Balkan endemic nephropathy: an update on its aetiology

The Impact of p53 on Aristolochic Acid I-Induced Gene Expression In Vivo

Exposure to aristolochic acid (AA) is linked to kidney disease and urothelial cancer in humans. The major carcinogenic component of the AA plant extract is aristolochic acid I (AAI). The tumour suppressor p53 is frequently mutated in AA-induced tumours. We previously showed that p53 protects from AAI-induced renal proximal tubular injury, but the underlying mechanism(s) involved remain to be further explored. In the present study, we investigated the impact of p53 on AAI-induced gene expression by treating Trp53(+/+), Trp53(+/-), and Trp53(-/-) mice with 3.5 mg/kg body weight (bw) AAI daily for six days. The Clariom™ S Assay microarray was used to elucidate gene expression profiles in mouse kidneys after AAI treatment. Analyses in Qlucore Omics Explorer showed that gene expression in AAI-exposed kidneys is treatment-dependent. However, gene expression profiles did not segregate in a clear-cut manner according to Trp53 genotype, hence further investigations were performed by pathway analysis with MetaCore™. Several pathways were significantly altered to varying degrees for AAI-exposed kidneys. Apoptotic pathways were modulated in Trp53(+/+) kidneys; whereas oncogenic and pro-survival pathways were significantly altered for Trp53(+/-) and Trp53(-/-) kidneys, respectively. Alterations of biological processes by AAI in mouse kidneys could explain the mechanisms by which p53 protects from or p53 loss drives AAI-induced renal injury in vivo.

Prevalence, clinicopathological features, and prognosis in upper tract urinary carcinoma patients with severe preoperative chronic kidney disease

BACKGROUND

Studies regarding the prevalence and factors associated with severe pre-operative chronic kidney disease (CKD) in upper tract urinary carcinoma (UTUC) patients were rare due to the low prevalence of UTUC. We conducted the present study to investigate the prevalence, clinicopathological features, and prognosis in UTUC patients with severe preoperative CKD.

METHODS

The study included 731 patients with UTUC treated with radical nephroureterectomy (RNU) in a large Chinese center. Estimated glomerular filtration rate (eGFR) was calculated by re-expressed Modification of Diet in Renal Disease (MDRD) formulas for the Chinese population. Severe preoperative CKD was defined as CKD stage 4-5 (eGFR <30 mL/min). Relationships of CKD stage 4-5 with clinicopathological characteristics, overall survival (OS), cancer-specific survival (CSS), contralateral recurrence-free survival and intravesical recurrence (IVR)-free survival were analyzed.

RESULTS

A total of 73 (10.0%) patients presented severe preoperative CKD in this cohort. Multivariate logistic analysis indicated that female gender (OR =1.791; 95% CI: 1.018-3.150; P=0.043), lower BMI (OR =0.452; 95% CI: 0.262-0.778; P=0.004), concomitant bladder tumor (OR =2.944; 95% CI: 1.360-6.373; P=0.006), lower pathological T stage (OR =0.578; 95% CI: 0.339-0.984; P=0.043), tumor necrosis (OR =2.764; 95% CI: 1.411-5.416; P=0.003), and exposure of aristolochic acid (AA) (OR =3.115; 95% CI: 1.536-6.316; P=0.002) were significantly related to severe CKD. Multivariate Cox's regression analysis showed that severe preoperative CKD was significantly associated with worse OS (HR =1.840; 95% CI: 1.150-2.944; P=0.011) and worse contralateral recurrence-free survival (HR =3.269; 95% CI: 1.607-6.650; P=0.001), while no statistical difference in terms of CSS or IVR-free survival were noticed.

CONCLUSIONS

Female gender, lower BMI, concomitant bladder tumor, lower pathological T stage, exposure of AA, and tumor necrosis were independently associated with severe preoperative CKD in UTUC patients. UTUC patients with severe preoperative CKD possess worse OS and higher possibility of contralateral upper urinary tract recurrence.

Characterising Mutational Spectra of Carcinogens in the Tumour Suppressor Gene TP53 Using Human TP53 Knock-in (Hupki) Mouse Embryo Fibroblasts

DNA in dividing cells is prone to mutagenesis, with mutations making key contributions to human disease including cancer. The tumour suppressor gene TP53 is the most frequently mutated gene in human tumours. Here, we present a robust protocol for studying TP53 mutagenesis utilising human TP53 knock-in (Hupki) mouse embryonic fibroblasts (HUFs). In the HUF immortalisation assay (HIMA), primary HUFs are treated with known or suspected carcinogens at 3% oxygen and then transferred to 20% atmospheric oxygen to induce senescence. Cells containing mutations (e.g., in TP53) that allow bypassing of senescence eventually emerge as immortalised clonal cell lines after 2-3 months of serial passaging. As not all immortalised HUF cells contain TP53 mutations, we developed a Nutlin-3a counter-screen to select for TP53-mutated clones prior to sequencing. TP53 mutation spectra generated can be compared with those of human tumours recorded in the International Agency for Research on Cancer TP53 mutation database. Environmental mutagens that have demonstrated and validated the utility of the HIMA include ultraviolet radiation, aristolochic acid, and benzo[a]pyrene. The TP53 mutation patterns induced by these mutagens in the HIMA corresponded to those found in human tumours from patients exposed to these mutagens. The approach presented helps to deepen our understanding of human cancer aetiology.

