Radiation-induced clastogenic factors: anticlastogenic effect of Ginkgo biloba extract

The copper-zinc superoxide dismutase activity in selected diseases

Copper-zinc superoxide dismutase (Cu,Zn-SOD) plays a protective role in various types of tissue protecting them from oxidative damage. Alterations in Cu,Zn-SOD (SOD1 and SOD3) activity and its expression have been observed in pathological occurrences most prevalent in modern society, including inflammatory bowel disease, obesity and its implications-diabetes and hypertension, and chronic obstructive pulmonary disease. Moreover, several SOD1 and SOD3 gene polymorphisms have been associated with the risk of developing a particular type of disease, or its exacerbation. This article features recent observations in this topic, aiming to show the importance of proper gene sequence and activity of Cu,Zn-SOD in the aforementioned diseases.

A historical and evolutionary perspective on the biological significance of circulating DNA and extracellular vesicles

The discovery of quantitative and qualitative differences of the circulating DNA (cirDNA) between healthy and diseased individuals inclined researchers to investigate these molecules as potential biomarkers for non-invasive diagnosis and prognosis of various pathologies. However, except for some prenatal tests, cirDNA analyses have not been readily translated to clinical practice due to a lack of knowledge regarding its composition, function, and biological and evolutionary origins. We believe that, to fully grasp the nature of cirDNA and the extracellular vesicles (EVs) and protein complexes with which it is associated, it is necessary to probe the early and badly neglected work that contributed to the discovery and development of these concepts. Accordingly, this review consists of a schematic summary of the major events that developed and integrated the concepts of heredity, genetic information, cirDNA, EVs, and protein complexes. CirDNA enters target cells and provokes a myriad of gene regulatory effects associated with the messaging functions of various natures, disease progression, somatic genome variation, and transgenerational inheritance. This challenges the traditional views on each of the former topics. All of these discoveries can be traced directly back to the iconic works of Darwin, Lamarck, and their followers. The history of cirDNA that has been revisited here is rich in information that should be considered in clinical practice, when designing new experiments, and should be very useful for generating an empirically up-to-date view of cirDNA and EVs. Furthermore, we hope that it will invite many flights of speculation and stimulate further inquiry into its biological and evolutionary origins.

Utilization of cytogenetic biomarkers as a tool for assessment of radiation injury and evaluation of radiomodulatory effects of various medicinal plants - a review

Systematic biological measurement of “cytogenetic endpoints” has helped phenomenally in assessment of risks associated with radiation exposure. There has been a surge in recent times for the usage of radioactive materials in health care, agriculture, industrial, and nuclear power sectors. The likelihood of radiation exposure from accidental or occupational means is always higher in an overburdened ecosystem that is continuously challenged to meet the population demands. Risks associated with radiation exposure in this era of modern industrial growth are minimal as international regulations for maintaining the safety standards are stringent and strictly adhered to, however, a recent disaster like “Fukushima” impels us to think beyond. The major objective of radiobiology is the development of an orally effective radio-modifier that provides protection from radiation exposure. Once available for mass usage, these compounds will not only be useful for providing selective protection against accidental and occupational radiation exposure but also help to permit use of higher doses of radiation during treatment of various malignancies curtailing unwarranted adverse effects imposed on normal tissues. Bio-active compounds isolated from natural sources enriched with antioxidants possess unique immune-modulating properties, thus providing a double edged benefit over synthetic radioprotectors. We aim to provide here a comprehensive overview of the various agents originating from plant sources that portrayed promising radioprotection in various experimental models with special emphasis on studies that used cytogenetic biomarkers. The agents will include crude extracts of various medicinal plants, purified fractions, and herbal preparations.

Effect of Butea monosperma leaf extracts on cyclophosphamide induced clastogenicity and oxidative stress in mice

Background:

Butea monosperma is a medium sized deciduous tree of family Fabaceae. It is widely used by rural people in India to cure many disorders. It possesses antioxidant and anticancer activity which is a prerequisite for anticlastogenic activity.

Objective:

To evaluate the effect of Butea monosperma leaf extracts on cyclophosphamide induced clastogenicity and oxidative stress in mice.

Materials and Methods:

The present study assessed the role of aqueous and ethanolic leaf extracts of B. monosperma (AQEBM and ETEBM) on cyclophosphamide (CP) induced oxidative stress and DNA damage in mice using micronucleus assay for anticlastogenic activity and biochemical estimation of malondialdehyde (MDA) and glutathione (GSH) for antioxidant activity. The frequency of the micronucleated erythrocytes and mitotic index was studied in peripheral blood and bone marrow after 24 and 48 h of clastogenic exposure.

Results:

CP treatment led to a significant (P < 0.001) increase in the frequency of micronuclei and decrease in the mitotic index (MI) in bone marrow and peripheral blood cells. Moreover, CP also significantly increased the lipid peroxidation as evidenced by an increase in the MDA content and decreased the antioxidant enzyme (GSH) in mice liver. Pretreatment with AQEBM and ETEBM reduced the frequency of micronuclei and increased the MI in the bone marrow and peripheral blood cells and also restored the MDA and GSH levels in mice liver.

