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Biomedical subjects

D P Clark

Publications and source records attributed to D P Clark.

At least 37 records · Page 2Linked to original sources
PubMed1998

Cryptosporidiosis in patients with AIDS: correlates of disease and survival.

Although 10%-15% of patients with AIDS in the United States may acquire cryptosporidium infection, little data exist on clinical or histological characteristics that differentiate clinical outcomes. A case-control study of 83 HIV-positive adult patients with cryptosporidiosis was conducted, as was a histopathologic review of data on gastrointestinal biopsy specimens from 30 patients. Four clinical syndromes were identified: chronic diarrhea (36% of patients), choleralike disease (33%), transient diarrhea (15%), and relapsing illness (15%). A multivariate analysis of data for cases and controls revealed that acquiring cryptosporidiosis was associated with the presence of candidal esophagitis (odds ratio [OR], 2.53; P < .002) and Caucasian race (OR, 6.71; P = .0001) but not with sexual orientation. Cases had a significantly shorter duration of survival from the time of diagnosis than did controls (240 vs. 666 days, respectively; P = .0004), which was independent of sex, race, or or injection drug use. Antiretroviral use was protective against disease (OR, 0.072; P = .0001). All four clinical syndromes were represented among the histological data. There was no statistically significant correlation between histological intensity of infection and clinical severity of illness.

AIDS-Related Opportunistic Infections↗
PubMed1998

Facial hypertrophic scarring from pulsed dye laser.

BACKGROUND: The 585-nm, 450-msec pulsed dye laser is widely used to treat benign vascular lesions. The biophysical interactive properties of this laser allow effective, precise small vessel ablation with very low incidence of pigmentary alteration and atrophic scarring side effects. OBJECTIVE: We are reporting a case of hypertrophic scar development on the upper lip of a patient whose facial hypertrophic port-wine stain was treated by pulsed dye laser. METHODS: The most effective energy fluence was determined by analysis of test areas treated at various fluences. This fluence was used for the initial full lesion treatment, with subsequent fluences chosen by treatment response at each 4-week follow-up visit. RESULTS: After the fourth treatment a hypertrophic scar developed on our patient's left cutaneous upper lip. CONCLUSIONS: This hypertrophic scar developed after pulsed dye laser treatment because the patient did not follow posttreatment care instructions, and because the initial treatment fluences of 8.0-8.5 J/cm2 may have been too high.

Cicatrix, Hypertrophic↗
PubMed1998

Enteric beta-defensin: molecular cloning and characterization of a gene with inducible intestinal epithelial cell expression associated with Cryptosporidium parvum infection.

A growing body of evidence suggests that endogenous antibiotics contribute to the innate defense of mammalian mucosal surfaces. In the cow, beta-defensins constitute a large family of antibiotic peptides whose members have been previously isolated from the respiratory and oral mucosa, as well as circulating phagocytic cells. A novel bovine genomic clone with beta-defensin-related sequence [corrected] related to those of these alpha-defensins was isolated and characterized. The corresponding cDNA was isolated from a small intestinal library; its open reading frame predicts a deduced sequence of a novel beta-defensin, which we designate enteric beta-defensin (EBD). Northern blot analysis of a variety of bovine tissues revealed that EBD mRNA is highly expressed in the distal small intestine and colon, anatomic locations distinct from those for previously characterized beta-defensins. EBD mRNA was further localized by in situ hybridization to epithelial cells of the colon and small intestinal crypts. Infection of two calves with the intestinal parasite Cryptosporidium parvum induced 5- and 10-fold increases above control levels of EBD mRNA in intestinal tissues. An anchored-PCR strategy was used to identify other beta-defensin mRNAs expressed in the intestine. In addition to that of EBD, several low-abundance cDNAs which corresponded to other beta-defensin mRNAs were cloned. Most of these clones encoded previously characterized beta-defensins or closely related isoforms, but two encoded a previously uncharacterized prepro-beta-defensin. Northern blot evidence supported that all of these other beta-defensin genes are expressed at levels lower than that of the EBD gene in enteric tissue. Furthermore, some of these beta-defensin mRNAs were abundant in bone marrow, suggesting that in enteric tissue their expression may be in cells of hematopoietic origin. Extracts of small intestinal mucosa obtained from healthy cows have numerous active chromatographic fractions as determined by an antibacterial assay, and one peptide was partially purified. The peptide corresponded to one of the low-abundance cDNAs. This study provides evidence of beta-defensin expression in enteric tissue and that the mRNA encoding a major beta-defensin of enteric tissue, EBD, is inducibly expressed in enteric epithelial cells. These findings support the proposal that beta-defensins may contribute to host defense of enteric mucosa.

