Agneta L. Sunehag

A 12-Week Aerobic Exercise Program Reduces Hepatic Fat Accumulation and Insulin Resistance in Obese, Hispanic Adolescents

The rise in obesity‐related morbidity in children and adolescents requires urgent prevention and treatment strategies. Currently, only limited data are available on the effects of exercise programs on insulin resistance, and visceral, hepatic, and intramyocellular fat accumulation. We hypothesized that a 12‐week controlled aerobic exercise program without weight loss reduces visceral, hepatic, and intramyocellular fat content and decreases insulin resistance in sedentary Hispanic adolescents. Twenty‐nine postpubertal (Tanner stage IV and V), Hispanic adolescents, 15 obese (7 boys, 8 girls; 15.6 ± 0.4 years; 33.7 ± 1.1 kg/m2; 38.3 ± 1.5% body fat) and 14 lean (10 boys, 4 girls; 15.1 ± 0.3 years; 20.6 ± 0.8 kg/m2; 18.9 ± 1.5% body fat), completed a 12‐week aerobic exercise program (4 × 30 min/week at ≥70% of peak oxygen consumption (VO2peak)). Measurements of cardiovascular fitness, visceral, hepatic, and intramyocellular fat content (magnetic resonance imaging (MRI)/magnetic resonance spectroscopy (MRS)), and insulin resistance were obtained at baseline and postexercise. In both groups, fitness increased (obese: 13 ± 2%, lean: 16 ± 4%; both P < 0.01). In obese participants, intramyocellular fat remained unchanged, whereas hepatic fat content decreased from 8.9 ± 3.2 to 5.6 ± 1.8%; P < 0.05 and visceral fat content from 54.7 ± 6.0 to 49.6 ± 5.5 cm2; P < 0.05. Insulin resistance decreased indicated by decreased fasting insulin (21.8 ± 2.7 to 18.2 ± 2.4 µU/ml; P < 0.01) and homeostasis model assessment of insulin resistance (HOMAIR) (4.9 ± 0.7 to 4.1 ± 0.6; P < 0.01). The decrease in visceral fat correlated with the decrease in fasting insulin (R2 = 0.40; P < 0.05). No significant changes were observed in any parameter in lean participants except a small increase in lean body mass (LBM). Thus, a controlled aerobic exercise program, without weight loss, reduced hepatic and visceral fat accumulation, and decreased insulin resistance in obese adolescents.

Strength exercise improves muscle mass and hepatic insulin sensitivity in obese youth.

INTRODUCTION Data on the metabolic effects of resistance exercise (strength training) in adolescents are limited. PURPOSE The objective of this study was to determine whether a controlled resistance exercise program without dietary intervention or weight loss reduces body fat accumulation, increases lean body mass, and improves insulin sensitivity and glucose metabolism in sedentary obese Hispanic adolescents. METHODS Twelve obese adolescents (age = 15.5 ± 0.5 yr, body mass index = 35.3 ± 0.8 kg·m; 40.8% ± 1.5% body fat) completed a 12-wk resistance exercise program (two times 1 h·wk, exercising all major muscle groups). At baseline and on completion of the program, body composition was measured by dual-energy x-ray absorptiometry, abdominal fat distribution was measured by magnetic resonance imaging, hepatic and intramyocellular fat was measured by magnetic resonance spectroscopy, peripheral insulin sensitivity was measured by the stable-label intravenous glucose tolerance test, and hepatic insulin sensitivity was measured by the hepatic insulin sensitivity index = 1000/(GPR × fasting insulin). Glucose production rate (GPR), gluconeogenesis, and glycogenolysis were quantified using stable isotope gas chromatography/mass spectrometry techniques. RESULTS All participants were normoglycemic. The exercise program resulted in significant strength gain in both upper and lower body muscle groups. Body weight increased from 97.0 ± 3.8 to 99.6 ± 4.2 kg (P < 0.01). The major part (∼80%) was accounted for by increased lean body mass (55.7 ± 2.8 to 57.9 ± 3.0 kg, P ≤ 0.01). Total, visceral, hepatic, and intramyocellular fat contents remained unchanged. Hepatic insulin sensitivity increased by 24% ± 9% (P < 0.05), whereas peripheral insulin sensitivity did not change significantly. GPR decreased by 8% ± 1% (P < 0.01) because of a 12% ± 5% decrease in glycogenolysis (P < 0.05). CONCLUSIONS We conclude that a controlled resistance exercise program without weight loss increases strength and lean body mass, improves hepatic insulin sensitivity, and decreases GPR without affecting total fat mass or visceral, hepatic, and intramyocellular fat contents.

