by Ruth Beran
Take two sugars. One of them, lactulose, is a much bigger sugar than the other, mannitol.
These sugars are different to ordinary sugars, like glucose, because they are not actively absorbed by the lining of the gut when ingested.
Instead, they are absorbed in the intestine by a process of diffusion. Mannitol and lactulose are also absorbed at different rates.
“Diffusion of course depends on the physical integrity and thickness of the lining of the gut,” says medical physiologist Prof Roger Lentle from Massey University. “Consequently by recording the rate at which it’s absorbed, it’s telling us something about the lining of the gut.”
Ivana Sequiera is a PhD student at Massey University who has been assessing how permeable the gut is by giving participants a solution containing the two sugars. It’s a common diagnostic tool known as the dual sugar absorption test, where a gross rate is usually measured in the urine after two to four hours, but Ivana’s been getting participants to provide a urine sample every 30 minutes to look at their rates of excretion.
From left to right: Ivana Sequeira and Roger Lentle Photo: RNZ / Ruth Beran
“Now this hasn’t been done before, surprisingly, even though these sugars have been used routinely to assess the health of the gut in the case of for example, people who have coeliac disease which is a gluten sensitivity, which affects your permeability of your gut,” says Roger.
Tracing the sugars as they’re excreted means it’s possible to now know when more of one sugar comes out than another. For example, the peak excretion for mannitol is two hours and lactulose is four hours.
“Mannitol is largely absorbed in the small intestine, whereas lactulose the greater absorption is in the colon,” says Ivana. “Ideally we wanted to choose, probes or marker sugars that are absorbed in specific segments of the gut to have site specific permeability measurements.”
The amount that is excreted tells a clinician how leaky or permeable the gut is.
However, with better standardisation, the test is now sensitive enough to pick up the effect of a single aspirin tablet. “So you give a person an aspirin tablet, and we can statistically identify that that’s the person who had the aspirin tablet because the pattern of sugar absorption is augmented, you get much more lactulose when you’ve had this dose of aspirin,” says Roger.
The purpose of this is to see how the gut responds to a challenge or perturbation.
“We want to look at measuring health in the intestine, not illness, and that’s classically what has been done,” says Ivana. But by mimicking what goes on in the intestine, and to see how quickly the gut maintains equilibrium after a noxious stimulus, it can give an indication of gut health.
“The lactulose goes through these little holes, if the asprin increases the number of holes…then your job as a gut cell is to repair the holes, and the quicker you repair the holes the more resilient you are, the more healthy you are,” says Roger.
From left to right: the Smart Pill, the sugars in solution and aspirin tablets Photo: RNZ / Ruth Beran
Ivana has also used a Smart Pill, a wireless motility capsule, to measure pressure, pH and temperature in the gut. The capsule is ingested at the same time as the sugar drink and then the changes in the profile of excretion of the two sugars can be matched with changes measured by the Smart Pill.
She now knows that the sugar probes reside in the small intestine between two and four hours. “So that’s a window period where I think you can start collecting samples, and even if you want to do a cumulative sample, it’s all fine because you know then that it resides in the small intenstine during that period,” says Ivana.
The sensitivity of the diagnostic tool may also allow other simple food components and chemicals to be tested to see if they influence the leakiness of the gut. For example, Ivana has been looking at Vitamin C and seen that a large single dose can temporarily increase the permeability of the gut.
“The test has got potential for testing individual components to see whether there having an effect on gut permeability,” says Roger.
The Ministry of Science and Innovation funded the research, which was awarded to Plant and Food Research.
