Biomedical subjects

M F Saad

Publications and source records attributed to M F Saad.

At least 19 recordsLinked to original sources

PubMed2005

Interstitial fluid glucose dynamics during insulin-induced hypoglycaemia.

AIMS/HYPOTHESIS: Glucose sensors often measure s.c. interstitial fluid (ISF) glucose rather than blood or plasma glucose. Putative differences between plasma and ISF glucose include a protracted delay during the recovery from hypoglycaemia and an increased gradient during hyperinsulinaemia. These have often been investigated using sensor systems that have delays due to signal smoothing, or require long equilibration times. The aim of the present study was to define these relationships during hypoglycaemia in a well-equilibrated system with no smoothing. METHODS: Hypoglycaemia was induced by i.v. insulin infusion (360 pmol.m(-2).min(-1)) in ten non-diabetic subjects. Glucose was sequentially clamped at approximately 5, 4.2 and 3.1 mmol/l and allowed to return to normoglycaemia. Subjects wore two s.c. glucose sensors (Medtronic MiniMed, Northridge, CA, USA) that had been inserted for more than 12 h. A two-compartment model was used to quantify the delay and gradient. RESULTS: The delay during the fall in plasma glucose was not different from the delay during recovery (8.3+/-0.67 vs 6.3+/-1.1 min; p=0.27) and no differences were observed in the ratio of sensor current to plasma glucose at basal insulin (2.7+/-0.25 nA.mmol(-1).l) compared with any of the hyperinsulinaemic clamp phases (2.8+/-0.18, 2.7+/-0.021, 2.9+/-0.21; p=NS). The ratio was significantly elevated following recovery to normoglycaemia (3.1+/-0.2 nA.mmol(-1).l; p<0.001). CONCLUSIONS/INTERPRETATION: The elevated ratio suggests that the plasma to ISF glucose gradient was decreased following hypoglycaemia, possibly due to increased skin blood flow. Recovery from hypoglycaemia is not accompanied by a protracted delay and insulin does not increase the plasma to s.c. ISF glucose gradient.

Adult↗

PubMed2005

Quantitative trait loci for abdominal fat and BMI in Hispanic-Americans and African-Americans: the IRAS Family study.

OBJECTIVE: To conduct linkage analysis for body mass index (BMI, kg/m2), waist-to-hip ratio (WHR), visceral adipose tissue mass (VAT, cm2) and subcutaneous adipose tissue mass (SAT, cm2) using a whole genome scan. DESIGN: Cross-sectional family study. STUDY SUBJECTS: African-American families from Los Angeles (AA, n=21 extended pedigrees) and Hispanic-American families (HA) from San Antonio, TX (HA-SA, n=33 extended pedigrees) and San Luis Valley, CO (HA-SLV, n=12 extended pedigrees), totaling 1049 individuals in the Insulin Resistance and Atherosclerosis (IRAS) Family Study. MEASUREMENTS: VAT and SAT were measured using a computed tomography scan obtained at the fourth and fifth lumbar vertebrae. All phenotypes were adjusted for age, gender, and study center. VAT, SAT, and WHR were analyzed both unadjusted and adjusted for BMI. RESULTS: Significant linkage to BMI was found at D3S2387 (LOD=3.67) in African-Americans, and at D17S1290 in Hispanic-Americans (LOD=2.76). BMI-adjusted WHR was linked to 12q13-21 (D12S297 (LOD=2.67) and D12S1052 (LOD=2.60)) in Hispanic-Americans. The peak LOD score for BMI-adjusted VAT was found at D11S2006 (2.36) in Hispanic families from San Antonio. BMI-adjusted SAT was linked to D5S820 in Hispanic families (LOD=2.64). Evidence supporting linkage of WHR at D11S2006, VAT at D17S1290, and SAT at D1S1609, D3S2387, and D6S1056 was dependent on BMI, such that the LOD scores became nonsignificant after adjustment of these phenotypes for BMI. CONCLUSIONS: Our findings both replicate previous linkage regions and suggest novel regions in the genome that may harbor quantitative trait locis contributing to variation in measures of adiposity.

