Altered arachidonic acid cascade enzymes in postmortem brain from bipolar disorder patients

Abstract

Mood stabilizers that are approved for treating bipolar disorder (BD), when given chronically to rats, decrease expression of markers of the brain arachidonic metabolic cascade, and reduce excitotoxicity and neuroinflammation-induced upregulation of these markers. These observations, plus evidence for neuroinflammation and excitotoxicity in BD, suggest that arachidonic acid (AA) cascade markers are upregulated in the BD brain. To test this hypothesis, these markers were measured in postmortem frontal cortex from 10 BD patients and 10 age-matched controls. Mean protein and mRNA levels of AA-selective cytosolic phospholipase A(2) (cPLA(2)) IVA, secretory sPLA(2) IIA, cyclooxygenase (COX)-2 and membrane prostaglandin E synthase (mPGES) were significantly elevated in the BD cortex. Levels of COX-1 and cytosolic PGES (cPGES) were significantly reduced relative to controls, whereas Ca(2+)-independent iPLA(2)VIA, 5-, 12-, and 15-lipoxygenase, thromboxane synthase and cytochrome p450 epoxygenase protein and mRNA levels were not significantly different. These results confirm that the brain AA cascade is disturbed in BD, and that certain enzymes associated with AA release from membrane phospholipid and with its downstream metabolism are upregulated. As mood stabilizers downregulate many of these brain enzymes in animal models, their clinical efficacy may depend on suppressing a pathologically upregulated cascade in BD. An upregulated cascade should be considered as a target for drug development and for neuroimaging in BD.

Figure 1

Schematic diagram of arachidonic acid cascade.

Figure 2. Protein and mRNA levels of PLA₂ enzymes

Mean cPLA₂ (A), sPLA₂ (B) and iPLA₂ (C) protein (with representative immunoblots) as percent of control in frontal cortex, from control (n = 10) and BD (n = 10) subjects. Data are optical densities relative to that of β-actin. Mean mRNA as percent of control of cPLA₂ (D), sPLA₂ (E) and iPLA₂ (F) in frontal cortex from control (n = 10) and BD (n =10) subjects, measured using RT-PCR. Data are normalized to the endogenous control (β-globulin) and expressed relative to the control (calibrator), using the ΔΔC_T method. Mean ± SEM, ** p < 0.01, ***p < 0.001.

Figure 3. Protein and mRNA levels of COX enzymes

Mean COX-2 (A) and COX-1 (C) protein (with representative immunoblots) as percent of control in frontal cortex, from control (n = 10) and BD (n = 10) subjects. Data are optical densities relative to that of β-actin. COX-2 (B) and COX-1 (D) mRNA levels in the frontal cortex from controls (n = 10) and BD patients (n = 10), measured using RT-PCR. Data are normalized to the endogenous control (β-globulin) and expressed relative to the control (calibrator), using the ΔΔC_T method. Mean ± SEM, * p < 0.05, **p < 0.01.

Figure 4. Protein and mRNA levels of PGES enzymes

Mean mPGES-1 (A) and cPGES- 2 (B) protein (with representative immunoblots) in control (n = 10) and BD (n = 10) frontal cortex. Data are optical densities of PGES protein to β-actin, expressed as percent of control. mRNA levels of mPGES-1 and cPGES-2 (C) in postmortem control (n = 10) and BD (n =10) frontal cortex, measured using RT-PCR. Data are levels of PGES in the BD patients normalized to the endogenous control (β-globulin) and relative to control level (calibrator), using the ΔΔC_T method. Mean ± SEM, ** p < 0.01.

Figure 5. Protein and mRNA levels of lipoxygenases

Mean 5 LOX (A), 12 LOX (B) and 15 LOX (C) protein levels (with representative immunoblots) in frontal cortex from control (n = 10) and BD (n = 10) subjects. Bar graphs are ratios of optical densities of LOXs to that of β-actin, expressed as percent of control. LOX mRNA (D) in postmortem frontal cortex from the control (n = 10) and BD (n = 10) subjects, measured using RT-PCR. Data are levels of LOXs in BD normalized to the endogenous control (β-globulin) and relative to the control (calibrator), using the ΔΔC_T method. Mean ± SEM.

Figure 6. Protein and mRNA levels of thromboxane synthase, P450 epoxygenase and neuron specific enolase

Mean TXS (A), P450 epoxygenase (B) and neuronal specific enolase (NSE) (C) protein in postmortem frontal cortex from control and BD subjects. Bar graph is ratio of optical density of each protein to that of β-actin, expressed as percent of control. TXS (D), P450 epoxygenase (E) and NSE mRNA (F) in postmortem frontal cortex from control (n = 10) and BD (n = 10) subjects, measured using RT-PCR. Data are level in the BD brain normalized to the endogenous control (β-globulin) and relative to control (calibrator), using the ΔΔC_T method. Mean ± SEM.