An experimentally supported, mathematical explanation of the gas chromatographic elution behaviour of the long-chain carbon members of the homologous series

By substituting the saturated vapour phase tension of the pure normal hydrocarbons described by the Clausius-Clapeyron law into the accepted expression of the specific retention volume (V_g,T), a theoretically coherent and relatively simple mathematical evidence of the elution behaviour of the homologous members has been deduced. It gives exponential retention time dependence on carbon number for isothermal, and nearly equidistant (i.e., approximately linear retention-time dependence on carbon number) elution for linear temperature programmed gas chromatographic runs. The final equations are in close correlation with the experimental results. Special emphasis is placed on the fact that a good approximation—not strict physical laws—have been found.     

A Comparison of Oral and Rectal Absorption of L-Dopa Esters in Rats and Mice

Short-chain alkyl esters of L-dopa were administered to rats and mice via oral and rectal routes. Plasma L-dopa esters and L-dopa were determined in the systemic and portal circulation by HPLC. A comparison of isopropyl, butyl, and 4-hydroxybutyl esters of L-dopa demonstrated significantly higher levels of the esters in both systemic and portal blood samples following rectal administration than following oral administration. In most cases, oral administration resulted in nondetectable (<0.01 µg/ml) levels of the esters in plasma. Correspondingly, the plasma levels of L-dopa itself were consistently higher following rectal administration. At very high oral doses (500 mg L-dopa equivalents/kg body weight), systemic plasma levels of the butyl ester could be detected (1.25 µg/ml at 10 min), which might indicate saturation of the esterase activity of the small intestine. These studies indicate that the systemic availability of L-dopa from short-chain alkyl esters of L-dopa may be best optimized by rectal administration, which avoids the relatively high esterase activity characteristic of the small intestine.     

Influence of insulin on cholesterol removal from macrophages and cholesterol ester uptake by HepG2 cells

The fact that an increased blood insulin level is observed in patients with coronary artery disease (CAD) confirms the hypothesis that insulin promotes the development of atherosclerosis. The low high-density lipoprotein (HDL) concentration observed in such patients may contribute to alteration in reverse cholesterol transport and promote the accumulation of sterols in vascular tissue. We examined the effect of insulin (20−1000μUmL⁻¹) on cholesterol efflux into HDL₃ particles from human blood monocyte/macrophages and rat peritoneal macrophages preloaded with labelled cholesterol esters, and the influence of insulin on the accumulation of sterols by rat liver cells and HepG2 cell line in vitro models. Insulin at concentrations up to 250μUmL⁻¹ inhibited the efflux of cholesterol from rat macrophages and promoted high uptake of sterols by both types of hepatic cells. Pharmacological concentrations higher than 250μU mL⁻¹ exerted the opposite effect. In the case of human macrophages, an insulin concentration of 20μUmL⁻¹ increased cholesterol removal, whereas 100−200μU mL⁻¹ insulin inhibited cholesterol removal from cells, and very high concentrations (>350μUmL⁻¹) again increased cholesterol removal. We have shown that insulin excess counteracts the beneficial effects of HDL in removing cellular cholesterol and, therefore, may promote development of atherogenesis.     

Cholesterol-based personal risk assessment in coronary heart disease

Using data from the National Health and Nutrition Examination Survey (NHANES II) 1976-1980, we demonstrate how cross-sectional total serum cholesterol surveillance data can be used by an individual to assess current and future personal cholesterol risk status. We propose statistical models, based on a person's current measured cholesterol level and the relationship between cross-sectional age and cholesterol percentile estimates, that will allow prediction of future cholesterol levels or the age at which specified cholesterol risk levels will be reached if no cholesterol-altering intervention is taken. These models incorporate the observed variation in the NHANES II data and expected intraperson biological variation and intralaboratory analytical variation. We illustrate the adequacy of the models using data from the longitudinal Framingham Study.     

