Biomedical subjects

A Ho

Publications and source records attributed to A Ho.

At least 37 records · Page 2Linked to original sources

PubMed2001

Collagen-induced arthritis in TNF receptor-1-deficient mice: TNF receptor-2 can modulate arthritis in the absence of TNF receptor-1.

TNF is a potent proinflammatory cytokine important for the development of arthritis in human and animals. We have investigated the roles of TNF receptor-1 (TNFR1) and TNF receptor-2 (TNFR2) in collagen-induced arthritis (CIA) by inducing CIA in mice genetically deficient in TNFR1. TNFR1-/- mice developed arthritis with similar incidence and severity as TNFR1+/- littermates, indicating that TNFR1 is redundant for the development of CIA. Anti-type II collagen (CII) antibody levels and T cell responses to CII did not differ between TNFR1-/- mice and controls. Neutralization of TNF with soluble TNF binding protein suppressed the development of arthritis in TNFR1+/- mice but not in TNFR1-/- mice, indicating that TNFR2 cannot substitute for TNFR1 for the proinflammatory function. To further investigate the functions of TNFR2, TNFR1-/- mice were injected with murine TNF-alpha at different stages during the course of CIA. Repeated TNF-alpha injection during the early induction phase enhanced the development of arthritis, but inhibited arthritis when administered during the late progression phase. These results show that the engagement of TNFR2 by TNF is involved in the development of CIA in the absence of TNFR1 and that opposing signals can be transduced by TNFR2.

Animals↗

PubMed2001

Predictable individual differences in the initiation of cocaine self-administration by rats under extended-access conditions are dose-dependent.

RATIONALE: The characterization of self-administration (SA) under extended access conditions is necessary for the development of addiction models. OBJECTIVE: The purposes of this experiment were to investigate: (1) dose effects on the initiation of cocaine SA under extended access conditions; (2) predictable individual differences in SA under these conditions and their relationships to neuroendocrine function and cocaine dose. METHODS: After they were tested for their locomotor responses to novelty and to cocaine and trained to lever-press under a food-reinforced schedule, male Sprague-Dawley rats were allowed to SA cocaine (0.25, 0.5, 1.0, or 2.0 mg/kg per infusion, IV) by lever-pressing under a FR1 schedule during five consecutive daily 10-h sessions. Plasma corticosterone (CORT) and prolactin (PRL) were measured throughout the experiment. RESULTS: Rats tested at higher cocaine doses more readily acquired and showed increased drug intake and more regular patterns of SA. High responders (HR) to novelty self-administered greater amounts of cocaine, acquired more rapidly and displayed more regular SA compared to LR rats, but only at the lowest cocaine dose tested (i.e., 0.25 mg/kg per infusion). HR rats also exhibited a greater high-dose escalation of SA compared to LR rats. Novelty-induced (but not cocaine-induced) locomotor activity, pre-SA plasma CORT, and pre-SA food-reinforced lever-pressing predicted SA, but only at the lowest cocaine dose tested. No differences in plasma CORT or PRL were observed between LR and HR rats. CONCLUSIONS: The present findings indicate that predictable individual differences in cocaine SA under extended access conditions are relevant only at low doses and are surmountable by increasing the available dose of cocaine.

Animals↗

PubMed2001

Mammary epithelial cell-cycle progression via the alpha(2)beta(1) integrin: unique and synergistic roles of the alpha(2) cytoplasmic domain.

The alpha(2)beta(1) integrin supports cell-cycle progression of mammary epithelial cells adherent to type I collagen matrices. Integrin collagen receptors containing the alpha(2) cytoplasmic domain stimulated expression of cyclin E and cyclin-dependent kinase (cdk)2, resulting in cyclin E/cdk2 activation in the absence of growth factors other than insulin. Integrin collagen receptors in which the alpha(2) cytoplasmic domain was replaced by the alpha(1) cytoplasmic domain or an alpha(2) subunit cytoplasmic domain truncated after the GFFKR sequence failed to stimulate cyclin E/cdk2 activation or entry into S phase in the absence of growth factors. Although overexpression of cyclins D or E or cdk2 in cells expressing the integrin collagen receptor with the alpha(1)-integrin cytoplasmic domain did not restore G(1) progression when mammary epithelial cells adhered to type I collagen, co-expression of cyclin E and cdk2 did rescue the ability of the transfectants to enter S phase. Activation of cyclin E/cdk2 complex by mammary epithelial cells required synergy between adhesion mediated by an integrin collagen receptor containing the alpha(2)-integrin subunit cytoplasmic domain and the insulin receptor.

