Diagnostic value of serum leptin and a promising novel diagnostic model for sepsis

Inflammatory biomarkers to predict the prognosis of acute bacterial and viral infections

Mortality in acute infections is mostly associated with sepsis, defined as 'life-threatening organ dysfunction caused by a dysregulated host response to infection'. It remains challenging to identify the patients with increased mortality risk due to the high heterogeneity in the dysregulated host immune response and disease progression. Biomarkers reflecting different pathways involved in the inflammatory response might improve prediction of mortality risk (prognostic enrichment) among patients with acute infections by reducing heterogeneity of the host response, as well as suggest novel strategies for patient stratification and treatment (predictive enrichment) through precision medicine approaches. The predictive value of inflammatory biomarkers has been extensively investigated in bacterial infections and the recent COVID-19 pandemic caused an increased interest in inflammatory biomarkers in this viral infection. However, limited research investigated whether the prognostic potential of these biomarkers differs between bacterial and viral infections. In this narrative review, we provide an overview of the value of various inflammatory biomarkers for the prediction of mortality in bacterial and viral infections.

Adipocytokine plasma concentrations reflect influence of inflammation but not body mass index (BMI) on clinical outcomes of COVID-19 patients: A prospective observational study from the Netherlands

Obesity is recognized as a risk factor for adverse outcome in COVID-19, but the molecular mechanisms underlying this relationship remain unknown. Adipose tissue functions as an endocrine organ by secreting multiple pro-inflammatory and anti-inflammatory factors, known as adipocytokines, which could be involved in COVID-19 severity. We explored the role of adipocytokines in COVID-19 and its association with BMI, clinical outcome, and inflammation. This is an observational study in 195 hospitalized COVID-19 patients. Serial plasma concentrations of the adipocytokines leptin, adiponectin, resistin, and various inflammatory cytokines were assessed. Adipocytokines were compared between patients with normal weight (BMI: 18.5-24.9 kg/m² ), overweight (BMI: 25.0-29.9 kg/m² ), and obesity (BMI ≥ 30 kg/m² ), between patients admitted to the ICU and to non-ICU clinical wards, and between survivors and non-survivors. Patients with overweight and obesity displayed higher leptin concentrations and lower adiponectin concentrations throughout hospital admission (p < .001), whereas resistin concentrations were not different from patients with normal weight (p = .12). Resistin concentrations correlated with inflammatory markers and were persistently higher in ICU patients and non-survivors compared to non-ICU patients and survivors, respectively (both p < .001), whereas no such relationships were found for the other adipocytokines. In conclusion, leptin and adiponectin are associated with BMI, but not with clinical outcomes and inflammation in COVID-19 patients. In contrast, resistin is not associated with BMI, but high concentrations are associated with worse clinical outcomes and more pronounced inflammation. Therefore, it is unlikely that BMI-related adipocytokines or differences in the inflammatory response underlie obesity as a risk factor for severe COVID-19.

THE ROLE OF OBESITY AND PLASMA ADIPOCYTOKINES IN IMMUNE DYSREGULATION IN SEPSIS PATIENTS

Introduction: The dysregulated immune response in sepsis is highly variable, ranging from hyperinflammation to immunoparalysis. Obesity is associated with the release of inflammatory mediators from adipose tissue, known as adipocytokines, causing a chronic inflammatory state. Perhaps counterintuitively, obesity is also associated with lower mortality in sepsis patients. We investigated the association between obesity, circulating adipocytokine concentrations, immune dysregulation, and outcome in sepsis patients. Methods In this secondary analysis of a prospective study, plasma concentrations of the adipocytokines leptin, adiponectin, and resistin were assessed in 167 patients at diagnosis of sepsis due to pneumonia, bacteremia, or acute cholangitis. Adipocytokines were compared between patients with normal weight (body mass index [BMI], 18.5-24.9 kg/m 2 ; n = 67), overweight (BMI, 25.0-29.9 kg/m 2 ; n = 56), and obesity (BMI ≥30 kg/m 2 ; n = 42), as well as between immunological endotypes: hyperinflammation (n = 40), immunoparalysis (n = 62), and unclassified (n = 55). Results: Higher circulating concentrations of leptin were observed in patients with obesity compared with patients with normal weight ( P = 0.008) and overweight ( P = 0.02), whereas adiponectin and resistin plasma concentrations were not different ( P = 0.08 and P = 0.85, respectively). Resistin concentrations were associated with immunological endotypes, with the highest levels found in hyperinflammatory patients ( P < 0.001). Furthermore, resistin concentrations were predictive for 28-day mortality (adjusted odds ratio, 1.03 per 10 ng/mL; P = 0.04). These associations were not found for leptin and adiponectin. Conclusion: Obesity and BMI-related adipocytokines are not related to the development of a hyperactive or suppressed immune response as defined by ferritin and mHLA-DR expression in sepsis patients. Although resistin is related to the immune response and an increased risk of adverse clinical outcomes, these associations are similar in patients with normal weight, overweight, and obesity. This implies that the relationship between resistin and clinical outcome is likely driven by the inflammatory response and not by obesity itself. Taken together, although there exists a strong association between inflammation and sepsis mortality, our results do not point toward a role for obesity and BMI-related adipocytokines in immune dysregulation in sepsis patients.