Conclusion:

The AQEBM and ETEBM do contain compounds capable of inhibiting the CP induced oxidative stress and subsequent DNA damage in both the peripheral blood and bone marrow cells in mice.

Embryos of the zebrafish Danio rerio in studies of non-targeted effects of ionizing radiation

The use of embryos of the zebrafish Danio rerio as an in vivo tumor model for studying non-targeted effects of ionizing radiation was reviewed. The zebrafish embryo is an animal model, which enables convenient studies on non-targeted effects of both high-linear-energy-transfer (LET) and low-LET radiation by making use of both broad-beam and microbeam radiation. Zebrafish is also a convenient embryo model for studying radiobiological effects of ionizing radiation on tumors. The embryonic origin of tumors has been gaining ground in the past decades, and efforts to fight cancer from the perspective of developmental biology are underway. Evidence for the involvement of radiation-induced genomic instability (RIGI) and the radiation-induced bystander effect (RIBE) in zebrafish embryos were subsequently given. The results of RIGI were obtained for the irradiation of all two-cell stage cells, as well as 1.5 hpf zebrafish embryos by microbeam protons and broad-beam alpha particles, respectively. In contrast, the RIBE was observed through the radioadaptive response (RAR), which was developed against a subsequent challenging dose that was applied at 10 hpf when <0.2% and <0.3% of the cells of 5 hpf zebrafish embryos were exposed to a priming dose, which was provided by microbeam protons and broad-beam alpha particles, respectively. Finally, a perspective on the field, the need for future studies and the significance of such studies were discussed.

Phase II study of Ginkgo biloba in irradiated brain tumor patients: effect on cognitive function, quality of life, and mood

Ginkgo biloba has been reported to improve cognitive function in older adults and patients with Alzheimer's disease and multi-infarct dementia. We conducted an open-label phase II study of this botanical product in symptomatic irradiated brain tumor survivors. Eligibility criteria included: life expectancy ≥30 weeks, partial or whole brain radiation ≥6 months before enrollment, no imaging evidence of tumor progression in previous 3 months, or stable or decreasing steroid dose, and no brain tumor treatment planned while on study. The Ginkgo biloba dose was 120 mg/day (40 mg t.i.d.) for 24 weeks followed by a 6-week washout period. Assessments performed at baseline, 12, 24 (end of treatment), and 30 weeks (end of washout) included KPS, Functional Assessment of Cancer Therapy-Brain (FACT-Br), Profile of Mood States, Mini-Mental Status Exam, Trail Making Test Parts A (TMT-A) and B (TMT-B), Digit Span Test, Modified Rey Osterrieth Complex Figure (ROCF), California Verbal Learning Test Part II, and the F-A-S Test.

RESULTS

Of the 34 patients enrolled on study, 23 (68 %) completed 12 weeks of treatment and 19 (56 %) completed 24 weeks of treatment. There were significant improvements at 24 weeks in: executive function (TMT-B) (p = 0.007), attention/concentration (TMT-A) (p = 0.002), and non-verbal memory (ROCF-immediate/delayed recall) (p = 0.001/0.002), mood (p = 0.002), FACT-Br subscale (p = 0.001), and the FACT physical subscale (p = 0.003).

CONCLUSIONS

Some improvement in quality of life and cognitive function were noted with Ginkgo biloba. However, treatment with Ginkgo biloba was associated with a high dropout rate.

The effect of Ginkgo biloba extract on genotoxic damage in patients with differentiated thyroid carcinoma receiving thyroid remnant ablation with iodine-131

BACKGROUND

Radioiodine ((131)I) therapy is usually performed in patients with differentiated thyroid cancer (DTC). Although (131)I is generally considered safe, genotoxic damage has been demonstrated both in vivo and in vitro. The aim of the current study was to evaluate the effect of Ginkgo biloba extract (GBE) on the time-course of appearance, after (131)I therapy for DTC, of plasma factors with chromosome-damaging properties (so-called "clastogenic" factors [CFs]) and of micronuclei (MN) in lymphocytes.

METHODS

Twenty-three patients (median age 42 years, range 18-73) with DTC receiving (131)I activity (3.7 GBq) for thyroid remnant ablation were randomly assigned to receive GBE (120 mg/day for one month; n=10) or placebo (n=13) in a double-blind manner. Blood samples were taken at various intervals (from baseline to 90 days) after (131)I therapy. The frequency of MN in blood lymphocytes was determined, and CFs were assayed in plasma by a method that used MN increase in lymphocytes from an healthy donor as the endpoint of the assay.

