ER signaling regulation drives the switch between autophagy and apoptosis in NRK-52E cells exposed to cisplatin

Role of renal tubular epithelial cells and macrophages in cisplatin-induced acute renal injury

Acute kidney injury (AKI) is a clinical syndrome characterized by a sudden and continuous decline in renal function. The drug cisplatin is commonly used as chemotherapy for solid tumors, and cisplatin-induced acute kidney injury (CI-AKI), which is characterized by acute tubular necrosis and inflammation, frequently occurs in tumor patients. Renal tubular epithelial cells (RTECs) are severely damaged early in this process and play an important role in renal tubular injury and the recruitment of immune cells. Macrophages are the most common infiltrating immune cells in the kidney and have a significant impact on CI-AKI and subsequent repair. This article reviews the latest research progress on the effects of RTECs and macrophages on CI-AKI and their interactions in AKI to provide a direction for identifying therapeutic targets for treating AKI.

Autophagy and necroptosis in cisplatin-induced acute kidney injury: Recent advances regarding their role and therapeutic potential

Cisplatin (CP) is a broad-spectrum antineoplastic agent, used to treat many different types of malignancies due to its high efficacy and low cost. However, its use is largely limited by acute kidney injury (AKI), which, if left untreated, may progress to cause irreversible chronic renal dysfunction. Despite substantial research, the exact mechanisms of CP-induced AKI are still so far unclear and effective therapies are lacking and desperately needed. In recent years, necroptosis, a novel subtype of regulated necrosis, and autophagy, a form of homeostatic housekeeping mechanism have witnessed a burgeoning interest owing to their potential to regulate and alleviate CP-induced AKI. In this review, we elucidate in detail the molecular mechanisms and potential roles of both autophagy and necroptosis in CP-induced AKI. We also explore the potential of targeting these pathways to overcome CP-induced AKI according to recent advances.

Autophagy in Cisplatin Nephrotoxicity during Cancer Therapy

Simple Summary

Cisplatin is a broadly used chemotherapy drug, but its use and efficacy are limited by its nephrotoxicity. Autophagy protects against kidney injury during cisplatin exposure but may reduce the efficacy of chemotherapy by protecting cancer cells. In this review, we describe the role and regulation of autophagy in cisplatin-induced nephrotoxicity and discuss the therapeutic advances and challenges of targeting autophagy in chemotherapy.

Abstract

Cisplatin is a widely used chemotherapeutic agent but its clinical use is often limited by nephrotoxicity. Autophagy is a lysosomal degradation pathway that removes protein aggregates and damaged or dysfunctional cellular organelles for maintaining cell homeostasis. Upon cisplatin exposure, autophagy is rapidly activated in renal tubule cells to protect against acute cisplatin nephrotoxicity. Mechanistically, the protective effect is mainly related to the clearance of damaged mitochondria via mitophagy. The role and regulation of autophagy in chronic kidney problems after cisplatin treatment are currently unclear, despite the significance of research in this area. In cancers, autophagy may prevent tumorigenesis, but autophagy may reduce the efficacy of chemotherapy by protecting cancer cells. Future research should focus on developing drugs that enhance the anti-tumor effects of cisplatin while protecting kidneys during cisplatin chemotherapy.

Panax notoginseng saponins reduces the cisplatin-induced acute renal injury by increasing HIF-1α/BNIP3 to inhibit mitochondrial apoptosis pathway

Cisplatin (CDDP) may induce apoptosis of renal tubular epithelial cells (RTEC) and cause CDDP-induced acute kidney injury (CAKI) during cancer treatment, but yet lack of preventive measures and effective treatment. As a new Chinese herbal preparation, Panax notoginseng saponins (PNS) has been found to mitigate CDDP-induced CAKI through elevating the expression of HIF-1α in the rat model, according to the data from our previous works. However, the underlying link between HIF-1α and apoptosis has not been well elucidated. The current study as a follow-up work, was aimed to reveal if PNS improves CAKI through HIF-1α-dependent apoptosis. A stably HIF-1α-knockdown human proximal tubular epithelial cell (HK-2) line was established by transfecting a HIF-1α-siRNA into HK-2 cells. Cell viability, mitochondrial function, cell apoptosis ratio and the expression of apoptosis-associated proteins (Cyt C, Bcl2, Bax, caspases 3) were determined. In order to elucidate the underlying mechanism, the expression of HIF-1α and BNIP3 were assessed. Our results showed that treatment of PNS rescued the cell viability of CDDP-injured HK-2 or HIF-1α-knockdown HK-2 cells, and increased the expression levels of ATP and MMP in HK-2 or HIF-1α-knockdown HK-2 cells which were reduced by CDDP. Moreover, PNS treatment decreased the CDDP or CDDP plus HIF-1α-knockdown-induced elevation of apoptosis and apoptosis-associated protein expressions. These findings demonstrate that PNS reduces CAKI through increasing HIF-1α to inhibit mitochondrial apoptosis pathway. Hence, we suggest PNS as a protective and therapeutic new drug for CDDP treatment of cancers, which might have significant meaning of further research and application potential.

Platinum drugs and taxanes: can we overcome resistance?

Cancer therapy is aimed at the elimination of tumor cells and acts via the cessation of cell proliferation and induction of cell death. Many research publications discussing the mechanisms of anticancer drugs use the terms "cell death" and "apoptosis" interchangeably, given that apoptotic pathways are the most common components of the action of targeted and cytotoxic compounds. However, there is sound evidence suggesting that other mechanisms of drug-induced cell death, such as necroptosis, ferroptosis, autophagy, etc. may significantly contribute to the fate of cancer cells. Molecular cross-talks between apoptotic and nonapoptotic death pathways underlie the successes and the failures of therapeutic interventions. Here we discuss the nuances of the antitumor action of two groups of the widely used anticancer drugs, i.e., platinum salts and taxane derivatives. The available data suggest that intelligent interference with the choice of cell death pathways may open novel opportunities for cancer treatment.

