Etiology Of Balkan Endemic Nephropathy Research Articles

EVALUATION of ARISTOLOCHOLIC ACID and LIGNITE HYPOTHESES on the ETIOLOGY of BALKAN ENDEMIC NEPHROPATHY

Balkan Endemik Nefropatisi (BEN), Balkanlar’da 1950’li yıllarda tanımlanmış, kronik bir böbrek rahatsızlığıdır. Bulgaristan, Romanya ve Sırbistan gibi ülkelerde Pliyosen yaşlı kömür yataklarının ve BEN’li alanların yayılımının aynı olması sebebiyle BEN etiyolojisi için linyit etkisi öne sürülmüştür. Bu hipotez, kömür ile ilişkili olan yeraltı suyunun linyitleri yıkayarak yapılarındaki toksik organik maddeleri bünyesine aldığını, bu suyun arıtılmadan kullanılmasıyla BEN geliştiğini önerir. Sonraki çalışmalar, bu hipotezin zayıf yanlarını ortaya çıkarırken, nefrotoksik/kanserojenik bazı toksinlere (Aristolokolik Asit ve Okratoksin; AA ve OTA) çeşitli yollarla maruz kalınmasının BEN etiyolojisinde önemli rol oynadığını ortaya çıkarmıştır.
 Linyit hipotezini zayıflatan en önemli bulgu, Pliyosen linyit yataklarının bulunduğu diğer ülkelerde benzer böbrek rahatsızlıklarının görülmemesidir. Benzer şekilde, BEN etiyolojisi sadece AA ve OTA’ya maruz kalmakla da açıklanamamıştır. Tek faktörlü etiyolojiyi zayıflatan en temel noktalar şunlardır: BEN-endemik bölgelerde yaşayan tüm bölge sakinlerinin hastalanmaması, BEN hastası olan bir evdeki tüm aile bireylerinin hastalanmaması ve kadınların erkeklere oranla daha fazla hastalanması.
 Sonuç olarak, yaygın olarak kabul edilen görüş, BEN gelişiminde çok faktörlü etiyolojinin etkin olduğudur. Çok temel olarak, linyit kaynaklı PAH’ların veya fenollerin, antropojenik kökenli fitalatların ve AA’nın toksik etkilerinin birleşmesi ve genetik yatkınlık gibi sebeplerle hastalığın geliştiği kabul edilmektedir. Bu çalışmada, BEN hastalığı ile linyit ve aristolokolik asit arasındaki ilişkinin incelendiği çalışmalar derlenmiştir.

Synergistic Interaction of Polycyclic Aromatic Hydrocarbons, Phthalate Esters, or Phenol on DNA Adduct Formation by Aristolochic Acid I: Insights into the Etiology of Balkan Endemic Nephropathy.

Balkan endemic nephropathy (BEN) is a multifactorial environmental disease, with chronic exposure to aristolochic acids (AAs) through AA-contaminated food being one of the major etiological mechanisms. However, the bulk of previous research has only focused on investigating the possible roles of individual pollutants in disease development and the etiological mechanism of BEN remains controversial. In this study, we investigated the exposure concentration and duration dependence of coexposure to phthalate esters and lignite coal-derived phenol and polycyclic aromatic hydrocarbons (PAHs) on the metabolism and DNA adduct formation of aristolochic acid I (AAI). Results showed that both the metabolic activation and DNA adduct formation of AAI in cultured human kidney cells were affected by their coexposure to the above-mentioned environmental pollutants. Furthermore, our results suggest that chemicals leached from lignite coal likely played a role by triggering AA-activating enzymes to produce more of the promutagenic DNA adducts, thus further elevating the nephrotoxicity and carcinogenicity of AAs and increasing the risk of BEN. It is believed that the results of this study provide a better understanding of the etiological mechanism of BEN and offer insights into methods and policies to lower the risk of this devastating disease.

Aristolochic acid I: an investigation into the role of food crops contamination, as a potential natural exposure pathway.

