Biomedical subjects

Daniel Bozinov

Publications and source records attributed to Daniel Bozinov.

6 recordsLinked to original sources

PubMed2005

Folate transport gene inactivation in mice increases sensitivity to colon carcinogenesis.

Low dietary folate intake is associated with an increased risk for colon cancer; however, relevant genetic animal models are lacking. We therefore investigated the effect of targeted ablation of two folate transport genes, folate binding protein 1 (Folbp1) and reduced folate carrier 1 (RFC1), on folate homeostasis to elucidate the molecular mechanisms of folate action on colonocyte cell proliferation, gene expression, and colon carcinogenesis. Targeted deletion of Folbp1 (Folbp1(+/-) and Folbp1(-/-)) significantly reduced (P < 0.05) colonic Folbp1 mRNA, colonic mucosa, and plasma folate concentration. In contrast, subtle changes in folate homeostasis resulted from targeted deletion of RFC1 (RFC1(+/-)). These animals had reduced (P < 0.05) colonic RFC1 mRNA and exhibited a 2-fold reduction in the plasma S-adenosylmethionine/S-adenosylhomocysteine. Folbp1(+/-) and Folbp1(-/-) mice had larger crypts expressed as greater (P < 0.05) numbers of cells per crypt column relative to Folbp1(+/+) mice. Colonic cell proliferation was increased in RFC1(+/-) mice relative to RFC1(+/+) mice. Microarray analysis of colonic mucosa showed distinct changes in gene expression specific to Folbp1 or RFC1 ablation. The effect of folate transporter gene ablation on colon carcinogenesis was evaluated 8 and 38 weeks post-azoxymethane injection in wild-type and heterozygous mice. Relative to RFC1(+/+) mice, RFC1(+/-) mice developed increased (P < 0.05) numbers of aberrant crypt foci at 8 weeks. At 38 weeks, RFC1(+/-) mice developed local inflammatory lesions with or without epithelial dysplasia as well as adenocarcinomas, which were larger relative to RFC1(+/+) mice. In contrast, Folbp1(+/-) mice developed 4-fold (P < 0.05) more lesions relative to Folbp1(+/+) mice. In conclusion, Folbp1 and RFC1 genetically modified mice exhibit distinct changes in colonocyte phenotype and therefore have utility as models to examine the role of folate homeostasis in colon cancer development.

Animals↗

PubMed2004

Hybrid clustering for microarray image analysis combining intensity and shape features.

BACKGROUND: Image analysis is the first crucial step to obtain reliable results from microarray experiments. First, areas in the image belonging to single spots have to be identified. Then, those target areas have to be partitioned into foreground and background. Finally, two scalar values for the intensities have to be extracted. These goals have been tackled either by spot shape methods or intensity histogram methods, but it would be desirable to have hybrid algorithms which combine the advantages of both approaches. RESULTS: A new robust and adaptive histogram type method is pixel clustering, which has been successfully applied for detecting and quantifying microarray spots. This paper demonstrates how the spot shape can be effectively integrated in this approach. Based on the clustering results, a bivalence mask is constructed. It estimates the expected spot shape and is used to filter the data, improving the results of the cluster algorithm. The quality measure 'stability' is defined and evaluated on a real data set. The improved clustering method is compared with the established Spot software on a data set with replicates. CONCLUSION: The new method presents a successful hybrid microarray image analysis solution. It incorporates both shape and histogram features and is specifically adapted to deal with typical microarray image characteristics. As a consequence of the filtering step pixels are divided into three groups, namely foreground, background and deletions. This allows a separate treatment of artifacts and their elimination from the further analysis.

Algorithms↗

PubMed2004

Folate-regulated changes in gene expression in the anterior neural tube of folate binding protein-1 (Folbp1)-deficient murine embryos.

Inactivation of the murine folate binding protein-1 (Folbp1) has been shown to play a vital role in embryonic development. Nullizygous embryos (Folbp1-/-) have significant malformations of the neural tube, craniofacies, and conotruncus, and invariably die in utero by gestational day (E) 10. Administration of 25 mg x kg(-1) x day(-1) folinic acid to dams prior to and throughout gestation rescues the majority of embryos from premature death; however, a portion of surviving embryos develops neural tube defects. Using antisense RNA amplification and cDNA microarrays, we examined the expression of approximately 5700 genes in the anterior neural tube of gestational day 9 Folbp1-/- embryos that were supplemented with folinic acid. Genes that appear to be folate regulated include transcription factors, G-proteins, growth factors, methyltransferases, and those that are related to cell proliferation. The potential impact of such changes during neural tube closure is considered in light of the phenotype of Folbp1-/- embryos.

