Mass spectrometry: a key metabolomics platform in metabolic diseases
Dr Annapaola Andolfo - San Raffaele Scientific Institute, Milan, Italy
I would say that mass spectrometry is a very useful tool and now there is a big development in metabolomics rather than only proteomics. So we are applying this tool in order to better understand what are the altered pathways that are involved in metabolic disease. So we are trying to combine our results using mass spectrometry applied to protein analysis and then also we are trying to understand which are the metabolites that are the real end product of metabolic pathways that are altered in metabolic disease. So our idea is to try to understand how can we explain what is altered in the disease status but also we are trying to understand how we can improve the treatment of patients affected by metabolic disease. So mass spectrometry is very useful because it gives us the possibility to analyse in a very sensitive and accurate way what are the molecules that are really playing a key role in metabolic disease.
What diseases are you focusing on?
We are now studying the ADA-SCID disease. So ADA-SCID is a severe combined immunodeficiency disease associated to a deficiency in the adenosine deaminase enzyme. We have genetic defects in the gene coding for this protein and this protein is an enzyme that is responsible for the conversion of adenosine into inosine and deoxyadenosine into deoxyinosine. What’s happening in patients is that upon these mutations in the gene coding for this protein we have the accumulation of adenosine and deoxyadenosine in plasma. So there is a huge problem in the patients because they suffer from recurrent infections because they have destruction of T-cells and B-cells. However, this metabolic disease is not only related to immunity because we have also other manifestations in other organs. So this is a systemic metabolic disease because we have manifestations also in kidney, lung, liver and now we are trying to understand what is happening in these patients since we observed a major incidence of urological defects in patients. Now patients can be treated with bone marrow transplantation or enzyme replacement so they can survive because they can really improve the detoxification of their plasma and they can live more. However, they have these long-term manifestations and in particular we are focussing our attention on urological defects. So these patients experience cryptorchidism so they have the undescended testes, one or both testes, so they can eventually terminate in infertility or even testes malignancy. So we are trying to understand what is happening in the testes in order to improve also the treatment of these patients for this kind of manifestation.
Are you using animal models?
Yes, we have an animal model and this was developed in 1998. The murine model was very helpful because it recapitulates all the manifestation, many features, of the human disease, so not only in the immune system but also for the other manifestations. So what we are studying now is our animal model and we actually applied a mass spectrometry based metabolomics approach in order to investigate what is changing in the testes of the mice at three weeks of age or at eight weeks of age. Why this? Because at three weeks of age the mice have immature testes so they can be easily compared to wild-type mice. On the other hand, mice can be treated with enzyme replacement so they are treated exactly as patients are treated with PEG-ADA treatment so they can live more otherwise they are lethal at three weeks of age. Then we can also compare the maturation of the testes in the treated mice for our animal model and the wild-type mice. Applying this approach we were able to not only verify that adenosine metabolism was altered at three weeks of age while it was not relevantly or significantly altered at eight weeks because of the treatment. But also we were able to identify other altered pathways that can indicate how can we treat the patients and eventually to rescue also the urological manifestation in these ADA-SCID patients.
Why are patients identified early?
They are identified early because now we have different tests that are performed during foetal life or also in the first days of life. But our approach is not intended to diagnosis this, rather than to treat in a late stage the patients.
