Soursop and its Powerful Anti-Cancer Compounds

The role of Soursop and its Powerful Anti-Cancer Compounds that Assists in Managing/Fighting Disease (Cancer/Diabetes)

Abstract

Annona muricata is a tropical fruit-bearing tree widely used in traditional medicine for treatment of a variety of diseases and health conditions. This reputation of A. muricata as a versatile medicinal plant has attracted considerable interest such that a number of studies have been done through the years to evaluate the claims of medicinal potential of this plant. According to multiple publications discussed in this paper, there are significant evidences to back the therapeutic potential of A. muricata against diabetes and several types of cancer such as breast, pancreatic, lung, liver, prostate and colon cancer. Active compounds such as acetogenins have been already identified and characterized. However, large-scale animal and human trials are still lacking which are necessary to firmly establish the anti-diabetic and anti-cancer properties of A. muricata to be able to proceed with developing A. muricata-based interventions. Therefore, further research and development are required in order to make A. muricata an available anti-cancer therapy option for diabetes and cancer patients.

Introduction

Annona muricata, also known as soursop or graviola, is a tropical fruit-bearing tree which is widely used in traditional medicine for treatment of a variety of diseases and health conditions that include fever, inflammation, skin illnesses, respiratory problems, hypertension, diabetes and cancer (Coria-Tellez et al. 2018). This reputation of A. muricata as a versatile medicinal plant has attracted considerable interest among the members of the general public as well as the scientific community. Therefore, a number of studies have recently been done to prove or disprove these claims of healing potential of A. muricata (Moghadamtousi et al. 2015a). This paper explores the medicinal properties of A. muricata, with an emphasis on cancer and diabetes, as evidenced by scientific research and publications. The botanical and horticultural characteristics as well as traditional uses around the world of A. muricata are first discussed. This is followed by an enumeration of the scientific evidences of its anti-diabetes and anti-cancer effects. Finally, recommendations and conclusions are presented.

Botanical and Physiochemical Characteristics of A. muricata

 Soursop or graviola belongs to a genus, with approximately 119 species, under the family Annonaceae. Only seven species and a single hybrid, however, are cultivated for consumption or commercial use. A. muricata trees are distributed widely throughout the tropical and frost-free subtropical regions of the world. The soursop tree is upright and low-branching with green, glossy dark-green leaves. Flowers occur randomly on the trunk and branches. Propagation of soursop is usually through seeds but can be achieved by cuttings. Soursop fruits are dark green, spiny fruits that are aggregate of berries fused along with flower parts. This fusion of fruitlets often results in oval, heart- or irregularly-shaped fruits reaching 4 kg in weight. The fruit is made up of white, fibrous, juicy segments with hard, smooth, black seeds (Badrie & Schauss 2010).

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  The composition of soursop fruit by weight is edible pulp (67.5%), peel (20%), seeds (8.5%) and core (4%). Most of the edible pulp is made up of water (80-81%) and the rest are carbohydrate (18%) and protein (1%). Other minerals and nutrients found in soursop fruit at low concentrations include calcium, phosphorus, iron, -carotene, thiamine, riboflavin, niacin, ascorbic acid, tryptophan, methionine and lysine. The seed and seed coat contain the following toxicants: tannin, phytate and cyanide. Compounds that have been extracted in soursop include alcohols, aldehydes, esters, ketones and terpenes (Badrie & Schauss 2010).

Uses of A. muricata in Traditional Medicine

 Medicinal applications of soursop are widely reported in countries where the tree naturally grows. In India, A. muricata leaves, bark, flowers, fruits and seeds are used to treat kidney problems, ulcers, wounds, dysentery, spasms and parasites. In some parts of the Caribbean Islands, the bark, fruit and its juice are used to treat parasites, diarrhea, fevers, heart conditions, respiratory problems, hypertension and difficult childbirth. In some countries in South America, the bark, leaves, fruit and its juice and seeds are used for diarrhea, dysentery, arthritis, rheumatism, neuralgia, spasms and diabetes (Badrie & Schauss 2010, Coria-Tellez et al. 2018).

Anti-Diabetic Effects of A. muricata

 Diabetes mellitus (DM) is often referred to simply as diabetes which is a syndrome of dysfunctional metabolism impacting the endocrine system. Diabetes is characterized by hyperglycemia or abnormally high blood glucose levels. Type 1 diabetes is associated with reduced insulin production while type 2 diabetes is characterized by an abnormal response to insulin linked with beta-cell abnormality. Treatment of type 2 diabetes includes lifestyle changes such as following a healthy diet and performing regular exercise. Medications such as metformin, inhibitors and related insulin-regulating and blood-sugar control drugs are other treatment options for diabetes (Bolen et al. 2007, Lin & Zhongjie 2009).

