Higher fasting serum insulin levels are associated with a better psychopathology profile in acutely ill non-diabetic inpatients with schizophrenia

New insights into the interaction between polycystic ovary syndrome and psychiatric disorders: A narrative review

Polycystic ovary syndrome (PCOS) is a prevalent endocrine disease characterized by hyperandrogenism, ovulatory dysfunction, and ovarian polycystic changes, which combines with reproductive problems, metabolic disorders, and psychological disorders to exhibit a far-reaching impact on the physical and mental health of women. We reviewed previous research and discovered that psychiatric disorders are more common in PCOS patients and their children, potentially exacerbating the condition and creating a vicious loop. To understand the reasons, relevant articles were collected following the Preferred Reporting Items for Systematic Reviews and Meta-analyses guidelines from PubMed, Web of Science, and Cochrane Library, through December 2022. Evidence suggested that PCOS-related clinical manifestations, hyperandrogenism, insulin resistance, obesity, gut dysbiosis, and other variables may increase the risk of psychiatric disorders in patients. In turn, psychiatric disorders may aggravate the pathologic process of PCOS and increase the difficulty of the treatment. We systematically reported the mechanisms underlying the psychiatric disorders-PCOS interactions, intending to provide potential ways to break the vicious cycle and lay the groundwork for future research. However, research on PCOS and psychiatric disorders were still in initial stages, which limited the scope of this review. More studies are needed to further verify our findings.

Body mass index, waist circumference, insulin, and leptin plasma levels differentiate between clozapine-responsive and clozapine-resistant schizophrenia

BACKGROUND

Between 25% and 50% of patients suffering from treatment-resistant schizophrenia fail to achieve a clinical response with clozapine. The rapid identification and treatment of this subgroup of patients represents a challenge for healthcare practice.

AIMS

To evaluate the relationship between metabolic alterations and the clinical response to clozapine.

METHODS

A multicenter, observational, case-control study was performed. Patients diagnosed with schizophrenia treated with clozapine were eligible (minimum dose 400 mg/d for at least 8 weeks and/or clozapine plasma levels ⩾ 350 µg/mL). According to the Positive and Negative Syndrome Scale (PANSS) total score, patients were classified as clozapine-responsive (CR) (<80 points) or clozapine non-responsive (CNR) (⩾80 points). Groups were compared based on demographic and treatment-related characteristics, together with body mass index (BMI), waist circumference, insulin, leptin, and C-reactive protein plasma levels. Plasma levels of clozapine and its main metabolite, nor-clozapine, were measured in all the participants. In addition, the potential relationship between PANSS scores and leptin or insulin plasma levels was assessed.

RESULTS

A total of 46 patients were included: 25 CR and 21 CNR. BMI and waist circumference, fasting insulin and leptin plasma levels were lower in the CNR group, while C-reactive protein was not different. Moreover, significant negative correlations were observed between PANSS positive and general psychopathology subscores, on one hand, and insulin and leptin plasma levels, on the other hand, as well as between PANSS negative subscores and leptin plasma levels.

CONCLUSIONS

Our results suggest that the lack of metabolic effect induced by clozapine is associated with the lack of clinical response.

Clinical improvement in schizophrenia during antipsychotic treatment in relation to changes in glucose parameters: A systematic review

Antipsychotics (APs) are the cornerstone of treatment for schizophrenia (SCZ) spectrum disorders. Previous research suggests that there may be a positive association between AP-induced weight gain and/or dyslipidemia and improvement in psychiatric symptoms, often referred to as a "metabolic threshold". To determine whether a similar relationship exists for glucose parameters, we conducted a systematic search in six databases from inception to June 2022 for all longitudinal studies that directly examined the relationship between changes in glucose-related outcomes and changes in psychopathology among patients with SCZ treated with APs. We identified 10 relevant studies and one additional study that considered cognition. In most cases, we found that increased levels of fasting glucose and insulin following treatment were associated with clinical improvement. These findings contribute to existing literature that could suggest a common mechanism between AP action and metabolic side effects and support a need for additional work aimed at exploring the validity of a glucose-psychopathology relation in SCZ.

