Amelioration of hyperoxaluria-induced kidney dysfunction by chemical chaperone 4-phenylbutyric acid

Reduction of excessive unfolded protein response by 4-phenylbutyric acid may mitigate procymidone-induced testicular damage in mice by changing the levels of circRNA Scar and circZc3h4

Procymidone (PCM) exposure below the no-observed-effect level triggers changes in circRNA Scar and circZc3h4 and overactivation of the unfolded protein response (UPR) in mice, culminating in testicular injury. The 4-phenyl butyric acid (4-PBA) is known to stabilize proteins and reduce the UPR. This study employed an in vitro system in which mouse testes were cultured with 1 × 10-5 M PCM and varying concentrations (0, 20, 40, and 80 mM) of 4-PBA; 4-week-old male mice were subsequently treated with 100 mg/kg/d PCM (suspended in corn oil) and/or 100 mg/kg/d 4-PBA for 21 d, consecutively. The treatments were as follows: the negative control (NC) group was orally administered corn oil; the positive control (PC) group was orally administered PCM; the 4-PBA group was intraperitoneally injected with 4-PBA; the 4-PBA-I group was orally administered PCM and 4-PBA simultaneously; the 4-PBA-II group received daily administration of 4-PBA 24 h prior to PCM; and the 4-PBA-III group was intraperitoneally injected with 4-PBA for 7 d after 21 d of PCM administration. However, the 4-PBA intervention groups showed no considerable changes in the overall or testicular appearance of mice. In vitro, 4-PBA inhibited the PCM-induced testicular injury, with the most significant effect observed at 80 mM. In vivo, the 4-PBA-III group exhibited the best in vivo effects. Our findings indicate that 4-PBA conferred testicular protection by decreasing PCM-induced circRNA Scar, elevating circZc3h4, and suppressing UPR both in vitro and in vivo. It has been hypothesized that 4-PBA mitigates testicular damage by reducing excessive UPR levels.

4-PBA Attenuates Fat Accumulation in Cultured Spotted Seabass Fed High-Fat-Diet via Regulating Endoplasmic Reticulum Stress

Excessive fat accumulation is a common phenomenon in cultured fish, which can cause metabolic disease such as fatty liver. However, the relative regulatory approach remains to be explored. Based on this, two feeding trials were conducted. Firstly, fish were fed either a normal-fat diet (NFD) or a high-fat diet (HFD) for eight weeks and sampled at the 2nd, 4th, 6th, and 8th week after feeding (Experiment I). In the first four weeks, fish fed an HFD grew faster than those fed an NFD. Conversely, the body weight and weight gain were higher in the NFD group at the 6th and 8th weeks. Under light and transmission electron microscopes, fat accumulation of the liver was accompanied by an obvious endoplasmic reticulum (ER) swell. Accordingly, the expressions of atf-6, ire-1, perk, eif-2α, atf-4, grp78, and chop showed that ER stress was activated at the 6th and 8th weeks. In Experiment II, 50 mg/kg 4-PBA (an ERs inhibitor) was supplemented to an HFD; this was named the 4-PBA group. Then, fish was fed with an NFD, an HFD, and a 4-PBA diet for eight weeks. As the result, the excessive fat deposition caused by an HFD was reversed by 4-PBA. The expression of ER stress-related proteins CHOP and GRP78 was down-regulated by 4-PBA, and the transmission electron microscope images also showed that 4-PBA alleviated ER stress induced by the feeding of an HFD. Furthermore, 4-PBA administration down-regulated SREBP-1C/ACC/FAS, the critical pathways of fat synthesis. In conclusion, the results confirmed that ER stress plays a contributor role in the fat deposition by activating the SREBP-1C/ACC/FAS pathway. 4-PBA as an ER stress inhibitor could reduce fat deposition caused by an HFD via regulating ER stress.

4-PBA rescues hyperoxaluria induced nephrolithiasis by modulating urinary glycoproteins: Cross talk between endoplasmic reticulum, calcium homeostasis and mitochondria

AIM

Urinary glycoproteins such as Tamm Horsfall Protein (THP) and Osteopontin (OPN) are well established key regulators of renal stone formation. Additionally, recent revelations have highlighted the influence of Endoplasmic Reticulum (ER) and mitochondria of crucial importance in nephrolithiasis. However, till date conclusive approach highlighting the influence of ER stress on urinary glycoproteins and chaperone in nephrolithiasis remains elusive. Therefore, the present study was focussed on deciphering the possible effect of 4-PBA mitigating ER stress on urinary glycoproteins and calnexin (chaperone) with emphasis on interlinking calcium homeostasis in hyperoxaluric rats.

