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Biomedical subjects

D M Mock

Publications and source records attributed to D M Mock.

At least 73 records · Page 4Linked to original sources
PubMed1990

Effect of aging on intestinal biotin transport in the rat.

The influence of aging of biotin intestinal transport was examined in Fisher 344 rats (3- 12- and 24-month old) using a brush border membrane vesicle (BBMV) technique. In all age groups examined, transport of biotin as a function of concentration was saturable in the presence of a Na+ gradient (out greater than in), but was lower and linear in the presence of a choline gradient (out greater than in.). The Vmax of the biotin transport process was found to be significantly (p less than 0.01) higher in 24-month-old rats compared to 3- and 12-month old rats. On the other hand, the apparent Km of the biotin transport system was similar in all age groups. We also measured plasma levels of biotin in the different age groups. The mean plasma levels of biotin in 24-month-old rats was found to be significantly higher than that of 3-month (p less than 0.005) and 12-month (p less than 0.025) old rats. These results demonstrate that aging is associated with an increase in biotin intestinal transport. This increase appears to be due to changes in the activity (and/or number) but not the affinity of the biotin transport system. Furthermore, an increase in plasma biotin levels was observed with aging, which might be a consequence to the increase in the vitamin's intestinal transport.

Aging↗
PubMed1990

Studies of the reversible binding of biotin to human plasma.

In this study we sought to determine the extent of the reversible binding of [3H]biotin to macromolecules (presumably proteins) of human plasma under physiologic conditions during physiologic time intervals ranging from minutes to days. Fresh, heparinized human plasma and [3H]biotin were incubated in 5% CO2, 95% N2 at 37 degrees C. After reaching equilibrium, free biotin was separated from bound biotin by centrifugal ultrafiltration (1500 x g for 60 min) using membranes with a molecular weight cutoff of 30,000. In a sample from a single individual, we detected a mean retentate:ultrafiltrate ratio of 1.20 +/- 0.03 (mean +/- SD, n = 14 determinations). In a group of 10 healthy adults, the mean retentate:ultrafiltrate ratio was 1.17 +/- 0.02; thus, approximately 8% of the biotin in the combined pool of free and reversibly bound biotin is bound. No consistent change in retentate:ultrafiltrate ratio was detected for total biotin concentrations ranging between 500 fmol/mL and 2 nmol/mL, but the ratio decreased to 1.1 at 400 nmol of biotin per mL. Thus, the biotin-binding system of human plasma appears to be a low affinity, high capacity system. A similar biotin-binding system was detected in experiments with purified human serum albumin. These results provide evidence that the majority of added [3H]biotin does not bind to plasma protein under physiologic conditions. To the extent that added [3H]biotin can be assumed to reflect reversible binding of endogenous unlabeled biotin, we infer that endogenous, reversibly bound biotin can account for no more than one-tenth of the increase in biotin detected after acid hydrolysis of plasma.

Adult↗
PubMed1990

Evidence for a pathogenic role of omega 6 polyunsaturated fatty acid in the cutaneous manifestations of biotin deficiency.

Abnormalities in fatty acid composition have been detected in biotin deficiency in humans and in the rat. However, the pathogenetic role of these abnormalities, if any, in the cutaneous manifestations of biotin deficiency is not clear. In a nutrient interaction experiment, we tested the hypothesis that an abnormality of omega 6 polyunsaturated fatty acid (PUFA) metabolism plays a pathogenetic role in the cutaneous manifestations. Five rats were fed an egg white diet that induces biotin deficiency; these rats developed the characteristic cutaneous abnormalities of biotin deficiency. Five additional rats were pair-fed the egg white diet and received Liposyn [77% linoleic acid (18:2 omega 6)]; these rats did not develop the cutaneous manifestations of biotin deficiency. The two groups had similar decreases in the rates of urinary excretion of biotin, the serum concentrations of biotin, the amounts of biotin in liver, and the hepatic activities of two biotin-dependent carboxylases; the two groups had similar increases in the rates of urinary excretion of 3-hydroxyisovaleric acid. These observations provide evidence that (a) some abnormality in omega 6 PUFA metabolism has a pathogenetic role in the cutaneous manifestations of biotin deficiency and (b) this pathogenetic role can not be explained as a difference in biotin nutritional status due to a biotin-sparing effect of Liposyn.

Animals↗
PubMed1989

Quantification of urinary 3-hydroxyisovaleric acid using deuterated 3-hydroxyisovaleric acid as internal standard.