Gene expression in the human mammary epithelium during lactation: the milk fat globule transcriptome

The molecular physiology underlying human milk production is largely unknown because of limitations in obtaining tissue samples. Determining gene expression in normal lactating women would be a potential step toward understanding why some women struggle with or fail at breastfeeding their infants. Recently, we demonstrated the utility of RNA obtained from breast milk fat globule (MFG) to detect mammary epithelial cell (MEC)-specific gene expression. We used MFG RNA to determine the gene expression profile of human MEC during lactation. Microarray studies were performed using Human Ref-8 BeadChip arrays (Illumina). MFG RNA was collected every 3 h for 24 h from five healthy, exclusively breastfeeding women. We determined that 14,070 transcripts were expressed and represented the MFG transcriptome. According to GeneSpring GX 9, 156 ontology terms were enriched (corrected P < 0.05), which include cellular (n = 3,379 genes) and metabolic (n = 2,656) processes as the most significantly enriched biological process terms. The top networks and pathways were associated primarily with cellular activities most likely involved with milk synthesis. Multiple sampling over 24 h enabled us to demonstrate core circadian clock gene expression and the periodicity of 1,029 genes (7%) enriched for molecular functions involved in cell development, growth, proliferation, and cell morphology. In addition, we found that the MFG transcriptome was comparable to the metabolic gene expression profile described for the lactating mouse mammary gland. This paper is the first to describe the MFG transcriptome in sequential human samples over a 24 h period, providing valuable insights into gene expression in the human MEC.

Metabolic Adaptations in the Absence of Perilipin INCREASED β-OXIDATION AND DECREASED HEPATIC GLUCOSE PRODUCTION ASSOCIATED WITH PERIPHERAL INSULIN RESISTANCE BUT NORMAL GLUCOSE TOLERANCE IN PERILIPIN-NULL MICE

Targeted disruption of the lipid droplet protein, perilipin, in mice leads to constitutional lipolysis associated with marked reduction in white adipose tissue as a result of unbridled lipolysis. To investigate the metabolic adaptations in response to the constitutive lipolysis, we studied perilipin-null (plin–/–) mice in terms of their fatty acid oxidation and glycerol and glucose metabolism homeostasis by using dynamic biochemical testing and clamp and tracer infusion methods. plin–/– mice showed increased β-oxidation in muscle, liver, and adipose tissue resulting from a coordinated regulation of the enzymes and proteins involved in β-oxidation. The increased β-oxidation helped remove the extra free fatty acids created by the constitutive lipolysis. An increase in the expression of the transcripts for uncoupling proteins-2 and -3 also accompanied this increase in fatty acid oxidation. Adult plin–/– mice had normal plasma glucose but a reduced basal hepatic glucose production (46% that of plin+/+). Insulin infusion during low dose hyperinsulinemic-euglycemic clamp further lowered the glucose production in plin–/– mice, but plin–/– mice also showed a 36% decrease (p < 0.007) in glucose disposal rate during the low dose insulin clamp, indicating peripheral insulin resistance. However, compared with plin+/+ mice, 14-week-old plin–/– mice showed no significant difference in glucose disposal rate during the high dose hyperinsulinemic clamp, whereas 42-week-old plin–/– mice displayed significant insulin resistance on high dose hyperinsulinemic clamp. Despite increasing insulin resistance with age, plin–/– mice at different ages maintained a normal glucose response during an intraperitoneal glucose tolerance curve, being compensated by the increased β-oxidation and reduced hepatic glucose production. These experiments uncover the metabolic adaptations associated with the constitutional lipolysis in plin–/– mice that allowed the mice to continue to exhibit normal glucose tolerance in the presence of peripheral insulin resistance.

Methionine transmethylation and transsulfuration in the piglet gastrointestinal tract

Methionine is an indispensable sulfur amino acid that functions as a key precursor for the synthesis of homocysteine and cysteine. Studies in adult humans suggest that splanchnic tissues convert dietary methionine to homocysteine and cysteine by means of transmethylation and transsulfuration, respectively. Studies in piglets show that significant metabolism of dietary indispensable amino acids occurs in the gastrointestinal tissues (GIT), yet the metabolic fate of methionine in GIT is unknown. We show here that 20% of the dietary methionine intake is metabolized by the GIT in piglets implanted with portal and arterial catheters and fed milk formula. Based on analyses from intraduodenal and intravenous infusions of [1-13C]methionine and [2H3]methionine, we found that the whole-body methionine transmethylation and remethylation rates were significantly higher during duodenal than intravenous tracer infusion. First-pass splanchnic metabolism accounted for 18% and 43% of the whole-body transmethylation and remethylation, respectively. Significant transmethylation and transsulfuration was demonstrated in the GIT, representing ≈27% and ≈23% of whole-body fluxes, respectively. The methionine used by the GIT was metabolized into homocysteine (31%), CO2 (40%), or tissue protein (29%). Cystathionine β-synthase mRNA and activity was present in multiple GITs, including intestinal epithelial cells, but was significantly lower than liver. We conclude that the GIT consumes 20% of the dietary methionine and is a significant site of net homocysteine production. Moreover, the GITs represent a significant site of whole-body transmethylation and transsulfuration, and these two pathways account for a majority of methionine used by the GITs.

