Quantitative analysis of electron transport inhibition of rat-liver mitochondrial cytochrome bc1 complex by nitrophenols

Reductive Dehalogenation of Oligocyclic Phenolic Bromoaromatics by Dehalococcoides mccartyi Strain CBDB1

Dehalococcoides mccartyi strains transform many halogenated compounds and are used for bioremediation. Such anaerobic transformations were intensively studied with chlorinated and simply structured compounds such as chlorinated benzenes, ethenes, and ethanes. However, many halogenated oligocyclic aromatic compounds occur in nature as either naturally produced materials or as part of commercial products such as pharmaceuticals, pesticides, or flame retardants. Here, we demonstrate that the D. mccartyi strain CBDB1 reductively debrominated two oligocyclic aromatic phenolic compounds, tetrabromobisphenol A (TBBPA) and bromophenol blue (BPB). The strain CBDB1 completely converted TBBPA to bisphenol A and BPB to phenol red with a stepwise removal of all bromide substituents. Debromination (but no cell growth) was detected in the cultures cultivated with TBBPA. In contrast, strain CBDB1 grew when interacting with BPB, demonstrating that this substrate was used as an electron acceptor for organobromine respiration. High doses of BPB delayed debromination and inhibited growth in the early cultivation phase. A higher toxicity of TBBPA compared with that of BPB might be due to the higher lipophilicity of TBBPA. Mass spectrometric analyses of whole-cell extracts demonstrated that two proteins encoded by the reductive dehalogenase homologous genes CbdbA1092 and CbdbA1503 were specifically induced by the used oligocyclic compounds, whereas others (e.g., CbdbA84 (CbrA)) were downregulated.

Mitochondrial targets of drug toxicity

Mitochondria have long been recognized as the generators of energy for the cell. Like any other power source, however, mitochondria are highly vulnerable to inhibition or uncoupling of the energy harnessing process and run a high risk for catastrophic damage to the cell. The exquisite structural and functional characteristics of mitochondria provide a number of primary targets for xenobiotic-induced bioenergetic failure. They also provide opportunities for selective delivery of drugs to the mitochondrion. In light of the large number of natural, commercial, pharmaceutical, and environmental chemicals that manifest their toxicity by interfering with mitochondrial bioenergetics, it is important to understand the underlying mechanisms. The significance is further underscored by the recent identification of bioenergetic control points for cell replication and differentiation and the realization that mitochondria play a determinant role in cell signaling and apoptotic modes of cell death.