Role of obesity on all-cause mortality in whites with type 2 diabetes from Italy

Mortality rate of diabetic patients is twice as much that of non-diabetic individuals. The role of obesity on mortality risk in patients with type 2 diabetes is controversial. Aim of our study was to address the relationship between obesity and all-cause mortality in a real-life set of white patients with type 2 diabetes from central-southern Italy from the Gargano Mortality Study (GMS). In addition, we used genetic data from genome-wide association studies (GWAs)-derived single nucleotide polymorphisms (SNPs) firmly associated with body mass index (BMI), in order to investigate the intrinsic nature of reduced mortality rate we, in fact, observed in obese patients. Study subjects with type 2 diabetes (n = 764) are part of the GMS, which is aimed at unraveling predictors of incident all-cause mortality. Time-to-death analyses were performed by Cox regression. Association between genotype risk score and obesity was tested by logistic regression. Of the 32 SNPs firmly associated with BMI, we investigated those with BMI β value ≥0.10 kg/m(2) and allele frequency ≥10 %. Genotyping was performed by KBioscience (http://www.lgcgenomics.com/). In GMS, obesity predicted a 45 % reduction in all-cause mortality. Individuals with high "obesity genetic load" (i.e., those carrying >9 risk alleles) were 60 % more likely to be obese as compared to individuals with low "obesity genetic load." Most importantly, mortality rate was not different in individuals with high and low "obesity genetic load," thus indicating no role of obesity genes on all-cause mortality and speaking against a cause-effect relationship underlying the association between obesity and reduced mortality rate.

Role of insulin resistance in kidney dysfunction: insights into the mechanism and epidemiological evidence

Several lines of evidence suggest a pathogenic role of insulin resistance on kidney dysfunction. Potential mechanisms are mostly due to the effect of single abnormalities related to insulin resistance and clustering into the metabolic syndrome. Hyperinsulinemia, which is inevitably associated to insulin resistance in non diabetic states, also appears to play a role on kidney function by inducing glomerular hyperfiltration and increased vascular permeability. More recently, adipocytokine which are linked to insulin resistance, low grade inflammation, endothelial dysfunction and vascular damage have been proposed as additional molecules able to modulate kidney function. In addition, recent evidences point also to a role of insulin resistance at the level of the podocyte, an important player in early phases of diabetic kidney damage, thus suggesting a new mechanism through which a reduction of insulin action can affect kidney function. In fact, mouse models not expressing the podocyte insulin receptor develop podocytes apoptosis, effacement of its foot processes along with thickening of the glomerular basement membrane, increased glomerulosclerosis and albuminuria. A great number of epidemiological studies have repeatedly reported the association between insulin resistance and kidney dysfunction in both non diabetic and diabetic subjects. Among these, studies addressing the impact of insulin resistance genes on kidney dysfunction have played the important role to help establish a cause-effect relationship between these two traits. Finally, numerous independent intervention studies have shown that a favourable modulation of insulin resistance has a positive effect also on urinary albumin and total protein excretion. In conclusion, several data of different nature consistently support the role of insulin resistance and related abnormalities on kidney dysfunction. Intervention trials designed to investigate whether treating insulin resistance ameliorates also hard renal end-points are both timely and needed.

Relationship between ADIPOQ gene, circulating high molecular weight adiponectin and albuminuria in individuals with normal kidney function: evidence from a family-based study

AIMS/HYPOTHESIS

Insulin resistance is associated with reduced serum adiponectin and increased albuminuria levels. Thus, one would anticipate an inverse relationship between circulating adiponectin and albuminuria. However, several studies have described a 'paradoxical' elevation of serum adiponectin in patients with elevated albuminuria. These findings may have been confounded by the presence of diseases and related treatments known to affect circulating adiponectin and albuminuria. We therefore studied the relationship between circulating adiponectin and albuminuria in the absence of such confounders.

METHODS

To this purpose, the relationship between adiponectin isoforms and albumin:creatinine ratio (ACR) was investigated in a family-based sample of 634 non-diabetic untreated white individuals with normal kidney function. We also investigated whether the two variables share a common genetic background and addressed the specific role of the gene encoding adiponectin on that background by genotyping several ADIPOQ single nucleotide polymorphisms (SNPs).

