A woman offered to help a man who, on his hands and knees under a street lamp, was frantically searching for his lost key. Frustrated after several unsuccessful minutes crawling under the bright light, the woman asked, “Where were you when you lost your key?” Pointing to a dark alley, the man answered, “over there.” “Then why aren’t you looking there?” she asked. “Because the light’s better here,” he replied.
Like the man under the light, are we focusing too intensely on glucose control?
PREMISE: The diabetes epidemic is exploding out of control. Whereas ten years ago type 2 or “adult-onset” diabetes was rare in individuals less than forty years-old, it is now epidemic even in children 1 . Generalized endothelial cell dysfunction and inflammation may be at the root of this condition. 2 Treatments focused on intensively controlling glucose at the expense of raising insulin levels and endothelial function contribute to this problem while failing to improve macrovascular disease or longevity. 3, 4 5, 6 Our genes haven’t changed in the past decades but food quality and diet have. Sedentary behavior combined with the enormous consumption of high glycemic carbohydrates, trans fats, and the increase in n-6/n-3 polyunsaturated fatty acid (PUFA) dietary ratio demand attention. Therein may be the solution. This is part 1 in a series that will explore these issues.
Is Hyperglycemia the Major Culprit in Diabetes or Simply a Marker of Endothelial Dysfunction?
From much of the media, public-service broadcasts, and, dare I say, most of the medical profession, we hear that controlling blood sugar (glucose) better will prolong life and improve its quality for most patients who have type-1 or type-2 diabetes. Contrary to popular belief, though, we have little evidence suggesting that lowering or normalizing blood sugar will correct atherosclerosis and heart disease, increase longevity, or improve quality of life. 5, 7-9 We have no clinical intervention trial data showing improvement in cardiovascular complication outcomes with glucose control. 6 Like the man searching for his key under the street lamp, for many years physicians have focused their light on tightly controlling their diabetic patients’ blood glucose. Too often results from large studies are interpreted to justify this approach. Clinical trials suggest treatments that raise insulin levels increase weight and worsen cardiovascular risk factors despite improving glycemia. For example, despite improving glycemia, patients treated intensively in the Veterans Affairs Diabetes Feasibility Trial had a trend toward more cardiovascular events. 3, 4
Syndrome X or insulin resistance syndrome (IRS) or metabolic syndrome includes insulin resistance, hyperinsulinemia, glucose intolerance, dyslipidemia, hypertension, and obesity. 10 These often play a role in the development of CHD even before hyperglycemia occurs or reaches the levels seen in diabetes. 11-13 Insulin-resistant humans demonstrate a delay in the delivery of insulin across the endothelium to the interstitial fluid leading to compensatory hyperinsulinemia until the beta cells are unable to continue to offset the demand 14-17 Hyperglycemia ensues leading to overt type 2 diabetes. 10
Don’t get me wrong — lowering blood glucose is a desirable goal for treatment. The endothelial cell is vulnerable to the metabolic byproducts of hyperinsulinemia and to high glucose levels. Elevated glucose can increase oxidation, 18, 19 , and chronic exposure to high glucose concentration impairs beta cells and worsens insulin resistance. 10, 20-22 Excess glucose has been shown to activate the enzyme protein kinase C (PKC) in endothelial cells, making them more permeable or leaky. 23 Moreover, prolonged hyperglycemia can alter proteins forming advanced glycosylated end products — AGEs, which especially injure the endothelial cells in small blood vessels, damaging the eyes, kidneys, and other organs. Cross-linking of AGEs with other proteins probably contributes to the basement membrane thickening associated with diabetes. 24
The endothelium is much more than a semi-permeable membrane. This single cell layer, which could cover 5,000 square meters, lines every blood vessel and is an active organ in its own right. In addition to transporting hormones such as insulin, the endothelial system also plays an important role in the regulation of blood flow, maintenance of vascular architecture, mononuclear cell (e.g., platelets and other leukocytes) migration, and hemostasis. 2, 25 Endothelial cells are constantly exposed to blood circulating toxins, inflammatory mediators, and lipoproteins, which appear to be irritating to the endothelium only when they are oxidized, e.g., OxLDL, OxChol are the main offenders. Acting as mechanosensors, endothelial cells sense changes in the shear stress of turbulent blood flow and responds by secreting factors that affect vessel tone and structure. 26 Endothelial cells regulate hemostasis by synthesizing a variety of pro-coagulant and anticoagulant factors, and they also regulate the inhibition of fibrinolysis. 25, 27, 28 In patients with type 2 diabetes and the insulin resistance syndrome or Syndrome X, several inhibiting and pro-coagulant factors are elevated. 28-31 Increased levels of the endothelial-derived pro-coagulant von Willebrand factor antedate microalbuminuria in type 2 diabetes which is consistent with generalized endothelial cell dysfunction. 32
Endothelial cells, vascular tone, and eicosanoids
The endothelial cells regulate vessel tone by releasing relaxing and contractile eicosanoids such as prostacyclin (PGI2) and thromboxane A2 (TXA2) which tend to have opposing biological functions. 27 Insulin stimulates the production of these arachidonic acid-derived eicosanoids. 33 In diabetes the equilibrium is pushed towards increased TXA2/PGI2 favoring vasoconstriction and hypertension. 27, 33, 34 A proposed mechanism for diabetic neuropathy involves the unopposed vasoconstriction action of TXA2 with ensuing ischemia. 35 Insulin inhibits PGI2 production in adipose tissue, therefore hyperinsulinemia associated with obesity could decrease PGI2 production and contribute to vasoconstriction and hypertension 33, 34 . Insulin also stimulates the endothelium to produce endothelin, a potent vasoconstrictor that is elevated in diabetes and directly stimulates smooth muscle proliferation of arterial walls 36-38 . Nitric oxide (NO), previously referred to as endothelium-dependent relaxing factor (EDRF), is synthesized in the endothelial cell from L-arginine and is the most potent endogenous vasodilator known. 25, 27 NO’s role in diabetes has been well-described.
