Transcranial direct current stimulation is more effective than pregabalin in controlling nociceptive and anxiety-like behaviors in a rat fibromyalgia-like model.

OBJECTIVES: Despite the fact that fibromyalgia, a widespread disease of the musculoskeletal system, has no specific treatment, patients have shown improvement after pharmacological intervention. Pregabalin has demonstrated efficacy; however, its adverse effects may reduce treatment adherence. In this context, neuromodulatory techniques such as transcranial direct current stimulation (tDCS) may be employed as a complementary pain-relieving method. Consequently, the purpose of this study was to evaluate the effect of pregabalin and tDCS treatments on the behavioral and biomarker parameters of rats submitted to a fibromyalgia-like model. METHODS: Forty adult male Wistar rats were divided into two groups: control and reserpine. Five days after the end of the administration of reserpine (1 mg/kg/3 days) to induce a fibromyalgia-like model, rats were randomly assigned to receive either vehicle or pregabalin (30 mg/kg) along with sham or active- tDCS treatments. The evaluated behavioral parameters included mechanical allodynia by von Frey test and anxiety-like behaviors by elevated plus-maze test (time spent in opened and closed arms, number of entries in opened and closed arms, protected head-dipping, unprotected head-dipping [NPHD], grooming, rearing, fecal boluses). The biomarker analysis (brain-derived neurotrophic factor [BDNF] and tumor necrosis factor-α [TNF-α]) was performed in brainstem and cerebral cortex and in serum. RESULTS: tDCS reversed the reduction in the mechanical nociceptive threshold and the decrease in the serum BDNF levels induced by the model of fibromyalgia; however, there was no effect of pregabalin in the mechanical threshold. There were no effects of pregabalin or tDCS found in TNF-α levels. The pain model induced an increase in grooming time and a decrease in NPHD and rearing; while tDCS reversed the increase in grooming, pregabalin reversed the decrease in NPHD. CONCLUSIONS: tDCS was more effective than pregabalin in controlling nociception and anxiety-like behavior in a rat model-like fibromyalgia. Considering the translational aspect, our findings suggest that tDCS could be a potential non-pharmacological treatment for fibromyalgia.

A next generation peripherally restricted Cavα2δ-1 ligand with inhibitory action on Cav2.2 channels and utility in neuropathic pain.

The Voltage-Gated Calcium Channel (VGCC) auxiliary subunit Cavα2δ-1 (CACNA2D1) is the target/receptor of gabapentinoids which are known therapeutics in epilepsy and neuropathic pain. Following damage to the peripheral sensory nervous system, Cavα2δ-1 is upregulated in dorsal root ganglion (DRG) neurons in several animal models of chronic neuropathic pain. Gabapentinoids, such as gabapentin and pregabalin, engage with Cavα2δ-1 via binding an arginine residue (R241) within an RRR motif located at the N-terminus of human Cavα2δ-1. A novel, next generation gabapentinoid, engineered not to penetrate the brain, was able to generate a strong analgesic response in Chronic Constriction Injury animal model of chronic neuropathic pain and showed binding specificity for Cavα2δ-1 versus the Cavα2δ-2 subunit. This novel non-brain penetrant gabapentinoid, binds to R241 and a novel binding site on Cavα2δ-1, which is located within the VGCC_α2 domain, identified as a lysine residue within an IKAK amino acid motif (K634). The overall whole cell current amplitudes were diminished by the compound, with these inhibitory effects being diminished in R241A mutant Cavα2δ-1 subunits. The functional effects occurred at lower concentrations than those needed for inhibition by gabapentin or pregabalin, which apparently bound the Cavα2δ-1 subunit only on the R241 and not on the K634 residue. Our work sets the stage for the identification and characterisation of novel compounds with therapeutic properties in neuropathic pain and possibly in other disorders and conditions which require engagement of the Cavα2δ-1 target.

Protective effect of pregabalin on renal and renal endothelial damage in sepsis induced by lipopolysaccharide.

