Central terminals of nociceptors are targets for nicotine suppression of inflammation

The Effect of Smoking on the Fusion Rate of Spinal Fusion Surgery: A Systematic Review and Meta-Analysis

OBJECTIVE

To conduct a systematic review and meta-analysis comparing the fusion rate after spinal fusion surgery between smokers and nonsmokers.

METHODS

We searched PubMed, Embase, Cochrane Library, and Web of Science electronic databases through March 10, 2021 for cohort and case-control studies assessing the effect of smoking on the fusion rate of spinal fusion surgery. Two researchers independently screened the literature and extracted data according to the inclusion and exclusion criteria. Statistical analysis was performed using RevMan, version 5.4.

RESULTS

A total of 26 studies, including 4 case-control studies and 22 cohort studies, with 4409 patients, were included in the present meta-analysis. Follow-up was at least 6 months. Overall, the pooled results demonstrated that the fusion rate of smokers after spinal fusion was significantly lower than that of nonsmokers. The odds ratio (OR) was 0.55 (95% confidence interval [CI] 0.45-0.67, P < 0.0001). Subgroup analyses by fusion level showed the adverse effect of smoking on the fusion rate at single level (OR 0.61, 95% CI 0.41-0.91, P = 0.02) was more significant than that of multiple levels (OR 0.55, 95% CI 0.38-0.80, P = 0.0010). Subgroup analysis according to the type of bone graft revealed an apparent association between smoking and fusion rate in the autograft subgroup (OR 0.47, 95% CI 0.33-0.66, P < 0.0001) but not in the allograft subgroup (OR 0.69, 95% CI 0.47-1.01, P = 0.06).

CONCLUSIONS

The fusion rate of smokers is significantly lower than that of nonsmokers in spinal fusion surgery. Smokers should be encouraged to quit smoking to improve the outcome of spinal fusion surgery.

Thumb Carpometacarpal Arthritis: Prognostic Indicators and Timing of Further Intervention Following Corticosteroid Injection

PURPOSE

Corticosteroid injections are commonly used to treat thumb carpometacarpal arthritis in adults. We aimed to define the timing of surgery following an initial corticosteroid injection and identify patient-specific factors that influence the likelihood of repeat injection or surgery.

METHODS

We performed a retrospective analysis of all patients who underwent a first-time corticosteroid injection for carpometacarpal arthritis between 2009 and 2017. Demographic information, radiographic classification, additional nonsurgical therapies, complications, and outcomes were collected. Primary outcomes were repeat injection and surgical reconstruction. Kaplan-Meier survival analysis was used to characterize the timing of surgical intervention and Cox regression modeling was used to identify predictors of subsequent intervention.

RESULTS

Two-hundred thirty-nine patients (average age, 62.9 years) were identified, of which 141 (59.0%) had a repeat injection and 90 (37.6%) underwent surgery. There were no patient-specific characteristics associated with repeat injection. Eaton stage III/IV arthritis at initial presentation, current smoking status, and prior ipsilateral hand surgery were associated with an increased likelihood of surgery. By Kaplan-Meier analyses, 87.7% of patients who presented with Eaton III/IV arthritis did not have surgery within a year and 66.7% of these patients did not have surgery within 5 years.

CONCLUSIONS

In this retrospective observational cohort study with 10-year follow-up from a 4-surgeon practice, advanced radiographic arthritis, current smoking status, and a history of ipsilateral hand surgery were patient-specific factors that predicted progression to surgery following injection. Of patients who presented with advanced radiographic arthritis, one-third underwent surgery within 5 years of initial injection. Although injection efficacy and causality cannot be inferred based on an observational longitudinal analysis, these data identify patient-specific factors that may have an impact on surgical decision-making and a potential timeframe for future intervention.

TYPE OF STUDY/LEVEL OF EVIDENCE

Prognostic IV.