AMPK/mTOR Signaling in Autophagy Regulation During Cisplatin-Induced Acute Kidney Injury

Autophagy is a conserved, multistep pathway that degrades and recycles dysfunctional organelles and macromolecules to maintain cellular homeostasis. Mammalian target of rapamycin (mTOR) and adenosine-monophosphate activated-protein kinase (AMPK) are major negative and positive regulators of autophagy, respectively. In cisplatin-induced acute kidney injury (AKI) or nephrotoxicity, autophagy is rapidly induced in renal tubular epithelial cells and acts as a cytoprotective mechanism for cell survival. Both mTOR and AMPK have been implicated in the regulation of autophagy in cisplatin-induced AKI. Targeting mTOR and/or AMPK may offer effective strategies for kidney protection during cisplatin-mediated chemotherapy.

NMR and LCMS analytical platforms exhibited the nephroprotective effect of Clinacanthus nutans in cisplatin-induced nephrotoxicity in the in vitro condition

Background

Clinacanthus nutans (C. nutans) Lind. locally known as Belalai Gajah or Sabah snake grass is a medicinal plant belonging to Acanthaceae family. In Asia, this plant is traditionally used for treating skin rashes, insects and snake bites, diabetes mellitus, fever and for diuretic effect. C. nutans has been reported to possess biological activities including anti-oxidant, anti-inflammation, anti-cancer, anti-diabetic and anti-viral activities.

Methods

Proton Nuclear Magnetic Resonance (¹H NMR) and Liquid Chromatography Mass Spectroscopy (LCMS) coupled with multivariate data analysis were employed to characterize the metabolic variations of intracellular metabolites and the compositional changes of the corresponding culture media in rat renal proximal tubular cells (NRK-52E).

Results

NMR and LCMS analysis highlighted choline, creatine, phosphocholine, valine, acetic acid, phenylalanine, leucine, glutamic acid, threonine, uridine and proline as the main metabolites which differentiated the cisplatin-induced group of NRK-52E from control cells extract. The corresponding media exhibited lactic acid, glutamine, glutamic acid and glucose-1-phosphate as the varied metabolites. The altered pathways perturbed by cisplatin nephrotoxic on NRK-52E cells included changes in amino acid metabolism, lipid metabolism and glycolysis.

Conclusion

The C. nutans aqueous extract (1000 μg/mL) exhibited the most potential nephroprotective effect against cisplatin toxicity on NRK-52E cell lines at 89% of viability. The protective effect could be seen through the changes of the metabolites such as choline, alanine and valine in the C. nutans pre-treated samples with those of the cisplatin-induced group.

Supplementary information

Supplementary information accompanies this paper at 10.1186/s12906-020-03067-3.

Taurine suppresses ROS-dependent autophagy via activating Akt/mTOR signaling pathway in calcium oxalate crystals-induced renal tubular epithelial cell injury

Oxidative stress and autophagy are the key promoters of calcium oxalate (CaOx) nephrolithiasis. Taurine is an antioxidant that plays a protective role in the pathogenesis of kidney disease. Previous studies found that taurine suppressed cellular oxidative stress, and inhibited autophagy activation. However, the effect of taurine on CaOx kidney stone formation remains unknown. In the present work, we explored the regulatory effects of taurine on CaOx crystals-induced HK-2 cell injury. Results showed that pretreatment with taurine significantly enhanced the viability of HK-2 cells and ameliorated kidney tissue injury induced by CaOx crystals. Taurine also markedly reduced the levels of inflammatory cytokines, apoptosis, and CaOx crystals deposition. Furthermore, we observed that taurine supplementation alleviated CaOx crystals-induced autophagy. Mechanism studies showed that taurine reduced oxidative stress via increasing SOD activity, reducing MDA concentration, alleviating mitochondrial oxidative injury, and decreasing the production of intracellular ROS. Taurine treatment also effectively activated Akt/mTOR signaling pathway in CaOx crystals-induced HK-2 cells both in vitro and in vivo. In summary, the current study shows that taurine inhibits ROS-dependent autophagy via activating Akt/mTOR signaling pathway in CaOx crystals-induced HK-2 cell and kidney injury, suggesting that taurine may serve as an effective therapeutic agent for the treatment of CaOx nephrolithiasis.

Autophagy in kidney homeostasis and disease

Autophagy is a conserved lysosomal pathway for the degradation of cytoplasmic components. Basal autophagy in kidney cells is essential for the maintenance of kidney homeostasis, structure and function. Under stress conditions, autophagy is altered as part of the adaptive response of kidney cells, in a process that is tightly regulated by signalling pathways that can modulate the cellular autophagic flux - mammalian target of rapamycin, AMP-activated protein kinase and sirtuins are key regulators of autophagy. Dysregulated autophagy contributes to the pathogenesis of acute kidney injury, to incomplete kidney repair after acute kidney injury and to chronic kidney disease of varied aetiologies, including diabetic kidney disease, focal segmental glomerulosclerosis and polycystic kidney disease. Autophagy also has a role in kidney ageing. However, questions remain about whether autophagy has a protective or a pathological role in kidney fibrosis, and about the precise mechanisms and signalling pathways underlying the autophagy response in different types of kidney cells and across the spectrum of kidney diseases. Further research is needed to gain insights into the regulation of autophagy in the kidneys and to enable the discovery of pathway-specific and kidney-selective therapies for kidney diseases and anti-ageing strategies.

Cisplatin-Induced Skeletal Muscle Dysfunction: Mechanisms and Counteracting Therapeutic Strategies

Among the severe side effects induced by cisplatin chemotherapy, muscle wasting is the most relevant one. This effect is a major cause for a clinical decline of cancer patients, since it is a negative predictor of treatment outcome and associated to increased mortality. However, despite its toxicity even at low doses, cisplatin remains the first-line therapy for several types of solid tumors. Thus, effective pharmacological treatments counteracting or minimizing cisplatin-induced muscle wasting are urgently needed. The dissection of the molecular pathways responsible for cisplatin-induced muscle dysfunction gives the possibility to identify novel promising therapeutic targets. In this context, the use of animal model of cisplatin-induced cachexia is very useful. Here, we report an update of the most relevant researches on the mechanisms underlying cisplatin-induced muscle wasting and on the most promising potential therapeutic options to preserve muscle mass and function.