Amino Acid Sequence↗
PubMed1997

Effect of chelating agents and respiratory inhibitors on regulation of the cadA gene in Escherichia coli.

The cadA gene that encodes lysine decarboxylase in Escherichia coli is induced by low pH and - during anaerobic growth - by the substrate, lysine. We used operon fusions of cadA to lacZ to investigate the effects of aeration on cadA regulation. When an insertion mutation in osmZ (= hns) was introduced, a cadA-lacZ fusion was derepressed in the presence of air to approximately the same level as seen during anaerobic growth. However, the pH-dependent regulation of cadA was not affected by osmZ. Introduction of mutations in rpoS, fur, or fnr had no significant effect on cadA expression. However, defects in arcB or arcA largely abolished expression of cadA during anaerobic growth. Nonetheless, strains defective in both arcB and osmZ showed the same high cadA-lac expression in air as seen in the single osmZ derivatives. Blocking the respiratory chain with mutations or chemical inhibitors also caused derepression of a cadA-lacZ fusion in air, while agents affecting the proton gradient had no effect. Derepression of cadA in air was also mediated by several chelating agents, in particular by methoxyindole carboxylic acid. Addition of Fe2+ overcame this effect. Chelating agents also abolished the expression during aerobic growth of several genes known to be under arcAB control and which are normally repressed during anaerobic growth but induced in the presence of air. This implies that the effect of chelating agents on cadA expression is mediated via the arcAB regulatory system.

Aluminum Silicates↗
PubMed1997

Polymerase chain reaction-based detection of B-cell clonality in the fine needle aspiration biopsy of a thyroid mucosa-associated lymphoid tissue (MALT) lymphoma.

Although it is possible to diagnose primary high-grade thyroid lymphoma from a fine needle aspiration (FNA) biopsy, the distinction of low-grade B-cell lymphoma of mucosa-associated lymphoid tissue (MALT) from lymphocytic thyroiditis is sometimes problematic. Definitive diagnosis of lymphoma on cytologic specimens may be facilitated by the documentation of a clonal lymphoid proliferation within the specimen by flow cytometric immunophenotyping or immunocytochemistry. Recently, molecular techniques have also been developed to detect clonal lymphoid proliferation based on immunoglobulin (Ig) or T-cell receptor gene rearrangement. We have used a polymerase chain reaction (PCR)-based assay for Ig heavy chain gene arrangement to identify a clonal population of lymphocytes within the thyroid FNA specimen from a low-grade thyroid MALT lymphoma. Using this assay, we identified no distinct clonal population in five cytologic specimens of lymphocytic thyroiditis. Therefore, this PCR-based clonality assay represents a potentially useful adjunct to the cytologic diagnosis of thyroid lymphoma.

Aged↗
PubMed1997

Polymerase chain reaction-based microsatellite analysis of fine-needle aspirations from Hürthle cell neoplasms.

