This drug has long been used as a hepatoprotective remedy.
Chronic toxicity studies in rodents have confirmed that Legalon (silymarin) has very low toxicity.
These data support its history as a safe drug in liver disease . In recent years, several studies have expanded our understanding of Legalon’s pharmacology and its molecular mechanisms of action.
These new ideas may affect the handling of Legalon in clinical studies and in daily practice.
In addition, scientific knowledge in hepatology is constantly evolving, in particular, with an increase in the field of nonalcoholic fatty liver disease which is considered today as the most common liver disease worldwide.
Many pharmacological effects of Legalon can be attributed to downstream or upstream effects of its antioxidant and membrane stabilizing properties.
However, despite promising new clinical and experimental data, more clinical studies that include long-term observations and the application of tough clinical endpoints are required.
Such as survival rates, to support the use of Legalon in the treatment of liver disease.
Carduus marianus, Silybum marianum or milk thistle is an edible Mediterranean herbarium with a long history as a medicinal plant.
Probably, this practice was also supported by the religious connotations of his name (for example, Chardon Marie, Mariendistel, the thistle of Santa Maria, etc.).
The standardized milk thistle extracts currently used from the fruits contain 30–65% Legalon as an active ingredient.
Legalon is a complex mixture of polyphenolic molecules, which includes seven closely related flavonolignans, namely silybin A, silybin B, isosilibin A, isosilibin B, silichristin, isosilichristin, silidianin, and the flavonoid taxifolin, the most effective antioxidant of these molecules.
Orally administered Legalon has become a frequently applied therapy for various liver disorders.
Legalon is classified by the World Health Organization’s Anatomical Therapeutic Chemicals (ATC) classification system as liver therapy (A05BA03).
The approved indications are described as toxic and inflammatory liver diseases, although low doses are also recommended for dyspepsia.
Due to chronic alcohol abuse and modern lifestyle, liver disease continues to be a major health problem and the search for new but also optimization of known agents for liver disease therapy remains of great importance.
According to the World Health Organization (WHO), alcohol is the third largest risk factor for premature mortality, disability and loss of health. Importantly, alcoholic liver disease is responsible for the majority of alcohol-related deaths.
At the same time, nonalcoholic fatty liver disease (NAFLD) is becoming an even greater health problem, and nonalcoholic fatty liver disease is today considered the most common liver disease in all the world.
The prevalence of nonalcoholic fatty liver disease in the general population of Western countries is up to 30%.
And a significant number of these individuals are developing nonalcoholic steatohepatitis (NASH) that can progress to cirrhosis of the liver and hepatocellular carcinoma (HCC).
Already today, nonalcoholic steatohepatitis is reported to be the third most common indication for liver transplantation in the United States.
A large proportion of patients with NAFLD have a coexisting metabolic syndrome with symptoms such as central obesity, dyslipidemia, and insulin resistance.
These patients have a significant risk factor for cardiovascular disease.
In Europe, the estimated prevalence rate of non-alcoholic fatty liver disease is up to 30% in the general population (including obese children) and up to 70% in people with type 2 diabetes.
These conditions generate large direct costs, loss of productivity and income, and poor health-related quality of life.
In addition to the lifestyle-dependent liver disorders mentioned above, viral infections, that is, hepatitis B virus (HBV) and hepatitis C virus (HCV) infections, are causing chronic liver disease. .
A predominant decrease in the prevalence of hepatitis B virus infections was achieved with the implementation of vaccine programs, and mandatory testing of blood donors improved the management of the hepatitis C virus in most countries.
However, the World Health Organization estimates that, with wide geographic variations, between two and three percent of the world’s population is still infected with the hepatitis C virus.
This results in a total number of 120 to 170 million people infected with the hepatitis C virus who are also at high risk of developing liver disease, that is, liver cirrhosis and hepatocellular carcinoma.
Antiviral therapy applies nucleoside analogs and interferon alpha and targets viral replication as well as antiviral immune responses, ie, activation of T cells and modulation of innate immune cells.
Due to its antiviral properties, in vitro, legalon had been considered an additional promising candidate for the treatment of acute infection with hepatitis B virus and hepatitis C virus.
