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Biomedical subjects

R B Brandt

Publications and source records attributed to R B Brandt.

15 recordsLinked to original sources
PubMed1992

The prevalence of oral lesions in smokeless tobacco users and an evaluation of risk factors.

BACKGROUND: The widespread use of smokeless tobacco (ST) has prompted concern in regard to the development of oral lesions in long-term users. METHODS: For inclusion in the current study, a subject must have used an ST product, either snuff or chewing tobacco, for at least 6 months. The subjects were recruited by advertising, and none was referred for the evaluation of an oral lesion. The following were performed on all subjects: assessment of exposure to ST, cigarettes, and alcohol; examination of the oral cavity; a biopsy, if an oral lesion was found; and analysis of a blood sample for beta-carotene. The dietary intake of most of the subjects was analyzed. RESULTS: Of the 347 ST users, all of whom were white male subjects, 45 (13.0%) had an oral lesion. Thirty-five of the lesions were hyperkeratosis and 10 were epithelial dysplasia. CONCLUSIONS: Snuff exposure was associated significantly with the presence of an oral lesion (P < 0.0001). A decreased vitamin C intake also was found among the ST users with oral lesions (P < 0.01). The ST users with epithelial dysplasia, as compared with those with hyperkeratotic lesions, were slightly older, had a lower intake of vitamin C (P < 0.05), and were more likely to have used chewing tobacco than snuff.

Adult↗
PubMed1992

Effects of proteolytic and thermal action on the activity of lactate dehydrogenase isozymes LD-1 and LD-5.

L-Lactate dehydrogenase (LD) catalyzes the interconversion of pyruvate and lactate. Using a spectrophotometric assay to determine LD activity, incubation of rabbit, porcine, and bovine LD-1 and LD-5 isozymes with the protease subtilisin (Carlsberg) gave first-order degradation kinetics. Degradation half-lives were significantly lower for the LD-5 isozymes from the three species when incubated with subtilisin at temperatures from 4 degrees C to 25 degrees C. The energy involved in the degradation process, however, was not different. The activation energy for the conversion of pyruvate to lactate by LD-1 at pH 7.4 was significantly higher than that for LD-5 for all three species examined (P less than 0.005). Thermocalorimetry showed that the LD-1 isozymes have both a higher mean temperature of denaturation and a higher heat uptake during the denaturation process than corresponding LD-5 forms. The results suggest that the LD-5 isozymes in the species studied are more metabolically efficient, whereas the LD-1 forms have greater structural stability.

Animals↗
PubMed1991

Evaluation of risk factors in smokeless tobacco-associated oral lesions.

Smokeless tobacco (ST) users and nonusers were recruited to evaluate the contribution of various risk factors (ST use, cigarettes, alcohol, and diet) in the development of oral mucosal lesions. Ninety-eight ST users with no lesion, 29 ST users with an oral lesion, and 33 nonusers were enrolled in the study. ST users with lesions, when compared with users with no lesion, were more likely to have used snuff than chewing tobacco (p = 0.01) and to have used more ST (p less than 0.01). Alcohol consumption, dietary intake of beta-carotene, and serum levels of beta-carotene were not related to an increased risk of lesion development. Our findings showed that the only significant risk factor for ST-associated oral lesions was the extent of ST exposure. Of 127 ST users, 29 (22.8%) had an oral lesion at the time of examination. Of these lesions, 23 (79.3%) were hyperkeratotic and 6 (20.7%) were epithelial dysplasia.

Adolescent↗
PubMed1987

Lactate dehydrogenase in rat mitochondria.

Small but persistent amounts of L-lactate dehydrogenase (LDH) activity were found in mitochondrial preparations isolated from rat heart, kidney, liver, and lymphocytes. Brain mitochondrial preparations were also isolated, but the results were inconclusive. A variety of cytosolic markers were used and it was found that essentially no cytosolic contamination was present except in brain preparations. A bacterial protease was used along with digitonin fractionation to determine localization of the mitochondrial LDH. Approximately 80% of the LDH activity associated with heart and kidney mitochondrial preparations was on the inside compared to about 40% for liver. Lymphocyte mitochondrial LDH activity was about 70% on the inside. Cytosolic LDH-5 preferentially adheres to outer mitochondrial membrane of liver, kidney, and heart. Agarose gel electrophoresis showed LDH isozymes in mitochondria qualitatively similar to that of the corresponding cytosol except in kidney mitochondrial preparations, where a specific electrophoretic band was found which did not correspond to any of the common LDH isozymes.

Animals↗
PubMed1987

Calculation of inhibitor Ki and inhibitor type from the concentration of inhibitor for 50% inhibition for Michaelis-Menten enzymes.

The use of I50 (concentration of inhibitor required for 50% inhibition) for enzyme or drug studies has the disadvantage of not allowing easy comparison among data from different laboratories or under different substrate conditions. Modifications of the Michaelis-Menten equation for treatment of inhibitors can allow both the determination of the type of inhibition (competitive, noncompetitive, and uncompetitive) and the Ki for the inhibitor. For competitive and uncompetitive inhibitors when the assay conditions are [S] = Km, then Ki = I50/2. For different conditions of [S] there is a divergence between competitive and uncompetitive inhibitors that may be used to identify the type of inhibitor. The equation for Ki also differs. For noncompetitive inhibitors the Ki = I50 and this relationship is valid with changing [S]. The equations developed require a single substrate, reversible-type inhibitors, and kinetics of the Michaelis-Menten type. Examples of the use of the equations are illustrated with experimental data from scientific publications.

