Genetic variation in the serotonin transporter and HTR1B receptor predicts reduced bone formation during serotonin reuptake inhibitor treatment in older adults

Identifying genetic variants associated with side effects of antidepressant treatment: A systematic review

Major Depressive Disorder (MDD) is one of the most prevalent neurobiological disorders globally. Antidepressant medications are the first-line treatment for managing symptoms. However, over time, pharmacotherapy has been linked to several challenges, primarily due to the wide array of side effects that often reduce patient adherence to treatment. The literature suggests that these side effects may be influenced by polymorphisms in genes related to the pharmacokinetics and pharmacodynamics of antidepressants. Thus, this systematic review aimed to identify studies that investigated the association between genetic variants and side effects resulting from antidepressant treatment in individuals with MDD. Original articles indexed in the electronic databases Cochrane Library, EMBASE, MEDLINE via PubMed, and Scopus were identified. A total of 55 studies were included in the review, and data regarding the outcomes of interest were extracted. Due to the exploratory nature of the review, a narrative/descriptive synthesis of the results was performed. The risk of bias was evaluated using the Joanna Briggs Institute's tools, tailored to the design of each study. Polymorphisms in 35 genes were statistically associated with the development of side effects. A subsequent Protein-Protein Interaction Network analysis helped elucidate the key biological pathways involved in antidepressant side effects, with a view toward exploring the potential application of pharmacogenetic markers in clinical practice.

Examining Whether Genetic Variants Moderate the Skeletal Effects of Selective Serotonin Reuptake Inhibitors in Older Adolescents and Young Adults

Objective: To examine whether serotonin (5-HT) related genetic variants moderate the effects of selective serotonin reuptake inhibitors (SSRIs) on skeletal outcomes. Methods: Trabecular bone mineral density (BMD) at the radius, lumbar spine (LS) BMD, total body less head (TBLH) bone mineral content (BMC) and markers of bone metabolism (osteocalcin, C-terminal telopeptide of type I collagen [CTX-1], and bone specific alkaline phosphatase to CTX-1 ratio) were examined in an observational study, enrolling 15- to 20-year-old participants, unmedicated or within a month of SSRI initiation. Variants in HTR1A (rs6295), HTR1B (rs6296), HTR1D (rs6300), HTR2A (rs6311 and rs6314), HTR2B (rs6736017), and the serotonin transporter intron 2 variable number tandem repeat (STin2 VNTR) were genotyped. Linear mixed-effects regression analysis examined associations between SSRI use, genetic variants, and skeletal outcomes. Results: After adjusting for relevant covariates, rs6295 CC and GC genotypes in 262 participants (60% female, mean ± SD age = 18.9 ± 1.6 years) were significantly associated with higher LS BMD compared to the GG genotype. Rs6311 GG SSRI users had greater LS BMD compared to nonusers (β = 0.18, p = <0.0001). Female SSRI users with the combination of rs6295 CC+GC and rs6311 GG genotypes had greater LS BMD than female SSRI nonusers (β = 0.29, p < 0.0001). SSRI users with the rs6295 GG genotype had higher trabecular BMD compared to nonusers (β = 3.60, p = 0.05). No significant interactions were found for TBLH BMC or bone turnover markers. After correcting for multiple comparisons, none of the results retained significance. Conclusions: In older adolescents and young adults, HTR1A (rs6295) and HTR2A (rs6311) variants may moderate the effect of SSRIs on BMD. Sex differences may exist and require further examination. Further research with larger sample sizes is needed to confirm our preliminary findings. Clinical Trial Registration: clinicaltrials.gov NCT02147184.

