Proinsulin-like molecules and plasminogen activator inhibitor type 1 (PAI-1) activity in diabetic and non-diabetic subjects with and without myocardial infarction

Glycaemic and insulinaemic impact of a diabetes-specific oral nutritional supplement with extra-virgin olive oil in patients with type 2 diabetes mellitus at nutritional risk: a randomized, double-blind, crossover, multicentre clinical trial (DIACARE)

Introduction

Introduction: there is controversy about the usefulness of specific enteral nutrition formulas in malnourished patients with diabetes. The effects on blood glucose and other aspects of metabolic control are not fully understood in the scientific literature. Objective: the aim of the study was to compare the glycaemic and insulinaemic response of patients with type 2 diabetes at risk of malnutrition after oral feed between a diabetes-specific formula with AOVE (DSF) and a standard one (STF). Methods: A randomized, double-blind, crossover, multicentre clinical trial was conducted in patients with type 2 diabetes at risk of malnutrition (SGA). The patients were randomized to receive either DSF or STF, a week apart. A glycaemia and insulinaemia curve was made at times 0 minutes, 30 min, 60 min, 90 min, 120 min, and 180 min after the patients drank 200 ml of the oral nutritional supplement (ONS). The principal variables were the area under the curve (AUC0-t) of glucose and insulin. Results: 29 patients (51 % women) were included, who were on average 68.84 (SD 11.37) years old. Regarding the degree of malnutrition, 86.2 % presented moderate malnutrition (B) and 13.8 % severe (C). When the patients received the DSF, they had a lower mean of glucose AUC0-t (-3,325.34 mg/min/dl [95 % CI: -4,3608.34 to -2,290.07]; p = 0.016) and also a lower mean of insulin AUC0-t (-451.14 uU/min/ml [95 % CI: -875,10 to -27.17]; p = 0.038). There were no differences in the degree of malnutrition. Conclusion: compared with STF, DSF with AOVE showed a better glycaemic and insulinaemic response in patients with type 2 diabetes at risk of malnutrition.

Association of vitronectin and plasminogen activator inhibitor-1 levels with the risk of metabolic syndrome and type 2 diabetes mellitus

It was the objective of this study to investigate the relation between vitronectin and plasminogen activator inhibitor (PAI)-1 plasma levels with nine-year incidences of the metabolic syndrome (MetS) and of type 2 diabetes mellitus (T2DM). Baseline plasma concentrations of vitronectin and PAI-1 were measured in 627 healthy participants from the prospective D.E.S.I.R. cohort who subsequently developed MetS (n=487) and T2DM (n=182) over a nine-year follow-up (42 presented both) and who were matched with two healthy control subjects each by use of a nested case-control design. Parameters composing the MetS explained about 20% of plasma vitronectin levels. An increase of one standard deviation of vitronectin was associated with increased risks of both the MetS (odds ratio [OR] = 1.21 [1.07 – 1.37], p = 0.003) and T2DM (OR = 1.24 [1.01 – 1.53], p = 0.045). Corresponding ORs for PAI-1 levels were 1.46 [1.27 – 1.68] (p < 10−4) and 1.40 [1.14 – 1.72] (p = 0.0012). However, the effects of vitronectin and PAI-1 levels on outcomes were not independent. The vitronectin–MetS association was restricted to individuals with low to modest PAI-1 levels (OR = 1.33 [1.14 – 1.54], p = 0.0003) while no association was observed in individuals with high PAI-1 levels (OR = 0.87 [0.68 – 1.10], p = 0.24), the test for interaction being highly significant (p = 0.0009). In conclusion, baseline plasma vitronectin is a marker of incident MetS at nine years. Its predictive ability for MetS and T2DM should not be assessed independently of PAI-1 levels.