雷帕霉素对炎性反应状态下肾小球系膜细胞内脂质稳态的影响

Objective To investigate the effect of rapamycin on cholesterol homeostasis of glomerular mesangial cells and the underlying mechanism. Methods Glomerular mesangial cell line (HMCL) cells were cultured and divided into control group, IL-1β group and different concentration rapamycin groups. Intracellular cholesterol accumulation was observed and measured by oil O staining and HPLC. Real-time quantitative PCR and Western blot were used to detect the mRNA and protein expression of LDLR, PPARγ, LXRα, ABCA1 in HMCL after the treatment with IL-1β and rapamycin. Results Rapamycin had no significant influence on intracellular cholesterol concentration under normal condition. IL-1β significantly increased the intracellular cholesterol concentration by 143％ of control (P<0.05), and 10, 50, 100 ?滋g/L rapamycin could significantly inhibit the effect of IL-1β (87％, 116％, 96％ of control respectively, all P<0.05). Rapamycin could suppress the increased expression of LDLR caused by IL-1β on both mRNA and protein level in a dose-dependent manner（P<0.01）. Rapamycin dose-dependently up-regulated the reduced mRNA and protein expression of ABCA1, the decreased mRNA expression of PPARγ and LXRα induced by IL-1β as well (P<0.01）. Conclusion Rapamycin may contribute to the maintenance of intracellular cholesterol homeostasis in glomerular mesangial cells under inflammatory state by both reducing cholesterol uptake and promoting cholesterol efflux.     

Effect of different phospholipid-cholesterol membrane compositions on liposome-mediated formation of calcium phosphates

Summary The present report compares the effects of different membrane phospholipid (PL)-cholesterol compositions on the kinetics of liposome-mediated formation of calcium phosphates from metastable solutions (2.25 mM CaCl₂; 1.5 mM KH₂PO₄) at 22°C, pH 7.4 and 240 mOsm. In most experiments, the liposomes were composed of 7:2:X mixtures of phosphatidylcholine (PC), neutral or acidic phospholipids, and cholesterol (Chol, X=0, 10, 35, or 50 mol%). The neutral phospholipids (NPL) examined, in addition to PC, were phosphatidylethanolamine (PE) and sphingomyelin (Sph), and the acidic phospholipids (APL) examined were dicetylphosphate (DCP), dioleolylphosphatidylglycerol (DOPG), dioleolylphosphatidic acid (DOPA), phosphatidylserine (PS) and phosphatidylinositol (PI). The 7:2:X liposomes did not initiate mineralization in metastable external solutions per se or, with the exception of DOPA, show extensive Ca-PL binding. However, solution Ca²⁺ losses due to precipitation occurred when the liposomes were encapsulated with 50 mM KH₂PO₄ and made permeable to external Ca²⁺ with X-537A. The extent of these Ca²⁺ losses was sensitive to both the phospholipid and Chol makeup of the membrane. Moderate-to-extensive intraliposomal precipitation occurred in all 7PC:2APL and 7PC:2NPL liposomes containing 0 or 10 mol% Chol. In contrast, at 50 mol% Chol, mineralization inside all liposomes was negligible. The only significant discriminating effect on internal mineralization among the different phospholipids was observed at 35 mol% Chol, where mineral accumulations ranged from negligible to moderate. At 0 or 10 mol% Chol, extraliposomal precipitation was extensive in all but DOPA- and PS-containing liposomes. However, onece intraliposomal yields declined at the higher Chol levels, external mineralization was either delayed or totally blocked in all liposome preparations. Other experiments showed that Sph substituted for PC in 7NPL:2DCP:1Chol liposomes totally blocked both intra- and extraliposomal precipitaiton. PE substituted in this manner, however, blocked only extraliposomal precipitation. The results of this study suggest that interference of the membrane transport processes controlling intraliposomal precipitation [15] by high (50 mol%) Chol levels is not significantly compromised by the specific APL or NPL incorporated in the membrane. Similarly, the data suggest that Chol does not directly affect the specfic interactions of the different membrane APLs with the mineral phase. On the other hand, the substitution of other NPLs for PC can affect the role of APLs such as DCP in liposome-mediated mineralization.     