OBJECTIVE: We investigated the protective effects of pregabalin (PRG) on kidney and renal endothelial damage in sepsis induced by Lipopolysaccharide (LPS). MATERIALS AND METHODS: Rats were randomly divided into three groups as control, LPS and LPS+PRG. Saline solution was administered 30 mg/kg orally and 5 mg/kg intraperitoneally (i.p.) to the control group. LPS was applied as 5 mg/kg, i.p. to the LPS group. In the LPS+PRG group, PRG at 30 mg/kg orally and one hour before LPS administration, one hour later 5 mg/kg i.p. LPS was applied. Rats were sacrificed 6 hours after LPS administration. RESULTS: White Blood Cell (WBC), granulocyte, Blood Urea Nitrogen (BUN), creatinine, uric asid, Total Oxidant Status (TOS) and Oxidative Stress Index (OSI) significantly increased (p<0.05); platelets (PLT), activated partial thromboplastin time (aPTT) and Total Antioxidant Status (TAS) significantly decreased in the LPS group compared to the control group (p<0.05). In the LPS+PRG group WBC, granulocyte, BUN, creatinine, uric asid, TOS and OSI significantly decreased (p<0.05); PLT, aPTT and TAS significantly increased compared to the LPS group(p<0.05). Histopathological examinations showed that kidney and renal endothelial damage in the LPS group decreased in the LPS+PRG group. Immunohistochemically IL1-ß, IL-6, IL-10, TNF-α expressions in kidney tissue and Toll-Like Receptors-4 (TLR-4) and NF-κB expressions in the renal endothelial tissue significantly increased in the LPS group compared to the control group and significantly decreased in the LPS+PRG group compared to the LPS group (p<0.001). CONCLUSIONS: Sepsis causes kidney and renal endothelial damage and PRG reduces this damage. Therefore PRG can be used in prophylactic treatment in sepsis, supported by more studies.

In this study, kidney and renal endothelial damage in sepsis was investigated. The effect of pregabalin on kidney and renal endothelial damage in sepsis was evaluated.

Pregabalin produces similar effects as gabapentin for preanesthetic sedation in cats.

OBJECTIVE: To compare the effects of oral pregabalin versus gabapentin on sedation quality and anesthesia recovery times in cats in a typical perioperative setting. ANIMALS: 50 healthy cats with > 1 kg body weight presenting for elective surgery. METHODS: In this randomized, prospective clinical trial, cats presenting to the University of California-Davis Veterinary Medical Teaching Hospital were assigned to receive buprenorphine 0.02 mg/kg IM followed by 1 of 2 oral sedation treatments: pregabalin 4 mg/kg or gabapentin 10 mg/kg. Cats were then anesthetized using a standardized protocol. Physical examination parameters and behavioral scores were measured by 2 treatment-blinded veterinarians to compare sedation levels before and after drug administration. Inadequate sedation for handling or IV catheter placement was addressed by dexmedetomidine administration. After surgery was completed, anesthesia recovery times and quality were assessed by the same veterinarians. The effects of pregabalin versus gabapentin on body temperature, respiratory rate, and heart rate were analyzed using Student t tests; behavioral assessments were analyzed using Wilcoxon signed-rank tests; and drug treatment effects on dexmedetomidine sedation rescue and frequency of delirium during anesthetic recovery were analyzed using Fisher exact tests. A P < .05 indicated statistical significance. RESULTS: There was no significant difference in change of physiologic parameters or sedation scores before and after sedation between groups. The need for rescue sedation for IV catheter placement and the incidence of emergence delirium were infrequent and similar for both treatments. CLINICAL RELEVANCE: At the doses studied, oral pregabalin and gabapentin produced indistinguishable effects as adjunctive perioperative sedation agents in cats.

Pregabalin alters reproductive performance in male mice and causes congenital anomalies in offspring.

