Metabolism of deltamethrin and cis- and trans-permethrin by human expressed cytochrome P450 and carboxylesterase enzymes

1. The metabolism of the pyrethroids deltamethrin (DLM), cis-permethrin (CPM) and trans-permethrin (TPM) was studied in human expressed cytochrome P450 (CYP) and carboxylesterase (CES) enzymes.

2. DLM, CPM and TPM were metabolised by human CYP2B6 and CYP2C19, with the highest apparent intrinsic clearance (CL_int) values for pyrethroid metabolism being observed with CYP2C19. Other CYP enzymes contributing to the metabolism of one or more of the three pyrethroids were CYP1A2, CYP2C8, CYP2C9*1, CYP2D6*1, CYP3A4 and CYP3A5. None of the pyrethroids were metabolised by CYP2A6, CYP2E1, CYP3A7 or CYP4A11.

3. DLM, CPM and TPM were metabolised by both human CES1 and CES2 enzymes.

4. Apparent CL_int values for pyrethroid metabolism by CYP and CES enzymes were scaled to per gram of adult human liver using abundance values for microsomal CYP enzymes and for CES enzymes in liver microsomes and cytosol. TPM had the highest and CPM the lowest apparent CL_int values for total metabolism (CYP and CES enzymes) per gram of adult human liver.

5. Due to their higher abundance, all three pyrethroids were extensively metabolised by CES enzymes in adult human liver, with CYP enzymes only accounting for 2%, 10% and 1% of total metabolism for DLM, CPM and TPM, respectively.

     

Nitric oxide synthesis in endothelial cytosol: Evidence for a calcium-dependent and a calcium-independent mechanism

Summary Release of nitric oxide (NO) from endothelial cells critically depends on a sustained increase in intracellular free calcium maintained by a transmembrane calcium influx into the cells. Therefore, we studied whether the free cytosolic calcium concentration directly affects the activity of the NO-forming enzyme(s) present in the cytosol from freshly harvested porcine aortic endothelial cells. NO was quantified by activation of a purified soluble guanylate cyclase coincubated with the cytosol. In the presence of 1 mM L-arginine, 0.1 mM NADPH and 0.1 mM EGTA, endothelial cytosol (0.2 mg of cytosolic protein per ml) stimulated the activity of guanylate cyclase 5.0 + 0.5-fold (from 31 + 9 to 153 + 15 nmol cyclic GMP formed per min per mg guanylate cyclase). Calcium chloride increased this stimulation further in a concentration-dependent fashion by up to 136 + 15% (with 2 M free calcium; EC₅₀ 0.3 M). The calcium-dependent and -independent activation of guanylate cyclase was enhanced by superoxide dismutase (0.3 M) and was inhibited by the stereospecifically acting inhibitor of L-arginine-dependent NO formation N^G-nitro-L-arginine (1 mM) and by LY 83583 (1 M), a generator of superoxide anions. Our findings suggest a calcium-dependent and -independent synthesis of NO from L-arginine by native porcine aortic endothelial cells. Send of fprint requests to A. Mülsch, at the above address     

Variable activation of lovastatin by hydrolytic enzymes in human plasma and liver

Lovastatin, widely used to lower cholesterol, is a pro-drug that requires metabolic activation through hydrolysis by carboxyesterases. There appear to be at least three distinct esterases in humans capable of catalysing this reaction, one in plasma and two in the liver.The rate of lovastatin hydroxy acid formation was measured as 15.8 pmol · ml^–1 · min^–1 in plasma, 2.13 pmol · mg^–1 protein · min^–1 in hepatic microsomes and 0.92 pmol · mg^–1 protein · min^–1 in cytosol. The data suggest that on average the three esterases together are capable of activating about 220 nmol (90 g) lovastatin per minute per person, to which the esterases of plasma, liver microsomes and liver cytosol contribute approximately 18, 15 and 67%, respectively.All three esterases showed evidence of inter-individual variability. In one of 17 livers, both cytosolic and microsomal esterase activity was completely missing, while two other liver specimens lacked one esterase.Such variability must be expected to influence the therapeutic efficacy of the drug, and they might be related to its occasional toxicity.     

Metabolism of deltamethrin and cis- and trans-permethrin by rat and human liver microsomes,liver cytosol and plasma preparations

1. The metabolism of deltamethrin (DLM), cis-permethrin (CPM) and trans-permethrin (TPM) was studied in liver microsomes, liver cytosol and plasma from male Sprague–Dawley rats aged 15, 21 and 90 days and from adult humans.

