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Biomedical subjects

R D Brown

Publications and source records attributed to R D Brown.

At least 217 records · Page 12Linked to original sources
PubMed1989

Evaluation of polyaza macrocyclic methylene phosphonate chelates of Gd3+ ions as MRI contrast agents.

Gd(DTPA)2- (diethylenetriaminepentaacetic acid) and the polyaza macrocyclic Gd(DOTA)- (1,4,7,10-tetraazacyclododecane-N,N',N'',N''') are paradigms of general purpose paramagnetic complexes useful for enhancing contrast in magnetic resonance imaging (MRI). It is of both fundamental and practical interest to determine how one might modify the chemical structure of these chelate complexes to improve their utility for MRI in specific circumstances. In the present work, we investigated polyaza methylene phosphonate complexes of Gd3+ ions to compare their NMRD profiles with those of their carboxylate analogs and with Gd(DTPA)2-. We find that the number q of exchangeable water molecules coordinated directly to the Gd3+ ions tends to be smaller in the phosphonates, in principle reducing their utility in MRI. However, these phosphonates have a tendency to oligomerize, and the resulting decrease in rotational mobility of the paramagnetic oligomers increases their relaxivity at higher fields, offsetting the effect of decreases in q. In particular, Gd(DOTRP)3- (1,5,9-triazacyclododecane-N,N',N'',-tris(methylenephosphonic++ + acid] would be an increasingly effective contrast agent above approximately 10 MHz if the oligomerization was stable in vivo (and the Gd3+ ions were sufficiently well bound). At lower fields, the relaxivity of these small chelate complexes is dominated by tau S0, the relaxation time of the spin moments of the paramagnetic ions. We find this to be favorably long for complexes of Gd3+ with the macrocyclic phosphonate ligands, as was found earlier by us for Gd(DOTA)-. This situation, ostensibly related to the relatively high symmetry and rigidity of the macrocyclic complexes, can increase the low-field relaxivity of the phosphonates almost a factor of 2 beyond that of Gd(DTPA)2-.

Chelating Agents↗
PubMed1989

Relaxometry of lens homogenates. II. Temperature dependence and comparison with other proteins.

We have extended our earlier work (C.F. Beaulieu, J.I. Clark, R.D. Brown III, M. Spiller, and S.H. Koenig, Magn. Reson. Med. 8, 45 (1988] on the magnetic field dependence of 1/T1 (NMRD profiles) of calf lens nuclear homogenates, at 25 degrees C, to 5 degrees C, and to other protein systems as well. These include concentrated solutions of myoglobin and bovine serum albumin, both globular proteins, the first compact and roughly spherical, the other extended, flexible, and with weak internal bonding; chicken lens homogenate, for which the dominant crystallins (lens proteins) are approximately 70% alpha-helical compared with calf crystallins, which are essentially all beta-sheet; and hen egg white, both native and heat-denatured. Our earlier conjectures regarding a reversible change in protein organization of the calf lens crystallins as a function of solute protein concentration is given added support. Our findings suggest that cytoplasmic homogenate can be characterized as a heterogeneous and polymorphic solution of crystallins. At high concentrations the NH moieties of the protein backbone become accessible to solvent with water (not NH proton) exchange rates greater than 10(4) s-1. This conclusion is based on two aspects of the observed NMRD profiles. At low crystallin concentration, the profiles of calf and chicken lens homogenates are similar in form to those of myoglobin and native hen egg white, a form that has been studied previously for a range of diamagnetic globular proteins and has been demonstrated to arise from the rotational thermal motion of the solute molecules. At high crystallin concentrations, the NMRD profiles of the lens homogenates develop a monotonic background (high rates at low fields), much like that of the heat-denatured egg-white sample and those of most tissues. In addition, there is a set of peaks in the central part of the profiles of the concentrated crystallins, seen also in the denatured egg white and some tissues but not in the myoglobin sample, which is known to arise from cross-relaxation interactions between the water protons and (through the intermediary of the NH proton) the 14N quadrupolar levels. The magnitude of these peaks, which is larger by an order of magnitude for native calf lens homogenates than for any tissue, requires that the majority of the NH moieties be accessible to water. Finally, going to 5 degrees C for the native calf lens homogenate takes the sample below the temperature of reversible phase separation, and it becomes opaque.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1989

The spore coat of a fucosylation mutant in Dictyostelium discoideum.

