Effects of prolonged recombinant human erythropoietin administration on muscle membrane transport systems and metabolic marker enzymes

Abstract

Adaptations to chronic hypoxia involve changes in membrane transport proteins. The underlying mechanism of this response may be related to concomitant occurring changes in erythropoietin (Epo) levels. We therefore tested the direct effects of recombinant human erythropoietin (rHuEpo) treatment on the expression of muscle membrane transport proteins. Likewise, improvements in performance may involve upregulation of metabolic enzymes. Since Epo is known to augment performance we tested the effect of rHuEpo on some marker enzymes that are related to aerobic capacity. For these purposes eight subjects received 5,000 IU rHuEpo every second day for 14 days, and subsequently a single dose of 5,000 IU weekly for 12 weeks. Muscle biopsies were obtained before and after 14 weeks of rHuEpo treatment. The treatment increased hematocrit (from 44.7 to 48.8%), maximal oxygen uptake by 8.1%, and submaximal performance by approximately 54%. Membrane transport systems and carbonic anhydrases involved in pH regulation remained unchanged. Of the Na(+), K(+)-pump isoforms only the density of the alpha2 subunit was decreased (by 22%) after treatment. The marker enzymes cytochrom c and hexokinase remained unchanged with the treatment. In conclusion, changes in muscle membrane transport proteins and selected muscle enzymes do not contribute to the Epo-induced improvement in performance.

Effects of an 8-weeks erythropoietin treatment on mitochondrial and whole body fat oxidation capacity during exercise in healthy males

“…In partial agreement with the thermogenesis theory suggested by the authors, we have previously reported higher uncoupled mitochondrial respiration in the same participants included in the present investigation (Plenge et al, 2012). On the contrary, some other studies have not found any effect of prolonged erythropoietin administration on muscle hexokinase or membrane transport system levels (Juel, Thomsen, Rentsch, & Lundby, 2007), erythropoietin receptormediated signalling cascades (Christensen, Lundby, et al, 2012), muscle phenotype and angiogenesis (Lundby, Hellsten, Jensen, Munch, & Pilegaard, 2008), suggesting that the effects of erythropoietin on skeletal muscle are likely indirect, i.e., through increased oxygen delivery. The results obtained from this investigation cannot rule out a possible indirect effect of erythropoietin on the skeletal muscle by means other than erythropoietin receptor, and further research is needed to elucidate the intracellular mechanisms responsible for the higher mitochondrial fat oxidation capacity observed.…”

Evaluation of Functional Erythropoietin Receptor Status in Skeletal Muscle In Vivo: Acute and Prolonged Studies in Healthy Human Subjects

“…Furthermore, over-expression of Epo in mice skeletal muscle tissue lead to up-regulation of genes involved in lipid metabolism while genes involved in glucose metabolism were down-regulated [37]. In contrast, 13 weeks of treatment with rHuEpo in humans did not lead to changes in levels of either hexokinase or cytochrome c [16].…”

“…Several studies have investigated changes in mRNA levels of pertinent proteins and structural changes in muscle after recombinant human Epo (rHuEpo) administration with conflicting results [13], [16], [17]. Thus, even though the Epo-R has been identified in human skeletal muscle tissue, its role remains incompletely understood.…”

Use of Erythropoietin as adjuvant therapy in nerve reconstruction

“…The data support the assumption that rHuEpo might evoke its effect independently from nerve regeneration in the graft by acting directly on the muscle or the neuromuscular junction. EpoR has recently been discovered in skeletal muscle and systemic rHuEpo treatment has shown to affect the expression of skeletal muscle proteins in vivo [27]. The fact that we did not detect reduced muscle atrophy in the conduit groups could imply that beginning re-innervation is needed for rHuEpo to render its supporting effect.…”