Effects of pituitary adenylate cyclase activating polypeptide on small intestinal INT 407 cells

Acrylamide-Induced Changes in the Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) Immunoreactivity in Small Intestinal Intramural Neurons in Pigs

BACKGROUND

A particularly pressing problem is determining consumer-safe doses of potentially health- and life-threatening substances, such as acrylamide. The aim of the study was to determine how acrylamide affects the pituitary adenylate cyclase-activating polypeptide (PACAP)-immunoreactive intramural neurons in the small intestine of sexually immature gilts.

METHODS

The study was conducted on 15 sexually immature Danish gilts receiving for 28 days empty gelatin capsules or acrylamide in low (0.5 µg/kg of body weight (b.w.)/day) and high (5 µg/kg b.w./day) doses. After euthanasia, intestinal sections were stained using the double immunofluorescence staining procedure.

RESULTS

Studies have shown that oral administration of acrylamide in both doses induced a response of intramural neurons expressed as an increase in the population of PACAP-immunoreactive neurons in the small intestine. In the duodenum, only in the myenteric plexus (MP) was an increase in the number of PACAP-immunoreactive (IR) neurons observed in both experimental groups, while in the outer submucous plexus (OSP) and inner submucous plexus (ISP), an increase was noted only in the high-dose group. In the jejunum, both doses of acrylamide led to an increase in the population of PACAP-IR neurons in each enteric plexus (MP, OSP, ISP), while in the ileum, only supplementation with the higher dose of acrylamide increased the number of PACAP-IR enteric neurons in the MP, OSP, and ISP.

CONCLUSIONS

The obtained results suggest the participation of PACAP in acrylamide-induced plasticity of enteric neurons, which may be an important line of defence from the harmful action of acrylamide on the small intestines.

Effects of Pituitary Adenylate Cyclase Activating Polypeptide on Cell Death

Pituitary adenylate cyclase activating polypeptide (PACAP) was first isolated as a hypothalamic peptide based on its efficacy to increase adenylate cyclase (AC) activity. It has a widespread distribution throughout the body including the nervous system and peripheral organs, where PACAP exerts protective effects both in vivo and in vitro through its anti-apoptotic, anti-inflammatory, and antioxidant functions. The aim of the present paper was to review the currently available literature regarding the effects of PACAP on cell death in vitro in neural and non-neural cells. Among others, its effect on apoptosis can be detected in cerebellar granule cells against different toxic stimuli. Different neural cell types from the cerebral cortex are also prevented from cell death. PACAP also shows effects on cell death in cells belonging to the peripheral nervous system and protects both neural and non-neural cells of sensory organs. In addition, cell survival-promoting effect can be observed in different peripheral organ systems including cardiovascular, immune, respiratory, gastrointestinal, urinary, and reproductive systems. The studies summarized here indicate its noteworthy effect on cell death in different in vitro models, suggesting PACAP’s potential therapeutic usage in several pathological conditions.

Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP) in Physiological and Pathological Processes within the Gastrointestinal Tract: A Review

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide widely distributed in the central nervous system (CNS) and many peripheral organs, such as the digestive tract, endocrine, reproductive and respiratory systems, where it plays different regulatory functions and exerts a cytoprotective effect. The multifarious physiological effects of PACAP are mediated through binding to different G protein-coupled receptors, including PAC1 (PAC1-R), VPAC1 (VPAC1-R) and VPAC2 (VPAC2-R) receptors. In the gastrointestinal (GI) tract, PACAP plays an important regulatory function. PACAP stimulates the secretion of digestive juices and hormone release, regulates smooth muscle contraction, local blood flow, cell migration and proliferation. Additionally, there are many reports confirming the involvement of PACAP in pathological processes within the GI tract, including inflammatory states, neuronal injury, diabetes, intoxication and neoplastic processes. The purpose of this review is to summarize the distribution and pleiotropic action of PACAP in the control of GI tract function and its cytoprotective effect in the course of GI tract disorders.

Diabetes Affects the Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP)-Like Immunoreactive Enteric Neurons in the Porcine Digestive Tract

Diabetic gastroenteropathy is a common complication, which develops in patients with long-term diabetes. The pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide known for its cytoprotective properties and plays an important role in neuronal development, neuromodulation and neuroprotection. The present study was designed to elucidate, for the first time, the impact of prolonged hyperglycaemia conditions on a population of PACAP-like immunoreactive neurons in selected parts of the porcine gastrointestinal tract. The experiment was conducted on 10 juvenile female pigs assigned to two experimental groups: The DM group (pigs with streptozocin-induced diabetes) and the C group (control pigs). Diabetes conditions were induced by a single intravenous injection of streptozocin. Six weeks after the induction of diabetes, all animals were euthanised and further collected, and fixed fragments of the stomach, duodenum, jejunum, ileum and descending colon were processed using the routine double-labelling immunofluorescence technique. Streptozotocin-induced hyperglycaemia caused a significant increase in the population of PACAP-containing enteric neurons in the porcine stomach, small intestines and descending colon. The recorded changes may result from the direct toxic effect of hyperglycaemia on the ENS neurons, oxidative stress or inflammatory conditions accompanying hyperglycaemia and suggest that PACAP is involved in regulatory processes of the GIT function in the course of diabetes.

