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Principal Investigator: VARMAN T SAMUEL
Organization: VA CONNECTICUT HEALTHCARE SYSTEM
Fiscal Year: 2024
Funding agency: Veterans Affairs
Increased fructose consumption has been implicated in many diseases, including type 2 diabetes, nonalcoholic
fatty liver disease and cardiovascular disease. Pharmaceutical companies are designing inhibitors against
ketohexokinase (KHK), the primary enzyme for fructose metabolism. Most studies have used higher doses of
fructose than humans consume. We do not fully understand the mechanisms by which moderate fructose
consumption impact metabolism and how KHK inhibition would improve metabolism in these conditions.
Preliminary data suggest that modest dietary fructose metabolism may primarily impair adipose, not hepatic,
function. Using an antisense oligonucleotide (ASO) against KHK, we studied rats fed: a low-fat “regular” chow
providing 15% calories from fructose and a high-fat diet providing 8% calories from fructose. KHK ASO improved
adipose insulin action in both conditions. Our overarching hypothesis is modest amounts of dietary fructose
increases hepatic VLDL production which can impair adipose insulin sensitivity leading to adipose dysfunction.
Fructose induced adipose dysfunction can then indirectly impact hepatic glucose and lipid metabolism. We will
leverage our expertise in in vivo metabolism and explorations of lipid mediated insulin resistance –that the
accumulation of sn 1,2 diacyglycerol (DAG) in the plasma membrane recruits protein kinase C ε (PKCε) which
then phosphorylates and impairs insulin receptor kinase (IRK) activation—to probe this novel aspect of fructose
metabolism. Aim 1) To determine the mechanism of fructose mediated adipose insulin resistance. We
will teAbsst the hypothesis that fructose mediated hepatic lipogenesis into VLDL triglyceride exceeds the
capacity for WAT esterification, leading to the accumulation of adipose sn 1,2 diacylglycerol and WAT insulin
resistance. Rats will be fed isocaloric low-fat diets with increasing sucrose content (accounting for 0, 5, 10 and
15% calories from fructose) to determine the threshold at which adipose sn 1,2 DAG accumulates and activates
PKCε in relation to insulin signaling and insulin action in vivo. Using KHK ASO, we will establish that blocking
fructose metabolism prevents adipose insulin resistance. We will further demonstrate that blocking hepatic KHK
is sufficient to prevent adipose insulin resistance using a liver-specific GalNAc modified ASO. Aim 2) To
determine the role of high-fat diets in potentiating fructose mediated adipose dysfunction. We will test
the hypothesis that the addition of dietary fat reduces the “safe threshold” for dietary fructose. Dietary fats may
constrain the ability of adipose tissue to handle fructose derived VLDL triglyceride. In addition, preliminary data
suggests the combination of fat and fructose increase expression of 11β hydroxysteroid dehydrogenase 1,
potentially another mechanism accounting for fructose induced adipose dysfunction and asses changes after a
long term (24 week) exposure to high-fat, fructose diets. Aim 3) To assess the mechanisms by which KHK
ASO impacts hepatic insulin action. KHK ASO decreases basal Gck expression and glycogen synthesis via
the direct pathway after an oral glucose load. Fructose metabolism will increase the concentration of hepatic
dihydroxyacetone phosphate, a putative activator of mTORC1. This in turn could increase SREBP1c mediated
activation of glucokinase (Gck) which would raise the capacity for glycogen synthesis via the direct pathway.
KHK inhibition may alter the pathways that support glycogen synthesis with an increase in the indirect, or
gluconeogenic pathway, balancing a decrease in the direct pathway (which is dependent on Gck). We will use
a combination of in vitro and in vivo approaches to establish the role of fructose metabolism in regulating Gck
expression through mTORC1 activation. Further, we will determine if KHK inhibition leads to increase Cori and
Cahill cycling and the potential for increased lactate flux when used with metformin.
