A study of the control of oral plaque biofilms via antibacterial photodynamic therapy

Aim: The aim of this study was to provide preliminary data on the most effective erythrosine concentration and light dose for the erythrosine-based photodynamic therapy (PDT) of oral plaque biofilms formed in vivo. Method: A randomized controlled study with 15 volunteers was carried out to investigate the effect of photosensitiser and light dose on the killing of bacteria in oral plaque biofilms formed in vivo. All volunteers wore a removable in situ appliance carrying 6 enamel slabs for two phases of two weeks each. During this time, plaque biofilms accumulated on the enamel slabs. The slabs were then removed from the appliances for PDT-treatment in vitro. In the first phase of the study, erythrosine doses of 22 and 220uM were used for the photodynamic treatment of the biofilms. In the second phase, the erythrosine concentration was kept constant, and the light dose was varied. Following treatment, the biofilms were disaggregated, and the total bacterial killing determined using colony counting. Results: The erythrosine dose of 220uM caused the most cell killing relative to controls. Fifteen minutes continuous irradiation with light and light fractionation of 5x1 minute irradiation separated by 2 minute dark recovery periods were found to be the most effective bactericidal regimes. Conclusion: Erythrosine-based PDT shows promise as an anti-bacterial treatment for oral plaque biofilms. Further research is needed to prove its clinical and cost-effectiveness compared with current best practice

Admixture Mapping Scans Identify a Locus Affecting Retinal Vascular Caliber in Hypertensive African Americans: the Atherosclerosis Risk in Communities (ARIC) Study

Retinal vascular caliber provides information about the structure and health of the microvascular system and is associated with cardiovascular and cerebrovascular diseases. Compared to European Americans, African Americans tend to have wider retinal arteriolar and venular caliber, even after controlling for cardiovascular risk factors. This has suggested the hypothesis that differences in genetic background may contribute to racial/ethnic differences in retinal vascular caliber. Using 1,365 ancestry-informative SNPs, we estimated the percentage of African ancestry (PAA) and conducted genome-wide admixture mapping scans in 1,737 African Americans from the Atherosclerosis Risk in Communities (ARIC) study. Central retinal artery equivalent (CRAE) and central retinal vein equivalent (CRVE) representing summary measures of retinal arteriolar and venular caliber, respectively, were measured from retinal photographs. PAA was significantly correlated with CRVE (ρ = 0.071, P = 0.003), but not CRAE (ρ = 0.032, P = 0.182). Using admixture mapping, we did not detect significant admixture association with either CRAE (genome-wide score = −0.73) or CRVE (genome-wide score = −0.69). An a priori subgroup analysis among hypertensive individuals detected a genome-wide significant association of CRVE with greater African ancestry at chromosome 6p21.1 (genome-wide score = 2.31, locus-specific LOD = 5.47). Each additional copy of an African ancestral allele at the 6p21.1 peak was associated with an average increase in CRVE of 6.14 µm in the hypertensives, but had no significant effects in the non-hypertensives (P for heterogeneity <0.001). Further mapping in the 6p21.1 region may uncover novel genetic variants affecting retinal vascular caliber and further insights into the interaction between genetic effects of the microvascular system and hypertension

Dynamics of DNA loop capture by the Sfil restriction endonuclease on supercoiled and relaxed DNA

The SfiI endonuclease is a prototype for DNA looping. It binds two copies of its recognition sequence and, if Mg2þ is present, cuts both concertedly. Looping was examined here on supercoiled and relaxed forms of a 5.5 kb plasmid with three SfiI sites: sites 1 and 2 were separated by 0.4 kb, and sites 2 and 3 by 2.0 kb. SfiI converted this plasmid directly to the products cut at all three sites, though DNA species cleaved at one or two sites were formed transiently during a burst phase. The burst revealed three sets of doubly cut products, corresponding to the three possible pairings of sites. The equilibrium distribution between the different loops was evalu-ated from the burst phases of reactions initiated by adding MgCl2 to SfiI bound to the plasmid. The short loop was favored over the longer loops, particularly on supercoiled DNA. The relative rates for loop capture were assessed after adding SfiI to solutions containing the plasmid and MgCl2. On both supercoiled and relaxed DNA, the rate of loop capture across 0.4 kb was only marginally faster than over 2.0 kb or 2.4 kb. The relative strengths and rates of looping were compared to computer simu-lations of conformational fluctuations in DNA. The simulations concurred broadly with the experimental data, though they predicted that increasing site separations should cause a shallower decline in the equilibrium con-stants than was observed but a slightly steeper decline in the rates for loop capture. Possible reasons for these discrepancies are discussed