Pharmacokinetics of a valpromide isomer,valnoctamide, in healthy subjects

Summary The pharmacokinetics of a single 400 mg oral dose of valnoctamide (VCD) has been investigated in seven healthy, adult, male volunteers. VCD was not biotransformed rapidly to its corresponding acid valnoctic acid (VCA), unlike its isomer valpromide (VPD). It had a mean residence time of 13.2 h and a terminal half-life of 9.3 h. Throughout the study, only low plasma levels of VCA could be detected. Thus, unlike VPD, which is a prodrug of the corresponding acid, (valproic acid, VPA). VCD appears to act as a drug in its own right, and it does not undergo similar hydrolysis. The pharmacokinetic difference may account for the different pharmacological activities of the two isomers.     

Effects of the superoxide dismutase-mimic compound TEMPOL on oxidant stress-mediated endothelial dysfunction

The aim of this study was to investigate the effects of oxidant stress on endothelium-dependent and endothelium-independent arterial relaxation. For this, oxidant stress was generated by preincubation of rat aortic rings (RARs) in either 25 mM glucose (mimicking hyperglycemic stress) or 0.5 mM pyrogallol (a superoxide generator) and the effects of the superoxide dismutase (SOD)-mimetic compound 4-hydroxy-2,2,6,6-tetramethylpiperidinyloxy free radical (TEMPOL) on the vasorelaxant and cGMP-producing effects of acetylcholine (ACh) and glyceryl trinitrate (GTN) in control RARs and RARs exposed to oxidant stress were examined. Pyrogallol, and to a lesser extent high glucose concentration, enhanced the contractile response of RARs to phenylephrine and markedly inhibited the vasorelaxant response to ACh. Although they existed, the inhibitory effects of high glucose and pyrogallol on the vasorelaxant response to GTN were less profound, especially with pyrogallol. Moreover, both pyrogallol and high glucose concentration inhibited the basal and the ACh-induced vascular cyclic guanosine monophosphate (cGMP) production. Treatment with TEMPOL (1-5 mM) slightly increased the ACh and GTN-induced cGMP levels in control RARs but had a significant effect in high glucose and pyrogallol-pretreated RARs. Additionally, concomitant treatment of RARs with TEMPOL (5 mM) abolished the difference in the relaxation response between control RARs and RARs exposed to either pyrogallol or high glucose concentration. These results further support the theory that reactive oxygen species (ROS), especially superoxide, play a key role in mediation of endothelial dysfunction accompanying diabetes, probably through their effects on the ability of the endothelium to synthesize, release or respond to endogenous nitric oxide (NO) or NO donated by nitrovasodilators.     

Pharmacokinetic Analysis and Antiepileptic Activity of Tetra-Methylcyclopropane Analogues of Valpromide

Purpose. The described structure pharmacokinetic pharmacodynamic relationships (SPPR) study explored the utilization of tetramethylcyclopropane analogues of valpromide (VPD), or tetra-methylcyclopropane carboxamide derivatives of valproic acid (VPA) as new antiepileptics. Methods. The study was carried out by investigating the pharmacokinetics in dogs and pharmacodynamics (anticonvulsant activity and neurotoxicity) of the following three cyclopropane analogues of VPD: 2,2,3,3-tetramethylcyclopropane carboxamide (TMCD), N-methyl TMCD (M-TMCD) and N-[(2,2,3,3-tetramethylcyclopropyl)carbonyl]-glycinamide (TMC-GLD). Results. The three investigated compounds showed a good anticonvulsant profile in mice and rats due to the fact that they were metabolically stable VPD analogues which were not biotransformed to their non-active acid, 2,2,3,3-tetramethylcyclopropane carboxylic acid (TMCA). M-TMCD was metabolized to TMCD and TMC-GLD underwent partial biotransformation to its glycine analogue N-[(2,2,3,3-tetramethylcyclopropyl)carbonyl]-glycine (TMC-GLN). Unlike TMC-GLN, the above mentioned amides had low clearance and a relatively long half life. Conclusions. In contrast to VPD which is biotransformed to VPA, the aforementioned cyclopropane derivatives were found to be stable to amide-acid biotransformation. TMCD and M-TMCD show that cyclic analogues of VPD, like its aliphatic isomers, must have either two substitutions at the position to the carbonyl, such as in the case of TMCD, or a substitution in the and in the positions like in the VPD isomer, valnoctamide (VCD). This paper discusses the antiepileptic potential of tetramethylcyclopropane analogues of VPD which are in animal models more potent than VPA and may be non-teratogenic and non-hepatotoxic.     

