Radiation protection of HepG2 cells by Podophyllum hexandrum Royale

Podophyllum hexandrum and its active constituents: Novel radioprotectants

Human exposure to radiation has expanded considerably in recent years, due to a wide range of medical, agricultural, and industrial applications. Despite its beneficial utilities, radiation is also known to have a deleterious effect on cells and tissues, largely through the creation of free radicals, which cause severe damage to biological systems through processes such as DNA double/single-strand fragmentation, protein modification, and upregulation of lipid peroxidation pathways. In addition, radiation damages genetic material while inducing hereditary genotoxicity. Developing measures to counter radiation-induced damage is thus considered to be of significant importance. Considering the inherent capability of plants to survive radiative conditions, certain plants and natural compounds have been the subject of investigations to explore and harness their natural radioprotective abilities. Podophyllum hexandrum, an Indian medicinal plant with several known traditional phytotherapeutic uses, is considered in particular to be of immense therapeutic importance. Recent studies have been conducted to validate its radioprotective potential alongside discovering its protective mechanisms following γ-radiation-induced mortality and disorder in both mice and human cells. These findings show that Podophyllum and its constituents/natural compounds protect the lungs, gastrointestinal tissues, hemopoietic system, and testis by inducing DNA repair pathways, apoptosis inhibition, free radical scavenging, metal chelation, anti-oxidation and anti-inflammatory mechanisms. In this review, we have provided an updated, comprehensive summary of ionizing radiations and their impacts on biological systems, highlighting the mechanistic and radioprotective role of natural compounds from Podophyllum hexandrum.

Prebiotic Mannan Oligosaccharide Pretreatment Improves Mice Survival Against Lethal Effects of Gamma Radiation by Protecting GI Tract and Hematopoietic Systems

Total body irradiation (TBI) results in critical injuries in a dose dependent manner that primarily damages highly proliferating tissues including hematopoietic stem cells (HSCs) and intestinal crypt stem cells etc. This may result in hematopoietic syndrome leading to bone marrow failure and gastrointestinal syndrome leading to chronic intestinal functional alterations. Death results from the gastrointestinal syndrome due to sepsis, bleeding, dehydration, and multi-system organ failure. We demonstrate that the prebiotic mannan oligosaccharide (MOS) pretreatment substantially prolongs survival in both male and female mice when administered 2 h prior to radiation either through oral or intraperitoneal route. The radioprotective efficacy of MOS was found to be age dependent and improves survival even in aged mice (12–13 months old). MOS pretreatment effectively abrogates radiation-induced hematopoietic injury and accelerates recovery of lymphocytes and WBCs and alleviates depletion of circulatory blood cells. Results also illustrate that MOS pretreatment abolishes crypt cell death and denudation of villi in comparison to the respective irradiated animals and ameliorates the overall radiation-induced damage to the GI system. MOS pretreatment facilitates intestinal recovery leading to enhanced animal survival demonstrating its protection efficacy against TBI induced mortality. Moreover, MOS pretreated animals show signs of accelerated recovery in terms of severity of radiation sickness symptoms including weight loss and completely abolish TBI associated mortality.

Mannan oligosaccharide requires functional ETC and TLR for biological radiation protection to normal cells

BACKGROUND

Low LET Ionizing radiation is known to alter intracellular redox balance by inducing free radical generation, which may cause oxidative modification of various cellular biomolecules. The extent of biomolecule-modifications/ damages and changes in vital processes (viz. cellular homeostasis, inter-/intra-cellular signaling, mitochondrial physiology/dynamics antioxidant defence systems) are crucial which in turn determine fate of cells.

RESULTS

In the present study, we expended TLR expressing (normal/ transformed) and TLR null cells; and we have shown that mannan pretreatment in TLR expressing normal cells offers survival advantage against lethal doses of ionizing radiation. On the contrary, mannan pretreatment does not offer any protection against radiation to TLR null cells, NKE ρ° cells and transformed cells. In normal cells, abrupt decrease in mitochondrial membrane potential and endogenous ROS levels occurs following treatment with mannan. We intend to irradiate mannan-pretreated cells at a specific stage of perturbed mitochondrial functioning and ROS levels to comprehend if mannan pretreatment offers any survival advantage against radiation exposure to cells. Interestingly, pre-irradiation treatment of cells with mannan activates NFκB, p38 and JNK, alters mitochondrial physiology, increases expression of Cu/ZnSOD and MnSOD, minimizes oxidation of mitochondrial phospholipids and offers survival advantage in comparison to irradiated group, in TLR expressing normal cells.

