BackgroundMany studies have focused on the challenges of small molecule uptake across the blood–brain barrier, whereas few in-depth studies have assessed the challenges with the uptake of antibodies into the central nervous system (CNS). In drug development, cerebrospinal fluid (CSF) sampling is routinely used as a surrogate for assessing CNS drug exposure and biomarker levels. In this report, we have studied the kinetic correlation between CSF and serum drug concentration–time profiles for five humanized monoclonal antibodies in rats and cynomolgus monkeys and analyzed factors that affect their CSF exposure.ResultsUpon intravenous (IV) bolus injection, antibodies entered the CNS slowly and reached maximum CSF concentration (CSFTmax) in one to several days in both rats and monkeys. Antibody serum and CSF concentration–time curves converged until they became parallel after CSFTmax was reached. Antibody half-lives in CSF (CSFt½) approximated their serum half-lives (serumt½). Although the intended targets of these antibodies were different, the steady-state CSF to serum concentration ratios were similar at 0.1–0.2% in both species. Independent of antibody target and serum concentration, CSF-to-serum concentration ratios for individual monkeys ranged by up to tenfold from 0.03 to 0.3%.ConclusionUpon systemic administration, average antibodies CSF-to-serum concentration ratios in rats and monkeys were 0.1–0.2%. The CSFt½ of the antibodies was largely determined by their long systemic t½ (systemict½).
Objective: The convective flow of CSF plays a crucial role for CNS to clear endogenous and xenobiotic substances. The objective of this study is to investigate the impact of modifying CSF flow with acetazolamide and arginine vasopressin (AVP) on the CNS clearance of ibuprofen and acetaminophen.Results.Microdialysis studies indicated that acetaminophen AUC ratio (K p,uu ) between brain ISF and unbound plasma increased from 0.40 ± 0.14 in the vehicle control group to 0.60 ± 0.27 in the acetazolamide treated group (P < 0.05). Conversely, acetaminophen's steady-state ISF C to unbound_plasma C ratio (K p,uu ) decreased from 0.44 ± 0.08 to 0.36 ± 0.07 upon IV infusion of 0.3 µg/hr AVP (P < 0.05). Using CSF concentration as a surrogate of unbound brain drug concentration, AVP treatment reduced the CSF AUC 0-5hr / unbound_plasma AUC 0-5hr ratio from 1.63 to 0.85 for acetaminophen, and the CSF C 4hr / unbound_plasma C 4hr ratio decreased from 0.91 ± 0.27 to 0.54 ± 0.12 for ibuprofen (P < 0.05).
Conclusion.We have demonstrated that acetazolamide decreases the CNS clearance of acetaminophen, while AVP increases the CNS clearance of both acetaminophen and ibuprofen. Such changes are caused by altering the CSF production rates.
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