GPX3 rs8177412 Polymorphism Modifies Risk of Upper Urothelial Tumors in Patients with Balkan Endemic Nephropathy

Current data suggest that aristolochic acid (AA) exposure is a putative cause of Balkan endemic nephropathy (BEN), a chronic kidney disease strongly associated with upper tract urothelial carcinoma. The cellular metabolism of AA is associated with the production of reactive oxygen species, resulting in oxidative distress. Purpose: Therefore, the aim of this study was to analyze individual, combined and cumulative effect of antioxidant gene polymorphisms (Nrf2 rs6721961, KEAP1 rs1048290, GSTP1AB rs1695, GSTP1CD rs1138272, GPX3 rs8177412 and MDR1 rs1045642), as well as GSTP1ABCD haplotypes with the risk for BEN development and associated urothelial cell carcinoma in 209 BEN patients and 140 controls from endemic areas. Experimental method: Genotyping was performed using polymerase chain reaction (PCR) and PCR with confronting two-pair primers (PCR-CTTP) methods. Results: We found that female patients carrying both variant GPX3 rs8177412 and MDR1 rs1045642 genotypes in combination exhibited significant risk towards BEN (OR 1 = 3.34, 95% CI = 1.16-9.60, p = 0.025; OR 2 = 3.79, 95% CI = 1.27-11.24, p = 0.016). Moreover, significant association was determined between GPX3rs8174412 polymorphism and risk for urothelial carcinoma. Carriers of variant GPX3*TC + CC genotype were at eight-fold increased risk of BEN-associated urothelial tumors development. There was no individual or combined impact on BEN development and BEN-associated tumors among all examined polymorphisms. The haplotype consisting of variant alleles for both polymorphisms G and T was associated with 1.6-fold increased risk although statistically insignificant (OR = 1.64; 95% CI = 0.75-3.58; p = 0.21). Conclusions: Regarding GPX3 rs8177412 polymorphism, the gene variant that confers lower expression is associated with significant increase in upper urothelial carcinoma risk. Therefore, BEN patients carrying variant GPX3 genotype should be more frequently monitored for possible upper tract urothelial carcinoma development.

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.

Genetic, Genomic and Epigenomic Studies of Balkan Endemic Nephropathy (Ben)

BEN is a primary, chronic tubulointerstitial nephritis characterized with chronic anemia, absence of edema, xantoderma, normal blood pressure and normal findings on the fundus oculi. The disease is distributed in restricted areas in Bulgaria, Romania, Croatia, Bosnia, Former Yugoslavia. Despite numerous studies on genetic and environmental factors and their possible involvement in BEN, its etiopathogenesis still remains elusive. Our recent study aim to elucidate the possible epigenetic component in BEN development. Whole genome DNA array methylation analysis was applied to compare the methylation profiles of male and female BEN patients from endemic regions in Bulgaria and Serbia and healthy controls. All three most prominent candidate genes with aberrations in the epigenetic profile discovered with this study are involved in the inflammatory/immune processes and oncogenesis. These data are in concordance with the reported pathological alterations in BEN. This research supports the role of epigenetic changes in BEN pathology. Exome sequencing of 22.000 genes with Illumina Nextera Exome Enrichment Kit revealed three mutant genes (CELA1, HSPG2, and KCNK5) in BEN patients which encode proteins involved in basement membrane/extracellular matrix and vascular tone, tightly connected to process of angiogenesis. We suggest that an abnormal process of angiogenesis plays a key role in the molecular pathogenesis of BEN.

Ochratoxin A: 50 Years of Research

Since ochratoxin A (OTA) was discovered, it has been ubiquitous as a natural contaminant of moldy food and feed. The multiple toxic effects of OTA are a real threat for human beings and animal health. For example, OTA can cause porcine nephropathy but can also damage poultries. Humans exposed to OTA can develop (notably by inhalation in the development of acute renal failure within 24 h) a range of chronic disorders such as upper urothelial carcinoma. OTA plays the main role in the pathogenesis of some renal diseases including Balkan endemic nephropathy, kidney tumors occurring in certain endemic regions of the Balkan Peninsula, and chronic interstitial nephropathy occurring in Northern African countries and likely in other parts of the world. OTA leads to DNA adduct formation, which is known for its genotoxicity and carcinogenicity. The present article discusses how renal carcinogenicity and nephrotoxicity cause both oxidative stress and direct genotoxicity. Careful analyses of the data show that OTA carcinogenic effects are due to combined direct and indirect mechanisms (e.g., genotoxicity, oxidative stress, epigenetic factors). Altogether this provides strong evidence that OTA carcinogenicity can also occur in humans.

Dominant-Negative Effect of a Missense Variant in the TASK-2 (KCNK5) K+ Channel Associated with Balkan Endemic Nephropathy

TASK-2, a member of the Two-Pore Domain (K2P) subfamily of K⁺ channels, is encoded by the KCNK5 gene. The channel is expressed primarily in renal epithelial tissues and a potentially deleterious missense variant in KCNK5 has recently been shown to be prevalent amongst patients predisposed to the development of Balkan Endemic Nephropathy (BEN), a chronic tubulointerstitial renal disease of unknown etiology. In this study we show that this variant (T108P) results in a complete loss of channel function and is associated with a major reduction in TASK-2 channel subunits at the cell surface. Furthermore, these mutant subunits have a suppressive or ‘dominant-negative’ effect on channel function when coexpressed with wild-type subunits. This missense variant is located at the extracellular surface of the M2 transmembrane helix and by using a combination of structural modelling and further functional analysis we also show that this highly-conserved threonine residue is critical for the correct function of other K2P channels. These results therefore provide further structural and functional insights into the possible pathophysiological effects of this missense variant in TASK-2.

