Biology subjects

Knop, F. K.

Publications and source records attributed to Knop, F. K..

6 recordsLinked to original sources

bioRxiv2026

Proteomic profiling of experimental acute alcohol intoxication reveals FGF21 as a specific ethanol-induced hormone

Background: The effects of acute alcohol intoxication on the human plasma proteome are still largely unexplored. Gaining insights into this relationship could identify factors that are influenced by and influence alcohol consumption. Fibroblast Growth Factor 21 (FGF21), a hormone produced by the liver and associated with alcohol preferences, is currently undergoing Phase 2 clinical trials for metabolic dysfunction and alcohol-related liver disease. We hypothesized that FGF21 is a key endocrine responsive hormone to alcohol in humans. Methods: In a post hoc analysis, we evaluated the effects of five standard units of alcoholic beverages on the plasma proteome in 12 healthy Caucasian men. Participants, fasting for 10 hours, received 0.7 g of alcohol per kg of body weight via gastric infusion, with blood samples collected before and after consumption. Results: The proteomic response to this level of alcohol intoxication was highly specific. Of 1,462 proteins measured, only 11 changed significantly and FGF21 exhibited by far the largest increase (10.5-fold). Conclusion: This study highlights a unique proteomic response to acute alcohol ingestion and supports further exploration of FGF21 mimetics as potential treatments for alcohol-related disorders.

physiology↗

bioRxiv2026

A loss-of-function variant in GFRAL associates with increased alcohol consumption in humans

Alcohol is an ancient and enduring component of the human diet, yet it is a dose-dependent cytotoxin and teratogen, raising the possibility that endogenous, state-dependent mechanisms constrain intake. Growth differentiation factor 15 (GDF15) is an endocrine hormone that rises during pregnancy--predominantly via secretion from blastocyst-derived placental trophoblasts into the maternal circulation--and is also induced in other tissues, particularly hepatocytes, by toxins and cellular stress. However, its function in humans remains unclear. Here, we show that circulating GDF15 levels are elevated 5-fold in individuals with alcohol dependence, identify a rare loss-of-function variant in the GDF15 receptor gene GFRAL associated with approximately 2.6 additional UK alcohol units ([~]21 g ethanol) per week, and demonstrate that recombinant GDF15 reduces alcohol drinking in mice. Collectively, these findings support a model in which GDF15 acts as an endocrine signal induced by chronic alcohol exposure--and potentially during pregnancy--to limit alcohol intake in humans. HighlightsO_LIGDF15 is markedly elevated in humans with alcohol dependence C_LIO_LIA truncating GFRAL variant associates with higher alcohol intake in UK Biobank C_LIO_LIGFRAL frameshift disrupts GDF15-RET signaling in vitro C_LIO_LIRecombinant GDF15 suppresses voluntary alcohol intake in mice C_LI Graphical abstract O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=152 SRC="FIGDIR/small/709997v1_ufig1.gif" ALT="Figure 1"> View larger version (50K): org.highwire.dtl.DTLVardef@13630fborg.highwire.dtl.DTLVardef@c9bebforg.highwire.dtl.DTLVardef@109fd63org.highwire.dtl.DTLVardef@da971f_HPS_FORMAT_FIGEXP M_FIG C_FIG

physiology↗

bioRxiv2024

Proinflammatory cytokine-induced alpha-cell impairment in human islet microtissues is partially restored by dual incretin receptor agonism

