Effects of various factors on steady state plasma concentrations of trazodone and its active metabolite m-chlorophenylpiperazine

Effects of various factors on steady state plasma concentrations of trazodone and its active metabolite m-chlorophenylpiperazine (mCPP) were studied in 43 depressed patients (19 males, 24 females) receiving trazodone 150 mg at bedtime for 1-3 weeks. Sixteen cases were smokers, and 19 cases were also receiving various benzodiazepines. The means (and ranges) of plasma concentrations of trazodone and mCPP, and the mCPP/trazodone ratio were 619 (251-1059) ng/ml, 59 (32-139) ng/ml and 0.100 (0.044-0.219), respectively. Smokers had significantly (p < 0.05) lower plasma concentrations of trazodone and higher mCPP/trazodone ratios than non-smokers. Age, sex and co-administration of benzodiazepines did not affect any plasma concentrations or the mCPP/trazodone ratio. In 11 cases where the dose was increased to 300 mg, neither plasma concentration/dose ratios nor the mCPP/trazodone ratio changed significantly. The present study thus suggests that: (1) there is a large Interindividual variation in the metabolism of trazodone; (2) smoking enhances the metabolism, but age, sex and co-administration of benzodiazepines do not affect it; (3) trazodone and mCPP have linear kinetics.

Reconstitution of the initial steps of mitochondrial protein import

We have reconstituted the initial steps of mitochondrial protein import with a purified precursor protein, a purified, ATP-dependent, cytosolic chaperone selective for mitochondrial precursors (mitochondrial import stimulating factor; MSF), and either intact mitochondria or intact or solubilized mitochondrial outer membranes. We show that the precursor-MSF complex first binds to the Mas37p/Mas70p subunits of the mitochondrial import receptor. After ATP-dependent release of MSF, the precursor is transferred from Mas37p/Mas70p to the Mas20p/Mas22p subunits of the receptor, and finally delivered to the import channel in the outer membrane. Import in the absence of the MSF bypasses Mas37p/Mas70p. The ATP-mediated transfer of a precursor from MSF to specific subunits of the import receptor is similar to the GTP-mediated transfer of precursors from the signal recognition particle to its receptor on the endoplasmic reticulum.

Inhibition of trazodone metabolism by thioridazine in humans

To clarify the involvement of cytochrome P4502D6 (CYP2D6) in the metabolism of trazodone, the effects of coadministration of thioridazine, which is an inhibitor of this isozyme, on plasma concentrations of trazodone and its active metabolite m-chlorophenylpiperazine (m-CPP) were studied. The subjects were 11 depressed patients receiving trazodone at bedtime for 1-18 weeks. The dose was 150 mg in 10 patients and 300 mg in one. Thioridazine 40 mg/day was coadministered for 1 week, and blood samplings were performed before and after the coadministration. Thioridazine significantly (p < 0.001) increased plasma concentrations of both trazodone (713 +/- 252 vs. 969 +/- 370 ng/ml) and m-CPP (61 +/- 22 vs. 94 +/- 34 ng/ml). The present study thus suggests that CYP2D6 is involved in the metabolism of trazodone.

Malfolded cytochrome P-450(M1) localized in unusual membrane structures of the endoplasmic reticulum in cultured animal cells

A conserved region containing three to five proline residues is present just behind the signal-anchor sequence in the amino terminal portion of most microsomal cytochrome P-450s. We have shown that the proline residues are crucial for correct folding in Schizosaccharomyces pombe cells by using mutants of P-450(M1) in which one to three of the proline residues were changed to alanine. To examine the effects of the mutations on the intracellular localization of P-450s, they were expressed in COS-7 cells. They were found to be localized only in the perinuclear loci as patched structures like the Golgi apparatus, while the wild-type P-450(M1) is localized in the reticular structures which are typical for the ER membrane. However, treatment of the cells with Brefeldin A had no effect on the patched structures. Upon co-expression with another ER membrane protein, CD4D, which possesses a double lysine motif, the expressed CD4D was localized not only in the patched structures as the mutated P-450(M1)s, but also in the reticular structures of ER. When the cells were homogenized and then fractionated, the mutated P-450(M1) was recovered mainly in the low-speed precipitate and in the fractions of much higher density than the normal ER membrane. On electron microscopic observation, unusual membranous bodies were observed near the nucleus only when the mutated P-450(M1) was expressed.(ABSTRACT TRUNCATED AT 250 WORDS)

