PubMed Health⌕ Search

Biomedical subjects

K A Meadows

Publications and source records attributed to K A Meadows.

At least 19 recordsLinked to original sources
PubMed2001

Insulin-like growth factors (IGF-I and IGF-II) inhibit C2 skeletal myoblast differentiation and enhance TNF alpha-induced apoptosis.

IGF-I and IGF-II are thought to be unique in their ability to promote muscle cell differentiation. Murine C2 myoblasts differentiate when placed into low serum media (LSM), accompanied by increased IGF-II and IGF binding protein-5 (IGFBP-5) production. Addition of 20 ng/ml TNF alpha on transfer into LSM blocked differentiation, IGF-II and IGFBP-5 secretion and induced apoptosis. We, therefore, wished to assess whether IGFs could protect against the effects of TNF alpha. Neither inhibition of differentiation or induction of apoptosis was rescued by co-incubation with IGF-I or IGF-II. A lower dose of TNF alpha (1 ng/ml) while not inducing apoptosis still inhibited myoblast differentiation by 56% +/- 12, (P < 0.001), indicating that induction of apoptosis is not the sole mechanism by which TNF alpha inhibits myoblast differentiation. Addition of IGF-I or IGF-II alone reduced differentiation by 49% +/- 15 and 33% +/- 20, respectively, (P < 0.001), although neither induced apoptosis. For muscle cells to differentiate, they must arrest in G0. We established that addition of IGF-I, IGF-II or TNF alpha to the myoblasts promoted proliferation. The myoblasts could not exit the cell cycle as efficiently as controls and differentiation was thus reduced. Unexpectedly, co-incubation of IGF-I or IGF-II with 1 ng/ml TNF alpha enhanced the inhibition of differentiation and induced apoptosis. In the absence of apoptosis we show an association between IGF-induced inhibition of differentiation and increased IGFBP-5 secretion. These results indicate that the effects of the IGFs on muscle may depend on the cytokine environment. In the absence of TNF alpha, the IGFs delay differentiation and promote myoblast proliferation whereas in the presence of TNF alpha the IGFs induce apoptosis.

Animals↗
PubMed2000

Tumor necrosis factor-alpha-induced apoptosis is associated with suppression of insulin-like growth factor binding protein-5 secretion in differentiating murine skeletal myoblasts.

Wasting of muscle and fat during cachexia exceeds that explained by reduced food intake alone. This wasting may result from an imbalanced cytokine environment, which could lead to increased protein catabolism. Supporting this, tumor necrosis factor-alpha (TNF-alpha) is raised in several animal models of cachectic muscle wasting. Therefore, we assessed the effects of TNF-alpha and its second messenger, ceramide, on the proliferation, differentiation, and survival of murine C2 skeletal myoblasts. Because insulin-like growth factor binding protein-5 (IGFBP-5) and insulin-like growth factor-II (IGF-II) are potent regulators of myoblast proliferation and differentiation, we monitored the ability of exogenous TNF-alpha to manipulate this system. Fibroblast growth factor (FGF) ceramide, or TNF-alpha suppressed differentiation of C2 cells compared with controls. All treatments suppressed IGF-II production but only TNF-alpha blocked IGFBP-5 secretion. TNF-alpha increased apoptotic cell death, which otherwise remained basal (low serum differentiation medium (LSM), FGF) or low (ceramide). Suppression of both IGFBP-5 and IGF-II secretion may explain why of all triggers tested, only TNF-alpha not only blocked differentiation, but also promoted cell death. This suggests a fundamental role of IGFBP-5 for maintaining muscle survival. Supporting this hypothesis, no increase in apoptosis was seen in IGFBP-5 cDNA tranfected C2 cells after TNF-alpha treatment. In summary, the IGF system is essential for maintaining skeletal muscle cell survival and differentiation, and its suppression by TNF-alpha is fundamental regarding muscle wasting, and may be associated in vivo with cancer cachexia.

