Key words L-methylfolate - depression - adjunct therapy
Introduction
Almost one in five people experience one episode of major depressive disorder (MDD)
at some point in their life that severely impacts psychosocial functioning and
diminishes their quality of life. In fact, depressive disorders represent an
increasing cause of disability worldwide and account for more disability-adjusted
life-years than substance use, stroke, diabetes, and chronic kidney disease in
individuals under 50 years of age [1 ].
Antidepressants represent the first-line pharmacotherapies for moderate-to-severe
MDD [2 ]. However, treatment response varies
considerably from person to person, with only 50% benefitting from their
first trial [3 ]
[4 ]. Among the potential causes of non-response
to antidepressant medications is the deficit in folate metabolism and
cycling/transport ([Fig. 1 ]) [5 ].
Fig. 1 Folate and methylation cycles.
The folate cycle is important for the synthesis of L-methylfolate, which is utilized
in the methylation cycle during DNA synthesis, homocysteine metabolism, and
neurotransmitter production [6 ]
[7 ]. Specifically, the enzyme
methylenetetrahydrofolate reductase (MTHFR) converts folic acid to L-methylfolate.
According to the 1000 Genomes Project Phase 3, between 9–47% of the
North American population have variants (e. g., C677T, A1298C) in the
MTHFR gene that reduce its enzymatic activity and have been proposed as
biomarkers for risk of depression [8 ]
[9 ]
[10 ]
[11 ]. Therefore, adjunctive
L-methylfolate in antidepressant-treated patients may increase the efficiency of
these cycles by bypassing the MTHFR-dependent conversion of folate to
L-methylfolate, putatively enhancing antidepressant response [12 ]. ([Tables
1 ]
[2 ])
Table 1 A summary of the characteristics of the studies
(n=10) included in the systematic review on L-methylfolate
augmentation in depressive disorders.
Study (First Author, Year)
Sample Size
Subject Characteristics (Age in years, Women%)
Study Design
Treatment
Treatment Duration
Comparator
Primary Outcome Measurement
Result
Ginsberg, 2011
242
43, 66.9%
Retrospective
L-methylfolate 7.5 or 15 mg+SSRI/SNRI
Minimum of 60 days
SSRI/SNRI
CGI-S
The treated group had greater improvement of symptoms versus the
comparator
*Godfrey, 1990
24 (patients with depression)
45.5, 54%
Double-blinded, randomized controlled trial
L-methylfolate 15 mg+psychotropic medication
6 months
Placebo+psychotropic medication
HAM-D17
The treated group trended towards having a greater reduction in
HAM-D versus the comparator
*Kakar, 2017
260
36.9, 53.5%
Double-blinded, randomized controlled trial
L-methylfolate 15 mg+escitalopram
30 days
Placebo+escitalopram
HAM-D17
Response in the treated was better than the comparator
Shelton, 2013
554
49.6, 76.5%
Prospective, naturalistic study
L-methylfolate 7.5 or 15 mg monotherapy or as an adjuvant
with SSRI, SNRI, or other psychotropic medications
90 days
None
PHQ-9
68.1% (n=342) responded and 45%
(n=226) achieved remission
Shelton, 2015
69 patients (same cohort as Papakostas trial 2)
Unable to calculate
Post-hoc analysis of double-blinded, randomized controlled
trial
L-methylfolate 15 mg+SSRI
60 days
Placebo+SSRI
HAM-D17/28
The treated group had a greater response than the comparator.