Strain HL250 of Dictyostelium discoideum cannot convert GDP-mannose to GDP-fucose, resulting in an inability to fucosylate protein. This affects a group of proteins which are normally fucosylated intracellularly and then secreted via prespore vesicles to become part of the outer lamina of the spore coat. We have found that strain HL250 nevertheless accumulates typical amounts of these proteins, stores them normally in prespore vesicles, and secretes them normally to become a part of the spore coat. However, affected proteins are proteolyzed after germination, the spore coat is more accessible to penetration by a macromolecular probe, and germination is inefficient in older spores. These findings can be explained by a dependence of the integrity of the outer layer of the spore coat on protein-linked fucose.

Antibodies, Monoclonal↗
PubMed1989

Toxicology studies of a chemical mixture of 25 groundwater contaminants. I. Chemistry development.

As part of an effort to evaluate the toxicology of a chemically defined mixture of 25 frequently detected groundwater contaminants, we report here the formulation and analytical chemistry of this mixture. Many problems were anticipated, including limitation of solubility, chemical interactions, and extreme volatility in the aqueous solution of 25 chemicals. The final technically achievable stock solution was prepared based on EPA survey concentrations of these chemicals in groundwater around hazardous waste disposal sites, their toxicity information, and solubility of the individual compounds in the matrix of the aqueous solution of these 25 chemicals. Because the anticipated animal studies were to be conducted at various laboratories, for ease of handling and maximum stability, the stock solution was stored or shipped as two substock solutions: an organic substock with 18 neat organic chemicals in a glass vial sealed with minimum headspace and an aqueous substock solution with 6 metals of various salt forms and phenol. The concentrations of the solutions were such that direct mixing of the organic and aqueous substocks produced the desired high dose level for the animal experiments. Analyses of all 25 chemicals in the drinking water mixture required six different chromatographic and spectroscopic methods. Some loss of organic volatiles during mixing of the substocks and during the first 24 hr following preparation did occur. However, the concentrations of acetone, phenol, and all the metals remained constant during preparation. Solutions held under simulated animal cage conditions for 96 hr showed losses of the organic volatiles; the majority of which occurred within the first 24 hr. This study shows that it is possible to conduct animal experiments on an aqueous mixture containing 25 groundwater contaminants. Furthermore, a reasonable estimate of intake of individual chemicals can be achieved provided that dosing solutions are prepared fresh at frequent intervals (e.g., 48 to 72 hr) and that comprehensive analyses are carried out.

Acetone↗
PubMed1989

Seasonal levels of cortisol, triiodothyronine and thyroxine in male axis deer.

1. Seasonal plasma levels of thyroxine (T4), triiodothyronine (T3) and cortisol were investigated between November and June in seven penned male Axis deer. 2. No distinct seasonal variation of cortisol has been detected. The levels oscillated between 1 and 5 micrograms/dl. 3. The stress of immobilization and sampling had little effect on cortisol levels. Concentrations remained mostly stable in three consecutive samples taken 10 min apart. 4. T3 concentrations were stable between November and March (average values 110-120 ng/dl). After a sharp decline in April (average 70 ng/dl), a strong rebound in May and June was observed. 5. A distinct seasonal peak of T4 (highest individual value, 12.1 micrograms/dl) was detected in March. After a sharp decline in April (lowest individual value, 4.5 micrograms/dl) a strong rebound followed in May.

Animals↗
PubMed1989

The effect of yohimbine on plasma levels of T3, T4 and cortisol in xylazine-immobilized white-tailed deer.

1. The effect of yohimbine (Y) on blood levels of thyroxine (T4), triiodothyronine (T3), and cortisol was investigated in 5 mature male white-tailed deer immobilized with xylazine hydrochloride (X). 2. T4 levels were erratic in X-treated deer, but stabilized in the X- and Y-treated deer. 3. T3 remained unchanged in both groups. 4. Cortisol levels have increased in X-treated deer, but declined in X- and Y-treated deer. 5. Yohimbine is a potent and safe antidote of X not affecting T3 and T4. Caution should be used in using R or Y in cortisol studies.

