Biomedical subjects

David Kaplan

Publications and source records attributed to David Kaplan.

12 recordsLinked to original sources

PubMed2003

GDNF promotes tubulogenesis of GFRalpha1-expressing MDCK cells by Src-mediated phosphorylation of Met receptor tyrosine kinase.

Glial cell line-derived neurotrophic factor (GDNF) and hepatocyte growth factor (HGF) are multifunctional signaling molecules in embryogenesis. HGF binds to and activates Met receptor tyrosine kinase. The signaling receptor complex for GDNF typically includes both GDNF family receptor alpha1 (GFRalpha1) and Ret receptor tyrosine kinase. GDNF can also signal independently of Ret via GFRalpha1, although the mechanism has remained unclear. We now show that GDNF partially restores ureteric branching morphogenesis in ret-deficient mice with severe renal hypodysplasia. The mechanism of Ret-independent effect of GDNF was therefore studied by the MDCK cell model. In MDCK cells expressing GFRalpha1 but no Ret, GDNF stimulates branching but not chemotactic migration, whereas both branching and chemotaxis are promoted by GDNF in the cells coexpressing Ret and GFRalpha1, mimicking HGF/Met responses in wild-type MDCK cells. Indeed, GDNF induces Met phosphorylation in several ret-deficient/GFRalpha1-positive and GFRalpha1/Ret-coexpressing cell lines. However, GDNF does not immunoprecipite Met, making a direct interaction between GDNF and Met highly improbable. Met activation is mediated by Src family kinases. The GDNF-induced branching of MDCK cells requires Src activation, whereas the HGF-induced branching does not. Our data show a mechanism for the GDNF-induced branching morphogenesis in non-Ret signaling.

Animals↗

PubMed2003

Arithmetic fact mastery in young children: a longitudinal investigation.

Children with poor arithmetic fact mastery (n=45) at the end of third grade were compared to grade-level peers with good arithmetic fact mastery (n=60) in competencies related to reading and mathematics. Children were assessed longitudinally across second and third grades. When predictor variables such as IQ were held constant, the poor fact mastery and good fact mastery groups performed at about the same level and progressed at a comparable rate on math story problems and on broad reading achievement. The groups also progressed at a comparable rate on broad math achievement, although children with poor fact mastery performed at a significantly lower level. Children with poor fact mastery showed remarkably little growth on timed number facts during the study period, despite normal growth in other areas of mathematics. Deficits in fact mastery are highly persistent and appear to be independent of reading and language abilities.

Child↗

PubMed2003

Use of health and mental health services by adolescents across multiple delivery sites.

PURPOSE: To assess the role that school-based health centers (SBHCs) play in facilitating access to care among low-income adolescents and the extent to which SBHCs and a community health center network (CHN) provide similar or complementary care. METHODS: A retrospective cohort design was used to compare health care service use among adolescents relying on SBHCs compared with adolescents relying on a CHN. The study sample consisted of 451 inner-city high school students who made 3469 visits between 1989 and 1993. Encounter data were abstracted from medical records. Frequency of use and reason for use are examined according to various sociodemographic and health insurance characteristics. RESULTS: SBHC users averaged 5.3 visits per year. Minority youth who used the SBHC had the highest visit rates (Hispanic, 6.6 visits/year; African-American, 10.6 visits/year). Visits to SBHCs were primarily for medical (66%, p <.001) and mental health services (34%, p <.001). Visits at CHN sites were 97% medical (p <.001). Visits by adolescents were 1.6 times more likely to be initiated for health maintenance reasons (p =.002; confidence interval [CI], 1.17-2.06) and 21 times more likely to be initiated for mental health reasons (p = <.001; CI, 14.76-28.86) at SBHCs than at CHN facilities. Urgent and emergent care use in the CHN system was four times more likely for adolescents who never used a SBHC (p <.001; CI, 3.44-5.47). CONCLUSIONS: This study supports the view that SBHCs provide complementary services. It also shows their unique role in improving utilization of mental health services by hard-to-reach populations. The extent to which community health centers and other health care providers, including managed care organizations, can build on the unique contributions of SBHCS may positively influence access and quality of care for adolescents in the future.

