Ochratoxin A and human chronic nephropathy in Tunisia: is the situation endemic?

Toxicities induced in cultured human hepatocarcinoma cells exposed to ochratoxin A: oxidative stress and apoptosis status

Ochratoxin A (OTA) is a mycotoxin currently detected in stored animal and human food supplies as well as in human sera worldwide. OTA has diverse toxicological effects; however, the most prominent one is the nephrotoxicity. The present investigation was conducted to determine the molecular aspects of OTA toxicity in cultured human hepatocellular carcinoma cells. With this aim, we have monitored the effects of OTA on (i) cell viability, (ii) heat shock protein expressions as a parameter of protective and adaptive response, (iii) oxidative damage, and (iv) cell death signaling pathway. Our results clearly showed that OTA treatment inhibits cell proliferation, downregulates Hsp 70 and Hsp 27 protein and mRNA levels, and did not induce a significant reactive oxygen species generation. We have also demonstrated a decrease in mitochondrial membrane potential, a cytochrome c release, and an activation of caspase 9 and caspase 3 in response to OTA exposure. Moreover, OTA activates p53 expression, while some of its transcriptional target genes (Bax, Bak, PUMA, and p21) were found to downregulate. According to these data, we concluded that OTA may exert an inhibitory action on the transcriptional process. Besides, oxidative damage is not a major contributor to OTA toxicity. This mycotoxin induces a mitochondrial and caspase-dependent apoptotic cell death, which seems to be mediated by p53 transcriptional independent activities.

Ochratoxin A: The Continuing Enigma

The mycotoxin ochratoxin A (OTA) has been linked to the genesis of several disease states in both animals and humans. It has been described as nephrotoxic, carcinogenic, teratogenic, immunotoxic, and hepatotoxic in laboratory and domestic animals, as well as being thought to be the probable causal agent in the development of nephropathies (Balkan Endemic Nephropathy, BEN and Chronic Interstitial Nephropathy, CIN) and urothelial tumors in humans. As a result, several international agencies are currently attempting to define safe legal limits for OTA concentration in foodstuffs (e.g., grain, meat, wine, and coffee), in processed foods, and in animal fodder. In order to achieve this goal, an accurate risk assessment of OTA toxicity including mechanistic and epidemiological studies must be carried out. Ochratoxin has been suggested by various researchers to mediate its toxic effects via induction of apoptosis, disruption of mitochondrial respiration and/or the cytoskeleton, or, indeed, via the generation of DNA adducts. Thus, it is still unclear if the predominant mechanism is of a genotoxic or an epigenetic nature. One aspect that is clear, however, is that the toxicity of OTA is subject to and characterized by large species- and sex-specific differences, as well as an apparently strict structure-activity relationship. These considerations could be crucial in the investigation of OTA-mediated toxicity. Furthermore, the use of appropriate in vivo and in vitro model systems appears to be vital in the generation of relevant experimental data. The intention of this review is to collate and discuss the currently available data on OTA-mediated toxicity with particular focus on their relevance for the in vivo situation, and also to suggest possible future strategies for unlocking the secrets of ochratoxin A.

Mycotoxins and child health: the need for health risk assessment

The occurrences of mycotoxins as food contaminants in different localities particularly in developing countries and the inevitable exposure of populations and children to these toxins with probable adverse outcomes need be scientifically and systematically assessed. Health risk assessment developed in the 1980s is separate from risk management, both with risk communication form the risk analysis framework adopted by the World Health Organization. The process contributes increasingly to policy development, public health decision making, the establishment of mycotoxin regulations and research planning. However, the exercise of the risk assessment structured approach is not simple and is faced up to lack of data, capable infrastructure facilities and need for trained personnel and resources. Furthermore, adopted methodologies need be developed focusing on child characteristics and health concerns.

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.

Trends of incident dialysis patients in Tunisia between 1992 and 2001

BACKGROUND

Reliable information about the burden of end-stage renal disease (ESRD) is still scarce in the developing world.

