Nonalcoholic fatty pancreas disease

BACKGROUND

Obesity leads to fat infiltration of multiple organs including the heart, kidneys, and liver. Under conditions of oxidative stress, fat-derived cytokines are released locally and result in an inflammatory process and organ dysfunction. In the liver, fat infiltration has been termed nonalcoholic fatty liver disease, which may lead to nonalcoholic steatohepatitis. No data are available, however, on the influence of obesity on pancreatic fat and cytokines, and nonalcoholic fatty pancreas disease (NAFPD) has not been described. Therefore, we designed a study to determine whether obesity is associated with increased pancreatic fat and cytokines.

MATERIALS AND METHODS

Thirty C57BL/6J lean control and 30 leptin-deficient obese female mice were fed a 15% fat diet for 4 weeks. At 12 weeks of age all animals underwent total pancreatectomy. Pancreata from each strain were pooled for measurement of a) wet and dry weight, b) histologic presence of fat, c) triglycerides, free fatty acids (FFAs), cholesterol, phospholipids, and total fat, and d) interleukin (IL)-1beta and tumor necrosis factor-alpha (TNF-alpha). Data were analyzed by Student's t test and Fisher's exact test.

RESULTS

Pancreata from obese mice were heavier (p<0.05) and had more fat histologically (p<0.05). Pancreata from obese mice had more triglycerides, FFAs, cholesterol, and total fat (p<0.05). Triglycerides represented 11% of pancreatic fat in lean mice compared with 67% of pancreatic fat in obese mice (p<0.01). Cytokines IL-1beta and TNF-alpha also were elevated in the pancreata of obese mice (p<0.05).

CONCLUSIONS

These data suggest that obese mice have 1) heavier pancreata, 2) more pancreatic fat, especially triglycerides and FFAs, and 3) increased cytokines. We conclude that obesity leads to nonalcoholic fatty pancreatic disease.

Bax is required for resection-induced changes in apoptosis, proliferation, and members of the extrinsic cell death pathways

BACKGROUND AND AIMS

To define better the homeostatic mechanisms contributing to small intestinal adaptation following partial resection, the relative contributions of apoptosis, cell proliferation, and enterocyte migration and the comparative roles of the intrinsic (mitochondrial) and extrinsic (death receptor-mediated) apoptotic pathways were assessed.

METHODS

After 50% jejunoileal resections or transections, adaptation was analyzed in duodenal-jejunal and ileal segments from C57BL/6 Bax(+/+) (16, 48, and 168 hours postoperative) and Bax(-/-) mice (168 hours).

RESULTS

Basal apoptotic rates were equivalent in all mice. By 1-week postresection, villus heights and crypt depths were increased in the duodenal-jejunal and ileal remnants of both genotypes. In Bax(+/+) mice, adaptation occurred in concert with increased crypt proliferative and apoptotic indices. Bax(-/-) mice did not show increases in proliferation or apoptosis, yet adaptive increases in villus height were enhanced relative to Bax(+/+) mice. Enterocyte migration increased in both genotypes. Postresection, the expression of caspases and genes involved in death receptor-mediated apoptosis was decreased in Bax(-/-) compared with Bax(+/+) mice.

CONCLUSIONS

Postresection adaptation involves parallel changes in crypt proliferation and apoptosis, but, as observed in Bax(-/-) mice, it can occur without increased proliferation. These studies demonstrate that spontaneous gut apoptosis is Bax independent, whereas adaptation-related apoptosis is Bax-dependent. Differences between resected Bax(+/+) and Bax(-/-) mice suggest that apoptosis in the adapting gut utilizes the extrinsic pathway, but this requires linkage to the mitochondrial pathway via Bax. The increased adaptive response in Bax(-/-) mice indicates that modulation of apoptosis may be useful for enhancing adaptation.

A murine model of obesity implicates the adipokine milieu in the pathogenesis of severe acute pancreatitis

Obesity is clearly an independent risk factor for increased severity of acute pancreatitis (AP), although the mechanisms underlying this association are unknown. Adipokines (including leptin and adiponectin) are pleiotropic molecules produced by adipocytes that are important regulators of the inflammatory response. We hypothesized that the altered adipokine milieu observed in obesity contributes to the increased severity of pancreatitis. Lean (C57BL/6J), obese leptin-deficient (LepOb), and obese hyperleptinemic (LepDb) mice were subjected to AP by six hourly intraperitoneal injections of cerulein (50 microg/kg). Severity of AP was assessed by histology and by measuring pancreatic concentration of the proinflammatory cytokines IL-1beta and IL-6, the chemokine MCP-1, and the marker of neutrophil activation MPO. Both congenitally obese strains of mice developed significantly more severe AP than wild-type lean animals. Severity of AP was not solely related to adipose tissue volume: LepOb mice were heaviest; however, LepDb mice developed the most severe AP both histologically and biochemically. Circulating adiponectin concentrations inversely mirrored the severity of pancreatitis. These data demonstrate that congenitally obese mice develop more severe AP than lean animals when challenged by cerulein hyperstimulation and suggest that alteration of the adipokine milieu exacerbates the severity of AP in obesity.

