Morgan‐Bathke, Maria

Background A multitude of studies have suggested that there is a link between obesity and inflammation. Various in vitro and animal studies have shown that saturated fatty acids are largely responsible for the induction of various pro‐inflammatory pathways. As vegetarians consume about half the amount of saturated fat as omnivores, we hypothesized that they would have less inflammation for any given amount of obesity. Objective To quantitate the inflammatory status of adipose tissue from obese vegetarians and omnivores. Methods The study included 8 obese vegetarians (1 male) and 8 obese omnivores matched for age, sex, and BMI. Body composition was measured by DXA. A blood sample was collected to measure plasma free fatty acids (FFA), subcutaneous adipose tissue biopsies to measure macrophage content and muscle biopsies to quantify diacylglycerol (DAG) and ceramide content. Each participant also completed a Food Frequency Questionnaire (FFQ) to determine their average dietary intake. Results By design there were no differences in age, weight, BMI, percentage body fat, fat free mass or adipocyte size between the omnivore and vegetarian group. We found that vegetarians consume lower amounts of saturated fatty acids and cholesterol while consuming higher amounts of fiber and vitamin C than the omnivore participants ( p = 0.06, 0.04, 0.004, 0.04 respectively). The plasma FFA of vegetarians revealed that they had greater proportions of the polyunsaturated fatty acids linoleic, linolenic ( p = 0.01, 0.02 respectively) as well as increased monounsaturated oleic acid ( p = 0.04). The inflammatory status of adipose tissue was quantified by measuring macrophage content (total, pro‐inflammatory M1, and anti‐inflammatory M2 macrophages). The vegetarian group had significantly lower adipose tissue total ( p = 0.004), M1 ( p = 0.002), and M2 ( p = 0.01) macrophage burden when compared the omnivore group. There was a difference, however, in muscle DAG and ceramide content between the two groups. Conclusions As expected, vegetarians consume a diet that varies in key macro‐ and micronutrients that may affect inflammatory status. Indeed, the vegetarian group had significantly lower adipose tissue macrophage burden than the omnivore participants despite their obese state. While these variations in dietary intake seem to have a positive impact on the adipose tissue immune cell milieu there was no difference in the potential inflammatory cell signaling components of the muscle tissue, DAGs and ceramides, between the two groups. These promising results display the importance of dietary intake in modulating adipose tissue inflammation and potentially chronic disease.

Background A multitude of studies have suggested that there is a link between obesity and inflammation. Various in vitro and animal studies have shown that saturated fatty acids are largely responsible for the induction of various pro‐inflammatory pathways. As vegetarians consume about half the amount of saturated fat as omnivores, we hypothesized that they would have less inflammation for any given amount of obesity. Objective To quantitate the inflammatory status of adipose tissue from obese vegetarians and omnivores. Methods The study included 8 obese vegetarians (1 male) and 8 obese omnivores matched for age, sex, and BMI. Body composition was measured by DXA. A blood sample to measure plasma free fatty acids (FFA) and abdominal and femoral subcutaneous adipose tissue biopsies to measure macrophage content, and the fatty acid composition were collected. Each participant also completed a Food Frequency Questionnaire (FFQ) to determine their average dietary intake. Results By design there were no differences in age, weight, BMI, percentage body fat, fat free mass or adipocyte size between the omnivore and vegetarian group. The plasma FFA of vegetarians revealed that they had greater proportions of the polyunsaturated fatty acids linoleic, linolenic and DHA ( p = 0.04, 0.05, 0.05 respectively ). Surprisingly, there was no difference in the fatty acid composition of the adipose tissue samples (abdominal or femoral) between the two groups. The FFQ data showed no significant difference in total fat, protein, or carbohydrate intake between the groups. However, the omnivore group had significantly greater intake of saturated fat and cholesterol than the vegetarian group ( p = 0.05, 0.04, respectively). The inflammatory status of adipose tissue was quantified by measuring macrophage content (total, pro‐inflammatory M1, and anti‐inflammatory M2 macrophages). There was no difference in total, M1 or M2 macrophage content between the vegetarian and omnivore groups. We also quantified the senescent cell population within the adipose tissue and again found no difference between the groups. Conclusions While vegetarians have significantly greater proportions of polyunsaturated fatty acids in plasma FFA than omnivores, this was not true for adipose tissue fatty acid composition. As expected, omnivores consume significantly greater amounts of saturated fatty acids, but there was no difference in adipose tissue inflammatory status between the two groups when measured using flow cytometry and senescent cell population. It is possible that the burden of obesity is more important than the consumption of saturated fatty acids in terms of human adipose tissue inflammation.