Photobiomodulation Decreases Hyperalgesia in Complex Regional Pain Syndrome: An Experimental Mouse Model Subjected to Nicotine

BACKGROUND AND OBJECTIVES

Complex regional pain syndrome (CRPS) is defined as an extreme and chronic pain condition, and photobiomodulation has relevance as a complementary treatment for CRPS. The objective of this study was to verify the effects of photobiomodulation (PBMT) therapy protocols at two wavelengths 660 and 830 nm, associated or not to nicotine in complex regional pain syndrome type I (CRPS-I).

STUDY DESIGN/MATERIALS AND METHODS

Sixty-four Swiss mice were divided into the following groups: (i) Naive, (ii) Sham, (iii) Control, (iv) 660 nm, (v) 830 nm, (vii) Nicotine, (vii) Nicotine/660 nm, and (viii) Nicotine/830 nm. CRPS-I was induced in an experimental ischemia/reperfusion model by affixing an elastic ring, proximal to the ankle joint of the right hind mouse paw, for 3 hours. Nicotine, in the respective groups was administered for 28 days prior to the induction of CRPS-I. PBMT was applied immediately after the procedure and for 20 consecutive days. The animals were evaluated for mechanical hyperalgesia, thermal hyperalgesia, paw edema at baseline and for 7, 14, and 21 days. Statistical analyses comprised a mixed-effects model, using the Tukey post hoc test (P < 0.05).

RESULTS

The PBMT wavelengths in 660 and 830 nm groups had beneficial effects (P < 0.05) in reducing mechanical and thermal hyperalgesia, but the effects at 660 nm were significantly better than 830 nm. At reducing edema, both wavelengths had significant effects statistically, absolutely no difference between them.

CONCLUSIONS

The use of PBMT (660 and 830 nm) was effective in reducing mechanical hyperalgesia and thermal hyperalgesia; however, PBMT at 660 nm generated significant results. In reducing edema, both wavelengths had similar effects, which were significant statistically. The deleterious effects of nicotine were evident statistically and were softened when treated with PBMT (P < 0.05). Lasers Surg. Med. © 2020 Wiley Periodicals, Inc.

Acute analgesic effects of nicotine and tobacco in humans: a meta-analysis

Although animal models have consistently demonstrated acute pain inhibitory effects of nicotine and tobacco, human experimental studies have yielded mixed results. The main goal of this meta-analysis was to quantify the effects of nicotine/tobacco administration on human experimental pain threshold and tolerance ratings. A search of PubMed and PsycINFO online databases identified 13 eligible articles, including k = 21 tests of pain tolerance (N = 393) and k = 15 tests of pain threshold (N = 339). Meta-analytic integration for both threshold and tolerance outcomes revealed that nicotine administered through tobacco smoke and other delivery systems (eg, patch, nasal spray) produced acute analgesic effects that may be characterized as small to medium in magnitude (Hedges g = 0.35, 95% confidence interval = 0.21-0.50). Publication bias-corrected estimates remained significant and indicated that these effects may be closer to small. Sex composition was observed to be a significant moderator, such that pain threshold effects were more robust among samples that included more men than women. These results help to clarify a mixed literature and may ultimately help to inform the treatment of both pain and nicotine dependence. Pain and tobacco smoking are both highly prevalent and comorbid conditions. Current smoking has been associated with more severe chronic pain and physical impairment. Acute nicotine-induced analgesia could make smoking more rewarding and harder to give up. Future research should use dynamic measures of experimental pain reactivity and further explore biopsychosocial mechanisms of action.

Distinct terminal and cell body mechanisms in the nociceptor mediate hyperalgesic priming

