Cognitive deficits associated with a high-fat diet and insulin resistance are potentiated by overexpression of ecto-nucleotide pyrophosphatase phosphodiesterase-1

There is growing evidence that over consumption of high-fat foods and insulin resistance may alter hippocampal-dependent cognitive function. To study the individual contributions of diet and peripheral insulin resistance to learning and memory, we used a transgenic mouse line that overexpresses ecto-nucleotide pyrophosphatase phosphodiesterase-1 in adipocytes, which inhibits the insulin receptor. Here, we demonstrate that a model of peripheral insulin resistance exacerbates high-fat diet induced deficits in performance on the Morris Water Maze task. This finding was then reviewed in the context of the greater literature to explore potential mechanisms including triglyceride storage, adiponectin, lipid composition, insulin signaling, oxidative stress, and hippocampal signaling. Together, these findings further our understanding of the complex relationship among peripheral insulin resistance, diet and memory.

Thyroid surgery in a district hospital in Southern Ethiopia: experience from a rural center

BACKGROUND

Diseases of the thyroid are not uncommon, particularly in the highlands of Ethiopia. The aim of the present study was to describe the experience of thyroid surgery in a rural hospital in Southern Ethiopia.

METHODS

The present study was based on review of surgical cases of thyroid diseases operated in a rural hospital in Southern Ethiopia during the period 2009-2010.

RESULTS

During the study period, 211 patients underwent surgery for goiter. The mean age was 31.9 years (range: 14-80 years). The sex ratio, M:F, was 1:9. A total of 103 patients had unilateral nodules, and in 108 patients the nodules were located bilaterally. The mean duration of symptoms was 5.7 years (range: 0.7-25 years). In total, 161 (76.7 %) subtotal thyroidectomy operations, and 50 (23.3 %) hemi-thyroidectomy operations were performed. Histological examination revealed multinodular goiters in 203 (96.2 %) cases. Papillary and follicular cancers were found in 7 (3.3 %) and 1 (0.5 %) cases, respectively.

CONCLUSIONS

Thyroid surgery is feasible in a small rural Ethiopian District Hospital. The provision of surgical services in rural areas of low income and middle income countries is extremely important and delivers more health opportunities to the local people.

The SH2B1 obesity locus and abnormal glucose homeostasis: lack of evidence for association from a meta-analysis in individuals of European ancestry

BACKGROUND/AIMS

The development of type 2 diabetes (T2D) is influenced both by environmental and by genetic determinants. Obesity is an important risk factor for T2D, mostly mediated by obesity-related insulin resistance. Obesity and insulin resistance are also modulated by the genetic milieu; thus, genes affecting risk of obesity and insulin resistance might also modulate risk of T2D. Recently, 32 loci have been associated with body mass index (BMI) by genome-wide studies, including one locus on chromosome 16p11 containing the SH2B1 gene. Animal studies have suggested that SH2B1 is a physiological enhancer of the insulin receptor and humans with rare deletions or mutations at SH2B1 are obese with a disproportionately high insulin resistance. Thus, the role of SH2B1 in both obesity and insulin resistance makes it a strong candidate for T2D. However, published data on the role of SH2B1 variability on the risk for T2D are conflicting, ranging from no effect at all to a robust association.

METHODS

The SH2B1 tag SNP rs4788102 (SNP, single nucleotide polymorphism) was genotyped in 6978 individuals from six studies for abnormal glucose homeostasis (AGH), including impaired fasting glucose, impaired glucose tolerance or T2D, from the GENetics of Type 2 Diabetes in Italy and the United States (GENIUS T2D) consortium. Data from these studies were then meta-analyzed, in a Bayesian fashion, with those from DIAGRAM+ (n = 47,117) and four other published studies (n = 39,448).

RESULTS

Variability at the SH2B1 obesity locus was not associated with AGH either in the GENIUS consortium (overall odds ratio (OR) = 0.96; 0.89-1.04) or in the meta-analysis (OR = 1.01; 0.98-1.05).

CONCLUSION

Our data exclude a role for the SH2B1 obesity locus in the modulation of AGH.

IRS1 G972R polymorphism and type 2 diabetes: a paradigm for the difficult ascertainment of the contribution to disease susceptibility of 'low-frequency-low-risk' variants

AIMS/HYPOTHESIS

The aim of the study was to determine the association between IRS1 G972R polymorphism and type 2 diabetes; published data concerning this association have been conflicting. To obtain further insight into this topic, we performed a meta-analysis of all available case-control studies.

METHODS

We performed a meta-analysis of 32 studies (12,076 cases and 11,285 controls).

