Evaluation of a new method for the analysis of free catecholamines in plasma using automated sample trace enrichment with dialysis and HPLC.
BACKGROUND: Analysis of urinary free catecholamines was automated recently, but analysis of plasma samples posed special difficulties. The present study was undertaken to evaluate a new method for the automated analysis of plasma catecholamines. METHODS: The procedure is based on an improved sample handling system that includes dialysis and sample clean-up on a strong cation trace-enrichment cartridge. The catecholamines norepinephrine, epinephrine, and dopamine are then separated by reversed-phase ion-pair chromatography and quantified by electrochemical detection. RESULTS: Use of a 740- microL sample is required to give the catecholamine detection limit of 0.05 nmol/L and analytical imprecision (CV) between 1.1% and 9.3%. The assay can be run unattended, although >12 h of analysis time is not recommended without cooling of the autosampler rack. Comparison (n = 68) of the automated cation-exchange clean-up with the well-established manual alumina procedure gave excellent agreement (mean, 3.78 +/- 2.76 and 3.8 +/- 2.89 nmol/L for norepinephrine and 0.99 +/- 1.72 and 1.08 +/- 1.78 nmol/L for epinephrine). Hemodialysis had no clear effect on plasma norepinephrine. Epinephrine concentrations were similar (0.05 < P < 0.1) in chronic renal failure patients (0.24 +/- 0.3 nmol/L; n = 15) and healthy controls (0.5 +/- 0.24 nmol/L; n = 31). Dopamine was not quantified, being usually <0.2 nmol/L. CONCLUSION: The availability of such a fully automated procedure should encourage the more widespread use of plasma catecholamine estimation, e.g., after dialysis, exercise, or trauma/surgery and in the investigation of catecholamine-secreting tumors, particularly in the anuric patient. (+info)
Inhibition of protein denaturation by fatty acids, bile salts and other natural substances: a new hypothesis for the mechanism of action of fish oil in rheumatic diseases.
Natural hydrophobic substances like bile salts (cholate, deoxycholate, chenodeoxycholate, lithocholate and their conjugates with glycine and taurine), fatty acids (caprylic, capric, lauric, myristic, palmitic, stearic, oleic, linoleic, arachidonic, eicosapentaenoic and docosahexaenoic acid) were much more active (EC50 approximately 10(-4)-10(-5) M) than selected amino acids (EC50 > 10(-2) M) and inorganic salts (EC50 approximately 10(-1) M) in inhibiting heat-induced denaturation of human serum albumin in vitro. Fish oil, rich in n-3-polyunsaturated acids such as eicosapentaenoic acid and docosahexaenoic acid, administered p.o. (1 ml/kg) in the rat, protected ex vivo (after 2 hr) serum against heat-induced denaturation more than bendazac, a known antidenaturant drug. Thus, we speculated that the antidenaturant activity of fish oil may be partly (in addition to the known effect on endogenous eicosanoid composition) responsible for its beneficial effects in rheumatoid arthritis and other rheumatic conditions. In this connection, it is of note that the in vitro antidenaturant activity of fish oil fatty acids was higher than that of known antidenaturant drugs such as bendazac and bindarit and nonsteroidal anti-inflammatory drugs like phenylbutazone and indomethacin which could exert beneficial effects in chronic inflammatory conditions by stabilizing endogenous proteins. (+info)
Kinetics and mechanism of exchange of apolipoprotein C-III molecules from very low density lipoprotein particles.
