Chronic interstitial nephritis in agricultural communities is a toxin-induced proximal tubular nephropathy.

Almost 30 years after the detection of chronic interstitial nephritis in agricultural communities (CINAC) its etiology remains unknown. To help define this we examined 34 renal biopsies from Sri Lanka, El Salvador, India and France of patients with chronic kidney disease 2-3 and diagnosed with CINAC by light and electron microscopy. In addition to known histopathology, we identified a unique constellation of proximal tubular cell findings including large dysmorphic lysosomes with a light-medium electron-dense matrix containing dispersed dark electron-dense non-membrane bound "aggregates". These aggregates associated with varying degrees of cellular/tubular atrophy, apparent cell fragment shedding and no-weak proximal tubular cell proliferative capacity. Identical lysosomal lesions, identifiable by electron microscopy, were observed in 9% of renal transplant implantation biopsies, but were more prevalent in six month (50%) and 12 month (67%) protocol biopsies and in indication biopsies (76%) of calcineurin inhibitor treated transplant patients. The phenotype was also found associated with nephrotoxic drugs (lomustine, clomiphene, lithium, cocaine) and in some patients with light chain tubulopathy, all conditions that can be directly or indirectly linked to calcineurin pathway inhibition or modulation. One hundred biopsies of normal kidneys, drug/toxin induced nephropathies, and overt proteinuric patients of different etiologies to some extent could demonstrate the light microscopic proximal tubular cell changes, but rarely the electron microscopic lysosomal features. Rats treated with the calcineurin inhibitor cyclosporine for four weeks developed similar proximal tubular cell lysosomal alterations, which were absent in a dehydration group. Overall, the finding of an identical proximal tubular cell (lysosomal) lesion in CINAC and calcineurin inhibitor nephrotoxicity in different geographic regions suggests a common paradigm where CINAC patients undergo a tubulotoxic mechanism similar to calcineurin inhibitor nephrotoxicity.

Chronic dehydration induces injury pathways in rats, but does not mimic histopathology of chronic interstitial nephritis in agricultural communities.

CINAC-patients present renal proximal tubular cell lysosomal lesions which are also observed in patients experiencing calcineurin inhibitor (CNI) nephrotoxicity, suggesting that CINAC is a toxin-induced nephropathy. An alternative hypothesis advocates chronic dehydration as a major etiological factor for CINAC. Here, we evaluated histological and molecular changes in dehydrated versus toxin exposed rats. Wistar rats were divided in 3 groups. Group 1 (n = 6) had free access to drinking water (control group). Group 2 (n = 8) was water deprived for 10 h per 24 h, 5 days/week and placed in an incubator (37 °C) for 30 min/h during water deprivation. Group 3 (n = 8) underwent daily oral gavage with cyclosporine (40 mg/kg body weight). After 28 days, renal function, histopathology and proteomic signatures were analysed. Cyclosporine-treated rats developed focal regions of atrophic proximal tubules with associated tubulo-interstitial fibrosis. PASM staining revealed enlarged argyrophilic granules in affected proximal tubules, identified as lysosomes by immunofluorescent staining. Electron microscopy confirmed the enlarged and dysmorphic phenotype of the lysosomes. Overall, these kidney lesions resemble those that have been previously documented in farmers with CINAC. Dehydration resulted in none of the above histopathological features. Proteomic analysis revealed that dehydration and cyclosporine both induce injury pathways, yet of a clear distinct nature with a signature of toxicity only for the cyclosporine group. In conclusion, both cyclosporine and dehydration are injurious to the kidney. However, dehydration alone does not result in kidney histopathology as observed in CINAC patients, whereas cyclosporine administration does. The histopathological analogy between CINAC and calcineurin inhibitor nephrotoxicity in rats and humans supports the involvement of an as-yet-unidentified environmental toxin in CINAC etiology.

Effects of medicagenic acid metabolites, originating from biotransformation of an Herniaria hirsuta extract, on calcium oxalate crystallization in vitro.

ETHNOPHARMACOLOGICAL RELEVANCE: Herniaria hirsuta is traditionally used in Moroccan folk medicine for treatment of urinary stones and as a diuretic. It is rich in saponins, which are known to be deglycosylated in the colon, whereafter aglycones such as medicagenic acid are absorbed and further metabolized in the liver. AIM OF THE STUDY: A sample of hepatic metabolites of medicagenic acid, with medicagenic acid glucuronide as the most abundant one, was evaluated for in vitro activity against urinary stones. A crystallization assay and a crystal-cell interaction assay were used to evaluate in vitro activity of hepatic metabolites of medicagenic acid on CaC2O4 (calciumoxalate) crystals, present in the majority of urinary stones. MATERIALS AND METHODS: In the crystallization assay the effects on nucleation of Ca2+ and C2O42- and aggregation of the CaC2O4 crystals are studied. In the crystal-cell interaction assay crystal retention is investigated by determining the amount of Ca2+ bound to injured monolayers of MDCK I cells. RESULTS: Results of the crystallization assay showed a tentative effect on crystal aggregation. The crystal-cell interaction assay showed a significant inhibition of crystal binding, which may reduce crystal retention in the urinary tract. CONCLUSIONS: As both formation of crystals by inhibiting aggregation and retention of crystals is affected, the beneficial effect of H. hirsuta against urinary stones may at least in part be attributed to medicagenic acid metabolites, indicating that saponins containing medicagenic acid may act as prodrugs.

Chronic interstitial nephritis in agricultural communities: a new perspective on etiology, diagnosis and mechanism.

Chronic interstitial nephritis in agricultural communities is a devastating kidney disease with a globally increasing prevalence. Its cause is unknown. Two predominant etiologies are hypothesised: recurrent episodes of dehydration and exposure to environmental toxins, such as agrochemicals and metals. In this review, we summarise arguments on: 1) why heat stress/dehydration is an unlikely cause of this disease and 2) why chronic interstitial nephritis in agricultural communities is to be considered a toxin-induced nephropathy. Mechanistically, we provide arguments for a putative role of pesticides on the one hand, and the calcineurin pathway on the other hand, both of which require further investigation. Finally, we summarise several important perspectives for research on chronic interstitial nephritis in agricultural communities.