CONTEXT: Pregabalin is an anticonvulsant drug with analgesic activity for the treatment of neuropathic pain. AIMS: To valuate the toxicity of pregabalin in reproductive parameters, spermatogenesis, and teratogenicity in the offspring of mice. METHODS: Twenty male mice were randomly distributed into two groups: PGB group and group C (n =10 per group). The animals in the PGB group received, via gavage, 200mg/kg of pregabalin diluted in distilled water daily, for a period of 45days. Group C received distilled water under the same experimental design. KEY RESULTS: In the paternal parameters of the PGB group, there was a significant increase in the size of the testicles, morphological alterations in the spermatozoa, a decrease in the Johnsen score, an increase in the Leydig cells, and a decrease in the serum level of testosterone. In the intrauterine development parameters of females mated with males from the PGB group, a significant decrease in placental weight, weight and length of fetuses, and fetal viability rate was observed. There was a significant increase in the number of resorptions and post-implantation losses. The significant anomalies observed in the offspring were alteration in the size of the kidneys, absent metacarpals and phalanges, alteration in the sternum, and supernumerary thoracic vertebrae. CONCLUSION: Results suggest that pregabalin had toxic effects on the reproductive function of male mice and teratogenic potential. IMPLICATIONS: The findings of this study may provide new hypotheses, taking into account the risk-benefit ratio for male reproduction and offspring health.

Pre-treatment with pregabalin reduces liver ischemia-reperfusion injury in rats: tissue protection with an analgesic.

OBJECTIVE: Ischemia-reperfusion injury is thought to be the most important factor affecting the success of liver surgery. Pregabalin has been studied to prevent ischemic reperfusion injury in many organs. The aim of this study was to investigate the role of pregabalin in preventing liver ischemic injury. MATERIALS AND METHODS: 40 male Wistar-Albino rats, 6-8 weeks old, were divided into 5 groups. Four groups other than the sham group were subjected to hepatic ischemia for 1 hour, followed by 2 hours of reperfusion. Effects of 30 mg/and 60 mg/kg pregabalin were evaluated by aspartate aminotransferase (AST), alanine aminotransferase (ALT), tumor necrosis factor α (TNF-α), nuclear factor-kappa B (NF-кB), interleukin (IL)-6 levels, measured in blood samples collected before and after ischemia. Apoptosis was measured by caspase-3, and tissue samples were evaluated for ischemia by histopathologic examination. RESULTS: The 60 mg pregabalin group was significantly superior (p=0.024) to the N-acetylcysteine group and the 30 mg pregabalin group for AST levels (p=0.612 and p=0.807, respectively). The difference between before and after ischemia-reperfusion blood TNF-α levels was higher in the 60 mg pregabalin group, but not significantly different from the 30 mg pregabalin and N-acetylcysteine groups (p>0.05). Tissue TNF-α levels showed that 60 mg and 30 mg pregabalin treatment was more effective than no-treatment (p=0.011, p=0.033, respectively), but not superior to N-acetylcysteine (p>0.05). CONCLUSIONS: It has been found that ischemia-reperfusion causes damage to the liver, and this damage may be irreversible if no treatment is given. Our study group, pregabalin molecule was found to be significantly effective in preventing ischemia-reperfusion injury and may have a therapeutic advantage over N-acetylcysteine.

Chronic pregabalin treatment protects against spreading depolarization and alters hippocampal synaptic characteristics in a model of familial hemiplegic migraine-type 1.

Familial hemiplegic migraine type-1 (FHM-1) is a form of migraine with aura caused by mutations in the P/Q-type (Cav2.1) voltage-gated calcium channel. Pregabalin, used clinically in the treatment of chronic pain and epilepsy, inhibits P/Q-type calcium channel activity and recent studies suggest that it may have potential for the treatment of migraine. Spreading Depolarization (SD) is a neurophysiological phenomenon that can occur during migraine with aura by propagating a wave of silenced neuronal function through cortex and sometimes subcortical brain structures. Here, utilizing an optogenetic stimulation technique optimized to allow for non-invasive initiation of cortical SD, we demonstrate that chronic pregabalin administration [12 mg/kg/day (s.c.)] in vivo increased the threshold for cortical spreading depolarization in transgenic mice harboring the clinically-relevant Cav2.1S218L mutation (S218L). In addition, chronic pregabalin treatment limited subcortical propagation of recurrent spreading depolarization events to the striatum and hippocampus in both wild-type and S218L mice. To examine contributing underlying mechanisms of action of chronic pregabalin, we performed whole-cell patch-clamp electrophysiology in CA1 neurons in ex vivo brain slices from mice treated with chronic pregabalin vs vehicle. In WT mice, chronic pregabalin produced a decrease in spontaneous excitatory postsynaptic current (sEPSC) amplitude with no effect on frequency. In contrast, in S218L mice chronic pregabalin produced an increase in sEPSC amplitude and decreased frequency. These electrophysiological findings suggest that in FHM-1 mice chronic pregabalin acts through both pre- and post-synaptic mechanisms in CA1 hippocampal neurons to elicit FHM-1 genotype-specific inhibitory action. The results highlight the potential of chronic pregabalin to limit recurrent SD to subcortical brain structures during pathophysiological events in both the genetically-normal and FHM-1 brain. The work further provides insights into FHM-1 pathophysiology and the potential for chronic pregabalin treatment to prevent SD in migraineurs.

