Antimicrobial-sensing proteins in obesity and type 2 diabetes: the buffering efficiency hypothesis

The relevance of intestinal barrier dysfunction, antimicrobial proteins and bacterial endotoxin in metabolic dysfunction-associated steatotic liver disease

BACKGROUND

Metabolic dysfunction-associated steatotic liver disease (MASLD) is a leading cause of end-stage liver disease associated with increased mortality and cardiovascular disease. Obesity and diabetes are the most important risk factors of MASLD. It is well-established that obesity-associated insulin resistance leads to a situation of tissue lipotoxicity characterized by an accumulation of excess fat in non-fat tissues such as the liver, promoting the development of MASLD, and its progression into metabolic dysfunction-associated steatohepatitis.

METHODS

Here, we aimed to review the impact of disrupted intestinal permeability, antimicrobial proteins and bacterial endotoxin in the development and progression of MASLD.

RESULTS AND CONCLUSION

Recent studies demonstrated that obesity- and obesogenic diets-associated alterations of intestinal microbiota along with the disruption of intestinal barrier integrity, the alteration in antimicrobial proteins and, in consequence, an enhanced translocation of bacterial endotoxin into bloodstream might contribute to this pathological process through to impacting liver metabolism and inflammation.

Host Defence Peptides in Diabetes Mellitus Type 2 Patients with Periodontal Disease. A Systematic Review

The aim of the study was to critically assess and review the latest evidence relating the associations between host defence peptides (HDPs), periodontal diseases (PD) and diabetes mellitus type 2 (DM2). To explore studies on HDPs, periodontal disease, and DM2, researchers utilised specific key phrases to search the electronic databases PubMed (National Library of Medicine), Embase (Ovid), Medline (EBSCO), and Dentistry and Oral Sciences (EBSCO). Quality assessment was conducted by means of the Newcastle Ottawa scale and the Systematic Review Centre for Laboratory Animal Experimentation (SYRCLE) tool. Following a thorough screening process, a total of 12 papers (4 case-control, 6 cross-sectional, 1 animal, and 1 in vitro) fulfilled the selection criteria and were included. The majority of research found that HDPs were upregulated in DM2 patients with PD. Three investigations, however, found that HDPs were downregulated in DM2 patients with PD. HDPs play a part in the pathophysiology of PD and DM2. Nonetheless, more human, animal and laboratory investigations are needed to fully understand validation of the link, as the evidence is limited. Understanding HDPs as common moderators is critical, aimed at unlocking their potential as therapeutic and diagnostic agents.

The Role of Obesity in the Immunopathogenesis of COVID-19 Respiratory Disease and Critical Illness

Coronavirus disease (COVID-19), the clinical syndrome caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), is currently a global health pandemic with substantial morbidity and mortality. COVID-19 has cast a shadow on nearly every aspect of society, straining health systems and economies across the world. Although it is widely accepted that a close relationship exists between obesity, cardiovascular disease, and metabolic disorders on infection, we are only beginning to understand ways in which the immunological sequelae of obesity functions as a predisposing factor related to poor clinical outcomes in COVID-19. As both the innate and adaptive immune systems are each primed by obesity, the alteration of key pathways results in both an immunosuppressed and hyperinflammatory state. The present review will discuss the cellular and molecular immunology of obesity in the context of its role as a risk factor for severe COVID-19, discuss the role of cytokine storm, and draw parallels to prior viral epidemics such as severe acute respiratory syndrome (SARS), Middle East respiratory syndrome (MERS), and 2009 H1N1.

Lysozyme is a component of the innate immune system linked to obesity associated-chronic low-grade inflammation and altered glucose tolerance

BACKGROUND & AIMS

Several proteins of the innate immune system are known to be deregulated with insulin resistance. We here aimed to investigate the relationship among circulating lysozyme (both plasma concentration and activity) and obesity-associated metabolic disturbances.

METHODS

Plasma lysozyme concentration was determined cross-sectionally in a discovery (Cohort 1, n = 137) and in a replication cohort (Cohort 2, n = 181), in which plasma lysozyme activity was also analyzed. Plasma lysozyme was also evaluated longitudinally in participants from the replication cohort (n = 93). Leukocyte lysozyme expression (LYZ mRNA) were also investigated in an independent cohort (Cohort 3, n = 76), and adipose tissue (AT) LYZ mRNA (n = 25) and plasma peptidoglycan levels (n = 61) in subcohorts from discovery cohort.

RESULTS

Translocation of peptidoglycan (as inferred from its increased circulating levels) was linked to plasma lysozyme, hyperinsulinemia and dyslipidemia in obese subjects. In both discovery and replication cohorts, plasma lysozyme levels and activity were significantly increased in obesity in direct association with obesity-associated metabolic disturbances and inflammatory parameters, being circulating lysozyme negatively correlated with fasting glucose, HbA1c and insulin resistance (HOMA-IR) in obese subjects. Of note, total cholesterol (p < 0.0001) and LDL cholesterol (p = 0.003) contributed independently to age-, gender- and BMI adjusted plasma lysozyme activity. Longitudinally, changes in HbA1c levels and serum LDL cholesterol were negatively associated with circulating lysozyme antimicrobial activity. On the contrary, the change in glucose infusion rate during the clamp (insulin sensitivity) was positively associated with lysozyme concentration.

