Connie Nosbisch

Transplacental pharmacokinetics of dideoxyinosine in pigtailed macaques.

To determine whether dideoxyinosine is actively transported across the placenta, four pregnant macques (Macaca nemestrina) near term and their fetuses were infused intravenously in random order with simultaneous doses of dideoxyinosine (42.5 micrograms/min/kg of body weight) and antipyrine (41.7 micrograms/min/kg) for 30 h. The infusions took place after the dams had been chronically catheterized at 128 +/- 0.8 days of gestation. In a third infusion, the dams alone received a higher dosage of dideoxyinosine (425 micrograms/min/kg) and the same dosage of antipyrine (41.7 micrograms/min/kg). Samples of maternal and fetal blood and amniotic fluid were collected at intervals for up to 30 h. The concentrations of dideoxyinosine and antipyrine were determined by high-performance liquid chromatography. The transplacental maternal-fetal drug clearances were compared by the paired Students t test. The ratio (mean +/- standard deviation) of the steady-state plasma dideoxyinosine concentration in the fetus to that in the dam was 0.49 +/- 0.10 at the low dideoxyinosine infusion rate and 0.51 +/- 0.00 at the high dideoxyinosine infusion rate. The clearance associated with maternal-fetal transfer of the drug, CLdf (0.38 +/- 0.21 ml/min/kg), was not significantly different (P > 0.05) from the clearance associated with fetal-maternal transfer of the drug, CLfd (0.56 +/- 0.27 ml/min/kg). Also, CLdf was not significantly different (P > 0.05) from CLfd when normalized with respect to the corresponding transplacental clearance of antipyrine (0.07 +/- 0.04 CLdf versus 0.09 +/- 0.04 CLfd). ur data indicate that passage of dideoxyinosine across the placenta in pregnant M. nemestrina near term is passive and constant over the dosage range studied.

Fetal, infant, and maternal toxicity of zidovudine (azidothymidine) administered throughout pregnancy in Macaca nemestrina

The toxicity of azidothymidine (AZT) was studied in monkey dams and fetuses that were exposed to the drug over the entire gestational period. Fourteen virus-free female macaques (Macaca nemestrina) were randomly assigned to AZT or control groups. AZT animals received the drug through a gastric catheter at a dose of 1.5 mg/kg every 4 hours, which produced plasma concentrations similar to those in humans taking 500 to 600 mg/day of AZT. Control animals received water placebo, also through gastric catheter. Some animals participated in both groups. All females were mated with the same male; 41 matings produced 20 pregnancies, of which 16 were carried to term (9 in AZT females; 7 in control females). The AZT animals developed an asymptomatic macrocytic anemia, but hematologic parameters returned to normal when AZT was discontinued. Total leukocyte count decreased during pregnancy and was further affected by AZT administration. AZT-exposed infants were mildly anemic at birth. AZT caused deficits in growth, rooting and snouting reflexes, and the ability to fixate and follow near stimuli visually, but the deficits disappeared over time. These data indicate that early exposure to AZT in utero should have no irreversible adverse effects on the fetus.

Development of a chronically catheterized maternal-fetal macaque model to study in utero mother-to-fetus HIV transmission: A preliminary report

Abstract: The lack of a representative animal model that permits frequent in utero fetal blood sampling is a major limiting factor for the study of maternal‐fetal HIV transmission. Therefore, we have developed a maternal‐fetal virus infection model using chronically catheterized macaques to simultaneously study the time‐course of viral infection in the mother and the response of the fetus to maternal HIV infection. Pregnant macaques were infected with 103 infectious units of HIV‐2287; every 3 days blood samples from both the mother and the fetus as well as amniotic fluid samples were collected. We found a varying degree of peak and time‐to‐peak virus load, virus‐infected PBMCs, and free virus (determined by QC‐RNA‐PCR method) in maternal blood. Two of the three mothers with more than 108 copies of viral RNA/ml of plasma at peak viremia transmitted the virus to their fetuses at about 14 days post‐infection. As observed with HIV‐2287 infected mothers, virus‐infected fetuses also produced a rapid rate of CD4+ cell decline in utero.

Effect of zidovudine on transplacental pharmacokinetics of ddI in the pigtailed macaque (Macaca nemestrina).