2. DLM and CPM were metabolised by rat hepatic microsomal cytochrome P450 (CYP) enzymes and to a lesser extent by microsomal and cytosolic carboxylesterase (CES) enzymes, whereas TPM was metabolised to a greater extent by CES enzymes.

3. In human liver, DLM and TPM were mainly metabolised by CES enzymes, whereas CPM was metabolised by CYP and CES enzymes.

4. The metabolism of pyrethroids by cytosolic CES enzymes contributes to the overall hepatic clearance of these compounds.

5. DLM, CPM and TPM were metabolised by rat, but not human, plasma CES enzymes.

6. This study demonstrates that the ability of male rats to metabolise DLM, CPM and TPM by hepatic CYP and CES enzymes and plasma CES enzymes increases with age. In all instances, apparent intrinsic clearance values were lower in 15 than in 90?day old rats. As pyrethroid-induced neurotoxicity is due to the parent compound, these results suggest that DLM, CPM and TPM may be more neurotoxic to juvenile than to adult rats.

     

Anti-Soluble Liver Antigen (SLA) Antibodies in Chronic HCV Infection

Hepatitis C infection is associated with autoimmune disorders, such as the production of autoantibodies. Anti-LKM1 and anti-LC1, immunomarkers of type 2 autoimmune hepatitis, have been previously associated with a HCV infection. Anti-Soluble-Liver-Antigen autoantibodies (SLA) are specifically associated with type 1 and type 2 autoimmune hepatitis and more closely related to patients who relapse after steroid therapy. The recent molecular cloning of the soluble liver antigen provides the opportunity to develop more specific tests for the detection of antibodies against it. The aim of this work is to characterize anti-soluble-liver autoantibodies in sera from patients chronically infected by HCV. A recombinant cDNA from activated Jurkat cells coding for the full length tRNP^(Ser)Sec/SLA antigen was obtained. ELISA, Western Blot and immunoprecipitation tests were developed and used to search for linear and conformational epitopes recognized by anti-SLA antibodies in sera from patients chronically infected by HCV. Anti-soluble liver antigen antibodies were found in sera from 10.4% of HCV-infected patients. The prevalence was significantly increased to 27% when anti-LKM1 was also present. Most anti-SLA reactivity was directed against conformational epitopes on the antigen. The means titers by ELISA were lower than those obtained in type 2 AIH. The result of autoantibody isotyping showed a subclass restriction to IgG1 and also IgG4. This study shows the presence of anti-SLA antibodies in approximately 10% of HCV infected patients. The prevalence of SLA autoantibodies in HCV infected patients increases when LKM1 autoantibodies are also present. The relationship between the prevalence of this characteristic autoimmune hepatitis autoantibody and the implication of an autoimmune phenomenon in the liver injury of patients chronically infected by HCV needs further investigation.     

Characteristics of an adenylate cyclase enhancing factor from mouse pancreatic islet cytosol

Summary The role of cytosolic components in the regulation of mouse pancreatic islet adenylate cyclase activity was studied. Addition of mouse islet cytosol (27000 g supernatant of mouse islet sonicate), devoid of adenylate cyclase activity itself, increased adenylate cyclase activity by 93±17% (n = 9) in the 27000 g total particulate fraction of mouse islets. Addition of GTP stimulated adenylate cyclase activity by 91±11% (n = 13) or to the same degree as cytosol. Like GTP, the substance causing the enhancing activity of the cytosol was found to be dialysable, resistant to heat, sensitive to charcoal treatment and alkaline phosphatase and insensitive to digestion with trypsin. However, in contrast to the stimulation by GTP, the stimulation by cytosol was not inhibited by guanosine 5-0-(2-thiodiphosphate), and furthermore, the effects of cytosol and GTP were additive. Neither NAD nor phosphoenolpyruvate stimulated adenylate cyclase activity. The cytosolic factor did not confer sensitivity towards glucose, Ca²⁺ or Ca²⁺-calmodulin on adenylate cyclase. The results demonstrate that mouse pancreatic islets contain a phosphocompound (or several compounds) distinct from GTP and capable of markedly stimulating adenylate cyclase. The identity of the compound and its physiological significance remain to be established.     

