Abstract
- Background
Lemon (Citrus limon) peel has long been utilized within traditional Chinese medicine systems for its broad medicinal properties. Flavonoids and polyphenolic compounds represent the most critical bioactive components of lemon peel, holding substantial promise for development as safe, natural therapeutics without adverse side effects. This study was designed to systematically investigate the protective effects of lemon peel polyphenols (LPP) against oxidative stress-induced cellular damage in human keratinocyte HaCaT cells, while identifying their specific active phytochemical constituents and underlying molecular mechanisms.
- Methods
The active phytochemical constituents of lemon peel polyphenols (LPP) were quantitatively and qualitatively determined using high-performance liquid chromatography (HPLC). The in vitro antioxidant capacity of LPP was evaluated by measuring their abilities to scavenge 1,1-diphenyl-2-picrylhydrazyl (DPPH) and 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) ($ABTS^+$) free radicals in comparison to vitamin C (Vc). Cell survival and viability rates were determined using the MTT assay. Intracellular antioxidant enzyme activities, oxidative stress markers, and biochemical indices—including superoxide dismutase (SOD), catalase (CAT), glutathione (GSH), lactate dehydrogenase (LDH), and malondialdehyde (MDA)—were quantified using commercial assay kits. Furthermore, the mRNA and protein expression levels of key regulatory markers, including Bcl-2-related X protein (Bax), caspase-3, B-cell lymphoma-2 (Bcl-2), nuclear factor erythroid 2-related factor 2 (Nrf2), and heme oxygenase-1 (HO-1), were assessed using quantitative PCR (qPCR) and Western blotting.
- Results
Phytochemical analyses revealed that LPP contains a rich profile of active substances, specifically including gallic acid, neochlorogenic acid, (+)-catechin, caffeic acid, (-)-catechin gallate, isochlorogenic acid A, rosmarinic acid, and protocatechuic acid. In antioxidant assays, the free radical scavenging capacities of LPP against DPPH and $ABTS^+$ radicals were superior to those of vitamin C at equivalent concentrations. Under oxidative stress conditions, the model group exhibited significantly decreased cell survival, elevated intracellular lactate dehydrogenase (LDH) and malondialdehyde (MDA) levels, and suppressed superoxide dismutase (SOD), catalase (CAT), and glutathione (GSH) concentrations compared to the normal control group. Molecular analyses demonstrated that LPP treatment effectively reversed these pathological alterations by improving cell survival rates, reducing intracellular LDH and MDA accumulation, and enhancing intracellular SOD, CAT, and GSH levels. Furthermore, treatment with LPP modulated apoptotic and cytoprotective protein expressions by down-regulating Bax, caspase-3, Nrf2, and HO-1, while up-regulating Bcl-2 expression.
- Conclusions
Lemon peel polyphenols (LPP) demonstrate exceptional in vitro antioxidant efficacy and protect human keratinocyte HaCaT cells against oxidative stress-induced damage. These protective effects are mediated through the regulation of the Nrf2/HO-1 signaling pathway facilitated by the eight identified active phytochemical substances, supporting the potential utilization of LPP as a valuable natural therapeutic agent in dermatological applications.
https://pmc.ncbi.nlm.nih.gov/articles/PMC7874231/