Impact of chronic nicotine on sciatic nerve injury in the rat

Consensus statement on smoking cessation in patients with pain

Smoking is closely associated with the development of various cancers and tobacco-related illnesses such as cardiovascular and respiratory disorders. However, data are scarce on the relationship between smoking and both acute and chronic pain. In addition to nicotine, tobacco smoke contains more than 4000 different compounds. Although nicotine is not the sole cause of smoking-induced diseases, it plays a critical role in pain-related pathophysiology. Despite the acute analgesic effects of nicotine, long-term exposure leads to tolerance and increased pain sensitivity due to nicotinic acetylcholine receptor desensitization and neuronal plastic changes. The purpose of smoking cessation interventions in smoking patients with pain is primarily not only to reduce their pain and associated limitations in activities of daily living, but also to improve the outcomes of underlying pain-causing conditions and reduce the risks of tobacco-related disorders. This statement aims to summarize the available evidence on the impact of smoking on pain and to inform medical professionals of the significance of smoking cessation in patients with pain.

Predictors of severe postoperative pain after orthopedic surgery in the immediate postoperative period

AIM

Severe pain in the immediate postoperative period can negatively affect patients' quality of recovery, prolong hospital stay, and increase the risk of developing persistent pain. This study aimed to examine the predictors of severe postoperative pain in the immediate postoperative period among orthopedic trauma patients.

METHODS

A prospective observational study design was used. Data were collected from 153 patients that underwent orthopedic surgery procedures. Pain scores were assessed by a numeric pain scale at 45 min in the Post Anesthesia Care Unit. Physical health status was measured by the American Society of Anesthesiologists Status Classification System, and total dose of opioids (converted to morphine equivalents) and other demographic and clinical characteristics were recorded from medical records.

RESULTS

Preoperative smoking and physical health status were statistically significant predictors of severe postoperative pain in the immediate postoperative period. The odds of severe postoperative pain for smokers were 2.42 times the odds of nonsmokers. Patients with severe systemic disease showed 4.27 times lower odds of severe pain than more healthy patients.

CONCLUSION

Preoperative predictors of severe postoperative pain should be considered when assessing and treating orthopedic patients postoperatively to assure adequate pain relief.

Nicotine induces P2X4 receptor, interleukin-1 beta, and brain-derived neurotrophic factor expression in BV2 microglia cells

OBJECTIVE

Upregulation of P2X4 receptor (P2X4R), brain-derived neurotrophic factor (BDNF), and interleukin-1 beta (IL-1β) in activated microglia is associated with hyperalgesia. This study investigated whether nicotine increases pain hypersensitivity by altering the expression of these molecules in microglia. We also examined the role of interferon regulatory factor 8 (IRF8) in this process.

METHODS

Experiments were performed in BV2 microglial cells. IRF8 was knocked down or overexpressed using lentiviruses harboring a short hairpin RNA targeting IRF8 or an IRF8 overexpression construct, respectively. P2X4R, BDNF, and IL-1β mRNA and protein levels were evaluated by real-time PCR and western blotting, respectively, and BDNF and IL-1β secretion was assessed by ELISA.

RESULTS

Chronic nicotine exposure enhanced the expression of P2X4R, BDNF, and IL-1β in BV2 cells, and stimulated the release of BDNF and IL-1β in the presence of ATP. IRF8 was found to mediate the nicotine-induced increases in BDNF and IL-1β mRNA and P2X4R protein levels in BV2 cells.

CONCLUSION

Nicotine may increase pain hypersensitivity by promoting the expression of P2X4R, BDNF, and IL-1β through modulation of IRF8 levels in microglial cells.

Tobacco use and neurogenesis: A theoretical review of pathophysiological mechanism affecting the outcome of peripheral nerve regeneration

Peripheral nerve injury often requires medical intervention. Unfortunately, many patients never have a full recovery, despite a multi-disciplinary approach, including operative intervention and physical and/or occupational therapy. Outcomes are multifactorial, but are largely affected by the original injury severity, and patient comorbidities. A lcoholism, diabetes mellitus and ageing may detrimentally affect the outcomes of nerve injury; however little is known about tobacco's potential impact on nerve regeneration. Tobacco has known immunomodulatory effects, which suggests that it might affect peripheral nerve regeneration and functional recovery following injury. This review characterizes the effects of tobacco use on the complex cellular and chemokine interactions in peripheral nerve regeneration.

