Santosa, Sylvia

Adult males and females have markedly different body composition, and energy expenditure and have different degrees of risk for metabolic diseases. A major aspect of metabolic regulation involves the appropriate storage and disposal of glucose and fatty acids. The use of sophisticated calorimetry, tracer, and imaging techniques has provided insight into the complex metabolism of these substrates showing that the regulation of these processes varies tremendously throughout the day, from the overnight fasting condition to meal ingestion, to the effects of physical activity. The sexual dimorphism in substrate metabolism is most readily observed in how fatty acids are stored and mobilized. The objective of this review is to provide a comprehensive and critical summary of the reported sex differences in the mobilization, oxidation, and storage of fat and carbohydrate in adipose tissue and skeletal muscle. We will describe how adipose tissue lipolysis differs between sexes and how this varies between fed, fasted, and exercise conditions. We will also review what is known about endogenous and exogenous fatty acid storage in adipose tissue and muscle, as well as how oxidation compares between men and women in response to exercise. What has been learned about the cellular level regulation of these processes will be described. Although glucose metabolism exhibits fewer differences between men and women, we will also review the existing knowledge on this topic.

AbstractObjectiveThe aim of this study was to determine the effect of age of obesity onset on senescence‐related markers in abdominal (AB) and femoral (FEM) subcutaneous adipose tissue (SAT) before and after moderate (~10%) weight loss.MethodsAB and FEM SAT were collected from human females with childhood‐onset obesity (CO) or adult‐onset obesity (AO) before and after diet‐ and exercise‐induced weight loss. Immunofluorescence analysis of γH2AX/RAD51 (DNA damage/repair markers) and p53/p21 (senescence markers) was conducted in cultured preadipocytes, and senescence‐associated β‐galactosidase (SA‐β‐gal) activity was measured in SAT.ResultsCO had proportionately more AB and FEM preadipocytes with DNA damage (γH2AX+) and senescence markers (p53+ and/or p21+) than AO at baseline. The proportion of γH2AX+ FEM preadipocytes declined with weight loss in CO and was similar between groups after weight loss. The number of γH2AX foci in γH2AX+ preadipocytes decreased similarly between groups and regions with weight loss in parallel with an increase in RAD51. The proportion of p53+ and p21+ preadipocytes and SA‐β‐gal+ cells in SAT did not change with weight loss, but the total p21 intensity in p53+/p21+ FEM preadipocytes declined in AO.ConclusionsThese results provide preliminary evidence that females with CO have an accelerated preadipocyte aging state that improves with weight loss in terms of DNA damage but not senescence.

Objectives: To determine whether meal fatty acid (FA) metabolism differs by sex and obesity phenotypes and to examine how weight loss (WtL) through diet and exercise affects meal FA trafficking. Methods: Before WtL (study 1) 13 obese men (ObM), 9 upper body obese (UbO) and 8 lower body obese (LbO) women consumed a standard meal containing [ 3 H]triolein followed by subcutaneous abdominal and gluteal fat biopsies. Indirect calorimetry was measured by 5 h substrate oxidation. Whole/regional fat distribution was measured using DXA and CT scan. Participants then enrolled in a structured WtL program, after which 23 returned for study 2. Results: There were no differences (p=0.32) in meal FA oxidation between groups. Abdominal uptake of meal FA in LOb was greater than in UOb (p=0.026) and ObM (p<0.001). LOb took up more meal FA in the lower body than ObM (p=0.001). Participants who returned for study 2 lost 14 ± 1.1 kg. After WtL, uptake of meal FA in upper body subcutaneous fat increased (p=0.028) in UOb and ObM (p=0.046) and decreased in lower body fat (p=0.025) in ObM. WtL led to reduced 5 h postprandial total fat oxidation and increased 24 h meal FA oxidation. Conclusion: Changes in uptake of meal FA after WtL followed a pattern indicative of body fat distribution maintenance. These results highlight the potential importance of meal fat uptake in modulating body fat distribution in obesity. Funding: NIH RO1 DK45343, DK50456 and R00585.

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.

Abstract Adult humans have a remarkable sexual dimorphism in body shape. Men tend to store relatively more fat in the upper body whereas women store more fat in the lower body. We do not have a complete understanding of the mechanisms underlying these differences, but we know that people who preferentially store abdominal fat are at greater risk of metabolic disease. It is also known that the changes in sex steroid concentrations during puberty and again with advancing age are accompanied by changes in body fat distribution. The objective of this review is to describe what has been learned regarding the mechanisms underlying changes in regional body fat distribution that occur as a result of changes in sex hormones and to delineate effects of sex steroids in modulating body composition.

Increases in weight have been associated with corresponding increases in insulin resistance in postmenopausal women. Although estrogen has significant impact on body fat and body fat distribution, the cellular mechanisms that influence this process are not yet known. We measured adipose tissue fatty acid (FA) storage and FA storage factors in 12 premenopausal and 11 postmenopausal women matched for age and body composition. Postmenopausal women had lower postprandial FA oxidation (indirect calorimetry), greater meal FA, and direct free FA (FFA) storage than premenopausal women, including two-fold greater meal FA storage in the femoral depot. The fed/fasted activities of adipose tissue lipoprotein lipase were not significantly different between premenopausal and postmenopausal women. In contrast, adipocyte acyl-CoA synthetase and diacylglycerol acyltransferase activities in postmenopausal women were significantly upregulated and were positively correlated with direct FFA storage rates. These findings suggest that the propensity for subcutaneous adipose tissue FA storage is increased in postmenopausal women, more so from changes in adipocyte FA storage factors than from adipose tissue lipoprotein lipase activity. Our results suggest that female sex steroids, most likely estrogen, have important effects on adipose tissue FA storage and FA oxidation that could promote fat gain in postmenopausal women.