Prognostic Significance of Murine Double Minute 2 Expression in Tumor Cells in Upper Tract Urothelial Carcinoma: An Analysis of 341 Cases in a Large Chinese Center

Aims: The prognostic significance of murine double minute 2 (MDM2) expression remains unknown in patients with upper tract urothelial carcinoma (UTUC). This study was designed to evaluate MDM2 expression and its association with clinicopathological characteristics and tumor outcomes in UTUC patients. Materials and Methods: Expression levels of MDM2 and p53 were determined by immunohistochemistry in a cohort of 341 UTUC patients. Associations of MDM2 and p53 expression levels with clinicopathological characteristics, disease-free survival (DFS), cancer-specific survival (CSS), and intravesical recurrence-free survival (IVRFS) were analyzed. Results: Nuclear expression of MDM2 and p53 were detected in the tumor cells of 129 (37.8%) and 203 (59.5%) patients, respectively. Decreased p53 expression was associated with positive MDM2 staining in tumor cells (p = 0.002). MDM2 expression was correlated with the exposure to aristolochic acids (p = 0.020), better preoperative renal function (p = 0.016), ureter location (p = 0.002), higher pathological T stage (p = 0.006), high tumor grade (p < 0.001), presence of glandular differentiation (p = 0.036), and sarcoma differentiation (p = 0.020). Kaplan-Meier analysis showed that positive MDM2 staining was associated with shorter CSS (p < 0.001), DFS (p < 0.001), and IVRFS (p = 0.020); MDM2+/p53- was associated with shorter CSS (p < 0.001) and DFS (p < 0.001), but not IVRFS (p = 0.145); while CSS, DFS, and IVRFS did not differ significantly between the p53+ and p53- patients (p = 0.307, 0.089, and 0.198, respectively). Multivariate analyses revealed that MDM2 expression in tumor cells independently predicted shorter CSS (p < 0.001; hazard ratio [HR] = 2.600; 95% confidence interval [CI]: 1.625-4.161) and DFS (p < 0.001; HR = 1.863; 95% CI: 1.314-2.641), excepting IVRFS (p = 0.092; HR = 1.590; 95% CI: 0.928-2.726). Conclusions: UTUC patients with elevated MDM2 expression may exhibit more aggressive biological features of the tumor and tend to have shorter CSS and DFS.

Analyses of biomarkers of exposure to nephrotoxic mycotoxins in a cohort of patients with renal tumours

The Czech Republic occupies the first place in the world in the frequency of renal and other urinary tract tumours, but their aetiology is unknown. To explore whether carcinogenic and nephrotoxic mycotoxins may contribute to kidney diseases in the Czech population, biomarkers of ochratoxin A (OTA) and citrinin (CIT) exposure were determined in biological specimens from a cohort of 50 patients with malignant renal tumours. Biomarker analyses in blood and urine samples used validated targeted methods for measuring OTA and CIT plus dihydrocitrinone (DH-CIT) after enrichment of analytes by specific immunoaffinity clean-up. OTA and CIT plus its metabolite DH-CIT were frequently detected in patient urine samples (OTA 62%; CIT 91%; DH-CIT 100%). The concentration ranges in urine were 1-27.8 ng/L for OTA, 2-87 ng/L for CIT and 2-160 ng/L for DH-CIT. The analyses of blood samples revealed also a frequent co-occurrence of OTA and CIT, in the ranges of 40-870 ng/L serum for OTA and 21-182 ng/L plasma for CIT. This first analysis of biomarkers in blood and urine samples of Czech patients revealed no major differences in comparison with published data for the general healthy Czech and European populations. Nonetheless, a frequent co-occurrence of CIT and OTA biomarkers in patient samples may be of interest with regard to potential interactions with other risk factors for renal disease.

The impact of p53 on aristolochic acid I-induced nephrotoxicity and DNA damage in vivo and in vitro

Exposure to aristolochic acid (AA) is associated with human nephropathy and urothelial cancer. The tumour suppressor TP53 is a critical gene in carcinogenesis and frequently mutated in AA-induced urothelial tumours. We investigated the impact of p53 on AAI-induced nephrotoxicity and DNA damage in vivo by treating Trp53(+/+), Trp53(+/-) and Trp53(-/-) mice with 3.5 mg/kg body weight (bw) AAI daily for 2 or 6 days. Renal histopathology showed a gradient of intensity in proximal tubular injury from Trp53(+/+) to Trp53(-/-) mice, especially after 6 days. The observed renal injury was supported by nuclear magnetic resonance (NMR)-based metabonomic measurements, where a consistent Trp53 genotype-dependent trend was observed for urinary metabolites that indicate aminoaciduria (i.e. alanine), lactic aciduria (i.e. lactate) and glycosuria (i.e. glucose). However, Trp53 genotype had no impact on AAI-DNA adduct levels, as measured by 32P-postlabelling, in either target (kidney and bladder) or non-target (liver) tissues, indicating that the underlying mechanisms of p53-related AAI-induced nephrotoxicity cannot be explained by differences in AAI genotoxicity. Performing gas chromatography-mass spectrometry (GC-MS) on kidney tissues showed metabolic pathways affected by AAI treatment, but again Trp53 status did not clearly impact on such metabolic profiles. We also cultured primary mouse embryonic fibroblasts (MEFs) derived from Trp53(+/+), Trp53(+/-) and Trp53(-/-) mice and exposed them to AAI in vitro (50 µM for up to 48 h). We found that Trp53 genotype impacted on the expression of NAD(P)H:quinone oxidoreductase (Nqo1), a key enzyme involved in AAI bioactivation. Nqo1 induction was highest in Trp53(+/+) MEFs and lowest in Trp53(-/-) MEFs; and it correlated with AAI-DNA adduct formation, with lowest adduct levels being observed in AAI-exposed Trp53(-/-) MEFs. Overall, our results clearly demonstrate that p53 status impacts on AAI-induced renal injury, but the underlying mechanism(s) involved remain to be further explored. Despite the impact of p53 on AAI bioactivation and DNA damage in vitro, such effects were not observed in vivo.

Geographic distribution and risk of upper urothelial carcinomas in Croatia, 2001-2011

BACKGROUND

Strong associations exist between Balkan endemic nephropathy (BEN) and upper urothelial carcinomas (UUCs). However, the common etiology between the two remains unclear and there are no studies to date that visualize UUC risks in Croatia. In Croatia, 14 villages in the southwestern part of Brod-Posavina County are considered endemic for BEN. The aim of this ecological study is to map cancer risks and describe the case distribution of UUCs in Croatia at the county level during 2001-2011.

METHODS

A total of 608 incident cases from the Croatian National Cancer Registry were identified. Indirect standardization was employed to compute standardized incidence ratios (SIRs).