RESULTS

MN in blood lymphocytes increased significantly after (131)I treatment in the placebo group, peaking at the 7th day (p=0.002) and slowly declining thereafter. In contrast, in similarly treated patients who were also treated with GBE both before and after (131)I treatment, a significant increase of blood lymphocyte MN level was not observed. In addition, only the placebo group showed a significant, progressive increase in CFs activity. This peaked at the 14th day (p=0.003 vs. baseline) and was still noted for the last plasma sample. The differences in the change in lymphocyte MN and CFs activity between the placebo and GBE-treated groups were significant (p<0.01 and p<0.05, respectively). Thyroid function tests, including serum thyroglobulin (Tg) and anti-Tg antibody levels, were never significantly different.

CONCLUSIONS

GBE may protect from possible oxidative and genotoxic damage associated with (131)I treatment in patients requiring (131)I therapy for thyroid cancer, without affecting the clinical outcome. Further studies with larger cohorts of patients are needed to confirm this report and verify the beneficial effect of GBE in patients requiring (131)I therapy, particularly for those in whom repeated treatments and high activities of (131)I are required.

Antioxidant activity and protecting health effects of common medicinal plants

Medicinal plants are traditionally used in folk medicine as natural healing remedies with therapeutic effects such as prevention of cardiovascular diseases, inflammation disorders, or reducing the risk of cancer. In addition, pharmacological industry utilizes medicinal plants due to the presence of active chemical substances as agents for drug synthesis. They are valuable also for food and cosmetic industry as additives, due to their preservative effects because of the presence of antioxidants and antimicrobial constituents. To commonly used medicinal plants with antioxidant activity known worldwide belong plants from several families, especially Lamiaceae (rosemary, sage, oregano, marjoram, basil, thyme, mints, balm), Apiaceae (cumin, fennel, caraway), and Zingiberaceae (turmeric, ginger). The antioxidant properties of medicinal plants depend on the plant, its variety, environmental conditions, climatic and seasonal variations, geographical regions of growth, degree of ripeness, growing practices, and many other factors such as postharvest treatment and processing. In addition, composition and concentration of present antioxidants, such as phenolic compounds, are related to antioxidant effect. For appropriate determination of antioxidant capacity, the extraction technique, its conditions, solvent used, and particular assay methodology are important.

Radioprotective Potential of Plants and Herbs against the Effects of Ionizing Radiation

Ionizing radiations produce deleterious effects in the living organisms and the rapid technological advancement has increased human exposure to ionizing radiations enormously. There is a need to protect humans against such effects of ionizing radiation. Attempts to protect against the deleterious effects of ionizing radiations by pharmacological intervention were made as early as 1949 and efforts are continued to search radioprotectors, which may be of great help for human application. This review mainly dwells on the radioprotective potential of plant and herbal extracts. The results obtained from in vitro and in vivo studies indicate that several botanicals such as Gingko biloba, Centella asiatica, Hippophae rhamnoides, Ocimum sanctum, Panax ginseng, Podophyllum hexandrum, Amaranthus paniculatus, Emblica officinalis, Phyllanthus amarus, Piper longum, Tinospora cordifoila, Mentha arvensis, Mentha piperita, Syzygium cumini, Zingiber officinale, Ageratum conyzoides, Aegle marmelos and Aphanamixis polystachya protect against radiation-induced lethality, lipid peroxidation and DNA damage. The fractionation-guided evaluation may help to develop new radioprotectors of desired activities.

Can the therapeutic gain of radiotherapy be increased by concurrent administration of Asian botanicals?

Therapeutic gain by radiotherapy can be achieved through improved targeting, selectively sensitizing malignant cells, or protecting normal tissue. The majority of synthetic chemical radiation sensitizers and normal tissue protectors have proved to be too toxic at effective clinical doses. However, Asian botanicals (from both Chinese and Ayurvedic medicine) are being evaluated for their ability to improve therapeutic gain through the modulation of reactive oxygen species. An increase in the efficacy of radiotherapy on tumor tissue allows a reduction in the dose applied to normal tissues. In addition, some botanicals may selectively protect normal tissue or increase its repair following radiation therapy. The results are promising enough to consider clinical trials.

Multiple factors conferring high radioresistance in insect Sf9 cells

Sf9, a lepidopteran cell line isolated from the fall armyworm, Spodoptera frugiperda, was shown to be significantly more resistant to growth inhibition and apoptosis induction effects of x-ray irradiation than several human cell lines of different origins. The single-cell electrophoresis technique revealed that Sf9 cells showed lower x-ray irradiation-induced DNA damage as well as better efficiency at repairing these damages. In addition, Sf9 cells were lower in both background and x-ray irradiation-induced intracellular oxidative stress, in which the higher intracellular level of reduced glutathione seemed to play a major role. The significance of oxidative stress in determining the radioresistance of Sf9 cells was confirmed by their being more resistant to hydrogen peroxide while equally susceptible to other non-reactive oxygen species of N-nitroso alkylating agents when compared with a human cell line. Although the Sf9 and human cell lines were equally susceptible to the lethal effects of N-nitroso alkylating agents, the components of DNA damage-induced and the repair enzymes involved significantly differ. This phenomenon is also discussed in this report.

