Implication of hyperoxaluria on osteopontin and ER stress mediated apoptosis in renal tissue of rats

Mitochondrial dysfunction and NLRP3 inflammasome: key players in kidney stone formation

The mitochondrion serves as a critical intracellular organelle, engaging in essential roles in the regulation of energy production, oxidative stress management, calcium homeostasis, and apoptosis. One such disease that has been particularly associated with these functions is kidney stone disease (KSD), specifically calcium oxalate (CaOx). It is underpinned by oxidative stress and tissue inflammation. Recent studies have shed light on the vital involvement of mitochondrial dysfunction, the nucleotide-binding domain and leucine-rich repeat containing protein 3 (NLRP3) inflammasome, endoplasmic reticulum stress and subsequent cell death in CaOx crystal retention and aggregation. These processes are pivotal in the pathogenesis of kidney stone formation. This review focuses on the pivotal roles of mitochondria in renal cell functions and provides an overview of the intricate interconnectedness between mitochondrial dysfunction and NLRP3 inflammasome activation in the context of KSD. It is essential to recognise the utmost significance of gaining a comprehensive understanding of the mechanisms that safeguard mitochondrial function and regulate the NLRP3 inflammasome. Such knowledge carries significant scientific implications and opens up promising avenues for the development of innovative strategies to prevent the formation of kidney stones.

Oxalate (dys)Metabolism: Person-to-Person Variability, Kidney and Cardiometabolic Toxicity

Oxalate is a metabolic end-product whose systemic concentrations are highly variable among individuals. Genetic (primary hyperoxaluria) and non-genetic (e.g., diet, microbiota, renal and metabolic disease) reasons underlie elevated plasma concentrations and tissue accumulation of oxalate, which is toxic to the body. A classic example is the triad of primary hyperoxaluria, nephrolithiasis, and kidney injury. Lessons learned from this example suggest further investigation of other putative factors associated with oxalate dysmetabolism, namely the identification of precursors (glyoxylate, aromatic amino acids, glyoxal and vitamin C), the regulation of the endogenous pathways that produce oxalate, or the microbiota's contribution to oxalate systemic availability. The association between secondary nephrolithiasis and cardiovascular and metabolic diseases (hypertension, type 2 diabetes, and obesity) inspired the authors to perform this comprehensive review about oxalate dysmetabolism and its relation to cardiometabolic toxicity. This perspective may offer something substantial that helps advance understanding of effective management and draws attention to the novel class of treatments available in clinical practice.

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.

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.

Downregulation of inflammatory mediators by ethanolic extract of Bergenia ligulata (Wall.) in oxalate injured renal epithelial cells

ETHNOPHARMACOLOGICAL RELEVANCE

In the Indian traditional system of medicine, Bergenia ligulata (Wall.) Engl. has been used for treatment of urolithiasis. Its efficacious nature has led to its incorporation in various commercial herbal formulations such as Cystone and Neeri which are prescribed for kidney related ailments.

AIM OF THE STUDY

To assess whether ethanolic extract of B. ligulata can mitigate the cascade of inflammatory responses that cause oxidative stress and ultimately cell death in renal epithelial cells exposed to hyperoxaluric conditions.

MATERIAL AND METHODS

Bioactivity guided fractionation using solvents of varying polarities was employed to evaluate the potential of the extracts of B. ligulata to inhibit the crystallization process. Modulation of crystal morphology was visualized through Scanning electron microscopy (SEM) analysis. Cell death was assessed using flow cytometry based assays. Alteration in the inflammatory mediators was evaluated using real time PCR and immunocytochemistry. Phytochemical characterization of the ethanolic extract was carried out using FTIR, LC-MS and GC-MS.

RESULTS

Bioactivity guided fractionation for the assessment of antilithiatic activity revealed dose dependent inhibition of nucleation and aggregation process of calcium oxalate crystals in the presence of various extracts, however ethanolic extract showed maximum inhibition and was chosen for further experiments. Studies on renal epithelial NRK-52E cells showed, cytoprotective efficacy of B. ligulata extract against oxalate injury. SEM anaysis further revealed the potential of the extract to modulate the crystal structure and adhesion to renal cell surface. Exposure of the renal cells to the extract led to conversion of the calcium oxalate monohydrate (COM) crystals to the less injurious calcium oxalate dihydrate (COD) form. Expression analysis for oxidative stress and inflammatory biomarkers in NRK-52E cells revealed up-regulation of Mitogen activated protein kinase (MAPK), Osteopontin (OPN) and Nuclear factor- ĸB (NF-ĸB), in response to calcium oxalate insult; which was drastically reduced in the presence of B. ligulata extract. Flow cytometric evaluation pointed to caspase 3 mediated apoptotic cell death in oxalate injured cells, which was attenuated by B. ligulata extract.

CONCLUSION

Considering the complex multifactorial etiology of urolithiasis, ethanolic extract from B. ligulata can be a promising option for the management of kidney stones, as it has the potential to limit inflammation and the subsequent cell death.

