银杏叶提取物对低氧复氧、H2O2和谷氨酸损伤时谷氨酸引起的大鼠星形胶质细胞［Ca2+］i变化的影响

目的研究银杏叶提取物对低氧复氧、H₂O₂和L-谷氨酸损伤时谷氨酸升高大鼠星形胶质细胞［Ca²⁺］_i的影响。方法钙荧光探针Fluo-3/AM标记胞浆内游离钙离子，激光扫描共聚焦显微镜测定［Ca²⁺］_i的变化。结果 在低氧复氧、H₂O₂以及高浓度的L-谷氨酸损伤后，外源性谷氨酸（27 μmol·L^-1）均不能引起培养乳大鼠星形胶质细胞正常的［Ca²⁺］_i升高，反而使［Ca²⁺］_i分别降低(3.3±1.6)%，(81±11)%和(81±7)%；损伤前预先给予GbE（10 mg·L^-1）不能明显改善星形胶质细胞的谷氨酸反应，但预先给予GbE（100 mg·L^-1）后，27 μmol·L^-1谷氨酸可使损伤的星形胶质细胞［Ca²⁺］_i分别升高(135±98)%，(117±93)%和(89±36)%。结论低氧复氧、H₂O₂以及高浓度的L-谷氨酸均能损伤星形胶质细胞的谷氨酸反应，影响神经细胞与胶质细胞的双向交流。GbE能明显逆转不同损伤后谷氨酸诱导星形胶质细胞［Ca²⁺］_i的异常变化，使星形胶质细胞在不同损伤时能维持正常功能，该作用可能与GbE的脑保护作用有关。     

新型奥沙利铂类似物的合成、表征与细胞毒性

目的合成并表征了一个新的奥沙利铂类似物，顺式-叶酸根·(1R,2R-环己二胺)合铂(II)(［Pt(DACH)FA］)，以期获得抗癌活性优于奥沙利铂的新铂配合物。方法采用MTT法，评价了［Pt(DACH)FA］对A549，BGC-823，HCT-116和COLO320人癌细胞株的体外抗癌活性。结果［Pt(DACH)FA］在HCT-116和COLO320细胞株中有活性，IC₅₀值分别为50.1 μmol·L^-1和 25.0 μmol·L^-1，而在A549和BGC-823细胞株中则活性很低。结论虽然［Pt(DACH)FA］在HCT-116和COLO320细胞株中有一定的抗癌活性，但是在所评价的细胞株中活性均小于阳性对照药奥沙利铂，说明用叶酸根作为解离基团降低了该铂配合物的细胞毒性。     

胰岛素吸入粉雾剂的体外沉降及大鼠体内吸收促进剂的药效学评价

目的采用喷雾干燥法制备胰岛素吸入粉雾剂，对吸入粉雾剂体外沉降性质进行考察，并对其吸收促进剂在大鼠体内的药效学进行初步研究。方法采用中国药典(2000版)附录XH的装置测定粉末的体外有效部位沉积量，以葡糖氧化酶法（GOD-PAP法）测定大鼠的血糖浓度来评价其降血糖效果。结果喷雾干燥法制得的胰岛素吸收粉雾剂沉积量在各湿度下均大于40％，在气流量≥18 L·min^-1的情况下其有效部位沉积量变化不大。8 mmol·L^-1/dose牛黄胆酸钠［PA=59.91%,C_nadir=(33±6)%］和10 mmol·L^-1/dose去氧胆酸钠［PA=47.46%，C _nadir=(32±7)%］对胰岛素肺部吸收促进作用明显。而1%辛酸钠、1%十二烷基硫酸钠、250 μg/dose卵磷脂和10 mmol·L^-1/dose EDTA并未显示明显效果。结论制得的胰岛素吸收粉雾剂沉积量受湿度影响小，环境湿度依赖性和吸气流量依赖性小。8 mmol·L^-1/dose牛黄胆酸钠和10 mmol·L^-1/dose去氧胆酸钠可有效促进胰岛素干粉吸入剂的降血糖效果。     