Antimutagenic in vitro activity of plant polyphenols: Pycnogenol and Ginkgo biloba extract (EGb 761)

Ofloxacin (15 microg/mL) and acridine orange (5 microg/mL) induce mutagenicity by different mechanisms in the photosynthetic flagellate Euglena gracilis. The present study examined whether Pycnogenol (PYC; 5-100 microg/mL) or Ginkgo biloba extract (EGb 761; 5-100 microg/mL) could protect against the mutagenic effects of each of the mutagens and the potential mechanisms underlying such protection. The highest concentration of PYC and EGb 761 effectively reduced the mutagenic activity of both ofloxacin and acridine orange by more than 99% (p < 0.001). Using luminol-dependent photochemical methodology it was demonstrated that EGb 761 and PYC were effective antioxidants. In addition, as determined by spectrophotometry, PYC and EGb 761 bound acridine orange. Both PYC and EGb 761 have been shown to produce dual antimutagenic effects, as evidenced by both antioxidant and physicochemical properties. The findings suggest that EGb 761 and PYC would thus be suitable for future study, not only as antioxidants, but also as antimutagenic agents.

Actions of radiation on living cells in the "post-bystander" era

Over the past 20 years there has been increasing evidence that cells and the progeny of cells surviving a dose of ionizing radiation can exhibit a wide range of effects inconsistent with the level of dose received. Recently, the cause of these delayed effects has been ascribed to so-called bystander effects, occurring in cells not directly hit by an ionizing track, but which are influenced by signals from irradiated cells. These effects are not necessarily deleterious, although most of the literature deals with adverse delayed effects. What is important to consider is what, if anything, these effects mean for what is still the central dogma of radiobiology and radiation protection, i.e., that DNA double-strand breaks are the primary radiation-induced lesion that can be quantifiably related to received dose, and which determine the probability that a cancer will result from a radiation exposure. In this chapter we review the history of radiation biology which led to the DNA paradigm. We explore the issues and the evidence which are now challenging the view that dose deposition in DNA is all important. We conclude that in the low-dose region, the primary determinant of radiation exposure outcome is the genetic and epigenetic background of the individual and not the dose. This effectively dissociates dose from effect as a quantitative relationship, but it does not necessarily mean that the effect is unrelated to DNA damage somewhere in the system.

An adjunctive preventive treatment for cancer: Ultraviolet light and ginkgo biloba, together with other antioxidants, are a safe and powerful, but largely ignored, treatment option for the prevention of cancer

Cancer has surpassed heart disease as the leading cause of death in the United States. The mortality rate for cancer is high (roughly 42%), and it increases dramatically with increasing age, especially in patients between the ages of 40 and 60 years old. Currently, the efforts at cancer prevention have been minimal. The drugs developed so far are expensive and have serious side effects. There are at least 18 vitamin D-sensitive cancers. Ultraviolet light, and specifically ultraviolet B (UVB), could reduce cancer by the limited exposure of suitable skin areas to UVB of an intensity and duration insufficient to produce skin cancer. An irrational fear of skin cancer is preventing this idea from being implemented. Though skin cancer incidence is significant, mortality from skin cancer is relatively rare. Roughly 1,000,000 Americans will be affected by skin cancer but only 10,000 deaths are expected in 2005 (a 1% mortality rate). Skin cancer is easily detected and often cured by excisional biopsy alone. Current practice among practicing clinicians is to use a prescription drug substitute for UV light, calcitriol (1-25 dihydroxycholcalciferol). However, high levels of (calcitriol) are dangerous, and there is no consensus on just what a high dose or a safe dose is. Apart from skin cancer, UV light exposure possesses few risks. Additionally, a number of botanical agents such as ginkgo biloba, vitamins E and C, carotenoids, selenium and proanthocyanidins can prevent the risk of skin cancer. Ginkgo biloba also possess the following additional cancer chemopreventive qualities: (1) promoting apoptosis of cancer cells; (2) an anti-clastogenic effect on chromosomes by repairing and reconstituting broken and damaged chromosomes; (3) a powerful therapeutic effect on the treatment of fibrosis-related cancer; (4) a therapeutic effect on free radical-induced cancer; (5) a therapeutic effect on the treatment of cancer incident to the result of numerous carcinogens; (6) a therapeutic effect on preventing free radical-induced cancer; (7) an enhancing effect on radiation therapy in the treatment of cancer; and (8) a therapeutic effect on reducing the size of cancer tumors. Ginkgo biloba is widely-used and has few adverse effects. The proposed preventive treatment for cancer consists of short intermittent exposure of the least sensitive areas of the body to sunlight and/or artificial ultraviolet light. The routine testing of plasma vitamin D levels help monitor the effectiveness of the treatment and periodic checkups with a dermatologist help monitor the safety.

