Genetic variants in nuclear-encoded mitochondrial proteins are associated with oxidative stress in obsessive compulsive disorders

The Oxidative Status and Na+/K+-ATPase Activity in Obsessive-Compulsive Disorder: A Case Control Study

Background

Oxidative stress is involved in pathogenesis of some psychiatric disorders. To examine the role of oxidative stress in the etiopathogenesis of obsessive-compulsive disorder (OCD), we aimed to determine oxidative stress indices, including malondialdehyde (MDA) levels in serum and red blood cells (RBC) membrane, total antioxidant capacity (TAC), serum glutathione (GSH) levels, serum antioxidant vitamins (A and E), and Na+/K+-ATPase activity, in patients with the mentioned disorder vs. healthy controls.

Method

39 OCD patients diagnosed based on Diagnostic and Statistical Manual of Mental Disorders (DSM-V) and 39 volunteer healthy subjects were included in this study. MDA levels in serum and RBC membrane were measured using fluorometric method. Serum TAC level, serum GSH level, and Na+/K+-ATPase activity were also measured using spectrophotometric methods. Serum levels of vitamins were calculated by reversed-phase high-performance liquid chromatography (RP-HPLC).

Result

There was a significantly higher MDA level in serum (p < 0.0001) and RBC membrane (p = 0.002) of OCD patients compared with those in controls. A significant reduction in vitamin A (p = 0.001) and vitamin E (p = 0.024) levels was found in OCD patients vs. controls. There was significantly lower activity of erythrocyte membrane Na+/K+-ATPase in RBC membrane of OCD patients vs. controls (p < 0.0001).

Conclusion

Our findings indicate significantly higher levels MDA in both serum and RBC membrane, lower levels of serum vitamins A and E, and lower activity of membrane Na+/K+-ATPase in OCD patients compared to controls. These suggest an imbalance between oxidant and antioxidant factors in OCD patients that might play a fundamental role in the etiopathogenesis of OCD.

Potential biomarkers and therapeutic targets for obsessive compulsive disorder: Evidences from clinical studies

Obsessive compulsive disorder (OCD) is a prevalent behavioral disorder with a complex etiology. However, the underlying pathogenic molecular pathways and the associated risk factors are largely obscure. This has hindered both the identification of relevant prognostic biomarkers and the development of effective treatment strategies. Because of the diverse range of clinical manifestations, not all patients benefit from therapies currently practiced in the clinical setting. Nevertheless, several lines of evidence indicate that neurotrophic, neurotransmitter, and oxidative signaling are involved in the pathophysiology of OCD. Based upon evidences from clinical (and pre-clinical studies), the present review paper sets out to decipher the utilities of three parameters (i.e. brain-derived neurotrophic factor; BDNF, noradrenalin-synthesizing enzyme dopamine beta-hydroxylase; DBH; and oxidative damage marker malondialdehyde; MDA) as diagnostic peripheral biomarkers as well as bio-targets for therapeutic strategies. While the data indicates promising results, there is necessitation for future studies to further confirm and establish these. Further, based again on the available clinical data, we investigated the possibilities of exploiting the etiological links between disruptions in the sleep-wake cycle and insulin signaling, and OCD for the identification of potential anti-OCD ameliorative agents with the ability to elicit multimodal effects, including attenuation of the alterations in BDNF, noradrenergic and redox pathways. In this respect, agomelatine and metformin may represent particularly interesting candidates; however, further clinical studies are warranted to establish these as singular or complementary medications in OCD subjects.

The Disease Model of Addiction: The Impact of Genetic Variability in the Oxidative Stress and Inflammation Pathways on Alcohol Dependance and Comorbid Psychosymptomatology

Oxidative stress and neuroinflammation are involved in the pathogenesis of alcohol addiction. However, little is known regarding the effect of genetic, behavioral, psychological, and environmental sources of origin on the inflammation and oxidative stress pathways of patients with alcohol addiction. Our study aimed to evaluate the impact of selected common functional single-nucleotide polymorphisms in inflammation and oxidative stress genes on alcohol addiction, and common comorbid psychosymptomatology. Our study included 89 hospitalized alcohol-addicted patients and 93 healthy individuals, all Slovenian males. Their DNA was isolated from peripheral blood and patients were genotyped for PON1 rs705379, rs705381, rs854560, and rs662, SOD2 rs4880, GPX1 rs1050450, IL1B rs1143623, rs16944, and rs1071676, IL6 rs1800795, IL6R rs2228145, and miR146a rs2910164. Kruskal-Wallis and Mann-Whitney tests were used for the additive and dominant genetic models, respectively. Our findings suggested the involvement of IL6 rs1800795 in alcohol addiction. Moreover, our data indicated that the genetic variability of SOD2 and PON1, as well as IL1B and IL6R, may be related to comorbid psychosymptomatology, revealing a potential indirect means of association of both the oxidative stress and inflammation pathways.

