Susan J. van Rensburg

The role of metals in neurodegenerative processes: aluminum, manganese, and zinc.

Until the last decade, little attention was given by the neuroscience community to the neurometabolism of metals. However, the neurobiology of heavy metals is now receiving growing interest, since it has been linked to major neurodegenerative diseases. In the present review some metals that could possibly be involved in neurodegeneration are discussed. Two of them, manganese and zinc, are essential metals while aluminum is non-essential. Aluminum has long been known as a neurotoxic agent. It is an etiopathogenic factor in diseases related to long-term dialysis treatment, and it has been controversially invoked as an aggravating factor or cofactor in Alzheimers disease as well as in other neurodegenerative diseases. Manganese exposure can play an important role in causing Parkinsonian disturbances, possibly enhancing physiological aging of the brain in conjunction with genetic predisposition. An increased environmental burden of manganese may have deleterious effects on more sensitive subgroups of the population, with sub-threshold neurodegeneration in the basal ganglia, generating a pre-Parkinsonian condition. In the case of zinc, there has as yet been no evidence that it is involved in the etiology of neurodegenerative diseases in humans. Zinc is redox-inactive and, as a result of efficient homeostatic control, does not accumulate in excess. However, adverse symptoms in humans are observed on inhalation of zinc fumes, or accidental ingestion of unusually large amounts of zinc. Also, high concentrations of zinc have been found to kill bacteria, viruses, and cultured cells. Some of the possible mechanisms for cell death are reviewed.

Maternal separation of rat pups increases the risk of developing depressive-like behavior after subsequent chronic stress by altering corticosterone and neurotrophin levels in the hippocampus

Children that are abused have an increased risk for developing psychiatric disorders later in life, because of the negative effects of stress on the developing brain. We used a maternal separation model in rats to see how neurotrophins, stress hormones, behavior and the anti-oxidant potential of serum are affected. Rat pups were separated from their mothers for 3h/day on days 2-14. Maternal separation caused changes in levels of NGF and NT-3 in the dorsal and ventral hippocampus, increased basal corticosterone levels and decreased ACTH levels after acute restraint stress. The anti-oxidant potential of the rat serum was significantly lower in the maternal separation group. Depressive-like behavior, measured during a forced swim test, was seen in maternally separated rats after additional chronic stress during adulthood. Maternal separation caused downregulation of neurotrophins in the ventral hippocampus, possibly as an effect of high corticosterone levels, but compensatory mechanisms against cell death may be involved as neurotrophin levels increased in the dorsal hippocampus. Decreased anti-oxidant potential of serum could have been an effect of downregulated neurotrophin levels.

The effects of eicosapentaenoic acid in tardive dyskinesia: A randomized, placebo-controlled trial

OBJECTIVE Worldwide, conventional antipsychotic medication continues to be used extensively, and tardive dyskinesia (TD) remains a serious complication. The primary objective of the present study was to compare the efficacy of EPA versus placebo in reducing symptoms of TD. METHOD This was a 12-week, double-blinded, randomized study of ethyl-EPA 2g/day versus placebo as supplemental medication, in patients with schizophrenia or schizoaffective disorder, with established TD. RESULTS Eighty-four subjects were randomized, of whom 77 were included in the analysis. Both the EPA and placebo groups displayed significant baseline to endpoint improvements in Extrapyramidal Symptom Rating Scale dyskinesia scores, but there were no significant between-group differences (p=0.4). Response rates (>or=30% improvement in TD symptoms) also did not differ significantly between EPA-treated subjects (45%) and placebo-treated subjects (32%) (p=0.6). However, a post-hoc linear mixed model repeated measures analysis of variance indicated an effect for treatment group and duration of TD. The EPA-treated patients had significantly greater mean reductions in dyskinesia scores initially, although this was not sustained beyond 6 weeks. CONCLUSIONS This trial failed to demonstrate an anti-dyskinetic effect for ethyl-EPA 2g/day on the primary efficacy measure. However, a modest and transient benefit is suggested in patients with more recent onset of TD. The lack of clear-cut efficacy could be explained on the basis of the dose of EPA being too low, the study being underpowered, TD being too chronic in the majority of cases, differences in dietary fatty acid intake, or that EPA lacks an anti-dyskinetic action.

