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A A Ismail

Publications and source records attributed to A A Ismail.

At least 37 records · Page 2Linked to original sources
PubMed2000

How many data sources are needed to determine diabetes prevalence by capture-recapture?

BACKGROUND: Capture-recapture (CR) methods are increasingly used to estimate the size of human populations, including those with diabetes. Few studies have examined the demographic details needed to match patients on the lists used in these techniques, or to determine the optimum number of lists. METHODS: Six lists of known diabetic patients attending different medical settings during the study year were obtained. The effects on total enumeration after aggregation of these lists were examined using increasing numbers of demographic data items as patient identifiers. The CR estimates of prevalence were obtained using 15 different combinations of two lists. Estimates were obtained after log-linear modelling for interdependence between different combinations of three and four lists, and after combining the six available lists into three logical lists. RESULTS: For matching patients, adding date of birth to first name and family name as matching criteria increased the total of identified patients from 2500 to 2585 (3% increase), corresponding to a period prevalence of 1.5% (95% CI : 1.41-1.52). Addition of further identifiers, such as partial postcode, only increased the estimate by a further 15 patients (0.5%), and more detailed matching with full postcode introduced uncertainty. The use of two-list CR yielded widely varying estimates of the total diabetic population from 1379 (95% CI : 435-2273) to 9554 (95% CI : 7291-10 983). Log-linear modelling using different combinations of three and four lists produced estimates of 5074 (95% CI : 4417-5947) and 5578 (95% CI : 4918-7081), respectively, after compensating for statistical interdependence between the lists used. The appropriate condensation of six available lists into three lists for modelling yielded estimates of 5492 (95% CI : 4870-6285), corresponding to a CR-adjusted period prevalence of 3.1% (95% CI : 3.03-3.19%). CONCLUSIONS: In a Western population, the only demographic data required for matching patients on lists used for CR methods are first name, family name and date of birth, if unique identifiers such as social security numbers are not available. Two lists alone do not produce reliable data, and at least three lists are needed to allow for modelling for 'dependence' between datasets. The use of more than three lists does not substantially alter the absolute value or confidence of enumeration, and multiple lists (if available) should be condensed into three lists for use in CR calculations.

Databases, Factual↗
PubMed1999

FTIR-monitored thermal titration reveals different mechanisms for the alkaline isomerization of tuna compared to horse and bovine cytochromes c.

Fourier transform infrared (FTIR) spectroscopy is used to compare the thermally induced conformational changes in horse, bovine and tuna ferricytochromes c in 50 mM phosphate/0.2 M KCl. Thermal titration in D2O at pD 7.0 of the amide II intensity of the buried peptide NH protons reveals tertiary structural transitions at 54 degrees C in horse and at 57 degrees C in bovine c. These transitions, which occur well before loss of secondary structure, are associated with the alkaline isomerization involving Met80 heme-ligand exchange. In tuna c, the amide-II-monitored alkaline isomerization occurs at 35 degrees C, followed by a second amide II transition at 50 degrees C revealing a hitherto unreported conformational change in this cytochrome. Amide II transitions at 50 degrees C (tuna) and 54 degrees C (horse) are also observed during the thermal titration of the CN(-)-ligated cytochromes (where CN- displaces the Met80 ligand), but a well-defined 35 degrees C amide II transition is absent from the titration curve of the CN- adduct of tuna c. The different mechanisms suggested by the FTIR data for the alkaline isomerization of tuna and the mammalian cytochromes c are discussed. After the alkaline isomerization, loss of secondary structure and protein aggregation occur within a 5 degrees C range with Tm values at 74 degrees C (bovine c), 70 degrees C (horse c) and 65 degrees C (tuna c), as monitored by changes in the amide I' bands. The FTIR spectra were also used to compare the secondary structures of the ferricytochromes c at 25 degrees C. Curve fitting of the amide I (H2O) and amide I' (D2O) bands reveals essentially identical secondary structure in horse and bovine c, whereas splitting of the alpha-helical absorption of tuna c indicates the presence of less-stable helical structures. CN- adduct formation results in no FTIR-detectable changes in the secondary structures of either tuna or horse c, indicating that Met80 ligation does not influence the secondary structural elements in these cytochromes. The data provided here demonstrate for the first time that the selective thermal titration of the amide II intensity of buried peptide NH protons in D2O is a powerful tool in protein conformational analysis.

