Abstract
Kahweol is a diterpene found in coffee beans and unfiltered coffee drinks. Several studies have demonstrated that kahweol induces the nuclear factor erythroid-2 related factor 2/ hemeoxygenase-1 (Nrf2/HO-1) pathway; however, the mechanisms involved are currently unknown. Kelch-like ECH-associated protein 1 (Keap1) is a major regulator of Nrf2 expression and is degraded mostly by autophagy. The p62 protein enhances binding to Keap1 and contributes to the activation of Nrf2. Here, we examined the role of Keap1 regulation in the effect of kahweol on the Nrf2/HO-1 pathway in hepatocytes. In AML12 cells and primary mouse hepatocytes, kahweol increased the levels of Nrf2 and HO-1 protein without increasing expression of the Nrf2 mRNA. In addition, kahweol reduced Keap1 protein levels significantly without decreasing Keap1 mRNA levels. Although regulation of the Keap1-Nrf2-pathway by p62-dependent autophagy is well known, we confirmed here that the reduction of Keap1 protein levels by kahweol does not involve p62-dependent autophagy degradation or ubiquitination. In conclusion, kahweol increases the expression of Nrf2 in hepatocytes by inhibiting translation of the Keap1 mRNA.
Highlights
As the main detoxification organ, the liver maintains metabolic homeostasis under normal conditions
In AML12 cells and primary mouse hepatocytes, kahweol increased the levels of nuclear factor erythroid-2 related factor 2 (Nrf2) and HO-1 protein without increasing expression of the Nrf2 mRNA
We found that kahweol increased the levels of Nrf2 and HO-1 in liver cells, indicating an antioxidant effect
Summary
As the main detoxification organ, the liver maintains metabolic homeostasis under normal conditions. Excessive ROS can interfere with liver homeostasis and cause oxidant stress, which plays an important role in the development of diseases such as viral hepatitis, nonalcoholic fatty liver disease, alcoholic liver disease, and drug-induced liver injury [3,4,5,6]. Oxidative stress activates the hepatic antioxidant defense system. The nuclear factor erythroid-2 related factor 2 (Nrf2)/Kelch-like ECH-associated protein 1 (Keap1) pathway plays a central role in protecting cells against oxidative stress. Nrf dissociates from Keap and enters the nucleus, where it regulates the expression of antioxidant genes such as hemeoxygenase-1 (HO-1) [7, 8].
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