Abstract
Although Aloe vera contains numerous bioactive components, the activity principles of widely used A. vera extracts are uncertain. Therefore, we analyzed the effects of genuine A. vera aqueous extract (AV) on human cells with respect to the effects of hydrogen peroxide (H2O2) and 4-hydroxynonenal (HNE). Fully developed A. vera leaves were harvested and analyzed for vitamin C, carotenoids, total soluble phenolic content, and antioxidant capacity. Furthermore, human cervical cancer (HeLa), human microvascular endothelial cells (HMEC), human keratinocytes (HaCat), and human osteosarcoma (HOS) cell cultures were treated with AV extract for one hour after treatment with H2O2 or HNE. The cell number and viability were determined using Trypan Blue, and endogenous reactive oxygen species (ROS) production was determined by fluorescence, while intracellular HNE–protein adducts were measured for the first time ever by genuine cell-based HNE–His ELISA. The AV extract expressed strong antioxidant capacities (1.1 mmol of Trolox eq/g fresh weight) and cell-type-specific influence on the cytotoxicity of H2O2, as well as on endogenous production of ROS and HNE–protein adducts induced by HNE treatment, while AV itself did not induce production of ROS or HNE–protein adducts at all. This study, for the first time, revealed the importance of HNE for the activity principles of AV. Since HMEC cells were the most sensitive to AV, the effects of AV on microvascular endothelia could be of particular importance for the activity principles of Aloe vera extracts.
Highlights
Aloe barbadensis Miller L. is one of more than 400 species of the Aloe genus belonging to family Liliaceae that originated in South Africa, but are indigenous to dry subtropical and tropical climates [1]
The results obtained in this study show that A. vera extract prepared from plant leaves has prominent antioxidant capacity, most likely reflecting the activities of various antioxidants produced prominent antioxidant capacity, most likely reflecting the activities of various antioxidants produced by the plant
AV treatment, we assume that such complex cell differences might reflect redox alterations differently expressed by different types of cells upon H2 O2 treatment interfering with antioxidants differently expressed by different types of cells upon H2O2 treatment interfering with antioxidants present in the AV extract, and might be, at least in a part, due to the lipid peroxidation chain present in the AV extract, and might be, at least in a part, due to the lipid peroxidation chain reactions that might generate HNE acting as a second messenger of free radicals
Summary
Aloe barbadensis Miller L. (trivially called A. vera) is one of more than 400 species of the Aloe genus belonging to family Liliaceae that originated in South Africa, but are indigenous to dry subtropical and tropical climates [1]. Antioxidants 2018, 7, 125 understanding of the activity principles that could make the basis for its therapeutic properties [2]. In addition to the medicinally most potent A. barbadensis Miller, at least three other species are known to have medicinal properties: Aloe perryi Baker, Aloe ferox, and Aloe arborescens [2]. It was claimed that the polysaccharides in A. vera gel have therapeutic properties such as immunostimulation, anti-inflammatory effects, wound healing, promotion of radiation damage repair, anti-bacterial, anti-viral, anti-diabetic, and anti-neoplastic activities, as well as stimulation of hematopoiesis and anti-oxidant effects [3]. Aloin is metabolized by the colonic flora to reactive aloe emodin, which is responsible for purgative activity. Aloe emodin inhibits colon cancer cell migration by downregulating matrix metalloproteinases 2 and 9 (MMP-2/9) [1,2,3]
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