Exploring Serum Biomarkers for Neuropathic Pain in Rat Models of Chemotherapy-Induced Peripheral Neuropathy: A Comparative Pilot Study with Oxaliplatin, Paclitaxel, Bortezomib, and Vincristine

Blood biomarkers, including neurofilament light chain (NfL), have garnered attention as potential indicators for chemotherapy-induced peripheral neuropathy (CIPN), a dose-limiting adverse effect of neurotoxic anticancer drugs. However, no blood biomarker has been established for routine application or translational research. This pilot study aimed to evaluate a limited panel of blood biomarkers in rat models of CIPN and their correlations with neuropathic pain. CIPN models were induced through repeated injections of oxaliplatin, paclitaxel, bortezomib, and vincristine. Electronic von Frey testing was used to assess tactile allodynia. Post anticancer injections, serum concentrations of 31 proteins were measured. Allodynia thresholds decreased in anticancer-treated animals compared to controls. No consistent modifications were observed in the biomarkers across CIPN models. The most noteworthy biomarkers with increased concentrations in at least two CIPN models were NfL (paclitaxel, vincristine), MCP-1, and RANTES (oxaliplatin, vincristine). Vincristine-treated animals exhibited strong correlations between LIX, MCP-1, NfL, and VEGF concentrations and tactile allodynia thresholds. No single biomarker can be recommended as a unique indicator of CIPN-related pain. Because of the study limitations (single dose of each anticancer drug, young animals, and single time measurement of biomarkers), further investigations are necessary to define the kinetics, specificities, and sensitivities of MCP-1, RANTES, and NfL.

Neurofilament light chain in plasma as a sensitive diagnostic biomarker of peripheral neurotoxicity: In Vivo mouse studies with oxaliplatin and paclitaxel - NeuroDeRisk project

Identifying compounds that are neurotoxic either toward the central or the peripheral nervous systems (CNS or PNS) would greatly benefit early stages of drug development by derisking liabilities and selecting safe compounds. Unfortunately, so far assays mostly rely on histopathology findings often identified after repeated-dose toxicity studies in animals. The European NeuroDeRisk project aimed to provide comprehensive tools to identify compounds likely inducing neurotoxicity. As part of this project, the present work aimed to identify diagnostic non-invasive biomarkers of PNS toxicity in mice. We used two neurotoxic drugs in vivo to correlate functional, histopathological and biological findings. CD1 male mice received repeated injections of oxaliplatin or paclitaxel followed by an assessment of drug exposure in CNS/PNS tissues. Functional signs of PNS toxicity were assessed using electronic von Frey and cold paw immersion tests (oxaliplatin), and functional observational battery, rotarod and cold plate tests (paclitaxel). Plasma concentrations of neurofilament light chain (NF-L) and vascular endothelial growth factor A (VEGF-A) were measured, and histopathological evaluations were performed on a comprehensive list of CNS and PNS tissues. Functional PNS toxicity was observed only in oxaliplatin-treated mice. Histopathological findings were observed dose-dependently only in paclitaxel groups. While no changes of VEGF-A concentrations was recorded, NF-L concentrations were increased only in paclitaxel-treated animals as early as 7 days after the onset of drug administration. These results show that plasma NF-L changes correlated with microscopic changes in the PNS, thus strongly suggesting that NF-L could be a sensitive and specific biomarker of PNS toxicity in mice.

Analgesic and preventive effects of donepezil in animal models of chemotherapy-induced peripheral neuropathy: Involvement of spinal muscarinic acetylcholine M2 receptors

BACKGROUND

Donepezil, a cholinesterase inhibitor approved in Alzheimer's disease, has demonstrated analgesic and preventive effects in animal models of oxaliplatin-induced neuropathy. To improve the clinical interest of donepezil for the management and prevention of chemotherapy-induced peripheral neuropathy (CIPN), a broader validation is required in different animal models of CIPN.

METHODS

using rat models of CIPN (bortezomib, paclitaxel, and vincristine), the analgesic and preventive efficacies of donepezil were evaluated on tactile, cold and heat hypersensitivities. The involvement of muscarinic M2 acetylcholine receptors (m2AChRs) in analgesic effects was investigated at the spinal level. The absence of interference of donepezil with the cytotoxic effect of chemotherapy has been controlled in cancer cell lines.

RESULTS

the analgesic efficacy of donepezil was demonstrated for all CIPN models, mainly on tactile hypersensitivity (maximal efficacy at 60 min, p < 0.05 vs. vehicle group). This effect was suppressed by an intrathecal injection of methoctramine (m2AChR antagonist). Regarding preventive effects, donepezil limited tactile hypersensitivity induced by paclitaxel, but not for other CIPN models. Donepezil did not modify the viability of cancer cells or the efficacy of anticancer drugs.

CONCLUSIONS

donepezil had a broad analgesic effect on animal models of CIPN and this effect involved spinal m2AChRs. This work validates the repositioning of donepezil in the management of CIPN.

Colorectal Cancer Survivors Suffering From Sensory Chemotherapy-Induced Peripheral Neuropathy Are Not a Homogenous Group: Secondary Analysis of Patients' Profiles With Oxaliplatin-Induced Peripheral Neuropathy

Oxaliplatin, a pivotal drug in the management of colorectal cancer, causes chemotherapy-induced peripheral neuropathy (CIPN) in a third of cancer survivors. Based on a previous cross-sectional study assessing oxaliplatin-related sensory CIPN in colorectal cancer survivors, a secondary analysis was designed to explore the possibility that different clusters of patients may co-exist among a cohort of patients with oxaliplatin-related CIPN. Other objectives were to characterize these clusters considering CIPN severity, anxiety, depression, health-related quality of life (HRQOL), patients’ characteristics and oxaliplatin treatments. Among the 96 patients analyzed, three clusters were identified (cluster 1: 52, cluster 2: 34, and cluster 3: 10 patients). Clusters were significantly different according to CIPN severity and the proportion of neuropathic pain (cluster 1: low, cluster 2: intermediate, and cluster 3: high). Anxiety, depressive disorders and HRQOL alteration were lower in cluster 1 in comparison to clusters 2 and 3, but not different between clusters 2 and 3. This study underlines that patients with CIPN are not a homogenous group, and that CIPN severity is associated with psychological distress and a decline of HRQOL. Further studies are needed to explore the relation between clusters and CIPN management.

