Carbamazepine and valproate monotherapy: feasibility, relative safety and efficacy, and therapeutic drug monitoring in manic disorder

RATIONALE

Search for alternatives to lithium therapy for mood disorders commenced with anticonvulsants, carbamazepine (CBZ) and valproic acid (VPA), in the late 1970s. The comparative safety and efficacy data of CBZ and VPA monotherapy in patients with bipolar disorder remain to be established.

OBJECTIVES

The main objectives of the study were to assess the relative antimanic efficacy and safety of CBZ and VPA; to study the feasibility of using either, as a first line anti-manic agent; to investigate and generate clinically relevant parameters involving therapeutic drug monitoring of the two drugs.

METHODS

After a 2-day screening period, suitable patients (n = 30) were randomly assigned to treatment with CBZ or VPA. Both the drugs were started with an average dose of approximately 20 mg/kg body weight per day. Further increment in dose was carried out at weekly intervals, guided by clinical improvement, serum levels and treatment emergent adverse events. The primary efficacy measure in the protocol was defined as a change from baseline to endpoint in total score on the Young Mania Rating Scale. A favourable clinical response was defined a priori as a decrease of more than 50% from baseline in Young Mania Rating Scale total score.

RESULTS

Both CBZ and VPA were found to be efficacious as single first-line anti-manic agents, however VPA proved to be better. Using the intent-to-treat analysis, the VPA group showed a significant fall in YMRS total scores after week 1 while the CBZ group showed a significant fall after week 2. In the primary efficacy analysis, valproate group experienced significantly greater mean improvement in Young Mania Rating Scale total score than the CBZ group. Of the VPA treated patients, 73% showed a favourable clinical response while 53% of the patients on CBZ responded favourably. In the CBZ group, significantly more patients received rescue medication during the week 2 and the requirement was quantitatively more as compared to the VPA group. The steady state serum concentration (Css) of CBZ ranged from 3 to 9 micrograms/ml; however, it did not appear to correlate with the dose or clinical response. The Css of VPA ranged from 50 to 100 micrograms/ml; a linear correlation was found between the dose and serum levels of VPA as well as between weekly rise in serum levels and clinical response. Weekly dose escalations of VPA also correlated positively with corresponding rise in serum levels. Significantly more patients in the CBZ group reported adverse events, including nausea, vomiting and dizziness, than VPA.

CONCLUSIONS

The findings from this study suggest that both CBZ and VPA monotherapy is feasible for treatment of acute mania; however, VPA is more efficacious in terms of its early onset of action, lesser requirement for rescue medication and better tolerability. Further work needs to be undertaken to characterise the manic patients in terms of their differential psychopharmacologic response profile.

Identification of amino acids in the tau 2-region of the mouse glucocorticoid receptor that contribute to hormone binding and transcriptional activation

The tau 2-region of steroid hormone receptors is a highly conserved region located at the extreme N-terminal end of the hormone-binding domain. A protein fragment encoding tau 2 has been shown to function as an independent transcriptional activation domain; however, because this region is essential for hormone binding, it has been difficult to determine whether the tau 2-region also contributes to the transactivation function of intact steroid receptors. In this study a series of amino acid substitutions were engineered at conserved positions in the tau 2-region of the mouse glucocorticoid receptor (mGR, amino acids 533-562) to map specific amino acid residues that contribute to the hormone-binding function, transcriptional activation, or both. Substitution of alanine or glycine for some amino acids (mutations E546G, P547A, and D555A) reduced or eliminated hormone binding, but the transactivation function of the intact GR and/or the minimum tau 2-fragment was unaffected for each of these mutants. Substitution of alanine for amino acid S561 reduced transactivation activity in the intact GR and the minimum tau 2-fragment but had no effect on hormone binding. The single mutation L550A and the double amino acid substitution L541G+L542G affected both hormone binding and transactivation. The fact that the S561A and L550A substitutions each caused a loss of transactivation activity in the minimum tau 2-fragment and the full-length GR indicated that the tau 2-region does contribute to the overall transactivation function of the full-length GR. Overall, the N-terminal portion of the tau 2-region (mGR 541-547) was primarily involved in hormone binding, whereas the C-terminal portion of the tau 2-region (mGR 548-561) was primarily involved in transactivation.