Decreased gallbladder response in leptin-deficient obese mice

Obesity is a major risk factor for gallstone formation, but the pathogenesis of this phenomenon remains unclear. Human data on gallbladder emptying are conflicting, and no animal data exist on the effect of obesity on gallbladder motility. Leptin, a hormone produced by adipocytes, is known to have central effects on neuropeptide Y and cholecystokinin, but the influence of leptin on the biliary effects of these hormones is unknown. Therefore we tested the hypothesis that leptin-deficient C57BL/6J-lep(ob) obese mice would have decreased gallbladder responses to excitatory stimuli. Twelve-week-old lean control (C57BL/6J) (n = 22) and C57BL/6J-lep(ob) obese (n = 20) female mice were fed a nonlithogenic diet. The mice were fasted overnight and underwent cholecystectomy. Whole gallbladders were placed in 3 ml muscle baths. After optimal length was determined with acetylcholine (10(-5) mol/L, responses to increasing doses of neuropeptide Y (10(-8) to 10(-6) mol/L) and cholecystokinin-8 (10(-10) to 10(-7) mol/L) were measured. Student's t test and two-way analysis of variance were used where appropriate. Results were expressed as Newtons per cross-sectional area. The lean control mice had significantly greater excitatory responses to acetylcholine than the obese mice (0.37 +/- 0.05 vs. 0.16 +/- 0.02, P < 0.01). The gallbladder responses were also greater when mice were treated with neuropeptide Y (10(-8) mol/L: 0.00 +/- 0.00 vs. 0.00 +/- 0.00, NS; 10(-7) mol/L: 0.12 +/- 0.02 vs. 0.05 +/- 0.01, P < 0.01; 10(-6) mol/L: 0.26 +/- 0.08 vs. 0.06 +/- 0.01, P < 0.01) and cholecystokinin (10(-10) mol/L: 0.27 +/- 0.04 vs. 0.13 +/- 0.02, P < 0.01; 10(-9) mol/L: 0.59 +/- 0.08 vs. 0.27 +/- 0.04, P < 0.01; 10(-8) mol/L: 0.80 +/- 0.11 vs. 0.37 +/- 0.05, P < 0.01; 10(-7) mol/L: 0.86 +/- 0.11 vs. 0.44 +/- 0.06, P < 0.01). These data suggest that genetically obese, leptin-deficient mice have decreased responses to acetylcholine, neuropeptide Y, and cholecystokinin. We conclude that decreased gallbladder motility contributes to the increased incidence of gallstones associated with obesity.

Insulin, leptin, and tumoral adipocytes promote murine pancreatic cancer growth

BACKGROUND

Obesity accelerates development and growth of human pancreatic cancer. We recently reported similar findings in a novel murine model of pancreatic cancer in congenitally obese mice. The current experiments were designed to evaluate the effects of diet-induced obesity on pancreatic cancer growth.

METHODS

Thirty C57BL/6J female mice were fed either control 10% fat (n = 10) or 60% fat diet (n = 20) starting at age 6 weeks. At 11 weeks, 2.5 × 10(5) PAN02 murine pancreatic cancer cells were inoculated. After 6 weeks, tumors were harvested. Serum adiponectin, leptin, insulin, and glucose concentrations were measured. Tumor proliferation, apoptosis, adipocyte content, and tumor-infiltrating lymphocytes were evaluated.

RESULTS

The diet-induced obesity diet led to significant weight gain (control 21.3 ± 0.6 g; diet-induced obesity 23.1 ± 0.5 g; p = 0.03). Mice heavier than 23.1 g were considered "Overweight." Tumors grew significantly larger in overweight (1.3 ± 0.3 g) compared to lean (0.5 ± 0.2 g; p = 0.03) mice; tumor size correlated positively with body weight (R = 0.56; p < 0.02). Serum leptin (3.1 ± 0.7 vs. 1.4 ± 0.2 ng/ml) and insulin (0.5 ± 0.2 vs. 0.18 ± 0.02 ng/ml) were significantly greater in overweight mice. Tumor proliferation, apoptosis, and tumor adipocyte volume were similar. T and B lymphocytes were observed infiltrating tumors from lean and overweight mice in similar number.

CONCLUSION

These data show that diet-induced obesity accelerates the growth of murine pancreatic cancer.

