Leber's hereditary optic atrophy: further evidence for a defect of cyanide metabolism?

Leber Hereditary Optic Neuropathy: Review of Treatment and Management

Leber hereditary optic neuropathy (LHON) is a maternally inherited mitochondrial disease that specifically targets the retinal ganglion cells by reducing their ability to produce enough energy to sustain. The mutations of the mitochondrial DNA that cause LHON are silent until an unknown trigger causes bilateral central visual scotoma. After the onset of loss of vision, most patients experience progressive worsening within the following months. Few of them regain some vision after a period of ~1 year. Management of LHON patients has been focused on understanding the triggers of the disease and its pathophysiology to prevent the onset of visual loss in a carrier. Medical treatment is recommended once visual loss has started in at least one eye. Research evaluated drugs that are thought to be able to restore the mitochondrial electron transport chain of the retinal ganglion cells. Significant advances were made in evaluating free radical cell scavengers and gene therapy as potential treatments for LHON. Although encouraging the results of clinical trial have been mixed in stopping the worsening of visual loss. In patients with chronic disease of over 1 year, efficient treatment that restores vision is yet to be discovered. In this review, we summarize the management strategies for patients with LHON before, during, and after the loss of vision, explain the rationale and effectiveness of previous and current treatments, and report findings about emerging treatments.

Leber's hereditary optic neuropathy with late disease onset: clinical and molecular characteristics of 20 patients

BACKGROUND

Leber's hereditary optic neuropathy (LHON) is a mitochondrial disease that typically causes bilateral blindness in young men. Here we describe the clinical and molecular characteristics of 20 patients with disease onset after the age of 50 years (late onset-LHON).

METHODS

From a cohort of 251 affected and 277 unaffected LHON carriers, we identified 20 patients with onset of visual loss after the age of 50 years. Using structured questionnaires, data including basic demographic details, age of onset, progression of visual loss and severity as well as exposure to possible environmental triggers including alcohol, smoking and illicit drugs were retrospectively collected. Groups were compared using the Mann-Whitney-U-Test for two independent groups of sampled data.

RESULTS

The proportion of late onset-LHON in our cohort was 8% (20 patients, 15 males, 5 females). The mtDNA mutations m.11778G > A and m.3460G > A were found in 16 and 4 patients, respectively. Among 89 asymptomatic carriers above the age of 50 years (28 males, 61 females), the mtDNA mutations m.11778G > A, m.3460G > A and m.14484 T > C were found in 60, 12 and 17 carriers, respectively. Late onset-LHON patients had significantly higher mean cumulative tobacco and alcohol consumption compared with unaffected carriers. However, there was no significant difference between late onset- and typical LHON patients with regard to daily tobacco and weekly alcohol consumption before disease onset.

CONCLUSION

As already shown for typical LHON, alcohol consumption and smoking are important trigger factors also for the late manifestation. LHON should be considered in the differential diagnosis of subacute blindness even in older patients.

Hydroquinone induces oxidative and mitochondrial damage to human retinal Müller cells (MIO-M1)

PURPOSE

Smoking is a risk factor in the development of a variety of neuroretinal diseases. Therefore, we have investigated the effects of hydroquinone (HQ), a toxicant that is present in high concentrations in cigarette smoke, on a human retinal Müller cell line (MIO-M1).

METHODS

MIO-M1 cells were treated for 24h with four different concentrations of HQ (200μM, 100μM, 50μM, and 25μM). Assays were used to measure cell viability, reactive oxygen/nitrogen species (ROS/RNS), mitochondrial dehydrogenase activity (WST assay), caspase-3/7 activity and lactate dehydrogenase (LDH) levels. Western blot analyses with anti-LC3 and anti-GAPDH antibodies were performed on HQ-treated samples. Some cultures were treated with 4μM rapamycin, to induce autophagy, with and without the autophagy inhibitor 3-methyl-adenine (3MA), and levels of ROS/RNS and LDH were measured.

RESULTS

Our findings show that HQ reduced cell viability at four different concentrations tested (200, 100, 50 and 25μM); decreased mitochondrial function at concentrations of 200 and 100μM; increased ROS/RNS activity at all the concentrations tested and increased LDH levels at concentrations of 200, 100 and 50μM. Caspase-3/7 activities were not modified by HQ. However, treatment of these cells with this agent resulted in the appearance of the autophagy associated LC3-II band. Pre-treatment with 3MA reduced the ROS/RNS and LDH levels of the HQ-treated and rapamycin-treated cells.

CONCLUSION

Our study suggests that HQ damages the MIO-M1 cells through oxidative, mitochondrial and autophagic pathways and not caspase-related apoptosis.

