Bilberry has a lot of beneficial effects on the human body. In particular, it is indicated for those conditions of extreme capillary fragility, and for disorders in microcirculation in general.
For example, a frequent advice that a doctor gives in case of frequent epistaxis is to drink a certain daily amount of bilberry juice. Why should a doctor give such an advice? The answer to this question lies in some distinctive compounds present in bilberry fruits: some colorful polyphenols belonging to the class of anthocyanins.
The pharmacological properties of these substances seem nowadays well ascertained. They are mainly linked to a strong antioxidant action, that helps to protect the endothelial cells from oxidative damage: they scavenge damaging particles like free radicals, helping prevent or reverse damage to cells.
But, beside this general protective action (that helps to protect the endothelial cells, but is not endothelium-specific), they also have a direct and specific vasoprotective action. These vasoprotective effects are mainly of 2 types:
-the anthocyanins enhance the resistance of endothelial cells plasma membranes to harmful stimuli
-the anthocyanins help to strengthen the extravascular connective tissue.
ANTHOCYANINS IN THE BILBERRY: STRUCTURE AND BIOSYNTHESIS
Anthocyanins are natural pigments. They belong to the class of flavonoids. Anthocyanins are glycosides of anthocyanidins, whose basic chemical structure is shown here.
Given this common basic chemical structure, there are more than 20 different anthocyanidin molecules. The most important ones are listed in the following table.
The anthocyanins are mostly 3-glycosides of the anthocyanidins. The sugar that is usually bound to these anthocyanidins is glucose, arabinose or galactose.
Their biosynthesis can be summarized as in the pathway below.
ABSORPTION AND BIOAVAILABILITY
The pharmacokinetics of anthocyanins was first investigated by Morazzoni et al. in 1991. This study showed that about 5% of the anthocyanins introduced with the diet is able to be absorbed by the small intestine. There is no hepatic first-pass effect, but their absolute bioavailability is still very low (1.2% of the total dietary intake). Despite that, the plasmatic peak levels (2-3 μg/ml) measured afterwards are in the range of biological activity reported for these substances. The elimination of the anthocyanins occurs mostly through urine and bile.
Vaccinium myrtillus anthocyanosides pharmacokinetics in rats, 2006
Anthocyanins are potent anti-oxidant and ROS scavengers. They have been shown to inhibit oxidation of lipids and LDLs. Some recent studies indicate that the single anthocyanin cyanindin-3-O-glucose chloride has a greater efficacy in protecting against oxidant degradation of LDLs than vitamins C, E, and beta-carotene combined. The anthocyanin concentration of fruit is highly correlated with the oxygen radical absorbance capacity (ORAC), with chokeberry, bilberry, and elderberry having the highest natural intrinsic total anthocyanin (Ta) content and ORAC of dozens of fruits and vegetables tested.
A recent study by Youdim et al. highlights the protective action that anthocyanins exerts on cultured endothelial cells against oxidant injuries. The authors show for the first time that vascular endothelial cells can incorporate anthocyanins into the membrane and cytosol, conferring significant protective effects against oxidative insult.
The incorporation of elderberry anthocyanins into endothelial cells was initially investigated using extract at 1 mg/ml. Results demonstrated that maximum incorporation was reached within 4h. A dose-response effect after 4h incubation was also investigated, as shown in the picture below (on the y-axis we have the anthocyanin concentration found in the endothelial cells after the incubation).
Separation of the cell membranes and cytosol showed that the anthocyanins were not only incorporated into the plasma membrane but also found to penetrate into the cell cytosol. However, their concentrations were found to be higher in the membrane fraction.
The endothelial cells were then exposed to different oxidative stressors for 2h. The cytotoxicity of control cells increased markedly in a concentration-dependent manner. However, endothelial cells supplemented with elderberry extract (0.05 mg/ml, 0.1mg/ml, 0.5mg/ml) appeared to be protected against all H2O2 concentrations examined, with cytotoxicity reduced between 20–40%.
Direct vasoactive and vasoprotective properties of anthocyanin-rich extracts, 2006
Incorporation of the elderberry anthocyanins by endothelial cells increases protection against oxidative stress, 2000
SPECIFIC VASOPROTECTIVE ACTIVITY
As we stated in the first paragraph, the anthocyanins protect the capillary wall through a double mechanism:
-increasing the endothelium barrier-effect through a stabilization of the membrane phospholipids
-protecting the extravascular matrix from the action of various proteinases.
Hystochemical and biochemical studies showed that anthocyanins interact with phospholipidic constituents of plasma membranes, potentially modifying their physical-chemical properties and enhancing their resistance to many types of stress. Studies on the influence of anthocyanins extract on membrane viscosity confirmed that anthocyanins were able to modify the membrane fluidity due to their high affinity for membrane phospholipids. Unfortunately, in these studies no direct evidence is reported describing the biological fate of these compounds. Lenne-Gouverneur et al. have shown, using a membrane fluorescent probe, that the membrane biophysical properties were altered following supplementation with flavonoids. Although no attempts were made to isolate these flavonoids from the membrane, the results strongly suggest direct association with(in) the plasma membrane. The authors claims that the molecular mechanism underlying this process is the formation of bridges between membrane phospholipids, bridges formed by anthocyanins phenolic groups. This association between anthocyanins and plasma membranes is strongly correlated with a reduction of membrane fluidity; a lower membrane fluidity results in a greater membrane lipidic order, and a greater membrane lipidic order results in an increased resistance to injurious stimuli.
Interactions of the monomeric and dimeric flavones apigenin and amentoflavone with the plasma membrane of L929 cells; a fluorescence study, 1999
In addition to this effect of membrane stabilization, anthocyanins inhibit the activities of various enzymes involved in the turnover of the main structural components of the extravascular matrix collagen, elastin and hyaluronic acid. In particular, they reduce the activity of proteolytic enzymes such as collagenase, elastase and metalloproteinases, and the activity of glycosidases such as hyaluronidase and beta-glucuronidase.
Some data demonstrating the reduction of the activity of MMP-1 and MMP-9 are shown in the chart below.
By inhibiting the mentioned proteases (collagenase, elastase and metalloproteinases), the anthocyanins contribute to make the pericapillary connective tissue more stable and elastic. By inhibiting the mentioned glycosidases (hyaluronidase and beta-glucuronidase), the anthocyanins help to keep intact the mucopolysaccharidic pericapillary sheat. Mucopolysaccharides, along with collagen and elastin, are recognized to play an important role in maintaining the integrity of both perivascular tissue and endothelial basal membrane. And a greater integrity of the perivascular tissue obviously results, again, in an increased capillary resistance to injurious stimuli.
Inhibition of host- and bacteria-derived proteinases by natural anthocyanins, 2011
Free radicals scavenging action and anti-enzyme activities of procyanidines from Vitis Vinifera. A mechanism for their capillary protective action, 1994