Lipoxygenase (LO) metabolizes AA to produce leukotrienes and products that play an important role in atherosclerosis by inducing oxidation of LDL and stimulating growth and migration of vascular smooth muscle cells. 39 40 LO products, e.g., the HPETEs and HETEs, also activate many of the pathways linked to increased vascular and renal disease. Elevated glucose has been shown to increase the activity of the LO enzymes and production of LO products 41 . Type 2 diabetes is characterized by the loss of first-phase insulin release in response to glucose and increased and sustained insulin secretion during the second phase. The AA metabolite PGE2 is a potent inhibitor of first-phase insulin release, whereas the AA lipoxygenase product (possibly 12-HETE) sustains increased second-phase insulin release. 42
Measuring endothelial function
The endothelium’s functioning is not yet routinely tested. Most of the practical techniques for directly measuring this activity use ultrasound to measure movement of blood in an artery after the flow has been altered either by injecting drugs that would normally dilate it, or by blocking the flow with a tourniquet. The more convenient and less invasive method usually involves applying a tourniquet to the forearm for one to five minutes to occlude the blood flow through the brachial artery. When the tourniquet is removed, normal endothelial cells respond by opening the vessel wider so that the blood flows faster than before the tourniquet was applied (a hyperemia response). This increase can be measured by ultrasound. 43, 44 If the endothelial cells are impaired, when the tourniquet is released they will not dilate the blood vessel more than before the tourniquet pinched the artery closed, and blood flow will not increase reflexively. The tourniquet creates shear stress (pressure and distortion from the force of the tourniquet and the resulting disrupted blood flow), and the normal endothelium will respond by releasing nitric oxide, causing the underlying smooth muscle to relax, and the artery to dilate.
A number of blood tests report on endothelial function, including concentration of insulin, clotting substances, inflammatory substances such as C-reactive protein, and the cholesterol profile, especially the triglyceride : high-density lipoprotein ratio (TG : HDL). One reasonable criticism aimed at blaming endothelial dysfunction for many of our woes, is that the condition is difficult to measure directly. True, but the evidence, circumstantial though it now is, overwhelmingly points to endothelial dysfunction as a large influence in diabetes, obesity, and other diseases. In fact, generalized endothelial dysfunction may be the cause behind most diseases.
Endothelial dysfunction precedes diabetes
Women who contract diabetes during pregnancy are said to have gestational diabetes. Although the condition often resolves after the baby is delivered, these women are known to be at greater risk for type-2 diabetes in the future. Anastasiou and colleagues published their observations on otherwise healthy women with a history of gestational diabetes. 45 The researchers studied both obese and nonobese women with that history but no present signs of diabetes, giving them a glucose-tolerance test to see how they tolerated large loads of glucose, and found that they already had abnormal endothelial function or endothelial dysfunction. These women currently showed no overt signs of diabetes but had endothelial dysfunction and were likely to contract diabetes.
In perhaps a more straightforward demonstration of endothelial dysfunction preceding the development of diabetes, Caballero et al used Laser Doppler and high resolution ultrasound to directly look for abnormalities in vascular reactivity in micro- and macrocirculation (respectively) in four age and sex comparable groups: 30 healthy normoglycemic subjects with no history of type 2 diabetes in a first-degree relative (controls), 39 healthy normoglycemic subjects with a history of type 2 diabetes in one or both parents (relatives), 32 subjects with impaired glucose tolerance (IGT), and 42 patients with type 2 diabetes without vascular complications. 46 They also measured the following blood tests as indicators for endothelial dysfunction: entothelin-1 (ET-1), von Willebrand factor (vWF), soluble adhesion molecules, and vascular cell adhesion molecules. Significantly less blood flow in both micro- and macrovasculature was observed in the group with type 2 diabetes, followed by the group with IGT and the group with a family history of IGT, than in the healthy control subjects. Patients with IGT and normoglycemic patients with a parental history of diabetes also had increased levels of ET-1 and cellular adhesion molecules consistent with increased activation of the endothelium. These results suggest that abnormalities in vascular reactivity and markers of endothelial cell activation are present early in individuals at risk of developing type 2 diabetes, even at a stage when normal glucose tolerance exists. 46
Many studies suggest that how elevated the blood glucose is matters less than how long the patient has had type-2 diabetes, suggesting a shared underlying pathophysiologic process—endothelial cell dysfunction. Enderle et al suggest that a longer period of undetected diabetes rather than poor glucose control impairs endothelial-dependent vasodilatation in type 2 diabetes. 47
Several studies show that risk factors for heart disease appear even before diabetes is recognizable. A 1998 study observing 17,000 men for twenty years found that those whose blood glucose was elevated but not high enough to meet the criteria for diabetes, had greater risk of dying from heart disease. 11 After following 2,000 nondiabetic, apparently healthy middle-aged men, for twenty-two years, Norwegian researchers found that, by themselves, fasting blood glucose values in the upper normal range accurately predicted death by a cardiac event. 48 An editorial accompanying the article on the smaller study suggests that even moderately elevated blood glucose increase the risk, and doctors should more aggressively treat elevated blood glucose in these patients even though they are not yet diabetic. 49 The editorialist’s logic is flawed, failing to appreciate that the moderate rise in blood glucose is not the villain but rather marks or results from a deeper problem — widespread damage to the endothelial cells that line all blood vessels. This damage contributes to insulin resistance, hypertension, dyslipidemia, proteinuria, atherosclerosis, and elevated glucose, which just happens to rise as these other conditions appear.
