Leptin plays an important role in energy intake and body weight homeostasis. Leptin is secreted mainly from white adipose tissue and circulates in the bloodstream, inhibiting food intake by activating the leptin receptor expressed on hypothalamic neurons. Recent studies have demonstrated leptin resistance as the main factor involved in the development of obesity. We and others have reported that leptin resistance is caused by endoplasmic reticulum (ER) stress due to the accumulation of unfolded protein in the ER. In the present study, we investigated whether isoflavones could affect ER stress and the subsequent development of leptin resistance. We showed that biochanin A, a family of isoflavones, strongly attenuated cell death induced by ER stress in neuronal cells, improved ER stress-induced impairments in leptin signaling, and suppressed ER stress-induced expression of glucose-regulated protein 78. These results suggest that biochanin A may have pharmacological properties that can ameliorate leptin resistance by reducing ER stress.

Insensitivity to the antiobesity hormone, leptin, has been suggested to be involved in the pathogenesis of obesity. However, the pathological mechanisms underlying the development of leptin resistance are not well-understood. This study aimed to examine the pathological mechanisms of leptin resistance in obesity. In the present study, we found that 4-hydroxy-2-nonenal (4-HNE), an aldehyde, may be involved in the development of leptin resistance. The SH-SY5Y-Ob-Rb human neuroblastoma cell line, transfected to express the Ob-Rb leptin receptor stably, was treated with 4-HNE, and leptin-induced signal transduction was analyzed. We found that 4-HNE dose- and time-dependently inhibited leptin-induced signal transducer and activator of transcription 3 (STAT3) phosphorylation, a major antiobesity signal of leptin. On the other hand, 4-HNE did not affect tyrosine phosphorylation of broad cellular proteins, suggesting that the inhibitory effect may be selective to leptin signaling. Mechanistically, 4-HNE induced the eukaryotic initiation factor 2α-CCAAT/enhancer-binding protein homologous protein arm of endoplasmic reticulum stress signaling, which may be involved in the pathogenesis of leptin resistance. Overall, these results suggest that 4-HNE may partly affect endoplasmic reticulum stress-induced unfolded protein response signaling and may be involved in the pathogenesis of leptin resistance.