Involvement of P2Y receptors in the protective effect of ATP towards the cell damage in HaCaT cells exposed to H₂O₂

Network pharmacology, molecular docking and in vivo and in vitro experiments to explore the molecular mechanism of licorice green tea beverage to scavenge oxygen free radicals

Excessive oxygen free radicals can lead to aging, cancer, and other diseases. Therefore, searching for effective antioxidants to scavenge oxygen free radicals has become the focus of modern medicine. In this study, the molecular mechanism of Licorice Green Tea Beverage (LGTB) in scavenging oxygen free radicals was investigated by means of network pharmacology, molecular docking and experimental verification. Network pharmacology studies have shown that paeonol, eugenol, cinnamaldehyde, swertisin, rutin, glycyrrhetinic acid, oleic, pelargonidin-3-O-glucoside and quercetin, kaferempol were the main active components of LGTB, and SOD and CAT are important targets for LGTB in scavenging oxygen free radicals. The results of molecular docking showed that these representative compounds had good affinity to SOD and CAT target proteins. In vitro free radical scavenging experiments showed that LTGB had significant scavenging effects on both DPPH and ABTS radicals, and had strong total reducing power. In vitro cell experiments showed that LGTB could protect HaCaT cells from oxidative stress induced by H₂ O₂ . The mechanism of LGTB was related to the increase of SOD and CAT activity. Western blotting showed that LGTB could inhibit PI3K/AKT/HIF-1 signaling pathway and improve the antioxidant capacity of HaCaT cells. In vivo experiments showed that LGTB could significantly increase mouse visceral index, increase serum SOD and GSH-Px activity, decrease the content of MDA, and improve liver and kidney pathological state. This study reported the molecular mechanism of LTGB scavenging oxygen free radicals, which provided scientific basis for the treatment and clinical research of aging and other diseases caused by excessive free radicals. PRACTICAL APPLICATIONS: Free radicals are produced by the normal response of cells during aerobic respiration and perform various functions, such as signaling and providing protection against infection. However, excessive free radicals can lead to aging, cancer, and other diseases. The antioxidant can overcome the harm caused by excessive free radicals. In this study, we investigated the molecular mechanism of scavenging oxygen free radicals of Licorice Green Tea Beverage (LGTB) through network pharmacology and molecular docking, and its efficacy was verified by free radical scavenging experiment in vitro, HaCaT cell oxidative stress injury induced by H₂ O₂ , D-galactose to establish an aging model in mice and Western blotting experiment. It not only elucidates its mechanism at the system level, but also proves its validity at the biological level. It provides the theoretical basis and experimental evidence for the follow-up research and promotion of the product.

Loss of P2Y1 receptors triggers glaucoma-like pathology in mice

BACKGROUND AND PURPOSE

Glaucoma, the leading cause of blindness, damages the retinal ganglion cells. Elevated intraocular pressure (IOP) is a high-risk factor for glaucoma, so topical hypotensive drugs are usually used for treatment. Because not all patients do not respond adequately to current treatments, there is a need to identify a new molecular target to reduce IOP. Here, we have assessed the role of P2Y1 receptors in mediating elevated IOP.

EXPERIMENTAL APPROACH

P2Y₁ receptor agonist was instilled into the eyes of mice, and the IOP changes were measured by a rebound-type tonometer. Expression of P2Y₁ receptors was estimated by immunohistochemistry. Ocular function was measured by a multifocal electroretinogram.

KEY RESULTS

A single dose of the P2Y₁ receptor agonist transiently reduced IOP and such effects were absent in P2Y₁ receptor-deficient (P2Y₁ KO) mice. P2Y₁ receptors were functionally expressed in the ciliary body, trabecular meshwork and Schlemm's canal. Activation of P2Y₁ receptors negatively regulated aquaporin 4 (AQP4) function but up-regulated endothelial NOS (eNOS). P2Y₁ KO mice showed chronic ocular hypertension regardless of age. P2Y₁ KO mice at 3 months old showed no damage to retinal ganglion cells, whereas 12-month-old mice showed a significant loss of these cells and impairment of ocular functions. Damage to retinal ganglion cells was attenuated by chronic administration of an IOP-reducing agent.