Adolescent↗

PubMed2003

Efficacy and tolerability of combined topical treatment of acne vulgaris with adapalene and clindamycin: a multicenter, randomized, investigator-blinded study.

This multicenter, randomized, investigator-blinded study investigated the efficacy and tolerability of adapalene gel 0.1% plus clindamycin phosphate lotion 1%, compared with clindamycin plus vehicle for the treatment of mild to moderate acne vulgaris. A total of 249 patients applied clindamycin lotion twice daily and adapalene (125 patients) or vehicle gel (124 patients) once daily for 12 weeks. A significantly greater reduction of total (P <.001), inflammatory (P =.004) and noninflammatory lesions (P <.001) was seen in the clindamycin plus adapalene group than in the clindamycin plus vehicle group. These significant treatment effects were observed as early as week 4 for both noninflammatory and total lesion counts. Both treatment regimens were well tolerated. Although the worst scores for scaling (P <.05), dryness (P <.01), and stinging/burning (P <.05) were higher in the clindamycin plus adapalene group than in the clindamycin plus vehicle group in patients with moderate or severe irritation; in most cases these symptoms were of mild intensity.

Acne Vulgaris↗

PubMed2003

CD34 expression on platelets.

Flow cytometric analysis of human platelets from healthy volunteers by high-resolution immunophenotyping accomplished with enzymatic amplification staining revealed the expression of CD34. Assessment of the platelets with five different monoclonal antibodies to the three different classes of CD34 epitopes suggested that platelets express a unique glycoform of the molecule. Expression of CD34 was verified by immunoblotting. Platelet activation resulted in a marked decrease in surface CD34. CD34 expression has significant implications for the function of platelets as well as for the determination of hematopoietic progenitor cells.

Antigens, CD↗

PubMed2002

Applications of enzymatic amplification staining in immunophenotyping hematopoietic cells.

Immunofluorescent staining of mammalian cells has provided a reliable approach for detection of specific antigen expression in situ. An advantage of fluorescent markers has been their applicability to automated, high-throughput cellular analysis by flow cytometry. Flow cytometry has thus become an integral component of clinical laboratory diagnostics, particularly in the areas of immunology and hematology. One of the major drawbacks of traditional immunofluorescent staining, even with flow cytometric detection, has been the difficulty in detecting low abundance cellular antigens, some of which may have clinical and scientific significance. To address these problems, staining techniques have recently been developed to increase the sensitivity of cellular antigen detection by flow cytometry. In this review we will describe a few of these techniques and focus on enzymatic amplification staining as a means to generate a highly augmented antigen-specific signal. We will also discuss practical applications of enzymatic amplification for immunostaining of clinical specimens.

Biotin↗

PubMed2002

Matrix-mediated cellular rejuvenation.

Biomaterial surface morphology and chemistry influence cell responses mediated via signaling cascades that regulate a wide range of metabolic processes. These responses may range from changes in surface adhesion and remodeling of the extracellular matrix to activation of cytokine, cytoskeletal and other biochemical pathways regulating or modulating cellular morphology and function. The present study has focused on collagen Type I, a key extracellular matrix protein, and its potential impact on the process of cellular aging. This study was undertaken for several reasons. First, several investigators reported that growth of cells on a collagen matrix markedly enhanced the resistance of cells to stresses. Second, a large body of accumulated data strongly indicated a relationship between the potential to respond to stresses and cellular aging with the former strongly influencing the rate of the latter. Finally, it has been recently demonstrated that in aged cells one of the key aging-related processes previously considered irreversible, attenuation of the expression of a major stress response protein, Hsp70, can be reversed. This fact together with a probable regulatory role of the stress response potential in cellular aging suggested a possibility that the cellular aging process as a whole can be altered. Indeed, in the present study, growth on a denatured collagen matrices reversed in aged cells not only the attenuation of Hsp70 expression but also other aging-related processes, such as beta-galactosidase expression, increase in protein oxidation and changes in cell morphology. Moreover, it appeared to reduce the rate of aging in young cells. Understanding the nature of collagen matrix-mediated cellular rejuvenation might suggest approaches for interfering with organismic aging. Some immediate applications include cell rejuvenation for purposes of cloning and reduction of the rate of aging during expansion of stem cells for purposes of tissue engineering.

