Protective effects of finasteride against testosterone-induced calcium oxalate crystallization and crystal-cell adhesion

Curcumin prevents high glucose-induced stimulatory effects of renal cell secretome on fibroblast activation via mitigating intracellular free radicals and TGF-β secretion

Diabetic kidney disease (DKD) is a leading cause of kidney failure. However, the involvement of renal fibroblasts and their communications with renal epithelial cells during DKD remain poorly understood. We investigated the potential role of renal proximal tubular epithelial cells (PTECs) in renal fibroblast activation that might lead to DKD. Additionally, the protective effects of curcumin, a known antioxidant, against renal fibroblast activation induced by high glucose-treated PTECs were investigated. Secretome was collected from HK-2 PTECs under normal glucose, high glucose, high glucose pretreated/cotreated with curcumin, or osmotic control condition for 24 h. Such secretome was then used to treat BHK-21 renal fibroblasts for 24 h. BHK-21 cells treated with high glucose-induced secretome had increased levels of fibroblast activation markers, including spindle index, F-actin, α-smooth muscle actin (α-SMA), fibronectin, collagen I, matrix metalloproteinase-2 (MMP-2) and MMP-9, as compared with normal glucose and osmotic control conditions. However, all these increases were successfully mitigated by curcumin. In addition, high glucose markedly increased intracellular reactive oxygen species (ROS) and transforming growth factor-β (TGF-β) secretion, but did not affect the secretion of platelet-derived growth factor A (PDGFA) and interleukin-1β (IL-1β), in HK-2 renal cells as compared with normal glucose and osmotic control conditions. Both intracellular ROS and secreted TGF-β levels were successfully mitigated by curcumin. Therefore, curcumin prevents the high glucose-induced stimulatory effects of renal cell secretome on fibroblast activation, at least in part, via mitigating intracellular ROS and TGF-β secretion.

The inhibitory effects of epigallocatechin-3-gallate on calcium oxalate monohydrate crystal growth, aggregation and crystal-cell adhesion

Epigallocatechin-3-gallate (EGCG), a predominant phytochemical in tea plant, has been reported to prevent kidney stone formation but with vague mechanism. We investigated modulatory effects of EGCG (at 0.1-100 µM) on calcium oxalate monohydrate (COM) crystals at various stages of kidney stone development. EGCG significantly increased crystal size (at 1-100 µM), but decreased crystal number (at 10-100 µM), resulting in unchanged crystal mass and volume. Interestingly, EGCG at 10-100 µM caused morphological change of the crystals from typical monoclinic prismatic to coffee-bean-like shape, which represented atypical/aberrant form of COM as confirmed by attenuated total reflection - Fourier transform infrared (ATR-FTIR) spectroscopy. EGCG at all concentrations significantly inhibited crystal growth in a concentration-dependent manner. However, only 100 µM and 10-100 µM of EGCG significantly inhibited crystal aggregation and crystal-cell adhesion, respectively. Immunofluorescence staining (without permeabilization) revealed that surface expression of heat shock protein 90 (HSP90) (a COM crystal receptor) on MDCK renal cells was significantly decreased by 10 µM EGCG, whereas other surface COM receptors (annexin A1, annexin A2, enolase 1 and ezrin) remained unchanged. Immunoblotting showed that 10 µM EGCG did not alter total level of HSP90 in MDCK cells, implicating that its decreased surface expression was due to translocation. Our data provide a piece of evidence explaining mechanism underlying the anti-lithiatic property of EGCG by inhibition of COM crystal growth, aggregation and crystal-cell adhesion via reduced surface expression of HSP90, which is an important COM crystal receptor.

