Joan Soler

Serum Ferritin as a Component of the Insulin Resistance Syndrome

OBJECTIVE In epidemiological studies, serum ferritin was the second-strongest determinant of blood glucose (after BMI) in regression models and the third-strongest determinant of serum insulin (after BMI and age). Its concentration also correlated positively with plasma triglycerides and apolipoprotein B concentrations, and negatively with HDL2 cholesterol. We hypothesized that serum ferritin could be a marker of insulin resistance. RESEARCH DESIGN AND METHODS Oral glucose tolerance and insulin sensitivity (SI, minimal model method) were prospectively evaluated in 36 healthy subjects. The relationship between serum ferritin and metabolic control (as measured by HbA1c levels) was also studied in 76 consecutive NIDDM patients. RESULTS In healthy subjects, log-transformed serum ferritin (LOGFER) correlated with basal serum glucose (r = 0.44, P = 0.007), but not with BMI, age, systolic or diastolic blood pressure, total cholesterol, VLDL cholesterol, HDL cholesterol, total triglycerides, VLDL triglycerides, serum insulin, or HbA1c (all P = NS). Identical results were obtained when the two lowest quartiles of serum ferritin were evaluated separately. However, in the two highest quartiles, LOGFER correlated with BMI (0.50, P = 0.02), diastolic blood pressure (r = 0.8, P < 0.0001), serum LDL cholesterol (r = 0.57, P = 0.01), VLDL cholesterol (r = 0.48, P = 0.03), total cholesterol and HDL2 and HDL3 subtractions of HDL cholesterol (r = −0.68, −0.76, −0.55, P = 0.001. < 0.0001, and 0.01, respectively), total triglycerides (r = 0.60, P = 0.006), HDL2/HDL3 quotient (P = −0.71, P = 0.001), VLDL triglycerides (r = 0.65, P = 0.004), and serum uric acid (r = 0.51, P = 0.03), but not with systolic blood pressure (r = 0.38, P = 0.15). After adjusting for BMI, only the correlations between LOGFER and diastolic blood pressure (r = 0.7, P = 0.002) and HDL2/HDL3 quotient (r = −0.63, P = 0.01) remained significant. Strong correlations between LOGFER and glucose area under the curve during oral glucose tolerance test (Pearsons r = 0.73, P = 0.001) and S1 (r = −0.68, P = 0.001), which remained significant after controlling for BMI, were observed. LOGFER (β = −0.44, P = 0.01) and BMI (β = −0.52, P = 0.004) constituted independent predictors of insulin sensitivity in a multivariate analysis (R2 = 0.68). In 76 consecutive NIDDM outpatients, serum glucose (P < 0.00001) and LOGFER (P = 0.03) independently predicted the value of HbA1c (R2 = 0.40) in a multiple linear regression analysis. CONCLUSIONS The correlations among serum ferritin and diastolic blood pressure, HDL quotient, glucose area under the curve, and S1 suggest that serum ferritin could be a marker of the insulin resistance syndrome. Serum ferritin may also be an independent determinant of poor metabolic control in the diabetic patient.

The TNF-alpha gene Nco I polymorphism influences the relationship among insulin resistance, percent body fat, and increased serum leptin levels.

