What is endometriosis?

Endometriosis is a condition where cells similar to those found within the lining of the uterus (womb) begin to grow in other areas of the body. The abnormal cells that characterise endometriosis react in the same way as  those found in the womb, building up tissue and then breaking down each month, causing bleeding. Unlike the cells that break down in the womb during a regular period, the abnormal and misplaced cells have no way to escape the body. Endometriosis causes a chronic inflammatory reaction that can lead to scar tissue within the pelvis and other parts of the body. Endometriosis is not limited to the area immediately in and around the womb and can spread across the body and affect other organs.

Endometriosis can affect people of all ages from puberty to menopause. Some can feel the effects of the condition for life. In the UK, around 1.5 million people have been diagnosed with endometriosis. The most common symptoms of endometriosis include:

• Chronic pain

• Fatigue/lack of energy

• Depression/isolation

• Problems with a couple’s sex life/relationships

• An inability to conceive

• Difficulty in fulfilling work and social commitments


What causes endometriosis?

The causes of endometriosis remain elusive to science, even though the disease was first identified more than 100 years ago. Endometriosis is a complex condition and the mechanisms underlying its development and progression are far from being understood. There are several theories about the cause of endometriosis but none fully explain why the disease occurs. Understanding the causes of endometriosis is essential to creating effective treatments for the condition.

So far, research has identified multiple areas as possible causes or contributors to endometriosis, including: retrograde menstruation; genetic predisposition; lymphatic or circulatory spread; immune dysfunction; environmental causes; and metaplasia.


Problems with diagnosing and observing endometriosis

Observing and diagnosing endometriosis in humans has proven difficult, especially in the early stages of the disease. In many cases, the condition is not diagnosed until it has progressed considerably. The only way to monitor the progression of endometriosis is through a surgical procedure, a laparoscopy, where a surgeon passes a thin tube through a small incision to look for patches of endometriosis tissue. It is impossible to monitor the progression of this disease without repeated laparoscopies.


Animal research and endometriosis

Various animal species have been used to study endometriosis including rats, mice, rabbits, hamsters, and monkeys. The most important difference amongst these species is their ability to spontaneously develop endometriosis. Rodents such as rats, mice, and hamsters do not spontaneously develop endometriosis, whereas monkeys do.

The diverse nature of endometriosis means that no single animal species is best suited to research in this area. Different animal species are used to model different aspects of the disease.


Endometriosis and research in mice and rats

Mice and rats have been used quite extensively to study endometriosis, including research into how the disease is caused, its progression and risk factors, and exploration and evaluation of potential treatments. Rodents do not develop endometriosis spontaneously, symptoms or characteristics of the disease are induced in the animals and studied independently.

Mice have also been used to study the link between endometriosis and genetics. Transgenic or knockout mice are used to study biological factors that may affect endometriosis, such as the role of the immune system and hormone imbalances. New insights into the genetics of endometriosis will improve our understanding of the disease and our ability to model it effectively in animals.

It is important to keep in mind that rodent models have limitations and do not mimic all aspects of human disease. Ideally, disease models should mimic human disease as much as possible to allow scientific investigation of the disease as a whole, but in many cases this is not possible. Rodent models will not reflect all aspects of human endometriosis, but they can still provide valuable information.

Read more detail on how rodents are used to model endometriosis on animalresearch.info

Read more on the use of mice in scientific research in the UK


Endometriosis and research in monkeys (non-human primates)

As primates, we share many biological similarities with monkeys, including spontaneous development of endometriosis. Monkeys are considered one of the most appropriate species to study endometriosis because of our biological similarities. Monkeys have been used to improve our understanding of endometriosis and how it affects the body, and to develop new treatments for people. However, using monkeys in scientific research comes with significant ethical concerns, and it is only allowed to take place when it is considered the only option. In addition, monkeys require large, costly enclosures and  specialist animal care staff with a deep understanding of their complex needs and behaviour.

The fact that monkeys naturally develop endometriosis would seem to make them the ideal species to research this disease, but the same difficulties in diagnosing and observing the disease that we face in humans are also present in monkeys, which limits their usefulness. Identifying spontaneous development of endometriosis in monkeys is not simple and, for many studies, a large number of animals would be needed. The law and ethical considerations require us to minimise the number of animals used in research wherever possible, especially when it comes to highly intelligent species such as monkeys, and so endometriosis research in monkeys remains minimal, usually occurring after substantial research has first taken place in rodents.

Read more detail on how monkeys are used to model endometriosis on animalresearch.info

Read more on the use monkeys in scientific research in the UK


Other animal species in endometriosis research

Other animals have been used to model specific aspects of endometriosis including chickens, rabbits, sheep, and cows. Chickens have been used to study specific mechanisms of endometriosis and rabbits and cows have been used to study the link between endometriosis and infertility.


Non-animal models and new approach methodologies (NAMs) in endometriosis research

Cell cultures, often based on cells collected from human biopsies, have been indispensable in uncovering the fundamental biological processes behind endometriosis. Cell cultures have shown us which cells assemble into tissues and organs, how these tissues function, and how that function becomes disrupted in disease. Findings that have emerged from in vitro observations have helped guide science to a whole new group of drugs for treating endometriosis.

However, these 2D models lack important features of cellular function, including their original microenvironment, their tissue-specific architecture, and blood flow perfusion. In the quest to create better models to observe cell to cell interaction, researchers have developed 3D cell models of endometriosis, with more realistic microenvironments. Commonly referred to as organoids, 3D cell models are made from artificially grown cells or tissue that resemble an organ. Organoids aim to provide an in vitro method of studying cellular behaviour and in some cases, they have been used successfully to reduce the number of animals used in scientific testing of this nature.

Read “Endometriosis: a painful lack of research”


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