Solving the riddle of Aguascalientes nephropathy: nephron number, environmental toxins and family clustering

Association of perinatal exposition to xenobiotics with kidney volume at birth

BACKGROUND

The state of Aguascalientes has the highest prevalence of kidney failure in young adults globally. A low nephron endowment has been suggested as a possible aetiology. This study aims to evaluate the association between exposure to xenobiotics and low kidney volume (KV) at birth.

METHODS

This is a cross-sectional, observational, descriptive study of at-term pregnant women with no comorbidities. We collected the mother's urine (MU) and amniotic fluid (AF) and the neonate's urine (NU). Metals and non-metals were measured with inductively coupled plasma mass spectrometry, pesticides with high-performance liquid chromatography and fluoride with ion-selective potentiometry. The total KV adjusted by body surface area (TKVBS) was calculated based on the kidney ultrasound.

RESULTS

Between March 2022 and July 2023, we included 299 women with an average age of 24.2 years [standard deviation (SD) 5.1]. A total of 54.2% of neonates were male with an average weight of 3266 g (SD 399). Factors associated with TKVBS ≤5th percentile were female sex, weight gain during pregnancy, glomerular filtration rate, methomyl concentration in AF {odds ratio [OR] 7.41 [95% confidence interval (CI) 2.31-23.8], P = .001}, 2,4-dichlorophenoxyacetic (2,4-D) >10 ng/ml in AF [OR 4.99 (95% CI 1.58-15.7), P = .002], MU [OR 6.1 (95% CI 1.9-19.7), P = 0.002] and NU [OR 5.1 (95% CI 1.10-26.2), P = .023] and fluoride in MU [OR 5.1 (95% CI 1.10-23.5), P = .010] and AF [OR 6.76 (95% CI 1.28-35.7), P = .024]. In all matrices (MU, AF and NU), exposure to pesticides was also significantly associated with greater concentrations of electrolytes (sodium, potassium, calcium, phosphate and magnesium) and trace elements (zinc and iron).

CONCLUSIONS

In neonates born to at-term women with no comorbidities, the presence of pesticides and fluoride was associated with low KV. The significant loss of electrolytes and trace elements associated with pesticides suggests proximal tubulopathy.

Pediatric kidney dimensions and risk of persistent albuminuria in Mexican adolescents

In Mexico, chronic kidney disease of unknown origin is highly prevalent. Screening studies in adolescents have shown persistent microalbuminuria (pACR), adaptive podocytopathy and decreased kidney volume (KV). Here, we sought to develop normality tables of kidney dimensions by ultrasound in the Mexican state of Aguascalientes pediatric population (0 to 18y) and evaluate the relationship between the KV and pACR among the region's adolescents in a cross-sectional study. Kidney length (KL) and KV were determined by ultrasound. Our findings were compared with those in international literature of different populations where tables and graphs of normal kidney dimensions by ultrasound were reported. We compared organ dimensions in individuals above the age of 11 without albuminuria with those in patients with pACR recruited through screening studies in adolescents in Aguascalientes. This included 1068 individuals to construct percentile tables and graphs of the KL. Kidney dimensions were significantly lower when compared with all international comparisons. From a total 14,805 screen individuals, we compared 218 adolescents with pACR and 377 individuals without significant albuminuria. The Total KV adjusted to body surface (TKVBS) was significantly associated with pACR (odds ratio 1.03, 95% confidence interval 1.02-1.03). The upper quartile of TKVBS was highly associated with pACR (7.57, 4.13-13.87), hypertension (2.53, 1.66-3.86), and hyperfiltration (26 vs 11.5%). Thus, TKVBS is directly associated with pACR while greater KV, arterial hypertension, and hyperfiltration in patients with pACR suggest that the increase in volume is secondary to kidney hypertrophy. Additionally, the adaptative podocytopathy with low fibrosis seen on kidney biopsy which was performed in a subset of patients, and the smaller kidney dimensions in our population point to prenatal oligonephronia as the primary cause of the detected kidney disease.

Oligonephronia: another piece in the CKDu jigsaw?

Rates of chronic kidney disease of unknown etiology are high in Aguascalientes, Mexico. Kidneys of adolescents are small by ultrasonography, compatible with oligonephronia, whereas proteinuria and higher estimated glomerular filtration rates and blood pressures among those with relatively higher kidney volumes probably flag relatively greater degrees of compensatory hypertrophy. Glomerulomegaly and podocytopathy, and later segmental glomerulosclerosis in biopsies, suggest a cascade driven by nephron deficiency. Better measures of glomerular number and volume should improve understanding, facilitate risk assessment, and guide interventions.

Insights into Repeated Renal Injury Using RNA-Seq with Two New RPTEC Cell Lines

Renal proximal tubule epithelial cells (RPTECs) are a primary site for kidney injury. We created two RPTEC lines from CD-1 mice immortalized with hTERT (human telomerase reverse transcriptase) or SV40 LgT antigen (Simian Virus 40 Large T antigen). Our hypothesis was that low-level, repeated exposure to subcytotoxic levels of 0.25-2.5 μM cisplatin (CisPt) or 12.5-100 μM aflatoxin B1 (AFB1) would activate distinctive genes and pathways in these two differently immortalized cell lines. RNA-seq showed only LgT cells responded to AFB1 with 1139 differentially expressed genes (DEGs) at 72 h. The data suggested that AFB1 had direct nephrotoxic properties on the LgT cells. However, both the cell lines responded to 2.5 μM CisPt from 3 to 96 h expressing 2000-5000 total DEGs. For CisPt, the findings indicated a coordinated transcriptional program of injury signals and repair from the expression of immune receptors with cytokine and chemokine secretion for leukocyte recruitment; robust expression of synaptic and substrate adhesion molecules (SAMs) facilitating the expression of neural and hormonal receptors, ion channels/transporters, and trophic factors; and the expression of nephrogenesis transcription factors. Pathway analysis supported the concept of a renal repair transcriptome. In summary, these cell lines provide in vitro models for the improved understanding of repeated renal injury and repair mechanisms. High-throughput screening against toxicant libraries should provide a wider perspective of their capabilities in nephrotoxicity.