Role of CYP3A in regulating hepatic clearance and hepatotoxicity of triptolide in rat liver microsomes and sandwich-cultured hepatocytes

Triptolide (TP) is an active component of Tripterygium wilfordii Hook. F and widely used to treat autoimmune and inflammatory diseases. It has been demonstrated that cytochrome P450 (CYP) are involved in the metabolism of TP. However, the underlying mechanisms of TP-induced toxicity mediated by hepatic CYP have not been well delineated. In this study, rat liver microsomes (RLM) and sandwich-cultured rat hepatocytes (SCRH) were used to identify the mechanism involving the CYP3A inhibition by TP and to evaluate TP-induced liver damage after CYP3A modulation by the known inhibitor, ketoconazole, and the known inducer, dexamethasone. The results showed that TP itself had a time- and concentration-dependent inhibitory effect on CYP3A. When the CYP3A inhibitor and inducer were added, the enzyme activity and hepatotoxicity changed significantly. The enzyme inducer increased CYP3A activity and decreased the metabolic half life (t_1/2) of TP when compared to the control group, while the enzyme inhibitor had an opposite effect. Our findings reveal that TP is a weak CYP3A inhibitor involving the time-dependent inhibition mechanism. The induction or inhibition of CYP3A played an important role in TP-induced hepatotoxicity. Clinicians should be aware of the metabolic characteristics of TP to maximize therapeutic efficacy and reduce TP-induced toxicity.     

Characterization of triptolide hydroxylation by cytochrome P450 in human and rat liver microsomes

Triptolide, the primary active component of a traditional Chinese medicine Tripterygium wilfordii Hook F, has a wide range of pharmacological activities. In the present study, the metabolism of triptolide by cytochrome P450s was investigated in human and rat liver microsomes. Triptolide was converted to four metabolites (M-1, M-2, M-3, and M-4) in rat liver microsomes and three (M-2, M-3, and M-4) in human liver microsomes. All the products were identified as mono-hydroxylated triptolides by liquid chromatography-mass spectrometry (LC-MS). The studies with chemical selective inhibitors, complementary DNA-expressed human cytochrome P450s, correlation analysis, and enzyme kinetics were also conducted. The results demonstrate that CYP3A4 and CYP2C19 could be involved in the metabolism of triptolide in human liver, and that CYP3A4 was the primary isoform responsible for its hydroxylation.     

Transport proteins and intestinal metabolism: P-glycoprotein and cytochrome P4503A

Although traditionally the liver was considered the main site of pharmacokinetic drug interactions, this view has been reexamined in light of the finding that cytochrome P4503A4 (CYP3A) enzymes are expressed at high levels in mature villus tip enterocytes. Because of their topographic location in small intestinal enterocytes and their overlap in substrates, functional interactions between P-glycoprotein and CYP3A were suggested. Although the functional interaction between CYP3A and P-glycoprotein is not yet completely understood, experimental evidence suggests several mechanisms: (1) CYP3A and P-glycoprotein are coregulated via the orphan nuclear receptor SXR/PXR; (2) drugs are repeatedly taken up and pumped out of the enterocytes by P-glycoprotein, and repeated exposure to CYP3A enzymes increases the probability of a drug being metabolized; (3) P-glycoprotein keeps intracellular drug concentrations within the linear range of CYP3A enzymes; (4) metabolism results in better substrates for P-glycoprotein; and (5) metabolism shifts affinity to other intestinal efflux transporters to avoid competitive interaction of metabolites with P-glycoprotein-mediated efflux of the parent drug.     

Comparative hepatotoxicity and metabolism of N-methylformamide in rats and mice

N-methylformamide (NMF) produced dose-dependent zone 3 haemorrhagic necrosis in mice; the threshold dose was 100–200 mg/kg. In rats a dose of 1000 mg/kg caused hepatic damage in some animals and slight elevations of plasma transaminases. A species difference in susceptibility to NMF-induced hepatotoxicity is clearly indicated. NMF depleted liver non-protein sulphydryl (NPSH) in a dose-dependent manner in mice, but not in rats. Depletion of liver glutathione by buthionine sulphoximine or diethylmaleate potentiated the hepatotoxicity of NMF in mice. [¹⁴C]-methyl NMF was metabolised by mice and rats and a number of urinary metabolites including an N-acetylcysteine conjugate, methylamine and N-hydroxymethylformamide were detected. There were no qualitative differences in the metabolites between rats and mice but mice metabolised NMF much faster and more extensively than rats.     