Zingiber officinale Rosc. modulates gamma radiation-induced conditioned taste aversion

The aim of the present study was to investigate the neurobehavioral protective efficacy of a hydroalcoholic extract of ginger (Zingiber officinale Rosc.) in mitigating gamma radiation-induced conditioned taste aversion in Sprague-Dawley rats. Administration of Zingiber extract 1 h before 2-Gy gamma irradiation was effective in blocking the saccharin avoidance response for 5 post-treatment observational days, both in a dose- and time-dependent manner, with 200 mg/kg b.w. i.p. being the most effective dose. Highest saccharin intake in all the groups was observed on the fifth post-treatment day. The potential of ginger extract to inhibit lipid peroxidation induced by radiation (2 Gy) and ascorbate-ion stress in brain homogenate and its ability to scavenge highly reactive superoxide anions were evaluated. The 1000-microg/ml and 2000-microg/ml concentration of ginger extract showed the highest efficiency in scavenging free radicals and in inhibiting lipid peroxidation. The lipid peroxidation and superoxide-anion scavenging ability of the extract further supports its radioprotective properties. The results clearly establish the neurobehavioral efficacy of ginger extract and the antioxidant properties appear to be a contributing factor in its overall ability to modulate radiation-induced conditioned taste aversion. Ginger extract has tremendous potential for clinical applications in mitigation of radiation-induced emesis in humans.

Radioprotection by plant products: present status and future prospects

The development of radioprotective agents has been the subject of intense research in view of their potential for use within a radiation environment, such as space exploration, radiotherapy and even nuclear war. However, no ideal, safe synthetic radioprotectors are available to date, so the search for alternative sources, including plants, has been on going for several decades. In Ayurveda, the traditional Indian system of medicine, several plants have been used to treat free radical-mediated ailments and, therefore, it is logical to expect that such plants may also render some protection against radiation damage. A systematic screening approach can provide leads to identifying potential new candidate drugs from plant sources, for mitigation of radiation injury. This article reviews some of the most promising plants, and their bioactive principles, that are widely used in traditional systems of medicine, and which have rendered significant radioprotection in both in vitro and in vivo model systems. Plants and their constituents with pharmacological activities that may be relevant to amelioration of radiation-mediated damage, including antiemetic, antiinflammatory, antioxidant, cell proliferative, wound healing and haemopoietic stimulatories are also discussed.

The effect of Ginkgo biloba in isolated ischemic/reperfused rat heart: a link between vitamin E preservation and prostaglandin biosynthesis

The effect of Ginkgo biloba extract (EGb 761) was studied in rat hearts submitted to ischemia/reperfusion. Isolated hearts perfused in Langendorff mode were subjected to 60 minutes of global ischemia and 15 minutes of reperfusion. EGb 761 was administered by chronic or acute treatment: intra-peritoneal injections of 5 mg/Kg extract for 5 days, or 100 mg /L extract addition to the perfusion buffer, respectively. In hearts not treated with EGb 761, ischemia induced a 20% decrease in the concentration of membrane alpha-tocopherol. This effect was not worsened by reperfusion. alpha-tocopherol consumption was accompanied by about 650% increase in 6-ketoPGF1alpha release within 3 minutes of reperfusion. Moreover, ischemia induced activation of transcription factor NF-kappaB, as compared with the untreated group. In both chronic and acute treatment with EGb 761, heart concentration of alpha-tocopherol was completely spared during ischemia as much as after reperfusion, and a significant decrease of 6-ketoPGF1alpha release was observed at 3 minutes of reperfusion. Nuclear translocation of NF-kappaB was lowered during ischemia. EGb 761 might act as direct free radical scavenger or as tocopheryl radical recycler; in both cases sparing membrane vitamin E should affect phospholipase A2 activity. Finally, EGb 761, by lowering ROS produced during ischemia, challenges nuclear translocation of NF-kappaB.

Oxidative metabolism, gap junctions and the ionizing radiation-induced bystander effect

Evidence accumulated over the past two decades has indicated that exposure of cell populations to ionizing radiation results in significant biological effects occurring in both the irradiated and nonirradiated cells in the population. This phenomenon, termed the 'bystander response', has been shown to occur both in vitro and in vivo and has been postulated to impact both the estimation of risks of exposure to low doses/low fluences of ionizing radiation and radiotherapy. Several mechanisms involving secreted soluble factors, oxidative metabolism and gap-junction intercellular communication have been proposed to regulate the radiation-induced bystander effect. Our current knowledge of the biochemical and molecular events involved in the latter two processes is reviewed in this article.