RESULTS

The relatively infrequent R972 variant was not significantly associated with type 2 diabetes (OR 1.09, 95% CI 0.96-1.23, p = 0.184 under a dominant model). Some evidence of heterogeneity was observed across studies (p = 0.1). In the 14 studies (9,713 individuals) in which the mean age at type 2 diabetes diagnosis was available, this variable explained 52% of the heterogeneity (p = 0.03). When these studies were subdivided into tertiles of mean age at diagnosis, the OR for diabetes was 1.48 (95% CI 1.17-1.87), 1.22 (95% CI 0.97-1.53) and 0.88 (95% CI 0.68-1.13) in the youngest, intermediate and oldest tertile, respectively (p = 0.0022 for trend of ORs).

CONCLUSIONS/INTERPRETATION

Our findings illustrate the difficulties of ascertaining the contribution of 'low-frequency-low-risk' variants to type 2 diabetes susceptibility. In the specific context of the R972 variant, approximately 200,000 study individuals would be needed to have 80% power to identify a 9% increase in diabetes risk at a genome-wide significance level. Under these circumstances, a strategy aimed at improving outcome definition and decreasing its heterogeneity may critically enhance our ability to detect genetic effects, thereby decreasing the required sample size. Our data suggest that focusing on early-onset diabetes, which is characterised by a stronger genetic background, may be part of such a strategy.

A double-blind, randomized study evaluating losartan potassium monotherapy or in combination with hydrochlorothiazide versus placebo in obese patients with hypertension

OBJECTIVES

The objective of this study was to evaluate the effects of losartan +/- hydrochlorothiazide (HCTZ) versus placebo in obese patients with systolic and diastolic hypertension.

RESEARCH DESIGN AND METHODS

Randomized patients (n = 261) were non-diabetic with systolic blood pressure (SBP) > or = 140 and < or = 180 mmHg and diastolic BP (DBP) > or = 95 and < or = 115 mmHg, body mass index > 30 kg/m(2), and waist circumference > 40 (males)/> 35 (females) inches. Patients were randomized to placebo or a forced titration of losartan 50 mg titrated at 4-week intervals to losartan 100 mg, losartan 100 mg/HCTZ 12.5 mg, and losartan 100 mg/HCTZ 25 mg. Primary efficacy measurements were change from baseline in SBP and DBP at 12 weeks. Secondary measurements were change from baseline in BPs at 8 and 16 weeks, percent responders at 12 and 16 weeks, and safety/tolerability. Post-hoc analyses were BP at 4 weeks and achievement of controlled BP (SBP < 140 and/or DBP < 90 mmHg) at 12 and 16 weeks.

RESULTS

Losartan 50 mg reduced BP from 151.6/99.2 mmHg at baseline to 140.1/89.8 mmHg at week 4 (post hoc), 139.5/89.6 mmHg with losartan 100 mg at week 8 (secondary), 134.3/85.9 mmHg with losartan 100 mg/HCTZ 12.5 mg at week 12 (primary), and 132.1/84.9 mmHg with losartan 100 mg/HCTZ 50 mg at week 16 (secondary) (all p < 0.05). Rates of clinical adverse experiences were similar between treatment groups. A limitation of these analyses is the relatively rapid rate of study drug titration, which may not have allowed for the evaluation of the full treatment effect at each titration step.

CONCLUSIONS

We conclude that losartan alone or in combination with HCTZ was generally well tolerated and effective in the treatment of elevated systolic and diastolic BP in obese patients with hypertension.

Ethnicity and type 2 diabetes: focus on Asian Indians

Though the overall prevalence of type 2 diabetes is increasing in US and in all other westernized countries, significant differences are noted among different ethnic groups. The reasons for ethnic differences in the risk of type 2 diabetes are not entirely understood. For example, Asian Indians (people from India, Pakistan, and Bangladesh) have remarkably high prevalence of type 2 diabetes compared to Caucasians. However, the incidence of obesity, an important risk factor in the development of type 2 diabetes, is significantly lower in Asian Indians compared to Caucasians. Though westernization of lifestyle with dietary changes and lack of exercise may play a role in increased prevalence of type 2 diabetes in migrant Asian Indians, various epidemiological studies have shown that these factors alone are not sufficient to explain this trend. One important factor contributing to increased type 2 diabetes in Asian Indians is excessive insulin resistance compared to Caucasians. This difference in the degree of insulin resistance may be explained by either an environmental or a genetic factor or by combination of both. The understanding of the etiology and mechanisms causing increased insulin resistance in Asian Indians will provide clues to more effective prevention and treatment of diabetes in this ethnic group. Furthermore, the information may help in understanding the pathophysiology of type 2 diabetes in other ethnic groups and improve methods of treatment and prevention in all ethnic groups. Since the ethnic mix of the US population is changing rapidly and it is estimated that by the year 2020, over 50% of US population will include non-Caucasian ethnicity, the identification of the mechanism involved in the excessive development of type 2 diabetes in non-Caucasians becomes important. In this review, possible etiology of excessive insulin resistance and role of free fatty acids (FFA) in insulin resistance in Asian Indians is discussed. Finally, the role of targeting insulin resistance in prevention and treatment of diabetes is discussed.