STUDY DESIGN

Observational study of a national dialysis registry.

SETTING & PARTICIPANTS

Patients incident to dialysis therapy captured in the Tunisian registry of renal replacement therapy (RRT).

PREDICTOR

Intervals from 1992 to 2001.

OUTCOMES

Incidence rates of patients beginning dialysis therapy by age, sex, primary cause of ESRD, and region.

RESULTS

The incidence of treated ESRD dramatically rose in Tunisia during the 10-year period to reach 158.8 cases/million people in 2000 to 2001. We hypothesize that the Tunisian population is experiencing better access to RRT, a decrease in mortality from other causes, and an increase in chronic kidney diseases from chronic disease causes. Chronic diseases that develop with aging and economic development prevailed in urban environments, with diabetic nephropathy rising at the rate of 16.1%/y, whereas renovascular diseases, which include hypertensive nephropathy, rose by 7.6% annually. Interestingly, tubulointerstitial nephropathies increased by 10.4% each year, which may be related to such environmental risk factors as dietary exposure to ochratoxin A, especially in rural settings. ESRD from unknown causes or with missing information about cause increased by 12.7% yearly. Large regional differences in total incidence persist despite constant efforts to level off inequalities in access to health care facilities and RRT treatment.

LIMITATIONS

Possible underreferral for RRT, underreporting of cases, and misdiagnosis.

CONCLUSIONS

The growing incidence of patients on dialysis therapy in Tunisia emphasizes that preventing chronic kidney disease and its progression should be a public health priority.

Incidence of ochratoxin A in rice and dried fruits from Rabat and Salé area, Morocco

One hundred samples of dried fruits (20 dried raisins, 20 walnuts, 20 peanuts, 20 dried figs and 20 pistachios) and 20 samples of rice purchased from retail shops in the Rabat and Salé area in Morocco were analysed for ochratoxin A (OTA) by immunoaffinity clean-up (IAC) and liquid chromatography (LC) with fluorescence detection. The limit of quantification (LOQ) (S/N = 10:1) of OTA was 0.02 ng g(-1) in rice, 0.03 ng g(-1) in pistachio, peanut and walnut, and 0.03 ng g(-1) in dried raisins and dried figs. The incidences of occurrence of OTA in dried raisins, walnuts, peanuts, dried figs and rice were 30, 35, 25, 65 and 90%, respectively. Analytical results showed that pistachio samples contained no detectable OTA, but concentrations ranged from 0.02 +/- 0.01 to 32.4 +/- 2.10 ng g(-1) in rice, from 0.10 +/- 0.05 to 2.36 +/- 0.75 in peanut, from 0.03 +/- 0.01 to 1.42 +/- 0.45 in dried figs, from 0.05 +/- 0.02 to 4.95 +/- 0.02 in dried raisins, and from 0.04 +/- 0.01 to 0.23 +/- 0.05 in walnuts. The results also showed that 15% of the total number of rice samples analysed exceeded the 2002 regulatory limit set by European Union regulations for cereals. This is the first report on the occurrence of OTA in dried fruits and rice available in Morocco.

Occurrence of ochratoxigenic fungi and ochratoxin A in grapes from a Tunisian vineyard

The occurrence of ochratoxin A (OTA) and the identification of the ochratoxigenic microbiota in Tunisian grapes were studied for the first time. Black aspergilli were the dominant genus among the filamentous fungi isolated from grapes and were the only potential OTA-producing fungi found. The most abundant species were member of Aspergillus niger aggregate (63%) and Aspergillus carbonarius (36%). Uniseriate aspergilli were rarely present (1%). Of the A. carbonarius isolates, 97% were OTA positive but only 3% of the A. niger aggregate isolates were OTA positive. During grape maturation, the frequency of black aspergilli increased due to increase of the numbers of A. carbonarius. Musts (n=24) obtained from grapes collected at the different sampling times were analyzed for their OTA content. Up to 37% of the musts contained OTA at levels varying between 0.59 and 2.57 microg/l. The amounts of OTA in musts increased as grapes matured. These results indicate that A. carbonarius is the main cause of OTA contamination of Tunisian grapes.

