Glucose transport and insulin secretion-molecular events-2024.pptx

This presentation discusses:glucose transport,transporters-insulin structure,function,receptor and signalling pathways-insulin resistance and metabolic syndrome.The molecular events controlling these events are discussed and the abnormalities and diagnostic approaches discussed.

1. بسم الله الرحمن الرحيم

2. EKBAL MOHAMED ABO-HASHEM (MD) Professor of Clinical Pathology Mansoura University-Egypt Glucose Transport and Insulin Secretion : Molecular Events

3. Outline : *Glucose transport across pancreatic B cell membrane –Glucose transporters *Insulin :historical background –structure-secretion –regulation of secretion - biological actions-degradation *The insulin –sensitive signalling system : insulin receptors and signalling pathways *Insulin resistance *Metabolic syndrome

4. The oxidation of glucose represents a major source of metabolic energy for mammalian cells. Because the plasma membrane is impermeable to polar molecules such as glucose, the cellular uptake of this important nutrient is accomplished by special carrier proteins called glucose transporters . These are integral membrane proteins located in the plasma membrane that bind glucose and transfer it across the lipid bilayer. The rate of glucose transport is limited by the number of glucose transporters on the cell surface and the affinity of the transporters for glucose. Glucose transport across the cell membrane :

5. 1.The Na+-glucose cotransporter or symporter is expressed by specialized epithelial (brush border) cells of the small intestine and the proximal tubule of the kidney and mediates an active, Na+-linked transport process against an electrochemical gradient . It actively transports glucose from the lumen of the intestine or the nephron against its concentration gradient by coupling glucose uptake with that of Na+, which is being transported down its concentration gradient. The Na+ gradient is maintained by the active transport of Na+ across the basolateral ( antiluminal ) surface of the brush border cells by membrane-bound Na+-K+- ATPase . There are two families of glucose transporters

6. There are twelve members of the human SGLT family in the human genome, including cotransporters for sugars, anions, vitamins, and short-chain fatty acids . The sugar transporters include SGLT1, SGLT2, SGLT4 and SGLT5, while SGLT3 functions as a glucose sensor .

7. There are 14 GLUT genes in the human genome of which 11 have been shown to catalyze sugar transport . The individual isotypes exhibit different substrate specificity, kinetic characteristics, and expression profiles, thereby allowing a tissue-specific adaptation of glucose uptake through regulation of their gene expression. These proteins mediate a bidirectional and energy-independent process of glucose transport in most tissues and cells where glucose is transported down its concentration gradient by facilitative diffusion. 2.The facilitative glucose transporters (GLUTs) :

8. The presence of GLUT1 and GLUT3 mRNA in all human tissues suggests that these facilitative glucose transporter isoforms mediate basal glucose uptake. In addition to catalyzing glucose entry into cells, some isotypes (GLUT2) seem to be involved in the mechanisms of glucosensing of pancreatic beta-cells, neuronal, or other cells, thereby playing a major role in the hormonal and neural control.

9. The molecular steps that couple the increment in extracellular glucose to insulin release are now well established . A rise in circulating glucose is detected by beta cells because the sugar rapidly diffuses through transport proteins into the cytoplasm. Here it is processed, resulting in a rise in free cytosolic [Ca2+], which plays a central role in facilitating the two phases of release of the insulin-containing secretory granules, that cumulatively ensure the appropriate level of insulin secretion.

10. The history of the discovery of insulin and its therapeutic utility defined a paradigm for the integration of physiologic and biochemical approaches in experimental medicine . At the end of the 19 th century Von Mering and Minkowski noted that removal of the pancreas led to the development of DM in dogs . In 1916 Schafer first speculated that an antidiabetic hormone, which he named “ insuline ,” was secreted from pancreatic islets . Barron noted in 1920 that ligation of the pancreatic duct, with destruction of the exocrine pancreas, only resulted in DM if the islets, so named by Langerhans in 1869 , were also destroyed . Insulin –historical background

