Robertas Petrolis

Small Aβ1–42 oligomer-induced membrane depolarization of neuronal and microglial cells: Role of N-methyl-D-aspartate receptors

Although it is well documented that soluble beta amyloid (Aβ) oligomers are critical factors in the pathogenesis of Alzheimers disease (AD) by causing synaptic dysfunction and neuronal death, the primary mechanisms by which Aβ oligomers trigger neurodegeneration are not entirely understood. We sought to investigate whether toxic small Aβ1–42 oligomers induce changes in plasma membrane potential of cultured neurons and glial cells in rat cerebellar granule cell cultures leading to neuronal death and whether these effects are sensitive to the N‐methyl‐D‐aspartate receptor (NMDA‐R) antagonist MK801. We found that small Aβ1–42 oligomers induced rapid, protracted membrane depolarization of both neurons and microglia, whereas there was no change in membrane potential of astrocytes. MK801 did not modulate Aβ‐induced neuronal depolarization. In contrast, Aβ1−42 oligomer‐induced decrease in plasma membrane potential of microglia was prevented by MK801. Small Aβ1–42 oligomers significantly elevated extracellular glutamate and caused neuronal necrosis, and both were prevented by MK801. Also, small Aβ1–42 oligomers decreased resistance of isolated brain mitochondria to calcium‐induced opening of mitochondrial permeability transition pore. In conclusion, the results suggest that the primary effect of toxic small Aβ oligomers on neurons is rapid, NMDA‐R‐independent plasma membrane depolarization, which leads to neuronal death. Aβ oligomers‐induced depolarization of microglial cells is NMDA‐R dependent.

Multistage principal component analysis based method for abdominal ECG decomposition.

Reflection of fetal heart electrical activity is present in registered abdominal ECG signals. However this signal component has noticeably less energy than concurrent signals, especially maternal ECG. Therefore traditionally recommended independent component analysis, fails to separate these two ECG signals. Multistage principal component analysis (PCA) is proposed for step-by-step extraction of abdominal ECG signal components. Truncated representation and subsequent subtraction of cardio cycles of maternal ECG are the first steps. The energy of fetal ECG component then becomes comparable or even exceeds energy of other components in the remaining signal. Second stage PCA concentrates energy of the sought signal in one principal component assuring its maximal amplitude regardless to the orientation of the fetus in multilead recordings. Third stage PCA is performed on signal excerpts representing detected fetal heart beats in aim to perform their truncated representation reconstructing their shape for further analysis. The algorithm was tested with PhysioNet Challenge 2013 signals and signals recorded in the Department of Obstetrics and Gynecology, Lithuanian University of Health Sciences. Results of our method in PhysioNet Challenge 2013 on open data set were: average score: 341.503 bpm(2) and 32.81 ms.

Detection and evaluation of ventricular repolarization alternans: an approach to combined ECG, thoracic impedance, and beat-to-beat heart rate variability analysis.

BACKGROUND AND OBJECTIVE Beat-to-beat alteration in ventricles repolarization reflected by alternans of amplitude and/or shape of ECG S-T,T segment (TWA) is known as phenomena related with risk of severe arrhythmias leading to sudden cardiac death. Technical difficulties have caused limited its usage in clinical diagnostics. Possibilities to register and analyze multimodal signals reflecting heart activity inspired search for new technical solutions. First objective of this study was to test whether thoracic impedance signal and beat-to-beat heart rate reflect repolarization alternans detected as TWA. The second objective was revelation of multimodal signal features more comprehensively representing the phenomena and increasing its prognostic usefulness. MATERIALS AND METHODS ECG, and thoracic impedance signal recordings made during 24h follow-up of the patients hospitalized in acute phase of myocardial infarction were used for investigation. Signal morphology variations reflecting estimates were obtained by the principal component analysis-based method. Clinical outcomes of patients (survival and/or rehospitalization in 6 and 12 months) were compared to repolarization alternans and heart rate variability estimates. RESULTS Repolarization alternans detected as TWA was also reflected in estimates of thoracic impedance signal shape and variation in beat-to-beat heart rate. All these parameters showed correlation with clinical outcomes of patients. The strongest significant correlation showed magnitude of alternans in estimates of thoracic impedance signal shape. CONCLUSIONS The features of ECG, thoracic impedance signal and beat-to-beat variability of heart rate, give comprehensive estimates of repolarization alternans, which correlate, with clinical outcomes of the patients and we recommend using them to improve diagnostic reliability.

SCARB1 rs5888 is associated with the risk of age-related macular degeneration susceptibility and an impaired macular area

ABSTRACT Background: Age-related macular degeneration (ARMD), a progressive retinal disease, is responsible for an impaired central vision in about 180 million people worldwide. Current options for ARMD prevention and treatment are limited due to an incomplete understanding of disease etiopathogenesis. We aimed to test the hypothesis that the single nucleotide polymorphism rs5888 of SCARB1 gene reflecting lipid and antioxidant micronutrient metabolism pathways is associated with ARMD susceptibility and to evaluate if there is any relation between SCARB1 rs5888 and the macular lesion area. Materials and methods: The prospective case-control study included patients with ARMD (n = 215) and the reference group (n = 238) drawn from a random sample of the Lithuanian population (n = 1436). The genotyping test of SCARB1 rs5888 was carried out using the real-time polymerase chain reaction method. Results: Regression analysis adjusted by gender and age demonstrated that SCARB1 rs5888 TT genotype significantly decreased the odds for ARMD development (OR: 0.61, 95%; CI: 0.380–0.981, p = 0.04). A smoking habit and leading an outdoor life are associated with larger macular lesion areas in ARMD patients (0.54 (0.00–39.06) vs. 3.09 (0.02–19.30) and 0.27 (0.00–34.57) vs. 0.75 (0.00–39.06), respectively). In late stage ARMD subjects with CT genotype, the macular lesion area was larger than in TT carriers (7.64 (0.49–39.06) mm2 vs. 5.02 (0.03–37.06) mm2, p = 0.006). Conclusions: SCARB1 rs5888 and environmental oxidative stress have a prominent role in ARMD susceptibility, early ARMD progression to advanced stage disease and even in the outcome of the disease—an area of macular lesion.

Principal Component Analysis based Colour Scheme Optimisation in Eye Fundus Images

Efficiency of the patient status monitoring in Age Related Macular Degeneration cases, based on evaluation of morphological properties eye fundus images, can be significantly increased by specific contrast enhancement in the images. Objects of interest - drusen (focal deposits of extracellular debris located between the basal lamina of the retinal pigment epithelium and the inner collagenous layer of Bruch membrane) usually are represented by various intensity but the same unique color in the image. Construction of the optimal color scheme to increase the contrast of drusen can be realized by means of Principal Component Analysis, which transforms original RGB color representation into principal components space. The study demonstrates that proposed method can increase contrast-to-noise ratio of the drusen areas 10-fold or more.