A number of pathological conditions caused by oxidative stress have been reported in uremic patients undergoing maintenance hemodialysis (HD). Enhanced lipid peroxidation was previously observed in peripheral blood mononuclear cells (PBMCs) of HD patients. Upregulation of 5-lipoxygenase (5-Lox) activity and protein content with enhanced production of leukotriene B(4) (LTB(4)) and membrane lipoperoxides was also shown in PBMCs of HD patients. Administration of free vitamin E specifically inhibited 5-Lox activity without affecting gene expression at the protein level. To assess whether oral or intramuscular (IM) administration of vitamin E may suppress 5-Lox in HD patients, PBMCs from 16 subjects on maintenance HD therapy for at least 6 months were investigated before and after a short course of IM or oral administration of vitamin E (8 patients per group). PBMCs from 13 healthy controls were also evaluated and assumed as the reference standard. Vitamin E significantly reduced lipid peroxidation, LTB(4) content, and 5-Lox activity in PBMCs, whereas 5-Lox gene expression at the protein level was not affected. There were no significant differences in these parameters between patients treated with IM or oral vitamin E. PBMCs of HD patients showed enhanced membrane lipid peroxidation and release of LTB(4), both linked to upregulation of 5-LOX: 5-Lox activity and related oxidative stress were significantly (although not completely) suppressed by vitamin E regardless of the administration route.

Lipid peroxidation was shown at the membrane level in peripheral blood cells of patients hemodialyzed on cuprophan dialyzers, and was mainly attributable to the generation of conjugated hydroperoxides in the lipid bilayer. The oxidative index (i.e., the A234/205 ratio) of membrane lipids was 3.2-fold higher in hemodialysis patients than in healthy control subjects, and also the level of leukotriene B4 was significantly increased (up to 1.7-fold over control). Both membrane peroxidation and release of leukotriene B4 were linked to upregulation of 5-lipoxygenase activity (up to 2.4-fold over control) and expression at the protein level (up to 1.9-fold). Vitamin E, the most important lipophilic antioxidant, prevented both membrane peroxidation and release of leukotriene B4 by inhibiting 5-lipoxygenase activity without affecting enzyme expression. Similar results were observed in patients hemodialyzed on polymethylmetacrylate membranes, but in this case the activation of 5-lipoxygenase was less pronounced. The use of a purified 5-lipoxygenase demonstrated that vitamin E was a reversible inhibitor of enzyme activity (IC50 = 35 +/- 4 microM), further characterized as noncompetitive (Ki = 30 +/- 3 microM). Taken together, the results reported here shed some light on the mechanism responsible for the oxidative damage in hemodialysis. Moreover, the beneficial effect of vitamin E described here may have relevance for the therapy of patients with kidney disease.

Cytokines, and interleukin-6 in particular, are inflammatory peptide mediators that are extensively studied as regulators of bone tissue homeostasis. They seem to be involved in osteoclast activation and bone resorption and probably play a role in osseointegrated implant rejection. In this study we investigate the ability of titanium implants to cause an imbalance in the homeostatic equilibrium of cytokines using the peritoneal cavity of DB-A2 mice as a model. The inflammatory response was evaluated as a messenger ribonucleic acid expression determined by the semiquantitative reverse transcriptase-polymerase chain reaction technique in peritoneal macrophages from titanium-implanted mice. Interleukin-6 release was detected by a specific quantitative enzyme-linked immunosorbent assay. Our results have shown that titanium implants do not significantly stimulate the proinflammatory cytokine system compared to the control group. The enzyme-linked immunosorbent assay test confirms, after a peak in secretion at day 1 compared with basal levels, a clear decrease in interleukin-6 at basal levels on following control at 6 and 9 days after implantation. The study of the interaction between implanted biomaterials and inflammatory mediators seems to be very promising.Perhaps a better understanding of the mechanisms of bone resorption could lead to finding a new clinical solution for patients with osseointegrated implant rejection.