James W. Osborne

The effect of pentoxifylline on early and late radiation injury following fractionated irradiation in C3H mice

An experiment was performed to test the effectiveness of pentoxifylline in reducing late radiation injury. One hundred and four C3H mice were randomized into eight groups of 13 mice each, and the right hind limbs were irradiated with 4000, 5000, 6000, or 7000 cGy in ten fractions. Each group was treated with once daily injections of either pentoxifylline or saline for 30+ weeks. An additional ten mice received daily injections of pentoxifylline or saline, but no irradiation. The pentoxifylline animals demonstrated significantly less late injury than the saline treated animals. The most obvious differences were observed in the 5000 and 6000 cGy groups. There were seven radiation related deaths in the saline treated control groups, but only one radiation related death in the pentoxifylline treated groups. Whereas 42% (20/48) of the saline treated animals had a late injury score of 3.0 or greater, only 8% (4/51) of the pentoxifylline treated animals had a late skin score as high as 3.0. Pentoxifylline had no effect on the acute radiation injury scores. The drug was well tolerated with no toxic effects noted. Pentoxifylline is a methyl xanthine derivative that is used to treat vascular occlusive disease in humans. It improves perfusion through small capillaries by improving the deformability of red blood cells, inhibiting platelet aggregation, and stimulating the release of prostacyclin. This study shows that the prophylactic administration of pentoxifylline can modify late radiation induced injury in the mouse extremity. It may have value in the prevention or treatment of late radiation induced injury in humans, and it could be a useful tool to help define the mechanisms of late radiation injury in specific organs.

Effects of accelerated fractionation on radiation injury of the small intestine: A new rat model

The present study assessed the influence of shortening the overall treatment time (accelerated fractionation) on radiation injury of the small intestine. A rat model which allowed repeated irradiation of a localized segment of small intestine was developed. Young adult male Sprague-Dawley rats were orchiectomized, and a loop of the distal ileum was transposed to the left part of the scrotum. The intestinal segment was irradiated with a total dose of 56 Gy, given in 20 fractions, the total treatment time being either 26, 12, or 7 days (i.e. 1, 2, or 3 fractions per day). Radiation injury was assessed by histopathologic examination at 6 hr and at 2 weeks after the last irradiation. The surgical procedure was without complications. Shortening the overall treatment time by giving more than one radiation dose per day resulted in markedly increased injury both at 6 hr and at 2 weeks. It is concluded that accelerated fractionation results in increased radiation injury of the intestine when compared with standard fractionation. Because there may be a relationship between early and late effects in the intestine, our results also indicate that increased late radiation enteropathy may result from accelerated fractionation.

CHANGES IN THE RAT INTESTINE AFTER X-IRRADIATION OF EXTERIORIZED SHORT SEGMENTS OF ILEUM.

Segments of rat ileum 2.5 or 7.5 cm in length were x-irradiated with 3000 R or 5000 R under conditions of normal or restricted blood flow to the intestine. Most animals were allowed to live their life span for mortality studies, but others were killed between Day 5 and Day 44 for an assessment of the progression of histological changes in the irradiated segment. Time of death after irradiation was variable in each treatment category. Most animals died between 10 and 100 days; some lived beyond 200 days. The blood flow-restriction procedure extended the life span in the 3000 R-7.5-cm group, but was ineffective at 5000 R regardless of segment length. A lesion characterized by serosal fibrosis apparently secondary to mucosal ulceration was always produced, but the latent period between the events and the extent of fibrosis varied considerably. Death was almost always due to bowel obstruction. In the 2.5-cm segment exposed to 5000 R, the mucosa did not regenerate in 44 days, but in some of the 7.5-cm segments...

Immunization of rhesus monkeys against schistosome infection by cercariae exposed to high doses of x-radiation.

Summary Strong acquired resistance against schistosome infection in rhesus monkeys can be induced by previous immunizations with cercariae exposed to large amounts of X-radiation; i.e., 24,000 or 48,000 R. This indicates that acquired resistance against schistosome infection can be induced exclusively from functional antigen produced after contact or deterioration of the schistosomular stage in the dermal tissues.

INTESTINAL COMPLICATIONS FOLLOWING ACCELERATED FRACTIONATED X-IRRADIATION An experimental study in the rat

Due to paucity of suitable animal models, it has been difficult to study the development of long-term intestinal complications following fractionated irradiation. We recently developed a model which allows multiple radiation exposures of a short segment of rat ileum without the need for repeated surgery. In the present series, this model was used to study the influence of shortening the total treatment time (accelerated fractionation) on development of radiation enteropathy. Male rats were orchiectomized and a short segment of distal ileum was transposed to the scrotum. Starting 3 weeks after surgery, the scrotum containing the intestinal segment was x-irradiated with 20 fractions of 2.8 Gy (total dose 56 Gy). Two fractionation schedules were compared: One fraction per day (total treatment time 26 days) and 3 fractions per day (total treatment time 7 days). Actuarial survival curves were obtained, and the degree of radiation injury was assessed 2, 8, and 26 weeks after the last radiation exposure using a semiquantitative histopathologic scoring system. There was no mortality from acute radiation injury in either treatment group. All animals of the 1-fraction/day group survived the observation period (26 weeks). In the 3-fraction/day group, there was significant mortality due to intestinal obstruction, and cumulative mortality at 26 weeks was 100%. Radiation injury, as assessed by the histopathologic scoring system, was also more pronounced in this group than in the 1-fraction/day group. We conclude that shortening the total treatment time significantly increases the severity of late intestinal complications. Our data are suggestive of an association between acute mucosal damage and chronic radiation injury of the small intestine.

