[Show abstract][Hide abstract] ABSTRACT: Hepatic lipotoxicity results from and contributes to obesity-related disorders. It is a challenge to study human metabolism of fatty acids (FAs) in the liver. We combined (11)C-palmitate imaging by positron emission tomography (PET) with compartmental modeling to determine rates of hepatic FA uptake, oxidation, and storage, as well as triglyceride release in pigs and human beings.
Anesthetized pigs underwent (11)C-palmitate PET imaging during fasting (n = 3) or euglycemic hyperinsulinemia (n = 3). Metabolic products of FAs were measured in arterial, portal, and hepatic venous blood. The imaging methodology then was tested in 15 human subjects (8 obese subjects); plasma (11)C-palmitate kinetic analyses were used to quantify systemic and visceral lipolysis.
In pigs, PET-derived and corresponding measured FA fluxes (FA uptake, esterification, and triglyceride FA release) did not differ and were correlated with each other. In human beings, obese subjects had increased hepatic FA oxidation compared with controls (mean +/- standard error of the mean, 0.16 +/- 0.01 vs 0.08 +/- 0.01 micromol/min/mL; P = .0007); FA uptake and esterification rates did not differ between obese subjects and controls. Liver FA oxidation correlated with plasma insulin levels (r = 0.61, P = .016), adipose tissue (r = 0.58, P = .024), and systemic insulin resistance (r = 0.62, P = .015). Hepatic FA esterification correlated with the systemic release of FA into plasma (r = 0.71, P = .003).
PET imaging can be used to measure FA metabolism in the liver. By using this technology, we found that obese individuals have increased hepatic oxidation of FA, in the context of adipose tissue insulin resistance, and increased FA flux from visceral fat. FA flux from visceral fat is proportional with the mass of the corresponding depot.
[Show abstract][Hide abstract] ABSTRACT: Objective. Rapid weight loss with very-low-calorie diet (VLCD) is known to improve insulin sensitivity and decrease adipose tissue masses. The aim was to investigate the effects of VLCD on adipose tissue regional glucose uptake (rGU) and perfusion and their association with adipokines. Research design and methods. Sixteen healthy obese (body mass index 33±1.1 kg/m2) subjects underwent VLCD for 6 weeks. RGU and perfusion were measured using [18F]-fluoro-deoxy-glucose, [15O]H2O and positron emission tomography. Results. Blood-flow and rGU expressed per gram of adipose tissue were higher in visceral fat compared to abdominal subcutaneous fat (P<0.01 for both). Dieting decreased weight by 11±0.9 kg (P<0.0001). Visceral adipose fat decreased by 25% (P<0.001) and abdominal subcutaneous fat by 16% (P<0.001). Whole body insulin sensitivity increased by 33% (P<0.01). Perfusion of both fat depots decreased (P<0.001), while rGU remained unchanged. Among the adipokines, leptin and interleukin-6 levels seemed to be associated with abdominal subcutaneous and intra-abdominal adipose tissue insulin resistance but not with adipose tissue perfusion. Conclusions. Abdominal adipose tissue perfusion and rGU are not related in obesity. Rapid weight loss decreases perfusion through adipose tissue depots but has no influence on rGU demonstrating the ‘sink’ role of adipose tissue.
[Show abstract][Hide abstract] ABSTRACT: The liver is perfused through the portal vein and hepatic artery. Quantification of hepatic glucose uptake (HGU) using PET requires the use of an input function for both the hepatic artery and portal vein. The former can be generally obtained invasively, but blood withdrawal from the portal vein is not practical in humans. The aim of this study was to develop and validate a new technique to obtain quantitative HGU by estimating the input function from PET images.
Normal pigs (n = 12) were studied with [18F]FDG PET, in which arterial and portal blood time-activity curves (TAC) were determined invasively to serve as reference measurements. The present technique consisted of two characteristics, i.e. using a model input function and simultaneously fitting multiple liver tissue TACs from images by minimizing the residual sum of square between the tissue TACs and fitted curves. The input function was obtained from the parameters determined from the fitting. The HGU values were computed by the estimated and measured input functions and compared between the methods.
