Topical Application Of Capsaicin Research Articles

Influence of topical application of capsaicin, menthol and local anesthetics on intraoral somatosensory sensitivity in healthy subjects: temporal and spatial aspects.

The aim of this study was to investigate temporal and spatial aspects of somatosensory changes after topical application of capsaicin, menthol and local anesthetics (LA) on the gingiva with the use of intraoral palpometers and thermal devices. Sixteen healthy volunteers (eight male, eight female) participated. Four topical preparations (capsaicin, menthol, LA and Vaseline as a control) were randomly applied to the gingiva around the first premolar in the upper jaw via individual oral templates, which allowed spatial mapping of somatosensory changes at and adjacent to the site of application. The topical drugs were applied for 15 min in a randomized and balanced sequence. The perceived preparation-evoked pain intensity was recorded with the use of 0-10 visual analog scales (VAS). Standardized mechanical and thermal stimuli were applied before, during and up to 30 min after the topical applications, and numerical rating scales (NRS) were used to score the perceived intensity of the stimuli. Peak VAS, area under the curve and mean VAS preparation-evoked pain scores for capsaicin, menthol, LA and control were compared with paired t tests. NRS scores for mechanical and thermal test stimuli were analyzed with four-way repeated measurements analyses of variance. Capsaicin evoked significantly higher VAS pain parameters as well as higher NRS scores to heat stimuli than control (P < 0.029). There were no significant differences in stimulus-evoked NRS scores between the menthol and control conditions (P = 0.518), but LA caused significantly lower stimulus-evoked NRS scores compared with control (P < 0.001). Post hoc tests showed that capsaicin caused sensitization to heat stimuli at and adjacent to the application area. In conclusion, this study for the first time demonstrates the time course of capsaicin-evoked heat hyperalgesia in and outside the site of application at the oral mucosa (primary and secondary hyperalgesia).

An equine pain face

ObjectiveThe objective of this study was to investigate the existence of an equine pain face and to describe this in detail. Study designSemi-randomized, controlled, crossover trial. AnimalsSix adult horses. MethodsPain was induced with two noxious stimuli, a tourniquet on the antebrachium and topical application of capsaicin. All horses participated in two control trials and received both noxious stimuli twice, once with and once without an observer present. During all sessions their pain state was scored. The horses were filmed and the close-up video recordings of the faces were analysed for alterations in behaviour and facial expressions. Still images from the trials were evaluated for the presence of each of the specific pain face features identified from the video analysis. ResultsBoth noxious challenges were effective in producing a pain response resulting in significantly increased pain scores. Alterations in facial expressions were observed in all horses during all noxious stimulations. The number of pain face features present on the still images from the noxious challenges were significantly higher than for the control trial (p = 0.0001). Facial expressions representative for control and pain trials were condensed into explanatory illustrations. During pain sessions with an observer present, the horses increased their contact-seeking behavior. Conclusions and clinical relevanceAn equine pain face comprising ‘low’ and/or ‘asymmetrical’ ears, an angled appearance of the eyes, a withdrawn and/or tense stare, mediolaterally dilated nostrils and tension of the lips, chin and certain facial muscles can be recognized in horses during induced acute pain. This description of an equine pain face may be useful for improving tools for pain recognition in horses with mild to moderate pain.

A novel method of selective ablation of afferent renal nerves by periaxonal application of capsaicin.

Renal denervation has been shown to lower arterial pressure in some hypertensive patients, yet it remains unclear whether this is due to ablation of afferent or efferent renal nerves. To investigate the role of afferent renal nerves in arterial pressure regulation, previous studies have used methods that disrupt both renal and nonrenal afferent signaling. The present study was conducted to develop and validate a technique for selective ablation of afferent renal nerves that does not disrupt other afferent pathways. To do this, we adapted a technique for sensory denervation of the adrenal gland by topical application of capsaicin and tested the hypothesis that exposure of the renal nerves to capsaicin (renal-CAP) causes ablation of afferent but not efferent renal nerves. Renal-CAP had no effect on renal content of the efferent nerve markers tyrosine hydroxylase and norepinephrine; however, the afferent nerve marker, calcitonin gene-related peptide was largely depleted from the kidney 10 days after intervention, but returned to roughly half of control levels by 7 wk postintervention. Moreover, renal-CAP abolished the cardiovascular responses to acute pharmacological stimulation of afferent renal nerves. Renal-CAP rats showed normal weight gain, as well as cardiovascular and fluid balance regulation during dietary sodium loading. To some extent, renal-CAP did blunt the bradycardic response and increase the dipsogenic response to increased salt intake. Lastly, renal-CAP significantly attenuated the development of deoxycorticosterone acetate-salt hypertension. These results demonstrate that renal-CAP effectively causes selective ablation of afferent renal nerves in rats.