Inflammatory and obesity-related factors were associated with
improved response in the treated group
*Papakostas (Trial 1), 2012
148
47.9, 69.5%
Double-blinded, randomized controlled trial
L-methylfolate 7.5/15 mg+SSRI
60 days
Placebo+SSRI
HAM-D17
No difference in response between treated and comparator
groups
*Papakostas (Trial 2), 2012
75
48.4, 70.6%
Double-blinded, randomized controlled trial
L-methylfolate 15 mg+SSRI
60 days
Placebo+SSRI
HAM-D17
The treated group had a greater response versus the comparator
group
Papakostas, 2014
74 provided data & 61 completed the study (same cohort as
Papakostas trial 2)
Unable to calculate
Post-hoc analysis of double-blinded, randomized controlled
trial
L-methylfolate 15 mg+SSRI
60 days
Placebo+SSRI
HAM-D28
The treated group had improved response versus the comparator
group when stratified by biological and genetic biomarkers
Wade, 2014
5,404
45.4, 74.5%
Retrospective
7.5 (96.5% of cohort) or 15 mg
L-methylfolate+SSRI/SNRI
>231 days of continuous augmentation
SSRI/SNRI+second-generation antipsychotic
NCQA mHEDIS AMM
The treated group had better adherence scores and lower total and
depression-related costs and utilization than the comparator
group
Zajecka, 2016
68 (same cohort as Papakostas trial 2)
48.3, 52.3%
Open-label follow-up
L-methylfolate 15 mg+SSRI
12 months
None
HAM-D17
38% (n=26) fully recovered with no recurrence of
MDD
*Included in the meta-analysis (n=4). Participants from all
studies were from European ancestry with the exception of Kakar et al. (East
Asian).22. Abbreviations: HAM-D17/28, Hamilton
Depression Rating Scale; SSRI, selective serotonin reuptake inhibitor; SNRI,
serotonin-norepinephrine reuptake inhibitor; NCQA, National Committee for
Quality Assurance; mHEDIS, modified Healthcare Effectiveness Data and
Information Set; AMM, Antidepressant Medication Management; MADRS,
Montgomery-Asberg Depression Rating Scale; MDD, major depressive disorder;
PHQ-9, 9-item Patient Health Questionnaire; CGI-S, Clinical Global
Impression – Severity.
Table 2 Cochrane risk of bias assessment [26 ] of included studies in the
meta-analysis (n=4).
Godfrey et al., 1990 [27 ]
Papakostas et al., 2012 (Trial 1, 7.5 mg) [22 ]
Papakostas et al., 2012 (Trial 2, 15 mg) [22 ]
Kaker et al., 2017 [20 ]
Random sequence generation
+
+
+
+
Allocation concealment
+
+
+
+
Blinding of participants and personnel
+
+
+
+
Blinding of outcome assessment
?
+
+
?
Incomplete outcome data
+
+
+
+
Selective reporting
+
+
+
?
Other sources of bias
+
-
-
+
(+) Low risk of bias; (-) High risk of bias, (?) Unknown risk of
bias.
L-methylfolate, the active form of folate that crosses the blood-brain barrier,
serves as a methyl donor in processes such as the folate and methylation cycles
([Fig. 1 ]) [13 ]. Recent reviews and meta-analyses have
recommended L-methylfolate augmentation for depression and emphasized the role of
L-methylfolate supplementation in the biochemical and physiological processes that
are relevant to the pathophysiology of mood disorders [13 ]
[14 ].
However, most clinical practice guidelines (i. e., Canadian Network for Mood
and Anxiety Treatments, American Psychiatric Association, National Institute for
Health and Care Excellence, and World Federation of Societies of Biological
Psychiatry) do not provide recommendations on L-methylfolate augmentation [15 ]
[16 ]
[17 ]
[18 ]. One exception is the British Association
for Psychopharmacology guidelines, which recommend L-methylfolate augmentation in
patients who are not responsive to selective serotonin reuptake inhibitors (SSRIs)
[19 ]. Further, the recent increased use of
pharmacogenomic tests for MTHFR and L-methylfolate augmentation makes it important
to understand what overall evidence exists for its use in MDD.
To aid efforts to determine the benefits of L-methylfolate augmentation to
antidepressants and its appropriateness in clinical practice, we systematically
searched the peer-reviewed literature and conducted meta-analyses on L-methylfolate
augmentation in adults with MDD using standardized tools and consensus criteria.
