Blood-to-brain transfer of various oxicams: effects of plasma binding on their brain delivery

Insights into the effect of glucose on the binding between human serum albumin and the nonsteroidal anti-inflammatory drug nimesulide

Glucose interacts with human serum albumin (HSA, the main protein responsible for the biodistribution of drugs in the bloodstream) and consequently affects the binding capacity of exogenous compounds. Thus, in this work, the interactive profile between HSA and the anti-inflammatory drug nimesulide (NMD, used mainly by patients with diabetic neuropathy to relieve acute or chronic pains) was characterized in nonglycemic, normoglycemic (80 mg/dL), and hyperglycemic (320 mg/dL) conditions by biophysics techniques. There is a spontaneous and ground-state association HSA:NMD under physiological conditions. Therefore, the Stern-Volmer constant (Ksv) can also be used to estimate the binding affinity. The Ksv values for nonglycemic, normoglycemic, and hyperglycemic conditions are around 104 M-1, indicating a moderate affinity of NMD to albumin that was slightly improved by glucose levels. Additionally, the binding is enthalpically and entropically driven mainly into subdomains IIA or IIIA. The binding perturbs weakly the α-helix content of albumin, however, glucose potentially stabilizes the tertiary structure, decreasing the structural perturbation upon NMD binding and improves the complex HSA:NMD stability. Overall, the biophysical characterization indicated that glucose levels might slightly positively impact the pharmacokinetic profile of NMD, allowing NMD to achieve its therapeutical potential without affecting drastically its effective dosages.

A Historical Review of Brain Drug Delivery

The history of brain drug delivery is reviewed beginning with the first demonstration, in 1914, that a drug for syphilis, salvarsan, did not enter the brain, due to the presence of a blood-brain barrier (BBB). Owing to restricted transport across the BBB, FDA-approved drugs for the CNS have been generally limited to lipid-soluble small molecules. Drugs that do not cross the BBB can be re-engineered for transport on endogenous BBB carrier-mediated transport and receptor-mediated transport systems, which were identified during the 1970s-1980s. By the 1990s, a multitude of brain drug delivery technologies emerged, including trans-cranial delivery, CSF delivery, BBB disruption, lipid carriers, prodrugs, stem cells, exosomes, nanoparticles, gene therapy, and biologics. The advantages and limitations of each of these brain drug delivery technologies are critically reviewed.

The hyperthermic effect of central cholecystokinin is mediated by the cyclooxygenase-2 pathway

Cholecystokinin (CCK) increases core body temperature via CCK₂ receptors when administered intracerebroventricularly (icv). The mechanisms of CCK-induced hyperthermia are unknown, and it is also unknown whether CCK contributes to the fever response to systemic inflammation. We studied the interaction between central CCK signaling and the cyclooxygenase (COX) pathway. Body temperature was measured in adult male Wistar rats pretreated with intraperitoneal infusion of the nonselective COX enzyme inhibitor metamizol (120 mg/kg) or a selective COX-2 inhibitor, meloxicam, or etoricoxib (10 mg/kg for both) and, 30 min later, treated with intracerebroventricular CCK (1.7 µg/kg). In separate experiments, CCK-induced neuronal activation (with and without COX inhibition) was studied in thermoregulation- and feeding-related nuclei with c-Fos immunohistochemistry. CCK increased body temperature by ∼0.4°C from 10 min postinfusion, which was attenuated by metamizol. CCK reduced the number of c-Fos-positive cells in the median preoptic area (by ∼70%) but increased it in the dorsal hypothalamic area and in the rostral raphe pallidus (by ∼50% in both); all these changes were completely blocked with metamizol. In contrast, CCK-induced satiety and neuronal activation in the ventromedial hypothalamus were not influenced by metamizol. CCK-induced hyperthermia was also completely blocked with both selective COX-2 inhibitors studied. Finally, the CCK₂ receptor antagonist YM022 (10 µg/kg icv) attenuated the late phases of fever induced by bacterial lipopolysaccharide (10 µg/kg; intravenously). We conclude that centrally administered CCK causes hyperthermia through changes in the activity of "classical" thermoeffector pathways and that the activation of COX-2 is required for the development of this response.NEW & NOTEWORTHY An association between central cholecystokinin signaling and the cyclooxygenase-prostaglandin E pathway has been proposed but remained poorly understood. We show that the hyperthermic response to the central administration of cholecystokinin alters the neuronal activity within efferent thermoeffector pathways and that these effects are fully blocked by the inhibition of cyclooxygenase. We also show that the activation of cyclooxygenase-2 is required for the hyperthermic effect of cholecystokinin and that cholecystokinin is a modulator of endotoxin-induced fever.

Biological barriers, and the influence of protein binding on the passage of drugs across them

Drug-protein binding plays a key role in determining the pharmacokinetics of a drug. The distribution and protein binding ability of a drug changes over a lifetime, and are important considerations during pregnancy and lactation. Although proteins are a significant fraction in plasma composition, they also exist beyond the bloodstream and bind with drugs in the skin, tissues or organs. Protein binding influences the bioavailability and distribution of active compounds, and is a limiting factor in the passage of drugs across biological membranes and barriers: drugs are often unable to cross membranes mainly due to the high molecular mass of the drug-protein complex, thus resulting in the accumulation of the active compounds and a significant reduction of their pharmacological activity. This review describes the consequences of drug-protein binding on drug transport across physiological barriers, whose role is to allow the passage of essential substances-such as nutrients or oxygen, but not of xenobiotics. The placental barrier regulates passage of xenobiotics into a fetus and protects the unborn organism. The blood-brain barrier is the most important barrier in the entire organism and the skin separates the human body from the environment.

