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Biomedical subjects

S Cohen

Publications and source records attributed to S Cohen.

At least 109 records · Page 6Linked to original sources
PubMed2000

The functional association of polymyxin B with bacterial lipopolysaccharide is stereospecific: studies on polymyxin B nonapeptide.

The Gram-negative bacterial endotoxin lipopolysaccharide (LPS) is a major inducer of sepsis. The natural cyclic peptide polymyxin B (PMB) is a potent antimicrobial agent, albeit highly toxic, by virtue of its capacity to neutralize the devastating effects of LPS. However, the exact mode of association between PMB and LPS is not clear. In this study, we have synthesized polymyxin B nonapeptide, the LPS-binding cyclic domain of PMB, and its enantiomeric analogue and studied several parameters related to their interaction with LPS and their capacity to sensitize Gram-negative bacteria toward hydrophobic antibiotics. The results suggest that whereas the binding of the two enantiomeric peptides to E. coli and to E. coli LPS is rather similar, functional association with the bacterial cell is stereospecific. Thus, the L-enantiomer is capable of synergism with the hydrophobic antimicrobial drugs novobiocin and erythromycin, whereas the D-enantiomer is devoid of such activity. The potential of understanding and consequently utilizing the PMB-LPS association for novel, nontoxic PMB-derived drugs is discussed.

Anti-Bacterial Agents↗
PubMed2000

Structure-function studies of polymyxin B nonapeptide: implications to sensitization of gram-negative bacteria.

Polymyxin B nonapeptide (PMBN), a cationic cyclic peptide derived by enzymatic processing from the naturally occurring peptide polymyxin B, is able to increase the permeability of the outer membrane of Gram-negative bacteria toward hydrophobic antibiotics probably by binding to the bacterial lipopolysaccharide (LPS). We have synthesized 11 cyclic analogues of PMBN and evaluated their activities compared to that of PMBN. The synthetic peptides were much less potent than PMBN in their capacity to sensitize Escherichia coli and Klebsiella pneumoniae toward novobiocin and to displace dansyl-PMBN from Escherichia coli LPS. Moreover, unlike PMBN, none of the analogues were able to inhibit the growth of Pseudomonas aeruginosa. The structural-functional features of PMBN were characterized and identified with regard to the ring size, the distance between positive charges and peptide backbone, the chirality of the DPhe-Leu domain, and the nature of the charged groups. Apparently, the structure of PMBN is highly specific for efficient perturbation of the outer membrane of Gram-negative bacteria as well as for LPS binding. The present study further increases our understanding of the complex PMBN-LPS and may, potentially, enable the design of compounds having enhanced permeabilization potency of the Gram-negative outer membrane.

Anti-Bacterial Agents↗
PubMed2000

Glycosyltransferase activity of Fringe modulates Notch-Delta interactions.

Ligands that are capable of activating Notch family receptors are broadly expressed in animal development, but their activity is tightly regulated to allow formation of tissue boundaries. Members of the fringe gene family have been implicated in limiting Notch activation during boundary formation, but the mechanism of Fringe function has not been determined. Here we present evidence that Fringe acts in the Golgi as a glycosyltransferase enzyme that modifies the epidermal growth factor (EGF) modules of Notch and alters the ability of Notch to bind its ligand Delta. Fringe catalyses the addition of N-acetylglucosamine to fucose, which is consistent with a role in the elongation of O-linked fucose O-glycosylation that is associated with EGF repeats. We suggest that cell-type-specific modification of glycosylation may provide a general mechanism to regulate ligand-receptor interactions in vivo.

Alkaline Phosphatase↗
PubMed2000

SMA-3 smad has specific and critical functions in DBL-1/SMA-6 TGFbeta-related signaling.

