Renal adaptive response to exposure to low doses of uranyl nitrate and sodium fluoride in mice

Role of uranium toxicity and uranium-induced oxidative stress in advancing kidney injury and endothelial inflammation in rats

OBJECTIVE

Uranium exposure may cause serious pathological injury to the body, which is attributed to oxidative stress and inflammation. However, the pathogenesis of uranium toxicity has not been clarified. Here, we evaluated the level of oxidative stress to determine the relationship between uranium exposure, nephrotoxic oxidative stress, and endothelial inflammation.

METHODS

Forty male Sprague-Dawley rats were divided into three experimental groups (U-24h, U-48h, and U-72h) and one control group. The three experimental groups were intraperitoneally injected with 2.0 mg/kg uranyl acetate, and tissue and serum samples were collected after 24, 48, and 72 h, respectively, whereas the control group was intraperitoneally injected with 1.0 ml/kg normal saline and samples were collected after 24 h. Then, we observed changes in the uranium levels and oxidative stress parameters, including the total oxidative state (TOS), total antioxidant state (TAS), and oxidative stress index (OSI) in kidney tissue and serum. We also detected the markers of kidney injury, namely urea (Ure), creatine (Cre), cystatin C (CysC), and neutrophil gelatinase-associated lipocalin (NGAL). The endothelial inflammatory markers, namely C-reactive protein (CRP), lipoprotein phospholipase A2 (Lp-PLA2), and homocysteine (Hcy), were also quantified. Finally, we analyzed the relationship among these parameters.

RESULTS

TOS (z = 3.949; P < 0.001), OSI (z = 5.576; P < 0.001), Ure (z = 3.559; P < 0.001), Cre (z = 3.476; P < 0.001), CysC (z = 4.052; P < 0.001), NGAL (z = 3.661; P < 0.001), and CRP (z = 5.286; P < 0.001) gradually increased after uranium exposure, whereas TAS (z = -3.823; P < 0.001), tissue U (z = -2.736; P = 0.001), Hcy (z = -2.794; P = 0.005), and Lp-PLA2 (z = -4.515; P < 0.001) gradually decreased. The serum U level showed a V-shape change (z = -1.655; P = 0.094). The uranium levels in the kidney tissue and serum were positively correlated with TOS (r = 0.440 and 0.424; P = 0.005 and 0.007) and OSI (r = 0.389 and 0.449; P = 0.013 and 0.004); however, serum U levels were negatively correlated with TAS (r = -0.349; P = 0.027). Partial correlation analysis revealed that NGAL was closely correlated to tissue U (rpartial = 0.455; P = 0.003), CysC was closely correlated to serum U (rpartial = 0.501; P = 0.001), and Lp-PLA2 was closely correlated to TOS (rpartial = 0.391; P = 0.014), TAS (rpartial = 0.569; P < 0.001), and OSI (rpartial = -0.494; P = 0.001). Pearson correlation analysis indicated that the Hcy levels were negatively correlated with tissue U (r = -0.344; P = 0.030) and positively correlated with TAS (r = 0.396; P = 0.011).

CONCLUSION

The uranium-induced oxidative injury may be mainly reflected in enhanced endothelial inflammation, and the direct chemical toxicity of uranium plays an important role in the process of kidney injury, especially in renal tubular injury. In addition, CysC may be a sensitive marker reflecting the nephrotoxicity of uranium; however, Hcy is not suitable for evaluating short-term endothelial inflammation involving oxidative stress.

Review of Knowledge of Uranium-Induced Kidney Toxicity for the Development of an Adverse Outcome Pathway to Renal Impairment

An adverse outcome pathway (AOP) is a conceptual construct of causally and sequentially linked events, which occur during exposure to stressors, with an adverse outcome relevant to risk assessment. The development of an AOP is a means of identifying knowledge gaps in order to prioritize research assessing the health risks associated with exposure to physical or chemical stressors. In this paper, a review of knowledge was proposed, examining experimental and epidemiological data, in order to identify relevant key events and potential key event relationships in an AOP for renal impairment, relevant to stressors such as uranium (U). Other stressors may promote similar pathways, and this review is a necessary step to compare and combine knowledge reported for nephrotoxicants. U metal ions are filtered through the glomerular membrane of the kidneys, then concentrate in the cortical and juxtaglomerular areas, and bind to the brush border membrane of the proximal convoluted tubules. U uptake by epithelial cells occurs through endocytosis and the sodium-dependent phosphate co-transporter (NaPi-IIa). The identified key events start with the inhibition of the mitochondria electron transfer chain and the collapse of mitochondrial membrane potential, due to cytochrome b5/cytochrome c disruption. In the nucleus, U directly interacts with negatively charged DNA phosphate, thereby inducing an adduct formation, and possibly DNA strand breaks or cross-links. U also compromises DNA repair by inhibiting zing finger proteins. Thereafter, U triggers the Nrf2, NF-κB, or endoplasmic reticulum stress pathways. The resulting cellular key events include oxidative stress, DNA strand breaks and chromosomal aberrations, apoptosis, and pro-inflammatory effects. Finally, the main adverse outcome is tubular damage of the S2 and S3 segments of the kidneys, leading to tubular cell death, and then kidney failure. The attribution of renal carcinogenesis due to U is controversial, and specific experimental or epidemiological studies must be conducted. A tentative construction of an AOP for uranium-induced kidney toxicity and failure was proposed.

The potential risks of chronic fluoride exposure on nephrotoxic via altering glucolipid metabolism and activating autophagy and apoptosis in ducks

Fluoride is one of the most widely distributed elements in nature, while some fluorine-containing compounds are toxic to several vertebrates at certain levels. The current study was performed to evaluate the nephrotoxic effects of fluoride exposure in ducks. The results showed that the renal index was decreased in NaF group, and fluoride exposure significantly decreased the levels of serum Albumin, Glucose, Total cholesterol, Urea, protein and Triglycerides, confirming that NaF exhibited adverse effects on the kidney. The overall structure of renal cells showed damage with the signs of nuclelytic, vacuolar degeneration, atrophy, renal cystic cavity widening after fluoride induction. Renal vascular growth was impaired as the expression of VEGF and HIF-1α decreased (p > 0.05). More importantly, autophagy and apoptosis levels of CYT C, LC3, p62, Beclin, M-TOR, Bax and Caspase-3 were increased (p < 0.05) in the NaF treated group. Interestingly, our results showed that Phosphatidylethanolamine (PE) and Phosphatidylcholine (PC) activated the M-TOR autophagy pathway. Meanwhile, the PE acted on Atg5/ LC3 autophagy factor, followed by the auto-phagosome generation and activation of cell autophagy. These results indicate that NaF exposure to duck induced nephron-toxicity by activating autophagy, apoptosis and glucolipid metabolism pathways, which suggest that fluorine exposure poses a risk of poisoning.