Mitochondrial abnormalities in lymphoblasts from autism

Background: Recent reports indicate role of oxidative stress in autism. Disturbance of energy metabolism has also been suggested in the brain of patients with autism. The free radicals, namely, reactive oxygen species (ROS) and reactive nitrogen species (RNS) are generated endogenously during oxidative metabolism and energy production by mitochondria in the body. While oxidative phosphorylation in the mitochondria generates superoxide anion, enzymatic oxidation of biogenic amines by monoamine oxidase in mitochondrial outer membrane produces H₂O₂. Damaged mitochondria not only produce more oxidants, but mitochondria are also vulnerable to oxidative stress. Additionally, alterations in mitochondrial membrane potential (MMP) are involved in both apoptotic and necrotic cell death. MMP creates an electrochemical gradient essential for ATP synthase activity in the oxidative phosphorylation pathway.

Objectives:   To study whether there is mitochondrial dysfunction in autism, mitochondrial free radicals generation and membrane potential were analyzed in the lymphoblasts.

Methods: The lymphoblasts from autistic and control subjects were obtained from Autism Genetic Resources Exchange Program, and the cell lysates and mitochondria were prepared. MMP was monitored using the fluorescent dye rhodamine123, a cell-permeable cationic dye, which preferentially partitions into mitochondria because of the highly negative MMP. ROS generation in the mitochondria was measured by the oxidation of dihydrorhodamine 123 to fluorescent rhodamine 123, while RNS were measured by using nitric oxide fluorometric assay kit.

Results: Elevated ROS and RNS levels were observed in the mitochondria of autistic lymphoblasts as compared with control lymphoblasts suggesting increased free radical generation by mitochondria in autism. The mitochondrial membrane potential was also reduced in lymphoblasts from autism than in controls.

Conclusions: Our results suggest increased mitochondrial oxidative stress and reduced MMP in autism. Such mitochondrial abnormalities may lead to defects in oxidative phosphorylation and energy metabolism in autism.