Obesity and cardiovascular disease. Pathogenetic role of the metabolic syndrome and therapeutic implications

Since obesity is a major risk factor for cardiovascular disease (CVD), the increasing prevalence and degree of obesity in all developed countries has the potential to significantly offset the current efforts to decrease CVD burden in our population. Obesity is pathogenetically related to several clinical and sub-clinical abnormalities that contribute to the development of atherosclerotic placks and their complication, leading to the onset of cardiovascular events. Obesity seems to interact with inheritable factors in determining the onset of insulin resistance, a metabolic abnormality that is responsible for altered glucose metabolism and predisposition to type 2 diabetes, but that also has a major role in the development of dyslipidemia, hypertension and many other sub-clinical abnormalities that contribute to the atherosclerotic process and onset of cardiovascular events. Inheritable factors seem to modulate the onset of type 2 diabetes, dyslipidemia, hypertension and various insulin resistance-related sub-clinical abnormalities, often in a clustering pattern that is commonly referred to as the "metabolic syndrome." Inheritable factors also are involved in the onset of CVD in a given population or individuals with various components of the metabolic syndrome. Intense research is currently undergoing to better understand the molecular mechanisms that could explain the relationship between environmental and inheritable factors that lead from obesity to atherosclerosis and cardiovascular event. The elucidation of these mechanisms will provide improved therapeutic strategies to reduce cardiovascular risk in the obese patients. However, effective therapeutic tools that control each of the known pathophysiological steps mediating CVD in obese patients are already available and should be used more aggressively. Patient education and coordinated approach of physicians, nurses and other health care providers in a multidisciplinary treatment of the obese patient is of fundamental importance to reduce CVD burden in our population.

Relationship between generalized and upper body obesity to insulin resistance in Asian Indian men

It has been proposed that excessive insulin resistance in Asian Indians living in urban areas or migrated to western countries is responsible for the higher incidence of type 2 diabetes and coronary heart disease observed in this population. To evaluate whether Asian Indians are more insulin resistant than Caucasians and to define the role of generalized and truncal adiposity, we performed hydrodensitometry, skinfold measurements, and euglycemic-hyperinsulinemic clamps in 21 healthy Asian Indian men and 23 Caucasian men of similar age and body fat content. The glucose disposal rate (Rd) was significantly lower in the Asian Indians than in the Caucasians (3.7+/-1.3 vs. 5.3+/-2.0 mg/min x kg lean body mass, respectively; P = 0.003). Despite similar total body fat content, Asian Indians had higher truncal adiposity than Caucasians (sum of truncal skinfolds, 117+/-37 and 92.4+/-38 mm, respectively). In both Asian Indians and Caucasians, the insulin sensitivity index (Rd/plasma insulin concentrations) was inversely correlated with both total body fat (r = -0.49; P<0.03 and r = -0.67; P<0.001, respectively) and sum of truncal skinfold thickness (r = -0.55; P<0.001 and r = -0.61; P<0.002, respectively). After adjustment for total body fat and truncal skinfold thickness, Asian Indians still had a significantly lower glucose disposal rate (P = 0.04). These results show that Asian Indian men are more insulin resistant than Caucasian men independently of generalized or truncal adiposity. The excessive insulin resistance in Asian Indians is probably a primary metabolic defect and may account for the excessive morbidity and mortality from diabetes and coronary heart disease in this population.

Relationship between generalized and upper body obesity to insulin resistance in Asian Indian men

It has been proposed that excessive insulin resistance in Asian Indians living in urban areas or migrated to western countries is responsible for the higher incidence of type 2 diabetes and coronary heart disease observed in this population. To evaluate whether Asian Indians are more insulin resistant than Caucasians and to define the role of generalized and truncal adiposity, we performed hydrodensitometry, skinfold measurements, and euglycemic-hyperinsulinemic clamps in 21 healthy Asian Indian men and 23 Caucasian men of similar age and body fat content. The glucose disposal rate (Rd) was significantly lower in the Asian Indians than in the Caucasians (3.7+/-1.3 vs. 5.3+/-2.0 mg/min x kg lean body mass, respectively; P = 0.003). Despite similar total body fat content, Asian Indians had higher truncal adiposity than Caucasians (sum of truncal skinfolds, 117+/-37 and 92.4+/-38 mm, respectively). In both Asian Indians and Caucasians, the insulin sensitivity index (Rd/plasma insulin concentrations) was inversely correlated with both total body fat (r = -0.49; P<0.03 and r = -0.67; P<0.001, respectively) and sum of truncal skinfold thickness (r = -0.55; P<0.001 and r = -0.61; P<0.002, respectively). After adjustment for total body fat and truncal skinfold thickness, Asian Indians still had a significantly lower glucose disposal rate (P = 0.04). These results show that Asian Indian men are more insulin resistant than Caucasian men independently of generalized or truncal adiposity. The excessive insulin resistance in Asian Indians is probably a primary metabolic defect and may account for the excessive morbidity and mortality from diabetes and coronary heart disease in this population.