Quercetin inhibits calcium oxalate crystallization and growth but promotes crystal aggregation and invasion

Recent evidence has shown an association between kidney stone pathogenesis and oxidative stress. Many anti-oxidants have been studied with an aim for stone prevention. Quercetin, a natural flavonol, is one among those eminent anti-oxidants with satisfactory anti-inflammatory property to cope with renal tissue injury in kidney stone disease. Nevertheless, its direct effect (if any) on calcium oxalate (CaOx) crystals and the stone formation mechanism had not been previously explored. This study has addressed the ability of quercetin at various concentrations (2.5, 5, 10, 20, 40, 80 and 160 μM) to directly modulate CaOx crystallization, growth, aggregation, adhesion on kidney cells, and invasion through the matrix. The data have shown that quercetin significantly inhibits CaOx crystallization and crystal growth but promotes crystal aggregation in concentration-dependent manner. However, quercetin at all these concentrations do not affect CaOx adhesion on kidney cells. For the invasion, quercetin at all concentrations constantly promotes CaOx invasion through the matrix without concentration-dependent pattern. These discoveries have demonstrated for the first time that quercetin has direct but dual modulatory effects on CaOx crystals. While quercetin inhibits CaOx crystallization and growth, on the other hand, it promotes CaOx crystal aggregation and invasion through the matrix. These data highlight the role for quercetin in direct modulation of the CaOx crystals that may intervene the stone pathogenesis.

Characterizations of annexin A1-interacting proteins in apical membrane and cytosolic compartments of renal tubular epithelial cells

Annexin A1 (ANXA1) is a multifunctional calcium-binding protein that can bind to membrane phospholipids. Under high-calcium condition, ANXA1 expression increases on renal epithelial cell surface, leading to enhanced adhesion of calcium oxalate (CaOx) crystal (stone material) onto the cells. To regulate various cellular processes, ANXA1 interacts with many other intracellular protein partners. However, components of the ANXA1-interacting protein complex remain unclear. Herein, we characterized the interacting complexes of apical membrane (ApANXA1) and cytosolic (cyANXA1) forms of ANXA1 in apical membrane and cytosolic compartments, respectively, of renal epithelial cells under high-calcium condition using proteomic and bioinformatic approaches. After fractionation, the ApANXA1- and CyANXA1-interacting partners were identified by immunoprecipitation followed by nanoLC‑ESI‑Qq-TOF tandem mass spectrometry (IP-MS/MS). The ANXA1-interacting partners that were common in both apical membrane and cytosolic compartments and those unique in each compartment were then analyzed for their physico-chemical properties (molecular weight, isoelectric point, amino acid contents, instability index, aliphatic index, and grand average of hydropathicity), secondary structure (α-helix, β-turn, random coil, and extended strand), molecular functions, biological processes, reactome pathways and KEGG pathways. The data demonstrated that each set of these interacting proteins exhibited common and unique characteristics and properties. The knowledge from this study may lead to better understanding of the ApANXA1 and CyAXNA1 biochemistry and functions as well as the pathophysiology of CaOx kidney stone formation induced by high-calcium condition.

Metabolic changes in kidney stone disease

Kidney stone disease (KSD) is one of the earliest medical diseases known, but the mechanism of its formation and metabolic changes remain unclear. The formation of kidney stones is a extensive and complicated process, which is regulated by metabolic changes in various substances. In this manuscript, we summarized the progress of research on metabolic changes in kidney stone disease and discuss the valuable role of some new potential targets. We reviewed the influence of metabolism of some common substances on stone formation, such as the regulation of oxalate, the release of reactive oxygen species (ROS), macrophage polarization, the levels of hormones, and the alternation of other substances. New insights into changes in substance metabolism changes in kidney stone disease, as well as emerging research techniques, will provide new directions in the treatment of stones. Reviewing the great progress that has been made in this field will help to improve the understanding by urologists, nephrologists, and health care providers of the metabolic changes in kidney stone disease, and contribute to explore new metabolic targets for clinical therapy.

Comparative analysis of markers for H2O2-induced senescence in renal tubular cells

To address what marker(s) is/are most suitable for determining renal cell senescence, cell area, granularity, cycle shift/arrest, SA-β-Gal, SIRT1 and p16 were evaluated after inducing senescence in HK-2 cells with 0.2-0.8 mM H₂O₂. Only cell area and granularity concentration-dependently increased at all time-points, whereas SA-β-Gal, SIRT1 and p16 showed significant coefficient of determination (R²) at two time-points. Cell granularity had significant correlation coefficient (R) with other six, whereas SA-β-Gal had significant R with five, and cell area, SIRT1 and p16 had significant R with four others. Comparing to SA-β-Gal, other markers had significantly lower fold-changes only at 72-h with 0.8 mM H₂O₂, whereas p16 provided greater fold-changes at 48-h with 0.4 and 0.8 mM H₂O₂. Therefore, cell area, granularity, SA-β-Gal and p16 may serve as the most suitable markers for determining H₂O₂-induced senescence in HK-2 renal cells, whereas other markers can be also used but with inferior quantitative precision.

