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Exposure-disease continuum for 2-chloro-2'-deoxyadenosine, a prototype ocular teratogen. 3. Intervention with PK11195
Jeffrey H Charlap1, Ronald J Donahue, Thomas B Knudsen
1Department of Pathology, Anatomy and Cell Biology, Jefferson Medical College, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
Background:
Treatment of pregnant mice with 2-chloro-2'-deoxyadenosine (2CdA) on Day 8 of gestation induces microphthalmia through a mechanism linked to the p53 tumor suppressor pathway. The present study defines the response of Day 8 mouse embryos through time with respect to pharmacologic intervention with PK11195, a ligand of the mitochondrial peripheral benzodiazepine receptor (Bzrp).
Methods:
Pregnant CD-1 mice dosed with 2CdA with or without PK11195 on gestation Day 8 provided fetuses for teratologic evaluation on Day 14 and Day 17; HPLC measured pyridine nucleotides (NADH/NAD+) at 1.5 hr, RT-PCR measured mitochondrial 16S rRNA abundance at 3.0 hr, and p53 protein induction was assessed with immunostaining at 4.5 hr postexposure.
Results:
The mean incidences of malformed fetuses were significantly higher in the 7.5 mg/kg 2CdA treatment group (50.2% malformed) vs. the 2CdA + 4.0 mg/kg PK11195 co-treatment group (4.4% malformed). Malformed fetuses displayed a range of ocular defects that included microphthalmia and keratolenticular dysgenesis (Peters anomaly). No malformations were observed in the control or PK11195 alone groups. PK11195 also protected litters from increased resorption rates and fetal weight reduction. It did not rescue early effects on NADH balance (1.5 hr) or 16S rRNA expression (3.0 hr); however, the p53 response (4.5 hr) was downgraded in 2CdA + PK11195 embryos vs. 2CdA alone. By delaying the administration of PK11195 in 1.5 hr intervals it was determined that the window for protection closed between 4.5 to 6.0 hr after 2CdA.
Conclusions:
The capacity of PK11195 to suppress the pathogenesis of microphthalmia implies a critical role for mitochondrial peripheral benzodiazepine receptors in the p53-dependent mode of action of 2CdA on ocular development.
Insights
PK11195 significantly reduced microphthalmia in mouse embryos exposed to 2-chloro-2'-deoxyadenosine (2CdA). This suggests mitochondrial peripheral benzodiazepine receptors are crucial for the p53-dependent developmental pathway.
Area of Science:
- Developmental biology
- Pharmacology
- Toxicology
Background:
- 2-chloro-2'-deoxyadenosine (2CdA) exposure during gestation induces microphthalmia in mouse embryos.
- The mechanism involves the p53 tumor suppressor pathway.
- PK11195, a ligand for mitochondrial peripheral benzodiazepine receptors, is investigated for its protective effects.
Purpose of the Study:
- To define the temporal response of Day 8 mouse embryos to 2CdA exposure.
- To evaluate the efficacy of PK11195 in preventing 2CdA-induced microphthalmia.
- To elucidate the role of mitochondrial peripheral benzodiazepine receptors in the observed teratogenesis.
Main Methods:
- Pregnant mice were treated with 2CdA with or without PK11195 on gestation Day 8.
- Fetal teratologic evaluation was performed on Days 14 and 17.
- Biochemical and molecular analyses included pyridine nucleotide levels, mitochondrial 16S rRNA abundance, and p53 protein induction.
Main Results:
- PK11195 co-treatment significantly reduced malformations (4.4%) compared to 2CdA alone (50.2%).
- PK11195 protected against increased resorption rates and reduced fetal weight.
- Protection was linked to the suppression of p53 induction, with a critical intervention window between 4.5 to 6.0 hours post-2CdA exposure.
Conclusions:
- PK11195 effectively suppresses the development of 2CdA-induced microphthalmia.
- Mitochondrial peripheral benzodiazepine receptors play a critical role in the p53-dependent teratogenic effects of 2CdA.
- Targeting these receptors may offer a therapeutic strategy for preventing developmental ocular defects.