Adipose Tissue↗

PubMed2005

Association of adipose tissue deposition and beta-2 adrenergic receptor variants: the IRAS family study.

OBJECTIVE: Adipose tissue distribution (visceral vs subcutaneous) has been shown to be an important predictor of insulin resistance, diabetes and cardiovascular disease, independent of body mass index. The beta-2 adrenergic receptor is a major lipolytic receptor in human fat cells and the gene that codes for this protein is an important candidate gene for measures of adiposity and fat deposition. We examined whether two common polymorphisms in codons 16 (Arg16Gly) and 27 (Gln27Glu) are associated with measures of fat distribution in participants of the IRAS Family Study. METHODS: We recruited African-American (AA) and Hispanic-American (HA) families from Los Angeles, CA, USA (18 pedigrees, 272 AA individuals), San Antonio, TX, USA (33 pedigrees, 448 HA individuals) and San Luis Valley, CO, USA (12 pedigrees, 272 HA individuals). We estimated adipose tissue distribution via computed tomography. To test for an association between adiposity measures and these polymorphisms, we used generalized estimating equations, adjusting for age, gender, clinical site (ethnicity), body mass index, and familial correlation. RESULTS: Of the 992 individuals genotyped for these polymorphisms, 57% were female and 15% had been diagnosed with type 2 diabetes mellitus. The mean age was 42.7+/-14.6 y. The Glu27 allele of the Gln27Glu polymorphism was positively associated with (P-value for recessive model): body mass index (0.025), visceral adipose tissue (<0.0001) and visceral-to-subcutaneous adipose ratio (0.009), but not with subcutaneous adipose tissue (0.952). The Arg16Gly polymorphism was not associated with any of the adiposity measures. CONCLUSIONS: These findings suggest that genetic variation in the beta-2 adrenergic receptor gene influences fat deposition and body size in AAs and HAs. In particular, these results support a role for the gene in the distribution of visceral adipose tissue but not subcutaneous adipose tissue.

Adipose Tissue↗

PubMed2005

Abdominal obesity predicts declining insulin sensitivity in non-obese normoglycaemics: the Insulin Resistance Atherosclerosis Study (IRAS).

AIM: Cross-sectional studies have demonstrated a relationship between obesity and insulin sensitivity (S(I)); however, there is a lack of evidence from longitudinal studies. METHODS: The Insulin Resistance Atherosclerosis Study (IRAS) estimated S(I) (x10(-4)/min.microU/ml) directly using a frequently sampled intravenous glucose tolerance test with minimal model analysis in 504 normoglycaemic subjects. Partial correlation coefficients (r) were calculated to compare the relationship of change in S(I) from baseline to 5 years later (DeltaS(I)) with baseline waist circumference (waist) as a measure of abdominal obesity and body mass index (BMI) as a measure of overall obesity. Mean DeltaS(I) was -1.06 (SD = 1.85). RESULTS: Higher baseline waist (r = -0.16; p = 0.0005), but not BMI (r = -0.005; p = 0.91), was associated with (-) DeltaS(I) in models including sex, ethnicity, clinical centre and baseline S(I), BMI, waist, age and physical activity. The waist-DeltaS(I) relationship differed across the levels of baseline BMI, being significant only in normal weight (r = -0.21) and overweight subjects (r = -0.16), but not in obese subjects. DeltaS(I) was correlated with a 5-year change in either obesity measure (Deltawaist: r = -0.22 and DeltaBMI: r = -0.20; p = 0.0001). CONCLUSIONS: Among non-diabetics, waist circumference was a strong predictor of declining S(I) among lean subjects, a modest predictor among overweight subjects, but was not predictive among obese individuals. Waist circumference should be considered, in addition to BMI, when identifying individuals at high risk of diabetes or the insulin resistance syndrome.

Abdomen↗

PubMed2005

Effects of liraglutide (NN2211), a long-acting GLP-1 analogue, on glycaemic control and bodyweight in subjects with Type 2 diabetes.

