Y. Oussoren

Repair of sublethal radiation injury after multiple small doses in mouse kidney: An estimate of flexure dose

Functional kidney damage in mice was measured after a series of fractionated X-irradiations. Doses per fraction of 0.75-12.5 Gy were given as 2, 5, 10, 30, 40, 60, or 80 equal doses in a total treatment time of 4 weeks. Renal function (measured by clearance of 51CrEDTA or hematocrit levels) deteriorated progressively, in a dose related manner, from 20 to 46 weeks after the start of treatment. The changes in renal function versus time were fitted by a polynomial regression through all data and interpolated values for 51CrEDTA clearance were then calculated at 30 and 40 weeks after treatment. Steep dose response curves were obtained and these were used to calculate isoeffective doses for the different fractionation schedules. There was a marked increase in total isoeffective doses from 2-30 fractions and these data were well described by a linear quadratic (L.Q.) expression for damage with an alpha/beta ratio of 2.3 +/- 0.2 Gy. There was only a slight increase in the total isoeffect dose as the size of the dose per fraction was decreased below 2 Gy and the measured isoeffect doses after 40 to 80 fractions were lower than predicted on the basis of an L.Q. model assuming complete repair between successive irradiations. The flexure dose for mouse kidneys irradiated 3 times per day was, effectively, 1 to 2 Gy and hyperfractionation using lower doses per fraction did not lead to significant, additional repair.

Early and late damage in the mouse rectum after irradiation andcis-diamminedichloroplatinum(II)

Summary The effects of radiation and cis -diamminedichloroplatinum(II) (c-DDP) in the mouse rectum were assessedusing two functional endpoints (anal discharge/diarrhoea and body weight changes), one lethal endpoint (obstructive rectal stenosis) and a microscopic endpoint (semiquantitative histological scoring). After irradiation, anal discharge, diarrhoea and lethal rectal stenosis were found to be the result of submucosal fibrosis with a secondary mucosal ulcer due to mechanical damage by the faeces. Weight loss at both early and late times after irradiation seemed to be related to epithelial cellular depletion. c-DDP, when given in combination with X-rays, did not enhance the incidence of late anal discharge, diarrhoea or rectal stenosis. Using an arbitrary semiquantitative scale for measuring the degree and extent of late rectal injury, c-DDP sometimes seemed to postpone the expression of radiation damage in the rectum. This effect, however, might also be the result only of interexperimental variation. An increase by c-DDP in the early body weight loss after irradiation was also observed which could be explained by an additive effect in the rectal epithelium.

Amelioration of Radiation Nephropathy by Acetylsalicylic Acid

This investigation was carried out to assess the amelioration by two antithrombotic drugs of radiation nephropathy in mice. Mouse kidneys were given split-dose irradiation to total doses between 17 and 22 Gy. A first group of animals was given acetylsalicylic acid (ASA) in drinking water, a second received daltroban, a thromboxane A2/prostaglandin H2 receptor antagonist, and a third received normal tap water, serving as a control. Both antithrombotic drugs were started 1 week prior to the irradiation and were given throughout the whole follow-up period. Renal function was assessed every 4 weeks from 18 weeks after the start of irradiation onwards by measuring the [51Cr] EDTA retention and haematocrit. The dose of ASA (600 mg/kg/day) caused an inhibition of thromboxane A2 and prostacyclin biosynthesis to 19 +/- 10 (mean +/- SEM) and 85 +/- 22%, respectively, as assessed by the excretion of their urinary metabolites. A significant sparing effect on the renal function after irradiation was observed in the ASA-treated animals. Using the latency time to reach 4% residual plasma activity of [51Cr] EDTA, a dose-modifying factor of 1.19 was calculated. No effect was seen with daltroban (10 mg/kg/day). Histopathological analysis of the kidneys at 12 months after irradiation demonstrated a substantially lower level of damage in the ASA-treated mice compared with daltroban-treated and radiation-only animals. These data indicate that long-term treatment with ASA is effective in reducing renal functional impairment after irradiation.

Mechanisms for optimising photodynamic therapy: second-generation photosensitisers in combination with mitomycin C

Mechanisms for improving photodynamic therapy (PDT) were investigated in the murine RIF1 tumour using meso-tetrahydroxyphenylchlorin (m-THPC) or bacteriochlorin a (BCA) as photosensitisers and comparing these results with Photofrin-mediated PDT. The 86Rb extraction technique was used to measure changes in perfusion at various times after interstitial PDT. Non-curative combinations of light doses with m-THPC and BCA PDT markedly decreased vascular perfusion. This decrease was more pronounced for both new photosensitisers than for Photofrin. Comparison of tumour perfusion after PDT with tumour response revealed an inverse correlation for all three photosensitisers, but the relationship was less clear for m-THPC and BCA. In vivo/in vitro experiments were performed after Photofrin or m-THPC PDT in order to assess direct tumour kill (immediate plating) vs indirect vascular effects (delayed plating). For both photosensitisers, there was little direct cell killing but clonogenic survival decreased as the interval between treatment and excision increased. When m-THPC PDT was combined with mitomycin C (MMC), light doses could be decreased by a factor of 2 for equal tumour effects. Lower light and m-THPC doses could be used compared with Photofrin PDT in combination with MMC. BCA PDT with MMC did not result in a greater tumour response compared with BCA PDT alone. Reduction in both light and photosensitiser does for effective PDT regimes in combination with MMC offers substantial clinical advantages, since both treatment time and skin photosensitisation will be reduced.

