Biomedical subjects
Publications and source records attributed to A Frazer.
This review covers mechanisms of action, efficacy, side effects, and toxicity of various classes of antidepressants: tricyclic antidepressants, monoamine oxidase inhibitors, second-generation antidepressants including the selective inhibitors of serotonin reuptake, and novel drugs such as mirtazapine, nefazodone, and venlafaxine.
Venlafaxine is a new antidepressant that inhibits the reuptake of both 5-hydroxytryptamine (serotonin; 5-HT) and noradrenaline (NA). It is somewhat more potent as an inhibitor of the reuptake of 5-HT than NA. Its potency to inhibit the reuptake of 5-HT is comparable to that of tricyclic antidepressants (TCAs) such as amitriptyline or imipramine, but it is less potent than these drugs at inhibiting the reuptake of NA. Consequently, at low doses, venlafaxine may be a more effective inhibitor of the reuptake of 5-HT than that of NA. The major metabolite of venlafaxine in humans, O-desmethylvenlafaxine, has comparable potency to the parent drug for inhibiting the reuptake of either NA or 5-HT in vitro, but it is less potent in vivo. Both venlafaxine and O-desmethylvenlafaxine are essentially devoid of activity at muscarinic cholinergic, H1 histaminergic, and 1-adrenoceptors. This probably accounts for venlafaxine having a side-effect profile similar to that of selective serotonin reuptake inhibitors (SSRIs) rather than that of TCAs. Venlafaxine is subject to extensive first-pass metabolism and is metabolised by the cytochrome P450 isoenzyme IID6 in the liver. The half-life of venlafaxine is 3-4 h and that of its principal metabolite is about 10 h. The daily dose of venlafaxine can be administered as either two or three divided doses without altering significantly the pharmacokinetics of venlafaxine. The most common side-effects of venlafaxine are nausea, sedation, dizziness, dry mouth and sweating, as well as sexual dysfunctions, primarily problems with erection and delayed ejaculation. In some patients, venlafaxine also causes sustained elevations in both systolic and diastolic blood pressure; this effect is dose-dependent. Venlafaxine is much safer in overdosage than the TCAs. Antidepressant efficacy of venlafaxine has been found both in out-patients and in-patients. In general, its efficacy is comparable to that of comparator drugs (primarily TCAs or SSRIs), and in some cases even greater, and its efficacy is greater than that measured with placebo.
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The annual regrowth of antlers in male deer is a unique example of complete bone regeneration occurring in an adult animal. Growth is initiated at the distal antler tip, which is similar to the epiphyseal growth plate in some respects. However, there is some debate as to whether this process represents "true" endochondral ossification. As part of the characterization of the developmental process in pre-osseus antler tissue, we have studied, by in situ hybridization, the spatial expression of mRNAs for types I, II, and X collagen. Viewed in a coronal plane, type I procollagen mRNA was observed in skin, the fibrous perichondrium, and the densely cellular area immediately adjacent to the perichondrium. Below this area, as cells began to assume a columnar arrangement and coincident with the appearance of a vasculature and synthesis of a cartilaginous matrix, transcripts for types I, IIA, IIB procollagen and X collagen were detected. Further down in the cartilage zone, the pattern of type I procollagen mRNA expression was altered. Here, the signal was detected only in a morphologically distinct subpopulation of small, flattened cells within the intercellular matrix at the periphery of the columns of chondrocytes. The alternative splice form of type II procollagen mRNA (IIA), characteristic of chondroprogenitor cells (Sandell et al. [1991] J. Cell Biol. 114:1307-1319), was expressed by a subset of cells in the upper region of the columns, indicating that this zone contains a population of prechondrocytic cells. Positive hybridization to type IIA was most abundant in these cells. In contrast, transcripts for the other procollagen splice form (IIB) and type X collagen were expressed by chondrocytes throughout the whole of the cartilage region studied. The translation and export of type II collagen and type X collagen were confirmed by detecting specific immunoreactivity for each. The spatial distribution of immunoreactivity for collagen types II and X was consistent with that of corresponding mRNAs. These data demonstrate for the first time the distinct pattern of expression of genes for major cartilage matrix macromolecules, the expression of the differentially spliced form of type II procollagen mRNA (IIA), and specifically the co-localization of types II and X collagen in the developing antler tip. Taken together, they strongly indicate that antler growth involves an endochondral process.
