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Animal studies suggest that the ion channels TRPV1, TRPA1 and TRPM3 are the relevant heat sensors. This study aims to validate these findings in humans.
Surprisingly, it is still not fully understood how humans perceive heat pain. There are several heat-sensitive ion channels whose manipulation in animals resulted in a more or less pronounced phenotype. However, complete blockade of heat sensation in animals has only recently been achieved. In triple knockout mice lacking TRPA1, TRPV1 and TRPM3, it was recently shown that only in the absence of all three receptors heat perception is largely abolished. Although the authors were unable to elucidate the underlying mechanism of this redundancy, the redundancy appears to have evolutionary value for protection against burns. In addition, recent evidence suggests that TRPV1 plays a role as a first-line defense against heat injury, i.e., that it encodes noninjurious heat injury in humans.
The goal of this study is to test whether the redundant functions of TRPV1, TRPA1 and TRPM3 observed in mice with respect to heat perception also apply to humans. More broadly, we want to understand which receptors enable humans to perceive heat pain. The study also aims to test if a chloride channel is involved in heat perception.
Design: Cross-over study with a Williams design group, 16 treatments incl. a placebo control.
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| Label | Type | Description | Intervention Names |
|---|---|---|---|
| Hot injection without TRP-channel inhibition | Placebo Comparator | Pain induced by an increasingly hot intradermal injection up to 52°C over 2 minutes. |
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| Hot injection with TRPA1-inhibition | Experimental | Pain is induced by an increasingly hot intradermal injection up to 52°C over 2 minutes, while TRPA1 is blocked pharmacologically by an antagonist dissolved in the hot fluid (synthetic interstitial fluid). The antagonist(s) have sufficient concentration to reliably block the channel. The total dose is in the range of a microdose trial. |
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| Hot injection with TRPV1-inhibition | Experimental | Pain is induced by an increasingly hot intradermal injection up to 52°C over 2 minutes, while TRPV1 is blocked pharmacologically by an antagonist dissolved in the hot fluid (synthetic interstitial fluid). The antagonist(s) have sufficient concentration to reliably block the channel. The total dose is in the range of a microdose trial. |
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| Hot injection with TRPM3-inhibition | Experimental | Pain is induced by an increasingly hot intradermal injection up to 52°C over 2 minutes, while TRPM3 is blocked pharmacologically by an antagonist dissolved in the hot fluid (synthetic interstitial fluid). The antagonist(s) have sufficient concentration to reliably block the channel. The total dose is in the range of a microdose trial. |
| Name | Type | Description | Arm Group Labels | Other Names |
|---|---|---|---|---|
| TRPA1-inhibitor | Drug | Pharmacological inhibition of TRPA1 during intradermal injection of hot synthetic interstitial fluid |
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| Measure | Description | Time Frame |
|---|---|---|
| HPI(50-52) - Heat pain inhibition in the range between 50°C and 52°C | 'Heat pain inhibition between 50 and 52 °C', abbreviated HPI(50-52). A value of 0% would indicate that for a given injection there was no inhibition between 50 and 52 °C, i.e. that the injection was equal to a heated control injection without substance. In contrast, a value of 100% would indicate that there was complete inhibition and the injection was as indistinguishable from the injection at room temperature. Of note, pain is rated during the application of the test substances. There are 2 experimental days with injections, separated by a few days, resulting in a time frame of 4 days on average. The principle of AUC calculations from pain ratings during injections is described in Heber et al. 2020 (PMID: 32107360 DOI: 0.1097/j.pain.0000000000001848) | Through study completion, on average 4 days. |
| Measure | Description | Time Frame |
|---|---|---|
| HPI - Heat pain inhibition | 'Heat pain inhibition between room temperature and 52 °C', abbreviated HPI. A value of 0% would indicate that for a given injection there was no inhibition, i.e. that the injection was equal to a heated control injection without substance. In contrast, a value of 100% would indicate that there was complete inhibition and the injection was as indistinguishable from the injection at room temperature. Of note, pain is rated during the application of the test substances. There are 2 experimental days with injections, separated by a few days, resulting in a time frame of 4 days on average. The principle of AUC calculations from pain ratings during injections is described in Heber et al. 2020 (PMID: 32107360 DOI: 0.1097/j.pain.0000000000001848) |
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Inclusion Criteria:
To ensure an equal number of each sex in the study population, only volunteers of one sex will be included as soon as the number of subjects with the other sex has reached half of the calculated sample size.