Whereas previous reviews and meta-analyses have focused on both folate and
L-methylfolate [14 ], we looked exclusively at
L-methylfolate augmentation and added an additional study that was not included in
previous studies [20 ].
Methods
Search Strategy
This systematic review and meta-analysis were conducted following the PRISMA
(Preferred Reporting Items for Systematic Reviews and Meta-Analyses)
recommendations and registered with PROSPERO (CRD42020218394) [21 ]. Two reviewers (AAM and LCB)
independently searched PubMed for published articles written in English up to
December 31, 2020. The search strategy was “((L-methylfolate OR Deplin
OR methylenetetrahydrofolate reductase OR MTHFR OR folate) AND (therapy OR
augmentation OR treatment OR adjuvant OR adjunctive OR supplementation) AND
(depression OR depressive* OR MDD OR antidepressant)).” Two
reviewers (AAM and LCB) independently searched the titles and abstracts of all
articles identified by the search strategies for eligibility. The full-text
copies of articles that met the inclusion criteria were assessed to ensure
consistency with the eligibility criteria. Bibliographies of all full-text
research articles and review articles were searched manually for additional
references not identified in the primary searches (AAM). Articles for which a
consensus between the two reviewers was not obtained were assessed by a third
reviewer (EAP). The articles that met the inclusion criteria were then selected
for data extraction. Extracted information included database ID, authors,
publication year, study title, subject characteristics, study design and sample
size, diagnosis studied, L-methylfolate dose and duration, comparator,
phenotypes investigated, how and what outcomes were measured, main findings,
safety/side effects, and conflicts of interest information.
Study Selection Criteria
Article inclusion criteria were: (1) examined L-methylfolate adjunctive therapy
in depressive disorders or its effect on antidepressant response in humans, (2)
published in a peer-reviewed, English-language journal, and (3) availability of
the full-text. Review articles, commentaries, books, book chapters, editorial
pieces, or any published material not deemed original research were excluded in
the evaluation. Case and single-arm studies of clinical relevance identified
from the systematic search are reviewed in the discussion section but were not
included as eligible studies in the systematic review and meta-analysis.
Meta-Analysis and Risk of Bias Assessment
Studies were reviewed to identify randomized controlled trials evaluating the use
of adjunctive L-methylfolate in the treatment of depressive disorders by two
independent reviewers (LCB and EAP). For meta-analyses, we only included studies
reporting Hamilton Rating Scale for Depression (HAM-D17) response or scores at
the trial endpoint. Random-effects models were utilized to determine the
relative risk (RR) of response for adjunctive L-methylfolate versus
antidepressant monotherapy. Using the Mantel-Haenszel meta-analytic method,
effect sizes were pooled with 95% confidence intervals (CI) and the
alpha threshold was set at 0.05. Fixed-effects models were performed as a
sensitivity analysis. A second meta-analysis was performed to determine the
standardized mean difference (SMD) of HAM-D17 scores at the trial endpoint.
Missing standard deviation values at the endpoint were estimated using baseline
scores. Using Hedge’s g as the meta-analytic method, effect sizes were
pooled with 95% CI and the alpha threshold was set at 0.05. For both
outcomes, a sensitivity meta-analysis was performed after removing one study
(that used 7.5 mg L-methylfolate) to mitigate variability between studies
regarding different L-methylfolate doses [22 ]. Response rates were pooled from the studies included in the
meta-analysis to calculate the number needed to treat with L-methylfolate
augmentation. Due to the lack of reporting of adverse events, the number needed
to harm was not calculated. Funnel plots and statistical testing for publication
bias were not performed as these techniques are discouraged when the number of
studies is less than 10 [23 ].
Random-effects models were performed as a sensitivity analysis. All analyses
were performed using the “meta” and “metafor”
packages in R version 4.0.3 (Vienna, Austria) [24 ]
[25 ]. The risk of bias of these trials was assessed using the Cochrane
risk of bias tool [26 ].
