The ketogenic diet (KD) is a high‐fat, low carbohydrate diet that is used as a therapy for intractable epilepsy. However, the mechanism(s) by which the KD achieves neuroprotection and/or seizure control are not yet known. We sought to determine whether the KD improves mitochondrial redox status. Adolescent Sprague–Dawley rats (P28) were fed a KD or control diet for 3 weeks and ketosis was confirmed by plasma levels of β‐hydroxybutyrate (BHB). KD‐fed rats showed a twofold increase in hippocampal mitochondrial GSH and GSH/GSSG ratios compared with control diet‐fed rats. To determine whether elevated mitochondrial GSH was associated with increased de novo synthesis, the enzymatic activity of glutamate cysteine ligase (GCL) (the rate‐limiting enzyme in GSH biosynthesis) and protein levels of the catalytic (GCLC) and modulatory (GCLM) subunits of GCL were analyzed. Increased GCL activity was observed in KD‐fed rats, as well as up‐regulated protein levels of GCL subunits. Reduced CoA (CoASH), an indicator of mitochondrial redox status, and lipoic acid, a thiol antioxidant, were also significantly increased in the hippocampus of KD‐fed rats compared with controls. As GSH is a major mitochondrial antioxidant that protects mitochondrial DNA (mtDNA) against oxidative damage, we measured mitochondrial H2O2 production and H2O2‐induced mtDNA damage. Isolated hippocampal mitochondria from KD‐fed rats showed functional consequences consistent with the improvement of mitochondrial redox status i.e. decreased H2O2 production and mtDNA damage. Together, the results demonstrate that the KD up‐regulates GSH biosynthesis, enhances mitochondrial antioxidant status, and protects mtDNA from oxidant‐induced damage.

The mechanisms underlying the efficacy of the ketogenic diet (KD) remain unknown. Recently, we showed that the KD increased glutathione (GSH) biosynthesis. Since the NF E2-related factor 2 (Nrf2) transcription factor is a primary responder to cellular stress and can upregulate GSH biosynthesis, we asked whether the KD activates the Nrf2 pathway. Here we report that rats consuming a KD show acute production of H2O2 from hippocampal mitochondria, which decreases below control levels by 3 weeks, suggestive of an adaptive response. 4-hydroxy-2-nonenal (4-HNE), an electrophilic lipid peroxidation end product known to activate the Nrf2 detoxification pathway was also acutely increased by the KD. Nrf2 nuclear accumulation was evident in both the hippocampus and liver, and the Nrf2 target, NAD(P)H:quinone oxidoreductase (NQO1), exhibited increased activity in both the hippocampus and liver after 3 weeks. We also found chronic depletion of liver tissue GSH, while liver mitochondrial antioxidant capacity was preserved. These data suggest that the KD initially produces mild oxidative and electrophilic stress which may systemically activate the Nrf2 pathway via redox signaling leading to chronic cellular adaptation, induction of protective proteins, and improvement of the mitochondrial redox state.

The ketogenic diet (KD) is a high-fat, low carbohydrate diet that is used as a therapy for intractable epilepsy. However, the mechanism(s) by which the KD achieves neuroprotection and/or seizure control are not yet known. The broad efficacy of the KD in diverse epilepsies coupled with its profound influence on metabolism suggests that mitochondrial functions may be critical in its mechanism(s) of seizure control. Mitochondria subserve important cellular functions that include the production of cellular ATP, control of apoptosis, maintenance of calcium homeostasis and the production and elimination of reactive oxygen species (ROS). This review will focus on recent literature reporting the regulation of mitochondrial functions and redox signaling by the KD. The review highlights a potential mechanism of the KD involving the production of low levels of redox signaling molecules such as H2O2 and electrophiles e.g. 4-hydroxynonenal (4-HNE), which in turn activate adaptive pathways such as the protective transcription factor, NF E2-related factor 2 (Nrf2). This can ultimately result in increased production of antioxidants (e.g. GSH) and detoxification enzymes which may be critical in mediating the protective effects of the KD.

Abnormal aggregation of human ␣-synuclein in Lewy bodies and Lewy neurites is a pathological hallmark of Parkinson disease and dementia with Lewy bodies. Studies have shown that oxidation and nitration of ␣-synuclein lead to the formation of stable dimers and oligomers through dityrosine cross-linking. Previously we have reported that tyrosine-to-cysteine mutations, particularly at the tyrosine 39 residue (Y39C), significantly enhanced ␣-synuclein fibril formation and neurotoxicity. In the current study, we have generated transgenic mice expressing the Y39C mutant human ␣-synuclein gene controlled by the mouse Thy1 promoter. Mutant human ␣-synuclein was widely expressed in transgenic mouse brain, resulting in 150% overexpression relative to endogenous mouse ␣-synuclein. At age 9 -12 months, transgenic mice began to display motor dysfunction in rotarod testing. Older animals aged 15-18 months showed progressive accumulation of human ␣-synuclein oligomers, associated with worse motor function and cognitive impairment in the Morris water maze. By age 21-24 months, ␣-synuclein aggregates were further increased, accompanied by severe behavioral deficits. At this age, transgenic mice developed neuropathology, such as Lewy body-like ␣-synuclein and ubiquitin-positive inclusions, phosphorylation at Ser 129 of human ␣-synuclein, and increased apoptotic cell death. In summary, Y39C human ␣-synuclein transgenic mice show age-dependent, progressive neuronal degeneration with motor and cognitive deficits similar to diffuse Lewy body disease. The time course of ␣-synuclein oligomer accumulation coincided with behavioral and pathological changes, indicating that these oligomers may initiate protein aggregation, disrupt cellular function, and eventually lead to neuronal death.