Mechanism of PA-induced hepatotoxicity
PA is widely distributed in various plant groups in nature. According to statistics, about 3% of flowering plants (about 6,000 species in total) contain PA, mainly distributed in Lithaceae, Compositae, Leguminosae, Orchidaceae, etc. Most PAs are formed by the condensation of two parts, an amino alcohol with a double-fused pyrrolidine ring (crack base) and an organic acid (crack acid). PA with a double bond at the 1, 2 position of the double-fused pyrrolidine ring is hepatotoxic, such as lilybase and senilin. So far, more than 120 hepatotoxic PAs have been isolated from plants, and it is one of the most important plant hepatotoxic components currently known [2|.
After ingesting Chinese herbal medicines containing PA, pyrrole alkaloids can be metabolized in the liver through two metabolic pathways: one is to form N monoxide through a mixed-function oxidase system, and the other is to form dehydrogenation through cytochrome P450 dehydrogenation. Alkaloids or pyrroles. PA itself and its conventional hydrolysis products are not toxic to the body, but when they reach the liver. Under the catalysis of cytochrome P450, it is first oxidized to unstable dehydropyrrolidine alkaloid (DHP), which can be further hydrolyzed to dehydrogenase (DHN). DHP and DHN have strong electrophilicity and can combine with macromolecules in the liver such as DNA/RNA to affect protein synthesis and cell division. The two can react with glutathione (GSH) or cysteine to form Less toxic or non-toxic products. When GSH content is reduced, the formation of toxic substances increases, resulting in cell damage . Hepatocytes in zone III of the hepatic lobule are rich in cytochrome P450, but the content of GSH is low. Cells are vulnerable to damage from toxic substances [H]. Some studies have found that monocrotaline, which belongs to the PA class, is metabolized by cytochrome P450 in the liver to the alkylating agent dehydro monocrotaline, which inhibits the activity of NADH dehydrogenase in the respiratory chain complex I, thereby causing animal and human inflammation. Liver injury, the mechanism may be related to the conformational change of respiratory chain complex I caused by the modification of cysteine sulfhydryl by metabolites.
Research status of experimental detection methods for PA
At present, the existing methods for detecting the hepatotoxicity of Chinese herbal medicines containing PA include in vitro and in vivo methods. The in vitro approach is to extract total alkaloids from suspected toxic herbs, and then use liquid chromatography-mass spectrometry (HPLC/MS) and other chromatographic analysis methods to determine whether they contain PA components, in order to provide an indirect diagnostic basis for the diagnosis of HVOD  ]. The in vivo approach is to detect the patient’s blood or urine and other biological samples, and apply chromatographic analysis methods to analyze and identify the PA components and their content in the blood samples.
During the analysis of PA metabolism in vivo, it was found that DHP and DHN generated by liver cytochrome P450 metabolism also entered the blood circulation and combined with the sulfhydryl group of cysteine residues in plasma proteins. Since the in vivo half-life of PA metabolites can be significantly prolonged after binding to plasma proteins, if the specific changes in plasma proteins after the interaction with PA metabolites can be found, it may be used as an ideal detection marker for detecting the hepatotoxicity of PA-containing herbs. Recent studies have reported [1 5|, after treating horse blood with PA active ingredient monocrotaline in vitro, panorama analysis by proteomics method found that a high molecular weight protein polymer appeared in horse serum protein spectrum; The main components of fibrinogen, serum albumin and transferrin were confirmed to be fibrinogen, serum albumin and transferrin, which cross-combined with PA metabolites to form high molecular weight protein polymers. Detection of this high-molecular-weight protein polymer present in blood may serve as a marker for horses eating PA-containing plants. Therefore, it is believed that in rodents and human-related diseases, PA can also change the binding state of plasma proteins. Using technical means such as proteomic panoramic analysis, it is possible to find its specific structural changes, in order to detect PA. In vivo biochemical markers.