Profile of cough triggers and their relationship with capsaicin cough sensitivity in chronic cough.

BACKGROUND: Cough hypersensitivity is an important part of the neurophysiology of cough, which presents with increased cough response to a lower level of stimuli or triggers. Classification of stimuli might bring about additional insight into the underlying mechanisms and management. OBJECTIVES: This study investigated the profile of cough triggers in chronic cough patients and their relationship with capsaicin cough sensitivity. DESIGN: This was a cross-sectional observational study. METHODS: We enrolled patients with different causes of chronic cough from 2006 to 2021. Cough triggers were defined as cough response to chemical triggers, mechanical triggers, meal triggers, or thermal trigger. Cough sensitivity to capsaicin was evaluated by the capsaicin challenge test, which was expressed as the lowest concentration of capsaicin inducing 5 or more coughing (C5). RESULTS: Among 1211 patients with chronic cough, 1107 (91.4%) patients reported at least one cough trigger. Chemical triggers (66.9%) were the most common cough triggers, followed by thermal exposure (50.6%), mechanical triggers (48.2%), and meal triggers (21.2%). There was no difference in the proportion of chemical triggers among different etiologies. Patients with refractory chronic cough reported the highest prevalence of cough triggers (97.1%). A higher number of meal triggers (34.9%) was associated with gastroesophageal reflux-related cough, and meal triggers and mechanical triggers were more common in refractory chronic cough. Among 254 patients who completed capsaicin challenge test, both the number of total triggers and the number of chemical triggers had a significant but mild correlation with capsaicin cough sensitivity. CONCLUSION: Cough hypersensitivity as reflected by a variety of cough triggers is a common feature in chronic cough patients, but different etiologies present specific profiles of cough triggers, which could not be evaluated comprehensively by capsaicin cough sensitivity.

Brainstem processing of cough sensory inputs in chronic cough hypersensitivity.

BACKGROUND: Chronic cough is a prevalent and difficult to treat condition often accompanied by cough hypersensitivity, characterised by cough triggered from exposure to low level sensory stimuli. The mechanisms underlying cough hypersensitivity may involve alterations in airway sensory nerve responsivity to tussive stimuli which would be accompanied by alterations in stimulus-induced brainstem activation, measurable with functional magnetic resonance imaging (fMRI). METHODS: We investigated brainstem responses during inhalation of capsaicin and adenosine triphosphate (ATP) in 29 participants with chronic cough and 29 age- and sex-matched controls. Psychophysical testing was performed to evaluate individual sensitivities to inhaled stimuli and fMRI was used to compare neural activation in participants with cough and control participants while inhaling stimulus concentrations that evoked equivalent levels of urge-to-cough sensation. FINDINGS: Participants with chronic cough were significantly more sensitive to inhaled capsaicin and ATP and showed a change in relationship between urge-to-cough perception and cough induction. When urge-to-cough levels were matched, participants with chronic cough displayed significantly less neural activation in medullary regions known to integrate airway sensory inputs. By contrast, neural activations did not differ significantly between the two groups in cortical brain regions known to encode cough sensations whereas activation in a midbrain region of participants with chronic cough was significantly increased compared to controls. INTERPRETATION: Cough hypersensitivity in some patients may occur in brain circuits above the level of the medulla, perhaps involving midbrain regions that amplify ascending sensory signals or change the efficacy of central inhibitory control systems that ordinarily serve to filter sensory inputs. FUNDING: Supported in part by a research grant from Investigator-Initiated Studies Program of Merck Sharp & Dohme Pty Ltd. The opinions expressed in this paper are those of the authors and do not necessarily represent those of Merck Sharp & Dohme (Australia) Pty Ltd.

Lactic acid sting test and capsaicin test differentially induce facial erythematous reaction in subjects with sensitive skin.

