Intraneuronal signaling pathways of metallothionein.

Metallothionein (MT) belongs to a family of metal-binding cysteine-rich proteins comprising several structurally related proteins implicated in tissue protection and regeneration after injuries and functioning as antiapoptotic antioxidants in neurological disorders. This has been demonstrated in animals receiving MT treatment and in mice with endogenous MT overexpression or null mutation during various experimental models of neuropathology, and also in patients with Alzheimer's disease and amyotrophic lateral sclerosis. Exogenously applied MT increases neurite outgrowth and neuronal survival in rat cerebellar, hippocampal, dopaminergic, and cortical neurons in vitro. In this study, the intraneuronal signaling involved in MT-mediated neuritogenesis was examined. The MT-induced neurite outgrowth in cultures of cerebellar granule neurons was dependent on activation of a heterotrimeric G-protein-coupled pathway but not on protein tyrosine kinases or on receptor tyrosine kinases. Activation of phospholipase C was necessary for MT-induced neurite outgrowth, and furthermore it was shown that inhibition of several intracellular protein kinases, such as protein kinase A, protein kinase C, phosphatidylinositol 3-kinase, Ca(2+)/calmodulin kinase-II, and mitogen-activated protein kinase kinase, abrogated the MT-mediated neuritogenic response. In addition, exogenously applied MT resulted in a decrease in phosphorylation of intraneuronal kinases implicated in proinflammatory reactions and apoptotic cell death, such as glycogen synthase-serine kinase 3alpha, Jun, and signal transducer and activator of transcription 3. This paper elucidates the intraneuronal molecular signaling involved in neuroprotective effects of MT.

Supplementation with vitamins C and E inhibits the release of interleukin-6 from contracting human skeletal muscle.

Contracting human skeletal muscle is a major contributor to the exercise-induced increase of plasma interleukin-6 (IL-6). Although antioxidants have been shown to attenuate the exercise-induced increase of plasma IL-6, it is unknown whether antioxidants inhibit transcription, translation or translocation of IL-6 within contracting human skeletal muscle. Using a single-blind placebo-controlled design with randomization, young healthy men received an oral supplementation with either a combination of ascorbic acid (500 mg day(-1)) and RRR-alpha-tocopherol (400 i.u. day(-1)) (Treatment, n= 7), or placebo (Control, n= 7). After 28 days of supplementation, the subjects performed 3 h of dynamic two-legged knee-extensor exercise at 50% of their individual maximal power output. Muscle biopsies from vastus lateralis were obtained at rest (0 h), immediately post exercise (3 h) and after 3 h of recovery (6 h). Leg blood flow was measured using Doppler ultrasonography. Plasma IL-6 concentration was measured in blood sampled from the femoral artery and vein. The net release of IL-6 was calculated using Fick's principle. Plasma vitamin C and E concentrations were elevated in Treatment compared to Control. Plasma 8-iso-prostaglandin F(2alpha), a marker of lipid peroxidation, increased in response to exercise in Control, but not in Treatment. In both Control and Treatment, skeletal muscle IL-6 mRNA and protein levels increased between 0 and 3 h. In contrast, the net release of IL-6 from the leg, which increased during exercise with a peak at 3.5 h in Control, was completely blunted during exercise in Treatment. The arterial plasma IL-6 concentration from 3 to 4 h, when the arterial IL-6 levels peaked in both groups, was approximately 50% lower in the Treatment group compared to Control (Treatment versus Control: 7.9 pg ml(-1), 95% confidence interval (CI) 6.0-10.7 pg ml(-1), versus 19.7 pg ml(-1), CI 13.8-29.4 pg ml(-1), at 3.5 h, P < 0.05 between groups). Moreover, plasma interleukin-1 receptor antagonist (IL-1ra), C-reactive protein and cortisol levels all increased after the exercise in Control, but not in Treatment. In conclusion, our results show that supplementation with vitamins C and E attenuated the systemic IL-6 response to exercise primarily via inhibition of the IL-6 protein release from the contracting skeletal muscle per se.