RESULTS

Counties with SIRs greater than 1 were concentrated around the agricultural region of Slavonia and the coastal region of Dalmatia. However, only Brod-Posavina County and Vukovar-Srijem County had a statistically significant risk of UUC development, where there were 390 and 210% more UUC cases observed than expected, respectively. Only unique to Brod-Posavina County, females were at higher risk (SIR 4.96; 95% CI 3.59-6.34) of developing UUCs than males (SIR 3.03; 95% CI 2.04-4.01) when compared to their Croatian counterparts. Although Brod-Posavina County only made up 3.7% of the total Croatian population (as of 2011), it had the highest frequency of incident UUC cases after the capital City of Zagreb. No elevated cancer risks were noted in the City of Zagreb, even after stratifying by sex.

CONCLUSION

Our findings suggest that Brod-Posavina County had the highest cancer risk for UUCs, especially among females, when compared to Croatia as a whole during 2001-2011. Given that a majority of BEN patients develop associated UUCs, concurrent screening programs for UUCs and BEN should be considered not only in endemic areas of BEN but also the surrounding rural areas and amongst at-risk groups such as those undergoing hemodialysis, who frequently develop UUCs, to help clarify BEN-UUC associations by identifying common risk factors while standardizing disease estimates across endemic regions for BEN.

The incidence, prevalence and trends of Chronic Kidney Disease and Chronic Kidney Disease of uncertain aetiology (CKDu) in the North Central Province of Sri Lanka: an analysis of 30,566 patients

Background

Chronic Kidney Disease (CKD) of uncertain origin (CKDu) has affected North Central Province (Anuradhapura and Polonnaruwa districts) of Sri Lanka. The cause is still unknown. The objective of this study was to describe the incidence, prevalence and trend of CKD/CKDu in North Central Province of Sri Lanka.

Methods

A cross sectional survey conducted in North Central Province with GPS mapping in CKDu highly affected areas. The diagnosis of CKD and staging were made according to the Kidney Disease: Improving Global Outcomes paper.

Descriptive statistics used with chi-square test for evaluating dichotomous variables. Log rank test was used to compare survival rates. The population data was obtained from the 2011 Census.

Results

There were 30,566 CKD/CKDu patients in the North Central Province. Incidence of 0.10 in 2009, 0.39 in 2016 in Anuradhapura district, decreased slightly to 0.29 in 2017. Incidence of 0.09 in 2009, 0.46 in 2016 in Polonnaruwa district, decreased slightly to 0.41 in 2017.

The point prevalence in high incidence areas ranged from 2.44–4.35. The 5 year survival rate was 71.2 (Anuradhapura 72.4 and Polonnaruwa 68.3, p = 0.0212).

More than 70, 40 and 33% of patients were over 50, 60 and 70 years of age respectively. A male preponderance was seen in all the divisional areas (ranging from 1.3:1 to 2.6:1) and in all the age groups. Farmers were the most affected (70.6% Anuradhapura district and 65.1% Polonnaruwa district). Majority in CKD stage I (4943, 69.6%).

There were 1685 deaths (17.5% of total CKD/CKDu patients, 67.6% of total deaths in CKD/CKDu patients) occurring within the first 3 years of diagnosis.

GPS mapping shows that there is a clustering of households with CKD/CKDu.

Conclusions

The incidence of CKD/CKDu increased up to 2016 with a slight decrease in 2017. The most vulnerable age group was 40 to 60 years. There is a male preponderance. Farmers at a higher risk. Majority were in CKD stage 1. More than two thirds of the deaths of CKD/CKDu patients occurred within three years of diagnosis with disparities in 5 year survival rate among the two districts. There is clustering of cases.

The incidence, prevalence and trends of Chronic Kidney Disease and Chronic Kidney Disease of uncertain aetiology (CKDu) in the North Central Province of Sri Lanka: an analysis of 30,566 patients

BACKGROUND

Chronic Kidney Disease (CKD) of uncertain origin (CKDu) has affected North Central Province (Anuradhapura and Polonnaruwa districts) of Sri Lanka. The cause is still unknown. The objective of this study was to describe the incidence, prevalence and trend of CKD/CKDu in North Central Province of Sri Lanka.

METHODS

A cross sectional survey conducted in North Central Province with GPS mapping in CKDu highly affected areas. The diagnosis of CKD and staging were made according to the Kidney Disease: Improving Global Outcomes paper. Descriptive statistics used with chi-square test for evaluating dichotomous variables. Log rank test was used to compare survival rates. The population data was obtained from the 2011 Census.

RESULTS

There were 30,566 CKD/CKDu patients in the North Central Province. Incidence of 0.10 in 2009, 0.39 in 2016 in Anuradhapura district, decreased slightly to 0.29 in 2017. Incidence of 0.09 in 2009, 0.46 in 2016 in Polonnaruwa district, decreased slightly to 0.41 in 2017. The point prevalence in high incidence areas ranged from 2.44-4.35. The 5 year survival rate was 71.2 (Anuradhapura 72.4 and Polonnaruwa 68.3, p = 0.0212). More than 70, 40 and 33% of patients were over 50, 60 and 70 years of age respectively. A male preponderance was seen in all the divisional areas (ranging from 1.3:1 to 2.6:1) and in all the age groups. Farmers were the most affected (70.6% Anuradhapura district and 65.1% Polonnaruwa district). Majority in CKD stage I (4943, 69.6%). There were 1685 deaths (17.5% of total CKD/CKDu patients, 67.6% of total deaths in CKD/CKDu patients) occurring within the first 3 years of diagnosis. GPS mapping shows that there is a clustering of households with CKD/CKDu.

CONCLUSIONS

The incidence of CKD/CKDu increased up to 2016 with a slight decrease in 2017. The most vulnerable age group was 40 to 60 years. There is a male preponderance. Farmers at a higher risk. Majority were in CKD stage 1. More than two thirds of the deaths of CKD/CKDu patients occurred within three years of diagnosis with disparities in 5 year survival rate among the two districts. There is clustering of cases.

