BJA/RCoA Project Grant
Improving opioid analgesia by targeting beta-arrestin2 signalling
Prof Tim Hales
Mu opioid receptor (MOPr) agonists, such as morphine, are the drugs of choice for treating severe pain. However, their effectiveness for chronic pain is compromised by side effects (including: tolerance, dependence, constipation and respiratory depression). Opioids also stimulate the reward pathway causing the hedonic effects underlying their abuse/addiction potential. Analgesic tolerance, the term used to describe the tendency for the pain killing action of opioids to wear off, is the probably the most problematic aspect of opioid analgesia. Tolerance leads to a requirement for increased doses to control persistent pain. Dose increases lead to a greater likelihood of additional adverse effects. Despite on-going attempts to develop alternative chronic pain killing drugs there is currently nothing likely to replace opioids in the treatment of severe pain. MOPrs are located throughout the pain pathway and may represent the best analgesic targets available. Rather than finding alternative targets we are seeking ways to improve opioid analgesia through mitigation of tolerance with an adjunct agent. Prior research highlights a role in tolerance for beta-arrestin2, a protein that interacts with MOPrs. We have found that beta-arrestin2 recruits c-Src, whose inhibition leads to sustained MOPr signalling which is a requirement for long lasting analgesia. The cellular kinase c-Src is named for its ability (in mutant form) to induce sarcomas. Several recent cancer therapies, including the drug dasatinib, inhibit c-Src activity. Dasatinib treatment is well tolerated despite the ubiquitous nature of c-Src expression. We will explore the effects of dasatinib on opioid analgesia in mice. We have several mutant mouse models available including mice engineered to lack either MOPrs or beta-arrestin2. These are useful tools that enable an investigation of the involvement of these proteins in any actions of c-Src inhibition.
The goals of this proposal are to:
1. Determine whether inhibition of c-Src reduces morphine tolerance and produces sustained analgesia
2. Examine whether c-Src inhibition disrupts opioid receptor signalling in the reward pathway
This preclinical study will explore the promise of antagonists of the beta-arrestin2/c-Src signalling pathway as adjuncts to improve opioid analgesia. Should the administration of dasatinib lead to sustained MOPr-mediated analgesia future experiments will test additional selective c-Src inhibitors. A clinical research project will be developed to examine pain in patients receiving c-Src inhibitors as anti-cancer drugs. A successful outcome could lead to changes in clinical practice in patients with cancer using c-Src inhibitors as part of a pain control regimen.
This work builds on the PhD study of Dr Fiona King (Trainee Anaesthetist). Support will enable the continued development of the project. Funding will enable Dr Daniel Baptista-Hon to perform the experiments described under the joint supervision of Dr King and Prof Hales.
Please see the NIAA's position statement on the use of animals in medical research.
MICROSHOCK: An observational pilot study of the effects of haemorrhagic shock and resuscitation on the microcirculation
Surg Cdr Sam Hutchings
Traumatic injury is the leading cause of death for adults under the age of 40 in the United Kingdom. The commonest accidents involve motor transportation or occur in the workplace. However, recent years have seen several incidents related to terrorist activity and, for the UK military, armed conflict that has lead to multiple fatalities. Many of these casualties have devastating injuries for which no treatment would have been effective. However, there is a group that die despite having potentially survivable injuries. Within this group the commonest mechanism of preventable death is massive blood loss. Over the last decade the Defence Medical Services of the United Kingdom have been at the forefront of treating massive blood loss due to their involvement in high intensity armed conflict. Advances in treatment have led to many lives being saved that would otherwise have been lost. There is an ongoing effort to understand the reasons why some patients who lose massive amounts of blood go on to recovery relatively quickly, whilst others, treated in the same way, die or take much longer to recover.
We know that some patients who survive their initial injuries go on to develop failure of some of the key organs of the body, such as the kidneys, and that this may be related to the way that blood flow to these organs is changed in the hours and days following injury. Of particularly interest is the network of tiny blood vessels that represent the final common pathway of oxygen and nutrient delivery to these organs; these vessels are termed the microcirculation. The microcirculation is difficult to examine and has tended to be overlooked by doctors treating patients with severe injuries, who have instead concentrated on measuring flow in the large blood vessels of the body. We believe that by targeting treatment to improve flow in these small vessels the impact of massive blood loss, in terms of organ damage, can be reduced. Very little research has been carried out in this area to date and before we can develop specific treatment recommendations we need to confirm our theory and develop some ideas about why the microcirculation is impaired in some patients but not in others.
To examine the microcirculation we will use a specialized medical camera, placed under the patient's tongue, which allows us to record very detailed images of blood flow. At the same time as we record these images we will be studying blood flow in the heart and larger blood vessels in order to examine the link between flow in small and large vessels. We will also take blood samples that will be studied to look at possible reasons why the microcirculation becomes impaired or damaged.
Our study is an early preliminary study, termed a pilot, designed to inform larger scale research in the future. It will be carried out at Kings College Hospital, London and will involve around ten patients over a two year period.