[Endemic nephropathy in Croatia]

Endemic nephropathy (EN) is a chronic tubulointerstitial aristolochic acid nephropathy (AAN) affecting residents of the certain villages in the valleys of the major tributaries of the Danube river in the south-east Europe including Croatia. Patients with EN have a significantly higher incidence of transitional cell carcinoma of the ureter than the general population. A-T transversion of the p53 gene is now considered to be a mutational "signature" of aristolochic acid, which is a cause of endemic nephropathy. Currently used diagnostic criteria for EN are outdated, uneven (three types of criteria) and are not in agreement with proposed new guidelines for kidney diseases. Therefore, based on current knowledge and expertise of a group of scientists and experts from all countries with EN as well as world where AAN has been reported, new diagnostic criteria and the new classification of the population of endemic villages were created at a symposium on EN. EN presents a major public health problem and current knowledge about this disease as well as new diagnostic criteria should help us in its early detection and treatment and maybe in a near future its eradication.

Is increased susceptibility to Balkan endemic nephropathy in carriers of common GSTA1 (*A/*B) polymorphism linked with the catalytic role of GSTA1 in ochratoxin a biotransformation? Serbian case control study and in silico analysis

Although recent data suggest aristolochic acid as a putative cause of Balkan endemic nephropathy (BEN), evidence also exists in favor of ochratoxin A (OTA) exposure as risk factor for the disease. The potential role of xenobiotic metabolizing enzymes, such as the glutathione transferases (GSTs), in OTA biotransformation is based on OTA glutathione adducts (OTHQ-SG and OTB-SG) in blood and urine of BEN patients. We aimed to analyze the association between common GSTA1, GSTM1, GSTT1, and GSTP1 polymorphisms and BEN susceptibility, and thereafter performed an in silico simulation of particular GST enzymes potentially involved in OTA transformations. GSTA1, GSTM1, GSTT1 and GSTP1 genotypes were determined in 207 BEN patients and 138 non-BEN healthy individuals from endemic regions by polymerase chain reaction (PCR). Molecular modeling in silico was performed for GSTA1 protein. Among the GST polymorphisms tested, only GSTA1 was significantly associated with a higher risk of BEN. Namely, carriers of the GSTA1*B gene variant, associated with lower transcriptional activation, were at a 1.6-fold higher BEN risk than those carrying the homozygous GSTA1*A/*A genotype (OR = 1.6; p = 0.037). In in silico modeling, we found four structures, two OTB-SG and two OTHQ-SG, bound in a GSTA1 monomer. We found that GSTA1 polymorphism was associated with increased risk of BEN, and suggested, according to the in silico simulation, that GSTA1-1 might be involved in catalyzing the formation of OTHQ-SG and OTB-SG conjugates.

NGS nominated CELA1, HSPG2, and KCNK5 as candidate genes for predisposition to Balkan endemic nephropathy

Balkan endemic nephropathy (BEN) is a familial chronic tubulointerstitial disease with insidious onset and slow progression leading to terminal renal failure. The results of molecular biological investigations propose that BEN is a multifactorial disease with genetic predisposition to environmental risk agents. Exome sequencing of 22 000 genes with Illumina Nextera Exome Enrichment Kit was performed on 22 DNA samples (11 Bulgarian patients and 11 Serbian patients). Software analysis was performed via NextGene, Provean, and PolyPhen. The frequency of all annotated genetic variants with deleterious/damaging effect was compared with those of European populations. Then we focused on nonannotated variants (with no data available about them and not found in healthy Bulgarian controls). There is no statistically significant difference between annotated variants in BEN patients and European populations. From nonannotated variants with more than 40% frequency in both patients' groups, we nominated 3 genes with possible deleterious/damaging variants--CELA1, HSPG2, and KCNK5. Mutant genes (CELA1, HSPG2, and KCNK5) in BEN patients encode proteins involved in basement membrane/extracellular matrix and vascular tone, tightly connected to process of angiogenesis. We suggest that an abnormal process of angiogenesis plays a key role in the molecular pathogenesis of BEN.

New generation genomic platforms in investigation of complex diseases and BEN

New generation genomic platforms enable us to decipher the complex genetic basis of complex diseases and Balkan Endemic Nephropathy (BEN) at a high-throughput basis. They give valuable information about predisposing Single Nucleotide Polymorphisms (SNPs), Copy Number Variations (CNVs) or Loss of Heterozygosity (LOH) (using SNP-array) and about disease-causing mutations along the whole sequence of candidate-genes (using Next Generation Sequencing). This information could be used for screening of individuals in risk families and moving the main medicine stream to the prevention. They also might have an impact on more effective treatment. Here we discuss these genomic platforms and report some applications of SNP-array technology in a case with familial nephrotic syndrome.

Endemic (Balkan) nephropathy is aristolochic acid nephropathy

Endemic nephropathy is a syndrome that comprises two entities: chronic interstitial nephropathy and urothelial cell cancers predominantly of the upper urinary tract. The etiological agent for the disease is aristolochic acid, a compound found in the plants of Aristolochia spp. The development of urothelial cancers is characterized by the formation of aristolactam DNA adducts leading to mutations, predominantly A: T->T: A transversions. In order to comprehensively understand the gene regulation programs in upper urothelial cancers we performed integrated miRNA and mRNA expression profiling of paired tumours and unaffected urothelium samples. The obtained data will help us to understand the carcinogenesis caused by aristolochic acid and might be the source for the design of a diagnostic biomarker.