Risk Factors for COVID-19: Diabetes, Hypertension, and Obesity

INTRODUCTION

The recent global pandemic of coronavirus disease 2019 (COVID-19), caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), has involved more than 7 million people worldwide and been associated with more than 400,000 deaths. No clear information is known about all the potential risk factors for COVID-19 or what factors adversely influence its clinical course and mortality. Therefore, we analyzed the role of obesity, type 2 diabetes, and hypertension as risk factors for COVID-19.

METHODS

We identified articles for inclusion by searching PubMed and Google Scholar (last accessed 15 June 2020). Retrospective review of literature. Analysis of epidemiological data concerning obesity prevalence and COVID-19 incidence, particularly in Italy and the USA.

RESULTS

Data from several retrospective studies of prevalence showed that patients with hypertension, type 2 diabetes, and obesity may have more severe COVID-19, intensive care unit admission, and higher mortality rates, but it is not definitively clear if this is an independent association. In general, the prevalence of obesity in patients with COVID-19 seems to be the same as that of the general population throughout the world; however, obesity seems to be associated with more severe disease and mortality in younger (< 60 years) patients. Similar effects seem to occur in patients with diabetes and/or hypertension but at older ages (> 60 years). In strict connection, it has been proposed that the use of drugs inhibiting angiotensin-converting enzyme 2 (ACE-2) or dipeptidyl dipeptidase 4 (DPP-4) might influence viral activity and disease severity since ACE-2 and DPP-4 receptors mediate SARS-CoV-2 entry into the host cells; however, no evidence exists to date that shows that this may be the case.

CONCLUSION

Overall, diabetes, hypertension, and obesity seem to negatively affect the clinical course and disease outcome in patients with COVID-19. However, these data need further confirmation by studies with more accurate data registration.

Serum Leptin Levels, Nutritional Status, and the Risk of Healthcare-Associated Infections in Hospitalized Older Adults

We aimed to determine whether serum leptin levels are predictive of the occurrence of healthcare-associated infections (HAIs) in hospitalized older patients. In a prospective cohort, 232 patients had available data for leptin and were monitored for HAIs for 3 months. Admission data included comorbidities, invasive procedures, the Mini Nutritional Assessment (MNA), BMI, leptin, albumin and C-reactive protein levels, and CD4 and CD8 T-cell counts. Multivariate logistic regression modelling was used to identify predictors of HAIs. Of the 232 patients (median age: 84.8; females: 72.4%), 89 (38.4%) experienced HAIs. The leptin level was associated with the BMI (p < 0.0001) and MNA (p < 0.0001) categories. Women who experienced HAIs had significantly lower leptin levels than those who did not (5.9 μg/L (2.6–17.7) and 11.8 (4.6–26.3), respectively; p = 0.01; odds ratio (OR) (95% confidence interval): 0.67 (0.49–0.90)); no such association was observed for men. In a multivariate analysis of the women, a lower leptin level was significantly associated with HAIs (OR = 0.70 (0.49–0.97)), independently of comorbidities, invasive medical procedures, and immune status. However, leptin was not significantly associated with HAIs after adjustments for malnutrition (p = 0.26) or albuminemia (p = 0.15)—suggesting that in older women, the association between serum leptin levels and subsequent HAIs is mediated by nutritional status.

Circulating leptin, soluble leptin receptor and free leptin index in critically ill patients with sepsis: a prospective observational study

BACKGROUND

Leptin, the prototype adipokine, exerts immunomodulatory actions being implicated in inflammatory responses during sepsis. Clinical evidence regarding its role in sepsis has been contradictory, while free leptin has not been studied. Our aim was to jointly investigate circulating total leptin, its soluble receptor (sOBR), and free leptin, as well as their kinetics in critically ill patients with sepsis regarding their diagnostic and prognostic value.