Expression of rat cathepsin D cDNA in Saccharomyces cerevisiae: implications for intracellular targeting of cathepsin D to vacuoles

To investigate the intracellular transport mechanisms of lysosomal cathepsin D in yeast cells, we produced cathepsin D in Saccharomyces cerevisiae by placing the coding region under the control of the promoter of the yeast glyceraldehyde-3-phosphate dehydrogenase (GAPDH) gene. Immunoblotting analysis by the use of an antibody specific for rat cathepsin D coding sequence produced an intermediate species which had a slightly higher molecular weight than that of the mature cathepsin D. Cell fractionation experiments demonstrated that the cathepsin D polypeptide was colocalized to the yeast vacuoles with the marker enzyme carboxypeptidase Y in a Ficoll step gradient. A biosynthesis study with pulse-chase kinetic analysis revealed that the precursor polypeptide was accurately sorted to the yeast vacuoles as determined by cell fractionation, and that N-linked carbohydrate modifications were not required for vacuolar sorting of this protein. To elucidate the role of the propeptide region of cathepsin D, which might function in the intracellular targeting to the vacuole, a deletion mutant of cathepsin D lacking the propeptide was prepared and its intracellular targeting was examined after transfection into yeast cells. Immunoblotting analysis demonstrated that the propeptide-deleted mutant protein was recovered in a low quantity as compared with that in the case of yeast cells expressing the wild-type protein in the isolated vacuolar fraction. Immunofluorescence analysis revealed that the deletion mutant protein appeared to be accumulated within the intracellular small vesicles but not in the carboxypeptidase Y-positive vacuoles. Overall, these results indicate that the rat cathepsin D precursor polypeptide is recognized by mechanisms similar to those involved in the intracellular sorting of vacuolar proteins through the ER/Golgi/vacuolar sorting pathway in yeast cells, and that the propeptide has an important function in translocation of the cathepsin D polypeptide to the vacuole.

Expression of CD21 antigen on myeloma cells and its involvement in their adhesion to bone marrow stromal cells

The mature myeloma cells express very late antigen 5 (VLA-5) and MPC-1 antigens on their surface and adhere to bone marrow (BM) stromal cells more tightly than the VLA-5-MPC-1- immature myeloma cells in vitro. The VLA-5 and MPC-1 antigens possibly function as two of the molecules responsible for interaction of mature myeloma cells with BM stromal cells. However, the immature myeloma cells do interact with BM stromal cells, and it is unclear which adhesion molecules mediate their interaction. In this study, we found that both immature and mature myeloma cells expressed CD21, an adhesion molecule known to bind to CD23. CD21 was also detected on normal plasma cells. To evaluate the role of CD21 expression on myeloma cells, two myeloma cell lines, NOP-2 (VLA-5-MPC-1-) and KMS-5 (VLA-5+MPC-1+), were used as representatives of immature and mature myeloma cell types, respectively, and an adhesion assay was performed between the myeloma cell lines and BM stromal cells. Antibody-blocking results showed that adhesion of the mature type KMS-5 to KM102, a human BM-derived stromal cell line, or to short-term cultured BM primary stromal cells was inhibited by monoclonal antibodies (MoAbs) against CD21, VLA-5, and MPC-1, and inhibition of adhesion of the immature type NOP-2 to KM102 by the anti-CD21 MoAb was observed as well. Furthermore, CD23 was detected on KM102. Treatment of KM102 with an anti-CD23 MoAb also inhibited adhesion of either KMS-5 or NOP-2 to KM102. Therefore, we propose that CD21 expressed on myeloma cells likely functions as a molecule responsible for the interaction of immature myeloma cells as well as mature myeloma cells with BM stromal cells, and CD23 may be the ligand on the stromal cells for the CD21-mediated adhesion.