BACKGROUND: Sensitivity skin (SS) is a common skin disorders, which have a various of clinical manifestation. Facial erythema is common objective symptom of SS. However, the reasons for the occurrence of erythema in sensitive skin are not fully understood. AIMS: In this study, we preliminarily explain the possible factors inducing erythema of sensitive skin by evaluating facial erythematous reaction to lactic acid sting test (LAST) and capsaicin test (CAT) in subjects with sensitive skin. METHODS: A total of 197 subjects were divided into five groups, that is, normal controls (NC), LAST-positive (LAST+ ), both LAST and CAT positive (L+ C+ ), both LAST and CAT negative (L- C- ) and CAT-positive (CAT+ ). Erythema index (EI), a* value, and tissue viability imaging (TIVI) were measured before and after LAST and CAT, The ΔEI, Δa*, and ΔTIVI before and after LAST and CAT were calculated, and the correlation between the scores of CAT, EI values, a* values, and TIVI values were analyzed to clarify the causes of facial erythema. RESULTS: Our results showed that EI values and a* values were significantly higher in the L+ C+ and CAT+ group than in NC group, TIVI values were higher in the L+ C+ group than in NC group. ΔEI and Δa* values after LAST did not differ significantly among five groups. However, ΔEI values in L+ C+ group were higher than that in L- C- group, while Δa* values were higher in CAT+ group than in NC. Moreover, ΔTIVI values in L+ C+ group and CAT+ group were also significantly higher than that in NC group after capsaicin stimulation. CAT scores correlated positively with EI, a* and TIVI values. CONCLUSION: Our results suggest that sensitive skin subjects with positive CAT are more likely to experience erythema reactions, and vasodilation is more pronounced after capsaicin stimulation. Reducing vascular and neural hyperreactivity could be therapeutic target in management of facial erythema in subjects with sensitive skin.

Modulation of the spinal N13 SEP component by high- and low-frequency electrical stimulation. Experimental pain models matter.

OBJECTIVE: The N13 component of somatosensory evoked potential (N13 SEP) represents the segmental response of cervical dorsal horn neurons. Neurophysiological studies in healthy participants showed that capsaicin-induced central sensitization causes an increase of the N13 SEP amplitude. Consequently, in human research, this spinal component may serve as a valuable readout of central sensitization. In this study, we wanted to verify if the sensitivity of the N13 SEP for detecting central sensitization is consistent across different experimental pain models inducing central sensitization and secondary hyperalgesia, namely high and low-frequency electrical stimulation (HFS and LFS). METHODS: In 18 healthy participants, we recorded SEP after bilateral ulnar nerve stimulation before and after secondary hyperalgesia was induced through HFS and LFS applied on the ulnar nerve territory of the hand of one side. The area of secondary hyperalgesia was mapped with a calibrated 128-mN pinprick probe, and the mechanical pain sensitivity with three calibrated 16-64-256-mN pinprick probes. RESULTS: Although both HFS and LFS successfully induced secondary hyperalgesia only LFS increased the amplitude of the N13 SEP. CONCLUSIONS: These findings suggest that the sensitivity of the N13 SEP for detecting dorsal horn excitability changes may critically depend on the different experimental pain models. SIGNIFICANCE: Our results indicate that LFS and HFS could trigger central sensitization at the dorsal horn level through distinct mechanisms, however this still needs confirmation by replication studies.

Painful diabetic peripheral neuropathy of the feet: integrating prescription-strength capsaicin into office procedures.

Prescription-strength (8%) capsaicin topical system is a US FDA-approved treatment for painful diabetic peripheral neuropathy of the feet. A 30 min application of the capsaicin 8% topical system can provide sustained (up to 3 months) local pain relief by desensitizing and reducing TRPV1-expressing cutaneous fibers. Capsaicin is not absorbed systemically; despite associated application-site discomfort, capsaicin 8% topical system is well tolerated, with no known drug interactions or contraindications, and could offer clinical advantages over oral options. Capsaicin 8% topical system are not for patient self-administration and require incorporation into office procedures, with the added benefit of treatment compliance. This article reviews existing literature and provides comprehensive, practical information regarding the integration of capsaicin 8% topical systems into office procedures.

Capsaicin 8% topical system is used to treat diabetic nerve pain of the feet. This in-office 30 min application can provide lasting relief of pain (for up to 3 months) by targeting the nerves damaged by diabetes. Since capsaicin acts at the site of diabetic nerve pain without being absorbed into the bloodstream, it is unlikely to interfere with other treatments and has few undesirable effects. Discomfort at the application site is the most commonly reported adverse event. Capsaicin 8% topical system must be applied by a healthcare professional and up to four topical systems can be used per treatment. Incorporating the use of capsaicin 8% topical systems into office procedures can help provide relief for patients living with diabetic nerve pain of the feet and may improve treatment compliance.

