Effects of 1,8-cineole on neuropathic pain mediated by P2X2 receptor in the spinal cord dorsal horn

Protective role of citronellol on antioxidant enzymes and oxidative damage induced by gentamicin in experimental nephrotoxic rats

BACKGROUND

Gentamicin leads to nephrotoxicity with increasing oxidative stress. In the present research the role of citronellol on oxidative damage induced by gentamicin in nephrotoxic rats was evaluated.

METHODS AND RESULTS

Forty-twomale Wistar rats were randomly divided into seven equal groups; healthy control, gentamicin, DMSO, citronellol 50, citronellol 100, citronellol 200 and vitamin E. The animals were anesthetized after 12 days of treatment. Kidney and serum samples were received for biochemical, histological changes, and gene expression assessments. The levels of serum glutathione (GSH), serum and kidney glutathione peroxidase (GPX) and the expression of GPX gene against gentamicin group were increased in citronellol treatment groups. The levels of serum and kidney malondialdehyde (MDA), urine protein, serum creatinine and the gene expression of inflammatory factors including tumor necrosis factor-alpha (TNF-α) and Interleukin 6 (IL-6) against gentamicin group were decreased in these groups. Moreover, recuperation in histological alterations was shown in three groups receiving citronellol compared to the gentamicin group.

CONCLUSIONS

Citronellol with its antioxidant and anti-inflammatory properties can decrease kidney damage caused by nephrotoxicity induced by gentamicin.

Eucalyptol alleviates cisplatin-induced kidney damage in rats

This study was aimed to explore the therapeutic effect of eucalyptol on cisplatin induced kidney damage in Wistar albino rats. The animals were divided into four groups: sham (S), eucalyptol (E), cisplatin (C), and cisplatin + eucalyptol (CE) randomly, six animals in each group. Groups C and CE were received cisplatin (12 mg/kg, a single dose, intraperitoneally (i.p.)). Groups E and CE were treated with eucalyptol (100 mg/kg, for seven days, orally). The blood samples and kidney tissues were collected following sacrification and analyzed histopathologically and biochemically. Histopathological results revealed tubular degeneration and necrosis, inflammatory cell infiltration, tubular lumen dilatation, enlargement of bowman's space and hyaline cast were significantly irregular in the group C than group S. However, eucalyptol treatment (CE) modulated the alterations in the group C. Serum levels of blood urea nitrogen (BUN) and creatinine (CRE) were considerably higher in the group C compared to the other groups. There was no significant difference among the other groups statistically (except group C) in terms of BUN and CRE values. Eucalyptol treatment (at 100 mg/kg, for seven days) decreased the cisplatin induced increase in serum BUN and CRE levels and restored the reduced Vit C level and CAT activity of kidneys caused by cisplatin. Thus, eucalyptol's antioxidative, nephroprotective, and curative effects indicated the potential for future drug development.

Mentha rotundifolia (L.) Huds. and Salvia officinalis L. hydrosols mitigate aging related comorbidities in rats

Introduction

Aging is often linked to oxidative stress, where the body experiences increased damage from free radicals. Plants are rich sources of antioxidants, playing a role in slowing down aging and supporting the proper functioning and longevity of cells. Our study focuses on exploring the impact of Mentha rotundifolia (MR) and Salvia officinalis (SO) hydrosols on aging-related comorbidities.

Methods

The chemical composition of MR and SO hydrosols was analyzed by gas chromatography coupled to mass spectrometry. 2,2-Diphenyl 1-picrylhydrazyl and 2,20-azino-bis 3-ethylbenzothiazoline-6-sulfonic acid radicals scavenging assays were used to assess their in vitro antioxidant activity, and heat induced albumin denaturation test was used to evaluate their anti-inflammatory activity. Subsequently, we administered 5% of each plant hydrosol in the drinking water of 18-month-old rats for six months. We then conducted behavioral tests, including open field, dark/light box, rotarod, and Y-maze assessments, and measured biochemical parameters in plasma, liver and brain tissues.

Results and discussion

At two years old, animals treated with MR and SO hydrosols displayed fewer physical and behavioral impairments, along with well-preserved redox homeostasis in comparison with animals in the control group. These results highlighted the significance of MR and SO hydrosols in addressing various aspects of age-related comorbidities. The study suggests that these plant-derived hydrosols may have potential applications in promoting healthy aging and mitigating associated health challenges.