The aim of this study was to investigate the effects of insulin-like growth factor-I, transforming growth factor-beta (TGF-beta), and interluekin-1 alpha (IL-1 alpha) on the deposition and degradation of a cartilage-like matrix in high-density pellet cultures of adult bovine chondrocytes. Proteoglycan was determined by toluidine blue staining and colorimetric assay. Type II collagen was determined by immunohistochemical staining and its unwinding in situ by a recently developed immunoassay. Bovine nasal chondrocytes cultured as pellets deposited a well-organized extracellular matrix of proteoglycan and type II collagen. Insulin-like growth factor-I (2-10 ng/ml) increased the synthesis and incorporation into the matrix of both these proteins. TGF-beta (2-10 ng/ml) also increased proteoglycan synthesis. However it inhibited proteoglycan deposition, presumably through increased degradation of the molecule, as shown by increased release of aggrecan fragments into the tissue culture medium. TGF-beta had no effect on type II collagen deposition. In pellet cultures of bovine nasal or articular chondrocytes, 20 ng/ml IL-1 alpha induced a significant degradation of both proteoglycan and type II collagen. The effect on collagen clearly involved proteolytic cleavage of its triple helix because there was an increase in the proportion of unwound type II collagen in the matrix, as well as a loss of total type II collagen. In explant cultures of intact bovine articular cartilage, incubation with 50 ng/ml IL-1 alpha stimulated significant degradation of the proteoglycan but no degradation of the type II collagen. These results demonstrate that although the articular chondrocytes are capable of degrading type II collagen when isolated, they do not do so in situ, presumably because of some inherent property of the mature extracellular matrix. This study demonstrates the utility of pellet cultures when investigating chondrocyte-mediated turnover of cartilage matrix and its modulation by cytokines and growth factors.
p-MPPI [4-(2'-methoxyphenyl)-1-[2'-[N-(2"-pyridinyl)-p-iodobenzamido] ethylpiperazine] and p-MPPF [4-(2'-methoxyphenyl)-1-[2'-[N-(2"-pyridinyl)-p- fluorobenzamido]ethyl]piperazine] competitively antagonized 5-HT1A receptor activation in the rat, as measured by hypothermia, forepaw treading and 5-HT turnover; they exhibited to partial agonist activity on any of these measures. When given i.p., p-MPPI and p-MPPF dose-dependently antagonized the hypothermia induced by 8-hydroxy-2- (di-n-propylamino)tetralin (8-OH-DPAT) (0.5 mg/kg), with approximate ID50 of 5 and 3 mg/kg, respectively. The inhibitory effect caused by a fixed dose of p-MPPI (6 mg/kg) or p-MPPF (3 mg/kg) was surmounted by higher doses of 8-OH-DPAT. p-MPPI and p-MPPF also attenuated the hypothermia induced by gepirone. Forepaw treading caused by 8-OH-DPAT (2 mg/kg) in reserpine-pretreated rats (1 mg/kg, s.c., 18-24 hr before the experiment) was dose-dependently antagonized by p-MPPI and p-MPPF with approximate ID50 of 3 and 0.7 mg/kg, respectively. p-MPPI also antagonized forepaw treading induced by 5-methoxy-N,N,-dimethyltryptamine (5-MeODMT) (5 mg/kg) and this antagonism was competitively overcome by higher doses of 5-methoxy-N,N,-dimethyltryptamine. p-MPPI and p-MPPF were able to antagonize the 8-OH-DPAT-(0.5 mg/kg) induced reduction in the 5-HIAA/5-HT ratio, a measure of 5-HT turnover in the hippocampus or striatum. No hypothermia or reciprocal forepaw treading was produced by either drug when given at doses as high as 10 mg/kg. Neither p-MPPI nor p-MPPF (10 mg/kg) given alone significantly altered the ratio of 5-HIAA/5-HT in the hippocampus or striatum. Also, binding of [3H]p-MPPF to hippocampal membranes was unaltered by the addition of 100 microM guanylyl-imidodiphosphate to the incubation medium. In conclusion, p-MPPI and p-MPPF behave, in vivo, as competitive antagonists of both postsynaptic 5-HT1A receptors and somatodendritic 5-HT1A autoreceptors.
