Inhibition of transport across the hepatocyte canalicular membrane by the antibiotic fusidate

Hyperbilirubinemia is a frequent side effect induced by long-term therapy with the antibiotic fusidate. The aim of this study was to elucidate the molecular mechanisms of fusidate-induced hyperbilirubinemia by investigating its influence on hepatic transport systems in the canalicular membrane. Using canalicular membrane vesicles from rat liver, we determined the effect of fusidate on the adenosine 5'-triphosphate (ATP)-dependent transport of substrates of the apical conjugate export pump, multi-drug resistance protein 2 (Mrp2, symbol Abcc2) and the bile salt export pump (Bsep, symbol Abcb11). Fusidate inhibited the ATP-dependent transport of the Mrp2 substrates 17beta-glucuronosyl estradiol and leukotriene C4, and the transport of cholyltaurine by Bsep with Ki values of 2.2+/-0.3, 7.6+/-1.3, and 5.5+/-0.8 microM, respectively. To elucidate the in vivo implication of these findings, the effect of fusidate treatment on the elimination of intravenously administered tracer doses of 17beta-glucuronosyl estradiol and cholyltaurine into bile was studied in rats. Treatment with fusidate (100 micromol/kg body weight) reduced the biliary excretion rate of 17beta-glucuronosyl [3H]estradiol and [3H]cholyltaurine by 75 and 80%, respectively. Extended treatment of rats with fusidate (100 micromol/kg body weight, three times daily i.p. for 3 days) reduced hepatic Mrp2 protein levels by 61% (P<0.001). Our data suggest that there are at least two different mechanisms involved in the impairment of transport processes and hepatobiliary elimination by fusidate, direct inhibition of transport of Mrp2 and Bsep substrates by competitive interaction and impairment by a decreased level of hepatic Mrp2.     

Structural and functional characterization of an acidic platelet aggregation inhibitor and hypotensive phospholipase A(2) from Bothrops jararacussu snake venom

An acidic (pI approximately 4.5) phospholipase A(2) (BthA-I-PLA(2)) was isolated from Bothrops jararacussu snake venom by ion-exchange chromatography on a CM-Sepharose column followed by reverse phase chromatography on an RP-HPLC C-18 column. It is an approximately 13.7kDa single chain Asp49 PLA(2) with approximately 122 amino acid residues, 7 disulfide bridges, and the following N-terminal sequence: 1SLWQFGKMINYVM-GESGVLQYLSYGCYCGLGGQGQPTDATDRCCFVHDCC(51). Crystals of this acidic protein diffracted beyond 2.0A resolution. These crystals are monoclinic and have unit cell dimensions of a=33.9, b=63.8, c=49.1A, and beta=104.0 degrees. Although not myotoxic, cytotoxic, or lethal, the protein was catalytically 3-4 times more active than BthTX-II, a basic D49 myotoxic PLA(2) from the same venom and other Bothrops venoms. Although it showed no toxic activity, it was able to induce time-independent edema, this activity being inhibited by EDTA. In addition, BthA-I-PLA(2) caused a hypotensive response in the rat and inhibited platelet aggregation. Catalytic, antiplatelet and other activities were abolished by chemical modification with 4-bromophenacyl bromide, which is known to covalently bind to His48 of the catalytic site. Antibodies raised against crude B. jararacussu venom recognized this acidic PLA(2), while anti-Asp49-BthTX-II recognized it weakly and anti-Lys49-BthTX-I showed the least cross-reaction. These data confirm that myotoxicity does not necessarily correlate with catalytic activity in native PLA(2) homologues and that either of these two activities may exist alone. BthA-I-PLA(2), in addition to representing a relevant molecular model of catalytic activity, is also a promising hypotensive agent and platelet aggregation inhibitor for further studies.     

Population pharmacokinetics model and limited sampling strategy for intravenous vinorelbine derived from phase I clinical trials

AIMS: a) To characterize the pharmacokinetics of intravenous vinorelbine, b) to use a population analysis for the identification of patient covariates that might appreciably influence its disposition and c) to define a limited sampling strategy for further Bayesian estimation of individual pharmacokinetic parameters. METHODS: All data were collected from 64 patients (99 courses) entered in three different phase I trials that have been previously reported. All patients received vinorelbine as a 20 min infusion with dose levels ranging from 20-45 mg m-2. The population pharmacokinetic model was built in a sequential manner on a subset of two-thirds of the data, starting with a covariate-free model then progressing to a covariate model using the nonlinear-mixed effect methodology. The remaining one-third of the data were used to validate several sparse sampling designs. RESULTS: A linear three-compartment model characterized vinorelbine blood concentrations (n=1228). Two primary pharmacokinetic parameters (total clearance and volume of distribution) were related to various combinations of covariates. The relationship for total clearance (CLtotal (l h-1)=29.2xBSAx(1-0.0090 Plt)+6.7xWt/Crs) was dependent on the patient's body surface area (BSA), weight (Wt), serum creatinine (Crs) and platelet count before administration (Plt). The optimal limited sampling strategy consisted of a combination of three measured blood concentrations; the first immediately before the end of infusion or 20 min later, the second at either 1 h, 3 h or 6 h and the third at 24 h after drug administration. CONCLUSIONS: A population pharmacokinetic model and a limited sampling strategy for intravenous vinorelbine have been developed. This is the first population analysis performed on the basis of a large phase I database that has identified clinical covariates influencing the disposition of i.v. vinorelbine. The model can be used to obtain accurate Bayesian estimates of pharmacokinetic parameters in situations where extensive pharmacokinetic sampling is not feasable.     