AIMS: Liraglutide (NN2211) is a long-acting GLP-1 analogue, with a pharmacokinetic profile suitable for once-daily administration. This multicentre, double-blind, parallel-group, double-dummy study explored the dose-response relationship of liraglutide effects on bodyweight and glycaemic control in subjects with Type 2 diabetes. METHODS: Subjects (BMI 27-42 kg/m(2)) with Type 2 diabetes who were previously treated with an OAD (oral anti-diabetic drug) monotherapy (69% with metformin), and had HbA(1c) < or = 10% were enrolled. After a 4-week metformin run-in period, 210 subjects (27-73 years, 60% female) were randomised to receive liraglutide (0.045-0.75 mg) once daily or continued on metformin 1000 mg b.d. for 12 weeks. RESULTS: Mean baseline values for the six treatment groups ranged from 6.8 to 7.5% for HbA(1c), and 8.06-9.44 mmol/l (145-170 mg/dl) for fasting plasma glucose. After 12-week treatment, a weight change of -0.05 to -1.9% was observed for the six treatment groups. Mean HbA(1c) changes from baseline for 0.045, 0.225, 0.45, 0.6, 0.75 mg liraglutide and metformin were +1.28%, +0.86%, +0.22%, +0.16%, +0.30% and +0.09%, respectively. No significant differences in HbA(1c) were observed between liraglutide and metformin groups at the three highest liraglutide dose levels (0.45, 0.6 and 0.75 mg). The lowest two liraglutide doses (0.045 mg and 0.225 mg) were not sufficient to maintain the fasting plasma glucose values achieved by metformin. No major hypoglycaemic episodes were reported. Episodes of nausea and/or vomiting were reported by 11 patients (6.3%) receiving liraglutide and three (8.8%) receiving metformin. CONCLUSIONS: Once-daily liraglutide improved glycaemic control and weight, in a comparable degree to metformin. Liraglutide appeared to be safe and generally well tolerated. Higher doses of liraglutide merit study in future clinical trials.

Adult↗

PubMed2004

Combination therapy for type 2 diabetes: repaglinide plus rosiglitazone.

AIMS: This 24-week, randomized, multicentre, open-label, parallel-group clinical trial compared efficacy and safety of repaglinide monotherapy, rosiglitazone monotherapy, and combination therapy (repaglinide plus rosiglitazone) in Type 2 diabetes after unsatisfactory response to sulphonylurea or metformin monotherapy. METHODS: Enrolled patients (n = 252) were adults having Type 2 diabetes for at least 1 year, with HbA(1c) values > 7.0% after previous monotherapy (sulphonylurea or metformin, >/= 50% maximal dose). Prior therapy was withdrawn for 2 weeks, followed by randomization to repaglinide, rosiglitazone, or repaglinide/rosiglitazone. Study treatments were initiated with a 12-week dose optimization period (doses optimized according to labelling), followed by a 12-week maintenance period. Efficacy endpoints were changes in HbA(1c) values (primary) or fasting plasma glucose values (secondary). RESULTS: Baseline HbA(1c) values were comparable (9.3% for repaglinide, 9.0% for rosiglitazone, 9.1% for combination). Mean changes in HbA(1c) values at the end of treatment were greater for repaglinide/rosiglitazone therapy (-1.43%) than for repaglinide (-0.17%) or rosiglitazone (-0.56%) monotherapy. Reductions of fasting plasma glucose values were also greater for combination therapy (-5.2 mmol/l, -94 mg/dl) than for repaglinide monotherapy (-3.0 mmol/l, -54 mg/dl) or rosiglitazone monotherapy (-3.7 mmol/l, -67 mg/dl). Minor hypoglycaemic events occurred in 9% of combination therapy patients, vs. 6% for repaglinide and 2% for rosiglitazone. Individual weight gains for combination therapy were correlated to HbA(1c) response. CONCLUSIONS: The combination therapy regimen was well tolerated. In patients previously showing unsatisfactory response to oral monotherapy, glycaemic reductions were greater for the repaglinide/rosiglitazone combination regimen than for use of either repaglinide or rosiglitazone alone.