My fear is that the “experts” are missing the boat: instead of recognizing that elevated glucose signals an underlying general problem, they will lower the criteria for diagnosing diabetes. Millions more will then be treated with drugs that elevate insulin, worsen endothelial-cell damage, make patients fatter and sicker, and cause more deaths. In other words, let’s focus on the problem, insulin resistance, not the result, which is the elevated blood glucose level.
Diabetes: an inflammatory condition
An accumulating body of evidence suggests that an inflammatory process plays a key role in developing the insulin resistance syndrome, 50, 51 type 2 diabetes 52, 53 and cardiovascular disease 54-56 In a recent prospective study, Pradhan et al followed over four years 27,628 women free of diagnosed diabetes, cardiovascular disease and cancer at baseline. 53 Elevated markers of systemic inflammation (C-reactive protein and interleukin 6) were able to powerfully predict the development of type 2 diabetes in these women. 53 Similar results were reported by Barzilay et al. 52 Consistent with this diabetes-inflammation connection is additional evidence showing elevated CRP associated with higher insulin and HbA1c among men and women 57 , and elevated leukocyte counts were significantly associated with diabetes incidence over a period of approximately 20 years. Participants’ risk of developing diabetes increased progressed as 58
C-reactive protein (CRP) Injured endothelial cells are linked to increased C-reactive protein in the blood, which can indicate generalized inflammation, and that can mean risk of death from stroke, MI, and other diseases. Elevated CRP is also associated with endothelial vasodilator dysfunction which could contribute to ischemic events. 59 Made in the liver, CRP is a marker or indicator for both chronic inflammation and acute or very recent injury. The protein binds to damaged tissue and resembles an antibody in that it helps activate inflammation.
Low-grade inflammation and an elevated CRP have been associated with at least doubled or tripled risk for heart attack, stroke, and atherosclerosis. Led by Paul Ridker, Harvard Medical School and director, Center for Cardiovascular Disease Prevention at Brigham & Women’s Hospital, researchers found that even tiny elevations in CRP powerfully predict who among groups of men and women are likely to have an MI. Of the twelve measures they looked at, including total cholesterol, LDL cholesterol, and the TG : HDL ratio, the CRP reading most effectively predicted risk. 55 Subsequently, Ridker and his colleagues have shown that elevated levels of CRP in previously healthy women predict the development of type 2 diabetes. 53
A research group led by John Yudkin established that CRP concentrations were related to insulin resistance as well as to such markers of endothelial dysfunction as low HDL, high TGs, and two substances produced by the endothelial cells that help increase blood’s tendency to clot. 60 These substances, von Willebrand factor and tissue plasminogen activator, are released into the blood by the damaged endothelium.
In patients with uncontrolled diabetes, CRP rises, a reaction significantly related to the rise in blood glucose. One possibility is that the increased blood glucose thickens the blood, increases the shear stress (forces acting on the endothelium as blood flows by), and this now-damaged and dysfunctional endothelium contributes to the inflammation in several ways, including secretion of sticky adhesion molecules, which can be induced by CRP. 61 These molecules act like flypaper, attracting inflammatory white blood cells and causing them to accumulate and stick to the endothelium’s surface This action can trigger release of a host of other substances that influence inflammation and blood-vessel leakage. That CRP is correlated with markers of endothelial dysfunction further suggests that endothelial triggering or activation is related to chronic inflammation.
