Mood disorder Flashcards
Axelrod 1970
Awarded Nobel Prize 1970 - for his work on catecholamine metabolism - showed that reuptake is a principal mechanism for NT inactivation (at the time, it was assumed that NTs were inactivated enzymatically only by MAO - however when MAO was almost completely ohibited in vivo, the physiological actions of injected NA were still ended - so must be other mechanisms) . His lab director provided hum with samples of [3H]adrenaline. When [3H]adrenaline or [3H]noradrenaline was injected intocats, the radiolabel concentrated in tissues enriched in sympathetic nerve endings (heart, spleen, salivary, adrenal glands), long after physiological effects ended (stay in the nerves). Then did unilateral lesions of the sympathic nerves.When [3H-noradrenaline was injected it accumulated on innervated side but not the denervated side. Showed stored in sympathetic nerves. Axelrod postulated reuptake. Then found ADs can act in this was, spawned the modern generation of ADs (e.g. fluoxetine)
Selikoff and Robitzek (1952)
- The monoamine hypothesis was based on the serendipitous discoveries of Selikoff and Robitzek (1952), who noted that patients in a tuberculosis chemotherapy trial testing hydrazine derivatives of isonicotinic acid “exhibited renewed vigor”.
Smith 1953
published a trial of 11 patients suffering from depression treated with iproniazid (a monoamine oxidase inhibitor, MAOI); 2 patients showed improvements in appetite, vitality and sleep.
Kuhn in 1958
he treated >500 psychiatric patients with imipramine (a tricyclic compound) and obtained the best results with endogenous depression, reducing fatigue, hopelessness, motor retardation and other symptoms of depression. o Although he noted the drug to have some efficacy in neurosis, schizophrenia and other forms of depression (especially in combination with chlorpromazine or ECT), it exacerbated psychosis in some cases of depression associated with organic brain damage or schizophrenic psychosis. He said → ‘The sense of oppression in the chest gives way to a feeling of relief’ In the 500 pts treated with imipramine, there were no serious side effects - vast improvement of MAOIs
Wong et al 1975
Control and drug-treated rats - synaptosomes were obtained via homogenisation and centrifugation-fractionation, then incubated with dopamine, NA , 5-HT. Observed that in vitro following intraperitoneal administration (did this before), the compound inhibited 5-HT reuptake but had no effect on other monoamines. they found this inhibition occurs significantly only 15 minutes after administration
Smith 1997 Lancet
showed that rapid depletion of tryptophan can induce relapse of depression in vulnerable individuals; tryptophan is the amino acid precursor of 5-HT and cannot be synthesized by the body (must be ingested to enable the formation of 5-HT) o Took 15 drug-free women who had suffered recurrent major depressive episodes but currently recovered gave them one of two AA mixtures in a double-blind fashion One = nutritionally balanced w tryptophan Other = identical but no tryptophan o After 7h, women who drunk tryptophan-free mixture experienced 75% decrease in tryptophan levels. 10/15 of them also scored sig higher on Hamilton rating scale for depression; showed temporary but clinically sig depressive symptoms • In contrast, no mood change observed after taking balanced mixture Limitation → trypophan depletion has since shown to affect women more - maybe this made the results seem more severe than they actually are?
Caspi et al 2003
showed, in a prospective-longitudinal study of a birth cohort of 847 subjects, that individuals who were homozygous or heterozygous for the s allele, were more likely to develop depressive symptoms, diagnosable depression and suicidality after stressful life events than individuals who were homozygous for the l allele
Culverhouse et al 2018
performed the largest study with consistent statistical analysis of all samples thus far, on the effect interaction between 5-HTTLPR genotype and stress exposure has on development of MDD, finding no statistically significant interaction. This collaborative group of authors concluded that if there is an interaction present, it must be of ‘modest effect size and only observable in limited situations’
Uher and McGuffin 2009
34 observational studies, demonstrated a relationship between the method used to assess environmental adversity and the results of studies linking such adversity and 5-HTTLPR to MDD
Bonk et al 2020
. The group used two different cohorts assessed using questionaries (BDI-II and PHQ-9) and interview procedures (DSM-IV). It was found that s allele carriers that had experienced childhood abuse and had low serum 25-hydroxyvitamin D (25(OH)D) levels had a higher BDI-II score than those with higher 25(OH)D levels, and this was not seen in ll carriers. They further used a functional polymorphism, rs4588, of vitamin D binding protein as a proxy for 25(OH)D serum levels to independently validate these results. This paper adds to the argument presented by Culverhouse et al. because the two-way GxE interaction of 5-HTTLPR and childhood trauma on BDI-II, when assessed in this paper, was also not significant, and only became significant when 25(OH)D serum level or different rs4588 genotypes were considered. Because 25(OH)D has been shown to stimulate the expression of the rate-limiting enzyme in 5-HT synthesis, tryptophan hydroxylase, the authors suggest that 5-HTTLRP genotype may only exert effects on mood when other threats to 5-HT homeostasis are present as well19. Although the limitations of this study include the fact that BDI-II only provides estimate for number of depressive symptoms and may not reflect clinical MDD, and the fact that different vitamin D metabolites were not considered, this study adds to evidence suggesting vitamin D supplementation as a treatment for depressive symptoms.
Van IJzendoorn et al. (2010)
used the Berkely Adult Attachment interview, used as a measure of a subject’s unresolved trauma, on 143 participants. They compared the results of this with the patient’s 5-HTT genotype and to the methylation ratios of the CpG residues, using quantitative mass spectrometry. It was found that more unresolved trauma in patients with the l variant was associated with higher methylation of SLC6A4, which the authors suggest augments the otherwise protective ll genotype.