Postinfectious Inflammation, Autoimmunity, and Obsessive-Compulsive Disorder: Sydenham Chorea, Pediatric Autoimmune Neuropsychiatric Disorder Associated with Streptococcal Infection, and Pediatric Acute-Onset Neuropsychiatric Disorder

Postinfectious neuroinflammation has been implicated in multiple models of acute-onset obsessive-compulsive disorder including Sydenham chorea (SC), pediatric acute-onset neuropsychiatric syndrome (PANS), and pediatric autoimmune neuropsychiatric disorders associated with streptococcal infection (PANDAS). These conditions are associated with a range of autoantibodies which are thought to be triggered by infections, most notably group A streptococci (GAS). Based on animal models using huma sera, these autoantibodies are thought to cross-react with neural antigens in the basal ganglia and modulate neuronal activity and behavior. As is true for many childhood neuroinflammatory diseases and rheumatological diseases, SC, PANS, and PANDAS lack clinically available, rigorous diagnostic biomarkers and randomized clinical trials. In this review article, we outline the accumulating evidence supporting the role neuroinflammation plays in these disorders. We describe work with animal models including patient-derived anti-neuronal autoantibodies, and we outline imaging studies that show alterations in the basal ganglia. In addition, we present research on metabolites, which are helpful in deciphering functional phenotypes, and on the implication of sleep in these disorders. Finally, we encourage future researchers to collaborate across medical specialties (e.g., pediatrics, psychiatry, rheumatology, immunology, and infectious disease) in order to further research on clinical syndromes presenting with neuropsychiatric manifestations.

Dietary quality and nutrient intake in adults with obsessive–compulsive disorder

Background

Many mental disorders, including depression, bipolar disorder and schizophrenia, are associated with poor dietary quality and nutrient intake. There is, however, a deficit of research looking at the relationship between obsessive–compulsive disorder (OCD) severity, nutrient intake and dietary quality.

Aims

This study aims to explore the relationship between OCD severity, nutrient intake and dietary quality.

Method

A post hoc regression analysis was conducted with data combined from two separate clinical trials that included 85 adults with diagnosed OCD, using the Structured Clinical Interview for DSM-5. Nutrient intakes were calculated from the Dietary Questionnaire for Epidemiological Studies version 3.2, and dietary quality was scored with the Healthy Eating Index for Australian Adults – 2013.

Results

Nutrient intake in the sample largely aligned with Australian dietary guidelines. Linear regression models adjusted for gender, age and total energy intake showed no significant associations between OCD severity, nutrient intake and dietary quality (all P > 0.05). However, OCD severity was inversely associated with caffeine (β = −15.50, 95% CI −28.88 to −2.11, P = 0.024) and magnesium (β = −6.63, 95% CI −12.72 to −0.53, P = 0.034) intake after adjusting for OCD treatment resistance.

Conclusions

This study showed OCD severity had little effect on nutrient intake and dietary quality. Dietary quality scores were higher than prior studies with healthy samples, but limitations must be noted regarding comparability. Future studies employing larger sample sizes, control groups and more accurate dietary intake measures will further elucidate the relationship between nutrient intake and dietary quality in patients with OCD.

Thiol/disulfide homeostasis in medication-naive children and adolescents with obsessive-compulsive disorder