Pregabalin inhibits purinergic P2Y2 receptor and TRPV4 to suppress astrocyte activation and to relieve neuropathic pain.

BACKGROUNDS: Transient receptor potential vanilloid 4 (TRPV4)-mediated astrocyte activation is critical to neuropathic pain. Pregabalin, a widely used drug to treat chronic pain, is reported to lower the intracellular calcium level. However, the molecular mechanism by which pregabalin decreases the intracellular calcium level remains unknown. Purinergic P2Y2 receptor-a member of the G protein-coupled receptor (GPCR) family-regulates calcium-related signal transduction in astrocyte activation. We investigated whether P2Y2 receptor is involved in the pharmacological effects of pregabalin on neuropathic pain. METHODS: Neuropathic pain was induced by chronic compression of the dorsal root ganglion (CCD) in rats. Paw withdrawal mechanical threshold (PWMT) was used for behavioral testing. Intracellular calcium concentration was measured using a fluorescent calcium indicator (Fluo-4 AM). RESULTS: We found that P2Y2 receptor protein was upregulated and astrocytes were activated in the experimental rats after CCD surgery. Lipopolysaccharide (LPS) increased the intracellular calcium concentration and induced astrocyte activation in cultured astrocytes but was prevented via P2Y2 receptor inhibitor AR-C118925 or pregabalin. Furthermore, plasmid-mediated P2Y2 receptor overexpression induced an elevation of the intracellular calcium levels and inflammation in astrocytes, which was abolished by the TRPV4 inhibitor HC-067047. AR-C118925, HC-067047, and pregabalin relieved neuropathic pain and inflammation in rats after CCD surgery. Finally, plasmid-mediated P2Y2 receptor overexpression induced neuropathic pain in rats, which was abolished by pregabalin administration. CONCLUSIONS: Pathophysiological variables that upregulated the P2Y2 receptor/TRPV4/calcium axis contribute to astrocyte activation in neuropathic pain. Pregabalin exerts an analgesic effect by inhibiting this pathway.

The investigation of antidepressant and anxiolytic effects of pregabalin and its mechanisms of action in rats.

OBJECTIVES: Pregabalin (PGB) is used in drug-resistant epilepsy. Also, it has analgesic effects in painful syndromes. Depression and anxiety are commonly seen in epilepsy and neuropathic pain patients. PGB is often combined with anxiolytics and antidepressants. We aimed to investigate the antidepressant and anxiolytic effects of PGB and compare its effects with those of antidepressant and anxiolytic drugs and their combined use. METHODS: Wistar Albino rats were used, and PGB (5, 10, 20, and 40 mg/kg), amitriptylin (AMT), fluoxetine (FLX), ketamine (KET), and diazepam (DZM), as well as combinations of PGB (20 mg/kg) with AMT, FLX, KET, and DZM, were administered. Elevated plus maze, forced swimming, and locomotor activity tests were performed. RESULTS: In the elevated plus maze, PGB10, 20, 40, AMT, FLX, and DZM increased open arm time. The PGB20+FLX combination increased compared to PGB20. In forced swimming, PGB doses increased immobility time. AMT, FLX, DZM, and KET decreased compared to control and PGB doses. Other combinations of PGB20 reversed immobility time, except FLX. In locomotor activity, PGB20, AMT, KET, and DZM decreased distance. CONCLUSION: PGB had a depressant effect in all doses and a dose-dependently anxiolytic effect. In combinations of PGB with AMT, KET, and DZM, it reversed their antidepressant effects. We assumed FLX could be preferred instead of AMT in patients using PGB. When PGB is used in combination, drug interactions should be considered. These results are also very remarkable in terms of pharmacoeconomics.