The influence of charge clustering on the anti-HIV-1 activity and in vivo distribution of negatively charged albumins

The substitution of human serum albumin with negatively charged molecules, such as succinic acid (Suc-HSA) or aconitic acid (Aco-HSA), resulted in proteins with potent anti-HIV activities, by binding to viral gp120 (V3 loop). The aim of the present study was to investigate whether the distribution of negative charges on the albumin backbone influences the anti-HIV activity. Therefore, we prepared albumins with clusters of negatively charged groups by coupling of heparin. The effects of this substitution on anti-HIV activity, in vivo distribution and the protein structure as compared to random succinylation were assessed. In vitro studies indicated that HSA-modified with heparin 6 or 13 kD displayed anti-HIV activity (IC50=660 and 37 nM, respectively) and exhibited affinity for gp120-V3 loop, although the activity was lower than that of Suc-HSA. Combined derivatization of HSA with heparin 13 kD and aconitic acid groups resulted in significantly increased inhibitory actions (IC50=2.8 nM). Structural analysis showed that modification of HSA with heparin did not lead to extensive unfolding of the protein, meaning that these modified proteins were still globular in structure. In contrast, succinylation of HSA resulted in a highly randomly coiled conformation. Dynamic light scattering experiments revealed that, at neutral pH, the heparin fragments attached to the protein were wrapped around the molecule rather than sticking out into the solution. In conclusion, coupling of sufficient clustered negative charges, by coupling of Hep-fragments, on HSA resulted in a clear anti-HIV activity of the protein. Yet, random distribution of anionic groups in the albumin seemed more optimal for in vitro anti-HIV activity. The higher plasma and lymphatic concentrations of Hep-HSA compared to Suc-HSA seemed more favorable for an anti-HIV activity in vivo.     

益肝康药物血清对大鼠肝星状细胞胞浆游离钙效应的抑制作用

目的研究益肝康药物血清是否具有抑制肝星状细胞(HSCs)胞浆游离钙([Ca2 ]i)增高的作用。方法将32只健康雄性SD大鼠按随机数字表分为4组:肝纤维化模型益肝康组(8只)皮下注射用精制橄榄油配制的40?L4溶液9周,然后灌服益肝康6d;肝纤维化模型对照组(8只)皮下注射用精制橄榄油配制的40?L4溶液9周,然后灌服0·9%氯化钠溶液6d;正常大鼠益肝康组(8只)皮下注射等量精制橄榄油9周,然后灌服益肝康6d;正常对照组(8只)皮下注射等量精制橄榄油9周,然后灌服0·9%氯化钠溶液6d。结束后经下腔静脉取血并分离血清。用盲法,采用上述10%血清培养HSCs24h并负载好Fluo-3/AM后,使用激光扫描共聚焦显微镜(LSCM)检测HSCs[Ca2 ]i。结果(1)经正常大鼠益肝康组及肝纤维化模型益肝康组大鼠血清预处理的HSCs,其[Ca2 ]i荧光强度相对值均明显低于肝纤维化模型对照组(P<0·05);且两者与正常对照组间差别均有显著性意义(P<0·05)。结论益肝康能抑制肝星状细胞[Ca2 ]i的升高,这可能是其发挥抗肝纤维化作用的重要途径之一。     

延长洛美利嗪作用时间可增加K562/A02细胞对阿霉素的敏感性

目的：研究洛美利嗪在高浓度、长时间作用于肿瘤细胞时，对多药耐药的逆转作用。探讨洛美利嗪逆转肿瘤细胞多药耐药的机制。方法：将不同浓度的洛美利嗪与人红白血病细胞系K562及其耐药细胞系K562／A02（耐阿霉素）共孵育24、48或72小时，然后分别向细胞中加入阿霉素，采用MTT法检测细胞毒作用；以流式细胞术测定两种细胞系内罗丹明123的潴留以反映P-糖蛋白的外排功能；利用Fluo-3／AM检测细胞内游离钙离子浓度。结果：细胞与洛美利嗪预温孵后，阿霉素对K562／A02细胞的IC50值减小，细胞内Rh123潴留增多，细胞内游离钙离子浓度明显升高。结论：洛美利嗪高浓度，长时间作用于K562／A02细胞，可以抑制细胞上P-糖蛋白的功能活性，使细胞对化疗药的敏感性增强，其机制可能与升高细胞内钙离子有关。     