Alkalies↗
PubMed1999

Number and type of vertebral deformities: epidemiological characteristics and relation to back pain and height loss. European Vertebral Osteoporosis Study Group.

Vertebral deformity is the classical hallmark of osteoporosis. Three types of vertebral deformity are usually described: crush, wedge and biconcave deformities. However, there are few data concerning the descriptive epidemiology of the individual deformity types, and differences in their underlying pathogenesis and clinical impact remain uncertain. The aim of this study was to compare the epidemiological characteristics of the three types of vertebral deformity and to explore the relationships of the number and type of deformity with back pain and height loss. Age-stratified random samples of men and women aged 50 years and over were recruited from population registers in 30 European centers (EVOS study). Subjects were invited to attend for an interviewer-administered questionnaire and lateral spinal radiographs. The presence, type and number of vertebral deformities was determined using the McCloskey-Kanis algorithm. A total of 13,562 men and women were studied; mean age in men was 64.4 years (SD 8.5), and in women 63.8 years (SD 8.5 years). There was evidence of variation in the occurrence of wedge, crush and biconcave deformity by age, sex and vertebral level. Wedge deformities were the most frequent deformity and tended to cluster at the mid-thoracic and thoraco-lumbar regions of the spine in both men and women. Similar predilection for these sites was observed for crush and to a lesser extent biconcave deformities though this was much less marked than for wedge deformities. In both sexes the frequency of biconcave deformities was higher in the lumbar than the thoracic spine and unlike the other deformity types it did not decline in frequency at lower lumbar vertebral levels. The prevalence of all three types of vertebral deformity increased with age and was more marked in women. There were no important differences in the effect of age on the different deformity types. All types of deformity were associated with height loss, which was greatest for individuals with crush deformity. Back pain was also associated with all types of deformity. Overall, these results do not suggest important differences in pathophysiology between the three deformity types. Biomechanical factors appear to be important in determining their distribution within the spine. All deformity types are linked with adverse outcomes, though crush deformities showed greater height loss than the other deformity types.

Age Factors↗
PubMed1999

Pressure-induced conformational changes of beta-lactoglobulin by variable-pressure Fourier transform infrared spectroscopy.

Pressure-induced conformational changes in D(2)O solutions of the two genetic variants of beta-lactoglobulin A (beta-lg A) and beta-lactoglobulin B (beta-lg B) and an equal mixture of both variants (beta-lg A+B) were studied by employing variable-pressure Fourier transform infrared (VP-FTIR) spectroscopy. Changes in the secondary structure of beta-lg A were observed at lower pressure compared to beta-lg B, indicating that beta-lg A had a more flexible structure. During the decompression cycle beta-lg A showed protein aggregation, accompanied by an increase in alpha-helical conformation. The changes in the secondary structure of beta-lg B with the pressure were minor and for the most part reversible. Upon decompression no aggregation in beta-lg B was observed. Increasing the pressure from 0.01 to 12.0 kbar of a solution containing beta-lg A+B resulted in substantial broadening of all major amide I bands. This effect was partially reversed by decreasing the hydrostatic pressure. beta-lg A+B underwent less aggregate formation than beta-lg A, possibly as a result of protein-protein interactions between beta-lg A and beta-lg B. Hence, it is likely that the functional or biological attributes of beta-lg proteins may be affected in different ways by hydrostatic pressure.

Deuterium↗
PubMed1999

Monitoring carbonyl-amine reaction and enolization of 1-hydroxy-2-propanone (Acetol) by FTIR spectroscopy.

Infrared absorption bands characteristic of the aldehydo, keto, and enediol forms of 1-hydroxy-2-propanone (acetol) were identified and used to study the effect of solvent on the absorption frequencies and the effect of temperature and acid/base catalysis on the enolization reactions. The data indicated that, in addition to water, acids and bases can catalyze the enolization of 1-hydroxy-2-propanone and that the temperature inversely effects the rate of enolization under basic conditions. However, under acidic conditions, increasing the temperature favors the enolization process. In addition, the reaction of 1-hydroxy-2-propanone with a primary and a secondary amine was also monitored by Fourier transform infrared spectroscopy. The data indicated that at room temperature the rate of amine reaction was faster than the rate of its catalysis of enolization; however, below room temperature, the rate of base-catalyzed enolization became comparable with the rate of carbonyl-amine reaction forming both Heyns and Amadori adducts.