PnPP-15, a Synthetic Peptide Derived from a Toxin from Phoneutria nigriventer Spider Venom, Alleviates Diabetic Neuropathic Pain and Acts Synergistically with Pregabalin in Mice.

Diabetic neuropathic pain is one of the complications that affect a wide variety of the diabetic population and is often difficult to treat. Only a small number of patients experience pain relief, which usually comes with onerous side effects and low levels of satisfaction. The search for new analgesic drugs is necessary, given the limitations that current drugs present. Combining drugs to treat neuropathic pain has been attracting interest to improve their efficacy compared to single-drug monotherapies while also reducing dose sizes to minimize side effects. The aim of our study was to verify the antinociceptive effect of a synthetic peptide, PnPP-15, alone and combined with pregabalin, in male Swiss diabetic mice using the von Frey method. PnPP-15 is a synthetic peptide derived from PnPP19, a peptide representing a discontinuous epitope of the primary structure of the toxin PnTx2-6 from the venom of the spider Phoneutria nigriventer. The antinociceptive activity of both compounds was dose-dependent and showed synergism, which was verified by isobolographic analysis. Treatment with PnPP-15 did not cause spontaneous or forced motor changes and did not cause any damage or signs of toxicity in the analyzed organs (pancreas, lung, heart, kidney, brain, or liver). In conclusion, PnPP-15 is a great candidate for an analgesic drug against neuropathic pain caused by diabetes and exerts a synergistic effect when combined with pregabalin, allowing for even more efficient treatment.

In-vivo anti-epileptic study of newly synthesized pregabalin derivatives based on docking studies.

OBJECTIVE: The goal of the present study is to examine pretreatment with Schiff bases and derivatives of pregabalin along with their metal (Zn and Cu) complexes on the severity of epilepsy, latency time, duration of convulsions, seizure score and survival rate in mice. METHODS: To achieve the goal, a molecular docking study of analogues was carried out on a specific molecular target, such as the alpha-2δ receptor (PDB ID: 6ND9); which revealed the significant binding affinity of the analogs to their respective target. Based on the docking information, all pregabalin derivatives were synthesized and in-vivo antiepileptic effect was confirmed by applying the PTZ model that prioritized the most crucial significant points responsible for biological activity. RESULTS: The test compounds markedly increased the latency of the first seizure and reduced the frequency of seizures throughout the body and frequent spinning and jumps. Additionally, treatment with pregabalin derivatives in mice that received PTZ significantly reduced the duration of seizures and seizure score. However, it increased the survival rate of the mice. DISCUSSION: Since the newly synthesized compounds were more active as compared to the parent drug in some respects; therefore, the expansion of the project can be planned to explore clinical side of the drugs in the future.

Docking studies of Schiff bases and derivatives of Pregabalin along with their Zn and Cu metal complexesPretreatment with Schiff bases and derivatives of pregabalin along with their metal (Zn and Cu)PTZ Model of epilepsyObservation of different parameters including; the severity of epilepsy, latency time, duration of convulsions, seizure score and survival rate in miceNewly synthesized compounds were more active as compared to the parent drug.

Pregabalin can interact synergistically with Kv7 channel openers to exert antinociception in mice.

Chronic pain is a common public health problem and remains an unmet medical need. Currently available analgesics usually have limited efficacy for the treatment of chronic pain, including neuropathic pain and persistent inflammatory pain, or they are accompanied by many adverse side effects. The voltage-gated calcium channel blocker (pregabalin) and potassium channel openers (flupirtine and retigabine) have been widely used for the management of chronic pain, but their effectiveness in combination is unclear. In this research, we evaluated the antinociceptive effects of pregabalin in combination with flupirtine or retigabine in carrageenan-induced inflammatory pain and paclitaxel-induced peripheral neuropathy in mice using the von Frey test. Isobolographic analysis indicated that pregabalin exerted synergistic antinociceptive effects when combined with flupirtine or retigabine in neuropathic and inflammatory pain models. Furthermore, the antinociceptive effects of pregabalin, flupirtine/retigabine, and their combinations were significantly attenuated by the Kv7 channel blocker XE991. The favored dose ratio between pregabalin and flupirtine/retigabine in combinations was also investigated. Finally, we evaluated the motor coordination of their combinations using the rotarod test, and the outcomes underpinned their safety. Collectively, our results support the potential use of pregabalin in combination with flupirtine or retigabine to alleviate chronic pain.