Association of SOD2 (rs4880) and GPX1 (rs1050450) Gene Polymorphisms with Risk of Balkan Endemic Nephropathy and its Related Tumors

Background: Experimental data show that superoxide dismutase 2 (SOD2) is involved in ochratoxin (OTA)-induced nephrotoxicity, whereas clinical data indicate the role of SOD2 rs4880 or glutathione peroxidase 1 (GPX1) rs1050450 polymorphisms in end-stage renal disease and urothelial carcinoma risk, known to be the major complications of Balkan endemic nephropathy (BEN). Therefore, we hypothesized that SOD2 and GPX1 gene polymorphisms would influence the risk of BEN and its associated tumors. Materials and Methods: The study was conducted in 207 BEN patients and 86 controls from endemic areas. Results: Individuals with both copies of variant SOD2 allele, known for lower mitochondrial antioxidant protection, are at a significantly higher BEN risk (OR = 2.6, p = 0.021). No association was observed between GPX1 gene polymorphism and BEN risk. Combining SOD2 and GPX1 genotypes did not alter the risk of BEN development. Regarding the risk of urothelial tumors in BEN patients, none of the polymorphisms studied was significantly associated with the risk of these tumors. Conclusions: Polymorphism in SOD2 rs4880 gene affects the risk of BEN development. Hence, SOD2 genotyping could, together with a panel of other enzymes, be used as a biomarker of susceptibility in BEN areas.

Genes and environment in chronic kidney disease hotspots

PURPOSE OF REVIEW

Chronic kidney disease (CKD) can cluster in geographic locations or in people of particular genetic ancestries. We explore APOL1 nephropathy and Balkan nephropathy as examples of CKD clustering that illustrate genetics and environment conspiring to cause high rates of kidney disease. Unexplained hotspots of kidney disease in Asia and Central America are then considered from the perspective of potential gene × environment interactions.

RECENT FINDINGS

We report on evidence supporting both genes and environment in these CKD hotspots. Differing genetic susceptibility between populations and within populations may explain why causal environmental risk factors have been so hard to identify conclusively. Similarly, one cannot explain why these epidemics of kidney disease are happening now without invoking environmental changes.

SUMMARY

Approaches to these CKD hotspots are of necessity becoming more holistic. Genetic studies may help us identify the environmental triggers by teaching us about disease biology and may empower environmental risk factor studies by allowing for stratification of study participants by genetic susceptibility.

The SLC22 Transporter Family: A Paradigm for the Impact of Drug Transporters on Metabolic Pathways, Signaling, and Disease

The SLC22 transporter family consists of more than two dozen members, which are expressed in the kidney, the liver, and other tissues. Evolutionary analysis indicates that SLC22 transporters fall into at least six subfamilies: OAT (organic anion transporter), OAT-like, OAT-related, OCT (organic cation transporter), OCTN (organic cation/carnitine transporter), and OCT/OCTN-related. Some-including OAT1 [SLC22A6 or NKT (novel kidney transporter)] and OAT3 (SLC22A8), as well as OCT1 (SLC22A1) and OCT2 (SLC22A2)-are widely studied drug transporters. Nevertheless, analyses of knockout mice and other data indicate that SLC22 transporters regulate key metabolic pathways and levels of signaling molecules (e.g., gut microbiome products, bile acids, tricarboxylic acid cycle intermediates, dietary flavonoids and other nutrients, prostaglandins, vitamins, short-chain fatty acids, urate, and ergothioneine), as well as uremic toxins associated with chronic kidney disease. Certain SLC22 transporters-such as URAT1 (SLC22A12) and OCTN2 (SLC22A5)-are mutated in inherited metabolic diseases. A new systems biology view of transporters is emerging. As proposed in the remote sensing and signaling hypothesis, SLC22 transporters, together with other SLC and ABC transporters, have key roles in interorgan and interorganism small-molecule communication and, together with the neuroendocrine, growth factor-cytokine, and other homeostatic systems, regulate local and whole-body homeostasis.

Systematic Overview of Aristolochic Acids: Nephrotoxicity, Carcinogenicity, and Underlying Mechanisms

Aristolochic acids (AAs) are a group of toxins commonly present in the plants of genus Aristolochia and Asarum, which are spread all over the world. Since the 1990s, AA-induced nephropathy (AAN) and upper tract urothelial carcinoma (UTUC) have been reported in many countries. The underlying mechanisms of AAN and AA-induced UTUC have been extensively investigated. AA-derived DNA adducts are recognized as specific biomarkers of AA exposure, and a mutational signature predominantly characterized by A→T transversions has been detected in AA-induced UTUC tumor tissues. In addition, various enzymes and organic anion transporters are involved in AA-induced adverse reactions. The progressive lesions and mutational events initiated by AAs are irreversible, and no effective therapeutic regimen for AAN and AA-induced UTUC has been established until now. Because of several warnings on the toxic effects of AAs by the US Food and Drug Administration and the regulatory authorities of some other countries, the sale and use of AA-containing products have been banned or restricted in most countries. However, AA-related adverse events still occur, especially in the Asian and Balkan regions. Therefore, the use of AA-containing herbal remedies and the consumption of food contaminated by AAs still carry high risk. More strict precautions should be taken to protect the public from AA exposure.

A Compendium of Mutational Signatures of Environmental Agents

Whole-genome-sequencing (WGS) of human tumors has revealed distinct mutation patterns that hint at the causative origins of cancer. We examined mutational signatures in 324 WGS human-induced pluripotent stem cells exposed to 79 known or suspected environmental carcinogens. Forty-one yielded characteristic substitution mutational signatures. Some were similar to signatures found in human tumors. Additionally, six agents produced double-substitution signatures and eight produced indel signatures. Investigating mutation asymmetries across genome topography revealed fully functional mismatch and transcription-coupled repair pathways. DNA damage induced by environmental mutagens can be resolved by disparate repair and/or replicative pathways, resulting in an assortment of signature outcomes even for a single agent. This compendium of experimentally induced mutational signatures permits further exploration of roles of environmental agents in cancer etiology and underscores how human stem cell DNA is directly vulnerable to environmental agents. VIDEO ABSTRACT.

