- Email: [email protected]
Endoscopic visceral fat removal as therapy for obesity and metabolic syndrome: a sham-controlled pilot study (with video)
THINKING OUTSIDE THE BOX
Endoscopic visceral fat removal as therapy for obesity and metabolic syndrome: a sham-controlled pilot study (with video) Background: Increased visceral adiposity is a key feature of obesity and metabolic syndrome. Previous studies have generated controversial results regarding visceral fat (VF) removal as a therapy for obesity and metabolic syndrome. Objective: To study the effect of surgical VF removal on metabolic profiles in a mouse model of diet-induced obesity and metabolic syndrome and to evaluate for the first time the feasibility of endoscopic omentectomy using natural orifice transluminal endoscopic surgery (NOTES) technique as treatment for obesity and metabolic syndrome in a feline model. Setting: The Johns Hopkins Hospital. Design: Sham-controlled study in a mouse model of metabolic syndrome and then pilot endoscopic shamcontrolled study in cats. Interventions: Partial or total surgical VF removal was performed in a high-fat diet-induced mouse model of obesity and metabolic syndrome, followed by measurements of metabolic profiles, and endoscopic omentectomy was performed in a feline model using the NOTES approach. Main Outcome Measurements: Weight loss and metabolic profiles. Results: In a mouse model of obesity, total but not partial VF removal significantly improved obesity and metabolic syndrome, including insulin resistance and hepatic steatosis (all P ⬍ .05 vs sham surgery). The improved metabolic syndrome was associated with significantly decreased inflammatory cytokines. In a feline model, endoscopic omentectomy was feasible and safe and resulted in a net weight loss compared with sham surgery (⫺387 ⫾ 437 g vs 233 ⫾ 351 g, P ⫽ .1, respectively). Limitations: Animal experiments. Conclusions: Endoscopic omentectomy is safe and feasible and has the potential to treat obesity and metabolic syndrome. Near-total VF removal is required to achieve net weight loss and improvement of metabolic syndrome. (Gastrointest Endosc 2011;74:637-44.)
Obesity and the related metabolic syndrome, including insulin resistance, type 2 diabetes, nonalcoholic fatty liver disease (NAFLD), atherosclerosis, and cardiovascular and cerebrovascular diseases, are increasing rapidly worldwide.1,2 Although the precise mechanisms underlying the pathogenesis of metabolic syndrome are still poorly understood, visceral fat (VF), rather than overall obesity, is closely correlated with insulin resistance, suggesting its pathogenic role in this syndrome.3,4 VF has been identified
Abbreviations: NAFLD, nonalcoholic fatty liver disease; NOTES, natural orifice transluminal endoscopic surgery; TNF, tumor necrosis factor; VF, visceral fat. Copyright © 2011 by the American Society for Gastrointestinal Endoscopy 0016-5107/$36.00 doi:10.1016/j.gie.2011.07.006
www.giejournal.org
as an independent risk factor for insulin resistance and NAFLD.5,6 The adverse metabolic impact of VF has been attributed to the distinct biological properties of visceral adipocytes compared with other fat cells. Visceral adipocytes show higher lipolytic rates in response to insulin7 and lower sensitivity to antilipolytic effects8 compared with subcutaneously derived fat cells. Visceral adipocytes also demonstrate a higher insulin-stimulated glucose uptake compared with subcutaneous fat cells both in vivo9 and in vitro.10 Increased visceral fat, manifested as central obesity, leads to a greater mobilization of free fatty acids into the portal circulation, contributing to NAFLD, systemic insulin resistance, and metabolic syndrome. Because of its critical role in the pathogenesis of metabolic syndrome, VF has been a target for therapies for obesity and metabolic syndrome. There is no specific medical therapy to reduce VF mass. Diet and lifestyle Volume 74, No. 3 : 2011 GASTROINTESTINAL ENDOSCOPY 637
Thinking Outside the Box
interventions are successful in ameliorating some aspects of the dysmetabolic phenotype.11,12 Surgical reduction of VF has been most extensively studied to achieve the therapeutic goal of weight loss and improvement of the metabolic syndrome. Several animal studies have shown that VF removal improves insulin resistance, one of the key markers of the metabolic syndrome.13,14 However, results from human studies of omentectomy in obese patients undergoing bariatric surgery have been mixed.15-17 The aims of this study were to study the effect of surgical VF removal on metabolic profiles in a mouse model of diet-induced obesity and metabolic syndrome and to evaluate for the first time the feasibility of endoscopic omentectomy using natural orifice transluminal endoscopic surgery (NOTES) technique as treatment of obesity and metabolic syndrome in a feline model.
METHODS This study was performed in 2 phases with 2 animal models. First, a mouse model of diet-induced obesity and metabolic syndrome was used to determine the metabolic effects of total versus partial surgical omentectomy. This was followed by a feasibility study of endoscopic omentectomy in a feline model using the NOTES technique. All animal experiments fulfilled National Institutes of Health and institutional criteria for the humane treatment of laboratory animals and were approved by The Johns Hopkins University School of Medicine Animal Care Institutional Review Board.
Mouse model experiments Adult (age 6-8 weeks) male wild-type C57BL-6 mice were purchased from Jackson Laboratories (Bar Harbor, Maine). The mice were fed with commercial diets with either normal or high-fat content as previously described.18 This high-fat diet–induced obese mouse model was used because it expresses many features of the human metabolic syndrome, such as obesity, insulin resistance, NAFLD, and hyperlipidemia.18 After 8 weeks, mice fed a high-fat diet were divided into 3 groups according to type of therapy received: (1) sham surgery in which animals were under anesthesia and had an abdominal incision but omentectomy was not performed; (2) partial omentectomy and unilateral epididymal fat pad removal (⬃50% of VF removed); or (3) total omentectomy and bilateral epididymal fat pad removal (total VF removal). After recovering from surgery, the animals were continued on a high-fat diet for an additional 4 weeks. At 4 weeks, animals were killed, and serum and liver tissue were collected for analysis. All mice were maintained in a temperature- and light-controlled facility and permitted ad libitum consumption of water and pellet chow. The effect of VF removal on the metabolic profiles and liver histology of the animals were tested as follows. Glucose tolerance test. After an overnight fast, a blood sample was obtained from each animal. Glucose was measured using an Accu-Check glucometer (Roche 638 GASTROINTESTINAL ENDOSCOPY Volume 74, No. 3 : 2011
Xia et al
Diagnostics, Indianapolis, IN) with a range of 20 to 600 mg/dL. Serum leptin and tumor necrosis factor ␣ levels. Serum leptin and tumor necrosis factor alpha (TNF)␣ levels were measured with a commercially available enzymelinked immunosorbent assay kit (R&D Systems, Minneapolis, Minn), using standards supplied by the manufacturer. Liver histology and triglyceride content. Thin slices of liver tissue were stained with hematoxylin. Total lipids were extracted from liver tissue according to a previously published technique.19 Triglyceride content was measured with a kit according to manufacturer’s instructions (TR0100; Sigma-Aldrich, St. Louis, Mo).
