Genotoxicity in Alzheimer's disease: role of amyloid

Alzheimer's disease (AD) is a complex neurodegenerative disorder pathologically identified by the presence of extracellular senile plaques (SP) with a proteinaceous core composed of aggregates of the amyloid peptide (Abeta) and intracellular aggregates of the microtubule-associated protein tau (tau) as neurofibrillary tangles (NFTs). These hallmarks consist of abnormally folded proteinaceous components that are believed to be neurotoxic in AD. The mechanisms of toxicity remain unclear although oxidative stress and inflammation are implicated as mediators of the toxicity and these lesions, in turn, are known to damage cellular components including proteins, lipids in the membrane and DNA. However effects on genotoxicity and its role in AD are less clear. The present review discusses various influences, in particular of amyloid, on the genetic material and their possible role in the neurodegeneration in AD. Further, the amalgamation of genomics and proteomics in understanding AD and therapeutic development is suggested.     

3-Chloro-2-methylphenyl-substituted semicarbazones: synthesis and anticonvulsant activity

A series of 3-chloro-2-methylphenyl substituted semicarbazones (3-33) was synthesized and evaluated for anticonvulsant and CNS activities. After intraperitoneal injection to mice or rats, the semicarbazone derivatives were examined in the maximal electroshock seizure (MES), subcutaneous pentylenetetrazole (scPTZ), and subcutaneous strychnine (scSTY)-induced seizure and neurotoxicity screens. The aryl urea (1) and the semicarbazide (2) showed anticonvulsant activity in the MES and scPTZ screens with acute neurotoxicity, whereas the semicarbazone derivatives showed good anticonvulsant potency in the scSTY screen with moderate activity against MES and scPTZ screens. Compound 21 exhibited anticonvulsant potency against all the three screens with lesser neurotoxicity. Some titled compounds exhibited lesser CNS depression and neurotoxicity compared to phenytoin or carbamazepine as was evident from the CNS studies.     

Akt-dependent anabolic activity of natural and synthetic brassinosteroids in rat skeletal muscle cells

Brassinosteroids are plant-derived polyhydroxylated derivatives of 5α-cholestane, structurally similar to cholesterol-derived animal steroid hormones and insect ecdysteroids. In this study, we synthesized a set of brassinosteroid analogues of a natural brassinosteroid (22S,23S)-homobrassinolide (HB, 1), including (22S,23S)-homocastasterone (2), (22S,23S)-3α-fluoro-homobrasinolide (3), (22S,23S)-3α-fluoro-homocastasterone (4), (22S,23S)-7-aza-homobrassinolide (5), and (22S,23S)-6-aza-homobrassinolide (6) and studied their anabolic efficacy in the L6 rat skeletal muscle cells in comparison to other synthetic and naturally occurring brassinosteroids (22R,23R)-homobrassinolide (7), (22S,23S)-epibrassinolide (8), and (22R,23R)-epibrassinolide (9). Presence of the 6-keto group in the B ring and stereochemistry of 22α,23α-vicinal hydroxyl groups in the side chain were critical for the anabolic activity, possibly due to higher cytotoxicity of the 22β,23β-hydroxylated brassinosteroids. All anabolic brassinosteroids tested in this study selectively activated PI3K/Akt signaling pathway as evident by increased Akt phosphorylation in vitro. Plant brassinosteroids and their synthetic derivatives may offer a novel therapeutic strategy for promoting growth, repair, and maintenance of skeletal muscles.     

Cholinergic degeneration and memory loss delayed by vitamin E in a Down syndrome mouse model

Down syndrome (DS) individuals develop several neuropathological hallmarks seen in Alzheimer's disease, including cognitive decline and the early loss of cholinergic markers in the basal forebrain. These deficits are replicated in the Ts65Dn mouse, which contains a partial trisomy of murine chromosome 16, the orthologous genetic segment to human chromosome 21. Oxidative stress levels are elevated early in DS, and may contribute to the neurodegeneration seen in these individuals. We evaluated oxidative stress in Ts65Dn mice, and assessed the efficacy of long-term antioxidant supplementation on memory and basal forebrain pathology. We report that oxidative stress was elevated in the adult Ts65Dn brain, and that supplementation with the antioxidant vitamin E effectively reduced these markers. Also, Ts65Dn mice receiving vitamin E exhibited improved performance on a spatial working memory task and showed an attenuation of cholinergic neuron pathology in the basal forebrain. This study provides evidence that vitamin E delays onset of cognitive and morphological abnormalities in a mouse model of DS, and may represent a safe and effective treatment early in the progression of DS neuropathology.     