Ginkgo biloba extracts and cancer: a research area in its infancy

Recent studies conducted with various molecular, cellular and whole animal models have revealed that leaf extracts of Ginkgo biloba may have anticancer (chemopreventive) properties that are related to their antioxidant, anti-angiogenic and gene-regulatory actions. The antioxidant and associated anti-lipoperoxidative effects of Ginkgo extracts appear to involve both their flavonoid and terpenoid constituents. The anti-angiogenic activity of the extracts may involve their antioxidant activity and their ability to inhibit both inducible and endothelial forms of nitric oxide synthase. With regard to gene expression, a Ginkgo extract and one of its terpenoid constituents, ginkgolide B, inhibited the proliferation of a highly aggressive human breast cancer cell line and xenografts of this cell line in nude mice. cDNA microarray analyses have shown that exposure of human breast cancer cells to a Ginkgo extract altered the expression of genes that are involved in the regulation of cell proliferation, cell differentiation or apoptosis, and that exposure of human bladder cancer cells to a Ginkgo extract produced an adaptive transcriptional response that augments antioxidant status and inhibits DNA damage. In humans, Ginkgo extracts inhibit the formation of radiation-induced (chromosome-damaging) clastogenic factors and ultraviolet light-induced oxidative stress - effects that may also be associated with anticancer activity. Flavonoid and terpenoid constituents of Ginkgo extracts may act in a complementary manner to inhibit several carcinogenesis-related processes, and therefore the total extracts may be required for producing optimal effects.

Biologic damage resulting from exposure to tobacco smoke and from radon: implication for preventive interventions

Cigarette smoking and residential radon are, respectively, the first and second leading cause of lung cancer in the United States today. Of the approximately 157 000 lung deaths occurring in 2000, approximately 90% can be attributed to cigarette smoking and 30% of the lung cancer deaths among non-smokers can be attributed to residential radon exposure. Although dwarfed by cigarette related lung cancer, lung cancer among lifetime non-smokers is a leading cause of death in the United States, and many other countries, accounting for approximately 16 000 deaths per year in the US. Laboratory studies and epidemiological investigations, particularly those conducted in the past decade, are yielding evidence that tobacco smoke and radon may share important elements of lung cancer's pathologic mechanism(s). Lung cancer prevention among smokers, ex-smokers and lifetime nonsmokers can be enhanced as we learn more about the etiologic mechanism(s) of lung cancer resulting from these and other exposures including diet, non-malignant respiratory diseases, occupational exposures, and susceptibility-gene. In this article we review both laboratory and epidemiologic data that gives insight into the biologic damage done to the lung from these exposures.

Inhibitory effect of herbal remedies on 12-O-tetradecanoylphorbol-13-acetate-promoted Epstein-Barr virus early antigen activation

For the past several years we have been evaluating natural products as potential cancer chemopreventive agents in a short term in vitro assay involving Epstein--Barr virus early antigen (EBV-EA) activation in Raji cells promoted by phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA). Because of the current interest in the use of herbal remedies, we considered examining them for their cancer chemopreventive activities, using their extracts with a view to uncovering such benefits (if any) these remedies might possess. Thirty-six extracts of 32 herbs belonging to 27 families in use as herbal remedies including those of gingko, black cohosh, echinacea, kava-kava, saw palmetto, turmeric, angelica, wild yam, cat's claw, passion flower, muira puama, feverfew, blueberry, chasteberry, licorice, nettle, golden seal, pygeum, ginger, valerian and hops were prepared and evaluated. Turmeric at a concentration of 10 microg x ml (-1)exhibited the most potent anti-EBV-EA activity, which is ten times more than passionflower, that is next in the order of activity. At the concentration level of 100 microg ml (-1), several of the herbal remedies tested inhibited the EBV-EA in Raji cells exposed to the tumor promoter TPA (32 pM) by more than 90%. We also report for the first time the activities of 16 new medicinal plants as potential cancer chemopreventive agents. Since inhibitors of EBV-EA promoted by TPA in vitro have been shown to be effective anti-tumor promoting agents in laboratory animal models, our results indicate new and potential applications of these herbal remedies as cancer chemopreventive agents since they are already in clinical use in the human population.

Radiation-induced bystander effects: past history and future directions

There has been a recent upsurge of interest in the phenomenon now known as radiation-induced bystander effects. This is largely due to the increased awareness of the contribution of indirect and delayed effects, such as genomic instability, to cellular outcomes after low-dose exposures. It is also due to the availability of tools such as the microbeam and advanced cell culture systems and to the ability to study end points such as gene or protein expression at low doses which were previously difficult to study. This review looks at the history of bystander effects in the earlier literature, in which the clastogenic effect of plasma from irradiated patients was well known. The effect was known to persist for several years and to cause transgenerational effects, making it similar to what we now call genomic instability. The review then examines the current data and controversies which are now beginning to resolve the questions concerning the mechanisms underlying the induction and transmission of both bystander effects and genomic instability. Finally, the possible impact of data concerning radiation-induced bystander effects on radiotherapy and radiation protection is discussed.