Canine Albumin Polymorphisms and Their Impact on Drug Plasma Protein Binding

Drug binding to plasma proteins is routinely determined during drug development. Albumin polymorphisms c.1075G>T (p.Ala359Ser) and c.1422A>T (p.Glu474Asp) were previously shown to alter plasma protein binding of a drug candidate (D01-4582, 4-[1-[3-chloro-4-[N′-(2-methylphenyl)ureido]phenylacetyl]-(4S)-fluoro-(2S)-pyrrolidine-2-yl]methoxybenzoic acid) in a colony of Beagles. Our study investigated the hypothesis that drug-protein binding in plasma from dogs with the albumin H1 (reference) allele would be greater than in plasma from dogs with the albumin H2 allele (c.1075G>T and c.1422A>T) (n = 6 per group). The plasma protein binding extent of four drugs (D01-4582, celecoxib, mycophenolic acid, and meloxicam) was evaluated using ultracentrifugation or equilibrium dialysis. Free and total drug concentrations were analyzed by liquid chromatography–mass spectrometry. The albumin gene coding region was sequenced in 100 dogs to detect novel gene variants, and H1/H2 allele frequency was determined in a large and varied population (n = 1446 from 61 breeds and mixed-breed dogs). For meloxicam, H1 allele plasma had statistically significant higher free drug fractions (P = 0.041) than H2 allele plasma. No significant difference was identified for plasma protein binding of D01-4582, celecoxib, or mycophenolic acid. c.1075G>T and c.1422A>T were the most common single nucleotide polymorphisms in canine albumin, present concurrently in most study dogs and occasionally identified independently. Our findings suggest a potential influence of c.1075G>T and c.1422A>T on plasma protein binding. This influence should be confirmed in vivo and for additional drugs. Based on our results, albumin genotyping should be considered for canine research subjects to improve interpretation of pharmacokinetic data generated during the drug development process for humans and dogs.

Meloxicam Improves Cognitive Impairment of Diabetic Rats through COX2-PGE2-EPs-cAMP/pPKA Pathway

Diabetics often face greater risk of cognitive impairment than nondiabetics. However, how to prevent this disease is still unconfirmed. In this study, we investigated the potential protection and mechanism of meloxicam on cognitive impairment in diabetic rats. The diabetic rat model was established with a high-fat diet and a small dose of streptozotocin (40 mg/kg). The changes of spatial learning and memory, histopathology, and the protein expressions of amyloid protein precursor (APP) and β-amyloid (Aβ) indicated that diabetic rats had neuronal injury and cognitive impairment. Tumor necrosis factor α (TNFα), interleukin 6 (IL-6), C reactive protein (CRP) and prostaglandin E2 (PGE2) levels, and microglial cell number were significantly increased in the diabetic rat brain. Meanwhile, the protein expressions of APP, Aβ, cyclooxygenases2 (COX2), E-type prostanoid recptors 1 (EP1) and EP2, and the level of cyclic adenosine monophosphate (cAMP) were significantly increased, while the protein expressions of EP3 and phosphorylated protein kinase A (pPKA) were significantly decreased in the diabetic rat hippocampus and cortex. However, the EP4 protein expression had no significant changes. Meloxicam significantly improved neuronal injury and cognitive impairment, and significantly decreased inflammatory cytokines levels. Meloxicam also significantly decreased the protein expressions of APP, Aβ, COX2, EP1 and EP2, and the level of cAMP and significantly increased the EP3 and pPKA protein expressions in rat hippocampus and cortex. However, meloxicam did not significantly influence the levels of blood glucose, lipids, and insulin of rats. Our results suggest that meloxicam could significantly protect diabetic rats from cognitive impairment via a mechanism that may be associated with rebalancing the COX2-PGE2-EPs-cAMP/PKA pathway.

The effect of surgery (Ovariohysterectomy) on the plasma disposition of meloxicam following intravenous administration in dogs

Background

Meloxicam (MLX) is a nonsteroidal anti-inflammatory drug used in the relief of postoperative pain for human and veterinary medicine. This study was designed to investigate the effect of surgery on the plasma disposition of MLX in dogs undergoing ovariohysterectomy following a single intravenous injection at a dose of 0.2 mg/kg bodyweight. Eight crossbred bitches were used in the study. A two-phase experimental design with a 10-day washout period was used. Pre-operative MLX was administered intravenously to 8 bitches about 10 days before surgery (Phase I, control) at a dose of 0.2 mg/kg bodyweight and peri-operative MLX was administered intravenously after anaesthesia and 15 min before the start of surgery (Phase II). Blood samples were collected from all animals at various times between 1 and 96 h after the drug administrations in both phases. The drug concentrations were analysed using high performance liquid chromatography.

Results

The volume of plasma MLX distribution at steady-state (Vd_ss) of the control group (Vd_ss: 263.0 ml/kg) was significantly greater (P < 0.05) compared to that of the surgery group (Vd_ss: 149.3 ml/kg). The AUC values were higher (29.5 vs. 23.0 μg.h²/ml) and the CL values were lower (7.7 vs. 10.5 ml.h/kg) in the surgery group compared to the control group, respectively, but differences were not significant.

Conclusions

The results of the present study indicated that surgery could alter the plasma disposition of MLX and thus the drug efficacy and side effects such as gastrointestinal ulceration, unusual bleeding and loss of kidney function/failure when repeated doses are used.