1,8-cineole (eucalyptol): A versatile phytochemical with therapeutic applications across multiple diseases

1,8-cineole (Eucalyptol), a naturally occurring compound derived from botanical sources such as eucalyptus, rosemary, and camphor laurel, has a long history of use in traditional medicine and exhibits an array of biological properties, including anti-inflammatory, antioxidant, antimicrobial, bronchodilatory, analgesic, and pro-apoptotic effects. Recent evidence has also indicated its potential role in managing conditions such as Alzheimer's disease, neuropathic pain, and cancer. This review spotlights the health advantages of 1,8-cineole, as demonstrated in clinical trials involving patients with respiratory disorders, including chronic obstructive pulmonary disease, asthma, bronchitis, and rhinosinusitis. In addition, we shed light on potential therapeutic applications of 1,8-cineole in various conditions, such as depression, epilepsy, peptic ulcer disease, diarrhea, cardiac-related heart diseases, and diabetes mellitus. A comprehensive understanding of 1,8-cineole's pharmacodynamics and safety aspects as well as developing effective formulations, might help to leverage its therapeutic value. This thorough review sets the stage for future research on diverse health benefits and potential uses of 1,8-cineole in tackling complex medical conditions.

Role and therapeutic target of P2X2/3 receptors in visceral pain

Visceral pain (VP) is caused by internal organ disease. VP is involved in nerve conduction and related signaling molecules, but its specific pathogenesis has not yet been fully elucidated. Currently, there are no effective methods for treating VP. The role of P2X2/3 in VP has progressed. After visceral organs are subjected to noxious stimulation, cells release ATP, activate P2X2/3, enhance the sensitivity of peripheral receptors and the plasticity of neurons, enhance sensory information transmission, sensitize the central nervous system, and play an important role in the development of VP. However, antagonists possess the pharmacological effect of relieving pain. Therefore, in this review, we summarize the biological functions of P2X2/3 and discuss the intrinsic link between P2X2/3 and VP. Moreover, we focus on the pharmacological effects of P2X2/3 antagonists on VP therapy and provide a theoretical basis for its targeted therapy.

The potential role of T-cell metabolism-related molecules in chronic neuropathic pain after nerve injury: a narrative review

Neuropathic pain is a common type of chronic pain, primarily caused by peripheral nerve injury. Different T-cell subtypes play various roles in neuropathic pain caused by peripheral nerve damage. Peripheral nerve damage can lead to co-infiltration of neurons and other inflammatory cells, thereby altering the cellular microenvironment and affecting cellular metabolism. By elaborating on the above, we first relate chronic pain to T-cell energy metabolism. Then we summarize the molecules that have affected T-cell energy metabolism in the past five years and divide them into two categories. The first category could play a role in neuropathic pain, and we explain their roles in T-cell function and chronic pain, respectively. The second category has not yet been involved in neuropathic pain, and we focus on how they affect T-cell function by influencing T-cell metabolism. By discussing the above content, this review provides a reference for studying the direct relationship between chronic pain and T-cell metabolism and searching for potential therapeutic targets for the treatment of chronic pain on the level of T-cell energy metabolism.

Dorsal root ganglia P2X4 and P2X7 receptors contribute to diabetes-induced hyperalgesia and the downregulation of electroacupuncture on P2X4 and P2X7

Diabetic neuropathic pain (DNP) is highly common in diabetes patients. P2X receptors play critical roles in pain sensitization. We previously showed that elevated P2X3 expression in dorsal root ganglion (DRG) contributes to DNP. However, the role of other P2X receptors in DNP is unclear. Here, we established the DNP model using a single high-dose streptozotocin (STZ) injection and investigated the expression of P2X genes in the DRG. Our data revealed elevated P2X2, P2X4, and P2X7 mRNA levels in DRG of DNP rats. The protein levels of P2X4 and P2X7 in DNP rats increased, but the P2X2 did not change significantly. To study the role of P2X4 and P2X7 in diabetes-induced hyperalgesia, we treated the DNP rats with TNP-ATP (2',3'-O-(2,4,6-trinitrophenyl)-adenosine 5'-triphosphate), a nonspecific P2X1-7 antagonist, and found that TNP-ATP alleviated thermal hyperalgesia in DNP rats. 2 Hz electroacupuncture is analgesic against DNP and could downregulate P2X4 and P2X7 expression in DRG. Our findings indicate that P2X4 and P2X7 in L4-L6 DRGs contribute to diabetes-induced hyperalgesia, and that EA reduces thermal hyperalgesia and the expression of P2X4 and P2X7.

