NEURAL REGULATION OF PANCREATIC FUNCTION
Principal Investigator: KIMBERLY SAUNDERS KIRKWOOD
Abstract: Acute pancreatitis is an inflammatory condition with 5-10% mortality rate. Severe abdominal pain is the most prominent symptom, however the mechanisms of pancreatic inflammatory pain are poorly understood and consequently the therapeutic strategies are unsophisticated. The long term goal of this proposal is to identify the major mediators of pancreatic neurogenic inflammation and pain and to develop novel therapies for these conditions. We propose to study pathways involved both in the initiation and termination of inflammatory pain in the pancreas. Although ion channels of the transient receptor potential (TRP) family are known to promote inflammation and pain in somatic models, and we have shown that TRPV1 mediates pancreatic inflammatory pain via the release of neuropeptides both in the pancreas and spinal cord, whether the newer ion channels TRPV4 and TRPA1 participate in pancreatic inflammation and pain is unknown. TRPV4 responds to mechanical sheer stress, osmotic changes, as well as certain arachidonic acid metabolites released during inflammation. TRPV4 is expressed by pancreatic sensory neurons and our preliminary results show that it mediates nociception since either injection of TRPV4 agonists into the pancreatic duct or initiation of experimental pancreatitis result in activation of nociceptive neurons in the spinal cord (assessed by fos expression) in wild-type mice with diminished effects in TRPV4-/- animals. Moreover, proteases such as trypsin, that are prematurely-activated in the inflamed pancreas and can cleave and activate protease activated receptor 2 (PAR2), sensitize TRPV4. Experiments are designed to define the mechanisms by which inflammatory mediators sensitize TRPV4 in pancreatic neurons to promote the release of neuropeptides that cause neurogenic inflammation and pain. We have recently discovered that 4-hydroxynonenal (HNE), an aldehyde generated by the action of reactive oxygen species (ROS) on membrane lipids, is an endogenous agonist of TRPA1 which causes peptide release, neurogenic inflammation and pain. TRPA1 promotes pancreatic inflammatory pain since our preliminary results show that intraductal agonists and experimental pancreatitis stimulate fos expression and inflammation in TRPA1 wild-type mice with markedly reduced effects in TRPA1-/- animals. Experiments are designed to define the expression of TRPA1 in pancreatic neurons, to determine the effects of lipid peroxidation products such as HNE on neurogenic pancreatic inflammation and nociception, to determine how the pro-inflammatory peptide bradykinin sensitizes TRPA1, and to investigate the contribution of TRPA1 to neurogenic inflammation and pain in several models of experimental pancreatitis. Finally we will investigate pathways that terminate pancreatic inflammation by examining the role of metalloendopeptidases that degrade proinflammatory peptides on the cell surface and in endosomes. We will determine whether neutral endopeptidase (NEP), a cell surface enzyme that degrades at least 11 peptides including substance P and bradykinin, attenuates pancreatic inflammation and pain, and to evaluate whether administration of recombinant human NEP is a novel anti-inflammatory and analgesic agent. We have recently discovered that endothelin converting enzyme-1 (ECE-1) degrades pro-inflammatory peptides in endosomes to thereby promote recycling and resensitization of endocytosed receptors. Experiments are designed to determine whether ECE-1 inhibitors, by preventing receptor recycling, inhibit resensitization of neurogenic inflammation in the pancreas, and are thus novel anti-inflammatory agents. PUBLIC HEALTH RELEVANCE: Pancreatic inflammation results in morbidity and mortality, with severe intractable pain. The mechanisms of acute pancreatitis and pancreatitis pain are very poorly understood. The overall objective of our proposal is to identify key mediators of pancreatic inflammation and pain, and to evaluate novel therapies for these conditions. Specifically, we will determine the role of newly-identified ion channels on pancreatic sensory nerves. Once activated or sensitized in the inflamed pancreas, these channels induce the release of neuropeptides from sensory nerves in the pancreas and the spinal cord, where peptides cause neurogenic inflammation and pain, respectively. Thus, antagonists of these channels may prevent pancreatic inflammatory pain. We will also evaluate whether recombinant human peptidases, which degrade proinflammatory and nociceptive peptides, ameliorate inflammatory pain, and are thus novel therapeutic agents. We determine whether inhibitors of peptidases in endosomes, that regulate the recycling and resensitization of neuropeptide receptors, prevent the sustained signaling of these peptides and thereby ameliorate neurogenic inflammation and pain.
Funding Period: 1995-10-01 - 2014-03-31
more information: NIH RePORT