Distinct Reactivity of Transient Receptor Potential Vanilloid Subtype 1 in a Murine Model of Atopic Dermatitis with Serious Scratching

Background: Abnormality in skin sensitivity may be responsible for unbearable itch in patients with atopic dermatitis (AD). Objectives: We evaluated reactivity of NC/Tnd mice, a model for human AD, against various experimental stimulations. Methods: Several behavioral tests were performed after external stimuli were applied to NC/Tnd mice. Transient receptor potential vanilloid subtype 1 (TRPV1) reactivity of neuronal cells collected from the dorsal root ganglions (DRG) was analyzed with a Ca++ influx test. Finally, we evaluated suppressive effect of capsaicin on atopic itch of NC/Tnd mice. Results: Pain responses to heat, acidic stimulation, and capsaicin injection, which are transduced through TRPV1, were decreased in NC/Tnd mice, when compared to two standard strains BALB/c and C57BL/6 mice. The reactivity of the primary neurons isolated from DRG to capsaicin was markedly reduced in NC/Tnd mice. Topical application of histamine evoked scratching in NC/Tnd mice as well as other two strains; however, the scratching intensities induced by nonhistamine pruritogens were significantly lower in NC/Tnd mice comparing to the two strains. In conventional NC/Tnd mice with AD, topical application of capsaicin reduced the scratching behavior. Conclusion: TRPV1 is associated with both pain and itch sensation; however, abnormalities in TRPV1 reactivity may involve in severe itch in NC/Tnd mice.

Z944: a first in class T-type calcium channel modulator for the treatment of pain.

Zalicus, Inc. is a small, publicly-traded biotech company in Cambridge, Massachusetts. The potential target for neuropathic pain lies in the T-type calcium channels, members of the low-voltage activated channel family. By opening at relatively negative membrane depolarizations, T-type channels can act as modulators of the threshold of the action potential by increasing the calcium current, leading to further depolarization of the cell and activation of other calcium channels, and ultimately, sodium and potassium channels. This is a target that is widely expressed in both the peripheral as well as the central nervous system (Zamponi et al., 2009). It is known that T-type calcium channel blockade can modulate pain behavior and disrupting this mechanism can reduce pain in neuropathic, inflammatory, and visceral pain models. There is evidence that the calcium channel protein itself as well as the current that is delivered by this channel is increased in certain pain models (Marger et al., 2011). Another important feature of this target is its central action. There are three subtypes of the T-type calcium channel, denoted Cav3.1, 3.2, and 3.3. They are expressed in different places in the thalamus, the cerebellum, and other parts of the brain. It is thought that they participate in the regulation of connectivity or crosstalk between the sensory nervous system and the cortex by promoting thalamic neuron burst firing and network oscillations important for relay and interpretation of signals to and by the cortex. A number of central nervous system (CNS) diseases have been linked to aberrant thalamocortical oscillations (thalamocortical dysrhythmia), and there is evidence that T-type calcium channel mutants can play a role in hyperexcitability disorders, for example, epilepsy syndromes. Some approved anticonvulsants also hit the T-type channel as part of their polypharmacology. Zalicus' approach has been to discover and develop a small molecule blocker of T-type calcium channels as a potential therapeutic for pain. The medication, Z944, is a novel, oral, state-dependent, selective T-type calcium channel blocker. This blocker has >150-fold selectivity vs. non-T-type voltage-gated ion channels and has been shown to inhibit native neuronal T-type currents at high potency. The blockade of Cav3.2 by Z944 is more pronounced during high-frequency firing and may provide some advantage to the molecule by selectively targeting a pathological state of the channel (Short et al., 2013). A phase 1, double-blind, placebo-controlled study to determine the safety, tolerability, and pharmacokinetics of single and multiple ascending doses of oral Z944 in healthy male subjects in the fed and fasted states using an immediate release formulation showed that the medication was safe and well tolerated. Mild and expected CNS side effects were observed; no serious adverse events were reported. A phase 1b clinical study utilized a state-of-the-art experimental clinical model measuring Laser-Evoked Potentials (LEP) from skin irritated following topical application of capsaicin (modeling neuropathic pain signaling and central sensitization) or exposure to UV light (modeling inflammatory pain signaling). Healthy volunteers received 20, 40, and 80 mg doses split in four administrations every 2 h vs. placebo. The data showed that Z944 reduced peak-to-peak amplitudes of LEPs from both capsaicin and UV irritated skin models and reduced subjective Visual Analog Scale (VAS) pain scores in both skin types. The noted adverse events were generally mild to moderate and primarily central nervous system related. No serious adverse events occurred in this study. On the basis of these findings, several modified release formulations of Z944 are currently being advanced in clinical development for pain indications.

