Magazine, Molecules

What is quercetin?

Whatis Quercetin Article image

Quercetin is an increasingly well-known member of the group of Polyphenols and Flavonoidswhich are natural dyes characterised in particular by their light yellow colour (from the Latin flavus; yellow). Flavonoids are biologically active plant compounds that have, for example, antioxidant and anti-inflammatory effects in humans. However, the body cannot produce quercetin itself and therefore absorbs it through food. A normal western diet contains about 15 mg to 40 mg quercetin daily.

Quercetin occurrence

The name quercetin is derived from the Latin word Quercētum, which means oak forest and underlines the plant origin. Larger amounts of the molecule are found in, for example, capers (234 mg per 100 g) and onions (11-33 mg per 100 g), apples and berries (both 2-5 mg per 100 g), and various teas (black tea 2 mg per 100 g). Quercetin accumulates mainly in the outer parts of the plant. In apples, it accumulates in the skin.

Onions peel quercetin
Onions (especially their peel) are particularly rich in the vital substance quercetin.

Quercetin in science and research

The molecule has been the subject of scientific scrutiny for some time. At the beginning of the 20th century, it was grouped together with other flavonoids as vitamin P. A designation that still appears occasionally, although it is inaccurate. Despite its long familiarity, there have been only a few studies to date in which effects on humans have been investigated. In essence, we are still dependent on laboratory studies or studies on animal models. However, there is hope that this will change in the near future. In the context of longevity research, the molecule is increasingly in the limelight because of its possible senolytic effect.

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Effects in the organism

Based on scientific research, quercetin is said to have antioxidant and anti-inflammatory effects. In addition, quercetin blocks the release of histamine in the cells. As a quick reminder, histamine is one of the body's responses to stress and the culprit behind annoying itching. Through this inhibition, quercetin has an anti-allergic effect on asthma and rhinitis or even joint pain. In addition, quercetin, like apigenin, naturally inhibits CD38. Blocking CD38 causes an increase in NAD+, a key molecule in the energy metabolism of our cells.

Via an enzyme with the complicated name AMPKis a molecular signalling pathway activated by quercetin that promises weight-loss and anti-diabetic effects. Together with mTOR, the sirtuins and NF-kB, AMPK is one of the four longevity pathways .

" Click here for the article on the four longevity paths.

But what about life extension? One possible explanation is the stimulation of proteasomes. These are also known as the cell's rubbish dumps and promote the degradation of defective protein structures, which increase significantly with age. One could regard it as a kind of cellular quality control. Nevertheless, another effect is particularly promising: senolysis.

Quercetin Banner Square

Cellular senescence

The term senolysis is composed of the two words senescence and lysis. While lysis is understood to mean dissolution or decay, the first part of the word tells us exactly what we are talking about. Senescence(from the Latin senescere; to age) plays an important role as the final stage of dozens of processes in the body.

Cellular senescence refers to a stable arrest of the cell cycle. Human cells can only complete a limited number of cell divisions before they suddenly stop and age. What is common today was once groundbreaking. Decades ago, science believed that all cells were immortal. Today we know that cancer cells in particular possess this characteristic. The phenomenon of the division ceiling is called replicative senescence, or after its discoverer: Hayflick limit. With increasing age, the number of senescent cells steadily increases, because too many of these dormant cells are produced and, on the other hand, too few are degraded.

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In old age, the number of senescent cells increases steadily. This is a normal process, but one that can be counteracted.

Quercetin as a Trojan horse

This dormant state sounds harmless and not very worrying at first. However, senescent cells can "infect" surrounding healthy cells and thus retire them prematurely. Certain substances produced by aged cells are responsible for this and are subsumed under the term "secretome". Aged cells also defend themselves against apoptosis, the natural cell death, by activating survival-promoting factors and inhibiting self-destructive signals.

Senolytically active substances such as quercetin are smuggled into the cell past the protective shield and can switch off the defence shield there from the inside. This happens by blocking an enzyme called PI3 kinase. This interrupts the chain that promotes survival and the senescent cell can die in a controlled manner and make room for new cells.

Qeurcetin cross

Results of initial laboratory studies are promising and give many scientific eyes a glimmer of hope. However, large-scale human studies are still needed to confirm the results and make further statements.

Literature

Hickson, L. J., Langhi Prata, L., et al. (2019). Senolytics decrease senescent cells in humans: Preliminary report from a clinical trial of * plus quercetin in individuals with diabetic kidney disease. EBioMedicine, 47, 446-456. https://doi.org/10.1016/j.ebiom.2019.08.069

Zhu, Y., Tchkonia, T., Pirtskhalava, T., et al. (2015). The Achilles' heel of senescent cells: from transcriptome to senolytic drugs. Aging cell, 14(4), 644-658. https://doi.org/10.1111/acel.12344

Kirkland, J. L., & Tchkonia, T. (2020). Senolytic drugs: from discovery to translation. Journal of internal medicine, 288(5), 518-536. https://doi.org/10.1111/joim.13141

Kang C. (2019). Senolytics and Senostatics: A Two-Pronged Approach to Target Cellular Senescence for Delaying Aging and Age-Related Diseases. Molecules and cells, 42(12), 821-827. https://doi.org/10.14348/molcells.2019.0298

Salehi, B., Machin, L., Monzote, L., et al. . (2020). Therapeutic Potential of Quercetin: New Insights and Perspectives for Human Health. ACS omega, 5(20), 11849-11872. https://doi.org/10.1021/acsomega.0c01818

Anand David, A. V., Arulmoli, R., & Parasuraman, S. (2016). Overviews of Biological Importance of Quercetin: A Bioactive Flavonoid. Pharmacognosy reviews, 10(20), 84-89. https://doi.org/10.4103/0973-7847.194044

Bhagwat, S., Haytowitz, D. B., & Holden, J. M. (2014). USDA database for the flavonoid content of selected foods, Release 3.1. US Department of Agriculture: Beltsville, MD, USA.

Costa, L. G., Garrick, J. M., Roquè, P. J., & Pellacani, C. (2016). Mechanisms of Neuroprotection by Quercetin: Counteracting Oxidative Stress and More. Oxidative medicine and cellular longevity, 2016, 2986796. https://doi.org/10.1155/2016/2986796

Escande, C., Nin, V., Price, N. L., et al. (2013). Flavonoid apigenin is an inhibitor of the NAD+ ase CD38: implications for cellular NAD+ metabolism, protein acetylation, and treatment of metabolic syndrome. Diabetes, 62(4), 1084-1093. https://doi.org/10.2337/db12-1139

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