Disruption of spindle checkpoint function in rats following 28 days of repeated administration of renal carcinogens.

We previously reported that 28-day exposure to hepatocarcinogens that facilitate cell proliferation specifically alters the expression of G1/S checkpoint-related genes and proteins, induces aberrant early expression of ubiquitin D (UBD) at the G2 phase, and increases apoptosis in the rat liver, indicating G1/S and spindle checkpoint dysfunction. The present study aimed to determine the time of onset of carcinogen-specific cell-cycle disruption after repeated administration of renal carcinogens for up to 28 days. Rats were orally administered the renal carcinogens nitrofurantoin (NFT), 1-amino-2,4-dibromoantraquinone (ADAQ), and 1,2,3-trichloropropane (TCP) or the non-carcinogenic renal toxicants 1-chloro-2-propanol, triamterene, and carboxin for 3, 7 or 28 days. Both immunohistochemical single-molecule analysis and real-time RT-PCR analysis revealed that carcinogen-specific expression changes were not observed after 28 days of administration. However, the renal carcinogens ADAQ and TCP specifically reduced the number of cells expressing phosphorylated-histone H3 at Ser10 in both UBD(+) cells and proliferating cells, suggestive of insufficient UBD expression at the M phase and early transition of proliferating cells from the M phase, without increasing apoptosis, after 28 days of administration. In contrast, NFT, which has marginal carcinogenic potential, did not induce such cellular responses. These results suggest that it may take 28 days to induce spindle checkpoint dysfunction by renal carcinogens; however, induction of apoptosis may not be essential. Thus, induction of spindle checkpoint dysfunction may be dependent on carcinogenic potential of carcinogen examined, and marginal carcinogens may not exert sufficient responses even after 28 days of administration.

In vitro antioxidant and photo-oxidant properties of dipyridamole.

The in vitro antioxidant and photo-oxidant activity of dipyridamole was studied by its effect on superoxide- and singlet oxygen-mediated photohemolysis and viability of neutrophils. Dipyridamole was found to be phototoxic when examined by the photohemolysis on human erythrocytes and on linoleic acid as lipid peroxidation model at concentrations above 3.0 x 10(-5) M. On the contrary, when lower concentrations (1.0 x 10(-5) to 1.0 x 10(-6) M) were used, dipyridamole showed a protector action against singlet oxygen-mediated photohemolysis by other phototoxic compounds like triamterene. This antioxidant property is proposed to result from quenching of triamterene mediated by fluorescence energy transfer. Auto-oxidation and fluorescence-energy transfer is clearly an important mechanism for protection for this drug.

Investigations on the acute toxicity of acidic and basic triamterene derivatives.

Acidic and basic triamterene derivatives were evaluated with respect to their acute toxicity. After single intravenous application in mice, derivatives with a basic side-chain were much more toxic than compounds with an acidic side-chain. There is a significant correlation between the potassium retaining properties (measured as ED50) and the acute toxicity (measured as LD50) of the substances. The low acute toxicity after oral application of the compounds can be explained by their low oral bioavailability.

Correlation between mechanistic biotransformation and biochemical toxicology of some antihypertensive drugs.

Mechanistic biochemistry (consideration of metabolism in the context of knowledge of contemporary biochemistry) was applied to propanolol (1), hydrochlorothiazide (2), hydralazine (3), and triamterene (4), representative of the main types of anti-hypertensive drugs in common use. Three routes of metabolism, that is, acetylation, generation of free radicals (leading to peroxidation of lipids), and osazone formation were considered in relation to the structures of these drugs. The possibility that acetylation can lead to hepatic toxicity, lipid peroxidation to membrane lesion, and osazone formation to glucose and energy depletion was highlighted. Hydralazine, with its potential for osazone formation and great susceptibility to acetylation and free radical formation, was judged most capable of giving rise to these side effects, in agreement with reported toxicity. Triamterene was judged less susceptible than hydralazine to acetylation and free radical formation, and hydrochlorothiazide even less so. Propanolol is immune to any of these consequences.

Lack of in vivo mutagenicity and testicular toxicity of triamterene in mice.

Triamterene (2,4,7-triamino-6-phenylpteridine), a widely used diuretic/antihypertensive agent with weak antifolate activity, has been found to be positive in several in vitro assays for mutagenicity. The present studies were undertaken to characterize the potential mutagenic and antifolate activity of triamterene in the bone marrow and testes of mice with in vivo treatment. Triamterene had no clastogenic effects on the bone marrow at 6, 16, or 24 hr after a single oral dose of 25, 125, or 250 mg/kg. No alterations in hematopoietic cell maturation characteristic of antifolate action were observed in a dose-range study in which triamterene was orally administered to mice at 5-300 mg/kg/day for 5 days. Triamterene had no adverse effects on mating or fertility and did not induce dominant lethal mutations in the germ cells of male mice when given for 5 days at 5-100 mg/kg/day. Oral exposure to mice under identical conditions had no effect on testicular weight, DNA content, or activity of the de novo pathway for thymidine synthesis from deoxy [6-3H]uridine. The present findings are consistent with an absence of mutagenic effect and antifolate action on the bone marrow and testes with in vivo administration.

Metabolic fate and solubility of triamterene--not an explanation for triamterene nephrolithiasis.

In an attempt to explain the triamterene stone diathesis, we studied the excretion and solubility of triamterene, 1, and its metabolite, the sulfate ester of the hydroxy derivative of triamterene, 3. The urinary excretion pattern and metabolism in stone formers was the same as in other chronic users of triamterene or healthy volunteers. The solubility of triamterene in urine was approximately one-half of its solubility in buffer solution, whereas the sulfate ester, 3, was nearly twice as soluble in urine as in the buffer solution. In the majority of the subjects studied, we found concentrations of 3 which approached or exceeded apparent solubility limits in urine. This was not true for triamterene where most measured urine concentrations were less than the apparent solubility as determined by equilibration. Alteration in the metabolism of triamterene is probably not a causative factor for triamterene nephrolithiasis. The saturation of urine with triamterene and especially with the sulfate ester, 3, may be related to stone formation, but other physical factors play a role in determining the relative amounts of drug found in calculus material.