Breast↗

PubMed2001

The Fc receptor for IgG (Fc gamma RII; CD32) on human neonatal B lymphocytes.

B cells express an Fc receptor for IgG (FcgammaRII; CD32) which is involved in feedback inhibition of antibody production. Engagement of FcgammaRII during ligation of the antigen receptor provides an inhibitory signal. FcgammaRII exists as several isoforms, with FcgammaRIIb (which carries an immunoreceptor tyrosine-based inhibition motif; ITIM) being predominant form on adult B cells. The inhibitory role of FcgammaRIIb may be unhelpful to the infant, since primary exposure to infectious agents is likely to be in the presence of maternal IgG. We hypothesized that neonatal B cells would be less susceptible to feedback inhibition by antibody, either through the expression of activation-competent FcgammaRII isoforms (FcgammaRIIa and FcgammaRIIc) or through reduced expression of the inhibitory FcgammaRIIb isoforms. Cord and adult B cells were examined for expression of FcgammaRII isoforms using monoclonal antibodies and RT-PCR. In vitro assays were performed to assess susceptibility of cord and adult cells to FcgammaRII-mediated suppression. Although there is no phenotypic difference in FcgammaRII expression (FcgammaRIIb predominating on both adult and cord B cells), FcgammaRIIb is expressed at lower levels on cord cells. This quantitative difference in FcgammaRIIb expression may explain the reduced susceptibility of cord B cells to antibody-mediated inhibition observed in these experiments.

Adult↗

PubMed2001

Altered HPA axis responsivity to metyrapone testing in methadone maintained former heroin addicts with ongoing cocaine addiction.

Metyrapone testing, a provocation of hypothalamic-pituitary-adrenocortical (HPA) axis function, was performed in 39 in-patient subjects: 10 stable methadone-maintained former heroin addicts without ongoing drug or alcohol abuse or dependence (MM), eight methadone- maintained former heroin addicts without ongoing drug or alcohol abuse or dependence other than ongoing cocaine dependence (C-MM), and 21 normal volunteers (NV). Plasma adrenocorticotrophic hormone (ACTH) levels were determined in samples drawn at 9A.M., just before administration of 2.25 g metyrapone orally and 4 and 8 hours afterward. Following metyrapone, C-MM had levels of ACTH that were significantly higher than both MM (p < .05) and NV (p < .01); whereas, MM and NV had levels that were comparable. Area under the plasma ACTH curves yielded similar results. This study documents hyper-responsivity to removal of glucocorticoid negative feedback associated with cocaine addiction, even in the setting of methadone maintenance for heroin addiction, which here and previously has been shown to be associated with normalization of HPA axis function.

Adolescent↗

PubMed2001

Lens prism in RGP manufacturing and its effect on edge quality.

Unwanted prism in lathe cut RGP lenses is most frequently caused by misalignment when re-blocking the button for cutting the front surface. The geometrical relationships in three types of alignment errors and the resulting variations in edge thickness were mathematically analysed and experimentally confirmed. The edge thickness variations in a prismatic lens along the circumference follow a cosine function. For a typical tri-curve lens design, an eccentric offset 30 microm between the front and the back surface can lead to a difference in edge thickness of more than 50 microm Edge thickness variations are greatest for high power minus lenses with prominent lenticulation. The polished edge shape is significantly compromised by inconsistent edge thickness. Typically, the thinner side has a sharp and pointed edge, while the thicker side is blunt.

Journal Article↗

PubMed2001

Ablation of pituitary pro-opiomelanocortin (POMC) cells produces alterations in hypothalamic POMC mRNA levels and midbrain mu opioid receptor binding in a conditional transgenic mouse model.

