Natural Radioprotective Agents: An Overview

Effect of reduced atmospheric pressure on growth and quality of two lettuce cultivars

Future space missions will likely include plants to provide fresh foods and bioregenerative life support capabilities. Current spacecraft such as the International Space Station (ISS) operate at 1 atm (101 kPa) pressure, but future missions will likely use reduced pressures to minimize gas leakage and facilitate rapid egress (space walks). Plants for these missions must be able to tolerate and grow reliably at these reduced pressures. We grew two lettuce cultivars, 'Flandria' a green bibb-type and 'Outredgeous,' a red, loose-leaf type, under three pressures: 96 kPa (ambient control), 67 kPa (2/3 atm), and 33 kPa (1/3 atm) for 21 days in rockwool using recirculating nutrient film technique hydroponics. Each treatment was repeated three times using a different hypobaric chamber each time. A daily light integral of 17.2 Moles Photosynthetically Active Radiation per day was provided with metal halide lamps set to deliver 300 µmol m-2s -1 photosynthetic photon flux (PPF) for a 16 h photoperiod at 22 °C. Oxygen was maintained at 21 kPa (equal to 21% at 1 atm) and CO2 at 0.12 kPa (equal to 1200 ppm at 1 atm). Leaf area for 'Outredgeous' was reduced 20% and 38% at 67 kPa and 33 kPa respectively; shoot fresh mass was reduced 22% and 41% at 67 kPa and 33 kPa respectively when compared to control plants at 96 kPa. These trends were not statistically significant at P ≥ 0.05. Leaf area for 'Flandria' showed no difference between 96 and 67 kPa but was reduced 31% at 33 kPa; shoot fresh mass was reduced 6% and 27% at 66 kPa and 33 kPa respectively compared to 96 kPa. There were 10% and 25% increases in anthocyanin concentration at 66 kPa and 33 kPa compared to 96 kPa, potentially increasing the bioprotective capacity of the plant. Previous studies with other cultivars of lettuce showed slight change in growth across this range of pressures, suggesting responses may vary among genotypes, hypobaric exposure treatments, and / or environmental conditions. Collectively, the findings suggest further testing is needed to understand the effects of atmospheric pressure on plant growth.

Radioprotective Role of Natural Polyphenols: From Sources to Mechanisms

The identification and development of radioprotective agents has emerged as a subject matter of research during recent years due to the growing usage of ionizing radiation in different areas of human life. Previous work on synthetic radioprotectors has achieved limited progress because of the numerous issues associated with toxicity. Compounds extracted from plants have potential to serve as lead candidates for developing ideal radioprotectors due to their low cost, safety and selectivity. Polyphenols are the most abundant and commonly dispersed group of biologically active molecules possessing broad range of pharmacological activities. Polyphenols have displayed efficacy for radioprotection during various investigations and can be administered at high doses with lesser toxicity. Detoxification of free radicals, modulating inflammatory responses, DNA repair, stimulation of hematopoietic recovery, and immune functions are the main mechanisms for radiation protection with polyphenols. Epicatechin, epigallocatechin-3-gallate, apigenin, caffeic acid phenylethylester, and silibinin provide cytoprotection together with the suppression of many pro-inflammatory cytokines owing to their free radical scavenging, anti-oxidant, and anti-inflammatory properties. Curcumin, resveratrol, quercetin, gallic acid, and rutin's radioprotective properties are regulated primarily by direct or indirect decline in cellular stress. Thus, polyphenols may serve as potential candidates for radioprotection in the near future, however, extensive investigations are still required to better understand their protection mechanisms.

