Acute, subacute, and chronic x-ray effects on glomerular hemodynamics in rats

Radioprotective Agents and Enhancers Factors. Preventive and Therapeutic Strategies for Oxidative Induced Radiotherapy Damages in Hematological Malignancies

Radiation therapy plays a critical role in the management of a wide range of hematologic malignancies. It is well known that the post-irradiation damages both in the bone marrow and in other organs are the main causes of post-irradiation morbidity and mortality. Tumor control without producing extensive damage to the surrounding normal cells, through the use of radioprotectors, is of special clinical relevance in radiotherapy. An increasing amount of data is helping to clarify the role of oxidative stress in toxicity and therapy response. Radioprotective agents are substances that moderate the oxidative effects of radiation on healthy normal tissues while preserving the sensitivity to radiation damage in tumor cells. As well as the substances capable of carrying out a protective action against the oxidative damage caused by radiotherapy, other substances have been identified as possible enhancers of the radiotherapy and cytotoxic activity via an oxidative effect. The purpose of this review was to examine the data in the literature on the possible use of old and new substances to increase the efficacy of radiation treatment in hematological diseases and to reduce the harmful effects of the treatment.

Platelet-rich plasma ameliorates gamma radiation-induced nephrotoxicity via modulating oxidative stress and apoptosis

AIMS

As a source of growth factors and with its cytoprotective properties, platelet-rich plasma (PRP) received considerable attention in regenerative medicine. Thus, this study was designed to evaluate the protective efficacy of PRP against γ-radiation-induced nephrotoxicity.

MAIN METHODS

Forty male rats were distributed in four groups: 1) control, 2) PRP, 3) Radiation, and 4) PRP + radiation. Nephrotoxicity was examined in rats after a whole body γ-irradiation at a single dose of 8 Gy. Activated PRP (0.5 ml/kg BW) was injected subcutaneously twice weekly for three successive weeks prior to γ-irradiation. At the end of the experiment, creatinine, urea, albumin, and neutrophil gelatinase-associated lipocalin (NGAL) serum levels, as well as renal relative gene expression level of kidney injury molecule-1 (KIM-1) were estimated. Further, malondialdehyde level, nitric oxide content and reduced glutathione content in addition to superoxide dismutase and catalase activities were measured. Moreover, the expression levels of B-cell lymphoma 2 (Bcl-2), Bcl-2-associated X (Bax), and caspase-3 proteins were assayed.

KEY FINDINGS

PRP pre-treatment significantly reduced the radiation-induced abnormalities in kidney histology and attenuated the induced cell injury. Furthermore, PRP notably ameliorated the state of oxidative stress and appeared to inhibit the induced apoptosis.

SIGNIFICANCE

This study lends a probable protective role of PRP against γ-radiation-induced nephrotoxicity which can highlight the possibilities of its application as a complementary procedure during radiotherapy.

Radiation-induced afferent arteriolar endothelial-dependent dysfunction involves decreased epoxygenase metabolites

Chronic kidney disease is a known complication of hematopoietic stem cell transplant (HSCT) and can be caused by irradiation at the time of the HSCT. In our rat model there is a 6- to 8-wk latent period after irradiation that leads to the development of proteinuria, azotemia, and hypertension. The current study tested the hypothesis that decreased endothelial-derived factors contribute to impaired afferent arteriolar function in rats exposed to total body irradiation (TBI). WAG/RijCmcr rats underwent 11 Gy TBI, and afferent arteriolar responses to acetylcholine were determined at 1, 3, and 6 wk. Blood pressure and blood urea nitrogen were not different between control and irradiated rats. Afferent arteriolar diameters were not altered in irradiated rats. Impaired endothelial-dependent responses to acetylcholine were evident at 3 and 6 wk following TBI. Nitric oxide synthase (NOS), cyclooxygenase (COX), and epoxygenase (EPOX) contribution to acetylcholine dilator responses were evaluated. NOS inhibition with N(G)-nitro-l-arginine methyl ester (l-NAME) reduced acetylcholine responses by 50% in controls and 90% in 3-wk TBI rats. COX inhibition with indomethacin did not significantly alter the acetylcholine response in the presence or absence of l-NAME. EPOX inhibition with N-methylsulfonyl-6-(2-propargyloxyphenyl)hexanamide significantly decreased acetylcholine responses (35%) in controls but did not significantly alter acetylcholine responses (4%) in TBI rats. Biochemical analysis revealed decreased urinary EPOX metabolites but no change in COX, NOS, or reactive oxygen species at 3 wk TBI. Taken together, these results indicate that afferent arteriolar endothelial dysfunction involves a decrease in EPOX metabolites that precedes the development of proteinuria, azotemia, and hypertension in irradiated rats.