Epigenetics Involvement in Oxaliplatin-Induced Potassium Channel Transcriptional Downregulation and Hypersensitivity

Peripheral neuropathy is the most frequent dose-limiting adverse effect of oxaliplatin. Acute pain symptoms that are induced or exacerbated by cold occur in almost all patients immediately following the first infusions. Evidence has shown that oxaliplatin causes ion channel expression modulations in dorsal root ganglia neurons, which are thought to contribute to peripheral hypersensitivity. Most dysregulated genes encode ion channels involved in cold and mechanical perception, noteworthy members of a sub-group of potassium channels of the K2P family, TREK and TRAAK. Downregulation of these K2P channels has been identified as an important tuner of acute oxaliplatin-induced hypersensitivity. We investigated the molecular mechanisms underlying this peripheral dysregulation in a murine model of neuropathic pain triggered by a single oxaliplatin administration. We found that oxaliplatin-mediated TREK-TRAAK downregulation, as well as downregulation of other K+ channels of the K2P and Kv families, involves a transcription factor known as the neuron-restrictive silencer factor (NRSF) and its epigenetic co-repressors histone deacetylases (HDACs). NRSF knockdown was able to prevent most of these K+ channel mRNA downregulation in mice dorsal root ganglion neurons as well as oxaliplatin-induced acute cold and mechanical hypersensitivity. Interestingly, pharmacological inhibition of class I HDAC reproduces the antinociceptive effects of NRSF knockdown and leads to an increased K+ channel expression in oxaliplatin-treated mice.

Prevalence of Chemotherapy-Induced Peripheral Neuropathy in Multiple Myeloma Patients and its Impact on Quality of Life: A Single Center Cross-Sectional Study

Bortezomib is a pivotal drug for the management of multiple myeloma. However, bortezomib is a neurotoxic anticancer drug responsible for chemotherapy-induced peripheral neuropathy (CIPN). CIPN is associated with psychological distress and a decrease of health-related quality of life (HRQoL), but little is known regarding bortezomib-related CIPN. This single center, cross-sectional study assessed the prevalence and severity of sensory/motor CIPN, neuropathic pain and ongoing pain medications, anxiety, depression, and HRQoL, in multiple myeloma patients after the end of bortezomib treatment. Paper questionnaires were sent to patients to record the scores of sensory and motor CIPNs (QLQ-CIPN20), neuropathic pain (visual analogue scale and DN4 interview), anxiety and depression (HADS), the scores of HRQoL (QLQ-C30 and QLQ-MY20) and ongoing pain medications. Oncological data were recorded using chemotherapy prescription software and patient medical records. The prevalence of sensory CIPN was 26.9% (95% CI 16.7; 39.1) among the 67 patients analyzed and for a mean time of 2.9 ± 2.8 years since the last bortezomib administration. The proportion of sensory CIPN was higher among patients treated by intravenous and subcutaneous routes than intravenous or subcutaneous routes (p = 0.003). QLQ-CIPN20 motor scores were higher for patients with a sensory CIPN than those without (p < 0.001) and were correlated with the duration of treatment and the cumulative dose of bortezomib (coefficient: 0.31 and 0.24, p = 0.01 and 0.0475, respectively), but not sensory scores. Neuropathic pain was screened in 44.4% of patients with sensory CIPN and 66.7% of them had ongoing pain medications, but none were treated with duloxetine (recommended drug). Multivariable analysis revealed that thalidomide treatment (odds-ratio: 6.7, 95% CI 1.3; 35.5, p = 0.03) and both routes of bortezomib administration (odds-ratio: 13.4, 95% CI 1.3; 139.1, p = 0.03) were associated with sensory CIPN. Sensory and motor CIPNs were associated with anxiety, depression, and deterioration of HRQoL. Sensory CIPN was identified in a quarter of patients after bortezomib treatment and associated with psychological distress that was far from being treated optimally. There is a need to improve the management of patients with CIPN, which may include better training of oncologists regarding its diagnosis and pharmacological treatment.

Prevention, diagnosis and management of chemotherapy-induced peripheral neuropathy: a cross-sectional study of French oncologists' professional practices

PURPOSE

Chemotherapy-induced peripheral neuropathy (CIPN) is challenging for oncologists. Many publications mention the high incidence of CIPN and the lack of effective preventive/management strategies and robust diagnostic tools. This cross-sectional study was aimed at assessing the practice of French oncologists for CIPN prevention, diagnosis and management.

METHODS

This web-based survey was sent to French oncologists by the regional cancer networks. Incidence and impact of CIPN were assessed using visual analogue scales (VAS) and diagnostic strategies were recorded. Also recorded were the drugs used to prevent or manage CIPN and their perceived efficacy and safety (VAS).

RESULTS

Among the 210 oncologists included, the perceived incidence of CIPN was about 36.2 ± 22.1% of patients. About 99.5% of oncologists declared that they assess CIPN during medical follow-up. The use of drugs to prevent CIPN was reported by 9.6% of oncologists (group B vitamins (35.0%) and calcium and magnesium infusion (25.0%)). In the case of CIPN, the therapeutic adjustment of neurotoxic anticancer drugs is performed by 99.0% of oncologists (chemotherapy change (49.8%), dose reduction (30.9%) or interruption (19.3%)). The pharmacological management of CIPN was declared by 72.9% of oncologists. The main drugs used are pregabalin (75.8%), amitriptyline (32.7%) and gabapentin (25.5%). Duloxetine (ASCO recommendation) is used by only 11.8% of oncologists.

CONCLUSION

Oncologists were clearly aware of CIPN risks, but its incidence tended to be underestimated and the ASCO recommendations for the management of CIPN were not followed. The prevention, diagnosis and management of CIPN remain problematic in clinical practice in France.