Geochemical characterization and renal cell toxicity of water-soluble extracts from U.S. Gulf Coast lignite

An assortment of organic material can leach from lignite (low-rank coal) in water, and the water-soluble fraction from lignite has been associated with adverse health effects in areas of the Balkans. Recent efforts have been made to evaluate this hypothesis in other areas where lignite is in contact with groundwater like in the U.S. Gulf Coast region. In this study, five Gulf Coast lignite samples were extracted with water, and the water-soluble portion of the coal was then characterized by total organic carbon, UV-Vis spectroscopy, and gas chromatography/mass spectrometry. Additionally, human kidney cells (HK-2) were exposed to water-soluble extracts of Gulf Coast lignite to assess toxicity. Cell viability was measured, and a dose-response curve was used to generate IC₅₀ values that ranged from 490 to 3000 ppm. The most toxic extract (Dolet Hills) was from Louisiana where lignite-derived organic material has been previously linked to high incidence of renal pelvic cancer. Concentrations of nephrotoxic metals (As, Cd, Co, Cu, Hg, Pb, V, Zn) were screened and were below those considered toxic to renal cells. We conclude that leachates from lignite do indeed have toxic affects on cultured human renal cells. Although the IC₅₀ values are higher than the concentration of organic matter in the local groundwater, typically < 5 ppm, the effects of long-term low-level exposure is not known.

Air pollution and kidney disease: review of current evidence

Along with amazing technological advances, the industrial revolution of the mid-19th century introduced new sources of pollution. By the mid-20th century, the effects of these changes were beginning to be felt around the world. Among these changes, health problems due to environmental air pollution are increasingly recognized. At the beginning, respiratory and cardiovascular diseases were emphasized. However, accumulated data indicate that every organ system in the body may be involved, and the kidney is no exception. Although research on air pollution and kidney damage is recent, there is now scientific evidence that air pollution harms the kidney. In this holistic review, we have summarized the epidemiology, disease states and mechanisms of air pollution and kidney damage.

The impact of p53 function on the metabolic activation of the carcinogenic air pollutant 3-nitrobenzanthrone and its metabolites 3-aminobenzanthrone and N-hydroxy-3-aminobenzanthrone in human cells

The tumour suppressor p53, encoded by TP53, is a key player in a wide network of signalling pathways. We investigated its role in the bioactivation of the environmental carcinogen 3-nitrobenzanthrone (3-NBA)found in diesel exhaust and its metabolites 3-aminobenzanthrone (3-ABA) and N-hydroxy-3-aminobenzanthrone (N-OH-3-ABA) in a panel of isogenic human colorectal HCT116 cells differing only with respect to their TP53 status [i.e. TP53(+/+), TP53(+/-), TP53(-/-), TP53(R248W/+) or TP53(R248W/-)]. As a measure of metabolic competence, DNA adduct formation was determined using 32P-postlabelling. Wild-type (WT) p53 did not affect the bioactivation of 3-NBA; no difference in DNA adduct formation was observed in TP53(+/+), TP53(+/-) and TP53(-/-) cells. Bioactivation of both metabolites 3-ABA and N-OH-3-ABA on the other hand was WT-TP53 dependent. Lower 3-ABA- and N-OH-3-ABA-DNA adduct levels were found in TP53(+/-) and TP53(-/-) cells compared to TP53(+/+) cells, and p53's impact was attributed to differences in cytochrome P450 (CYP) 1A1 expression for 3-ABA whereas for N-OH-3-ABA, an impact of this tumour suppressor on sulphotransferase (SULT) 1A1/3 expression was detected. Mutant R248W-p53 protein function was similar to or exceeded the ability of WT-p53 in activating 3-NBA and its metabolites, measured as DNA adducts. However, identification of the xenobiotic-metabolising enzyme(s) (XMEs), through which mutant-p53 regulates these responses, proved difficult to decipher. For example, although both mutant cell lines exhibited higher CYP1A1 induction after 3-NBA treatment compared to TP53(+/+) cells, 3-NBA-derived DNA adduct levels were only higher in TP53(R248W/-) cells but not in TP53(R248W/+) cells. Our results show that p53's influence on carcinogen activation depends on the agent studied and thereby on the XMEs that mediate the bioactivation of that particular compound. The phenomenon of p53 regulating CYP1A1 expression in human cells is consistent with other recent findings; however, this is the first study highlighting the impact of p53 on sulphotransferase-mediated (i.e. SULT1A1) carcinogen metabolism in human cells.

Balkan endemic nephropathy and aristolochic acid I: an investigation into the role of soil and soil organic matter contamination, as a potential natural exposure pathway

Aristolochic acids (AAs) are carcinogenic and nephrotoxic plant alkaloids present in Aristolochia species, used in traditional medicine. Recent biomolecular and environmental studies have incriminated these toxins as an etiological agent in Balkan endemic nephropathy (BEN), a severe kidney disease occurring in the Balkan Peninsula. The questions on how the susceptible populations are exposed to these toxins have not yet been clearly answered. Exposure to AAs through the food chain, and environmental pollution (soil/dust), could provide an explanation for the presence of BEN in the countries where no folkloric use of the plant has been documented (Bulgaria, Croatia). Additional exposure pathways are likely to occur, and we have shown previously that AAs can contaminate crop plants through absorption from soil, under controlled laboratory environment. Here, we attempt to provide additional support to this potential exposure pathway, by revealing the presence of AAI in soil and soil organic matter samples collected from BEN and non-BEN areas. The samples were processed in order to be analyzed by high-pressure liquid chromatography, and ion trap mass spectrometry. Our results showed the presence of AAI in small concentrations, both in BEN and non-BEN soils, especially where Aristolochia plants and seeds were present.