Retinoic acid stimulates early cellular proliferation in the adapting remnant rat small intestine after partial resection

Following loss of small bowel surface area, the remnant intestine undergoes a remarkable adaptive response. To define more fully the underlying molecular mechanisms, we have identified genes that are specifically induced in the adapting remnant after partial small bowel resection. Several of these, including cellular retinol binding protein II (CRBP II) and apolipoprotein (apo) AI, participate in vitamin A and lipid trafficking. The CRBP II and apo A-I promoters contain response elements for the nuclear retinoid X receptor RXR-alpha. It is well established that vitamin A is essential for normal cell growth, differentiation and maintenance of epithelial tissues and that CRBP II functions to facilitate intestinal vitamin A absorption and metabolism. On the basis of these considerations, changes in CRBP II and apo A-I mRNA levels could reflect a role for retinoids in modulating the intestinal adaptive response. To explore this hypothesis, we used a rat resection model of intestinal adaptation to examine the temporal patterns of CRBP II, apo A-I and RXR-alpha expression postresection. CRBP II and apo A-I mRNA levels were increased in the remnant intestine in distinct temporal patterns, whereas RXR-alpha expression was unchanged. To address directly the effects of vitamin A in adaptation, retinoic acid or vehicle was administered intravenously to rats immediately after 70% small bowel resection. Compared with vehicle, all-trans-retinoic acid significantly stimulated crypt cell proliferation in the adapting remnant intestine by 6 h after surgery. These data suggest that retinoic acid acts to modulate intestinal proliferation in the adapting small intestine after loss of functional small bowel surface area.

Vitamin A deficiency inhibits intestinal adaptation by modulating apoptosis, proliferation, and enterocyte migration

In a prior study, vitamin A-deficient rats subjected to submassive small bowel resections did not mount a normal intestinal adaptive response by 10 days postoperatively, although adaptive increases in crypt cell proliferation were not attenuated and there were no differences in apoptotic indexes. The present study was designed to address the mechanisms by which vitamin A status effects adaptation by analyzing proliferation, apoptosis, and enterocyte migration in the early postoperative period (16 and 48 h) in vitamin A-sufficient, -deficient, and partially replenished sham-resected and resected rats. At 16 h postresection, apoptosis was significantly greater in the remnant ileum of resected vitamin A-deficient rats compared with the sufficient controls. Crypt cell proliferation was increased by resection in all dietary groups at both timepoints. However, at 48 h postresection, proliferation was significantly decreased in the vitamin A-deficient and partially replenished rats. By 48 h after resection, vitamin A deficiency also reduced enterocyte migration rates by 44%. This occurred in conjunction with decreased immunoreactive collagen IV at 48 h and 10 days postoperation. Laminin expression was also reduced by deficiency at 10 days postresection, whereas fibronectin and pancadherin were unchanged at 48 h and 10 days. These studies indicate that vitamin A deficiency inhibits intestinal adaptation following partial small bowel resection by reducing crypt cell proliferation, by enhancing early crypt cell apoptosis, and by markedly reducing enterocyte migration rates, which may be related to changes in the expression of collagen IV and other extracellular matrix components.

Diabetes and hyperlipidemia correlate with gallbladder contractility in leptin-related murine obesity

Obesity is associated with many comorbid conditions including diabetes, hyperlipidemia, and gallstones. However, the interaction among these modalities remains unclear. We recently demonstrated that both leptin-deficient and leptin-resistant obese mice have impaired biliary motility. These obese mice also are diabetic and hyperlipidemic. Therefore, we tested the hypothesis that serum glucose, insulin, cholesterol, and triglyceride levels would correlate with gallbladder contractility. Thirty-four lean control, 10 lean heterozygous leptin-deficient, 18 obese homozygous leptin-deficient, and 12 obese homozygous leptin-resistant mice were fed a nonlithogenic chow diet while nine lean control and nine obese homozygous leptin-deficient mice were fed a high-cholesterol diet for 4 weeks. In vitro gallbladder responses to cholecystokinin (CCK; 10(-8) mol/L), acetylcholine (ACh; 10(-5) mol/L), and neuropeptide Y (NPY; 10(-6) mol/L) were measured. Serum glucose, insulin, cholesterol, and triglyceride levels were measured from pooled serum from an additional 704 animals. Gallbladder responses were greatest for CCK, intermediate for ACh, and least for NPY. Serum glucose, insulin, cholesterol, and triglyceride levels and body weight all correlated similarly, negatively, and significantly (P<0.001) with gallbladder contractility. Hyperglycemia, insulin-resistance, hyperlipidemia, and body weight in obese mice with leptin dysfunction are associated with poor gallbladder contractility, which in turn may contribute to the association between obesity and gallstone formation.

Nuclear magnetic resonance spectroscopy-based metabolomics of the fatty pancreas: implicating fat in pancreatic pathology

BACKGROUND

Obesity is a worldwide epidemic and a significant risk factor for pancreatic diseases including pancreatitis and pancreatic cancer; the mechanisms underlying this association are unknown. Metabolomics is a powerful new analytical approach for describing the metabolome (compliment of small molecules) of cells, tissue or biofluids at any given time. Our aim was to analyze pancreatic fat content in lean and congenitally obese mice using both metabolomic analysis and conventional chromatography.

METHODS

The pancreatic fat content of 12 lean (C57BL/6J), 12 obese leptin-deficient (Lep(ob)) and 12 obese hyperleptinemic (Lep(db)) mice was evaluated by metabolomic analysis, thin-layer and gas chromatography.

