Concentration- and time-dependent effects of gamma-linolenic acid supplementation to tumor cells in culture

The Influence of long-chain polyunsaturated fatty acids on total lipid fatty acid composition of a canine mastocytoma cell line

Cutaneous mast cells are considered as key immune effectors in the pathogenesis of canine atopic dermatitis (CAD). These cells release immediate-phase and late-phase mediators of inflammation. Dietary fatty acids are incorporated in cellular membranes and seem to influence mediator production and release. A dietary intervention with n6- and n3-fatty acids is thought to alleviate clinical symptoms in atopic dogs. The purpose of this study was to examine the effects of n6- and n3-fatty acids on the fatty acid composition of canine mastocytoma cells (C2) as a possible model for CAD. The C2 was cultured in a basic medium called Dulbecco's modified Eagle's medium (DEH) or with additional 14 mum linoleate (C18:2n6, DEH-LA), gamma-linolenate (C18:3n6, DEH-GLA), arachidonate (C20:4n6, DEH-AA), alpha-linolenate (C18:3n3, DEH-LnA), eicosapentaenoate (C20:5n3, DEH-EPA) or docosahexaenoate (C22:6n3, DEH-DHA). Cell growth was examined for 11 days in all media. Cell growth increased from days 1 to 8 and decreased thereafter in all media conditions. The fatty acids supplied did not influence cell growth. The cells were harvested after 8 days for fatty acid analysis. The fatty acid composition was determined by gas chromatography after extraction and trans-esterification of the lipids. The added fatty acids increased the concentration of these fatty acids in C2 differently (LA 4.9-fold, GLA 6.9-fold, AA 6-fold, LNA 9.3-fold, EPA 6.5-fold and DHA 8.4-fold). Furthermore, elongated and Delta6-desaturated products of the corresponding fatty acids were significantly elevated. However, Delta5-desaturated products were not measurable. These results let us assume that C2 has no measurable activity of the Delta5-desaturase. In case the low activity of Delta5-desaturase is one of the mechanisms underlying the pathogenesis of CAD, C2 seems to be an adequate model for investigations in CAD.

Differential antiproliferative activity of new benzimidazole-4,7-diones

Ten benzimidazole-4,7-diones were synthesized and tested in vitro on two tumor cell lines. Several compounds showed a significant antiproliferative activity on K562 cells, although to a different extent, whereas compound 1i showed a highly significant activity on SW620 cells, comparable to that of doxorubicin. Both the substituents in the quinone ring and the position of the nitrogen atom in the pyridine moiety play a crucial role for the biological activity.

Synthesis and antiproliferative activity of some thiazolylbenzimidazole-4,7-diones

Some thiazolylbenzimidazole-4,7-diones were synthesized and tested in vitro on two tumor cell lines. Compounds 2d and 2e show a very good activity on K562 cells, whereas compounds 2a and 2b are active on SW620 cells. The importance of the methoxy group on the quinone moiety is confirmed and the function at 4-position of the thiazole ring plays a determining role for the activity.

Repression of cellular anaplerosis as the hypothesized mechanism of gamma-linolenic acid-induced toxicity to tumor cells

In in vitro cultures, the cell is virtually isolated and can no longer rely on mechanisms for physiological regulation of substrate availability found in tissues. More emphasis is laid on utilization of preponderant substrate in a proposed reciprocal relationship between glycolysis and free fatty acid (FFA) oxidation for energy. Supraphysiological concentrations of gamma-linolenic acid and some other polyunsaturated fatty acids (PUFAs) therefore suppress glycolysis but also inhibit FFA oxidation initiated through a cytochrome P450-mediated epoxidation of PUFA to inhibit fatty acid synthase (FAS) activity. FAS inhibition accumulates malonyl CoA which inhibits carnitine palmitoyl transferase I and prevents FFA oxidation. The cell is starved of energy and anabolic intermediates, leading to decreased proliferation or death for tumor cells. Tumor cells are more vulnerable to this induced toxicity due to possession of specific phenotypes of elevated expression for FAS and pyruvate kinase, type M2, both factors inducing tumor cell apoptosis on inhibition.

Role of gamma-linolenic acid in counteracting doxorubicin-induced damage in cultured rat cardiomyocytes

The clinical usefulness of doxorubicin is limited by cardiotoxicity. We have demonstrated that doxorubicin has a dual negative effect on myocardial lipids, acting against highly unsaturated fatty acids (HUFAs) directly and desaturating/elongating enzymes required for their biosynthesis, thus decreasing linoleic and alpha -linolenic conversion to higher metabolites. Primary cultures of rat cardiomyocytes were challenged with different doxorubicin concentrations and doxorubicin exposure was followed by a 24-h recovery period in the absence or presence of serum, and of gamma -linolenic acid. Serum in the recovery medium did not appear to be essential for the restoration of the desaturating/elongating activities, and gamma -linolenic acid supplementation influenced only alpha -linolenic acid conversion. Serum, and particularly gamma-linolenic acid, were very important in increasing HUFA levels behind the pure biosynthesis. HUFA biosynthesis plays a role in counteracting doxorubicin toxicity, but it cannot completely overcome the depletion of these fatty acids; serum and exogenous gamma-linolenate are critical in filling the decreased HUFA pool.

The impairment of essential fatty acid metabolism as a key factor in doxorubicin-induced damage in cultured rat cardiomyocytes

The clinical use of the antitumoral doxorubicin (DOX) is limited by its cardiotoxicity, which is mediated through different mechanisms. The membrane lipid peroxidation induced by DOX may cause disruption of the unsaturated fatty acyl chains; in the endoplasmic reticulum, containing the system catalyzing the desaturation/elongation of fatty acids, DOX could interfere with the metabolism of linoleic and alpha-linolenic acids. Using primary cultures of neonatal rat cardiomyocytes we demonstrated that the exposure to different concentrations of DOX (10(-5) and 10(-7) M) for 24 h caused an increase in the production of conjugated dienes, an impairment in the desaturation/elongation of essential fatty acids, and a reduction in the cellular content of highly unsaturated fatty acids. Conversely, 1 h exposure to 10(-5) M DOX was sufficient to induce alterations in the desaturation/elongation of linoleic and alpha-linolenic acids, but did not cause either formation of conjugated dienes or modification of the fatty acyl pattern. Therefore, DOX has a dual negative effect, depending on its concentration and on the time of exposure, one directed against the membrane highly unsaturated fatty acids, the other against the system which is required for the synthesis of these fatty acids themselves. These two effects synergically act in causing heart cell damage.