Mitral valve repair with leaflet resection versus preservation for degenerative posterior leaflet prolapse.

OBJECTIVES: The optimal technique for repairing posterior mitral valve leaflet prolapse remains undetermined. We aimed to compare leaflet resection and neochordae implantation in patients undergoing mitral valve repair for posterior leaflet prolapse, focusing on transmitral pressure gradient and recurrence of mitral regurgitation. METHODS: We enrolled patients undergoing mitral valve repair using either leaflet resection or neochordae implantation for single-segment prolapse of posterior mitral valve leaflet between 2000 and 2021 at our institution. Longitudinal outcomes were evaluated after adjustments with inverse-probability-of-treatment weighting. Repeat echocardiographic measurements (n = 3473, 5.4/patient) of transmitral pressure gradient and significant (moderate or severe) mitral regurgitation recurrence were estimated using nonlinear mixed-effect models. Subgroup analyses were conducted based on the size and type of prosthesis. RESULTS: Among 639 patients, leaflet resection was used in 479 (75.0%) and neochordae implantation was used in 160 (25.0%). In the inverse-probability-of-treatment weighting adjusted cohort, the risk of death (P = .623) and mitral valve reoperation (P = .340) did not significantly differ between the 2 groups during a median follow-up of 97.3 months. Echocardiographic data showed comparable mean (at 5 years, 3.8 vs 4.0 mm Hg; P = .442) and peak (9.6 vs 10.4 mm Hg; P = .131) pressure gradients between groups, which persisted in most subgroup analyses. However, neochordae implantation was associated with a higher probability of significant mitral regurgitation recurrence compared with leaflet resection (at 5 years, 16.1% vs 7.0%; P < .001). CONCLUSIONS: Leaflet resection yielded similar clinical outcomes and transmitral pressure gradients compared with neochordae implantation after mitral valve repair, with a lower mitral regurgitation recurrence rate. These findings underscore the need to reassess the efficacy of neochordae implantation relative to leaflet resection.

Time to initiation of extracorporeal membrane oxygenation in conventional cardiopulmonary resuscitation affects the patient survival prognosis.

BACKGROUND: Cardiopulmonary resuscitation (CPR) is the cornerstone intervention for cardiac arrest, with extracorporeal CPR (ECPR) demonstrating enhanced survival and neurologic outcomes in in-hospital cardiac arrest. This study explores the time interval between CPR initiation and the onset of extracorporeal membrane oxygenation (ECMO) in ECPR recipients, investigating its impact on survival outcomes. METHODS: This retrospective analysis included 1950 adults who received CPR at a single medical center between March 2019 and April 2023. Data from 198 adult patients who had ECMO inserted during CPR were analyzed. The interval from CPR initiation to ECMO initiation was quantified and categorized as ≤20, 20-40, and >40 min. Cox regression analysis assessed associations between CPR-to-ECMO time and short- and long-term mortalities. RESULTS: Among the 198 patients who underwent ECPR, 116 (58.6%) experienced 30-day mortality. Initiation of ECMO within 20 min occurred in 46 (23.2%), whereas 74 (37.4%) had ECMO initiated after 40 min. Cox regression revealed a significant association between time from CPR to ECMO initiation and 30-day mortality (adjusted hazard ratio [HR]: 2.20 in >40 min, HR: 2.63 in 20-40 min, p = 0.006) and 6-month mortality (HR: 1.81, in >40 min, HR: 1.99 in 20-40 min, p = 0.021). CONCLUSIONS: This study revealed that, in ECPR recipients, a shorter duration between CPR initiation and ECMO flow commencement is associated with improved short- and long-term patient prognoses. These findings emphasize the critical role of timely ECMO application in optimizing outcomes for patients undergoing ECPR.

Pharmacologic inhibition of Il6st/gp130 improves dermatological inflammation and pruritus.

Chronic dermatitis is a disease with large unmet need for pharmacological improvement. Dermatitis conditions are maintained and exacerbated by various cytokine actions in the context of inflammation. Interleukin 6 signal transducer (Il6st), also known as glycoprotein 130 (Gp130), is a key component for surface reception of a multitude of cytokines and transduction and amplification of their pro-inflammatory signals. We hypothesized accordingly that pharmacological inhibition of Il6st can alter dermatitis pathology. Treatment with SC-144 and bazedoxifene, two representative small molecule Il6st inhibitors with different binding modes led to moderate but significant improvement of skin conditions in a 1-chloro-2,4-dinitrobenzene animal model. Part of cytokine expressions indicating the dermatological index were normalized particularly when treated with SC-144. Pruritic behaviors were blunted, also possibly giving limited contribution to disease improvement. In psoriatic skin and itch of an imiquimod animal model, those two treatments appeared to be relatively moderate. Collectively, pharmacological inhibition of Il6st seems to lessen pathological irritation. Inversely, this experimental attempt newly implies that Il6st participates in pathological mechanisms. In conclusion, we suggest Il6st as a novel target for improving dermatitis, and that agents with suitable efficacy and safety for its modulation are translatable.

