Jensen, Michael D.

PET radiopharmaceuticals can noninvasively measure free fatty acid (FFA) tissue uptake. Investigators often use PET scan-derived data to calculate FFA flux. We tested whether the [1-11C]palmitate PET measures of palmitate flux provide results equivalent to a continuous infusion of [U-13C]palmitate. Nine volunteers participated in study 1 to evaluate whether a rapidly (10–20 s) given bolus of [1-11C]palmitate affects calculated flux results. Thirty volunteers participated in study 2, which was identical to study 1 except that the [1-11C]palmitate bolus was given over 1 min. Volunteers in both studies also received a continuous intravenous infusion of [U-13C]palmitate. Plasma palmitate concentrations and enrichment were measured by liquid chromatography-mass spectrometry. The PET/CT images were analyzed on a workstation running PMOD. Palmitate flux was estimated using PET time-activity curve (TAC) data from regions of interest in the left ventricle (LV) and aorta both with and without hybrid TACs that employed the11CO2-corrected data for the first 5 min and the11CO2-corrected blood radioactivity for the remainder of the PET scan. Palmitate flux in study 1 measured with PET [1-11C]palmitate and [U-13C]palmitate were not correlated, and the PET [1-11C]palmitate flux was significantly less than the [U-13C]palmitate measured flux. In study 2, the palmitate flux using PET [1-11C]palmitate hybrid LV models provided closer mean estimates of [U-13C]palmitate measured flux. The best PET calculation approaches predicted 64% of the interindividual variance in [U-13C]palmitate measured flux. Palmitate kinetics measured using [1-11C]palmitate/PET do not provide the same palmitate kinetic results as the continuous infusion [U-13C]palmitate approach.

ObjectiveThe relationship between inflammation, obesity, and adverse metabolic conditions is associated with adipose tissue macrophages (ATM). This study compared the measurements of human ATM using flow cytometry, immunohistochemistry (IHC), and real‐time polymerase chain reaction (RT‐PCR) of ATM markers.MethodsA new software program (AMCounter) was evaluated to help measure ATM using IHC, and this was compared to flow cytometry and RT‐PCR.ResultsIHC had good intraindividual reproducibility for total (CD68), proinflammatory (CD14), and anti‐inflammatory (CD206) ATM. The AMCounter improved interreader agreement and was more time efficient. Flow cytometry had acceptable intraindividual reproducibility for the percentage of CD68+ cells that were CD14+ or CD206+, but not for ATMs per gram of tissue. ATMs per gram of tissue was much greater using IHC than flow cytometry. The flow cytometry and IHC measures of ATM from the same biopsies were not correlated. There were statistically significant correlations between RT‐PCR CD68 and IHC CD68, CD14, and CD206 ATMs per 100 adipocytes. Also of interest were statistically significant correlations between RT‐PCR CD68 and IHC CD68, CD14, and adipose flow cytometry measures of CD68+, CD68+/CD14+, and CD68+/CD206+ ATMs per gram of tissue.ConclusionsThe AMCounter software helps provide reproducible and efficient measures of IHC ATMs. Flow cytometry, IHC, and RT‐PCR measures of adipose inflammation provide somewhat different information.

We investigated the effects of meal ingestion on intramyofibrillar (IMF) and subsarcolemmal (SS) ceramide metabolism in volunteers ranging from lean to obese. Thirty-eight women and men underwent a steady-state meal ingestion protocol that included a 6.5-h infusion of [U-13C]palmitate and muscle biopsies 1.5 and 6.5 h after starting the tracer infusion. We measured IMF and SS sphingolipid concentrations and the contribution of plasma palmitate to intramyocellular C16:0 ceramide by use of LC-MS-MS. In response to meal ingestion SS C24 ceramide concentrations, but not C14-C20 concentrations, increased significantly. IMF ceramide concentrations did not change. The increases in SS C24 ceramides were negatively related to parameters of insulin resistance. The fractional contribution of plasma palmitate to intramyocellular C16:0 ceramides in both IMF and SS fractions was inversely related to overweight status (β = –0.432, P = 0.0095 and β = –0.443, P = 0.0058, respectively). These data indicate that meal ingestion has differing effects on SS ceramide subspecies and suggest that the fractional de novo synthesis of intramyocellular ceramide from plasma palmitate in the postprandial condition is reduced in those who are overweight.

