Vascular read-out for TRP channel functionality on distal peripheral nerve endings in healthy men.

BACKGROUND: Quantification of the vasodilation after topical application of capsaicin or cinnamaldehyde is often implemented to indirectly assess Transient Receptor Potential (TRP) Vanilloid 1 (TRPV1) or Ankyrin 1 (TRPA1) functionality respectively. This method has been well-established on the human forearm. However, to enable TRP functionality assessments in distal peripheral neuropathy, the vascular response upon TRP activation on dorsal finger skin was characterized. METHODS: Two doses of cinnamaldehyde (3 % and 10 % v/v) and capsaicin (300 µg and 1000 µg) were topically applied (20 µL) on the skin of the mid three proximal phalanges in 17 healthy men. The dose-response, and inter-hand and inter-period reproducibility of the dermal blood flow (DBF) increase was assessed using Laser Speckle Contrast Imaging (LSCI) during 60 min post-application. Linear mixed models explored dose-driven differences, whereas the intra-class correlation coefficient (ICC) estimated the reproducibility of the vascular response. RESULTS: Both doses of cinnamaldehyde and capsaicin induced a robust, dose-dependent increase in DBF. The vascular response to cinnamaldehyde 10 % on finger skin, expressed as area under the curve, correlated well over time (ICC = 0.66) and excellently between hands (ICC = 0.87). Similarly, the response to capsaicin 1000 µg correlated moderately over time (ICC = 0.50) and well between hands (ICC = 0.73). CONCLUSION: The vascular response upon topical cinnamaldehyde and capsaicin application on finger skin is an alternative approach for measurements on forearm skin. Thereby, it is a promising vascular read-out to investigate the pathophysiology, and TRP involvement in particular, of specific peripheral neuropathic pain syndromes.

Validation of laser doppler flowmetry to measure dermal blood flow of the pinnae in dogs with pinnal alopecia.

BACKGROUND: Laser Doppler flowmetry (LDF) is a noninvasive method of measuring regional blood flow in humans. However, this method has not been widely applied to measure blood flow in dogs. HYPOTHESIS/OBJECTIVES: We hypothesised that LDF can measure changes in blood flow in canine pinnae accurately. The objectives were to determine whether LDF could accurately detect dermal blood flow changes in canine pinnae caused by haemodynamic drugs and characterize the dermal blood flow in dogs with pinnal alopecia. ANIMALS: Sixteen laboratory-owned healthy dogs, 25 client-owned healthy control dogs and six dogs with pinnal alopecia suspected to be secondary to ischaemic dermatoses. MATERIALS AND METHODS: Clinical doses of the haemodynamic drugs atropine, medetomidine and dibutyryl cyclic adenosine monophosphate (dBcAMP), as well as topical dBcAMP, were administered to healthy beagles. Subsequently, an LDF apparatus was attached to the pinnae to analyse changes in dermal blood flow. Finally, LDF was used to measure auricular dermal blood flow in dogs with pinnal alopecia compared to healthy dogs. RESULTS: Dermal blood flow increased after atropine injection, during dBcAMP infusion and after topical dBcAMP ointment application, and decreased after medetomidine injection. Auricular dermal blood flow (in mL/min/100 g tissue) was significantly (p < 0.05) lower in dogs with pinnal alopecia than in healthy dogs. CONCLUSIONS AND CLINICAL RELEVANCE: Laser Doppler flowmetry is useful for measuring dermal blood flow in canine pinnae; it can be a noninvasive method to monitor ischaemic conditions of dog skin.

Optimization of capsaicin-induced dermal blood flow measurement by laser Doppler imaging in cynomolgus macaque.

BACKGROUND: Capsaicin is used in several areas of non-human primate research including allodynia and dermal blood flow (DBF). The capsaicin-induced DBF increase was measured using laser Doppler imaging (LDI), but this response is known to diminish upon repeated topical applications. Refinement of the experimental procedures could improve the rigor and reproducibility of the DBF migraine model. METHODS: Optimal anatomical site in cynomolgus was determined, and conditions and experimental settings for DBF measurement using LDI were established. Then, two study design trial structures were compared. RESULTS: Medial thigh was the preferrable site, and an ethanol-Tween 20 formulation of capsaicin was desirable. A 1-week washout for contralateral side or 2-week washout for ipsilateral side was necessary to eradicate capsaicin desensitization. CONCLUSIONS: With the established technicality in DBF measurements in cynomolgus macaques, the capsaicin-induced DBF model may be utilized in translational medical research in developing migraine therapeutics.