Hyperalgesic priming, a form of neuroplasticity in nociceptors, is a model of the transition from acute to chronic pain in the rat, which involves signaling from the site of an acute tissue insult in the vicinity of the peripheral terminal of a nociceptor to its cell body that, in turn, induces a signal that travels back to the terminal to mediate a marked prolongation of prostaglandin E2-induced hyperalgesia. In the present experiments, we studied the underlying mechanisms in the cell body and compared them to the mechanisms in the nerve terminal. Injection of a cell-permeant cAMP analog, 8-bromo cAMP, into the dorsal root ganglion induced mechanical hyperalgesia and priming with an onset more rapid than when induced at the peripheral terminal. Priming induced by intraganglion 8-bromo cAMP was prevented by an oligodeoxynucleotide antisense to mRNA for a transcription factor, cAMP response element-binding protein (CREB), and by an inhibitor of importin, which is required for activated CREB to get into the nucleus. While peripheral administration of 8-bromo cAMP also produced hyperalgesia, it did not produce priming. Conversely, interventions administered in the vicinity of the peripheral terminal of the nociceptor that induces priming-PKCε activator, NGF, and TNF-α-when injected into the ganglion produce hyperalgesia but not priming. The protein translation inhibitor cordycepin, injected at the peripheral terminal but not into the ganglion, reverses priming induced at either the ganglion or peripheral terminal of the nociceptor. These data implicate different mechanisms in the soma and terminal in the transition to chronic pain.

Smoking and osteoarthritis: a review of the evidence and its implications

A number of reports including a recent publication in Osteoarthritis and Cartilage have suggested that smokers have a lower than expected prevalence of osteoarthritis (OA) than nonsmokers. We review the evidence linking smoking with OA, suggest approaches whereby the direct and indirect effects of smoking on OA might be distinguished, highlight two diseases, ulcerative colitis and Parkinson's disease, where smoking is protective, discuss mechanisms by which nicotine might act and lastly explore the association of smoking with enhanced musculoskeletal pain.

Role of α5-containing nicotinic receptors in neuropathic pain and response to nicotine

Nicotinic receptors in the central nervous system (nAChRs) are known to play important roles in pain processing and modulate behavioral responses to analgesic drugs, including nicotine. The presence of the α5-neuronal nicotinic accessory subunit in the nicotinic receptor complex is increasingly understood to modulate reward and aversive states, addiction, and possibly pathological pain. In the current study, using α5-knockout (KO) mice and subunit-specific antibodies, we assess the role of α5-containing neuronal nicotinic receptors in neuropathic pain and in the analgesic response to nicotine. After chronic constriction injury (CCI) or partial sciatic nerve ligation (PSNL), no differences in mechanical, heat, or cold hyperalgesia were found in wild-type (WT) versus α5-KO littermate mice. The number of α5-containing nAChRs was decreased (rather than increased) after CCI in the spinal cord and in the thalamus. Nevertheless, thermal analgesic response to nicotine was marginally reduced in CCI α5-KO mice at 4 days after CCI, but not at later timepoints or after PSNL. Interestingly, upon daily intermittent nicotine injections in unoperated mice, WT animals developed tolerance to nicotine-induced analgesia to a larger extent than α5-KO mice. Our results suggest that α5-containing nAChRs mediate analgesic tolerance to nicotine but do not play a major role in neuropathic pain.

Effects of α7 positive allosteric modulators in murine inflammatory and chronic neuropathic pain models

Agonists and positive allosteric modulators (PAMs) of α7 nicotinic acetylcholine receptors (nAChRs) are currently being considered as novel therapeutic approaches for managing cognitive deficits in schizophrenia and Alzheimer's disease. Though α7 agonists were recently found to possess antinociceptive and anti-inflammatory properties in rodent models of chronic neuropathic pain and inflammation, the effects of α7 nAChRs PAMs on chronic pain and inflammation remain largely unknown. The present study investigated whether PAMs, by increasing endogenous cholinergic tone, potentiate α7 nAChRs function to attenuate inflammatory and chronic neuropathic pain in mice. We tested two types of PAMS, type I (NS1738) and type II (PNU-120596) in carrageenan-induced inflammatory pain and chronic constriction injury (CCI) neuropathic pain models. We found that both NS1738 and PNU-120596 significantly reduced thermal hyperalgesia, while only PNU-120596 significantly reduced edema caused by a hind paw infusion of carrageenan. Importantly, PNU-120596 reversed established thermal hyperalgesia and edema induced by carrageenan. In the CCI model, PNU-120596 had long-lasting (up to 6 h), dose-dependent anti-hyperalgesic and anti-allodynic effects after a single injection, while NS1738 was inactive. Systemic administration of the α7 nAChR antagonist MLA reversed PNU-120596's effects, suggesting the involvement of central and peripheral α7 nAChRs. Furthermore, PNU-120596 enhanced an ineffective dose of selective agonist PHA-543613 to produce anti-allodynic effects in the CCI model. Our results indicate that the type II α7 nAChRs PAM PNU-120596, but not the type I α7 nAChRs PAM NS1738, shows significant anti-edematous and anti-allodynic effects in inflammatory and CCI pain models in mice.

