Inaugural Lecture | Matej Orešič

Metabolome is an intermediary linking environmental exposures and life-course health. I have been involved in the study of metabolites, which are small molecules of molecular weight of less than 1500 dalton, for over 20 years. Metabolites are intermediaries and products of metabolism. Many of them are very well known to you, such as, for example, glucose, cholesterol, lactate or glutamate. And each of them, measuring them, for example, from blood, does inform us about the status of the body. It could be, for example, health and disease, such as in case of glucose, if it's high, it may mean diabetes, or if you are a professional cyclist racing in Tour de France, you do want to know what is your level of lactate, because that may tell you what is your lactate clearance capacity, and that may further tell you how good chances you have the next day when you have to climb the mountains again. Complete collection of metabolites in a given biological system, from cells, tissues, to whole organism, is referred to as metabolome. The metabolome is very diverse chemically, functionally, as well as in terms of concentration range. Metabolites are typically in concentration from milligram per millilitre, down to picogram per millilitre, thus spanning several orders of magnitude. These involve, for example, many classes of lipids, amino acids, nucleotides, steroids, eicosanoids, which are involved in immune response, neurotransmitters, et cetera. And they all are important in various biological processes, either metabolic processes, could be cell signalling, could be, for example, immune regulation, and many others. Thus, in order to study the metabolome, it's not only about studying and measuring metabolites. We want to know also how these metabolites are transformed biochemically. That means which enzymes are regulating specific metabolic reactions. And then also, we want to know what are the genes coding for these enzymes. So, we need to deal also with genetics, proteomics, and then, of course, metabolomics. So, there are many fields that contribute to the field that is called metabolomics. Additionally, we also know that we are colonized by thousands of microbes across the gastrointestinal tract and also elsewhere. And these microbes are also producing metabolites, and they are also transforming our metabolites, meaning that the gut microbiome is a major contributor to our host metabolism, and many metabolites we measure, for example, from tissues and blood, are actually either direct products of gut microbiota, or they are being transformed by the gut microbiota. Bile acids, for example, is one class of metabolites that is currently of great interest, being involved not only in the digestion of lipids, but also in the cellular signalling, and increasingly recognised also in the regulation of the immune response.

The question then is, if you have so many metabolites, and they are so important, we do want to know their amounts, not only their identity, thus how do we measure them? And this is what we do in our research on a daily basis. We use the so-called mass spectrometry for measuring the metabolites. That means also identifying and then also quantifying, to determine the amount of these metabolites. Mass spectrometry is an old technique, but the instruments are getting better and better. The fundamental principle of mass spectrometry is that as an input to the mass spectrometer, your molecules will get charged, then they will fly through the mass spectrometer, there are different ways to do that, and then at the end, there is a detector which will determine the specific molecule based on the charge and based on the mass. So, it is, in a way, a very sophisticated weight scale that costs roughly about the cost of the house. It's a very expensive equipment, but it's highly, highly sensitive, highly accurate, and also with a very high mass resolution. So, this is something that is being done by us and many others in metabolomics research. And there are, of course, other techniques that are available, such as nuclear magnetic resonance, which is less sensitive, but does have some advantages for specific kinds of studies. Now, since the metabolites are so important in health and disease, involved in so many different processes, we call it as a certain intermediate phenotype, we do want to understand what is affecting the metabolome. So, what factors are driving it? The gut microbiome, as I said, is already there, so we consider that more of an internal environment. But then, there are many external factors that are also important. And this is what, today, we call in totality, the environment is the exposome. And this includes not only the general external environment, such as the light or noise or the pollution, air pollution or social networks, et cetera, but also the specific external environment, such as chemical exposures or lifestyles, like smoking or diet, and then when we talk about chemical exposures, this is usually linked to the food, the water, drinking water, the diet itself, and then the consumer products we are exposed to when we do the packaging, et cetera, and cleaning reagents, and these are all containing certain industrial chemicals that may be affecting also your metabolome. So, this is the area where we have been particularly interested, and these exposures are not only one-time exposures. Of course, we ideally would understand these exposures over the life course, and not only during the life, but also before life. Because we think, and we know that exposure starts already in the womb, that means in utero in other words. Just as one example, those who were in utero during the five days of Great Smog of London in 1952, they have 8% increase in childhood asthma. Even before they were born, they acquired the risk that quite importantly increases the risk of the disease. Those who were, for example, in their first year of life during these five days, they had 20% increase of childhood asthma later on. And even significant fraction also was having increased risk of adulthood asthma. That means that decades later since they were born, they actually acquired this disease because of these five days of exposure to the smog.

