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Comparative Analysis of Experimental Methods to Quantify Animal Activity in <em>Caenorhabditis elegans</em> Models of Mitochondrial Disease

Caenorhabditis elegans is widely recognized for its central utility as a translational animal model to efficiently interrogate mechanisms and therapies of ...

The Children’s Hospital of Philadelphia

Cysteamine bitartrate is a US Food and Drug Administration-approved therapy for nephropathic cystinosis also postulated to enhance glutathione biosynthesis. We hypothesized this antioxidant effect may reduce oxidative stress in primary mitochondrial respiratory chain (RC) disease, improving cellular viability and organismal health. Here, we systematically evaluated the therapeutic potential of cysteamine bitartrate in RC disease models spanning three evolutionarily distinct species. These pre-clinical studies demonstrated the narrow therapeutic window of cysteamine bitartrate, with toxicity at millimolar levels directly correlating with marked induction of hydrogen peroxide production. Micromolar range cysteamine bitartrate treatment in Caenorhabditis elegans gas-1(fc21) RC complex I (NDUFS2-/-) disease invertebrate worms significantly improved mitochondrial membrane potential and oxidative stress, with corresponding modest improvement in fecundity but not lifespan. At 10 to 100 μm concentrations, cysteamine bitartrate improved multiple RC complex disease FBXL4 human fibroblast survival, and protected both complex I (rotenone) and complex IV (azide) Danio rerio vertebrate zebrafish disease models from brain death. Mechanistic profiling of cysteamine bitartrate effects showed it increases aspartate levels and flux, without increasing total glutathione levels. Transcriptional normalization of broadly dysregulated intermediary metabolic, glutathione, cell defense, DNA, and immune pathways was greater in RC disease human cells than in C. elegans, with similar rescue in both models of downregulated ribosomal and proteasomal pathway expression. Overall, these data suggest cysteamine bitartrate may hold therapeutic potential in RC disease, although not through obvious modulation of total glutathione levels. Careful consideration is required to determine safe and effective cysteamine bitartrate concentrations to further evaluate in clinical trials of human subjects with primary mitochondrial RC disease.

Pre-clinical evaluation of cysteamine bitartrate as a therapeutic agent for mitochondrial respiratory chain disease.

Mitochondrial respiratory chain disorders are empirically managed with variable antioxidant, cofactor, and vitamin 'cocktails'. However, clinical trial validated and approved compounds, or doses, do not exist for any single or combinatorial mitochondrial disease therapy. Here, we sought to pre-clinically evaluate whether rationally-designed mitochondrial medicine combinatorial regimens might synergistically improve survival, health, and physiology in translational animal models of respiratory chain complex I disease. Having previously demonstrated that gas-1(fc21) complex I subunit NDUFS2-/-  C. elegans have short lifespan that can be significantly rescued with 17 different metabolic modifiers, signaling modifiers, or antioxidants, here we evaluated 11 random combinations of these 3 treatment classes on gas-1(fc21) lifespan. Synergistic rescue occurred only with glucose, nicotinic acid, and N-acetylcysteine (Glu + NA + NAC), yielding improved mitochondrial membrane potential that reflects integrated respiratory chain function, without exacerbating oxidative stress and while reducing mitochondrial stress (UPRmt) and improving intermediary metabolic disruptions at the levels of the transcriptome, steady-state metabolites, and intermediary metabolic flux. Equimolar Glu + NA + NAC dosing in a zebrafish vertebrate model of rotenone-based complex I inhibition synergistically rescued larval activity, brain death, lactate, ATP, and glutathione levels. Overall, these data provide objective preclinical evidence in two evolutionary-divergent animal models of mitochondrial complex I disease to demonstrate that combinatorial Glu + NA + NAC therapy significantly improved animal resiliency in the face of stressors that exacerbate their underlying metabolic deficiency, thereby preventing acute neurologic and biochemical decompensation. Clinical trials are warranted to evaluate the efficacy of this lead combinatorial therapy regimen to improve resiliency and health outcomes in human subjects with mitochondrial disease.

Combinatorial glucose, nicotinic acid, and N-acetylcysteine therapy has synergistic effect in preclinical C. elegans and zebrafish models of mitochondrial complex I disease.

Neal D. Mathew

Mitochondrial Medicine Frontier Program,
Division of Human Genetics,
Department of Pediatrics,
Mitochondrial Medicine Frontier Program, Division of Human Genetics, Department of Pediatrics

The Children’s Hospital of Philadelphia

Comparative Analysis of Experimental Methods to Quantify Animal Activity in Caenorhabditis elegans Models of Mitochondrial Disease

Neal D. Mathew

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The Children’s Hospital of Philadelphia

Comparative Analysis of Experimental Methods to Quantify Animal Activity in Caenorhabditis elegans Models of Mitochondrial Disease

Mitochondrial Medicine Frontier Program,
Division of Human Genetics,
Department of Pediatrics,
Mitochondrial Medicine Frontier Program, Division of Human Genetics, Department of Pediatrics