Pain, nicotine, and smoking: research findings and mechanistic considerations

Tobacco addiction and chronic pain represent 2 highly prevalent and comorbid conditions that engender substantial burdens upon individuals and systems. Interrelations between pain and smoking have been of clinical and empirical interest for decades, and research in this area has increased dramatically over the past 5 years. We conceptualize the interaction of pain and smoking as a prototypical example of the biopsychosocial model. Accordingly, we extrapolated from behavioral, cognitive, affective, biomedical, and social perspectives to propose causal mechanisms that may contribute to the observed comorbidity between these 2 conditions. The extant literature was 1st dichotomized into investigations of either effects of smoking on pain or effects of pain on smoking. We then integrated these findings to present a reciprocal model of pain and smoking that is hypothesized to interact in the manner of a positive feedback loop, resulting in greater pain and increased smoking. Finally, we proposed directions for future research and discussed clinical implications for smokers with comorbid pain disorders. We observed modest evidence that smoking may be a risk factor in the multifactorial etiology of some chronically painful conditions and that pain may come to serve as a potent motivator of smoking. We also found that whereas animal studies yielded consistent support for direct pain-inhibitory effects of nicotine and tobacco, results from human studies were much less consistent. Future research in the emerging area of pain and smoking has the potential to inform theoretical and clinical applications with respect to tobacco smoking, chronic pain, and their comorbid presentation. (PsycINFO Database Record (c) 2011 APA, all rights reserved).

Antinociceptive and anti-inflammatory effects of choline in a mouse model of postoperative pain

BACKGROUND

Choline is a dietary supplement that activates alpha7 nicotinic receptors. alpha7 nicotinic activation reduces cytokine production by macrophages and has antinociceptive activity in inflammatory pain models. We hypothesized that systemic administration of choline would reduce the inflammatory response from macrophages and have antinociceptive efficacy in a murine model of postoperative pain.

METHODS

We studied the response of wild-type and alpha7 nicotinic knockout mice to heat and punctate pressure after a model surgical procedure. We investigated the effect of genotype and choline treatment on alpha-bungarotoxin binding to, and their production of tumour necrosis factor (TNF) from, macrophages.

RESULTS

Choline provided moderate antinociception. The ED(50) for choline inhibition of heat-induced allodynia was 1.7 mg kg(-1) h(-1). The ED(50) for punctate pressure threshold was 4.7 mg kg(-1) h(-1) choline. alpha7 nicotinic knockout mice had no change in hypersensitivity to heat or pressure and were significantly different from littermate controls when treated with choline 5 mg kg(-1) h(-1) (P<0.05, 0.01). Choline 100 mM reduced binding of alpha-bungarotoxin to macrophages by 72% and decreased their release of TNF by up to 51 (sd 11)%. There was no difference by genotype in the inhibition of TNF release by choline.

CONCLUSIONS

Systemic choline is a moderately effective analgesic via activation of alpha7 nicotinic acetylcholine receptors. The antinocicepive effect may not be mediated by a reduction of TNF pathway cytokine release from macrophages. Although choline at millimolar concentrations clearly inhibits the release of TNF, this effect is not alpha7 subunit-dependent and occurs at concentrations likely higher than reached systemically in vivo.