Inflammation, diabetes, and obesity
One study found that eighteen obese, premenopausal women with no other medical problems had impaired blood flow or impaired endothelial-dependent vasodilation (dilation of blood vessels), suggesting that by itself uncomplicated obesity influences endothelial dysfunction or damage to blood vessels. The more fat around the abdomen and internal organs the greater the endothelial dysfunction, and also the higher the concentration of insulin. In fact, insulin resistance and endothelial dysfunction increase as girth at the waist increases. 62 Compared to people of normal weight, even those who are young and overweight or obese (ages seventeen to thirty-nine) have been found to have elevated CRP or higher prevalence of generalized low-grade inflammation. In a 1999 study, Marjolein Visser and her colleagues showed that waist size and CRP were directly related — the bigger the belly, the greater the inflammation. 63 Visser et al’s subsequent research has shown that in children 8 to 16 years of age, overweight is associated with higher CRP concentrations and higher white blood cell counts. 64 Analyzed results from thousands of adult 65 and children 66 participants in NHANES III provided clear evidence of a relationship between BMI and plasma CRP levels. Together these studies suggest that insulin resistance, inflammation, and endothelial dysfunction increase as body fat, and especially girth at the waist, increases. 63
Tumor necrosis factor-alpha (TNF-a)
Tumor necrosis factor-alpha is a cytokine secreted in proportion to the percentage of body fat. 67 It can damage the insulin-producing beta cells in the pancreas, inhibit secretion of insulin, and may also produce resistance to insulin, especially in fat and muscle. . 67 . 68, 69 It also activates phospholipase A2 and synthesis of arachidonic and metabolites in endothelial cells which can play a role in inflammation, vasoconstriction, and thrombosis. 68, 69 TNFa can incite the immune system to attack healthy tissue throughout the body. Elevated TNF-a can cause diffuse inflammation that may result in painful arthritis along with vascular (blood-vessel) complications. It also induces breakdown of muscle, causing the cachexia or wasting that occurs in such chronic diseases as congestive heart failure, cancer, and pathological aging. 70-73
Fat’s role in inflammation
CRP and therefore inflammation are related to insulin resistance as well as to waist size and abdominal fat. These stores of fat are not just innocent bystanders hanging around doing nothing. Stored fat or adipose tissue contributes heavily to a low-level, chronic inflammatory state. Besides its connection to CRP, fatty tissue produces and releases other inflammatory substances, including interleukin-6 (IL-6) 63 and tumor necrosis factor alpha (TNFa) into the circulation. Omental or visceral fat cells in vitro have been shown to secrete as much as two to three times more IL-6 than cells derived from subcutaneous fat stores. 74 This may shed light on the connection between excess abdominal fat and insulin resistance in the liver and other metabolically active tissues since venous drainage from omental fat provides direct access to the liver’s portal system. 53 TNFa produced by fat cells also appears to be implicated in inducing resistance to insulin. 75, 76 Thus overweight people have excess body fat, which produces inflammatory substances and low-level, chronic inflammation that may induce endothelial dysfunction and resistance to insulin. This process links these conditions (endothelial dysfunction and insulin resistance) to obesity, cardiovascular disease, and diabetes.
At least 90 percent of patients with type 2 diabetes are overweight. While simply being overweight is a risk for type 2 diabetes, one must also bear in mind that a subset of non-obese adults without apparent glucose abnormalities can rapidly develop type 2 diabetes which may be attributable to an autoimmune and inflammatory process. 77 Barzilay et al found that in those with lower BMI (less overweight), there was a stronger association with inflammation as glucose levels progressed. This suggests that inflammation in leaner patients with type 2 diabetes might not be due entirely to the production of inflammatory cytokines by fat cells. 52 However, even modest weight loss can prevent and reverse type 2 diabetes, 78 and sustained weight loss in obese women results in a reduction in elevated inflammatory cytokine levels and an amelioration of endothelial dysfunction. 79 Surgical removal of visceral fat may reduce insulin resistance and plasma insulin levels. 80
Reconsidering cholesterol and atherosclerosis
Consider the following facts. More than half of all MIs occur in people with normal plasma lipid levels and 40 percent have no warning symptoms 81 In fact, angiographic studies indicate that the average stenosis of lesions leading to acute MI is less than 50 percent, with infarction occurring due to rupture of non-occlusive plaques triggering acute thrombosis. 82 The beneficial effects of statin agents may be independent of serum lipid levels and can occur before lipid lowering. 83-86 In the CARE and other trials, the risk of an MI was reduced to the same degree whether the cholesterol level was lowered by a large or small amount, i.e., “lack of exposure response.” 87 While a number of factors can damage the endothelium and accelerate atherosclerosis, oxidants and free radicals are major initiators of vessel wall damage as we will discuss below. Statins have been shown to prevent the activation of monocytes into macrophages, inhibit the production of pro-inflammatory cytokines, C- reactive protein, and cellular adhesion molecules, and decrease the adhesion of monocyte to endothelial cells. 88 The benefit of statins may be their anti-inflammatory effect, and the lowering of cholesterol may be an interesting side effect. LDLs appear to be harmful when they are oxidized. Without a pro-oxidant or pro-inflammatory environment perhaps elevated lipids are significantly less of a threat.