Protective Effects of PACAP in Peripheral Organs

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide widely distributed in the nervous system, where it exerts strong neuroprotective effects. PACAP is also expressed in peripheral organs but its peripheral protective effects have not been summarized so far. Therefore, the aim of the present paper is to review the existing literature regarding the cytoprotective effects of PACAP in non-neuronal cell types, peripheral tissues, and organs. Among others, PACAP has widespread expression in the digestive system, where it shows protective effects in various intestinal pathologies, such as duodenal ulcer, small bowel ischemia, and intestinal inflammation. PACAP is present in both the exocrine and endocrine pancreas as well as liver where it reduces inflammation and steatosis by interfering with hepatic pathology related to obesity. It is found in several exocrine glands and also in urinary organs, where, with its protective effects being mainly published regarding renal pathologies, PACAP is protective in numerous conditions. PACAP displays anti-inflammatory effects in upper and lower airways of the respiratory system. In the skin, it is involved in the development of inflammatory pathology such as psoriasis and also has anti-allergic effects in a model of contact dermatitis. In the non-neuronal part of the visual system, PACAP showed protective effects in pathological conditions of the cornea and retinal pigment epithelial cells. The positive role of PACAP has been demonstrated on the formation and healing processes of cartilage and bone where it also prevents osteoarthritis and rheumatoid arthritis development. The protective role of PACAP was also demonstrated in the cardiovascular system in different pathological processes including hyperglycaemia-induced endothelial dysfunction and age-related vascular changes. In the heart, PACAP protects against ischemia, oxidative stress, and cardiomyopathies. PACAP is also involved in the protection against the development of pre-senile systemic amyloidosis, which is presented in various peripheral organs in PACAP-deficient mice. The studies summarized here provide strong evidence for the cytoprotective effects of the peptide. The survival-promoting effects of PACAP depend on a number of factors which are also shortly discussed in the present review.

Altered Notch Signaling in Developing Molar Teeth of Pituitary Adenylate Cyclase-Activating Polypeptide (PACAP)-Deficient Mice

Pituitary adenylate cyclase-activating polypeptide (PACAP) is a neuropeptide with neuroprotective and neurotrophic effects. This suggests its influence on the development of teeth, which are, similarly to the nervous system, ectoderm and neural crest derivatives. Our earlier studies have shown morphological differences between wild-type (WT) and PACAP-deficient mice, with upregulated sonic hedgehog (SHH) signaling in the lack of PACAP. Notch signaling is a key element of proper tooth development by regulating apoptosis and cell proliferation. In this study, our main goal was to evaluate the possible effects of PACAP on Notch signaling pathway. Immunohistochemical staining was performed of Notch receptors (Notch1, 2, 3, 4), their ligands [delta-like protein (DLL)1, 3, 4, Jagged1, 2], and intracellular target molecules [CSL (CBF1 humans/Su (H) Drosophila/LAG1 Caenorhabditis elegans transcription factor); TACE (TNF-α converting enzyme), NUMB] in molar teeth of 5-day-old WT, and homozygous and heterozygous PACAP-deficient mice. We measured immunopositivity in the enamel-producing ameloblasts and dentin-producing odontoblasts. Notch2 receptor and DLL1 expression were elevated in ameloblasts of PACAP-deficient mice compared to those in WT ones. The expression of CSL showed similar results both in the ameloblasts and odontoblasts. Jagged1 ligand expression was elevated in the odontoblasts of homozygous PACAP-deficient mice compared to WT mice. Other Notch pathway elements did not show significant differences between the genotype groups. The lack of PACAP leads to upregulation of Notch pathway elements in the odontoblast and ameloblast cells. The underlying molecular mechanisms are yet to be elucidated; however, we propose SHH-dependent and independent processes. We hypothesize that this compensatory upregulation of Notch signaling by the lack of PACAP could represent a salvage pathway in PACAP-deficient animals.

Presence and Effects of Pituitary Adenylate Cyclase Activating Polypeptide Under Physiological and Pathological Conditions in the Stomach

Pituitary adenylate cyclase activating polypeptide (PACAP) is a multifunctional neuropeptide with widespread occurrence throughout the body including the gastrointestinal system. In the small and large intestine, effects of PACAP on cell proliferation, secretion, motility, gut immunology and blood flow, as well as its importance in bowel inflammatory reactions and cancer development have been shown and reviewed earlier. However, no current review is available on the actions of PACAP in the stomach in spite of numerous data published on the gastric presence and actions of the peptide. Therefore, the aim of the present review is to summarize currently available data on the distribution and effects of PACAP in the stomach. We review data on the localization of PACAP and its receptors in the stomach wall of various mammalian and non-mammalian species, we then give an overview on PACAP's effects on secretion of gastric acid and various hormones. Effects on cell proliferation, differentiation, blood flow and gastric motility are also reviewed. Finally, we outline PACAP's involvement and changes in various human pathological conditions.