Podophyllum hexandrum modulates gamma radiation-induced immunosuppression in Balb/c mice: Implications in radioprotection

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.

Podophyllotoxin and Rutin Modulate M1 (iNOS+) Macrophages and Mitigate Lethal Radiation (LR) Induced Inflammatory Responses in Mice

Accidental exposure to lethal doses of Gamma radiation leads to the systemic inflammatory syndrome which causes mortality. In view of this, management of hemopoietic syndrome by modulating pro-inflammatory response in clinically manageable time period seems to be the most appropriate strategy for encountering radiation induced damage and recovery. As both tissue and peripheral macrophages are critical for the management of radiation induced injuries, we have unraveled the immunomodulatory potential of radioprotective formulation (G-003M) on peripheral macrophages populations in this study. G-003M inhibited lethal radiation induced NO and Th1 effector cytokines in the exposed macrophages indicating its M1 dim polarizing capacity. In similar lines, conditioning of mice with G-003M before lethal irradiation (LR) inhibited LR induced titre of Th1 effector cytokines in both serums as well as in lung, small intestine, and spleen tissue confirming its immunomodulatory potential. G-003M potentially down modulated inflammatory response in LPS induced inflammatory model and enhanced M2 polarization of iNOS+ M1 effector macrophages providing a molecular hint on G-003M mechanism of action on macrophages. These observations revealed that G-003M potentially modulate pro-inflammatory programming of macrophages and mitigate radiation-induced inflammatory stress which is believed to contribute significantly to radioprotective attribute of G-003M. In this study, we demonstrate that Rutin and Podophyllotoxin drive M1^dim/M2 polarization of LR primed macrophages apart from protecting DNA from radiation. These drugs have the capacity to programme innate immune cells like macrophages which may be involved in homeostasis during recovery.

Therapeutic potential of natural plant products and their metabolites in preventing radiation enteropathy resulting from abdominal or pelvic irradiation

Radiation-induced gastrointestinal injury or radiation enteropathy is an imminent risk during radiation therapy of abdominal or pelvic tumors. Despite remarkable technological advancements in image-guided radiation delivery techniques, the risk of intestinal injury after radiotherapy for abdominal or pelvic cancers has not been completely eliminated. The irradiated intestine undergoes varying degrees of adverse structural and functional changes, which can result in transient or long-term complications. The risk of development of enteropathy depends on dose, fractionation, and quality of radiation. Moreover, the patients' medical condition, age, inter-individual sensitivity to radiation and size of the treatment area are also risk factors of radiation enteropathy. Therefore, strategies are needed to prevent radiotherapy-induced undesirable alteration in the gastrointestinal tract. Many natural plant products, by virtue of their plethora of biological activities, alleviate the adverse effects of radiation-induced injury. The current review discusses potential roles and possible mechanisms of natural plant products in suppressing radiation enteropathy. Natural plant products have the potential to suppress intestinal radiation toxicity.

Phloroglucinol protects small intestines of mice from ionizing radiation by regulating apoptosis-related molecules: a comparative immunohistochemical study

Phloroglucinol (PG) is a phenolic compound isolated from Ecklonia cava, a brown algae abundant on Jeju island, Korea. Previous reports have suggested that PG exerts antioxidative and cytoprotective effects against oxidative stress. In this study, we confirmed that PG protected against small intestinal damage caused by ionizing radiation, and we investigated its protective mechanism in detail. Regeneration of intestinal crypts in the PG-treated irradiated group was significantly promoted compared with that in irradiated controls. The expression level of proapoptotic molecules such as p53, Bax, and Bak in the small intestine was downregulated and that of antiapoptotic molecules such as Bcl-2 and Bcl-X(S/L) was augmented in the PG-treated group. On histological observation of the small intestine, PG inhibited the immunoreactivity of p53, Bax, and Bak and increased that of Bcl-2 and Bcl-X(S/L). These results demonstrate the protective mechanisms of PG in mice against intestinal damage from ionizing radiation, providing the benefit of raising the apoptosis threshold of jejunal crypt cells.

Hydrogen-rich saline protects immunocytes from radiation-induced apoptosis

Background

Radiation often causes depletion of immunocytes in tissues and blood, which results in immunosuppression. Molecular hydrogen (H₂) has been shown in recent studies to have potential as a safe and effective radioprotective agent through scavenging free radicals. This study was designed to test the hypothesis that H₂ could protect immunocytes from ionizing radiation (IR).

Material/Methods

H₂ was dissolved in physiological saline or medium using an apparatus produced by our department. A 2-[6-(4′-hydroxy) phenoxy-3H-xanthen-3-on-9-yl] benzoate (HPF) probe was used to detect intracellular hydroxyl radicals (•OH). Cell apoptosis was evaluated by annexin V-FITC and Propidium iodide (PI) staining as well as the caspase 3 activity. Finally, we examined the hematological changes using an automatic Sysmex XE 2100 hematology analyzer.