Carbamazepine-Valnoctamide Interaction in Epileptic Patients: In Vitro/In Vivo Correlation

Six patients stabilized with carbamazepine (CBZ) therapy received an 8-day “add-on” supplement of valnoctamide (VCD), a tranquilizer available over the counter (OTC) in several European countries that exhibits promising anticonvulsant activity in animal models. During VCD intake, serum levels of the active CBZ metabolite, carbamazepine-10,ll-epoxide (CBZ-E), increased fivefold from 1.5 ± 0.7 μg/ml at baseline to 7.4 ± 4.4 μg/ml after 4 days of VCD therapy and 7.7 ± 3.1 ^g/ml after 7 days of VCD therapy (means ± SD, p < 0.01). In 4 patients, the increase in serum CBZ-E levels was associated with clinical signs of CBZ intoxication. CBZ-E levels returned to baseline after VCD therapy was discontinued. Serum CBZ levels remained stable throughout the study. The interaction observed in this study is similar to that described in patients treated with CBZ and valpromide (VPD, an isomer of VCD). In a mechanistic study, therapeutic concentrations of VCD inhibited hydrolysis of styrene oxide in human liver mi-crosome preparations. Thus, VCD is a potent inhibitor of microsomal epoxide hydrolase (IC₅₀ 15 μM). There was a striking similarity between in vitro and in vivo inhibition potencies. In this study, VCD clearance was higher in epileptic patients (treated with CBZ) than in healthy subjects.     

Can we develop improved derivatives of valproic acid?

Valproic acid is one of the major antiepileptic drugs. In animal models, valproate showed less anticonvulsant potency than the other three established antiepileptic drugs: phenobarbital, phenytoin and carbamazepine. In addition, two major side-effects, teratogenicity and hepatotoxicity, have been associated with valproate Iherapy. Due to the above and the shortage of new antiepileptic drugs there is a substantial need to develop improved derivatives of valproate. This paper analyses three kinds of valproate derivatives: valpromide, the primary amide of valproate, and its analogues; monoester prodrugs of valproate and an active metabolite of valproate, 2-n-propyl-2-pentenoate. The comparative evaluation was carried out by pharmacokinetic and pharmacodynamic analyses in animals. From the data accumulated so far, we can conclude that 2-n-propyl-2-pentenoatc and/or a valpromide isomer, which does not undergo amide acid biotransformation and preferably is not an epoxide hydrolase inhibitor, may prove to be improved derivatives of the parent compound valproic acid.     

Microassay of superoxide anion scavenging activity in vitro

We have developed a photometric, platereader-based microassay for superoxide anion scavening activity in vitro. Superoxide anions were generated using a xanthine oxidase/hypoxanthine system and detected by following the reduction of ferricytochrome c at 550 nM. Inhibitory activity was assessed for superoxide dismutase (SOD) and the superoxide anion scavengers tiron and TEMPO together with a number of TEMPO derivatives. The initial rate of change in optical density (OD) at 550 nm, i.e., initial reaction rate, generated by xanthine oxidase (20 mU/ml)/hypoxanthine (100 μM) coupled to ferricytochrome c (100 μM) was effectively abolished by SOD (200 U/ml), tiron (10 mM) and TEMPO (0.3 mM), indicating the involvement of superoxide anions. TEMPO derivatives inhibited the initial reaction rate with the potency order: TEMPO > 4-hydroxy-TEMPO = 4-carboxy-TEMPO. In contrast, 4-hydroxy-TEMPO, which lacks the free radical nitroxide function, was inactive up to 1 mM.     

Effects of the superoxide dismutase-mimetic compound tempol on endothelial dysfunction in streptozotocin-induced diabetic rats

Evidence exists to support the beneficial effects of superoxide dismutase on endothelial dysfunction induced by hyperglycemia in vitro. In vivo, however, studies of the effects of native superoxide dismutase preparations on the vascular complications accompanying diabetes are limited, and their therapeutic application potential has so far been disappointing. The objective of this study was to evaluate, for the first time in vivo, the effects of long-term administration of tempol, a stable superoxide dismutase-mimic compound, on diabetes-induced endothelial dysfunction in rats. Diabetes was induced by streptozotocin and rats were monitored for 8 weeks with or without treatment with tempol (100 mg/kg, s.c., b.i.d). Diabetic rats showed increased vascular levels of superoxide, which was accompanied by increased levels of the oxidative stress markers malondialdehyde and 8-epi-prostaglandin F(2alpha). In addition, the vasorelaxant as well as the cGMP-producing effects of acetylcholine and glyceryl trinitrate were reduced in diabetic rats. Treatment with tempol abolished not only the differences in the vascular content of superoxide, malondialdehyde and 8-epi-prostaglandin F(2alpha), but also the differences in the relaxation and cGMP responses of aortic rings to both acetylcholine and glyceryl trinitrate between control and diabetic rats. These results support the involvement of reactive oxygen species in mediation of hyperglycemia-induced endothelial dysfunction in vivo, and provide the rationale for potential utilization of stable superoxide dismutase-mimic nitroxides for the prevention of the vascular complications accompanying diabetes.     

