A nonhuman primate model of vertical sleeve gastrectomy facilitates mechanistic and translational research in human obesity

Abstract

The obesity epidemic significantly contributes to overall morbidity and mortality. Bariatric surgery is the gold standard treatment for obesity and metabolic dysfunction, yet the mechanisms by which it exerts metabolic benefit remain unclear. Here, we demonstrate a model of vertical sleeve gastrectomy (VSG) in nonhuman primates (NHP) that mimics the complexity and outcomes in humans. We also show that VSG confers weight loss and durable metabolic benefit, where equivalent caloric intake in shams resulted in significant weight gain following surgery. Furthermore, we show that VSG is associated with early, weight-independent increases in bile acids, short-chain fatty acids, and reduced visceral adipose tissue (VAT) inflammation with a polarization of VAT-resident immunocytes toward highly regulatory myeloid cells and Tregs. These data demonstrate that this strongly translational NHP model can be used to interrogate factors driving successful intervention to unravel the interplay between physiologic systems and improve therapies for obesity and metabolic syndrome.

Keywords: Immunology; Obesity medicine; Surgery.

Graphical abstract

Figure 1

Surgical approach and intraoperative photographs of sham surgery and VSG in the NHP (A–G) VSG was performed laparoscopically in the usual fashion (A), while sham surgery replicated surgical stress without anatomic alterations (A). Port placement was the same as in humans (B), and dissection occurred along the greater curvature of the stomach with the division of the short gastric arteries (C). Sham surgery was concluded without stomach stapling, while VSG proceeded with mobilization of the esophageal hiatus (D) and stapled sleeve gastrectomy (E–G). (H) Removed stomach specimen. (I–K) (I) Endoscopic view with intact staple line. At baseline, CLSs of macrophage inflammation in AT were observed (J, representative image, IBA-1 stain, 40x magnification, scale bar = 0.05 mm). AT morphology was homologous to humans (K) (representative image, IBA-1 stain, 4x magnification, scale bar = 0.5 mm). See also Figure S12.

Figure 2

Weight loss, feeding patterns, and glucose metabolism one year after VSG in NHPs (A) Study design schematic of the long-term study. (B–D) VSG resulted in weight loss (B) even with equivalent caloric intake postoperatively. When allowed to eat to caloric excess after D180, VSG animals' body weights increased slightly but still remained at a net negative weight from baseline (B). One animal in the sham group did become hyperglycemic and thus lost weight, and as such was excluded from the calculations in (B). Metabolic control as measured by HgbA1c (C) and HOMA-IR (D) was stable for animals who underwent VSG throughout the study year, even with weight regain by the VSG cohort after D180. ∗p < 0.05, ∗∗p < 0.005, sham vs. VSG. Data reported as group average ±SEM. See also Figures S1, S2, S4, S10, and S11 and Tables S2, S3, and S7.

Figure 3

Macrophage phenotypes, CLSs, and T cell infiltration in AT one year after VSG (A and B) Tissue-resident macrophages (CD64⁺CD45⁺ stromal vascular cells) in VAT were significantly suppressed after VSG (n = 3) compared to sham (n = 3) (A), with less CD206 expression (a classic M2 macrophage marker) and less expression of activation markers CD11c, HLA-DR, and CD169 (B). (C–F) (C) CLS density (expressed as Δchange from D0) trended to slightly increased after sham surgery, but was significantly reduced in VAT after VSG suggested reduced inflammation in the VAT. This was VAT-compartment specific, with SAT (D) demonstrating increases in CLSs after both sham surgery and VSG. Similar trends were seen with CD3⁺ T cells, with a decrease after VSG in VAT (E) but not SAT (F). ∗p < 0.05, sham vs. VSG; #p = 0.05, sham vs. VSG. Data reported as group average ±SEM. See also Figure S3.

Figure 4

Peripheral serum metabolite changes after VSG (A) The secondary BA lithocholic acid was significantly increased after VSG compared to sham at D21 and equalized by D90. (B) The SCFA butyric acid trended toward increased at D21 after VSG. ∗p < 0.05 sham vs. VSG. Data reported as group average ±SEM. See also Figures S5, S6, and Table S4.

Figure 5

Diversity of myeloid and lymphoid immune cells one month after VSG (A–C) Our short-term study (A) was designed to characterize early immunocyte changes in a group of animals with matched weight loss following VSG to the long-term study (B). VSG promoted M2-like macrophage polarization, increased the number of regulatory T cells, and decreased the number of proliferating T cells in the adipose tissue. Fold-change from baseline in PBLs, SAT, and VAT in the ratio of: (C) M2/M1 macrophages (M1: CD206⁺CD11c⁺, M2: CD206⁺CD11c⁻ of CD14⁺CD68⁺CD3^- lym), M2/M1 in SAT n = 1, all others n = 2. (D) Tregs (FoxP3⁺CD4⁺ of CD3⁺ lym). (E) t-SNE projection of 26,400 myeloid cells (CD3⁻CD20^-/CD45⁺ lym) sampled equally from PBLs (n = 2), SAT (n = 2), and VAT (n = 2) at D0 and D28 after VSG. (F) 12 individual FlowSOM-identified myeloid populations from the t-SNE projection in (E) as fold change from D0. (G) Heatmap showing mean expression of indicated markers across the 12 FlowSOM myeloid populations. (H) t-SNE projection of 4860 Tregs (CD25⁺CD127^-/CD4⁺ lym) sampled equally from PBLs (n = 2), SAT (n = 2), and VAT (n = 2) at D0 and D28 after VSG. (I) Six individual FlowSOM-identified Treg populations from the t-SNE projects in (H) as fold change from D0. (J) Heatmap showing mean expression of indicated markers across the six FlowSOM Treg populations. Data reported as group average ±SEM. See also Figures S7, S8, and S9, and Tables S5 and S6.

Figure 6

Serum incretins during OGTTs (A–U) Major incretins in peripheral serum were measured via multiplex assay during OGTTs preoperatively and at D150. Pancreatic polypeptide (A–C) and peptide YY (D–F) were significantly increased and GLP-1 (total) (G–I) trended toward increased after VSG but not after sham surgery. Leptin (J–L), GIP (M–O), glucagon (P–R), and insulin (S–U) were not markedly changed by sham surgery or VSG. ∗p < 0.05, #p = 0.05, sham vs. VSG; ˆp < 0.05, preop vs. D150. Data reported as group average ±SEM. See also Table S8.