Delayed renal injury in survivors of hematologic acute radiation syndrome

Abstract

Purpose: A mass casualty disaster involving radiological or nuclear agents continues to be a public health concern which requires consideration of both acute and late tissue toxicities in exposed victims. With the advent of advanced treatment options for the mitigation of hematological injuries, there are likely to be survivors of total body irradiation (TBI) exposures as high as 8-10 Gy. These survivors are at risk for a range of delayed multi-organ morbidities including progressive renal failure.

Material and methods: Here, we established the WAG/RijCmcr rat as an effective model for the evaluation of medical countermeasures (MCM) for acute hematologic radiation syndrome (H-ARS). The LD_50/30 dose for adult and pediatric WAG/RijCmcr rats was determined for both sexes. We then confirmed the FDA-approved MCM pegfilgrastim (peg-GCSF, Neulasta®) mitigates H-ARS in adult male and female rats. Finally, we evaluated survival and renal dysfunction up to 300 d post-TBI in male and female adult rats.

Results: In the WAG/RijCmcr rat model, 87.5% and 100% of adult rats succumb to lethal hematopoietic acute radiation syndrome (H-ARS) at TBI doses of 8 and 8.5 Gy, respectively. A single dose of the hematopoietic growth factor peg-GCSF administered at 24 h post-TBI improved survival during H-ARS. Peg-GCSF treatment improved 30 d survival from 12.5% to 83% at 8 Gy and from 0% to 63% at 8.5 Gy. We then followed survivors of H-ARS through day 300. Rats exposed to TBI doses greater than 8 Gy had a 26% reduction in survival over days 30-300 compared to rats exposed to 7.75 Gy TBI. Concurrent with the reduction in long-term survival, a dose-dependent impairment of renal function as assessed by blood urea nitrogen (BUN) and urine protein to urine creatinine ratio (UP:UC) was observed.

Conclusion: Together, these data show survivors of H-ARS are at risk for the development of delayed renal toxicity and emphasize the need for the development of medical countermeasures for delayed renal injury.

Keywords: Acute radiation syndrome (ARS); growth factors; haematology – radiation; multiple organ failure (MOF); radiation-induced tissue toxicity; total body irradiation (TBI).

Figure 1.

Dose-dependent lethality observed after total body irradiation in female and male WAG/RijCmcr rats. (A) Survival and (B) percent body weight change in adult (11–12-week-old) female rats which received TBI at doses ranging from 6.5 to 8.5 Gy. (C) Survival and (D) percent body weight change in adult (11–12-week-old) male rats which received TBI at doses ranging from 6.5 to 8.5 Gy. (E) Survival and (F) percent body weight change in pediatric (5–6-week-old) female rats which received TBI at doses ranging from 5.5 to 7.0 Gy. (G) Survival and (H) percent body weight change in pediatric (5–6-week-old) male rats which received TBI at doses ranging from 5.5 to 7.5 Gy.

Figure 2.

Age Related Differences in LD_50/30. (A) Percent morbidity in pediatric and adult female rats (individual data points) was fit with a probit regression analysis (solid line) to determine the expected percent mortality as a function of radiation dose. The calculated LD_50/30 (red dashed line) with 95% confidence interval (gray region) for adult and pediatric female rats are 7.71 (CI: 7.61–7.85) Gy and 6.47 (CI: 6.14–8.12), respectively. The dose modifying factor (DMF) for female rats is 1.19. (B) Percent morbidity in pediatric and adult male rats (individual data points) was fit with a probit regression analysis (solid line) to determine the expected percent mortality as a function of radiation dose. The calculated LD_50/30 (red dashed line) with 95% confidence interval (gray region) for adult and pediatric male rats are 7.71 Gy (CI: 7.62–7.81) Gy and LD_50/30 of 6.45 (CI: 6.01–7.11) Gy, respectively. The dose modifying factor (DMF) for male rats is 1.19.

Figure 3.

Time courses for white blood cell, lymphocyte, neutrophil, and platelet counts at the LD_50/30 for female and male, adult (7.75 Gy) and pediatric (6.5Gy) rats are shown in panels A-H. Complete blood counts were assessed from day 3 to 30 after TBI. Data are presented as means and 95% CI for non-irradiated rats (open symbols) and TBI rats (solid symbols).

Figure 4.

Kaplan-Meier (KM) survival plots after TBI (A) in adult female and (B) male WAG/RijCmcr rats treated with peg-GCSF (dashed lines) subcutaneously at 24 hours after TBI. For comparison, survival curves from untreated female and male rats exposed to 8 and 8.5 Gy are included for comparison (solid lines). Peg-G-CSF significantly improves survival at the 8 and 8.5 Gy doses. Log-rank p-values for 8 Gy + peg-G-CSF versus 8 Gy alone for female and male rats are 0.0389 and 0.0009, respectively. Log-rank p-values for 8.5 Gy + peg-G-CSF versus 8.5 Gy alone for female and male rats are 0.05 and 0.0016, respectively. (B) Percent morbidity in pooled male and female rats (solid points) was fit with a probit regression analysis (solid line) to determine the expected percent mortality as a function of radiation dose. The calculated LD_50/30 (red dashed line) with 95% confidence interval (gray region) for untreated adult rats was 7.71 (7.6–7.8) Gy and for peg-G-CSF treated rats was 8.41 (8.2–8.6) Gy. The dose modifying factor (DMF) for Neulasta treatment is 1.09.

Figure 5.

(A) Kaplan-Meier (KM) survival plots days 30–300 in pooled male and female adult WAG/RijCmcr rats exposed to either 7.75 Gy (black line) or 8–8.5 Gy (peg-GCSF treated, red line). Survival at doses above 8 Gy is significantly reduced by about 26% with a log-rank p-value of 0.025. (B) Representative Masson’s trichrome staining of kidneys from a non-irradiated aged rat (left) and a rat euthanized at day 265 following 8.5 Gy TBI (right). Dashed white region indicates fibrotic Trichrome-stained glomeruli. Scale bar = 150 μm. (C) Urine protein/creatinine ratio measured at day 300 in female and male rats. (8 and 8.5 Gy doses received peg-GCSF). (D) BUN levels measured at day 300 in female and male rats. (8 and 8.5 Gy doses received peg-GCSF).