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Aβ2M (β2-microglobulin-related) amyloidosis is a frequent and serious complication in patients on long-term dialysis. Partial unfolding of β2-m (β2-microglobulin) may be essential to its assembly into Aβ2M amyloid fibrils in vivo. Although SDS around the critical micelle concentration induces partial unfolding of β2-m to an α-helix-containing aggregation-prone amyloidogenic conformer and subsequent amyloid fibril formation in vitro, the biological molecules with similar activity under near-physiological conditions are still unknown. The effect of various NEFAs (non-esterified fatty acids), which are representative anionic amphipathic compounds in the circulation, on the growth of Aβ2M amyloid fibrils at a neutral pH was examined using fluorescence spectroscopy with thioflavin T, CD spectroscopy, and electron microscopy. Physiologically relevant concentrations of laurate, myristate, oleate, linoleate, and mixtures of palmitate, stearate, oleate and linoleate, induced the growth of fibrils at a neutral pH by partially unfolding the compact structure of β2-m to an aggregation-prone amyloidogenic conformer. In the presence of human serum albumin, these NEFAs also induced the growth of fibrils when their concentrations exceeded the binding capacity of albumin, indicating that the unbound NEFAs rather than albumin-bound NEFAs induce the fibril growth reaction in vitro. These results suggest the involvement of NEFAs in the development of Aβ2M amyloidosis, and in the pathogenesis of Aβ2M amyloidosis. [ABSTRACT FROM AUTHOR]