Diabetes and vascular disease
Each hour, 178 people die from complications set off by diabetes. For 80 percent of these patients the killer is atherosclerosis involving the large blood vessels supplying heart and brain. Patients with diabetes are four times as likely as nondiabetic individuals to die of an MI. With endothelial dysfunction a primary cause, type-2 diabetes is a high-risk condition for heart attack and stroke. The American Diabetes Association is launching a program “Make the Link!” a new initiative aimed at making patients aware of the association between diabetes and cardiovascular disease. But these two entities might not be separate diseases at all but rather part of the same disease process. Besides being involved in mediating inflammation, endothelial dysfunction (perhaps from inflammation) may lead to increased coagulation of blood, leaky blood vessels, increased vascular tone or constriction causing hypertension, elevated TGs and lowered HDL. The dysfunctional endothelium also secretes growth factors that stimulate blood-vessel walls to expand or hypertrophy, narrowing the blood vessels’ opening. Leaky endothelium and diminished peripheral blood flow may limit insulin delivery and promote insulin resistance. 53
Diabetes is a huge risk factor for coronary-artery disease. The risk for heart MI is higher for diabetic patients with no prior MI than for nondiabetic patients who have survived a prior MI. The greater risk is by no means clearly understood, but can be better appreciated if we assume that atherosclerosis-related heart disease and diabetes share an underlying pathology: endothelial dysfunction and inflammation.
Generalized Endothelial Dysfunction– This common underlying pathology explains microalbuminuria, elevated triglycerides, low HDL, and insulin resistance.
Microalbuminuria (MA) is a powerful independent risk factor for CHD and is closely linked to the insulin resistance syndrome (IRS) while an elevated plasma triglyceride (TG) to HDL ratio (TG:HDL) is an independent predictor of MA that is also associated with insulin resistance 2, 89-91 and CHD. 92 The high TG and low HDL levels found in those with insulin resistance is associated with low lipoprotein lipase ( LPL) activity. 93, 94 Widespread endothelial damage occurs in patients with insulin resistance leading to MA and a decrease in the lipoprotein lipase moiety (LPL) bound to the endothelium. 32, 90 This impairs the clearing and catabolism of TG-rich lipoproteins allowing TGs to rise. 90 The TG:HDL ratio is a strong predictor of MI, 92 perhaps because it reflects endothelial function.
The Characteristic Dyslipidemia of Diabetes –
The characteristic dyslipidemia of insulin resistance and diabetes consists of elevated TGs and low HDL 10 . There is some evidence that in the insulin-resistance syndrome increased free fatty-acid flux from the adipose tissue causes the liver to secrete more TG-rich VLDL particles. This effect may be additive to the means by which impaired LPL also contributes to decreased clearance of TGs. The numerous TGs used to make LDL and HDL cholesteryl esters are mediated by cholesterol ester transfer protein (CETP). These now TG-rich LDL and HDL particles are susceptible to hydrolysis by hepatic lipases, resulting in small, dense LDLs, and small HDLs. The small, dense LDLs are more vulnerable to oxidation and are more atherogenic than large, buoyant LDL particles. Small HDLs are more easily cleared from the plasma (they have lower affinity for apoprotein A-I, leading to rapid dissociation). This sequence results in fewer HDL particles in the blood, a condition indicating high risk for a cardiovascular event.
Although LDL levels may be normal, elevated, or low, they are usually the small, dense, more atherogenic LDL which are independently associated with insulin resistance and hyperinsulinemia 95, 96 97 . These LDL can more easily penetrate damaged endothelium where they become oxidized. The injured endothelium then secretes white blood cell adhesion molecules 98, 99 27 inflammatory substances, and procoagulants, which create a plaque that is likely to rupture, thrombose, and cause a cardiovascular event. 100, 101 In patients with diabetes the type of plaque may be more important than the extent of advanced atherosclerotic lesions. Existing vascular lesions may be more likely to rupture.
Lowering TGs is accompanied by increase in size of LDL particles, but this result will not be obvious until TGs are low enough, usually less than 100. Note also that LDL is not routinely measured directly—it is calculated using the Friedwald equation: LDL = total cholesterol – HDL – TG/5. Therefore, the common “LDL measurement” on a typical lab slip includes the sum of LDL, plus other things like Lp(a), and IDL (intermediate-density lipoprotein). If TG-lowering efforts are effective, the LDL level may calculate to be greater, even though it hasn’t changed, simply because the equation needs to be balanced. Increases in the percentage of large, buoyant LDL particles is associated with a decrease in TG:HDL, insulin resistance, and improvement in endothelial function. 102-105 Unlike their small, dense counterparts, these LDLs are less likely to become oxidized and induce an cardiac event 106 Yet LDL particles are rarely measured directly and an elevated LDL automatically triggers a drug prescription. Also, if HDL increases, total cholesterol has to increase. Therefore cardiac risk may decrease in the face of increasing total cholesterol.
LDL is not a strong predictor of CHD—further evidence
A team led by Antonio Gotto, past president of the American Heart Association, examined the 5-year histories of over 6,600 men and women between 45 and 73 years of age and found that blood levels of LDL cholesterol, according to Gotto, “didn’t predict MI risk at all.” Low HDL cholesterol levels which may be a better indicator of endothelial dysfunction, were fouind to be fairly good predictors of risk. 107 In 1993 in the same journal (Circulation: Journal of the American Heart Association) Phillips et al. followed 335 patients with established atherosclerosis of the coronary arteries. Angiography was performed every two years over a four to six year period> Similar to Gotto’s findings, decreased levels of HDL was associated with progression of coronary atherosclerosis, but they found no such relation for the level of LDL. It should also be noted that LDL is not routinely measured but rather it is calculated using the Friedwald equation: LDL = total cholesterol – HDL – TG/5. From this you can see that as triglycerides (TG) drop, LDL automatically go up, but these are the larger, fluffy, buoyant, and the kind less likely to oxidize and cause problems. In fact, what is commonly regarded as LDL-cholesterol includes particles other than LDL. It is actually the sum of LDL plus Lp(a) and imtermediate density lipoprotein (IDL). These are lipid puls protein molecules (lipoproteins) that are associated with increased risk of atherosclerosis.
