DNA damage, DNA repair and the genetic basis of Alzheimer's disease

Assessment of DNA damage and repair efficiency in drug naïve schizophrenia using comet assay

The etiology of schizophrenia continues to be confounding and elusive. Some knowledge gaps exist in the neurodegenerative theory of schizophrenia. Oxidative DNA damage and repair deficits are relevant to the mechanisms of neurodegeneration but have not been studied in drug naïve schizophrenia. The present study used the comet assay technique to study the extent of DNA damage in circulating peripheral lymphocytes of patients with drug naïve schizophrenia (n = 40) along with an age and gender matched control group (n = 40). We also assessed the DNA repair efficiency in cases following incubation in a nutrient medium. All the assayed comet parameters demonstrated significantly greater baseline DNA damage in cases in comparison to the controls except for head diameter (p < 0.001 for all significant results, p = 0.32 for head diameter). Gender, age and duration of illness (p = 0.21, 0.69 and 0.12 respectively for tail length) did not influence any of the parameters significantly. Significant decrease was noted in the comet tail length and percentage of DNA in comet tail (p < 0.001 for both) in cases following incubation suggesting that the DNA repair machinery was preserved. No difference in DNA repair efficiency was noted between the genders (p = 0.23 for tail length). Our findings confirm the presence of significant baseline DNA damage in schizophrenia even prior to the initiation of anti-psychotic treatment. Additionally, intact genomic repair efficiency was noted in this group as a whole. These results provide some evidence for oxidative DNA damage as molecular link underpinning neurodegeneration in drug naïve schizophrenia.

Endobiogeny: a global approach to systems biology (part 1 of 2)

Endobiogeny is a global systems approach to human biology that may offer an advancement in clinical medicine based in scientific principles of rigor and experimentation and the humanistic principles of individualization of care and alleviation of suffering with minimization of harm. Endobiogeny is neither a movement away from modern science nor an uncritical embracing of pre-rational methods of inquiry but a synthesis of quantitative and qualitative relationships reflected in a systems-approach to life and based on new mathematical paradigms of pattern recognition.

DNA damage and repair efficiency in lymphocytes from schizophrenic patients

In the present study we examined schizophrenic patients' lymphocytes sensitivity to the effects of external factors, such as hydrogen peroxide and gamma-irradiation and also their repair efficiency with the comet assay. Our results did no show any difference in basal levels of DNA damage between schizophrenic and normal populations. The slightly increased sensitivity of the schizophrenic population to the externally induced DNA damage compared to controls was not statistically significant. Also the small reduction in the DNA repair efficiency in schizophrenics in comparison to normal population was found to be not statistically significant. Finally, patients with heritable predisposition to schizophrenia did not show any difference in their response from the other schizophrenics.

Hyperphosphorylation of RNA polymerase II and reduced neuronal RNA levels precede neurofibrillary tangles in Alzheimer disease

Affected neurons of Alzheimer disease (AD) brain are distinguished by the presence of the cell cycle cdc2 kinase and mitotic phosphoepitopes. A significant body of previous data has documented a decrease in neuronal RNA levels and nucleolar volume in AD brain. Here we present evidence that integrates these seemingly distinct findings and offers an explanation for the degenerative outcome of the disease. During mitosis cdc2 phosphorylates and inhibits the major transcriptional regulator RNA polymerase II (RNAP II). We therefore investigated cdc2 phosphorylation of RNAP II in AD brain. Using the H5 and H14 monoclonal antibodies specific for the cdc2-phosphorylated sites in RNAP II, we found that the polymerase is highly phosphorylated in AD. Moreover, RNAP II in AD translocates from its normally nuclear compartment to the cytoplasm of affected neurons, where it colocalizes with cdc2. These M phase-like changes in RNAP II correlate with decreased levels of poly-A RNA in affected neurons. Significantly, they precede tau phosphorylation and neurofibrillary tangle formation. Our data support the hypothesis that inappropriate activation of the cell cycle cdc2 kinase in differentiated neurons contributes to neuronal dysfunction and degeneration in part by inhibiting RNAP II and cellular processes dependent on transcription.