Aristolochic acid I (AAI) is a potent nephrotoxic and carcinogenic compound produced by plants of the Aristolochiaceae family and thoroughly investigated as a main culprit in the etiology of Balkan endemic nephropathy (BEN). So far, the AAI exposure was demonstrated to occur through the consumption of Aristolochia clematitis plants as traditional remedies, and through the contamination of the surrounding environment in endemic areas: soil, food and water contamination. Our study investigated for the first time the level of AAI contamination in 141 soil and vegetable samples from two cultivated gardens in non-endemic areas, A. clematitis being present in only one of the gardens. We developed and validated a simple and sensitive ultra-high-performance liquid chromatography-ion trap mass spectrometry method for qualitative and quantitative AAI analysis. The results confirmed the presence of AAI at nanogram levels in soil and vegetable samples collected from the non-endemic garden, where A. clematitis grows. These findings provide additional evidence that the presence of A. clematitis can cause food crops and soil contamination and unveil the pathway through which AAI could move from A. clematitis to other plant species via a common matrix: the soil. Another issue regarding the presence of AAI, in a non-endemic BEN area from Romania, could underlie a more widespread environmental exposure to AAI and explain certain BEN-like cases in areas where BEN has not been initially described.

Octanol–Water Partition Coefficients of Aristolochic Acids and Implications to the Etiology of Balkan Endemic Nephropathy

The octanol–water partition coefficients (Kow) of the aristolochic acids, AA I and AA II, were determined using the traditional shake-flask method as a function of pH and ionic strength. These compounds have been implicated in the etiology of Balkan endemic nephropathy, but evidence of a plausible exposure pathway remains elusive, and research is constrained by the absence of critical physical–chemical parameters on these compounds. Apparent Kow values were determined across a range of pH and ionic strength conditions. The results show that the apparent Kow decreased by approximately four orders of magnitude as pH increased from 2 to 9. The pH dependence was well described by a simple model that calculated the apparent Kow based on the ionization fractions and intrinsic Kow values for the neutral and ionized species. Higher ionic strength solutions resulted in higher Kow values at high pH, but had no effect at low pH. These results suggest that transport of aristolochic acids will be highly dependent on pH and ionic strength, with significant aqueous-phase transport at neutral to slightly alkaline conditions, with the highest mobility occurring under low ionic strength conditions, and the possibility of significant partitioning to nonpolar phases, such as soil organic matter or plant material, at low pH. Much of the region where BEN is prevalent is a karst environment, and pH values are generally above 8, thus leaching and groundwater transport are favored, which can suggest possible exposure routes.

SILICON: ITS BIOLOGICAL IMPACT UNDER DIETARY INTAKE AND HYGIENIC STANDARDIZATION OF ITS CONTENT IN DRINKING WATER. A REVIEW

By the prevalence in the earth’s crust, silicon occupies the second place after oxygen. In different quantities silicon always presents in water and food products.The average daily dietary intake of silicon in Western world is about 20-50 mg/day. The biological role of silicon in human organism is still not clear, but it assumed to be necessary for processes of bone mineralization, collagen synthesis, it has a positive effect on the state of skin, hair, and nails, contributes to the prevention of atherosclerosis and Alzheimer disease. A number of scientific research is devoted to biological effects of silicon in animals and human subjects under intake with food and water, and substantiation of silicon (maximum admissible concentrations (MAC) in drinking water. In Chuvashia there was investigated the regional (geographical) pathology, which may be related with an increased silicon intake in association with the sharp imbalances of trace and macro elements in drinking water. Some measures were implemented to identify the possible role of silicon in etiology of Balkan endemic nephropathy. Organization for Economic Co-operation and Development (OECD) report summarized materials for the experimental evaluation of the toxicity and harmless levels of silicon intake with food and water in animals. A series of studies was executed to simulate the development of silicon urolithiasis and for the elucidation of the role of macro- and microelements accompanying the intake of silicon into the body in stone formation. There are studied potential therapeutic effects of water soluble silicon compounds on human health. The standards of silicon in drinking water are regulated only in Russia and Australia. At the same time in our country there were formed two opposing points of view in relation to the hygienic standardization of silicon. The first is one - MAC of silicon in drinking water needs to be cancelled, the second - MAC of silicon in the water needs to be tightened. To resolve the contradictions it is advisable to use both the experience of harmonization of standards with international requirements, and the principle of silicon regional standardization, taking into consideration the biogeochemical characteristics of geographic areas. When searching the literature databases PubMed and CyberLeninka were used.

