Pathophysiological Alterations of Redox Signaling and Endocannabinoid System in Granulocytes and Plasma of Psoriatic Patients

Abstract

Inflammatory granulocytes are characterized by an oxidative burst, which may promote oxidative stress and lipid modification both in affected tissues and on a systemic level. On the other hand, redox signaling involving lipid peroxidation products acting as second messengers of free radicals play important yet not fully understood roles in the pathophysiology of inflammation and various stress-associated disorders. Therefore, the aim of this study was to evaluate the onset of oxidative stress and alterations of enzyme-dependent lipid metabolism resulting from redox imbalance in granulocytes and plasma obtained from patients with psoriasis vulgaris or psoriatic arthritis in comparison to the healthy subjects. The results obtained revealed enhanced activity of pro-oxidant enzymes nicotinamide adenine dinucleotide phosphate (NADPH) and xanthine oxidases in granulocytes with a decrease of enzymatic and non-enzymatic antioxidants in the plasma of psoriatic patients. The nuclear factor erythroid 2⁻related factor 2 (Nrf2) and its regulators were increased in both forms of psoriasis while heme oxygenase 1 levels were increased only in psoriasis vulgaris. The redox imbalance was associated with decreased levels of phospholipids and of free polyunsaturated fatty acids but with enhanced activity of enzymes involved in lipid metabolism (phospholipase A2, acetylhydrolase PAF, cyclooxygenases 1 and 2) and increased lipid peroxidation products 4-hydroxynonenal, isoprostanes, and neuroprostanes. Increased endocannabinoids and G protein-coupled receptor 55 were observed in both forms of the disease while expression of the cannabinoid type 1 receptor (CB1) was increased only in patients with psoriatic arthritis, which is opposite to the cannabinoid type 2 receptor. This receptor was increased only in psoriasis vulgaris. Changes in protein expression promoted the apoptosis of granulocytes by increased caspases mainly in psoriasis vulgaris. This study indicates that inhibition of the Nrf2 pathway in psoriatic arthritis promotes a redox imbalance. In addition, increased expression of CB1 receptors leads to increased oxidative stress, lipid modifications, and inflammation, which, in turn, may promote the progression of psoriasis into the advanced, arthritic form of the disease.

Keywords: 4-hydroxynonenal; arthritis; endocannabinoid system; granulocytes; inflammation; lipid peroxidation; lipids; oxidative stress; psoriasis; redox signaling.

Figure 1

The level of the Nrf2 pathway factors in granulocytes from healthy subjects (n = 8) and psoriatic patients (psoriasis vulgaris (n = 16) or psoriatic arthritis (n = 8)). ^a p < 0.05 when compared with healthy subjects. ^x p < 0.05 when compared with patients with psoriasis vulgaris.

Figure 2

(A) Partial least squares-discriminate analysis (PLS-DA) plot of the phospholipid species and relative abundance determined by HILIC-LC-MS in the plasma of healthy people and both groups of psoriatic patients. The red triangles indicate healthy subjects (n = 34) while the green and blue crosses represent patients with psoriasis vulgaris (n = 68) and psoriatic arthritis (n = 34), respectively. (B) Graphical presentation of the regulation of phospholipids with VIP score ≥1, which differentiate healthy subjects and patients with psoriasis vulgaris and psoriatic arthritis.

Figure 3

Endocannabinoid system receptor expression in granulocytes* of healthy subjects (n = 8) and patients with psoriasis vulgaris (n = 16) and psoriatic arthritis (n = 8) (A), endocannabinoid levels, (C) and activity of enzymes metabolizing endocannabinoids in plasma (B) of healthy subjects (n = 34) and patients with psoriasis vulgaris (n = 68) and psoriatic arthritis (n = 34). ^a p < 0.05 when compared with healthy subjects and ^x p < 0.05 when compared with patients with psoriasis.

Figure 3

Endocannabinoid system receptor expression in granulocytes* of healthy subjects (n = 8) and patients with psoriasis vulgaris (n = 16) and psoriatic arthritis (n = 8) (A), endocannabinoid levels, (C) and activity of enzymes metabolizing endocannabinoids in plasma (B) of healthy subjects (n = 34) and patients with psoriasis vulgaris (n = 68) and psoriatic arthritis (n = 34). ^a p < 0.05 when compared with healthy subjects and ^x p < 0.05 when compared with patients with psoriasis.

Figure 4

The level of pro-apoptotic proteases (caspase-8, caspase-9, caspase-3) and proteins involved in cell death (Bcl2 and cytochrome c) in granulocytes from healthy subjects (n = 8) and patients with psoriasis vulgaris (n = 16) and psoriatic arthritis (n = 8). ^a p < 0.05 when compared with healthy subjects. ^x p < 0.05 when compared with patients with psoriatic vulgaris.

Figure 5

The levels of interleukins and pro-inflammatory mediators in plasma or granulocytes* from healthy subjects (n = 8) and patients with psoriasis vulgaris (n = 16) and psoriatic arthritis (n = 8). ^a p < 0.05 when compared with healthy subjects. ^x p < 0.05 when compared with patients with psoriasis vulgaris.