Modulation of glucose metabolism in isolated rat hepatocytes by 1,1,1,2-tetrafluoroethane.
The thermodynamic behavior and lack of ozone-depleting potential of 1,1,1,2-tetrafluoroethane (R-134a) suggest it as a likely replacement for dichlorodifluoromethane (R-12), now used as the refrigerant in many air-conditioning systems. To further the presently incomplete toxicological analysis of R-134a, the effects of R-134a on cell viability and functional competence of glucose metabolism were evaluated in suspension cultures of hepatocytes derived from fed or fasted rats. R-134a concentrations up to and including 75% (750,000 ppm) in the gas phase of sealed culture flasks did not produce evidence of cytolethality (LDH leakage) following 2 hr of exposure; in contrast, halothane (1,1,1-trifluoro-2-bromo-2-chloroethane) caused cell death at a gas phase concentration of only 1250 ppm. In hepatocytes isolated from fed rats. R-134a at concentrations of 12.5 to 75% increased glycolysis (production of lactate + pyruvate) in a concentration-dependent manner; no effect was observed at 5%. At 25%, R-12 and 1,1,2,2-tetrafluoro-1,2-dichloroethane (R-114) were of equal potency to R-134a in stimulating glycolysis: 1,1,1,2,2-pentafluoro-2-chloroethane (R-115) depressed glycolysis slightly. Halothane, at concentrations as low as 300 ppm, markedly increased rates of glycolysis. Glucose production by hepatocytes of fed rats was decreased by R-134, R-12, and R-114 only at concentrations of 25% or more. On the other hand, halothane (greater than or equal to 300 ppm) potently decreased glucose production by hepatocytes. In cells isolated from livers of fasted rats, R-134a exposure inhibited gluconeogenesis in a concentration-dependent manner although this effect was not significant until R-134a concentrations reached 12.5%. Comparative potency studies showed that R-134a, R-12, or R-114 (25% gas phase) inhibited gluconeogenesis about equally while as little as 300 ppm halothane was effective and R-115 (25%) was without effect. Considering that the threshold for alteration of the rate of glucose metabolism in this in vitro paradigm is about 12.5% R-134a, we conclude that toxicologically significant alteration of glucose-linked bioenergetics is unlikely at the levels of R-134a exposure anticipated in workplace or environment.
Olson
M J
MJ
Biomedical Science Department, General Motors Research Laboratories, Warren, Michigan 48090.
Reidy
C A
CA
Johnson
J T
JT
D000818:Animals; D015687:Cell Hypoxia / Q000187:drug effects; D002470:Cell Survival / Q000187:drug effects; D002849:Chromatography, Gas; D003470:Culture Media / Q000032:analysis; D005260:Female; D005943:Gluconeogenesis / Q000187:drug effects; D005947:Glucose / Q000378:metabolism*; D006019:Glycolysis / Q000187:drug effects; D006221:Halothane / Q000633:toxicity; D006845:Hydrocarbons, Fluorinated / Q000032:analysis / Q000633:toxicity*; D006846:Hydrocarbons, Halogenated / Q000633:toxicity; D066298:In Vitro Techniques; D007700:Kinetics; D008099:Liver / Q000166:cytology / Q000378:metabolism*; D051381:Rats; D011916:Rats, Inbred F344; D004980:Ethane / Q000031:analogs & derivatives; D005466:Fluorocarbons
D003470:Culture Media; D005947:Glucose; D006221:Halothane; D006845:Hydrocarbons, Fluorinated; D006846:Hydrocarbons, Halogenated; C063006:norflurane; D004980:Ethane; D005466:Fluorocarbons