Loss of Reirradiation Tolerance in the Kidney with Increasing Time after Single or Fractionated Partial Tolerance Doses

The aim was to determine the influence of initial dose and dose per fractionation on retreatment tolerance of the kidney. Mouse kidney was bilaterally irradiated with various single or fractionated X-ray doses equivalent to about 12-70% of a defined response dose. The mice were retreated with a range of single doses after 2 or 26 weeks. The development of functional kidney damage was followed by monthly testing of clearance of 51CrEDTA until the animals expressed overt renal dysfunction (maximum follow-up 70 weeks after retreatment). Reirradiation tolerance was assessed by probit analysis and Kaplan-Meier actuarial estimates of the incidence of a defined level of renal damage at 40 weeks after retreatment. Doses required to give a 50% incidence of damage (RD50) were compared for animals that had received previous single dose or fractionated irradiations, or that were previously unirradiated. Multivariate analysis of time to expression of renal damage (latency) was also done using the Cox Proportional Hazards model. Results demonstrated that previous irradiation always compromised retreatment tolerance, even for intervals of 26 weeks after initial treatments with < 20% full response dose. Reirradiation tolerance was inversely related to the initial dose and tolerance decreased significantly with increasing interval between treatments, suggesting progression rather than recovery from the initial damage. Linear-quadratic analysis of the data for reirradiation at 26 weeks after partial-response doses gave an alpha/beta = 1.4 Gy. This was significantly lower than the alpha/beta = 3.3 Gy obtained for initial treatments alone (no retreatment), indicating a larger fractionation-sparing effect for the retreatment situation.

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 alpha/beta ratio of 7.7 Gy, which is significantly greater than the alpha/beta 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.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.

Acute and late radiation damage in mouse bladder: A comparison of urination frequency and cystometry

Functional damage in the mouse bladder was measured sequentially from 1 to 53 weeks after irradiation with a range of X ray doses (10 to 30 Gy). Damage was assessed from the independent assays of urination frequency and cystometric measurement of bladder volume at a constant intravesical pressure. There was an early, transient wave of damage from 1 to 3 weeks after bladder irradiation. During this period the urination frequency was increased to greater than or equal to 2 times control levels in 20 to 70% of the mice (depending on dose) after 15 to 30 Gy. Bladder volume was reduced to less than or equal to 50% of control values in 20 to 40% of the mice after doses of 20 to 30 Gy. This early damage usually lasted for less than 1 week and occurred at times ranging from 5 to 21 days, independent of dose. There was no significant correlation between response as measured by the two assays on an individual animal basis during the early period. The incidence of reduced bladder volume, measured cystometrically in anesthetized mice, tended to be less than the incidence of increased urination frequency, measured in non-anesthetized animals. Late bladder damage developed from 16 to 40 weeks after doses of greater than or equal to 20 Gy, and the time of onset was inversely related to dose. Less than 20% of mice treated with 10 to 15 Gy developed late bladder damage as assessed by increased urination frequency or reduced bladder volume. Late bladder damage was irreversible and there was a good correlation between response of individual animals as measured by the two assays. We conclude that changes in both urination frequency and bladder volume can be used as quantitative measures of early and late functional damage after bladder irradiation. The early, transient damage was not associated with changes in the urothelium or muscle layers of the bladder, whereas the late, persistent damage was accompanied by epithelial denudation and focal hyperplasia, with fibrosis and ulceration after higher doses.

Dose and time effects of cis-diamminedichloroplatinum(II) and radiation on mouse duodenal crypts

The effect of cis-platinum and radiation on mouse duodenal crypts was assessed using the microcolony assay. The diameters of regenerating crypts were measured at various times after X-rays and cis-platinum given either alone or in combination. It appeared that the appropriate time of assay after any of these treatments was 88 h. When 10 mg/kg of cis-platinum was administered 24 h before, 0.5 h before or 10 min after radiation, the X-ray survival curve for crypt stem cells was shifted towards lower doses, with a Dose Effect Factor (DEF) of 1.2-1.3. When the drug was given one week before X-rays, no effect on the survival curve was observed. The slope of the X-ray survival curve was not modified by cis-platinum. When the drug was given within 6 h time of X-rays, the increased killing of crypt cells by cis-platinum was the same irrespective of the sequence of administration. These data suggest that cis-platinum and radiation kill crypt cells by independent cellular mechanisms. A survival curve for crypt cells was also obtained after graded doses of cis-platinum alone. It was characterised by a D0 of 3.18 +/- 0.40 mg/kg (1 S.E.) and an extrapolation number N of 2.9 X 10(4). When the drug treatment was combined with a single dose of X-rays, this survival curve was shifted towards lower drug doses without a significant change in the slope (D0 = 2.87 +/- 0.37 mg/kg). This suggests that independent killing of crypt cells by the two agents occurred over a wide range of drug doses.

