Biomedical subjects

K Robertson

Publications and source records attributed to K Robertson.

At least 37 records · Page 2Linked to original sources

PubMed2001

Acute anorectic effect of single and combined drugs in mice using a non-deprivation protocol.

RATIONALE: Studies of the effect of anorectic drugs such as fenfluramine in mice have indicated the desirability of using experimental protocols that do not involve deprivation. OBJECTIVE: We have developed a non-deprivation or "dessert" protocol for use in mice that are maintained in standard housing conditions, and examine the effects of a serotonergic agent dexfenfluramine (DFEN), a dopaminergic agent phentermine (PHEN), and a selective norepinephrine uptake inhibitor thionisoxetine (TNIX) alone and in combination. METHODS: Female C57BL/6J mice were adapted to 30 min daily presentation of a gelatinized form of sweetened milk using a holder that hooks over the side of the cage during tests; food spillage and contamination are minimal. Dose-inhibition curves were determined for DFEN, PHEN, and TNIX alone and for fixed ratio combinations of DFEN with either PHEN or TNIX. RESULTS: Each drug produced a near linear dose-inhibition curve with the 50% inhibitory doses (DI50) of 5.6, 3.2 and 12.2 mg/kg, respectively. By isobolographic analysis, the effects of the drug combinations were strictly additive. CONCLUSION: The procedure described is highly suitable for testing anorectic drugs in mice and is adaptable to a variety of housing conditions and diets. The DFEN+ PHEN combination was additive, which contrasts with its reported supra-additive effect in rats.

Animals↗

PubMed2001

Mre11 protein complex prevents double-strand break accumulation during chromosomal DNA replication.

Mre11 complex promotes repair of DNA double-strand breaks (DSBs). Xenopus Mre11 (X-Mre11) has been cloned, and its role in DNA replication and DNA damage checkpoint studied in cell-free extracts. DSBs stimulate the phosphorylation and 3'-5' exonuclease activity of X-Mre11 complex. This induced phosphorylation is ATM independent. Phosphorylated X-Mre11 is found associated with replicating nuclei. X-Mre11 complex is required to yield normal DNA replication products. Genomic DNA replicated in extracts immunodepleted of X-Mre11 complex accumulates DSBs as demonstrated by TUNEL assay and reactivity to phosphorylated histone H2AX antibodies. In contrast, the ATM-dependent DNA damage checkpoint that blocks DNA replication initiation is X-Mre11 independent. These results strongly suggest that the function of X-Mre11 complex is to repair DSBs that arise during normal DNA replication, thus unraveling a critical link between recombination-dependent repair and DNA replication.

Amino Acid Sequence↗

PubMed2001

Angiotensin-converting enzyme activity and the ACE Alu polymorphism in autosomal dominant polycystic kidney disease.

BACKGROUND: Previous studies concerning Alu I/D polymorphism in the ACE gene and ADPKD severity have used the Alu genotypes as a representative of the true biological variable, namely ACE activity. However, wide individual and ethnic differences in the proportion of variance in ACE activity explained by the I/D genotype may have confounded these studies. This investigation examines the association between ADPKD severity and ACE in terms of plasma enzyme activity and I/D genotypes in individuals from three different countries. METHODS: Blood samples were collected from 307 ADPKD patients (116 Australian, 124 Bulgarian and 67 Polish) for determination of ACE activity levels and I/D genotypes. Chronic renal failure (CRF) was present in 117 patients and end-stage renal failure (ESRF) in 68 patients. RESULTS: ACE activity was related to the I/D genotype, showing a dosage effect of the D allele (P=0.006). The proportion of variance due to the Alu polymorphism was 14%. No difference in ACE activity and I/D genotype distribution was found between patients with CRF versus normal renal function (P=0.494; P=0.576) or between those with ESRF versus those without ESRF (P=0.872; P=0.825). No effect of the I/D genotype on age at development and progression to renal failure (CRF; ESRF) was detected in the overall group, and in subgroups based on ethnic origin, linkage status and sex. CONCLUSION: ACE is not likely to play a role as a determinant of ADPKD phenotype severity.

Adolescent↗

PubMed2001

Estuary-associated syndrome in North Carolina: an occupational prevalence study.