Plasminogen activator inhibitor-1 and type 2 diabetes: a systematic review and meta-analysis of observational studies

An emerging body of evidence has implicated plasminogen activator inhibitor-1 (PAI-1) in the development of type 2 diabetes (T2D), though findings have not always been consistent. We systematically reviewed epidemiological studies examining the association of PAI-1 with T2D. EMBASE, PubMed, Web of Science, and the Cochrane Library were searched to identify studies for inclusion. Fifty-two studies (44 cross-sectional with 47 unique analytical comparisons and 8 prospective) were included. In pooled random-effects analyses of prospective studies, a comparison of the top third vs. bottom third of baseline PAI-1 values generated a RR of T2D of 1.67 (95% CI 1.28–2.18) with moderate heterogeneity (I² = 38%). Additionally, of 47 cross-sectional comparisons, 34(72%) reported significantly elevated PAI-1 among diabetes cases versus controls, 2(4%) reported significantly elevated PAI-1 among controls, and 11(24%) reported null effects. Results from pooled analyses of prospective studies did not differ substantially by study design, length of follow-up, adjustment for various putative confounding factors, or study quality, and were robust to sensitivity analyses. Findings from this systematic review of the available epidemiological literature support a link between PAI-1 and T2D, independent of established diabetes risk factors. Given the moderate size of the association and heterogeneity across studies, future prospective studies are warranted.

Plasminogen activator inhibitor-1 is associated with coronary artery calcium in Type 1 diabetes

BACKGROUND

Elevated levels of plasminogen activator inhibitor-1 (PAI-1), the major inhibitor of fibrinolysis, is associated with coronary artery disease (CAD). This association may not be independent of factors related to insulin resistance (IR). Patients with Type 1 diabetes mellitus have increased CAD and an increase in sub-clinical CAD which develops earlier in life. It is not known if PAI-1 is associated with sub-clinical CAD in Type 1 diabetes or if this association is independent of IR.

METHODS AND RESULTS

Type 1 diabetes patients (n=560) and participants without diabetes (n=693) were assessed for coronary artery calcium (CAC), a surrogate for subclinical CAD, by electron-beam computed tomography. PAI-1 was associated with CAC in both Type 1 diabetes (OR=1.32, 95% CI=1.12-1.58) and non-diabetes (OR=1.34, 95% CI=1.13-1.58), after controlling for traditional risk factors not associated with IR. In Type 1 diabetes, the relationship between PAI-1 and CAC was strongest for younger participants (P=.02 for PAI-1-by-age interaction) after controlling for factors related to IR. PAI-1 was positively associated with CAC for Type 1 diabetes participants younger than 45 years of age.

CONCLUSION

PAI-1 levels are independently related to CAC in younger Type 1 diabetes participants. PAI-1 levels were not independently related to CAC in non-diabetes participants.

Multimarker approach to evaluate the incidence of the metabolic syndrome and longitudinal changes in metabolic risk factors: the Framingham Offspring Study

BACKGROUND

The metabolic syndrome (MetS) is associated with increased cardiovascular risk. We evaluated the relative contributions of circulating biomarkers representing distinct biological pathways to the incidence of MetS and to longitudinal changes of its constituent risk factors.

METHODS AND RESULTS

We measured 8 circulating biomarkers reflecting inflammation (C-reactive protein), hemostasis (plasminogen activator inhibitor-1, fibrinogen), neurohormonal activity (aldosterone, renin, B-type natriuretic peptide, N-terminal proatrial natriuretic peptide), and endothelial dysfunction (homocysteine) in 2292 Framingham Offspring Study participants (mean age, 57 years; 56% women). We related the biomarker panel to incidence of MetS on follow-up initially and then related biomarkers associated with incident MetS to longitudinal change in its components. On follow-up (mean, 2.9 years), 282 participants (of 1473 participants without prevalent MetS at baseline) developed MetS. After adjustment for clinical risk factors, the biomarker panel was associated with incident MetS (P=0.008). On backward elimination, plasminogen activator inhibitor-1 and aldosterone remained associated with incident MetS (multivariable-adjusted odds ratio per 1-SD increment log marker, 1.31 [P=0.004] and 1.21 [P=0.015], respectively). In multivariable analyses evaluating longitudinal change in MetS components (analyzed as continuous variables), plasminogen activator inhibitor-1 was significantly and positively associated with changes in fasting glucose, systolic blood pressure, and triglycerides (all P<0.05). Serum aldosterone was associated positively with change in systolic blood pressure (P=0.023) and inversely with change in high-density lipoprotein cholesterol (P=0.001).

