Uptake of rosuvastatin by isolated rat hepatocytes: comparison with pravastatin.

1. The liver is the target organ for the lipid-regulating effect of rosuvastatin, a new 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, and liver-selective uptake of this drug is therefore a desirable property. The uptake kinetics of rosuvastatin were investigated and compared with those of pravastatin using isolated rat hepatocytes. 2. Uptake for both drugs involved both active transport and passive diffusion processes. The Michaelis constant (K(m)) of uptake rate for rosuvastatin (9.17 micro M) was approximately half that for pravastatin (16.5 micro M). However, the maximum uptake rate (V(max)) and carrier-mediated uptake clearance (V(max)/K(m)) of rosuvastatin were significantly (p < 0.01) greater than those of pravastatin, and a larger contribution of carrier-mediated uptake clearance to total uptake clearance was shown for rosuvastatin (contribution ratio 0.903 versus pravastatin 0.654). 3. Sodium and chloride ions did not play a significant role in the uptake of rosuvastatin and pravastatin, but the uptake of both drugs was inhibited both by depletion of cellular ATP and by organic anions such as bromosulfophthalein. 4. Rosuvastatin competitively inhibited the uptake of pravastatin, with an inhibition constant (K(i)) (2.75 micro M) relatively similar to its K(m). 5. The results suggest that an organic anion transport protein is the main mediator of the hepatic uptake of rosuvastatin and pravastatin, which occurs in an ATP-dependent manner. Our results indicated that rosuvastatin was taken up by the hepatocytes via the same transport systems as pravastatin, but with a greater affinity and efficiency than pravastatin.

Pharmacokinetics and disposition of rosuvastatin, a new 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, in rat.

1. The pharmacokinetics and disposition of rosuvastatin, a new 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase inhibitor, were investigated following single administration of (14)C-rosuvastatin in the Sprague-Dawley rat. 2. Following oral administration of (14)C-rosuvastatin at 1, 5 and 25 mg kg(-1), the C(max) and AUC of the radioactivity in the plasma increased more than the increase in dose ratio. 3. Excretion of radioactivity was 98.0% of the dose in the faeces and 0.4% in the urine up to 168 h after oral administration in the intact rat, and was 55.1% in the bile and 0.5% in the urine up to 48 h post-dosing in the bile duct-cannulated rat. The unchanged compound mainly accounted for the radioactivity in the bile and faeces. 4. In the tissue distribution study, the concentration of the radioactivity in the liver was markedly higher than those in the other tissues, and the radioactivity concentration ratios of the liver to the plasma were between 8 and 25 up to 48 h after oral administration. The liver-specific distribution of rosuvastatin was similarly recognized in whole-body autoradiography. 5. Metabolic profiling studies indicated that rosuvastatin would not be metabolized by CYP enzymes. 6. These results clarified that rosuvastatin selectively distributed in the liver - the target organ - and was excreted in the bile mainly as the unchanged compound.

Pharmacokinetics of a novel benzodiazepine partial inverse agonist in the F344 rat, SD rat and B6C3F1 mouse.

1. The pharmacokinetics of a novel benzodiazepine partial inverse agonist (S-8510) were studied in the Fischer 344 (F344) rat and B6C3F1 mouse to obtain information for the planning of carcinogenicity studies. Sprague-Dawley (SD) rats were also included for comparison. 2. Clear non-linear elimination of S-8510 was observed after single oral administration of S-8510 in all animals tested (F344 rat, 1-50 mg/kg; SD rat and B6C3F1 mouse, 1-150 mg/kg). 3. Exposure of S-8510 after single oral administration was in the order F344 rat > B6C3F1 mouse > SD rat. 4. Multiple oral administration to F344 rat and B6C3F1 mouse decreased the exposure to S-8510. 5. These results indicate that it is very important to evaluate pharmacological and toxicological studies based on exposure and to be careful in selecting the species and strains of animal used in toxicology studies.

Stereoselective uptake of an organic anion across the renal basolateral membrane in isolated perfused rat kidney.

To clarify which process in renal secretion is responsible for the stereoselective renal secretion of organic anions, the renal handling of enantiomers of 5-monomethylsulfamoyl-6,7-dichloro-2, 3-dihydrobenzofuran-2-carboxylic acid (MBCA) was studied by the multiple-indicator dilution method, using isolated perfused rat kidney. After bolus injection of (R)-(+)-[14C]MBCA or (S)-(-)-[14C]MBCA into the renal artery, the outflow patterns for the perfusate and the urinary excretion rate profiles were estimated by statistical moment analysis. AUC values and mean transit times in kidney for the MBCA enantiomers indicated that (R)-(+)-MBCA was excreted much more extensively in urine and that it had a higher affinity for renal tissue than did (S)-(-)-MBCA. A significantly larger intrinsic clearance of secretion for (R)-(+)-MBCA attested to the R-(+)-preferential renal secretion. The uptake rate constant across the basolateral membrane, the ratio of the uptake rate constant to the free fraction in the perfusate, and the intracellular distribution volume were significantly larger for (R)-(+)-MBCA than for (S)-(-)-MBCA, indicating that uptake across the basolateral membrane and intracellular distribution were R-(+)-preferential. However, the mean time across renal epithelial cells for secreted molecules, the single-pass mean residence time in renal epithelial cells, and the rate constant for secretion across the brush-border membrane were not significantly different between enantiomers. The simultaneous presence of (R)-(+)-MBCA decreased the intrinsic clearance of secretion, the ratio of the uptake rate constant to the free fraction in the perfusate, and the intracellular distribution volume for (S)-(-)-[14C]MBCA, although the secretion rate constant, the mean time across renal epithelial cells for secreted molecules, and the single-pass mean residence time in renal epithelial cells were not influenced by (R)-(+)-MBCA, confirming that uptake across the basolateral membrane and intracellular distribution were stereoselective processes.