The hypothalamic-pituitary-adrenal (HPA) axis is regulated by stress-related excitatory inputs, and various inhibitory and negative-feedback controls by glucocorticoids and opioids, including pro-opiomelanocortin (POMC)-derived peptides. The role of POMC-derived peptides of pituitary origin in the modulation of brain POMC mRNA expression and opioid receptor binding was investigated using a line of transgenic mice that express a fusion gene composed of the pituitary expression-specific promoter region of the POMC gene driving the herpes simplex viral-1 thymidine kinase (TK). Male adult mice were treated with the antiherpes agent ganciclovir that selectively ablates cells expressing TK. Following treatment, POMC mRNA levels, measured by quantitative solution hybridization/RNase protection assays, were decreased by 48% in the pituitary of the TK+/+ mice, reflecting an expected loss of the pituitary corticotrope POMC cells. This treatment also significantly lowered pituitary beta-endorphin immunoreactivity content and plasma concentrations of corticosterone. In contrast, POMC mRNA levels were increased by 79% in the hypothalamus of the TK+/+ mice with pituitary POMC cell ablation. Binding of [(3)H]DAMGO to mu opioid receptors, as measured by quantitative autoradiography, was significantly reduced in several brain regions including the central grey, median raphe and superficial grey layer of the superior colliculus. These regions are innervated by hypothalamic POMC neurones. No significant differences in binding to either kappa or delta opioid receptors were found in the brain regions studied. These results suggest that POMC-derived peptides of pituitary origin may exert a tonic negative-feedback effect on hypothalamic POMC neurones. In turn, the downregulation of central mu opioid receptors in this model may be mediated through a mechanism related to hypothalamic POMC overexpression.

Amygdala↗

PubMed2001

Theoretical analysis of accommodation amplitude and ametropia correction by varying refractive index in Phaco-Ersatz.

Phaco-Ersatz is a surgical procedure for restoring accommodation in which the presbyopic crystalline lens is replaced by a flexible polymer gel in the lens capsule. We assessed the feasibility of simultaneously correcting ametropia while restoring accommodation using Phaco-Ersatz by utilizing polymer gel of the appropriate refractive index. Computation results using paraxial equations and ray tracing on two model eyes indicate that although this approach might be feasible for the hypermetrope, its usefulness for correcting myopia is limited, principally due to significant reductions in the resultant amplitude of accommodation.

Accommodation, Ocular↗

PubMed2001

Differential regulation of retinoblastoma tumor suppressor protein by G(1) cyclin-dependent kinase complexes in vivo.

The retinoblastoma tumor suppressor protein (pRB) negatively regulates early-G(1) cell cycle progression, in part, by sequestering E2F transcription factors and repressing E2F-responsive genes. Although pRB is phosphorylated on up to 16 cyclin-dependent kinase (Cdk) sites by multiple G(1) cyclin-Cdk complexes, the active form(s) of pRB in vivo remains unknown. pRB is present as an unphosphorylated protein in G(0) quiescent cells and becomes hypophosphorylated (approximately 2 mol of PO(4) to 1 mol of pRB) in early G(1) and hyperphosphorylated (approximately 10 mol of PO(4) to 1 mol of pRB) in late G(1) phase. Here, we report that hypophosphorylated pRB, present in early G(1), represents the biologically active form of pRB in vivo that is assembled with E2Fs and E1A but that both unphosphorylated pRB in G(0) and hyperphosphorylated pRB in late G(1) fail to become assembled with E2Fs and E1A. Furthermore, using transducible dominant-negative TAT fusion proteins that differentially target cyclin D-Cdk4 or cyclin D-Cdk6 (cyclin D-Cdk4/6) and cyclin E-Cdk2 complexes, namely, TAT-p16 and TAT-dominant-negative Cdk2, respectively, we found that, in vivo, cyclin D-Cdk4/6 complexes hypophosphorylate pRB in early G(1) and that cyclin E-Cdk2 complexes inactivate pRB by hyperphosphorylation in late G(1). Moreover, we found that cycling human tumor cells expressing deregulated cyclin D-Cdk4/6 complexes, due to deletion of the p16(INK4a) gene, contained hypophosphorylated pRB that was bound to E2Fs in early G(1) and that E2F-responsive genes, including those for dihydrofolate reductase and cyclin E, were transcriptionally repressed. Thus, we conclude that, physiologically, pRB is differentially regulated by G(1) cyclin-Cdk complexes.

