Experimental evidence that monocarboxylic long-chain hydroxy fatty acids accumulating in MTP and LCHAD deficiencies markedly disrupt mitochondrial bioenergetics in rat skeletal muscle

Alexandre Umpierrez Amaral1*, Cristiane Cecatto1, Kálita dos Santos Godoy1 Ana Paula de Abreu Lopes1, Janaína Camacho da Silva1, Moacir Wajner1,2

1Departamento de Bioquímica, Instituto de Ciências Básicas da Saúde, Universidade

Federal do Rio Grande do Sul, Porto Alegre, RS, Brazil

2Serviço de Genética Médica, Hospital de Clínicas de Porto Alegre, Porto Alegre, RS,

Brazil*

email: alexandreuamaral@gmail.com Tel: +55 51 98378489

We studied the effects of the major monocarboxylic 3-hydroxylated fatty acids (LCHFA) accumulating in these disorders, namely 3-hydroxytetradecanoic (3HTA) and 3-hydroxypalmitic (3HPA) acids, on important mitochondrial functions in rat skeletal muscle since muscular symptoms and recurrent rhabdomyolysis affect patients with mitochondrial trifunctional protein (MTP) and long-chain 3-hydroxy-acyl-CoA dehydrogenase (LCHAD) deficiencies. These LCHFA markedly increased resting (state 4) respiration, decreased ADP-stimulated (state 3), uncoupled respiration and the respiratory control ratio (RCR). Similar effects were provoked by 3HPA in permeabilized skeletal muscle fibers, an integrated cellular system, validating the results obtained in isolated mitochondria. 3HTA and 3HPA also markedly decreased mitochondrial membrane potential, NAD(P)H content and Ca2+ retention capacity in Ca2+-loaded skeletal muscle mitochondria. These effects were totally prevented by the classical mitochondrial permeability transition (mPT) inhibitors cyclosporin A and ADP, as well as by ruthenium red, a mitochondrial Ca2+ uptake blocker, indicating the involvement of mPT and the participation of Ca2+ in 3HPA-induced deleterious effects. Mitochondrial membrane fluidity was also increased by 3HPA probably contributing to the nonselective permeabilization provoked by the LCHFA. In contrast and of interest, the dicarboxylic analogue of 3HTA, 3HTDA, was not able to alter any of the tested parameters, suggesting a selective action for the monocarboxylic LCHFA. These data indicate that the major fatty acids accumulating in MTP and LCHAD deficiencies behave as metabolic inhibitors, uncouplers of oxidative phosphorylation and mPT inducers in skeletal muscle. It is proposed that disturbance of mitochondrial homeostasis may be involved in the muscular symptoms and episodes of rhabdomyolysis characteristic of patients affected by these diseases

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Financial support: We thank PROPESQ/UFRGS, FAPERGS and CNPq.