CONCLUSIONS

Higher circulating plasminogen activator inhibitor-1 and aldosterone levels are associated with the development of MetS and with longitudinal change of its components, suggesting that these biomarkers and related pathways play a key role in mediating metabolic risk.

Impaired fibrinolysis and risk for cardiovascular disease in the metabolic syndrome and type 2 diabetes

Patients with the metabolic syndrome are insulin resistant and manifest a cluster of risk factors for cardiovascular disease. Impaired fibrinolysis and increased concentrations in blood of plasminogen activator inhibitor-1 (PAI-1) are related to insulin resistance and abdominal obesity and may contribute to the increased risk for cardiovascular disease in this group. Weight loss, metformin, and thiazolidinediones ameliorate insulin resistance and decrease concentrations of PAI-1. Thus, they may lower risk in patients with the metabolic syndrome.

IRIS II Study: Sensitivity and specificity of intact proinsulin, adiponectin, and the proinsulin/adiponectin ratio as markers for insulin resistance

OBJECTIVE

This study was performed to compare the specificity and sensitivity of intact proinsulin, adiponectin, and their ratio (proinsulin/adiponectin) in the prediction of insulin resistance as assessed by the homeostasis model assessment (HOMA) score (> or =2 = resistant).

RESEARCH DESIGN AND METHODS

Using a cross-sectional approach, 500 orally treated patients with type 2 diabetes (272 women, 238 men; mean +/- SD age, 64.8 +/- 11.6 years; hemoglobin A1c, 7.0 +/- 1.5%; disease duration, 5.8 +/- 6.1 years) were investigated. Various cutoffs for body mass index-adjusted adiponectin and proinsulin/adiponectin were compared with the established cutoff value of 10 pmol/L for fasting proinsulin.

RESULTS

Fasting proinsulin correlated more closely with the HOMA score (r = 0.560, P < 0.001) than fasting adiponectin (r = -0.204, P < 0.001) or proinsulin/adiponectin (r = 0.355, P < 0.001). For proinsulin, specificity and sensitivity for insulin resistance in correlation to the HOMA score results were 96% and 70%, respectively. At a comparable specificity level to proinsulin, adiponectin did not reach a comparable sensitivity (14%), while the proinsulin/adiponectin ratio almost reached the same sensitivity (65%). Overall, patients with elevated proinsulin had a higher prevalence of micro- and macrovascular disease [odds ratio 1.47 (adiponectin, 1.08; proinsulin/ adiponectin, 1.48) and 1.34 (adiponectin, 1.32; proinsulin/adiponectin, 1.27), respectively].

CONCLUSIONS

Elevation of fasting intact proinsulin seems to be the more specific marker for insulin resistance and increased cardiovascular risk than suppression of fasting adiponectin. Formation of the ratio does not lead to a further increase in the predictive value.

Evaluation of a scoring scheme, including proinsulin and the apolipoprotein B/apolipoprotein A1 ratio, for the risk of acute coronary events in middle-aged men: Uppsala Longitudinal Study of Adult Men (ULSAM)

BACKGROUND

In recent years, the importance of circulating levels of proinsulin and apolipoproteins as risk factors for myocardial infarction (MI) has been highlighted. The aims of the current study were to investigate whether introduction of these new markers of coronary risk could improve the performance of a risk prediction score and to compare this new score with traditional scoring schemes, such as the Framingham Study and the Prospective Cardiovascular Munster (PROCAM) Study schemes.

METHODS

From 1970 to 1973 all 50-year-old men in Uppsala, Sweden, were invited to participate in a health survey aimed at identifying risk factors for cardiovascular disease (the Uppsala Longitudinal Study of Adult Men [ULSAM] cohort). The current study investigated metabolic characteristics at baseline and the incidence of fatal and nonfatal MI (n = 251) during 28.7 years of follow-up in 1108 men who were free of coronary heart disease at baseline.