CDC2-CDC28 Kinases↗

PubMed2001

Biological methods for cell-cycle synchronization of mammalian cells.

Understanding the molecular and biochemical basis of cellular growth and division involves the investigation of regulatory events that most often occur in a cell-cycle phase-dependent fashion. Studies examining cell-cycle regulatory mechanisms and progression invariably require cell-cycle synchronization of cell populations. Thus, many methods have been established to synchronize cells at specific phases of the cell cycle. Several of the common methods involve pharmacological agents, which act at various points throughout the cell cycle. Because of adverse cellular perturbations resulting from many of the synchronizing drugs used, other synchrony methods that involve less perturbation of biological systems, such as serum deprivation, contact inhibition, and centrifugal elutriation have a significant advantage. The advantages and disadvantages of these cell synchronization methods are discussed in this review.

Animals↗

PubMed2001

Tear exchange under hydrogel contact lenses: methodological considerations.

PURPOSE: To characterize hydrogel lens tear exchange and to apply an optimized method to compare tear exchange of a marketed hydrogel lens to that measured with a prototype silicone hydrogel lens. METHODS: Fluorophotometry and a nonpenetrating tracer (70-kDa FITC-dextran) were used with a single extended-wear soft contact lens (EWSCL) material on 11 subjects to characterize tear-exchange kinetics. Twenty to 30 measurements were obtained over a 30-minute period to allow accurate modeling and estimation of the several tear-exchange parameters. Calculated values included tear-replenishment rate (TRR), elimination rate (ER), and the time for 95% of the signal to be eliminated (T(95)). Major experiments were (1) comparison of ER under controlled and physiological conditions, (2) comparison of right and left eyes, (3) repeatability of ER and T(95) on five occasions, and (4) comparison of a marketed lens (oxygen permeability [Dk] 28 x 10(-9) [cm/sec][ml O(2)/ml mm Hg]) to a prototype silicone hydrogel lens (Dk 140 x 10(-9) [cm/sec][ml O(2)/ml mm Hg]). RESULTS: Tracer elimination behind a hydrogel contact lens (CL), up to 30 minutes after insertion, was optimally described by double-exponential kinetics. Physiological ER (5-30 minutes after CL insertion) was optimally described by single-exponential kinetics. Overall, physiological ER was 8.8% +/- 3.8% per minute, and T(95) was 31.0 +/- 16.1 minutes (n = 76 and 72 determinations, respectively). Differences between right and left eyes in ER and T(95) were not significant at the 0.05 level. No difference in ER or T(95) was found between habitual and controlled blinking. Mean TRR was 0.67% +/- 0.26% per blink (n = 11 determinations). No differences were shown between ER or T(95) measurements over time. A prototype highly oxygen-permeable silicone hydrogel lens showed higher ER than did a marketed hydrogel lens (P < 0.01). CONCLUSIONS: Estimates of postlens tear exchange using a slit lamp fluorophotometer are similar to previously reported rates using similar fluorophotometric techniques. Fluorescent decay behind a hydrogel lens is most precisely described using a double-exponential curve equation and tear exchange may be described using ER, TRR and T(95), although the T(95) may be the least reliable of these measures. The technique appears capable of discriminating between lens types.

Adult↗

PubMed2000

Colorectal carcinomas in mice lacking the catalytic subunit of PI(3)Kgamma.

Phosphoinositide-3-OH kinases (PI(3)Ks) constitute a family of evolutionarily conserved lipid kinases that regulate a vast array of fundamental cellular responses, including proliferation, transformation, differentiation and protection from apoptosis. PI(3)K-mediated activation of the cell survival kinase PKB/Akt, and negative regulation of PI(3)K signalling by the tumour suppressor PTEN (refs 3, 4) are key regulatory events in tumorigenesis. Thus, a model has arisen that PI(3)Ks promote development of cancers. Here we report that genetic inactivation of the p110gamma catalytic subunit of PI(3)Kgamma (ref. 8) leads to development of invasive colorectal adenocarcinomas in mice. In humans, p110gamma protein expression is lost in primary colorectal adenocarcinomas from patients and in colon cancer cell lines. Overexpression of wild-type or kinase-dead p110gamma in human colon cancer cells with mutations of the tumour suppressors APC and p53, or the oncogenes beta-catenin and Ki-ras, suppressed tumorigenesis. Thus, loss of p110gamma in mice leads to spontaneous, malignant epithelial tumours in the colorectum and p110gamma can block the growth of human colon cancer cells.

