Development Of Radiation Nephropathy Research Articles

Targeting of Heparanase in the Murine Model Protects against Radiation-Induced Nephropathy

<h3>Purpose/Objective(s)</h3> Adverse effects are common in virtually all types of treatment modalities in cancer including that of radiation therapy. Several agents are clinically used to aid in the reduction of side effects of anti-cancer therapy, however these agents <i>per se</i> are typically not endowed with tumor-suppressing properties. Herein we report that the extracellular matrix (ECM)-degrading enzyme heparanase (a valid target for anti-cancer drug development) is also a promising candidate for interventions aimed at preventing development of radiation nephropathy - a significant side effect of radiation therapy in the treatment of abdominal/pelvic malignancies. Heparanase is the sole mammalian endoglucuronidase that cleaves heparan sulfate in the ECM. The enzymatic action of heparanase has not only been found to promote tumor development and progression at various anatomic sites but is upregulated in essentially all tumor types found in the abdominal/pelvic cavity, whose radiation treatment may result in the development of radiation nephropathy. <h3>Materials/Methods</h3> Eleven-week-old female C3H/HeNHsd mice were administered 10 Gy of radiation using brachytherapy to induce radiation nephropathy. Subcutaneous injections of Roneparstat, a specific heparanase inhibitor, were administered to the mice and urine samples were collected over 24h. Urinary albumin was measured using an ELISA kit. Prior to and following irradiation, heparanase and early growth response (Egr1) transcription factor mRNA levels were determined by qRT-PCR in both HK-2 human proximal tubule epithelial cells and HEK-293 human embryonic kidney cells. <h3>Results</h3> In this study, we evaluated the potential of targeting heparanase to diminish radiation therapy-induced kidney damage. We demonstrated that clinically relevant doses of ionizing radiation upregulate heparanase expression in renal cells (most likely through a transcription factor Egr 1 –dependent mechanism). Moreover, utilizing a murine model of abdominal radiation therapy, we found that the specific heparanase inhibitor, Roneparstat, abolished radiation-induced albuminurea –the hallmark of radiation nephropathy. <h3>Conclusion</h3> Given the well-documented anti-cancer effects of heparanase inhibition, our present findings attest this enzyme as a unique target in the landscape of cancer therapy due to its dual action. Indeed, targeting of heparanase exerts not only direct anti-tumor effects but also protects from kidney damage induced by radiation - the backbone of cancer therapy across a broad range of abdominal/pelvic malignancies.

Impact of angiotensin II type 2 receptor blockade on experimental radiation nephropathy.

In the rat, blockade of angiotensin II type 1 receptors diminishes the functional changes that occur after kidney irradiation. It has been hypothesized that some of the beneficial effects of angiotensin II type 1 blockers in renal disease are caused by a rise in angiotensin II that stimulates the angiotensin II type 2 receptor. If this hypothesis applied in this model, blockade of the type 2 receptor should exacerbate radiation nephropathy and/or counteract the beneficial effects of type 1 receptor blockade. To assess this hypothesis, rats were given total-body irradiation plus bone marrow transplantation and then treated for 12 weeks with a type 1 receptor blocker (L158,809), a type 2 blocker (PD123319), both blockers, or no blockers. Rats were assessed for renal function (proteinuria, hypertension, azotemia) and renal failure for up to 62 weeks. Contrary to the hypothesis, the type 2 blocker alone produced a temporary delay in the development of radiation nephropathy, and it substantially enhanced the efficacy of the type 1 blocker. This implies that both type 1 and type 2 angiotensin receptors need to be blocked to achieve the maximum level of prophylaxis of radiation nephropathy. We speculate that the beneficial effect of the angiotensin II type 2 receptor blocker is due to a reduction in radiation-induced renal cell proliferation or fibrosis.

Dietary sodium modification and experimental radiation nephropathy

Purpose : To determine whether suppression of the reninangiotensin system (RAS) with high dietary sodium (salt) has the same beneficial effect on radiation nephropathy as suppression of the RAS with angiotensin-converting-enzyme (ACE) inhibitors or angiotensin II (AII) receptor antagonists. Materials and methods : Normal and irradiated rats were placed on high- or low-salt diets and assessed for effects on blood pressure, on AII levels and on the development of radiation nephropathy. Results : In unirradiated animals, a high-salt diet suppressed AII and caused hypertension, while a low-salt diet produced no detectable effects. Use of a high-salt diet 3-9 weeks after irradiation exacerbated radiation-induced hypertension but attenuated the development of radiation nephropathy. Continuous use of a high-salt diet slowed the progression of radiation nephropathy, but eventually exacerbated radiationinduced hypertension and accelerated renal failure. Use of a high-salt diet in animals with established radiation nephropathy was deleterious. A low-salt diet had no effect on the development of radiation nephropathy. Conclusions : These studies provide further support for the hypothesis that the beneficial effect of AII receptor antagonists, ACE inhibitors and high dietary sodium in the prophylaxis of radiation nephropathy is due to their suppression of the RAS, not to their anti-hypertensive effects.

