Nonylphenol ethoxylate plastic additives inhibit mitochondrial respiratory chain complex I.

The first and major entry point of electrons into the mitochondrial respiratory chain (MRC) 1 occurs through NADH-coenzyme Q reduc-tase (complex I). Decreased complex I activity is associated with a wide range of conditions, including inherited mitochondrial diseases and neu-rodegenerative conditions such as Parkinson disease (1–2). More than 60 natural and commercial compounds are reported to inhibit complex I activity, among them certain pesticides, agrochemicals, and MPTP (1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine), a neurotoxin that induces parkinsonism in humans ; thus, exposure to these compounds may be harmful (3). We report here that nonylphenol ethoxylate (NP) surfactants leach from disposable laboratory plastic-ware and inhibit mitochondrial complex I. During a routine diagnostic workup designed to diagnose mi-tochondrial diseases from patients' muscle biopsy samples, we observed a substantial (50%–66%) decrease of mitochondrial enzy-matic activities related to complex I compared with historical values determined spectrophotometri-cally in our laboratory. Furthermore , a 71% decrease in complex I–dependent oxygen consumption was also observed with gluta-mate ϩ malate as substrates (Oxy-graph, Hansatech Instruments) (2). Notably, other MRC activities, as well as citrate synthase, a mito-chondrial marker enzyme, were largely unaffected. It was determined that inhibition resulted from a single brief period of contact between assay reagents and blue polypropylene 1-mL pipette tips (" blue tips ") manufactured by Scientific Specialties (Table 1). Methanol washes of blue tips were subjected to positive ion–mode electrospray mass spectrometry (Waters Mariner BioSpectrometry Workstation oa-TOF); these analyses confirmed the presence of NP compounds, marketed as surfactants from the Tergitol NP series. The prevalent ion at m/z 683.5 was consistent with the use of NP-10 as a dye-solubilizing agent in the plastic manufacturing process, whereas m/z peaks indicative of shorter (NP-9) and longer (NP-11) side-chain surfactants are characteristic of mass spectral data for these compounds (4). Subsequently we evaluated MRC function in the presence of commercial samples of NP-10 and NP-9 and detected inhibition of complex I enzymatic activity, with IC 50 values of 4 ␮mol/L and 3.7 ␮mol/L, respectively. Other respiratory chain complexes were unaffected in the presence of these surfactants at 10 ␮mol/L; however, a marked decrease in complex I–dependent oxygen consumption was evident (Table 1). Oxygen consumption with complex I–independent sub-strates was not affected (not shown). The inhibition of oxygen consumption in whole mitochondria by NP-10 and NP-9 indicates that these compounds penetrate the inner mi-tochondrial membrane. We also studied the impact of leachate from blue tips and of NP surfactants on growing …