Tumor necrosis factor alpha derived from classically activated "M1" macrophages reduces interstitial cell of Cajal numbers.

BACKGROUND: Delayed gastric emptying in diabetic mice and humans is associated with changes in macrophage phenotype and loss of interstitial cells of Cajal (ICC) in the gastric muscle layers. In diabetic mice, classically activated M1 macrophages are associated with delayed gastric emptying, whereas alternatively activated M2 macrophages are associated with normal gastric emptying. This study aimed to determine if secreted factors from M1 macrophages could injure mouse ICC in primary culture. METHODS: Cultures of gastric ICC were treated with conditioned medium (CM) from activated bone marrow-derived macrophages (BMDMs) and the effect of CM was quantified by counting ICC per high-powered field. KEY RESULTS: Bone marrow-derived macrophages were activated to a M1 or M2 phenotype confirmed by qRT-PCR. Conditioned medium from M1 macrophages reduced ICC numbers by 41.1%, whereas M2-CM had no effect as compared to unconditioned, control media. Immunoblot analysis of 40 chemokines/cytokines found 12 that were significantly increased in M1-CM, including tumor necrosis factor alpha (TNF-α). ELISA detected 0.697±0.03 ng mL-1 TNF-α in M1-CM. Recombinant mouse TNF-α reduced Kit expression and ICC numbers in a concentration-dependent manner (EC50 = 0.817 ng mL-1 ). Blocking M1-CM TNF-α with a neutralizing antibody preserved ICC numbers. The caspase inhibitor Z-VAD.fmk partly preserved ICC numbers (cells/field; 6.63±1.04, 9.82±1.80 w/Z-VAD.fmk, n=6, P<.05). CONCLUSIONS & INFERENCES: This work demonstrates that TNF-α secreted from M1 macrophages can result in Kit loss and directly injure ICC in vitro partly through caspase-dependent apoptosis and may play an important role in ICC depletion in diabetic gastroparesis.

Review article: carbon monoxide in gastrointestinal physiology and its potential in therapeutics.

BACKGROUND: While carbon monoxide (CO) is a known toxin, it is now recognised that CO is also an important signalling molecule involved in physiology and pathophysiology. AIMS: To summarise our current understanding of the role of endogenous CO in the regulation of gastrointestinal physiology and pathophysiology, and to potential therapeutic applications of modulating CO. METHODS: This review is based on a comprehensive search of the Ovid Medline comprehensive database and supplemented by our ongoing studies evaluating the role of CO in gastrointestinal physiology and pathophysiology. RESULTS: Carbon monoxide derived from haem oxygenase (HO)-2 is predominantly involved in neuromodulation and in setting the smooth muscle membrane potential, while CO derived from HO-1 has anti-inflammatory and antioxidative properties, which protect gastrointestinal smooth muscle from damage caused by injury or inflammation. Exogenous CO is being explored as a therapeutic agent in a variety of gastrointestinal disorders, including diabetic gastroparesis, post-operative ileus, organ transplantation, inflammatory bowel disease and sepsis. However, identifying the appropriate mechanism for safely delivering CO in humans is a major challenge. CONCLUSIONS: Carbon monoxide is an important regulator of gastrointestinal function and protects the gastrointestinal tract against noxious injury. CO is a promising therapeutic target in conditions associated with gastrointestinal injury and inflammation. Elucidating the mechanisms by which CO works and developing safe CO delivery mechanisms are necessary to refine therapeutic strategies.

Role of the AMP-activated protein kinase (AMPK) signaling pathway in the orexigenic effects of endogenous ghrelin.

Ghrelin, released from the stomach, stimulates food intake through activation of the ghrelin receptor (GHS-R) located on neuropeptide Y (NPY)/agouti-related peptide (AgRP) neurons in the hypothalamus. A role for the energy sensor AMP-activated protein kinase (AMPK) and its downstream effector uncoupling protein 2 (UCP2) in the stimulatory effect of exogenous ghrelin on NPY/AgRP expression and food intake has been suggested. This study aimed to investigate whether a rise in endogenous ghrelin levels is able to influence hypothalamic AMPK activity, pACC, UCP2 and NPY/AgRP expression through activation of GHS-R. An increase in endogenous ghrelin levels was established by fasting (24h) or by induction of streptozotocin(STZ)-diabetes (15 days) in GHS-R(+/+) and GHS-R(-/-) mice. GHS-R(+/+) mice showed a significant increase in AgRP and NPY mRNA expression after fasting, which was not observed in GHS-R(-/-) mice. Fasting did not affect AMPK activity nor ACC phosphorylation in both genotypes and increased UCP2 mRNA expression. The hyperghrelinemia associated with STZ-induced diabetes was accompanied by an increased NPY and AgRP expression in GHS-R(+/+) but not in GHS-R(-/-) mice. AMPK activity and UCP2 expression in GHS-R(+/+) mice after induction of diabetes were decreased to a similar extent in both genotypes. Exogenous ghrelin administration tended to decrease hypothalamic AMPK activity. In conclusion, an increase in endogenous ghrelin levels triggered by fasting or STZ-induced diabetes stimulates the expression of AgRP and NPY via interaction with the GHS-R. The changes in AMPK activity, pACC and UCP2 occur independently from GHS-R suggesting that they do not play a major role in the orexigenic effect of endogenous ghrelin.

