Ciliary neurotrophic factor restores gallbladder contractility in leptin-resistant obese diabetic mice

Mechanisms underlying the roles of nervous and humoral factors in the pathogenesis of gallstones

Gallstone disease is a common disorder with an incidence rate of about 10%. Recent research has revealed that nervous and humoral factors are involved in the pathogenesis of gallstone disease. This article focuses on the mechanisms underlying the roles of parasympathetic nerve, sympathetic nerve, non-adrenergic non-cholinergic nerve, cholecystokinin, gastrin, bombesin, gastrin-releasing peptide, motilin, vasoactive intestinal polypeptide, somatostatin, pancreatic polypeptide, substance P, secretin, neurotensin, opioid peptide, nitric oxide, estrogen, thyroxine, and leptin in the pathogenesis of gallstones.

Cholecystosteatosis: an explanation for increased cholecystectomy rates

INTRODUCTION

Over the past decade, obesity has become epidemic, and the number of cholecystectomies as well as the percentage with acalculous cholecystitis have increased. We have recently reported that congenitally obese mice and lean mice fed a high fat diet have increased gallbladder wall lipids and poor gallbladder emptying. Therefore, we tested the hypothesis that compared to patients with a normal gallbladder, patients with both acalculous and calculous cholecystitis would have increased gallbladder wall fat.

METHODS

Sixteen patients who underwent cholecystectomy for acalculous cholecystitis were identified. Sixteen nondiseased controls who underwent incidental cholecystectomy during surgery for liver or pancreatic disease and 16 diseased controls whose gallbladder was removed for chronic calculous cholecystitis were chosen to match the acalculous patients for gender and Body Mass Index. Pathology specimens were reviewed in a blinded fashion for gallbladder wall fat, thickness, and inflammation.

RESULTS

Acalculous cholecystitis patients were younger (p < 0.01) than nondiseased or diseased controls. Gallbladder wall fat was significantly increased (p < 0.02) in the acalculous and calculous cholecystitis patients compared to the nondiseased controls. Gallbladder wall thickness (p < 0.02) and inflammatory score (p < 0.01) were highest in the calculous cholecystitis patients.

CONCLUSIONS

These data suggest that compared to nondiseased controls, (1) patients with acalculous cholecystitis are younger and have increased gallbladder fat and (2) patients with calculous cholecystitis have increased gallbladder fat and inflammation. We conclude that increased gallbladder fat may lead to poor gallbladder emptying and biliary symptoms. Thus, cholecystosteatosis may explain, in part, the increased need for cholecystectomy and the higher percentage of these patients with acalculous cholecystitis.

Leptin regulates gallbladder genes related to absorption and secretion

Dysregulation of gallbladder ion and water absorption and/or secretion has been linked to cholesterol crystal and gallstone formation. We have recently demonstrated that obese, leptin-deficient (Lep(ob)) mice have enlarged gallbladder volumes and decreased gallbladder contractility and that leptin administration to these mice normalizes gallbladder function. However, the effect of leptin on gallbladder absorption/secretion is not known. Therefore, we sought to determine whether leptin would alter the expression of genes involved in water and ion transport across the gallbladder epithelium. Affymetrix oligonucleotide microarrays representing 39,000 transcripts were used to compare gallbladder gene-expression profiles from 12-wk-old control saline-treated Lep(ob) and from leptin-treated Lep(ob) female mice. Leptin administration to Lep(ob) mice decreased gallbladder volume, bile sodium concentration, and pH. Leptin repletion upregulated the expression of aquaporin 1 water channel by 1.3-fold and downregulated aquaporin 4 by 2.3-fold. A number of genes involved in sodium transport were also influenced by leptin replacement. Epithelial sodium channel-alpha and sodium hydrogen exchangers 1 and 3 were moderately downregulated by 2.0-, 1.6-, and 1.3-fold, respectively. Carbonic anhydrase-IV, which plays a role in the acidification of bile, was upregulated 3.7-fold. In addition, a number of inflammatory cytokines that are known to influence gallbladder epithelial cell absorption and secretion were upregulated. Thus leptin, an adipocyte-derived cytokine involved with satiety and energy balance, influences gallbladder bile volume, sodium, and pH as well as multiple inflammatory cytokine genes and genes related to water, sodium, chloride, and bicarbonate transport.

