Nephrotoxic Effects of Paraoxon in Three Rat Models of Acute Intoxication

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.

Molecular Mechanisms of Acute Organophosphate Nephrotoxicity

“…In our studies after acute poisoning of rats with POX, a decrease in endogenous creatinine clearance (ECC) within 24 h was found, irrespective of the method of carboxylesterase inhibition. At 3 and 7 days after poisoning, ECC in poisoned rats did not differ from those of intact controls [ 61 ]. This may indicate a decrease in GFR in the early period after poisoning, with subsequent recovery of filtration levels.…”

“…Thus, hyperglycaemia is one of the factors of oxidative stress mechanism in OP poisoning [ 134 ]. In our studies in rats, 24 h after acute poisoning with POX, glucosuria was observed without an increase in blood glucose level, indicating its renal origin [ 61 ]. It should be noted that glycosuria without associated hyperglycaemia after OP poisoning has also been described in humans [ 211 , 212 ].…”

“…Each representative of OPs has a unique toxicity profile, and therefore nephrotoxicity and histopathological changes in the kidneys may differ when poisoned by different OPs. In the last few years, isolated reports of observed changes in renal morphology when exposed to OPs, such as malathion, fentione, diisopropylfluorophosphate (DFP), and paraoxon, continue to be published [ 32 , 40 , 53 , 60 , 61 ]. The pathomorphophysiological changes in renal tissue in OP-treated rats include shrinkage of glomeruli; dilation of the urinary space; infiltration of interstitial tissue with inflammatory cells; pycnotic nuclei; vacuolisation of renal tubule cytoplasm; deposition of hyaline material in the lumen of some tubules; dilation and occlusion of blood vessels; degeneration of renal tubule epithelium; deposition of epithelial casts in some tubule lumen; and tearing of Bowman capsule [ 61 , 203 ].…”

“…Earlier, we proposed two models of acute poisoning of rats by OPs, with preliminary inhibition of CEs by administration of 2-(o-cresyl)-4H-1,3,2-benzodioxaphosphorin-2-oxide (CBDP) or fractional administration of a total dose of OPs under study [ 57 ]. The models allow effective assessment of various aspects of OP toxicity manifestation in rats, comparable to human poisoning [ 58 , 59 , 60 , 61 ]. It is advisable that choice of animal species and poisoning model should take into account the potential effect of different OPs on the target organs.…”

“…It is advisable that choice of animal species and poisoning model should take into account the potential effect of different OPs on the target organs. In our studies, it was shown that some OPs, such as paraoxon, show signs of nephrotoxicity even at a single exposure, regardless of prior inhibition of CE activity [ 61 ].…”