Mechanism of action of intracisternal apolipoprotein A-IV in inhibiting gastric acid secretion in rats

Transcriptome Reveals 1400-Fold Upregulation of APOA4-APOC3 and 1100-Fold Downregulation of GIF in the Patients with Polycythemia-Induced Gastric Injury

High-altitude polycythemia (HAPC) inducing gastric mucosal lesion (GML) is still out of control and molecular mechanisms remain widely unknown. To address the issues, endoscopy and histopathological analyses were performed. Meanwhile, microarray-based transcriptome profiling was conducted in the gastric mucosa from 3 pairs of healthy subjects and HAPC-induced GML patients. HAPC caused morphological changes and pathological damages of the gastric mucosa of GML patients. A total of 10304 differentially expressed genes (DEGs) were identified, including 4941 up-regulated and 5363 down-regulated DEGs in gastric mucosa of GML patients compared with healthy controls (fold change ≥2, P<0.01 and FDR <0.01). Particularly, apolipoprotein genes APOA4 and APOC3 were 1473-fold and 1468-fold up-regulated in GML patients compared with the controls. In contrast, gastric intrinsic factor (GIF) was 1102-fold down-regulated in GML patients compared with the controls. APOA4 (chr11:116691770–116691711), APOC3 (chr11:116703530–116703589) and GIF (chr11:59603362–59603303) genes are all located on chromosome 11. APOA4 and APOC3 act as an inhibitor of gastric acid secretion while gastric acid promotes ulceration. GIF deficiency activates a program of acute anemia, which may antagonize polycythemia while polycythemia raises the risk of GML. Therefore, the present findings reveal that HAPC-induced GML inspires the protection responses by up-regulating APOA4 and APOC3, and down-regulating GIF. These results may offer the basic information for the treatment of HAPC-induced gastric lesion in the future.

Apolipoprotein A-IV: a protein intimately involved in metabolism

The purpose of this review is to summarize our current understanding of the physiological roles of apoA-IV in metabolism, and to underscore the potential for apoA-IV to be a focus for new therapies aimed at the treatment of diabetes and obesity-related disorders. ApoA-IV is primarily synthesized by the small intestine, attached to chylomicrons by enterocytes, and secreted into intestinal lymph during fat absorption. In circulation, apoA-IV is associated with HDL and chylomicron remnants, but a large portion is lipoprotein free. Due to its anti-oxidative and anti-inflammatory properties, and because it can mediate reverse-cholesterol transport, proposed functions of circulating apoA-IV have been related to protection from cardiovascular disease. This review, however, focuses primarily on several properties of apoA-IV that impact other metabolic functions related to food intake, obesity, and diabetes. In addition to participating in triglyceride absorption, apoA-IV can act as an acute satiation factor through both peripheral and central routes of action. It also modulates glucose homeostasis through incretin-like effects on insulin secretion, and by moderating hepatic glucose production. While apoA-IV receptors remain to be conclusively identified, the latter modes of action suggest that this protein holds therapeutic promise for treating metabolic disease.

Effect of peripheral administration of cholecystokinin on food intake in apolipoprotein AIV knockout mice

Apolipoprotein AIV (apo AIV) and cholecystokinin (CCK) are satiation factors secreted by the small intestine in response to lipid meals. Apo AIV and CCK-8 has an additive effect to suppress food intake relative to apo AIV or CCK-8 alone. In this study, we determined whether CCK-8 (1, 3, or 5 μg/kg ip) reduces food intake in fasted apo AIV knockout (KO) mice as effectively as in fasted wild-type (WT) mice. Food intake was monitored by the DietMax food system. Apo AIV KO mice had significantly reduced 30-min food intake following all doses of CCK-8, whereas WT mice had reduced food intake only at doses of 3 μg/kg and above. Post hoc analysis revealed that the reduction of 10-min and 30-min food intake elicited by each dose of CCK-8 was significantly larger in the apo AIV KO mice than in the WT mice. Peripheral CCK 1 receptor (CCK1R) gene expression (mRNA) in the duodenum and gallbladder of the fasted apo AIV KO mice was comparable to that in WT mice. In contrast, CCK1R mRNA in nodose ganglia of the apo AIV KO mice was upregulated relative to WT animals. Similarly, upregulated CCK1R gene expression was found in the brain stem of apo AIV KO mice by in situ hybridization. Although it is possible that the increased satiating potency of CCK in apo AIV KO mice is mediated by upregulation of CCK 1R in the nodose ganglia and nucleus tractus solitarius, additional experiments are required to confirm such a mechanism.

