Benefit of doxycycline treatment on articular disability caused by dialysis related amyloidosis.

Abstract Doxycycline inhibits amyloid formation in vitro and its therapeutic efficacy is under evaluation in clinical trials for different protein conformational diseases, including prion diseases, Alzheimer's disease and transthyretin amyloidosis. In patients on chronic hemodialysis, a persistently high concentration of ß2-microglobulin causes a form of amyloidosis (dialysis-related amyloidosis, DRA) localized in bones and ligaments. Since doxycycline inhibits ß2-microglobulin fibrillogenesis in vitro and accumulates in bones, DRA represents an ideal form of amyloidosis where doxycycline may reach a therapeutic concentration at the site of amyloid deposition. Three patients on long-term dialysis with severe articular impairment and uncontrollable pain due to DRA were treated with 100 mg of doxycycline daily. Pharmacokinetics and safety of treatment were conducted. Plasmatic levels of the drug reached a plateau after one week (1.1-2.3 µg/ml). Treatment was well tolerated in two patients for a year, while one was suspended after 5 months due to mild esophagitis. Treatment was associated with a significant reduction in articular pain and with a significant and measurable improvement in passive and active movements in all cases, despite the persistence of unchanged amyloid deposits measured by magnetic resonance imaging.

Determinants of drug brain uptake in a rat model of seizure-associated malformations of cortical development.

We examined the blood-brain barrier (BBB) function in methylazoxymethanol acetate (MAM)-treated rats, a model of human developmental brain malformations. We found aberrant vessels morphology and serum albumin leakage in the heterotopic (malformed) hippocampus; these changes were associated with a significant increase in endothelial P-glycoprotein (P-gp) expression. Seizures exacerbated BBB leakage and greatly augmented P-gp expression in vessels and additionally in perivascular/parenchymal astrocytes. The effects of seizures were observed to a much larger extent in malformed than in normal brain tissue. The intrinsic changes in BBB function in MAM-exposed rats were associated with increased blood-to-brain penetration of ondansetron, a P-gp substrate. However, a marked reduction in drug brain levels was provoked by seizures, and this effect was reversed by selective blockade of P-gp activity with tariquidar. Changes in BBB function may critically contribute to determine the brain uptake and distribution of P-gp substrates in epileptic tissue associated with developmental malformations.

A pilot study on brain-to-plasma partition of 10,11-dyhydro-10-hydroxy-5H-dibenzo(b,f)azepine-5-carboxamide and MDR1 brain expression in epilepsy patients not responding to oxcarbazepine.

PURPOSE: We measured the brain-to-plasma partition of 10,11-dihydro-10-hydroxy-5H-dibenzo(b,f)azepine-5-carboxamide (10-OHCBZ) in epilepsy patients undergoing surgery to alleviate drug-resistant seizures and administered with different oral doses of oxcarbazepine (OXC). We addressed the possible contribution of the multidrug transporter P-glycoprotein (P-gp or MDR1) in determining 10-OHCBZ brain levels by measuring whether this active metabolite is a substrate of P-gp and the relation between the level of expression of MDR1 and the drug concentration in the same brain tissue specimens. METHODS: Steady-state plasma and brain concentrations (C(ss)) of 10-OHCBZ were determined intraoperatively in 11 patients by high-performance liquid chromatography (HPLC) with UV detection. The level of expression of MDR1 mRNA was measured in surgically resected brain tissue by reverse transcriptase polymerase chain reaction (RT-PCR). The ability of 10-OHCBZ to act as substate of P-gp was evaluated by measuring its uptake in cell lines expressing different levels of P-gp, in the presence or absence of a selective P-gp inhibitor. RESULTS: OXC was converted to 10-OHCBZ and to Di-OHCBZ, the two main metabolites measured in plasma. The brain concentrations of the active metabolite 10-OHCBZ did not reflect plasma C(ss). A significant inverse linear correlation was found between 10-OHCBZ brain-to-plasma concentration ratio and the level of brain expression of MDR1 mRNA. In vitro uptake studies demonstrated lower intracellular 10-OHCBZ levels in cells with higher P-gp expression. Intracellular drug concentration was increased by XR9576, a specific P-gp blocker. CONCLUSIONS: Pharmacologic failure of OXC in pharmacoresistant epilepsy is unlikely to be due to alterations in drug metabolism. 10-OHCBZ does not appear to cross the blood-brain barrier by simple diffusion, and it acts as a substrate of P-gp. The level of expression of MDR1 is inversely correlated with 10-OHCBZ concentration in the epileptic tissue. P-gp may play a role in the pharmacoresistance to OXC by determining the attainment of insufficient concentrations of its active metabolite at neuronal targets.

Limbic seizures induce P-glycoprotein in rodent brain: functional implications for pharmacoresistance.

The causes and mechanisms underlying multidrug resistance (MDR) in epilepsy are still elusive and may depend on inadequate drug concentration in crucial brain areas. We studied whether limbic seizures or anticonvulsant drug treatments in rodents enhance the brain expression of the MDR gene (mdr) encoding a permeability glycoprotein (P-gp) involved in MDR to various cancer chemotherapeutic agents. We also investigated whether changes in P-gp levels affect anticonvulsant drug concentrations in the brain. Mdr mRNA measured by RT-PCR increased by 85% on average in the mouse hippocampus 3-24 hr after kainic acid-induced limbic seizures, returning to control levels by 72 hr. Treatment with therapeutic doses of phenytoin or carbamazepine for 7 d did not change mdr mRNA expression in the mouse hippocampus 1-72 hr after the last drug administration. Six hours after seizures, the brain/plasma ratio of phenytoin was reduced by 30% and its extracellular concentration estimated by microdialysis was increased by twofold compared with control mice. Knock-out mice (mdr1a/b -/-) lacking P-gp protein showed a 46% increase in phenytoin concentrations in the hippocampus 1 and 4 hr after injection compared with wild-type mice. A significant 23% increase was found in the cerebellum at 1 hr and in the cortex at 4 hr. Carbamazepine concentrations were measurable in the hippocampus at 3 hr in mdr1a/b -/- mice, whereas they were undetectable at the same time interval in wild-type mice. In rats having spontaneous seizures 3 months after electrically induced status epilepticus, mdr1 mRNA levels were enhanced by 1.8-fold and fivefold on average in the hippocampus and entorhinal cortex, respectively. Thus, changes in P-gp mRNA levels occur in limbic areas after both acute and chronic epileptic activity. P-gp alterations significantly affect antiepileptic drugs concentrations in the brain, suggesting that seizure-induced mdr mRNA expression contributes to MDR in epilepsy.