Acute Pain Clinical Trial
Official title:
An Exploratory Study of the Epigenetic Influences on Post-Surgical Acute and Chronic Pain
Pain is the way our brain interprets certain bodily sensations. It is very difficult to
describe or to put into words as perception and tolerance of pain varies widely between
individuals. It is known that age, gender and past experience and memory of past experience
all contribute to patients' feelings of discomfort and tolerance of pain, but the reason why
some patients actually do not experience any pain at all post surgery is still unknown.
Because pain affects every person at some point in their lives, it is of utmost importance
that we can find more effective analgesic methods, and provide analgesia tailored to an
individual's need as well as discovering new methods which may be able to identify those
individuals who are more prone to suffering serious, or chronic pain. It has been proposed
that epigenetic modifications may play a role in sensitivity to analgesia and response to
trauma, such as post surgery. The effects of epigenetic changes on key genes and the role
this plays in analgesia sensitivity and pain perception is deserving of further research.
Epigenetics is a growing field of study in which there are genetic modifications that do not
involve changes to base sequences in a gene, but that result nonetheless in changes to gene
expression. It has long been known that changes in gene expression play an important role in
the establishment of pain states. But it is not known whether a priming injury can induce
lasting epigenetic marks which would result in an increase in both postoperative acute pain
and the risk for chronic pain. Only by fully understanding these epigenetic mechanisms will
we be able to offer better drugs for the treatment of pain, and to identify those at high
risk of postoperative pain and postsurgical chronic pain.
The purpose of this study is to determine whether severity of pain following surgical
procedures, such as third molar surgery is related to baseline methylation status of the
promoter region of IL-6 and TNF-α and changes in methylation status post surgery.
(i) Subjects: Sixty subjects who will be undergoing third molar surgery (hereafter known as
'cases') will be recruited from The Queen Mary Hospital and The Prince Philip Dental
Hospital and sixty, aged and sex matched controls who will not be undergoing surgery in the
next 3 months, nor have undergone surgery in the past year (hereafter known as 'controls')
will also be recruited from the Outpatients department of the same hospital.
(ii) Methods: The study aims and details will be explained to each subject and informed
consent will be sought from each of them. A pain diaryquestionnaire developed by our group
will be adapted for the use of assessing pain experienced by each subject pre and post
surgery. Research personnel will accompany each case subject, and fill out the pain
diaryquestionnaire with them during the visit when the patients' blood is taken.
The following health questionaires will be completed by the subjects recruites:
SF-36: 8-scale profile of functional health and well-being scores as well as
psychometrically-based physical and mental health summary measures HADS: Assessment of the
psychological status of the subjects (anxiety & depression)
Pain assessment:
Pain at rest and during opening will be assessed using a numerical rating scale (NRS, 1= no
pain, 10 = most severe pain) at the following time points:
1. Before surgery
2. 4 hourly after surgery for 16 hours
3. At 24th, 48th and 72nd after surgery
4. 1 month after surgery by telephone interview.
5. 3 month after surgery by telephone interview. If pain is present, questions about
neuropathic pain will be asked.
Venous EDTA blood (10ml) on each occacasion will be drawn from each case one hour prior to
surgery, 1 hour and 3 hours post surgery. Then they will be asked to return to the hospital
3 to 5 days post surgery for one more blood taking, and macrophages will be separated from
the blood and total RNA will be extracted as soon as possible after blood taking from half
the total cells. The remainder of the cells (macrophages) will be stored at -80oC and
batched for DNA extraction. Venous EDTA blood (20ml) will be drawn from each control subject
at a time convenient to them and again, 3 to 5 days post first blood taking. The blood taken
from the control subjects will be treated in exactly the same way as with blood taken from
the case subjects. Therefore, four samples in total will be obtained from each case and
control subject.
The size of the IL-6 and TNF-α promoter regions spanning the sequences upstream of the
transcriptional start site as well as part of the first exon will be determined from
literature search and using a database for reference, CpG islands will be first identified
for primer design (http://www.cpgislands.com/). For analysis of methylation, a commercial
kit will be used (EpiTect Plus LyseAll Bisulfite Kit from Qiagen, Hilden, Germany).
Samples will undergo bisulfite-conversion, and unmethylated cytosines will be deaminated,
forming uracils. Methylated cytosines will remain unchanged. The location of the methylated
cytosine of the gene sequence and the amount of methylated cytosine will be identified and
quantitated by Pyrosequencing using established techniques. Results will be expressed as %
methylation in the promoter region of IL-6 and NF-ĸB.
Note: The pyrosequencing technique can only analyse fragments of DNA of up to 50 base pairs
in one reaction. According to data from CpG Island Searcher, and when the % GC was set at
55%, observed CpG/expected CpG set at 0.65 and gaps between adjacent islands set at 100bp,
no CpG islands can by found in either the IL-6, or the TNFα promoter. Therefore, the
methylation status of the whole promoter region in both genes will be studied using 40 pairs
of primers for each gene (in order to cover 2kb of the promoter region). This approach is
adopted as it is the most sensitive and reliable for determination of site specific DNA
methylation in an extended region such as a promoter region.
(iii) Study design: This is a case-control study. The samples used in this study will be
whole blood samples taken pre- and post- surgery from the cases, and at a matched time, from
the controls.
Power calculations: No data exist on the level of DNA methylation in the promoter region of
IL-6 and TNF-α in normal healthy subjects. Power calculations reveal that 51 subjects in
each group are required to have an 80% power to detect a true difference in the variable of
interest at 5% significance level (calculations using G*Power software, version 3.1). A
total of 60 subjects will be recruited into each group to take into consideration drop out
rates.
(iv) Data processing and analysis: Paired t-test (or non-parametric equivalent) will be
performed to investigate differences in level of DNA methylation pre- and post- surgery.
Unpaired t-test will be used to investigate difference in the level of DNA methylation
between cases and controls. Correlational analysis will be used to investigate relationships
between methylation status and IL-6 and TNF-α expression. Descriptive statistics will be
employed to describe the changes in methylation status (i.e., if different sites in the CpG
island are methylated) in the promoter region of IL-6 and TNF-α B, pre-post surgery and in
the two different sampling time points of the control subjects.
Purpose and potential: This is a pilot, exploratory environmental-epigenetics study on the
effect of bilateral third molar surgery on DNA methylation changes in the promoter region of
IL-6 and NF-ĸB, and the influence of methylation status on gene expression. The results will
provide insight and promote understanding into the molecular mechanisms through which the
methylation status of inflammatory genes can affect the experience of pain post surgery.
;
Observational Model: Case Control, Time Perspective: Prospective
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