MECHANISM OF ACTION OF ELECTROCONVULSIVE THERAPY (ECT): A NEUROIMMUNOCHEMICAL APPROACH

Background: Electroconvulsive therapy (ECT) is one of the most effective and fast acting therapeutic options for treatment-resistant psychiatric diseases, in particular mood disorders. Mood disorders are highly heterogeneous, disabling and severe mental illness, at still unknown etiology, which have been associated with a multifaceted pathogenesis, encompassing genetic, epigenetic and metabolic vulnerabilities together psychosocial/lifestyle factors. Among the various biological patterns thought to be involved in the physiopathology of dysthymia, major depression, cyclothymia, bipolar I, II, mixed states and related disorders, alterations in the neuroendocrine and immune systems have been also evidenced. Additionally, an increasing number of studies have highlighted the relevance of impaired mechanisms of defense against reactive oxygen species (ROS) in the progression and severity of BD. Oxidative stress and redox states are indeed part of the metabolic and chemical networks of the immune/inflammation response. Despite such evidences, few studies have examined, by now, the impact of ECT on specific neuroendocrine, immune and oxidative stress paths in patients undergoing this therapy. It has been reported that ECT-induced epileptic seizures stimulate the intra-cerebral release of cytokines, including the cytokine network associated with the pathophysiology of affective disorders. It is therefore challenging to consider that the therapeutic efficacy of ECT may reside on the degree of activation of the immune/inflammatory system and that patients, under depressive, hypomanic, manic or mixed states, may change their specific profile of biochemical/immunological markers by ECT. ECT would thus act on complex biochemical cascades, formed by several neurotransmitters, neuro-hormones, neurotrophic factors and metabolic substrates, playing a significant therapeutic role. Hypothesis: Beside possible neurotransmitter and neurotrophin variations, mood disorder patients would also present significant changes of peripheral cytokine and oxidative stress profiles, before and after ECT; it might be thus possible to identify specific redox chemical and immune features related to the response/Non-response to this treatment. Such a result could also considerably help to detect peripheral molecular correlates of immunochemical dysregulation, refractory symptoms and ECT therapeutic benefits or adverse effects in mood disorders. Aims: The foremost aims of this study were: 1) to explore the degree of expression/activity of peripheral immune and oxidative stress markers during the course of ECT in bipolar patients; 2) to possibly evidence differences of these biochemical parameters among Remitter and Non-Remitter patients, assessed by means of suitable examinations and psychometric questionnaires, administered to recruited patients before, during and after ECT. Methods: From 2016 to 2018, we recruited and investigated 17 consecutive patients with a BD diagnosis accordingly to DSM-V diagnostic criteria, all treated by ECT at the Psychiatry section of the Department of Clinical and Experimental Medicine of the University of Pisa. All patients were examined during three main phases of ECT course, following this schedule: 1) at T0, by both psychometric and biochemical evaluations, before the first application; 2) at T1, by biochemical evaluations carried out 3 hours after the first application; 3) at T2, at the end of the treatment, by both psychometric and biochemical examinations. A forth biochemical assessment was carried out also at T3, 3 hours after the last application, in order to possible appraise a different reactivity of immune/oxidative stress patterns at the end of ECT applications. To constantly monitor patients, psychiatric and physical examinations were always performed for the duration of the study. Psychometric questionnaires carried out prior to (T0) and after (T3) the ECT course, consisted into: the Hamilton Depression Rating Scale-17 (HAM-D), Young Mania Rating Scale (YMRS), Brief Psychiatric Rating Scale (BPRS) and Clinical Global Improvement Impression (CGI) scale. The CGI subscale “global improvement”, final HAM-D and YMRS total scores were used to identify Remitter and Non-Remitter groups . Biochemical investigations, performed after blood samplings carried out at the 4 scheduled times, T0, T1, T2 and T3, were: 1)-the plasma levels of the immune/inflammatory cytokines IL-6, IL-8 and TNFα; 2)-the plasma levels/ activity of the antioxidant enzymes catalase (CAT) and superoxide dismutase (SOD), total thiols (R-SH), the ferric reducing ability of plasma (FRAP), uric acid as well as an index of oxidative damage, the advanced oxidation plasma protein products (AOPP). Results: At the end of therapy, about the 53% of ECT-treated BD patients was found to remit. Concerning biochemical investigation, we observed that, globally, in 17 subjects, 3 hours after ECT (T1), the activity of SOD in plasma increased nearly attaining the statistical significance, while FRAP was found significantly decreased; when analyzing Remitters and Non-Remitters separately, the nearly significant increased SOD reported in all patients at T1, after the first ECT application, was due to a greater enzyme activity in Remitters, while the global T1 FRAP reduction was due to the significant decrease of plasma ferric reducing power in Non-Remitters only. We also reported that Non-Remitters had a significantly reduced CAT activity both at T1 and in the long term, at the end of ECT course (T2), and a higher percent of responce in uric acid and IL 8 after the last ECT (T3 vs. T2). Also, Non-Remitters tended to concomitantly have, at T2, higher plasma FRAP, SOD,IL6 and lower CAT, Thiols in respect to baseline (T0) values as well as in respect to Remitters. No significant effect on the plasma level of AOPP was observed at any scheduled time in all patients, indicating that no relevant protein damage, due to ROS was reported during ECT sessions. Limitations: The study, at the present stage, had a small sample size; moreover the patient group was heterogeneous, consisting of treatment resistant bipolar patients in different phases of illness and with different pharmacological regimes. Conclusions: According to literature, we showed that ECT is an effective and safe treatment able to heal drug-resistant bipolar patients with very severe clinical presentation and risk of suicide, in all phases of the illness. Preliminary results suggest that ECT can induce changes of the antioxidant system: an increased ROS scavenging activity at T1 seems to be an index of favorable response. The diminuition of antioxidant defense system would be conversely linked to reduced benefits deriving from this therapy. The recruitment of a larger cohort of patients is needed to confirm and pursue this useful investigation of peripheral biomarkers of ECT response. This will permit to perform more robust statistical tests as multivariate regression or principal component analyses and to possibly define peculiar immunochemical changes related to the clinical response.