Relationship of anterior and posterior subcutaneous abdominal fat to insulin sensitivity in nondiabetic men

Recent studies from our reveal that adipose tissue (AT) in the subcutaneous abdominal region is the most important determinant of peripheral and hepatic insulin sensitivity. Because of different anatomic and physiologic characteristics of anterior and posterior subcutaneous abdominal AT, we investigated the relationship of the masses of each compartment, as determined by magnetic resonance imaging, to insulin sensitivity (using euglycemic hyperinsulinemic glucose clamp technique), and other anthropometric variables. Thirty-four healthy men with varying ranges of obesity were recruited for the study. The mass of posterior subcutaneous abdominal AT was approximately 1.6 times more than that of the anterior compartment, and these masses accounted for 12.9% and 8.2% of the total body fat mass, respectively. All anthropometric variables, including body mass index (BMI), waist-to-hip circumference ratio (WHR), skin-fold thicknesses, and intraperitoneal AT mass were more significantly related to the posterior than the anterior subcutaneous abdominal AT mass. Compared to the anterior compartment mass, the posterior compartment mass displayed stronger relationship with insulin-mediated glucose disposal (Rd) (r = -0.44, p = 0.009, and r = -0.76, p = 0.0001, respectively) as well as with residual hepatic glucose output during the 40 mU.m-2.min-1 insulin infusion (r = 0.39, p = 0.02, and r = 0.53, p = 0.001, respectively). After adjusting for total body fat, the Rd values showed a significant partial correlation with the posterior subcutaneous abdominal AT mass (r = 0.52, p = 0.002). To conclude, posterior subcutaneous abdominal AT mass is more important determinant of peripheral and hepatic insulin sensitivity than the anterior subcutaneous abdominal AT.

Prediction of total subcutaneous abdominal, intraperitoneal, and retroperitoneal adipose tissue masses in men by a single axial magnetic resonance imaging slice

To develop a simplified but accurate method for determining the masses of various abdominal adipose tissue compartments, we studied the predictive value of masses of intraperitoneal, retroperitoneal, and subcutaneous abdominal adipose tissue determined on single axial abdominal magnetic resonance imaging (MRI) slices taken at various intervertebral levels from the 12th thoracic to 1st sacral vertebra (identified on a sagittal section) for the respective total masses of each compartment calculated from contiguous 10-mm thick MRI slices covering the entire abdomen in 49 men (26 without diabetes and 23 with non-insulin-dependent diabetes mellitus). The MRI slice at the intervertebral level between the lumbar (L) 2 and 3 vertebrae showed the highest and most consistent predictive value for all three compartments (R2 = 0.85 for all). Furthermore, compared with other intervertebral levels, the L2-L3 level had a higher amount of intraperitoneal and retroperitoneal adipose tissue mass. We conclude that determining the masses of various abdominal adipose tissue compartments at the L2-L3 intervertebral level by MRI is an acceptably reliable and accurate method for studying abdominal adiposity in men.

Relationship of generalized and regional adiposity to insulin sensitivity in men with NIDDM

Abdominal obesity, particularly excess intraperitoneal fat, is considered to play a major role in causing insulin resistance and NIDDM. To determine if NIDDM patients accumulate excess intraperitoneal fat, and whether this contributes significantly to their insulin resistance, 31 men with mild NIDDM with a wide range of adiposity were compared with 39 nondiabetic, control subjects for insulin sensitivity (measured using euglycemic-hyperinsulinemic clamp technique with [3-3H]glucose turnover) and total and regional adiposity (assessed by hydrodensitometry and by measuring subcutaneous abdominal, intraperitoneal, and retroperitoneal fat masses using magnetic resonance imaging [MRI], and truncal and peripheral skinfold thicknesses using calipers). MRI analysis revealed that intraperitoneal fat was not increased in NIDDM patients compared with control subjects; in both groups it averaged 11% of total body fat. NIDDM patients, however, had increased truncal-to-peripheral skinfolds thickness ratios. In NIDDM patients, as in control subjects, amounts of truncal subcutaneous fat showed a stronger correlation with glucose disposal rate than intraperitoneal or retroperitoneal fat; however, NIDDM patients were more insulin resistant at every level of total or regional adiposity. Further, no particular influence of excess intraperitoneal fat on hepatic insulin sensitivity was noted. We conclude that NIDDM patients do not have excess intraperitoneal fat, but that their fat distribution favors more truncal and less peripheral subcutaneous fat. Moreover, for each level of total and regional adiposity, NIDDM patients have a heightened state of insulin resistance.