 Most of the studies investigating the anti-diabetic effects of A. muricata have been performed in the laboratory and mainly on diabetic rats. For instance, Adewole & Caxton-Martins (2006) reported that aqueous extract from leaves of A. muricata affected the morphology of pancreatic beta-cells and blood sugar levels of diabetic rats. More specifically, the authors found that A. muricata extract induced viable pancreatic cellularity with distinct beta-cell mass in treated rats. In addition, blood glucose levels of diabetic rats were found to have significantly decreased with the administration of A. muricata extract. Pancreatic and serum insulin contents as well as antioxidant activities were also found to be boosted by the extract from A. muricata. These effects were reported by the authors as a reaction to A. muricata extracts directly quenching lipid peroxides while indirectly inducing synthesis of endogenous antioxidants.

 Methanolic extracts of A. muricata were used by Adeyemi et al. (2009) to determine its anti-hyperglycemic effects on diabetic rats. Powdered A. muricata leaves were soaked in 70% methanol to obtain extracts of the plant that were injected in adult Wistar rats. Mean body weight and blood glucose level of the rats were then measured. Results showed that significant reduction in mean body weight and mean glucose concentration occurred in A. muricata-treated diabetic rats compared to control and untreated diabetic rats. The authors suggested that these observed effects indicate that A. muricata has anti-hyperglycemic activities potentially useful in treating diabetes.

 Using the bark, Ahalya et al. (2014) demonstrated the hypoglycemic and anti-diabetic activity of A. muricata in diabetic albino rats. The ethanolic A. muricata bark extract was found to significantly reduce the fasting blood glucose levels of diabetic rats. The authors noted that polysaccharides, terpenes, tannins, steroids as well as alkaloids could be involved in the anti-diabetic effects of plants such as A. muricata.

 A more specific investigation was undertaken by Adefegha et al. (2015) to determine the anti-diabetic potentials of A. muricata. The study used aqueous fruit extracts for alpha-amylase inhibition assay and alpha-glucosidase inhibition assays as well as other assays for determining antioxidative properties of A. muricata. Their results showed that A. muricata extracts inhibited alpha-amylase and alpha-glucosidase activities in a dose-dependent manner (Fig. 1). The study also reported that the pericarp extract of A. muricata showed the highest alpha-amylase and alpha-glucosidase inhibitory activities. Furthermore, the inhibitory effects on the enzymes were attributed to the phenolic distributions of the extract which, according to the authors, serve as basis for potential diabetes and hypertension treatment strategies.

Fig. 1. Inhibition of -amylase (A) and -glucosidase (B) by extracts from A. muricata. Figures borrowed from Adefegha et al. (2015).

 The most recent study done by Sovia et al. (2017) also reported hypoglycemic effects of A. muricata leaf ethanol extract in diabetic rats. The authors observed a significant decrease in blood glucose levels in diabetic rats treated with A. muricata extracts that were found to contain tannins, saponins, flavonoids, phytosterols as well as phenols. However, A. muricata extracts showed no ameliorative effect on the damaged pancreatic islet, a condition that is associated with type 1 diabetes.

Anti-Cancer Effects of A. muricata

 According to GLOBOCAN 2018, there will be approximately 18.1 million new cases of cancer in 2018 while around 9.6 million cancer deaths will be recorded in the same year. Of the different types of cancer, lung cancer is the most common and leading cause of cancer death worldwide. This is followed by female breast cancer, prostate cancer, colorectal cancer, stomach cancer and liver cancer (Bray et al. 2018). Available options for cancer treatment depend on the type of cancer but typically include surgery, chemotherapy, radiotherapy and other drugs (Biemar & Foti 2013). However, these treatment strategies come with serious side effects such as risk of infection, anemia, bruising, bleeding, hair loss, fatigue, mouth ulcers, nausea, loss of appetite, change in taste perception, diarrhea and constipation (National Cancer Institute 2018). Therefore, researchers have been actively searching for less intrusive cancer treatments that could come from natural sources such as plants and animals. There are a number of studies already done focusing on the anti-cancer properties of A. muricata (Table 1). Most of these studies have been performed on specific cancer cells such as breast, pancreatic, lung, liver, prostate and colon cancer cells which are updated and further discussed below.