Blood Glucose↗

PubMed2000

Hepatic glucokinase promoter polymorphism is associated with hepatic insulin resistance in Asian Indians.

BACKGROUND: The role of glucokinase (GCK) in the pathogenesis of maturity-onset diabetes of the young is well established. However, its role in the common form of type 2 diabetes is far from convincing. We investigated the role of the G-to-A polymorphism in the hepatic GCK promoter on insulin sensitivity and beta cell function in 63 normotensive Asian Indians with normal glucose tolerance. As proposed by Matsuda and DeFronzo, hepatic insulin sensitivity (ISIH) and total body insulin sensitivity (ISIM) were estimated from the oral glucose tolerance test. Beta cell function was estimated using %B from the Homeostasis Model Assessment and insulingenic index (dI/dG). RESULT: We identified 38 GG, 24 GA, and one AA subjects. The AA subject was pooled with the GA subjects during the analysis. No difference was noted in the demographic features between the two genotypic groups (GG vs. GA/AA). Compared to the GG group, the GA/AA group had a lower ISIH (p=0.002), a lower ISIM (p=0.009), a higher %B (p=0.014), and a higher dI/dG (p=0.030). Multivariate analysis revealed that this polymorphism is an independent determinant for ISIH (p=0.019) and along with age, waist-hip ratio, gender, and diastolic blood pressure accounted for 51.5% of the variation of ISIH. However, this polymorphism was a weak, but independent determinant for ISIM (p=0.089) and %B (p=0.083). Furthermore, it had no independent effect on dI/dG (p=0.135). CONCLUSIONS: These data suggest that the G-to-A polymorphism in the hepatic GCK promoter is associated with hepatic insulin resistance in Asian Indians.

Adult↗

PubMed2000

Carotid artery atherosclerosis in type-2 diabetic and nondiabetic subjects with and without symptomatic coronary artery disease (The Insulin Resistance Atherosclerosis Study).

Type-2 diabetes mellitus is associated with a 2- to 4-fold increase in the risk of clinical coronary artery disease (CAD). It has been suggested that diabetic subjects without clinical CAD should be treated as aggressively for cardiovascular risk factors as subjects with CAD. This would be warranted if diabetic subjects without clinical CAD would have accelerated CAD similar to that of nondiabetic subjects with symptomatic CAD. To assess this suggestion, we compared the intima-media wall thickness in the common carotid artery (CCA) and internal carotid artery (ICA) in 43 diabetic subjects with clinical CAD, 446 diabetic subjects without clinical CAD, 47 nondiabetic subjects with clinical CAD, and 975 nondiabetic subjects without clinical CAD (all aged 40 to 70 years) in the Insulin Resistance Atherosclerosis Study. All data were adjusted for age, gender, ethnicity, and clinical results. Both diabetes and CAD were associated with increased atherosclerosis in the CCA. Likewise, diabetes was significantly associated with increased atherosclerosis in the ICA; however, CAD was not associated with ICA intima-media wall thickness. As expected, diabetic subjects with CAD had the greatest intima-media wall thickness, whereas nondiabetic subjects without CAD had the least atherosclerosis. Subjects with diabetes but without CAD had slightly greater intima-media wall thickness than nondiabetic subjects with CAD, although these differences were not statistically significant. Thus, diabetic subjects even without CAD had extensive atherosclerosis in the carotid artery. These results support the suggestion that diabetic subjects should be treated as aggressively for cardiovascular risk factor management as subjects with pre-existing CAD.

Adult↗

PubMed2000

Insulin sensitivity is inversely correlated with plasma intact parathyroid hormone level.

