Plasma and cerebrospinal fluid pharmacokinetics of valproic acid after oral administration in non-human primates

Design of experiment (DoE) of mucoadhesive valproic acid-loaded nanostructured lipid carriers (NLC) for potential nose-to-brain application

Epilepsy is a highly prevalent neurological disease and valproic acid (VPA) is used as a first-line chronic treatment. However, this drug has poor oral bioavailability, which requires the administration of high doses, resulting in adverse effects. Alternative routes of VPA administration have therefore been investigated, such as the nose-to-brain route, which allows the drug to be transported directly from the nasal cavity to the brain. Here, the use of nanostructured lipid carriers (NLC) to encapsulate drugs administered in the nasal cavity has proved advantageous. The aim of this work was to optimise a mucoadhesive formulation of VPA-loaded NLC for intranasal administration to improve the treatment of epilepsy. The Design of Experiment (DoE) was used to optimise the formulation, starting with component optimisation using Mixture Design (MD), followed by optimisation of the manufacturing process parameters using Central Composite Design (CCD). The optimised VPA-loaded NLC had a particle size of 76.1 ± 2.8 nm, a polydispersity index of 0.190 ± 0.027, a zeta potential of 28.1 ± 2.0 mV and an encapsulation efficiency of 85.4 ± 0.8%. The in vitro release study showed VPA release from the NLC of 50 % after 6 h and 100 % after 24 h. The in vitro biocompatibility experiments in various cell lines have shown that the optimised VPA-loaded NLC formulation is safe up to 75 µg/mL, in neuronal (SH-SY5Y), nasal (RPMI 2650) and hepatic (HepG2) cells. Finally, the interaction of the optimised VPA-loaded NLC formulation with nasal mucus was investigated and mucoadhesive properties were observed. The results of this study suggest that the use of intranasal VPA-loaded NLC may be a promising alternative to promote VPA targeting to the brain, thereby improving bioavailability and minimising adverse effects.

Anti-seizure therapy with a long-term, implanted intra-cerebroventricular delivery system for drug-resistant epilepsy: A first-in-man study

BACKGROUND

A clinical feasibility study was undertaken at a single center of long-term intra-cerebroventricular drug delivery of the anti-seizure medication valproic acid, into the cerebrospinal fluid (CSF) in order to treat drug resistant focal seizures, using an implantable infusion system. The primary objective was to establish the dose range of VPA administered in this manner. Secondarily, safety, pharmacokinetics (PK) and a preliminary estimate of effectiveness were evaluated.

METHODS

In this single arm study, five adult subjects, with 29-234 focal onset seizures per month from a seizure focus involving the mesial temporal lobe were implanted with the system (clinicaltrials.gov identifier NCT02899611). Oral valproic acid (VPA) had previously been ineffective in all subjects. Post-surgery, pharmacokinetic studies of CSF infused VPA were performed. Valproic acid doses were increased stepwise in a standardised protocol.

FINDINGS

The procedure and implantation were well-tolerated by all subjects. Four subjects responded with > 50% seizure reduction at the highest tested dose of 160 mg/day. Two subjects experienced extended periods of complete seizure freedom. All five subjects reported significant quality of life improvement. No clinical dose limiting side effects were encountered and there was no evidence of local periventricular toxicity in three subjects who were evaluated with imaging (T2 MRI). Side effects included nausea and appetite loss but were not dose-limiting. Mean CSF valproic acid levels were 45 μg per ml (range 20-120 μg per ml), with corresponding serum levels of 4-14 μg per ml.  Subjects have received therapy for up to 2.5 years in total . The efficacy analysis presented focuses on the period of time with the current pump with a mean 12.5 months, range 11.5-15 months. Pump failure requiring reimplantation was a significant initial issue in all subjects but resolved with use of pumps suitably compatible with long-term exposure to valproic acid.

INTERPRETATION

The study demonstrated that chronic intraventricular administration of valproic acid is safe and effective in subjects with medically refractory epilepsy over many months. The procedure for implanting the infusion system is safe and well-tolerated. High CSF levels are achieved with corresponding low serum levels and this therapy is shown to be effective despite unsuccessful earlier use of oral valproate preparations. Drug side effects were minimal.

FUNDING

The study was funded by Cerebral Therapeutics Inc., Suite 137 12635 East Montview Blvd Aurora CO 80045.