Abnormal cholesterol distribution among lipoprotein fractions in normolipidemic patients with mild NIDDM

This study was carried out to identify and define lipoprotein abnormalities in patients with noninsulin-dependent diabetes mellitus (NIDDM) who do not have clinical elevations of cholesterol or triglycerides. Thirty-four male patients with mild NIDDM and normolipidemia (plasma cholesterol < or = 240 mg/dl and triglycerides < or = 250 mg/dl) were compared with 35 healthy male normolipidemic subjects. The two groups had similar age and body mass index. Measurements in the two groups included concentrations and chemical composition of lipoproteins and sizing of low-density lipoprotein (LDL) particles. The patients with NIDDM, compared to control subjects, had two distinct lipoprotein abnormalities: first a significantly reduced level of high-density lipoprotein (HDL) cholesterol (mean +/- S.D., 35 +/- 8 mg/dl vs. 41 +/-10 mg/dl, respectively; P = 0.006), and second, a high cholesterol-to-apolipoprotein (apo) B ratio both in a very low density lipoprotein (VLDL) + intermediate density lipoprotein (IDL) fraction (mean +/- S.D.; 3.2 +/- 0.8 vs. 2.8 +/- 0.9, respectively; P = 0.02) and in LDL fraction (mean +/- S.D.; 1.61 +/- 0.11 vs. 1.52 +/- 0.13, respectively; P = 0.003). Increased cholesterol content in LDL was mainly due to free cholesterol. No differences were detected between the two groups in the frequency of LDL pattern A (major LDL peak > 255 A) and pattern B (major LDL peak < or = 255 A). However, a higher frequency of LDL pattern B was found in NIDDM patients with low plasma total triglyceride concentrations ( < 150 mg/dl) compared to the to the control subjects (45% vs. 7%, P = 0.02). Thus in normolipidemic patients with mild NIDDM, the major lipoprotein abnormalities were a low level of HDL cholesterol and compositional changes in LDL and VLDL + IDL fractions. Compositional abnormalities included enrichment of apo B-containing lipoproteins with cholesterol. These lipoprotein abnormalities could have atherogenic potential in patients with mild NIDDM and normolipidemia.

Regulation of bile acid synthesis in humans: studies on cholesterol 7 alpha-hydroxylation in vivo

Over the last few years important progress has been made on the quantitation of cholesterol 7 alpha-hydroxylation, the rate-limiting step of bile acid synthesis. The use of a technique based on the determination of body water tritium enrichment after i.v. administration of [7 alpha-3H] cholesterol has allowed in vivo investigation of this step in humans in different experimental conditions. The cholesterol 7 alpha-hydroxylation rate was not affected by the administration of the hydrophilic bile acid ursodeoxycholic acid (UDCA) whereas it was significantly reduced by the more hydrophobic chenodeoxycholic acid (CDCA) and even more so by the strongly hydrophobic deoxycholic acid (DCA). The administration of cholestyramine induced a significant dose-related increase of 7 alpha-hydroxylation along with a correspondent decrease in plasma cholesterol. The administration of simvastatin exerted no effect on cholesterol 7 alpha-hydroxylation despite a marked decrease in serum cholesterol. Treatment with fibrates reduced plasma lipid levels and 7 alpha-hydroxylation rates. Hydroxylation rates were unchanged in familial hypercholesterolaemia and increased in familial combined hyperlipidaemia. These data suggest that in humans bile acid synthesis can be affected by quantitative and qualitative alterations of the enterohepatic circulation of bile acids. Changes in cholesterol 7 alpha-hydroxylation rates may be associated with alterations in plasma lipid levels, but such a relationship is ill-defined and seems to vary with the different experimental models.

Effects of different phenotypes of hyperlipoproteinemia and of treatment with fibric acid derivatives on the rates of cholesterol 7 alpha-hydroxylation in humans

