Unraveling the interplay between dipeptidyl peptidase 4 and the renin-angiotensin system in heart failure

Impact of Proximal Tubule-Specific Deletion of Dipeptidyl Peptidase 4 on Blood Pressure, Renal Sodium Handling, and NHE3 Phosphorylation

Dipeptidyl peptidase 4 (DPP4) is a transmembrane serine exopeptidase abundantly expressed in the kidneys, predominantly in the proximal tubule (PT); however, its non-enzymatic functions in this nephron segment remain poorly understood. While DPP4 physically associates with the Na+/H+ exchanger isoform 3 (NHE3) and its inhibitors exert natriuretic effects, the DPP4 role in blood pressure (BP) regulation remains controversial. This study investigated the effects of PT-specific Dpp4 deletion (Dpp4 ΔPT) and global Dpp4 deletion (Dpp4 -/-) on systolic blood pressure (SBP), natriuresis, and NHE3 regulation under baseline and angiotensin II (Ang II)-stimulated conditions in both male and female mice. Global and PT-specific Dpp4 deletion increased diuretic and natriuretic responses to acute saline loading, correlating with enhanced phosphorylation of NHE3 at serine 552 (pS552-NHE3). However, baseline SBP remained unchanged. Ang II stimulation increased DPP4 activity in control mice, with a greater effect in males than in females, reflecting sex-dependent regulation of renal DPP4. In Dpp4 ΔPT mice, residual kidney DPP4 was unresponsive to Ang II, indicating that PT DPP4, rather than DPP4 in other nephron segments, is regulated by Ang II. Ang II administration increased SBP in all groups; however, the pressor response was significantly attenuated in both Dpp4 ΔPT and Dpp4 -/- mice, coinciding with sustained elevated levels of pS552-NHE3. Collectively, these findings demonstrate that PT DPP4 modulates NHE3 activity through mechanisms that prevent the accumulation of pS552-NHE3, exerting an anti-natriuretic effect. In the absence of DPP4, these mechanisms are disrupted, reducing Ang II sensitivity and maintaining high pS552-NHE3 levels, underscoring the role of DPP4 in PT signaling and function.

Aprotinin (II): Inhalational Administration for the Treatment of COVID-19 and Other Viral Conditions

Aprotinin is a broad-spectrum inhibitor of human proteases that has been approved for the treatment of bleeding in single coronary artery bypass surgery because of its potent antifibrinolytic actions. Following the outbreak of the COVID-19 pandemic, there was an urgent need to find new antiviral drugs. Aprotinin is a good candidate for therapeutic repositioning as a broad-spectrum antiviral drug and for treating the symptomatic processes that characterise viral respiratory diseases, including COVID-19. This is due to its strong pharmacological ability to inhibit a plethora of host proteases used by respiratory viruses in their infective mechanisms. The proteases allow the cleavage and conformational change of proteins that make up their viral capsid, and thus enable them to anchor themselves by recognition of their target in the epithelial cell. In addition, the activation of these proteases initiates the inflammatory process that triggers the infection. The attraction of the drug is not only its pharmacodynamic characteristics but also the possibility of administration by the inhalation route, avoiding unwanted systemic effects. This, together with the low cost of treatment (≈2 Euro/dose), makes it a good candidate to reach countries with lower economic means. In this article, we will discuss the pharmacodynamic, pharmacokinetic, and toxicological characteristics of aprotinin administered by the inhalation route; analyse the main advances in our knowledge of this medication; and the future directions that should be taken in research in order to reposition this medication in therapeutics.