The estimated input functions were well reproduced. The HGU values, ranging from 0.005 to 0.02 ml/min per ml, were not significantly different between the two methods (r = 0.95, p < 0.001). A Bland-Altman plot demonstrated a small overestimation by the image-derived method with a bias of 0.00052 ml/min per g for HGU.
The results presented demonstrate that the input function can be estimated directly from the PET image, supporting the fully non-invasive assessment of liver glucose metabolism in human studies.
No preview · Article · Jul 2009 · European Journal of Nuclear Medicine
[Show abstract][Hide abstract] ABSTRACT: Obesity is associated with increased fatty acid uptake in the myocardium, and this may have deleterious effects on cardiac function. The aim of this study was to evaluate how weight loss influences myocardial metabolism and cardiac work in obese adults. Thirty-four obese (mean body mass index 33.7 +/- 0.7 kg/m(2)) but otherwise healthy subjects consumed a very low calorie diet for 6 weeks. Cardiac substrate metabolism and work were measured before and after the diet. Myocardial fatty acid uptake was measured in 18 subjects using fluorine-18-fluoro-6-thia-heptadecanoic acid and positron emission tomography, and myocardial glucose uptake was measured in 16 subjects using fluorine-18-2-fluoro-2-deoxyglucose. Myocardial structure and cardiac function were measured using magnetic resonance imaging. Consumption of the very low calorie diet decreased weight (-11.2 +/- 0.6 kg, p <0.0001). Myocardial fatty acid uptake decreased from 4.2 +/- 0.4 to 2.9 +/- 0.2 micromol/100 g/min (p <0.0001). Myocardial mass decreased by 7% (p <0.005), and cardiac work decreased by 26% (p <0.0001). Whole-body insulin sensitivity increased by 33% (p <0.01), but insulin-stimulated myocardial glucose uptake remained unchanged (p = 0.90). Myocardial triglyceride content decreased by 31% (n = 8, p = 0.076). In conclusion, weight reduction decreases myocardial fatty acid uptake in parallel with myocardial mass and cardiac work. These results show that the increased fatty acid uptake found in the hearts of obese patients can be reversed by weight loss.
No preview · Article · Jun 2009 · The American journal of cardiology
[Show abstract][Hide abstract] ABSTRACT: Even minor renal dysfunction is a powerful cardiovascular risk factor. The abnormalities in coronary and peripheral artery function in different stages of chronic kidney disease (CKD) remain poorly understood. Our aim was to test by a positron emission tomography (PET)-based method whether microvascular dysfunction, an early marker of coronary dysfunction, exists already in early stages of CKD.
Myocardial blood flow was measured at baseline and during dipyridamole-induced hyperaemia by PET. Peripheral artery endothelial function was examined by measuring flow-mediated dilatation (FMD) of the brachial artery at rest and during reactive hyperaemia. Twenty-two patients with moderate to severe kidney failure and 10 healthy controls were investigated. Diabetic patients were excluded. Baseline characteristics were similar between the groups with the exception of antihypertensive medication in all CKD patients.
The basal myocardial perfusion was statistically significantly higher in CKD patients than observed values in similarly aged controls. There was a statistically significant negative correlation between the baseline myocardial perfusion and the estimated glomerular filtration rate. Coronary flow reserve was comparable to healthy controls in all patients. FMD was significantly reduced in all patients with CKD regardless of the stage of kidney failure.
Coronary flow reserve was normal although baseline myocardial blood flow was increased in all CKD patients as compared to healthy controls. Peripheral endothelial dysfunction was detected in all patients. Our findings suggest that coronary perfusion and peripheral vascular function are disturbed by different mechanisms in patients with CKD.
