Toxicity assessment of pramipexole in juvenile rhesus monkeys.

Pramipexole (PPX) is a dopamine agonist approved for the treatment of the signs and symptoms of idiopathic Parkinson's disease as well as restless leg syndrome. The objective of this study was to investigate the toxicity of PPX when administered orally to juvenile rhesus monkeys once daily for 30 weeks, and to assess the reversibility of toxicity during a 12-week recovery. Rhesus monkeys (N=4 males and 4 females/group; 22-24 months of age) were orally treated daily for 30 weeks with 0.0, 0.1, 0.5 or 2.0 mg/kg PPX, and subjects were assessed daily using the NCTR Operant Test Battery (OTB). Clinical chemistry, hematology, ophthalmology and other standard postmortem toxicological evaluations, including histopathology and neuropathology as well as toxicokinetics were performed. The systemic exposure to PPX was higher than that at therapeutic doses in man and AUC(0-24 h)-data increased proportionally to dose. Blood pressure significantly decreased over time in all groups including control. Near the end of treatment, there were statistically significant decreases in heart rate for the 0.5 and 2.0 mg/kg/day groups compared to control. After 4 weeks of dosing, serum prolactin was significantly decreased in all treatment groups compared to control. This decrease remained at the end of treatment in the 0.5 and 2.0 mg/kg/day groups. In summary, administration of PPX at doses of up to 2.0 mg/kg/day for 30 weeks to juvenile rhesus monkeys produced adverse findings which were attributable to its pharmacological properties, including hypoprolactinemia.

The dipeptidyl peptidase-4 inhibitor linagliptin exhibits time- and dose-dependent localization in kidney, liver, and intestine after intravenous dosing: results from high resolution autoradiography in rats.

Linagliptin is an orally active dipeptidyl peptidase-4 (DPP-4) inhibitor that is under development for the treatment of type 2 diabetes and shows dose-dependent pharmacokinetics in rats and humans. With microscopic autoradiography, the dose dependence of cellular distribution of [(3)H]linagliptin-related radioactivity was investigated in kidney at 3 h after intravenous injection of 7.4, 100, and 2000 microg/kg [(3)H]linagliptin. Furthermore, distribution of radioactivity in kidney, liver, and small intestine was investigated in relation to time (2 min, 3 h, and 192 h) after intravenous injection of 7.4 microg/kg [(3)H]linagliptin. The localization of radioactivity in the kidney at 3 h after administration of 7.4, 100, and 2000 microg/kg [(3)H]linagliptin changed with increasing dose from cortical glomeruli and parts of proximal tubule parts to parts of medullar proximal tubule. In addition, the compound distribution in the kidney shifted with time after administration of 7.4 microg/kg [(3)H]linagliptin from glomeruli (2 min) to the lower parts of proximal tubules (192 h). The radioactivity within proximal tubules was located primarily in the brush border. In the liver, the radioactivity persisted mainly around the portal triads and in the bile duct from 2 min to 192 h. In the small intestine, the radioactivity shifted from the lamina propria (2 min) to the surface of the villi and/or intestinal lumen (192 h). In conclusion, the cellular distribution pattern of [(3)H]linagliptin-related radioactivity reflected the known distribution of DPP-4. Together with the persistence of binding, this result supports the high relevance of DPP-4 binding of linagliptin for its pharmacokinetics and pharmacodynamics.

Binding to dipeptidyl peptidase-4 determines the disposition of linagliptin (BI 1356)--investigations in DPP-4 deficient and wildtype rats.

Linagliptin (BI 1356) is a novel dipeptidyl peptidase-4 (DPP-4) inhibitor in clinical development for the treatment of type 2 diabetes. It exhibits non-linear pharmacokinetics and shows concentration-dependent plasma protein binding to its target, DPP-4. The aim of this study was to investigate the impact of saturable binding of linagliptin to plasma and tissue DPP-4 by comparing the pharmacokinetics of linagliptin in wildtype and DPP-4 deficient Fischer rats using non-compartmental and model-based data analysis. The non-compartmental analysis revealed a significantly reduced AUC in DPP-4 deficient rats compared with wildtype rats when single intravenous doses

Tissue distribution of the novel DPP-4 inhibitor BI 1356 is dominated by saturable binding to its target in rats.