Ochratoxin A in nephropathic patients from two cities of central zone in Portugal

Ochratoxin A (OTA) produced by Aspergillus and Penicillium genera contaminates several foods. OTA is nephrotoxic to all animal species studied so far, and most likely to humans, who show the longest half-life for elimination of this toxin among all examined species. OTA has other toxic effects such as teratogenicity, immunotoxicity, genotoxicity, and is also mutagenic and carcinogenic, all of which lead to life-threatening pathologies through several molecular pathways. A sensitive, specific and rapid method applying high performance liquid chromatography coupled to a spectrofluorimeter for the determination of ochratoxin A in human serum was validated. Serum samples were extracted with chloroform-orthophosphoric acid, and cleaned-up through immunoaffinity column (IAC). The separation and identification was performed by HPLC coupled to a spectrofluorimeter, and, after OTA methylation, the confirmation was achieved. Chromatographic separation of the analyte was performed on a reverse phase column with a mobile phase of water:acetonitrile:glacial acetic acid (49.5:49.5:1.0). Linearity was established between the range of 1 and 10 ng/ml. Under the optimized conditions, the recoveries were higher than 83.0% for all fortification levels. The intra-day precision oscillated between 8.0 and 5.0% at levels of 0.25 and 0.5 microg/l, while the inter-day precision was in the range of 10.7-16.0%. The limit of quantification of the method was 0.05 microg/l. The method is appropriate for quantitative determination of OTA in human serum and has been successfully applied to the analysis of OTA in haemodialysis patients from two principal cities of Portugal, in order to evaluate its exposure degree. Levels of OTA in Coimbra were higher than in Aveiro, 0.50 microg/l versus 0.49 microg/l. In respect to gender, levels of OTA were higher in males from Aveiro than in females, 0.52 microg/l versus 0.44 microg/l, and in Coimbra were similar, 0.50 microg/l versus 0.51 microg/l. However, in none of the cases, significant statistical differences were found.

Biomarkers of human exposure to ochratoxin A

Low blood serum/plasma concentrations of ochratoxin A (OTA) have been reported for healthy persons in more than 20 countries. Epidemiology studies in Bulgaria, Romania, Spain, the Czech Republic, Turkey, Italy, Egypt, Algeria and Tunisia have found significantly higher serum or plasma levels of OTA in patients with certain kidney disorders compared to healthy people, although the association may not be a causal one. Regional variations within one country, seasonal differences and variation within one person were found in some studies. Correlations with age and gender have not usually been detected. Detection limits using liquid chromatographic methods are about 0.02-0.1 ng ml(-1) plasma/serum so that incidences of positives often are 50-100%, reflecting widespread and continuous exposure of humans to OTA. In a study in the UK, OTA in urine was found to be a better indicator of OTA consumption than OTA in plasma. Nevertheless, blood plasma concentrations have been widely used to estimate dietary intake of OTA, using equations relating it with plasma concentration, plasma clearance and bioavailability. A further source of human exposure is airborne dust. OTA has been detected in human milk in several countries and comparisons with serum/blood levels have been made in Germany and Sweden.