Developmental toxicity of 4-ring polycyclic aromatic hydrocarbons in zebrafish is differentially dependent on AH receptor isoforms and hepatic cytochrome P4501A metabolism

Polycyclic aromatic hydrocarbons (PAHs) derived from fossil fuels are ubiquitous contaminants and occur in aquatic habitats as highly variable and complex mixtures of compounds containing 2 to 6 rings. For aquatic species, PAHs are generally accepted as acting through either of two modes of action: (1) "dioxin-like" toxicity mediated by activation of the aryl hydrocarbon receptor (AHR), which controls a battery of genes involved in PAH metabolism, such as cytochrome P4501A (CYP1A) and (2) "nonpolar narcosis", in which tissue uptake is dependent solely on hydrophobicity and toxicity is mediated through non-specific partitioning into lipid bilayers. As part of a systematic analysis of mechanisms of PAH developmental toxicity in zebrafish, we show here that three tetracyclic PAHs (pyrene, chrysene, and benz[a]anthracene) activate the AHR pathway tissue-specifically to induce distinct patterns of CYP1A expression. Using morpholino knockdown of ahr1a, ahr2, and cyp1a, we show that distinct embryolarval syndromes induced by exposure to two of these compounds are differentially dependent on tissue-specific activation of AHR isoforms or metabolism by CYP1A. Exposure of embryos with and without circulation (silent heart morphants) resulted in dramatically different patterns of CYP1A induction, with circulation required to deliver some compounds to internal tissues. Therefore, biological effects of PAHs cannot be predicted simply by quantitative measures of AHR activity or a compound's hydrophobicity. These results indicate that current models of PAH toxicity in fish are greatly oversimplified and that individual PAHs are pharmacologically active compounds with distinct and specific cellular targets.     

红酒多酚对细胞色素P4503A4介导的硝苯地平代谢的影响

目的体外研究红酒多酚成分对细胞色素P4503A4(CYP3A4)介导的硝苯地平代谢的影响。方法将红酒多酚、人肝微粒体及探针底物睾酮孵育后,用高效液相色谱法测定代谢产物6β-羟基睾酮的生成量,用来考察红酒多酚对CYP3A4抑制的浓度依赖性。将不同浓度红酒多酚、人肝微粒体与硝苯地平孵育,测定硝苯地平的减少率并计算IC₅₀值。在不同浓度硝苯地平存在下,绘制米氏曲线,得到红酒多酚存在时硝苯地平的代谢清除率CL_红酒(K_m-红酒/V_max-红酒),对比空白组,考察红酒多酚对硝苯地平代谢的影响。结果红酒多酚对CYP3A4存在明显的浓度依赖抑制效应(IC₅₀=18.29%)。在以硝苯地平为底物时,IC₅₀为25.04%。红酒多酚对硝苯地平的代谢清除率CL_红酒为14μL·min^-1·mg^-1,显著低于空白组(640μL·min^-1·mg^-1)。结论红酒多酚可通过抑制CYP3A4的活性,减少其对硝苯地平的代谢,具有诱导食物-药物不良反应的风险。     

雷公藤内酯醇对哮喘豚鼠血浆和肺组织内皮素1的影响

目的探讨雷公藤内酯醇(TP)干预对哮喘脉鼠血浆和肺组织中内皮素1(ET—1)水平的影响。方法42只脉鼠随机分为对照组(C)6只、哮喘组(A)18只，干预组(T)18只。后两组依次分为4小时组(A4、T4)、8小时组(A8、T8)及慢性组(A2w、T2w)，每组6只。建立哮喘模型，放免法测定血浆和肺组织ET—1。结果A4、T4、A8组肺组织ET—1显高于血浆，C、T2w组血浆ET—1显高于肺组织。较C组，A4、T4、A8、T8、A2w组肺组织及A8、T8组血浆ET—1显增加。各干预组肺组织ET—1显低于哮喘组。结论推测抑制肺组织ET—1的合成与分泌及其生物学效应等，可能是雷公藤治疗哮喘的机制之一。     

