PRESENTED BY
MARC DE BROE AND BENJAMIN VERVAET

Presentation Summary

Written by Jasna Trbojevic-Stankovic
Reviewed by Marc De Broe and Benjamin Vervaet

Chronic interstitial nephritis in agricultural communities (CINAC)
In 1995 an outbreak of acute kidney injury manifesting with chronic nephritis and resulting in chronic kidney disease (CKD) has been noticed in Central America, Sri Lanka and other tropical countries. The condition has been named chronic interstitial nephritis in agricultural communities (CINAC), since it predominantly appeared in farming communities. The established minimal set of clinical diagnostic criteria for CINAC included: residence in agricultural communities in tropical climate, predominance of young males, and absence of diabetes, hypertension, glomerulopathies or other known causes of CKD (1).

A quarter of the century later, etiology of CINAC is still obscure. The condition appears to be multifactorial, with various hypotheses being proposed. Several factors have been suggested as possible triggers, including heat stress, episodes of repeated dehydration, and exposures to toxic agrochemicals through work, ingestion of contaminated food and water, or by inhalation of toxic substances in the agricultural communities. Evidence supports occupational and environmental toxins as the primary trigger (1). However, diagnosis is still based on exclusion criteria.

Renal biopsy study of CINAC patients
Renal biopsies and patohysiological analysis are of crucial importance in patients presenting with clinical symptoms suggestive of CINAC. Analysis of collections of kidney biopsies from patients with clinical manifestation of CINAC from El Salvador, France, India and Sri Lanka returned compelling results, as presented on Figure 1. The most remarkable feature observed with light microscopy in virtually all examined samples was a remarkable accumulation of large granules in proximal tubular cells, with some granules demonstrating clear dysmorphia and containing dispersed intragranular aggregates (2).

Figure 1. Jones-stained sections revealed prominent accumulation of intracellular granules (identified as lysosomes) with different phenotypic appearances. Prominent enlarged granules, some with irregular/dysmorphic shapes and heterogenous content. B and D respresent the squares in A and C, respectively. Image Images from Sri Lankan CINAC patients. Image C and D reproduced from supplemental figure S2 of Vervaet et al., who published as an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

The immunofluorescence microscopy analysis revealed autofluorescence of the observed granules. Furthermore, when stained with Jones silver staining, the granules, predominantly present in the proximal tubular cells from segment S1 to S3, showed notable argyrophilia. Other observed features on proximal tubular cells included conserved height, but noticeable atrophy, apical blebbing, thickening of the basement membrane, interstitial expansion, fibrosis and defective proliferation. All these alterations suggested a remarkable deterioration of regenerative capacity (2).

Further investigation addressed the origin of the CINAC granules. They exhibited positive staining for Cathepsin B and lysosome-associated membrane protein 1 (LAMP-1). Electron microscopy analysis demonstrated dysmorphic intracellular granules containing dispersed electron dense aggregates in the proximal tubular epithelial cells (Figure 2). The observations were comparable with light microscopy, but there was still insufficient data to confirm these were lysosomes. The final confirmation came from a specific technique, called the Transmission Electron Microscopy Energy-Dispersive X-ray spectroscopy (TEM-EDX), which was applied on the Jones stained tissue section, verifying that observed granules in fact originated from lysosomes.

The connection between lesions in CINAC patients and patients treated with calcineurin-inhibitors
Analysis of biopsy samples from patients with suspected CINAC from different parts of the world showed remarkable similarity, suggesting an epidemic of very large proportion (Figure 2).

Figure 2. CINAC patients across the world have the same histopathological appearance. Panels A, C, E, G are Jones stainined sections; panels B, D, F, H are electronmicroscopic images. Images A-H reproduced from figure 11 of Vervaet et al., who published as an open access article under the CC BY- NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Furthermore, when samples from patients with CINAC, non- CINAC nephropathies and normal controls were compared, a striking similarity was observed between the lesions in CINAC patients and transplant patients on calcineurin inhibitors (CIN) therapy (6-9). This led to a conclusion that possible toxic cause of CINAC promotes the same alterations of tissue morphology as CIN (5-8). The CIN-related tissue alterations, including the appearance of dysmorphic lysosomes, eventually progress over time, probably due to the acquired phenotype associated with exposure to nephrotoxic drugs that inhibit calcineurin (10-13).

The search for the connection between the CINAC and CIN-related lesions returned several possible reciprocities. Certain pesticides, such as synthetic pyrethroids and chlorinated hydrocarbon insecticides, exhibit direct inhibition on calcineurin (14). Moreover, they activate reactive oxygen species (ROS), which also impede calcineurin effects (15-17). Furthermore, several agrochemicals, such as paraquat, roundup and several others, are able to induce ROS (18-21). These mechanisms might represent the possible link between agrochemicals and CIN.

References

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