CONCLUSION AND IMPLICATIONS

Activation of P2Y₁ receptors reduced IOP via dual pathways including AQP4 and eNOS. Loss of P2Y₁ receptors resulted in glaucomatous optic neuropathy, suggesting that P2Y₁ receptors might provide an effective target in the treatment of glaucoma.

Hydroquinone Induces NLRP3-Independent IL-18 Release from ARPE-19 Cells

Age-related macular degeneration (AMD) is a retinal disease leading to impaired vision. Cigarette smoke increases the risk for developing AMD by causing increased reactive oxygen species (ROS) production and damage in the retinal pigment epithelium (RPE). We have previously shown that the cigarette tar component hydroquinone causes oxidative stress in human RPE cells. In the present study, we investigated the propensity of hydroquinone to induce the secretion of interleukin (IL)-1β and IL-18. The activation of these cytokines is usually regulated by the Nucleotide-binding domain, Leucine-rich repeat, and Pyrin domain 3 (NLRP3) inflammasome. ARPE-19 cells were exposed to hydroquinone, and cell viability was monitored using the lactate dehydrogenase (LDH) and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide salt (MTT) assays. Enzyme-linked immunosorbent assays (ELISAs) were used to measure the levels of proinflammatory cytokines IL-1β and IL-18 as well as NLRP3, caspase-1, and poly (ADP-ribose) polymerase (PARP). Hydroquinone did not change IL-1β release but significantly increased the secretion of IL-18. Cytoplasmic NLRP3 levels increased after the hydroquinone treatment of IL-1α-primed RPE cells, but IL-18 was equally released from primed and nonprimed cells. Hydroquinone reduced the intracellular levels of PARP, which were restored by treatment with the ROS scavenger N-acetyl-cysteine (NAC). NAC concurrently reduced the NLRP3 levels but had no effect on IL-18 release. In contrast, the NADPH oxidase inhibitor ammonium pyrrolidinedithiocarbamate (APDC) reduced the release of IL-18 but had no effect on the NLRP3 levels. Collectively, hydroquinone caused DNA damage seen as reduced intracellular PARP levels and induced NLRP3-independent IL-18 secretion in human RPE cells.

Effects of Resvega on Inflammasome Activation in Conjunction with Dysfunctional Intracellular Clearance in Retinal Pigment Epithelial (RPE) Cells

Age-related macular degeneration (AMD) is an eye disease in which retinal pigment epithelium (RPE) cells play a crucial role in maintaining retinal homeostasis and photoreceptors’ functionality. During disease progression, there is increased inflammation with nucleotide-binding domain, leucine-rich repeat, and Pyrin domain 3 (NLRP3) inflammasome activation, oxidative stress, and impaired autophagy in RPE cells. Previously, we have shown that the dietary supplement Resvega reduces reactive oxygen species (ROS) production and induces autophagy in RPE cells. Here, we investigated the ability of Resvega to prevent NLRP3 inflammasome activation with impaired protein clearance in human RPE cells. Cell viability was measured using the lactate dehydrogenase (LDH) and the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assays. Enzyme-linked immunosorbent assays (ELISA) were utilized to determine the secretion of cytokines, NLRP3, and vascular endothelial growth factor (VEGF). Caspase-1 activity was measured with a fluorescent labeled inhibitor of caspase-1 (FLICA; FAM-YVAD-FMK) and detected microscopically. Resvega improved the cell membrane integrity, which was evident as reduced LDH leakage from cells. In addition, the caspase-1 activity and NLRP3 release were reduced, as was the secretion of two inflammatory cytokines, interleukin (IL)-1β and IL-8, in IL-1α-primed ARPE-19 cells. According to our results, Resvega can potentially reduce NLRP3 inflammasome-mediated inflammation in RPE cells with impaired protein clearance.

