Interview with Prof. Eugeni Roura on the role of nutrient-sensing mechanisms

Van Zele: Hello everyone and thank you once again for joining us today. I'm your host Delphine Van Zele, swine product manager EMEA. Connecting with us today, we have professor Eugeni Roura from the University of Queensland. Professor, may I say Eugeni?

Prof. Roura: Hi Delphine, yes, please call me Eugeni if you're comfortable with that. Thanks.

Van Zele: Ok, thank you. Thank you for taking the time also to share your insights on nutrient-sensing mechanisms and how these impact the gut-brain axis.

Well Eugeni, you appear to be quite the world traveler. First, earning your degree in veterinary science from the Universitat Autonoma de Barcelona, Spain, before achieving a postgraduate in nutrition from the University of California Davis. Now you are in Australia, working with the University of Queensland as a professor of the Centre for Nutrition and Food Sciences.

Through all these moves, I've noticed two trends. One is the focus of your research on the popularly termed gut-brain axis and the second is your preference for warm and sunny places. Do I have all this right, or is there anything more you'd like to add?

Prof. Roura: Thanks so much for having me. Good observation, certainly, I'm always looking for sun and good weather… enjoying the outdoors, right? So, that's certainly something that helps me enjoy life outside the lab and the classrooms. In addition, I would also like to add something that may not be that apparent to you but it is important. I think I've been very lucky and I feel fortunate because I have also been interacting with the three institutions that you named and they are all excellent institutions.

The Universitat Autonoma Barcelona, the vet school is one of the top vet schools in the world. Needless to say, the University of California, Davis is a world top-ranking institution; particularly in agriculture and food sciences. And that's also true for the University of Queensland. Our university is one of the top fifty universities in the world and, in terms of agriculture and food science, is actually amongst the top ten too. So, I am very fortunate and honored to have been able to travel the “academic” world as a member of these three outstanding Universities.

Also trying to find scientific excellence in addition to sun and good weather. Maybe they are related? But I am sure there are many exceptions. Ha, ha, ha….

Van Zele: OK, sounds great. So, three top schools with a lot of scientific experience. So, I would say let's jump right into that. Now, we touched already a little bit, but you are specializing in the function of nutrient sensing mechanisms present in the gastrointestinal tract. What are these mechanisms and what role do they play in nutrition and performance?

Prof. Roura: That's a very good question. And you're right, that has probably been a main driver of my professional career at least over the last, I would say twenty-four years or so.

As a nutritionist and digestive physiologist, I want to understand how feeds and foods are being digested, how are they being absorbed, and how this then leads to satiation and a satiety state. And, how is that happening? When you start looking at these different processes you will soon observe intermediate steps and mechanisms that actually need to be activated for all of this to happen.

For example, how does the pancreas know that it's time to release pancreatic enzymes? Well, there has got to be some signaling that when we start eating something is telling the pancreas, “Hey buddy! Start synthesizing and releasing pancreatic enzymes because there's food coming”, right?

And that's not magic and it's not that the pancreas is secreting enzymes all the time either, which would be a waste, right? In fact, the pancreas will only release enzymes when there is food coming. So, it is obvious that there has to be a communication, a talk, a chemical talk if you want, between different parts of the digestive system when food is entering through the mouth. The mouth somehow is talking to the pancreas so that the pancreas says ‘Yep, it's time to secrete all these enzymes for digestion’.

The same happens with things such as how do we absorb nutrients. So, if we think that the enterocytes in the small intestine have always the means ready to absorb… well no! The process of absorption could potentially cost energy, as well, right? So, it's not that the gut and the intestines are constantly activated to absorb nutrients because that would be inefficient. On the contrary, they will only activate the absorption function when the time is right, when there are nutrients to be absorbed. And that's what we call chemo-sensing. So, we are studying all these processes that in fact are like the vocabulary, a dictionary of how different parts/tissues of the body talk to each other. How does the mouth talk to the gut and how does the gut talk to the brain?

In other words, we're trying to understand these communication pathways between foods and exogenous income, and internal organs. And the only way that that communication is possible is through chemosensory mechanisms. Over the past couple of decades, we have understood what are the main receptors and how they interact with the amino acids and carbohydrates and fats present in food. And how the activation of these receptors implies changes in the cellular metabolism that prepares the enterocyte to absorb amino acids, for example. Or activating specialized cells which are able to secrete gut peptides, hormones that will talk to the hypothalamus, the hypothalamus being the main organ in the control of feed and food intake. That's nutrient sensing. That's nutritional chemosensory science.

Van Zele: A very fascinating system, that we can say, I think.

So, speaking about that signaling and giving a signal towards the gut and from the gut to the brain, you were also touching about the influence of the absorption of nutrients as well as digesting the food, that it is not going all the time.

Is there also somewhere then a correlation with them? How it is going and how the passage rate is going in the digestive tract?

Prof. Roura: Absolutely, it will be no surprise to nutritionists that the passage rate has a massive influence on the way and how efficiently we are in digesting feeds and foods.

But if there's something that we need to keep in mind, it is that if there is one organ that is crucial when it comes to defining passage rate, it is the stomach. Many of us, I believe, have been assuming that the most limiting passage rate is in the small intestine. This would make sense, I guess, given that it is the longest part of the gastrointestinal tract.  But this is far from reality. In fact, the most critical decision-making organ in terms of passage rate is the stomach.