Ochratoxin A in foods of animal origin

Ochratoxin A (OTA) is a mycotoxin produced by the fungi Aspergillus ochraceus καιPénicillium verrucosum. OTA shows a nephrotoxic, teratogenic, immunotoxic and carcinogenic action against animals and humans. In humans, OTA is implicated in the aetiology of Balkan endemic nephropathy. OTA can be mainly found in foods of animal origin as a result of indirect transmission from animals exposed to naturally contaminated feed. Results from research works in various countries showed that the pork meat was the most important source of human contamination with OTA, as compared to other products of animal origin. Sausages containing blood or pork kidney presented the highest amounts of OTA among other food products of animal origin. The presence of OTA in cow's milk was rather low, since the bacteria in the rumen of ruminants are capable of splitting OTA to ochratoxin a, which is generally accepted as no toxic metabolite. The European Union has not yet set limits of ochratoxin in foods of animal origin, in contrast to these of limits in foods of plant origin.

Balkan endemic nephropathy: an update on its aetiology.

Balkan endemic nephropathy (BEN) is a unique, chronic renal disease frequently associated with upper urothelial cancer (UUC). It only affects residents of specific farming villages located along tributaries of the Danube River in Bosnia-Herzegovina, Croatia, Macedonia, Serbia, Bulgaria, and Romania where it is estimated that ~100,000 individuals are at risk of BEN, while ~25,000 have the disease. This review summarises current findings on the aetiology of BEN. Over the last 50 years, several hypotheses on the cause of BEN have been formulated, including mycotoxins, heavy metals, viruses, and trace-element insufficiencies. However, recent molecular epidemiological studies provide a strong case that chronic dietary exposure to aristolochic acid (AA) a principal component of Aristolochia clematitis which grows as a weed in the wheat fields of the endemic regions is the cause of BEN and associated UUC. One of the still enigmatic features of BEN that need to be resolved is why the prevalence of BEN is only 3–7 %. This suggests that individual genetic susceptibilities to AA exist in humans. In fact dietary ingestion of AA along with individual genetic susceptibility provides a scenario that plausibly can explain all the peculiarities of BEN such as geographical distribution and high risk of urothelial cancer. For the countries harbouring BEN implementing public health measures to avoid AA exposure is of the utmost importance because this seems to be the best way to eradicate this once mysterious disease to which the residents of BEN villages have been completely and utterly at mercy for so long.

Quantitation of Aristolochic Acids in Corn, Wheat Grain, and Soil Samples Collected in Serbia: Identifying a Novel Exposure Pathway in the Etiology of Balkan Endemic Nephropathy.

While to date investigations provided convincing evidence on the role of aristolochic acids (AAs) in the etiology of Balkan endemic nephropathy (BEN) and upper urothelial cancer (UUC), the exposure pathways by which AAs enter human bodies to cause BEN and UUC remain obscure. The goal of this study is to test the hypothesis that environmental pollution by AAs and root uptake of AAs in the polluted soil may be one of the pathways by which AAs enter the human food chain. The hypothesis driving this study was that the decay of Aristolochia clematitis L., a AA-containing herbaceous plant that is found growing widespread in the endemic regions, could release free AAs to the soil, which could be taken up by food crops growing nearby, thereby transferring this potent human nephrotoxin and carcinogen into their edible parts. Using the highly sensitive and selective high-performance liquid chromatography coupled with fluorescence detection method, we identified and quantitated in this study for the first time AAs in corn, wheat grain, and soil samples collected from the endemic village Kutles in Serbia. Our results provide the first direct evidence that food crops and soil in the Balkans are contaminated with AAs. It is possible that the presence of AAs in edible parts of crops originating from the AA-contaminated soil could be one of the major pathways by which humans become exposed to AAs.

MicroRNA Profiling in Patients with Upper Tract Urothelial Carcinoma Associated with Balkan Endemic Nephropathy.

