Changes in cytokine levels in major depression and during treatment have been reported in adults. However, few studies have examined cytokine levels in an adolescent sample despite this being a common age of onset.
MDD is a world health problem that affects people of all ages. In adolescents, MDD has increased significantly in the past ten years, with estimated prevalence rates ranging between 2 and 5.6% [
Currently, there are few works on children and adolescents in relation to cytokine profiles and their corresponding clinical follow-up. Some works performed in children and adolescents have reported cytokine disturbances similar to those described in adults, such as the case of IL-1
This work aimed at detecting alterations in the cytokine profiles of adolescents with a first episode of MDD during eight weeks of clinical follow-up (treatment with fluoxetine) as well as the correlation between symptomatology and inflammatory profiles.
The Adolescent Clinic of Instituto Nacional de Psiquiatría Ramón de la Fuente, Mexico City, assessed 337 individuals and recruited a total of 22 patients that met the inclusion criteria from January 2006 to December 2008. The inclusion criteria consisted of patients between ages 14 and 19 diagnosed with moderate MDD according to the DSM-IV-TR. The patients had a minimum baseline score in the HDRS equal or higher than 14.
All included patients agreed to participate in this study and signed the informed consent forms. Patient recruitment was done following the experimental clinical procedures of the INPRF-2035 research protocol and approved by the ethics committee of Instituto Nacional de Psiquiatría, México. Eighteen healthy volunteers (HV) aged between 14 and 19 participated in this study and were considered the reference group.
Psychiatrists diagnosed all the subjects, while the clinical status of adolescents with MDD was determined using the validated Spanish version of the 21-item HDRS [
Throughout the study, all patients were evaluated monthly by their psychiatrist, who applied the HDRS. Blood samples were taken from patients at baseline (week 0, W0) and weeks 4 (W4) and 8 (W8) of antidepressant treatment. Figure
Flow diagram of eight-week fluoxetine treatment in adolescents with major depressive disorder.
Fluoxetine dose was 20 mg/day. The dose was established for each patient by their psychiatrist and was adjusted when necessary throughout the study. All patients purchased their drug.
Peripheral blood (10 mL) was collected by venipuncture from the ratio humeral venous plexus into Vacutainer® SST™ tubes with gel for serum separation (REF: 367988 BD Vacutainer System, Franklin Lakes, NJ. USA). Blood samples were centrifuged immediately (1125 × g) at 4°C for 15 minutes to obtain serum. Serum samples were separated into aliquots and stored at −80°C until analysis.
Levels of human cytokines (IL-2, IFN-
Statistical analysis of HDRS results was performed by one-way ANOVA for repeated measures with Bonferroni’s
Twenty-two adolescents with MDD who met the inclusion criteria participated in this study. The demographic characteristics of the patients group as well as the reference group with 18 healthy volunteers are described in Table
Demographic data.
Healthy volunteers; |
MDD adolescents; | |
---|---|---|
Age (years) | 18.9 ± 1.2 | 17.1 ± 2.3 |
Gender (male/female) | 4/14 | 4/18 |
BMI (kg/m2) | 23.2 ± 2.1 | 23.1 ± 2.1 |
Education (years) | 12.9 ± 1.2 | 11.5 ± 2.6 |
Family history (yes/no) | 3/15 | 8/14 |
First episode | NA | 8 |
Recurrent episode | NA | 14 |
Values are presented as mean ± standard deviation. Statistical analysis was performed by Student’s
The results of the HDRS scale show that the adolescents had improvement in the symptomatology of MDD at four (W4) and eight weeks (W8) of treatment with fluoxetine. One-way ANOVA for repeated measures showed a significant difference between treatments with an
Clinical score of HDRS test in adolescents with MDD during eight weeks of clinical follow-up with fluoxetine. W0: baseline; W4: four weeks of fluoxetine treatment; W4: eight weeks of fluoxetine treatment. Statistical analysis was performed by one-way ANOVA with Bonferroni’s
The cytokine levels in the serum of MDD adolescents were measured at baseline (W0) and weeks four (W4) and eight (W8) of treatment. The results are described below. Figures
Proinflammatory cytokine serum level comparison between healthy volunteers and adolescents with MDD at baseline (previous to fluoxetine treatment).
Proinflammatory cytokine serum levels of adolescents with MDD during eight weeks of treatment with fluoxetine. W0: baseline; W4: four weeks of fluoxetine treatment; W8: eight weeks of fluoxetine treatment. Statistical analysis was performed by one-way ANOVA for repeated measures using Dunnett’s
Anti-inflammatory cytokine serum level comparison between healthy volunteers and adolescents with MDD at baseline (without fluoxetine treatment).