CONCLUSION

The study demonstrates that TLR and mitochondrial ETC functions are inevitable in radio-protective efficacy exhibited by mannan.

DRDO Herbal Technologies: Military and Civil Applications

The novel herbal technologies developed by India’s Defence Research and Development Organization are discussed with a view to improving the lives of soldiers and civilians. The life sciences laboratories of DRDO are engaged in R&D with the aim to develop processes, products and technologies and effective strategies to protect and enhance the operational efficiency of the Indian Armed Forces. Over the last five decades, the endeavours have resulted in creating specialized human capital through selection and training; enhancing efficiency through customized nutrition; optimizing human efficiency through traditional systems; optimizing performance through human engineering approach; protecting against health hazards like CBRN and vectors; reducing combat stress by counselling, training and resilience building; reinforcing adaptation through acclimatization processes and saving lives through life support systems. Several technologies with holistic and pragmatic applications for defence and civil sector from a herbal perspective are presented.

Appraisal of biochemical classes of radioprotectors: evidence, current status and guidelines for future development

The search for efficient radioprotective agents to protect from radiation-induced toxicity, due to planned or accidental radiation exposure, is still ongoing worldwide. Despite decades of research and development of widely different biochemical classes of natural and derivative compounds, a safe and effective radioprotector is largely unmet. In this comprehensive review, we evaluated the evidence for the radioprotective performance of classical thiols, vitamins, minerals, dietary antioxidants, phytochemicals, botanical and bacterial preparations, DNA-binding agents, cytokines, and chelators including adaptogens. Where radioprotection was demonstrated, the compounds have shown moderate dose modifying factors ranging from 1.1 to 2.7. To date, only few compounds found way to clinic with limited margin of dose prescription due to side effects. Most of these compounds (amifostine, filgratism, pegfilgrastim, sargramostim, palifermin, recombinant salmonella flagellin, Prussian blue, potassium iodide) act primarily via scavenging of free radicals, modulation of oxidative stress, signal transduction, cell proliferation or enhance radionuclide elimination. However, the gain in radioprotection remains hampered with low margin of tolerance. Future development of more effective radioprotectors requires an appropriate nontoxic compound, a model system and biomarkers of radiation exposure. These are important to test the effectiveness of radioprotection on physiological tissues during radiotherapy and field application in cases of nuclear eventualities.

Studies on radiation sensitization efficacy by silymarin in colon carcinoma cells

Recent reports demonstrated the role of silymarin as a cytoprotective agent for normal cells against ionizing or non-ionizing (UV) radiation, and in inhibiting the chemically initiated or promoted carcinogenesis in several malignancies, such as skin or prostate cancers. Silymarin is a plant flavonoid obtained from milk thistle; the main active principles in milk thistle are silybin (silibinin), sylichrisitin and silydianin, commonly referred as silymarin. In the present study, we aimed to investigate the radiation modulatory effects of silymarin on cancer cells. For this, we used the HCT-15 and RKO colon cancer cell lines as a model. Pre-irradiation treatment of cells with silymarin (20 mg/ml) followed by radiation exposure inhibits colon cancer cell proliferation and enhances cell death in a time-dependent manner. We have also examined the changes in p53 phosphorylation at Ser15, phosphorylation of p38 and their association with DNA damage. Silymarin was found to reduce proliferation of the human colon carcinoma cells in a concentration and time-dependent manner. Moreover, percentage of cell death was also increased in combined treatment (20µg/ml of silymarin + radiation). Our studies indicate that the combination increases the arrest of cells in G2/M phase of cell cycle, DNA damage-induced decrease in mitochondrial membrane potential (MMP) and a decrease of the reactive oxygen species (ROS) levels, which are associated with an increase in cell death. Altogether, these results suggest that silymarin sensitizes colon cancer cells to radiation, strategy with potential for colon cancer treatment. Noteworthy, since silymarin was previously shown to confer protection against radiation in at least some types of normal tissues, additional studies are needed to further investigate the potential of silymarin in colon cancer therapy when combined with radiation, its potential protective effects on normal tissues and its mechanisms of action.