Feline model experiments: endoscopic omentectomy Eight adult (aged 5 years) domestic shorthair cats were obtained from Liberty Research (Waverly, NY). Each cat was housed separately in cages and provided unlimited access to water and a commercial high-fat diet (Iams Ocean Fish and Rice) for 8 weeks. Animals were then divided into 2 groups: sham surgery or partial (subtotal) endoscopic omentectomy. After overnight fasting, cats were put under general anesthesia by a professional veterinarian. All experiments were performed under standard sterile techniques. A forward-viewing double-channel endoscope was introduced into the stomach. The gastric cavity was irrigated with dilute povidone iodine. The anterior gastric wall at the junction of the body and the antrum was punctured with a needle-knife and then dilated using a controlled radial expansion balloon to 15 mm. The endoscope was advanced into the peritoneal cavity, which was systematically explored. For omentectomy, part of the greater omentum was grasped with a forceps, brought back to the gastric cavity, and excised with a snare. Repeated similar steps were performed until approximately 75% of the omentum was removed (Video 1, available online at www.giejournal.org). For sham surgery, the endoscope was introduced into the peritoneal cavity after gastrotomy and maintained in the peritoneal cavity for a duration of time similar to that for the omentectomy group. After omentectomy or sham surgery, the endoscope was withdrawn into the stomach. The gastric wall incision was closed with endoscopic clips (Video 1). The excised omentum was removed with a Roth basket (US Endoscopy, Mentor, OH) along with the withdrawal of the endoscope. The cats recovered from the anesthesia and fed with a pureed diet the night of the operation. The cats resumed normal solid diets on the following day and fed for another 4 weeks before necropsy. The dietary intake of cats was closely monitored but not restricted. Serum samples were collected at the time of endoscopic procedures and then immediately before they were killed. Postmortem examination was performed to reveal any evidence of intra-abdominal injuries or infection, and liver tissue was collected for analysis. www.giejournal.org
Xia et al
Thinking Outside the Box
TABLE 1. Surgical total versus partial VF removal in a mouse model
VF removed
Total (n ⴝ 5)
Partial (n ⴝ 5)
P value
Weight of VF removed, g, ⫾ SD
2.1 ⫾ 0.35 0.85 ⫾ 0.24 ⬍.01
% of body weight, ⫾ SD
4.91 ⫾ 0.47 2.12 ⫾ 0.46 ⬍.01
VF, Visceral fat; SD, standard deviation.
Statistical analysis All values are expressed as mean ⫾ standard deviation. Treatment-related differences were evaluated by analysis of variance. The paired-individual means were compared by a t test. P values ⬍.05 were considered statistically significant.
RESULTS Total but not partial VF removal improves obesity and metabolic syndrome The weight of the omentum removed was 2.1 ⫾ 0.35 g in the total omentectomy group and 0.85 ⫾ 0.24 g in the partial omentectomy group (Table 1). Only animals that had total VF removal surgery lost significant net weight 4 weeks after surgery (⫺13.04 ⫾ 2.57 g, P ⬍ .001 vs both sham surgery and partial omentectomy groups) (Fig. 1A). The weight loss was sustained and significantly larger than can be accounted for by the weight of fat removed (Fig. 1B, Table 1). On the other hand, animals that underwent sham surgery or partial omentectomy gained weight (10.44 ⫾ 7.23 g and 13.87 ⫾ 0.99 g, respectively). Animals that underwent total VF removal also had significantly improved glucose tolerance test results (P ⬍ .05 vs sham) (Fig. 1C). In addition, the homeostasis model assessment insulin resistance (⫽ glucose ⫻ insulin/405), a wellestablished index for insulin sensitivity and insulin resistance,20 showed a close to normal improvement in animals that underwent total omentectomy (P ⬍ .05 vs sham) (Fig. 1D). Partial VF removal had little impact on animal weight, glucose tolerance, and insulin resistance (Fig. 1A-D). One phenomenon that is frequently associated with obesity and metabolic syndrome is fatty liver disease. Visceral adiposity is closely related to fatty liver disease.21 To evaluate the impact of VF removal on fatty liver disease, the liver histology and triglyceride content were examined. Total VF removal significantly improved hepatic steatosis and reduced hepatic triglyceride content (P ⬍ .05 vs sham) (Fig. 2A, B). Again, the benefit of improved fatty liver was noted in animals that received near-total VF removal but not in animals that had partial VF removal. www.giejournal.org
The improvement of obesity and metabolic syndrome by total VF removal is associated with an improved cytokine profile VF secretes many cytokines that regulate inflammatory signaling and influence insulin sensitivity. Among them, TNF␣, leptin, and adiponectin play important roles in modulating obesity and metabolic syndrome.22-24 A recent study has shown that their levels are closely correlated with visceral adiposity.25 Serum levels of TNF␣, leptin, and adiponectin were evaluated. Total VF removal significantly reduced leptin and TNF␣ levels (P ⬍ .05 vs sham) (Fig. 3A, B) but did not alter adiponectin level (Fig. 3C).
Endoscopic omentectomy is a safe and feasible method for VF removal To test the feasibility of endoscopic VF removal as treatment of obesity and metabolic syndrome, endoscopic omentectomy and a sham procedure were performed in a total of 8 cats using the NOTES technique. One cat died before the endoscopic procedure of complications from anesthesia. Three cats had sham surgeries and 4 had partial (near total) endoscopic omentectomy. On average, it took less than 2 hours to remove the majority of the omentum (Table 2, Fig. 1). Endoscopic omentectomy was feasible and was performed safely without any complication (Video 1). The average weight of the omentum removed was 37.24 ⫾ 6.09 g. All cats recovered well from surgery and resumed their diet on the same day of surgery. Postmortem examination 4 weeks after surgery showed no signs of infection or other organ injury. Overall, cats that underwent omentectomy lost more net weight than cats that underwent sham surgery (Table 2, Fig. 4), although the difference did not reach statistical significance (⫺387 ⫾ 437 g vs 233 ⫾ 351 g, P ⫽ .1, respectively).
DISCUSSION The prevalence of obesity and its associated metabolic syndrome, including fatty liver disease and insulin resistance, has increased rapidly.1,2 Because VF plays a key role in the pathogenesis of obesity and metabolic syndrome,26 VF removal has been studied as a therapeutic method to improve obesity and metabolic syndrome. Previous studies have shown that VF removal improves the metabolic syndrome in animal models.13,14 However, human studies of surgical omentectomy have generated inconsistent results.15,16 Recently, Fabbrini et al17 demonstrated, in both a randomized, controlled trial and a longitudinal single-arm study, that VF removal did not add additional benefit in obese patients who underwent gastric bypass surgeries. The reasons for these contradictive results are unclear. The current study, however, provides a potential mechanism to explain the amount of VF that needs to be removed to achieve the therapeutic goal of a significant net weight loss and improvement of metabolic syndrome. We used a Volume 74, No. 3 : 2011 GASTROINTESTINAL ENDOSCOPY 639
Thinking Outside the Box
Xia et al
Figure 1. Total but not partial visceral fat (VF) removal improves obesity and insulin resistance. A, The weight of the animal before (open bar) and 4 weeks after (solid bar) VF removal surgery (*P ⬍ .05 vs before surgery). B, Percentage of weight change before and 4 weeks after surgery (*P ⬍ .05 vs sham). C, Glucose tolerance tests 4 weeks after surgery (*P ⬍ .05 vs HF; #P ⬍ .05 vs sham). D, Homeostasis model assessment-insulin resistance (HOME-IR) 4 weeks after surgery (*P ⬍ .05 vs HF; #P ⬍ .05 vs sham). ND, normal diet control; HF, high-fat diet control; HF ⫹ sham, high-fat diet with sham surgery; HF ⫹ partial, high-fat diet with partial VF removal; HF ⫹ total, high-fat diet with near-total VF removal (5 per group).
Figure 2. Total but not partial visceral fat (VF) removal improves hepatic steatosis. A, Representative liver histology with hematoxylin and eosin stains (orig. mag. ⫻160). B, Hepatic triglyceride contents (5 per group vs high fat [HF], *P ⬍ .05 vs HF; #P ⬍ .05 vs sham). ND, normal diet.
mouse model of high-fat diet–induced obesity and metabolic syndrome that resembles human disease. In mice, there are 4 VF depots: (1) the paired gonadal depots are attached to the uterus and ovaries in females and the 640 GASTROINTESTINAL ENDOSCOPY Volume 74, No. 3 : 2011
epididymis and testes in males; (2) the paired retroperitoneal depots are found along the dorsal wall of the abdomen surrounding the kidney; (3) the mesenteric depot supports the intestines; and (4) the omental depot is near www.giejournal.org
Xia et al
Thinking Outside the Box
Figure 3. Effect of visceral fat (VF) removal on cytokine profiles. Serum levels of leptin (A), tumor necrosis factor ␣ (TNF␣) (B), and adiponectin (C) were measured by commercially available enzyme-linked immunosorbent assay (5 per group, *P ⬍ .05; **P ⬍ .01 vs high fat (HF); #P ⬍ .05 vs sham).
