Kenneth R. Scott

Enhancing the permeation of marker compounds and enaminone anticonvulsants across Caco-2 monolayers by modulating tight junctions using zonula occludens toxin

Zonula occludens toxin (Zot), a protein elaborated from Vibrio cholerae, has been shown to be capable of reversibly opening tight junctions between intestinal cells The objective of this study was to examine the effect of Zot on the flux of various molecules across Caco-2 cell monolayers. In addition, the transport of a series of anticonvulsants, the enaminones was also evaluated in the presence of Zot. The flux of [(14)C]mannitol, [(14)C]inulin and various enaminones across Caco-2 cell monolayers (n=6) was examined after pre-incubation for 1h with Zot (0 or 4000ng/ml) or phosphate-buffered saline (PBS). At the end of the incubation period, the flux of radiolabeled compounds or enaminones (1x10(-4)M) was assessed over a 2-h period. In addition, dose-response studies with Zot (0, 1000, 2000 or 4000ng/ml) were performed using mannitol. The flux of both mannitol and inulin significantly increased (P<0.05) in the presence of Zot. The transport of the enaminones with Zot ranged from 9.42 to 26.83x10(-5)cm/s vs. 4.68 to 13.83x10(-5)cm/s without Zot. Zot significantly increased the transport of all agents tested. This suggests that the co-administration of drugs with Zot may be a useful delivery strategy to increase the intestinal permeability and hence oral absorption of poorly bioavailable agents.

Profile of Anticonvulsant Activity and Minimal Toxicity of Methyl 4-[(p-Chlorophenyl)amino]-6-Methyl-2-Oxo-Cyclohex-3-En-l-Oate and Some Prototype Antiepileptic Drugs in Mice and Rats

The anticonvulsant and toxic properties of methyl 4‐[(p‐chlorophenyl)amino]‐6‐methyl‐2‐oxo‐cyclohex‐3‐en‐l‐oate (ADD 196022), were compared with those of phenytoin (PHT), carbamazepine (CBZ), and valproate (VPA). These compounds were evaluated in mice and rats using well‐standardized anticonvulsant testing procedures. Results indicate that ADD 196022 is a very potent anticonvulsant in the maximal electroshock seizure (MES) model. The compound was effective in nontoxic doses after intraperitoneal (i.p.) administration in mice and oral administration in rats. In mice, i.p. administration of ADD 196022 resulted in an ED50 value of 26.2 mg/kg as compared with a value of 6.48 mg/kg for PHT in the same assay. ADD 196022 was more potent that PHT in the oral rat model, having an ED50 value of 5.79 mg/kg as compared to 23.2 mg/kg for PHT. ADD 196022 was ineffective in nontoxic doses against all other seizure models evaluated and thus has a pharmacologic profile similar to that of PHT.

Multidrug resistance and anticonvulsants: new studies with some enaminones.

The multidrug resistance (MDR), often conferred by the active extrusion of drugs from the cell, is a phenomenon often seen in cancer cells that may become resistant to a wide spectrum of drugs with varying chemical structures or cellular targets. This event has recently been reported for anticonvulsants. Studies in our laboratories on this occurrence with some enaminones have shown that the enaminones display high efflux ratios and are recognized by P-glycoprotein (P-gp) and/or the multidrug resistance protein (MRP), which have been reported as the main efflux transporters responsible for the development of MDR. Recent studies have uncovered interesting structural analogues that can modulate the functional activity of P-gp, suggesting a possible increase in the bioavailabillity of P-gp substrate drugs when administered concurrently.

Development of carbamazepine:phospholipid solid dispersion formulations

Abstract This study is concerned with the development of a carbamazepine (CBZ):phospholipid (PL) solid dispersion formulation with improved dissolution characteristics. CBZ powders were blended with PL to produce CBZ:PL physical mixtures or made into solid dispersions with PL by the solvent method. CBZ exhibited significantly improved dissolution rates in PL coprecipitate (coppt) as compared to the physical mixtures or CBZ alone. Dissolution studies suggested that less than 10:1 ratio of CBZ to PL (9.1% PL) was required to disperse amorphous CBZ completely in the carrier. The coppt yielded a 3.6-fold greater initial dissolution rate (computed over the 5 min of dissolution) than the pure CBZ. Also, the total amount dissolved after 60 min was 2.1-fold greater at a CBZ:dimyristoylphosphatidylglycerol (DMPG) of 10:1 ratio (9.1% DMPG) than for the corresponding pure drug. Increasing the DMPG concentration to 4:1 (20% DMPG) compositions resulted in only a further 10% increase in the initial dissolution rate and 8.5% increase in the limiting concentration. Thus, a small amount of PL improved the dissolution of CBZ to a significant level. Some effect was also observed by changing the composition of the PLs. The coppts were formulated into tablets in order to compare the dissolution profile with that of TegretolR, a commercially available tablet of CBZ. It was found that the total amount dissolved after 60 min was two-fold higher in our tablet formulation than the commercial product, TegretolR. Powder X-ray diffraction spectra showed no changes in the diffraction patterns of CBZ in the coppt. It is concluded that CBZ:PL solid dispersions may have clinical advantages of quick in-vivo release to yield better bioavailability than existing commercial formulations.

