Introduction
Bariatric surgery is the most effective medical option to achieve sustained weight loss in severe obesity. Besides traditional procedures such as laparoscopic Roux-en-Y gastric bypass (RYGB), vertical sleeve gastrectomy (VSG) and adjustable gastric banding (LAGB), less invasive options are available such as the (transorally placed) duodenal-jejunal bypass sleeve (DJBS). In general, these procedures lead to a loss of body fat, a reduction of comorbidities and improvement of long-term health risks. Remarkably, the mechanisms behind these outcomes are still poorly understood, and it is conceivable that these comprise different combinations of biological adaptations [
1]. This is reflected in the markedly different immediate effects on glycaemic control following different procedures [
2]. Recently, endoscopic gastroplication has become available as a new minimal invasive technique. The articulating circular endoscopic (ACE) stapler is used to reduce the volume of the stomach without removing tissue or bypassing other intestinal regions. For this procedure, no skin incisions are necessary; it is performed via a transoral route. This procedure results in a median 34.9 % (IQR 17.8–46.6) loss of excess weight in the first year. Moreover, only mild adverse effects were reported so far [
3]. Although several studies have described metabolic and anti-inflammatory effects of bariatric surgery at a molecular level, studies on these processes within the gastrointestinal (GI) tract are still limited. This holds particularly true for the upper GI tract, as most studies in this field have focussed on the mid or lower gastrointestinal tract [
4‐
6]. Moreover, these studies concern effects of RYGB, a procedure extensively changing GI anatomy and physiology. The present study was undertaken to gain more insight in the long-term effects and underlying mechanisms of gastroplication in the upper GI tract: the stomach (fundus and antrum) and the duodenum, and to relate these to general health outcomes, including parameters of inflammation. To this end, transcriptome and gene set enrichment analysis was performed with biopsies obtained before and 1 year following gastroplication.
Conclusions
Results of the present study add important physiological background information to the clinical outcomes observed in patients after undergoing ACE stapler gastroplication. Our plasma analyses revealed beneficial effects on HbA1c and adiponectin levels 1 year after surgery, indicating an improvement of glycaemic control and a favourable shift in adipose tissue mass and/or inflammatory status, respectively. This rise in plasma adiponectin and reduction of HbA1c is in line with previous studies in which a loss of excess body fat was achieved, including those involving other surgical and non-surgical weight loss interventions [
14‐
17]. We also found tendencies for reduced plasma IL-6 and MCP-1 levels, 1 year after intervention. Reduced levels of inflammatory markers are generally assumed to result from a reduction of visceral fat mass in particular, which plays a major role in the low grade inflammatory state associated with obesity [
18]. The total number of patients in our study population is quite small, and it is conceivable that statistical significance might have been reached with a larger patient group. Several other studies have found significant reductions in inflammatory markers like CRP, MCP-1 and IL-6 after bariatric surgery, while others did not find such an effect [
19‐
21].
To our knowledge, this study is the first to analyse long-term whole transcriptome changes in the upper gastrointestinal tract after a new transoral bariatric procedure. Gastroplication reduces gastric volume without altering intestinal anatomy, as is the case with RYGB. In contrast to bypass surgery, exposure of the intestinal epithelium to nutrients and their metabolites is largely maintained after this endoscopic gastroplication. At the same time, small changes related to different GI transit characteristics or changes in the microbiome might still occur.
Analysis of the large amount of data using unbiased transcriptome analysis clearly pointed towards a reduction in inflammatory tone in the fundus and duodenum tissues as manifested by the downregulation of a wide variety of inflammation-related gene sets. The downregulated gene sets in the fundus were mostly related to innate immunity, and particularly associated with downregulation of the complement system, presentation and recognition of antigens (self or pathogenic), IFN-γ signalling and T cell receptor signalling. In the duodenum, the main downregulated gene set was associated with the complement system. Moreover, the top 20 highly changed genes in these locations also suggest notable downregulation of many immune-related processes, of which several were related to chemokines, complement system, interferon signalling and immunoglobulins. These results coincided with the weight loss, improvement of HbA1c levels and decrease of whole-body inflammatory tone in these patients.
Based on the present study, we cannot establish whether the apparent reduction of inflammatory tone in the upper GI tract has a predominantly local cause, i.e. due to a changed food-intake pattern or digestion process, or whether it is related to a reduction of low-grade systemic inflammation due to the reduction of body fat mass.