极谱法研究辅酶Q10与β-环糊精的包结行为

目的研究辅酶Q_{10与β-环糊精(β-CD)的包结行为。方法用极谱法考察主体分子β-CD与电活性客体分子辅酶Q10发生包结反应时，包结物还原波峰电流随时间的变化，峰电位随β-CD浓度的变化，并在自然光照条件下分别考察辅酶Q10和包结物的还原波峰电流随时间的变化。结果在0.1 mol·L^-1 HAc/NaAc (pH 4.7)的乙醇-水(60∶40)介质中，辅酶Q10与β-CD形成1∶1的包结物，测得其包结常数kf为1.26×10⁴ L·mol^-1，包结反应的表观速率常数k为6.64×10^-2 min^-1。并测得辅酶Q10的光降解表观速率常数k为7.77×10^-3 min^-1，辅酶Q10-β-CD包结物的k为3.38×10^-3 min^-1。结论辅酶Q10和β-CD可形成包结物，并在一定程度上提高了辅酶Q10的光稳定性。}     

小檗碱与大黄酸沉淀作用的毛细管电泳法

目的研究大黄酸和小檗碱沉淀反应的热力学和动力学性质，为深入研究中药复方泻心汤和芍药汤提供依据。方法用毛细管电泳法测定在不同条件下沉淀反应溶液中两组分的平衡浓度，研究沉淀反应的热力学和动力学。结果沉淀中两组分摩尔比1∶1，20 ℃时溶度积常数k_sp=［B］［R］=(3.29±0.19)×10^-9mol²·L^-2。沉淀反应为吸热过程，k_sp受温度的影响不大。沉淀反应在混合时很快发生，然后是沉淀的陈化过程。结论中药复方泻心汤和芍药汤在煎煮过程中产生的来自于大黄蒽醌和生物碱的沉淀有一定的溶解度。毛细管电泳采用加大进样量后用峰高定量的方法有助于提高简单样品测定结果的重现性。     

基于溶解氧乙酰螺旋霉素极谱平行催化氢波的研究

目的提出一种极谱测定乙酰螺旋霉素(ASPM)的新方法。方法应用单扫描极谱法,在含溶解氧的0.1 mol·L^-1 NH₄Cl-NH₃·H₂O(pH 8.9)缓冲液中ASPM产生1个灵敏的平行催化氢波［峰电位E_p=-1.63 V(vs SCE)］。结果该平行催化氢波的二阶导数峰峰电流i″与ASPM浓度在1.74×10^-3～3.48 μg·mL^-1呈良好线性关系(r=0.997 9,n=13),检出限为5.80×10^-4 μg·mL^-1(3σ)。对0.871 μg·mL^-1 ASPM溶液进行13次平行测定,RSD为1.24%。结论本方法可用于ASPM片剂中ASPM含量的测定。     

HPLC/MS法研究左旋黄皮酰胺及其代谢物在Beagle犬血浆中的药代动力学HPLC/MS法研究左旋黄皮酰胺及其代谢物在Beagle犬血浆中的药代动力学

目的用HPLC/MS法研究左旋黄皮酰胺［(-)-clau］及其代谢物6-羟基-黄皮酰胺(6-OH-clau)在Beagle犬血浆中的药代动力学过程。方法Beagle犬灌胃左旋黄皮酰胺30 mg·kg^-1，采集静脉血样，血浆经乙酸乙酯萃取分离后，用HPLC/MS选择性正离子检测内标(格列吡嗪，［M+H］⁺，m/z 446)法测定左旋黄皮酰胺(［M+H］⁺，m/z 298)及6-羟基-黄皮酰胺(［M+H-H₂O］⁺，m/z 296)的浓度，以甲醇-水-冰醋酸(60∶40∶0.8)为流动相，流速1.0 mL·min^-1。用3P97软件计算药代动力学参数。结果左旋黄皮酰胺和6-羟基-黄皮酰胺分别在1.0～200 ng·mL^-1和0.2～40.0 ng·mL^-1线性关系良好(r>0.999)，萃取回收率均大于85%。原药及其代谢物的体内过程均符合二室模型；左旋黄皮酰胺及6-羟基-黄皮酰胺的C_max分别为(21±10) ng·mL^-1和(3.9±2.2) ng·mL^-1；T_max分别为(0.8±0.5) h和(1.3±0.5) h；T_1/2α分别为(0.9±0.6) h和(1.4±0.6) h；T_1/2β分别为(19±23) h和(13±12) h；AUC_{0-24 h}分别为(69±14) h·ng·mL^-1和(12±7) h·ng·mL^-1。结论Beagle犬灌胃左旋黄皮酰胺后迅速吸收，血药浓度一相消除很快，但末端消除较慢；其代谢物6-羟基-黄皮酰胺血药浓度经时过程与左旋黄皮酰胺相似，但血药浓度相对较小。     