One class of chemicals that we have been particularly interested in are per- and polyfluorinated alkyl substances, or PFAS. These are a group of man-made chemicals that have been widely used since the 1950s in various household and industrial products. They were made to resist heat, oil stains, grease and water, and we are exposed to them through the diet, food packaging, non-stick cookware, various clothing, cleaners, firefighting foams, et cetera. The most common one, the first one that was really widely used is called PFOS, and it was actually phased out already in early 21st century, 2002 specifically, yet it's still very widely detected in our bodies and also in the environment. There are others, and currently, EU is pushing for the complete ban of PFAS as a class, which has not yet happened, and we still have a lot of new PFAS coming to the market. So, this is still an unresolved issue, and we know that they are harmful for the health. For example, in our research, which was published recently, we were studying how the exposure prenatally affects the metabolism of human foetus. We have collaborated with partners in Aberdeen, where we studied 78 livers of human foetuses. The foetuses were from the elective abortions at gestational ages of 12 to 19 weeks. The key finding there was, looking at the comprehensive metabolomics and chemical exposures, that higher exposures to PFAS had a major impact on the hepatic metabolism. Many of the hepatic metabolites, such as bile acids, for example, or lipids, were strongly affected by the higher exposure to PFAS. And this is evidence that already in the first trimester of gestation there is PFAS exposure detected in the human foetus, which probably comes through the placenta, and also these PFAS have a major impact on metabolism. In fact, the metabolic changes that we observed in the human foetal liver are similar to what we have observed in other studies, for example, in studies of fatty liver disease in adults. Therefore, it does seem that there is a sort of metabolic imprinting that affects the risk of disease future in life. Thus, this may be similar to the story about the asthma and smog. It seems that there is a lot more to it in terms of what exposures do already at the foetal stage.

One last thing about the research that we are doing, among the main lines of research is type 1 diabetes. That has been going on for nearly 20 years already in our research group. The highest incidence of type 1 diabetes in the world is actually in Finland. Nearly 1% of all population of Finland is affected by this disease. Type 1 diabetes has a strong genetic component, but only 3-7% of those at genetic risk do develop disease actually, so there is clearly a major impact of the environment. One of the early signs of disease progression is islet autoantibody positivity, i.e. an autoimmune resonse, but it may take months to years before the disease develops. What is important in our research is that we found that already before the autoimmunity, you see the metabolic changes that are associated with later progression to type 1 diabetes. And further, our most recent study suggests that these metabolic changes are actually driven by the environmental exposures in utero, including the PFAS in this case. This is an ongoing investigation, so we are currently studying bigger populations, but generally, it seems that environment is a contributor, not a cause necessarily, but a contributor to the increased risk to diabetes. This is in fact the main subject of the research going on now in our research group. And that's part of an EU project called INITIALISE, which I'm coordinating, and the University of Turku is a coordinating institution, and altogether involves 12 partners from EU, UK and US. Our overall aim here is to improve life course health by focusing on shaping of the immune system in the early, most vulnerable period of life, including prenatal period. We include multiple clinical cohorts as well as various mechanistic studies. We investigate gut microbiome, the metabolome, immune system measured through various kinds of markers, and then proteome in general, and how these factors play together during early life in utero as well as first years of life, and how they then contribute to the risk of diseases later in life. And we are not only focusing here on type 1 diabetes. We focus on actually several immune mediated disorders, including allergies. Then, we also focus on obesity, specifically childhood obesity, which is then the major predictor of the future risk of diabetes and cardiovascular disease. And then also, on the various neurocognitive outcomes, such as ADHD and autism. So, this will keep us busy for several years now when this project is ongoing.