Zareen Amtul

Neuroprotective Mechanism Conferred by 17beta-estradiol on the Biochemical Basis of Alzheimer's Disease

Estrogen (17beta-estradiol) plays key regulatory roles in a variety of physiological and biological processes. Several lines of evidence also support its role as a protective factor in Alzheimers disease; however, the basis of this effect is unclear. Here we show that an early-onset Alzheimers disease transgenic mouse model expressing the double-mutant form of human amyloid precursor protein (APP); Swedish (K670N/M671L) and Indiana (V717F) undergoing treatment with 17beta-estradiol show significantly lower levels of APP processing through beta-secretase and enhanced alpha-secretase processing resulting in marked reductions of APP-CTFbeta, Abeta42 and plaque burden, along with increased levels of the non-amyloidogenic sAPPalpha. Moreover, 17beta-estradiol resulted in elevated brain levels of transthyretin, which inhibits aggregation of Abeta into plaques; though the insulin-degrading enzyme, which breaks down Abeta, was significantly reduced. These results illustrate a multifaceted effect of 17beta-estradiol on the biochemical basis of Alzheimers disease, through effects on APP processing, Abeta levels and factors that affect its clearance and aggregation. Overall, these results support the need for further long-term longitudinal studies to elucidate consequences of menopause as well as hormone therapy on Alzheimers disease, and explore its potential as a therapeutic avenue for the disease.

Detrimental effects of arachidonic acid and its metabolites in cellular and mouse models of Alzheimer's disease: structural insight

Inflammation is believed to be integral to the pathogenesis of Alzheimers disease (AD). Arachidonic acid (AA) is the most important omega-6 fatty acid and a mediator of inflammatory pathways. High-sensitivity enzyme linked immunosorbent assay shows that AA and its various metabolites; prostaglandins, thromboxanes, and leukotriene B4 resulted in significantly higher secretion of both Abeta40 and 42 peptides. A combination of identical number of alternate cis and trans double bonds either at positions Δ5 or 7Z,13 or 15E (such as PGE(2), PGF(2α), THXB2 and PGF(2α)EA) or at positions Δ6Z,8E,10E,14Z (such as LB4) built in the 3-dimensional structure of 20-carbon fatty acyl chains believed to be responsible for their detrimental action. CP 24,879 and sesamin, 2 inhibitors of the AA pathway suppressed the production of amyloid-beta (Aβ) peptides. Immunoblotting experiments and use of SP-C99 transfected COS-7 cells suggested that AA and its metabolites-driven altered production of Aβ is mediated through gamma-secretase cleavage of amyloid precursor protein (APP). An early-onset AD transgenic mouse model expressing the double-mutant form of human amyloid precursor protein, Swedish (K670N/M671L) and Indiana (V717F), corroborated our in vitro findings by showing higher levels of Abeta and amyloid plaques in the brains, when they were fed chow supplemented with 2% AA. Our work not only supports that AA and its metabolites are involved in the production of Aβ and in the pathogenesis of AD but also contributes to clarify aspects of structure-activity relationship helpful for future nonsteroidal anti-inflammatory drugs (NSAIDs) research.

Comorbid Aβ toxicity and stroke: hippocampal atrophy, pathology, and cognitive deficit.

Numerous clinical and epidemiological reports indicate that patients with history of vascular illness such as stroke are more likely to develop dementia as the clinical manifestation of Alzheimers disease. However, there are little data regarding the pathologic mechanisms that link vascular risk factors to the factors associated with dementia onset. We provide evidence that suggests intriguing detrimental interactions between stroke and β-amyloid (Aβ) toxicity in the hippocampus. Stroke was induced by unilateral striatal injection of endothelin-1, the potent vasoconstrictor. Aβ toxicity was modeled by bilateral intracerebroventricular injections of the toxic fragment Aβ. Gross morphologic changes in comorbid Aβ and stroke rats were enlargement of the lateral ventricles with concomitant shrinkage of the hippocampus. The hippocampus displayed a series of synergistic biochemical alterations, including microgliosis, deposition of Aβ precursor protein fragments, and cellular degeneration. In addition, there was bilateral induction of connexin43, reduced neuronal survival, and impaired dendritic development of adult-born immature neurons in the dentate gyrus of these rats compared with either rats alone. Behaviorally, there was impairment in the hippocampal-based discriminative fear-conditioning to context task indicating learning and memory deficit. These results suggest an insight into the relationship between hippocampal atrophy, pathology, and functional impairment. Our work not only highlights the exacerbated pathology that emerges when Aβ toxicity and stroke occur comorbidly but also demonstrates that this comorbid rat model exhibits physiopathology that is highly characteristic of the human condition.

