Adrenomedullin Therapy in Moderate to Severe COVID-19

A Focus on the Pathophysiology of Adrenomedullin Expression: Endothelitis and Organ Damage in Severe Viral and Bacterial Infections

Adrenomedullin (ADM) is a peptide hormone produced primarily in the adrenal glands, playing a crucial role in various physiological processes. As well as improving vascular integrity and decreasing vascular permeability, ADM acts as a vasodilator, positive inotrope, diuretic, natriuretic and bronchodilator, antagonizing angiotensin II by inhibiting aldosterone secretion. ADM also has antihypertrophic, anti-apoptotic, antifibrotic, antioxidant, angiogenic and immunoregulatory effects and antimicrobial properties. ADM expression is upregulated by hypoxia, inflammation-inducing cytokines, viral or bacterial substances, strength of shear stress, and leakage of blood vessels. These pathological conditions are established during systemic inflammation that can result from infections, surgery, trauma/accidents or burns. The ability to rapidly identify infections and the prognostic, predictive power makes it a valuable tool in severe viral and bacterial infections burdened by high incidence and mortality. This review sheds light on the pathophysiological processes that in severe viral or bacterial infections cause endothelitis up to the development of organ damage, the resulting increase in ADM levels dosed through its more stable peptide mid-regional proadrenomedullin (MR-proADM), the most significant studies that attest to its diagnostic and prognostic accuracy in highlighting the severity of viral or bacterial infections and appropriate therapeutic insights.

Receptor activity-modifying proteins of adrenomedullin (RAMP2/3): Roles in the pathogenesis of ARDS

Acute respiratory distress syndrome (ARDS) is a life-threatening lung condition characterized by widespread inflammation and pulmonary edema. Adrenomedullin (AM), a bioactive peptide with various functions, is expected to be applied in treating ARDS. Its functions are regulated primarily by two receptor activity-modifying proteins, RAMP2 and RAMP3, which bind to the AM receptor calcitonin receptor-like receptor (CLR). However, the roles of RAMP2 and RAMP3 in ARDS remain unclear. We generated a mouse model of ARDS via intratracheal administration of lipopolysaccharide (LPS), and analyzed the pathophysiological significance of RAMP2 and RAMP3. RAMP2 expression declined with LPS administration, whereas RAMP3 expression increased at low doses and decreased at high doses of LPS. After LPS administration, drug-inducible vascular endothelial cell-specific RAMP2 knockout mice (DI-E-RAMP2-/-) showed reduced survival, increased lung weight, and had more apoptotic cells in the lungs. DI-E-RAMP2-/- mice exhibited reduced expression of Epac1 (which regulates vascular endothelial cell barrier function), while RAMP3 was upregulated in compensation. In contrast, after LPS administration, RAMP3-/- mice showed no significant changes in survival, lung weight, or lung pathology, although they exhibited significant downregulation of iNOS, TNF-α, and NLRP3 during the later stages of inflammation. Based on transcriptomic analysis, RAMP2 contributed more to the circulation-regulating effects of AM, whereas RAMP3 contributed more to its inflammation-regulating effects. These findings indicate that, while both RAMP2 and RAMP3 participate in ARDS pathogenesis, their functions differ distinctly. Further elucidation of the pathophysiological significance and functional differences between RAMP2 and RAMP3 is critical for the future therapeutic application of AM in ARDS.

Mid-Regional Pro-Adrenomedullin Can Predict Organ Failure and Prognosis in Sepsis?