Balkan endemic nephropathy (BEN) is a disease that affects people that live in the alluvial plains along the tributaries of the Danube River in the Balkan region. BEN is a chronic tubulointerstitial disease with a slow progression to terminal renal failure and has strong association with upper tract urothelial carcinoma (UTUC). There are several hypotheses about the etiology of BEN, but only the toxic effect of aristolochic acid has been confirmed as a risk factor in the occurrence of the disease. Aberrantly expressed miRNAs have been shown to be associated with many types of cancers. A number of studies have investigated the expression of microRNAs in urothelial carcinoma, mainly on urothelial bladder cancer, and only a few have included patients with UTUC. Here we present the first study of microRNA profiling in UTUC tissues from patients with BEN (BEN-UTUC) and patients with UTUC from nonendemic Balkan regions (non-BEN-UTUC) in comparison to normal kidney tissues. We found 10 miRNAs that were differentially expressed in patients with BEN-UTUC and 15 miRNAs in patients with non-BEN-UTUC. miRNA signature determined in BEN-UTUC patients differs from the non-BEN-UTUC patients; only miR-205-5p was mutual in both groups.

Limitations and plausibility of the Pliocene lignite hypothesis in explaining the etiology of Balkan endemic nephropathy

Balkan endemic nephropathy (BEN) is a chronic, tubulointerstitial renal disease often accompanied by urothelial cancer that has a lethality of nearly 100%. One of the many factors that have been proposed to play an etiological role in BEN is exposure to organic compounds from Pliocene lignite coal deposits via the drinking water in endemic areas. The objective of this study was to systematically evaluate the role of the tenets of the Pliocene lignite hypothesis in the etiology of BEN in order to provide an improved understanding of the hypothesis for colleagues and patients alike. A comprehensive compilation of the possible limitations of the hypothesis, with each limitation addressed in turn is presented. The Pliocene lignite hypothesis can best account for, is consistent with, or has the potential to explain the evidence associated with the myriad of factors related to BEN. Residents of endemic areas are exposed to complex mixtures containing hundreds of organic compounds at varying doses and their potentially more toxic (including nephrotoxic) and/or carcinogenic metabolites; however, a multifactorial etiology of BEN appears most likely.

Organic compounds in water extracts of coal: links to Balkan endemic nephropathy

The Pliocene lignite hypothesis is an environmental hypothesis that has been proposed to explain the etiology of Balkan endemic nephropathy (BEN). Aqueous leaching experiments were conducted on a variety of coal samples in order to simulate groundwater leaching of organic compounds, and to further test the role of the Pliocene lignite hypothesis in the etiology of BEN. Experiments were performed on lignite coal samples from endemic BEN areas in Romania and Serbia, and lignite and bituminous coals from nonendemic regions in Romania and the USA. Room temperature, hot water bath, and Soxhlet aqueous extraction experiments were conducted between 25 and 80 °C, and from 5 to 128 days in duration. A greater number of organic compounds and in higher concentrations were present in all three types of leaching experiments involving endemic area Pliocene lignite samples compared to all other coals examined. A BEN causing molecule or molecules may be among phenols, PAHs, benzenes, and/or lignin degradation compounds. The proposed transport pathway of the Pliocene lignite hypothesis for organic compound exposure from endemic area Pliocene lignite coals to well and spring drinking water, is likely. Aromatic compounds leached by groundwater from Pliocene lignite deposits in the vicinity of endemic BEN areas may play a role in the etiology of the disease. A better understanding of organic compounds leached by groundwater from Pliocene lignite deposits may potentially lead to the identification and implementation of effective strategies for the prevention of exposure to the causative agent(s) for BEN, and in turn, prevention of the disease.

Evidence of exposure to aristolochic acid in patients with urothelial cancer from a Balkan endemic nephropathy region of Romania