TRIAL REGISTRATION

ClinicalTrials.gov : NCT03854864.

The Safety of Medications used to Treat Peripheral Neuropathic Pain, Part 2 (Opioids, Cannabinoids and Other Drugs): review of Double-Blind, Placebo-Controlled, Randomized Clinical Trials

INTRODUCTION

Peripheral neuropathic pain is a disabling condition for patients and a challenge for physicians. Although many drugs have been assessed in scientific studies, few have demonstrated clear clinical efficacy against neuropathic pain. Moreover, the paucity of data regarding their safety raises the question of the benefit-risk ratio when used in patients experiencing peripheral neuropathies.

AREAS COVERED

We conducted a review of double-blind, placebo-controlled, randomized clinical trials to assess the safety of medications used to treat peripheral neuropathic pain. This second review was focused on opioids, cannabinoids, and other medications. The aim was to provide an overview of the treatment-emergent adverse events (TEAEs) (≥10%) and the serious adverse effects described in clinical trials.

EXPERT OPINION

Opioids and cannabinoids had significantly more TEAEs than placebos. Locally administered analgesics, such as capsaicin, lidocaine, botulinum toxin A seemed to have the most acceptable safety with only local adverse effects. The results for NMDA antagonists were inconclusive since no safety report was available. Less than half of the studies included presented a good description of TEAEs that included a statistical comparison versus a placebo group. Major methodological improvements must be made to ameliorate the assessment of medication safety in future clinical trials.

TREK1 channel activation as a new analgesic strategy devoid of opioid adverse effects

BACKGROUND AND PURPOSE

Opioids are effective painkillers. However, their risk-benefit ratio is dampened by numerous adverse effects and opioid misuse has led to a public health crisis. Safer alternatives are required, but isolating the antinociceptive effect of opioids from their adverse effects is a pharmacological challenge because activation of the μ opioid receptor triggers both the antinociceptive and adverse effects of opioids.

EXPERIMENTAL APPROACH

The TREK1 potassium channel is activated downstream of μ receptor and involved in the antinociceptive activity of morphine but not in its adverse effects. Bypassing the μ opioid receptor to directly activate TREK1 could therefore be a safer analgesic strategy.

KEY RESULTS

We developed a selective TREK1 activator, RNE28, with antinociceptive activity in naive rodents and in models of inflammatory and neuropathic pain. This activity was lost in TREK1 knockout mice or wild-type mice treated with the TREK1 blocker spadin, showing that TREK1 is required for the antinociceptive activity of RNE28. RNE28 did not induce respiratory depression, constipation, rewarding effects, or sedation at the analgesic doses tested.

CONCLUSION AND IMPLICATIONS

This proof-of-concept study shows that TREK1 activators could constitute a novel class of painkillers, inspired by the mechanism of action of opioids but devoid of their adverse effects.

The safety of medications used to treat peripheral neuropathic pain, part 1 (antidepressants and antiepileptics): review of double-blind, placebo-controlled, randomized clinical trials

INTRODUCTION

Peripheral neuropathic pain is a highly disabling condition for patients and a challenge for neurologists and pain physicians. Although many drugs have been assessed in scientific studies, few have demonstrated a clear clinical efficacy against neuropathic pain. Moreover, the paucity of data regarding their safety raised the question on the benefit-risk ratio when used in patients experiencing peripheral neuropathies.

AREAS COVERED

The authors conducted a review of double-blind, placebo-controlled, randomized clinical trials to assess the safety of medications used to treat neuropathic pain. This first review was focused on antidepressant and antiepileptic medications. The aim was to provide an overview of the treatment-emergent adverse events (≥10%) and the serious adverse effects described in clinical trials.

EXPERT OPINION

Among antiepileptics and antidepressants, duloxetine appeared to have the most detailed safety for the treatment of peripheral neuropathic pain. Over all studies, the most commonly reported adverse effects were dizziness, drowsiness, nausea, and constipation. Only 20.0% of the included studies (N = 90) presented a good description of adverse effects that included a statistical comparison vers usa placebo group. Important methodological improvements must be made to improve the assessment of medication safety in future clinical trials.

Testosterone-androgen receptor: The steroid link inhibiting TRPM8-mediated cold sensitivity

Recent studies have revealed gender differences in cold perception, and pointed to a possible direct action of testosterone (TST) on the cold-activated TRPM8 (Transient Receptor Potential Melastatin Member 8) channel. However, the mechanisms by which TST influences TRPM8-mediated sensory functions remain elusive. Here, we show that TST inhibits TRPM8-mediated mild-cold perception through the noncanonical engagement of the Androgen Receptor (AR). Castration of both male rats and mice increases sensitivity to mild cold, and this effect depends on the presence of intact TRPM8 and AR. TST in nanomolar concentrations suppresses whole-cell TRPM8-mediated currents and single-channel activity in native dorsal root ganglion (DRG) neurons and HEK293 cells co-expressing recombinant TRPM8 and AR, but not TRPM8 alone. AR cloned from rat DRGs shows no difference from standard AR. However, biochemical assays and confocal imaging reveal the presence of AR on the cell surface and its interaction with TRPM8 in response to TST, leading to an inhibition of channel activity.

Replacement of current opioid drugs focusing on MOR-related strategies

The scarcity and limited risk/benefit ratio of painkillers available on the market, in addition to the opioid crisis, warrant reflection on new innovation strategies. The pharmacopoeia of analgesics is based on products that are often old and derived from clinical empiricism, with limited efficacy or spectrum of action, or resulting in an unsatisfactory tolerability profile. Although they are reference analgesics for nociceptive pain, opioids are subject to the same criticism. The use of opium as an analgesic is historical. Morphine was synthesized at the beginning of the 19th century. The efficacy of opioids is limited in certain painful contexts and these drugs can induce potentially serious and fatal adverse effects. The current North American opioid crisis, with an ever-rising number of deaths by opioid overdose, is a tragic illustration of this. It is therefore legitimate to develop research into molecules likely to maintain or increase opioid efficacy while improving their tolerability. Several avenues are being explored including targeting of the mu opioid receptor (MOR) splice variants, developing biased agonists or targeting of other receptors such as heteromers with MOR. Ion channels acting as MOR effectors, are also targeted in order to offer compounds without MOR-dependent adverse effects. Another route is to develop opioid analgesics with peripheral action or limited central nervous system (CNS) access. Finally, endogenous opioids used as drugs or compounds that modify the metabolism of endogenous opioids (Dual ENKephalinase Inhibitors) are being developed. The aim of the present review is to present these various targets/strategies with reference to current indications for opioids, concerns about their widespread use, particularly in chronic non-cancer pains, and ways of limiting the risk of opioid abuse and misuse.

