Bariatric surgery reduces visceral adipose inflammation and improves endothelial function in type 2 diabetic mice

Abstract

Objective: Bariatric surgery is emerging as an effective method to alleviate a multitude of medical conditions associated with morbid obesity and type 2 diabetes. However, little is known about the effects and mechanisms of bariatric surgery on visceral fat inflammation and endothelial dysfunction in type 2 diabetes. We hypothesize that bariatric surgery ameliorates interferon-γ-mediated adipose tissue inflammation/oxidative stress and improves endothelial function in type 2 diabetic mice.

Methods and results: Control mice (m Lepr(db)) and diabetic mice (Lepr(db)) were treated with either sham surgery or improved gastric bypass surgery and then were evaluated at 5, 10, 20, and 30 days to assess postsurgical effects. Surgery reduced body weight, abdominal adiposity, blood glucose level, and food intake in Lepr(db). The surgery-induced decrease in visceral adiposity was accompanied by amelioration of T-lymphocytes and macrophage infiltration, as well as reduction in the expression of interferon-γ and other inflammatory cytokines in the mesenteric adipose tissue (MAT) of Lepr(db) mice. Furthermore, surgery improved endothelium-dependent, but not endothelium-independent, vasorelaxation in small mesenteric arteries (SMA) of Lepr(db) mice. The improvement in endothelial function was largely attenuated by nitric oxide synthase inhibitor (L-NAME) incubation. Interferon-γ treatment increased the mRNA expression of tumor necrosis factor-α in the MAT of control mice and incubation of SMA of control mice with tumor necrosis factor-α caused impairment of endothelial function. Superoxide production in MAT/SMA and nitrotyrosine protein level in SMA were elevated in diabetic mice. Surgery reduced MAT/SMA oxidative stress in Lepr(db) mice.

Conclusions: The amelioration of adipose tissue inflammation and the improvement of endothelial function may represent important mechanisms that result in cardiovascular benefits after bariatric surgery.

Figure 1

Improved Gastric Bypass Surgery (IGBS) reduced T-lymphocyte infiltration and IFNγ expression in mesenteric adipose tissue (MAT) of diabetic mice. A, Immunohistochemical staining was performed in control (m Lepr^db) and diabetic (Lepr^db) mice treated with either sham surgery or IGBS. Lepr^db mice were assessed 5, 10, 20, and 30 days post IGBS (P5, P10, P20, and P30), or 20 days after sham surgery. m Lepr^db mice were assessed 20 days after either sham surgery or IGBS. The results show that CD3 positive T-lymphocyte infiltration in MAT was higher in Lepr^db+Sham versus IGBS. Data shown are representative of 4 separate experiments. B, mRNA expression of CD3 increased in MAT of Lepr^db+Sham. IGBS significantly reduced CD3 mRNA levels in MAT. The mRNA (C) and protein (D) expression of T-lymphocyte hallmark cytokine, IFNγ, increased in MAT of Lepr^db+Sham. IGBS decreased the mRNA and protein expression of IFNγ. Data represent mean±SEM, n=4-12 mice. *P<0.05 compared with m Lepr^db+Sham surgery; ^#P<0.05 compared with Lepr^db+Sham surgery.

Figure 2

IGBS reduced macrophage infiltration and MCP-1 expression in MAT of diabetic mice. A, Immunohistochemical staining shows that Mac-3 positive macrophage infiltration in MAT was higher in Lepr^db+Sham versus IGBS. Data shown are representative of 4 separate experiments. B, mRNA expression of CD68 was increased in MAT of Lepr^db+Sham. IGBS significantly reduced CD68 mRNA levels in MAT. The mRNA (C) and protein (D) expression of MCP-1 were increased in MAT of Lepr^db+Sham, and were reduced by IGBS. Data represent mean±SEM, n=4-12 mice. *P<0.05 compared with m Lepr^db+Sham surgery; # P<0.05 compared with Lepr^db+Sham surgery.

Figure 3

IGBS improved endothelium-dependent vasorelaxation to acetylcholine (ACh) in small mesentery arteries (SMA) of Lepr^db mice. Data represent mean±SEM. n=6-31 rings from 4-18 mice (1 or 2 rings per mouse). *P<0.05 compared with m Lepr^db+Sham surgery; # P<0.05 compared with Lepr^db+Sham surgery.

Figure 4

Incubation with nitric oxide synthase inhibitor, L-NAME, largely attenuated the improvement of SMA endothelial function in surgery-treated diabetic mice. Data represent mean±SEM. n=6-31 rings from 4-18 mice (1 or 2 rings per mouse).

Figure 5

IFNγ stimulated the expression of proinflammatory cytokine TNFα, which impaired endothelial function of SMA. A. mRNA expression of TNFα increased in the MAT of m Lepr^db mice treated with IFNγ. Data represent mean±SEM, n=6-8 mice. *P<0.05 compared with m Lepr^db. B, 1 ng/ml recombinant TNFα incubation (90 minutes) only slightly impaired endothelial function of m Lepr^db mice. 10 ng/ml TNFα incubation significantly impaired endothelial function. n=4-5 rings from 4-5 mice (1 ring per mouse). *P<0.05 compared with m Lepr^db.

Figure 6

IGBS ameliorated MAT/SMA oxidative stress. A and B, IGBS reduced superoxide level in MAT and SMA of Lepr^db mice. Data represent mean±SEM. n=6-8 mice. *P<0.05 compared with m Lepr^db+Sham surgery; # P<0.05 compared with Lepr^db+Sham surgery. C, IGBS decreased protein expression of nitrotyrosine in SMA of diabetic mice. Data shown are representative of 3 separate experiments.