NAD(P)H:quinone oxidoreductase expression in Cyp1a-knockout and CYP1A-humanized mouse lines and its effect on bioactivation of the carcinogen aristolochic acid I

Aristolochic acid causes a specific nephropathy (AAN), Balkan endemic nephropathy, and urothelial malignancies. Using Western blotting suitable to determine protein expression, we investigated in several transgenic mouse lines expression of NAD(P)H:quinone oxidoreductase (NQO1)-the most efficient cytosolic enzyme that reductively activates aristolochic acid I (AAI). The mouse tissues used were from previous studies [Arlt et al., Chem. Res. Toxicol. 24 (2011) 1710; Stiborova et al., Toxicol. Sci. 125 (2012) 345], in which the role of microsomal cytochrome P450 (CYP) enzymes in AAI metabolism in vivo had been determined. We found that NQO1 levels in liver, kidney and lung of Cyp1a1⁻/⁻, Cyp1a2⁻/⁻ and Cyp1a1/1a2⁻/⁻ knockout mouse lines, as well as in two CYP1A-humanized mouse lines harboring functional human CYP1A1 and CYP1A2 and lacking the mouse Cyp1a1/1a2 orthologs, differed from NQO1 levels in wild-type mice. NQO1 protein and enzymic activity were induced in hepatic and renal cytosolic fractions isolated from AAI-pretreated mice, compared with those in untreated mice. Furthermore, this increase in hepatic NQO1 enzyme activity was associated with bioactivation of AAI and elevated AAI-DNA adduct levels in ex vivo incubations of cytosolic fractions with DNA and AAI. In conclusion, AAI appears to increase its own metabolic activation by inducing NQO1, thereby enhancing its own genotoxic potential.

Angiotensin-converting enzyme gene polymorphism and N-Acetyl-β-D-glucosaminidase excretion in endemic nephropathy

BACKGROUND

Tubular proteinuria and enzymuria are hallmarks of endemic nephropathy (EN). The role of I/D angiotensin convertase (ACE) gene polymorphism has not yet been elucidated in this peculiar chronic tubulointerstitial nephritis, and our aim was to investigate the role of this polymorphism in EN focusing on the urinary N-acetyl-β-D-glucosaminidase (NAG) excretion, a biomarker of proximal tubular damage.

METHODS

ACE genotype and allele frequencies were determined in 229 farmers (147 women and 82 men) from an endemic Croatian village. The farmers were stratified according to the WHO criteria into the following subgroups: those 'at risk' for EN (n = 37), 'suspected of having EN' (n = 57), and 'others' (n = 135).

RESULTS

There were 74 (32.3%) subjects homozygous for the D allele, 99 (43.2%) heterozygous (ID genotype) and 56 (24.4%) homozygous for the I allele. No differences in allele frequency were found between the established WHO subgroups (p > 0.05). In the whole group, DD subjects had significantly higher values of diastolic blood pressure (p = 0.003) and urinary NAG than subjects with ID and II genotype (5.5 ± 1.2 vs. 4.0 ± 3.0 vs. 3.8 ± 4.2, respectively; p = 0.023). The highest values of serum creatinine (p = 0.02), proteinuria (p = 0.03) and urinary NAG (6.0 ± 3.7 vs. 3.7 ± 2.1 vs. 3.0 ± 1.6, respectively; p = 0.008) were observed in those suspected of having EN group with the DD genotype.

CONCLUSION

ACE gene polymorphism is not a risk factor for EN. However, it might influence the clinical course of EN, and increased excretion of NAG might be a prognostic marker of this chronic tubulointerstitial nephritis.

p53 mutations as fingerprints for aristolochic acid: an environmental carcinogen in endemic (Balkan) nephropathy

The activation of protooncogenes and inactivation of tumor suppressor genes are considered to be the main molecular events in the multistep process of carcinogenesis. Mutations of the TP53 tumor suppressor gene have been found in nearly all tumor types and are estimated to contribute to more than 50% of all cancers. Most mutations lead to the synthesis of highly stable, inactive proteins that accumulate in the nucleus of cancer cells. Among the 393 codons of the human p53 gene, 222 are targets of 698 different types of mutations. Alterations of codons 175, 248, 273 and 282 correspond to 19% of all mutations and are considered general hot spot mutations. Dietary exposure to aristolochic acid (AA), an established nephrotoxin and human carcinogen found in all Aristolochia species was shown to be the causative agent of aristolochic acid nephropathy (previously called Chinese herbs nephropathy). This syndrome is characterized by proximal tubular damage, renal interstitial fibrosis, slow progression to the end stage renal disease and a high prevalence of upper urinary tract urothelial carcinoma (otherwise a highly unusual location). AA preferentially binds to purines in DNA and is associated with a high frequency of A-->T transversions in the p53 gene. Rats treated with AA develop A:T-->T:A mutations in codon 61. The pathological and clinical features of endemic (Balkan) nephropathy closely resemble those associated with aristolochic acid nephropathy except for the slower progression to end stage renal disease and longer cumulative period before the appearance of urothelial cancer. Recently, we reported the presence of AA-DNA adducts in renal cortex and A-->T p53 mutations in tumor tissue of patients from Croatia and Bosnia with endemic nephropathy. These data support the hypothesis that dietary exposure to AA is a major risk factor for endemic (Balkan) nephropathy.

