Are apples (apple polyphenol) ok for the liver？

In recent years, with the booming development of the plant extract industry and the continuous deepening of life science research, the anti-inflammatory properties of apple polyphenols and their protective effects on specific organs, especially the kidneys, have become the focus of global researchers' attention.

Apple Polyphenols (AP) are not a single compound, but a collective term for a series of polyphenolic substances present in apples. These substances are mainly distributed in the peel and flesh of apples, with the peel having a much higher content than the flesh. Its main components include flavonols (such as quercetin and its glycosides), catechins (such as epicatechin and epigallocatechin), anthocyanins (mainly found in red-skinned apples), phenolic acids (such as chlorogenic acid), and dihydrochalcones (such as puerarin). It is the synergistic effect of these diverse compounds that endows apple polyphenols with extensive biological activity.

In the plant extract industry, apple polyphenols are usually prepared from fresh apples or apple pomace through advanced extraction and purification processes, forming standardized extract products. These products are widely used in the fields of functional foods, health products, and cosmetics due to their clear active ingredient content and stable efficacy. At present, there are enterprise standards and group standards (such as T/CCCMHPIE 1.36-2018) in the industry to regulate its production and quality.

Inflammation is the body's normal defense response to injury or infection. Still, chronic, uncontrolled inflammation is the common pathological basis of many chronic diseases, including kidney disease, cardiovascular disease, and diabetes. A large number of cell and animal studies have confirmed that apple polyphenols have significant anti-inflammatory activity, and their mechanism of action is complex and multi-target, mainly focusing on the following aspects:

The nuclear factor kappa B (NF-κB) signaling pathway is the core hub for regulating inflammatory responses. In an inflammatory state, NF-κB is activated and enters the nucleus to initiate transcription of various pro-inflammatory cytokine genes, such as tumor necrosis factor-α (TNF-α), interleukin-1β (IL-1β), and interleukin-6 (IL-6). Multiple studies have shown that apple polyphenols can effectively inhibit the activation of the NF-κB pathway, thereby reducing the production and release of these key pro-inflammatory cytokines from the source and achieving a drastic anti-inflammatory effect.

Cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) are two key enzymes in the inflammatory process. COX-2 catalyzes the synthesis of prostaglandin E2 (PGE2), which is an important mediator in causing pain, fever, and inflammation. INOS produces a large amount of nitric oxide (NO), exacerbating oxidative stress and tissue damage. Apple polyphenols have been shown to significantly downregulate the expression and activity of COX-2 and iNOS, thereby directly reducing the production of inflammatory mediators and alleviating inflammatory symptoms.

Oxidative stress and inflammatory response are closely related, and the two promote each other, forming a vicious cycle. Apple polyphenols are not only powerful antioxidants that can directly eliminate free radicals, but more importantly, they can activate the "commander-in-chief" antioxidant pathway in cells - the Nrf2 (nuclear factor E2 related factor 2) signaling pathway. Activated Nrf2 promotes the expression of a series of downstream antioxidant enzymes (such as heme oxygenase-1, HMOX1), thereby enhancing the cell's own antioxidant defense ability and indirectly inhibiting the inflammatory response induced by oxidative stress.

Based on the existing scientific evidence, we can draw the following conclusion:

Apple polyphenols exhibit strong anti-inflammatory effects in vitro and animal models by inhibiting the NF-κB pathway, regulating inflammation-related enzymes such as COX-2 and iNOS, and activating the Nrf2 antioxidant pathway through multiple mechanisms.
For the plant extract industry, apple polyphenols are undoubtedly a star ingredient with great market potential. With the increasing demand of consumers for natural and healthy products, as well as the continuous deepening of scientific research, the application of apple polyphenols in functional foods and dietary supplements will become more widespread.

For more details about apple polyphenols, connect with Serrisha from APPCHEM. (Email: cwj@appchem.cn; +86-138-0919-0407)

Reference

[1]Advances in the Astonishing World of Phytochemicals: State-of-the-Art for Antioxidants. Antonella D'Anneo et al. [2023]

[2]Targeting Nrf2 and NF-κB Signaling Pathways in Inflammatory Pain: The Role of Polyphenols from Thinned Apples. Livia Interdonato et al. [2023-07-13]

[3]J. González‐Gallego, M. García‐Mediavilla et al. "Fruit polyphenols, immunity and inflammation." British Journal of Nutrition (2010). [2010-10-01]

[4]T. Yue, Xuelian Bai et al. "Fractionation and anti-inflammatory effects of polyphenol-enriched extracts from apple pomace." Bangladesh Journal of Pharmacology (2012). [2012-03-28]

[5]M. Jung, S. Triebel et al. "Influence of apple polyphenols on inflammatory gene expression.." Molecular nutrition & food research (2009). [2009-10-01]