Glucose Production, Gluconeogenesis, and Insulin Sensitivity in Children and Adolescents: An Evaluation of Their Reproducibility

The prevalence of overweight and obese children has doubled, and the incidence of type 2 diabetes in children (0–19 y) has increased 4-fold during the past several decades. As a result we can anticipate an increased number of metabolic studies in children. There are few data on measures of glucose metabolism in normal children, and virtually none relating to their reproducibility. The aims of this study were 1) to provide new data on energy expenditure and glucose, lipid, and protein metabolism in nonobese, healthy children and adolescents;2) to evaluate their reproducibility; and 3) on the basis of these data, to perform power calculations for metabolic studies. Eight nonobese subjects (8–16 y) were studied on two occasions, preceded by 7 d of a diet with identical energy content and macronutrient distribution. Gluconeogenesis, measured by deuterium oxide, accounted for 50% of glucose production. Insulin sensitivity, measured by the labeled minimal model, averaged 4.9 × 10−4 mL(mU·min)−1. Glucose appearance rate was significantly higher (p < 0.01) in the children than in the adolescents. Furthermore, we demonstrated that for energy intake and expenditure, plasma concentrations of glucose and C-peptide, and rates of appearance of glucose and leucine, a 10% difference can be detected in fewer than five subjects with a power of 80% and a type I error of 5%. Insulin concentration, gluconeogenesis, insulin secretory indices, insulin sensitivity, and glucose effectiveness were more variable, but with the above power a difference of 25% could be detected in 7–11 subjects using a paired study design.

Glucose Production Rate in Extremely Immature Neonates (<28 Weeks) Studied by Use of Deuterated Glucose

ABSTRACT: Neonatal hypoglycemia is a frequent complication in immature infants. This may be due to small substrate stores, a high brain:body weight ratio, and immature enzyme systems. The purpose of the present study was to investigate the rate of glucose production in newborn infants with gestational ages of less than 28 wk. The subjects were 10 newborn infants delivered after 25 to 26 gestational wk. Their mean birth weight was 772 g (range 588–1000 g), and their mean postnatal age at the time of the study was 15 h (range 4–24 h). An isotopic compound (d-6,6-2H2-glucose) was given as a constant-rate i.v. infusion. In addition to dideuteroglucose, eight of the infants also received an i.v. infusion of unlabeled glucose at a rate of 1.4–2.6 mg·kg−1·min−1. Blood samples for determination of the concentration and isotopic enrichment of plasma glucose were obtained every 15 min in a 2-h period. Isotopic enrichment, measured by gas chromatography/mass spectrometry, was used for calculating the glucose production rate. The mean glucose production rate related to body weight (± SD) was 6.1 ± 1.5 mg·kg−1·min−1. The results show that infants born at <28 gestational wk have a capacity to produce glucose on their 1st d of life at rates close to or even exceeding those reported in term infants.

Aerobic exercise increases peripheral and hepatic insulin sensitivity in sedentary adolescents.

CONTEXT Data are limited on the effects of controlled aerobic exercise programs (without weight loss) on insulin sensitivity and glucose metabolism in children and adolescents. OBJECTIVE To determine whether a controlled aerobic exercise program (without weight loss) improves peripheral and hepatic insulin sensitivity and affects glucose production (GPR), gluconeogenesis and glycogenolysis in sedentary lean and obese Hispanic adolescents. PATIENTS AND DESIGN Twenty-nine post-pubertal adolescents (14 lean: 15.1 +/- 0.3 y; 20.6 +/- 0.8 kg/m(2); 18.9+/-1.5% body fat and 15 obese: 15.6 +/- 0.4 y; 33.2 +/- 0.9 kg/m(2); 38.4 +/- 1.4% body fat) (mean +/- SE), completed a 12 wk aerobic exercise program (4 x 30 min/week at >or=70% of VO(2) peak). Peripheral and hepatic insulin sensitivity and glucose kinetics were quantified using GCMS pre- and post-exercise. RESULTS No weight loss occurred. Lean and obese participants complied well with the program ( approximately 90% of the exercise sessions attended, resulting in approximately 15% increase in fitness in both groups). Peripheral and hepatic insulin sensitivity were higher in lean than obese adolescents but increased in both groups; peripheral insulin sensitivity by 35 +/- 14% (lean) (p < 0.05) and 59 +/- 19% (obese) (p < 0.01) and hepatic insulin sensitivity by 19 +/- 7% (lean) (p < 0.05) and 23 +/- 4% (obese) (p < 0.01). GPR, gluconeogenesis and glycogenolysis did not differ between the groups. GPR decreased slightly, 3 +/- 1% (lean) (p < 0.05) and 4 +/- 1% (obese) (p < 0.01). Gluconeogenesis remained unchanged, while glycogenolysis decreased slightly in the obese group (p < 0.01). CONCLUSION This well accepted aerobic exercise program, without weight loss, is a promising strategy to improve peripheral and hepatic insulin sensitivity in lean and obese sedentary adolescents. The small decrease in GPR is probably of limited clinical relevance.