Exclusion Criteria:
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| Name | Affiliation | Role |
|---|---|---|
| Michael JM Fischer, Professor MD | Medical University of Vienna | Study Chair |
| Facility | Status | City | State | ZIP | Country | Contacts |
|---|---|---|---|---|---|---|
| Medical University of Vienna | Vienna | 1090 | Austria |
| PubMed Identifier | Type | Citation | Retractions |
|---|---|---|---|
| 41118703 | Derived | Chubanov V, Grimm C, Hill K, Schaefer M, Kottgen M, Storch U, Mederos Y Schnitzler M, Kudrina V, Erbacher A, Gudermann T. Physiological functions and pharmacological targeting of transient receptor potential channels. Pharmacol Rev. 2025 Nov;77(6):100089. doi: 10.1016/j.pharmr.2025.100089. Epub 2025 Sep 13. |
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All raw data will be shared with other researches upon reasonable request
As soon as the study is published.
Access will be granted to other researchers as well as clinicians.
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| ID | Term |
|---|---|
| D010146 | Pain |
| ID | Term |
|---|---|
| D009461 | Neurologic Manifestations |
| D012816 | Signs and Symptoms |
| D013568 | Pathological Conditions, Signs and Symptoms |
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Factorial: There are 4 treatments (TRPV1-, TRPA1-, TRPM3- and chloride channel inhibition). These will be applied in all possible combinations (16). Each healthy volunteer will receive 8 of these 16 combinations in a sequence defined by a Williams square (Hinkelmann, K., and Kempthorne, O. (2005). Design and Analysis of Experiments Vol. 2 - Advanced Experimental Design (Wiley))
Randomized: Volunteers will be randomly assigned to a pre-specified sequence.
Placebo-controlled: One of the 16 combinations includes none of the three treatments, i.e., can be regarded as placebo control.
Adaptive: Due to the complex study design, a priori assumptions about the distribution and correlation of data could not be made reliably. Therefore, after 16 volunteers, the responsible bio-statistician will simulate how much more patients are necessary to detect the a priori defined effect size with the until then observed data
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| Hot injection with TRPA1- and TRPV1-inhibition | Experimental | Pain is induced by an increasingly hot intradermal injection up to 52°C over 2 minutes, while TRPA1 and TRPV1 are blocked pharmacologically by an antagonist dissolved in the hot fluid (synthetic interstitial fluid). The antagonist(s) have sufficient concentration to reliably block the channel. The total dose is in the range of a microdose trial. |
|
| Hot injection with TRPA1- and TRPM3-inhibition | Experimental | Pain is induced by an increasingly hot intradermal injection up to 52°C over 2 minutes, while TRPA1 and TRPM3 are blocked pharmacologically by an antagonist dissolved in the hot fluid (synthetic interstitial fluid). The antagonist(s) have sufficient concentration to reliably block the channel. The total dose is in the range of a microdose trial. |
|
| Hot injection with TRPM3- and TRPV1-inhibition | Experimental | Pain is induced by an increasingly hot intradermal injection up to 52°C over 2 minutes, while TRPM3 and TRPV1 are blocked pharmacologically by an antagonist dissolved in the hot fluid (synthetic interstitial fluid). The antagonist(s) have sufficient concentration to reliably block the channel. The total dose is in the range of a microdose trial. |
|
| Hot injection with TRPA1-, TRPV1 and TRPM3-inhibition | Experimental | Pain is induced by an increasingly hot intradermal injection up to 52°C over 2 minutes, while TRPA1, TRPV1 and TRPM3 are blocked pharmacologically by an antagonist dissolved in the hot fluid (synthetic interstitial fluid). The antagonist(s) have sufficient concentration to reliably block the channel. The total dose is in the range of a microdose trial. |
|
