Substance P, neurokinin A, vasoactive intestinal polypeptide and gastrin releasing peptide in the intestine and pancreas of spontaneously obese-diabetic mice

Syringaldehyde promoting intestinal motility with suppressing α-amylase hinders starch digestion in diabetic mice

The antihyperglycemic potential of syringaldehyde has been previously investigated; however, the underlying mechanism remains unclear. In this study, we performed a postprandial glucose test (in vivo) including oral glucose tolerance test (OGTT) and oral starch tolerance test (OSTT) in fructose-induced diabetic mice on a high-fat diet for mimicking type 2 diabetes to explore the hypoglycemic efficacy of syringaldehyde and the underlined molecular involvement of syringaldehyde in a glucose-lowering effect. The results revealed that syringaldehyde dose-dependently suppressed blood glucose in both the OSTT and OGTT when referenced to acarbose and metformin, respectively. Surprisingly, syringaldehyde triggered jejunum motility (ex vivo) via activation of the muscarinic-type acetylcholine receptor. By performing virtual screening with molecular docking, the data showed that syringaldehyde nicely interacted with glucagon-like peptide 1 receptor (GLP-1R), peroxisome proliferator-activated receptor (PPAR), dipeptidyl peptidase-IV (DPP-4), acetylcholine M2 receptor, and acetylcholinesterase. These results showed that syringaldehyde can potentiate intestinal contractility to abolish the α-amylase reaction when concurrently reducing retention time and glucose absorption to achieve a glucose-lowering effect in diabetic mice, suggesting its potential therapeutic benefits with improvement for use as a prophylactic and treatment.

NFAT5 Is Involved in GRP-Enhanced Secretion of GLP-1 by Sodium

Gastrin, secreted by G-cells, and glucagon-like peptide-1 (GLP-1), secreted by L-cells, may participate in the regulation of sodium balance. We studied the effect of sodium in mice in vivo and mouse ileum and human L-cells, on GLP-1 secretion, and the role of NFAT5 and gastrin-releasing peptide receptor (GRPR) in this process. A high-sodium diet increases serum GLP-1 levels in mice. Increasing sodium concentration stimulates GLP-1 secretion from mouse ileum and L-cells. GRP enhances the high sodium-induced increase in GLP-1 secretion. High sodium increases cellular GLP-1 expression, while low and high sodium concentrations increase NFAT5 and GRPR expression. Silencing NFAT5 in L-cells abrogates the stimulatory effect of GRP on the high sodium-induced GLP-1 secretion and protein expression, and the sodium-induced increase in GRPR expression. GLP-1 and gastrin decrease the expression of Na⁺-K⁺/ATPase and increase the phosphorylation of sodium/hydrogen exchanger type 3 (NHE3) in human renal proximal tubule cells (hRPTCs). This study gives a new perspective on the mechanisms of GLP-1 secretion, especially that engendered by ingested sodium, and the ability of GLP-1, with gastrin, to decrease Na⁺-K⁺/ATPase expression and NHE3 function in hRPTCs. These results may contribute to the better utilization of current and future GLP-1-based drugs in the treatment of hypertension.

Apelin-13 analogues show potent in vitro and in vivo insulinotropic and glucose lowering actions

Nine structurally modified apelin-13 analogues were assessed for their in vitro and acute in vivo antidiabetic potential. Stability was assessed in mouse plasma and insulinotropic efficacy tested in cultured pancreatic BRIN-BD11 cells and isolated mouse pancreatic islets. Intracellular Ca²⁺ and cAMP production in BRIN-BD11 cells was determined, as was glucose uptake in 3T3-L1 adipocytes. Acute antihyperglycemic effects of apelin analogues were assessed following i.p. glucose tolerance tests (ipGGT, 18 mmol/kg) in normal and diet-induced-obese (DIO) mice and on food intake in normal mice. Apelin analogues all showed enhanced in vitro stability (up to 5.8-fold, t½ = 12.8 h) in mouse plasma compared to native apelin-13 (t½ = 2.1 h). Compared to glucose controls, stable analogues exhibited enhanced insulinotropic responses from BRIN-BD11 cells (up to 4.7-fold, p < 0.001) and isolated mouse islets (up to 5.3-fold) for 10^-7 M apelin-13 amide (versus 7.6-fold for 10^-7 M GLP-1). Activation of APJ receptors on BRIN-BD11 cells increased intracellular Ca²⁺ (up to 3.0-fold, p < 0.001) and cAMP (up to 1.7-fold, p < 0.01). Acute ipGTT showed improved insulinotropic and glucose disposal responses in normal and DIO mice (p < 0.05 and p < 0.01, respectively). Apelin-13 amide and (pGlu)apelin-13 amide were the most effective analogues exhibiting acute, dose-dependent and persistent biological actions. Both analogues stimulated insulin-independent glucose uptake by differentiated adipocytes (2.9-3.3-fold, p < 0.05) and inhibited food intake (26-33%, p < 0.001), up to 180 min in mice, versus saline. In contrast, (Ala¹³)apelin-13 and (Val¹³)apelin-13 inhibited insulin secretion, suppressed beta-cell signal transduction and stimulated food intake in mice. Thus, stable analogues of apelin-13 have potential for diabetes/obesity therapy.