Sepsis causes immune dysregulation and endotheliitis, with an increase in mid-regional pro-adrenomedullin (MR-proADM). The aim of the study is to determine an MR-proADM value that, in addition to clinical diagnosis, can identify patients with localized infection or those with sepsis/septic shock, with specific organ damage or with the need for intensive care unit (ICU) transfer and prognosis. The secondary aim is to correlate the MR-proADM value with the length of stay (LOS). In total, 301 subjects with sepsis (124/301 with septic shock) and 126 with localized infection were retrospectively included. In sepsis, MR-proADM ≥ 3.39 ng/mL identified acute kidney injury (AKI); ≥2.99 ng/mL acute respiratory distress syndrome (ARDS); ≥2.28 ng/mL acute heart failure (AHF); ≥2.55 ng/mL Glascow Coma Scale (GCS) < 15; ≥3.38 multi-organ involvement; ≥3.33 need for ICU transfer; ≥2.0 Sequential Organ Failure Assessment (SOFA) score ≥ 2; and ≥3.15 ng/mL non-survivors. The multivariate analysis showed that MR-proADM ≥ 2 ng/mL correlates with AKI, anemia and SOFA score ≥ 2, and MR-proADM ≥ 3 ng/mL correlates with AKI, GCS < 15 and SOFA score ≥ 2. A correlation between mortality and AKI, GCS < 15, ICU transfer and cathecolamine administration was found. In localized infection, MR-proADM at admission ≥ 1.44 ng/mL identified patients with AKI; ≥1.0 ng/mL with AHF; and ≥1.44 ng/mL with anemia and SOFA score ≥ 2. In the multivariate analysis, MR-proADM ≥ 1.44 ng/mL correlated with AKI, anemia, SOFA score ≥ 2 and AHF. MR-proADM is a marker of oxidative stress due to an infection, reflecting severity proportionally to organ damage.

Mid-Regional Proadrenomedullin in COVID-19-May It Act as a Predictor of Prolonged Cardiovascular Complications?

The rising prevalence of cardiovascular disease (CVD) and the impact of the SARS-CoV-2 pandemic have both led to increased mortality rates, affecting public health and the global economy. Therefore, it is essential to find accessible, non-invasive prognostic markers capable of identifying patients at high risk. One encouraging avenue of exploration is the potential of mid-regional proadrenomedullin (MR-proADM) as a biomarker in various health conditions, especially in the context of CVD and COVID-19. MR-proADM presents the ability to predict mortality, heart failure, and adverse outcomes in CVD, offering promise for improved risk assessment and treatment strategies. On the other hand, an elevated MR-proADM level is associated with disease severity and cytokine storms in patients with COVID-19, making it a predictive indicator for intensive care unit admissions and mortality rates. Moreover, MR-proADM may have relevance in long COVID, aiding in the risk assessment, triage, and monitoring of individuals at increased risk of developing prolonged cardiac issues. Our review explores the potential of MR-proADM as a predictor of enduring cardiovascular complications following COVID-19 infection.

Aspartate aminotransferase to platelet ratio index has utility as a biomarker of COVID-19 severity in patients with nonalcoholic fatty liver disease

AIM

Patients with nonalcoholic fatty liver disease (NAFLD) are reported to have greater coronavirus disease 2019 (COVID-19) severity compared with patients without NAFLD. Previous studies have reported that noninvasive liver fibrosis scores, including the Fibrosis-4 index, NAFLD fibrosis score, and aspartate aminotransferase to platelet ratio index (APRI), have utility in predicting COVID-19 mortality and disease severity in patients without NAFLD. However, the utility of liver fibrosis scores in predicting COVID-19 mortality and disease severity among patients with NAFLD infected with SARS-CoV-2 has yet to be evaluated.

METHODS

This retrospective observational study comprised 126 patients with NAFLD and active SARS-CoV-2 infection. Patients were classified into low COVID-19 severity (mild or moderate I disease) and high COVID-19 severity (moderate II or severe disease) groups based on the therapeutic guideline implemented by the Ministry of Health, Labor, and Welfare of Japan.

RESULTS

Of the 126 patients, only one had been diagnosed with NAFLD before admission. Age; levels of serum aspartate aminotransferase, γ-glutamyl transpeptidase, lactate dehydrogenase, blood urea nitrogen, and serum C-reactive protein; Fibrosis-4 index; NAFLD fibrosis score; and APRI levels on admission were higher in the high COVID-19 severity group compared with the low COVID-19 severity group. Serum albumin levels, platelet counts, and lymphocyte counts on admission were lower in the high COVID-19 severity group compared with the low COVID-19 severity group. Univariate and multivariate analysis revealed that APRI values were significantly associated with COVID-19 severity and hospitalization duration for COVID-19.

CONCLUSIONS

APRI was independently associated with COVID-19 severity and hospitalization duration for COVID-19 in patients with NAFLD.

Endotheliopathy in Acute COVID-19 and Long COVID

The pulmonary endothelium is a highly regulated organ that performs a wide range of functions under physiological and pathological conditions. Since endothelial dysfunction has been demonstrated to play a direct role in sepsis and acute respiratory distress syndrome, its role in COVID-19 has also been extensively investigated. Indeed, apart from the COVID-19-associated coagulopathy biomarkers, new biomarkers were recognised early during the pandemic, including markers of endothelial cell activation or injury. We systematically searched the literature up to 10 March 2023 for studies examining the association between acute and long COVID-19 severity and outcomes and endothelial biomarkers.