CONCLUSIONS

Increased plasma lysozyme levels and activity are found in obese subjects. The longitudinal findings suggest that plasma lysozyme might be protective on the development of obesity-associated metabolic disturbances.

Culture characterization of the skin microbiome in Type 2 diabetes mellitus: A focus on the role of innate immunity

AIMS

The current study aimed at determining the differences between the cutaneous microbial flora of patients with Type 2 diabetes mellitus (T2DM) and those without, and thus evaluate for cutaneous microbiome dysbiosis in diabetes.

METHODS

We employed a case-control study design with 41 participants in each group. The skin over the toe-web space was swabbed and cultured aerobically. Data was analyzed for differences in microbial prevalences and growths between the two groups. Predictors for heavy colonization by microbes were analysed using logistic regression.

RESULTS

We found significantly higher prevalences of Staphylococcus epidermidis among patients with T2DM (77.5% vs. 53.7%, p=0.02). Further, when prevalent, these bacteria showed a significantly greater degree of skin colonization i.e. CFUs/cm² among these patients, p=0.03. Highly pathogenic bacteria such as S. aureus were more prevalent among patients with T2DM. The regression model determined a significant association between T2DM status and heavy colonization by S. epidermidis (OR - 5.40, p=0.02). Also, agricultural workers were significantly more likely to have heavy colonization by S. epidermidis (OR - 3.75, p=0.02). Other predictor variables did not show significant association with heavy colonization by any of the isolated microbes.

CONCLUSIONS

Our findings support the existence of cutaneous microbiome dysbiosis among patients with T2DM. Literature suggests that microbiome dybiosis in T2DM could stem from the same activated innate immune response that is thought to be central to the development of T2DM. This dysbiosis could increase the risk of developing skin infections.

Genetic variations of the bitter taste receptor TAS2R38 are associated with obesity and impact on single immune traits

SCOPE

Changes in genetic variations affecting the taste receptor, type 2, member 38 (TAS2R38) may identify the interacting mechanism leading to obesity and potential associations with proteins partaking in innate immunity, such as surfactant protein D (SPD) and mannan-binding lectin (MBL).

METHODS AND RESULTS

We evaluated haplotypes of the bitter-taste receptor TAS2R38 in an identification sample of 210 women in different weight conditions, including anorexia nervosa and obesity. The association with SPD and MBL was tested in an independent sample picturing general population (n = 534). The relationship with obesity was validated in an extended final sample of 1319 participants. In the sample comprised of women in extreme weight conditions, increased obesity was identified in AVI/AVI subjects (OR = 2.5 [1.06-6.11], p = 0.035). In the sample picturing general population, increased SPD and MBL concentrations were found in nonsmoking AVI carriers. In this cohort, smoking and obesity blunted associations between TAS2R38 haplotypes and SPD and MBL. In the extended sample, the association of AVI/AVI haplotypes with increased obesity was also identified (OR = 1.4 [0.99/1.85], p = 0.049), being more robust in subjects aged <40 years (OR = 1.9 [1.06/3.42], p = 0.031).

CONCLUSION

Current data reinforce the impact of TAS2R38 gene on phenotypic and clinical outputs affecting obesity, showing significant associations with extreme weight conditions (i.e., obesity and anorexia nervosa), and changes in both olfactory capacity and immune traits.

The Ligands of Neutrophil Gelatinase-Associated Lipocalin

Neutrophil gelatinase associated lipocalin (NGAL), was originally identified in neutrophil granules as a heterodimer complex with gelatinase B (matrix metalloproteinase 9, MMP9), but more recently has been found to be secreted by damaged epithelial cells. Ngal is a member of the lipocalin family and subsequently named as lipocalin 2 on the basis of structural similarity with other members of the lipocalin family and its potential association with hydrophobic retinol and cholesterol oleate more strongly than their hydrophilic counterparts. In 2002, a landmark paper suggested that Ngal is a bacteriostatic agent which blocks iron acquisition by interacting with a number of bacterial siderophores, especially enterobactin. Since then, more siderophore-carrying functions have been reported than the possibility of hydrophobic ligand transport. In this setting, Ngal was renamed Siderocalin. Functions of siderocalin include not only bacteriostatic activity but potentially as a mediator of cell growth and differentiation; some of these functions appear to be referable to the holo siderocalin:siderophore:iron complex and recent work suggests that metabolic products may act as mammalian siderophores bound by Ngal. While still speculative, it may be that the mammalian siderophores can establish the missing link between Ngal and a number of its functions in vivo. This review provides an overview of the discoveries of the different ligands of Ngal and consequently related functions. Hydrophobic ligands, bacterial siderophores as well as their modified structures (synthetic siderophores), and mammalian siderophores are summarized.

