Encyclopedia
Please note this is a comparison between Version 1 by Yulia Merkher and Version 2 by Jessie Wu.
Flaxseed has been recognized as a valuable source of nutrients and bioactive compounds, including proteins that possess various health benefits. In recent years, studies have shown that flaxseed proteins, including albumins, globulins, glutelin, and prolamins, possess anti-cancer properties. These properties are attributed to their ability to inhibit cancer cell proliferation, induce apoptosis, and interfere with cancer cell signaling pathways, ultimately leading to the inhibition of metastasis.
- flaxseed proteins
- cancer treatment
- radiotherapy
- mechanobiology
- proteoform level analysis
- metastasis
- : metastasis
- flaxseed proteins
1. Flaxseed Proteins
Flaxseed comprises 30–41% fat, 20–35% dietary fiber, 20–30% protein, 4–8% moisture, 3–4% ash, and 1% simple sugars [1][23]. Recently, researchers have begun exploring the anti-cancer properties of flaxseed proteins, uncovering various ways in which they may exhibit such properties. For instance, flaxseed stands out as a significant dietary source of lignans, a type of phytoestrogen recognized for its anti-cancer attributes [2][24]. Lignans have been found to inhibit the growth of hormone-sensitive cancers, such as breast and prostate cancers, by interfering with the effects of estrogen on these tissues [3][25]. Additionally, flaxseed offers an abundant supply of alpha-linolenic acid—an omega-3 fatty acid. Omega-3 fatty acids are known for their anti-inflammatory effects, potentially reducing cancer risk [4][5][26,27]. Moreover, there is speculation that omega-3 fatty acids could hinder or limit the proliferation and dissemination of certain types of cancer cells [6][28]. The rich antioxidant content in flaxseed contributes to cellular protection against damage induced by free radicals [7][8][29,30]. Free radicals, unstable molecules, can induce cellular damage and escalate cancer risk. Certain studies have even indicated that flaxseed proteins might possess anti-angiogenic properties, impeding the formation of new blood vessels essential for tumor growth [9][21].
The composition of flaxseed proteins can fluctuate based on factors such as flax variety, growth conditions, and processing techniques. However, on average, flaxseed proteins comprise roughly 15–25% albumins, 43–80% globulins, 4–10% prolamins, and up to 10% other proteins [10][11][12][13][14][15][16][17][31,32,33,34,35,36,37,38], as illustrated in Figure 1.
Figure 1.
Flaxseed protein composition. Note: percentages may vary depending on the source and processing of the flaxseed.
The level and composition of flaxseed proteome depends on many factors, for example, cultivars, environmental conditions, and processing methods [16][37]. Flaxseed proteins mainly consist of 11S globulin and 2S albumin (Table 1). The 11S globulin is a salt-soluble protein; it has high molecular weight (252–298 kDa). The 2S albumin is a water-soluble protein; it has low molecular weight (16–17 kDa) [12][16][18][33,37,39].
Table 1. Proteome components found in flaxseed, and their potential heals benefits. Images prepared using Mol* Viewer 1.1, RCSB Protein Data Bank software (RCSB PDB, Piscataway, NJ, USA).
| Proteome Component |
Structure | Percentage of Total Protein | Potential Health Benefits |
|---|---|---|---|
| 11S Globulin |  |
43–48% | Contains anti-cancer peptides [19][20][21][40,41,42]; may have anti-inflammatory and antioxidant effects [22][23][43,44] |
| 2S Albumin |  |
16–18% | Contains peptides with potential anti-cancer and anti-inflammatory effects [21][24][25][42,45,46]; may have cholesterol-lowering effects [26][47] |
| 7S Vicilin-Like Globulin |  |
11–13% | May have antioxidant and anti-inflammatory effects [23][27][44,48]; contains peptides with potential anti-cancer effects [28][49] |
| Prolamin |  |
4–6% | Contains peptides with potential anti-cancer effects [29][30][50,51] |
| Glutelin-Like Protein |  |
2–3% | May have antioxidant and anti-inflammatory effects [31][32][52,53] |
| Other Proteins |  |
10–15% | May include lignans, which have antioxidant and anti-inflammatory and thus potential anti-cancer effects [33][34][54,55] |
2. Albumins of Flaxseed
Albumin, a type of protein present in various foods such as egg whites and whey protein, is recognized for its water-soluble nature and high digestibility, making it a valuable source of essential amino acids. While flaxseed albumin has not been as extensively studied as other components like lignans or omega-3 fatty acids, there exists some evidence to suggest its potential anti-cancer properties. Functioning as a potent antioxidant, albumin aids in neutralizing free radicals—unstable molecules responsible for cellular damage and heightened cancer risk [7][29]. Furthermore, albumin plays a pivotal role in immune system functionality, safeguarding against endothelial dysfunction through immunomodulation and antioxidant mechanisms [35][56]. Diminished albumin levels could potentially trigger inflammation and an increase in leukocyte count [36][57]. As a significant source of amino acids, albumin contributes to essential protein synthesis required for healthy cell growth and division; deficiencies in this synthesis have been correlated with an elevated cancer risk [37][38][58,59]. Albumin is also responsible for transporting vital nutrients, including vitamins and minerals, throughout the body [39][60], which is crucial for maintaining a robust immune system and minimizing cancer risk. Beyond these roles, albumin can serve as a carrier for chemotherapy drugs, enhancing their targeted delivery to tumor sites and potentially lowering metastasis risk [40][61].