Gastric secretions affected by esophageal distention in the rat

BACKGROUND

The effect of esophageal distention (ED) on gastric motility has been well documented, but only a few investigations have been carried out about the effect of ED on gastric secretions. The aim of this study was to investigate the effect of ED on gastric acid and pepsin secretions and the mechanisms involved.

METHODS

Male adult Wistar rats (200-240 g) were anesthetized by urethane [1.2 g/kg, intraperitoneally (i.p.)] and underwent tracheostomy and laparotomy. A catheter was inserted in the stomach through the duodenum for gastric washout and distention followed by the esophageal distention by a balloon (0.3 ml, 10 min). Gastric acid secretion was stimulated by gastric distension (1.5 ml/100 g body weight), pentagastrin (20 microg/kg, i.p.), or insulin (0.6 IU/kg, i.p.). Pepsin secretion was stimulated by carbachol (20 microg/kg, i.p.). Effects of cervical vagotomy and reserpine (1 mg/kg, i.p.) were also investigated.

RESULTS

Gastric distention-, pentagastrin-, and insulin-stimulated gastric acid secretion was reduced by esophageal distention (P < 0.001, P < 0.05, and P < 0.05, respectively). Carbachol-induced pepsin secretion was also attenuated by esophageal distention (P < 0.05). Cervical vagotomy abolished the inhibitory effect of ED on pentagastrin-induced gastric acid secretion. In reserpinized rats, ED reduced the basal gastric acid secretion (P < 0.05).

CONCLUSIONS

These results indicate that the vagus nerves are involved in the inhibitory effect of esophageal distension on gastric secretory function.

Stimulation of Apolipoprotein A-IV expression in Caco-2/TC7 enterocytes and reduction of triglyceride formation in 3T3-L1 adipocytes by potential anti-obesity Chinese herbal medicines

BACKGROUND

Chinese medicine has been proposed as a novel strategy for the prevention of metabolic disorders such as obesity. The present study tested 17 Chinese medicinal herbs were tested for their potential anti-obesity effects.

METHODS

The herbs were evaluated in terms of their abilities to stimulate the transcription of Apolipoprotein A-IV (ApoA-IV) in cultured Caco-2/TC7 enterocytes. The herbs that showed stimulating effects on ApoA-IV transcription were further evaluated in terms of their abilities to reduce the formation of triglyceride in differentiated 3T3-L1 adipocytes.

RESULTS

ApoA-IV transcription was stimulated by Rhizoma Alismatis and Radix Angelica Sinensis in a dose- and time-dependent manner in cultured Caco-2/TC7 cells. Moreover, these two herbs reduced the amount of triglyceride in differentiated 3T3-L1 adipocytes.

CONCLUSION

The results suggest that Rhizoma Alistmatis and Radix Angelica Sinensis may have potential anti-obesity effects as they stimulate ApoA-IV transcription and reduce triglyceride formation.

Apolipoprotein A-IV is involved in detection of lipid in the rat intestine

Long chain triglyceride (>C12) in the intestinal lumen potently inhibits gastric emptying and acid secretion via the vagal afferent pathway. While the mechanism of inhibition involves the formation of chylomicrons, the essential role of the apolipoprotein apo A-IV is unclear. Using apo A-IV(-/-) mice, we tested the hypothesis that inhibition of gastric emptying and gastric acid secretion in response to dietary lipid is dependent upon apo A-IV. As measured by nuclear scintigraphy in awake mice, gastric emptying of an ingested whole-egg meal was significantly faster in apo A-IV(-/-) knockout versus A-IV(+/+) controls (34 +/- 1 versus 54 +/- 3 min, P < 0.0001). In anaesthetized A-IV(+/+) mice, meal-stimulated gastric acid secretion was 59% inhibited by intestinal lipid infusion; this was abolished in apo A-IV(-/-) mice. Oral gavage of lipid in awake mice activated neurones throughout the nucleus of the solitary tract (NTS) in A-IV(+/+) mice, measured by immunohistochemical localization of Fos protein expression. However, in the mid region of the NTS (bregma -7.32 to -7.76 mm), Fos expression in response to intestinal lipid was significantly decreased by 50% in apo A-IV(-/-) mice compared to A-IV(+/+) controls. We conclude that activation of the vagal afferent pathway and inhibition of gastric function in response to dietary lipid is partly dependent upon apo A-IV.