TABLE 2. Endoscopic omentectomy in a feline model Sham surgery
Omentectomy
Weight preop, kg
4.67 ⫾ 0.50
5.25 ⫾ 0.37
Weight postop,* kg
4.90 ⫾ 0.85
4.83 ⫾ 0.78
Weight change, kg
0.23 ⫾ 0.35
⫺0.43 ⫾ 0.44
BMI preop
50.03 ⫾ 6.42
52.53 ⫾ 10.01
BMI postop*
52.53 ⫾ 10.01
49.68 ⫾ 5.47
BMI change
2.50 ⫾ 3.90
⫺4.58 ⫾ 4.80
Matched
112.5 ⫾ 15
N/A
37.24 ⫾ 6.09
Serum glucose preop, mg/dL
80.3 ⫾ 5.7
98.0 ⫾ 12.7
Serum glucose postop, mg/dL
97.0 ⫾ 17.1
94.5 ⫾ 18.4
Serum ALT preop, U/L
58.7 ⫾ 15.5
55.5 ⫾ 12.3
Serum ALT postop, U/L
58.3 ⫾ 17.2
43.0 ⫾ 7.5
Serum AST preop, U/L
22.3 ⫾ 5.7
22.3 ⫾ 6.6
Serum AST postop, U/L
22 ⫾ 17.2
17 ⫾ 3.4
Serum cholesterol preop, mg/dL
98.7 ⫾ 7.6
118.3 ⫾ 38.1
Serum cholesterol postop, mg/dL
123.0 ⫾ 14.7
117.0 ⫾ 43.7
Serum triglyceride preop, mg/dL
31.7 ⫾ 6.4
30.7 ⫾ 2.3
Serum triglyceride postop, mg/dL
40.8 ⫾ 18.3
37.3 ⫾ 10.4
Liver triglyceride content postop, mg/g of tissue
18.9 ⫾ 3.4
19.8 ⫾ 3.0
Operation time, min Omental fat removed, g
Preop, Preoperatively; postop, postoperatively; BMI, body mass index; ALT, alanine aminotransferase; AST, aspartate aminotransferase. *Postmortem examination was performed 4 weeks after surgery.
www.giejournal.org
the stomach and spleen. In high-fat diet–induced obesity model, the majority of fat is in gonadal and mesenteric depots.27 We evaluated the effect of near-total (bilateral gonadal depots and the whole mesenteric depot) or partial (unilateral gonadal depot and half of mesenteric depot) VF removal. Our study shows that only near-total, but not partial, VF removal asserts its benefit through an improved proinflammatory cytokine profile. The fact that partial omentectomy was performed in most published human studies may explain the suboptimal results in these studies. In fact, Fabbrini et al17 acknowledged that removing a greater amount of VF could have resulted in beneficial metabolic effects. Endoscopic removal of more VF than the greater omentum has not been studied. In the current study, an average of about 2 hours was needed to remove approximately 35 g of omental fat. An average obese human omentum weighs about 800 g.17 The main current limitation to all NOTES procedures, including that described in the current study, is the lack of optimal instruments and accessories necessary to achieve efficient NOTES interventions. A flexible laparoscope with variable stiffness properties and large therapeutic channel will be necessary to achieve rapid endoscopic omentectomy. Therefore, better instrumentation is needed to render complete endoscopic omentectomy efficient and ready for clinical trials. The TNF␣ signaling pathway has been shown to mediate obesity-related insulin resistance.28 Inhibition of TNF␣ signaling pathway improves obesity-related insulin resistance.29 Therefore, we believe that the reduced TNF␣ level and activity observed in the current study may have contributed to the improved metabolic profile exerted by total VF removal. On the other hand, leptin plays an important role in the pathogenesis of obesity by mediating the neuroendocrine response to food deprivation.23 Serum leptin levels decrease exponentially with reduced total fat mass.30 The decreased leptin level after total VF removal reflects the reduction of total body fat mass in these animals. In all, improved cytokine profile, especially reduced Volume 74, No. 3 : 2011 GASTROINTESTINAL ENDOSCOPY 641
Thinking Outside the Box
Xia et al
Figure 4. Effect of endoscopic omentectomy. Representative images of greater omentum of sham surgery (A) and omentectomy (B) are shown. Individual animal weight (C) and body mass index (BMI) (D) before (pre-op) and at the time of postmortem examination (post-op) are graphed.
TNF␣, may contribute to the positive effect of VF removal on obesity and metabolic syndrome. There has been a growing interest in endoluminal and transgastric devices for preoperative or stand-alone weight loss procedures.31 Here, we provide a proof-of-concept study that endoscopic omentectomy, using standard NOTES techniques and conventional instruments, is safe, feasible, and effective. We chose domestic cats as our endoscopic omentectomy model, because (1) cats are one of few animal species that can have obesity with changes in fat metabolism similar to those in human beings32; (2) the upper GI anatomy and physiology of the cat closely simulates the human GI system, making it an appropriate animal candidate for GI endoscopic research33; and (3) cats have tendency to become obese by overfeeding within a short period of time, owing to their energy metabolism characteristic.34 Although endoscopic omentectomy resulted in net weight loss, it did not reach statistical significance. This is likely attributable to the small sample size in this pilot study. The weight lost far exceeded the amount of omental fat removed (Table 2). In addition, endoscopic omentectomy improved some of metabolic markers (eg, glucose, cholesterol), but none of them reached statistical significance (Table 2). 642 GASTROINTESTINAL ENDOSCOPY Volume 74, No. 3 : 2011
All endoscopic omentectomy procedures were performed safely without any complications. All cats resumed feeding on same day of the procedures. There was never any significant bleeding. Snaring of the omentum was performed with a blended current. If bleeding did occur, we were prepared to treat it using standard endoscopic cautery devices Successful gastrotomy closure was performed by using endoscopic clips in all procedures. Other closure methods, such as the use of over-the-scope clips, is likely a more reliable closure method. However, the use of simple clips for access closure is still the most widely used technique, probably because of ease of use, wide availability, and relatively low cost. A main limitation of the current study is the use of 2 different animal models. The mouse model is not appropriate for endoscopic interventions. The feline model was used to prove the concept that endoscopic omentectomy is feasible. However, the feline model has its limitations when it comes to metabolic profile analysis, including lack of reagents for detailed metabolic and inflammatory cytokine analysis. The mouse model of obesity and metabolic syndrome is well established with widely available commercial reagents for detailed analysis. It was used for proof of principle that near-total VF removal was necessary to www.giejournal.org
Xia et al