NF-kB as a key player in regulation of cellular radiation responses and identification of radiation countermeasures

Nuclear factor (NF)-κB is a transcription factor that plays significant role in immunity, cellular survival and inhibition of apoptosis, through the induction of genetic networks. Depending on the stimulus and the cell type, the members of NF-κB related family (RelA, c-Rel, RelB, p50, and p52), forms different combinations of homo and hetero-dimers. The activated complexes (Es) translocate into the nucleus and bind to the 10bp κB site of promoter region of target genes in stimulus specific manner. In response to radiation, NF-κB is known to reduce cell death by promoting the expression of anti-apoptotic proteins and activation of cellular antioxidant defense system. Constitutive activation of NF-κB associated genes in tumour cells are known to enhance radiation resistance, whereas deletion in mice results in hypersensitivity to IR-induced GI damage. NF-κB is also known to regulate the production of a wide variety of cytokines and chemokines, which contribute in enhancing cell proliferation and tissue regeneration in various organs, such as the GI crypts stem cells, bone marrow etc., following exposure to IR. Several other cytokines are also known to exert potent pro-inflammatory effects that may contribute to the increase of tissue damage following exposure to ionizing radiation. Till date there are a series of molecules or group of compounds that have been evaluated for their radio-protective potential, and very few have reached clinical trials. The failure or less success of identified agents in humans could be due to their reduced radiation protection efficacy. In this review we have considered activation of NF-κB as a potential marker in screening of radiation countermeasure agents (RCAs) and cellular radiation responses. Moreover, we have also focused on associated mechanisms of activation of NF-κB signaling and their specified family member activation with respect to stimuli. Furthermore, we have categorized their regulated gene expressions and their function in radiation response or modulation. In addition, we have discussed some recently developed radiation countermeasures in relation to NF-κB activation

Podophyllum hexandrum-Mediated Survival Protection and Restoration of Other Cellular Injuries in Lethally Irradiated Mice

This study aims at the development of a safe and effective formulation to counter the effects of lethal irradiation. The sub-fraction (G-001M), prepared from Podophyllum hexandrum has rendered high degree of survival (>90%) at a dose of 6 mg kg(-1) body weight (intramuscular) in lethally irradiated mice. Therapeutic dose of G-001M, at about 20 times lower concentration than its LD(100), has revealed a DRF of 1.62. Comet assay studies in peripheral blood leukocytes have reflected that, treatment of G-001M before irradiation has significantly reduced DNA tail length (P < .001) and DNA damage score (P < .001), as compared to radiation-only group. Spleen cell counts in irradiated animals had declined drastically at the very first day of exposure, and the fall continued till the 5th day (P < .001). In the treated irradiated groups, there was a steep reduction in the counts initially, but this phase did not prolong. More than 60% decline in thymocytes of irradiated group animals was registered at 5 h of irradiation when compared with controls, and the fall progressed further downwards with the similar pace till 5th day of exposure (P < .001). At later intervals, thymus was found fully regressed. In G-001M pre-treated irradiated groups also, thymocytes decreased till the 5th day but thereafter rejuvenated and within 30 days of treatment the values were close to normal. Current studies have explicitly indicated that, G-001M in very small doses has not only rendered high survivability in lethally irradiated mice, but also protected their cellular DNA, besides supporting fast replenishment of the immune system.

Protection of mitochondrial system by Hippophae rhamnoides L. against radiation-induced oxidative damage in mice

The whole extract of the fresh berries of Hippophae rhamnoides L. (RH−3), which has been reported to provide protection to whole mice, various tissues, cells and cell organelles against lethal irradiation, was further investigated for its effects on mitochondria isolated from mouse liver. Superoxide anion, reduced (GSH) and oxidized glutathione (GSSG) levels, NADH-ubiquinone oxidoreductase (complex I), NADH-cytochrome c oxidoreductase (complex I/II), succinate-cytochrome c oxidoreductase (complex II/III), mitochondrial membrane potential (MMP), lipid peroxidation (LPx) and protein oxidation (PO) were determined for RH-3-mediated radioprotective manifestation. Pre-irradiation treatment of mice with RH-3 (30 mg kg−1, i.p.; single dose; −30 min) significantly inhibited the radiation-induced increase in superoxide anions, GSSG, thiobarbituric acid reactive substances (TBARS), complex I, complex I/III activity and MMP maximally at 4 h (P &lt; 0.05). This treatment inhibited the oxidation of proteins (P &lt; 0.05) at all the time periods studied here. This study suggests that pre-irradiation treatment of mice with RH-3 protects the functional integrity of mitochondria from radiation-induced oxidative stress.

