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Biomedical subjects

M Stefansson

Publications and source records attributed to M Stefansson.

11 recordsLinked to original sources
PubMed1998

Reconstitution of opsonizing activity by infusion of mannan-binding lectin (MBL) to MBL-deficient humans.

Mannan-binding lectin (MBL, previously named mannan-binding protein, MBP) is a serum collectin, which activates complement upon binding to microbial carbohydrates. This results in opsonization of the microorganisms as well as direct complement-mediated killing. Clinical evidence indicates that MBL has an important role in the innate immune defence against various pathogens. Genetically determined MBL deficiency is associated with increased susceptibility to infections. We have infused two MBL-deficient individuals with clinical grade MBL, purified from pooled donor plasma, in doses sufficient to attain normal concentration of MBL in serum. This resulted in normalization of complement-mediated opsonization. An initial rapid decrease in the serum concentration of MBL was followed by a slower decline with an estimated half-life of about 6 days. No adverse effects were observed and anti-MBL antibodies could not be detected following several MBL infusions. One of the two MBL recipient, a two-year-old girl, who had been suffering from repeated infections from the age of 4 months, was given a total of six MBL infusions. She has subsequently remained healthy for more than three years.

Adult↗
PubMed1994

Modification of the electrophoretic mobility of neutral and charged polysaccharides.

Suitable buffer additives can either induce or reduce the electrophoretic mobility of certain polysaccharides during capillary electrophoresis. With water-soluble cellulose derivatives, adsorption of detergents on the analyte molecules governs the migration rates. Different types of adsorption sites, including multilayer formation, were found to be present on the cellulose-derived polymers. For highly charged polysaccharides (heparins), the electrophoretic mobility can be controlled by the use of ion-pairing reagents. The concentration and number of cationic charges appear useful in optimizing the separation selectivity. Migration models based on secondary thermodynamic equilibria are presented and evaluated for different polysaccharides.

Carbohydrate Sequence↗
PubMed1994

Maltooligosaccharides as chiral selectors for the separation of pharmaceuticals by capillary electrophoresis.

Complexation between the linear maltodextrin oligosaccharides and certain enantiomeric compounds of pharmaceutical interest in buffered solutions can lead to an analytically desirable chiral recognition. Different maltodextrins were assessed in their capacity to cause enantiomeric separations under various conditions of capillary electrophoresis. The mechanism of chiral recognition has been probed through electrophoretic mobility and selectivity measurements for different buffer solutions and organic solvent additives. A differential interaction of chiral solutes with the maltodextrin helical entities emerges as the basis of such enantioselectivity. This notion is further supported by 1H- and 13C-NMR experiments. Optimized separations of simendan, ibuprofen, warfarin, and ketoprofen enantiomers are demonstrated together with a chiral determination of ibuprofen in a blood serum sample at the therapeutic level.

Blood Chemical Analysis↗
PubMed1994

Resolution of the branched forms of oligosaccharides by high-performance capillary electrophoresis.

The heterogeneous nature of most polysaccharides found in nature includes distribution in molecular weight, primary sequence, and branching. The analytical methodology used in the characterization of these structural aspects must ensure high separation efficiency and selectivity. This paper reports on the high-performance capillary electrophoresis (HPCE) separation of branched forms of oligosaccharides as well as some variants in the primary structure. Oligosaccharide maps were obtained after selective debranching using isoamylase, laminarinase, and cellulase enzymes. The samples investigated were alpha-D-glucans (amylose, amylopectin, and pullulan) and beta-D-glucans (exemplified by lichenan). The solutes were separated as fluorescent derivatives with 8-aminonaphthalene-1,3,6-trisulfonate (ANTS) and detected by laser-induced fluorescence at 514 nm using a He/Cd laser (excitation at 325 nm). The number of theoretical plates was in excess of one million per meter. Baseline resolution of oligosaccharides with a degree of polymerization approximately 70 was obtained within 15 min using borate buffer as the electrolyte.

Amylopectin↗
PubMed1994

Separation of complex oligosaccharide mixtures by capillary electrophoresis in the open-tubular format.

The fluorescent derivatives of complex oligosaccharide mixtures from different origins are separated in open capillaries. The number of negatively charged sulfonate groups in the tag molecule strongly affects separation efficiency and selectivity. Coating of the capillary surface with linear polyacrylamide has been essential to ensure fast and stable migration velocities. Efficiencies in excess of 1 million plates/m have been achieved, facilitating resolution of branched oligosaccharides. The effects of field strength and buffer composition on the apparent electrophoretic mobility of dextran and dextrin oligomers are discussed, with relation to borate complexation. Preliminary examples of applications to monitoring the action of hydrolytic and synthesizing enzymes are also described.