Increasing evidence points to a link between intestinal inflammation status in general, obesity and (or) diabetes. In obesity, increased innate cell densities, among which macrophages, natural killer cells and T cells, especially the proportion of cytotoxic CD8 T cells, have been observed in the jejunal epithelium. These epithelial T cells were found to be associated with local and systemic comorbidities. Furthermore, isolated T cells from obese patients decreased insulin sensitivity of epithelial cells in vitro [
22]. Another study reported that diet-induced weight loss resulted in a downregulation of inflammatory pathways and inflammatory cytokines IL-8, TNF-α, MCP-1 and IL-1β, in recto-sigmoid mucosal tissue [
23]. Moreover, increased intestinal inflammatory gene expression of TNF-α, IL-6, ICAM and PTGS-2 was found in insulin-resistant obese patients compared to non-insulin-resistant obese patients, suggesting that intestinal inflammation is involved in diabetes during obesity [
24,
25]. A prominent feature of the immune system in the gastrointestinal tract is to provide adequate protection without stimulating excessive inflammation, thereby maintaining a fine balance [
26,
27]. A pro-inflammatory immune status of the gastrointestinal tract in obese patients might be protective against increased luminal challenges associated within obesity but deteriorating for insulin resistance [
22]. Furthermore, this pro-inflammatory status might be linked to the increased prevalence of inflammatory bowel disease and cancer in obese patients [
28‐
30]. In summary, we can only speculate whether the reduced inflammatory microenvironment in gastric and duodenal tissue found after gastroplication can be considered as a positive or negative outcome.
In the antral tissue, gene sets related to cell cycle processes and extracellular matrix were increased. This might be explained by dilation of the stomach, a common observation after gastric volume reduction [
31‐
34]. While gastric volume was not quantified, we perceived the stomach as larger at 1-year follow-up than immediately after gastroplication.
An interesting observation was that the mean gene expression of ghrelin and the enzyme GOAT, responsible for ghrelin acylation, decreased after gastroplication in some of the tissues. At the same time, plasma fasted active ghrelin was increased, and there was a positive correlation between the gene expression of ghrelin and plasma values of active ghrelin. Ghrelin is one of the most prominent hormones secreted from the upper gastrointestinal tract and does not only play a role in appetite regulation but also in inflammation [
13]. Consistent with our results, in RYGB patients, significant lower levels of jejunal ghrelin gene expression have been reported after 10 months [
6]. Furthermore, GOAT mRNA expression and GOAT-positive cell numbers were lower in a non-obese group compared to morbidly obese patients, although no changes in jejunal ghrelin expression were detected [
35]. Moreover, more ghrelin positive cells were found in the stomach of morbidly obese and overweight patients compared to healthy normal weight controls [
36,
37], which might indicate that with weight loss, the number of ghrelin-releasing cells will decrease. The discrepancy with ghrelin expression in the gastrointestinal tract and plasma ghrelin values might be explained by a reduced secretory activity of (a higher number of) ghrelin producing cells in obesity, as suggested by Widmayer et al. [
36]. However, within our patients, there was a positive correlation between its gene expression and plasma levels, indicating that upregulated expression of ghrelin in the fundus was associated with greater increase in fasted ghrelin levels and downregulated expression with a smaller increase 1 year after gastroplication. The underlying cause of the observed changes cannot be pinpointed in our study. It is possible that the changes in ghrelin are dependent on the surgical procedure, which takes place at the main site of ghrelin secretion. Furthermore, the implications of these changes in ghrelin are not fully understood and need further investigation to crystallize the underlying mechanism and to explore the potential of these changes in obesity treatment.
There are some strengths and limitations to this study. The within-person measurement of changes in gastrointestinal gene expression is unique as most studies in this field are observational. By applying a prospective design, we were able to perform paired analysis and look specifically for changes induced by the gastroplication treatment instead of comparing obese subjects with lean controls. Whole transcriptome analysis enabled us to investigate changes in an unbiased manner. One of the limitations of this study is that it was not powered to find differences in inflammatory markers. Therefore, the inclusion of more patients could have strengthened the study. Furthermore, a control group on a lifestyle intervention program could help differentiate between weight loss effects and strictly procedural effects.
This study presents the long-term effects of a new transoral gastroplication treatment in morbidly obese patients. We show that this recently developed ACE stapler procedure was not only effective in reducing body weight as presented before [
3], but also improved glycated haemoglobin levels and increased plasma adiponectin. Furthermore, whole transcriptome analysis suggested a marked downregulation of inflammatory gene sets in both the fundus and duodenum, coinciding with changes in plasma cytokines. Moreover, gene expression of ghrelin and its activating enzyme GOAT were reduced after gastroplication. The apparent reduction of inflammatory tone in the upper GI tract may be a consequence of an improved metabolic health status as associated with weight loss, or alternatively caused by the procedure itself.
In conclusion, this new transoral gastroplication treatment which induced significant weight loss and improved plasma levels of adiponectin and glycated haemoglobin coincides with a reduced inflammatory tone in the upper GI tract. The clinical relevance of our findings remains to be established, as there is still limited knowledge on the role of inflammatory pathways in the upper GI tract in obesity.