Search PubMed⌕ Search

Biomedical subjects

M A Clark

Publications and source records attributed to M A Clark.

At least 19 recordsLinked to original sources
PubMed2000

Lectin-mediated mucosal delivery of drugs and microparticles.

Absorption of drugs and vaccines at mucosal surfaces may be enhanced by conjugation to appropriate bioadhesins which bind to mucosal epithelia. Bioadhesins might also permit cell- and site-selective targeting. One approach is to exploit surface carbohydrates on mucosal epithelial cells for lectin-mediated delivery. We review work supporting the use of lectins as mucosal bioadhesins in the gastrointestinal and respiratory tracts, the oral cavity and the eye. The gastrointestinal tract is particularly favoured for mucosal delivery. Many studies have demonstrated that the antigen sampling intestinal M cells offer a portal for absorption of colloidal delivery vehicles. Evidence is presented that M cell targeting may be achieved using M cell-specific lectins, microbial adhesins or immunoglobulins. While many hurdles must be overcome before mucosal bioadhesins can guarantee consistent, safe, effective mucosal delivery, this is an exciting area of research that has important implications for future drug and vaccine formulation.

Animals↗
PubMed2000

Pharmacokinetics and microdistribution of polyethylene glycol-modified humanized A33 antibody targeting colon cancer xenografts.

Therapeutic proteins have been conjugated with polyethylene glycol (PEGylation) to reduce immunogenicity and enhance circulating dose. Here we have investigated the effect of PEGylation on immunogenicity, pharmacokinetics, and histologic microdistribution of tumor-targeting antibodies with humanized A33 antibody (huA33) as a model system. Conjugation of huA33 with methoxy-PEG of M(r) 5,000 (32%-34% of primary amines modified) or M(r) 20,000 (16%-18% modification) preserved >50% of native huA33 binding to SW1222 colon cancer cells. In mice, both PEGylated forms cleared from serum moderately slower than native huA33. After repeated immunization with PEG-huA33, antiantibody titers in immunocompetent mice were <5% of those in huA33-treated controls. Both PEG-huA33 forms reached approx. 75% of the maximum tumor dose of huA33 in SW1222-xenografted mice, but their tumor:blood ratios were considerably reduced. To demonstrate immunologic specificity of PEG-huA33 targeting in SW1222 tumor-bearing mice, antigenic sites were presaturated by injecting excess native huA33. This reduced subsequent uptake of PEG-huA33 by up to 80%, whereas presaturation with hu3S193 control antibody had no significant effect. To assess the microdistribution of antibody uptake in the same xenograft model, tumor tissue resected at different time points after antibody administration was examined for human IgG by immunohistochemistry. Both PEG preparations achieved the same peak staining intensity and homogeneity as native huA33 with a delay of several hours. Given the measured reduction in immunoreactivity in vitro, these results demonstrate that the tumor targeting potential of huA33 in vivo is preserved at PEGylation levels sufficient to suppress immunogenicity.

Adenocarcinoma↗
PubMed2000

Stereoselective synthetic approaches to highly substituted cyclopentanes via electrophilic additions to mono-, di-, and trisubstituted cyclopentenes.

Electrophilic additions to allylically substituted alkenes are of broad synthetic utility. The control of stereoselectivity in such reactions has attracted considerable interest. However, the effect of allylic and homoallylic substituents in cyclopentenyl systems has not been investigated systematically. Studies on a series of mono, di-, and trisubstituted cyclopentenes are reported in which trans-vicinal-additions favor a syn-selective approach of electrophiles to the cyclopentene system. The formal addition of HOBr, HOCl, CH(3)SCl, and dimethyl(methylthio)sulfonium tetrafluoroborate (DMTSF)/NaN(3) with a variety of cyclopentene substrates has been carried out, and the effects of various allylic substituents on these selectivities have been examined. Additions of HOBr, HOCl, and DMTSF to highly functionalized substrates proceed predictably with syn selectivity, giving predominantly or exclusively one product. Methanesulfenyl chloride additions are less predictable, but can be tuned by suitable alteration of solvent and substrate. Results have proven useful in total syntheses of (+)-trehazolin and (+)-allosamidin.

Cyclopentanes↗
PubMed2000

Wound healing associated with severe surgical illness.

Severe injury or infection is associated with a hypermetabolic response that, when excessive, results in impaired wound healing and as a consequence increased morbidity and mortality. The objective examination of wound healing in humans is difficult and generally requires the use of models. Evidence is accumulating that nutritional and growth factors play important roles in improving the wound healing response, particularly after thermal injury and uncomplicated major surgery. The septic patient represents the biggest challenge to those seeking to optimize wound healing capacity. Advances in molecular biology have provided promising therapies in experimental studies of wound healing that await clinical investigation.

