Diabetes Primes Neutrophils for Neutrophil Extracellular Trap Formation through Trained Immunity.

Neutrophils are primed for neutrophil extracellular trap (NET) formation during diabetes, and excessive NET formation from primed neutrophils compromises wound healing in patients with diabetes. Here, we demonstrate that trained immunity mediates diabetes-induced NET priming in neutrophils. Under diabetic conditions, neutrophils exhibit robust metabolic reprogramming comprising enhanced glycolysis via the pentose phosphate pathway and fatty acid oxidation, which result in the accumulation of acetyl-coenzyme A. Adenosine 5'-triphosphate-citrate lyase-mediated accumulation of acetyl-coenzyme A and histone acetyltransferases further induce the acetylation of lysine residues on histone 3 (AcH3K9, AcH3K14, and AcH3K27) and histone 4 (AcH4K8). The pharmacological inhibition of adenosine 5'-triphosphate-citrate lyase and histone acetyltransferases completely inhibited high-glucose-induced NET priming. The trained immunity of neutrophils was further confirmed in neutrophils isolated from patients with diabetes. Our findings suggest that trained immunity mediates functional changes in neutrophils in diabetic environments, and targeting neutrophil-trained immunity may be a potential therapeutic target for controlling inflammatory complications of diabetes.

Comprehensive overview of the role of mitochondrial dysfunction in the pathogenesis of acute kidney ischemia-reperfusion injury: a narrative review.

Acute kidney ischemia-reperfusion (IR) injury is a life-threatening condition that predisposes individuals to chronic kidney disease. Since the kidney is one of the most energy-demanding organs in the human body and mitochondria are the powerhouse of cells, mitochondrial dysfunction plays a central role in the pathogenesis of IR-induced acute kidney injury. Mitochondrial dysfunction causes a reduction in adenosine triphosphate production, loss of mitochondrial dynamics (represented by persistent fragmentation), and impaired mitophagy. Furthermore, the pathological accumulation of succinate resulting from fumarate reduction under oxygen deprivation (ischemia) in the reverse flux of the Krebs cycle can eventually lead to a burst of reactive oxygen species driven by reverse electron transfer during the reperfusion phase. Accumulating evidence indicates that improving mitochondrial function, biogenesis, and dynamics, and normalizing metabolic reprogramming within the mitochondria have the potential to preserve kidney function during IR injury and prevent progression to chronic kidney disease. In this review, we summarize recent advances in understanding the detrimental role of metabolic reprogramming and mitochondrial dysfunction in IR injury and explore potential therapeutic strategies for treating kidney IR injury.

Reducing Oxidative Stress and Inflammation by Pyruvate Dehydrogenase Kinase 4 Inhibition Is Important in Prevention of Renal Ischemia-Reperfusion Injury in Diabetic Mice.

Background: Reactive oxygen species (ROS) and inflammation are reported to have a fundamental role in the pathogenesis of ischemia-reperfusion (IR) injury, a leading cause of acute kidney injury. The present study investigated the role of pyruvate dehydrogenase kinase 4 (PDK4) in ROS production and inflammation following IR injury. Methods: We used a streptozotocin-induced diabetic C57BL6/J mouse model, which was subjected to IR by clamping both renal pedicles. Cellular apoptosis and inflammatory markers were evaluated in NRK-52E cells and mouse primary tubular cells after hypoxia and reoxygenation using a hypoxia work station. Results: Following IR injury in diabetic mice, the expression of PDK4, rather than the other PDK isoforms, was induced with a marked increase in pyruvate dehydrogenase E1α (PDHE1α) phosphorylation. This was accompanied by a pronounced ROS activation, as well as tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6), interleukin-1ß (IL-1ß), and monocyte chemoattractant protein-1 (MCP-1) production. Notably, sodium dichloroacetate (DCA) attenuated renal IR injury-induced apoptosis which can be attributed to reducing PDK4 expression and PDHE1α phosphorylation levels. DCA or shPdk4 treatment reduced oxidative stress and decreased TNF-α, IL-6, IL-1ß, and MCP-1 production after IR or hypoxia-reoxygenation injury. Conclusion: PDK4 inhibition alleviated renal injury with decreased ROS production and inflammation, supporting a critical role for PDK4 in IR mediated damage. This result indicates another potential target for reno-protection during IR injury; accordingly, the role of PDK4 inhibition needs to be comprehensively elucidated in terms of mitochondrial function during renal IR injury.