Little is known about the relationships between hyperlipidemia and bile acid metabolism. However, hypolipidemic treatment with fibric acid derivatives has been shown to increase biliary cholesterol secretion, presumably by reducing bile acid synthesis. To clarify such relationships, we investigated the effects of different hyperlipoproteinemic conditions and of treatment with fibric acid derivatives on the rates of cholesterol 7 alpha-hydroxylation (the limiting step of bile acid synthesis) in humans. We studied 10 patients (aged 36 to 68 years) with lipoprotein phenotype IIa and with a clinical diagnosis of heterozygous familial hypercholesterolemia, a condition of reduced activity of LDL receptors, and 11 patients (aged 48 to 70 years) with lipoprotein phenotype IIb or IV and clinical diagnosis of familial combined hyperlipidemia, a condition probably related to increased hepatic lipoprotein synthesis. Cholesterol 7 alpha-hydroxylation rates were assayed in vivo by tritium release assay after an intravenous injection of [7 alpha-3H]cholesterol. The results were compared by ANOVA to the values obtained in a group of 28 normolipidemic patients (aged 34 to 83 years), with age as the covariate. Six patients were also studied after treatment with gemfibrozil (900 to 1200 mg/d for 6 to 8 weeks) and 5 patients were studied after treatment with bezafibrate (400 mg/d for 6 to 8 weeks). Hydroxylation rates were 0.82 +/- 0.22 mmol/d in the familial hypercholesterolemia group and 1.30 +/- 0.47 mmol/d in the familial combined hyperlipidemia group (P < .05 between the two groups and between patients with familial combined hyperlipidemia and control subjects; P = NS between patients with familial hypercholesterolemia and control subjects, as determined by ANOVA).(ABSTRACT TRUNCATED AT 250 WORDS)

Physico-chemical properties of low density lipoproteins in normolipidemic Asian Indian men

The present study investigated whether a predisposition to high frequency of small, dense low density lipoproteins (LDL) could be an additional coronary risk factor in migrant Asian Indians. Ninety-three normolipidemic (fasting plasma cholesterol levels < or = 240 mg/dl and triglyceride levels < or = 250 mg/dl) adult Asian Indian men residing in the U.S. were compared to a group of 59 Caucasian men for the prevalence of LDL electrophoretic patterns A and B (size of major LDL peak > or = 255 A for LDL pattern A and < 255 A for LDL pattern B). Compared to the Caucasians, the Asian Indians had larger LDL size (mean +/- SD; 260.1 +/- 12.8 A vs 267.7 +/- 11.4 A, respectively; p = 0.0002), an increased frequency of LDL pattern A (59% vs 85%, respectively) and a lower frequency of LDL pattern B (41% vs 15%, respectively) (p = 0.0005). The difference in LDL size in the two study groups persisted after adjusting for the various confounding variables, such as age, plasma triglycerides, high-density lipoprotein cholesterol and dietary habits. We conclude that compared to Caucasians, Asian Indian men have larger LDL particles and a lower prevalence of LDL phenotype B in the presence of normolipidemia. Therefore, we exclude a genetic predisposition to atherogenic LDL phenotype as a factor contributing to the high incidence of coronary heart disease in migrant Asian Indians.

Relationships of generalized and regional adiposity to insulin sensitivity in men

The relative impacts of regional and generalized adiposity on insulin sensitivity have not been fully defined. Therefore, we investigated the relationship of insulin sensitivity (measured using hyperinsulinemic, euglycemic clamp technique with [3-3H]glucose turnover) to total body adiposity (determined by hydrodensitometry) and regional adiposity. The latter was assessed by determining subcutaneous abdominal, intraperitoneal, and retroperitoneal fat masses (using magnetic resonance imaging) and the sum of truncal and peripheral skinfold thicknesses. 39 healthy middle-aged men with a wide range of adiposity were studied. Overall, the intraperitoneal and retroperitoneal fat constituted only 11 and 7% of the total body fat. Glucose disposal rate (Rd) and residual hepatic glucose output (rHGO) values during the 40 mU/m2.min insulin infusion correlated significantly with total body fat (r = -0.61 and 0.50, respectively), subcutaneous abdominal fat (r = -0.62 and 0.50, respectively), sum of truncal skinfold thickness (r = -0.72 and 0.57, respectively), and intraperitoneal fat (r = -0.51 and 0.44, respectively) but not to retroperitoneal fat. After adjusting for total body fat, the Rd and rHGO values showed the highest correlation with the sum of truncal skinfold thickness (partial r = -0.40 and 0.33, respectively). We conclude that subcutaneous truncal fat plays a major role in obesity-related insulin resistance in men, whereas intraperitoneal fat and retroperitoneal fat have a lesser role.

Heterogeneity in adipose tissue metabolism: causes, implications and management of regional adiposity

The observation that different patterns of adipose tissue distribution are associated with different metabolic abnormalities, has recently given new impetus to research in obesity. Due to several methodologic problems, however, many aspects of regional excess of adipose tissue are still poorly understood. Among them, the causes and the metabolic consequences of regional adiposity are particularly important. Heterogeneity in adipose tissue distribution may be determined by a combination of genetic and hormonal causes. Both factors may determine differences in metabolism of various adipose tissue compartments primarily by regulating LPL production, storage and release of triacylglycerols, and aromatization of androgens. Furthermore, changes in adipocyte sensitivity to hormones such as, sex steroids, glucocorticoids, insulin and adrenergic hormones may also regulate fat distribution in various adipose tissue compartments. The metabolic heterogeneity of adipose tissue from various compartments, particularly the differences between the "portal" and subcutaneous adipose tissues, may account for several metabolic abnormalities associated with "upper body adiposity". However, no direct evidence is available to confirm this hypothesis. Recent advances in the methodology to study adipose tissue distribution (mainly CT and MRI) may provide the necessary tools to evaluate the true impact of adiposity in various compartments on intermediary metabolism and to identify a "morbid" adipose tissue compartment. These observations may help in designing better therapeutic strategies targeted towards regional adiposity and its metabolic complications.