Clinical potential of omega-3 fatty acids in the treatment of schizophrenia.

The phospholipids in the neuronal membranes of the brain are rich in highly unsaturated essential fatty acids (EFAs). It has been hypothesised that abnormalities of phospholipid metabolism are present in patients with schizophrenia and that the EFAs omega-3 polyunsaturated fatty acids, and eicosapentaenoic acid (EPA) in particular, may have a role in treating this illness. Considerable preclinical and clinical evidence provides support for this proposal. An epidemiological study reported a better outcome for patients with schizophrenia in countries where the diet is rich in unsaturated fatty acids. Evidence of abnormalities of EFAs has been found in erythrocyte membranes and cultured skin fibroblasts of patients with schizophrenia, and abnormal retinal function and niacin skin flush tests (markers of omega-3 polyunsaturated fatty acid depletion) have also been reported. Case reports and an open-label clinical trial reported efficacy for EPA in schizophrenia. Four randomised, controlled trials of EPA versus placebo as supplemental medication have now been reported. Two of these trials showed significant benefit with EPA on the positive and negative symptom scale total scores, whereas the other two did not show any effects on this primary efficacy measure. One study also reported a beneficial effect on dyskinesia. In the only published trial in which EPA was used as monotherapy versus placebo in schizophrenia, some evidence was found to suggest antipsychotic activity. Taken together, there is considerable evidence to suggest abnormalities of EFAs in cell membranes of patients with schizophrenia, and there is preliminary evidence that EPA is an effective adjunct to antipsychotics.

Genetic variability in CHMP2B and frontotemporal dementia.

A nonsense/protein chain-terminating mutation in the CHMP2B gene has recently been reported as a cause of frontotemporal dementia (FTD) in the single large family known to show linkage to chromosome 3. Screening for mutations in this gene in a large series of FTD families and individual patients led to the identification of a protein-truncating mutation in 2 unaffected members of an Afrikaner family with FTD, but not in their affected relatives. The putative pathogenicity of CHMP2B mutations for dementia is discussed.

Membrane fluidity of platelets and erythrocytes in patients with Alzheimer's disease and the effect of small amounts of aluminium on platelet and erythrocyte membranes

The membrane fluidity of platelet and erythrocyte membranes in 10 Alzheimers disease patients and 9 age-matched controls was studied. The platelet membranes of patients with Alzheimers disease were found to be significantly more fluid than those of controls (p<0.02). However, erythrocyte membranes of Alzheimer patients were less fluid (more viscous) than those of controls (p<0.05). On further investigation of platelet and erythrocyte membranes obtained from healthy volunteers, the fluidity was found to change with increasing aluminium concentrations. When aluminium ammonium sulphate (0.01–10 μM) was added to membrane suspensions, the fluidity of platelet membranes was increased, whereas the fluidity of erythrocyte membranes was decreased (i.e. the microviscosity was increased).

Safety of the omega-3 fatty acid, eicosapentaenoic acid (EPA) in psychiatric patients : Results from a randomized, placebo-controlled trial

Omega-3 fatty acids, particularly eicosapentaenoic acid (EPA), are increasingly being used by psychiatric patients. Most studies have concentrated on efficacy aspects, while little is known about their safety and tolerability in psychiatric populations. This study aimed to assess the effects of EPA treatment on body mass, glucose metabolism, lipid profiles, prolactin secretion, bleeding time, haematology and liver functions. Eighty-four subjects with schizophrenia were treated with either EPA 2 g/day or placebo in addition to their antipsychotic medication for 12 weeks, in a randomized, controlled trial. Forty-seven entered a 40-week open-label extension phase of EPA 2 g/day. Seventy-four patients were included in the analysis. Six patients discontinued from the EPA group and 14 in the placebo group. Adverse event reporting was similar for the two groups. While there were no significant between-group differences, in the blinded phase the EPA group showed a significant increase in body mass index (BMI) and bleeding time. In the open-label extension, there was again a modest increase in BMI. Total cholesterol and HDL levels were significantly decreased. EPA 2 g/day is generally well tolerated. Clinicians should be aware of possible increases in bleeding time, as well as changes in weight and lipid metabolism.

