Influence of various combinations of specific antibody dose and affinity on tissue imipramine redistribution.

1. This study was designed to evaluate the distribution kinetics of imipramine (Imip) in the brain and the main peripheral organs (heart, kidney, liver and lung) of rats, and to establish the relationship between the redistribution of Imip from these tissues and the immunoreactive capacity (dose and affinity) of anti-TCA IgG. 2. [3H]-Imip (1 nmol kg(-1) body weight) was injected intravenously 6 min before the i.v. injection of antibodies. At this time, the concentrations of Imip and its main metabolites in plasma were determined. The radioactivity measured corresponded to 91.7% Imip, indicating that the pharmacokinetics reflected essentially Imip. Plasma and tissue Imip contents were measured over the interval 1 to 90 min in control and in treated rats. The antibodies used were a murine monoclonal IgG1 (Ka=3.8 10(7) M(-1)) at an IgG1/Imip molar ratio of 1000 (IgG1 1000), and a sheep polyclonal IgG (TAb, Ka=1.3 10(10) M(-1)) at IgG/ Imip molar ratios of 1, 10 and 100 (TAb1, TAb10 and TAb100). 3. The anti-TCA IgG increased the plasma [3H]-Imip concentrations: the AUC1-->60 min for [3H]-Imip were 4 (IgG1 1000), 9 (TAb1), 33.9 (TAb10) and 41.4 (TAb100) times higher in the treated groups than in the controls. The opposite effect occurred in the brain, heart and lungs, with large, rapid decreases in Imip. The increase in plasma Imip and the decrease in tissue Imip depended on the immunoreactive capacity (NKa) of the antibody, where N=molar concentration of IgG binding sites and Ka=IgG affinity constant. Maximal plasma and tissue redistribution occurred when NKa=33.8 x 10(4). 4. Imip redistribution can be controlled using various doses or affinities of specific antibodies, and the resulting rapid, extensive Imip redistribution from the main target organs could be very promising for TCA detoxification.

Simultaneous microdialysis in brain and blood of the mouse: extracellular and intracellular brain colchicine disposition.

A simultaneous brain and blood microdialysis system was developed to study the passage of colchicine through the blood-brain barrier in the mouse. Colchicine was administered as a bolus in the jugular vein (1.5 mg kg-1) and its hippocampal extracellular fluid (ECF) and blood kinetics were determined over a 4 h period using two microdialysis probes, one in the dorsal hippocampus, the other in the inferior vena cava. Colchicine rapidly diffused into the hippocampus (maximum concentration in the first dialysate sample) and brain and blood concentrations declined in parallel, suggesting rapid equilibration between these two compartments. However, only 6. 7% of total blood colchicine, 14% of unbound colchicine was present in the hippocampus suggesting that the P-glycoprotein efflux pump limits colchicine uptake by the brain. We also found, using conventional tissue homogenate analysis in parallel, that the concentration of colchicine in the hippocampal ECF was 10 times less than that in the intracellular space and that the hippocampus colchicine concentration was 2.8 times higher than that of the rest of the brain. This study shows that the simultaneous brain and blood microdialysis can be used to measure the passage of colchicine through the blood-brain barrier and to estimate the brain extra- and intracellular distribution of colchicine.

Redistribution of imipramine from regions of the brain under the influence of circulating specific antibodies.

The kinetics of brain-to-blood redistribution of imipramine (IMI) was assessed in nine brain regions of control rats and rats given anti-tricyclic antidepressant (anti-TCA) antibody. Two antibodies were given intravenously 6 min after intravenous [3H]IMI (1 nmol/kg). One was a murine monoclonal IgG1 (Ka = 3.8 x 10(7) M(-1)) at an IgG/IMI molar ratio of 1,000 (IgG1,000), and the other was a sheep polyclonal IgG (TAb; Ka = 1.3 x 10(10) M(-1)) at IgG/IMI molar ratios of 1, 10, and 100 (TAb1, TAb10, and TAb100). In the control rats, IMI was rapidly taken up by the brain (Cmax at 5 min) with no significant differences among the brain regions (4.1 +/- 0.4 to 5.4 +/- 0.6 pmol/ g), and brain IMI then declined monoexponentially with a half-life of 44.2 min (cerebellum) to 77.3 min (hippocampus). The greatest IMI content was in the frontal cortex and the lowest in the cerebellum. The antibodies (except TAb1) stimulated the extent and rate of IMI redistribution from all the brain regions depending on the immunoreactive capacity (NKa) of the antibody. The antibody with the highest NKa (TAb100) had the greatest effect. The fraction of IMI removed from the brain was 58-74%, and the redistribution half-life was 7.9-15.6 min; the mean residence time was reduced by 66-75% (11.8-23.9 min). These results demonstrate that circulating anti-TCA IgG rapidly and reliably removes IMI from the brain, indicating that immunotoxicotherapy could be an efficient procedure for accelerating the removal of TCA from the brain.

Facilitation of imipramine efflux from the brain by systemic specific antibodies.

1. This study investigated the capacity of circulating anti-tricyclic antidepressant (TCA) IgG to increase the efflux of imipramine (Imip) from the rat brain. 2. A tracer amount of [3H]-Imip (40 pmol) was injected into the cerebral lateral ventricle and its efflux was determined in control rats and in rats given anti-TCA antibody. The monoclonal anti-TCA IgG1 was injected i.v. 48 h before Imip at 4 IgG:Imip molar ratios (10, 100, 1000 and 10,000). The [3H]-Imip in arterial and venous plasma was measured for up to 60 min, and in the brain and peripheral organs (heart, liver, lung, kidney) 5 and 60 min after Imip injection. 3. The arterial plasma concentration of Imip in control rats was significantly higher (26.7 +/- 2.1 pM) than the venous one (17.7 +/- 2.0 pM) at 5 min, indicating that Imip released from brain becomes distributed in peripheral tissues. These concentrations were not significantly different at 60 min suggesting that Imip was, at this time, redistributing from extravascular tissues to the blood. In rats given anti-TCA IgG, any Imip leaving the brain was immediately bound by the circulating antibody at 5 min. This greatly reduced the Imip in the heart (63.9%) and lung (61.3%) at the highest IgG:Imip ratio. The brain Imip was markedly lower at 60 min (31.5% with an IgG Imip ratio of 1000 and 57.5% at a ratio of 10,000). The two lowest IgG:Imip ratios had less effect on the plasma Imip because of the relative low affinity of the anti-TCA IgG (3.8 x 10(7) M-1). 4. These data indicate that the anti-TCA IgG facilitated the efflux of Imip from the brain, even though these antibodies cannot cross the blood-brain barrier. This may be an efficient system for increasing drug organ clearance, as more than half the Imip in the brain was actively removed by the antibody in 1 h.