A new phenotypic classification of bone marrow plasmacytosis

Here, we propose a new phenotypic classification of bone marrow plasmacytosis. By 2-color phenotypic analysis with FITC anti-CD38 and PE anti-CD19, -CD56, -VLA-5 or MPC-1 antibody, plasma cells are easily identified on the histogram, even though no more than 1% of plasma cells are found in the bone marrow. Hence, plasma cells are phenotypically classified into polyclonal (reactive) (CD19+CD56-) or monoclonal (neoplastic) plasma cells (mostly CD19-CD56+), and furthermore immature (VLA-5-MPC-1-), intermediate (VLA-5-MPC-1+) and mature plasma cells (VLA-5+MPC-1+). According to these findings, plasmacytosis in the bone marrow can be classified into polyclonal marrow plasmacytosis (POMP) and monoclonal marrow plasmacytosis (MOMP) states. The MOMP state is further subclassified into MOMP-1 and MOMP-2, MOMP-3 and MOMP-4; MOMP-1 is defined by co-existence of monoclonal plasma cells and polyclonal plasma cells, and MOMP-2 to MOMP-4 are dependent on increased proportions of VLA-5-MPC-1- immature myeloma (plasma) cells. We found that the cases of benign monoclonal gammopathy (BMG) according to the conventional classification were in the MOMP-1 state, and myelomas could be classified into the MOMP-2 to MOMP-4 state. Subclassification of the MOMP state may be useful in determining the prognosis of myelomas, where an increase in immature myeloma cells is reported to correlate well with their aggravation during the clinical courses. Therefore, this new phenotypic classification of bone marrow plasmacytosis (POMP and MOMP-1 to MOMP-4) will contribute to differential diagnosis and understanding of therapeutic responses and prognosis in myelomas.

Two-dimensional electrophoretic analysis of down-regulated proteins in human fibroblasts immortalized by treatment with either 4-nitroquinoline 1-oxide or 60Co gamma rays

Cellular proteins were examined by two-dimensional polyacrylamide gel electrophoresis (2-D PAGE) in order to determine the mechanisms of cellular aging and immortalization of human fibroblasts. A total of 10 cell lines were studied, four of which were immortalized. OUMS-24F and SUSM-1 cells were immortalized by repeated treatment with 4-nitroquinoline 1-oxide (4NQO), KMST-6 cells were immortalized by intermittent exposure to 60Co-gamma rays, and IMR-90/SV40 cells were immortalized with simian virus 40 (SV40). None of these immortalized cells were tumorigenic. Four normal human fibroblast cell lines, OUMS-24, AD 387, KMS-6 and IMR-90, and two human cervical cancer cell lines, HeLa and A-431, were also studied. Applying 2-D PAGE, the down-regulation of the identical proteins was observed in the four immortalized cell lines and in the two human cancer cell lines. Their molecular masses were about 80 kDa and the isoelectric points ranged between 5.5 and 6.3. We could not find any information on our proteins from the recent protein data bases. Further characterization of the proteins indicated that they might be phosphorylated cytoskeletal proteins.

High-performance liquid chromatographic determination of trazodone and 1-m-chlorophenylpiperazine with ultraviolet and electrochemical detector

A high-performance liquid chromatographic (HPLC) assay was developed for the determination of trazodone and its metabolite, 1-m-chlorophenylpiperazine (m-CPP), in plasma. The high level of trazodone in plasma was detected by ultraviolet absorbance at 254 nm and the low level of m-CPP in plasma was detected by coulometric electrochemical detection at 840 mV on the series arrangement of two detectors. Pilsicainide as an internal standard for both compounds was monitored by both detectors. Trazodone and m-CPP in plasma were extracted by a rapid and simple procedure based on CN bonded-phase extraction, and C8 reversed-phase HPLC separation. Determination was possible for trazodone in the concentration range 100-2000 ng mL-1 and for m-CPP in the concentration range 5-100 ng mL-1. The recoveries of trazodone and m-CPP added to plasma were 81.0-84.2 and 68.0-73.2%, respectively, with coefficients of variation of less than 7.3 and 8.2%, respectively. The method is applicable to high level monitoring of trazodone and low level monitoring of m-CPP in plasma of healthy volunteers and patients treated with trazodone.