Breast Cancer

 A study by Fidianingsih & Handayani (2015) investigated the antiproliferative properties of A. muricata on breast cancer cells. Their research used leaves, fruits and seeds of A. muricata to obtain infusions for cytotoxicity tests on T47D cells and proliferative inhibition tests through a 3-(4, 5-dimethylthiazol-2-yl)-2, 5-diphenyltetrazolium bromide (MTT) assay. The authors reported that the aqueous extracts significantly inhibited T47D cell proliferation. More specifically, they found that theleaves were particularly potent compared to fruits and seed extracts. Another study using breast cancer cell lines and A. muricata crude extract was done by Najmuddin et al. (2016). This study also investigated the anti-proliferative and anti-cancer activities of A. muricata on MCF-7, MDA-MB-231 and 4T1 breast cancer cell lines using MTT assay and anti-cancer assays. Results showed that the A. muricata crude extract possessed varying levels of cytotoxicity to breast cancer cell lines. The extracts also reduced the size and weight of the tumor while exhibiting anti-metastatic properties and apoptosis induction activities in vitro and in vivo. Furthermore, the extracts were able to increase white blood cell, T-cell and natural killer cell levels.

Table 1. Anticancer studies on A. muricata. Table borrowed from Moghadamtousi et al. (2015a).

Tests on rats also showed promising results for A. muricata against breast cancer. Sulistyoningrum et al. (2017) used DMBA-induced breast cancer in rats to demonstrate the cytotoxic properties of A. muricata leaf extract. The study showed that the extracts improved the histological integrity of DMBA-induced breast cancer while reducing proliferative indices of the breast cancer cell lines. The anti-proliferative properties of A. muricata was attributed to the presence of annonaceous acetogenins in the leaves which are thought to inhibit the function of mitochondrial complex I, reducing ATP production, thus, causing cellular apoptosis. Reduction of ATP has also been known to induce intracellular hypoxia, further activating p53 tumor suppressor genes which halts the cell cycle of breast cancer cells at G1 stage.

Pancreatic Cancer

 Cytotoxicity, tumorigenicity, metastatic and related properties of pancreatic cancer cells were evaluated against the effects of A. muricata extracts by Torres et al. (2012). The authors reported that A. muricata displayed cytotoxicity (Fig. 2) and induced pancreatic cell necrosis through the inhibition of cellular metabolism. The extract was also found to cause down-regulation of the expression in pancreatic cells of proteins associated with glycolysis and hypoxia such as HIF-1, NF-_kB, HKII, GLUT1, GLUT4 and LDHA. Tumorigenic properties of pancreatic cancer cells were also inhibited by A. muricata extracts. Therefore, these results indicated that A. muricata extracts are capable of inhibiting multiple signaling pathways regulating metabolism, survival, cell cycle and metastasis of pancreatic cancer cells, thus, reducing their tumorigenicty and metastatic mechanisms.

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 Rosdi et al. (2015) have likewise reported that A. muricata extracts promote anti-proliferative and anti-cancer activities in pancreatic cell lines. This study used leaf extracts to test the viability of Capan-1 pancreatic cell lines through an MTT assay. Results indicated that A. muricata extracts are able to generate mild cytotoxicity to cells in pancreatic cancer. Such anti-cancer activities have been attributed to the flavonoid content of A. muricata leaves.

Fig. 2. Percent cytotoxicity of A. muricata extract to pancreatic cancer cells. Figure borrowed from Torres et al. (2012).

Lung Cancer

 To determine the effect of A. muricata on lung cancer cells, Moghadamtousi et al. (2014) used leaf ethyl acetate extracts on A549 lung cancer cells in an MTT assay. The authors reported that leaf extracts possessed selective cytotoxic effects on lung cancer cells. The extracts also significantly raised the reactive oxygen species (ROS) formation in A549 cells, inducing cell death. The study also noted that A. muricata leaf extract-induced apoptosis was associated with cell cycle arrest at the G₀/G₁. Furthermore, leaf extracts also promoted the cytoplasm-to-nucleus translocation of NF-_kB.

Liver Cancer

 Liu et al. (2016) have reported that A. muricata induces apoptosis in liver cancer cells. The research team used A. muricata ethanol leaf extracts on HepG2 liver cancer cells and MTT to determine cell viability. Flow cytometry, TUNEL assays and functional proteomics were done to confirm apoptosis and to delineate molecular pathways regulating apoptosis. Results showed that A. muricata extract can reduce liver cancer cell viability while triggering apoptosis in these cells. The study was also able to identify 14 proteins involved in apoptosis induced by the extract such as HSP70, GRP94 and DPI-related protein 5. The authors concluded that A. muricata leaf extract induces apoptosis of liver cancer cells via the endoplasmic reticulum stress pathway.