INTESTINAL FLORA IN WHOLE-BODY AND INTESTINAL X-IRRADIATED RATS.

Striking changes occurred in mid-small intestinal and cecal flora of rats after exposure to 1400 R of whole-body irradiation or 2000 R of intestinal irradiation delivered at 250 kVp and 30 mA. The changes reached a maximum 3 days after irradiation. A consistent 100- to 10,000-fold increase in coliforms and enterococci occurred at both sites, and similar increases in proteus occurred in most animals. The normally predominant lactobacilli decreased slightly in numbers or remained unchanged. Other organisms participated less constantly in the overgrowth. Massive bacterial invasion of the severely injured small intestinal mucosa did not occur. There was no difference in bacterial invasion of mesenteric lymph nodes, spleen, liver, or heart blood between control and irradiated animals. The bacterial overgrowth in the intestines was effectively prevented by orally administered neomycin-polymyxin B-bacitracin without altering mortality. The findings indicate that massive intestinal flora changes occur in rats wit...

The prevalence and severity of late effects in normal rat duodenum following intraoperative irradiation.

In humans, a portion of the duodenum is often at risk for radiation-induced complications following intraoperative radiation therapy for pancreatic carcinoma. To determine experimentally the prevalence and severity of late effects in the normal mammalian duodenum, 190 rats received single doses of 0, 15, 20, 25, 30, or 40 Gy orthovoltage X rays to temporarily exteriorized 3 cm circumferential segments of duodenum. The animals were killed 2, 6, 8, or 10 months later. Actuarial survival, change in body weight, and a radiation injury score based on eight histopathologic alterations were used as endpoints. Epithelial atypia, intestinal wall fibrosis, serosal thickening, and vascular sclerosis were the dominant histopathologic alterations at all dose levels throughout the 10-month observation period. The prevalence and severity of histologic radiation injury showed sigmoidal dose-response relationships with the plateaus starting at 20 Gy. Doses of 20 Gy or greater also resulted in a substantial loss of body weight and a high level of early deaths (20-80 days). All endpoints indicate that intraoperative doses of 20 Gy or greater are associated with unacceptable risks of late and irreversible complications.

The Kinetics of Cellular Recovery in Locally X-Irradiated Rat Ileum

treated and control animals were given tritiated thymidine ip and killed one hour later. The irradiated or sham-irradiated segment and segments of shielded intestine 5 cm and 10 cm distal to the irradiated or sham-irradiated segments were removed and appropriately processed for histologic and autoradiographic studies. At each time sampled, the number of total cells per crypt section in both the irradiated segment and the shielded segment 5 cm distally was greater than in the respective control segments. The differences between treated and control values decreased with time after irradiation. The percent labeled cells per crypt section for samples from the irradiated area and from the segment located 5 cm distally were not different from controls. The total cells, labeled cells, and percent labeled cells per crypt section in the segment located 10 cm distally were not different from the respective control values. The results obtained indicate that local irradiation of the intestine does not change the relative size of the proliferative compartment. This is in contrast to the situation which exists after whole-body exposure to 1000 R in which the entire crypt becomes proliferative. The mucosal cell proliferation rate is slightly increased in a shielded ileal segment 5 cm from the site of local irradiation, suggesting that there is an attempt by adjacent unirradiated tissue to compensate for the temporary loss of functional crypts. The compensatory increase in cellularity in both the irradiated and shielded intestine, followed by a decrease toward control values with time after irradiation and increased distance from the irradiation site, suggests a local, temporary influence associated with

Erythropoietic stimulating factor (ESF) as a stimulant of tumor growth.

Summary Four experimental procedures have been tested for ability to increase ESF concentrations (as measured by Fe59 uptake) and increase tumor growth. It was concluded that ESF extracts prepared by a modified method of Borsook or the method of White and procedures which increase endogenous ESF production (partial hepatectomy and cobalt chloride administration) are capable of stimulating Novikoff hepatoma growth in rats.

Induced Hypoxia in Rat Pulp and Periapex Demonstrated by 3H-Misonidazole Retention

Cellular hypoxia may be a useful indication of tissue distress in the dental pulp that could be used to investigate the early stages of pulpal responses. Tritiated misonidazole (3H-MISO) is a marker which preferentially labels cells with decreased oxygen tension (hypoxia). The experiments reported here were carried out to determine whether this agent could distinguish between hypoxic and normoxic pulp and periapical tissues. Rats were injected intra-peritoneally with either 3H-MISO, unlabeled MISO, or saline, then divided into normoxic, hypoxic, and control groups. Normoxic animals were maintained at ambient pressure. We induced hypoxia by maintaining animals in a hypobaric chamber at 0.5 atm for 24 hrs. 3H-MISO retention was assessed by quantitative analysis of tissue autoradiographs. 3H-MISO retention rates in normoxic animals showed little variation except for increased retention in mature ameloblasts and immature odontoblasts in the continually erupting incisor. In both incisor and molar pulps, hypobaric hypoxia significantly increased 3H-MISO retention when compared with normoxic controls. Hypobaric hypoxia also resulted in intense 3H-MISO retention in cellular cementum, periodontal ligament, osteocytes, and, occasionally, in molar pulp horn odontoblasts. This study demonstrated that, with standard autoradiographic techniques, 3H-MISO can label induced hypoxic disturbances in the pulp and surrounding periodontium.