Adipocyte P2Y14 receptors play a key role in regulating whole-body glucose and lipid homeostasis

Chimeras Derived from a P2Y14 Receptor Antagonist and UDP-Sugar Agonists for Potential Treatment of Inflammation

Tethered glycoconjugates of a naphthalene- and piperidine-containing antagonist of the P2Y14 receptor (PPTN) were synthesized, and their nM receptor binding affinity was determined using a fluorescent tracer in hP2Y14R-expressing whole CHO cells. The rationale for preparing mono- and disaccharide conjugates of the antagonists was to explore the receptor binding site, which we know recognizes a glucose moiety on the native agonist (UDP-glucose), as well as enhance aqueous solubility and pharmacokinetics, including kidney excretion to potentially counteract sterile inflammation. Glycoconjugates with varied linker length, including PEG chains, were compared in hP2Y14R binding, suggesting that an optimal affinity (IC50, nM) in the piperidine series was achieved for triazolyl N-linked glucose conjugates having one (8a, MRS4872, 3.21) or two (7a, MRS4865, 2.40) methylene spacers. In comparison of different carbohydrate conjugates lacking a piperidine moiety but containing triazole spacers, optimal hP2Y14R affinity (IC50, nM) was achieved with N-linked glycosides of fucose 10f (6.19) and lactose 10h (1.88), and C-linked glucose 11a (5.30). Selected compounds were examined in mouse models of conditions known to be ameliorated by P2Y14R antagonists. Two glycoconjugates that lacked a piperidine moiety, N-linked glucose derivative 10a and the isomeric C-linked glucose derivative 11a, were protective in a mouse model of allergic asthma. Piperidine-containing glucose conjugate 7a of intermediate linker length and corresponding glucuronide 7b (MRS4866) protected against neuropathic pain. Thus, glycoconjugation of a known antagonist scaffold has produced less hydrophobic P2Y14R antagonists having substantial in vitro and in vivo activity.

Obesity-induced chronic low-grade inflammation in adipose tissue: A pathway to Alzheimer's disease

Alzheimer's disease (AD) is a leading cause of cognitive impairment worldwide. Overweight and obesity are strongly associated with comorbidities, such as hypertension, diabetes, and insulin resistance (IR), which contribute substantially to the development of AD and subsequent morbidity and mortality. Adipose tissue (AT) is a highly dynamic organ composed of a diverse array of cell types, which can be classified based on their anatomic localization or cellular composition. The expansion and remodeling of AT in the context of obesity involves immunometabolic and functional shifts steered by the intertwined actions of multiple immune cells and cytokine signaling within AT, which contribute to the development of metabolic disorders, IR, and systemic markers of chronic low-grade inflammation. Chronic low-grade inflammation, a prolonged, low-dose stimulation by specific immunogens that can progress from localized sites and affect multiple organs throughout the body, leads to neurodystrophy, increased apoptosis, and disruption of homeostasis, manifesting as brain atrophy and AD-related pathology. In this review, we sought to elucidate the mechanisms by which AT contributes to the onset and progression of AD in obesity through the mediation of chronic low-grade inflammation, particularly focusing on the roles of adipokines and AT-resident immune cells.

P2Y13 receptor deficiency favors adipose tissue lipolysis and worsens insulin resistance and fatty liver disease

