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Biomedical subjects

M Randolph

Publications and source records attributed to M Randolph.

At least 19 recordsLinked to original sources
PubMed2001

Defining the minimal length of sequence homology required for selective gene isolation by TAR cloning.

The transformation-associated recombination (TAR) cloning technique allows selective and accurate isolation of chromosomal regions and genes from complex genomes. The technique is based on in vivo recombination between genomic DNA and a linearized vector containing homologous sequences, or hooks, to the gene of interest. The recombination occurs during transformation of yeast spheroplasts that results in the generation of a yeast artificial chromosome (YAC) containing the gene of interest. To further enhance and refine the TAR cloning technology, we determined the minimal size of a specific hook required for gene isolation utilizing the Tg.AC mouse transgene as a targeted region. For this purpose a set of vectors containing a B1 repeat hook and a Tg.AC-specific hook of variable sizes (from 20 to 800 bp) was constructed and checked for efficiency of transgene isolation by a radial TAR cloning. When vectors with a specific hook that was >/=60 bp were utilized, approximately 2% of transformants contained circular YACs with the Tg.AC transgene sequences. Efficiency of cloning dramatically decreased when the TAR vector contained a hook of 40 bp or less. Thus, the minimal length of a unique sequence required for gene isolation by TAR is approximately 60 bp. No transgene-positive YAC clones were detected when an ARS element was incorporated into a vector, demonstrating that the absence of a yeast origin of replication in a vector is a prerequisite for efficient gene isolation by TAR cloning.

Animals↗
PubMed1999

Transdermal photopolymerization for minimally invasive implantation.

Photopolymerizations are widely used in medicine to create polymer networks for use in applications such as bone restorations and coatings for artificial implants. These photopolymerizations occur by directly exposing materials to light in "open" environments such as the oral cavity or during invasive procedures such as surgery. We hypothesized that light, which penetrates tissue including skin, could cause a photopolymerization indirectly. Liquid materials then could be injected s.c. and solidified by exposing the exterior surface of the skin to light. To test this hypothesis, the penetration of UVA and visible light through skin was studied. Modeling predicted the feasibility of transdermal polymerization with only 2 min of light exposure required to photopolymerize an implant underneath human skin. To establish the validity of these modeling studies, transdermal photopolymerization first was applied to tissue engineering by using "injectable" cartilage as a model system. Polymer/chondrocyte constructs were injected s.c. and transdermally photopolymerized. Implants harvested at 2, 4, and 7 weeks demonstrated collagen and proteoglycan production and histology with tissue structure comparable to native neocartilage. To further examine this phenomenon and test the applicability of transdermal photopolymerization for drug release devices, albumin, a model protein, was released for 1 week from photopolymerized hydrogels. With further study, transdermal photpolymerization potentially could be used to create a variety of new, minimally invasive surgical procedures in applications ranging from plastic and orthopedic surgery to tissue engineering and drug delivery.

Animals↗
PubMed1999

Transdermal photopolymerization of poly(ethylene oxide)-based injectable hydrogels for tissue-engineered cartilage.

Transdermal photopolymerization, a minimally invasive method for implantation, was used to subcutaneously place a mixture of polymer and isolated chondrocytes to regenerate cartilage tissue in vivo. Semi-interpenetrating networks of varying proportions of poly(ethylene oxide)-dimethacrylate and poly(ethylene oxide) and primary bovine articular chondrocytes were implanted in athymic mice. Four mice (12 implants) were harvested at 2, 4, and 7 weeks. Chondrocytes survived implantation and photopolymerization and formed neocartilage containing 1.5 to 2.9% wet weight collagen and 4 to 7% glycosaminoglycan. Thirty-five percent of the total collagen was type II collagen. Histologic analysis exhibited tissue structure resembling neocartilage, and safranin O staining demonstrated glycosaminoglycan distribution throughout the hydrogels. This study demonstrates the potential use of transdermal photopolymerization for minimally invasive subcutaneous implantation of hydrogels and chondrocytes for in vivo cartilage regeneration.

Animals↗
PubMed1996

Mechanical analysis of explanted silicone breast implants.