Fine-needle aspiration (FNA) of the thyroid is the sine qua non in the preoperative evaluation of thyroid nodules. Despite this, cytological examination of FNA cannot differentiate malignant from benign Hürthle cell neoplasms. We have previously shown that Hürthle cell carcinomas harbor more genetic alterations on chromosomal arms 1q and 2p than Hürthle cell adenomas, and that all Hürthle cell neoplasms have a significantly higher frequency of alterations on chromosomal arm 1p compared with normal thyroid. To determine if these genetic alterations could be detected in FNA samples, we examined DNA from FNAs that were available from eight Hürthle cell neoplasms. Polymerase chain reaction (PCR) amplification of DNA demonstrated either direct correlation with alterations seen in the tumor samples or in some instances, additional chromosomal alterations. We conclude that PCR-based microsatellite DNA analysis of preoperative FNA samples from Hürthle cell neoplasms can potentially distinguish Hürthle cell carcinomas from adenomas and that with further validation and perfection, this technique may allow more optimal surgical management of patients with these lesions.

Adenocarcinoma↗
PubMed1997

Cutaneous micrographic surgery for atypical fibroxanthoma.

BACKGROUND: Atypical fibroxanthoma is a locally aggressive cutaneous tumor of the head and neck. Reported treatments include simple excision, cryosurgery, radiation, and cutaneous micrographic surgery. OBJECTIVE: We wish to further document the use of cutaneous micrographic surgery for local control of atypical fibroxanthoma. METHODS: A retrospective study of six cases from the University of Missouri-Columbia and a review of the literature. RESULTS: Five (84%) of our cases were on the heads of elderly patients with strong evidence of photodamage. Subclinical extension of atypical fibroxanthoma required surgical margins averaging 9 mm. Cutaneous micrographic surgery has been associated with no recurrences. CONCLUSION: The results of our data demonstrate cutaneous micrographic surgery to be an excellent modality to address this locally aggressive tumor. Cutaneous micrographic surgery is an advantageous therapy for this tumor because of its meticulous tissue removal, tissue mapping, and tissue sparing qualities.

Aged↗
PubMed1997

Bacteroides fragilis toxin exhibits polar activity on monolayers of human intestinal epithelial cells (T84 cells) in vitro.

Strains of Bacteroides fragilis associated with diarrhea in children (termed enterotoxigenic B. fragilis, or ETBF) produce a heat-labile ca. 20-kDa protein toxin (BFT). The purpose of this study was to examine the activity of BFT on polarized monolayers of human intestinal epithelial cells (T84 cells). In Ussing chambers, BFT had two effects. First, BFT applied to either the apical or basolateral surfaces of T84 monolayers diminished monolayer resistance. However, the time course, magnitude, and concentration dependency differed when BFT was applied to the apical versus basolateral membranes. Second, only basolateral BFT stimulated a concentration-dependent and short-lived increase in short circuit current (Isc; indicative of C1- secretion). Time course experiments indicated that Isc returned to baseline as resistance continued to decrease, indicating that these two electrophysiologic responses to BFT are distinct. Light microscopic studies of BFT-treated monolayers revealed only localized cellular changes after apical BFT, whereas basolateral BFT rapidly altered the morphology of nearly every cell in the monolayer. Transmission and scanning electron microscopy after basolateral BFT confirmed a striking loss of cellular microvilli and complete dissolution of some tight junctions (zonula occludens) and zonula adherens without loss of desmosomes. The F-actin structure of BFT-treated monolayers (stained with rhodamine-phalloidin) revealed diminished and flocculated staining at the apical tight junctional ring and thickening of F-actin microfilaments in focal contacts at the basolateral monolayer surface compared to those in similarly stained control monolayers. BFT did not injure T84 monolayers, as assessed by lactic dehydrogenase release and protein synthesis assays. These studies indicate that BFT is a nonlethal toxin which acts in a polar manner on T84 monolayers to stimulate C1- secretion and to diminish monolayer resistance by altering the apical F-actin structure of these cells. BFT may contribute to diarrheal disease associated with ETBF infection by altering epithelial barrier function and stimulating C1- secretion.

Actins↗
PubMed1997

Characterization of anaerobic fermentative growth of Bacillus subtilis: identification of fermentation end products and genes required for growth.