, Aberg et al. (2018)
Irecently published the first large-scale methylome-wide association study (MWAS) for MDD
- compiled using both blood samples from 1132 individuals and identifying regions of overlap between CpG sites of these and post-mortem brain samples from 61 individuals with MDD.
- Most notably, they identified three novel differentially methylated loci associated with MDD, that overlapped with the blood and the brain; these were an intergenic region on chromosome 2, GABBR2 (coding for a GABAB receptor), and RUFY3 (implicated in normal axon elongation)25. This study identified methylation sites in the blood, which overlap with methylation sites in the brain, that have potential serve as biomarkers for MDD and may expand on current mechanism underpinning the disorder.
- However, certain limitations of this study must also be considered, such as the fact that samples were taken from bulk tissues rather than specific cell types and that brain methylation profiles have been shown to complex and may also include methylation outside of CpG sites and hypermethylation.
Parsey 2006
used PET imaging with the 11[C]-WAY-100635 radioligand to determine 5-HT1A binding potential o Found sig greater binding potential in brains of medication-free MDD subjects during a major depressive episode compared to controls o Since 5-HT1A is a presynaptic inhibitory autoreceptor, this indicates greater autoinhibition of 5-HT release in MDD individuals would reduce 5-HT release
Meyer 2006
used 11[C]-harmine to label MAO-A in a group undergoing a major depressive episode + a healthy group o They found elevated MAO-A density by an average of 34% in the depressive group compared to control o Since MAO-A breaks down monoamines, this supports the MA hypothesis
Santarelli et al 2003
chronic, but not acute fluoxetine (SSRI) administration increased the number of BrdU-positive cells in the dentate gyrus of mice, indicating increased neurogenesis. They further disrupted neurogenesis by X-irradiation and found that chronic treatment with fluoxetine reduced latency to feeding in novelty-suppressed feeding tests, and also improved fur condition due to increase grooming in chronic unpredictable stress tests in sham mice; these changes were absent in irradiation mice, indicating that antidepressants require neurogenesis in order to mediate their effects
Snyder et al 2011
produced selective depletion of dividing hippocampal dentate gyrus stem cells by administering valganciclovir to mice expressing HSV-thymidine kinase under the GFAP promoter (expressed by SCs and astrocytes, although no of astrocytes was unaltered). TK renders mitotic cells sensitive to valganciclovir by spares post-mitotic cells. These mice showed significantly greater immobility in the forced swim test and significantly reduced sucrose preference. However, these mice only showed increased latency to feed after restraint stress, indicating that the there is an interaction between lack of neurogenesis and environmental factors in this particular test
Vetencourt 2008
Chronic administration of fluoxetine reinstates ocular dominance plasticity in adulthood and promotes the recovery of visual functions in adult amblyopic animals, as tested electrophysiologically and behaviourally
Siuciak et al 1997
rats preconditioned to learned helplessness box 2 compartemtns, continually shocked every minute for 2 hours regardless of compartment Then moved to similar box but only shocked in one compartment Preconditioned animals escape with 47% less frequency and 5x more latency than controls However, infusion of BDNF into rats midbrain reversed these effects no sig difference
Tsankova et al 2006
demonstrated that chronic social defeat in mice was associated with a significant decrease in BDNF III and IV expression, and, using hippocampal ChIP assays they found significantly higher H3-K27 and H3-K9 dimethylation at BDNF III and IV promoters. These epigenetic modifications indicate transcriptional repression and were reversed following chronic tricyclic antidepressant (imipramine) administration31. This demonstrates a role for epigenetic modification of BDNF in mechanisms underlying depression
Chottekalapanda et al 2020
Using qPCR that c-Fos, which forms the AP-1 dimer with c-Jun, was the earliest induced TF (induced after 9 days) in mice in response to fluoxetine
used Ingenuity Pathway Analysis to implicate that overlapping gene targets of both c-Fos and c-Jun these regulate pathways such as neuronal morphology, remodelling and homeostasis. They then tested whether MDD-associated genes identified in previous GWAS studies had any overlap with the gene targets of the two transcription factors and found in particular Bdnf and S100a10 (p11) which had known links to depression and antidepressant responses, with the interaction between AP-1 and S100a10 confirmed by ChIP-seq
Casarotto et al 2021
Background: BDNF mediates effects through tyrosine kinase receptor 2 (TRKB). They did a series of elegant studies setting out to investigate whether ADs have direct action on BDNF-TRKB system and to clarify modulators of this function - e.g. cholesterol
Key: That ADs can directly bind to and cause membrane translocation of TRKB. Did ligand binding assays in cell lines expressing TRKB. Saw that biotinylated fluoxetine binds to immunoprecipitated TRKB with a LOW MICROMOLAR AFFINITY but not to TRKA or lysates from non-transfected cells (cells lacking both receptors). Also did not bind to TRKB lacking the TMD or TRKB (chimeric w TRKA) ~ this was the binding site ~ bound even when EC and IC domains were deleted and only the TMD remained. This was confirmed using an MST and PLA assay and also confirmed with other ADs (incl imipramine, ket and RR-HNK). Further showed that binding of labelled FLX was displaced by unlabelled FLX, imipramine, RR-HNK, KET and esketamine – have at least overlapping sites - first unifying mechanism for biological actvity
Hypothesized direct interaction between TRKB and cholesterol. Showed TRKB also binds chol. Using MST - microscale thermophoresis - they showed that chol direct interacts with GFP-TRKB in cell lysates with an affinity of ~20um. Mutation in TMD region of TRKB suspected to bind chol blocks this interaction in MST (Y334F). Mutation of this residue also abolished AD binding and AD effects.
