Multiparameter Analysis of Clastogenic Factors, Pro-oxidant Cytokines, and Inflammatory Markers in HIV-1-Infected Patients with Asymptomatic Disease, Opportunistic Infections, and Malignancies

Developments in Neuroprotection for HIV-Associated Neurocognitive Disorders (HAND)

PURPOSE OF REVIEW

Reducing the risk of HIV-associated neurocognitive disorders (HAND) is an elusive treatment goal for people living with HIV. Combination antiretroviral therapy (cART) has reduced the prevalence of HIV-associated dementia, but milder, disabling HAND is an unmet challenge. As newer cART regimens that more consistently suppress central nervous system (CNS) HIV replication are developed, the testing of adjunctive neuroprotective therapies must accelerate.

RECENT FINDINGS

Successes in modifying cART regimens for CNS efficacy (penetrance, chemokine receptor targeting) and delivery (nanoformulations) in pilot studies suggest that improving cART neuroprotection and reducing HAND risk is achievable. Additionally, drugs currently used in neuroinflammatory, neuropsychiatric, and metabolic disorders show promise as adjuncts to cART, likely by broadly targeting neuroinflammation, oxidative stress, aerobic metabolism, and/or neurotransmitter metabolism. Adjunctive cognitive brain therapy and aerobic exercise may provide additional efficacy. Adjunctive neuroprotective therapies, including available FDA-approved drugs, cognitive therapy, and aerobic exercise combined with improved cART offer plausible strategies for optimizing the prevention and treatment of HAND.

Clastogenic Factors as Potential Biomarkers of Increased Superoxide Production

The formation of clastogenic factors (CF) and their damaging effects are mediated by superoxide, since superoxide dismutase is regularly protective. CF are produced via superoxide and stimulate the production of superoxide by monocytes and neutrophils. This results in a selfsustaining and longlasting process of clastogenesis, which may exceed the DNA repair system and ultimately lead to cancer (Emerit, 1994). An increased cancer risk is indeed observed in conditions accompanied by CF formation. These include irradiated persons, patients with chronic inflammatory diseases, HIV-infected persons and the chromosomal breakage syndromes ataxia telangiectasia, Bloom's syndrome and Fanconi's anemia. Biochemical analysis has identified lipid peroxidation products, arachidonic acid metabolites, nucleotides of inosine and cytokines, in particular tumor necrosis factor alpha, as the clastogenic and also superoxide stimulating components of CF. Due to their chromosome damaging effects, these oxidants can be detected with classical cytogenetic techniques. Their synergistic action renders the CF-test particularly sensitive for the detection of a pro-oxidant state. Correlations were observed between CF and other biomarkers of oxidative stress such as decreases in total plasma thiols or increases in TBARS or chemiluminescence. Correlations between CF and disease activity, between CF and radiation exposure, suggest the study of CF for monitoring these conditions. CF may also be useful as biochemical markers and intermediate endpoints for the evaluation of promising antioxidant drugs.

CF formation represents a link between chronic inflammation and carcinogenesis. Prophylactic use of superoxide scavengers as anticarcinogens is therefore suggested.

Bystander effects as manifestation of intercellular communication of DNA damage and of the cellular oxidative status

It is becoming increasingly clear that cells exposed to ionizing radiation (IR) and other genotoxic agents (targeted cells) can communicate their DNA damage response (DDR) status to cells that have not been directly irradiated (bystander cells). The term radiation-induced bystander effects (RIBE) describes facets of this phenomenon, but its molecular underpinnings are incompletely characterized. Consequences of DDR in bystander cells have been extensively studied and include transformation and mutation induction; micronuclei, chromosome aberration and sister chromatid exchange formation; as well as modulations in gene expression, proliferation and differentiation patterns. A fundamental question arising from such observations is why targeted cells induce DNA damage in non-targeted, bystander cells threatening thus their genomic stability and risking the induction of cancer. Here, we review and synthesize available literature to gather support for a model according to which targeted cells modulate as part of DDR their redox status and use it as a source to generate signals for neighboring cells. Such signals can be either small molecules transported to adjacent non-targeted cells via gap-junction intercellular communication (GJIC), or secreted factors that can reach remote, non-targeted cells by diffusion or through the circulation. We review evidence that such signals can induce in the recipient cell modulations of redox status similar to those seen in the originating targeted cell - occasionally though self-amplifying feedback loops. The resulting increase of oxidative stress in bystander cells induces, often in conjunction with DNA replication, the observed DDR-like responses that are at times strong enough to cause apoptosis. We reason that RIBE reflect the function of intercellular communication mechanisms designed to spread within tissues, or the entire organism, information about DNA damage inflicted to individual, constituent cells. Such responses are thought to protect the organism by enhancing repair in a community of cells and by eliminating severely damaged cells.