Topical capsaicin for the management of painful diabetic neuropathy: a narrative systematic review.

Aim: To investigate the potential benefit of topical capsaicin formulations. Materials & methods: A narrative systematic review was employed. Results: About 8% capsaicin patches were found to significantly reduce symptoms of diabetic peripheral neuropathy. Capsaicin was found to improve sleep quality (p = 0.02). Capsaicin patch exposure for 60 min showed significant reduction in symptoms (-32.8%). Capsaicin cream significantly reduced pain at weeks two and six (p = 0.003 and p = 0.03, respectively), but not at week eight in comparative studies. 0.025% capsaicin gel had an insignificant reduction in pain compared with placebo (p = 0.53), however 0.075% was found to be significant (p = 0.038). Capsaicin cream did not have superior improvement of pain as compared with clonidine gel (p = 0.931). The most common adverse events included application site discomfort, erythema and burning. Conclusion: Topical capsaicin treatments are a potentially beneficial peripherally acting medication. Further research is needed to determine the best means of ameliorating the side effects of treatments.

Painful diabetic neuropathy (DPN) is a serious and common problem affecting those suffering from diabetes. Current treatments of DPN include medications that act on the CNS, rather than the distally affected nerves. Topical capsaicin patches and creams offer potential as alternative treatments to centrally acting neuropathy medications. Topical capsaicin depletes the neurotransmitter for pain signaling at the distally affected nerves. Topical capsaicin in all formulations has been shown to be beneficial in reduction of DPN. However, capsaicin treatments are often irritating to the skin, causing burning and redness at the application site.

Botanical Briefs: Handling the Heat From Capsicum Peppers.

Capsicum peppers-including chili peppers, paprika, and red peppers-are native to the Americas but used worldwide in spicy dishes. Capsaicin, the active ingredient of Capsicum peppers, is used topically to treat musculoskeletal pain, neuropathy, and other conditions. Capsaicin binds the transient receptor potential vanilloid 1 (TRPV1), releasing substance P and desensitizing nerves with long-term use. Capsicum peppers and capsaicin products (eg, medications, cosmetics, pepper sprays) can provoke an irritant contact dermatitis, causing erythema and cutaneous burning. Capsaicin-induced dermatitis can be relieved by washing the area with soap, detergents, or oily compounds. Ice water or high-potency topical steroids also can help. Capsaicin is available in creams, lotions, and patches. Synthetic TRPV1-agonist injectables based on capsaicin are in clinical trials for use in localized pain. Capsaicin is a neuropeptide-active compound found in Capsicum peppers with many promising applications; however, dermatologists should be aware of possible skin reactions to these plants and medications derived from them.

A pilot randomized control trial of topical capsaicin as adjunctive therapy for nausea and vomiting of pregnancy.

BACKGROUND: Nausea and vomiting is one of the most common complications of pregnancy, affecting 50% to 80% of pregnant persons. Moreover, despite its prevalence, it remains a challenging condition to treat. Treatment often involves oral and intravenous medications with potential side effects, particularly when taken in combination. Capsaicin cream is proven to decrease nausea and vomiting in cyclic vomiting syndrome; however, its use has not been well studied among pregnant patients. OBJECTIVE: This study aimed to test the feasibility of the off-label use of capsaicin for the treatment of nausea and vomiting in pregnancy. STUDY DESIGN: This was a double-blinded randomized controlled trial of pregnant individuals in their first trimester of pregnancy seeking care at a tertiary care hospital for nausea and vomiting. Consenting participants were randomized to abdominal application of topical capsaicin vs placebo. All participants received intravenous hydration and metoclopramide. The primary outcome, total treatment time, was recorded for all participants. In addition, symptom severity was assessed every 30 minutes using a visual analog scale. Data were analyzed using the Wilcoxon rank-sum test for continuous variables and the Fisher exact test for binary variables. RESULTS: Of the 38 eligible individuals approached, 30 were randomized. There was a trend toward decreased mean treatment time in the capsaicin group compared with the placebo group (79.9 vs 97.3 minutes; P=.1). There was no significant difference in visual analog scale scores at any time point between groups. Furthermore, capsaicin was well tolerated, with only 1 individual requesting the medication be removed. CONCLUSION: This study demonstrated that capsaicin is an acceptable treatment of nausea and vomiting in pregnancy and additional explorations of its use as treatment are feasible. A larger randomized controlled trial is needed to determine the efficacy of capsaicin in this population.

