Proteinase-activated Receptor 1 Contributed to Up-regulation of Enkephalin in Keratinocytes of Patients with Obstructive Jaundice

The Local Neuropeptide System of Keratinocytes

Neuropeptides have been known for over 50 years as chemical signals in the brain. However, it is now well established that the synthesis of this class of peptides is not restricted to neurons. For example, human skin not only expresses several functional receptors for neuropeptides but, also, can serve as a local source of neuroactive molecules such as corticotropin-releasing hormone, melanocortins, and β-endorphin. In contrast, an equivalent of the hypothalamic-pituitary axis in the oral mucosa has not been well characterized to date. In view of the differences in the morphology and function of oral mucosal and skin cells, in this review I surveyed the existing evidence for a local synthesis of hypothalamic-pituitary, opiate, neurohypophyseal, and neuroendocrine neuropeptides in both epidermal and oral keratinocytes.

Protease Activated Receptors and Arthritis

The catabolic and destructive activity of serine proteases in arthritic joints is well known; however, these enzymes can also signal pain and inflammation in joints. For example, thrombin, trypsin, tryptase, and neutrophil elastase cleave the extracellular N-terminus of a family of G protein-coupled receptors and the remaining tethered ligand sequence then binds to the same receptor to initiate a series of molecular signalling processes. These protease activated receptors (PARs) pervade multiple tissues and cells throughout joints where they have the potential to regulate joint homeostasis. Overall, joint PARs contribute to pain, inflammation, and structural integrity by altering vascular reactivity, nociceptor sensitivity, and tissue remodelling. This review highlights the therapeutic potential of targeting PARs to alleviate the pain and destructive nature of elevated proteases in various arthritic conditions.

Cannabinoid Receptor-2 Activation in Keratinocytes Contributes to Elevated Peripheral β-Endorphin Levels in Patients With Obstructive Jaundice

BACKGROUND

Cholestatic diseases are often accompanied by elevated plasma levels of endogenous opioid peptides, but it is still unclear whether central or peripheral mechanisms are involved in this process, and little is known about the change of pain threshold in these patients. The purpose of this study was to determine the preoperative pain threshold, postoperative morphine consumption, and central and peripheral β-endorphin levels in patients with obstructive jaundice. This study also tests the hypothesis that activation of the cannabinoid receptor-2 (CB2R) in skin keratinocytes by endocannabinoids is the mechanism underlying circulating β-endorphin elevation in patients with obstructive jaundice.

METHODS

The electrical pain thresholds, 48-hour postoperative morphine consumption, concentrations of β-endorphin in plasma and cerebrospinal fluid, skin and liver β-endorphin expression, and plasma levels of endocannabinoids were measured in jaundiced (n = 32) and control (n = 32) patients. Male Sprague-Dawley rats and human keratinocytes (human immortalized keratinocyte cell line [HaCaT]) were used for the in vivo and in vitro experiments, respectively. Mechanical and thermal withdrawal latency, plasma level, and skin expression of β-endorphin were measured in CB2R-antagonist-treated and control bile duct-ligated (BDL) rats. In cultured keratinocytes, the effect of CB2R agonist AM1241-induced β-endorphin expression was observed and the phosphorylation of extracellular-regulated protein kinases 1/2, p38, and signal transducer and activator of transcription (STAT) pathways were investigated.

RESULTS

This study found (1) the plasma level of β-endorphin (mean ± standard error of the mean [SEM]) was 193.9 ± 9.6 pg/mL in control patients, while it was significantly increased in jaundiced patients (286.6 ± 14.5 pg/mL); (2) the electrical pain perception threshold and the electrical pain tolerance threshold were higher in patients with obstructive jaundice compared with controls, while the 48-hour postoperative morphine consumption was lower in the jaundiced patients; (3) there was no correlation between plasma β-endorphin levels, electrical pain thresholds, and 48-hour postoperative morphine consumption in patients with obstructive jaundice; (4) the plasma level of the endogenous cannabinoid anandamide was increased in the jaundiced patients; (5) CB2R antagonist treatment of the BDL rats reduced β-endorphin levels in plasma and skin keratinocytes, while it did not alter the nociceptive thresholds in BDL and control rats; (6) the endocannabinoid anandamide-induced β-endorphin synthesis and release via CB2R in cultured keratinocytes; and (7) phosphorylation of extracellular-regulated protein kinases 1/2 is involved in the CB2R-agonist-induced β-endorphin expression in keratinocytes.