Tautomeric transformations of piroxicam in solution: a combined experimental and theoretical study

Piroxicam tautomerism was studied in solution. Enol-amide tautomer is presented mainly as a sandwich type dimer in ethanol and DMSO. The addition of water leads to gradual shift of the equilibrium towards the zwitterionic tautomer.

The effect of manganese on the olfactory bulb of adult male albino rat and the role of meloxicam: A histological and immunohistochemical study

Manganese (Mn) is an essential metal commonly found in the environment and is used for industrial purposes. Exposure to excessively high Mn levels may induce neurotoxicity referred to as manganism. This work was conducted to study the effect of manganese on the olfactory bulb of adult male albino rat and the possible protective role of meloxicam. Forty adult male albino rats were equally divided into four groups: control group, meloxicam-treated group (5 mg/kg/day orally for 4 weeks), MnCl₂-treated group (10 mg/kg/day orally for 4 weeks), and the fourth group received both meloxicam and MnCl₂ at the same doses and duration. Specimens of the olfactory bulbs were prepared for light and electron microscopy. An immunohistochemical study with a quantitative morphometry was performed using antibodies against glial fibrillary acidic protein (GFAP). The control group and meloxicam-treated group showed the same normal structure. MnCl₂-treated group showed shrinkage of mitral nerve cells with dark peripheral nuclei as well as disorganization of mitral and granule nerve cells. The surrounding neuropil showed vacuolar spaces. Ultrastructurally, the mitral cells showed accumulation of lysosomes, swelling of mitochondria and irregularity of the nuclei. The nerve fibers contained swollen mitochondria with splitting and irregularity of the surrounding myelin sheaths. GFAP immunoreaction showed a highly significant increase compared to control group. On the other hand, the group that received both meloxicam and MnCl₂ showed less marked histological changes. It was concluded that manganese induced structural changes in the olfactory bulb of albino rat that were ameliorated by concomitant use of meloxicam.

Development of a physiologically-based pharmacokinetic model of the rat central nervous system

Central nervous system (CNS) drug disposition is dictated by a drug's physicochemical properties and its ability to permeate physiological barriers. The blood-brain barrier (BBB), blood-cerebrospinal fluid barrier and centrally located drug transporter proteins influence drug disposition within the central nervous system. Attainment of adequate brain-to-plasma and cerebrospinal fluid-to-plasma partitioning is important in determining the efficacy of centrally acting therapeutics. We have developed a physiologically-based pharmacokinetic model of the rat CNS which incorporates brain interstitial fluid (ISF), choroidal epithelial and total cerebrospinal fluid (CSF) compartments and accurately predicts CNS pharmacokinetics. The model yielded reasonable predictions of unbound brain-to-plasma partition ratio (Kpuu,brain) and CSF:plasma ratio (CSF:Plasmau) using a series of in vitro permeability and unbound fraction parameters. When using in vitro permeability data obtained from L-mdr1a cells to estimate rat in vivo permeability, the model successfully predicted, to within 4-fold, Kpuu,brain and CSF:Plasmau for 81.5% of compounds simulated. The model presented allows for simultaneous simulation and analysis of both brain biophase and CSF to accurately predict CNS pharmacokinetics from preclinical drug parameters routinely available during discovery and development pathways.

Transport rankings of non-steroidal antiinflammatory drugs across blood-brain barrier in vitro models

The aim of this work was to conduct a comprehensive study about the transport properties of NSAIDs across the blood-brain barrier (BBB) in vitro. Transport studies with celecoxib, diclofenac, ibuprofen, meloxicam, piroxicam and tenoxicam were accomplished across Transwell models based on cell line PBMEC/C1-2, ECV304 or primary rat brain endothelial cells. Single as well as group substance studies were carried out. In group studies substance group compositions, transport medium and serum content were varied, transport inhibitors verapamil and probenecid were added. Resulted permeability coefficients were compared and normalized to internal standards diazepam and carboxyfluorescein. Transport rankings of NSAIDs across each model were obtained. Single substance studies showed similar rankings as corresponding group studies across PBMEC/C1-2 or ECV304 cell layers. Serum content, glioma conditioned medium and inhibitors probenecid and verapamil influenced resulted permeability significantly. Basic differences of transport properties of the investigated NSAIDs were similar comparing all three in vitro BBB models. Different substance combinations in the group studies and addition of probenecid and verapamil suggested that transporter proteins are involved in the transport of every tested NSAID. Results especially underlined the importance of same experimental conditions (transport medium, serum content, species origin, cell line) for proper data comparison.

The mastermind approach to CNS drug therapy: translational prediction of human brain distribution, target site kinetics, and therapeutic effects