Animals↗
PubMed1989

Human cardiolipin as the antigen in an ELISA to detect anticardiolipin antibodies.

Human cardiolipin was purified from cadaver heart tissue and used as the antigen in an enzyme-linked immunoassay (ELISA) for anticardiolipin antibodies. The correlation between assays using human and bovine cardiolipin was r = 0.90. Of the lupus anticoagulant positive patients 88% had antibodies to the human antigen and 75% had antibodies to the bovine antigen. Six of 45 samples contained antibodies which only reacted with the human antigen. All six samples remained positive when retested with a different human cardiolipin preparation and were negative when tested against a preparation of sheep cardiolipin. These studies suggest that there was increased specificity when human cardiolipin was used as the phospholipid antigen.

Animals↗
PubMed1989

Sources of the increased longitudinal relaxation rates observed in melanotic melanoma. An in vitro study of synthetic melanins.

Researchers have suggested that the increased longitudinal relaxation rates (1/T1) of solvent water protons often found in melanoma result either from the paramagnetism of stable free radicals occurring in melanin or from that of methemoglobin in nonacute hemorrhagic regions of the tumor. However, field-cycling relaxometry and model solutions of synthetic melanin produced data which show that free radicals in melanin do not contribute significantly to 1/T1; instead, aggregation of melanin into macromolecular particles and binding of biologically-common paramagnetic metal ions (ie Fe3+, Mn2+, and Cu2+) to melanin effectively do increase 1/T1. These data have been combined with published histochemical data on melanin-containing tissues, while disregarding any additional effect related to hemorrhage. The result indicates that in melanoma the expected contribution of melanin-bound Fe3+ to 1/T1, at typical imaging fields, predominates under estimated in vivo conditions; furthermore, the total contribution from all sources, specifically due to the presence of melanin, is sufficient to account for reported measurements of 1/T1 in melanoma. Comparing the latter results with published data on T1 relaxation in model solutions of methemoglobin suggests that co-existing regions of nonacute microhemorrhage also may contribute significantly to 1/T1 under certain conditions. Finally, the implications for 1/T2 of melanin occurring in vivo within discrete melanosomes is discussed.

Chemical Phenomena↗
PubMed1989

Serum thymidine kinase as a marker of disease activity in patients with multiple myeloma.

Serum thymidine kinase (STK) levels have recently been used to detect tumour regression and progression in a number of hematological malignancies. In this study, patients with myeloma were monitored longitudinally for STK and several other potentially useful tumour markers to determine which laboratory parameters are the most useful for differentiating between stable and progressive disease. STK was determined by radioenzyme assay, lymphocyte surface markers were analysed by flowcytometry, plasma cell labelling index (LI) by immunofluorescence with anti BU-1, serum B2-microglobulin (SB2M) by radioimmunoassay and M proteins by radial immunodiffusion. Detailed multiparameter longitudinal investigations of 5 patients and ongoing studies of 70 other patients suggest that STK is a more reliable marker of progressive disease than either SB2M, LI, M-protein or CD10 positive lymphocytes. A rise in STK during the emergence of progressive disease at least paralleled and usually preceded any change in the other parameters which often did not change at all. All samples from patients with progressive disease (n = 29) had a STK above the normal range (0-5U/l) whereas 76% of patients in clear stable disease had a STK within the normal range. All samples (n = 34) from patients with light chain isotype suppression (LCIS) had STK values of less than 12 U/L and 82% of samples (n = 33) from patients without LCIS had a STK above the normal range (0-5U/L). The correlation between STK and LI was r = 0.65; p less than 0.001 (n = 21). The radioenzyme assay for STK is simple, reproducible and a valuable tool for monitoring patients with myeloma and when used in conjunction with other clinical and laboratory investigations, aids in the separation of patients with stable myeloma from patients whose disease is progressive.

Antigens, Differentiation↗
PubMed1989

Visual toxicity of synthetic retinoids.

Twelve patients treated with isotretinoin, a synthetic vitamin A analogue, were assessed before, during, and after therapy. Significant falls occurred in the amplitude of the a waves of the scotopic electroretinogram.

Electroretinography↗
PubMed1989

Antimicrobial therapy in neonates, infants and children.