The role of parenteral lipids in supporting gluconeogenesis in very premature infants

We have previously demonstrated that very premature infants receiving glucose at 17 μmol/kg min plus appropriate supply of parenteral lipids (Intralipid®) and amino acids (TrophAmine®) maintained normoglycemia by glucose produced primarily via gluconeogenesis. The present study addressed the individual roles of parenteral lipids and amino acids in supporting gluconeogenesis. Fourteen premature infants (993 ± 36 g 27 ± 1 wk) (mean ± SE) were studied for 8 h on d 5 ± 1 of life. All infants were receiving standard TPN prior to the study. At start of study, the glucose infusion rate was decreased to ∼17 μmol/kg min and either Intralipid® (g + AA; n = 8) or TrophAmine® (g + IL; n = 6) was discontinued. Data from 14 previously studied infants receiving glucose (∼17 μmol/kg min) + TrophAmine® + Intralipid® (g + AA + IL) are included for comparison. Gluconeogenesis was measured by [U-13 C]glucose, (g + AA) and (8 infants of the g + AA + IL group) or [2-13C]glycerol, (g + IL) and (6 infants of the g + AA + IL group). Infants studied by the same method were compared. Withdrawal of Intralipid® resulted in decreased gluconeogenesis, 6.3 ± 0.9 (g +AA) vs. 8.4 ± 0.7 μmol/kg min (g + AA + IL) (p = 0.03). Withdrawal of TrophAmine® affected neither total gluconeogenesis, 7.5 ± 0.8 vs. 7.9 ± 0.9 μmol/kg min nor gluconeogenesis from glycerol, 4.4 ± 0.6 vs. 4.9 ± 0.7 μmol/kg min (g+ IL and g + AA + IL groups, respectively). In conclusion, in parenterally fed very premature infants, lipids play a primary role in supporting gluconeogenesis.

Effect of dietary macronutrient composition under moderate hypocaloric intake on maternal adaptation during lactation

BACKGROUND No evidence-based recommendations exist concerning what dietary macronutrient composition optimizes weight loss during lactation while maintaining milk production. OBJECTIVES The study was designed to test the following hypotheses: compared with a reduced-calorie, high-carbohydrate (H-CHO) diet, an isonitrogenous, isocaloric high-fat (H-F) diet will decrease milk production and carbohydrate oxidation, increase gluconeogenesis and hexoneogenesis, and not affect energy balance. DESIGN Seven healthy lactating mothers and their infants were studied on 2 occasions in random order for 8 d separated by 1-2 wk. On one occasion, the subjects received the H-F (30% of energy as carbohydrate and 55% as fat) diet and on the other occasion received the H-CHO (60% of energy as carbohydrate and 25% as fat) diet. Milk production, infant intakes, and substrate and hormone concentrations were measured. Glucose rates of appearance, production, gluconeogenesis, glycogenolysis, and hexoneogenesis were measured by using stable-isotope gas chromatography-mass spectrometric techniques, and energy expenditure and substrate oxidation were measured by using indirect calorimetry. RESULTS Milk volume, lactose, and protein concentrations were unaffected. Milk fat, energy, and infant intakes were higher (P < 0.05) during the H-F diet. Neither gluconeogenesis nor hexoneogenesis was different. During the H-F diet, energy expenditure and fat and protein oxidation rates were higher (P < 0.05), and the daily energy balance deficit was greater (P < 0.01). CONCLUSIONS Milk fat, energy output, and energy expenditure were higher during the H-F diet, which resulted in a greater negative energy balance. The lactating mothers adapted to a low carbohydrate intake by decreasing carbohydrate oxidation. Additional studies are warranted to determine whether a hypocaloric H-F diet might promote weight loss to a greater extent than the H-CHO diet while maintaining milk production.