Vitamin D insufficiency and cognitive impairment in Asians: a multi-ethnic population-based study and meta-analysis.

BACKGROUND: The relationship between vitamin D insufficiency and cognitive impairment remains equivocal in Asians. We examined the association between circulating 25-hydroxyvitamin D (25OHD) concentration and cognitive performance in a large multi-ethnic Singaporean population-based study. We also conducted a meta-analysis of 25OHD concentrations amongst cognitively impaired older adults in Asia. METHODS: Our population-based cross-sectional study included 2273 persons ≥60 years of age from the Singapore Epidemiology of Eye Diseases (SEED) study (mean ± SD age 70.4 ± 6.2 years; 44.7% female), who were categorized according to 25OHD concentration (i.e. ≤10, 10.1-20 and >20 ng mL(-1) ). The 25OHD concentration was measured and adjusted to reflect a deseasonalized value. Cognition was assessed using the total and domain scores of the Abbreviated Mental Test (AMT). Global cognitive impairment was defined as AMT score of ≤6 if 0-6 years of education and AMT score of ≤8 if >7 years of education. Fully adjusted multivariate models were used. We included seven studies in a meta-analysis of 25OHD and cognition in Asia (6068 participants; 1179 cognitively impaired cases). RESULTS: Participants with 25OHD levels >20 ng mL(-1) (n = 1302) had higher AMT total scores (mean ± SD 8.5 ± 1.9) and were less likely to have cognitive impairment (14.1%) than participants with lower 25OHD levels (overall P < 0.001, P-trend < 0.001). Deseasonalized 25OHD concentration was associated with AMT score (ß = 0.10 per 10 ng mL(-1) , P = 0.035). Vitamin D insufficiency (25OHD ≤20 ng mL(-1) ) was associated with global cognitive impairment (OR 1.56, P = 0.028). Specifically, 25OHD concentration correlated with semantic memory (r = 0.08, P = 0.009) and orientation in time (r = 0.09, P = 0.003). In the meta-analysis, the pooled mean 25OHD difference was -6.83 ng mL(-1) (95% confidence interval -11.36; -2.30), indicating lower 25OHD concentrations amongst cognitively impaired compared to cognitively healthy participants in Asia. CONCLUSION: Vitamin D insufficiency is associated with a greater likelihood of and more severe cognitive impairment in Asian populations.

Using total internal reflection fluorescence microscopy to visualize rhodopsin-containing cells.

Sunlight is captured and converted to chemical energy in illuminated environments. Although (bacterio)chlorophyll-based photosystems have been characterized in detail, retinal-based photosystems, rhodopsins, have only recently been identified as important mediators of light energy capture and conversion. Recent estimates suggest that up to 70% of cells in some environments harbor rhodopsins. However, because rhodopsin autofluorescence is low-comparable to that of carotenoids and significantly less than that of (bacterio)chlorophylls-these estimates are based on metagenomic sequence data, not direct observation. We report here the use of ultrasensitive total internal reflection fluorescence (TIRF) microscopy to distinguish between unpigmented, carotenoid-producing, and rhodopsin-expressing bacteria. Escherichia coli cells were engineered to produce lycopene, ß-carotene, or retinal. A gene encoding an uncharacterized rhodopsin, actinorhodopsin, was cloned into retinal-producing E. coli. The production of correctly folded and membrane-incorporated actinorhodopsin was confirmed via development of pink color in E. coli and SDS-PAGE. Cells expressing carotenoids or actinorhodopsin were imaged by TIRF microscopy. The 561-nm excitation laser specifically illuminated rhodopsin-containing cells, allowing them to be differentiated from unpigmented and carotenoid-containing cells. Furthermore, water samples collected from the Delaware River were shown by PCR to have rhodopsin-containing organisms and were examined by TIRF microscopy. Individual microorganisms that fluoresced under illumination from the 561-nm laser were identified. These results verify the sensitivity of the TIRF microscopy method for visualizing and distinguishing between different molecules with low autofluorescence, making it useful for analyzing natural samples.

Serum C-reactive protein level and prehypertension in two Asian populations.