Lithium targeting of AMPK protects against cisplatin-induced acute kidney injury by enhancing autophagy in renal proximal tubular epithelial cells

Autophagy has been demonstrated to be vital for kidney homeostasis and is centrally implicated in the pathogenesis of cisplatin-induced acute kidney injury (AKI). Lithium is a potent autophagy inducer in a number of cell types. However, it remains uncertain whether its autophagic activity is associated with a beneficial effect on renal tubular cells in AKI. This study aimed to examine the effect of lithium on renal autophagy in cisplatin-induced AKI. Mice or renal proximal tubular epithelial cells in culture were exposed to cisplatin-induced acute injury in the presence or absence of lithium treatment. AKI or tubular cell injury was evaluated, and cell signaling associated with autophagy was examined. Lithium pretreatment prominently ameliorated acute renal tubular damage in mice exposed to cisplatin insult, associated with enhanced autophagy in renal tubules, as assessed by measuring microtubule-associated protein 1A/1B-light chain 3 (LC3)BII/I expression and autophagosome formation. Consistently, in cisplatin-injured renal tubular cells in vitro, lithium enhanced autophagic activities, improved cell viability, and attenuated cell death. Mechanistically, lithium triggered AMPK-α phosphorylation and activation, which in turn positively correlated with the induced expression of autophagy-related molecules, like mammalian target of rapamycin and LC3BII/I. AMPK-α activation is likely required for lithium-induced tubular cell autophagy and protection in cisplatin-induced AKI because blockade of AMPK-α phosphorylation by compound C markedly abrogated lithium-induced autophagosome formation and mitigated the protective effect of lithium on AKI. Our findings suggest that lithium represents a promising therapeutic strategy for protecting renal tubular cells against cisplatin-induced AKI by enhancing autophagy via AMPK-α activation.-Bao, H., Zhang, Q., Liu, X., Song, Y., Li, X., Wang, Z., Li, C., Peng, A., Gong, R. Lithium targeting of AMPK protects against cisplatin-induced acute kidney injury by enhancing autophagy in renal proximal tubular epithelial cells.

Low‑intensity pulsed ultrasound promotes apoptosis and inhibits angiogenesis via p38 signaling‑mediated endoplasmic reticulum stress in human endothelial cells

Aberrant increase in angiogenesis contributes to the progression of malignant solid tumors. An alternative anti-angiogenesis therapy is critical for cancer, since the current anti-angiogenesis drugs lack specificity for tumor cells. In the present study, the effects and mechanisms of low-intensity pulsed ultrasound (LIPUS) on human umbilical vein endothelial cells (HUVECs) and human microvascular endothelial cells (HMECs) were investigated, and the therapeutic potential of this technology was assessed. HUVECs and HMECs were treated with LIPUS (0.5 MHz; 210 mW/cm²) for 1 min and cultured for 24 h. Flow cytometry and Cell Counting Kit-8 assays demonstrated that LIPUS treatment at a dose of 210 mW/cm² promoted apoptosis and decreased the viability in HUVECs and HMECs. Real-time cell analysis also revealed that LIPUS did not affect the proliferation or migration of HUVECs. An endothelial cell tube formation assay indicated that LIPUS treatment inhibited the angiogenic ability of HUVECs and HMECs. Furthermore, LIPUS increased the protein levels of the apoptosis-associated cleaved Caspase-3 and decreased the B-cell lymphoma-2 levels. LIPUS increased the phosphorylation of p38 mitogen-activated protein kinase (MAPK), and the levels of endoplasmic reticulum (ER) stress-associated markers, including activating transcription factor-4 (ATF-4) and phosphorylated eukaryotic initiation factor 2α (eIF2α). The p38 inhibitor SB203580 reversed the pro-apoptotic and anti-angiogenic effects of LIPUS in cells. Finally, inhibition of p38 decreased the LIPUS-induced elevation of p-eIF2α and ATF-4 levels. Taken together, these results suggested that LIPUS promoted apoptosis and inhibited angiogenesis in human endothelial cells via the activation of p38 MAPK-mediated ER stress signaling.

Endoplasmic reticulum stress in ischemic and nephrotoxic acute kidney injury

Acute kidney injury (AKI) is a medical condition characterized by kidney damage with a rapid decline of renal function, which is associated with high mortality and morbidity. Recent research has further established an intimate relationship between AKI and chronic kidney disease. Perturbations of kidney cells in AKI result in the accumulation of unfolded and misfolded proteins in the endoplasmic reticulum (ER), leading to unfolded protein response (UPR) or ER stress. In this review, we analyze the role and regulation of ER stress in AKI triggered by renal ischemia-reperfusion and cisplatin nephrotoxicity. The balance between the two major components of UPR, the adaptive pathway and the apoptotic pathway, plays a critical role in determining the cell fate in ER stress. The adaptive pathway is evoked to attenuate translation, induce chaperones, maintain protein homeostasis and promote cell survival. Prolonged ER stress activates the apoptotic pathway, resulting in the elimination of dysfunctional cells. Therefore, regulating ER stress in kidney cells may provide a therapeutic target in AKI. KEY MESSAGES Perturbations of kidney cells in acute kidney injury result in the accumulation of unfolded and misfolded proteins in ER, leading to unfolded protein response (UPR) or ER stress. The balance between the adaptive pathway and the apoptotic pathway of UPR plays a critical role in determining the cell fate in ER stress. Modulation of ER stress in kidney cells may provide a therapeutic strategy for acute kidney injury.