A TGFbeta signal transduction cascade controls body size and male tail morphogenesis in the nematode Caenorhabditis elegans. We have analyzed the function of the sma-3 Smad gene, one of three Smad genes that function in this pathway. Null mutations in sma-3 are at least as severe as null mutations in the ligand and type I receptor genes, dbl-1 and sma-6, indicating that the other Smads do not function in the absence of SMA-3. Furthermore, null mutations in sma-3 do not cause defects in egg laying or in regulation of the developmentally arrested dauer larva stage, indicating no overlapping function with another C. elegans TGFbeta signaling pathway. The sma-3 gene is widely expressed at all developmental stages in hermaphrodites and males. The molecular lesions associated with eight sma-3 alleles of varying severity have been determined. The missense mutations cluster in two previously identified regions important for Smad function.

Alleles↗
PubMed2000

Interactions between the exocytic and endocytic pathways in polarized Madin-Darby canine kidney cells.

The compartments involved in polarized exocytosis of membrane proteins are not well defined. In this study we hypothesized that newly synthesized polymeric immunoglobulin receptors are targeted from the trans-Golgi network to endosomes prior to their appearance on the basolateral cell surface of polarized Madin-Darby canine kidney cells. To examine this hypothesis, we have used an assay designed to measure the meeting of newly synthesized receptors with a selective population of apical or basolateral endosomes loaded with horseradish peroxidase. We found that in the course of basolateral exocytosis, the wild-type polymeric immunoglobulin receptor is targeted from the trans-Golgi network to apical and basolateral endosomes. Phosphorylation of a Ser residue in the cytoplasmic tail of the receptor is implicated in this process. The biosynthetic pathway of apically sorted polymeric immunoglobulin receptor mutants similarly traversed apical endosomes, raising the possibility that apical receptors are segregated from basolateral receptors in apical endosomes. The post-endocytic pathway of transcytosing and recycling receptors also passed through apical endosomes. Together, these observations are consistent with the possibility that the biosynthetic and endocytic routes merge into endosomes and justify a model suggesting that endosomal recycling processes govern polarized trafficking of proteins traveling in both pathways.

Amino Acid Sequence↗
PubMed2000

Oriented crystalline monolayers and bilayers of 2 x 2 silver(I) grid architectures at the air-solution interface: their assembly and crystal structure elucidation

Oriented crystalline monolayers, approximately 14 A thick, of a 2 x 2 Ag+ grid complex, self-assembled at the air-solution interface starting from an water-insoluble ligand 3,6-bis[2-(6-phenylpyridine)]pyridazine spread on silver-ion-containing solutions, were examined by grazing-incidence X-ray diffraction and specular X-ray reflectivity using synchrotron radiation. The monolayer structure was refined, including a determination of the positions of the counter-ions, with the SHELX-97 computer program. The monolayers were transferred from the interface onto various solid supports and visualized by scanning force microscopy, and characterized by X-ray photoelectron spectroscopy in terms of molecular structure. On surface compression, the initial self-assembled monolayer undergoes a transition to a crystalline bilayer in which the two layers, almost retaining the original arrangement, are in registry. Such a phase transition is of relevance to the understanding of crystal nucleation.

Journal Article↗
PubMed2000

Hepatocyte behavior within three-dimensional porous alginate scaffolds.

A potential approach to facilitate the performance of implanted hepatocytes is to enable their aggregation and re-expression of their differentiated function prior to implantation. Here we examined the behavior of freshly isolated rat adult hepatocytes seeded within a novel three-dimensional (3-D) scaffold based on alginate. The attractive features of this scaffold include a highly porous structure (sponge-like) with interconnecting pores, and pore sizes with diameters of 100-150 microm. Due to their hydrophilic nature, seeding hepatocytes onto the alginate sponges was efficient. DNA measurements showed that the total cell number within the sponges did not change over 2 weeks, indicating that hepatocytes do not proliferate under these culture conditions. Nearly all seeded cells maintained viability, according to the MTT assay. Within 24 h post-seeding, small clusters of viable cells, were seen scattered within the sponge. More than 90% of the seeded cells participated in the aggregation; the high efficiency is attributed to the non-adherent nature of alginate. The spheroids had smooth boundaries and by day 4 in culture reached an average diameter of 100 microm, which is at the same magnitude of the sponge pore size. The cells appeared to synthesize fibronectin which was deposited on the spheroids. No laminin or collagen type IV were detected in the deposit. The 3-D arrangement of hepatocytes within the alginate sponges promoted their functional expression; within a week the cells secreted the maximal albumin secretion rate of 60 microg albumin/10(6) cells/day. Urea secretion rate did not depend on cell aggregation and was similar to that obtained when hepatocytes were cultured on collagen type I coated dishes (100 microg/10(6) cells/day). Our studies show that alginate sponges can provide a conducive environment to facilitate the performance of cultured hepatocytes by enhancing their aggregation.

