T-2 toxin effect on the ultrastructure of myocardial microvasculature.

The effect of T-2 toxin on the ultrastructure of coronary microvasculature was studied in rats injected intraperitoneally and in rats hearts perfused with the toxin. The capillaries were most severely damaged and were often disrupted. The plasma membrane of endothelial cells seemed to be the first structure affected. A direct cytotoxicity of T-2 toxin to the myocardial capillary lining cells seems to be the pathogenical mechanism of injury. The abundance of mast cells in several of the hearts examined suggests a role for their vasoactive products in the genesis of the capillary lesions.     

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.     

New CNS-active drugs which are second-generation valproic acid: can they lead to the development of a magic bullet?

PURPOSE OF REVIEW: Valproic acid (VPA) is one of the four first line antiepileptic drugs (AEDs). VPA is also an effective drug in migraine prophylaxis and in treatment of bipolar disorders. The use of VPA is limited by its two rare but potentially life-threatening side effects, teratogenicity and hepatotoxicity, and it is the least potent of the established AEDs. Consequently, there is an incentive to develop a second-generation VPA. A successful, second-generation VPA would need to possess the following characteristics: broad-spectrum antiepileptic activity; better potency than VPA; and lack of teratogenicity and hepatotoxicity. These characteristics would give such a drug the potential to be utilized in epilepsy and other CNS disorders. RECENT FINDINGS: Intensive research has been carried out in order to develop a second-generation VPA that would be more potent and safer than VPA. Amide derivatives of VPA have shown particular value as potential follow-up compounds and have better in-vivo performance than VPA. Several CNS-active valproylamides are more potent as antiepileptics than VPA, they possess broad-spectrum antiepileptic activity, and have been found to be nonteratogenic in animal models. The amide analogues of VPA that emerged from structure-pharmacokinetic-pharmacodynamic relationship studies as promising second-generation compounds are: N-methyl-tetramethylcyclopropane carboxamide, (2S,3S)-valnoctamide, (R)-propylisopropyl acetamide and valproyl glycinamide. SUMMARY: At present there are three compounds in clinical trials in patients with epilepsy that can be regarded as second-generation VPA: valproyl glycinamide, 3-methylbutanamide or isovaleramide and SPD421 (DP-VPA). For any one of these second-generation valproic acids to become a successful follow-up compound to VPA, it has to fulfil the above criteria and also possess favorable pharmacokinetics.     

Intoxication produced by toxic fungi Fusarium poae and F. sporotrichioides on chicks

Strains of F. poae No. 958 and F. sporotrichioides No. 921 were involved in fatal outbreaks of alimentary toxic aleukia in man. Mixed moldy diet, crude extracts containing T-2 toxin 4β, 15-diacetoxy-8α-(3-methylbutyryloxy)-12, 13-epoxytrichothec-9-en-3α-ol) from these fungi, and pure T-2 toxin isolated from F. sporotrichioides No. 921 were used for an extensive toxicological study on New Hampshire chicks. The cultures were grown on sterile moist wheat grains at 12°C for 21 days. The experiments were performed on a total of 300 chicks, divided into 18 groups of control and of treated chicks being fed the toxic diet. The treated chicks showed reduction of weight gains, clinical and gross pathological changes and severe hematopoietic damage, which were also the principal features of alimentary toxic aleukia in man. The control groups administered the same diet without toxic material, remained healthy and showed no clinical or pathological changes.     

Efficacy of antiepileptic tetramethylcyclopropyl analogues of valproic acid amides in a rat model of neuropathic pain

Antiepileptic drugs (AEDs) are widely utilized in the management of neuropathic pain. The AED valproic acid (VPA) holds out particular promise as it engages a variety of different anticonvulsant mechanisms simultaneously. However, the clinical use of VPA is limited by two rare but potentially life-threatening side effects: teratogenicity and hepatotoxicity. We have synthesized several tetramethylcyclopropyl analogues of VPA amides that are non-teratogenic, and are likely to be non-hepatotoxic, and that exhibit good antiepileptic efficacy. In the present study we have assessed the antiallodynic activity of these compounds in comparison to VPA and gabapentin (GBP) using the rat spinal nerve ligation (SNL) model of neuropathic pain. TMCA (2,2,3,3-tetramethylcyclopropanecarboxylic acid, 100–250 mg/kg), TMCD (2,2,3,3-tetramethylcyclopropanecarboxamide, 40–150 mg/kg), MTMCD (N-methyl-TMCD, 20–100 mg/kg), and TMCU (2,2,3,3-tetramethylcyclopropanecarbonylurea, 40–240 mg/kg) all showed dose-related reversal of tactile allodynia, with ED₅₀ values of 181, 85, 41, and 171 mg/kg i.p., respectively. All were more potent than VPA (ED₅₀ = 269 mg/kg). An antiallodynic effect was obtained for TMCD, MTMCD and TMCU at plasma concentrations as low as 23, 6 and 22 mg/L, respectively. MTMCD was found to be non-toxic, non-sedative and equipotent to gabapentin, currently the leading AED in neuropathic pain treatment. Tetramethylcyclopropyl analogues of VPA amides have potential to become a new series of drugs for neuropathic pain treatment.     