Results
Systematic Review
The article selection process is summarized as a PRISMA flowchart in [Fig. 2 ]. In total, 800 articles were
identified through PubMed database searches and an additional 16 articles were
identified through manual searches of review article bibliographies, resulting
in a total of 810 articles after duplicates were removed. Seventeen articles
were included for full-text screening. Bibliographies of all full-text research
articles were searched manually for additional references; however, no
additional articles were identified. After the full-text screening, 9 articles
were included in the systematic review, and three articles were identified for
meta-analyses. One article provided data from two independent randomized
controlled trials and both trials met inclusion criteria for the systematic
review and meta-analysis [22 ]. Therefore,
10 studies were included for the systematic review and four studies for the
meta-analyses. Four studies were double-blind, randomized controlled trials,
with three additional studies reporting results from a post-hoc analysis
of one of the trials [22 ]
[27 ]
[28 ]
[29 ]
[30 ]. All studies involving clinical trial
data used HAM-D17 as the primary outcome measurement. One additional study used
a prospective, naturalistic study design and did not have a comparator group
[31 ]. Lastly, two studies were
retrospective case-controlled studies, one of which evaluated the efficacy of
adjunctive L-methylfolate in combination with SSRIs or serotonin-norepinephrine
reuptake inhibitor (SNRI) whereas the other study evaluated adherence and
cost-utilization [32 ]
[33 ]. All studies used L-methylfolate doses
of either 7.5 or 15 mg/day.
Fig. 2 Preferred Reporting Items for Systematic Reviews and
Meta-Analyses (PRISMA) flow chart detailing the article selection
process.
Summary of Included Studies
The largest studies of L-methylfolate augmentation included two randomized,
double-blind, parallel-sequential trials of augmentation with L-methylfolate
(7.5 mg and 15 mg) in adults with partial SSRI response [28 ]. In the first trial, 7.5 mg
L-methylfolate augmentation did not differ from placebo in terms of treatment
efficacy as measured by HAM-D17 in 148 MDD patients. In the second trial, 15 mg
L-methylfolate augmentation to SSRI treatment in adults with MDD (N=75)
produced greater symptomatic improvement (–5.58 vs. –3.04,
p =0.05) and response rates (32.3% vs. 14.6%,
p =0.04) on the HAM-D17 compared to SSRI therapy plus placebo.
Taken together, these studies suggest that augmentation of 15 mg L-methylfolate
with SSRIs may improve outcomes for individuals with MDD and inadequate response
to SSRIs. Two other studies also investigated the efficacy of L-methylfolate
augmentation in patients with MDD. Kakar and colleagues reported that
augmentation with escitalopram and L-methylfolate improved outcomes compared to
placebo in patients with MDD (N=260) [20 ]. Godfrey and colleagues found that L-methylfolate augmentation
over six months improved clinical symptoms compared to placebo in depressed
adults (N=24), but the improvement in HAM-D17 score was not significant
despite lower scores in the L-methylfolate arm [27 ].
In an open-label, naturalistic trial, patients with depression who were treated
with L-methylfolate (7.5 mg or 15 mg) monotherapy or as
augmentation had improved Patient Health Questionnaire-9 scores and improved
functioning [31 ]. However, without a
comparison group, it is difficult to determine if L-methylfolate would
outperform placebo in these patients. Interestingly, one study sought to
understand the economic effects of adjunctive L-methylfolate compared to
antipsychotics. In a large registry of SSRI- and SNRI-treated patients who
received adjunctive L-methylfolate or antipsychotics, patients who received
L-methylfolate had improved adherence scores, as well as lower medical
utilization and depression-related costs compared to those who receive
augmentation with second generations antipsychotics [33 ]. This indicates that L-methylfolate
augmentation may have greater economic savings than adjunctive antipsychotic
therapy in patients with MDD who are treated with SSRIs and SNRIs.
