxy-D-glucose positron emission tomography/computed tomography (FDG-PET/CT) is used for staging classical Hodgkin lymphoma (cHL) with high sensitivity for skeletal involvement. However, it is unclear whether a single bone lesion carries the same adverse prognosis as multifocal lesions and if this is affected by type of chemotherapy [ABVD (adriamycin, bleomycin, vincristine, dacarbazine) versus BEACOPP (bleomycin, etoposide, adriamycin, cyclophosphamide, vincristine, procarbazine, prednisone)]. We reviewed the clinico-pathological and outcome data from 209 patients with newly diagnosed cHL staged by FDG-PET/CT. Patterns of skeletal/bone marrow uptake (BMU) were divided into 'low' and 'high' diffuse BMU (i.e. without focal lesions), and unifocal or multifocal lesions. Additional separate survival analysis was performed, taking type of chemotherapy into account. Forty patients (19·2%) had skeletal lesions (20 unifocal, 20 multifocal). The 3-year progression-free-survival (PFS) was 80% for patients with 'low BMU', 87% for 'high BMU', 69% for 'unifocal' and 51% for 'multifocal' lesions; median follow-up was 38 months. The presence of bone lesions, both uni- and multifocal, was associated with significantly inferior PFS (log rank P = 0·0001), independent of chemotherapy type. Thus, increased diffuse BMU should not be considered as a risk factor in cHL, whereas unifocal or multifocal bone lesions should be regarded as important predictors of adverse outcome, irrespective of the chemotherapy regimen used.

A comparative study of standardized quantitative and visual assessment for predicting tumor volume and outcome in newly diagnosed diffuse large B-cell lymphoma staged with 18F-FDG PET/CT

Background

Semi-automated quantitative measurement of metabolic tumor volume (MTV) for prognosis in diffuse large B-Cell lymphoma (DLBCL) has gained considerable interest lately. However, simple tumor volume measures may be inadequate for assessment of prognosis in DLBCL as other characteristics such as growth pattern and metabolic heterogeneity may be just as important. In addition, MTV measurements require delineation of tumor lesions by semi-automated software, which can be time-consuming. We hypothesized that a simple visual assessment of tumor volume performs as well as standardized MTV measurements in DLBCL prognostication.

Materials and methods

Quantitative and visual analyses of pre-therapy 18F-FDG PET/CT scans in 118 patients with newly diagnosed DLBCL were conducted. Quantitative analyses were performed using Hermes TumourFinder® to obtain MTV^2.5 (SUV 2.5 cut-off) and MTV⁴¹ (41% SUVmax isocontour cut-off). Visual assessments included a binary prediction (good/poor prognosis) as well as tumor burden based on a visual analog scale (MTV^VAS) and an estimated volume (eMTV). Three experienced nuclear medicine physicians who were blinded to clinical outcome performed visual evaluations. Progression-free survival was evaluated by Kaplan-Meier curves and log-rank test. Inter-observer variability was evaluated by Fleiss’ kappa for multiple observers.

Results

In the quantitative analysis, a ROC-determined MTV^2.5 cut-off (log-rank p = 0.11) seemed to outperform MTV⁴¹ (log-rank p = 0.76) for PFS prediction. TLG2.5 (log-rank p = 0.14) and TLG41 (log-rank p = 0.34) were not associated with outcomes. By visual analysis, all three reviewers were able to stratify patients into good/poor prognosis (reviewer A log-rank p = 0.002, reviewer B log-rank p = 0.016, and reviewer C log-rank p = 0.012) with fair inter-observer agreement (Fleiss’ kappa 0.47). MTV^VAS and eMTV were not consistently correlated with the outcome.

Conclusion

Predictions of outcome after first-line treatment for DLBCL were surprisingly good when left to the unsupervised, subjective judgment of experienced readers of lymphoma 18F-FDG-PET/CT. The study highlights the importance of non-standardized clinical judgments and shows potential loss of valuable prognostic information when relying solely on semi-automated MTV measurements.

