Pituitary adenylate cyclase activating-peptide and its receptor antagonists in development of acute pancreatitis in rats

Pituitary Adenylate Cyclase-Activating Polypeptide: 30 Years in Research Spotlight and 600 Million Years in Service

Emerging from the depths of evolution, pituitary adenylate cyclase-activating polypeptide (PACAP) and its receptors (i.e., PAC1, VPAC1, VPAC2) are present in multicellular organisms from Tunicates to humans and govern a remarkable number of physiological processes. Consequently, the clinical relevance of PACAP systems spans a multifaceted palette that includes more than 40 disorders. We aimed to present the versatility of PACAP1-38 actions with a focus on three aspects: (1) when PACAP1-38 could be a cause of a malfunction, (2) when PACAP1-38 could be the cure for a malfunction, and (3) when PACAP1-38 could either improve or impair biology. PACAP1-38 is implicated in the pathophysiology of migraine and post-traumatic stress disorder whereas an outstanding protective potential has been established in ischemia and in Alzheimer’s disease. Lastly, PACAP receptors could mediate opposing effects both in cancers and in inflammation. In the light of the above, the duration and concentrations of PACAP agents must be carefully set at any application to avoid unwanted consequences. An enormous amount of data accumulated since its discovery (1989) and the first clinical trials are dated in 2017. Thus in the field of PACAP research: “this is not the end, not even the beginning of the end, but maybe the end of the beginning.”

Comparison of the effects of PACAP-38 and its analog, acetyl-[Ala15, Ala20] PACAP-38-propylamide, on spatial memory, post-learning BDNF expression and oxidative stress in rat

We compared the effects of single intraveinous injection of pituitary adenylate cyclase-activating polypeptide-38 (P38) to those of its analog, acetyl-[Ala¹⁵, Ala²⁰]PACAP-38-propylamide (P38-alg) on spatial memory in the Morris water maze (MWM) using a weak massed-learning procedure, post-training brain derived neurotrophic factor (BDNF) and post-training oxidative stress biomarker assays in male Wistar rats. Acquisition of the MWM task following P38 (30 μg/kg) and P38-alg (30 μg/kg) treatments was similar to control group (Saline: 0.9% NaCl) and there was no interaction between treatments and performance. However, in the probe test, P38-treated group showed a specific interest for the target quadrant whereas the two other groups exhibited less focused place searching behavior. Moreover, P38 had an anxiogenic effect as measured by the distribution of swimming at the periphery of the pool. The swimming test resulted in a decrease in BDNF contents in the hippocampus. P38 but not P38-alg treatment restored BDNF expression. In terms of oxidative stress, both P38 and P38-alg treatments had antioxidative effects. The activity of antioxidative enzymes in the neocortex was increased. However only P38 reduced the levels of carbonylated proteins (CP). These data show that P38 and P38-alg have different behavioral and neurobiological effects. Thus, P38-alg and other analogs with specific functional profiles, inducing beneficial central effects (e.g. neuroprotection) while minimizing undesired peripheral effects may be useful for potential therapeutical use.

Buyang Huanwu decoction increases the expression of glutamate transporter-1 and glutamate synthetase in association with PACAP-38 following focal ischemia

The neuroprotective role of Buyang Huanwu decoction (BYHWD) in focal ischemia is associated with decreasing glutamate concentration. However, the mechanisms are not fully understood. The present study aimed to explore whether glutamate transporter-1 (GLT-1) and glutamine synthetase (GS) participated in the decreased level of glutamate and whether pituitary adenylate cyclase-activating polypeptide-38 (PACAP-38) was involved in this process. BYHWD was found to significantly upregulate the expression of GLT-1 and GS in the hippocampal CA1 area compared to the ischemia group, with the difference on day 3 being most significant. BYHWD increased the level of PACAP-38, and PACAP-(6-38) (PACAP receptor antagonist) significantly attenuated the effect of BYHWD on GLT-1 and GS, suggesting that PACAP-38 was involved in the upregulation of GLT-1 and GS induced by BYHWD. In addition, as GLT-1 and GS are mainly located in astrocytes, the changes of astrocytes were detected by glial fibrillary acidic protein (GFAP; an astrocytic marker) immunostaining. The results showed that BYHWD inhibited the expression of GFAP compared with the ischemia group, however, co-administration with PACAP-(6-38), which inhibited the effect of BYHWD on GLT-1 and GS in astrocytes, attenuated this effect, indicating that astrocytes participated in the protective role of BYHWD following focal ischemia. These results provided the evidence for the first time that not only neurons but also astrocytes contribute to the protective role of BYHWD, which opposes previous studies and may be a starting point for traditional medicine.

