Lysophospholipase activity in rat brain subcellular fractions

Lysophospholipase activity in brain subcellular fractions was measured by the release of myristic acid from 1-myristoylglycerophosphocholine or through the formation of [32P]glycerophosphocholine from [32P]lysophosphatidylcholine. Although the lysophospholipase activity was highest in microsomes, considerable enzyme activity was also found in other subcellular membrane fractions. The pH optimum for the microsomal enzyme was around 7, whereas the synaptosomes and non-synaptic plasma membranes exhibited a pH maximum around 8. Although the enzyme did not require divalent cations for activity, divalent cations (1 mM) such as Hg2+, Cu2+, and Zn2+ inhibited potently the enzyme activity. Enzyme activity was also partially inhibited by both saturated and polyunsaturated fatty acids (25-200 microM), and the inhibition seemed to be greater in the membrane than in the cytosolic fractions. Ionic detergents such as deoxycholate and taurocholate inhibited the lysophospholipase. On the other hand, the effect of Triton X-100 was biphasic, i.e., stimulation at concentrations below 100 micrograms/mg protein and inhibition at higher concentrations. Addition of cholesterol (50-250 micrograms/ml), but not cholesteryl esters, also potently inhibited enzyme activity. The presence of active lysophospholipase(s) in brain is probably an important mechanism for preventing unnecessary accumulation of lysophospholipids which may exert a deleterious effect on the membranes because of their detergent properties.

Acidic phospholipids, diacylglycerols, and free fatty acids in gerbil brain: a comparison of ischemic changes resulting from carotid ligation and decapitation

The levels of brain acidic phospholipids (poly-PI, PI, PA, and PS), DG, and FFA and their acyl group profiles were determined after induction of ischemia in gerbils by ligation of the common carotid arteries and decapitation. Ischemia induced by both procedures resulted in a significant decrease in poly-PI (20% for 1-min decapitation and 1-min ligation). Except for a 16% increase in PI in the 5-min decapitation group, no apparent change was found in other phospholipids after either ischemic condition. The level of DG was increased one- and three-fold after 1 and 5 min, respectively, of decapitative ischemic treatment. Ligation of the carotid arteries for 1 min resulted also in a one-fold increase in the DG level. The decapitative model resulted in a one- and five-fold increase in FFA level (with respect to 1 and 5 min, respectively), whereas ligation for 1 min resulted in an increase of 42% of the FFA. The acyl groups of poly-PI and PI in the control gerbil brain are enriched in 18:0 and 20:4, but those of DG, FFA, and PA have a higher proportion of 16:0 besides 18:0 and 20:4. However, a preferential increase in the proportion of 18:0 and 20:4 was shown for the DG and FFA in both types of ischemic treatments. It is concluded from the results that both models of ischemic treatment elicit a similar decrease in poly-PI and increase in DG, but differ in the amount of FFA release. The higher level of FFA release in the decapitative model suggests that other biochemical mechanisms may be activated to cause the additional release.

Progression-linked properties of specific-lesion cell populations from 7,12-dimethylbenz[a]anthracene-exposed rat tracheal implants

The purpose of this study was to determine whether there are any relationships between the morphological expressions of the progression of neoplasia in tracheal epithelium in vivo, and the increased in vitro growth autonomy expressed by carcinogen-altered cell populations isolated from the same tracheas. Rat tracheal implants were exposed for 2 weeks or 4 weeks to 200 micrograms 7,12-dimethylbenz[a]anthracene (DMBA)-beeswax pellets. In the first phase of this study reported earlier (1), the numbers of carcinogen-altered cell populations, identified by their lack of need for exogenous pyruvate and insulin for survival in cell culture, were quantitated 2, 6 and 9 months after the start of the exposures. Before generating the cell cultures, lesions on the pieces of pre-exposed tracheal implants were identified by placing them in organ culture for 24 h and collecting the exfoliated cells from the medium for diagnostic cytopathology. Although the pieces of 2-week DMBA-exposed tracheas had not developed any markedly atypical lesions by 9 months, there was a progressive increase in the growth autonomy of the small number of subculturable cell populations (approximately 1/trachea) obtained from this exposure group. This was seen in the decreased time needed in culture to expand the population for testing anchorage-independent growth and tumorigenicity in nude mice. Also, anchorage-independent growth was markedly enhanced from 25 to 80% between 2 and 6 months and then to 100% at 9 months. Tumorigenicity did not show an increase. In the 4-week DMBA-exposed group, 74% of the large number of subculturable cell populations (approximately 5.0/trachea) already showed anchorage-independent growth at 2 months. This percentage increased to 94-100% at 6 and 9 months. A progressive increase in tumorigenic cell populations was also clearly seen. At 2 months, 26% of the cell populations inoculated into nude mice formed tumors. This number increased from 45 to 61% at 6 and 9 months, respectively. The pieces of tracheas taken at 2 months after the start of the 4-week DMBA exposure had no markedly atypical lesions. At 6 months one marked atypia was detected, and at 9 months five markedly atypical lesions and two carcinomas in situ were present. The cell populations derived from the explants harboring these lesions showed a high incidence of growth autonomy, e.g. anchorage-independent growth and tumor formation, indicating a close relationship between these properties and the evolving morphological manifestations of tumor development.

Selection of carcinogen-altered rat tracheal epithelial cells preexposed to 7,12-dimethylbenz[a]anthracene by their loss of a need for pyruvate to survive in culture

Normal rat tracheal epithelial cells require exogenous pyruvate to survive in culture while carcinogen-altered cells do not. The aims of our study were, (i) to utilize this loss of requirement for pyruvate by carcinogen-altered cells as a way of selecting out and quantitating the numbers of altered cell populations induced in tracheas exposed to 200 micrograms 7,12-dimethylbenz[a]-anthracene (DMBA)-beeswax pellets for different lengths of time, (ii) to determine the constancy of these numbers at increasing time intervals after the exposure, (iii) to look for distinctive growth properties in cell populations that may be related to the exposure conditions. Tracheal implants were exposed for 2 weeks, 4 weeks or continuously to the 200 micrograms DMBA. At 2, 6 and 9 months after the start of exposure, the tracheas were cut into pieces and primary cultures established from outgrowths in an enriched Waymouth's medium. After 2 weeks, pyruvate and insulin were removed from the medium for 2 weeks to kill the normal cells and leave the altered, i.e., the selected cell populations (SPC). The pyruvate and insulin were then returned to the medium to stimulate rapid expansion of the SPC. The length of DMBA exposure had a marked effect on the number of SPC induced in the tracheas. There were 1.8 SPC/trachea 2 months after the 2 weeks exposure, while 5.0 and 7.2 SPC were obtained from the 4 weeks and continuously exposed tracheas, respectively, at this time. The numbers of SPC did not increase with time after exposure indicating that the maximal number of initiation sites was fixed. Between 2 and 9 months the number of subculturable SPC increased from 67 to 88% in the 2 week exposed group, while 93-100% of the SPC were subculturable after the longer DMBA exposures. Only the SPC from the 2 week DMBA--2 month group were distinguished by smaller numbers of cells surviving the selection medium and by a slower average growth rate compared to all the other experimental conditions.