CONCLUSIONS

CB2R activation in keratinocytes by the endocannabinoid anandamide may play an important role in the peripheral elevation of β-endorphin during obstructive jaundice.

Bilirubin Induces Pain Desensitization in Cholestasis by Activating 5-Hydroxytryptamine 3A Receptor in Spinal Cord

Background

Cholestasis patients often suffer from pain desensitization, resulting in serious complications in perioperative period. This study was aim to investigate the mechanism of bilirubin in cholestasis mediating pain desensitization through 5-hydroxytryptamine 3A (5-HT_3A ) receptor activation in spinal dorsal horn (SDH).

Methods

A cholestasis model was established by bile duct ligation (BDL) in rats. Pain thresholds of rats were measured after BDL or intrathecally injecting bilirubin in the presence or absence of agonist (mCPBG) and antagonists (ondansetron, bicuculline, or CGP55845). Expression of 5-HT₃ receptors, and the affinity and binding mode of bilirubin to 5-HT_3A receptor were determined. Effects of bilirubin on γ-aminobutyric acid (GABA) pathway and the interactions with 5-HT_3A receptor were tested.

Results

Bilirubin was elevated significantly in both serum and CSF in BDL rats, accompanied with the up-regulation of pain thresholds. Both of 5-HT_3A receptor and GABA _A receptor antagonists could reverse the increased pain threshold in BDL rats. Further, 5-HT_3A and GABA _A receptor expressions were increased in BDL rats or intervention with bilirubin. Molecular docking suggested that bilirubin entered the hydrophobic pocket pre-formed in 5-HT_3A receptor with potential hydrogen bonding. Bilirubin also increased GABA concentrations in CSF and GABAergic spontaneous inhibitory postsynaptic current in spinal cord, and directly induced inward currents in HEK293 cells which were overexpressed 5-HT_3A receptor by lentivirus.

Conclusion

In conclusion, bilirubin induced pain desensitization in cholestasis by activating 5-HT_3A receptor in spinal cord. The activation of 5-HT_3A receptor might regulate pain threshold by acting on the GABA pathway.

Inhibition of the norepinephrine transporter rescues vascular hyporeactivity to catecholamine in obstructive jaundice

In patients with obstructive jaundice, the cardiovascular system exhibits hypotension and vascular hyporeactivity. Most norepinephrine is taken up through the neuronal norepinephrine transporter (NET), which is implicated in cardiovascular diseases. A previous study demonstrated that pharmacological NET inhibition could increase resting blood pressure. However, the role of NETs in vascular hyporeactivity induced by obstructive jaundice is poorly understood. This study used the NET inhibitor nisoxetine and a rat model of bile duct ligation (BDL) to investigate whether NET is associated with BDL-induced vascular hyporeactivity. Rats were injected with nisoxetine via the tail vein for 7 consecutive days after BDL. Samples of the superior cervical sympathetic ganglion (SCG) and thoracic aortic rings were processed for investigations. Our results showed that NET expression in the SCG was significantly increased after BDL. Nisoxetine prevented the augmentation of NET expression, increased α₁-adrenoceptor activation, and enhanced the weakened contractile responses of thoracic aortic rings after BDL. Our study demonstrates that nisoxetine plays a protective role in BDL-induced vascular hyporeactivity through increased α₁-adrenoceptor activation in rats.

Recent advances in understanding the molecular mechanisms of cholestatic pruritus: A review

Cholestasis, a condition characterized by an abnormal decrease in bile flow, is accompanied by various symptoms such as pruritus. Although cholestatic pruritus is a prominent condition, its precise mechanisms have largely been elusive. Recently, advancements have been made for understanding the etiology and pathogenesis of cholestatic pruritus. The current review therefore focuses on summarizing the overall progress made in the elucidation of its molecular mechanisms. We have reviewed the available animal models on cholestasis to compare the differences between them, characterized potential pruritogens involved in cholestatic pruritus, and have summarized the receptor and ion channels implicated in the condition. Finally, we have discussed the available treatment options for alleviation of cholestatic pruritus. As our understanding of the mechanisms of cholestatic pruritus deepens, novel strategies to cure this condition are awaited.