Acetone↗
PubMed1999

Fourier transform infrared spectroscopic investigation of temperature- and pressure-induced disaggregation of amyloid A.

The conformation-sensitive amide I band in the Fourier transform infrared (FTIR) spectra of amyloid A suspensions in D2O was examined as a function of temperature (25-95 degrees C) and applied hydrostatic pressure (1-12 kbar) to assess the stability of the peptide. The principal changes observed upon heating were a significant loss of intermolecular beta-sheet structure, and an increase in the broad band centred at 1644 cm(-1) assigned to unordered structure and alpha-helices of the dissociated species. Application of hydrostatic pressure at ambient temperature resulted in a limited degree of aggregate dissociation. These structural changes were partially reversible with cooling or release of the applied pressure. Dissolving the aggregated peptide in alkaline solution (pH 12) also resulted in disaggregation. Dissociation of organ-deposited amyloid substance bears clinical relevance. The present data indicate that residual amounts of undissociated amyloid in the milieu at physiological and acidic pH may act as nucleating foci rendering dissociated amyloid to reaggregate into organized amyloid.

Amino Acid Sequence↗
PubMed1999

The epidemiology of Type 2 diabetes and its current measurement.

Type 2 diabetes is globally increasing in prevalence and is widely recognized as a major cause of morbidity and mortality, as well as being a burden to the health-care services. Planning for current and future diabetes services requires up-to-date prevalence information. The enumeration of Type 2 diabetes is, however, surprisingly difficult. Large numbers of people are undiagnosed, and those known cases have variable loci of care. Traditional techniques include cross-sectional diagnostic surveys, postal or house-to-house surveys and cohort surveys. All are time-consuming and expensive, and may potentially undercount. The use of multiple patient lists (e.g. hospital clinic data, general practitioner (GP) lists, prescribing information, etc.) can, however, increase accuracy and, if the data are computerized, may be rapid and inexpensive. A new and potentially exciting tool to utilize multiple lists in Type 2 diabetes prevalence assessment is known as 'capture-recapture'. In this, statistical models are used to estimate prevalence from the degree of overlap between lists. Capture-recapture is emerging as a valuable tool in the epidemiological assessment of Type 2 diabetes.

Animals↗
PubMed1999

Capture-recapture-adjusted prevalence rates of type 2 diabetes are related to social deprivation.

We examined the prevalence of type 2 diabetes and social deprivation in one urban district in Liverpool from October 1995 to September 1996 inclusive. This area has a stable Caucasian population of 176, 682. Lists were made of all known diabetics attending six different medical points of contact during the year, and were condensed and aggregated to eliminate duplicates. From postcode data, each patient was assigned to residence in one of the 14 electoral wards in the district, for which demographic structure and standardized measures of social deprivation were known (Townsend index). The crude period prevalences of type 1 and type 2 diabetes were estimated for each ward. Crude prevalence data were then corrected by applying capture-recapture (CR) techniques to the different patient datasets to allow for undercount. The crude period prevalence (95%CI) of diabetes was 1.5% (1.4-1.5%), or 2585/176, 682. The mean age of people with diabetes was not significantly different between electoral wards. The crude period prevalence of type 2 diabetes within individual wards ranged from 0.4% (0.3-0.6%) in the least deprived area to 4.1% (3.6-4.6%) in the most deprived area. The corresponding range of CR-adjusted period prevalence rates of type 2 diabetes was from 3.2% (2.8-3.6%) to 6.7% (6.1-7.4%), and there was strong correlation between both crude and CR-adjusted prevalence and social deprivation in each ward (r=0.76, p<0.001 for crude; and r=0. 49, p<0.005 for CR-adjusted prevalence). There was no correlation between the crude or CR-adjusted period prevalence rates of type 1 diabetes and Townsend index (r=0.14, p=NS). This strong correlation between the prevalence of type 2 diabetes and social deprivation has important implications for the planning of health-care delivery.

