Role of Oxidative Stress, Methionine Oxidation and Methionine Sulfoxide Reductases (MSR) in Alzheimer's Disease

A major contributor to dementia seen in aging is Alzheimer's disease (AD). Amyloid beta (Aβ), a main component of senile plaques (SPs) in AD, induces neuronal death through damage to cellular organelles and structures, caused by oxidation of important molecules such as proteins by reactive oxygen species (ROS). Hyperphosphorylation and accumulation of the protein tau in the microtubules within the brain also promote ROS production. Methionine, a residue of proteins, is particularly sensitive to oxidation by ROS. One of the enzyme systems that reverses the oxidative damage in mammalian cells is the enzyme system known as Methionine Sulfoxide Reductases (MSRs). The components of the MSR system, namely MSRA and MSRB, reduce oxidized forms of methionine (Met-(o)) in proteins back to methionine (Met). Furthermore, the MSRs scavenge ROS by allowing methionine residues in proteins to utilize their antioxidant properties. This review aims to improve the understanding of the role of the MSR system of enzymes in reducing cellular oxidative damage and AD pathogenesis, which may contribute to effective therapeutic approaches for AD by targeting the MSR system.

Sulindac enhances the killing of cancer cells exposed to oxidative stress

Background

Sulindac is an FDA-approved non-steroidal anti-inflammatory drug (NSAID) that affects prostaglandin production by inhibiting cyclooxygenases (COX) 1 and 2. Sulindac has also been of interest for more than decade as a chemopreventive for adenomatous colorectal polyps and colon cancer.

Principal Findings

Pretreatment of human colon and lung cancer cells with sulindac enhances killing by an oxidizing agent such as tert-butyl hydroperoxide (TBHP) or hydrogen peroxide. This effect does not involve cyclooxygenase (COX) inhibition. However, under the conditions used, there is a significant increase in reactive oxygen species (ROS) within the cancer cells and a loss of mitochondrial membrane potential, suggesting that cell death is due to apoptosis, which was confirmed by Tunel assay. In contrast, this enhanced killing was not observed with normal lung or colon cells.

Significance

These results indicate that normal and cancer cells handle oxidative stress in different ways and sulindac can enhance this difference. The combination of sulindac and an oxidizing agent could have therapeutic value.

Topical sulindac combined with hydrogen peroxide in the treatment of actinic keratoses

BACKGROUND

Actinic keratoses (AKs) are a precancerous condition of the skin that have the potential to become squamous cell cancer (SCC). Sulindac is a Food and Drug Administration (FDA)-approved nonsteroidal anti-inflammatory drug (NSAID) that has been shown to have clinically significant anticancer effects. Malignant cells may have a different response to oxidative stress than normal cells.

OBJECTIVE

To establish a role of increased reactive oxygen species (ROS) in the mechanism of cancer killing by sulindac in the presence of an oxidizing agent. To assess the tolerability and efficacy of the combination of gels containing sulindac and hydrogen peroxide in the treatment of patients with AKs.

METHODS

Cell culture studies were performed using a skin SCC cell line and normal human epidermal keratinocytes. After treatment with sulindac and an oxidizing agent, cell viability, and intracellular ROS levels were measured. An open-label clinical trial was performed using sulindac and hydrogen peroxide gels daily for 3 weeks on AKs involving the upper extremities.

RESULTS

In SCC cells, a combination of sulindac and an oxidizing agent lead to 400 to 500% increases in intracellular ROS, which resulted in significant cell death. In sharp contrast, normal keratinocytes did not show increases in ROS levels and were not killed. A clinical trial using the combination of sulindac and hydrogen peroxide therapy in 5 patients with AKs revealed that 60% of the treated AKs responded and 50% showed no residual AK on histopathology specimens after skin biopsy.

LIMITATIONS

The small number of patients and the lack of a placebo group.

CONCLUSION

Increased levels of ROS appear to be important in the selective killing of cancer cells in the presence of sulindac and oxidizing agents. Further studies are necessary to define the role of the combination of sulindac and oxidizing agent therapy in patients with AKs and skin cancer.

