Is Silymarin Hepatoprotective in Alcoholic Liver Disease?

Abstract

Silymarin is the main active complex extracted from the milk thistle (Silybum marianum L.), an annual plant that has been used by herbalists since antiquity. Pharmacologic evidence from numerous studies in the last few decades supports potential therapeutic benefits of milk thistle and silymarin in liver necroinflammation and fibrogenesis given its free-radical scavenging, antioxidant, anti-inflammatory, immunomodulatory, iron chelating, and membrane stabilizing properties as well as its purported ability to selectively stimulate hepatocyte proliferation. Current knowledge of the role of oxidative stress in the pathogenesis of alcohol liver disease (ALD), suggests that silymarin’s pharmacological properties may have potential therapeutic value in ALD. Since the 1960s, milk thistle products have been prescribed by physicians in Europe for ALD as well as other liver-related conditions. Several European manufacturers have developed pharmaceutical grade milk thistle products standardized to a higher content of silymarin (70%–80%) than in non-standardized herbal preparations (≈5%), mainly because of silymarin’s poor oral bioavailability. As part of pharmaceutical development, several clinical studies have been conducted in Europe to assess the efficacy of oral milk thistle products in liver diseases of diverse etiology. Recently, a systematic review sponsored by the Agency for Healthcare Research and Quality (AHRQ) selectively analyzed 16 prospective randomized placebo-controlled European trials in terms of the efficacy and safety of milk thistle products in alcohol, viral or toxin-related liver diseases. Six of the selected trials evaluated ALD using various doses of Legalon, a milk thistle product standardized to 80% silymarin manufactured in by Madhaus AG (Cologne, Germany). The reviewers found these trials difficult to interpret due to unclear and variable definitions of disease chronicity and severity. Some of the studies included liver diseases of various etiologies. None of the studies stratified patients by presence or absence of ongoing alcohol consumption or chronic hepatitis C infection as potential confounders. All 6 studies on silymarin and ALD found at least 1 biochemical parameter of liver function or liver histology that improved significantly with silymarin compared with placebo. The parameters that were significant varied from study to study. Importantly, 1 of the 6 studies showed significant improvement in overall survival among cirrhotic patients treated with silymarin, a second study showed a non-statistical trend toward improved survival and yet another study showed no improvement in overall survival in silymarin compared with placebo. No relationship was found between duration of therapy and improvement in liver function, although 3 of the reports did not clearly describe the duration of therapy. The previous data on silymarin in ALD along with current evidence on the potential benefit of antioxidant therapies in ALD, justify a more systematic assessment of silymarin in ALD. Furthermore, an evidence-based approach to the evaluation of the safety and efficacy is crucial because at least 1 multicenter survey has shown that milk thistle is the most frequently used supplement in patients with liver disease. In 2001, milk thistle products ranked 12th in the list of supplements sold in the US surpassing 7 million dollars.