RESULTS

Pancreata of congenitally obese mice had significantly more total pancreatic fat, triglycerides and free fatty acids, but significantly less phospholipids and cholesterol than those of lean mice. Metabolomic analysis showed excellent correlation with thin-layer and gas chromatography in measuring total fat, triglycerides and phospholipids.

CONCLUSIONS

Differences in pancreatic fat content and character may have important implications when considering the local pancreatic proinflammatory milieu in obesity. Metabolomic analysis is a valid, powerful tool with which to further define the mechanisms by which fat impacts pancreatic disease.

Altered intestinal motility in leptin-deficient obese mice

INTRODUCTION

Leptin is produced by adipocytes and causes satiety by regulating hypothalamic neurotransmission and energy expenditure. Leptin functions through the active long form of its receptor, which is expressed throughout the gastrointestinal tract, including the vagal neurons concerned with small intestinal motility. However, the role of leptin in small intestinal motility is poorly understood. Therefore, we hypothesized that leptin-deficient (Lepob) obese mice would have altered small intestinal response to neurotransmitters and transit time.

MATERIALS AND METHODS

Responses of jejunal and ileal segments from lean control and leptin-deficient obese animals to acetylcholine (ACh) and cholecystokinin (CCK) were determined in an organ bath. In addition, gastric emptying was determined as the amount of gavaged liquid diet remaining in the stomach after 1 h, and intestinal transit time was determined by calculating the geometric center (GC) of passage of a fluorescent-labeled marker.

RESULTS

Leptin deficiency resulted in increased jejunal responses to CCK (P <0.05) and a similar response to ACh compared to lean controls. Also, gastric emptying (97% versus 91%, P <0.001) in obese mice was greater. Overall small intestinal transit (GC) in obese mice was decreased (7.3 versus 8.4, P <0.05) even though proximal transit was increased (5.3 versus 1.5, P <0.06).

CONCLUSIONS

These studies indicate that leptin-deficient (Lepob) obese mice have an increased jejunal response to CCK as well as an increased proximal intestinal transit, but an overall decrease in small intestinal transit.

Ezetimibe ameliorates cholecystosteatosis

BACKGROUND

Cholecystosteatosis is the accumulation of gallbladder wall fats leading to decreased gallbladder emptying. Ezetimibe inhibits intestinal fat absorption and prevents murine gallstone formation. However, the influence of ezetimibe on gallbladder emptying and cholecystosteatosis has not been studied. Therefore, we tested the hypothesis that ezetimibe would improve gallbladder motility by preventing the buildup of fats in the gallbladder wall.

METHODS

Forty lean female mice were fed either a control diet or a lithogenic diet for 6 weeks. Half of the mice on each diet received ezetimibe. At 11 weeks of age, all mice were fasted overnight and underwent gallbladder ultrasonography to determine ejection fraction. One week later, the mice were fasted and underwent cholecystectomy. Bile was examined for cholesterol crystals. The gallbladders were snap-frozen for lipid analysis.

RESULTS

The lithogenic diet significantly (P < 0.05) increased serum cholesterol, biliary crystals, gallbladder wall cholesterol and cholesterol/phospholipid ratio, and decreased gallbladder ejection fraction. All of these abnormalities were reversed (P < 0.05) by the addition of ezetimibe to the diet.

CONCLUSIONS

These data suggest that ezetimibe lowers serum cholesterol, prevents biliary crystals, and normalizes gallbladder wall fat and function. We conclude that ezetimibe ameliorates cholecystosteatosis and may be an effective agent for gallstone prevention.

Nonalcoholic Fatty gallbladder disease: the influence of diet in lean and obese mice

The obesity epidemic has contributed to an increased prevalence of gallstones and a higher percentage of chronic acalculous cholecystitis. Obesity is associated with Type II diabetes and hyperlipidemia in murine models. In addition, we have previously demonstrated that serum glucose, insulin, cholesterol, and triglycerides correlated with gallbladder contractility in murine models. However, the relative role of insulin resistance and gallbladder fat infiltration in this phenomenon remain unclear. Therefore, we tested the hypothesis that gallbladder wall lipids are related to obesity and diet and are inversely correlated with gallbladder contractility. One hundred lean control (C7BL/6J) and 36 obese leptin-deficient (Lep(ob)) 8-week-old female mice were fed either a chow diet or a 1.0% cholesterol, 15% butterfat (high-lipid) diet for four weeks. Pooled gallbladders were then analyzed for free fatty acids (FFA), phospholipids (PL), total cholesterol (TC), and triglycerides (TG). Cholesterol/phospholipid ratios were then calculated. The Lep(ob) mice fed a chow diet had significantly higher (P < 0.01) gallbladder lipids than the three other groups. The lean mice that were fed a high-lipid diet had increased (P < 0.05) gallbladder TC compared to the lean mice on a chow diet. In addition, the cholesterol/phospholipid ratio was significantly increased (P < 0.01) in the lean mice fed a high-lipid diet compared to the other three groups. Finally, the high-lipid diet decreased gallbladder FFA (P < 0.01), PL (P = 0.08), and TC (P < 0.05) in Lep(ob) mice. These data suggest that (1) obese mice have increased gallbladder lipids; (2) a high-cholesterol, high-fat diet increases gallbladder lipids and the cholesterol/phospholipid ratio in lean mice; but (3) decreases gallbladder fatty acids, phospholipids, and cholesterol in obese mice. Prior studies have documented similarly decreased gallbladder response to neurotransmitters in obese mice on a chow diet, as well as lean and obese mice on a high-lipid diet. Therefore, we conclude that leptin-deficient obesity and/or a high-fat diet causes nonalcoholic fatty gallbladder disease, which is manifested by diminished gallbladder contractility.