Animals↗
PubMed2000

The impact of different response alternatives on responders' reporting of health-related behaviour in a postal survey.

Previous experimental research in other topic areas has shown that the choice of response alternatives can influence respondents' reporting of the frequency of vaguely defined events and that the set of response alternatives is treated as information in the interpretation of the question. The aim of this study was to examine whether such affects would occur in the context of respondents reporting of health-related events using high and medium frequency closed format response categories, which might be used interchangeably by researchers. The study consisted of a postal survey of n = 518 patients aged > or = 18 years randomly selected from the patient list of a diabetes centre and who were equally and randomly allocated to one of three conditions (Condition A: high frequency response alternatives/horizontal orientation; condition B: medium frequency response alternatives/horizontal orientations; condition C: high frequency response alternatives/vertical orientation). Testing for the effect of response alternatives for the combined responses of five vaguely defined questions between conditions A and B was chi 2 = 5.5, p = 0.019, for the difference in proportions, indicating that overall, those respondents presented with response alternatives discriminating at medium frequency, reported significantly fewer target events than those presented with high frequency response alternatives. Testing for the effect of orientation of the combined question responses between conditions A and C, differences in proportions between conditions, did not reach statistical significance (p > 0.05). Findings from this and previous studies indicate that response alternatives provide information on the interpretation of vaguely defined questionnaire items and that their choice should not be left to intuition alone when designing questionnaire items.

Adult↗
PubMed2000

Adaptation of the Diabetes Health Profile (DHP-1) for use with patients with Type 2 diabetes mellitus: psychometric evaluation and cross-cultural comparison.

AIMS: To adapt the Diabetes Health Profile (DHP-1) for use with English speaking patients with Type 2 diabetes mellitus and to evaluate the psychometric properties of the adapted measure in a UK and Danish sample of insulin, tablet and diet-treated patients with Type 2 diabetes. METHODS: Following linguistic adaptation using the forward-backward translation procedure, the 32-item DHP-1 was sent to 650 and 800 consecutively selected UK and Danish patients with Type 2 diabetes. Construct validity was assessed using principal axis factoring. Factor stability was assessed across language groups using the coefficient of congruence. Reliability was evaluated using Cronbach's alpha and multi-trait analysis, including item convergent/discriminant validity. Subscale discriminant validity was assessed through known groups with one-way ANOVA and post hoc Scheffe tests for multiple comparisons. RESULTS: Eighteen items (56.25%) were retained following initial item analysis. A three-factor solution accounting for 45.6% and 40.3% of the total explained variance was identified in the UK and Danish samples, respectively. Factors were interpreted as psychological distress (PD), barriers to activity (BA) and disinhibited eating (DE). Factor congruence between language groups ranged from 0.98 to 0.99 and Cronbach's alpha ranged between 0.70 and 0.88. Item scaling success for both language versions was 88.9%. BA scores discriminated between treatment groups in both language groups (F = 24.24, P < 0.001; F = 7.68, P < 0.001) and PD scores in the UK sample (F = 20.97, P < 0.001). CONCLUSIONS: The DHP-18 developed for use with patients with Type 2 diabetes has been shown to have satisfactory internal reliability and validity and measurement equivalence across language groups.

Affect↗
PubMed1998

Reconstitution of core light-harvesting complexes of photosynthetic bacteria using chemically synthesized polypeptides. 1. Minimal requirements for subunit formation.