Despite enormous advances in CNS research, CNS disorders remain the world's leading cause of disability. This accounts for more hospitalizations and prolonged care than almost all other diseases combined, and indicates a high unmet need for good CNS drugs and drug therapies.Following dosing, not only the chemical properties of the drug and blood-brain barrier (BBB) transport, but also many other processes will ultimately determine brain target site kinetics and consequently the CNS effects. The rate and extent of all these processes are regulated dynamically, and thus condition dependent. Therefore, heterogenious conditions such as species, gender, genetic background, tissue, age, diet, disease, drug treatment etc., result in considerable inter-individual and intra-individual variation, often encountered in CNS drug therapy.For effective therapy, drugs should access the CNS "at the right place, at the right time, and at the right concentration". To improve CNS therapies and drug development, details of inter-species and inter-condition variations are needed to enable target site pharmacokinetics and associated CNS effects to be translated between species and between disease states. Specifically, such studies need to include information about unbound drug concentrations which drive the effects. To date the only technique that can obtain unbound drug concentrations in brain is microdialysis. This (minimally) invasive technique cannot be readily applied to humans, and we need to rely on translational approaches to predict human brain distribution, target site kinetics, and therapeutic effects of CNS drugs.In this review the term "Mastermind approach" is introduced, for strategic and systematic CNS drug research using advanced preclinical experimental designs and mathematical modeling. In this way, knowledge can be obtained about the contributions and variability of individual processes on the causal path between drug dosing and CNS effect in animals that can be translated to the human situation. On the basis of a few advanced preclinical microdialysis based investigations it will be shown that the "Mastermind approach" has a high potential for the prediction of human CNS drug effects.

Meloxicam improves object recognition memory and modulates glial activation after splenectomy in mice

CONTEXT

Surgery-induced neuroinflammation has been implicated in the development of postoperative cognitive dysfunction (POCD).

OBJECTIVE

To test the hypothesis that meloxicam, a selective cyclooxygenase (COX)-2 inhibitor, preserves postoperative cognitive function and inhibits surgery-induced neuroinflammation in a mouse model.

DESIGN

A mouse model of splenectomy-induced inflammation.

METHODS

Sixty Swiss Webster male mice (6-8 week old) were randomised into six groups that underwent splenectomy. Animals in groups 1-4 were tested once on day 1, 5, 9 or 14 to determine the time course of delayed transient cognitive dysfunction associated with splenectomy. Animals in groups 5 and 6 were tested once on day 5 or 9 to determine the ability of the NSAID meloxicam to attenuate cognitive dysfunction.

INTERVENTION

Animals in groups 1-4 received one dose 500 μl intraperitoneal physiological saline 24 h after splenectomy. Animals in groups 5 and 6 received one dose of intraperitoneal meloxicam (60 mg kg in 500 μl saline) 24 h after splenectomy.

MAIN OUTCOME MEASURES

Short-term working memory as determined by Object Recognition Test (ORT) index on days 1, 5, 9 and 14 was the first main outcome. Tomato lectin staining histochemistry of glial cells was assessed on days 1, 5, 9 and 14 as a second main outcome.

RESULTS

Compared with day 1 (group 1), the mean ORT indices at day 5 (group 2) and day 9 (group 3) were decreased by 27.5% [95% confidence interval (CI): 0.9 to 54.1%, P = 0.04] and 23.8% (95% CI, 4.3 to 51.9%, P = 0.09), respectively. At day 5 (group 5) and day 9 (group 6), the ORT indices in the meloxicam groups were reduced by 6.6% (95% CI: -11.4 to 24.5%) and 4.3% (95% CI: -25.3 to 34.0). Thus, the administration of meloxicam attenuated the decrease in ORT indices (P = 0.031). Histochemical staining with tomato lectin showed features of microglia activation at day 5 and 9, which was reduced by the administration of meloxicam.

CONCLUSION

These findings suggest that COX-2-dependent mechanisms may play a role in the development of POCD. This effect may be dependent on the modulation of glial cell activation.

Is there a role for PGE2 in urinary concentration?

Prostanoids are prominent, yet complex, components in the maintenance of body water homeostasis. Recent functional and molecular studies have revealed that the local lipid mediator PGE2 is involved both in water excretion and absorption. The biologic actions of PGE2 are exerted through four different G-protein-coupled receptors; designated EP1-4, which couple to separate intracellular signaling pathways. Here, we discuss new developments in our understanding of the actions of PGE2 that have been uncovered utilizing receptor specific agonists and antagonists, EP receptor and PG synthase knockout mice, polyuric animal models, and the new understanding of the molecular regulation of collecting duct water permeability. The role of PGE2 in urinary concentration comprises a variety of mechanisms, which are not fully understood and likely depend on which receptor is activated under a particular physiologic condition. EP3 and microsomal PG synthase type 1 play a role in decreasing collecting duct water permeability and increasing water excretion, whereas EP2 and EP4 can bypass vasopressin signaling and increase water reabsorption through two different intracellular signaling pathways. PGE2 has an intricate role in urinary concentration, and we now suggest how targeting specific prostanoid receptor signaling pathways could be exploited for the treatment of disorders in water balance.

Differentiating oxicam nonsteroidal anti-inflammatory drugs in phosphoglyceride monolayers

Meloxicam, piroxicam, and tenoxicam belong to a highly potent oxicam group of nonsteroidal anti-inflammatory drugs. Whereas the structurally similar oxicams have different pharmacokinetics, treatment efficiency, and adverse effects, their common mechanism of action is the inhibition of a membrane enzyme, cyclooxygenase. Because the prerequisite for accessing the cyclooxygenase by the drugs is interaction with the membrane, the focus of the current study was a comparison of how meloxicam, piroxicam, and tenoxicam interact with lipid monolayers used as models of biological membranes. The monolayers were formed with 1,2-dipalmitoyl-sn-glycero-3-phospho-rac-(1-glycerol), 1,2-dipalmitoyl-sn-glycero-3-phospho-l-serine, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine, 1,2-dipalmitoyl-sn-glycero-3-phosphoethanolamine, 1,2-myristoyl-sn-glycero-3-phosphoethanolamine, and 1,2-dilauroyl-sn-glycero-3-phosphoethanolamine. These systems were examined via surface pressure and surface electrical potential measurements, polarization modulation infrared reflection adsorption spectra, and Brewster angle microscopy. The three oxicams are differentiated in the monolayers; meloxicam shows the highest ability to modify membrane fluidity and surface potential, followed by piroxicam and tenoxicam. The dissimilarity of the biological activity of the oxicams may be linked to different interaction with the membrane, as revealed by the present study.