Discovery of a peripheral 5HT2A antagonist as a clinical candidate for metabolic dysfunction-associated steatohepatitis.

Metabolic Dysfunction-Associated Steatotic Liver Disease (MASLD) is currently the leading cause of chronic liver disease worldwide. Metabolic Dysfunction-Associated Steatohepatitis (MASH), an advanced form of MASLD, can progress to liver fibrosis, cirrhosis, and hepatocellular carcinoma. Based on recent findings by our team that liver 5HT2A knockout male mice suppressed steatosis and reduced fibrosis-related gene expression, we developed a peripheral 5HT2A antagonist, compound 11c for MASH. It shows good in vitro activity, stability, and in vivo pharmacokinetics (PK) in rats and dogs. Compound 11c also shows good in vivo efficacy in a diet-induced obesity (DIO) male mice model and in a choline-deficient, L-amino acid-defined, high-fat diet (CDAHFD) male mice model, effectively improving histologic features of MASH and fibrosis. According to the tissue distribution study using [14C]-labeled 11c, the compound was determined to be a peripheral 5HT2A antagonist. Collectively, first-in-class compound 11c shows promise as a therapeutic agent for the treatment of MASLD and MASH.

Mitochondrial dysfunctions in T cells: focus on inflammatory bowel disease.

Mitochondria has emerged as a critical ruler of metabolic reprogramming in immune responses and inflammation. In the context of colitogenic T cells and IBD, there has been increasing research interest in the metabolic pathways of glycolysis, pyruvate oxidation, and glutaminolysis. These pathways have been shown to play a crucial role in the metabolic reprogramming of colitogenic T cells, leading to increased inflammatory cytokine production and tissue damage. In addition to metabolic reprogramming, mitochondrial dysfunction has also been implicated in the pathogenesis of IBD. Studies have shown that colitogenic T cells exhibit impaired mitochondrial respiration, elevated levels of mROS, alterations in calcium homeostasis, impaired mitochondrial biogenesis, and aberrant mitochondria-associated membrane formation. Here, we discuss our current knowledge of the metabolic reprogramming and mitochondrial dysfunctions in colitogenic T cells, as well as the potential therapeutic applications for treating IBD with evidence from animal experiments.

Synthesis and biological evaluation of xanthine derivatives with phenacyl group as tryptophan hydroxylase 1 (TPH1) inhibitors for obesity and fatty liver disease.

Tryptophan hydroxylase 1 (TPH1) has emerged as a target for the treatment of metabolic diseases including obesity and fatty liver disease. A series of xanthine derivatives were synthesized and evaluated for their TPH1 inhibition. Among the synthesized compounds, compound 40 showed good in vitro activity and liver microsomal stability. Docking studies revealed that compound 40 showed better binding to TPH1 via key intermolecular interactions involving the xanthine scaffold, imidazo-thiazolyl ring, and hydroxyl-containing phenacyl moiety. In addition, compound 40 effectively suppressed the adipocyte differentiation of 3 T3-L1 cells.

Inhibition of pyruvate dehydrogenase kinase 4 ameliorates kidney ischemia-reperfusion injury by reducing succinate accumulation during ischemia and preserving mitochondrial function during reperfusion.