Decreased capsaicin cough reflex sensitivity predicts hospitalisation due to COPD.

INTRODUCTION: Patients with chronic obstructive pulmonary disease (COPD) are often hospitalised due to severe acute exacerbation (AE) or community-acquired pneumonia (CAP). Previous studies revealed the association of cough reflex sensitivity with the pathophysiology of COPD and pneumonia. We hypothesised that cough reflex sensitivity may be associated with severe AE or CAP requiring hospitalisation in patients with COPD. METHODS: We prospectively recruited 68 patients with COPD between June 2018 and January 2020. Patient characteristics, lung and cardiac functions, and biomarkers, including capsaicin cough reflex sensitivity and blood eosinophil count, were evaluated at enrolment. All participants were monitored for AE or CAP requiring hospitalisation for 12 months. We determined the risk factors and ORs for hospitalisation in patients with COPD using a multivariate analysis. RESULTS: Eight patients experienced AE (n=3) or CAP (n=5) and required hospitalisation during follow-up. Patients in the hospitalisation+ group had higher modified Medical Research Council scores and blood eosinophil counts (≥300 µL) than those in the hospitalisation- group. Capsaicin cough reflex sensitivity tended to decrease in the hospitalisation+ group compared with that in the hospitalisation- group. Multivariate analysis revealed that a decreased capsaicin cough reflex and high eosinophil count (≥300 µL) were predictive risk factors for future hospitalisation due to AE-COPD or CAP. CONCLUSION: In addition to eosinophils, decreased capsaicin cough reflex sensitivity was associated with hospitalisation due to AE-COPD or CAP. Capsaicin cough reflex sensitivity in patients with COPD may play a role in the prevention of severe AE or pneumonia requiring hospitalisation. TRIAL REGISTRATION NUMBER: UMIN000032497.

Characterization of Ethyl Butyrate-Induced Cough Before and After Breath Control Techniques in Healthy Adults.

PURPOSE: Methods for cough elicitation frequently involve aerosolized tussive agents. Here, we sought to determine whether healthy individuals demonstrate a quantifiable cough response after inhaling a volatile ester and if breath control techniques modify this chemically induced cough response. METHOD: Sixty adult male and female participants inhaled prepared liquid dilutions of ethyl butyrate dissolved in paraffin oil at 20%, 40%, and 60% v/v concentrations in triplicate, with presentation order randomized. We delivered stimuli through a face mask connected to an olfactometer and respiratory pneumotachograph. Participants rated sensations of their urge to cough and pleasantness of the odor while cough airflow was measured. Following baseline testing, participants were randomized to implement pursed-lip breathing or slow-paced breathing after inhaling ethyl butyrate to determine the effects of breath control on cough measures. RESULTS: Inhaled ethyl butyrate elicited cough in 70% of participants. Higher concentrations of ethyl butyrate resulted in significantly greater sensation of the urge to cough, F(2, 80) = 10.72, p < .001, and significantly more generated coughs, F(2, 63) = 13.14, p < .001. Compared to baseline, participants rated significantly decreased urge to cough during breath control techniques, F(1, 40) = 11.01, p = .0019. No significant changes were observed in the number of generated coughs between baseline and breath control techniques, F(1, 31) = 7.23, p = .01. CONCLUSIONS: Airborne ethyl butyrate is a tussigenic agent in humans. Our findings provide opportunities for future research directions in normal and disordered cough responses to volatile compounds.

Small Synthetic Hyaluronan Disaccharide BIS014 Mitigates Neuropathic Pain in Mice.