Abstract 3217: Capsaicin inhibits proliferation and chemosensitizes gastric carcinoma cells to 5-Fluorouracil

Abstract Background: Capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide) is the principal pungent component in hot peppers. The role of capsaicin in carcinogenic processes is quite controversial. Although some investigators suspect that capsaicin is a carcinogen, co-carcinogen, or tumor promoter, others have reported that it has chemopreventive and chemotherapeutic effects. Interestingly, capsaicin has been found to preferentially repress the growth of some transformed human and mouse cells. Although the antiproliferative activity of capsaicin has been ascribed to its ability to induce apoptosis. For example, The American Association for Cancer Research reports studies suggesting capsaicin is able to kill prostate cancer and lung cancer cells by causing them to undergo apoptosis. The present study aimed to evaluate the cytotoxicity and chemosensitizing activities of capsaicin alone and on 5-Flourouracil (5-FU) treated gastric carcinoma cells. Material and methods: In this study, the gastric cancer cell line HGC-27 was used. Cytotoxicity and chemosensitizing activities were analyzed with MTT assay. Capsaicin used a chemosensitizer and 5-FU was used as chemotherapeutic agent. Supernatant levels of Lactate dehydrogenases (LDH), Glucose (GLU) were detected as biochemical markers of cell viability. Additionally, cytochrome c and apoptosis inducing factor (AIF) were evaluated with western blot. Colonigenic assay and wound healing assays were also employed. Results: Capsaicin and 5-FU both detected cytotoxic and anticolonigenic on HGC-27 cells dose dependent manner after 24h/48h incubation. Both compounds were found more effective at 48h incubation. Furthermore, it is observed that the concentration of capsaicin higher than 12 µM may cause sensitization to 5-FU. Results suggested that capsaicin had significant anticancer and chemosensitizing abilities; such capsaicin were capable of causing multi-fold decreases in the half maximal inhibitory concentration IC50 value of 5-FU. The chemosensitizing ability of the capsaicin on HGC-27 metastatic lymph node from a gastric cancer patient diagnosed histological as undifferentiated carcinoma cells, in the present study is notable. The cytotoxic effect of capsaicin was observed cytochrome c activation dependent pathway. Conclusions: The continuing controversy surrounding consumption or topical application of capsaicin clearly suggests that more well-controlled epidemiologic studies are needed to evaluate the safety and efficacy of capsaicin use. In summary, the present study demonstrated that capsaicin has the potential to be used in chemosensitization for treating gastric carcinoma in vitro. Citation Format: Gorkem Kismali, Merve Alpay, Ogunc Meral, Funda Kosova, Dilek Ulker Cakir, Tevhide Sel. Capsaicin inhibits proliferation and chemosensitizes gastric carcinoma cells to 5-Fluorouracil. [abstract]. In: Proceedings of the 105th Annual Meeting of the American Association for Cancer Research; 2014 Apr 5-9; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2014;74(19 Suppl):Abstract nr 3217. doi:10.1158/1538-7445.AM2014-3217

