Effects of co-administration of vitamin E and lithium chloride on chronic constriction injury-induced neuropathy in male Wistar rats: Focus on antioxidant and anti-inflammatory mechanisms

Virtual screening and molecular dynamics investigations using natural compounds against autotaxin for the treatment of chronic pain

Chronic pain is a common and debilitating condition with a huge social and economic burden worldwide. Currently, available drugs in clinics are not adequately effective and possess a variety of severe side effects leading to treatment withdrawal and poor quality of life. Recent findings highlight the potential role of autotaxin (ATX) as a promising novel target for chronic pain management, extending beyond its previously established involvement in arthritis and other neurological disorders, such as Alzheimer's disease. In the present study, we used a virtual screening strategy by targeting ATX against commercially available natural compounds (enamine- phenotypic screening library) to identify the potential inhibitors for the treatment of chronic pain. After initial identification using molecular docking based virtual screening, molecular mechanics (MM/GBSA), ADMET profiling and molecular dynamics simulation were performed to verify top hits. The computational screening resulted in the identification of fifteen top scoring structurally diverse hits that have free energy of binding (ΔG) values in the range of -25.792 (for compound Enamine_1850) to -74.722 Kcal/mol (for compound Enamine_1687). Moreover, the top-scoring hits have favourable ADME properties as calculated using in-silico algorithms. Additionally, the molecular dynamics simulation revealed the stable nature of protein-ligand interaction and provided information about amino acid residues involved in binding. This study led to the identification of potential autotaxin inhibitors with favourable pharmacokinetic properties. Identified hits may further be investigated for their safety and efficacy potential using in-vitro and in-vivo models of chronic pain.Communicated by Ramaswamy H. Sarma.

Bergenin ameliorates chemotherapy-induced neuropathic pain in rats by modulating TRPA1/TRPV1/NR2B signalling

Chemotherapy-induced neuropathic pain (CINP) is one of the most prominent and incapacitating complication associated with chemotherapeutic regimens. The exact mechanisms underlying CINP are not fully understood yet, which hampers the development of effective therapeutics. The current study has been designed to investigate the effect of bergenin on CINP and dissect the underlying cellular and molecular mechanisms. Behavioural responsiveness assays were conducted in rats before and after CINP induction and at different time points post-bergenin treatment. We also measured alterations in tight junction proteins, pro-inflammatory cytokines, microglia activity, transient receptor potential (TRP) channels (TRPV1, TRPA1 and TRPM8) and N-methyl-D-aspartate receptor subtype 2 (NR2B) in dorsal root ganglion (DRG) and spinal tissues of neuropathic rats. Bergenin treatment leads to a significant and dose-dependent reduction in evoked and spontaneous ongoing pain without causing central side effects in neuropathic rats. Furthermore, treatment with bergenin and gabapentin did not affect the baseline pain threshold in healthy, non-chemotherapy-treated rats, as evaluated through tail-flick and tail-clip assays. Chemotherapy administration leads to a significant activation of TRP channels, concurrent with microglial activation, disruption of spinal cord tight junction proteins, and subsequent infiltration of pro-inflammatory cytokines, as well as NR2B activation. Notably, bergenin treatment effectively reversed all of these alterations, with the exception of TRPM8, in both the DRG and spinal cord of neuropathic rats. Findings from the present study suggests that bergenin mitigates neuropathic pain by modulating the TRPA1/TRPV1/NR2B signalling and presents a promising therapeutic avenue for the treatment of chemotherapy-induced neuropathic pain.

Vitamins in neuropathy: pathophysiological and therapeutic roles

PURPOSE OF REVIEW

Vitamin deficiency is a risk factor in the development of peripheral neuropathy, which leads to complex and severe diseases. This review provides an update overview of the literature on the roles of vitamins in peripheral neuropathy, highlighting their pathophysiological and therapeutic roles.

