2.4 Animal study
To test whether chronic arsenic exposure upregulates β-endorphin, 18
C57BL/6J male mice (6–8 week) were purchased from the Department of
Laboratory Animal Medicine of Central South University and raised under
a controlled environment with constant temperature (22±2 °C) and a
12-hour light-dark cycle. The mice were randomly assigned to vehicle
control, 5 mg/L arsenite-treated group, or 15 mg/L arsenite-treated
group, and each group contained 6 mice. The arsenite-treated mice were
administered arsenite for 6 months
by the drinking water. Mice in vehicle control group were fed with
sterilized water correspondingly. Arsenic trioxide was purchased from
Sigma-Aldrich (St. Louis, MO, USA). After 6 months treatment, the mice
were killed and blood sampled by eyeball extirpating for the detection
of β-endorphin.
2.5 Randomized,
double-blind, placebo-controlled trial
To test whether the inhibition of β-endorphin (μ-opioid) receptor
alleviates itch in patients under chronic arsenic exposure, we conducted
a randomized, double-blind, placebo-controlled trial (ClinicalTrial.gov
ID: NCT03751111). We randomly assigned patients to naloxone (0.4 mg/qd,
sublingual) and placebo (0.4 mg/qd, sublingual) using a
computer-generated sequence of random numbers during January 2019 to
March 2019. The trial consisted of a one-week treatment period and a
one-week withdrawl period. The primary outcome (severity of itch) was
evaluated using the NRS through a face-to-face interview on baseline
(Day 0) and the last day of the treatment period (Day 7), and a
telephone interview on the last day of the withdrawl period (Day 14).
The participants were also inquired about the possible adverse events of
naloxone such as headache, sleep difficulty, sickness, and dizziness in
each interview.
The inclusion criteria can be found in the protocol (supplementary file
S1). In brief, the participants must be above 18 years, be able to
understand the study protocol and sign informed consent voluntarily, and
report moderate-to-severe itch (NRS≥3). Participants were excluded if
they used anti-histamines, anti-inflammatory, anti-pruritic, analgesic,
antidepressant, or anti-epileptic agents within 2 weeks prior to the
study, or had a history of pruritic skin diseases such as eczema and
psoriasis.