11. Subsequently, the work of Banting, Best, Collip and MacCleod in the early 1920′s resulted in the identification of a substance in extracts of pancreas that had the remarkable ability to reduce blood glucose levels in diabetic animals . By 1923 these pancreatic extracts were employed to successfully treat patients with DM. The dramatic clinical utility of insulin encouraged broad public support for medical research

12. The insulin molecule Human insulin is a protein consisting of an A-chain with 21 amino acids, and a B-chain with 30 amino acids ,linked by the connecting (c-peptide). The chains are linked by two disulfide bridges between the cysteine residues at positions A7 and B7, and A20 and C19. Human insulin aggregates to dimers, hexamers and more complex crystalline structures in the presence of zinc ions and low pH, as found in the secretory granule Insulin has a molecular weight of 5808. Its iso -electric point (point of least ionisation/ water solubility) is at a pH of 5.4. An additional disulfide-bridge connects the cysteine residues at A6 and A11, which is important for determining the tertiary structure and receptor binding of the molecule.

13. Insulin secretion The mature beta-granules form a large storage pool for insulin, well in excess of the daily requirement. Insulin is released into the circulation by fusion of the granules with the beta-cell membrane and exocytosis. A series of events triggers insulin secretion. Physiologically, glucose enters the beta-cell through an insulin independent process (probably involving the glucose transporter 1, GLUT-1). There it is phosphorylated by the enzyme glucokinase and metabolized through glycolysis and entry into the mitochondrial TCA cycle. This results in the generation of ATP which is transferred back to the cytosol and increases the ATP/ADP ratio.

14. Glucose-induced insulin secretion-a

15. This increased ATP/ADP ratio leads to closure of the ATP-dependent potassium channel (K ATP channel) which leads to depolarisation of the beta-cell membrane. The depolarisation of the cell membrane activates voltage-sensitive Ca 2+ channels, leading to an influx of Ca 2+ into the cell. This forms the final trigger for insulin exocytosis. The granule membrane is recycled to the Golgi apparatus following release of insulin. (Cont.)

16. Glucose-induced insulin secretion-b

17. Glucose-induced insulin secretion-c

18. The beta-cell KATP channel is a complex octameric unit of 2 different proteins: the sulfonylurea receptor (SUR-1) and an inward rectifier (Kir6.2). The sulfonylurea receptor belongs to a superfamily of ATP-binding cassette proteins and contains the binding site for sulfonylurea drugs and nucleotides. The inward rectifier represents the K+ conducting pore and is also regulated by ATP. The Importance of KATP Channels

19.     The KATP channels play an integral role in glucose-stimulated insulin secretion by serving as the transducer of a glucose-generated metabolic signal ( ie , ATP) to cell electrical activity (membrane depolarization). Thus, like neurons, beta cells are electrically excitable and capable of generating Ca2+ action potentials that are important in synchronizing islet cell activity and insulin release. In addition to being signal targets for glucose, KATP channels are the targets for sulfonylureas, which are commonly prescribed oral agents in the treatment of type 2 diabetes. The sulfonylureas, like glucose, induce closure of KATP channels and stimulate insulin secretion.

20. Voltage-Dependent Ca2+ Channels: Novel Regulators Extracellular Ca2+ influx through L-type voltage-dependent Ca2+ channels (VDCC) raises free cytoplasmic Ca2+ levels and triggers insulin secretion. The structure of the VDCC is complex and consists of 5 subunits: alpha1, alpha2, beta, gamma, and delta units. The alpha subunit constitutes the ion-conducting pore, whereas the other units serve a regulatory role.