| Hot injection with TRPA1-, TRPM3- and chloride channel inhibition | Experimental | Pain is induced by an increasingly hot intradermal injection up to 52°C over 2 minutes, while TRPA1, TRPM3 and a chloride channel are blocked pharmacologically by an antagonist dissolved in the hot fluid (synthetic interstitial fluid). The antagonist(s) have sufficient concentration to reliably block the channel. The total dose is in the range of a microdose trial. |
|
| Hot injection with TRPV1-, TRPM3- and chloride channel inhibition | Experimental | Pain is induced by an increasingly hot intradermal injection up to 52°C over 2 minutes, while TRPV1, TRPM3 and a chloride channel are blocked pharmacologically by an antagonist dissolved in the hot fluid (synthetic interstitial fluid). The antagonist(s) have sufficient concentration to reliably block the channel. The total dose is in the range of a microdose trial. |
|
| Hot injection with TRPA1- and chloride channel inhibition | Experimental | Pain is induced by an increasingly hot intradermal injection up to 52°C over 2 minutes, while TRPA1 and a chloride channel are blocked pharmacologically by an antagonist dissolved in the hot fluid (synthetic interstitial fluid). The antagonist(s) have sufficient concentration to reliably block the channel. The total dose is in the range of a microdose trial. |
|
| Hot injection with TRPV1- and chloride channel inhibition | Experimental | Pain is induced by an increasingly hot intradermal injection up to 52°C over 2 minutes, while TRPV1 and a chloride channel are blocked pharmacologically by an antagonist dissolved in the hot fluid (synthetic interstitial fluid). The antagonist(s) have sufficient concentration to reliably block the channel. The total dose is in the range of a microdose trial. |
|
| Hot injection with TRPV1-, TRPA1, TRPM3- and chloride channel inhibition | Experimental | Pain is induced by an increasingly hot intradermal injection up to 52°C over 2 minutes, while TRPV1, TRPA1, TRPM3 and a chloride channel are blocked pharmacologically by an antagonist dissolved in the hot fluid (synthetic interstitial fluid). The antagonist(s) have sufficient concentration to reliably block the channel. The total dose is in the range of a microdose trial. |
|
| Hot injection with TRPM3- and chloride channel inhibition | Experimental | Pain is induced by an increasingly hot intradermal injection up to 52°C over 2 minutes, while TRPM3 and a chloride channel are blocked pharmacologically by an antagonist dissolved in the hot fluid (synthetic interstitial fluid). The antagonist(s) have sufficient concentration to reliably block the channel. The total dose is in the range of a microdose trial. |
|
| Hot injection with TRPV1-, TRPA1, and chloride channel inhibition | Experimental | Pain is induced by an increasingly hot intradermal injection up to 52°C over 2 minutes, while TRPV1, TRPA1, and a chloride channel are blocked pharmacologically by an antagonist dissolved in the hot fluid (synthetic interstitial fluid). The antagonist(s) have sufficient concentration to reliably block the channel. The total dose is in the range of a microdose trial. |
|
| Hot injection with chloride channel inhibition | Experimental | Pain is induced by an increasingly hot intradermal injection up to 52°C over 2 minutes, while a chloride channel is blocked pharmacologically by an antagonist dissolved in the hot fluid (synthetic interstitial fluid). The antagonist(s) have sufficient concentration to reliably block the channel. The total dose is in the range of a microdose trial. |
|
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| TRPV1-inhibitor | Drug | Pharmacological inhibition of TRPV1 during intradermal injection of hot synthetic interstitial fluid |
|
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| TRPM3-inhibitor | Drug | Pharmacological inhibition of TRPM3 during intradermal injection of hot synthetic interstitial fluid |
|
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| Placebo | Drug | No pharmacological intervention |
|
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| Chloride-channel inhibitor | Drug | Pharmacological inhibition of a chloride channel during intradermal injection of hot synthetic interstitial fluid |
|
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| Through study completion, on average 4 days. |