Described are the chemical synthesis, isolation and characterization of each of three polypeptides whose amino acid sequences reproduce portions of the amino acid sequence of the beta-polypeptides of the core light-harvesting complex (LH1) of Rhodobacter sphaeroides or Rhodospirillum rubrum. The native beta-polypeptides of LH1 of these organisms contain 48 and 54 amino acids, respectively. The smallest synthetic polypeptide had an amino acid sequence identical to that of the last 16 amino acids of the beta-polypeptide of Rb. sphaeroides (sph beta 16) but failed to form either a subunit- or LH1-type complex under reconstitution conditions. Also, this polypeptide, lengthened on the N terminus by adding the sequence Lys-Ile-Ser-Lys to enhance solubility, failed to form a subunit- or LH1-type complex. In contrast, polypeptides containing either the 31 amino acids at the C terminus of the beta-polypeptide of Rb. sphaeroides (sph beta 31) or the equivalent 31 amino acids of the beta-polypeptide of Rs. rubrum (rr beta 31) were fully competent in forming a subunit-type complex and exhibited association constants for complex formation comparable to or exceeding those of the native beta-polypeptides. The absorption and CD spectra of these subunit-type complexes were nearly identical to those of subunit complexes formed with native beta-polypeptides. It may be concluded that all structural features required to make the subunit complex are present in the well-defined, chemically synthesized polypeptides. Neither polypeptide appeared to interact with the native alpha-polypeptides to form a LH1-type complex. However, sph beta 31 formed a LH1-type complex absorbing at 849 nm without an alpha-polypeptide. Although chemical syntheses of polypeptides of this size are common, the purification of membrane-spanning segments is much more challenging because the polypeptides lack solubility in water. The chemical syntheses reported here represent the first such syntheses of membrane-spanning polypeptides which display native activity upon reconstitution.

Amino Acid Sequence↗
PubMed1998

Reconstitution of core light-harvesting complexes of photosynthetic bacteria using chemically synthesized polypeptides. 2. Determination of structural features that stabilize complex formation and their implications for the structure of the subunit complex.

Chemically synthesized polypeptides have been utilized with a reconstitution assay to determine the role of specific amino acid side chains in stabilizing the core light-harvesting complex (LH1) of photosynthetic bacteria and its subunit complex. In the preceding paper [Meadows, K. A., Parkes-Loach, P. S., Kehoe, J. W., and Loach, P. A. (1998) Biochemistry 37, 3411-3417], it was demonstrated that 31-residue polypeptides (compared to 48 and 54 amino acids in the native polypeptides) having the same sequence as the core region of the beta-polypeptide of Rhodobacter sphaeroides (sph beta 31) or Rhodospirillum rubrum (rr beta 31) could form subunit-type complexes. However, neither polypeptide interacted with the native alpha-polypeptides to form a native LH1 complex. In this paper, it is demonstrated that larger segments of the native Rb. sphaeroides beta-polypeptide possess native behavior in LH1 formation. Polypeptides were synthesized that were six (sph beta 37) and ten amino acids (sph beta 41) longer than sph beta 31. Although sph beta 37 exhibited behavior nearly identical to that of sph beta 31, sph beta 41 behaved more like the native polypeptide. In the case of rr beta 31, a polypeptide with four additional amino acids toward the C terminus was synthesized (rr beta 35). Because LH1-forming behavior was not recovered with this longer polypeptide, one or more of the three remaining amino acids at the C-terminal end of the native beta-polypeptide seem to play an important role in LH1 stabilization in Rs. rubrum. Three analogues of the core region of the Rb. sphaeroides beta-polypeptide were synthesized, in each of which one highly conserved amino acid was changed. Evidence was obtained that the penultimate amino acid, a Trp residue, is especially important for subunit formation. When it was changed to Phe, the lambda Max of the subunit shifted from 823 to 811 nm and the association constant decreased about 500-fold. Changing each of two other amino acids had smaller effects on subunit formation. Changing Trp to Phe at the location six amino acid residues toward the C terminus from the His coordinated to Bchl resulted in an approximately 10-fold decrease in the association constant for subunit formation but did not affect the formation of a LH1-type complex compared to sph beta 31. Finally, changing Arg to Leu at the location seven amino acid residues toward the C terminus from the His coordinated to Bchl decreased the association constant for subunit formation by about 30-fold. In this case, no LH1-type complex could be formed. On the basis of these results, in comparison with the crystal structure of the LH2 beta-polypeptide of Rhodospirillum molischianum, two possible structures for the subunit complex are suggested.