Brain insulin action: Implications for the treatment of schizophrenia

Insulin action in the central nervous system is a major regulator of energy balance and cognitive processes. The development of central insulin resistance is associated with alterations in dopaminergic reward systems and homeostatic signals affecting food intake, glucose metabolism, body weight and cognitive performance. Emerging evidence has highlighted a role for antipsychotics (APs) to modulate central insulin-mediated pathways. Although APs remain the cornerstone treatment for schizophrenia they are associated with severe metabolic complications and fail to address premorbid cognitive deficits, which characterize the disorder of schizophrenia. In this review, we first explore how the hypothesized association between schizophrenia and CNS insulin dysregulation aligns with the use of APs. We then investigate the proposed relationship between CNS insulin action and AP-mediated effects on metabolic homeostasis, and different domains of psychopathology, including cognition. We briefly discuss a potential role of CNS insulin signaling to explain the hypothesized, but somewhat controversial association between therapeutic efficacy and metabolic side effects of APs. Finally, we propose how this knowledge might inform novel treatment strategies to target difficult to treat domains of schizophrenia. This article is part of the issue entitled 'Special Issue on Antipsychotics'.

Reduced insulin sensitivity may be related to less striatal glutamate: An 1H-MRS study in healthy non-obese humans

Levels of striatal dopamine (DA) may be positively correlated with levels of striatal glutamate (Glu). While reduced insulin sensitivity (%S) has been associated with reduced striatal DA levels in healthy non-obese persons, whether reduced %S is also associated with reduced striatal Glu levels has not yet been established. Using ¹H-MRS, we measured levels of several neurometabolites in the striatum and dorsolateral prefrontal cortex (DLPFC) of seventeen healthy non-obese persons (9 female, mean age: 28.35 ± 9.53). Insulin sensitivity was estimated for each subject from fasting plasma glucose and insulin using the Homeostasis Model Assessment II. We hypothesized that %S would be positively related with levels of Glu and Glu + glutamine (Glx) in the striatum. Exploratory analyses were also conducted between other fasting markers of metabolic health and neurometabolites measured with ¹H-MRS. In the right striatum, %S was positively correlated with levels of Glu (r(15) = .49, p = .04) and Glx (r(15) = .50, p = .04). In the left striatum, there was a trend positive correlation between %S and Glu (r(15) = .46, p = .06), but not Glx levels (r(15) = .20, p = .44). The relationships between %S and striatal Glu levels remained after controlling for age, sex, and BMI (right: r(12) = .73, β = .52, t = 2.55, p = .03; left: (r(12) = .63, β = .53, t = 2.25, p = .04) These preliminary findings suggest that %S may be related to markers of glutamatergic functioning in the striatum of healthy non-obese persons. These findings warrant replication in larger samples and extension into neuropsychiatric populations where altered striatal DA, Glu, and %S are implicated.

The Complex Relationship between Antipsychotic-Induced Weight Gain and Therapeutic Benefits: A Systematic Review and Implications for Treatment

Background: Antipsychotic-induced weight gain (AIWG) and other adverse metabolic effects represent serious side effects faced by many patients with psychosis that can lead to numerous comorbidities and which reduce the lifespan. While the pathophysiology of AIWG remains poorly understood, numerous studies have reported a positive association between AIWG and the therapeutic benefit of antipsychotic medications.

Objectives: To review the literature to (1) determine if AIWG is consistently associated with therapeutic benefit and (2) investigate which variables may mediate such an association.

Data Sources: MEDLINE, Google Scholar, Cochrane Database and PsycINFO databases were searched for articles containing all the following exploded MESH terms: schizophrenia [AND] antipsychotic agents/neuroleptics [AND] (weight gain [OR] lipids [OR] insulin [OR] leptin) [AND] treatment outcome. Results were limited to full-text, English journal articles.