Leber's hereditary optic neuropathy triggered by antiretroviral therapy for human immunodeficiency virus

PURPOSE

To describe the clinical features of two cases of Leber's hereditary optic neuropathy (LHON) precipitated by antiretroviral treatment for human immunodeficiency virus (HIV) infection.

METHODS

Two cases of LHON (from an expected four new cases a year throughout Australia) were identified in men on treatment for HIV infection.

RESULTS

Two HIV-infected men were receiving combination antiretroviral therapy that included nucleoside analogues. Both patients carried the 14 484 mitochondrial DNA mutation and were distantly related (seventh cousins). Although both men presented with sequential visual loss typical of LHON and one had a known close relative affected by LHON, the correct diagnosis was delayed in both cases. The final visual outcome was profoundly reduced in both instances and cessation of antiretroviral therapy did not result in recovery of vision in one patient.

CONCLUSION

Patients with a family history of LHON who require antiretroviral treatment should be warned of the high risk of severe visual loss. The underlying mechanism of antiretroviral side effects may help characterize the other trigger factors for LHON.

Ocular motility in North Carolina autosomal dominant ataxia

The term "vestibulocerebellar ataxia" has been applied to a rare, autosomal dominant, late-onset disease with unusual ocular motility findings. We examined the ocular motility of 18 family members from two different kindreds and found 11 affected individuals. Both families in the present study, one of which was originally described by Farmer and Mustian, as well as the family reported by Farris et al., originated from Johnston County, North Carolina. We suspect that all three of these families have a common ancestral origin. The age of onset of the disorder was 31-60 years in the individuals examined. Ataxia, vertigo, diplopia, oscillopsia, and tinnitus were common complaints. Although a variety of eye movement abnormalities have previously been described in this disease, the most prominent and consistent findings in our patients were (a) abnormal smooth pursuits, (b) inability to suppress the vestibuloocular reflex (VOR), and (c) gaze-evoked nystagmus. These findings suggest that the cerebellar flocculus may be the primary site of pathology.

Epidemic neuropathy in Cuba not associated with mitochondrial DNA mutations found in Leber's hereditary optic neuropathy patients. Cuba Neuropathy Field Investigation Team

An epidemic neuropathy in Cuba has caused bilateral optic neuropathies in more than 26,000 people during the past three years. Various pathogenetic factors have been proposed, including toxins, nutritional deficiencies, and an underlying genetic predisposition involving mitochondrial DNA. As part of a case-control collaborative investigation, 135 Cuban blood samples were analyzed for the most common mitochondrial DNA mutations associated with Leber's hereditary optic neuropathy. None of the participants tested were found to have the mitochondrial DNA mutations at nucleotide positions 11778, 3460, 14484, 7444, or 9804. Of 57 definite case subjects and 69 normal control subjects, three case and three control subjects had the mutation at nucleotide position 9438, three different case and three different control subjects had the mutation at position 13708, and one case and one control subject had the mutation at position 15257 in association with the mutation at position 13708. The most common mitochondrial DNA mutations associated with Leber's hereditary optic neuropathy do not appear to be contributing factors in the epidemic neuropathy in Cuba. We also identified a large Cuban family with maternally related members who experienced visual loss consistent with the diagnosis of Leber's hereditary optic neuropathy. Maternal family members harbored the highly pathogenetic mutation at nucleotide position 11778.

Leber's hereditary optic neuropathy and complex I deficiency in muscle

We investigated a family with Leber's hereditary optic neuropathy in which affected individuals were homoplasmic for the point mutation of the NADH-dehydrogenase 4 gene of mitochondrial DNA, described by Wallace and colleagues in 1988. The proband had bilateral optic atrophy, tremor, dystonia, and sharply defined lesions in the putamen on magnetic resonance images. Optic atrophy was found in another 3 of 13 investigated relatives on the maternal side. Additional neurological signs were found but only in patients with optic neuropathy. The morphological appearance and the respiratory chain function of muscle tissue were investigated in the proband, his mother, and 3 siblings. Polarographic measurements revealed complex I deficiency in the 5 investigated subjects. Morphological changes of mitochondria were found in 4 of these subjects. There was no decrease in complex I activity measured as NADH ferricyanide reductase or rotenone-sensitive NADH cytochrome c reductase activities. In other cases with complex I deficiency, good agreement between polarographic and spectrophotometric measurements was found. This study showed that there is decreased activity of complex I of the respiratory chain in muscle and that cerebral striatal lesions occur in Leber's hereditary optic neuropathy with the NADH-dehydrogenase 4 gene point mutation.