Evaluation of various PAMPA models to identify the most discriminating method for the prediction of BBB permeability

The Parallel Artificial Membrane Permeability Assay (PAMPA) has been successfully introduced into the pharmaceutical industry to allow useful predictions of passive oral absorption. Over the last 5 years, researchers have modified the PAMPA such that it can also evaluate passive blood-brain barrier (BBB) permeability. This paper compares the permeability of 19 structurally diverse, commercially available drugs assessed in four different PAMPA models: (1) a PAMPA-BLM (black lipid membrane) model, (2) a PAMPA-DS (Double Sink) model, (3) a PAMPA-BBB model and (4) a PAMPA-BBB-UWL (unstirred water layer) model in order to find the most discriminating method for the prediction of BBB permeability. Both the PAMPA-BBB model and the PAMPA-BLM model accurately identified compounds which pass the BBB (BBB+) and those which poorly penetrate the BBB (BBB-). For these models, BBB+ and BBB- classification ranges, in terms of permeability values, could be defined, offering the opportunity to validate the paradigm with in vivo data. The PAMPA models were subsequently applied to a set of 14 structurally diverse internal J&J candidates with known log (brain/blood concentration) (LogBB) values. Based on these LogBB values, BBB classifications were established (BBB+: LogBB0 >or=; BBB-: LogBB<0). PAMPA-BLM resulted in three false positive identifications, while PAMPA-BBB misclassified only one compound. Additionally, a Caco-2 assay was performed to determine the efflux ratio of all compounds in the test set. The false positive that occurred in both models was shown to be related to an increased efflux ratio. Both the PAMPA-BLM and the PAMPA-BBB models can be used to predict BBB permeability of compounds in combination with an assay that provides p-gp efflux data, such as the Caco-2 assay.

Intracarotid delivery of drugs: the potential and the pitfalls

The major efforts to selectively deliver drugs to the brain in the past decade have relied on smart molecular techniques to penetrate the blood-brain barrier, whereas intraarterial drug delivery has drawn relatively little attention. Meanwhile, rapid progress has been made in the field of endovascular surgery. Modern endovascular procedures can permit highly targeted drug delivery by the intracarotid route. Intracarotid drug delivery can be the primary route of drug delivery or it could be used to facilitate the delivery of smart neuropharmaceuticals. There have been few attempts to systematically understand the kinetics of intracarotid drugs. Anecdotal data suggest that intracarotid drug delivery is effective in the treatment of cerebral vasospasm, thromboembolic strokes, and neoplasms. Neuroanesthesiologists are frequently involved in the care of such high-risk patients. Therefore, it is necessary to understand the applications of intracarotid drug delivery and the unusual kinetics of intracarotid drugs.

Targeting the brain: rationalizing the novel methods of drug delivery to the central nervous system

Drug delivery to the brain has remained one of the most vexing problems in translational neuroscience research. This review rationalizes the strategies to target drugs to the brain. Factors such as the speed of intervention, the scale of intervention, the state of BBB, and the permissible risks, will all be critical in deciding how best to deliver drugs to a target site in the brain for a specific clinical situation.

Rapid Screening of Blood-Brain Barrier Penetration of Drugs Using the Immobilized Artificial Membrane Phosphatidylcholine Column Chromatography

The chromatographic capacity factors (kIAM) of 23 structurally diverse drugs were measured by the immobilized artificial membrane (kIAM) phosphatidylcholine chromatography for the prediction of blood-brain barrier (BBB) penetration. The kIAM was determined using themobile phase consisting of acetonitrile:DPBS (20:80 v/v) and corrected for the molar volume of the solutes (kIAM/MWn). The correlation between kIAM/MWn and CNS penetration was highest when measured at pH 5.5 with the power function of n = 4. This in vitro predictionmethod was validated with 7 newly synthesized PDE-4 inhibitors. The relationship between in vivo plasma-to-brain concentration ratios and in vitro CNS penetration was excellent ( r= 0.959). The developed in vitro prediction method may be used as a rapid screening tool for BBB penetration of drugs with passive transport mechanism, with high success, low cost, and reproducibility.

Toward the prediction of CNS drug-effect profiles in physiological and pathological conditions using microdialysis and mechanism-based pharmacokinetic-pharmacodynamic modeling

Our ultimate goal is to develop mechanism-based pharmacokinetic (PK)-pharmacodynamic (PD) models to characterize and to predict CNS drug responses in both physiologic and pathologic conditions. To this end, it is essential to have information on the biophase pharmacokinetics, because these may significantly differ from plasma pharmacokinetics. It is anticipated that biophase kinetics of CNS drugs are strongly influenced by transport across the blood-brain barrier (BBB). The special role of microdialysis in PK/PD modeling of CNS drugs lies in the fact that it enables the determination of free-drug concentrations as a function of time in plasma and in extracellular fluid of the brain, thereby providing important data to determine BBB transport characteristics of drugs. Also, the concentrations of (potential) extracellular biomarkers of drug effects or disease can be monitored with this technique. Here we describe our studies including microdialysis on the following: (1) the evaluation of the free drug hypothesis; (2) the role of BBB transport on the central effects of opioids; (3) changes in BBB transport and biophase equilibration of anti-epileptic drugs; and (4) the relation among neurodegeneration, BBB transport, and drug effects in Parkinson's disease progression.

