How phenols from plants pass through the kidneys
The possible effects of biogenic medicinal products containing plant phenols are not only derived from epidemiological data. Tests are usually also carried out in test tubes, as Dr. Markus Veit from the Chair of Pharmaceutical Biology at the University of Würzburg explains: In such experiments, plant phenols influence a number of human enzymes. "Activities are then often improperly derived from such enzyme models and a number of pharmacological effects are ascribed to plant phenols without studies having been carried out on humans," criticizes Dr. Vit. It is currently not even known whether the tested substances are actually available for the body after oral intake.
In order to prepare appropriate investigations into the active principle of medicinal plants and medicinal products made from them, Dr. Veit conducted a pilot study. It was investigated how certain phenols (caffeic acid conjugates and quercetin glycosides) are excreted via the kidneys after oral intake. An extract from horsetail was tested because it is a very good model: Its phenol pattern is typical for a number of medicinal plants, but it also corresponds to that of important food plants such as lettuce.
Nine men and two women between the ages of 23 and 37 took part in the study. These volunteers followed a flavonoid-free diet for nine days. On the fourth day, the flavonoid content in the urine was determined as a reference value, because the metabolites of interest can also arise from the breakdown of endogenous substances. On the three following days, the subjects then drank five times 1.0 gram of a standardized horsetail extract in the form of a tea infusion. That was the only flavonoid intake at that time. The subsequent two-day wash-out phase took into account the delayed metabolism.
Dr. Veit: "In no case could flavonoids be detected unchanged or in conjugated form in the urine, which we interpret as an indication of extensive degradation by the microflora in the intestine." A final clarification of the question of whether flavonoids or only their metabolites in the intestine be resorbed and thus be responsible for an effect, could only be achieved via blood analyses. They should be an important part of the subsequent work.
The study also found very large inter-individual fluctuations: According to Dr. Very different. Apparently a number of parameters influence the uptake, distribution and excretion of the administered phenols. The researchers also want to characterize such parameters in further investigations. The investigations are carried out with finished medicinal products from hawthorn (flowers, leaves and fruits of Crataegus species), artichoke (leaves of Cynara scolymus), goldenrod (herb of Solidago species) and various foods.
Finally, Dr. Veit a completely different, but highly interesting aspect of the effect of flavonoids from food plants: Under the influence of increased UV radiation, the pattern of leaf flavonoids changes. This could affect the effects that can be expected after consuming plant-based foods. The Würzburg scientist emphasizes that higher UV radiation apparently leads to a component spectrum that is pharmacologically more active, at least in test tube experiments, and could therefore possibly contribute to better protection against cardiovascular diseases. This would probably be the first positive aspect that one could gain from the decrease in stratospheric ozone and the associated increase in UV radiation.