Adiponectin receptor-1 expression is decreased in the pancreas of obese mice

BACKGROUND

Obesity is epidemic in the 21st century and has been shown to be a risk factor for developing severe acute pancreatitis. Adipose tissue produces small molecules called adipokines, which are important in modulating metabolism and inflammation. The anti-inflammatory adipokine adiponectin is decreased in obesity and inversely mirrors the severity of pancreatitis in a murine experimental model. Adiponectin acts through two receptors, AdipoR1 and AdipoR2; no data are currently available regarding adiponection receptor expression in the obese murine pancreas.

MATERIALS AND METHODS

Immunohistochemical and reverse transcription-polymerase chain reaction analysis were undertaken to determine expression of adiponectin receptors AdipoR1 and AdipoR2 in the pancreas and liver of lean (C57BL/6J) and congenitally obese (Lep(Ob) and Lep(Db)) mice.

RESULTS

Immunohistochemistry confirmed expression of both AdipoR1 and AdipoR2 in the pancreas of all three murine strains. Staining was positive in acinar cells and to a lesser extent in islet cells. Pancreatic gene expression of AdipoR2 was similar among lean and obese mice. AdipoR1 gene expression, however, was significantly (P < 0.001) decreased in the pancreas of both Lep(Ob) and Lep(Db) mice compared to wild-type lean animals. Gene expression of both AdipoR1 and AdipoR2 was significantly less in the liver of obese (Lep(Ob) and Lep(Db)) mice compared to wild-type lean animals (P < 0.001).

CONCLUSIONS

These data show for the first time that the adiponectin receptors AdipoR1 and AdipoR2 are expressed in the obese murine pancreas. The paucity of AdipoR1 receptors may be important when considering the role played by adipokines in the genesis of severe pancreatitis in obesity.

Gallbladder motility in agouti-yellow and leptin-resistant obese mice

BACKGROUND

Obesity is a polygenic disorder that is associated with gallstone disease. We have previously shown that leptin deficiency in obese mice correlates with decreased gallbladder motility, suggesting that leptin plays a role in the link between gallstone disease and obesity. However, most obese humans are leptin-resistant, and relatively few are leptin-deficient. To confirm that leptin dysfunction is responsible for impaired gallbladder motility in obese mice, we hypothesized that leptin-resistant obese mice (Lep(db)) would have abnormal gallbladder motility while obese mice with intact leptin function (Agouti Yellow, A(y)) would have normal gallbladder motility.

MATERIALS AND METHODS

Eighteen lean control (C57BL/6J), 10 A(y) and 12 Lep(db) female mice were fasted overnight, weighed, and livers and gallbladders were harvested. Liver weights and gallbladder volumes were measured. Gallbladder contractile responses (N/cm(2)) to acetylcholine (10(-5)M), neuropeptide Y (10(-8,-7,-6) M) and cholecystokinin (10(-10,-9,-8,-7)M) were determined in muscle bath chambers. Results were analyzed by analysis of various (ANOVA) and with the Mann-Whitney Rank Sum Test.

RESULTS

Both Agouti yellow (A(y)) and leptin-resistant (Lep(db)) obese mice had body weights, liver weights and gallbladder volumes that were significantly greater (P < 0.01) than lean control mice. Leptin-resistant obese mice had gallbladder responses to acetylcholine, neuropeptide Y and cholecystokinin that were significantly less (P < 0.01) than both lean control and Agouti yellow obese mice.

CONCLUSIONS

These data suggest that (1). leptin-resistant obese mice (Lep(db)) have abnormal gallbladder motility and (2). obese mice with normal leptin metabolism (A(y)) have normal gallbladder response to neurotransmitters. We conclude that leptin represents a link between obesity, gallbladder motility and gallstone formation.

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.

Iron deficiency diminishes gallbladder neuronal nitric oxide synthase

BACKGROUND

Iron deficiency has been demonstrated in the prairie dog to result in cholesterol crystal formation and altered biliary motility. Gallbladder filling and emptying are influenced by both inhibitory and excitatory stimuli, with nitric oxide (NO) playing a key role in normal relaxation. Iron is a cofactor for nitric oxide synthase. Therefore, we tested the hypothesis that iron deficiency would result in diminished levels of gallbladder neuronal nitric oxide synthase (nNOS) but would not influence the gallbladder's response to excitatory stimuli.

