Bioavailability of dietary polyphenols: Factors contributing to their clinical application in CNS diseases.

The anatomical location of the central nervous system (CNS) renders it immunologically and pharmacologically privileged due to the blood brain barrier (BBB). Although this limits the transport of unfavorable molecules to the CNS, the ensuing privilege could be disadvantageous for therapeutic compounds. Hence, the greatest challenge in the pharmacotherapy of CNS diseases is to ensure efficient brain targeting and drug delivery. Research evidences indicate that dietary polyphenols have neuroprotective potential against CNS diseases. However, their selective permeability across BBB, poor absorption, rapid metabolism and systemic elimination limit their bioavailability and therapeutic efficacy. Consequently, the beneficial effects of these orally administered agents in the CNS still remain a subject of debate. This has also limited its clinical application either as independent or adjunctive therapy. Improving the in vivo bioavailability by novel methods could improve the therapeutic feasibility of polyphenols and assist in evolving novel drugs and their derivatives with improved efficacy in vivo. Here we review the mechanistic and pharmacological issues related to the bioavailability of polyphenols with therapeutic implications for CNS diseases. We surmise that improving the bioavailability of polyphenols entails efficient in vivo transport across BBB, biochemical stability, improved half-life and persistent neuroprotection in the CNS.

Curcumin: a potential neuroprotective agent in Parkinson's disease.

Parkinson's disease (PD) is an age-associated neurodegenerative disease clinically characterized as a movement disorder. The motor symptoms in PD arise due to selective degeneration of dopaminergic neurons in the substantia nigra of the ventral midbrain thereby depleting the dopamine levels in the striatum. Most of the current pharmacotherapeutic approaches in PD are aimed at replenishing the striatal dopamine. Although these drugs provide symptomatic relief during early PD, many patients develop motor complications with long-term treatment. Further, PD medications do not effectively tackle tremor, postural instability and cognitive deficits. Most importantly, most of these drugs do not exhibit neuroprotective effects in patients. Consequently, novel therapies involving natural antioxidants and plant products/molecules with neuroprotective properties are being exploited for adjunctive therapy. Curcumin is a polyphenol and an active component of turmeric (Curcuma longa), a dietary spice used in Indian cuisine and medicine. Curcumin exhibits antioxidant, anti-inflammatory and anti-cancer properties, crosses the blood-brain barrier and is neuroprotective in neurological disorders. Several studies in different experimental models of PD strongly support the clinical application of curcumin in PD. The current review explores the therapeutic potential of curcumin in PD.

Muscarinic receptor 1 agonist activity of novel N-aryl carboxamide substituted 3-morpholino arecoline derivatives in Alzheimer's presenile dementia models.

Earlier we have reported the effect of arecoline thiazolidinone and morpholino arecoline derivatives as muscarinic receptor 1 agonists in Alzheimer's presenile dementia models. To elucidate further our Structure-Activity Relationship (SAR) studies on the chemistry and muscarinic receptor 1 binding efficacy, a series of novel carboxamide derivatives of 2-(1-methyl-1,2,5,6-tetrahydropyridin-3-yl)morpholine molecule have been designed and synthesized as a new class of M1 receptor agonists with a low toxicity effect profile that enhances memory function in animal models of Alzheimer's presenile dementia and also modulates the APP secretion from rat brain cerebrocortical slices by activating M1 receptor in vitro. Results suggest that compound 9b having methyl group at the para position of the aryl group attached to the carboxamide of morpholino arecoline could emerge as a potent molecule having antidementia activity.

Biochemical analysis of protein stability in human brain collected at different post-mortem intervals.

BACKGROUND & OBJECTIVES: Rising prevalence of neurodegenerative disorders with a steady increase in aged-population necessitates studies of the human brain to understand their pathophysiology. As animal models are not available, medical centers have established "brain banks" to provide autopsy brain samples for such research. Frozen tissues must be of optimal quality to permit molecular and protein studies. Post-mortem interval (PMI) is an important factor affecting tissue quality although its effects on brain physiology are unclear. We undertook this study to analyze the biochemical effects of PMI on protein stability in human brains collected at autopsy and stored at the brain bank of a tertiary care neurosciences institute in south India. METHODS: Different neuroanatomical areas including frontal cortex (FC), cerebellum (CB), caudate nucleus (CD) and substantia nigra (SN) from autopsy human brains (n=9) with varying PMI (4-18 h) were analyzed for pH, protein insolubility, protein oxidation/ nitration and protein expression of glial fibrillary acidic protein (GFAP), synatophysin and neurofilament (NF). Histological changes at different PMI were also assessed. RESULTS: An increase in tissue pH was noted with increasing PMI. Although there was no significant alteration in solubility of proteins, SN showed increased protein oxidation/nitration events, GFAP and NF expression with increasing PMI. No major abnormalities in cell morphology or tissue integrity were noted. Immunohistochemistry with GFAP and NF did not show any significant increase in signal in FC at high PMI. INTERPRETATION & CONCLUSION: In post-mortem human brains, although there were no gross structural changes at the tissue level with increasing PMI, biochemical events such as oxidative and nitrosative damage of cellular proteins, tissue pH could be considered as markers of tissue quality for biochemical research. Further, SN was found to be most susceptible to PMI related changes.

Integrating glutathione metabolism and mitochondrial dysfunction with implications for Parkinson's disease: a dynamic model.

UNLABELLED: Oxidative/nitrosative stress and mitochondrial dysfunction have been implicated in the degeneration of dopaminergic neurons in the substantia nigra during Parkinson's disease (PD). During early stages of PD, there is a significant depletion of the thiol antioxidant glutathione (GSH), which may lead to oxidative stress, mitochondrial dysfunction, and ultimately neuronal cell death. Mitochondrial complex I (CI) is believed to be the central player to the mitochondrial dysfunction occurring in PD. We have generated a dynamic, mechanistic model for mitochondrial dysfunction associated with PD progression that is activated by rotenone, GSH depletion, increased nitric oxide and peroxynitrite. The potential insults independently inhibit CI and other complexes of the electron transport chain, drop the proton motive force, and reduce ATP production, ultimately affecting the overall mitochondrial performance. We show that mitochondrial dysfunction significantly affects glutathione synthesis thereby increasing the oxidative damage and further exacerbating the toxicities of these mitochondrial agents resulting in neurodegeneration. Rat dopaminergic neuronal cell culture and in vitro experiments using mouse brain mitochondria were employed to validate important features of the model. MAJOR CONCLUSIONS: Using a combination of experimental and in silico modeling approaches, we have demonstrated the interdependence of mitochondrial function with GSH metabolism in relation to neurodegeneration in PD.