Sodium activates human monocytes via the NADPH oxidase and isolevuglandin formation

Abstract

Aims Prior studies have focused on the role of the kidney and vasculature in salt-induced modulation of blood pressure, however recent data indicate that sodium accumulates in tissues and can activate immune cells. We sought to examine mechanisms by which salt causes activation of human monocytes both in vivo and in vitro. Methods and Results To study the effect of salt in human monocytes, monocytes were isolated from volunteers to perform several in vitro experiments. Exposure of human monocytes to elevated Na+ ex vivo caused a coordinated response involving isolevuglandin (IsoLG)-adduct formation, acquisition of a dendritic cell-like morphology, expression of activation markers CD83 and CD16, and increased production of pro-inflammatory cytokines TNF-α, IL-6 and IL-1β. High salt also caused a marked change in monocyte gene expression as detected by RNA sequencing and enhanced monocyte migration to the chemokine CC motif chemokine ligand 5. NADPH-oxidase inhibition attenuated monocyte activation and IsoLG-adduct formation. The increase in IsoLG-adducts correlated with risk factors including body mass index, pulse pressure, total cholesterol and glucose. Monocytes exposed to high salt stimulated IL-17A production from autologous CD4+ and CD8+ T cells. In addition, to evaluate the effect of salt in vivo, monocytes and T cells isolated from humans were adoptively transferred to immunodeficient NSG mice. Salt feeding of humanized mice caused monocyte-dependent activation of human T cells reflected by proliferation and accumulation of T cells in the bone marrow. Moreover, we performed a cross-sectional study in 70 prehypertensive subjects. Blood was collected for flow cytometric analysis and 23Na MRI was performed for tissue sodium measurements. Monocytes from humans with high skin Na+ exhibited increased IsoLG-adduct accumulation and CD83 expression. Conclusions Human monocytes exhibit coordinated increases in parameters of activation, conversion to a DC-like phenotype and ability to activate T cells upon both in vitro and in vivo sodium exposure. The ability of monocytes to be activated by sodium is related to in vivo cardiovascular disease risk factors. We therefore propose that in addition to the kidney and vasculature, immune cells like monocytes convey salt-induced cardiovascular risk in humans. Translational perspective Immune cells like monocytes convey salt-sensitivity to humans and this is associated with cardiovascular risk factors. Our research provides a new mechanism by which a high salt diet may induce inflammation and hypertension and support the current recommendations of a low sodium consumption, especially in subjects with elevated cardiovascular risk. Our data indicates that scavenging IsoLGs or targeting monocytes may be therapeutically beneficial in salt-sensitive hypertension.

DC ENaC-Dependent Inflammasome Activation Contributes to Salt-Sensitive Hypertension

“…High sodium exposure increased expression of NOX subunit p91 phox (CYBB [cytochrome b-245 beta chain]; Figure 1E) but not NOX1, NOX4, p47 phox (NCF1 [neutrophil cytosolic factor 1]), p22 phox (CYBA), or p67 phox (NCF2; Figure 1E). We found that expression of genes associated with activation of the NLRP3 inflammasome including IL-1β (IL1B), which we have previously published, 26 IL-18 (IL-18), and IL18R1 (IL-18 receptor; Figure 1F), inflammatory caspase CASP1 (caspase-1), and the initiator and executioner caspases, CASP2 (Figure 1H through 1J) and CASP7 (Figure 1J) were increased in response to elevated sodium exposure. Upon investigation of other NLR proteins, including NLRP1, NLRC4, and NLRP12, in addition to non-NLR proteins such as AIM2 (absent in melanoma 2) and IFI16 (interferon gamma inducible protein 16), known to assemble into inflammasome complexes, we found that NLRP1, NLRP12, and AIM2 were all significantly downregulated in response to salt (Figure 1G).…”

The modulatory effect of high salt on immune cells and related diseases

“…A recent study found that high salt can drive human monocytes to a DC‐like phenotype, characterized by the formation of isolevuglandin (IsoLG) adducts, expression of CD83 and increased production of IL‐1β. These responses induced subsequent T‐cell activation with increased IL‐17A production 104 . Consistently, monocytes from humans with high skin sodium exhibited enhanced IsoLG adduct accumulation and CD83 expression 104 .…”

Coupling of phagocytic NADPH oxidase activity and mitochondrial superoxide production

“…The role of inflammation and immunity in hypertension has been recently described ( 23 ). It was found that phagocytic NADPH oxidase in immune cells plays a critical role in the development of hypertension ( 4 ). Interestingly, treatment of T cells isolated from hypertensive mice with mitochondria-targeted superoxide scavenger mitoTEMPO significantly abrogated the pro-hypertensive response of immune cells ( 24 ).…”

“…Inflammatory cells represent a critical source of superoxide not only in inflammatory conditions but also in metabolic conditions, cardiovascular disease, hypertension, and end-organ damage ( 1 ). Activation of immune cells is associated with increased superoxide production and leads to release of pro-inflammatory cytokines such as IL-17A and TNFα which contribute to development of pathological conditions ( 4 ). Understanding the redox regulation of immune cells activity can allow a better therapeutic targeting of immune system reducing the inflammatory injury.…”