Identification of cytochrome P4503A as the major subfamily responsible for the metabolism of roquinimex in man

1. Roquinimex, a novel immunomodulator, is metabolized in liver microsomes from mouse and rat via cytochrome P450s to four hydroxylated and two demethylated metabolites (R1-6). The study investigated which cytochrome P450 enzyme(s) is responsible for the metabolism of roquinimex in man. 2. Enzyme kinetic analysis demonstrated an apparent Km = 1.28-7.00 mM and Vmax = 50-159 pmol x mg(-1) microsomal protein x min(-1) for the primary metabolites in human liver microsomes. The sum of Cl(int) for the primary pathways was 0.167 microl x mg(-1) microsomal protein x min(-1). 3. A correlation between the formation rate of R1-6 and 6beta-hydroxylation of testosterone was obtained within a panel of liver microsomes from 11 individuals (r2 = 0.72-0.97). Furthermore, significant inhibition (>90%) of roquinimex primary metabolism was demonstrated by ketoconazole and troleandomycin, specific inhibitors of CYP3A4 as well as with anti-CYP3A4 antibodies. Moreover, a similar metabolite pattern was produced from roquinimex by incubation with cDNA-expressed CYP3A4 as by human liver microsomes. 4. In conclusion, these data indicate a major role for CYP3A4 in the formation of roquinimex primary metabolites in human liver microsomes.     

Identification of cytochrome P4503A as the major subfamily responsible for the metabolism of roquinimex in man

1. Roquinimex, a novel immunomodulator, is metabolized in liver microsomes from mouse and rat via cytochrome P450s to four hydroxylated and two demethylated metabolites (R1?6). The study investigated which cytochrome P450 enzyme(s) is responsible for the metabolism of roquinimex in man. 2. Enzyme kinetic analysis demonstrated an apparent K_m = 1.28-7.00?mm and V_max = 50-159 pmol·mg^?1 microsomal protein·min^?1 for the primary metabolites in human liver microsomes. The sum of Cl_int for the primary pathways was 0.167 μl·mg^?1 microsomal protein·min^?1. 3. A correlation between the formation rate of R1-6 and 6β-hydroxylation of testosterone was obtained within a panel of liver microsomes from 11 individuals (r² = 0.72-0.97). Furthermore, significant inhibition (<90%) of roquinimex primary metabolism was demonstrated by ketoconazole and troleandomycin, specific inhibitors of CYP3A4 as well as with anti-CYP3A4 antibodies. Moreover, a similar metabolite pattern was produced from roquinimex by incubation with cDNA-expressed CYP3A4 as by human liver microsomes. 4. In conclusion, these data indicate a major role for CYP3A4 in the formation of roquinimex primary metabolites in human liver microsomes.     

Protein expression of kidney and liver bilitranslocase in rats exposed to mercuric chloride—A potential tissular biomarker of toxicity

Bilitranslocase (BTL) is a plasma membrane carrier that transports organic anions of physiological and pharmacological interest. It is expressed in basolateral plasma membrane of kidney and liver. BTL has been recently described as a marker of transition from normal tissue to its neoplastic transformation in human kidney. Inorganic mercury is a major environmental contaminant that produces many toxic effects. Previous reports have described an interaction between BTL and mercuric ions. This study was designed to evaluate the renal and hepatic expression of BTL in rats exposed to a nephrotoxic and hepatotoxic dose of HgCl₂. Male rats were treated with a single injection of HgCl₂ at a dose of 4 mg/kg body wt, i.p. (HgCl₂ group). Control rats received the vehicle alone (Control group). Studies were carried out 18 h after injection. Afterwards, the kidneys and livers were excised and processed for histopathological studies or immunoblot (homogenates and crude membranes) techniques. In rats treated with HgCl₂, immunoblotting showed a significant decrease in the abundance of BTL in homogenates and plasma membranes from kidney and liver. BTL decrease of expression might reflect the grade of damage in renal tubule cells and in hepatocytes. Thus, BTL might be postulated as a new biomarker of tissue toxicity induced by mercury.     