Dextrans↗
PubMed1992

Direct coupled column separation and determination of the diastereomeric glucuronides of almokalant, a new class III antiarrhythmic drug, in human urine.

A reversed-phase coupled column separation (CCS) system for the analysis of two diastereomeric glucuronides of almokalant, a new class III antiarrhythmic drug, in human urine is described. After direct injection of urine samples (50 microliters) the glucuronides were isolated by complex formation on a terbium(III) loaded strong cation exchanger at alkaline pH. The solutes were eluted from the precolumn by an acidic mobile phase, enriched and separated on Hypercarb (porous graphitic carbon) as analytical column with 0.1 M acetic acid pH 2.8 and 30% acetonitrile as mobile phase. The calibration graph was linear (r2 = 0.9999) and the detection limits were in the low picomole (UV) or femtomole (fluorescence) range. Optimization of the analytical column revealed that elution order and selectivity for the glucuronides were dependent on the buffer agent and temperature used. By appropriate choice of mobile phase conditions all four diastereomers could be separated.

Anti-Arrhythmia Agents↗
PubMed1992

Separation of glucuronides from urine by coupled-column separation using underivatized silica as precolumn.

Glucuronides are separated from urine by coupled-column separations (CCSs). The fraction containing the glucuronide(s) is transferred on-line from a silica precolumn to the analytical column (octadecyl derivatized silica), enriched, and separated by ion-pair chromatography. The retention and selectivity on the precolumn are controlled by pH, buffer components, organic modifier, and ion-pair agent. After the injection of filtered urine samples, glucuronides with different chemical properties can be separated. The total analysis of morphine-3-glucuronide and morphine-6-glucuronide is accomplished in less than six minutes, with UV detection at 210 nm.

Buffers↗
PubMed1976

Acute myopericarditis. A long-term follow-up study.

A follow-up study was made of 29 patients aged 21 to 45 years, some 15-158 months after acute myopericarditis. The mean follow-up period was 72.9 months. The follow-up investigation included recording of history, physical examination, laboratory tests, radiologic examination of the heart and lungs and electrocardiography. All but one of the patients were fit for fulltime work. Nine had residual cardiac symptoms, but the physical examination was negative in all but 2 of them. One patient had chronic cardiac insufficiency and hepatic enlargement. Another had sinus tachycardia and cardiac enlargement of moderate degree and impaired working capacity in relation to heart size. Cardiac murmurs without clinical significance were audible in three cases. The resting ECG was pathologic in only 6 cases. Orthostatic ECG evoked ECG abnormalities in 6 more cases. Exercise tolerance tests showed reduced working capacity in relation to heart volume in 5 of the 29 cases (17%). Four of these 5 patients had cardiac enlargement. There was thus good correlation between increase in heart volume and reduction of physical capacity. The prognosis in regard to cardiac function was good, as was also found in other comparable series in which the observation time was somewhat shorter.

Acute Disease↗
PubMed1976

Co-trimoxazole and nitrofurantoin in urinary-tract infections: a controlled clinical study.

The clinical efficacies of co-trimoxazole and nitrofurantoin were compared in patients with urinary-tract infections associated with significant bacteriuria with coliform bacteria tested and found to be sensitive to both drugs. Of 27 patients treated with co-trimoxazole, 23 were cured after 10 days' treatment with 320 mg trimethoprim and 1600 mg sulphamethoxazole daily (85%). Of 18 patients treated with nitrofurantoin (200 mg/day for 10 days), 7 were cured (39%). Thus, cotrimoxazole was significantly superior (p less than 0.01) in this study. A significant (p less than 0.001) but temporary and modest rise of the serum-creatinine levels was noted after 5 days' treatment with co-trimoxazole. Such a rise was not observed in the nitrofurantoin group. Only a few minor side effects were noted in both groups.

Bacterial Infections↗
PubMedDate not supplied

An unusual inhibition of an anti-P1.

Tests for unexpected antibodies using commercially prepared red blood cells demonstrated no agglutination even though crossmatching and testing with saline washed commercially prepared reagent red blood cells identified an anti-P1. This antibody was inhibited when tested with red blood cells suspended in a modified Alsever's solution and several commercially prepared reagent red blood cell diluents. The inhibitory substance was identified as inosine. Hypoxanthine, adenine, and thymine also inhibited the anti-P1. Partial inhibition was produced by uracil, 5-methylcytosine, and xanthine. No other example of anti-P1 has been found to exhibit this unusual inhibiting characteristic.

Antibodies↗