Lymphocyte-derived and lipoprotein-derived inflammatory ratios as biomarkers in bipolar disorder type I: Characteristics, predictive values, and influence of current psychopharmacological treatments.

Purpose Of This Research: The purpose of this research was to investigate peripheral inflammation by analyzing lymphocyte and lipoprotein-derived inflammatory ratios in patients with bipolar disorder type I (BD-I) and healthy controls (HCs), considering mood stabilizer drug treatments, sex and clinical trajectories.

Methods: This was a cross-sectional case-control study of BD-I patients (n=252) and healthy controls (n=62). We investigated peripheral inflammation biomarkers through blood count values (CBCs), lipoproteins and a complex panel of inflammatory ratios, including the neutrophil-to-lymphocyte ratio (NLR), monocyte-to-lymphocyte ratio (MLR), platelet-to-lymphocyte ratio (PLR), systemic immune-inflammation index (SII), systemic inflammation response index (SIRI), neutrophil-to-HDL ratio (NHR), monocyte-to-HDL ratio (MHR), platelet-to-HDL ratio (PHR) and lymphocyte-to-HDL ratio (LHR). Furthermore, we examined the effects of sex, drug treatment and clinical outcome on the inflammatory profile.

Results: We found that the monocyte-to-lymphocyte ratio (MLR) and lipoprotein-derived inflammatory ratio (NHR, MHR, PHR, and LHR) were significantly greater in BD-I patients than in control individuals. The monocyte-to-HDL ratio (MHR) showed acceptable accuracy as a disease predictor. Logistic regression analysis adjusted for sex, age and BMI indicated that the risk of having a BD-I diagnosis was greater for participants with MHR levels in quartiles 3 (OR= 5.2, p=0.001) and 4 (OR=13, p<0.001). There was a strong association between lithium treatment and increased inflammation represented by elevated lymphocyte-derived inflammatory ratios (NLR, MLR, PLR, SII, and SIRI) in lithium-treated BD-I patients compared to those in lithium-free or lithium treatment-naïve BD-I patients. The main limitations are the cross-sectional nature of the study and limited sample size of HCs.

Major Conclusions: Several CBCs, lipoproteins, and a complex panel of inflammatory ratios, including lymphocyte-derived inflammatory ratios (NLR, MLR, PLR, SII, and SIRI) and lipoprotein-derived inflammatory ratios (NHR, MHR, PHR, and LHR), are altered in individuals diagnosed with BD-I. The monocyte-to-HDL ratio (MHR) emerged as a disease predictor in our BD-I sample. A remarkable finding is the association of lithium and valproate treatment with the inflammatory state. Considering the study limitations, our results underscore the importance of pharmacological treatments when researching inflammation markers in mood disorders. Lymphocyte-derived and lipoprotein-derived inflammatory ratios are easy-to-implement and relevant biomarkers in BD-I patients.