Apolipoprotein A-IV, food intake, and obesity

Apolipoprotein A-IV (apo A-IV) is secreted by the intestine associated with chylomicron. Intestinal apo A-IV synthesis is stimulated by fat absorption, which is probably mediated by chylomicron formation. The stimulation of apo A-IV synthesis in the jejunum and ileum is attenuated by intravenous leptin infusion. Intestinal apo A-IV synthesis is also stimulated by a factor from the ileum, probably peptide tyrosine-tyrosine (PYY), which has been demonstrated to affect satiety. Apo A-IV has been proposed to physiologically control food intake, a function not shared by apo A-I, and this inhibitory effect is centrally mediated. Recently, apo A-IV was demonstrated in the hypothalamus. The hypothalamic apo A-IV level was reduced by food deprivation and restored by lipid feeding. Intracerebroventricular administration of apo A-IV antiserum increased feeding and decreased the hypothalamic apo A-IV mRNA level, implying that feeding is normally limited by endogenous apo A-IV. Central administration of neuropeptide Y (NPY) significantly increased hypothalamic apo A-IV mRNA levels in a dose-dependent manner. The stimulation of intestinal synthesis and secretion of apo A-IV by lipid absorption are rapid; thus, apo A-IV is capable of short-term regulation of food intake. Evidence also suggests apo A-IV's involvement in the long-term regulation of food intake and body weight. Chronic ingestion of high fat blunts the hypothalamic apo A-IV response to lipid feeding and may therefore explain why chronic intake of high fat predisposes animals and humans to obesity.

A selective orexin-1 receptor antagonist, SB334867, blocks 2-DG-induced gastric acid secretion in rats

We have previously demonstrated that intracisternal orexin-A potently stimulated gastric acid secretion through the vagus nerve. Considering its stimulatory action on feeding, we hypothesized that orexin-A is a candidate mediator of cephalic phase gastric secretion. It has also been suggested that the stimulation of acid by central orexin-A may be mediated by orexin 1 receptor (OX1R) in the brain. In the present study, we tried to clarify whether endogenously released orexin-A in the brain indeed plays a physiological role in gastric secretion. To address the question, the effects of OX1R antagonist on gastric acid secretion was examined in rats. Intraperitoneal administration of SB334867, a specific OX1R antagonist, by itself did not change gastric acid secretion in pylorus-ligated conscious rats. Pretreatment with SB334867 in a dose of 10 mg/kg completely blocked the stimulated acid output by intracisternal orexin-A but not thyrotropin-releasing hormone, suggesting that SB334867 specifically blocked the action of orexin-A in the brain. 2-Deoxy-D-glucose (2-DG)-induced stimulation of gastric acid output was significantly blocked by pretreatment with intraperitoneal administration of SB334867. These results suggest that endogenously released orexin-A in the brain plays a vital role in central regulation of gastric secretion. Since 2-DG induces central glucoprivation as a hunger state, the present study furthermore supports the speculation that orexin-A may be an important molecule that triggers the cephalic phase gastric acid secretion.

Diurnal changes in intestinal apolipoprotein A-IV and its relation to food intake and corticosterone in rats

To further investigate the role of intestinal aplipoprotein A-IV (apo A-IV) in the management of daily food intake, we examined the diurnal patterns in apo A-IV gene and protein expression in freely feeding (FF) and food-restricted (FR; food provided 4 h daily for 4 wk) rats that were killed at 3-h intervals throughout the 24-h diurnal cycle. In FF rats, the intestinal apo A-IV mRNA and protein levels showed a circadian rhythm concomitant with the feeding pattern. The daily pattern of fluctuation of apo A-IV, however, was altered in FR rats, which had a marked increase in intestinal apo A-IV levels during the 4-h feeding period of light phase. In both FF and FR rats, increased plasma corticosterone (Cort) levels temporally coincided with the increasing phase of intestinal apo A-IV mRNA and protein expression. Depletion of Cort by adrenalectomy abolished the diurnal rhythm by decreasing the apo A-IV expression during the dark period but did not change the feeding rhythm. Exposure of adrenalectomized rats to consistent Cort level (50-mg continuous release Cort pellet) resulted in fixed apo A-IV levels throughout the day. These results indicate that intestinal apo A-IV exhibits a diurnal rhythm, which can be regulated by endogenous Cort independently of the light-dark cue. The fact that intestinal apo A-IV levels were consistent with the food intake during the normal diurnal cycle as well as during the cycle of 4-h feeding each day suggests that intestinal apo A-IV is involved in the regulation of daily food intake.

