Network


Latest external collaboration on country level. Dive into details by clicking on the dots.

Hotspot


Dive into the research topics where Donald M. Mock is active.

Publication


Featured researches published by Donald M. Mock.


Pediatrics | 2005

Randomized trial of liberal versus restrictive guidelines for red blood cell transfusion in preterm infants.

Edward F. Bell; Ronald G. Strauss; John A. Widness; Larry T. Mahoney; Donald M. Mock; Victoria J. Seward; Gretchen A. Cress; Karen J. Johnson; Irma J. Kromer; M. Bridget Zimmerman

Objective. Although many centers have introduced more restrictive transfusion policies for preterm infants in recent years, the benefits and adverse consequences of allowing lower hematocrit levels have not been systematically evaluated. The objective of this study was to determine if restrictive guidelines for red blood cell (RBC) transfusions for preterm infants can reduce the number of transfusions without adverse consequences. Design, Setting, and Patients. We enrolled 100 hospitalized preterm infants with birth weights of 500 to 1300 g into a randomized clinical trial comparing 2 levels of hematocrit threshold for RBC transfusion. Intervention. The infants were assigned randomly to either the liberal- or the restrictive-transfusion group. For each group, transfusions were given only when the hematocrit level fell below the assigned value. In each group, the transfusion threshold levels decreased with improving clinical status. Main Outcome Measures. We recorded the number of transfusions, the number of donor exposures, and various clinical and physiologic outcomes. Results. Infants in the liberal-transfusion group received more RBC transfusions (5.2 ± 4.5 [mean ± SD] vs 3.3 ± 2.9 in the restrictive-transfusion group). However, the number of donors to whom the infants were exposed was not significantly different (2.8 ± 2.5 vs 2.2 ± 2.0). There was no difference between the groups in the percentage of infants who avoided transfusions altogether (12% in the liberal-transfusion group versus 10% in the restrictive-transfusion group). Infants in the restrictive-transfusion group were more likely to have intraparenchymal brain hemorrhage or periventricular leukomalacia, and they had more frequent episodes of apnea, including both mild and severe episodes. Conclusions. Although both transfusion programs were well tolerated, our finding of more frequent major adverse neurologic events in the restrictive RBC-transfusion group suggests that the practice of restrictive transfusions may be harmful to preterm infants.


Molecular and Cellular Biology | 1989

High incidence of lung, bone, and lymphoid tumors in transgenic mice overexpressing mutant alleles of the p53 oncogene.

A Lavigueur; V. Maltby; Donald M. Mock; J. Rossant; Tony Pawson; Alan Bernstein

We have investigated the role of the p53 gene in oncogenesis in vivo by generating transgenic mice carrying murine p53 genomic fragments isolated from a mouse Friend erythroleukemia cell line or BALB/c mouse liver DNA. Elevated levels of p53 mRNA were detected in several tissues of two transgenic lines tested. Increased levels of p53 protein were also detected in most of the tissues analyzed by Western blotting (immunoblotting). Because both transgenes encoded p53 proteins that were antigenically distinct from wild-type p53, it was possible to demonstrate that overexpression of the p53 protein was mostly, if not entirely, due to the expression of the transgenes. Neoplasms developed in 20% of the transgenic mice, with a high incidence of lung adenocarcinomas, osteosarcomas, and lymphomas. Tissues such as ovaries that expressed the transgene at high levels were not at higher risk of malignant transformation than tissues expressing p53 protein at much lower levels. The long latent period and low penetrance suggest that overexpression of p53 alone is not sufficient to induce malignancies and that additional events are required. These observations provide direct evidence that mutant alleles of the p53 oncogene have oncogenic potential in vivo and that different cell types show intrinsic differences in susceptibility to malignant transformation by p53. Since recent data suggest that p53 may be a recessive oncogene, it is possible that the elevated tumor incidence results from functional inactivation of endogenous p53 by overexpression of the mutant transgene. The high incidence of lung and bone tumors suggests that p53 transgenic mice may provide a useful model to investigate the molecular events that underlie these malignancies in humans.


The New England Journal of Medicine | 1981

Biotin Deficiency: An Unusual Complication of Parenteral Alimentation

Donald M. Mock; Alfred A. deLorimer; William M. Liebman; Lawrence Sweetman; Herman Baker

BIOTIN deficiency has been documented in human beings only in association with prolonged ingestion of raw egg white. In this paper, we report that clinically important biotin deficiency occurred in...


