Diabetes Mellitus: Intracellular & Metabolic Pathways
| Sorbitol Osmotic Damage: | Aldose Reductase (Glucose → Sorbitol) |
| DKA Ketogenesis Marker: | HMG-CoA Synthase (Mitochondrial rate-limiting step) |
| Plasma Lipid Elevation Mechanism: | Hormone-Sensitive Lipase (HSL) (Unchecked lipolysis) |
| Long-Term Tissue Marker: | Advanced Glycation End-products (AGEs) (Non-enzymatic) |
High-Yield Core Realities:
- The Polyol Pathway Trap: Lens, retina, kidneys, and Schwann cells lack Sorbitol Dehydrogenase. In severe hyperglycemia, intracellular glucose shifts to Aldose Reductase, generating sorbitol. Sorbitol cannot cross membranes, driving osmotic fluid shifts that lead to cataracts, retinopathy, nephropathy, and peripheral neuropathy.
- Diabetic Ketoacidosis (DKA) Shift: Complete insulin deficiency yields hyperactive Hormone-Sensitive Lipase (HSL) in adipose tissue. Free fatty acids pour into the liver and undergo β-oxidation, generating excess Acetyl-CoA that overwhelms the TCA cycle and diverts exclusively into producing Acetoacetate and β-Hydroxybutyrate.
- Non-Enzymatic Glycation (AGEs): Chronic hyperglycemia drives a direct, chemical bond between glucose and amino groups on proteins (e.g., hemoglobin → HbA1c). AGEs cross-link collagen in basement membranes, causing microvascular basement membrane thickening and accelerated atherosclerosis.
- Counter-Regulatory Hormone Surge: The absence of effective insulin signaling triggers massive secretion of glucagon, epinephrine, and cortisol, upregulating Pyruvate Carboxylase and PEPCK to drive unchecked hepatic gluconeogenesis, compounding systemic hyperglycemia.
- Intracellular Protein Kinase C (PKC) Activation: Elevated glucose shifts intermediates into the diacylglycerol (DAG) pathway, activating PKC. This triggers increased synthesis of VEGF (causing diabetic retinopathy neovascularization) and endothelin-1 (inducing microvascular vasoconstriction).