The effects of two putative 5-HT1A antagonists, 4-(2'-methoxyphenyl)-1- [2'-[N-(2"-pyridinyl)-p-iodobenzamido]ethyl]piperazine (p-MPPI) and 4-(2'-methoxyphenyl)-1-[2'-[N-(2"-pyridinyl)-p- fluorobenzamido]ethyl]piperazine (p-MPPF), were examined in vivo in two tests of postsynaptic 5-HT1A receptor activation, hypothermia and reciprocal forepaw treading, in the rat. Both p-MPPI (10 mg/kg, i.p.) and p-MPPF (10 mg/kg, i.p.) antagonized the hypothermia induced by the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) (0.5 mg/kg, s.c.). Neither p-MPPI nor p-MPPF administered alone at a dose of 10 mg/kg (i.p.) induced hypothermia. Similarly, both p-MPPI (10 mg/kg, i.p.) and p-MPPF (2.5 mg/kg, i.p.) completely antagonized 8-OH-DPAT (2 mg/kg, s.c.)-induced forepaw treading in rats pretreated with reserpine (1 mg/kg, s.c., 18-24 hours prior to the experiment). p-MPPI and p-MPPF, at doses of 10 mg/kg (i.p.) did not induce forepaw treading in reserpine pretreated animals. The results of the present study demonstrate that p-MPPI and p-MPPF act as 5-HT1A receptor antagonists in these measures of postsynaptic 5-HT1A receptor activation.
This is a study of the regulation of human articular chondrocyte proliferation by transforming growth factor beta (TGF beta) and interleukin-1 beta (IL-1 beta) in vitro. Human articular chondrocytes were cultured at different cell densities on plastic and on a collagen substratum, in the presence and absence of serum. The effects of TGF beta and IL-1 beta on proliferation of chondrocytes, as determined by [3H]thymidine incorporation, under these conditions of culture were examined. TGF beta was found to have both stimulatory and inhibitory effects on chondrocytes in vitro. Interactions between TGF beta and growth factors present in serum influence the modulation of chondrocyte proliferation by TGF beta. IL-1 beta caused a significant reduction of the TGF beta-stimulated increase in chondrocyte proliferation. The complex inter-relationships between TGF beta and IL-1 beta on chondrocytes have implications for cartilage repair.
The binding of 3H-CN-IMI to 5-HT uptake sites, as measured by quantitative autoradiography, was used as a marker of serotonergic neurons. Within the dorsal raphe nucleus the binding of 3H-CN-IMI was compared in adjacent coronal sections of rat brain to the binding of 3H-DPAT to 5-HT1A receptors, which have a known somatodendritic localization. The heterogeneous pattern of binding of these two radioligands within the dorsal raphe nucleus was similar and corresponded to the distribution of serotonergic cell bodies as visualized by 5-HT immunohistochemistry. Intracerebroventricular administration of 5,7-dihydroxytryptamine (5,7-DHT), which caused a dramatic loss of 5-HT immunoreactivity and 3H-DPAT binding to 5-HT1A receptors, resulted in a marked reduction of 3H-CN-IMI binding in this nucleus. Treatment of rats with a dose of para-chloroamphetamine (PCA) which has been reported to selectively lesion serotonergic processes arising from the dorsal raphe nucleus, while sparing serotonergic cell bodies and projections from the median raphe nucleus, did not alter the binding of 3H-DPAT or 3H-CN-IMI in the dorsal raphe nucleus; serotonergic cell bodies appeared morphologically unaffected. The lack of effect of PCA treatment on the binding of 3H-DPAT and 3H-CN-IMI is consistent with a somatodendritic localization of the 5-HT transporter in the dorsal raphe nucleus. PCA treatment appeared to produce a moderate loss of serotonergic innervation in serotonergic terminal field areas as visualized by serotonin immunohistochemistry. The reductions in 3H-CN-IMI binding observed in terminal field areas (24 to 69%) following treatment of rats with PCA did not reflect a marked differential innervation of forebrain areas by the dorsal and medial raphe nuclei as expected from previous biochemical studies, and were not entirely consistent with the findings of neuroanatomical studies using histochemical techniques. Site-specific injection of 5,7-DHT into the dorsal raphe nucleus produced an 80 +/- 11% reduction in the binding of 3H-CN-IMI in this nucleus, whereas the binding of 3H-CN-IMI in the median raphe nucleus was not reduced.(ABSTRACT TRUNCATED AT 400 WORDS)