Neuropathic pain (NP) is a challenging condition to treat, as the need for new drugs to treat NP is an unmet goal. We investigated the analgesic potential of a new sulfated disaccharide compound, named BIS014. Oral administration (p.o.) of this compound induced ameliorative effects in formalin-induced nociception and capsaicin-induced secondary mechanical hypersensitivity in mice, but also after partial sciatic nerve transection (spared nerve injury), chemotherapy (paclitaxel)-induced NP, and diabetic neuropathy induced by streptozotocin. Importantly, BIS014, at doses active on neuropathic hypersensitivity (60 mg/kg/p.o.), did not alter exploratory activity or motor coordination (in the rotarod test), unlike a standard dose of gabapentin (40 mg/kg/p.o.) which although inducing antiallodynic effects on the NP models, it also markedly decreased exploration and motor coordination. In docking and molecular dynamic simulation studies, BIS014 interacted with TRPV1, a receptor involved in pain transmission where it behaved as a partial agonist. Additionally, similar to capsaicin, BIS014 increased cytosolic Ca2+ concentration ([Ca2+]c) in neuroblastoma cells expressing TRPV1 receptors; these elevations were blocked by ruthenium red. BIS014 did not block capsaicin-elicited [Ca2+]c transients, but inhibited the increase in the firing rate of action potentials in bradykinin-sensitized dorsal root ganglion neurons stimulated with capsaicin. Perspective: We report that the oral administration of a new sulfated disaccharide compound, named BIS014, decreases neuropathic pain from diverse etiology in mice. Unlike the comparator gabapentin, BIS014 does not induce sedation. Thus, BIS014 has the potential to become a new efficacious non-sedative oral medication for the treatment of neuropathic pain.

Emodin Reduces Inflammatory and Nociceptive Responses in Different Pain-and Inflammation-Induced Mouse Models.

AIMS: Different nociceptive models induced with heat and chemicals were used to assess the potency of emodin in alleviating pain. The anti-inflammatory properties of emodin at different doses were also assessed using different anti-inflammatory in vivo models. OBJECTIVE: Pain management is a global problem nowadays, and nonsteroidal anti-inflammatory drugs (NSAIDs) are commonly prescribed to assuage inflammation and alleviate pain. Prolonged usage of these NSAIDs triggers various adverse drug reactions (ADRs). The dose-dependent effect of emodin was assessed by treating mice with three different doses (5, 10, and 20 mg/kg bwt) of emodin. METHODS: The effects of emodin in various nociceptive and inflammatory models were assessed. The anti-nociceptive potential of emodin was evaluated with the hot plate and tail immersion tests. The effects of emodin on acetic acid-, glutamate-, capsaicin-, and formalin-stimulated pain models were examined. The anti-inflammatory potency of emodin was examined in a carrageenan-induced inflammatory model. The sedative effect of emodin was assessed by an open field test. RESULTS: Emodin potentially prevented the nociception provoked by thermal stressors during the hot plate and tail immersion methods and from chemical stressors such as acetic acid, formalin, capsaicin, and glutamate. The anti-inflammatory action of emodin was evidenced by carrageenaninduced paw edema and peritoneal leukocyte penetration. The open field results confirmed that emodin induced a mild sedative effect on the treated mice. CONCLUSION: Our overall results obtained from this study confirmed that emodin exhibits potent anti- nociceptive and anti-inflammatory effects.

Capsaicin affects macrophage anti-inflammatory activity via the MAPK and NF-κB signaling pathways.

Capsaicin, the main constituent in chili, is an extremely spicy vanillin alkaloid and is found in several Capsicum species in China. Traditionally, it has been used to treat inflammatory diseases such as allergic rhinitis, neuralgia after shingles, refractory female urethral syndrome, spontaneous recalcitrant anal pruritus, and solid tumors. Constant stimulation of the body by inflammatory factors can lead to chronic inflammation. Capsaicin possesses anti-inflammatory activity; however, the underlying mechanism is unknown. We investigated the effect of capsaicin on the secretion of macrophage inflammatory factors in a lipopolysaccharide-induced inflammation model using 56 healthy, SPF grade, BALB/c mice. To this end, mice peritoneal macrophages were isolated and stimulated with lipopolysaccharide (1 µg/mL) and capsaicin (25, 50, 75, or 100 µg/mL) for 24 h. At all concentrations tested, capsaicin significantly promoted the phagocytosis of neutral red dye by macrophages. Furthermore, the gene expression and secretion of inflammatory cytokines significantly increased after induction with lipopolysaccharide (P<0.01); the interleukin (IL)-6 level was 204 µg/mL, tumor necrosis factor (TNF)-α level was 860 µg/mL, and nitric oxide (NO) level was 19.8 µg/mL. However, the treatment with capsaicin reduced their levels (P<0.01) and protein expression of lipopolysaccharide-induced extracellular signal-related kinase 1/2 and p65 (P<0.05). Overall, capsaicin reduced the secretion of inflammatory cytokines (P<0.01), interleukins, TNF-α (P<0.01), and NO by inhibiting the nuclear factor-kappa B and microtubule-associated protein kinase signaling pathways, and thereby reduced lipopolysaccharide-induced inflammatory response in macrophages.

