Neurotoxicity in all prion disorders is believed to result from the accumulation of PrP-scrapie (PrPSc), a β-sheet rich isoform of a normal cell-surface glycoprotein, the prion protein (PrPC). Limited reports suggest imbalance of brain iron homeostasis as a significant associated cause of neurotoxicity in prion-infected cell and mouse models. However, systematic studies on the generality of this phenomenon and the underlying mechanism(s) leading to iron dyshomeostasis in diseased brains are lacking. In this report, we demonstrate that prion disease–affected human, hamster, and mouse brains show increased total and redox-active Fe (II) iron, and a paradoxical increase in major iron uptake proteins transferrin (Tf) and transferrin receptor (TfR) at the end stage of disease. Furthermore, examination of scrapie-inoculated hamster brains at different timepoints following infection shows increased levels of Tf with time, suggesting increasing iron deficiency with disease progression. Sporadic Creutzfeldt-Jakob disease (sCJD)–affected human brains show a similar increase in total iron and a direct correlation between PrP and Tf levels, implicating PrPSc as the underlying cause of iron deficiency. Increased binding of Tf to the cerebellar Purkinje cell neurons of sCJD brains further indicates upregulation of TfR and a phenotype of neuronal iron deficiency in diseased brains despite increased iron levels. The likely cause of this phenotype is sequestration of iron in brain ferritin that becomes detergent-insoluble in PrPSc-infected cell lines and sCJD brain homogenates. These results suggest that sequestration of iron in PrPSc–ferritin complexes induces a state of iron bio-insufficiency in prion disease–affected brains, resulting in increased uptake and a state of iron dyshomeostasis. An additional unexpected observation is the resistance of Tf to digestion by proteinase-K, providing a reliable marker for iron levels in postmortem human brains. These data implicate redox-iron in prion disease–associated neurotoxicity, a novel observation with significant implications for prion disease pathogenesis.

Converging evidence leaves little doubt that a change in the conformation of prion protein (PrPC) from a mainly α-helical to a β-sheet rich PrP-scrapie (PrPSc) form is the main event responsible for prion disease associated neurotoxicity. However, neither the mechanism of toxicity by PrPSc, nor the normal function of PrPC is entirely clear. Recent reports suggest that imbalance of iron homeostasis is a common feature of prion infected cells and mouse models, implicating redox-iron in prion disease pathogenesis. In this report, we provide evidence that PrPC mediates cellular iron uptake and transport, and mutant PrP forms alter cellular iron levels differentially. Using human neuroblastoma cells as models, we demonstrate that over-expression of PrPC increases intra-cellular iron relative to non-transfected controls as indicated by an increase in total cellular iron, the cellular labile iron pool (LIP), and iron content of ferritin. As a result, the levels of iron uptake proteins transferrin (Tf) and transferrin receptor (TfR) are decreased, and expression of iron storage protein ferritin is increased. The positive effect of PrPC on ferritin iron content is enhanced by stimulating PrPC endocytosis, and reversed by cross-linking PrPC on the plasma membrane. Expression of mutant PrP forms lacking the octapeptide-repeats, the membrane anchor, or carrying the pathogenic mutation PrP102L decreases ferritin iron content significantly relative to PrPC expressing cells, but the effect on cellular LIP and levels of Tf, TfR, and ferritin is complex, varying with the mutation. Neither PrPC nor the mutant PrP forms influence the rate or amount of iron released into the medium, suggesting a functional role for PrPC in cellular iron uptake and transport to ferritin, and dysfunction of PrPC as a significant contributing factor of brain iron imbalance in prion disorders.