Finasteride Alleviates High Fat Associated Protein-Overload Nephropathy by Inhibiting Trimethylamine N-Oxide Synthesis and Regulating Gut Microbiota

Unhealthy diet especially high-fat diet (HFD) is the major cause of hyperlipidemia leading to deterioration of chronic kidney diseases (CKD) in patients. Trimethylamine N-oxide (TMAO) is a gut-derived uremic toxin. Our previous clinical study demonstrated that the elevation of TMAO was positively correlated with CKD progression. Finasteride, a competitive and specific inhibitor of type II 5a-reductase, has been reported recently to be able to downregulate plasma TMAO level thus preventing the onset of atherosclerosis by our research group. In this study, we established a protein-overload nephropathy CKD mouse model by bovine serum albumin (BSA) injection to investigate whether hyperlipidemia could accelerate CKD progression and the underlying mechanisms. Finasteride was administrated to explore its potential therapeutic effects. The results of biochemical analyses and pathological examination showed that HFD-induced hyperlipidemia led to aggravated protein-overload nephropathy in mice along with an elevated level of circulating TMAO, which can be alleviated by finasteride treatment possibly through inhibition of Fmo3 in liver. The 16 S rRNA sequencing results indicated that HFD feeding altered the composition and distribution of gut microbiota in CKD mice contributing to the enhanced level of TMAO precursor TMA, while finasteride could exert beneficial effects via promoting the abundance of Alistipes_senegalensis and Akkermansia_muciniphila. Immunofluorescence staining (IF) and qRT-PCR results demonstrated the disruption of intestinal barrier by decreased expression of tight junction proteins including Claudin-1 and Zo-1 in HFD-fed CKD mice, which can be rescued by finasteride treatment. Cytokine arrays and redox status analyses revealed an upregulated inflammatory level and oxidative stress after HFD feeding in CKO mice, and finasteride-treatment could alleviate these lesions. To summarize, our study suggested that finasteride could alleviate HFD-associated deterioration of protein-overload nephropathy in mice by inhibition of TMAO synthesis and regulation of gut microbiota.

Roles of heat-shock protein 90 and its four domains (N, LR, M and C) in calcium oxalate stone-forming processes

Human heat-shock protein 90 (HSP90) has four functional domains, including NH₂-terminal (N), charged linker region (LR), middle (M) and COOH-terminal (C) domains. In kidney stone disease (or nephrolithiasis/urolithiasis), HSP90 serves as a receptor for calcium oxalate monohydrate (COM), which is the most common crystal to form kidney stones. Nevertheless, roles of HSP90 and its four domains in kidney stone formation remained unclear and under-investigated. We thus examined and compared their effects on COM crystals during physical (crystallization, growth and aggregation) and biological (crystal–cell adhesion and crystal invasion through extracellular matrix (ECM)) pathogenic processes of kidney stone formation. The analyses revealed that full-length (FL) HSP90 obviously increased COM crystal size and abundance during crystallization and markedly promoted crystal growth, aggregation, adhesion onto renal cells and ECM invasion. Comparing among four individual domains, N and C domains exhibited the strongest promoting effects, whereas LR domain had the weakest promoting effects on COM crystals. In summary, our findings indicate that FL-HSP90 and its four domains (N, LR, M and C) promote COM crystallization, crystal growth, aggregation, adhesion onto renal cells and invasion through the ECM, all of which are the important physical and biological pathogenic processes of kidney stone formation.

