Central nervous system action of bombesin to influence gastric secretion and ulceration

Stable Gastric Pentadecapeptide BPC 157, Robert's Stomach Cytoprotection/Adaptive Cytoprotection/Organoprotection, and Selye's Stress Coping Response: Progress, Achievements, and the Future

We reviewed again the significance of the stable gastric pentadecapeptide BPC 157 as a likely mediator of Robert's stomach cytoprotection/adaptive cytoprotection and organoprotection and as novel mediator of Selye's stress coping response to reestablish homeostasis. Specific points of BPC 157 therapy and the original concept of Robert's cytoprotection/adaptive cytoprotection/organoprotection are discussed, including the beneficial effects of BPC 157. First, BPC 157 protects stomach cells and maintains gastric integrity against various noxious agents (Robert's killing cell by contact) and is continuously present in the gastric mucosa and gastric juice. Additionally, BPC 157 protects against the adverse effects of alcohol and nonsteroidal anti-inflammatory drugs on the gastric epithelium and other epithelia, that is, skin, liver, pancreas, heart (organoprotection), and brain, thereby suggesting its use in wound healing. Additionally, BPC 157 counteracts gastric endothelial injury that precedes and induces damage to the gastric epithelium and generalizes "gastric endothelial protection" to protection of the endothelium of other vessels (thrombosis, prolonged bleeding, and thrombocytopenia). BPC 157 also has an effect on blood vessels, resulting in vessel recruitment that circumvents vessel occlusion and the development of additional shunting and rapid bypass loops to rapidly reestablish the integrity of blood flow (ischemic/reperfusion colitis, duodenal lesions, cecal perforation, and inferior vena caval occlusion). Lastly, BPC 157 counteracts tumor cachexia, muscle wasting, and increases in pro-inflammatory/procachectic cytokines, such as interleukin-6 and tumor necrosis factor-α, and significantly corrects deranged muscle proliferation and myogenesis through changes in the expression of FoxO3a, p-AKT, p-mTOR, and p-GSK-3β (mitigating cancer cachexia).

Brain-gut Axis and Pentadecapeptide BPC 157: Theoretical and Practical Implications

BACKGROUND

Brain-gut interaction involves, among others, peptidergic growth factors which are native in GI tract and have strong antiulcer potency and thus could from periphery beneficially affect CNS-disorders. We focused on the stable gastric pentadecapeptide BPC 157, an antiulcer peptidergic agent, safe in inflammatory bowel disease trials and now in multiple sclerosis trial, native and stable in human gastric juice.

METHODS

Review of our research on BPC 157 in terms of brain-gut axis.

RESULTS

BPC 157 may serve as a novel mediator of Robert's cytoprotection, involved in maintaining of GI mucosa integrity, with no toxic effect. BPC 157 was successful in the therapy of GI tract, periodontitis, liver and pancreas lesions, and in the healing of various tissues and wounds. Stimulated Egr-1 gene, NAB2, FAK-paxillin and JAK-2 pathways are hitherto implicated. Initially corresponding beneficial central influence was seen when BPC 157 was given peripherally and a serotonin release in particular brain areas, mostly nigrostriatal, was changed. BPC 157 modulates serotonergic and dopaminergic systems, beneficially affects various behavioral disturbances that otherwise appeared due to specifically (over)stimulated/damaged neurotransmitters systems. Besides, BPC 157 has neuroprotective effects: protects somatosensory neurons; peripheral nerve regeneration appearent after transection; after traumatic brain injury counteracts the otherwise progressing course, in rat spinal cord compression with tail paralysis, axonal and neuronal necrosis, demyelination, cyst formation and rescues tail function in both short-terms and long-terms; after NSAIDs or insulin overdose or cuprizone encephalopathies were attenuated along with GI, liver and vascular injuries.

CONCLUSION

BPC 157, a gastric peptide, may serve as remedy in various CNS-disorders.

Bombesin and the brain-gut axis

Bombesin is the first peptide shown to act in the brain to influence gastric function and the most potent peptide to inhibit acid secretion when injected into the cerebrospinal fluid (CSF) in rats and dogs. Bombesin responsive sites include specific hypothalamic nuclei (paraventricular nucleus, preoptic area and anterior hypothalamus), the dorsal vagal complex as well as spinal sites at T9-T10. The antisecretory effect of central bombesin encompasses a variety of endocrine/paracrine (gastrin, histamine) or neuronal stimulants. Bombesin into the CSF induces an integrated gastric response (increase in bicarbonate, and mucus, inhibition of acid, pepsin, vagally mediated contractions) enhancing the resistance of the mucosa to injury through autonomic pathways. The physiological significance of central action of bombesin on gastric function is still to be unraveled.