Influence of Cardiac CT based disease severity and clinical symptoms on the diagnostic performance of myocardial perfusion

We aimed to identify factors influencing the sensitivity of perfusion imaging after an initial positive coronary computed tomography angiography (CCTA) using invasive coronary angiography (ICA) with conditional fractional flow reserve (FFR) as reference. Secondly we aimed to identify factors associated with revascularisation and to evaluate treatment outcome after ICA. We analysed 292 consecutive patients with suspected significant coronary artery disease (CAD) at CCTA, who underwent perfusion imaging with either cardiac magnetic resonance (CMR) or myocardial perfusion scintigraphy (MPS) followed by ICA with conditional FFR. Stratified analysis and uni- and multiple logistic regression analyses were performed to identify predictors of diagnostic agreement between perfusion scans and ICA and predictors of revascularisation. Myocardial ischemia evaluated with perfusion scans was present in 65/292 (22%) while 117/292 (40%) had obstructive CAD evaluated by ICA. Revascularisation rate was 90/292 (31%). The overall sensitivity for perfusion scans was 39% (30-48), specificity 89% (83-93), PPV 69% (57-80) and NPV 68% (62-74). Stratified analysis showed higher sensitivities in patients with multi-vessel disease at CCTA 49% (37-60) and typical chest pain 50% (37-60). Predictors of revascularisation were multi-vessel disease by CCTA (OR 3.51 [1.91-6.48]) and a positive perfusion scan (OR 4.69 [2.49-8.83]). The sensitivity for perfusion scans after CCTA was highest in patients with typical angina and multiple lesions at CCTA and predicted diagnostic agreement between perfusion scans and ICA. Abnormal perfusion and multi vessel disease at CCTA predicted revascularisation.

FDG-PET/CT in the management of lymphomas: current status and future directions

FDG-PET/CT is the current state-of-the-art imaging in lymphoma and plays a central role in treatment decisions. At diagnosis, accurate staging is crucial for appropriate therapy selection: FDG-PET/CT can identify areas of lymphoma missed by CT alone and avoid under-treatment of patients with advanced disease stage who would have been misclassified as having limited stage disease by CT. Particularly in Hodgkin lymphoma, positive interim FDG-PET/CT scans are adversely prognostic for clinical outcomes and can inform PET-adapted treatment strategies, but such data are less consistent in diffuse large B-cell lymphoma. The use of quantitative FDG-PET/CT metrics using metabolic tumour volume, possibly in combination with other biomarkers, may better define prognostic subgroups and thus facilitate better treatment selection. After chemotherapy, FDG-PET/CT response is predictive of outcome and may identify a subgroup who benefit from consolidative radiotherapy. Novel therapies, in particular immunotherapies, exhibit different response patterns than conventional chemotherapy, which has led to modified response criteria that take into account the risk of transient pseudo-progression. In relapsed lymphoma, FDG-PET/CT after second-line therapy and prior to high-dose therapy is also strongly associated with outcome and may be used to guide intensity of salvage therapy in relapsed Hodgkin lymphoma. Currently, FDG-PET/CT has no role in the routine follow-up after complete metabolic response to therapy, but it remains a powerful tool for excluding relapse if patients develop clinical features suggestive of disease relapse. In conclusion, FDG-PET/CT plays major roles in the various phases of management of lymphoma and constitutes a step towards the pursuit of personalized treatment.

Metformin targets brown adipose tissue in vivo and reduces oxygen consumption in vitro

AIMS

To test the hypothesis that brown adipose tissue (BAT) is a metformin target tissue by investigating in vivo uptake of [¹¹ C]-metformin tracer in mice and studying in vitro effects of metformin on cultured human brown adipocytes.

MATERIALS AND METHODS

Tissue-specific uptake of metformin was assessed in mice by PET/CT imaging after injection of [¹¹ C]-metformin. Human brown adipose tissue was obtained from elective neck surgery and metformin transporter expression levels in human and murine BAT were determined by qPCR. Oxygen consumption in metformin-treated human brown adipocyte cell models was assessed by Seahorse XF technology.

RESULTS

Injected [¹¹ C]-metformin showed avid uptake in the murine interscapular BAT depot. Metformin exposure in BAT was similar to hepatic exposure. Non-specific inhibition of the organic cation transporter (OCT) protein by cimetidine administration eliminated BAT exposure to metformin, demonstrating OCT-mediated uptake. Gene expression profiles of OCTs in BAT revealed ample OCT3 expression in both human and mouse BAT. Incubation of a human brown adipocyte cell models with metformin reduced cellular oxygen consumption in a dose-dependent manner.

CONCLUSION

These results support BAT as a putative metformin target.

Whole-Body Biodistribution, Dosimetry, and Metabolite Correction of [11C]Palmitate: A PET Tracer for Imaging of Fatty Acid Metabolism

INTRODUCTION

Despite the decades long use of [¹¹C]palmitate positron emission tomography (PET)/computed tomography in basic metabolism studies, only personal communications regarding dosimetry and biodistribution data have been published.