Valproic acid derivatives signal for apoptosis and repair in vitro

Purpose

To determine the cytotoxicity of valproic acid (VPA) and its derivatives in human hepatoblastoma (HepG2) cells, and to study the possible toxicity of these compounds in human lymphocytes from patients with known hypersensitivity syndrome reactions (HSRs) to other medication.

Methods

Cells were exposed to physiological doses of VPA, valnoctamide (VCD) and its one carbon homologue sec-Butyl-propyl-acetamide (SPD) for 2 h and for 24 h. Cell viability was measured using succinate dehydrogenase activity for hepatocytes and lymphocyte toxicity assay (LTA) for lymphocytes. Cytokines and apoptosis [cytokeratine 18 (cCK18-M30)] markers were quantitated by ELISA.

Results

VCD and SPD presented lower cytotoxicity compared to VPA in cultured HepG2 cells. SPD led to cytotoxicity in lymphocytes. VPA and its derivatives increased the release of interferon (IFN)-γ and tumor necrosis factor (TNF)-α in media, but had no influence on the release of either interleukin (IL)-1 or IL-6. Significant increases in the release of IFN-γ and TNF-α were observed in lymphocytes exposed to high doses of VPA, and this increased further with exposure time.

Significance

HepG2 cells exposed to VCD and SPD experienced lower direct cytotoxicity than those treated with VPA. Lymphocytes from patients that experienced HSR to other medication have shown cytotoxicity to VPA and its VPA derivatives-induced. High levels of pro-inflammatory cytokines were released in the cell culture media, suggesting that inflammation plays a key role in VPA-derivatives induced lymphocyte toxicity.     

Syntheses and evaluation of anticonvulsant activity of novel branched alkyl carbamates

A novel class of 19 carbamates was synthesized, and their anticonvulsant activity was comparatively evaluated in the rat maximal electroshock (MES) and subcutaneous metrazol (scMet) seizure tests and pilocarpine-induced status epilepticus (SE) model. In spite of the alkyl-carbamates' close structural features, only compounds 34, 38, and 40 were active at the MES test. The analogues 2-ethyl-3-methyl-butyl-carbamate (34) and 2-ethyl-3-methyl-pentyl-carbamate (38) also exhibited potent activity in the pilocarpine-SE model 30 min postseizure onset. Extending the aliphatic side chains of homologous carbamates from 7 to 8 (34 to 35) and from 8 to 9 carbons in the homologues 38 and 43 decreased the activity in the pilocarpine-SE model from ED(50) = 81 mg/kg (34) to 94 mg/kg (35) and from 96 mg/kg (38) to 114 mg/kg (43), respectively. The most potent carbamate, phenyl-ethyl-carbamate (47) (MES ED(50) = 16 mg/kg) contains an aromatic moiety in its structure. Compounds 34, 38, 40, and 47 offer the optimal efficacy-safety profile and, consequently, are promising candidates for development as new antiepileptics.     

Cutaneous injury by topical T-2 toxin: involvement of microvessels and mast cells

Topical applications of various doses of T-2 toxin to rats led to delayed skin reactions. Following a dose-dependent latent period of 12-24 hr, there appeared vascular dilation, stasis, edema and mononuclear cell infiltration, with many degranulating mast cells. These signs were earliest and strongest in the subcutis. Epidermal necrosis occurred 1-2 days later and was probably caused secondarily by ischemia, due to microcirculatory failure. Ultrastructurally, endothelial cells of small vessels were the earliest sites of change. While intercellular junctions remained closed and pinocytosis decreased, the cytoplasm contained many ribosomes, vacuoles, and abnormal mitochondria. Another early effect of topical T-2 toxin was an increase in number and degranulation of mast cells, especially in the subcutis. The resemblance of the skin injury to that produced by irradiation is noted.     

Metabolism of T-2 toxin by rat brain homogenate

HT-2 toxin was the sole metabolite formed when T-2 toxin was treated with homogenate from brain without its blood content. Homogenate from brain with its full blood content produced--besides HT-2 toxin--T-2 triol, neosolaniol, 4-deacetylneosolaniol and T-2 tetraol, i.e. the same metabolites formed by incubation of T-2 toxin with whole rat blood.