Synthesis of nitric oxide in the dorsal motor nucleus of the vagus mediates the inhibition of gastric acid secretion by central bombesin

1. Central administration of bombesin inhibits gastric acid production independently of the centrally or peripherally-acting stimuli employed. This study evaluates the role and location of the cerebral nitric oxide (NO) implicated in the inhibitory effect of central bombesin on in vivo rat gastric acid secretion, as induced by distension with 15 cm H2O, insulin (0.75 u.i. kg-1 i.p.) TRH (1.2 microg kg-1, i.c.) or pentagastrin (100 microg kg-1, i.p.). 2. The acid-inhibitory effect of i.c. bombesin (40 ng kg-1) was prevented by prior administration of L-NAME (80 microg kg-1) in the dorsal motor nucleus of the vagus (DMN). This dose of L-NAME when administered into the nucleus of the tractus solitarious (NTS) did not influence the effects of bombesin. Administration of L-arginine (400 microg kg-1) into the DMN restored the acid-inhibitory effect of i.c. bombesin in animals treated with L-NAME. 3. Microinjection of bombesin (12 ng kg-1) into the paraventricular nucleus of the hypothalamus (PvN) inhibits acid secretion stimulated by pentagastrin. This inhibitory effect was prevented by a previous injection of L-NAME (80 microg kg-1) into the DMN. 4. The release of NO in the DMN following i.c. administration of bombesin was confirmed by in vivo electrochemical detection. 5. Administration by microdialysis in the DMN of the NO-donor SNAP (25 mM in 1.5 microl min-1) into the DMN inhibits pentagastrin-stimulated gastric acid secretion. 6. The present study suggests that nNOS-containing neurons in the DMN have an inhibitory role in the control of gastric acid responses.

Ultrastructure of bombesin-like immunoreactive nerve terminals in the nucleus of the solitary tract and the dorsal motor nucleus

Bombesin (gastrin-releasing peptide 14-27) inhibits gastric function and feeding when microinjected into the nucleus of the solitary tract (NTS)/dorsal motor nucleus of the vagus (DMV) complex. We performed a preembedding immunoelectron microscopic study in rats to describe the bombesin containing nerve terminals and to characterize their postsynaptic structures. 228 bombesin-L1 nerve terminals which made synaptic contacts in the NTS/DMV complex were studied. Labeling was heaviest over dense core vesicles and lighter over small clear vesicles. The dense core vesicles were typically located along the plasmalemma away from the synaptic face, a finding that is typical of neuropeptide containing nerve terminals. The postsynaptic structures were most often medium sized dendrites (56%) and small sized dendrites (27%), with similar percentages in the NTS and DMV. In the DMV, synapses on cell bodies (8%) were more frequent than in the NTS (1%). In the NTS, synapses on dendritic spines (10%) were more frequent than in the DMV (4%). Only a single axo-axonal contact was identified. These findings add to the increasing body of evidence that bombesin is a neurotransmitter/neuromodulator in the NTS/DMV complex. Bombesin rarely makes presynaptic (axo-axonal) contacts that might inhibit the release of excitatory neurotransmitters, but rather makes postsynaptic contacts potentially effecting vagal motoneurons.

Use of animal models in peptic ulcer disease

Considerable progress has been made in the understanding of the formation of gastric erosions by the use of animals. The role of gastric acid secretion in their pathogenesis has been clarified. Gastric erosions are associated with the presence of acid in the stomach and slow gastric contractions. With several different experimental procedures, the animal's body temperature falls; preventing the fall averts erosions. A fall in body temperature or exposure to cold are associated with the secretion of thyrotropin-releasing hormone (TRH), and both increased and decreased concentration of corticotropin-releasing factor (CRH) in discrete regions of rat brains. Thyrotropin-releasing hormone when injected into specific sites in the brain produces gastric erosions and increases acid secretion and slow contractions, whereas CRH has the opposite effects. One of the major sites of interaction of the two peptides is in the dorsal motor complex of the vagus nerve. Thyrotropin-releasing hormone increases serotonin (5-HT) secretion into the stomach. Serotonin counter-regulates acid secretion and slow contractions. Many other peptides injected into discrete brain sites stimulate or inhibit gastric acid secretion.