Transfected mutant p53 gene increases X-ray-induced cell killing and mutation in human fibroblasts immortalized with 4-nitroquinoline 1-oxide but does not induce neoplastic transformation of the cells

We introduced the mutant p53 gene (codon 273Arg-His) into human fibroblasts (SUSM-I cells) previously immortalized with 4-nitroquinoline I-oxide (4NQO) and obtained 2 clonal cell lines (SUSM-i/p53-1 and SUSM-1/p53-6) expressing the mutant p53. Since the genetic background of SUSM-1/p53 is the same as that of SUSM-1 except for the presence of the mutant p53, we expected to obtain more information on the mechanisms of p53 functions without the influence of other genetic differences by comparing cellular characteristics of both cell lines. SUSM-1/p53 cells became about twice as sensitive to the cytotoxic effects of X-rays as their parent SUSM-1 cells. Mutation frequency was determined by the appearance of hypoxanthine guanine phosphoribosyl transferase deficient (6-thioguanine resistant) cells. As a result, the mutation frequency of SUSM-1/p53 cells was about 5 times that of SUSM-1 cells transfected with or without the vector plasmid alone. Furthermore, when the SUSM-1/p53 cells were exposed to X-rays, the mutation frequency increased to about twice that of the non-irradiated SUSM-1/p53 cells. However, SUSM-1/p53 cells showed neither anchorage-independent growth in soft agar nor tumorigenicity in nude mice. These results indicate that the mutant p53 gene itself, which generally works in a dominant-negative way on cellular carcinogenesis, is not sufficient for neoplastic transformation of immortalized human cells, and that additional genetic change(s) may be necessary for transformation.

[Phenotypic analysis of myeloma cells]

Recent 2-color phenotypic analysis using anti-CD38 antibody reveals that plasma cells alone locate at CD38strong positive (CD38++) fraction and expression of adhesion molecules such as VLA-5 and MPC-1 can define VLA-5-MPC-1- immature, VLA-5-MPC-1+ intermediate and VLA-5+ MPC-1+ mature plasma (myeloma) cells. Furthermore, phenotypic analysis of plasma cells with anti-CD19 and -CD56 antibodies can distinguish normal (polyclonal) plasma cells from malignant (monoclonal) plasma cells; normal plasma cells from various tissues are all CD19+ CD56-, while malignant plasma cells are mostly CD19- CD56+. Therefore, this 2-color phenotypic analysis is very useful for differential diagnosis of bone marrow plasmacytosis, that is, myeloma, benign monoclonal gammopathy or polyclonal gammopathy, and furthermore contributes to understanding of differentiated stages of myeloma cells (immature, intermediate or mature myeloma cells).

Human fibroblasts (KMST-6/RAS cell line) transformed with 60Co gamma-rays and c-Ha-ras oncogene produce a large amount of granulocyte colony-stimulating factor (G-CSF); production is enhanced by cAMP, theophylline, and butyrate

Human fibroblasts (KMST-6/RAS cell line), which was malignantly transformed in vitro with 60Co gamma-rays and the c-Ha-ras oncogene, produced a large amount of granulocyte colony-stimulating factor (G-CSF). The production was greater during the logarithmic growth phase than during the stationary phase. cAMP and theophylline, alone or in combination, and butyrate significantly enhanced G-CSF production, but dexamethasone or 5-azacytidine did not. Enhanced production of G-CSF by these agents was regulated at the posttranscriptional level. Neither the expression of the ras oncogene nor the tumorigenicity of the cells correlated with the production of G-CSF.

Differentiation of early plasma cells on bone marrow stromal cells requires interleukin-6 for escaping from apoptosis

The bone marrow (BM) is well known to be the major site of Ig production in secondary immune responses; thus, the microenvironment of BM is considered to be essential for final differentiation of plasma cells. We identified in the peripheral blood (PB) early plasma cells (CD38++CD19+VLA-5-) committed to entering the BM. The sorted early plasma cells rapidly entered apoptosis in vitro, but these cells could survive and further differentiate into mature plasma cells (CD38 CD19+) just as BM plasma cells in the presence of a BM-derived stromal cell line (KM-102). Culture supernatants of KM-102 cell lines could also support survival of these cells, and antibody to interleukin-6 (IL-6) completely blocked the effect of these supernatants. Furthermore, recombinant IL-6, but not IL-1 or IL-3, could support their survival and their differentiation into mature plasma cells (CD38 CD19+VLA-5+) with expression of VLA-5 mRNA. Therefore, here is direct evidence that early plasma cells found in the PB differentiated into mature plasma cells with stromal cell-derived IL-6 in vitro; thus, BM stromal cells control the final checkpoint of plasma cell differentiation with secretion of IL-6 in the BM.

