Pharmacological Toxicological Effects 41 Antimicrobial Activity

Controversy exists on the pharmacological mechanism of cranberry. In the mid-19th century, German researchers discovered hippuric acid in the urine of people who ate cranberries (2). From the 1920s through the 1970s, many researchers thought that hippuric acid produced a bacteriostatic effect by acidifying the urine (11,14,15). The ability of cranberry to prevent renal calculi has also been attributed to its ability to decrease urine pH and inhibit bacterial growth (7,8,16). Not all studies documented a change in urinary pH with cranberry administration, so a parallel line of thinking suggested that hippuric acid, which was structurally similar to mandelic acid, inhibited bacterial multiplication (15). It was found that the concentration of hippuric acid in the urine rarely reached a concentration necessary for bacteriostatic effects (15). Because hippuric acid is a weak acid, it exists in equilibrium with its conjugate base, and requires a urine pH of at least 5.0 to produce the minimum bacteriostatic hippuric acid concentration. Thus, these researchers felt that both urine pH and hippuric acid concentration were important for the bacteriostatic effect of cranberry. More recently, however, studies have shown that the mechanism of action of cranberry is the inhibition of bacterial adherence to mucosal surfaces (3,11,17-19). One study proposed that there are two substances in cranberry juice cocktail, fructose and a glycoprotein, responsible for inhibiting adherence of Escherichia coli to mucosal cells (18).

E. coli is responsible for 85% of urinary tract infections (20). Virtually all E. coli express type 1 fimbrae, and most uropathogenic E. coli express P fimbriae, which are responsible for mediating the adherence of the bacteria to uroepithelial cells (18). Fructose is responsible for inhibiting the adherence of type-1-fimbriated E. coli, whereas a polymeric compound inhibits P-fim-briated E. coli (18). Recently, a study (21) identified this polymeric compound as condensed tannins (proanthocyanidins) based on the ability of proanthocyanidins purified from cranberries to inhibit the ability of P-fimbri-ated E. coli to attach to isolated uroepithelial cells at concentrations of 10-50 ^g/mL. Blueberries, another member of the Vaccinium genus, may be a more palatable source of proanthicyanidins.

Epidemiological data (22) and data from a double-blind, placebo-controlled trial (11) support the use of cranberry juice to prevent urinary tract infections, although in the latter study differences in baseline characteristics between study groups may have influenced the results. Cranberry extract in capsule form was more effective than placebo in preventing recurrent urinary tract infections in a small study (23).

Another potential benefit to the use of cranberry is its antiviral effect. One study (24) evaluated the ability of various commercial juices and beverages to inactivate poliovirus type I (Sabin) in vitro. Cranberry juice had some antiviral activity that was noted to be enhanced at pH 7.0 (24). The antiviral effect of commercial juices is thought to be caused by polyphenols, including tannins, which form complexes with viruses (24).

Berry Boosters

Berry Boosters

Acai, Maqui And Many Other Popular Berries That Will Change Your Life And Health. Berries have been demonstrated to be some of the healthiest foods on the planet. Each month or so it seems fresh research is being brought out and new berries are being exposed and analyzed for their health giving attributes.

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