High sensitivity liquid phase measurements using broadband cavity enhanced absorption spectroscopy (BBCEAS) featuring a low cost webcam based prism spectrometer.

Cavity enhanced techniques enable high sensitivity absorption measurements in the liquid phase but are typically more complex, and much more expensive, to perform than conventional absorption methods. The latter attributes have so far prevented a wide spread use of these methods in the analytical sciences. In this study we demonstrate a novel BBCEAS instrument that is sensitive, yet simple and economical to set up and operate. We use a prism spectrometer with a low cost webcam as the detector in conjunction with an optical cavity consisting of two R = 0.99 dielectric mirrors and a white light LED source for illumination. High sensitivity liquid phase measurements were made on samples contained in 1 cm quartz cuvettes placed at normal incidence to the light beam in the optical cavity. The cavity enhancement factor (CEF) with water as the solvent was determined directly by phase shift cavity ring down spectroscopy (PS-CRDS) and also by calibration with Rhodamine 6G solutions. Both methods yielded closely matching CEF values of ~60. The minimum detectable change in absorption (αmin) was determined to be 6.5 × 10(-5) cm(-1) at 527 nm and was limited only by the 8 bit resolution of the particular webcam detector used, thus offering scope for further improvement. The instrument was used to make representative measurements on dye solutions and in the determination of nitrite concentrations in a variation of the widely used Griess Assay. Limits of detection (LOD) were ~850 pM for Rhodamine 6G and 3.7 nM for nitrite, respectively. The sensitivity of the instrument compares favourably with previous cavity based liquid phase studies whilst being achieved at a small fraction of the cost hitherto reported, thus opening the door to widespread use in the community. Further means of improving sensitivity are discussed in the paper.

Tailored internet-delivered cognitive behavioral therapy for individuals experiencing psychological distress associated with climate change: A pilot randomized controlled trial.

Even among people who are not directly impacted by the consequences of climate change, perceptions about the ongoing crisis can have a negative effect on mental health and well-being. However, empirical evidence on interventions aiming to provide support is currently scarce. In order to address this issue, a pilot-RCT was carried out to investigate the effects of a novel ICBT treatment program. Sixty participants (23-73 years) were recruited and randomly allocated to eight weeks of therapist-supported ICBT (n = 30) or a wait-list control condition (n = 30). Measures of depressive symptoms, stress, and quality of life were used as primary outcomes, while measures of anxiety, insomnia, climate change-related distress, pro-environmental behaviour, and alcohol use were used as secondary outcomes. The treatment group had moderate to large between-group effects compared to the waitlist group on measures of depression (d = 0.87), stress (d = 0.76), quality of life (d = 0.79) and climate change-related distress (d = 0.79). There were no significant between-group differences on the other outcome measures. The results from this pilot-RCT indicate that individually tailored ICBT can be an effective way to reduce psychological distress associated with climate change without reducing pro-environmental behaviour.

Regulation of targeted gene repair by intrinsic cellular processes.

Targeted gene alteration (TGA) is a strategy for correcting single base mutations in the DNA of human cells that cause inherited disorders. TGA aims to reverse a phenotype by repairing the mutant base within the chromosome itself, avoiding the introduction of exogenous genes. The process of how to accurately repair a genetic mutation is elucidated through the use of single-stranded DNA oligonucleotides (ODNs) that can enter the cell and migrate to the nucleus. These specifically designed ODNs hybridize to the target sequence and act as a beacon for nucleotide exchange. The key to this reaction is the frequency with which the base is corrected; this will determine whether the approach becomes clinically relevant or not. Over the course of the last five years, workers have been uncovering the role played by the cells in regulating the gene repair process. In this essay, we discuss how the impact of the cell on TGA has evolved through the years and illustrate ways that inherent cellular pathways could be used to enhance TGA activity. We also describe the cost to cell metabolism and survival when certain processes are altered to achieve a higher frequency of repair.

Recovery of cell cycle delay following targeted gene repair by oligonucleotides.

