Berberine, a bioactive alkaloid isolated from several herbal substances, possesses multiple pharmacological effects, including antimicrobial, antidiabetic, anticancer activities. Meanwhile, berberine undergoes extensive metabolism after oral administration which results in its extremely low plasma exposure. Therefore, it is believed that the metabolites of berberine also contribute a lot to its pharmacological effects. Along these lines, this review covers the metabolism studies of berberine in terms of its metabolic pathways and metabolic organs based on the identified metabolites, and it also covers the pharmacological activities of its active metabolites. In brief, the predominant metabolic pathways of berberine are demethylation, demethylenation, reduction, hydroxylation and subsequent conjugation in vivo. Active metabolites such as columbamine, berberrubine and demethyleneberberine also exhibit similar pharmacological effects by comparison with berberine, such as antioxidant, anti-inflammatory, antitumor, antimicrobial, hepatoprotective, neuroprotective, hypolipidemic and hypoglycemic effects. Overall, berberine together with its metabolites formed the material basis of berberine in vivo.

As a sugar additive, fructose is widely used in processed foods and beverages. Excessive fructose consumption can cause hepatic steatosis and dyslipidemia, leading to the development of metabolic syndrome. Recent research revealed that fructose-induced nonalcoholic fatty liver disease (NAFLD) is related to several pathological processes, including: (1) augmenting lipogenesis; (2) leading to mitochondrial dysfunction; (3) stimulating the activation of inflammatory pathways; and (4) causing insulin resistance. Cellular signaling research indicated that partial factors play significant roles in fructose-induced NAFLD, involving liver X receptor (LXR)α, sterol regulatory element binding protein (SREBP)-1/1c, acetyl-CoA carboxylase (ACC), fatty acid synthase (FAS), stearoyl-CoA desaturase (SCD), peroxisome proliferator–activated receptor α (PPARα), leptin nuclear factor-erythroid 2-related factor 2 (Nrf2), nuclear factor kappa B (NF-κB), tumor necrosis factor α (TNF-α), c-Jun amino terminal kinase (JNK), phosphatidylinositol 3-kinase (PI3K) and adenosine 5′-monophosphate (AMP)-activated protein kinase (AMPK). Until now, a series of natural products have been reported as regulators of NAFLD in vivo and in vitro. This paper reviews the natural products (e.g., curcumin, resveratrol, and (−)-epicatechin) and their mechanisms of ameliorating fructose-induced NAFLD over the past years. Although, as lead compounds, natural products usually have fewer activities compared with synthesized compounds, it will shed light on studies aiming to discover new drugs for NAFLD.

Berberine, a well-known alkaloid, has been proved to possess various pharmacological activities. Previous studies demonstrated that berberine could be extensively metabolized and the metabolites also contributed to its therapeutic effects. However, as for berberine’s metabolites, especially phase II metabolites, pharmacokinetics and excretion studies were rarely reported. The objective of this study was to thoroughly investigate the pharmacokinetic and excretion profiles of berberine and its nine metabolites, namely, berberrubine (M1), demethyleneberberine (M2), jatrorrhizine (M3), jatrorrhizine-3-O-β-D-glucuronide (M4), jatrorrhizine-3-O-sulfate (M5), thalfendine-10-O-β-D-glucuronide (M6), berberrubine-9-O-β-D-glucuronide (M7), demethyleneberberine-2-O-sulfate (M8) and demethyleneberberine-2-O-β-D-glucuronide (M9) in rats. An accurate and reliable LC-MS/MS method was developed and validated for the determination of berberine and its nine metabolites in rat biosamples. Pharmacokinetic profiles of berberine and its nine metabolites were obtained after a single intravenous administration (4.0 mg/kg) and oral administration (48.2, 120 or 240 mg/kg) of berberine in rats. For excretion study, rats were intragastrically administered a single dose of 48.2 mg/kg berberine. Our results showed that berberine could be metabolized rapidly and all the nine metabolites could be detected in vivo. The absolute bioavailability of berberine was 0.37 ± 0.11%. As for the AUC_0–48 h values, phase II metabolites were much higher than those of phase I metabolites, suggesting that phase II metabolites were the major metabolites exist in blood circulation. 18.6% of the berberine was excreted in feces as berberrubine (M1). The total recovery of berberine and its nine metabolites from urine, bile and feces was 41.2%. This is the first systematic study about the pharmacokinetics and excretion of berberine and its nine metabolites, which will be beneficial for both better understanding the clinical effects and further development of berberine.