Obesity and nutrition in acute respiratory distress syndrome

This article discusses obesity, its contribution to clinical outcomes, and the current literature on nutrition. More than one third of Americans are obese. Literature suggests that, among critically ill patients, the relationship between obesity and outcomes is complex. Obese patients may be at greater risk of developing acute respiratory distress syndrome (ARDS) than normal weight patients. Although obesity may confer greater morbidity in intensive care, it seems to decrease mortality. ARDS is a catabolic state; patients demonstrate a profound inflammatory response, multiple organ dysfunction, and hypermetabolism, often with malnutrition. The concept of pharmaconutrition has emerged.

The gut microbiota profile is associated with insulin action in humans

The role of the gut microbiota in the induction of metabolic diseases has now been increasingly recognized worldwide. Indeed, a specific gut microbiota has been shown to characterize lean versus obese phenotypes both in humans and mice. We have also recently demonstrated that a precise gut microbiota is associated with the host's responsiveness to a high-fat diet. Therefore, we hypothesized that insulin resistance in humans could also be linked to a specific gut microbiota. To this aim, microbial DNA and RNA were extracted from the appendix contents of insulin-resistant versus insulin-sensitive obese subjects, matched for body mass index and age, and analyzed by DNA- and RNA-DGGE. Microbial DNA analysis showed that the patients fully segregated according to their degree of insulin action. Conversely, microbial RNA investigation showed that some degree of homology still existed between insulin-sensitive and insulin-resistant patients. Quantitative trait analysis, ordinary least squares regression, principal components regression, partial least squares, canonical correlation analysis, and canonical correspondence analysis also showed a net separation of the two phenotypes analyzed. We conclude that a specific gut microbial profile is associated with insulin action in humans.

Common genetic variants of surfactant protein-D (SP-D) are associated with type 2 diabetes

Context

Surfactant protein-D (SP-D) is a primordial component of the innate immune system intrinsically linked to metabolic pathways. We aimed to study the association of single nucleotide polymorphisms (SNPs) affecting SP-D with insulin resistance and type 2 diabetes (T2D).

Research Design and Methods

We evaluated a common genetic variant located in the SP-D coding region (rs721917, Met³¹Thr) in a sample of T2D patients and non-diabetic controls (n = 2,711). In a subset of subjects (n = 1,062), this SNP was analyzed in association with circulating SP-D concentrations, insulin resistance, and T2D. This SNP and others were also screened in the publicly available Genome Wide Association (GWA) database of the Meta-Analyses of Glucose and Insulin-related traits Consortium (MAGIC).

Results

We found the significant association of rs721917 with circulating SP-D, parameters of insulin resistance and T2D. Indeed, G carriers showed decreased circulating SP-D (p = 0.004), decreased fasting glucose (p = 0.0002), glycated hemoglobin (p = 0.0005), and 33% (p = 0.002) lower prevalence of T2D, estimated under a dominant model, especially among women. Interestingly, these differences remained significant after controlling for origin, age, gender, and circulating SP-D. Moreover, this SNP and others within the SP-D genomic region (i.e. rs10887344) were significantly associated with quantitative measures of glucose homeostasis, insulin sensitivity, and T2D, according to GWAS datasets from MAGIC.

Conclusions

SP-D gene polymorphisms are associated with insulin resistance and T2D. These associations are independent of circulating SP-D concentrations.

Activation of human neutrophils by Esenbeckia leiocarpa: comparison between the crude hydroalcoholic extract (CHE) and an alkaloid (Alk) fraction

Esenbeckia leiocarpa, a wide spread native Brazilian tree, was reported recently to possess anti-inflammatory effects in vivo, but the mechanisms involved are still not fully understood and its role in neutrophils is poorly documented. The aim of this study was to compare the effects of a crude hydroalcoholic extract (CHE) and an alkaloid-enriched (Alk) fraction obtained from Esenbeckia leiocarpa bark on human neutrophils by investigating the effect of each fraction alone or in a mixture with classical neutrophil agonists. CHE inhibited intracellular reactive oxygen species (ROS) production but increased the extracellular superoxide (O2-) production, while Alk increased the former and also slightly increased O2- production. We found that CHE and Alk also induced phagocytosis accompanied by Syk activation, adhesion and degranulation. However, neither CHE nor Alk potentiated the effect of classical neutrophil agonists, namely the cytokines GM-CSF for phagocytosis and TNF-α for adhesion or N-formyl-methionyl-leucyl-phenylalanine (fMLP) for degranulation. In addition, based on catalase treatment, CHE and Alk induced neutrophil apoptosis by a hydrogen peroxide (H2O2)-dependent mechanism. Since the elimination of apoptotic neutrophils by professional phagocytes is important for the resolution of inflammation, the ability of CHE and Alk to induce neutrophil apoptosis has to be considered as one possible mechanism associated with the anti-inflammatory activity of these fractions previously reported in vivo.