Clinical and preclinical evidence that angiotensin-converting enzyme inhibitors and angiotensin receptor blockers prevent diabetic peripheral neuropathy

Given possible involvement of the central and peripheral angiotensin system in pain processing, we conducted clinical and preclinical studies to test whether pharmacological inhibition of the angiotensin system would prevent diabetic peripheral neuropathy (DPN) accompanying type 2 diabetes mellitus (T2DM). In the preclinical study, the nociceptive sensitivity was determined in leptin-deficient ob/ob mice, a T2DM model. A clinical retrospective cohort study was conducted, using the medical records of T2DM patients receiving antihypertensives at three hospitals for nearly a decade. In the ob/ob mice, daily treatment with perindopril, an angiotensin-converting enzyme inhibitor (ACEI), or telmisartan, an angiotensin receptor blocker (ARB), but not amlodipine, an L-type calcium channel blocker (CaB), significantly inhibited DPN development without affecting the hyperglycemia. In the clinical study, the enrolled 7464 patients were divided into three groups receiving ACEIs, ARBs and the others (non-ACEI, non-ARB antihypertensives). Bonferroni's test indicated significantly later DPN development in the ARB and ACEI groups than the others group. The multivariate Cox proportional analysis detected significant negative association of the prescription of ACEIs or ARBs and β-blockers, but not CaBs or diuretics, with DPN development. Thus, our study suggests that pharmacological inhibition of the angiotensin system is beneficial to prevent DPN accompanying T2DM.

Cav3.2-dependent hyperalgesia/allodynia following intrathecal and intraplantar zinc chelator administration in rodents

Ca_v3.2, a T-type calcium channel (T-channel) family member, is expressed in the nociceptors and spinal cord, and its activity is largely suppressed by zinc under physiological conditions. In rats, intrathecal and intraplantar administration of a zinc chelator, TPEN, caused T-channel-dependent mechanical hyperalgesia, and the intraplantar, but not intrathecal, TPEN induced Ca_v3.2 upregulation in the dorsal root ganglion. In mice, intraplantar TPEN also caused mechanical allodynia, which was abolished by T-channel inhibitors or Ca_v3.2 gene deletion. Together, spinal and peripheral zinc deficiency appears to enhance Ca_v3.2 activity in the spinal postsynaptic neurons and nociceptors, respectively, thereby promoting pain.

A hydrolysate of poly-trans-[(2-carboxyethyl)germasesquioxane] (Ge-132) suppresses Cav3.2-dependent pain by sequestering exogenous and endogenous sulfide

Poly-trans-[(2-carboxyethyl)germasesquioxane] (Ge-132), an organogermanium, is hydrolyzed to 3-(trihydroxygermyl)propanoic acid (THGP) in aqueous solutions, and reduces inflammation, pain and cancer, whereas the underlying mechanisms remain unknown. Sulfides including H2S, a gasotransmitter, generated from l-cysteine by some enzymes including cystathionine-γ-lyase (CSE), are pro-nociceptive, since they enhance Cav3.2 T-type Ca2+ channel activity expressed in the primary afferents, most probably by canceling the channel inhibition by Zn2+ linked via coordinate bonding to His191 of Cav3.2. Given that germanium is reactive to sulfur, we tested whether THGP would directly trap sulfide, and inhibit sulfide-induced enhancement of Cav3.2 activity and sulfide-dependent pain in mice. Using mass spectrometry and 1H NMR techniques, we demonstrated that THGP directly reacted with sulfides including Na2S and NaSH, and formed a sulfur-containing reaction product, which decreased in the presence of ZnCl2. In Cav3.2-transfected HEK293 cells, THGP inhibited the sulfide-induced enhancement of T-type Ca2+ channel-dependent membrane currents. In mice, THGP, administered systemically or locally, inhibited the mechanical allodynia caused by intraplantar Na2S. In the mice with cyclophosphamide-induced cystitis and cerulein-induced pancreatitis, which exhibited upregulation of CSE in the bladder and pancreas, respectively, systemic administration of THGP as well as a selective T-type Ca2+ channel inhibitor suppressed the cystitis-related and pancreatitis-related visceral pain. These data suggest that THGP traps sulfide and inhibits sulfide-induced enhancement of Cav3.2 activity, leading to suppression of Cav3.2-dependent pain caused by sulfide applied exogenously and generated endogenously.

Opioid modulation of T-type Ca2+ channel-dependent neuritogenesis/neurite outgrowth through the prostaglandin E2/EP4 receptor/protein kinase A pathway in mouse dorsal root ganglion neurons

Irregular regeneration or inappropriate remodeling of the axons of the primary afferent neurons after peripheral nerve trauma could be associated with the development of neuropathic pain. We analyzed the molecular mechanisms for the neuritogenesis and neurite outgrowth caused by prostaglandin E2 (PGE2) in mouse dorsal root ganglion (DRG) neurons, and evaluated their opioid modulation. PGE2 in combination with IBMX, a phosphodiesterase inhibitor, caused neuritogenesis/neurite outgrowth in DRG cells, an effect abolished by a prostanoid EP4, but not EP2, receptor antagonist, and inhibitors of adenylyl cyclase or protein kinase A (PKA). Blockers of T-type Ca2+ channels (T-channels), that are responsible for window currents involving the sustained low-level Ca2+ entry at voltages near the resting membrane potentials and can be functionally upregulated by PKA, inhibited the neuritogenesis/neurite outgrowth caused by PGE2/IBMX or dibutylyl cyclic AMP, a PKA activator, in DRG neurons, an inhibitory effect mimicked by ZnCl2 and ascorbic acid that block Cav3.2, but not Cav3.1 or Cav3.3, T-channels. Morphine and DAMGO, μ-opioid receptor (MOR) agonists, suppressed the neuritogenesis and/or neurite outgrowth induced by PGE2/IBMX in DRG neurons and also DRG neuron-like ND7/23 cells, an effect reversed by naloxone or β-funaltrexamine, a selective MOR antagonist. Our data suggest that the EP4 receptor/PKA/Cav3.2 pathway is involved in the PGE2-induced neuritogenesis/neurite outgrowth in DRG neurons, which can be suppressed by MOR stimulation. We propose that MOR agonists including morphine in the early phase after peripheral nerve trauma might delay the axonal regeneration of the primary afferent neurons but prevent the development of neuropathic pain.

Dietary Zinc Deficiency Induces Cav3.2-Dependent Nociceptive Hypersensitivity in Mice

Cav3.2 channels belong to the T-type calcium channel (T-channel) family, i.e., low voltage-activated calcium channels, and are abundantly expressed in the nociceptors, playing a principal role in the development of pathological pain. The channel activity of Cav3.2 is suppressed by zinc under physiological conditions. We thus tested whether dietary zinc deficiency would cause Cav3.2-dependent nociceptive hypersensitivity in mice. In the mice fed with zinc deficient diet for 2 weeks, plasma zinc levels declined by more than half, and mechanical allodynia developed. The dietary zinc deficiency-induced allodynia was restored by T-channel inhibitors or by Cav3.2 gene silencing. These data demonstrate that zinc deficiency induces Cav3.2-dependent nociceptive hypersensitivity in mice, thereby suggesting that pain experienced by patients with diseases accompanied by zinc deficiency (e.g., chronic kidney disease) might involve the increased Cav3.2 activity.