21. 1 . Glucose is transported into beta cells through facilitated diffusion of GLUT2 glucose transporters. 2 . Intracellular glucose is metabolized to ATP. 3 . Elevation in the ATP/ADP ratio induces closure of cell-surface ATP-sensitive K+ (KATP) channels, leading to cell membrane depolarization. 4 . Cell-surface voltage-dependent Ca2+ channels (VDCC) are opened, facilitating extracellular Ca2+ influx into the beta cell. 5 . A rise in free cytosolic Ca2+ triggers the exocytosis of insulin. A widely accepted sequence of events involved in glucose-induced insulin secretion is as follows:

22. Insulin is produced by the beta-cells in the pancreatic islets. Its synthesis involves sequential cleavage of its two precursor molecules preproinsulin and proinsulin . The gene encoding preproinsulin is located on the short arm of chromosome 11. Following synthesis the preproinsulin molecule undergoes rapid enzymatic cleavage to proinsulin . Proinsulin consists of three domains: an amino-terminal B chain, a carboxy -terminal A chain and a connecting peptide in the middle known as the C peptide Insulin synthesis :

23. Proinsulin is packaged into small granules within the Golgi complex, which then migrate towards the cell surface. As the granules mature, proteases split proinsulin into equal amounts of insulin and C-peptide, allowing the insulin molecule, consisting of A and B chains linked by two disulfide bridges, to assume its active configuration. Insulin forms microcrystals around zinc ions within the secretory granules, producing hexamers which separate rapidly following release.

24. Insulin stored in secretory vesicles has to undergo preparatory steps upon translocation to the plasma membrane which include docking and priming before being released by exocytosis. A better understanding of the molecules involved in these steps is required to determine the rate limiting factors for sustained secretion. These processes were studied in real time using total internal reflection fluorescence microscopy, which enables observation of insulin granules localized at the plasma membrane.

25. In the final series of steps proinsulin is transported to the Golgi apparatus where it is packaged into secretory granules and converted to native insulin and C-peptide. The conversion process may begin in the trans Golgi network but continues in the condensing vacuoles (early secretory granules), and the products are stored in mature secretory vesicles, and secreted in equimolar amounts along with small amounts (ca. 2-3%) of proinsulin and intermediate cleavage products . Glucose, in addition to stimulating insulin secretion by β-cells, also activates insulin gene transcription, enhances insulin mRNA stability, and stimulates its translation

26. INSULIN BIOSYNTHESIS

27. The linking of the plasma membrane proteins syntaxin and SNAP-25 to vesicle protein VAMP-2/synaptobrevin-2 cause the docking of the vesicle, bringing insulin granules in close contact with the plasma membrane and calcium channels, after opening of calcium channels, the readily releasable pool (RRP) insulin granules located nearby are exposed to high level of Ca2+, resulting in RRP granule exocytosis. Insulin granules in reserve pool must undergo acidification to gain secretion competence.

28. This mobilization or priming process is dependent on the simultaneous operation of a V-type H+-ATPase and ClC-3 Cl - channels. Cl - uptake determines the extent of granular acidification by providing a counter-ion required to allow continuous H+ pumping. ADP can inhibit Cl - channel activity, however, glucose metabolism reduces the ADP level, leading to the loss of inhibition to Cl - channels, so insulin secretory granules undergo acidification and the secretion process is augmented.

29. These mechanisms were studied using a newly developed red fluorescent probe - NPY-tdmOrange2 which was the most reliable pH sensitive red granule marker to label insulin granules. Overall these data give new insights into the molecular mechanisms involved in biphasic insulin secretion. Disturbances in the secretion at the level of granule docking and fusion may contribute to the early manifestations of type-2 diabetes.

30. Pancreatic beta mass is regulated by: a) beta-cell replication, b) beta-cell size, c) beta-cell neogenesis , and d) beta-cell apoptosis. Beta-cell mass

31. The beta-cell mass adapts to an increased metabolic load caused by insulin resistance. The onset of type-2 diabetes is accompanied by a progressive decrease in the beta-cell mass that arises from a marked increase of beta-cell apoptosis prevailing over beta-cell replication and neogenesis. Similar mechanisms to those produced by cytokines and free fatty acids on insulin signaling in the peripheral tissues affect IRS-2 activity in beta cells and could account for the acquired beta cell secretory dysfunction.