The extracellular matrix (ECM), a complex network of proteins and molecules surrounding cells, plays a pivotal role in cancer progression and metastasis. Evidence indicates that albumin interacts with and regulates ECM components, potentially inhibiting cancer cell invasion and metastasis. Albumin’s interactions encompass key proteins involved in cancer cell invasion, like matrix metalloproteinases (MMPs) and urokinase-type plasminogen activator (uPA) [41][42][62,63]. Moreover, albumin can engage with other ECM proteins, such as laminin and fibronectin, contributing to the inhibition of cancer cell invasion [43][44][45][64,65,66].
The primary form of albumin in flaxseed is 2S albumin, a seed storage protein. Although the precise physiological and metabolic role of 2S albumins remains to be definitively described, evidence based on their amino acid composition and mobilization during germination suggests their function as nitrogen and sulfur donors [46][67]. Typically existing as heterodimers, these proteins consist of 8–16 kDa water-soluble polypeptides [46][67], connected by two disulfide bonds resistant to pepsin and trypsin. While the subunit compositions and structures of 2S albumins differ, their 3D form is generally a compact sphere enriched in α-helices [47][48][68,69]. An extensively studied anti-cancer peptide derived from plants is lunasin, a small peptide from the 2S albumin family, containing 43–44 amino acid residues [24][45]. Lunasin encompasses multiple functional domains, including an aspartic acid tail, an RGD domain, and a chromatin-binding helical domain [49][70]. Lunasin exhibits a wide-ranging therapeutic effect against cancer in both laboratory and live models, encompassing lung cancer, colon cancer, leukemia, melanoma, and breast cancer [50][51][71,72]. This protein holds the potential to hinder cancer cell invasion and migration (Table 2) and represents a promising avenue for further research in developing novel cancer treatments.
Table 2.
Anti-metastatic action of 2S albumin component–Lunasin.
| Action | Mode of Action | Evidence |
|---|---|---|
| Inhibits cancer proliferation and induce apoptosis | Interaction with the αvβ3 integrin via the FAK/ERK/NF-κB signaling pathway; activation of caspase-3 and cleavage of PARP [52][53][73,74] | Inhibited the proliferation and the tumorsphere-forming capacity of colon cancer HCT-116 cells [54][75]. Increased the amount of colon cancer cells KM12L4 undergoing apoptosis twofold [55][76]. Reduced tumor growth in NSCLC and melanoma xenografts [51][72]. |
| Inhibits cancer cell invasion and migration | Interaction with cellular receptors (integrins and EGFR); disrupts the activity of key signaling proteins (MMP-2/-9) via the FAK/Akt/ERK and NF-κB signaling pathways [56][77] | Caused a reduction in the migration (scratch assay) of HCT-116 and KM12L4 colon cancer cells [53][74]. Inhibited the migration and invasion activity in MDA-MB-231 and MCF-7 breast cancer cell lines [56][77]. Inhibited the invasion of melanoma A375 and B16-F10 cells to matrigel [50][71]. |
| Reduces inflammation and oxidation | Reduction in the production of certain inflammatory markers (ROS, TNF-α and IL-6) [57][58][78,79] | Mouse macrophage cells (LPS-stimulated RAW 264.7) reduced the production of certain inflammatory markers (ROS, TNF-α and IL-6) [59][80]. |
| Reduces cancer cells colonization | Reduction in phosphorylation of the intracellular kinases FAK and AKT; reduction in histone acetylation of lysine residues in H3 and H4 histones [50][71] | Reduced pulmonary colonization after injection of highly metastatic B16-F10 . |
| Arrest cell cycle | Arrests the cell cycle at the G2/M and G1/S phase; altered the expression of the G1 specific cyclin-dependent kinase complex components, increased levels of p27Kip1, reduced levels of phosphorylated Akt [55][60][76,81] | Inhibited cell cycle progression at the G1/S phase for NSCLC H661 cells [60][81]. Lunasin treatment of MDA-MB-231 breast cancer cells resulted in a notable increase in RB1 level, which lead to arrest of G1 phase [61][82] |
Overall, while further research is required to comprehensively comprehend the potential anti-cancer effects of 2S albumin, this protein shows promise in potentially inhibiting cancer cell invasion and migration. Thus, it stands as a promising realm of investigation for the advancement of novel cancer treatments.
