OBES SURG (2008) 18:1246–1250 DOI 10.1007/s11695-008-9556-1
RESEARCH ARTICLE
Gastric Bypass Surgery in Rats Produces Weight Loss Modeling after Human Gastric Bypass David S. Tichansky & John D. Boughter Jr. & Jason Harper & A. Rebecca Glatt & Atul K. Madan
Received: 1 February 2008 / Accepted: 5 May 2008 / Published online: 25 June 2008 # Springer Science + Business Media, LLC 2008
Abstract Background The study of the mechanisms of weight loss after bariatric surgery requires an animal model that mimics the human procedure and subsequent weight loss. A rat model eliminates the cognitive efforts associated with human weight loss and gain. Methods A technique for gastric bypass (Roux-en-Y gastric bypass [RYGB]) was developed in Sprague–Dawley rats. A 1- to 2-cc pouch is created from the uppermost stomach using a linear stapler. A 10-cm biliopancreatic limb and 15-cm Roux limb are anastomosed side to side with running nonabsorbable suture. The gastrojejunostomy is created with a single layer of running nonabsorbable suture. Four rats underwent RYGB. Weight loss was compared to four sham rats that had a midline incision and left 60 min with an open abdomen before closure. Results RYGB rats lost an average of 16.5% body weight (BW) at 1 week, 22% BW at 2 weeks, 20% BW at 3 weeks, Presented at the 24th Annual Meeting of the American Society for Bariatric Surgery; June 16, 2007; San Diego, CA. D. S. Tichansky (*) : J. Harper Section of Minimally Invasive Surgery, Department of Surgery, College of Medicine, University of Tennessee Health Science Center, 910 Madison Ave., Suite 208, Memphis, TN 38163, USA e-mail:
[email protected] J. D. Boughter Jr. : A. R. Glatt Department of Anatomy and Neurobiology, College of Medicine, University of Tennessee Health Science Center, Memphis, TN, USA A. K. Madan Division of Laparoendoscopic and Bariatric Surgery, University of Miami Miller School of Medicine, Miami, FL, USA
and 11% BW at 4 weeks. The RYGB rat’s weight was basically level after 4 weeks. The shams lost an average of 4% BW at 1 week, 1% BW at 2 weeks, and 0% BW at 3 weeks and gained an average of 2% at weeks. Subjectively, the RYGB rats were less interested in chow and frequently had chow left in their cage. Conclusion A Sprague–Dawley rat model for gastric bypass has been developed and yields approximately 11% BW loss. This will allow investigators to objectively view factors associated with weight loss without the confounding cognitive factors in humans. Keywords Gastric bypass . Rat model . Weight loss
Introduction In spite of increased public awareness, the obesity epidemic continues to grow. In the quest to significantly impact and reverse the trends in obesity, treatments to substitute surgery or avoid morbid obesity altogether must be found. Even though the most effective form of treatment for morbidly obese individuals is bariatric surgery [1] and weight loss after Roux-en-Y gastric bypass (RYGB) is generally dramatic and sustained [2–4], some individuals cannot tolerate the surgery because of overall poor health. Others are not overweight enough to qualify as a candidate in accordance with the National Institutes of Health guidelines [5]. In lieu of surgery, there are behavior modifications. Effective behavioral modifications must include meaningful dietary modification. To augment will power, medications have been developed to curb appetite (i.e., Meridia). For failure of will power, medications have been developed to cause malabsorption (i.e. Xenical). No medication has been significantly effective long term.
