Dual effects of silymarin on nasopharyngeal carcinoma cells (NPC-TW01)

Role of Silymarin in Cancer Treatment: Facts, Hypotheses, and Questions

The flavonoid silymarin extracted from the seeds of Sylibum marianum is a mixture of 6 flavolignan isomers. The 3 more important isomers are silybin (or silibinin), silydianin, and silychristin. Silybin is functionally the most active of these compounds. This group of flavonoids has been extensively studied and they have been used as hepato-protective substances for the mushroom Amanita phalloides intoxication and mainly chronic liver diseases such as alcoholic cirrhosis and nonalcoholic fatty liver. Hepatitis C progression is not, or slightly, modified by silymarin. Recently, it has also been proposed for SARS COVID-19 infection therapy. The biochemical and molecular mechanisms of action of these substances in cancer are subjects of ongoing research. Paradoxically, many of its identified actions such as antioxidant, promoter of ribosomal synthesis, and mitochondrial membrane stabilization, may seem protumoral at first sight, however, silymarin compounds have clear anticancer effects. Some of them are: decreasing migration through multiple targeting, decreasing hypoxia inducible factor-1α expression, inducing apoptosis in some malignant cells, and inhibiting promitotic signaling among others. Interestingly, the antitumoral activity of silymarin compounds is limited to malignant cells while the nonmalignant cells seem not to be affected. Furthermore, there is a long history of silymarin use in human diseases without toxicity after prolonged administration. The ample distribution and easy accessibility to milk thistle-the source of silymarin compounds, its over the counter availability, the fact that it is a weed, some controversial issues regarding bioavailability, and being a nutraceutical rather than a drug, has somehow led medical professionals to view its anticancer effects with skepticism. This is a fundamental reason why it never achieved bedside status in cancer treatment. However, in spite of all the antitumoral effects, silymarin actually has dual effects and in some cases such as pancreatic cancer it can promote stemness. This review deals with recent investigations to elucidate the molecular actions of this flavonoid in cancer, and to consider the possibility of repurposing it. Particular attention is dedicated to silymarin's dual role in cancer and to some controversies of its real effectiveness.

Health Benefits of Silybum marianum: Phytochemistry, Pharmacology, and Applications

Silybum marianum (SM), a well-known plant used as both a medicine and a food, has been widely used to treat various diseases, especially hepatic diseases. The seeds and fruits of SM contain a flavonolignan complex called silymarin, the active compounds of which include silybin, isosilybin, silychristin, dihydrosilybin, silydianin, and so on. In this review, we thoroughly summarize high-quality publications related to the pharmacological effects and underlying mechanisms of SM. SM has antimicrobial, anticancer, hepatoprotective, cardiovascular-protective, neuroprotective, skin-protective, antidiabetic, and other effects. Importantly, SM also counteracts the toxicities of antibiotics, metals, and pesticides. The diverse pharmacological activities of SM provide scientific evidence supporting its use in both humans and animals. Multiple signaling pathways associated with oxidative stress and inflammation are the common molecular targets of SM. Moreover, the flavonolignans of SM are potential agonists of PPARγ and ABCA1, PTP1B inhibitors, and metal chelators. At the end of the review, the potential and perspectives of SM are discussed, and these insights are expected to facilitate the application of SM and the discovery and development of new drugs. We conclude that SM is an interesting dietary medicine for health enhancement and drug discovery and warrants further investigation.

Silymarin-Loaded, Lactobionic Acid-Conjugated Porous PLGA Nanoparticles Induce Apoptosis in Liver Cancer Cells

HepG2 cells (HCC), characterized by epithelial-like morphology, high proliferation rates, and nontumorigenicity, require cost-effective and efficient treatment. Silymarin, a flavonoid extract of Silybum marianum, is effective in the treatment of HCC. Here, we have reported a comparative anticancer study of the well-characterized nanoformulations of lactobionic acid-adorned porous PLGA-encapsulated silymarin (LA-PLGA-Sil) with only porous PLGA-encapsulated silymarin (PLGA-Sil) against HepG2 cells. Treatment of HepG2 cells with LA-PLGA-Sil produced a significant deterioration in cell viability at an essentially low dose as compared with PLGA-Sil, due to the adorned lactobionic acid moiety, which results in better targeting. p53, a tumor suppressor gene, essentially initiates apoptosis in cells procuring wild-type p53 (p53 +/+). In our report, treatment of HepG2 cells (p53 +/+) with LA-PLGA-Sil activated p53, which in turn inhibited the proliferation of cells by instigating cell-cycle arrest and apoptosis in a concentration-dependent manner and simultaneously stabilized the nuclear translocation of NFκB-p65. To explore the effect of LA-PLGA-Sil on the expression of microRNA, we observed that LA-PLGA-Sil markedly upregulated the miR-29b in human HCC cells. Reactivation of the p53 gene by miR-29b targeted Bcl-2 and triggered the sequential activation of mediators such as proapoptotic Bax protein, release of cytochrome c, and the activation of caspase proteins (caspase-3 and caspase-9). Furthermore, the overexpression of NFκB-p65 in HepG2 cells reversed the repression, and this stabilization effect of LA-PLGA-Sil on the nuclear translocation of p65 led to the significant downregulation of miR-29b and successively decreased the p53 expression in LA-PLGA-Sil-treated cells, thereby providing a survival mechanism to HepG2. In entirety, our study demonstrated the extensive potential of LA-PLGA-Sil to instigate the cell death of HepG2 cells via apoptosis by targeting the miR-29b/p53 axis through the stabilization of NFκB. It also impaired the migratory activity of HepG2 cells and thereby furnished a comprehensive way to HCC therapeutic treatment.

Hepatoprotective effect of silymarin

The use of medicinal plants in treating illnesses has been reported since ancestral times. In the case of hepatic diseases, several species such as Silybum marianum, Phyllanthus niruri, and Panus giganteus (Berk.) have been shown to ameliorate hepatic lesions. Silymarin is a natural compound derived from the species Silybum marianum, which is commonly known as Milk thistle. This plant contains at least seven flavoligands and the flavonoid taxifolin. The hepatoprotective and antioxidant activity of silymarin is caused by its ability to inhibit the free radicals that are produced from the metabolism of toxic substances such as ethanol, acetaminophen, and carbon tetrachloride. The generation of free radicals is known to damage cellular membranes and cause lipoperoxidation. Silymarin enhances hepatic glutathione and may contribute to the antioxidant defense of the liver. It has also been shown that silymarin increases protein synthesis in hepatocytes by stimulating RNA polymerase I activity. A previous study on humans reported that silymarin treatment caused a slight increase in the survival of patients with cirrhotic alcoholism compared with untreated controls.