Growth Substances↗
PubMed2000

Secondary endosymbionts of psyllids have been acquired multiple times.

Previous studies have established that psyllids (Hemiptera, Psylloidea) contain primary endosymbionts, designated as Carsonella ruddii, which cospeciate with the psyllid host. This association appears to be the consequence of a single infection of a psyllid ancestor with a bacterium. Some psyllids may have additional secondary (S-) endosymbionts. We have cloned and sequenced the 16S-23S ribosomal RNA genes of seven representative psyllid S-endosymbionts. Comparison of the S-endosymbiont phylogenetic trees with those of C. ruddii indicates a lack of congruence, a finding consistent with multiple infections of psyllids with different precursors of the S-endosymbionts and/or possible horizontal transmission. Additional comparisons indicate that the S-endosymbionts are related to members of the Enterobacteriaceae as well as to several other endosymbionts and insect-associated bacteria.

Animals↗
PubMed2000

Protein carbonyl measurements show evidence of early oxidative stress in critically ill patients.

OBJECTIVE: To determine whether there is evidence of oxidative injury in patients who are critically ill with severe sepsis or major trauma, by measuring protein and lipid oxidation products. DESIGN: A prospective, observational study. SETTING: Critical care unit at a university teaching hospital. PATIENTS: Twenty-two patients with severe sepsis (Acute Physiology and Chronic Health Evaluation II score 15-34) and eight patients with major trauma (Injury Severity Score 26-50). INTERVENTIONS: Plasma and bronchoalveolar lavage fluid was collected regularly during the first 10 days after trauma or onset of sepsis. Both fluids were analyzed for protein carbonyl concentrations as a measure of protein oxidation and thiobarbituric acid-reactive substances as a measure of lipid peroxidation. Myeloperoxidase concentrations were measured as an index of neutrophil activation. MEASUREMENTS AND MAIN RESULTS: Protein carbonyl concentrations were initially highly elevated compared with those in healthy adults in the plasma of both patient groups. They fell significantly within the first few days but remained above control values. Protein carbonyl concentrations were also high initially in bronchoalveolar lavage fluid and fell significantly with time. Thiobarbituric acid-reactive substances were not increased in plasma, and varied over a wide concentration range in lavage fluid. Myeloperoxidase activity reached micromolar levels in the lavage fluid when corrected for dilution, and was significantly higher in the plasma of the sepsis patients who subsequently died. There was a strong correlation between carbonyl concentrations in lavage fluid and plasma, and between protein carbonyls, thiobarbituric acid-reactive substances and myeloperoxidase in the lungs. CONCLUSIONS: Our results provide evidence of oxidation occurring early in severe sepsis and major trauma patients, with protein carbonyl measurements providing a sensitive index of this process. High protein carbonyl concentrations in plasma as well as bronchial aspirates indicate that oxidation is not restricted to the lungs. The correlation between oxidative measures and myeloperoxidase concentrations in the lung indicates that neutrophil oxidants could be responsible for the injury.

APACHE↗
PubMed2000

Cospeciation between bacterial endosymbionts (Buchnera) and a recent radiation of aphids (Uroleucon) and pitfalls of testing for phylogenetic congruence.

Previous studies of phylogenetic congruence between aphids and their symbiotic bacteria (Buchnera) supported long-term vertical transmission of symbionts. However, those studies were based on distantly related aphids and would not have revealed horizontal transfer of symbionts among closely related hosts. Aphid species of the genus Uroleucon are closely related phylogenetically and overlap in geographic ranges, habitats, and parasitoids. To examine support for congruence of phylogenies of Buchnera and Uroleucon, sequences from four mitochondrial, one nuclear, and one endosymbiont gene (trpB) were obtained. Congruence of phylogenies based on pooled aphid genes with phylogenies based on trpB was highly significant: Most nodes resolved by trpB corresponded to nodes resolved by the pooled aphid genes. Furthermore, no nodes were both inconsistent between the trees and strongly supported in both trees. Two kinds of analyses testing the null hypothesis of perfect congruence between pairwise combinations of datasets and tree topologies were performed: the Kishino-Hasegawa test and the likelihood-ratio test. Both tests indicated significant disagreement among most pairwise combinations of mitochondrial, nuclear, and symbiont datasets. Because rampant recombination among mitochondrial genomes of different aphid species is unlikely, inaccurate assumptions in the evolutionary models underlying these tests appear to be causing the hypothesis of a shared history to be incorrectly rejected. Moreover, trpB was more consistent with the aphid genes as a set than any single aphid gene was with the others, suggesting that the symbionts show the same phylogeny as the aphids. Overall, analyses support the interpretation that symbionts and aphids have undergone strict cospeciation, with no horizontal transmission of symbionts even among closely related, ecologically similar aphid hosts.