Pharmacogenomics in pain treatment

The experience of chronic pain is one of the commonest reasons for seeking medical attention, being a major issue in clinical practice. While pain is a universal experience, only a small proportion of people who felt pain develop pain syndromes. In addition, painkillers are associated with wide inter-individual variability in the analgesic response. This may be partly explained by the presence of single nucleotide polymorphisms in genes encoding molecular entities involved in pharmacodynamics and pharmacokinetics. However, uptake of this information has been slow due in large part to the lack of robust evidences demonstrating clinical utility. Furthermore, novel therapies, including targeting of epigenetic changes and gene therapy-based approaches are further broadening future options for the treatment of chronic pain. The aim of this article is to review the evidences behind pharmacogenetics (PGx) to individualize therapy (boosting the efficacy and minimizing potential toxicity) and genes implicated in pain medicine, in two parts: (i) genetic variability with pain sensitivity and analgesic response; and (ii) pharmacological concepts applied on PGx.

New Insight in Cold Pain: Role of Ion Channels, Modulation, and Clinical Perspectives

Cold temperature detection involves the process of sensory transduction in cutaneous primary sensory nerve terminals, which converts thermal stimuli into depolarizations of the membrane. This transformation into electrical signals is followed by the subsequent propagation of action potentials in cold-sensitive afferent nerve fibers. A large array of ion channels shapes this process; however, the precise contribution of specific ion channel subtypes to cold perception and cold pain remains elusive. This review aims at giving an update on our current understanding of the role played by TRPs, leak K+ and voltage-gated Na+ and K+ channels in the transduction of cold by nociceptors and in cold-induced pain.

The Nav1.9 channel is a key determinant of cold pain sensation and cold allodynia

Cold-triggered pain is essential to avoid prolonged exposure to harmfully low temperatures. However, the molecular basis of noxious cold sensing in mammals is still not completely understood. Here, we show that the voltage-gated Nav1.9 sodium channel is important for the perception of pain in response to noxious cold. Nav1.9 activity is upregulated in a subpopulation of damage-sensing sensory neurons responding to cooling, which allows the channel to amplify subthreshold depolarizations generated by the activation of cold transducers. Consequently, cold-triggered firing is impaired in Nav1.9(-/-) neurons, and Nav1.9 null mice and knockdown rats show increased cold pain thresholds. Disrupting Nav1.9 expression in rodents also alleviates cold pain hypersensitivity induced by the antineoplastic agent oxaliplatin. We conclude that Nav1.9 acts as a subthreshold amplifier in cold-sensitive nociceptive neurons and is required for the perception of cold pain under normal and pathological conditions.

Peripheral contribution of NGF and ASIC1a to colonic hypersensitivity in a rat model of irritable bowel syndrome

BACKGROUND

Irritable bowel syndrome (IBS) is a functional gastrointestinal disorder associated with idiopathic colonic hypersensitivity (CHS). However, recent studies suggest that low-grade inflammation could underlie CHS in IBS. The pro-inflammatory mediator nerve growth factor (NGF) plays a key role in the sensitization of peripheral pain pathways and several studies have reported its contribution to visceral pain development. NGF modulates the expression of Acid-Sensing Ion Channels (ASICs), which are proton sensors involved in sensory neurons sensitization. This study examined the peripheral contribution of NGF and ASICs to IBS-like CHS induced by butyrate enemas in the rat colon.

METHODS

Colorectal distension and immunohistochemical staining of sensory neurons were used to evaluate NGF and ASICs contribution to the development of butyrate-induced CHS.

KEY RESULTS

Systemic injection of anti-NGF antibodies or the ASICs inhibitor amiloride prevented the development of butyrate-induced CHS. A significant increase in NGF and ASIC1a protein expression levels was observed in sensory neurons of rats displaying butyrate-induced CHS. This increase was specific of small- and medium-diameter L1 + S1 sensory neurons, where ASIC1a was co-expressed with NGF or trkA in CGRP-immunoreactive somas. ASIC1a was also overexpressed in retrogradely labeled colon sensory neurons. Interestingly, anti-NGF antibody administration prevented ASIC1a overexpression in sensory neurons of butyrate-treated rats.

CONCLUSIONS & INFERENCES

Our data suggest that peripheral NGF and ASIC1a concomitantly contribute to the development of butyrate-induced CHS NGF-ASIC1a interplay may have a pivotal role in the sensitization of colonic sensory neurons and as such, could be considered as a potential new therapeutic target for IBS treatment.

Complex modulation of TRPM8 cold receptor by volatile anaesthetics and role in complications of general anaesthesia

The mechanisms by which volatile general anaesthetics (VAs) produce a depression of central nervous system are beginning to be better understood, but little is known about a number of side effects. Here, we show that the cold receptor, TRPM8, is complexly modulated by clinical concentration of VAs in dorsal root ganglion neurons and HEK-293 cells heterologously expressing TRPM8. VAs produced transient enhancement of TRPM8 via a depolarizing shift of its activation towards physiological membrane potentials, followed by a sustained TRPM8 inhibition. Stimulatory action of VAs engaged molecular determinants distinct from those used by the TRPM8 agonist. Transient TRPM8 activation by VAs could explain such side effects as inhibition of respiratory drive, shivering and cooling sensation during the beginning of anaesthesia, whereas the second phase of VA action associated with sustained TRPM8 inhibition may be responsible for hypothermia. Consistent with this, both hypothermia and inhibition of respiratory drive induced by VAs are partially abolished in TRPM8-null animals. Thus, we propose TRPM8 as a new clinical target for diminishing common and serious complications of general anaesthesia.

