Researchers at the National Heart and Lung Institute have found more efficient ways to study tissues and cells. As a result, we can learn more about cardiovascular health whilst using fewer animals.
When scientists set out to investigate a complex health issue, no single approach will deliver all the answers. “We always look for the best way to test each individual research question,” says Dr Nick Kirkby,
from the Cardio-Respiratory Interface section at Imperial’s National Heart and Lung Institute. “That might mean very simple studies with cultured cells, or using many types of cultured cells together, or animal models, or small clinical studies with patients.”
Each line of enquiry will deliver different, complementary information, which together builds into a better understanding of the question. In this case, the goal is to understand how blood vessels function in healthy and unhealthy bodies, and how drugs can control those processes. “What we want is to create a window into the circulation,” says Dr Blerina Ahmetaj- Shala, a colleague working in the same area.
The challenge when studying blood vessels is that they are complex structures, made up of different types of cells and tissues. These interact together, and with the tissues that the vessels supply with blood. If you break these structures down in order to study them, or take the blood vessels out of context, then you risk not getting the whole picture. A common thread in Nick and Blerina’s work is that they are looking for ways to preserve this natural complexity as much as possible.
Nick’s research focuses on drugs like aspirin and ibuprofen. “People take aspirin to protect against heart disease. It’s a very good drug, but some people taking aspirin still have heart attacks and strokes, so we think there is potential to improve it. Then with ibuprofen-like drugs, which people take for painful conditions such as arthritis, the problem is that they can actually cause heart attacks and strokes in some people. We would like to solve those problems.”
Whole animal studies can provide the big picture, for instance how a particular drug affects blood pressure and other cardiovascular indicators, but they are also time-consuming and can involve a lot of animals, which is not ethically desirable. In addition, this approach does not reveal in detail how blood vessels are behaving to control these effects.
While it has long been possible to study large blood vessels, which are easily accessible, they do not tell us everything about the finer points of vascular behaviour. “They are essentially hosepipes that take the blood around the body. We’ve learnt a lot from studying them but they are quite different from the much smaller blood vessels that are inside your tissues and organs,” Nick explains. “These small vessels are really important in controlling your blood pressure and your cardiovascular risk and there is still a lot we don’t know about them.”
So he and his colleagues came up with a compromise method, in which fine slices are taken from tissues and kept alive in a petri dish. “We can observe the small blood vessels within each slice, while they are still influenced by all the other components of that tissue. We can look at each slice under a microscope and watch the blood vessels contract and relax as we add different substances.”
Lots of slices can be taken from each organ to profile different drug responses, and several organs can be studied from the same animal. “This is a stepping stone that allows us to retain the complexity of a whole-animal system, while getting much more information and using fewer animals,” says Nick. “We can also use the technique to study human tissues biopsies and so avoid the need to use animals altogether.”
Efforts are also made to get even more information from each piece of tissue, using ‘omic’ technologies, where hundreds or thousands of molecules can be measured in the blood vessels at the same time. “Even if you start the study with a very specific question, using these approaches we can often make completely unexpected discoveries, which is really exciting. And by getting so much information at the same time we add extra value to the animal studies that we do.”
This work mainly involves mice and human tissue, although sometimes rats or spare tissue from pigs collected as a by-product of other research or food production are studied. “Wherever animals are used for research, it is our obligation to make sure we use as few as possible, and do it with as little impact on their welfare as possible.”
This tissue slicing method has been used to examine the adverse effects of ibuprofen-like drugs in different tissues. “We found that they have a very negative effect on the blood vessels in the kidney,” Nick says. “People don’t necessarily think of the kidney as part of the cardiovascular system, but it is really important in controlling cardiovascular health.”
His group is now pursuing this lead with other basic science studies, as well as through clinical studies. “We have samples from a big clinical trial of people taking ibuprofen-like drugs, and we want to see if changes in kidney function markers in the blood predict whether or not the person is likely to go on to have a heart attack.”
This research may also result in better treatments. “Ultimately we hope we can develop a new drug, or say that a particular drug combination lowers a patient’s risk of heart attack.”
Blerina is approaching the question of blood vessel complexity from the other side, with research into how studies of cells from blood vessels cultured in the laboratory can be improved. The tissue that lines blood vessels, called the endothelium, can be grown under laboratory conditions, but these cell cultures change over time and so may not function in a dish the same way that they do in the body. This also removes them from the smooth muscle cells that they would normally be attached to in a blood vessel in the body.
Her approach involves isolating progenitor cells from the human blood stream, which can then be grown into endothelial and smooth muscle cells. Cultures of these cells are fresh, and therefore behave as they do in the human body. More importantly, they can be combined so that the interactions present in the body between the two kinds of cells are also present in the dish. “We’ve created a model where we can layer both of the cell types together,” she says. “When we add dierent drugs to that model, the cells respond in a similar way to what is expected in the body.”
Since the progenitor cells can be isolated from simple blood samples they can be studied from dierent people and patient groups. “If we know that endothelial or smooth muscle cells are aected by certain diseases, like pulmonary hypertension, then we can isolate these cells from patients who have these diseases, compare them to healthy patients, look for dierences and then test potential drugs that are available and see which works best.”
This is a stepping stone that allows us to retain the complexity of a whole- animal system, while getting much more information and using fewer animals.”
– Dr Nick Kirkby, Faculty of Medicine, National Heart and Lung Institute
Another possible application that Blerina is using these cells to investigate is diabetes. “Cardiovascular issues are a big problem for patients with diabetes, with 80% of diabetic patients dying from cardiovascular complications. So, we want to isolate these cells from diabetic patients to understand what goes wrong in the blood vessels of these people and how we could reverse or prevent that.”
In addition to answering questions about diseases in general, this approach could make treatments much more personal. Once a blood vessel model has been created for a specific patient it can be stored for future use, to test new treatments as they are developed. “If you give me a blood sample, I can grow your endothelial cells and your smooth muscle cells, then use them together in a personalised medicine approach to see which drugs your cells respond to best before you start taking them.”
In the long term, this technology could also make it possible to build three- dimensional blood vessels, which could be transplanted into patients to replaced damaged blood vessels. “This will not be easy, however, and will require help from engineers and a range of other researchers.”
The relationship between this research with cell cultures and the research with animals is not simply that one can replace the other. Instead, there is an exchange of information, with each approach capable of influencing the other. “There are many diseases where we are not sure of the mechanism, so by getting cells from people who have these diseases we can learn more about these mechanisms, and then use animal models to test potential treatments and therapies that target them,” says Blerina.
And unless you know which factors are involved in a biological process, you cannot begin to make a cell culture model. This is where an animal study may hold the key. “Once you realise that a pathology or a drug response is driven by interactions between, say, endothelial cells, smooth muscle cells and white blood cells, then you can address that with human cells in a dish, and you no longer have to use animals,” Nick says.