BAM8-22 and its receptor MRGPRX1 may attribute to cholestatic pruritus

Pruritus is an unexpected symptom observed in cholestasis and its mechanism is still unclear. Here, we show that bovine adrenal medulla (BAM) 8-22, an endogenous itch-inducing peptide, could be involved in cholestatic pruritus. It was found that bile duct ligation (BDL) mice, an obstructive cholestasis model, showed increased spontaneous scratching behaviour. Importantly, the mRNA level of proenkephalin, a precursor polypeptide of BAM8-22, was significantly increased in the skin of BDL mice. Furthermore, the mRNA level of Mrgprx1, which encodes a receptor for BAM8-22, was significantly increased in the dorsal root ganglia (DRG) of BDL mice. This was further confirmed by elevation of intracellular calcium levels upon BAM8-22 treatment in primarily-cultured DRG neurons. In addition, BDL mice showed augmented scratching behaviour by BAM8-22, indicating enhanced activity of MRGPRX1. Moreover, the skin homogenate of BDL mice induced elevation of intracellular calcium levels through MRGPRX1. Finally, among the various bile acids, chenodeoxycholic acid significantly increased proenkephalin transcription in a human keratinocyte cell line (HaCaT). In conclusion, cholestatic pruritus could be attributed in part to enhanced action of both BAM8-22 in the skin and its receptor MRGPRX1 in sensory neurons.

Spironolactone rescues renal dysfunction in obstructive jaundice rats by upregulating ACE2 expression

Postoperative acute renal failure in patients with obstructive jaundice is still a serious clinically complication, yet the mechanisms remain unclear. Renin-angiotensin-aldosterone system (RAAS) plays a central role in renal disease progression. Several lines of evidence shows that angiotensin-converting-enzyme-2 (ACE2), a main effector of RAAS acts as a local regulator for renal protection. This study aims to investigate the role of ACE2 and the effect of spironolactone treatment in obstructive jaundice(OJ) rats with renal injury. The rats with obstructive jaundice were established by bile duct ligation. Total bilirubin (TBil), serum creatinine (Scr) and the expression of ACE2 in kidney tissue of obstructive jaundice rats were detected. Comparatively, the expression of ACE2, renin, angiotensin II (AngII), angiotensin-(1-7)[Ang-(1-7)], aldosterone and intercellular adhesion molecule 1 (ICAM-1) in kidney tissues after spironolactone administration were measured by ELISA. Renal necrosis, inflammation and fibrosis induced by OJ were also measured by HE staining and Masson staining. The correlation between the expression of ACE2 and TBil, also the Scr level were investigated. With the time of common bile duct ligation prolonged, the TBil and Scr concentration increased while the expression of ACE2 in OJ rats' kidney tissues decreased. However, after spironolactone intervention, the expressions of ACE2, renin, AngII, Ang-(1-7), aldosterone and ICAM-1 in kidney tissue were changed, moreover, necrotic, inflammatory and fibrotic condition was also decreased. The relationship between the mRNA expression of ACE2 and TBil/Scr was observed to be moderately negatively correlated (r = -0.516, R² = 0.292, P < 0.01), (r = -0.576, R² = 0.332, P < 0.01), respectively. RAAS exerted an important effect in the renal damage caused by OJ. Spironolactone intervention not only improved the degree of renal fibrosis induced by OJ, but also upregulated the ACE2 expression in the kidney of OJ rats and rescued the renal function.

Altered expression of differential gene and lncRNA in the lower thoracic spinal cord on different time courses of experimental obstructive jaundice model accompanied with altered peripheral nociception in rats

The spinal origin of jaundice-induced altered peripheral nociceptive response poorly understood. In the current study, we aimed to first validate rats with bile duct ligation (BDL) as a jaundice model accompanied by altered peripheral nociceptive response, and then to analyze differential gene and lncRNA expression patterns in the lower thoracic spinal cord on different time courses after BDL operation by using high-throughput RNA sequencing. The differentially expressed genes (DEGs) identified using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) analysis, followed by clustering analysis, Gene Ontology analysis and pathway analysis. As a result, a total of 2033 lncRNAs were differentially expressed 28d after BDL, in which 1545 probe sets were up-regulated and 488 probe sets were down-regulated, whereas a total of 2800 mRNAs were differentially expressed, in which 1548 probe sets were up-regulated and 1252 probe sets were down-regulated. The RNAseq data of select mRNAs and lncRNAs was validated by RT-qPCR. 28d after BDL, the expressions of lncRNA NONRATT002335 and NONRATT018085 were significantly up-regulated whereas the expression of lncRNA NONRATT025415, NONRATT025388 and NONRATT025409 was significantly down-regulated. 14d after BDL, the expressions of lncRNA NONRATT002335 and NONRATT018085 were significantly up-regulated; the expression of lncRNA NONRATT025415, NONRATT025388 and NONRATT025409 was significantly down-regulated. In conclusion, the present study showed that jaundice accompanied with decreased peripheral nociception involved in the changes of gene and lncRNA expression profiles in spinal cord. These findings extend current understanding of spinal mechanism for obstructive jaundice accompanied by decreased peripheral nociception.