Radiation Nephropathy&The Link Between Functional Damage and Vascular Mediated Inflammatory and Thrombotic Changes

The extent of radiation-induced nephropathy, which develops progressively over periods of months to years after treatment, is strongly influenced by both total dose and dose per fraction. In this study we examined the relationship between the early expression of various thrombotic and inflammatory markers of endothelial cell (EC) damage in irradiated mouse kidneys and the subsequent development of nephropathy. Decreased levels of glomerular ADPase and increased levels of glomerular Vwf were seen from 4 or 20 weeks after irradiation, respectively. These pro-thrombotic changes were associated with increased fibrin fibrinogen deposits, indicative of microthrombus formation, at later times. These events were, however, not sensitive to changes in total dose or dose per fraction, therefore they cannot be quantitatively linked to the development of radiation nephropathy. Increased leucocyte invasion of the renal cortex was also seen after irradiation; this was quantitatively dependent on both total dose and dose per fraction. Linear quadratic analysis of the leucocyte dose-response curves yielded an f / g ratio of 7.7 Gy, which is significantly greater than the f / g ratio or 2.7 Gy determined for nephropathy, indicating less fractionation sensitivity for the inflammatory response. We conclude that inflammatory changes contribute to, but do not entirely explain, radiation nephropathy. The role of thrombotic changes is less clear.

A morphometric analysis of glomerular and tubular alterations following fast-neutron irradiation of the pig and monkey kidney

Purpose: The morphologic responses of the pig and monkey kidney to fractionated fast-neutron irradiation were assessed. Methods and Materials: The right kidney of approximately 14-week-old female Large White pigs was irradiated with 6.6–12.2 Gy of fast neutrons (42 MeV d→Be) given as 12 fractions over 18 days; the left kidney served as the contralateral unirradiated kidney. Both kidneys were removed at necropsy 2 years postirradiation. In addition, the remaining hypertrophied kidney of four unilaterally nephrectomized adult rhesus monkeys was irradiated with a total dose of 11.0 Gy fast neutrons (45 MeV p→Be) given in an identical fractionation regimen to that used in the pig studies. These kidneys were removed when the animals exhibited renal failure, between 32–94 weeks postirradiation. Glomeruli were assessed for the presence of pathologic features, including intercapillary eosinophilic material (ICE), ectatic capillaries, thrombi, hemorrhage, and sclerosis. The relative proportion of renal cortex occupied by glomeruli, interstitium, normal, or abnormal tubules was determined using a Chalkley point grid. Results: The incidence of normal glomeruli, ectatic capillaries, thrombosis, and periglomerular fibrosis were significantly different in the irradiated pig kidneys compared with the unirradiated contralateral kidneys ( p ≤ 0.02). Linear regression analysis demonstrated a significant dose relationship in terms of normal glomeruli, ectatic capillaries, and ICE ( r ≥ 0.64; p ≤ 0.04). Irradiation was also associated with a significant ( p < 0.0001) decrease and increase in the volume of renal cortex occupied by normal and abnormal tubules, respectively. Similar morphometric changes were noted in the irradiated monkey kidneys. Conclusions: The morphologic changes seen in the pig and monkey kidney after fractionated irradiation with fast neutrons are similar to those previously noted after single-dose or fractionated-photon irradiation. These findings support the hypothesis that the development of radiation nephropathy in these various models involves common pathophysiological mechanisms.

Angiotensin II Receptor Antagonists in the Prevention of Radiation Nephropathy

Angiotensin-converting enzyme (ACE) inhibitors can be used to prevent the development of radiation nephropathy. Current studies were designed to determine whether blocking the angiotensin II (AII) receptor, rather than preventing the creation of AII, would be effective in the prophylaxis of radiation nephropathy. Rats received 17 Gy total-body irradiation (TBI) in six fractions followed by syngeneic bone marrow transplantation (BMT). Prior to TBI the rats were randomized to groups receiving an ACE inhibitor (captopril), an AII type 1 (AT1) receptor antagonist (L-158,809) or no treatment. Renal function was assessed over 40 weeks, and a subset of animals were sacrificed for histopathology at 33 weeks. Renal function deteriorated progressively in animals receiving TBI alone, leading to renal failure by 34 weeks. Renal function was significantly better in animals receiving either captopril or L-158,809, and none of these animals had progressed to renal failure by 43 weeks. Analysis of both renal function and histopathology shows that the AII receptor antagonist is more effective than the ACE inhibitor in the prophylaxis of BMT nephropathy. This indicates that a reduction of activation of the AT1 receptor by AII, by itself, is sufficient for the prophylaxis of radiation nephropathy.