We have previously shown that activation of the homologous recombinational repair pathway leads to a block of cell division in corrected cells, possibly through the activity of checkpoint proteins Chk1 and Chk2. In this study, we examine the long-term impact of this stalling on the growth of cells that have enabled gene repair events. Using a mutated eGFP gene as an episomal reporter, we show that corrected (eGFP-positive) cells contain only a few active replication templates 2 weeks after electroporation, yet do not display an apoptotic or senescent phenotype. By 6 weeks after electroporation, cells resume active replication with a cell cycle profile that is comparable to that of the non-corrected (eGFP-negative) population. These results indicate that the initial stalling is transient and eGFP-positive cells eventually resume a normal phenotypic growth pattern, allowing for passaging and expansion in vitro.

Manipulation of cell cycle progression can counteract the apparent loss of correction frequency following oligonucleotide-directed gene repair.

BACKGROUND: Single-stranded oligonucleotides (ssODN) are used routinely to direct specific base alterations within mammalian genomes that result in the restoration of a functional gene. Despite success with the technique, recent studies have revealed that following repair events, correction frequencies decrease as a function of time, possibly due to a sustained activation of damage response signals in corrected cells that lead to a selective stalling. In this study, we use thymidine to slow down the replication rate to enhance repair frequency and to maintain substantial levels of correction over time. RESULTS: First, we utilized thymidine to arrest cells in G1 and released the cells into S phase, at which point specific ssODNs direct the highest level of correction. Next, we devised a protocol in which cells are maintained in thymidine following the repair reaction, in which the replication is slowed in both corrected and non-corrected cells and the initial correction frequency is retained. We also present evidence that cells enter a senescence state upon prolonged treatment with thymidine but this passage can be avoided by removing thymidine at 48 hours. CONCLUSION: Taken together, we believe that thymidine may be used in a therapeutic fashion to enable the maintenance of high levels of treated cells bearing repaired genes.

The effect of hydroxyurea and trichostatin a on targeted nucleotide exchange in yeast and Mammalian cells.

Targeted nucleotide exchange (TNE) is a process by which a synthetic DNA oligonucleotide, partially complementary to a site in a chromosomal or an episomal gene directs the reversal of a single nucleotide at a specific site. To protect against nuclease digestion, the oligonucleotide is modified with derivative linkages among the terminal bases. We have termed these molecules modified single-stranded oligonucleotides (MSOs). Current models suggest that the reaction occurs in two steps. The first, DNA pairing, involves the alignment of the MSO with the target site and its assimilation into the target helix forming a D-loop. The second phase centers around the repair of a single base mismatch formed between the MSO and its complementary strand in the D-loop. Nucleotide exchange is promoted in all likelihood by the mismatch repair system. A critical feature of successful TNE is the accessibility of the target site for the MSO and the factors that increase the dynamic nature of the chromatin that will likely increase the frequency. Here, we report that two factors, trichostatin A and hydroxyurea, elevate gene repair of a mutant hygromycin gene in Saccharomyces cerevisiae and a mutant eGFP gene in a mammalian cell line, MCF-10AT1 cells. Trichostatin A (TSA) acts by preventing the deacetylation of histones while hydroxyurea (HU) reduces the rate of replication. Both of these activities, by their very nature, create a more open configuration of the MSO into the target site.

DNA replication, cell cycle progression and the targeted gene repair reaction.

Single-stranded oligonucleotides (ssODNs) can direct base changes in mammalian cells and influence changes in phenotype. The mechanism by which ssODNs alters the sequence is being revealed by studies carried out in model systems. In the long run, this information will provide the basis for clinical protocols designed to target genetic diseases. It is now clear that DNA replication plays an important part in the gene repair reaction. Here, we examine gene repair as a function of the amount of cells passing through S phase. We find that cells in mid to late S are most amenable to gene repair, and reaction manipulations that enrich the population of cells in S phase naturally lead to elevated correction frequencies. Our data suggest that these intra-S sub phases support higher levels of repair independent of transfection efficiencies or the rates of replication. A preliminary gene expression profile of cells in the most amenable correction phase indicates that the levels of cyclin G(2), cyclin H, CDK12A and CDK12B are raised significantly. Taken together, our data identify sections of S phase that enable higher levels of gene repair and establish a mechanistic framework for the use of gene repair in clinical setup.