Abstract Background Over recent decades, significant progress has been made in the pharmacological management of Inflammatory Bowel Diseases (IBD). However, the sustained efficacy of existing anti-inflammatory therapies remains suboptimal, highlighting the urgent need for novel treatments. Recent studies have implicated the coagulation pathway, particularly Plasminogen Activator Inhibitor 1 (PAI-1), as a crucial link between epithelium and inflammation in IBD. Genetic deletion of PAI-1 has been shown to reduce experimental colitis severity in mice. Based on these findings, we aimed to develop and evaluate novel PAI-1 inhibitors for IBD treatment. Methods Using the A3SMO® platform, we synthesized LDN-071, an amino acid-based PAI-1 inhibitor, and assessed its inhibitory potential and cytotoxicity in vitro. Acute and chronic colitis models were induced in mice using DSS, with 10 mg/bwkg LDN-071 administered orally. Body weight, spleen weight, and colon length were monitored, while colon histology was analysed. Cytokine expression was measured via ELISA and qRT-PCR, and collagen deposition was quantified using a hydroxyproline assay. Human colon organoid (HCO) and fibroblast (FB) cultures from IBD patients were used to evaluate LDN-071’s effects. Toxicity was assessed in vivo in mice. Results LDN-071 effectively inhibited PAI-1 in vitro without cytotoxicity (1µM–1mM). In DSS-treated mice, 10 mg/bwkg LDN-071 prevented body weight loss, bloody diarrhea, colon shortening, and spleen enlargement. Histological analysis showed that PAI-1 inhibition significantly reduced severe inflammation, ulceration, crypt structure loss, and goblet cell depletion in acute and chronic colitis models. Additionally, PAI-1 inhibition reduced mucosal TNF-α, IL-1β, and IL-6 expression during acute inflammation. In chronic colitis, LDN-071 decreased inflammation, epithelial erosion, and fibrosis while significantly lowering collagen deposition. Importantly, no toxicity was observed at 100 mg/bwkg LDN-071 for seven days. In vitro, LDN-071 reduced pro-inflammatory cytokine expression in HCOs from IBD patients and significantly decreased fibrosis-related gene expression in patient-derived FB cultures. Conclusion Our results showed that LDN-071, a novel amino acid-based inhibitor of PAI-1, significantly ameliorated the severity of acute and chronic colitis in mice. However, the LDN-071 reduced the expression of inflammation- and fibrosis-related genes and proteins in vitro human models. We propose that the inhibition of PAI-1 could be a potential novel therapeutic strategy in IBD.

Abstract Background Inflammatory Bowel Diseases (IBD) are chronic inflammatory disorders characterised by alterations of acute relapses and remission. The past decades have brought substantial advances in the pharmacological management of IBD by wide range of medicines. Although, the sustained efficacy of the currently available anti-inflammatory therapies is still far from optimal. Therefore, the development of novel therapies represents a major unmet clinical need in this field. Recently the enrichment of the coagulation pathway genes and among these, Plasminogen activator inhibitor 1 (PAI-1) was described in IBD, whereas PAI-1 emerged as a link between the epithelium and inflammation. Moreover, the genetic deletion of PAI-1 impaired the severity of experimental colitis in mice. Based on these, our aim was to develop and test novel PAI-1 inhibitors for the treatment of IBD. Methods Novel, amino acid-based PAI-1 inhibitors were synthetized by A3SMO® platform. The inhibitory potential and cytotoxicity effects of the peptides were determined by in vitro assays. Based on the in vitro results LDN-071 was selected for further analysis. Experimental colitis was induced in mice with 3% DSS and after the induction of colitis 10 mg/bwkg LDN-071 was administered per os for four consecutive days. The changes of body weight, spleen weight and colon length were measured. Haematoxylin eosin (HE) and Periodic acid-Schiff (PAS) staining were performed for histology. ELISA and qRT-PCR measurements were applied to analyse the mucosal cytokine expressions. In vivo toxicity of LDN-071 was determined in mice. Results LDN-071 significantly inhibited PAI-1 in vitro without decreasing the cell viability in a concentration range of 1µM-1mM. The administration of 10 mg/bwkg LDN-071 in the DSS-treated mice prevented the body weight loss, the development of bloody diarrhoea, the decrease of colon length and increase of the spleen weight, which were displayed by the DSS+vehicle-treated animals. The histological analysis of the colon revealed that DSS treatment induced a severe transmural inflammation, ulceration, loss of crypt structures and goblet cell depletion. Importantly, all of these parameters were significantly impaired by the administration of 10 mg/bwkg LDN-071. Additionally, mucosal gene and protein expressions of TNF-α, IL-1β and IL-6 were significantly impaired by PAI-1 inhibition. Importantly, no signs of toxicity were LDN-071 observed in mice exposed to 100 mg/bwkg LDN-071 for 7 days. Conclusion Our results showed that LDN-071, a novel amino acid-based inhibitor of PAI-1. It significantly reduces the severity of experimental colitis in mice. We propose that the inhibition of PAI-1 could be a potential novel therapeutic strategy in IBD.

