Characterization of temperature-dependent drug release from liposomes using electron spin resonance

Liposome blood clearance and temperature-dependent drug release were studied using an electron spin resonance technique on whole blood samples. Temperature-sensitive liposomes composed of dipalmitoylphosphatidylcholine and dipalmitoylphosphatidylglycerol (4:1 by weight) were formed by reversed-phase evaporation. The liposomes were stable in the blood for greater than 2 h after iv injection. Liposome blood clearance exhibited a fast and slow component which may be due to the presence of both large and small liposomes in the preparation. The onset temperature for liposome release of the water-soluble nitroxide spin label was reduced from 40 degrees C in Hepes buffered saline to 38 degrees C in the rat blood, and the total release in the blood was approximately 25% greater than that measured in saline. These results show the influence of blood constituents on temperature-dependent drug release from liposomes.

Delivery of nitroxide spin label to cultured cells by liposomes

The positively charged nitroxide spin label, 2,2,6,6-tetramethyl-piperidine-N-oxyl-4-trimethylammonium (Cat1), was encapsulated in two types of liposomes, phosphatidylserine/phosphatidylcholine (PS/PC) and phosphatidylserine/distearoylphosphatidylcholine/dipalmitoylphosphatidyl choline (PS/DSPC/DPPC). The liposomes were incubated with mouse thymus-bone marrow (TB) cells to study the uptake and metabolism of nitroxides entrapped in liposomes. The effects of temperature, metabolic inhibitors, and fixation of cells were investigated. The results indicate that different mechanisms are involved in the uptake of these two types of liposomes. PS/PC liposomes interact predominantely with the plasma membrane of TB cells and release Cat1 continuously, whereas the majority of PS/DSPC/DPPC liposomes are taken into the cells intact via endocytosis. These findings suggest that it may be possible to deliver nitroxides selectively, either to the membrane of cells or to their interior by manipulating the lipid composition of the liposomes. This study also found that the rate of reduction of Cat1 delivered using liposomes was increased under hypoxic conditions. Thus, the use of liposomes for in vivo delivery of nitroxides has the potential to provide NMR contrast that reflects different metabolic conditions.

Classification of resistance to passive motion using minimum probability of error criterion

Neurologists diagnose many muscular and nerve disorders by classifying the resistance to passive motion of patients' limbs. Over the past several years, a computer-based instrument has been developed for automated measurement and parameterization of this resistance. In the device, a voluntarily relaxed lower extremity is moved at constant velocity by a motorized driver. The torque exerted on the extremity by the machine is sampled, along with the angle of the extremity. In this paper a computerized technique is described for classifying a patient's condition as 'Normal' or 'Parkinson disease' (rigidity), from the torque versus angle curve for the knee joint. A Legendre polynomial, fit to the curve, is used to calculate a set of eight normally distributed features of the curve. The minimum probability of error approach is used to classify the curve as being from a normal or Parkinson disease patient. Data collected from 44 different subjects was processes and the results were compared with an independent physician's subjective assessment of rigidity. There is agreement in better than 95% of the cases, when all of the features are used.

Selective effects of N-acetylcysteine stereoisomers on hepatic glutathione and plasma sulfate in mice

Administration of 1200 mg/kg N-acetyl-L-acetyl-L-cysteine to mice apparently increased the rate of glutathione synthesis resulting in prolonged elevation of the hepatic glutathione pool. At 3 hr, peak glutathione concentrations nearly doubled. The fraction of glutathione in the oxidized state remained at normally low values over this period. The L isomer also significantly increased plasma and urinary concentrations of inorganic sulfate. Plasma concentrations nearly doubled at their peak and urinary excretion over 24 hr rose some threefold above control. Consistent with the known stereoselectivity of many biological processes, the unnatural D isomer of N-acetylcysteine failed to increase hepatic glutathione. Liver concentrations remained similar to control suggesting that the D isomer was unable to increase the rate of glutathione synthesis. The D isomer further differed from its L enantiomer in failing to increase the plasma concentration and the urinary excretion of inorganic sulfate. Congruent with these observations, much more N-acetyl-D-cysteine (47% of dose) was recovered unchanged in 24 hr urine than N-acetyl-L-cysteine (6.1% of dose). These findings are of toxicologic interest because they identify the N-acetylcysteine stereoisomers as a pair of agents that may be useful in separating biologic effects of sulfhydryls that are related primarily to their physical properties (i.e. reduction, radical scavenging) from those that accrue from their ability to increase glutathione and sulfate availability in vivo.

Liposome delivery of NMR contrast agents for improved tissue imaging

Large unilamellar liposomes containing the paramagnetic contrast agent manganese chloride were shown to selectively enhance the intensity of the proton NMR signal from the livers of experimental mice. The kinetics of the observed effect indicate that the liposomes are rapidly removed from the circulation and deposited in high concentration within the liver. This process is known to involve the phagocytic activity of macrophages. These results show that liposomes could provide a useful and efficient vehicle for delivering NMR contrast agents to organs like the liver, spleen, and bone marrow. It may also be possible to use liposomes to selectively deliver contrast agents to tissue regions of developing pathology that are rich in macrophage activity.

HLA and systemic lupus erythematosus in Chinese

Seventy-five unrelated Chinese SLE patients were HLA typed and subdivided into mild and severe disease. The HLA-B13 was associated with mild disease. Fourteen of 30 (46.7%) mild disease patients had B13 compared to 63/330 (19.1%) normal subjects (p less than 0.0005, corrected p less than 0.013, RR = 3.7). The HLA-B17 on the other hand was observed in 29% of 45 severe disease patients compared to 13.9% of 330 normal subjects (p less than 0.01, RR = 2.5). The frequency of HLA-B17 in 11 patients who died was even higher (45.5%).