Bacillus subtilis can grow anaerobically by respiration with nitrate as a terminal electron acceptor. In the absence of external electron acceptors, it grows by fermentation. Identification of fermentation products by using in vivo nuclear magnetic resonance scans of whole cultures indicated that B. subtilis grows by mixed acid-butanediol fermentation but that no formate is produced. An ace mutant that lacks pyruvate dehydrogenase (PDH) activity was unable to grow anaerobically and produced hardly any fermentation product. These results suggest that PDH is involved in most or all acetyl coenzyme A production in B. subtilis under anaerobic conditions, unlike Escherichia coli, which uses pyruvate formate lyase. Nitrate respiration was previously shown to require the ResDE two-component signal transduction system and an anaerobic gene regulator, FNR. Also required are respiratory nitrate reductase, encoded by the narGHJI operon, and moaA, involved in biosynthesis of a molybdopterin cofactor of nitrate reductase. The resD and resDE mutations were shown to moderately affect fermentation, but nitrate reductase activity and fnr are dispensable for fermentative growth. A search for genes involved in fermentation indicated that ftsH is required, and is also needed to a lesser extent for nitrate respiration. These results show that nitrate respiration and fermentation of B. subtilis are governed by divergent regulatory pathways.

ATP-Dependent Proteases↗
PubMed1997

Papillary carcinoma of the thyroid: can operative management be based solely on fine-needle aspiration?

BACKGROUND: Fine-needle aspiration cytology is sensitive for detecting malignancies such as papillary carcinoma of the thyroid gland. Because fine-needle aspiration specificity for papillary carcinoma of the thyroid is variable, routine intraoperative frozen section is often advocated. STUDY DESIGN: To define the roles of fine-needle aspiration and frozen section in papillary carcinoma of the thyroid gland, we reviewed data from 82 patients who underwent thyroidectomy between August 1989 and August 1995 for papillary carcinoma of the thyroid cytology. Results of fine-needle aspirations were grouped into three categories: diagnostic of papillary carcinoma of the thyroid; diagnostic of follicular-variant of papillary carcinoma of the thyroid; or suspicious for papillary carcinoma of the thyroid. Definitive diagnoses were made on permanent histology. RESULTS: A fine-needle aspiration revealing papillary carcinoma of the thyroid was 98 percent specific for cancer or 100 percent specific for follicular-variant of papillary carcinoma of the thyroid. A fine-needle aspiration that was suspicious for papillary carcinoma of the thyroid (n = 24) was only 54 percent specific for cancer. On the basis of gross intraoperative findings, 5 of these 24 patients underwent total thyroidectomy without frozen section, and all had carcinoma. The other 19 had frozen section analysis. Of the 5 patients with cancer detected by frozen section, 4 had cancer on permanent histology. Findings on frozen section demonstrated a follicular neoplasm in the other 14 patients, of which 4 ultimately were cancer. CONCLUSIONS: When papillary carcinoma of the thyroid or follicular-variant of papillary carcinoma of the thyroid is definitively diagnosed on fine-needle aspiration, the surgeon can perform definitive thyroidectomy without frozen section because of the high specificity for cancer. If the fine-needle aspiration is suspicious for papillary carcinoma of the thyroid, the incidence of cancer is 54 percent, and patients with these conditions should undergo surgery with frozen section. When either gross findings or frozen sections suggest malignancy, definitive thyroidectomy can be performed because 90 percent of such cases will be cancer. If frozen section is not diagnostic of malignancy, a thyroid lobectomy/isthmusectomy is recommended because 71 percent have a benign lesion. This systematic approach to papillary carcinoma of the thyroid will obviate unnecessary frozen sections while maintaining excellent diagnostic specificity.

Adolescent↗
PubMed1996

The pathogenesis of cryptosporidiosis.