ATP and ADP enhance DNA damage repair in γ-irradiated BEAS-2B human bronchial epithelial cells through activation of P2X7 and P2Y12 receptors

Agents that promote DNA repair may be useful as radioprotectants to minimize side effects such as radiation pneumonia caused by damage to normal cells during radiation therapy to treat lung cancer. We have reported that extracellular nucleotides and nucleosides are involved in the P2 or P1 receptor-mediated DNA damage response (DDR) after γ-irradiation. Here, we investigated the effects of ATP, UTP, GTP, ITP and their metabolites on the γH2AX/53BP1 focus formation in nuclei (a measure of γ-irradiation-induced DDR) and the survival of γ-irradiated immortalized human bronchial epithelial (BEAS-2B) cells. Fluorescence immunostaining showed that ATP and ADP increase DDR and DNA repair, and exhibit radioprotective effects as evaluated by colony formation assay. These effects of ATP or ADP were blocked by inhibitors of P2X7 or P2Y12 receptor, respectively, and by ERK1/2 inhibitor. ATP and ADP enhanced phosphorylation of ERK1/2 by suppressing MKP-1 and MKP-3 expression after γ-irradiation. These results indicate that ATP and ADP exhibit radioprotective effects by phosphorylation of ERK1/2 via activation of P2X7 and P2Y12 receptors, respectively, to promote γ-irradiation-induced DDR and DNA repair. ATP and ADP appear to be candidates for radioprotectants to reduce damage to non-cancerous cells during lung cancer radiotherapy by promoting DDR and DNA repair.

House dust mite allergens induce interleukin 33 (IL-33) synthesis and release from keratinocytes via ATP-mediated extracellular signaling

In atopic diseases, the epithelium releases cytokines and chemokines that initiate skin inflammation. Atopic dermatitis (AD) is characterized by a disrupted epidermal barrier and is triggered or exacerbated by environmental stimuli such as house dust mite (HDM) allergens. The proinflammatory cytokine interleukin 33 (IL-33) plays an important role in the pathogenesis of AD, but how IL-33 production in keratinocytes is elicited by HDM is unknown. To that end, here we stimulated monolayer-cultured human keratinocytes and human living skin equivalents with Dermatophagoides pteronyssinus HDM extract to investigate its effects on IL-33 production from keratinocytes. The HDM extract induced intracellular expression of IL-33 and modulated its processing and maturation, triggering rapid IL-33 release from keratinocytes. Group 1 HDM allergen but not group 2 HDM allergen elicited IL-33 production. An ATP assay of keratinocyte culture supernatants revealed an acute and transient accumulation of extracellular ATP immediately after the HDM extract stimulation. Using the broad-spectrum P2 antagonist suramin, the specific purinergic receptor P2Y2 (P2RY2) antagonist AR-C118925XX, and P2RY2-specific siRNA, we discovered that the HDM extract-induced IL-33 expression was mainly dependent on extracellular ATP/P2Y2 signaling mediated by transactivation of epidermal growth factor receptor, followed by activation of the ERK kinase signaling pathway. Moreover, HDM extract-induced release of 25-kDa IL-33 from the keratinocytes depended on an extracellular ATP/P2 signaling-mediated intracellular Ca²⁺ increase. Our study demonstrates the new mechanism controlling the induction and maturation of keratinocyte-produced IL-33 by HDM allergens, an innate immune process that might play a role in AD development or severity.

The Metabolism of Methazolamide in Immortalized Human Keratinocytes, HaCaT Cells

OBJECTIVE

Drug therapy is occasionally accompanied by an idiosyncratic severe toxicity, which occurs very rarely, but can lead to patient mortality. Methazolamide, an anti-glaucomatous agent, could cause severe skin eruptions called Stevens-Johnson syndrome/toxic epidermal necrolyis (SJS/TEN). Its precise etiology is still uncertain. In this study, the metabolism of methazolamide was investigated in immortalized human keratinocytes to reveal the possible mechanism which causes SJS/TEN.