Type II collagen and aggrecan are major components of the extracellular matrix of articular cartilage. Their biosynthesis and catabolism are regulated by chondrocytes. They may be used as markers of chondrocyte phenotype for cells cultured in vitro. Type II collagen gene expression was detected by amplification of type II collagen-specific sequences, using cDNA produced by reverse transcription of mRNA extracted from freshly isolated and cultured human articular chondrocytes by the polymerase chain reaction (PCR). The synthesis of gene product was confirmed by immunohistochemical localization of type II collagen in cartilage sections and in cultured chondrocytes. Aggrecan core protein was also immunolocalized in cartilage sections and in chondrocytes in culture. Expression of type II collagen or aggrecan was not detected immunohistochemically in skin or bone. These results demonstrate that human articular chondrocytes can be characterized in culture, by the combined application of PCR and immunohistochemistry. Interleukin-1beta (IL-1beta) may play an important role in the destruction of cartilage matrix in arthritis, whereas transforming growth factor-beta (TGFbeta) may have an opposing effect and their combined actions may modulate chondrocyte phenotype. The effect of rhIL-1beta and rhTGFbeta on the production of type II collagen by chondrocytes in culture was investigated. It was shown that TGFbeta enhanced the production of type II collagen, localized immunocytochemically, in cultured chondrocytes. IL-1beta inhibited expression of mRNA for type II collagen. The implications of this study, in terms of a better understanding of degenerative cartilage disease, are discussed.
Despite cumulative evidence that the tricyclic drugs result in significant changes in the functioning of brain serotonergic (5-HT) and nordrenergic (NE) systems, such changes have not been found to be associated with recovery from depression. Based upon evidence that the 5-HT and NE systems were associated with different emotions, it was hypothesized that changes in these systems were associated with different components of behavior in drug-responsive patients and not with changes in the "whole" disorder. Findings from this multihospital study of 104 unipolar and bipolar depressed patients showed early drug-associated reductions in anxiety and hostility in treatment responders to precede changes in motor retardation and depressed mood. Adopting this approach of looking for relationships between changes in components of major depression and changes in neurotransmitter system function, decreases in 5-HT and NE metabolite concentrations in cerebrospinal fluid (CSF) in patients treated with tricyclics, were found to be correlated with changes in specific behaviors. Results indicated the following: (1) drug-induced changes in the 5-HT system to be associated with mood aspects, notably anxiety, and depressed mood; changes in NE primarily with the psychomotor, secondarily with the mood components of the depressed state; (2) the pattern of relationships between changes in 5-HT and in mood in the unipolar was different than that in the bipolar subtype. The results indicate that in determining the relationships of biochemical changes to behavioral ones, that it is important to take into account the type of depression (bipolar or unipolar), as well as examining individually and over time those components that make up the disorder of depression. These results support evidence that tricyclics have multiple behavioral actions, that response is mediated through changes in specific behaviors and that this approach warrants further application in prospective studies of antidepressant drug mechanisms and their therapeutic actions.
