Claes Engelbrecht

Modulation of 5-fluorouracil metabolism by thymidine: In vivo and in vitro studies on RNA-directed effects in rat liver and hepatoma

The effects of thymidine (TdR) co-administration on the cytotoxicity and incorporation of 5-fluorouracil (5-FU) into RNA of various tissues was studied in rats bearing an ascites hepatoma (AH 130). The role of pyrimidine degradation in determining the modulating effects of TdR on the formation of FU-RNA was studied in hepatocytes and AH 130 cells in vitro. TdR (500 mg/kg) potentiated the antitumour effect of 5-FU (150 mg/kg) and also increased host toxicity as judged by changes in body weight. TdR given alone did not significantly affect tumour growth and body weight gain. Examination of the effect of TdR on the incorporation of 5-FU into RNA revealed a differential modulation of RNA-directed toxicity in different tissues. Incorporation of 5-FU into RNA in tumour and bone marrow was increased 2- and 4-fold, respectively. In spleen and kidney the incorporation increased by approximately 50%, but the values did not reach statistical significance. In contrast, the incorporation into RNA of liver and intestinal mucosa was decreased to ca 35% of the control. TdR at concentrations of 40 microM-40 mM progressively inhibited the degradation of 5-FU and decreased the incorporation of 5-FU into RNA of hepatocytes in vitro. In AH 130 cells in vitro TdR did not significantly influence the metabolism of 5-FU and the incorporation into RNA. These results demonstrate that the enhanced incorporation of 5-FU into tumour RNA in vivo after pretreatment with TdR is related not to local effects on the tumour cells but rather to an increased bioavailability of the drug. Although co-administration of TdR did not selectively enhance the antitumour effect of 5-FU, a differential toxicity in host tissues was indicated by the modulated incorporation of 5-FU into RNA.

Effects of partial hepatectomy on the utilization of 3h-thymidine in mice

Abstract 1. 1. Thymidine availability and specificity for DNA synthesis in various organs of hepatectomized and intact mice and the magnitude of catabolism of administered 3H-thymidine were investigated. 2. 2. The serum thymidine radioactivity 5 min after administration was 1.5 % of the total administered dose. The radioactivity decreased rapidly and was reduced to 1 % of the 5 min value after 2hr. 3. 3. β-AIB accumulated m serum until 20 min after injection and then its level decreased. The levels of thymidine and β-AIB radioactivity were increased 2–3 times after partial hepatectomy. 4. 4. Volatile radioactivity constituted 90% of the total serum radioactivity 60 min after injection. 5. 5. The level of acid soluble radioactivity in liver and kidney was higher, whilst that in spleen, thymus and cerebrum was lower than the serum acid soluble radioactivity until 60 min after injection. Liver and kidney acid soluble radioactivity was increased, but that of spleen, thymus and cerebrum was unaffected by partial hepatectomy. 6. 6. Sixty minutes after injection, the radioactivity in RNA was 1–10% of that in DNA per gram of spleen, thymus and regenerating liver, but 25 and 50 % of that in kidney and intact liver respectively. Incorporation of 3H-activity into liver RNA was increased 48 hr after partial hepatectomy; no difference was obtained in other organs. 7. 7. The main incorporation of 3H-thymidine into DNA was confined to the first 20 min after injection. The DNA radioactivity of the spleen was 2.3 %, thymus 0.4%, kidney 0.2% and that of intact liver 0.6 % of the total injected dose 60 min after injection. Forty-eight hours after partial hepatectomy the DNA radioactivity in the liver was 5 times that of control liver. At 24–72 hr after resection, incorporation of 3H-thymidine into DNA/g of liver was in the same range as that of thymus and spleen. The radioactivity of thymus and kidney DNA was reduced while that of liver DNA was at a maximum.

Urinary polyamine excretion as related to cell death and cell proliferation induced by carbon tetrachloride intoxication

This study addresses the question whether urinary polyamine excretion is related to cell death or cell proliferation. CCl4 intoxication of the rat was used as the experimental model. Treatment with CCl4, a hepatotoxic haloalkane, produces an initial phase of liver cell death succeeded by a regenerative phase of growth, during which the liver is restored. The highest rate of putrescine (and spermidine) excretion occurred during the first 24 hr of CCl4 intoxication and coincided with the period of maximum liver damage. During subsequent liver regeneration the rate of excretion of both polyamines decreased.

Serum and liver radioactivity levels in mice after intraperitoneal and subcutaneous injection of [14C]orotic acid

[14C]Orotic acid was rapidly distributed in blood after, both i.p. and s.c. injection but was not completely absorbed from the peritoneal cavity until 20 min after injection. S.c. injection should be an acceptable alternative to i.p. injection although the incorporation into the liver acid soluble- and RNA-fractions was somewhat delayed after the s.c. injection.

Utilization of labelled uridine, cytidine and orotic acid for determination of ribonucleic acid synthesis in mouse liver

[3H]uridine and [3H]orotic acid were equally utilized for labelling of RNA in mouse liver. Incorporation of [3H]cytidine was 2-3 times as high as that of [3H]-labelled uridine or orotic acid. These results differ from findings in rat liver, where both cytidine and orotic acid are better utilized for RNA labelling than is uridine. The ratio between liver RNA [3H]-activity and volatile [3H]-activity was 2, 3 and 13, respectively, at 300 min after injection of labelled uridine, orotic acid and cytidine, indicating an efficient chanelling of cytidine into liver anabolic pathways.

Concentration of uracil nucleotides and UDP-glucose in mouse liver after partial hepatectomy

Abstract 1. 1. The UTP and UDP concentration of mouse liver was not significantly affected by the partial hepatectomy, whereas the size of the UMP pool increased 3- to 4-fold when compared to unoperated controls. 2. 2. In regenerating liver, the UDP-glucose concentration decreased by 20% or more when compared to unoperated controls. 3. 3. The analysed metabolites were affected to the same extent by partial hepatectomy and by shamoperation.

Metabolism of uridine and determination of liver ribonucleic acid synthesis in developing and adult mice.

The metabolism of [5-3H]uridine and the incorporation of the precursor into liver RNA was studied in developing (13-day-old) and adult (45-day-old) mice. Different time-courses of labelling and increased amounts of labelled catabolic products of uridine were found in liver and blood of developing mice compared with adult animals. This is suggested to be a consequence of enlarged metabolite pools resulting from a lower total amount of uracil-degrading enzymes in the developing mice. The labelling of the uracil nucleotides was decreased in the developing liver. However, in spite of a lower specific radioactivity of UTP, the RNA-specific radioactivity of developing liver was increased compared with adult liver. Also the labelling of liver RNA with [6-14C]orotic acid was found to be increased in developing mice, thus indicating a higher rate of RNA synthesis in these animals. A more pronounced difference in liver RNA labelling between the developing and the adult mice obtained with the use of [14C]orotic acid than with [3H]uridine may suggest that the de novo pathway, relative to the salvage pathways, is more important in developing than in adult liver.