Synthesis and Evaluation of Amino Analogues of Valproic Acid

Valproic acid, an antiepileptic drug, is extensively metabolized in humans. Two putative metabolites, 2-n-propyl-3-aminopentanoic acid (3-aminovalproic acid, 3-amino-VPA; 2a) and 2-n-propyl-4-aminopentanoic acid (4-amino-valproic acid, 4-amino-VPA; 4a), which may result from the transamination of the respective keto acids 1a and 3a may explain the unusual extended seizure protection elicited by valproic acid. The title compounds were synthesized as their diasteriomeric ethyl esters 2b and 4b and submitted for anticonvulsant evaluation by the Antiepileptic Drug Development Program of the National Institute of Neurological and Communicative Disorders and Stroke. The results verified our hypothesis, as 4b was active in the subcutaneous pentylenetetrazol (scMet) evaluation at 30 mg/kg. Both compounds were highly toxic at 300 mg/kg.

Pharmacokinetics and Pharmacodynamics of Valproate Analogues in Rats. I. Spiro[4.6]Undecane-2-Carboxylic Acid

Summary: The pharmacokinetic and pharmacodynamic properties of the spiro carboxylic acid, spiro[4.6]un‐decane‐2‐carboxylic acid (SUCA, ADD 93024), were investigated in rats and compared with those of the standard anticonvulsant carboxylic acid, valproate (VPA). The clearance of SUCA was dose‐dependent, although the observed nonlinearity did not appear to be due to classical saturable elimination. The change in clearance across doses was consistent with end‐product inhibition or cosubstrate depletion. The volume of distribution of the spiro compound also evidenced nonlinearity, possibly due to concentration‐dependent binding to serum proteins. In contrast, the dose‐dependent clearance displayed by VPA was composed of both saturable and non‐saturable components. Furthermore, the disposition of VPA was characterized by a significant enterohepatic recirculation, whereas no such recirculatory process was apparent for SUCA. Both compounds afforded significant protection from pentylenetetrazol (PTZ)‐induced seizures, and the time course of anticonvulsant effect did not correspond to that of drug concentrations in serum for either anticonvulsant. The apparent dissociation between the pharmacokinetics and pharmacodynamics of VPA may be a function of the mechanism of antiepileptic action and not due to the presence of active metabolites of the drug

5,5-Dimethyl-3-(5-methyl­isoxazol-3-yl)cyclo­hex-2-enone

The X-ray crystal structure of the title compound, C12H16N2O2, has been determined and its structure correlated with its antixadconvulsant activity in mice and rats. In each of the two molecules of the asymmetric unit, the two rings are linked by an intramolecular C—H⋯N hydrogen bond.

Effect of cyclic analogues of valproic acid on glutamic acid decarboxylase activity as determined by different methods

Abstract In order to study the anticonvulsant activity of cyclic analogues of valproic acid, the effects of sodium valproate, sodium spiro (4:6) undecane-2-carboxylate, and sodium spiro (4:6) undecane-2-acetate were observed on the L -glutamic acid decarboxylase (GAD) activity of E. coli and C. welchii by radioisotopic, volumetric, and gravimetric methods. The results indicated that these compounds potentiated enzyme activity at low concentrations but higher concentrations exhibited an inhibitory effect. Fifty percent enzyme inhibition ( ID 5O ) ranges were 200–250 μg/ml, 50–75 μg/ml, and 150–200 μg/ml, for the three compounds respectively as determined by the radioisotopic method. While the radioisotopic was used as a conventional method, the microvolumetric and microgravimetric methods were developed for the first time and found to be applicable in determining the effect of the compounds on enzyme activity. The advantages of the latter two methods are that they are simple, safe, and inexpensive as compared to the radioisotopic method. The results by these methods indicated that the second compound was the strongest inhibitor of GAD activity.