MATERIALS AND METHODS

Twenty adult female prairie dogs were fed either an iron-supplemented (Fe(+)) (200 ppm) control diet (n = 10) or an iron-deficient (Fe-) (8 ppm) diet (n = 10) for 8 weeks. Fasting gallbladder volume was measured. Gallbladder muscle strips were harvested for response to excitatory stimuli and measurement of nNOS protein levels by Western blotting. Muscle strip response to a spectrum of doses of cholecystokinin, acetylcholine, and electrical field stimuli was determined, and the areas under the response curves were calculated.

RESULTS

Gallbladder volume increased in the iron-deficient prairie dogs compared with the iron-supplemented group (1.45 +/- 0.27 mL vs 0.80 +/- 0.13 mL, P < 0.05). Iron deficiency diminished the ratio of gallbladder nNOS to beta-actin protein levels (0.05 +/- 0.01 vs 3.48 +/- 1.02, P < 0.05) but resulted in a normal response to excitatory stimuli.

CONCLUSIONS

We conclude that diminished gallbladder neuronal nitric oxide synthase contributes to the gallbladder stasis that occurs with iron deficiency. This phenomenon may contribute to the increased incidence of gallstones in premenopausal women.

Leptin-resistant obese mice have paradoxically low biliary cholesterol saturation

BACKGROUND

Human obesity is associated with leptin resistance, elevated serum glucose and lipids, hepatic steatosis, and cholesterol gallstone formation. These gallstones are thought to result from hypersecretion of biliary cholesterol as well as biliary stasis. Leptin-resistant Lep(db) obese mice, which are known to have elevated serum leptin, glucose, and lipids, as well as hepatic steatosis, should be an appropriate model for human gallstone formation. Therefore, we tested the hypothesis that leptin-resistant mice would have increased gallbladder volume, biliary cholesterol saturation, and cholesterol crystal formation.

METHODS

Sixty lean control mice and 60 Lep(db) obese mice on a low cholesterol chow diet were studied. Gallbladder volumes were measured and bile was pooled to calculate cholesterol saturation index. Serum cholesterol, glucose, and leptin levels were determined from pooled serum. Hepatic fat vacuoles were counted. Bile from a second group of 90 lean control and 59 obese mice was observed microscopically for cholesterol crystal formation.

RESULTS

Leptin-resistant obese mice have significantly higher serum cholesterol, glucose, and leptin levels, hepatic fat vacuoles, and gallbladder volume than lean control mice. However, biliary cholesterol saturation index and cholesterol crystal formation were significantly diminished in the obese mice.

CONCLUSIONS

These data suggest that leptin-resistant Lep(db) obese mice have (1) increased gallbladder volume, (2) decreased biliary cholesterol saturation despite elevated serum cholesterol and hepatic steatosis, and (3) decreased in vitro cholesterol crystal formation. We conclude that the link between obesity and gallstone formation does not require hypersecretion of biliary cholesterol.

Vitamin A status modulates intestinal adaptation after partial small bowel resection

BACKGROUND

Intestinal adaptation after loss of functional small bowel surface area is characterized by cellular hyperplasia and increased absorptive function. Interventions to enhance the adaptive response are needed to decrease the morbidity and mortality associated with short bowel syndrome. Retinoic acid was shown to stimulate crypt cell proliferation in the adapting remnant rat ileum by 6 hours after resection. Thus, vitamin A, which is required for normal epithelial cell proliferation and differentiation and which can modulate programmed cell death, may play an important role in the adapting intestine. On the basis of these observations, the effects of vitamin A deficiency on intestinal morphology, epithelial cell proliferation, and apoptosis in the adapting intestine after resection were investigated.

METHODS

Weanling male Sprague-Dawley rats fed either a vitamin A-deficient or -sufficient diet for 58 days underwent 70% proximal small bowel resection. The deficient rats were divided into cohorts that were either maintained on the experimental diet after surgery or replenished with vitamin A 20 hours before surgery and switched to the control diet after surgery.

RESULTS

Ten days after resection, vitamin A-deficient rats exhibited a markedly blunted adaptive response. The adaptive increase in villus height and crypt depth was absent in the deficient rats. However, adaptive increases in crypt cell proliferation were not attenuated by vitamin A deficiency, and there were no differences in apoptotic indices.

CONCLUSIONS

Vitamin A deficiency inhibits the adaptive response to partial small bowel resection, supporting a role for vitamin A in the adaptive process. Changes in cellular proliferation or programmed cell death are not sufficient to account for this inhibition. This model system will be useful for examining the role of other mechanisms, such as changes in cell-cell and cell-extracellular matrix interactions, and rates of epithelial cell migration and cell extrusion.

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.