Homocysteine – a forgotten major risk factor
Several studies have targeted the effects of homocysteine on the vascular endothelium. Folate deficiency may predispose endothelial cells to damage and homocysteine may have a direct cytotoxic effect on vascular endothelium. Impaired endothelium vasodilation has also been observed in patients with elevated homocysteine levels, which may possibly be the result of decreased nitric oxide bioavailability induced by homocysteine’s toxic effects. Homocysteine plasma levels are independently associated with insulin resistance in apparently healthy normal weight, overweight and obese pre-menopausal women, thus suggesting a possible role of insulin resistance and/or hyperinsulinaemia in increasing homocysteine plasma levels. Since homocysteine is a well-known cardiovascular risk factor, higher homocysteine plasma levels may well be a further mechanism explaining the higher risk of coronary heart disease in patients affected by insulin resistance. 108
Free radicals and insulin resistance
Free radicals are molecules that are highly reactive because of their unpaired electrons; they are effective in many cellular processes that generate energy, and they protect us by attacking invading bacteria and viruses. In excess, though, the highly reactive free radicals steal electrons or “oxidize” and damage proteins, fats, and DNA, causing widespread damage to cells and contributing to more than a hundred disease states. Free radicals can oxidize LDL cholesterol particles, making them directly toxic to endothelial cells. Oxidation is everywhere, from rusted iron to butter left out overnight that turns rancid. Fortunately, we have a defense force of antioxidants for the counterattack. Among these include a number of enzymes and assorted molecules, including vitamins C and E, that can intercept these oxidizing free radicals by binding to them before they reach cells, preventing damage to human tissue, including endothelial cells. Because it interfaces with the blood and other tissues and directly contacts free radicals in the blood, the endothelium is especially vulnerable.
Several studies show that people with diabetes have excessive free radicals or oxidants and are deficient in antioxidants. Gerald Reaven’s group at Stanford established that not only do patients with diabetes experience more oxidation, but that even apparently healthy nondiabetic individuals can reveal evidence of increased oxidation that is directly related to their risk for contracting diabetes. 19 These people had early, mild resistance to insulin and normal glucose tolerance. This finding suggests that increased free-radical activity and oxidation occur very early in those who are insulin resistant, even before diabetes appears. The more resistant subjects were to insulin, the higher the quantity of oxidation. Degree of resistance to insulin is also related to consumption of such antioxidant vitamins as vitamin E and others supplied by the diet. Low vitamin E concentrations are more common in insulin- resistant people and can help in predicting diabetes, whereas consuming more raw vegetables, which are rich in E and other antioxidant vitamins, has been linked to decreased risk for diabetes. Healthy endothelial cells carry an arsenal of various antioxidants and antioxidant co-factors including: vitamins C and E, glutathione, the enzymes superoxide dismutase, catalase, and co-factors such as selenium and magnesium, which is technically not an antioxidant co-factor but if deficient can lead to increased insulin resistance and thromboxane synthesis. 109 Mohanty et al demonstrated the protective effect of antioxidants on endothelial function in healthy volunteers. Challenged with an oral glucose load (75 grams) the subjects demonstrated impaired endothelial function and increased free radicals (oxidative stress), both of which were prevented for those who first ingested 2 grams of vitamin C and 800 international units (IU) of vitamin E. 18 Of note, statin agents such as simvastatin lower vitamin E, CoQ-10, beta carotene, and raise insulin levels. 110
Nitric oxide (NO)
A diabetic environment high in free radicals and low in antioxidants may disrupt endothelial function. A highly active regulatory organ, the endothelium senses and assesses signals to which it is constantly exposed by the blood, and responds by secreting factors that affect blood vessels’ tone and structure. 26 On the endothelial cell’s surface specific receptors sense such changes as shear stress or force of blood turbulence acting on the endothelium as it flows by, oxidized LDLs, and inflammatory mediators. The endothelial receptors use a number of pathways to translate signals from their environment and make adjustments. One of these, the L-arginine pathway, generates nitric oxide (NO), a gas that protects the vessel wall’s health. 111 When endothelial cells produce NO, it dilates (opens) blood vessels and delivers more blood. Nitric oxide also combats oxidation and can be depleted or elevated in diseases related to endothelial dysfunction. Concentrations of NO were found to be higher in a group of patients with insulin resistance, possibly because the endothelium was compensating to overcome the unfavorable effects of insulin resistance and high insulin concentration (hyperinsulinemia).
Adequate intracellular supplies of L-arginine are believed to be critical in forming enough NO. Though plenty of L-arginine usually seems to be available, small supplements may increase the endothelium’s production of NO in patients with high cholesterol and diabetes 112 , and long-term supplementing with l-arginine has been shown to improve endothelial function in the small arteries that supply the heart. 113 Supplementing also shows promise in preventing atherosclerosis-related heart disease 114, 115 .