The effect of gabapentin and pregabalin administration on memory in clinical and preclinical studies: a meta-analysis and systematic review.

BACKGROUND: Today, gabapentinoids such as Gabapentin (GBP) and pregabalin (PGB) are widely used as painkillers. This may alter the function of the nervous system; hence their results may include a difference in memory and processes that end in memory formation. This study aims to conclude whether gabapentinoids can alter memory or not by reviewing and analyzing clinical and preclinical studies. MATERIAL AND METHODS: A comprehensive search was carried out in databases including PUBMED, EMBASE, SCOPUS, and Web of Science. In the included studies, memory was measured as an outcome variable in clinical or preclinical studies. RESULT: A total of 21 articles (4 clinical, 17 preclinical) were included in the meta-analysis by STATA Software. The results showed that memory changes under the influence of GBP. Both the administrated dosage and the time of administration are important in the final results and latency time of retention. GBP administration in healthy animals increased latency time, whereas if the administration of GBP took place exactly before training, the latency time increased slightly. Short-term administration of PGB in healthy volunteers is accompanied by transient side effects on the CNS. However, the number and homogeneity of the studies were not such that a meta-analysis could be performed on them. CONCLUSION: Clinical and preclinical studies showed that PGB administration did not confirm its improving memory effect. GBP administration in healthy animals increased latency time and improved memory. Although it depended on the time of administration.

Pregabalin Silences Oxaliplatin-Activated Sensory Neurons to Relieve Cold Allodynia.

Oxaliplatin is a platinum-based chemotherapeutic agent that causes cold and mechanical allodynia in up to 90% of patients. Silent Nav1.8-positive nociceptive cold sensors have been shown to be unmasked by oxaliplatin, and this event has been causally linked to the development of cold allodynia. We examined the effects of pregabalin on oxaliplatin-evoked unmasking of cold sensitive neurons using mice expressing GCaMP-3 in all sensory neurons. Intravenous injection of pregabalin significantly ameliorates cold allodynia, while decreasing the number of cold sensitive neurons by altering their excitability and temperature thresholds. The silenced neurons are predominantly medium/large mechano-cold sensitive neurons, corresponding to the "silent" cold sensors activated during neuropathy. Deletion of α2δ1 subunits abolished the effects of pregabalin on both cold allodynia and the silencing of sensory neurons. Thus, these results define a novel, peripheral inhibitory effect of pregabalin on the excitability of "silent" cold-sensing neurons in a model of oxaliplatin-dependent cold allodynia.

Effect of amoxicillin/clavulanic acid in attenuating pregabalin-induced condition place preference.

Substance abuse is a worldwide problem with serious repercussions for patients and the communities where they live. Pregabalin (Lyrica), is a medication commonly used to treat neuropathic pain. Like other analgesic medications there has been concern about pregabalin abuse and misuse. Although it was initially suggested that pregabalin, like other gabapentinoids, has limited abuse liability, questions still remain concerning this inquiry. Changes in glutamate system homeostasis are a hallmark of adaptations underlying drug dependence, including down-regulation of the glutamate transporter 1 (GLT-1; SLC1A2) and the cystine/glutamate antiporter (xCT; SLC7A11). In this study, it was found that pregabalin (90 mg/kg) produces a conditioned place preference (CPP), indicative of reinforcing effects that suggest a potential for abuse liability. Moreover, like other drugs of abuse, pregabalin also produced alterations in glutamate homeostasis, reducing the mRNA expression of Slc1a2 and Slc7a11 in the nucleus accumbens (NAc) and medial prefrontal cortex (mPFC). Amoxicillin clavulanic acid, a ß-lactam antibiotic, blocked the reinforcing effects of pregabalin and normalized glutamate homeostasis. These results suggest that pregabalin has abuse potential that should be examined more critically, and that, moreover, the mechanisms underlying these effects are similar to those of other drugs of abuse, such as heroin and cocaine. Additionally, these results support previous findings showing normalization of glutamate homeostasis by ß-lactam drugs that provides a novel potential therapeutic approach for the treatment of drug abuse and dependence.

