Papers of the Week

Despite the requirement for effective medication against neuropathic pain associated with type 2 diabetes-mellitus (T2DM), mechanism-based pharmacotherapy has yet to be established. Given that long-lasting neuroinflammation, driven by inflammatory macrophages in the peripheral nerves, plays a pivotal role in intractable pain, it is important to determine whether inflammatory macrophages contribute to neuropathic pain associated with T2DM. To generate an experimental model of T2DM, C57BL/6J mice were fed a high-fat diet (HFD) ad libitum. Compared to control diet-feeding, obesity and hyperglycemia were observed after HFD-feeding, and the mechanical pain threshold evaluated using the von Frey test was found to be decreased, indicating the development of mechanical allodynia. The expression of mRNA markers for macrophages, inflammatory cytokines, and chemokines were significantly upregulated in the sciatic nerve (SCN) following HFD-feeding. Perineural (p.n.) administration of saporin-conjugated anti-Mac1 antibody (Mac1-Sap) improved HFD-induced mechanical allodynia. Moreover, treatment of Mac1-Sap decreased the accumulation of F4/80+ macrophages and the upregulation of inflammatory mediators in the SCN after HFD-feeding. Inoculation of lipopolysaccharide-activated peritoneal macrophages in tissue surrounding the SCN elicited mechanical allodynia. Furthermore, pharmacological inhibition of inflammatory macrophages by either p.n. or systemic administration of TC-2559, a α4β2 nicotinic acetylcholine receptor selective agonist, relieved HFD-induced mechanical allodynia. Taken together, inflammatory macrophages accumulated in the SCN mediate the pathophysiology of neuropathic pain associated with T2DM. Inhibitory agents for macrophage-driven neuroinflammation could be potential candidates for novel pharmacotherapy against intractable neuropathic pain.