Epoxyeicosatrienoic acid analogue mitigates kidney injury in a rat model of radiation nephropathy

Arachidonic acid is metabolized to epoxyeicosatrienoic acids (EETs) by CYP epoxygenases, and EETs are kidney protective in multiple pathologies. We determined the ability of an EET analogue, EET-A, to mitigate experimental radiation nephropathy. The kidney expression of the EET producing enzyme CYP2C11 was lower in rats that received total body irradiation (TBI rat) compared with non-irradiated control. At 12 weeks after TBI, the rats had higher systolic blood pressure and impaired renal afferent arteriolar function compared with control, and EET-A or captopril mitigated these abnormalities. The TBI rats had 3-fold higher blood urea nitrogen (BUN) compared with control, and EET-A or captopril decreased BUN by 40-60%. The urine albumin/creatinine ratio was increased 94-fold in TBI rats, and EET-A or captopril attenuated that increase by 60-90%. In TBI rats, nephrinuria was elevated 30-fold and EET-A or captopril decreased it by 50-90%. Renal interstitial fibrosis, tubular and glomerular injury were present in the TBI rats, and each was decreased by EET-A or captopril. We further demonstrated elevated renal parenchymal apoptosis in TBI rats, which was mitigated by EET-A or captopril. Additional studies revealed that captopril or EET-A mitigated renal apoptosis by acting on the p53/Fas/FasL (Fas ligand) apoptotic pathway. The present study demonstrates a novel EET analogue-based strategy for mitigation of experimental radiation nephropathy by improving renal afferent arteriolar function and by decreasing renal apoptosis.

Early detection of radiation-induced glomerular injury by albumin permeability assay

Renal irradiation leads predictably to glomerular vascular injury, cell lysis, matrix accumulation, sclerosis and loss of renal function. The immediate effects of renal irradiation that may be associated with glomerular pathology and proteinuria are not clear in the human disease or its rat model. We hypothesized that radiation-induced injury causes immediate and subtle alterations in glomerular physiology independent of the neurohumoral and hemodynamic regulatory mechanisms. We employed a sensitive in vitro functional assay of glomerular albumin permeability (P(alb)) to demonstrate radiation-induced damage to the glomerular filtration barrier immediately after total-body irradiation of rats. In blinded experiments, control rats were sham-treated, and experimental rats received 9.5 Gy X rays. Rats were killed humanely at 1 h to 9 weeks after irradiation and glomeruli were isolated. In parallel experiments, glomeruli were isolated from normal rats and irradiated in vitro. The change in glomerular capillary permeability due to an experimental oncotic gradient was determined using videomicroscopy and P(alb) was calculated. Results show that in vivo or in vitro irradiation of glomeruli caused an increased P(alb) at 1 h. Increased P(alb) was observed up to 3 weeks after irradiation. Glomeruli from mice irradiated with 9.5 or 19.0 Gy X rays did not show increased P(alb) at 1 h postirradiation. We conclude that glomerular protein permeability of irradiated rats increases in a dose-dependent manner immediately after irradiation and that it appears to be independent of hemodynamic or systemic influences.