Drug metabolism studies can explore drug toxicity and toxic mechanism of action.

 In drug development, many compounds often die in clinical trials because of the toxicity or safety of their metabolites, among which the active metabolites formed by drug molecules activated by human liver metabolism are more likely to be an important cause of toxicity. 

In vivo or in vitro metabolite analysis of drugs can be used to determine an early stage whether a compound is toxic and suitable for further development, thus minimizing unnecessary losses.

In preclinical drug metabolite analysis and metabolite structure identification to evaluate the safety of a drug metabolite, one can identify an animal species in a routine toxicology test in which adequate exposure levels of that metabolite can be formed, which is comparable to or higher than human exposure, and then study the drug toxicity in that animal species.

Alternatively, if a relevant animal species cannot be identified that forms the metabolite, the metabolite can be synthesized, and further safety evaluations can be conducted by infiltration or direct administration.

For example, a previous study by a group that used the biological activity tracking method combined with the primary rat liver cell model to finally screen out the prenyl flavonoids with substantial hepatotoxicity in Sophora flavescens - matrine (Kur), dihydrogen flavonoid G (SFG), and the in vivo and in vitro metabolism research of matrine, the hepatotoxic component of Sophora flavescens[1]. 

To further investigate the human hepatotoxicity parameters of hepatotoxic compounds and their metabolic toxicity mechanisms and to provide an experimental basis for the safety and quality control of bitter ginseng-containing formulations, the investigators first used semi-preparative HPLC to prepare the monomeric compounds and then performed human hepatotoxicity assays after structural identification of the monomeric compounds, and then conducted in vitro metabolism studies of the more abundant kur using rat and human liver microsomes. 

Then, a series of studies were worked to investigate the relationship between metabolism and toxicity and finally to study the toxicokinetics of Kur in rats. It was found that the toxic effects of bitter ginseng alcohol extract on rats were mainly in the liver, with no significant damage to the heart and kidney. The liver damage of bitter ginseng alcohol extract in rats was manifested by elevated transaminases and steatosis of liver tissue.

In drug metabolite analysis, metabolic characterization can be accomplished by in vitro and in vivo test methods. In vitro tests can be performed using liver microsomes, liver sections, and hepatocytes from different animals and humans. Medicilon Pharmacokinetics Lab has passed the GLP certification by NMPA, Following the guiding principles of ICH, NMPA, and FDA. The lab offers in vivo and in vitro pharmacokinetic tests according to the needs of our clients and provides them with complete sets of pharmacokinetic evaluation and optimization services.

Some researchers have researched the toxic substance basis and poisoning mechanism of the traditional Chinese medicine Fructus xanthii[2]. The researchers first used acute toxicity experiments in mice to clarify that the target organ of Fructus xanthii toxic damage is mainly the liver, used in vitro hepatocyte experiments to screen the toxic components, and conducted the overall animal toxicity evaluation of the target components; based on this, using metabolomics technology, the toxicological mechanism of Fructus xanthii was explored to provide a scientific basis for the rational application of Fructus xanthii. 

It was found that the target organ of the toxic effect of Fructus xanthii was mainly the liver, and the shellac enzymes were the main harmful components, and their poisonous products were related to the lipid peroxidation damage caused by Fructus xanthii in the liver, and the mechanism affecting the energy metabolism of hepatocytes.

The hepatic cytochrome P450 enzyme system (CYPs) is responsible for more than 90% human drug metabolism.

Therefore, in vitro metabolic reaction systems (e.g., liver microsomes) to obtain hepatic pharmacokinetic parameters to predict or extrapolate drug biotransformation behavior in vivo has become an essential element in current new drug development. Several researchers have also conducted studies on the metabolism of drugs in cytochrome P450 enzymes and the analysis of their metabolites.

Based on the fact that cytochrome P450 enzymes(CYP enzymes) play an essential role in the attenuation of drugs and mediate the mechanism of attenuation of many toxic herbal medicines, the investigators

mainly conducted the CYP enzyme metabolism of Gelsemine and its toxicity correlation by using three harmful components (Kelkinin (KOU), Kelkinin A (GA), and Humenine A (HMT)) in Kelkinin, aiming to provide a reference for revealing the scientific connotation of Kelkinin attenuation and improving drug efficacy and safety[3]. 

This study demonstrated for the first time that the metabolic pathways of Gelsemine in human and murine liver particles are mainly demethylation, dehydrogenation, hydroxylation, dimethyl dehydrogenation, and oxidation, and the most critical metabolic enzyme isoforms involved are CYP3A4/5. It was also demonstrated that the toxicity of Gelsemine was significantly reduced after metabolism by CYP3A4/5. 

The results of this study can provide a theoretical basis for Gelsemine's toxicity warning and clinical safety application.

After entering the human body, drugs may be metabolized and activated to produce toxicity, so drug metabolism studies are needed to explore the toxicity of drugs and their toxic mechanisms of action.

In short, drug metabolism studies are throughout the new drug development chain and play a significant role in drug discovery and development.

[1] In vitro and in vivo metabolism study of bitter ginseng hepatotoxic components of bitter ginseng ketone [J].

[2] Study the toxic substance basis and poisoning mechanism of the Chinese herbal medicine Fructus xanthii[J].

[3] Study the metabolism of P450 enzymes and their toxicity relevance of Gelsemine [J].