Spirulina platensis organic extract increases spare respiratory capacity in RAW 264.7 macrophages to exert an anti‐inflammatory effect

Abstract

Recent evidence supports that crosstalk between energy metabolism and inflammatory processes is a critical determinant for macrophage phenotype. Macrophage energy metabolism greatly influences their activation state. For example, M1, pro‐inflammatory macrophages largely depend on glycolysis while M2, anti‐inflammatory macrophages prefer mitochondrial oxidative phosphorylation (OXPHOS) for their energy generation. We previously demonstrated that organic extract of Spirulina platensis (SPE), a blue‐green algae, exerts a potent anti‐inflammatory effect in vitro and ex vivo. Our recent study also suggests that the anti‐inflammatory effect of SPE is at least partly attributable to the induction of an endotoxin tolerance‐like state in macrophages. Interestingly, although SPE repressed LPS‐induced pro‐inflammatory gene expression as potently as endotoxin tolerant (ET) macrophages, there were some differences between SPE‐treated and ET macrophages. The objective of this study was to determine if SPE alters macrophage energy metabolism to exert its anti‐inflammatory effect in addition to its role in endotoxin tolerance. To determine the energy phenotype, we measured oxygen consumption rate (OCR) and extra cellular acidification rate (ECAR) of naïve, SPE‐treated, and ET macrophages by XF Mito Stress tests using a Seahorse XFe24 Analyzer. Treatment of RAW 264.7 macrophages with 25 mg/mL of SPE or endotoxin tolerization with 10 ng/mL of lipopolysaccharide (LPS) for 12 h increased basal ECAR compared to naïve cells with concomitant increases in the expression of interleukin‐1β and tumor necrosis factor‐α, suggesting that both SPE and LPS activated macrophages to a certain degree. The basal OCR values of naïve cells were the highest, followed by SPE‐treated and then ET cells, which indicates that SPE and LPS decreased cell's dependence on OXPHOS. Interestingly, RAW 264.7 macrophages treated with 25 mg/mL of SPE had the highest spare respiratory capacity (SRC), which is a measure of how much ATP may be produced through OXPHOS in response to a sudden increase in energy demand. When naïve, SPE‐pretreated and ET RAW 264.7 macrophages were stimulated with 100 ng/mL of LPS for 12 h, the SRC was significantly reduced in all treatment groups. During LPS‐stimulation, SPE‐pretreated cells may be better off to meet the energy demands of LPS stimulation as SPE pretreatment significantly increased the SRC. In conclusion, we found that SPE‐pretreated macrophage, but not ET macrophages, had increased the SRC, which may contribute to the potent anti‐inflammatory effects of SPE in macrophages.Support or Funding InformationUSDA AFRI (2014‐01870)