Role of Brain Derived Extracellular Vesicles in Decoding Sex Differences Associated with Nicotine Self-Administration

Smoking remains a significant health and economic concern in the United States. Furthermore, the emerging pattern of nicotine intake between sexes further adds a layer of complexity. Nicotine is a potent psychostimulant with a high addiction liability that can significantly alter brain function. However, the neurobiological mechanisms underlying nicotine’s impact on brain function and behavior remain unclear. Elucidation of these mechanisms is of high clinical importance and may lead to improved therapeutics for smoking cessation. To fill in this critical knowledge gap, our current study focused on identifying sex-specific brain-derived extracellular vesicles (BDEV) signatures in male and female rats post nicotine self-administration. Extracellular vesicles (EVs) are comprised of phospholipid nanovesicles such as apoptotic bodies, microvesicles (MVs), and exosomes based on their origin or size. EVs are garnering significant attention as molecules involved in cell–cell communication and thus regulating the pathophysiology of several diseases. Interestingly, females post nicotine self-administration, showed larger BDEV sizes, along with impaired EV biogenesis compared to males. Next, using quantitative mass spectrometry-based proteomics, we identified BDEV signatures, including distinct molecular pathways, impacted between males and females. In summary, this study has identified sex-specific changes in BDEV biogenesis, protein cargo signatures, and molecular pathways associated with long-term nicotine self-administration.

Relationship between pain outcomes and smoking history following video-assisted thoracic surgery for lobectomy: a retrospective study

Purpose

The relationship between chronic smoking history and postoperative pain remains controversial. This study aimed to elucidate this relationship in non-small cell lung cancer (NSCLC) patients who underwent video-assisted thoracic surgery (VATS) lobectomy.

Patients and methods

This retrospective observational study included NSCLC patients treated with VATS lobectomy between January 2011 and July 2017. Demographic and clinical information, including preoperative smoking history, was collected. The primary goal was to investigate the relationship between smoking history and postoperative pain outcomes (oral morphine equivalent [OME] consumption and pain score). Multivariate linear regression analysis was performed, and P<0.05 was considered as statistically significant.

Results

A total of 1,785 patients were included in the final analysis. Multivariate linear regression analysis revealed that total smoking amount (in packs), status as current smoker, and cessation time did not have an association with OME consumption (mg) or pain scores on postoperative days 0–2 (P>0.05). However, patients who had never smoked consumed less morphine equivalent analgesics (mg) on postoperative days 0–2 (coefficient: −17.48, 95% CI [−33.83, −1.13], P=0.036) compared to patients who had a history of smoking.

Conclusion

Patients who had never smoked had lower opioid analgesics consumption on the days immediately following surgery, while being a current smoker or the total amount of smoking in packs did not affect postoperative pain outcomes after VATS lung lobectomy.

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.

Smoking is associated with reduced leptin and neuropeptide Y levels and higher pain experience in patients with fibromyalgia

Smoking deregulates neuroendocrine responses to pain supporting production of neuropeptide Y (NpY) by direct stimulation of nicotinic receptors or by inhibiting adipokine leptin. Present study addressed the effect of cigarette smoking on adipokines and pain parameters, in 62 women with fibromyalgia (FM) pain syndrome with unknown etiology. Pain was characterized by a visual analogue scale, tender point (TP) counts, pressure pain threshold, and neuroendocrine markers NpY and substance P (sP). Levels of IGF-1, leptin, resistin, visfatin, and adiponectin were measured in blood and cerebrospinal fluid. Current smokers (n = 18) had lower levels of leptin compared to ex-smokers (n = 25, P = 0.002), while the expected NpY increase was absent in FM patients. In smokers, this was transcribed in higher VAS-pain (P = 0.04) and TP count (P = 0.03), lower pain threshold (P = 0.01), since NpY levels were directly related to the pain threshold (rho = 0.414) and inversely related to TP counts (rho = −0.375). This study shows that patients with FM have no increase of NpY levels in response to smoking despite the low levels of leptin. Deregulation of the balance between leptin and neuropeptide Y may be one of the essential mechanisms of chronic pain in FM.

Increased pain in response to mechanical or thermal stimulation in a rat model of incision-induced pain with nicotine dependence and withdrawal

The aim of this study was to observe the changes in mechanical withdrawal threshold (MWT) and thermal withdrawal latency (TWL) in a rat model of incisional pain with nicotine dependence and withdrawal. Twelve Wistar rats were randomly divided into a control and a withdrawal group, with 6 rats per group. In the control group, the rats were raised in normal conditions for 7 days without any treatment. A model of plantar incisional pain was established in the right lower extremity and changes in the plantar MWT and TWL of the healthy and operative sides were observed for 7 successive days. In the withdrawal group, the rats were raised in normal conditions and treated with a subcutaneous injection of pure nicotine (3 mg/kg), 3 times each day for 7 days. The model of plantar incisional pain in the right lower extremity was established, and changes in bilateral plantar MWT and TWL were observed for 7 days. The operative side plantar MWT and TWL in the withdrawal group were significantly lower than those in the control group on postoperative days 1–7, respectively (P<0.05). Compared with the healthy side in the control group, the healthy plantar MWT was significantly reduced on postoperative days 1–7 (P<0.05) and TWL was significantly decreased in postoperative days 1–6 (P<0.05) in the withdrawal group. The pain sensitivity to mechanical and thermal stimulation significantly increased in the rat model of incisional pain with nicotine dependence and withdrawal. This is consistent with the clinical increase of postoperative pain observed in patients after quitting smoking.