ESRD and ESRD-DM associated with lignite-containing aquifers in the U.S. Gulf Coast region of Arkansas, Louisiana, and Texas

Balkan endemic nephropathy (BEN) is an irreversible, lethal kidney disease that occurs in regions of the Balkans where residents drink untreated well water. A key factor contributing to the development of BEN may be consumption of dissolved organic matter leached from low-rank coal called lignite. This hypothesis-known as lignite-water hypothesis-was first posed for areas of the Balkans. It is possible that a BEN-like condition exists in the United States (US) Gulf Coast region in parts of the Mississippi Embayment and the Texas Coastal Uplands aquifers -Arkansas, Louisiana, and Texas, for instance-that rely heavily on groundwater from aquifers that contain lignite. This study utilizes a geographic information system (GIS) to map the distributions of end-stage renal disease (ESRD) in relation to water from lignite-containing aquifers in the tri-state region. Regional patterns emerged from geospatial analysis, suggesting that counties that relied on lignite-containing aquifers for their main water source had higher rates of ESRD in comparison to other populations in the region that rely on other water sources, including surface water and groundwater from aquifers not associated with lignite seams. Statewide rates of ESRD and diabetes associated ESRD (ESRD-DM) showed strong correlations to the percent of families at or below poverty level and the percentage of African Americans. These confounding factors somewhat mitigate the association seen between ESRD and lignite-containing regions at the state level. However, at the larger tri-state view, there is a significant (p = 0.002) increase in incidence rates where groundwater is connected to lignite-containing aquifers when considering both race and poverty. Additionally, no relationship was observed between the rate of public water supply withdrawal from lignite-bearing aquifers and rates of ESRD or ESRD-DM at the state or tri-state regions, supporting the observation that the risk associated with water from lignite-containing aquifers is limited to water from untreated domestic supply.

Cooking methods employing natural anti-oxidant food additives effectively reduced concentration of nephrotoxic and carcinogenic aristolochic acids in contaminated food grains

Emerging evidence suggests that aristolochic acids (AA) produced naturally by a common weed Aristolochia clematitis in the cultivation fields is contaminating the food products in Balkan Peninsula and acting as the etiological agent in the development of Balkan endemic nephropathy. In this study, we investigated the combined use of natural anti-oxidative "food additives" and different cooking methods to find a solution for the widespread contamination of AA in food products. The results indicated that the addition of healthy dietary supplements (such as cysteine, glutathione, ascorbic acid, citric acid and magnesium) during cooking, is a highly efficient method in lowering the concentration of AA in the final food products. Because previous observation indicated one of the toxicological mechanisms by which AA exert its toxicity is to induce oxidative stress in internal organs, it is anticipated that these added anti-oxidants will also help to attenuate the nephrotoxicity of AA.

Carcinogens that induce the A:T > T:A nucleotide substitutions in the genome

Recently, Ng et al. reported that the A:T > T:A substitutions, proposed to be a signature of aristolochic acid (AA) exposure, were detected in 76/98 (78%) of patients with hepatocellular carcinoma (HCC) from the Taiwan Province of China, and 47% to 1.7% of HCCs from the Chinese mainland and other countries harbored the nucleotide changes. However, other carcinogens, e.g., tobacco carcinogens 4-aminobiphenyl and 1,3-butadiene, air toxic vinyl chloride and its reactive metabolites chloroethylene oxide, melphalan and chlorambucil, also cause this signature in the genome. Since tobacco smoke is a worldwide public health threat and vinyl chloride distributes globally and is an air pollutant in Taiwan Province, the estimation of the patients' exposure history is the key to determine the "culprit" of the A:T > T:A mutations. Apparently, without estimation of the patients' exposure history, the conclusion of Ng et al. is unpersuasive and misleading.

Formation of Covalent DNA Adducts by Enzymatically Activated Carcinogens and Drugs In Vitro and Their Determination by 32P-postlabeling

Covalent DNA adducts formed by chemicals or drugs with carcinogenic potency are judged as one of the most important factors in the initiation phase of carcinogenic processes. This covalent binding, which is considered the cause of tumorigenesis, is now evaluated as a central dogma of chemical carcinogenesis. Here, methods are described employing the reactions catalyzed by cytochrome P450 and additional biotransformation enzymes to investigate the potency of chemicals or drugs for their activation to metabolites forming these DNA adducts. Procedures are presented describing the isolation of cellular fractions possessing biotransformation enzymes (microsomal and cytosolic samples with cytochromes P450 or other biotransformation enzymes, i.e., peroxidases, NADPH:cytochrome P450 oxidoreductase, NAD(P)H:quinone oxidoreductase, or xanthine oxidase). Furthermore, methods are described that can be used for the metabolic activation of analyzed chemicals by these enzymes as well as those for isolation of DNA. Further, the appropriate methods capable of detecting and quantifying chemical/drug-derived DNA adducts, i.e., different modifications of the ³²P-postlabeling technique and employment of radioactive-labeled analyzed chemicals, are shown in detail.

Environmental pollution and kidney diseases

The burden of disease and death attributable to environmental pollution is becoming a public health challenge worldwide, especially in developing countries. The kidney is vulnerable to environmental pollutants because most environmental toxins are concentrated by the kidney during filtration. Given the high mortality and morbidity of kidney disease, environmental risk factors and their effect on kidney disease need to be identified. In this Review, we highlight epidemiological evidence for the association between kidney disease and environmental pollutants, including air pollution, heavy metal pollution and other environmental risk factors. We discuss the potential biological mechanisms that link exposure to environmental pollutants to kidney damage and emphasize the contribution of environmental pollution to kidney disease. Regulatory efforts should be made to control environmental pollution and limit individual exposure to preventable or avoidable environmental risk. Population studies with accurate quantification of environmental exposure in polluted regions, particularly in developing countries, might aid our understanding of the dose-response relationship between pollutants and kidney diseases.