Ingested fat and satiety

Apolipoprotein A-IV (apo A-IV) is secreted by the intestine associated with chylomicron. Intestinal apo A-IV synthesis is stimulated by fat absorption, probably mediated by chylomicron formation. The stimulation of apo A-IV synthesis in the jejunum and ileum is attenuated by intravenous leptin infusion. Intestinal apo A-IV synthesis is also stimulated by a factor from the ileum, probably peptide tyrosine-tyrosine (PYY), which has been demonstrated to affect satiety. Apo A-IV has been proposed to physiologically control food intake, and this inhibitory effect is centrally mediated. Recently, apo A-IV was demonstrated in the hypothalamus. The hypothalamic apo A-IV level was reduced by food deprivation and restored by lipid feeding. Intracerebroventricular administration of apo A-IV antiserum stimulated feeding and decreased the hypothalamic apo A-IV mRNA level, implying that feeding is normally limited by endogenous apo A-IV. Central administration of neuropeptide Y (NPY) significantly increased hypothalamic apo A-IV mRNA levels in a dose-dependent manner. The stimulation of intestinal synthesis and secretion of apo A-IV by lipid absorption are rapid; thus, apo A-IV is capable of short-term regulation of food intake. Evidence also suggests apo A-IV's involvement in long-term regulation of food intake and bodyweight. The chronic ingestion of high fat blunts the intestinal apo A-IV response to lipid feeding and may therefore explain why chronic intake of high fat predisposes animals and humans to obesity.

Apolipoprotein A-IV stimulates duodenal vagal afferent activity to inhibit gastric motility via a CCK1 pathway

Apolipoprotein A-IV (apo A-IV), a peptide expressed by enterocytes in the mammalian small intestine and released in response to long-chain triglyceride absorption, may be involved in the regulation of gastric acid secretion and gastric motility. The specific aim of the present study was to determine the pathway involved in mediating inhibition of gastric motility produced by apo A-IV. Gastric motility was measured manometrically in response to injections of either recombinant purified apo A-IV (200 μg) or apo A-I, the structurally similar intestinal apolipoprotein not regulated by triglyceride absorption, close to the upper gastrointestinal tract in urethane-anesthetized rats. Injection of apo A-IV significantly inhibited gastric motility compared with apo A-I or vehicle injections. The response to exogenous apo A-IV injections was significantly reduced by 77 and 55%, respectively, in rats treated with the CCK1 receptor blocker devazepide or after functional vagal deafferentation by perineural capsaicin treatment. In electrophysiological experiments, isolated proximal duodenal vagal afferent fibers were recorded in vitro in response to close-arterial injection of vehicle, apo A-IV (200 μg), or CCK (10 pmol). Apo A-IV stimulated the discharge of duodenal vagal afferent fibers, significantly increasing the discharge in 4/7 CCK-responsive units, and the response was abolished by CCK1 receptor blockade with devazepide. These data suggest that apo A-IV released from the intestinal mucosa during lipid absorption stimulates the release of endogenous CCK that activates CCK1 receptors on vagal afferent nerve terminals initiating feedback inhibition of gastric motility.

Neuromedin U acts in the central nervous system to inhibit gastric acid secretion via CRH system

Neuromedin U (NMU) is a hypothalamic peptide involved in energy homeostasis and stress responses. NMU, when administered intracerebroventricularly, decreases food intake and body weight while increasing body temperature and heat production. In addition, NMU, acting via the corticotropin-releasing hormone (CRH) system, induces gross locomotor activity and stress responses. We studied the effect of intracerebroventricularly administered NMU (0.5-4 nmol) in the regulation of gastric functions in conscious rats. Intracerebroventricular administration of NMU significantly decreased gastric acid output to 30-60% and gastric emptying to 35-70% in a dose-dependent manner. Vagotomy did not abolish the inhibitory effect of NMU on pentagastrin-induced gastric acid secretion. Pretreatment with indomethacin (10 mg/kg), an inhibitor of prostaglandin synthesis, also did not affect NMU-induced acid inhibition. Pretreatment with anti-CRH IgG (1 microg/rat), however, completely blocked NMU-induced acid inhibition (P < 0.01). Administration of yohimbine (4 mg/kg), an alpha(2)-adrenergic receptor antagonist, also abolished NMU-induced acid inhibition (P < 0.01). These findings suggest that NMU is critical in the central regulation of gastric acid secretion via CRH.

Neuropeptide Y and lipid increase apolipoprotein AIV gene expression in rat hypothalamus

Apolipoprotein AIV (apo AIV) is a circulating signal released from intestinal cells in response to lipid feeding and contributes to the anorectic effect of a lipid meal. We have demonstrated that apo AIV is also synthesized in the hypothalamus, and that hypothalamic apo AIV gene expression is regulated physiologically. Neuropeptide Y (NPY) is a hypothalamic neuropeptide with broad regulatory actions in the central nervous system. In the present studies, the effects of intracerebroventricular (i.v.t.) administration of NPY and of intraduodenal lipid infusion on hypothalamic apo AIV gene expression were determined using competitive RT-PCR in fasted rats. I.v.t. injection of NPY alone significantly increased apo AIV mRNA levels in the hypothalamus in a dose-dependent manner. Intraduodenal infusion of lipid also stimulated the gene expression of hypothalamic apo AIV, but no further significant increment occurred when i.v.t. injection of NPY was combined with lipid infusion. These results suggest that NPY and lipid may regulate apo AIV gene expression in the rat hypothalamus.