Albumins↗
PubMed2000

Expression of a PKR dominant-negative mutant in myogenic cells interferes with the myogenic process.

In this study, we explored the possibility that PKR, a dsRNA-activated regulatory protein, is an essential component in the differentiation program of myogenic cells in vitro. For this purpose, we used a retroviral expression vector pMV7, harboring the PKR dominant-negative mutant PKRDelta6 (pMV7-p68Delta6). Murine C2C12 myogenic cells were transfected either with pMV7 or with pMV7-p68Delta6. Neomycin-resistant clones from both types were isolated and expanded and the results obtained with the representative clones C2-NEO (transfected with pMV7) and clone 17 and clone 22 (both transfected with pMV7-p68Delta6) are presented. In clone 17 and 22 cells, regardless of IFN treatment, a similar level of the transfected human p68 PKR mutant was detected. This protein was absent in C2-NEO cells. In parallel, in all types of cells, a low basal level of the endogenous murine p65 PKR protein was observed, which was further induced by IFN. However, PKR enzymatic activity was significantly induced by IFN only in C2-NEO cells, while it was hardly detected in both clones 17 and 22, even after IFN treatment. Furthermore, in contrast to C2-NEO cells, only a slight to moderate increase in enzymatic activity was observed in clone 17 and 22 differentiating cells. Next, cells were grown either in growth medium (GM) or differentiation medium (DM), and the progression of the myogenic program was studied. An inhibition in myotube formation in clone 17 versus C2-NEO cells cultivated in DM was clearly observed. Furthermore, while the growth rate and thymidine incorporation were reduced in C2-NEO cells grown in DM, both clone 17 and 22 cells were less affected under the same conditions. Similarly, a delay in the accumulation of the transcription factors MyoD and myogenin, as well as in creatine kinase activity and accumulation of troponin T, was detected in DM-cultivated clone 17 and clone 22 cells. Moreover, a delay in the induction of p21 (WAF1), in down-regulation of cyclin D1 and c-myc, and in the accumulation of the underphosphorylated form of pRb was also observed in clone 17 cells. We conclude that inhibition of endogenous PKR activity by a PKR dominant-negative mutant interferes with the myogenic program of murine C2C12 myogenic cells.

Animals↗
PubMed2000

Enhancing the immunogenicity of liposomal hepatitis B surface antigen (HBsAg) by controlling its delivery from polymeric microspheres.

Microencapsulated liposome systems (MELs) were investigated as a potential immunization carrier for a recombinant 22-nm hepatitis B surface antigen (HBsAg) particle. MELs were prepared by first entrapping the HBsAg particles within liposomes composed of phosphatidylcholine:cholesterol (1:1 molar ratio), which were then encapsulated within alginate-poly(L-lysine) (PLL) hydrogel microspheres. The entrapped HBsAg particles retained immunoreactivity, as judged by an enzyme-linked immunosorbent assay (ELISA). Direct imaging of HBsAg particles and HBsAg incorporated into liposomes by cryo-transmission electron microscopy (cryo-TEM) indicated that HBsAg is embedded in the liposomal membrane. The antigenic particles were released from MELs mainly within the context of liposomes. The release rates in vitro and in vivo depended on the molecular weight of PLL used for MEL coating; MELs-214, coated with 214 kDa PLL, released the liposomal HBsAg at much higher rates than MELs-25, which was coated with 25 kDa PLL. Concomitantly, the specific anti-HBsAg titers in mice receiving HBsAg in MELs-214 were higher than those induced by MELs-25. MELs-214 were more efficient than conventional liposomes or alum in eliciting higher and prolonged antibody levels in mice. The ability of MELs to provide an HBsAg depot as well as a sustained release of liposomal HBsAg suggests that these carriers may be an ideal immunoadjuvant.