Aims/hypothesisIn type 1 diabetes, the counterregulatory glucagon response to low plasma glucose is impaired. The resulting increased risk of hypoglycaemia necessitates novel strategies to ameliorate alpha-cell impairment. Here, we aimed to establish an in vitro model of alpha-cell impairment in type 1 diabetes using human islet microtissues (MTs) exposed to proinflammatory cytokines. Additionally, we investigated the therapeutic potential of incretin receptor agonists in improving alpha-cell responses to low glucose. MethodsHuman islet MTs were exposed to proinflammatory cytokines (IL-1{beta}, IFN-{gamma}, and TNF-) for 1 day (short-term) and 6 days (long-term). Alpha-cell function was assessed by sequential glucose-dependent secretion assays at 2.8 and 16.7 mmol/l glucose, followed by glucagon measurements. Additional evaluations included ATP content, caspase-3/7 activity, chemokine secretion, and expression of islet transcription factors and hormones. The effects of incretin receptor agonist treatment (glucose-dependent insulinotropic polypeptide (GIP) analogue [D-Ala2]-GIP {+/-} liraglutide) alongside or after cytokine exposure were also investigated, focusing on low glucose-dependent glucagon secretion. ResultsShort-term cytokine exposure increased glucagon secretion at both 2.8 and 16.7 mmol/l glucose. In contrast, long-term cytokine exposure caused dose-dependent suppression of glucagon secretion at 2.8 mmol/l glucose, resembling a type 1 diabetes phenotype. Long-term cytokine exposure also diminished somatostatin secretion, reduced ATP content, increased caspase 3/7 activity, and decreased islet transcription factor and hormone expression. Despite cytokine-induced impairment, alpha cells partially retained secretory capacity to L-arginine stimulation. Treatment with incretin receptor agonists during long-term cytokine exposure did not prevent alpha-cell impairment. However, acute treatment with [D-Ala2]-GIP {+/-} liraglutide or the single-molecule dual agonist tirzepatide partially restored glucagon secretion at low glucose. Conclusions/interpretationLong-term cytokine exposure of human islet MTs impaired glucagon secretion to low glucose, creating a type 1 diabetes alpha-cell phenotype. This cytokine-induced alpha-cell impairment was partially restored by [D-Ala2]-GIP {+/-} liraglutide and tirzepatide, respectively. Research in contextO_ST_ABSWhat is already known about this subject?C_ST_ABSO_LIThe counterregulatory alpha-cell response to low glucose is impaired in type 1 diabetes, increasing the risk of hypoglycaemia. C_LIO_LILimited translatability of rodent islet findings highlights the need for human islet models. C_LIO_LIActions of the incretin hormones glucose-dependent insulinotropic polypeptide (GIP) and glucagon-like peptide 1 (GLP-1) have mainly been studied in the context of type 2 diabetes and hyperglycaemia but less in type 1 diabetes and hypoglycaemia. C_LI What is the key question?O_LICan alpha-cell impairment in type 1 diabetes be modelled in vitro by exposing human islet microtissues (MTs) to proinflammatory cytokines, and could incretins protect against this? C_LI What are the new findings?O_LILong-term (6-day) exposure to proinflammatory cytokines produces a type 1 diabetes phenotype of alpha-cell impairment to low glucose in islet MTs C_LIO_LIAcute dual treatment with incretin receptor agonists partially restored glucose-dependent glucagon secretion in cytokine-exposed islet MTs -- an effect mainly carried by GIP receptor agonism and not opposed by GLP-1 receptor agonism. C_LI How might this impact on clinical practice in the foreseeable future?O_LIInvestigating incretin receptor agonists in a preclinical in vitro model of alpha-cell impairment may reveal their potential and fast-track their use as safeguards against hypoglycaemia in type 1 diabetes. C_LI

cell biology↗

bioRxiv2024

Exploring the functional, protective, and transcriptomic effects of GIP on cytokine-exposed human pancreatic islets and EndoC-βH5 cells

Immune-mediated beta-cell destruction and lack of alpha-cell responsiveness to hypoglycaemia are hallmarks of type 1 diabetes pathology. The incretin hormone glucose-dependent insulinotropic polypeptide (GIP) may hold therapeutic potential for type 1 diabetes due to its insulinotropic and glucagonotropic effects, as well as its beta-cell protective effects shown in rodent islets. Here, we examined the functional, protective, and transcriptomic effects of GIP treatment upon diabetogenic cytokine exposure to interleukin (IL)-1{beta} {+/-} interferon (IFN)-{gamma} in human EndoC-{beta}H5 beta cells and isolated human islets, respectively. GIP dose-dependently augmented glucose-stimulated insulin secretion from EndoC-{beta}H5 cells and increased insulin and glucagon secretion from human islets during high and low glucose concentrations, respectively. The insulinotropic effect of GIP in EndoC-{beta}H5 cells was abrogated by KN-93, an inhibitor of calcium/calmodulin-dependent protein kinase 2 (CaMK2). GIP did not prevent cytokine-induced apoptosis or cytokine-induced functional impairment of human EndoC-{beta}H5 cells. GIP also did not prevent cytokine-induced apoptosis in human islets. GIP treatment of human islets with or without cytokines for 24 hours did not significantly impact the transcriptome. GIP potentiated cytokine-induced secretion of IL-10 and c-c motif chemokine ligand (CCL)-2 from human islets while decreasing the secretion of c-x-c motif chemokine ligand (CXCL)-8. In EndoC-{beta}H5 cells, GIP reduced IFN-{gamma}-induced secretion of tumor necrosis factor (TNF)-, IL-2, IL-6, and IL-10 but increased the secretion of CXCL8, CCL2, CCL4, and CCL11. In conclusion, our results suggest that the insulinotropic effect of GIP is CaMK2-dependent. Furthermore, our results indicate that GIP does not provide substantial cytoprotective effects against diabetogenic cytokine challenge or significantly modulate the transcriptome of human islets when applied at a supraphysiological level. GIP may, however, still exert selective inflammation-modulatory effects upon diabetogenic cytokine exposure.