METHODS

The metabolism of methazolamide was studied using immortalized human keratinocytes, HaCaT cells. HPLC was used to isolate a metabolite from the culture medium. Mass spectrometry (LCMS/ MS) was employed for its characterization. Three typical chemical inducers were assessed for the inducibility of cytochrome P450, and methimazole was used as the inhibitor of flavin-containing monooxygenase (FMO).

RESULTS

A sulfonic acid, N-[3-methyl-5-sulfo-1,3,4-thiadiazol-2(3H)-ylidene]acetamide (MSO) was identified as the final metabolite. Dexamethasone and β-naphthoflavone behaved as an inducer of cytochrome P450 in the metabolism, but isoniazid did not. The effect of methimazole was not consistent. We did not detect any glucuronide nor any mercapturic acid (N-acetylcysteine conjugate).

CONCLUSION

N-[3-methyl-5-sulfo-1,3,4-thiadiazol-2(3H)-ylidene]acetamide (MSO) is not considered to be a direct product of an enzymatic reaction, but rather an auto-oxidation product of N-[3-methyl-5- sulfe-1,3,4-thiadiazol-2(3H)-ylidene]acetamide, a chemically unstable sulfenic acid, which is produced by cytochrome P450 from the β-lyase product of cysteine conjugate of methazolamide. MSO is considered to be susceptible to glutathione and to return to glutathione conjugate of methazolamide, forming a futile cycle. A hypothetical scenario is presented as to the onset of the disease.

Ecto-nucleoside triphosphate diphosphohydrolase 2 modulates local ATP-induced calcium signaling in human HaCaT keratinocytes

Keratinocytes are the major building blocks of the human epidermis. In many physiological and pathophysiological conditions, keratinocytes release adenosine triphosphate (ATP) as an autocrine/paracrine mediator that regulates cell proliferation, differentiation, and migration. ATP receptors have been identified in various epidermal cell types; therefore, extracellular ATP homeostasis likely determines its long-term, trophic effects on skin health. We investigated the possibility that human keratinocytes express surface-located enzymes that modulate ATP concentration, as well as the corresponding receptor activation, in the pericellular microenvironment. We observed that the human keratinocyte cell line HaCaT released ATP and hydrolyzed extracellular ATP. Interestingly, ATP hydrolysis resulted in adenosine diphosphate (ADP) accumulation in the extracellular space. Pharmacological inhibition by ARL 67156 or gene silencing of the endogenous ecto-nucleoside triphosphate diphosphohydrolase (NTPDase) isoform 2 resulted in a 25% reduction in both ATP hydrolysis and ADP formation. Using intracellular calcium as a reporter, we found that although NTPDase2 hydrolyzed ATP and generated sustainable ADP levels, only ATP contributed to increased intracellular calcium via P2Y2 receptor activation. Furthermore, knocking down NTPDase2 potentiated the nanomolar ATP-induced intracellular calcium increase, suggesting that NTPDase2 globally attenuates nucleotide concentration in the pericellular microenvironment as well as locally shields receptors in the vicinity from being activated by extracellular ATP. Our findings reveal an important role of human keratinocyte NTPDase2 in modulating nucleotide signaling in the extracellular milieu of human epidermis.

Involvement of P2Y13 receptor in suppression of neuronal differentiation

We examined the receptor-mediated effects of extracellular ATP on neuronal differentiation of PC12 cells, Neuro2a cells and MEB5 cells by using a series of receptor antagonists. The P2Y13 receptor antagonist MRS2211 significantly accelerated neurite outgrowth in all cases. Treatment with nerve growth factor (NGF) alone activated ERK1/2 in PC12 cells, and the activation was further increased by MRS2211. These results suggest involvement of P2Y13 receptor in suppression of neuronal differentiation. Thus, P2Y13 receptor antagonists might be candidates for treatment of neurodegenerative diseases.