Deficiency of biotin at the tissue level can be assessed indirectly by measuring the urinary excretion of 3-hydroxyisovaleric acid. This paper describes the application of an improved method of quantifying urinary 3-hydroxyisovaleric acid using unlabeled and uniformly deuterated 3-hydroxyisovaleric acid. These compounds were synthesized by a modification of the lithioacetic acid method for generation of beta-hydroxy acids. Elemental analysis, nuclear magnetic resonance, gas chromatographic and gas chromatographic/mass spectrometric data demonstrated that the compounds are greater than 95% pure. Mass spectrometry confirmed the identity of the unlabeled compound, demonstrated that the deuterated compound is uniformly labeled, and offered insight into the pattern of mass fragmentation. The method for determination of the concentration of 3-hydroxyisovaleric acid in rat urine uses gas chromatographic/mass spectrometric quantification of the di-trimethylsilyl derivative with the deuterated compound as the internal standard. Results provide evidence that this method is more accurate than a previously published method that did not utilize the unlabeled and deuterated standards.

Animals↗
PubMed1989

Biotin nutritional status of vegans, lactoovovegetarians, and nonvegetarians.

Urinary excretion of biotin (total avidin-binding substances) was measured in adults and children who were adhering to one of the following self-selected diets: strict vegetarian (vegan), lactoovovegetarian, or mixed (containing meat and dairy products as well as plant-derived foods). In a subset of subjects, plasma biotin concentrations were also measured. In adults the biotin excretion rate was significantly greater in the vegan group than in either the lactoovovegetarian or the mixed-diet groups; the latter were not significantly different from one another. In children the biotin excretion rates in both the vegan group and the lactoovovegetarin group were significantly greater than in the mixed-diet group. A similar trend (vegan greater than lactoovovegetarian greater than mixed) was detected in the plasma concentrations of biotin of adults and children but differences were not generally statistically significant. These observations provide evidence that the biotin nutritional status of vegans is not impaired.

Adult↗
PubMed1989

Biotin analysis of commercial vitamin and other nutritional supplements.

Because previous observations suggest that biotin may be present in vitamin preparations not labeled as containing biotin, we determined the biotin content of several over-the-counter vitamin and nutritional supplements said to contain biotin (group 1) and several in which biotin content was not specified (group 2). Biotin concentration was measured using the 125I-avidin assay which detects total avidin-binding substances. Water extracts were assayed for free biotin and acid hydrolysates were assayed for total biotin. The results of the 125I-avidin assay agreed with the stated biotin content for most vitamin and nutritional supplements in group 1. Biotin was the only avidin-binding substance in the preparations from group 1, based on reversed-phase chromatography. However, some vitamin and nutritional supplements in group 2 contained nutritionally significant amounts of biotin, particularly if the supplement contained liver or yeast extract. Total biotin was significantly higher than free biotin in one supplement; the difference was attributable to release of biotin rather than a biotin analog. We conclude that biotin may be present in some vitamin and nutritional supplements not labeled as containing biotin; biotin intake might be under-estimated if the subject is receiving a nutritional supplement containing extracts of liver or yeast.

Acids↗
PubMed1989

Regulation of intestinal biotin transport in the rat: effect of biotin deficiency and supplementation.

The effect of biotin deficiency and supplementation at pharmacological doses on the intestinal transport of the vitamin was examined in the rat using a brush-border membrane vesicle (BBMV) technique. Transport of biotin in both jejunal and ileal BBMV was significantly (P less than 0.05-0.01) higher in biotin-deficient rats compared with control (pair-fed) rats. This increase in biotin transport appeared to be specific because transport of D-glucose was similar in the two rat groups. The increase in biotin transport in the deficient rats appeared to be mediated through a marked increase (146-230%) in the Vmax of the biotin transport process (with minimal change in the apparent Km), suggesting an increase in the number of the transport carriers. In contrast, supplementation at pharmacological doses of biotin caused significant (P less than 0.05-0.01) and specific decrease (suppression) in biotin transport compared with (unsupplemented) controls. The suppression of biotin transport in the supplemented rats appeared to be mediated through a marked decrease (58%) in the Vmax of the biotin transport process (with minimal change in the apparent Km), suggesting a decrease in the number of the transport carriers. These results provide evidence that biotin transport in the intestine is regulated by the level of the vitamin in the diet (and/or body stores). Furthermore, the results demonstrate the ability of the small intestine to adapt to the challenge of deficiency of an essential nutrient, a capability that may be crucial for the survival of the animal.

