Dipeptidyl peptidase 4 (DPP4) is a molecule implicated in the regulation of metabolic homeostasis and inflammatory processes, and it exerts its main action through its enzymatic activity. DPP4 represents the enzyme most involved in the catabolism of incretin hormones; thus, its activity impacts appetite, energy balance, and the fine regulation of glucose homeostasis. Indeed, DPP4 inhibitors represent a class of antidiabetic agents widely used for the treatment of Type 2 diabetes mellitus (T2DM). DPP4 also acts as an adipokine and is mainly secreted by the adipose tissue, mostly from mature adipocytes of the visceral compartment, where it exerts autocrine and paracrine activities. DPP4 can disrupt insulin signaling within the adipocyte and in other target cells and tissues, where it also favors the development of a proinflammatory environment. This is likely at the basis of the presence of elevated circulating DPP4 levels in several metabolic diseases. In this review, we summarize the most recent evidence of the role of the DPP4 as an adipokine-regulating glucose/insulin metabolism and fat homeostasis, with a particular focus on clinical outcomes associated with its increased secretion in the presence of adipose tissue accumulation and dysfunction.

Type 2 diabetes mellitus (T2DM) is associated with an increased fracture risk. Our study aimed to explore differences in bone alterations between T2DM women and controls and to assess clinical predictors of bone impairment in T2DM. For this observational case control study, we recruited 126 T2DM female patients and 117 non-diabetic, age- and BMI-comparable women, who underwent clinical examination, routine biochemistry and dual-energy X-ray absorptiometry (DXA) scans for bone mineral density (BMD) and trabecular bone score (TBS) assessment-derived indexes. These were correlated to metabolic parameters, such as glycemic control and lipid profile, by bivariate analyses, and significant variables were entered in multivariate adjusted models to detect independent determinants of altered bone status in diabetes. The T2DM patients were less represented in the normal bone category compared with controls (5% vs. 12%; p = 0.04); T2DM was associated with low TBS (OR: 2.47, C.I. 95%: 1.19–5.16, p = 0.016) in a regression model adjusted for age, menopausal status and BMI. In women with T2DM, TBS directly correlated with plasma high-density lipoprotein cholesterol (HDL-c) (p = 0.029) and vitamin D (p = 0.017) levels. An inverse association was observed with menopausal status (p < 0.001), metabolic syndrome (p = 0.014), BMI (p = 0.005), and waist circumference (p < 0.001). In the multivariate regression analysis, lower HDL-c represented the main predictor of altered bone quality in T2DM, regardless of age, menopausal status, BMI, waist circumference, statin treatment, physical activity, and vitamin D (p = 0.029; R² = 0.47), which likely underlies common pathways between metabolic disease and bone health in diabetes.

Type 2 diabetes mellitus (T2DM) is characterized by disrupted glucose homeostasis and metabolic abnormalities, with oxidative stress and inflammation playing pivotal roles in its pathophysiology. Poly(ADP-ribosyl)ation (PARylation) is a post-translational process involving the addition of ADP-ribose polymers (PAR) to target proteins. While preclinical studies have implicated PARylation in the interplay between oxidative stress and inflammation in T2DM, direct clinical evidence in humans remains limited. This study investigates the relationship between oxidative stress, PARylation, and inflammatory response in T2DM patients. This cross-sectional investigation involved 61 T2DM patients and 48 controls. PAR levels were determined in peripheral blood cells (PBMC) by ELISA-based methodologies. Oxidative stress was assessed in plasma and PBMC. In plasma, we monitored reactive oxygen metabolites (d-ROMs) and ferric-reducing antioxidant power. In PBMC, we measured the expression of antioxidant enzymes SOD1, GPX1 and CAT by qPCR. Further, we evaluated the expression of inflammatory mediators such as IL6, TNF-α, CD68 and MCP1 by qPCR in PBMC. T2DM patients exhibited elevated PAR levels in PBMC and increased d-ROMs in plasma. Positive associations were found between PAR levels and d-ROMs, suggesting a link between oxidative stress and altered PAR metabolism. Mediation analysis revealed that d-ROMs mediate the association between HbA1c levels and PAR, indicating oxidative stress as a potential driver of increased PARylation in T2DM. Furthermore, elevated PAR levels were found to be associated with increased expression of pro-inflammatory cytokines IL6 and TNF-α in the PBMC of T2DM patients. This study highlights that hyperactivation of PARylation is associated with poor glycemic control and the resultant oxidative stress in T2DM. The increase of PAR levels is correlated with the upregulation of key mediators of the inflammatory response. Further research is warranted to validate these findings and explore their clinical implications.

