Handbook of Neurochemistry And Molecular Neurobiology

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Chiral Interface of Amyloid Beta (Aβ): Relevance to Protein Aging, Aggregation and Neurodegeneration

Biochirality is the subject of distinct branches of science, including biophysics, biochemistry, the stereochemistry of protein folding, neuroscience, brain functional laterality and bioinformatics. At the protein level, biochirality is closely associated with various post-translational modifications (PTMs) accompanied by the non-equilibrium phase transitions (PhTs NE). PTMs NE support the dynamic balance of the prevalent chirality of enzymes and their substrates. The stereoselective nature of most biochemical reactions is evident in the enzymatic (Enz) and spontaneous (Sp) PTMs (PTMs Enz and PTMs Sp) of proteins. Protein chirality, which embraces biophysics and biochemistry, is a subject of this review. In this broad field, we focus attention to the amyloid-beta (Aβ) peptide, known for its essential cellular functions and associations with neuropathology. The widely discussed amyloid cascade hypothesis (ACH) of Alzheimer’s disease (AD) states that disease pathogenesis is initiated by the oligomerization and subsequent aggregation of the Aβ peptide into plaques. The racemization-induced aggregation of protein and RNA have been extensively studied in the search for the contribution of spontaneous stochastic stereo-specific mechanisms that are common for both kinds of biomolecules. The failure of numerous Aβ drug-targeting therapies requires the reconsolidation of the ACH with the concept of PTMs Sp. The progress in methods of chiral discrimination can help overcome previous limitations in the understanding of AD pathogenesis. The primary target of attention becomes the network of stereospecific PTMs that affect the aggregation of many pathogenic agents, including Aβ. Extensive recent experimental results describe the truncated, isomerized and racemized forms of Aβ and the interplay between enzymatic and PTMs Sp. Currently, accumulated data suggest that non-enzymatic PTMs Sp occur in parallel to an existing metabolic network of enzymatic pathways, meaning that the presence and activity of enzymes does not prevent non-enzymatic reactions from occurring. PTMs Sp impact the functions of many proteins and peptides, including Aβ. This is in logical agreement with the silently accepted racemization hypothesis of protein aggregation (RHPA). Therefore, the ACH of AD should be complemented by the concept of PTMs Sp and RHPA

Varenicline Effects on Smoking, Cognition, and Psychiatric Symptoms in Schizophrenia: A Double-Blind Randomized Trial

<div><p>Schizophrenic patients have a high rate of smoking and cognitive deficits which may be related to a decreased number or responsiveness of nicotinic receptors in their brains. Varenicline is a partial nicotinic agonist which is effective as an antismoking drug in cigarette smokers, although concerns have been raised about potential psychiatric side-effects. We conducted a double-blind placebo controlled study in 87 schizophrenic smokers to evaluate the effects of varenicline (2 mg/day) on measures of smoking, cognition, psychiatric symptoms, and side-effects in schizophrenic patients who were cigarette smokers. Varenicline significantly decreased cotinine levels (P<0.001), and other objective and subjective measures of smoking (P < .01), and responses on a smoking urges scale (P = .02), more than placebo. Varenicline did not improve scores on a cognitive battery designed to test the effect of drugs on cognitive performance in schizophrenia (the MATRICS battery), either in overall MATRICS battery Composite or individual Domain scores, more than placebo. There were no significant differences between varenicline vs. placebo effects on total symptom scores on psychiatric rating scales, PANSS, SANS, or Calgary Depression scales, and there were no significant drug effects in any of these scales sub-scores when we used Benjamin-Hochberg corrected significance levels (α = .05). Varenicline patients did not show greater side-effects than placebo treated patients at any time point when controlled for baseline side-effect scores. Our study supports the use of varenicline as a safe drug for smoking reduction in schizophrenia but not as a cognitive enhancer.</p><p><b><i>Trial Registration</i>:</b> ClinicalTrials.gov <a href="https://clinicaltrials.gov/ct2/show/NCT00802919?term=00802919&rank=1" target="_blank">00802919</a></p></div

Comparison of MATRICS Battery Domain and Overall Composite Scores In varenicline- and placebo- treated patients.

<p>N's are shown in figure. Each value represents mean ± s.e.m. of Domain or Composite scores of subjects who had complete values on all Domain scores at baseline and week 8. Mean scores are <i>not</i> adjusted for baseline covariate value or site effects. Abbreviations of Domain and Composite scores in figure: SP = speed of processing, AV = attention-vigilance, WM = working memory, VERBL = verbal learning, VISL = visual learning, RP = reasoning-problem solving, COMP = overall composite. Significance of difference for specific Domain or Composite score between baseline and 8 week value: *P < .05, by paired t-test.</p

Effect of varenicline and placebo on PANSS Total and Depression Scores.

<p>N = 77, Varenicline = 38, Placebo = 39. Each value represents model adjusted least square mean score ± s.e.m. for that week, from mixed model ANCOVA. Overall Drug Effect between varenicline and placebo: PANSS Total F = 2.11, DF = 1, 71, P = 0.151; PANSS Depression Factor F = 4.79, df = 1,71, P = 0.032. Significance of difference from same drug baseline in varenicline treated patients by least square means t-test: * P<0.05, **P<0.01.</p