BrdU incorporation – FLX sig increased survival of newborn hippocampal neurons in wt mice but not in the DG of mice with the mutant unable to bind chol and ADs
Experiments looking at ocular dominance (OD) - OD shift following monocular deprivation usually - FLX given to mice for 4 weeks given FLX = shift to the open eye, same for KET and R,R-HNK - This shift was lost in mutant mice and wt mice treated with pravastatin (HMG CoA reductase inhibitor) – indicating plasticity effects of ADs may be mediated by direct binding to TRKB
They gave fluoxetine for 7 days to mice and then did the object location memory test (OLM). One group had wt TRKB and the other had TRKB mutant unable to bind cholesterol and ADs (elucidated to bind ADs through molecular dynamics simulations)
- Found that mutant = impaired long-term memory following fluoxetine, suggesting no LTP/plasticity
- Fluoxetine also did not enhance memory in BDNF haploinsufficient mice, 5-HTT KO mice and mice cotreated with HMG-CoA reductase
- Fluoxetine and ket reduce immobility time in FST and enhanced fear extinction in wt but not mutant mice where TRKB is unable to respond to cholesterol
Criticisms: see AR spreadsheet
Future: Design of TrkB modulators - now an attractive target
Fava et al 2016
described a placebo-controlled double-blind phase 1b trial involving 24 patients with MDD. They investigated the effects of daily dosing of NSI-189, a compound that had previously been shown to stimulate neurogenesis of human hippocampus-derived neural stem cells in vitro and neurogenesis in mouse hippocampus in vivo. The group observed a clinically meaningly reduction in depressive and cognitive symptoms following 28 days of treatment
Berman et al 2000
First placebo controlled trial of ketamine 7 patients w MDD IV ket vs placebo Sig improvment in depressive symptoms with 72 hours after ketamine on Hamilton Depression Rating Scale
Zarate et al 2006
Study of 17 pts with TRMDD - 71% of participants had >50% reduction in depressive symptoms within 24 hours of ketamine whereas the same pts had no chnages in symptoms after placebo saline. The response was sustained for 1 week of follow-up in about a third of participants
Breier et al 1997
PET to determine metabolic activity in 17 healthy volunteers while being given subanasthetic doses of ketamine - found ketamine produced focal increases in metabolic activity in the PFC
Moghaddam et al 1997
Ketamine administration in rats results in a significant increase in EC glutamate levels in the PFC - used intracerebral microdialysis in the awake rat
Laje et al 2012
major depressed pts carrying the Met rs6265 allele do not respond to ketamine - this is a SNP that induces deficits in BDNF processing - further suggests BDNF synthesis is important for ketamine
Pozzi et al 2014
Mice lacking NMDAR (subunit GluN1) in parvalbumin-expressing interneurons, designed to mimic disinhibition of pyramidal cell activity, retained ketamine induced AD activity (no differences in repeated FST or in a sucrose preference test)
Autry et al 2011
- Administered ket to BDNF to inducible KO BDNF mice
- Looked at FST behaviour
- WT controls showed reductions in immobility (AD effect) whereas ket had no effect on the KOs (no AD effect)
- BDNF protein synthesis increased following ketamine treatment as shown by Western blot at 30 minutes in hippocampal cells
- Whole-cell patch-clamp recordings - in hippocampal neurons in vitro they recorded NMDA-mEPSCs after ketamine infusion - detected a significant decrease of mEPSCs within minutes
- Then did Western blot and after 30 mins of ket administration there were rapid decreases in phosphorylated eEF2 in HC compared to vehicle-treated cells → suggested that ketamine leads to dephosphorylation of eEF2
- They then administered eEFK2 inhibitors to normal mice = AD response. When they administered to BDNF KOs and tested FST behaviour. This was ineffective in BDNF KOs - shows requirement for increased BDNF expression upon eEF2 inhibition to produce AD-like behavior
- Supports the hypothesis that ket inhibits spontaneous NMDA-mEPSCs, leading to decerased eEF2 kinase activity, permitting rapid increased in BDNF translation which may exert strong influences on synaptic strength
Abdallah et al 2020 Nature
20 pts suffering major depressive episode were pretreated with oral rapamycin or placebo 2h prior to IV ketamine. Depression severity assessed using Mongomery-Asberg Rating Scale. 2 major findings Rapamycin pts saw the same benefit of ketamine as those who received placebo at 24h - rapamycin did not block the effects of ketamine as seen in animal studies When patients took rapamycin prior to receiving ketamine, 41% still showed a clinical antidepressant response after two weeks, with 29% in full remission. This compared with 13% response and 7% remission when placebo was given prior to ketamine instead of rapamycin. In other words, rapamycin pretreatment apparently extended ketamine’s antidepressant effectiveness, for at least some patients. Limitations - Anti-inflammatory (immune suppressive kidney transplant) - may be anti-depressive and confound
Zanos 2016
Chemically altered ketamine via deuteration at the C6 position, which did not change its binding affinity for the NMDAR but dramatically decreased its in vivo metabolism to HNK. This manipulation prevent ketamine’s AD actions in mice - no AD actions in FST or LH 24 hours after administration
Greater AD behavioural responses of a single administration of ketamine have been observed in female compared to male rats and mice - in mice this behavioural effect was associated with (3 fold) higher brain levels of HNK, but not ketamine or norketamine levels, supporting the role of this metabolite in the AD actions of ketamine