Population-genetic study of Balkan endemic nephropathy in Serbia

The study of Balkan Endemic Nephropathy (BEN) in the affected localities of southern Serbia shows population-genetic difference between samples of BEN affected individuals and control group consisting of non-affected individuals from the same localities. Detailed population-genetic study in village Chepure, which includes 20 large families where BEN is present in 646 (from first to fourth degree) relatives of probants, shows familial character of disease as well as significant genetic influences in expression of the illness. Our study of genetic homozygosity degree includes an analysis of the presence, distribution and individual combination of 20 to 30 selected genetically controlled morpho-physiological traits in the sample of BEN patients and in the control-healthy group. Assuming that BEN is genetically controlled disease, we made a hypothesis that an increased homozygosity level, as well as the changed variability among the patients, could be population-genetic parameter for the prediction of the illness. Taking into consideration our experience, as well as the experience of numerous scientists who studied the nature of the inheritance of mono- and oligo-genically controlled qualitative traits, we applied a methodology to estimate the proportion of such homozygously recessive characters (HRC-test). This population-genetic study did not only show statistically significant difference of the mean values of genetic homozygosity (BEN - 8.7 +/- 0.3; control - 7.6 +/- 0.3), but of the differences in the type of distribution too, as well as the differences in the presence of certain individual combinations of such traits.

Increased blood pressure in adult offspring of families with Balkan endemic nephropathy: a prospective study

BACKGROUND

Previous studies have linked smaller kidney dimensions to increased blood pressure. However, patients with Balkan Endemic Nephropathy (BEN), whose kidneys shrink during the course of the disease, do not manifest increased blood pressure. The authors evaluated the relationship between kidney cortex width, kidney length, and blood pressure in the offspring of BEN patients and controls.

METHODS

102 offspring of BEN patients and 99 control offspring of non-BEN hospital patients in the Vratza District, Bulgaria, were enrolled in a prospective study and examined twice (2003/04 and 2004/05). Kidney dimensions were determined using ultrasound, blood pressure was measured, and medical information was collected. The parental disease of BEN was categorized into three groups: mother, father, or both parents. Repeated measurements were analyzed with mixed regression models.

RESULTS

In all participants, a decrease in minimal kidney cortex width of 1 mm was related to an increase in systolic blood pressure of 1.4 mm Hg (p = 0.005). There was no association between kidney length and blood pressure. A maternal history of BEN was associated with an increase in systolic blood pressure of 6.7 mm Hg (p = 0.03); paternal BEN, +3.2 mm Hg (p = 0.35); or both parents affected, +9.9 mm Hg (p = 0.002). There was a similar relation of kidney cortex width and parental history of BEN with pulse pressure; however, no association with diastolic blood pressure was found.

CONCLUSION

In BEN and control offspring, a smaller kidney cortex width predisposed to higher blood pressure. Unexpectedly, a maternal history of BEN was associated with average increased systolic blood pressure in offspring.

Clinical markers in adult offspring of families with and without Balkan Endemic Nephropathy

Balkan Endemic Nephropathy (BEN) is a kidney disease that progresses slowly. Only a few studies have investigated renal clinical markers in offspring of BEN families before the onset of the disease. This project aimed to determine whether kidney function and structure are altered in BEN offspring compared with non-BEN offspring. The study population consisted of 102 adult BEN offspring and a control group of 99 non-BEN offspring. We collected urine and blood samples, and conducted face-to-face interviews, physical examinations and ultrasound measurements of the kidney. Total protein, albumin, beta2-microglobulin and creatinine in urine, creatinine and urea in serum, and creatinine clearance (CCR) were determined. Two risk factors were assessed: first, the overall status of being an offspring from a BEN family, and second, the specific status of a mother and/or father with BEN. The data were analyzed using linear regression. After adjusting for confounders, we found that kidney length and minimal cortex width in BEN offspring were significantly decreased. Urine concentrations of total protein, albumin, and beta2-microglobulin were higher in BEN offspring. Regarding parental history, the associations were statistically significant only for the offspring of mothers who had BEN, with the exception of minimal cortex width, which showed no parental difference. For CCR, we did not identify a statistically significant effect for BEN offspring status nor for parental history. In conclusion, adult offspring of BEN families can be characterized by shorter kidney length and an increased excretion of albumin, total protein, and beta2-microglobulin, in particular, when the mother had BEN.

Etiology of Balkan endemic nephropathy and associated urothelial cancer

Balkan endemic nephropathy (BEN) is a familial chronic tubulointerstitial disease with insidious onset and slow progression to terminal renal failure. Evidence has accumulated that BEN is an environmentally induced disease. There are three actual theories attempting to explain the environmental cause of this disease: (1) the aristolochic acid hypothesis, which considers that the disease is produced by chronic intoxication with Aristolochia, (2) the mycotoxin hypothesis, which considers that BEN is produced by ochratoxin A, and (3) the Pliocene lignite hypothesis, which proposes that the disease is caused by long-term exposure to polycyclic aromatic hydrocarbons and other toxic organic compounds leaching into the well drinking water from low-rank coals in the vicinity to the endemic settlements. Moreover, it was suggested that BEN risk is influenced by inherited susceptibility. Therefore, it has been expected that molecular biological investigations will discover genetic markers of BEN and associated urothelial cancer, permitting early identification of susceptible individuals who may be at risk of exposure to the environmental agents. Since kidney pathophysiology is complex, gene expression analysis and highly throughput proteomic technology can identify candidate genes, proteins and molecule networks that eventually could play a role in BEN development. Investigation of gene-gene and gene-environment interactions could be the content of further studies determining the precise risk for BEN.

Germline p53 single-base changes associated with Balkan endemic nephropathy

The Balkan endemic nephropathy (BEN) is a significant clinical and scientific problem in need of novel effective therapies. Though many genetic and environmental factors have been investigated the basis, cause, and predisposition to BEN are still unclear. In this study, based on the hypothesis that the genetic pathways leading to BEN might be associated with p53 dysfunction, we screened for p53 gene mutations 90 Bulgarian BEN patients using optimized PCR-SSCP-sequencing analysis. Germline p53 single-base changes were found in blood samples in 10% of BEN cases. Three of them caused amino acid substitutions (p.Arg283Cys, p.Gln317His, and p.Lys321Glu); the other six were either synonymous amino acid substitutions (p.Arg213Arg) or intron polymorphisms (T14766C). To the best of our knowledge, these are the first data investigating tumor suppressor gene mutations in patients with BEN. The obtained results are in support of our hypothesis that p53 gene alterations are possibly involved in BEN genetic pathways.

