Pathogenesis of nephrolithiasis

Ambra1 in exosomes secreted by HK-2 cells damaged by supersaturated oxalate induce mitophagy and autophagy-ferroptosis in normal HK-2 cells to participate in the occurrence of kidney stones

Injury to the renal tubular epithelium has emerged as a leading factor underlying the formation of kidney stones. Indeed, epithelial cell damage contributes to the adherence and aggregation of crystals, thereby accelerating the formation of renal stones. Meanwhile, exosomes play an instrumental role in cellular communication, including DNA, RNA, mRNA, etc. In this study, homogenous cells were treated with exosomes derived from damaged cells in an attempt to establish "positive feedback" of cell damage, and the desired results were achieved. To begin, a serum-free medium and supersaturated concentrations of oxalate were added to the HK-2 cell line, and then exosomes were isolated from the two groups for analysis and comparison, and the autophagy-related gene Ambra1 (autophagy and beclin-1 regulator 1) was detected. Subsequently, normal HK-2 cells were treated with exosomes, and the related indexes of autophagy, ferroptosis and mitophagy were determined. Thereafter, Ambra1 was knocked down in exosome-derived HK-2 cells, resulting in the down-regulation of Ambra1 expression in exosomes produced by HK-2 cells following oxalate intervention. Thereafter, the ability of exosomes to stimulate autophagy, mitophagy and ferroptosis was re-evaluated in HK-2 cells after Ambra1 knockdown. The results corroborated that exosomes secreted by oxalate-treated HK-2 can directly elevate autophagy, ferroptosis and mitophagy levels in normal cells, and this effect was significantly mitigated following Ambra1 knockdown within exosomes. Meanwhile, exosomes-induced autophagy and ferroptosis were alleviated after knockdown of beclin-1 in recipient HK-2 cells. These results further suggest that beclin-1 plays a critical role in the process of exosome-induced autophagy-ferroptosis.

Renal sarcoidosis

Sarcoidosis is a systemic inflammatory disease of unknown etiology. The pathogenesis rests on an aberrant T cell response to unidentified antigens in individuals predisposed by genetic and environmental factors. Increased expression of polarized macrophages and disequilibrium between effector and regulator T cells contribute to the formation of noncaseating granulomas, that are frequently found in affected organs. The main kidney abnormalities in sarcoidosis are granulomatous interstitial nephritis (GIN) and hypercalcemia-related disorders. The clinical diagnosis is difficult. The outcome is variable, ranging from spontaneous remission to end-stage kidney disease (ESKD). Early diagnosis and prompt treatment with corticosteroids can improve the prognosis. Hypercalcemia may be responsible for acute kidney injury (AKI) caused by vasoconstriction of afferent arterioles. Complications of persistent hypercalcemia include nephrocalcinosis and renal stones. In patients with ESKD, dialysis and transplantation can offer results comparable to those observed in patients with other causes of kidney failure. Based on a review of the literature, we present an overview of the etiopathogenesis, the renal manifestations of sarcoidosis and their complications, management and prognosis.

Exosomes derived from calcium oxalate-treated macrophages promote apoptosis of HK-2 cells by promoting autophagy

Calcium oxalate (CaOx) crystals are the main component of kidney stones. Macrophages have the function of eliminating these crystals, and the underlying mechanism remains unclear. Here, we attempted to determine the role of macrophage-derived exosomes exposed to CaOx crystals in regulating apoptosis of human proximal tubular cells (HK-2). Exosomes (CaOx-Exo) were isolated from CaOx-treated macrophages and then incubated with HK-2 cells. CaOx-Exo treatment reduced cell viability and promoted apoptosis of HK-2 cells. The expression of Caspase-3 and Bax was increased, and Bcl-2 expression was decreased in HK-2 cells following CaOx-Exo treatment. Moreover, CaOx-Exo treatment caused an increase of LC3-II/LC3-I ratio and Beclin-1 expression and a downregulation of p62 in HK-2 cells. GFP-LC3 puncta were increased in HK-2 cells following CaOx-Exo treatment. Additionally, CaOx-Exo-treated HK-2 cells were treated with 3-methyladenine (3-MA) to inhibit autophagy activity. 3-MA treatment weakened the impact of CaOx-Exo on cell viability and apoptosis of HK-2 cells. 3-MA treatment also reduced the LC3-II/LC3-I ratio and Beclin-1 expression and enhanced p62 expression in CaOx-Exo-treated HK-2 cells. In conclusion, these data demonstrated that exosomes derived from CaOx-treated macrophages promote apoptosis of HK-2 cells by promoting autophagy. Thus, this work suggests that macrophage-derived exosomes may play a vital role in CaOx-induced human proximal tubular cell damage.