The stomach is the no-return point. Once food (and feed) passes through the pylorus into the small intestine, there's no way back. On the contrary, while the food is in the stomach, we can still reject it. We can vomit and we can just get rid of something that the stomach feels may not be safe.

The stomach also makes decisions on when to let the content continue the journey into the small intestine, and how much is released at any time point. A good part of the decision-making process is particle size. We know that only small particles will be let through the pylorus into the small intestine because what we really need is a particle size in the small intestine for fast (and complete) digestion. As you noticed, I am emphasizing ‘fast’, and fast means really fast. Something that we have learned is that the passage rate through the small intestine is very quick.

Many of us have been thinking that the passage rate of the gut content through the small intestine would take a long time because of the need of actually digesting the food. The enzymes need to get into the particles and digest them bit by bit and that takes a long time. Well, it doesn't actually happen that way and that's a crucial concept to understand. The stomach releases small particle sizes that will travel very fast through the small intestine, and fast means ten to twenty (or even more) meters per hour.

Meters per hour… let’s think about it. That means, for example, that a young pig with a small intestine of say ten meters will take less than one hour for feed to go through. So very quick indeed, certainly quicker than most of us had been previously thinking, right? It is important to emphasize this, because what it means is that once you get into the small intestine, you need the nutrients to be digested and absorbed very fast. Otherwise, they go all the way through to the large intestine where they will be fermented by bacteria. And to some extent, that's a loss.

So, the most significant time constraints of the digestion process are either in the stomach or in the large intestine where feed can spend hours. But not in the small intestine where the passage rate is really quick.

Van Zele: Interesting, really. For some of us for sure, new information as well, not yet known. So, we were already touching the passage rate as well as the nutrient absorption and we can all relate this to nutrient sensing. So, for me, it sounds like you and your team, plus for sure many others in the field of research, have discovered a lot about how pigs are perceiving feed. Where do you see then the future of research?

Prof. Roura: That's a very good question and, like everything in life, there is a sequence. And, almost, life takes you to the next stage, right? Let me explain what I mean in terms of our research area. When it comes to nutrient sensing, it all started in the oral cavity. I started developing my professional research career at least in the oral cavity, taste and smell and other oral sensing mechanisms. At that time we didn't even know the molecular mechanisms of taste. We started to understand about the existence of taste receptors and where they were expressed around the turn of the century in the year 2000. Only then we realized that these taste receptors discovered in the tongue were actually the same receptors that are present in the stomach, small intestine, large intestine, et cetera.

Then we started to wonder what these “taste” receptors were doing in the intestines. In fact, they do the same thing that they do in the tongue, they sense nutrients. If you think about the taste, sweet taste is about simple carbohydrates (this is, sensing the carbohydrate fraction of the diet). If we think about the savory taste, the umami taste, relates to the protein fraction of the diet: the amino acids, glutamic acid, and so on. I could go on, we have the fatty acid sensing, dietary fats, right? Et cetera, et cetera. So, for every nutrient, there is a type of taste and sensing [receptor], and those receptors are also present in the small intestine, stomach…. And those are the ones that will be mediating the gut sensing and the gut-brain communication responses.

From the oral cavity into the gut and then from the gut, the same senses will mediate the release of gut peptides. And what gut peptides do is communicate with the brain. So, that's where the gut-brain axis comes into place. We start in the oral cavity, we continue into the digestive system, and then we go into the gut-brain axis and then the next stage, that's where the next stage comes logically, the brain.

Consequently, what we're interested in now is how do we understand this brain response? How is the brain deciding or giving us the good versus unpleasant feelings? Where is the decision coming from? How is that brain hardwired and what's the process? And we have realized that at least some of these processes of hardwiring how the brain responds to nutrient sensing will be influenced during embryonic development.

In other words, how the environment affects mum while pregnant will be transferred into making the fetus understand what is waiting in the outside world. In terms of nutrition, the embryo or the fetus is getting ready for what's coming in the outer world through the perception of mum and the nutrients (or lack of) that mum is ingesting. For example, if the sow in the wild is having a rough diet because there's drought, and there are not enough proteins found, it's got a low protein diet. Well, we know that the progeny will be more adapted to a low crude protein diet through maternal conditioning.

This is the adaptation to harsh or special requirements starts in the womb. Progeny adaptive mechanisms influenced by mum’s environment is what we call transgeneration, because it takes more than one generation. That transgeneration mechanism has a tremendous impact because one individual, one sow or one hen, has the potential to impact tens, if not hundreds, of progeny. Transgenerational research has the potential to influence lots of individuals by only affecting one individual. This is a multiplication effect, what brings me to believe this is going to be an important strategic area of future research. That's where we're going. I hope I explained it plainly and that it makes sense.

Van Zele: Yes, so very interesting. Wow. Also, you are very passionate as well.

Prof. Roura: Well, passion is me. Look, it fascinates me… AND this is a fundamental aspect, if I'm not passionate about what I do, I don't think I would be doing a good job. I need to be passionate about things.

Van Zele: Well, I for one cannot wait to hear what you find and then discover how to utilize it in the industry. But, unfortunately, Eugeni, it looks like we are running low on time. But thank you for also sharing about parental transgeneration. We wish you all the best with your future research and are looking forward to it.

Prof. Roura: Well thank you so much for giving me this opportunity and the same to you all. All the best to you and really a pleasure to be here. Honored to be part of this interview and anytime.

Van Zele: Thank you Eugeni, and thank you to our audience for joining us. We hope you enjoy today's topic and can apply it to raise healthy pigs, right from the start.