Nav1.9 channel contributes to mechanical and heat pain hypersensitivity induced by subacute and chronic inflammation

Inflammation is known to be responsible for the sensitization of peripheral sensory neurons, leading to spontaneous pain and invalidating pain hypersensitivity. Given its role in regulating neuronal excitability, the voltage-gated Nav1.9 channel is a potential target for the treatment of pathological pain, but its implication in inflammatory pain is yet not fully described. In the present study, we examined the role of the Nav1.9 channel in acute, subacute and chronic inflammatory pain using Nav1.9-null mice and Nav1.9 knock-down rats. In mice we found that, although the Nav1.9 channel does not contribute to basal pain thresholds, it plays an important role in heat pain hypersensitivity induced by subacute paw inflammation (intraplantar carrageenan) and chronic ankle inflammation (complete Freund's adjuvant-induced monoarthritis). We showed for the first time that Nav1.9 also contributes to mechanical hypersensitivity in both models, as assessed using von Frey and dynamic weight bearing tests. Consistently, antisense-based Nav1.9 gene silencing in rats reduced carrageenan-induced heat and mechanical pain hypersensitivity. While no changes in Nav1.9 mRNA levels were detected in dorsal root ganglia (DRGs) during subacute and chronic inflammation, a significant increase in Nav1.9 immunoreactivity was observed in ipsilateral DRGs 24 hours following carrageenan injection. This was correlated with an increase in Nav1.9 immunolabeling in nerve fibers surrounding the inflamed area. No change in Nav1.9 current density could be detected in the soma of retrolabeled DRG neurons innervating inflamed tissues, suggesting that newly produced channels may be non-functional at this level and rather contribute to the observed increase in axonal transport. Our results provide evidence that Nav1.9 plays a crucial role in the generation of heat and mechanical pain hypersensitivity, both in subacute and chronic inflammatory pain models, and bring new elements for the understanding of its regulation in those models.

Oxaliplatin-induced cold hypersensitivity is due to remodelling of ion channel expression in nociceptors

Cold hypersensitivity is the hallmark of oxaliplatin-induced neuropathy, which develops in nearly all patients under this chemotherapy. To date, pain management strategies have failed to alleviate these symptoms, hence development of adapted analgesics is needed. Here, we report that oxaliplatin exaggerates cold perception in mice as well as in patients. These symptoms are mediated by primary afferent sensory neurons expressing the thermoreceptor TRPM8. Mechanistically, oxaliplatin promotes over-excitability by drastically lowering the expression of distinct potassium channels (TREK1, TRAAK) and by increasing the expression of pro-excitatory channels such as the hyperpolarization-activated channels (HCNs). These findings are corroborated by the analysis of TREK1-TRAAK null mice and use of the specific HCN inhibitor ivabradine, which abolishes the oxaliplatin-induced cold hypersensibility. These results suggest that oxaliplatin exacerbates cold perception by modulating the transcription of distinct ionic conductances that together shape sensory neuron responses to cold. The translational and clinical implication of these findings would be that ivabradine may represent a tailored treatment for oxaliplatin-induced neuropathy.

The transient receptor potential channel TRPM8 is inhibited via the alpha 2A adrenoreceptor signaling pathway

The transient receptor potential channel melastatin member 8 (TRPM8) is expressed in sensory neurons, where it constitutes the main receptor of environmental innocuous cold (10-25 degrees C). Among several types of G protein-coupled receptors expressed in sensory neurons, G(i)-coupled alpha 2A-adrenoreceptor (alpha 2A-AR), is known to be involved in thermoregulation; however, the underlying molecular mechanisms remain poorly understood. Here we demonstrated that stimulation of alpha 2A-AR inhibited TRPM8 in sensory neurons from rat dorsal root ganglia (DRG). In addition, using specific pharmacological and molecular tools combined with patch-clamp current recordings, we found that in heterologously expressed HEK-293 (human embryonic kidney) cells, TRPM8 channel is inhibited by the G(i) protein/adenylate cyclase (AC)/cAMP/protein kinase A (PKA) signaling cascade. We further identified the TRPM8 S9 and T17 as two key PKA phosphorylation sites regulating TRPM8 channel activity. We therefore propose that inhibition of TRPM8 through the alpha 2A-AR signaling cascade could constitute a new mechanism of modulation of thermosensation in both physiological and pathological conditions.

Short-term consumption of a high-sucrose diet has a pro-oxidant effect in rats

The underlying mechanisms for the detrimental consequences of a high-fructose diet in animal models are not clear. However, the possibility exists that fructose feeding facilitates oxidative damage. Thus, the aim of the present study was to assess, in weaning rats, the effect of a high-sucrose diet v. starch diet for 2 weeks on oxidative stress variables. Plasma lipid levels were measured and lipid peroxidation was evaluated by urine and plasma thiobarbituric acid-reactive substances (TBARS). The susceptibilities of several tissues to peroxidation were determined in tissue homogenates after in vitro lipid peroxidation. Antioxidant defence variables were evaluated by measuring plasma and heart vitamin E levels, and heart superoxide dismutase (SOD) and glutathione peroxidase (GPX) activities. Higher plasma triacylglycerol (P<0·01) and TBARS (P<0·01) levels were found in rats fed the sucrose diet as compared with the starch-fed group, whereas plasma α-tocopherol levels were significantly decreased in the sucrose-fed group compared with the starch-fed group (P<0·01). Higher urine TBARS (P<0·01) were found in the sucrose-fed group compared with the starch-fed group, suggesting increased production of these substances from lipid peroxidation in vivo. Higher susceptibility to peroxidation in heart, thymus and pancreas was also found in the sucrose-fed group v. the starch-fed group. No statistical differences were observed for liver TBARS level between the two groups. Heart SOD activity was significantly decreased (P<0·001) in the sucrose-fed group compared with the starch-fed group, whereas heart vitamin E level and GPX activity were not different between the groups. However, the in vitro generation of superoxide radical in heart homogenate, measured by electron spin resonance detection and spin trapping, was not increased in the sucrose-fed group compared with starch-fed rats. Altogether, the results indicate that a short-term consumption of a high-sucrose diet negatively affects the balance of free radical production and antioxidant defence in rats, leading to increased lipid susceptibility to peroxidation.