Many antimicrobial medications may be administered to paediatric patients with a degree of impunity because they are relatively non-toxic and have a wide therapeutic margin. However, because of different pharmacokinetics from those in adults, the potential for toxicity exists with the use of some of these agents. Drug absorption in paediatric patients, either orally or parenterally, is generally similar to that in adults, except among neonates and, particularly, premature neonates. Similarly, in neonates, drug distribution is altered, plasma protein binding is decreased and hepatic metabolism and renal excretory capacity are limited by physiological immaturity. Thus, in neonates, only drugs that have pharmacokinetically derived dosage schedules should be used, and therapeutic monitoring of plasma drug concentrations is recommended during therapy with aminoglycosides, vancomycin and chloramphenicol. In older infants and children, the pharmacokinetics of antimicrobial drugs generally approximate those in adults, and recommended dosages have been determined relative to bodyweight. Therapeutic monitoring of plasma drug concentrations may be important in certain patients, such as those with major organ failure, and may be useful in cases of suspected noncompliance. Additional pharmacokinetic considerations concerning antimicrobial medication and paediatric patients are the extent to which drug therapy penetrates the cerebrospinal fluid in meningitis, and the potential for and implications of exposure of infants to antimicrobial medications excreted in breast milk.

Anti-Infective Agents↗
PubMed1989

Multiple myeloma: evidence that light chains play an immunoregulatory role in B-cell regulation.

Supernatants from human lymphoblastoid and plasma cell lines were added to cultures of normal cells stimulated with pokeweed mitogen (PWM) with the aim of providing an in vitro model for light chain isotype suppression (LCIS). Supernatants from the kappa-secreting cell line LICR-LON-HMY2 were specifically able to block the secretion of kappa-associated immunoglobulin and supernatants from the lambda-secreting cell line U266 were specifically able to block the secretion of lambda-associated immunoglobulin without any effect on the secretion of the other light chain isotype. Supernatant from a human leukemia line, HL60, did not block either kappa or lambda immunoglobulin secretion. Purging studies where kappa or lambda light chains were removed from supernatants of these cell lines suggest that this is a direct effect of light chain and not due to any other nonspecific inhibitory material which may be present.

B-Lymphocytes↗
PubMed1988

A new interstellar polyatomic molecule: detection of propynal in the cold cloud TMC-1.

We report the detection of the acetylene derivative propynal (HC triple bond CCHO) in the cold cloud TMC-1, with an abundance that is very close to that for the related species tricarbon monoxide (C3O). Propadienone, an isomer of propynal with the formula H2C=C=C=O, was not detected and is hence less abundant than either C3O or HC2CHO.

Aldehydes↗
PubMed1988

Effects of cisplatin and thiosulfate upon auditory brainstem responses of guinea pigs.

Two side effects which limit the use of cisplatin in cancer chemotherapy are severe nephrotoxicity and ototoxicity. The concurrent administration of sodium thiosulfate with cisplatin reportedly protects from cisplatin nephrotoxicity, however, protection from ototoxicity has not been documented. The purpose of this study was to examine the efficacy of using thiosulfate to ameliorate the ototoxic effects of cisplatin. Toward this end, the effects of cisplatin alone, cisplatin administered concurrently with sodium thiosulfate (CIS/THIO), and sodium thiosulfate alone on the auditory brainstem response (ABR) of guinea pigs were compared. ABR waveforms, comparing latencies, amplitudes and response thresholds, were monitored before, immediately after, and 30 days post treatment. Sodium thiosulfate administered with cisplatin (CIS/THIO) consistently protected animals from hearing loss and surprisingly yielded significant increases in amplitude when compared to baseline and saline controls. However, ABRs of CIS/THIO animals returned toward baseline values after 30 days.

Animals↗
PubMed1988

The oligosaccharide component of alpha 1-adrenergic receptors from BC3H1 and DDT1 muscle cells. Studies with glycosidases and photoaffinity labelling of intact cells.