Cell Line↗

PubMed2002

Adjuvant activity of emulsan, a secreted lipopolysaccharide from acinetobacter calcoaceticus.

Several promising adjuvant candidates have been studied over the past 75 years; however, only alum is currently approved for human use. The complex acylated polysaccharide emulsan, secreted from Acinetobacter calcoaceticus, represents a new candidate. Unique features of this family of polymers are their amenability to structural tailoring and their emulsification behavior. We demonstrate that emulsan activates macrophages in a dose-dependent manner. This activation is dependent on the presence of the fatty acid side chains that decorate the polysaccharide backbone, and, furthermore, the level of activation can be affected by changes in the chemical characteristics of emulsan structural variants. One emulsan variant was examined in a classical hapten carrier immunization protocol and demonstrated significant adjuvant activity as determined by hapten-specific antibody titers. This immune response was characterized by a high immunoglobulin G2a titer, consistent with a Th1 response. The significant immunopotentiation demonstrated by this complex polymer establishes emulsan as an exciting new candidate adjuvant. Furthermore, by manipulating the chemical structure of this compound, we can explore the physical basis of pattern recognition receptors and macrophage activation.

Adjuvants, Immunologic↗

PubMed2002

Adolescent preventive services for girls.

Adolescence is a complex and often confusing time in the life of a girl as she undergoes significant physical, emotional, and cognitive development. Because most causes of teen morbidity and mortality are behavioral, preventive health visits should address psychosocial issues such as substance abuse, sexuality, and emotional health in a confidential and age-appropriate manner. Assessment and management strategies for providing preventive health services for adolescent girls are offered in this article.

Adolescent↗

PubMedDate not supplied

Comorbidity of irritable bowel syndrome in psychiatric patients: a review.

Irritable bowel syndrome (IBS), a functional gastrointestinal disorder, is present in 10% to 20% of the U.S. adult population. The syndrome is best defined as chronic abdominal discomfort with changes in stool frequency, consistency, and passage, with associated symptoms such as abdominal bloating or presence of mucus in stools. Several studies have shown that up to 70% to 90% of patients with IBS who seek treatment have psychiatric comorbidity, most notably mood and anxiety disorders. Recent studies have shown a high prevalence of IBS in psychiatric patients who seek treatment, with a prevalence of 19% in schizophrenia, 29% in major depression, and 46% in panic disorder among other disorders. Our article reviews the comorbidity of IBS in psychiatric patients and discusses implications for treatment.

Colonic Diseases, Functional↗

PubMedDate not supplied

A longitudinal study of mathematical competencies in children with specific mathematics difficulties versus children with comorbid mathematics and reading difficulties.

Mathematical competencies of 180 children were examined at 4 points between 2nd and 3rd grades (age range between 7 and 9 years). Children were initially classified into one of 4 groups: math difficulties but normal reading (MD only), math and reading difficulties (MD-RD), reading difficulties but normal math (RD only), and normal achievement in math and reading (NA). The groups did not differ significantly in rate of development. However, at the end of 3rd grade the MD only group performed better than the MD-RD group in problem solving but not in calculation. The NA and RD only groups performed better than the MD-RD group in most areas. Deficiencies in fact mastery and calculation fluency, in particular, are defining features of MD, with or without RD.

Aptitude↗

PubMedDate not supplied

Does a preexisting anxiety disorder predict response to paroxetine in irritable bowel syndrome?

Irritable bowel syndrome (IBS) is the most common disorder in patients seen by gastroenterologists. Twenty subjects with IBS diagnosed with the Rome criteria were treated for 12 weeks with 20-40 mg/day of paroxetine (mean dose=31 mg/day). At baseline, 10 patients had a lifetime history of an anxiety disorder, and 10 patients did not have such a history. Both groups had similar improvement in abdominal pain, constipation, diarrhea, incomplete emptying, and bloating/ abdominal distension. Paroxetine was very well tolerated.

Adult↗