Animals↗
PubMed1988

Isolation and characterization of highly purified streptavidin obtained in a two-step purification procedure from Streptomyces avidinii grown in a synthetic medium.

A method is described for isolation of streptavidin from cultures of Streptomyces avidinii grown in a synthetic culture medium for 6-10 days. Streptavidin is precipitated directly from culture supernatant fluid using 80% ammonium sulfate, and the precipitate is dialyzed against water and centrifuged at 40,000 X g for 60 min. The absorbency coefficient at 280 nm of purified streptavidin was estimated to be 31.7142 +/- 0.1806 for a 1% solution. The protein appeared to be greater than 90% homogeneous by gel permeation chromatography and polyacrylamide gel electrophoresis. No biotin-binding molecules less than 70 kDa in size were detected at any step during the purification of streptavidin. Streptavidin was able to maintain a stable crosslink between two biotinylated molecules in a solid-phase assay. Streptavidin purified by this method was stable in 50% glycerol/water at -20 degrees C for more than 1 year. Lyophilization or iodination did not produce apparent damage to the protein.

Bacterial Proteins↗
PubMed1988

A study of the interaction of avidin with 2-anilinonaphthalene-6-sulfonic acid as a probe of the biotin binding site.

The environment of the biotin binding site on avidin was investigated by determining the fluorescence enhancement of a series of fluorescent probes that are anilinonaphthalene sulfonic acid derivatives. Of the compounds tested, 2-anilinonaphthalene-6-sulfonic acid (2,6-ANS) exhibited the greatest enhancement under the conditions used (which would reflect both molar fluorescence enhancement and binding affinity) and exhibited more than 95% reversal upon addition of biotin. Thus, 2,6-ANS was chosen for more detailed characterization of the interaction with avidin. Only a single class of binding sites for 2,6-ANS was identified; the mean value for the Kd was 203 +/- 16 microM (X +/- 1 S.D.), and the molar ratio of 2,6-ANS binding sites to biotin binding sites was approx. 1. These results provide evidence that the biotin binding site and the 2,6-ANS binding site are at least partially overlapping, but the possibility that the probe binding site is altered by a conformational change induced by biotin binding cannot be excluded. At excitation = 328 nm and emission = 408 nm, the molar fluorescence of the bound probe was 6.8 +/- 1.0 microM-1 and that of the free probe was 0.061 +/- 0.008 microM-1 giving an enhancement ratio (molar fluorescence of bound probe/molar fluorescence of free probe) of 111 +/- 22. Upon binding, the wavelength of maximum fluorescence decreases. These findings also provide evidence that the fluorescence enhancement associated with the interaction of 2,6-ANS and avidin reflects the environment of the biotin binding site. The Kosower's Z factor, an empirical index of apolarity, was 82.1 for the 2,6-ANS binding site on avidin. This value reflects a degree of apolarity that is similar to apolar environments observed for substrate binding sites on several enzymes; although not the dominant factor, this environment may contribute to the strong binding of biotin.

Anilino Naphthalenesulfonates↗
PubMed1988

Biotin transport and metabolism in the central nervous system.

The mechanisms by which biotin enters and leaves brain, choroid plexus and cerebrospinal fluid (CSF) were investigated by injecting [3H]biotin either intravenously or intraventricularly into adult rabbits. [3H] biotin, either alone or together with unlabeled biotin was infused at a constant rate into conscious rabbits. At 180 minutes, [3H]biotin had entered CSF, choroid plexus, and brain. In brain, CSF, and plasma, greater than 90% of the nonvolatile 3H was associated with [3H]biotin. The addition of 400 mumol/kg unlabeled biotin to the infusion syringe decreased the penetration of [3H]biotin into brain and CSF by approximately 70 percent. Two hours after an intraventricular injection, [3H]biotin was cleared from the CSF more rapidly than mannitol and minimal metabolism of the [3H]biotin had occurred in brain. However, 18 hours after an intraventricular injection, approximately 35% of the [3H]biotin remaining in brain had been covalently incorporated into proteins, presumably into carboxylase apoenzymes. These results show that biotin enters CSF and brain by saturable transport systems that do not depend on metabolism of the biotin. However, [3H]biotin is very slowly incorporated covalently into proteins in brain in vivo.