Human infection with the protozoan parasite Cryptosporidium parvum has recently emerged as a global public health problem. Although infection is unrelenting in patients classically regarded as immunocompromised, a tantalizing observation is that infection with this parasite results in both acute self-limited as well as chronic diarrhea in young children. Recent data have begun to elucidate multiple potential mechanisms by which parasitism of the intestinal epithelium may yield an intestinal secretory response. However, a central issue for future studies is to understand how Cryptosporidium infection in young children results in such a broad spectrum of clinical presentation. An answer to this question is likely to result through a dual understanding of how systemic or enteric immunity impacts on intestinal secretory responses and how intra-cellular parasitism alters intestinal epithelial cell function and signals the submucosal intestinal compartment. The virulence factors of Cryptosporidium mediating these events need to be identified. Douglas Clark and Cynthia Sears here review the current understanding of the pathogenesis of intestinal secretion in response to Cryptosporidium infection, and discuss key questions requiring additional study.

Journal Article↗
PubMed1996

Role of NAD in regulating the adhE gene of Escherichia coli.

The fermentative alcohol dehydrogenase of Escherichia coli is encoded by the adhE gene, which is induced under anaerobic conditions but repressed in air. Previous work suggested that induction of adhE might depend on NADH levels. We therefore directly measured the NAD+ and NADH levels for cultures growing aerobically and anaerobically on a series of carbon sources whose metabolism generates different relative amounts of NADH. Expression of adhE was monitored both by assay of alcohol dehydrogenase activity and by expression of phi(adhE'-lacZ) gene fusions. The expression of the adhE gene correlated with the ratio of NADH to NAD+. The role of NADH in eliciting adhE induction was supported by a variety of treatments known to change the ratio of NADH to NAD+ or alter the total NAD+-plus-NADH pool. Blocking the electron transport chain, either by mutation or by chemical inhibitors, resulted in the artificial induction of the adhE gene under aerobic conditions. Conversely, limiting NAD synthesis, by introducing mutational blocks into the biosynthetic pathway for nicotinic acid, decreased the expression of adhE under anaerobic conditions. This, in turn, was reversed by supplementation with exogenous NAD or nicotinic acid. In merodiploid strains carrying deletion or insertion mutations abolishing the synthesis of AdhE protein, an adhE-lacZ fusion was expressed at nearly 10-fold the level observed in an adhE+ background. Introduction of mutant adhE alleles producing high levels of inactive AdhE protein gave results equivalent to those seen in absence of the AdhE protein. This finding implies that it is the buildup of NADH due to lack of enzyme activity, rather than the absence of the AdhE protein per se, which causes increased induction of the phi(adhE'-lacZ) fusion. Moreover, mutations giving elevated levels of active AdhE protein decreased the induction of the phi(adhE'-lacZ) fusion. This finding suggests that the enzymatic activity of the AdhE protein modulates the level of NADH under anaerobic conditions, thus indirectly regulating its own expression.

Aerobiosis↗
PubMed1995

Prevention of breast tumour development in vivo by downregulation of the p185neu receptor.

Certain strains of transgenic mice that express the rat neu oncogene (neuT) in mammary epithelial cells develop breast tumours at an average of 44 weeks of age. In this study, intraperitoneal injection of a monoclonal anti-receptor antibody specific for the rat neuT oncogene product dramatically affected tumour development in these transgenic mice in a dose-dependent manner. A significant proportion (50%) of mice, when injected with anti-receptor antibodies, did not develop tumours even after 90 weeks of age. The phosphotyrosine levels of the membrane fraction of breast tissues in the anti-receptor antibody-treated mice were almost completely abolished when a higher dose of antibodies was used. This study demonstrates, for the first time, that immunologic manipulation of an oncogene product can effectively prevent the development of tumours in a rodent transgenic model.

Animals↗
PubMed1994

Chromate reductase activity of Enterobacter aerogenes is induced by nitrite.