Excessive lipolysis in white adipose tissue (WAT) leads to insulin resistance (IR) and ectopic fat accumulation in insulin-sensitive tissues. However, the impact of Gi-coupled receptors in restraining adipocyte lipolysis through inhibition of cAMP production remained poorly elucidated. Given that the Gi-coupled P2Y13 receptor (P2Y13-R) is a purinergic receptor expressed in WAT, we investigated its role in adipocyte lipolysis and its effect on IR and metabolic dysfunction-associated steatotic liver disease (MASLD). In humans, mRNA expression of P2Y13-R in WAT was negatively correlated to adipocyte lipolysis. In mice, adipocytes lacking P2Y13-R displayed higher intracellular cAMP levels, indicating impaired Gi signaling. Consistently, the absence of P2Y13-R was linked to increased lipolysis in adipocytes and WAT explants via hormone-sensitive lipase activation. Metabolic studies indicated that mice lacking P2Y13-R showed a greater susceptibility to diet-induced IR, systemic inflammation, and MASLD compared with their wild-type counterparts. Assays conducted on precision-cut liver slices exposed to WAT conditioned medium and on liver-specific P2Y13-R-knockdown mice suggested that P2Y13-R activity in WAT protects from hepatic steatosis, independently of liver P2Y13-R expression. In conclusion, our findings support the idea that targeting adipose P2Y13-R activity may represent a pharmacological strategy to prevent obesity-associated disorders, including type 2 diabetes and MASLD.

The role of P2Y6 receptor in the pathogenesis of cardiovascular and inflammatory diseases

The purinergic receptor P2Y6 receptor (P2Y6R) is a member of the G protein-coupled receptors (GPCR) family. P2Y6R is widely expressed in various cell types and plays a critical role in physiological processes, where it is activated by extracellular uridine diphosphate (UDP) and mobilizes Ca2+ via the Gαq/11 protein pathway. We have recently discovered the pathophysiological role of P2Y6R in cardiovascular and inflammatory diseases, including inflammatory bowel disease and non-alcoholic fatty liver disease. Furthermore, we uncovered the redox-dependent internalization of P2Y6R. In this review, we provide a comprehensive overview of the pathophysiological activity of P2Y6R in cardiovascular and inflammatory diseases. Additionally, we discuss the concept of atypical internalization control of GPCRs, which may be applied in the prevention and treatment of intestinal inflammation and cardiovascular remodeling.

Alicyclic Ring Size Variation of 4-Phenyl-2-naphthoic Acid Derivatives as P2Y14 Receptor Antagonists

P2Y14 receptor (P2Y14R) is activated by extracellular UDP-glucose, a damage-associated molecular pattern that promotes inflammation in the kidney, lung, fat tissue, and elsewhere. Thus, selective P2Y14R antagonists are potentially useful for inflammatory and metabolic diseases. The piperidine ring size of potent, competitive P2Y14R antagonist (4-phenyl-2-naphthoic acid derivative) PPTN 1 was varied from 4- to 8-membered rings, with bridging/functional substitution. Conformationally and sterically modified isosteres included N-containing spirocyclic (6-9), fused (11-13), and bridged (14, 15) or large (16-20) ring systems, either saturated or containing alkene or hydroxy/methoxy groups. The alicyclic amines displayed structural preference. An α-hydroxyl group increased the affinity of 4-(4-((1R,5S,6r)-6-hydroxy-3-azabicyclo[3.1.1]heptan-6-yl)phenyl)-7-(4-(trifluoromethyl)phenyl)-2-naphthoic acid 15 (MRS4833) compared to 14 by 89-fold. 15 but not its double prodrug 50 reduced airway eosinophilia in a protease-mediated asthma model, and orally administered 15 and prodrugs reversed chronic neuropathic pain (mouse CCI model). Thus, we identified novel drug leads having in vivo efficacy.