Characterization of Potentially Inappropriate Medications That Need Special Attention in the Elderly with Dementia by Analyzing Pharmacy Claims Data

Community pharmacists may play a key role in promoting deprescribing of potential inappropriate medications (PIMs) that are highly prevalent among community-dwelling elderly with dementia. To characterize PIMs categories that need a special attention for dementia patients, in the present study, we analyzed the anonymized pharmacy claims data of patients aged 65 years and older (n = 333869) who visited nationwide 905 community-based pharmacies of Sugi Pharmacy Co., Ltd. during December 1-31, 2019. A dementia group was defined as patients who received typical dementia medications marketed in Japan, i.e., donepezil, galantamine, memantine or rivastigmine, and a non-dementia group was defined as patients who received no such medications. After propensity score matching on the basis of patients' age, gender and home healthcare insurance usage, the data of 11486 patients in each group were subjected to logistic regression analyses, to identify PIMs categories particularly important for dementia patients. Univariate analysis indicated that the proportions of dementia patients who received 1 and 2≤ of PIMs were significantly (p < 0.001) greater than those of non-dementia patients (odds ratios were 1.35 and 1.47, respectively). Multivariate analyses identified 5 categories of PIMs that were significantly more frequently prescribed in dementia patients, i.e., 'H2 blockers,' 'drugs for overactive bladder,' 'anti-diabetes drugs' and 'sulpiride' listed as PIMs categories for non-specific cases (adjusted odds ratios (aORs): 1.29, 1.91, 1.17, and 1.38, respectively), in addition to 'antipsychotics' listed only for dementia patients (aOR: 4.29). These results provide useful information to establish strategies for pharmacist-led deprescribing of PIMs in dementia patients.

Development of hepatic impairment aggravates chemotherapy-induced peripheral neuropathy following oxaliplatin treatment: Evidence from clinical and preclinical studies

Oxaliplatin often induces peripheral neuropathy, a dose-limiting adverse reaction, and in rare cases leads to sinusoidal obstruction syndrome. We thus conducted a retrospective cohort study to examine the relationship between oxaliplatin-induced peripheral neuropathy (OIPN) and hepatic impairment, and then perform a fundamental study to analyze the underlying mechanisms. Analysis of medical records in cancer patients treated with oxaliplatin indicated that laboratory test parameters of hepatic impairment including AST, ALT and APRI (AST to platelet ratio index) moderately increased during oxaliplatin treatment, which was positively correlated with the severity of OIPN (grades 1-4), and associated with later incidence of survivors with OIPN grades ≥2. In mice, hepatic injury induced by CCl4 or ethanol accelerated OIPN in mice, an effect prevented by inactivation of high mobility group box 1 (HMGB1), known to participate in OIPN, by the neutralizing antibody or thrombomodulin alfa capable of promoting its thrombin-dependent degradation. Oxaliplatin also aggravated the hepatic injury in mice. CCl4 released HMGB1 from cultured hepatic parenchymal cells, and oxaliplatin at clinically achievable concentrations released HMGB1 from hepatic parenchymal and non-parenchymal cells. Our clinical and preclinical data suggest that the development of mild hepatic impairment during oxaliplatin treatment is associated with later aggravation of OIPN.

Risk factors and pharmacotherapy for chemotherapy-induced peripheral neuropathy in paclitaxel-treated female cancer survivors: A retrospective study in Japan

Chemotherapy-induced peripheral neuropathy (CIPN) is a dose-limiting adverse reaction in cancer patients treated with several cytotoxic anticancer agents including paclitaxel. Duloxetine, an antidepressant known as a serotonin-noradrenalin reuptake inhibitor, is the only agent that has moderate evidence for the use to treat painful CIPN. The present retrospective cohort study aimed to analyze risk factors for paclitaxel-induced peripheral neuropathy (PIPN), and investigate ongoing prescription drug use for PIPN in Japan. Female breast and gynecologic cancer patients who underwent paclitaxel-based chemotherapy at a single center in Japan between January 2016 and December 2019 were enrolled in this study. Patients’ information obtained from electronic medical records were statistically analyzed to test possible risk factors on PIPN diagnosis. Patients’ age, total paclitaxel dose, the history of female hormone-related diseases, hypertension and body mass index (BMI), but not additional platinum agents, were significantly associated with increased PIPN diagnosis. Drugs prescribed for PIPN included duloxetine, pregabalin, mecobalamin and Goshajinkigan, a polyherbal medicine, regardless of poor evidence for their effectiveness against CIPN, and were greatly different between breast and gynecologic cancer patients diagnosed with PIPN at the departments of Surgery and Gynecology, respectively. Thus, older age, greater total paclitaxel dose, the history of estrogen-related diseases, hypertension and BMI are considered risk factors for PIPN in paclitaxel-based chemotherapy of female cancer patients. It appears an urgent need to establish a guideline of evidence-based pharmacotherapy for PIPN.

Role of neuron-derived ATP in paclitaxel-induced HMGB1 release from macrophages and peripheral neuropathy

We examined the role of ATP and high mobility group box 1 (HMGB1) in paclitaxel-induced peripheral neuropathy (PIPN). PIPN in mice was prevented by HMGB1 neutralization, macrophage depletion, and P2X₇ or P2X₄ blockade. Paclitaxel and ATP synergistically released HMGB1 from macrophage-like RAW264.7 cells, but not neuron-like NG108-15 cells. The paclitaxel-induced HMGB1 release from RAW264.7 cells was accelerated by co-culture with NG108-15 cells in a manner dependent on P2X₇ or P2X₄. Paclitaxel released ATP from NG108-15 cells, but not RAW264.7 cells. Thus, PIPN is considered to involve acceleration of HMGB1 release from macrophages through P2X₇ and P2X₄ activation by neuron-derived ATP.

