Pharmacokinetics

The anthocyanins present in bilberry are thought to cross the blood-brain barrier (21). To date, no human studies have been published regarding the pharmacokinetics of the anthocyanins present in bilberry. However, studies have been conducted using other sources of anthocyanins, such as blueberries, elderberries, and blackcurrant juice. Mazza and colleagues (22) studied the absorption of anthocyanins from a freeze-dried blueberry preparation in five human subjects. Following administration of 100 g of blueberry supplement containing 1.2 g of anthocyanins, serum concentrations of 11 anthocyanins were measured at 1, 2, 3, and 4 hours postdose. Serum concentrations of each of the anthocyanins ranged from 0.23 to 3.68 ng/mL, suggesting very low absorption of anthocyanidins from this preparation. However, urinary excretion was not measured, precluding an accurate assessment of absorption. The concentration of total anthocyanins ranged from 6.6 ng/mL at 1 hour to 9.6, 12.1, and 13.1 ng/mL at 2, 3, and 4 hours, respectively.

In a more complete pharmacokinetic study, Cao et al. (23) studied the plasma and urine pharmacokinetics of 720 mg of anthocyanins from an elderberry extract in four elderly women. Blood and urine samples were collected over 24 hours. These investigators found primarily two anthocyanins (cyani-din 3-sambubioside and cyanidin 3-glucoside) present in both blood and urine. The time to maximum concentration (tmax) of total anthocyanidins was approx 1 hour and the Cmax was 97 nmol/L. The average half-life for total anthocyanidins was approx 130 minutes, with the mean half-life of cyanidin 3-sambubioside being 170 minutes and that of cyanidin 3-glucoside being 100 minutes. In concurrence with the results of Mazza et al. (22), less than 0.001% of the dose of anthocyanins was recovered in the urine within 24 hours, again indicative of poor absorption of these compounds. However, no attempts were made to analyze for potential glucuronide or sulfate conjugate metabolites of these compounds, and thus a more complete absorption picture is not available.

Another study in six healthy volunteers studied the pharmacokinetics and bioavailability of anthocyanidin-3-glycosides from either blackcurrant juice or elderberries (24). As with other studies listed previously, these investigators found very little (~0.04% from blackcurrant juice to 0.4% from elderberry extract) of the dose recovered in the urine, suggesting low bioavailability. Though the half-life of the anthocyanidins was similar regard less of preparation, the area under the curve and amount of anthocyanidins excreted were approx 10-fold higher in the subjects administered the elderberry extract as compared with those receiving blackcurrant juice. The halflife (~1.7 hours) was comparable to that in the aforementioned study by Cao et al. (23), but the recovery of anthocyanins in the previous study by Cao et al. administering elderberry extract was substantially lower (~400-fold lower) than that observed in this study. The reason for this discrepancy in amount recovered is unclear from the information given in the articles, but may relate to how the elderberry extract is formulated.

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