Cerulein-induced acute pancreatitis in PACAP knockout mice

In our previous study, we reported that cerulein-induced acute pancreatitis is aggravated in pancreatic β-cell-specific pituitary adenylate cyclase-activating polypeptide (PACAP) transgenic mice, showing that an increase in pancreatic PACAP is a risk factor for progression of acute pancreatitis. Accordingly, in this study, we examined the progression of cerulein-induced acute pancreatitis in PACAP knockout (KO) mice. Unexpectedly, after cerulein, about 60% of the KO mice showed severe hypothermia below 30°C by 12 h and most of them died within 72 h. In contrast, the remaining KO and wild-type mice showed normothermia with no mortality. Thus, KO mice could be classified into two groups as hypothermic (HT-KO) and normothermic (NT-KO) to cerulein. Only HT-KO mice subsequently showed severe mortality, although both HT-KO and NT-KO mice exhibited similar susceptibility of lungs to cerulein toxicity, comparable to that in wild-type mice. Regarding pancreatitis, HT-KO mice showed ameliorated pancreatic damage without any rise in serum enzyme activities, whereas NT-KO mice exhibited a similar degree of pancreatitis to wild-type mice. Taken together, the present results indicate that lack of pancreatic PACAP did not aggravate, but rather ameliorated, cerulein-induced pancreatitis. In addition, about half of KO mice showed a novel phenotype in which cerulein caused rapid and severe hypothermia, followed by death.

Over-expression of pancreatic pituitary adenylate cyclase-activating polypeptide (PACAP) aggravates cerulein-induced acute pancreatitis in mice

Development of human chronic pancreatitis is associated with intrapancreatic accumulation of pituitary adenylate cyclase-activating polypeptide (PACAP) accompanied with an altered inflammatory response (Michalski et al., Am J Physiol Gastrointest Liver Physiol. 2008;294:G50-G57). To investigate the role of pancreatic PACAP in the development of acute pancreatitis, we employed transgenic mice over-expressing PACAP in pancreatic beta-cells (PACAP-Tg). In comparison to wild-type mice, PACAP-Tg mice exhibited more severe pathophysiological signs of the cerulein-induced pancreatitis at 12 h, as evidenced by higher serum amylase and lipase levels accompanied by the exacerbation of pancreatic edema, necrosis, and inflammation. Cerulein treatment increased mRNA expression of several proinflammatory cytokines (TNFalpha, IL-1beta, and IL-6) at 12 h with similar magnitude both in wild-type and PACAP-Tg mice. In addition, the mRNA and protein levels of regenerating gene III beta (RegIIIbeta), a key factor in the pancreatic response to acute pancreatitis, were up-regulated at 24 h in wild-type mice upon cerulein administration, whereas they were attenuated in PACAP-Tg mice. These data indicate that over-expressed PACAP in pancreas enhances the cerulein-induced inflammatory response of both acinar cells, leading to aggravated acute pancreatitis, which was accompanied by a down-regulation of RegIIIbeta, an anti-inflammatory factor.

Beneficial effects of vasodilators in preventing severe acute pancreatitis shock

OBJECTIVES

To investigate the effect of treatment with several vasodilatory substance on the changes in mean arterial pressure (MAP) of severe acute pancreatitis.

METHODS

Pancreatitis was induced in rats by 5% sodium taurocholate retrograde infusion through the pancreatic duct, which produces a significant decrease in arterial blood pressure.

RESULTS

Three hours after the induction of pancreatitis, a fall of approximately 25 mm Hg in MAP was observed, with no changes of MAP in untreated controls. The administration of the nitric oxide synthesis inhibitor, N-nitro-L-arginine methyl ester (25 mg/kg), previously to the induction of pancreatitis, produced a marked fall in MAP leading to the death of all the animals. When several vasodilatory substances, S-nitroso-N-acetylpenicillamine (200 microg x kg x h), calcitonin gene-related peptide (10 microg/kg), and vasoactive intestinal polypeptide (8 microg x kg x h) were administered previously to the induction of pancreatitis, the MAP fall induced by pancreatitis was not observed. The improvement of physiological conditions observed in vasodilator-treated animals is in agreement with histological data, which show only minor structural changes in the pancreas from these animals, in contrast with the severe alterations observed in untreated pancreatitic rats.

CONCLUSION

: Vasodilation confers protection against the systemic circulatory derangement derived from the development of severe acute pancreatitis.