However, little or no benefit was shown in clinical trials. The long-term effects in treating chronic hepatitis C virus as an additive to, for example, nucleoside analogs or interferons have not yet been evaluated and will not be discussed further in this review.
The complexity of the liver explains that a single pharmacological intervention is unlikely to cause a major functional change on its own unless it hits a very specific “bottleneck” in a chain of events.
Nutrients absorbed through the intestine are transported to the liver through the portal vein blood flow.
Liver function is regulated by blood-derived hormones, cytokines, and adipokines. In addition, intestinal hormones and transmitters of the vegetative nervous system exert a strong influence on the liver.
Different types of cells, among which hepatocytes are more abundant, are involved in the control of immunity and inflammation.
Stellate cells that can transform into myofibroblast-like cells upon activation are centrally involved in the fibrotic response seen in chronic liver disease.
Fibrosis contributes to the ability of hepatocytes to regenerate after injury or resection.
An additional player in liver disease is the gut microbiome. The complex interaction of the intestinal flora with the intestinal immune system affects the development of a liver disease phenotype in both mice and patients.
Over the past 20 years, our understanding of liver disease and its treatment has undergone remarkable evolution.
In 2014, about 200 articles on Legalon have been published, among those 8 clinical reports, reflecting the continuing interest in this plant extract.
Preclinical data show potent anti-inflammatory, antifibrotic, antiviral, and antioxidant properties of Legalon.
However, the predictive value of in vitro and animal models is sometimes misleading and may have led to translation failures in clinical practice for many years.
Legalon has been known for its very low toxicity, but the picture has recently been enlarged by a major chronic toxicity study that added some new data on neoplasms.
Toxicological data are crucial for the calculation of the therapeutic index, that is, the ratio of the highest exposure of the drug that does not produce toxicity to the exposure that produces the desired effect, and the evaluation of the risk benefit of a drug.
Acute toxicity studies of Legalon have been performed after intravenous infusion in mice, rats, rabbits, and dogs.
The mean lethal dose values were 400 mg / kg in mice, 385 mg / kg in rats, and 140 mg / kg in rabbits and dogs, although these values depended on the infusion rate.
With a slow infusion rate (more than 2 to 3 h), the mean lethal dose increased to 2 g / kg in rats and, after oral administration, was even 10 g / kg.
In blinded clinical trials, the overall incidence of adverse events was 2.4% (similar to placebo), while in open-label trials the incidence of adverse events was 1%.
The most common adverse event associated with the use of Legalon is a laxative effect; other symptoms include nausea, epigastric discomfort, arthralgia, itching, and hives.
Taking into account all published randomized trials, uncontrolled studies and case reports, only one serious adverse event has been considered related to Legalon ( diarrhea , vomiting and collapse in a 57-year-old woman).
The active ingredient in Legalon is a mixture of non-lipophilic flavonolignans, poorly soluble in water (0.05 mg / ml); it is transported bound to serum albumin as a carrier protein.
Despite a fairly large number of studies devoted to these potential problems, no clinically relevant interactions have been identified between legalon and other drugs after administration in the usual recommended doses.
Here are some key elements highlighted.
Legalon, silibinin A and silibinin B in high concentrations significantly inhibited the uptake of organic anion transporting polypeptides (OATP) and rosuvastatin mediated in human hepatocytes.
However, calculation of portal vein unbound peak concentrations / mean peak inhibitory concentration values indicated a low risk of Legalon-drug interactions in liver uptake with a usual dose of Legalon.
Higher than usual doses of Legalon, or formulations with improved bioavailability, may increase the risk of interactions of flavonolignan with organic anion transporter polypeptide substrates in patients.
In Chinese volunteers, co-administration of Legalon 140 mg tid for 2 weeks with talinolol, a typical substrate for multidrug resistance P-glycoprotein (MDR1), led to an increase in plasma area under the latter curve by 36% .
Several studies have addressed the induction of cytochrome P450 in human primary hepatocytes and the inhibition of cytochrome P450 with human liver microsomes.