In the rat, activation of 5-hydroxytryptamine1A (5-HT1A) receptors causes hypothermia and the 5-HT syndrome. The effects of three chemically dissimilar 5-HT1A agonists administered s.c. [8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), gepirone, and (+)4-[n-5-(methoxychroman-3-yl)n-propylamino]butyl-8-azaspiro++ +[4,5] decane-7,adione ((+) S-20499)] on both of these responses were studied. The same maximal drop in body temperature (approximately 2.5 degrees C) was elicited by all three agonists, 8-OH-DPAT being the most potent (EC50 = 0.05 mg/kg), followed by gepirone (1.8 mg/kg) and (+) S-20499 (8 mg/kg). Both pindolol, a nonselective 5-HT1A receptor/beta adrenoceptor antagonist and n-t-butyl,-3-[1-[4-(2-methoxy)phenyl]piperazinyl]-1-phenylpropionamid e [(+) WAY 100135], a more selective 5-HT1A receptor antagonist, dose dependently attenuated the hypothermia induced by all three agonists. From these data, we inferred that all three agonists caused hypothermia via activation of 5-HT1A receptors. The syndrome was observed reliably in rats at doses of 2 to 4 mg/kg 8-OH-DPAT; doses up to 100 mg/kg of gepirone or (+) S-20499 did not produce the syndrome. In reserpine-pretreated animals, 8-OH-DPAT (maximal effect at 2-4 mg/kg) and 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) (5 mg/kg) induced forepaw treading, whereas gepirone (10 mg/kg) and (+) S-20499 (75 mg/kg) did not. (+) WAY 100135 competitively antagonized the forepaw treading caused by 8-OH-DPAT in reserpine-pretreated rats. This indicates that forepaw treading, like hypothermia, is mediated by activation of 5-HT1A receptors. Gepirone (5-10 mg/kg) attenuated the forepaw treading induced by either 8-OH-DPAT (4 mg/kg) or 5-MeODMT (5 mg/kg); by contrast, (+) S-20499, at doses up to 75 mg/kg, did not attenuate the forepaw treading induced by either 8-OH-DPAT or 5-MeODMT. The inability of (+) S-20499 either to induce the 5-HT syndrome or forepaw treading or to attenuate the forepaw treading induced by other agonists could be due to several factors, one of which is that different subtypes of the 5-HT1A receptor mediate hypothermia and the 5-HT syndrome.
The density of alpha 2-adrenoceptors, using 3H-idazoxan as the radioligand, was determined by quantitative autoradiography in the locus coeruleus and in 13 noradrenergic projection fields following chronic administration of drugs acting on noradrenergic and/or serotonergic neurons. Protriptyline, an inhibitor of the uptake or norepinephrine, and mianserin, an alpha 2-adrenoceptor antagonist, reduced the binding of 3H-idazoxan only in the locus coeruleus. Phenelzine, an inhibitor of both type A and type B monoamine oxidase (MAO), reduced the binding of 3H-idazoxan in the locus coeruleus and in several areas with noradrenergic innervation from tegmental cell bodies. Clorgyline, a selective inhibitor of type A MAO, had no effect. Of the two selective inhibitors of serotonin uptake, citalopram caused a modest increase in binding only in one terminal field area, whereas sertraline had no effect. Although these antidepressants did not produce consistent effects on alpha 2-adrenoceptors, protriptyline, mianserin, and phenelzine were similar in that they all decreased the binding of 3H-idazoxan in the locus coeruleus without widely affecting its binding in the coerulean terminal fields. Deprenyl, a selective inhibitor of type B MAO, the only drug in this study without proven antidepressant efficacy, differed from all other drugs in that it decreased the binding of 3H-idazoxan both in the locus coeruleus as well as in most terminal fields with primarily coerulean noradrenergic innervation.