Results: Our literature search uncovered 31 independent studies which investigated an AIWG-therapeutic benefit association with a total of 6063 enrolled individuals diagnosed with schizophrenia or another serious mental illness receiving antipsychotic medications. Twenty-two studies found a positive association while, 10 studies found no association and one study reported a negative association. Study variables including medication compliance, sex, ethnicity, or prior antipsychotic exposure did not appear to consistently affect the AIWG-therapeutic benefit relationship. In contrast, there was some evidence that controlling for baseline BMI/psychopathology, duration of treatment and specific agent studied [i.e., olanzapine (OLZ) or clozapine (CLZ)] strengthened the relationship between AIWG and therapeutic benefit.

Limitations: There were limitations of the reviewed studies in that many had small sample sizes, and/or were retrospective. The heterogeneity of the studies also made comparisons difficult and publication bias was not controlled for.

Conclusions: An AIWG-therapeutic benefit association may exist and is most likely to be observed in OLZ and CLZ-treated patients. The clinical meaningfulness of this association remains unclear and weight gain and other metabolic comorbidities should be identified and treated to the same targets as the general population. Further research should continue to explore the links between therapeutic benefit and metabolic health with emphasis on both pre-clinical work and well-designed prospective clinical trials examining metabolic parameters associated, but also occurring independently to AIWG.

Exploring the Relationship Between Body Mass Index and Positive Symptom Severity in Persons at Clinical High Risk for Psychosis

Metabolic health and positive symptom severity has been investigated in schizophrenia, but not in clinical high risk (CHR) patients. We hypothesized that greater body mass index (BMI) in CHR patients would be related to less positive symptoms. We examined this relationship in CHR patients being treated with 1) no psychotropic medications (n = 58), 2) an antipsychotic (n = 14), or 3) an antidepressant without an antipsychotic (n = 10). We found no relationship between BMI and positive symptoms in unmedicated CHR patients, the majority of whom had a narrow BMI range between 20 and 30. However, in the smaller sample of CHR patients taking an antidepressant or antipsychotic, BMI was negatively correlated with positive symptoms. Although potentially underpowered, these preliminary findings provide initial steps in elucidating the relationships between metabolic health, neurochemistry, and symptom severity in CHR patients.

Reduced insulin-receptor mediated modulation of striatal dopamine release by basal insulin as a possible contributing factor to hyperdopaminergia in schizophrenia

Schizophrenia is a severe and chronic neuropsychiatric disorder which affects 1% of the world population. Using the brain imaging technique positron emission tomography (PET) it has been demonstrated that persons with schizophrenia have greater dopamine transmission in the striatum compared to healthy controls. However, little progress has been made as to elucidating other biological mechanisms which may account for this hyperdopaminergic state in this disease. Studies in animals have demonstrated that insulin receptors are expressed on midbrain dopamine neurons, and that insulin from the periphery acts on these receptors to modify dopamine transmission in the striatum. This is pertinent given that several lines of evidence suggest that insulin receptor functioning may be abnormal in the brains of persons with schizophrenia. Post-mortem studies have shown that persons with schizophrenia have less than half the number of cortical insulin receptors compared to healthy persons. Moreover, these post-mortem findings are unlikely due to the effects of antipsychotic treatment; studies in cell lines and animals suggest antipsychotics enhance insulin receptor functioning. Further, hyperinsulinemia - even prior to antipsychotic use - seems to be related to less psychotic symptoms in patients with schizophrenia. Collectively, these data suggest that midbrain insulin receptor functioning may be abnormal in persons with schizophrenia, resulting in reduced insulin-mediated regulation of dopamine transmission in the striatum. Such a deficit may account for the hyperdopaminergic state observed in these patients and would help guide the development of novel treatment strategies. We hypothesize that, (i) insulin receptor expression and/or function is reduced in midbrain dopamine neurons in persons with schizophrenia, (ii) basal insulin should reduce dopaminergic transmission in the striatum via these receptors, and (iii) this modulation of dopaminergic transmission by basal insulin is reduced in the brains of persons with schizophrenia.