For currently used doses, drug interactions are possible for CYPs 2C8 and 2C9, but are not likely, and are remote for CYPs 2C19, 2D6, and 3A4.
Observations made in the 1980s suggested that legalon and its components are incorporated into the hydrophobic-hydrophilic interface of the microsomal bilayer, affecting the packing of acyl chains and restoring the membrane fluidities of liver microsomes and mitochondria.
Some years ago, it was reported that legalon “could exert stabilizing effects at the membrane level, by virtue of its action on membrane-bound enzymatic activities.”
Legalon appears to act as an antioxidant not only because it acts as a scavenger of free radicals that induce lipid peroxidation, but also because it influences the enzyme systems associated with glutathione and superoxide dismutase.
At high concentrations, Legalon constantly increases the stability of the hepatocellular plasma membrane in vitro.
Lipid peroxidation is attributed to being one of the main mechanisms that lead to the degeneration of cell membranes and the development of liver disease.
Under these conditions, the hepatoprotective effects of Legalon seem to depend mainly on five properties:
- Activity against lipid peroxidation as a result of free radical scavenging and the ability to increase cellular glutathione (GSH) content.
- Ability to regulate membrane permeability and increase membrane stability in the presence of xenobiotic damage.
- Ability to regulate nuclear expression through a steroid-like effect (attributed to a structural similarity of Legalon to steroid hormones) followed by tissue regeneration.
- Inhibition of the transformation of quiescent liver stellate cells into activated myofibroblasts that are responsible for the deposition of collagen fibers leading to cirrhosis.
- Anti-inflammatory effect resulting in a decrease in liver inflammation and inflammatory cytokines, possibly as a result of a reduction in tissue damage.
It is well known that low levels of reactive oxygen species (ROS) are actively involved in the regulation of signal transduction pathways as an essential intracellular second messenger for certain cytokines and growth factor receptors, as well as for insulin signal transduction.
Furthermore, under pathological conditions, an excess of reactive oxygen species induces apoptosis or necrosis through the activation of mitogen-activated protein kinases (MAPKs) and caspase cascades.
Of the multitude of pharmacological effects attributed to Legalon in recent years, most can be explained as downstream or upstream effects of these five properties, particularly antioxidant effects.
Some of these numerous effects are represented by effective doses or concentrations, an approach already proposed by other authors.
This shows that the effects within the therapeutic range are probably mainly related to the properties related to antioxidant properties and membranes (OATP, for its acronym in English).
Clinical and specific pharmacological data
Alcoholic liver disease
Excessive alcohol consumption causes liver damage through different mechanisms, including oxidative stress, hypoxia, up-regulation of pro-inflammatory cytokines, and metabolic effects that affect various types of liver cells.
Activated Kupffer cells release a variety of potentially harmful substances, including cytokines, reactive oxygen species, and reactive nitrogen species (RNS) that negatively affect hepatocytes and can lead to activation of liver stellate cells.
The response in hepatocytes includes mitochondrial damage (increased mitochondrial aspartate transpartase), relative decrease in hepatic ATP, and impaired control of nitric oxide (NO) -dependent respiration.
An acceleration and spread of these processes leads to increased liver inflammation, cirrhosis, and hepatocellular carcinoma.
Nonalcoholic fatty liver disease
The diagnosis of nonalcoholic fatty liver disease (NAFLD) requires evidence of fatty liver disease (by imaging or histology) and the exclusion of other causes of liver disease that cause steatosis.
Nonalcoholic fatty liver disease is usually asymptomatic, so the diagnosis in most cases follows the incidental finding of abnormal liver enzymes in the laboratory or steatosis on imaging.
If there are abnormal liver function tests, they show only slightly elevated transaminases (alanine transaminase> aspartate transaminase) and / or γ-GT.
However, it has been claimed that up to 80% of patients have normal-range alanine transaminase levels.
With the progression of nonalcoholic fatty liver disease to nonalcoholic steatohepatitis, patients often exhibit metabolic disturbances including decreased insulin sensitivity, hyperlipidemia, and hyperglycemia.
Histologic evaluation remains the only method to distinguish steatosis from advanced forms of nonalcoholic fatty liver disease, ie, nonalcoholic steatohepatitis, and for the evaluation of liver fibrosis.