Laser speckle contrast imaging, the future DBF imaging technique for TRP target engagement biomarker assays.

A comparison was made between the established laser Doppler imaging (LDI) technique and the more recently developed laser speckle contrast imaging (LSCI) method to measure changes in capsaicin- and cinnamaldehyde-induced dermal blood flow (DBF) as an indicator of TRPV1 and TRPA1 activation, respectively. METHODS: Capsaicin (1000 µg/20 µl) and cinnamaldehyde (10%) solutions were applied on the forearm of 16 healthy male volunteers, alongside their corresponding vehicle solutions. Pre challenge and 10, 20, 30, 40 and 60 min post challenge application, changes in DBF were assessed with the LSCI technique, followed by LDI. The area under the curve from 0 to 60 min (AUC0-60) post capsaicin and cinnamaldehyde application was calculated as a summary measure of the response. Correlation between the LDI and LSCI instrument was assessed using a simple linear regression analysis. Sample size calculations (SSC) were performed for future studies using either the LDI or LSCI technique. RESULTS: Higher arbitrary perfusion values were obtained with LDI compared to LSCI, yet a complete discrimination between the challenge and vehicle responses was achieved with both techniques. A strong degree of correlation was observed between LDI and LSCI measurements of the capsaicin- (R = 0.84 at Tmax and R = 0.92 for AUC0-60) and cinnamaldehyde-induced (R = 0.78 at Tmax and R = 0.81 for AUC0-60) increase in DBF. SSC revealed that LSCI requires considerably less subjects to obtain a power of 80% (about 15 versus 27 subjects in case of capsaicin and 7 versus 13 for cinnamaladehyde). CONCLUSIONS: The LSCI technique was identified as the preferred method to capture capsaicin- and cinnamaldehyde-induced changes in DBF. Besides its reduced variability, the shorter scan time provides a major advantage, allowing real-time DBF measurements.

Novel capsaicin-induced parameters of microcirculation in migraine patients revealed by imaging photoplethysmography.

BACKGROUND: The non-invasive biomarkers of migraine can help to develop the personalized medication of this disorder. In testing of the antimigraine drugs the capsaicin-induced skin redness with activated TRPV1 receptors in sensory neurons associated with the release of the migraine mediator CGRP has already been widely used. METHODS: Fourteen migraine patients (mean age 34.6 ± 10.2 years) and 14 healthy volunteers (mean age 29.9 ± 9.7 years) participated in the experiment. A new arrangement of imaging photoplethysmography recently developed by us was used here to discover novel sensitive parameters of dermal blood flow during capsaicin applications in migraine patients. RESULTS: Blood pulsation amplitude (BPA) observed as optical-intensity waveform varying synchronously with heartbeat was used for detailed exploration of microcirculatory perfusion induced by capsicum patch application. The BPA signals, once having appeared after certain latent period, were progressively rising until being saturated. Capsaicin-induced high BPA areas were distributed unevenly under the patch, forming "hot spots." Interestingly the hot spots were much more variable in migraine patients than in the control group. In contrast to BPA, a slow component of waveforms related to the skin redness changed significantly less than BPA highlighting the latter parameter as the potential sensitive biomarker of capsaicin-induced activation of the blood flow. Thus, in migraine patients, there is a non-uniform (both in space and in time) reaction to capsaicin, resulting in highly variable openings of skin capillaries. CONCLUSION: BPA dynamics measured by imaging photoplethysmography could serve as a novel sensitive non-invasive biomarker of migraine-associated changes in microcirculation.

Pharmacokinetic-Pharmacodynamic Relationship of Erenumab (AMG 334) and Capsaicin-Induced Dermal Blood Flow in Healthy and Migraine Subjects.