Fifty years of Balkan endemic nephropathy: daunting questions, elusive answers

Balkan endemic nephropathy (BEN) has remained a geographically constant endemic for 50 years. Despite extensive research, its etiology remains unknown. In the current issue, in a study in one of the earliest sites where the endemic was first recognized, Dimitrov et al. confirm the persistance of the endemic into a new generation and also identify a maternal link in the pathogenesis of BEN. This intriguing finding needs to be confirmed in other endemic areas.

Genetic polymorphisms of cytochrome P450 among patients with Balkan endemic nephropathy (BEN)

OBJECTIVES

The concept of multifactorial etiology of BEN anticipates that a combination of polymorphic gene variants and various environmental factors causes an increased risk for the disease. CYP enzymes play a key role in the metabolic activation of environmental chemicals and toxins. CYP3A enzymes are particularly relevant for xenobiotic metabolism because of their broad substrate specificity and abundant expression in the human liver, intestine, and kidney. Previous phenotyping analysis on CYP2D6 enzyme activity in BEN patients proposed a modifying effect of CYP2D6 gene variants on BEN risk, but it was not approved with molecular-genetic methods. The aim of the current case-control study was to compare the frequency of CYP2D6 and CYP3A5 polymorphisms, as well as one CYP3A4 promoter variant in BEN patients and controls in order to investigate a possible association between individual genetic variations in these genes and susceptibility to BEN.

DESIGN AND METHODS

Ninety-six nonrelated Bulgarian BEN patients from endemic villages in the Vratza district and 112 healthy Bulgarians from nonendemic areas (controls) were genotyped. Identification of alleles was done by allele-specific PCR or by rapid-cycle amplification on the LightCycler, followed by sequence-specific detection.

RESULTS

The UM, PM, and EM + IM genotype frequencies of CYP2D6 did not differ significantly between the two groups (P > 0.05). The CYP3A4*1B allele was only found in the heterozygous form, with allelic frequencies of 5.21% in the patients and 2.23% in the healthy individuals (P = 0.11). The CYP3A5*1 allele was more prevalent in BEN patients with a frequency of 9.38% compared to 5.36% in the controls and was associated with a higher risk for BEN (OR 2.41, 95% CI 1.09-5.33) (P = 0.02).

CONCLUSIONS

Our results demonstrate that the CYP3A5*1 allele, previously reported as a marker for CYP3A5 expression in human kidney, is associated with increased risk for BEN, while CYP3A4*1B and CYP2D6 genotypes do not significantly modify the risk for the disease.

Detection of renal dysfunctions in family members of patients with Balkan endemic nephropathy

BACKGROUND/AIM

Recent studies have questioned whether new cases of Balkan endemic nephropathy (BEN) are occurring. The aim of the present study was to find out whether new members with renal dysfunctions can be identified among family members of BEN patients from the Kolubara region.

METHODS

The study included 47 family members of 5 BEN patients on hemodialysis (HD) and 17 members of 3 non-BEN patients on HD. Their medical and epidemiological histories were taken, an objective survey made, and all persons were examined for global and tubular kidney function.

RESULTS

Seven BEN family members (2 with previously known BEN) had creatinine clearance (Ccr) below the 75th percentile rank according to sex and age. All non-BEN family members had normal Ccr and no evidence of previous renal disorders. Hypertension was found in 20 (43%) BEN and 6 (35%) non-BEN family members. No significant differences in the frequency of renal function disorders (proteinuria, alpha1-microglobulinuria, urine specific gravity, osmolality, functional excretion of sodium, tubular phosphate resorption) or anemia were found between the groups. Renal disorders were detected in 18 BEN family members without previously detected disease, 3 of whom fulfilled criteria for a diagnosis of BEN and another 2 for BEN-suspected persons.

CONCLUSION

New cases of BEN are still arising among the affected families in the Kolubara region.

Balkan endemic nephropathy and genetic variants of glutathione S-transferases

BACKGROUND

Balkan endemic nephropathy (BEN) is a non-inflammatory, chronic, slow progressing kidney disease, frequently associated with urinary tract tumors. BEN displays familial clustering without an apparent Mendelian inheritance pattern. It has been suggested that environmental toxicants damage urothelial cells in genetically susceptible individuals, which could be the cause of BEN. The metabolism of some substrates that are mediated by glutathione S-transferases (GST), which are polymorphic enzymes, results in nephrotoxic products. To evaluate whether GST genetic heterogeneity could be involved in BEN, we launched a case-control study concerning the association of the most common polymorphic GST variants with BEN.

METHODS

DNA was extracted from venous blood samples from 54 unrelated BEN patients and 104 controls inhabiting the same endemic region. GSTM1 and GSTT1 null deletions were identified simultaneously by a triplex polymerase chain reaction (PCR) procedure, and GSTP1 polymorphism was analyzed by PCR-restriction fragment length polymorphism (PCR-RFLP) using Alw261.

RESULTS

Carriers of at least one GSTM1 wild type allele (wt-allele) were more prevalent among BEN patients compared to controls (chi2=7.92, p=0.005). The GSTT1 and GSTP1 genotype distributions did not demonstrate statistically significant differences between the groups. The carriers of at least one GSTM1 wt-allele among BEN patients were more prevalent in comparison with controls when the GSTM1 genotypes were combined in pairs with all GSTT1 (chi2=9.52, p=0.023) and GSTP1 (chi2=11.92, p=0.036) genotypes. The combined genotype distributions of the three GST genes studied among BEN patients and controls showed that the frequency of carriers of at least one GSTM1 wt-allele among BEN patients was higher or at least equal to the corresponding frequency among controls in all triple combinations. However, this difference did not reach statistical significance (chi2=14.06, p=0.170).