Alum Compounds↗
PubMed2000

Macrophage activation for the production of immunostimulatory cytokines by delivering interleukin 1 via biodegradable microspheres.

Interleukin 1alpha (IL-1alpha), a pleiotropic cytokine with multiple anti-tumour activities, has been investigated in our laboratory for its potential to serve as an immunotherapeutic agent. In the present study, an attempt was made to direct IL-1alpha to macrophages, in order to induce their immunoregulatory activities. For that purpose, IL-1alpha was encapsulated within biodegradable poly(lactic/glycolic acid) microspheres, 1-5 microm diameter in size. The microspheres were efficiently taken-up by macrophages in culture and after intraperitoneal injection into mice. In culture, phagocytosis of the microspheres reached saturation within 3 h and there was no apparent effect of polymer type on the extent of uptake. In vivo uptake of human IL-1alpha-microspheres by the macrophages lead to cell activation, as evidenced by the enhanced production of murine IL-1alpha, IL-6 and IL-12. Control microspheres, containing bovine serum albumin, induced only background to low levels of cytokine production. These cytokines, when expressed by or secreted from macrophages, may stimulate in situ diverse immune and inflammatory responses, including T cell-mediated immune responses, such as the development of Th(1)cells and cytotoxic lymphocytes. Thus, directing IL-1alpha into macrophages, via the appropriate microspheres, may serve as a unique mean to activate these cells to participate in anti-tumour immune responses in situ.

Animals↗
PubMed2000

The stability of and intercorrelations among cardiovascular, immune, endocrine, and psychological reactivity.

One hundred fifteen college students were exposed to an evaluative speech task twice, separated by 2 weeks. At both sessions, we assessed cardiovascular, endocrine, immune, and psychological response at baseline and during the task. We found stability across sessions for stress-induced increases in anxiety and task engagement, heart rate, blood pressure, norepinephrine (but not epinephrine), cortisol, natural killer cell cytotoxicity, and numbers of circulating CD3+, CD8+, and CD56+ (but not CD4+ or CD19+) lymphocytes. The stable cardiovascular, immune, and endocrine reactivities were intercorrelated, providing evidence of a unified physiological stress response across these outcomes. Although stable stress-induced increases in task engagement were associated with the physiological stress responses, stress-induced anxiety was not.

Adolescent↗
PubMed2000

Effects of risedronate treatment on bone density and vertebral fracture in patients on corticosteroid therapy.

Men and women (n = 518) receiving moderate-to-high doses of corticosteroids were enrolled in two studies with similar protocols and randomly assigned to receive either placebo or risedronate (2.5 or 5 mg) for 1 year. All patients received daily calcium supplementation (500-1000 mg), and most also received supplemental vitamin D (400 IU). The primary endpoint was the difference between the placebo and active groups in lumbar spine bone mineral density (BMD) at 1 year; changes in BMD at other sites, biochemical markers of bone turnover, and the incidence of vertebral fractures were also assessed. In the overall population, the mean (SE) lumbar spine BMD increased 1.9 +/- 0.38% from baseline in the risedronate 5 mg group (P < 0.001) and decreased 1.0 +/- 0.4% in the placebo group (P = 0. 005). BMD at the femoral neck, trochanter, and distal radius increased or was maintained with risedronate 5 mg treatment, but decreased in the placebo group. Midshaft radius BMD did not change significantly in either treatment group. The difference in BMD between the risedronate 5 mg and placebo groups was significant at all skeletal sites (P < 0.05) except the midshaft radius at 1 year. The 2.5 mg dose also had a positive effect on BMD, although of a lesser magnitude than that seen with risedronate 5 mg. A significant reduction of 70% in vertebral fracture risk was observed in the risedronate 5 mg group compared with the placebo group (P = 0.01). Risedronate was efficacious in both men and women, irrespective of underlying disease and duration of corticosteroid therapy, and had a favorable safety profile, with a similar incidence of upper gastrointestinal adverse events in the placebo and active treatment groups. Daily treatment with risedronate 5 mg significantly increases BMD and decreases vertebral fracture risk in patients receiving moderate-to-high doses of corticosteroid therapy.