Taurine Supplementation Alleviates Puromycin Aminonucleoside Damage by Modulating Endoplasmic Reticulum Stress and Mitochondrial-Related Apoptosis in Rat Kidney

Taurine (TAU) is a sulfur-containing beta amino acid that is not involved in protein composition and anabolism, conditionally essential in mammals provided through diet. Growing evidence supports a protective role of TAU supply in osmoregulation, calcium flux, and reduction of inflammation and oxidant damage in renal diseases like diabetes. Endoplasmic reticulum (ER) stress, due to abnormal proteostasis, is a contributor to nephrotic syndrome and related renal damage. Here, we investigated the effect of dietary TAU (1.5% in drinking water for 15 days) in an established rat model that mimics human minimal change nephrosis, consisting of a single puromycin aminonucleoside (PAN) injection (intraperitoneally 15 mg/100 g body weight), with sacrifice after eight days. TAU limited proteinuria and podocytes foot processes effacement, and balanced slit diaphragm nephrin and glomerular claudin 1 expressions. In cortical proximal tubules, TAU improved lysosomal density, ER perimeter, restored proper ER-mitochondria tethering and mitochondrial cristae, and decreased inflammation. Remarkably, TAU downregulated glomerular ER stress markers (GRP78, GRP94), pro-apoptotic C/EBP homologous protein, activated caspase 3, tubular caspase1, and mitochondrial chaperone GRP75, but maintained anti-apoptotic HSP25. In conclusion, TAU, by targeting upstream ER stress separate from mitochondria dysfunctions at crucial renal sites, might be a promising dietary supplement in the treatment of the drug-resistant nephrotic syndrome.

Ameliorative effects of taurine against diabetes: a review

Diets in rats and humans have shown promising results. Taurine improved glucagon activity, promoted glycemic stability, modified glucose levels, successfully addressed hyperglycemia via advanced glycation end-product control, improved insulin secretion and had a beneficial effect on insulin resistance. Taurine treatment performed well against oxidative stress in brain, increased the secretion of required hormones and protected against neuropathy, retinopathy and nephropathy in diabetes compared with the control. Taurine has been observed to be effective in treatments against diabetic hepatotoxicity, vascular problems and heart injury in diabetes. Taurine was shown to be effective against oxidative stress. The mechanism of action of taurine cannot be explained by one pathway, as it has many effects. Several of the pathways are the advanced glycation end-product pathway, PI3-kinase/AKT pathway and mitochondrial apoptosis pathway. The worldwide threat of diabetes underscores the urgent need for novel therapeutic measures against this disorder. Taurine (2-aminoethane sulfonic acid) is a natural compound that has been studied in diabetes and diabetes-induced complications.

Morin hydrate ameliorates cisplatin-induced ER stress, inflammation and autophagy in HEK-293 cells and mice kidney via PARP-1 regulation

The present study assessed the possible therapeutic potential of a natural flavonoid morin hydrate (MH), against cisplatin (CP) induced toxicity in HEK-293 cells and mice kidney. Herein, we observed that exposure of HEK-293 cells to CP (20 μM, 24 h) reduced the cell viability, and increased the intracellular ROS generation, nuclear DNA damage, Ca⁺⁺ release, and accumulation of acidic vacuoles. Concomitantly, acute exposure of CP (30 mg/kg, 72 h) to male ICR mice induced histopathological changes in kidney tissue, and alterations in serum creatinine and blood urea nitrogen (BUN) levels. Oxidative stress mediated ER-stress was evidenced by the reduced expression of antioxidant enzymes such as SOD-1, SOD-2, GR, and Trx, and increased expression levels of CytP450, IRE1-α, PERK, and CHOP. The expression levels of major inflammatory response markers such as NF-κB, TNF-α, IL-1β, COX-2 and iNOS were significantly increased in the HEK-293 cells and mice kidney. Temporal up-regulation of p-AMPK and LC3I/II, and down regulation of mTOR was also noticed after CP treatment. CP-induced DNA damage led to activation of PARP-1, which plays a crucial role in inflammation, apoptosis and autophagy activation. Concurrently, co-treatment of CP-MH and CP-ANI (PARP-1 inhibitor) significantly attenuated the expression level of PARP-1, reduced cellular death, alleviated inflammatory responses, and inhibited autophagy stimulation in HEK-293 cells and mice kidney. On the basis of above findings, we suggest MH as a potential therapeutic agent against CP-induced nephrotoxicity.

Autophagy: A new treatment strategy for MSC-based therapy in acute kidney injury (Review)

Acute kidney injury (AKI) is a common and serious medical condition associated with poor health outcomes. Autophagy is a conserved multistep pathway that serves a major role in many biological processes and diseases. Recent studies have demonstrated that autophagy is induced in proximal tubular cells during AKI. Autophagy serves a pro‑survival or pro‑death role under certain conditions. Furthermore, mesenchymal stem cells (MSCs) have therapeutic potential in the repair of renal injury. This review summarizes the recent progress on the role of autophagy in AKI and MSCs‑based therapy for AKI. Further research is expected to prevent and treat acute kidney injury.

Panax notoginseng saponins mitigate cisplatin induced nephrotoxicity by inducing mitophagy via HIF-1α

We investigated the role of HIF-1α in the mitigation of cisplatin-induced nephrotoxicity by Panax notoginseng saponins (PNS) in a rat model. Serum creatinine (Scr), blood urea nitrogen (BUN) and urinary N-acetyl-β-D-glucosaminidase (NAG) levels were all elevated in cisplatin treated rats. PNS reduced Scr, BUN and NAG levels in the presence or absence of the HIF-1α inhibitor 2-methoxyestradiol (2ME2). PNS also reduced the high tubular injury scores, which corresponded to renal tubular damage in cisplatin-treated rats and which were exacerbated by 2ME2. Renal tissues from PNS-treated rats showed increased HIF-1α mRNA and nuclear localized HIF-1α protein. Moreover, PNS treatment increased BNIP3 mRNA as well as LC3-II, BNIP3 and Beclin-1 proteins and the LC3-II/LC3-I ratio in rat renal tissues. This suggested that PNS treatment enhanced HIF-1α, which in turn increased autophagy. This was confirmed in transmission electron micrographs of renal tissues that showed autophagosomes in PNS-treated renal tissues. These findings demonstrate that PNS mitigates cisplatin-induced nephrotoxicity by enhancing mitophagy via a HIF-1α/BNIP3/Beclin-1 signaling pathway.