When production of NO is inhibited, the endothelium triggers secretion of adhesion molecules that attract white blood cells and cause them to stick to the endothelial surface along the blood-vessel wall. This sequence is part of inflammation, but NO also prevents inflammation by keeping circulating white blood cells from attaching to vessel walls.
Throughout the body tiny blood clots commonly form but are quickly broken down and rendered harmless. Clots are of course necessary to protect against significant bleeding, but syndrome X (metabolic syndrome) and diabetes heighten the tendency for blood to clot, and increase risk for stroke and myocardial infarction (MI). Measures of body fat are strongly associated with circulating levels of fibrinogen, 116 which plays a critical role in clotting. Even those who apparently are healthy but whose blood insulin is high have been found to impair ability to dissolve blood clots (fibrinolysis). The endothelium is mainly responsible for the delicate balance of fibrinolysis. Plasminogen activator (tPA), a natural tissue enzyme that dissolves blood clots, is used in treating patients suffering from acute heart attack. Fat cells as well as endothelial cells secrete plasminogen activator inhibitor-1 (PAI-1), which increases with obesity and, as its name implies, inhibits plasminogen activator. 76 Damaged or dysfunctional endothelial cells also are linked to increased PAI-1. When PAI-1 is over-expressed, blood clots (thromboses) form more readily, a major event leading to atherosclerosis. But NO helps keep PAI-1 under control and so prevents life and limb-threatening thromboses, life-threatening clots that can wholly block a blood vessel. 117
Risks in “improving” control of blood glucose
Elevated insulin by itself is a predictor of CHD and death. 97, 118-121 Injected insulin, drugs, and diets that raise insulin concentrations are harmful. Adverse effects include: cost, patient inconvenience, consumption of medical resources, hypoglycemia, weight gain , early worsening of angiopathy 122 and lipid profiles, increased blood pressure, 123 ( 124 drug side effects, and unknown drug interactions. In the United Kingdom Prospective Diabetes Study fasting insulin levels at nine years were higher in patients assigned to sulfonylurea and insulin therapy than those assigned to conventional therapy, 125 placing them at higher risk for CHD. 126 Sulfonylurea therapy in the University Group Diabetes Program study also was associated with an increase in cardiovascular events. 127 A 1997 study demonstrates that insulin therapy requires expensive resources and is rarely effective in decreasing risk of severe complications. 128 Commenting on the 1997 article, the American Diabetes Association’s chief scientific and medical officer comments, “Intuitively, people thought, of course if you give insulin, people will do better. But this shows we’re not doing so great.”
Patients are encouraged to think they can make up for that extra- rich dessert simply by injecting a little extra insulin to avoid “risking” higher blood glucose. 129, 130 This mindset is a risky proposition. In fact, studies such as the Veterans Affairs Cooperative Study on Glycemic Control and Complications in Diabetes Mellitus, examined intensive treatment with oral drugs, insulin, or both —compared to those treated less aggressively. They found that more people who were intensively treated and had “more improved” blood glucose concentrations (HgA1C) died, 4 and fibrinogen levels were increased which increases the risk of thrombosis and CHD. 131 “Better” control of blood sugar with medication also carries a risk for dangerously low blood glucose (hypoglycemia) a condition that leaves patients prone to act bizarrely, lose consciousness, and suffer brain damage or death. Recurrent hypoglycemia can result in cognitive dysfunction and non-cognitive psychological abnormalities. Self-monitoring blood glucose remains open to debate. While for some patients self-monitoring may improve blood glucose, in patients not treated with insulin, self-monitoring is associated with higher HbA(1c) levels and psychological burden. 132 In a meta-analysis of four randomized controlled studies comparing the effects of glucose monitoring with no self-monitoring, the authors concluded, “The results do not provide evidence for clinical effectiveness of an item of care with appreciable costs. Further work is needed to evaluate self-monitoring so that resources for diabetes care can be used more efficiently.” 133 Meanwhile, self-monitoring is not widely practiced 134, 135 I am not saying it is not important to monitor blood glucose, but it is, perhaps, more important to educate our patients and ourselves and appreciate that glucose is but one marker of and contributor to a diffuse, complex disease and not an isolated target to be treated in a vacuum.