exert the therapeutic benefit of improving metabolic syndrome. In summary, endoscopic omentectomy is safe and feasible and has the potential to treat obesity and metabolic syndrome. Near-total VF removal is required to achieve net weight loss and improvement of metabolic syndrome, which is likely attributable to an improved proinflammatory cytokine profile. Superior instrumentation is needed to render complete endoscopic omentectomy efficient and ready for clinical trials. DISCLOSURE The following author disclosed financial relationships relevant to this publication: Dr. Kalloo: founding member of, equity holder in, and consultant for Apollo Endosurgery. The other authors disclosed no financial relationships relevant to this publication. This work was supported by a research grant from NIH/NIDDK R01DK075990 (Z.L.). ACKNOWLEDGMENTS We thank James Potter for his insightful suggestions and editorial assistance and Ron Wroblewski for providing technical assistant. Lu Xia, MD, PhD The Johns Hopkins University Baltimore, Maryland, USA Ruijin Hospital Shanghai Jiaotong University School of Medicine Shanghai, China Jing Hua, MD, PhD Renji Hospital Shanghai Jiaotong University School of Medicine Shanghai, China Xavier Dray, MD Hôpital Lariboisière APHP University of Paris Paris, France Mouen A. Khashab, MD The Johns Hopkins University Baltimore, Maryland, USA Shuwen Liang, PhD The Johns Hopkins University Baltimore, Maryland, USA Yong-sik Kim, MD Korea University College of Medicine Seoul, Korea Cristina Jimeno-Ayllon, MD Hospital Virgen de la Luz Cuenca, Spain www.giejournal.org
Thinking Outside the Box
Anthony N. Kalloo, MD The Johns Hopkins University Baltimore, Maryland, USA Zhiping Li, MD The Johns Hopkins University Baltimore, Maryland, USA REFERENCES 1. Clark JM, Brancati FL, Diehl AM. The prevalence and etiology of elevated aminotransferase levels in the United States. Am J Gastroenterol 2003; 98:960-7. 2. Farrell GC, Chitturi S, Lau GK, et al. Guidelines for the assessment and management of non-alcoholic fatty liver disease in the Asia-Pacific region: executive summary. J Gastroenterol Hepatol 2007;22:775-7. 3. Bray GA, Jablonski KA, Fujimoto WY, et al. Relation of central adiposity and body mass index to the development of diabetes in the Diabetes Prevention Program. Am J Clin Nutr 2008;87:1212-8. 4. Fox CS, Massaro JM, Hoffmann U, et al. Abdominal visceral and subcutaneous adipose tissue compartments: association with metabolic risk factors in the Framingham Heart Study. Circulation 2007;116:39-48. 5. Poirier P, Lemieux I, Mauriege P, et al. Impact of waist circumference on the relationship between blood pressure and insulin: the Quebec Health Survey. Hypertension 2005;45:363-7. 6. Jakobsen MU, Berentzen T, Sorensen TI, et al. Abdominal obesity and fatty liver. Epidemiol Rev 2007;29:77-87. 7. Zierath JR, Livingston JN, Thorne A, et al. Regional difference in insulin inhibition of non-esterified fatty acid release from human adipocytes: relation to insulin receptor phosphorylation and intracellular signalling through the insulin receptor substrate-1 pathway. Diabetologia 1998; 41:1343-54. 8. Vikman HL, Savola JM, Raasmaja A, et al. Alpha 2A-adrenergic regulation of cyclic AMP accumulation and lipolysis in human omental and subcutaneous adipocytes. Int J Obes Relat Metab Disord 1996;20:185-9. 9. Virtanen KA, Hallsten K, Parkkola R, et al. Differential effects of rosiglitazone and metformin on adipose tissue distribution and glucose uptake in type 2 diabetic subjects. Diabetes 2003;52:283-90. 10. Lundgren M, Buren J, Ruge T, et al. Glucocorticoids down-regulate glucose uptake capacity and insulin-signaling proteins in omental but not subcutaneous human adipocytes. J Clin Endocrinol Metab 2004;89: 2989-97. 11. Knowler WC, Barrett-Connor E, Fowler SE, et al. Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. N Engl J Med 2002;346:393-403. 12. Lindstrom J, Eriksson JG, Valle TT, et al. Prevention of diabetes mellitus in subjects with impaired glucose tolerance in the Finnish Diabetes Prevention Study: results from a randomized clinical trial. J Am Soc Nephrol 2003;14:S108-13. 13. Lottati M, Kolka CM, Stefanovski D, et al. Greater omentectomy improves insulin sensitivity in nonobese dogs. Obesity (Silver Spring) 2009;17:674-80. 14. Gabriely I, Ma XH, Yang XM, et al. Removal of visceral fat prevents insulin resistance and glucose intolerance of aging: an adipokine-mediated process? Diabetes 2002;51:2951-8. 15. Thorne A, Lonnqvist F, Apelman J, et al. A pilot study of long-term effects of a novel obesity treatment: omentectomy in connection with adjustable gastric banding. Int J Obes Relat Metab Disord 2002;26:193-9. 16. Csendes A, Maluenda F, Burgos AM. A prospective randomized study comparing patients with morbid obesity submitted to laparotomic gastric bypass with or without omentectomy. Obes Surg 2009;19:490-4. 17. Fabbrini E, Tamboli RA, Magkos F, et al. Surgical removal of omental fat does not improve insulin sensitivity and cardiovascular risk factors in obese adults. Gastroenterology 2010;139:448-55. 18. Li Z, Soloski MJ, Diehl AM. Dietary factors alter hepatic innate immune system in mice with nonalcoholic fatty liver disease. Hepatology 2005; 42:880-5.
Volume 74, No. 3 : 2011 GASTROINTESTINAL ENDOSCOPY 643
Thinking Outside the Box
19. Folch J, Lees M, Sloane-Stanley GH. A simple method for the isolation and purification of total lipids from animal tissues. J Biol Chem 1957;226: 457-509. 20. Radziuk J. Insulin sensitivity and its measurement: structural commonalities among the methods. J Clin Endocrinol Metab 2000;85:4426-33. 21. Guerrero R, Vega GL, Grundy SM, et al. Ethnic differences in hepatic steatosis: an insulin resistance paradox? Hepatology 2009;49:791-801. 22. Nieto-Vazquez I, Fernandez-Veledo S, Kramer DK, et al. Insulin resistance associated to obesity: the link TNF-alpha. Arch Physiol Biochem 2008; 114:183-94. 23. Mantzoros CS. The role of leptin in human obesity and disease: a review of current evidence. Ann Intern Med 1999;130:671-80. 24. Pajvani UB, Du X, Combs TP, et al. Structure-function studies of the adipocyte-secreted hormone Acrp30/adiponectin. Implications fpr metabolic regulation and bioactivity. J Biol Chem 2003;278:9073-85. 25. Lira FS, Rosa JC, Dos Santos RV, et al. Visceral fat decreased by long-term interdisciplinary lifestyle therapy correlated positively with interleukin-6 and tumor necrosis factor-alpha and negatively with adiponectin levels in obese adolescents. Metabolism 2011;60:359-65. 26. Despres JP, Lemieux I. Abdominal obesity and metabolic syndrome. Nature 2006;444:881-7.
644 GASTROINTESTINAL ENDOSCOPY Volume 74, No. 3 : 2011
Xia et al
27. Bachmanov AA, Reed DR, Tordoff MG, et al. Nutrient preference and diet-induced adiposity in C57BL/6ByJ and 129P3/J mice. Physiol Behav 2001;72:603-13. 28. Hotamisligil GS, Shargill NS, Spiegelman BM. Adipose expression of tumor necrosis factor-alpha: direct role in obesity-linked insulin resistance. Science 1993;259:87-91. 29. Yuan M, Konstantopoulos N, Lee J, et al. Reversal of obesity- and dietinduced insulin resistance with salicylates or targeted disruption of IKKbeta. Science 2001;293:1673-7. 30. Considine RV, Sinha MK, Heiman ML, et al. Serum immunoreactiveleptin concentrations in normal-weight and obese humans. N Engl J Med 1996;334:292-5. 31. Cote GA, Edmundowicz SA. Emerging technology: endoluminal treatment of obesity. Gastrointest Endosc 2009;70:991-9. 32. Hoenig M, Hall G, Ferguson D, et al. A feline model of experimentally induced islet amyloidosis. Am J Pathol 2000;157:2143-50. 33. Moore LE. The advantages and disadvantages of endoscopy. Clin Tech Small Anim Pract 2003;18:250-3. 34. Kley S, Hoenig M, Glushka J, et al. The impact of obesity, sex, and diet on hepatic glucose production in cats. Am J Physiol Regul Integr Comp Physiol 2009;296:R936-43.