Therapeutic efficacy of Picroliv in chronic cadmium toxicity

Cadmium (Cd), an industrial and environmental pollutant, is toxic to several tissues, most notably causing hepatotoxicity on acute administration and nephrotoxicity following chronic exposure. The therapeutic efficacy of Picroliv – a standardized fraction of Picrorhiza kurroa, was investigated in male rats treated with Cd as CdCl₂ (0.5 mg/kg, sc) 5 days/week for 24 weeks and Picroliv at two doses (6 and 12 mg/kg, p.o.) was given during the last 4 weeks.     

TM208在大鼠肝微粒体中代谢产物与细胞色素P450亚型代谢酶鉴别研究

在大鼠肝微粒体的体外代谢中研究作用于TM208的细胞色素P450亚型代谢酶。以不含细胞色素P450化学抑制剂的样品为对照，研究不同细胞色素P450亚型选择性化学抑制剂对TM208代谢转化率的影响。CYP2D和CYP2B的选择性抑制剂对TM208的代谢表现出浓度依赖性较强抑制作用，CYP1A的选择性抑制剂对TM208的代谢表现出一定抑制作用。CYP3A的选择性抑制剂对TM208的代谢没有表现出明显的抑制作用。TM208在人鼠肝微粒体体外代谢中主要通过CYP2D和CYP2B两种细胞色素P450亚型代谢酶参与代谢。     

Acute and subacute toxicity studies on triptolide and triptolide-loaded polymeric micelles following intravenous administration in rodents

Except its anti-tumour effects, triptolide (TP) also shows multiple pharmacological side activities, such as immune-suppressive and male anti-fertility. To increase the therapeutic index of TP, a novel polymeric micelle system containing TP (TP-PM) has been developed to treat tumour. Our previous studies have demonstrated the good anti-tumour efficacy of TP-PM. This paper investigated the acute toxicity in mice and subacute toxicity in rats of TP-PM and TP. Results demonstrated that the LD₅₀ for TP-PM and TP administered intravenously were 1.06 mg/kg and 0.83 mg/kg in mice, respectively. In subacute toxicity study, TP-PM and TP were administered intravenously at the dose levels of 0.1 mg/kg and 0.3 mg/kg for 14 d. Compared to the control, there was significant decrease in the serum AST activities, the testis ACP activities, thymus index, testis index, and significant increase in spleen index, and obvious histopathological changes in rats treated with TP, however, the toxicities of TP-PM on liver, kidney, testis and spleen are slighter than TP. Compared to TP, TP-PM significantly increased the ACP activity of the testis and decreased the MDA level in serum. So, the polymeric micelles may be a novel drug delivery carrier of TP for reducing the toxicities of TP.     

Dendritic cell combination therapy reduces the toxicity of triptolide and ameliorates colitis in murine models

Triptolide (TP) exerts a promising effect in the treatment of ulcerative colitis (UC). However, its toxicity seriously hinders its application in the clinic. Previous studies indicated that dendritic cells (DCs) are the main target through which TP exerts its immunoregulatory effect. Thus, we designed an approach to target DCs in vitro to avoid the direct exposure of organs to TP. Our results revealed that DCs pretreated with TP (DCTP) exerted satisfactory therapeutic effects in mice with colitis, resulting in improved colonic inflammation and alleviated local lesion damage. In addition, no obvious toxicity was observed. DCTP also reshaped the immune milieu by decreasing CD4⁺ T cell numbers and increasing regulatory T cell numbers in the spleen, mesenteric lymph nodes, peripheral blood and colon; these effects were further confirmed in vitro. Downregulation of CD80/86, ICAM-1, MHCI, TLR2/4, TNF-α, and IL-6 expression and upregulation of programmed cell death ligand 1 (PDL1) and IL-10 expression were observed, indicating that DCs were converted into tolerogenic DCs. In conclusion, DCTP can effectively reduce toxicity and alleviate colonic inflammation and local lesion damage in mice with colitis. The immune mechanism underlying the effects of DCTP included the conversion of DCs into tolerogenic DCs and the alteration of T cell differentiation to produce immunoinhibitory rather than immunostimulatory T cells.     