Electroacupuncture Alleviates Diabetic Neuropathic Pain and Downregulates p-PKC and TRPV1 in Dorsal Root Ganglions and Spinal Cord Dorsal Horn

Diabetic neuropathic pain (DNP) is a common complication of diabetes. Streptozotocin (STZ)-induced changes of protein in dorsal root ganglion (DRG) and spinal cord dorsal horn (SCDH) are critical for DNP genesis. However, which proteins change remains elusive. Here, the DNP model was established by a single intraperitoneal injection of STZ, accompanied by increased fasting blood glucose (FBG), decreased body weight (BW), and decreased paw withdrawal latency (PWL). Proteins change in L4-L6 DRGs and SCDH of rats were detected. Western blot and immunofluorescence results showed that expression levels of phosphorylated protein kinase C (p-PKC), transient receptor potential vanilloid-1 (TRPV1), Substance P (SP) and calcitonin gene-related peptide (CGRP) in the DRG and the SCDH of rats were increased after STZ injection. A preliminary study from our previous study showed that 2 Hz electroacupuncture (EA) effectively alleviates DNP. However, the analgesic mechanism of EA needs further elucidation. Here, EA at the bilateral Zusanli (ST36) and KunLun (BL60) acupoints was applied for one week, and to investigate the effect on DNP. EA reversed thermal hyperalgesia in DNP rats and downregulated the expression of p-PKC, TRPV1, SP, and CGRP in DRG and SCDH.

Transcriptome Analysis Reveals the Anti-Tumor Mechanism of Eucalyptol Treatment on Neuroblastoma Cell Line SH-SY5Y

Eucalyptol (1.8-cineole), an active component in traditional Chinese medicine Artemisia argyi for moxibustion. Previous studies have shown that eucalyptol has anti-tumor effects on leukemia and colon cancer. Nonetheless, the effect and mechanism of eucalyptol on neuroblastoma remains unclear. In the present study, we intended to reveal the effect and mechanism of eucalyptol treatment on the neuroblastoma cell line SH-SY5Y through transcriptome analysis. In the group treated with eucalyptol, 566 brain genes were up-regulated, while 757 genes were down-regulated. GO function analysis showed that positive regulation of cell cycle was down-regulated in biological processes. Meanwhile, cancer-related pathways were identified in KEGG (Kyoto Encyclopedia of Genes and Genomes) enrichment analysis, including pathways in cancer, PI3K-Akt signaling pathway, cAMP signaling pathway, TGF-beta signaling pathway, Hippo signaling pathway, p53 signaling pathway, and additional pathways. Furthermore, we found a key gene, such as MYC, by constructing a network of cancer related pathways with differentially expressed genes and transcription factor analysis. In conclusion, our research indicates that MYC might play a central role in the anit-tumor mechanisms of eucalyptol.

Essential Oils and Neuropathic Pain

Neuropathic pain is one of the most prominent chronic pain syndromes, affecting almost 10% of the United States population. While there are a variety of established pharmacologic and non-pharmacologic treatment options, including tricyclic antidepressants (TCAs), serotonin-noradrenaline reuptake inhibitors, anticonvulsants, trigger point injections, and spinal cord stimulators, many patients continue to have chronic pain or suboptimal symptom control. This has led to an increased interest in alternative solutions for neuropathic pain such as nutritional supplements and essential oils. In this review, we explore the literature on the most commonly cited essential oils, including lavender, bergamot, rosemary, nutmeg, Billy goat weed, and eucalyptus. However, the literature is limited and largely comprised of preclinical animal models and a few experimental studies, some of which were poorly designed and did not clearly isolate the effects of the essential oil treatment. Additionally, no standardized method of dosing or route of administration has been established. Further randomized control studies isolating the active components of various essential oils are needed to provide conclusive evidence on the use of essential oils for neuropathic pain. In this review, we explore the basis behind some of the essential oils of interest to patients with neuropathic pain seen in rheumatology clinics.

