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Metabolism Master Chart Study Notes

Section 1: Hepatic–Adipose Axis & Gluconeogenesis Control

  • Adiponectin Effects
    • Activates AMPK
    • ext{AMPK}
      ightarrow ext{decreased Malonyl-CoA}
      ightarrow ext{increased } eta ext{-oxidation}
    • Analogy: "AMPK flips switch: burns fat, lowers glu"
    • Effects in Insulin-Resistant Hepatocytes
    • FOXO1 Failure:
      • Failed to exit the nucleus. This failure leads to:
      • extIncreasedPEPCK+extG6PaseremainONext{Increased PEPCK} + ext{G6Pase remain ON}
      • Analogy: "Fox keeps faucet on"
  • ACC Gain-of-Function
    • Functionality: Increases Malonyl-CoA levels leading to:
    • ext{decreased CPT1}
      ightarrow ext{decreased } eta ext{-oxidation, increased fatty acid synthesis}
    • Analogy: "More ACC → fat storage, less burn"

Section 2: CNS & Neuroendocrine Regulation

  • Insulin's Effect on POMC Neurons
    • Mechanism: Vagal efferents are involved in inhibiting hepatic gluconeogenic genes.
    • Analogy: "Brain tells liver to chill"
  • Leptin Resistance
    • Consequences:
    • NPY/AgRP (neuropeptide Y/Agouti-related peptide) are not suppressed.
    • Leads to:
      • Increased feeding
      • Increased insulin demand
    • Analogy: "Leptin mute → hunger & hyperinsulin"

Section 3: Skeletal Muscle Mitochondrial Defects

  • Reduced PGC-1α in Muscle
    • Effect: Decrease in mitochondrial biogenesis leading to:
    • Increased DAG (Diacylglycerol) and Ceramide levels leading to:
      • extdecreasedAktext{decreased Akt}
      • Analogy: "Weak mitochondria → IR → fat backup → sig"
  • High ATP:ADP Ratio in Muscle
    • Consequences:
    • Inhibits hexokinase leading to:
      • extdecreasedglucosephosphorylationext{decreased glucose phosphorylation}
      • Analogy: "High energy = no sugar entry"
  • Uptake Decrease: Resulting reduction in glucose uptake.

Section 4: Renal Glucose Metabolism Beyond SGLT2

  • Poorly Controlled T2DM Kidneys
    • Mechanism:
    • Increased PEPCK and SGLT2 leading to:
      • Increased gluconeogenesis and reabsorption
      • Analogy: "Kidney joins liver in making sugar"
  • Metformin + SGLT2i
    • Mechanism:
    • Decreases hepatic gluconeogenesis while increasing urinary glucose excretion.
    • Analogy: "Double attack: liver + pee out sugar"

Section 5: β-Cell Stress, UPR, Apoptosis

  • Chronic ER Stress
    • Pathway: Involves PERK–eIF2A α–CHOP leading to:
    • Translational arrest
    • Activation of pro-apoptotic genes
    • Analogy: "ER stress hits beta-cells hard"
  • Role of IL-1β Cytokines
    • Mechanism:
    • Inducible nitric oxide synthase (iNOS) produces nitric oxide leading to:
      • Mitochondrial damage and dysfunction
    • Analogy: "Cytokine sabotage → beta-cells suffer"

Section 6: Lipid–Glucose Cross-Talk & Metabolic Integration

  • Randle Cycle FFA Effect
    • Consequences:
    • High free fatty acids (FFA) result in increased citrate, which leads to:
      • Inhibition of PFK-1 (Phosphofructokinase-1) and PDH (Pyruvate dehydrogenase)
      • Analogy: "Fat blocks sugar burning"
  • Excess Citrate Export
    • Mechanism:
    • Activates ACC leading to increased lipogenesis.
    • Analogy: "Citrate → fat factory"

Section 7: Molecular Pharmacology of Antidiabetic Drugs

  • DPP-4 Inhibitors
    • Functionality:
    • Prevent degradation of cytokines leading to alterations in T-cell signaling.
    • Analogy: "Keeps cytokines in check"
  • Dual SGLT1/2 Inhibitors
    • GI Effects:
    • Block SGLT1 leading to less intestinal glucose absorption.
    • Analogy: "Sugar stays in gut → fermentation → bloating"

Section 8: Systemic Integration & Clinical Research Logic

  • AMPK Activation Metabolites
    • Effects:
    • Decreased levels of glucose, triglycerides (TG), FFAs and increased lactate.
    • Analogy: "AMPK cleans up sugar & fat"
  • Hepatic Glycogen in Early T2DM
    • Observation:
    • Insulin continues to stimulate glycogen synthase despite ongoing gluconeogenesis.
    • Analogy: "Liver hoards sugar"
  • Endothelial Dysfunction
    • Consequences: Decreased eNOS (endothelial nitric oxide synthase), increased ET-1 (endothelin-1) and ROS (reactive oxygen species) leading to vascular insulin resistance.
    • Analogy: "Vessels under attack"

Section 9: Integrative Research & Translational Concepts

  • Metformin + GLP-1 Agonist
    • Mechanism:
    • Targets AMPK–mTOR (mammalian Target of Rapamycin) and cAMP–PKA–CREB pathways for liver and beta-cell benefits.
    • Analogy: "Double pathway therapy"

Additional Insights

  • Insulin + Glucagon Paradox in Hepatocytes
    • Observation:
    • There is simultaneous lipogenesis and gluconeogenesis occurring in the liver, leading to confusion within the metabolic pathways.
    • Analogy: "Liver confused: make fat & sugar"