The demographic profile of the population that was used in this analysis can be seen in . For the sample of individuals with major depression and their matched controls, there were no differences in age (p = 0.93), race (p = 1.00) or years of education (p = .15). Individuals with major depression exhibited a significantly higher body mass index (BMI; p = 0.001) compared with their matched controls, and they were also more likely to be daily smokers (p = 0.02). The number of alcoholic drinks consumed in a week was higher, but not significantly, in individuals with major depression (p = 0.07). For the sample of individuals with minor depression and their matched controls, there were no differences between the two groups on age (p = 0.80), race (p = 0.84), percentage of daily smokers (p = 0.17) or alcoholic drinks consumed per week (p = 0.62), however years of total education was non-significantly lower in individuals with minor depression (p = 0.06).
Demographic characteristics of sample population (mean variable +/− SD)
In women with major depression, serum 2-AG was significantly reduced [t (30) = 2.098, p = 0.04; ] (serum 2-AG for major depression: 12.5 +/− 5.6 pmol/ml serum vs. matched controls: 19.6 +/− 12.5 pmol/ml serum), with an effect size of 0.57 standard deviations. This effect was marginally reduced by controlling for tobacco use (p = 0.08), and marginally enhanced by controlling for BMI (p = 0.03).
Figure 1 Serum content of the endocannabinoids anandamide (AEA) and 2-arachidonylglycerol (2-AG) in women with: a) major depression and their matched controls (n=16/group); or b) women with minor depression and their matched controls (n=12 for minor depression; (more ...)
To examine if this reduction in serum 2-AG was related to severity, chronicity or symptom profile of major depression, we examined the correlation of serum 2-AG to each of these variables in the major depression cohort. Serum 2-AG content was found to exhibit a significant negative correlation with duration of current depressive episode (r = −.492, p = 0.05; ). Within the sample of subjects with major depression, there was no difference in serum 2-AG between those with recurrent major depression and those in their first episode [t (14) = 0.133, p = 0.90]. Serum 2-AG did not significantly correlate with total Hamilton score (r = −.09, p = 0.74), suggesting that this reduction of 2-AG was not directly related to depression severity.
Serum content of the endocannabinoid 2-arachidonlyglycerol (2-AG) exhibited a significant negative correlation (r = −.492) with the duration of the current depressive episode (in weeks).
Serum AEA content did not differ between subjects with major depression and their matched controls [t (30) = 0.205, p = 0.84; ] (serum AEA for major depression: 0.74 +/− 0.32 pmol/ml serum vs. matched controls: 0.72 +/− 0.29 pmol/ml serum). While serum AEA was not correlated with total Hamilton score (r = −.24, p = 0.38), serum AEA exhibited a highly significant, negative correlation with scores on both the Hamilton variable for cognitive anxiety (r = −.647, p < 0.01; ) and somatic anxiety (r = −.674, p < 0.01; ), such that individuals who demonstrated higher measures of anxiety, exhibited lower serum AEA content. Serum AEA content did not correlate with any other Hamilton rating. Serum AEA did not correlate with duration of current depressive episode (r = .30, p = 0.25), nor did serum AEA content differ between subjects who experienced recurrent depression as opposed to those who were experiencing their first episode [t (14) = 1.12, p = 0.28].
(a) Serum content of the endocannabinoid N-arachidonylethanolamine (anandamide; AEA) exhibited a significant negative correlation (r = −.647) with Hamilton ratings for cognitive anxiety.
Serum AEA content was significantly increased in patients with minor depression compared to their matched controls [t (21) = 2.48, p = 0.02; ] (serum AEA for minor depression: 0.95 +/− 0.44 pmol/ml serum vs. matched controls: 0.60 +/− 0.18 pmol/ml serum), with a robust effect size of 1.96 standard deviations. Serum 2-AG was higher in patients with minor depression; however, this was not significant [t (21) = 1.26, p = 0.22; ] (2-AG in minor depression: 26.4 +/− 18.32 pmol/ml serum vs matched controls: 18.18 +/− 12.37 pmol/ml serum, effect size = 0.67 standard deviations). The length of the current depressive episode appeared to correlate with both serum AEA (r = .51, p = .09) and serum 2-AG (r = .50, p = .10), such that serum contents of both these molecules were higher the longer the duration of the episode. However, because of the small number of patients in these analyses, these effects were not statistically significant. There were no significant differences in serum AEA [t (10) = −.169, p = .12] or serum 2-AG [t (10) = 1.76, p = .11] between those experiencing a first episode of depression versus recurrent depression. There was no significant correlation between total Hamilton score and serum AEA (r = −.19, p = .55). The correlation between total Hamilton scores and serum 2-AG content was positive (r = .51, p = .10), but nonsignificant because of the sample size of 12 subjects. It should be noted that one sample from the control group to the minor depression patients was compromised during the extraction procedure and thus data from this individual is not included in the data set.