Study supports anti-diabetic potential of lupin

The study published in Food Chemistry​ demonstrates that the glycoprotein gamma-conglutin found in lupin seeds can effectively cross the intestinal barrier, where it may be able to provide anti-diabetic, glucose reducing effects.

“Although the action mechanism of this dietary protein is still far from being understood, these experimental findings represent the rationale behind the attribution of anti-diabetic properties to lupin seeds,”​ stated the authors, led by Jessica Capraro from the Università degli Studi di Milano in Italy.

Biological response​

Gamma-conglutin (gamma-conglutin) is a glycoprotein which accounts for about four percent of total lupin seed protein.

According to the researchers is the only protein known to elicit a significant glucose decrease response – as observed in both animal and human glucose overload studies.

Previous research has shown orally-administered lupin gamma-conglutin to have two major biological responses, an immuno-competent reaction in rats and a decrease in blood glucose concentration in both animals and humans.

The authors reported the glycoprotein to have also been previously found to display insulin mimetic activity in myocyte models, and reduce plasma glucose concentration when orally administered to both rats and humans.

Although it is a prerequisite for the elicitation of its biological activity, the authors noted that the absorption of gamma-conglutin by the intestinal epithelium has never been studied before.

The new researched aimed to assess gamma-conglutin transit through the intestine using both in vitro​ cell and ex vivo​ tissue models to monitor its transit.

Intact transit​

The in vitro​ approach showed that the intact protein can transit from the apical to the basolateral side of the cell layers in the gut.

The researchers also demonstrated transit of the intact protein through a simulated intestinal barrier. Adding that quantification of the protein collected allowed an estimate of the transit at about one percent of the applied protein.

“The demonstrated ability of intact gamma-conglutin to transit through human Caco-2 monolayers and the intestinal epithelium fit well with the reported gamma-conglutin biological responses,”​ noted the researchers.

However they said the physiological amounts of γ-conglutin capable of triggering a plasma glucose lowering effect – as well the underlying mechanisms – are a matter for further research.

In addition the authors stated that the modality of γ-conglutin transit, i.e. receptor-mediated transport vs. endocytic mechanism, can not be drawn from the present results.

Food potential​

Lupin is the major grain legume grown in Australia, where production exceeds 800,000 tons per year. It is used mainly for animal feed; however since 2001 lupin bran and flour have been used as a substitute in food formulations for more expensive traditional cereal grains.

Given that lupin seeds have the full range of essential amino acids and that they can be grown in more temperate to cool climates, lupins are becoming increasingly recognized a readily available alternative to soy.

The average protein content of lupin is just over 30 per cent – compared with 44 to 48 per cent in soybeans. In Europe, lupin flour is already being used in bakery and pasta products, and additional potential uses of lupins are in crunchy cereals and snacks, baby formula, soups and salads.

Source: Food Chemistry​
Published online ahead of print, doi: 10.1016/j.foodchem.2010.10.073
“Assessment of the lupin seed glucose-lowering protein intestinal absorption by using in vitro and ex vivo models”​
Authors: J. Capraro, A. Clemente, L.A. Rubio, C. Magni, A. Scarafoni, M. Duranti