Obsessive-compulsive disorder (OCD) causes significant psychic distress and affects children's social and academic functioning. Approximately 80% of OCD cases begin in childhood. Earlier onset is associated with more severe OC symptoms, poorer treatment response, and a more unfavorable clinical course. A particular oxidative stress marker, thiol/disulfide homeostasis, using a new, comparatively inexpensive, easily calculated, easily accessible, repeatable, and fully automated method was investigated between pediatric patients diagnosed with OCD and a healthy control group in this study. This study is the first to address this subject in pediatric patients with OCD and aims to contribute to our knowledge of the etiopathogenesis and treatment of pediatric OCD. The study included children with OCD (n = 35, 52.2%) (drug free, comorbidity free) between 11 and 18 years of age and age- and sex-matched healthy controls (n = 32, 47.8%). The total thiol (p = 0.025) and disulfide (p = 0.001) levels and the disulfide/native thiol (p = 0.001) and disulfide/total thiol ratios (p = 0.001) were significantly different between the groups. Also, in the patient group, biochemical analysis revealed that the disulfide level (p = 0.05) and the disulfide/native thiol (p = 0.034) and disulfide/total thiol ratios (p = 0.039) differed significantly according to the presence of a family history of psychiatric disorders. Consequently, the results of our study show that thiol/disulfide homeostasis may affect the etiopathogenesis of pediatric OCD and can be utilized as a new method when evaluating oxidative stress.

Malondialdehyde concentrations in obsessive-compulsive disorder: a systematic review and meta-analysis

BACKGROUND

This meta-analysis aimed to investigate serum and plasma malondialdehyde (MDA) levels in patients with obsessive-compulsive disorder (OCD) in comparison to healthy controls.

METHODS

Following the PRISMA protocol, we searched for the relevant studies through the databases of Scopus, PubMed, Google Scholar, and web of science until September 2019 with no time restriction. Overall, nine studies were included in the current meta-analysis. Data were pooled using a random-effects model; in addition, standard mean difference (SMD) and/or weight mean difference (WMD) was calculated. Cochran's Q test and I-square (I2) statistics were used to evaluate between-study heterogeneity. The Newcastle-Ottawa scale (NOS) was used to evaluate the quality of the included studies. Statistical analyses were done using the STATA version 14.

RESULTS

Our systematic review included nine case-control studies (including 367 cases and 337 controls). Pooling findings from these studies showed a significantly higher MDA level in OCD patient compared to control groups (SMD = 1.62; 95% CI [0.53, 2.72]; I2 = 96.9%; Pheterogeneity (Ph) < 0.001). This finding remained unchanged among studies which reported MDA in the same unit (WMD = 1.93; 95% CI [0.27, 3.59]; I2 = 99.2%; Ph < 0.001). Subgroup analysis by the study location and sample size revealed findings that were also significant.

CONCLUSION

We found that MDA levels are higher in OCD patients than healthy controls. This finding highlights the importance of inflammatory responses in OCD patients that should be considered for future investigations. Further studies are recommended to expand current knowledge on this issue.

Increased Production of the Potent Oxidant Peroxynitrite in the Serum of Obsessive-Compulsive Disorder Patients

Background: There is growing evidence that oxidative stress may play a principal role in the etiology of psychiatric disorders, such as obsessive-compulsive disorder (OCD). The potent oxidant peroxynitrite (ONOO-) is the final yield of rapid reaction nitric oxide (NO) and superoxide anions. Objectives: The present study aimed to investigate whether serum peroxynitrite levels in patients with OCD disorder can be used as an oxidative biomarker Methods: Twenty-one patients with freshly diagnosed OCD and not using any drugs and 19 healthy volunteers were enrolled in this study. Serum peroxynitrite levels were measured in the control and OCD groups. Results: Serum peroxynitrite values in patients with newly diagnosed OCD were significantly increased compared to the control group (7.968 ± 2.576 µmol/L in patients and 4.983 ± 1.300 µmol/L in the control) and were significantly correlated with Yale-Brown Obsession Compulsion Scale scores. However, they were not significantly different between male and female groups. Conclusions: Our findings revealed a correlation between increased peroxynitrite level and OCD. Serum peroxynitrite level may be considered an oxidative biomarker for OCD patients in the future. It seems that using drugs with antioxidant properties can be used for the prevention of further damage by oxidants in the treatment of OCD patients.

Riding the tiger - physiological and pathological effects of superoxide and hydrogen peroxide generated in the mitochondrial matrix