Tailored surgical strategies for mini-access open total arch repair.

Objective: Open arch repair is perceived as a challenging, high-risk procedure, with a barrier against the use of a minimally invasive approach. We aimed to present a mini-access total arch replacement performed by stratified approaches and to evaluate perioperative outcomes to contribute to the body of evidence. Methods: We evaluated 40 consecutive patients (aged 69.5 years; interquartile range, 65.6-76.3 years) undergoing elective total arch replacement using 5- to 8-cm upper mini-sternotomy between 2018 and 2022. Surgical strategies, including arterial inflow site and methods of branching vessel reconstruction, were systematically selected at the individual level. To evaluate comparative outcomes, contemporary cases undergoing total arch replacement via sternotomy with similar eligibility criteria served as a control group, and the inverse-treatment-weighting method was used to adjust for baseline characteristics. Results: Arch-first anastomosis using trifurcate graft, distal-first anastomosis using 4-branch graft, and island anastomosis were used in 18 (45%), 12 (30.0%), and 10 (25%) patients, respectively. Lower body and cardiac ischemic times were 23.4 minutes (interquartile range, 18.0-29.0 minutes) and 66.7 minutes (interquartile range, 50.1-78.2 minutes). There was no early (30-day or in-hospital) mortality, and 2 patients experienced disabling stroke (5.0%). The contemporary control group comprised 55 patients. After an adjustment, a mini-access group showed lower risks of stroke (odds ratio, 0.88; 95% CI, 0.78-1.00; P = .049) and a composite of major complications (odds ratio, 0.79; 95% CI, 0.68-0.92; P = .003), compared with a sternotomy approach. Conclusions: Based on present results, mini-access total arch replacement may be performed with reasonable safety and efficiency.

Chemical tools to define and manipulate interferon-inducible Ubl protease USP18.

Ubiquitin-specific protease 18 (USP18) is a multifunctional cysteine protease primarily responsible for deconjugating interferon-inducible ubiquitin-like (Ubl) modifier ISG15 from protein substrates. Here, we report the design and synthesis of activity-based probes (ABPs) capable of selectively detecting USP18 activity over other ISG15 cross-reactive deubiquitinases (DUBs) by incorporating unnatural amino acids into the C-terminal tail of ISG15. Combining with a ubiquitin-based DUB ABP, the selective USP18 ABP is employed in a chemoproteomic screening platform to identify and assess inhibitors of DUBs including USP18. We further demonstrate that USP18 ABPs can be utilized to profile differential activities of USP18 in lung cancer cell lines, providing a strategy that will help define the activity-related landscape of USP18 in different disease states and unravel important (de)ISGylation-dependent biological processes.

Discovery of a Tunable Heterocyclic Electrophile 4-Chloro-pyrazolopyridine That Defines a Unique Subset of Ligandable Cysteines.

Electrophilic small molecules with novel reactivity are powerful tools that enable activity-based protein profiling and covalent inhibitor discovery. Here, we report a reactive heterocyclic scaffold, 4-chloro-pyrazolopyridine (CPzP) for selective modification of proteins via a nucleophilic aromatic substitution (SNAr) mechanism. Chemoproteomic profiling reveals that CPzPs engage cysteines within functionally diverse protein sites including ribosomal protein S5 (RPS5), inosine monophosphate dehydrogenase 2 (IMPDH2), and heat shock protein 60 (HSP60). Through the optimization of appended recognition elements, we demonstrate the utility of CPzP for covalent inhibition of prolyl endopeptidase (PREP) by targeting a noncatalytic active-site cysteine. This study suggests that the proteome reactivity of CPzPs can be modulated by both electronic and steric features of the ring system, providing a new tunable electrophile for applications in chemoproteomics and covalent inhibitor design.

Identification of plastic-degrading bacteria in the human gut.