Thrombin inhibitory constituents from Duranta repens

The C-alkylated flavonoids 3,7,4′-trihydroxy-3′-(4-hydroxy-3-methylbutyl)-5,6-dimethoxyflavone (1), 3,7-dihydroxy-3′-(4-hydroxy-3-methylbutyl)-5,6,4′-trimethoxyflavone (2) and the trans-clerodane diterpenoids 6β-hydroxy-15,16-epoxy-5β,8β,9β,10α-cleroda-3,13(16),14-trien-18-oic acid (3) and 2β-hydroxy-15,16-epoxy-5β,8β,9β,10α-cleroda-3,13(16),14-trien-18-oic acid (4) were isolated from Duranta repens. Their structures and the relative configuration of 3 and 4 were determined by spectroscopic methods (1H- and 13C-NMR, IR, and MS) and 2D-NMR experiments. The known flavonoid 5 is also reported for the first time from this species. The compounds 1, 3, and 5 showed significant enzyme-inhibitory activity against thrombin.

Structural Insight into the Differential Effects of Omega-3 and Omega-6 Fatty Acids on the Production of Aβ Peptides and Amyloid Plaques

Several studies have shown the protective effects of dietary enrichment of various lipids in several late-onset animal models of Alzheimer Disease (AD); however, none of the studies has determined which structure within a lipid determines its detrimental or beneficial effects on AD. High-sensitivity enzyme-linked immunosorbent assay (ELISA) shows that saturated fatty acids (SFAs), upstream omega-3 FAs, and arachidonic acid (AA) resulted in significantly higher secretion of both Aβ 40 and 42 peptides compared with long chain downstream omega-3 and monounsaturated FAs (MUFA). Their distinct detrimental action is believed to be due to a structural template found in their fatty acyl chains that lack SFAs, upstream omega-3 FAs, and AA. Immunoblotting experiments and use of APP-C99-transfected COS-7 cells suggest that FA-driven altered production of Aβ is mediated through γ-secretase cleavage of APP. An early-onset AD transgenic mouse model expressing the double-mutant form of human amyloid precursor protein (APP); Swedish (K670N/M671L) and Indiana (V717F), corroborated in vitro findings by showing lower levels of Aβ and amyloid plaques in the brain, when they were fed a low fat diet enriched in DHA. Our work contributes to the clarification of aspects of structure-activity relationships.

Comorbid Rat Model of Ischemia and β-Amyloid Toxicity: Striatal and Cortical Degeneration

Levels of cerebral amyloid, presumably β‐amyloid (Abeta), toxicity and the incidence of cortical and subcortical ischemia increases with age. However, little is known about the severe pathological condition and dementia that occur as a result of the comorbid occurrence of this vascular risk factor and Abeta toxicity. Clinical studies have indicated that small ischemic lesions in the striatum are particularly important in generating dementia in combination with minor amyloid lesions. These cognitive deficits are highly likely to be caused by changes in the cortex. In this study, we examined the viability and morphological changes in microglial and neuronal cells, gap junction proteins (connexin43) and neuritic/axonal retraction (Fer Kinase) in the striatum and cerebral cortex using a comorbid rat model of striatal injections of endothelin‐1 (ET1) and Abeta toxicity. The results demonstrated ventricular enlargement, striatal atrophy, substantial increases in β‐amyloid, ramified microglia and increases in neuritic retraction in the combined models of stroke and Abeta toxicity. Changes in connexin43 occurred equally in both groups of Abeta‐treated rats, with and without focal ischemia. Although previous behavioral tests demonstrated impairment in memory and learning, the visual discrimination radial maze task did not show significant difference, suggesting the cognitive impairment in these models is not related to damage to the dorsolateral striatum. These results suggest an insight into the relationship between cortical/striatal atrophy, pathology and functional impairment.