Abnormal glucose metabolism and a high prevalence of diabetes have been reported in patients with primary and secondary hyperparathyroidism. We hypothesize that plasma intact parathyroid hormone (iPTH) level is a determinant of either insulin sensitivity or beta-cell function. The study included 52 normotensive, healthy subjects with glucose tolerance. Insulin sensitivity and beta-cell function were assessed using a hyperglycemic clamp. Fasting plasma iPTH was determined. The relationships between its level and insulin sensitivity index and beta-cell function were examined. Insulin sensitivity index was inversely correlated with plasma iPTH level (r2 = .104, P = .020). The first phase insulin response was positively correlated with plasma iPTH level (r2 = .098, P = .023), but no correlation existed with the second phase insulin response. After adjusting for age, gender, ethnicity, and waist-to-hip ratio, plasma iPTH level was an independent determinant of insulin sensitivity index (P = .019). However, no independent relationship between plasma iPTH level and beta-cell function (the first phase and second phase insulin response) was found. In normotensive, glucose-tolerant, and healthy subjects, plasma iPTH level accounts for 10.4% of the variation in insulin sensitivity index. For each pg/mL increment in plasma iPTH level, there is a decrease of 0.247 micromol/L/m2/min/pmol/L in insulin sensitivity index. Although the molecular basis of this relationship is not clear, our results indicate that plasma iPTH level is inversely correlated with insulin sensitivity index.

Adult↗

PubMed2000

The I27L amino acid polymorphism of hepatic nuclear factor-1alpha is associated with insulin resistance.

Mutations of the hepatic nuclear factor-1alpha (HNF-1alpha) gene have been found in patients with maturity-onset diabetes of the young. We examined the relation between the I27L polymorphism of HNF-1alpha and insulin sensitivity and beta-cell function assessed by a hyperglycemic clamp. This study included 52 healthy glucose-tolerant and normotensive subjects (age, 19-40 yr; body mass index, 17.58-35.61 kg/m2; waist/hip ratio, 0.65-1.03). We identified 19 LL subjects, 24 IL, and 9 II subjects. No difference was noted in the demographic features among the three genotypes. The LL group had the highest postchallenge insulin levels at 30 and 90 min (P = 0.038 and P = 0.015, respectively) and also the highest insulin area under curve (P = 0.009) among the three genotypes. The LL group was more insulin resistant than the IL and II groups (P = 0.042 for insulin sensitivity index). After adjusting for age, gender, obesity, and ethnicity, the I27L polymorphism was an independent determinant of the insulin sensitivity index (P = 0.001). However, it had no impact on either the first or second phase insulin response. Therefore, we conclude that the I27L polymorphism is associated with insulin resistance, but not beta-cell function. The mechanism of this association is unclear, but HNF-1alpha may play a role in regulating hepatic glucose metabolism.

Adult↗

PubMed2000

Lipoprotein concentrations and carotid atherosclerosis by diabetes status: results from the Insulin Resistance Atherosclerosis Study.

OBJECTIVE: Lipoprotein concentrations are associated with the development of atherosclerosis in people with and without diabetes. The relative strength of these associations could differ by diabetes status as a result of diabetes-related lipoprotein modifications. RESEARCH DESIGN AND METHODS: The associations between lipoprotein concentrations and internal and common carotid artery intimal-medial thickness (IMT) assessed by B-mode ultrasonography were examined by diabetes status in a cross-sectional analysis among 1,391 participants in the Insulin Resistance Atherosclerosis Study. Participants included 442 individuals with type 2 diabetes, 308 with impaired glucose tolerance, and 641 with normal glucose tolerance. RESULTS: The differences in internal and common carotid IMT between the highest and lowest tertiles of LDL were 58.1 microm (P = 0.054) and 51.0 microm (P < 0.001), respectively. The differences in internal and common carotid IMT between the lowest and highest tertiles of HDL were 56.2 microm (P = 0.07) and 37.8 microm (P = 0.003), respectively Triglycerides and VLDL were not associated with IMT. These associations did not differ significantly because of diabetes status. CONCLUSIONS: These results support the importance of dyslipidemia as a major risk factor for atherosclerosis in people with diabetes. Future research in humans should measure lipoprotein oxidizability, glycation, size, and composition directly in people of differing glucose tolerance status to address the importance of diabetes-related lipoprotein modifications more conclusively.

