Cancer is one of the leading causes of human death worldwide.[44] Different factors that can decrease the incidence of chronic diseases could contribute to a significant increase in health and longevity. According to numerous reliable studies from Europe and the USA, higher consumption of fruits and vegetables were associated with a lower risk of total mortality.[45, 46] In this regard, there has been growing epidemiological and experimental studies that suggest vegetables and fruits intake has an inverse relationship with chronic diseases such as cancer.[44, 45, 47–49] Recently, betalains as natural antioxidants with free radical scavenging and potential health benefits have been considered by supplements manufacturers.[32, 50–52] Numerous investigations showed that the extract of red beetroot (Beta vulgaris L.), the FDA approved red food color E162, can reduce the incidence of some experimental tumors in skin, lung, liver and esophagus in vivo and is considered as new natural product with chemopreventive and/or chemotherapeutic activity opposing human cancers. [28, 36, 38] Likewise, our results showed that the beetroot hydro-alcoholic extract and its main constituent, betanin, can reduce the cell proliferation (in different doses) in the colorectal cancer cell lines via induction of apoptosis. Interestingly, the KDR/293 cells as a normal control group that treated with similar doses of beetroot hydro-alcoholic extract and betanin were intact in the determined treatment time point. The beetroot hydro-alcoholic extract inhibited cell proliferation in the HT-29 cells by a dose of 92 µg/mL, as well in the Caco-2 cells by a dose of 107 µg/mL at 48 h time-point. Also, betanin, triggered cell apoptosis with lower doses than beetroot hydro-alcoholic extract in HT-29 (64 µg/mL) and Caco-2 (90 µg/mL) cell lines without considerable adverse effects on normal KDR/293 cells.
Previous investigations showed that Red beetroot extract (Beta vulgaris. L) has effective chemopreventive activity and can decrease cell proliferation, angiogenesis, inflammation and also can induce apoptosis in different cancer cell lines such as Human lymphoma cells (Raji cells),[38] Human melanoma cells (B16F10),[53] Human chronic myeloid leukemia cells (K562),[40] Human colonic adenocarcinoma cells (HT-29), Human liver hepatoma cells (Huh7) [54] and Human breast cancer cell line (MCF-7).[37, 55] Indeed, various in-vitro and in-vivo investigations suggested that betacyanins, isobetanin and betanin as the main constituent of red beetroot, reduce cancer cell proliferation with different IC50s and possess anti-inflammatory, hepatoprotective, radioprotective, neuroprotective, diuretic, hypolipidemic, osteoarthritis pain reliever and anti-diabetic effects in different doses and time-points.[40, 56] Moreover, the antiproliferative effects of red beetroot extract have been proven on androgen-independent human prostate (PC-3) and breast cancer cells (MCF-7) without considerable adverse effects on normal human skin (FC) and liver (HC) cells.[37] As well, betanin that makes more than 95% of the total betacyanins (300–600 mg/kg) and known as the most principal and effective compound of the red beetroot is nontoxic, in different concentrations, on human umbilical vein endothelial cells (HUVECs) and normal human fibroblasts cells and also significantly inhibits ROS production, decreases the intracellular ROS level about 3 fold,[18, 20, 57] enhances the caspase-3 activity in stimulated neutrophils with the doses within range of 100–300 mM.[55, 57, 58] Likewise, treatment of MCF-7 cells with betanin-enriched red beetroot (Beta vulgaris L.) extract increased the expression level of apoptosis-related proteins (Bad, TRAILR4, FAS, p53) and altered the mitochondrial membrane potential. These alterations confirm the involvement of both intrinsic and extrinsic apoptosis pathways due to red beetroot extract treatment.[55] However, beetroot extract showed lower cytotoxicity on normal cells in comparison with doxorubicin (Adriamycin) as familiar chemotherapeutic agent.[37, 59] In another in-vitro study, Sreekanth et al. showed that betanin, isolated from the fruits of Opuntia ficus-indica decreases cell proliferation of human chronic myeloid leukemia cell line (K562) with an IC50 of 40 µM. Also, betanin induced intrinsic apoptosis pathway that is mediated by the release of cytochrome c from mitochondria into the cytosol, poly (ADP) ribose polymerase (PARP), downregulation of Bcl-2, reduction in the membrane potentials and qualitatively causing chromatin condensation, cell shrinkage and membrane blebbing.[40] Similarly, our investigation demonstrated that red beetroot hydro-alcoholic extract and betanin can inhibit cell proliferation and can induce apoptosis in treated HT-29 and Caco-2 cancer cell lines.
Besides, several in-vivo studies reported that red beetroot and betanin significantly decreased tumor multiplicity (20%) and tumor load in the female A/J mice lung cancer model. Accordingly, betanin in the drinking water of mice lung cancer model inhibited the angiogenesis and increased the expression level of caspase-3 resulted in induction of apoptosis. Betanin also triggered apoptosis via activated caspase-3, -7, -9, and PARP in human lung cancer cell lines.[35] Lechner et al. showed that regular oral consumption of red beetroot food color (78 µg/mL) decreased the number of NMBA-induced esophageal papilloma tumors by 45% and reduced cell proliferation in both precancerous esophageal lesions and in papillomas of NMBA-treated rats. Also, the levels of angiogenesis and inflammation in the beetroot color-consuming rats were decreased, and the apoptotic rates were increased significantly.[36]
Although the beneficial effects of red beetroot and betanin on different cancers have been proven by numerous studies, the precise mechanisms of these effects are still unclear .Based on several in-vitro and in-vivo studies it can be hypothesized that the betacyanins and betanin possessed chemotherapeutic and antiproliferative activities through their antioxidative activity and decrease the level of reactive oxygen species to minimum level that can’t stimulate proliferation by inappropriate signal transduction in that levels.[60]
Apoptosis as an accurate programmed cell death removes damaged cells via precisely regulated genes and plays an important role in the development and homeostasis of normal tissues.[61, 62] The least defect in this system can cause cancer or autoimmunity, while the improvement of apoptosis in some cases may cause degenerative diseases.[63] Indeed, suppression of apoptosis in the carcinogenesis process is supposed to play a crucial role in the development and progression of some cancers.[64] This exact mechanism induced in malignant cells via either the caspase-mediated extrinsic or mitochondrial intrinsic pathways. Activation of effector caspases in both pathways resulting in morphological and biochemical cellular alterations like membrane blebbing, cell shrinkage, nuclear fragmentation, chromatin condensation, chromosomal DNA fragmentation, and global mRNA decay.[61, 65] However, the significant role of pro/anti-apoptotic proteins and over/down expression of their effective genes by natural anticancer compounds is very important in the cell survival and apoptosis.[42, 43, 66–68] During the process of preventing cancer cell formation, the DNA damage in precancerous lesions triggers apoptosis pathways with the purpose of removing potentially harmful cells and blocking tumor growth. Nevertheless, deregulation of this exact death process by different carcinogenic factors resulted in uncontrolled cell proliferation, progress, and development of cancerous cells and also predisposed to resistance against drug therapies.[69, 70]
Thus, the previous studies suggested that the betalains are the most principal and potent anticancer constituents of the red beetroot extract.[18, 36, 71–73]