Study of ochratoxin A as an environmental risk that causes renal injury in breast-fed Egyptian infants

Ochratoxin A (OTA) constitutes a real human threat. Its presence in human milk has previously been reported in different countries. This study is the first Egyptian report on the presence of OTA in both mothers' milk and infants' sera, addressing its correlation with infants' kidney functions, which was not previously addressed in the literature. Fifty healthy breast-lactating mothers and their infants who were exclusively breast-fed for at least 4 months were included. All of them were subjected to a thorough laboratory evaluation including determination of OTA concentration by high-performance liquid chromatography. Thirty-six mothers (72%) and their infants had been contaminated with OTA. Univariate analysis showed that the presence of OTA was associated with significantly higher levels of urinary beta2 microglobulin and microalbuminuria. Multivariate logistic regression analysis showed that there was a significant correlation between a higher OTA level in infants' sera and the degree of microalbuminuria. Mothers and their infants in our locality are exposed to a high OTA contamination rate (72%). To establish the role of OTA in causation of future renal dysfunction for infants, large controlled studies are warranted.

Nephrotoxicity associated with exposure to plant toxins, with particular reference to Africa

Acute renal failure is a frequent cause of morbidity and mortality in the hospitalized population worldwide. In Africa, apart from hemodynamic causes and infections, herbal remedies contribute to both morbidity and mortality, although these causes often go unrecognized. This paper reviews reports of herbal remedies that have been shown to result in nephrotoxicity. The indications for use of the remedies, signs and symptoms in poisoned patients, and the methods used to detect toxic compounds in plant specimens or in biological fluids are covered.

Ochratoxin A blood concentration in healthy subjects and bladder cancer cases from Pakistan

ASTRACT: The mycotoxin ochratoxin A (OTA) is a public health issue in many countries. Data on OTA concentrations in foods and in blood are available for several European countries including the Balkan area, as well as for Canada and Japan. Yet, for developing countries such data are scarce. In this study we determined OTA blood levels as biomarker of exposure in bladder cancer patients and in healthy controls from Pakistan. OTA in blood was analyzed after extraction by HPLC with fluorescence detection (limit of detection: <0.03 ng/mL) in 96 patients and in 31 controls. Over 92% of all blood samples (87 patients, 30 controls) contained quantifiable amounts of OTA: The mean OTA concentrations were 0.33 ng/mL (SD 0.42; range: 0.03 to 3.41 ng/mL) in bladder cancer patients, and 0.31 ng/mL (SD 0.29; range: 0.04 to 1.25 ng/mL) in healthy controls. These OTA concentrations are comparable to those reported for the general population in the European Union.

Karyomegaly of tubular kidney cells in human chronic interstitial nephropathy in Tunisia: respective role of Ochratoxin A and possible genetic predisposition

Karyomegalic nephropathy associated to bizarre enlargement of nuclei in renal tubular epithelial cells was first described by Mihatch in 1979. We present herein additional cases occurring in three siblings suffering from chronic interstitial nephropathy (CIN) of unknown aetiology where the renal biopsies showed numerous enlarged and hyperchromatic nuclei. CIN of unknown aetiology has been previously characterized and showed striking similarities with Balkan Endemic Nephropathy (BEN). Ochratoxin A (OTA) is a nephrotoxic mycotoxin suspected to be the causal agent of the BEN as well as the Tunisian CIN of unknown aetiology. OTA is incriminated in the onset of these disclosed cases of karyomegalic nephropathy since high OTA concentrations were found in blood (505.83 ng/ml, 102.63 ng/ml and 1023 ng/ml) and in urine (94.40 ng/ml and 10.18 ng/ml) of two of them. Moreover, we have investigated OTA in blood and urine as well as in food samples of the entire household (21 people). Our findings suggest (i) a link between OTA and the outcome of this karyomegalic nephropathy, and (ii) the possible involvement of a genetic factor since the three cases have the same haplotype B27/35.

How much should we involve genetic and environmental factors in the risk assessment of mycotoxins in humans?