Recently, chronic Aristolochia poisoning was found responsible for the aetiology of Balkan endemic nephropathy (BEN) in Croatia, Serbia, and Bosnia, and diet was the likely route of exposure to aristolochic acid (AA). BEN, often associated with an increased incidence of upper urinary tract carcinoma (UUC), also affects residents of certain rural villages in Romania. AA is a nephrotoxin and human carcinogen that forms DNA adducts after metabolic activation, which induce characteristic TP53 mutations in urothelial tumours. Here we present the first evidence linking AA exposure to UUC in residents of an endemic region in the Romanian Mehedinti County. DNA was extracted from kidney and tumour tissue of seven patients who underwent nephroureterectomy for UUC and resided in BEN villages (endemic group). Five patients with UUC from nonendemic villages served as controls. AA-DNA adducts (7-(deoxyadenosin-N(6) -yl)-aristolactam I), established biomarkers of AA exposure, were identified by (32)P-postlabelling in renal DNA of six patients from the endemic group and in one of the nonendemic group (adduct levels ranged from 0.3 to 6.5 adducts per 10(8) nucleotides). Additionally, an A to T transversion in TP53, a base substitution characteristic of AA mutagenic activity was found in urothelial tumour DNA of one patient from the endemic group. Our results provide a molecular link to the cause of urothelial tumours in BEN regions of Romania indicating that AA is the common aetiological agent for BEN across its numerous geographical foci.

Pro- and Antiapoptotic Markers in Upper Tract Urothelial Carcinoma Associated with Balkan Endemic Nephropathy

The role of aristolochic acid in the etiology of Balkan endemic nephropathy (BEN) and associated upper-tract urothelial carcinoma (UTUC) has been recently confirmed. The aim of this study was to determine apoptosis-related marker(s) specific for BEN-associated UTUC. Present investigation included 105 patients with UTUC, 44 from BEN region and 61 control tumors. Altered expression of Survivin was more often present in BEN UTUC with high grade and solid growth (P < 0.005; P < 0.05) than in control tumors. Significantly lower expression of proapoptotic marker Bax was found in BEN tumors with high grade, high stage, necrosis, and without metaplastic change (P < 0.05; 0.05; 0.05; 0.05) compared to control tumors with the same features. Group (BEN-related/control), stage, growth pattern, and caspase 3 activity were significantly associated with the expression of Bax (P = 0.002, 0.034, 0.047, 0.028, resp.,). This investigation identifies Bax as specific marker of BEN-associated UTUC. Decrease of pro-apoptotic protein Bax together with alteration of Survivin may be indicative for specific disturbances of intrinsic apoptotic pathway in UTUC arising in endemic areas.

Ochratoxin a: general overview and actual molecular status.

Ochratoxin A (OTA) is a mycotoxin produced by several species of Aspergillus and Penicillium fungi that structurally consists of a para-chlorophenolic group containing a dihydroisocoumarin moiety that is amide-linked to L-phenylalanine. OTA is detected worldwide in various food and feed sources. Studies show that this molecule can have several toxicological effects such as nephrotoxic, hepatotoxic, neurotoxic, teratogenic and immunotoxic. A role in the etiology of Balkan endemic nephropathy and its association to urinary tract tumors has been also proved. In this review, we will explore the general aspect of OTA: physico-chemical properties, toxicological profile, OTA producing fungi, contaminated food, regulation, legislation and analytical methods. Due to lack of sufficient information related to the molecular background, this paper will discuss in detail the recent advances in molecular biology of OTA biosynthesis, based on information and on new data about identification and characterization of ochratoxin biosynthetic genes in both Penicillium and Aspergillus species. This review will also cover the development of the molecular methods for the detection and quantification of OTA producing fungi in various foodstuffs.

Investigation of Balkan endemic nephropathy in Serbia: How to proceed?

Balkan endemic nephropathy (BEN) presents an unsolved puzzle despite fifty years of its investigation. Academy of Medical Sciences of the Serbian Medical Society organized a round table discussion on current unsolved problems related to BEN. The present paper summarizes presentations, discussion and conclusions of this meeting. During the last fifty years, the course of BEN prolonged and it shifted towards the older age in all endemic foci. Data on the incidence of BEN have been controversial and frequently based on the data on the number of BEN patients starting haemodialysis treatment. In Serbia, BEN patients present 6.5% of haemodialysis population and this percentage differs among different centres ranging from 5% (Leskovac) to 46% (Lazarevac). Maintenance of high prevalence of BEN patients on regular haemodialysis indicates that BEN is not an expiring disease. In addition, recent data have shown more frequent microalbuminuria and low-molecular weight proteinuria in children from endemic than from nonendemic families. Aetiology of BEN is still unknown despite numerous investigations of environmental and genetic factors. Today, there is a very current hypothesis on the aetiological role of aristolochic acid but the role of viruses, geochemical factors and genetic factors must not be neglected. Morphological features of BEN are nonspecific and characterized by acellular interstitial fibrosis, tubular atrophy and changes on pre- and postglomerular vessels. New immunohistochemical and molecular biology methods offer a new approach to BEN investigation. Association of BEN with high incidence of upper-urothelial tumours is well-known. Recent studies have shown significant changes of demographic characteristics of patients suffering upper-urothelial tumours, their prevalence in different endemic foci and characteristics of tumours. Further studies of BEN should be directed to determination of incidence and prevalence of disease in different endemic foci, investigations of different insufficiently examined aetiological factors as well as pathomorphological features of the disease by the use of modern methods.

