Diabetes and schizophrenia: genes or zinc deficiency?

Inter-relationships of risk factors and pathways associated with all-cause mortality in patients with chronic schizophrenia

Introduction

Of all psychiatric disorders, schizophrenia is associated with the highest risk of all-cause mortality. This study aimed to investigate independent risk factors for all-cause mortality in patients with chronic schizophrenia. In addition, the possible causal inter-relationships among these independent risk factors and all-cause mortality were also explored.

Methods

We conducted an analysis of 1,126 patients with chronic schizophrenia from our psychiatric department from April 2003 to August 2022, and retrospectively reviewed their medical records. The study endpoint was all-cause mortality. Baseline clinical characteristics including sociodemographic data, biochemical data, lifestyle factors, comorbidities and antipsychotic treatment were examined with Cox proportional hazards analysis.

Results

The all-cause mortality rate was 3.9% (44 patients). Multivariate Cox regression analysis revealed that several factors were independently associated with all-cause mortality, including diabetes mellitus (DM), hypertension, heart failure, gastroesophageal reflux disease (GERD), peptic ulcer disease, ileus, underweight, fasting glucose, triglycerides, albumin, and hemoglobin. Structural equation modeling (SEM) analysis revealed that several factors had statistically significant direct effects on all-cause mortality. Heart failure, hypertension, underweight, age at onset, and ileus showed positive direct effects, while albumin and hemoglobin demonstrated negative direct effects. In addition, several factors had indirect effects on all-cause mortality. GERD indirectly affected all-cause mortality through ileus, and peptic ulcer disease had indirect effects through albumin and ileus. Ileus, underweight, DM, and hypertension also exhibited indirect effects through various pathways involving albumin, hemoglobin, and heart failure. Overall, the final model, which included these factors, explained 13% of the variability in all-cause mortality.

Discussion

These results collectively suggest that the presence of DM, hypertension, heart failure, GERD, peptic ulcer disease, ileus, and underweight, along with lower levels of albumin or hemoglobin, were independently associated with all-cause mortality. The SEM analysis further revealed potential causal pathways and inter-relationships among these risk factors contributing to all-cause mortality in patients with chronic schizophrenia.

An overview of diabetes management in schizophrenia patients: office based strategies for primary care practitioners and endocrinologists

Diabetes is common and seen in one in five patients with schizophrenia. It is more prevalent than in the general population and contributes to the increased morbidity and shortened lifespan seen in this population. However, screening and treatment for diabetes and other metabolic conditions remain poor for these patients. Multiple factors including genetic risk, neurobiologic mechanisms, psychotropic medications, and environmental factors contribute to the increased prevalence of diabetes. Primary care physicians should be aware of adverse effects of psychotropic medications that can cause or exacerbate diabetes and its complications. Management of diabetes requires physicians to tailor treatment recommendations to address special needs of this population. In addition to behavioral interventions, medications such as metformin have shown promise in attenuating weight loss and preventing hyperglycemia in those patients being treated with antipsychotic medications. Targeted diabetes prevention and treatment is critical in patients with schizophrenia and evidence-based interventions should be considered early in the course of treatment. This paper reviews the prevalence, etiology, and treatment of diabetes in schizophrenia and outlines office based interventions for physicians treating this vulnerable population.

Clioquinol synergistically augments rescue by zinc supplementation in a mouse model of acrodermatitis enteropathica

Background

Zinc deficiency due to poor nutrition or genetic mutations in zinc transporters is a global health problem and approaches to providing effective dietary zinc supplementation while avoiding potential toxic side effects are needed.

Methods/Principal Findings

Conditional knockout of the intestinal zinc transporter Zip4 (Slc39a4) in mice creates a model of the lethal human genetic disease acrodermatitis enteropathica (AE). This knockout leads to acute zinc deficiency resulting in rapid weight loss, disrupted intestine integrity and eventually lethality, and therefore provides a model system in which to examine novel approaches to zinc supplementation. We examined the efficacy of dietary clioquinol (CQ), a well characterized zinc chelator/ionophore, in rescuing the Zip4^{intest KO} phenotype. By 8 days after initiation of the knockout neither dietary CQ nor zinc supplementation in the drinking water was found to be effective at improving this phenotype. In contrast, dietary CQ in conjunction with zinc supplementation was highly effective. Dietary CQ with zinc supplementation rapidly restored intestine stem cell division and differentiation of secretory and the absorptive cells. These changes were accompanied by rapid growth and dramatically increased longevity in the majority of mice, as well as the apparent restoration of the homeostasis of several essential metals in the liver.

Conclusions

These studies suggest that oral CQ (or other 8-hydroxyquinolines) coupled with zinc supplementation could provide a facile approach toward treating zinc deficiency in humans by stimulating stem cell proliferation and differentiation of intestinal epithelial cells.