Identification of Remaining Life Expectancy Less Than Two Weeks by C-Reactive Protein/Albumin Ratio, Prognostic Nutritional Index, Fibrosis-4 Index, and Albumin-Bilirubin Score in Terminal Cancer Patients

Background: Accurate prognosis in terminal cancer patients is useful to improve their quality of life and also to decide the cessation of fluid administration. Nonetheless, few prognostic indicators are available for prediction of such a short-term life expectancy. Objectives: The present study aimed at evaluating the efficacy of C-reactive protein (CRP)/albumin (CRP/Alb) ratio, prognostic nutritional index (PNI), fibrosis-4 (FIB-4) index, and albumin-bilirubin (ALBI) score in identifying terminal cancer patients who have a life expectancy less than two weeks. Design: Retrospective study. Setting/Subjects: Of 483 patients who died between April 2019 and March 2020 at a single center in Japan, 102 who met the inclusion criteria were enrolled in this study. Measurements: CRP/Alb, PNI, FIB-4, and ALBI were calculated from the laboratory data collected 1-13, 14-27, 28-83, and 168-365 days before death and subjected to statistical analyses. Results: CRP/Alb, PNI, FIB-4, and ALBI values were significantly associated with the time before death during terminal 365 days. CRP/Alb ≥4.4, PNI <30, FIB-4 ≥ 9.4, and ALBI ≥ -1.26 were significantly associated with the transition from the first half to the second half of terminal four weeks. Of those prognostic indicators, three and four combinations provided significantly reliable estimation of a life expectancy less than two weeks. Conclusions: CRP/Alb, PNI, FIB-4, ALBI, and their combinations are considered to help identify cancer patients who have a life expectancy less than two weeks, which is useful to make appropriate end-stage treatment decisions, for example, cessation of artificial hydration therapy.

Caspase-Dependent HMGB1 Release from Macrophages Participates in Peripheral Neuropathy Caused by Bortezomib, a Proteasome-Inhibiting Chemotherapeutic Agent, in Mice

Given the role of macrophage-derived high mobility group box 1 (HMGB1) in chemotherapy-induced peripheral neuropathy (CIPN) caused by paclitaxel, we analyzed the role of HMGB1 and macrophages in the CIPN caused by bortezomib, a proteasome-inhibiting chemotherapeutic agent used for the treatment of multiple myeloma. Repeated administration of bortezomib caused CIPN accompanied by early-stage macrophage accumulation in the dorsal root ganglion. This CIPN was prevented by an anti-HMGB1-neutralizing antibody, thrombomodulin alfa capable of accelerating thrombin-dependent degradation of HMGB1, antagonists of the receptor for advanced glycation end-products (RAGE) and C-X-C motif chemokine receptor 4 (CXCR4), known as HMGB1-targeted membrane receptors, or macrophage depletion with liposomal clodronate, as reported in a CIPN model caused by paclitaxel. In macrophage-like RAW264.7 cells, bortezomib as well as MG132, a well-known proteasome inhibitor, caused HMGB1 release, an effect inhibited by caspase inhibitors but not inhibitors of NF-κB and p38 MAP kinase, known to mediate paclitaxel-induced HMGB1 release from macrophages. Bortezomib increased cleaved products of caspase-8 and caused nuclear fragmentation or condensation in macrophages. Repeated treatment with the caspase inhibitor prevented CIPN caused by bortezomib in mice. Our findings suggest that bortezomib causes caspase-dependent release of HMGB1 from macrophages, leading to the development of CIPN via activation of RAGE and CXCR4.

Effects of Bepridil and Pimozide, Existing Medicines Capable of Blocking T-Type Ca2+ Channels, on Visceral Pain in Mice

T-Type Ca²⁺ channels (T-channels), particularly Ca_v3.2, are now considered as therapeutic targets for treatment of intractable pain including visceral pain. Among existing medicines, bepridil, a multi-channel blocker, used for treatment of arrhythmia and angina, and pimozide, a dopamine D₂ receptor antagonist, known as a typical antipsychotic, have potent T-channel blocking activity. We thus tested whether bepridil and pimozide could suppress visceral pain in mice. Colonic and bladder pain were induced by intracolonic administration of 2,4,6-trinitrobenzene sulfonic acid (TNBS) and systemic administration of cyclophosphamide (CPA), respectively. Referred hyperalgesia was assessed by von Frey test, and colonic hypersensitivity to distension by a volume load with intracolonic water injection and spontaneous bladder pain were evaluated by observing nociceptive behaviors in conscious mice. The mice exhibited referred hyperalgesia and colonic hypersensitivity to distension on day 6 after TNBS treatment. Systemic administration of bepridil at 10-20 mg/kg or pimozide at 0.1-0.5 mg/kg strongly reduced the referred hyperalgesia on the TNBS-induced referred hyperalgesia and colonic hypersensitivity to distension. CPA treatment caused bladder pain-like nociceptive behavior and referred hyperalgesia, which were reversed by bepridil at 10-20 mg/kg or pimozide at 0.5-1 mg/kg. Our data thus suggest that bepridil and pimozide, existing medicines capable of blocking T-channels, are useful for treatment of colonic and bladder pain, and serve as seeds for the development of new medicines for visceral pain treatment.

Role of HMGB1 in Chemotherapy-Induced Peripheral Neuropathy

Chemotherapy-induced peripheral neuropathy (CIPN), one of major dose-limiting side effects of first-line chemotherapeutic agents such as paclitaxel, oxaliplatin, vincristine, and bortezomib is resistant to most of existing medicines. The molecular mechanisms of CIPN have not been fully understood. High mobility group box 1 (HMGB1), a nuclear protein, is a damage-associated molecular pattern protein now considered to function as a pro-nociceptive mediator once released to the extracellular space. Most interestingly, HMGB1 plays a key role in the development of CIPN. Soluble thrombomodulin (TMα), known to degrade HMGB1 in a thrombin-dependent manner, prevents CIPN in rodents treated with paclitaxel, oxaliplatin, or vincristine and in patients with colorectal cancer undergoing oxaliplatin-based chemotherapy. In this review, we describe the role of HMGB1 and its upstream/downstream mechanisms in the development of CIPN and show drug candidates that inhibit the HMGB1 pathway, possibly useful for prevention of CIPN.

Cav3.2 overexpression in L4 dorsal root ganglion neurons after L5 spinal nerve cutting involves Egr-1, USP5 and HMGB1 in rats: An emerging signaling pathway for neuropathic pain

Overexpression of Ca_v3.2 T-type Ca²⁺ channels in L4 dorsal root ganglion (DRG) participates in neuropathic pain after L5 spinal nerve cutting (L5SNC) in rats. The L5SNC-induced neuropathic pain also involves high mobility group box 1 (HMGB1), a damage-associated molecular pattern protein, and its target, the receptor for advanced glycation end-products (RAGE). We thus studied the molecular mechanisms for the L5SNC-induced Ca_v3.2 overexpression as well as neuropathic pain in rats by focusing on; 1) possible involvement of early growth response 1 (Egr-1), known to regulate transcriptional expression of Ca_v3.2, and ubiquitin-specific protease 5 (USP5) that protects Ca_v3.2 from proteasomal degradation, and 2) possible role of HMGB1/RAGE as an upstream signal. Protein levels of Ca_v3.2 as well as Egr-1 in L4 DRG significantly increased in the early (day 6) and persistent (day 14) phases of neuropathy after L5SNC, while USP5 protein in L4 DRG did not increase on day 6, but day 14. An anti-HMGB1-neutralizing antibody or a low molecular weight heparin, a RAGE antagonist, prevented the development of neuropathic pain and upregulation of Egr-1 and Ca_v3.2 in L4 DRG after L5SNC. L5SNC increased macrophages accumulating in the sciatic nerves, and the cytoplasm/nuclear ratio of immunoreactive HMGB1 in those macrophages. Our findings suggest that L5SNC-induced Ca_v3.2 overexpression in L4 DRG and neuropathic pain involves Egr-1 upregulation downstream of the macrophage-derived HMGB1/RAGE pathway, and that the delayed upregulation of USP5 might contribute to the persistent Ca_v3.2 overexpression and neuropathy.