接受室溶液电导率对盐酸丁卡因离子导入的影响

目的研究接受室溶液电导率对离子导入渗透速率的影响和作用机理。方法以盐酸丁卡因为模型药物,采用Valia-chien双室扩散池,供应室组成恒定,分别测定不同组成和不同浓度的接受室溶液下的离子导入渗透速率,并测定供应室和接受室的离子电导率。结果盐酸丁卡因离子导入渗透随着接受室阴离子(Cl^-)浓度的减少而增加。当电流强度恒定,盐酸丁卡因的离子导入增渗倍数(ER,ER=离子导入渗透速率/被动扩散渗透速率)与供应室和接受室电导率和的倒数［1/(k_s,d+k_s,r),k_s,d和k_s,r分别是供应室和接受室的电导率］成线性关系。结论接受室离子电导率可能是离子导入的重要影响因素。     

谷胱甘肽在10-甲基吩噻嗪修饰碳糊电极上的电催化氧化及电分析方法

研究了谷胱甘肽(还原型, glutathione, GSH)在10-甲基吩噻嗪(10-methylphenothiazine, MPT)修饰碳糊电极(MPT/CPE)上的电催化氧化行为。GSH在裸碳糊电极(carbon paste electrode， CPE)上的直接电化学氧化过程十分迟缓， 但在MPT/CPE上于0.702 V处出现一个不可逆氧化峰， 氧化电流大幅度增大。计时电流(chronoamperometry， CA)实验测得该电催化氧化反应速率常数k为(5.44±0.03)×10² (mol·L^-1)^-1·s^-1。用线性扫描伏安法(linear sweep voltammetry, LSV)测得催化氧化峰电流与GSH在5.0×10^-6～2.0×10^-3 mol·L^-1呈良好的线性关系， 线性回归方程I_pa=3.536c+2.117， r=0.999 0， 检测限为1.0×10^-6 mol·L^-1。同时用本方法对含GSH的市售药品进行了含量测定， 结果可靠。     

毒毛旋花子苷元对豚鼠心室肌细胞内钙浓度的影响

观察毒毛旋花子苷元(strophanthidin, Str)对分离豚鼠心室肌细胞内游离钙浓度(［Ca²⁺］_i)的影响。酶解分离豚鼠心室肌细胞, 用Fluo 3-AM负载, 激光共聚焦显微镜法测定单个豚鼠心室肌细胞［Ca²⁺］_i的荧光密度。Str可浓度依赖性地升高［Ca²⁺］_i, Str (10 μmol·L^-1)在［Ca²⁺］_i升高达峰值时, 可使细胞挛缩, 而Str (1和10 nmol·L^-1)对细胞形态无影响。TTX、 尼索地平或升高细胞外钙可影响Str (1和100 nmol·L^-1)对［Ca²⁺］_i的升高作用,而对Str (10 μmol·L^-1)无明显影响。在外液中加入ryanodine或去除细胞外钙, 则3个检测浓度的Str升高［Ca²⁺］_i作用均被明显抑制。在无K⁺、 无Na⁺液中, 10 μmol·L^-1 Str升高［Ca²⁺］_i的作用减弱, 而Str (1和100 nmol·L^-1)升高［Ca²⁺］_i的作用无明显影响。加入TTX、 尼索地平或增加细胞外的钙离子浓度, 则3个检测浓度Str的作用均受到影响。提示低浓度Str对［Ca²⁺］_i的升高作用与抑制Na⁺、K⁺-ATP酶活性无关, 而与促进L-型钙通道和TTX敏感性钠通道的“slip-mode”钙电导有关; 高浓度Str升高［Ca²⁺］_i的作用则是抑制Na⁺、K⁺-ATP酶的结果。此外, Str对［Ca²⁺］_i的升高作用还与直接作用于ryanodine受体促进内钙释放有关。     