RESULTS

The risk prediction score was derived from one half of the population sample from the ULSAM cohort and included systolic blood pressure, smoking, family history of MI, serum proinsulin, and the ratio between apolipoprotein B and apolipoprotein A1. The score was highly predictive for future MI (hazard ratio, 1.77 for a 1 SD increase; 95% CI, 1.49 to 2.10, P <.0001) in the other half of the population that was not used for generating the score. The ULSAM score performed slightly better than the Framingham and PROCAM scores (evaluated as areas under the receiver operating curves; Framingham, 61%; PROCAM, 63%; ULSAM, 66%; P =.08).

CONCLUSIONS

A risk prediction score for MI including proinsulin and the ratio between apolipoprotein B and apolipoprotein A1 was developed in middle-aged men. This score was highly predictive for future fatal and nonfatal MI and proved to be at least as good as the Framingham and the PROCAM scores, being based on traditional risk factors.

Hypofibrinolysis in the insulin resistance syndrome: implication in cardiovascular diseases

Insulin resistance syndrome (IRS) is associated with increased cardiovascular morbidity and mortality. IRS is becoming one of the major health problems as its prevalence grows rapidly. Accelerated atherothrombotic process in the IRS is attributed to metabolic abnormalities, inflammation and to impaired fibrinolysis due to increased plasma plasminogen activator inhibitor type 1 (PAI-1) levels. Proinflammatory cytokines may have an important role in PAI-1 overexpression, particularly in the adipose tissue. Studies in genetically modified mice indicate that PAI-1 might be involved in the aetiopathogenesis of obesity. Modifying PAI-1 expression by PAI-1 inhibitors may open a new field of research and may reveal the true role of PAI-1 in atherosclerotic and insulin resistance processes.

Cardiovascular risk factors for stable angina pectoris versus unheralded myocardial infarction

BACKGROUND

Ischemic heart disease can vary substantially in its clinical presentation. Some patients have acute myocardial infarction (MI) without any previous signs of myocardial ischemia, whereas other patients may have stable angina pectoris for years without periods of acute unstability. This study compared baseline risk factors between subjects in whom stable angina pectoris developed and subjects in whom unheralded fatal or nonfatal MI developed during the follow-up period.

METHODS

In 1970 to 1973, all 50-year-old men in Uppsala, Sweden, were invited to participate in a health survey aimed at identifying risk factors for cardiovascular disease. The present study is a nested case-control study of subjects who were free of coronary heart disease (CHD) at baseline and who then underwent revascularization (percutaneous transluminal coronary angioplasty or coronary artery bypass grafting) because of angina pectoris without preceding MI (n = 70) or in whom fatal or nonfatal MI developed without prior known CHD (n = 372) during the period until 1998.

RESULTS

In multivariate Cox proportional hazard models, low-density lipoprotein and high-density lipoprotein levels (protective) were significant independent risk factors for stable angina pectoris demanding revascularization, whereas smoking, diastolic blood pressure, serum proinsulin levels, and serum lipid levels were significant independent predictors of subsequent unheralded MI. When comparing hazard ratios (HR), significantly higher HR for diastolic blood pressure (1.40 vs 1.00, for 1 SD increase) and serum proinsulin (1.82 vs1.20, for 1 SD increase) were found in the group in which unheralded MI developed than in the group with stable angina pectoris.

CONCLUSIONS

Serum lipid levels were important risk factors for the development of both stable and acute coronary heart disease. In addition, proinsulin levels and blood pressure were independent predictors of unheralded MI only, which suggests that these factors are involved in thrombosis, plaque rupture, or both.

Plasminogen activator inhibitor-1, inflammation, obesity, insulin resistance and vascular risk

Elevated plasma plasminogen activator inhibitor-1 (PAI-1) level is a core feature of insulin-resistance syndrome (IRS). Atherothrombotic complications in IRS are partly attributed to impaired fibrinolysis caused by increased plasma PAI-1 levels. Although the etiology of IRS is far from being explained, the clustering of inflammation, adipose tissue accumulation and insulin resistance suggests an etiopathological link. Proinflammatory cytokines might regulate PAI-1 expression in IRS; however, more studies are needed to confirm this complex mechanism in humans. Furthermore, modifying PAI-1 expression by PAI-1 inhibitors provides a new challenge and may reveal the true role of PAI-1 in atherosclerotic and insulin resistance processes.