Evaluation of sodium valproate loaded nanoparticles in acute and chronic pentylenetetrazole induced seizure models

BACKGROUND AND PURPOSE

Efficacy of sodium valproate in epilepsy is limited by its poor blood brain barrier penetration and side effects. Nanoparticles may offer a better drug delivery system to overcome these limitations. This study evaluated the efficacy of sodium valproate encapsulated in nanoparticles in pentylenetetrazole (PTZ) induced acute and kindling models of seizures in male Wistar rats.

METHODS

Poly lactic-co-glycolic acid (PLGA) based, polysorbate 80 stabilized sodium valproate loaded nanoparticles (nano sodium valproate) and rhodamine loaded nanoparticles (RLN) were formulated by double emulsion- solvent evaporation method and characterized for their size, shape, zeta potential and drug loading percentage. RLN was used to demonstrate blood brain barrier (BBB) permeability of nanoparticles. Serum drug levels were estimated using high performance liquid chromatography. The efficacy of standard sodium valproate (300 mg/kg) and nano sodium valproate (∼300, ∼150 and ∼75 mg/kg of sodium valproate) were evaluated in experimental animal models of seizures along with their effects on behavioral and oxidative stress parameters. Drugs were administered 60 min before PTZ in acute model. In the kindling model, drugs were administered every day while PTZ was administered on alternate days 60 min after drug administration. All the study drugs/compounds were administered intraperitoneally.

RESULTS

RLN were observed to be clustered in cortex which implied that the nanoparticles crossed BBB. Both standard sodium valproate and nano sodium valproate reached therapeutic serum level at 15 min and 1 h, but were undetectable in serum at 24 h. In acute PTZ (60 mg/kg) model, nano sodium valproate (∼300 mg/kg of sodium valproate) and standard sodium valproate showed protection against seizures till 6 h and 4 h, respectively. There were significant behavioral impairment and oxidative stress with standard sodium valproate in acute model as compared to nano sodium valproate at 6 h. In kindling model, induced with PTZ (30 mg/kg, every alternate day for 42 days), complete protection from seizures was observed with nano sodium valproate (∼150 mg/kg and ∼75 mg/kg of sodium valproate) and standard sodium valproate (300 mg/kg). Similarly, significant protection from behavioral impairment and oxidative stress was observed with standard sodium valproate and nano sodium valproate as compared to PTZ.

CONCLUSION

When compared to conventional therapy, nano sodium valproate showed protection from seizures at reduced doses and for a longer duration in animal models of epilepsy. This study suggests the potential of nano sodium valproate in the treatment of epilepsy.

Plasma and cerebrospinal fluid pharmacokinetics of select chemotherapeutic agents following intranasal delivery in a non-human primate model

The blood-brain barrier (BBB) limits entry of most chemotherapeutic agents into the CNS, resulting in inadequate exposure within CNS tumor tissue. Intranasal administration is a proposed means of delivery that can bypass the BBB, potentially resulting in more effective chemotherapeutic exposure at the tumor site. The objective of this study was to evaluate the feasibility and pharmacokinetics (plasma and CSF) of intranasal delivery using select chemotherapeutic agents in a non-human primate (NHP) model. Three chemotherapeutic agents with known differences in CNS penetration were selected for intranasal administration in a NHP model to determine proof of principle of CNS delivery, assess tolerability and feasibility, and to evaluate whether certain drug characteristics were associated with increased CNS exposure. Intravenous (IV) temozolomide (TMZ), oral (PO) valproic acid, and PO perifosine were administered to adult male rhesus macaques. The animals received a single dose of each agent systemically and intranasally in separate experiments, with each animal acting as his own control. The dose of the agents administered systemically was the human equivalent of a clinically appropriate dose, while the intranasal dose was the maximum achievable dose based on the volume limitation of 1 mL. Multiple serial paired plasma and CSF samples were collected and quantified using a validated uHPLC/tandem mass spectrometry assay after each drug administration. Pharmacokinetic parameters were estimated using non-compartmental analysis. CSF penetration was calculated from the ratio of areas under the concentration-time curves for CSF and plasma (AUC_CSF:plasma). Intranasal administration was feasible and tolerable for all agents with no significant toxicities observed. For TMZ, the degrees of CSF drug penetration after intranasal and IV administration were 36 (32-57) and 22 (20-41)%, respectively. Although maximum TMZ drug concentration in the CSF (C_max) was lower after intranasal delivery compared to IV administration due to the lower dose administered, clinically significant exposure was achieved in the CSF after intranasal administration with the lower doses. This was associated with lower systemic exposure, suggesting increased efficiency and potentially lower toxicities of TMZ after intranasal delivery. For valproic acid and perifosine, CSF penetration after intranasal delivery was similar to systemic administration. Although this study demonstrates feasibility and safety of intranasal drug administration, further agent-specific studies are necessary to optimize agent selection and dosing to achieve clinically-relevant CSF exposures.