Urinary metabolomics reveals the therapeutic effect of HuangQi Injections in cisplatin-induced nephrotoxic rats

The side effects of cisplatin (CDDP), notably nephrotoxicity, greatly limited its use in clinical chemotherapy. HuangQi Injections (HI), a commonly used preparation of the well-known Chinese herbal medicine Astragali radix, appeared to be promising treatment for nephrotoxicity without compromising the anti-tumor activity of CDDP. In this study, the urinary metabolomics approach using liquid chromatography time of flight mass spectrometry (LC-TOF/MS) was developed to assess the toxicity-attenuation effects and corresponding mechanisms of HI on CDDP-exposed rats. As a result, successive administration of HI significantly recovered the decline of body weight and downregulated the abnormal increase of serum creatinine and urea. HI partly restored the CDDP-induced alteration of metabolic profiling back into normal condition. Totally 43 toxicity-attenuation potential biomarkers were screened and tentatively identified, which were involved in important metabolic pathways such as amino acid metabolism, TCA cycle, fatty acid metabolism, vitamin B6 metabolism and purine metabolism. The results clearly revealed that HI could alleviate CDDP-induced nephrotoxicity and improve the disturbed metabolic balance induced by repeated CDDP exposure. The present study provided reliable evidence for the protective effect of HI on CDDP-induced toxicity with the multi-target pharmacological characteristics.

Structure-activity relationship of piperine and its synthetic amide analogs for therapeutic potential to prevent experimentally induced ER stress in vitro

Endoplasmic reticulum (ER) is the key organelle involved in protein folding and maturation. Emerging studies implicate the role of ER stress in the development of chronic kidney disease. Thus, there is an urgent need for compounds that could ameliorate ER stress and prevent CKD. Piperine and its analogs have been reported to exhibit multiple pharmacological activities; however, their efficacy against ER stress in kidney cells has not been studied yet. Hence, the goal of this study was to synthesize amide-substituted piperine analogs and screen them for pharmacological activity to relieve ER stress using an in vitro model of tunicamycin-induced ER stress using normal rat kidney (NRK-52E) cells. Five amide-substituted piperine analogs were synthesized and their chemical structures were elucidated by pertinent spectroscopic techniques. An in vitro model of ER stress was developed using tunicamycin, and the compounds of interest were screened for their effect on cell viability, and the expression of ER chaperone GRP78, the pro-apoptotic ER stress marker CHOP, and apoptotic caspases 3 and 12 (via western blotting). Our findings indicate that exposure to tunicamycin (0.5 μg/mL) for 2 h induces the expression of GRP78 and CHOP, and apoptotic markers (caspase-3 and caspase-12) and causes a significant reduction in renal cell viability. Pre-treatment of cells with piperine and its cyclohexylamino analog decreased the tunicamycin-induced upregulation of GRP78 and CHOP and cell death. Taken together, our findings demonstrate that piperine and its analogs differentially regulate ER stress, and thus represent potential therapeutic agents to treat ER stress-related renal disorders. Graphical Abstract Piperine (PIP) reduces the expression of ER stress markers (GRP78 and CHOP) induced by pathologic stimuli and consequently decreases the activation of apoptotic caspase-12 and caspase-3; all of which contributes to its chemical chaperone and cytoprotective properties to protect renal cells against ER stress and ER stress-induced cell death, and would ultimately prevent the development of chronic kidney disease.

Autophagy and Tubular Cell Death in the Kidney

Many common renal insults such as ischemia and toxic injury primarily target the tubular epithelial cells, especially the highly metabolically active proximal tubular segment. Tubular epithelial cells are particularly dependent on autophagy to maintain homeostasis and respond to stressors. The pattern of autophagy in the kidney has a unique spatial and chronologic signature. Recent evidence has shown that there is complex cross-talk between autophagy and various cell death pathways. This review specifically discusses the interplay between autophagy and cell death in the renal tubular epithelia. It is imperative to review this topic because recent discoveries have improved our mechanistic understanding of the autophagic process and have highlighted its broad clinical applications, making autophagy a major target for drug development.

Emodin ameliorates cisplatin-induced apoptosis of rat renal tubular cells in vitro by activating autophagy

AIM

A previous report shows that emodin extracted from the Chinese herbs rhubarb and giant knotweed rhizome can ameliorate the anticancer drug cisplatin-induced injury of HEK293 cells. In this study, we investigated whether and how emodin could protect renal tubular epithelial cells against cisplatin-induced nephrotoxicity in vitro.

METHODS

The viability and apoptosis of normal rat renal tubular epithelial cells (NRK-52E) were detected using formazan assay and flow cytometry analysis, respectively. The expression levels of cleaved caspase-3, autophagy maker LC3 I/II, and AMPK/mTOR signaling pathway-related proteins were measured with Western blot analysis. The changes of morphology and RFP-LC3 fluorescence were observed under microscopy.

RESULTS

Cisplatin (10-50 μmol/L) dose-dependently induced cell damage and apoptosis in NRK-52E cells, whereas emodin (10 and 100 μmol/L) significantly ameliorated cisplatin-induced cell damage, apoptosis and caspase-3 cleavage. Emodin dose-dependently increased LC3-II levels and induced RFP-LC3-containing punctate structures in NRK-52E cells. Furthermore, the protective effects of emodin were abolished by bafilomycin A1 (10 nmol/L), and mimicked by rapamycin (100 nmol/L). Moreover, emodin increased the phosphorylation of AMPK and suppressed the phosphorylation of mTOR. The AMPK inhibitor compound C (10 μmol/L) not only abolished emodin-induced autophagy activation, but also emodin-induced anti-apoptotic effects.

CONCLUSION

Emodin ameliorates cisplatin-induced apoptosis of rat renal tubular cells in vitro through modulating the AMPK/mTOR signaling pathways and activating autophagy. Emodin may have therapeutic potential for the prevention of cisplatin-induced nephrotoxicity.