Ischemia-reperfusion (IR) injury, a leading cause of acute kidney injury (AKI), is still without effective therapies. Succinate accumulation during ischemia followed by its oxidation during reperfusion leads to excessive reactive oxygen species (ROS) and severe kidney damage. Consequently, the targeting of succinate accumulation may represent a rational approach to the prevention of IR-induced kidney injury. Since ROS are generated primarily in mitochondria, which are abundant in the proximal tubule of the kidney, we explored the role of pyruvate dehydrogenase kinase 4 (PDK4), a mitochondrial enzyme, in IR-induced kidney injury using proximal tubule cell-specific Pdk4 knockout (Pdk4ptKO) mice. Knockout or pharmacological inhibition of PDK4 ameliorated IR-induced kidney damage. Succinate accumulation during ischemia, which is responsible for mitochondrial ROS production during reperfusion, was reduced by PDK4 inhibition. PDK4 deficiency established conditions prior to ischemia resulting in less succinate accumulation, possibly because of a reduction in electron flow reversal in complex II, which provides electrons for the reduction of fumarate to succinate by succinate dehydrogenase during ischemia. The administration of dimethyl succinate, a cell-permeable form of succinate, attenuated the beneficial effects of PDK4 deficiency, suggesting that the kidney-protective effect is succinate-dependent. Finally, genetic or pharmacological inhibition of PDK4 prevented IR-induced mitochondrial damage in mice and normalized mitochondrial function in an in vitro model of IR injury. Thus, inhibition of PDK4 represents a novel means of preventing IR-induced kidney injury, and involves the inhibition of ROS-induced kidney toxicity through reduction in succinate accumulation and mitochondrial dysfunction.

Upregulation of the ERRγ-VDAC1 axis underlies the molecular pathogenesis of pancreatitis.

Emerging evidence suggest that transcription factors play multiple roles in the development of pancreatitis, a necroinflammatory condition lacking specific therapy. Estrogen-related receptor γ (ERRγ), a pleiotropic transcription factor, has been reported to play a vital role in pancreatic acinar cell (PAC) homeostasis. However, the role of ERRγ in PAC dysfunction remains hitherto unknown. Here, we demonstrated in both mice models and human cohorts that pancreatitis is associated with an increase in ERRγ gene expression via activation of STAT3. Acinar-specific ERRγ haploinsufficiency or pharmacological inhibition of ERRγ significantly impaired the progression of pancreatitis both in vitro and in vivo. Using systematic transcriptomic analysis, we identified that voltage-dependent anion channel 1 (VDAC1) acts as a molecular mediator of ERRγ. Mechanistically, we showed that induction of ERRγ in cultured acinar cells and mouse pancreata enhanced VDAC1 expression by directly binding to specific site of the Vdac1 gene promoter and resulted in VDAC1 oligomerization. Notably, VDAC1, whose expression and oligomerization were dependent on ERRγ, modulates mitochondrial Ca2+ and ROS levels. Inhibition of the ERRγ-VDAC1 axis could alleviate mitochondrial Ca2+ accumulation, ROS formation and inhibit progression of pancreatitis. Using two different mouse models of pancreatitis, we showed that pharmacological blockade of ERRγ-VDAC1 pathway has therapeutic benefits in mitigating progression of pancreatitis. Likewise, using PRSS1R122H-Tg mice to mimic human hereditary pancreatitis, we demonstrated that ERRγ inhibitor also alleviated pancreatitis. Our findings highlight the importance of ERRγ in pancreatitis progression and suggests its therapeutic intervention for prevention and treatment of pancreatitis.

Thyroid storm caused by metastatic papillary thyroid carcinoma tissue after total thyroidectomy: a case report.

