Variants in PDE11A and PDE1A are not associated with citalopram response

Phosphodiesterase inhibitors in psychiatric disorders

RATIONALE

Challenges in drug development for psychiatric disorders have left much room for the introduction of novel treatments with better therapeutic efficacies and indices. As a result, intense research has focused on identifying new targets for developing such pharmacotherapies. One of these targets may be the phosphodiesterase (PDE) class of enzymes, which play important roles in intracellular signaling. Due to their critical roles in cellular pathways, these enzymes affect diverse neurobiological functions from learning and memory formation to neuroinflammation.

OBJECTIVES

In this paper, we reviewed studies on the use of PDE inhibitors (PDEIs) in preclinical models and clinical trials of psychiatric disorders including depression, anxiety, schizophrenia, post-traumatic stress disorder (PTSD), bipolar disorder (BP), sexual dysfunction, and feeding disorders.

RESULTS

PDEIs are able to improve symptoms of psychiatric disorders in preclinical models through activating the cAMP-PKA-CREB and cGMP-PKG pathways, attenuating neuroinflammation and oxidative stress, and stimulating neural plasticity. The most promising therapeutic candidates to emerge from these preclinical studies are PDE2 and PDE4 inhibitors for depression and anxiety and PDE1 and PDE10 inhibitors for schizophrenia. Furthermore, PDE3 and 4 inhibitors have shown promising results in clinical trials in patients with depression and schizophrenia.

CONCLUSIONS

Larger and better designed clinical studies of PDEIs in schizophrenia, depression, and anxiety are warranted to facilitate their translation into the clinic. Regarding the other conditions discussed in this review (most notably PTSD and BP), better characterization of the effects of PDEIs in preclinical models is required before clinical studies.

cGMP Signaling, Phosphodiesterases and Major Depressive Disorder

Deficits in neuroplasticity are hypothesized to underlie the pathophysiology of major depressive disorder (MDD): the effectiveness of antidepressants is thought to be related to the normalization of disrupted synaptic transmission and neurogenesis. The cyclic adenosine monophosphate (cAMP) signaling cascade has received considerable attention for its role in neuroplasticity and MDD. However components of a closely related pathway, the cyclic guanosine monophosphate (cGMP) have been studied with much lower intensity, even though this signaling transduction cascade is also expressed in the brain and the activity of this pathway has been implicated in learning and memory processes. Cyclic GMP acts as a second messenger; it amplifies signals received at postsynaptic receptors and activates downstream effector molecules resulting in gene expression changes and neuronal responses. Phosphodiesterase (PDE) enzymes degrade cGMP into 5’GMP and therefore they are involved in the regulation of intracellular levels of cGMP. Here we review a growing body of evidence suggesting that the cGMP signaling cascade warrants further investigation for its involvement in MDD and antidepressant action.

Genetic variation in phosphodiesterase (PDE) 7B in chronic lymphocytic leukemia: overview of genetic variants of cyclic nucleotide PDEs in human disease

Expression of cyclic adenosine monophosphate-specific phosphodiesterase 7B (PDE7B) mRNA is increased in patients with chronic lymphocytic leukemia (CLL), thus suggesting that variation may occur in the PDE7B gene in CLL. As genetic variation in other PDE family members has been shown to associate with numerous clinical disorders (reviewed in this manuscript), we sought to identify single-nucleotide polymorphisms (SNPs) in the PDE7B gene promoter and coding region of 93 control subjects and 154 CLL patients. We found that the PDE7B gene has a 5' non-coding region SNP -347C>T that occurs with similar frequency in CLL patients (1.9%) and controls (2.7%). Tested in vitro, -347C>T has less promoter activity than a wild-type construct. The low frequency of this 5' untranslated region variant indicates that it does not explain the higher PDE7B expression in patients with CLL but it has the potential to influence other settings that involve a role for PDE7B.

Pharmacogenetics studies in STAR*D: strengths, limitations, and results

Several lines of evidence support an important genetic contribution to the wide individual variation in therapeutic response to antidepressant medications. The Sequenced Treatment Alternatives to Relieve Depression (STAR*D) study provided the largest cohort assembled to date of DNA from patients with nonpsychotic major depressive disorder, uniformly treated with citalopram and followed prospectively for up to 12 weeks. This pivotal study changed the face of pharmacogenetics research by increasing the sample size by an order of magnitude as well as by providing detailed prospective information about antidepressant response and tolerability. Several groups have identified markers in genes and tested the replication of previous findings of genes associated with outcome and side effects of antidepressant treatment. Variants in HTR2A, GRIK4, and KCNK2 were associated with citalopram treatment outcome. Replication was achieved in markers in the FKBP5 gene. Other findings in PDE11A and BDNF were not successfully replicated, and reports of potential confounders in previous associations with serotonin transporter variation (SLC6A4) were identified. Polymorphisms in pharmacokinetic genes involved in metabolism and transmembrane transport were also not associated with antidepressant response. Adverse events were also tested. Treatment-emergent suicidal ideation was associated with GRIK2, GRIA3, PAPLN, IL28RA, and CREB1. Sexual dysfunction was linked with variation in GRIN3A, GRIA1 GRIA3, and GRIK2. Reported and future findings of pharmacogenetics studies in STAR*D could help elucidate pathways involved in major depression and those pertinent to antidepressant outcome and side effects. Replication of these findings in independent samples could lead to the development of new treatments and to optimization of available treatments.

