Predictive factors of speech understanding in adults with cochlear implants

OBJECTIVE

The aim of this study was to analyse the factors that influenced speech recognition scores in quiet conditions and speech reception threshold levels (SRT) in fixed noise conditions, after cochlear implant (CI) surgery in adults with postlinguistic deafness.

STUDY DESIGN

Combined retrospective and prospective study in a tertiary referral centre.

METHODS

We included 66 patients that received implants between 2002 and 2013. We retrospectively collected speech recognition scores and 14 demographic, audiological, and technical factors, including gender, age at implantation, aetiology, hearing loss progression, preoperative Pure Tone Average (PTA), hearing loss onset age and duration, duration and use of hearing aids (HAs); implantation in the best or worst ear; implantation on the right or left side; use of HA after implantation; and the duration and type of CI. We prospectively tested a subgroup of 21 patients for SRT in fixed noise.

RESULTS

The hearing loss duration significantly affected speech recognition scores in quiet conditions (H (4) = 10.567, p =0.032) and SRTs in fixed noise conditions (rs = 0.466, p = 0.033). The PTA of the better ear significantly affected only the SRT in fixed noise conditions (rs = 0.57 1, p = 0.007).

CONCLUSION

The duration of hearing loss and the PTA of the best ear had significant effects on the outcomes of speech recognition and SRT in quiet and fixed noise conditions, respectively. These findings are important for counselling CI candidates. Further studies in larger study populations are warranted.

Synthesis and photophysical characterisation of new fluorescent triazole adenine analogues

Fluorescent nucleic acid base analogues are powerful probes of DNA structure. Here we describe the synthesis and photo-physical characterisation of a series of 2-(4-amino-5-(1H-1,2,3-triazol-4-yl)-7H-pyrrolo[2,3-d]pyrimidin-7-yl) and 2-(4-amino-3-(1H-1,2,3-triazol-4-yl)-1H-pyrazolo[3,4-d]pyrimidin-1-yl) analogues via Sonogashira cross-coupling and [3 + 2]-cycloaddition reactions as the key steps in the synthesis. Compounds with a nitrogen atom in position 8 showed an approximately ten-fold increase in quantum yield and decreased Stokes shift compared to analogues with a carbon atom in position 8. Furthermore, the analogues containing nitrogen in the 8-position showed a more red-shifted and structured absorption as opposed to those which have a carbon incorporated in the same position. Compared to the previously characterised C8-triazole modified adenine, the emissive potential was significantly lower (tenfold or more) for this new family of triazoles-adenine compounds. However, three of the compounds have photophysical properties which will make them interesting to monitor inside DNA.

The amino terminal extension of mammalian mitochondrial RNA polymerase ensures promoter specific transcription initiation

Mammalian mitochondrial transcription is executed by a single subunit mitochondrial RNA polymerase (Polrmt) and its two accessory factors, mitochondrial transcription factors A and B2 (Tfam and Tfb2m). Polrmt is structurally related to single-subunit phage RNA polymerases, but it also contains a unique N-terminal extension (NTE) of unknown function. We here demonstrate that the NTE functions together with Tfam to ensure promoter-specific transcription. When the NTE is deleted, Polrmt can initiate transcription in the absence of Tfam, both from promoters and non-specific DNA sequences. Additionally, when in presence of Tfam and a mitochondrial promoter, the NTE-deleted mutant has an even higher transcription activity than wild-type polymerase, indicating that the NTE functions as an inhibitory domain. Our studies lead to a model according to which Tfam specifically recruits wild-type Polrmt to promoter sequences, relieving the inhibitory effect of the NTE, as a first step in transcription initiation. In the second step, Tfb2m is recruited into the complex and transcription is initiated.