3. Globulins of Flaxseed
Globulins form a diverse family of proteins present in various foods, including legumes, nuts, and animal products. Among flaxseed proteins, globulin takes precedence as the principal component, its size being reported to be in the range of 252–298 kDa (for 11–12 S Globulins). Comprising about 3% α-helical and 17% β-structures [62][63][64][83,84,85], globulins, akin to albumins, have not undergone extensive examination for their anti-cancer attributes. Nevertheless, some evidence indicates the potential anti-cancer properties of globulins.
Globulins play a pivotal role in the immune system, actively combating infections and diseases, including cancer. There has been a suggestion that globulins might stimulate white blood cell production, contributing to the battle against cancer cells [65][86]. Certain globulins have been shown to impede the activity of enzymes linked to tumor growth and metastasis. For instance, soybean globulins have been observed to hinder the action of tyrosine kinase, an enzyme central to cancer cell proliferation [66][67][87,88]. Certain globulins, like whey protein, boast significant antioxidant content that aids in neutralizing free radicals and guarding against cellular damage that could lead to cancer [68][89]. Moreover, globulins partake in regulating hormone levels within the body [69][70][71][90,91,92]. Given that hormones can influence the development and progression of specific cancers, modulating their levels might yield anti-cancer effects as well.
Predominantly, flaxseed’s major globulin type is the 11S globulin (comprising over 85% of all globulins), while the 7S (less than 2%) and 2S Vicilin-like globulins (less than 4%) are considered minor [72][93]. The non-reduced 11S globulin reveals five polypeptide bands, including a basic subunit (18–20 kDa), an acidic subunit (30–40 kDa), and additional polypeptides with molecular weights of 47, 80, 120, and 160 kDa. Studies exploring the distinct biological properties of flaxseed protein digests have yielded varied results, contingent on the methods employed. For example, the highest antioxidant activity (90%) and effective fungal inhibition were observed with glutelin hydrolysates, whereas intact glutelin protein exhibited the highest angiotensin-converting enzyme-inhibiting (60%) activity [13][34]. There is some evidence suggesting that 11S globulin (also referred to as glutelin [73][94]), a major storage protein in flaxseed, might possess anti-cancer properties, potentially inhibiting cancer cell proliferation and inducing apoptosis (Table 3). However, it is crucial to acknowledge that these investigations were conducted in vitro (within a laboratory setting using cell cultures), and further research is necessary to ascertain the potential effects of glutelin in vivo (within living organisms).
Table 3.
Anti-tumor action of 11S globulin components.