PURPOSE: Capsaicin-induced dermal blood flow (CIDBF) is a validated biomarker used to evaluate the target engagement of potential calcitonin gene-related peptide-blocking therapeutics for migraine. To characterize the pharmacokinetics (PK) and quantify the inhibitory effects of erenumab (AMG 334) on CIDBF, CIDBF data were pooled from a single- and a multiple-dose study in healthy and migraine subjects. METHODS: Repeated capsaicin challenges and DBF measurements were performed and serum erenumab concentrations determined. A population analysis was conducted using a nonlinear mixed-effects modeling approach. Effects of body weight, gender, and age on model parameters were evaluated. RESULTS: Two-compartment target-mediated drug disposition (TMDD) model assuming binding of erenumab in the central compartment best described the nonlinear PK of erenumab. Subcutaneous absorption half-life was 1.6 days and bioavailability was 74%. Erenumab produced a maximum inhibition of 89% (95% confidence interval: 87-91%). Erenumab concentrations required for 50% and 99% of maximum inhibition were 255 ng/mL and 1134 ng/mL, respectively. Increased body weight was associated with increased erenumab clearance but had no effect on the inhibitory effect on CIDBF. CONCLUSIONS: Our results show that erenumab pharmacokinetics was best characterized by a TMDD model and resulted in potent inhibition of CIDBF.

Quantification of Dermal Microcirculatory Changes after Topical Administration of Capsaicin: A Randomized Placebo-Controlled Study in 46 Subjects.

BACKGROUND: Dermal blood flow is crucial for wound healing and survival of flaps in dermatologic surgery. To improve flap viability in cases of compromised perfusion topical agents can easily be applied. The aim of this placebo-controlled study was to characterize changes of DBF in healthy subjects by quantitatively assessing perfusion dynamics after application of capsaicin to establish a reference for measurements at injured sites. METHODS: In 46 healthy subjects perfusion dynamics after local application with capsaicin and placebo was noninvasively assessed, determining cutaneous oxygen saturation, relative hemoglobin count and blood flow using an Oxygen-to-See device. RESULTS: A significant raise in superficial (162% p = 0.000) and deep (144%, p = 0.000) skin oxygenation after 30 min was provoked. A highly significant raise in measurements of flow and velocity was present in superficial (523%, p = 0.000) and deep (242%, p = 0.000) sites. CONCLUSION: With the introduced model applied to observe changes in parameters of dermal blood flow in healthy subjects the authors can reliably monitor effects of topically administered capsaicin. This baseline can be used as reference for further studies in the settings of endangered flap survival or critically perfused wounds as has been proven in animal studies.

Safety, Tolerability, Pharmacokinetics, and Pharmacodynamics of the CGRP Binding Monoclonal Antibody LY2951742 (Galcanezumab) in Healthy Volunteers.

Background: Calcitonin gene-related peptide (CGRP) is pivotal in the pathophysiology of migraine headaches and represents a promising target for migraine treatment. The humanized monoclonal antibody galcanezumab (LY2951742) binds to CGRP and may be effective in migraine prophylaxis. Objectives: The primary objective was to evaluate the safety and tolerability of single and multiple doses of galcanezumab in humans. Secondary objectives included assessing the pharmacokinetics and evaluating target engagement. Methods: A double-blind, randomized, placebo-controlled study (NCT 01337596) with single escalating and multiple subcutaneous (SC) doses of galcanezumab was performed in healthy male volunteers. Single doses of 1, 5, 25, 75, 200, and 600 mg of galcanezumab (n = 7/dose) or placebo (n = 2/dose) were injected SC in six consecutive cohorts of nine subjects each. One cohort of nine subjects received multiple (4) 150 mg doses of galcanezumab or placebo every other week. Target engagement was evaluated by measuring inhibition of capsaicin-induced increase in dermal blood flow (DBF). Findings: Sixty-three subjects were randomized and included in the safety analyses. Galcanezumab was well tolerated in single doses (1-600 mg SC) and consecutive doses (150 mg SC). There was no dose-dependent difference in type or frequency of treatment-emergent adverse events, and no clinically meaningful difference when compared with placebo. Pharmacokinetics were linear. Galcanezumab induced a robust, dose-dependent, and durable inhibition of capsaicin-induced increase in DBF, supporting the continued clinical development of galcanezumab for prophylaxis in migraine patients.