ABSTRACT
It must be assumed that current petri dish primary hepatocyte culture models do not supply sufficient amounts of oxygen and thus cause anaerobic metabolism of the cells. This is contrary to the physiologic state of the cells. In vivo the liver is a highly vascularized organ with a rather high blood flow rate of a mixture of arterial and venous blood. The aim of the present study was to show the oxygen dependence of primary rat hepatocytes in long-term culture and to define appropriate conditions that could allow hepatocytes to maintain tissue specific functions in an aerobic environment. To this purpose matrix overlaid hepatocytes were either cultured on gas-permeable (fluorinated hydrocarbon films) or gas-impermeable (polystyrene) supports at 10% and 20% ambient oxygen concentration (v/v), respectively. Tissue-specific functions were assessed by studying albumin and urea secretion as well as xenobiotic metabolism. The mRNA expression and catalytic activities of the cytoprotective antioxidant enzymes mitochondrial manganese superoxide dismutase (MnSOD), cytosolic copper and zinc superoxide dismutase, peroxisomal catalase, and cytosolic glutathione peroxidase were investigated to assess intracellular responses to the defined variations in oxygen supply. Hepatocytes could successfully be maintained at aerobic conditions in long-term culture on gas-permeable PTFE films. At 50% (10%, v/v) of currently used oxygen levels lactate accumulation was prevented, a plateau-like albumin secretion reestablished, urea secretion improved, and xenobiotic metabolism proceeded at physiological rates. mRNA expression of cytoprotective enzymes responded to the pericellular availability of oxygen and was most pronounced in the case of MnSOD. However, the biggest stress factor for the hepatocytes still appeared to be the isolation procedure, as mRNA expression and catalytic activities were most elevated shortly thereafter. In conclusion, this study clearly shows the oxygen dependence of primary rat hepatocytes in long-term culture and indicates means to establish appropriate conditions for the aerobic culture of primary rat sandwich hepatocytes with full maintenance of function. The long-term culture of hepatocytes on oxygenating supports at in vivo-like oxygen tensions therefore appears to be more physiologic and beneficial for the cells.