Full-text · Article · May 2009 · Nephrology Dialysis Transplantation
[Show abstract][Hide abstract] ABSTRACT: PurposeThe liver is perfused through the portal vein and the hepatic artery. When its perfusion is assessed using positron emission
tomography (PET) and 15O-labeled water (H2
15O), calculations require a dual blood input function (DIF), i.e., arterial and portal blood activity curves. The former can
be generally obtained invasively, but blood withdrawal from the portal vein is not feasible in humans. The aim of the present
study was to develop a new technique to estimate quantitative liver perfusion from H2
15O PET images with a completely non-invasive approach.
MethodsWe studied normal pigs (n = 14) in which arterial and portal blood tracer concentrations and Doppler ultrasonography flow rates were determined invasively
to serve as reference measurements. Our technique consisted of using model DIF to create tissue model function and the latter
method to simultaneously fit multiple liver time–activity curves from images. The parameters obtained reproduced the DIF.
Simulation studies were performed to examine the magnitude of potential biases in the flow values and to optimize the extraction
of multiple tissue curves from the image.
ResultsThe simulation showed that the error associated with assumed parameters was <10%, and the optimal number of tissue curves
was between 10 and 20. The estimated DIFs were well reproduced against the measured ones. In addition, the calculated liver
perfusion values were not different between the methods and showed a tight correlation (r = 0.90).
ConclusionIn conclusion, our results demonstrate that DIF can be estimated directly from tissue curves obtained through H2
15O PET imaging. This suggests the possibility to enable completely non-invasive technique to assess liver perfusion in patho-physiological
Full-text · Article · Oct 2008 · European journal of nuclear medicine and molecular imaging
[Show abstract][Hide abstract] ABSTRACT: Rapid weight loss with very-low-calorie diet (VLCD) is known to improve insulin sensitivity and decrease adipose tissue masses. The aim was to investigate the effects of VLCD on adipose tissue regional glucose uptake (rGU) and perfusion and their association with adipokines.
Sixteen healthy obese (body mass index 33+/-1.1 kg/m(2)) subjects underwent VLCD for 6 weeks. RGU and perfusion were measured using [(18)F]-fluoro-deoxy-glucose, [(15)O]H(2)O and positron emission tomography.
Blood-flow and rGU expressed per gram of adipose tissue were higher in visceral fat compared to abdominal subcutaneous fat (P<0.01 for both). Dieting decreased weight by 11+/-0.9 kg (P<0.0001). Visceral adipose fat decreased by 25% (P<0.001) and abdominal subcutaneous fat by 16% (P<0.001). Whole body insulin sensitivity increased by 33% (P<0.01). Perfusion of both fat depots decreased (P<0.001), while rGU remained unchanged. Among the adipokines, leptin and interleukin-6 levels seemed to be associated with abdominal subcutaneous and intra-abdominal adipose tissue insulin resistance but not with adipose tissue perfusion.
Abdominal adipose tissue perfusion and rGU are not related in obesity. Rapid weight loss decreases perfusion through adipose tissue depots but has no influence on rGU demonstrating the 'sink' role of adipose tissue.
No preview · Article · Oct 2008 · Annals of Medicine
[Show abstract][Hide abstract] ABSTRACT: Weight loss has been shown to decrease liver fat content and whole-body insulin resistance. The current study was conducted to investigate the simultaneous effects of rapid weight reduction with a very-low-calorie diet on liver glucose and fatty acid metabolism and liver adiposity.
We hypothesized that liver insulin resistance and free fatty acid uptake would decrease after weight loss and that they are associated with reduction of liver fat content.
Thirty-four healthy obese subjects (body mass index, 33.7 +/- 8.0 kg/m(2)) were studied before and after a very-low-calorie diet for 6 wk. Hepatic glucose uptake and endogenous glucose production were measured with [(18)F]fluorodeoxyglucose during hyperinsulinemic euglycemia and fasting hepatic fatty acid uptake with [(18)F]fluoro-6-thia-heptadecanoic acid and positron emission tomography. Liver volume and fat content were measured using magnetic resonance imaging and spectroscopy.