AbstractContextAlthough the long-term effects of testosterone on adipose tissue lipid metabolism in men have been defined, the short-term regulation of these effects is not well understood.ObjectiveWe examined the effects of acute testosterone withdrawal on subcutaneous abdominal and femoral adipose tissue fatty acid (FA) storage and cellular mechanisms.DesignThis was a prospective, randomized trial.SettingMayo Clinic Clinical Research Unit.Patients or ParticipantsThirty-two male volunteers ages 18 to 50 participated in these studies.InterventionsVolunteers were randomized to receive (1) no treatment (control), (2) injections (7.5 mg) of Lupron®, or (3) Lupron and testosterone (L+T) replacement for 49 days, resulting in 4 weeks of sex steroid suppression in the Lupron group.Main Outcome MeasuresWe measured body composition, fat cell size, adipose tissue meal FA and direct free FA storage, lipoprotein lipase (LPL), acyl coenzyme A synthetase (ACS), diacylglycerol acyltransferase activities, and CD36 content.ResultsCompared with control and L+T groups, acute testosterone deficiency resulted in greater femoral adipose tissue meal FA storage rates, fasting and fed LPL activity, and ACS activity.ConclusionsThese results suggest that in men, testosterone plays a tonic role in restraining FA storage in femoral adipose tissue via suppression of LPL and ACS activities. FA storage mechanisms in men appear sensitive to short-term changes in testosterone concentrations.

We investigated the relationship between insulin resistance markers and subsarcolemmal (SS) and intramyofibrillar (IMF) ceramide concentrations, as well as the contribution of plasma palmitate (6.5-h infusion of [U-13C]palmitate) to intramyocellular ceramides. Seventy-six postabsorptive men and women had muscle biopsies 1.5, 6.5, and 24 h after starting the tracer infusion. Concentrations and enrichment of muscle ceramides were measured by liquid chromatography-tandem mass spectrometry. We found that HOMA of insulin resistance, plasma insulin, and triglyceride concentrations were positively correlated with SS C16:0 and C18:1 ceramide, but not SS C14:0-Cer, C20:0-Cer, C24:0-Cer, and C24:1-Cer concentrations; IMF ceramide concentrations were not correlated with any metabolic parameters. The fractional contribution of plasma palmitate to 16:0 ceramide was greater in SS than IMF (SS, 18.2% vs. IMF, 8.7%; P = 0.0006). Plasma insulin concentrations correlated positively with the fractional contribution of plasma palmitate to SS 16:0 ceramide. The fractional contribution of plasma palmitate to intramyocellular SS 16:0 ceramide was positively correlated with SS C16:0 ceramide concentrations (γ = 0.435; P = 0.002). We conclude that skeletal muscle SS ceramides, especially C16 to C18 chain lengths and the de novo synthesis of intramyocellular ceramide from plasma palmitate are associated with markers of insulin resistance.

Abstract Context and Objective: Adipose tissue insulin resistance may cause hepatic and skeletal muscle insulin resistance by releasing excess free fatty acids (FFAs). Because no consensus exists on how to quantify adipose tissue insulin sensitivity we compared three methods for measuring adipose tissue insulin sensitivity: the single step insulin clamp, the multistep pancreatic clamp, and the adipose tissue insulin resistance index (Adipo-IR). Design and Participants: We studied insulin sensitivity in 25 adults by measuring the insulin concentration resulting in 50% suppression of palmitate flux (IC50) using both a multistep pancreatic clamp and a one-step hyperinsulinemic-euglycemic clamp. Palmitate kinetics were measured using a continuous infusion of [U-13C]palmitate. Adipo-IR was calculated from fasting insulin and fasting FFA concentrations. Results: Adipo-IR was reproducible (sample coefficient of variability, 10.0%) and correlated with the IC50 measured by the multistep pancreatic clamp technique (r, 0.86; P < 0.001). Age and physical fitness were significant predictors of the residual variation between Adipo-IR and IC50, with a positive relationship with age (r, 0.47; P = 0.02) and a negative association with VO2 peak (r, −0.46; P = 0.02). Likewise, IC50 measured by the multistep pancreatic clamp technique correlated with IC50 measured using the one-step hyperinsulinemic-euglycemic clamp technique (r, 0.73; P < 0.001). Conclusion: Adipo-IR and the one-step hyperinsulinemic-euglycemic clamp technique using a palmitate tracer are good predictors of a gold standard measure of adipose tissue insulin sensitivity. However, age and physical fitness systematically affect the predictive values. Although Adipo-IR is suitable for larger population studies, the multistep pancreatic clamp technique is probably needed for mechanistic studies of adipose tissue insulin action.