Adolescent↗
PubMed1999

Relationship between unexplained infertility and human leukocyte antigens and expression of circulating autogeneic and allogeneic antisperm antibodies.

PURPOSE: The association between unexplained infertility, human leukocyte antigens (HLA) and expression of circulating antisperm antibodies was studied in 52 couples with unexplained infertility and 15 infertile and 9 fertile couples. METHODOLOGY: Evaluation parameters included Terasaki's HLA microlymphocytotoxicity test, circulating antisperm antibodies using immunofluorescence technique. RESULTS: Fifty-two couples (8.7%) out of 600 consecutive clinic attendants had unexplained infertility. Unexplained infertility was associated with circulating antisperm antibodies (22 versus 13 and 0% for men and 18.5 versus 13 and 0% for women). HLA class 1 B6 and B52 and Cw7 and HLA class 2 DR4 and DR6 and sharing of HLA B6, DR4 and DR6 were found more in couples with unexplained infertility. Combined expression of antisperm antibodies by couples, demonstrated more homozygosity for HLA B6 and DR4. CONCLUSION: Homozygosity for these antigens, B6, DR4 and DR6, may enhance the expression of antisperm antibodies, and cause infertility.

Antibodies↗
PubMed1998

Mortality associated with vertebral deformity in men and women: results from the European Prospective Osteoporosis Study (EPOS).

Clinically apparent vertebral deformities are associated with reduced survival. The majority of subjects with radiographic vertebral deformity do not, however, come to medical attention. The aim of this study was to determine the association between radiographic vertebral deformity and subsequent mortality. The subjects who took part in the analysis were recruited for participation in a multicentre population-based survey of vertebral osteoporosis in Europe. Men and women aged 50 years and over were invited to attend for an interviewer-administered questionnaire and lateral spinal radiographs. Radiographs were evaluated morphometrically and vertebral deformity defined according to established criteria. The participants have been followed by annual postal questionnaire--the European Prospective Osteoporosis Study (EPOS). Information concerning the vital status of participants was available from 6480 subjects, aged 50-79 years, from 14 of the participating centres. One hundred and eighty-nine deaths (56 women and 133 men) occurred during a total of 14,380 person-years of follow-up (median 2.3 years). In women, after age adjustment, there was a modest excess mortality in those with, compared with those without, vertebral deformity: rate ratio (RR) = 1.9 (95% confidence interval (CI) 1.0,3.4). In men, the excess risk was smaller and non-significant RR = 1.3 (95% CI 0.9,2.0). After further adjusting for smoking, alcohol consumption, previous hip fracture, general health, body mass index and steroid use, the excess risk was reduced and non-significant in both sexes: women, RR = 1.6 (95% CI 0.9,3.0); men RR = 1.2 (95% CI 0.7,1.8). Radiographic vertebral deformity is associated with a modest excess mortality, particularly in women. Part of this excess can be explained by an association with other adverse health and lifestyle factors linked to mortality.

Aged↗
PubMed1996

FTIR study of the thermal denaturation of horseradish and cytochrome c peroxidases in D2O.

Fourier transform infrared (FTIR) spectroscopy was employed to examine the thermal denaturation of the Fe(III), Fe(II), and Fe(II)-CO forms of cytochrome c peroxidase and horseradish peroxidase in phosphate buffer at pD 7.0. The amide I' regions of the deconvolved spectra are consistent with predominantly alpha-helical secondary structure around room temperature, but the alpha-helical absorption of the two peroxidases differs significantly; bands assigned to alpha-helical components occur at 1659 and 1649 cm-1 in horseradish peroxidase and at 1652 and 1637 cm-1 in cytochrome c peroxidase. The thermal denaturation mechanisms of the peroxidases also vary. All three forms of cytochrome c peroxidase retain their secondary structure up to 50 degrees C, when bands characteristic of aggregation (1616 and 1684 cm-1) appear in the amide I' region, and above 55 degrees C rapid loss of secondary structure is accompanied by enhanced aggregation. In horseradish peroxidase, on the other hand, the Fe(III) and Fe(II) states exhibit dissimilar denaturation mechanisms. Slow, gradual alteration of secondary structure is observed for Fe(III) horseradish peroxidase on heating, and polypeptide unfolding appears to be complete around 90 degrees C, without aggregation. In Fe(II) and Fe(II)-CO horseradish peroxidase, aggregation bands appear at approximately 55 degrees C, signaling the onset of denaturation. Frequency shifts in the v(CO) bands above room temperature reveal the conformational changes in the heme cavity precede global conformational changes in cytochrome c peroxidase but not in horseradish peroxidase. The reduction in amide II intensities, due to peptide H-D exchange on heating the peroxidases in D2O, indicates the formation above room temperature of partially unfolded states with increased solvent accessibility but intact secondary structures.