Estimation of adipose tissue mass by magnetic resonance imaging: validation against dissection in human cadavers

The evaluation of adipose tissue distribution has become an essential component of investigations on the complications of obesity. However, a major limitation is lack of methodology for accurate estimation of adipose tissue mass in the different regions of the body. Therefore, we have tested the accuracy and precision of magnetic resonance imaging (MRI) as a method to measure adipose tissue mass in regions of the body not accessible with standard anthropometric methods. The mass of subcutaneous and intraabdominal adipose tissue estimated by MRI was compared with that obtained by direct weighing of the same adipose tissue compartments after dissection in human cadavers. MRI was performed on three unembalmed cadavers (two males, one female) who were subsequently dissected to isolate intraperitoneal, retroperitoneal, and subcutaneous adipose tissues. These same components were delineated by MRI. The results of the two methods were highly congruent. For the various compartments, the mean of the difference between the two methods was only 0.076 kg (95% confidence interval + 0.005 kg and + 0.147 kg). The "limits of agreement" between the two techniques were -0.066 kg and +0.218 kg. Multiple repeated estimates of mass of adipose tissue compartments were made to determine reproducibility of the MRI measurement; the coefficient of variation for repeated measures was below 14%. The results of this study show that MRI is an accurate and precise technique to evaluate adipose tissue mass in subcutaneous and intraabdominal compartments. Furthermore, MRI was found to be a valid method to separately evaluate the mass of intraabdominal subcompartments of intraperitoneal and retroperitoneal adipose tissue.

Effect of chenodeoxycholic acid and ursodeoxycholic acid administration on acyl-CoA: cholesterol acyltransferase activity in human liver

In order to investigate the relationship between bile acid pool composition and hepatic cholesterol metabolism in humans, we studied the effect of chronic feeding of chenodeoxycholic (CDCA) or ursodeoxycholic acid (UDCA) on the hepatic activity of acyl-CoA: cholesterol acyltransferase (ACAT) evaluated "in vitro". Twenty-eight gallstone patients were admitted to the study: 15 were untreated subjects, 8 were treated with UDCA (10 mg/kg/day for 15-20 days) and 5 were treated with CDCA (15 mg/kg/day for 15-20 days). A liver specimen and a bile sample were obtained during laparotomy for elective cholecystectomy. Untreated subjects had bile supersaturated with cholesterol (mean saturation index: 1.35 +/- 0.31) whereas subjects treated with either UDCA or CDCA had bile unsaturated with cholesterol (mean saturation index: 0.66 +/- 0.1 and 0.75 +/- 0.06 respectively). In all treated subjects the bile acid administered became predominant in bile. ACAT activity was 14% lower in subjects treated with UDCA and 16% lower in those treated with CDCA compared to controls; the differences did not achieve statistical significance. Microsomal cholesterol content did not differ between the groups (75.4 +/- 7.2 nmol/mg protein in control group; 86.5 +/- 7.0 nmol/mg protein in CDCA treated group; 83.4 +/- 7.0 nmol/mg protein in UDCA treated group). Our data show that the cholesterol esterifying activity of human liver is not affected by changes in bile acid pool composition.

Variability in cholesterol content and physical properties of lipoproteins containing apolipoprotein B-100

The primary objective of this study was to determine the variability in cholesterol carrying capacity of low density lipoproteins (LDLs) and other apolipoprotein B (apo B)-containing lipoproteins in normolipidemic men. One hundred and fifty-nine normolipidemic men, ages 21 to 73 years, were enrolled. In addition to determining plasma lipids and lipoproteins, three primary measurements were made: ratios of cholesterol to apo B in LDL; the electrophoretic pattern of LDL, i.e. pattern A, AB, or B; and levels of cholesterol in all lipoproteins other than high density lipoproteins (nonHDL-cholesterol) along with total apo B. First, the data revealed that about 85% of the variability of LDL-cholesterol levels can be accounted for by LDL-apo B levels, whereas the remaining 15% can be explained by differences in LDL-cholesterol/apo B ratios. Second, LDL electrophoretic pattern A was the predominant pattern in young adult men, but in older men the pattern shifted increasingly to AB and B. And third, there was a high correlation between nonHDL-cholesterol levels and total apo B levels, which suggests that nonHDL-cholesterol can be used as a relatively accurate surrogate for total apo B levels in normolipidemic individuals.