MATERIAL AND METHODS

Post 9 days of treatment, animals were sacrificed, and renal tissues were investigated for urinary glycoproteins, calnexin, calcium homeostasis, ER environment, redox status, and mitochondrial linkage.

KEY FINDINGS

4-PBA appreciably reversed the altered levels of THP, OPN, and calnexin observed along with curtailing the disrupted calcium homeostasis when assessed for SERCA activity and intra-cellular calcium levels. Additionally, significant improvement in the perturbed ER environment as verified by escalated ER stress markers, disturbed protein folding-aggregation-degradation (congo red assay) pathway, and redox status was found post 4-PBA intervention. Interestingly, linkage of ER stress and mitochondria was established under hyperoxaluric conditions when assessed for protein levels of VDAC1 and GRP75.

SIGNIFICANCE

4-PBA treatment resulted in rectifying the repercussions of ER-mitochondrial caused distress when assessed for protein folding/aggregation/degradation events along with disturbed calcium homeostasis. The present study advocates the necessity to adopt a holistic vision towards hyperoxaluria with emphasis on glycoproteins and ER environment.

Protective effect of bee pollen in acute kidney injury, proteinuria, and crystalluria induced by ethylene glycol ingestion in rats

Oxidative stress plays a role in hyperoxaluria-induced kidney injury and crystallization. Bee pollen is a hive product with a high content of antioxidants. The antioxidant content and protective effect of bee pollen extract (BPE) against ethylene glycol (EG) induced crystalluria, and acute kidney injury (AKI) were investigated. The effect of BPE on the EG-induced liver injury and proteinuria was also examined. Ten groups of male Wister rats were treated daily with vehicle, cystone, BPE (100, 250, and 500 mg/kg b.wt.), and group 6–9 treated with EG, EG + BPE (100, 250, and 500 mg/kg b.wt.) and group 10 EG + cystone. The dose of EG was 0.75% v/v, and the dose of cystone was 500 mg/kg b.wt. On day 30, blood and urine samples were collected for analysis. Kidneys were removed for histopathological study. The antioxidant activity of BPE was assessed, and its total phenols and flavonoids were determined. EG significantly increased urine parameters (pH, volume, calcium, phosphorus, uric acid, and protein), blood urea, creatinine, and liver enzymes (P < 0.05). EG decreased creatinine clearance and urine magnesium and caused crystalluria. Treatment with BPE or cystone mitigates EG's effect; BPE was more potent than cystone (P < 0.05). BPE increases urine volume, sodium, and magnesium compared to the control and EG treated groups. BPE reduces proteinuria and prevents AKI, crystalluria, liver injury, and histopathological changes in the kidney tissue caused by EG. BPE might have a protective effect against EG-induced AKI, crystalluria, proteinuria, and stone deposition, most likely by its antioxidant content and activity.

β-Caryophyllene may attenuate hyperoxaluria-induced kidney dysfunction in rats by regulating stress marker KIM-1/MCP-1 and NF-κB signaling pathway

β-Caryophyllene (BCP), a bicyclic sesquiterpene, has proved to exhibit antioxidant and anti-inflammatory activities. The present study is carried out to investigate BCP impact on hyperoxaluria-induced kidney dysfunction in male Wistar rats. The animals were categorized into four groups, namely, Group I, control rats; Group II, ethylene glycol (inducer); Group III, inducer + BCP (100 µM/kg bw); Group IV, BCP alone. After the treatment period, the rate of creatinine clearance and the concentration of urea in urine and serum were assessed. Histopathology reports were conducted to study renal and liver tissues, while the reverse transcription-polymerase chain reaction studies were carried out for messenger RNA expression of inflammatory (nuclear factor kappa B) and endoplasmic reticulum (ER) stress (kidney dysfunction molecule-1, monocyte chemoattractant protein-1, glucose binding protein 78, CHOP, activating factor 4, and X-box binding protein-1) markers as well as antioxidant activity for the hyperoxaluric rats. Western blot was performed to investigate the level of protein expression by the treatment group on apoptotic (Bcl-2, Bax, caspase-3, and caspase-9) proteins. The results show BCP to possess a renoprotective effect under hyperoxaluric conditions by decreasing the level of the inflammatory and ER stress markers and restoring the enzymes' antioxidant activities. The histology reports depicted the satisfactory morphology of glomerulus in diseased rats. Furthermore, the results of Western blot suggested that BCP may possess inhibitory action on apoptosis by affecting the mitochondrial-dependent apoptotic pathway. Therefore, BCP can be considered as a potential candidate for the therapy of hyperoxaluric-induced kidney complications.

