Gale B. Carey

Mechanisms Regulating Adipocyte Lipolysis

Mechanisms regulating adipocyte lipolysis are reviewed in three stages. The first stage examines plasma membrane hormone receptors and G-proteins. The primary regulators of adipose tissue lipolysis, the catecholamines, bind to the alpha 2, beta 1, beta 2, and beta 3 adrenergic receptors. The alpha 2 receptor couples with Gi-proteins to inhibit cyclic AMP formation and lipolysis, while the beta receptors couple with Gs-proteins to stimulate cyclic AMP formation and lipolysis. The beta 1 receptor may mediate low level catecholamine stimulation, while the beta 3 receptor, which is activated by higher levels of catecholamines, may deliver a more sustained signal. The second stage examines the regulation of cyclic AMP, the intracellular messenger that activates protein kinase A. Adenylyl cyclase synthesizes cyclic AMP from ATP and is regulated by the G-proteins. Phosphodiesterase 3B hydrolyzes cyclic AMP to AMP and is activated and phosphorylated by both insulin and the catecholamines norepinephrine and epinephrine. The third stage focuses on the rate-limiting enzyme of lipolysis, hormone-sensitive lipase (HSL). This 82 to 88 kDa protein is regulated by reversible phosphorylation. Protein kinase A activates and phosphorylates the enzyme at 2 sites, and 3 phosphatases have been implicated in HSL dephosphorylation. The translocation of HSL from the cytosol to the lipid droplet in response to lipolytic stimulation may be facilitated by a family of lipid-associated droplets called perilipins that are heavily phosphorylated by protein kinase A and dephosphorylated by insulin. As the mechanisms regulating adipocyte lipolysis continue to be uncovered, we look forward to the challenges of integrating these findings with research at the in situ and in vivo levels.

Polybrominated Diphenyl Ethers as Endocrine Disruptors of Adipocyte Metabolism

Objective: Obesity is thought to result from poor diet and insufficient exercise. An additional factor may be endocrine‐disrupting environmental chemicals that contaminate the air, water, and food supply. We tested the hypothesis that a class of lipid‐soluble flame retardant chemicals known to accumulate in adipose tissue, polybrominated diphenyl ethers (PBDEs), disrupts insulin and isoproterenol sensitivity of isolated rat adipocytes.

Polybrominated Diphenyl Ethers Alter Hepatic Phosphoenolpyruvate Carboxykinase Enzyme Kinetics in Male Wistar Rats: Implications for Lipid and Glucose Metabolism

Xenobiotics such as phenobarbital, 2,3,7,8-tetrachlorodibenzo-p-dioxin, and Aroclor 1254 significantly suppress the activity of a key gluconeogenic and glyceroneogenic enzyme, phosphoenolpyruvate carboxykinase (PEPCK), suggesting that xenobiotics disrupt hepatic glucose and fat metabolism. The effects of polybrominated diphenyl ethers (PBDE), a family of synthetic flame-retardant chemicals, on PEPCK activity is unknown. This study investigated the effect of DE-71, a commercial PBDE mixture, on PEPCK enzyme kinetics. Forty-eight 1-mo-old male Wistar rats were gavaged daily with either corn oil or corn oil containing 14 mg/kg DE-71 for 3, 14, or 28 d (n = 8/group). At each time point, fasting plasma glucose, insulin, and C-peptide were measured and hepatic PEPCK activity, lipid content, and three cytochrome P-450 enzymes (CYP1A, -2B, and -3A) were assayed. PBDE treatment for 28 d significantly decreased PEPCK Vmax (μmol/min/g liver weight) by 43% and increased liver lipid by 20%, compared to control. CYP1A, -2B, and -3A Vmax values were enhanced by 5-, 6-, and 39-fold, respectively, at both 14 and 28 d in treated rats compared to control. There was a significant inverse and temporal correlation between CYP3A and PEPCK Vmax for the treatment group. Fasting plasma glucose, insulin, and C-peptide levels were not markedly affected by treatment, but the glucose:insulin ratio was significantly higher in treated compared to control rats. Data suggest that in vivo PBDE treatment compromises liver glucose and lipid metabolism, and may influence whole-body insulin sensitivity.