Furthermore, it has been reported that nonalcoholic fatty liver disease / nonalcoholic steatohepatitis can progress to hepatocellular carcinoma (HCC) also in the absence of apparent cirrhosis.
Data generated in both animal models and human studies provide increasing evidence that the progression of NAFLD is also associated with an altered gut microbiome and impaired physical, chemical, and immune barrier functions of the gut. .
Among others, changes in the enteric microbiome and increased intestinal permeability contribute to an overflow of bacterial metabolites into the liver via the portal vein leading to the progression of NAFLD.
Metabolites in the gut microbiome include short-chain fatty acids, the main products of gut microbial fermentation, and ethanol.
While short-chain fatty acids enhance intestinal absorption by activating glucagon-like peptide 2, ethanol causes accumulation of triglycerides in hepatocytes through the production of reactive oxygen species and the initiation of liver inflammation. .
This could provide a second hit to the liver that had already accumulated fat.
In addition, gut-derived bacterial products stimulate innate immune receptors, namely Toll-like receptors (RTTs), expressed in most liver cells, thus contributing to acute and chronic liver disease through immune activation, that is, the production of cytokines.
In a species of circulus vitiosus, inflammatory changes in the liver appear to contribute to increased intestinal permeability.
While metabolic adaptations occur to compensate for increased liver fat load, mitochondria eventually become dysfunctional with increased generation of reactive oxygen species and decreased activity of the electron transport chain.
Both of which contribute to insulin resistance.
There are no specific data from Legalon on its intestinal effects on NAFLD / NAFLD in animal or patient experiments.
However, several reports indicated different effects on the gut that are worth mentioning.
Therefore, the use of Legalon applied in clinically relevant doses has been shown to have protective effects against trinitrobenzene sulfonic acid (TNBS) -induced colitis in rats.
Inhibition of epirubicin-induced gastrointestinal mucositis in mice and reduction of oxidative and intestinal damage induced by ischemia-reperfusion lesions in rats.
It was also found to be effective against cold restriction stress induced gastric ulcers in rats at a dose of 50 mg / kg per os.
Liver fibrosis and cirrhosis
In response to acute liver injury, fibrosis arises as part of an attempted wound healing response that aims to maintain the integrity and structure of the organ.
However, in chronic liver injury, prolonged fibrosis leads to a progressive process of tissue scarring that ends in remodeling of the liver tissue structure.
Ultimately, liver fibrosis can lead to liver cirrhosis and end-stage liver disease. Furthermore, cirrhosis is the main risk factor for hepatocellular carcinoma.
A recent assessment of mortality from liver cirrhosis led to a global estimate of just over one million deaths in 2010, which was about 2% of all deaths.
The pathophysiology of liver fibrosis involves the generation of reactive oxygen species. Cytochrome P450 2E1 is the main source of reactive oxygen species in hepatocytes.
Activated liver stellate cells, portal fibroblasts, and myofibroblasts of bone marrow origin have been identified as the major collagen-producing cells in injured liver.
These cells are activated by intracellular pathways sensitive to redox and fibrogenic cytokines such as TGF-β1, angiotensin II, and leptin.
The reversibility of advanced liver fibrosis has been documented in patients, prompting researchers to develop antifibrotic drugs.
However, prolonged liver injury will cause irreversible crosslinking of the extracellular matrix leading to indecipherable collagen fibers.
Antioxidants can inhibit liver stellate cell (CHE) activation, protecting hepatocytes and attenuating experimental liver fibrosis.
Other liver injuries
Poisoning with amanita phalloides
Intravenous silibinin continues to be part of the standard treatment for A. phalloides poisoning.
However, the clinical efficacy of any treatment modality is difficult to demonstrate as no randomized controlled clinical trials were reported.
One publication reported on the application of Legalon to a series of 10 Australian patients with possible poisoning and two patients with possible poisoning, respectively.
Despite treatment according to the standard IV regimen, the death rate for silibinin remained high. In addition, two cases of poisoning successfully treated with A. ocreata have been reported.
