Incorporation of zidovudine into cord blood DNA of infants and peripheral blood DNA of their HIV-1-positive mothers

The nucleoside analogue 3'-azido-3'-deoxythymidine (AZT) is a weak carcinogen in adult female mice and a moderately strong carcinogen in the offspring of female mice given the drug during gestation. In addition, incorporation of AZT into DNA was observed in multiple organs of transplacentally exposed newborn mice. Here we investigate the incorporation of AZT into peripheral leukocyte DNA of HIV-1-positive adult pregnant women given AZT for variable times during gestation and cord blood of infants exposed to AZT in utero. The length of treatment varied between 10 days and 9 months. High molecular weight DNA was extracted from maternal peripheral blood mononuclear cells (PBMC) and infant cord blood. A specific AZT-DNA radioimmunoassay was used to determine the amount of AZT incorporated into leukocyte DNA. Incorporation of AZT into DNA ranged up to 183.3 and 344.5 molecules of AZT/10(6) nucleotides in the mothers and infants, respectively, and was detected in about 70% of samples. Therefore, AZT-induced mutagenic events are possible in the majority of adults and infants. No correlation was found between level of incorporation and length of AZT treatment, suggesting that the differences observed among the individuals arise from variability in AZT metabolism. These data support previous observations that a high degree of inter-individual variability in AZT phosphorylation occurs in primates.

Incorporation of zidovudine into leukocyte DNA from HIV-1-positive adults and pregnant women, and cord blood from infants exposed in utero

OBJECTIVE

The nucleoside analog 3'-azido-3'-deoxythymidine (ZDV) has widespread clinical use but also is carcinogenic in newborn mice exposed to the drug in utero and becomes incorporated into newborn mouse DNA. This pilot study was designed to determine ZDV incorporation into human blood cell DNA from adults and newborn infants.

DESIGN

In this prospective cohort study, peripheral blood mononuclear cells (PBMC) were obtained from 28 non-pregnant adults and 12 pregnant women given ZDV therapy, six non-pregnant adults with no exposure to ZDV, and six non-pregnant adults who last received ZDV > or = 6 months previously. In addition, cord blood leukocytes were obtained from 22 infants of HIV-1-positive, ZDV-exposed women and from 12 infants unexposed to ZDV. There were 11 mother-infant pairs involving HIV-1 -positive women.

METHODS

DNA was extracted from PBMC obtained from non-pregnant HIV-1-positive adults taking ZDV, pregnant HIV-1-positive women given ZDV during pregnancy, and from adults not taking ZDV. Cord blood leukocytes were examined from infants exposed to ZDV in utero and from unexposed controls. DNA samples were assayed for ZDV incorporation by anti-ZDV radioimmunoassay (RIA).

RESULTS

The majority (76%) of samples from ZDV-exposed individuals, pregnant women (8 of 12), non-pregnant adults (24 of 28), or infants at delivery (15 of 22), had detectable ZDV-DNA levels. The range of positive values for ZDV-treated adults and infants was 25-544 and 22-452 molecules ZDV/10(6) nucleotides, respectively. Analysis of 11 mother-infant pairs showed variable ZDV-DNA incorporation in both, with no correlation by pair or by duration of drug treatment during pregnancy. Two of the 24 samples from individuals designated as controls were positive by anti-ZDV RIA. The 20-fold range for ZDV-DNA values in both adults and infants suggested large interindividual differences in ZDV phosphorylation.

CONCLUSIONS

Incorporation of ZDV into DNA was detected in most of the samples from ZDV-exposed adults and infants. Therefore, the biologic significance of ZDV-DNA damage and potential subsequent events, such as mutagenicity, should be

Screen of five alkyl carbamates for initiating and promoting activity in rat liver

Five alkyl carbamates, methyl, ethyl, propyl, hydroxypropyl and ethylhexyl, were tested for initiating and promoting activity in rat liver. The test for initiating activity consisted of administering the carbamate by gavage to male Sprague--Dawley rats at either 6 or 18 h after a 2/3 partial hepatectomy. One week later, the rats received 500 ppm sodium phenobarbital in their drinking water until killed 10 weeks later. None of the carbamates at 1/5 the LD50 induced gamma-glutamyltranspeptidase (GGT)-positive foci, indicating the lack of initiating activity. The tumor promoting activity test consisted of initiation with 80 mmol/kg diethylnitrosamine administered 18 h after a partial hepatectomy. One week later, the rats received one of the the carbamates at either 1/10 or 1/20 the LD50 5 days per week until sacrificed 10 weeks later. The alkyl carbamates increased the volume of the foci, the percent of the liver occupied by the foci, the number of foci/cm3 (except ethylhexyl carbamate), and the number of foci/liver (except ethylhexyl carbamate). These results suggest that the alkyl carbamates are tumor promoters and not tumor initiators in rat liver.