cell biology↗

bioRxiv2020

AVP-induced counter-regulatory glucagon is diminished in type 1 diabetes

Insulin-induced hypoglycemia is a major barrier to the treatment of type-1 diabetes (T1D). Accordingly, it is important that we understand the mechanisms regulating the circulating levels of glucagon - the bodys principal blood glucose-elevating hormone which is secreted from alpha-cells of the pancreatic islets. Varying glucose over the range of concentrations that occur physiologically between the fed and fuel-deprived states (from 8 to 4 mM) has no significant effect on glucagon secretion in isolated islets (in vitro) and yet associates with dramatic changes in plasma glucagon in vivo. The identity of the systemic factor(s) that stimulates glucagon secretion remains unknown. Here, we show that arginine-vasopressin (AVP), secreted from the posterior pituitary, stimulates glucagon secretion. Glucagon-secreting alpha-cells express high levels of the vasopressin 1b receptor gene (Avpr1b). Activation of AVP neurons in vivo increased circulating copeptin (the C-terminal segment of the AVP precursor peptide, a stable surrogate marker of AVP) and increased blood glucose; effects blocked by pharmacological antagonism of either the glucagon receptor or vasopressin 1b receptor. AVP also mediates the stimulatory effects of hypoglycemia produced by exogenous insulin and 2-deoxy-D-glucose on glucagon secretion. We show that the A1/C1 neurons of the medulla oblongata drive AVP neuron activation in response to insulin-induced hypoglycemia. Exogenous injection of AVP in vivo increased cytoplasmic Ca2+ in alpha-cells (implanted into the anterior chamber of the eye) and glucagon release. Hypoglycemia also increases circulating levels of AVP in humans and this hormone stimulates glucagon secretion from isolated human islets. In patients with T1D, hypoglycemia failed to increase both plasma copeptin and glucagon levels. These findings suggest that AVP is a physiological systemic regulator of glucagon secretion and that this mechanism becomes impaired in T1D.

cell biology↗

bioRxiv2018

FGF21, a liver hormone that inhibits alcohol intake in mice, increases in human circulation after acute alcohol ingestion and sustained binge drinking at Oktoberfest

ObjectiveExcessive alcohol consumption is a leading cause of global morbidity and mortality. However, knowledge of the biological factors that influence ad libitum alcohol intake may be incomplete. Two large studies recently linked variants in the KLB locus with levels of alcohol intake in humans. KLB encodes {beta}-klotho, co-receptor for the liver-derived hormone fibroblast growth factor 21 (FGF21). In mice, FGF21 reduces alcohol intake, and human Fgf21 variants are enriched among heavy drinkers. Thus, the liver may limit alcohol consumption by secreting FGF21. However, whether full-length, active plasma FGF21 (FGF21 (1-181)) levels in humans increase acutely or sub-chronically in response to alcohol ingestion is uncertain.\n\nMethodsWe recruited 10 healthy, fasted male subjects to receive an oral water or alcohol bolus with concurrent blood sampling for FGF21 (1-181) measurement in plasma. In addition, we measured circulating FGF21 (1-181) levels, liver stiffness, triglyceride, and other metabolic parameters in three healthy Danish men before and after consuming an average of 22.6 beers/person/day (4.4 g/kg/day of ethanol) for three days during Oktoberfest 2017 in Munich, Germany. We further correlated fasting FGF21 (1-181) levels in 49 healthy, non-alcoholic subjects of mixed sex with self-reports of alcohol-related behaviors, emotional responses, and problems. Finally, we characterized the effect of recombinant human FGF21 injection on ad libitum alcohol intake in mice.\n\nResultsWe show that alcohol ingestion (25.3 grams or ~2.5 standard drinks) acutely increases plasma levels of FGF21 (1-181) 3.4-fold in fasting humans. We also find that binge drinking for three days at Oktoberfest is associated with a 2.1-fold increase in baseline FGF21 (1-181) levels, in contrast to minor deteriorations in metabolic and hepatic biomarkers. However, basal FGF21 (1-181) levels were not correlated with differences in alcohol-related behaviors, emotional responses, or problems in our non-alcoholic subjects. Finally, we show that once-daily injection of recombinant human FGF21 reduces ad libitum alcohol intake by 21% in mice.\n\nConclusionsFGF21 (1-181) is markedly increased in circulation by both acute and sub-chronic alcohol intake in humans, and reduces alcohol intake in mice. These observations are consistent with a role for FGF21 as an endocrine inhibitor of alcohol appetite in humans.

physiology↗