Acute, Subacute, and Chronic X-ray Effects on Glomerular Hemodynamics in Rats

In order to evaluate the effects of x-rays on glomerular hemodynamics, surgically exposed left kidneys of Munich-Wistar rats were irradiated with 15 Gy in a single dose. The animals were studied 45 min (acute group, n = 8), 14 days (subacute group, n = 7), and 60 days (chronic group, n = 7) after irradiation and compared with their respective controls. A decrease in total glomerular filtration (55%) and renal plasma flow (40%) rates with marked elevation of total renal vascular resistance (180%), p < 0.05, occurred within 45 min. Significant changes also occurred in the microcirculation; i.e., single-nephron glomerular filtration (SNGFR), glomerular plasma flow (QA), and glomerular capillary hydraulic pressure (PGC) declined by 35%, 40%, and 12%, respectively, due to an increase in total arteriolar resistance (90%), p < 0.05. Within 14 days, SNGFR was similar to control in spite of a moderate elevation of afferent arteriolar resistance (26%) and reduction in PGC (11%), p < 0.05, and QA (20%). Kf was significantly elevated (46%), p < 0.05. The chronic group presented a response pattern similar to that of the acute group, although less severe. Histopathological changes were not relevant and were restricted to tubules. The present results suggest that: (a) Acutely, there was a marked reduction in filtration, flow, and PGC with significant elevation of resistances. (b) Within 14 days, the maintenance of SNGFR was probably the result of an offsetting effect between QA and PGC decreases and Kf elevation. (c) After 60 days, the homeostatic mechanism was not sufficient to maintain normal renal function. (d) A functional effect is probably the most important pathogenetic mechanism, at least during the initial phase, for the development of radiation nephropathy since no morphological alterations were observed.

Effects of Dexamethasone on the Development of Radiation Nephropathy in the Rat

Low-dose, chronic administration of the synthetic glucocorticoid, dexamethasone, to male CD-I rats in the drinking water or by osmotic minipumps implanted subcutaneously after supralethal irradiation of the kidneys (20 Gy) was studied. The effectiveness of treatment with dexamethasone in the drinking water at concentrations of 23 micrograms/l to 188 micrograms/l and treatment times varying from 33 to 166 days was evaluated. At monthly intervals kidney function was assayed by measuring the clearance of 51Cr-ethylenediaminetetraacetic acid. All dexamethasone treatment regimens increased survival times significantly and delayed the development of kidney dysfunction. The most effective combination of concentration of dexamethasone in drinking water and treatment interval after irradiation with respect to survival was 94 micrograms/l and 88 days. However, a slightly longer survival and a better functional result was obtained if an equivalent amount of dexamethasone was administered by minipumps. Shielding the adrenal glands during kidney irradiation did not prolong survival. This shows that the beneficial effect of dexamethasone is not due to compensation for reduced adrenal glucocorticoid production resulting from concomitant exposures of these glands during kidney irradiation.

A Morphological Study of Radiation Nephropathy in the Pig

Both kidneys of mature pigs received a single dose of 9.8 Gy 60Co gamma rays. Pigs were killed between 2 and 24 weeks after irradiation and the kidneys examined histologically. Glomerular and tubular changes were observed within 2 weeks of irradiation. Neutrophils and other leukocytes were seen within glomerular capillary loops; mesangial matrix and cell number increased. A progressive increase in thickening of the basement membrane and a decrease in capillary lumina were then noted. Basement membrane duplication occurred within 12 weeks. By 24 weeks these lesions had increased in severity, sclerotic endstage glomeruli, predominantly subcapsular or juxtamedullary, being evident. Tubular lesions initially consisted of focal areas of tubular atrophy in the juxtamedullary region. By 6 weeks subcapsular foci of tubular degeneration, regeneration, and necrosis were found; these appeared to resolve 12 weeks after irradiation. At later times the severity of the tubular lesions varied between pigs, with some exhibiting interstitial fibrosis involving a complete band of subcapsular tissue, while others showed relatively mild changes. There was no apparent change in the vasculature. These findings indicate that (a) there is no one target or dose-limiting cell, and (b) the vasculature does not play a primary role in the development of radiation nephropathy.