Analytical strategies for therapeutic monitoring of drugs and metabolites in biological fluids : Plenary lecture

Therapeutic drug monitoring can involve quantitation in either microgram, nanogram or picogram concentrations present in a complex biological matrix (whole blood, urine or tissue).The chemical structure of a compound influences not only the analytical method best suited to its quantitation, but also its acid/base character (PK_a) and its extractability. The dose administered, the bioavailability of the dosage form, and the pharmacokinetic profile of the drug govern the circulating concentrations of either the parent drug and/or its metabolites present in vivo, and dictate the ultimate sensitivity and specificity required of the analytical method.The degree of sample preparation required is dependent on the analytical method used (gas—liquid chromatography, thin-layer chromatography, high-performance liquid chromatography) and on the tolerance of the specific type of detection system to contamination. Factors leading to compound losses during sample preparation (adsorption, stability) are critical at low concentrations and can adversely affect the reliability of an assay, therefore maximizing the overall recovery of the assay is essential not only for high sensitivity but also for good precision and accuracy. Therefore, the criteria to be used in sample preparation should aim to optimize all of the above factors in the overall development of a reliable and validated method for the compound suitable for use in clinical therapeutic monitoring.     

Growth and fermentation characteristics of new selected strains of Saccharomyces at high temperatures and high cell densities

Maintenance of high cell viability was the main characteristic of our new strains of thermotolerant Saccharomyces. Total sugar conversion to ethanol was observed for sugarcane juice fermentation at 38-40 degrees C in less than 10 h and without continuous aeration of the culture. Invertase activity differed among the selected strains and increased during fermentation but was not dependent on cell viability. Invertase activity of the cells and optimum temperature for growth, as well as velocity of ethanol formation, were dependent on medium composition and the type of strain used. At high sugarcane syrup concentrations, the best temperature for ethanol formation by strain 781 was 35 degrees C. Distinct differences among the velocities of ethanol production using selected strains were also observed in sugarcane syrup at 35-38 degrees C.     

Presynaptic Mechanism of Action of 4-Aminopyridine: Changes in Intracellular Free Ca2+ Concentration and Its Relationship to B-50 (GAP-43) Phosphorylation

Abstract: Recently we have shown that 4-aminopyridine (4-AP), a drug known to enhance transmitter release, stimulates the phosphorylation of the protein kinase C substrate B-50 (GAP-43) in rat brain synaptosomes and that this effect is dependent on the presence of extracellular Ca²⁺. Hence, we were interested in the relationship between changes induced by 4-AP in the intracellular free Ca²⁺ concentration ([Ca²⁺]_i) and B-50 phosphorylation in synaptosomes. 4-AP (100 μ M ) elevates the [Ca²⁺]_i (as determined with fura-2) to approximately the same extent as depolarization with 30 m M K⁺ (from an initial resting level of 240 n M to ∼480 n M after treatment). However, the underlying mechanisms appear to be different: In the presence of 4-AP, depolarization with K⁺ still evoked an increase in [Ca²⁺]_i, which was additive to the elevation caused by 4-AP. Several Ca²⁺ channel antagonists (CdCl₂, LaCl₃, and diphenylhydantoin) inhibited the increase in B-50 phosphorylation by 4-AP. It is interesting that the increase in [Ca²⁺]_i and the increase in B-50 phosphorylation by 4-AP were attenuated by tetrodotoxin, a finding pointing to a possible involvement of Na⁺ channels in this action. These results suggest that 4-AP (indirectly) stimulates both Ca²⁺ influx and B-50 phosphorylation through voltage-dependent channels by a mechanism dependent on Na⁺ channel activity.     

Calcium binding induces conformational changes in muscle regulatory proteins.

Calcium binding to proteins containing the 'EF-hand' structural motif regulates a variety of biochemical processes including muscle contraction. Techniques such as protein crystallography, site-directed mutagenesis and domain transplantation experiments are being used to unravel the conformational changes induced by calcium binding.     

Enhancement of Endogenous Release of Glutamate and γ-Aminobutyric Acid from Hippocampus CA1 Slices After In Vivo Long-Term Potentiation

The effect of long-term potentiation (LTP) on endogenous amino acid release from rat hippocampus slices was studied. LTP was induced in vivo by application of a tetanus (200 Hz, 200 ms) to the Schaffer collateral fibers in unanesthetized rats. Endogenous release of glutamate and gamma-aminobutyric acid (GABA) was investigated 60 min after tetanization in CA1 subslices of potentiated and control rats. No significant effects of LTP were observed in basal and K(+)-induced Ca(2+)-independent release components of these amino acids. In contrast, K(+)-induced Ca(2+)-dependent release of both glutamate and GABA increased approximately 100% in slices from potentiated rats. No differences were observed in total content of glutamate and GABA between the subslices from control and LTP animals. These results suggest a persistent increase in the recruitment of the presynaptic vesicular pool of glutamate and GABA during LTP.     

Effects of hydrostatic pressure on a membrane-enveloped virus: high immunogenicity of the pressure-inactivated virus.

A new approach to the preparation of antiviral vaccines relying on the inactivation of the virus particle by hydrostatic pressure is described. The enveloped virus vesicular stomatitis virus was utilized as a model; a pressure of 260 MPa applied for 12 h reduced infectivity by a factor of 10(4), and the antibodies against pressurized material were as effective as those against the intact virus when measured by their neutralization titer. Fluorescence measurements indicate that application of pressure results in perturbations of the particle interactions that permit binding of specific molecular probes. Electron microscopy showed that the membrane of the pressurized virus was partially preserved, presenting the spike pattern of the membrane G protein. Unlike the icosahedral viruses, dissociation into smaller particles was not observed, but a constant change in the morphology was the presence of a bulge in the surface of the pressurized virus, indicating a displacement of the capsid subunits, retained under the lipid and protein membrane.     

Water utilization of tropical hardwood hammocks of the Lower Florida Keys

Summary Predawn water potential of representative plant species, together with stable isotope composition of stem water and potential water sources were investigated in four low-elevation tropical hardwood hammocks in the Lower Florida Keys, during a one year period. Hammock species had the lowest water potentials when soil water content was low and/or soil salinity was high, but differences in groundwater salinity had no effect on the water potential. Comparison of D/H ratio of plant stem water with soil and ground water corroborates the conclusion that they are primarily utilizing soil water and not groundwater. Thus, tropical hardwood hammocks are buffered from saline groundwater, and are able to thrive in areas where groundwater salinity is as high as 25. The effect of sea level rise on these forests may depend more on changes in the frequency of tidal inundation of the soil surface than on changes in groundwater salinity.     

Living immobilized Acetobacter in Ca-alginate in vinegar production: Perliminary study on optimum conditions for immobilization

Summary The optimum conditions forAcetobacter immobilization were investigated. The results show that: 1) the maximum oxygen uptake rate (OURm) and cell release are related to alginate and cell concentration in the gel; 2)different alginate concentration does not affect cell viability, but long storage in CaCl₂ reduces the number of living cells; 3)the double alginate gel layers had no influence on cell viability and on the OURm and prevented cell leakage from the gel matrix.