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The effect of nitroso-chloramphenicol on mitochondrial DNA polymerase activity
Abstract:
We studied the effects of nitroso-chloramphenicol, chloramphenicol, amino-chloramphenicol, and thiamphenicol on the activity of mitochondrial DNA polymerase of rat liver. 3H-thymidine triphosphate incorporation into DNA was used to measure the DNA polymerase activity in the mitochondrial matrix fraction. This fraction was in the supernatant of sonicated mitochondria obtained by ultracentrifugation. Under standard experimental conditions, thymidine triphosphate incorporation was time dependent up to 10 minutes. This activity was enhanced by beta-mercaptoethanol and was blocked by the known polymerase inhibitors ethidium bromide and 2',3'-dideoxythymidine 5'-triphosphate. Chloramphenicol and its analogues, amino-chloramphenicol and thiamphenicol, did not have a significant effect on the polymerase activity, whereas nitroso-chloramphenicol was inhibitory. The degree of inhibition was dependent on the experimental conditions. Thus, in the absence of beta-mercaptoethanol, nitroso-chloramphenicol caused inhibition; however, in its presence, there was no significant inhibitory effect. Under similar conditions, the addition of dithiothreitol also provided partial protection. On the other hand, the inhibition by nitroso-chloramphenicol was significantly enhanced with its preincubation in the mitochondrial matrix fraction before the addition of nucleotides and DNA; thus after 40 minutes of preincubation, nitroso-chloramphenicol at a concentration of 200 mumol/L gave 53% inhibition, and produced total inhibition at 600 mumol/L. The addition of NADH or NADPH to the preincubation medium produced substantial protection against nitroso-chloramphenicol, whereas nicotinamide-adenine dinucleotide had no effect. These results suggest that mitochondrial DNA polymerase may be a target for nitroso-chloramphenicol action. The potentiation of that action by preincubation and the protection against it by NADH and NADPH suggest the involvement of intermediate metabolic steps for maximal inhibition.
Insights
Nitroso-chloramphenicol inhibits rat liver mitochondrial DNA polymerase activity, unlike its analogues. This inhibition is dependent on experimental conditions and may involve metabolic steps, suggesting it as a potential drug target.
Area of Science:
- Biochemistry
- Molecular Biology
- Pharmacology
Background:
- Mitochondrial DNA polymerase is crucial for mitochondrial genome replication and maintenance.
- Chloramphenicol and its analogues are antibiotics with varying effects on cellular processes.
- Understanding drug interactions with mitochondrial enzymes is vital for assessing potential toxicity and therapeutic applications.
Purpose of the Study:
- To investigate the impact of chloramphenicol and its derivatives (amino-chloramphenicol, thiamphenicol, and nitroso-chloramphenicol) on rat liver mitochondrial DNA polymerase activity.
- To elucidate the mechanism and conditions influencing the interaction between nitroso-chloramphenicol and mitochondrial DNA polymerase.
Main Methods:
- Assessed mitochondrial DNA polymerase activity by measuring 3H-thymidine triphosphate incorporation into DNA.
- Utilized isolated rat liver mitochondrial matrix fraction obtained through sonication and ultracentrifugation.
- Examined the effects of various compounds, including chloramphenicol analogues, reducing agents (beta-mercaptoethanol, dithiothreitol), and cofactors (NADH, NADPH, nicotinamide-adenine dinucleotide) under different preincubation conditions.
Main Results:
- Chloramphenicol, amino-chloramphenicol, and thiamphenicol showed no significant effect on mitochondrial DNA polymerase activity.
- Nitroso-chloramphenicol demonstrated inhibitory effects on polymerase activity, which were dependent on experimental conditions.
- Inhibition by nitroso-chloramphenicol was potentiated by preincubation and partially reversed by reducing agents and specific cofactors like NADH and NADPH.
Conclusions:
- Nitroso-chloramphenicol, but not its analogues, significantly inhibits rat liver mitochondrial DNA polymerase.
- The inhibitory action of nitroso-chloramphenicol is modulated by preincubation, reducing agents, and specific cofactors, suggesting a complex interaction.
- Mitochondrial DNA polymerase is a potential molecular target for nitroso-chloramphenicol, warranting further investigation into its pharmacological and toxicological implications.