The contractile and inflammatory actions of the cysteinyl leukotrienes (CysLTs), LTC₄, LTD₄, and LTE₄, are thought to be mediated through at least two distinct but related CysLT G protein-coupled receptors. The human CysLT₁ receptor has been recently cloned and characterized. We describe here the cloning and characterization of the second cysteinyl leukotriene receptor, CysLT₂, a 346-amino acid protein with 38% amino acid identity to the CysLT₁ receptor. The recombinant human CysLT₂ receptor was expressed in Xenopusoocytes and HEK293T cells and shown to couple to elevation of intracellular calcium when activated by LTC₄, LTD₄, or LTE₄. Analyses of radiolabeled LTD₄ binding to the recombinant CysLT₂ receptor demonstrated high affinity binding and a rank order of potency for competition of LTC₄ = LTD₄ ≫ LTE₄. In contrast to the dual CysLT₁/CysLT₂ antagonist, BAY u9773, the CysLT₁ receptor-selective antagonists MK-571, montelukast (Singulair^TM), zafirlukast (Accolate^TM), and pranlukast (Onon^TM) exhibited low potency in competition for LTD₄ binding and as antagonists of CysLT₂receptor signaling. CysLT₂ receptor mRNA was detected in lung macrophages and airway smooth muscle, cardiac Purkinje cells, adrenal medulla cells, peripheral blood leukocytes, and brain, and the receptor gene was mapped to chromosome 13q14, a region linked to atopic asthma.

Age-associated chronic inflammation is characterized by unresolved and uncontrolled inflammation with multivariable low-grade, chronic and systemic responses that exacerbate the aging process and age-related chronic diseases. Currently, there are two major hypotheses related to the involvement of chronic inflammation in the aging process: molecular inflammation of aging and inflammaging. However, neither of these hypotheses satisfactorily addresses age-related chronic inflammation, considering the recent advances that have been made in inflammation research. A more comprehensive view of age-related inflammation, that has a scope beyond the conventional view, is therefore required. In this review, we discuss newly emerging data on multi-phase inflammatory networks and proinflammatory pathways as they relate to aging. We describe the age-related upregulation of nuclear factor (NF)-κB signaling, cytokines/chemokines, endoplasmic reticulum (ER) stress, inflammasome, and lipid accumulation. The later sections of this review present our expanded view of age-related senescent inflammation, a process we term "senoinflammation", that we propose here as a novel concept. As described in the discussion, senoinflammation provides a schema highlighting the important and ever-increasing roles of proinflammatory senescence-associated secretome, inflammasome, ER stress, TLRs, and microRNAs, which support the senoinflammation concept. It is hoped that this new concept of senoinflammation opens wider and deeper avenues for basic inflammation research and provides new insights into the anti-inflammatory therapeutic strategies targeting the multiple proinflammatory pathways and mediators and mediators that underlie the pathophysiological aging process.

Lysophosphatidic acid (LPA) exerts a variety of biological responses through specific receptors: three subtypes of the EDG-family receptors, LPA₁, LPA₂, and LPA₃ (formerly known as EDG-2, EDG-4, and EDG-7, respectively), and LPA₄/GPR23, structurally distinct from the EDG-family receptors, have so far been identified. In the present study, we characterized the action mechanisms of 3-(4-[4-([1-(2-chlorophenyl)ethoxy]carbonyl amino)-3-methyl-5-isoxazolyl] benzylsulfanyl) propanoic acid (Ki16425) on the EDG-family LPA receptors. Ki16425 inhibited several responses specific to LPA, depending on the cell types, without any appreciable effect on the responses to other related lipid receptor agonists, including sphingosine 1-phosphate. With the cells overexpressing LPA₁, LPA₂, or LPA₃, we examined the selectivity and mode of inhibition by Ki16425 against the LPA-induced actions and compared them with those of dioctyl glycerol pyrophosphate (DGPP 8:0), a recently identified antagonist for LPA receptors. Ki16425 inhibited the LPA-induced response in the decreasing order of LPA₁ ≥ LPA₃ » LPA₂, whereas DGPP 8:0 preferentially inhibited the LPA₃-induced actions. Ki16425 inhibited LPA-induced guanosine 5′-O-(3-thio)triphosphate binding as well as LPA receptor binding to membrane fractions with a same pharmacological specificity as in intact cells. The difference in the inhibition profile of Ki16425 and DGPP 8:0 was exploited for the evaluation of receptor subtypes involved in responses to LPA in A431 cells. Finally, Ki16425 also inhibited LPA-induced long-term responses, including DNA synthesis and cell migration. In conclusion, Ki16425 selectively inhibits LPA receptor-mediated actions, especially through LPA₁ and LPA₃; therefore, it may be useful in evaluating the role of LPA and its receptor subtypes involved in biological actions.

Three G protein-coupled receptors (Edg-1, Edg-3, and Edg-5) for the lysolipid phosphoric acid mediator sphingosine 1-phosphate have been described by molecular cloning. Using a similar sequence that we found in the expressed sequence tag data base, we cloned and characterized of a fourth, high affinity, rat brain sphingosine 1-phosphate receptor, Edg-8. When HEK293T cells were co-transfected with Edg-8 and G protein DNAs, prepared membranes showed sphingosine 1- phosphate-dependent increases in [³⁵S]guanosine 5′-(3-O-thio)triphosphate binding with an EC₅₀of 90 nm. In a rat hepatoma Rh7777 cell line that exhibits modest endogenous responses to sphingosine 1-phosphate, this lipid mediator inhibited forskolin-driven rises in cAMP by greater than 90% when the cells were transfected with Edg-8 DNA (IC₅₀ 0.7 nm). This response is blocked fully by prior treatment of cultures with pertussis toxin, thus implicating signaling through G_i/oα proteins. Furthermore, Xenopus oocytes exhibit a calcium response to sphingosine 1-phosphate after injection of Edg-8 mRNA, but only when oocytes are co-injected with chimeric G_q/iα protein mRNA. Membranes from HEK293T and Rh7777 cell cultures expressing Edg-8 exhibited high affinity (K _D = 2 nm) binding for radiolabeled sphingosine 1-phosphate. Rat Edg-8 RNA is expressed in spleen and throughout adult rat brain where in situ hybridization revealed it to be associated with white matter. Together our data demonstrate that Edg-8 is a high affinity sphingosine 1-phosphate receptor that couples to G_i/oα proteins and is expressed predominantly by oligodendrocytes and/or fibrous astrocytes in the rat brain.

Panax ginseng, also known as Korean ginseng, is a famous medicinal plant used for the treatment of many inflammatory diseases. Ginsenosides (ginseng saponins) are the main class of active constituents of ginseng. The anti-inflammatory effects of ginseng extracts were proven with purified ginsenosides, such as ginsenosides Rb1, Rg1, Rg3, and Rh2, as well as compound K. The negative regulation of pro-inflammatory cytokine expressions (TNF-α, IL-1β, and IL-6) and enzyme expressions (iNOS and COX-2) was found as the anti-inflammatory mechanism of ginsenosides in M1-polarized macrophages and microglia. Recently, another action mechanism emerged explaining the anti-inflammatory effect of ginseng. This is a pro-resolution of inflammation derived by M2-polarized macrophages. Direct and indirect evidence supports how several ginsenosides (ginsenoside Rg3, Rb1, and Rg1) induce the M2 polarization of macrophages and microglia, and how these M2-polarized cells contribute to the suppression of inflammation progression and promotion of inflammation resolution. In this review, the new action mechanism of ginseng anti-inflammation is summarized.