Persistent Escherichia coli infection in renal tubular cells enhances calcium oxalate crystal-cell adhesion by inducing ezrin translocation to apical membranes via Rho/ROCK pathway

Recent evidence has suggested that recurrent urinary tract infection (UTI) can cause not only infection stones but also metabolic stones (e.g., those containing calcium oxalate monohydrate or COM). However, precise mechanisms underlying UTI-induced metabolic stones remained unknown. In this study, Escherichia coli, the most common bacterium found in recurrent UTI was used to establish the in vitro model for persistent infection of renal epithelial cells. The promoting effects of persistent E. coli infection on kidney stone formation were validated by COM crystal-cell adhesion assay, followed by immunofluorescence study for changes in surface expression of the known COM crystal receptors. Among the five receptors examined, only ezrin had significantly increased level on the surface of persistently infected cells without change in its total level. Such translocation of ezrin to apical membranes was confirmed by Western blotting of apical membrane and cytosolic fractions and confocal microscopic examination. Additionally, persistent infection increased phosphorylation (Thr567) of ezrin. However, all of these changes induced by persistent E. coli infection were significantly inhibited by small-interfering RNA (siRNA) specific for ezrin or a Rho-associated kinase (ROCK)-specific inhibitor (Y-27632). In summary, this study provides a piece of evidence demonstrating that persistent infection by E. coli, one of the non-urease-producing bacteria, may contribute to COM metabolic stone formation by translocation of ezrin to apical membranes, thereby promoting COM crystal-cell adhesion. Such ezrin translocation was mediated via Rho/ROCK signaling pathway. These findings may, at least in part, explain the pathogenic mechanisms underlying recurrent UTI-induced metabolic kidney stone disease.

Oxidized forms of uromodulin promote calcium oxalate crystallization and growth, but not aggregation

Roles of an abundant human urinary protein, uromodulin (UMOD), in kidney stone disease were previously controversial. Recently, we have demonstrated that oxidative modification reverses overall modulatory activity of whole urinary proteins, from inhibition to promotion of calcium oxalate (CaOx) stone-forming processes. We thus hypothesized that oxidation is one of the factors causing those previously controversial UMOD data on stone modulation. Herein, we addressed effects of performic-induced oxidation on CaOx crystal modulatory activity of UMOD. Sequence analyses revealed two EGF-like calcium-binding domains (65th-107th and 108th-149th), two other calcium-binding motifs (65th-92nd and 108th-135th), and three oxalate-binding motifs (199th-207th, 361st-368th and 601st-609th) in UMOD molecule. Analysis of tandem mass spectrometric dataset of whole urinary proteins confirmed marked increases in oxidation, dioxidation and trioxidation of UMOD in the performic-modified urine samples. UMOD was then purified from the normal urine and underwent performic-induced oxidative modification, which was confirmed by Oxyblotting. The oxidized UMOD significantly promoted CaOx crystallization and crystal growth, whereas the unmodified native UMOD inhibited CaOx crystal growth. However, the oxidized UMOD did not affect CaOx crystal aggregation. Therefore, our data indicate that oxidized forms of UMOD promote CaOx crystallization and crystal growth, which are the important processes for CaOx kidney stone formation.

Trigonelline prevents kidney stone formation processes by inhibiting calcium oxalate crystallization, growth and crystal-cell adhesion, and downregulating crystal receptors

Trigonelline is the second most abundant bioactive alkaloid found in coffee. It is classified as a phytoestrogen with similar structure as of estradiol and exhibits an estrogenic effect. A previous study has reported that fenugreek seed extract rich with trigonelline can reduce renal crystal deposition in ethylene glycol-induced nephrolithiatic rats. However, direct evidence of such anti-lithogenic effects of trigonelline and underlying mechanisms have not previously been reported. Our study therefore addressed the protective effects and mechanisms of trigonelline against kidney stone-forming processes using crystallization, crystal growth, aggregation and crystal-cell adhesion assays. Also, proteomics was applied to identify changes in receptors for calcium oxalate monohydrate (COM), the most common stone-forming crystal, on apical membranes of trigonelline-treated renal tubular cells. The analyses revealed that trigonelline significantly reduced COM crystal size, number and mass during crystallization. Additionally, trigonelline dose-dependently inhibited crystal growth and crystal-cell adhesion, but did not affect crystal aggregation. Mass spectrometric protein identification showed the smaller number of COM crystal receptors on apical membranes of the trigonelline-treated cells. Western blotting confirmed the decreased levels of some of these crystal receptors by trigonelline. These data highlight the protective mechanisms of trigonelline against kidney stone development by inhibiting COM crystallization, crystal growth and crystal-cell adhesion via downregulation of the crystal receptors on apical membranes of renal tubular cells.