www.giejournal.org
Endoscopic visceral fat removal as therapy for obesity and metabolic syndrome: a sham-controlled pilot study (with video) Background: Increased visceral adiposity is a key feature of obesity and metabolic syndrome. Previous studies have generated controversial results regarding visceral fat (VF) removal as a therapy for obesity and metabolic syndrome. Objective: To study the effect of surgical VF removal on metabolic profiles in a mouse model of diet-induced obesity and metabolic syndrome and to evaluate for the first time the feasibility of endoscopic omentectomy using natural orifice transluminal endoscopic surgery (NOTES) technique as treatment for obesity and metabolic syndrome in a feline model. Setting: The Johns Hopkins Hospital. Design: Sham-controlled study in a mouse model of metabolic syndrome and then pilot endoscopic shamcontrolled study in cats. Interventions: Partial or total surgical VF removal was performed in a high-fat diet-induced mouse model of obesity and metabolic syndrome, followed by measurements of metabolic profiles, and endoscopic omentectomy was performed in a feline model using the NOTES approach. Main Outcome Measurements: Weight loss and metabolic profiles. Results: In a mouse model of obesity, total but not partial VF removal significantly improved obesity and metabolic syndrome, including insulin resistance and hepatic steatosis (all P ⬍ .05 vs sham surgery). The improved metabolic syndrome was associated with significantly decreased inflammatory cytokines. In a feline model, endoscopic omentectomy was feasible and safe and resulted in a net weight loss compared with sham surgery (⫺387 ⫾ 437 g vs 233 ⫾ 351 g, P ⫽ .1, respectively). Limitations: Animal experiments. Conclusions: Endoscopic omentectomy is safe and feasible and has the potential to treat obesity and metabolic syndrome. Near-total VF removal is required to achieve net weight loss and improvement of metabolic syndrome. (Gastrointest Endosc 2011;74:637-44.)
Obesity and the related metabolic syndrome, including insulin resistance, type 2 diabetes, nonalcoholic fatty liver disease (NAFLD), atherosclerosis, and cardiovascular and cerebrovascular diseases, are increasing rapidly worldwide.1,2 Although the precise mechanisms underlying the pathogenesis of metabolic syndrome are still poorly understood, visceral fat (VF), rather than overall obesity, is closely correlated with insulin resistance, suggesting its pathogenic role in this syndrome.3,4 VF has been identified
Abbreviations: NAFLD, nonalcoholic fatty liver disease; NOTES, natural orifice transluminal endoscopic surgery; TNF, tumor necrosis factor; VF, visceral fat. Copyright © 2011 by the American Society for Gastrointestinal Endoscopy 0016-5107/$36.00 doi:10.1016/j.gie.2011.07.006
www.giejournal.org
as an independent risk factor for insulin resistance and NAFLD.5,6 The adverse metabolic impact of VF has been attributed to the distinct biological properties of visceral adipocytes compared with other fat cells. Visceral adipocytes show higher lipolytic rates in response to insulin7 and lower sensitivity to antilipolytic effects8 compared with subcutaneously derived fat cells. Visceral adipocytes also demonstrate a higher insulin-stimulated glucose uptake compared with subcutaneous fat cells both in vivo9 and in vitro.10 Increased visceral fat, manifested as central obesity, leads to a greater mobilization of free fatty acids into the portal circulation, contributing to NAFLD, systemic insulin resistance, and metabolic syndrome. Because of its critical role in the pathogenesis of metabolic syndrome, VF has been a target for therapies for obesity and metabolic syndrome. There is no specific medical therapy to reduce VF mass. Diet and lifestyle Volume 74, No. 3 : 2011 GASTROINTESTINAL ENDOSCOPY 637
Thinking Outside the Box
interventions are successful in ameliorating some aspects of the dysmetabolic phenotype.11,12 Surgical reduction of VF has been most extensively studied to achieve the therapeutic goal of weight loss and improvement of the metabolic syndrome. Several animal studies have shown that VF removal improves insulin resistance, one of the key markers of the metabolic syndrome.13,14 However, results from human studies of omentectomy in obese patients undergoing bariatric surgery have been mixed.15-17 The aims of this study were to study the effect of surgical VF removal on metabolic profiles in a mouse model of diet-induced obesity and metabolic syndrome and to evaluate for the first time the feasibility of endoscopic omentectomy using natural orifice transluminal endoscopic surgery (NOTES) technique as treatment of obesity and metabolic syndrome in a feline model.
METHODS This study was performed in 2 phases with 2 animal models. First, a mouse model of diet-induced obesity and metabolic syndrome was used to determine the metabolic effects of total versus partial surgical omentectomy. This was followed by a feasibility study of endoscopic omentectomy in a feline model using the NOTES technique. All animal experiments fulfilled National Institutes of Health and institutional criteria for the humane treatment of laboratory animals and were approved by The Johns Hopkins University School of Medicine Animal Care Institutional Review Board.
Mouse model experiments Adult (age 6-8 weeks) male wild-type C57BL-6 mice were purchased from Jackson Laboratories (Bar Harbor, Maine). The mice were fed with commercial diets with either normal or high-fat content as previously described.18 This high-fat diet–induced obese mouse model was used because it expresses many features of the human metabolic syndrome, such as obesity, insulin resistance, NAFLD, and hyperlipidemia.18 After 8 weeks, mice fed a high-fat diet were divided into 3 groups according to type of therapy received: (1) sham surgery in which animals were under anesthesia and had an abdominal incision but omentectomy was not performed; (2) partial omentectomy and unilateral epididymal fat pad removal (⬃50% of VF removed); or (3) total omentectomy and bilateral epididymal fat pad removal (total VF removal). After recovering from surgery, the animals were continued on a high-fat diet for an additional 4 weeks. At 4 weeks, animals were killed, and serum and liver tissue were collected for analysis. All mice were maintained in a temperature- and light-controlled facility and permitted ad libitum consumption of water and pellet chow. The effect of VF removal on the metabolic profiles and liver histology of the animals were tested as follows. Glucose tolerance test. After an overnight fast, a blood sample was obtained from each animal. Glucose was measured using an Accu-Check glucometer (Roche 638 GASTROINTESTINAL ENDOSCOPY Volume 74, No. 3 : 2011
Xia et al
Diagnostics, Indianapolis, IN) with a range of 20 to 600 mg/dL. Serum leptin and tumor necrosis factor ␣ levels. Serum leptin and tumor necrosis factor alpha (TNF)␣ levels were measured with a commercially available enzymelinked immunosorbent assay kit (R&D Systems, Minneapolis, Minn), using standards supplied by the manufacturer. Liver histology and triglyceride content. Thin slices of liver tissue were stained with hematoxylin. Total lipids were extracted from liver tissue according to a previously published technique.19 Triglyceride content was measured with a kit according to manufacturer’s instructions (TR0100; Sigma-Aldrich, St. Louis, Mo).