Changes in Percutaneous Absorption of Fentanyl Patches in Rats Treated with a Sebum-Like Secretion

The percutaneous absorption of a fentanyl (FEN)-patch is affected by various external factors including the volume of sebum secretion, which causes changes in the skin surface environment. In this study, we prepared a lard-based sebum-like secretion (SLS), and applied it to investigate the effect of different skin surface conditions on the drug penetration of a FEN-patch. In vitro work to test drug release using the Franz diffusion cell indicated that drug release was significantly suppressed by treatment with 5% SLS, which is equivalent to the amount of daily human sebum secretion. Conversely, in ex vivo experiments using rat skin, the amount of FEN that accumulated in the skin tissue of the 5% SLS-treated rats was higher in comparison with the non-SLS treated group. Furthermore, in vivo experiments indicated that the plasma FEN concentration in rats treated with the FEN-patch was significantly increased by treatment with 5% SLS. These results suggest that the sebum affected the release, accumulation, and absorption of FEN from the FEN-patch, and the FEN concentration in the blood was reflected by the balance of the suppression of drug release and the enhancement of drug accumulation in the skin with SLS.

Role of high-mobility group box 1 and its modulation by thrombomodulin/thrombin axis in neuropathic and inflammatory pain

High-mobility group box 1 (HMGB1), a nuclear protein, once released to the extracellular space, facilitates pain signals as well as inflammation. Intraplantar or intraspinal application of HMGB1 elicits hyperalgesia/allodynia in rodents by activating the advanced glycosylation end-product specific receptor (receptor for advanced glycation end-products; RAGE) or Toll-like receptor 4 (TLR4). Endogenous HMGB1 derived from neurons, perineuronal cells or immune cells accumulating in the dorsal root ganglion or sensory nerves participates in somatic and visceral pain consisting of neuropathic and/or inflammatory components. Endothelial thrombomodulin (TM) and recombinant human soluble TM, TMα, markedly increase thrombin-dependent degradation of HMGB1, and systemic administration of TMα prevents and reverses various HMGB1-dependent pathological pain. Low MW compounds that directly inactivate HMGB1 or antagonize HMGB1-targeted receptors would be useful to reduce various forms of intractable pain. Thus, HMGB1 and its receptors are considered to serve as promising targets in developing novel agents to prevent or treat pathological pain. LINKED ARTICLES: This article is part of a themed issue on Neurochemistry in Japan. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v178.4/issuetoc.

HMGB1 and its membrane receptors as therapeutic targets in an intravesical substance P-induced bladder pain syndrome mouse model

HMGB1, a nuclear protein, once released to the extracellular space, promotes somatic and visceral pain signals. We thus analyzed the role of HMGB1 in an intravesical substance P-induced bladder pain syndrome (BPS) mouse model. Intravesical administration of substance P caused referred hyperalgesia/allodynia in the lower abdomen and hindpaw without producing severe urothelial damage, which was prevented by an anti-HMGB1-neutralizing antibody, thrombomodulin α capable of inactivating HMGB1 and antagonists of RAGE or CXCR4. The HMGB1 inactivation or RAGE blockade also reversed the established bladder pain symptoms. HMGB1 and RAGE are thus considered to serve as therapeutic targets for BPS.

[HMGB1 as a target for prevention of chemotherapy-induced peripheral neuropathy]

Chemotherapy-induced peripheral neuropathy (CIPN) considerably impairs cancer patients' QOL, and may lead to discontinuation of drug treatment of cancer. Currently, there is no effective strategy against CIPN. Therefore, it is an urgent issue to develop clinically available drugs that prevent or treat CIPN. We have shown that high mobility group box 1 (HMGB1), a damage-associated molecular pattern (DAMP) molecule, plays an essential role in the development of CIPN. Most interestingly, thrombomodulin α, approved as a medicine for treatment of disseminated intravascular coagulation (DIC) in Japan, causes thrombin-dependent degradation of extracellular HMGB1 that is released in response to chemotherapeutics, and prevents CIPN. Thus, we expect that targeting HMGB1 or its receptors would lead to prevention of CIPN in cancer patients in near future.

Role of non-macrophage cell-derived HMGB1 in oxaliplatin-induced peripheral neuropathy and its prevention by the thrombin/thrombomodulin system in rodents: negative impact of anticoagulants

Background

Macrophage-derived high mobility group box 1 (HMGB1), a damage-associated molecular pattern (DAMP) protein, plays a key role in the development of chemotherapy-induced peripheral neuropathy (CIPN) caused by paclitaxel in rodents. Endothelial thrombomodulin (TM) promotes thrombin-induced degradation of HMGB1, and TMα, a recombinant human soluble TM, abolishes peripheral HMGB1-induced allodynia in mice. We thus examined whether HMGB1, particularly derived from macrophages, contributes to oxaliplatin-induced neuropathy in mice and analyzed the anti-neuropathic activity of the TM/thrombin system.

Methods

CIPN models were created by the administration of oxaliplatin in mice and rats, and the nociceptive threshold was assessed by von Frey test or paw pressure test. Macrophage-like RAW264.7 cells were stimulated with oxaliplatin in vitro. Proteins were detected and/or quantified by Western blotting, immunostaining, or enzyme-linked immunosorbent assay.

Results

Intraperitoneal administration of an anti-HMGB1-neutralizing antibody (AB) at 1 mg/kg prevented the oxaliplatin-induced allodynia in mice and rats. Antagonists of Toll-like receptor (TLR) 4, receptor for advanced glycation end products (RAGE) and CXCR4 among the HMGB1-targeted pro-nociceptive receptors, also mimicked the anti-neuropathic activity of AB in mice. Macrophage accumulation in the sciatic nerve was observed in mice treated with paclitaxel, but not oxaliplatin, and neither macrophage depletion nor inhibitors of macrophage activation affected oxaliplatin-induced allodynia. Oxaliplatin was 10- to 100-fold less potent than paclitaxel in releasing HMGB1 from macrophage-like RAW264.7 cells. Like AB, TMα at 10 mg/kg prevented the oxaliplatin-induced allodynia in mice as well as rats, an effect abolished by argatroban at 10 mg/kg, a thrombin inhibitor. The anti-neuropathic activity of TMα in oxaliplatin-treated mice was suppressed by oral anticoagulants such as warfarin at 1 mg/kg, dabigatran at 75 mg/kg, and rivaroxaban at 10 mg/kg, but not antiplatelet agents such as aspirin at 50 mg/kg and clopidogrel at 10 mg/kg. Repeated administration of the anticoagulants gradually developed neuropathic allodynia and elevated plasma HMGB1 levels in mice treated with a subeffective dose of oxaliplatin.

