Growth of cultured rabbit renal tubular cells does not require exogenous glutamine

Generation and partial characterization of a transformed cetacean cell line

A primary epithelial cell line, DK1, established from renal tissue of a spontaneously aborted female Atlantic bottlenose dolphin was transfected with linearized pSV3.neo, an SV40 virus-derived plasmid encoding large tumor antigen (Tag). Transfected cells were grown in cetacean culture medium supplemented with 400 microg/ml geneticin (G418), and individual clones were selected using cloning rings. DKN1 was the first clone to be evaluated for future research use, and has been continuously cultured for 8 years. Intracellular cytokeratin and the expression of Tag were determined in DKN1, and cell growth was evaluated under different concentrations of l-glutamine, glutathione, and N-acetylcysteine. DKN1 cells did not require high levels of l-glutamine as previously reported for cetacean cells, and addition of antioxidants at the concentrations used in this study (2.0mM) decreased the rate of cell division. These data suggest strongly that these immortalized bottlenose dolphin epithelial cells have different levels of, and requirements for, glutathione than would be considered normal for terrestrial mammalian cells, do not require high levels of l-glutamine as previously suggested for dolphin cells, and exhibit decreased levels of cell growth and viability in high levels of the antioxidant GSH and its precursor, NAC.

Glycolysis inhibition by palmitate in renal cells cultured in a two-chamber system

A major shortcoming of renal proximal tubular cells (RPTC) in culture is the gradual modification of their energy metabolism from the oxidative type to the glycolytic type. To test the possible reduction of glycolysis by naturally occurring long-chain fatty acids, RPTC were cultured in a two-chamber system, with albumin-bound palmitate (0.4 mM) added to the basolateral chamber after confluency. Twenty-four hours of contact with palmitate decreased glycolysis by 38% provided that carnitine was present; lactate production was decreased by 38%, and the decrease in glycolysis resulted from a similar decrease of basolateral and apical net uptake of glucose. In contrast to the previously described effect of the nonphysiological oxidative substrate heptanoate, palmitate promoted a long-term decrease in lactate production and sustained excellent cellular growth. After 4 days of contact, decreased glycolysis was maintained even in the absence of carnitine and resulted from a decrease of basolateral uptake only, suggestive of long-term regulation different from the earlier effects. Thus, although cultured RPTC lost their oxidative phenotype, they exhibited a type of regulation (Randle effect) that is found in the oxidative-type but not in the glycolytic-type tissues, therefore unmasking a regulative capacity barely detectable in fresh RPTC. Low PO2 (50 mmHg in the apical chamber) could be a major cause of elevated glycolysis and could hinder the effects of palmitate.

Advantages and limitations of the use of isolated kidney tubules in pharmacotoxicology

Among the cellular models used in in vitro renal pharmacotoxicology, isolated kidney tubules, used as suspensions mainly of proximal tubules, offer important advantages. They can be prepared in large amounts under nonsterile conditions within 1-2 h; thus, it is possible to employ a great number of experimental conditions simultaneously and to obtain rapidly many experimental results. Kidney tubules can be prepared from the kidney of many animal species and also from the human kidney; given the very limited availability of healthy human renal tissue, it is therefore possible to choose the most appropriate species for the study of a particular problem encountered in man. Kidney tubules can be used for screening and prevention of nephrotoxic effects and to identify their mechanisms as well as to study the renal metabolism of xenobiotics. When compared with cultured renal cell, a major advantage of kidney tubules is that they remain differentiated. The main limitations of the use of kidney tubules in pharmacotoxicology are (1) the necessity to prepare them as soon as the renal tissue sample is obtained; (2) their limited viability, which is restricted to 2-3 h; (3) the inability to expose them chronically to a potential nephrotoxic drug; (4) the inability to study transepithelial transport; and (5) the uncertainty in the extrapolation to man of the results obtained using animal kidney tubules. These advantages and limitations of the use of human and animal kidney tubules in pharmacotoxicology are illustrated mainly by the results of experiments performed with valproate, an antiepileptic and moderately hyperammonemic agent. The fact that kidney tubules, unlike cultured renal cells, retain key metabolic properties is also shown to be of the utmost importance in detecting certain nephrotoxic effects.