Feline model experiments: endoscopic omentectomy Eight adult (aged 5 years) domestic shorthair cats were obtained from Liberty Research (Waverly, NY). Each cat was housed separately in cages and provided unlimited access to water and a commercial high-fat diet (Iams Ocean Fish and Rice) for 8 weeks. Animals were then divided into 2 groups: sham surgery or partial (subtotal) endoscopic omentectomy. After overnight fasting, cats were put under general anesthesia by a professional veterinarian. All experiments were performed under standard sterile techniques. A forward-viewing double-channel endoscope was introduced into the stomach. The gastric cavity was irrigated with dilute povidone iodine. The anterior gastric wall at the junction of the body and the antrum was punctured with a needle-knife and then dilated using a controlled radial expansion balloon to 15 mm. The endoscope was advanced into the peritoneal cavity, which was systematically explored. For omentectomy, part of the greater omentum was grasped with a forceps, brought back to the gastric cavity, and excised with a snare. Repeated similar steps were performed until approximately 75% of the omentum was removed (Video 1, available online at www.giejournal.org). For sham surgery, the endoscope was introduced into the peritoneal cavity after gastrotomy and maintained in the peritoneal cavity for a duration of time similar to that for the omentectomy group. After omentectomy or sham surgery, the endoscope was withdrawn into the stomach. The gastric wall incision was closed with endoscopic clips (Video 1). The excised omentum was removed with a Roth basket (US Endoscopy, Mentor, OH) along with the withdrawal of the endoscope. The cats recovered from the anesthesia and fed with a pureed diet the night of the operation. The cats resumed normal solid diets on the following day and fed for another 4 weeks before necropsy. The dietary intake of cats was closely monitored but not restricted. Serum samples were collected at the time of endoscopic procedures and then immediately before they were killed. Postmortem examination was performed to reveal any evidence of intra-abdominal injuries or infection, and liver tissue was collected for analysis. www.giejournal.org
Xia et al
Thinking Outside the Box
TABLE 1. Surgical total versus partial VF removal in a mouse model
VF removed
Total (n ⴝ 5)
Partial (n ⴝ 5)
P value
Weight of VF removed, g, ⫾ SD
2.1 ⫾ 0.35 0.85 ⫾ 0.24 ⬍.01
% of body weight, ⫾ SD
4.91 ⫾ 0.47 2.12 ⫾ 0.46 ⬍.01
VF, Visceral fat; SD, standard deviation.
Statistical analysis All values are expressed as mean ⫾ standard deviation. Treatment-related differences were evaluated by analysis of variance. The paired-individual means were compared by a t test. P values ⬍.05 were considered statistically significant.
RESULTS Total but not partial VF removal improves obesity and metabolic syndrome The weight of the omentum removed was 2.1 ⫾ 0.35 g in the total omentectomy group and 0.85 ⫾ 0.24 g in the partial omentectomy group (Table 1). Only animals that had total VF removal surgery lost significant net weight 4 weeks after surgery (⫺13.04 ⫾ 2.57 g, P ⬍ .001 vs both sham surgery and partial omentectomy groups) (Fig. 1A). The weight loss was sustained and significantly larger than can be accounted for by the weight of fat removed (Fig. 1B, Table 1). On the other hand, animals that underwent sham surgery or partial omentectomy gained weight (10.44 ⫾ 7.23 g and 13.87 ⫾ 0.99 g, respectively). Animals that underwent total VF removal also had significantly improved glucose tolerance test results (P ⬍ .05 vs sham) (Fig. 1C). In addition, the homeostasis model assessment insulin resistance (⫽ glucose ⫻ insulin/405), a wellestablished index for insulin sensitivity and insulin resistance,20 showed a close to normal improvement in animals that underwent total omentectomy (P ⬍ .05 vs sham) (Fig. 1D). Partial VF removal had little impact on animal weight, glucose tolerance, and insulin resistance (Fig. 1A-D). One phenomenon that is frequently associated with obesity and metabolic syndrome is fatty liver disease. Visceral adiposity is closely related to fatty liver disease.21 To evaluate the impact of VF removal on fatty liver disease, the liver histology and triglyceride content were examined. Total VF removal significantly improved hepatic steatosis and reduced hepatic triglyceride content (P ⬍ .05 vs sham) (Fig. 2A, B). Again, the benefit of improved fatty liver was noted in animals that received near-total VF removal but not in animals that had partial VF removal. www.giejournal.org
The improvement of obesity and metabolic syndrome by total VF removal is associated with an improved cytokine profile VF secretes many cytokines that regulate inflammatory signaling and influence insulin sensitivity. Among them, TNF␣, leptin, and adiponectin play important roles in modulating obesity and metabolic syndrome.22-24 A recent study has shown that their levels are closely correlated with visceral adiposity.25 Serum levels of TNF␣, leptin, and adiponectin were evaluated. Total VF removal significantly reduced leptin and TNF␣ levels (P ⬍ .05 vs sham) (Fig. 3A, B) but did not alter adiponectin level (Fig. 3C).
Endoscopic omentectomy is a safe and feasible method for VF removal To test the feasibility of endoscopic VF removal as treatment of obesity and metabolic syndrome, endoscopic omentectomy and a sham procedure were performed in a total of 8 cats using the NOTES technique. One cat died before the endoscopic procedure of complications from anesthesia. Three cats had sham surgeries and 4 had partial (near total) endoscopic omentectomy. On average, it took less than 2 hours to remove the majority of the omentum (Table 2, Fig. 1). Endoscopic omentectomy was feasible and was performed safely without any complication (Video 1). The average weight of the omentum removed was 37.24 ⫾ 6.09 g. All cats recovered well from surgery and resumed their diet on the same day of surgery. Postmortem examination 4 weeks after surgery showed no signs of infection or other organ injury. Overall, cats that underwent omentectomy lost more net weight than cats that underwent sham surgery (Table 2, Fig. 4), although the difference did not reach statistical significance (⫺387 ⫾ 437 g vs 233 ⫾ 351 g, P ⫽ .1, respectively).
DISCUSSION The prevalence of obesity and its associated metabolic syndrome, including fatty liver disease and insulin resistance, has increased rapidly.1,2 Because VF plays a key role in the pathogenesis of obesity and metabolic syndrome,26 VF removal has been studied as a therapeutic method to improve obesity and metabolic syndrome. Previous studies have shown that VF removal improves the metabolic syndrome in animal models.13,14 However, human studies of surgical omentectomy have generated inconsistent results.15,16 Recently, Fabbrini et al17 demonstrated, in both a randomized, controlled trial and a longitudinal single-arm study, that VF removal did not add additional benefit in obese patients who underwent gastric bypass surgeries. The reasons for these contradictive results are unclear. The current study, however, provides a potential mechanism to explain the amount of VF that needs to be removed to achieve the therapeutic goal of a significant net weight loss and improvement of metabolic syndrome. We used a Volume 74, No. 3 : 2011 GASTROINTESTINAL ENDOSCOPY 639
Thinking Outside the Box
Xia et al
Figure 1. Total but not partial visceral fat (VF) removal improves obesity and insulin resistance. A, The weight of the animal before (open bar) and 4 weeks after (solid bar) VF removal surgery (*P ⬍ .05 vs before surgery). B, Percentage of weight change before and 4 weeks after surgery (*P ⬍ .05 vs sham). C, Glucose tolerance tests 4 weeks after surgery (*P ⬍ .05 vs HF; #P ⬍ .05 vs sham). D, Homeostasis model assessment-insulin resistance (HOME-IR) 4 weeks after surgery (*P ⬍ .05 vs HF; #P ⬍ .05 vs sham). ND, normal diet control; HF, high-fat diet control; HF ⫹ sham, high-fat diet with sham surgery; HF ⫹ partial, high-fat diet with partial VF removal; HF ⫹ total, high-fat diet with near-total VF removal (5 per group).
Figure 2. Total but not partial visceral fat (VF) removal improves hepatic steatosis. A, Representative liver histology with hematoxylin and eosin stains (orig. mag. ⫻160). B, Hepatic triglyceride contents (5 per group vs high fat [HF], *P ⬍ .05 vs HF; #P ⬍ .05 vs sham). ND, normal diet.
mouse model of high-fat diet–induced obesity and metabolic syndrome that resembles human disease. In mice, there are 4 VF depots: (1) the paired gonadal depots are attached to the uterus and ovaries in females and the 640 GASTROINTESTINAL ENDOSCOPY Volume 74, No. 3 : 2011
epididymis and testes in males; (2) the paired retroperitoneal depots are found along the dorsal wall of the abdomen surrounding the kidney; (3) the mesenteric depot supports the intestines; and (4) the omental depot is near www.giejournal.org
Xia et al
Thinking Outside the Box
Figure 3. Effect of visceral fat (VF) removal on cytokine profiles. Serum levels of leptin (A), tumor necrosis factor ␣ (TNF␣) (B), and adiponectin (C) were measured by commercially available enzyme-linked immunosorbent assay (5 per group, *P ⬍ .05; **P ⬍ .01 vs high fat (HF); #P ⬍ .05 vs sham).