The swine as a model for studying exercise-induced changes in lipid metabolism

The swine has many similarities to humans, making it an excellent research model in which to study the role of exercise on lipid metabolism. Swine adapt to exercise-training by increasing muscle oxidative enzymes, maximal stroke volume, cardiac output, VO2max, and high density lipoprotein cholesterol levels, while decreasing total cholesterol levels and resting heart rate. The lipoprotein profile of swine and humans is also similar, and low density lipoprotein is the major cholesterol transporting lipoprotein in both species. Several studies in swine report conflicting results on the effect of exercise-training on lipoprotein profile and atherosclerotic lesion appearance. This may result from differences in total exercise time between the studies. With sufficient total exercise, atherosclerosis was reduced and high density lipoprotein cholesterol levels were increased. Exercise may also play a role in reducing obesity, a risk factor for cardiovascular disease, by enhancing lipid mobilization from adipocytes. Recent research suggests that swine adipocyte sensitivity to adenosine, a locally-produced antilipolytic agent, is reduced after exercise treatment. Cellular mechanisms responsible for this metabolic change include a reduction in adenosine A1 receptor number. Current studies are examining the transport of extracellular cyclic AMP from adipocytes and its role as a potential adenosine precursor.

Assessment of the dining environment on and near the campuses of fifteen post-secondary institutions

OBJECTIVE The present study evaluated the restaurant and dining venues on and near post-secondary campuses varying in institution size. DESIGN The Nutrition Environment Measures Survey for Restaurants (NEMS-R) was modified to evaluate restaurants as fast food, sit down and fast casual; and campus dining venues as dining halls, student unions and snack bar/cafe´s. ANOVA with post hoc Tukey’s B and T tests were used to distinguish differences between dining venues and associated institutions by size. SETTING The study was conducted at fifteen US post-secondary institutions, 2009–2011. SUBJECTS Data presented are from a sample of 175 restaurants and sixty-eight on-campus dining venues. RESULTS There were minimal differences in dining halls by institution size, although medium-sized institutions as compared with small-sized institutions offered significantly more healthful side dish/salad bar items. Dining halls scored significantly higher than student unions or snack bar/cafe´s on healthful entre´es, side dish/salad bar and beverages offerings, but they also had the most barriers to healthful dietary habits (i.e. all-you-can-eat). No differences were found by restaurant type for NEMS-R scores for total restaurant dining environment or healthful entre´es and barriers. Snack bars had more healthful side dishes (P50?002) and fast-food restaurants had the highest level of facilitators (i.e. nutrition information; P50?002). CONCLUSIONS Based on this evaluation in fifteen institutions, the full campus dining environment provides limited support for healthy eating and obesity prevention. The quality of campus dining environments can be improved via healthful offerings, providing nutrition information and other supports to facilitate healthy eating and prevent unwanted weight gain.

Does exercise intensity or diet influence lactic acid accumulation in breast milk

PURPOSE This study examined the relationships among diet, exercise intensity, and breast milk composition in lactating women. METHODS Twelve lactating women were randomly assigned to either a high (N = 6; 5.03 g carbohydrate (CHO) x kg body mass (BM)(-1)) or moderate (N = 6; 3.89 g CHO x kg BM(-1)) carbohydrate diet. Milk and blood samples were collected before and after a nonexercise session (control) and maximal, lactic acid-threshold (LAT), and 20% below the LAT (LAT-20) intensities. RESULTS The 30-min exercise LAT bout was more stressful than the 30-min LAT-20 bout (rating of perceived exertion (RPE) = 15 vs 12, respectively, P < 0.05). Milk LA was significantly higher at 0 min following maximal exercise in the high and moderate CHO groups (1.27+/-0.56 and 1.52+/-0.49 mM, respectively) and following LAT exercise (0.19+/-0.16 and 0.25+/-0.12 mM, respectively), when compared with the control session (0.08+/-0.03 and 0.09+/-0.05 mM, respectively). This was not observed following the LAT-20 exercise in the high and moderate CHO groups (0.11+/-0.04 and 0.12+/-0.08 mM, respectively). Elevated milk LA persisted in the 30-min collection point after maximal exercise only. There was no significant effect of dietary treatment on milk or blood LA at any of the collection points. CONCLUSIONS In lactating women whose caloric needs are being met: 1) dietary CHO intake, within a practical range, does not influence LA levels in breast milk at rest or after exercise; 2) LA appearance in the milk is a function of exercise intensity; and 3) moderate intensity exercise (RPE = 12) will not increase breast milk LA levels.

