A Transmembrane Single-Polypeptide-Chain (sc) Linker to Connect the Two G-Protein–Coupled Receptors in Tandem and the Design for an In Vivo Analysis of Their Allosteric Receptor- Receptor Interactions

A transmembrane (TM) single-polypeptide-chain (sc) linker can connect two G-protein–coupled receptors (GPCRs) in tandem. The priority of a gene-fusion strategy for any two class A GPCRs has been demonstrated. In the striatal function, dopamine (DA) plays a critical role. In the striatum, how the GPCR for adenosine, subtype A2A (A2AR), contributes to the DA neurotransmission in the “volume transmission”/dual-transmission model has been studied extensively. In addition to the fusion receptor, i.e., the prototype scA2AR/D2R complex (the GPCR for DA, subtype D2), several types were created and tested experimentally. To further elucidate this in vivo, we designed a new molecular tool, namely, the supermolecule scA2AR/D2R. Here, no experiments on its expression were done. However, the TM linker to connect the nonobligate dimer as the transient class A GPCR nanocluster that has not been identified at the cell surface membrane deserves discussion through scA2AR/D2R. Supramolecular designs, are experimentally testable and will be used to confirm in vivo the functions of the two GPCRs interactive in such a low specific signal to the nonspecific noise (S/N) ratio in the neurotransmission in the brain. The sc also has, at last, become straightforward in the field of GPCRs, similar to in the field of antibody

Effects of Bepridil on Spiral Reentry

Bepridil is effective for conversion of atrial fibrillation to sinus rhythm and in the treatment of drug-refractory ventricular tachyarrhythmias. We investigated the effects of bepridil on electrophysiological properties and spiral-wave (SW) reentry in a 2-dimensional ventricular muscle layer of isolated rabbit hearts by optical mapping. Ventricular tachycardia (VT) induced in the presence of bepridil (1 μM) terminated earlier than in the control. Bepridil increased action potential duration (APD) by 5% – 8% under constant pacing and significantly increased the space constant. There was a linear relationship between the wavefront curvature (κ) and local conduction velocity: LCV = LCV0 − D·κ (D, diffusion coefficient; LCV0, LCV at κ = 0). Bepridil significantly increased D and LCV0. The regression lines with and without bepridil crossed at κ = 20 – 40 cm−1, resulting in a paradoxical decrease of LCV at κ > 40 cm−1. Dye transfer assay in cultured rat cardiomyocytes confirmed that bepridil increased intercellular coupling. SW reentry in the presence of bepridil was characterized by decremental conduction near the rotation center, prominent drift, and self-termination by collision with boundaries. These results indicate that bepridil causes an increase of intercellular coupling and a moderate APD prolongation, and this combination compromises wavefront propagation near the rotation center of SW reentry, leading to its drift and early termination

Effect of febuxostat on left ventricular diastolic function in patients with asymptomatic hyperuricemia : a sub analysis of the PRIZE Study

Hyperuricemia is related to an increased risk of cardiovascular events from a meta-analysis and antihyperuricemia agents may influence to cardiac function. We evaluated the effect of febuxostat on echocardiographic parameters of diastolic function in patients with asymptomatic hyperuricemia as a prespecified endpoint in the subanalysis of the PRIZE study. Patients in the PRIZE study were assigned randomly to either add-on febuxostat treatment group or control group with only appropriate lifestyle modification. Of the 514 patients in the overall study, 65 patients (31 in the febuxostat group and 34 in the control group) who had complete follow-up echocardiographic data of the ratio of peak early diastolic transmitral flow velocity (E) to peak early diastolic mitral annular velocity (e′) at baseline and after 12 and 24 months were included. The primary endpoint was a comparison of the changes in the E/e′ between the two groups from baseline to 24 months. Interestingly, e′ was slightly decreased in the control group compared with in the febuxostat group (treatment p = 0.068, time, p = 0.337, treatment × Time, p = 0.217). As a result, there were significant increases in E/e′ (treatment p = 0.045, time, p = 0.177, treatment × time, p = 0.137) after 24 months in the control group compared with the febuxostat group. There was no significant difference in the serum levels of N-terminal-pro brain natriuretic peptide and high-sensitive troponin I between the two groups during the study period. In conclusions, additional febuxostat treatment in patients with asymptomatic hyperuricemia for 24 months might have a potential of preventable effects on the impaired diastolic dysfunction