Animals↗
PubMed2000

Breast and cervical cancer screening: associations with personal, spouse's, and combined smoking status.

The objective of this study was to examine the association of women's cancer screenings with both personal and spouses' smoking status, as well as with the broader context of household smoking, in a United States national-level sample of women aged 42-75 years. Data were from the 1994 National Health Interview Survey Health Promotion Supplement. The sample included 1586 women who reported they were married and living with a spouse in a two-person household. Three measures of smoking status were used: personal smoking status, smoking status of spouse, and household smoking status (self and spouse smoked, spouse only smoked, self only smoked, and both nonsmokers). Using logistic regression modeling, associations were examined between the smoking status measures and three cancer screening indicators: mammogram < or =2 years, clinical breast exam < or =2 years, and Pap test < or =3 years. The both nonsmokers group consistently had the highest screening rates for all three exams. The spouse only smoking group was 10-12% less likely to obtain all three cancer screening tests compared to the both nonsmokers group. The self and spouse group was less likely to report a recent mammogram and clinical breast exam. The self only group did not differ significantly from the both nonsmokers group on any of the cancer screening measures. Results suggest that smoking status of a spouse may be an important correlate of women's cancer screenings.

Adult↗
PubMed1999

Generation of anti-p53 Fab fragments from individuals with colorectal cancer using phage display.

Although many individuals with malignancy develop Abs against p53, little is currently known of the structural features, V gene usage, and degree of somatic mutation of these Abs. Such information is critical to any meaningful understanding of the nature and significance of this humoral immune response to p53. We have constructed phage display libraries from six individuals with colorectal cancer and a demonstrable serum immune response against p53. Following panning with recombinant p53, a total of 43 binding Fab were identified. Four of these Abs bound with high affinity to wild-type denatured p53 (1.19 x 10-8 - 1.57 x 10-8), as determined by BIAcore analysis, and were highly specific for both recombinant and cell line-derived p53, as determined by ELISA and immunoprecipitation. Epitope mapping showed they were reactive with the N terminus of human p53 between residues 27 and 44. Sequence analysis showed that the heavy chains were derived from the VH1 gene family, and the light chains from VL4. The pattern of replacement and silent mutations in the Fab sequence indicated that negative selection had occurred in the framework regions of all the VH genes. We show that lymphocytes from individuals with cancer represent a valuable source of high affinity human Abs against p53. This approach provides an opportunity to examine the genetic structure of these naturally occurring Abs, and to draw inferences regarding the nature of the immune response that produced them. Abs identified in this way have a number of potential therapeutic applications.

Amino Acid Sequence↗
PubMed1999

Smoking and cancer screening for women ages 42-75: associations in the 1990-1994 National Health Interview Surveys.

BACKGROUND: Previous studies have found an association between current smoking and lower rates of mammography and Pap testing. The objective of this study was to investigate the association of smoking status with breast and cervical cancer screening across the 1990-1994 National Health Interview Surveys (NHIS). The NHIS provides a consistent set of independent and dependent variables across several surveys, with data collected by a similar in-person interview methodology from year to year. This report employs more databases than have been used in other analyses that have examined associations between smoking and cancer screening. METHODS: Data were from the health promotion and cancer control supplements to the 1990-1994 NHIS. The target population was women ages 42-75. Associations were examined between smoking status (never, former, <1 pack/day, >/=1 pack/day) and three screening indicators: ever had a mammogram, mammogram in the past 2 years, and Pap test in the past 3 years. Sample sizes ranged from about 3,000 to over 10,800 depending on the respective NHIS survey and dependent variable. Data analyses were conducted by bivariate and multiple logistic regression. RESULTS: Women who smoked >/=1 pack of cigarettes per day were significantly less likely to have had mammography screening in all NHIS surveys, compared to women who never smoked. Adjusted odds ratios were 0.63 to 0.74 for ever had a mammogram, and 0.56 to 0.66 for mammography in the past 2 years. Women who smoked >/=1 pack per day also had lower Pap test rates than women who never smoked in 1992-1994 (adjusted odds ratios of 0.51-0.71). Results for lighter smokers were not as consistent. Former smokers often had significantly higher screening rates than never smokers. CONCLUSIONS: Research still needs to identify reasons for lower screening among women who smoke. Factors to explore include the social networks of smokers and broader health behavior patterns. Clinicians should consider heavier smoking as a marker for risk of not obtaining screening and make assessment of screening status a priority at each visit.