AbstractContext:Lipoprotein lipase (LPL) activity is considered the rate-limiting step of very-low-density-lipoprotein triglycerides (VLDL-TG) tissue storage, and has been suggested to relate to the development of obesity as well as insulin resistance and type 2 diabetes.Objective:The objective of the study was to assess the relationship between the quantitative storage of VLDL-TG fatty acids and LPL activity and other storage factors in muscle and adipose tissue. In addition, we examine whether such relations were influenced by type 2 diabetes.Design:We recruited 23 men (12 with type 2 diabetes, 11 nondiabetic) matched for age and body mass index. Postabsorptive VLDL-TG muscle and subcutaneous adipose tissue (abdominal and leg) quantitative storage was measured using tissue biopsies in combination with a primed-constant infusion of ex vivo triolein labeled [1-14C]VLDL-TG and a bolus infusion of ex vivo triolein labeled [9,10-3H]VLDL-TG. Biopsies were analyzed for LPL activity and cellular storage factors.Results:VLDL-TG storage rate was significantly greater in men with type 2 diabetes compared with nondiabetic men in muscle tissue (P = 0.02). We found no significant relationship between VLDL-TG storage rate and LPL activity or other storage factors in muscle or adipose tissue. However, LPL activity correlated with fractional VLDL-TG storage in abdominal fat (P = 0.04).Conclusions:Men with type 2 diabetes have increased VLDL-TG storage in muscle tissue, potentially contributing to increased intramyocellular triglyceride and ectopic lipid deposition. Neither muscle nor adipose tissue storage rates were related to LPL activity. This argues against LPL as a rate-limiting step in the postabsorptive quantitative storage of VLDL-TG.

OBJECTIVE We compared 3-year achievement of an American Diabetes Association composite treatment goal (HbA1c <7.0%, LDL cholesterol <100 mg/dL, and systolic blood pressure <130 mmHg) after 2 years of intensive lifestyle-medical management intervention, with and without Roux-en-Y gastric bypass, with one additional year of usual care. RESEARCH DESIGN AND METHODS A total of 120 adult participants, with BMI 30.0–39.9 kg/m2 and HbA1c ≥8.0%, were randomized 1:1 to two treatment arms at three clinical sites in the U.S. and one in Taiwan. All patients received the lifestyle-medical management intervention for 24 months; half were randomized to also receive gastric bypass. RESULTS At 36 months, the triple end point goal was met in 9% of lifestyle-medical management patients and 28% of gastric bypass patients (P = 0.01): 10% and 19% lower than at 12 months. Mean (SD) HbA1c values at 3 years were 8.6% (3.5) and 6.7% (2.0) (P < 0.001). No lifestyle-medical management patient had remission of diabetes at 36 months, whereas 17% of gastric bypass patients had full remission and 19% had partial remission. Lifestyle-medical management patients used more medications than gastric bypass patients: mean (SD) 3.8 (3.3) vs. 1.8 (2.4). Percent weight loss was mean (SD) 6.3% (16.1) in lifestyle-medical management vs. 21.0% (14.5) in gastric bypass (P < 0.001). Over 3 years, 24 serious or clinically significant adverse events were observed in lifestyle-medical management vs. 51 with gastric bypass. CONCLUSIONS Gastric bypass is more effective than lifestyle-medical management intervention in achieving diabetes treatment goals, mainly by improved glycemic control. However, the effect of surgery diminishes with time and is associated with more adverse events.