METHODS

In a prospective study, serum total leptin, sOBR and free leptin index (FLI) were determined in 102 critically ill patients with sepsis within 48 hours from sepsis onset and one week after enrollment, and in 102 age and gender-matched healthy controls.

RESULTS

Upon enrollment, total leptin, sOB-R and FLI were significantly higher in septic patients compared to controls and they were positively correlated with sepsis severity scores, while they presented a significant decrease during the first week (p<0.001). The decrease in total leptin and sOB-R was significantly higher in patients with sepsis compared to septic shock and in survivors compared to nonsurvivors at 28 days (p<0.001). Higher serum total leptin was independently associated with survival at 28 days (enrollment: HR 0.86, p=0.03; one week after: HR 0.77, p<0.001). Higher kinetics of total leptin (but not FLI) was independently associated with survival after adjustment (HR: 0.48, p=0.001).

CONCLUSIONS

Higher circulating total leptin and its higher kinetics during the first week from sepsis onset independently predict 28 day survival in critically ill patients. Free leptin did not present any additional diagnostic and prognostic value in sepsis.

Biomarkers of inflammation and the etiology of sepsis

Sepsis is characterized as a life-threatening organ dysfunction syndrome that is caused by a dysregulated host response to infection. The main etiological causes of sepsis are bacterial, fungal, and viral infections. Last decades clinical and preclinical research contributed to a better understanding of pathophysiology of sepsis. The dysregulated host response in sepsis is complex, with both pathogen-related factors contributing to disease, as well as immune-cell mediated inflammatory responses that can lead to adverse outcomes in early or advanced stages of disease. Due to its heterogenous nature, clinical diagnosis remains challenging and sepsis-specific treatment options are still lacking. Classification and early identification of patient subgroups may aid clinical decisions and improve outcome in sepsis patients. The initial clinical presentation is rather similar in sepsis of different etiologies, however, inflammatory profiles may be able to distinguish between different etiologies of infections. In this review, we summarize the role and the discriminating potency of host-derived inflammatory biomarkers in the context of the main etiological types of sepsis.

The Role of Adipose Tissue and Adipokines in Sepsis: Inflammatory and Metabolic Considerations, and the Obesity Paradox

PURPOSE

Sepsis has become a global health problem with rising incidence and high mortality, creating a substantial social and economic burden. Early diagnosis and treatment can improve outcome, but reliable sepsis biomarkers are lacking. This review summarizes current evidence of the pathophysiological mechanisms linking adipose tissue to sepsis and presents experimental and clinical data on adipokines and sepsis along with important insights into the obesity paradox in sepsis survival.

RECENT FINDINGS

Sepsis is characterized by significant alterations in circulating cytokines and adipokines, biologically active molecules produced by the adipose tissue, being implicated in metabolic and inflammatory processes. Although data are inconclusive regarding classic adipokines such as leptin and adiponectin, recent evidence have highlighted the striking elevation of resistin and visfatin in critical illness and sepsis as well as their association with sepsis severity and outcomes. Given that inflammatory and metabolic pathways are involved in sepsis, studying adipokines presents an attractive, innovative, and promising research field that may provide more powerful diagnostic and prognostic biomarkers as well as novel therapeutic targets, empowering the therapeutic armamentarium for sepsis management in order to improve survival.

The Role of Adipokines as Circulating Biomarkers in Critical Illness and Sepsis

Sepsis represents a major global health burden. Early diagnosis of sepsis as well as guiding early therapeutic decisions in septic patients still represent major clinical challenges. In this context, a whole plethora of different clinical and serum-based markers have been tested regarding their potential for early detection of sepsis and their ability to stratify patients according to their probability to survive critical illness and sepsis. Adipokines represent a fast-growing class of proteins that have gained an increasing interest with respect to their potential to modulate immune responses in inflammatory and infectious diseases. We review current knowledge on the role of different adipokines in diagnostic work-up and risk stratification of sepsis as well as critical illness. We discuss recent data from animal models as well as from clinical studies and finally highlight the limitations of these analyses that currently prevent the use of adipokines as biomarkers in daily practice.

Comparison of biomarkers adiponectin, leptin, C-reactive protein, S100A12, and the Acute Patient Physiologic and Laboratory Evaluation (APPLE) score as mortality predictors in critically ill dogs

OBJECTIVES

To determine if selected serum biomarkers are superior to the acute patient physiologic and laboratory evaluation (APPLE) complete score in predicting 30-day mortality in a non-homogeneous disease population of critically ill dogs.

