Porphyrin loading of lipofuscin granules in inflamed striated muscle

To further the understanding of oxidative effects on inflammation injury to muscle fiber structure, fluorescent imaging analysis of human striated muscle tissues from a variety of inflammatory or postinflammatory etiologies was undertaken in a search for accumulated coproporphyrin, a red autofluorescent byproduct of heme biosynthesis that would theoretically be formed under oxidative insult. Using a differential excitation method of in situ analysis, porphyrin autofluorescence was detected in intact fibers within the context of the yellow autofluorescent subsarcolemmal lipofuscin granules. Relative measurements of porphyrin concentration in the granules from different patients indicated that the acute/subacute inflammatory specimens grouped significantly higher than the more chronic inflammatory and nonpathological specimens. Myoglobin was also found to be associated with the granules. Myoglobin heme iron could potentially serve as a Fenton reagent for the intracellular generation of hydroxyl radicals, which are responsible for the oxidation of the porphyrinogens. High-performance liquid chromatography analysis of extracted dense particles revealed coproporphyrin as the sole porphyrin present. The observation of coproporphyrin within lipofuscin granules, previously unreported, suggests that lipofuscin accumulation in striated muscle may begin under conditions of acute oxidative stress, as marked by the oxidation of extramitochondrial porphyrinogens that are immediately incorporated into the granules.