Recognition of mitochondria-targeting signals by a cytosolic import stimulation factor, MSF

MSF, a mitochondrial import stimulation factor purified from rat liver cytosol, is an ATP-dependent precursor protein conformational modulator. As a step toward understanding the specificity of substrate recognition by MSF, various synthetic peptides were examined for their ability to induce MSF ATPase activity. The peptides corresponding to various mitochondria-targeting signal sequences elicited significant ATPase activity. MSF bound the synthetic mitochondrial signal peptides, and ATP hydrolysis caused dissociation of the peptides from MSF. Basic amino acid residues in the signal peptides seemed to be essential for recognition. Thus, MSF is a member of the polypeptide chain-binding protein family with unique recognition specificity and is distinct from the hsp70 family of proteins.

MSF, a novel cytoplasmic chaperone which functions in precursor targeting to mitochondria

Mitochondrial import stimulation factor (MSF) unfolds wheat germ lysate synthesized aggregated mitochondrial precursor proteins and stimulates their mitochondrial import in an ATP dependent manner. Here we analysed the function of MSF mainly by utilizing chemically pure adrenodoxin precursor (pAd). MSF bound to the unfolded pAd and prevented it from losing import competence and also restored the import competence of the aggregated pAd dependent on ATP hydrolysis. The import incompetent aggregated mitochondrial precursors induced the ATPase activity of MSF and the activity was strongly inhibited by isolated mitochondrial outer membrane (OM) but not by trypsin treated outer membrane (tOM). The precursor induced ATPase activity of N-ethylmaleimide (NEM)-treated MSF was not inhibited by OM. In this context, the MSF-precursor complex specifically bound to OM and binding was abolished both by the treatment of OM with trypsin and by the treatment of MSF with NEM. These results show that MSF is a novel cytoplasmic chaperone protein with a mitochondrial precursor-targeting function.

Structural requirement for recognition of the precursor proteins by the mitochondrial processing peptidase

We examined the structural characteristics of the extension peptides responsible for the recognition by the mitochondrial processing peptidase by using preadrenodoxin, which has a long extension peptide of 58 amino acid residues, as the substrate. The deletion of various parts of the extension peptide of pre-adrenodoxin indicated that more than 40 amino acid residues and the presence of basic amino acid residues in the distal portion (20-40 amino acid residues upstream of the cleavage site) were necessary for the recognition of the precursor by the peptidase. The processing of preadrenodoxin was strongly inhibited by the synthetic peptide corresponding to the middle portion of the extension peptide, whereas the peptide corresponding to the amino-terminal portion exhibited weak inhibition of the processing. The replacement of arginine residues in the middle portion of the extension peptide with neutral amino acids resulted in a great decrease in the processing. We conclude that basic amino acids at a position distal to the cleavage site are necessary for the recognition of the precursor proteins by the processing peptidase and that basic amino acids required for the mitochondrial targeting and those for the recognition by the peptidase are separately located in the extension peptide of pre-adrenodoxin.

cDNA cloning and characterization of mitochondrial import stimulation factor (MSF) purified from rat liver cytosol

We identified a liver cytosolic protein factor that stimulated the import of wheat germ lysate-synthesized precursor proteins into mitochondria. It was termed mitochondrial import stimulation factor or MSF [Hachiya, N. et al. (1993) EMBO J. 12, 1579-1586]. It consisted of 32-kDa (MSFL) and 30-kDa (MSFS) polypeptides as assessed by SDS-PAGE. MSF recognized the presequence portion of mitochondrial precursor proteins and catalyzed the depolymerization and unfolding of in vitro synthesized mitochondrial precursor proteins in an ATP-dependent manner. We report here the cDNA cloning and characterization of MSF. Microsequencing of MSFL and MSFS showed that they belonged to a highly conserved, widely distributed eukaryotic protein family, collectively designated as 14-3-3 proteins. We cloned the cDNA of MSFL and that of one component of MSFS (MSFS1) from a rat liver cDNA library. The cloned cDNAs were separately expressed in Escherichia coli and the expressed proteins were purified to homogeneity. The purified recombinant MSFL and MSFS1 stimulated mitochondrial import of adrenodoxin precursor (pAd) synthesized in vitro with wheat germ lysate translation system. Recombinant MSFL or MSFS1 had the ability to bind with denatured pAd and they kept the precursor in an import-competent state. Rabbit polyclonal antibodies raised against the recombinant proteins inhibited the import-stimulation activity of rat liver cytosol as well as that of authentic purified MSF. Identification of MSF as 14-3-3 proteins establishes a novel function for this family of proteins and indicates their role as cytosolic chaperones to aid many important cellular events.