Metabolic-associated steatotic liver disease (MASLD) represents the most common chronic hepatopathy worldwide and an independent risk factor for cardiovascular disease and mortality, particularly when liver fibrosis occurs. Epigenetic alterations, such as DNA methylation, may influence MASLD susceptibility and progression; yet mechanisms underlying this process are limited. This study aimed to investigate whether active DNA demethylation in peripheral blood mononuclear cells (PBMCs) from individuals with MASLD, alongside the methylation and mRNA levels of inflammation- and fibrosis-related candidate genes, is associated with liver fibrosis. For this study, global demethylation intermediates (5-hydroxymethylcytosine [5hmC], 5-formylcytosine [5fC]) were quantified in PBMCs from 89 individuals with/without MASLD using ELISA. Site-specific DNA methylation of SOCS3, SREBF1, and TXNIP was analyzed by mass spectrometry-based bisulfite sequencing; mRNA expression was assessed via RT-PCR. Individuals with MASLD and moderate-to-high fibrosis risk (estimated by the fibrosis non-alcoholic steatohepatitis (NASH) index, FNI) progressively exhibited greater global 5hmC and 5fC levels. Higher FNI was associated with reduced methylation of the SOCS3 gene and increased mRNA expression of the SOCS3, TXNIP, IL-6, and MCP-1 genes. In conclusion, elevated fibrosis risk in MASLD is associated with active global DNA demethylation, as well as differential methylation and expression patterns of genes, which are key regulators of inflammation and fibrosis. These epigenetic alterations in PBMCs may mirror DNA methylation changes in the liver, which may potentially contribute to liver fibrogenesis and represent novel biomarkers for MASLD progression toward fibrosis.

Neurotensin (NT) is a small protein implicated in the regulation of energy balance which acts as both a neurotransmitter in the central nervous system and as a gastrointestinal peptide. In the gut, NT is secreted after fat ingestion and promotes the absorption of fatty acids. The circulating levels of its precursor, pro-NT, predicts the presence and development of metabolic and cardiovascular diseases. Despite the extensive knowledge on the dynamic changes that occur to pro-NT = after fat load, the determinants of fasting pro-NT are unknown. The aim of this study was to determine the possible genetic regulation of plasma pro-NT. The NT gene (NTS) was sequenced for potential functional variants, evaluating its entire genomic and potentially regulatory regions, in DNA from 28 individuals, stratified by low and high pro-NT levels. The identified variant differently distributed in the two pro-NT subgroups was genotyped in a cohort of nine hundred and thirty-two overweight/obese children and adolescents. A total of seven sequence variations across the NTS gene, none of them located in coding regions, were identified. The rs2234762 polymorphism, sited in the NTS gene promoter, was statistically more frequent in the lowest pro-NTS level group. Carriers of the rs2234762 variant showed lower pro-NT levels, after adjusting for sex, age, BMI, triglycerides and the Tanner stage. Having NTS rs2234762 predicted less pronounced insulin resistance at the 6.5-year follow-up with OR: 0.46 (0.216–0.983), at the logistic regression analysis adjusted for age, sex and BMI. In conclusion, the NTS rs2234762 gene variant is a determinant of reduced circulating pro-NT levels in overweight and obese children, which predisposes this group to a more favorable metabolic profile and a reduced insulin resistance later in life, independently from metabolic confounders.

Increased intestinal permeability has been implicated in metabolic dysfunction-associated steatotic liver disease (MASLD), but its relationship with liver fibrosis independent of metabolic risk factors remains unclear. The aim of this study was to investigate the relationship between markers of gut-derived immune activation and liver fibrosis in individuals with metabolic disease. We enrolled 139 adults (48.8 ± 11 years; BMI 33.7 ± 9.5 kg/m²; 50% type 2 diabetes); liver steatosis and fibrosis were estimated using the Hepatic Steatosis Index (HSI) and Fibrotic NASH Index (FNI); liver biopsies were available in a bariatric subgroup. Plasma soluble CD14 (sCD14) and lipopolysaccharide-binding protein (LBP) levels were measured by ELISA kits, and the LBP/sCD14 ratio was calculated. MASLD was present in 78% of participants; in these individuals, sCD14 levels correlated with HSI and FNI (both p < 0.01). In multivariable analysis adjusting for age, sex, BMI, waist circumference, and type 2 diabetes, sCD14 was independently associated with advanced fibrosis (OR: 3.16, 95% CI 1.32–7.55; p = 0.010). This association was confirmed by histology (p = 0.02). Overall, these findings point to a link between gut-derived immune activation and fibrotic burden in MASLD and provide insight into the pathophysiological relevance of the gut–liver axis in metabolic disease.