Elevated mitochondrial matrix superoxide and/or hydrogen peroxide concentrations drive a wide range of physiological responses and pathologies. Concentrations of superoxide and hydrogen peroxide in the mitochondrial matrix are set mainly by rates of production, the activities of superoxide dismutase-2 (SOD2) and peroxiredoxin-3 (PRDX3), and by diffusion of hydrogen peroxide to the cytosol. These considerations can be used to generate criteria for assessing whether changes in matrix superoxide or hydrogen peroxide are both necessary and sufficient to drive redox signaling and pathology: is a phenotype affected by suppressing superoxide and hydrogen peroxide production; by manipulating the levels of SOD2, PRDX3 or mitochondria-targeted catalase; and by adding mitochondria-targeted SOD/catalase mimetics or mitochondria-targeted antioxidants? Is the pathology associated with variants in SOD2 and PRDX3 genes? Filtering the large literature on mitochondrial redox signaling using these criteria highlights considerable evidence that mitochondrial superoxide and hydrogen peroxide drive physiological responses involved in cellular stress management, including apoptosis, autophagy, propagation of endoplasmic reticulum stress, cellular senescence, HIF1α signaling, and immune responses. They also affect cell proliferation, migration, differentiation, and the cell cycle. Filtering the huge literature on pathologies highlights strong experimental evidence that 30-40 pathologies may be driven by mitochondrial matrix superoxide or hydrogen peroxide. These can be grouped into overlapping and interacting categories: metabolic, cardiovascular, inflammatory, and neurological diseases; cancer; ischemia/reperfusion injury; aging and its diseases; external insults, and genetic diseases. Understanding the involvement of mitochondrial matrix superoxide and hydrogen peroxide concentrations in these diseases can facilitate the rational development of appropriate therapies.

Converging evidence points towards a role of insulin signaling in regulating compulsive behavior

Obsessive-compulsive disorder (OCD) is a neuropsychiatric disorder with childhood onset, and is characterized by intrusive thoughts and fears (obsessions) that lead to repetitive behaviors (compulsions). Previously, we identified insulin signaling being associated with OCD and here, we aim to further investigate this link in vivo. We studied TALLYHO/JngJ (TH) mice, a model of type 2 diabetes mellitus, to (1) assess compulsive and anxious behaviors, (2) determine neuro-metabolite levels by 1 H magnetic resonance spectroscopy (MRS) and brain structural connectivity by diffusion tensor imaging (DTI), and (3) investigate plasma and brain protein levels for molecules previously associated with OCD (insulin, Igf1, Kcnq1, and Bdnf) in these subjects. TH mice showed increased compulsivity-like behavior (reduced spontaneous alternation in the Y-maze) and more anxiety (less time spent in the open arms of the elevated plus maze). In parallel, their brains differed in the white matter microstructure measures fractional anisotropy (FA) and mean diffusivity (MD) in the midline corpus callosum (increased FA and decreased MD), in myelinated fibers of the dorsomedial striatum (decreased FA and MD), and superior cerebellar peduncles (decreased FA and MD). MRS revealed increased glucose levels in the dorsomedial striatum and increased glutathione levels in the anterior cingulate cortex in the TH mice relative to their controls. Igf1 expression was reduced in the cerebellum of TH mice but increased in the plasma. In conclusion, our data indicates a role of (abnormal) insulin signaling in compulsivity-like behavior.

Oxidative and nitrosative stress markers in obsessive-compulsive disorder: a systematic review and meta-analysis

OBJECTIVE

Obsessive-compulsive disorder (OCD) is a chronic, prevalent, and highly impairing psychiatric illness. Although the pathophysiology of OCD remains unknown, pathways involved in oxidative and nitrosative stress (O&NS) have been implicated. The present study aims to systematically review the literature for quantitative evidence that patients with OCD have altered measures of blood O&NS markers.

METHODS

Independent random-effects meta-analyses using standardized mean differences were conducted to assess each marker separately. Additionally, data from multiple markers were pooled together in a meta-analysis for measures of oxidant activity and another for measures of antioxidant activity.

RESULTS

Thirteen studies met inclusion criteria, involving 433 OCD patients and 459 controls. Eleven blood O&NS markers were eligible for independent quantitative analyses. We found that, in OCD patients, the oxidant markers 8-hydroxydeoxyguanosine and malondialdehyde, and the antioxidants glutathione peroxidase and superoxide dismutase, were significantly increased while total antioxidant status, vitamin C, and vitamin E were significantly decreased, when comparing with controls. Regarding pooled meta-analyses, we found a statistically significant increase in oxidant markers, but non-significant results regarding antioxidant markers.

CONCLUSIONS

Our meta-analysis suggests that OCD patients have a systemic oxidative imbalance that is not adequately buffered by the antioxidant system. Additional studies are needed in order to support this association.