TABLE 2. Endoscopic omentectomy in a feline model Sham surgery
Omentectomy
Weight preop, kg
4.67 ⫾ 0.50
5.25 ⫾ 0.37
Weight postop,* kg
4.90 ⫾ 0.85
4.83 ⫾ 0.78
Weight change, kg
0.23 ⫾ 0.35
⫺0.43 ⫾ 0.44
BMI preop
50.03 ⫾ 6.42
52.53 ⫾ 10.01
BMI postop*
52.53 ⫾ 10.01
49.68 ⫾ 5.47
BMI change
2.50 ⫾ 3.90
⫺4.58 ⫾ 4.80
Matched
112.5 ⫾ 15
N/A
37.24 ⫾ 6.09
Serum glucose preop, mg/dL
80.3 ⫾ 5.7
98.0 ⫾ 12.7
Serum glucose postop, mg/dL
97.0 ⫾ 17.1
94.5 ⫾ 18.4
Serum ALT preop, U/L
58.7 ⫾ 15.5
55.5 ⫾ 12.3
Serum ALT postop, U/L
58.3 ⫾ 17.2
43.0 ⫾ 7.5
Serum AST preop, U/L
22.3 ⫾ 5.7
22.3 ⫾ 6.6
Serum AST postop, U/L
22 ⫾ 17.2
17 ⫾ 3.4
Serum cholesterol preop, mg/dL
98.7 ⫾ 7.6
118.3 ⫾ 38.1
Serum cholesterol postop, mg/dL
123.0 ⫾ 14.7
117.0 ⫾ 43.7
Serum triglyceride preop, mg/dL
31.7 ⫾ 6.4
30.7 ⫾ 2.3
Serum triglyceride postop, mg/dL
40.8 ⫾ 18.3
37.3 ⫾ 10.4
Liver triglyceride content postop, mg/g of tissue
18.9 ⫾ 3.4
19.8 ⫾ 3.0
Operation time, min Omental fat removed, g
Preop, Preoperatively; postop, postoperatively; BMI, body mass index; ALT, alanine aminotransferase; AST, aspartate aminotransferase. *Postmortem examination was performed 4 weeks after surgery.
www.giejournal.org
the stomach and spleen. In high-fat diet–induced obesity model, the majority of fat is in gonadal and mesenteric depots.27 We evaluated the effect of near-total (bilateral gonadal depots and the whole mesenteric depot) or partial (unilateral gonadal depot and half of mesenteric depot) VF removal. Our study shows that only near-total, but not partial, VF removal asserts its benefit through an improved proinflammatory cytokine profile. The fact that partial omentectomy was performed in most published human studies may explain the suboptimal results in these studies. In fact, Fabbrini et al17 acknowledged that removing a greater amount of VF could have resulted in beneficial metabolic effects. Endoscopic removal of more VF than the greater omentum has not been studied. In the current study, an average of about 2 hours was needed to remove approximately 35 g of omental fat. An average obese human omentum weighs about 800 g.17 The main current limitation to all NOTES procedures, including that described in the current study, is the lack of optimal instruments and accessories necessary to achieve efficient NOTES interventions. A flexible laparoscope with variable stiffness properties and large therapeutic channel will be necessary to achieve rapid endoscopic omentectomy. Therefore, better instrumentation is needed to render complete endoscopic omentectomy efficient and ready for clinical trials. The TNF␣ signaling pathway has been shown to mediate obesity-related insulin resistance.28 Inhibition of TNF␣ signaling pathway improves obesity-related insulin resistance.29 Therefore, we believe that the reduced TNF␣ level and activity observed in the current study may have contributed to the improved metabolic profile exerted by total VF removal. On the other hand, leptin plays an important role in the pathogenesis of obesity by mediating the neuroendocrine response to food deprivation.23 Serum leptin levels decrease exponentially with reduced total fat mass.30 The decreased leptin level after total VF removal reflects the reduction of total body fat mass in these animals. In all, improved cytokine profile, especially reduced Volume 74, No. 3 : 2011 GASTROINTESTINAL ENDOSCOPY 641
Thinking Outside the Box
Xia et al
Figure 4. Effect of endoscopic omentectomy. Representative images of greater omentum of sham surgery (A) and omentectomy (B) are shown. Individual animal weight (C) and body mass index (BMI) (D) before (pre-op) and at the time of postmortem examination (post-op) are graphed.
TNF␣, may contribute to the positive effect of VF removal on obesity and metabolic syndrome. There has been a growing interest in endoluminal and transgastric devices for preoperative or stand-alone weight loss procedures.31 Here, we provide a proof-of-concept study that endoscopic omentectomy, using standard NOTES techniques and conventional instruments, is safe, feasible, and effective. We chose domestic cats as our endoscopic omentectomy model, because (1) cats are one of few animal species that can have obesity with changes in fat metabolism similar to those in human beings32; (2) the upper GI anatomy and physiology of the cat closely simulates the human GI system, making it an appropriate animal candidate for GI endoscopic research33; and (3) cats have tendency to become obese by overfeeding within a short period of time, owing to their energy metabolism characteristic.34 Although endoscopic omentectomy resulted in net weight loss, it did not reach statistical significance. This is likely attributable to the small sample size in this pilot study. The weight lost far exceeded the amount of omental fat removed (Table 2). In addition, endoscopic omentectomy improved some of metabolic markers (eg, glucose, cholesterol), but none of them reached statistical significance (Table 2). 642 GASTROINTESTINAL ENDOSCOPY Volume 74, No. 3 : 2011
All endoscopic omentectomy procedures were performed safely without any complications. All cats resumed feeding on same day of the procedures. There was never any significant bleeding. Snaring of the omentum was performed with a blended current. If bleeding did occur, we were prepared to treat it using standard endoscopic cautery devices Successful gastrotomy closure was performed by using endoscopic clips in all procedures. Other closure methods, such as the use of over-the-scope clips, is likely a more reliable closure method. However, the use of simple clips for access closure is still the most widely used technique, probably because of ease of use, wide availability, and relatively low cost. A main limitation of the current study is the use of 2 different animal models. The mouse model is not appropriate for endoscopic interventions. The feline model was used to prove the concept that endoscopic omentectomy is feasible. However, the feline model has its limitations when it comes to metabolic profile analysis, including lack of reagents for detailed metabolic and inflammatory cytokine analysis. The mouse model of obesity and metabolic syndrome is well established with widely available commercial reagents for detailed analysis. It was used for proof of principle that near-total VF removal was necessary to www.giejournal.org
Xia et al