An increase in Abeta42 in the prefrontal cortex is associated with a reversal-learning impairment in Alzheimer's disease model Tg2576 APPsw mice

The medial temporal lobe-dependent memory loss associated with Alzheimer's disease (AD) is often accompanied by a loss of prefrontal cortex-dependent cognitive domains that fall under the broad category of executive function. In this study, we examined the relationship between one type of prefrontal-dependent executive function, discrimination reversal-learning, and levels of the amyloid beta protein (Abeta) of 40 and 42 residues in a transgenic mouse model (Tg2576) of the over-expression of the familial AD mutant form of the amyloid precursor protein (APPsw). Tg2576 and their non-transgenic (NTg) littermates were assessed at 3 and 6 months of age when there is little to no amyloid plaque deposition. After reversal-learning assessment, Abeta40 and Abeta42 were quantified in the prefrontal cortex and hippocampus. Tg2576 mice were impaired in reversal-learning at 6 but not 3 months of age when compared to the NTg group. Coincidently, there was a corresponding approximately 3-fold increase of Abeta42 levels in the prefrontal cortex of 6- compared to 3-month-old Tg2576 mice. In addition, the prefrontal cortex contained higher levels of Abeta42 compared to the hippocampus at both 3 and 6 months of age, regardless of genotype, indicating a high vulnerability of this brain region to Abeta42 accumulation. These data suggest that the early emergence of reversal-learning deficits in the Tg2576 mouse may be due to the localized increase of Abeta42 in the prefrontal cortex.     

Synthesis and anticonvulsant and neurotoxicity evaluation of N4-phthalimido phenyl (thio) semicarbazides.

The phenyl (thio) semicarbazide derivatives of phthalimido pharmacophore were synthesized and evaluated for their anticonvulsant and neurotoxic properties. Initial anticonvulsant screening was performed using intraperitoneal (i.p.), maximal electroshock-induced seizure (MES), subcutaneous pentylenetetrazole (scPTZ) and subcutaneous strychnine (sc STY)-induced seizure threshold tests in mice. Compound 2c afforded protection in all the three screens. Compounds except 1d, 2a and 2d showed no neurotoxicity up to 300 mg/kg. Compounds 1a, 1b, 2c, 2d, 2g and 2i were found to show oral MES activity. The compounds exhibited CNS depression and behavioral despair side effects, lesser than the conventional antiepileptic drugs.     

Plasma and RBCs antioxidant status in occupational male pesticide sprayers

A total of forty-one (n=41) male, healthy agricultural sprayers, exposed to pesticides for 5 years, were compared with twenty one (n=21) controls matched for age and economic status with respect to free radical generation, lipid peroxidation, antioxidant status and concentration of cellular enzymes were determined. Significantly increased TBARS (thiobarbituric acid reactive substances) were observed (P<0.001) in sprayer populations when compared to controls. The concentration of antioxidants such as glutathione (GSH), -tocopherol, ascorbic acid and ceruloplasmin were significantly altered when compared to controls, and the activities of antioxidant enzymes were remarkably elevated (P<0.001) in sprayer populations, when compared to controls.     

Triamcinolone-loaded glutaraldehyde cross-linked chitosan microspheres: prolonged release approach for the treatment of rheumatoid arthritis

The use of glucocorticoids in the treatment of rheumatoid arthritis has been widely employed, but, owing to their systemic side-effects and also their susceptibility to the first pass metabolism, their use is being discouraged. To circumvent this, triamcinolone (TA) were encapsulated in chitosan microspheres with glutaraldehyde as the cross-linking agent to achieve a prolonged drug release. The percentage of drug loading, encapsulation efficiency, and surface morphology by Scanning electron microscopy (SEM), Phase transition by Differential scanning colorimetry (DSC), as well as Fourier transform infrared spectroscopy (FTIR) studies was carried out to characterize the chitosan microspheres. In-vitro and in-vivo release studies revealed that microspheres were able to control the release of TA with a uniform release pattern up to a period of 36 days and thereafter an extended release up to 63 days. The clinical parameters were investigated for changes in paw volume, hematological parameters like Erythrocyte sedimentation rate (ESR), Paced cell volume (PCV), Total leucocyte count (TLC), Hb, and Differential cell count (DCC) in Fruend's complete adjuvant induced arthritic rats. Histopathological findings as well as radiology (X-ray) further confirmed the effectiveness of TA encapsulated microspheres in mitigating the rat arthritic model.