CONCLUSIONS

GSTM1 wt-allele associates with BEN. The significantly lower prevalence of the GSTM1 deletion homozygotes among BEN patients suggests that individuals bearing the GSTM1 null genotype could be better protected.

Identification of NQO1 and GSTs genotype frequencies in Bulgarian patients with Balkan endemic nephropathy

BACKGROUND

Polymorphisms in NAD[P]H:quinone oxidoreductase (NQO1) and glutathione S-transferases (GSTs) have been reported to be associated with an increased risk for environmentally and/or occupationally induced renal and bladder cancers. Genetic factors related to chronic nephropathy and to urinary bladder or renal cancer development in Balkan endemic nephropathy (BEN) is unknown. In order to evaluate their possible role in BEN susceptibility, we determined the frequencies of NQO1 alleles *1, *2 and *3, as well as the GSTT1 and GSTM1 null genotypes in BEN patients and healthy subjects from a non-endemic region of Bulgaria.

METHODS

The respective genotypes of 95 unrelated Bulgarian BEN patients and of 112 healthy individuals (control group) were determined by rapid cycle polymerase chain reaction (PCR) and detected with either SYBR green I fluorescent dye or melting curve analysis using allele specific probes.

RESULTS

NQO1 genotyping showed a higher NQO1*2 allele frequency (23.68%) in BEN patients compared to controls (18.75%; p=0.219), while NQO1*3 allele frequencies were similar in both groups (2.63% in BEN patients vs. 2.23% in controls; p=0.791). The GSTT1 deficiencywas observed in 20% of BEN patients vs. 16.1% of controls (p=0.613). The GSTM1 null genotype was found in 45.3% of BEN patients vs. 51.8% of controls (p=0.674). There was no influence of NQO1 and GSTs genotypes found on BEN risk.

CONCLUSIONS

Our results established that alleles NQO1*2 and NQO1*3, as well as lack of GSTT1 and GSTM1 did not influence the BEN risk. These findings provide novel information on the genetic heterogeneity in the healthy Bulgarian population.

MDR1 Haplotypes Modify BEN Disease Risk: A Study in Bulgarian Patients with Balkan Endemic Nephropathy Compared to Healthy Controls

BACKGROUND

Balkan endemic nephropathy (BEN) is a slow progressive nephropathy with frequent occurrence of uroepithelial tumors in the upper urinary tract. Genetic factors involved in xenobiotic detoxification mechanisms may cause genetic predisposition to BEN and influence the risk for this disease. Polymorphic MDR1 variants with decreased P-glycoprotein (P-gp) activity modulate the risk for renal neoplasm. We have therefore investigated the impact of MDR1 polymorphisms on BEN manifestation.

METHODS

The constitutional genotype frequencies of two SNPs (C3435T and G2677T) in the MDR1 gene in 112 healthy control subjects were investigated and compared with those of 96 patients with BEN. Identification of the SNPs was done with rapid cycle real-time PCR and melting curve analysis with allele-specific probes.

RESULTS

The frequency of mutant alleles was comparable in both groups. Significant differences were revealed when the MDR1 haplotypes were analyzed. Individuals with a predicted haplotype 12 (2677G/3435T) were less frequent in BEN cases (frequency 7.3%) than in controls (16.1%, p = 0.006). We found that carriers of the haplotype 12 had a decreased risk for BEN (OR = 0.411; 0.21-0.78).

CONCLUSIONS

The data suggest that haplotype 12 is protective against BEN. There is no clear molecular explanation of the MDR1 haplotype effects on the protein activity, which can explain the modified effect of the haplotype 12 on BEN risk.

Increased urinary albumin excretion in children from families with Balkan nephropathy

Balkan nephropathy (BN) has not been described in children. However, some previous studies have revealed abnormalities of the urinary tract in children from families with BN. In the present study, urinary excretion of albumin was studied in 703 healthy children, age 9-13 years, from endemic and non-endemic settlements around the South Morava River. Since BN is an environmentally induced disease, with possible seasonal variation of toxicant(s), children were studied three times a year: spring, autumn, and winter. After a water load of 15 ml/kg body weight, a 3-h urine sample was collected, from 7 to 10 a.m. Albumin excretion in urine was highest in children from families with BN in all three periods investigated. It was significantly different from excretion in children from the city, and in autumn it was also different ( P<0.01) from children in non-endemic families. Correlation analysis of albumin excretion with some urinary markers of tubular nephrotoxicity shows the highest correlation with both beta(2)-microglobulin and N-acetyl-beta-D-glucosaminidase in endemic villages in autumn. If the upper limit of albumin excretion is set at 8.5 mg/mmol creatinine, then in autumn increased albumin excretion was found in 15 of 229 children from endemic settlements and in only 5 of 454 children from non-endemic areas ( P<0.0001). Evidence is presented that in autumn children from families with BN excreted significantly more albumin than those from non-endemic families but living in the same settlements, or from children living outside of the endemic region in the city of Nis.

Genetic changes in uroepithelial tumors of patients with Balkan endemic nephropathy

BACKGROUND

Balkan endemic nephropathy (BEN) is seen in certain regions of the Balkan Peninsula. The patients are predisposed to epithelial cell tumors of the urinary tract. These tumors have not been genetically investigated so far.

METHODS

We studied the loss of heterozygosity (LOH) in three BEN-associated tumors at seven microsatellite loci at 3q21.3 - 3q27.3. Comparative genomic hybridization (CGH) was also done and one of the tumors was investigated by 24-color FISH as well.