Light Emitting Diodes (LEDs) as Agricultural Lighting: Impact and Its Potential on Improving Physiology, Flowering, and Secondary Metabolites of Crops

A reduction in crop productivity in cultivable land and challenging environmental factors have directed advancement in indoor cultivation systems, such that the yield parameters are higher in outdoor cultivation systems. In wake of this situation, light emitting diode (LED) lighting has proved to be promising in the field of agricultural lighting. Properties such as energy efficiency, long lifetime, photon flux efficacy and flexibility in application make LEDs better suited for future agricultural lighting systems over traditional lighting systems. Different LED spectrums have varied effects on the morphogenesis and photosynthetic responses in plants. LEDs have a profound effect on plant growth and development and also control key physiological processes such as phototropism, the immigration of chloroplasts, day/night period control and the opening/closing of stomata. Moreover, the synthesis of bioactive compounds and antioxidants on exposure to LED spectrum also provides information on the possible regulation of antioxidative defense genes to protect the cells from oxidative damage. Similarly, LEDs are also seen to escalate the nutrient metabolism in plants and flower initiation, thus improving the quality of the crops as well. However, the complete management of the irradiance and wavelength is the key to maximize the economic efficacy of crop production, quality, and the nutrition potential of plants grown in controlled environments. This review aims to summarize the various advancements made in the area of LED technology in agriculture, focusing on key processes such as morphological changes, photosynthetic activity, nutrient metabolism, antioxidant capacity and flowering in plants. Emphasis is also made on the variation in activities of different LED spectra between different plant species. In addition, research gaps and future perspectives are also discussed of this emerging multidisciplinary field of research and its development.

Radioprotective effect of chloropyllin, protoporphyrin-IX and bilirubin compared with amifostine® in Drosophila melanogaster

The identification of substances that prevent or minimize the detrimental effects of ionizing radiation is an essential undertaking. The aim of this paper was to evaluate and compare the radioprotective potential of chlorophyllin, protoporphyrin and bilirubin, with amifostine®, an US Food & Drug Administration approved radioprotector Using the somatic mutation and recombination assay in the Drosophila melanogaster wing, it was found that pretreatment (1-9 h) with any of the porphyrins or amifostine® alone, did not affect the larva-adult viability or the basal frequency of mutation. However, they were associated with significant reductions in frequency of somatic mutation and recombination compared with the gamma-irradiated (20 Gy) control as follows: bilirubin (69.3 %)> chlorophyllin (40.0 %)> protoporphyrin (39.0 %)> amifostine® (19.7 %). Bilirubin also caused a 16 % increase in larva-adult viability with 3 h of pretreatment respect to percentage induced in 20 Gy control group. Whilst amifostine® was associated with lower genetic damage after pre-treatment of 1 and 3 h, this did not attain significance. These findings suggest that the tested porphyrins may have some potential as radioprotectant agents.

Radiation protective effects of baclofen predicted by a computational drug repurposing strategy

Exposure to ionizing radiation causes damage to living tissues; however, only a small number of agents have been approved for use in radiation injuries. Radioprotector is the primary countermeasure to radiation injury and none radioprotector has indeed reached the drug development stage. Repurposing the long list of approved, non-radioprotective drugs is an attractive strategy to find new radioprotective agents. Here, we applied a computational approach to discover new radioprotectors in silico by comparing publicly available gene expression data of ionizing radiation-treated samples from the Gene Expression Omnibus (GEO) database with gene expression signatures of more than 1309 small-molecule compounds from the Connectivity Map (cmap) dataset. Among the best compounds predicted to be therapeutic for ionizing radiation damage by this approach were some previously reported radioprotectors and baclofen (P<0.01), a chemical that was not previously used as radioprotector. Validation using a cell-based model and a rodent in vivo model demonstrated that treatment with baclofen reduced radiation-induced cytotoxicity in vitro (P<0.01), attenuated bone marrow damage and increased survival in vivo (P<0.05). These findings suggest that baclofen might serve as a radioprotector. The drug repurposing strategy by connecting the GEO data and cmap can be used to identify known drugs as potential radioprotective agents.

