Porphyrin Loading of Lipofuscin Granules in Inflamed Striated Muscle

Abstract

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.

Purinergic receptors expressed in human skeletal muscle fibres

“…This is due to the presence of small autofluorescence structures, lipofuscin granules, which are very "eye-catching", and which may easily be mistaken for true positive specific staining. Lipofuscin inclusions are formed from damaged cell components and accumulated in postmitotic cells in relation to oxidative stress and ageing [33][34][35][36]. In contrast hereto, lipofuscin granules are absent in healthy muscle in laboratory animals like rats and mice.…”

Technical Advance: Autofluorescence as a tool for myeloid cell analysis

“…However, given the subcellular localization and fluorescence properties, as well as the known functions of these cells, it seems likely to originate from a mix of phagocytosed cellular breakdown products. Potential contributors to this are ceroid/lipofuscin, which has an emission maximum Ͻ600 nm [30], heme breakdown products such as bilirubin (maximum emission 500 -550 nm) [31], and porphyrins [8,32], which emit at wavelengths Ͼ600 nm.…”

“…Although efforts have been made to incorporate AF into myeloid analysis strategies, these have been sporadic and restricted to individual cell types [3][4][5]. One reason for the lack of any systematic use of AF in analysis is its heterogeneous nature: It may derive from NAD(P)H [6], flavins [7], porphyrin [8], and lipofuscin [9], among other sources. Each of these endogenous fluorophores has distinct excitation and emission characteristics.…”

Genomic organization, alternative splicing, and expression of human and mouse N‐RAP, a nebulin‐related LIM protein of striated muscle

“…N-RAP is concentrated at the intercalated disks (arrowheads). Autofluorescent, phase dense lipofuscin granules [Kiefer et al, 1998] are also visible (arrows). antibodies against sarcomeric ␣-actinin.…”