In this study, the radiolabeled 5-hydroxytryptamine1A agonist, [3H]8-hydroxy-N,N-dipropylamino tetralin ([3H]8-OH-DPAT), was shown to have both a high (Kd, 0.7 +/- 0.2 nM) and a low (Kd, 17 +/- 4 nM) affinity binding component in rat hippocampal homogenate preparations in the absence of guanine nucleotides. The high-affinity binding component was markedly reduced by the elimination of Mg++ from the incubation medium and the addition of both the nonhydrolyzable guanine nucleotide guanylylimidodiphosphate (Gpp(NH)p) (100 microM) and 1.0 mM EDTA to the incubation medium. Under these latter conditions, a single binding affinity component was observed with a Kd of 11 +/- 1 nM, a value in good agreement with the value for the low-affinity component measured in the absence of Gpp(NH)p. Further, the Bmax value for the single low-affinity binding component measured in the presence of Gpp(NH)p was essentially equivalent to the total of the two Bmax values found in the absence of Gpp(NH)p. A binding assay was developed using 15 nM [3H]8-OH-DPAT to determine the affinities of serotonergic drugs for the low-affinity component of [3H]8-OH-DPAT binding and these values were compared with their affinities for the high-affinity binding component as well as their potencies in a hippocampal adenylyl cyclase assay. For agonists, the Ki value for the high-affinity binding component was always less than the low-affinity Ki value, whereas the antagonist spiperone had similar values for both the high-affinity and low-affinity binding components.(ABSTRACT TRUNCATED AT 250 WORDS)
In order to develop selective radioactive ligands for the study of presynaptic monoamine uptake sites, iodinated derivatives of tomoxetine were synthesized and evaluated in radioligand binding assays. Iodotomoxetine derivatives showed high affinity for serotonin (5-HT) uptake sites using a rat cortical membrane preparation. Compound 1R,(R)-(-)-N-methyl-3-(4-iodo-2-methylphenoxy)-3-phenylpropanamine , was the most potent and showed high stereoselectivity for 5-HT uptake sites (Ki, R isomer = 0.65 nM, S isomer = 13.9 nM). Changing the position of the methyl group or eliminating the methyl group at the phenoxy ring resulted in a loss of stereoselectivity. Substitution of the methyl group of tomoxetine with iodine gave the R and S isomers of N-methyl-3-(2-iodophenoxy)-3-phenylpropanamine 4R and 4S. These compounds displayed stereoselectivity for the norepinephrine (NE) (Ki values = 0.24 and 9.35 nM for R and S isomers, respectively). The in vitro binding data suggest that 1R and 4R are potential radioiodinated ligands for pharmacological studies of 5-HT and NE uptake sites, respectively.
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The Transforming Growth Factor-beta (TGF beta) family of polypeptides elicits diverse biological actions on a wide range of cell types. There are known to be several isoforms of TGF beta coded for by different genes, with possibly differential expression and potencies. We have demonstrated that there is constitutive expression of three forms of transforming growth factor beta in adult human articular chondrocytes. The presence of 10% fetal calf serum in the culture medium may influence expression. The addition of transforming growth factor beta or interleukin 1 beta to the culture medium does not appear to consistently influence the expression of TGF beta by the cells.
1-Isoproterenol has equal affinity for beta 1- and beta 2-adrenoceptors and is a full agonist at both subtypes. However, when infused in vivo into the rat brain, it has been shown to induce a preferential reduction of central beta 2-adrenoceptors. To investigate this phenomenon further, in the present study rats were infused centrally with higher doses of 1-isoproterenol (15 or 45 micrograms/h). Furthermore, isoproterenol was infused into rats lesioned neonatally with 6-hydroxydopamine (6-OHDA). Subtypes of beta-adrenoceptors were measured by quantitative autoradiography of the binding of [125I]iodopindolol ([125I]IPIN). In sham lesioned rats, infusions of isoproterenol at both doses caused comparable reductions in the density of [125I]IPIN binding sites in many brain regions. The binding to beta 2-adrenoceptors was decreased in a larger number of brain areas than the binding to beta 1-adrenoceptors and the magnitude of the reduction was greater for beta 2- than for beta 1-adrenoceptors. However, isoproterenol at these doses did produce greater effects on the beta 1-subtype than those found previously with a lower dose. Treatment with 6-OHDA induced significant increases in the binding of [125I]IPIN to both beta 1- and beta 2-adrenoceptors in cerebral cortical and hippocampal areas, indicating that endogenous norepinephrine may regulate both subtypes in these regions. Even in the 6-OHDA-lesioned rats, the binding of [125I]IPIN to beta 2-adrenoceptors was reduced to a greater extent that the binding to beta 1-adrenoceptors. Thus, these studies demonstrate that the non-selective beta-adrenergic agonist isoproterenol induces a preferential regulation of beta 2-adrenoceptors, even at relatively high doses and in norepinephrine-depleted animals.