Effects of omega-3 fatty acids on components of the transforming growth factor beta-1 pathway: implication for dietary modification and prevention in ovarian cancer

OBJECTIVE

We previously demonstrated that omega-3 fatty acids (OM-3FAs) have definitive inhibitory effects on ovarian cancer cell lines. We sought to determine whether the inhibitory effects of OM-3FAs were mediated by the transforming growth factor (TGF)-beta1 signaling pathway.

STUDY DESIGN

Ovarian cancer cell lines were grown at 37 degrees C in 5% CO(2) and treated with OM-3FAs, omega-6 fatty acids, and control at different concentrations for 24-72 hours. Enzyme-linked immunosorbent assay (ELISA) assay and Western blot analysis were used to measure TGF-beta1, phosphorylated mothers against decapentaplegic (Smad)-3 and p21 protein levels.

RESULTS

An ELISA assay demonstrated that OM-3FA treatment increased TGF-beta1 in all 3 Hey cell lines (P < .05). In both SKOV-3 and OVCAR-3 cells, TGF-beta1 levels were not significantly increased. Western blots confirmed increases in TGF-beta1, Smad-3 and p21 protein levels in Hey and HeyC2 but not SKOV-3 and OVCAR-3 cells.

CONCLUSION

OM-3FAs increased the level of TGF-beta1, Smad-3, and p21 protein in ovarian cancer cells known to be more sensitive to their inhibitory effect.

Amino acid transporters involved in luminal transport of mercuric conjugates of cysteine in rabbit proximal tubule

The primary aim of the present study was to test the hypothesis that amino acid transport systems are involved in absorptive transport of dicysteinylmercury (cysteine-Hg-cysteine). Luminal disappearance flux [JD, fmol x min(-1) (mm tubular length)(-1)] of inorganic mercury (Hg2+), in the form of dicysteinylmercury, was measured in isolated perfused S2 segments with various amino acids or amino acid analogs in the luminal compartment under one of two conditions, in the presence or absence of Na+. The control perfusion fluid contained 20 microM dicysteinylmercury. Replacing Na+ in both the bathing and perfusing solutions with N-methyl-D-glucamine reduced the JD of Hg2+ by about 40%. Nine amino acids and two amino acid analogs were coperfused individually (at millimolar concentrations) with dicysteinylmercury. The amino acids and amino acid analogs that had the greatest effect on the JD of Hg2+ were L-cystine, L-serine, L-histidine, L-tryptophan, and 2-(-)-endoamino-bicycloheptane-2-carboxylic acid. The greatest reduction (76%) in the total JD of Hg2+ occurred when L-cystine was coperfused with dicysteinylmercury in the presence of Na+. Overall, the current findings indicate that Hg2+ is transported from the lumen into proximal tubular epithelial cells via amino acid transporters that recognize dicysteinylmercury. In addition, the data indicate that multiple amino acid transporters are involved in the luminal uptake of dicysteinylmercury, including the Na+-dependent low-affinity L-cystine, B(0), and ASC systems and the Na+-independent L-system. Furthermore, the transport data obtained when L-cystine was added to the luminal fluid indicate strongly that dicysteinylmercury is likely transported as a molecular homolog of L-cystine.

Molecular homology and the luminal transport of Hg2+ in the renal proximal tubule

The aim of this study was to define mechanisms involved in the luminal uptake of inorganic mercury in the kidney using isolated perfused straight (S2) segments of the proximal tubule. When mercuric conjugates of glutathione (GSH), cysteinylglycine. or cysteine (containing 203Hg2+) were perfused through the lumen, the rates of luminal disappearance flux (JD) of inorganic mercury were approximately 39, 53, and 102 fmol/min per' min, respectively. Thus, the rates of luminal uptake of mercury are greater when the mercury is in the form of a mercuric conjugate of cysteine than in the form of a mercuric conjugate of cysteinylglycine or GSH. Addition of acivicin to the perfusate, to inhibit activity of the y-glutamyltransferase, caused significant reductions in the J,, for mercury in tubules perfused with mercuric conjugates of GSH. Addition of cilastatin, an inhibitor of dehydropeptidase- l (cysteinylglycinase) activity, caused significant reductions in the uptake of mercury in tubules perfused with mercuric conjugates of cysteinylglycine. These findings indicate that a significant amount of the luminal uptake of mercury, when mercuric conjugates of GSH are present in the lumen, is dependent on the activity of both y-glutamyltransferase and cysteinylglycinase. Finally, the JD for mercury in tubules perfused with mercuric conjugates of cysteine was reduced by approximately 50% when 3.0 mM L-lysine or 5.0 mM cycloleucine was added to the perfusate. It is concluded that these findings indicate that at least some of the luminal uptake of mercuric conjugates of cysteine occurs at the site of one or more amino acid transporters via a mechanism involving molecular homology.

Mechanisms of action of 2,3-dimercaptopropane-1-sulfonate and the transport, disposition, and toxicity of inorganic mercury in isolated perfused segments of rabbit proximal tubules

Mechanisms by which the dithiol chelating agent 2, 3-dimercaptopropane-1-sulfonate (DMPS) significantly alters the renal tubular transport, accumulation, and toxicity of inorganic mercury were studied in isolated perfused pars recta (S2) segments of proximal tubules of rabbits. Addition of 200 microM DMPS to the bath provided complete protection from the toxic effects of 20 microM inorganic mercury in the lumen. The protection was linked to decreased uptake and accumulation of mercury. Additional data indicated that, when DMPS and inorganic mercury were coperfused through the lumen, very little inorganic mercury was taken up from the lumen. We also obtained data indicating that DMPS is transported by the organic anion transport system and that this transport is linked to the therapeutic effects of DMPS. Interestingly, very little inorganic mercury was taken up and no cellular pathological changes were detected when inorganic mercury and DMPS were added to the bath. We also tested the hypothesis that DMPS can extract cellular mercury while being transported from the bath into the luminal compartment. Our findings showed that, when DMPS was applied to the basolateral membranes of S2 segments after they had been exposed to mercuric conjugates of glutathione of the laminal membrane, the tubular content of mercury was greatly reduced and the rates of disappearance of mercury from the lumen changed from positive values to markedly negative values. We conclude that inorganic mercury is extracted from proximal tubular cells by a transport process involving the movement of DMPS from the bathing compartment to the luminal compartment.