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We previously reported that subjective taste changes occur after gastric bypass surgery [6]. Others have also found that taste changes after gastric bypass surgery occur [7–9]. The proportion to which these changes are psychologically versus physiologically based is unknown. The realm of psychological issues and pathology contributing to obesity is vast. However, if the physiological basis of taste changes could be defined, this could be the target of new treatments to pharmacologically alter food taste making it less appealing. Patients have said that they will eat less after weight loss surgery simply because the food does not taste good [6]. To well study the physiologic aspects of taste, change in the absence of individual psychological issues requires an animal model. Others have previously developed rat models for weight loss surgery. Sclafani [10] developed a jejuno-ileal bypass model and found feeding pattern changes and decreased intake leading to weight loss. Mequid et al. [11] reported some of several variations their group evolved through in the development of a gastric bypass model in rats. They report four successive modifications and ended up with a reliable model with weight loss sustained greater than 2 months. They started with an undivided stapled gastric pouch, a 16-cm biliary–pancreatic limb, and a 10-cm alimentary limb. This achieved weight loss, however, gastrogastric fistulas occurred. They next divided the stomach and were still unsatisfied with the duration of weight loss. Their third variation utilized a longer (30 cm) biliary–pancreatic limb, thus shortening the common chananel and improving the durability of weight loss at 28 days. Lastly, they divided the stomach ‘between two rows of staples’, which lengthened the durability of weight loss beyond 2 months. An important point to introduce is that 60 days is approximately equal to five to six ‘rat years’ [12]. Thus, even weight loss at 21 days is approximately equivalent to 2-year human weight loss data. Although little is known about the mechanisms underlying taste change after gastric bypass in humans, it is clear that an animal model that removes the cerebral issues associated with human weight loss will be very helpful in determining some of these mechanisms. In this investigation, we set forth to develop a reliable rat model of RYGB in an effort to later define these mechanisms and develop nonsurgical treatments for obesity equivalent to gastric bypass surgery.
Methods Development of this model went through many iterations, as described by others [11]. For all procedures, the rats used were diet-induced obese Sprague–Dawley (SD) rats. SD
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rats were purchased at 3–4 weeks of age. The rats were individually housed and placed on a high-fat, high-energy diet for 7 weeks consisting of high-fat chow (D12266B; Research Labs, New Brunswick, NJ, USA) together with a liquid diet (Boost Plus, Mead Johnson). All rats were given ad lib access to diets and tap water. For all procedures, the rats were anesthetized using an intraperitoneal injection of a ketamine/xylazine (75:10 mg/ml) mixture that is administered per kilogram body weight (BW). The abdomen is then shaved and sterilely prepped with alcohol and betadine and draped. To achieve appropriate visualization of the structures, surgeons wore loupes for these procedures. A 3- to 4-cm upper midline incision is made with a scalpel, and any bleeding was controlled with cautery or ties. The procedure is performed as expeditiously as possible. The details of each of the multiple variations utilized during the evolution of this procedure are described below. At the end of each procedure, the midline incision is sutured closed at the fascial level with absorbable (4–0 vicryl; Ethicon) suture and at the skin level using nonabsorbable (4–0 silk; Ethicon) suture. Initially, to show the feasibility of performing these procedures in our facility, we performed a jejuno-ileal bypass. First, the stomach was exposed and the anatomy identified. The small intestine was transected 10-cm distal to the end of the duodenum by placing two absorbable (4–0 vicryl; Ethicon) ties and dividing the bowel between the ties. The proximal cut end was then anastomosed to the jejunum 15-cm downstream to form a side-to-side jejunojejunostomy in a single-layer handsewn technique. A running 5–0 prolene suture (Ethicon) was used with a lacrimal probe to act as a stent when needed. The best descriptive surgical analogy to this anastomosis is the creation of a Cimino arteriovenous fistula. After uneventful survival of this jejuno-ileal bypass animal, we next showed the feasibility of performing division of the stomach in these rats by performing a sleeve gastrectomy. After skin incision and exposure of the stomach, all greater curvature vessels were ligated with absorbable (4–0 vicryl; Ethicon) ties and divided. The stomach was then transected longitudinally using a linearcutting stapler (Ethicon endopath ETS45 2.0 mm) to create a gastric sleeve approximately 4 mm in width along the lesser curvature. After uneventful survival of this sleeve gastrectomy animal, we began developing the gastric bypass model. The first version of the gastric bypass performed was similar to that developed by Meguid’s group [11, 13]. The skin was incised, and the stomach was exposed. All greater curvature vessels were ligated with absorbable (4–0 vicryl; Ethicon) ties and divided. The stomach was then transected transversely to create an approximately 1- to 2-ml pouch (Fig. 1). This pouch is approximately 10% of the original stomach size and retains its original connection to the esophagus. A linear-cutting stapler was utilized to divide