Autophagy in acute kidney injury

Autophagy is a conserved multistep pathway that degrades and recycles damaged organelles and macromolecules to maintain intracellular homeostasis. The autophagy pathway is upregulated under stress conditions including cell starvation, hypoxia, nutrient and growth-factor deprivation, endoplasmic reticulum stress, and oxidant injury, most of which are involved in the pathogenesis of acute kidney injury (AKI). Recent studies demonstrate that basal autophagy in the kidney is vital for the normal homeostasis of the proximal tubules. Deletion of key autophagy proteins impaired renal function and increased p62 levels and oxidative stress. In models of AKI, autophagy deletion in proximal tubules worsened tubular injury and renal function, highlighting that autophagy is renoprotective in models of AKI. In addition to nonselective sequestration of autophagic cargo, autophagy can facilitate selective degradation of damaged organelles, particularly mitochondrial degradation through the process of mitophagy. Damaged mitochondria accumulate in autophagy-deficient kidneys of mice subjected to ischemia-reperfusion injury, but the precise mechanisms of regulation of mitophagy in AKI are not yet elucidated. Recent progress in identifying the interplay of autophagy, apoptosis, and regulated necrosis has revived interest in examining shared pathways/molecules in this crosstalk during the pathogenesis of AKI. Autophagy and its associated pathways pose potentially unique targets for therapeutic interventions in AKI.

Lovastatin prevents cisplatin-induced activation of pro-apoptotic DNA damage response (DDR) of renal tubular epithelial cells

The platinating agent cisplatin (CisPt) is commonly used in the therapy of various types of solid tumors. The anticancer efficacy of CisPt largely depends on the formation of bivalent DNA intrastrand crosslinks, which stimulate mechanisms of the DNA damage response (DDR), thereby triggering checkpoint activation, gene expression and cell death. The clinically most relevant adverse effect associated with CisPt treatment is nephrotoxicity that results from damage to renal tubular epithelial cells. Here, we addressed the question whether the HMG-CoA-reductase inhibitor lovastatin affects the DDR of renal cells by employing rat renal proximal tubular epithelial (NRK-52E) cells as in vitro model. The data show that lovastatin has extensive inhibitory effects on CisPt-stimulated DDR of NRK-52E cells as reflected on the levels of phosphorylated ATM, Chk1, Chk2, p53 and Kap1. Mitigation of CisPt-induced DDR by lovastatin was independent of the formation of DNA damage as demonstrated by (i) the analysis of Pt-(GpG) intrastrand crosslink formation by Southwestern blot analyses and (ii) the generation of DNA strand breaks as analyzed on the level of nuclear γH2AX foci and employing the alkaline comet assay. Lovastatin protected NRK-52E cells from the cytotoxicity of high CisPt doses as shown by measuring cell viability, cellular impedance and flow cytometry-based analyses of cell death. Importantly, the statin also reduced the level of kidney DNA damage and apoptosis triggered by CisPt treatment of mice. The data show that the lipid-lowering drug lovastatin extensively counteracts pro-apoptotic signal mechanisms of the DDR of tubular epithelial cells following CisPt injury.

Advances and New Concepts in Alcohol-Induced Organelle Stress, Unfolded Protein Responses and Organ Damage

Alcohol is a simple and consumable biomolecule yet its excessive consumption disturbs numerous biological pathways damaging nearly all organs of the human body. One of the essential biological processes affected by the harmful effects of alcohol is proteostasis, which regulates the balance between biogenesis and turnover of proteins within and outside the cell. A significant amount of published evidence indicates that alcohol and its metabolites directly or indirectly interfere with protein homeostasis in the endoplasmic reticulum (ER) causing an accumulation of unfolded or misfolded proteins, which triggers the unfolded protein response (UPR) leading to either restoration of homeostasis or cell death, inflammation and other pathologies under severe and chronic alcohol conditions. The UPR senses the abnormal protein accumulation and activates transcription factors that regulate nuclear transcription of genes related to ER function. Similarly, this kind of protein stress response can occur in other cellular organelles, which is an evolving field of interest. Here, I review recent advances in the alcohol-induced ER stress response as well as discuss new concepts on alcohol-induced mitochondrial, Golgi and lysosomal stress responses and injuries.

Basic mechanisms in endoplasmic reticulum stress and relation to cardiovascular diseases

The folding process is an important step in protein synthesis for the functional shape or conformation of the protein. The endoplasmic reticulum (ER) is the main organelle for the correct folding procedure, which maintains the homeostasis of the organism. This process is normally well organized under unstressed conditions, whereas it may fail under oxidative and ER stress. The unfolded protein response (UPR) is a defense mechanism that removes the unfolded/misfolded proteins to prevent their accumulation, and two main degradation systems are involved in this defense, including the proteasome and autophagy. Cells decide which mechanism to use according to the type, severity, and duration of the stress. If the stress is too severe and in excess, the capacity of these degradation mechanisms, proteasomal degradation and autophagy, is not sufficient and the cell switches to apoptotic death. Because the accumulation of the improperly folded proteins leads to several diseases, it is important for the body to maintain this balance. Cardiovascular diseases are one of the important disorders related to failure of the UPR. Especially, protection mechanisms and the transition to apoptotic pathways have crucial roles in cardiac failure and should be highlighted in detailed studies to understand the mechanisms involved. This review is focused on the involvement of the proteasome, autophagy, and apoptosis in the UPR and the roles of these pathways in cardiovascular diseases.

Mechanism of cisplatin proximal tubule toxicity revealed by integrating transcriptomics, proteomics, metabolomics and biokinetics

Cisplatin is one of the most widely used chemotherapeutic agents for the treatment of solid tumours. The major dose-limiting factor is nephrotoxicity, in particular in the proximal tubule. Here, we use an integrated omics approach, including transcriptomics, proteomics and metabolomics coupled to biokinetics to identify cell stress response pathways induced by cisplatin. The human renal proximal tubular cell line RPTEC/TERT1 was treated with sub-cytotoxic concentrations of cisplatin (0.5 and 2 μM) in a daily repeat dose treating regime for up to 14 days. Biokinetic analysis showed that cisplatin was taken up from the basolateral compartment, transported to the apical compartment, and accumulated in cells over time. This is in line with basolateral uptake of cisplatin via organic cation transporter 2 and bioactivation via gamma-glutamyl transpeptidase located on the apical side of proximal tubular cells. Cisplatin affected several pathways including, p53 signalling, Nrf2 mediated oxidative stress response, mitochondrial processes, mTOR and AMPK signalling. In addition, we identified novel pathways changed by cisplatin, including eIF2 signalling, actin nucleation via the ARP/WASP complex and regulation of cell polarization. In conclusion, using an integrated omic approach together with biokinetics we have identified both novel and established mechanisms of cisplatin toxicity.