Unraveling the Cardiac Matrix: From Diabetes to Heart Failure, Exploring Pathways and Potential Medications

Myocardial infarction (MI) often leads to heart failure (HF) through acute or chronic maladaptive remodeling processes. This establishes coronary artery disease (CAD) and HF as significant contributors to cardiovascular illness and death. Therefore, treatment strategies for patients with CAD primarily focus on preventing MI and lessening the impact of HF after an MI event. Myocardial fibrosis, characterized by abnormal extracellular matrix (ECM) deposition, is central to cardiac remodeling. Understanding these processes is key to identifying new treatment targets. Recent studies highlight SGLT2 inhibitors (SGLT2i) and GLP-1 receptor agonists (GLP1-RAs) as favorable options in managing type 2 diabetes due to their low hypoglycemic risk and cardiovascular benefits. This review explores inflammation's role in cardiac fibrosis and evaluates emerging anti-diabetic medications' effectiveness, such as SGLT2i, GLP1-RAs, and dipeptidyl peptidase-4 inhibitors (DPP4i), in preventing fibrosis in patients with diabetes post-acute MI. Recent studies were analyzed to identify effective medications in reducing fibrosis risk in these patients. By addressing these areas, we can advance our understanding of the potential benefits of anti-diabetic medications in reducing cardiac fibrosis post-MI and improve patient outcomes in individuals with diabetes at risk of HF.

Bidirectional relation between dipeptidyl peptidase 4 and angiotensin II type I receptor signaling

Cardiometabolic diseases are often associated with heightened levels of angiotensin II (Ang II), which accounts for the observed oxidative stress, inflammation, and fibrosis. Accumulating evidence indicates a parallel upregulation of dipeptidyl dipeptidase 4 (DPP4) activity in cardiometabolic diseases, with its inhibition shown to mitigate oxidative stress, inflammation, and fibrosis. These findings highlight an overlap between the pathophysiological mechanisms used by Ang II and DPP4. Recent evidence demonstrates that targeted inhibition of DPP4 prevents the rise in Ang II and its associated molecules in experimental models of cardiometabolic diseases. Similarly, inhibitors of the angiotensin I-converting enzyme (ACE) or Ang II type 1 receptor (AT1R) blockers downregulate DPP4 activity, establishing a bidirectional relationship between DPP4 and Ang II. Here, we discuss the current evidence supporting the cross talk between Ang II and DPP4, along with the potential mechanisms promoting this cross regulation. A comprehensive analysis of this bidirectional relationship across tissues will advance our understanding of how DPP4 and Ang II collectively promote the development and progression of cardiometabolic diseases.

A systematic review on the clinical pharmacokinetics of vildagliptin in healthy and disease populations

INTRODUCTION

Vildagliptin, a dipeptidyl peptidase-4 inhibitor, is indicated to cure type 2 diabetes mellitus (T2DM). This systematic literature search aims to assess the current knowledge about the clinical pharmacokinetics (PK) of vildagliptin to provide recommendations for clinical use to prevent the harmful effects of this drug.

METHODS

The PubMed, Science Direct, EBSCO, Cochrane Central Register of Controlled Trials, and Google Scholar databases were screened for articles related to the clinical PK of vildagliptin using systematic search strategies.

RESULTS

The literature search identified 2118 records, among which 28 were subsumed in this systematic review that fulfilled the inclusion standards.

CONCLUSIONS

This systematic review can help dose optimization among critically ill patients (e.g. renal impairment) without exposing them to the drug's toxic effects.

The role of glucose in cardiac physiology and pathophysiology

PURPOSE OF REVIEW

Heart failure is one of the major causes of death worldwide and continues to increase despite therapeutics and pharmacology advances. Fatty acids and glucose are used as ATP-producing fuels in heart to meet its energy demands. However, dysregulation of metabolites' use plays a pivotal role in cardiac diseases. How glucose becomes toxic or drives cardiac dysfunction is incompletely understood. In the present review, we summarize the recent findings on cardiac cellular and molecular events that are driven by glucose during pathologic conditions and potential therapeutic strategies to tackle hyperglycemia-mediated cardiac dysfunction.

RECENT FINDINGS

Several studies have emerged recently, demonstrating that excessive glucose utilization has been correlated with impairment of cellular metabolic homeostasis primarily driven by mitochondrial dysfunction and damage, oxidative stress, and abnormal redox signaling. This disturbance is associated with cardiac remodeling, hypertrophy, and systolic and diastolic dysfunction. Both human and animal heart failure studies, report that glucose is a preferable fuel at the expense of fatty acid oxidation during ischemia and hypertrophy, but the opposite happens in diabetic hearts, which warrants further investigation.