Genetic clues to the etiology of Balkan endemic nephropathy: Investigating the role of ACE and AT1R polymorphisms

Balkan endemic nephropathy (BEN) was recognized as a distinct entity more than 50 years ago, but the exact environmental and genetic causes of the disease remain elusive. Considering the role of the renin-angiotensin system (RAS) in the emergence of various nephropathies, in the present study we evaluated the possible association with BEN of polymorphisms in two RAS genes: I/D ACE (an angiotensin-converting enzyme) and A1166C AT1R (an angiotensin type 1 receptor). The study groups consisted of 48 BEN patients from the endemic region in the district of Kolubara, Serbia, 33 patients with other nephropathies and 42 healthy individuals. The ACE DD genotype was significantly more represented in the NBEN group (OR=5.447; 95%CI=1.862-15.932, p&lt;0.01). The frequency of the AT1R CC genotype was higher in BEN patients compared to controls (0.104 vs. 0.048), but the difference was not significant. Though the analyzed polymorphisms are associated with certain nephropathies, we found no support for their specific role in BEN susceptibility.

Molecular Markers in Upper Urothelial Carcinoma Associated to Balkan Endemic Nephropathy. Aristolochic Acid as the Major Risk Factor of the Worldwide Disease

The role of aristolochic acid in the etiology of Balkan endemic nephropathy (BEN) and associated upper urothelial carcinoma (UUC) was recently confirmed. The aim of this study was to determine the marker(s) specific for BEN-associated UUC. A total of 82 patients with UUC (38 from the BEN region and 44 control tumors) were included in the study. The Ki-67 index in BEN tumors correlated with the grade and multifocality (p < 0.05), but in regression analysis, only the grade of BEN tumor. The p53 index was significantly higher in BEN than in control tumors (p < 0.05), as well as the alteration of p53 (p < 0.05). BEN low-stage tumors, tumors without limphovascular invasion (LVI), and tumors of the renal pelvis had a higher p53 index than the control tumors (p < 0.05, 0.01, 0.05, respectively). The Ki-67 index was higher in control tumors with high-stage and solid growth than in BEN UUC (p < 0.050, 0.005). The Ki-67 correlated with the grade, growth, stage, LVI, and multifocality of UUC on the best way, but not with the group. In regression analysis, only multifocality of UUC had predictive influence on Ki-67 activity (p < 0.001). P53 correlated with the grade, growth, and group (p < 0.05). This investigation identifies the p53 pathway as the specific cell cycle marker involved in BEN-associated UUC.

Balkan Nephropathy: Evolution of Our Knowledge

Balkan endemic nephropathy (BEN), originally described in the late 1950s as a chronic tubulointerstitial kidney disease, is identified by its unique epidemiological features. The most remarkable characteristic of BEN is the focal topographical nature that characterizes its occurrence at the global, national, and even household level. BEN affects only certain endemic rural foci along tributaries of the Danube River in the Balkan countries of Bosnia, Bulgaria, Croatia, Romania, and Serbia. The spatial distribution has remained astonishingly unchanged with time because the disease affects the same endemic clusters as 50 years ago. The natural course of the disease is characterized by universal development of end-stage renal disease and the frequent development of upper urinary tract tumors, posing a substantial disease burden to the afflicted areas. The greatest challenge in the study of BEN has been the elucidation of its cause. The unique features of the disease, in particular its endemic nature and the long incubation period required for the disease to develop, have led to the proposal that BEN represents a unique environmental disease. The quest for the responsible environmental factor has been long and diverse, and although no definitive answer has been provided to date, converging lines of evidence support the theory that long-term consumption of food contaminated with aristolochic acid underlies the pathogenesis of BEN. The present review describes the evolution of our knowledge of BEN in relation to the development of the main theories for its pathogenesis.