Subjects lost weight (11.2 +/- 2.9 kg; P < 0.0001). Liver volume decreased by 11% (P < 0.002), which was partly explained by decreased liver fat content (P < 0.0001). Liver free fatty acid uptake was 26% lower after weight loss (P < 0.003) and correlated with the decrement in liver fat content (r = 0.54; P < 0.03). Hepatic glucose uptake during insulin stimulation was unchanged, but the endogenous glucose production decreased by 40% (P < 0.04), and hepatic insulin resistance by 40% (P < 0.05).
The liver responds to a 6-wk period of calorie restriction with a parallel reduction in lipid uptake and storage, accompanied by enhancement of hepatic insulin sensitivity and clearance.
Full-text · Article · Oct 2008 · Journal of Clinical Endocrinology & Metabolism
[Show abstract][Hide abstract] ABSTRACT: Children with persistent Chlamydia pneumoniae infection may be at increased risk for atherosclerosis. The impact of antimicrobial therapy for primary prevention of atherosclerotic cardiovascular disease is unsolved.
The purpose of this study was to determine whether treatment with antimicrobial agents effective against C pneumoniae during childhood, regardless of indication, has a favorable influence on the arterial wall-thickness in children by the time they reach adolescence.
The association of macrolide, tetracycline, quinolone, and rifamycin use (number of exposure events) between ages 5 and 13 years with carotid and aortic intima-media thickness at age 13 years was investigated among 508 healthy children. Information about the use of medications was obtained from the Finnish prescription register. Arterial intima-media thickness was measured with a high-resolution ultrasound.
Mean aortic intima-media thickness showed a significant direct association with the number of antichlamydial antimicrobial exposure events also after controlling for established atherosclerotic risk factors. Elevated C-reactive protein level had an additional effect on aortic intima-media thickness in a multivariable model. Carotid intima-media thickness was not associated with the number of preceding antichlamydial treatments.
Recurrent antichlamydial treatments in childhood have no favorable influence on early vascular changes but are associated with increased intima-media thickness in the abdominal aorta. These findings suggest that the use of antimicrobial agents does not offer protection against the potential atherogenicity of repeated infectious insults.
[Show abstract][Hide abstract] ABSTRACT: Breast feeding in infancy may be associated with reduced cardiovascular morbidity in adulthood. We examined the association between breast feeding in infancy and arterial function and structure in adulthood in a population-based cohort of Finnish adults.
Noninvasive ultrasound was used to measure brachial artery flow-mediated dilatation (FMD), carotid artery intima-media thickness (IMT) and carotid artery compliance (CAC) in 1667 young adults participating in the Cardiovascular Risk in Young Finns Study with data on early nutrition.
Maximal FMD was higher in breast-fed men compared to formula-fed men (7.2+/-4.0 vs 5.9+/-3.4%, P=0.029) while no differences were seen between breast-fed and formula-fed women (8.9+/-4.5 vs 8.8+/-5.0%, P=0.84). In men, the multivariable correlates of FMD included the group variable for breast feeding (P=0.014), birth weight (P=0.043), waist circumference (P<0.001) and baseline brachial artery diameter (P<0.001). In women, the multivariable correlates of FMD were birth weight (P=0.02), waist circumference (P<0.001) and brachial artery baseline diameter (P<0.001). Breast feeding was not significantly associated with IMT or CAC in multivariable models.
Adult men who have been breast fed have better brachial endothelial function compared to men who have been formula fed.