Background/Objectives: Type 1 diabetes affects cytokines as potential inducers of NFκB signalling involved in inflammation and neuronal survival. Our goal was to assess the expression of NFκB p65 and its negative regulator, Nrf2, in myenteric neurons and adjacent smooth muscle of different gut segments after chronic hyperglycaemia and immediate insulin treatment. Methods: After ten weeks of hyperglycaemia, intestinal samples of control, streptozotocin-induced diabetic and insulin-treated diabetic rats were prepared for fluorescent immunohistochemistry, immunogold electron microscopy, ELISA and qPCR. Results: In the diabetic rats, the proportion of NFκB p65-immunoreactive myenteric neurons decreased significantly in the duodenum and increased in the ileum. The density of NFκB p65-labelling gold particles increased in the ileal but remained unchanged in the duodenal ganglia. Meanwhile, both total and nuclear Nrf2 density increased in the myenteric neurons of the diabetic duodenum. In smooth muscle, NFκB p65 and Nrf2 density increased in the small intestine of diabetic rats. While on the mRNA level, NFκB p65 and Nrf2 were induced, on the protein level, NFκB p65 increased and Nrf2 decreased in muscle/myenteric plexus homogenates. Insulin treatment had protective effects. Conclusions: Our findings reveal a segment-specific NFκB and Nrf expression in myenteric neurons and ganglionic muscular environments, which may contribute to regional neuronal survival and motility disturbances in diabetes.

Toll-like receptor 4 (TLR4) can activate pro-inflammatory cascades in the gastrointestinal tract. Our aim was to determine TLR4 expression in myenteric neurons of different gut regions using a type 1 diabetic model. Ten weeks after the onset of hyperglycemia, myenteric whole-mount preparations from the duodenum, ileum and colon of streptozotocin-induced diabetic, insulin-treated diabetic and control rats were prepared for TLR4/peripherin double-labelling fluorescent immunohistochemistry. Immunogold electron microscopy was applied to evaluate TLR4 expression in the myenteric perikaryon and neuropil. Tissue TLR4 levels were measured by enzyme-linked immunosorbent assay. In controls, the number and proportion of the TLR4-immunoreactive myenteric neurons showed an increasing tendency to aboral direction. These values were significantly higher in diabetics compared to controls in the duodenum and ileum, but were significantly lower in the colon. In diabetics, the distribution of TLR4-labelling gold particles between the perikaryon and neuropil of myenteric neurons varied in a different way by intestinal segment. TLR4 tissue concentration changed only in the diabetic duodenum, and it decreased in muscle/myenteric plexus-containing homogenates, while it increased in mucosa/submucosa/submucous plexus-containing samples relative to controls. Insulin had beneficial effects on TLR4 expression. These findings support that chronic hyperglycemia has segment-specific effects on TLR4 expression, contributing to gastrointestinal disorders in diabetic patients.