Hesperidin alleviates acetaminophen induced toxicity in Wistar rats by abrogation of oxidative stress, apoptosis and inflammation

Acetaminophen (APAP) is a widely used analgesic and antipyretic drug, but at high dose it leads to undesirable side effects, such as hepatotoxicity and nephrotoxicity. The present study demonstrates the comparative hepatoprotective and nephroprotective activity of hesperidin (HD), a naturally occurring bioflavonoid against APAP induced toxicity. APAP induces hepatotoxicity and nephrotoxicity as was evident by abnormal deviation in the levels of antioxidant enzymes. Moreover, APAP induced renal damage by inducing apoptotic death and inflammation in renal tubular cells, manifested by an increase in the expression of caspase-3, caspase-9, NFkB, iNOS, Kim-1 and decrease in Bcl-2 expression. These results were further supported by the histopathological examination of kidney. All these features of APAP toxicity were reversed by the co-administration of HD. Therefore, our study favors the view that HD may be a useful modulator in alleviating APAP induced oxidative stress and toxicity.     

Characterization of human cytochrome P450 enzymes involved in the metabolism of cyamemazine

Recombinant human liver microsomal enzymes of the cytochrome P450 family (CYP1A2, CYP2A6, CYP3A4, CYP2B6, CYP2C8, CYP2C9, CYP2C19, CYP2D6, CYP2E1) were used to determine the metabolic fate of the antipsychotic anxiolytic agent cyamemazine. An LC/MS–MS tandem methodology was developed specifically for identifying the presence of cyamemazine and its metabolites in reaction media. All P450 enzymes investigated, with the exception of CYP2A6 and CYP2E1, degraded cyamemazine, albeit to a different extent, with CYP1A2, CYP2C8 and CYP2C19 being the most efficient (>80%). However, in microsomes prepared from native human hepatocytes, only relatively specific competitors (inhibitors and/or substrates) of CYP1A2, CYP2C8, CYP2C9 and CYP3A4 reduced notably the degradation cyamemazine. The main routes of cyamemazine biotransformation are N-mono-demethylation (CYP1A2, CYP3A4 and CYP2C8) and mono-oxidation (either S-oxidized or hydroxylated derivatives which could not be discriminated because characterized by the same mass value) by CYP1A2 and CYP2C9. Secondary metabolic routes yields N,N-di-demethylated and N-demethylated mono-oxidized products. Thus, under in vitro conditions, cyamemazine is extensively degraded by at least four distinct P450 enzymes, into two primary hydrophilic metabolites. These results suggest that cyamemazine detoxification process is unlikely to be significantly impaired by co-administration of therapeutic agents that are substrates of the CYP metabolic system.     

雷公藤多苷治疗糖尿病肾病Ⅲ期疗效分析

目的 观察雷公藤多苷治疗糖尿病肾病(DN)Ⅲ期的疗效.方法 75例2型糖尿病并DNⅢ期患者,完全随机分为观察组(40例)和对照组(35例).观察组予以雷公藤多苷60 mg/d及氯沙坦100 mg/d,对照组给予氯沙坦100 mg/d,总疗程12周.治疗前后进行24h尿微量白蛋白(24 h Alb)、层黏连蛋白(LN)、Ⅳ型胶原(C-Ⅳ)、血浆高敏C反应蛋白(hs-CRP)的定量测定及尿中足细胞计数.结果 治疗后2组24 h Alb、尿中足细胞计数、LN、C-Ⅳ、hs-CRP均明显下降[对照组:(117±30) mg比(173±35) mg,(1.2±0.6)个/ml比(1.7±0.8)个/ml,(127±25) μg比(144±26) μg,(248±25)μg比(274±27) μg,(4.3±1.4) mg/L比(5.0±1.7) mg/L;观察组:(104±20)mg比(169±27) mg,(1.1±0.4)个/ml比(1.8±0.7)个/ml,(125±27)μg比(145±28) μg,(253±74) μg比(282±74) μg,(3.8±1.2) mg/L比(4.9±1.7)mg/L,均P＜0.05],且观察组下降更明显,其中24 h Alb、尿足细胞计数及C-Ⅳ减少差异具有统计学意义(均P＜0.05);2组均无严重不良反应发生.结论 雷公藤多苷可以减少DNⅢ期患者尿微量白蛋白及足细胞的凋亡,炎症因子在DN的发生发展中起重要的作用.     