Conclusions

Our data thus suggests a causative role of HMGB1 derived from non-macrophage cells in oxaliplatin-induced peripheral neuropathy and a thrombin-dependent anti-neuropathic activity of exogenous TMα and, most probably, endogenous TM.

[Role of Cav3.2 T-type Ca2+ channels in prostate cancer cells]

Among voltage-gated Ca²⁺ channels, T-type Ca²⁺ channels, which are activated by low voltages, regulate neuronal excitability, spontaneous neurotransmitter release, hormone secretion, etc. and also participate in proliferation of distinct cancer cells. Among three isoforms of T-type Ca²⁺ channels, Ca_v3.2 is detectable in 100% of biopsy samples from prostate cancer patients. In general, prostate cancer cells are highly sensitive to androgen deprivation therapy, but often acquire hormone-therapy resistance. The androgen deprivation may trigger neuroendocrine (NE)-like differentiation of some prostate cancer cells. We have analyzed the expression and function of Ca_v3.2 in human prostate cancer LNCaP cells during NE-like differentiation. NE-like LNCaP cells overexpress Ca_v3.2 through the CREB/Egr-1 pathway and also cystathionine-γ-lyase (CSE), which generates H₂S that enhances the channel activity of Ca_v3.2. H₂S generated by upregulated CSE appears to enhance the activity of upregulated Ca_v3.2 after the differentiation. The enhanced Ca_v3.2 activity in NE-like cells may contribute to increased secretion of mitogenic factors essential for androgen-independent proliferation of surrounding prostate cancer cells. It is known that increased extracellular glucose levels enhance Ca_v3.2 activity through asparagine (N)-linked glycosylation of Ca_v3.2, which might contribute to diabetic neuropathy. We then found that high glucose accelerates the enhanced channel function and overexpression of Ca_v3.2 in NE-like LNCaP cells, which might be associated with clinical evidence for diabetes-related poor prognosis of prostate cancer and development of hormone therapy resistance. Thus, Ca_v3.2 is considered to play a role in the pathophysiology of prostate cancer, and may serve as a therapeutic target.

Prenylflavanones as Novel T-Type Calcium Channel Blockers Useful for Pain Therapy

Prenylated flavonoids have attracted much attention due to their promising and diverse bioactivities on multitarget tissues. To the best of our knowledge, our recent studies demonstrated first that (2 S)-6-prenylnaringenin (6-PNG), a hop component, blocks Cav3.2 T-type calcium channels (T-channels) and alleviates neuropathic and visceral pain with little side effects; it also indicated first that other natural prenylflavanones (PFVNs), such as sophoraflavanone G and (2 S)-8-PNG, or synthetic 6-PFVNs including (2 R/S)-6-PNG and its derivatives are capable of blocking T-channels and useful for pain therapy. Through the structure-activity relationship studies on the synthetic 6-PFVNs, we identified 6-(3-ethylpent-2-enyl)-5,7-dihydroxy-2-(2-hydroxyphenyl)chroman-4-one (8j or KTt-45) as the most potent blocker of Cav3.2 T-channels. It is interesting to recognize a prenylated flavonoid, belonging to other sub-classes, as a novel T-channel blocker. Therefore, this article will review some of our recent studies to introduce a new branch to researchers studying on prenylated flavonoids.

Genetic deletion of Cav3.2 T-type calcium channels abolishes H2S-dependent somatic and visceral pain signaling in C57BL/6 mice

We tested whether genetic deletion of Ca_v3.2 T-type Ca²⁺ channels abolishes hydrogen sulfide (H₂S)-mediated pain signals in mice. In Ca_v3.2-expressing HEK293 cells, Na₂S, an H₂S donor, at 100 μM clearly increased Ba²⁺ currents, as assessed by whole-cell patch-clamp recordings. In wild-type C57BL/6 mice, intraplantar and intracolonic administration of Na₂S evoked mechanical allodynia and visceral nociceptive behavior, respectively, which were abolished by TTA-A2, a T-type Ca²⁺ channel blocker. In Ca_v3.2-knockout mice of a C57BL/6 background, Na₂S caused neither somatic allodynia nor colonic nociception. Our study thus provides definitive evidence for an essential role of Ca_v3.2 in H₂S-dependent somatic and colonic pain.

NNC 55-0396, a T-type calcium channel blocker, protects against the brain injury induced by middle cerebral artery occlusion and reperfusion in mice

We tested whether NNC 55-0396 (NNC), a T-type calcium channel (T-channel) blocker, reduces the brain injury caused by middle cerebral artery occlusion and reperfusion (MCAO/R) in mice. NNC, administered i.c.v. before the occlusion, greatly reduced the MCAO/R-induced brain infarct and neurological dysfunctions, although it, given toward the end of occlusion, was less effective. Systemic administration of NNC before the occlusion also attenuated the infarct and neurological dysfunctions. Our data imply that blood-brain-barrier-permeable T-channel blockers such as NNC are capable of reducing MCAO/R-induced brain damage, and that T-channels are involved in neuronal damage induced by ischemia rather than reperfusion.

Dietary ascorbic acid restriction in GNL/SMP30-knockout mice unveils the role of ascorbic acid in regulation of somatic and visceral pain sensitivity

Ca_v3.2 T-type Ca²⁺ channels are expressed in the primary afferents and play a pronociceptive role. The activity of Ca_v3.2 is enhanced by H₂S, a gasotransmitter, and suppressed by ascorbic acid (vitamin C) through metal-catalyzed oxidation of the Zn²⁺-binding His¹⁹¹ in Ca_v3.2. Since rodents, but not humans, are capable of synthesizing ascorbic acid, the present study examined the role of ascorbic acid in nociceptive processing, using the mice lacking GNL/SMP30, an enzyme essential for ascorbic acid biosynthesis. Intraplantar and intracolonic administration of NaHS, an H₂S donor, caused somatic allodynia and referred hyperalgesia, respectively, and repeated treatment with paclitaxel produced neuropathic allodynia in wild-type mice, all of which were suppressed by ascorbic acid or T-type Ca²⁺ channel blockers. Dietary ascorbic acid restriction caused dramatic decreases in plasma and tissue ascorbic acid levels in GNL/SMP30-knockout, but not wild-type, mice. The ascorbic acid restriction enhanced the somatic and visceral hypersensitivity following intraplantar and intracolonic NaHS, respectively, and paclitaxel-induced neuropathy in GNL/SMP30-knockout mice, while it had no such effect in wild-type mice. Together, our data unveil the critical role of ascorbic acid in regulating somatic and visceral pain sensitivity and support accumulating clinical evidence for the usefulness of ascorbic acid in pain management.