Cav - Studies in mice have inherent difficulties in translation into therapeutic mechanism into humans… 10uM used is approx 60-fold higher than plasma than the plasma Cmax (peak serum conc) observed in bipolar depressed pts receiving 0.5mg/kg ketamine IV… this was when assessing transmission in rat hippocampal slices…also no data of intraperitoneal administration of ketamine in humans - might differ
Williams 2018
RCT trying to determine if opoid receptor antagonism prior to IV ket attenuates AD effects - pts treated with ketamine + opoid antagonist or ketamine +placebo - treated with opoid antagonist/placebo prior to ketamine, in 12 pts, ketamine +naloxone Hamilton Depression rating cale was sig lower than ket + placebo post-infusion days 1 and 3. Concluded ketamines AD effect appears to require opioid system activation. Limitations - there was no placebo control arm for the ketamine infusion (e.g. naltrexone + IV saline and placebo + IV saline) impedes evaluation of the specificity of the antagonist + ketamine effect, also, they could have included pharmacodynamic markers of keta opioid essay, for example, they could have looked that miosis and see if this is blocked by naltrexone Future - Human radioligand PET studies with mu-opioid tracers should examine ketamne’s binding affinity at clinically relevant doses
Ed Domino
largely responsible for introducing ketamine into clinic practice as an anaethetic - described individuals who received ketamine as ‘disconnected from their environment somehow’
Davis et al 2020
Two doses of psilocybin and supportive psychotherapy resulted in rapid, significant AD effects. Around 67% of participants experienced a 50% reduction in symptoms. These effects appear to be lasting. By 4 weeks after treatment, 54% of the participants were no longer depressed. 24 people involved with long-term his Small + preliminary, need to be validated in a sham-controlled study - cant give it to addicts, schizophrenics and prdromal schizophrenics Perhaps a psychodelic experience?
Klein et al 2020
Ket does not act as an opiate but requires both NMDA and opiate receptors. They found that opiate antagonist pretreatment blocked acute effects of ketamine in congenitally learned helplessness (cLH) mice. Lateral habenula hyperactivity known to occur rin animals with depressive-like behaviours. Then saw that ket blocks hyperactivity in lateral habeula neurons from cLH rats, and this was blocked by opiate antagonist. Opiate antagonist alone did not have an effect on lateral habenula. Specific NDMA antagonist decreased LHb activity to as similar degree as ket and adding ket after did not decrease it more. Opioid receptors needed but not sufficient alone for the AD effect - shown both cellularly and behaviourally
Cav - Ket is known to have lasting (up to 1 week) effects - sustained effects were not trested in cLH rats, general drawbacks of cLH as opposed to inescapable shock-induced LH model = you cant compare LH and non-LH (resilient rats), genetic basis of cLH is unknown
Future direction - effects on depression-like behaviours in rodents exposed to stress needed
Mathai et al 2020
They did a systematic review that demonstrated inconsistent relationship between ketamine’s dissociative and AD effects. Looked at 8 studies in total. Found that only 3 of these observed a relationship between Clinician-Administered Dissociative States Scale (CADSS) and AD response. Within the papers that reported a significant relationship, the explained vriance of dissociative experiences for AD response was 12-21%
Musselman 2001
conducted a double-blind study on 40 patients with malignant melanoma who received IFN-α therapy; half the group was given paroxetine (SSRI) and the other half was given placebo. Development of depressive symptoms was significantly reduced in the paroxetine group compared to control, showing that the IFN-α behavioural syndrome is sensitive to regular antidepressants.
Köhler et al. (2014) –
“carried out systematic review including 10 trials investigating NSAIDS + 4 trials investigating cytokine inhibitors as potential ADs o They found evidence that anti-inflammatory treatment, particularly celecoxib, reduced depressive symptoms”
Singh et al 2013
screened a clinical collection of around 450 drugs for efficacy at inhibiting inositol monophosphatase, identified organic molecule called ebselen able to do this, which could inhibit in vitro and in vivo with similar effects to lithium & used a human IMPase assay to demonstrate IMPase inhibition by ebselen. • Ebselen reduced manic-like behaviour in mice, including rearing in the open field test and amphetamine-induced hyperactivity • To confirm the importance of inositol depletion, intracerebroventricular injection of inositol reversed the behavioural effects of ebselen.
Fava et al 2020
TRD individuals randomined to get IV ket (0.1, 0.2, 0.5 or 1.0 mg/kg) ro active control (midazolam). Higher doses produced higher CADSS scores than lower but higher did not result in greater AD efficacy than the 0.5mg/kg dose. No sig correlation between CADSS and HAM-D-6 score.
cav - Small sample size and the fact that concomitant medication was allowed
September 2021 Cochrane Review
Looked at 31 studies of ketamine and other glutamate receptor modulators for MDD. Concludes that symptoms of depression reduced and agrees with use of ket for MDD but states all trials were short term (don’t know long-term effects), inflated bias, problems with IV. Not many trials in each meta-analysis. Say confidence in findings is limited.
