OU-MRU Vol.10 Apr 2015

Okayama University Medical Research Updates （OU-MRU）

2015.04 Vol.10

Source: Okayama University, Center for Public Affairs and Communications

For immediate release: 27 April 2015
Okayama University research: Enzyme-inhibitors treat drug-resistant epilepsy(Okayama, 28 April) Studies reveal how high-fat low-carb diets affect brain activity andhighlight an approach for treating epilepsy with metabolic drugs.

One percent of the world’s population suffer from epilepsy, and a third of sufferers cannot
be treated with antiepileptic drugs. Diet control has been used to treat patients sufferingfrom drug-resistant epilepsy since the 1920s, but how metabolic processes affect epilepsy
has not been fully understood. Now researchers at Okayama University and Kawasaki
Medical School have identified the metabolic pathways altered by diet treatments, theenzymes that can control them and potential metabolic drugs that may be effective fortreating types of epilepsy that are resistant to other drugs.

‘Ketogenic’ diets used to treat epilepsy are high in fat and low in carbohydrate. Due to thescarcity of glucose available as a result, the brain metabolises ketones, which uses adifferent metabolic pathway.

Tsuyoshi Inoue and his team examined neural cells in an artificial cerebrospinal fluid
solution switched from glucose to ketones. When glucose was switched to ketones the cells
became hyperpolarized - a change in the cell’s membrane potential that makes neurons lessprone to becoming excited and active.

The researchers further broke down the processes in the metabolism of glucose andidentified a crucial enzyme – lactate dehydrogenase (LDH). Blocking LDH mimicked theswitch from glucose to ketones in vitro. Further in vivo tests on mice confirmed the effect.

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OU-MRU Vol.10 Apr 2015

By testing the drugs already in use they identified LDH inhibitory action in stiripentol, a drug
used for a rare form of the epilepsy. By modifying its chemical structure, they found analternative LDH inhibitor with a similar structure that was more effective for in vivo tests onmice. They conclude, “Our study opens a realistic path to develop compounds for drugresistant epilepsy by targeting LDH enzymes with stiripentol derivatives.”

Background
Epilepsy
Epilepsy describes the neurological disorder that results in seizures that have no otherknown cause. The seizures result from excessive excitation in the cortical nerve in the brain
and the length and severity of the seizures may vary.

The transmission of signals by neurons relies on the rapid rise and fall of the membranepotential, and is affected by cell polarization. When the cell membrane becomes
hyperpolarized, a greater stimulus is required to produce an action potential. As a result
hyperpolarization can prevent the excessive cortical activity that causes epileptic seizures.

Glucose and ketone metabolic pathways
Ketones directly activate the tricarboxylic acid (TCA) cycle that generates energy in aerobic
respiration. In contrast glucose and lactate are converted to pyruvate in glycolysis, which
are then used as the main input and intermediates of the TCA cycle.

The researchers studied the activity of neural cells from the basal ganglia – a region of thebrain that is important for the propagation of seizures - in artificial cerebrospinal fluid invitro. They found that the replacement of glucose with ketones led to hyperpolarization of
the cell membrane. The hyperpolarization was recovered by the addition of lactate,suggesting that inhibitors of the enzyme LDH - which catalyses the conversion of lactate into
pyruvate - may have the same effect on epilepsy as ketogenic diets.

Stiripentol and analog
Stiripentol is an antiepileptic drug found to be effective for a particular type of epilepsy,
Dravet syndrome. The chemical structure of stiripentol differs to most antiepileptic drugs,
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OU-MRU Vol.10 Apr 2015

prompting the researchers to explore other chemicals with a similar structure that have LDH
inhibiting and antiepileptic actions.

Isosafrole has a similar structure to stiripentol but with certain parts of the chemicalstructure absent (i.e. the hydroxyl and tertiary-butyl groups). The researchers found thatisosafrole strongly inhibited LDH and suppressed signs of seizure such as spontaneous highvoltage spikes and paroxysmal discharges in mice tests. The results suggest that LDHinhibitors may be effective for types of epilepsy that cannot be treated with traditional
drugs.

Figure caption
A scheme of energy metabolic pathways in the brain. Glucose is transported into neurons
and converted to pyruvate in glycolysis (pathway 1, brown). Ketone bodies directly activate
the TCA cycle in neurons (pathway 2, green). Glucose is also transported into astrocytes (atype of glial cell) and converted to lactate by LDH, which is then released to neurons andconverted to pyruvate by LDH (pathway 3, blue; the astrocyte-neuron lactate shuttle).

Reference
Nagisa Sada, Suni Lee, Takashi Katsu, Takemi Otsuki, Tsuyoshi Inoue. Targeting LDH Enzymes
with a Stiripentol Analog to Treat Epilepsy. Science (March 20, 2015) Vol. 347 no. 6228 pp.
1362-1367
DOI: 10.1126/science.aaa1299
http://www.ncbi.nlm.nih.gov/pubmed/25792327

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OU-MRU Vol.10 Apr 2015

Correspondence toAssociate Professor Tsuyoshi Inoue, Ph.D.
Department of Biophysical Chemistry, Graduate School ofMedicine, Dentistry and Pharmaceutical Sciences, Okayama
University, Okayama 700-8530, Japan.
E-mail: tinoue@pharm.okayama-u.ac.jp

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1-1-1 Tsushima-naka, Kita-ku, Okayama 700-8530 Japan© OKAYAMA University

OU-MRU Vol.10 Apr 2015

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About Okayama University
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