[Kidney diseases caused by drugs]

Biotransformation and Toxicities of Aristolochic Acids

Environmental and iatrogenic exposures contribute significantly to human diseases, including cancer. The list of known human carcinogens has recently been extended by the addition of aristolochic acids (AAs). AAs occur primarily in Aristolochia herbs, which are used extensively in folk medicines, including Traditional Chinese Medicine. Ingestion of AAs results in chronic renal disease and cancer. Despite importation bans imposed by certain countries, herbal remedies containing AAs are readily available for purchase through the internet. With recent advancements in mass spectrometry, next generation sequencing, and the development of integrated organs-on-chips, our knowledge of cancers associated with AA exposure, and of the mechanisms involved in AA toxicities, has significantly improved. DNA adduction plays a central role in AA-induced cancers; however, significant gaps remain in our knowledge as to how cellular enzymes promote activation of AAs and how the reactive species selectively bind to DNA and kidney proteins. In this review, I describe pathways for AAs biotransformation, adduction, and mutagenesis, emphasizing novel methods and ideas contributing to our present understanding of AA toxicities in humans.

Renal toxicity of aristolochic acid in rats as an example of nephrotoxicity testing in routine toxicology

The nephrotoxic action of aristolochic acid (AA) was investigated in female Wistar rats given single doses of 10, 50 or 100 mg/kg by gastric tube. Renal lesions developed within 3 days, the effect being dose-dependent. Histologically, there was evidence of necrosis of the epithelium of the renal tubules, and functionally, there were rises in plasma creatinine and urea together with increases in urinary glucose, protein, N-acetyl-beta-glucosaminidase, gammaglutamyl transferase and malate dehydrogenase. Taking AA as an example, the aim of the present study was to consider the suitability of this model, based on a combination of histology and laboratory investigations, as a short-term test for the detection of nephrotoxic agents.

Acute toxicity of aristolochic acid in rodents

The acute toxic effects of aristolochic acid (AA) were tested in rats and mice of both sexes. Oral or intravenous administration in high doses was followed by death from acute renal failure within 15 days. Histologically, the predominant features were severe necrosis affecting the renal tubules, atrophy of the lymphatic organs and large areas of superficial ulceration in the forestomach, followed by hyperplasia and hyperkeratosis of the squamous epithelium. The LD50 ranged from 56 to 203 mg/kg orally or 38 to 83 mg/kg intravenously, depending on species and sex.

Analgesic-associated nephropathy

Although the question of whether or not analgesic abuse leads to a certain type of nephropathy has been investigated since 1953, no conclusive answer has been forthcoming. Epidemiologic investigations on the correlation between analgesic abuse and renal function as well as experimental animal studies have given contradictory results concerning the possibility of analgesic-associated kidney damage. However, studies on the correlation between analgesic abuse and papillary necrosis have demonstrated that this lesion coincides in 69% of the cases with an analgesic history. Follow-up studies of patients with analgesic nephropathy have shown that renal function deteriorates in 60% of the patients with continued abuse and that it stabilizes in 80% of the patients after cessation of abuse. Studies on the legislative restriction of phenacetin/acetaminophen, carried out mostly in Scandinavian countries since 1965, show a 50%-90% decline in signs of analgesic nephropathy (papillary necrosis) following a reduction in the sale of these drugs. The prevalence of analgesic abuse may be underestimated, since up to 80% of the abusers tend to deny their analgesic intake. Obviously, only a small percentage of analgesic abusers (approximately 1%) finally develop nephropathy. Even though the results of epidemiologic and experimental studies are contradictory, the results of investigations on papillary necrosis and on legislative prevention as well as of patient follow-ups tend to indicate a correlation between analgesic abuse and a well-defined type of nephropathy.

Aristolochic acid induces 6-thioguanine-resistant mutants in an extrahepatic tissue in rats after oral application

The mutagenic activity of the natural plant product aristolochic acid (AA) was tested in the Granuloma Pouch Assay, which detects gene mutations induced in a subcutaneous granuloma tissue of rats. After direct exposure of the target tissue, AA induced high frequencies of mutants at a relatively low cytostatic/cytotoxic level. AA was more potent that N-methyl-N'-nitro-N-nitrosoguanidine (MNNG) at equimolar doses. After oral application of AA, a dose-dependent mutagenic activity was seen. In contrast a very weak and inconsistent mutagenic effect was seen after systemic application of MNNG. These observations suggest that after oral application AA is not detoxified efficiently and can exert its mutagenic activity in extrahepatic tissues whereas MNNG is detoxified to a large extent at the site of administration.

On the histopathogenesis of rat forestomach carcinoma caused by aristolochic acid

The histopathogenesis of rat forestomach carcinoma induced experimentally with aristolochic acid was investigated. The intragastric administration of 10 mg/kg/day caused extensive necrosis of the squamous epithelium, followed by regeneration and hyperplasia, papilloma formation and ultimately by invasive squamous cell carcinoma.