Protective Effect of Lycopene against Radiation-Induced Hepatic Toxicity in Rats

The radioprotective effect of lycopene against liver damage was investigated in 80 female Sprague Dawley rats (10 per group). Early-group rats included: controls (group 1), lycopene (group 2), radiotherapy alone (group 3), and lycopene + radiotherapy (group 4). Lycopene (5 mg/kg per day) was administered orally for 7 days; single-fraction 8 Gy abdominopelvic radiotherapy was administered on day 8. Early-group rats were sacrificed on day 10. Late-group rats (groups 5 – 8) underwent treatment with the same regimens but, in groups 6 and 8, lycopene was administered until all rats were sacrificed, 60 days postradiotherapy. Liver malondialdehyde levels increased significantly and glutathione (GSH) levels, GSH-peroxidase (GSH-Px) and superoxide dismutase (SOD) activity decreased significantly in radiotherapy versus control groups. In lycopene + radiotherapy groups, malondialdehyde levels decreased significantly and GSH levels, GSH-Px and SOD activity increased significantly compared with radiotherapy groups. No significant between-group histopathological differences were observed in early groups; in late groups, histopathological changes increased significantly in the radiotherapy group versus control group. A significant decrease in histopathological changes occurred in the lycopene + radiotherapy group compared with the radiotherapy group. Lycopene supplementation significantly reduced radiotherapy-induced oxidative liver injury.

Radioprotective and antioxidant activity of fractionated extracts of berries of Hippophae rhamnoides

Plants are an abundant source of medicinal compounds, some of which are useful in combating free radical-mediated oxidative stress. In the present study, initially two fractions designated REC-1001 (flavonoid-rich fraction) and REC-1002 (flavonoid-poor fraction) of Hippophae rhamnoides were screened on the basis of their reducing power in the aqueous phase. REC-1001 was selected for further study, since it exhibited 27.38 times higher antioxidant activity than REC-1002. REC-1001 also showed significant (P < .05) membrane protection potential at 50 microg/mL, which was attributed to its ability to scavenge peroxyl radicals (64.82 +/- 1.25% scavenging within 1,440 min). A significant (P < .05) difference of 67.02% in free radical scavenging activity at 1,000 ng/mL between REC-1001 and vitamin E demonstrated the extract fraction's worth in radiation protection. Such activities were attributed to the presence of quercetin, isorhamnetin, and kaempferol in this fraction. Further, REC-1001 was found to be nontoxic up to 200 mg/kg of body weight. This research suggests that the REC-1001 fraction of H. rhamnoides extract is a safe and effective antioxidant nutraceutical product.

Metabolic remodeling of malignant gliomas for enhanced sensitization during radiotherapy: an in vitro study

OBJECTIVE

To investigate a novel method to enhance radiosensitivity of gliomas via modification of metabolite flux immediately before radiotherapy. Malignant gliomas are highly glycolytic and produce copious amounts of lactic acid, which is effluxed to the tumor microenvironment via lactate transporters. We hypothesized that inhibition of lactic acid efflux would alter glioma metabolite profiles, including those that are radioprotective. H magnetic resonance spectroscopy (MRS) was used to quantify key metabolites, including those most effective for induction of low-dose radiation-induced cell death.

METHODS

We inhibited lactate transport in U87-MG gliomas with alpha-cyano-4-hydroxycinnamic acid (ACCA). Flow cytometry was used to assess induction of cell death in treated cells. Cells were analyzed by MRS after ACCA treatment. Control and treated cells were subjected to low-dose irradiation, and the surviving fractions of cells were determined by clonogenic assays.

RESULTS

MRS revealed changes to intracellular lactate on treatment with ACCA. Significant decreases in the metabolites taurine, glutamate, glutathione, alanine, and glycine were observed, along with inversion of the choline/phosphocholine profile. On exposure to low-dose radiation, ACCA-pretreated U-87MG cells underwent rapid morphological changes, which were followed by apoptotic cell death.

CONCLUSION

Inhibition of lactate efflux in malignant gliomas results in alterations of glycolytic metabolism, including decreased levels of the antioxidants taurine and glutathione and enhanced radiosensitivity of ACCA-treated cells. Thus, in situ application of lactate transport inhibitors such as ACCA as a novel adjunctive therapeutic strategy against glial tumors may greatly enhance the level of radiation-induced cell killing during a combined radio- and chemotherapeutic regimen.