Taurine rescues cisplatin-induced muscle atrophy in vitro: a morphological study

Cisplatin (CisPt) is a widely used chemotherapeutic drug whose side effects include muscle weakness and cachexia. Here we analysed CisPt-induced atrophy in C2C12 myotubes by a multidisciplinary morphological approach, focusing on the onset and progression of autophagy, a protective cellular process that, when excessively activated, may trigger protein hypercatabolism and atrophy in skeletal muscle. To visualize autophagy we used confocal and transmission electron microscopy at different times of treatment and doses of CisPt. Moreover we evaluated the effects of taurine, a cytoprotective beta-amino acid able to counteract oxidative stress, apoptosis, and endoplasmic reticulum stress in different tissues and organs. Our microscopic results indicate that autophagy occurs very early in 50  μM CisPt challenged myotubes (4 h-8 h) before overt atrophy but it persists even at 24 h, when several autophagic vesicles, damaged mitochondria, and sarcoplasmic blebbings engulf the sarcoplasm. Differently, 25 mM taurine pretreatment rescues the majority of myotubes size upon 50  μM CisPt at 24 h. Taurine appears to counteract atrophy by restoring regular microtubular apparatus and mitochondria and reducing the overload and the localization of autophagolysosomes. Such a promising taurine action in preventing atrophy needs further molecular and biochemical studies to best define its impact on muscle homeostasis and the maintenance of an adequate skeletal mass in vivo.

Autophagy in kidney health and disease

SIGNIFICANCE

Autophagy is emerging as an important pathway in many biological processes and diseases. This review summarizes the current progress on the role of autophagy in renal physiology and pathology.

RECENT ADVANCES

Studies from renal cells in culture, human kidney tissues, and experimental animal models implicate that autophagy regulates many critical aspects of normal and disease conditions in the kidney, such as diabetic nephropathy and other glomerular diseases, tubular injuries, kidney development and aging, cancer, and genetic diseases associated with the kidney.

CRITICAL ISSUES

The importance of autophagy in the kidney has just started to be elucidated. How the process of autophagy is altered in the pathogenesis of kidney diseases and how this alteration is beneficial or detrimental to kidney functions still need to be fully understood.

FUTURE DIRECTIONS

Investigations that uncover the precise mechanism and regulation of autophagy in various kidney diseases may lead to new strategies for therapeutic modulation.

Autophagy in acute kidney injury

Acute kidney injury is a major kidney disease associated with poor clinical outcomes. The pathogenesis of acute kidney injury is multifactorial and is characterized by tubular cell injury and death. Recent studies have shown autophagy induction in proximal tubular cells during acute kidney injury. The regulatory mechanisms of tubular cell autophagy are poorly understood; however, some recent findings have set up a foundation for further investigation. Although autophagy may promote cell death under certain experimental conditions, pharmacologic and autophagy-related gene knockout studies have established a renoprotective role for autophagy in acute kidney injury. The mechanisms by which autophagy protects cells from injury and how, possibly, its pro-survival role switches to pro-death under certain conditions are discussed. Further research is expected to help us understand the regulatory network of tubular cell autophagy, define its precise roles in the specific context of acute kidney injury, and identify autophagy-targeting strategies for the prevention and treatment of acute kidney injury.

A new strategy of promoting cisplatin chemotherapeutic efficiency by targeting endoplasmic reticulum stress

Cisplatin (cis-diamminedichloroplatinum II, CDDP) is one of the most effective chemotherapeutic agents and is widely used in the treatment of solid tumors. However, its side effects and acquired resistance gained during the course of treatment may limit its usage. It is generally considered to be a cytotoxic drug that kills cancer cells by damaging their DNA and inhibiting DNA synthesis to induce apoptosis via the mitochondrial death pathway or through plasma membrane disruption, triggering the Fas death receptor pathway. The endoplasmic reticulum (ER) is one of the most important protein-folding compartments within the cell and an intracellular Ca²⁺ storage organelle. The ER contains a number of molecular chaperones, which may play an important role in determining cellular sensitivity to ER stress and apoptosis. The aim of this review was to summarize our current understanding regarding the mechanisms of ER stress response by which cisplatin induces cell death and the basis for cisplatin resistance. Various aspects were addressed, including the two-way regulation of ER stress, the involvement of ER stress in cisplatin-induced cell death and drug resistance and the drugs enhancing cisplatin-induced cell death by interfering with ER stress. An understanding of how ER stress signaling pathways regulate cisplatin-induced cell death may enable the development of more effective therapeutic strategies for the treatment of cancer.

Saxifragifolin D induces the interplay between apoptosis and autophagy in breast cancer cells through ROS-dependent endoplasmic reticulum stress

Breast cancer is the leading cause of cancer death among females, and novel chemotherapeutic drugs for treating breast cancer are needed urgently. Saxifragifolin D (SD) was isolated by our group from Androsace umbellata which is commonly used to treat solid tumor. In this study, we evaluated its growth inhibitory effect on breast cancer cells and explored the underlying molecular mechanisms. Our results showed that SD inhibited the growth of both MCF-7 and MDA-MB-231 cells significantly. Mechanistic studies demonstrated that SD induced apoptosis through mitochondrial apoptotic pathway. Evidence of SD-induced autophagy included the occurrence of autophagic vacuoles, up-regulation of LC3-II, Beclin1 and Vps34. Inhibition of autophagy by bafilomycin A1 or Beclin1 siRNA pretreatment decreased the ratio of apoptosis, indicating that autophagy induction contributes to apoptosis and is required for the latter. SD was also found to induce endoplasmic reticulum stress, accompanied by ROS production, increase of intracellular calcium and up-regulation of Bip, IRE1α and XBP-1s. Inhibition of endoplasmic reticulum stress by N-acetyl-l-cysteine, tauroursodeoxycholic acid or IRE1α siRNA pretreatment could suppress both apoptosis and autophagy. Besides, increases in CHOP, calnexin, calpain, p-JNK and p-Bcl-2 were followed by subsequent dissociation of Beclin1 from Bcl-2, further suggesting endoplasmic reticulum stress to be the common signaling pathway shared by SD-induced apoptosis and autophagy. In conclusion, SD inhibits breast cancer cell growth and induces interplay between apoptosis and autophagy through ROS-mediated endoplasmic reticulum stress. It will provide molecular bases for developing SD into a drug candidate for the treatment of breast cancer.