Plasminogen activator inhibitor type-1 in cardiovascular disease. Status report 2001

Plasminogen activator inhibitor type-1 (PAI-1) is known to contribute to thrombus formation and to the development and the clinical course of acute and chronic cardiovascular disease, as well as of other arterial and venous thromboembolic diseases. Recently, an important role of elevated pretreatment levels of PAI-1 for failure of thrombolytic therapy of acute myocardial infarction has been discussed. PAI-1 plasma levels depend on the one hand on gene regulation but are related on the other hand to known risk factors of atherosclerosis like insulin resistance, diabetes or hypertriglyceridemia, respectively. Furthermore, an activated renin-angiotensin-aldosterone system (RAAS) significantly contributes to the upregulation of PAI-1 concentration via a receptor-mediated mechanism. In accordance to the known mechanisms of regulation of PAI-1 plasma levels, the use of specific agents like antidiabetic drugs, fibrates, statins, ACE inhibitors and angiotensin II type-1 receptor-blockers may contribute to the downregulation of circulating PAI-1 and, therefore, increase the fibrinolytic capacity and consecutively counteract the thrombotic tendency. To further improve the efficacy of thrombolytic therapy, a PAI-1 resistant variant of t-PA, TNK-t-PA, has been developed and is now available for acute myocardial infarction.

Cross-sectional and prospective associations between proinsulin and cardiovascular disease risk factors in a population experiencing rapid cultural transition

OBJECTIVE

To examine cross-sectional and prospective associations between proinsulin and cardiovascular disease risk factors using data from a population-based study of type 2 diabetes among Native Canadians.

RESEARCH DESIGN AND METHODS

Between 1993 and 1995, 72% of eligible members of a Native Canadian community participated in a baseline diabetes prevalence survey. Fasting samples were collected for glucose, C-peptide, proinsulin, lipids, and apolipoproteins. A 75-g oral glucose tolerance test was administered, and a second sample for glucose was drawn after 120 min. Blood pressure and waist circumference were determined. In the present study, subjects with normal glucose tolerance (NGT) (n = 505) and impaired glucose tolerance (IGT) (n = 74) were included in cross-sectional analyses. In 1998, 95 individuals who had IGT or NGT at baseline with an elevated 2-h glucose concentration (> or = 7.0 mmol/l) participated in a follow-up evaluation using the protocol used at baseline. Cross-sectional and prospective associations between proinsulin and cardiovascular risk factors were assessed using correlation and multiple linear regression analyses.

RESULTS

After adjustment for covariates including age, sex, C-peptide, waist circumference, and glucose tolerance status, fasting proinsulin concentration was significantly associated with concurrently measured lipid and apolipoprotein concentrations (triglycerides: r = 0.18, P < 0.0001; total cholesterol: r = 0.10, P = 0.02; LDL cholesterol: r = 0.11, P = 0.01; HDL cholesterol: r = -0.16, P = 0.0002; apolipoprotein (apo) B: r = 0.17, P < 0.0001; apoAI: r = -0.11, P = 0.008). In the adjusted prospective analysis, baseline triglycerides, HDL cholesterol, and apoB were associated with changes over time in proinsulin (r = 0.23, P = 0.04; r = -0.30, P = 0.01; r = 0.23, P = 0.04; respectively).

CONCLUSIONS

These results confirm previously reported cross-sectional associations between proinsulin and lipid concentrations. In addition, an unexpected association between baseline lipids and proinsulin change was documented.

Plasminogen activator inhibitor type-1 (part one): basic mechanisms, regulation, and role for thromboembolic disease

Plasminogen activator inhibitor type-1 (PAI-1) is a rapid inhibitor of tissue plasminogen activator (tPA) in circulation. Evidence suggests that the PAI-1 concentration is responsible for the regulation of the endogenous fibrinolytic system through its tPA/PAI-1 interactions. Accordingly, increased levels of PAI-1 have emerged as a masker for an increased thrombolic risk. This article represents a status report of mechanism of action, regulation of plasma levels, as well as the role of PAI-1 in arterial and venous thromboembolic disease.