Since zidovudine and ddI may be used in combination in the future to treat pregnant women who are human immunodeficiency virus positive, we conducted a study to determine whether zidovudine affects the transfer of ddI across the placenta. Zidovudine and ddI were infused simultaneously to three near-term pregnant macaques (Macaca nemestrina) at 156 +/- 1.5 days of gestation. Samples of maternal and fetal blood and amniotic fluid were drawn at intervals for 30 h. The steady-state dideoxyinosine concentrations in the plasma of the dam (Cssd), the fetus (Cssf), and the amniotic fluid (Cssa) and the ratios Cssf/Cssd and Cssa/Cssf were found to be not significantly different from the values previously determined after the administration of ddI alone during the same pregnancy. We conclude that concurrent zidovudine administration does not affect the transfer of ddI across the placenta in near-term Macaca nemestrina.

Pharmacokinetics of dideoxyinosine in neonatal pigtailed macaques.

To determine whether age affects the pharmacokinetics of dideoxyinosine in neonatal pigtailed macaques (Macaca nemestrina), dideoxyinosine (10 mg/kg of body weight) was administered as a single intravenous bolus to macaques at ages < 1 week, 1 month, and 4 months. Clearance from plasma at < 1 week of age was significantly lower (P < 0.05) and the terminal half-life was significantly higher than the corresponding values obtained at 1 month and 4 months of age. Our data indicate that the pharmacokinetics of dideoxyinosine change significantly with age in M. nemestrina.

Characterization of a maternal-fetal HIV transmission model using pregnant macaques infected with HIV-2287

Abstract: To study mechanisms involved in mother‐to‐fetus transmission of human immunodeficiency virus (HIV) in utero, we have developed a chronically catheterized pregnant macaque model that permits simultaneous and sequential determination of virus in maternal and fetal blood and amniotic fluid during pregnancy. In this report, we have characterized this model using three groups of pregnant macaques designed to sample: (1) maternal blood, fetal blood, and amniotic fluid (n = 6); (2) maternal blood and amniotic fluid (n = 6); or (3) maternal blood only (n = 2). After inoculation with the highly pathogenic HIV‐2287, all pregnant macaques developed brief but intense viremias followed by precipitous CD4+ T‐cell declines within 2–3 weeks. While all the infants born to dams of the three groups were HIV positive, the degree of infection and outcome of HIV infection varied. All infants were shown to be HIV‐RNA‐positive by reverse transcriptase‐polymerase chain reaction (RT‐PCR). However, HIV‐infected cells were detected only in the blood of those born to dams enrolled in groups 1 and 2: most of these infants progressed to CD4+ T‐cell depletion. The infants in group 3 exhibited HIV‐RNA in plasma, although neither HIV‐infected cells nor CD4+ T‐cell depletion was detectable. However, all infants developed HIV‐2‐specific antibody at various levels by 2 months of age. Together, the data suggest that, while the degree of instrumentation may modulate intensity of virus transmission to fetus, the highly pathogenic HIV‐2287 exhibited a high frequency of virus transmission from the mother to fetus.

Suppression of maternal virus load with zidovudine, didanosine, and indinavir combination therapy prevents mother-to-fetus HIV transmission in macaques

&NA;Recently, we developed a maternal‐fetal macaque model using a highly pathogenic HIV‐2 strain, HIV‐2287, to study the time course of HIV transmission in utero. Most pregnant macaques (Macaca nemestrina) infected with HIV‐2287 (10‐103 infective doses) transmitted HIV to their fetuses, as verified by positive identification of virus‐infected mononuclear cells and free viral RNA in fetal blood. To determine whether an antiretroviral drug combination therapy composed of two dideoxynucleosides, azidothymidine (15 mg/kg) and dideoxyinosine (15 mg/kg), and a protease inhibitor, indinavir (25 mg/kg), could completely inhibit mother‐to‐fetus HIV transmission, we administered these drugs orally through gastric catheters to five pregnant macaques infected with 10 infective doses of HIV‐2287. Beginning 30 minutes after HIV inoculation, the dams were given the combination antiviral therapy three times daily until delivery by cesarean section. Drug treatment reduced the maternal virus load to a minimally detectable level but did not prevent primary HIV‐2287 infection. All fetal and infant blood samples were virus negative by internally controlled RNA polymerase chain reaction (QC‐RNA‐PCR) and virus coculture assays. Fetal and infant CD4+ T‐cell levels remained normal throughout the experiment. These findings strongly suggest that combination chemotherapy with azidothymidine, dideoxyinosine, and indinavir can suppress maternal viral load enough to prevent mother‐to‐fetus transmission of HIV.