Gene specific DNA repair of damage induced in familial Alzheimer disease cells by ultraviolet irradiation or by nitrogen mustard

We have measured gene specific DNA repair in a normal human fibroblast cell line, and in fibroblast lines from two patients with familial Alzheimer disease (AD). Cells were treated with either ultraviolet radiation (UV) or the chemotherapeutic alkylating agent, nitrogen mustard (HN2). DNA damage formation and repair were studied in the active dihydrofolate reductase (DHFR) gene for the main lesions introduced by each of these two types of DNA damaging agents. The gene specific repair of UV induced cyclobutane pyrimidine dimers in the human DHFR gene was 86% complete in the AD cells after 24 h of repair incubation. This repair efficiency was similar to what we and others have found in normal human fibroblasts. After treatment of the AD cells with HN2, we found the frequency of HN2 induced lesions in the DHFR gene to be similar to the frequency in the transcriptionally inactive delta-globin gene. The gene specific repair of HN2 induced lesions in the DHFR gene was completed within 8-24 h in the normal fibroblast line and in the familial AD line, and the repair kinetics were similar for both cell lines. These results indicate that familial AD fibroblasts have normal gene specific repair of both UV induced and HN2 induced DNA damage in active genes.

Slowed synthesis of DNA and methionine is a pathogenetic mechanism common to dementia in Down's syndrome, AIDS and Alzheimer's disease?

This is a presentation of the hypothesis of a pathogenetic mechanism common to the dementia seen in Alzheimer's disease (AD), Down's Syndrome (DS) and the acquired immunodeficiency syndrome (AIDS). As there is experimental evidence of defective DNA repair capacity in AD and DS, unrepaired damage to DNA occurs in these diseases and may lead to complete breakdown of cellular function and ultimate cell death. Cobalamin and folate are coordinated in a vulnerable key position in the synthesis of DNA and S-adenosylmethionine (SAM). Cobalamin/folate deficiency, a significant feature in senile dementia of Alzheimer type and in AIDS-related dementia complex, will result in concomitant slowed synthesis of DNA and SAM. The enzyme cystathionine-beta-synthetase (CBS) has been localized to the chromosome band 21q22.3. Owing to gene dosage, CBS activity is increased in trisomy 21. As a consequence, cobalamin/folate metabolism is inhibited, which leads to slowing of DNA and SAM synthesis in DS patients. Amyloidosis is a hallmark of AD and DS brain neuropathology and recent experimental findings support the view that amyloid or amyloid precursors stimulate DNA synthesis, which is in agreement with the hypothesis presented in this paper. In summary, demented patients with cobalamin/folate deficiency, trisomy 21 and human immunodeficiency virus (HIV) infection display a simultaneous downregulation of DNA and SAM synthesis, which may indicate a pathway common to the dementia seen in AD, DS and AIDS.

DNA repair and mutant frequency in schizophrenia

The in vivo frequency of mutants resulting from mutation at the hprt locus in human T-lymphocytes was determined with a cloning assay. T-lymphocytes were obtained from 14 individuals diagnosed with schizophrenia and 5 controls. No significant difference in mutant frequency was observed between the 2 groups. In addition, DNA-repair capacity was measured with the unscheduled DNA synthesis technique in lymphocytes from 7 individuals diagnosed with schizophrenia and 7 controls. Repair capacity was determined following treatment with MMS, MNNG, and 20 J/m2 ultraviolet light. No significant differences in DNA repair were observed between the patient and control groups in response to any of the 3 DNA-damaging agents. These results argue against differences between normal and schizophrenic individuals with respect to in vivo mutant frequency or their capacity to repair DNA lesions induced by MMS, MNNG, or ultraviolet radiation.