In this study, we clarify the structural aspects of the oligosaccharides associated with the alpha 1-adrenergic receptor in two muscle cell lines. Photoaffinity labelling of intact BC3H1 or DDT1 muscle cells with 2-[4-(4-azido-3-[125I]iodobenzoyl)piperazin-1-yl]-4-amino-6, 7-dimethoxyquinazoline ([125I]azidoprazosin) followed by SDS/polyacrylamide-gel electrophoresis (PAGE) and autoradiography revealed specifically labelled proteins of molecular mass = 87,000 and 81,000, respectively. Treatment of photoaffinity-labelled receptors in DDT1 cells with 33 u. of endoglycosidase F/ml for 24 h resulted in the loss of the 81 kDa receptor and the appearance of a 52.5 kDa protein. When lower concentrations of glycosidase or shorter incubation times were used, the 81 kDa receptor was converted to a 66 kDa protein. Treatment of the photoaffinity-labelled BC3H1 receptor with endoglycosidase F resulted in the appearance of a 50.5 kDa protein. Neither alpha-mannosidase nor endoglycosidase H had an effect on the photoaffinity labelling patterns of the receptor from the two cell types. alpha 1-Adrenergic receptors, solubilized from membranes prepared from BC3H1 and DDT1 cells, bound to wheat germ agglutinin-Sepharose and were displaced by N-acetylglucosamine. Taken together, these results indicate that alpha 1-adrenergic receptors in BC3H1 and DDT1 cells contain complex, but not high, mannose oligosaccharide chains; differences in the composition or number of chains partially accounts for the different molecular mass of the receptor in the two cell lines. The results further indicate that the oligosaccharide chains contribute substantially to the apparent molecular mass of alpha 1-adrenergic receptors, as detected by SDS/PAGE, and that the protein backbone of these receptors is likely to be approximately 50 kDa.

Acetylglucosaminidase↗
PubMed1988

Enzyme-gold affinity labelling of cellulose.

The enzyme-linked colloidal gold affinity labelling technique was tested as a method to localize cellulose on thin sections of plant cell walls and slime mold spores. Commercially available cellulase from cultures of Trichoderma reesei, the main components being cellobiohydrolase I and II (CBH I, CBH II) and endoglucanase (EG), was linked to colloidal gold by using standard techniques and applied as a dilute, buffered suspension to thin sections. After brief exposure, e.g., 15-30 minutes, cellulose exposed on the surface of sections was labelled with the enzyme-gold complex. Poststaining did not appear to have a deleterious effect on the labelled sections. The specificity of labelling was demonstrated by its complete inhibition when carboxymethylcellulose was incorporated in the labelling mixture, by lack of labelling of 1,4-beta-mannans or 1,3-beta-xylans in noncellulosic walls of marine algae, by lack of labelling of 1,4-beta-glucans in chitin, by much lower labelling density when done at 4 degrees C, and by lack of labelling when sections were predigested with cellulase. Labelling with the crude commercial cellulase was compared to labelling with purified CBH I-, CBH II-, and EG-linked colloidal gold, and the labelling pattern was similar. This method was found useful on conventionally fixed material and required no special preparation other than the use of inert (Ni or Au) grids and 0.5% gelatin to reduce nonspecific binding of the gold complex. Labelling was similar in the several embedding resins tested: LR White, Lowicryl K4M, Epon 812, and Spurr's.(ABSTRACT TRUNCATED AT 250 WORDS)

Affinity Labels↗
PubMed1988

Relaxivity and binding of Mn2+ ions in solutions of phosphatidylserine vesicles.

We report the magnetic field dependence (NMRD profiles) of 1/T1 of solvent protons in solutions of unilamellar phosphatidylserine vesicles with added Mn2+ ions, including studies of the variation of the profiles with temperature, extent of coverage of available binding sites by Mn2+ ions, ionic strength, and competition with (nonparamagnetic) Ca2+ ions. ions. In addition, we sketch the theory of screening of the negative surface charges of the vesicles due to both specific binding of Mn2+ ions and nonspecific effects of other mobile solute ions. The major result is that the NMRD profiles, although qualitatively similar, vary systematically as the parameters of the solutions are altered, in a manner consistent with the theory of screening. The profiles of the Mn2+-vesicle complexes are much like those of Mn2+-protein complexes that have the ions in an octahedral ligand environment. In addition, we find that the profiles are similar to those reported for Mn2+ ions in packed liver cells and liver tissue, supporting a previous conjecture that available Mn2+ in liver binds to the polar head groups of cell membranes, saturating these sites before binding elsewhere. Again, it is evident that results for in vitro model systems can be extrapolated reliably to tissue behavior.

Contrast Media↗