Structure of the processive rubber oxygenase RoxA from Xanthomonas sp

Rubber oxygenase A (RoxA) is one of only two known enzymes able to catalyze the oxidative cleavage of latex for biodegradation. RoxA acts as a processive dioxygenase to yield the predominant product 12-oxo-4,8-dimethyl-trideca-4,8-diene-1-al (ODTD), a tri-isoprene unit. Here we present a structural analysis of RoxA from Xanthomonas sp. strain 35Y at a resolution of 1.8 Å. The enzyme is a 75-kDa diheme c-type cytochrome with an unusually low degree of secondary structure. Analysis of the heme group arrangement and peptide chain topology of RoxA confirmed a distant kinship with diheme peroxidases of the CcpA family, but the proteins are functionally distinct, and the extracellular RoxA has evolved to have twice the molecular mass by successively accumulating extensions of peripheral loops. RoxA incorporates both oxygen atoms of its cosubstrate dioxygen into the rubber cleavage product ODTD, and we show that RoxA is isolated with O₂ stably bound to the active site heme iron. Activation and cleavage of O₂ require binding of polyisoprene, and thus the substrate needs to use hydrophobic access channels to reach the deeply buried active site of RoxA. The location and nature of these channels support a processive mechanism of latex cleavage.     

Sex Differences in the Behavioral,Molecular, and Structural Effects of Ketamine Treatment in Depression

Major depressive disorder (MDD) is a common psychiatric illness that manifests in sex-influenced ways. Men and women may experience depression differently and also respond to various antidepressant treatments in sex-influenced ways. Ketamine, which is now being used as a rapid-acting antidepressant, is likely the same. To date, the majority of studies investigating treatment outcomes in MDD do not disaggregate the findings in males and females, and this is also true for ketamine. This review aims to highlight that gap by exploring pre-clinical data—at a behavioral, molecular, and structural level—and recent clinical trials. Sex hormones, particularly estrogen and progesterone, influence the response at all levels examined, and sex is therefore a critical factor to examine when looking at ketamine response. Taken together, the data show females are more sensitive to ketamine than males, and it might be possible to monitor the phase of the menstrual cycle to mitigate some risks associated with the use of ketamine for females with MDD. Based on the studies reviewed in this article, we suggest that ketamine should be administered adhering to sex-specific considerations.     

瑞舒伐他汀和阿托伐他汀对氯吡格雷抗血小板活性的影响

目的观察瑞舒伐他汀和阿托伐他汀对氯吡格雷抗血小板活性的影响。方法选择60例冠心病患者接受阿司匹林100mg/d、氯吡格雷75 mg/d及低分子肝素5000 U/12 h治疗,5 d后随机分为阿托伐他汀20mg/d(阿托伐他汀组,30例)和瑞舒伐他汀10 mg/d(瑞舒伐他汀组,30例)。在服用氯吡格雷之前(基线值)、加用他汀类药物之前及服用他汀类药物3d后,用全血阻抗法分别测定不同浓度二磷酸腺苷(5、10、20μmol/L)诱导的血小板聚集率。结果与基线值比较,服用氯吡格雷5 d后和加服他汀类药物治疗3 d后,2组患者血小板聚集率明显降低,差异有统计学意义(P<0.05);与治疗前比较,阿托伐他汀组患者血小板聚集率有所升高,而瑞舒伐他汀组患者血小板聚集率有所下降,但差异无统计学意义(P>0.05)。结论经细胞色素3A4途径代谢的阿托伐他汀及不经细胞色素3A4代谢的瑞舒伐他汀,短期内对氯吡格雷抗血小板活性无影响。     