Second-degree burn induced by high-concentration topical capsaicin with mobility sequelae: A case report.

High-concentration topical capsaicin is used as a second-line treatment for neuropathic pain. Transient, mild burning sensation and erythema are expected adverse drug reactions. Here, we report the first case of second degree burn after the application of a high-concentration topical capsaicin patch with secondary mobility sequelae. Nine months after the application, neuropathic pain still remained and the patient described mobility difficulties in daily activities, preventing her from returning to work. This report aims to raise the question of the benefit/risk ratio of high concentration topical capsaicin.

Sprayable NAHAO® hydrogel alleviates pain and accelerates rat oral mucositis wound healing.

OBJECTIVE: To investigate the promote healing and analgesic effects of NAHAO® Brand Nazhen oral antibacterial care solution (NAHAO® spray) on the 5-fluorouracil-induced oral mucositis in rats. MATERIAL AND METHOD: Sixty male SD rats were randomly divided into normal group, model group, recombinant human epidermal growth factor (rhEGF) group, NAHAO® spray group, and 1/3 concentration of NAHAO® spray group. 5-FU was injected intraperitoneally on the first and third days of the experimental model, and OM was induced using mechanical trauma on the third and fifth days. Wound healing quality was assessed by the appearance of mucosa and histological images on day6 and day10. Pain is measured by facial grooming behavior stimulated by capsaicin, the alternation of body weight and food intake was also recorded to reflect the OM pain. To examine the involvement of the cyclooxygenase pathway in the mechanism underlying oral mucositis, we detected the expression of cyclooxygenase2(COX-2) and matrix metalloproteinase 9(MMP9) via immunohistochemical staining and determined the PGE2 concentrations in rats' serum during healing of oral mucositis. RESULTS: NAHAO® spray attenuated pathological damage and reduced pain sensitivity effectively. COX-2 expression levels were inhibited in the NAHAO® spray-treated group. The concentration of PGE2 and the expression of MMP9 were inhibited in NAHAO®-treated rats. Compared with normal rats, the elevated rubbing time following capsaicin stimulation in the model was completely inhibited after being treated with NAHAO® spray. CONCLUSION: NAHAO® spray alleviated OM-induced pain and promoted wound healing partly by inhibiting the cyclooxygenase-related pathway.

Role of dairy proteins in the reduction of capsaicin-induced oral burning pain.