The carbon monoxide-releasing molecule CORM-2 inhibits the inflammatory response induced by cytokines in Caco-2 cells

BACKGROUND AND PURPOSE

Recent evidence indicates that carbon monoxide-releasing molecules (CO-RMs) exhibit potential anti-inflammatory properties. In the present study, we have investigated whether tricarbonyl dichloro ruthenium(II) dimer (CORM-2) can control the inflammatory response induced by cytokines in a human colonic epithelial cell line, Caco-2.

EXPERIMENTAL APPROACH

Caco-2 cells were preincubated with CORM-2 for 30 minutes and then stimulated with interleukin (IL)-1beta, tumor necrosis factor-alpha and interferon-gamma for different times. Gene expression was analyzed by real-time PCR. Protein expression was investigated by Western blot and ELISA. Transcription factor activation was determined by the luciferase method.

KEY RESULTS

We have shown that CORM-2 significantly decreased the mRNA expression of nitric oxide synthase-2 (NOS-2) and the production of nitrite, in Caco-2 cells stimulated with cytokines. IL-8, IL-6 and metalloproteinase-7 (MMP-7) mRNA and protein were also significantly reduced by CORM-2. Time-course and small interfering RNA studies suggest that inhibition of IL-6 plays a role in the regulation of MMP-7 expression by CORM-2. These effects of CORM-2 can be dependent on the modulation of nuclear factor-kappaB (NF-kappaB), activator protein-1, CCAT/enhancer binding protein and the phosphorylated forms of NF-kappaB inhibitory protein-alpha, c-Jun N-terminal protein kinase 1/2, p38 and extracellular signal-regulated kinase 1/2.

CONCLUSIONS AND IMPLICATIONS

CORM-2 can regulate a number of genes relevant in intestinal inflammation and cancer progression. These findings provide new insights into the anti-inflammatory properties and potential applications of this class of compounds.

In vivo antioxidant activity of procyanidin-rich extracts from grape seed and pine (Pinus maritima) bark in rats

BACKGROUND

In vitro evidence exists for the potential antioxidant benefits of procyanidin-rich extracts, but in vivo studies are scarce. We have evaluated the effects of selected procyanidin-rich extracts on oxidative stress in rats in condition of prolonged consumption of these compounds and also after single administration i.e. in postprandial conditions.

METHODS

Rats were fed for 8 weeks with diets supplemented with either a grape seed extract (GE), a pine bark extract (PE), or a high-degree polymerized pine bark extract (HPE). An additional study was performed in order to assess the postprandial effect of these extracts on plasma antioxidant capacity. The ferric-reducing antioxidant power (FRAP) and thiobarbituric acid-reactive substances (TBARS) were determined in plasma. For lipid peroxidation study of heart tissue, homogenates were prepared and TBARS were measured after lipid peroxidation induced by FeSO4-ascorbate.

RESULTS

After 8 weeks of dietary treatment, total antioxidant capacity in plasma was significantly higher in the GE and PE groups as compared with the other two groups. Plasma TBARS concentrations and heart susceptibility to peroxidation were not significantly different between the groups. In the postprandial state, by comparing plasma antioxidant capacity 2 hours after ingestion of the different procyanidin-rich extracts (500 mg/kg body weight), we observed that FRAP values were higher in the procyanidin-rich extracts groups as compared with the control group. Moreover, plasma FRAP concentration was significantly higher in the GE group as compared with the other groups.

CONCLUSION

The results of the present experiment constitute positive evidence for an in vivo antioxidant effect at the plasma level of procyanidin-containing plant extracts.

Heme oxygenase-1 inhibits apoptosis in Caco-2 cells via activation of Akt pathway

Heme oxygenase-1 can play a protective role against cellular stress. In colon cancer cells, these effects would be relevant to oncogenesis and resistance to chemotherapy. The aim of the study was to examine the effects of heme oxygenase-1 induction on cell survival in a human colon cancer cell line, Caco-2. Serum deprivation induced apoptosis, reduced Akt and p38 phosphorylation, and increased p21(Cip/WAF1) levels. Heme oxygenase-1 induction by treatment with cobalt protoporphyrin IX resulted in resistance to apoptosis, activation of Akt, reduction in p21(Cip/WAF1) levels and modification of bcl2/bax ratio towards survival. Indomethacin reduced apoptosis but in contrast to heme oxygenase-1, arrested cells in G0/G1. Apoptosis was also inhibited by the heme oxygenase metabolites bilirubin and biliverdin but the CO donor tricarbonyldichlororuthenium(II) dimer did not exert significant effects. Protection against apoptosis in cells treated with cobalt protoporphyrin IX was reverted by incubation with heme oxygenase-1 small interfering RNA. This study shows an antiapoptotic effect of heme oxygenase-1 in colon cancer cells which could be mediated by the formation of bilirubin and biliverdin. Our results support an antiapoptotic role for HO-1 in these cells and provide a mechanism by which overexpression of HO-1 may promote tumor resistance to stress in conditions of limited nutrient supply. We have extended these observations by demonstrating that these effects are independent of p38 but are mediated via Akt pathway.

Activity of lupane triterpenoids from Maytenus species as inhibitors of nitric oxide and prostaglandin E2

In the present study, we report that three new lupane triterpenes (1-3), in addition to 16 known ones (4-19), were isolated from the root bark of Maytenus cuzcoina and the leaves of Maytenus chiapensis. Their structures were elucidated by spectral analysis, including homonuclear and heteronuclear correlation NMR experiments (COSY, ROESY, HSQC, and HMBC). The natural compounds and derivatives 6a, 6b, 9a, and 9b have been tested for potential anti-inflammatory activity, and several compounds including 3-epicalenduladiol (2), 11alpha-hydroxy-glochidone (3), rigidenol (6), acetoxy-rigidenol (6a), 11alpha-acetoxy-30-chloro-3-oxo-lup-20(29)-ene (6b), betulin (9), 28-acetoxy-betulin (9a), epibetulin (12), epibetulinic acid (13), and betulonic acid (16) exhibited potent inhibitory effects on NO and prostaglandin E(2) production in mouse macrophages (RAW 264.7) stimulated with bacterial endotoxin. The structure-activity relationship is discussed in detail.