Mineralogy, geochemistry, 13C and 16O isotopic characteristics of urinary stones in Iran, a case study of Lorestan Province

Owing to the importance of urinary stones as one of the biominerals in the human body, it is necessary to investigate their chemical composition and mineralogy. In this matter, a mineralogical study using X-ray diffraction and scanning electron microscopy indicated that urinary stones in Lorestan Province were divided into 5 groups of calcium oxalate, urate, cysteine, phosphate and mixed stones (Whewellite, uric acid, phosphate). In this regard, the microscopic studies revealed that Whewellite was the most important mineral phase among various phases. In the following, the major and rare elements of each group were determined by inductively coupled plasma mass spectrometry (ICP-MS) and X-ray fluorescence analysis. The obtained results demonstrated that Ca was found the most abundant element in urinary stones. In the analysis results of the major oxides, compared to other major oxides, CaO had the highest frequency in urinary stones. The reason was due to the role of calcium in most of the basic functions in cell metabolism. The average values of isotope ¹³C and ¹⁶O in the studied urinary stones were obtained - 33.71 and - 20.57, respectively. Overall, the values of ¹³C isotope in urinary stones were lower than those in the similar stones and human hard tissues in other countries.

Mineralogical, compositional and isotope characterization of human kidney stones (urolithiasis) in a Sri Lankan population

In order to understand the processes of stone formation, compositional, spectroscopic, mineralogical and crystallographic characteristics of human urinary stones collected from patients in Sri Lanka were investigated in detail. The data showed that the majority of urinary calculi were calcium oxalate, either whewellite or weddellite. Other solid phases of stones were composed of struvite, uricite and hydroxylapatite. However, mixed compositions were common except for whewellite stones which occur frequently in pure form. Scanning electron microscope observations and associated energy-dispersive X-ray analyses revealed that whewellite or weddellite was well crystalized compared to other stones types, while phosphate stones were mostly cryptocrystalline. The average δ¹³C and δ¹⁸O of stones were - 32.2‰ (- 37.3 to - 17.4‰) and - 24.2‰ (- 26.7‰ to - 8.9‰), respectively. The δ¹³C values were highly depleted compared to North American and European urinary stones. This may be due to food habits of Asians who consume rice as the staple food.

Endoscopic and histologic findings in a cohort of uric acid and calcium oxalate stone formers

OBJECTIVE

To characterize the endoscopic and histologic renal papillary lesions in a cohort of uric acid (UA) stone formers (SF).

METHODS

Data were prospectively obtained during percutaneous nephrolithotomy between 2009 and 2013. Renal papillae were endoscopically analyzed to quantitate surface area occupied by plaque or plug, and biopsies were obtained. UA SF were compared with non-SF controls and patients with >50% calcium oxalate (CaOx) in the absence of UA.

RESULTS

There were 23 UA SF; of which 19 stones (83%) were admixed with CaOx and 4 (17%) were pure. Compared with CaOx SF and controls, UA SF had a higher prevalence of diabetes and obesity, greater serum creatinine and UA levels, lower estimated glomerular filtration rate and urine pH, and elevated UA supersaturation. Characteristics of UA SF were compared with 95 CaOx SF and 19 controls. Overall, 23 (100%) UA SF had endoscopic plaque and 13 (57%) plugs. Endoscopically, UA SF displayed a greater incidence of plugging (57% vs 45% vs 11%; P = .006) relative to CaOx SF and controls. Likewise, UA SF had a greater percentage surface area of plugging (0.1 vs 0.0; P = .002) and plaque (2.0 vs 0.9; P = .006) than controls but similar amounts to CaOx SF. Histologic plugs were similar in UA and CaOx SF, although CaOx SF demonstrated greater interstitial inflammation on endoscopic biopsy.

CONCLUSION

UA and CaOx SF have similar amounts of plaque, whereas UA SF have more endoscopic but not histologic collecting duct plugs. These data suggest an overlap between the pathogenesis of UA and CaOx stones. The anchoring site for UA stones remains uncertain.

[Nephrolithiasis: metabolic defects and terapeutic implications]

Over the past 10 years, major progress has been made in the knowledge of urinary lithogenesis, including the potential pathogenetic role of Randall's plaques and renal tubular crystal retention. Urine supersaturation is the driving force of this process and can be induced by some risk factors, including low urine volume, high urinary excretion of calcium oxalate and uric acid and low urinary excretion of citrate. Primary hypercalciuria can be due to intestinal overabsorption renal leak and bone reabsorption of calcium. Prophilaxis is mainly conducted with thiazides and low calcium diet which is indicated only in the intestinal form. Primary hyperoxaluria is treated with pyridoxine and may require in the severe forms simultaneous renal and liver transplantation. Enteric hyperoxaluria is secondary to fatty acids malabsorption and requires diet, oral calcium and cholestiramine. Hyperuricosuria is caused by diet endogenous overproduction, mainly due to enzymatic defects or high renal excretion of uric acid. Urine alkalinization with K or K and Mg citrate can prevent stone formation even in idiopathic uric acid nephrolithiasis, in which a defect of urine acidification is supposed to be the main abnormality, and in hypocitraturic patients. Cystinuria is a rare inherited defect with an intense clinical impact. It can be classified in three forms and urinary stone formation is the role. Increased solubility and conversion of cystine in a more soluble form are the main goals of the prophylaxis which includes K citrate and thiol agents administration. Tiopronin is preferred to D-penicillamine due to its lower side effects.