Thyroid storm is a life-threatening form of thyrotoxicosis and an endocrinological emergency. We present a case of thyroid storm in a patient with metastatic papillary thyroid cancer. A 67-year-old woman with a history of total thyroidectomy 4 years prior to presentation was admitted with deteriorating mental status, fever, and tachycardia. Laboratory tests revealed severe thyrotoxicosis. Although the patient had no residual thyroid tissue after total thyroidectomy, she had a previously diagnosed metastatic thyroid cancer lesion in the pelvic bone. Despite initial treatment with a standard thyroid storm regimen, the patient died 6 days after hospitalization. The patient had no history of Graves disease; however, a thyroxine receptor antibody was detected postmortem. The patient had a history of exposure to an iodine contrast agent, which is a rare cause of thyrotoxicosis. Thyroxine production from a differentiated thyroid carcinoma is rare but can be a source of clinically significant thyrotoxicosis in patients post-thyroidectomy. Overlapping Graves disease is a common stimulus; however, other causes, such as exogenous iodine, cannot be excluded. This case demonstrates that in the setting of metastatic thyroid carcinoma, thyrotoxicosis cannot be completely ruled out as a cause of suspicious symptoms, even in patients with a history of total thyroidectomy.

CycloZ Improves Hyperglycemia and Lipid Metabolism by Modulating Lysine Acetylation in KK-Ay Mice.

BACKGRUOUND: CycloZ, a combination of cyclo-His-Pro and zinc, has anti-diabetic activity. However, its exact mode of action remains to be elucidated. METHODS: KK-Ay mice, a type 2 diabetes mellitus (T2DM) model, were administered CycloZ either as a preventive intervention, or as a therapy. Glycemic control was evaluated using the oral glucose tolerance test (OGTT), and glycosylated hemoglobin (HbA1c) levels. Liver and visceral adipose tissues (VATs) were used for histological evaluation, gene expression analysis, and protein expression analysis. RESULTS: CycloZ administration improved glycemic control in KK-Ay mice in both prophylactic and therapeutic studies. Lysine acetylation of peroxisome proliferator-activated receptor gamma coactivator 1-alpha, liver kinase B1, and nuclear factor-κB p65 was decreased in the liver and VATs in CycloZ-treated mice. In addition, CycloZ treatment improved mitochondrial function, lipid oxidation, and inflammation in the liver and VATs of mice. CycloZ treatment also increased the level of ß-nicotinamide adenine dinucleotide (NAD+), which affected the activity of deacetylases, such as sirtuin 1 (Sirt1). CONCLUSION: Our findings suggest that the beneficial effects of CycloZ on diabetes and obesity occur through increased NAD+ synthesis, which modulates Sirt1 deacetylase activity in the liver and VATs. Given that the mode of action of an NAD+ booster or Sirt1 deacetylase activator is different from that of traditional T2DM drugs, CycloZ would be considered a novel therapeutic option for the treatment of T2DM.

Enhanced Ca2+-channeling complex formation at the ER-mitochondria interface underlies the pathogenesis of alcohol-associated liver disease.

Ca2+ overload-induced mitochondrial dysfunction is considered as a major contributing factor in the pathogenesis of alcohol-associated liver disease (ALD). However, the initiating factors that drive mitochondrial Ca2+ accumulation in ALD remain elusive. Here, we demonstrate that an aberrant increase in hepatic GRP75-mediated mitochondria-associated ER membrane (MAM) Ca2+-channeling (MCC) complex formation promotes mitochondrial dysfunction in vitro and in male mouse model of ALD. Unbiased transcriptomic analysis reveals PDK4 as a prominently inducible MAM kinase in ALD. Analysis of human ALD cohorts further corroborate these findings. Additional mass spectrometry analysis unveils GRP75 as a downstream phosphorylation target of PDK4. Conversely, non-phosphorylatable GRP75 mutation or genetic ablation of PDK4 prevents alcohol-induced MCC complex formation and subsequent mitochondrial Ca2+ accumulation and dysfunction. Finally, ectopic induction of MAM formation reverses the protective effect of PDK4 deficiency in alcohol-induced liver injury. Together, our study defines a mediatory role of PDK4 in promoting mitochondrial dysfunction in ALD.

The Link between Mitochondrial Dysfunction and Sarcopenia: An Update Focusing on the Role of Pyruvate Dehydrogenase Kinase 4.