Effects of heme oxygenase-1 inducers on established rat adjuvant arthritis

Heme oxygenase-1 (HO-1) activity can inhibit inflammatory and immune responses. We have examined the influence of HO-1 induction on the established rat adjuvant arthritis model of chronic inflammation. Therapeutic administration of cobalt protoporphyrin IX (CoPP; 5 mg/kg/day i.p.) from day 17 to 23 significantly reduced the inflammatory response, with partial inhibition of hind paw edema and the production of some inflammatory mediators such as nitric oxide metabolites and tumor necrosis factor-alpha, although joint erosion was observed. Hemin administration (26 mg/kg/day i.p.) during the same time period was ineffective on these parameters. Western blot analysis of hind paw homogenates revealed a weaker induction of HO-1 by this compound in comparison with CoPP. Our data indicate that pharmacological HO-1 induction after the establishment of adjuvant arthritis partially reduced the inflammatory response but it was not sufficient to control joint erosion in our experimental conditions.

Protection against 2,4,6-trinitrobenzenesulphonic acid-induced colonic inflammation in mice by the marine products bolinaquinone and petrosaspongiolide M

Proinflammatory mediators, namely eicosanoids, reactive oxygen and nitrogen species and cytokines, are clearly involved in the pathogenesis of intestinal bowel disease. bolinaquinone (BQ) and petrosaspongiolide M (PT), two marine products with potent anti-inflammatory action, have been shown to control the production of mediators in acute and chronic inflammatory processes. Hence, we have tested here the hypothesis that BQ and PT could ameliorate inflammation and oxidative stress parameters in 2,4,6-trinitrobenzenesulphonic acid (TNBS)-induced colitis in Balb/c mice. BQ and PT were given orally in doses of 10 or 20mg/kg/day. Treatment of the animals with BQ or PT at the highest dose significantly protected against TNBS-induced inflammation, as assessed by a reduced colonic weight/length ratio and histological scoring. Neutrophilic infiltration, interleukin (IL)-1beta and prostaglandin E(2) (PGE(2)) levels, as well as cyclooxygenase-2 (COX-2) protein expression were inhibited by both compounds. Colonic nitrite and nitrate levels and protein expression of inducible nitric oxide synthase (iNOS) were also lower in the treated groups in comparison to the TNBS control. BQ and PT reduced nitrotyrosine immunodetection and colonic superoxide anion production. Neither compound inhibited the expression of the protective protein heme oxygenase-1 (HO-1), although they reduced the extension of apoptosis. Our study also indicated that PT could interfere with the translocation of p65 into the nucleus, a key step in nuclear factor-kappaB (NF-kappaB) activation. Altogether, the results suggest that BQ and PT can have potential protective actions in intestinal inflammatory diseases.

Oligofructose protects against the hypertriglyceridemic and pro-oxidative effects of a high fructose diet in rats

Recent findings indicate that in addition to its hyperlipemic effect, a high fructose diet has a pro-oxidant effect in rats compared with a starch-based diet. Oligofructose (OFS) has already been shown to decrease plasma lipids in rats. We assessed the impact of fructose on oxidative stress by supplementing a high fructose diet with OFS. Rats were fed either a high fructose diet or a starch-based diet, with or without supplementation of 10 g/100 g oligofructose for 4 wk. Regardless of the type of carbohydrate, OFS in the diet produced an enlargement of the cecum and led to a significant increase in the SCFA cecum pool. Fructose feeding was associated with significantly higher insulin plasma concentrations (+63%) in the control groups, whereas insulin plasma concentrations did not differ in rats fed the fructose diet supplemented with OFS. Plasma leptin concentration was significantly lower (approximately 50%) in the OFS-supplemented fructose group compared with the other three groups. Fructose feeding in rats also significantly increased plasma (P < 0.001) and liver (P < 0.001) triglyceride (TG) concentrations and the addition of OFS prevented the TG accumulation induced by fructose in the liver (P < 0.05) and hyperlipemia (P < 0.05). OFS consumption prevented (P < 0.05) the lower plasma vitamin E/TG ratio in rats fed the fructose diet. Control rats fed the fructose diet had high plasma TBARS values compared with rats fed the starch diet, whereas TBARS values remained unchanged when rats were supplemented with OFS. Control rats fed the fructose diet had higher TBARS urine values and higher heart tissue susceptibility to peroxidation compared with rats fed the starch diet, and this effect was significantly reduced by OFS consumption. Further studies are required to identify the mechanisms underlying the protective effect of OFS against the pro-oxidant effect of fructose. However, the potential nutritional benefits of OFS supplementation in fructose-rich diets are suggested.

High fructose feeding of magnesium deficient rats is associated with increased plasma triglyceride concentration and increased oxidative stress

The purpose of this study was to assess whether dietary carbohydrate could differentially influence the consequences of magnesium deficiency with particular emphasis on lipid metabolism and oxidative stress. Rats were fed a sucrose based or starch based diet either adequate or deficient in magnesium for two weeks. Magnesium deficient rats, as compared with rats fed magnesium adequate diets, displayed the usual decrease in plasma magnesium concentration. The classic symptoms of inflammation including hyperaemia, increased number of blood leukocytes and enlarged spleen weight were observed in these rats. Plasma TG and plasma apo B concentrations were also significantly increased. In addition, magnesium-deficient animals presented an increased susceptibility to lipid peroxidation of heart and liver tissues as shown by TBARS concentration. Regardless of magnesium status, sucrose feeding did not affect the magnesium plasma level and inflammatory parameters. Feeding rats the sucrose diets induced hypertriglyceridaemia and increased plasma apo B concentration. Heart and liver susceptibility to lipid peroxidation were significantly increased in rats fed the sucrose diets as compared with those fed the starch diets. Sucrose feeding in magnesium deficient rats was associated with higher plasma triglycerides concentration and higher tissue susceptibility to peroxidation as compared with magnesium deficient rats fed the starch diet. The results emphasised the potential detrimental and additional effect of sucrose feeding and magnesium deficiency on cardiovascular risk. Since the intake of magnesium has been reduced appreciably in industrialised countries while fructose consumption has been rapidly increased, the impact of this eating pattern should be clarified in humans.