DHA Supplemented in Peptamen Diet Offers No Advantage in Pathways to Amyloidosis: Is It Time to Evaluate Composite Lipid Diet?

Numerous reports have documented the beneficial effects of dietary docosahexaenoic acid (DHA) on beta-amyloid production and Alzheimers disease (AD). However, none of these studies have examined and compared DHA, in combination with other dietary nutrients, for its effects on plaque pathogenesis. Potential interactions of DHA with other dietary nutrients and fatty acids are conventionally ignored. Here we investigated DHA with two dietary regimes; peptamen (pep+DHA) and low fat diet (low fat+DHA). Peptamen base liquid diet is a standard sole-source nutrition for patients with gastrointestinal dysfunction. Here we demonstrate that a robust AD transgenic mouse model shows an increased tendency to produce beta-amyloid peptides and amyloid plaques when fed a pep+DHA diet. The increase in beta-amyloid peptides was due to an elevated trend in the levels of beta-secretase amyloid precursor protein (APP) cleaving enzyme (BACE), the proteolytic C-terminal fragment beta of APP and reduced levels of insulin degrading enzyme that endoproteolyse beta-amyloid. On the contrary, TgCRND8 mice on low fat+DHA diet (based on an approximately 18% reduction of fat intake) ameliorate the production of abeta peptides and consequently amyloid plaques. Our work not only demonstrates that DHA when taken with peptamen may have a tendency to confer a detrimental affect on the amyloid plaque build up but also reinforces the importance of studying composite lipids or nutrients rather than single lipids or nutrients for their effects on pathways important to plaque development.

New antibacterial steroidal alkaloids from Sarcococca brevifolia

Abstract Three new steroidal alkaloids, epipachysamine-E-5-ene-4-one (1), N b-demethylepipachysamine-E-5-ene-4-one (2) and iso-N-formylchonemorphine (3) have been isolated from Sarcococca brevifolia. Structures of these compounds were determined by spectroscopic studies. Compounds 1 and 3 exhibited strong antibacterial activity against Bacillus cereus, Escherichia coli, Staphylococcus aureus, Klebsiella pneumoniae, Proteus mirabilis, Corynebacterium diphtheriae and Pseudomonas aeruginosa.

Additive effects of fatty acid mixtures on the levels and ratio of amyloid β40/42 peptides differ from the effects of individual fatty acids.

Several studies have shown the protective and/or deleterious effects of dietary enrichment of single fatty acids (FAs) in several animal and cell‐culture models of Alzheimers disease (AD). However, potential interactions among dietary fatty acids are traditionally ignored. None of these studies has examined and compared the differential effects of FAs in combination, as well as alone, for their effects on amyloid β production or AD. Here we investigated the effects of omega‐9 (oleic acid) and omega‐6 (linoleic and arachidonic acids) fatty acids, either alone or combined, on Aβ production by APP‐695 and SP‐C99 transfected COS‐7 cells. Overall, our results are the first to demonstrate that mixtures of FAs alter the production of Aβ40 and Aβ42 peptides and consequently the Aβ40:42 ratio differently from individual FAs. Here we show that the effects of a single lipid on Aβ production are not attributed to that single FA alone. Rather, the overall lipid composition influences the specificity and level of the regulated intramembranous proteolysis of APP by the γ‐secretase complex. Our results reinforce the importance of studying composite lipids/nutrients rather than single lipids or nutrients.

Why therapies for Alzheimer’s disease do not work: Do we have consensus over the path to follow?

Alzheimers disease (AD) represents a personal tragedy of enormous magnitude, which imposes a daunting worldwide challenge for health-care providers and society as well. In last five decades, global research in clinics and laboratories has illuminated many features of this sinister and eventually fatal disease. Notwithstanding this development, the Alzheimers research apparently has come across a phase of disappointment and a little reservation about the direction to follow. Persistently distressing controversies and a significant number of missing facts shed further uncertainty about the path forward. A detailed description of some of the main controversies in AD research may assist the field towards finding a resolution. Here I reviewed some alarming concerns or controversies related to these primary issues and emphasized on a possible mechanism to settle them.