Few previous studies in Western populations have reported an association between C-reactive protein (CRP) and prehypertension. However, no previous study has examined this association in Asians. We examined individuals who were free of hypertension from two independent population-based studies in Singapore: the Singapore Prospective Study Programme (SP2, n=2843 Chinese, Malay and Indians aged 24 years) and the Singapore Malay Eye Study (SiMES, n=957 Malays, aged 40-80 years). Prehypertension was defined as systolic blood pressure (BP) 120-139 mm Hg or diastolic BP 80-89 mm Hg. CRP was analyzed as categories (<1, 1-3, >3 mg l(-1)). The prevalence of prehypertension increased with increasing categories of CRP in both cohorts (P for trend <0.05 in both cohorts). After adjusting for potential confounders including body mass index (BMI), smoking and diabetes, persons with higher levels of CRP were more likely to have prehypertension in both SP2 (compared with CRP <1 mg l(-1), odds ratio (OR) 1.23, 95% confidence interval (CI) 1.03-1.48 for CRP 1-3 and OR 1.67, 95% CI 1.32-2.10 for >3 mg l(-1)) and SiMES (OR 1.45, 95% CI 1.04-2.01 and OR 1.56, 95% CI 1.07-2.27) respectively. In conclusion, data from two population-based Asian cohorts suggest that elevated serum CRP levels are associated with prehypertension.

Serum C-reactive protein level and prediabetes in two Asian populations.

AIMS/HYPOTHESIS: Prediabetes, an early stage in the hyperglycaemic continuum, increases the future risk of developing diabetes and cardiovascular disease (CVD). C-reactive protein (CRP), a marker of inflammation, is associated with diabetes and CVD. However, studies examining the association between CRP and prediabetes among participants without diabetes are limited. METHODS: We analysed data from two large population-based studies in Singapore: the Singapore Prospective Study Programme (SP2, n = 4,252 Chinese, Malay and Indians aged ≥ 24 years) and the Singapore Malay Eye Study (SiMES, n = 2,337 Malays aged 40-80 years), participants of which were free of diabetes mellitus. Prediabetes was defined as glycated haemoglobin of 5.7-6.4% in SiMES (n = 1,231); fasting plasma glucose of 5.6-6.9 mmol/l in SP2 (n = 386). RESULTS: Elevated high sensitivity CRP (hsCRP) levels were found to be associated with prediabetes after adjusting for age, sex, race-ethnicity, education, smoking, alcohol consumption, hypertension, BMI and total cholesterol. Comparing those with hsCRP <1 mg/l (referent), the OR (95% confidence interval) of prediabetes in persons with hsCRP 1-3 mg/l and >3 mg/l was 1.31 (0.99-1.74) and 2.17 (1.61-2.92), p (trend) < 0.0001 in SP2; 1.23 (1.00-1.52) and 1.31 (1.06-1.64), p (trend) = 0.02 in SiMES. In subgroup analysis, the association was stronger in women, Chinese and Malays, and participants with BMI < 25 kg/m(2). CONCLUSIONS: Data from two population-based Asian cohorts suggest that elevated serum hsCRP levels are associated with prediabetes.

Relationship between glycated haemoglobin and microvascular complications: is there a natural cut-off point for the diagnosis of diabetes?

AIMS/HYPOTHESIS: This study was designed to determine whether the relationship of glycated haemoglobin to diabetic microvascular complications shows any natural thresholds that could be useful in diagnosing diabetes. METHODS: We examined a population-based sample of 3,190 Malay adults aged 40-80 years in Singapore. The microvascular outcomes of interest were: (1) any retinopathy, defined from fundus photographs; (2) mild retinopathy, defined as in (1); (3) moderate retinopathy, defined as in (1); (4) chronic kidney disease, defined from estimated glomerular filtration rate; (5) micro- or macroalbuminuria, defined from urinary albumin to creatinine ratio; and (6) peripheral neuropathy, defined from neurothesiometer or monofilament sensory testing. RESULTS: Increasing HbA(1c) was associated with all microvascular complications. The optimal cut-off points for detecting mild and moderate retinopathy were 6.6% (87.0% sensitivity, 77.1% specificity and area under the receiver operating characteristics [ROC] curve 0.899) and 7.0% (82.9% sensitivity, 82.3% specificity and area under ROC curve 0.904). The prevalences of mild and moderate retinopathy were <1% below the optimal cut-off points. For other complications, the association with HbA(1c) was linear without evidence of a distinct threshold. Although ROC analysis for these other complications also suggested optimal cut-off points between 6.6% and 7.0%, the sensitivity at these cut-off points was considerably lower than for mild and moderate retinopathy, ranging from 31.8% to 66.5%. CONCLUSIONS/INTERPRETATION: Higher levels of HbA(1c) were associated with microvascular complications. Our data support use of an HbA(1c) cut-off point of between 6.6 and 7.0% in diagnosing diabetes. Cut-off points in this range were best for the identification of individuals with mild and moderate retinopathy. Any retinopathy, chronic kidney disease, albuminuria and peripheral neuropathy are less well detected at these cut-off points.