Sarcopenia, defined as a progressive loss of muscle mass and function, is typified by mitochondrial dysfunction and loss of mitochondrial resilience. Sarcopenia is associated not only with aging, but also with various metabolic diseases characterized by mitochondrial dyshomeostasis. Pyruvate dehydrogenase kinases (PDKs) are mitochondrial enzymes that inhibit the pyruvate dehydrogenase complex, which controls pyruvate entry into the tricarboxylic acid cycle and the subsequent adenosine triphosphate production required for normal cellular activities. PDK4 is upregulated in mitochondrial dysfunction-related metabolic diseases, especially pathologic muscle conditions associated with enhanced muscle proteolysis and aberrant myogenesis. Increases in PDK4 are associated with perturbation of mitochondria-associated membranes and mitochondrial quality control, which are emerging as a central mechanism in the pathogenesis of metabolic disease-associated muscle atrophy. Here, we review how mitochondrial dysfunction affects sarcopenia, focusing on the role of PDK4 in mitochondrial homeostasis. We discuss the molecular mechanisms underlying the effects of PDK4 on mitochondrial dysfunction in sarcopenia and show that targeting mitochondria could be a therapeutic target for treating sarcopenia.

Relationship between the High Fatty Liver Index and Risk of Fracture.

Background/Aims: The prevalence of nonalcoholic fatty liver disease (NAFLD) has increased rapidly as a consequence of more sedentary lifestyles and a Westernized diet. Fracture is a major clinical problem in older people, but few large-scale cohort studies have evaluated the relationship between NAFLD and fracture. Therefore, we aimed to determine whether the fatty liver index (FLI), which represents the severity of NAFLD, can predict fracture risk. Methods: We analyzed the relationship between the FLI and incident fracture using multivariate Cox proportional hazards models and data for 180,519 individuals who underwent National Health check-ups in the Republic of Korea between 2009 and 2014. Results: A total of 2,720 participants (1.5%) were newly diagnosed with fracture during the study period (median 4.6 years). The participants were grouped according to FLI quartiles (Q1, 0 to <5.653; Q2, 5.653 to <15.245; Q3, 15.245 to <37.199; and Q4 ≥37.199). The cumulative fracture incidence was significantly higher in the highest FLI group than in the lowest FLI group (Q4, 986 [2.2%] and Q1, 323 [0.7%]; p<0.001). The adjusted hazard ratio indicated that the highest FLI group was independently associated with a higher incidence of fracture (hazard ratio for Q4 vs Q1, 2.956; 95% confidence interval, 2.606 to 3.351; p<0.001). FLI was significantly associated with a higher incidence of fracture, independent of the baseline characteristics of the participants. Conclusions: Our data imply that the higher the FLI of a Korean patient is, the higher their risk of osteoporotic fracture, independent of key confounding factors. (Gut Liver, Published online July 27, 2022).

Inhibition of Pyruvate Dehydrogenase Kinase 4 in CD4+ T Cells Ameliorates Intestinal Inflammation.

BACKGROUND & AIMS: Despite recent evidence supporting the metabolic plasticity of CD4+ T cells, it is uncertain whether the metabolic checkpoint pyruvate dehydrogenase kinase (PDK) in T cells plays a role in the pathogenesis of colitis. METHODS: To investigate the role of PDK4 in colitis, we used dextran sulfate sodium (DSS)-induced colitis and T-cell transfer colitis models based on mice with constitutive knockout (KO) or CD4+ T-cell-specific KO of PDK4 (Pdk4fl/flCD4Cre). The effect of PDK4 deletion on T-cell activation was also studied in vitro. Furthermore, we examined the effects of a pharmacologic inhibitor of PDK4 on colitis. RESULTS: Expression of PDK4 increased during colitis development in a DSS-induced colitis model. Phosphorylated PDHE1α, a substrate of PDK4, accumulated in CD4+ T cells in the lamina propria of patients with inflammatory bowel disease. Both constitutive KO and CD4+ T-cell-specific deletion of PDK4 delayed DSS-induced colitis. Adoptive transfer of PDK4-deficient CD4+ T cells attenuated murine colitis, and PDK4 deficiency resulted in decreased activation of CD4+ T cells and attenuated aerobic glycolysis. Mechanistically, there were fewer endoplasmic reticulum-mitochondria contact sites, which are responsible for interorganelle calcium transfer, in PDK4-deficient CD4+ T cells. Consistent with this, GM-10395, a novel inhibitor of PDK4, suppressed T-cell activation by reducing endoplasmic reticulum-mitochondria calcium transfer, thereby ameliorating murine colitis. CONCLUSIONS: PDK4 deletion from CD4+ T cells mitigates colitis by metabolic and calcium signaling modulation, suggesting PDK4 as a potential therapeutic target for IBD.