Sharpley 2020
60 BPD pts treated with the drug or placebo - outcome determined on Young Mania Rating Scale and showed a 4.2 point difference in reduction (0<0.058, not sig) – numerical but not statistical significance - althoguh CGI-s score was significantly lower (Clinical GLobal impression) secondary outcome - better controlled studies needed for this
Awarded Nobel Prize 1970 - for his work on catecholamine metabolism - showed that reuptake is a principal mechanism for NT inactivation (at the time, it was assumed that NTs were inactivated enzymatically only by MAO - however when MAO was almost completely ohibited in vivo, the physiological actions of injected NA were still ended - so must be other mechanisms) . His lab director provided hum with samples of [3H]adrenaline. When [3H]adrenaline or [3H]noradrenaline was injected intocats, the radiolabel concentrated in tissues enriched in sympathetic nerve endings (heart, spleen, salivary, adrenal glands), long after physiological effects ended (stay in the nerves). Then did unilateral lesions of the sympathic nerves.When [3H-noradrenaline was injected it accumulated on innervated side but not the denervated side. Showed stored in sympathetic nerves. Axelrod postulated reuptake. Then found ADs can act in this was, spawned the modern generation of ADs (e.g. fluoxetine)
Axelrod 1970
- The monoamine hypothesis was based on the serendipitous discoveries of Selikoff and Robitzek (1952), who noted that patients in a tuberculosis chemotherapy trial testing hydrazine derivatives of isonicotinic acid “exhibited renewed vigor”.
Selikoff and Robitzek (1952)
published a trial of 11 patients suffering from depression treated with iproniazid (a monoamine oxidase inhibitor, MAOI); 2 patients showed improvements in appetite, vitality and sleep.
Smith 1953
he treated >500 psychiatric patients with imipramine (a tricyclic compound) and obtained the best results with endogenous depression, reducing fatigue, hopelessness, motor retardation and other symptoms of depression. o Although he noted the drug to have some efficacy in neurosis, schizophrenia and other forms of depression (especially in combination with chlorpromazine or ECT), it exacerbated psychosis in some cases of depression associated with organic brain damage or schizophrenic psychosis. He said → ‘The sense of oppression in the chest gives way to a feeling of relief’ In the 500 pts treated with imipramine, there were no serious side effects - vast improvement of MAOIs
Kuhn in 1958
Control and drug-treated rats - synaptosomes were obtained via homogenisation and centrifugation-fractionation, then incubated with dopamine, NA , 5-HT. Observed that in vitro following intraperitoneal administration (did this before), the compound inhibited 5-HT reuptake but had no effect on other monoamines. they found this inhibition occurs significantly only 15 minutes after administration
Wong et al 1975
showed that rapid depletion of tryptophan can induce relapse of depression in vulnerable individuals; tryptophan is the amino acid precursor of 5-HT and cannot be synthesized by the body (must be ingested to enable the formation of 5-HT) o Took 15 drug-free women who had suffered recurrent major depressive episodes but currently recovered gave them one of two AA mixtures in a double-blind fashion One = nutritionally balanced w tryptophan Other = identical but no tryptophan o After 7h, women who drunk tryptophan-free mixture experienced 75% decrease in tryptophan levels. 10/15 of them also scored sig higher on Hamilton rating scale for depression; showed temporary but clinically sig depressive symptoms • In contrast, no mood change observed after taking balanced mixture Limitation → trypophan depletion has since shown to affect women more - maybe this made the results seem more severe than they actually are?
Smith 1997 Lancet
showed, in a prospective-longitudinal study of a birth cohort of 847 subjects, that individuals who were homozygous or heterozygous for the s allele, were more likely to develop depressive symptoms, diagnosable depression and suicidality after stressful life events than individuals who were homozygous for the l allele
Caspi et al 2003
performed the largest study with consistent statistical analysis of all samples thus far, on the effect interaction between 5-HTTLPR genotype and stress exposure has on development of MDD, finding no statistically significant interaction. This collaborative group of authors concluded that if there is an interaction present, it must be of ‘modest effect size and only observable in limited situations’
Culverhouse et al 2018
34 observational studies, demonstrated a relationship between the method used to assess environmental adversity and the results of studies linking such adversity and 5-HTTLPR to MDD
Uher and McGuffin 2009
. The group used two different cohorts assessed using questionaries (BDI-II and PHQ-9) and interview procedures (DSM-IV). It was found that s allele carriers that had experienced childhood abuse and had low serum 25-hydroxyvitamin D (25(OH)D) levels had a higher BDI-II score than those with higher 25(OH)D levels, and this was not seen in ll carriers. They further used a functional polymorphism, rs4588, of vitamin D binding protein as a proxy for 25(OH)D serum levels to independently validate these results. This paper adds to the argument presented by Culverhouse et al. because the two-way GxE interaction of 5-HTTLPR and childhood trauma on BDI-II, when assessed in this paper, was also not significant, and only became significant when 25(OH)D serum level or different rs4588 genotypes were considered. Because 25(OH)D has been shown to stimulate the expression of the rate-limiting enzyme in 5-HT synthesis, tryptophan hydroxylase, the authors suggest that 5-HTTLRP genotype may only exert effects on mood when other threats to 5-HT homeostasis are present as well19. Although the limitations of this study include the fact that BDI-II only provides estimate for number of depressive symptoms and may not reflect clinical MDD, and the fact that different vitamin D metabolites were not considered, this study adds to evidence suggesting vitamin D supplementation as a treatment for depressive symptoms.
Bonk et al 2020
used the Berkely Adult Attachment interview, used as a measure of a subject’s unresolved trauma, on 143 participants. They compared the results of this with the patient’s 5-HTT genotype and to the methylation ratios of the CpG residues, using quantitative mass spectrometry. It was found that more unresolved trauma in patients with the l variant was associated with higher methylation of SLC6A4, which the authors suggest augments the otherwise protective ll genotype.