Cytotoxic and radioprotective effects of Podophyllum hexandrum

Podophyllum hexandrum, a herb thriving in Himalayas has already been reported to exhibit antitumor and radioprotective properties. Present study was undertaken to unravel the possible mechanism responsible for the cytotoxic and radioprotective properties of REC-2001, a fraction isolated from the rhizome of P. hexandrum using murine peritoneal macrophages and plasmid DNA as model systems. Cell death, levels of intracellular reactive oxygen species (ROS) and apoptosis were studied employing trypan blue exclusion assay, dichlorofluorescein diacetate and DNA fragmentation assay, respectively. Superoxide anions, hydroxyl radicals and DNA damage were estimated following nitroblue tetrazolium, 2-deoxyribose degradation and plasmid DNA relaxation assays, respectively. Pre-irradiation administration of REC-2001 to peritoneal macrophages in the concentration range of 25-200μg/ml significantly reduced radiation induced ROS generation, DNA damage, apoptosis and cell killing in comparison to radiation control group indicating radioprotective potential. Studies with plasmid DNA indicated the ability of REC-2001 to inhibit 20Gy induced single and double strand breaks further supporting the antioxidative potential. However, REC-2001 in a dose-dependent fashion induced cell death, ROS and DNA fragmentation indicating the cytotoxic nature. REC-2001, in presence of 100μM copper sulfate, generated significant amount of hydroxyl radicals and superoxide anions indicating ability to act as a pro-oxidant in presence of metal ions. The superoxide anion generation was found to be sensitive to metal chelators like EDTA and deferoxamine mesylate (DFR). These results suggest that the ability of REC-2001 to act as a pro-oxidant in presence of metal ions and antioxidant in presence of free radicals might be responsible for cytotoxic and radioprotective properties.

Podophyllum hexandrum Offers Radioprotection by Modulating Free Radical Flux: Role of Aryl-Tetralin Lignans

We have evaluated the effect of variation in aryl-tetralin lignans on the radioprotective properties of Podophyllum hexandrum. Two fractionated fractions of P. hexandrum [methanolic (S1) and chloroform fractions (S2)], with varying aryl-tetralin lignan content were utilized for the present study. The peroxyl ion scavenging potentials of S1 and S2 were found to be comparable [i.e. 45.88% (S1) and 41% (S2)] after a 48 h interval in a time-dependent study, whereas in a 2 h study, S2 exhibited significant (P < 0.05) antioxidant activity in different metal ion + flux states. In the aqueous phase, S2 exhibited non-site-specific reactive oxygen species scavenging activity, i.e. 73.12% inhibition at 500 μg ml⁻¹. S1 exhibited 58.40 ± 0.8% inhibition (at 0.025 μg ml⁻¹) of the formation of reactive nitrite radicals, comparable to S2 (52.45 ± 0.825%), and also showed 45.01% site-specific activity (1000 μg ml⁻¹), along with significant (P < 0.05) electron donation potential (50–2000 μg ml⁻¹) compared to S2. Such activities of S1 could be attributed to the significantly (P < 0.05) higher levels of podophyllotoxin β-d-glucopyranoside (16.5 times) and demethyl podophyllotoxin glucoside (2.9 times) compared with S2. Together, these findings clearly prove that aryl-tetralin lignan content influences the radiation protective potential of the Podophyllum fractions to a great extent.

Zingiber officinale exhibits behavioral radioprotection against radiation-induced CTA in a gender-specific manner

At the organismic level, exposure to radiation can produce taste aversion (CTA) learning and emesis, which have been proposed as behavioral endpoints that are mediated by harmful effects of radiations on peripheral systems, primarily the gastrointestinal system. Thus, the aim of the present investigation was to study the gastroprotective action of hydroalcoholic extract of zingiber rhizome (Zingiber officinale Rosc.) against radiation-induced conditioned taste aversion (CTA) in both male and female species of animals, for testing its potential as a behavioral radioprotector. Administration of zingiber extract 1 h before 2-Gy gamma-radiation was significantly effective in blocking the saccharin avoidance response, with 200 and 250 mg/kg b.wt. i.p., being the most effective doses for male and female rats, respectively. A comparison of the efficacy of zingiber extract with two antiemetic drugs, ondansteron and dexamethasone, revealed that the extract rendered comparable protection against radiation-induced CTA. Our experiments also confirmed the existence of sex dichotomy (i.e., the sex of animal greatly influenced response towards radiation exposure) in relation to behavioral responses (CTA) or differential metabolism. The observed gender variations were hypothesized to be a result of hormonal fluctuations and differences in pharmacological parameters in male and female rats. To correlate the mechanism of action, the free-radical-scavenging potential of zingiber extract to scavenge hydroxyl ion and nitric oxide was also tested, in cell-free system and a concentration of 1000 microg/ml, was found to be the most potent, which has been proposed as one the many activities assisting in its overall ability to modulate radiation-induced taste aversion. The results demonstrate that Z. officinale possesses antioxidant, radioprotective and neuromodulatory properties that can be effectively utilized for behavioral radioprotection and for efficiently mitigating radiation-induced CTA in both males and females species.