[Regulation of Cav3.2-mediated pain signals by hydrogen sulfide]

Hydrogen sulfide (H₂S), an endogenous gasotransmitter, is generated from L-cysteine by 3 distinct enzymes including cystathionine-γ-lyase (CSE), and targets multiple molecules, thereby playing various roles in health and disease. H₂S triggers or accelerates somatic pain and visceral nociceptive signals in the pancreas, colon and bladder by enhancing the activity of Ca_v3.2 T-type calcium channels. H₂S also activates TRPA1, which participates in H₂S-induced somatic pain signaling. However, Ca_v3.2 predominantly mediates colonic nociception by H₂S, because genetic deletion of TRPA1 does not reduce H₂S-induced colonic pain. The functional upregulation of the CSE/H₂S/Ca_v3.2 system is involved in neuropathic pain and visceral pain accompanying pancreatitis and cystitis. Ca_v3.2 also appears to participate in irritable bowel syndrome (IBS), although the role of endogenous H₂S generation by CSE in IBS is still open to question. In this review, we describe how H₂S regulates pain signals, particularly by interacting with Ca_v3.2.

Critical role of Cav3.2 T-type calcium channels in the peripheral neuropathy induced by bortezomib, a proteasome-inhibiting chemotherapeutic agent, in mice

Bortezomib, a first-line agent for treatment of multiple myeloma, exhibits anticancer activity through proteasome inhibition. However, bortezomib-induced peripheral neuropathy (BIPN) is one of the most serious side effects. Since decreased proteasomal degradation of Ca_v3.2 T-type calcium channels in the primary afferents is involved in persistent pain, we investigated whether BIPN involves increased protein levels of Ca_v3.2 in mice. Six repeated i.p. administrations of bortezomib for 12 days developed persistent mechanical allodynia. Systemic administration of novel T-type calcium channel blockers, (2R/S)-6-prenylnaringenin and KTt-45, and of TTA-A2, the well-known blocker, reversed the BIPN. Ascorbic acid, known to block Ca_v3.2, but not Ca_v3.1 or 3.3, and silencing of Ca_v3.2 gene also suppressed BIPN. Protein levels of Ca_v3.2 in the dorsal root ganglion (DRG) at L4-L6 levels increased throughout days 1-21 after the onset of bortezomib treatment. Protein levels of USP5, a deubiquitinating enzyme that specifically inhibits proteasomal degradation of Ca_v3.2, increased in DRG on days 3-21, but not day 1, in bortezomib-treated mice. In DRG-derived ND7/23 cells, bortezomib increased protein levels of Ca_v3.2 and T-channel-dependent currents, as assessed by a patch-clamp method, but did not upregulate expression of Ca_v3.2 mRNA or USP5 protein. MG-132, another proteasome inhibitor, also increased Ca_v3.2 protein levels in the cultured cells. Given the previous evidence for USP5 induction following nociceptor excitation, our data suggest that BIPN involves the increased protein levels of Ca_v3.2 in nociceptors through inhibition of proteasomal degradation of Ca_v3.2 by bortezomib itself and then by USP5 that is upregulated probably in an activity-dependent manner.

Paclitaxel-induced HMGB1 release from macrophages and its implication for peripheral neuropathy in mice: Evidence for a neuroimmune crosstalk

Given our recent evidence for the role of high mobility group box 1 (HMGB1) in chemotherapy-induced peripheral neuropathy (CIPN) in rats, we examined the origin of HMGB1 and the upstream and downstream mechanisms of HMGB1 release involved in paclitaxel-induced neuropathy in mice. Paclitaxel treatment developed mechanical allodynia in mice, as assessed by von Frey test, which was prevented by an anti-HMGB1-neutralizing antibody or thrombomodulin alfa capable of inactivating HMGB1. RAGE or CXCR4 antagonists, ethyl pyruvate or minocycline, known to inhibit HMGB1 release from macrophages, and liposomal clodronate, a macrophage depletor, prevented the paclitaxel-induced allodynia. Paclitaxel caused upregulation of RAGE and CXCR4 in the dorsal root ganglia and macrophage accumulation in the sciatic nerve. In macrophage-like RAW264.7 cells, paclitaxel evoked cytoplasmic translocation of nuclear HMGB1 followed by its extracellular release, and overexpression of CBP and PCAF, histone acetyltransferases (HATs), known to cause acetylation and cytoplasmic translocation of HMGB1, which were suppressed by ethyl pyruvate, N-acetyl-l-cysteine, an anti-oxidant, and SB203580 and PDTC, inhibitors of p38 MAP kinase (p38MAPK) and NF-κB, respectively. Paclitaxel increased accumulation of reactive oxygen species (ROS) and phosphorylation of p38MAPK, NF-κB p65 and I-κB in RAW264.7 cells. In mice, N-acetyl-l-cysteine or PDTC prevented the paclitaxel-induced allodynia. Co-culture of neuron-like NG108-15 cells or stimulation with their conditioned medium promoted paclitaxel-induced HMGB1 release from RAW264.7 cells. Our data indicate that HMGB1 released from macrophages through the ROS/p38MAPK/NF-κB/HAT pathway participates in the paclitaxel-induced peripheral neuropathy in mice, and unveils an emerging therapeutic avenue targeting a neuroimmune crosstalk in CIPN.

Involvement of Voltage-Gated Calcium Channels in Inflammation and Inflammatory Pain

Voltage-gated calcium channels (VGCCs) are classified into high-voltage-activated (HVA) channels and low-voltage-activated channels consisting of Ca_v3.1-3.3, known as T ("transient")-type VGCC. There is evidence that certain types of HVA channels are involved in neurogenic inflammation and inflammatory pain, in agreement with reports indicating the therapeutic effectiveness of gabapentinoids, ligands for the α₂δ subunit of HVA, in treating not only neuropathic, but also inflammatory, pain. Among the Ca_v3 family members, Ca_v3.2 is abundantly expressed in the primary afferents, regulating both neuronal excitability at the peripheral terminals and spontaneous neurotransmitter release at the spinal terminals. The function and expression of Ca_v3.2 are modulated by a variety of inflammatory mediators including prostanoids and hydrogen sulfide (H₂S), a gasotransmitter. The increased activity of Ca_v3.2 by H₂S participates in colonic, bladder and pancreatic pain, and regulates visceral inflammation. Together, VGCCs are involved in inflammation and inflammatory pain, and Ca_v3.2 T-type VGCC is especially a promising therapeutic target for the treatment of visceral inflammatory pain in patients with irritable bowel syndrome, interstitial cystitis/bladder pain syndrome, pancreatitis, etc., in addition to neuropathic pain.