| Action | Mode of Action | Evidence | |
|---|---|---|---|
| Inhibits cancer cell growth and proliferation | Lectin was responsible for the antiproliferative activity of the MPI-h [74][95]. Acid fraction of glycinin, composed of low molecular weight peptides, was able to inhibit cancer cells growth [75][96]. | Inhibited the proliferation of UMR106 rat osteosarcoma-derived cells [74][95] and inhibited the growth of cervical cancer HeLa cells in a dose-dependent manner [75][96]. | |
| Antioxidant effect | Small (~1 kDa) peptides generated from 11S globulin inhibit the formation of hydroxyl radicals by reaction of H2O2 and Co+2 and decreasing ROS [20][41] | Demonstrated peroxyl radical scavenging activity dependent on the structure of peptides in human adenocarcinoma cell line, Caco-2 TC7 [20][41] | |
| Induces cancer cell death (apoptosis) | Increased the expression levels of apoptosis-related spot-like protein (ASC), caspase-1, the cleaved gasdermin D, and interleukin-1β [76][97]. Flaxseed orbitides influence mitochondrial- and death receptor-mediated intrinsic and extrinsic pathways [77][98]. | Glutelin extracts induced the apoptosis of cervical cancer HeLa cells [78][99]. Human gastric SGC-7901 cell apoptosis was induced by linusorb B3 flaxseed orbitides [77][98] | |
| Arresting cell cycle | Linoorbitides arrested the cell at the G1 phase by downregulation of CDK2/4 and overexpression of p21WAF1/CIP1 and p27KIP1 genes [79][100]. | melanoma cells [50][51][71,72]. Inhibited formation of liver metastasis in murine model | Cyclolinopeptides/linusorbs are capable of arresting cell cycle, and thus reduce metastasis spreading in human gastric SGC-7901 cells [79][53][74][100]. |
| Cytotoxic effect on cancer cells | Linoorbitides have strong cytotoxic effect probably due to its binding abilities to human serum albumin [11][32]. | Linusorb B3 is cytotoxic to human melanoma cells A375 and breast cancer cells Sk-Br-3 and MCF7 at high concentration [80][101]. |
4. The Combined Anti-Cancer Action of Flaxseed Proteins
Flaxseed proteins can be consumed as part of the diet and subsequently absorbed within the digestive tract. Once absorbed, they can enter the bloodstream and circulate throughout the body, potentially reaching cancer cells. There is also the possibility of delivering flaxseed proteins directly to cancer cells through targeted drug delivery systems or nanoparticle formulations. Moreover, the topical application of flaxseed oil, which contains certain proteins present in flaxseed, has been explored as a potential method for delivering these proteins to skin cancer cells [81][82][142,143].
The efficacy of flaxseed proteins in various cancer cell lines, such as breast [83][144], skin [50][71], prostate, and colon [53][74] cancer cells, has been demonstrated. Flaxseed proteins have exhibited anti-tumor activity by inducing cell cycle arrest and promoting apoptosis (programmed cell death) [11][32]. Notably, flaxseed proteins possess the capacity to modulate the immune system, which holds a pivotal role in cancer surveillance and elimination [81][142]. Furthermore, flaxseed proteins have been observed to enhance the effectiveness of chemotherapy drugs across different cancer cell lines [5][84][27,145].
According to the ClinicalTrials.gov database, there are no past or current clinical trials specifically focused on cancer treatment using proteins from flaxseed. However, 21 clinical trials have been conducted to explore the biological effects of dietary flaxseed, either alone or in combination with chemotherapy or radiotherapy, on cancer patients (only 3 of them—with results and none of them on phase 4). Unfortunately, no significant positive results or in-depth investigations into the underlying mechanisms of action have been recorded. For instance, there were no notable effects of flaxseed on aromatase inhibitors’ activity concerning selected breast tumor characteristics or serum steroid hormone levels [85][146]. In patients with locally advanced or metastatic non-small cell lung cancer (NSCLC) undergoing radiotherapy, the daily intake of flaxseed led to noteworthy treatment-related gastrointestinal toxicities, even though there was a low reported incidence of acute radiation-induced complications [86][147]. On the other hand, there is an indication that a dietary milled sesame/pumpkin/flax seed mixture, added to a habitual diet, lowered triglyceride and CRP, TNF-alpha, and IL-6 levels, affected glycemic control, and improved fatty acid profile and pruritus symptoms [87][148]. Currently (2023), there are only two ongoing clinical trials investigating the use of flaxseed in cancer treatment.
In essence, the potential advantages of utilizing extracted and especially selected flaxseed proteins in cancer treatment are indeed promising (Figure 24). However, further research is imperative to fully elucidate their underlying mechanisms of action and gauge their clinical effectiveness in treating cancer.
Figure 24.
Anti-cancer action of main flaxseed proteins.