Tumor necrosis factor-α (TNF-α), acting as a modulator of gene expression in adipocytes, is implicated in the development of insulin resistance and obesity. The aim of this study was to investigate whether the Nco I polymorphism of the TNF-a gene influences the relationship among insulin resistance, percent body fat, and serum leptin levels. A sample of 38 subjects (19 men, mean age 36.2 ± 1.9 years, BMI 28.8 ± 1.2 kg/m2, range 22.2–35.7; and 19 women, age 34.9 ± 1.4 years, BMI 28.1 ± 0.8 kg/m2, range 19–37.9) was divided into two groups on the basis of the Nco I genotype. Twenty-three subjects were (+/+) homozygotes for the presence of the Nco I restriction site that is associated with a guanine at position −308 of the TNF-a promoter. Of the other subjects, 12 were (+/−) heterozygotes and 3 (−/−) homozygotes for the absence of the restriction site, resulting from a guanine-to-adenine substitution at position −308 of the TNF-a promoter. This substitution (termed TNF-2) leads to higher rate of transcription of TNF-a than the wild-type allele TNF-1 in vitro. TNF-1 (+/+) and TNF-2 (+/− and −/−) groups of subjects were comparable in sex, age, BMI, waist-to-hip ratio, and several skinfold measurements. Basal serum insulin was greater (14.2 ± 2 vs. 9.2 ± 0.9 mlM, P = 0.041) in the TNF-2 group in the presence of comparable serum glucose concentration. The integrated area under the curve of serum insulin concentrations, measured in response to a 75-g oral glucose challenge, and the percent body fat, measured by bioelectric impedance, were significantly increased in TNF-2 subjects (226.8 ± 33 vs. 139.4 ± 17.8 mU/l, P = 0.032; 33.6 ± 2.8 vs. 24.9 ± 2%, P = 0.01). TNF-2 subjects also showed a decreased insulin sensitivity index, as determined by the frequently sampled intravenous glucose tolerance test with minimal model analysis (1.9 ± 0.4 vs. 3.05 ± 0.3 min−1 · mU−1 · 1−1 P = 0.03). These differences were more marked among women. Paralleling the known relationship between insulin and leptin levels, serum leptin concentration was clearly increased in the TNF-2 group (19.6 ± 3.4 vs. 11.1 ± 1.5 ng/ml, P = 0.03). Therefore, (+/−) heterozygotes and (−/−) homozygotes may be more susceptible to developing insulin resistance and increased percent body fat. Results of the present study suggest that TNF-αNco I polymorphism may exacerbate the alterations in leptin levels normally found among insulin-resistant subjects.

Low 25-hydroxyvitamin D concentrations in obese women: Their clinical significance and relationship with anthropometric and body composition variables

Obesity is associated with low concentrations of 25-hydroxyvitamin D [25(OH) D]. However, conflicting results have been found regarding the relationship of 25(OH) D with anthropometric and adiposity parameters. The aim of our study was to analyze the association between 25(OH) D and body fat (BF) in a homogeneous cohort of non-obese, obese, and morbidly obese Caucasian women. The study was performed in L’Hospitalet de Llobregat, a city adjacent to Barcelona with a latitude of 41 degrees, 22 minutes, and 5 seconds north. Materials and methods: Plasma concentrations of 25(OH) D were determined and body composition was evaluated by bioelectrical impedance in a group of 43 women with morbid obesity, 28 non-morbidly obese, and 50 non-obese women matched for age. Results: Morbidly obese women showed lower 25(OH) D concentrations compared to non-morbidly and non-obese women (37.9±16 vs 40.2±13 vs 56.7±21 nmol/l, p=0.001). Fifty-one percent of morbidly obese women had vitamin D deficiency [25(OH) D<38 nmol/l] compared to 22% of non-obese patients, (p=0.004). In the bivariate correlation analysis 25(OH) D was inversely associated with weight (r=−0.41, p=0.001), body mass index (BMI) (r=−0.432, p=0.001 ), waist to hip ratio (WHR)(r=−0.40, p=0.001 ), BF (r=−0.53, p=0001 ), fat mass (r=−0.44, p=0.0001), fat-free mass (r=−0.35, p=0.001). In the multivariate general linear model analysis, 25(OH) D was associated with season of examination (p=0.001) and was negatively associated with BF (β=−0.75, p=0.001), after adjusting for age, BMI, and WHR. Conclusions: 25(OH) D concentrations are associated with body composition variables especially by BF, independently of seasonal variability. Therefore, body adiposity should be considered when assessing vitamin D requirements in obese patients.

Blood Volumes and Renal Function in Overt and Subclinical Primary Hypothyroidism

INTRODUCTION Thyroid dysfunction is associated with marked alterations in cardiovascular and renal functions. In hypothyroidism, myocardial contractility, cardiac output, and oxygen consumption are decreased, whereas peripheral resistance is increased. METHODS We assessed blood volumes and effective renal plasma blood flow (ERPF) and glomerular filtration rate (GFR) in 17 patients with overt primary hypothyroidism and in 15 of these patients when in euthyroid state after substitutive therapy. We performed the same measurements in eight patients with subclinical hypothyroidism. RESULTS In the hypothyroid state, the plasma volume measured by dilution of 125I-albumin (APV) was higher than the calculated plasma volume (CPV) from packed red cell mass, suggesting an extravascular escape of albumin. After substitutive therapy, the CPV showed a statistical increase (P < 0.05), whereas APV remained unchanged. Both ERPF and GFR increased after thyroxine therapy (p < 0.05). In the subclinical group, blood volumes and renal function were similar to those found in the other group of patients when in the euthyroid state. CONCLUSIONS We conclude that in primary hypothyroidism, ERPF and GFR are low, but that these values improve with substitutive therapy. CPV is a better index of the current plasma volume than APV. The difference between these two parameters suggests that the escape of albumin into the extravascular space in primary hypothyroidism is terminated by treatment. There are no clear abnormalities either in blood volumes or in renal function in subclinical hypothyroidism.