Environmental pollution caused by the excessive use of plastics has resulted in the inflow of microplastics into the human body. However, the effects of microplastics on the human gut microbiota still need to be better understood. To determine whether plastic-degrading bacteria exist in the human gut, we collected the feces of six human individuals, did enrichment cultures and screened for bacterial species with a low-density polyethylene (LDPE) or polypropylene (PP)-degrading activity using a micro-spray method. We successfully isolated four bacterial species with an LDPE-degrading activity and three with a PP-degrading activity. Notably, all bacterial species identified with an LDPE or PP-degrading activity were opportunistic pathogens. We analyzed the microbial degradation of the LDPE or PP surface using scanning electron microscopy and confirmed that each bacterial species caused the physical changes. Chemical structural changes were further investigated using X-ray photoelectron spectroscopy and Fourier-transform-infrared spectroscopy, confirming the oxidation of the LDPE or PP surface with the formation of carbonyl groups (C=O), ester groups (CO), and hydroxyl groups (-OH) by each bacterial species. Finally, high temperature gel permeation chromatography (HT-GPC) analysis showed that these bacterial species performed to a limited extent depolymerization. These results indicate that, as a single species, these opportunistic pathogens in the human gut have a complete set of enzymes and other components required to initiate the oxidation of the carbon chains of LDPE or PP and to degrade them. Furthermore, these findings suggest that these bacterial species can potentially biodegrade and metabolize microplastics in the human gut.

Cardiovascular outcomes in solid organ transplant recipients undergoing cardiac surgery: A matched pair analysis.

INTRODUCTION: This study aimed to compare postoperative outcomes after cardiac surgery in solid-organ transplant recipients and nontransplant patients. METHODS: We performed a retrospective analysis of 78 consecutive transplant recipients who underwent cardiac surgery at Asan Medical Center between 2000 and 2022 and were matched with 312 nontransplant patients who underwent cardiac surgery at a 1:4 ratio. The outcomes included 30-day mortality, all-cause death, cardiac death, readmission, and cardiac readmission. RESULTS: There was no significant difference in baseline characteristics between the two groups. The most common type of cardiac surgery performed in solid organ transplant recipients was isolated valve surgery, followed by isolated CABG. The 30-day mortality was not significantly different between transplant recipients and nontransplant patients (3.9% vs. 3.5%; P > .99). Solid organ transplant recipients showed a higher all-cause mortality compared to nontransplant patients (29.1% vs. 14.3% at 5 years; P = .001); however, there was no significant difference in cardiac death between the two groups (2.6% vs. 3.2% at 5 years; P = .80). In addition, the readmission and cardiac readmission rates showed comparable findings to that of mortality. CONCLUSION: Cardiac surgery can be performed safely in solid organ transplant recipients, with postoperative cardiovascular outcomes comparable to those observed in nontransplant patients.

Mechanical versus Bioprosthetic Aortic Valve Replacement in Patients Aged 50 to 70 Years.

Background: This study compared the outcomes of surgical aortic valve replacement (AVR) in patients aged 50 to 70 years based on the type of prosthetic valve used. Methods: We compared patients who underwent mechanical AVR to those who underwent bioprosthetic AVR at our institution between January 2000 and March 2019. Competing risk analysis and the inverse probability of treatment weighting (IPTW) method based on propensity score were employed for comparisons. Results: A total of 1,580 patients (984 patients with mechanical AVR; 596 patients with bioprosthetic AVR) were enrolled. There was no significant difference in early mortality between the mechanical AVR and bioprosthetic AVR groups (0.9% vs. 1.7%, p=0.177). After IPTW adjustment, the risk of all-cause mortality was significantly higher in the bioprosthetic AVR group than in the mechanical AVR group (hazard ratio [HR], 1.39; 95% confidence interval [CI], 1.07-1.80; p=0.014). Competing risk analysis revealed lower risks of stroke (sub-distributional hazard ratio [sHR], 0.44; 95% CI, 0.28-0.67; p<0.001) and anticoagulation- related bleeding (sHR, 0.35; 95% CI, 0.23-0.53; p<0.001) in the bioprosthetic AVR group. Conversely, the risk of aortic valve (AV) reintervention was higher in the bioprosthetic AVR group (sHR, 6.14; 95% CI, 3.17-11.93; p<0.001). Conclusion: Among patients aged 50 to 70 years who underwent surgical AVR, those receiving mechanical valves showed better survival than those with bioprosthetic valves. The mechanical AVR group exhibited a higher risk of stroke and anticoagulation-related bleeding, while the bioprosthetic AVR group showed a higher risk of AV reintervention.

Recent Outcomes of Surgical Redo Aortic Valve Replacement in Prosthetic Valve Failure.