exert the therapeutic benefit of improving metabolic syndrome. In summary, endoscopic omentectomy is safe and feasible and has the potential to treat obesity and metabolic syndrome. Near-total VF removal is required to achieve net weight loss and improvement of metabolic syndrome, which is likely attributable to an improved proinflammatory cytokine profile. Superior instrumentation is needed to render complete endoscopic omentectomy efficient and ready for clinical trials. DISCLOSURE The following author disclosed financial relationships relevant to this publication: Dr. Kalloo: founding member of, equity holder in, and consultant for Apollo Endosurgery. The other authors disclosed no financial relationships relevant to this publication. This work was supported by a research grant from NIH/NIDDK R01DK075990 (Z.L.). ACKNOWLEDGMENTS We thank James Potter for his insightful suggestions and editorial assistance and Ron Wroblewski for providing technical assistant. Lu Xia, MD, PhD The Johns Hopkins University Baltimore, Maryland, USA Ruijin Hospital Shanghai Jiaotong University School of Medicine Shanghai, China Jing Hua, MD, PhD Renji Hospital Shanghai Jiaotong University School of Medicine Shanghai, China Xavier Dray, MD Hôpital Lariboisière APHP University of Paris Paris, France Mouen A. Khashab, MD The Johns Hopkins University Baltimore, Maryland, USA Shuwen Liang, PhD The Johns Hopkins University Baltimore, Maryland, USA Yong-sik Kim, MD Korea University College of Medicine Seoul, Korea Cristina Jimeno-Ayllon, MD Hospital Virgen de la Luz Cuenca, Spain www.giejournal.org
Thinking Outside the Box
Anthony N. Kalloo, MD The Johns Hopkins University Baltimore, Maryland, USA Zhiping Li, MD The Johns Hopkins University Baltimore, Maryland, USA REFERENCES 1. Clark JM, Brancati FL, Diehl AM. The prevalence and etiology of elevated aminotransferase levels in the United States. Am J Gastroenterol 2003; 98:960-7. 2. Farrell GC, Chitturi S, Lau GK, et al. Guidelines for the assessment and management of non-alcoholic fatty liver disease in the Asia-Pacific region: executive summary. J Gastroenterol Hepatol 2007;22:775-7. 3. Bray GA, Jablonski KA, Fujimoto WY, et al. Relation of central adiposity and body mass index to the development of diabetes in the Diabetes Prevention Program. Am J Clin Nutr 2008;87:1212-8. 4. Fox CS, Massaro JM, Hoffmann U, et al. Abdominal visceral and subcutaneous adipose tissue compartments: association with metabolic risk factors in the Framingham Heart Study. Circulation 2007;116:39-48. 5. Poirier P, Lemieux I, Mauriege P, et al. Impact of waist circumference on the relationship between blood pressure and insulin: the Quebec Health Survey. Hypertension 2005;45:363-7. 6. Jakobsen MU, Berentzen T, Sorensen TI, et al. Abdominal obesity and fatty liver. Epidemiol Rev 2007;29:77-87. 7. Zierath JR, Livingston JN, Thorne A, et al. Regional difference in insulin inhibition of non-esterified fatty acid release from human adipocytes: relation to insulin receptor phosphorylation and intracellular signalling through the insulin receptor substrate-1 pathway. Diabetologia 1998; 41:1343-54. 8. Vikman HL, Savola JM, Raasmaja A, et al. Alpha 2A-adrenergic regulation of cyclic AMP accumulation and lipolysis in human omental and subcutaneous adipocytes. Int J Obes Relat Metab Disord 1996;20:185-9. 9. Virtanen KA, Hallsten K, Parkkola R, et al. Differential effects of rosiglitazone and metformin on adipose tissue distribution and glucose uptake in type 2 diabetic subjects. Diabetes 2003;52:283-90. 10. Lundgren M, Buren J, Ruge T, et al. Glucocorticoids down-regulate glucose uptake capacity and insulin-signaling proteins in omental but not subcutaneous human adipocytes. J Clin Endocrinol Metab 2004;89: 2989-97. 11. Knowler WC, Barrett-Connor E, Fowler SE, et al. Reduction in the incidence of type 2 diabetes with lifestyle intervention or metformin. N Engl J Med 2002;346:393-403. 12. Lindstrom J, Eriksson JG, Valle TT, et al. Prevention of diabetes mellitus in subjects with impaired glucose tolerance in the Finnish Diabetes Prevention Study: results from a randomized clinical trial. J Am Soc Nephrol 2003;14:S108-13. 13. Lottati M, Kolka CM, Stefanovski D, et al. Greater omentectomy improves insulin sensitivity in nonobese dogs. Obesity (Silver Spring) 2009;17:674-80. 14. Gabriely I, Ma XH, Yang XM, et al. Removal of visceral fat prevents insulin resistance and glucose intolerance of aging: an adipokine-mediated process? Diabetes 2002;51:2951-8. 15. Thorne A, Lonnqvist F, Apelman J, et al. A pilot study of long-term effects of a novel obesity treatment: omentectomy in connection with adjustable gastric banding. Int J Obes Relat Metab Disord 2002;26:193-9. 16. Csendes A, Maluenda F, Burgos AM. A prospective randomized study comparing patients with morbid obesity submitted to laparotomic gastric bypass with or without omentectomy. Obes Surg 2009;19:490-4. 17. Fabbrini E, Tamboli RA, Magkos F, et al. Surgical removal of omental fat does not improve insulin sensitivity and cardiovascular risk factors in obese adults. Gastroenterology 2010;139:448-55. 18. Li Z, Soloski MJ, Diehl AM. Dietary factors alter hepatic innate immune system in mice with nonalcoholic fatty liver disease. Hepatology 2005; 42:880-5.
Volume 74, No. 3 : 2011 GASTROINTESTINAL ENDOSCOPY 643
Thinking Outside the Box
19. Folch J, Lees M, Sloane-Stanley GH. A simple method for the isolation and purification of total lipids from animal tissues. J Biol Chem 1957;226: 457-509. 20. Radziuk J. Insulin sensitivity and its measurement: structural commonalities among the methods. J Clin Endocrinol Metab 2000;85:4426-33. 21. Guerrero R, Vega GL, Grundy SM, et al. Ethnic differences in hepatic steatosis: an insulin resistance paradox? Hepatology 2009;49:791-801. 22. Nieto-Vazquez I, Fernandez-Veledo S, Kramer DK, et al. Insulin resistance associated to obesity: the link TNF-alpha. Arch Physiol Biochem 2008; 114:183-94. 23. Mantzoros CS. The role of leptin in human obesity and disease: a review of current evidence. Ann Intern Med 1999;130:671-80. 24. Pajvani UB, Du X, Combs TP, et al. Structure-function studies of the adipocyte-secreted hormone Acrp30/adiponectin. Implications fpr metabolic regulation and bioactivity. J Biol Chem 2003;278:9073-85. 25. Lira FS, Rosa JC, Dos Santos RV, et al. Visceral fat decreased by long-term interdisciplinary lifestyle therapy correlated positively with interleukin-6 and tumor necrosis factor-alpha and negatively with adiponectin levels in obese adolescents. Metabolism 2011;60:359-65. 26. Despres JP, Lemieux I. Abdominal obesity and metabolic syndrome. Nature 2006;444:881-7.
644 GASTROINTESTINAL ENDOSCOPY Volume 74, No. 3 : 2011
Xia et al
27. Bachmanov AA, Reed DR, Tordoff MG, et al. Nutrient preference and diet-induced adiposity in C57BL/6ByJ and 129P3/J mice. Physiol Behav 2001;72:603-13. 28. Hotamisligil GS, Shargill NS, Spiegelman BM. Adipose expression of tumor necrosis factor-alpha: direct role in obesity-linked insulin resistance. Science 1993;259:87-91. 29. Yuan M, Konstantopoulos N, Lee J, et al. Reversal of obesity- and dietinduced insulin resistance with salicylates or targeted disruption of IKKbeta. Science 2001;293:1673-7. 30. Considine RV, Sinha MK, Heiman ML, et al. Serum immunoreactiveleptin concentrations in normal-weight and obese humans. N Engl J Med 1996;334:292-5. 31. Cote GA, Edmundowicz SA. Emerging technology: endoluminal treatment of obesity. Gastrointest Endosc 2009;70:991-9. 32. Hoenig M, Hall G, Ferguson D, et al. A feline model of experimentally induced islet amyloidosis. Am J Pathol 2000;157:2143-50. 33. Moore LE. The advantages and disadvantages of endoscopy. Clin Tech Small Anim Pract 2003;18:250-3. 34. Kley S, Hoenig M, Glushka J, et al. The impact of obesity, sex, and diet on hepatic glucose production in cats. Am J Physiol Regul Integr Comp Physiol 2009;296:R936-43.
www.giejournal.org