Death receptor signalling in acute respiratory distress syndrome
Dr Brijesh Patel
The lung consists of airspaces (alveoli). Each of these airspaces is similar to a dam - with air on one side and blood on the other. The 'bricks' of this dam are called alveolar epithelial cells (AECs) and are bound very tightly together. AECs facilitate gas exchange: transfer of oxygen from air to blood and carbon dioxide from blood to air. In health, the bond between AECs prevents tissue fluid moving into the airspaces; and channels on AECs pump fluid out of the airspaces keeping them dry.
Damage to AECs leads to flooding of airspaces with tissue fluid causing life-threateningly low oxygen levels in the blood. Furthermore, the damage to the lungs initially attracts immune cells from the blood that compound the injury. This constitutes the acute respiratory distress syndrome (ARDS) and can be triggered by a variety of insults (pneumonia, inhalation of stomach contents) and carries a 40% death rate. It has no treatments, with only life-support on intensive care, with the hope that lungs repair themselves. Damage to AECs is thought to occur through molecules that induce programmed cell death. This process is a highly co-ordinated process whereby a cell is slowly dismantled and is called apoptosis.
We have established a model of ARDS in mice which reproduces many features of human ARDS and was featured as an editorial entitled "Progress in modelling acute lung injury in a pre-clinical mouse model" by Professor Michael Matthay (UCSF), an internationally renowned ARDS investigator, who stated 'the report by Patel provides an excellent, comprehensive model of ARDS in mice that should be of substantial value to investigators in the field'.
We recently showed that during the early hours of ARDS in mice, death signals within AECs induce leak of tissue fluid into alveoli. Historically, it has been thought that this leak is a direct consequence of cells dying but our work shows, for the first time, that the death signal itself, not the death of the cell, causes ARDS. This concept, which we have called 'apoptosis limbo', suggests that if AECs are not dead then we can potentially find treatments to revive, reanimate, and restore epithelial function in ARDS.
Apoptosis is integral to normal organ function and repair and recovery from disease. We will examine the death and survival balance in different cells and investigate the beneficial and detrimental effects of blocking death signals. We shall use genetically modified mice and drugs, to establish the benefits and side effects of modulating death signalling. In particular, we will see how blocking death signals delays the clearance of harmful immune cells that are attracted to the lung during ARDS. In contrast, during later stages of ARDS reparative immune cells enter the lungs and facilitate recovery and we believe these cells influence recovery through deactivation of death signalling.
Overall, our aim is to find mechanisms and therapeutic targets to stop cracks developing, helping to re-build the dam in ARDS.
Please see the NIAA's position statement on the use of animals in medical research.
Optimising translational capacity of melatonin administration for chemotherapy induced neuropathic pain
Dr Carole Torsney
Background
Cancer chemotherapy often causes side effects, which include pain and altered skin sensation. These symptoms, called chemotherapy induced neuropathic pain- or CINP- are difficult to treat and may be so severe that lifesaving cancer treatment has to be stopped. The symptoms can also go on long after the chemotherapy has finished. We currently have no way of identifying who is most likely to suffer from CINP before they develop it.
Some common chemotherapy drugs have been shown in laboratory experiments to cause something called oxidative stress, which can be prevented by antioxidants. Melatonin is a natural substance produced in the brain. It is a very good antioxidant which can be given orally in large doses with minimal side effects. We have recently completed a study in rats, showing that the side effects of chemotherapy were reduced when melatonin was given to the rats in their drinking water. We therefore think that melatonin may be helpful to prevent or reduce the painful side effects in cancer patients getting chemotherapy. Before we can undertake a clinical trial of melatonin however, we need to further study how it acts in rats. This will help direct us in developing its potential use in the clinic. This will be complemented by studying samples from patients undergoing neurotoxic chemotherapy, to try and identify a marker in the blood that will help identify those most at risk.
The aim of this proposal is to undertake a study using rats to determine if CINP can be reduced by oral melatonin, what the optimum dose and dosing interval is, and the effects in both male and female animals.
Method
The study will be in 3 parts. In the first we will determine the levels of melatonin and also of the related substances which are produced when the melatonin is metabolised, as these are also good antioxidants. In the second part of the study we will measure the pain reducing effects of different doses of melatonin and different timings of treatments and we will do all of this in both male and female animals. In addition we will conduct experiments to try and find a biochemical substance in the blood which we can then use to measure the effects of the melatonin in patients in the future.
Rats will be given melatonin in doses prepared in flavoured jelly. This approach has been used before to give drugs to rats and is more like giving a capsule of medicine to humans than giving the melatonin in drinking water. The chemotherapy drug will be given to the rats by injection and the pain side effects profile will be measured using well established techniques that monitor the rats' behaviour. At the end of the experiments the rats will be killed and blood and nerves will be removed for testing. The entire study will be done in a mix of males and females and the study is designed to mimic the approach we would use in patients.
Please see the NIAA's position statement on the use of animals in medical research.