Dietary Genistein Influences Number of Acetylcholine Receptors in Female Diabetic Jejunum

BACKGROUND

Intestinal dysfunction in the ob/ob mouse model of diabetes mimics that seen clinically.

METHODS

We determined the effects of a 4-week genistein diet (600 mg genistein/kg food) on intestinal function (contractility, morphology, AChR, and motility) in female ob/ob and lean mice.

RESULTS

Contractility of the jejunum in response to incrementally increasing concentrations of KCl was comparable in ob/ob females and lean controls regardless of a genistein-diet. There were no changes in the wall thickness measured. We assessed the number of clusters of AChR in the jejunum wall; AChR were decreased by 48% in ob/ob mice versus leans, and the genistein diet reversed this. In utilizing a video-imaging system to evaluate gastrointestinal motility, we determined that the distance between consecutive contractile events was significantly increased by 1.87-fold in ob/ob mice versus leans, and the genistein diet was without effect.

CONCLUSIONS

These data suggest that slowed intestinal transit in the diabetic ob/ob mouse may be due in part to decreased AChR and decreased contraction events occurring per unit time. A genistein diet rescues the number of AChR to levels of leans yet did not change the number of contractile events. Feeding ob/ob mice a genistein-rich diet has potential therapeutic benefits towards improving the debilitating diabetes-related gastrointestinal dysfunction.

Decreased basal chloride secretion and altered cystic fibrosis transmembrane conductance regulatory protein, Villin, GLUT5 protein expression in jejunum from leptin-deficient mice

Patients with diabetes and obesity are at increased risk of developing disturbances in intestinal function. In this study, we characterized jejunal function in the clinically relevant leptin-deficient ob/ob mouse, a model of diabetes and obesity. We measured transepithelial short circuit current (Isc), across freshly isolated segments of jejunum from 12-week-old ob/ob and lean C57BL/6J (female and male) mice. The basal Isc was significantly decreased (~30%) in the ob/ob mice (66.5±5.7 μA/cm(2) [n=20]) (P< 0.05) compared with their lean counterparts (95.1±9.1 μA/cm(2) [n=19]). Inhibition with clotrimazole (100 μM, applied bilaterally) was significantly reduced in the ob/ob mice (-7.92%±3.67% [n=15]) (P<0.05) compared with the lean mice (10.44%±7.92% [n=15]), indicating a decreased contribution of Ca(2+)-activated K(+) (KCa) channels in the ob/ob mice. Inhibition with ouabain (100 μM, applied serosally) was significantly reduced in the ob/ob mice (1.40%±3.61%, n=13) (P< 0.05) versus the lean mice (18.93%±3.76% [n=18]), suggesting a potential defect in the Na(+)/K(+)-adenosine triphosphate (ATP)ase pump with leptin-deficiency. Expression of cystic fibrosis transmembrane conductance regulatory protein (CFTR) (normalized to glyceraldehyde-3-phosphate dehydrogenase [GAPDH]) was significantly decreased ~twofold (P<0.05) in the ob/ob mice compared with the leans, whilst crypt depth was unchanged. Villi length was significantly increased by ~25% (P<0.05) in the ob/ob mice compared with the leans and was associated with an increase in Villin and GLUT5 expression. GLUT2 and SGLT-1 expression were both unchanged. Our data suggests that reduced basal jejunal Isc in ob/ob mice is likely a consequence of reduced CFTR expression and decreased activity of the basolateral KCa channel and Na(+)/K(+)-ATPase. Understanding intestinal dysfunctions in ob/ob jejunum may allow for the development of novel drug targets to treat obesity and diabetes.

