Metabolism of flavonoids and lignans by lactobacilli and bifidobacteria strains improves the nutritional properties of flaxseed-enriched beverages

Regular consumption of flavonoids may reduce the risk for CVD. However, the effects of individual flavonoids, for example, quercetin, remain unclear. The present study was undertaken to examine the effects of quercetin supplementation on blood pressure, lipid metabolism, markers of oxidative stress, inflammation, and body composition in an at-risk population of ninety-three overweight or obese subjects aged 25-65 years with metabolic syndrome traits. Subjects were randomised to receive 150 mg quercetin/d in a double-blinded, placebo-controlled cross-over trial with 6-week treatment periods separated by a 5-week washout period. Mean fasting plasma quercetin concentrations increased from 71 to 269 nmol/l (P < 0.001) during quercetin treatment. In contrast to placebo, quercetin decreased systolic blood pressure (SBP) by 2.6 mmHg (P < 0.01) in the entire study group, by 2.9 mmHg (P < 0.01) in the subgroup of hypertensive subjects and by 3.7 mmHg (P < 0.001) in the subgroup of younger adults aged 25-50 years. Quercetin decreased serum HDL-cholesterol concentrations (P < 0.001), while total cholesterol, TAG and the LDL:HDL-cholesterol and TAG:HDL-cholesterol ratios were unaltered. Quercetin significantly decreased plasma concentrations of atherogenic oxidised LDL, but did not affect TNF-alpha and C-reactive protein when compared with placebo. Quercetin supplementation had no effects on nutritional status. Blood parameters of liver and kidney function, haematology and serum electrolytes did not reveal any adverse effects of quercetin. In conclusion, quercetin reduced SBP and plasma oxidised LDL concentrations in overweight subjects with a high-CVD risk phenotype. Our findings provide further evidence that quercetin may provide protection against CVD.

Inflammation is an important process of human healing response, wherein the tissues respond to injuries induced by many agents including pathogens. It is characterized by pain, redness and heat in the injured tissues. Chronic inflammation seems to be associated with different types of diseases such as arthritis, allergies, atherosclerosis, and even cancer. In recent years natural product based drugs are considered as the novel therapeutic strategy for prevention and treatment of inflammatory diseases. Among the different types of phyto-constituents present in natural products, flavonoids which occur in many vegetable foods and herbal medicines are considered as the most active constituent, which has the potency to ameliorate inflammation under both in vitro and in vivo conditions. Kaempferol is a natural flavonol present in different plant species, which has been described to possess potent anti-inflammatory properties. Despite the voluminous literature on the anti-inflammatory effects of kaempferol, only very limited review articles has been published on this topic. Hence the present review is aimed to provide a critical overview on the anti-inflammatory effects and the mechanisms of action of kaempferol, based on the current scientific literature. In addition, emphasis is also given on the chemistry, natural sources, bioavailability and toxicity of kaempferol.

Gamma-amino butyric acid (GABA) is an active biogenic substance synthesized in plants, fungi, vertebrate animals and bacteria. Lactic acid bacteria are considered the main producers of GABA among bacteria. GABA-producing lactobacilli are isolated from food products such as cheese, yogurt, sourdough, etc. and are the source of bioactive properties assigned to those foods. The ability of human-derived lactobacilli and bifidobacteria to synthesize GABA remains poorly characterized. In this paper, we screened our collection of 135 human-derived Lactobacillus and Bifidobacterium strains for their ability to produce GABA from its precursor monosodium glutamate. Fifty eight strains were able to produce GABA. The most efficient GABA-producers were Bifidobacterium strains (up to 6 g/L). Time profiles of cell growth and GABA production as well as the influence of pyridoxal phosphate on GABA production were studied for L. plantarum 90sk, L. brevis 15f, B. adolescentis 150 and B. angulatum GT102. DNA of these strains was sequenced; the gadB and gadC genes were identified. The presence of these genes was analyzed in 14 metagenomes of healthy individuals. The genes were found in the following genera of bacteria: Bacteroidetes (Bacteroides, Parabacteroides, Alistipes, Odoribacter, Prevotella), Proteobacterium (Esherichia), Firmicutes (Enterococcus), Actinobacteria (Bifidobacterium). These data indicate that gad genes as well as the ability to produce GABA are widely distributed among lactobacilli and bifidobacteria (mainly in L. plantarum, L. brevis, B. adolescentis, B. angulatum, B. dentium) and other gut-derived bacterial species. Perhaps, GABA is involved in the interaction of gut microbiota with the macroorganism and the ability to synthesize GABA may be an important feature in the selection of bacterial strains - psychobiotics.