Cyclosporine nephrotoxicity: comparative cytochemical study of rat kidney and human allograft biopsies.

The aim of this study was to detect early renal changes in the rat. Female Wistar rats received oral doses of cyclosporine (12.5, 25 or 50 mg/kg daily). The duration of the experiment was 1, 2, and 3 weeks. Controls received the vehicle only (olive oil). The following alterations were seen by light microscopy: Hypertrophy of the juxtaglomerular apparatus (PAS stain). Cytoplasmic droplets of neutral fat (Oil Red 0) in clusters of cortical tubules, probably belonging to the same nephron. Both the above phenomena increased with dosage and duration of treatment and were absent in controls. In the fat containing tubulus (FCT) brush border staining (alkaline phosphatase) was decreased or absent. Since after PAS the brush border was visualized in many FCT, it is concluded that many FCT were proximal tubulus (PT) of which the brush border has been damaged. In FCT mitochondrial staining (Cytochrome oxidase activity) was strongly decreased or absent. Mean lysosomal volume (acid phosphatase and dipeptidase II) is increased in the PT; in some cyclosporine animals, lysosomes were enlarged, while in others they were comparable to controls. Electron microscopy showed in some PT cells an increased number of empty vacuoles and focal alteration of mitochondria. Normal mitochondria were present next to grossly altered mitochondria. Autophagocytosis of mitochondria was clearly present. The lysosomes appeared swollen and contained electron dense material, not organised in the typical 50 A pattern of myeloid figures. These morphological changes suggest a defect of mitochondrial metabolism, leading to lipid deposition in PT. The mitochondrial metabolism can be disturbed by a direct toxic effect of cyclosporine or indirectly via ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal cortical uptake kinetics of gentamicin in rats with impaired renal function.

The renal cortical uptake kinetics of the aminoglycoside antibiotic gentamicin was determined in the remnant kidney model. Renal failure was induced by partial ablation of the right kidney followed by left nephrectomy in female Wistar rats. The animals received a six-hour gentamicin infusion at a constant rate yielding steady-state serum concentrations ranging from 0.5 to 150 micrograms/mL. The renal cortical gentamicin concentrations were determined and related to the serum concentrations achieved. This relationship was nonlinear and followed Michaelis-Menten kinetics. Gentamicin cortical uptake rate, however, did not show clear saturation in the range of gentamicin serum levels studied as was observed in rats with normal renal function. The Michaelis-Menten parameters determined by nonlinear regression were Km = 15.0, 73.9, and 135.7 micrograms/mL; and Vmax = 149.9, 213.7, and 239.2 micrograms/g cortex/h, respectively, for controls, rats with serum creatinine levels between 0.9 and 1.2 mg/dL, and those with levels between 1.3 and 1.8 mg/dL. It is concluded that at serum levels below 100 micrograms/mL, the gentamicin renal cortical uptake is diminished in rats with renal failure. This decrease in renal cortical uptake is more pronounced in the group of rats with more severe renal failure.

Effect of hyperfiltration, proteinuria and diabetes mellitus on the uptake kinetics of gentamicin in the kidney cortex of rats.

The influence of hyperfiltration-hypertrophy, proteinuria and glucosuria on the renal cortical uptake of gentamicin was studied in several experimental models. Two groups of remnant kidney rats, one fed a standard protein diet and one a low protein diet, heavy proteinuric rats (adriamycin) and diabetic rats, each with their own control group, were treated with increasing doses of gentamicin, given as a continuous infusion over 6 hr. The relationship between increasing steady-state serum levels (ranged from 1 to 100 micrograms/ml) and the cortical gentamicin concentrations at the end of the infusions was examined by means of Michaelis-Menten kinetics. The uptake curves were compared to their respective control curves. It was demonstrated that gentamicin uptake was reduced in remnant kidney rats fed standard diet (showing hyperfiltration and heavy proteinuria), in adriamycin rats (showing heavy proteinuria in the absence of hyperfiltration) and in diabetic rats. Uptake of gentamicin in remnant kidney rats fed low protein diet (showing hyperfiltration and slight proteinuria) was comparable to controls. It appeared that among the pathophysiological factors examined, proteinuria is the most important in decreasing the cortical uptake of gentamicin. It is suggested that high levels of proteins in the proximal tubular fluid interfere with the adsorptive endocytic process, involved in the uptake of both proteins and gentamicin.

Recovery of cortical phospholipidosis and necrosis after acute gentamicin loading in rats.

The recovery from gentamicin-induced phospholipidosis in the rat kidney cortex was characterized both morphologically and biochemically after a single 12-hr drug infusion. Total dosages administered were 10, 60, or 140 mg/kg, achieving constant serum concentrations of 3, 11, and 27 micrograms/ml, respectively. At the end of the 12-hr infusion, the cortical drug concentrations corresponding to the three dosages were 124, 450, and 993 micrograms/g of wet tissue. At the low dose (10 mg/kg), myeloid bodies were seen inside lysosomes of proximal tubular cells, along with a modest decrease of lysosomal sphingomyelinase activity. The cortical drug level declined steadily following first-order kinetics along with a disappearance of myeloid bodies and return of sphingomyelinase activity to control levels. At the high dose (140 mg/kg), we observed a sustained loss of sphingomyelinase activity (37% of controls), a subsequent increase of phospholipid concentration in the kidney cortex (up to 117% of controls 2 days after) and a prominent accumulation of myeloid bodies inside the lysosomes of proximal tubular cells (up to 4% of cell volume). Tubular regeneration and interstitial infiltration became detectable by histology and the increase of DNA synthesis as from day 1, along with an apparent reduction of the phospholipidosis at days 3 and 4. Drug cortical concentrations showed a sharp decline 2 days after infusion. An intermediate behavior was observed at 60 mg/kg. It is concluded that the proximal tubular cells behave in a fundamentally different way after gentamicin loading with low and high doses. At the low dose there is a regression of the drug-induced changes in the absence of any sign of necrosis-regeneration. Above a threshold in cortical drug concentration there is further development of the alterations leading to cell death-regeneration.