Effect of magnesium ammonium phosphate on the expression of adhesion molecules in sheep renal tubular epithelial cells

Adhesion molecules play an important role in urinary calculus formation. The expressions of adhesion molecules in renal tubular has been reported in some animals. However, the role of adhesion molecules in the process of sheep urinary calculus formation is still unclear. The magnesium ammonium phosphate (MAP) is the main component of sheep urinary calculus. In this paper, the sheep renal tubular epithelial cells (RTECs) were isolated and treated with MAP, the expressions of osteopontin (OPN), intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1) and apoptosis-related indicators caspase-3, Bcl-2 and Bax in RTECs were observed, the viability of RTECs was detected by Cell Counting Kit-8 (CCK-8). The levels of superoxide dismutase (SOD) and malondialdehyde (MDA), and the expressions of inflammatory factors Interleukin-6 (IL-6), Interleukin-1 (IL-1), Interleukin-17 (IL-17) and tumor necrosis factor-α (TNF-α) were measured by enzyme-linked immunosorbent (ELISA). The histopathological observation of kidney in urolithiasis sheep was made. The results showed that MAP could reduce the viability and SOD activity, enhance the activity of MDA significantly and promote the expressions of IL-1, IL-6, IL-17 and TNF-α of RTECs. By western blot and qPCR methods, the expressions of ICAM-1, VCAM-1 and OPN increased in 48 h. In addition, the expression of caspase-3 increased significantly and the ratio of Bcl-2/Bax reduced with exposure to MAP. The renal tissue structure was seriously damaged, the RTECs in urolithiasis sheep were degenerative and necrotic.

iTRAQ-Based Comparative Proteomics Analysis of Urolithiasis Rats Induced by Ethylene Glycol

Nephrolithiasis is a frequent chronic urological condition with a high prevalence and recurrence rate. Proteomics studies on urolithiasis rat models are highly important in characterizing the pathophysiology of kidney stones and identifying potential approaches for preventing and treating kidney stones. The isobaric tags for relative and absolute quantification (iTRAQ) were performed to identify differentially expressed proteins (DEPs) in the kidney between urolithiasis rats and control rats. The results showed that 127 DEPs (85 upregulated and 42 downregulated) were identified in urolithiasis and control rats. The functions of DEPs were predicted by Gene Ontology (GO) analysis, Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analysis, and protein-protein interaction (PPI) network analysis. The expression of four upregulated proteins (Tagln, Akr1c9, Spp1, and Fbn1) and four downregulated proteins (Hbb, Epb42, Hmgcs2, and Ca1) were validated by parallel reaction monitoring (PRM). Proteomics studies of ethylene glycol-induced urolithiasis rat models using iTRAQ and PRM helped to elucidate the molecular mechanism governing nephrolithiasis and to identify candidate proteins for the treatment of kidney stones.

Oxidative stress and endoplasmic stress in calcium oxalate stone disease: the chicken or the egg?

Crystal modulators play a significant role in the formation of calcium oxalate stone disease. When renal cells are subjected to oxalate stress, the loss in cell integrity leads to exposure of multiple proteins that assist and/or inhibit crystal attachment and retention. Contact between oxalate and calcium oxalate with urothelium proves fatal to cells as a result of reactive oxygen species generation and onset of oxidative stress. Hence, as a therapeutic strategy it was hypothesised that supplementation of antioxidants would suffice. On the contrary to popular belief, the detection of oxalate induced endoplasmic reticulum mediated apoptosis proved the ineffectiveness of antioxidant therapy alone. Thus, the inadequacy of antioxidant supplementation in oxalate stress invoked the presence of an alternative pathway for the induction of kidney fibrosis in hyperoxaluric rats. In addition to settling this query, the link between oxidative stress and ER stress is not well understood, especially in urolithiasis.

Modulatory effect of 4-phenyl butyric acid on hyperoxaluria-induced renal injury and inflammation

Hyperoxaluria-associated deposition of calcium oxalate crystals results from oxalate-induced renal injury and inflammation. The present study was designed to evaluate the effect of 4-Phenyl butyric acid (4-PBA), a chemical chaperone, in ethylene glycol-induced hyperoxaluria and compare its effect with antioxidant, N-acetyl cysteine (NAC). Male Sprague-Dawley rats were given ethylene glycol in drinking water for 28 days to induce hyperoxaluria. 4-PBA and NAC were given by oral gavage. Effect of 4-PBA was analyzed in both prophylactic and curative regimens. After every 7 days, 24-h urine samples were analyzed for kidney injury and inflammation markers. Increased amounts of kidney injury markers like Kidney injury molecule-1, Lactate dehydrogenase, and N-acetyl-β-glucoseaminidase were found in the urine of hyperoxaluric rats which were significantly reduced by 4-PBA treatment in both prophylactic and curative regimens. Inflammatory markers IL-1β, IL-6, and MCP-1 were also raised in the urine of hyperoxaluric rats which were significantly decreased by 4-PBA treatment. Hyperoxaluria was accompanied with renal oxidative stress as reflected by decreased glutathione redox status and increased reactive oxygen species which was significantly reduced by 4-PBA treatment. Histological study with H&E and Pizzolato staining showed numerous calcium oxalate crystal deposits in the renal tissues of hyperoxaluric rats. However, no significant crystal deposits were seen in the 4-PBA-treated hyperoxaluric rats. N-acetyl cysteine treatment effectively decreased renal oxidative stress but did not alter the production of inflammatory markers. Collectively, the present study suggested the potential protective effect of 4-PBA in hyperoxaluria-induced renal injury and inflammation.