Insulin resistance
See Article on insulin, if necessary, to better understand present article.
As described in the 2013 Medical Subject Headings of the National Library of Medicine, insulin resistance consists of
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Diminished effectiveness of insulin in lowering blood sugar [glucose][Note 1] levels: requiring the use of 200 units or more of insulin per day to prevent hyperglycemia or ketosis.[1] |
Christos Mantzoros, writing in UpToDate, offers:[2]
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Insulin resistance can be broadly defined as a subnormal biological response to normal insulin concentrations. By this definition, it may pertain to many biological actions of insulin in many tissues of the body. Typically, however, in clinical practice, insulin resistance refers to a state in which a given concentration of insulin is associated with a subnormal glucose response [i.e., subnormal reduction in plasma glucose concentration] [cites: Moller DE, Flier JS. Insulin resistance--mechanisms, syndromes, and implications. N Engl J Med 1991; 325:938.]. |
Insulin resistance consists in part of reduced action of insulin on its major target tissues involved in glucose homeostasis—skeletal muscle, adipose tissue, and liver. Insulin resistance manifests as reduced insulin-induced uptake of glucose, largely in skeletal muscle.[3] In people who have not developed the characteristic phenotype of type 2 diabetes mellitus (T2DM), prospective studies reveal insulin resistance as the strongest predictor of T2DM subsequent development. (See[4] and the references cited therein.) (See also[5]).
Metabolic and physiologic consequences of pathologic insulin resistance
The normal action of insulin to increase cellular uptake of glucose from plasma involves the delivery of an intracellular glucose transporter, a protein called GLUT4, to the cell membrane. GLUT4 proteins remain in storage in intracellular vesicles, endosomes, until insulin, through a series of biochemical steps initiated by insulin acting on its cell membrane receptor, stimulates the GLUT4-containing endosomes to deliver the glucose uptake transporter to the cell membrane. In the circumstance of insulin resistance, characterized by abnormally high plasma glucose concentrations, maintaining an adequate delivery of GLUT4 to the cell membrane to facilitate glucose uptake requires abnormally high plasma insulin concentrations. The hyperglycemia that results from insulin resistance helps to achieve those abnormally high plasma insulin concentrations by overstimulation of insulin secretion by cells in the pancreas. Over time, insulin resistant persons experience abnormally high integrated levels of both glucose and insulin in the systemic circulation, accompanied by multi-system glucose and insulin toxicity.
Hyperglycemia toxicity
Hyperinsulinemia toxicity
Causes of insulin resistance
It can be caused by the presence of insulin antibodies or the abnormalities in insulin receptors (receptor, insulin) on target cell surfaces. It is often associated with obesity; diabetic ketoacidosis; infection; and certain rare conditions.
Role of obesity
Role of Inflammation
Role of lipid metabolism
Role of gastrointestinal microbiota
Role of systemic acid-base status
Role of potassium
Methods of detecting and quantifying insulin resistance
• Euglycemic hyperinsulinemic clamp
• HOMA-IR: homeostasis model assessment of insulin resistance
Insulin resistance (HOMA-IR) can be measured by:[6]
• HOMA2
HOMA calculator.[7]
• Hyperglycemic clamp
• Oral glucose tolerance test
• Intravenous glucose tolerance test
Notes
- ↑ Glucose belongs to the class of nutrients called carbohydrates, combinations of carbon (C) and water (H2O):
C6(H20)6
C6H12O6
Molecular weight (molar mass) of glucose: 180.15588 (~180.2) g/mol, or 180.2 mg/mmol, calculated as the sum of the number of atoms per molecule of glucose times the atomic weights of: carbon (C) * 6, hydrogen (H) * 12, oxygen (O) * 6: (12 * 6) + (1 * 12) + (16 * 6) = ~180.2
The concentration of glucose in blood plasma, usually expressed in U.S. as milligrams/deciliter (mg/dl), where deciliter equals one-tenth of a liter (L), or 100 milliliters (100 ml).
However, the standard unit for plasma glucose: mmol/L.
To convert mg/dl to mmol/L, divide by 18:
- N mg glucose/dL = N mg glucose/100 ml
- N mg glucose/100 ml = N mg glucose/ 0.1 L
- N mg glucose/0.1 L / 180.2 mg glucose/mmol glucose = N mmol glucose/0.1 *180.2 mmol glucose/L
- N mmol glucose/0.1 *180.2 mmol glucose/L = N mmol glucose/L/0.1*180.2
- N mmol glucose/L/0.1*180.2 = (N/18) mmol glucose
Conversely, to convert mmol glucose/L to mg glucose/dl, multiply by 18.
References
- ↑ Insulin Resistance. National Library of Medicine.
- ↑ Mantzoros C. (2012) Insulin resistance: Definition and clinical spectrum. UpToDate. Topic 1762. Version 4.
- ↑
Shulman GI, Rothman DL, Jue T, Stein P, DeFronzo RA, Shulman RG. (1990) Quantitation of muscle glycogen synthesis in normal subjects and subjects with non-insulin-dependent diabetes by 13C nuclear magnetic resonance spectroscopy. N Engl J Med 322:223-8.
- The mean glucose uptake was markedly reduced in the diabetic (30±4 mumol per kilogram per minute) as compared with the normal subjects (51±3 mumol per kilogram per minute; P less than 0.005). The mean rate of nonoxidative glucose metabolism was 22±4 mumol per kilogram per minute in the diabetic subjects and 42±4 mumol per kilogram per minute in the normal subjects (P less than 0.005). When these rates are extrapolated to apply to the whole body, the synthesis of muscle glycogen would account for most of the total-body glucose uptake and all of the nonoxidative glucose metabolism in both normal and diabetic subjects. We conclude that muscle glycogen synthesis is the principal pathway of glucose disposal in both normal and diabetic subjects and that defects in muscle glycogen synthesis have a dominant role in the insulin resistance that occurs in persons with NIDDM.
- ↑ Lillioja S, Mott DM, Spraul M, Ferraro R, Foley JE, Ravussin E, Knowler WE, Bennett PH, Bogardus C. (1993) Insulin resistance and insulin secretory dysfunction as precursors of non-insulin-dependent diabetes mellitus. Prospective studies of Pima Indians. N. Engl. J. Med. 329:1988–1992.
- ↑
Martin BC, Warram JH, Krolewski AS, Soeldner JS, Kahn CR, Martin BC, Bergman RN. (1992) Role of glucose and insulin resistance in development of type 2 diabetes mellitus: results of a 25-year follow-up study. Lancet; 340:925-29.
- The development of type 2 diabetes is preceded by and predicted by defects in both insulin-dependent and insulin-independent glucose uptake; the defects are detectable when the patients are normoglycaemic and in most cases more than a decade before diagnosis of disease.
- ↑ Matthews DR, Hosker JP, Rudenski AS, Naylor BA, Treacher DF, Turner RC. (1985) Homeostasis model assessment: insulin resistance and beta-cell function from fasting plasma glucose and insulin concentrations in man. Diabetologia 28:412-419. PMID 3899825.
- ↑ HOMA Calculator. Diabetes Trial Unit. University of Oxford.