BACKGROUND: As redo surgical aortic valve replacement (AVR) is relatively high risk, valve-in-valve transcatheter AVR has emerged as an alternative for failed prostheses. However, the majority of studies are outdated. This study assessed the current clinical outcomes of redo AVR. METHODS AND RESULTS: This study enrolled 324 patients who underwent redo AVR due to prosthetic valve failure from 2010 to 2021 in four tertiary centers. The primary outcome was operative mortality. The secondary outcomes were overall survival, cardiac death, and aortic valve-related events. Logistic regression analysis, clustered Cox proportional hazards models, and competing risk analysis were used to evaluate the independent risk factors. Redo AVR was performed in 242 patients without endocarditis and 82 patients with endocarditis. Overall operative mortality was 4.6% (15 deaths). Excluding patients with endocarditis, the operative mortality of redo AVR decreased to 2.5%. Multivariate analyses demonstrated that endocarditis (hazard ratio [HR]: 3.990, p = 0.014), longer cardiopulmonary bypass time (HR: 1.006, p = 0.037), and lower left ventricular ejection fraction (LVEF) (HR: 0.956, p = 0.034) were risk factors of operative mortality. Endocarditis and lower LVEF were independent predictors of overall survival. CONCLUSION: The relatively high risk of redo AVR was due to reoperation for prosthetic valve endocarditis. The outcomes of redo AVR for nonendocarditis are excellent. Our findings suggest that patients without endocarditis, especially with acceptable LVEF, can be treated safely with redo AVR.

SP-8356 inhibits acute lung injury by suppressing inflammatory cytokine production and immune cell infiltration.

This study investigated the anti-inflammatory and protective properties of SP-8356, a synthetic derivative of (1S)-(-)-verbenone, in a mouse model of LPS-induced acute lung injury (ALI). By targeting intracellular signaling pathways and inflammatory responses, SP-8356 demonstrated a potent ability to attenuate deleterious effects of proinflammatory stimuli. Specifically, SP-8356 effectively inhibited the activation of crucial signaling molecules such as NF-κB and Akt, and subsequently dampened the expression of inflammatory cytokines in various lung cellular components. Intervention with SP-8356 treatment also preserved the structural integrity of the epithelial and endothelial barriers. By reducing immune cell infiltration into inflamed lung tissue, SP-8356 exerted a broad protective effect against ALI. These findings position SP-8356 as a promising therapeutic candidate for pulmonary inflammatory diseases that cause ALI.

Surgical Outcomes of Centrifugal Continuous-Flow Implantable Left Ventricular Assist Devices: Heartmate 3 versus Heartware Ventricular Assist Device.

Background: Left ventricular assist devices (LVADs) are widely employed as a therapeutic option for end-stage heart failure. We evaluated the outcomes associated with centrifugal-flow LVAD implantation, comparing 2 device models: the Heartmate 3 (HM3) and the Heartware Ventricular Assist Device (HVAD). Methods: Data were collected from patients who underwent LVAD implantation between June 1, 2015 and December 31, 2022. We analyzed overall survival, first rehospitalization, and early, late, and LVAD-related complications. Results: In total, 74 patients underwent LVAD implantation, with 42 receiving the HM3 and 32 the HVAD. A mild Interagency Registry for Mechanically Assisted Circulatory Support score was more common among HM3 than HVAD recipients (p=0.006), and patients receiving the HM3 exhibited lower rates of preoperative ventilator use (p=0.010) and extracorporeal membrane oxygenation (p=0.039). The overall early mortality rate was 5.4% (4 of 74 patients), with no significant difference between groups. Regarding early right ventricular (RV) failure, HM3 implantation was associated with a lower rate (13 of 42 [31.0%]) than HVAD implantation (18 of 32 [56.2%], p=0.051). The median rehospitalization-free period was longer for HM3 recipients (16.9 months) than HVAD recipients (5.3 months, p=0.013). Furthermore, HM3 recipients displayed a lower incidence of late hemorrhagic stroke (p=0.016). In the multivariable analysis, preoperative use of continuous renal replacement therapy (odds ratio, 22.31; p=0.002) was the only significant predictor of postoperative RV failure. Conclusion: The LVAD models (HM3 and HVAD) demonstrated comparable overall survival rates. However, the HM3 was associated with a lower risk of late hemorrhagic stroke.

Prognostic impact of the E/e' ratio in patients with chronic severe aortic regurgitation undergoing aortic valve replacement.