Studying Axonal Degeneration and Regeneration Using In Vitro and In Vivo Models: the Translational Potential

ABSTRACT: Since the initial studies by Cajal, multiple models of peripheral nerve degeneration and regeneration have been developed to address the ever-increasing complexity of the mechanisms involved in regeneration. In vitro models offer the principal benefit of a system that can be readily manipulated to address specific mechanistic questions in a deconstructed system. However, in vitro models can be overly simplified and intricacies of the interactions between neurons and glia can be lost. In vivo animal models seek to remedy some of these shortcomings, but most in vivo animal systems fail to precisely model human nerve regeneration. Rodent models of chronic nerve regeneration have been developed to better recapitulate human nerve regeneration, but are not widely used. An important development in the field has been the establishment of experimental nerve regeneration in humans, involving the reinnervation of the epidermis after cutaneous axotomy or topical capsaicin application. Use of such human models will likely accelerate the development and evaluation of new drugs that enhance peripheral nerve regeneration.

Capsaicin-induced cardioprotection. Is hypothermia or the salvage kinase pathway involved?

Topical capsaicin application was shown to reduce infarct size in experimental animal models. We hypothesized that cardioprotective properties of topical capsaicin application could be related to its hypothermic effect. In the first arm of the study, anesthetized rats received capsaicin cream (Caps group) or vehicle (Control group, Ctrl) applied either 15 or 30min prior to a 30-min coronary artery occlusion followed by 2-h reperfusion. Core body temperature was allowed to run its course, and was monitored via rectal probe. At the end of the protocol, hearts were excised and risk zone and infarct size were measured. In an additional set of animals, hearts were excised immediately after a 15-min application of capsaicin/vehicle, and were used to measure phosphorylated Akt and Erk1/2 with western blots. In the second arm of the study Ctrl (n = 6) and Caps-treated (n = 5) animals were subjected to the same protocol as rats in the first arm, but core body temperature was maintained at 36°C. In the first arm of the study, capsaicin produced a rapid decrease in rectal temperature ranging from 0.22 to 1.78°C at pre-occlusion, with a median level of 0.97°C. A capsaicin-induced temperature decrease of >0.97°C was associated with a 31.2% smaller infarct compared to the control group. Capsaicin treatment induced an increase in the levels of phosphorylated Akt and Erk1/2 at the end of capsaicin cream application. No increase in the phosphorylation of downstream p70S6 was observed. Levels of phosphorylated Akt- and Erk1/2 did not correlate with temperature changes after treatment. In the second arm of the study, in which body core temperature was maintained at 36°C, no change in the infarct size was observed in the capsaicin vs. control group. In the current study we for the first time demonstrated that the capsaicin induced cardioprotective effect might be related to mild hypothermia, caused by capsaicin topical application. The salvage kinase pathway appears not to be critical for capsaicin-induced cardioprotection.

Anti-inflammatory effects of Bryophyllum pinnatum (Lam.) Oken ethanol extract in acute and chronic cutaneous inflammation