Amino Acid Sequence↗
PubMed1998

Alterations in the insulin-like growth factor system during the menstrual cycle in normal women.

OBJECTIVES: To evaluate the effects of endogenous estrogens and progestins on the IGF-system during the normal menstrual cycle in healthy premenopausal women not using contraceptive drugs. METHODS: Nine women had fasting blood samples obtained at 2-3 days intervals during a 5 week study period. Plasma levels of IGF-I, IGF-II, IGFBP-I, IGFBP-3, estradiol and progesterone were measured by radioimmunoassay (RIA) in each sample. IGFBP-3 was also evaluated by Western ligand blot (WLB) and immunoblot. Any differences between the menstrual phase (defined as day 1-5), follicular and luteal phases (separation based on plasma estradiol and progesterone values) were evaluated by the Friedman test. RESULTS: A small but significant difference in plasma levels of IGF-I (P < 0.01) and IGFBP-d (P < 0.05) measured by RIA between the three phases were seen with the highest levels found during the follicular phase. No change in plasma levels of IGFBP-1 and IGF-II was found and immunoblots did not reveal any alteration in the ratio of fragmented to intact IGFBP-3 during the menstrual cycle. A positive correlation between plasma levels of IGF-I and estradiol was seen in 8 out of 9 patients (P = 0.012). CONCLUSIONS: The finding of a slight but significant higher level of plasma IGF-I in the follicular and luteal phases compared with the menstrual phase suggests plasma estradiol may influence the level of this growth factor. This hypothesis is further supported by the finding of a correlation between plasma levels of IGF-I and estradiol but not progesterone in individual patients at different times during the menstrual cycle.

Adult↗
PubMed1998

Re-examination of factors associated with expansion of CGG repeats using a single nucleotide polymorphism in FMR1.

In at least 98% of fragile X syndrome cases, the disease results from expansion of the CGG repeat in the 5' end of FMR1. The use of microsatellite markers in the FMR1 region has revealed a disparity of risk between haplotypes for CGG repeat expansion. Although instability appears to depend on both the haplotype and the AGG interspersion pattern of the repeat, these factors alone do not completely describe the molecular basis for the linkage disequilibrium between normal and fragile X chromosomes, in part due to instability of the marker loci themselves. In an effort to better understand the mechanism of dynamic mutagenesis, we have searched for and discovered a single nucleotide polymorphism in intron 1 of FMR1 and characterized this marker, called ATL1, in 564 normal and 152 fragile X chromosomes. The G allele of this marker is found in 40% of normal chromosomes, in contrast to 83% of fragile X chromosomes. Not only is the G allele exclusively linked to haplotypes over-represented in fragile X syndrome, but G allele chromosomes also appear to transition to instability at a higher rate on haplotypes negatively associated with risk of expansion. The two alleles of ATL1 also reveal a highly significant linkage disequilibrium between unstable chromosomes and the 5' end of the CGG repeat itself, specifically the position of the first AGG interruption. The data expand the number of haplotypes associated with FMR1 and specifically allow discrimination, by ATL1 alleles, of single haplotypes with differing predispositions to expansion. Such haplotypes should prove useful in further defining the mechanism of dynamic mutagenesis.

Adenine Nucleotides↗
PubMed1998

Attitudes to the use of health outcome questionnaires in the routine care of patients with diabetes: a survey of general practitioners and practice nurses.