Occurrence of Ochratoxins, Fumonisin B2 , Aflatoxins (B1 and B2 ), and Other Secondary Fungal Metabolites in Dried Date Palm Fruits from Egypt: A Mini-Survey

This study was conducted to investigate the natural co-occurrence of 295 fungal and bacterial metabolites in 28 samples of dried date palm fruits collected from different shops distributed in Assiut Governorate, Upper Egypt in 2016. Extraction and quantification of the target analytes were done using the "dilute and shoot" approach followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS) analysis. In total, 30 toxic fungal metabolites were detected. Among these metabolites, 4 types of ochratoxins including ochratoxin type A and B were quantified in 3 samples (11%) with a contamination range from 1.48 to 6070 μg/kg for ochratoxin A and from 0.28 to 692 μg/kg for ochratoxin B. In addition, fumonisin B₂ was observed in 2 (7%) samples with contamination levels ranging from 4.99 to 16.2 μg/kg. The simultaneous detection of fumonisin B₂ in the same contaminated samples with ochratoxins indicates the fungal attack by Aspergillus niger species during storage. Only 1 sample was contaminated with aflatoxin B₁ (14.4 μg/kg) and B₂ (2.44 μg/kg). The highest maximum concentration (90400 μg/kg) was for kojic acid that contaminated 43% of the samples. To the best of the authors' knowledge, this is the first report of the natural co-occurrence of fumonisin B₂ and ochratoxin A and B in addition to a wide range of other fungal metabolites in date palm fruits.

PRACTICAL APPLICATION

Mycotoxins are secondary metabolites produced by different fungi. These metabolites pose a potential risk on human health since they contaminate many food commodities. Among these, date palm fruits which are an integral part of diet in several countries. Therefore, detection of mycotoxins is a prerequisite to insure the safety of food. Here, different types of mycotoxins have been detected in levels that may have health hazard.

DNA Adducts Formed by Aristolochic Acid Are Unique Biomarkers of Exposure and Explain the Initiation Phase of Upper Urothelial Cancer

Aristolochic acid (AA) is a plant alkaloid that causes aristolochic acid nephropathy (AAN) and Balkan endemic nephropathy (BEN), unique renal diseases frequently associated with upper urothelial cancer (UUC). This review summarizes the significance of AA-derived DNA adducts in the aetiology of UUC leading to specific A:T to T:A transversion mutations (mutational signature) in AAN/BEN-associated tumours, which are otherwise rare in individuals with UCC not exposed to AA. Therefore, such DNA damage produced by AA-DNA adducts is one rare example of the direct association of exposure and cancer development (UUC) in humans, confirming that the covalent binding of carcinogens to DNA is causally related to tumourigenesis. Although aristolochic acid I (AAI), the major component of the natural plant extract AA, might directly cause interstitial nephropathy, enzymatic activation of AAI to reactive intermediates capable of binding to DNA is a necessary step leading to the formation of AA-DNA adducts and subsequently AA-induced malignant transformation. Therefore, AA-DNA adducts can not only be utilized as biomarkers for the assessment of AA exposure and markers of AA-induced UUC, but also be used for the mechanistic evaluation of its enzymatic activation and detoxification. Differences in AA metabolism might be one of the reasons for an individual’s susceptibility in the multi-step process of AA carcinogenesis and studying associations between activities and/or polymorphisms of the enzymes metabolising AA is an important determinant to identify individuals having a high risk of developing AA-mediated UUC.

Restored nitric oxide bioavailability reduces the severity of acute-to-chronic transition in a mouse model of aristolochic acid nephropathy

Aristolochic Acid (AA) nephropathy (AAN) is a progressive tubulointerstitial nephritis characterized by an early phase of acute kidney injury (AKI) leading to chronic kidney disease (CKD). The reduced nitric oxide (NO) bioavailability reported in AAN might contribute to renal function impairment and progression of the disease. We previously demonstrated that L-arginine (L-Arg) supplementation is protective in AA-induced AKI. Since the severity of AKI may be considered a strong predictor of progression to CKD, the present study aims to assess the potential benefit of L-Arg supplementation during the transition from the acute phase to the chronic phase of AAN. C57BL/6J male mice were randomly subjected to daily i.p. injections of vehicle or AA for 4 days. To determine whether renal AA-induced injuries were linked to reduced NO production, L-Arg was added to drinking water from 7 days before starting i.p. injections, until the end of the protocol. Mice were euthanized 5, 10 and 20 days after vehicle or AA administration. AA-treated mice displayed marked renal injury and reduced NO bioavailability, while histopathological features of AAN were reproduced, including interstitial cell infiltration and tubulointerstitial fibrosis. L-Arg treatment restored renal NO bioavailability and reduced the severity of AA-induced injury, inflammation and fibrosis. We concluded that reduced renal NO bioavailability contributes to the processes underlying AAN. Furthermore, L-Arg shows nephroprotective effects by decreasing the severity of acute-to-chronic transition in experimental AAN and might represent a potential therapeutic tool in the future.

Protective effects of cyclic helix B peptide on aristolochic acid induced acute kidney injury

BACKGROUND

Aristolochic acid (AA) injuries remain a serious condition associated with acute renal dysfunction. Herein, the effect and mechanism of a novel tissue protective peptide, cyclic helical B-peptide (CHBP) derived from erythropoietin, were investigated in a mice model.

METHODS

Mice were randomly divided into four groups, receiving the following treatments (1: saline; 2: AA 10mg/kg; 3: AA 10mg/kg +CHBP 4nmol/kg; 4: AA 10mg/kg +CHBP 8nmol/kg).

RESULTS

Blood urea nitrogen and serum creatinine was increased by AA but decreased by CHBP in a dose-dependent fashion. CHBP also significantly improved renal tubular injury and inflammatory infiltration, which was gradually increased by AA. Apoptotic cells, infiltrating inflammatory cells, and active caspase-3+ cells were greatly reduced by CHBP. In addition, CHBP inhibited caspase-3, 9 and improved bcl-2, bcl-xl protein expression in vivo.

CONCLUSION

Taken together, we demonstrated, for the first time, that CHBP effectively improved renal function and tissue damage caused by AA, which maybe through reducing caspase-3 activation, apoptosis, and inflammation.