RESULTS

ACR was directly associated with high molecular weight (HMW) adiponectin isoform (p = 0.024). The two variables shared some genetic correlation (ρ(g) = 0.38, p = 0.04). ADIPOQ promoter SNP rs17300539 was associated with HMW adiponectin (p = 4.8 × 10(-5)) and ACR (p =0.0027). The genetic correlation between HMW adiponectin and ACR was no longer significant when SNP rs17300539 was added to the model, thus reinforcing the role of this SNP in determining both traits.

CONCLUSIONS/INTERPRETATION

Our study shows a positive, independent correlation between HWM adiponectin and ACR. ADIPOQ variability is associated with HMW adiponectin and ACR, and explains some of the common genetic background shared by these traits, thus suggesting that ADIPOQ and HMW adiponectin modulate albuminuria levels.

Circulating high molecular weight adiponectin isoform is heritable and shares a common genetic background with insulin resistance in nondiabetic White Caucasians from Italy: evidence from a family-based study

OBJECTIVE

Reduced circulating adiponectin levels contribute to the aetiology of insulin resistance. Adiponectin circulates in three different isoforms: high molecular weight (HMW), medium molecular weight (MMW) and low molecular weight (LMW) isoforms. The genetics of adiponectin isoforms is mostly unknown. Our aim was to investigate whether and to which extent circulating adiponectin isoforms are heritable and whether they share common genetic backgrounds with insulin resistance-related traits.

METHODS

In a family-based sample of 640 nondiabetic White Caucasians from Italy, serum adiponectin isoforms concentrations were measured by ELISA. Three single nucleotide polymorphisms (SNPs) in the ADIPOQ gene previously reported to affect total adiponectin levels (rs17300539, rs1501299 and rs677395) were genotyped. The heritability of adiponectin isoform levels was assessed by variance component analysis. A linear mixed effects model was used to test the association between SNPs and adiponectin isoforms. Bivariate analyses were conducted to study genetic correlations between adiponectin isoforms levels and other insulin resistance-related traits.

RESULTS

All isoforms were highly heritable (h(2) = 0.60-0.80, P = 1.0 x 10(-13)-1.0 x 10(-23)). SNPs rs17300539, rs1501299 and rs6773957 explained a significant proportion of HMW variance (2-9%, P = 1.0 x 10(-3)-1.0 x 10(-5)). In a multiple-SNP model, only rs17300539 and rs1501299 remained associated with HMW adiponectin (P = 3.0 x 10(-4) and 2.0 x 10(-2)). Significant genetic correlations (P = 1.0 x 10(-2)-1.0 x 10(-5)) were observed between HMW adiponectin and fasting insulin, homeostasis model assessment of insulin resistance, HDL cholesterol and the metabolic syndrome score. Only rs1501299 partly accounted for these genetic correlations.

CONCLUSION

Circulating levels of adiponectin isoforms are highly heritable. The genetic control of HMW adiponectin is shared in part with insulin resistance-related traits and involves, but is not limited to, the ADIPOQ locus.

Multigenic control of serum adiponectin levels: evidence for a role of the APM1 gene and a locus on 14q13

Adiponectin is a circulating enhancer of insulin action that is secreted by the adipose tissue. In epidemiological studies, serum levels of this protein predict the risk of type 2 diabetes and cardiovascular events. Serum adiponectin levels have been associated with variants at the adiponectin (APM1) and PPARgamma2 loci and have also been linked to markers on 5p15 and 14q13. We investigated the role of these four loci in regulating serum adiponectin in a Caucasian population from Italy. Four haplotype-tagging single-nucleotide polymorphisms (ht-SNPs) (-11377 C>G, -4041 A>C, +45 T>G, and +276 G>T) at the APM1 locus and the PPARgamma2 Pro12Ala polymorphism were examined for association with serum adiponectin in 413 unrelated, nondiabetic individuals. Of the five SNPs tested, +276G>T was the only one to be associated with serum adiponectin (P = 0.032), with "TT" individuals having higher adiponectin levels than other subjects. In a variance-components analysis of 737 nondiabetic members of 264 nuclear families, adiponectin heritability was 30%, with a small but significant proportion explained by the +276 genotype ( P = 0.0034). Suggestive evidence of linkage with adiponectin levels was observed on chromosome 14q13, with a LOD of 2.92 (P = 0.000057) after including the APM1 +276 genotype in the model. No linkage was observed at 5p15. Our data indicate a strong genetic control of serum adiponectin. A small proportion of this can be attributed in our population to variability at the APM1 locus, but an as yet unidentified gene on 14q13 appears to play a much bigger role.