Adult↗
PubMed1999

Providers' smoking cessation attitudes and practices for older patients.

A mail survey of 136 providers in a health maintenance organization in the Chicago metropolitan area examined smoking cessation attitudes and performance of the 4As protocol (asking, advising, assisting, arranging) for patients aged 50 years or older. Asking about smoking was most frequent, followed by arranging, advising, and assisting. Physicians and nurse practitioners performed each of the 4As more often than did registered and licensed practical nurses. In multiple logistic regression analyses, provider type was the only significant predictor of asking about smoking. Advising, assisting, and arranging follow-ups were more likely to be performed by providers who perceived a sense of professional responsibility about older patients' smoking; advising was more likely for providers who perceived that they had enough time to advise older patients about smoking; and assisting and arranging were more likely for providers with a stronger sense of self-efficacy for helping older patients stop smoking.

Aging↗
PubMed1999

Sequence evolution in bacterial endosymbionts having extreme base compositions.

A major limitation on ability to reconstruct bacterial evolution is the lack of dated ancestors that might be used to evaluate and calibrate molecular clocks. Vertically transmitted symbionts that have cospeciated with animal hosts offer a firm basis for calibrating sequence evolution in bacteria, since fossils of the hosts can be used to date divergence events. Sequences for a functionally diverse set of genes have been obtained for bacterial endosymbionts (Buchnera) from two pairs of aphid host species, each pair diverging 50-70 MYA. Using these dates and estimated numbers of Buchnera generations per year, we calculated rates of base substitution for neutral and selected sites of protein-coding genes and overall rates for rRNA genes. Buchnera shows homogeneity among loci with regard to synonymous rate. The Buchnera synonymous rate is about twice that for low-codon-bias genes of Escherichia coli-Salmonella typhimurium on an absolute timescale, and fourfold higher on a generational timescale. Nonsynonymous substitutions show a greater rate disparity in favor of Buchnera, a result consistent with a genomewide decrease in selection efficiency in Buchnera. Ratios of synonymous to nonsynonymous substitutions differ for the two pairs of Buchnera, indicating that selection efficiency varies among lineages. Like numerous other intracellular bacteria, such as Rickettsia and Wolbachia, Buchnera has accumulated amino acids with codons rich in A or T. Phylogenetic reconstruction of amino acid replacements indicates that replacements yielding increased A + T predominated early in the evolution of Buchnera, with the trend slowing or stopping during the last 50 Myr. This suggests that base composition in Buchnera has approached a limit enforced by selective constraint acting on protein function.

AT Rich Sequence↗
PubMed1999

Screening for breast and cervical cancers: the importance of knowledge and perceived cancer survivability.

INTRODUCTION: This study examines the association between recent screening for breast and cervical cancers, knowledge of cancer risk factors, and perceptions of surviving cancer. METHODS: Data were from the Cancer Control Supplement to the 1992 National Health Interview Survey (NHIS-CCS). The dependent variable combined breast and cervical cancer screening practices into a single composite index. Two independent variables combined women's knowledge about breast and cervical cancers into single indicators--one representing risk factor knowledge, the other representing perceived likelihood of surviving breast and cervical cancers following early detection. RESULTS: Multivariate analysis showed that recency of screening for both breast and cervical cancers was associated with knowledge of cancer risk factors and perceptions of surviving cancer. Education, household income, and smoking status also were correlates of comprehensive screening. Significant interactions between income and perceived survivability, and between education and perceived survivability suggested that the effects of income and education on comprehensive screening varied with perceptions about surviving cancer. CONCLUSION: The study suggests that knowledge and attitudinal questions can be combined for two diseases to enhance understanding of who is most likely to be screened comprehensively for breast and cervical cancers. Although national trends show that large percentages of women over age 50 are having mammograms and Pap tests, this progress is not likely to be sustained unless existing barriers are eliminated. Limited knowledge about breast and cervical cancer risk factors and misperceptions about survival from cancer represent two of these barriers.

Aged↗
PubMed1999

The use of fluconazole as a local irrigant for nephrostomy tubes.

