The Functional Consequences of the CTNS-deletion for the TRPV1-receptor in Cystinosis Patients

Summary

Cystinosis is a rare autosomal recessive disorder, characterized by the abnormal accumulation of cystine in the lysosomes. Cystinosis is mostly caused by mutations in the cystinosin gene (CTNS). The major mutation, which is present in almost 50% of the cystinosis patients, is a 57-kb deletion. This deletion removes the first 9 exons and a part of exon 10 of the CTNS gene. Exon 10 of the CTNS gene is a upstream 5' region that encodes for the CARKL gene and also for the first two noncoding exons of the transient receptor potential channel, vanilloid subfamily member 1 (TRPV1) gene.

TRPV1 belongs to the transient receptor potential (TRP) superfamily of cation channels. TRPV1 is primarily expressed in sensory nerves and is activated by heating (\>43°C) and a wide range of chemical stimuli. One of these chemical stimuli is capsaicin, the pungent ingredient in hot chilli peppers. The effect of binding of the exogenous ligand capsaicin with the TRPV1 receptor is well known to provoke the release of a number of bioactive substances including calcitonin gene-related peptide (CGRP). These substances, in turn, act on target cells in the surrounding tissue such as mast cells, immune cells and vascular smooth muscle cells. The resulting response is characterized by redness and warmth (secondary to vasodilatation), swelling (secondary to plasma extravasation) and allodynia (i.e. hypersensitivity to heat and touch secondary to alterations in the excitability of primary sensory neurons).

The present study wants to test the following hypotheses:

(i) The DBF response to topical applied capsaicin is decreased in cystinosis patients, compared to matched control subjects.

(ii) The skin sensitivity response after topical applied capsaicin is decreased in cystinosis patients, compared to matched control subjects.

(iii) The temperature sensitivity is decreased in cystinosis patients, compared to matched control subjects.

Conditions

• Cystinosis

Interventions

OTHER

Challenge agent: capsaicin

During the study period (Day 1), in each subject 3 equally spaced (minimum distance of 4 cm) 10-mm rubber O-rings (8 mm inner diameter) will be placed on the volar surface of the forearm. The most proximal ring (i.e. at least 15 cm proximal of the wrist crease) is referred to as ring number 1; the most distal ring is referred to as ring number 3; in between is ring number 2. In ring number 1 and 2, subjects will receive a topical dose of 1000 µg/20 µL capsaicin (single-blind). Change in dermal blood flow induced by capsaicin will be measured with Laser Doppler Imaging.

OTHER

Challenge agent: placebo

During the study period (Day 1), in each subject 3 equally spaced (minimum distance of 4 cm) 10-mm rubber O-rings (8 mm inner diameter) will be placed on the volar surface of the forearm. The most proximal ring (i.e. at least 15 cm proximal of the wrist crease) is referred to as ring number 1; the most distal ring is referred to as ring number 3; in between is ring number 2. In ring number 3, subjects will receive a topical dose of placebo (single-blind).Change in dermal blood flow induced by placebo will be measured with Laser Doppler Imaging.

DEVICE

Mechanical stimulation with Von Frey filaments

Von Frey filaments will be used to measured the mechanical detection and pain threshold of the volunteers. The Von Frey filaments will be applied on the upper capsaicin spot in sequential order. The subject will be asked to indicate when he feels the application of the Von Frey filaments and when it hurts.

DEVICE

Temperature sensitivity measurement with Advanced Thermal Stimulation

Temperature sensitivity (detection and pain threshold) will be determined using Advanced Thermal stimulation. A thermode will be attached to the hand of the volunteer with a baseline temperature of 32°C. The thermode will heat up and cool down with a rate of 1°C/second and the volunteer will be asked to click on a computer mouse when he feels the change in temperature and when it hurts.

Sponsors & Collaborators

• Universitaire Ziekenhuizen KU Leuven

  lead OTHER

Study Design

Allocation

NON_RANDOMIZED

Purpose

BASIC_SCIENCE

Masking

NONE

Model

PARALLEL

Eligibility

Min Age

8 Years

Sex

ALL

Healthy Volunteers

Yes

Timeline & Regulatory

Start

2014-11-30

Primary Completion

2015-07-31

Completion

2015-07-31

Countries

• Belgium

Study Locations