Indian Indigenous Fruits as Radioprotective Agents: Past, Present and Future

Ionising radiation has been an important modality in cancer treatment and its value is immense when surgical intervention is risky or might debilitate/adversely affect the patient. However, the beneficial effect of radiation modality is negated by the damage to the adjacent healthy tissue in the field of radiation. Under these situations, the use of radioprotective compounds that can selectively protect normal tissues against radiation injury is considered very useful. However, research spanning over half a century has shown that there are no ideal radioprotectors available. The United States Food and Drug Administration (FDA or USFDA) approved amifostine or WR-2721 (Walter Reed-2721) [chemically S-2-(3-aminopropyl-amino) ethyl phosphorothioic acid] is toxic at their optimal concentrations. This has necessitated the need for agents that are safe and easily acceptable to humans.

BACKGROUND

Dietary agents with beneficial effects like free radical scavenging, antioxidant and immunomodulatory effects are recognized as applicable and have been investigated for their radioprotective properties. Studies in these lines have shown that the fruits of Aegle marmelos (stone apple or bael), Emblica officinalis or Phyllanthus emblica(Indian gooseberry/amla), Eugenia jambolana or Syzygium jambolana (black plum / jamun), Mangifera indica (mango) and Grewia asiatica (phalsa or falsa) that are originally reported to be indigenous to India have been investigated for their usefulness as a radioprotective agent.

OBJECTIVE

The objective of this review is to summarize beneficial effects of the Indian indigenous fruits stone apple, mango, Indian gooseberry, black plum, and phalsa in mitigating radiation-induced side effects, emphasize the underlying mechanism of action for the beneficial effects and address aspects that merit detail investigations for these fruits to move towards clinical application in the near future.

METHODS

The authors data mined in Google Scholar, PubMed, Embase, and the Cochrane Library for publications in the field from 1981 up to July 2020. The focus was on the radioprotection and the mechanism responsible for the beneficial effects, and accordingly, the articles were collated and analyzed.

RESULTS

This article emphasizes the usefulness of stone apple, mango, Indian gooseberry, black plum, and phalsa as radioprotective agents. From a mechanistic view, reports are suggestive that the beneficial effects are mediated by triggering free radical scavenging, antioxidant, anti-mutagenic and anti-inflammatory effects.

CONCLUSION

For the first time, this review addresses the beneficial effects of mango, Indian gooseberry, black plum, stone apple and phalsa as radioprotective agents. The authors suggest that future studies should be directed at understanding the selective radioprotective effects with tumor-bearing laboratory animals to understand their usefulness as radioprotective drug/s during radiotherapy and as a food supplement to protect people getting exposed to low doses of radiation in occupational settings. Phase I clinical trial studies are also required to ascertain the optimal dose and the schedule to be followed with the standardized extract of these fruits. The most important aspect is that these fruits are a part of the diet, have been consumed since the beginning of mankind, are non-toxic, possess diverse medicinal properties, have easy acceptability all of which will help take research forward and be of benefit to patients, occupational workers, agribased sectors and pharma industries.

Radioprotection and Radiomitigation: From the Bench to Clinical Practice

The development of protective agents against harmful radiations has been a subject of investigation for decades. However, effective (ideal) radioprotectors and radiomitigators remain an unsolved problem. Because ionizing radiation-induced cellular damage is primarily attributed to free radicals, radical scavengers are promising as potential radioprotectors. Early development of such agents focused on thiol synthetic compounds, e.g., amifostine (2-(3-aminopropylamino) ethylsulfanylphosphonic acid), approved as a radioprotector by the Food and Drug Administration (FDA, USA) but for limited clinical indications and not for nonclinical uses. To date, no new chemical entity has been approved by the FDA as a radiation countermeasure for acute radiation syndrome (ARS). All FDA-approved radiation countermeasures (filgrastim, a recombinant DNA form of the naturally occurring granulocyte colony-stimulating factor, G-CSF; pegfilgrastim, a PEGylated form of the recombinant human G-CSF; sargramostim, a recombinant granulocyte macrophage colony-stimulating factor, GM-CSF) are classified as radiomitigators. No radioprotector that can be administered prior to exposure has been approved for ARS. This differentiates radioprotectors (reduce direct damage caused by radiation) and radiomitigators (minimize toxicity even after radiation has been delivered). Molecules under development with the aim of reaching clinical practice and other nonclinical applications are discussed. Assays to evaluate the biological effects of ionizing radiations are also analyzed.