Cytochrome-c Peroxidase↗
PubMed1996

Effects of physicochemical factors on the secondary structure of beta-lactoglobulin.

Fourier transform infrared spectroscopy and differential scanning calorimetry were used as complementary techniques to study changes in the secondary structure of beta-lactoglobulin under various physicochemical conditions. The effects of pH (3-9), NaCl (0-2 M), and lactose, glucose and sucrose (100-500 g/l) in the temperature range 25-100 degrees C on the conformation sensitive amide I band in the i.r. spectrum of beta-lactoglobulin in D2O solution were examined. The 1692 cm-1 band in the amide I band profile had not been definitively assigned in previous studies of the i.r. spectrum of beta-lactoglobulin. The decrease in this band at ambient temperature with time or upon mild heating was attributed to slow H-D exchange, indicating that it was due to a structure buried deep within the protein. The disappearance of the 1692 cm-1 band on heating was accompanied by the appearance of two bands at 1684 and 1629 cm-1, assigned to beta-sheets. The 1692 cm-1 band was therefore attributed to a beta-type structure. beta-Lactoglobulin showed maximum thermal stability at pH 3 and was easily denatured at pH 9. On denaturation, the protein unfolded into more extensive random coil structures at pH 9 than at pH 3. After 10 h at pH 9 (25 degrees C), beta-lactoglobulin was partly denatured. Heating to 60-80 degrees C generally resulted in the loss of secondary structure. At all pH values studied, two new bands at 1618 and 1684 cm-1, characteristic of intermolecular beta-sheet structure and associated with aggregation, were observed after the initial denaturation. Differential scanning calorimetry studies indicated that the thermal stability of beta-lactoglobulin was enhanced in the presence of sugars. The Fourier transform i.r. results obtained provide evidence that sugars promoted the unfolding of beta-lactoglobulin via multiple transition pathways leading to a transition state resisting aggregation.

Calorimetry, Differential Scanning↗
PubMed1996

Ligand-induced conformational change in the ferrichrome-iron receptor of Escherichia coli K-12.

Ferrichrome-iron is actively transported across the outer membrane of Escherichia coli by the TonB-dependent receptor FhuA. To obtain FhuA in a form suitable for secondary-structure analyses, a hexahistidine tag was inserted into a surface-located site and the recombinant protein was purified by metal chelate chromatography. Functional studies indicated that the presence of the hexahistidine tag did not interfere with FhuA localization or with ligand-binding activity. Ferrichrome protected lysine 67 but not lysine 5 of purified recombinant FhuA from trypsinolysis. Results from trypsin digestion were interpreted as a conformational change in FhuA which had occurred upon ferrichrome binding, thereby preventing access of trypsin to lysine 67. Circular dichroism and Fourier transform infrared spectroscopy revealed a predominance of beta-sheet structure for the purified protein. In the presence of ferrichrome, FhuA exhibited a secondary structure and a thermostability which were similar to FhuA without ligand. The addition of ferrichrome to purified FhuA reduced the ability of certain anti-FhuA monoclonal antibodies to bind to the receptor. All antibodies which could in this manner discriminate between FhuA and FhuA bound to ferrichrome had their determinants within a loop which is toward the N-terminus and which is exposed to the periplasm. These data indicate that the binding of ferrichrome induces a structural change that is propogated across the outer membrane and results in an altered conformation of a periplasmically exposed loop of FhuA. It is proposed that by such an alteration of FhuA conformation, TonB is triggered to energize the active transport of the bound ligand across the outer membrane.

Antibodies, Monoclonal↗