Do polygenic risk and stressful life events predict pharmacological treatment response in obsessive compulsive disorder? A gene-environment interaction approach

The rate of response to pharmacological treatment in Obsessive-compulsive disorder (OCD) oscillates between 40 and 70%. Genetic and environmental factors have been associated with treatment response in OCD. This study analyzes the predictive ability of a polygenic risk score (PRS) built from OCD-risk variants, for treatment response in OCD, and the modulation role of stressful life events (SLEs) at the onset of the disorder. PRSs were calculated for a sample of 103 patients. Yale-Brown Obsessive Compulsive Scale (YBOCS) scores were obtained before and after a 12-week treatment. Regression analyses were performed to analyze the influence of the PRS and SLEs at onset on treatment response. PRS did not predict treatment response. The best predictive model for post-treatment YBOCS (post YBOCS) included basal YBOCS and age. PRS appeared as a predictor for basal and post YBOCS. SLEs at onset were not a predictor for treatment response when included in the regression model. No evidence for PRS predictive ability for treatment response was found. The best predictor for treatment response was age, agreeing with previous literature specific for SRI treatment. Suggestions are made on the possible role of neuroplasticity as a mediator on this association. PRS significantly predicted OCD severity independent on pharmacological treatment. SLE at onset modulation role was not evidenced. Further research is needed to elucidate the genetic and environmental bases of treatment response in OCD.

Oxidative Stress Implications in the Affective Disorders: Main Biomarkers, Animal Models Relevance, Genetic Perspectives, and Antioxidant Approaches

The correlation between the affective disorders and the almost ubiquitous pathological oxidative stress can be described in a multifactorial way, as an important mechanism of central nervous system impairment. Whether the obvious changes which occur in oxidative balance of the affective disorders are a part of the constitutive mechanism or a collateral effect yet remains as an interesting question. However it is now clear that oxidative stress is a component of these disorders, being characterized by different aspects in a disease-dependent manner. Still, there are a lot of controversies regarding the relevance of the oxidative stress status in most of the affective disorders and despite the fact that most of the studies are showing that the affective disorders development can be correlated to increased oxidative levels, there are various studies stating that oxidative stress is not linked with the mood changing tendencies. Thus, in this minireview we decided to describe the way in which oxidative stress is involved in the affective disorders development, by focusing on the main oxidative stress markers that could be used mechanistically and therapeutically in these deficiencies, the genetic perspectives, some antioxidant approaches, and the relevance of some animal models studies in this context.

LOWER POSTERIOR CINGULATE CORTEX GLUTATHIONE LEVELS IN OBSESSIVE-COMPULSIVE DISORDER

BACKGROUND

Several lines of evidence support the hypothesis that lower cerebral levels of glutathione (GSH), associated with increased oxidative stress, may contribute to obsessive-compulsive disorder (OCD). However, no studies to date have investigated brain GSH levels in individuals with OCD.

METHODS

Twenty-nine individuals with OCD and 25 age-, sex-, and race-matched comparison individuals without OCD underwent single voxel 2D J-resolved proton magnetic resonance spectroscopy (MRS) to examine GSH levels in the posterior cingulate cortex (PCC). MRS data were analyzed using LCModel and a simulated basis set. Group metabolite differences referenced to total creatine (Cr), as well as relationships between metabolite ratios and symptom severity as measured by the Yale-Brown Obsessive-Compulsive Scale (Y-BOCS), were analyzed using linear regression with adjustment for age, sex, and race.

RESULTS

One OCD participant failed to produce usable PCC MRS data. We found significantly lower PCC GSH/Cr in OCD participants compared with non-OCD participants (β = -0.027 [95% CI: -0.049 to -5.9 × 10^-3]; P = 0.014). PCC GSH/Cr was not significantly associated with total Y-BOCS score in the OCD group (β = 5.7 × 10^-4 [95% CI: -4.8 × 10^-3 to 5.9 × 10^-3]; P = 0.83).

CONCLUSIONS

Lower PCC GSH/Cr may be indicative of increased oxidative stress secondary to hypermetabolism in this brain region in OCD. Future MRS studies are warranted to investigate GSH levels in other brain regions that comprise the cortico-striato-thalamo-cortical circuit thought to be abnormal in OCD.

Striatal magnetic resonance spectroscopy abnormalities in young adult SAPAP3 knockout mice

BACKGROUND

Obsessive compulsive disorder (OCD) is a debilitating condition with lifetime prevalence of 1-3%. OCD typically arises in youth but delays in diagnosis impede optimal treatment and developmental studies of the disorder. Research using genetically modified rodents may provide models of etiology that enable earlier detection and intervention. The SAPAP3 knockout (KO) transgenic mouse was developed as an animal model of OCD and related disorders (OCRD). KO mice exhibit compulsive self-grooming behavior analogous to behaviors found in people with OCRD. Striatal hyperactivity has been reported in these mice and in humans with OCD.

