De goede eigenschappen van cranberry’s.*

Cranberry’s staan bekend om geneeskrachtige eigenschappen om urineweginfecties en bacteriën in de het spijsverteringskanaal zoals E-coli en Heliobacter te bestrijden.

Cranberry’s doen dit door het “plakken” van de bacteriën tegen te gaan. Het is het enige fruit wat dit doet. Daarvoor heeft het een speciale bioactieve stof, een A type proanthocyanidine. In ander fruit , zoals druiven, zitten proanthocyanidinen van het type B.

Vanwege deze eigenschappen wordt in het laboratorium nu bij het maken van biologische assays het sap van cranberry’s gebruikt.

Cranberry sauce, cranberry jelly, and the smell of cranberry bread often bring thoughts of Thanksgiving meals and celebrations to families in the United States. But mention cranberry juice, and many would associate it, not with holiday dinners, but drinking it to treat urinary tract infections. Food, medicine, pretty good success for a berry. But the berry may have a new use, this time in the laboratory. 

Its new use is related to the cranberry’s medicinal properties. Cranberry juice has been shown to inhibit bacteria, including E. coli, from adhering to the urinary tract, explaining its historical use for urinary tract infection. The juice also inhibits the adhesion to the stomach and intestines of ulcer-causing bacteria, such as Helicobacter, and it may even be effective in other parts of the body, such as keeping bacteria off of teeth. 

Researchers at the U.S. Naval Research Laboratory have now applied cranberry juice’s bacterial adhesion fighting properties to combat bacterial adhesion on biological assays. Assays are used to find out if specific biological molecules are present in a sample, which can mean that certain microbes or human cells are present. Making an assay begins with immobilizing proteins, DNA, or antibodies on a surface, such as a microscope slide. These immobilized molecules will bind with molecules of interest if they are present in the sample. Once the assay is made, a sample containing the animal, plant, bacterial, or viral material being analyzed is washed over the surface and followed by fluorescent tags that will let the researchers determine the presence of any captured molecules. 

However, some samples pose problems for assays because portions of the sample can adhere to the surface where nothing should stick. This problem, called non-specific adhesion, clutters the assay and makes it difficult to analyze. In addition, some cases of non-specific adhesion can even cause false-positive results. If non-specific adhesion could be reduced, smaller concentrations of molecules could be detected and more difficult samples could be analyzed. 

Francis Ligler and colleagues at the Naval Research Laboratory investigated the possibility that compounds in cranberries could prevent non-specific adhesion. In their very tasty study, the researchers used Ocean Spray Premium 100% Juice Cranberry & Concord Grape Juice, Ocean Spray Premium 100% Juice White Cranberry Blend, and Langer’s Frozen Cranberry Concentrate. Each juice contained approximately 27% cranberry juice, primarily because cranberry juice is very tart and other juices are added to make it taste better. Grape juice, apple juice, and orange juice were used as controls. Several types of assays were run, including an E. coli assay that is considered to have significant problems with non-specific adhesion.

The addition of cranberry juice to the E. coli assay produced dramatically improved results. Adding 10 to 50 percent of cranberry juice to the sample caused the locations where molecules were supposed to bind to become brighter and well- defined. And the results improved as the concentration of cranberry juice increased. The improvements in other assays were less significant, in part because those assays had fewer problems with non-specific adhesion before the juice was added. 

Grape, apple, and orange juice did not have an effect on non-specific adhesion and although the white cranberry juice inhibited adhesion, it interfered with the fluorescent tags. Therefore, thanks to good old cranberries, researchers have a new way to get the most out of biological assays. And its not very often that you can say this about laboratory tools: I think I’ll go drink a glass. 

The secret sauce

What makes cranberry juice good at inhibiting adhesion? Researchers have narrowed the likely compounds down to a class of molecules called proanthocyanidins, also known as tannins. Proanthocyanidins are found in a wide range of foods from grapes and wine to chocolate, but cranberries have proanthocyanidins that contain a unique subunit called an A-type inter-flavanoid (Proanthocyanidins are polymers of flavanoids). These A-type proanthocyanidins appear to inhibit bacterial adhesion, while fruit containing just the B-type proanthocyanidins do not. 

To add further evidence that it is the tannins that provide the anti-adhesion properties of cranberry juice, Francis Ligler and colleagues used dialysis and HPCL to obtain concentrated cranberry tannins. The fraction with tannins that were retained for longer periods of time in the HPLC produced results similar to the cranberry juices. This experiment also proved that sugars, once though to be part of the cranberry’s anti-adhesion properties, do not play a role. The authors said, “Sugars are clearly not responsible for the reduction in cell adhesion.” If cranberry juice is good for you, and good for the lab, then maybe I should start drinking it too. ( Maart 2006)