RESULTS

LOH in locus D3S1299 (3q24) was established in one case. CGH showed genetic gains at 1q, 3q, 7p, 7q, 15q, and 19q in at least two of the three tumors. Genetic loss was found in one case at 4q. Most frequent aberrations detected by 24-color FISH were der(X), der(X)t(X;18), der(16), der(3)t(3;15) and der(12).

CONCLUSION

The LOH suggests the presence of a new, so far unidentified tumor-suppressor gene at 3q24. In pTa BEN tumor CGH showed genome instability was extremely high. The 24-color FISH indicated highly complex chromosomal rearrangements. Chromosome 3 anomalies support our previous data on 3q24 - 3q26.3 association with BEN.

Urinary creatinine excretion in children from families with Balkan endemic nephropathy: evidence for genetic predisposition to the disease

Balkan endemic nephropathy (BEN) is a chronic tubulointerstitial kidney disease prevalent in Serbia, Bosnia, Croatia, Bulgaria and Romania. Genetic studies have supported the genetic predisposition to BEN, and some studies in Bulgaria and in the Kolubara region of Serbia have revealed abnormalities of the urinary tract in up to 46% of children from families with BEN. In the present study, urinary excretion of creatinine, an index of muscle mass, was studied in 703 healthy children from endemic and non-endemic areas around the South Morava River. The survey covered a three-year period, and the children were studied three times a year: in the spring, autumn and winter. A urine sample for the period corresponding to 7-10 a.m. was collected during each study period. Evidence has been presented that children from families with BEN excrete significantly less creatinine than those from families without BEN living in the same area, or than children living in villages outside the endemic region or in the city of Nis. This study supports the view that genetic predisposition to BEN is indicated by a smaller muscle mass, although the effect of living conditions and nutrition may also contribute to this.

Balkan endemic nephropathy: a need for novel aetiological approaches

Aetiology remains the main unanswered problem in Balkan endemic nephropathy (BEN) despite investigations into the roles of genetic factors, environmental agents and immune mechanisms. Evidence has accumulated that BEN is an environmentally-induced disease. Weathering of low-rank coals near to the villages where BEN is endemic produces water-soluble polycyclic aromatic hydrocarbons and aromatic amines, similar to metabolic products of acetaminophen that cause analgesic nephropathy. Many of these compounds are known to be carcinogenic and could also cause urothelial cancer. Genetic studies have supported genetic predisposition to BEN. The candidate genes have been localized to a region between 3q25 and 3q26, the 3q BEN marker being detected in both BEN patients and in some healthy relatives with initial morphological changes peculiar to BEN. Three bands with increased frequencies of spontaneous and induced aberrations contain oncogenes. The frequent association of BEN and urinary tract tumours (UTT) can be explained by the chromosomal hypothesis of oncogenesis. The results of molecular biological investigations will allow the identification of genetic markers of BEN, permitting early detection of BEN-predisposing mutations and identification of susceptible individuals who may be at risk of exposure to the environmental agents. An increased incidence of tumours of renal pelvis and ureter in patients with BEN and in population from endemic settlements has been observed. Familial clustering of the UTT was also reported. The frequency of urinary bladder tumours in BEN-endemic settlements is also increased compared with the non-endemic villages and cities. The geographic correlation between BEN and UTT supports the speculation that these diseases share a common aetiology.

Genetic predisposition to Balkan endemic nephropathy

This study is the first cytogenetic investigation of healthy relatives of patients with Balkan endemic nephropathy (BEN) who were born in nonendemic areas. Characteristics of BEN No. 3 chromosomal anomalies (extremely high frequencies of 3q25 homologue discordance - 68.5 +/- (SD) 5.03% vs. 6.65 +/- 0.95% in controls, p < 0.001; chromosome breaks at 3q25 band - 0.79 +/- 0.25% vs. 0.01% in controls, p < 0.001; structural aberrations affecting 3q25 band), very high frequency of acquired chromosomal aberrations (5.74 +/- 0.64% vs. 1.72 +/- 0.3% in controls) and a family history with 1 or 2 BEN parents were identified in 5 relatives. It is proposed that they are at high risk for developing the disease and that a genetic mechanism might be involved in the etiology of BEN.

Spontaneous and induced chromosome aberrations in Balkan endemic nephropathy

The aim of the present study was to investigate the spontaneous aberrations and chromosome breakages induced by X-rays and folic acid deficiency. In patients with Balkan endemic nephropathy (BEN) a higher frequency of spontaneous aberrations and chromosome lesions in medium TC 199 and radiation induced breakages were found compared with the healthy individuals. In BEN patients the 3q25 band was most frequently involved in the aberrations. These results support the idea that 3q25 may play a specific role and be a marker for BEN. Three of the additional five bands with increased frequencies of lesions in BEN patients contain oncogenes: 1q36-c src, 3p25-raf-1, and 6q23-myb. The frequent association of BEN and cancer can be explained by the chromosomal hypothesis of oncogenesis.

Induction of characteristic chromosomal aberrations, particularly X-trisomy, in cultured human lymphocytes treated by ochratoxin A, a mycotoxin implicated in Balkan endemic nephropathy

Ochratoxin A (OA), a mycotoxin which induces nephropathy and kidney tumours in rats and mice, is a contaminant of food consumed by a population with a high incidence of endemic nephropathy (EN). It was therefore tested in vitro for its ability to induce chromosomal aberrations in human peripheral lymphocytes in a small number of subjects, in the presence or absence of a kidney microsomal metabolic activation system. OA was found to induce aberrations on X chromosomes of similar types to those previously detected in lymphocytes from patients suffering from endemic nephropathy.