Terms: <1,2,3-Propanetriol><1,2,3-Trihydroxypropane><1,2-Diacylglycerol Kinase><1,2-diacylglycerol><ADD-1 protein><ADD1 protein><Accounting><Adipocytes><Adipose Cell><Adipose tissue><Adult-Onset Diabetes Mellitus><Affect><Alanine><Antisense Agent><Antisense Oligonucleotides><Biological><Body Tissues><Calories><Cardiovascular Diseases><Causality><Cell Communication and Signaling><Cell Signaling><Cell membrane><Chylomicrons><Common Rat Strains><Consumption><Cytoplasmic Membrane><D-Glucose><DAG Kinase><Data><Dextrose><Diacylglycerol Kinase><Diacylglycerols><Diet><Dietary Fats><Diglyceride Kinase><Diglycerides><Dihydroxyacetone Phosphate><Dimethylbiguanidine><Dimethylguanylguanidine><Disease><Disorder><Dose><Dysfunction><Enzyme Gene><Enzymes><Esterification><Etiology><Euglycemic Clamping><Exposure to><Fat Cells><Fat-Restricted Diet><Fats><Fatty Tissue><Fatty acid glycerol esters><Fructose><Functional disorder><Glucokinase><Glucose><Glucose Clamp><Glycerin><Glycerol><Glycogen><Hepatic><Hepatic Glycogen><High Fat Diet><Human><Humulin R><Hydroxysteroid Dehydrogenases><Hyperinsulinemia><Hyperinsulinism><Impairment><In Vitro><Inflammation><Insulin><Insulin Receptor><Insulin Receptor Protein-Tyrosine Kinase><Insulin Resistance><Insulin-Dependent Tyrosine Protein Kinase><Intermediary Metabolism><Intestinal><Intestines><Intracellular Communication and Signaling><Investigators><Isoforms><Isotopes><Ketohexokinase><Ketosis-Resistant Diabetes Mellitus><Kidney><Kidney Urinary System><Kinases><Leucine><Levulose><Link><Lipids><Lipocytes><Lipolysis><Liver><Liver Glycogen><Low-Fat Diet><Mature Lipocyte><Mature fat cell><Maturity-Onset Diabetes Mellitus><Mediating><Metabolic Diseases><Metabolic Disorder><Metabolic Processes><Metabolism><Metformin><Modern Man><Molecular Analysis><N,N-dimethyl-imidodicarbonimidic diamide><NAFLD><NIDDM><Non-Insulin Dependent Diabetes><Non-Insulin-Dependent Diabetes Mellitus><Noninsulin Dependent Diabetes><Noninsulin Dependent Diabetes Mellitus><Novolin R><Nutrient><Oral><PKC epsilon><Pathway interactions><Pharmaceutical Agent><Pharmaceuticals><Pharmacologic Substance><Pharmacological Substance><Phosphorylation><Phosphotransferase Gene><Phosphotransferases><Physiopathology><Plasma Membrane><Prebeta-Lipoproteins><Production><Protein Isoforms><Protein Phosphorylation><Rat><Rats Mammals><Rattus><Regular Insulin><Research Personnel><Researchers><Rodent><Rodentia><Rodents Mammals><Role><SREBP-1c><Saccharose><Signal Transduction><Signal Transduction Systems><Signaling><Slow-Onset Diabetes Mellitus><Stable Diabetes Mellitus><Sucrose><T2 DM><T2D><T2DM><Techniques><Testing><Thesaurismosis><Tissues><Transphosphorylases><Triacylglycerol><Triglycerides><Type 2 Diabetes Mellitus><Type 2 diabetes><Type II Diabetes Mellitus><Type II diabetes><VLDL><VLDL Lipoproteins><VLDL triacylglycerol><VLDL triglyceride><VLDL triglyceride lipoprotein><Very low density lipoprotein><adipogenesis><adipose><adult onset diabetes><antisense oligo><biologic><biological signal transduction><bowel><cardiovascular disorder><causation><design><designing><diacylglycerol><dietary><dietary lipid><diets><diglyceride><disease causation><fat metabolism><glucose metabolism><glucose uptake><hepatic body system><hepatic metabolism><hepatic organ system><improved><in vivo><inhibitor><insight><insulin resistant><insulin sensitivity><insulin signaling><insulin tolerance><ketosis resistant diabetes><lipid biosynthesis><lipid metabolism><lipidomics><lipogenesis><liver metabolism><maturity onset diabetes><metabolism disorder><non-alcohol fatty liver disease><non-alcoholic fatty liver disease><non-alcoholic liver disease><nonalcoholic fatty liver disease><novel><obesigenic><obesogenic><pathophysiology><pathway><pharmaceutical><plasmalemma><prevent><preventing><protein kinase C epsilon><recruit><renal><social role><sterol regulatory element binding protein-1c><sugar><transcription factor ADD1><type 2 DM><type II DM><type two diabetes><uptake><very low density lipoprotein triglyceride><white adipose tissue><yellow adipose tissue>