Case Series: Synergistic Effect of Gabapentin and Adjuvant Pregabalin in Neuropathic Pain.

Gabapentin and pregabalin both exert high affinity to the α2δ subunit of the voltage-gated calcium channels which inhibits excitatory neurotransmitter release. The synergistic mechanism was described in rats given combinations of gabapentin and pregabalin. In this case series, we described 2 cases which may illustrate the synergistic effect of gabapentin and pregabalin in treatment resistant neuropathic pain. Low dose pregabalin was added to therapeutic gabapentin to achieve appreciable pain reduction in one case and improved quality of life in another case. Further research with more enrollment and longer study duration may help elucidate the appropriate dosing and potential associated side effects.

Anti-neuropathic Pain Mechanistic Study on A. conyzoides Essential Oil, Precocene II, Caryophyllene, or Longifolene as Single Agents and in Combination with Pregabalin.

BACKGROUND: Neuropathic pain has become a contributor to the global burden of illness. However, the currently available drugs exhibit inadequate pain relief and significant side effects. Our previous study demonstrated that the essential oil of Ageratum conyzoides exerts potent antineuropathic pain activity through opioid receptor activation. Precocene II, longifolene, and caryophyllene are the largest component of the A. conyzoides essential oil. OBJECTIVE: The objective of the study was to determine the anti-neuropathic pain activity of precocene II, longifolene, and caryophyllene as single agents and in combination with pregabalin. Possible mechanisms of action involving the opioid receptor, ATP-sensitive potassium channel, and gammaaminobutyric acid (GABA) were further investigated. METHODS: The experimental animals (male mice Swiss Webster) were divided randomly into seven groups, namely, Normal control (naïve mice), Negative control (CMC 1%), Sham (CMC 1%), Positive control (Pregabalin 0,195 mg/ 20 g BW of mice), Test I (Precocene II 21.09 mg/Kg BW), Test II (Longifolene 9.94 mg/Kg BW), and Test III (Caryophyllene 3.64 mg/Kg BW). Each group contained 3 animals. The test groups that demonstrated anti-neuropathic pain activity were further tested in combination with pregabalin, followed by mechanistic studies. The negative, positive, and test I-III groups were induced with chronic constriction injury. RESULTS: The results of the study demonstrated that caryophyllene and longifolene, but not precocene II, exerted anti-neuropathic pain activity. The caryophyllene was shown to involve in the activation of opioid receptors and ATP-sensitive potassium channels. It was also reported to increase GABA concentration in the spinal cord. We further found that longifolene exerted its action via opioid receptor activation. The combination of A. conyzoides essential oil, longifolene, or caryophyllene with pregabalin demonstrated additive anti-neuropathic pain activity. CONCLUSION: Taken together, the results of the present study suggested that the A. conyzoides essential oil and caryophyllene have the potential to be developed as novel drugs to treat neuropathic pain.

Response profile in a rat model of exercise-induced hypoalgesia is associated with duloxetine, pregabalin and diclofenac effect on constriction-induced neuropathy.