Metabolism of digoxin and digoxigenin digitoxosides in rat liver microsomes: involvement of cytochrome P4503A

1. The sequential metabolism of digoxin (Dg3) to digoxigenin bis-digitoxoside (Dg2), digoxigenin mono-digitoxoside (Dg1) and digoxigenin (Dg0) was investigated in rat liver microsomes. 2. Kinetic studies produced results consistent with a single enzyme mechanism describing the successive oxidative cleavages. Formation of Dg2 was catalysed with mean (+/-SD) Km and Vmax of 125 +/- 22 microM and 362 +/- 37 pmol/min/mg protein, respectively. The corresponding values for the formation of Dg1 were 61 +/- 5 microM and 7 +/-1 pmol/min/mg protein. Dg0 formation was catalysed with the apparent values of 30 +/- 9 microM and 310 +/- 30 pmol/min/mg protein. 3. Chemical inhibition of cytochrome P450 (CYP) 3A subfamily with ketoconazole and triacetyoleandomycin decreased the formation of Dg2 and Dg1 by up to 90%. Antibodies specific to rat CYP3A2 lowered the rate of oxidative cleavage of Dg3 and Dg2 by up to 85%. Inhibition of CYP2E1, CYP2C subfamily and CYP1A2 by chemical and immuno-inhibition did not affect initial rates of metabolism of Dg3 and Dg2. In contrast, Dg1 metabolism was not affected by triacetyloleandomycin as well as by antibodies to CYP3A2, CYP2C11, CYP2E1, CYP2B1/2B2 and CYP1A2. It was however inhibited by >80% by gestodene and 17alpha-ethynylestradiol (selective inhibitors of human CYP3A). 4. Collectively, these data support the involvement of CYP3A in the cleavage of Dg3 and Dg2 in rat liver microsomes. The enzyme-metabolizing Dg1 remains to be identified.     

Identification of the rat liver cytochrome P450 enzymes involved in the metabolism of the calcium channel blocker dipfluzine hydrochloride

This study aimed to identify the specific cytochrome P450 (CYP450) enzymes involved in the metabolism of dipfluzine hydrochloride using the combination of a chemical inhibition study, a correlation analysis and a panel of recombinant rat CYP450 enzymes. The incubation of Dip with rat liver microsomes yielded four metabolites, which were identified by liquid chromatography-coupled tandem mass spectrometry (LC/MS/MS). The results from the assays involving eight selective inhibitors indicated that CYP3A and CYP2A1 contributed most to the metabolism of Dip, followed by CYP2C11, CYP2E1 and CYP1A2; however, CYP2B1, CYP2C6 and CYP2D1 did not contribute to the formation of the metabolites. The results of the correlation analysis and the assays involving the recombinant CYP450 enzymes further confirmed the above results and concluded that CYP3A2 contributed more than CYP3A1. The results will be valuable in understanding drug–drug interactions when Dip is coadministered with other drugs.     

体外观察雷公藤内酯醇对乳腺癌细胞MCF-7增殖及凋亡的影响

目的:探讨雷公藤内酯醇(triptolide,TP)对人乳腺癌细胞MCF-7增殖及凋亡的影响。方法:MTT法检测不同条件下TP对MCF-7细胞的增殖抑制作用;倒置显微镜观察TP对MCF-7细胞形态学影响;流式细胞仪检测MCF-7细胞的凋亡情况;Caspase检测试剂盒测定Caspase-3,9的变化。结果:TP以剂量及时间依赖性方式明显抑制MCF-7细胞的增殖;TP作用MCF-7细胞后,细胞出现明显的形态学改变(形态不规则、脱落,细胞碎片等)。流式细胞仪检测5μg/mL的TP明显诱导MCF-7细胞凋亡;Caspase-3,9表达水平明显升高,和对照组相比差异有统计学意义(P<0.05)。结论:TP可能通过线粒体通路诱导MCF-7细胞凋亡而发挥其抑制作用。