Atlantic coast estuaries recently have experienced fish kills and fish with lesions attributed to Pfiesteria piscicida and related dinoflagellates. Human health effects have been reported from laboratory exposure and from a 1997 Maryland fish kill. North Carolina has recorded Pfiesteria-related fish kill events over the past decade, but human health effects from environmental exposure have not been systematically investigated or documented here. At the request of the state health agency, comprehensive examinations were conducted in a cross-sectional prevalence study of watermen working where Pfiesteria exposure may occur: waters where diseased or stressed fish were reported from June to September 1997, and where Pfiesteria had been identified in the past. Controls worked on unaffected waterways. The study was conducted 3 months after the last documented Pfiesteria-related fish kill. The goal was to document any persistent health effects from recent or remote contact with fish kills, fish with lesions, or affected waterways, using the 1997 U.S. Centers for Disease Control and Prevention case description for estuary-associated syndrome (EAS). Examinations included comprehensive medical, occupational, and environmental history, general medical, dermatologic, and neurologic examinations, vision testing, and neuropsychologic evaluations. Seventeen of 22 watermen working in affected waters and 11 of 21 in unaffected waters reported exposure to a fish kill or to fish with lesions. We found no pattern of abnormalities on medical, neurologic, neuropsychologic, or NES-2 evaluation. By history, one subject in each group met the EAS criteria, neither of whom had significant neuropsychological impairment when examined. Watermen from affected waterways had a significant reduction in visual contrast sensitivity (VCS) at the midspatial frequencies, but we did not identify a specific factor or exposure associated with this reduction. The cohorts did not differ in reported occupational exposure to solvents (qualitative) or to other neurotoxicants; however, exposure history was not sufficiently detailed to measure or control for solvent exposure. This small prevalence study in watermen, conducted 3 months after the last documented fish kill related to Pfiesteria, did not identify an increased risk of estuary-associated syndrome in those working on affected waterways. A significant difference between the estuary and ocean watermen was found on VCS, which could not be attributed to any specific factor or exposure. VCS may be affected by chemicals, drugs, alcohol, and several developmental and degenerative conditions; it has not been validated as being affected by known exposure to dinoflagellate secretions. VCS should be considered for inclusion in further studies, together with documentation or quantification of its potential confounders, to assess whether it has utility in relationship to dinoflagellate exposure.

Adult↗

PubMed2001

Good metabolic control is associated with better quality of life in 2,101 adolescents with type 1 diabetes.

OBJECTIVE: It is unclear whether the demands of good metabolic control or the consequences of poor control have a greater influence on quality of life (QOL) for adolescents with diabetes. This study aimed to assess these relations in a large international cohort of adolescents with diabetes and their families. RESEARCH DESIGN AND METHODS: The study involved 2,101 adolescents, aged 10-18 years, from 21 centers in 17 countries in Europe, Japan, and North America. Clinical and demographic data were collected from March through August 1998. HbA(1c) was analyzed centrally (normal range 4.4-6.3%; mean 5.4%). Adolescent QOL was assessed by a previously developed Diabetes Quality of Life (DQOL) questionnaire for adolescents, measuring the impact of diabetes, worries about diabetes, satisfaction with life, and health perception. Parents and health professionals assessed family burden using newly constructed questionnaires. RESULTS: Mean HbA(1c) was 8.7% (range 4.8-17.4). Lower HbA(1c) was associated with lower impact (P < 0.0001), fewer worries (P < 0.05), greater satisfaction (P < 0.0001), and better health perception (P < 0.0001) for adolescents. Girls showed increased worries (P < 0.01), less satisfaction, and poorer health perception (P < 0.01) earlier than boys. Parent and health professional perceptions of burden decreased with age of adolescent (P < 0.0001). Patients from ethnic minorities had poorer scores for impact (P < 0.0001), worries (P < 0.05), and health perception (P < 0.01). There was no correlation between adolescent and parent or between adolescent and professional scores. CONCLUSIONS: In a multiple regression model, lower HbA(1c) was significantly associated with better adolescent-rated QOL on all four subscales and with lower perceived family burden as assessed by parents and health professionals.

Adolescent↗

PubMed2001

Pituitary-adrenal function in uncomplicated falciparum malaria.

