Consider 3 observations:
- Evidence is mounting that cytokine abnormalities are present in schizophrenia (Box1-8).
- Reduced arterial compliance (change in volume divided by change in pressure [ΔV/ΔP] in an artery during the cardiac cycle) is an early marker of cardiovascular disease (CVD) and a robust predictor of mortality, and is associated with cytokine abnormalities.
- People with schizophrenia experience increased mortality from CVD.
Taken together, the 3 statements hint at a hypothesis: a common inflammatory process involving cytokine imbalance is associated with symptoms of schizophrenia, reduced arterial compliance, and CVD.
Anti-inflammatory therapeutics that target specific cytokines might both decrease psychiatric symptoms and reduce cardiac mortality in people with schizophrenia. In this article, we (1) highlight the potential role of anti-inflammatory medications in reducing both psychiatric symptoms and cardiac mortality in people with schizophrenia and (2) review the pathophysiological basis of this inflammatory commonality and the evidence for its presence in schizophrenia.
The ‘membrane hypothesis’ of schizophrenia
In this hypothesis, a disturbance in the synthesis and structure of membrane phospholipids results in a subsequent disturbance in the function of neuronal membrane proteins, which might be associated with symptoms and mortality in schizophrenia.9-12 The synaptic vesicle protein synaptophysin, a marker for synaptic density, was found to be decreased in postmortem tissue from the gyrus cinguli in 11 patients with schizophrenia, compared with 13 controls.10 Intracellular phospholipases A2 (inPLA2) act as key enzymes in cell membrane repair and remodeling and in neuroplasticity, neurodevelopment, apoptosis, synaptic pruning, neurodegenerative processes, and neuroinflammation.
In a study, people with first-episode schizophrenia (n = 24) who were drug-naïve or off antipsychotic medication were compared with 25 healthy controls using voxel-based morphometry analysis of T1 high-resolution MRI. inPLA2 activity was increased in the patient group compared with controls; the analysis revealed abnormalities of the frontal and medial temporal cortices, hippocampus, and left-middle and superior temporal gyri in first-episode patients.11 In another study, inPLA2 activity was increased in 35 people with first-episode schizophrenia, compared with 22 controls, and was associated with symptom severity and outcome after 12 weeks of antipsychotic treatment.12
Early CVD mortality in schizophrenia
People with schizophrenia have an elevated rate of CVD compared with the general population; in part, this elevation is linked to magnified risk factors for CVD, including obesity, metabolic syndrome, cigarette smoking, and diabetes13-17; furthermore, most antipsychotics can cause or worsen metabolic syndrome.17
CVD is one of the most common causes of death among people with schizophrenia.17,18 Their life expectancy is reported to be 51 to 61 years—20 to 25 years less than what is seen in the general population.19-21
Arterial compliance in schizophrenia
Reduced arterial compliance has been found to be a robust predictor of atherosclerosis, stroke, and myocardial infarction22-29:
- In 376 subjects who had routine diagnostic coronary angiography associated with coronary stenosis, arterial compliance was reduced significantly—even after controlling for age, sex, smoking, diabetes, hypertension, hyperlipidemia, and obesity.24
In a cross-sectional study, 63 male U.S. veterans age 18 to 70 who had a psychiatric diagnosis (16 taking quetiapine, 19 taking risperidone, and 28 treated in the past but off antipsychotics for 2 months) had significantly reduced compliance in thigh- and calf-level arteries than male controls (n = 111), adjusting for body mass index and Framingham Risk Score (FRS). Of the 63 patients, 23 had a diagnosis of schizophrenia or schizoaffective disorder.30 (The FRS is an estimate of a person’s 10-year cardiovascular risk, calculated using age, sex, total cholesterol, high-density lipoprotein, smoker or not, systolic blood pressure, and whether taking an antihypertensive or not. Compliance was measured using computerized plethysmography). Although not statistically significant, secondary analyses from this data set (n = 77, including men for whom factors for metabolic syndrome were available) showed that calf-level compliance (1.82 vs 2.06 mL) and thigh-level compliance (3.6 vs 4.26 mL; P = .06) were reduced in subjects with schizophrenia, compared with those who had another psychiatric diagnosis.31
- In another study, arterial compliance was significantly reduced in 10 subjects with schizophrenia, compared with 10 healthy controls.32
- Last, reduced total arterial compliance has been shown to be a robust predictor of mortality in older people, compared with reduced local or regional arterial compliance.33
Cytokine abnormalities in arterial compliance
The mechanism by which reduced arterial compliance is associated with cardiovascular pathology is not entirely clear. Arterial compliance is a predictor of cardiovascular disorders independent of hypertension.34 Two studies show that vascular inflammation is associated with reduced arterial compliance.35,36 Reduced arterial compliance is associated with increased angiotensin II activity; increased nicotinamide adenine dinucleotide phosphate oxidase activity; reduced nitric oxide activity; and increased reactive oxygen species.37-39 Angiotensin-II signaling activates transforming growth factor-β, tumor necrosis factor (TNF)-α, interleukin (IL)-1, IL-17, IL-6, and C-reactive protein (CRP)—all of which are associated with reduced arterial compliance.39-46 In addition, high-sensitivity CRP is significantly associated with reduced arterial compliance.47-49