GRIP1, a transcriptional coactivator for the AF-2 transactivation domain of steroid, thyroid, retinoid, and vitamin D receptors

After binding to enhancer elements, transcription factors require transcriptional coactivator proteins to mediate their stimulation of transcription initiation. A search for possible coactivators for steroid hormone receptors resulted in identification of glucocorticoid receptor interacting protein 1 (GRIP1). The complete coding sequence for GRIP1, isolated from a mouse brain cDNA library, contains an open reading frame of 1,462 codons. GRIP1 is the probable ortholog of the subsequently identified human protein transcription intermediary factor 2 (TIF2) and is also partially homologous to steroid receptor coactivator 1 (SRC-1). The full-length GRIP1 interacted with the hormone binding domains (HBDs) of all five steroid receptors in a hormone-dependent manner and also with HBDs of class II nuclear receptors, including thyroid receptor alpha, vitamin D receptor, retinoic acid receptor alpha, and retinoid X receptor alpha. In contrast to agonists, glucocorticoid antagonists did not promote interaction between the glucocorticoid receptor and GRIP1. In yeast cells, GRIP1 dramatically enhanced the transcriptional activation function of proteins containing the HBDs of any of the above-named receptors fused to the GAL4 DNA binding domain and thus served as a transcriptional coactivator for them. This finding contrasts with previous reports of TIF2 and SRC-1, which in mammalian cells enhanced the transactivation activities of only a subset of the steroid and nuclear receptors that they physically interacted with. GRIP1 also enhanced the hormone-dependent transactivation activity of intact glucocorticoid receptor, estrogen receptor, and mineralocorticoid receptor. Experiments with glucocorticoid receptor truncation and point mutants indicated that GRIP1 interacted with and enhanced the activity of the C-terminal AF-2 but not the N-terminal AF-1 transactivation domain of the glucocorticoid receptor. These results demonstrate directly that AF-1 and AF-2 domains accomplish their transactivation activities through different mechanisms: AF-2 requires GRIP1 as a coactivator, but AF-1 does not.

Fluoride uptake by proximal surfaces from professionally applied fluorides: an in vitro study

This study was performed to examine the uptake of fluoride by mesial enamel surfaces of extracted teeth from different types of topical fluoride. Forty-eight extracted human molars and twelve premolars were randomly divided into four groups and mounted in twelve wax blocks with five teeth in proximal contact in each block. Each group was treated for four minutes with either 1.23 percent acidulated phosphofluoride conventional gel, thixotropic gel, or foam in lined trays, or 2 percent neutral sodium fluoride solution applied with a cotton tip applicator. Acid-etch biopsies were performed three times to indicate the amount of fluoride uptake at three different depths. The results demonstrated that there was a statistically significant increase in fluoride uptake in the surface layer with both gels and foam (1150, 1058 and 1120 ppm F), whereas there was an insignificant increase with the fluoride solution (27 ppm F). In the deepest layer, the thixotropic fluoride produced the greatest fluoride uptake (919 ppm F) in comparison with the uptake from conventional gel (383 ppm F), foam (297 ppm F), or solution (118 ppm F).

GRIP1, a novel mouse protein that serves as a transcriptional coactivator in yeast for the hormone binding domains of steroid receptors

The yeast two-hybrid system was used to isolate a clone from a 17-day-old mouse embryo cDNA library that codes for a novel 812-aa long protein fragment, glucocorticoid receptor-interacting protein 1 (GRIP1), that can interact with the hormone binding domain (HBD) of the glucocorticoid receptor. In the yeast two-hybrid system and in vitro, GRIP1 interacted with the HBDs of the glucocorticoid, estrogen, and androgen receptors in a hormone-regulated manner. When fused to the DNA binding domain of a heterologous protein, the GRIP1 fragment activated a reporter gene containing a suitable enhancer site in yeast cells and in mammalian cells, indicating that GRIP1 contains a transcriptional activation domain. Overexpression of the GRIP1 fragment in mammalian cells interfered with hormone-regulated expression of mouse mammary tumor virus-chloramphenicol acetyltransferase gene and constitutive expression of cytomegalovirus-beta-galactosidase reporter gene, but not constitutive expression from a tRNA gene promoter. This selective squelching activity suggests that GRIM can interact with an essential component of the RNA polymerase II transcription machinery. Finally, while a steroid receptor HBD fused with a GAL4 DNA binding domain did not, by itself, activate transcription of a reporter gene in yeast, coexpression of this fusion protein with GRIP1 strongly activated the reporter gene. Thus, in yeast, GRIP1 can serve as a coactivator, potentiating the transactivation functions in steroid receptor HBDs, possibly by acting as a bridge between HBDs of the receptors and the basal transcription machinery.