A chromate resistant mutant of Enterobacter aerogenes manifested its chromate resistance only under aerobic conditions. Both parent and mutant showed substantial levels of anaerobic chromate reductase activity when grown on glycerol plus fumarate. The chromate reductase was further induced by growth in the presence of nitrite but was repressed by nitrate. The chromate reductase activity paralleled that of the formate-linked nitrite reductase. There was no significant difference in chromate reductase levels between the parent and its chromate resistant mutant, indicating that this enzyme activity is not, in fact responsible for chromate resistance as was suggested previously by others.

Chromates↗
PubMed1994

Ranalexin. A novel antimicrobial peptide from bullfrog (Rana catesbeiana) skin, structurally related to the bacterial antibiotic, polymyxin.

Antimicrobial peptides comprise a diverse class of molecules used in host defense by plants, insects, and animals. In this study we have isolated a novel antimicrobial peptide from the skin of the bullfrog, Rana catesbeiana. This 20 amino acid peptide, which we have termed Ranalexin, has the amino acid sequence: NH2-Phe-Leu-Gly-Gly-Leu-Ile-Lys-Ile-Val-Pro-Ala-Met-Ile-Cys-Ala-Val-Thr- Lys-Lys - Cys-COOH, and it contains a single intramolecular disulfide bond which forms a heptapeptide ring within the molecule. Structurally, Ranalexin resembles the bacterial antibiotic, polymyxin, which contains a similar heptapeptide ring. We have also cloned the cDNA for Ranalexin from a metamorphic R. catesbeiana tadpole cDNA library. Based on the cDNA sequence, it appears that Ranalexin is initially synthesized as a propeptide with a putative signal sequence and an acidic amino acid-rich region at its amino-terminal end. Interestingly, the putative signal sequence of the Ranalexin cDNA is strikingly similar to the signal sequence of opioid peptide precursors isolated from the skin of the South American frogs Phyllomedusa sauvagei and Phyllomedusa bicolor. Northern blot analysis and in situ hybridization experiments demonstrated that Ranalexin mRNA is first expressed in R. catesbeiana skin at metamorphosis and continues to be expressed into adulthood.

Amino Acid Sequence↗
PubMed1994

Human neonatal thymic organ culture: an ex vivo model of thymocyte ontogeny and HIV-1 infection.

An intact thymic microenvironment is required for the normal maturation and selection of thymocytes. This process is directed by the interaction of thymocyte progenitors with molecules on the surface of thymic stromal cells and with cytokines. The precise nature of these events is poorly understood in humans. We have developed a technique of human neonatal thymic organ culture (hNTOC) that enabled thymocyte development for up to 14 days of ex vivo culture. hNTOC supported the maturation of CD4+CD8+ double-positive cells into both CD4+CD8- and CD4-CD8+ single-positive thymocytes. hNTOC was also used to examine infection with HIV-1, as a means to address the thymic pathology of HIV-1. These results establish an experimental system for the analysis of human thymic ontogeny and for the experimental manipulation of these events by ex vivo administration of cytokines, drugs or infectious agents.

Flow Cytometry↗
PubMed1993

A natural isolate of Pseudomonas maltophila which degrades aromatic sulfonic acids.

A natural isolate, designated BSA56, which was originally selected for growth with benzene sulfonic acid as sole carbon and energy source, was identified as a strain of Pseudomonas maltophila. Strain BSA56 grew on a wide range of aromatic sulfonic acids and was shown to release sulfite from benzene sulfonic acid and 2-naphthalene sulfonic acid. Although it also grew on toluene sulfonic acid and pyridine sulfonic acid, no significant sulfite release was observed with these substrates. Release of sulfite from benzene sulfonic acid was greatly promoted by the presence of glycerol. The ability to release sulfite was induced by growth in the presence of benzene sulfonic acid and was repressed almost entirely by substrates allowing rapid growth such as acetate. Strain BSA56 grew better at 30 degrees C than 37 degrees C on most aromatic substrates, but the reverse was true for most aromatic sulfonates. Several mutants of BSA56 were isolated with defects in benzoate, salicylate, or gentisate metabolism. However, all these mutants retained the ability to degrade the aromatic sulfonates.

Benzenesulfonates↗