DNA damage evaluated by alkaline single cell gel electrophoresis (SCGE) in children of Chernobyl, 10 years after the disaster

Using the alkaline single cell gel electrophoresis (Comet) assay, the extent of DNA damage was evaluated in leukocytes of 43 Belarussian children (16 healthy and 27 affected by thyroid cancer). Thirty-nine healthy children from Pisa (Italy) were enrolled in the study as controls. In addition to basal levels of DNA damage, leukocytes were treated in vitro with bleomycin (BLM), a radiomimetic drug, to evaluate a possible adaptive response in different groups of children. Results with the Comet assay indicated an increased level of DNA damage (P=0.037) in leukocytes of Belarussian children compared to the Italian control group. In addition, within the Belarus group, lower basal levels of DNA damage (P<0.001) were found in children with cancer compared to healthy children. Tumor affected children were living in less radiocontaminated areas (P<0.04) than the healthy children and there was a significant relationship (P=0.03) between the amount of environmental radiocontamination and DNA damage in leukocytes. There were no differences in the sensitivity of leukocytes from different groups of children to BLM, indicating the absence of an adaptive response. The lack of an adaptive response may have been due to the use of noncycling cells and/or the bleomycin dose chosen. Tests for the presence of clastogenic factors (CF) in the blood serum of children showed that 39% of the tumor affected children and 19% of the healthy children in the exposed group were positive as compared to the Italian control group (0%) (Chi-square test, P<0.04). The higher levels of genomic damage in children evaluated 10 years after the Chernobyl disaster could be related to the increased incidence of individuals with CF.

A threshold concept for cancer therapy

Oxygen free radicals have been implicated in many disease processes, including aging and carcinogenesis, and have been associated with a variety of complications resulting from the treatment of cancer. As a result, the treatment of free radical-induced disease with antioxidants or free radical scavengers has become an important therapeutic modality. Ironically, these same oxygen free radicals also play a critical role in anti-cancer therapies. The use of antioxidants such as superoxide dismutase (SOD), in this setting, has been found to decrease the efficacy of anti-tumor therapies, which depend on free radical generation for their action. In addition, increased antioxidant activity can often be utilized by the tumor cell to favor increased growth. Therefore, the appropriate application of oxygen free radicals and antioxidants seems to be critically important in designing proper strategies for both prevention and treatment of malignant disorders. This review will summarize free radical and antioxidant regimens that have been employed to date, examine some of the problems associated with these regimens, introduce the 'threshold concept' explaining the dual effects of oxygen free radicals and antioxidants, and discuss a novel hypothesis regarding therapy that could potentially improve outcome in cancer patients.

Potential role for Ginkgo biloba extract in the treatment of glaucoma

Glaucoma is becoming recognized as a condition for which not only elevated intraocular pressure, but also non-pressure-dependent risk factors are responsible. New avenues of treatment into which investigations are being initiated include agents which could possibly improve blood flow to the eye and neuroprotective drugs. Only calcium channel blockers are presently available for such treatment in glaucoma, and these have not been widely adopted, in contrast to clinical trials involving a number of neuroprotectants in other neurologic disorders. Ginkgo biloba extract is freely available and has several biological actions which combine to make it a potentially important agent in the treatment of glaucoma: improvement of central and peripheral blood flow, reduction of vasospasm, reduction of serum viscosity, antioxidant activity, platelet activating factor inhibitory activity, inhibition of apoptosis, and inhibition of excitotoxicity. The effect of Ginkgo biloba extract as a potential antiglaucoma therapy deserves intensive scrutiny.

Anticlastogenic effects of Ginkgo biloba extract (EGb 761) and some of its constituents in irradiated rats

In a previous study we reported that radiation-induced clastogenic factors (CF) are found in the plasma of Chernobyl accident recovery workers and that their chromosome damaging effects are inhibited by antioxidant treatment with a Ginkgo biloba extract (EGb761). In the present study, we induced CF in rats with a radiation dose of 4.5 Gy. The protective effects of the complete extract were compared to those obtained with the extract devoid of its terpene fraction (CP205), with isolated ginkgolides A+B and bilobalide at the concentrations present in EGb761. The pretreatment samples were taken at day 22 postirradiation, the posttreatment samples the day following arrest of the 3-week treatment. The adjusted clastogenic score (ACS) were reduced from 11.71+/-3.55 to 2.00+/-2.83 after treatment with 100 mg/kg and from 13.43+/-2.23 to 4.29+/-2.14 with 50 mg/kg of the complete extract (p<0.0001). Similar protective effects were observed with CP205, ginkgolides and bilobalide (p<0. 001), while the reduction of ACS in placebo-treated rats was not statistically significant (12.80+/-1.79 and 9.20+/-2.68). However, if the efficacy of the treatment was compared to placebo, only the complete extract was significantly protective. While all components exerted anticlastogenic effects at the concentrations present in the complete extract, the comparison of the different groups by analysis of variance did not reveal significant differences. This may be due to to the small number of animals available in each treatment group. The complete extract reduced the ACS by 83% at the dose of 100 mg/kg, while the lower dose of 50 mg/kg and the three components reached only 66%-68% reduction. The better protection provided by the complete extract is due to synergistic rather than to additive effects.