Evaluation of Bone Mineral Density Loss in Morbidly Obese Women After Gastric Bypass: 3-Year Follow-Up

Studies that evaluate the influence of gastric bypass (RYGP) on bone mass are limited to short-term follow-up. We analysed changes in bone mineral density (BMD) three years after surgery and evaluated the main determinants of the development of bone disease. Prospective study of 59 morbidly obese white women aged 46 ± 8 years. BMD scanning using DEXA and plasma determinations of calcium, parathyroid hormone, 25-hydroxyvitamin D and insulin-like growth factor-I were made prior, at 12 months and 3 years after surgery. In the first postoperative year BMD decreased at femoral neck (FN) 10.2 % and in the lumbar spine (LS) 3.2 %, in the third year it additionally decreased 2.7 % and 3.1 %, respectively. BMD at both sites remained above the values of women of the same age. In the follow-up, 1.7 % developed osteoporosis at FN and 6.8 % at LS. Patients with bone disease were older, the percentage of women with menopause was greater in this group and had lower initial and final values of lean mass. The percentage of BMD loss at FN remained positively associated with the percentage of lean mass loss [β 0.304, p = 0.045], and menopause [β 0.337, p = 0.025]. Major osteoporotic fracture and hip fracture risk was low even in menopausal patients (3.1 % and 0.40 %, respectively). After RYGP menopausal women and those with greater lean mass loss are at higher risk of BMD loss but progression to osteoporosis is uncommon and the risk of fracture is low.

Distribution and determinants of adiponectin, resistin and ghrelin in a randomly selected healthy population

Objective  Adiponectin, resistin, ghrelin and the IGF‐I system seem to play an important role in the regulation of body composition throughout life, but the mechanisms are not well understood. The aim of our study was to analyse the distribution among sexes and all decades of the adult life of adiponectin, resistin and ghrelin and their relationship with anthropometric, body composition parameters and the IGF‐I system.

Effect of weight loss induced by gastric bypass on proinflammatory interleukin‐18, soluble tumour necrosis factor‐α receptors, C‐reactive protein and adiponectin in morbidly obese patients

Objective  Interleukin‐18 (IL‐18) is a potent proinflammatory cytokine whose role in human obesity has recently been suggested. The aim of our study was to analyse in morbidly obese patients undergoing gastric bypass, the relationship of IL‐18 with insulin resistance and with proinflammatory cytokines (tumour necrosis factor‐α receptors, sTNFR), C‐reactive protein (CRP) and with adiponectin.

Improved outcome of islet transplantation in insulin-treated diabetic mice : effects on beta-cell mass and function

Summary Insulin treatment may improve the outcome of islet transplantation. To determine the effects of insulin treatment on transplanted islets, 4 groups of streptozotocin-diabetic C57BL/6 mice were transplanted with 100 islets, an insufficient beta-cell mass to restore normoglycaemia. Groups 1 (n = 12) and 2 (n = 12), were kept normoglycaemic with insulin treatment from day 10 before transplantation to day 14 after transplantation; groups 3 (n = 12) and 4 (n = 18), were not treated with insulin. Grafts were harvested 14 (groups 1 and 3) or 60 (groups 2 and 4) days after transplantation and beta-cell mass and replication were measured. When insulin was discontinued all mice maintained normoglycaemia; in contrast, non-insulin-treated groups remained hyperglycaemic throughout the study. Fourteen days after transplantation the beta-cell mass was reduced both in group 1 (0.09 ± 0.01 mg) and group 3 (0.14 ± 0.02 mg) compared to the initially transplanted mass (0.22 ± 0.02 mg, p < 0.01); beta-cell replication and area did not change in group 1, but were increased in group 3. Insulin content, expressed as a function of beta-cell mass, was maintained in group 1 grafts (12.5 ± 2.0 μg/mg), but was severely reduced in group 3 (1.0 ± 0.2 μg/mg) compared to non-transplanted islets (20.4 ± 3.3 μm/mg). In group 2, beta-cell mass increased when insulin was discontinued; 60 days after transplantation beta-cell mass was similar to the initially transplanted mass (0.23 ± 0.04 mg), glucose levels after an intraperitoneal glucose challenge were normal, and insulin content was preserved (19.6 ± 2.7 μg/mg). In contrast, beta-cell mass was progressively reduced in group 4 (0.08 ± 0.02 mg, p < 0.001). In summary, insulin treatment reduced the beta-cell mass needed to achieve normoglycaemia in islet transplantation. Islets transplanted to insulin-treated mice showed better beta-cell function, preserved insulin content, and were able to increase their beta-cell mass to meet an increased functional demand. [Diabetologia (1997) 40: 1004–1010]