Transfer of apolipoprotein (apo) molecules between lipoprotein particles is an important factor in modulating the metabolism of the particles. Although the phenomenon is well established, the kinetics and molecular mechanism of passive apo exchange/transfer have not been defined in detail. In this study, the kinetic parameters governing the movement of radiolabeled apoC molecules from human very low density lipoprotein (VLDL) to high density lipoprotein (HDL3) particles were measured using a manganese phosphate precipitation assay to rapidly separate the two types of lipoprotein particles. In the case of VLDL labeled with human [14C]apoCIII1, a large fraction of the apoCIII1 transfers to HDL3 within 1 minute of mixing the two lipoproteins at either 4 degrees or 37 degrees C. As the diameter of the VLDL donor particles is decreased from 42-59 to 23-25 nm, the size of this rapidly transferring apoCIII1 pool increases from about 50% to 85%. There is also a pool of apoCIII1 existing on the donor VLDL particles that transfers more slowly. This slow transfer follows a monoexponential rate equation; for 35-40 nm donor VLDL particles the pool size is approximately 20% and the t1/2 is approximately 3 h. The flux of apoCIII molecules between VLDL and HDL3 is bidirectional and all of the apoCIII seems to be available for exchange so that equilibrium is attained. It is likely that the two kinetic pools of apoCIII are related to conformational variations of individual apo molecules on the surface of VLDL particles. The rate of slow transfer of apoCIII1 from donor VLDL (35-40 nm) to acceptor HDL3 is unaffected by an increase in the acceptor to donor ratio, indicating that the transfer is not dependent on collisions between donor and acceptor particles. Consistent with this, apoCIII1 molecules can transfer from donor VLDL to acceptor HDL3 particles across a 50 kDa molecular mass cutoff semipermeable membrane separating the lipoprotein particles. These results indicate that apoC molecules transfer between VLDL and HDL3 particles by an aqueous diffusion mechanism. (+info)
Isolation and characterization of a Ca2+ -binding polysaccharide associated with coccoliths of Emiliania huxleyi (Lohmann) Kamptner.
C-occolithophoridae, a group of mostly unicellular algae, possess a cell wall containing calcified plates, called coccoliths. The coccoliths from the species Emilania huxleyi (Lohmann) Kamptner contain a water-soluble acid polysaccharide. In this paper we describe the isolation and some characteristic properties of the polysaccharide, in particular its Ca2+ -binding capacity. A large-scale cultivation of the Coccolithophoridae was worked out and a new procedure for isolating coccoliths was developed. The polysaccharide obtained from the coccoliths contained two types of monobasic acid groups in a total amount of 1.8 mumol/mg polysaccharide. One type consisted of weakly acid groups which were identified as uronic acids. The nature of the stronger acid groups remains to be established. The ratio between the respective groups was 1:0.8. Studies with 45Ca2+ demonstrated that the isolated polysaccharide is capable of binding Ca2+. Equilibrium dialysis revealed that the maximum amount of Ca2+ which can be bound in 0.92 +/- 0.05 mumol/mg polysaccharide. Flow-rate dialysis experiments strongly suggested the presence of two classes of Ca2+ -binding sites differing in affinity for Ca2+. High-affinity sites (dissociation constant Kd for Ca2+ :2.2 +/- 1.0 X 10(-5) M) were found to be present in amounts (0.38 +/- 0.04 mumol/mg polysaccharide) approximately equivalent to the strongly acid monovalent groups mentioned above (0.8 mumol/mg polysaccharide). Low-affinity sites (Kd for Ca2+: -11 +/- 39 X 10(-5) M) were estimated at 0.74 +/- 0.11 mumol/mg polysaccharide. Although this figure could be determined less accurately, it is suggested that the uronic acids (1.0 mumol/mg polysaccharide) are identical to the low-affinity sites. Preferential binding of Ca2+ occurred in a 100-fold excess of Na+ and Mg2+ as was shown by gel filtration. A 100-fold excess of Sr2+ inhibited Ca2+ binding to a great extent while no Ca2+ was bound in the presence of an equimolar amount of La3+. The dissociation constants of the high-affinity sites for Na+, Mg2+, Sr2+ and La3+ (in the presence of Ca2+) were determined with the flow-rate dialysis technique. They confirm the order of binding preference found with gel filtration. A polysaccharide with similar properties could be isolated from subfossil coccoliths of E. hyxleyi (about 1000 years old). The possible role of the polysaccharide as a heterogeneous matrix in coccolith formation is discussed. (+info)
Polyamine-dependent deoxyribonuclease activity from rat-liver nuclei.