Systematic analysis of modulating activities of native human urinary Tamm-Horsfall protein on calcium oxalate crystallization, growth, aggregation, crystal-cell adhesion and invasion through extracellular matrix

Functions of Tamm-Horsfall protein (THP), the most abundant human urinary protein, have been studied for decades. However, its precise roles in kidney stone formation remain controversial. In this study, we aimed to clarify the roles of native human urinary THP in calcium oxalate monohydrate (COM) kidney stone formation. THP was purified from the human urine by adsorption method using diatomaceous earth (DE). Its effects on stone formation processes, including COM crystallization, crystal growth, aggregation, crystal-cell adhesion and invasion through extracellular matrix (ECM), were examined. SDS-PAGE and Western blotting confirmed that DE adsorption yielded 84.9% purity of the native THP isolated from the human urine. Systematic analyses revealed that THP (at 0.4-40 μg/ml) concentration-dependently reduced COM crystal size but did not affect the crystal mass during initial crystallization. At later steps, THP concentration-dependently inhibited COM crystal growth and aggregation, and prevented crystal-cell adhesion only at 40 μg/ml. However, THP did not affect crystal invasion through the ECM. Sequence analysis revealed two large calcium-binding domains (residues 65-107 and 108-149) and three small oxalate-binding domains (residues 199-207, 361-368 and 601-609) in human THP. Immunofluorescence study confirmed the binding of THP to COM crystals. Analyses for calcium-affinity and/or oxalate-affinity demonstrated that THP exerted a high affinity with only calcium, not oxalate. Functional validation revealed that saturation of THP with calcium, not with oxalate, could abolish the inhibitory effects of THP on COM crystal growth, aggregation and crystal-cell adhesion. These data highlight the inhibitory roles of the native human urinary THP in COM crystal growth, aggregation and crystal-cell adhesion, which are the important processes for kidney stone formation. Such inhibitory effects of THP are most likely mediated via its high affinity with calcium ions.

Oxidative Modifications Switch Modulatory Activities of Urinary Proteins From Inhibiting to Promoting Calcium Oxalate Crystallization, Growth, and Aggregation

The incidence/prevalence of kidney stone disease has been increasing around the globe, but its pathogenic mechanisms remained unclear. We evaluated effects of oxidative modifications of urinary proteins on calcium oxalate (CaOx) stone formation processes. Urinary proteins derived from 20 healthy individuals were modified by performic oxidation, and the presence of oxidatively modified urinary proteins was verified, quantified, and characterized by Oxyblot assay and tandem MS (nanoLC-electrospray ionization-linear trap quadrupole-Orbitrap-MS/MS). Subsequently, activities of oxidatively modified urinary proteins on CaOx stone formation processes were examined. Oxyblot assay confirmed the marked increase in protein oxidation level in the modified urine. NanoLC-electrospray ionization-linear trap quadrupole-Orbitrap-MS/MS identified a total of 193 and 220 urinary proteins in nonmodified and modified urine samples, respectively. Among these, there were 1121 and 5297 unambiguous oxidatively modified peptides representing 42 and 136 oxidatively modified proteins in the nonmodified and modified urine samples, respectively. Crystal assays revealed that oxidatively modified urinary proteins significantly promoted CaOx crystallization, crystal growth, and aggregation. By contrast, the nonmodified urinary proteins had inhibitory activities. This is the first direct evidence demonstrating that oxidative modifications of urinary proteins increase the risk of kidney stone disease by switching their modulatory activities from inhibiting to promoting CaOx crystallization, crystal growth, and aggregation.