Short-Term Culture with the Caspase Inhibitor z-VAD.fmk Reduces Beta Cell Apoptosis in Transplanted Islets and Improves the Metabolic Outcome of the Graft:

In the initial days after transplantation islets are particularly vulnerable and show increased apoptosis and necrosis. We have studied the effects of caspase inhibition on this early beta cell death in syngeneically transplanted islets. Streptozotocin-diabetic C57BL/6 mice were transplanted with 150 syngeneic islets, an insufficient mass to restore normoglycemia, preincubated with or without the pan-caspase inhibitor z-VAD. fmk 2 h before transplantation. Beta cell apoptosis was increased in control islets on day 3 after transplantation (0.28 ± 0.02%) compared with freshly isolated islets (0.08 ± 0.02%, p< 0.001), and was partially reduced in transplanted islets preincubated with z-VAD.fmk 200 μM (0.14 ± 0.02%, p = 0.003) or with z-VAD.fmk 500 μM (0.17 ± 0.01%, p = 0.012), but not with a lower z-VAD.fmk (100 μM) concentration. Diabetic mice transplanted with islets preincubated with z-VAD.fmk 500 μM showed an improved metabolic evolution compared with control and z-VAD.fmk 200 μM groups. The z-VAD.fmk 500 μM group showed an overall lower blood glucose after transplantation (p = 0.02), and at the end of the study blood glucose values were reduced compared with transplantation day (15.7 ± 3.6 vs. 32.5 ± 0.5 mmol/L, p = 0.001). In contrast, blood glucose was not significantly changed in control and z-VAD.fmk 200 μM groups. Four weeks after transplantation beta cell mass was higher in z-VAD.fmk 500 μM group (0.15 ± 0.02 mg) than in the control group (0.10 ± 0.02 mg) (p = 0.043). In summary, the treatment of freshly isolated islets with the caspase inhibitor z-VAD.fmk reduced the subsequent apoptosis of the islets once they were transplanted and improved the outcome of the graft.

Optimal insulin treatment in syngeneic islet transplantation.

Insulin-induced normoglycemia has shown to have a beneficial effect on the outcome of pancreatic islets transplanted to diabetic recipients. The aim of the study was to identify the insulin treatment that can maximize its beneficial effect on islet transplants. Six groups of streptozotocin diabetic C57B1/6 mice were transplanted (Tx) with 100 syngeneic islets, an insufficient beta cell mass to restore normoglycemia, and were treated with insulin as follows: group 1 (n = 9): from day 10 before Tx to day 14 after Tx; group 2 (n = 11): from day 6 before Tx to Tx day; group 3 (n = 11): from Tx day to day 6 after Tx; group 4 (n = 7): from Tx day to day 14 after Tx; group 5 (n = 8): from day 10 to day 24 after Tx; group 6 (n = 18): Tx mice were not treated with insulin. Sixty days after Tx, normoglycemia was achieved in 100% of mice in groups 1, 4, and 5, in 73% of mice in group 2, and in only 45% and 33% of mice in groups 3 and 6, respectively (p < 0.01). Intraperitoneal glucose tolerance, determined only in normoglycemic mice, was similar in groups 1, 2, 4, and normal controls. In contrast, normoglycemic mice from groups 3, 5, and 6, exposed to more severe and prolonged hyperglycemia after Tx, showed higher glucose values after glucose injection, suggesting that hyperglycemia had a long-lasting deleterious effect on transplanted beta cell function. The initially transplanted beta cell mass was maintained in the grafts of normoglycemic mice, but was severely reduced in hyperglycemic mice. Transplanted beta cell mass was similar in normoglycemic groups with normal or impaired glucose tolerance, indicating that impaired glucose tolerance was not due to reduced beta cell mass. In summary, the beneficial effect of insulin-induced normoglycemia on transplanted islets was maximal when insulin treatment was maintained the initial 14 days after transplantation. Exposure to sustained hyperglycemia initially after transplantation had a long-lasting deleterious effect on transplanted islets.