Trypsin-protease activated receptor-2 signaling contributes to pancreatic cancer pain

Pain treatment is a critical aspect of pancreatic cancer patient clinical care. This study investigated the role of trypsin-protease activated receptor-2 (PAR-2) in pancreatic cancer pain. Pancreatic tissue samples were collected from pancreatic cancer (n=22) and control patients (n=22). Immunofluorescence analyses confirmed colocalization of PAR-2 and neuronal markers in pancreatic cancer tissues. Trypsin levels and protease activities were higher in pancreatic cancer tissue specimens than in the controls. Supernatants from cultured human pancreatic cancer tissues (PC supernatants) induced substance P and calcitonin gene-related peptide release in dorsal root ganglia (DRG) neurons, and FS-NH₂, a selective PAR-2 antagonist, inhibited this effect. A BALB/c nude mouse orthotopic tumor model was used to confirm the role of PAR-2 signaling in pancreatic cancer visceral pain, and male Sprague-Dawley rats were used to assess ambulatory pain. FS-NH₂ treatment decreased hunch scores, mechanical hyperalgesia, and visceromotor reflex responses in tumor-bearing mice. In rats, subcutaneous injection of PC supernatant induced pain behavior, which was alleviated by treatment with FS-NH₂ or FUT-175, a broad-spectrum serine protease inhibitor. Our findings suggest that trypsin-PAR-2 signaling contributes to pancreatic cancer pain in vivo. Treatment strategies targeting PAR-2 or its downstream signaling molecules might effectively relieve pancreatic cancer pain.

Validation of the Mandarin Chinese Version of the Pain Sensitivity Questionnaire

BACKGROUND AND AIM

The Pain Sensitivity Questionnaire (PSQ), a self-reported scale, has been used to assess the pain sensitivity level in a Caucasian population. However, a validated Mandarin Chinese version of the PSQ is not available. This study was aimed to translate the PSQ into Mandarin Chinese (PSQ-C) and validate it to measure pain sensitivity among Chinese people.

METHODS

The English version of the PSQ has been translated into Mandarin Chinese (PSQ-C), according to the standard steps of cross-cultural adaptation of self-reported scales. Three of the 17 items were revised owing to cultural adaptation. The final version was validated on a population of 182 Chinese people in Changsha City, China, during October to December 2015. The participants underwent electrical experimental pain testing. The psychometric properties of the PSQ-C and its subscales were examined.

RESULTS

The Cronbach's alpha coefficients for the PSQ-C-total, PSQ-C-moderate, and PSQ-C-minor were 0.90, 0.86, and 0.81, respectively. Acceptable test-retest reliability, content validity, and construct validity were demonstrated. Concurrent validity was shown via significant positive correlations between PSQ-C scores and perceived pain intensity at pain threshold and during pain stimulation with a fixed intensity. Convergent validity was shown via significant positive correlations between Pain Catastrophizing Scale scores and PSQ-C scores. Known group validity was demonstrated via higher PSQ-C-total and PSQ-C-moderate scores among those with high neuroticism scores. These results indicate that the PSQ-C has reasonably good psychometric properties, similar to the original English and German versions.

CONCLUSION

The PSQ-C is a reliable and useful tool to assess pain sensitivity levels in a Chinese population.

Endogenous opiates and behavior: 2014

This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants). This paper is the thirty-seventh consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2014 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (endogenous opioids and receptors), and the roles of these opioid peptides and receptors in pain and analgesia (pain and analgesia); stress and social status (human studies); tolerance and dependence (opioid mediation of other analgesic responses); learning and memory (stress and social status); eating and drinking (stress-induced analgesia); alcohol and drugs of abuse (emotional responses in opioid-mediated behaviors); sexual activity and hormones, pregnancy, development and endocrinology (opioid involvement in stress response regulation); mental illness and mood (tolerance and dependence); seizures and neurologic disorders (learning and memory); electrical-related activity and neurophysiology (opiates and conditioned place preferences (CPP)); general activity and locomotion (eating and drinking); gastrointestinal, renal and hepatic functions (alcohol and drugs of abuse); cardiovascular responses (opiates and ethanol); respiration and thermoregulation (opiates and THC); and immunological responses (opiates and stimulants).