Design and synthesis of novel anti-hyperalgesic agents based on 6-prenylnaringenin as the T-type calcium channel blockers

Since 6-prenylnaringenin (6-PNG) was recently identified as a novel T-type calcium channel blocker with the IC₅₀ value around 1 µM, a series of flavanone derivatives were designed, synthesized and subsequently evaluated for T-channel-blocking activity in HEK293 cells transfected with Ca_v3.2 T-type channels using a patch-clamp technique. As a result, several new flavanones blocked Ca_v3.2-dependent T-currents more potently than 6-PNG. In the synthesized compounds, 6-(3-ethylpent-2-enyl)-5,7-dihydroxy-2-(2-hydroxyphenyl)chroman-4-one 8j, 6-(3-ethylpent-2-enyl)-5,7-dihydroxy-2-(4-hydroxyphenyl)chroman-4-one 11b, 6-(2-cyclopentylideneethyl)-5,7-dihydroxy-2-(4-hydroxyphenyl)chroman-4-one 11d, and 6-(2-Cyclopentylethyl)-5,7-dihydroxy-2-(4-hydroxyphenyl)chroman-4-one 12c were more potent blocker than 6-PNG with the IC₅₀ value of 0.39, 0.26, 0.46, and 0.50 µM, respectively. Among the above four derivatives, the compound 8j provided the best result in the in vivo experiments; i.e. systemic administration of 8j at the minimum dose completely restored neuropathic pain induced by partial sciatic nerve ligation in mice.

Blockade of T-type calcium channels by 6-prenylnaringenin, a hop component, alleviates neuropathic and visceral pain in mice

Since Ca_v3.2 T-type Ca²⁺ channels (T-channels) expressed in the primary afferents and CNS contribute to intractable pain, we explored T-channel-blocking components in distinct herbal extracts using a whole-cell patch-clamp technique in HEK293 cells stably expressing Ca_v3.2 or Ca_v3.1, and purified and identified sophoraflavanone G (SG) as an active compound from SOPHORAE RADIX (SR). Interestingly, hop-derived SG analogues, (2S)-6-prenylnaringenin (6-PNG) and (2S)-8-PNG, but not naringenin, also blocked T-channels; IC₅₀ (μM) of SG, (2S)-6-PNG and (2S)-8-PNG was 0.68-0.75 for Ca_v3.2 and 0.99-1.41 for Ca_v3.1. (2S)-6-PNG and (2S)-8-PNG, but not SG, exhibited reversible inhibition. The racemic (2R/S)-6-PNG as well as (2S)-6-PNG potently blocked Ca_v3.2, but exhibited minor effect on high-voltage-activated Ca²⁺ channels and voltage-gated Na⁺ channels in differentiated NG108-15 cells. In mice, the mechanical allodynia following intraplantar (i.pl.) administration of an H₂S donor was abolished by oral or i.p. SR extract and by i.pl. SG, (2S)-6-PNG or (2S)-8-PNG, but not naringenin. Intraperitoneal (2R/S)-6-PNG strongly suppressed visceral pain and spinal ERK phosphorylation following intracolonic administration of an H₂S donor in mice. (2R/S)-6-PNG, administered i.pl. or i.p., suppressed the neuropathic allodynia induced by partial sciatic nerve ligation or oxaliplatin, an anti-cancer agent, in mice. (2R/S)-6-PNG had little or no effect on open-field behavior, motor performance or cardiovascular function in mice, and on the contractility of isolated rat aorta. (2R/S)-6-PNG, but not SG, was detectable in the brain after their i.p. administration in mice. Our data suggest that 6-PNG, a hop component, blocks T-channels, and alleviates neuropathic and visceral pain with little side effects.

Involvement of the cystathionine-γ-lyase/Cav3.2 pathway in substance P-induced bladder pain in the mouse, a model for nonulcerative bladder pain syndrome

Hydrogen sulfide (H₂S) formed by cystathionine-γ-lyase (CSE) enhances the activity of Ca_v3.2 T-type Ca²⁺ channels, contributing to the bladder pain accompanying hemorrhagic cystitis caused by systemic administration of cyclophosphamide (CPA) in mice. Given clinical and fundamental evidence for the involvement of the substance P/NK₁ receptor systems in bladder pain syndrome (BPS)/interstitial cystitis (IC), we created an intravesical substance P-induced bladder pain model in mice and analyzed the possible involvement of the CSE/Ca_v3.2 pathway. Bladder pain/cystitis was induced by i.p. CPA or intravesical substance P in female mice. Bladder pain was evaluated by counting nociceptive behavior and by detecting referred hyperalgesia in the lower abdomen and hindpaw. The isolated bladder tissue was weighed to estimate bladder swelling and subjected to histological observation and Western blotting. Intravesical substance P caused profound referred hyperalgesia accompanied by little bladder swelling or edema 6-24 h after the administration, in contrast to i.p. CPA-induced nociceptive behavior/referred hyperalgesia with remarkable bladder swelling/edema and urothelial damage. The bladder pain and/or cystitis symptoms caused by substance P or CPA were prevented by the NK₁ receptor antagonist. CSE in the bladder was upregulated by substance P or CPA, and the NK₁ antagonist prevented the CPA-induced CSE upregulation. A CSE inhibitor, a T-type Ca²⁺ channel blocker and gene silencing of Ca_v3.2 abolished the intravesical substance P-induced referred hyperalgesia. The intravesical substance P-induced pain in mice is useful as a model for nonulcerative BPS, and involves the activation of the NK₁ receptor/CSE/H₂S/Ca_v3.2 cascade.

Involvement of NF-κB in the upregulation of cystathionine-γ-lyase, a hydrogen sulfide-forming enzyme, and bladder pain accompanying cystitis in mice

Hydrogen sulfide (H₂ S) is generated from l-cysteine by multiple enzymes including cystathionine-γ-lyase (CSE), and promotes nociception by targeting multiple molecules such as Ca_v 3.2 T-type Ca²⁺ channels. Bladder pain accompanying cyclophosphamide (CPA)-induced cystitis in mice has been shown to involve the functional upregulation of the CSE/H₂ S/Ca_v 3.2 pathway. Therefore, we investigated whether NF-κB, as an upstream signal of the CSE/H₂ S system, contributes to bladder pain in mice with CPA-induced cystitis. Bladder pain-like nociceptive behaviour was observed in CPA-treated mice, and referred hyperalgesia was evaluated by the von Frey test. Isolated bladder weights were assessed to estimate bladder swelling, and protein levels were measured by Western blotting. CPA, administered intraperitoneally, induced nociceptive behaviour, referred hyperalgesia and increased bladder weights in mice. β-Cyano-l-alanine, a reversible selective CSE inhibitor, prevented CPA-induced nociceptive behaviour, referred hyperalgesia, and, in part, increases in bladder weight. CPA markedly increased phosphorylated NF-κB p65 levels in the bladder, an effect that was prevented by pyrrolidine dithiocarbamate (PDTC), an NF-κB inhibitor. PDTC and curcumin, which inhibits NF-κB signals, abolished CPA-induced nociceptive behaviour, referred hyperalgesia and, in part, increases in bladder weight. CPA caused the overexpression of CSE in the bladder, and this was prevented by PDTC or curcumin. The CPA-induced activation of NF-κB signals appeared to cause CSE overexpression in the bladder, contributing to bladder pain and in part swelling, possibly through H₂ S/Ca_v 3.2 signaling. Therefore, NF-κB-inhibiting compounds including curcumin may be useful for the treatment of cystitis-related bladder pain.