Obesity, but not high-fat diet, promotes murine pancreatic cancer growth

BACKGROUND

Obesity accelerates pancreatic cancer growth; the mechanisms underlying this association are poorly understood. This study evaluated the hypothesis that obesity, rather than high-fat diet, is responsible for accelerated pancreatic cancer growth.

METHODS

Male C57BL/6J mice were studied after 19 weeks of high-fat (60 % fat; n = 20) or low-fat (10 % fat; n = 10) diet and 5 weeks of Pan02 murine pancreatic cancer growth (flank).

RESULTS

By two-way ANOVA, diet did not (p = 0.58), but body weight, significantly influenced tumor weight (p = 0.01). Tumor weight correlated positively with body weight (R (2) = 0.562; p < 0.001). Tumors in overweight mice were twice as large as those growing in lean mice (1.2 ± 0.2 g vs. 0.6 ± .01 g, p < 0.01), had significantly fewer apoptotic cells than those in lean mice (0.8 ± 0.4 vs 2.4 ± 0.5; p < 0.05), and greater adipocyte volume (3.7 vs. 2.2 %, p < 0.05). Apoptosis (R (2) = 0.472; p = 0.008) and serum adiponectin correlated negatively with tumor weight (R = 0.45; p < 0.05).

CONCLUSIONS

These data suggest that body weight, and not high-fat diet, is responsible for accelerated murine pancreatic cancer growth observed in this model of diet-induced obesity. Decreased tumor apoptosis appears to play an important mechanistic role in this process. The concept that decreased apoptosis is potentiated by hypoadiponectinemia (seen in obesity) deserves further investigation.

Adipocytes enhance murine pancreatic cancer growth via a hepatocyte growth factor (HGF)-mediated mechanism

INTRODUCTION

Obesity accelerates the development and progression of pancreatic cancer, though the mechanisms underlying this association are unclear. Adipocytes are biologically active, producing factors such as hepatocyte growth factor (HGF) that may influence tumor progression. We therefore sought to test the hypothesis that adipocyte-secreted factors including HGF accelerate pancreatic cancer cell proliferation.

MATERIAL AND METHODS

Murine pancreatic cancer cells (Pan02 and TGP-47) were grown in a) conditioned medium (CM) from murine F442A preadipocytes, b) HGF-knockdown preadipocyte CM, c) recombinant murine HGF at increasing doses, and d) CM plus HGF-receptor (c-met) inhibitor. Cell proliferation was measured using the MTT assay. ANOVA and t-test were applied; p < 0.05 considered significant.

RESULTS

Wild-type preadipocyte CM accelerated Pan02 and TGP-47 cell proliferation relative to control (59 ± 12% and 34 ± 12%, p < 0.01, respectively). Knockdown of preadipocyte HGF resulted in attenuated proliferation vs. wild type CM in Pan02 cells (35 ± 5% vs. 68 ± 14% greater than control; p < 0.05), but proliferation in TGP-47 cells remained unchanged. Recombinant HGF dose-dependently increased Pan02, but not TGP-47, proliferation (p < 0.05). Inhibition of HGF receptor, c-met, resulted in attenuated proliferation versus control in Pan02 cells, but not TGP-47 cells.

CONCLUSIONS

These experiments demonstrate that adipocyte-derived factors accelerate murine pancreatic cancer proliferation. In the case of Pan02 cells, HGF is responsible, in part, for this proliferation.

Altered small intestinal absorptive enzyme activities in leptin-deficient obese mice: influence of bowel resection

BACKGROUND

Residual bowel increases absorption after massive small bowel resection. Leptin affects intestinal adaptation, carbohydrate, peptide, and lipid handling. Sucrase, peptidase, and acyl coenzyme A:monoacylglycerol acyltransferase (MGAT) are involved in carbohydrate, protein, and lipid absorption. We hypothesized that leptin-deficient obese mice would have altered absorptive enzymes compared with controls before and after small bowel resection.

METHODS

Sucrase, peptidase (aminopeptidase N [ApN], dipeptidyl peptidase IV [DPPIV]), and MGAT activities were determined from lean control (C57BL/6J, n = 16) and leptin-deficient (Lep(ob), n = 16) mice small bowel before and after 50% resection.

RESULTS

Ileal sucrase activity was greater in obese mice before and after resection. Jejunal ApN and DPPIV activities were lower for obese mice before resection; ileal ApN activity was unaltered after resection for both strains. Resection increased DPPIV activity in both strains. Jejunal MGAT in obese mice decreased postresection. In both strains, ileal MGAT activity decreased after resection, and obese mice had greater activity in remnant ileum.

CONCLUSIONS

After small bowel resection, leptin-deficient mice have increased sucrase activity and diminished ileal ApN, DPPIV, and MGAT activity compared with controls. Therefore, we conclude that leptin deficiency alters intestinal enzyme activity in unresected animals and after small bowel resection. Altered handling of carbohydrate, protein, and lipid may contribute to obesity and diabetes in leptin-deficient mice.