RECENT FINDINGS

The importance and clinical manifestations and implications of the vitamins and vitamin deficiencies are further demonstrated in peripheral neuropathy and the associated diseases. Vitamin deficiency is common in various severe and complex diseases such as diabetes, chemotherapy, acute nutritional axonal neuropathy, dermatitis, complex regional pain syndrome, postherpetic neuralgia, carpal tunnel syndrome, and so forth and some rare clinical case reports. There is evidence that deficiencies of almost all vitamins are associated with diabetic neuropathy. Vitamin supplementation may serve as an effective therapeutic strategy.

SUMMARY

The vitamins play critical roles in maintaining physiological functions, and vitamin deficiencies cause peripheral neuropathy with various severe and complex diseases. The therapeutic benefits of vitamins and further understanding of the mechanisms for vitamin treatment effects should be emphasized and highlighted. More clinical trials are needed to establish optimal treatment strategies for vitamins in the various neuropathies. A large range of people/patients screening for vitamin deficiencies may be considered in order to provide early diagnosis and timely medical assistance.

Intraganglionic reactive oxygen species mediate inflammatory pain and hyperalgesia through TRPA1 in the rat

Reactive oxygen species (ROS) are generated in nociceptive pathways in response to inflammation and injury. ROS are accumulated within the sensory ganglia following peripheral inflammation, but the functional role of intraganlionic ROS in inflammatory pain is not clearly understood. The aims of this study were to investigate whether peripheral inflammation leads to prolonged ROS accumulation within the trigeminal ganglia (TG), whether intraganglionic ROS mediate pain hypersensitivity via activation of TRPA1, and whether TRPA1 expression is upregulated in TG during inflammatory conditions by ROS. We demonstrated that peripheral inflammation causes excess ROS production within TG during the period when inflammatory mechanical hyperalgesia is most prominent. Additionally, scavenging intraganglionic ROS attenuated inflammatory mechanical hyperalgesia and a pharmacological blockade of TRPA1 localized within TG also mitigated inflammatory mechanical hyperalgesia. Interestingly, exogenous administration of ROS into TG elicited mechanical hyperalgesia and spontaneous pain-like responses via TRPA1, and intraganglionic ROS induced TRPA1 upregulation in TG. These results collectively suggest that ROS accumulation in TG during peripheral inflammation contributes to pain and hyperalgesia in a TRPA1 dependent manner, and that ROS further exacerbate pathological pain responses by upregulating TRPA1 expression. Therefore, any conditions that exacerbate ROS accumulation within somatic sensory ganglia can aggravate pain responses and treatments reducing ganglionic ROS may help alleviate inflammatory pain.

Effect of chronic lithium on mechanical sensitivity and trabecular bone loss induced by type-1 diabetes mellitus in mice

Type-1 diabetes mellitus (T1DM) is a chronic condition characterized by long-term hyperglycemia that results in several complications such as painful peripheral neuropathy, bone deterioration, and increased risk of bone fractures. Lithium, a first-line therapy for bipolar disorder, has become an attractive agent for attenuating peripheral neuropathy and menopause-induced bone loss. Therefore, our aim was to determine the effect of chronic lithium treatment on mechanical hypersensitivity and trabecular bone loss induced by T1DM in mice. T1DM was induced in male C57BL/6J mice by intraperitoneal injection of streptozotocin (STZ, 50 mg/kg/day, for 5 consecutive days). 12 weeks after T1DM-induction, mice received a daily intraperitoneal injection of vehicle, 30 or 60 mg/kg lithium (as LiCl) for 6 weeks. Throughout the treatment period, blood glucose levels and mechanical sensitivity were evaluated every 2 weeks. After lithium treatment, the femur and L5 vertebra were harvested for microcomputed tomography (microCT) analysis. T1DM mice showed significant hyperglycemia, mechanical hypersensitivity, and significant trabecular bone loss as compared with the control group. Chronic lithium treatment did not revert the hindpaw mechanical hypersensitivity nor hyperglycemia associated to T1DM induced by STZ. In contrast, microCT analysis revealed that lithium reverted, in a dose-dependent manner, the loss of trabecular bone associated to T1DM induced by STZ at both the distal femur and L5 vertebra. Lithium treatment by itself did not affect any trabecular bone parameter in non-diabetic mice.