Grape harvest season is almost over in Italy. Let’s have a look at a popular compound from grapes and wine: resveratrol, a chemical with many biological activities.
This phenolic compound is a stilbenoid present in grapes and several berries (blueberries, raspberries, mulberries, etc.), but also in peanuts. It is found in white, rosé and red wines, but the highest concentration is usually detected in red wines. Much of the resveratrol is indeed in the grape’s skin, which is fermented together with the flesh when making red wine. It is also important to point out that the concentration of resveratrol in grapes, and therefore in wines, also depends on many factors (like the effects of biotic or abiotic stress) and can therefore be very variable.
A miraculous compound in vitro…
Resveratrol is extensively used in the cosmetic industry due to its antiaging effect . However, great interest is directed towards its impact on human health. It has been suggested, base on in vitro studies, to be a preventive agent of several important pathologies: vascular diseases, cancer, and neurodegenerative processes among others [2,3]. It is also considered anti‐inflammatory, anti-obesity and anti-diabetic .
The list of potential beneficial effects would be actually very long. However, it has been suggested that its protective effects are a result of the antioxidant and anti‐inflammatory properties .
…not keeping up with the expectations in vivo.
While there are many studies on its effects in vitro, more studies are needed to prove its actions in vivo. Most of the proposed activities were not confirmed in clinical trials, so far. Furthermore, one of the main problems is related to resveratrol bioavailability (i.e., it is not able to reach the sites where it should exert its activity at relevant doses).
Cells in the intestine rapidly absorb resveratrol which then reaches the liver and is converted into different derivatives [4,5]. Along with rapid metabolism, resveratrol also undergoes rapid excretion , leading to an irrelevant in vivo effect by oral administration as compared to the powerful in vitro efficacy . This surely undermines the benefits of resveratrol intake with food. On the other hand, this issue with its bioavailability has prompted great efforts in the search for ways to improve it, that include the development of specific formulations and delivery systems .
Biosynthesis and functions in planta
Plant specialized metabolites are built using specific building blocks. For resveratrol, one piece comes from the polyketide pathway and the other one from the shikimate pathway. The compound exists as two isomers, cis- and trans-resveratrol, but the latter (the most stable one) is the main form.
Why do plants produce resveratrol? This compound is commonly referred to as a phytoalexin, which means that it is an antimicrobial compound produced upon infection. However, the synthesis of resveratrol is initiated in response to several abiotic (e.g., ultraviolet irradiation) or biotic stress, including the interaction of the plant with pathogens such as Botrytis cinerea .
Botrytis cinerea is a fungus that causes grey mould and affects not only grape quality, but also the winemaking process and of course the quality of the final product. Resveratrol is produced in response to the fungal attack as a defence compound and it inhibits the germination and growth of the fungus [7,8]. However, B. cinerea also fights back, with a few mechanisms to circumvent the antimicrobial activity of the compound . Noteworthy, other stilbene compounds found in grapes, like pterostilbenes and viniferins, show even more pronounced effects towards the fungus, but they are present in much lower amount compared to resveratrol, which seems to be their precursor .
It is suggested that resveratrol might have a defensive role also towards other pathogens, like Plasmopara viticola, the causing agent of grapevine downy mildew .
Resveratrol is a great example of a chemical produced by plants for their own defence from biotic and abiotic stress, which displays several biological activities and potential application to human health. Although further in vivo studies are needed and its bioavailability has to be improved, the current evidence is encouraging.
Let’s toast to resveratrol with a glass of red wine!