| Neuropathic pain(NP)is one of the most difficult diseases to conquer.Belonging to chronic pain,NP is characterized by spontaneous pain,hyperalgesia,allodynia,and paresthesia.According to the location of the primary lesion or dysfunction,it can be classified into peripheral neuropathic pain and central neuropathic pain.As a clinical entity,NP presents unique diagnostic and therapeutic challenges,affecting 3.0 % to 8.0 % of the population.The treatments of NP are usually grouped around three categories,pharmacological,interventional and other nonpharmacological treatment.Unfortunately,quite a few patients have to seek for treatments pressingly and repeatedly,since the existing therapies are usually limited.Discovered since 19 th centrry,ozone therapy is seldom used to treat NP,let alone the related basic researches.It usually refers to oxygen-ozone mixture that can be generated by ozone generator,because the pure ozone does not exist under either natural or artificial conditions,on account of its active chemical and biological property.Currently,ozone therapy has been mainly used for treatment or prevention of intervertebral disc herniation and some conditions in the field of stomatology.Not until the last decades did some physicians also try to use ozone therapy to treat lower back pain and knee osteoarthritis through intraforamenal or intraarticular injection.Recently,to treat NP,a five-year follow-up study was conducted by Wang Jiashuang,in a hospital of southern China.It was shown that intervertebral foramen(I.V.F.)injection of ozone at the involved segmental levels for once or twice could significantly relieve pain intensity and frequency,and reduce the daily oral dose of gabapentin,which was an anticonvulsant drug.Simultaneously,life quality including sleep,emotion,and daily activities was improved markedly.However,a lack of proof-of-concept studies in animals and basic researches hinders this medical use to be studied through multicenter clinical trials.To investigate whether I.V.F.injection of ozone has analgesic effects,animal models of both neuropathic and inflammatory pain were used in the current study.Besides,the comparison between the effects of ozone(I.V.F.)and other selective molecular target drugs(I.V.F.)was conducted.Our results suggested the minimally-invasive I.V.F.injection of ozone could specifically and efficiently ease NP for a relatively long period of time,and the clinical practice should be evaluated by multicenter clinical trials.The followings are the main results:1.Minimally-invasive I.V.F.injection of ozone has no effect on mechanical and thermal pain sensitivity of na?ve Sprague-Dawley(SD)rats.Under general anesthesia,5 ?l DiI(2.5%)was injected respectively into L4 and L5 intervertebral foramen,by introducing the needle through specific points(for detail,see below).Rapid superfusion with physiological saline,the fixation with 4 % paraformaldehyde in 0.1 M PB solution,dehydration by 30% sucrose solution,and frozen section were conducted in sequence.The presence of Di I in injected DRGs by eyes and extensive red fluorescence labling cells by microscope indicated the accurate localization.Then,SD rats were randomly divided into two groups to compare the effects of air(n=8)and ozone(n=8)on the pain behavior of normal rats.After 14 days' observation,it was found that there was no significant difference between the effects of air and ozone on the paw withdrawal mechanical threshold(PWMT)or paw withdrawal thermal latency(PWTL).2.Minimally-invasive I.V.F.injection of ozone or other selective molecular target drugs has significant analgesic effect on neuropathic pain,while the former's effect lasts much longer.As for SD rats with spared nerve injury(SNI),the decreased ipsilateral paw withdrawal mechanical threshold(PWMT)could maintain more than 6 weeks.After the pain hypersensitivity reached peak and stable,single I.V.F.injection of ozone(n=15),AMD3100(Stromal cell-derived factor 1 receptor CXCR4 antagonists,n=8),A803467(selective Nav1.8 blocker,n=8),rapamycin(mammalian target of rapamycin inhibitor,n=8),or MGCD0103(selective class I histone deacetylase inhibitor,n=8)was conducted.The analgesic effect appeared just 1 day after ozone(I.V.F.)injection,peaked at 5 days after injection,maintained at least 10 days,and returned to control level 14 days after injection.However,ozone(I.V.F.)had no effect on the contralateral PWMTs.In the meanwhile,I.V.F.delivery of other four selective molecular target drugs had analgesic effect no more than 72 h,thouth each of them had significant analgesic effect in SNI rats.3.Minimally-invasive I.V.F.injection of ozone has no analgesic effect on rats with acute or chronic inflammatory pain.As for acute inflammatory pain,the bee venom(BV,n=9)model was used.The pre-treatment of ozone(I.V.F.)didn't relieve the mechanical and thermal pain hypersensitivity and spontaneous pain behaviors.As for chronic inflammatory pain,the complete Freund's adjuvant(CFA,n=9)model was used.Ozone(I.V.F.)had no significant analgesic effect on neither of mechanical and thermal pain hypersensitivity induced by CFA during the 14 days' observing.4.Pretreatment with inimally-invasive I.V.F.injection of ozone can inhance intraperitoneal injection of gabapentin's efficacy,prolongs the analgesic effect duration,suggests its synergistic effects with gabapentin.Intraperitoneal(i.p.)injection of gabapentin alone(n=8)had obvious analgesic effect on SNI rats 1.5 h after injection,and maintained till 2 h after injection.However,i.p.injection of gabapentin 5 days after ozone(I.V.F.),showed obvious analgesic effect 1 h after injection,and maintained till 3 h after injection(n=8).Furthermore,the pain reversal percentage of gabapentin on the basis of ozone(I.V.F.)was much higher(about 3-4 times)than gabapentin alone.In addition,gabapentin(i.p.)had systemic effects,while ozone(I.V.F.)didn't.Conclusions1)Minimally-invasive I.V.F.injection of ozone could significantly relieve neuropathic pain,and had no significant effect on inflammatory pain.2)Compared with other four selective molecular target drugs,minimally-invasive I.V.F.injection of ozone had analgesic effect for a much longer period.3)Minimally-invasive I.V.F.injection of ozone could inhance the analgesic effect by systemic administration of gabapentin,and prolong its duration.4)Minimally-invasive targeted I.V.F.injection of ozone had no effect on pain sensitivity of na?ve SD rats. |
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