Distribution of bombesin-like immunoreactivity in the nucleus of the solitary tract and dorsal motor nucleus of the rat and human: colocalization with tyrosine hydroxylase

Bombesin is a peptide neurotransmitter/neuromodulator with important autonomic and behavioral effects that are mediated, at least in part, by bombesin-containing neurons and nerve terminals in the nucleus of the solitary tract (NTS) and the dorsal motor nucleus of the vagus (DMV). The distribution of bombesin-like immunoreactive nerve terminals/fibers and cell bodies in relation to a viscerotopically relevant subnuclear map of this region was studied by using an immunoperoxidase technique. In the rat, bombesin fiber/terminal staining was heavy in an area that included the medial subnucleus of the NTS and the DMV over their full rostral-caudal extent. Distinctly void of staining were the gelatinous, central, and rostral commissural subnuclei and the periventricular area of the NTS, regions to which gastric, esophageal, cecal, and colonic primary afferents preferentially project. The caudal commissural and dorsal subnuclei had light bombesin fiber/terminal staining, as did the intermediate, interstitial, ventral, and ventrolateral subnuclei. With colchicine pretreatment, numerous cell bodies were stained in the medial and dorsal subnuclei, with fewer neurons in the caudal commissural, intermediate, interstitial, ventral, and ventrolateral subnuclei. Bombesin-like immunoreactive neurons were found in numerous other areas of the brain, including the ventrolateral medulla, the parabrachial nucleus, and the medial geniculate body. In the human NTS/DMV complex, the distribution of bombesin fiber/terminal staining was very similar to the rat. In addition, occasional bombesin-like immunoreactive neurons were labeled in a number of subnuclei, with clusters of neurons labeled in the dorsal and ventrolateral subnuclei. Double immunofluorescence studies in rat demonstrated that bombesin colocalizes with tyrosine hydroxylase in neurons in the dorsal subnucleus of the NTS. Bombesin does not colocalize with tyrosine hydroxylase in any other location in the brain. In conclusion, the distribution of bombesin in the NTS adheres to a viscerotopically relevant map. This is the anatomical substrate for the effects of bombesin on gastrointestinal function and satiety and its likely role in concluding a meal. The anatomic similarities between human and rat suggest that bombesin has similar functions in the visceral neuraxis of these two species. Bombesin coexists with catecholamines in neurons in the dorsal subnucleus, which likely mediate, in part, the cardiovascular effects of bombesin.

Somatostatin antibody does not influence bombesin-induced inhibition of gastric acid secretion in rats

The influence of peripheral somatostatin immunoneutralization on intravenous (i.v.) and intracerebroventricular (ICV) bombesin-induced inhibition of gastric acid secretion (GAS) was investigated with the somatostatin monoclonal antibody, CURE.S6, in rats. The somatostatin antibody, injected i.v. in conscious rats with a chronic gastric fistula and i.v. catheter, did not modify basal GAS, whereas in urethane-anesthetized rats the basal GAS was increased by 150%. In conscious rats, somatostatin (15 micrograms/kg/h, i.v.) inhibited basal GAS by 50% after injection of control antibody but not after pretreatment with the somatostatin antibody. With pretreatment with a control antibody, bombesin (10 micrograms/kg/h, i.v.) inhibited basal GAS by 60% in conscious rats and by 50% the acid response to pentagastrin infusion in urethane-anesthetized rats. Bombesin injected ICV (3 and 10 ng/10 microliters/rat) inhibited basal GAS by 50% and 70%, respectively, in conscious rats pretreated with a control antibody. The somatostatin antibody injected i.v. before i.v. or ICV injection of bombesin did not influence bombesin-induced inhibition of GAS in conscious or anesthetized rats. These results show that peripheral somatostatin does not play a major role in the inhibition of gastric acid secretion induced either by ICV or i.v. administration of bombesin or basal acid secretion in conscious rats.

Local and commissural neuropeptide-containing projections of the nucleus of the solitary tract to the dorsal vagal complex in the pigeon