Carotid Arteries↗

PubMed1999

LDL size in African Americans, Hispanics, and non-Hispanic whites : the insulin resistance atherosclerosis study.

The prevalence of cardiovascular disease (CVD) and atherosclerosis varies among several minority ethnic groups in the United States. Recently, small, dense low density lipoprotein (LDL) particle size has been recognized as a risk factor for CVD. We examined LDL size as a possible explanation for differences in CVD rates in 1571 subjects from the Insulin Resistance Atherosclerosis Study (IRAS), a multiethnic study of insulin resistance and cardiovascular risk factors. LDL size (A) was significantly different by ethnic group (African Americans 262.1+/-0.6, Hispanics 257.6+/-0.6, and non-Hispanic whites 259.2+/-0.4, P<0.001). Ethnic differences in LDL size continued to be statistically significant after adjustment for upper body adiposity, insulin resistance, and glucose tolerance status. However, after further adjustment for other cardiovascular risk factors, especially ethnic differences in triglyceride and high density lipoprotein (HDL) cholesterol levels, the ethnic differences in LDL size were markedly attenuated and in general no longer statistically significant. The relation of triglyceride, HDL cholesterol, insulin resistance, and adiposity to LDL size in each ethnic group was similar. LDL size differs by ethnic group, which is independent of obesity or insulin resistance. These ethnic differences appear to be due to ethnic variations in dyslipidemia (especially differences in triglyceride levels); ethnic differences in LDL size are not consistent with previously reported ethnic dissimilarities in CVD or atherosclerosis.

Adipose Tissue↗

PubMed1999

Changes in plasma leptin during the treatment of diabetic ketoacidosis.

To test the hypothesis that insulin regulates leptin, we measured the plasma leptin concentration before and during treatment of diabetic ketoacidosis (DKA), a condition characterized by extreme insulin deficiency. The study included 17 patients with type 1 diabetes (7 males and 10 females), aged 10+/-1 yr (mean +/- SE), with a body mass index of 17.6+/-1.9 kg/m2. Patients were treated with continuous insulin infusion and fluid and electrolyte replacement. Plasma leptin was measured every 6 h in the first 24 h, during which patients received a total insulin dose of 0.6-2.0 U/kg. Plasma leptin concentrations were also measured in a control group of 29 stable type 1 diabetic children (12 males and 17 females) and 25 healthy children (11 males and 14 females), aged 11+/-1 yr, with a body mass index of 18.5+/-1.1 kg/m2. Before treatment, plasma leptin concentrations were significantly lower in patients with DKA than those in diabetic and healthy controls (4.9+/-1.2 vs. 9.0+/-1.8 and 11.2+/-2.1 ng/mL, respectively; P < 0.05). In the DKA patients, plasma leptin increased to 6.4+/-1.5, 7.5+/-1.9, 9.1+/-2.7, and 8.9+/-2.5 at 6, 12, 18, and 24 h, respectively, after starting treatment (P = 0.001). Thus, leptin levels increased by 38+/-10% and 92+/-38% within 6 and 24 h of starting treatment. There was no difference in the change in plasma leptin by 24 h between subjects who could eat (n = 7) and those who could not (n = 10). The plasma leptin increase was paralleled by a rise in insulin level and a decline in glucose and cortisol levels at 6 and 24 h. In conclusion, DKA was associated with decreased plasma leptin concentrations. Treatment resulted in a significant increase in plasma leptin, which may be due to the effect of insulin on leptin production. Our data lend support to the hypothesis that insulin is the link between caloric intake and plasma leptin.

Blood Glucose↗

PubMed1999

Insulin sensitivity in subjects with type 2 diabetes. Relationship to cardiovascular risk factors: the Insulin Resistance Atherosclerosis Study.