Further evidence for the association between obesity-related traits and the apolipoprotein A-IV gene

OBJECTIVE

To investigate associations and gene-environment interactions of APOA-IV gene polymorphisms with obesity-related phenotypes in a Brazilian population.

METHODS

A total of 391 individuals (171 men and 220 women) were genotyped for Xbal, Thr347Ser and Gln360His polymorphisms by PCR-RFLP methods. Adjusted body mass index (BMI) and waist circumference (WC) were compared among genotypes/haplotypes by unpaired t-test or analysis of variance. Gene-environment interactions were tested by analysis of variance using a general linear model.

RESULTS

Analysis of the APOA-IV gene variants separately showed that X*2 and 347Ser alleles were associated with higher BMI (P=0.02 for both polymorphisms). Haplotype analysis confirmed this association. For these polymorphisms, the effect on BMI appeared to depend on smoking status (test for interaction, P=0.007 and 0.02, respectively), the Thr347Ser variant was associated with a BMI increase in smokers only (P=0.002). At the single-locus level no association was observed between 360His allele and BMI; however, haplotype analyses showed an association of this gene variant and higher BMI. A trend for association with WC (P=0.05) was observed in male carriers of the 360His allele. The effect of this polymorphism also depended on smoking status (test for interaction, P=0.018). Nonsmoker male carriers of the 360His allele had a larger waist circumference than homozygotes for the Gln allele (P=0.003).

CONCLUSION

Our data suggest that the APOA-IV gene polymorphisms investigated are associated with obesity-related traits. The effects of X*2 and 347Ser variants on BMI and the 360His variant on waist circumference depended on smoking status.

Apo A-IV: an update on regulation and physiologic functions

Apolipoprotein (apo) A-IV, first identified 28 years ago as a plasma lipoprotein moiety, is now known to participate in the regulation of various metabolic pathways. It is synthesized primarily in the enterocytes of the small intestine during fat absorption. After entry into the bloodstream, the 46-kDa glycoprotein apo A-IV appears associated with chylomicrons, high-density lipoproteins, and in the lipoprotein-free fraction. It has a role in lipid absorption, transport and metabolism, and may act as a post-prandial satiety signal, an anti-oxidant and a major factor in the prevention of atherosclerosis. After summarizing and discussing these functions for reader's comprehension, the current review focuses on the regulation of apo A-IV by nutrients, biliary components, drugs, hormones and gastrointestinal peptides. The understanding of the involved mechanisms that underline apo A-IV regulation may in the long run allow us to switch on its gene, which may confer multiple beneficial effects, including the protection from atherosclerosis.

The role of apolipoprotein A-IV in the regulation of food intake

Apolipoprotein A-IV (apo A-IV) is a glycoprotein synthesized by the human intestine. In rodents, both the small intestine and liver secrete apo A-IV, but the small intestine is the major organ responsible for the circulating apo A-IV. Intestinal apo A-IV synthesis is markedly stimulated by fat absorption and appears not to be mediated by the uptake or reesterification of fatty acids to form triglycerides. Rather, the formation of chylomicrons acts as a signal for the induction of intestinal apo A-IV synthesis. Intestinal apo A-IV synthesis is also enhanced by a factor from the ileum, probably peptide tyrosine-tyrosine. The inhibition of food intake by apo A-IV is mediated centrally. The stimulation of intestinal synthesis and the secretion of apo A-IV by lipid absorption are rapid; thus, apo A-IV likely plays a role in the short-term regulation of food intake. Other evidence suggests that apo A-IV may also be involved in the long-term regulation of food intake and body weight. Chronic ingestion of a high-fat diet blunts the intestinal apo A-IV response to lipid feeding and may explain why the chronic ingestion of a high-fat diet predisposes both animals and humans to obesity.

Effect of leptin on intestinal apolipoprotein AIV in response to lipid feeding

We determined apolipoprotein AIV (apo AIV) content in intestinal epithelial cells using immunohistochemistry when leptin was administered intravenously. Most of the apo AIV immunoreactivity in the untreated intestine was located in the villous cells as opposed to the crypt cells. Regional distribution of apo AIV immunostaining revealed low apo AIV content in the duodenum and high content in the jejunum that gradually decreases caudally toward the ileum. Intraduodenal infusion of lipid (4 h) significantly increased apo AIV immunoreactivity in the jejunum and ileum. Simultaneous intravenous leptin infusion plus duodenal lipid infusion markedly suppressed apo AIV immunoreactivity. Duodenal lipid infusion increased plasma apo AIV significantly (measured by ELISA), whereas simultaneous leptin infusion attenuated the increase. These findings suggest that leptin may regulate circulating apo AIV by suppressing apo AIV synthesis in the small intestine.