Peripheral nerve injury alters spinal nicotinic acetylcholine receptor pharmacology

Nicotinic acetylcholine receptors are widely expressed in the rat spinal cord and modulate innocuous and nociceptive transmission. The present studies were designed to investigate the plasticity of spinal nicotinic acetylcholine receptors modulating mechanosensitive information following spinal nerve ligation. A tonic inhibitory cholinergic tone mediated by dihydro-beta-erythroidine- (DHbetaE) and methyllycaconitine- (MLA) sensitive nicotinic acetylcholine receptors was identified in the normal rat spinal cord and cholinergic tone at both populations of nicotinic acetylcholine receptors was lost ipsilateral to spinal nerve ligation. The administration of intrathecal nicotinic acetylcholine receptor agonists reduced mechanical paw pressure thresholds with a potency of epibatidine=A-85380>>nicotine>choline in the normal rat. Following spinal nerve ligation, intrathecal epibatidine and nicotine produced an ipsilateral antinociception, but intrathecal A-85380 and choline did not. The antinociceptive response to intrathecal nicotine was blocked with the alpha7 and alpha9alpha10-selective nicotinic acetylcholine receptor antagonist, MLA, and the alphabeta heteromeric nicotinic acetylcholine receptor antagonist, DHbetaE. The antinociceptive effects of both intrathecal nicotine and epibatidine were mediated by GABA(A) receptors. Spinal [(3)H]epibatidine saturation binding was unchanged in spinal nerve-ligated rats, but spinal nerve ligation did increase the ability of nicotine to displace [(3)H]epibatidine from spinal cord membranes. Spinal nerve ligation altered the expression of nicotinic acetylcholine receptor subunits ipsilaterally, with a large increase in the modulatory alpha5 subunit. Taken together these results suggest that pro- and antinociceptive populations of spinal nicotinic acetylcholine receptors modulate the transmission of mechanosensitive information and that spinal nerve ligation-induced changes in spinal nicotinic acetylcholine receptors likely result from a change in subunit composition rather than overt loss of nicotinic acetylcholine receptor subtypes.

Cigarette smoking and radiographic progression in rheumatoid arthritis

BACKGROUND

Smoking is a well-established environmental risk factor for the development of rheumatoid arthritis (RA). However, it remains unclear whether smoking influences RA disease progression and whether smokers have more radiographic damage progression than non-smokers over time.

OBJECTIVE

To compare the rates of radiographic damage progression in current smokers and non-smokers in a large prospective RA cohort.

METHODS

The SCQM-RA is a population-based registry monitoring disease activity, radiographic damage and symptoms at regular intervals. All patients in the SCQM-RA database with sequential plain radiographs were included. Joint erosions were assessed in 38 hand and foot joints with a validated scoring method. The rate of erosion progression was analysed using multivariate longitudinal regression models and adjusted for potential confounders.

RESULTS

2004 RA patients with a mean of 3.6 sequential radiographs and 3.1 years of follow-up were included. The 545 (27%) current smokers smoked on average 16 cigarettes per day and had a mean past smoking exposure of 20.6 pack-years. Radiographic joint damage progressed at a similar rate in current smokers and non-smokers (p = 0.26). However, smoking intensity was associated with a significant inverse dose-response; heavy smokers (>1 pack-day) progressed significantly less than non-smokers or moderate smokers (p<0.001).

CONCLUSION

Radiographic joint damage progressed at an equivalent rate in smokers and non-smokers. Furthermore, a significant trend was observed for reduced radiographic progression and generally more favourable functional scores among heavy smokers, suggesting that cigarette smoke does not accelerate RA disease progression.

The efficacy of rhBMP-2 for posterolateral lumbar fusion in smokers

STUDY DESIGN

Retrospective review of prospectively collected data, as part of an IRB-approved, FDA-regulated, randomized, nonblinded IDE trial of rhBMP-2 matrix for lumbar spinal fusion.

OBJECTIVES

The purpose of this study is to examine the influence of smoking on fusion rate and outcome in a large series of patients treated with an rhBMP-2 matrix (AMPLIFY) or iliac crest bone graft as part of a randomized IDE trial for single-level lumbar fusion.