成核效应蛋白在泡凝聚融合过程中作用的初步研究

为了探讨成核效应蛋白在泡凝聚、融合过程中的作用，作者研究了胆汁中主要的促成核蛋白系统—ＣｏｎＡ结合蛋白对模拟胆汁泡的形态与脂类组成的影响，发现ＣｏｎＡ结合蛋白在加快泡凝聚与融合的同时，也使泡胆固醇增加，磷脂减少，泡胆固醇／磷脂比增高，认为成核效应蛋白促泡凝聚与融合的本质是改变了泡胆固醇饱和度。作者的初步研究还发现泡相蛋白虽量微却具有强的促成核活性；几种已知的成核效应蛋白在泡相与微胶粒相的分布有差异；胆固醇结石患者与色素结石患者相比，泡蛋白的量与促成核活性均增高。通过泡蛋白亲和染色技术，还发现ＣｏｎＡ结合蛋白能与模拟胆汁泡形成脂质－蛋白复合体。作者认为，泡中成核效应蛋白的存在或量与质的改变，在泡凝聚与融合过程中起重要作用。     

胆汁胆固醇对胆囊收缩素受体表达的影响

目的：探讨胆汁胆固醇对胆囊收缩素受体（CCK－R）表达的影响。方法 采用放射免疫分析法和受体放射配基结合法检测对照组、高胆固醇组、自然恢复组及治疗组豚鼠门静脉血CCK水平、胆囊CCK－R的最大结合容量（Bmax）和亲和力（Kd），同时观察空腹胆囊体积（FV）、胆囊胆汁量（FB）和餐后胆囊体积（RV）、胆囊胆汁量（RB）及胆囊收缩率（E％）、胆汁胆固醇浓度的变化。结果 与对照组比较，高胆固醇组豚鼠FV、FB增大（P＜0.05），RV、RB也增大，胆囊收缩率下降（P＜0.01），胆汁胆固醇浓度升高（P＜0.05），门静脉血CCK水平及CCK－R的Kd无改变，而CCK－R的Bmax下降（P＜0.01）；治疗组上述各项指标正常。结论 胆汁中的高胆固醇通过下调胆囊CCK－R表达而导致胆囊收缩功能障碍，降低胆汁高胆固醇浓度可以促进胆囊动力功能的恢复。     

Simplified determination of serum cholesterol sulfate by gas-liquid chromatography combined with cyclohexylsilane-bonded phase column purification

Summary A new gas-liquid chromatographic (GLC) determination of cholesterol sulfate (CS) and dehydroepiandrosterone sulfate (DHEAS) for a biochemical diagnosis of recessive X-linked ichthyosis (RXLI) is described. Although the GLC method for determination of CS is known to be more sensitive than the thin layer chromatographic (TLC) method, the former method has not been widely employed because of its complicated pre-purification steps. The present method allows us to measure the serum levels of CS and DHEAS without tedious purification steps such as multiple conventional column chromatography and preparative thin layer chromatography. Sulfated steroids are rapidly purified with a commercially available mini disposable cyclohexylsilane-bonded phase (CH) column, CH BOND ELUT, and the purified steroids after desulfation are converted to water-resistant tert-butyldimethylsilyl ether derivatives for the GLC analysis on dual 2 m glass columns packed with 2% XE-60 on Chromosorb W.By the present method, serum CS concentrations in RXLI patients were shown to be about 10 times higher than those in patients with ichthyosis vulgaris, carriers of RXLI, and healthy subjects. This method is more suitable not only for a biochemical diagnosis of RXLI but also for studies on the metabolism of sulfated steroids than the previous time-consuming GLC methods.