Preview · Article · Mar 2008 · European journal of clinical nutrition
[Show abstract][Hide abstract] ABSTRACT: Exercise training seems to restore impaired vascular function in both peripheral and myocardial vessels in patients with coronary artery and peripheral vascular disease or in patients with risk factors for these diseases. However, the results on the effects of exercise training on vascular function in apparently healthy subjects are controversial. We studied the effects of long-term volitionally increased physical activity on peripheral and myocardial vascular function in nine young healthy male monozygotic twin pairs discordant for physical activity and fitness. The brothers were divided into more (MAG) and less active groups according to physical activity and fitness. The difference between groups in VO(2max) was 18+/-10% (P<0.001). Myocardial perfusion at rest, during adenosine-induced vasodilatation and during cold-pressor test and myocardial oxygen consumption were measured with positron emission tomography. In addition, endothelial function was measured using ultrasound in brachial and left anterior descending coronary arteries, and standard echocardiographic measures were taken. No differences were observed in myocardial perfusion measurements between groups. MAG tended to have a lower oxygen extraction fraction (P=0.06), but oxygen consumption was similar between the groups. No differences were found in coronary artery, myocardial resistance vessel or peripheral endothelial function between groups. These results suggest that when the effects of heredity are controlled, myocardial perfusion reserve and endothelial function, both in peripheral arteries and myocardial vessels, are not enhanced by increased physical activity and fitness in young healthy adult men.
Full-text · Article · Apr 2007 · Scandinavian Journal of Medicine and Science in Sports
[Show abstract][Hide abstract] ABSTRACT: Alterations of free fatty acid (FA) metabolism in several organs are implicated in the pathogenesis of chronic disorders. The aim of this study was to investigate the biodistribution and partitioning of the FA analog, 14(R,S)-(18)F-fluoro-6-thia-heptadecanoic acid ((18)F-FTHA), across different lipid pools in plasma and in metabolically important organs and its response to insulin.
Eight anesthetized pigs were studied during fasting or euglycemic insulin stimulation. Plasma samples from the carotid artery, hepatic vein, and portal vein were collected at 10 and 40 min after (18)F-FTHA injection via indwelling catheters. The animals were then sacrificed and tissue biopsies rapidly obtained from the heart, brain, liver, subcutaneous and visceral fat, pancreas, intestine, and skeletal muscle. Radioactivity was assessed in the FA, phospholipid, and triglyceride or glycerol ester pools.
The tissue-to-plasma intact (18)F-FTHA ratio was high in all tissues, with the highest values being in the heart and liver; (18)F-FTHA accumulated in the brain to a significant extent. Hyperinsulinemia was associated with higher plasma (18)F-FTHA clearance (P < 0.05) and lower labeled triglyceride appearance (P <or= 0.01) than those associated with fasting, indicating faster tissue removal and suppressed hepatic triglyceride release. Tracer retention was enhanced in skeletal muscle, pancreas, and visceral fat (P < 0.05 vs. fasting). Under both study conditions, tissue radioactivity was greatly accounted for by glycerol ester.
(18)F-FTHA is a promising tracer in PET imaging of metabolically important organs, which are currently inaccessible in vivo. Physiologic hyperinsulinemia enhances plasma tracer clearance in fat, skeletal muscle, and pancreas.
No preview · Article · Mar 2007 · Journal of Nuclear Medicine
[Show abstract][Hide abstract] ABSTRACT: The levels of the surrogate markers of cholesterol absorption (cholestanol and plant sterols) and synthesis (cholesterol precursors) in serum have suggested that in adult type 1 diabetes, cholesterol absorption is high and synthesis is low compared with type 2 diabetic or control subjects. Accordingly, these findings were further studied in children with type 1 diabetes.
Forty-eight children with diabetes were compared with 79 age- and sex-matched control subjects. The serum ratios of cholesterol absorption and synthesis markers were measured with gas-liquid chromatography. The study population was divided into triads (combining the two lowest triads) by serum cholestanol ratios of the control subjects indicating low to high cholesterol absorption efficiency.
The ratios of the absorption and synthesis markers were similar in case and control subjects, and they were negatively related to each other in control subjects, being less consistent in diabetic patients. Thus, high cholesterol absorption was associated with low synthesis. Plant sterol ratios increased significantly with increasing cholestanol triads in both groups, but the values in the lowest triads were higher in case versus control subjects.
Homeostasis between cholesterol absorption and synthesis is maintained in control children and somewhat less consistently in those with diabetes. The higher plant sterol ratios in diabetic versus control subjects in the lowest cholestanol triads suggest that cholesterol absorption is higher in children with diabetes versus control subjects but only within the range of low cholesterol absorption.