Blockage of HCN Channels Inhibits the Function of P2X Receptors in Rat Dorsal Root Ganglion Neurons

Hyperpolarization-activated cyclic nucleotide-gated channels and purinergic P2X receptors play critical roles in the nerve injury-induced pain hypersensitivity. Both HCN channels and P2XR are expressed in dorsal root ganglia sensory neurons. However, it is not clear whether the expression and function of P2X2 and P2X3 receptors can be modulated by HCN channel activity. For this reason, in rats with chronic constriction injury of sciatic nerve, we evaluated the effect of intrathecal administration of HCN channel blocker ZD7288 on nociceptive behavior and the expression of P2X2 and P2X3 in rat DRG. The mechanical withdrawal threshold was measured to evaluate pain behavior in rats. The protein expression of P2X2 and P2X3 receptor in rat DRG was observed by using Western Blot. The level of cAMP in rat DRG was measured by ELISA. As a result, decreased MWT was observed in CCI rats on 1 d after surgery, and the allodynia was sustained throughout the experimental period. In addition, CCI rats presented increased expression of P2X2 and P2X3 receptor in the ipsilateral DRG at 7 d and 14 d after CCI operation. Intrathecal injection of ZD7288 significantly reversed CCI-induced mechanical hyperalgesia, and attenuated the increased expression of P2X2 and P2X3 receptor in rat DRG, which open up the possibility that the expression of P2X2 and P2X3 receptor in DRG is down-regulated by HCN channel blocker ZD7288 in CCI rats. Furthermore, the level of cAMP in rat DRG significantly increased after nerve injury. Intrathecal administration of ZD7288 attenuated the increase of cAMP in DRG caused by nerve injury. Subsequently, effects of HCN channel activity on ATP-induced current (I_ATP) in rat DRG neurons were explored by using whole-cell patch-clamp techniques. ATP (100 μM) elicited three types of currents (fast, slow and mixed I_ATP) in cultured DRG neurons. Pretreatment with ZD7288 concentration-dependently inhibited three types of ATP-activated currents. On the other hand, pretreatment with 8-Br-cAMP (a cell-permeable cAMP analog, also known as an activator of PKA) significantly increased the amplitude of fast, slow and mixed I_ATP in DRG neurons. The enhanced effect of 8-Br-cAMP on ATP-activated currents could be reversed by ZD7288. In a summary, our observations suggest that the opening of HCN channels could enhance the expression and function of P2X2 and P2X3 receptor via the cAMP-PKA signaling pathway. This may be important for pathophysiological events occurring within the DRG, for where it is implicated in nerve injury-induced pain hypersensitivity.

1,8-cineole ameliorates ischaemic brain damage via TRPC6/CREB pathways in rats

OBJECTIVES

A previous in vitro study reported that the monoterpene oxide 1,8-cineole (cineole) attenuates neuronal caused by oxygen-glucose deprivation/reoxygenation in culture. However, to date, there is no in vivo evidence showing neuroprotective effects of cineole against stroke. This study aimed to investigate whether cineole attenuates cerebral ischaemic damage in rats.

METHODS

A rat model of middle cerebral artery occlusion (MCAO) followed by 24 h reperfusion was applied. Male rats were treated with oral cineole (100 mg/kg) for 7 consecutive days, then subjected to MCAO surgery. Infarct volume, neurologic deficits, apoptosis and expression levels of all-spectrin breakdown products of 145 kDa (SBDP145), transient receptor potential canonical (subtype) 6 (TRPC6) and phosphorylated CREB (p-CREB) were measured in ischaemic brain tissues.

KEY FINDINGS

Cineole treatment significantly reduced infarct volume, neurological dysfunction, neuronal apoptosis, SBDP145 formation and TRPC6 degradation and enhanced p-CREB expression in MCAO rats compared with vehicle treatment. These neuroprotective effects were markedly suppressed by pharmacological inhibition of MEK or CaMKIV signalling.

CONCLUSIONS

Our study provides in vivo evidence demonstrating that cineole pretreatment attenuates ischaemic stroke-induced brain damage, mainly through blocking calpain-induced TRPC6 degradation and activating CREB via MEK/CREB and CaMKIV/CREB signalling pathways.