Fluctuation correlation spectroscopy and photon histogram analysis of light scattered by gold nanospheres.

Fluorescence correlation spectroscopy (FCS) is a valuable tool in biological research. In recent years there has been growing interest in using light scattered from metallic colloids in place of organic fluorophores. Metallic colloids display optical cross sections for scattering that are orders of magnitude brighter than fluorophores. We used the FCS method to study the scattering properties of varying sizes of gold colloids 38-100 nm in diameter. The optical cross sections of the gold colloids increase rapidly with size, as can be seen by both the G(0) value of the autocorrelation function and the scattering intensity distributions. In mixtures of different size gold colloids the autocorrelation function is dominated by the larger (brighter) colloids, even when present at a small fractional population. We show that it is possible to detect one 100 nm gold colloid in the presence of 10(3)-10(4)smaller 39 nm diameter colloids. Because the scattering cross sections of colloids will increase with aggregation, we believe that FCS can be used to detect a small number of associated bio-labeled colloids in the presence of a much larger population of non-associated colloids.

Oligonucleotide immobilization on micropatterned streptavidin surfaces.

We describe a simple procedure for photolithographic patterning of streptavidin on silicon substrates. Long wavelength UV (365 nm) light was used to direct the covalent attachment of photoactivatable biotin onto silylated silicon wafers. Fluorescently labeled streptavidin was found to bind only in areas exposed to the light. We used this procedure to selectively pattern streptavidin inside microwells etched in silicon, and we investigated the binding characteristics of biotinylated oligonucleotides of lengths, n = 16, 54 and 99 bases. The binding curves were found to fit the functional form of the Langmuir isotherm, with binding saturation proportional to n(-3/4).

Real-time velocity of DNA bands during field-inversion gel electrophoresis.

The velocity v of bands of double-stranded, linear DNAs containing 48.5-5700 kbp was determined with 0.3 s resolution during field-inversion agarose gel electrophoresis (FIGE) for a broad range of the forward pulse period T+, keeping the duration of the backward pulse T- = T+/3. Within 0.6 s or less after the field changed sign from-to +, the velocity showed a sharp positive peak; a similar spike, but with negative velocity, occurred immediately after the field changed from + to -. For long pulses, the magnitude of this spike increased with M0.36, reaching ten times the steady-state velocity for M = 5.7 kbp. After this spike, the velocity dipped to 55-75% of its value in a steady field, then increased to a small secondary peak before reaching a steady-state plateau. The duration of the velocity trough, and the time of the small peak, increased as M1. For standard FIGE conditions (ratio of forward:reverse pulse duration, T+:T- = 3:1; equal forward and reverse field amplitudes, E+ = E-), the mobility mu = integral of vdt over a complete cycle was a minimum when E+ terminated at the end of the velocity trough. The minimum occurred because the velocity during E+ sampled primarily the trough, and because the backward velocity during E- was exceptionally large; the negative velocity spike was maximized when T+ terminated at the end of the velocity trough. Computer simulations of FIGE by Zimm (J. Chem. Phys. 1991, 94, 2187-2206) and by Duke and Viovy (J. Chem. Phys. 1992, 96, 8552-8563) generate real-time velocities that are in excellent agreement with our experimental data.