The neuropeptide content of neurons of the nucleus of the solitary tract (NTS), which have local and commissural projections to the dorsal motor nucleus of the vagus (DMNX) and to NTS, were demonstrated in the pigeon (Columba livia) by using a combined fluorescein-bead retrograde-transport-immunofluorescence technique. The specific peptides studied were bombesin, cholecystokinin, enkephalin, galanin, neuropeptide Y, neurotensin, and substance P. Perikarya immunoreactive for bombesin were located in medial tier subnuclei of NTS and the caudal NTS. Most galanin- and substance P-immunoreactive cells were found in subnucleus medialis ventralis. Cells immunoreactive for neuropeptide Y were found in the medial tier of NTS and in the lateral tier, especially in subnucleus lateralis dorsalis intermedius. The majority of enkephalin- and neurotensin-immunoreactive cells were found centrally in subnuclei medialis dorsalis and medialis intermedius. Cells immunoreactive for cholecystokinin were located in subnuclei lateralis dorsalis pars anterior, medialis superficialis, and the caudal NTS. Based on the presence of retrogradely labeled cells, numerous neurons of the medial tier of NTS, but extremely few lateral tier NTS neurons, had projections to the ipsilateral and contralateral DMNX and NTS. The number of retrogradely labeled NTS cells was always greater ipsilaterally than contralaterally. The percentages of peptide-immunoreactive NTS cells that projected to the ipsilateral and contralateral DMNX were in the ranges of 29-61% and 10-48%, respectively. The percentages of peptide-immunoreactive NTS cells that projected to the contralateral NTS ranged from 13 to 60%. Peptide-immunoreactive NTS cells that have local and commissural projections to DMNX and NTS may act as interneurons in vagovagal reflex pathways and in the integration of visceral sensory and forebrain input to NTS and DMNX.

Bombesin acts in the brain to decrease gastric vagal efferent discharge in rats

The central nervous system action of bombesin to influence basal gastric vagal efferent discharge (GVED) was investigated in urethane-anesthetized rats. Bombesin (62, 620, and 6200 pmol) injected intracisternally (IC) decreased GVED to 78 +/- 10%, 50 +/- 4%, and 43 +/- 3% of preinjection levels, respectively. Bombesin (620 pmol) injected IV also reduced GVED to 36 +/- 6%. Pretreatment with bombesin monoclonal antibody 2A11 completely prevented the decrease in GVED induced by bombesin (620 pmol) given IV but not IC. These data indicate that both IC and IV injections of bombesin decrease basal GVED, and that the inhibitory effect of IC injection represents a central nervous system-mediated action.

N-acetyl-GRP(20-26)-O-CH3 reverses intracisternal bombesin-induced inhibition of gastric acid secretion in rats

Intracisternal injection of 19 pmoles of bombesin in light-ether-anesthetized rats, five minutes after intracisternal vehicle, produced a 75% and 63% inhibition in gastric acid output and concentration, respectively, in 2-hour pylorus-ligated rats. Pretreatment of rats with the characterized peripheral bombesin antagonist N-acetyl-GRP(20-26)-O-CH3 (1 nmole) reversed the inhibitory effect of bombesin on gastric acid output and concentration. In contrast, the related bombesin antagonist N-acetyl-GRP-O-CH2-CH3 (1 nmole) was ineffective in this system. In urethane-anesthetized, acute gastric fistula rats infused with pentagastrin, intracisternal N-acetyl-GRP(20-26)-O-CH3 protected against the inhibition in gastric acid output produced by intracisternal bombesin (19 pmoles). Thus the recently characterized peripheral bombesin antagonist N-acetyl-GRP(20-26)-O-CH3 also appears to be effective in antagonizing central bombesin-induced inhibition in gastric acid secretion in two models. This represents a first report of a synthetic bombesin antagonist effective in reversing central bombesin-induced effects on gastric function.

Medullary sites of action of the TRH analogue, RX 77368, for stimulation of gastric acid secretion in the rat

Brain and spinal sites of action of the stable thyrotropin-releasing hormone (TRH) analogue, RX 77368 [pGlu-His-(3,3'-dimethyl)-Pro-NH2], for stimulation of gastric acid secretion have been investigated in urethane-anesthetized rats with gastric fistula. RX 77368 microinjected at a 7.7-pmol dose into the dorsal vagal complex or nucleus ambiguus stimulated gastric acid secretion to 62.2 +/- 15.9 and 45.3 +/- 14.3 mumol/h, respectively, whereas in the vehicle-treated group acid secretion was 0.5 +/- 1.0 mumol/h. A 10-fold higher dose of RX 77368 was inefficient when microinjected into the medial septum, central amygdala, or lateral hypothalamus. The gastric secretory response to microinjection of RX 77368 into the nucleus ambiguus was dose related (0.7-77 pmol), long-lasting (greater than 90 min), and blocked by vagotomy. TRH (144 pmol) injected into the nucleus ambiguus also stimulated gastric acid secretion but was less potent than the stable TRH analogue, whereas the unrelated peptide, oxytocin, was inactive. Intrathecal injection of RX 77368 at doses up to 2500 pmol did not modify gastric acid secretion. These results demonstrate that the dorsal vagal complex and nucleus ambiguus are TRH sites of action for stimulation of gastric acid secretion through vagal dependent pathways. These findings, added to the high concentrations of TRH-like immunoreactivity and receptors present in these nuclei, suggest a possible role of medullary TRH in the vagal regulation of gastric acid secretion.