The role of energy metabolism dysfunction and oxidative stress in schizophrenia revealed by proteomics

Schizophrenia is a psychiatric illness that affects approximately 30 million people worldwide. Converging lines of evidence suggest that mitochondrial function may be compromised in this disorder, and this can lead to perturbations in calcium buffering, oxidative phosphorylation, increased production of reactive oxygen species, and apoptotic factors, which can, in turn, affect neuronal processes such as neurotransmitter synthesis and synaptic plasticity. Proteomics studies in brain and peripheral tissues of schizophrenia patients have provided considerable evidence and identified biomarker fingerprints corresponding to such pathways. Here we review the results of these studies with a focus on the biomarker pattern depicting alterations in energy metabolism and oxidative stress in this debilitating illness.

Converging evidence of blood-based biomarkers for schizophrenia: an update

This chapter has carried out a review of the literature and combined this with the results of in-house studies to identify candidate blood-based biomarkers for schizophrenia and antipsychotic drug response. Literature searches retrieved 185 publications describing a total of 273 schizophrenia biomarkers identified in serum and/or plasma. Examination of seven in-house multicenter studies resulted in the identification of 137 serum/plasma biomarkers. Taken together, the findings suggested an ongoing immunological and inflammatory process in schizophrenia. This was accompanied by altered cortisol levels which suggested activated stress response and altered hypothalamic-pituitary-adrenal axis function in these patients. The authors conclude that such biomarkers may prove useful as additional parameters for characterizing specific immune and/or metabolic or hormonal subsystems in schizophrenia and might, therefore, facilitate the development of future patient stratification and personalized medicine strategies.

S100B Serum Levels in Schizophrenia Are Presumably Related to Visceral Obesity and Insulin Resistance

Elevated blood levels of S100B in schizophrenia have so far been mainly attributed to glial pathology, as S100B is produced by astro- and oligodendroglial cells and is thought to act as a neurotrophic factor with effects on synaptogenesis, dopaminergic and glutamatergic neutrotransmission. However, adipocytes are another important source of S100B since the concentration of S100B in adipose tissue is as high as in nervous tissue. Insulin is downregulating S100B in adipocytes, astrocyte cultures and rat brain. As reviewed in this paper, our recent studies suggest that overweight, visceral obesity, and peripheral/cerebral insulin resistance may be pivotal for at least part of the elevated S100B serum levels in schizophrenia. In the context of this recently identified framework of metabolic disturbances accompanying S100B elevation in schizophrenia, it rather has to be attributed to systemic alterations in glucose metabolism than to be considered a surrogate marker for astrocyte-specific pathologies.

Clozapine interaction with phosphatidyl inositol 3-kinase (PI3K)/insulin-signaling pathway in Caenorhabditis elegans

Clozapine has superior and unique effects as an antipsychotic agent, but the mediators of these effects are not known. We studied behavioral and developmental effects of clozapine in Caenorhabditis elegans, as a model system to identify previously undiscovered mechanisms of drug action. Clozapine induced early larval arrest, a phenotype that was also seen with the clozapine metabolite N-desmethyl clozapine but not with any other typical or atypical antipsychotic drug tested. Mutations in the insulin receptor/daf-2 and phosphatidyl inositol 3-kinase (PI3K)/age-1 suppressed clozapine-induced larval arrest, suggesting that clozapine may activate the insulin-signaling pathway. Consistent with this notion, clozapine also increased the expression of an age-1::GFP reporter. Activation of the insulin-signaling pathway leads to cytoplasmic localization of the fork head transcription factor FOXO/daf-16. Clozapine produced cytoplasmic localization of DAF-16::GFP in arrested L1 larvae, in contrast to stressors such as starvation or high temperature, which produce nuclear localization of DAF-16::GFP in arrested L1 larvae. Clozapine also inhibited pharyngeal pumping in C. elegans, an effect that may contribute to, but did not explain, clozapine-induced larval arrest. Our findings demonstrate a drug-specific interaction between clozapine and the PI3K/insulin-signaling pathway in C. elegans. As this pathway is conserved across species, the results may have implications for understanding the unique effects of clozapine in humans.