Research reportThe expression of genes encoding for COX-2, MPO, iNOS, and sPLA2-IIA in patients with recurrent depressive disorder
Introduction
Depressive disorder is the heterogenic disease. Activation of inflammatory, oxidative, and nitrosative stress (IO&NS) pathways plays an important role in the pathophysiology (Maes et al., 2011a). There is evidence showing that the production of free radicals and their derivatives is increased in depression (Gałecki et al., 2009, Kodydková et al., 2009, Kotan et al., 2011). Increased levels of proinflammatory mediators are now well established in depression (Maes, 2011). There are also results showing that key inflammatory enzymes, including cyclooxygenase-2 (COX-2), myeloperoxidase (MPO), inducible nitric oxide synthase (iNOS) are involved in the disease in question (Guo et al., 2009, Vaccarino et al., 2008, Wang et al., 2008). The aforementioned enzymes not only contribute to inflammatory processes, but also participate in the production of free radicals and damage to fatty acids, DNA and proteins (Aktan, 2004, Dubois et al., 1998, Hansson et al., 2006, Kuehl and Egan, 1980, Valko et al., 2007, Winterbourn, 2002).
COX-2 enzyme is one of the two isoforms of COX producing prostaglandins from arachidonic acid. The level of COX-2 is raised in chronic inflammatory diseases and may be induced by cytokines (Dubois et al., 1998). There is also evidence that COX-2 may participate in neurodegenerative processes (Mirjany et al., 2002) but it also plays a role in brain physiology (Minghetti, 2004). The expression of COX-2 is observed not only in inflammatory cells, but also in the central nervous system (CNS) (Yasojima et al., 1999). The importance of COX-2 in depression is indicated by the therapeutic effectiveness of COX-2 inhibitors in the treatment of depression and in animal models (Müller et al., 2006, Myint et al., 2007). Moreover, in animal model of depression increased expression of mRNA for COX-2 was observed in hippocampal region (Cassano et al., 2006).
MPO is a heme enzyme expressed in brain cells (Jolivalt et al., 1996) and in immune cells and that plays an important role in the regulation of inflammatory processes and causes oxidative damage (Hansson et al., 2006). Activation of MPO leads to the production of hypochlorous acid and other toxic oxidants (Winterbourn, 2002) that function as antimicrobial agents (Heinecke, 1999, Podrez et al., 2000). There are studies showing that low levels of MPO reduces the risk of cardiovascular diseases (CVD) (Zhang et al., 2001), an inflammatory disorder (Carr and Frei, 2000) that co-exists with depression (Maes et al., 2011b, McCaffery et al., 2006). MPO deficiency also attenuates cytokine production (Haegens et al., 2009). Recently Vaccarino et al. (2008) found that higher MPO is one of the biomarkers of inflammation in depression. Additionally, increased expression in brain region is related to neurodegeneration (Green et al., 2004), a process that also accompanies depressive disorder (Maes et al., 2011a).
The next enzyme involved in inflammation and oxidative stress is iNOS producing nitric oxide (NO). The molecule is important in many physiological and pathological processes including inflammation and oxidative stress (Hirst and Robson, 2011). iNOS constitutes an inducible form, which expression is present in numerous inflammatory cells in the periphery and in brain. iNOS expression is also observed in neurons following biological stimuli including proinflammatory cytokines, lipopolysacharides, and stress as well (Aktan, 2004, Heneka and Feinstein, 2001, Kleinert et al., 2004). All those factors play a role in the onset of depression (Kubera et al., 2011, Maes, 2011). Evidence for the involvement of iNOS includes: increased level of iNOS-derived NO in patients suffering from depression (Suzuki et al., 2001), inhibition of the iNOS that lowers the depressive-like behaviors (Wang et al., 2008), reduced NOS activity followed by antidepressant treatment (Wegener et al., 2003), both performed on animal model.
Secretory phospholipases A2 (sPLA2s) are important enzymes detected in blood of patients with inflammatory disorders. These enzymes catalyze the reaction of fatty acids production from phospholipids (Triggiani et al., 2006). sPLA2s produce other inflammatory mediators and reactive oxygen species (Adibhatla and Hatcher, 2008, Triggiani et al., 2006). The expression of sPLA2 is low in resting inflammatory peripheral cells, but their release is mediated by pro-inflammatory factors (Balboa and Balsinde, 2006). The mainly investigated type of sPLA2s that is involved in inflammation is type IIA (sPLA2-IIA) enzyme. In the brain, mRNA for sPLA2-IIA is observed (Sun et al., 2004) and activation of sPLA2 type IIA contributes to neuronal death (Schaeffer et al., 2010). Moreover, sPLA-IIA appears to be a risk factor of CVD (Koenig et al., 2009), because sPLA2-IIA makes oxidized LDL more atherogenic (Divchev and Schieffer, 2008).
Recently, biological studies observed that polymorphism of the genes encoding COX-2, MPO and iNOS are related to the risk of recurrent depressive disorder (rDD) (Gałecki et al., 2010a, Gałecki et al., 2010b, Gałecki et al., 2011).
The aim of the present study was to investigate mRNA expression of PTGS2, MPO, NOS2A, PLA2G2A coding aforementioned four enzymes in patients suffering from rDD versus normal controls.
The reason to investigate the gene expression in the whole blood resulted from the fact that all these enzymes are not only expressed in brain but mainly in the periphery. There is also strong evidence that peripheral molecules might affect brain cells. Moreover, whole blood is more accessible. Peripheral blood cells share more than 80% of the transcriptome with nine tissues including brain (Mehta et al., 2010).
Section snippets
Subjects
A group of 181 patients, treated for rDD (102 females; 56.4%), were enrolled into the study. The mean age in that group was 42.6 ± 8.2 years (mean ± SD). The diagnosis was established according to ICD-10 criteria (F33.0–F33.8) (World Health Organization, 1992). In all qualified cases, medical history was obtained, using the standardized Composite International Diagnostic Interview (CIDI) (World Health Organization, 1992). Additionally, the number of depressive episodes, duration of the disease and
Results
There were no differences in age and gender between depressed patients and controls. Table 1 and Fig. 1 show significantly higher mRNA expression for COX-2, MPO, iNOS and sPLA2 in rDD patients than in control subjects.
Relationships were not also observed between mRNA expression levels and such clinical variables as the age at disease onset, disease duration and the number of episodes (Mann–Whitney U-test; p > 0.05).
Discussion
The major finding of this study is that the mRNA expressions of the genes encoding COX-2, MPO, iNOS, and sPLA2 were significantly higher in rDD than in controls. This is a first study showing increased expression of mRNA of these genes in depressive disorders. Our results collaborate those of previous studies which showed that the levels or activities of all four enzymes are significantly increased in depressive disorder and/or processes characteristic for depression (Balboa and Balsinde, 2006,
Conclusion
Our study suggests that COX-2, MPO, iNOS and sPLA2-IIA expression is increased during depression in the peripheral cells. The data indicate that increased expression of COX-2, MPO, iNOS, and sPLA2-IIA, which are key IO&NS enzymes, might be one of the mechanisms of underpinning the pathophysiology of rDD. Our results further extent the role of inflammation and O&NS in the etiology of depression. Our findings suggest that peripheral IO&NS gene expression may explain the molecular mechanism and be
Role of funding source
All the researches were financed from the resources of Medical University of Łódź, No 502-03/5-062-02/502-54-016.
Conflict of interest
No conflicts of interest were declared.
Acknowledgment
None.
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Both authors contributed equally to this work.