A quantitative trait locus on chromosome 18q for physical activity and dietary intake in Hispanic children

OBJECTIVE

Genetic components of energy homeostasis contributing to childhood obesity are poorly understood. Genome scans were performed to identify chromosomal regions contributing to physical activity and dietary intake traits in Hispanic children participating in the VIVA LA FAMILIA Study.

RESEARCH METHODS AND PROCEDURES

We report linkage findings on chromosome 18 for physical activity and dietary intake in 1030 siblings from 319 Hispanic families. Measurements entailed physical activity by accelerometry, dietary intake by two 24-hour recalls, and genetic linkage analyses using SOLAR software.

RESULTS

Significant heritabilities were seen for physical activity and dietary intake, ranging from 0.46 to 0.69, except for vigorous activity (h2 = 0.18). Percentage time in sedentary activity mapped to markers D18S1102-D18S64 on chromosome 18 [logarithm of the odds (LOD) score = 4.07], where melanocortin 4 receptor gene (MC4R) resides. Quantitative trait loci (QTLs) for total activity counts, percentage time in light or in moderate activity, and carbohydrate intake and percentage of energy intake from carbohydrates were detected in the same region (LOD = 2.28, 2.79, 2.2, 1.84, and 1.51, respectively). A novel loss of function mutation in MC4R (G55V) was detected in six obese relatives, but not in the rest of the cohort. Removal of these MC4R-deficient subjects from the analysis reduced the LOD score for sedentary activity to 3.94.

DISCUSSION

Given its role in the regulation of food intake and energy expenditure, MC4R is a strong positional candidate gene for the QTL on chromosome 18 detected for physical activity and dietary intake in Hispanic children.

Tachykinins in the gut. Part II. Roles in neural excitation, secretion and inflammation

The preprotachykinin-A gene-derived peptides substance (substance P; SP) and neurokinin (NK) A are expressed in intrinsic enteric neurons, which supply all layers of the gut, and extrinsic primary afferent nerve fibers, which innervate primarily the arterial vascular system. The actions of tachykinins on the digestive effector systems are mediated by three different types of tachykinin receptor, termed NK1, NK2 and NK3 receptors. Within the enteric nervous system, SP and NKA are likely to mediate, or comediate, slow synaptic transmission and to modulate neuronal excitability via stimulation of NK3 and NK1 receptors. In the intestinal mucosa, tachykinins cause net secretion of fluid and electrolytes, and it appears as if SP and NKA play a messenger role in intramural secretory reflex pathways. Secretory processes in the salivary glands and pancreas are likewise influenced by tachykinins. The gastrointestinal arterial system may be dilated or constricted by tachykinins, whereas constriction and an increase in the vascular permeability are the only effects seen in the venous system. Various gastrointestinal disorders are associated with distinct changes in the tachykinin system, and there is increasing evidence that tachykinins participate in the hypersecretory, vascular and immunological disturbances associated with infection and inflammatory bowel disease. In a therapeutic perspective, it would seem conceivable that tachykinin antagonists could be exploited as antidiarrheal, antiinflammatory and antinociceptive drugs.

Impairment of nitrergic-mediated relaxation of rat isolated duodenum by experimental diabetes

1. Diabetes mellitus is associated with changes in gastrointestinal motility. The effects of experimental diabetes, induced by streptozotocin administration to rats 3-4 weeks previously, on the nitric oxide (NO)-mediated (nitrergic) relaxation of the duodenum have now been investigated. 2. The non-adrenergic, non-cholinergic (NANC) relaxation of the isolated duodenum induced by nicotine (0.3-10 microM) or the nicotinic agonist, 1,1-dimethyl-4-phenylpiperazinium (DMPP; 10 microM) was inhibited by the NO synthase inhibitor, NG-nitro-L-arginine (3-100 microM). 3. This nitrergic relaxation induced by nicotine or DMPP of the duodenum from diabetic rats was substantially smaller than that of the tissue from control rats. 4. By contrast, the relaxation of the duodenum from diabetic rats to the NO donor, nitroprusside (0.3-10 microM) was similar to that of control tissue, whereas the relaxation to ATP (0.1-3 microM) was enhanced to a small but significant degree. 5. Incubation of duodenal tissue from control rats at 4 degrees C for 72 h, which leads to neuronal disruption, significantly attenuated the relaxation to nicotine or DMPP whereas the relaxation induced by nitroprusside or ATP was not affected. Comparable cold-storage did not affect the endothelium-dependent relaxation of rat aortic rings induced by acetylcholine (0.01-2 microM). 6. The calcium-dependent NO synthase activity in duodenal tissue, determined by the conversion of radiolabelled L-arginine to citrulline, was significantly reduced in cold-stored tissue and in tissue obtained from diabetic rats. 7. These findings in the rat duodenum indicate that a reduction in intestinal NO synthase activity is associated with an impairment of the NANC relaxation. A defect in the intestinal nitrergic innervation could thus contribute to the motility dysfunction observed in diabetes.