The beneficial effects of l-cysteine on brain antioxidants of rats affected by sodium valproate

Oxidative stress caused by sodium valproate (SV) is known to play a key role in the pathogenesis of brain tissue. The present study was designed to evaluate the protective effect of l-cysteine (LC) on the antioxidants of brain tissue of rats. The animals were divided into six groups: control group 1 was treated with saline as vehicle, groups 2 and 3 were treated with low and high doses of SV (100 and 500 mg/kg, respectively), group 4 was treated with LC (100 mg/kg), and groups 5 and 6 were treated with low-dose SV + LC and high-dose SV + LC, respectively. All the groups were treated orally by gastric tube for 30 successive days. Some antioxidant parameters were determined. Brain tissue (cerebral cortex) of SV-treated animals showed an increase in lipid peroxidation (LPO) and reduction in activity of enzymatic antioxidant and total antioxidant levels. Histopathological examination of cerebral cortex of SV rats showed astrocytic swelling, inflammation, and necrosis. After 4 weeks of the combination treatment of SV and LC daily, results showed significant improvement in the activity of cathepsin marker enzymes and restored the structure of the brain. LC was able to ameliorate oxidative stress deficits observed in SV rats. LC decreased LPO level and was also able to restore the activity of antioxidant enzymes as well as structural deficits observed in the brain of SV animals. The protective effect of LC in SV-treated rats is mediated through attenuation of oxidative stress, suggesting a therapeutic role for LC in individuals treated with SV.

Valproate induces epigenetic modifications in lymphomonocytes from epileptic patients

Valproate (VPA) is an anti-epileptic and mood-stabilizing drug with a broad range of action and which mechanism of action still remains in part elusive. Recently the discovery that VPA modifies the epigenome increasing the transcriptional rate of target genes raises the issue of understanding the exact role of this mechanism. In this work we tested the possibility that VPA could modify the epigenome of lymphomonocytes (PBMC) obtained from epileptic patients chronically treated in monotherapy with VPA and phenobarbital. Acetyl-histone H3 expression was assessed by western blotting and global DNA methylation by incorporation of [³H]dCTP. A significant increase in histone acetylation and a correlated decrease of global DNA methylation were shown at VPA therapeutically relevant plasma concentrations. This effect was drug-related, since it was not demonstrated in PBMC obtained from phenobarbital-treated patients. Moreover, a VPA dose-response curve was performed on PBMC obtained from healthy controls, demonstrating an increase of acetyl-histone H3 content. We suggest that the epigenetic properties of VPA expressed on PBMC at these concentrations might be operative in different tissues, with possible implications for the field of neuropsychiatric disorders.

An improved method of transcutaneous cisterna magna puncture for cerebrospinal fluid sampling in rats

A simple, reproducible and chronic technique of cerebrospinal fluid (CSF) collection in rats was developed by direct cisterna magna (CM) puncture utilizing stereotaxic apparatus. CSF collection apparatus was constructed using 1 mL syringe, silicone tubing, 21G disposable needle and water. Animal was placed on an elevated platform over stereotaxic apparatus base and puncture site was identified with the aid of stereotaxic co-ordinates. The volume of CSF collected varied from 100 to 180 μL with mean CSF volume of 150 μL. Neurological deficits were recorded according to the modified Bederson's scoring system 24h post CSF collection and differential cell count in CSF samples was performed. Animals continued to be normal with regular feed intake and gained body weight (∼24%) even after repeated sampling for four weeks and showed no severe neurological deficits (mean Bederson score<1 for four weeks). Neuropharmacokinetic data for Phenytoin sodium, MS 275 and Valproic acid (VPA) demonstrated CSF uptake with CSF(AUC)/plasma(AUC) ratio (K(p,CSF)) of 0.09, 0.01 and 0.33, respectively. This model exemplifies the 3R's of animal use and has been successfully implemented at Orchid Chemicals and Pharmaceuticals Limited for lead optimization of CNS penetrating HDAC inhibitors.