Tacrolimus Triggers Transient Receptor Potential Vanilloid-1-Dependent Relapse of Pancreatitis-Related Pain in Mice

Transient receptor potential vanilloid-1 (TRPV1) expressed in nociceptors is directly phosphorylated and activated by protein kinase C, and involved in the signaling of pancreatic pain. On the other hand, Cav3.2 T-type Ca2+ channels expressed in nociceptors are functionally upregulated by phosphorylation with protein kinase A and also play a role in pancreatitis-related pain. Calcineurin, a phosphatase, negatively regulates various channel functions including TRPV1, and calcineurin inhibitor-induced pain syndrome by tacrolimus, a calcineurin inhibitor, used as an immunosuppressant, has been a clinical problem. We thus examined the effect of tacrolimus on pancreatitis-related pain in mice. Repeated treatment with cerulein caused referred hyperalgesia accompanying acute pancreatitis, which was unaffected by tacrolimus. Pancreatitis-related symptoms disappeared in 24 h, whereas the referred hyperalgesia recurred following the administration of tacrolimus, which was abolished by the blockers of TRPV1 but not T-type Ca2+ channels. Thus, tacrolimus appears to cause the TRPV1-dependent relapse of pancreatitis-related pain, suggesting the involvement of calcineurin in the termination of pancreatic pain.

Repeated Cold Stress Reduces Cyclophosphamide-Induced Cystitis/Bladder Pain and Macrophage Activity in Mice

We examined the effect of repeated cold (RC) stress on cyclophosphamide (CPA)-induced cystitis/bladder pain in mice, in relation to macrophage activity. CPA, given i.p. at 400 mg/kg, caused bladder pain symptoms accompanying cystitis in both unstressed and RC-stressed mice, which were prevented by the macrophage inhibitor minocycline. A low dose, that is, 200 mg/kg, of CPA still produced bladder pain symptoms in unstressed but not RC-stressed mice. Lipopolysaccharide-induced cytokine production in peritoneal macrophages from RC-stressed mice was less than that from unstressed mice. Thus, RC stress appears to reduce CPA-induced bladder pain in mice, which may be associated with the decreased macrophage activity.

Endogenous Hydrogen Sulfide Enhances Cell Proliferation of Human Gastric Cancer AGS Cells

Hydrogen sulfide (H2S), the third gasotransmitter, is endogenously generated by certain H2S synthesizing enzymes, including cystathionine-γ-lyase (CSE) and cystathionine-β-synthase (CBS) from L-cysteine in the mammalian body. Several studies have shown that endogenous and exogenous H2S affects the proliferation of cancer cells, although the effects of H2S appear to vary with cell type, being either promotive or suppressive. In the present study, we determined whether endogenously formed H2S regulates proliferation in human gastric cancer AGS cells. CSE, but not CBS, was expressed in AGS cells. CSE inhibitors, DL-propargylglycine (PPG) and β-cyano-L-alanine (BCA), significantly suppressed the proliferation of AGS cells in a concentration-dependent manner. CSE inhibitors did not increase lactate dehydrogenase (LDH) release in the same concentration range. The inhibitory effects of PPG and BCA on cell proliferation were reversed by repetitive application of NaHS, a donor of H2S. Interestingly, nuclear condensation and fragmentation were detected in AGS cells treated with PPG or BCA. These results suggest that endogenous H2S produced by CSE may contribute to the proliferation of gastric cancer AGS cells, most probably through anti-apoptotic actions.

Involvement of high mobility group box 1 in the development and maintenance of chemotherapy-induced peripheral neuropathy in rats

Given that high mobility group box 1 (HMGB1), a nuclear protein, once released to the extracellular space, promotes nociception, we asked if inactivation of HMGB1 prevents or reverses chemotherapy-induced painful neuropathy in rats and also examined possible involvement of Toll-like receptor 4 (TLR4) and the receptor for advanced glycation endproduct (RAGE), known as targets for HMGB1. Painful neuropathy was produced by repeated i.p. administration of paclitaxel or vincristine in rats. Nociceptive threshold was determined by the paw pressure method and/or von Frey test in the hindpaw. Tissue protein levels were determined by immunoblotting. Repeated i.p. administration of the anti-HMGB1-neutralizing antibody or recombinant human soluble thrombomodulin (rhsTM), known to inactivate HMGB1, prevented the development of hyperalgesia and/or allodynia induced by paclitaxel or vincristine in rats. A single i.p. or intraplantar (i.pl.) administration of the antibody or rhsTM reversed the chemotherapy-induced neuropathy. A single i.pl. administration of a TLR4 antagonist or low molecular weight heparin, known to inhibit RAGE, attenuated the hyperalgesia caused by i.pl. HMGB1 and also the chemotherapy-induced painful neuropathy. Paclitaxel or vincristine treatment significantly decreased protein levels of HMGB1 in the dorsal root ganglia, but not sciatic nerves. HMGB1 thus participates in both development and maintenance of chemotherapy-induced painful neuropathy, in part through RAGE and TLR4. HMGB1 inactivation is considered useful to prevent and treat the chemotherapy-induced painful neuropathy.

The prostaglandin E2/EP4 receptor/cyclic AMP/T-type Ca(2+) channel pathway mediates neuritogenesis in sensory neuron-like ND7/23 cells

We investigated mechanisms for the neuritogenesis caused by prostaglandin E2 (PGE2) or intracellular cyclic AMP (cAMP) in sensory neuron-like ND7/23 cells. PGE2 caused neuritogenesis, an effect abolished by an EP4 receptor antagonist or inhibitors of adenylyl cyclase (AC) or protein kinase A (PKA) and mimicked by the AC activator forskolin, dibutyryl cAMP (db-cAMP), and selective activators of PKA or Epac. ND7/23 cells expressed both Cav3.1 and Cav3.2 T-type Ca(2+) channels (T-channels). The neuritogenesis induced by db-cAMP or PGE2 was abolished by T-channel blockers. T-channels were functionally upregulated by db-cAMP. The PGE2/EP4/cAMP/T-channel pathway thus appears to mediate neuritogenesis in sensory neurons.

Selective sensitization of C-fiber nociceptors by hydrogen sulfide

We examined the effects of intraplantar (i.pl.) administration of NaHS, an H2S donor, known to cause T-type Ca(2+) channel (T-channel)-dependent mechanical hyperalgesia, on responsiveness to electric stimulation with 5, 250 and 2000 Hz sine waves (SW) that selectively excites C, Aδ and Aβ fibers, respectively. NaHS, given i.pl., caused behavioral hypersensitivity to SW stimulation at 5 Hz, but not 250 or 2000 Hz, in rats. NaHS also enhanced phosphorylation of spinal ERK following 5 Hz SW stimulation. Three distinct T-channel blockers abolished the NaHS-induced behavioral hypersensitivity to 5 Hz SW stimulation. Thus, H2S selectively sensitizes C-fiber nociceptors via T-channels.