Results

We demonstrated H₂-rich medium pretreatment reduced •OH level in AHH-1 cells. We also showed H₂ reduced radiation-induced apoptosis in thymocytes and splenocytes in living mice. Radiation-induced caspase 3 activation was also attenuated by H₂ treatment. Finally, we found that H₂ rescued the radiation-caused depletion of white blood cells (WBC) and platelets (PLT).

Conclusions

This study suggests that H₂ protected the immune system and alleviated the hematological injury induced by IR.

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.

Acidic polysaccharide of Panax ginseng as a defense against small intestinal damage by whole-body gamma irradiation of mice

An acidic polysaccharide of Panax ginseng (APG), ginsan, has been reported to protect the hematopoietic system by increasing the number of bone marrow cells and spleen cells. Therefore, we evaluated the ability of APG to protect mice from radiation-induced damage of the small intestine. APG treatment caused the lengthening of villi and a numerical increase of crypt cells in the small intestine at 3.5 days after 7Gy irradiation compared to irradiated, non-treated controls. In addition, APG significantly inhibited irradiation-induced apoptosis by decreasing the amount of pro-apoptotic p53 and Bax as well as augmenting that of anti-apoptotic Bcl-2 at 24h after irradiation. These results indicate that APG might be a useful adjunct to therapeutic irradiation as a protective agent for the gastrointestinal tract of cancer patients.

Hematopoiesis in the thymidine kinase 2 deficient mouse model of mitochondrial DNA depletion syndrome

Mitochondria are important for normal blood-cell development, and several diseases linked to mitochondrial DNA (mtDNA) show hematological manifestations. We recently generated a mouse strain deficient in expression of the mitochondrial pyrimidine nucleoside kinase thymidine kinase 2 (Tk2), showing that these mice exhibit progressive mtDNA depletion in multiple organs. We used this mouse strain as a model for mtDNA depletion syndromes to investigate the effects of mtDNA depletion on hematopoiesis. MtDNA levels in spleen from the Tk2-deficient mice were decreased 50%, but in contrast to all other investigated organs, both thymus and peripheral blood leukocytes showed normal mtDNA levels. Analysis of peripheral blood and cell populations in spleen, thymus, and bone marrow showed normal findings in the Tk2-deficient mice. The total rates of thymidine phosphorylation-which also include phosphorylation catalyzed by cytosolic Tk 1-in both spleen and thymus from wild-type mice were >50-fold higher than in liver, brain, and muscle. In summary, our data show that blood cells are less dependent on mitochondrial Tk2 compared with several other tissues and that these cells can synthesize deoxyribonucleotides required for mtDNA replication by alternative pathways such as phosphorylation of thymidine by cytosolic Tk1.

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.

Modulation of apoptosis of eckol against ionizing radiation in mice

To investigate the radioprotective potential of eckol, a component of the seaweed Ecklonia cava, against radiation in vivo, we evaluated the effect of eckol on cyto- and histo-protective capability of the lymphocytes and intestine against damage induced by a single whole body irradiation (WBI) in vivo. Here, we ascertained that eckol protected the lymphocytes' viability and rescued intestinal cells from radiation-induced apoptosis by decreasing the amount of pro-apoptotic p53 and Bax and increasing that of anti-apoptotic Bcl-2. These findings indicate that the overexpression of anti-apoptotic protein, which may lead to resistance to DNA damage, is involved deeply in protection of gastrointestinal cells after irradiation. Thus, eckol that can protect cells and tissues against ionizing radiation may have considerable potential as adjuncts to successful radiotherapy.

Differential susceptibility of C57BL/6NCr and B6.Cg-Ptprca mice to commensal bacteria after whole body irradiation in translational bone marrow transplant studies

Background

The mouse is an important and widely utilized animal model for bone marrow transplant (BMT) translational studies. Here, we document the course of an unexpected increase in mortality of congenic mice that underwent BMT.

Methods

Thirty five BMTs were analyzed for survival differences utilizing the Log Rank test. Affected animals were evaluated by physical examination, necropsy, histopathology, serology for antibodies to infectious disease, and bacterial cultures.

Results

Severe bacteremia was identified as the main cause of death. Gastrointestinal (GI) damage was observed in histopathology. The bacteremia was most likely caused by the translocation of bacteria from the GI tract and immunosuppression caused by the myeloablative irradiation. Variability in groups of animals affected was caused by increased levels of gamma and X-ray radiation and the differing sensitivity of the two nearly genetically identical mouse strains used in the studies.

Conclusion

Our retrospective analysis of thirty five murine BMTs performed in three different laboratories, identified C57BL/6NCr (Ly5.1) as being more radiation sensitive than B6.Cg-Ptprc^a/NCr (Ly5.2). This is the first report documenting a measurable difference in radiation sensitivity and its effects between an inbred strain of mice and its congenic counterpart eventually succumbing to sepsis after BMT.