Van IJzendoorn et al. (2010)
Irecently published the first large-scale methylome-wide association study (MWAS) for MDD
- compiled using both blood samples from 1132 individuals and identifying regions of overlap between CpG sites of these and post-mortem brain samples from 61 individuals with MDD.
- Most notably, they identified three novel differentially methylated loci associated with MDD, that overlapped with the blood and the brain; these were an intergenic region on chromosome 2, GABBR2 (coding for a GABAB receptor), and RUFY3 (implicated in normal axon elongation)25. This study identified methylation sites in the blood, which overlap with methylation sites in the brain, that have potential serve as biomarkers for MDD and may expand on current mechanism underpinning the disorder.
- However, certain limitations of this study must also be considered, such as the fact that samples were taken from bulk tissues rather than specific cell types and that brain methylation profiles have been shown to complex and may also include methylation outside of CpG sites and hypermethylation.
, Aberg et al. (2018)
used PET imaging with the 11[C]-WAY-100635 radioligand to determine 5-HT1A binding potential o Found sig greater binding potential in brains of medication-free MDD subjects during a major depressive episode compared to controls o Since 5-HT1A is a presynaptic inhibitory autoreceptor, this indicates greater autoinhibition of 5-HT release in MDD individuals would reduce 5-HT release
Parsey 2006
used 11[C]-harmine to label MAO-A in a group undergoing a major depressive episode + a healthy group o They found elevated MAO-A density by an average of 34% in the depressive group compared to control o Since MAO-A breaks down monoamines, this supports the MA hypothesis
Meyer 2006
chronic, but not acute fluoxetine (SSRI) administration increased the number of BrdU-positive cells in the dentate gyrus of mice, indicating increased neurogenesis. They further disrupted neurogenesis by X-irradiation and found that chronic treatment with fluoxetine reduced latency to feeding in novelty-suppressed feeding tests, and also improved fur condition due to increase grooming in chronic unpredictable stress tests in sham mice; these changes were absent in irradiation mice, indicating that antidepressants require neurogenesis in order to mediate their effects
Santarelli et al 2003
produced selective depletion of dividing hippocampal dentate gyrus stem cells by administering valganciclovir to mice expressing HSV-thymidine kinase under the GFAP promoter (expressed by SCs and astrocytes, although no of astrocytes was unaltered). TK renders mitotic cells sensitive to valganciclovir by spares post-mitotic cells. These mice showed significantly greater immobility in the forced swim test and significantly reduced sucrose preference. However, these mice only showed increased latency to feed after restraint stress, indicating that the there is an interaction between lack of neurogenesis and environmental factors in this particular test
Snyder et al 2011
Chronic administration of fluoxetine reinstates ocular dominance plasticity in adulthood and promotes the recovery of visual functions in adult amblyopic animals, as tested electrophysiologically and behaviourally
Vetencourt 2008
rats preconditioned to learned helplessness box 2 compartemtns, continually shocked every minute for 2 hours regardless of compartment Then moved to similar box but only shocked in one compartment Preconditioned animals escape with 47% less frequency and 5x more latency than controls However, infusion of BDNF into rats midbrain reversed these effects no sig difference
Siuciak et al 1997
demonstrated that chronic social defeat in mice was associated with a significant decrease in BDNF III and IV expression, and, using hippocampal ChIP assays they found significantly higher H3-K27 and H3-K9 dimethylation at BDNF III and IV promoters. These epigenetic modifications indicate transcriptional repression and were reversed following chronic tricyclic antidepressant (imipramine) administration31. This demonstrates a role for epigenetic modification of BDNF in mechanisms underlying depression
Tsankova et al 2006
Using qPCR that c-Fos, which forms the AP-1 dimer with c-Jun, was the earliest induced TF (induced after 9 days) in mice in response to fluoxetine
used Ingenuity Pathway Analysis to implicate that overlapping gene targets of both c-Fos and c-Jun these regulate pathways such as neuronal morphology, remodelling and homeostasis. They then tested whether MDD-associated genes identified in previous GWAS studies had any overlap with the gene targets of the two transcription factors and found in particular Bdnf and S100a10 (p11) which had known links to depression and antidepressant responses, with the interaction between AP-1 and S100a10 confirmed by ChIP-seq
Chottekalapanda et al 2020
Background: BDNF mediates effects through tyrosine kinase receptor 2 (TRKB). They did a series of elegant studies setting out to investigate whether ADs have direct action on BDNF-TRKB system and to clarify modulators of this function - e.g. cholesterol
Key: That ADs can directly bind to and cause membrane translocation of TRKB. Did ligand binding assays in cell lines expressing TRKB. Saw that biotinylated fluoxetine binds to immunoprecipitated TRKB with a LOW MICROMOLAR AFFINITY but not to TRKA or lysates from non-transfected cells (cells lacking both receptors). Also did not bind to TRKB lacking the TMD or TRKB (chimeric w TRKA) ~ this was the binding site ~ bound even when EC and IC domains were deleted and only the TMD remained. This was confirmed using an MST and PLA assay and also confirmed with other ADs (incl imipramine, ket and RR-HNK). Further showed that binding of labelled FLX was displaced by unlabelled FLX, imipramine, RR-HNK, KET and esketamine – have at least overlapping sites - first unifying mechanism for biological actvity
Hypothesized direct interaction between TRKB and cholesterol. Showed TRKB also binds chol. Using MST - microscale thermophoresis - they showed that chol direct interacts with GFP-TRKB in cell lysates with an affinity of ~20um. Mutation in TMD region of TRKB suspected to bind chol blocks this interaction in MST (Y334F). Mutation of this residue also abolished AD binding and AD effects.