Human apolipoprotein A-IV metabolism within triglyceride-rich lipoproteins and plasma

In order to investigate the metabolism of apo A-IV within TRL and plasma, we assessed TRL and plasma apo A-IV kinetics in 19 and 4 subjects, respectively, consuming an average US diet for a 6-week period. At the end of this diet study, each subject received a primed-constant infusion of deuterated leucine over a 15 h time period with hourly feeding, and blood samples were drawn at 10 time points. TRL was separated by ultracentrifugation. Apo A-IV was isolated by immunoprecipitation and/or SDS-PAGE. Apo A-IV concentrations were determined by immunoelectrophoresis. Stable isotope tracer/tracee ratios were measured by gas chromatography/mass spectrometry, and the data were analyzed by multicompartmental modeling. The mean concentrations of plasma and TRL apo A-IV during the isotope infusion period were 21.0+/-3.2 and 0.66+/-0.25 mg/dl, respectively, and these values were 11.5 and 30.5% higher than those of fasting samples. The mean TRL and plasma apo A-IV residence times (RT) were 1.97+/-0.57 and 2.71+/-0.65 days, and transport rates (TR) were 0.17+/-0.19 and 3.90+/-1.24 mg/kg per day, respectively. There were significant correlations between TRL apo A-IV concentrations and TR (r(2)=0.79, P<0.001), and between TRL apo A-IV pool size and TRL cholesterol levels (r(2)=0.29, P=0.02). Our data indicated that; (1) TRL apo A-IV has a RT of 1.97 days which is similar to that earlier reported for HDL apo A-IV; (2) Apo A-IV recirculates between TRL and other slowly turning over pools; (3) the primary determinant of TRL apo A-IV levels is its TR; and (4) there is no correlation between TRL apo A-IV and apo B48 fractional catabolism in TRL.

Effects of age, gender, and lifestyle factors on plasma apolipoprotein A-IV concentrations

Apolipoprotein (apo) A-IV is a protein component of triglyceride (TG)-rich lipoproteins and high density lipoproteins (HDL). Plasma apo A-IV levels were measured by immunoelectrophoresis and these values were related to other biological variables in 723 middle aged and elderly men and women (more than 90% of them were Caucasian) prior to participation in a lifestyle modification program. Apo A-IV may play an important function in regulating lipid absorption, reverse cholesterol transport, and food intake. The data are consistent with the following concepts: (1) apo A-IV levels are significantly and positively correlated with age (r = 0.159, P < 0.05) in all subjects, with plasma apo A-I levels in both men (r = 0.194, P < 0.001) and women (r = 0.213, P < 0.001), and with apo E (r=0.111, P<0.05) and TG levels (r =0.120, P <0.05) in men; (2) apo A-IV levels are inversely correlated with body mass index (r = 0.170, P <0.05) in women; (3) female subjects on hormone replacement therapy have significantly lower plasma apo A-IV levels (by 4.1%, P < 0.05) than normal controls; (4) diabetic subjects have significantly higher apo A-IV levels (by 21%, P < 0.01) than normal subjects; (5) there is no significant effect of smoking, alcohol intake, and apo A-IV-1/2 genotype on apo A-IV levels. The data indicate that plasma apo A-IV levels are significantly affected by age, diabetes, and hormone replacement therapy.

Cocaine-amphetamine-regulated transcript (CART) acts in the central nervous system to inhibit gastric acid secretion via brain corticotropin-releasing factor system

Recent study has indicated that cocaine-amphetamine-regulated transcript (CART) is an anorectic chemical in the brain. In the present study, we examined the hypothesis that CART may act in the central nervous system to alter gastric function. Food consumption, gastric acid secretion, and gastric emptying were measured after injection of CART into the cerebrospinal fluid in 24-h fasted Sprague Dawley rats. Central injection of CART inhibited food intake, gastric acid secretion, and gastric emptying. In contrast, ip injection of CART failed to inhibit gastric acid secretion and gastric emptying, suggesting that CART acts in the brain to suppress gastric acid secretion and gastric emptying. In the vagotomized animals, centrally administered CART did inhibit pentagastrin-stimulated gastric acid secretion. The CART-induced acid inhibition was also observed in rats treated with indomethacin, a cyclooxygenase inhibitor. In contrast, pretreatment with central administration of a CRF receptor antagonist, alpha-helical CRF9-41, completely blocked the central CART-induced inhibition of gastric acid secretion. All these results suggest that CART acts in the brain to inhibit gastric function via brain CRF system. The vagal pathway and the prostaglandin system are not involved in the acid inhibition.

