Carboxylesterase catalyzed 18O-labeling of carboxylic acid and its potential application in LC-MS/MS based quantification of drug metabolites

LC-MS quantification of drug metabolites is sometimes impeded by the availability of internal standards that often requires customized synthesis and/or extensive purification. Although isotopically labeled internal standards are considered ideal for LC-MS/MS based quantification, de novo synthesis using costly isotope-enriched starting materials makes it impractical for early stage of drug discovery. Therefore, quick access to these isotope-enriched compounds without chemical derivatization and purification will greatly facilitate LC-MS/MS based quantification. Herein, we report a novel ¹⁸O-labeling technique using metabolizing enzyme carboxylesterase (CES) and its potential application in metabolites quantification study. Substrates of CES typically undergo a two-step oxygen exchange with H₂¹⁸O in the presence of the enzyme, generating singly- and doubly-¹⁸O-labeled carboxylic acids; however, unexpected hydrolytic behavior was observed for three of the test compounds – indomethacin, piperacillin and clopidogrel. These unusual observations led to the discovery of several novel hydrolytic mechanisms. Finally, when used as internal standard for LC-MS/MS based quantification, these in situ labeled compounds generated accurate quantitation comparable to the conventional standard curve method. The preliminary results suggest that this method has potential to eliminate laborious chemical synthesis of isotope-labeled internal standards for carboxylic acid-containing compounds, and can be developed to facilitate quantitative analysis in early-stage drug discovery.     

瘦蛋白的分子生物学特性研究进展

瘦蛋白 (leptin)是由肥胖基因编码、脂肪细胞分泌的一种分子量为 16kDa的蛋白质 ,是一种重要的代谢调节信号 ,对人和动物的采食量、能量代谢、繁殖性能等具有重要调节功能 ,对人肥胖病的治疗和改善动物的生产性能、胴体组成等有良好的潜在应用前景 .主要概述了瘦蛋白基因的克隆、转录、表达调控以及瘦蛋白受体与信号转导等分子生物学特性     

Bioavailability and Pharmacokinetics of a New Sustained-Release Potassium Chloride Tablet

The bioavailability of a new sustained-release potassium chloride (KC1) tablet, designed for once-a-day dosing, was compared to a KC1 elixir using urinary excretion data. The study utilized 25 male volunteers dosed in a crossover design in a dietary/activity-controlled environment. The regimens consisted of a total of 80 mEq of potassium in three equally divided doses of elixir every 6 hr and a single 80-mEq dose using four 20-mEq sustained-release (SR) tablets. The mean time to maximum rate of potassium urinary excretion was 2.2 hr for the first elixir dose and 5.5 hr after the SR tablet (P < 0.01), thereby supporting the prolonged-release properties of this formulation. After correction for baseline urinary potassium excretion, the mean total 24-hr urinary potassium excretion was 42.18 mEq for the elixir and 40.41 mEq for the SR tablet. The results indicate that the absorption pattern from the SR tablet is equal to three doses of KC1 elixir dosed 6 hr apart.     

脂肪族聚酯与高氯酸锂络合物的结构与导电性

本文通过酯交换反应合成了一系列脂肪族聚丁二酸酯,对他们的结构和性能作了表征。发现聚酯存在多晶现象,其熔点有奇偶性变化规律。探索了由此系列聚酯与高氯酸锂形成的固体电解质的结构和离子导电性。无机盐的加入提高了电解质的玻璃化温度但降低了聚酯的熔点及结晶度。聚酯电解质的晶体类似于聚酯,其无机盐主要溶解于聚酯的无定形区域。聚酯系列电解质的导电率也有偶奇效应,与熔点变化相反;熔点高的电解质导电率低,熔点低的电解质导电率高。电解质的导电率随温度改变而变化,在室温下电解质的导电率可达10~(-6)s/cm。高分子链上侧基的引入将大大降低电解质的导电性。     

关附甲素对豚鼠乳头肌动作电位最大除极速度的频率依赖性抑制作用

应用标准微电极技术，研究了关附甲素对豚鼠右心室乳头肌动作电位最大除极速率(V_max)的频率依赖性抑制作用(RDB)，并与美西律，奎尼丁，劳卡尼进行了比较. 在相同刺激间隔(300 ms)，产生50%左右RDB的药物浓度下，美西律的RDB开始最快，其第2个V_max所产生的抑制已占RDB的64%，奎尼丁，劳卡尼和关附甲素的RDB开始速率常数分别为每个动作电位0.165, 0.076和0.136. 美西律，奎尼丁，劳卡尼和关附甲素产生RDB的恢复时间常数分别为1.4, 9.0, 18.2和44.0 s，而且它们的恢复时间常数是不依赖于药物浓度而变化的，结果提示，关附甲素是一个慢动力学钠通道阻滞剂.     