BACKGROUND: Despite the increasing availability of multidimensional health status and outcome measures of the patient's physical and emotional functioning, and a number of national initiatives to promote their use, little is known about the attitudes and behaviour of general practitioners (GPs) and practice nurses (PNs) regarding their use in evaluating the effectiveness of health care. What evidence there is remains largely anecdotal but supports the view that health outcome data is currently not used in the routine management of the patient. AIM: To investigate the attitudes and behaviour of GPs and PNs regarding the use of health outcome data in the routine care of patients with diabetes. METHOD: A questionnaire comprising 20 attitudinal and behavioural statements covering the use and benefits of health outcome data in the routine care of patients with diabetes were sent to 156 GPs and 114 PNs in the Doncaster area together with a covering letter and two examples of multidimensional health outcome measures. RESULTS: Completed questionnaires were received from 90 (58%) GPs and 49 (50% corrected for out of scope) nurses. Median response scores showed that both GPs and nurses expressed a positive overall attitude towards health outcome measurement giving responses favourable to it in 15 (75%) and 18 (90%) of the statements respectively. A key finding was that 48% and 46% of GPs and PNs were unclear as to how they would use health outcome data. CONCLUSION: While our findings reflect a favourable view towards the use of health outcome data for the routine management of the patient with diabetes in a general practice setting, a number of important barriers to their implementation have been identified. These include insufficient knowledge on their use, the need for easily interpretable data, and a lack of resources.

Adult↗
PubMed1996

Insulin-like growth factor binding protein-3 in breast cyst fluid: relationships with insulin-like growth factors I and II and transforming growth factor-beta 1 and 2.

Women who have palpable breast cysts with intracystic Na/K > 3 may have a lower risk of developing breast cancer than those with intracystic Na/K < 3. In this study significantly higher concentrations of insulin-like growth factor-binding protein-3 (IGFBP-3), insulin-like growth factors I and II (IGF-I, IGF-II) and transforming growth factor-beta 2 (TGF-beta2) were found in the Na/K > 3 sub-group. No difference was found in transforming-growth factor-beta 1 (TGF-beta1) levels between the two sub-groups of breast cysts. A positive correlation was obtained for IGFBP-3 and TGF-beta1 in the Na/ K > 3 sub-group consistent with reports that TGF-beta1 may regulate the production of IGFBP-3. Equimolar amounts of total IGFs and IGFBP-3 in breast cyst fluid imply that most, if not all, of these IGFs are protein-bound. The significantly higher concentrations of TGF-beta2 in the Na/K > 3 sub-group may partly explain the lower risk of breast cancer in this group of women.

Exudates and Transudates↗
PubMed1996

Comparison of the structural requirements for bacteriochlorophyll binding in the core light-harvesting complexes of Rhodospirillum rubrum and Rhodospirillum sphaeroides using reconstitution methodology with bacteriochlorophyll analogs.

Bacteriochlorophyll (BChl) structural requirements for formation of the core light-harvesting complex (LH1) and its structural subunit complex were examined by reconstitution with BChl analogs and the alpha- and beta-polypeptides of Rhodospirillum rubrum and Rhodobacter sphaeroides. Comparable results were obtained with most of the BChl analogs and the polypeptides of each bacterium, indicating the conservation of BChl binding sites. These systems showed the following common requirements for formation of the subunit complex and LH1: (1) Mg or a metal of similar size and coordination chemistry (e.g., Zn, Cd, Ni), (2) a bacteriochlorin oxidation state of the macrocyclic ring, (3) a 13(2)-carbomethoxy group, and (4) an intact ring V. Some structural features were not as critically important. For example, the subunit complex and LH1 could be formed with both sets of polypeptides and BChl b, as well as with analogs containing either short (ethanol) or long (phytol) esterifying alcohols. Two derivatives were identified that behave differently with the two sets of polypeptides. The 3-acetyl group is required to form LH1 in both bacteria, although a subunit-type complex was readily formed with [3-vinyl]BChl a and the polypeptides of Rs. rubrum but formed only slightly under special conditions with polypeptides of Rb. sphaeroides. [13(2)-OH]BChl a(p) formed both subunit- and LH1-type complexes with the alpha- and beta-polypeptides of Rb. sphaeroides but not with those of Rs. rubrum. Thus, some subtle differences in the BChl binding sites exist in the LH1 complexes of these two bacteria.

Amino Acid Sequence↗
PubMed1995

Enzymatic and chemical cleavage of the core light-harvesting polypeptides of photosynthetic bacteria: determination of the minimal polypeptide size and structure required for subunit and light-harvesting complex formation.