The photoinduced transformation of fluorescent DNA base analogue tC triggers DNA melting

While fluorescent analogues of the canonical nucleobases have proven to be highly valuable in a large number of applications, up until today, fluorescent DNA base analogues remain virtually inapplicable for single-molecule fluorescence experiments which require extremely bright and photostable dyes. Insight into the photodegradation processes of these fluorophores is thus a key step in the continuous development towards dyes with improved performances. Here, we show that the commercially available fluorescent nucleobase analogue tC under intense long-term illumination and in the presence of O2 is degraded to form a single photoreaction product which we suggest to be the sulfoxide form of tC. The photoproduct is characterized by a blue-shifted absorption and a less intense fluorescence compared to that of tC. Interestingly, when tC is positioned inside double-stranded DNA this photodriven conversion of tC to its photoproduct greatly reduces the duplex stability of the overall double helix in which the probe is positioned. Since tC can be excited selectively at 400 nm, well outside the absorption band of the natural DNA bases, this observation points towards the application of tC as a general light-triggered switch of DNA duplex stability.

Quadracyclic adenine: a non-perturbing fluorescent adenine analogue

Fluorescent-base analogues (FBAs) comprise a group of increasingly important molecules for the investigation of nucleic acid structure and dynamics as well as of interactions between nucleic acids and other molecules. Here, we report on the synthesis, detailed spectroscopic characterisation and base-pairing properties of a new environment-sensitive fluorescent adenine analogue, quadracyclic adenine (qA). After developing an efficient route of synthesis for the phosphoramidite of qA it was incorporated into DNA in high yield by using standard solid-phase synthesis procedures. In DNA qA serves as an adenine analogue that preserves the B-form and, in contrast to most currently available FBAs, maintains or even increases the stability of the duplex. We demonstrate that, unlike fluorescent adenine analogues, such as the most commonly used one, 2-aminopurine, and the recently developed triazole adenine, qA shows highly specific base-pairing with thymine. Moreover, qA has an absorption band outside the absorption of the natural nucleobases (>300 nm) and can thus be selectively excited. Upon excitation the qA monomer displays a fluorescence quantum yield of 6.8 % with an emission maximum at 456 nm. More importantly, upon incorporation into DNA the fluorescence of qA is significantly less quenched than most FBAs. This results in quantum yields that in some sequences reach values that are up to fourfold higher than maximum values reported for 2-aminopurine. To facilitate future utilisation of qA in biochemical and biophysical studies we investigated its fluorescence properties in greater detail and resolved its absorption band outside the DNA absorption region into distinct transition dipole moments. In conclusion, the unique combination of properties of qA make it a promising alternative to current fluorescent adenine analogues for future detailed studies of nucleic acid-containing systems.

Characterization of photophysical and base-mimicking properties of a novel fluorescent adenine analogue in DNA

To increase the diversity of fluorescent base analogues with improved properties, we here present the straightforward click-chemistry-based synthesis of a novel fluorescent adenine-analogue triazole adenine (A^T) and its photophysical characterization inside DNA. A^T shows promising properties compared to the widely used adenine analogue 2-aminopurine. Quantum yields reach >20% and >5% in single- and double-stranded DNA, respectively, and show dependence on neighbouring bases. Moreover, A^T shows only a minor destabilization of DNA duplexes, comparable to 2-aminopurine, and circular dichroism investigations suggest that A^T only causes minimal structural perturbations to normal B-DNA. Furthermore, we find that A^T shows favourable base-pairing properties with thymine and more surprisingly also with normal adenine. In conclusion, A^T shows strong potential as a new fluorescent adenine analogue for monitoring changes within its microenvironment in DNA.

Uranium release from boom clay in bicarbonate media

The release of natural uranium from Boom Clay was studied to better understand the mechanisms governing the solid-liquid partitioning of uranium. Batch leaching experiments suggested that the portion of natural uranium released from clay is associated with colloids at a low bicarbonate concentration prevailing in Boom Clay. At increased bicarbonate concentrations, uranium was present predominantly as dissolved species indicating a formation of uranium carbonate complexes. Thein situaqueous uranium concentration,i.e., the concentration in the pore waters collected by piezometers was found to be 2 to 3 orders of magnitudes lower than the one measured by the batch techniques. These results illustrated that the batch techniques may cause a remobilization of uranium containing colloids from clay surfaces into solution when clay is suspended, agitated, and mechanically perturbed. These colloids are attributed to artefacts and are not considered to existin situbecause of the high compaction of Boom Clay. Due to the presence of colloids, a laboratory derived solid-liquid partitioning coefficient is not equivalent to and cannot simply be converted to the distribution coefficientKdcurrently used in performance assessment calculations.