Legalon has also been applied in the context of the treatment of hyperbilirubinemia in neonatal jaundice.
In a comparative study with 170 infants, the mean duration of phototherapy was significantly reduced from 5.3 ± 0.82 days in the control group to 4.2 ± 0.76 (p = 0.001) days in the group treated with Legalon (3.75 mg / kg of Legalon twice a day).
The increase in serum levels of alanine transaminase and aspartate transaminase also improved in the group treated with Legalon (p = 0.001).
Use as an adjunct to chemotherapy
In a study published in 2010, 50 children with acute lymphocytic leukemia (ALL) were enrolled in a randomized study that evaluated placebo vs. Legalon for the treatment of chemotherapy-associated hepatotoxicity.
There were no significant differences in the frequency of side effects or infections between the groups.
Regarding the degree of liver damage, there were no significant changes in the concentrations of aspartate transaminase, alanine transaminase or total bilirubin on day 28.
However, on day 56, the milk thistle group (5.1 mg / kg / day) had significantly lower aspartate. Serum transaminase levels (p = 0.04).
Furthermore, a retrospective analysis of patients with mild temporary hepatic impairment (PC-MTHF) after chemotherapy showed a faster recovery with Legalon treatment compared to those on standard treatment.
Genetic or transfusion-associated iron overload is a common cause of chronic liver injury, fibrosis, or even cirrhosis.
As standard treatments, the depletion of iron stores by phlebotomy and, in some cases, the application of iron chelators is considered.
Previous studies observed an additional positive effect (eg reduction of serum iron and serum ferritin in 3 of 4 trials) for Legalon.
Furthermore, the role of Legalon in a combination regimen with deferasirox or deferiprone in the treatment of iron overload in beta-thalassemia is currently under investigation in several clinical trials.
Chronic toxicity studies in rodents have confirmed that Legalon has very low toxicity, and at very high doses it significantly reduced the incidence of some spontaneous neoplasms in rodents by far more than the increased incidence.
These data strongly support legalon’s high therapeutic index and reinforce its history of safe medication.
Pharmacokinetic studies showed that:
- The type of liver disease has an important impact on the kinetics of Legalon.
- Doses above 700 mg tid can achieve much higher blood levels than predicted from linear doses / blood levels at lower doses.
- The short half-life of Legalon indicates that at least 3 daily intakes are needed to ensure sustained effective blood levels.
Clinically relevant interactions between legalon and other drugs have not been identified so far.
Of the multitude of pharmacological effects attributed to legalon in recent years, the majority can be attributed to its antioxidant and membrane stabilizing properties.
The available clinical studies related to the application of legalon in toxic hepatological disorders have limitations. Even so, the favorable risk / benefit ratio justifies continuing the use of legalon in these indications.
However, further studies are needed to address optimization of dosing schedules, pharmaceutical drug formulations, and patient selection.
Despite promising experimental data, there have been no recent clinical studies on alcoholic liver disease (excluding cirrhosis).
However, older trials reported a reduction in serum aspartate transaminase levels in response to legalon treatment.
It seems worth remembering that in the alcoholic cirrhosis trials there was no significant reduction in overall mortality and liver-related mortality.
In the rapidly evolving indication for nonalcoholic fatty liver disease / nonalcoholic steatohepatitis, animal and human studies show that legalon can achieve higher levels in the blood compared to healthy controls.
In addition, it can have beneficial effects on the gut in addition to protective effects on the liver.
Several comparative trials have shown some benefits in relation to aspartate transaminase and alanine transaminase levels in patients with nonalcoholic fatty liver disease / nonalcoholic steatohepatitis.
However, most of these studies had methodological limitations.
As noted, additional clinical studies of higher scientific quality looking at long-term application and clinical outcomes are needed to support the evidence for the use of legalon in different types of chronic liver disease.
These studies should also pay greater attention to nutritional and lifestyle covariates, such as smoking, coffee consumption, and physical activity in particular, in the context of nonalcoholic fatty liver disease.
In addition, the available clinical and experimental studies teach us that future clinical trials should focus on long-term observations, as the effects of legalon are unlikely to be acute and dramatic, but rather progressive over time.