32. Mechanisms of Insulin Secretion The secretion of insulin from pancreatic beta cells is a complex process involving the integration and interaction of multiple external and internal stimuli. Thus, nutrients, hormones, neurotransmitters, and drugs all activate -- or inhibit -- insulin release. The primary stimulus for insulin secretion is the beta-cell response to changes in ambient glucose.

33. Normally, glucose induces a biphasic pattern of insulin release. First-phase insulin release occurs within the first few minutes after exposure to an elevated glucose level; this is followed by a more enduring second phase of insulin release. It is observed that first-phase insulin secretion is lost in patients with type 2 diabetes. Thus, molecular mechanisms involved in phasic insulin secretion are important.

34.   Beta-Cell Dysfunction in Type 2 Diabetes: Role of Insulin Secretion Type 2 diabetes is a heterogeneous disorder with varying degrees of insulin resistance and insulin secretion. Traditionally, insulin resistance has been considered to play the more prominent role in the causation of type 2 diabetes. A progressive impairment in pancreatic islet function occurs during the course of the disease, implicating an important role for beta-cell failure in the pathogenesis of type 2 diabetes.

35. High ambient glucose concentration in the islets promotes insulin biosynthesis and is the primary regulator of secretion. Elevated glucose concentrations cause an increase in cAMP levels by a mechanism that does not appear to involve activation of adenylate cyclase . cAMP then exerts its effects via a mechanism involving protein kinase A (PKA), leading to the phosphorylation and activation of certain key proteins . Through this complex chain of events, glucose and cAMP (and possibly contributions from the rise in intracellular free calcium and IP3) rapidly increase translation and transcription of insulin mRNA .

36. Other hormones and chemical substances also play an important role in the regulation of insulin secretion , including glucagon, which is secreted by α -cells in pancreatic islets ; glucagon-like peptide (GLP-1 )cholecystokinin ; and gastric inhibitory peptide all acting via specific receptors on the β-cell. Inhibitors of insulin secretion include catecholamines (adrenaline and noradrenaline) which interact with adrenergic receptors on the β-cell membrane , and somatostatin which is secreted by -cells of the pancreatic islets . Amylin is also secreted by the β -cell although the regulatory mechanisms for amylin co-secretion are not well understood.

37. Type 2 diabetes progresses from a stage of normal glucose tolerance through prediabetes to overt type 2 diabetes. This progression is associated with minimal changes in the degree of insulin resistance; however, insulin secretion is progressively blunted with transition from prediabetes to overt diabetes. Thus, beta-cell failure or dysfunction is inherently associated with type 2 diabetes and may precede the onset of hyperglycemia . There is also evidence that beta-cell mass is reduced in type 2 diabetes.

38. Insulin enhances glucose uptake by increasing the number of transporters in the plasma membrane of target cells. This was first demonstrated in adipocytes and subsequently in skeletal and cardiac muscle . Insulin stimulation of such cells mobilizes transporters from intracellular compartments to the plasma membrane to facilitate glucose transport. Translocation of receptors to the plasma membrane occurs within 30 seconds of insulin stimulation ; as the stimulus dissipates the decrease in the number of plasma membrane receptors declines coincident with a decline in glucose transport .

39. Metabolic perturbations -- including hyperglycemia itself – are important causative factors for beta cell dysfunction. Thus, therapeutic interventions to maintain euglycemia during the prediabetes stage may "protect" beta cells from failing. When the beta cells do fail, overt type 2 diabetes results. These facts highlight the importance of studying the mechanisms that regulate beta-cell function, since knowledge of these processes may aid our understanding of the pathophysiology of beta-cell dysfunction and aid in the development of new therapeutic agents to prevent or reverse these defects. Further, successful genetic-engineering approaches to the development of new sources of islet cells for transplantation will require a better understanding of the biology of beta cells.

