Early changes in immune cell metabolism and function are a hallmark of sleeve gastrectomy: a prospective human study

Abstract

Objective: To characterize longitudinal changes in blood biomarkers, leukocyte composition, and gene expression following laparoscopic sleeve gastrectomy (LSG).

Background: LSG is an effective treatment for obesity, leading to sustainable weight loss and improvements in obesity-related co-morbidities and inflammatory profiles. However, the effects of LSG on immune function and metabolism remain uncertain.

Methods: Prospective data was collected from 23 enrolled human subjects from a single institution. Parameters of weight, co-morbidities, and trends in blood biomarkers and leukocyte subsets were observed from pre-operative baseline to one year in three-month follow-up intervals. RNA-sequencing was performed on pairs of whole blood samples from the first six subjects of the study (baseline and three months post-surgery) to identify genome-wide gene expression changes associated with undergoing LSG.

Results: LSG led to a significant decrease in mean total body weight loss (18.1%) at three months and among diabetic subjects a reduction in HbA1c. Improvements in clinical inflammatory and hormonal biomarkers were demonstrated as early as three months after LSG. A reduction in neutrophil-lymphocyte ratio was observed, driven by a reduction in absolute neutrophil counts. Gene set enrichment analyses of differential whole blood gene expression demonstrated that after three months, LSG induced transcriptomic changes not only in inflammatory cytokine pathways but also in several key metabolic pathways related to energy metabolism.

Conclusions: LSG induces significant changes in the composition and metabolism of immune cells as early as three months post-operatively. Further evaluation is required of bariatric surgery's effects on immunometabolism and consequences for host defense and metabolic disease.

Figure 1.

Weight change (A) and percent total body weight loss (TBWL) (B) for each subject over 12 months following sleeve gastrectomy. Serum insulin levels in subjects with T2D (C) over 12 months post operatively. Comparison of HbA1C (%) levels in subjects with T2D (D) at three months to baseline. Dark blue dots indicate values measured at baseline (pre-operatively) and dark red dots indicate values measured during follow-up (post-operatively). Dashed lines between dots indicate missing data for a given subject. Data for each timepoint are summarized as means and 95% confidence intervals. In panel D, the two dark red horizontal lines indicate the HbA1C thresholds for defining prediabetes (bottom, dot-dashed, HbA1C = 5.7%) and diabetes (top, dashed, HbA1C = 6.5%). Significant differences adjusted for multiple testing were marked with the following thresholds: *P < 0.05; **P < 0.01, ***P < 0.001, ****P < 0.0001. T0, baseline; T3, 3 months post-op; T6, 6 months; T9, 9 months; T12, 12 months.

Figure 2.

Changes in key serum clinical inflammatory markers and leukocytes composition: white blood cells (A), C reactive protein (B), interleukin-6 (C), neutrophil counts (D), lymphocyte counts (E) and neutrophil to lymphocyte ratio (F) from baseline to 12 months after undergoing sleeve gastrectomy. Dark blue dots indicate values measured at baseline (pre-operatively) and dark red dots indicate values measured during follow-up (post-operatively). Dashed lines between dots indicate missing data for a given subject. Data for each timepoint are summarized as means and 95% confidence intervals. Significant differences adjusted for multiple testing were marked with the following thresholds: *P < 0.05; **P < 0.01, ***P < 0.001, ****P < 0.0001. T0, baseline; T3, 3 months post-op; T6, 6 months; T9, 9 months; T12, 12 months.

Figure 3.

Changes in serum levels of adiponectin (A), resistin (B), leptin (C) and ghrelin (D) from baseline to 12 months after undergoing sleeve gastrectomy. Blue bars indicate values at baseline (preoperatively). Dark blue dots indicate values measured at baseline (pre-operatively) and dark red dots indicate values measured during follow-up (post-operatively). Dashed lines between dots indicate missing data for a given subject. Data for each timepoint are summarized as means and 95% confidence intervals. Significant differences adjusted for multiple testing were marked with the following thresholds: *P < 0.05; **P < 0.01, ***P < 0.001, ****P < 0.0001. T0, baseline; T3, 3 months post-op; T6, 6 months; T9, 9 months; T12, 12 months.

Figure 4.

Differential expression of 36,593 gene transcripts in whole blood from six subjects at three months following sleeve gastrectomy. The dashed horizontal line corresponds to a false discovery rate (FDR) of 5% (corresponding to nominal P = 0.0093). The dashed vertical line corresponds to a log₂ fold-change (FC) = 1.0. Transcripts showing significant and substantive differential expression (FDR < 5%, log₂ FC > 1.0) are plotted in red. All other transcripts not meeting these two criteria are plotted in light gray. Transcripts of interest are annotated with their respective gene names and are described in the main text (IL27, EGR1, SLCO2A1, IGF2, PDPK2P).

Figure 5.

Heatmap of 112 individual transcript counts from strongest differential expression results in whole blood from six subjects at three months following sleeve gastrectomy (T3). Transcripts showing significant and substantive differential expression (false-discovery rate < 5%, log₂ fold-change > 1.635) were chosen for display. All expression values are centered on the mean values across all six baseline (T0) samples. Red coloring in the heatmap indicates increased expression compared to the baseline mean (beige) across all subjects and blue indicates decreased expression. Samples (columns) are also annotated according to their timepoint: T0 (dark blue) and T3 (dark red).

Figure 6.

A set of 28 hallmark gene sets significantly enriched for differential expression in whole blood from six subjects at three months following sleeve gastrectomy at a false discovery rate (FDR) < 5%. Negative normalized enrichment scores indicate decreased expression of genes in the set following surgery, and positive score indicate increased expression. MSigDB, Molecular Signatures Database.