Ethnopharmacological relevanceBryophyllum pinnatum (Lam.) Oken (Crassulaceae), popularly known in Brazil as “folha-da-fortuna”, is a plant species used in folk medicine for the external and internal treatment of inflammation, infection, wound, burn, boil, ulcers and gastritis, and several other diseases. The present study aimed to perform the chemical characterization and the evaluation of the topical anti-inflammatory effect of the ethanol extract of Bryophyllum pinnatum leaves (EEBP) in acute and chronic mice ear edema models induced by different irritant agents. Materials and methodsThe EEBP chemical characterization was performed by HPLC–UV DAD. Ear edema on Swiss mice was induced by the topical application of Croton oil (single and multiple applications), arachidonic acid, phenol, capsaicin and ethyl phenylpropiolate (EPP). The topical anti-inflammatory effect of EEBP was evaluated by measuring the ear weight (acute inflammation models) and thickness (chronic inflammation model). Histopathological analyses of ear tissue samples sensitized with Croton oil (single and multiple applications) were also performed. ResultsThe flavonoids rutin, quercetin, luteolin and luteolin7-O-β-d-glucoside were detected in EEBP. Topical application of EEBP significantly (P<0.001) inhibited the ear edema induced by Croton oil single application (inhibition of 57%), arachidonic acid (inhibition of 67%), phenol (inhibition of 80%), capsaicin (inhibition of 72%), EPP (inhibition of 75%) and Croton oil multiple application (55% after 9 days). Histopathological analyses confirmed the topical anti-inflammatory effect of EEBP since it was observed reduction of edema, epidermal hyperplasia, inflammatory cells infiltration and vasodilation. ConclusionsThe results suggest that EEBP is effective as a topical anti-inflammatory agent in acute and chronic inflammatory processes possibly due to inhibition of arachidonic acid pathway, which justify the traditional use of Bryophyllum pinnatum as a remedy for skin disorders.

Capsaicin-induced neurogenic inflammation in pig skin: A behavioural study

Topical capsaicin is a well-established model of experimental hyperalgesia. Its application to the study of animals has been limited to few species. The effect of topical capsaicin on hyperalgesia in porcine skin was evaluated as part of a study of inflammatory pain in the pig. Two experiments were carried out on pigs of 27 ± 5 kg (n = 8) and 57 ± 3 kg (n = 16). Thermal and mechanical noxious stimuli were provided (CO2 laser and Pressure Application Measurement device) to assess avoidance behaviours. Capsaicin induced significant thermal hyperalgesia in the smaller pigs (P < 0.05), while no mechanical hyperalgesia was observed in either animal group. The present model of topical capsaicin application may be useful to investigate the mechanisms of primary hyperalgesia in this species, although some experimental conditions, such as the administration route and cutaneous morphology, need to be evaluated.

Capsaicin‐induced cardioprotection is driven by its hypothermic effect (1154.1)

Objective. We hypothesized that cardioprotective properties of topical capsaicin (CAP) application are related to its hypothermic effect.Methods. Anesthetized rats received CAP cream or vehicle (VCL) applied 15‐30 minutes before a 30‐minute coronary artery occlusion followed by 2‐hour reperfusion. At the end of the protocol, hearts were excised and the area at risk (AR), area of necrosis (AN) and infarct size (AN/AR) were measured. In additional set of animals, hearts were excised at the end of CAP/VCL application, and used for Western Blot assay of p‐Akt and p‐Erk1/2.Results. CAP cream produced a rapid decrease in pre‐occlusion core temperature, ranging from 0.22 to 1.78°C, with a median reduction of 0.97°C. In a CAP subgroup with a temperature decrease of &gt; 0.97°C, AN/AR was decreased by 31% (from 56±4% in the VCL group to 38±4% in the CAP group, p&lt;0.05). In the CAP subgroup with temperature decrease &lt; 0.97°C no difference in the infarct size was observed. CAP induced an increase in p‐Akt and p‐Erk1/2. Phosphorylation of downstream p70S6 was unaffected. Levels of p‐Akt‐ and p‐Erk1/2 did not correlate with temperature at pre‐occlusion.Conclusion. In the current study we for the first time demonstrated that cardioprotective effect of capsaicin might be related to mild hypothermia, caused by its topical application. Salvage kinase pathway appears not to be critical for the cardioprotective effects of capsaicin.

