Abstract
BackgroundCurrent treatments for idiopathic inflammatory myopathies (collectively called myositis) focus on the suppression of an autoimmune inflammatory response within the skeletal muscle. However, it has been observed that there is a poor correlation between the successful suppression of muscle inflammation and an improvement in muscle function. Some evidence in the literature suggests that metabolic abnormalities in the skeletal muscle underlie the weakness that continues despite successful immunosuppression. We have previously shown that decreased expression of a purine nucleotide cycle enzyme, adenosine monophosphate deaminase (AMPD1), leads to muscle weakness in a mouse model of myositis and may provide a mechanistic basis for muscle weakness. One of the downstream metabolites of this pathway, D-ribose, has been reported to alleviate symptoms of myalgia in patients with a congenital loss of AMPD1. Therefore, we hypothesized that supplementing exogenous D-ribose would improve muscle function in the mouse model of myositis. We treated normal and myositis mice with daily doses of D-ribose (4 mg/kg) over a 6-week time period and assessed its effects using a battery of behavioral, functional, histological and molecular measures.ResultsTreatment with D-ribose was found to have no statistically significant effects on body weight, grip strength, open field behavioral activity, maximal and specific forces of EDL, soleus muscles, or histological features. Histological and gene expression analysis indicated that muscle tissues remained inflamed despite treatment. Gene expression analysis also suggested that low levels of the ribokinase enzyme in the skeletal muscle might prevent skeletal muscle tissue from effectively utilizing D-ribose.ConclusionsTreatment with daily oral doses of D-ribose showed no significant effect on either disease progression or muscle function in the mouse model of myositis.
Highlights
Idiopathic inflammatory myopathies are characterized by symmetrical muscle weakness and easy fatigability
There is evidence in the literature to suggest that metabolic abnormalities in the skeletal muscle of myositis patients may contribute to muscle weakness independent of the inflammation and damage caused by autoimmune response [1,2,3]
It was previously observed that muscle weakness is associated with an acquired deficiency of the adenosine monophosphate deaminase (AMPD1) enzyme [4,5]
Summary
Idiopathic inflammatory myopathies are characterized by symmetrical muscle weakness and easy fatigability. There is evidence in the literature to suggest that metabolic abnormalities in the skeletal muscle of myositis patients may contribute to muscle weakness independent of the inflammation and damage caused by autoimmune response [1,2,3]. It was previously observed that muscle weakness is associated with an acquired deficiency of the adenosine monophosphate deaminase (AMPD1) enzyme [4,5]. We recently confirmed these findings in the MHC class I transgenic mouse model of myositis [6]. We treated normal and myositis mice with daily doses of D-ribose (4 mg/kg) over a 6-week time period and assessed its effects using a battery of behavioral, functional, histological and molecular measures
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