Clinical trial experience in Japan and future issues in developing drugs to treat COVID-19

The National Center for Global Health and Medicine plays a central role in the treatment and research of infectious diseases in Japan. It has conducted various research and development activities on drugs to treat coronavirus disease 2019 (COVID-19) with clinical questions as starting points. Clinical trials are essential in developing new treatment modalities, but we have noticed some characteristic difficulties in clinical trials on emerging and re-emerging infectious diseases. For example, since there is no standard of care when an emerging infectious disease starts to spread, establishing an appropriate control group is complicated, and many things are hurried at the start of trials. This means there is little time to arrange a placebo, and conducting blinded, randomized, controlled trials has been difficult. Another issue characteristic of infectious disease has been that progress in enrolling subjects is affected by the spread of the disease. It was also a struggle to select institutions that provide medical care on the front lines of infectious disease and conduct clinical trials regularly. To start multicenter clinical trials expeditiously, a regulated and structured network is thus considered necessary. From the perspective of implementation, it is preferable to conduct decentralized clinical trials (DCTs) that do not depend on people coming to the medical institution, while from the perspective of preventing infections during the spread of COVID-19, wide adoption of eConsent is desirable. Based on the experience of COVID-19, new measures must be taken to prepare for emerging and re-emerging infectious diseases in the future.

Procalcitonin and Adrenomedullin in Infectious Diseases

Calcitonin (CT) and adrenomedullin (ADM) are members of the CT family. Procalcitonin (PCT) is a prohormone of CT. Elevations in serum PCT and ADM levels are associated with severe sepsis and coronavirus disease 2019 (COVID-19). PCT enhances sepsis mortality and it binds to the CGRP receptor, which is a heterodimer of CT receptor-like receptor and receptor activity-modifying protein 1. The N-terminal truncated form of PCT, PCT3-116, is produced by the cleavage of PCT by dipeptidyl peptidase 4 (DPP-4) and is the main form of PCT in serum during sepsis, inducing microvascular permeability. Mid-regional pro-adrenomedullin (MR-proADM) is used instead of ADM as a biological indicator because ADM is rapidly degraded, and MR-proADM is released at the same rate as ADM. ADM reduces endothelial permeability and promotes endothelial stability. Endothelial dysfunction is responsible for multiple organ failure in sepsis and COVID-19 patients. Therefore, ADM may be an important molecule for improving the severity associated with sepsis and COVID-19. This review focuses on the current knowledge of PCT and ADM in sepsis and COVID-19.

Elucidating the Interactome of G Protein-Coupled Receptors and Receptor Activity-Modifying Proteins

G protein-coupled receptors (GPCRs) are known to interact with several other classes of integral membrane proteins that modulate their biology and pharmacology. However, the extent of these interactions and the mechanisms of their effects are not well understood. For example, one class of GPCR-interacting proteins, receptor activity-modifying proteins (RAMPs), comprise three related and ubiquitously expressed single-transmembrane span proteins. The RAMP family was discovered more than two decades ago, and since then GPCR-RAMP interactions and their functional consequences on receptor trafficking and ligand selectivity have been documented for several secretin (class B) GPCRs, most notably the calcitonin receptor-like receptor. Recent bioinformatics and multiplexed experimental studies suggest that GPCR-RAMP interactions might be much more widespread than previously anticipated. Recently, cryo-electron microscopy has provided high-resolution structures of GPCR-RAMP-ligand complexes, and drugs have been developed that target GPCR-RAMP complexes. In this review, we provide a summary of recent advances in techniques that allow the discovery of GPCR-RAMP interactions and their functional consequences and highlight prospects for future advances. We also provide an up-to-date list of reported GPCR-RAMP interactions based on a review of the current literature. SIGNIFICANCE STATEMENT: Receptor activity-modifying proteins (RAMPs) have emerged as modulators of many aspects of G protein-coupled receptor (GPCR)biology and pharmacology. The application of new methodologies to study membrane protein-protein interactions suggests that RAMPs interact with many more GPCRs than had been previously known. These findings, especially when combined with structural studies of membrane protein complexes, have significant implications for advancing GPCR-targeted drug discovery and the understanding of GPCR pharmacology, biology, and regulation.