Effects of secretome derived from macrophages exposed to calcium oxalate crystals on renal fibroblast activation

The association between kidney stone disease and renal fibrosis has been widely explored in recent years but its underlying mechanisms remain far from complete understanding. Using label-free quantitative proteomics (nanoLC-ESI-LTQ-Orbitrap MS/MS), this study identified 23 significantly altered secreted proteins from calcium oxalate monohydrate (COM)-exposed macrophages (COM-MP) compared with control macrophages (Ctrl-MP) secretome. Functional annotation and protein-protein interactions network analysis revealed that these altered secreted proteins were involved mainly in inflammatory response and fibroblast activation. BHK-21 renal fibroblasts treated with COM-MP secretome had more spindle-shaped morphology with greater spindle index. Immunofluorescence study and gelatin zymography revealed increased levels of fibroblast activation markers (α-smooth muscle actin and F-actin) and fibrotic factors (fibronectin and matrix metalloproteinase-9 and -2) in the COM-MP secretome-treated fibroblasts. Our findings indicate that proteins secreted from macrophages exposed to COM crystals induce renal fibroblast activation and may play important roles in renal fibrogenesis in kidney stone disease.

Kidney stone proteomics: an update and perspectives

INTRODUCTION

Main problems of kidney stone disease are its increasing prevalence and high recurrence rate after calculi removal in almost all areas around the globe. Despite enormous efforts in the past, its pathogenic mechanisms remain unclear and need further elucidations. Proteomics has thus become an essential tool to unravel such sophisticated disease mechanisms at cellular, subcellular, molecular, tissue, and whole organism levels.

AREAS COVERED

This review provides abrief overview of kidney stone disease followed by updates on proteomics for investigating urinary stone modulators, matrix proteins, cellular responses to different types/doses of calcium oxalate (CaOx) crystals, sex hormones and other stimuli, crystal-cell interactions, crystal receptors, secretome, and extracellular vesicles (EVs), all of which lead to better understanding of the disease mechanisms. Finally, the future challenges and translation of these obtained data to the clinic are discussed.

EXPERT OPINION

Knowledge from urinary proteomics for exploring the important stone modulators (either inhibitors or promoters) will be helpful for early detection of asymptomatic cases for prompt prevention of symptoms, complications, and new stone formation. Moreover, these modulators may serve as the new therapeutic targets in the future for successful treatment and prevention of kidney stone disease by medications or other means of intervention.

Caffeine prevents oxalate-induced epithelial-mesenchymal transition of renal tubular cells by its anti-oxidative property through activation of Nrf2 signaling and suppression of Snail1 transcription factor

Caffeine is an active ingredient found in coffee and energy beverages. Its hepatoprotective effects against liver fibrosis are well-documented. Nonetheless, its renoprotective effects against renal fibrogenesis and epithelial-mesenchymal transition (EMT) processes remain unclear and under-investigated. In this study, the protective effects of caffeine against oxalate-induced EMT in renal tubular cells were evaluated by various assays to measure expression levels of epithelial and mesenchymal markers, cell migrating activity, level of oxidized proteins, and expression of Nrf2 and Snail1. Oxalate at sublethal dose significantly suppressed cell proliferation but increased cell elongation, spindle index and migration. Oxalate also decreased expression of epithelial markers (zonula occludens-1 (ZO-1) and E-cadherin) but increased expression of mesenchymal markers (fibronectin, vimentin and α-smooth muscle actin (α-SMA)). All of these EMT-inducing effects of oxalate could be prevented by pretreatment with caffeine. While oxalate increased oxidized proteins and Snail1 levels, it decreased Nrf2 expression. Caffeine could preserve all these molecules to their basal (control) levels. Finally, silencing of Nrf2 expression by small interfering RNA (siRNA) could abolish such protective effects of caffeine on oxalate-induced EMT. Our data indicate that the renoprotective effects of caffeine against oxalate-induced EMT is mediated, at least in part, by its anti-oxidative property through activation of Nrf2 signaling and suppression of Snail1 transcription factor.