SUMMARY OF BACKGROUND DATA

Preclinical studies suggest that bone morphogenetic proteins (BMPs) are able to reverse the negative influence of nicotine on fusion healing in animal models. It remains unclear if a similar benefit will be seen in humans, and if so, what formulation and amount of BMP will be required to achieve that improvement.

METHODS

We reviewed the clinical and radiographic records of 148 patients who underwent single-level instrumented lumbar fusion at three spine centers as part of an ongoing FDA-regulated IDE trial. Clinical outcome measures included Oswestry Disability Index, SF-36, back, and leg pain scores. Radiographic measures were plain radiographs with flexion-extension views and fine cut computed tomography scans with sagittal and coronal reconstruction. Fusion success was determined by independent radiologist readings.

RESULTS

At 2 years postoperatively, solid fusion was demonstrated in all 55 nonsmokers in the rhBMP-2 group (100%). Successful fusion was seen in 20 of 21 smokers in the rhBMP-2 group (95.2%). Fusion was achieved in 48 of 51 nonsmokers in the iliac crest bone graft (ICBG) group (94.1%), but only 16 of 21 smokers (76.2%) in the ICBG group.

CONCLUSIONS

The results of this study suggest that rhBMP-2 may enhance fusion rate in cigarette smokers undergoing single-level instrumented posterolateral lumbar fusion. Despite the improvement in fusion rate with rhBMP-2, clinical outcomes measures were still adversely affected in smokers.

Fine specificity of the Ro/SSA autoantibody response in relation to serological and clinical findings in 96 patients with self-reported cutaneous symptoms induced by the sun

Anti-Ro/SSA assays assist the clinician in distinguishing autoimmune diseases such as Sjögrenś syndrome (SS), systemic lupus erythematosus (SLE) and subacute cutaneous lupus erythematosus (SCLE). The objective of the study was to investigate the fine specificity of the autoantibodies in relation to clinical presentation as well as environmental and endogenous factors such as photosensitivity, smoking and immunoglobulin (Ig) levels in patients with Ro/SSA autoantibodies. Serum samples from 96 anti-Ro/SSA positive photosensitive patients were tested for autoantibody levels by enzyme-linked immunosorbent assay (ELISA) using purified recombinant Ro52 kd, Ro60 kd and La proteins as antigens. The highest levels of anti-Ro52 and anti-La were observed in patients with primary SS, and the lowest levels of anti-Ro52 in chronic cutaneous lupus erythematosus (CCLE). SCLE patients with systemic disease (SLE and/or SS) showed higher levels of anti-Ro52 than SCLE limited to the skin. A correlation between high serum levels of IgG and anti-Ro52 (P < 0.01) and between IgA and anti-Ro52 (P < 0.05) and anti-Ro60 (P < 0.05) was found. Polymorphic light eruption (PLE) was common in all diagnostic groups but did not correlate with autoantibody levels. Smoking was more common in lupus patients than in SS patients. Our findings thus propose different mechanisms for different clinical presentations of Ro/SSA positive patients. The testing of anti-Ro52 antibodies might serve as a prognostic tool in photosensitive cutaneous diseases.

Inflammatory, autoimmune, chronic diseases: bad diet and physical inactivity are causes or effects?

It is now well established that most chronic diseases, especially those identified as inflammatory, are statistically correlated with some typical dietary excesses and physical inactivity. But do really these habits cause the diseases, or they result from them? Current opinion favours the first option, but fails to explain why the satisfaction of eating, naturally evolved in our brains to produce health, apparently induces countless millions of people to eat unrestrictedly until becoming mortally sick, whereas trying to keep a theoretically healthy diet is most often a real torture. The inverse explanation makes much more sense: since inflammation produces much heat, calorie-rich diets are required. An inflamed digestive tract lacks digestive power and is easily irritated or damaged by solid objects, therefore requiring a refined, concentrated, low-fibre diet. And inflamed or merely sick organisms are easily exhausted by physical effort, hence physical inactivity. This study confirms that, most probably, the primary causes of inflammatory diseases are always external inflammatory agents, like infectious micro-organisms or toxic substances, of which a particularly ubiquitous example is nicotine. High-calorie/low-fibre diets and physical inactivity are direct consequences of generalised inflammation. Inversely, in most cases, physical exercise and moderation in eating, by themselves, cannot substantially suppress inflammations, but they can prevent them from being further reinforced by the neural reward system. Moreover, diets and exercise causing important suffering will usually do more harm than good, especially to children and young people, not to mention pregnant or nursing women. Only the identification and elimination of the inflammatory agents can efficiently prevent and cure inflammatory diseases, and currently nicotine, absorbed intentionally or passively, from tobacco or other sources, must be considered the chief suspect because of its inflammatory power, ubiquity and addictive properties.