The transmembrane region of microsomal cytochrome P450 identified as the endoplasmic reticulum retention signal

Microsomal-type cytochrome P450s are integral membrane proteins bound to the membrane through their N-terminal transmembrane hydrophobic segment, the signal anchor sequence. To elucidate the determinants that enable the P450s to be located in the ER, we constructed cDNAs encoding chimeric proteins in which a secretory form of carboxyesterase, carboxyesterase Sec, was connected to the N-terminus of the full-length or truncated forms of a microsomal-type P450, P450(M1), and the constructed plasmids were expressed in COS cells. Since carboxyesterase Sec is an N-glycosylated secretory protein, endo H treatment could be used to determine whether these chimeric proteins were located in the ER or not. Carboxyesterase Sec with the N-terminal 20 amino acids, containing the transmembrane region, of P450(M1), was located in the ER, as determined from the endo H sensitivity of the expressed protein and immunofluorescence staining of the cells. As the expressed protein exhibited carboxyesterase activity, it was not retained in the ER through the BiP-dependent quality control system recognizing unfolded proteins. Another chimeric protein construct in which carboxyesterase Sec was connected to the C-terminal region of rat UDP-glucuronosyltransferase (UDP-GT), that contained a double-lysin ER retention motif, was also located in the ER, as determined from the endo H sensitivity and immunofluorescence staining. On the other hand, the sugar moiety of the carboxyesterase Sec connected to the transmembrane segment of UDP-GT, Sec/GTd, was partially resistant to the endo H treatment. From the results of immunofluorescent staining and cell fractionation, it was concluded that the Sec/GTd product was located in the Golgi apparatus. These observations indicated that the N-terminal hydrophobic segment of P450(M1) is sufficient for the ER membrane retention, whereas the transmembrane segment of UDP-GT is not. To determine whether microsomal P450s are recycled between the ER and Golgi compartments or not, a DNA construct encoding cathepsin D connected to the N-terminus of P450(M1) was prepared and expressed in COS cells. The fusion protein was phosphorylated, but the phosphorylation was sensitive to alkaline phosphatase. As a control, authentic cathepsin D was subjected to phosphorylation of its oligosaccharide chain that was resistant to the alkaline phosphatase treatment. Since GlcNAc-P-transferase, which forms the alkaline phosphatase-resistant phosphodiester in the sugar chains of lysosome-targeting proteins, is located in the Golgi apparatus, it was concluded that the oligosaccharide chain of the cathepsin D portion of the fusion protein was not phosphorylated, and that the chimeric protein did not go to the Golgi apparatus.(ABSTRACT TRUNCATED AT 400 WORDS)

Reconstitution of import-competent outer membrane vesicles from mammalian mitochondria

Protein insertion into mitochondrial outer membrane (OM) vesicles isolated from Neurospora crassa has recently been reported. The N. crassa OM vesicles retained the features of the intact mitochondria concerning the dependency of insertion on the receptor protein [A. Mayer et al. (1993) J. Cell Biol. 121, 1233-1243]. In this study, OM vesicles were purified from bovine adrenal cortex mitochondria, and unilamellar proteoliposomes were reconstituted from OM vesicles using heptyl beta-thioglucoside. Both OM vesicles and the reconstituted outer membrane vesicles (ROM) were able to import porin, but unable to import the precursor of adrenodoxin, which translocates across both the outer and inner membranes of intact mitochondria. Porin insertion into both OM vesicles and ROM was inhibited in the presence of purified recombinant adrenodoxin precursor and also by ATP depletion, and was dependent on the trypsin-sensitive membrane surface factor, suggesting that the purified OM vesicles as well as ROM retained the properties of the intact OM concerning porin insertion. The protein import machinery of OM seems to be functional for the outer membrane protein without the participation of the inner membrane. The successful reconstitution of the protein import activity from solubilized OM will pave the way for further biochemical characterization of the protein import machinery of OM.