Identification of the chemical constituents of <i>Juglans regia</i> ethanol extract by L-MS/MS and its effects on 5-FU-induced autophagy, oxidative stress, and apoptosis

5-fluorouracil (5-FU) is an important chemotherapeutic agent that has been used alone or in combination with other chemotherapeutics for years in the treatment of various malignancies. However, as with other chemotherapeutic agents, the disadvantage of 5-FU is that it damages healthy cells as well as cancer cells. Natural compounds are the first option that comes to mind to reduce and/or prevent undesirable side effects of chemotherapeutics. In this study, we aimed to determine the effects of <i>Juglans regia</i> extract (JR), whose antioxidant, anti-inflammatory, anti-diabetic, and antimicrobial effects were previously determined, on 5-FU-induced autophagy, oxidative stress, and apoptosis after its constituents were determined by LC-MS/MS. Experimental groups were formed as Control (C), JR, 5-FU, and JR + 5-FU. Rats were pretreated with JR at a dose of 200 mg/kg for seven days, and on the eighth day, a single dose of 100 mg/kg 5-FU was administered intraperitoneally to the JR + 5-FU and 5-FU groups. 5-FU disturbed the oxidant-antioxidant balance by increasing Keap1, TOS, and 8-OHdG levels and decreasing TAS levels and triggered cellular autophagy and apoptosis by increasing LC3B, Bax, and Caspase-3 levels and decreasing Bcl-2. JR pretreatment was shown to have modulating effects on the Keap1/Nrf2 pathway in the reorganization of the oxidant-antioxidant balance, to show anti-apoptotic activity, and to partially alleviate autophagy. JR’s bioactive components were shown to alleviate oxidative stress and associated DNA damage via Keap1/Nrf2 and also attenuate fluorouracil-induced kidney damage by reducing autophagy and apoptosis, two important forms of programmed cell death, and have a promising potential against nephrotoxicity.