Effect of aging on cholesterol 7 alpha-hydroxylation in humans

In order to investigate the alterations of bile acid synthesis in aging, we studied the rates of cholesterol 7 alpha-hydroxylation, the rate-limiting step, in 28 patients of different ages (34-83 years old, 14 below and 14 above the age of 65) of both sexes. Hydroxylation rates were determined by tritium release assay after an intravenous bolus of [7 alpha-3H]cholesterol. Cholesterol 7 alpha-hydroxylation was significantly decreased in the older age group, compared to middle-aged subjects, both in males and females; moreover, a significant inverse correlation between hydroxylation rates and age was found in the whole sample (r = -0.56; P < 0.01) and in females, but not in males. The percent concentration of deoxycholic acid in plasma (determined by gas-liquid chromatography) was increased in older subjects. Plasma cholesterol and triglyceride levels were not related with age even though triglyceride concentrations tended to be lower in the older age group. Triglyceride, but not cholesterol levels, were directly correlated with hydroxylation rates (r = 0.45, P < 0.05). After cholestyramine treatment (8-12 g/day for 4 weeks) a sharp increase in 7 alpha-hydroxylation rates was observed in three elderly patients, accompanied by reduced levels of dihydroxylated bile acids. Our data are consistent with a reduced rate of conversion of cholesterol to bile acids with aging, particularly in females, and suggest a coordinate reduction of triglyceride production. Alterations of the quantitative and/or qualitative pattern of the bile acid pool recirculating to the liver may be responsible, at least in part, for the changes observed.

Regulation of bile acid synthesis in humans: effect of treatment with bile acids, cholestyramine or simvastatin on cholesterol 7 alpha-hydroxylation rates in vivo

The rates of cholesterol 7 alpha-hydroxylation (the first and rate-limiting step of bile acid synthesis from cholesterol) were evaluated in vivo in patients administered bile acids with different structural properties, cholestyramine or simvastatin, a competitive inhibitor of 3-hydroxy-3-methylglutaryl-coenzyme A reductase. Twenty-three subjects, with normal hepatic and intestinal functions, were studied in basal conditions and after one of the following treatment schedules, lasting 4 to 6 weeks: cholestyramine, 4 and 12 gm/day (four patients); ursodeoxycholic acid, 9 to 11 mg/kg/day (four patients); chenodeoxycholic acid, 12 to 15 mg/kg/day (five patients); deoxycholic acid, 8 to 10 mg/kg/day (four patients); and simvastatin, 40 mg/day (six patients). 7 alpha-Hydroxylation of cholesterol was assayed by measuring the increase in body water tritium after intravenous bolus of cholesterol tritiated at the 7 alpha position. Plasma bile acid composition, evaluated by gas-liquid chromatography, revealed a substantial enrichment of the recirculating pool by the administered bile acid, whereas treatment with cholestyramine decreased the content of dihydroxylated bile acids. Cholesterol 7 alpha-hydroxylation increased in a dose-related manner after cholestyramine, in parallel with a decrease of cholesterol in total plasma and low-density lipoproteins (1.006 to 1.063 gm/ml). Hydroxylation rates decreased by an average of 47% with chenodeoxycholic acid and by an average of 78% with deoxycholic acid; ursodeoxycholic acid treatment did not affect 7 alpha-hydroxylation significantly. Simvastatin markedly reduced plasma total and low-density lipoprotein-cholesterol but exerted no change on 7 alpha-hydroxylation rates.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of bile acid pool composition on hepatic metabolism of cholesterol in man

This work reviews the evidence concerning the role of the bile acid pool composition in the regulation of the overall hepatic metabolism of cholesterol in man. It has been known that bile acids regulate bile secretion, biliary lipid transport and hepatic cholesterol metabolism. However, the intimate mechanisms of these regulatory functions are not well understood. Current thinking attributes most of this regulation to the size of the bile acid pool. A typical example is represented by the negative feed-back mechanism by which bile acids returning to the liver control their own synthesis. Recent evidence however tend to suggest that not only the size but also the composition contributes to the regulatory activity of the bile acid pool. Specifically the hydrophobic-hydrophilic balance of the pool, as resulting from the characteristics and the proportions of the individual bile acids present within the pool, seems to dictate most of the effects of bile acids on hepatic cholesterol metabolism. Thus abundance within the pool of hydrophobic bile acids, such as deoxycholic or chenodeoxycholic acid, seems to induce a greater biliary lipid secretion and to exert inhibition of cholesterol and bile acid synthesis whereas hydrophilic bile acids such as ursodeoxycholic acid seem to be uneffective. It follows that by changing the composition of the bile acid pool it is possible to influence the hepatic metabolism of cholesterol.