Capsaicin inhibits cell proliferation by cytochrome c release in gastric cancer cells

Capsaicin (trans-8-methyl-N-vanillyl-6-nonenamide) is the principal pungent component in hot peppers. The role of capsaicin in carcinogenesis is quite controversial. Although some investigators suspect that capsaicin is a carcinogen, co-carcinogen, or tumor promoter, others have reported that it has chemopreventive and chemotherapeutic effects. The present study aimed to evaluate the cytotoxicity and chemosensitizing activities of capsaicin alone and on 5-flourouracil (5-FU)-treated gastric cancer cells. In this study, the gastric cancer cell line HGC-27 was used and capsaicin used as a chemosensitizer and 5-flourouracil (5-FU) was used as chemotherapeutic. Cytotoxicity and chemosensitizing activities were analyzed with MTT assay; supernatant levels of LDH and glucose were detected as biochemical markers of cell viability; cytochrome c and AIF were evaluated with western blot; and additionally, wound-healing assays were employed. Results suggested that capsaicin had significant anticancer abilities; such capsaicin were capable of causing multifold decreases in the half maximal inhibitory concentration IC50 value of 5-FU. The continuing controversy surrounding consumption or topical application of capsaicin clearly suggests that more well-controlled epidemiologic studies are needed to evaluate the safety and efficacy of capsaicin use. In summary, the present study demonstrated that capsaicin has the potential to be used for treating gastric carcinoma with 5-FU in vitro.

Development of an experimental model to study trigeminal nerve-mediated vasodilation on the human forehead

During migraine, trigeminal sensory nerve terminals release calcitonin gene-related peptide (CGRP), inducing nociception and vasodilation. Applied on the skin, capsaicin activates the transient receptor potential vanilloid type 1 (TRPV1) channel and releases CGRP from sensory nerve terminals, thus increasing dermal blood flow (DBF). Using capsaicin application and electrical stimulation of the forehead skin, a trigeminal nerve-innervated dermatome, we aimed to develop a model to measure trigeminal nerve-mediated vasodilation in humans. Using laser Doppler imaging, forehead DBF responses to application of capsaicin (0.06 mg/ml and 6.0 mg/ml) and saline, with and without iontophoresis, were studied in healthy subjects. The within-subject coefficient of variation (WCV) of repeated DBF measurements was calculated to assess reproducibility. Maximal DBF responses to 6.0 mg/ml capsaicin with and without iontophoresis did not differ (Emax 459 ± 32 and 424 ± 32 arbitrary units (a.u.), WCV 6 ± 4%). In contrast, DBF responses to 0.06 mg/ml capsaicin were significantly larger with than without iontophoresis (Emax 307 ± 60 versus 187 ± 21 a.u., WCV 21 ± 13%). Saline with iontophoresis significantly increased DBF (Emax: 245 ± 26 a.u, WCV 11 ± 8%), while saline application without iontophoresis did not affect DBF. Topical application of capsaicin and electrical stimulation induce reproducible forehead DBF increases and therefore are suitable to study trigeminal nerve-mediated vasodilation in humans.

No association of polymorphisms in the serotonin transporter gene with thermal pain sensation in healthy individuals.

BackgroundRecent studies have suggested an association between genotypes affecting the expression of the serotonin transporter and thermal pain perception and the thermal grill. The aim of this study was to investigate differences in thermal and mechanical pain perception and the thermal grill in two groups of healthy volunteers according to their genotype, associated with either high (n = 40) or low (n = 40) expression of the serotonin transporter and according to gender. Cold and warm detection and pain thresholds, pressure pain threshold and cold, warm and pain sensations to single or alternating stimuli with cold (20°C) and warm (40°C) temperatures (known as the thermal grill) were determined. In addition, intensity of ongoing pain and area and intensity of pinprick hyperalgesia in the secondary hyperalgesic area following topical application of capsaicin and vehicle control (ethanol) were determined.ResultsNo significant differences in detection and pain thresholds for cold and warm temperatures, presence of paradoxical heat sensation, pressure pain threshold and pain responses to suprathreshold thermal stimuli were observed. There was also no difference in capsaicin-evoked ongoing pain and secondary hyperalgesia between the two genotype groups (p >0.4), also when subdivided by gender (p >0.17). In addition, there were no significant differences in the perception of the thermal grill between the two genotypes (p >0.5), also when subdivided by gender.ConclusionsGenotypes associated with high or low expression of the serotonin transporter were not associated with thermal pain thresholds, pressure pain threshold, pain after capsaicin application or responses to the thermal grill.The present results do not support that the investigated genotypes play a major role in thermal pain perception among healthy individuals.

