The 481 patients with inflammatory marker data were evaluated between 23 and 120 days after hospital discharge (mean=59.7 days). Their mean age was 60 years (range=26–90), and 18.9% were women. Most (81.7%) had had an acute myocardial infarction (Q-wave myocardial infarction, 22.5%) at the time of the index hospitalization, 19.3% had undergone coronary artery bypass surgery at that time, and 49.1% were classified as having the metabolic syndrome. The DSM-IV criteria for a current major depressive episode were met by 7.3% of the study group, with 4.4% experiencing a first depression. The overall lifetime prevalence of major depression was 21.2%.
The levels of the three inflammatory markers were significantly related, and the correlation between IL-6 and C-reactive protein (r=0.58, N=481, p<0.001) was somewhat higher than the correlation between sICAM-1 and IL-6 (r=0.17, N=481, p<0.001) or between sICAM-1 and C-reactive protein (r=0.21, N=481, p<0.001).
+Table 1 shows the mean values of the inflammatory markers and other baseline characteristics for subjects with current major depression and those without.
sICAM-1 was the only inflammatory marker significantly related to current major depression (
+Table 1) . There was also a significant interaction between current and past depression (F=3.98, df=1, 477, p=0.05). To illustrate this interaction,
+Figure 1 uses the group’s upper quartile of sICAM-1 levels (≥210 ng/ml) since there are no established cutoff values for high sICAM-1 levels. Although the currently depressed patients tended to have higher sICAM-1 levels regardless of whether or not they had a previous depression (main effect from ANOVA: F=9.18, df=1, 477, p=0.003), the link between current depression and sICAM-1 was much more marked in the individuals with a first depression. None of the interactions between age or sex and current depression for the inflammatory markers had a p value less than 0.20.
Besides having higher levels of sICAM-1, the depressed were also more likely to be women, to have had a previous depression, and to smoke daily, as well as to take antidepressants (
+Table 1). In addition, there was a significantly higher rate of metabolic syndrome among the depressed, largely due to a higher rate of hypertriglyceridemia and a nonsignificantly higher rate of abdominal obesity. The depressed and nondepressed patients did not differ significantly in body mass index, insulin level, diagnosis at the time of the index admission, or the number of major blockages on the cardiac angiogram.
In addition to the diagnosis of major depression, sICAM-1 levels were significantly related to older age (r=0.11, N=481, p=0.02), female sex (F=13.79, df=1, 479, p<0.001), smoking (F=7.03, df=1, 479, p=0.008), previous myocardial infarction or coronary revascularization procedure (F=7.84, df=1, 479, p=0.005), and the metabolic syndrome (F=18.76, df=1, 479, p<0.001), including all of its individual components except hypertension (p=0.15). Body mass index was also significantly related to sICAM-1 (r=0.14, N=481, p=0.002). Patients taking adenosine diphosphate (ADP) inhibitors had significantly higher sICAM-1 levels than other patients (F=5.69, df=1, 479, p=0.02). Those taking antidepressants (F=2.81, df=1, 479, p=0.10) and those not receiving statin therapy (F=3.40, df=1, 479, p=0.07) had marginally higher sICAM-1 levels. The sICAM-1 level was not significantly related to past depression, left ventricular ejection fraction, number of vessels blocked on the coronary angiogram, coronary bypass surgery at index hospitalization, or prescription of aspirin, beta-blockers, or ACE inhibitors (for all, p>0.40).
Variables that were at least marginally related to both sICAM-1 level and major depression (p<0.10) were selected as potential confounders of the observed link between the two and entered in the first step of a multiple linear regression analysis to predict sICAM-1 level. Major depression was entered in the second step. As shown in
+Table 2, the difference in sICAM-1 levels between patients with major depression and those without remained significant (p=0.04) after statistical control for sex, current smoking, and the presence of the metabolic syndrome, suggesting that the link between depression and sICAM-1 was not explained by these factors. The relationship was slightly attenuated when antidepressant treatment was added to the model (p=0.06). The results were similar when abdominal obesity and hypertriglyceridemia were substituted for the metabolic syndrome classification. The interaction between current and past depression remained at least marginally significant after adjustment for the covariates in all models (for all, p<0.07).
All patients had documented coronary artery disease, and although they were stable, their cardiac medications could not be safely withdrawn. These medications included statins, which are known to influence inflammatory markers
+(28). It is conceivable that statin treatment reduced levels of inflammatory markers in our study group and obscured differences between the depressed and nondepressed groups. In fact, prescription of statins showed a nearly significant association with all three markers. To determine whether statin therapy may have masked the relationship between depression and inflammation, we used ANOVA to assess the two-way interaction between depression and statins for each of the three inflammatory markers. The interaction for C-reactive protein was significant (F=6.35, df=1, 477, p=0.02). This interaction is illustrated in
+Figure 1, for which a cutoff value of 3.0 mg/liter was used to determine high levels of C-reactive protein, as suggested by Liuzzo and Biasucci
+(9). While depression was associated with higher levels of C-reactive protein in patients not taking statins (for continuous log-transformed data, F=7.10, df=1, 148, p=0.009), there was no relationship in those receiving statin therapy (p=0.41). The interactions for IL-6 (p=0.59) and sICAM-1 (p=0.11) were not significant.
Higher levels of C-reactive protein were significantly associated with age (r=0.10, N=481, p=0.03), female sex (F=5.29, df=1, 479, p=0.03), previous myocardial infarction or coronary revascularization procedure (F=5.97, df=1, 479, p=0.02), the metabolic syndrome (F=11.24, df=1, 479, p=0.001) (including all components except triglyceride and HDL levels), and body mass index (r=0.25, N=481, p<0.001). When the factors significantly related to CRP and to major depression (sex and metabolic syndrome) were entered along with major depression and statin use into the first step of a multiple linear regression analysis, with the interaction entered in the second step, the interaction of C-reactive protein and statin use remained significant (F=6.57, df=1, 475, p=0.01).