No effect of CYP450 and P-glycoprotein on hydroxyurea in vitro metabolism

Our objectives were (1) to study the HU metabolism via human cytochromes and (2) to test if HU is a substrate of P-gp. HU metabolism was investigated by determining the appearance of urea and HU decreasing upon incubation with human liver microsomes. Quantification was determined using HPLC coupled with UV-detection at 449 nm. Our method was linear between 5 and 1000 μ m , precise (coefficients of variation ranging from 1.7 to 9.9%), accurate (97.7–103.9%). The limit of quantification was 7 μ m . The ATPase activity of human P-gp membranes was determined by measuring inorganic phosphate liberation. HU and urea measurements in microsomes were not different between 0 and 60 min whatever HU concentration used from 30 to 300 μ m . The presence of NADPH in the medium has no effect on HU and urea measurements. In the absence of verapamil, the ATPase activity was unaffected by HU at concentrations of 10, 30, 100 and 300 μ m . HU is unlikely to cause clinically relevant drug interactions with the substrates of these enzymes/transporters. However, it will be necessary to validate these in vitro data in patients with sickle cell anemia to evaluate the impact of genetic polymorphisms of these enzymes in a black population.     

Phenytoin-associated severe hypocalcemia with seizures in a patient with a TSC2-PKD1 contiguous gene syndrome

Abstract

We report the case of an inaugural episode of generalized seizures in a 40-year-old male with a history of chronic kidney disease associated with TSC2-PKD1 contiguous gene syndrome. This patient was under prophylactic treatment of phenytoin since 2 years because of a subarachnoid hemorrhage due to a ruptured cerebral aneurysm. Laboratory results revealed therapeutic range of phenytoin levels, but severe hypocalcemia associated with profound vitamin D deficiency that could not be explained by secondary hyperparathyroidism alone. The interaction of phenytoin on the P-450 cytochromes activity has been demonstrated to accelerate the rate of 25-hydroxivitamin D₃ and 1α,25-dihydroxivitamin D₃ catabolism into inactive metabolites, leading to hypocalcemia. Physicians should be aware of significant phenytoin interactions on vitamin D metabolism which may lead to symptomatic hypocalcemia in patients with chronic kidney disease.     

The effects of 2,2 diethylallylacetamide on hepatic cytochromes in rats and in vitro

The application of 0.15 and 0.3% of diethylallylacetamide (DA) in the drinking water to rats during 10 days increased the relative liver weight, the yield of hepatic microsomes, and cytochromes P-450 and b₅.Single s.c. doses of 400 mg DA per kg reduced cytochrome P-450 concentrations in the hepatic endoplasmic reticulum of rats. This effect was considerably more pronounced in rats pretreated with phenobarbital. The activity of 5-aminolaevulinic acid synthesis in liver mitochondria, and total liver porphyrins increased.In incubations of metabolizing hepatic microsomes from rabbits pretreated with phenobarbital 75% of 0.1 mM DA was degraded after 1 h. The aerobic incubation of 0.1 mM DA with rabbit hepatic microsomes in the presence of NADPH produced 50% destruction of cytochrome P-450 within 1 h. Addition of EDTA revealed that a part of this destruction cannot be explained by accelerated lipid peroxidation.This work was supported by the Deutsche Forschungsgemeinschaft.     

Influence of piecemeal necrosis on the compensatory increase of mitochondrial respiratory enzymes of the tumour-bearing liver: Clinical study of 53 surgical cases

The relationships between histological findings, adaptively increased cytochrome a(+a3) levels in chronic liver disease and complications after hepatectomy were studied in order to clarify the mechanism of mitochondrial derangement. The liver specimens of 53 hepatectomized patients were randomly evaluated by three independent hepatopathologists and were compared with cytochrome a(+a3) levels in the biopsied liver, the extent of operation and postoperative complications. The cytochrome a(+a3) concentrations did not show any significant difference between cases of chronic hepatitis and liver cirrhosis nor groups classified by regeneration. Severity of piecemeal necrosis was categorized into three groups: group A--minimal (n = 20); group B--moderate (n = 19); and group C--severe (n = 14). There were significant differences (P less than 0.01) in cytochrome a(+a3) concentrations between the groups (A: 99 +/- 9; B: 135 +/- 6; C: 155 +/- 10 pmol/mg of mitochondrial protein). Extensive hepatectomy, involving segmentectomy or more, was frequently complicated (four of nine, 44.4%) in group C, whereas there were few complications (two of 16, 12.5%) in group A cases in which extensive hepatectomy was performed. Evidence will be presented which will show that deranged liver function, as indicated by cytochrome a(+a3) levels, is closely correlated with piecemeal necrosis. This may be attributed to the damage of periportal hepatocytes which are the main sites of oxidative phosphorylation.     