Understanding the mechanisms of zinc-sensing by metal-response element binding transcription factor-1 (MTF-1)

The regulation of divalent zinc has been observed in a wide range of organisms. Since this metal is an essential nutrient, but also toxic in excess, zinc homeostasis is crucial for normal cellular functioning. The metal-responsive-element-binding transcription factor-1 (MTF-1) is a key regulator of zinc in higher eukaryotes ranging from insects to mammals. MTF-1 controls the expression of metallothioneins (MTs) and a number of other genes directly involved in the intracellular sequestration and transport of zinc. Although the diverse functions of MTF-1 extend well beyond zinc homeostasis to include stress-responses to heavy metal toxicity, oxidative stress, and selected chemical agents, in this review we focus on the recent advances in understanding the mechanisms whereby MTF-1 regulates MT gene expression to protect the cell from fluctuations in environmental zinc. Particular emphasis is devoted to recent studies involving the Cys2His2 zinc finger DNA-binding domain of MTF-1, which is an important contributor to the zinc-sensing and metal-dependent transcriptional activation functions of this protein.

Schizophrenia and diabetes: epidemiological data

The association of diabetes mellitus and mental illness, in particular, schizophrenia, has been remarked upon for over a century. Recent epidemiological studies have shown the age- and sex-matched prevalence of diabetes in patients with schizophrenia to be 1.5-2 times those in the general population. This difference is particularly noticeable in younger patients. The explanation for this finding probably resides in both environmental and biological factors. Patients with schizophrenia tend to be sedentary and have a poor diet, which are both known risk factors for diabetes. However, familial studies have indicated a heritable component to the risk of diabetes in patients with schizophrenia. A number of biological mechanisms have been proposed to explain this, including neuroendocrine changes and neurodevelopmental anomalies, but none are entirely satisfactory. In addition, it has been suggested that treatment with antipsychotic medication may potentially increase the risk of diabetes and account for some of the increased prevalence seen in patients with schizophrenia. It has been suggested that different antipsychotic drugs may differ in their ability to facilitate the emergence of poor glycaemic control in patients with schizophrenia. However, the situation is far from clear and more work is required to accurately assess the potential risk associated with different antipsychotic drugs.

MouseZIP1 andZIP3 genes together are essential for adaptation to dietary zinc deficiency during pregnancy

Subfamily II of the solute-linked carrier 39A superfamily contains three well-conserved zinc transporters (ZIPs1, 2, 3) whose physiological functions are unknown. We generated mice homozygous for knockout alleles of ZIP1 and both ZIP1 and ZIP 3 (double-knockout). These mice were apparently normal when dietary zinc was replete, but when dietary zinc was limited during pregnancy embryos from ZIP1 or ZIP3 knockout mice were two to three times more likely to develop abnormally than those in wildtype mice, and 91% (71/78) of embryos developed abnormally in ZIP1, ZIP3 double-knockout mice. Analysis of the patterns of expression of these genes in mice revealed predominate expression in intestinal stromal cells, nephric-tubular epithelial cells, pancreatic ductal epithelial cells, and hepatocytes surrounding the central vein. This suggests that these zinc transporters function, at least in part, in the redistribution and/or retention of zinc rather than its acquisition from the diet. In conclusion, mutations in the ZIP1 and ZIP3 zinc transporter genes are silent when dietary intake of zinc is normal, but can dramatically compromise the success of pregnancy when dietary intake of zinc is limiting.

Neurobiological plausibility of prenatal nutritional deprivation as a risk factor for schizophrenia

Emerging evidence indicates that schizophrenia may in some cases be a neurodevelopmental disorder, resulting in part from the effects of prenatal exposures. Studies by our group have focused attention on the potential role of prenatal nutritional deficiency as a potential etiological factor. Therefore, we sought to examine the biological plausibility of prenatal nutritional deprivation in the etiopathogenesis of schizophrenia. We conducted a review of the pertinent literature. Four lines of evidence support prenatal nutritional deficiencies as a plausible set of risk factors for schizophrenia: a) their effects are not incompatible with the epidemiology of schizophrenia; b) they have adverse effects on brain development; c) general malnutrition results in neuropathological anomalies of brain regions implicated in schizophrenia; and d) prenatal malnutrition affects maternal systems critical to the developing fetal nervous system. There is sufficient evidence to warrant further studies of prenatal nutritional deficits as risk factors for schizophrenia. A strategy for testing these hypotheses is outlined.

Zinc is required for the expression of ornithine decarboxylase in a difluoromethylornithine-resistant cell line

Dilution of quiescent L1210-DFMOr (difluoromethylornithine-resistant) cells in fresh medium containing serum led to the induction of ornithine decarboxylase (ODC) and to the expression of its mRNA, as determined by a sensitive solution-hybridization-RNase-protection assay. Addition of the chelating agent diethylenetriaminepentaacetic acid (DTPA) at seeding time caused an inhibition of the induction of ODC activity by up to 90%, and only Zn2+ of the bivalent metal ions tested was effective in reversing this effect. The inhibition of the induction of ODC activity was accompanied by a marked decrease, prevented by Zn2+ supplementation, of the accumulation of immunoreactive ODC protein and ODC mRNA. DTPA treatment also caused a slight acceleration of ODC turnover. These results indicate that a restricted Zn2+ availability in L1210-DFMOr cells impairs ODC induction remarkably, mainly by affecting the expression of the messenger.