Perfluorodecanoic acid inactivation of a channel for 2-aminopurine in the L5178Y cell membrane and recovery of the channel

Comparison of the elimination between perfluorinated fatty acids with different carbon chain length in rats

Elimination in urine and feces was compared between four perfluorinated fatty acids (PFCAs) with different carbon chain length. In male rats, perfluoroheptanoic acid (PFHA) was rapidly eliminated in urine with the proportion of 92% of the dose being eliminated within 120 h after an intraperitoneal injection. Perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA) was eliminated in urine with the proportions of 55, 2.0 and 0.2% of the dose, respectively. By contrast, four PFCAs were eliminated in feces with the proportion of less than 5% of the dose within 120 h after an injection. In female rats, the proportions of PFOA and PFNA eliminated in urine within 120 h were 80% and 51% of the dose, respectively, which were significantly higher compared with those in male rats. There was the tendency that PFCA with longer carbon chain length is less eliminated in urine in both male and female rats. Fecal elimination of PFCAs was not different between PFCAs in female rats and comparable to those in male rats. The rates of biliary excretion of PFCAs in male rats were slower than those in female rats. Sex-related difference in urinary elimination of PFOA was abolished when male rats had been castrated. On the contrary, treatment with testosterone suppressed the elimination of PFOA in urine in both castrated male rats and female rats. The effect of testosterone was in a time- and dose-dependent manner. These results suggest that PFCAs are distinguished by their carbon chain length by a renal excretion system, which is regulated by testosterone.

Induction by perfluorinated fatty acids with different carbon chain length of peroxisomal beta-oxidation in the liver of rats

The potency of the induction of peroxisomal beta-oxidation was compared between perfluorinated fatty acids (PFCAs) with different carbon chain lengths in the liver of male and female rats. In male rats, perfluoroheptanoic acid (PFHA) has little effect, although perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA) and perfluorodecanoic acid (PFDA) potentially induced the activity. By contrast, PFHA and PFOA did not induce the activity of peroxisomal beta-oxidation in the liver of female rats while PFNA and PFDA effectively induced the activity. The induction of the activity by these PFCAs was in a dose-dependent manner, and there is a highly significant correlation between the induction and hepatic concentrations of PFCAs in the liver regardless of their carbon chain lengths. These results strongly suggest that the difference in their chemical structure is not the cause of the difference in the potency of the induction. Hepatic concentrations of PFOA and PFNA was markedly higher in male compared with female rats. Castration of male rats reduced the concentration of PFNA in the liver and treatment with testosterone entirely restored the reduction. In contrast to the results obtained from the in vivo experiments, the activity of peroxisomal beta-oxidation was induced by PFDA and PFOA to the same extent in cultured hepatocytes prepared from both male and female rats. These results, taken together, indicate that difference in accumulation between PFCAs in the liver was responsible for the different potency of the induction of peroxisomal beta-oxidation between PFCAs with different carbon chain lengths and between sexes.

Reversal agent inhibition of the multidrug resistance pump in human leukemic lymphoblasts

Multidrug resistant cancer cells of the MDR-1 phenotype utilize an ATP-dependent pump to excrete toxic drugs. Rhodamine 123 (R123) is a fluorescent substrate of the MDR pump. An assay for the ATP-dependent initial efflux of R123 from CEM/VLB100 human leukemic lymphoblasts has been developed. The MDR-1 cells were treated with a reversal agent and preloaded with 40.0 nM R123 in buffer at 30 degrees C that contained sodium azide and 2-deoxyglucose. The cells were rinsed with cold buffer and resuspended in L-glutamine/glucose solution at 23 degrees C. The cell suspension was passed through a filter and R123 in the filtrate was detected at 2-s intervals by fluorescence. Efflux of R123 was inhibited by the reversal agents amiodarone, cyclosporin A, Ro11-2933 (DMDP), quinidine, and the optical isomers of propranolol. The MDR pump is stereospecific for the (R)-diastereomer quinidine; however, the (S)-diastereomer quinine is a relatively weak inhibitor of the pump. Cyclosporin A was the most potent inhibitor tested against the efflux of R123 by the MDR pump.

Inhibition of the multidrug resistance efflux pump

An ATP-dependent efflux pump is found in the plasma membrane of certain multidrug resistant (MDR) cancer cells. Drug resistance is due to decreased intracellular drug levels that have been reduced to subcytotoxic concentrations. Inhibition of the MDR efflux pump with a reversal agent may 'trap' the cytotoxic drug inside the cell; thus, cellular drug resistance is reversed. Although many different lipophilic substances exhibit reversal activity, inhibition of the pump is stereospecific with respect to the chiral agent cinchonine. In this article, several methods for the estimation of reversal potency are reviewed. Furthermore, information on the transport characteristics of reversal agents is presented. The rate equations for ATP-dependent drug efflux, competitive inhibition of the MDR pump, and noncompetitive inhibition of the pump are derived. A method is presented that discriminates between competitive or noncompetitive inhibition of the pump. These studies show the potential contribution of fundamental inhibition studies to the design of clinical reversal protocols.

Effects of perfluoro-n-decanoic acid on the respiratory activity of isolated rat liver mitochondria

The toxic responses of rats to a single dose of perfluorodecanoic acid (PFDA) include reduced food consumption, severe body weight loss ("wasting syndrome"), and hypothermia. Recent studies have suggested that some of these effects may be due to alterations of basic metabolic processes in animals treated with PFDA. In order to test this hypothesis the effects of PFDA on respiratory activity of isolated rat liver mitochondria were examined. PFDA concentrations up to 87.5 micrograms/ml produced a linear increase in oxygen consumption during state 4 (nonphosphorylating) respiration. This suggested uncoupling of electron transport and oxidative phosphorylation was supported by the observation that PFDA released mitochondrial state 3 respiration from inhibition by oligomycin and stimulated latent ATPase activity. Concentrations of PFDA greater than 87.5 micrograms/ml produced progressively less increase in state 4 oxygen consumption, and a single high concentrations (150 micrograms/ml) completely inhibited state 3 respiration and prevented the uncoupling effect of 2,4-dinitrophenol. These observations suggest that in addition to uncoupling electron transport and oxidative phosphorylation PFDA may affect other energy-transducing functions of liver mitochondria such as inhibiting electron transport. These effects on mitochondrial respiration may help to explain the "wasting syndrome" characteristic of PFDA toxicity.

Cytotoxic and cytolytic activity of nonadecafluoro-n-decanoic acid on Acholeplasma laidlawii

We studied the interactions between the perfluorinated fatty acid nonadecafluoro-n-decanoic acid (NDFDA) and the cell wall-less procaryote Acholeplasma laidlawii, which were cultured in an identical medium base but with different serum supplements. When grown in mycoplasma media supplemented with PPLO serum fraction (Difco Laboratories, Detroit, Mich.), A. laidlawii was rapidly killed by low concentrations of toxicant (less than 1.0 mM). At higher concentrations (greater than 10 mM), NDFDA treatment appeared to lyse cells. A. laidlawii cells grown in horse serum-supplemented mycoplasma media were both killed and lysed at the same NDFDA concentration (greater than 10 mM). These data suggest that this perfluorinated fatty acid can be cytotoxic and cytolytic to mycoplasmas. Changes in active concentrations occurred in parallel with changes in growth medium serum supplementation, which is known to alter mycoplasma membrane composition. We propose that NDFDA interacts with the membranes of A. laidlawii cells, resulting in cell death or cell lysis or both.