UDP-glucose sensing P2Y14R: A novel target for inflammation

Uridine 5'-diphosphoglucose (UDP-G) as a preferential agonist, but also other UDP-sugars, such as UDP galactose, function as extracellular signaling molecules under conditions of cell injury and apoptosis. Consequently, UDP-G is regarded to function as a damage-associated molecular pattern (DAMP), regulating immune responses. UDP-G promotes neutrophil recruitment, leading to the release of pro-inflammatory chemokines. As a potent endogenous agonist with the highest affinity for the P2Y₁₄ receptor (R), it accomplishes an exclusive relationship between P2Y₁₄Rs in regulating inflammation via cyclic adenosine monophosphate (cAMP), nod-like receptor protein 3 (NLRP3) inflammasome, mitogen-activated protein kinases (MAPKs), and signal transducer and activator of transcription 1 (STAT1) pathways. In this review, we initially present a brief introduction into the expression and function of P2Y₁₄Rs in combination with UDP-G. Subsequently, we summarize emerging roles of UDP-G/P2Y₁₄R signaling pathways that modulate inflammatory responses in diverse systems, and discuss the underlying mechanisms of P2Y₁₄R activation in inflammation-related diseases. Moreover, we also refer to the applications as well as effects of novel agonists/antagonists of P2Y₁₄Rs in inflammatory conditions. In conclusion, due to the role of the P2Y₁₄R in the immune system and inflammatory pathways, it may represent a novel target for anti-inflammatory therapy.

A purinergic mechanism underlying metformin regulation of hyperglycemia

Metformin, created in 1922, has been the first-line therapy for treating type 2 diabetes mellitus for almost 70 years; however, its mechanism of action remains controversial, partly because most prior studies used supratherapeutic concentrations exceeding 1 mM despite therapeutical blood concentrations of metformin being less than 40 μM. Here we report metformin, at 10-30 μM, blocks high glucose-stimulated ATP secretion from hepatocytes mediating its antihyperglycemic action. Following glucose administration, mice demonstrate increased circulating ATP, which is prevented by metformin. Extracellular ATP through P2Y₂ receptors (P2Y₂R) suppresses PIP₃ production, compromising insulin-induced AKT activation while promoting hepatic glucose production. Furthermore, metformin-dependent improvements in glucose tolerance are abolished in P2Y₂R-null mice. Thus, removing the target of extracellular ATP, P2Y₂R, mimics the effects of metformin, revealing a new purinergic antidiabetic mechanism for metformin. Besides unraveling long-standing questions in purinergic control of glucose homeostasis, our findings provide new insights into the pleiotropic actions of metformin.

Natural Flavonoids and Ferroptosis: Potential Therapeutic Opportunities for Human Diseases

Flavonoids are a class of bioactive phytochemicals containing a core 2-phenylchromone skeleton and are widely found in fruits, vegetables, and herbs. Such natural compounds have gained significant attention due to their various health benefits. Ferroptosis is a recently discovered unique iron-dependent mode of cell death. Unlike traditional regulated cell death (RCD), ferroptosis is associated with excessive lipid peroxidation on cellular membranes. Accumulating evidence suggests that this form of RCD is involved in a variety of physiological and pathological processes. Notably, multiple flavonoids have been shown to be effective in preventing and treating diverse human diseases by regulating ferroptosis. In this review, we introduce the key molecular mechanisms of ferroptosis, including iron metabolism, lipid metabolism, and several major antioxidant systems. Additionally, we summarize the promising flavonoids targeting ferroptosis, which provides novel ideas for the management of diseases such as cancer, acute liver injury, neurodegenerative diseases, and ischemia/reperfusion (I/R) injury.

Purinergic receptor: a crucial regulator of adipose tissue functions

Obesity is a public-health challenge resulting from an imbalance between energy expenditure and calorie intake. This health problem exacerbates a variety of metabolic complications worldwide. Adipose tissue is an essential regulator of energy homeostasis, and the functions within it are regulated by purinergic receptors. A₁R, P2X7R, and P2YR mainly mediate energy homeostasis primarily through regulating energy storage and adipokines secretion in white adipose tissue (WAT). P2X5R is a novel-specific cell surface marker in brown/beige adipocytes. A₂R is a promising therapeutic target for stimulating energy expenditure in brown adipose tissue (BAT) and also mediating WAT browning. Based on these features, purinergic receptors may be an appropriate target in treating obesity. In this review, the role of purinergic receptors in different types of adipose tissue is summarized. An improved understanding of purinergic receptor functions in adipose tissue may lead to more effective treatment interventions for obesity and its related metabolic disorders.