BrdU incorporation – FLX sig increased survival of newborn hippocampal neurons in wt mice but not in the DG of mice with the mutant unable to bind chol and ADs
Experiments looking at ocular dominance (OD) - OD shift following monocular deprivation usually - FLX given to mice for 4 weeks given FLX = shift to the open eye, same for KET and R,R-HNK - This shift was lost in mutant mice and wt mice treated with pravastatin (HMG CoA reductase inhibitor) – indicating plasticity effects of ADs may be mediated by direct binding to TRKB
They gave fluoxetine for 7 days to mice and then did the object location memory test (OLM). One group had wt TRKB and the other had TRKB mutant unable to bind cholesterol and ADs (elucidated to bind ADs through molecular dynamics simulations)
- Found that mutant = impaired long-term memory following fluoxetine, suggesting no LTP/plasticity
- Fluoxetine also did not enhance memory in BDNF haploinsufficient mice, 5-HTT KO mice and mice cotreated with HMG-CoA reductase
- Fluoxetine and ket reduce immobility time in FST and enhanced fear extinction in wt but not mutant mice where TRKB is unable to respond to cholesterol
Criticisms: see AR spreadsheet
Future: Design of TrkB modulators - now an attractive target
Casarotto et al 2021
described a placebo-controlled double-blind phase 1b trial involving 24 patients with MDD. They investigated the effects of daily dosing of NSI-189, a compound that had previously been shown to stimulate neurogenesis of human hippocampus-derived neural stem cells in vitro and neurogenesis in mouse hippocampus in vivo. The group observed a clinically meaningly reduction in depressive and cognitive symptoms following 28 days of treatment
Fava et al 2016
First placebo controlled trial of ketamine 7 patients w MDD IV ket vs placebo Sig improvment in depressive symptoms with 72 hours after ketamine on Hamilton Depression Rating Scale
Berman et al 2000
Study of 17 pts with TRMDD - 71% of participants had >50% reduction in depressive symptoms within 24 hours of ketamine whereas the same pts had no chnages in symptoms after placebo saline. The response was sustained for 1 week of follow-up in about a third of participants
Zarate et al 2006
PET to determine metabolic activity in 17 healthy volunteers while being given subanasthetic doses of ketamine - found ketamine produced focal increases in metabolic activity in the PFC
Breier et al 1997
Ketamine administration in rats results in a significant increase in EC glutamate levels in the PFC - used intracerebral microdialysis in the awake rat
Moghaddam et al 1997
major depressed pts carrying the Met rs6265 allele do not respond to ketamine - this is a SNP that induces deficits in BDNF processing - further suggests BDNF synthesis is important for ketamine
Laje et al 2012
Mice lacking NMDAR (subunit GluN1) in parvalbumin-expressing interneurons, designed to mimic disinhibition of pyramidal cell activity, retained ketamine induced AD activity (no differences in repeated FST or in a sucrose preference test)
Pozzi et al 2014
- Administered ket to BDNF to inducible KO BDNF mice
- Looked at FST behaviour
- WT controls showed reductions in immobility (AD effect) whereas ket had no effect on the KOs (no AD effect)
- BDNF protein synthesis increased following ketamine treatment as shown by Western blot at 30 minutes in hippocampal cells
- Whole-cell patch-clamp recordings - in hippocampal neurons in vitro they recorded NMDA-mEPSCs after ketamine infusion - detected a significant decrease of mEPSCs within minutes
- Then did Western blot and after 30 mins of ket administration there were rapid decreases in phosphorylated eEF2 in HC compared to vehicle-treated cells → suggested that ketamine leads to dephosphorylation of eEF2
- They then administered eEFK2 inhibitors to normal mice = AD response. When they administered to BDNF KOs and tested FST behaviour. This was ineffective in BDNF KOs - shows requirement for increased BDNF expression upon eEF2 inhibition to produce AD-like behavior
- Supports the hypothesis that ket inhibits spontaneous NMDA-mEPSCs, leading to decerased eEF2 kinase activity, permitting rapid increased in BDNF translation which may exert strong influences on synaptic strength
Autry et al 2011
20 pts suffering major depressive episode were pretreated with oral rapamycin or placebo 2h prior to IV ketamine. Depression severity assessed using Mongomery-Asberg Rating Scale. 2 major findings Rapamycin pts saw the same benefit of ketamine as those who received placebo at 24h - rapamycin did not block the effects of ketamine as seen in animal studies When patients took rapamycin prior to receiving ketamine, 41% still showed a clinical antidepressant response after two weeks, with 29% in full remission. This compared with 13% response and 7% remission when placebo was given prior to ketamine instead of rapamycin. In other words, rapamycin pretreatment apparently extended ketamine’s antidepressant effectiveness, for at least some patients. Limitations - Anti-inflammatory (immune suppressive kidney transplant) - may be anti-depressive and confound
Abdallah et al 2020 Nature
Chemically altered ketamine via deuteration at the C6 position, which did not change its binding affinity for the NMDAR but dramatically decreased its in vivo metabolism to HNK. This manipulation prevent ketamine’s AD actions in mice - no AD actions in FST or LH 24 hours after administration
Greater AD behavioural responses of a single administration of ketamine have been observed in female compared to male rats and mice - in mice this behavioural effect was associated with (3 fold) higher brain levels of HNK, but not ketamine or norketamine levels, supporting the role of this metabolite in the AD actions of ketamine