While MTHFR is crucial to converting folic acid to L-methylfolate ([Fig. 1 ]) and may play a role in depression
and antidepressant response, only one of the included studies sought to
determine if genetic variations in MTHFR play a role in treatment
response with L-methylfolate [28 ]. The
authors reported that carriers of the 677 T variant trended towards more
improvement; however, the result was not significant, and neither was the
response rate. The A1298C variant also did not correlate with improvement or
response. Therefore, whether MTHFR variants play a role in response to
L-methylfolate augmentation is not known and additional studies are needed.
Meta-Analysis
For the meta-analysis focusing on HAM-D17 response, two articles reporting three
independent trials were included [20 ]
[22 ]. No heterogeneity between the included
studies was detected (I2= 0%, p =0.43).
However, heterogeneity across the studies is likely present despite the lack of
statistical proof of such heterogeneity. The random-effects model revealed a
25% greater likelihood of response among those receiving L-methylfolate
augmentation compared to those that received SSRI or SNRI monotherapy ([Fig. 3a ], RR=1.25, 95%
CI=1.08 to 1.46, p= 0.004). Further, a fixed-effects model
maintained this significant association (RR=1.26, 95% CI: [1.07
to 1.48], p= 0.005). A sensitivity analysis after removing the one
trial that evaluated adjunctive L-methylfolate at a dose of 7.5 mg,
thereby only including the two trials assessing a 15 mg dose of
L-methylfolate doses, did not result in a significant effect ([Fig. 3b ], RR=1.38, 95%
CI=0.90 to 2.11, p= 0.14) [18 ].
Fig. 3 Hamilton Rating Scale for Depression-17 (HAM-D17) response
meta-analysis of L-methylfolate augmentation studies. (a ) All
controlled studies (N=3), (b ) Only 15 mg of
L-methylfolate augmentation (N=2).
For the meta-analysis focusing on HAM-D17 scores at trial endpoint, three
articles reporting four independent trials were included [20 ]
[22 ]
[27 ]. There was minimal
heterogeneity between the included studies (I2= 16%,
p= 0.31). The random-effects model showed an effect size of
SMD=−0.38 ([Fig. 4a ],
95% CI=−0.59 to −0.17, p= 0.0003).
A fixed-effects model maintained this significant association
(SMD=−0.39, 95% CI=−0.58 to
−0.21, p <0.0001). A sensitivity analysis after removing
the one trial that evaluated adjunctive L-methylfolate at a dose of
7.5 mg, thereby only including the two trials assessing a 15 mg
dose of L-methylfolate doses, resulted in a similar significant effect ([Fig. 4b ], SMD=−0.49,
95% CI=−0.71 to −0.28,
p <0.0001).
Fig. 4 Hamilton Rating Scale for Depression-17 (HAM-D17) scores at
trial endpoint meta-analysis of L-methylfolate augmentation studies.
(a ) All controlled studies (N=4), (b ) Only
15 mg of L-methylfolate augmentation (N=3).
Risk of Bias
The risk of bias was analyzed based on the Cochrane risk of bias assessment tool
[26 ] and a consensus was reached by
all authors. The included studies have a moderate to high risk of bias. It is
not known whether the studies by Godfrey et al. [27 ] and Kakar et al. [20 ] were
blinded. No dropouts were reported in the study by Kakar et al. [20 ]. An author in the studies by Papakostas
also held a patent for the trial design which may present some risk of bias as
well [22 ]
[30 ].
Discussion
The findings from our systematic review and meta-analysis favor the use of
L-methylfolate as an adjunct to antidepressant (i. e., SSRI, SNRI) therapy
for the treatment of MDD. However, the effect sizes were notably small and were
derived from a modest number of patients. Our findings concur with a previous
meta-analysis of folate and its derivatives and the British Association for
Psychopharmacology guidelines for the treatment of depression, which recommended to
(1) not prescribe L-methylfolate as monotherapy in patients with MDD and (2)
consider 15 mg as an adjunct to an SSRI for the treatment of MDD [14 ]
[19 ].