40. Insulin and glucose metabolism

41. Biological actions

42. Insulin degradation Insulin has a short half-life in the circulation following release, estimated at 4-6 minutes, allowing minute-to-minute regulation of metabolism. Circulating insulin is cleared by the liver as it passes through the portal circulation, which means that portal levels of insulin are higher than those in the systemic circulation. The kidney is largely responsible for insulin clearance in the systemic circulation, and delayed insulin clearance may cause problems with control in those with kidney disease.

43. Some degradation occurs within the insulin granule, and insulin is degraded in other tissues after binding to the insulin receptor. In this receptor-mediated degradation, the insulin-insulin receptor complexes come together on the plasma membrane of the target cell, forming groups that are sequestered in so-called coated-pits. These invaginate to fuse with intracellular lysosomes, in which the insulin is enzymatically degraded.

44. The Insulin-sensitive Signaling System

45. Insulin Receptor/Insulin Receptor Tyrosine Kinase The insulin receptor is a glycoprotein consisting of two α subunits and two β subunits linked by disulfide bonds . The α subunit of the insulin receptor is entirely extracellular and contains the insulin-binding domain. The β subunit has an extracellular domain, a transcellular domain, and an intracellular domain that express insulin-stimulated kinase activity directed toward its own tyrosine residues. Insulin receptor phosphorylation of the β subunit, with subsequent activation of insulin receptor tyrosine kinase, represents the first step in the action of insulin on glucose metabolism.

46. Phe 25B is the active site of insulin. Insulin makes contact with the insulin receptor in a hydrophobic pocket.  This causes the C-terminus of the B chain to separate from the N-terminus of the A chain.  This allows for more binding and reactions to occur. Although insulin stimulates a vast array of responses in its target tissues skeletal muscle, adipose tissue and the liver, they all appear to be initiated by an interaction between insulin and a protein receptor located on the cell membranes of these tissues.  The insulin receptor protein can only be found on these tissues, which explains the specificity of the action.  When insulin binds it induces a conformational change within the receptor, known as oligomerization , which leads to autophosphorylation of specific tyrosine residues in the cytoplasmic domains of the receptors Insulin Receptors (cont.)

47. Binding of insulin leads to phosphorylation of several intracellular substrates, including, insulin receptor substrates (IRS1, 2, 3, 4), SHC, GAB1, CBL and other signaling intermediates. Each of these phosphorylated proteins serve as docking proteins for other signaling proteins that contain Src-homology-2 domains (SH2 domain) that specifically recognize different phosphotyrosine residues, including the p85 regulatory subunit of PI3K and SHP2. Function

48. Phosphorylation of IRSs proteins lead to the activation of two main signaling pathways: the PI3K-AKT/PKB pathway, which is responsible for most of the metabolic actions of insulin: and the Ras-MAPK pathway , which regulates expression of some genes and cooperates with the PI3K pathway to control cell growth and differentiation.

49. Binding of the SH2 domains of PI3K to phosphotyrosines on IRS1 leads to the activation of PI3K and the generation of phosphatidylinositol-(3, 4, 5)-triphosphate (PIP3), a lipid second messenger, which activates several PIP3-dependent serine/threonine kinases, such as PDPK1 and subsequently AKT/PKB. The net effect of this pathway is to produce a translocation of the glucose transporter SLC2A4/GLUT4 from cytoplasmic vesicles to the cell membrane to facilitate glucose transport.

50. Moreover, upon insulin stimulation, activated AKT/PKB is responsible for: anti-apoptotic effect of insulin by inducing phosphorylation of BAD; regulates the expression of gluconeogenic and lipogenic enzymes. Another pathway regulated by PI3K-AKT/PKB activation is mTORC1 signaling pathway which regulates cell growth and metabolism and integrates signals from insulin. AKT mediates insulin-stimulated protein synthesis by phosphorylating TSC2 thereby activating mTORC1 pathway.

51. The Ras/RAF/MAP2K/MAPK pathway is mainly involved in mediating cell growth, survival and cellular differentiation of insulin. Phosphorylated IRS1 recruits GRB2/SOS complex, which triggers the activation of the Ras/RAF/MAP2K/MAPK pathway. In addition to binding insulin, the insulin receptor can bind insulin-like growth factors (IGFI and IGFII).