Diabetes and endothelial dysfunction: a clinical perspective

The main etiology for mortality and a great percent of morbidity in patients with diabetes mellitus is atherosclerosis. A hypothesis for the initial lesion of atherosclerosis is endothelial dysfunction, defined pragmatically as changes in the concentration of the chemical messengers produced by the endothelial cell and/or by blunting of the nitric oxide-dependent vasodilatory response to acetylcholine or hyperemia. Endothelial dysfunction has been documented in patients with diabetes and in individuals with insulin resistance or at high risk for developing type 2 diabetes. Factors associated with endothelial dysfunction in diabetes include activation of protein kinase C, overexpression of growth factors and/or cytokines, and oxidative stress. Several therapeutic interventions have been tested in clinical trials aimed at improving endothelial function in patients with diabetes. Insulin sensitizers may have a beneficial effect in the short term, but the virtual absence of trials with cardiovascular end-points preclude any definitive conclusion. Two trials offer optimism that treatment with ACE inhibitors may have a positive impact on the progression of atherosclerosis. Although widely used, the effect of hypolipidemic agents on endothelial function in diabetes is not clear. The role of antioxidant therapy is controversial. No data have been published regarding the effects of hormonal replacement therapy on endothelial dysfunction in postmenopausal women with type 2 diabetes.

Relationship between lipoprotein(a) phenotypes and plaminogen activator inhibitor type 1 in diabetic patients

It has been demonstrated in vitro that lipoprotein(a) [Lp(a)] increases the endothelial synthesis of plasminogen activator inhibitor 1 (PAI-1). However, this effect in vivo is controversial, and the possible relationship between PAI-1 and Lp(a) phenotypes has not been evaluated. The aim of the study was to determine the influence of Lp(a) and its phenotypes on PAI-1 serum concentrations in diabetic patients. For this purpose we include 75 Caucasian diabetic patients (34 consecutive type I and 41 consecutive type II) without late diabetic complications. Lp(a) and PAI-1 were assessed by ELISA. Lp(a) phenotypes were determined by SDS-PAGE followed by immunoblotting, and grouped according to size in small (F,B,S1,S2), big (S3,S4), and null. A linear correlation between Lp(a) and PAI-1 was not observed either as a whole or when type I and type II diabetic patients were analyzed separately. However, significant differences were detected in PAI-1 levels when Lp(a) phenotypes were considered (small: 42.1+/-31.8 ng/mL; big: 37.2+/-26.1 ng/mL; null: 14.4+/-14.4; p< 0.05). The significant differences were due to the low PAI-1 concentrations observed in patients with null phenotype. Our results suggest that fibrinolytic activity might be preserved in diabetic patients with null Lp(a) phenotype. Furthermore, it could be speculated that diabetic patients with null phenotype should be considered at low risk to develop cardiovascular disease.

Effect of tumor necrosis factor alpha and transforming growth factor beta 1 on plasminogen activator inhibitor-1 secretion from subcutaneous and omental human fat cells in suspension culture

Elevated levels of plasminogen activator inhibitor-1 (PAI-1) are characteristic of the obese state and may contribute to the association between obesity and cardiovascular disease. In this study, we measured the rate of secretion of PAI-1 antigen in isolated subcutaneous and omental abdominal adipocytes from severely obese and non-obese individuals and studied the effect of selected cytokines on PAI-1 release using a suspension culture technique. PAI-1 secretion was approximately 2-fold greater in isolated fat cells from the obese versus non-obese subjects. In addition, PAI-1 mRNA levels were higher in adipose tissue samples from obese versus non-obese individuals (P < .05). PAI-1 release was also approximately 2-fold greater in omental versus subcutaneous adipocytes from both obese and non-obese subjects (each P < .05). A 24-hour exposure to 1 nmol/L tumor necrosis factor alpha (TNF-alpha) slightly increased PAI-1 release from both subcutaneous and omental adipocytes (30% +/- 21% and 17% +/- 18%, respectively, nonsignificant [NS]). Transforming growth factor beta 1 (TGF-beta1) induced a significant dose-dependent increase of PAI-1 release into the medium. Exposure to 400 pmol/L TGF-beta1 of subcutaneous and omental fat cells from both obese and non-obese individuals elevated PAI-1 secretion by 2-fold. These data provide evidence that human fat cells release a substantial amount of PAI-1 in a depot-specific manner and that TGF-beta1 particularly contributes to the regulation of PAI-1 secretion.