Interleukin 1β (IL1β) is a pro-inflammatory cytokine that may play a crucial role in enteric neuroinflammation in type 1 diabetes. Therefore, our goal is to evaluate the effects of chronic hyperglycemia and insulin treatment on IL1β immunoreactivity in myenteric neurons and their different subpopulations along the duodenum–ileum–colon axis. Fluorescent immunohistochemistry was used to count IL1β expressing neurons as well as the neuronal nitric oxide synthase (nNOS)- and calcitonin gene-related peptide (CGRP)-immunoreactive myenteric neurons within this group. Tissue IL1β level was measured by ELISA in muscle/myenteric plexus-containing homogenates. IL1β mRNA was detected by RNAscope in different intestinal layers. The proportion of IL1β-immunoreactive myenteric neurons was significantly higher in the colon than in the small intestine of controls. In diabetics, this proportion significantly increased in all gut segments, which was prevented by insulin treatment. The proportion of IL1β-nNOS-immunoreactive neurons only increased in the diabetic colon, while the proportion of IL1β-CGRP-immunoreactive neurons only increased in the diabetic ileum. Elevated IL1β levels were also confirmed in tissue homogenates. IL1β mRNA induction was detected in the myenteric ganglia, smooth muscle and intestinal mucosa of diabetics. These findings support that diabetes-related IL1β induction is specific for the different myenteric neuronal subpopulations, which may contribute to diabetic motility disturbances.

BACKGROUND Cytokines are essential in autoimmune inflammatory processes that accompany type 1 diabetes. Tumor necrosis factor alpha plays a key role among others in modulating enteric neuroinflammation, however, it has a dual role in cell degeneration or survival depending on different TNFRs. In general, TNFR1 is believed to trigger apoptosis, while TNFR2 promotes cell regeneration. The importance of the neuronal microenvironment has been recently highlighted in gut region-specific diabetic enteric neuropathy, however, the expression and alterations of different TNFRs in the gastrointestinal tract has not been reported. AIM To investigate the TNFR1 and TNFR2 expression in myenteric ganglia and their environment in different intestinal segments of diabetic rats. METHODS Ten weeks after the onset of hyperglycemia, gut segments were taken from the duodenum, ileum and colon of streptozotocin-induced (60 mg/body weight kg i.p.) diabetic (n = 17), insulin-treated diabetic (n = 15) and sex- and age-matched control (n = 15) rats. Myenteric plexus whole-mount preparations were prepared from different gut regions for TNFR1/HuCD or TNFR2/HuCD double-labeling fluorescent immunohistochemistry. TNFR1 and TNFR2 expression was evaluated by post-embedding immunogold electron microscopy on ultrathin sections of myenteric ganglia. TNFRs levels were measured by enzyme-linked immun-osorbent assay in muscle/myenteric plexus-containing (MUSCLE-MP) tissue homogenates from different gut segments and experimental conditions. RESULTS A distinct region-dependent TNFRs expression was detected in controls. The density of TNFR1-labeling gold particles was lowest, while TNFR2 density was highest in duodenal ganglia and a decreased TNFRs expression from proximal to distal segments was observed in MUSCLE-MP homogenates. In diabetics, the TNFR2 density was only significantly altered in the duodenum with decrease in the ganglia (0.32 ± 0.02 vs 0.45 ± 0.04, P < 0.05), while no significant changes in TNFR1 density was observed. In diabetic MUSCLE-MP homogenates, both TNFRs levels significantly decreased in the duodenum (TNFR1: 4.06 ± 0.65 vs 20.32 ± 3.1, P < 0.001; TNFR2: 11.72 ± 0.39 vs 15.91 ± 1.04, P < 0.01), which markedly influenced the TNFR2/TNFR1 proportion in both the ganglia and their muscular environment. Insulin treatment had controversial effects on TNFR expression. CONCLUSION Our findings show diabetes-related region-dependent changes in TNFR expression and suggest that TNFR2 is more affected than TNFR1 in myenteric ganglia in the duodenum of type 1 diabetic rats.