[Show abstract][Hide abstract] ABSTRACT: To describe the background and assessment of inflammatory markers and endothelial function in atherosclerosis.
Recent observations have related several inflammation markers, including cytokines and chemokines, soluble adhesion molecules, and acute-phase reactants, to the pathophysiology of atherosclerosis. Chronic inflammatory states such as rheumatoid arthritis and systemic lupus erythematosus have been identified as independent risk factors for early atherosclerosis. The role of endothelial function in atherosclerosis has been elucidated by clinical studies that have demonstrated that the status of vascular endothelium may modify the effects of risk factors on the development of atherosclerosis. These observations support the response-to-injury theory of atherosclerosis that emphasizes the role of endothelium in atherosclerosis.
Inflammation and endothelial function play significant roles in the pathogenesis of atherosclerosis. Elevations in certain inflammatory mediators as well as evidence of endothelial dysfunction are related to increased risk of future cardiovascular morbidity. The value of measuring inflammatory markers and endothelial function in clinical practice remains to be defined.
No preview · Article · Oct 2006 · Current Opinion in Clinical Nutrition and Metabolic Care
[Show abstract][Hide abstract] ABSTRACT: The glucose analog (18)F-FDG is commonly used to quantify regional glucose uptake in vivo. The aim of this study was to test whether the analysis of plasma (18)F-FDG kinetics could be used to estimate endogenous glucose production (EGP) and the total rate of appearance (Ra), total rate of disappearance (Rd), and the metabolic clearance rate (MCR) of glucose.
Fourteen pigs were coinjected with (18)F-FDG and 6,6-(2)H-glucose ((2)H-G) during fasting (n = 6) and during physiologic (1.0 mU.kg(-1).min(-1), n = 4) and supraphysiologic (5.0 mU.kg(-1).min(-1), n = 4) euglycemic hyperinsulinemia. Arterial plasma was sampled for 180 min to quantify the parameters for the 2 tracers.
Fasting Rd((2))(H-G) and Rd(FDG) were 12.3 +/- 2.1 and 13.3 +/- 1.3 micromol.kg(-1).min(-1) (difference not statistically significant [NS]). M values were more than doubled between the 2 clamp studies (P < 0.0001). Rd((2))(H-G) and Rd(FDG) were dose-dependently higher during the hyperinsulinemic state (19.8 +/- 3.7 vs. 18.9 +/- 1.1 and 31.4 +/- 4.1 vs. 31.9 +/- 2.3 in 1.0 and 5.0 mU.kg(-1).min(-1) studies, respectively; difference between tracers NS) than during the fasting state, with a parallel suppression of EGP((2))(H-G) and EGP(FDG). Parameters estimated by (18)F-FDG and (2)H-G were equivalent in all groups; their agreement was confirmed by Bland-Altman examination. Total Rd(FDG) correlated with Rd((2))(H-G) (r = 0.74; P = 0.003), M (r = 0.92; P = 0.001), MCR((2))(H-G) (r = 0.52; P = 0.037), and EGP((2))(H-G) (r = -0.71; P = 0.004). EGP(FDG) correlated with EGP((2))(H-G) (r = 0.62; P = 0.018), Rd((2))(H-G) (r = -0.78; P = 0.001), and MCR((2))(H-G) (r = -0.67; P = 0.008). The (18)F-FDG mean transit time correlated inversely with the M and Rd values and positively with EGP.
The glucose analog (18)F-FDG can be used in the simultaneous estimation of whole-body glucose turnover and production and regional (18)F-FDG PET measurements under both fasting and insulin-stimulated conditions.