Recent advances on the mechanisms of kidney stone formation (Review)

Kidney stone disease is one of the oldest diseases known to medicine; however, the mechanisms of stone formation and development remain largely unclear. Over the past decades, a variety of theories and strategies have been developed and utilized in the surgical management of kidney stones, as a result of recent technological advances. Observations from the authors and other research groups suggest that there are five entirely different main mechanisms for kidney stone formation. Urinary supersaturation and crystallization are the driving force for intrarenal crystal precipitation. Randall's plaques are recognized as the origin of calcium oxalate stone formation. Sex hormones may be key players in the development of nephrolithiasis and may thus be potential targets for new drugs to suppress kidney stone formation. The microbiome, including urease-producing bacteria, nanobacteria and intestinal microbiota, is likely to have a profound effect on urological health, both positive and negative, owing to its metabolic output and other contributions. Lastly, the immune response, and particularly macrophage differentiation, play crucial roles in renal calcium oxalate crystal formation. In the present study, the current knowledge for each of these five aspects of kidney stone formation is reviewed. This knowledge may be used to explore novel research opportunities and improve the understanding of the initiation and development of kidney stones for urologists, nephrologists and primary care.

Controversies in Testosterone Therapy

INTRODUCTION

Testosterone prescriptions have increased dramatically in recent years, largely because of changes in expert guidelines. Concerns have been raised that testosterone therapy (TTh) may be associated with an increased incidence of conditions such as cardiovascular (CV) disease, thromboembolic events, obstructive sleep apnea (OSA), benign prostatic hyperplasia (BPH), and prostate cancer (PCa) and also may be a beneficial therapy in the management of prediabetes. As such, considerable debate remains regarding which hypogonadal populations are appropriate candidates for TTh.

OBJECTIVES

This systematic review aims to affirm or refute, using the most current evidence, the published concerns surrounding TTh and its potential increased risk of conditions such as CV disease, thromboembolic events, OSA, urolithiasis, BPH, and PCa, as well as its role as a potential tool for managing prediabetes.

METHODS

A systematic review of literature surrounding TTh and its impact on increasing risk for the adverse conditions mentioned previously was performed. 62 publications were selected for inclusion based on their relevance to the effects and risks of TTh. Evidence is current through December 2019.

RESULTS

Evidence demonstrates that positive associations exist between TTh and OSA, erythrocytosis, as well as urolithiasis. TTh may potentially be used to treat hypogonadal men with prediabetes. While low testosterone is positively correlated with adverse CV events, TTh in hypogonadal men either has no effect or decreases such risk. TTh is likely not associated with increased risk of PCa incidence or recurrence.

CONCLUSIONS

Despite historical beliefs that TTh increases the risk of CV disease, thromboembolic events, BPH, and PCa, recent evidence suggests that TTh conveys less risk than previously perceived. While caution should continue to be exercised, evidence suggests that TTh is a reasonable treatment option in many hypogonadal men who were previously excluded from TTh based on risk factors and prior health histories. Twitchell DK, Pastuszak AW, Khera M. Controversies in Testosterone Therapy. Sex Med Rev 2021;9:149-159.

Differential bound proteins and adhesive capabilities of calcium oxalate monohydrate crystals with various sizes

Adhesion of calcium oxalate (CaOx) crystals onto renal tubular epithelial cells is one of the critical steps in kidney stone formation. However, effects of crystal size on the crystal adhesive capability remained unclear. This study compared the adhesive capabilities of CaOx monohydrate (COM) crystals with various sizes (<10 μm, 20-30 μm, 50-60 μm, and > 80 μm). Crystal-cell adhesion assay showed size-dependent increase of COM crystal adhesion onto epithelial cell surface using the larger crystals. Identification of apical membrane proteins that could bind to COM crystals by tandem mass spectrometry (nanoLC-ESI-ETD MS/MS) demonstrated size-specific sets of the COM crystal-binding proteins. Among these, numbers of known oxalate-binding proteins and COM crystal receptors were greatest in the set of the largest size (>80 μm). Atomic force microscopy (AFM) revealed that adhesive forces between carboxylic-immobilized AFM tip and COM crystal surface and between COM-mounted AFM tip and renal epithelial cell surface were size-dependent (greater for the larger crystals). In summary, the adhesive capability of COM crystals is size-dependent - the larger the greater adhesive capability. These data may help better understanding of the pathogenic mechanisms of kidney stone formation at an initial stage when renal tubular cells are exposed to various sizes of COM crystals.