Adenocarcinoma↗

PubMed2000

Effects of the androgenic anabolic steroid, nandrolone decanoate, on adrenocorticotropin hormone, corticosterone and proopiomelanocortin, corticotropin releasing factor (CRF) and CRF receptor1 mRNA levels in the hypothalamus, pituitary and amygdala of the rat.

There is increasing abuse of androgenic anabolic steroids (AAS) by non-athletes. AAS abuse has been associated with psychiatric symptoms such as mania, major depression and aggression and the development of dependence. Little is known about the effects of AAS on hypothalamic-pituitary-adrenal axis function or corticotropin releasing factor, which may be involved in mediating some of the psychiatric symptoms associated with AAS abuse. Male Sprague-Dawley rats received one daily intra-muscular injection of the AAS nandrolone decanoate (ND, 15 mg/kg) or vehicle for 3 days. Animals were sacrificed either 1 h or 24 h after the last injection, brain regions dissected and trunk blood collected. Corticotropin releasing factor (CRF), CRF receptor1 (CRF-R1) and proopiomelanocortin (POMC) mRNAs were measured with solution hybridization/RNase protection. Circulating levels of corticosterone and adrenocorticotropin hormone (ACTH) were determined using radioimmunoassays. One hour following the last injection, ND significantly increased circulating levels of both corticosterone and ACTH levels. In the amygdala, CRF mRNA levels were unchanged 1 h after the last injection of ND but were significantly reduced at 24 h. The same was found for hypothalamic POMC. No significant AAS effects were observed on: hypothalamic CRF mRNA; POMC mRNA in the amygdala or CRF R1 mRNA in the anterior pituitary.

Adrenocorticotropic Hormone↗

PubMed2000

Chronic 'binge' pattern cocaine alters the neuroendocrine profile of pregnant rats.

Pregnant Fischer rats injected with cocaine in a 'binge' pattern (3x15 mg/kg, i.p.) from gestational days 8 through 17, had significantly higher levels of progesterone (212.12+/-22.50 vs. 91. 99+/-15.41 ng/ml) and corticosterone (257.99+/-21.76 ng/ml vs. 31. 70+/-7.93, respectively) than saline-treated dams. No significant differences in prolactin were observed (2.36+/-0.17 vs. 2.17+/-0.19 ng rPrl132/ml). Correlation analysis indicated that there is a significant relationship between plasma levels of progesterone and corticosterone and the quality of nests built by the dams. No correlation was found within animals between prolactin plasma levels and the nest quality. Thus, cocaine's effect on progesterone and corticosterone may contribute to the series of behavioral alterations associated with cocaine exposure during pregnancy.

Animals↗

PubMed2000

Prognostic relevance of serum levels of the angiogenic peptide bFGF in advanced carcinoma of the head and neck treated by primary radiochemotherapy.

BACKGROUND: The objective of this trial was to analyze the prognostic relevance of the angiogenic peptides basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), and matrix metalloproteinase-2 (MMP-2) in the serum of patients with advanced carcinoma of the head and neck treated by primary radiochemotherapy. METHODS: From 1992 to 1995, 26 patients with advanced head and neck cancer (25 stage IV, 1 stage III UICC) were treated according to the protocol of radiochemotherapy with carboplatin. The pretreatment serum levels VEGF, bFGF, and MMP-2 were measured by ELISA, and data were correlated with tumor characteristics and followed up (median time of follow up, 60 months). RESULTS: An increase in bFGF serum level above the upper limit of normal controls showed a significant correlation with shorter time the of locoregional control (p =.036). In covariant analysis bFGF serum concentration proved to be independent of other prognostic factors like tumor site, age, total tumor volume, and response to therapy. No prognostic relevance of VEGF and MMP-2 serum levels could be determined. CONCLUSIONS: The results of this pilot study indicate that the serum concentration of bFGF has prognostic relevance for advanced head and neck cancer.