METHODS

Striatal and medial frontal cortex 9.4 Tesla proton spectra were acquired from young adult SAPAP3 KO and wild-type control mice to determine whether KO mice have metabolic and neurochemical abnormalities.

RESULTS

Young adult KO mice had lower striatal lactate (P=0.006) and glutathione (P=0.039) levels. Among all mice, striatal lactate and glutathione levels were associated (R=0.73, P=0.007). We found no group differences in medial frontal cortex metabolites. At the age range studied, only 1 of 8 KO mice had skin lesions indicative of severe compulsive grooming.

CONCLUSION

Young adult SAPAP3 KO mice have striatal but not medial frontal cortex MRS abnormalities that may reflect striatal hypermetabolism accompanied by oxidative stress. These abnormalities typically preceded the onset of severe compulsive grooming. Our findings are consistent with striatal hypermetabolism in OCD. Together, these results suggest that striatal MRS measures of lactate or glutathione might be useful biomarkers for early detection of risk for developing compulsive behavior disorders.

Oxidative stress and mitochondrial dysfunction across broad-ranging pathologies: toward mitochondria-targeted clinical strategies

Beyond the disorders recognized as mitochondrial diseases, abnormalities in function and/or ultrastructure of mitochondria have been reported in several unrelated pathologies. These encompass ageing, malformations, and a number of genetic or acquired diseases, as diabetes and cardiologic, haematologic, organ-specific (e.g., eye or liver), neurologic and psychiatric, autoimmune, and dermatologic disorders. The mechanistic grounds for mitochondrial dysfunction (MDF) along with the occurrence of oxidative stress (OS) have been investigated within the pathogenesis of individual disorders or in groups of interrelated disorders. We attempt to review broad-ranging pathologies that involve mitochondrial-specific deficiencies or rely on cytosol-derived prooxidant states or on autoimmune-induced mitochondrial damage. The established knowledge in these subjects warrants studies aimed at elucidating several open questions that are highlighted in the present review. The relevance of OS and MDF in different pathologies may establish the grounds for chemoprevention trials aimed at compensating OS/MDF by means of antioxidants and mitochondrial nutrients.

Oxidative imbalance in child and adolescent patients with obsessive compulsive disorder

Various psychological, social, genetic and biochemical factors are thought to be involved in etiology of obsessive-compulsive disorder (OCD). To the best of our knowledge there are no studies investigating the effects of free radicals in children and adolescents with OCD. This study evaluated total oxidant and antioxidant status, oxidative stress index, and arylesterase and paraoxonase activity in children and adolescents with OCD. The study included 28 patients diagnosed with OCD and 36 healthy children as an age- and sex-matched control group. Their serum total oxidant status (TOS) and total antioxidant status (TAS) were measured and the oxidative stress index (OSI) was calculated. Although serum TOS and OSI values in the OCD patients were significantly higher than those in the control group (p = 0.008, p < 0.001, respectively), TAS and paraxonase activity were significantly lower ( p < 0.001 for both). However, no statistically significant difference in arylesterase activity was found (p > 0.05). The increase in oxidative status and decrease in antioxidants in patients with OCD demonstrate that oxidative stress may have an important role in the pathophysiology of the disease. It has been suggested that drugs that contain antioxidants should be added to conventional pharmacotherapy during follow-up.

A critical review of magnetic resonance spectroscopy studies of obsessive-compulsive disorder

Functional neuroimaging studies have converged to suggest that cortico-striatal-thalamo-cortical (CSTC) circuit dysfunction is a core pathophysiologic feature of obsessive-compulsive disorder (OCD). Now, complementary approaches examining regional neurochemistry are beginning to yield additional insights with regard to the neurobiology of aberrant CSTC circuitry in OCD. In particular, proton magnetic resonance spectroscopy, which allows for the in vivo quantification of various neurochemicals in the CSTC circuit and other brain regions, has recently been used extensively in studies of OCD patients. In this review, we summarize the diverse and often seemingly inconsistent findings of these studies, consider methodological factors that might help to explain these inconsistencies, and discuss several convergent findings that tentatively seem to be emerging. We conclude with suggestions for possible future proton magnetic resonance spectroscopy studies in OCD.