To investigate pituitary-adrenal function in acute uncomplicated falciparum malaria, we performed an overnight dexamethasone suppression test in 13 Vietnamese adults with acute malaria and 6 healthy controls. After blood samples were taken for serum cortisol and plasma ACTH at 23.00 hours on the admission day, 1 mg dexamethasone was given and further samples were taken at 08.00, 16.00 and 23.00 hours the next day. The patients received conventional antimalarial and supportive treatment. Baseline plasma ACTH concentrations in the patients [3.9 (0.2-41.2) pmol/l] and controls [3.4 (1.1-4.3) pmol/l] were similar (p=0.51), and exhibited a similar fall after dexamethasone to 0.6 (0.2-2.5) and 0.9 (0.7-1.6) pmol/l at 08.00 hours respectively (p<0.03 vs 23.00 hour values). Serum cortisol levels before dexamethasone were higher in the patients than in the controls [456 (102-821) vs 145 (64-183) nmol/l respectively; p=0.007] and the overnight fall was less in the patients [208 (26-340) and 23 (15-46) nmol/l at 08.00 hours respectively; p<0.001 vs 23.00 hour values and between groups]. Between 08.00 and 23.00 hours, plasma ACTH and serum cortisol remained suppressed in the controls. In the patients, the serum cortisol continued to fall progressively towards control values. These data suggest that there is a raised set point for cortisol inhibition of ACTH secretion but normal corticotrophin responsiveness to dexamethasone in uncomplicated malaria. A raised serum cortisol after dexamethasone in the patients might reflect the combination of a prolonged cortisol half-life and the stimulatory effects of cytokines on the adrenal cortex, with a consequent protective effect against complications such as hypoglycemia.

Adrenal Glands↗

PubMed2000

Reaction of phenylaminoethyl selenides with peroxynitrite and hydrogen peroxide.

Peroxynitrite, a reactive cytotoxic species generated by the reaction of superoxide with nitric oxide, rapidly oxidizes phenylaminoethyl selenide (PAESe) and its para-substituted derivatives with second-order rate constants ranging from 900 to 3000 M(-1) s(-1) at neutral pH (pH 7.0) and 25 degrees C. These values are approximately 3 x 10(4) times greater than the corresponding rate constants for the reactions of selenides with hydrogen peroxide. The peroxynitrite reaction was also studied at alkaline pH. HPLC analysis confirms that both the peroxynitrite and hydrogen peroxide reactions produced the corresponding phenylaminoethyl selenoxide (PAESeO) as the sole selenium-containing product, with a stoichiometry of 1 mol of PAESe oxidized per 1 mol of PAESeO formed per 1 mol of oxidant reacted. The influence of para-substituents on the rate constants was investigated using Hammett plots; in both cases the data are consistent with an S(N)2-type mechanism, wherein the selenium atom acts as the nucleophile. Our results provide further evidence that organoselenium compounds may play a protective role in the defense against the many reactive oxidizing species produced in cellular metabolism.

Antihypertensive Agents↗

PubMed2000

Expression and subcellular localization of X-ATM during early Xenopus development.

ATM, the gene mutated in ataxia telangiectasia, is a protein essential for handling DNA strand breaks. We recently isolated the Xenopus homologue of ATM, X-ATM and we report here the detailed expression pattern of the protein and the mRNA during early Xenopus development. During the cleavage stages, ATM protein was concentrated in and around the nuclei of all cells with low levels of expression also detected in the cytoplasm. Following neurulation, increased protein levels were detected in the nuclei of developing somites and in the central nervous system. Areas of high protein expression correlated with areas of increased mRNA expression which was detected in the nuclei of somites and the developing lens.

Animals↗

PubMed2000

The role of local estrogen biosynthesis in males and females.

Natural (human) and experimental (mouse) models of estrogen insufficiency have revealed hitherto unexpected roles for estrogens in both males and females. In postmenopausal women, and in men, estrogen no longer has a major role as a circulating hormone, but rather it functions locally as a paracrine or even 'intracrine' factor in tissue sites where it is formed. As a consequence, the tissue-specific nature of aromatase production assumes physiological and pathophysiological significance. The availability of circulating precursors is also important in sites where there is no local supply of C19 precursors, particularly in elderly women. The potential clinical significance of these findings in terms of the development of new therapeutic modalities is discussed.

Adipose Tissue↗

PubMed2000

Reconstitution of an ATM-dependent checkpoint that inhibits chromosomal DNA replication following DNA damage.

Cell cycle checkpoints lead to the inhibition of cell cycle progression following DNA damage. A cell-free system derived from Xenopus eggs has been established that reconstitutes the checkpoint pathway inhibiting DNA replication initiation. DNA containing double-strand breaks inhibits replication initiation in a dose-dependent manner. Upon checkpoint activation, a prereplicative complex is assembled that contains ORC, Cdc6, Cdc7, and MCM proteins but lacks Cdc45. The checkpoint is ATM dependent. Cdk2/CyclinE acts downstream of ATM and is downregulated by Cdk2 phosphorylation on tyrosine 15. Cdk2AF/CyclinE is refractory to checkpoint signaling, and Cdc25A overrides the checkpoint and restores DNA replication. This report provides the description of a DNA damage checkpoint pathway that prevents the onset of S phase independently of the transcriptional function of p53 in a vertebrate organism.

