March 2016 Update:
Following the 2016 Prosper Meniere’s Society Meeting in Austria, it is probably a good time to provide an update of the current research being performed at The University of Sydney, Meniere’s Laboratory.
There are numerous lines of research that we have either undertaken over last few years, or are currently undertaking. Here‘s a brief summary of each project for the layman. As you can see, the below list of recent projects is extensive, and given that the research team consists mostly of Dr Brown, a couple of students, and a couple of clinical collaborators, it is perhaps easy to appreciate the slow-progress of the research overall. That is, we appreciate that Meniere’s sufferers are desperate for a glorious breakthrough, but this is unlikely to happen overnight, and the Laboratory does not currently have the resources most people in the public may perceive that it does. At one level, we punch-above-our weight, but we are still hamstrung by the moderate nature of the laboratory’s team. This is, however, rapidly changing, as the laboratory establishes more of a profile at the University and Internationally. What is needed, and what the MRFI are now looking towards, is to grow the lab team, by recruiting additional, experienced laboratory researchers to compliment Dr Brown’s program.
Aquaporin over-expression as a model for Hydrops.
Over the last 15 years, several researchers have focused on the idea that many forms of Meniere’s disease may be due to an abnormal expression of water transport channels called aquaporins. Specifically, a number of studies have reported that experimental animals who have been treated with hormones that up-regulate the expression of aquaporins develop endolymphatic hydrops, and related hearing and balance symptoms. Between 2012-2013 we explored this animal model by chronically implanting mini-osmotic pumps into guinea pigs to deliver vasopressin (a hormone that upregulates aquaporin expression) over a 2-3 week period (Chihara et al., 2013). Ultimately, we found the effects to be minimal, and most likely insufficient to explain the symptoms observed in Meniere’s disease patients. We subsequently moved on from this model, but in the subsequent years others have continued to explore the involvement of aquaporins in Meniere’s, demonstrating new findings that may entice us to revisit the model in the future. For now, we think that it is unlikely that an abnormal level of hormones that regulate aquaporin expression is the cause of Meniere’s disease in a relevant number of sufferers.
Cause of Vertigo attacks
One main-stay of our research over the last few years has been the investigation of the link between endolymphatic hydrops, and the symptoms of Meniere’s disease. Arguably, from 2005 until the last couple of years, many researchers felt that endolymphatic hydrops was not the cause of Meniere’s symptoms, but rather just an epiphenomenon. This view resulted from a seminal study by Merchant et al., (2005), who examined temporal boned from deceased people, and reported that whilst all Meniere’s sufferers had hydrops, many people who were not diagnoses with Meniere’s disease also had hydrops. This report was heavily cited, and ‘became clouded’ in the research world to be taken as though hydrops doesn’t cause hearing or balance symptoms, and that normally hearing/balance people can have hydrops.
However, a close inspection of the Merchant study reveals that the non-Meniere’s ears with hydrops all had some form of hearing or balance disorder, it’s just that they didn’t fit the criteria for a Meniere’s diagnosis. More recently, MRI studies have demonstrated a clear association between endolymphatic hydrops and Meniere’s disease (or related inner ear problems).
Additionally, we have performed numerous studies where we have artificially created endolymphatic hydrops in the inner ears of experimental animals, demonstrating that hydrops can indeed underlie the symptoms of Meniere’s, including the sudden episodes of vestibular dysfunction. Traditionally, it was thought that hydrops (a swelling of the membranous labyrinth) eventually caused a rupture of the membranous labyrinth, resulting in a mixing of the inner ear fluids (perilymph and endolymph), and a transient potassium toxicity of the vestibular hair cells. This is known as the “Rupture Theory”. We have performed an extensive, if not exhaustive series of experiments to determine if a rupture of the membranous labyrinth causes sudden vestibular problems… ultimately, we have failed to find sufficient evidence that ruptures underlie the episodes of vestibular dysfunction. Rather, our research points towards a sudden re-distribution of the endolymph fluid within the membranous labyrinth, possibly involving the action of various morphological ‘valves’ that separate portions of the inner ear (Brown et al., 2013a,b; Brown et al., 2016). It seems as though endolymph volume builds up in one part of the ear (the cochlea), increasing fluid pressure and disturbing cochlear hair cells, until the pressure forces open one of these valves, releasing pressure in one compartment, but increasing it in another (also causing a sudden ionic disturbance).
The importance of understanding the role hydrops plays in hearing and balance symptoms is two-fold. First, we can now focus on researching disorders that may cause abnormal fluid volume regulation per se, rather than researching disorders that cause fluctuating hearing and balance symptoms – but may or may not lead to hydrops (e.g. a viral infection of the VIIIth nerve).
It seems everyone wants to see more randomized, placebo controlled trials of treatments for Meniere’s. First, it’s important to understand that such trials are difficult to get going, and almost always require the involvement of multiple hospitals/specialized clinics, with nurses, clinicians, and biostatisticians who are experienced in running such trials. Secondly, because Meniere’s symptoms naturally fluctuate, the trial must be maintained over a long period of time (>6 months at least) to ensure efficacy, you need close to a hundred or more participants, and you must make sure that all those participants have Meniere’s disease of the ‘right’ kind. Trials are particularly difficult here because we lack a tool for the simple diagnosis of the disease itself. That is, we cannot simply rely on patients providing feedback about how they are feeling, because the placebo effect in Meniere’s disease is very large.
If we had a tool whereby we could easily measure Meniere’s disease, or if you like, hydrops (assuming hydrops directly correlates with the course of the disease), then trials would be an order of magnitude easier to perform, because we wouldn’t need a placebo group, and we wouldn’t need to wait for the full progression of symptoms.
In 2012 we developed a non-invasive method of objectively estimating the level of hydrops in Meniere’s sufferers. This test involves using low-frequency modulated ‘Distortion Product Otoacoustic Emissions’ (DPOAE-bias). The test works really well in people who still have good hearing, and involves just an ear-canalphone like setup. We are currently looking for industry partners who can help develop the test into standard audiometric equipment, so that we can test many more people, and incorporate the test into clinical trials.
Still working on the following updates… more to come….
Light Sheet Fluorescent Microscope
UVL plus CI
CI impedance Fluctuation
Scala Media Pressure Regulation
Vestibular Efferent System
LPS induced Hydrops
Comparison of membranous labyrinth in MD patients vs. pre-clinical models