Chemical Chaperones Modulate the Formation of Metabolite Assemblies

The formation of amyloid-like structures by metabolites is associated with several inborn errors of metabolism (IEMs). These structures display most of the biological, chemical and physical properties of protein amyloids. However, the molecular interactions underlying the assembly remain elusive, and so far, no modulating therapeutic agents are available for clinical use. Chemical chaperones are known to inhibit protein and peptide amyloid formation and stabilize misfolded enzymes. Here, we provide an in-depth characterization of the inhibitory effect of osmolytes and hydrophobic chemical chaperones on metabolite assemblies, thus extending their functional repertoire. We applied a combined in vivo-in vitro-in silico approach and show their ability to inhibit metabolite amyloid-induced toxicity and reduce cellular amyloid content in yeast. We further used various biophysical techniques demonstrating direct inhibition of adenine self-assembly and alteration of fibril morphology by chemical chaperones. Using a scaffold-based approach, we analyzed the physiochemical properties of various dimethyl sulfoxide derivatives and their role in inhibiting metabolite self-assembly. Lastly, we employed whole-atom molecular dynamics simulations to elucidate the role of hydrogen bonds in osmolyte inhibition. Our results imply a dual mode of action of chemical chaperones as IEMs therapeutics, that could be implemented in the rational design of novel lead-like molecules.

A deleterious interplay between endoplasmic reticulum stress and its functional linkage to mitochondria in nephrolithiasis

Hyperoxaluria is one of the leading causes of calcium oxalate stone formation in the kidney. Since hyperoxaluria produces Endoplasmic Reticulum (ER) stress in the kidney, it is thus likely that the adaptive unfolded protein response might affect the mitochondrial population as ER and mitochondria share close physical and functional interactions mandatory for several biological processes. Thus this work was designed to study the putative effects of endoplasmic reticulum stress on the renal mitochondria during hyperoxaluria-induced nephrolithiasis. The results showed that hyperoxaluria induced an ER stress led to the unfolded protein response in the renal tissue of experimental rats. Hampered mitochondrion functioning was detected with decreased mitochondrial membrane potential and upsurged mitochondria calcium. These changes in the mitochondria function and ER stress are preceded by apoptosis. The expression of Sigma-1 receptor protein found in the Mitochondria associated ER membranes, the connecting link between ER and mitochondria was found to decrease in the hyperoxaluric rats. Inhibition of ER stress by 4-Phenylbutyric acid prevented the decrease in mitochondria membrane potential and increase in mitochondria calcium observed in hyperoxaluric rats. Also, it restored the protein expression of the sigma-1 receptor protein. On the other hand, N-acetyl cysteine had a nominal impact on the reduction of the ER stress-induced mitochondrial dysfunction. In conclusion, our data showed that hyperoxaluria induces renal ER stress which triggers mitochondria dysfunction, might be via alteration in the sigma-1 receptor protein in the mitochondria-associated ER membranes, which leads to apoptosis, renal injury, and calcium oxalate crystal deposition.

Regulation of endoplasmic reticulum stress on the damage and apoptosis of renal tubular epithelial cells induced by calcium oxalate crystals