Enhanced stability of codeine sulfate: effect of pH, buffer, and temperature on the degradation of codeine in aqueous solution

In the absence of strong buffer catalysts, the degradation of codeine sulfate (7,8-didehydro-4,5 alpha-epoxy-3-methoxy-17-methylmorphinan-6 alpha-ol sulfate) in aqueous solution is described by the expression kobs = kH+ [H+] + k0 + kHO-[HO-], where kH+ = (3.9 +/- 1.3) X 10(-8) M-1 X S-1, k0 = (2.7 +/- 0.5) X 10(-8) S-1, and kHO- = (5.1 +/- 1.0) X 10(-6) M-1 X S-1 at 80 degrees C. The activation energies associated with these rate constants are 27.7, 21.0, and 28.3 kcal X mol-1, respectively. In the absence of buffer catalysis, codeine sulfate is predicted to have a room temperature shelf life of approximately 44 years between pH 1 and 10, significantly longer than the 1.1 year shelf life of codeine phosphate reported earlier.     

Temperature and pH Dependence of Fluocinolone Acetonide Degradation in a Topical Cream Formulation

We investigated the degradation of fluocinolone acetonide (FA) incorporated into an oil-in-water cream base. The study examined the influence of temperature (23 to 80 degrees C) and cream pH (pH 2.3 to 6) on FA degradation rates. FA degradation followed pseudo-first-order kinetics and adhered to the Arrhenius expression over the entire temperature range investigated. At all temperatures, the pH strongly influenced the observed degradation rate constant (kobs) values, with rate minima observed near pH 4. The FA log(degradation rate)-pH profiles were consistent with a reaction mechanism requiring drug hydrolysis catalyzed by hydroxide and hydrogen ions. Taking into account both the temperature and the pH dependence of FA degradation permits calculating kobs values from the following equation: kobs = exp[22.5 - (17,200/RT)] + exp[38.7 - (22,200/RT)] x [H+] + exp[49.5 - (21,100/RT)] x [OH-] where the three bracketed terms represent Arrhenius expressions for neutral, acid-catalyzed, and base-catalyzed hydrolysis reactions. FA degradation in the cream base parallels the degradation of a related steroid (triamcinolone acetonide) in an aqueous alcohol solution. The equivalence between FA and triamcinolone acetonide kinetics in the different reaction media suggests that in the cream base, FA degradation is limited to an aqueous phase largely unperturbed by the presence of nonaqueous constituents that comprise the cream formulation.     

Factors affecting the inactivation of human placental glutathione S-transferase pi. The kinetic mechanism and pH-dependence of solvational and 1-chloro-2,4-dinitrobenzene-mediated inactivation of the enzyme

The kinetics of the inactivation of human placental GSH S-transferase pi has been studied at 25 degrees in the pH range 6.5 less than or equal to pH less than or equal to 9. At pH values less than or equal to 7.0 the inactivation of GSH S-transferase pi incubated in the absence of GSH and (i) in the absence or (ii) in the presence of CDNB (0-1.5 X 10(-3) mol/dm3) exhibited pseudo first-order kinetics with kobs for (i) and (ii) approximately equal (approximately 0.002 sec-1). The extent of inactivation in (i) approached a limiting value of 50% at infinite dilution of the enzyme; while in the presence of CDNB the extent of inactivation approached 100%. At any given pH such that 7 less than pH less than or equal to 9 the pseudo first-order inactivation rate constant, kobs, exhibits a linear dependence on [CDNB] (Eqn 1): kobs = k1 + k2 [CDNB] (1) where k1 is invariant with pH and approximately equal to 0.002 sec-1. The first-(k1) and second-(k2)-order components of kobs suggest at least two mechanisms for the inactivation of GST by CDNB, these are: (i) a pH-invariant facilitation of solvational inactivation and (ii) a pH-dependent nucleophilic reaction of a thiol group (pKa = 8.85 +/- 0.08) at or spatially close to the active site of the enzyme. A mechanistic rationale for the enzyme functioning as a dimer is discussed in detail.     

Radioligand and functional estimates of the interaction of the 1,4-dihydropyridines, isradipine and lacidipine, with calcium channels in smooth muscle.

