Elsevier

Biomedicine & Pharmacotherapy

Volume 93, September 2017, Pages 976-984
Biomedicine & Pharmacotherapy

Original article
The extract from Punica granatum (pomegranate) peel induces apoptosis and impairs metastasis in prostate cancer cells

https://doi.org/10.1016/j.biopha.2017.07.008Get rights and content

Abstract

Prostate cancer is a big threat to male for its poor prognosis and high mortality rate. Natural compounds are important resources of many anticancer drugs. Pomegranate is a kind of antioxidant-rich fruit and its peel and seed has potential anticancer activities. In this study, we aimed to investigate the effects of pomegranate peel extract (PoPx) on the apoptosis and metastasis of prostate cancer cells and the related mechanism. We found that PoPx showed growth inhibition on prostate cancer cells. Nuclei morphological and flow cytometer (FCM) analysis indicated that PoPx could induce prostate cancer apoptosis. Further investigation indicated that mitochondrial mediated intrinsic pathway is involved in the apoptosis. Exposure to PoPx led to loss of mitochondrial transmembrane potential (Δym), accumulation of reactive oxygen species (ROS). Western blot analysis showed that PoPx could increase the expression ratio of Bax/Bcl2 and activation of apoptosis executor caspase 3. Wound healing assay and transwell migration and invasion assay implied that PoPx has the potential to inhibit migration and invasion, two critical steps in prostate cancer metastasis. Downregulation of MMP2/MMP9 and upregulation of TIMP2 showed accordance with the inhibition of migration and invasion. In summary, the present data showed that PoPx could be a promising drug candidate to treat prostate cancer, showing us a better way to develop novel drugs from natural compounds.

Introduction

Cancer is the leading cause of death in the 21st century. According to American Cancer Society, prostate cancer is the most common form of cancer in male, accounting for 1 in 5 new cancer diagnoses in men and ranking the second leading cause of cancer related mortality [1]. Unfortunately, the majority of prostate cancer patients are diagnosed at a late stage with distant metastasis but its pathogenesis is not fully understood yet, resulting a high mortality [2], [3]. Thus, there is an urgent need to uncover the molecular mechanisms of prostate cancer (PCa) and to develop some novel and better therapeutic approaches.

Punica granatum (Pomegranate) is one member of Punicaceae. The peel juice and seed oil of the pomegranate fruit is an important source of antioxidants with known anti-cancer activities [4]. Numerous current researches have demonstrated that antioxidants in some fruits and vegetables can defend human cells from oxidative damage and prevent aging, resulting in a decreased incidence of tumors and infections [5]. There are plenty of bioactive components presented in pomegranate peel, such as tannins, flavonoids, polyphenols, anthocyanins, etc. [4]. They have been proposed to have various pharmacological activities, including anticancer activity.

Evasion of apoptosis is one hallmark of maybe all types of cancer [6]. Deregulation of apoptosis resulted in uncontrolled growth of cancer and development of resistance to treatment. Therefore, drugs that could restore cancer cell apoptosis may be effective against many types of cancer, making this a promising strategy to treat cancer [7]. On April 11, 2016, the U. S. Food and Drug Administration approved Venclexta for treating chronic lymphocytic leukemia (CML) patients. This is a Bcl2 inhibitor that specifically targeted to the apoptosis pathway.

It has been proved in earlier studies that pomegranate peel could inhibit prostate cancer growth by inducing cell apoptosis [8]. However, the mechanism of pomegranate peel induced apoptosis has not been delineated clearly yet. Metastasis is the main cause of PCa related mortality. Migration and invasion are two critical steps in metastasis. Numerous proteins are involved in the metastasis cascades. Among them, matrix metalloproteinases could destruct the integraty of extracellular matrix in the microenvironment to facilitate metastasis [9], [10]. It’s still unknown whether pomegranate peel extract (PoPx) could inhibit PCa metastasis cascades. Hence, this study is aimed to investigate the effects of PoPx on PCa cells and provide evidence for the further application of PoPx in inhibiting PCa growth and metastasis. The effects of PoPx were assessed on several PCa cells and the preliminary molecular mechanism was explored in our study.

Section snippets

Preparation of pomegranate peel extract (PoPx)

Pomegranate peel of Tunisia soft-seed pomegranate was purchased from Yuzhuang Ecological Green Industry Co. (Qianxi County, Guizhou Province, China). The preparation of pomegranate peel extract was done as previously described with minor modifications. Firstly, 400 g fresh peel was cut into pieces of 0.5 cm in size and extracted with a combination of 1550 mL ethanol and 480 mL H2O followed by soaking for 2 h at 60 °C. The crude extracts were then filtered and concentrated under vacuum to produce a

Analysis of punicalagin and ellagic acid in PoPx by HPLC and MS

PoPx was comprehensively analyzed by the combination of HPLC and MS. The prepared PoPx sample was firstly analyzed by using the optimized HPLC method and the component were matched by the Similarity Evaluation System for Chromatographic Fingerprint of Traditional Chinese Medicine (Version 2012A). As shown in Fig. 1A, the main constituents of PoPx were determined as punicalagin (PC, peak 1 and peak 2) and ellagic acid (EA, peak 3) by comparing their retention time with standard substance. The

Discussion

Prostate cancer is a big threat to male and lacks effective treatment option. And a lot of pharmaceutical companies and institutes are trying to find novel drugs to treat this devastating disease. Numerous research reports that natural compounds from plants can trigger apoptosis in a lot of cancer cells with different histologic origin [18]. This inspires us to investigate the pharmacological activities of extracts from pomegranate peels on prostate cancer.

Dysregulation of apoptosis is a

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    These authors contribute equally to this study.

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