Pharmacogenetics in Primary Headache Disorders

Primary headache disorders, such as migraine, tension-type headache (TTH), and cluster headache, belong to the most common neurological disorders affecting a high percentage of people worldwide. Headache induces a high burden for the affected individuals on the personal level, with a strong impact on life quality, daily life management, and causes immense costs for the healthcare systems. Although a relatively broad spectrum of different pharmacological classes for the treatment of headache disorders are available, treatment effectiveness is often limited by high variances in therapy responses. Genetic variants can influence the individual treatment success by influencing pharmacokinetics or pharmacodynamics of the therapeutic as investigated in the research field of pharmacogenetics. This review summarizes the current knowledge on important primary headache disorders, including migraine, TTH, and cluster headache. We also summarize current acute and preventive treatment options for the three headache disorders based on drug classes and compounds taking important therapy guidelines into consideration. Importantly, the work summarizes and discusses the role of genetic polymorphisms regarding their impact on metabolism safety and the effect of therapeutics that are used to treat migraine, cluster headache, and TTH exploring drug classes such as nonsteroidal anti-inflammatory drugs, triptans, antidepressants, anticonvulsants, calcium channel blockers, drugs with effect on the renin-angiotensin system, and novel headache therapeutics such as ditans, anti-calcitonin-gene-related peptide antibodies, and gepants. Genetic variants in important phase I-, II-, and III-associated genes such as cytochrome P450 genes, UGT genes, and different transporter genes are scrutinized as well as variants in genes important for pharmacodynamics and several functions outside the pharmacokinetic and pharmacodynamic spectrum. Finally, the article evaluates the potential and limitations of pharmacogenetic approaches for individual therapy adjustments in headache disorders.

Pharmacogenetic Implications for Antidepressant Pharmacotherapy in Late-Life Depression: A Systematic Review of the Literature for Response, Pharmacokinetics and Adverse Drug Reactions

Affecting up to 15% of older adults, late-life depression (LLD) is characterized by the occurrence of depressive symptoms after the age of 50-65 years and maybe pathophysiologically distinct from depression in younger adults. Therefore, LLD is challenging to treat, and predictive genetic testing might be essential to improve treatment in this vulnerable population. The current review aims to provide a summary of the literature exploring genetic associations with antidepressant treatment outcomes in late-life. We conducted a systematic search of three integrated electronic databases. We identified 29 articles investigating genetic associations with antidepressant treatment outcomes, pharmacokinetic parameters, and adverse drug reactions in older adults. Given the small number of investigations conducted in older adults, it is difficult to conclude the presence or absence of genetic associations with the outcomes of interest. In sum, the most substantial amount of evidence exists for the CYP2D6 metabolizer status, SLC6A4 5-HTTLPR, and BDNF rs6265. These findings are consistent in the literature when not restricting to older adults, suggesting that similar treatment recommendations may be provided for older adults regarding genetic variation, such as those outlined for CYP2D6 by the Clinical Pharmacogenetics Implementation Consortium. Nonetheless, further studies are required in well-characterized samples, including genome-wide data, to validate if similar treatment adjustments are appropriate in older adults, given that there appear to be significant effects of genetic variation on antidepressant treatment factors.

Venlafaxine pharmacogenetics: a comprehensive review

Antidepressant response could be from 42 to 50% genetically determined. Venlafaxine (VEN) was the sixth most-prescribed antidepressant in the USA in 2017. Therefore, we reviewed studies which focused on the pharmacogenetics of VEN and found that there is a lack of guidelines for pharmacogenetic testing for VEN. Within investigated genetic polymorphisms, few of them can be indicated as potential predictors of VEN efficacy and tolerance. However, additional pharmacogenetic studies of VEN should be performed to reproduce already obtained results or explain contradictory ones. The individualization of pharmacotherapy is a key issue in providing patients with the highest possible quality of treatment, therefore pharmacogenetic studies should be one of the components of therapy optimization.