A Role for the Nonsense-Mediated mRNA Decay Pathway in Maintaining Genome Stability in Caenorhabditis elegans

Ionizing radiation (IR) is commonly used in cancer therapy and is a main source of DNA double-strand breaks (DSBs), one of the most toxic forms of DNA damage. We have used Caenorhabditis elegans as an invertebrate model to identify novel factors required for repair of DNA damage inflicted by IR. We have performed an unbiased genetic screen, finding that smg-1 mutations confer strong hyper-sensitivity to IR. SMG-1 is a phosphoinositide-3 kinase (PI3K) involved in mediating nonsense-mediated mRNA decay (NMD) of transcripts containing premature stop codons and related to the ATM and ATR kinases which are at the apex of DNA damage signaling pathways. Hyper-sensitivity to IR also occurs when other genes mediating NMD are mutated. The hyper-sensitivity to bleomycin, a drug known to induce DSBs, further supports that NMD pathway mutants are defective in DSB repair. Hyper-sensitivity was not observed upon treatment with alkylating agents or UV irradiation. We show that SMG-1 mainly acts in mitotically dividing germ cells, and during late embryonic and larval development. Based on epistasis experiments, SMG-1 does not appear to act in any of the three major pathways known to mend DNA DSBs, namely homologous recombination (HR), nonhomologous end-joining (NHEJ), and microhomology-mediated end-joining (MMEJ). We speculate that SMG-1 kinase activity could be activated following DNA damage to phosphorylate specific DNA repair proteins and/or that NMD inactivation may lead to aberrant mRNAs leading to synthesis of malfunctioning DNA repair proteins.

Comparison of the oxidation of carcinogenic aristolochic acid I and II by microsomal cytochromes P450 in vitro: experimental and theoretical approaches

Abstract

The herbal drug aristolochic acid, a natural mixture of 8-methoxy-6-nitrophenanthro[3,4-d]-1,3-dioxole-5-carboxylic acid (AAI) and 6-nitrophenanthro[3,4-d]-1,3-dioxole-5-carboxylic acid (AAII), is derived from Aristolochia species and is the cause of two nephropathies. Ingestion of aristolochic acid is associated with the development of urothelial tumors linked with aristolochic acid nephropathy and is implicated in the development of Balkan endemic nephropathy-associated urothelial tumors. The O-demethylated metabolite of AAI, 8-hydroxyaristolochic acid (AAIa), is the detoxification product of AAI generated by its oxidative metabolism. Whereas the formation of AAIa from AAI by cytochrome P450 (CYP) enzymes has been found in vitro and in vivo, this metabolite has not been found from AAII as yet. Therefore, the present study has been designed to compare the amenability of AAI and AAII to oxidation; experimental and theoretical approaches were used for such a study. In the case of experimental approaches, the enzyme (CYP)-mediated formation of AAIa from both carcinogens was investigated using CYP enzymes present in subcellular microsomal fractions and recombinant CYP enzymes. We found that in contrast to AAI, AAII is oxidized only by several CYP enzymatic systems and their efficiency is much lower for oxidation of AAII than AAI. Using the theoretical approaches, such as flexible in silico docking methods and ab initio calculations, contribution to explanation of these differences was established. Indeed, the results found by both used approaches determined the reasons why AAI is better oxidized than AAII; the key factor causing the differences in AAI and AAII oxidation is their different amenability to chemical oxidation.

Graphical abstract

Ochratoxin A and its metabolites in urines of German adults-An assessment of variables in biomarker analysis

Ochratoxin A (OTA), a mycotoxin known for its nephrotoxic and carcinogenic properties, is a worldwide occurring contaminant in a variety of food commodities. Biomonitoring (i.e. analysis in biological fluids) can serve to assess human internal exposure from all consumed foods and beverages. We now determined the concentration of OTA and its metabolite ochratoxin alpha (OTα) in plasma and in urine of two male volunteers with different food habits, in order to assess intra-individual temporal fluctuations and inter-individual differences in their biomarker levels. Moreover, the urinary levels of both OTA and OTα were analyzed in a cohort of German adults (23 males, 27 females) on their regular diet. All samples were subjected to an enzymatic hydrolysis of biomarker conjugates prior to clean-up by liquid-liquid extraction and HPLC-FD analysis. The profile in the first individual showed small fluctuations over time: mean levels in plasma were 0.42 and 0.45ng/mL for OTA and OTα, respectively, and in urine means of 0.06ng/mL for both analytes. The other individual had mean levels of 1.64 and 0.20ng/mL for OTA and OTα in plasma, and 0.24 and 2.22ng/mL for these analytes in urine. It is concluded that inter-individual differences in biomarker levels reflect dissimilar dietary exposure and/or disposition of ingested mycotoxin, with an apparently more efficient detoxification of OTA to OTα in the second individual. In the German cohort (n=50), analytes were detected in 100% (OTA: range 0.02-1.82ng/mL mean level 0.21±0.31ng/mL) and 78% (OTα: range 0.01-14.25ng/mL, mean level 1.33±2.63ng/mL) of all urines. Parameters such as gender, age and body mass index did not show a significant association with urine biomarker levels. This study indicates frequent exposure to OTA among German adults. The new results are discussed in the context of biomarker data from other countries and some methodological issues.

An Integrated View of Aristolochic Acid Nephropathy: Update of the Literature

The term “aristolochic acid nephropathy” (AAN) is used to include any form of toxic interstitial nephropathy that is caused either by ingestion of plants containing aristolochic acids (AA) as part of traditional phytotherapies (formerly known as “Chinese herbs nephropathy”), or by the environmental contaminants in food (Balkan endemic nephropathy). It is frequently associated with urothelial malignancies. Although products containing AA have been banned in most of countries, AAN cases remain regularly reported all over the world. Moreover, AAN incidence is probably highly underestimated given the presence of AA in traditional herbal remedies worldwide and the weak awareness of the disease. During these two past decades, animal models for AAN have been developed to investigate underlying molecular and cellular mechanisms involved in AAN pathogenesis. Indeed, a more-in-depth understanding of these processes is essential to develop therapeutic strategies aimed to reduce the global and underestimated burden of this disease. In this regard, our purpose was to build a broad overview of what is currently known about AAN. To achieve this goal, we aimed to summarize the latest data available about underlying pathophysiological mechanisms leading to AAN development with a particular emphasis on the imbalance between vasoactive factors as well as a focus on the vascular events often not considered in AAN.