Impaired intestinal cell proliferation and cell death in leptin-deficient obese mice

BACKGROUND

After massive small-bowel resection and loss of absorptive capacity, residual intestine has compensatory ability to adapt by cellular hyperplasia and increased absorptive function. Growth factors have been shown to enhance intestinal adaptation, but the mechanisms involved are not well defined. Leptin has been shown to function as a trophic factor in the intestine and enhances carbohydrate absorption after small-bowel resection. Therefore, we hypothesized that leptin deficiency may impair the adaptive response by modulating cellular proliferation or cell death after small-bowel resection.

METHODS

Twelve-week-old male lean control (C57BL/6J, n = 28) and leptin-deficient (Lep(ob), n = 24) obese mice underwent sham laparotomy, intestinal transection, or 50% proximal small-bowel resection. Mice were killed at 48 hours postresection, and remnant intestine was harvested. Phenotypic analysis to assess adaptation included characterization of cell proliferation (percentage BrdU incorporation), apoptosis (terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nickend labeling assay), and morphometric response (villus height, crypt depth).

RESULTS

The percentage S-bromodeoxyuridine (BrdU) incorporation and apoptotic indices of obese transected mice were significantly lower than lean transected mice (7.3 vs 21.9% and 0.70 vs 1.53% respectively, p < .05). In resected animals, the percentage BrdU incorporation and apoptotic indices of obese resected mice were significantly lower than for lean resected (6.1 vs 22.0% and 0.93 vs 1.80% respectively, p < .05). No differences between groups, regardless of surgery, were identified in villus height or crypt depth.

CONCLUSIONS

Therefore, we conclude that leptin deficiency impairs both cell proliferation and cell death in the early adaptive period after either small-bowel transection or resection.

Cannabinoid receptor-1 blockade attenuates acute pancreatitis in obesity by an adiponectin mediated mechanism

BACKGROUND

Obesity is a risk factor for increased severity of acute pancreatitis. Adipocytes produce adiponectin, an anti-inflammatory molecule that is paradoxically decreased in the setting of obesity. We have shown that adiponectin concentration inversely mirrors the severity of pancreatitis in obese mice. Cannabinoid receptor CB-1 blockade increases circulating adiponectin concentration. We, therefore, hypothesize that blockade of CB-1 would increase adiponectin and attenuate pancreatitis severity.

METHODS

Forty lean (C57BL/6J) and 40 obese (Lep(Db)) mice were studied. Half of the mice in each strain received intraperitoneal injection of the CB-1 antagonist rimonabant (10 mg/kg daily for 7 days); the others received vehicle. Pancreatitis was induced by intraperitoneal injection of cerulein (50 microg/g hourly x 6). Pancreatitis severity was determined by histology. Pancreatic chemokine and proinflammatory cytokine concentrations were measured by ELISA.

RESULTS

Rimonabant treatment significantly increased circulating adiponectin concentration in obese mice (p < 0.03 vs. vehicle). After induction of pancreatitis, obese mice treated with rimonabant had significantly decreased histologic pancreatitis (p < 0.001), significantly lower pancreatic tissue levels of monocyte chemoattractant protein-1 (p = 0.03), tumor necrosis factor-alpha (p < 0.001), interleukin-6 (p < 0.001), and myeloperoxidase (p = 0.006) relative to vehicle-treated animals.

CONCLUSIONS

In obese mice, cannabinoid receptor CB-1 blockade with rimonabant attenuates the severity of acute pancreatitis by an adiponectin-mediated mechanism.

High dietary carbohydrates decrease gallbladder volume and enhance cholesterol crystal formation

BACKGROUND

Animal and human data suggest that a diet high in refined carbohydrates leads to gallstone formation. However, no data are available on the role of dietary carbohydrates on gallbladder volume or on cholesterol crystal formation. Therefore, we tested the hypothesis that a high carbohydrate diet would alter gallbladder volume and enhance cholesterol crystal formation.

METHODS

At 8 weeks of age, 60 lean and 36 obese leptin-deficient female mice were fed a 45% carbohydrate diet while an equal number of lean and obese mice were fed a 75% carbohydrate diet for 4 weeks. All animals then underwent cholecystectomy, and gallbladder bile volume was recorded. Bile was pooled, filtered, and maintained in a water bath at 37 degrees C for 14 days. Birefringent cholesterol crystals in bile were counted daily; crystal observation time and crystal mass were determined.

RESULTS

The crystal observation time was significantly shortened in both lean and obese mice on the 75% diet compared with their counterparts on the 45% diet. The crystal mass was significantly increased in the lean mice on the 75% diet compared with the 45% diet. Gallbladder volumes were significantly reduced in both lean and obese mice on the 75% diet compared with their counterparts on the 45% diet.

CONCLUSIONS

These data suggest that a high carbohydrate diet decreases gallbladder volume, shortens cholesterol crystal observation time, and increases crystal mass. We conclude that dietary carbohydrates may play a role in cholesterol gallstone formation by altering biliary motility and by enhancing crystal formation.