Association of the serotonin transporter-linked polymorphic region genotype with lower bone mineral density

The serotonin transporter-linked polymorphic region (5-HTTLPR) of the serotonin transporter gene (SLC6A4) S allele is linked to pathogenesis of depression and slower response to selective serotonin reuptake inhibitors (SSRIs); depression and SSRIs are independently associated with bone loss. We aimed to determine whether 5-HTTLPR was associated with bone loss. This cross-sectional study included psychiatric patients with both 5-HTTLPR analysis and bone mineral density (BMD) assessment (hip and spine Z-scores if age <50 years and T-scores if ⩾50 years). BMD association with 5-HTTLPR was evaluated under models with additive allele effects and dominant S allele effects using linear regression models. Patients were stratified by age (<50 and ⩾50 years) and sex. Of 3016 patients with 5-HTTLPR genotyping, 239 had BMD assessments. Among the younger patients, the S allele was associated with lower Z-scores at the hip (P=0.002, dominant S allele effects; P=0.004, additive allele effects) and spine (P=0.0006, dominant S allele effects; P=0.01, additive allele effects). In sex-stratified analyses, the association of the S allele with lower BMD in the younger patients was also significant in the subset of women (P⩽0.003 for both hip and spine BMD under the additive allele effect model). In the small group of men younger than 50 years, the S allele was marginally associated with higher spine BMD (P=0.05). BMD T-scores were not associated with 5-HTTLPR genotypes in patients 50 years or older. The 5-HTTLPR variants may modify serotonin effects on bone with sex-specific effects.

Non-conventional features of peripheral serotonin signalling - the gut and beyond

Serotonin was first discovered in the gut, and its conventional actions as an intercellular signalling molecule in the intrinsic and extrinsic enteric reflexes are well recognized, as are a number of serotonin signalling pharmacotherapeutic targets for treatment of nausea, diarrhoea or constipation. The latest discoveries have greatly broadened our understanding of non-conventional actions of peripheral serotonin within the gastrointestinal tract and in a number of other tissues. For example, it is now clear that bacteria within the lumen of the bowel influence serotonin synthesis and release by enterochromaffin cells. Also, serotonin can act both as a pro-inflammatory and anti-inflammatory signalling molecule in the intestinal mucosa via activation of serotonin receptors (5-HT₇ or 5-HT₄ receptors, respectively). For decades, serotonin receptors have been known to exist in a variety of tissues other than the gut, but studies have now provided strong evidence for physiological roles of serotonin in several important processes, including haematopoiesis, metabolic homeostasis and bone metabolism. Furthermore, evidence for serotonin synthesis in peripheral tissues outside of the gut is emerging. In this Review, we expand the discussion beyond gastrointestinal functions to highlight the roles of peripheral serotonin in colitis, haematopoiesis, energy and bone metabolism, and how serotonin is influenced by the gut microbiota.

Bone Turnover with Venlafaxine Treatment in Older Adults with Depression

OBJECTIVES

Epidemiologic data suggest older adults receiving serotonergic antidepressants may have accelerated bone loss. We examined bone turnover marker changes and patient-level variables associated with these changes in older adults receiving protocolized antidepressant treatment.

DESIGN

Open-label, protocolized treatment study.

SETTING

Medical centers in Pittsburgh, St Louis, and Toronto.

PARTICIPANTS

Older adults with major depression (N = 168).

MEASUREMENTS

Serum levels of the bone resorption marker C-terminal cross-linking telopeptide of type 1 collagen (CTX) and the bone formation marker procollagen type 1 N propeptide (P1NP) were assayed before and after 12 weeks of treatment with venlafaxine. Whether CTX and P1NP changes were associated with depression remission and duration of depression and genetic polymorphisms in the serotonin transporter (5HTTLPR) and 1B receptor (HTR1B) were also examined.

RESULTS

CTX increased and P1NP decreased during venlafaxine treatment, a profile consistent with accelerated bone loss. Two individual-level clinical variables were correlated with bone turnover; participants whose depression did not go into remission had higher CTX levels, and those with chronic depression had lower P1NP levels. HTR1B genotype predicted P1NP change, whereas 5HTTLPR genotype was unrelated to either biomarker.