The effect of single versus split doses of diethylnitrosamine on the induction of gamma-glutamyltranspeptidase-foci in the livers of adult and juvenile rats

The induction of gamma-glutamyltranspeptidase (GGT)-foci by single and by split doses of diethylnitrosamine (DENA) was evaluated in the livers of juvenile and young adult male, Sprague-Dawley rats. A single dose of DENA was administered at either 32, 41, 46, 52 or 56 days of age and followed by a promoting regimen of sodium phenobarbital in the drinking water. In 32 days old rats, DENA resulted in a higher incidence of GGT-foci/cm3 than was observed when it was administered to 41 or 46 day old rats. The same dose of DENA was inactive in 52 or 60 day old rats. In rats initiated with DENA on day 32 of age, starting the phenobarbital promotion at 41 days of age resulted in a higher incidence of GGT-foci than when the phenobarbital treatment was begun at 60 days of age. When the dose of DENA was split into five daily doses of DENA starting on day 32 of age, the incidence of GGT-foci/cm3 was equivalent to the single dose given on day 32 of age. However, when the five daily doses were started on 48 days of age, the incidence of GGT-foci/cm3 was less than the five doses of DENA started on day 32 of age. Hence, juvenile rats were more sensitive to both single and split doses of DENA than adult rats. The dose-response relationship was also determined in juvenile rats for a single and for up to 64 daily doses of 3 mg/kg DENA started on day 32 of age. The dose-response relationship for a single dose of 3-96 mg/kg DENA was equivalent to the relationship of one to 32 daily 3 mg/kg doses. Thus, low daily doses of DENA were additive when started in juvenile rats. Neither a threshold nor a plateau was obtained for the dose-response relationship of DENA initiation of GGT-foci.

Effect of coadministration of phenobarbital sodium on N-nitrosodiethylamine-induced gamma-glutamyltransferase-positive foci and hepatocellular carcinoma in rats

The effect of concurrent administration of phenobarbital on the hepatocarcinogenicity of N-nitrosodiethylamine (diethylnitrosamine; DENA) in rats was investigated by determination of the incidence of gamma-glutamyltransferase (gamma-glutamyltranspeptidase) (GGT)-positive foci and liver tumors. Male outbred Sprague-Dawley rats received either a weekly oral dose of DENA (0.08 mol/kg), phenobarbital sodium (500 ppm) in their drinking water, or DENA and phenobarbital sodium concurrently. After 16 weeks, only the animals treated concurrently with DENA and phenobarbital sodium had GGT-positive foci (3.65 foci/cm2). At 30 weeks, the group treated with DENA and phenobarbital sodium exhibited more foci (23.6 foci/cm2) compared to the group that received only DENA (3.08 foci/cm2). The average size of foci in both of the DENA-treated groups was the same. The tumors in the group that received DENA plus phenobarbital sodium showed a greater incidence of GGT activity compared to the tumors in the DENA group. Under the conditions of this study the incidence of GGT-positive foci did not predict the incidence of hepatocellular carcinomas.

Effects of strain, sex, route of administration and partial hepatectomy on the induction by chemical carcinogens of gamma-glutamyltranspeptidase foci in rat liver

The incidence of gamma-glutamyltranspeptidase (GGT)-positive foci induced by 0.3 mmol/kg diethylnitrosamine (DENA) followed by promotion with 500 ppm sodium phenobarbital in drinking water and was the same in Fischer 344, Sprague-Dawley and Wistar-Lewis rats. There was no difference in the level of GGT-foci initiated by DENA, 7,12-dimethylbenz[a]-anthracene (DMBA), or 1,2-dimethylhydrazine (DMH) followed by promotion with phenobarbital with respect to sex or route of administration including gavage and intraperitoneal injection. Maximal stimulation by partial hepatectomy of DENA initiation of GGT-foci occurred when the DENA was administered 18 h after the operation. Our results indicate that the optimal protocol for the rat liver foci assay consists of using partial hepatectomized rats of 1 of the 3 strains and of either sex. The test substance should be administered by either gavage or intraperitoneal injection so that maximal DNA binding coincides with the maximal rate of DNA replication resulting from partial hepatectomy.

Promotion by polychlorinated biphenyls of enzyme-altered foci in rat liver

Aroclor 1254 is a complex mixture of polychlorinated biphenyls (PCB) that upon prolonged administration has been reported to produce hepatic tumors in mice and rats. The ability of Aroclor 1254 to promote enzyme-altered foci was determined in an initiation/promotion bioassay in rat liver. Initiation was accomplished in rats that received a 2/3 partial hepatectomy followed in 24 h by diethylnitrosamine (DENA). Aroclor 1254 was administered to each rat 7, 28 and 49 days after the DENA and some of the rats were killed 21 days after each dose of Aroclor. The liver of rats that received Aroclor 1254 on either day 7 or on day 7 and 28 contained an increased incidence of gamma-glutamyltranspeptidase (GGTase)-positive foci compared to partial hepatectomized and DENA treated rats given tricaprylin (the solvent for Aroclor 1254). Therefore, Aroclor 1254 was demonstrated to enhance the appearance of enzyme-altered foci after only a single oral dose.

Sex difference in enhancement of GGTase-positive foci by hexachlorobenzene and lindane in rat liver

The ability of hexachlorobenzene and lindane in diethylnitrosamine (DENA) pretreated rats to enhance the incidence of gamma-glutamyltranspeptidase (GGTase)-positive foci was determined. In rats that received either DENA followed by a basal agar diet or hexachlorobenzene or lindane without prior administration of DENA, the incidence of GGTase-positive foci was negligible. When hexachlorobenzene or lindane were administered in the diet to rats that previously received a 2/3 partial hepatectomy prior to the DENA. The results suggest that hepatocarcinogenicity of hexachlorobenzene and lindane results from tumor promotion.