Androstadienes↗

PubMed2000

Quantitation of human immunodeficiency virus type 1 RNA in different biological compartments.

Little information is available describing viral loads in body fluids other than blood. In addition, the suitability of commercially available assays for human immunodeficiency virus type 1 (HIV-1) RNA quantitation has not been evaluated in most nonblood fluids. We compared Organon Teknika's nucleic acid sequence-based amplification method (NASBA) and Roche's Amplicor HIV-1 Monitor (reverse transcriptase PCR [RT-PCR]) for quantitating HIV-1 RNA in cerebrospinal fluid (CSF), saliva, breast milk, seminal plasma, and cervical-vaginal lavage fluid (CVL). Saliva and breast milk frequently demonstrated some inhibition in the RT-PCR assay, similar to the inhibition previously described in seminal plasma. Inhibition of the RT-PCR assay was not observed with CSF or CVL, nor in any of the NASBA assays. When fluids from HIV-infected individuals were tested by RT-PCR and NASBA, 73 and 27% of CSF samples and 60 and 40% of breast milk specimens had detectable RNA, respectively. These differences were not statistically significant. In cross-sectional studies using RT-PCR to measure viral RNA in paired blood plasma and CSF samples, 71% of blood plasma samples and 42% of CSF samples were positive. A similar analysis using NASBA with paired blood plasma and CVL, saliva, or seminal plasma samples revealed 91% were blood plasma positive and 55% were CVL positive, 76% were blood plasma positive and 46% were saliva positive, and 83% were blood plasma positive and 63% were seminal plasma positive. NASBA worked fairly well to quantitate HIV-1 RNA from all fluids without apparent inhibition. RT-PCR performed well on CVL and CSF, frequently with greater sensitivity, although its use in other fluids appears limited due to the presence of inhibitors. These studies demonstrate that viral loads in nonblood fluids were generally lower than in blood.

Body Fluids↗

PubMed2000

The Prince Edward Island Conceptual Model for Nursing: a nursing perspective of primary health care.

The philosophy of primary health care (PHC) recognizes that health is a product of individual, social, economic, and political factors and that people have a right and a duty, individually and collectively, to participate in the course of their own health. The majority of nursing models cast the client in a dependent role and do not conceptualize health in a social, economic, and political context. The Prince Edward Island Conceptual Model for Nursing is congruent with the international move towards PHC. It guides the nurse in practising in the social and political environment in which nursing and health care take place. This model features a nurse/client partnership, the goal being to encourage clients to act on their own behalf. The conceptualization of the environment as the collective influence of the determinants of health gives both nurse and client a prominent position in the sociopolitical arena of health and health care.

Family Nursing↗

PubMed1999

Isolation and characterization of Xenopus ATM (X-ATM): expression, localization, and complex formation during oogenesis and early development.

ATM, the gene product mutated in Ataxia Telangiectasia (A-T) encodes a 350-kDa protein involved in the regulation of several cellular responses to DNA breaks. We used a degenerate PCR-based strategy to isolate a partial clone of X-ATM, the Xenopus homologue of human ATM. Sequence analysis and confirmed that the clone was most closely related to human ATM. Xenopus ATM protein (X-ATM) is 85% identical to human ATM within the kinase domain and 71% identical over the carboxyl-terminal half of the protein. Polyclonal antibodies raised against recombinant X-ATM are highly specific for the ATM protein and recognize a single polypeptide of 370-kDa in oocytes, embryos, egg extracts and a Xenopus cell line. We found that X-ATM was expressed maternally in eggs and as early as stage II pre-vitellogenic oocytes, and the protein and mRNA were present at relatively constant levels throughout development. Subcellular fractionation showed that the protein was nuclear in both the female and male germlines. The level of X-ATM protein did not change throughout the meiotic divisions or the synchronous mitotic cycles of cleavage stage embryos. In addition, we did not observe any change in the level or mobility of X-ATM protein following gamma-irradiation of embryos. Finally, we also demonstrated that X-ATM was present in a high molecular weight complex of approximately 500 kDa containing the X-ATM protein and other, as yet unidentified component(s).

Amino Acid Sequence↗

PubMed1999

Properties of adenosine deaminase from Candida albicans.

