Lymphovenous Canada: New Research Developments in Understanding Lymphovenous Disorders - update

In recent years I've moved out of the traditional lymphatic area by focusing on the brain, and looking at how cerebrospinal fluid is absorbed into the lymphatic system. Quite remarkably our research has pointed us in an entirely different direction from the conventional view. The conventional view is that cerebral spinal fluid (CSF), which is part of the brain, is drained from the subarachnoid space into the venous sinuses of the brain.

That may be true to some extent but all of our research tends to point the fact the majority of cerebral spinal fluid enters lymphatic vessels at the base of the brain. We've been able to apply a number of quantitative measures, and some new imaging techniques with contrast agents to show a highly specialized network of lymphatic vessels in the olfactory and respiratory passages that have important function in absorbing cerebral spinal fluids. So what we're trying to do now is link this, if possible, to disease.

We're developing some models with collaborators in the United States, where we induce hydrocephalus in rats. One of our graduate students is testing the concept that an impediment to the absorption to CSF into the lymphatics contributes in some way to hydrocephalus. We're also looking into a project about aging. One of the things that happens as people get older is that they seem to absorb less spinal fluid, and no one understands why, although this been linked possibly to Alzheimer's and normal pressure hydrocephalus. CSF turnover seems to be impaired in the elderly. This may cause the accumulation of toxic metabolic substances that would have normally been vented out more effectively in the younger ages.

Our preliminary studies seem to show quite convincingly that in the aged animals there is less lymphatic update of the cerebral spinal fluid. So we're moving from physiology into a consideration of the pathological implications.

Related to this research is the FOXC2 gene which has been found to be responsible for mutations in the lymphatic system. What's of great interest to us is that mutations in a related gene - FOXC1 - causes some skeletal anomalies in the head, particularly with the bones at the base of the skull. In research done by Dr. Marlys Witte at the University of Arizona lab animals affected by this gene also had lymphedema and hydrocephalus.

The other project we have undertaken is a lymphangiogenesis study. Lymphangiogenesis is a term that refers to the regeneration of lymphatic vessels. In commonly used approaches, investigators surgically destroy an area of tissue and then use fairly crude measures to assess whether tissue drainage has been restored. The ultimate goal is to manipulate this process with molecular factors.

Lymphatic vessels regenerate rapidly under most conditions. However, we don't know whether these new vessels function normally. For example, are they hyperpermeable (allow protein to pass through their vessel walls), is the architecture of the newly formed ducts conducive to lymph transport etc.

It is very difficult to study these issues in a mouse, which is the animal most commonly used by researchers. They are too small to allow individual vessels to be studied. So, we returned to sheep, which are large and allow us to access these ducts conveniently. We've developed a single vessel model of lymphangiogenesis in which a large postnodal duct is ligated to obstruct flow. New vessels sprout from the upstream end to bridge the gap presumably in an attempt to re-establish flow across the ligature.

Because we can do this in very large lymphatics, we can perform perfusion studies and employ other techniques to investigate the biomechanical properties of these vessels. That's where our work has been moving. We are particularly interested in the role of the lymph node in tissue fluid balance.

The lymph node has an important role to play in the generation of immune responses. However, most people ignore the lymph node as having any relevant fluid transport properties. Nonetheless, there is some reason to believe that the node may be a critical element in establishing anatomical cues to orient the architecture of a lymphatic network.

Secondly, there is evidence to suggest that the lymph node is a fluid exchange chamber. Water is absorbed out of the lymph into the vasculature of the node and that means that what comes out in the post-nodal lymph is quite different from what went in. The removal of water seems to reduce the pressure and stress on downstream elements. If you remove the lymph node that dissipation of energy will not occur. We think this might adversely affect the functioning of system in post-surgical lymphedema patients.

We're now trying to think of ways of testing this by transplanting lymph nodes into areas where the nodes have been excised.

