Brown atrophy is due to accumulation of

Lipofuscin, or "wear-and-tear pigment," is an insoluble brownish-yellow granular intracellular material that accumulates in a variety of tissues (paicularly the hea, liver, and brain) as a function of age or atrophy. Lipofuscin is complexes of lipid and protein that derive from the free radical-catalyzed peroxidation of polyunsaturated lipids of subcellular membranes. It is not injurious to the cell but is a marker of past free radical injury. The brown pigment, when present in large amounts, impas an appearance to the tissue that is called brown atrophy.( Robbins Basic Pathology, 9th edition, page 24 )