Knockout of Purinergic P2Y6 Receptor Fails to Improve Liver Injury and Inflammation in Non-Alcoholic Steatohepatitis

Nonalcoholic steatohepatitis (NASH) is a disease that progresses from nonalcoholic fatty liver (NAFL) and which is characterized by inflammation and fibrosis. The purinergic P2Y₆ receptor (P2Y₆R) is a pro-inflammatory G_q/G₁₂ family protein-coupled receptor and reportedly contributes to intestinal inflammation and cardiovascular fibrosis, but its role in liver pathogenesis is unknown. Human genomics data analysis revealed that the liver P2Y₆R mRNA expression level is increased during the progression from NAFL to NASH, which positively correlates with inductions of C-C motif chemokine 2 (CCL2) and collagen type I α1 chain (Col1a1) mRNAs. Therefore, we examined the impact of P2Y₆R functional deficiency in mice crossed with a NASH model using a choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD). Feeding CDAHFD for 6 weeks markedly increased P2Y₆R expression level in mouse liver, which was positively correlated with CCL2 mRNA induction. Unexpectedly, the CDAHFD treatment for 6 weeks increased liver weights with severe steatosis in both wild-type (WT) and P2Y₆R knockout (KO) mice, while the disease marker levels such as serum AST and liver CCL2 mRNA in CDAHFD-treated P2Y₆R KO mice were rather aggravated compared with those of CDAHFD-treated WT mice. Thus, P2Y₆R may not contribute to the progression of liver injury, despite increased expression in NASH liver.

HQL6 serves as a novel P2Y14 receptor antagonist to ameliorate acute gouty arthritis through inhibiting macrophage pyroptosis

Acute gouty arthritis (AGA) has been classified as an autoinflammatory disease caused by deposition of monosodium urate crystals (MSU), accompanied by swellingofjoint and severe pain. Limited clinical therapy and highincidence indicate that the development of effective drugs for AGA is an urgent need. Our previous study found that P2Y₁₄ receptor (P2Y₁₄R) was a potential target in anti-gout treatment through regulating pyroptosis of macrophages under exposure of MSU. Based on previous work, we carried out further structure modifications and led to a more effective antagonist HQL6 with IC₅₀ of 3.007 nM. Extensive profiling of HQL6 has demonstrated that its high selectivity, good pharmacokinetic properties, and reliable in vivo anti-gout efficacy. Moreover, P2Y₁₄R has been demonstrated to be the key target of HQL6 since the diminished effects on adenylate cyclase inhibitor-induced acute gouty arthritis in P2Y₁₄R knockout rats. More importantly, results of single point mutant experiments exhibited that HQL6 might interact with Lys277 as favorable residue in the binding pocket of P2Y₁₄R. Therefore, we confirmed that P2Y₁₄R was a promising drug target for AGA, and HQL6 would be an available candidate for further drug development.

Adipocyte purinergic receptors activated by uracil nucleotides as obesity and type 2 diabetes targets

Extracellular uridine nucleotides regulate physiological and pathophysiological metabolic processes through the activation of P2Y₂, P2Y₄, P2Y₆ and P2Y₁₄ purinergic receptors, which play a key role in adipogenesis, glucose uptake, lipolysis and adipokine secretion. Using adipocyte-specific knockout mouse models, it has been demonstrated that lack of the P2Y₆R or P2Y₁₄R can protect against diet-induced obesity and improve whole-body glucose metabolism. The P2Y₂R facilitated adipogenesis and inflammation, and the loss of P2Y₄R or P2Y₁₄R raised the levels of the protective endocrine factor adiponectin. Hence, potent antagonists for these receptors may be tested to identify drug candidates for the treatment of obesity and type 2 diabetes. However, future studies are required to provide insight into purinergic regulation of brown adipocytes and their role in thermogenesis. This review summarizes the current studies on uridine nucleotide-activated P2YRs and their role in adipocyte function, diet-induced obesity and associated metabolic deficits.