Pyruvate dehydrogenase kinase 4 promotes ubiquitin-proteasome system-dependent muscle atrophy.

BACKGROUND: Muscle atrophy, leading to muscular dysfunction and weakness, is an adverse outcome of sustained period of glucocorticoids usage. However, the molecular mechanism underlying this detrimental condition is currently unclear. Pyruvate dehydrogenase kinase 4 (PDK4), a central regulator of cellular energy metabolism, is highly expressed in skeletal muscle and has been implicated in the pathogenesis of several diseases. The current study was designed to investigated and delineate the role of PDK4 in the context of muscle atrophy, which could be identified as a potential therapeutic avenue to protect against dexamethasone-induced muscle wasting. METHODS: The dexamethasone-induced muscle atrophy in C2C12 myotubes was evaluated at the molecular level by expression of key genes and proteins involved in myogenesis, using immunoblotting and qPCR analyses. Muscle dysfunction was studied in vivo in wild-type and PDK4 knockout mice treated with dexamethasone (25 mg/kg body weight, i.p., 10 days). Body weight, grip strength, muscle weight and muscle histology were assessed. The expression of myogenesis markers were analysed using qPCR, immunoblotting and immunoprecipitation. The study was extended to in vitro human skeletal muscle atrophy analysis. RESULTS: Knockdown of PDK4 was found to prevent glucocorticoid-induced muscle atrophy and dysfunction in C2C12 myotubes, which was indicated by induction of myogenin (0.3271 ± 0.102 vs 2.163 ± 0.192, ****P < 0.0001) and myosin heavy chain (0.3901 ± 0.047 vs. 0.7222 ± 0.082, **P < 0.01) protein levels and reduction of muscle atrophy F-box (10.77 ± 2.674 vs. 1.518 ± 0.172, **P < 0.01) expression. In dexamethasone-induced muscle atrophy model, mice with genetic ablation of PDK4 revealed increased muscle strength (162.1 ± 22.75 vs. 200.1 ± 37.09 g, ***P < 0.001) and muscle fibres (54.20 ± 11.85% vs. 84.07 ± 28.41%, ****P < 0.0001). To explore the mechanism, we performed coimmunoprecipitation and liquid chromatography-mass spectrometry analysis and found that myogenin is novel substrate of PDK4. PDK4 phosphorylates myogenin at S43/T57 amino acid residues, which facilitates the recruitment of muscle atrophy F-box to myogenin and leads to its subsequent ubiquitination and degradation. Finally, overexpression of non-phosphorylatable myogenin mutant using intramuscular injection prevented dexamethasone-induced muscle atrophy and preserved muscle fibres. CONCLUSIONS: We have demonstrated that PDK4 mediates dexamethasone-induced skeletal muscle atrophy. Mechanistically, PDK4 phosphorylates and degrades myogenin via recruitment of E3 ubiquitin ligase, muscle atrophy F-box. Rescue of muscle regeneration by genetic ablation of PDK4 or overexpression of non-phosphorylatable myogenin mutant indicates PDK4 as an amenable therapeutic target in muscle atrophy.

Noncanonical PDK4 action alters mitochondrial dynamics to affect the cellular respiratory status.