脑心通胶囊对血管性痴呆模型大鼠海马神经细胞静息态[Ca2+]i的影响

目的观察脑心通胶囊对血管性痴呆模型大鼠海马神经细胞静息态游离Ca2+浓度 ([Ca2+]i) 的影响,初步探讨脑心通胶囊治疗血管性痴呆的机制.方法采用大脑中动脉闭塞法(MCAO)制作血管性痴呆动物模型;使用胰蛋白酶消化法制备海马组织单细胞悬液,Fura-2/AM负载分离的神经细胞,双波长荧光法测定海马神经细胞内静息态[Ca2+]i.结果模型组大鼠海马神经细胞静息态[Ca2+]i为437.42±32.14nmol/L,显著高于假手术组189.83±18.57 nmol/L(P<0.05);脑心通组和喜德镇组大鼠海马神经细胞静息态[Ca2+]i为252.61±20.15 nmol/L、237.34±19.83 nmol/L,较模型组显著降低(P<0.05).结论 脑心通胶囊可降低血管性痴呆模型大鼠海马神经细胞静息态[Ca2+]i,这可能是脑心通胶囊治疗血管性痴呆的作用机制之一.     

PGF_(2α)对NIT-1β细胞葡萄糖刺激性胰岛素分泌的影响

目的探讨PGF2α对葡萄糖刺激性胰岛素分泌和[Ca2+]i变化的影响。方法运用放免方法检测不同浓度的PGF2α在不同情况下对NIT-1β细胞葡萄糖刺激性胰岛素分泌量的变化,并以F luo-3AM为探针,利用激光共聚焦显微镜检测细胞内钙的改变。结果在16.5 mmol.L-1葡萄糖刺激下,0.1、1、5μmol.L-1的PGF2α剂量依赖性的促进了NIT-1β细胞葡萄糖刺激性胰岛素分泌,其中5μmol.L-1时作用最强(P<0.01),而在10μmol.L-1时,PGF2α却抑制了葡萄糖刺激的胰岛素分泌(P<0.05);预先加入0.5 mmol.L-1EGTA后,5μmol.L-1的PGF2α不能促进胰岛素分泌,同样在预先加入n ifed ip ine或EGTA+n ifed ip ine后,PGF2α也无促进胰岛素分泌(P>0.05)。在0、5.5 mmol.L-1葡萄糖刺激下,5μmol.L-1的PGF2α无促进胰岛素分泌作用(P>0.05)。另外,应用5μmol.L-1的PGF2α能够引起β细胞内钙升高(P<0.01),在无钙环境下,PGF2α只引起缓慢的幅度较小的细胞内钙升高,恢复细胞外钙浓度时,β细胞内钙升高(P<0.01)。结论在NIT-1β细胞,一定范围浓度的PGF2α能够促进高浓度葡萄糖刺激下的胰岛素分泌,可能与PGF2α增加细胞外钙内流有关。     

丹参对胆源性胰腺炎的防治作用

目的 探讨胆源性胰腺炎（ＢＰ）的发病过程中,胰腺泡细胞内游离钙离子〔Ｃａ＾２＋〕;浓度的变化机制及丹参对ＢＰ的防治作用。方法 采用流式细胞仪（ＦＣＭ）和细胞内〔Ｃａ＾２＋〕;探针Ｆｌｕｏ－３－ＡＭ检测胆胰管结扎组（Ａ组）及其加丹参组（Ｂ组,丹参注射剂量为５ｇ／ｋｇ）、ＣＣＫ－ＯＰ静脉输液组（Ｃ组）及其加丹参组（Ｄ组）和对照组（Ｅ组）ＳＤ大鼠胰腺泡细胞内〔Ｃａ＾２＋〕;浓度,并检测血淀粉酶、血清钙离     

血管紧张素Ⅱ对人精子顶体反应的影响

目的 :探讨血管紧张素 (angiotensin ,Ang )对人精子顶体反应的影响及其可能机制。方法 :检测不同浓度 Ang 诱发的人精子顶体反应率和 Ang 引起的精子胞内钙离子的变化 ,以及血管紧张素受体 AT1拮抗剂 Losartan对其的抑制作用。结果 :Ang 在 1 0 nmol/L和 1 0 0 nmol/L时均可显著增加人精子顶体反应率 ,并引起精子胞内钙离子短暂快速升高 ,Losartan可以明显抑制这些过程。结论 :Ang 可以诱发人精子顶体反应 ,这一作用可能经 AT1受体介导 ,通过引起精子胞内钙离子升高而实现。