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Difficulty: HardCellular Injury and Adaptation

A 76-year-old man with a 25-year history of poorly controlled essential hypertension and osteoarthritis dies from complications of a massive subarachnoid hemorrhage. Postmortem examination reveals a markedly enlarged heart with concentric left ventricular thickening. Light microscopy of the myocardium demonstrates widened myocytes containing enlarged, hyperchromatic 'boxcar' nuclei. High-power examination of these cells reveals the presence of a finely granular, yellow-brown perinuclear pigment. This pigment is strongly positive for Sudan Black B and periodic acid-Schiff (PAS) staining, but it is negative for Prussian blue staining. Which of the following pathophysiologic processes is most directly responsible for the accumulation of this intracellular material?

  1. A
    Lysosomal accumulation of degraded iron-storage macromolecular complexes
  2. B
    Extracellular aggregation of misfolded polypeptides in a beta-pleated sheet conformation
  3. Autophagic sequestration of free radical-peroxidized subcellular membranesAnswer
  4. D
    Massive cytosolic calcium influx with activation of endogenous phospholipases
  5. E
    Unregulated activation of the coagulation cascade resulting in microvascular ischemic damage

Answer

Autophagic sequestration of free radical-peroxidized subcellular membranes
The correct answer accurately describes the formation of lipofuscin. The vignette describes a patient with long-standing hypertension leading to left ventricular hypertrophy (enlarged myocytes with 'boxcar' nuclei). The yellow-brown, perinuclear pigment that is Sudan Black B positive (indicating lipid content) and Prussian blue negative (indicating lack of iron) is lipofuscin. Lipofuscin is an insoluble wear-and-tear pigment composed of polymers of lipids and phospholipids complexed with protein. It results from free radical-catalyzed lipid peroxidation of subcellular membranes and accumulates within autophagolysosomes of long-lived cells (like cardiomyocytes and neurons) as a marker of cellular aging.

Step-by-Step Solution

1
Identify the primary pathological finding from the biopsy description.
The presence of widened myocytes with 'boxcar' nuclei indicates cellular hypertrophy. The key finding to identify is the yellow-brown perinuclear pigment.
Establishing the nature of the intracellular material is required to determine its underlying mechanism.
2
Differentiate the pigment based on its histochemical staining profile.
The pigment is Sudan Black B positive (indicating lipid content) and Prussian blue negative (ruling out iron/hemosiderin). This profile confirms it is lipofuscin.
Different yellow-brown pigments (e.g., lipofuscin, hemosiderin, melanin) have distinct compositions and causes.
3
Determine the pathophysiologic origin of lipofuscin.
Lipofuscin forms via free radical-induced lipid peroxidation of subcellular membranes, which undergo autophagocytosis.
Connecting the identified pigment to its subcellular mechanism of formation directly answers the question.

Key Concept

Lipofuscin formation via lipid peroxidation in cellular aging and adaptation
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Topics

Cellular Injury and Adaptation

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