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Novel therapeutic approaches for Leber's hereditary optic neuropathy.

ABSTRACT: Many human childhood mitochondrial disorders result from abnormal mitochondrial DNA (mtDNA) and altered bioenergetics. These abnormalities span most of the mtDNA, demonstrating that there are no "unique" positions on the mitochondrial genome that when deleted or mutated produce a disease phenotype. This diversity implies that the relationship between mitochondrial genotype and clinical phenotype is very complex. The origins of clinical phenotypes are thus unclear, fundamentally difficult-to-treat, and are usually clinically devastating. Current treatment is largely supportive and the disorders progress relentlessly causing significant morbidity and mortality. Vitamin supplements and pharmacological agents have been used in isolated cases and clinical trials, but the efficacy of these interventions is unclear. In spite of recent advances in the understanding of the pathogenesis of mitochondrial diseases, a cure remains elusive. An optimal cure would be gene therapy, which involves introducing the missing gene(s) into the mitochondria to complement the defect. Our recent research results indicate the feasibility of an innovative protein-transduction ("protofection") technology, consisting of a recombinant mitochondrial transcription factor A (TFAM) that avidly binds mtDNA and permits efficient targeting into mitochondria in situ and in vivo. Thus, the development of gene therapy for treating mitochondrial disease offers promise, because it may circumvent the clinical abnormalities and the current inability to treat individual disorders in affected individuals. This review aims to focus on current treatment options and future therapeutics in mitochondrial disease treatment with a special emphasis on Leber's hereditary optic neuropathy.

SUBMITTER: Iyer S

PROVIDER: S-EPMC5652312 | biostudies-literature | 2013 Mar

REPOSITORIES: biostudies-literature

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Novel therapeutic approaches for Leber's hereditary optic neuropathy.

Iyer Shilpa S

Discovery medicine 20130301 82

Many human childhood mitochondrial disorders result from abnormal mitochondrial DNA (mtDNA) and altered bioenergetics. These abnormalities span most of the mtDNA, demonstrating that there are no "unique" positions on the mitochondrial genome that when deleted or mutated produce a disease phenotype. This diversity implies that the relationship between mitochondrial genotype and clinical phenotype is very complex. The origins of clinical phenotypes are thus unclear, fundamentally difficult-to-trea ...[more]

PMID: 23545042

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Project description:PurposeTo screen mitochondrial DNA (mtDNA) variations in Leber hereditary optic neuropathy (LHON).MethodsTen LHON patients were selected from neuro-ophthalmology clinics of All India Institute of Medical Sciences (AIIMS), New Delhi, India. Clinical evaluation included slit-lamp biomicroscopy, fundus examination, and neuroimaging. DNA was isolated from whole blood samples. The entire coding region of the mitochondrial genome was amplified by PCR in ten patients and 20 controls. The full mtDNA genome except D-loop was sequenced. All sequences were analyzed against mitochondrial reference sequence NC_012920.ResultsMtDNA sequencing revealed a total of 30 nucleotide variations in the ten LHON patients and 29 in the 20 controls. Of 30 changes, 30.00% (9/30) were nonsynonymous, and the remaining 70.00% (21/30) were synonymous. In controls, a total of five changes were nonsynonymous. Out of the total 14 nonsynonymous changes observed in cases and controls, four (p.A52T in nicotinamide adenine dinucleotide [NADH] dehydrogenase [ND1] protein; p.L128Q in ND2; p.W48R in ATPase6; p.R340H in ND4 protein) were pathogenic. Four patients were positive for either of pathogenic changes. In total, 16.66% (5/30) variations were novel out of which 40.00% (2/5) were nonsynonymous. All novel variations were submitted to the GenBank database, and accession numbers were obtained. Primary LHON mutations in complex I genes have been considered a hallmark feature of LHON patients, and primary LHON mutations were present in two cases in this study. Mutations in complex I genes (ND genes) account for 50%-90% of LHON pedigrees in different ethnic pedigrees. In this study the highest numbers of changes were also present in complex I genes (46.66%; 14/30) followed by complex IV (30.00%; 9/30), complex III (16.66%; 5/30), and then complex V (6.66%; 2/30). Complex I had 5/30 (16.66%) nonsynonymous changes, complex III had 1/30 (3.33%), complex IV had 1/30 (3.33%), and complex V had 2/30 (6.66%) nonsynonymous changes. Nonsynonymous mutations in cytochrome c oxidase (COX) genes have been reported previously in LHON patients. Nonsynonymous mtDNA variations may adversely affect the respiratory chain and impair the oxidative phosphorylation (OXPHOS) pathway, resulting in low ATP production and elevated reactive oxygen species (ROS) levels, which cause oxidative stress. It has previously been reported that oxidative stress (OS) leads to oxidative damage of cellular macromolecules, such as mitochondrial and nuclear DNA, proteins, and lipids along with energy depletion and a local imbalance of calcium homeostasis, resulting in neuronal degeneration. OS is the underlying etiology in several ocular diseases and also plays an essential role in LHON.ConclusionsA total of five novel mtDNA variations were identified in this study. Nonsynonymous mtDNA variations may adversely affect the respiratory chain and impair the OXPHOS pathway, resulting in low ATP production and elevated ROS levels. OS further damages both nuclear and mtDNA. This preliminary study describes mtDNA sequence variations in a relatively small number of LHON patients of north Indian ethnic origin. However, these results should be confirmed in other populations. Early diagnosis of mtDNA variations and prompt anti-oxidant administration in these cases may delay OS-induced injury to retinal ganglion cells (RGCs) and hence improve visual prognosis.

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Novel therapeutic approaches for Leber's hereditary optic neuropathy.

Publications

Novel therapeutic approaches for Leber's hereditary optic neuropathy.

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