Pharmacogenomics of antidepressant drugs

While antidepressant pharmacotherapy is an effective treatment of depression, it is still hampered by the slow onset of appreciable clinical improvement and a series of side effects. Moreover, a substantial group of patients does not achieve remission or fails to respond at all. One possible source accounting for these variations in treatment outcome are genetic differences. In recent years a number of pharmacogenetic studies on antidepressant drugs have been published. This manuscript summarizes findings related to the pharmacogenetics of genes involved in the pharmacokinetics as well as pharmacodynamics of antidepressants to date. Illustrated by examples from current candidate gene- and whole genome association studies, this manuscript critically discusses aspects of pharmacogenetic studies in antidepressant response related to study design and clinical relevance.

Association study of phosphodiesterase genes in the Sequenced Treatment Alternatives to Relieve Depression sample

A recent study has reported a significant association of variants in phosphodiesterase (PDE) genes with antidepressant treatment outcome in a Mexican American sample. We set out to investigate these findings in a large sample of patients from the Sequenced Treatment Alternatives to Relieve Depression (STAR*D) study. STAR*D is a longitudinal study of antidepressant outcome in depressed outpatients. We genotyped three single nucleotide polymorphisms (SNPs) in PDE11A (rs1880916), PDE1A (rs1549870), and PDE9A (rs729861) for replication and we also report three additional SNPs in PDE11A (rs3770016, rs4893975, rs6433687) that had been genotyped for a previous study. Single marker analysis of remission within the Hispanic subsamples (n=268) revealed no significant evidence of association with markers in PDE11A, PDE9A, or PDE1A. Additional analyses of remission within the total STAR*D sample (n=1914) were also largely negative, as were analyses utilizing a narrower definition of remission. Haplotype analyses were carried out with the four PDE11A SNPs we genotyped; these also failed to show significant evidence of association in the STAR*D sample. In conclusion, we could not reproduce the reported association between PDE genes and antidepressant outcome in a sample of participants comparable to that reported previously. We conclude that PDE11A, PDE9A, and PDE1A are unlikely to play an important role in antidepressant outcome in this sample.

Phosphodiesterase genes and antidepressant treatment response: a review

Depression results in a tremendous burden to individuals suffering from the disorder and to the global health economy. Available pharmacologic treatments for depression target monoamine levels and monoamine receptors. However, delayed onset of effect, partial or inadequate treatment response, and side-effects are significant limitations of current therapies. The search for a better understanding of mechanisms of depression and for new treatment targets has turned attention to intracellular mediators. Phosphodiesterases (PDEs) are enzymes that break down the intracellular second messenger mononucleotides cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP). Recent data from animal and human studies indicate that PDEs may play a role in depression and in related stress conditions. PDE genes have been linked directly to depression and to other genes associated with psychiatric disorders.

Association of PDE11A global haplotype with major depression and antidepressant drug response

Cyclic nucleotide phosphodiesterases (PDEs) hydrolyze the intracellular second messengers cAMP and cGMP to their corresponding monophosphates. PDEs play an important role in signal transduction by regulating the intracellular concentration of cyclic nucleotides. We have previously shown that the individual haplotype GAACC in the PDE11A gene was associated with major depressive disorder (MDD) based on block-by-block analysis. There are two PDE genes, PDE11A and PDE1A, located in chromosome 2q31-q32. In this study, we have further explored whether the whole region 2q31-q32 contribute to MDD or antidepressant response 278 depressed Mexican-American participants and 321 matched healthy controls. Although there is no significant interaction between the two genes, the remission rate of individual carrying the combination genotype at rs1880916 (AG/AA) and rs1549870 (GG) is significantly increased. We analyzed the global haplotype by examining 16 single-nucleotide polymorphisms (SNPs) in PDE11A and six SNPs in PDE1A. None of the haplotypes consisting of six SNPs in the PDE1A have a significant difference between depressed and control groups. Among haplotypes consisting of 16 SNPs across 440 kb in the PDE11A gene, 18 common haplotypes (with frequency higher than 0.8%) have been found in the studied population. Six haplotypes showed significantly different frequencies between the MDD group and the control group. The phylogenetic network result for the 16 SNPs showed that several historic recombination events have happened in the PDE11A gene. The frequency of one haplotype is significantly lower in the remitter group than in the nonremitter group for the depressed participants treated with either desipramine or fluoxetine. Thus, our data suggest that the PDE11A global haplotype is associated with both MDD and antidepressant drug response.

Pharmacogenomics with antidepressants in the STAR*D study

Major depressive disorder is one of the most common psychiatric disorders worldwide. No single antidepressant has been shown to be more effective than any other in lifting depression, and the effectiveness of any particular antidepressant in an individual is difficult to predict; therefore, doctors must prescribe antidepressants based on educated guesses. SNPs can be used in clinical association studies to determine the contribution of genes to drug efficacy. Evidence is accumulating to suggest that the efficacy of antidepressants results from the combined effects of a number of genetic variants, such as SNPs. Although there are not enough data currently available to prove this hypothesis, an increasing number of genetic variants associated with antidepressant response are being discovered. In this article, we review the pharmacogenomics of the drug efficacy of antidepressants in major depressive disorder. First, we survey the SNPs and genes identified as genetic markers that are correlated and associated with the drug efficacy of antidepressants in the Sequenced Treatment Alternatives for Depression (STAR*D) study. Second, we investigate candidate genes that have been suggested as contributing to treatment-emergent suicidal ideation during the course of antidepressant treatment in the STAR*D study. Third, we briefly describe the pharmacokinetic genes examined in the STAR*D study, and finally, we summarize the limitations with respect to the pharmacogenomics studies in the STAR*D study. Future research with independent replication in large sample sizes is needed to confirm the role of the candidate genes identified in the STAR*D study in antidepressant treatment response.