Flaxseed (Linum usitatissimum L.) extract as well as(+)-secoisolaric- iresinol diglucoside and its mammalian derivatives are potent inhibitors of a-amylase activity.

Type 2 diabetes mellitus (T2DM) is one of the common global diseases.  Flaxseed is by far the richest source of the dietary lignans (i.e.,secoisolariciresinol diglucoside)which have been shown to delay the development of T2DM in animal models.  Herein, we propose the first evidences for a mechanism of action involving the inhibition of the pancreatic a amylase by flaxseed-derived lignans that could therefore constitute a promising nutraceutical for the prevention and the treatment of T2DM. (Authors Abstract)

T2DM (formerly called non-insulin-dependent or adult onset ) results from the body’s ineffective use of insulin and is characterized by hyperglycemia, impaired glucose tolerance, insulin resistance and hyper lipidemia.  T2DM is largely the result of excess body weight and physical inactivity and is associated with a reduced quality of life and increased risk of mortality and morbidity.  Diabetes and its complications have also a significant economic impact on individuals, families, health systems and countries. Acting as key enzymes for carbohydrate digestion and absorption, intestinal  aglucosidase  and pancreatic a amylase have been identified as important therapeutic targets for the modulation of the pathologic postprandial hyperglycemia observed for T2DM suffering patients. Important steps of the starch digestion occur in the small intestine through the action of soluble a-amylase of pancreatic origin, yielding to linear maltose and branched isomaltose oligosaccharides. These iso maltose oligosaccharides are then further digested by a glucosidases anchored in the membrane of the epithelium of the small intestine and lead to the release of absorbable monosaccharides. In such context, inhibitors of intestinal aglucosidase and pancreatic a amylase can effectively retard the digestion and assimilation at the early steps of starch digestion and thus succeed in a significant delay of postprandial hyperglycemia and have a beneficial effect on insulin resistance and glycemic index control. For this purpose inhibitors such as a carbose, voglibose or miglitol are clinically used.  Natural aglucosidase and a amylase inhibitors, from food sources notably, have become an attractive therapeutic approach in complement to or in replacement of the current inhibitors.   The aim of the present work was to determine the potential inhibitory effect on a glucosidase and a-amylase activities of flax seed extract, and pure  or derived compounds  in order to clarify the biochemical mechanism by which flax seed extract and may developed their hypoglycemic effect. The flax seed coat extract (FSE) as well as the extraction and purification were performed by microwave assisted extraction and enzymatic assisted release, respectively.   FSE was able to inhibit both soluble aglucosidase and aamylase in a dose dependent way.  However, using immobilized a glucosidase a large decrease (loss of 30percent) in the inhibitory capacity of FSE was noted. These results indicate that the observed hypoglycemic potential of flax seed could depend mostly on their inhibitory capacities toward the pancreatic a-amylase. This was confirmed by the dose response curves representing the inhibition of the pancreatic a-amylase as a function of the concentration and by the determination of the IC50 values14 for each compound. Comparable IC50 values were found for (3), (2) and (4), with 8.6,9.5 and 10.9 lM, respectively,where as a higher value of15.7 lM was calculated for (1). Calculation on thermo dynamic parameters for the interaction between flavonoids (quercetin and derived compounds ) and aamylase have revealed that the main driving force of this interaction is hydrophobic. As the higher inhibitory effect was observed with (3) and in order to get an insight in the possible mechanism s by which this compound could inhibit the a-amylase from porcine pancreas, this enzymatic activity in absence or presence of different concentrations of this molecule were measured. The determined Km values,19 using 4NPM as substrate ,14 were 716.6 lM under control conditions and 431.7 and 416.4 lM in presence of 50and 100 lM of (3), respectively. The determined Vmax values19 were 11.25 lmolmn 1 for control and 5.23 and 3.28 lmol min  1 in presence of 50and 100 lM of (3), respectively . As a consequence double reciprocal plots obtained in presence of different concentrations of (3) revealed a mixed inhibition mode diagnosed by the decrease of both Vmax and Km . These results indicated that the inhibition can arise in different ways.  Compound  could interact directly with the enzyme forming an inactive enzyme inhibitor (EI)complex and inducing an enzyme conformation change that prevent the enzyme substrate (ES)intermediate to be formed  could also interact with the form ES intermediate to give a sterile ternary enzyme substrate inhibitor (ESI) complex. The authors propose the first evidences for a third mechanism through the inhibition of pancreatic a-amylase. FSE as well as its derived metabolites have been shown to efficiently reduce the a-amylase activity which partly could at least explain the observed hypoglycemic effect of dietary supplementation in T2DM animal model. It is alos demonstrated here that the most active form is the circulating form metabolized by the human intestinal microbiota.  In human intestine the conversion of (1) into (2) and finally to (3) and (4) results in an increase of the inhibition capacity of this natural compound. The inhibition mechanism was also studied: a mixed inhibition mode for (3) was deduced which indicates that it retards a-amylase activity by preferentially interfering with the free enzyme. To conclude, flax seed could be associated with a potent inhibitor such as a carbose in order to reduce its side effects. (Editors comments)