The short-term and long-term effects of bariatric/metabolic surgery on subcutaneous adipose tissue inflammation in humans

CONTEXT

The mechanisms mediating the short- and long-term improvements in glucose homeostasis following bariatric/metabolic surgery remain incompletely understood.

OBJECTIVE

To investigate whether a reduction in adipose tissue inflammation plays a role in the metabolic improvements seen after bariatric/metabolic surgery, both in the short-term and longer-term.

DESIGN

Fasting blood and subcutaneous abdominal adipose tissue were obtained before (n=14), at one month (n=9), and 6-12months (n=14) after bariatric/metabolic surgery from individuals with obesity who were not on insulin or anti-diabetes medication. Adipose tissue inflammation was assessed by a combination of whole-tissue gene expression and flow cytometry-based quantification of tissue leukocytes.

RESULTS

One month after surgery, body weight was reduced by 13.5±4.4kg (p<0.001), with improvements in glucose tolerance reflected by a decrease in area-under-the-curve (AUC) glucose in 3-h oral glucose tolerance tests (-105±98mmol/L * min; p=0.009) and enhanced pancreatic β-cell function (insulinogenic index: +0.8±0.9pmol/mmol; p=0.032), but no change in estimated insulin sensitivity (Matsuda insulin sensitivity index [ISI]; p=0.720). Furthermore, although biomarkers of systemic inflammation and pro-inflammatory gene expression in adipose tissue remained unchanged, the number of neutrophils increased in adipose tissue 15-20 fold (p<0.001), with less substantial increases in other leukocyte populations. By the 6-12month follow-up visit, body weight was reduced by 34.8±10.8kg (p<0.001) relative to baseline, and glucose tolerance was further improved (AUC glucose -276±229; p<0.001) along with estimated insulin sensitivity (Matsuda ISI: +4.6±3.2; p<0.001). In addition, improvements in systemic inflammation were reflected by reductions in circulating C-reactive protein (CRP; -2.0±5.3mg/dL; p=0.002), and increased serum adiponectin (+1358±1406pg/mL; p=0.003). However, leukocyte infiltration of adipose tissue remained elevated relative to baseline, with pro-inflammatory cytokine mRNA expression unchanged, while adiponectin mRNA expression trended downward (p=0.069).

CONCLUSION

Both the short- and longer-term metabolic improvements following bariatric/metabolic surgery occur without significant reductions in measures of adipose tissue inflammation, as assessed by measuring the expression of genes encoding key mediators of inflammation and by flow cytometric immunophenotyping and quantification of adipose tissue leukocytes.

Improvements in glycemic control after gastric bypass occur despite persistent adipose tissue inflammation

OBJECTIVE

Type 2 diabetes commonly goes into remission following Roux-en-Y gastric bypass (RYGB). As the mechanisms remain incompletely understood, a reduction in adipose tissue inflammation may contribute to these metabolic improvements. Therefore, whether RYGB reduces adipose tissue inflammation compared with equivalent weight loss from an intensive lifestyle intervention was investigated.

METHODS

Sixteen people with obesity and type 2 diabetes were randomized to RYGB or lifestyle intervention. Fasting blood and subcutaneous abdominal adipose tissue were obtained before and after the loss of ∼7% of baseline weight. Adipose tissue inflammation was assessed by whole-tissue gene expression and flow cytometry-based quantification of tissue leukocytes.

RESULTS

At 7% weight loss, insulin and metformin use were reduced among the RYGB but not the Lifestyle cohort, while fasting glucose and insulin declined in both. Adipose tissue inflammation increased modestly after RYGB and to a similar extent following nonsurgical weight loss. In both groups, the number of neutrophils increased severalfold (P < 0.001), mRNA levels of the proinflammatory cytokine interleukin-1β increased (P = 0.037), and mRNA expression of the anti-inflammatory and insulin-sensitizing adipokine adiponectin decreased (P = 0.010).