Adult↗

PubMed2000

A study to examine the accuracy of potassium measurements in clinical laboratories across Canada.

OBJECTIVE: To assess the accuracy of potassium measurements in clinical laboratories across Canada. DESIGN AND METHOD: The flame atomic emission spectrophotometry reference method for the determination of potassium was established at the Canadian Reference Laboratory by using National Institute of Science and Technology standard reference materials. The method was subsequently used to assign target values for potassium to Canadian Reference Laboratory's External Quality Assessment human-serum-based testing material. A total of 503 laboratories participated and 9,279 individual External Quality Assessment test results were included in the study. Bias was determined by using difference plots. RESULTS: Clinically significant bias (>1.6%) was observed in 45.9% of the laboratories. Bias ranged from 0.34 mmol/L to -0.54 mmol/L. At low concentrations (<3.5 mmol/L) a positive bias was most frequently observed (14.7% of analytical systems). At high potassium concentrations (>5.1 mmol/L) a negative bias was most frequently observed (31.4% of analytical systems). CONCLUSION: Inaccuracy in potassium results can contribute to test redundancy and mismanagement of patients, while prohibiting the merger of laboratory data from disparate testing sites for the purpose of trending and consolidation within a "universal health record." Inaccurate test results and the lack of standardization among laboratories adversely impact our ability to establish common reference intervals and critical limits. This inability has an adverse effect on medical decisions and patient care.

Bias↗

PubMed2000

Cocaine affects progesterone plasma levels in female rats.

Female Fischer rats injected with cocaine in a "binge" pattern (15 mg/kg, IP, three times a day, at 1-h intervals) for 1 day had significantly higher levels of progesterone than saline-treated controls (p < 0.001). When analyzed by the stage of the estrous cycle, animals in proestrus showed significantly higher cocaine-induced progesterone plasma levels than those in other stages of the cycle (p < 0.01). Progesterone plasma levels were also increased after a single dose of cocaine (15 mg/kg). However, 3 h postinjection progesterone plasma levels had returned to normal. Thus, cocaine modulation of progesterone plasma levels appears to be an acute effect. In ovariectomized rats pretreated with estrogen, progesterone, or estrogen + progesterone, no significant differences were observed in progesterone plasma levels after acute "binge" pattern cocaine administration. Thus, acute cocaine induced increases in progesterone plasma levels in intact female rats are probably due to an increase in secretion rates of progesterone rather than an acceleration of its biotransformation. Due to the profound effects of progesterone in the modulation of CNS plasticity, the modulation of progesterone plasma level by cocaine may have implications for reproductive processes and neuronal functions of women. Moreover, cocaine may affect the progesterone levels in women utilizing progesterone-based contraception or steroid replacement treatment after menopause.

Animals↗

PubMed2000

Ovarian hormone replacement affects cocaine-induced behaviors in ovariectomized female rats.

To determine whether cocaine-induced behavioral alterations are modulated by ovarian hormones, ovariectomized rats were randomly assigned to one of two drug treatment conditions: "binge" cocaine (three 15-mg/kg intraperitoneal (ip) injections, 1 h apart) or saline administration; and four hormone pretreatment sub-groups: vehicle control, estrogen, progesterone, or estrogen+progesterone. Cocaine-treated animals displayed more locomotor activity than saline-treated animals and locomotor activity was higher after the third injection than after the first two injections. When analyzed according to hormone group, the administration of estrogen+progestrone suppressed cocaine-induced locomotion after the first injection; this effect was significant when compared to estrogen-pretreated animals. While in each condition cocaine-treated animals displayed significantly higher stereotypic activity than saline-treated animals, in the estrogen+progesterone replacement group, there was more activity after the second injection of cocaine than after the first. Interestingly, animals in the estrogen+progesterone group had significantly lower plasma levels of the cocaine metabolite, benzoylecgonine, than animals in the progesterone or estrogen groups. These results extend our earlier findings in the intact female rat, which suggest an interaction between the endocrine environment, cocaine metabolism, and cocaine-induced behaviors. These effects may underlie reported sex and estrous cycle differences in cocaine-induced behavioral activity.

Animals↗