In vivo and in vitro assessment of brain bioenergetics in aging rats

Abstract

Brain energy disorders can be present in aged men and animals. To this respect, the mitochondrial and free radical theory of aging postulates that age-associated brain energy disorders are caused by an imbalance between pro- and anti-oxidants that can result in oxidative stress. Our study was designed to investigate brain energy metabolism and the activity of endogenous antioxidants during their lifespan in male Wistar rats. In vivo brain bioenergetics were measured using ³¹P nuclear magnetic resonance (NMR) spectroscopy and in vitro by polarographic analysis of mitochondrial oxidative phosphorylation. When compared to the young controls, a significant decrease of age-dependent mitochondrial respiration and adenosine-3-phosphate (ATP) production measured in vitro correlated with significant reduction of forward creatine kinase reaction (kfor) and with an increase in phosphocreatine (PCr)/ATP, PCr/Pi and PME/ATP ratio measured in vivo. The levels of enzymatic antioxidants catalase, GPx and GST significantly decreased in the brain tissue as well as in the peripheral blood of aged rats. We suppose that mitochondrial dysfunction and oxidative inactivation of endogenous enzymes may participate in age-related disorders of brain energy metabolism.

Fig 1

Changes of brain bioenergetics measured in vivo by ³¹P MRS in aged (36 months old) compared to young (3 months old) male Wistar rats. MRS, magnetic resonance spectroscopy; PCr/ATP, phosphocreatine to adenosine three phosphate ratio; PCr/Pi, PCr to inorganic phosphate ratio; PME/ATP, phosphate monoester to ATP ratio; kfor, forward rate constant of CK and pHi, intracellular pH. ***P < 0.001, **P < 0.01, *P < 0.05.

Fig 2

Percentual changes of in vitro measured OXPHOS parameters in brain mitochondria from young (3 months old), adult (17 months old) and aged (36 months old) male Wistar rats. (A) Complex I–sodium glutamate / malic acid NAD substrate, (B) Complex II–succinate FAD substrate (respectively, A and B). ***P < 0.001, **P < 0.01, *P < 0.05 versus 3 months old rats. ++P < 0.01, +P < 0.05 versus 17 months old rats.

Fig 3

Percentual changes of endogenous antioxidants activity in brain tissue (A) and in peripheral blood (B) of aged (36 months old) compared to adult (10 months old) male Wistar rats. (A) (brain) ***P < 0.001, *P < 0.05, (B) (blood) ***P < 0.001, **P < 0.01.