When nuclei isolated from rat liver in a low salt buffer were washed with 0.1 M NaCl solution, the supernatant showed a deoxyribonuclease (DNase) activity. The activity required Mg2+ and in addition spermine or spermidine, and its optimal pH was 7.2-7.4. The activity was higher on denatured (single stranded) DNA than on double-helical DNA. With both substrates the activity was highest at a polyamine concentration at which the DNA-polyamine complex began to precipitate. No Mg2++Ca2+ dependent DNase activity was detected in the preparation. (+info)
Tissue distribution and characteristics of xanthine oxidase and allopurinol oxidizing enzyme.
Tissue distribution and levels of allopurinol oxidizing enzyme and xanthine oxidase with hypoxanthine as a substrate were compared with supernatant fractions from various tissues of mice and from liver of mice, rats, guinea pigs and rabbits. The allopurinol oxidizing enzyme activities in liver were quite different among the species and the sex difference of the enzyme activity only in mouse liver. In mice, the highest activity of allopurinol oxidizing enzyme was found in the liver with a trace value in lung, but the enzyme activity was not detected in brain, small intestine and kidney, while the highest activity of xanthine oxidase was detected in small intestine, lung, liver and kidney in that sequence. The allopurinol oxidizing enzyme activity in mouse liver supernatant fraction did not change after storage at -20 degrees C or dialysis against 0.1 M Tris-HCl containing 1.15% KCl, but the activity markedly decreased after dialysis against 0.1 M Tris-HCl. On the contrary, the xanthine oxidase was activated 2 to 3 times the usual activity after storage at -20 degrees C or dialysis of the enzyme preparation. These results indicated that allopurinol was hydroxylated to oxipurinol mainly by the enzyme which is not identical to xanthine oxidase in vivo. A possible role of aldehyde oxidase involved in the allopurinol oxidation in liver supernatant fraction was dicussed. (+info)
Early requirement for alpha-SNAP and NSF in the secretory cascade in chromaffin cells.
NSF and alpha-SNAP have been shown to be required for SNARE complex disassembly and exocytosis. However, the exact requirement for NSF and alpha-SNAP in vesicular traffic through the secretory pathway remains controversial. We performed a study on the kinetics of exocytosis from bovine chromaffin cells using high time resolution capacitance measurement and electrochemical amperometry, combined with flash photolysis of caged Ca2+ as a fast stimulus. alpha-SNAP, a C-terminal mutant of alpha-SNAP, and NEM were assayed for their effects on secretion kinetics. Two kinetically distinct components of catecholamine release can be observed upon fast step-like elevation of [Ca2+]i. One is the exocytotic burst, thought to represent the readily releasable pool of vesicles. Following the exocytotic burst, secretion proceeds slowly at maintained high [Ca2+]i, which may represent vesicle maturation/recruitment, i.e. some priming steps after docking. alpha-SNAP increased the amplitude of both the exocytotic burst and the slow component but did not change their kinetics, which we examined with millisecond time resolution. In addition, NEM only partially inhibited the slow component without altering the exocytotic burst, fusion kinetics and the rate of endocytosis. These results suggest a role for alpha-SNAP/NSF in priming granules for release at an early step, but not modifying the fusion of readily releasable granules. (+info)
Daunomycin-induced unfolding and aggregation of chromatin.
Using equilibrium dialysis and sedimentation velocity analysis, we have characterized the binding of the anti-tumor drug daunomycin to chicken erythrocyte chromatin before and after depletion of linker histones and to its constitutive DNA under several ionic strengths (5, 25, and 75 mM NaCl). The equilibrium dialysis experiments reveal that the drug binds cooperatively to both the chromatin fractions and to the DNA counterpart within the range of ionic strength used in this study. A significant decrease in the binding affinity was observed at 75 mM NaCl. At any given salt concentration, daunomycin exhibits higher binding affinity for DNA than for linker histone-depleted chromatin or chromatin (in decreasing order). Binding of daunomycin to DNA does not significantly affect the sedimentation coefficient of the molecule. This is in contrast to binding to chromatin and to its linker histone-depleted counterpart. In these instances, preferential binding of the drug to the linker DNA regions induces an unfolding of the chromatin fiber that is followed by aggregation, presumably because of histone-DNA interfiber interactions. (+info)