Rational drug therapy as evaluated from student's clinical case reports

210 prescriptions selected by students from Sucheta Kriplani and R.M.L. Hospitals were subjected to audit prescription in a group discussion with faculty members in the Department of Pharmacology of Lady Hardinge Medical College, New Delhi. It was observed that inadequate treatment was prescribed to the patients suffering from common diseases like amoebiasis, tuberculosis and typhoid fever. Indiscriminate use of antibiotics, antihistaminics, NSAID, vitamins and haematinics was a common observation.

A somatic cell genetic method for identification of untargeted mutations in the glucocorticoid receptor that cause hormone binding deficiencies

Mouse T lymphoma cell line W7MG1, which is killed by physiological concentrations of glucocorticoid agonists, was used as a convenient genetic system for isolating sublines containing mutant glucocorticoid receptors (GR) with hormone-binding deficiencies. Partially hormone-resistant cell clones were derived from chemically mutagenized cell populations by selecting for growth in moderate concentrations of dexamethasone (Dex) and then screening for failure to grow in high Dex concentrations. Such clones are likely to have mutant GR. In GR cDNA clones from the partially resistant cell sublines, three different functionally significant mutations in the hormone-binding domain were identified: Leu-569 changed to Phe (L569F), Leu-670 to Phe (L670F), and Met-672 to Ile (M672I). Dose-response analyses with Dex and affinity labeling studies with dexamethasone 21-mesylate in transiently transfected cells indicated that all three mutant GR species had hormone-binding deficiencies. However, at saturating Dex concentrations the mutant and wild type GR activated a hormone-inducible reporter gene to the same extent; thus, these three mutations did not affect the ability of GR to activate transcription of the reporter gene after hormone was bound. In dose-response curves conducted with several glucocorticoid agonists, mutations L670F and M672I caused no change in ligand-binding specificities, while mutation L569F caused a modest change in specificity. Quantitative hormone-binding studies conducted with mutant GR synthesized in cell-free reactions showed that mutant GR species L569F and M672I had reduced Dex-binding affinities both at 0 C and at 22 C in the presence of molybdate. In contrast, for the L670F mutant, which exhibited the severest deficiency in vivo, the hormone-binding deficiency in the cell-free system was evident only at 26-37 C and primarily in the absence of molybdate. We propose that the L670F GR is an activation-labile type of mutant, which binds hormone normally in the presence of heat shock protein 90 but loses hormone rapidly after dissociation from heat shock protein 90. These three mutations define two new subregions of the GR polypeptide that are important for hormone binding.

Genetic analysis of the N-terminal end of the glucocorticoid receptor hormone binding domain

Four site-directed missense mutations were constructed at the N-terminal end of the mouse glucocorticoid receptor (GR) hormone binding domain. This small subdomain is highly conserved among the steroid hormone receptors and is within a larger subregion believed to be important for hormone binding, transcriptional activation, and hsp90 binding. The ability of mutant and wild type GR to activate a reporter gene in response to various concentrations of dexamethasone was examined in transiently transfected COS-7 cells. Mutant GR species V544G (valine-544 changes to glycine) and V549G activated the reporter gene to approximately the same extent as wild type GR, but required approx. 7 and 23 times greater hormone concentrations, respectively. In contrast, double mutant LL541/2GG (leucines changed to glycines) could not activate transcription even at 10 microM dexamethasone or deacylcortivazol, while E543A (glutamic acid to alanine) was functionally indistinguishable from wild type GR. GR mutants LL541/2GG and V549G had reduced abilities to bind covalently to affinity label dexamethasone 21-mesylate. The partially and fully functional mutant GR species had no deficiency in transcriptional transactivation activity in the presence of saturating concentrations of agonist.

Phenylalanine-780 near the C-terminus of the mouse glucocorticoid receptor is important for ligand binding affinity and specificity

Site-directed mutagenesis was employed to make two single amino acid substitutions for highly conserved amino acid residues near the C-terminus of the 783-amino acid mouse glucocorticoid receptor. Substitution of leucine for histidine-781 caused little or no change in the concentration of dexamethasone required for half-maximal activation of a chloramphenicol acetyltransferase reporter gene expressed from a mouse mammary tumor virus promoter. However, when phenylalanine-780 was changed to alanine, the half-maximal concentrations of various agonists were increased as follows, compared with the wild-type glucocorticoid receptor: triamcinolone acetonide by 7-fold, dexamethasone by 25-fold, and hydrocortisone and deoxycorticosterone by more than 150-fold. Binding of labeled steroids by the mutant receptor in vitro and in vivo was also decreased. In contrast, this mutation caused a small decrease in the concentration of RU486 required for antagonist or partial agonist activity. Thus, the phenyl group of phenylalanine-780 of the mouse glucocorticoid receptor is an important determinant of ligand binding affinity and specificity.