METHODS

Dosimetry and biodistribution studies were performed in 2 pigs and 2 healthy volunteers by whole-body [¹¹C]palmitate PET scans. Metabolite studies were performed in 40 participants (healthy and with type 2 diabetes) under basal and hyperinsulinemic conditions. Metabolites were estimated using 2 approaches and subsequently compared: Indirect [¹¹C]CO₂ release and parent [¹¹C]palmitate measured by a solid-phase extraction (SPE) method. Finally, myocardial fatty acid uptake was calculated in a patient cohort using input functions derived from individual metabolite correction compared with population-based metabolite correction.

RESULTS

In humans, mean effective dose was 3.23 (0.02) µSv/MBq, with the liver and myocardium receiving the highest absorbed doses. Metabolite correction using only [¹¹C]CO₂ estimates underestimated the fraction of metabolites in studies lasting more than 20 minutes. Population-based metabolite correction showed excellent correlation with individual metabolite correction in the cardiac PET validation cohort.

CONCLUSION

First, mean effective dose of [¹¹C]palmitate is 3.23 (0.02) µSv/MBq in humans allowing multiple scans using ∼300 MBq [¹¹C]palmitate, and secondly, population-based metabolite correction compares well with individual correction.

Metformin does not affect postabsorptive hepatic free fatty acid uptake, oxidation or resecretion in humans: A 3-month placebo-controlled clinical trial in patients with type 2 diabetes and healthy controls

AIMS

To explore whether the pre-clinical findings that metformin improves lipid metabolism, possibly through modulation of intrahepatic partitioning of fatty acids towards oxidation and away from re-esterification and resecretion as triglycerides (TGs), can be translated to a human setting.

MATERIALS AND METHODS

We performed a 3-month randomized, placebo-controlled, parallel-group clinical trial in patients with type 2 diabetes (T2D; n = 24) and healthy controls (n = 12). Patients with T2D received either placebo (placebo group) or 1000 mg metformin twice daily (metformin group), while healthy subjects were all treated with metformin (control group). Hepatic fatty acid metabolism was measured by [¹¹ C]palmitate positron-emission tomography, hepatic TG secretion and peripheral oxidation by ex vivo labelled [1-¹⁴ C]VLDL-TG and VLDL particle size by TG/apolipoprotein B ratio. Body composition was assessed by dual-energy X-ray and whole-body lipid oxidation by indirect calorimetry.

RESULTS

Metformin treatment for 3 months produced the anticipated decrease in fasting plasma glucose (FPG) in the metformin group (FPG 7.9 ± 1.8 mM [study day 1] vs 6.4 ± 1.1 mM [study day 2]), whereas patients in the placebo group and healthy controls had similar FPG levels before and after the trial (mixed model group vs time interaction; P = .003); however, contrary to our hypothesis, metformin treatment did not affect hepatic lipid metabolism or peripheral oxidation.

CONCLUSION

The observed beneficial effects on lipid metabolism during metformin treatment in humans appear to be secondary to long-term alterations in body composition or glucose homeostasis.

Quantitative PET of liver functions

Improved understanding of liver physiology and pathophysiology is urgently needed to assist the choice of new and upcoming therapeutic modalities for patients with liver diseases. In this review, we focus on functional PET of the liver: 1) Dynamic PET with 2-deoxy-2-[18F]fluoro-D-galactose (18F-FDGal) provides quantitative images of the hepatic metabolic clearance Kmet (mL blood/min/mL liver tissue) of regional and whole-liver hepatic metabolic function. Standard-uptake-value (SUV) from a static liver 18F-FDGal PET/CT scan can replace Kmet and is currently used clinically. 2) Dynamic liver PET/CT in humans with 11C-palmitate and with the conjugated bile acid tracer [N-methyl-11C]cholylsarcosine (11C-CSar) can distinguish between individual intrahepatic transport steps in hepatic lipid metabolism and in hepatic transport of bile acid from blood to bile, respectively, showing diagnostic potential for individual patients. 3) Standard compartment analysis of dynamic PET data can lead to physiological inconsistencies, such as a unidirectional hepatic clearance of tracer from blood (K1; mL blood/min/mL liver tissue) greater than the hepatic blood perfusion. We developed a new microvascular compartment model with more physiology, by including tracer uptake into the hepatocytes from the blood flowing through the sinusoids, backflux from hepatocytes into the sinusoidal blood, and re-uptake along the sinusoidal path. Dynamic PET data include information on liver physiology which cannot be extracted using a standard compartment model. In conclusion, SUV of non-invasive static PET with 18F-FDGal provides a clinically useful measurement of regional and whole-liver hepatic metabolic function. Secondly, assessment of individual intrahepatic transport steps is a notable feature of dynamic liver PET.