BI 1356 (INN: linagliptin) is an inhibitor of dipeptidyl peptidase-4 (DPP-4). This study investigated whether saturable binding of BI 1356 to its target DPP-4 occurs in tissues and whether drug accumulation occurs at these sites in vivo. In order to test these hypotheses, the tissue distribution of BI 1356 was determined in wild-type and DPP-4 deficient rats at different dose levels by means of whole body autoradiography and measurement of tissue radioactivity concentrations after single i.v. dosing of [(14)C]-radio labeled BI 1356. The accumulation behavior of drug-related radioactivity in tissues was further explored in an oral repeat dose study. Tissue levels of [(14)C]BI 1356 related radioactivity were markedly lower in all investigated tissues of the DPP-4 deficient rats and the difference of the dose-dependent increase of radioactivity tissue levels between both rat strains indicates that tissue distribution at low doses of BI 1356 is dominated by binding of BI 1356 to DPP-4 in tissues. As the binding to DPP-4 is strong but reversible, the tissue binding results in a long terminal half-life in several tissues including plasma. The binding capacity to DPP-4 is, however, limited. In the rat, saturation of DPP-4 binding is suggested at an intravenous dose above 0.01-0.1 mg/kg [(14)C]BI 1356. As the DPP-4 binding capacity is saturated already at low doses, accumulation of BI 1356 in tissues is unlikely, despite the long persistence of low amounts in the body.

Concentration-dependent plasma protein binding of the novel dipeptidyl peptidase 4 inhibitor BI 1356 due to saturable binding to its target in plasma of mice, rats and humans.

OBJECTIVES: The purpose of this study was to characterise the plasma protein binding of BI 1356. METHODS: BI 1356 (proposed trade name ONDERO) is a novel dipeptidyl peptidase 4 (DPP-4) inhibitor, which is under clinical development for the treatment of type 2 diabetes. DPP-4 is expressed in various tissues but soluble DPP-4 is also present in plasma. Therefore, binding to soluble DPP-4 may influence the pharmacokinetics of BI 1356. Plasma protein binding of BI 1356 was determined in vitro for wild type mice and rats and the results compared with those for DPP-4 knockout mice and DPP-4 deficient Fischer rats. In addition, protein binding of BI 1356 was examined in plasma from healthy human volunteers and renal excretion of the compound in the DPP-4 knockout mice was compared with that occurring in wild type mice. KEY FINDINGS: The results showed that BI 1356 exhibited a prominent concentration-dependent plasma protein binding due to a saturable high affinity binding to the DPP-4 target in plasma. Differences in renal excretion of BI 1356 between DPP-4 knockout mice and wild type mice suggested that saturable binding of BI 1356 to DPP-4 in the body also influenced elimination. CONCLUSIONS: High affinity, but readily saturable binding of BI 1356 to its target DPP-4 accounted primarily for the concentration-dependent plasma protein binding at therapeutic plasma concentrations of BI 1356.

Altered drug disposition of the platelet activating factor antagonist apafant in mdr1a knockout mice.

The aim of the present study was to determine a potential impact of P-glycoprotein (P-gp) on the tissue distribution and disposition of apafant (WEB 2086, CAS 105219-56-5), a selective platelet-activating factor antagonist, and on digoxin in mdr1a(-/-) and wildtype mice. Transport experiments in Caco-2 monolayers at low concentrations (<10 microM) showed that the secretory flux of [(14)C]apafant and [(3)H]digoxin exceeded the absorptive flux nine times. This efflux was concentration dependent and subject to inhibition by the P-gp substrates verapamil and cyclosporin A. This indicates that active drug transporter P-gp was involved in apafant and digoxin absorption. Mdr1a(-/-) mice showed a more than 70-fold higher concentration of digoxin-related radioactivity (P<0.001) in the brain than wildtype mice after intravenous doses of 0.05 mg/kg [(3)H]digoxin. Differences were less pronounced in other tissues. Both liquid scintillation counting and whole body autoradiography yielded comparable results and they also matched recently published data. Apafant-related radioactivity was about ten-fold higher in the brain of mdr1a(-/-) mice compared to wildtype mice following intravenous doses of 2 mg/kg radiolabelled apafant. Only slight or negligible differences were observed in other tissues. In wildtype mice, intestinal excretion of [(14)C]apafant (54.9%) exceeded biliary excretion (26.5%). However, in mdr1a(-/-) mice biliary excretion (50.7%) exceeded intestinal excretion (6.8%). These differences were mirrored in the urinary and faecal excretion. Pharmacokinetic parameters of apafant and radioactivity did not differ between wildtype and mdr1a(-/-) mice. The conclusions were: (1) apafant and digoxin are P-gp substrates, and (2) absence of mdr1a encoded P-gp significantly alters tissue distribution (especially in brain) and excretion routes (biliary and intestinal) of apafant.