52. i Insulin signaling pathways

53. The cellular events that initiate the crosstalk between insulin and its receptors are present in the specific surface of skeletal muscle cells. The insulin receptor consists of two subunits ( 𝛼 and 𝛽 ) linked by disulfide bonds lying in the extracellular environment sarcoplasmic membrane. The binding of insulin with its receptor leads to phosphorylation of the 𝛽 -subunit in several tyrosine residues as the insulin receptor has kinase activity . However, due to the hydrophilic characteristic of the glucosemolecule , it does not diffuse through the lipid layer of cell membrane. Therefore, it is necessary a membrane transporter to make possible the uptake of glucose by the cell. In humans, these proteins constitute a family of transporters (GLUT) . GLUT-4 express is the major transporter in skeletal muscle, activated (and translocated) to the surface of the cellular membrane in response to insulin and exercise . The GLUT-4 translocation is stimulated by insulin in skeletal muscle and the reduced speed-determining step in the glycogen synthesis are observed in T2DMpatients

54. Figure 4: In brief, the insulin binds with its membrane receptor which has intrinsic tyrosine kinase activity, triggers a signaling cascade to downstream substrates resulting in glucose transport. Subsequently, tyrosine phosphorylated IRS (IRS-1/2) recruits signaling molecules incluinding phosphoinositide 3-kinase (PI3k). After a activation of PI3k a complex formation of phosphatidylinositol-3,4,5-trisphosphate (PI3P) that serves as regulator of phosphoinositide-dependent kinase (PDK) which was later shown to activate others prototypes proteins kinase (e.g., PKC). With this, the protein Akt is activated and propagates the hormonal signal to activate protein AS160 (GTPase activating protein of 160 kDa ), which in turn sensitizes the glucose transporter in skeletal muscle (GLUT-4) to the translocation process to the lipid membrane to glucose uptake .

55. Two major cascades of protein-protein interactions mediate intracellular insulin action: one pathway is involved in regulating intermediary metabolism and the other plays a role in controlling growth processes and mitoses. The regulation of these two distinct pathways can be dissociated. Indeed, some data suggest that the pathway regulating intermediary metabolism is diminished in type 2 diabetes while that regulating growth processes and mitoses is normal

56. Insulin Resistance Insulin resistance is defined clinically as the inability of a known quantity of exogenous or endogenous insulin to increase glucose uptake and utilization in an individual as much as it does in a normal population. Insulin action is the consequence of insulin binding to its plasma membrane receptor and is transmitted through the cell by a series of protein-protein interactions. Insulin resistance: The diminished ability of cells to respond to the action of insulin in transporting glucose (sugar) from the bloodstream into muscle and other tissues

57. Insulin resistance typically develops with obesity and heralds the onset of type 2 diabetes . It is as if insulin is "knocking" on the door of muscle. The muscle hears the knock, opens up, and lets glucose in. But with insulin resistance, the muscle cannot hear the knocking of the insulin (the muscle is "resistant"). The pancreas makes more insulin, which increases insulin levels in the blood and causes a louder "knock." Eventually, the pancreas produces far more insulin than normal and the muscles continue to be resistant to the knock. As long as one can produce enough insulin to overcome this resistance, blood glucose levels remain normal. Once the pancreas is no longer able to keep up, blood glucose starts to rise, initially after meals, eventually even in the fasting state.

58. Etiology Insulin resistance results from inherited and acquired influences. Hereditary causes include mutations of insulin receptor, glucose transporter, and signaling proteins, although the common forms are largely unidentified. Acquired causes include physical inactivity, diet, medications, hyperglycemia (glucose toxicity), increased free fatty acids, and the aging process .