Bioactivation and DNA adduction as a rationale for ochratoxin A carcinogenesis

Ochratoxin A (OTA) is a para-chlorophenolic mycotoxin produced by strains of Aspergillus and Penicillium that is widely found as a contaminant of improperly stored food products. The toxin is a potent renal carcinogen in rats, especially male, and has an implicated role in the etiology of Balkan endemic nephropathy and its associated urinary tract tumours. Although the mechanism of OTA-mediated tumour formation is not fully understood, and represents a hotly debated topic, bioactivation and subsequent DNA adduction through covalent attachment of electrophilic OTA species remains a viable mechanism for OTA-mediated carcinogenesis. In this paper we outline the established chemistry for the bioactivation of chlorophenol carcinogens and demonstrate how this chemistry relates to the bioactivation of OTA. From this basis it is predicted that OTA will form a benzoquinone electrophile following activation by cytochrome P450 enzymes and radical species following activation by enzymes with peroxidase activities. These electrophiles react preferentially with deoxyguanosine (dG) to form benzetheno adducts and C8- dG adducts, respectively. Analysis of OTA-mediated DNA adduction using the 32P-postlabelling method correlates with OTA chemistry and adduct spots derived from the quinone electrophile are generated following activation by cytochrome P450, while a C8-OTA adduct is formed following activation of OTA by peroxidase enzymes. These same adduct spots are also produced in animal (rat and pig) and human tumoral kidney tissue. This model for OTAmediated carcinogenesis is consistent with established structure-activity relationships for covalent attachment of OTA analogues and OTA toxicity. The model also provides a rationale for the synergistic effect observed for OTA in the presence of the mycotoxin citrinin and for the sexual differences observed in rat carcinogenesis where the male is particularly susceptible to OTA-mediated tumour formation.

Metals and kidney markers in adult offspring of endemic nephropathy patients and controls: a two-year follow-up study.

BackgroundThe etiology of Balkan Endemic Nephropathy, (BEN), a tubulointerstitial kidney disease, is unknown. Although this disease is endemic in rural areas of Bosnia, Bulgaria, Croatia, Romania, and Serbia, similar manifestations are reported to occur in other regions, for instance Tunisia and Sri Lanka. A number of explanations have been stated including lignites, aristolochic acid, ochratoxin A, metals, and metalloids. Etiologic claims are often based on one or a few studies without sound scientific evidence. In this systematic study, we tested whether exposures to metals (cadmium and lead) and metalloids (arsenic and selenium) are related to Balkan Endemic Nephropathy.MethodsIn 2003/04 we recruited 102 adults whose parents had BEN and who resided in one of three communities (Vratza, Bistretz, or Beli Izvor, Bulgaria). A control group comprised of 99 adults having non-BEN hospitalized parents was enrolled in the study during the same time. We conducted face-to-face interviews, ultrasound kidney measurements, and determined kidney function in two consecutive investigations (2003/04 and 2004/05). Metals and metalloids were measured in urine and blood samples. To assess the agreement between these consecutive measurements, we calculated intraclass correlation coefficients. Repeated measurement data were analyzed using mixed models.ResultsWe found that cadmium and arsenic were associated with neither kidney size nor function. Lead had a significant but negligible effect on creatinine clearance. Selenium showed a weak but significant negative association with two of the four kidney parameters, namely creatinine clearance and β2-microglobulin. It was positively related to kidney length. These associations were not restricted to the offspring of BEN patients. Adding credence to these findings are reports showing comparable kidney effects in animals exposed to selenium.ConclusionThe findings of this 2-year follow-up study indicate that metals and metalloids do not play a role in the etiology of Balkan Endemic Nephropathy. Against the assumption in the literature, selenium was not protective but a risk factor. Since comparable associations were observed in animals, future studies are needed to explore whether selenium may have adverse renal effects in humans.