Absorptiometry, Photon↗
PubMed2000

Combined leukocyte and erythrocyte aggregation in the peripheral venous blood during sepsis. An indication of commonly shared adhesive protein(s).

We have used a simple slide test and image analysis to reveal the state of leukocyte and erythrocyte adhesiveness/aggregation in the peripheral blood of 28 patients with sepsis and 28 controls. A significant (P<0.00001) increment in both leukocyte and erythrocyte adhesiveness/aggregation was noted in patients compared with controls. Moreover, a significant (r=0.73, n=56, P<0.001) correlation was noted between the two adhesiveness/aggregation variables themselves, suggesting a common mechanism responsible for these adhesive phenomena. The significant correlation with fibrinogen suggests that this protein might be such a "non-specific glue." Our results indicate that a simple slide technique and image analysis can assess the aggregability of both white and red blood cells in septic patients. This might have clinical application when interventions to reduce cell aggregability are planned in order to improve blood flow in the microcirculation.

Adult↗
PubMed2000

Issues of aging and adherence to health interventions.

This review article describes several processes and considerations that are important to adherence in aging research and potential strategies that could be used to facilitate adherence among older adults. In many large aging trials participants are purposefully selected to reduce the risk of suboptimal adherence and retention. This selection often involves screening out those with barriers such as transportation needs, sensory deficits, functional dependence, major diseases limiting life expectancy, or apparent psychological distress. However, trends toward extending interventions to the general population of older adults require specific knowledge about the circumstances and processes that support adherence among older adults or the conditions that make them vulnerable to adherence problems. Addressing the diversity of needs, expectations, and capabilities of older adults that promote adherence is a key consideration in aging research. Control Clin Trials 2000;21:171S-183S

Aged↗
PubMed2000

Incorporating physical activity advice into primary care: physician-delivered advice within the activity counseling trial.

INTRODUCTION: The Activity Counseling Trial (ACT) was designed to compare the effectiveness of physician advice alone with physician advice plus behavioral counseling, provided by ACT-trained health educators, to increase levels of physical activity in healthy, sedentary patients. The objective was to determine health care providers' adherence to the ACT protocol for delivering initial "physician" advice on physical activity and to determine providers' satisfaction with the protocol. METHODS: Fifty-four physicians or physician assistants from 11 primary care practices located in California, Texas, and Tennessee volunteered to participate as ACT-trained physicians. Providers were trained to integrate 3 to 4 minutes of initial physical activity advice into the routine office visits of sedentary patients, aged 35 to 75 years, with no acute or serious chronic conditions. This advice included assessment of current physical activities, advising the patient about an appropriate physical activity goal, and referring the patient to the health educator. Providers initialed forms to document delivery of advice, and ACT health educators recorded their advice on a computerized tracking system. A provider survey measured length of time spent advising patients about physical activity and provider satisfaction with the program. RESULTS: Ninety-nine percent of patients received the initial physician advice about physical activity. Eighty-three percent of the providers spent less than 5 to 6 minutes, and 46% spent the recommended 3 to 4 minutes providing advice. Sixty-three percent said the advice resulted in little or no increase in the length of an office visit, and 83% said participation was an asset to their clinics. CONCLUSIONS: Providers incorporated brief physical activity advice into routine primary care visits with little disruption. Their response to the ACT advice protocol was positive and participation in the study was viewed as beneficial.

Adult↗