Capsaicin-induced burning sensation in the oral mucosa can be relieved by skimmed and whole milk. The mechanism behind this effect, however, is unknown. This study aimed to asses the role of milk proteins in reducing capsaicin-induced oral burning sensation. 24 healthy participants were included in this single-blinded cross-over study consisting of four sessions. In each sessions, mucosal burning sensation was evoked by having the participants dip their tongues in a cup containing 0.1% capsaicin gel for a total of 8 min. The perceived levels of unpleasantness and burning intensity were scored on two different numerical rating scales. After capsaicin exposure, the participants rinsed their mouth for 10 s with a different solution in each session (3.5% casein, 3.5% whey, 3.5% lactose (non-protein control) and skimmed milk (active/positive control)). Mechanical (64, 128 and 256 mN pinprick) and thermal (5, 40, 45 and 50 ̊C) sensitivity of the tongue was measured using semi-quantative sensory testing at baseline, immediately after capsaicin exposure and when the scores for unpleasantness and burning intensity reached the minimum value of 0. Thermographic images of the tongue were taken at the same time-points. Overall, no statistically significant difference in unpleasantness and burning intensity was found between the four sessions (P ≥ 0.070). Explorative pair-wise comparisons, however, showed slight short-term reduction in unpleasantness and burning intensity when comparing the casein solution with the lactose solution (P ≤ 0.020). Scores for burning intensity and unpleasantness varied over time (P ≤ 0.001). Statistically significant changes in heat and mechanical sensitivity was observed between time-points (P < 0.001) but not sessions (P ≥ 0.410). An increased sensitivity towards heat and a decreased sensitivity towards mechanical stimuli was observed after capsaicin exposure compared with baseline (P < 0.001). Similarly, changes in thermographic temperature of the tongue was observed between time-points (P < 0.001), but not sessions (P ≥ 0.827). An increased maximum, minimum and average temperature of the tongue was observed immediately after capsaicin exposure compared with baseline (P < 0.001). In conclusion, short-term rinsing with room temperature milk proteins did not robustly alter capsaicin-induced oral burning sensation, unpleasantness, somatosensory changes or tongue temperature compared with control. Further studies exploring the effects of increased rinsing time and concentrations are needed in the future.

The role of topical capsaicin gel in pain management during microfocused ultrasound treatment for neck laxity.

BACKGROUND: The transient receptor potential vanilloid 1 (TRPV1) provides a heat and pain sensation (nociception). Capsaicin, a TRPV1 agonist, has been shown to induce a refractory period in the nerve terminal expressing TRPV1 and create long-term nerve terminal defunctionalization. OBJECTIVE: To evaluate the efficacy of capsaicin for pain reduction during microfocused ultrasound with visualization (MFU-V) treatment. METHODS AND MATERIALS: A randomized, split-side study including 24 subjects was conducted. A combined 0.025% capsaicin gel and topical anesthetic were randomly applied on one side of the neck, and a topical anesthetic monotherapy was applied on the contralateral side for 30 min before MFU-V treatment. Pain score (visual analog scale, 0-10) was evaluated at T1 (before MFU-V), T2a (after the 4.5-mm transducer treatment), T2b (after the 3.0-mm transducer treatment), and T3 (after the entire treatment). Side effects were recorded. RESULTS: Mean pain scores at T2a for combined and single regimens were 5.19 (±2.26) and 6.91 (±1.72), respectively (p < 0.001). The capsaicin-treated side had a lower pain score at T2b and T3 (p < 0.001). Redness was longer on the capsaicin-treated side (112.67 vs. 10.68 min, p < 0.001). No other adverse events including contact dermatitis were reported. CONCLUSION: A single application of a combined 0.025% capsaicin gel with topical anesthesia produces a significantly lesser pain score during the MFU-V treatment. Defunctionalization of TRPV1 may explain the alleviation of painful sensations caused by heat from MFU-V.

Neuropharmacological Study on Capsaicin in Scopolamine-injected Mice.

AIM: To evaluate the potential beneficial role of Capsaicin in cognitive dysfunction, mitochondrial impairment, and oxidative damage induced by scopolamine in mice. BACKGROUND: Capsaicin is the chief phenolic component present in red chili and is responsible for its pungent and spicy flavor. It affects TRPV1 channels in nociceptive sensory neurons and is present in the hippocampus, and hypothalamus of the brains of rodents and humans. OBJECTIVE: The main objective is to investigate the effective role of capsaicin in attenuating cognitive dysfunction, mitochondrial impairment, and oxidative damage induced by scopolamine in mice and examine the feasible mechanisms. METHODS: Various doses of capsaicin (5, 10, and 20 mg/kg) were given orally to mice daily for 7 consecutive days after the administration of scopolamine. Various behavioral tests (motor coordination, locomotor counts, hole board test) and biochemical assay (Pro-inflammatory cytokines, catalase, lipid peroxidation, nitrite, reduced glutathione, and superoxide dismutase), mitochondrial complex (I, II, III, and IV) enzyme activities, and mitochondrial permeability transition were evaluated in the distinct regions of the brain. RESULTS: Scopolamine-treated mice showed a considerable reduction in the entries and duration in the light zone as well as in open arms of the elevated plus maze. Interestingly, capsaicin at different doses reversed the anxiety, depressive-like behaviors, and learning and memory impairment effects of scopolamine. Scopolamine-administered mice demonstrated substantially increased pro-inflammatory cytokines levels, impaired mitochondrial enzyme complex activities, and increased oxidative damage compared to the normal control group. Capsaicin treatment reinstated the reduced lipid peroxidation, nitric oxide, catalase, superoxide dismutase, reduced glutathione activity, decreasing pro-inflammatory cytokines and restoring mitochondrial complex enzyme activities (I, II, III, and IV) as well as mitochondrial permeability. Moreover, the IL-1ß level was restored at a dose of capsaicin (10 and 20 mg/kg) only. Capsaicin reduced the scopolamine-induced acetylcholinesterase activity, thereby raising the acetylcholine concentration in the hippocampal tissues of mice. Preservation of neuronal cell morphology was also confirmed by capsaicin in histological studies. From the above experimental results, capsaicin at a dose of 10 mg/kg, p.o. for seven consecutive days was found to be the most effective dose. CONCLUSION: The experiential neuroprotective effect of capsaicin through the restoration of mitochondrial functions, antioxidant effects, and modulation of pro-inflammatory cytokines makes it a promising candidate for further drug development through clinical setup.