Clinical evaluation of a potassium nitrate dentifrice for the treatment of dentinal hypersensitivity

Abstract The effectiveness of a 5% potassium nitrate dentifrice as a daily home treatment for dentinal hypersensitivity was evaluated in a double-blind study in 36 Japanese subjects who complained of cold and/or tactile hypersensitivity. The subjects were divided into 2 groups, with 18 being given a 5% potassium nitrate dentifrice (treated group) and the other 18 a vehicle paste (control group). Both groups were instructed to brush their teeth 2 × a day. The hypersensitivity levels of the affected teeth were assessed by 2 stimuli, one tactile and the other cold air, and by the perception of pain. The results of all 3 assessment methods indicated that the potassium nitrate dentifrice significantly decreased the level of hypersensitivity at weeks 4, 8, and 12. In the treated group, a rapid decrease of positive scores for both the cold air stimulus and the subjective symptoms appeared from week 2. Although a significant decrease of the assessment score was also observed in the control group, the reduction rate of the score was much greater in the treated group by ail 3 assessment methods at weeks 4, 8, and 12. Complete relief of subjective symptoms throughout the 12 weeks’examination was noted in 67% of the subjects in the treated group, but in only 6% in the control group. These results suggest the usefulness of a 5% potassium nitrate dentifrice in Japanese patients with dentinal hypersensitivity.     

Repetitive firing properties in subpopulations of the chick Edinger Westphal nucleus.

The avian Edinger Westphal nucleus, through the ciliary ganglion, controls accommodation, iris constriction, and blood flow through the choroid. In live brainstem slices, the nucleus is easily identifiable as an olive-shaped cluster of neurons dorsal to the oculomotor nerve and nucleus. Intracellular recordings from neurons in the nucleus identified two classes of responses to sustained (300 to 500 ms) injections of depolarizing current. One set of cells fired action potentials for the duration of the pulse while a second set of cells fired action potentials only transiently, during the first 50 to 100 ms, after which they remained silent regardless of the size of the depolarization. Intracellular recordings followed by injections of the fluorescent dye lucifer yellow revealed that repetitively firing cells were located in the lateral half of the nucleus while non-repetitively or transiently firing cells were located in the medial half. These locations correspond to different Edinger Westphal subdivisions which have distinct inputs and target populations. The varying firing patterns are discussed with reference to the known functions of the subdivisions in which they occur. Replacement of calcium by magnesium in the extracellular medium had no effect on the number of action potentials fired by non-repetitively firing cells, suggesting that a calcium-activated potassium current is not responsible for suppressing repetitive firing in these cells. In contrast, in repetitively firing cells removal of extracellular calcium increased the frequency of action potential discharge and decreased the amplitude of afterhyperpolarizations following single action potentials. Addition of cadmium to the bath medium had similar effects.(ABSTRACT TRUNCATED AT 250 WORDS)     

Reduction in sodium chloride intake: effects on urinary Na, K and aldosterone output in healthy free-living adults

Eleven healthy free-living adults (six women, five men) weighed and recorded all food and drink consumed and collected all urine for two non-consecutive 7-day periods whilst eating their usual diet (Period 1) and attempting to reduce salt intake (Period 2). Bread (including pitta bread) provided on average a quarter of total Na intake of subjects in Period 1 so that wholemeal bread made without added salt was made available in Period 2. All subjects achieved substantial reductions (mean 65%) in Na intake in Period 2 with no change in K intake so that the Na:K molar ratio fell from 1.3 to 0.5. Urinary Na output closely followed intakes and there was a large increase (mean 11.2 μg/d) in aldosterone excretion with a non-significant increase in K output. Simple linear relationships which allow prediction of Na and K intake from the more easily measured urinary output were derived.     

Hereditary Hypertriglyceridemic Rat: A New Animal Model of Metabolic Alterations in Hypertension

Hereditary hypertriglyceridemic rats (hHTg) were developed as a new genetic model for the study of relationships between blood pressure (BP) and metabolic abnormalities. This strain has been produced by selective inbreeding from Wistar rats according to the rise of plasma triglycerides induced by a high-sucrose diet. Though hHTg rats display hypertriglyceridemia, impaired glucose tolerrance, hyperinsulinemia, insulin resistance and increased BP even without nutritional stimuli, high sucrose feeding further aggravates these symptoms. High plasma triglycerides levels in hHTg rats seem to be a consequence of their hyperproduction. Impaired insulin action is responsible for the defective glucoregulation in this strain. The loss of insulin responsiveness might be due to a reduction in the number of glucose transporters. Highly significant relationships among plasma triglycerides, ouabain-resistant Na⁺ transport and BP were demonstrated in the hHTg rats. Segregating populations (F2 hybrids) should be used for genetic analysis of the primary role of lipid and/or ion transport abnormalities in the pathogenesis of this form of genetic hypertension.