5- and 6-Glycosylation of transferrin in patients with Alzheimer's Disease.

Transferrin is a glycosylated metal-carrying serum protein. One of the biological functions of glycosylation is to regulate the life span of proteins, less glycosylation leading to a faster clearance of a protein from the circulation. In the case of transferrin, this would indirectly also influence iron homeostasis. Higher glycosylation has been demonstrated in patients with Parkinsons disease and rheumatoid arthritis. A genetic variant of transferrin, TfC2, occurs with increased frequency in patients with Alzheimers disease (AD), rheumatoid arthritis, and other diseases associated with a free radical etiology. Investigations have so far not revealed the reason for the pro-oxidative qualities of TfC2. In this study the glycosylation of Tf in AD (TfC1 homozygotes and TfC1C2 heterozygotes) was compared with alcohol-induced dementia (AID) patients and nondemented, age-matched controls, using isoelectric focusing followed by blotting with anti-Tf antibodies. In TfC1 homozygotes a shift was found toward higher sialylation, but in TfC1C2 heterozygotes the 5- and 6-sialylated bands were less concentrated. The decreased sialalytion found for TfC1C2 heterozygotes, may indicate that the pro-oxidative TfC2 molecules are removed from the circulation at a faster rate than TfC1. This may be of benefit to AD patients having TfC2, but still does not explain why this Tf variant is pro-oxidative.

Biochemical Model for Inflammation of the Brain: The Effect of Iron and Transferrin on Monocytes and Lipid Peroxidation

Cerebral inflammation plays a role in diseases such as multiple sclerosis (MS), Alzheimers disease (AD), and depression. Iron is involved in infection and inflammation through free radical production. Theoretically transferrin should prohibit iron from participating in oxidative reactions, but transferrin has also been found to promote free radical damage. We reported previously that isolation of transferrin from plasma by ion exchange column chromatography produced a broad pink protein band that subsequently separated on a gel filtration column into three proteins containing many metals. In this study some properties of the three proteins were studied in 20 volunteers. Protein 3 (identified as transferrin by nephelometry) contained the most iron while Protein 1 (called “toxiferrin”) contained significantly less iron (p < 0.00001). Plasma from volunteers obtained under conditions of infection/inflammation with fever (n = 5) had a significantly increased toxiferrin to transferrin ratio compared to healthy volunteers (n = 15; p < 0.001). In vitro, Protein 2 and transferrin inhibited lipid peroxidation, while toxiferrin (possibly a protease degradation product of transferrin), enhanced lipid peroxidation. Also, toxiferrin (1 mg/mL) caused a significant increase in viability of monocytes as measured by the 3-(4,5-dimethyl-thiazol-2-yl) 2,5-diphenyl tetrazolium bromide (MTT) reduction test, as well as the morphological transformation of monocytes to macrophages.

A mechanism for zinc toxicity in neuroblastoma cells

Zinc is an important component of proteins essential for normal functioning of the brain. However, it has been shown in vitro that this metal, at elevated levels, can be toxic to cells leading to their death. We investigated possible mechanisms of cell death caused by zinc: firstly, generation of reactive oxygen species, and secondly, the activation of the MAP-kinase pathway. Cell viability was assessed by means of the methyl-thiazolyl tetrazolium salt (MTT) assay and confirmed by tetramethylrhodamine methyl ester (TMRM) staining. We measured the phosphorylation status of Erk and p38 as indicators of MAP-kinase activity, using Western Blot techniques. A time curve was established when neuroblastoma (N2α) cells were exposed to 100 μM of zinc for 4, 12, and 24 h. Zinc caused a significant reduction in cell viability as early as 4 h, and indirectly stimulated the accumulation of reactive oxygen species as determined by 2.7 dichlorodihydrofluorescein diacetate (DCDHF) staining and confocal microscopy. Investigation of the MAP-kinase pathway indicated that Erk was downregulated, while p38 was stimulated. Our results therefore led us to conclude that in vitro, zinc toxicity involved the generation of reactive oxygen species and the activation of the MAP-kinase pathway.