OBJECTIVES: Few data exist concerning the combined use of fluconazole systemically and as an irrigant for nephrostomy tubes in a patient with renal candidiasis. The patient described here presented with renal fungal balls obstructing the drainage of urine from her nephrostomy tubes. METHODS: Twelve months after chemoradiation for a stage IIB squamous cell carcinoma of the uterine cervix, a 35-year-old woman presented with renal obstruction necessitating insertion of ureteral stents. After 6 months of chemotherapy, the patient developed uremia. After nephrostomy tubes were placed, renal candidiasis was noted, and fluconazole was begun systemically. When the renal candidiasis failed to clear, nephrostomy tube irrigations were begun. RESULTS: Fourteen days of therapy with fluconazole resulted in the resolution of the uremia. The patient died 6 months later with her nephrostomy tubes in situ and without evidence of candidiasis in her urinary tract. CONCLUSIONS: The patient described was successfully treated without having to remove her nephrostomy tubes. Two other authors have reported the successful use of fluconazole irrigation to treat candidiasis in nephrostomy tubes that was unresponsive to systemic fluconazole. Before the appearance of these reports, the best results were obtained with removal of the catheter in renal candidiasis.

Adult↗
PubMed1998

Sequence analysis of a 34.7-kb DNA segment from the genome of Buchnera aphidicola (endosymbiont of aphids) containing groEL, dnaA, the atp operon, gidA, and rho.

Buchnera aphidicola is a prokaryotic endosymbiont of the aphid Schizaphis graminum. From past and present nucleotide sequence analyses of the B. aphidicola genome, we have assembled a 34. 7-kilobase (kb) DNA segment. This segment contains genes coding for 32 open reading frames (ORFs), which corresponded to 89.9% of the DNA. All of these ORFs could be identified with homologous regions of the Escherichia coli genome. The order of the genes with established functions was groELS-trmE-rnpA-rpmH-dnaA-dnaN-gyrB-atpCDGAH FEB-gidA-fdx-hscA- hscB-nifS-ilvDC-rep-trxA-rho. The order of genes in small DNA fragments was conserved in both B. aphidicola and E. coli. Most of these fragments were in approximately the same region of the E. coli genome. The latter organism, however, contained many additional inserted genes within and between the fragments. The results of the B. aphidicola genome analyses indicate that the endosymbiont has many properties of free-living bacteria.

Algal Proteins↗
PubMed1998

Buchnera aphidicola (Aphid endosymbiont) contains genes encoding enzymes of histidine biosynthesis.

Buchnera aphidicola is an endosymbiont of aphids. One of its functions appears to be the synthesis of essential amino acids for the aphid host. A 12.8-kilobase B. aphidicola DNA fragment has been cloned and sequenced. It contains genes encoding all of the enzymes required for the biosynthesis of the essential amino acid histidine. The order of the genes, hisGDCBHAFI, is the same as that found in Escherichia coli and is consistent with their constituting a single transcription unit. The DNA fragment also contained genes involved in aromatic amino acid biosynthesis (aroC), the oxidative pentose pathway (gnd), and 2'-deoxyribonucleotide metabolism (dcd), as well as a tRNA synthase (metG).

Animals↗
PubMed1998

Ulex europaeus 1 lectin targets microspheres to mouse Peyer's patch M-cells in vivo.

The interaction of latex microspheres with mouse Peyer's patch membranous M-cells was studied in a mouse gut loop model after the microspheres were coated with a variety of agents. Carboxylated microspheres (diameter 0.5 micron) were covalently coated with lectins Ulex europaeus 1, Concanavalin A, Euonymus europaeus and Bandeiraea simplicifolia 1 isolectin-B4, human immunoglobulin A or bovine serum albumin. Of the treatments examined, only Ulex europaeus (UEA1) resulted in significant selective binding of microspheres to M-cells. UEA1-coated microspheres bound to M-cells at a level 100-fold greater than BSA-coated microspheres, but binding to enterocytes was unaffected. Incubation of UEA1-coated microspheres with alpha-L-fucose reduced M-cell binding to a level comparable with BSA-coated microspheres. This indicated that targeting by UEA1 was via a carbohydrate receptor on the M-cell surface. Adherence of UEA1-coated microspheres to M-cells occurred within 10 min of inoculation into mouse gut loops and UEA1-coated microspheres were transported to 10 microns below the apical surface of M-cells within 60 min of inoculation. UEA1-coated microspheres also targeted mouse Peyer's patch M-cells after intragastric administration. These results demonstrated that altering the surface chemistry of carboxylated polystyrene microspheres increased M-cell targeting, suggesting a strategy to enhance delivery of vaccine antigens to the mucosal immune system.

Analysis of Variance↗