Abstract
Lemon peel can be used as traditional Chinese medicine. Flavonoids are the most important components in lemon peel, which can be developed as natural medicine without side effects. This study investigated the protective effect of lemon peel polyphenols (LPP) on human keratinocyte HaCaT cells under oxidative stress. The active components of LPP were determined by high performance liquid chromatography. The abilities of LPP to scavenge DPPH and ABTS+ free radicals were studied for detection of antioxidation in vitro. Cell survival rates were determined by MTT assay. The antioxidant enzyme activity and antioxidant index of cells were determined using kit. The mRNA and protein expression of cells were determined by qPCR and western blot. The ability of LPP to scavenge DPPH and ABTS+ free radicals were stronger than those of vitamin C (Vc) at the same concentration. As expected, compared with the normal group of cells, the model group had decreased cell survival, increased lactate dehydrogenase (LDH), decreased levels of superoxide dismutase (SOD), catalase (CAT) and glutathione (GSH), and increased malondialdehyde (MDA) content. qPCR and western blot results indicated that the expression of Bcl-2-related X protein (Bax), caspases-3, erythroid-derived nuclear factor 2-related factor 2 (Nrf2), and heme oxygenase-1 (HO-1) were decreased and the expression of B-cell lymphoma-2 (Bcl-2) was increased in the model group, compared with the normal group. LPP treatment improved cell survival rate, reduced intracellular LDH and MDA levels, increased intracellular SOD, CAT, GSH levels, down-regulated Bax, caspases-3, Nrf2, HO-1 expression, and up-regulated Bcl-2 expression. Component analyses found that LPP contains gallic acid, neochlorogenic acid, (+)-catechin, caffeic acid, (−)-Catechin gallate, isochlorogenic acid A, rosmarinic acid, and protocatechuic acid. LPP was found to regulate the Nrf2/HO-1 signaling pathway through 8 active substances to protect HaCaT cells against oxidative stress in vitro.
Highlights
Lemon is a high-yielding crop that is widely consumed as a fruit and processed into a variety of juice, jam, and other food products [1]
DPPH and ABTS+ are both organic free radicals commonly used to quantify the antioxidant effects of active substances
This study confirms that H2O2 leads to a decrease in the survival rate of HaCaT cells, but lemon peel polyphenols (LPP) protects HaCaT cells and improves the survival rate after H2O2-induced oxidative damage
Summary
Lemon is a high-yielding crop that is widely consumed as a fruit and processed into a variety of juice, jam, and other food products [1]. At present, it is planted in all provinces in southwest China, with Sichuan as the greatest produce [2]. Lemon pulp contains multiple active ingredients including dietary fiber, vitamins, flavonoids, phenolic derivatives, limonoids, minerals, and others [3]. Lemon pulp is commonly used, but lemon peel is not widely used in traditional processing applications because it is thick and rough. The lemon peel contains various active substances, including polyphenols [3], which may offer significant therapeutic benefits
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