Bioactive Alginates and Obesity

Obesity is one of the fastest growing medical issues across the western world and it is fast becoming one of the leading causes of mortality worldwide. At least one in thirteen annual deaths in the European Union are likely to be related to overweight. That is 337,000 deaths/year and Britain leads the E.U. table of deaths related to excess body weight. Half the adults in the U.K. are overweight and around one in four is obese. Obesity increases the risk of high blood pressure, heart disease and late onset diabetes with an estimated cost to the economy of £2 Billion/year. In general, women have a greater body mass index (BMI) distribution and higher obesity rate compared to men. Obesity is a condition associated with poverty and a poor diet in both the developed and developing nations. It is therefore particularly important that if treatment/prevention is delivered via diet that the foods should be affordable and acceptable e.g. bread, the vehicle we intend to trial. Because eating is a pleasurable experience and humans tend to over eat if food is available in excess, in particular high energy foods which are often rich in fat. Reducing fat metabolism and uptake is one approach to reducing weight gain. Therefore chemically synthesised inhibitors of the fat digesting enzymes, lipases are currently being used to treat obesity. At present the major lipase inhibitor available on prescription in the U.K. is orlistat (Xenical) which will reduce fat absorption by up to 30%. However side effects such as oily stools, flatulence and diarrhoea have meant reduced acceptability. Interestingly these side effects can be significantly reduced if the lipase inhibitor is taken with a dietary fibre supplement. Therefore a good solution would be a dietary fibre with lipase inhibitory activity. Alginate, a natural fibre from seaweed has these properties. We have demonstrated in our lab that alginates have a similar ability to inhibit lipase as orlistat. We therefore aim to screen a bank of alginates (over 20), some of which are already used in the food industry at low levels and other naturally occurring biopolymers to determine the best lipase inhibitor profile using a lab based colorimetric assay. Using the best inhibitors we will demonstrate their ability to inhibit lipase activity in conditions as close as possible to those in the gut, i.e. with other food components etc. The best candidate/s from the above studies will then be tested (delivered in bread in the first instance) in human volunteers. A group of healthy subjects will be used to determine acceptability of the biopolymer in the food vehicle and to determine the best balance between lipase inhibition and levels of biopolymer intake. Our preliminary studies showed no acceptability problems with alginate levels as high as 10% by weight in bread. Following the studies with the healthy subjects the biopolymer enriched foods will be tested to demonstrate calorific intake reduction in ileostomy patients. This study has the potential to provide evidence that normal foods supplemented with fibre biopolymers can be used to treat obesity/overweight and allow this to be translated by the food industry into the development of a range of other tasty and affordable food products. Such a range would have the potential to reduce calorific intake, as well as include the health benefits of dietary fibre.

Objective 1: To screen a bank of alginates and other biopolymers for their ability to inhibit gastro-intestinal lipase. Lipase activity will be measured in a colorimetric assay using the synthetic substrate1,2-o-Dilauryl-RAC-glycerol-3-glutaric acid-6'-methylresorufin ester. The mechanism of inhibition will be determined, and as it is likely to be reversible, kinetic studies will determine the class of inhibition. Factors such as viscosity, soluble vs insoluble fractions and calcium binding will be investigated. The information generated will be used to match the best alginate with the structure and composition of naturally occurring alginates or alginate mixtures which are available as food additives with extensive safety data. Objective 2: To test the biopolymers identified from objective 1 in conditions of the digestive tract. This will be achieved by lipase inhibition studies with the synthetic substrate and a tryglyceride substrate in the presence of other nutrients. The lipid substrate +/- the inhibitor is suspended in artificial saliva pH 7-8 containing amylase and agitated for 5min at 37oC. The resulting suspension is mixed 1:3 (saliva: gastric juice, vol/vol) with artificial gastric juice pH 1-2 containing pepsin and agitated at 37oC for 1hour. This is then mixed with artificial pancreatic juice and pig bile in the ratio of 15:6:18 (gastric/saliva mixture: pig bile :pancreatic juice) containing amylase, trypsin and chymotrypsin. At this stage the lipase and co-lipase are added and incubated for 1.5 hours at 37oC. Aliquots will be removed at 10min intervals to measure, using GLC free fatty acids, tri, di and monoacylglycerols and glycerol. Using this methodology optimum alginate: lipase ratios will be determined. Objective 3: To demonstrate efficacy of the inhibitor in vivo. This will be achieved with human volunteer studies including (10) healthy and (40) ileostomy patients using questionaires and lipid determination to quantify calorie reductions.