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Fig. 1 Division of stomach. Arrow shows staple line at transverse division point
Fig. 3 Completed procedure. The procedure is completed with creation of the jejunojenunostomy. Arrows show the two anastomoses
the stomach (Ethicon endopath ETS45 2.0 mm). Next, the small intestine was transected 10-cm distal to the end of the duodenum. The point of division is determined at an area where the mesenteric arcades are closest to the bowel (Fig. 2). The distal cut end was anastomosed to the stomach pouch forming a gastrojejunostomy in a single-layer handsewn technique with a running 5–0 prolene suture (Ethicon). The proximal cut end is then anastomosed to this Roux limb 15-cm downstream from the gastrojejunostomy, thus forming a jejunojejunostomy in a single-layer handsewn technique with a running 5–0 prolene (Ethicon) suture. The completed procedure is shown in Fig. 3. The bypassed remainder of the stomach, the so-called excluded stomach, remains in continuity with the duodenum. Modifications made to this original procedure were all complication specific. First, to reduce critical staple line bleeding (0.05). Subjectively, the RYGB rats were less interested in chow and frequently had chow left in their cage. Autopsy results in all four RYGB animals revealed a dilated gastric pouch approximately two to three times the post-surgical volume, but otherwise intact, gastric bypass anatomy.
Discussion Development of a gastric bypass model in rats has been achieved by our group and others [11, 13, 14]. In their study, Suzuki et al. found a statistically significant weight loss difference between RYGB- and sham-operated rats at 4 weeks where we did not. This may be attributable to sample size or the fact that the average starting weight of the rats used in that study were approximately 300 g (40%) larger than ours. Similar to their study, all rats lost weight initially because of postoperative stress. The shams start gaining weight back within the first week and were back to their original weight by week 3. The RYGB rats regained some weight between weeks 3 and 4 but did not return to their original weight. The complexity of such a model is deep. Although the rats fulfill our ultimate goal of a gastric bypass patient without psychological influence, physiologically, they are delicate. Unlike humans, the rats are adversely affected by
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the speed at which obesity is induced, the anesthetic that is used, the pain that they feel, the preoperative diet restriction, and even the smallest degree of blood loss. Any of these stresses placed upon the animal usually results in death. As stated, our model went through many variations before achieving rats capable of further testing. Any institution embarking on this extensive surgery on rats will ultimately need to overcome a large learning curve. However, by allowing investigators to objectively view factors associated with weight loss without the confounding cognitive factors in humans, the rewards may be limitless to the field of bariatric medicine. By removing the psychological issues of obesity and weight loss surgery frequently encountered in human patients, true physiologic studies can be performed. Although there are hormonal changes found in humans after gastric bypass [15–17], could these also be psychologically influenced? Eating behavior is unquestionably psychologically modulated. Newman et al. [18] found food intake to increase proportionately with an increase in the number of daily ‘hassles’. While Goldfield and Legg [19] found that anxiety may have an effect on the value of snack food in low restraint eaters. Masheb [20] examined emotional overeating and found it to be associated with depression and not body mass index or gender. Lastly, sibutramine (Meridia) is a serotonin and norepinephrine reuptake inhibitor not very dissimilar from selective serotonin reuptake inhibitors used to treat depression [21]. Perhaps, psychological issues are the major problems to be conquered in the battle against obesity. Clearly, to make a significant impact on obesity without surgery, this disease will need to be fought on both psychological and physiological grounds. Only by separating the two can we be assured that new treatments can be successful. This animal model will hopefully open the door to nonsurgical physiological targeted treatments in the future.
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