 Another study on the effect of A. muricata on liver cancer cells was done by Banerjee et al. (2017). The authors used leaf aqueousextracts on Huh-7 liver cancer cells through an MTT assay. In addition, they analyzed the expression of apoptotic genes Bax and Bcl-2 gene using RT-PCR. Huh-7 cells were also assessed for DNA damage and apoptosis using Comet assay. Results indicated that the leaf extract has cytotoxic effect on Huh-7 cells. Also, down and up regulation of Bax and Bcl-2 confirmed their roles in anti-apoptotic and pro-apoptotic mechanisms in cells. Furthermore, the extract was found to cause DNA damage and apoptosis to liver cancer cells. Therefore, A. muricata has potential to treat liver cancer cells through apoptosis.

Prostate Cancer

 Leaf extracts were used by Yang et al. (2015) to test anti-proliferative, cytotoxic and clonogenic effects of A. muricata on prostate cancer cells. They first prepared flavonoid-enriched and acetogenin-enriched fractions from leaf extracts. The authors reported presence of rutin and quercetin-3-glucoside in the extracts. Results showed that rutin and acetogenin in the extracts contributed maximum efficiency to the anti-cancer properties of A. muricata.

 Another study on the A. muricata effects on prostate cancer cell proliferation and clonogenicity showed promising results. The study done by Deep et al. (2016) used A. muricata pulp extract containing specific acetogenins (Fig. 3) with reportedly potent anti-cancer effects. Results showed inhibition of hypoxia-induced NOX activity in prostate cancer cells such as PC3, LNCAP and 22Rv1. Inhibition of hypoxia-induced NOX activity was associated with a reduction in NOX1, NOX2 and p47^phox expression. The authors also reported significant reduction in nuclear H1F-1 levels accompanying the decrease in the proliferation and clonogenic potential of prostate cancer cells. They concluded that A. muricata extract is potentially useful, through inhibition of NOX activity, in the control of prostate cancer progression.

Fig. 3. Chemical structure and fragmentation patterns of acetogenins. Figure borrowed from Deep et al. (2016).

Colon Cancer

 To determine the anticancer activity of A. muricata, Venkateshwarlu et al. (2014) introduced ethanolic extract of the plant to Wistar albino rats with induced colon cancer. The authors reported that 300 mg/kg of the ethanolic A. muricata extract reduced the development of aberrant crypt foci and the quantity of aberrant crypts. The extract was also found to increase the apoptosis index while promoting weight gain and improving histopathological parameters. The anticancer properties of A. muricata were attributed by the authors to the presence of acetogenins, adding that the primary anticancer compound is annonacin.

 Moghadamtousi et al. (2015b) have likewise reported a chemopotential property of A. muricata against colon cancer in rats. Their study used ethyl acetate A. muricata leaf extracts on azoxymethane-induced colonic aberrant crypt foci in rats. In addition, extracts were evaluated for apoptosis-inductive effects against HT-29 colon cancer cell lines. Results showed that A. muricata extracts significantly reduced the development of colonic aberrant crypt foci including an increase in enzymatic antioxidant levels, suppression of lipid peroxidation, arrest of G1 cell cycle and apoptosis induction in HT-29 cells as well as activation of several related pathways, indicating the anticancer activity of A. muricata.

Recommendations

 The studies reported in this paper are mostly at the level of laboratory stage of experimentation. According to the assays involving cancer cell lines and trials using rats, the anti-diabetic and anti-cancer properties of A. muricata are backed by evidences. However, large-scale animal and human trials are lacking. These advanced stages of research are necessary to establish the anti-diabetic and anti-cancer merits of A. muricata. Therefore, increased awareness and resources towards gathering more credible results should place A. muricata alongside highly promising or available anti-cancer therapy options in the near future.

Conclusion

 The healing properties of A. muricata have long been known among locals where the fruit tree grows. As a response, a number of researchers have attempted to provide scientific evidences for the claimed medicinal properties of A. muricata. According to multiple sources discussed in this paper, there are significant evidences to back the therapeutic potential of A. muricata against diabetes and cancer. Active compounds have been likewise identified and characterized. However, these studies are still in their early stages. Further research and development are, therefore, needed to fully understand and exploit the medicinal uses of A. muricata.

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