Mutational analysis of the simian immunodeficiency virus SIVmac nef gene

We are using site-directed mutagenesis of single viral genes to identify and analyze the genetic determinants of human and simian immunodeficiency virus pathogenicity. In a first approach, we have constructed a series of simian immunodeficiency virus SIVmac nef mutants by partial deletion and insertions in the nef gene, as this gene is a candidate gene for the establishment and maintenance of latency. nef insertion mutants replicated faster than wild-type SIVmac, suggesting that the nef gene product acts as a negative factor for replication. Surface phenotyping revealed that cultures permanently infected with nef mutants exhibit an enhanced expression of viral proteins on the outer cell surface. We have analyzed the properties of the mutant viruses in cell culture and intend to use rapidly replicating mutants (putatively unable to undergo latency) as model vaccine viruses in the rhesus monkey.

The quest for an AIDS vaccine: the state of the art and current challenges

Despite intense efforts worldwide, using state-of-the-art methods and techniques and despite ever-increasing knowledge about the molecular and structural make-up of HIV, a practical vaccine against acquired immunodeficiency syndrome (AIDS) has yet to be developed. The increasing use of recombinant DNA techniques and synthetic peptide technology has allowed many groups to identify at the epitope level the regions of HIV proteins which act as targets for (and stimulate) the immune response. Epitopes which stimulate and bind neutralizing antibodies have been examined in detail and an ever-increasing number of antibody-dependent cellular cytotoxicity (ADCC) and cytotoxic T lymphocytes (CTL) epitopes are being defined, as are potentially harmful (immunosuppressive or enhancing) domains. It still is not clear which of the different immune responses (or combinations thereof) it will be necessary to stimulate in order to protect from infection. Infected humans develop neutralizing antibodies, ADCC-inducing antibodies and CTL responses against a variety of viral proteins but it is not known which of these can control or prevent infection in vivo. The extensive knowledge of HIV and the immune response it elicits is being used to design and produce a wide variety of putative vaccines, ranging from whole inactivated virus, through recombinant organisms/proteins, to synthetic peptides although each has its inherent advantages and disadvantages. The very nature of HIV makes vaccine development difficult at best. However, recent successes using whole inactivated virus or virus-infected cells in the macaque simian immunodeficiency virus (SIVmac) model system at least show that protection against lethal lentivirus infection can be achieved.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of SV40 DNA replication by Rous sarcoma virus LTR enhancer

Simian virus 40 (SV40) late region recombinant constructs containing the Rous sarcoma virus (RSV) src gene along with RSV enhancer stimulated expression but completely abolished SV40 DNA replication. Constructs, in which the heterologous enhancer sequences were omitted, did replicate normally in African green monkey kidney cells and, in the presence of helper virus, gave rise to infectious progeny. Inhibition of SV40 DNA replication follows a cis-acting mechanism and is most likely due to a conformational change of the SV40 chromatin structure.

Coordinate regulation of polypeptide chain initiation and elongation in rabbit reticulocytes

Under normal conditions, reticulocytes synthesize alpha- and beta-globin polypeptides at equal rates. Incubation in the absence of hemin or under anoxia or hypertonic stress (100 mM excess NaCl) reduces the rate of protein synthesis to 30-50% of control levels. However, only hemin deprivation causes a reduction in polyribosome size and preferential inhibition of alpha-globin synthesis consistent with specific reduction in the rate of polypeptide chain initiation. Polyribosomal profiles are unaffected by anoxic or hypertonic stress and the ratio of alpha:beta globin synthesis remains close to unity. Measurement of ribosome transit time indicates that anoxic or hypertonic stress causes a decrease in the rate of polypeptide chain elongation that varies with the degree of inhibition of protein synthesis. Ribosomes isolated from stressed cells exhibit a reduced ability to bind 35S-met-tRNAf, suggesting that the ability to form initiation complexes is also impaired. These results suggest that reticulocytes, unlike nucleated cell lines, can coordinately reduce rates of initiation and elongation in response to certain physiological stresses.