IKs Block and Spiral-Wave Reentry

We tested a hypothesis that an enhancement of IKs may play a pivotal role in ventricular proarrhythmia under high sympathetic activity. A 2-dimensional ventricular muscle layer was prepared in rabbit hearts, and action potential signals were analyzed by optical mapping. During constant stimulation, isoproterenol (ISP, 0.1 μM) significantly shortened action potential duration (APD); chromanol 293B (30 μM), a selective IKs-blocker, reversed the APD shortening. VTs induced in the presence of ISP lasted longer than in the control, and this was reversed by 293B. E-4031 (0.1 μM), a selective IKr-blocker, did not cause such reversal. Spiral-wave (SW) reentry with ISP was characterized by more stable rotation around a shorter functional block line (FBL) than in the control. After application of 293B, SW reentry was destabilized, and rotation around a longer FBL with prominent drift reappeared. The APD abbreviation by ISP close to the rotation center was more pronounced than in the periphery, leading to an opposite APD gradient (center < periphery) compared with controls. This effect was also reversed by 293B. In conclusion, β-adrenergic stimulation stabilizes SW reentry most likely though an enhancement of IKs. Blockade of IKs may be a promising therapeutic modality in prevention of ventricular tachyarrhythmias under high sympathetic activity

Impact of glycemic control with sitagliptin on the 2‑year progression of arterial stiffness : a sub‑analysis of the PROLOGUE study

Background: No conclusive evidence has been obtained yet on the significance of the effects of dipeptidyl peptidase-4 (DPP-4 inhibitor) treatment on the arterial stiffness in clinical settings. In addition, the effects of good glycemic control on the arterial stiffness have also not been clarified yet. As a sub-analysis of the PROLOGUE study, we examined the effect of a DPP-4 inhibitor (sitagliptin) on the 2-year progression of the arterial stiffness and also to determine the effect of good glycemic control on the rate of progression of the arterial stiffness. Methods: In the PROLOGUE study, the study participants were either allocated to add-on sitagliptin treatment or to continued treatment with conventional anti-diabetic agents. Among the 463 participants of the PROLOGUE study, we succeeded in measuring the brachial-ankle pulse wave velocity (baPWV) at least two times during the 2-year study period in 96 subjects. Results: The changes in the baPWV during the study period were similar between the both groups (i.e., with/without staglipitin), overall. On the other hand, when the study subjects were divided into two groups according to the glycemic control status during the study period {good glycemic control group (GC) = hemoglobin (Hb)A1c <7.0 at both 12 and 24 months after the treatment randomization; poor glycemic control group (PC) = HbA1c ≥7.0 at either 12 months, 24 months, or both}, the 2-year increase of the baPWV was marginally significantly larger in the PC group (144 ± 235 cm/s) as compared to that the GC group (−10 ± 282 cm/s) (p = 0.036). Conclusion: While the present study could not confirm the beneficial effect of sitagliptin per se on the arterial stiffness, the results suggested that good glycemic control appears to be beneficial for delaying the annual progression of the arterial stiffness

Effect of sitagliptin on the echocardiographic parameters of left ventricular diastolic function in patients with type 2 diabetes : a subgroup analysis of the PROLOGUE study

Background: Diabetes is associated closely with an increased risk of cardiovascular events, including diastolic dysfunction and heart failure that leads to a shortening of life expectancy. It is therefore extremely valuable to evaluate the impact of antidiabetic agents on cardiac function. However, the influence of dipeptidyl peptidase 4 inhibitors on cardiac function is controversial and a major matter of clinical concern. We therefore evaluated the effect of sitagliptin on echocardiographic parameters of diastolic function in patients with type 2 diabetes as a sub-analysis of the PROLOGUE study. Methods: Patients in the PROLOGUE study were assigned randomly to either add-on sitagliptin treatment or conventional antidiabetic treatment. Of the 463 patients in the overall study, 115 patients (55 in the sitagliptin group and 60 in the conventional group) who had complete echocardiographic data of the ratio of peak early diastolic transmitral flow velocity (E) to peak early diastolic mitral annular velocity (e′) at baseline and after 12 and 24 months were included in this study. The primary endpoint of this post hoc sub-analysis was a comparison of the changes in the ratio of E to e′ (E/e′) between the two groups from baseline to 24 months. Results: The baseline-adjusted change in E/e′ during 24 months was significantly lower in the sitagliptin group than in the conventional group (−0.18 ± 0.55 vs. 1.91 ± 0.53, p = 0.008), irrespective of a higher E/e′ value at baseline in the sitagliptin group. In analysis of covariance, sitagliptin treatment was significantly associated with change in E/e′ over 24 months (β = −9.959, p = 0.001), independent of other clinical variables at baseline such as blood pressure, HbA1c, and medications for diabetes. Changes in other clinical variables including blood pressure and glycemic parameters, and echocardiographic parameters, such as cardiac structure and systolic function, were comparable between the two groups. There was also no significant difference in the serum levels of N-terminal-pro brain natriuretic peptide and high-sensitive C-reactive protein between the two groups during the study period. Conclusions: Adding sitagliptin to conventional antidiabetic regimens in patients with T2DM for 24 months attenuated the annual exacerbation in the echocardiographic parameter of diastolic dysfunction (E/e′) independent of other clinical variables such as blood pressure and glycemic control