The role of adipose tissue (AT) inflammation in AT function in humans is unclear. We tested whether AT macrophage (ATM) content, cytokine gene expression, and senescent cell burden (markers of AT inflammation) predict AT insulin resistance measured as the insulin concentration that suppresses lipolysis by 50% (IC50). We studied 86 volunteers with normal weight or obesity at baseline and a subgroup of 25 volunteers with obesity before and after weight loss. There was a strong positive relationship between IC50 and abdominal subcutaneous and femoral fat cell size (FCS). The positive, univariate relationships between IC50 and abdominal AT inflammatory markers CD68, CD14, CD206 ATM/100 adipocytes, senescent cells, IL-6, and TNF-α mRNA were not significant after adjustment for FCS. A 10% weight loss significantly reduced IC50; however, there was no reduction in adipose ATM content, senescent cells, or cytokine gene expression. Our study suggests that commonly used markers of AT inflammation are not causally linked to AT insulin resistance, whereas FCS is a strong predictor of AT insulin resistance with respect to lipolysis.

AbstractObjectiveAdipose tissue (AT) senescence is associated with AT dysfunction in rodents, but little is known about human AT senescence. The study goal was to define the distribution of senescent cells in two subcutaneous depots and understand relationships with adiposity and inflammation.MethodsSixty‐three volunteers (48 females) underwent abdominal and femoral subcutaneous fat biopsies. Fat cell size, senescent cells using senescence‐associated β‐galactosidase staining per 100 nucleated cells (percentage), and mRNA expression of four cytokines were measured.ResultsThere was a larger proportion of senescent cells in femoral than abdominal subcutaneous AT (mean difference 1.6% [95% CI: 0.98%‐2.3%], p < 0.001), and the percentage of femoral AT senescent cells was greater in women than men (median 3.9% vs. 2.1%, p < 0.01). There was a positive correlation between senescence and fat cell size in abdominal (rs = 0.44, p < 0.001) and femoral (rs = 0.35, p = 0.007) AT depots. Abdominal AT tumor necrosis factor alpha (rs = 0.49, p < 0.01) and interleukin‐1β (rs = 0.44, p = 0.01) expression was positively correlated with abdominal, but not femoral, AT senescence.ConclusionsIn human subcutaneous AT, there are more senescent cells in femoral than abdominal depots; abdominal AT senescent cells are more associated with inflammatory signals than femoral AT senescent cells.

Adipose tissue inflammation, as defined by macrophage accumulation, is proposed to cause insulin resistance and systemic inflammation. Because the strength of this relationship for humans is unclear, we tested whether adipose tissue macrophage (ATM) burden is correlated with these health indicators. Using immunohistochemistry, we measured abdominal subcutaneous CD68+ (total ATM), CD14+ (proinflammatory/M1), and CD206+ (anti-inflammatory/M2) ATM in 97 volunteers (BMI 20–38 kg/m 2 , in addition to body composition, adipocyte size, homeostasis model assessment of insulin resistance, ADIPO-IR, adipose tissue insulin resistance measured by palmitate, plasma lipids, TNF, and IL-6 concentrations. There were several significant univariate correlations between metabolic parameters to IL-6 and ATM per 100 adipocytes, but not ATM per gram tissue; adipocyte size was a confounding variable. We used matching strategies and multivariate regression analyses to investigate the relationships between ATM and inflammatory/metabolic parameters independent of adipocyte size. Matching approaches revealed that the groups discordant for CD206 but concordant for adipocyte size had significantly different fasting insulin and IL-6 concentrations. However, groups discordant for adipocyte size but concordent for ATM differeded in that visceral fat, plasma triglyceride, glucose, and TNF concentrations were greater in those with large adipocytes. Multivariate regression analysis indicated that indexes of insulin resistance and fasting triglycerides were predicted by body composition; the predictive value of ATM per 100 adipocytes or per gram tissue was variable between males and females. We conclude that the relationship between ATM burden and metabolic/inflammatory variables is confounded by adipocyte size/body composition and that ATM do not predict insulin resistance, systemic inflammation, or dyslipidemia. ATM may primarily play a role in tissue remodeling rather than in metabolic pathology.

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.

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 &lt; 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 &lt; 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.

Adipose tissue fatty acid storage varies according to sex, adipose tissue depot, and degree of fat gain. However, the mechanism(s) for these variations is not completely understood. We examined whether differences in adipose tissue glycerol-3-phosphate acyltransferase (GPAT) might play a role in these variations. We optimized an enzyme activity assay for total GPAT and GPAT1 activity in human adipose tissue and measured GPAT activity. Omental and subcutaneous adipose tissue was collected from obese and nonobese adults for measures of GPAT and GPAT1 activities, ex vivo palmitate storage, acyl-CoA synthetase (ACS) and diacylglycerol-acyltransferase (DGAT) activities, and CD36 protein. Total GPAT and GPAT1 activities decreased as a function of adipocyte size in both omental ( r = −0.71, P = 0.003) and subcutaneous ( r = −0.58, P = 0.04) fat. The relative contribution of GPAT1 to total GPAT activity increased as a function of adipocyte size, accounting for up to 60% of GPAT activity in those with the largest adipocytes. We found strong, positive correlations between ACS, GPAT, and DGAT activities for both sexes and depots ( r values 0.58–0.91) and between these storage factors and palmitate storage rates into TAG ( r values 0.55–0.90). We conclude that: 1) total GPAT activity decreases as a function of adipocyte size; 2) GPAT1 can account for over half of adipose GPAT activity in hypertrophic obesity; and 3) ACS, GPAT, and DGAT are coordinately regulated.