Full-text · Article · Jun 2006 · Journal of Nuclear Medicine
[Show abstract][Hide abstract] ABSTRACT: Brachial artery FMD (flow-mediated dilatation) is widely used as a marker of systemic arterial endothelial function. FMD, however, shows considerable 25% day-to-day variation that hinders its clinical use. The reasons for this variability are poorly characterized. Therefore the present study was designed to clarify factors responsible for the hourly variation in endothelial function, including consuming a low-fat meal and circadian rhythms in endogenous hormonal levels. Brachial artery FMD, along with serum glucose, triacylglycerols (triglycerides) and levels of several hormones were measured six times per day on two separate days 1 week apart. On one day, the subjects (healthy males: n=12, mean age, 24 years) ate a light breakfast and a standardized lunch (23.5% fat, 48.7% carbohydrate and 27.8% protein). On the other day, they had a similar breakfast after which they fasted. Postprandial FMD values (both after breakfast and after lunch) were similar to baseline FMD. FMD showed a 28% hourly variation and 27% weekly variation. Variation in plasma levels of insulin (P=0.02) associated negatively and DHPG (3,4-dihydroxyphenylglycol) (P=0.001), a marker of sympathetic nervous activation, associated positively with variation in FMD. The effects of DHPG and insulin on FMD were independent of changes in baseline brachial artery diameter, although DHPG was also inversely associated with baseline diameter. Eating a regular low-fat meal does not have any measurable effects on brachial artery endothelial function. These data suggest that strict requirements for fasting conditions may be unnecessary when measuring peripheral endothelial function using the ultrasound technique. Circadian variation in serum insulin and sympathetic tone are physiological determinants of endothelial function.
[Show abstract][Hide abstract] ABSTRACT: The liver is fundamental in regulating lipid metabolism, and it supplies fatty acids (FA) to the rest of the body in the form of triglycerides (TG); the time-related relevance of this process is incompletely defined. The aim of the study was to investigate the appearance of labeled TG in the hepatic vascular bed after [11C]palmitate injection during fasting and insulin stimulation.
Plasma [11C]palmitate kinetics in arterial, portal and hepatic venous lipid fractions was studied in eight anesthetized pigs during fasting or euglycemic hyperinsulinemia. Plasma analyses were conducted at 10 and 40 min after tracer injection. Corresponding liver positron emission tomography (PET) images were acquired for the semiquantitative determination of hepatic FA uptake.
At 10 min, plasma levels of unchanged [11C]palmitate were lower in hyperinsulinemic than in fasting experiments in the artery and in the portal vein (P< or=.03), suggesting faster clearance. Levels of unmetabolized [11C]palmitate did not differ between portal and arterial plasma. In the fasting state, a tendency to a positive arterial and portal vs. hepatic venous gradient was observed, indicative of net hepatic [11C]palmitate extraction. Labeled TG were already detectable at 10 min (fasting vs. hyperinsulinemia, ns) and were higher in fasting than in hyperinsulinemic animals at 40 min (92+/-1% and 82+/-6% of arterial plasma radioactivity). Higher proportions of labeled TG were recovered in portal vein plasma, suggesting release by the gut. The portal and the arterial-portal vs. hepatic venous TG gradient tended to be positive. Accordingly, hepatic FA uptake was higher, but declined more rapidly during fasting than during hyperinsulinemia.
The study indicates that the redistribution of [11C]palmitate between different lipid pools occurs within the short time interval of most PET experiments and is strongly influenced by insulin. Labeled TG constitute an additional [11C]palmitate source in the modeling of PET data.
No preview · Article · May 2006 · Nuclear Medicine and Biology
[Show abstract][Hide abstract] ABSTRACT: The relationship between Chlamydia pneumoniae (Cpn) infection and arterial measures of preclinical atherosclerosis has remained controversial. Because atherogenesis begins in early life, we examined whether carotid and aortic intima-media thickness (IMT) and brachial artery endothelial function are associated with Cpn seropositivity in children.