OBJECTIVE: Among nondiabetic subjects, insulin resistance has been associated with increased cardiovascular risk factors, including dyslipidemia, hypertension, impaired fibrinolysis, and coagulation. Less is known about the relationship between insulin resistance and cardiovascular risk factors in subjects with type 2 diabetes. RESEARCH DESIGN AND METHODS: To examine this issue, we determined insulin sensitivity (SI) in 479 type 2 diabetic subjects by minimal model analyses of frequently sampled intravenous glucose tolerance tests in the Insulin Resistance Atherosclerosis Study (IRAS), a large multicenter study of insulin sensitivity and cardiovascular disease in African-Americans, Hispanics, and non-Hispanic whites. We defined insulin-sensitive subjects as having SI > or = 1.61 x 10(-4) min-1.microU-1.ml-1 (above median in nondiabetic subjects of all ethnic groups in the IRAS). Using this definition, only 37 type 2 diabetic subjects were insulin sensitive, and the remaining 442 were insulin resistant. RESULTS: After adjustment for age, sex, ethnicity, and clinic, insulin resistance was significantly correlated with total triglycerides, VLDL cholesterol, VLDL triglyceride, fibrinogen, PAI-1, and fasting glucose, and was inversely correlated with HDL cholesterol level and LDL size. Carotid intimal-medial thickness was greater in insulin-resistant than in insulin-sensitive subjects, but this difference was not statistically significant. After further adjustment for waist circumference (marker of visceral adiposity), insulin-resistant subjects continued to have higher plasminogen activator inhibitor 1 and VLDL triglyceride levels, lower HDL cholesterol levels, and smaller LDL particle size than did insulin-sensitive subjects. After further adjustment for fasting glucose levels, these results were very similar. CONCLUSIONS: We conclude that insulin-resistant type 2 diabetic subjects have more atherogenic cardiovascular risk factor profiles than insulin-sensitive type 2 diabetic subjects and that this is only partially related to increased obesity and an adverse body fat distribution.

Black or African American↗

PubMed1998

Relationships between insulin resistance and lipoproteins in nondiabetic African Americans, Hispanics, and non-Hispanic whites: the Insulin Resistance Atherosclerosis Study.

The study purpose was to explore the association between dyslipidemia and insulin resistance in three ethnic groups. The Insulin Resistance Atherosclerosis Study (IRAS) is a multicenter epidemiologic study conducted at four clinical centers in California, Texas, and Colorado. The study population for this analysis consisted of 931 non-Hispanic white, African American, and Hispanic men and women (aged 45 to 64 years) without diabetes. The IRAS clinical examinations included lipoprotein measures, a 75-g glucose tolerance test, and the frequently sampled intravenous glucose tolerance (FSIGT) test. The results show a consistent relationship between insulin-mediated glucose disposal and dyslipidemia in African American, Hispanic, and non-Hispanic white men and women. Further, LDL size was inversely associated with insulin resistance in all three ethnic groups. These findings indicate that dyslipidemia is a fundamental part of the insulin resistance syndrome in all of the ethnic groups studied.

Adult↗

PubMed1998

Ability of alternative indices of insulin sensitivity to predict cardiovascular risk: comparison with the "minimal model". Insulin Resistance Atherosclerosis Study (IRAS) Investigators.

INTRODUCTION: Although recognition of insulin sensitivity as a risk factor for cardiovascular disease is growing, a deeper understanding of its role is impeded by the cost and complexity of currently available measures. This report evaluates previously described alternative indices of insulin sensitivity with the goal of identifying a reliable, but logistically simpler, alternative. METHODS: Data from 1460 participants in the Insulin Resistance Atherosclerosis Study (IRAS) were used to assess the proportion of the relationship between a recognized measure of insulin sensitivity (Bergman's SI) and cardiovascular risk factors that is contained in each of nine alternative measures. RESULTS: A number of the alternative indices contained a substantial proportion of the information available in Bergman's SI. The Galvin's index and the homeostasis model were most promising. However, there remained a significant amount of the information in Bergman's SI that was not contained in any of the alternative indices. DISCUSSION: There are simpler alternative indices of insulin sensitivity for use in epidemiological studies, but each alternative is associated with some loss of information. It may be possible that this loss can be overcome with an increased sample size; however, using the alternative indices may also confound the assessment of insulin sensitivity with other underlying factors (i.e., hyperinsulinemia). The alternative indices are not recommended for the clinical assessment of insulin sensitivity for an individual patient or subject.