5. Flaxseed Proteome Effect on Anti-Cancer Radiotherapy
Radiotherapy (RT) stands as a prominent method for cancer treatment, functioning by inducing DNA damage within cancer cells. This complex medical procedure necessitates meticulous planning and monitoring. However, despite advancements in RT techniques, certain tumors display notable radio resistance, leading to elevated rates of treatment failure and tumor relapse [88][89][149,150]. Upon encountering DNA damage, cancer cells elevate their antioxidant activity [90][151] and metabolic processes, encompassing glucose flux, amino acid metabolism, and fatty acid utilization. This metabolic response provides the necessary substrates and energy for the repair of DNA damage [91][152].
Although research specifically focusing on the impact of flaxseed proteins on radiotherapy remains limited, it is crucial to recognize that flaxseed proteins could potentially offer benefits during radiotherapy due to their antioxidant and anti-inflammatory properties. Flaxseed 2S-albumin, akin to other albumin proteins, possesses antioxidant attributes (Table 1 and Table 2). Antioxidants play a role in neutralizing the free radicals generated during radiotherapy [92][153], thereby reducing oxidative stress and potential harm to healthy tissues. Through its scavenging action against free radicals, flaxseed 2S-albumin might confer protective effects on cells exposed to radiation.
Some studies propose that specific globulin proteins exhibit anti-inflammatory characteristics (Table 1 and Table 3). Inflammation is a natural reaction to radiation exposure [93][154], but excessive or prolonged inflammation could contribute to tissue damage. By lessening inflammation, flaxseed 11S-globulin might potentially alleviate some of the detrimental effects of radiotherapy on healthy tissues.
Flaxseed proteins, including 2S-albumin and 11S-globulin, furnish essential amino acids and contribute to nutritional support for the body. Maintaining sufficient protein intake is vital during radiotherapy to facilitate tissue repair and overall well-being [94][155]. Flaxseed proteins can play a role in meeting the nutritional requirements of individuals undergoing radiotherapy, potentially supporting recovery and minimizing treatment-related complications.
Previous research has demonstrated that the intake of flaxseed oil increased the survival rate of rats exposed to 8 Gy gamma radiation. However, this effect was hypothesized to stem from indirect biological mechanisms, such as impacts on the gut microbiota, rather than the direct radioprotective qualities of flaxseed oil [95][156]. For instance, after being metabolized by the intestinal microbiota, flax components could modify mammary gland miRNAs, potentially reducing the risk of adult breast cancer [96][157]. Flaxseed has also shown potential in mitigating side effects induced by radiotherapy. In mice subjected to a combination of thoracic radiation therapy and a flaxseed diet, a decrease in p53-responsive miR-34a was observed. This miRNA is associated with cellular maturity and apoptosis regulation [97][158]. Mice fed with flaxseed exhibited reduced expression of lung injury biomarkers (Bax, p21, and TGF-beta1), oxidative lung damage, lung fibrosis, and inflammatory cell influx into lungs following 13.5 Gy thoracic X-ray radiation exposure. However, the radioprotective effect of flaxseed on Lewis Lung carcinoma was not observed [98][99][159,160]. Consequently, targeting tumor metabolism through the flaxseed proteome presents a promising therapeutic avenue for safeguarding normal cells during radiation while sensitizing cancer cells to its effects.
6. Conclusions
Nutrition plays a crucial role in the overall well-being of cancer patients and can significantly contribute to reducing complications during treatment [168,169]. In recent years, there has been a growing focus on plant-based nutrition as a means to protect against a range of leading causes of death, including various types of cancer such as breast, prostate, colorectal, and gastrointestinal cancers. Plant-based diets comprising whole foods have demonstrated substantial protective effects against these cancers and other chronic diseases. These diets can serve as disease-modifying agents, enhancing the management and treatment of these conditions. Consequently, interventions involving nutrition in the prevention of diverse cancers offer a notable complement to existing medical therapies.
Addressing the current gaps in knowledge about flaxseed proteins is crucial for advancing both cancer treatment and overall health. Firstly, the limited representation of flaxseed proteins in existing databases underscores the need for a more comprehensive inclusion of this vital information. Additionally, the absence of established sequences for flaxseed proteins poses a challenge in understanding their biological activities. Furthermore, the scarcity of research on the properties of flaxseed for cancer treatment emphasizes the importance of exploring these avenues. The development of a compatible nutraceutical enriched with flaxseed proteins and the analysis of its anti-metastatic effects contribute significantly to promoting healthy aging. These initiatives not only address existing gaps but also pave the way for novel strategies that can enhance both cancer treatment and overall well-being.