Afferent signals regulating food intake

Food intake is a regulated system. Afferent signals provide information to the central nervous system, which is the centre for the control of satiety or food seeking. Such signals can begin even before food is ingested through visual, auditory and olfactory stimuli. One of the recent interesting findings is the demonstration that there are selective fatty acid taste receptors on the tongue of rodents. The suppression of food intake by essential fatty acids infused into the stomach and the suppression of electrical signals in taste buds reflect activation of a K rectifier channel (K 1.5). In animals that become fat eating a high-fat diet the suppression of this current by linoleic acid is less than that in animals that are resistant to obesity induced by dietary fat. Inhibition of fatty acid oxidation with either mercaptoacetate (which blocks acetyl-CoA dehydrogenase) or methylpalmoxirate will increase food intake. When animals have a choice of food, mercaptoacetate stimulates the intake of protein and carbohydrate, but not fat. Afferent gut signals also signal satiety. The first of these gut signals to be identified was cholecystokinin (CCK). When CCK acts on CCK-A receptors in the gastrointestinal tract, food intake is suppressed. These signals are transmitted by the vagus nerve to the nucleus tractus solitarius and thence to higher centres including the lateral parabrachial nucleus, amygdala, and other sites. Rats that lack the CCK-A receptor become obese, but transgenic mice lacking CCK-A receptors do not become obese. CCK inhibits food intake in human subjects. Enterostatin, the pentapeptide produced when pancreatic colipase is cleaved in the gut, has been shown to reduce food intake. This peptide differs in its action from CCK by selectively reducing fat intake. Enterostatin reduces hunger ratings in human subjects. Bombesin and its human analogue, gastrin inhibitory peptide (also gastrin-insulin peptide), reduce food intake in obese and lean subjects. Animals lacking bombesin-3 receptor become obese, suggesting that this peptide may also be important. Circulating glucose concentrations show a dip before the onset of most meals in human subjects and rodents. When the glucose dip is prevented, the next meal is delayed. The dip in glucose is preceded by a rise in insulin, and stimulating insulin release will decrease circulating glucose and lead to food intake. Pyruvate and lactate inhibit food intake differently in animals that become obese compared with lean animals. Leptin released from fat cells is an important peripheral signal from fat stores which modulates food intake. Leptin deficiency or leptin receptor defects produce massive obesity. This peptide signals a variety of central mechanisms by acting on receptors in the arcuate nucleus and hypothalamus. Pancreatic hormones including glucagon, amylin and pancreatic polypeptide reduce food intake. Four pituitary peptides also modify food intake. Vasopressin decreases feeding. In contrast, injections of desacetyl melanocyte-stimulating hormone, growth hormone and prolactin are associated with increased food intake. Finally, there are a group of miscellaneous peptides that modulate feeding. beta-Casomorphin, a heptapeptide produced during the hydrolysis of casein, stimulates food intake in experimental animals. In contrast, the other peptides in this group, including calcitonin, apolipoprotein A-IV, the cyclized form of histidyl-proline, several cytokines and thyrotropin-releasing hormone, all decrease food intake. Many of these peptides act on gastrointestinal or hepatic receptors that relay messages to the brain via the afferent vagus nerve. As a group they provide a number of leads for potential drug development.

Human apolipoprotein A-IV reduces gastric acid secretion and diminishes ulcer formation in transgenic mice

We have investigated the involvement of human apolipoprotein A-IV (apoA-IV) in gastric acid secretion and ulcer formation in recently generated apoA-IV transgenic mice. Compared to control littermates, transgenic animals showed a gastric acid secretion decreased by 43-77% whereas only slight variations were observed in the different cell population densities within the gastric mucosa. In addition, no variation in gastrin levels was observed. Transgenics were protected against indomethacin-induced ulcer formation, with lesions diminishing by 45 to 64% compared to controls. These results indicate that endogenous apoA-IV expression can regulate gastric acid secretion and ulcer development.

The role of enterostatin and apolipoprotein AIV on the control of food intake

Procolipase is secreted as a protein consisting of 101 amino acids. In the intestinal lumen, procolipase is activated by trypsin and cleaves to form the active colipase and the pentapeptide from the amino terminus. This pentapeptide is called enterostatin. Pancreatic procolipase synthesis is stimulated by a high-fat diet. A large body of evidence has been gathered in the past decade demonstrating the role of enterostatin in the inhibition of food intake; in particular, fat intake. This aspect of enterostatin will be discussed in this review. Other functions of enterostatin such as the inhibition of insulin secretion, will not. Apolipoprotein AIV is a protein synthesized by the human intestine. Similar to procolipase, the synthesis and secretion of apo AIV are also stimulated by fat absorption. In 1992, Fujimoto et al. first demonstrated that apo AIV is a satiety signal secreted by the small intestine following the ingestion of a lipid meal. Subsequently, this initial observation was followed by a number of studies supporting apo AIV's role in the inhibition of food intake. This review will discuss the role of apo AIV in inhibiting food intake.