Transfusion | 2008

A randomized clinical trial comparing immediate versus delayed clamping of the umbilical cord in preterm infants: short-term clinical and laboratory endpoints

Ronald G. Strauss; Donald M. Mock; Karen J. Johnson; Gretchen A. Cress; Leon F. Burmeister; M. Bridget Zimmerman; Edward F. Bell; Asha Rijhsinghani

BACKGROUND: Most neonates less than 1.0 kg birth weight need red blood cell (RBC) transfusions. Delayed clamping of the umbilical cord 1 minute after delivery transfuses the neonate with autologous placental blood to expand blood volume and provide 60 percent more RBCs than after immediate clamping. This study compared hematologic and clinical effects of delayed versus immediate cord clamping.


Transfusion | 1999

Measurement of red cell survival using biotin-labeled red cells: validation against 51Cr-labeled red cells

Donald M. Mock; Gary L. Lankford; John A. Widness; Leon F. Burmeister; Daniel Kahn; Ronald G. Strauss

BACKGROUND: Anemia is a serious problem in the fetus and preterm infant. To investigate the physiology and pathophysiology of anemia and to assess responses to blood transfusions and erythropoietin therapy, measurement of circulating red cell survival would be useful.


Journal of Nutritional Biochemistry | 1999

Biotin biochemistry and human requirements

Janos Zempleni; Donald M. Mock

Human biotin turnover and requirements can be estimated on the basis of (1) concentrations of biotin and metabolites in body fluids, (2) activities of biotin-dependent carboxylases, and (3) the urinary excretion of organic acids that are formed at increased rates if carboxylase activities are reduced. Recent studies suggest that the urinary excretions of biotin and its metabolite bisnorbiotin, activities of propionyl-CoA carboxylase and beta-methylcrotonyl-CoA carboxylase in lymphocytes, and urinary excretion of 3-hydroxyisovaleric acid are good indicators of marginal biotin deficiency. On the basis of studies using these indicators of biotin deficiency, an adequate intake of 30 microg (123 nmoles) of biotin per day is currently recommended for adults. The dietary biotin intake in Western populations has been estimated to be 35 to 70 microg/d (143-287 nmol/d). Recent studies suggest that humans absorb biotin nearly completely. Conditions that may increase biotin requirements in humans include pregnancy, lactation, and therapy with anticonvulsants or lipoic acid.


American Journal of Physiology-cell Physiology | 1998

Uptake and metabolism of biotin by human peripheral blood mononuclear cells

Janos Zempleni; Donald M. Mock

We studied the uptake of biotin into human peripheral blood mononuclear cells (PBMC) using [3H]biotin and studied the catabolism of biotin in PBMC using [14C]biotin. Over 30 min, [3H]biotin uptake was greater at 37°C than at 25°C ( K T = 2.6 ± 0.4 nM, maximal velocity = 2.9 ± 0.2 fmol ⋅ 106cells-1 ⋅ 30 min-1). Ouabain reduced [3H]biotin uptake to 65% of control values, suggesting that biotin uptake is Na-K-ATPase dependent. Unlabeled biotin and biotin analogs reduced the uptake of [3H]biotin to 22-70% of control values, suggesting the presence of a competition for a structurally specific biotin transporter. When endocytosis by PBMC was stimulated by various acyl glycerols, [3H]biotin uptake was 40-73% of control values; these data are consistent with the hypothesis that stimulated endocytosis reduces biotin transporter density on the cell surface. During a 168-h incubation, PBMC did not catabolize [14C]biotin.We studied the uptake of biotin into human peripheral blood mononuclear cells (PBMC) using [3H]biotin and studied the catabolism of biotin in PBMC using [14C]biotin. Over 30 min, [3H]biotin uptake was greater at 37 degrees C than at 25 degrees C (KT = 2.6 +/- 0.4 nM, maximal velocity = 2.9 +/- 0.2 fmol . 10(6) cells-1 . 30 min-1). Ouabain reduced [3H]biotin uptake to 65% of control values, suggesting that biotin uptake is Na-K-ATPase dependent. Unlabeled biotin and biotin analogs reduced the uptake of [3H]biotin to 22-70% of control values, suggesting the presence of a competition for a structurally specific biotin transporter. When endocytosis by PBMC was stimulated by various acyl glycerols, [3H]biotin uptake was 40-73% of control values; these data are consistent with the hypothesis that stimulated endocytosis reduces biotin transporter density on the cell surface. During a 168-h incubation, PBMC did not catabolize [14C]biotin.