Smooth-walled silicone gel breast implants (n = 25) were removed from 15 women after implantation times that varied from 23 to 216 months (mean = 117 months; SEM = 12.9). Strips of implant shells were tested to failure by computer-controlled tensiometer. Regression analysis revealed significant negative correlation between age of implantation and shell strength (p < 0.05), shell toughness (p < 0.05), and shell elasticity (p < 0.05). These data suggest that exposure to the in vivo environment weakens silicone gel breast implant shells over time.

Breast Implants↗
PubMed1994

Retrospective description and experimental reconstitution of three different responses of the baboon to lethal E. coli.

This paper is divided into a retrospective descriptive section in which we report on three distinctly different and spontaneous responses of the baboon to LD100 Eschericia coli observed over the last 6 years. This section is followed by an experimental section in which we reproduce the immediate and delayed responses based on hypothetical mechanisms. In the descriptive section, we arbitrarily divided all the non-survivor animals on which we had sufficient data into three groups based on duration of survival (i.e., 12 hr or less, immediate, 12 to 30 hr, intermediate, and 30 hr or more, delayed). The natural history and pathophysiology of the 12 hr or less group matched that of capillary leak syndrome with a rapid fall in blood pressure, rise in hematocrit, massive edema, and congestion with leukocyte sequestration in both lung and liver, with only limited adrenal cortical hemorrhage. The 12 to 30 hr group matched the natural history of a consumptive hemorrhagic diatheses with a biophasic blood pressure response, limited change in hematocrit, a severe consumptive coagulopathy, severe adrenal cortical hemorrhage, and a moderate renal cortical tubular necrosis, but limited renal cortical thrombosis. The greater than 30 hr group matched the natural history of a microvascular thrombotic (hemolytic uremic) syndrome with a stable blood pressure, a fall in hematocrit associated with a massive renal cortical thrombosis with a severe medullary, and cortical tubular necrosis. We did not analyze these groups further (i.e., type of intervention etc.) once we found that time of survival correlated with a unique clinical syndrome, because based on these observations, we hypothesized that we could reproduce the immediate capillary leak and pulmonary failure, and the delayed microvascular thrombosis and renal failure syndromes experimentally. We reproduced the immediate (< 12 hr) and delayed (> 30 hr) responses by infusion of either tumor necrosis factor or C4b binding protein with sublethal E. coli. This provides models of the immediate and delayed as well as the intermediate responses to E. coli for study of mechanism and the efficacy of therapeutic interventions.

Animals↗
PubMed1991

Effect of intravenous cocaine on uterine blood flow in the gravid baboon.

Cocaine abuse during pregnancy is associated with adverse perinatal outcome, believed to be a result of potent vasoconstrictive effects that cocaine has on the maternal cardiovascular system. The direct effect of cocaine on the pregnant, nonhuman primates' uterine vasculature in vivo has not been examined. We investigated the effects of intravenous cocaine on maternal arterial blood pressure, uterine blood flow, and uterine vascular resistance in four unanesthetized, chronically instrumented pregnant baboons. Baboons were instrumented during the latter half of pregnancy, placing an ultrasonic flow probe around one uterine artery and catheters in the maternal inferior vena cava and aorta. Bolus intravenous cocaine hydrochloride doses of 0.05 mg/kg, 0.1 mg/kg, and 0.3 mg/kg by maternal weight were infused 30 minutes apart at least 5 days after surgical instrumentation. The maternal blood pressure rose 7.3% and 12.0% after the 0.1 mg/kg and 0.3 mg/kg cocaine infusions, respectively, and the uterine blood flow fell in a dose-dependent fashion 13.1% and 22.7%. Plasma norepinephrine levels rose in response to the 0.3 mg/kg cocaine infusion. These studies show that low doses of cocaine significantly reduce uterine blood flow in the pregnant baboon in a dose-dependent manner by increasing uterine vascular resistance.

Animals↗
PubMed1990

Comparison of epidemic and endemic group G streptococci by restriction enzyme analysis.

