The mechanism of excretion of trientine from the rat kidney: trientine is not recognized by the H+/organic cation transporter

Triethylenetetramine pharmacology and its clinical applications

Triethylenetetramine (TETA), a Cu(II)-selective chelator, is commonly used for the treatment of Wilson's disease. Recently, it has been shown that TETA can be used in the treatment of cancer because it possesses telomerase inhibiting and anti-angiogenesis properties. Although TETA has been used in the treatment of Wilson's disease for decades, a comprehensive review on TETA pharmacology does not exist. TETA is poorly absorbed with a bioavailability of 8 to 30%. It is widely distributed in tissues with relatively high concentrations measured in liver, heart, and kidney. It is mainly metabolized via acetylation, and two major acetylated metabolites exist in human serum and urine. It is mainly excreted in urine as the unchanged parent drug and two acetylated metabolites. It has a relatively short half-life (2 to 4 hours) in humans. The most recent discoveries in TETA pharmacology show that the major pharmacokinetic parameters are not associated with the acetylation phenotype of N-acetyltransferase 2, the traditionally regarded drug acetylation enzyme, and the TETA-metabolizing enzyme is actually spermidine/spermine acetyltransferase. This review also covers the current preclinical and clinical application of TETA. A much needed overview and up-to-date information on TETA pharmacology is provided for clinicians or cancer researchers who intend to embark on cancer clinical trials using TETA or its close structural analogs.

Inhibitory effects of trientine, a copper-chelating agent, on induction of DNA strand breaks in kidney cells of Long-Evans Cinnamon (LEC) rats

The effects of treatment with trientine, a specific copper-chelating agent, on the accumulation of copper and induction of DNA strand breaks were investigated in Long-Evans Cinnamon (LEC) rats, an animal model for human Wilson's disease. Copper accumulated in the kidneys of LEC rats in an age-dependent manner from 12 to 18 weeks of age. When LEC rats were treated with trientine from 10 weeks of age, renal copper contents did not increase and were maintained at the same levels as those in 4-week-old LEC rats. Estimation of the amounts of DNA single-strand breaks (SSBs) by comet assay showed that SSBs of DNA were induced in a substantial population of LEC rat renal cortex cells around 12 weeks of age and that the amounts of SSBs increased in an age-dependent manner from 12 to 18 weeks of age. When LEC rats were treated with trientine from 10 weeks of age, the observed number of cells with DNA damage decreased, suggesting that induction of SSBs of DNA was inhibited and/or SSBs were repaired during the period of treatment with trientine. The results show that SSBs of DNA in LEC rat kidney cells are induced prior to occurrence of clinical signs of hepatic injury and that treatment of LEC rats with trientine decreases the number of DNA strand breaks.

Inhibitory effects of trientine, a copper-chelating agent, on induction of DNA strand breaks in hepatic cells of Long-Evans Cinnamon rats

Effects of treatment with trientine, a specific copper-chelating agent, on accumulation of copper and induction of DNA strand breaks were investigated in Long-Evans Cinnamon (LEC) rats, an animal model for human Wilson's disease. Copper accumulated in the livers of LEC rats in an age-dependent manner from 4 to 13 weeks of age. When LEC rats were treated with trientine from 10 weeks of age, hepatic copper contents did not increase and were maintained at the same levels as those in 10-week-old LEC rats. When the amounts of DNA single-strand breaks (SSBs) were estimated by a comet assay, SSBs of DNA were induced in a substantial population of LEC rat hepatic cells around 8 weeks of age and the amounts of SSBs increased in an age-dependent manner from 8 to 15 weeks of age. When LEC rats were treated with trientine from 10 weeks of age, the observed number of cells with DNA damage decreased dramatically, suggesting that induction of SSBs of DNA was inhibited and/or SSBs were repaired during the period of treatment with trientine. The results show that treatment of LEC rats with trientine decreases the number of DNA strand breaks observed, although copper contents remain high in the liver.

[The transport mechanism of polycationic compounds across intestinal and renal cell membrane]

This article reviewed the transport mechanism of polycationic compounds across rat intestinal and renal cell membranes. The inside-negative diffusion potential stimulated the initial uptake of dicationic compounds into intestinal brush-border membrane vesicles, and a good correlation was observed between lipophilicity and the amount of diffusion potential-dependent transport of the dications. On the other hand, tri- and tetracationic compounds were not affected by the diffusion potential because of their much lower lipophilicity. The membrane surface potential affected to the transport of polycationic compounds, similar to monocationic compounds. Therefore it appears that the membrane surface potential plays a common role in the transport of mono- and polycationic compounds across cell membranes. On the intestinal basolateral membrane, it was found that there was a Na+/putrescine symporter. This recognized dicationic compounds and transported them from the blood into intestinal cells. This transporter did not recognize spermine and spermidine. Furthermore, we found a novel transport system, a Na+/spermine antiporter, on the rat renal brush-border membrane. This transporter recognized aliphatic polycation, which has more than four amino groups, and actively secreted spermine and trientine into the renal proximal tubules in vitro and in vivo. However, this transporter did not recognize trientine-copper complex. These results are useful for the prediction of the intestinal absorption and renal excretion of polyamine derivatives.

Effects of interactions between drugs on the renal excretion of trientine in rats--acetazolamide and furosemide increase trientine excretion

PURPOSE

To elucidate the effects of drug interactions on the urinary excretion of trientine in rats.

METHOD

Trientine and various other drugs were intravenously administered to rats and the urinary excretion of trientine was investigated. To clarify the mechanisms of drug-drug interactions, we also investigated the effects of various drugs on spermine uptake by rat renal brushborder membrane vesicles.

RESULTS

Cimetidine, a substrate of the H+/organic cation antiporter, and aminoglycoside antibiotics did not affect trientine excretion, while acetazolamide and furosemide, which increase the concentration of sodium ions in renal proximal tubules, increased the excretion of trientine. However, trichlormethiazide, which acts in renal distal tubules, did not affect trientine excretion. Acetazolamide and furosemide did not directly affect the Na+/spermine transporter because these diuretics had no effect on the uptake of spermine into the rat renal brush-border membrane vesicles.

CONCLUSIONS

There is no interaction between trientine and the substrate of the H+/organic cation antiporter or aminoglycoside antibiotics. However, drugs that change the concentration of sodium ions in renal proximal tubules, such as diuretics, can increase the trientine excretion since the increase in the luminal concentration of sodium ion accelerates the Na+/spermine antiporter.

The presence of an Na+/spermine antiporter in the rat renal brush-border membrane

This study was aimed at determining the driving force for spermine transport in rat renal proximal tubular brush-border membrane. The uptake of spermine and trientine, a spermine-like drug used for treating Wilson's disease, into rat renal brush-border membrane vesicles was significantly stimulated by an outwardly directed Na+ gradient. The Na+-dependent uptake was temperature dependent and saturable. A kinetic analysis of the initial uptake of spermine with an Na+ gradient gave a Km value of 1.44 microM and a Vmax value of 6.31 pmol (mg protein)(-1)/30s. The Na+ dependent uptake of [3H]spermine was inhibited by spermine, trientine and tetraethylene-pentamine. Substrates of the H+/organic cation transporter (cimetidine and tetraethyl-ammonium), physiological polyamines (putrescine and spermidine) with 2 or 3 amino groups and aminoglycosides (amikacin and tobramicin) with 4 or 5 cationic amines did not affect the uptake of spermine in the presence of an outwardly directed Na+ gradient. These results suggest that the renal tubular secretion of spermine is mediated by an Na+/spermine antiport system which is specific for a straight-chain polyamine compound with more than 4 amino groups.