XBP1 mRNA splicing triggers an autophagic response in endothelial cells through BECLIN-1 transcriptional activation

Sustained activation of X-box-binding protein 1 (XBP1) results in endothelial cell (EC) apoptosis and atherosclerosis development. The present study provides evidence that XBP1 mRNA splicing triggered an autophagic response in ECs by inducing autophagic vesicle formation and markers of autophagy BECLIN-1 and microtubule-associated protein 1 light chain 3β (LC3-βII). Endostatin activated autophagic gene expression through XBP1 mRNA splicing in an inositol-requiring enzyme 1α (IRE1α)-dependent manner. Knockdown of XBP1 or IRE1α by shRNA in ECs ablated endostatin-induced autophagosome formation. Importantly, data from arterial vessels from XBP1 EC conditional knock-out (XBP1eko) mice demonstrated that XBP1 deficiency in ECs reduced the basal level of LC3β expression and ablated response to endostatin. Chromatin immunoprecipitation assays further revealed that the spliced XBP1 isoform bound directly to the BECLIN-1 promoter at the region from nt -537 to -755. BECLIN-1 deficiency in ECs abolished the XBP1-induced autophagy response, whereas spliced XBP1 did not induce transcriptional activation of a truncated BECLIN-1 promoter. These results suggest that XBP1 mRNA splicing triggers an autophagic signal pathway through transcriptional regulation of BECLIN-1.

Apoptosis induced by adenosine involves endoplasmic reticulum stress in EC109 cells

Apoptosis plays a critical role in the development and homeostasis of multicellular organisms, and endoplasmic reticulum stress (ERS) is one of the intrinsic apoptosis pathways. Previous studies have shown that adenosine induces apoptosis in several cancer cell lines. However, the molecular mechanism remains poorly understood. In this study, we explored whether adenosine triggers apoptosis of EC109 esophageal carcinoma (EC) cells by ERS. The MTT assay was used to determine cell proliferation; cell cycle detection (FCM) and terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling (TUNEL) assay were performed to determine cell apoptosis. The subcellular distribution and expression of the ERS-related proteins GRP78, cleaved caspase-3, cleaved caspase-4, CHOP and NF-κB p65 were detected by western blot techniques. NF-κB activation was measured by electrophoretic mobility shift assay (EMSA). The MTT assay demonstrated that adenosine inhibited EC109 cell proliferation in a dose- and time-dependent manner. FCM and TUNEL assay verified that adenosine caused an apoptotic peak in cell cycle arrest and a higher percentage of apoptotic cells. Western blot analysis confirmed that the expression of GRP78, cleaved caspase-4, CHOP, NF-κB p65 and cleaved caspase-3 were upregulated in a dose-dependent manner after adenosine treatment. EMSA revealed that adenosine activated NF-κB p65. This is the first demonstration that adenosine inhibits cell proliferation, increases GRP78 and NF-κB p65 expression and induces apoptosis by CHOP and caspase-4 pathways. The ERS pathway is involved in adenosine-induced apoptosis in EC109 cells.

Involvement of endoplasmic reticulum and autophagy in microcystin-LR toxicity in Vero-E6 and HepG2 cell lines

This work investigates the involvement of the endoplasmic reticulum (ER) and autophagy in microcystin-LR (MCLR) toxicity in Vero-E6 and HepG2 cell lines. Additionally, morphological alterations induced by MCLR in lysosomes and mitochondria were studied. Cytotoxicity evaluation showed that pure MCLR and MCLR from LMECYA110 extract induce concentration dependent viability decays after 24h exposure. HepG2 cells showed an increased sensitivity to MCLR than Vero cells, with lower cytotoxic thresholds and EC(50) values. Conversely, LC3B immunofluorescence showed that autophagy is triggered in both cell lines as a survival response to low MCLR concentrations. Furthermore, MCLR induced a MCLR concentration-dependent decrease of GRP94 expression in HepG2 cells while in Vero cells no alteration was observed. This suggests the involvement of the ER in HepG2 apoptosis elicited by MCLR, while in Vero cells ER destructuration could be a consequence of cytoskeleton inflicted damages. Additionally, in both cell lines, lysosomal destabilization preceded mitochondrial impairment which occurred at high toxin concentrations. Although not an early cellular target of MCLR, mitochondria appears to serve as central mediators of different signaling pathways elicited by the organelles involved in MCLR toxicity. As a result, kidney and hepatic cell lines exhibit cell type and dose-dependent mechanisms to overcome MCLR toxicity.

Expression of PAFR as part of a prosurvival response to chemotherapy: a novel target for combination therapy in melanoma

Melanoma cells express the platelet-activating factor receptor (PAFR) and, thus, respond to PAF, a bioactive lipid produced by both tumour cells and those in the tumour microenvironment such as macrophages. Here, we show that treatment of a human melanoma SKmel37 cell line with cisplatin led to increased expression of PAFR and its accumulation. In the presence of exogenous PAF, melanoma cells were significantly more resistant to cisplatin-induced cell death. Inhibition of PAFR-dependent signalling pathways by a PAFR antagonist (WEB2086) showed chemosensitisation of melanoma cells in vitro. Nude mice were inoculated with SKmel37 cells and treated with cisplatin and WEB2086. Animals treated with both agents showed significantly decreased tumour growth compared to the control group and groups treated with only one agent. PAFR accumulation and signalling are part of a prosurvival program of melanoma cells, therefore constituting a promising target for combination therapy for melanomas.