Mitochondrial Lipofuscin and Thermomitochondrial Lipofuscin in Homogenates of Rat Organs

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Abstract—The amounts of lipofuscin (age pigment) were compared in four organs of rats: the liver, the kidney, the heart muscle, and the brain, as well as in a suspension of ghosts of hepatic mitochondria. It was shown that liver lipofuscin, which absorbs UV light at 360 nm and fluoresces at 460 nm, is predominantly formed due to mitochondrial processes. The lowest lipofuscin content was observed in the heart muscle; in the other organs studied, the levels of lipofuscin calculated per mg of protein were approximately the same. The spectral data and the lifetime of the excited state suggest that a considerable contribution to the fluorescence of lipofuscin in various organs belongs to mitochondrial lipofuscin. Along with lipofuscin, a fluorescent pigment, all organs were shown to contain non-fluorescent protein aggregates: their level was the highest in the heart muscle and the lowest in the liver. Among them, a significant portion were covalently cross-linked aggregates that were not destroyed by detergent treatment. Moderate heating of the organ homogenates caused the formation of thermolipofuscin. The level of thermolipofuscin production was the highest in the brain and the lowest in the heart. Apparently, a significant portion of the thermolipofuscin that formed in organ homogenates was thermomitochondrial lipofuscin from the membranes of damaged mitochondria. The formation of thermolipofuscin strongly involved aromatic residues: tyrosine and tryptophan.