Mechanism of interaction of the non-steroidal antiinflammatory drugs meloxicam and nimesulide with serum albumin

The mechanism of interaction of the non-steroidal antiinflammatory drugs meloxicam and nimesulide with human and bovine serum albumin has been studied using fluorescence spectroscopy. There was only one high affinity site on serum albumin for both the drugs with association constants of the order of 10(5). Negative enthalpy (DeltaH(0)) and positive entropy (DeltaS(0)) values in the case of both meloxicam and nimesulide showed that both hydrogen bonding and hydrophobic interactions play a role in the binding of these drugs. Binding studies in the presence of the hydrophobic probe 1-anilinonaphthalene-8-sulfonate (ANS) showed that the binding of meloxicam and nimesulide to serum albumin involves predominantly hydrophobic interactions. Stern-Volmer analysis of the quenching data showed that quenching is highly efficient and that the tryptophan residues in hydrophobic regions of the proteins are fully exposed to the drugs. Thus these drugs are bound to albumin by hydrophobic interactions as well as hydrogen bonding at a site, which is close to the tryptophan residues. An increase of the pH and ionic strength caused an increase in the concentration of free drug, although the effect was not very significant.

COX-dependent mechanisms involved in the antinociceptive action of NSAIDs at central and peripheral sites

Despite the diverse chemical structure of aspirin-like drugs, the antinociceptive effect of NSAIDs is mainly due to their common property of inhibiting cyclooxygenases involved in the formation of prostaglandins. Prostaglandins are potent hyperalgesic mediators which modulate multiple sites along the nociceptive pathway and enhance both transduction (peripheral sensitizing effect) and transmission (central sensitizing effect) of nociceptive information. Inhibition of the formation of prostaglandins at peripheral and central sites by NSAIDs thus leads to the normalisation of the increased pain threshold associated with inflammation. The contribution of peripheral and central mechanisms to the overall antinociceptive action of NSAIDs depends on several factors including the location of the targets of drug action, the site of drug delivery and the uptake and distribution to the site of action. The present work reviews the data on the regulation and location of cyclooxygenases at central and peripheral sites of the nociceptive pathway and focuses on the role of COX in the generation and maintenance of pain hypersensitivity. Experimental and clinical evidences are used to evaluate the significance of the peripheral and central antihyperalgesic effects of NSAIDs.

Inefficient central nervous system delivery limits the use of ibuprofen in neurodegenerative diseases

Chronic use of non-steroidal anti-inflammatory drugs may reduce the risk or delay the onset of Alzheimer's disease. To date, only limited information exists on the brain distribution of these drugs. The objective of this study was to determine the absolute brain delivery of ibuprofen by using constant in vivo infusion in rats. Ibuprofen was infused to steady-state concentrations both in plasma and brain tissue. Ibuprofen levels in plasma and brain tissue were measured by RP-HPLC after the plasma and the brain samples were purified by protein precipitation and solid phase extraction, respectively. Results indicate that both plasma and brain concentrations reached steady-state within 6h, and that the brain to plasma ratio of ibuprofen was only 0.02. Thus, limited brain penetration prevents the possible use of ibuprofen in treating or preventing neurodegenerative disorders such as Alzheimer's disease.

Contribution of ionization and lipophilicity to drug binding to albumin: a preliminary step toward biodistribution prediction

Understanding the molecular mechanisms governing albumin binding is a major challenge in absorption-distribution-metabolism-excretion prediction. To gain insight into this complex field, an ultracentrifugation method to measure the drug fraction bound to bovine serum albumin [%B(DAB)] is presented. The second part of the study shows the dependence of the experimental binding parameter on ionization and lipophilicity descriptors (pK(a) and log D(oct)(7.4) for a series of 14 structurally diverse drugs. Finally, a docking strategy is used to rationalize the findings; the results confirm the mostly nonspecific nature of the interaction of albumin with neutral ligands.

What is the role of NSAIDs in pre-emptive analgesia?

NSAIDs inhibit the cyclo-oxygenase enzymes, and decrease peripheral and central prostaglandin production. In addition to reducing the inflammation that accompanies tissue injury, decreasing prostaglandin production attenuates the response of the peripheral and central components of the nervous system to noxious stimuli. Such a reduction in the response to pain can reduce the peripheral and central sensitisation induced by noxious stimuli, and reduce the pain experienced in response to subsequent noxious stimuli. These properties would seem to make NSAIDs ideal drugs to use in a pre-emptive fashion, where analgesics are administered prior to a noxious stimulus, such as surgery, with the expectation that reduction in peripheral and central sensitisation will lead to a decrease of pain.However, the available perioperative trials of pre-emptive NSAID use have yielded modest or equivocal results, and these may be due, in part, to controversy associated with the definition of pre-emptive analgesia and how to conduct the corresponding clinical trials. Although NSAIDs may have a limited ability by themselves to induce a pre-emptive analgesic effect, the available trials suggest how the perioperative use of these drugs may be made more effective. It is expected that NSAIDs will play an increasing role in multimodal analgesia and pain relief in general.