1. The present experiments were undertaken in order to characterize further the apparently irreversible inhibition of the contraction of depolarized rat aorta caused by lacidipine, a 1,4-dihydropyridine calcium antagonist. 2. We studied the effect of lacidipine on contraction evoked by 100 mM KCl solution in rat aorta, treated by N omega-nitro-L-arginine (0.1 mM), an inhibitor of nitric oxide (NO) synthesis. We compared the effect of prolonged depolarization on lacidipine and (+)-isradipine inhibition and the reversal of this inhibition after washout in the absence of dihydropyridines. Assuming that the onset of lacidipine-evoked inhibition was a pseudo-first order association kinetics, we estimated the dissociation rate constant (k-1 = 0.031 min-1), the association rate constant (k1 = 2.70 x 10(8) M-1 min-1) and the dissociation constant (KD = k-1/k1 = 115 pM) which was close to the IC50 value in steady-state conditions (160 pM). 3. The inhibitory effects of lacidipine and (+)-isradipine on rat aorta contraction were reversibly enhanced after preincubation with the drug in a 40 mM KCl-solution. Washout with drug-free 40 mM K(+)-depolarizing solution reversed inhibition in the (+)-isradipine-treated preparations, but not in the lacidipine-treated ones. 4. Radioligand binding studies were performed with [3H]-lacidipine and [3H]-isradipine in microsomes from rat aorta and rat ileum.(ABSTRACT TRUNCATED AT 250 WORDS)     

Characterization of bradykinin B2 receptors on human IMR-90 lung fibroblasts: stimulation of 45Ca2+ efflux by D-Phe substituted bradykinin analogues.

[3H]Bradykinin binds to intact human IMR-90 fetal lung fibroblasts in a time and dose-dependent manner. Binding equilibrium was attained by 120 minutes at 4 degrees C. [3H]Bradykinin binding was saturable; Scatchard analysis of saturation binding data demonstrated a single binding site having a KD = 1.8 +/- 0.2 nM and a receptor concentration of 17.4 +/- 4.0 fmol/10(5) cells. The calculated value for KD(k-1/k1) from the association (k1 = 4.71 x 10(6) mol-1 min-1) and dissociation (k-1 = 1.13 x 10(-2) min-1) rate constants was 2.4 nM. The rank order of potency observed for bradykinin peptide agonists, bradykinin > Lys-bradykinin > Met,Lys-bradykinin > Ile,Ser-bradykinin > des-Arg9-bradykinin, is consistent with that of a bradykinin B2 receptor. Bradykinin stimulated efflux of 45Ca2+ from IMR-90 cells dose dependently with an EC50 = 331 +/- 50 pM. 45Ca2+ efflux was also demonstrated with Lys-bradykinin and Met-Lys-bradykinin but not by des-Arg10-kallidin (100 nM) or NKA (1 microM). Hoe-140 inhibited bradykinin-induced 45Ca2+ efflux (IC50 = 3 +/- 2 nM). D-Phe7-substituted bradykinin analogues stimulated 45Ca2+ efflux dose dependently and this stimulation of 45Ca2+ efflux was inhibited by Hoe-140. These results suggest that D-Phe7 substituted bradykinin analogues are agonists at the bradykinin B2 receptor in IMR-90 cells.     

Reactive sulfur species: kinetics and mechanism of the oxidation of cystine by hypochlorous acid to give N,N'-dichlorocystine