CONCLUSION

Bone turnover markers change with antidepressant treatment in a pattern that suggests accelerated bone loss, although the clinical significance of these changes is unclear. These data are preliminary and argue for a larger, controlled study to confirm whether antidepressants are harmful to bone metabolism and whether certain individuals might be at increased risk.

Pharmacogenetics and Imaging-Pharmacogenetics of Antidepressant Response: Towards Translational Strategies

Genetic variation underlies both the response to antidepressant treatment and the occurrence of side effects. Over the past two decades, a number of pharmacogenetic variants, among these the SCL6A4, BDNF, FKBP5, GNB3, GRIK4, and ABCB1 genes, have come to the forefront in this regard. However, small effects sizes, mixed results in independent samples, and conflicting meta-analyses results led to inherent difficulties in the field of pharmacogenetics translating these findings into clinical practice. Nearly all antidepressant pharmacogenetic variants have potentially pleiotropic effects in which they are associated with major depressive disorder, intermediate phenotypes involved in emotional processes, and brain areas affected by antidepressant treatment. The purpose of this article is to provide a comprehensive review of the advances made in the field of pharmacogenetics of antidepressant efficacy and side effects, imaging findings of antidepressant response, and the latest results in the expanding field of imaging-pharmacogenetics studies. We suggest there is mounting evidence that genetic factors exert their impact on treatment response by influencing brain structural and functional changes during antidepressant treatment, and combining neuroimaging and genetic methods may be a more powerful way to detect biological mechanisms of response than either method alone. The most promising imaging-pharmacogenetics findings exist for the SCL6A4 gene, with converging associations with antidepressant response, frontolimbic predictors of affective symptoms, and normalization of frontolimbic activity following antidepressant treatment. More research is required before imaging-pharmacogenetics informed personalized medicine can be applied to antidepressant treatment; nevertheless, inroads have been made towards assessing genetic and neuroanatomical liability and potential clinical application.

Bone growth in juvenile rhesus monkeys is influenced by 5HTTLPR polymorphisms and interactions between 5HTTLPR polymorphisms and fluoxetine

Male rhesus monkeys received a therapeutic oral dose of the selective serotonin reuptake inhibitor (SSRI) fluoxetine daily from 1 to 3 years of age. Puberty is typically initiated between 2 and 3 years of age in male rhesus and reproductive maturity is reached at 4 years. The study group was genotyped for polymorphisms in the monoamine oxidase A (MAOA) and serotonin transporter (SERT) genes that affect serotonin neurotransmission. Growth was assessed with morphometrics at 4 month intervals and radiographs of long bones were taken at 12 month intervals to evaluate skeletal growth and maturation. No effects of fluoxetine, or MAOA or SERT genotype were found for growth during the first year of the study. Linear growth began to slow during the second year of the study and serotonin reuptake transporter (SERT) long polymorphic region (5HTTLPR) polymorphism effects with drug interactions emerged. Monkeys with two SERT 5HTTLPR L alleles (LL, putative greater transcription) had 25-39% less long bone growth, depending on the bone, than monkeys with one S and one L allele (SL). More advanced skeletal maturity was also seen in the LL group, suggesting earlier onset of puberty. An interaction between 5HTTLPR polymorphisms and fluoxetine was identified for femur and tibia growth; the 5HTTLPR effect was seen in controls (40% less growth for LL) but not in the fluoxetine treated group (10% less growth for LL). A role for serotonin in peripubertal skeletal growth and maturation has not previously been investigated but may be relevant to treatment of children with SSRIs.

