The Involvement Of PAR-2 Mechanism In Pancreatic Cancer Pain

Objective:Pain is one of the most common and untolerated syndromes for cancer patients.Some patients are even more fear to pain than to death since pain will severely depress their living quality.There are even some cancer patients who have refused therapeutics or even suicide for cancer pain.That is also true in patients with pancreatic carcinoma.Pain in terminal pancreatic carcinoma is very severe and is not only a physical pain but also an omnibearing pain involved social,psychological and mental indisposition. And this kind of pain is often complicated with autonomic nerve system and mental abnormalities.Therefore,pain control has become one of the important parts of alleviative treatment of pancreatic carcinoma.The ideal pain control strategy should be based on the pain mechanism,but unfortunately,mechanisms underlying pancreatic cancer pain remain unclear now.Protease activated receptors(PARs) is a kind of G-protein coupled receptor.There are 4 members in PARs family,ie,PAR-1,PAR-2,PAR-3 and PAR-4,PAR-2 mainly express in airway,epidermis,gastrointestinal tract, pancreas,cardiovascular and nervous system.Trypsin is the most powerful PAR-2 agonist.It was reported that PAR-2 may play an important role in visceral pain of pancreatic carcinoma.Many studies verified that PAR-2 is dose-dependently expressed in thoracic and lumbar dorsal root ganglion.Injection of trypsin or PAR-2 specific agonist into pancreatic duct will evoke pain behaviors in rats. And pre-injection of PAR-2 specific agonist analogue will eliminate the pain reaction.These results show that activation of PAR-2 by the activated trypsin may be one of main mechanisms of pancreatitis pain.There are no definite studies on role of PAR-2 in pain mechanisms of pancreatic carcinoma.But high trypsin is found in most of pancreatic carcinoma patients.Therefore,the role of PAR-2 in pain of pancreatic carcinoma should be studied. Methods:In our study,methods of biochemistry,molecular biology,patch clamp, primary neuron culture and animal behavior studies were employed to:(1) Collect specimen of pancreatic tumor and pathological test;(2) Identify and quantitate the release of trypsin of pancreatic tumor tissue and the level of proteolytic activity;(3) Study the effect of culture supernatants of pancreatic tumor tissue on thermal and mechanical pain of rats and its mechanism;(4) Study the effect of culture supernatants of pancreatic tumor tissue on electrophysiology of cultured DRG neuron membrane and its mechanism.Results:The main results of these studies are:(1) Patients displayed persistent full pain on mid-superior belly,jaundice, extenuation etc.and a＞5 VAS score preoperatively.The specimen was pathologically identified to be caput pancreatis carcinomas with moderate cell differentiation.(2) The expression of trypsin is significantly higher in pancreatic tumor tissue than in normal pancreatic tissue.After incubation in HBSS culture solution,release of proteolytic enzyme of pancreatic tumor tissue is significantly higher than that of normal tissue.(3) Injection of trypsin or incubation supernatant of pancreatic tumor tissue into rats footplate causes obviously thermal hyperalgesia and mechanical allodynia.After added with broad spectrum serine stretch proteinase inhibitor,FUT-175,supernatant of pancreatic tumor tissue causes significant lower thermal and mechanical pain.And incubation supernatant of normal pancreatic tissue shows no difference to saline or negtive control in this study.(4) In cultured DRG neuron of new neonat rats,pre-conditioning with supernatant of pancreatic tumor tissue causes an increase of capsaicin sensitive current.Trypsin and PAR-2 receptor agonist SL-NH₂ peptide causes the same reaction.But the control peptide LR-NH₂,which has no proteolytic activity,has no effect on the current.And pre-conditioning with synthetic PAR-2 receptor antagonist FSLLRY-NH₂ peptide effectively inhibits the promotion effect of supernatant of pancreatic tumor tissue on the current.Conclusion:It is indicated in these results that in this pancreatic tumor tissue the expression of trypsin and the proteolytic activity enzyme increase.And the supernatant of tumor tissue may activates the nociceptive neuron in vivo and causes nociceptive behavior,which has relationship with the proteolytic activity.In cultured DRG neurons,supernatant of pancreatic tumor tissue causes increase of TRPV current,and PAR-2 receptor antagonist FSLLRY-NH₂ may inhibit this promotion effect,which indicates that the supernatant activates the nociceptive neuron through a mechanism involved with PAR-2.Therefore,PAR-2 may play an important role in the pain mechanism of pancreatic carcinoma.