Bridged Piperidine Analogues of a High Affinity Naphthalene-Based P2Y14R Antagonist

High affinity phenyl-piperidine P2Y₁₄R antagonist 1 (PPTN) was modified with piperidine bridging moieties to probe receptor affinity and hydrophobicity. Various 2-azanorbornane, nortropane, isonortropane, isoquinuclidine, and ring-opened cyclopentylamino derivatives preserved human P2Y₁₄R affinity (fluorescence binding assay), and their pharmacophoric overlay was compared. Enantiomeric 2-azabicyclo[2.2.1]hept-5-en-3-one precursors assured stereochemically unambiguous, diverse products. Pure (S,S,S) 2-azanorbornane enantiomer 15 (MRS4738) displayed higher affinity than 1 (3-fold higher affinity than enantiomer 16) and in vivo antihyperallodynic and antiasthmatic activity. Its double prodrug 143 (MRS4815) dramatically reduced lung inflammation in a mouse asthma model. Related lactams 21-24 and dicarboxylate 42 displayed intermediate affinity and enhanced aqueous solubility. Isoquinuclidine 34 (IC₅₀ 15.6 nM) and isonortropanol 30 (IC₅₀ 21.3 nM) had lower lipophilicity than 1. In general, rigidified piperidine derivatives did not lower lipophilicity dramatically, except those rings with multiple polar groups. P2Y₁₄R molecular modeling based on a P2Y₁₂R structure showed stable and persistent key interactions for compound 15.

Adenosine A1 receptor is dispensable for hepatocyte glucose metabolism and insulin sensitivity

Hepatic insulin resistance (IR) and enhanced hepatic glucose production (HGP) are key features of type 2 diabetes (T2D), contributing to fasting hyperglycemia. Adenosine receptors (ARs) are G protein-coupled and expressed in hepatocytes. Here, we explored the role of hepatic Gi/o-coupled A1AR on insulin resistance and glucose fluxes associated with obesity. We generated a mouse model with hepatocyte-specific deletion of A1AR (A1LΔ/Δ), which was compared with whole body knockout of A1AR or A1AR/A3AR (both Gi-coupled). Selective deletion of hepatic A1AR resulted in a modest improvement in insulin sensitivity. In addition, HFD A1LΔ/Δ mice showed decreased fasting glucose levels. Hyperinsulinemic-euglycemic clamp studies demonstrated enhanced insulin sensitivity with no change in HGP in HFD A1LΔ/Δ mice. Similar to A1LΔ/Δ, fasting blood glucose levels were significantly reduced in whole body A1Δ/Δ and A1Δ/ΔA3Δ/Δ compared to wild-type mice. Taken together, our data support the concept that blocking hepatic A1AR may decrease fasting blood glucose levels without directly affecting hepatocyte glucose metabolism and insulin sensitivity.

Purinergic Signaling in Liver Pathophysiology

Extracellular nucleosides and nucleotides activate a group of G protein-coupled receptors (GPCRs) known as purinergic receptors, comprising adenosine and P2Y receptors. Furthermore, purinergic P2X ion channels are activated by ATP. These receptors are expressed in liver resident cells and play a critical role in maintaining liver function. In the normal physiology, these receptors regulate hepatic metabolic processes such as insulin responsiveness, glycogen and lipid metabolism, and bile secretion. In disease states, ATP and other nucleotides serve as danger signals and modulate purinergic responses in the cells. Recent studies have demonstrated that purinergic receptors play a significant role in the development of metabolic syndrome associated non-alcoholic fatty liver disease (NAFLD), non-alcoholic steatohepatitis (NASH), fibrosis, hepatocellular carcinoma (HCC) and liver inflammation. In this concise review, we dissect the role of purinergic signaling in different liver resident cells involved in maintaining healthy liver function and in the development of the above-mentioned liver pathologies. Moreover, we discuss potential therapeutic strategies for liver diseases by targeting adenosine, P2Y and P2X receptors.