Cpn-specific IgG and IgA antibodies were assessed by enzyme immunoassay in 199 healthy children followed-up annually from 7 to 11 years of age. Carotid (cIMT) and aortic IMT (aIMT), and brachial artery flow-mediated dilatation (FMD) were measured in 137 of the 199 children at the age of 11 years using high-resolution ultrasound. Children with persistent IgG and/or IgA seropositivity to Cpn had significantly increased aIMT compared with seronegative children (IgG< or =45 and IgA< or =12 enzyme immunounits) or children with transient Cpn seropositivity (seronegative, 0.496 [0.054]; transient, 0.494 [0.061]; and persistent, 0.532 [0.086] mm; P<0.05 for trend). This trend was not explained by traditional atherosclerotic risk factors or pubertal stage. cIMT and FMD were not associated with Cpn seropositivity.
Eleven-year-old children with persistent Cpn seropositivity show increased aIMT but not cIMT, suggesting that Cpn may affect the aortic wall, the site where the earliest atherosclerotic lesions are known to occur, in otherwise healthy children.
Full-text · Article · Mar 2006 · Arteriosclerosis Thrombosis and Vascular Biology
[Show abstract][Hide abstract] ABSTRACT: Patient motion during dynamic PET studies is a well-documented source of errors. The purpose of this study was to investigate the incidence of frame-to-frame motion in dynamic ( 15)O-water myocardial perfusion PET studies, to test the efficacy of motion correction methods and to study whether implementation of motion correction would have an impact on the perfusion results.
We developed a motion detection procedure using external radioactive skin markers and frame-to-frame alignment. To evaluate motion, marker coordinates inside the field of view were determined in each frame for each study. The highest number of frames with identical spatial coordinates during the study were defined as "non-moved". Movement was considered present if even one marker changed position, by one pixel/frame compared with reference, in one axis, and such frames were defined as "moved". We tested manual, in-house-developed motion correction software and an automatic motion correction using a rigid body point model implemented in MIPAV (Medical Image Processing, Analysis and Visualisation) software. After motion correction, remaining motion was re-analysed. Myocardial blood flow (MBF) values were calculated for both non-corrected and motion-corrected datasets.
At rest, patient motion was found in 18% of the frames, but during pharmacological stress the fraction increased to 45% and during physical exercise it rose to 80%. Both motion correction algorithms significantly decreased (p<0.006) the number of moved frames and the amplitude of motion (p<0.04). Motion correction significantly increased MBF results during bicycle exercise (p<0.02). At rest or during adenosine infusion, the motion correction had no significant effects on MBF values.
Significant motion is a common phenomenon in dynamic cardiac studies during adenosine infusion but especially during exercise. Applying motion correction for the data acquired during exercise clearly changed the MBF results, indicating that motion correction is required for these studies.
Full-text · Article · Jan 2006 · European journal of nuclear medicine and molecular imaging
[Show abstract][Hide abstract] ABSTRACT: Early childhood introduction of nutritional habits aimed at atherosclerosis prevention reduces children's serum total cholesterol concentration, but its effect on vascular endothelial function is unknown.
Between 1990 and 1992, we randomized healthy 7-month-old infants (n=1062) to intervention (low-saturated-fat diet) and control (unrestricted diet) groups. At the age of 11 years, endothelium-dependent (flow-mediated) and endothelium-independent (nitrate-mediated) vasodilatory responses of the brachial artery were measured with high-resolution ultrasound in 179 intervention and 190 control children. The effect of intervention on endothelial function was significant in boys (P=0.0034) but not in girls (P=0.69). The maximum endothelium-dependent dilation response (mean+/-SD) was 9.62+/-3.53% and 8.36+/-3.85% in intervention boys and control boys and 8.84+/-4.00% and 8.44+/-3.60% in intervention girls and control girls, respectively. Intervention had no effect on nitrate-mediated dilation. The difference in endothelial function in boys remained significant after adjustment for current serum total or LDL cholesterol but became nonsignificant after adjustment for mean cholesterol measured under 3 years of age (adjusted means: 9.46% [CI 8.68% to 10.24%] versus 8.54% [CI 7.75% to 9.32%], P=0.11).
A low-saturated-fat diet introduced in infancy and maintained during the first decade of life is associated with enhanced endothelial function in boys. The effect is explained in part by the diet-induced reduction in serum cholesterol concentration.