CONCLUSIONS

A reduction in adipose tissue inflammation is not one of the acute weight loss-independent mechanisms through which RYGB exerts its antidiabetes effects.

Macrophage metalloelastase (MMP12) regulates adipose tissue expansion, insulin sensitivity, and expression of inducible nitric oxide synthase

Macrophage metalloelastase, a matrix metallopeptidase (MMP12) predominantly expressed by mature tissue macrophages, is implicated in pathological processes. However, physiological functions for MMP12 have not been described. Because mRNA levels for the enzyme increase markedly in adipose tissue of obese mice, we investigated the role of MMP12 in adipose tissue expansion and insulin resistance. In humans, MMP12 expression correlated positively and significantly with insulin resistance, TNF-α expression, and the number of CD14(+)CD206(+) macrophages in adipose tissue. MMP12 was the most abundant matrix metallopeptidase detected by proteomic analysis of conditioned medium of M2 macrophages and dendritic cells. In contrast, it was detected only at low levels in bone marrow derived macrophages and M1 macrophages. When mice received a high-fat diet, adipose tissue mass increased and CD11b(+)F4/80(+)CD11c(-) macrophages accumulated to a greater extent in MMP12-deficient (Mmp12(-/-)) mice than in wild-type mice (Mmp12(+/+)). Despite being markedly more obese, fat-fed Mmp12(-/-) mice were more insulin sensitive than fat-fed Mmp12(+/+) mice. Expression of inducible nitric oxide synthase (Nos2) by Mmp12(-/-) macrophages was significantly impaired both in vivo and in vitro, suggesting that MMP12 might mediate nitric oxide production during inflammation. We propose that MMP12 acts as a double-edged sword by promoting insulin resistance while combatting adipose tissue expansion.

n3 PUFAs do not affect adipose tissue inflammation in overweight to moderately obese men and women

Recent studies have indicated that omega-3 (n3) polyunsaturated fatty acids (PUFAs) decrease adipose tissue inflammation in rodents and in morbidly obese humans. We investigated whether a diet rich in n3 PUFAs from both marine and plant sources reduces adipose tissue and systemic inflammation in overweight to moderately obese adults. We conducted a randomized, single-blind, parallel-design, placebo-controlled feeding trial. Healthy men and women with a body mass index between 28 and 33 kg/m(2) consumed a diet rich in n3 PUFAs (3.5% of energy intake; n = 11) from plant and marine sources or a control diet (0.5% of energy intake from n3 PUFAs; n = 13). These diets were consumed for 14 wk (ad libitum for 12 wk). All foods were provided for the entire study period. Subcutaneous abdominal adipose tissue and fasting plasma were collected after the first 2 wk with the control diet and again at the end of the 14-wk dietary period. The primary outcome of this ex post analysis was the adipose tissue gene expression of 13 key mediators of inflammation. Adipose tissue gene expression of inflammatory mediators did not differ between the 2 groups, after adjustment for weight change. Furthermore, none of the 5 plasma markers of systemic inflammation differed significantly as an effect of diet treatment. We conclude that a relatively high dose of n3 PUFAs from plant and marine sources did not significantly lower adipose tissue or systemic inflammation in overweight to moderately obese healthy men and women over 14 wk.

Relationship of ovesity and disease in 73,532 weight-conscious women

The relationship between obesity and 18 different disease conditions was examined in a cross-sectional study of 73,000 weight-conscious women (TOPS Club members). The women reported an average of 1.6 disease conditions each (based on their responses on a questionnaire). Age-specific rates of occurrence for the age group 30-49 years were calculated for each disease condition. The conditions that were found to be significantly (P smaller than 0.001) correlated with obesity were diabetes, high blood pressure, gallbladder disease, gout, thyroid disease, heart disease, arthritis, and jaundice. When the crude relative risks of obesity for each disease condition were calculated, diabetes was found to be the highest (4.5), high blood pressure was second (3.3), and gallbladder disease was third (2.7).