SUMMARY

A better understanding of glucose metabolism and its fate during distinct types of heart disease will contribute to developing novel therapeutic options for the prevention and treatment of heart failure.

Angiotensin II-Related Activation of Scleral Fibroblasts and Their Role on Retinal Ganglion Cell Death in Glaucoma

We identify the angiotensin II (AngII)-associated changes in the extracellular matrix (ECM) and the biomechanical properties of the sclera after systemic hypotension. Systemic hypotension was induced by administering oral hydrochlorothiazide. AngII receptor levels and ECM components in the sclera and biomechanical properties were evaluated based on the stress–strain relationship after systemic hypotension. The effect of inhibiting the AngII receptor with losartan was determined in the systemic hypotensive animal model and the cultured scleral fibroblasts from this model. The effect of losartan on retinal ganglion cell (RGC) death was evaluated in the retina. Both AngII receptor type I (AT-1R) and type II (AT-2R) increased in the sclera after systemic hypotension. Proteins related to the activation of fibroblasts (transforming growth factor [TGF]-β1 and TGF-β2) indicated that transformation to myofibroblasts (α smooth muscle actin [SMA]), and the major ECM protein (collagen type I) increased in the sclera after systemic hypotension. These changes were associated with stiffening of the sclera in the biomechanical analysis. Administering losartan in the sub-Tenon tissue significantly decreased the expression of AT-1R, αSMA, TGF-β, and collagen type I in the cultured scleral fibroblasts and the sclera of systemic hypotensive rats. The sclera became less stiff after the losartan treatment. A significant increase in the number of RGCs and decrease in glial cell activation was found in the retina after the losartan treatment. These findings suggest that AngII plays a role in scleral fibrosis after systemic hypotension and that inhibiting AngII could modulate the tissue properties of the sclera, resulting in the protection of RGCs.

Dipeptidyl peptidase 4 inhibition rescues PKA-eNOS signaling and suppresses aortic hypercontractility in male rats with heart failure

AIMS

Vascular dysfunction and elevated circulating dipeptidyl peptidase 4 (DPP4) activity are both reported to be involved in the progression of heart failure (HF). While the cardiac benefits of DPP4 inhibitors (DPP4i) have been extensively studied, little is known about the effects of DPP4i on vascular dysfunction in nondiabetic HF. This study tested the hypothesis that vildagliptin (DPP4i) mitigates aortic hyperreactivity in male HF rats.

MATERIALS AND METHODS

Male Wistar rats were subjected to left ventricle (LV) radiofrequency ablation to HF induction or sham operation (SO). Six weeks after surgery, radiofrequency-ablated rats who developed HF were treated with vildagliptin (120 mg⸱kg^-1⸱day^-1) or vehicle for 4 weeks. Thoracic aorta reactivity, dihydroethidium fluorescence, immunoblotting experiments, and enzyme-linked immunosorbent assays were performed.

KEY FINDINGS

DPP4i ameliorated the hypercontractility of HF aortas to the α-adrenoceptor agonist phenylephrine towards SO levels. In HF, the reduced endothelium and nitric oxide (NO) anticontractile effect on phenylephrine response was restored by DPP4i. At the molecular level, this vasoprotective effect of DPP4i was accompanied by (i) reduced oxidative stress and NADPH oxidase 2 (Nox2) expression, (ii) enhanced total endothelial nitric oxide synthase (eNOS) expression and phosphorylation at Ser1177, and (iii) increased PKA activation, which acts upstream of eNOS. Additionally, DPP4i restored the higher serum angiotensin II concentration towards SO.

SIGNIFICANCE

Our data demonstrate that DPP4i ameliorates aortic hypercontractility, most likely by enhancing NO bioavailability, showing that the DPP4i-induced cardioprotection in male HF may arise from effects not only in the heart but also in conductance arteries.