Proceedings of the Society for Experimental Biology and Medicine. Society for Experimental Biology and Medicine (New York, N.Y.) | 2000

Marginal biotin deficiency is teratogenic.

Janos Zempleni; Donald M. Mock

Recent studies of biotin status during pregnancy provide evidence that a marginal degree of biotin develops in a substantial proportion of women during normal pregnancy. Several lines of evidence suggest that, although the degree of biotin deficiency is not severe enough to produce the classic cutaneous and behavioral manifestations of biotin deficiency, the deficiency is severe enough to produce metabolic derangements in women and that characteristic fetal malformations occur at a high rate in some mammals. Moreover, our analysis of data from a published multivitamin supplementation study provide significant albeit indirect evidence that the marginal degree of biotin deficiency that occurs spontaneously in normal human gestation is teratogenic. Investigation of potential mechanisms provides evidence that biotin transport by the human placenta is weak. Further, proliferating cells accumulate biotin at a rate five times faster than quiescent cells; this observation suggests that there is an increased biotin requirement associated with cell proliferation. Perhaps this requirement arises from the need to synthesize additional biotin-dependent holocarboxylases or provide additional biotin as a substrate for biotinylation of cellular histones. Reduced activity of the biotin-dependent enzymes acetyl-CoA carboxylase and propionyl-CoA carboxylase can cause alterations of lipid metabolism and might theoretically lead to alterations of polyunsaturated fatty acid and prostaglandin metabolism that derange normal skeletal development.


Journal of Neurochemistry | 1987

Biotin transport through the blood-brain barrier

Reynold Spector; Donald M. Mock

Abstract: The unidirectional influx of biotin across cerebral capillaries, the anatomical locus of the blood‐brain barrier, was measured with an in situ rat brain perfusion technique employing [3H]biotin. Biotin was transported across the blood‐brain barrier by a saturable system with a one‐half saturation concentration of ∼ 100 μM. The permeability‐surface area products were 10−4 s−1 with a biotin concentration of 0.02 μM in the perfusate. Probenecid, pantothenic acid, and nonanoic acid but not biocytin or biotin methyles‐ter (all 250μM) inhibited biotin transfer through the blood‐brain barrier. The isolated rabbit choroid plexus was unable to concentrate [3H]biotin from medium containing 1 nM [3H]biotin. These observations provide evidence that: (1) biotin is transported through the blood‐brain barrier by a saturable transport system that depends on a free carboxylic acid group, and (2) the choroid plexus is probably not involved in the transfer of biotin between blood and cerebro‐spinal fluid.


Neurology | 1997

Biotin catabolism is accelerated in adults receiving long-term therapy with anticonvulsants

Donald M. Mock; Mark Eric Dyken

Using serum biotin concentration as the indicator, a previous study reported biotin deficiency resulting from long-term anticonvulsant therapy. However, serum biotin may not be a good indicator of tissue biotin status. Using better indicators of biotin status in anticonvulsant-treated subjects, we found increased urinary excretion of biotin catabolites and 3-hydroxyisovaleric acid, an organic acid produced in greater quantities secondary to reduced activity of a biotin-dependent carboxylase. We conclude that anticonvulsant treatment led to increased biotin catabolism and probably to reduced biotin status.

Collaboration


Dive into the Donald M. Mock's collaboration.

Top Co-Authors

Avatar
Top Co-Authors

Avatar

Nell I. Mock

University of Arkansas for Medical Sciences

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar

Nell I. Matthews

University of Arkansas for Medical Sciences

View shared research outputs
Top Co-Authors

Avatar

Janos Zempleni

University of Texas Health Science Center at San Antonio

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar

Shawna L. Stratton

University of Arkansas for Medical Sciences

View shared research outputs
Top Co-Authors

Avatar

Anna Bogusiewicz

University of Arkansas for Medical Sciences

View shared research outputs
Top Co-Authors

Avatar
Top Co-Authors

Avatar
Researchain Logo
Decentralizing Knowledge