Effects of glutamine on simulated microgravity induced cardiac oxidative stress

  AIM   To investigate the effects of glutamine (Gln) on simulated microgravity induced oxidative stress in the heart.

  METHODS   Microgravity was simulated by tail suspension. Eighteen male Sprague-Dawley rats were randomly assigned into a control group (Control), a tail suspension group (HU) and a Gln-treated tail suspension group (HU + Gln). After 4 weeks of tail suspension, cardiac functions and contents of dihydroethidium (DHE) labeled superoxide anion, malondialdehyde (MDA), glutathione (GSH) and hydrogen peroxide (H₂O₂) in myocardial tissues were detected. Neonatal rat cardiomyocytes and adult rat cardiomyocytes were isolated and divided into 4 groups: a control group (Control), a Gln-treated group (Gln), a H₂O₂ group (H₂O₂) and a Gln-treated H₂O₂ group (H₂O₂ + Gln). Flow cytometry was used to detect myocardial apoptosis in different groups. The contents of MDA and GSH in adult rat cardiomyocytes were detected. Intracellular Ca²⁺ were stained with fluo-4, and then myocardial contraction amplitude and Ca²⁺ transient amplitude were detected by laser confocal microscope.

  RESULTS   Compared with those in the control group, the DHE fluorescence intensity, MDA content and H₂O₂ content were increased (all P < 0.01), and GSH content was decreased in the HU group (P < 0.01), indicating an increased oxidative stress level. Gln treatment decreased the DHE fluorescence intensity, MDA content and H₂O₂ content (P < 0.05), but increased GSH content (P < 0.05). Gln also restored the impaired cardiac functions induced by HU, as manifested by increased left ventricular ejection fraction, fractional shortening and cardiac output (all P < 0.05). In neonatal rat cardiomyocytes, Gln significantly reduced the increased apoptosis induced by H₂O₂ treatment (P < 0.01). In adult rat ventricular cardiomyocytes, Gln treatment significantly alleviated the increased oxidative stress level (P < 0.05) and enhanced the decreased myocardial contraction amplitude (P < 0.01) and Ca²⁺ transient amplitude (P < 0.05) induced by H₂O₂ treatment.

  CONCLUSION   Gln treatment significantly alleviates cardiac oxidative stress and improves the impaired cardiac functions induced by simulated microgravity probably through promoting GSH synthesis in cardiomyocytes.