Association between mitochondrial DNA and cognitive impairment in schizophrenia: study protocol for a Mexican population

Differences in cognitive impairment and its correlation with circulating cell-free mitochondrial DNA in medication-free depression and bipolar depression patients

OBJECTIVE

This study aimed to investigate whether there are differences in cognitive impairment between medication-free patients with bipolar depression (BD) and major depressive disorder (MDD) and whether these differences are related to circulating cell-free mtDNA (ccf-mtDNA).

METHODS

For this cross-sectional study, 76 outpatients with BD, 86 outpatients with MDD and 70 healthy controls (HCs) were enrolled. Sociodemographic and clinical data were collected. The Repeatable Battery for the Assessment of Neuropsychological Status (RBANS) and the Stroop Color-Word Test were used to assess cognitive function. Plasma ccf-mtDNA levels were measured via qPCR.

RESULTS

BD and MDD patients had similar scores for immediate memory, language, attention, delayed memory, the RBANS total score, Stroop color, Stroop word, and Stroop total score, which were significantly lower than the HCs. The visuospatial/constructive scores of the BD patients were significantly lower than those of the HCs (p < 0.001) and MDD patients (p = 0.008), but there was no difference between the HCs and MDD patients. The ccf-mtDNA levels in the BD and MDD patient groups were significantly higher than those in the HC group, and those in the MDD group were higher than those in the BD group (p = 0.016). Multiple stepwise regression analysis showed that ccf-mtDNA was negatively correlated with language in patients with depression (t = -2.11, p = 0.039).

CONCLUSION

There were differences in specific cognitive dimensions between patients with BD and MDD. Increased ccf-mtDNA levels were found in BD and MDD patients, suggesting ccf-mtDNA may be involved in the pathophysiology of MDD and BD.

Circulating Cell-Free Mitochondrial DNA in Plasma of Individuals with Schizophrenia and Cognitive Deficit in Mexican Population

Purpose

Cognitive domains are affected in patients with schizophrenia. Mitochondrial dysfunction has been proposed as a possible origin of these symptoms. Cell-free mitochondrial DNA (cf-mtDNA) is an indicator of cellular stress, and it can be identified in individuals with age-associated disorders, this study aimed to explore the presence of cf-mtDNA in plasma of schizophrenia patients and its association with cognitive deficit.

Patients and Methods

Ninety-nine subjects were clinically evaluated; the case group included 60 patients diagnosed with schizophrenia and 39 randomly-individuals without psychiatric disorders were included in the comparison group. Cognitive status (MoCA scale) and cell-free mtDNA in blood plasma were assessed and quantified in both groups.

Results

From the original sample, cf-mtDNA was identified in 43 subjects, 40 patients with schizophrenia and 3 controls (Χ2 = 31.10, p-value < 0.0001). Thirty-nine out of forty patients with schizophrenia had a cognitive deficit.

Conclusion

According to our findings, cognitive impairment and presence of cf-mtDNA were related in subjects with schizophrenia. Thus, while the cognitive deficit might reflect an accelerated aging process, the cf-mtDNA plays a role as a potential biomarker in this mechanism.

Association of Urinary Biomarkers of Renal Tubular Injury with Cognitive Dysfunction in Older Patients with Chronic Kidney Disease: A Cross-Sectional Observational Study

Epidemiological data suggest that individuals in all stages of chronic kidney disease (CKD) have higher risks of developing cognitive impairment. The relationship between CKD and cognition has been assessed exclusively using glomerular function markers; however, kidney tubule injury has not been assessed. We assessed the association between urinary biomarkers of renal tubular injury and cognitive dysfunction in older patients with CKD Stages 3–4. According to the Montreal Cognitive Assessment, participants were divided into cognitive dysfunction and control groups. Compared with the control group, the cognitive dysfunction group had significantly higher percentages of smokers, noticeably lower average education, and higher mitochondrial DNA (mtDNA) levels in the peripheral blood. Spearman correlation analysis showed that higher urine neutrophil gelatinase-associated lipocalin, kidney injury molecule-1, and beta-2 microglobulin (β2M) levels were significantly associated with lower cognitive scores. Multivariate logistic regression analysis showed that only increased urinary β2M levels were independently associated with cognitive worsening in CKD after adjusting for confounders. Logistic regression identified a promising role of urinary β2M combined with smoking and education for predicting cognitive impairment in CKD. Urinary β2M and cognitive function negatively correlated with mtDNA content, suggesting that mitochondrial dysfunction is a common pathophysiological mechanism linking CKD and cognitive dysfunction.

Neurobiological Highlights of Cognitive Impairment in Psychiatric Disorders

This review is focused on several psychiatric disorders in which cognitive impairment is a major component of the disease, influencing life quality. There are plenty of data proving that cognitive impairment accompanies and even underlies some psychiatric disorders. In addition, sources provide information on the biological background of cognitive problems associated with mental illness. This scientific review aims to summarize the current knowledge about neurobiological mechanisms of cognitive impairment in people with schizophrenia, depression, mild cognitive impairment and dementia (including Alzheimer's disease).The review provides data about the prevalence of cognitive impairment in people with mental illness and associated biological markers.

Evidence for the Role of Mitochondrial DNA Release in the Inflammatory Response in Neurological Disorders

Mitochondria are regarded as the metabolic centers of cells and are integral in many other cell processes, including the immune response. Each mitochondrion contains numerous copies of mitochondrial DNA (mtDNA), a small, circular, and bacterial-like DNA. In response to cellular damage or stress, mtDNA can be released from the mitochondrion and trigger immune and inflammatory responses. mtDNA release into the cytosol or bloodstream can occur as a response to hypoxia, sepsis, traumatic injury, excitatory cytotoxicity, or drastic mitochondrial membrane potential changes, some of which are hallmarks of neurodegenerative and mood disorders. Released mtDNA can mediate inflammatory responses observed in many neurological and mood disorders by driving the expression of inflammatory cytokines and the interferon response system. The current understanding of the role of mtDNA release in affective mood disorders and neurodegenerative diseases will be discussed.

Mitochondrial Dysfunction and Changes in High-Energy Compounds in Different Cellular Models Associated to Hypoxia: Implication to Schizophrenia

Schizophrenia (SZ) is a multifactorial mental disorder, which has been associated with a number of environmental factors, such as hypoxia. Considering that numerous neural mechanisms depends on energetic supply (ATP synthesis), the maintenance of mitochondrial metabolism is essential to keep cellular balance and survival. Therefore, in the present work, we evaluated functional parameters related to mitochondrial function, namely calcium levels, mitochondrial membrane potential, redox homeostasis, high-energy compounds levels and oxygen consumption, in astrocytes from control (Wistar) and Spontaneously Hypertensive Rats (SHR) animals exposed both to chemical and gaseous hypoxia. We show that astrocytes after hypoxia presented depolarized mitochondria, disturbances in Ca²⁺ handling, destabilization in redox system and alterations in ATP, ADP, Pyruvate and Lactate levels, in addition to modification in NAD⁺/NADH ratio, and Nfe2l2 and Nrf1 expression. Interestingly, intrauterine hypoxia also induced augmentation in mitochondrial biogenesis and content. Altogether, our data suggest that hypoxia can induce mitochondrial deregulation and a decrease in energy metabolism in the most prevalent cell type in the brain, astrocytes. Since SHR are also considered an animal model of SZ, our results can likewise be related to their phenotypic alterations and, therefore, our work also allow an increase in the knowledge of this burdensome disorder.