Increased Expression of Glomerular von Willebrand Factor after Irradiation of the Mouse Kidney

Ionizing irradiation has been shown to induce an increased release of von Willebrand factor (vWF) in human endothelial cells in vitro. The present study was undertaken to investigate whether an increase in expression of vWF also occurs in glomerular endothelial cells in vivo after irradiation of the kidney. Increased expression of vWF may initiate prothrombotic changes, and the resultant vascular damage could cause renal failure. The amount of adherent leukocytes in the renal cortex after irradiation was also quantified, since this may contribute to the histological changes that occur after irradiation. Changes in expression of glomerular vWF and in the amount of leukocytes were related to the development of impairment of renal function, as assessed with the [51Cr]EDTA retention assay. Mice were given bilateral irradiation (single dose of 16 Gy) or were sham-irradiated and were sacrificed at intervals of 1 day to 40 weeks after irradiation. Immunohistochemical analysis of kidney cryosections was performed using a polyclonal vWF antibody or monoclonal CD45 antibody (leukocyte common antigen). The amount of glomerular vWF staining and CD45 staining in the renal cortex (percentage surface coverage) was quantified using a computerized image analyzer. The mean glomerular vWF staining in the nonirradiated kidneys was 34.4 +/- 6.2% (mean +/- SEM, 10 weeks after sham treatment). After irradiation, the expression of glomerular vWF increased gradually from 10 weeks to 53.4 +/- 3.6% at 40 weeks. The total number of leukocytes in the renal cortex of nonirradiated mice at 10 weeks after sham treatment was low, with a mean area of 1.0 +/- 0.09%, whereas in the irradiated kidneys the relative tissue area covered by leukocytes increased to 7.6 +/- 2.1% at 40 weeks. These alterations preceded impairment of renal function. The extent to which these changes are causally related to impairment of function will be the subject of future study using specific antithrombotic and anti-inflammatory agents.

Long-term effects of total-body irradiation on the kidney of Rhesus monkeys

PURPOSE To investigate the long-term effects of total-body irradiation (TBI) on kidneys in non-human primates. METHODS AND MATERIALS The kidneys of Rhesus monkeys were histologically examined at 6-8 years after TBI with low single doses of 4.5-8.5Gy or two fractions of 5.4Gy. The kidneys of age-matched non-irradiated monkeys served as controls. Irradiation was performed on adult monkeys aged about 3 years; 6-8 years later animals were sacrificed and the kidneys removed and processed for histology. A semi-quantitative scoring system was used to evaluate overall histological damage. Glomerular changes were also morphometrically analysed according to previously published criteria. In selected dose groups (pro)thrombotic and inflammatory changes were investigated by immunostaining cryosections with antibodies against von Willebrand factor (vWF), leukocytes and macrophages. RESULTS Histological changes were generally mild and only seen in kidneys irradiated with doses higher than 7 Gy. Glomerular changes were characterized by increased mesangial matrix and capillary dilatation. Tubulo-interstitial changes included hypercellularity, fibrosis and mild tubular atrophy. The mean glomerular area expressing vWF protein in the irradiated kidneys was not different from that in the age-matched controls. Numbers of infiltrating leukocytes were not significantly different between irradiated kidneys and controls. However, slightly increased numbers of macrophages were present in the renal cortex after irradiation. CONCLUSIONS Renal damage after TBI of Rhesus monkeys with single doses of 4.5-8.5 Gy or two fractions of 5.4 Gy was mild, even after follow-up times of 6-8 years.Purpose : To investigate the long-term effects of total-body irradiation (TBI) on kidneys in non-human primates. Methods and materials : The kidneys of Rhesus monkeys were histologically examined at 6–8 years after TBI with low single doses of 4.5–8.5 Gy or two fractions of 5.4 Gy. The kidneys of age-matched non-irradiated monkeys served as controls. Irradiation was performed on adult monkeys aged about 3 years; 6–8 years later animals were sacrificed and the kidneys removed and processed for histology. A semi-quantitative scoring system was used to evaluate overall histological damage. Glomerular changes were also morphometrically analysed according to previously published criteria. In selected dose groups (pro)thrombotic and inflammatory changes were investigated by immunostaining cryosections with antibodies against von Willebrand factor (vWF), leukocytes and macrophages. Results : Histological changes were generally mild and only seen in kidneys irradiated with doses higher than 7 Gy. Glomerular changes were characterized by increased mesangial matrix and capillary dilatation. Tubulo-interstitial changes included hypercellularity, fibrosis and mild tubular atrophy. The mean glomerular area expressing vWF protein in the irradiated kidneys was not different from that in the age-matched controls. Numbers of infiltrating leukocytes were not significantly different between irradiated kidneys and controls. However, slightly increased numbers of macrophages were present in the renal cortex after irradiation. Conclusions : Renal damage after TBI of Rhesus monkeys with single doses of 4.5–8.5Gy or two fractions of 5.4Gy was mild, even after follow-up times of 6–8 years.