Tumour necrosis factor alpha (TNFα) is essential in neuroinflammatory modulation. Therefore, the goal of this study is to reveal the effects of chronic hyperglycaemia and insulin treatment on TNFα expression in different gut segments and intestinal wall layers. TNFα expression was mapped by fluorescent immunohistochemistry and quantitative immunogold electron microscopy in myenteric ganglia of duodenum, ileum and colon. Tissue TNFα levels were measured by enzyme-linked immunosorbent assays in muscle/myenteric plexus-containing (MUSCLE-MP) and mucosa/submucosa/submucous plexus-containing (MUC-SUBMUC-SP) homogenates. Increasing density of TNFα-labelling gold particles is observed in myenteric ganglia from proximal to distal segments and TNFα tissue levels are much more elevated in MUSCLE-MP homogenates than in MUC-SUBMUC-SP samples in healthy controls. In the diabetics, the number of TNFα gold labels is significantly increased in the duodenum, decreased in the colon and remained unchanged in the ileal ganglia, while insulin does not prevent these diabetes-related TNFα changes. TNFα tissue concentration is also increased in MUSCLE-MP homogenates of diabetic duodenum, while decreased in MUC-SUBMUC-SP samples of diabetic ileum and colon. These findings support that type 1 diabetes has region-specific and intestinal layer-dependent effects on TNFα expression, contributing to the regional damage of myenteric neurons and their intestinal milieu.

BACKGROUND The importance of the neuronal microenvironment has been recently highlighted in gut region-specific diabetic enteric neuropathy. Regionally distinct thickening of endothelial basement membrane (BM) of intestinal capillaries supplying the myenteric ganglia coincide with neuronal damage in different intestinal segments. Accelerated synthesis of matrix molecules and reduced degradation of matrix components may also contribute to the imbalance of extracellular matrix dynamics resulting in BM thickening. Among the matrix degrading proteinases, matrix metalloproteinase 9 (MMP9) and its tissue inhibitor (TIMP1) are essential in regulating extracellular matrix remodelling. AIM To evaluate the intestinal segment-specific effects of diabetes and insulin replacement on ganglionic BM thickness, MMP9 and TIMP1 expression. METHODS Ten weeks after the onset of hyperglycaemia gut segments were taken from the duodenum and ileum of streptozotocin-induced diabetic, insulin-treated diabetic and sex- and age-matched control rats. The thickness of BM surrounding myenteric ganglia was measured by electron microscopic morphometry. Whole-mount preparations of myenteric plexus were prepared from the different gut regions for MMP9/TIMP1 double-labelling fluorescent immunohistochemistry. Post-embedding immunogold electron microscopy was applied on ultrathin sections to evaluate the MMP9 and TIMP1 expression in myenteric ganglia and their microenvironment from different gut segments and conditions. The MMP9 and TIMP1 messenger ribonucleic acid (mRNA) level was measured by quantitative polymerase chain reaction. RESULTS Ten weeks after the onset of hyperglycaemia, the ganglionic BM was significantly thickened in the diabetic ileum, while it remained intact in the duodenum. The immediate insulin treatment prevented the diabetes-related thickening of the BM surrounding the ileal myenteric ganglia. Quantification of particle density showed an increasing tendency for MMP9 and a decreasing tendency for TIMP1 from the proximal to the distal small intestine under control conditions. In the diabetic ileum, the number of MMP9-indicating gold particles decreased in myenteric ganglia, endothelial cells of capillaries and intestinal smooth muscle cells, however, it remained unchanged in all duodenal compartments. The MMP9/TIMP1 ratio was also decreased in ileal ganglia only. However, a marked segment-specific induction was revealed in MMP9 and TIMP1 at the mRNA levels. CONCLUSION These findings support that the regional decrease in MMP9 expression in myenteric ganglia and their microenvironment may contribute to extracellular matrix accumulation, resulting in a region-specific thickening of ganglionic BM.