Effect of long-term treatment with trivalent chromium on erythropoietin production in HepG2 cells.

Trivalent chromium (Cr(III)) is sometimes taken as a long-term supplement, but its effectiveness is unclear. Recently, Cr(III) reportedly modulates peroxisome proliferator-activated receptor gamma (PPARγ) expression. Our previous study reported that increased PPARγ after 24 h Cr(III) treatment promoted erythropoietin (EPO) production in HepG2 cells. In the current study, we analyzed 4-week Cr(III) treatment effects on PPARγ and EPO production in HepG2 cells. Long-term Cr(III) treatment resulted in significantly elevated mRNA expression levels of PPARγ and EPO compared to controls. Additionally, treatment with a PPARγ inhibitor suppressed EPO mRNA expression. Increased EPO mRNA expression due to stimulation with hypoxia or cobalt was unaffected by long-term Cr(III) treatment. Administration of lipopolysaccharide and pyocyanin which causes oxidative stress, promoted EPO production, but this effect was attenuated in cells treated with Cr(III). Long-term Cr(III) treatment increased hypoxia inducible factor (HIF)-1α and 2α mRNA expression and protein levels. Increased PPARγ, induced by long-term Cr(III) treatment, suppressed sirtuin1 (SIRT1) mRNA expression and increased EPO mRNA expression, suggesting that increased PPARγ attenuated the suppressive effect of SIRT1 on HIF. These results suggest that the sustained increase in PPARγ during long-term Cr(III) treatment maintains increased EPO production through a mechanism different from that observed under hypoxia.

Enzymatic, alkaline, and autocatalytic degradation of poly(L-lactic acid): effects of biaxial orientation.

The hydrolytic degradation of biaxially oriented and de-oriented (melt-crystallized) poly(l-lactic acid) (PLLA) films was investigated in Tris-HCl-buffered solution (pH 8.6) with proteinase K, alkaline solution, and phosphate-buffered solution (pH 7.4) by the use of gravimetry, gel permeation chromatography, differential scanning calorimetry, and scanning electron microscopy. Biaxial orientation disturbed the proteinase K-catalyzed enzymatic degradation of PLLA films and the effects of biaxial orientation overcame those of crystallinity. The former may be due to the fact the enzyme cannot attach to the extended (strained) chains in the amorphous regions of the biaxially oriented PLLA film or cannot catalyze the cleavage of the strained chains. Another probable cause is that the enzyme can act only at the film surface of the biaxially oriented PLLA film, in marked contrast with the case of the de-oriented PLLA films where enzymatic degradation can proceed beneath the spherulitic crystalline residues. The effects of biaxial orientation on the alkaline and autocatalytic degradation of the PLLA films were insignificant for the periods studied here. The crystallinity rather than the biaxial orientation seems to determine the alkaline and autocatalytic degradation rates of the PLLA films. The accumulation of crystalline residues formed as a result of selective cleavage and removal of the amorphous chains was observed for the de-oriented PLLA films, but not for the biaxially oriented PLLA film, when degraded in the presence of proteinase K. This means the facile release of formed crystalline residues from the surface of the biaxially oriented PLLA film during enzymatic degradation, due to the fact that the crystalline regions of the biaxially oriented PLLA film were oriented with their c axis parallel to the film surface.