Combination of quercetin, cinnamaldehyde and hirudin protects rat dorsal root ganglion neurons against high glucose-induced injury through Nrf-2/HO-1 activation and NF-κB inhibition

To examine the effects of the combination of quercetin (Q), cinnamaldehyde (C) and hirudin (H), a Chinese medicine formula on high glucose (HG)-induced apoptosis of cultured dorsal root ganglion (DRG) neurons. DRG neurons exposed to HG (45 mmol/L) for 24 h were employed as an in vitro model of diabetic neuropathy. Cell viability, reactive oxygen species (ROS) level and apoptosis were determined. The expression of nuclear factor of Kappa B (NF-kappa B), inhibitory kappa B alpha(I kappa B alpha), phosphorylated I kappa B alpha and Nf-E2 related factor 2 (Nrf2) were examined using reverse transcription-polymerase chain reaction (RT-PCR) and Western blot assay. The expression of hemeoxygenase-1 (HO-1), interleukin-6 (IL-6), tumor necrosis factor (TNF-alpha) and caspase-3 were also examined by RT-PCR and Western blot assay. HG treatment markedly increased DRG neuron apoptosis via increasing intracellular ROS level and activating the NF-kappa B signaling pathway (P < 0.05). Co-treatment with Q, C, H and their combination decreased HG-induced caspase-3 activation and apoptosis (P < 0.05 or P < 0.01). The expressions of NF-kappa B, IL-6 and TNF-alpha were down-regulated, and Nrf2/HO-1 expression was up-regulated (P < 0.05 or P < 0.01). QCH has better effect in scavenging ROS, activating Nrf-2/HO-1, and down-regulating the NF-kappa B pathway than other treatment group. DRG neurons' apoptosis was increased in diabetic conditions, which was reduced by QCH formula treatment. The possible reason could be activating Nrf-2/HO-1 pathway, scavenging ROS, and inhibition of NF-kappa B activation. The effect of QCH combination was better than each monomer or the combination of the two monomers.