Localization of neurokinin A and chromogranin A immunoreactivity in the developing porcine adrenal medulla

The presence of neurokinin A immunoreactivity was studied in the chromaffin cells of the porcine adrenal medulla and in the nerve fibres innervating the adrenal gland during ontogenic development. For comparison, chromogranin A immunoreactivity was used as a marker for chromaffin cells. Whereas chromogranin A was found in chromaffin cells through all steps in embryonic development, three developmental stages of neurokinin A immunoreactivity could be distinguished. In the first and second trimester of gestation, neurokinin A was observed in some groups of chromaffin cells, but no neurokinin-immunoreactive nerve fibres could be detected. In the last trimester of gestation, neurokinin A-reactive chromaffin cells and nerve fibres were both found in adrenal glands. However, in adrenal glands of neonatal piglets, neurokinin A was found only in nerve fibres and not in chromaffin cells. From these results a hypothesis is proposed that neurokinin A might act as a neurotrophic factor in the early stages of the developing porcine chromaffin cells. Biochemical studies are being performed in order to confirm these morphological results and to study the possible role of neurokinin A as a neurotrophic factor in the adrenal gland.

Neuropeptide content in pancreas and pituitary of obese and diabetes mutant mice: strain and sex differences

The nature of the primary genetic defects in ob/ob and db/db mice are unknown. Both the obese (ob) and diabetes (db) mutations produce similar, multicomponent obese-hyperinsulinemic syndromes when maintained in the same strain of mouse. In an attempt to find differences between these mutations in neuroendocrine function affecting the islets of Langerhans or the pituitary, tissue content of four neuropeptides that are known to be capable of influencing the rate of insulin secretion was examined in obese (ob/ob) and diabetes (db/db) mice. In the first study, C57BL/6Job/ob and control males were studied at 3, 4, and 11 weeks of age. In the second study, db/db mice of both sexes and two inbred strains (C57BL/6J and C57BL/KsJ), which differ markedly in the severity of expression of the diabetes phenotype, were studied at 3 weeks of age, before the development of hyperglycemia and secondary consequences thereof. Immunoreactive peptides were measured in acetic acid extracts of pancreas and pituitary. No differences between male ob/ob and db/db mice of the C57BL/6J strain were found. Marked sex differences in lean control mice were found at 3 weeks of age in pancreatic Met-enkephalin-LI and galanin-LI (with two- to threefold higher content in males). Low pancreatic content (50% to 70% lower than in control mice) of galanin-LI, Met-enkephalin-LI and Leu-enkephalin-LI was associated with hyperinsulinemia in male B6 ob/ob and db/db mice at 3 weeks of age, though not in B6 db/db females and not in BKs db/db mice of either sex.(ABSTRACT TRUNCATED AT 250 WORDS)

Glucoregulatory effects of bombesin in lean and genetically obese hyperglycaemic (ob/ob) mice

1. Plasma glucose and insulin responses to bombesin were examined in 12-15-week-old 12 hr fasted lean and genetically obese hyperglycaemic (ob/ob) mice. 2. Bombesin (1 mg/kg ip) produced a prompt but transient increase of plasma insulin in lean mice (maximum increase of 50% at 5 min), and a more slowly generated but protracted insulin response in ob/ob mice (maximum increase of 80% at 30 min). Plasma glucose concentrations of both groups of mice were increased by bombesin (maximum increases of 40 and 48% respectively in lean and ob/ob mice at 15 min). 3. When administered with glucose (2 g/kg ip), bombesin (1 mg/kg ip) rapidly increased insulin concentrations of lean and ob/ob mice (maximum increases of 39 and 63% respectively at 5 min). Bombesin did not significantly alter the rise of plasma glucose after exogenous glucose administration to these mice. 4. The results indicate that bombesin exerts an insulin-releasing effect in lean and ob/ob mice. The greater insulin-releasing effect in ob/ob mice renders bombesin a possible component of the overactive entero-insular axis in the ob/ob mutant, especially if it acts within the islets as a neurotransmitter or paracrine agent.