Insulin modulates PC-1 processing and recruitment in cultured human cells

We evaluated whether insulin signaling modulates plasma cell glycoprotein (PC-1) plasma membrane recruitment, posttranslational processing, and gene expression in human cultured cell lines. Insulin induced a fourfold increase (P < 0.01) of membrane PC-1 expression by rapid and sensitive mechanism(s). This effect was reduced (P < 0.05-0.01) by inhibition of phosphatidylinositol 3-kinase (200 nmol/l wortmannin) and S6 kinase (50 nmol/l rapamycin) activities and intracellular trafficking (50 micromol/l monensin) and was not accompanied by PC-1 gene expression changes. Moreover, at Western blot, insulin elicited the appearance, in both plasma membrane and cytosol, of a PC-1-related 146-kDa band (in addition to bands of 163, 117, 106, and 97 kDa observed also in absence of insulin) that was sensitive to endoglycosidase H. Finally, inhibition of PC-1 translocation to plasma membrane, by wortmannin pretreatment, increases insulin-stimulated receptor autophosphorylation. Our data indicate that insulin stimulates PC-1 posttranslational processing and translocation to the plasma membrane, which in turn impairs insulin receptor signaling. Bidirectional cross talk between insulin and PC-1, therefore, takes place, which may be part of the hormone self-desensitization mechanism.

T426I a new mutation in the thyroid hormone receptor beta gene in a sporadic patient with resistance to thyroid hormone and dysmorphism. Mutations in brief no. 192. Online

Resistance to thyroid hormone (RTH) is a rare inherited autosomal syndrome caused by mutations in the thyroid hormone receptor beta (TRb) gene. Although RTH is generally a familiar disease, 15% of sporadic cases have been also reported. So far, about 80 different mutations of TRb gene have been identified in patients affected by RTH. All these mutations localize to the binding domain and most of them cluster within two "hot spots" (codons 310-349 and codons 429-460). Here we describe in a patient with RTH, a new mutation in codon 426 (T426I) of the TRb gene leading to a threonine to isoleucine substitution. This is a "de nova" mutation which localizes in the so-called "cold" region, outside the two known "hot spots". The patient had the hallmark of RTH: elevated FT3 and FT4, normal TSH, and clinical features of both hypo and hyperthyroidism. Moreover, several dysmorphisms were present including triangular face appearance, synophris, low set ears, micrognathia with malocclusion, large upper incisors and apparent lack of lower cuspids which have not previously described in RTH patients.

Graves' immunoglobulins activate phospholipase A2 by recognizing specific epitopes on thyrotropin receptor

Thyroid-stimulating IgG from Graves' patients bind to the TSH receptor and activate both adenylyl cyclase (AC) and phospholipase A2 (PLA2) in FRTL5 thyroid cells. Both activities have been associated with increased thyroid cell growth and function; evidence exists that subpopulations of Graves' IgG can stimulate either AC or PLA2 cascades and that the activation of both is associated with the largest goiters in patients. Studies using chimeras of the human TSHR receptor (hTSHR) and the LH-CG receptor show that most patients with Graves' disease have cAMP-stimulating IgG that require epitopes on the N-terminal portion of the TSHR extracellular domain; epitopes associated with PLA2 activation are not clear. To address this question we used stably transfected Chinese hamster ovary (CHO) cells containing the wild-type hTSHR and the hTSHR chimera with residues 8-165 (Mc1+2) substituted by equivalent residues of the LH-CG receptor. PLA2 activity, measured as arachidonic acid (AA) release, was determined in 32 patients with Graves' disease. We show that 72% of Graves' patients have IgG able to stimulate PLA2 in CHO cells transfected with the TSHR and that AA release induced by Graves' IgG was significantly reduced (P = 0.022) in the CHO-Mc1+2-transfected cells (193 +/- 88% vs. 131 +/- 67%, respectively). Unlike IgG, the effect of TSH was not modified in the CHO-Mc1+2-transfected cells. When we compared the AC- and PLA2-stimulating activities of these 32 IgG in wild-type TSHR transfectants, we found that 63% of Graves' patients have antibodies able to stimulate both PLA2 and AC, whereas some patients' IgG were active only in AC or PLA2 assays. Of the patients with IgG having activity in both assays in wild-type TSHR transfectants, 50% of the IgG lost their stimulatory activities in both AA release and cAMP assays in Mc1+2 cells. Of the remainder, some IgG maintained their activity in one (AA release) or the other (cAMP) assay when measured in Mc1+2 chimeras. Thus, our data show that the N-terminal portion of extracellular domain of the TSHR is required for PLA2 as well as AC activation by IgG from patients with Graves' disease. These data also demonstrate that patients with Graves' disease have heterogeneous autoantibodies that selectively activate AC and PLA2 pathways and suggest that patients with autoantibodies active in both assays have more severe disease, with higher thyroid hormone levels and larger goiters.