Cystine and HOCl (a neutrophil-derived oxidant) react to form an intermediate that has a half-life of ca. 5 min at pH 7.5. The intermediate subsequently decomposes to eventually yield a mixture of cystine, higher oxides of Cys, and other uncharacterized species. Spectral titrations, transitory (1)H NMR and UV-vis spectra, and the reaction properties of the intermediate are consistent with a formulation of N,N'-dichlorocystine {NDC = [-SCH(2)CH(NHCl)(CO(2)H)](2)}. The reaction of equimolar amounts of HOCl with cystine at pH 11.3 does not yield N-chlorocystine [NCC = (-O2C)(H3N+)CHCH(2)SSCH(2)CH(NHCl)(CO(2)H)] but rather a 1:1 mixture of NDC and cystine. This result could be explained by two mechanisms: rapid disproportionation of NCC to produce NDC and cystine or a faster reaction of the second equivalent of HOCl with NCC than the first equivalent of HOCl reacts with cystine. The latter mechanism is favored because of our observation by NMR spectroscopy that NDC decomposes via a species that we have assigned as NCC. Thus, disproportionation of NCC is apparently a relatively slow process. The rates of reaction of cystine(0) = [-SCH(2)CH(NH(3)(+))(CO(2)(-))](2) degrees , cystine(1-) = [((-)O(2)C)(H(2)N)CHCH(2)SSCH(2)CH(NH(3)(+))(CO(2)(-))](-), and cystine(2-) = [-SCH(2)CH(NH2)(CO2)(-))]2(2-) have been investigated, and it is clear that cystine(0) is unreactive, whereas cystine(2-) is about four times more reactive than cystine(1-). Accordingly, the following mechanism is proposed (constants for 5 degrees C): HOCl = H+ + OCl-, pK1 = 7.47; cystine(0) = cystine(1-) + H+, pK2 = 8.15; cystine(1-) = cystine(2-) + H+, pK3 = 9.00; cystine(1-) + HOCl --> NCC(1-) + H2O, k4 = 4.3(2) x 10(6) M(-1) s(-1); cystine(2-) + HOCl --> NCC(2)(-) + H2O, k5 = 1.6(2) x 10(7) M(-1) s(-1); NCC(1-) --> NCC(2-) + H+, k6 = fast; NCC(2-) + HOCl --> NDC(2-) + H2O, k7 = fast. At physiologic pH, the k4 pathway dominates. The generation of long-lived chloramine derivatives of cystine may have physiological consequences, since such compounds are known to react with nucleophiles via mechanisms that are also characteristic of HOCl, electrophilic transfer C+.     

Alkaline hydrolysis of oxaliplatin--isolation and identification of the oxalato monodentate intermediate

The alkaline degradation of the chemotherapeutic agent oxaliplatin has been studied using liquid chromatography. The oxalato ligand is lost in two consecutive steps. First, the oxalato ring is opened, forming an oxalato monodentate intermediate, as identified by electrospray ionization mass spectrometry. Subsequently, the oxalato ligand is lost and the dihydrated oxaliplatin complex is formed. The observed rate constants for the first step (k(1)) and the second step (k(2)) follow the equation k(1) or k(2) = k(0) + k(OH(-) )[OH(-)], where k(0) is the rate constant for the degradation catalyzed by water and k(OH(-) ) represents the second-order rate constant for the degradation catalyzed by the hydroxide ion. At 37 degrees C the rate constants for the first step are k(OH(-) ) = 5.5 x 10(-2) min(-1) M(-1) [95% confidence interval (CI), 2.7 x 10(-2) to 8.4 x 10(-2) min(-1) M(-1)] and k(0) = 4.3 x 10(-2) min(-1) (95% CI, 4.0 x 10(-2) to 4.7 x 10(-2) min(-1)). For the second step the rate constants are k(OH(-) ) = 1.1 x 10(-3) min(-1) M(-1) (95% CI, -1.1 x 10(-3) to 3.3 x 10(-3)) min(-1) M(-1) and k(0) = 7.5 x 10(-3) min(-1) (95% CI, 7.2 x 10(-3) to 7.8 x 10(-3) min(-1)). Thus, the ring-opening step is nearly six times faster than the step involving the loss of the oxalato ligand.     

Kinetics and mechanism of the oxidation of the glutathione dimer by hypochlorous Acid and catalytic reduction of the chloroamine product by glutathione reductase