Major depressive disorder in older adults: benefits and hazards of prolonged treatment

Antidepressants have been shown to reduce the risk of depression recurrence in adults, justifying prolonged antidepressant maintenance therapy for most if not all patients. However, older depressed adults may be at increased risk for antidepressant adverse effects. This article discusses the benefits and hazards of continued treatment in elderly depressed patients, and indicates which patients should and should not receive maintenance phase antidepressants. Most clinical trials conducted so far suggest that prolonged antidepressant use in older adults is efficacious to reduce recurrence rates. The benefits of prolonged antidepressant use may not be restricted to preventing recurrence but also include preservation of overall well-being, social functioning, reduced mortality risk from medical disorders, and reduced risk of dementia. Although generally safe, the prolonged use of antidepressants has been associated with higher risk of osteopenia/osteoporosis (in particular the selective serotonin reuptake inhibitors) and cardiovascular toxicity (tricyclic antidepressants). Fewer data are available for special populations, like those with multiple medical comorbidities or those with dementia; thus, the benefits of prolonged antidepressant use are not clear in these individuals.

Interaction between 5-HTTLPR and 5-HT1B genotype status enhances cerebral 5-HT1A receptor binding

Serotonergic neurotransmission is thought to underlie a dynamic interrelation between different key structures of the serotonin system. The serotonin transporter (SERT), which is responsible for the reuptake of serotonin from the synaptic cleft into the neuron, as well as the serotonin-1A (5-HT1A) and -1B (5-HT1B) receptors, inhibitory auto-receptors in the raphe region and projection areas, respectively, are likely to determine serotonin release. Thereby, they are involved in the regulation of extracellular serotonin concentrations and the extent of serotonergic effects in respective projection areas. Complex receptor interactions can be assessed in vivo with positron emission tomography (PET) and single-nucleotide-polymorphisms, which are thought to alter protein expression levels. Due to the complexity of the serotonergic system, gene × gene interactions are likely to regulate transporter and receptor expression and therefore subsequently serotonergic transmission. In this context, we measured 51 healthy subjects (mean age 45.5 ± 12.9, 38 female) with PET using [carbonyl-(11)C]WAY-100635 to determine 5-HT1A receptor binding potential (5-HT1A BPND). Genotyping for rs6296 (HTR1B) and 5-HTTLPR (SERT gene promoter polymorphism) was performed using DNA isolated from whole blood. Voxel-wise whole-brain ANOVA revealed a positive interaction effect of genotype groups (5-HTTLPR: LL, LS+SS and HTR1B: rs6296: CC, GC+GG) on 5-HT1A BPND with peak t-values in the bilateral parahippocampal gyrus. More specifically, highest 5-HT1A BPND was identified for individuals homozygous for both the L-allele of 5-HTTLPR and the C-allele of rs6296. This finding suggests that the interaction between two major serotonergic structures involved in serotonin release, specifically the SERT and 5-HT1B receptor, results in a modification of the inhibitory serotonergic tone mediated via 5-HT1A receptors.

Depression, antidepressants, and bone health in older adults: a systematic review

OBJECTIVES

To examine the association between depression, antidepressant use, and bone health in older adults and the implications for treatment.

DESIGN

Systematic review.

SETTING

All studies that measured depression or antidepressant exposure and bone mineral density (BMD).

PARTICIPANTS

Adults aged 60 and older.

MEASUREMENTS

Age, site of BMD measurement using dual-energy X-ray absorptiometry (DXA), measure of depression or depressive symptoms, association between BMD changes, and depression or antidepressant use.

RESULTS

Nineteen observational studies met the final inclusion criteria; no experimental studies were found. Several cross-sectional and longitudinal studies found that depression or depressive symptoms were associated with a decrease in BMD. Few studies and only two longitudinal studies addressed the association between serotonin reuptake inhibitor (SRI) antidepressant use and a decrease in BMD and they had conflicting results.

CONCLUSION

Depression and depressive symptoms are associated with low bone mass and accelerated bone loss in older adults; putative mechanisms underlying this relationship are discussed. There is insufficient evidence that SRI antidepressants adversely affect bone health. Thus, a change in current recommendations for the use of antidepressants in older adults is not justified at the present time. Given the high public health significance of this question, more studies are required to determine whether (and in whom) antidepressants may be deleterious for bone health.