To ascertain the minimal structural requirements for formation of the subunit and core light-harvesting complex (LH1), the alpha- and beta-polypeptides of the LH1 from three purple photosynthetic bacteria were enzymatically or chemically truncated or modified. These polypeptides were then used in reconstitution experiments with bacteriochlorophyll a (BChla), and the formation of subunit and LH1 complexes was evaluated using absorbance and circular dichroism spectroscopies. Truncation or modification outside of the conserved core sequence region of the polypeptides had no effect on subunit or LH1 formation. However, the extent of formation and stability of the subunit and LH1 decreased as the polypeptide was shortened inside the core region within the N-terminal domain. This behavior was suggested to be due to the loss of potential ion-pairing and/or hydrogen-bonding interactions between the polypeptides. While the spectroscopic properties of the subunit complexes generated using truncated polypeptides were analogous to those obtained using native polypeptides, in some cases the resulting LH1 complex absorption was blue-shifted relative to the control. Thus, truncation within the N-terminal domain may have long-range effects on the immediate BChla binding environment, since the putative BChla binding site resides near the C-terminal end of the polypeptides. It was also demonstrated that the His located within the membrane-spanning domain on the N-terminal end of the beta-polypeptide is not participating in ligation of the BChla in the reconstituted subunit and therefore probably not in LH1.

Amino Acid Sequence↗
PubMed1995

Developing outcome measures for ambulatory care--an application to asthma and diabetes.

Increasing emphasis is now being placed on the assessment of patient outcomes, both in evaluating medical interventions and in quality assurance initiatives. Clinicians, purchasers, managers and researchers need outcome measures that are valid, reliable and responsive. This paper describes the theory and practice underlying the development of outcome measures for two chronic conditions, asthma and diabetes, for application in ambulatory settings. Existing generic and condition-specific health status and health-related quality-of-life measures were administered to almost 1300 patients. The psychometric properties of these measures were examined to identify those that were of adequate validity and reliability in these population groups. Step-wise regression procedures were then used to identify a core set of scales that best predicted patients' general health perceptions, which could be used in measuring general health outcomes for each of these groups. These core sets consist of up to 40 items, spanning physical function, energy and vitality, emotional well-being and condition-specific aspects of health such as symptom control. Further analysis is being carried out to assess the responsiveness to change of these core item sets.

Activities of Daily Living↗
PubMed1994

Development of a symptom based outcome measure for asthma.

Measuring symptom specific health outcome is complex, but the methodologies now exist to develop measures with the appropriate properties. As one element of a major programme to develop multidomain health outcome measures for chronic disease, a symptom based measure for asthma care has been developed for use in general practice and outpatient departments. This article outlines the development process, which used a framework recently described in the theoretical literature to show the constraints that scientific criteria place on the development of outcome measures and the means of overcoming such limiting factors. Although substantial effort is required to undertake a rigorous process of development, useful tools are the result. Two five item, symptom based outcome measures for adult asthma are described.

Ambulatory Care↗
PubMed1991

Copper transfer from Rhus vernicifera laccase.

Tree laccase, a multi-copper oxidase, has been studied as a copper donor in conjunction with the demetalated forms of three blue copper proteins. Copper transfer could be observed under reducing conditions in the absence of air. Only about 10% of the total copper in laccase could be transferred regardless of the amount of acceptor present in solution, hence, the laccase is heterogeneous as isolated. Potential sources of the heterogeneity are considered. After transfer, laccase could be partially resolved into copper-deficient and nearly holoprotein fractions that would not donate copper when recombined with acceptor protein. EPR results in conjunction with thiol titrations indicate that there is no net loss of type 1 copper from laccase but that there is loss of type 2 copper as well as a small amount of type 3 copper. Very little transfer is observed when type 2-depleted laccase is used as the donor. Finally, the implications that these results could have in the elucidation of possibly more physiologically relevant processes are briefly summarized.

Copper↗