59. The underlying causes of insulin-resistant states may also be categorized according to whether their primary effect is before, at, or after the insulin receptor Prereceptor causes of insulin resistance include the following: Abnormal insulin (mutations) Anti-insulin antibodies Receptor causes include the following: Decreased number of receptors (mainly, failure to activate tyrosine kinase) Reduced binding of insulin Insulin receptor mutations Insulin receptor–blocking antibodies

60. Postreceptor causes include the following: Defective signal transduction Mutations of GLUT4 (in theory, these mutations could cause insulin resistance, but polymorphisms in the GLUT4 gene are rare. Combinations of causes are common. For example, obesity, the most common cause of insulin resistance, is associated mainly with postreceptor abnormality but is also associated with a decreased number of insulin receptors.

61. There are several methods for detecting IR, such as : The hyperinsulinemic -euglycemic clamp technique, The fasting insulin, The homeostatic model assessment of IR (HOMA-IR), The quantitative insulin sensitivity check index (QUICKI), and The frequent sample IV glucose tolerance test (FSIVGTT).

62. Specific conditions and agents that may cause insulin resistance include the following: Aging : This may cause insulin resistance through a decreased production of GLUT-4. Increased production of insulin antagonists : A number of disorders are associated with this effect, such as Cushing syndrome, acromegaly, and stress states, such as trauma, surgery, diabetes ketoacidosis, severe infection, uremia , and liver cirrhosis. Specific causes of insulin resistance

63. Medications : Agents associated with insulin resistance syndrome include glucocorticoids (Cushing syndrome), cyclosporine, niacin, and protease inhibitors. Glucocorticoid therapy is a common cause of glucose intolerance; impairment of glucose tolerance may occur even at low doses when administered long term. Sodium: High sodium intake has been associated with increased glucocorticoid production and insulin resistance.

64. Anti-HIV therapy : Protease inhibitor–associated lipodystrophy is a recognized entity. Nucleoside analogues have also been implicated in the development of insulin resistance. Androgen-deprivation therapy : This therapy causes severe hypogonadism with unfavorable metabolic changes.

65. Insulin therapy : Low-titer immunoglobulin G ( IgG ) anti-insulin antibody levels are present in most patients who receive insulin. Rarely, the antibodies result in significant prereceptor insulin resistance. Patients with a history of interrupted exposure to beef insulin treatment are particularly prone to this resistance. Clinically significant resistance usually occurs in patients with preexisting, significant tissue insensitivity to insulin. Enhanced destruction of insulin at the subcutaneous injection site has also been implicated in resistance.

66. Metabolic syndrome Metabolic syndrome ( MetS ) is a cluster of metabolic abnormalities that includes hypertension, central obesity, insulin resistance, and atherogenic dyslipidemia . MetS is strongly associated with an increased risk of developing atherosclerotic cardiovascular disease (CVD). The pathogenesis of MetS involves both genetic and acquired factors that play a role in the final pathway of inflammation that leads to CVD. MetS has become increasingly relevant in recent times due to the exponential increase in obesity worldwide. Early diagnosis is important in order to employ effective lifestyle and risk factor modification.

67. Interaction of cytokines,adipokines ,and inflammatory markers to the metabolic syndrome

68. Cont.)

69. Concentrations of pro-inflammatory cytokines (IL-6, TNF- α ), markers of pro-oxidant status ( OxLDL , uric acid), and prothrombic factors (PAI-1) are elevated in metabolic syndrome. Additionally, leptin concentrations are found to be elevated, likely due to leptin resistance. In contrast, concentrations of anti-inflammatory cytokines (IL-10), ghrelin, adiponectin, and antioxidant factors (PON-1) are decreased .The leptin:adiponectin ratio (LAR) is better than any of them alone . Biomarkers of metabolic syndrome

70. The potential for using multiple biomarkers for diagnosis and early detection, and subsequent customization of treatment and risk management, is a promising field for research ,especially the implications of using multiple biomarkers. These biomarkers correlate significantly with metabolic syndrome and could provide a minimally-invasive means for early detection and specific treatment of these disorders

71. Creating such a panel could provide a relatively easy and minimally-invasive way to detect metabolic syndrome and possibly indicate the severity, depending on the combination of aberrations.