Search for clastogenic factors in the plasma of locally irradiated individuals

In studies reported in the 1960s and in several investigations since, plasma from irradiated individuals was shown to induce chromosomal aberrations when transferred into normal blood cultures. In the present study, the aim was to investigate the occurrence of these clastogenic factors (CF) using markers representing DNA damage produced in reporter lymphocytes that are treated with plasma from locally exposed individuals. Blood plasma was obtained from clinical patients with benign conditions before and after they had received radiation to small treatment volumes. Three patient groups were studied: (I) marginal resected basal cell carcinoma, (II) painful osteoarthritis of the knee, and (III) painful tendinitis of the elbow or the heel. Patients in each treatment group obtained the same fractionated treatment regimen, ranging from a total dose of 40 Gy (8 × 5 Gy, 2 factions/week) to a very small volume (1-3.5 cm³) in group I to a total dose of 6 Gy (6 × 1 Gy, 2 fractions/week) for groups II and III (treatment volumes 800-1150 cm³ and 80-160 cm³, respectively). The presence of CF in the plasma was investigated through cytogenetic (chromosomal aberrations, micronuclei) assays and kinetics of early DNA damage (γ-H2AX foci) in reporter cells. With the experimental settings applied, local radiation exposure had no apparent effect on the induction of CF in patient plasma; no deviations in chromosomal aberrations or micronucleus or focus induction were observed in reporter cells treated with postexposure plasma with respect to pre-exposure samples when the mean values of the groups were compared. However, there was a large interindividual variation in the plasma-induced DNA-damaging effects. Steroid treatment of patients was demonstrated to be the most influential factor affecting the occurrence of plasma factors; plasma from patients treated with steroids led to significant reductions of γ-H2AX foci and reduced numbers of chromatid aberrations in reporter cells. In addition to the locally exposed patients, newly obtained plasma samples from three radiological accident victims exposed in 1994 were examined. In contrast to the patient data, a significant increase in chromosomal aberrations was induced with plasma from two accident victims.

Clastogenic plasma factors: a short overview

A large number of studies have revealed that irradiated subjects produce soluble factors found in their blood plasma which, when transferred into cell cultures from non-irradiated individuals, show clastogenic (chromosome breaking) activity. Increased yields of chromatid-type aberrations have been characteristic in most of these studies. Exposed cohorts of various origins have revealed to possess this feature: from A-bomb survivors to patients treated with radiotherapy. It is apparent that the plasma factors are sustainable for long time periods. On the other hand, they seem to be produced very fast after exposure. Considerable variation in the effect has been found between individuals with similar radiation exposure. Further, the phenomenon is not restricted to irradiated populations. Clastogenic plasma has also been observed in patients with inflammatory diseases or congenital chromosome breakage syndromes as well in subjects exposed to other agents than ionizing radiation. Chromosomal aberration inducing substances have been detected not only in vivo, but also in vitro. A common feature to all the conditions is that they are associated with oxidative stress. Studies on the biochemical nature of the clastogenic factor(s) have been conducted, and tumor necrosis factor alpha and lipid peroxidation products, among others, have been suggested as good candidates. The relevance of the plasma factors to health effects remains open. The aim of the paper is to give a short overview on the phenomenon of clastogenic factors--their occurrence and formation as well as possible effectors.