High throughput artificial membrane permeability assay for blood-brain barrier

The recent advances in high throughput screening for biological activities and combinatorial chemistry have greatly expanded the number of drug candidates. Rapid screening for BBB penetration potential early in drug discovery programs provides important information for compound selection and guidance of synthesis for desirable CNS properties. In this paper, we discuss a modification of the parallel artificial membrane permeation assay (PAMPA) for the prediction of blood-brain barrier penetration (PAMPA-BBB). The assay was developed with 30 structurally diverse commercial drugs and validated with 14 Wyeth Research compounds. The PAMPA-BBB assay has the advantages of: predicting passive blood-brain barrier penetration with high success, high throughput, low cost, and reproducibility.

Considerations in the use of cerebrospinal fluid pharmacokinetics to predict brain target concentrations in the clinical setting: implications of the barriers between blood and brain

In the clinical setting, drug concentrations in cerebrospinal fluid (CSF) are sometimes used as a surrogate for drug concentrations at the target site within the brain. However, the brain consists of multiple compartments and many factors are involved in the transport of drugs from plasma into the brain and the distribution within the brain. In particular, active transport processes at the level of the blood-brain barrier and blood-CSF barrier, such as those mediated by P-glycoprotein, may lead to complex relationships between concentrations in plasma, ventricular and lumbar CSF, and other brain compartments. Therefore, CSF concentrations may be difficult to interpret and may have limited value. Pharmacokinetic data obtained by intracerebral microdialysis monitoring may be used instead, providing more valuable information. As non-invasive alternative techniques, positron emission tomography or magnetic resonance spectroscopy may be of added value.

Influence of a polymeric formulation of ketoprofen on its diffusion into cerebrospinal fluid in rats

Poly(D,L)lactide nanocapsules (NCs) have been proposed as an alternative carrier for many drugs. We investigated the influence of this formulation on the pharmacokinetics of ketoprofen in the plasma and cerebrospinal fluid (CSF). Male Wistar rats were given intraperitoneal dose of ketoprofen (5 mg/kg) in a suspension of NCs or in a carboxymethylcellulose (CMC) solution (reference preparation). Blood and CSF samples were collected at different times up to 24 h after dosing. The unbound fraction of ketoprofen in plasma (f(u)) was determined using ultrafiltration. The total (C(T)) and free (C(F)) concentrations of ketoprofen in plasma and the simultaneous CSF concentrations (C(CSF)) were measured by a HPLC method and the areas under the curve (AUC(T), AUC(F), AUC(CSF)) were calculated. AUC(T) of ketoprofen-loaded NCs in plasma was similar to that of the reference solution, while AUC(F) of the former (5.41 mg/l x h) was higher than that produced by the latter (4.03 mg/l x h). Accordingly, the unbound fraction (f(u)) was higher after administration of NCs than that of the solution (2.5 and 1.8%, respectively). Finally, AUC(CSF) were identical for both formulations. These findings suggest that the binding of ketoprofen to plasma proteins is not the major factor that governs its blood-to-CSF exchanges.

Predicting blood-brain barrier permeation from three-dimensional molecular structure

Predicting blood-brain barrier (BBB) permeation remains a challenge in drug design. Since it is impossible to determine experimentally the BBB partitioning of large numbers of preclinical candidates, alternative evaluation methods based on computerized models are desirable. The present study was conducted to demonstrate the value of descriptors derived from 3D molecular fields in estimating the BBB permeation of a large set of compounds and to produce a simple mathematical model suitable for external prediction. The method used (VolSurf) transforms 3D fields into descriptors and correlates them to the experimental permeation by a discriminant partial least squares procedure. The model obtained here correctly predicts more than 90% of the BBB permeation data. By quantifying the favorable and unfavorable contributions of physicochemical and structural properties, it also offers valuable insights for drug design, pharmacological profiling, and screening. The computational procedure is fully automated and quite fast. The method thus appears as a valuable new tool in virtual screening where selection or prioritization of candidates is required from large collections of compounds.

Structure-property relationships on histamine H3-antagonists: binding of phenyl-substituted alkylthioimidazole derivatives to rat plasma proteins

The binding of a series of H3-antagonists to rat plasma proteins was investigated by dialysis experiments, with RP-HPLC measurement of the free ligand. The series was composed of 4(5)-phenyl-2-[[2-[4(5)-imidazolyl]ethyl]thio]imidazoles having, on the phenyl ring, meta- and para-substituents, with different physico-chemical characteristics. As high protein binding had been proposed as being one of the features limiting brain access for the reference H3-antagonist thioperamide, the title series was employed to test the possibility of achieving lower protein binding by modulation of lipophilicity, while maintaining good receptor affinity. The compounds tested showed quotas of bound drug ranging from 60 to 97.5%, while for thioperamide a 78% bound drug quota was observed at high total concentrations, with a steep increase in bound percentage at lower concentrations. Two of the tested compounds, having a carboxamide substituent, showed lower protein binding compared to thioperamide over a wide range of total concentration, without a significant loss in affinity with respect to the parent compound. A strict dependence of protein binding on lipophilicity was observed, and a QSPR model was derived which could also account for the protein binding observed for thioperamide, while receptor affinity had been reported to be quite insensitive to phenyl ring substitution. It is therefore possible to modulate protein binding of these H3-antagonists, through lipophilicity adjustment, without losing receptor affinity; this finding could help in the design of new compounds with improved brain access.