Substituting honey for refined carbohydrates protects rats from hypertriglyceridemic and prooxidative effects of fructose

Recent findings indicate that a high fructose diet has a prooxidant effect in rats compared with a starch diet. Because honey is rich in fructose, the aim of this study was to assess the effect of substituting honey for refined carbohydrates on lipid metabolism and oxidative stress. Rats were fed for 2 wk purified diets containing 65 g/100 g carbohydrates as wheat starch or a combination of fructose and glucose or a honey-based diet prepared by substituting honey for refined carbohydrates (n = 9/group). The same amount of fructose was provided by the honey and fructose diets. The hypertriglyceridemic effect of fructose was not observed when fructose was provided by honey. Compared with those fed starch, fructose-fed rats had a lower plasma alpha-tocopherol level, higher plasma nitrite and nitrate (NOx) levels and were less protected from lipid peroxidation as indicated by heart homogenate TBARS concentration. Compared with those fed fructose, honey-fed rats had a higher plasma alpha-tocopherol level, a higher alpha-tocopherol/triacylglycerol ratio, lower plasma NOx concentrations and a lower susceptibility of heart to lipid peroxidation. Further studies are required to identify the mechanism underlying the antioxidant effect of honey but the data suggest a potential nutritional benefit of substituting honey for fructose in the diet.

Metabolic syndrome in the rat: females are protected against the pro-oxidant effect of a high sucrose diet

Metabolic syndrome is more prevalent in men than in women. In an experimental dietary model of metabolic syndrome, the high-fructose-fed rat, oxidative stress has been observed in males. Given that estradiol has been documented to exert an antioxidant effect, we investigated whether female rats were better protected than males against the adverse effects of a high-sucrose diet, and we studied the influence of hormonal status in female rats. Males and females were first fed a sucrose-based or starch-based diet for 2 weeks. In the males, the plasma triglyceride (TG)-raising effect of sucrose was accompanied by significantly lowered plasma alpha-tocopherol and a significantly lowered alpha-tocopherol/TG ratio (30%), suggesting that vitamin E depletion may predispose lipoproteins to subsequent oxidative stress. In males, after exposure of heart tissue homogenate to iron-induced lipid peroxidation, thiobarbituric reactive substances were significantly higher in the sucrose-fed than in the starch-fed rats. In contrast, in sucrose-fed females, neither a decrease in vitamin E/TG ratio nor an increased susceptibility of heart tissue to peroxidation was observed, despite both a significantly decreased heart superoxide dismutase activity (14%) and a significant 3-fold increase in plasma nitric oxide concentration compared with starch-fed females. The influence of hormonal status in female rats was then assessed using intact, ovariectomized, or estradiol-supplemented ovariectomized female rats fed the sucrose or starch diet for 2 weeks. After exposure of heart tissue to iron-induced lipid peroxidation, higher susceptibility to peroxidation was found only in ovariectomized females fed the sucrose diet compared with the starch group and not in intact females or ovariectomized females supplemented with estradiol. Thus, estrogens, by their effects on antioxidant capacity, might explain the sexual difference in the pro-oxidant effect of sucrose diet resulting in metabolic syndrome in rats.

Rats fed a high sucrose diet have altered heart antioxidant enzyme activity and gene expression

Several studies in human and animal models have shown that consumption of fructose facilitates oxidative damage but the mechanisms involved are unclear. In this study, the effects of two weeks of high sucrose on both oxidative stress parameters and stress-related gene expression, using a cDNA array, were investigated in rat heart. Both increased TBARS and lower Cu-Zn-SOD activity were found in heart from high sucrose fed rats compared to rats on a starch diet. Higher plasma NO level was also found in the high sucrose group, corroborating the pro-oxidant effect of fructose. The Cu-Zn-SOD mRNA level was also greater in the high sucrose group; the Mn-SOD, GPX and catalase were not different between the two groups. Increased HSP70 and decreased COMT genes expression were observed, underlying the hypertensive effect of dietary fructose. These findings confirm the pro-oxidant effect of high sucrose feeding to rats and highlight the NO/O(2)(*-) balance importance in oxidative homeostasis.

Lyophilized apple counteracts the development of hypercholesterolemia, oxidative stress, and renal dysfunction in obese Zucker rats

Apples may have selective effects on abnormalities associated with the plurimetabolic syndrome. Therefore, the effects of 20% lyophilized apple supplementation on plasma and tissue lipids and on protection against susceptibility to oxidative stress and renal dysfunction were investigated in Zucker lean (Fa/-) or obese (fa/fa) rats. The experimental diets were equilibrated for sugar supply, contained 0.25 g/100 g cholesterol and provided only one third of the vitamin E requirement. Obese Zucker rats were hypercholesterolemic with cholesterol accumulation in LDL and HDL fractions. The apple diet lowered plasma and LDL cholesterol (-22 and -70%, respectively, P < 0.01) in obese Zucker rats and, in parallel, reduced triglyceride accumulation in heart and liver. Zucker rats fed the apple diet also had a larger intestinal pool and greater fecal excretion of bile acids. The heart concentration and urinary excretion of malondialdehyde were reduced by apple consumption in obese Zucker rats, suggesting better protection against peroxidation. Glucosuria and proteinuria in obese Zucker rats were also suppressed by the apple diet. In conclusion, despite their moderate fiber content, apples improve substantially the lipid status and peroxidative parameters in obese Zucker rats, suggesting that other plant constituents such as polyphenols are involved in these effects.