Impulse Conduction Increases Mitochondrial Transport in Adult Mammalian Peripheral Nerves In Vivo

Author SummaryAs mitochondria are the main power source for most cells, their correct localization is vital for cellular homeostasis. The morphological and functional complexity of neurons, and the unpredictability of energy demand resulting from sustained impulse activity, means that correct mitochondrial function and location is particularly important for these cells. However, it is unclear how mitochondrial transport responds to the wide range of physiological conduction frequencies experienced by an intact nervous system. Here we image mitochondria moving along mouse saphenous nerve axons in vivo and observe the effects of sustained trains of impulses, evoked either by electrical stimulation of myelinated axons at physiological frequencies (1 and 50 Hz), or chemical stimulation (cutaneous capsaicin) in unmyelinated axons. We find that the number and speed of mitochondria moving towards the peripheral sensory terminals dramatically increases in active axons. The increased numbers of mobile mitochondria seem to originate from “pinched off” segments of stationary mitochondria (mitochondrial fission), and from recruitment of small stationary mitochondria. The transported mitochondria appear to accumulate in sensory nerve terminals in the skin. This study suggests that mitochondrial fission is involved in rapidly supplying mobile mitochondria to aid their re-distribution to regions of increased metabolic demand along axons.

Activation of primary sensory neurons by the topical application of capsaicin on the epidermis of a re‐innervated organotypic human skin model

Using an ex vivo skin-nerve preparation, skin and nerve cells were reconstituted into a single unit and maintained in a nutrient medium bath until required experimentally. Our objective was to use the epidermis as a relay for the induction of an electric current to the neurons following the topical application of capsaicin on the skin epidermis of the skin explant, an agonist of the TRPV1 channel implicated in pruritus and pain. After 10-20 days of coculture to form the re-innervated skin model, we applied a solution of capsaicin directly on the epidermis of the skin explant (4 μm). The resulting current was recorded using a path-clamp technique on the neuronal fibres. Following the topical application of capsaicin, spontaneous activity was triggered, as characterised by repetitive spikes with periods of 125, 225 or 275 ms. This study demonstrates that the skin explant and nerve cells preparation may receive stimuli and be used to screen molecules or to study signal transmission.

The anti-inflammatory effect of diclofenac is considerably augmented by topical capsaicinoids-containing patch in carrageenan-induced paw oedema of rat

Nonsteroidal anti-inflammatory drugs (NSAIDs) are the most used drugs in musculoskeletal disorders, but their systemic adverse effects limit their therapeutic benefit in local inflammation. On the other hand, topical preparations of capsaicinoids are widely used for musculoskeletal disorders as a complementary therapy. In this study, the effects of both topical capsaicinoids-containing patch and local subcutaneous capsaicin application on the anti-inflammatory action of NSAID were examined. Carrageenan-induced paw oedema of rats was used as the inflammation model. The volume and weight of the paw oedema and plasma extravasation in the paw were determined after carrageenan injection. The systemic application of diclofenac (3 mg/kg), which is an NSAID, significantly decreased the volume and weight of the paw oedema. Topical capsaicinoids-containing patch application or local capsaicin injection (2, 10, 20 μg/paw) alone did not cause any effect on oedema volume and weight. However, the combination of diclofenac with topical capsaicinoids-containing patch significantly increased the effectiveness of diclofenac on inflammation. Evans blue content of the paws that represents plasma extravasation was decreased by capsaicinoids-containing patch with and without diclofenac and diclofenac combination with the lowest dose of capsaicin injection. The results of this study indicate that topical application of capsaicinoids-containing patch enhances the anti-inflammatory effect of diclofenac and its beneficial effect may not purely relate to its capsaicin content. In the treatment of local inflammatory disorders, the combination of NSAID with topical capsaicinoids-containing patch could increase the anti-inflammatory efficiency of drug without systemic side effects.