Despite consented efforts in prevention, mycotoxins remain a problem of human health concern in several parts of the world including developed countries. Within the same range of toxins concentrations in the blood some people develop a disease while others do not. Could this inequality in front of mycotoxins effects be explained by environment factors and/or genetic predisposition? Among recent advances in environmental health research Correlation between chronic diseases and mycotoxins in humans deserves attention through several questions: Are genetic factors involved in disease causation of mycotoxins? How much are these factors currently taken into account for mycotoxins risk assessment and how much should we involve them? Answers are still to come. Genetic and environment factors deserve therefore more attention when dealing with regulatory limits, since among the general population, those who are at risk and will develop specific diseases are likely those bearing genetic predispositions. We have addressed these questions for the specific case of ochratoxin A in humans by investigating in Tunisia, county of Jelma, in four rural families forming a household of 21 persons all exposed to ochratoxin A in diet. Our results confirm that ochratoxin A induces chronic tubular nephropathy in humans and mainly point at those having the HLA haplotype A3, B27/35, DR7 to be more sensitive to the disease for quantitatively similar or lower exposure. Persons with such haplotype were found to bear chronic interstitial nephropathy with tubular karyomegalic cells while others were apparently healthy. Godin et al. (1996) in France have also found in sibling (a sister and her brother from urban area) that have similar HLA haplotype B35-patern, OTA-related renal tubulopathy with mild proteinuria including beta2-microglobulinuria. Several mechanisms are discussed that could be put ahead to explain how the HLA haplotype could lead to tubular cells lyses and renal failure. In the mean time it is urgent to search for mass screening biomarkers for mycotoxins in humans and related genetic factors to set-up more appropriate regulation.

Ochratoxin A levels in human plasma and foods in Lebanon

Ochratoxin A (OTA) is a widespread mycotoxin which contaminates food such as cereals, beer, coffee, wine and products of animal origin. OTA is known for its nephrotoxic, immunotoxic and carcinogenic properties. The prevalence of OTA in human blood and foodstuffs has been investigated in many countries. In this study, exposure of the Lebanese population to OTA was evaluated and the contamination of the most commonly consumed foods in Lebanon by OTA was assessed. Plasma samples from healthy individuals and also cereals and beer samples obtained from markets were collected from the different regions of Lebanon. OTA was detectable in 33% of tested plasma samples (n =250) with a concentration ranging from 0.1 to 0.87 ng/mL and a mean of 0.17+/-0.01ng/mL. No sex and age differences were found. The frequency of OTA-positive plasma samples obtained in the South of Lebanon and in the Bekaa valley (50 and 47%, respectively) was significantly higher compared to plasma samples obtained in the Beirut/Mount Lebanon region (19%). Food analyses showed that wheat, burghul and beer were contaminated with a mean value of 0.15+/-0.03 microg/kg, 0.21+/-0.04 microg/kg and 0.19+/-0.12 ng/mL, respectively. These data suggest that the Lebanese population is exposed to OTA through food ingestion at concentrations lower than the tolerable daily intake.

Ochratoxin A and β2-microglobulinuria in healthy individuals and in chronic interstitial nephropathy patients in the Centre of Tunisia: a hot spot of Ochratoxin A exposure

Ochratoxin A (OTA) is a nephrotoxic mycotoxin considered to be the causal agent of the Balkan endemic nephropathy (BEN). In Tunisia, a chronic interstitial nephropathy (CIN) of unknown aetiology, resembling BEN, has been characterised wherein OTA seems to be implicated too. However, despite the considerable number of investigations conducted so far, the role of OTA in the outcome of this human nephropathy is still uncertain. In this study, an attempt is being made to consolidate the link between OTA and the Tunisian CIN of unknown aetiology. Blood OTA and beta(2)-microglobulinuria levels were measured in several groups of healthy individuals and patients having different renal diseases of known and unknown aetiologies (100 nephropathy patients and 40 healthy subjects). The high blood OTA and beta(2)-microglobulinuria levels seem to be strongly associated to the CIN of unknown aetiology. Our results support the involvement of this nephrotoxic agent in the outcome of this particular human nephropathy and underline furthermore the importance of beta(2)-microglobulinuria in the characterization of this disease.