Cardioprotective properties of O-(beta-hydroxyethyl)-rutosides in doxorubicin-pretreated BALB/c mice.

Chronic doxorubicin-induced cardiotoxicity is believed to be caused by the formation of oxygen free radicals. Thus O-(beta-hydroxyethyl)-rutosides, a standardized flavonoid mixture (Venoruton) with iron chelating and radical scavenging activity, might provide protection. Therefore, we investigated the (cardio)protective effect of Venoruton (1.5 g/kg injected i.p. on days 1-5, 8-12, 15-19, and 22-26) in BALB/c mice treated with doxorubicin (4 mg/kg injected i.v. on days 1, 8, 15, and 22) compared with mice treated with doxorubicin alone. Saline-treated animals served as controls. No mortality was encountered in either of the groups; weight gain data suggest little general toxicity of this dose schedule. The basal frequency of the isolated right atria was increased in doxorubicin-pretreated animals as compared to control animals (468 +/- 22 and 366 +/- 20 beats/min, respectively). Venoruton coadministration diminished this increase (373 +/- 17 beats/min). The -log of the concentration giving 50% effect of l-isoprenaline on the right atrium was changed after doxorubicin pretreatment (8.33 +/- 0.04 versus 8.86 +/- 0.06 for control animals). Venoruton coadministration resulted in a smaller shift in the -log of the concentration giving 50% effect (8.51 +/- 0.10) than with doxorubicin alone. The extent of cardiotoxicity found in the functional studies was confirmed by histological scoring of heart ventricle damage. It can be concluded that Venoruton has the potential to protect against doxorubicin-induced cardiotoxicity.

Fractionation effects and repair kinetics in rat kidney.

Rat kidneys were unilaterally irradiated with up to 40 fractions of X rays. Fractionation regimens were given either with long intervals of 6-24 hr between fractions, resulting in complete recovery from sublethal damage, or with 1-hr intervals, resulting in largely incomplete repair. The non-irradiated kidney was surgically removed 4 weeks after the last fraction. The development of radiation-induced kidney damage was monitored by regular assessment of three different parameters indicative of kidney function: serum urea, the total volume of urine excreted in 24 hr and urine osmolality. At the end of the observation period, 18 months after treatment, the kidney was removed. The hydroxyproline content was determined and a histopathological analysis was performed. Since the 20 and 40-fraction data indicated a higher effectiveness of these regimens than would be expected on the basis of the LQ model, the data were divided in two subsets, 2-10 fractions (high doses per fraction) and 10-40 fractions (low doses per fraction), and analyzed separately. The time course of alpha/beta and T1/2 values was determined for each functional parameter separately, and for the data from the three parameters combined. A complex pattern was found, with the values for alpha/beta as well as T1/2 differing between the two data subsets between about 20 and 40 weeks after treatment. For the lower doses per fraction the alpha/beta values were generally higher and the repair half-times longer. After 40 weeks no significant differences were observed between the two data subsets. If the differences found earlier are ignored, overall alpha/beta and T1/2 values can be calculated. For early endpoints the alpha/beta was 1.69 (1.45, 1.90) Gy (95% confidence limits in parentheses), for late endpoints it was 1.77 (1.56, 2.00) Gy. The corresponding T1/2 values were 1.57 (1.44, 1.73) hr for early endpoints, and 2.10 (1.90, 2.34) hr for late endpoints. Hence, the alpha/beta values do not alter in time, but the T1/2 value for late damage might be higher than that for early damage.

Early and late effects of fractionated irradiation and the kinetics of repair in rat lung.

The thorax of WAG/Rij rats was irradiated with fractionated doses of X rays. Irradiation schedules were designed either to allow virtually complete repair of sublethal damage between subsequent fractions by fractionating at 6-h intervals, or to result in incomplete repair by allowing only 1-h intervals between subsequent fractions. Combination of the data from both experimental series permitted the calculation of alpha/beta ratios and values for the repair halftime T1/2. The animals were monitored by assessment of the breathing frequency and by recording deaths. At the end of the experiments, 18 months after treatment, the hydroxyproline content of the lung tissue was determined as a biochemical indicator of radiation-induced fibrosis, and an histopathological analysis was performed. Early endpoints, indicative of radiation-induced pneumonitis, resulted in an alpha/beta ratio of 3.5 Gy and a T1/2 value of 0.95 h. Late endpoints were presumed to be indicative of radiation-induced fibrosis. Based on the combined analysis of data from three different late endpoints, the mean alpha/beta ratio was 2.3 Gy, and the T1/2 value was 1.13 h. The difference in alpha/beta ratio and T1/2 value between early and late endpoints was not significant, since the 95% confidence limits were overlapping. For each individual early or late endpoint as well as for the two early or the three late endpoints combined, there was a trend for lower alpha/beta ratios and higher T1/2 values associated with low doses per fraction. However, widely overlapping confidence limits indicated that again the differences were not significant.

Effects of multifraction irradiation on the rat kidney.

Wag/Rij female rats were irradiated to the left kidney with single doses or 2, 4, 10, 20, or 40 equal dose fractions. The right kidney was removed 4 weeks after the last fraction. The kidney function was determined using three different parameters. The serum urea content indicated glomerular function. Urine osmolality and the total volume of urine excreted in 24 hr indicated tubular function. The onset as well as the rate of expression of radiation-induced kidney damage was dose-dependent. The kidney function decreased continuously. Differences in expression of damage between glomerular and tubular parameters were not observed. All parameters indicated marked sparing of the kidney by fractionation. In general, the data could be fitted to the linear-quadratic model, if the single dose data were not included in the analyses. However, the fit greatly improved when data obtained with high and low doses per fraction were analyzed separately. The Direct Analysis method was used to determine the alpha/beta ratios. No significant differences were observed between the alpha/beta ratios calculated for the different parameters. The ratios also did not change with increasing time after treatment. The alpha/beta for high doses per fraction was between 0.6 and 2.7 Gy, and that for low doses per fraction, with fractional doses in the clinical range, was between 0.5 and 3.8 Gy. The alpha/beta values for low doses per fraction were generally lower than those for high doses per fraction. These observations indicate a strong dependence of radiation-induced damage in the rat kidney on the size of the dose per fraction.