OBJECTIVES: The study objective was to evaluate the clinical implication of left ventricular diastolic dysfunction in patients with chronic severe aortic regurgitation undergoing aortic valve replacement. METHODS: We reviewed the medical records of 323 patients (age, 56.3 ± 14.1 years; 111 female) who underwent aortic valve replacement for chronic severe aortic regurgitation between 2005 and 2019. Left ventricular diastolic dysfunction was assessed by the ratio of peak left ventricular inflow velocity over mitral annular velocity (E/e'). The study end point was the composite of death and heart failure requiring hospital admission. RESULTS: The E/e' ratio was significantly correlated with age, left atrial dimension, left ventricular end-diastolic volume, mitral regurgitation grade, and tricuspid regurgitation grade (all P < .001). During follow-up (1748.3 patient-years), death and heart failure occurred in 36 patients (2.06/patient-year) and 9 patients (0.53/patient-year), respectively. In multivariable analysis, E/e' ratio (per 5 increment, hazard ratio, 1.32; 95% confidence interval, 1.02-1.71; P = .03), age (hazard ratio, 1.06; 95% confidence interval, 1.03-1.10; P < .001), and left ventricular ejection fraction (hazard ratio, 0.94; 95% confidence interval, 0.90-0.98; P = .002) were independent predictors of death and heart failure. The 5-year heart failure-free survival was 94.9% ± 1.7% in patients with E/e' less than 15% and 84.2% ± 4.2% in patients with E/e' 15 or greater (P < .001). CONCLUSIONS: The E/e' ratio was significantly associated with adverse outcomes in patients with chronic severe aortic regurgitation undergoing aortic valve replacement and may be useful as a prognostic marker in such patients.

Synthesis of 9-Cinnamyl-9H-purine Derivatives as Novel TLR4/MyD88/NF-κB Pathway Inhibitors for Anti-inflammatory Effects.

The novel 9-cinnamyl-9H-purine skeleton, inspired by resveratrol and curcumin, was developed to avoid a pan-assay interference compound (PAINS) related to invalid metabolic pancreas activity (IMPS). It replaced the phenol group with purine analogues, the building blocks of DNA and RNA. Alterations to the hydroxyl group in the cinnamyl group, such as H, Me, or F substitutions, were made to impede its oxidation to a PAINS-associated quinone. Among the compounds tested, 5e significantly inhibited nitric oxide production in LPS-induced macrophages (IC50: 6.4 vs 26.4 µM for resveratrol). 5e also reduced pro-inflammatory cytokine levels (IL-6, TNF-α, IL-1ß) and lowered iNOS and COX-2 protein levels. Mechanistically, 5e disrupted the TLR4-MyD88 protein interaction, leading to the suppression of the NF-κB signaling pathway suppression. In an atopic dermatitis mouse model, 5e reduced ear edema and inflammation. These findings indicate that the novel 9-cinnamyl-9H-purine skeleton provides therapeutic insight into treating various human diseases by regulating inflammation.

Discovery of Chemical Scaffolds as Lysophosphatidic Acid Receptor 1 Antagonists: Virtual Screening, In Vitro Validation, and Molecular Dynamics Analysis.

Lysophosphatidic acid receptor 1 (LPAR1) is an emerging therapeutic target for numerous human diseases including fibrosis. However, the limited number of available core structures of LPAR1 antagonists has prompted the need for novel chemical templates. In this study, we conducted a high-throughput virtual screening to discover potential new scaffolds. We tested three existing crystal structures alongside an AlphaFold model to evaluate their suitability in structure-based virtual screening, finding that the crystal structures show superior performance compared with the predictive model. Furthermore, we also found that enhancing the precision in the screening process did not necessarily improve the enrichment of hits. From the screening campaign, we identified five structures that were validated using an LPAR1-dependent calcium flux assay. To gain a deeper insight into the protein-ligand interaction, we extensively analyzed the binding modes of these compounds using in silico techniques, laying the groundwork for the discovery of novel LPAR1 antagonists.

Bovine pericardial versus porcine bioprosthetic aortic valves: A nationwide population-based cohort study in Korea.