GPR39, a receptor of the ghrelin receptor family, plays a role in the regulation of glucose homeostasis in a mouse model of early onset diet-induced obesity.

GPR39, which may function as a Zn(2+) sensor, is a member of the G protein-coupled receptor family that also includes the receptor for the hunger hormone ghrelin. The down-regulation of GPR39 mRNA in adipose tissue of obese type 2 diabetic patients suggests that GPR39 may contribute to the pathogenesis of the disease. The present study aimed to investigate the role of GPR39 in the regulation of energy balance and glucose homeostasis in wild-type (GPR39(+/+) ) and GPR39 knockout mice (GPR39(-/-) ) with obesity-related type 2 diabetes. GPR39 mRNA levels in adipose tissue of fasted GPR39(+/+) mice fed a high-fat diet (HFD) for 30 weeks were reduced and correlated positively with blood glucose levels. Body weight, fat percentage and energy intake were increased in the HFD group but did not differ between both genotypes. Within the HFD group, blood glucose levels were lower in GPR39(-/-) than in GPR39(+/+) mice, despite significant reductions in prandial plasma insulin levels. The latter may not be a result of changes in ß-cell hyperplasia because immunohistochemical staining of pancreata of mice on a HFD showed no differences between genotypes. The lower blood glucose levels may involve alterations in insulin sensitivity as revealed by glucose tolerance tests and respiratory quotient measurements that showed a preference of obese GPR39(-/-) mice for the use of carbohydrates as metabolic fuel. The increase in plasma ghrelin levels in GPR39(-/-) mice fed a HFD may contribute to the alterations in glucose homeostasis, whereas changes in gastric emptying or intestinal Zn(2+) absorption are not involved. The results obtained in the present study suggest that GPR39 plays a role in the pathogenesis of obesity-related type 2 diabetes by affecting the regulation of glucose homeostasis.

Further investigations on the role of diet-induced thermogenesis in the regulation of feed intake in chickens: comparison of adult cockerels of lines selected for high or low residual feed intake.

The main objective of this study was to investigate the role of diet-induced thermogenesis (DIT) in feed intake regulation in cockerels selected for high (R+) or low (R-) residual feed intake. The selection criterion was defined as the difference between observed feed intake and feed intake predicted by regression between feed intake and BW, BW gain, and egg mass production. Furthermore, the effect of genotype on postprandial oxidation of U-(13)C(6)-glucose, decarboxylation of 1-(13)C(1)-Leu, and key metabolites and hormones was analyzed. Thirty 24-wk-old cockerels of both lines were kept in battery cages under standard conditions on a commercial diet. Three cockerels per genotype were examined twice weekly from wk 30 through 34 in open-circuit respiratory cells. After adaptation, cockerels were feed deprived for 24 h and heat production was measured. During the subsequent 7-h refeeding period, DIT and feed intake, as well as glucose oxidation and Leu decarboxylation were assessed by using breath tests. Blood samples were collected after fasting and refeeding. Finally, 10 animals per genotype were killed to record abdominal fat weight. Body composition of 6 different chickens per genotype was determined by using dual-energy x-ray absorptiometry. During feed deprivation, the R+ cockerels had a significantly higher heat production than their R- counterparts, which was even more pronounced during refeeding. Consequently, the R+ cockerels had a significantly increased DIT and a higher feed intake than the R- cockerels. Thus, no evidence of a feedback effect of DIT on feed intake was observed. The oxidation of U-(13)C(6)-glucose was significantly higher in the R+ cockerels, confirming their higher respiratory quotient values and the augmented fat deposition in the R- chickens, as assessed by abdominal fat weight and dual-energy x-ray absorptiometry measurements. No significant genotype effect on 1-(13)C(1)-Leu decarboxylation was observed, despite increased circulating uric acid levels in the R+ chickens. Genotype did not influence plasma levels of triglycerides, free fatty acids, glucose, triiodothyronine, or thyroxine after refeeding, whereas plasma leptin levels were significantly higher in the R+ cockerels.