Abstract
The delayed effects of acute intoxication by organophosphates (OPs) are poorly understood, and the various experimental animal models often do not take into account species characteristics. The principal biochemical feature of rodents is the presence of carboxylesterase in blood plasma, which is a target for OPs and can greatly distort their specific effects. The present study was designed to investigate the nephrotoxic effects of paraoxon (O,O-diethyl O-(4-nitrophenyl) phosphate, POX) using three models of acute poisoning in outbred Wistar rats. In the first model (M1, POX2x group), POX was administered twice at doses 110 µg/kg and 130 µg/kg subcutaneously, with an interval of 1 h. In the second model (M2, CBPOX group), 1 h prior to POX poisoning at a dose of 130 µg/kg subcutaneously, carboxylesterase activity was pre-inhibited by administration of specific inhibitor cresylbenzodioxaphosphorin oxide (CBDP, 3.3 mg/kg intraperitoneally). In the third model (M3), POX was administered subcutaneously just once at doses of LD16 (241 µg/kg), LD50 (250 µg/kg), and LD84 (259 µg/kg). Animal observation and sampling were performed 1, 3, and 7 days after the exposure. Endogenous creatinine clearance (ECC) decreased in 24 h in the POX2x group (p = 0.011). Glucosuria was observed in rats 24 h after exposure to POX in both M1 and M2 models. After 3 days, an increase in urinary excretion of chondroitin sulfate (CS, p = 0.024) and calbindin (p = 0.006) was observed in rats of the CBPOX group. Morphometric analysis revealed a number of differences most significant for rats in the CBPOX group. Furthermore, there was an increase in the area of the renal corpuscles (p = 0.0006), an increase in the diameter of the lumen of the proximal convoluted tubules (PCT, p = 0.0006), and narrowing of the diameter of the distal tubules (p = 0.001). After 7 days, the diameter of the PCT lumen was still increased in the nephrons of the CBPOX group (p = 0.0009). In the M3 model, histopathological and ultrastructural changes in the kidneys were revealed after the exposure to POX at doses of LD50 and LD84. Over a period from 24 h to 3 days, a significant (p = 0.018) expansion of Bowman’s capsule was observed in the kidneys of rats of both the LD50 and LD84 groups. In the epithelium of the proximal tubules, stretching of the basal labyrinth, pycnotic nuclei, and desquamation of microvilli on the apical surface were revealed. In the epithelium of the distal tubules, partial swelling and destruction of mitochondria and pycnotic nuclei was observed, and nuclei were displaced towards the apical surface of cells. After 7 days of the exposure to POX, an increase in the thickness of the glomerular basement membrane (GBM) was observed in the LD50 and LD84 groups (p = 0.019 and 0.026, respectively). Moreover, signs of damage to tubular epithelial cells persisted with blockage of the tubule lumen by cellular detritus and local destruction of the surface of apical cells. Comparison of results from the three models demonstrates that the nephrotoxic effects of POX, evaluated at 1 and 3 days, appear regardless of prior inhibition of carboxylesterase activity.
Highlights
The kidneys of humans and animals are susceptible to the toxic effects of chemicals because they are continuously supplied with large volumes of blood, ranging from 15 to 25% of cardiac output [1]
Of the 27 biochemical parameters, changes in plasma creatinine, urea, and uric acid were the most likely indicators of renal dysfunction. This was the case 3 h after poisoning creatinine level had already increased by 35–40% in the CBPOX group (p < 0.05)
At 7 days after the poisoning, there was no significant difference in the urinary Chondroitin Sulphate (CS) content in the poisoned rats: 5.2 ± 0.9 in the POX2x group, 6.6 ± 1.5 in the CBPOX group, and 5.9 ± 1.7 mg CS/mol creatinine in the control group
Summary
The kidneys of humans and animals are susceptible to the toxic effects of chemicals because they are continuously supplied with large volumes of blood, ranging from 15 to 25% of cardiac output [1]. Renal secretion and reabsorption mechanisms providing high concentrations of blood-borne toxic compounds in the tubules or interstitium can lead to their accumulation in renal cells and tissues. The primary mechanism of OPs toxicity in humans and animals is the irreversible inhibition of cholinesterases, leading to the accumulation of acetylcholine in the synaptic cleft, causing overstimulation of nicotinic and muscarinic receptors in the central and peripheral nervous system [5]. This stimulation leads to a variety of clinical symptoms of OPs poisoning, including salivation, lacrimation, exophthalamus, diarrhoea, miosis, hypothermia, muscle fasciculations, bradycardia, bronchospasm, pulmonary edema, pneumonia, pancreatitis, and renal failure
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