If you think about it, lymphatic vessels are damaged all the time by surgeons - every time they go into a body they're cutting lymphatic vessels. But the vessels regenerate and apart from an acute edema, lymphedema is not a characteristic feature of any kind of heart surgery, or liver transplantation.

So what is the key in the surgical removal of cancers such as that which occurs in breast cancer? It's the removal of the lymph node, which doesn't occur, in other types of surgical procedures. There's already some clinical evidence that the node may be key. The issue is that we really have to test whether putting the node back or an artificial substitute, will improve the situation. There is some literature on this and the literature seems positive.

There are reports in experimental animals that if you auto-transplant a node back into the incision site there is considerable improvement compared to not putting the node back in. I think that the molecular biologist are so concerned at developing new molecular concepts that we may be ignoring the broad physiological context in which lymphedema develops.

The node itself probably isn't facilitating the spread of the cancer, in fact, if anything it's blocking it. The node filters out cells and node staging is often used to determine how far the cancer has spread. Once these nodes are removed however, the lymphatics regenerate whether the node is put back in or not.

Based on the few reports that I have seen,
the transplanting of nodes in some people
with lymphedema has been beneficial.

Radiation seems to increase the risk for lymphedema considerably. Nobody is quite certain why but presumably the radiation prevents the re-growth of vessels or the newly formed vessels are damaged in some way. Transplantation of autologous lymph nodes may help in two ways.

Firstly, the node may provide structural orientation for the new vessels. In the absence of nodes, we know there is a haphazard connection of vessels that link up but these do not seem to provide a smooth transfer of tissue fluid back to the venous system.

The lymph node provides a focal point to anchor the prenodal and postnodal ducts. By providing these structural cues - and this is something we can test - the presence of a lymph node might help to return fluid balance close to its original state. As part of this process, the loss of water in the node might remove some of the stress on the downstream elements.

Based on the few reports that I have seen, the transplanting of nodes in some people with lymphedema has been beneficial. However, the advantage to the patient may depend to some extent on the timing of the node transplantation. If the nodes were to be transplanted long after lymphedema had been established, this procedure would probably have less effect. In comparison, if the nodes were replaced shortly after nodal dissection for cancer therapy, the presence of the node might actually prevent the generation of lymphedema.

The situation with hereditary lymphedema is probably more complex. Even though some of the genes have been identified there are probably many factors involved in the pathogenesis. Hopefully, with further research we will understand what these factors are and be in a position to develop new therapies as appropriate.

If we take a step back and look at lymphatic research in general it is certainly much improved over where it was 10-20 years ago. Speaking to my clinical colleagues, I understand the number of cases of post surgical lymphedema is on the rise. No doubt, this is contributing to a greater awareness of lymphedema and several agencies are putting more into lymphatic research.

On the other hand, while the improved funding for the Canadian Institute for Health Research (CIHR) is commendable, the base budget for operating grants does not seem to be keeping up with the number of applications submitted. This is really discouraging as scientists may have their grants ranked excellent and yet, they don't get their projects funded.

And when times are tough, topics that are considered less fashionable - like lymphedema - are at risk of losing some of the funding to projects that are higher up on the radar screen of biomedical research.

It is unfortunate that many scientists will only publish in what they consider high impact journals. This approach causes pain for some of the smaller journals especially those new journals that don't even have an impact factor yet. It takes a number of years before they generate a certain reputation in the field. In my view, there is no such thing as a good journal or a bad journal - there are only good papers and bad papers. One can see all kinds of silly papers in great journals as well as superb papers. The journal is not the critical thing it's the quality of the paper that is important.

Improving the research and treatments in this area will come through a combination of patient empowerment, patient knowledge and new research initiatives. Patient advocates are having a big impact - through education and the development of web sites. So congratulations to you and your colleagues.

Toronto scientist, Professor Miles Johnston, receives CBCRA funding to determine how damaged lymphatic vessels repair and stabilize newly formed ducts.