This study aimed to observe whether calcium oxalate (CaOx) crystals can induce the activation of endoplasmic reticulum (ER) stress in human renal cortex proximal tubule epithelial (HK-2) cells and to explore the regulatory of ER stress on the damage and apoptosis of HK-2 cells induced by CaOx crystals. We detected the optimal CaOx crystal concentration and intervention time by Western blot. ER stress modifiers tunicamycin (TM) and 4-phenylbutyric acid (4-PBA) were used to regulate the ER stress of HK-2 cells. The activities of ER stress marker proteins GRP78 and CHOP were evaluated by Western blot and immunohistochemistry. Western blot and TUNEL staining were used to detect cell apoptosis. We observed cell-crystal adhesion with an optical microscope. Lactate dehydrogenase (LDH) test kit and IL-1β enzyme-linked immunosorbent assay kit were used to detect and evaluate HK-2 cell damage. We found that the expression of ER stress marker proteins GRP78 and CHOP gradually increased with the increase in CaOx crystal concentration and intervention time and reached the maximum at 2.0 mmol/L and 24 h. The use of ER stress modifiers TM and 4-PBA can effectively regulate the ER stress level induced by CaOx crystals, and the level of apoptosis is positively correlated with the level of ER stress. 4-PBA pretreatment remarkably reduced cell-crystal adhesion and the secretions of IL-1β and LDH, whereas the results of TM pretreatment were the opposite. In summary, the damage and apoptosis of HK-2 cells induced by CaOx crystals are closely related to the level of ER stress. Inhibiting the ER stress of HK-2 cells can substantially reduce the cell damage and apoptosis induced by CaOx crystals.

Nephroprotective Effect of Pleurotus ostreatus and Agaricus bisporus Extracts and Carvedilol on Ethylene Glycol-Induced Urolithiasis: Roles of NF-κB, p53, Bcl-2, Bax and Bak

This study was designed to assess the nephroprotective effects of Pleurotus ostreatus and Agaricus bisporus aqueous extracts and carvedilol on hyperoxaluria-induced urolithiasis and to scrutinize the possible roles of NF-κB, p53, Bcl-2, Bax and Bak. Phytochemical screening and GC-MS analysis of mushrooms’ aqueous extracts were also performed and revealed the presence of multiple antioxidant and anti-inflammatory components. Hyperoxaluria was induced in Wistar rats through the addition of 0.75% (v/v) ethylene glycol in drinking water for nine weeks. The ethylene glycol-administered rats were orally treated with Pleurotus ostreatus and Agaricus bisporus aqueous extracts (100 mg/kg) and carvedilol (30 mg/kg) daily during the last seven weeks. The study showed that Pleurotus ostreatus, Agaricus bisporus and carvedilol all successfully inhibited ethylene glycol-induced histological perturbations and the elevation of serum creatinine, serum urea, serum and urinary uric acid, serum, urinary and kidney oxalate, urine specific gravity, kidney calcium, kidney NF-κB, NF-κB p65, NF-κB p50, p53, Bax and Bak expressions as well as serum TNF-α and IL-1β levels. Moreover, the treatment decreased the reduction in urinary creatinine, urinary urea, ratios of urinary creatinine to serum creatinine and urinary urea to serum urea, Fex Urea and Bcl-2 expression in kidney. In conclusion, although Pleurotus ostreatus and Agaricus bisporus extracts and carvedilol all significantly inhibited the progression of nephrolithiasis and showed nephroprotective effects against ethylene glycol-induced kidney dysfunction, Pleurotus ostreatus and Agaricus bisporus seemed to be more effective than carvedilol. Moreover, the nephroprotective effects may be mediated via affecting NF-κB activation, extrinsic apoptosis and intrinsic apoptosis pathways.

Effect of endoplasmic reticulum stress-mediated excessive autophagy on apoptosis and formation of kidney stones

AIMS

This study was designed to reveal the role and underlying mechanism of excessive autophagy mediated by ERS via the PERK-eIF2α pathway in the apoptosis and formation of CaOx kidney stones.

MAIN METHODS

Ethylene glycol (EG) was used to establish a rat model of CaOx kidney stones, and 100 mg/kg of ERS inhibitor 4-phenylbutyric acid (4-PBA) or 60 mg/kg of autophagy inhibitor chloroquine (CQ) was administered daily to the rats. Four weeks after administration, we collected blood and kidney tissues to analyze the occurrence of ERS and autophagy, apoptosis, renal function, renal tubular crystal deposition, and kidney damage, respectively.

KEY FINDINGS

We observed that both 4-PBA and CQ treatment significantly inhibited the excessive autophagy and reduced apoptosis as well as decreasing p-PERK and p-eIF2α expressions. Meanwhile, the proportion of kidney weight, contents of creatinine and blood urea nitrogen, excretion of neutrophil gelatinase-associated lipocalin and kidney injury molecule 1, and renal tubular deposition were markedly down-regulated.

SIGNIFICANCE

The findings in this study suggested that ERS induced excessive autophagy via the PERK-eIF2α pathway, regulating cell damage and apoptosis. ERS-mediated inhibition of excessive autophagy effectively protected kidney function and prevented the apoptosis and formation of kidney stones.