Antioxidant inhibitors for cancer therapy

Built-in cellular defense mechanisms play a major role in a tumor's protection against non-surgical antineoplastic therapies. Of these, the overexpression of antioxidants such as superoxide dismutase (SOD) may be the most important. Oxygen radicals are highly toxic, and have been implicated in various diseases, including carcinogenesis and aging. They produce a variety of pathological changes through lipid peroxidation and DNA damage. Therefore, treating free-radical-induced diseases with antioxidants has been an accepted therapeutic approach. Ironically, however, the underlying mechanism that most chemotherapeutic agents and ionizing radiation exert on tumor cell kill is not increased antioxidation but rather the production of more free radicals leading to irreversible tissue injury. A small increase in reactive oxygen species (ROS) following non-surgical antineoplastic therapies induces the expression of antioxidants such as SOD, but overproduction of ROS, conversely, exhausts the production of SOD and other adaptive antioxidant defenses. Based on these considerations, we hypothesize that the appropriate administration of antioxidant inhibitors and/or free-radical-generating compounds may be a useful strategy in the treatment of solid tumors.

A new mechanism for DNA alterations induced by alpha particles such as those emitted by radon and radon progeny

The mechanism(s) by which alpha (alpha) particles like those emitted from inhaled radon and radon progeny cause their carcinogenic effects in the lung remains unclear. Although direct nuclear traversals by alpha-particles may be involved in mediating these outcomes, increasing evidence indicates that a particles can cause alterations in DNA in the absence of direct hits to cell nuclei. Using the occurrence of excessive sister chromatid exchanges (SCE) as an index of DNA damage in human lung fibroblasts, we investigated the hypothesis that alpha-particles may induce DNA damage through the generation of extracellular factors. We have found that a relatively low dose of alpha-particles can result in the generation of extracellular factors, which, upon transfer to unexposed normal human cells, can cause excessive SCE to an extent equivalent to that observed when the cells are directly irradiated with the same irradiation dose. A short-lived, SCE-inducing factor(s) is generated in alpha-irradiated culture medium containing serum in the absence of cells. A more persistent SCE-inducing factor(s), which can survive freeze-thaw and is heat labile is produced by fibroblasts after exposure to the alpha-particles. These results indicate that the initiating target for alpha-particle-induced genetic changes can be larger than a cell's nucleus or even a whole cell. How transmissible factors like those observed here in vitro may extend to the in vivo condition in the context of a-particle-induced carcinogenesis in the respiratory tract remains to be determined.

Clastogenic factors in the plasma of children exposed at Chernobyl

Clastogenic factors (CFs), as they were described previously in accidentally or therapeutically irradiated persons, in A-bomb survivors and in liquidators of the Chernobyl nuclear power plant, were also detected in the plasma of Chernobyl-exposed children. A high percentage of plasma ultrafiltrates from 170 children, immigrated to Israel in 1990, exerted clastogenic effects in test cultures set up with blood from healthy donors. The differences were highly significant in comparison to children immigrated from 'clean' cities of the former Soviet Union or children born in Israel. The percentage of CF-positive children and the mean values of the adjusted clastogenic scores (ACS) were higher for those coming from Gomel and Mozyr, which are high exposure sites (IAEA measurements), compared to those coming from Kiev. There was no correlation between residual 137-Caesium body burden and presence of CFs. However, both measurements were not done at the same time (in 1990 and 1992-1994, respectively). Also no relationship could be revealed between enlargement of the thyroid gland and CF-positivity. CFs are not only observed after irradiation, but in a variety of chronic inflammatory diseases with autoimmune reactions. They were also described in the congenital breakage syndromes, which are hereditary diseases with the highest cancer incidence in humans. Whether the clastogenic effects continuously produced by circulating CFs represent a risk factor for malignant late effects deserves further study and follow-up. Since CF formation and CF action are mediated by superoxide radicals, prophylactic treatment with antioxidants may be suggested for Chernobyl-exposed children, whose plasma induces a strongly positive CF-test.

Clastogenic factors in plasma of HIV-1 infected patients activate HIV-1 replication in vitro: inhibition by superoxide dismutase

The frequent neoplastic disorders present in HIV-infected patients and the implication of oxidative stress in AIDS-Kaposi's sarcoma pathogenesis prompted us to study whether the mechanisms implicated in genotoxic effects of clastogenic factors (CFs) (i.e., chromosome damaging materials released by cells under conditions of oxidant stress) can play a role in HIV-1 expression and whether exogenous superoxide dismutase can inhibit the clastogenic and HIV-inducing effects of CFs. CFs were found in the plasma of all HIV-1 infected patients (n = 21) of this study group, in asymptomatic (CDC II) as well as in symptomatic patients (CDC IV). In addition to their chromosome damaging effect, CFs are able to upregulate HIV-1 expression in U1 cells and in PBMCs activated with PHA and IL2 at all time points (p < .05). Their formation, therefore, is an early event in the disease. It occured despite antiviral medication in these patients. Superoxide dismutase inhibited the clastogenic and the viral inducing effects (p < .05). On the basis of our findings, association of SOD mimetics or superoxide scavengers with antiviral drugs may be a new therapeutic approach. This polytherapy, if started early enough after infection, may prolong the latency period and limit the emergence of drug-resistant viral strains.