Animals↗

PubMed2003

Autonomous system for Web-based microarray image analysis.

Software-based feature extraction from DNA microarray images still requires human intervention on various levels. Manual adjustment of grid and metagrid parameters, precise alignment of superimposed grid templates and gene spots, or simply identification of large-scale artifacts have to be performed beforehand to reliably analyze DNA signals and correctly quantify their expression values. Ideally, a Web-based system with input solely confined to a single microarray image and a data table as output containing measurements for all gene spots would directly transform raw image data into abstracted gene expression tables. Sophisticated algorithms with advanced procedures for iterative correction function can overcome imminent challenges in image processing. Herein is introduced an integrated software system with a Java-based interface on the client side that allows for decentralized access and furthermore enables the scientist to instantly employ the most updated software version at any given time. This software tool is extended from PixClust as used in Extractiff incorporated with Java Web Start deployment technology. Ultimately, this setup is destined for high-throughput pipelines in genome-wide medical diagnostics labs or microarray core facilities aimed at providing fully automated service to its users.

Algorithms↗

PubMed2002

Unsupervised technique for robust target separation and analysis of DNA microarray spots through adaptive pixel clustering.

MOTIVATION: Microarray images challenge existing analytical methods in many ways given that gene spots are often comprised of characteristic imperfections. Irregular contours, donut shapes, artifacts, and low or heterogeneous expression impair corresponding values for red and green intensities as well as their ratio R/G. New approaches are needed to ensure accurate data extraction from these images. RESULTS: Herein we introduce a novel method for intensity assessment of gene spots. The technique is based on clustering pixels of a target area into foreground and background. For this purpose we implemented two clustering algorithms derived from k-means and Partitioning Around Medoids (PAM), respectively. Results from the analysis of real gene spots indicate that our approach performs superior to other existing analytical methods. This is particularly true for spots generally considered as problematic due to imperfections or almost absent expression. Both PX(PAM) and PX(KMEANS) prove to be highly robust against various types of artifacts through adaptive partitioning, which more correctly assesses expression intensity values. AVAILABILITY: The implementation of this method is a combination of two complementary tools Extractiff (Java) and Pixclust (free statistical language R), which are available upon request from the authors.

Algorithms↗

PubMedDate not supplied

Nitrous oxide concentrations in the posterior nasopharynx during administration by nasal mask.

PURPOSE: Nitrous oxide (N2O) administration with nasal mask produces variable outcomes in dental patients. This study describes a novel sampling method to measure actual inspired/expired N2O concentrations ([N2O]). METHODS: Fifteen adult volunteers (32.5 +/- 8.5 years) underwent placement of a nasopharyngeal probe. With a nasal mask, 100% oxygen (O2) was administered for 2 minutes. N2O was introduced incrementally every 2 minutes for a final flowmeter [N2O] of 50% and subsequently decreased in the same manner. Anesthesia gas monitors analyzed inspired/expired [N2O], [O2], and PETCO2 from the nasopharynx and end-inspired/expired [N2O] in the mask. Data were measured every 20 seconds and analyzed. Inspired/expired nasopharyngeal and nasal mask [N2O] and [O2] were expressed as the median value at each time point for all subjects and plotted against flowmeter settings. RESULTS: Average inspired nasal mask [N2O] was 31% lower than flowmeter settings and decreased by another 19% on the way to the nasopharyngeal sampling site. During the phase of increasing N2O, average expired nasopharyngeal [N2O] was 22% lower than inspired [N2O]. When N2O was decreased, the effect was reversed and average expired [N2O] was 18% higher than inspired. Expired [N2O] was on average 51% lower than flowmeter settings. Mean PETCO2 was 39.7 +/- 1.4 mm Hg. CONCLUSIONS: Nasopharyngeal end-expired [N2O] varied markedly from flowmeter settings. Correlation of PETCO2 with expected physiologic values validates sampling methodology. This method allows accurate, continuous, and actual measurements of inhaled/exhaled gases in awake patients as well as decision-making/analysis of effectiveness of mask type to determine average [N2O] during administration by nasal mask.

Adult↗