Animals↗
PubMed1988

Effects of biotin deficiency on serum fatty acid composition: evidence for abnormalities in humans.

In three patients who developed biotin deficiency during parenteral alimentation, serum fatty acid compositions of the four major lipid classes (phospholipid, cholesteryl ester, triglyceride and free fatty acid) were measured. Relative to the normal range, percent compositions of an odd-chain fatty acid (either 15:0 or 17:0 or both) were increased in each class of lipid, and these abnormalities generally returned to normal or decreased toward normal with biotin therapy. Abnormalities in particular fatty acids in the omega 6, omega 3 and omega 9 pathways were also found, but these abnormalities did not resolve with biotin therapy. These data provide evidence in favor of the conclusion that biotin deficiency causes increases in the composition of some odd-chain fatty acids in humans, perhaps by the same mechanism that leads to odd-chain fatty acidemia in the inborn deficiency of the biotin-dependent enzyme propionyl-CoA carboxylase.

Acetyl-CoA Carboxylase↗
PubMed1988

Effects of biotin deficiency on plasma and tissue fatty acid composition: evidence for abnormalities in rats.

Abnormalities of fatty acid composition have been detected in the plasma of patients who developed frank biotin deficiency during parenteral nutrition. We sought to determine which abnormalities of fatty acid composition, if any, would be replicated in the biotin-deficient rat and to determine the relative temporal relationships of these abnormalities to biotin nutritional status. We measured fatty acid compositions of the phospholipids extracted from plasma, heart, and liver and assessed biotin nutritional status longitudinally in biotin-deficient and biotin-treated rats during progressive biotin deficiency. In the biotin-deficient group, significant increases relative to the biotin-treated group were detected in all three tissues in the odd-chain fatty acids 15:0 and 17:0. In the biotin-deficient rats, significant increases in 18:2 omega 6 in liver and 18:3 omega 6 in plasma and liver and significant decreases in 22:5 omega 6 were detected in plasma and liver. The constellation of fatty acid abnormalities observed in the biotin-deficient rats was not identical to that observed in biotin-deficient patients, but abnormalities in composition of odd-chain fatty acids were detected in both human and rat and therefore are attributable to biotin deficiency per se. The abnormalities in fatty acid composition were already present by wk 4 on the egg white diet; the cutaneous findings appeared between wk 3 and 6. These observations are consistent with the hypothesis that an abnormality in fatty acid metabolism may play a pathogenetic role in the cutaneous manifestations of biotin deficiency.

Animals↗
PubMed1988

Abnormal organic aciduria in biotin deficiency: the rat is similar to the human.

We sought to determine whether the biotin-deficient rat excretes the same constellation of abnormal organic acids in urine that has been reported for biotin deficiency in humans and, if so, to determine the variation of the abnormal organic aciduria with time during progressive biotin deficiency. Biotin deficiency was induced by a 30% egg white diet. Gas chromatography-mass spectrometry was used to identify and quantitate the trimethylsilyl derivatives of the organic acids extracted from urine. We detected a progressive increase in the urinary excretion of 3-hydroxyisovaleric acid that was highly significant (p less than 0.0001). Abnormal excretion of 3-hydroxyisovaleric acid was detectable in some biotin-deficient rats as early as week 1; by week 5, all biotin-deficient rats had abnormally increased excretion of 3-hydroxyisovaleric acid. We also detected a highly significant increase (p less than 0.0001) in the urinary excretion of 3-methylcrotonylglycine. We conclude that biotin deficiency in the rat causes abnormal organic aciduria similar but not identical to that caused by biotin deficiency in humans. We speculate that this abnormal organic aciduria may serve as a useful index of biotin deficiency at the tissue level.

Animals↗
PubMed1987

Pancreatitis and alcoholism disorder the renal tubule and impair reclamation of some low molecular weight proteins.