A Study on Cough Sensitivity and Airway Inflammation in Patients with Sinobronchial Syndrome.

Objective: This study aimed to clarify the characteristics of cough-reflex sensitivity and airway inflammation in patients with sinobronchial syndrome (SBS). Methods: 39 patients with SBS, 53 patients with upper airway cough syndrome (UACS) induced by rhinitis, 33 patients with chronic sinusitis without cough, and 39 healthy controls (HCs) were enrolled between January 2013 and December 2018. All participants underwent a capsaicin cough-sensitivity test and cytology of induced sputum. The concentration of calcitonin-gene-related peptide (CGPR), histamine, prostaglandin (PG) E2, and eosinophil cationic protein (ECP) in induced sputum were measured using enzyme-linked immunosorbent assays (ELISAs). Results: The lowest concentration of capsaicin solution that induced ≥5 coughs (C5) was decreased markedly in patients with UACS induced by rhinitis compared with SBS patients (1.95 ± 2.92 vs. 31.2 ± 58.6 mol/L, P < 0.001), indicating higher cough-reflex sensitivity among UACS patients induced by rhinitis. However, there was no difference of these threshold between SBS patients and patients with sinusitis without cough and HCs. The percentage of neutrophils in sputum was increased remarkably in patients with SBS compared with HCs (40.0 ± 48.5% vs. 5.5 ± 9.0%, P < 0.001). A higher concentration of CGPR, histamine, and PGE2 was observed in induced sputum from patients with UACS induced by rhinitis than that in controls, and the ECP level was increased significantly in UACS induced by rhinitis compared with that in the other three groups. Conclusions: Cough-reflex sensitivity and airway inflammation in patients with SBS were different in patients with UACS induced by rhinitis. Thus, the mechanism of cough in those two patient populations might differ. Our study is registered in the Chinese Clinical Trials Register (https://www.chictr.org.cn/) as ChiCTR-TRC-00000152.

Capsaicin, its clinical significance in patients with painful diabetic neuropathy.

Diabetic neuropathy is a risk factor for developing complications such as autonomic cardiovascular disease, osteoarthropathy, foot ulcers, and infections, which may be the direct cause of death. Even worse, patients plagued by this condition display painful neuropathic symptoms that are usually severe and frequently lead to depression, anxiety, and sleep disarrays, eventually leading to a poor quality of life. There is a general interest in evaluating the therapeutic properties of topical capsaicin cream as an effective agent for pain relief in these patients. As such, the current review makes use of major search engines like PubMed and Google Scholar, to bring an updated analysis of clinical studies reporting on the therapeutic effects of capsaicin in patients with painful diabetic neuropathy. In fact, most of the summarized literature indicates that topical capsaicin (0.075 %) cream, when applied to the painful areas for approximately 8 weeks, can reduce pain, which may lead to clinical improvements in walking, working, and sleeping in patients with painful diabetic neuropathy. The current review also discusses essential information on capsaicin, including its source, bioavailability profile, as well as treatment doses and duration, to highlight its therapeutic potential.