The effect of barbiturates on microtubular assembly

Anesthetic pentobarbital inhibits proliferation and migration of malignant glioma cells

Malignant gliomas are common and aggressive brain tumors in adults. The rapid proliferation and diffuse brain migration are main obstacles to successful treatment. Here we show that pentobarbital, a central depressant introduced clinically a century ago, is capable of suppressing proliferation and migration of C6 malignant glioma cells in a concentration-dependent manner. Pentobarbital also leads to a G1 phase cell cycle arrest accompanied by suppressed G1 cell cycle regulatory proteins Cyclin D1, Cyclin D3, CDK2 and phosphorylated Rb. In addition, noticeable morphological changes and interrupted alpha-tubulin microtubule assembly are induced by pentobarbital exposure. Intracellular signal pathways involved in the effect of pentobarbital is concerned with inactivation of ERK, c-Jun and Akt. Together, these findings suggest anti-proliferation and anti-migration effects of pentobarbital on malignant gliomas, most likely by arresting cell cycle and interfering microtubule. ERK, c-Jun MAPK and PI3K/Akt are possible signaling pathways involved.

Inhibition of Activator Protein 1 by Barbiturates Is Mediated by Differential Effects on Mitogen-Activated Protein Kinases and the Small G Proteins Ras and Rac-1

Barbiturates are known to suppress protective immunity, and their therapeutic use is associated with nosocomial infections. Although barbiturates inhibit T cell proliferation, differentiation, and cytokine synthesis, only thiobarbiturates markedly reduce the activation of immune regulatory transcription factors such as nuclear factor-kappaB and nuclear factor of activated T cells. In this study, we investigated barbiturate-mediated effects on the regulation of the transcription factor activator protein 1 (AP-1) in primary T lymphocytes. We show that both thiobarbiturates and their oxy-analogs inhibit AP-1-dependent gene expression and AP-1 complex formation at clinically relevant doses. Furthermore, mitogen-activated protein (MAP) kinase activity, which transcriptionally and posttranslationally regulates AP-1 complex formation, is suppressed by most barbiturates. CD3/CD28- or phorbol 12-myristate 13-acetate (PMA)/ionomycin-induced p38 and extracellular signal-regulated kinase 1/2 phosphorylation or c-jun NH2-terminal kinase (JNK) 1/2 kinase activity was significantly diminished by pentobarbital, thiamylal, secobarbital, or methohexital treatment. These barbiturates also inhibited the initiators of the MAP kinase cascade, the small G proteins ras and rac-1, and prevented binding to their partners raf-1 and PAK, respectively. Thiopental, unlike the other barbiturates, only reduced ras and JNK activity upon direct CD3/CD28 receptor engagement. Contrarily, upon PMA/ionomycin stimulation, thiopental blocked AP-1-dependent gene expression independently of the small G protein ras and MAP kinases, thus suggesting an additional, unknown mechanism of AP-1 regulation. In conclusion, our results contribute to the explanation of a clinically manifested immune suppression in barbiturate-treated patients and support the idea of a MAP kinase-independent regulation of AP-1 by PKC and calcium in human T cells.

Effect of rifampicin on the biological activity of tubulin

The effect of rifampicin on the biological properties of bovine brain tubulin was investigated. Assembly of microtubules was almost completely blocked by rifampicin, whereas the depolymerization was not affected. The drug was found to inhibit both colchicine and GTP binding to tubulin. Association of rifampicin with tubulin was confirmed by spectrophotometric method. Binding of rifampicin was found to be dependent both on temperature and time. At 0 degrees for 1 hr 0.84 moles of rifampicin were bound per mole of tubulin.

Colchicine-induced appearance (proliferation) of smooth sarcoplasmic reticulum in arterial smooth muscle cells

Colchicine treatment resulted in the appearance and proliferation of smooth sarcoplasmic reticulum in some smooth muscle cells of the aortic and pulmonary trunk walls in the rabbit. The significance of cytoplasmic microtubules and/or membrane-bound tubulin for the morphogenesis, functioning and control of smooth endoplasmic reticulum in different kinds of cells is discussed.