Upper urothelial tumours and the Balkan nephropathy. Inference from the study of a family pedigree

In an area heavily affected by both Balkan nephropathy (BN) and upper urothelial tumours (UUT), an outbreak of UUT (followed later by BN) affected at least four of five siblings. Their cousins developed BN in a high proportion but no one of them had any sign of UUT. It has been suggested that host factors determine the outcome of exposure to the same agent(s) responsible for both diseases.

[Activity of delta-aminolevulinate dehydratase and glutathione levels in the erythrocytes of patients with endemic nephropathy and in healthymembers of their families]

In a previous paper a markedly decreased activity of delta-aminolevulinate dehydratase (ALA-D) in patients with endemic nephropathy and in 24.6% of their healthy family members, was found. In this study the possible mechanisms of the decreased enzyme activity and the level of erythrocyte glutathione in patients and in healthy members from nephropathic families, were studied. We established decreased ALA-D activity in endemic nephropathy patients and in some healthy persons from their families. The normal concentration of erythrocyte glutathione was found in all groups. However, it was possible to reactivate the ALA-D enzyme in vitro by addition of exogenous glutathione. The obtained results suggested a normal synthesis of ALA-D apoenzyme and the existence of some factors whose effect upon enzyme activity was mediated through a binding to the reactive groups in the active centre of his enzyme or by oxidation of he reactive groups. Therefore, increased concentrations of sulfhydryl compounds, mostly of reduced glutathione are necessary for an optimal ALA-D activity.

Aetiology of Balkan nephropathy: a reappraisal after 30 years

Balkan nephropathy (BN) has been a complete aetiological puzzle for many years. Intense research produced many controversial results, but also helped some clues to be traced. Thus, it became rather obvious that the disease is caused by environmental factors (though it may be, to some extent, genetically controlled). Among live agents, slow viruses are the only (and theoretically very attractive) possible cause of both BN and urothelial tumours, which occur frequently in BN endemic areas. Apart from occasional visualization of virus-like particles, other evidence supporting this hypothesis has been lacking. The role biological products, particularly fungal toxins, needs to be further defined. An excess of any heavy metal or radioactive substance as a cause of BN is very unlikely indeed; however, a deficiency of a bio-essential element could not be ruled out. Many epidemiological data indicate that water might be a transmitter of the agent(s). A wide range of ions and minerals have been incriminated, but up to now most of the studies have provided negative or inconclusive results. Organic compounds in well water have never been sufficiently considered. Another ignored area are unstable and, particularly, photosensitive substances. Fertilizers, pesticides, analgesics, local herbs and teas have no causal relation to BN.

Ochratoxin A in human blood in relation to Balkan endemic nephropathy and urinary system tumours in Bulgaria

In continuing the effort to provide further evidence for the hypothesis that ochratoxin A might be involved in the aetiology of Balkan endemic nephropathy and the associated urinary system tumours, a survey to determine the occurrence of ochratoxin A in human blood was conducted in affected and unaffected areas of Bulgaria, where both diseases are prevalent. Ochratoxin A, positive samples, were present more often in blood from affected patients and the contamination levels were generally higher.

Cytogenetic studies in Balkan endemic nephropathy

The G band characteristic of chromosomes in 15 patients with Balkan endemic nephropathy (BEN), 20 relatives with no features of the disease and 25 healthy controls were investigated by cytogenetic analysis of lymphocyte cultures from peripheral blood. A specific chromosome marker in BEN was established in one No. 3 chromosome homologue characterized by a discordance in the banding patterns of the long arm, shortening the band 3q25 with faster fusion of subbands q26.1 and q26.3, and lack of differentiation of q24. Among the patients there were a mosaic case with a caryotype: 46,XY/46,XY,t(1;3) (q11.2;q25) and another one with a t(2;3)(p11.2; q25) in a tetraploid lymphocyte cell. The evidence of shortening of q25 and postzygotic mutations for 1/3 translocation and 2/3 translocation with the breakpoints on chromosome 3 being in 3q25 suggested that the critical band for BEN is 3q25.

An etiological approach to Balkan endemic nephropathy based on the investigation of two genetically different populations

The direct inheritance as a possible etiologic factor of Balkan endemic nephropathy (BEN) has been studied in an endemic area in the district of Slavonski Brod (Croatia-Yugoslavia). The basis for the investigation was given by a natural experiment induced by immigration of people from Ukraina to the endemic and nonendemic areas near Slavonski Brod. 1,536 persons in endemic villages and 733 inhabitants from the villages, where BEN has not been found, were studied with the aim of establishing diagnosis or excluding BEN. The generally adopted criteria enabling to classify the examined persons into the following 3 groups have been used: (a) diseased of BEN; (b) suspect to be diseased of BEN, and (c) individuals without signs of a renal disease. In the endemic villages among the population of Croatian aborigines, 12,1% diseased and suspects have been revealed. Among the Ukrainian immigrants and their offsprings, 10.5% diseased and suspects have been found. The difference is not significant (t = 0.7, p greater than 0.05). On the other hand, in nonendemic villages there were no diseased nor suspect BEN patients among the indigenous people as well as among the Ukrainians. The inference is suggested that the factors of the direct inheritance do not play a decisive role in the etiopathogenesis of BEN.

Clustering of the upper urothelial tumours in a family

In a Balkan nephropathy endemic area, 5 siblings developed haematuria over a period of 10 years. 4 of them were operated on and pathohystological examination revealed papillary transitional cell tumours of the renal pelvis and/or ureters. Both these tumours and the Balkan nephropathy affected only 1 generation of the family members. This fact, as well as the other relevant evidence, indicated that environmental factors played an important role in the process of carcinogenesis.