Attenuated nitric oxide synthase activity and protein expression accompany intestinal ischemia/reperfusion injury in rats

Intestinal ischemia/reperfusion (I/R) leads to bowel impairment via the release of reactive oxygen species (ROS) and neutrophil infiltration. In addition to modulating intestinal integrity, nitric oxide (NO(*)) inhibits neutrophil activation and scavenges ROS. Attenuated endogenous NO(*) formation may result in the accrual of these deleterious stimuli. Therefore, we determined nitric oxide synthase (NOS) activity in anesthetized rats subjected to 1 h of superior mesenteric ischemia or ischemia followed by reflow. NOS activity was measured in intestinal tissue homogenates as the conversion rate of (3)H-L-arginine to (3)H-L-citrulline. Our results demonstrate that intestinal ischemia leads to a decrease in NOS activity indicating lower NO(*) formation in the animal model. The attenuation in NOS activity was not reversed following 4 h of reperfusion. Western blot analysis revealed that the decline in enzyme activity was accompanied by reduced intestinal NOS III (endothelial constitutive NOS) expression. These findings provide biochemical evidence for impaired NO(*) formation machinery in intestinal I/R injury.

Drug transfer across the blood-brain barrier and improvement of brain delivery

The blood-brain barrier is formed by the endothelial cells of the brain capillaries. Its primary characteristic is the impermeability of the capillary wall due to the presence of complex tight junctions and a low endocytic activity. Essential nutrients are delivered to the brain by selective transport mechanisms, such as the glucose transporter and a variety of amino acid transporters. Although most drugs enter the brain by passive diffusion through the endothelial cells depending on their lipophilicity, degree of ionization, molecular weight, relative brain tissue and plasma bindings, some others can use specific endogenous transporters. In such cases, binding competition on the transporter with endogenous products or nutrients can occur and limits drug transfer. The blood-brain barrier can be a major impediment for the treatment of diseases of the central nervous system, since many drugs are unable to reach this organ at therapeutic concentrations. Various attempts have been made to overcome the limiting access of drugs to the brain, e.g. chemical modification, development of more hydrophobic analogs or linking an active compound to a specific carrier. Transient opening of the blood-brain barrier in humans has been achieved by intracarotid infusion of hypertonic mannitol solutions or of bradykinin analogs. Another way to increase or decrease brain delivery of drugs is to modulate the P-glycoprotein (P-gp) whose substrates are actively pumped out the cell into the capillary lumen. Many P-gp inhibitors or inducers are available to enhance the therapeutic effects of centrally acting drugs or to decrease central adverse effects of peripherally active drugs.

The genetic variant A of human alpha 1-acid glycoprotein limits the blood to brain transfer of drugs it binds

The objective of this work was to check the effects of alpha-1 acid glycoprotein (AAG) and of its components, A and F1/S genetic variants, on the brain transfer of drugs they bind in plasma. The relevant extractions of six basic drugs, highly bound to AAG, were measured. We chose three drugs selectively bound to the A variant, disopyramide, imipramine and methadone, one drug mainly bound to the mixture F1/S, mifepristone, and two drugs which were simultaneously bound to the variant A and the mixture F1/S, propranolol and chlorpromazine. Their brain extraction were investigated in rats using the carotid injection technique and the capillary depletion method. Injected drugs were dissolved either in buffer, either in native AAG containing the three variants (A, F1 and S), either in variant A or in variant F1/S solutions. Brain extractions of disopyramide, imipramine and methadone were significantly reduced by native AAG and by variant A. Drug's plasma retention was related to their preferential and almost exclusive binding to A variant, both of them exhibiting the same decrease in brain transfer as compared to a buffered solution. At the opposite, there were no significative differences between the extraction either in buffer, either in AAG or in F1/S solutions, of drugs both bound to A variant and F1/S mixture (chlorpromazine and propranolol) or to the F1/S mixture (mifepristone). In serum, the retentional effect of the A variant on the extraction of disopyramide and imipramine was counteracted by the presence of albumin and lipoproteins, which simultaneously bind these two drugs at a high extent and act as permissive binders. We conclude that AAG binding decreases brain drug transfer when the A variant is mainly and almost exclusively involved in the binding. On the contrary, the entire fraction of the tested drugs when bound exclusively or partly to the mixture F1/S is available for transfer into the brain.

Molecular properties and pharmacokinetic behavior of cetirizine, a zwitterionic H1-receptor antagonist

The ionization and lipophilicity behavior of the antihistamine (H1-receptor antagonist) cetirizine was investigated, showing the drug to exist almost exclusively as a zwitterion in the pH region 3.5-7.5. In this pH range, its octanol/water lipophilicity is constant and low compared to cationic antihistamines (log D = log PZ = 1.5), whereas its H-bonding capacity is relatively large (delta log PZ > or = 3.1). Conformational, electronic, and lipophilicity potential calculations revealed that zwitterionic cetirizine experiences partial intramolecular charge neutralization in folded conformers of lower polarity. Pharmacokinetic investigations have shown the drug to be highly bound to blood proteins, mainly serum albumin, and to have a low brain uptake, explaining its lack of sedative effects. As such, cetirizine does not differ from "second-generation" antihistamines. In contrast, its very low apparent volume of distribution in humans (0.4 L kg-1, smaller than that of exchangeable water) implies a low affinity for lean tissues such as the myocardium and is compatible with the absence of cardiotoxicity of the drug. The zwitterionic nature and modest lipophilicity of cetirizine may account for this pharmacokinetic behavior. The suggestion is offered that cetirizine and analogous zwitterions, whose physicochemical, pharmacokinetic, and pharmacodynamic properties differ from those of "first-" and "second-generation" drugs in this class, could be considered as "third-generation" antihistamines.