Endogenous opiates and behavior: 2004

This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Neuronal nicotinic receptors as targets for novel analgesics

The potential use of nicotinic acetylcholine receptor agonists has been the subject of a number of recent reviews. Despite the promises of better things to come, few new compounds have been identified that circumvent the issues hindering the widespread use of the previously described nicotinic analgesics, mainly a narrow therapeutic window between analgesic efficacy and toxicity, and a lack of knowledge of native nicotinic acetylcholine receptor expression. However, several recent developments have potentially opened new windows of opportunity in the use of nicotinic agents for analgesia. A small number of laboratories have reported that peripheral nerve injury alters the pharmacology of nicotinic receptors, resulting in a leftward shift of analgesic potency but not of toxicity. Another important development in the pathophysiology of neuropathic pain is the reliance of nerve injury-induced behavioural hypersensitivity on both peripheral and central neural immune interactions. Finally, the reported neuroprotective effects of nicotine following spinal cord injury may provide an opportunity for the development of selective nicotinic agonists that are capable of attenuating chronic pain. The current review will attempt to highlight these recent developments and outline key findings that demonstrate further opportunity for the development of nicotinic agonists as novel analgesics.

Exposure to nicotine is probably a major cause of inflammatory diseases among non-smokers

This article assesses the hypothesis that most inflammatory diseases are conditioned responses caused by the psychoactive action of nicotine. Even in very 'light' passive smokers, the repeated nicotinic stimulation of the reward system can produce, through classical and subsequent operant conditioning, unconscious addiction to most relevant perceptions occurring simultaneously, including the artificial, non-localised sensation of pain or sickness caused by the action of nicotine on the nociceptive 'cholinergic anti-inflammatory pathway'. During nicotine abstinence and especially under stress, the brain previously addicted to this pain is compelled to reproduce it by the only method available without nicotine: causing lesions or cellular stress in one's organism, for example, by triggering intense inflammations. The author's observations and two independent studies have confirmed that nicotine withdrawal causes inflammatory crises. Furthermore, there is evidence that severe inflammations can be triggered even by almost unnoticeable exposures to nicotine, for example, by staying several minutes outdoors at a few metres from smokers. This has been clearly observed by one patient and can be deduced from theoretical considerations (sensitivity of neural pathways and cumulativeness of conditioning processes) and an animal experimental reference, and is confirmed by the fact that most inflammatory diseases affect similarly all non-smokers regardless of their apparent exposure to nicotine, despite the proven relation between nicotine withdrawal and inflammation. This sensitivity implies that the outdoors atmosphere of most densely populated urban areas represents now a serious health hazard, probably requiring the prohibition of all smokable forms of nicotine. The usual anti-smoking measures focused on closed spaces are inefficient against this danger.

Nicotine effects on skin: Are they positive or negative?

The adverse effects of tobacco on the skin are well known but the role of nicotine is more controversial. Nicotinic receptors are expressed in the skin, on keratinocytes, fibroblasts and blood vessels. Nicotine induces vasoconstriction associated with local hyperaemia. It inhibits inflammation through effects on central and peripheral nervous system and through direct effect on immune cells. It delays wound healing and accelerates skin aging. The role of nicotine on skin diseases remains unclear. Therapeutic effects of nicotine could be possible and this a new stimulating field of research.