We sought to determine whether the clinical setting in which pancreatitis occurs affects the incidence and distribution of increased values of renal clearance of amylase relative to creatinine, CAm/CCr, and whether the increased values reflect a tubular disorder that impairs renal reclamation of certain low molecular weight proteins. We measured the renal clearance of three low molecular weight proteins (amylase, beta 2-microglobulin, and lysozyme) and urinary excretion of three lysosomal enzymes that originate from the renal tubule in three groups of patients (alcoholic pancreatitis, pancreatitis without alcoholism, and alcoholism without pancreatitis). When compared to normal controls, the mean CAm/CCr was significantly elevated in alcoholic pancreatitis (p less than 0.05) but not in equally severe pancreatitis without alcoholism nor in alcoholism without pancreatitis. The clearance ratio of beta 2-microglobulin was significantly increased in each of the three patient groups; mean clearance ratio of lysozyme was not significantly increased in any of the patient groups. Excretion of each of the three lysosomal enzymes was significantly increased in each of the patient groups. We conclude that the etiology of pancreatitis affects the distribution of values for CAm/CCr, impaired tubular reclamation of amylase is the mechanism of the increase in CAm/CCr, and a factor or factors associated with both pancreatitis and with alcoholism per se appear to disorder the renal tubule and to impair tubular reclamation of some but not all low molecular weight proteins-a novel finding of considerable potential significance.

Acetylglucosaminidase↗
PubMed1986

A sequential, solid-phase assay for biotin in physiologic fluids that correlates with expected biotin status.

Interest in accurate measurement of biotin concentrations in plasma and urine has been stimulated by recent advances in the understanding of biotin-responsive inborn errors of metabolism and by several reports describing acquired biotin deficiency during parenteral alimentation. This paper presents a biotin assay utilizing radiolabeled avidin in a sequential, solid-phase method; the assay has increased sensitivity compared to previous methods (greater than or equal to 10 fmol/tube), correlates with expected trends in biotin concentrations in blood and urine in a rat model of biotin deficiency, and can utilize commercially available radiolabeled avidin.

Animals↗
PubMed1986

Coordinately increased lysozymuria and lysosomal enzymuria induced by maleic acid.

During the acute renal tubular dysfunction of Fanconi syndrome and type 2 renal tubular acidosis (FS/RTA2) induced by maleic acid in the unanesthetized dog, we observed: 30 minutes after the onset of FS/RTA2, the urinary excretion of lysosomal enzymes, N-acetyl-beta-glucosaminidase (NAG), beta-glucuronidase (beta-gluc) and beta-galactosidase (beta-galac), increased simultaneously with the anticipated increase in renal clearance of lysozyme; the severities of all these hyperenzymurias increased rapidly, progressively, and in parallel, all reaching a peak some 60 to 80 minutes after their onset; thereafter, while the FS/RTA2 continued undiminished in severity, the severity of the hyperenzymurias decreased rapidly, greatly, progressively, and in parallel; and sodium phosphate loading strikingly attenuated the FS/RTA2 and the hyperenzymurias. Thus, the maleic acid-induced FS/RTA2 is attended by an acute reversible-complex derangement in the renal tubular processing of proteins that: affects not only lysozyme which is normally filtered, but also NAG and other lysosomal enzymes, which are not; and is to some extent functionally separable from that of FS/RTA2. The findings suggest that the derangements in renal processing of lysozyme and lysosomal enzymes are linked, and that a phosphate-dependent metabolic abnormality in the proximal tubule can participate in the pathogenesis of both these derangements and the FS/RTA2.

Acetylglucosaminidase↗
PubMed1985

A fluorometric assay for the biotin-avidin interaction based on displacement of the fluorescent probe 2-anilinonaphthalene-6-sulfonic acid.

Avidin and biotin can be sensitively and accurately quantitated using the fluorescent probe 2-anilinonaphthalene-6-sulfonic acid (2,6-ANS). In the presence of avidin, the fluorescence of 2,6-ANS is blue shifted with a large increase in quantum yield. Biotin binding causes complete displacement of the bound fluorophore with concomitant quenching of the fluorescence. The fluorometric monitoring of the displacement of 2,6-ANS can be used as a facile method of measuring the biotin-avidin interaction. 2,6-ANS displacement gives the same stoichiometry as the method using 4'-hydroxyazobenzene-2-carboxylic acid. Our initial studies of an affinity-purified avidin revealed that, of the four binding sites on the avidin tetramer, a mean of three remain available for biotin (or dye) binding; this finding highlights a caveat concerning the use of affinity-purified oligomeric-binding proteins with multiple sites. As compared with previous fluorescence methods, the use of 2,6-ANS gives high sensitivity without the necessity of preparing and purifying a covalent avidin conjugate. In addition, the present method;:is potentially more sensitive than those based on optical absorbance; uses a probe that has increased stability and a larger Stokes shift compared with fluorescein; is not subject to protein interference; and gives accurate results over a wide range of 2,6-ANS and avidin concentrations.

Anilino Naphthalenesulfonates↗