Oxidized glutathione (GSSG) reacts with two molar equivalents of HOCl/OCl- (a neutrophil-derived oxidant and a common biocide) to form the dichloro (bis-N-chloro-gamma-l-glutamyl) derivative (NDG). The reaction of less than two molar equivalents of HOCl with GSSG does not yield the unsymmetrical monochloro derivative (NCG) but rather a stoichiometric amount of NDG and GSSG. This result is explained by a faster reaction of the second equivalent of HOCl with NCG than that of the first equivalent of HOCl with GSSG. The rates of reaction of GSSG2-, GSSG3-, and GSSG4- (successive deprotonation of the ammonium groups) have been investigated, and it is clear that GSSG2- is unreactive, whereas GSSG4- is about twice as reactive as GSSG3-. Accordingly, the following mechanism is proposed (constants for 5 degrees C): H+ + OCl- = HOCl, pK1 = -7.47; GSSG2- = GSSG3- + H+, pK2 = 8.5; GSSG3- = GSSG4- + H+, pK3 = 9.5; GSSG3- + HOCl --> NCG3- + H2O, k4 = 2.7(2) x 106 M-1 s-1; GSSG4- + HOCl --> NCG4- + H2O, k5 = 3.5(3) x 107 M-1 s-1; NCG3- --> NDG4- + H+, k6 = fast; and NCG4- + HOCl --> NDG4- + H2O, k7 = fast. At physiologic pH, the k4 pathway dominates. NDG decomposes at pH 7.4 in a first-order process with kdec = 4.22(1) x 10-4 s-1 (t1/2 = 27 min). Glutathione reductase (EC 1.6.4.2) is capable of catalyzing the reduction of NDG by NADPH. The only NDG-derived product that is observed (by NMR) after the reduction by NADPH is GSH. Thus, in the presence of the GOR/NADPH system, GSH is capable of redox buffering a 3/2 mol equiv of HOCl rather than a 1/2 mol equiv as previously assumed.     

Disproportionation of clozapine radical: a link between one-electron oxidation of clozapine and formation of its nitrenium cation

The primary products of one-electron oxidation of clozapine and olanzapine, very effective atypical antipsychotic drugs, have been spectroscopically characterized. The oxidation process has been studied under glassy matrix conditions and by a pulse radiolysis technique in aqueous solution. The rate constants for the oxidation of clozapine with dibromide radical anion ( k = 2 x 10 (9) M (-1) s (-1)) and azide radical ( k = 2.3 x 10 (9) M (-1) s (-1)) in aqueous solution were measured. The computational DFT results support the identification of the transient species. The mechanistic aspects of reactivity of radical cations, radicals, and nitrenium cations have been investigated. A disproportionation reaction ( k > or = 1 x 10 (8) M (-1) s (-1)) was proposed as a link between the products of one-electron oxidation and formation of the nitrenium cations of clozapine and olanzapine, products likely responsible for the pathogenesis of adverse drug reactions. The rate constants for the reactions of nitrenium cation of clozapine with glutathione ( k = 3.4 x 10 (4) M (-1) s (-1)) and cysteine ( k = 9.8 x 10 (4) M (-1) s (-1)) were determined.     

p-[125I]iodoclonidine, a novel radiolabeled agonist for studying central alpha 2-adrenergic receptors

Unlabeled p-iodoclonidine was efficacious in attenuating forskolin-stimulated cAMP accumulation in SK-N-SH neuroblastoma cells. Maximal attenuation was 76 +/- 3%, with an EC50 of 347 +/- 60 nM. Comparable values of epinephrine were 72 +/- 3% and 122 +/- 22 nM. Responses to both agonists were abolished by 10 microM phentolamine. Therefore, p-iodoclonidine is an agonist in a cell culture model system of the neuronal alpha 2-adrenergic receptor. p-[125I]Iodoclonidine binding to membranes were measured using various regions of the rat brain. The agonist labeled a single population of sites present on cerebral cortical membranes, which was saturable (Bmax = 230 fmol/mg of protein) and possessed high affinity for the ligand (Kd = 0.6 nM). Binding was largely specific (93% at 0.6 nM). A variety of alpha 2-adrenergic agonists and antagonists were shown to compete for the binding of the radioligand. The binding of p-[125I]iodoclonidine was much less sensitive to agents that interact with alpha 1-adrenergic, serotonergic, and dopaminergic receptors. Approximately 65% of the binding was sensitive to guanine nucleotides. Association kinetics using 0.4 nM radioligand were biphasic (37% associate rapidly, with kobs = 0.96 min-1, with the remainder binding more slowly, with kobs = 0.031 min-1) and reached a plateau by 90 min at 25 degrees. Dissociation kinetics were also biphasic, with 30% of the binding dissociating rapidly (k1 = 0.32 min-1) and the remainder dissociating 50-fold more slowly (k2 = 0.006 min-1). Agonist binding is, therefore, uniquely complex and probably reflects the conformational changes that accompany receptor activation.