Nephrotic syndrome associated with N-hydroxyureas, inhibitors of 5-lipoxygenase.

The N-hydroxyurea derivatives 70C ((E)-N-[3-[3- (4-fluorophenoxy)phenyl[-1-(R,S)-methylprop-2-enyl]-N-hydroxyurea) and its (R) 225C and (S) 404C enantiomers, which were being developed as 5-lipoxygenase inhibitors for the treatment of certain allergic and inflammatory conditions, were found to cause severe glomerulonephropathy in the rat. The lesion appeared to be of greater severity in female rats compared with male rats. In addition, 70C and 225C treated animals appeared more severely affected than 404C treated animals. Detailed examination of the lesion in animals dosed with 225C showed that there was a clear relationship between the onset of the lesion and the dose given, i.e. the higher the dose the sooner the lesion developed. The earliest changes detected in the kidney by transmission electron microscopy were noted in the glomeruli, in which the visceral cells appeared enlarged and showed varying degrees of foot process loss. In the more advanced lesion, the degree of foot process loss became more obvious and changes in the kidney tubules were seen by light microscopy. The morphological changes were mirrored by a dose-related increase in water consumption, an increased kidney to body weight ratio and gastrointestinal oedema, suggesting impaired renal function. Shortly after the onset of foot process loss, decreases in the total plasma protein and albumin and increases in the plasma cholesterol, triglycerides, urea and creatinine were recorded. These changes, particularly the foot-process loss, together with increased proteinuria, hypoalbuminaemia, hypercholesterolaemia and lipaemia, are all characteristic of "minimal change nephrotic syndrome". Because of the serious nature of the kidney lesion caused by these N-hydroxyureas in the rat, it was considered that it precluded their development as therapeutic agents for use in man.

Induction and exacerbation of hyaline droplet formation in the proximal tubular cells of the kidneys from male rats receiving a variety of pharmacological agents.

Kidneys from male and female Wistar rats dosed with 1 of 3 chemically unrelated pharmacological agents, a pyrazoline BW540C, a naphthoquinone BW58C and the levoisomer of tetramisole, levamisole or the light hydrocarbon Decalin, were examined by light and electron microscopy. Paraffin histology showed that all 4 agents induced and exacerbated hyaline droplet accumulation in the renal proximal tubular cells of the male rats. Resin histology at both the light and electron microscope level, along with cytochemical procedures for acid phosphatase and the protein 'alpha 2U globulin', helped further in the characterisation of these cytoplasmic inclusions. These techniques confirmed that the accumulation of hyaline droplets seen by paraffin histology represented an increase in the size and number of secondary lysosomes which have been shown to be involved in protein uptake and metabolism. Time course studies showed that increased numbers of small dense lysosomes appear first, which then increase in size, presumably by fusion. Crystalloid bodies form in these large lysosomes eventually giving rise to rectilinear bodies. The accumulation of these protein laden secondary lysosomes took place primarily in the cells of the S1 and S2 segments of the proximal tubules. In extreme cases of lysosomal accumulation however, loading of the S3 segments was noted. In tubules where cellular inclusion loading was heavy, there was evidence of increased cell turnover. The kidneys of female rats dosed with any one of the 4 agents appeared normal.

Kanamycin induced ototoxicity in the laboratory rat. A comparative morphological and audiometric study.

Two comparative experiments on the behavioural, audiometric and histological effects of kanamycin-induced cochleotoxicity in the Wistar rat are reported. In the first experiment kanamycin 400-1,500 mg/kg/day was injected subcutaneously for 20 days and the morphological damage to the organ of Corti assessed. In the second experiment the progression of damage to the organ of Corti was examined in animals given kanamycin 700 mg/kg/day for 4-20 days. Behavioural audiometric studies of threshold shift were undertaken throughout both experiments. In the first study, all the animals were killed after a recovery period of 20 days from the last injection, i.e., day 40, and in the second study groups of animals were killed at 4-day intervals between days 4 and 20 of dosing. One cochlea from each animal was critical point-dried, dissected to expose the organ of Corti and examined by scanning electron microscopy. A vertical section through the contralateral cochlea was examined by light microscopy. The results of the morphological examination of the cochleas were collated with the behavioural audiometry. The morphological damage to the organ of Corti followed a stereotyped pattern of degeneration, the extent of which appeared to be determined both by the number and concentration of the kanamycin administrations. The collateral audiometric examinations indicated that extensive damage had taken place before a shift in the behavioural auditory threshold could be detected by observation of the Preyer reflex.

Improved morphological techniques for screening potentially ototoxic compounds in laboratory animals.

A technique is described for morphological examination of the organ of Corti which can be used in routine toxicological studies. This involves the dissection of a critical point-dried cochlea and examination of a surface preparation of the entire organ by scanning electron microscopy. The procedure is simple and far less time consuming than that previously used for light microscopy. Quantitative estimates of damage induced in the organ of Corti either by the administration of ototoxic compounds or as a response to noise-induced or age-related changes can be obtained. Details are given for the application of this technique to two species commonly used in toxicity studies. With minor modifications it could be applied to many other species of animal.