Cardiovascular Diseases↗

PubMed1998

Proinsulin and insulin concentrations in relation to carotid wall thickness: Insulin Resistance Atherosclerosis Study.

BACKGROUND AND PURPOSE: Insulin resistance and hyperinsulinemia have been associated with atherosclerosis. Recent attention has focused on the possible role of proinsulin because most radioimmunoassays for insulin cross-react with proinsulin. Therefore, it is not known which of the two, insulin per se or proinsulin, is more strongly related to atherosclerosis. METHODS: We examined the relation between fasting proinsulin, fasting split proinsulin, fasting and 2-hour insulin (after oral glucose load), and intima-media wall thickness (IMT) in the common carotid artery (CCA) and internal carotid artery (ICA) in 985 nondiabetic subjects from the Insulin Resistance Atherosclerosis Study, a multiethnic study of insulin resistance and atherosclerosis. RESULTS: In the overall population, a weak but significant relation between proinsulin and CCA IMT was observed (r=0.07, P=0.029). However, the relation between proinsulin and IMT was stronger in Hispanics and non-Hispanic whites than in African Americans. In non-Hispanic whites and Hispanics, significant correlations between CCA and proinsulin (r=0.087) and between ICA and proinsulin (r=0.101), split proinsulin (r = 0.092), and fasting insulin (r = 0.087) were observed. The significant correlations became more attenuated (and nonsignificant) after adjustment for cardiovascular risk factors, especially plasminogen activator inhibitor-1 (PAI-1). CONCLUSIONS: The association between proinsulin and IMT, while weak, appears to be stronger than the association between insulin and IMT. Adjustment for PAI-1 markedly attenuated the association between proinsulin and IMT, suggesting a possible mediating role for PAI-1 in this association. It is possible that proinsulin may represent a marker of atherosclerosis rather than a causal factor for atherosclerosis. Studies of the insulin resistance syndrome and atherosclerosis that use insulin as a surrogate for insulin resistance should consider the use of specific insulin assays as well as determination of proinsulin concentrations.

Arteriosclerosis↗

PubMed1998

Diurnal and ultradian rhythmicity of plasma leptin: effects of gender and adiposity.

Plasma leptin shows a nocturnal rise and a pulsatile pattern. This work was undertaken to determine the effects of gender and obesity on this pattern. Twenty-four-hour leptin profiles were evaluated in 31 subjects [17 male, 14 female; age: 36 +/- 2 yr (mean +/- SEM); body mass index: 27.5 +/- 1.0 kg/m2]. Plasma leptin profiles were higher in obese (body mass index > 27 kg/m2) than in lean subjects and higher in women than in men, regardless of fat mass. Leptin showed diurnal rhythmicity with peaks between 2200-0300 (median: 0120) and nadirs between 0800 and 1740 (median: 1033). Spectral analysis revealed 2 components (periodicities: 24 and 12 h) with higher relative amplitudes in lean than in obese subjects. The relative diurnal amplitude also was higher in men than in women, controlling for adiposity. Insulinemia, female sex, and age were negative determinants of diurnal rhythm relative amplitude. Pulse analysis revealed 3.6 +/- 0.3 pulses/24 h, occurring mostly 2-3 h after meals. Pulse frequency correlated negatively with fat mass and insulinemia (Spearman's r = -0.54 and -0.37, respectively; P < 0.05 for each). Thus, obesity is associated not only with higher leptin levels but also with blunted diurnal excursions and dampened pulsatility. This abnormal rhythmicity may contribute to leptin resistance in obesity. The significance of the sexual dimorphism in the diurnal amplitude is unclear, but it may be related to leptin's putative role as a metabolic signal to the reproductive axis.

Adipose Tissue↗