Anti-inflammatory cytokine serum levels of adolescents with MDD during eight-week treatment with fluoxetine. W0: baseline; W4: four weeks of fluoxetine treatment; W8: eight weeks of fluoxetine treatment. Statistical analysis was performed by one-way ANOVA for repeated measures using Dunnett’s
Dunnett’s multiple comparisons showed that IL-2 significantly increased (
Dunnett’s multiple comparisons showed that IL-1Ra levels significantly decreased (
MDD has been little studied in adolescents; therefore, there are scarce reports on cytokine profiles along drug treatment. Most of the works on MDD are
In this work, we present the proinflammatory (IL-2, IFN-
Several clinical studies have reported disturbances in the levels of IL-2 in either adult or adolescent MDD patients. In this study, we observed that IL-2 was significantly higher in MDD adolescents than in healthy volunteers, which is in agreement with previous reports in adolescents with mood disorders [
Just like IL-2, disturbances in IFN-γ levels have been reported in MDD patients. In our work, IFN-γ was significantly higher in MDD adolescents, as previously reported [
IFN-
Significantly high levels of IL-1
Concerning our work, it is likely that extended clinical follow-up times might be useful to detect a clearer effect of fluoxetine on concentrations of IL-1
In our work, we found a significant increase in TNF-
Several clinical trials using monoclonal anti-TNF-
In children and adolescents, IL-6 has been identified as a good biomarker of psychopathology. The levels of IL-6 are significantly higher in patients with a diagnosis of affective, anxiety, adjustment, psychotic, obsessive-compulsive, and Tourette disorders [
Therapy with tocilizumab, a monoclonal antibody against the IL-6 receptor, showed improvement in fatigue symptomatology among patients with rheumatoid arthritis, a disorder strongly related to depression, which positions IL-6 as a therapeutic target of depression [
The levels of IL-12p70 that we determined in this work were significantly higher in MDD adolescents regarding the control group. To date, we are not aware of other studies evaluating IL-12p70 in MDD adolescents, but the reports in adults correspond with our results, showing significantly higher levels of IL-12 in MDD patients, as compared with the control group [
Little is known about the role of IL-15 in MDD; to the best of our knowledge, this is the first report in adolescents. In adults, Simon et al. reported increased IL-15 in MDD patients [
Studies in rodents have shown that both IL-15 and IL-15 receptor (IL-15R
The role of IL-4 in depression is not yet well established. Most of the research on IL-4 in MDD provides reports on adults, with a small number on adolescents. In our work, we found increased levels of IL-4 in MDD adolescents, which contradicts previous reports on patients with psychopathology [
The role of IL-5 in MDD adolescents has been scarcely studied. In 2015, Gariup et al. (2015) performed a study in children and adolescents with acute psychopathology in which a set of twelve cytokines, including IL-5, was evaluated. However, they did not find significant differences between IL-5 in patients and controls. In this work, we found elevated levels of IL-5 in MDD adolescents, as compared to healthy volunteers, which correspond to previous works in adults [
Previous studies have revealed an increase of circulatory levels of IL-13 in MDD adults when compared to healthy volunteers [
The role of IL-1Ra in the development of depression has been evidenced in a model of depression in mice, in which it has been demonstrated that the IL-1/IL-1Ra signaling induces depressive-like symptoms by two potential mechanisms: the reduction of adrenocortical activation and the reduction of hippocampal neurogenesis [
IL-10 alterations have been associated with depressive symptoms such as fatigue, loss of appetite, and anhedonia [
Alterations in cytokine levels and depression are closely related, especially in adolescents. Although the direct connection is not fully clear yet, some factors have been suggested to link them. For example, genetic polymorphisms in IL-10 and IL-6 have been associated with a higher risk of suffering depression [
In general, we reported that MDD adolescents have higher levels of proinflammatory and anti-inflammatory cytokines than healthy volunteers, except for IL-10 and IL-1Ra. Up to now, the mechanism by which fluoxetine affects cytokine levels remains unclear. However, a temporary effect or fluctuations in cytokine levels has been observed during clinical follow-up in previous works [
Week eight has been considered by several groups as a suitable time to evaluate the therapeutic efficacy of fluoxetine in MDD adolescents given the possibility of observing an improvement in the symptomatology at this time [
It should be noted that some discrepancies in our results with respect to other reports may make sense if we consider the heterogeneity of sample sources, demographic data, sampling times, and diversity in analytical procedures used in each study.
Despite that our cytokine determinations were performed at systemic level, it is well known that chronic elevations in systemic cytokine levels impairs the permeability of the blood-brain barrier, facilitating the entry of cytokines into the brain [
It is important to consider that some of the patients initially diagnosed with first-episode depression may later exhibit bipolar disorder. Therefore, we consider that an 8-week follow-up is a limitation to evaluate the probability of a change of diagnosis in this population (conversion to activation syndrome or bipolar disorder); however, none of our patients presented symptoms of activation syndrome or bipolar disorder during the treatment period. Although it has been reported that this conversion can occur at any time during SSRI treatment, there seems to be a tendency for it to appear during the first 2 or 3 weeks after drug initiation [
In this work, we found that MDD adolescents have higher levels of proinflammatory and anti-inflammatory cytokines than the healthy volunteers, except for IL-10 and IL-1Ra. To the best of our knowledge, this is the first report in adolescents with MDD in which alterations of IL-12, IL-13, and IL-15 are reported. Moreover, we described that fluoxetine treatment affects proinflammatory and anti-inflammatory cytokines in a temporal manner; however, no correlation was detected between the cytokine levels and the HDRS clinical score. The background of the relationship between cytokines and depression suggests that the altered inflammatory profiles that we observed in MDD adolescents may be contributing to the physiopathology of this disorder, although these inflammatory molecules are only one of the multiple biological alterations present in this disease.
The group of healthy volunteers had to include subjects of legal age (age 18+), according to Mexican law; otherwise, recruiting healthy underaged adolescents willing to take part in the study would have been complicated since the authorization of parents or guardian is required. In fact, recruiting underaged adolescents with MDD was complicated since the authorization of parents or guardian is required; thus, the sample size obtained was small.
The cytokine levels and psychiatric values used to support the findings of this study are available from the corresponding author upon request.
The authors declare no conflicts of interest associated with the present manuscript.
GPS, EBV, RA, GML, CTS, MEHG, MAVV, SAH, CCF, FP, and LP drafted the paper. All authors reviewed the paper and approved the final version.
This work was supported in part by the Instituto Nacional de Psiquiatría Ramón de la Fuente Muñiz: Project NC150048SECITI, SECITI 0048/2014, and NC16044.0 and Proyect FT-IPN: IC-10-002. We appreciate the assistance of Erick Hernandez Ferreira, Guadalupe López Bello, Ericka Flores Ortega, and Eliuth Juárez Cruz.