Abstract
Background and Aims
Renal hypoxia plays a key role in the pathophysiology of acute kidney injury and in the progression of chronic kidney disease, potentiating other important risk factors for renal disease, such as oxidative stress, renal fibrosis, and inflammation. Hydroxytyrosol (HT) is a phenolic compound extracted from olives and olive-derived products, that has been shown to detain potent in vitro antioxidant and anti-inflammatory activity. The aim of this study was to evaluate the preventive therapeutic potential of HT on a cellular model of renal hypoxia.
Method
A cell line of normal adult proximal tubular epithelium (HK-2 cell line) was used to determine the effects of the chemical induction of hypoxia with cobalt chloride (CoCl2), as well as the preventive potential of HT on the elicited effects. For this purpose, HK-2 cells were exposed for 24 h to 254 µM CoCl2, to mimic the hypoxic conditions, or pre-incubated for 1 h with 5 µM HT and further exposed to the CoCl2 for 24 h more. Cell viability was assessed by the thiazolyl blue tetrazolium bromide reduction assay. Oxidative status was evaluated by the measurement of reactive oxygen and nitrogen species (ROS and RNS) and reduced glutathione (GSH) levels, by using standardized fluorometric and colorimetric assays. The expression of several genes related to the hypoxic, inflammatory, and fibrotic responses was determined by quantitative polymerase chain reaction (PCR).
Results
CoCl2-exposed HK-2 cells (hypoxic conditions) showed a significant decrease in cell viability (p < 0.0001 vs. control), and a disruption of the oxidative status, characterized by an increase of ROS and RNS production of about 6-fold over control cells (p < 0.0001) and a decrease in GSH intracellular levels of nearly 50 % (p < 0.05). Although the pre-exposure to HT showed no significant effects on the loss of cell viability elicited by CoCl2, the presence of HT prior to induction of hypoxia reduced the generation of ROS and RNS (p < 0.05 for HT + CoCl2 vs. CoCl2) and prevented the GSH depletion (GSH levels for HT + CoCl2 were similar to those of control) elicited by CoCl2. When compared to control cells, CoCl2-exposed HK-2 cells also showed increased expression of genes related to hypoxia (HIF1A, p < 0.05; GAPDH, p < 0.0001), as well as of modulators of inflammation (IL6, p < 0.0001) and fibrosis (TGFB1, p < 0.05). Importantly, the expression of these genes was partially or even totally suppressed by the pre-exposure of cells to HT (GAPDH, p < 0.01 for HT + CoCl2 vs. CoCl2; expression of HIF1A, IL6 and TGFB1 for HT + CoCl2 was similar to that of control).
Conclusion
Our data supports the potential for a multiplicity of preventive effects of HT, providing antioxidant, anti-inflammatory and anti-fibrotic defenses to renal cells under hypoxic conditions. Importantly, the development of safe and effective therapeutic approaches based on phytochemicals such as HT, may present substantial advantages for renal patients over synthetic drugs, including fewer side effects, significantly lower price, and ease of administration in the form of dietary supplements.
Acknowledgments
This work was supported by Applied Molecular Biosciences Unit (UCIBIO), financed by national funds from FCT/MCTES (UIDB/04378/2020), by North Portugal Regional Coordination and Development Commission (CCDR-N)/NORTE2020/Portugal 2020 (Norte-01-0145-FEDER-000024), and co-financed by FCT/MCTES (PTDC/OCE-ETA/32492/2017) and FEDER/COMPETE 2020 (POCI-01-0145-FEDER-032492).
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