DESIGN

Prospective cohort study comparing the serum biomarkers adiponectin, leptin, C-reactive protein, and S100A12 concentrations between surviving and nonsurviving critically ill dogs.

SETTING

University small animal teaching hospital.

ANIMALS

Seventy critically ill dogs were prospectively recruited, and an APPLE complete score was calculated within 24 hours of being admitted to the intensive care unit. Logistic regression models were fit to estimate the association between biomarkers and 30-day survival. Results were interpreted at the 5% level of significance.

MEASUREMENTS AND MAIN RESULTS

Leptin was the only biomarker that was significantly correlated with the APPLE complete score (P < 0.001). Only the APPLE complete score (P = 0.003) and illness duration of < 1 day (P = 0.043) were significantly associated with outcome.

CONCLUSION

Based on the results of this study, there appears to be no benefit in using biomarkers over the APPLE score for disease severity stratification. Serum leptin concentration was significantly correlated with disease severity as determined by APPLE scoring. Longer duration of illness prior to admission was associated with a higher risk of death. APPLE scores were highest in dogs with infectious and immune-mediated diseases and bite wounds.

Preventive Leptin Administration Protects Against Sepsis Through Improving Hypotension, Tachycardia, Oxidative Stress Burst, Multiple Organ Dysfunction, and Increasing Survival

Sepsis syndrome is the most important cause of mortality in critically ill patients admitted to intensive care units (ICUs). However, current therapies for its prevention and treatment are still unsatisfactory, and the mortality rate is still high. Non-septic ICU patients are vulnerable to acquire sepsis syndrome. Thus, a preventive treatment for this population is needed. During sepsis syndrome and endotoxemia, severe hypotension, tachycardia, oxidative and immune response increase, multiple organ dysfunction syndrome (MODS) and decreased survival are observed. Leptin administration protects against negative effects of sepsis syndrome and endotoxemia. Furthermore, it is has been reported that leptin elevates blood pressure mediated by sympathetic nervous system activation. However, whether leptin administration before sepsis induction mediates its protective effects during sepsis through blood pressure regulation is not known. Therefore, we investigated whether pre-treatment of leptin improves blood pressure and MODS, resulting in survival increase during endotoxemia. The results showed that leptin administration before endotoxemia induction reduced both the hypotension and tachycardia characteristically observed during endotoxemia. Notably, this protective effect was observed early and late in the course of endotoxemia. Endotoxemia-induced MODS decreased in leptin-treated rats, which was reflected in normal values for liver and kidney function, inhibition of muscle mass wasting and maintenance of glycemia. Furthermore, leptin pre-treatment decreased the oxidative stress burst in blood and blunted the increased pro-inflammatory cytokines TNF-α, IL-1β, and IL-6 observed during endotoxemia. Remarkably, according to the leptin-induced increase in survival, leptin pre-administration decreased the risk for death associated with sepsis syndrome at early and late times after endotoxemia induction. These results show a potential preventive therapy against sepsis syndrome and endotoxemia in vulnerable patients, based in the beneficial actions of leptin.

Leptin Functions in Infectious Diseases

Leptin, a pleiotropic protein has long been recognized to play an important role in the regulation of energy homeostasis, metabolism, neuroendocrine function, and other physiological functions through its effects on the central nervous system (CNS) and peripheral tissues. Leptin is secreted by adipose tissue and encoded by the obese (ob) gene. Leptin acts as a central mediator which regulates immunity as well as nutrition. Importantly, leptin can modulate both innate and adaptive immune responses. Leptin deficiency/resistance is associated with dysregulation of cytokine production, increased susceptibility toward infectious diseases, autoimmune disorders, malnutrition and inflammatory responses. Malnutrition induces a state of immunodeficiency and an inclination to death from communicable diseases. Infectious diseases are the disease of poor who invariably suffer from malnutrition that could result from reduced serum leptin levels. Thus, leptin has been placed at the center of many interrelated functions in various pathogenic conditions, such as bacterial, viruses and parasitic infections. We review herein, the recent advances on the role of leptin in malnutrition in pathogenesis of infectious diseases with a particular emphasis on parasitic diseases such as Leishmaniasis, Trypanosomiasis, Amoebiasis, and Malaria.