BACKGROUND: Exercise is a known trigger of the inhibitory pain modulation system and its analgesic effect is termed exercise-induced hypoalgesia (EIH). Previous studies have demonstrated that rats with deficient analgesic response following exercise develop more significant hypersensitivity following nerve injury compared to rats with substantial analgesic response following exercise. OBJECTIVES: A rat model of EIH as an indicator of the pain inhibitory system's efficiency was used to explore the association between EIH profiles and the effect of pharmacotherapy on rat's neuropathic pain. METHODS: EIH profiles were assessed by evaluating paw responses to mechanical stimuli before and after exercise on a rotating rod. Rats with a reduction of ≤33% in responses were classified as low EIH and those with ≥67% as high EIH. Low and high EIH rats underwent sciatic nerve chronic constriction injury (CCI). Paw responses to mechanical stimuli were measured at baseline, following CCI, and after treatment with diclofenac, duloxetine or pregabalin. In a different group of low and high EIH rats, EIH was measured before and following treatment with the same medications. RESULTS: Low EIH rats developed more significant hypersensitivity following CCI. Duloxetine and pregabalin successfully reduced hypersensitivity, although significantly more so in low EIH rats. Diclofenac had limited effects, and only on low EIH rats. Four days of duloxetine administration transformed low EIH rats' profiles to high EIH. CONCLUSIONS: The findings of this study suggest that EIH profiles in rats can not only predict the development of hypersensitivity following injury but may also support targeted pharmacological treatment. SIGNIFICANCE: Exercise is a known trigger of the inhibitory pain modulation. Rats with deficient analgesic response following exercise develop more significant hypersensitivity following nerve injury. Pain modulation profiles in rats can also support targeted pharmacological treatment; rats with deficient analgesic response following exercise benefit more from treatment with duloxetine and gabapentin. Treatment with duloxetine can improve pain modulation profile.

Pregabalin Mediates Retinal Ganglion Cell Survival From Retinal Ischemia/Reperfusion Injury Via the Akt/GSK3ß/ß-Catenin Signaling Pathway.

Purpose: Progressive retinal ganglion cell (RGC) loss induced by retinal ischemia/reperfusion (RIR) injury leads to irreversible visual impairment. Pregabalin (PGB) is a promising drug for neurodegenerative diseases. However, with regard to RGC survival, its specific role and exact mechanism after RIR injury remain unclear. In this study, we sought to investigate whether PGB could protect RGCs from mitochondria-related apoptosis induced by RIR and explore the possible mechanisms. Methods: C57BL/6J mice and primary RGCs were pretreated with PGB prior to ischemia/reperfusion modeling. The retinal structure and cell morphology were assessed by immunochemical assays and optical coherence tomography. CCK8 was used to assay cell viability, and an electroretinogram was performed to detect RGC function. Mitochondrial damage was assessed by a reactive oxygen species (ROS) assay kit and transmission electron microscopy. Western blot and immunofluorescence assays quantified the expression of proteins associated with the Akt/GSK3ß/ß-catenin pathway. Results: Treatment with PGB increased the viability of RGCs in vitro. Consistently, PGB preserved the normal thickness of the retina, upregulated Bcl-2, reduced the ratio of cleaved caspase-3/caspase-3 and the expression of Bax in vivo. Meanwhile, PGB improved mitochondrial structure and prevented excessive ROS production. Moreover, PGB restored the amplitudes of oscillatory potentials and photopic negative responses following RIR. The mechanisms underlying its neuroprotective effects were attributed to upregulation of the Akt/GSK3ß/ß-catenin pathway. However, PGB-mediated neuroprotection was suppressed when using MK2206 (an Akt inhibitor), whereas it was preserved when treated with TWS119 (a GSK3ß inhibitor). Conclusions: PGB exerts a protective effect against RGC apoptosis induced by RIR injury, mediated by the Akt/GSK3ß/ß-catenin pathway.

The Acute Antiallodynic Effect of Tolperisone in Rat Neuropathic Pain and Evaluation of Its Mechanism of Action.

Current treatment approaches to manage neuropathic pain have a slow onset and their use is largely hampered by side-effects, thus there is a significant need for finding new medications. Tolperisone, a centrally acting muscle relaxant with a favorable side effect profile, has been reported to affect ion channels, which are targets for current first-line medications in neuropathic pain. Our aim was to explore its antinociceptive potency in rats developing neuropathic pain evoked by partial sciatic nerve ligation and the mechanisms involved. Acute oral tolperisone restores both the decreased paw pressure threshold and the elevated glutamate level in cerebrospinal fluid in neuropathic rats. These effects were comparable to those of pregabalin, a first-line medication in neuropathy. Tolperisone also inhibits release of glutamate from rat brain synaptosomes primarily by blockade of voltage-dependent sodium channels, although inhibition of calcium channels may also be involved at higher concentrations. However, pregabalin fails to affect glutamate release under our present conditions, indicating a different mechanism of action. These results lay the foundation of the avenue for repurposing tolperisone as an analgesic drug to relieve neuropathic pain.