Adenosine deaminase (ADA; adenosine aminohydrolase, E.C. 3.5.4.4), a purine catabolic enzyme, was studied in Candida albicans, an opportunistic yeast that causes diseases ranging from superficial infections to the deep systemic disease, candidiasis, in immunosuppressed humans. The fungus was grown as a yeast form in LEE's synthetic medium, pH 4.5, at room temperature for various growth periods. Adenosine deaminase (ADA) activity was determined from the cell free extract by measuring the change in absorbance 265 nm resulting from the deamination of adenosine. In yeast form, maximum growth and ADA activity were found at 72 and 24 hours, respectively, whereas in the mycelial form both the growth and ADA activity were maximum after 48 hours. Among the three media tested, tryptic soy broth supported maximum growth and enzyme production, compared to LEE synthetic medium or SABOURAUD dextrose broth. The enzyme was active over the pH range 4-8 and the optimum temperature for ADA activity was found to be 37 degrees C.

Adenosine Deaminase↗

PubMed1999

Local estrogen biosynthesis in males and females.

It is now apparent that in men and in postmenopausal women, estrogens have important physiological and pathophysiological roles. However, importantly, these actions are at a local level, namely paracrine, autocrine, and even 'intracrine' rather than endocrine in the classical sense. Thus for example local estrogen biosynthesis in the bones of men plays a hitherto unsuspected role in the maintenance of bone mineralization and in epiphyseal fusion; and in the testes, estrogen is essential for male germ cell development. On the other hand, in postmenopausal women, the mesenchymal cells of the breast are the major source of estrogen responsible for breast cancer development. This realization points to the importance of circulating C19 precursors in the maintenance of adequate estrogen biosynthesis in extragonadal sites and suggests the possibility of new therapies to block estrogen synthesis in a tissue-specific fashion.

Adipose Tissue↗

PubMed1999

Neurotoxicity of CSF from HIV-infected humans.

Approximately 15-20% of individuals infected with the human immunodeficiency virus will develop severe neurological disease. This may be due in part to virus-induced release of a number of putative neurotoxins. However, there is little information to predict which individuals will progress to dementia or the precise mechanisms that drive pathogenesis. In an effort to identify early markers of neurological disease progression we used an in vitro bioassay with rat cortical neurons to test for the presence of toxins in CSF from 40 HIV-infected humans with mild, minimal or no neurological disease. A subset of HIV-infected individuals was found to have significant toxic activity in CSF indicating that toxic factors may be circulating prior to the development of dementia. The toxicity was concentration dependent and due to a factor with a molecular mass of less than 30 kDa. Only a small proportion of the cell death appeared to be due to apoptosis. Neuronal toxicity was associated with a gradual accumulation of intracellular calcium in a subset of cortical neurons over a period of 1-2 h and in the absence of a significant acute response. Individuals with both high viral burden and high CSF toxicity were significantly more likely to have neurological symptoms. These initial analyses indicate that toxic factors are present in the CSF of HIV-infected patients that could serve as useful markers of neurological disease progression and provide insights into pathogenic mechanisms in vivo.

Acquired Immunodeficiency Syndrome↗

PubMed1999

Trauma nursing: an advanced practice case study.

Trauma is the leading cause of death in people less than 40 years of age. Blunt or penetrating trauma injuries may be a result of gunshot wounds, stabbings, head injuries,burns, falls or motor vehicle collisions. Unlike other patients entering the health care system, trauma victims have no time for hospital preparation. The physiologic and psychosocial complications resulting directly from the traumatic incident provide response patterns not typical of other patients. Further to this unpredictability, the trauma patient usually sustains multiple system injuries, making it difficult to design critical pathways in care plans. The complexity is heightened by the patient's unique perception of the traumatic event, which can be even more important than the physical injury in determining the ultimate impact of the trauma.

Adaptation, Psychological↗

PubMed1998

HIV-infected subjects with the E4 allele for APOE have excess dementia and peripheral neuropathy.

HIV produces a chronic viral infection of the central nervous system that elicits chronic glial activation and overexpression of glial cytokines that are also implicated in Alzheimer disease (AD) pathogenesis. A genetic risk factor for AD is the E4 isoform for apolipoprotein E (APOE). Here we compare the frequency of neurologic symptoms for subjects with and without the E4 isoform (E4(+)and E4(-), respectively) in an HIV cohort. Compared with E4(-) subjects, twice as many E4(+) subjects were demented (30% compared with 15%) or had peripheral neuropathy (70% compared with 39%) at least once, and they had threefold more symptomatic examinations (13% compared with 3% and 42% compared with 14%, respectively)(P < 0.0001). Thus, neurologic symptoms for HIV-infection and AD are linked through an etiologic risk factor. Long-term survivors of HIV infection with E4 may be at high risk for AD; conversely, gene-viral interactions may speed AD pathogenesis.

AIDS Dementia Complex↗