Probiotics do not enhance anti-hypertensive effect of blueberry diets in hypertensive rats

Previously we showed that feeding polyphenol-rich wild blueberries (BB) to hypertensive rats lowered systolic blood pressure (BP). Since probiotic bacteria produce secondary metabolites from berry polyphenols which augment the health benefits of berry consumption, we hypothesized that adding probiotics to a BB-enriched diet would augment the anti-hypertensive effects of BB. Male spontaneously hypertensive rats were fed different AIN93G-based diets for 8 weeks (n=8 rats each diet): Control; 3% freeze-dried wild BB; 1% probiotic bacteria (PRO); or 3% BB + 1% PRO. BP was measured biweekly by the tail-cuff method, and urine was collected twice to determine markers of oxidative stress [F2-isoprostanes], nitric oxide synthesis [nitrites] and polyphenol metabolism [hippuric acid]. Systolic BP at week 8, but not sooner, was lower in the BB and PRO groups (163+5.9 mmHg and 168+6.2 mmHg, respectively) compared to the control diet (188+7.6 mmHg; p=0.04). Diet had main effects on diastolic BP at week 8 as well (p<0.05). In contrast, the combined BB + PRO diet produced no significant effects on BP. Hippuric acid excretion, a marker of polyphenol metabolism, was 91% higher after 4 weeks and 74% higher after 8 weeks in BB-fed rats compared to CON (p=0.0006). PRO by itself had no effect on urinary hippuric acid, and BB+PRO diet did not reduce the magnitude of the BB effect. Excretion of isoprostanes (p=0.989) and nitrite (p=0.373) did not differ across diet groups. Thus adding probiotics to a blueberry-enriched diet does not enhance and actually may impair the antihypertensive effect of BB consumption. However, probiotic bacteria are not interfering with metabolism of BB polyphenols into hippuric acid.