Resistin-like molecule alpha reduces gallbladder optimal tension

INTRODUCTION

Insulin resistance is associated with increased gallbladder volume and impaired gallbladder emptying. Resistin and resistin-like molecule alpha (RELM-alpha) are adipose-derived hormones that are believed to mediate insulin resistance. Therefore, we tested the hypothesis that administration of resistin or RELM-alpha would cause insulin resistance and diminish gallbladder contractility.

METHODS

In two sequential studies 40 eight-week-old nondiabetic lean mice were fed a chow diet for 4 weeks. In Study A, 10 mice received 20 microg of resistin IP, while in Study B 10 mice received 20 microg of RELM-alpha IP for seven days. In each study, 10 control mice received an equal volume of saline IP for seven days. At 12 weeks animals were fasted and underwent cholecystectomy, and in vitro gallbladder response to neurotransmitters was determined. Serum resistin, RELM-alpha, glucose, and insulin levels were measured. HOMA index, a measure of insulin resistance, was calculated.

RESULTS

RELM-alpha significantly increased HOMA index. RELM-alpha decreased gallbladder optimal tension, but did not alter responses to neurotransmitters. Resistin had no effect on HOMA index or on gallbladder optimal tension or response.

CONCLUSION

These data suggest that in nondiabetic lean mice: 1) resistin does not alter insulin resistance or gallbladder optimal tension, but 2) RELM-alpha increases insulin resistance and reduces gallbladder optimal tension. Therefore, we concluded that RELM-alpha may play a role in insulin-resistance mediated gallbladder dysmotility.

Pioglitazone Increases Gallbladder Volume in Insulin-Resistant Obese Mice

BACKGROUND

Both obesity and diabetes are associated with an increased incidence of gallstones. Recent animal and human data from our laboratory suggest that insulin resistance is associated with increased gallbladder volume and/or impaired gallbladder emptying. Pioglitazone is a thiazolidinedione that has been shown to improve insulin resistance. Therefore, we tested the hypothesis that pioglitazone would improve insulin resistance, decrease resting gallbladder volume and improve gallbladder response to neurotransmitters in insulin-resistant obese mice fed a 25% carbohydrate diet.

MATERIALS AND METHODS

Twenty eight-week-old insulin-resistant obese (Lep(ob)) mice fed a 25% carbohydrate diet for 4 weeks. Half of the animals had 0.3 g/kg pioglitazone added to their diet. At 12 weeks all animals were fasted and underwent cholecystectomy. Gallbladder volume and weight were measured, and fresh gallbladders were placed in a muscle bath to assess response to acetylcholine (ACh 10(-5)M), neuropeptide Y (NPY 10(-8,-7,-6)M) and cholecystokinin (CCK 10(-10,-9,-8,-7)M). Serum glucose and insulin were measured, and HOMA Index, a measure of insulin resistance, was calculated.

RESULTS

Fasting serum insulin and HOMA Index were significantly decreased (P < 0.03), but gallbladder volume was significantly increased (P < 0.03) in the pioglitazone treated group. Pioglitazone did not alter gallbladder weight or response to ACh, NPY, or CCK.

CONCLUSION

These data suggest that in insulin-resistant obese mice pioglitazone 1) lowers insulin-resistance, 2) increases resting gallbladder volume, and 3) does not alter gallbladder response to neurotransmitters. Therefore, we conclude that pioglitazone, while improving insulin resistance, paradoxically increases gallbladder volume and, thereby, may increase the propensity for gallstone formation by enhancing gallbladder stasis.