Dynamic regulation of mitochondrial morphology provides cells with the flexibility required to adapt and respond to electron transport chain (ETC) toxins and mitochondrial DNA-linked disease mutations, yet the mechanisms underpinning the regulation of mitochondrial dynamics machinery by these stimuli is poorly understood. Here, we show that pyruvate dehydrogenase kinase 4 (PDK4) is genetically required for cells to undergo rapid mitochondrial fragmentation when challenged with ETC toxins. Moreover, PDK4 overexpression was sufficient to promote mitochondrial fission even in the absence of mitochondrial stress. Importantly, we observed that the PDK4-mediated regulation of mitochondrial fission was independent of its canonical function, i.e., inhibitory phosphorylation of the pyruvate dehydrogenase complex (PDC). Phosphoproteomic screen for PDK4 substrates, followed by nonphosphorylatable and phosphomimetic mutations of the PDK4 site revealed cytoplasmic GTPase, Septin 2 (SEPT2), as the key effector molecule that acts as a receptor for DRP1 in the outer mitochondrial membrane to promote mitochondrial fission. Conversely, inhibition of the PDK4-SEPT2 axis could restore the balance in mitochondrial dynamics and reinvigorates cellular respiration in mitochondrial fusion factor, mitofusin 2-deficient cells. Furthermore, PDK4-mediated mitochondrial reshaping limits mitochondrial bioenergetics and supports cancer cell growth. Our results identify the PDK4-SEPT2-DRP1 axis as a regulator of mitochondrial function at the interface between cellular bioenergetics and mitochondrial dynamics.

Identification of New Non-BBB Permeable Tryptophan Hydroxylase Inhibitors for Treating Obesity and Fatty Liver Disease.

Serotonin (5-hydroxytryptophan) is a hormone that regulates emotions in the central nervous system. However, serotonin in the peripheral system is associated with obesity and fatty liver disease. Because serotonin cannot cross the blood-brain barrier (BBB), we focused on identifying new tryptophan hydroxylase type I (TPH1) inhibitors that act only in peripheral tissues for treating obesity and fatty liver disease without affecting the central nervous system. Structural optimization inspired by para-chlorophenylalanine (pCPA) resulted in the identification of a series of oxyphenylalanine and heterocyclic phenylalanine derivatives as TPH1 inhibitors. Among these compounds, compound 18i with an IC50 value of 37 nM was the most active in vitro. Additionally, compound 18i showed good liver microsomal stability and did not significantly inhibit CYP and Herg. Furthermore, this TPH1 inhibitor was able to actively interact with the peripheral system without penetrating the BBB. Compound 18i and its prodrug reduced body weight gain in mammals and decreased in vivo fat accumulation.

Synthesis and biological evaluation of tyrosine derivatives as peripheral 5HT2A receptor antagonists for nonalcoholic fatty liver disease.

Non-alcoholic fatty liver disease (NAFLD), attributed to excessive fat accumulation in the liver, is reportedly prevalent worldwide. NAFLD is one of the leading causes of chronic liver disease, including non-alcoholic steatohepatitis (NASH), cirrhosis, and hepatic cellular carcinoma (HCC). The peripheral roles of serotonin (5-hydroxytryptamine, 5HT) were found to regulate hepatic lipid metabolism. Among serotonin receptor subtypes, 5HT2A receptor is known to regulate hepatic lipid metabolism. Hepatic lipid accumulation and hepatic triglyceride (TG) were reduced in liver-specific 5HT2A receptor knockout (5HT2A receptor LKO) mice upon high-fat diet (HFD) feeding. In the present study, we explored a series of new peripherally acting 5HT2A receptor antagonists. Compound 14a displayed good in vitro activity, with an IC50 value of 0.17 nM. Compound 14a exhibited good microsomal stability, no significant CYP and hERG inhibition, and 5HT receptor subtype selectivity. The brain-to-plasma ratio of 14a was below the lower limit of quantification, indicating limited blood-brain barrier (BBB) penetration. HFD-fed 14a treated mice showed decreased liver steatosis and lobular inflammation. These results demonstrate the potential of newly synthesized peripheral 5HT2A receptor antagonists for treating NAFLD.