High proinsulin concentration precedes acute myocardial infarction in a nondiabetic population

Hyperinsulinemia has been shown to have strong and consistent associations with a cluster of cardiovascular risk factors. Yet the associations between hyperinsulinemia and coronary heart disease (CHD) have been weak, at best, and often inconsistent. Most previous studies have analyzed the insulin level using a radioimmunoassay method, which does not separate proinsulin from intact (true) insulin. New methods separating the two have demonstrated that proinsulin may be at least as strongly or even more strongly associated than intact insulin with a CHD-promoting risk factor profile. In this incident case-control study of a nondiabetic population, 67 cases of first acute myocardial infarction (AMI) were compared with 127 individually age- and sex-matched controls. Blood sampling was collected prior to disease outcome. Proinsulin and intact insulin levels were measured using highly sensitive two-site sandwich enzyme-linked immunosorbent assays (ELISAs). The highest quartile of proinsulin, in contrast to intact insulin, showed a greater than threefold increase in AMI compared with the lowest quartile, with an odds ratio (OR) and 95% confidence interval (CI) of 3.5 and 1.2 to 9.9, respectively. The increased risk of AMI persisted after controlling for total cholesterol, smoking status, diastolic blood pressure, and antihypertensive medication, and disappeared after additional control was used for the body mass index. High levels of proinsulin, even in a nondiabetic population, seem to be a strong and independent risk factor for AMI. The mechanism underlying the relationship may be direct via effects on fibrinolysis or, probably more plausibly, indirect, where proinsulin is a marker of an underlying metabolic disturbance.

Relative contribution of insulin and its precursors to fibrinogen and PAI-1 in a large population with different states of glucose tolerance. The Insulin Resistance Atherosclerosis Study (IRAS)

Hyperinsulinemia is associated with the development of coronary heart disease. However, the underlying mechanisms are still poorly understood. Hypercoagulability and impaired fibrinolysis are possible candidates linking hyperinsulinism with atherosclerotic disease, and it has been suggested that proinsulin rather than insulin is the crucial pathophysiological agent. The aim of this study was to investigate the relationship of insulin and its precursors to markers of coagulation and fibrinolysis in a large triethnic population. A strong and independent relationship between plasminogen activator inhibitor-1 (PAI-1) antigen and insulin and its precursors (proinsulin, 32-33 split proinsulin) was found consistently across varying states of glucose tolerance (PAI-1 versus fasting insulin [proinsulin], r=0.38 [r=0.34] in normal glucose tolerance; r=0.42 [r=0.43] in impaired glucose tolerance; and r=0.38 [r=0.26] in type 2 diabetes; all P<0.001). The relationship remained highly significant even after accounting for insulin sensitivity as measured by a frequently sampled intravenous glucose tolerance test. In a stepwise multiple regression model after adjusting for age, sex, ethnicity, and clinic, both insulin and its precursors were significantly associated with PAI-1 levels. The relationship between fibrinogen and insulin and its precursors was significant in the overall population (r=0.20 for insulin and proinsulin; each P<0.001) but showed a more inconsistent pattern in subgroup analysis and after adjustments for demographic and metabolic variables. Stepwise multiple regression analysis showed that proinsulin (split products) but not fasting insulin significantly contributed to fibrinogen levels after adjustment for age, sex, clinic, and ethnicity. Decreased insulin sensitivity was independently associated with higher PAI-1 and fibrinogen levels. In summary, we were able to demonstrate an independent relationship of 2 crucial factors of hemostasis, fibrinogen and PAI-1, to insulin and its precursors. These findings may have important clinical implications in the risk assessment and prevention of macrovascular disease, not only in patients with overt diabetes but also in nondiabetic subjects who are hyperinsulinemic.