Inhibitory effect of EGTA on serotonin transport into rabbit blood platelets: possible involvement of the glycoprotein IIb/IIIa complex.

We reported previously that serotonin (5-HT) transport was attenuated by treatment of platelets with EGTA, and that this inhibitory effect of EGTA was restored by CaCl2. In the present study, the inhibitory effect of EGTA was found to be uncompetitive, and no inhibitory effect was observed when EGTA was added at 20 degrees C. Genistein and thyrphostin A47, both protein tyrosine kinase inhibitors, inhibited Ca(2+)-induced restoration of 5-HT transport. In contrast, the protein tyrosine phosphatase inhibitor phenylarsine oxide significantly augmented Ca(2+)-induced restoration of 5-HT transport. These results might support the hypothesis that the glycoprotein (GP) IIb/IIIa complex, a platelet membrane integrin protein, might regulate 5-HT transport into blood platelets. It is conceivable that Ca2+ chelation by EGTA might cause temperature-dependent dissociation of the GP IIb/IIIa complex, which results in the reduction of 5-HT transport. Rearrangement of the GP IIb/IIIa complex by replenishment of the Ca2+ binding sites might restore the EGTA-induced reduction of 5-HT transport.

Effects of thimerosal, an organic sulfhydryl modifying agent, on serotonin transport activity into rabbit blood platelets.

The effects of the sulfhydryl group inhibitor thimerosal on serotonin (5-HT) transport activity into rabbit blood platelets were investigated, along with its effects on the intracellular concentration of Ca2+ ([Ca2+]i). 3H-5-HT transport activity into rabbit blood platelets was inhibited by treatment with 10(-5) M thimerosal for 30 min, which did not cause 5-HT release from platelets. The thimerosal-induced inhibition of 5-HT transport was antagonized by dithiotheritol. It was suggested that the thimerosal acts as a sulfhydryl inhibitor and inhibits 5-HT transport activity independently of the 5-HT release reaction in our experiment using rabbit blood platelets. As aspirin did not affect thimerosal-induced 5-HT transport inhibition, it was suggested that the thromboxane A2-generating system does not operate in the effect of thimerosal on 5-HT transport into blood platelets. Furthermore, thimerosal induced a transient elevation of [Ca2+]i, which was followed by a sustained increase. In the absence of extracellular Ca2+, thimerosal caused only a transient increase in [Ca2+]i. It was suggested that the elevation of [Ca2+]i consisted of two phases, e.g. a transient phase induced by Ca2+ mobilization from the intracellular store sites and a sustained phase which might be explained by Ca2+ influx from the extracellular environment. In conclusion, thimerosal inhibited 5-HT transport into blood platelets at a concentration which did not induce 5-HT release, and intracellular Ca2+ mobilization might mediate the inhibitory effect of thimerosal on 5-HT transport.

Role of calcium ion in platelet serotonin uptake regulation.

It is generally accepted that intracellular Ca2+ is a key substance in the intracellular signal transducing mechanism of platelets. We investigated the possibility that extracellular and/or intracellular Ca2+ might regulate the transport activity of serotonin (5-HT) into platelets. We found that extracellular Ca2+ chelation with EGTA caused inhibition of 5HT uptake activity, which was recovered by extracellulary applied excess Ca2+. Intracellular Ca2+ chelation with acetoxymethyl bis(O-aminophenoxy)ethane-N,N,N'-tetraacetate (BAPTA-AM) did not, however, have any inhibitory effect on 5HT uptake activity in the presence of extracellular Ca2+. In the absence of extracellular Ca2+, BAPTA-AM significantly inhibited 5-HT uptake. The restorative effect of Ca2+ on 5-HT transport into EGTA-treated platelets was mimicked by Ba2+, but not by Sr2+. It was antagonised by inorganic Ca2+ channel antagonist including Ni2+, La3+ and Gd3+, but not by organic Ca2+ channel blockers including verapamil, nifedipine, diltiazem, omega-conotoxin GVIA and omega-agatoxin IVA. Furthermore, 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester hydrochloride (TMB-8), an intracellular Ca2+ antagonist, was found to inhibit the restorative effect of Ca2+. These results have led to the suggestion that depletion of intracellular Ca2+ pool(s) by EGTA might result in a reduction of 5-HT uptake activity. Thus, the intracellular Ca2+ pool(s) susceptible to EGTA might have a regulatory role in maintaining 5-HT transport into blood platelets.