Differential cellular localization of antioxidant enzymes in the trigeminal ganglion

Because of its high oxygen demands, neural tissue is predisposed to oxidative stress. Here, our aim was to clarify the cellular localization of antioxidant enzymes in the trigeminal ganglion. We found that the transcriptional factor Sox10 is localized exclusively in satellite glial cells (SGCs) in the adult trigeminal ganglion. The use of transgenic mice that express the fluorescent protein Venus under the Sox10 promoter enabled us to distinguish between neurons and SGCs. Although both superoxide dismutases 1 and 2 were present in the neurons, only superoxide dismutase 1 was identified in SGCs. The enzymes relevant to hydrogen peroxide degradation displayed differential cellular localization, such that neurons were endowed with glutathione peroxidase 1 and thioredoxin 2, and catalase and thioredoxin 2 were present in SGCs. Our immunohistochemical finding showed that only SGCs were labeled by the oxidative damage marker 8-hydroxy-2′-deoxyguanosine, which indicates that the antioxidant systems of SGCs were less potent. The transient receptor potential vanilloid subfamily member 1 (TRPV1), the capsaicin receptor, is implicated in inflammatory hyperalgesia, and we demonstrated that topical capsaicin application causes short-lasting mechanical hyperalgesia in the face. Our cell-based assay revealed that TRPV1 agonist stimulation in the presence of TRPV1 overexpression caused reactive oxygen species-mediated caspase-3 activation. Moreover, capsaicin induced the cellular demise of primary TRPV1-positive trigeminal ganglion neurons in a dose-dependent manner, and this effect was inhibited by a free radical scavenger and a pancaspase inhibitor. This study delineates the localization of antioxidative stress-related enzymes in the trigeminal ganglion and reveals the importance of the pivotal role of reactive oxygen species in the TRPV1-mediated caspase-dependent cell death of trigeminal ganglion neurons. Therapeutic measures for antioxidative stress should be taken to prevent damage to trigeminal primary sensory neurons in inflammatory pain disorders.

NON-INVASIVE EVALUATION OF NERVE CONDUCTION IN SMALL DIAMETER FIBERS IN THE RAT.

A novel non-invasive technique was applied to measure velocity within slow conducting axons in the distal extreme of the sciatic nerve (i.e., digital nerve) in a rat model. The technique is based on the extraction of rectified multiple unit activity (MUA) from in vivo whole nerve compound responses. This method reliably identifies compound action potentials in thinly myelinated fibers conducting at a range of 9-18 m/s (Aδ axons), as well as in a subgroup of unmylinated C fibers conducting at approximately 1-2 m/s. The sensitivity of the method to C-fiber conduction was confirmed by the progressive decrement of the responses in the 1-2 m/s range over a 20-day period following the topical application of capsaicin (ANOVA p<0.03). Increasing the frequency of applied repetitive stimulation over a range of 0.75 Hz to 6.0 Hz produced slowing of conduction and a significant decrease in the magnitude of the compound C-fiber response (ANOVA p<0.01). This technique offers a unique opportunity for the non-invasive, repeatable, and quantitative assessment of velocity in the subsets of Aδ and C fibers in parallel with evaluation of fast nerve conduction.

A Human Model of Small Fiber Neuropathy to Study Wound Healing

The aim of this study was to develop a human model of acute wound healing that isolated the effects of small fiber neuropathy on the healing process. Twenty-five healthy subjects had the transient receptor vanilloid 1 agonist capsaicin and placebo creams topically applied to contralateral areas on the skin of the thigh for 48 hours. Subjects had shallow (1.2 millimeter) and deep (>3 millimeter) punch skin biopsies from each thigh on days 1 and 14. Biopsy wound healing was monitored photographically until closure. Intra-epidermal and sweat-gland nerve fiber densities were measured for each biopsy. Shallow wounds in capsaicin-treated sites healed more slowly than in placebo treated skin with biopsies taken on day 1 (P<0.001) and day 14 (P<0.001). Deep biopsies in the capsaicin and placebo areas healed at similar rates at both time points. Nerve fiber densities were reduced only in capsaicin treated regions (P<0.01). In conclusion, topical application of capsaicin causes a small fiber neuropathy and is associated with a delay in healing of shallow, but not deep wounds. This novel human model may prove valuable in the study of wound healing in patients with neuropathy.