Studies on antioxidants as neuroprotective agents have been hampered by the impermeability of the blood brain barrier (BBB) to many compounds. However, previous studies have shown that a group of tea flavonoids, the catechins, are brain permeable and neuroprotective. Despite this remarkable observation, there exist no data on the bioavailability and pharmacological benefits of tea anthocyanins (ACNs) in the brain tissue. This study investigated the ability of Kenyan purple tea ACNs to cross the BBB and boost the brain antioxidant capacity. Mice were orally administered with purified and characterized Kenyan purple tea ACNs or a combination of Kenyan purple tea ACNs and coenzyme-Q10 at a dose of 200 mg/kg body weight in an experiment that lasted for 15 days. Twenty-four hours post the last dosage of antioxidants, CO2 was used to euthanize the mice after which the brain was excised and used for various biochemical analyses. Brain extracts were analysed by high-performance liquid chromatography for ACN metabolites and spectrophotometry for cellular glutathione (GSH). Kenyan purple tea ACNs significantly (P < 0.05) raised brain GSH levels implying boost in brain antioxidant capacity. However, co-administration of both antioxidants caused a reduction of these beneficial effects implying a negative interaction. Notably, ACN metabolites were detected in brain tissue of ACN-fed mice. Our results constitute the first demonstration that Kenyan purple tea ACNs can cross the BBB reinforcing the brain's antioxidant capacity. Hence, the need to study them as suitable candidates for dietary supplements that could support antioxidant capacity in the brain and have potential to provide neuroprotection in neurodegenerative conditions.

Adding indinavir 400 mg twice daily to lopinavir/ritonavir-containing regimens did not significantly alter the median lopinavir PK parameters. However, wide interpatient variability in lopinavir concentrations was seen. In contrast plasma indinavir levels were >80 ng/mL in seven of eight plasma samples, and all CSF and semen samples collected.

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Peroxisome proliferator-activated receptors (PPARs) play roles in neural cells by regulating energy balance, cell proliferation and anti-oxidant responses although the molecular mechanisms underlying such roles are unclear. Chronic exposure to excess manganese (Mn) leads to neurotoxicity, although Mn-induced neurotoxic mechanisms have not been fully elucidated. We hypothesized Mn neurotoxicity differentially alters the expression of PPARs. We investigated the effects of manganese chloride treatment (0.01-4 mM) on protein expression of PPAR isoforms (alpha, beta, and gamma) in human astrocytoma (U87) and neuroblastoma (SK-N-SH) cells. The two cell types expressed the 3 PPAR isoforms differentially: their expression of the PPARs was altered by Mn-treatment. Furthermore, nuclear and cytosolic fractions derived from the 2 cell types, with and without Mn-treatment, exhibited marked differences in the protein content of PPARs. Our results constitute the first demonstration that the PPAR signaling pathway may assume pathophysiological importance in Mn neurotoxicity.

BackgroundAnopheles gambiae, one of the main Afro-tropical mosquito vector of malaria, has adapted to heavy metals in its natural habitat, and developed resistance to most conventional insecticides. Investigations were conducted to establish an association between tolerance to cadmium or lead-heavy metals, and expression of specific genes for cytochrome p450 enzymes associated with pyrethroid resistance in the mosquito.MethodsJuvenile aquatic stages of the mosquito were selected for tolerance to cadmiun or lead through chronic exposure of the stages to maximum acceptable toxicant concentrations (MATCs) of the metals. Using real-time quantitative polymerase chain reaction (qPCR), three replicates each of male or female cadmium or lead-tolerant individuals and relevant controls were separately screened for expression of CYP6M2, CYP6P3 and CYP6Z1 genes. The variance in expression levels of the genes amongst the treatments was compared by ANOVA statistical tool.ResultsExpressions of all the genes were significantly lower (P <0.05) in females than in males. Within gender, there 1.3 - 2.3 or 3.1-4.2-fold reduction in expression of the genes in cadmium or lead selected than respective control populations. Expression of all the classes of gene was elevated in cadmium selected female populations relative to their respective controls.ConclusionThese findings suggest that tolerance to cadmium or lead in the mosquito can influence response in cytochrome p450 genes associated with metabolism of pyrethroids in the mosquito in a sex-specific manner. This can, in turn, affect sensitivity of the mosquito to pyrethroids and other xenobiotics associated with these genes, with potential implications in mosquito vector control operations.