Estimation of the Unbound Brain Concentration of P-Glycoprotein Substrates or Nonsubstrates by a Serial Cerebrospinal Fluid Sampling Technique in Rats

Abstract

The unbound concentration in plasma drives the transport of the drug into the brain, and the unbound drug concentration in the central nervous system (CNS) drives the interaction with the target eliciting the pharmacological effect. Delivery of the drug to the CNS is a challenge because of the unique neurovascular unit, which restricts the passage of drugs into the brain. The efflux transporters [especially P-glycoprotein (P-gp)] present at the blood-brain barrier (BBB) act as one of the major detractors for keeping drugs outside the CNS. The cerebrospinal fluid (CSF) drug concentration has been used as a surrogate for unbound brain concentrations and has proven to be a good indicator to relate to CNS activity. Herein, we have established a serial CSF sampling technique in rats, which allowed CSF sampling from a single animal and reduced the number of animals required, as well as the interanimal variance associated with a composite/terminal study design. Concentrations in the CSF sampled from the cisterna magna serially from the same rat were compared with the concentrations obtained from discrete CSF sampling and with brain concentrations. The serial CSF sampling technique was also authenticated by ensuring no change in the barrier without any indication of damage caused by the repeated puncture of cisterna magna. This technique was corroborated using three passively permeable compounds (carbamazepine, theophylline, and propranolol), three P-gp substrates (quinidine, verapamil, and digoxin), and one l-amino acid uptake transporter substrate (gabapentin). The P-gp substrates were also used in separate studies with the P-gp inhibitor elacridar to assess the effect on CSF concentration versus brain concentration on P-gp inhibition. The CSF concentration and unbound brain concentration were comparable (within 3-fold) for all compounds, including P-gp substrates even in the presence of elacridar. Therefore, this technique can prove to be beneficial for predicting the unbound drug concentrations in the brain from the CSF concentrations and reduce the cost incurred in preclinical animal models. Chemical inhibition by elacridar and prediction of the brain unbound concentrations from the serial CSF sampling of P-gp substrates in the rat may be an attractive alternative to the use of genetically knocked out rodents.

Propofol attenuates inflammatory damage on neurons following cerebral infarction by inhibiting excessive activation of microglia

“…ELISA. At 12 h after tMCAO, the cerebrospinal fluid (CSF) of SD rats was extracted following a previously described method (27). Subsequently, the levels of interleukin (IL)-1β, IL-6 and tumor necrosis factor-α (TNF-α) in the CSF were measured using ELISA kits (cat.…”

Unmasking the Role of Uptake Transporters for Digoxin Uptake Across the Barriers of the Central Nervous System in Rat

“…The different patterns of digoxin uptake in the presence and absence of individual or dual transporter inhibition suggest differential orientation of efflux and uptake transporters at the BCSFB compared with the BBB and BSCB. 15 As opposed to the BBB and BSCB, the role of uptake transporters was evident even in the presence of efflux (P-gp), suggesting that at the BCSFB the direction of transport of the Oatps is mainly from the CSF to the blood side.…”

“…13,14 The P-gp is localized on the BCSFB, but it has been suggested that the orientation of the efflux transporter may enable the transport from the blood to the CSF instead of effluxing drugs out of the CSF. 14,15 …”

Acute or chronic use of lacosamide does not alter its distribution between serum and cerebrospinal fluid

“…Because measurement of drug concentration in the interstitial fluid (ISF) in the brain of human patients is impractical, cerebrospinal fluid (CSF) concentration is typically used as a surrogate. Studies of both rats and nonhuman primates have demonstrated that CSF concentration corresponded to the ISF concentration of AED carbamazepine (which is not a substrate for efflux transport) . More compelling is a recent published study in patients with epilepsy who were chronically treated with LCM as part of their maintenance drug regimen.…”

“…Studies of both rats and nonhuman primates have demonstrated that CSF concentration corresponded to the ISF concentration of AED carbamazepine (which is not a substrate for efflux transport). 8,9 More compelling is a recent published study in patients with epilepsy who were chronically treated with LCM as part of their maintenance drug regimen. In this study, LCM concentrations in the CSF reached~85% of the serum concentration.…”