Impairment of glycoprotein secretion by phenobarbital in rat liver slices

The effects of phenobarbital on protein and glycoprotein synthesis and secretion were studied in rat liver slices. Phenobarbital (2 mM) decreased [14C]glucosamine and [14C]leucine incorporation into liver proteins and markedly inhibited their incorporation into medium (secretory) proteins. The inhibitory effect of phenobarbital was dose dependent and not reversible under the conditions of this study. In the presence of cycloheximide, an inhibitor of peptide synthesis, phenobarbital still inhibited the release of glycoproteins into the medium; however, the specific activity of liver glycoproteins was increased. The effects of phenobarbital on hepatic macromolecular secretion, independent of its effects on synthesis, were determined by prelabeling proteins in a liver slice system with either [14C]leucine or [14C]glucosamine. When phenobarbital was present, the secretion of these prelabeled proteins into the medium was inpaired. 12 h after intraperitoneal injections of phenobarbital, glycoprotein secretion was inhibited from liver slices prepared from the pretreated rats. This inhibition of secretion occurred even though protein synthesis was stimulated and intracellular glycosylations unaffected. The results of this study indicate that phenobarbital impairs the secretion of glycoproteins by the liver.

Rotenone inhibition of tubulin self-assembly

Rotenone effectively inhibits the in vitro formation of microtubules from tubulin containing or lacking microtubule-associated proteins. In both cases a concentration of rotenone equal to that of tubulin present completely blocks assembly. The inhibition can be reversed by the addition of dimethylsulfoxide or by removing rotenone with charcoal.

An ultrastructural study into the effects of pentobarbitone on synaptic organization

A series of adult male rats was analyzed to test the effects of varying doses of pentobarbitone sodium on the ultrastructure of synapses in the molecular layer of the parietal cortex. The rats were divided into the following categories: unanaesthetized stunned, unanaesthetized cannulated and those subjected to 40, 80, 160, 300, or 400 mg/kg pentobarbitone. All material was examined both qualitatively and quantitatively after aldehyde-OsO4 or ethanolic phosphotungstic acid (E-PTA) treatment. The principal qualitative observations were: the preponderance in the unanaesthetized stunned and 160-400 mg/kg material of a variety of intraterminal profiles including synaptic vesicles, mitochondria, coated vesicles, tubular profiles, vacuoles, cisterns and double membrane profiles; the presence of exocytotic sites along the presynaptic membrane in the unanaesthetized stunned and cannulated material; the presence of endocytotic sites over the limiting membrane of the terminal away from the cleft in the unanaesthetized stunned and 160-400 mg/kg material; the prominence of the presynaptic network in the unanaesthetized and 40 mg/kg E-PTA material; discontinuity of the cleft material in the 40-160 mg/kg material. Findings to emerge from the quantitative aspect of the study show that pentobarbitone influences synaptic curvature, with a marked increase in curvature negativity over the 0-80 mg/kg dose range and a decrease in negativity at higher dose levels. The increase in curvature negativity is accompanied by an increase in synaptic length and dense projection numbers, with a consonant increase in the perimeter and area of the presynaptic terminal. Reversal of the negativity trend at higher dose levels is parallelled by reversal of these accompanying trends. Both sets of findings can be accounted for by membrane recycling within the terminal, supporting a membrane redistribution hypothesis.

Microtubules associated with postsynaptic 'thickenings'

Using a new albumin technique, microtubules can be seen closely related to or associated with the postsynaptic 'thickening' of mature and immature central nervous synapses. Thus in conventionally fixed synapses (without albumin pretreatment) where microtubules cannot usually be observed running into the postsynaptic dense material, this material could perhaps, in part, consist of the debris of in vivo microtubules. Smooth endoplasmic reticulum (ER) is often seen associated with the microtubules near the postsynaptic 'thickening'. Microtubules, and possibly smooth ER, may have an important role in the initiation of synapse formation and in the maintenance of mature synapses.