The decision to utilize L-methylfolate as an augmentation strategy, however, should
be considered in light of several caveats of the current evidence. First, the
patients included in published studies to date may not be representative of all MDD
patients. The majority were women of European background in their 40’s, who
had experienced an inadequate response to multiple antidepressant medication trials,
potentially owing to treatment-resistant depression. Whether L-methylfolate
augmentation varies by age, sex, ethnicity, disease severity, or stage of treatment
has yet to be determined and warrants further study. Second, it is unclear whether
specific SSRIs or SNRIs are superior for L-methylfolate augmentation. Among the RCTs
we identified, SSRIs were the most common antidepressants examined but head-to-head
trials will be required to determine superiority. There is also no data on the
efficacy of L-methylfolate augmentation for other antidepressant classes
(e. g., tricyclics). Third, we did not meta-analytically examine adverse
drug reactions or side effects due to the lack of available data in the included
trials. However, adjunctive L-methylfolate appears to be well-tolerated, with
gastrointestinal and somatic adverse events being the most common [20 ]
[22 ]
[30 ]. Previous work has also
suggested tolerability does not vary by MTHFR genotypes [22 ]. Fourth, the impact of MTHFR genetic
variation on adjunctive L-methylfolate efficacy is unclear. Despite strong
biological plausibility, the evidence to date is inconclusive. We only identified
one small study (N=75) that met our inclusion criteria, which failed to find
an association between the C677T polymorphism and response to L-methylfolate
augmentation. Likewise, a recent large study of 426 children and adolescents with
mood disorders, reported that neither improvement nor response to adjunctive
L-methylfolate was influenced by C677T MTHFR genotype [34 ]. Fifth, we did not perform a
meta-regression to adjust for methodological differences across included studies,
given the minimal number of studies included. Sixth, our systematic review and
meta-analysis focused exclusively on adults with MDD. While most of the studies with
L-methylfolate augmentation have been studied in adult patients with MDD, one small
open-label registry study of L-methylfolate in ten patients with bipolar depression
found improvement in outcomes [35 ]. Likewise,
in a case series of 10 adolescents with treatment-resistant depression, 80%
showed improvement with adjunctive L-methylfolate and another study of 190 children
and adolescents with anxiety and mood disorders found fewer adverse events in the
L-methylfolate group compared to the comparator arm [36 ]
[37 ]. However, in 426 children
and adolescents with mood disorders, neither improvement nor response was influenced
by adjunctive L-methylfolate use [34 ]. These
initial findings suggest the need for additional research to understand the effect
of L-methylfolate in other disorders and examine developmental factors that may
contribute to differences in response in pediatric patients. Finally, the study by
Kakar et al. [20 ] had several methodological
issues, e. g., they reported the study as an augmentation study although,
they introduced L-methylfolate as a combination with SSRIs. Moreover, the study did
not have a detailed statistical analysis plan and did not report any dropouts.
Given the limited evidence and modest effect size, this study precludes a thorough
discussion of the clinical considerations for L-methylfolate. While L-methylfolate
appears to play a role in the pathophysiology and treatment of MDD, establishing its
specific place within the psychopharmacologic armamentarium is an ongoing challenge.
Further understanding this heterogeneity of treatment response, especially in
patients with treatment-resistant depression, is of critical importance.
We meta-analytically identified the effects of L-methylfolate on endpoint HAM-D17
response and HAM-D17 score at trial endpoints in patients with MDD. While endpoint
differences are important, faster improvement is also very important for clinicians,
particularly as patients with treatment-resistant depression who improve earlier
have triple the likelihood of achieving remission over longer-term follow-up [38 ]. The time course of response to adjunctive
L-methylfolate remains unclear. Relatedly, the role of L-methylfolate within
sequential or staged approaches warrants further study. Should L-methylfolate be
added early in treatment or after less than predicted improvement over the first 4
weeks and should this differ based on genotype or other factors? Answering these
questions by understanding the trajectory and heterogeneity of L-methylfolate
response will be critical to determining the specific role of L-methylfolate in
MDD.