The influence of distributional kinetics into a peripheral compartment on the pharmacokinetics of substrate partitioning between blood and brain tissue

Development of CNS-targeted agents often focuses on identifying compounds with "good" CNS exposure (brain-to-blood partitioning >1). Some compounds undergoing enterohepatic recycling (ER) evidence a partition coefficient, K (p,brain) (expressed as C (brain) /C (plasma)), that exceeds and then decreases to (i.e., overshoots) a plateau (distribution equilibrium) value, rather than increasing monotonically to this value. This study tested the hypothesis that overshoot in K (p,brain) is due to substrate residence in a peripheral compartment. Simulations were based on a 3-compartment model with distributional clearances between central and brain (CL (br)) and central and peripheral (CL (d)) compartments and irreversible clearance from the central compartment (CL). Parameters were varied to investigate the relationship between overshoot and peripheral compartment volume (V (p)), and how this relationship was modulated by other model parameters. Overshoot magnitude and duration were characterized as peak C (brain)/C (plasma) relative to the plateau value (%OS) and time to reach plateau (TRP). Except for systems with high CL (d), increasing V (p) increased TRP and %OS. Increasing brain (V (br)) or central (V (c)) distribution volumes eliminated V (p)-related OS. Parallel increases in all clearances shortened TRP, but did not alter %OS. Increasing either CL or CL (d) individually increased %OS related to V (p), while increasing CL (br) decreased %OS. Under realistic peripheral distribution scenarios, C (brain)/C (plasma) may overshoot substantially K (p,brain) at distribution equilibrium. This observation suggests potential for erroneous assessment of brain disposition, particularly for compounds which exhibit a large apparent V (p), and emphasizes the need for complete understanding of distributional kinetics when evaluating brain uptake.

Brain delivery of valproic acid via intranasal administration of nanostructured lipid carriers: in vivo pharmacodynamic studies using rat electroshock model

The treatment of brain disorders is one of the greatest challenges in drug delivery because of a variety of main barriers in effective drug transport and maintaining therapeutic concentrations in the brain for a prolonged period. The objective of this study was delivery of valproic acid (VPA) to the brain by intranasal route. For this purpose, nanostructured lipid carriers (NLCs) were prepared by solvent diffusion method followed by ultrasonication and characterized for size, zeta potential, drug-loading percentage, and release. Six groups of rats each containing six animals received drug-loaded NLCs intraperitoneally (IP) or intranasally. Brain responses were then examined by using maximal electroshock (MES). The hind limb tonic extension:flexion inhibition ratio was measured at 15-, 30-, 60-, 90-, and 120-minute intervals. The drug concentration was also measured in plasma and brain at the most protective point using gas chromatography method. The particle size of NLCs was 154 ± 16 nm with drug-loading percentage of 47% ± 0.8% and drug release of 75% ± 1.9% after 21 days. In vivo results showed that there was a significant difference between protective effects of NLCs of VPA and control group 15, 30, 60, and 90 minutes after treatment via intranasal route (P < 0.05). Similar protective effect was observed in rats treated with NLCs of VPA in intranasal route and positive control in IP route (P > 0.05). Results of drug determination in brain and plasma showed that brain:plasma concentration ratio was much higher after intranasal administration of NLCs of VPA than the positive control group (IP route). In conclusion, intranasal administration of NLCs of VPA provided a better protection against MES seizure.

New histone deacetylase inhibitors as potential therapeutic tools for advanced prostate carcinoma

The anti-epileptic drug valproic acid is also under trial as an anti-cancer agent due to its histone deacetylase (HDAC) inhibitory properties. However, the effects of valproic acid (VPA) are limited and concentrations required for exerting anti-neoplastic effects in vitro may not be reached in tumour patients. In this study, we tested in vitro and in vivo effects of two VPA-derivatives (ACS2, ACS33) on pre-clinical prostate cancer models. PC3 and DU-145 prostate tumour cell lines were treated with various concentrations of ACS2 or ACS33 to perform in vitro cell proliferation 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays and to evaluate tumour cell adhesion to endothelial cell monolayers. Analysis of acetylated histones H3 and H4 protein expression was performed by western blotting. In vivo tumour growth was conducted in subcutaneous xenograft mouse models. Tumour sections were assessed by immunohistochemistry for histone H3 acetylation and proliferation. ACS2 and ACS33 significantly up-regulated histone H3 and H4 acetylation in prostate cancer cell lines. In micromolar concentrations both compounds exerted growth arrest in PC3 and DU-145 cells and prevented tumour cell attachment to endothelium. In vivo, ACS33 inhibited the growth of PC3 in subcutaneous xenografts. Immunohistochemistry and western blotting confirmed increased histone H3 acetylation and reduced proliferation. ACS2 and ACS33 represent novel VPA derivatives with superior anti-tumoural activities, compared to the mother compound. This investigation lends support to the clinical testing of ACS2 or ACS33 for the treatment of prostate cancer.