OBJECTIVE: To compare the clinical outcomes of aortic valve replacement (AVR) using bovine pericardial and porcine bioprostheses, utilizing a nationwide administrative claims database. METHODS: Adult patients (age ≥40 years) who underwent bioprosthetic AVR, without other valve replacements, between 2003 and 2018 were identified from the Korean National Health Insurance Service database. The outcomes of interest were all-cause mortality, cardiac mortality, and valve-related events, including the incidence of reoperation, endocarditis, systemic thromboembolism, and major bleeding. Baseline adjustment was performed using propensity score matching. Time-related outcomes were evaluated using a competing risk analysis, with death as a competing risk. RESULTS: Among the 7714 patients who underwent bioprosthetic AVR, 5621 (72.9%) received bovine pericardial prostheses and 2093 (27.1%) received porcine bioprostheses. After matching, 1937 pairs were included in the final analysis. During follow-up (median, 4.49 years; interquartile range, 2.83-8.20 years), the use of porcine bioprostheses was associated with a higher risk of aortic valve reoperation (adjusted hazard ratio [HR], 1.87; 95% confidence interval [CI], 1.16 to 3.01); however, no significant differences were observed in cumulative incidences of all-cause mortality, cardiac mortality, thromboembolism, or major bleeding. Subgroup analyses revealed that the use of bovine valves was associated with improved survival in patients with diabetes mellitus, whereas in patients undergoing dialysis, porcine valves exhibited better survival than bovine valves. CONCLUSIONS: In this large nationwide cohort study of patients undergoing bioprosthetic aortic valve replacement, the use of porcine prostheses was significantly associated with an increased risk of reoperation compared with the use of bovine prostheses, supporting previous findings.

Defect-Passivated Photosensor Based on Cesium Lead Bromide (CsPbBr3) Perovskite Quantum Dots for Microbial Detection.

A defect-passivated photosensor based on cesium lead bromide (CsPbBr3) perovskite quantum dots (QD) was fabricated using parylene films, and the photosensor was applied for the microbial detection. The CsPbBr3 perovskite QDs were synthesized to be homogeneous in size under thermodynamic control, and the perovskite QD-based photosensor was fabricated using MoS2 flakes as the electron transfer layer. In this work, a parylene film with functional groups was deposited on a photosensor for physical protection (waterproof) and defect (halide vacancy) passivation of the perovskite QD. As the first effect of the parylene film, the physical protection of the perovskite QD from water was estimated by comparing the photosensor performance after incubation in water. As the second effect of the parylene, the interaction between the functional groups of the parylene film and the halide vacancies of the perovskite QDs was investigated through the bandgap, crystal structure, and trap-state density analysis. Additionally, density functional theory analysis on Mulliken charges, lattice parameters, and Gibbs free energy demonstrated the effect of the defect passivation by parylene films. Finally, the parylene-passivated QD-based photosensor was applied to the detection of two kinds of food-poisoning and gastroduodenal disease bacteria (Listeria monocytogenes and Helicobacter pylori).

Neurokinin-2 receptor negatively modulates substance P responses by forming complex with Neurokinin-1 receptor.

BACKGROUND: Tachykinins and their cognate receptors, neurokinin receptors (NKs) including NK1, NK2, and NK3 play vital roles in regulating various physiological processes including neurotransmission, nociception, inflammation, smooth muscle contractility, and stimulation of endocrine and exocrine gland secretion. Their abnormal expression has been reported to be associated with neurological disorders, inflammation, and cancer. Even though NKs are expressed in the same cells with their expression being inversely correlated in some conditions, there is no direct evidence to prove their interaction. Understanding the functional crosstalk between NKs in mediated downstream signaling and cellular responses may elucidate the roles of each receptor in pathophysiology. RESULTS: In this study, we showed that NKs were co-expressed in some cells. However, different from NK3, which only forms homodimerization, we demonstrated a direct interaction between NK1 and NK2 at the protein level using co-immunoprecipitation and NanoBiT-based protein interaction analysis. Through heterodimerization, NK2 downregulated substance P-stimulated NK1 signals, such as intracellular Ca2+ mobilization and ERK phosphorylation, by enhancing ß-arrestin recruitment, even at the ligand concentration that could not activate NK2 itself or in the presence of NK1 specific antagonist, aprepitant. In A549 cells with receptors deleted and reconstituted, NK2 exerted a negative effect on substance P/NK1-mediated cell migration. CONCLUSION: Our study has provided the first direct evidence of an interaction between NK1 and NK2, which highlights the functional relevance of their heterodimerization in cellular responses. Our findings demonstrated that through dimerization, NK2 exerts negative effects on downstream signaling and cellular response mediated by NK1. Moreover, this study has significant implications for understanding the complexity of GPCR dimerization and its effect on downstream signaling and cellular responses. Given the important roles of tachykinins and NKs in pathophysiology, these insights may provide clues for developing NKs-targeting drugs.