Leptin levels after subarachnoid haemorrhage are gender dependent

Background

Subarachnoid hemorrhage (SAH) is a neurological disease where the majority of the patients are critically ill. The adipokine leptin has in cerebral emergencies been related to severity of disease and to adverse outcome. The aim of this study was to examine leptin levels over time after SAH and associations to gender, age, body mass index, severity of disease, parenteral lipids, systemic organ failure and outcome.

Methods

Prospective observational study in 56 patients. Leptin was obtained 0–240 h after SAH, in 48 h intervals. Severity of disease was assessed with the Hunt and Hess score, organ failure with the sequential organ failure assessment score, and outcome with Glasgow outcome scale. Leptin levels in the SAH group were compared with controls from the same geographical area.

Results

At admission, Leptin was significantly higher in SAH patients compared to controls, both in female (28.6 ± 25.6 vs 13.0 ± 2.3 ng/mL, p = 0.001) and male patients (13.3 ± 8.4 vs 4.3 ± 0.7 ng/mL, p = 0.001). Leptin levels remained stable over time. Female patients had significantly higher leptin levels than male patients, and deceased female patients had higher leptin levels than female survivors (85.5 ± 20.5 vs 50.5 ± 34.6, n = 4/35, p < 0.05). Leptin levels did not differ between male survivors and non-survivors. Leptin levels were not associated with severity of disease, organ failure or parenteral lipids.

Conclusion

Leptin levels were significantly higher in both male and female patients compared to controls. Higher leptin levels were related to outcome and organ failure in women but not in men. When analysing leptin levels gender-related differences should be considered.

Clinical associations of host genetic variations in the genes of cytokines in critically ill patients

Host genetic variations may influence a changing profile of biochemical markers and outcome in patients with trauma/injury. The objective of this study was to assess clinical associations of single nucleotide polymorphisms (SNPs) in the genes of cytokines in critically ill patients. A total of 430 patients were genotyped for SNPs in the genes of pro- (IL1B, IL6, IL8) and anti-inflammatory (IL4, IL10, IL13) cytokines. The main end-points were sepsis, mortality and adult respiratory distress syndrome (ARDS). We evaluated the dynamic levels of bilirubin, blood urea nitrogen, creatine kinase, creatinine and lactate dehydrogenase in five points of measurements (between 1 and 14 days after admission) and correlated them with SNPs. High-producing alleles of proinflammatory cytokines protected patients against sepsis (IL1B -511A and IL8 -251A) and mortality (IL1B -511A). High-producing alleles of anti-inflammatory cytokines IL4 -589T and IL13 431A (144Gln) were less frequent in ARDS patients. The carriers of IL6 -174C/C genotypes were prone to the increased levels of biochemical markers and acute kidney and liver insufficiency. Genotype-dependent differences in the levels of biochemical indicators gradually increased to a maximal value on the 14th day after admission. These findings suggest that genetic variability in pro- and anti-inflammatory cytokines may contribute to different clinical phenotypes in patients at high risk of critical illness.

Endocrine dysfunction in sepsis: a beneficial or deleterious host response?

Sepsis is a systemic, deleterious inflammatory host response triggered by an infective agent leading to severe sepsis, septic shock and multi-organ failure. The host response to infection involves a complex, organized and coherent interaction between immune, autonomic, neuroendocrine and behavioral systems. Recent data have confirmed that disturbances of the autonomic nervous and neuroendocrine systems could contribute to sepsis-induced organ dysfunction. Through this review, we aimed to summarize the current knowledge about the endocrine dysfunction as response to sepsis, specifically addressed to vasopressin, copeptin, cortisol, insulin and leptin. We searched the following readily accessible, clinically relevant databases: PubMed, UpToDate, BioMed Central. The immune system could be regarded as a "diffuse sensory organ" that signals the presence of pathogens to the brain through different pathways, such as the vagus nerve, endothelial activation/dysfunction, cytokines and neurotoxic mediators and the circumventricular organs, especially the neurohypophysis. The hormonal profile changes substantially as a consequence of inflammatory mediators and microorganism products leading to inappropriately low levels of vasopressin, sick euthyroid syndrome, reduced adrenal responsiveness to ACTH, insulin resistance, hyperglycemia as well as hyperleptinemia. In conclusion, clinical diagnosis of this "pan-endocrine illness" is frequently challenging due to the many limiting factors. The most important benefits of endocrine markers in the management of sepsis may be reflected by their potential to be used as biomarkers in different scoring systems to estimate the severity of the disease and the risk of death.