Leukotriene B4 12-hydroxydehydrogenase/15-ketoprostaglandinΔ13-reductase (LTB4 12-HD/PGR) responsible for the reduction of a double-bond of the α,β-unsaturated ketone of an aryl propionic acid non-steroidal anti-inflammatory agent CS-670

CS-670 is a non-steroidal anti-inflammatory agent with an α,β-unsaturated ketone structure. It exerts its pharmacological activity after being transformed to the active metabolite (2S,1′R,2′S)-trans-alcohol. Two consecutive reductions are needed for the formation of the active metabolite, reduction of the double-bond of the α,β-unsaturated ketone moiety, followed by reduction of the resulting saturated ketone. The objective of the current study was to identify the enzyme responsible for reduction of the double-bond. An enzyme purified from rat liver cytosol as a single band on sodium dodecylsulphate-polyacrylamide gel electrophoresis (SDS-PAGE) was analysed by a Mascot database search of nano-LC tandem mass spectrometry (MS/MS) data and the enzyme was identified as 2-alkenal reductase (EC 1.3.1.74), which is known as an β-nicotinamide adenine dinucleotide phosphate (NADPH)-dependent alkenal/one oxidoreductase and has a role for leukotriene B₄ 12-hydroxydehydrogenase/15-ketoprostaglandinΔ13-reductase (LTB₄ 12-HD/PGR). The identification was confirmed by cloning LTB₄ 12-HD/PGR cDNA from rat liver, expressing it in Escherichia coli, and characterizing the properties of the enzyme. The identity was further supported by the subcellular localization in cytosol, a cofactor requirement for NADPH, substrate specificity, and substantial inhibition by 15-ketoPGF_2α, benzylideneacetophenone, indomethacin, and quercitrin. In addition to catalysing the biological reduction of eicosanoids, including prostaglandins, leukotrienes, and lipoxins, LTB₄ 12-HD/PGR was also determined to function as a xenobiotic-metabolizing enzyme.     

Clinical significance of autoantibodies in autoimmune hepatitis

The accurate diagnosis and classification of autoimmune hepatitis (AIH) rely upon the detection of characteristic autoantibodies. Positivity for anti-nuclear (ANA) and/or anti-smooth muscle (SMA) autoantibodies defines AIH type 1 (AIH-1), whereas anti-liver kidney microsomal type 1 (anti-LKM1) and/or anti-liver cytosol type 1 (anti-LC1) define AIH type 2 (AIH-2). ANA and SMA, and less commonly anti-LKM1, have also been detected in de-novo autoimmune hepatitis developing after liver transplantation, a condition that may affect patients transplanted for non-autoimmune liver disease. The diagnostic autoantibodies associated with AIH-1 are also detected in the paediatric AIH/sclerosing cholangitis overlap syndrome, referred to as autoimmune sclerosing cholangitis (ASC). ASC, like adult primary sclerosing cholangitis, is often associated with atypical perinuclear anti-neutrophil cytoplasmic autoantibodies (p-ANCA), although p-ANCA are also detected in other autoimmune liver diseases. These associations highlight the necessity for simple and prompt diagnostic autoantibody testing, and the requirement for the accurate interpretation of the results of the tests in the clinical context. Fine-mapping of antigenic autoantibody targets has facilitated the development of rapid molecular assays that have the potential to revolutionise the field if properly standardised and when used in combination with classical immunofluorescence. Despite their diagnostic significance, the pathogenic role of the various autoantibodies and the mechanisms by which they can potentially inflict damage onto the liver cell remain a topic for further research.     

胎肝细胞质液对小鼠IL－2系统的影响

用自制胎肝细胞质液（ＦＬＣ）对小鼠ＩＬ ２系统的影响进行研究，结果表明ＦＬＣ对正常小鼠体内Ｔ淋巴细胞有诱生ＩＬ ２的作用（Ｐ＜００５），可明显促进淋巴细胞ｍＩＬ ２Ｒ的表达（Ｐ＜００１）和血清ｓＩＬ ２Ｒ水平的降低（Ｐ＜００５）；对环磷酰胺免疫抑制后小鼠的ＩＬ ２诱生、ｍＩＬ ２Ｒ表达均有所改善（分别为Ｐ＜００５，Ｐ＜００１），提示ＦＬＣ对小鼠Ｔ淋巴细胞有一定程度活化和诱导ＩＬ ２产生的作用，可降低小鼠血清ｓＩＬ ２Ｒ水平。     

A novel soluble brain-specific protein (Sy-1) : Identification and partial characterization

A novel brain-specific antigen, called Sy-1, has been identified in whole rat brain hypotonic extracts by means of an antiserum produced in rabbits against the synaptosomal cytosol. Sy-1 is an acidic protein (pI 4.7) present exclusively in a soluble form and it does not carry any sugar moiety. Sy-1 is found only in rat brain and, in a partially identical form, in mouse brain. In rat brain the antigen is more concentrated in the brainstem than in the forebrain and cerebellum. On the basis of immunological, physico-chemical and biological criteria Sy-1 differs from other, already described, brain-specific proteins.