Binding, Competitive↗
PubMed1986

Localization of L-lactate dehydrogenase in mitochondria.

Relatively small but persistent amounts of L-lactate dehydrogenase (LDH) activity were found in mitochondrial preparations isolated from liver of the rat. Using a variety of cytosolic markers, it was found that essentially no cytosolic contamination was present. Respiratory velocities and respiratory control with L-lactate were somewhat lower than with glutamate, but equal or superior to those with pyruvate. Agarose gel electrophoresis showed LDH isoenzymes in mitochondria similar to that in corresponding cytosol. Subtilisin BPN', a bacterial protease, was incubated with intact mitochondria and enzyme activities were measured. Following mitochondrial disruption, the proteolytic treatment was repeated. Digitonin was also used in the fractionation of mitochondria. These techniques helped to determine the location of the LDH in the mitochondria as being mainly in the outer membrane and periplasmic space.

Animals↗
PubMed1986

Nicotinic acid or N-methyl nicotinamide prolongs elevated brain dopa and dopamine in L-dopa treatment.

A peripheral dopa decarboxylase inhibitor, benserazide, was given ip, followed by intubation with L-dopa. Brain dopa and DA levels were elevated maximally between 0.5-2.5 hr and 1.0-2.5 hr, respectively. Dopa in serum, liver, and brain were at control values after 4 hr. Supplementation of dopa with NAM or NAC, as possible methyl group acceptors to lower catabolism of DA, showed that NAM had no effect on DA levels or on SAM. However, with both NAC and N-methyl NAM (a methylated compound intended as a control) at time periods where dopa and DA were normally decreasing, the brain levels were increased over control values with benserazide and dopa alone. NAC or N-methyl NAM appeared to extend the period of elevated brain DA levels with L-dopa treatment. The mechanism responsible for these results is uncertain.

Animals↗
PubMed1978

Methylglyoxal production in human blood.

The research of Szent-Györgyi and others has suggested that the three-carbon ketoaldehyde methylglyoxal has a potential role in the control of cell growth. Its metabolism to D-lactate (not the L-lactate of glycolysis) is catalysed by the mammalian enzymes glyoxalase I (S-lactoyl-glutathione methylglyoxal-lyase, isomerizing; EC 4.4.1.5) and glyoxalase II (S-2-hydroxyacylglutathione hydrolase; 3.1.2.6), with glutathione as a coenzyme. Direct determination of methylglyoxal in biological tissues is difficult because of the active glyoxalase system. However, the product of the glyoxalase system, D-lactate, should indicate formed or added methylglyoxal. A stereospecific assay was used to measure D-lactate in human plasma; it involved the spectrophotometric analysis of NADH at 340 nm catalysed by D-lactate dehydrogenase (D-lactate:NAD+ oxidoreductase; EC 1.1.1.28) from Lactobacillus leichmannii. Blood collected by venepuncture was used for the determination of the plasma concentration of D-lactate. The mean concentration for seven normal subjects was 0.023 mM +/- 0.002 S.E.M. When the glycolytic pathway in whole blood was inhibited in vitro with fluoride, a significant increase in D-lactate was found (about 0.15 mM/hour at 37 degrees C). Added methylglyoxal also produced an increase in D-lactate formation. Some specific precursors of L-lactate (dihydroxyacetone phosphate, for example) added to whole blood produced an increased concentration of D-lactate, even when glycolysis was not inhibited. This finding indicates that catabolites of glucose lead to methylglyoxal synthesis and suggest a control function for the glyoxalase enzyme system in glycolysis that could be exploited for cancer therapy.

Adult↗
PubMed1978

Serum vitamin A in premature and term neonates.

Serum vitamin A was determined in premature and term neonates by a specific spectrofluorometric method. Premature neonates (N = 42; gestational age = 32 +/- 0.4 weeks) had a serum vitamin A level (14.9 +/- 0.98 microgram/dl) significantly lower (P less than 0.001) than that of term neonates (N = 51; 22.4 +/- 0.99 microgram/dl). The vitamin A mean serum values of infants of 36 weeks' gestational age were not statistically different from those of the term neonates. Linear regression analysis for serum vitamin A values vs gestational age showed no significant correlation. A linear correlation (P less than 0.05), however, was found between serum vitamin A and serum protein protein concentrations, perhaps indicative of a lower concentration of retinol-binding protein. Since vitamin A is involved in the promotion of mucous-secreting cells, the premature neonate may be at greater risk than the term infant for diseases involving the mucosal epithelium, including necrotizing enterocolitis.

Enterocolitis, Pseudomembranous↗
PubMedDate not supplied

Decrease of available vitamin A in parenteral nutrition solutions.

The efficiency of vitamin A delivery in total parenteral nutrition solutions was determined using spectrofluorometric and radioisotope assays. Experiments incubating total parenteral nutrition solutions in intravenous tubing demonstrated that an 88% decrease in vitamin A content from solution occurred over a 5-hr period. This decrease was independent of the method of assay and was not due to photodecomposition. Recovery of vitamin A from hexane rinses of the intravenous tubing demonstrated that the vitamin decrease was due to uptake by the tubing. Experiments simulating clinical practice situations showed saturation of these binding sites, with mean decrease of 26 to 67% of the vitamin, which were partially dependent on flow-rate. Clinical samples analyzed for comparison showed a greater loss of vitamin (77-98%) from the intravenous solutions. A decrease of vitamin A from solution should be a consideration when using parenteral nutrition.

Biological Availability↗