.Despite improving blood glucose concentrations in patients with type 2 diabetes by using either insulin or an oral drug (sulfonylurea), Yudkin and colleagues were unable to show improvement in markers of endothelial dysfunction (von Willebrand factor, cellular fibronectin, thrombomodulin, tissue plasminogen activator, soluble E-selectin or soluble intercellular adhesion molecule-1 or in urinary albumin excretion rate) after either treatment period. 29 In another study forty-three patients with type 2 diabetes and glycosylated hemoglobin (HbA1c) greater than 8.9 percent were randomized to either improved glycemic control or usual control for 20 weeks. 136 Despite significant lowering of HbA1c in the improved group (IC) there was no improvement in endothelial function as determined by measuring brachial artery flow-mediated dilatation. Furthermore, in the IC group weight increased by 3.2 kg after 20 weeks compared to less than 1.0 kg for the unimproved HbA1c group. In 1998, an ancillary study of the Diabetes Control and Complications Trial (DCCT) suggested that using insulin to tightly control glucose in patients with type-1 diabetes increases body fat and worsens risk factors for CHD (elevated triglycerides, more cholesterol in small dense LDL sub-fractions, lower HDL levels, and higher blood pressure) by increasing insulin resistance. 123 This sequence is very similar to that observed in patients with type-2 diabetes whose bodies make insulin but whose cells are resistant to it, suggesting that excessive use of insulin to lower or “improve” blood glucose may actually increase the risk for CHD. 137
United Kingdom Prospective Diabetes Study (UKPDS) — a different perspective
Currently hailed as a landmark inquiry, the UKPDS followed 5,102 patients with newly diagnosed type-2 diabetes in twenty-three British healthcare centers for an average of ten years. The study was designed to determine whether intensively applying drugs to lower blood glucose would lessen complications from diabetes. Although the small blood vessels supplying the eyes and kidneys seemed to improve somewhat, lowering blood glucose did not significantly improve the complications caused by atherosclerosis involving the large blood vessels that supply the heart, brain, and legs.
The UKPDS is fraught with problems. Drugs were administered in combinations, patients were crossed over into different treatment groups, and the diet group was not kept pure because 80 percent of them ultimately received one or more drugs. It is also unclear which diet was followed. Such confusion prompted the American Diabetes Association (ADA) to comment in December 1998 “the prevalence of treatment crossovers and additions reduces our confidence in the differences observed, or not detected, among the various pharmacological agents.” One subgroup assigned to receive a commonly prescribed combination of two drugs (a sulfonylurea and metformin) had a 96 percent increase in diabetes-related deaths and a 60 percent increase in death from any cause. And yet, the ADA’s position statement concludes that “nothing should stop practitioners from pursuing the American Diabetes Association’s goals for glycemia…,” 5 which supports tight control with drugs.
What about microvascular disease?
Elevated glucose causes the blood to become more viscous, which especially affects the small blood vessels supplying the eyes and kidneys. These tiny blood vessels have endothelial cells that differ a bit from those in larger vessels, and these changes in the blood are more likely to increase the pressure (transcapillary pressure). Consequent transcapillary passage of macromolecules, including leakage of plasma protein may ensue, 138, 139 which may explain microalbuminuria in diabetes. Also, high extracellular glucose concentration directly increases vascular endothelial growth factor (VEGF), which induces angiogenesis and increases endothelial permeability and dysfunction. 140 This can lead to microvascular disease of the eye with neovascularization and retinopathy. 141 In the UKPDS the main effect of glucose control after 10.5 years was only a 3/1,000 reduction in photocoagulation for retinal disease (from 1.1% in the standard arm to 0.8% in the intensive arm). Glucose control did not have an effect on clinical end points, such as visual acuity. 6 Lowering blood glucose with drugs may improve microvascular conditions, 5, 142 143 144 but, in many cases, for only a short time. Although glucose impairs endothelial cells, neither quickly lowering blood glucose by itself, nor tight control, have been shown to prevent continuing damage to the endothelial cells in the large blood vessels supplying heart and brain, nor does it lower insulin or improve inflammation. 127 4, 5, 7 Glucose control in the UKPDS failed to show a significant improvement in macrovascular diseases. One needs to reverse these afflictions to make a difference in the goals that really count — decreasing heart disease, stroke, leg amputation, prolonging life, and improving its quality. Different endothelial processes may contribute to atherombotic disease of the larger blood vessels. For example, macrovascular endothelial cells seem to be more affected by LDL oxidation than those of the microvasculature. 145 Drugs may have a function but the answer is not simply better drug therapy, but better-informed nutrition along with moderate exercise and avoiding cigarette smoke.
Here’s the secret: If you administer too much insulin or other drugs to lower blood glucose, you may pay a price —if insulin levels go up you can end up with worse endothelial dysfunction and insulin resistance and make patients fatter and sicker. Despite, or perhaps by, implementing insulin therapy in patients with type 2 diabetes we are worsening macrovascular disease. This is supported by the following report from diabetesincontrol.com,(November 14, 2001, Issue 78) “The number of lower-extremity amputations among diabetic patients in the U.S .increased from 36,000 in 1980 to 86,000 in 1996…Fifty-five percent of deaths in people with diabetes are caused by cardiovascular disease.” Likewise we are not very successful. The immediate and often angry response to this is often, “so what would you do, not treat them and let their eye disease deteriorate?” No. Lower blood glucose by methods that have been proven safe—lifestyle changes. The reply—“that’s not very easy to do.” Therein lies the challenge we will explore. There is no other rational choice, just like there is no magic pill, nor is there likely to ever be one.
Eric S. Freedland, MD graduated from University of Rochester School of Medicine in 1982, trained in internal medicine at Mt. Auburn Hospital in Cambridge, MA, and emergency medicine at Harbor-UCLA Medical Center in Torrance, CA, and has held faculty positions at Harvard Medical School (1990-1991) and Boston University School of Medicine (1992-1997). Dr. Freedland has developed a nutrition-centered model of disease with a special emphasis on diabetes. A staunch advocate for prescribing lifestyle changes before drugs, Dr. Freedland has written and lectured extensively on this subject.
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