Restriction enzyme profiles of group G beta-hemolytic streptococci associated with a point source outbreak and an outbreak of sporadic pharyngitis in two different communities were compared. To asses the epidemiologic utility of this approach for studying group G streptococci, DNA fingerprints of strains responsible for a point source outbreak of pharyngitis associated with the consumption of contaminated food were compared with DNA fingerprints of pharyngeal isolates from children with pharyngitis seen at a pediatric practice during a 6-month period. In each epidemiologic situation, a single strain characterized by a unique restriction enzyme pattern predominated. The results are compatible with the conclusion that human infections could be limited to a few strains of group G streptococci which have the capacity to spread through a given population. The restriction enzyme profiles proved to be a highly specific and precise means of evaluating strain relatedness and of providing further understanding of the epidemiology of group G streptococcal infections.

Connecticut↗
PubMed1986

Persistence of antibody and response to booster dose of Haemophilus influenzae type b polysaccharide diphtheria toxoid conjugate vaccine in infants immunized at 9 to 15 months of age.

At approximately 2 years of age, 27 infants previously immunized at 9 to 15 months of age with two doses of polyribosylribitol phosphate-diphtheria toxoid conjugate vaccine (PRP-D) and 23 infants immunized with polyribosylribitol phosphate (PRP) vaccine were given a single injection of PRP-D. Pre- and post-immunization sera were obtained. No serious local or systemic reactions were observed. The PRP-D recipients had a geometric mean anti-PRP antibody level of 4.8 micrograms/ml 1 month after the second primary injection, retained 1.2 microgram/ml 1 year later, and had a level of 71 micrograms/ml after the booster immunization. In contrast, PRP recipients had a geometric mean level of 0.083 microgram/ml 1 month after the second primary injection, retained 0.042 microgram/ml 1 year later, and after a single dose of PRP-D at approximately 2 years of age had a geometric mean level of 8.6 micrograms/ml. The significantly higher antibody response in the prior PRP-D recipients suggests the recall of immunologic memory induced by the PRP-D vaccine.

Antibodies, Bacterial↗
PubMed1978

Carriage of Neisseria meningitidis and Neisseria lactamica in infants and children.

Asymptomatic carriage of Neisseria meningitidis and Neisseria lactamica was studied in a total of 2,969 healthy infants and children in Danbury, Conn., between October 1971 and June 1975. The prevalence of N. meningitidis averaged 0.71% during the first four years of life and increased to 5.4% by 14--17 years. Rates of carriage of N. lactamica increased from 3.8% in three-month-old infants to a peak of 21.0% at 18 months and then declined to 1.8% by 14--17 years of age. Of the children who acquired N. lactamica, 66% developed fourfold or greater rises in titers of IgG antibody to groups A, B, and/or C meningococci as determined by immunofluorescence compared with only 5% of control children. Of new carriers of N. lactamica, 40% developed increased titers of bactericidal antibody to groups A, B, and/or C meningococci as compared with 7% of noncarriers. Carriage of N. lactamica may assist in the development of natural immunity to N. meningitidis by induction of cross-reactive antibodies.

Aging↗
PubMed1977

Persistence of antibody following immunization of children with groups A and C meningococcal polysaccharide vaccines.

Persistence of antibody following immunization with groups A and C meningococcal polysaccharides was studied in two groups of children. Cohort 1 (20 children, 2 to 11 years of age) received two doses of A vaccine three years apart; cohort 2 (1,345 children, 6 to 8 years of age) received A or C vaccine initially and the heterologous vaccine one year later. No significant reactions were observed. Geometric mean anti-A concentrations one month after primary and booster immunization in cohort 1 were 8.77 and 13.08 microgram/ml, respectively. Mean anti-A concentration declined 32% one year after booster immunization, but then stabilized. Mean anti-A and anti-C concentrations in cohort 2 were 9.35 and 9.12 microgram/ml, respectively, one month after primary immunization. Mean anti-A concentration declined to 5.54 and 3.62 microgram/ml while anti-C levels fell to 2.35 and 1.47 microgram/ml one and four years after immunization. The proportion of children in cohort 2 with greater than or equal to 2.0 microgram/ml of anti-A and anti-C four years after immunization were 80% and 40%, respectively. An antibody concentration greater than or equal to 2.0 microgram/ml has been associated with protection against meningococcal disease. The results suggest that routine immunization of young infants with group A vaccine may result in long-lasting immunity. The usefulness of the presently available group C vaccine appears to be limited to the control of epidemics.

Antibodies, Bacterial↗