Experimental lipid storage myopathy. A quantitative ultrastructural and biochemical study

Area of Science:

• Biochemistry
• Cell Biology
• Toxicology

Background:

• Lipid storage myopathies are a group of neuromuscular disorders characterized by abnormal lipid accumulation in muscle fibers.
• The precise mechanisms underlying lipid accumulation in certain types of lipid storage myopathies remain unclear, particularly those not linked to carnitine metabolism defects.

Purpose of the Study:

• To investigate the biochemical basis of lipid storage myopathy induced by brominated vegetable oil in a rat model.
• To explore the role of fatty acid oxidation pathways in the pathogenesis of this induced myopathy.
• To propose a diagnostic approach for human lipid storage myopathies unrelated to carnitine system dysfunction.

Main Methods:

• Induction of lipid storage myopathy in rats using daily doses of brominated vegetable oil (2.5 g/kg).
• Histopathological examination of muscle fibers, focusing on type I fibers and mitochondrial distribution.
• Assessment of substrate oxidation rates (palmitate, octanoate, beta-hydroxybutyrate, pyruvate, succinate) using radiolabeled compounds.
• Measurement of carnitine acyltransferase activities and muscle carnitine levels.

Main Results:

• Brominated vegetable oil induced selective and severe type I fiber damage with lipid deposits surrounded by increased mitochondria.
• Oxidation of medium-chain and short-chain fatty acids (octanoate, beta-hydroxybutyrate) was significantly impaired.
• Oxidation of long-chain fatty acids (palmitate) and other substrates (pyruvate, succinate) remained normal.
• Muscle carnitine levels and carnitine acyltransferase activities were within normal ranges.

Conclusions:

• The induced lipid storage myopathy in rats is attributed to impaired beta-oxidation of medium- and short-chain fatty acyl residues.
• This model highlights a potential mechanism for human lipid storage myopathies not caused by carnitine system defects.
• Suggests focusing on fatty acid oxidation pathway analysis for investigating such myopathies.