Involvement of P2X2 receptor in the medial prefrontal cortex in ATP modulation of the passive coping response to behavioral challenge

P2X2 and P2X3 receptors are widely expressed in both the peripheral nervous system and the central nervous system and have been proven to participate in different peripheral sensory functions, but there are few studies on the involvement of P2X2 and P2X3 receptors in animal behaviors. Here we used P2X2 and P2X3 knockout mice to address this issue. P2X2 knockout mice showed normal motor function, exploratory behavior, anxiety-like behaviors, learning and memory behaviors and passive coping response to behavioral challenge. Nevertheless, the effect of ATP infusion in the medial prefrontal cortex (mPFC) on the passive coping response was blocked by P2X2 but not P2X3 receptor deletion. Additionally, no deficits in a wide variety of behavioral tests were observed in P2X3 knockout mice. These findings demonstrate a role of P2X2 receptor in the mPFC in adenosine-5'-triphosphate modulation of the passive coping response to behavioral challenge and show that the P2X2/P2X3 receptor is dispensable for behaviors.

Inhalation Administration of the Bicyclic Ethers 1,8- and 1,4-cineole Prevent Anxiety and Depressive-Like Behaviours in Mice

The anxiolytic and antidepressant-like activities of the naturally occurring monoterpene 1,8-cineole and its structural isomer 1,4-cineole were evaluated in mice via inhalation administration at doses ranging from 4 × 10-6 to 4 × 10-1 mg per 400 μL of triethyl citrate. Mice were tested for anxiety-like behaviours by using the light-dark box test (LDB) and marble-burying test (MBT) and for depression-like symptoms by using the forced swimming test (FST) and tail suspension test (TST). Diazepam and fluoxetine were used as standard drugs for anxiolytic and antidepressant tests, respectively. The results showed that 1,8-cineole at 4 × 10-4 mg, and 1,4-cineole at 4 × 10-4 and 4 × 10-3 mg significantly increased the amount of time spent in the light box and the number of entries in the light box in the LDB as well as reduced the number of marbles buried in the MBT relative to those in the control, suggesting an anxiolytic effect. Similarly, 1,8-cineole at 4 × 10-4 and 4 × 10-2 mg and 1,4-cineole at doses of 4 × 10-4 to 4 × 10-2 mg significantly reduced immobility times in the FST and TST relative to those of the control, suggesting an antidepressant activity. The role of the GABAA/benzodiazepine receptor system in the anxiolytic effects of 1,8- and 1,4-cineole was investigated through co-administration of flumazenil, a GABAergic system antagonist. Flumazenil reversed the effects of diazepam and 1,8-cineole, suggesting that 1,8-cineole affects the GABAA/benzodiazepine receptors. Collectively, the results suggest that inhaled 1,8- and 1,4-cineole prevented anxiety and depressive-like symptoms in classic mice models.

Electroacupuncture Stimulation Alleviates CFA-Induced Inflammatory Pain Via Suppressing P2X3 Expression

Chronic inflammatory pain is one of the most common complaints that seriously affects patients’ quality of life. Previous studies have demonstrated that the analgesic effect of electroacupuncture (EA) stimulation on inflammatory pain is related to its frequency. In this study, we focused on whether the analgesic effects of EA are related to the period of stimulation. Purinergic receptor P2X3 (P2X3) is involved in the pathological process underlying chronic inflammatory pain and neuropathic pain. We hypothesized that 100 Hz EA stimulation alleviated Freund’s complete adjuvant (CFA) induced inflammatory pain via regulating P2X3 expression in the dorsal root ganglion (DRG) and/or spinal cord dorsal horn (SCDH). We also assumed that the analgesic effect of EA might be related to the period of stimulation. We found that both short-term (three day) and long-term (14 day) 100 Hz EA stimulation effectively increased the paw withdrawal threshold (PWT) and reversed the elevation of P2X3 in the DRG and SCDH of CFA rats. However, the analgesic effects of 100 Hz EA were not dependent on the period of stimulation. Moreover, P2X3 inhibition or activation may contribute to or attenuate the analgesic effects of 100 Hz EA on CFA-induced inflammatory pain. This result indicated that EA reduced pain hypersensitivity through P2X3 modulation.