CYP2D6基因G4268C和ERCC1基因C8092A位点的单核苷酸多态性与肺癌遗传易感性

目的：探讨辽宁地区CYP2D6基因G4268C和ERCC1基因C8092A位点的单核苷酸多态性对肺癌发生的影响。方法：采用病例-对照研究方法,选取肺癌患者和健康对照者各200例。应用KI法快速抽提人外周血基因组DNA,PCR-RFLP的方法检测CYP2D6基因G4268C和ERCC1基因C8092A位点的单核苷酸多态性。结果：G4268/G、G4268/C和C4268/C这3种基因型在病例和对照组的分布频率分别为1.50%、58.00%、40.50%和2.50%、44.00%、53.50%,非C4268/C基因型的个体发生肺癌的风险是C4268/C基因型个体的1.73倍（95%CI=1.02-2.95）,在腺癌中OR=2.75（95%CI=1.27-5.94）;按吸烟情况进行分层分析后发现不吸烟者及轻度吸烟者中携带非C4268/C基因型的个体患肺癌的风险显著增高,OR值为2.09（95%CI=1.09-4.25）和3.41（95%CI=1.24-9.93）;非A8092/A基因型的个体发生肺癌的风险是A8092/A基因型个体的0.98倍（95%CI=0.52-2.17）。结论：C4268/C基因型在不吸烟者和轻度吸烟者中可能作为保护因素而降低肺癌的易感性,ERCC1 C8092A多态性与肺癌易感性无相关性。     

Lead acetate does not inhibit dimethylnitrosamine activation and interacts with phenobarbital which is genotoxic in the ST cross of the Drosophila wing spot test

Lead acetate (PbAc) is known to inhibit the synthesis of the heme group, needed for hemeproteins like Cytochromes P450 (CYP450s). Dimethylnitrosamine (DMN) requires metabolic activation by CYP450s. The Drosophila wing spot test was performed to establish whether PbAc inhibits DMN activation in the standard (ST) and high bioactivation (HB) crosses, with different levels of CYP450s. Phenobarbital (PH) was used as an antagonist for its ability to induce CYP450s synthesis. PbAc (0.01, 0.1, 1.0 mM) produced significant small spots frequencies in the ST cross, indicating a possible genotoxic activity, however, the total spots frequency was negative at all concentrations. DMN (0.076 mM) was genotoxic in both crosses; surprisingly, PH (12 mM) was genotoxic and the PH-DMN treatment resulted synergic in the ST cross. Interestingly, the PbAc-PH pre-co-treatments showed a possible interaction in the ST cross. The GC-MS analysis showed a drop in the PH content as the PbAc concentration increased. PbAc also seemed to inhibit the genotoxic activity of PH, except at 0.01 mM. It is concluded that PbAc does not inhibit DMN activation by CYP450s in both crosses since it exerted a clear genotoxicity and that PH is genotoxic and interacts with PbAc in the ST but not the HB cross.     

The pathogenesis of inflammatory disease: Surgical shock and multiple system organ failure

Chronic inflammatory disease, embracing rheumatoid arthritis (RA), inflammatory bowel disease (IBD), hepatitis, asthma, atherosclerosis, multiple system organ failure (MSOF), etc., is mediated by reactive oxygen species (ROS). These ROS originate from activated neutrophils in infections and in immune and autoimmune reactions, from tissue deposits of ferritin, and from futile cycling of cytochrome P450 (CYP) following exposure to persistent chemicals, and may be perpetuated by the actions of complement, cytokines and eicosanoids. Acute inflammation is normally arrested by removal of ROS by tissue glutathione (GSH) and the antioxidant vitamins, A, C and E, all of which are regenerated by NADH and NADPH. Failure of this antioxidant defence system can lead to oxidative stress and to chronic inflammatory disease, including surgical shock and MSOF. The roles of oxidative stress and microcirculatory arrest in promoting MSOF, and of GSH, the antioxidant defence system, and fibronectin in preventing this, are reviewed in the light of recent experimental studies of surgical shock, including fasting, anaesthesia, hepatic ischaemia and reperfusion.