The endophytic fungus Trametes hirsuta as a novel alternative source of podophyllotoxin and related aryl tetralin lignans

The aryl tetralin lignans are synthesized by Podophyllum sps. and are in great demand worldwide due to their use in synthesis of topoisomerase inhibitors. However, the sustained production of these aryl tetralin lignans requires large-scale harvesting from the natural environments, which has resulted in the plant-endangered status. In view of the difficulties in their total chemical synthesis, cultivation and failure of metabolic engineering approaches, there is a need to search for alternative sources of production of aryl tetralin lignans. We unequivocally established the methodology for isolation, identification, and characterization of a novel fungal endophyte (Trametes hirsuta) that produces aryl tetralin lignans consistently as shown by HPLC, LC-MS, LC/MS-MS and (1)H NMR. The lignans produced by the microorganism are biologically active, and exhibit potent antioxidant, anticancer and radioprotective properties. This strategy promises to improve the production of these therapeutically important compounds at lower costs.

Antioxidant activity of fractionated extracts of rhizomes of high-altitude Podophyllum hexandrum: Role in radiation protection

Whole extract of rhizomes of Podophyllum hexandrum has been reported earlier by our group to render whole-body radioprotection. High-altitude P. hexandrum (HAPH) was therefore fractionated using solvents of varying polarity (non-polar to polar) and the different fractions were designated as, n-hexane (HE), chloroform (CE), alcohol (AE), hydro-alcohol (HA) and water (WE). The total polyphenolic content (mg% of quercetin) was determined spectrophotometrically, while. The major constituents present in each fraction were identified and characterized using LC-APCI/MS/MS. In vitro screening of the individual fractions, rich in polyphenols and lignans, revealed several bioactivities of direct relevance to radioprotection e.g. metal-chelation activity, antioxidant activity, DNA protection, inhibition of radiation (250 Gy) and iron/ascorbate-induced lipid peroxidation (LPO). CE exhibited maximum protection to plasmid (pBR322) DNA in the plasmid relaxation assay (68.09% of SC form retention). It also showed maximal metal chelation activity (41.59%), evaluated using 2,2'-bipyridyl assay, followed by AE (31.25%), which exhibited maximum antioxidant potential (lowest absorption unit value: 0.0389 +/- 0.00717) in the reducing power assay. AE also maximally inhibited iron/ascorbate-induced and radiation-induced LPO (99.76 and 92.249%, respectively, at 2000 microg/ml) in mouse liver homogenate. Under conditions of combined stress (radiation (250 Gy) + iron/ascorbate), at a concentration of 2000 microg/ml, HA exhibited higher percentage of inhibition (93.05%) of LPO activity. HA was found to be effective in significantly (p < 0.05) lowering LPO activity over a wide range of concentrations as compared to AE. The present comparative study indicated that alcoholic (AE) and hydro-alcoholic (HA) fractions are the most promising fractions, which can effectively tackle radiation-induced oxidative stress.

Mitochondrial involvement in RP-1 mediated apoptosis in U 87 cells

The aqueous extract of RP-1, which rendered significant protection to whole body irradiated mice, was found to be tumoricidal. The mode of cytotoxic action of RP-1 attributing to its antitumor action was investigated in U 87 cells with special reference to mitochondrial contribution. RP-1 doses above 0.5 microg/ml reduced colonogenic survival (maximum reduction of 62% at 10 microg/ml) and increased the free radical generation, G2/M fraction and apoptotic frequency. Prolonged exposure to RP-1 rendered significant increase in mitochondrial mass. It also reduced mitochondrial membrane potential in a dose and time dependent manner that was restored by verapamil, a Ca+2 channel blocker. Mitochondrial anti-apoptotic proteins Bcl-2 and Hsp-70 levels were also reduced by RP-1 treatment in a dose and time dependent manner. The ability of RP-1 to disrupt mitochondrial structure and function could be responsible for its cytotoxic action.