Association between an R338L mutation in the thyroid hormone receptor-beta gene and thyrotoxic features in two unrelated kindreds with resistance to thyroid hormone

Resistance to thyroid hormone (RTH) is a rare syndrome characterized by reduced sensitivity to thyroid hormone due to thyroid hormone receptor-beta (TRbeta) gene mutations or deletion. RTH has been classified on the basis of clinical features into generalized (GRTH) and pituitary (PRTH) resistance. There is, however, overlap of clinical and biochemical findings in patients with the two forms of resistance, and similar TRbeta gene mutations have been identified in both. The 2 subtypes of RTH, therefore, are considered to be different manifestations of a single genetic entity. We report a mutation of the TRbeta gene, an arginine to leucine substitution at codon 338 (R338L), in 2 unrelated RTH kindreds of northern Italian ancestry. The same mutation was already reported in a single unrelated kindred affected by PRTH. Five individuals, 3 in the first and 2 in the second family, were clinically evaluated and followed for 3-11 years. During the long-term follow-up, the patients manifested symptoms and signs of hyperthyroidism including palpitations, fine tremors, heat intolerance, increased sweating, increased deep tendon reflexes, moist and warm skin, cardiac rhythm abnormalities, reduced body weight, and reduced bone mineral density. The clinical features of these kindreds are consistent with a predominant PRTH phenotype.

Cyclooxygenase-dependent thyroid cell proliferation induced by immunoglobulins from patients with Graves' disease

IgG associated with Graves' disease bind to the TSH receptor and alter thyroid growth and function, mainly through the stimulation of adenylyl cyclase. In addition, Graves' IgG are able to interact with the phospholipase C (PLC)/Ca2+ and phospholipase A2 (PLA2)/arachidonic acid (AA) cascades. The activation of this latter pathway leads to thyroid cell growth in vitro. The elucidation of additional mechanisms of action of Graves' IgG has made possible the identification of four subgroups of patients, characterized by IgG with different biochemical activities (extent of cAMP and AA release stimulation in in vitro assays). On the basis of these results, a novel therapeutic approach could be proposed based on the inhibition of PLA2 and AA metabolism. To test this hypothesis, the ability of IgG from 56 Graves' patients to stimulate [3H]thymidine incorporation in FRTL5 thyroid cells in the presence and absence of the cyclooxygenase inhibitor indomethacin (2.5 x 10(-6) mol/L) was measured. A significant reduction in [3H]thymidine incorporation was found (33% inhibition; P < 0.0001) upon pretreatment with indomethacin, suggesting that in vitro thyroid cell growth is regulated by cyclooxygenase metabolites. This strengthens the argument for involvement of the PLA2/AA cascade in the pathophysiology of Graves' disease and the proposal for novel selective pharmacological treatments of these patients.

Steroid gradients across the cancerous breast: an index of altered steroid metabolism in breast cancer?

The concentrations of 17 beta-estradiol, estrone, testosterone (T), dehydroepiandrosterone (DHEA), dehydroepiandrosterone sulphate, androstenedione (A), cortisol and prolactin (PRL) were determined in the peripheral venous blood and in the lateral thoracic vein of 14 premenopausal and 34 postmenopausal women who underwent surgery for a breast carcinoma. The difference between the two blood samples, defined as concentration gradient across the cancerous breast, was calculated for all hormones. A significant peripheral-local concentration gradient was found for DHEA and A both in pre- and postmenopausal patients, whereas for T it was observed only in postmenopausal subjects. Furthermore, DHEA and A gradients were correlated to the presence of estrogen receptors as determined by a radioligand binding assay. An inverse relationship between DHEA gradient and the expression of estrogen receptors was observed in premenopausal women, whereas in postmenopausal patients an opposite, although not significant, trend was found. These results suggest that in the cancerous breast: (1) DHEA, A and T (the latter only in postmenopause) could be taken up from plasma, and thus there could be a storage of these steroids inside the breast tissue and/or perhaps some alterations in their local metabolism; (2) androgens could play a different role in breast carcinogenesis in relation to the estrogen circulating levels and to the expression of estrogen receptors.