Cav - Studies in mice have inherent difficulties in translation into therapeutic mechanism into humans… 10uM used is approx 60-fold higher than plasma than the plasma Cmax (peak serum conc) observed in bipolar depressed pts receiving 0.5mg/kg ketamine IV… this was when assessing transmission in rat hippocampal slices…also no data of intraperitoneal administration of ketamine in humans - might differ
Zanos 2016
RCT trying to determine if opoid receptor antagonism prior to IV ket attenuates AD effects - pts treated with ketamine + opoid antagonist or ketamine +placebo - treated with opoid antagonist/placebo prior to ketamine, in 12 pts, ketamine +naloxone Hamilton Depression rating cale was sig lower than ket + placebo post-infusion days 1 and 3. Concluded ketamines AD effect appears to require opioid system activation. Limitations - there was no placebo control arm for the ketamine infusion (e.g. naltrexone + IV saline and placebo + IV saline) impedes evaluation of the specificity of the antagonist + ketamine effect, also, they could have included pharmacodynamic markers of keta opioid essay, for example, they could have looked that miosis and see if this is blocked by naltrexone Future - Human radioligand PET studies with mu-opioid tracers should examine ketamne’s binding affinity at clinically relevant doses
Williams 2018
largely responsible for introducing ketamine into clinic practice as an anaethetic - described individuals who received ketamine as ‘disconnected from their environment somehow’
Ed Domino
Two doses of psilocybin and supportive psychotherapy resulted in rapid, significant AD effects. Around 67% of participants experienced a 50% reduction in symptoms. These effects appear to be lasting. By 4 weeks after treatment, 54% of the participants were no longer depressed. 24 people involved with long-term his Small + preliminary, need to be validated in a sham-controlled study - cant give it to addicts, schizophrenics and prdromal schizophrenics Perhaps a psychodelic experience?
Davis et al 2020
Ket does not act as an opiate but requires both NMDA and opiate receptors. They found that opiate antagonist pretreatment blocked acute effects of ketamine in congenitally learned helplessness (cLH) mice. Lateral habenula hyperactivity known to occur rin animals with depressive-like behaviours. Then saw that ket blocks hyperactivity in lateral habeula neurons from cLH rats, and this was blocked by opiate antagonist. Opiate antagonist alone did not have an effect on lateral habenula. Specific NDMA antagonist decreased LHb activity to as similar degree as ket and adding ket after did not decrease it more. Opioid receptors needed but not sufficient alone for the AD effect - shown both cellularly and behaviourally
Cav - Ket is known to have lasting (up to 1 week) effects - sustained effects were not trested in cLH rats, general drawbacks of cLH as opposed to inescapable shock-induced LH model = you cant compare LH and non-LH (resilient rats), genetic basis of cLH is unknown
Future direction - effects on depression-like behaviours in rodents exposed to stress needed
Klein et al 2020
They did a systematic review that demonstrated inconsistent relationship between ketamine’s dissociative and AD effects. Looked at 8 studies in total. Found that only 3 of these observed a relationship between Clinician-Administered Dissociative States Scale (CADSS) and AD response. Within the papers that reported a significant relationship, the explained vriance of dissociative experiences for AD response was 12-21%
Mathai et al 2020
“carried out systematic review including 10 trials investigating NSAIDS + 4 trials investigating cytokine inhibitors as potential ADs o They found evidence that anti-inflammatory treatment, particularly celecoxib, reduced depressive symptoms”
Köhler et al. (2014) –
screened a clinical collection of around 450 drugs for efficacy at inhibiting inositol monophosphatase, identified organic molecule called ebselen able to do this, which could inhibit in vitro and in vivo with similar effects to lithium & used a human IMPase assay to demonstrate IMPase inhibition by ebselen. • Ebselen reduced manic-like behaviour in mice, including rearing in the open field test and amphetamine-induced hyperactivity • To confirm the importance of inositol depletion, intracerebroventricular injection of inositol reversed the behavioural effects of ebselen.
Singh et al 2013
TRD individuals randomined to get IV ket (0.1, 0.2, 0.5 or 1.0 mg/kg) ro active control (midazolam). Higher doses produced higher CADSS scores than lower but higher did not result in greater AD efficacy than the 0.5mg/kg dose. No sig correlation between CADSS and HAM-D-6 score.
cav - Small sample size and the fact that concomitant medication was allowed
Fava et al 2020
Looked at 31 studies of ketamine and other glutamate receptor modulators for MDD. Concludes that symptoms of depression reduced and agrees with use of ket for MDD but states all trials were short term (don’t know long-term effects), inflated bias, problems with IV. Not many trials in each meta-analysis. Say confidence in findings is limited.
September 2021 Cochrane Review
60 BPD pts treated with the drug or placebo - outcome determined on Young Mania Rating Scale and showed a 4.2 point difference in reduction (0<0.058, not sig) – numerical but not statistical significance - althoguh CGI-s score was significantly lower (Clinical GLobal impression) secondary outcome - better controlled studies needed for this
Sharpley 2020
conducted a double-blind study on 40 patients with malignant melanoma who received IFN-α therapy; half the group was given paroxetine (SSRI) and the other half was given placebo. Development of depressive symptoms was significantly reduced in the paroxetine group compared to control, showing that the IFN-α behavioural syndrome is sensitive to regular antidepressants.
Musselman 2001