Sea Buckthorn Leaf Extract Protects Jejunum and Bone Marrow of (60)Cobalt-Gamma-Irradiated Mice by Regulating Apoptosis and Tissue Regeneration

A single dose (30 mg/kg body weight) of standardized sea buckthorn leaf extract (SBL-1), administered 30 min before whole body ⁶⁰Co-gamma-irradiation (lethal dose, 10 Gy), protected >90% of mice population. The purpose of this study was to investigate the mechanism of action of SBL-1 on jejunum and bone marrow, quantify key bioactive compounds, and analyze chemical composition of SBL-1. Study with 9-week-old inbred male Swiss albino Strain ‘A' mice demonstrated that SBL-1 treatment before ⁶⁰Co-gamma-irradiation (10 Gy) significantly (p < 0.05) countered radiation induced decreases in jejunum crypts (1.27-fold), villi number (1.41-fold), villus height (1.25-fold), villus cellularity (2.27-fold), cryptal Paneth cells (1.89-fold), and Bcl2 level (1.54-fold). It countered radiation induced increases in cryptal apoptotic cells (1.64-fold) and Bax levels (1.88-fold). It also countered radiation (2 Gy and 3 Gy) induced bone marrow apoptosis (1.59-fold and 1.85-fold) and micronuclei frequency (1.72-fold and 2.6-fold). SBL-1 rendered radiation protection by promoting cryptal stem cells proliferation, by regulating apoptosis, and by countering radiation induced chromosomal damage. Quercetin, Ellagic acid, Gallic acid, high contents polyphenols, tannins, and thiols detected in SBL-1 may have contributed to radiation protection by neutralization of radiation induced oxidative species, supporting stem cell proliferation and tissue regeneration.

In vivo radioprotective potential of thymol, a monoterpene phenol derivative of cymene

The radioprotective and anticlastogenic potential of a phenol derivative monoterpene thymol(TOH), against whole-body gamma radiation was studied in Swiss albino mice. Acute toxicity of TOH, with an LD(50(14)) of 1134.03mg/kgbwt., was observed when administered intra-peritoneally (i.p.). The radioprotective potential of TOH was evaluated using the optimal dose of 10mg/kgbwt. TOH, which increased the LD(50/30) by 2.17Gy and resulted in a dose reduction factor (DRF) of 1.25. A significant (p<0.01) reduction in micronucleated, polychromatic erythrocytes (PCE), normochromatic erythrocytes (NCE), and an increased PCE/NCE ratio was also observed after administration of 10mg/kg.b.wt. TOH prior to gamma radiation, indicating its antigenotoxic effect. TOH pre-treatment significantly (p<0.01) elevated reduced glutathione, glutathione-S-transferase, catalase, and superoxide dismutase levels and decreased lipid peroxidation levels in mouse liver homogenates at 24 and 48h after exposure to 4.5Gy of radiation. Further, TOH treatment before exposure to 7.5Gy of gamma radiation resulted in a significant (p<0.01) increase in hematological parameters at various post-treatment time points, with increased numbers of endogenous spleen colonies as well. The histological observations indicated a decline in villus heights and crypt numbers in mouse jejunum and were accompanied by a significant decrease in bone marrow nucleated cells in the irradiated group, which was almost normalized by pre-treatment with TOH. Our study clearly documents the antioxidant, anticlastogenic and radioprotective potentials of TOH, which may be attributed to several possible mechanisms, such as normalization of intracellular antioxidant levels and free radical scavenging activities by TOH.

Bevacizumab as a treatment option for radiation-induced cerebral necrosis

Radiation necrosis of normal CNS tissue represents one of the main risk factors of brain irradiation, occurring more frequently and earlier at higher total doses and higher doses per fraction. At present, it is believed that the necrosis results due to increasing capillary permeability caused by cytokine release leading to extracellular edema. This process is sustained by endothelial dysfunction, tissue hypoxia, and subsequent necrosis. Consequently, blocking the vascular endothelial growth factor (VEGF) at an early stage could be an option to reduce the development of radiation necrosis by decreasing the vascular permeability. This might help to reverse the pathological mechanisms, improve the symptoms and prevent further progression. A patient with radiationinduced necrosis was treated with an anti-VEGF antibody (bevacizumab), in whom neurologic signs and symptoms improved in accordance with a decrease in T1-weighted fluid-attenuated inversion recovery signals. Our case report together with the current literature suggests bevacizumab as a treatment option for patients with symptoms and radiological signs of cerebral necrosis induced by radiotherapy.

Protection of Mouse Bone Marrow against Radiation-Induced Chromosome Damage and Stem Cell Death by the Ocimum Flavonoids Orientin and Vicenin

In a previous study, orientin and vicenin, the water-soluble plant flavonoids, protected mice against radiation lethality (Uma Devi et al., Radiat. Res. 151, 74-78, 1999). To study bone marrow protection, adult Swiss mice were exposed to 0-6 Gy 60Co gamma rays 30 min after an intraperitoneal injection of 50 microg/ kg body weight of orientin/vicenin. Chromosomal aberrations in bone marrow were studied at 24 h postirradiation. Stem cell survival was studied using the exogenous spleen colony (CFU-S) assay. Radiation produced a dose-dependent increase in aberrant cells as well as in the yield of the different types of aberrations (breaks, fragments, rings and dicentrics) and a decrease in CFU-S. Pretreatment with either flavonoid significantly reduced the aberrant cells and different aberrations and increased the number of CFU-S compared to the respective radiation-alone groups. The dose modification factors for 50% reductions in the number of CFU-S were 1.6 for orientin and 1.7 for vicenin. The present finding that very low nontoxic doses of orientin and vicenin provide efficient protection against bone marrow damage at clinically relevant radiation doses suggests their potential for protection of normal tissues in radiotherapy.