Pharmacokinetic Analysis of the Structural Requirements for Forming “Stable” Analogues of Valpromide

The following valpromide (VPD) analogues were synthesized and their structure-pharmacokinetic relationships explored: 3-ethyl pentanamide (EPD), methylneopentylacetamide (MND), 1-methyl cyclohexanecarboxamide (MCD), cycloheptanecarboxamide (CHD), and t-butylacetamide (TBD). Two aliphatic (EPD and MND) and two cyclic amides (MCD and CHD) underwent complete or partial conversion to their corresponding acids. The only amide found in this study to be stable to the amide-acid biotransformation was TBD. It also had the lowest clearance and the longest half-life and mean residence time. Unlike the other investigated amides, TBD contained two substitutions of two methyl moieties at the position of its chemical structure. A stable valpromide analogue must have either two substitutions at the position, such as in the case of TBD, or a substitution in the and positions, such as in the case of the VPD isomer valnoctamide (VCD). This paper discusses the antiepileptic potential of stable VPD analogues which may be more potent and less teratogenic than their biotransformed isomers.     

Structure–Pharmacokinetic Relationships in a Series of Valpromide Derivatives with Antiepileptic Activity

The following valpromide (VPD) derivatives were synthesized and their structure–pharmacokinetic relationships explored: ethylbutylacetamide (EBD), methylpentylacetamide (MPD), propylisopropylacetamide (PID), and propylallylacetamide (PAD). In addition, the anticonvulsant activity of these compounds was evaluated and compared to that of VPD, valnoctamide (VCD), and valproic acid (VPA). MPD, the least-branched compound had the largest clearance and shortest half-life of all the amides investigated and was the least active. All other amides had similar pharmacokinetic parameters. Unlike the other amides, PID and VCD did not metabolize to their respective homologous acids and were the most active compounds. Our study showed that these amides need an unsubstituted position in their aliphatic side chain in order to biotransform to their homologous acids. An amide which is not metabolized is more potent as an anticonvulsant than its biotransformed isomer. All amides were more active than their respective homologous acids. In this particular series of aliphatic amides, which were derived from short-branched fatty acids, the anticonvulsant activity was affected by the pharmacokinetics in general and by the biotransformation of the amide to its homologous acid in particular. This amide–acid biotransformation appeared to be dependent upon the chemical structure, especially upon the substitution at position of the molecule.     

Human alpha-defensin regulates smooth muscle cell contraction: a role for low-density lipoprotein receptor-related protein/alpha 2-macroglobulin receptor

We have previously identified alpha-defensin in association with medial smooth muscle cells (SMCs) in human coronary arteries. In the present paper we report that alpha-defensin, at concentrations below those found in pathological conditions, inhibits phenylephrine (PE)-induced contraction of rat aortic rings. Addition of 1 microM alpha-defensin increased the half-maximal effective concentration (EC(50)) of PE on denuded aortic rings from 32 to 630 nM. The effect of alpha-defensin was dose dependent and saturable, with a half-maximal effect at 1 microM. alpha-Defensin binds to human umbilical vein SMCs in a specific manner. The presence of 1 microM alpha-defensin inhibited the PE-mediated Ca(++) mobilization in SMCs by more than 80%. The inhibitory effect of alpha-defensin on contraction of aortic rings and Ca(++) mobilization was completely abolished by anti-low-density lipoprotein receptor-related protein/alpha(2-)macroglobulin receptor (LRP) antibodies as well as by the antagonist receptor-associated protein (RAP). alpha-Defensin binds directly to isolated LRP in a specific and dose-dependent manner; the binding was inhibited by RAP as well as by anti-LRP antibodies. alpha-Defensin is internalized by SMCs and interacts with 2 intracellular subtypes of protein kinase C (PKC) involved in muscle contraction, alpha and beta. RAP and anti-LRP antibodies inhibited the binding and internalization of alpha-defensin by SMCs and its interaction with intracellular PKCs. These observations suggest that binding of alpha-defensin to LRP expressed in SMCs leads to its internalization; internalized alpha-defensin binds to PKC and inhibits its enzymatic activity, leading to decreased Ca(++) mobilization and SMC contraction in response to PE.