The role of apolipoprotein A-IV in food intake regulation

Apolipoprotein (apo) A-IV is a glycoprotein synthesized by the human intestine. In rodents, both the small intestine and the liver secrete apo A-IV; the small intestine, however, is by far the major organ responsible for the circulating apo A-IV. Intestinal apo A-IV synthesis is markedly stimulated by fat absorption and appears not to be mediated by the uptake or reesterification of fatty acids to form triglycerides. Rather, it is the formation of chylomicrons that acts as a signal for the induction of intestinal apo A-IV synthesis. Intestinal apo A-IV synthesis is also enhanced by a factor from the ileum and that factor is probably peptide tyrosine-tyrosine (PYY). The inhibition of food intake by apo A-IV is probably mediated centrally. The stimulation of intestinal synthesis and secretion of apo A-IV by lipid absorption are rapid; thus, apo A-IV likely plays a role in the short-term regulation of food intake. Other evidence suggests that apo A-IV may also be involved in the long-term regulation of food intake and body weight. Chronic ingestion of a high fat diet blunts the intestinal apo A-IV response to lipid feeding and may explain why the chronic ingestion of a high fat diet predisposes both animals and humans to obesity.

Stimulation of gastric acid secretion by centrally administered orexin-A in conscious rats

Orexins are novel neuropeptides that are localized in neurons within the lateral hypothalamus and regulate feeding behavior. The lateral hypothalamus also plays an important role in the central regulation of gut function. We therefore hypothesized that orexins might be involved in the central control of gastric acid secretion. To address this question, we examined the effect of central injection of orexins on gastric acid secretion in rats. Intracisternal injection of synthetic orexin-A but not orexin-B dose-dependently stimulated acid secretion while intraperitoneal administration of orexin-A failed to stimulate acid secretion. Vagotomy or atropine abolished the action by central orexin-A. These data suggest for the first time that orexin-A may act in the brain to stimulate gastric acid secretion by modulating the vagal system. Considering its stimulatory action on feeding, we hypothesize here that orexin-A is a candidate mediator of cephalic phase gastric secretion.

Helicobacter pylori lipopolysaccharide inhibits acid secretion in pylorus-ligated conscious rats

To examine the effect of Helicobacter pylori lipopolysaccharide on gastric secretion, the present study was carried out using pylorus ligated conscious rats. Intraperitoneal administration of Helicobacter pylori lipopolysaccharide significantly inhibited gastric acid secretion (4 hr) in a dose-dependent manner (0.033-1.0 mg/rat). The Helicobacter pylori lipopolysaccharide (1 mg/rat)-induced acid inhibition was still observed 8 hr after injection. Gastric acid secretion (4 hr) was compared in the rats that had received intraperitoneal administration of 1 mg/rat dose of Helicobacter pylori lipopolysaccharide or saline alone 24 hr before. There was no significant difference in gastric acid secretion between the saline- and H. pylori lipopolysaccharide-treated rats. These results suggest for the first time that H. pylori lipopolysaccharide may inhibit acid production, and this acid inhibition may be long-lasting. It is also demonstrated that this anti-secretory action of H. pylori lipopolysaccharide has a reversible effect on gastric secretion. All these results suggest that H. pylori lipopolysaccharide might be involved in the low acid secretory function seen in patients with acute H. pylori infection.

Intraduodenal lipid does not inhibit acid secretion in OLETF rats not expressing CCK-A receptor gene

Gastric acid secretion in response to pylorus-ligation and duodenal fat feeding in Otsuka Long-Evans Tokushima Fatty (OLETF) rats without cholecystokinin-A receptor was examined. Acidity of gastric juice obtained from pylorus-ligated OLETF rats was significantly lower than that of control LETO rats. Gastric acid secretion in response to bethanechol, pentagastrin, or atropine was maintained in both OLETF and LETO rats. Intraduodenal lipid injection strongly inhibited gastric acid secretion in control LETO rats. In contrast, administration of lipid into the duodenum failed to inhibit acid secretion in OLETF rats. These results suggest that basal gastric acid secretion may be impaired in OLETF rats and that the cholecystokinin-A receptor is involved in lipid-induced acid inhibition.