Breast Milk Composition After Exercise of Different Intensities

The purpose of this study was to determine if breast milk composition changed significantly following exercise conducted at different intensities. Nine postpartum women exercised on a treadmill up to maximal oxygen uptake (100% of VO2max) on the first laboratory visit, for 30 minutes on two subsequent occasions (50% and 75% of VO2max) and also performed a nonexercise control session. Blood and breast milk were collected prior to exercise, immediately after exercise, and at 30, 60, and 90 minutes postexercise. Blood samples were analyzed for lactic acid (LA) while milk samples were analyzed for LA, pH, lipid, ammonium, and urea. Milk LA after the 100% intensity session was significantly elevated through 90 minutes postexercise, while there was no significant increase in milk LA at any collection time after the 50% or 75% intensity sessions. There were no significant uifferences in milk pH, lipid, ammonium, or urea measurements after any of the exercise sessions. These data show that unlike maximum intensity exercise, moderate intensity exercise does not increase breast milk LA content.

Cardiovascular Fitness, Activity, and Metabolic Syndrome Among College Men and Women

BACKGROUND The purpose of this cross-sectional study was to examine the impact of below-average cardiovascular fitness and inactivity on the metabolic syndrome among an understudied population-undergraduate men and women, ages 18-24 years. METHODS Between January, 2010, and May, 2012, we assessed anthropometric, biochemical, and clinical measures in a convenience sample of students (n=1610) enrolled in an introductory nutrition course at a public university. We quantified the prevalence of metabolic syndrome criteria, estimated cardiovascular fitness via a 1-mile Rockport Walk Test, and evaluated daily activity via pedometer. Subjects were classified as below-average, average, and above-average fitness based upon the Rockport Walk Test; activity levels were classified as low active, somewhat active, active, or highly active according to average steps per day. RESULTS Those with below-average fitness (10%) were at increased risk for being overfat, having abdominal obesity, and having the metabolic syndrome as compared to those with average or above-average fitness (odds ratio: 12.4, 10.0, and 4.7, respectively; all P<0.01). Twenty percent of subjects were low active (<7500 steps/day) and had a greater number of metabolic syndrome criteria as compared to very active subjects (>12,500 steps/day) (0.94±0.05 vs. 0.73±0.05, P=0.01). CONCLUSIONS Young, college-age adults with below-average cardiovascular fitness and/or low activity levels are at increased risk for obesity and the metabolic syndrome. Future studies should examine how promoting lifestyle habits that increase physical activity and reduce sedentary behaviors during the young adult years can improve metabolic health.

Characterization of the swine adipocyte A1 adenosine receptor using an optimized assay system.

The radioligand binding assay of A1 adenosine receptors in adipocyte crude plasma membrane from Yucatan miniature swine was optimized by evaluating 17 factors involved in the assay. Significant effects of CHAPS, adenosine deaminase, EDTA, pre-rinsing glass fiber filters and pH were found for the binding measurements. Using the optimized procedure, [3H]8-cyclopentyl-1,3-dipropylxanthine, ([3H]-DPCPX) binding to A1 adenosine receptors in swine subcutaneous adipocyte crude plasma membrane was measured; Bmax and Kd values were 479 +/- 77 fmol/mg protein and 0.87 +/- 0.10 nM, respectively. Values for mesenteric adipose tissue from sedentary swine and subcutaneous adipose tissue from exercise-trained swine were also measured.

Human breast milk enrichment in conjugated linoleic acid after consumption of a conjugated linoleic acid-rich food product: a pilot study ☆

Human breast milk is a complex mixture of organic and inorganic compounds. Some compounds, such as conjugated linoleic acid (CLA), come partly from the mothers diet and are produced by the mothers body and secreted into the milk. Although several studies have examined the effect of chronic CLA supplementation on breast milk CLA appearance, little is known about the transfer of food CLA to breast milk over the short term. The objective of this study was to conduct a preliminary analysis of the kinetics of CLA appearance in breast milk over the short term. Seven women expressed breast milk at 4- to 6-hour intervals for 2 days after eating either CLA-enriched (1912 mg CLA) or control (231 mg CLA) cookies. Milk samples were freeze-dried, fatty acid methyl esters were prepared using methanolic-potassium hydroxide (KOH), and CLA isomers were quantified by gas chromatography. Analysis revealed the following: (1) CLA enrichment of total fatty acids in the breast milk for 48 hours post ingestion of the CLA-enriched cookies was 2.9-fold above control; (2) total breast milk CLA content for 48 hours post CLA-enriched cookies ingestion was 46% greater than post CLA-moderate cookies ingestion; (3) after ingestion of the CLA-enriched cookies, breast milk CLA enrichment plateaued between 8 to 28 hours. This preliminary study suggests that breast milk fatty acids are enriched in CLA compared to control within 28 hours after the ingestion of a CLA-rich food product and invites further research on the extent and timing with which breast milk composition reflects dietary CLA content.