Total, free and bound leptin and thyroid function in elderly women with different body weights

Association Between Red Blood Cell Distribution Width and Thyroid Function

AIM

Red blood cell distribution width (RDW) is an important parameter with broad biological implications. However, the study investigating the association between RDW and thyroid function remains sparse and inconsistent. We aimed to investigate the association between RDW and thyroid function in the US population.

METHODS

A cross-sectional analysis was performed using the data from the National Health and Nutrition Examination Survey (NHANES) conducted from 2007 to 2010. The thyroid parameters investigated were mainly free triiodothyronine (fT3), free thyroxine (fT4), thyroid-stimulating hormone (TSH), antithyroglobulin antibody (TgAb), and antithyroperoxidase antibody (TPOAb). In the 6,895 adults aged 18 years or older, logistic regression modeling was applied to estimate the association between RDW quartiles and thyroid parameters. Smooth curve fittings and generalized additive models were then performed to address the nonlinear relationship.

RESULTS

The association between RDW and TSH followed a J-shaped curve, and a significant positive relationship existed in the 12.5%-17.5% range of RDW (β  = 0.350, 95% confidence interval (CI): 0.225 to 0.474), which was prominent in females. We further demonstrated a negative association (β = -0.018, 95% CI: -0.030 to -0.005) between RDW and fT3. Moreover, elevated RDW was more likely to be subclinical hypothyroidism. However, there was no obvious association between RDW and fT4.

CONCLUSION

This study confirmed a significant association between RDW and TSH, and future studies are needed to elucidate the underlying mechanisms of the peculiar RDW-fT3 relationship. RDW may be a significant clinical marker of subclinical hypothyroidism.

Translating the biology of adipokines in atherosclerosis and cardiovascular diseases: Gaps and open questions

AIM

Critically discuss the available data, to identify the current gaps and to provide key concepts that will help clinicians in translating the biology of adipokines in the context of atherosclerosis and cardio-metabolic diseases.

DATA SYNTHESIS

Adipose tissue is nowadays recognized as an active endocrine organ, a function related to the ability to secrete adipokines (such as leptin and adiponectin) and pro-inflammatory cytokines (tumor necrosis factor alpha and resistin). Studies in vitro and in animal models have observed that obesity status presents a chronic low-grade inflammation as the consequence of the immune cells infiltrating the adipose tissue as well as adipocytes. This inflammatory signature is often related to the presence of cardiovascular diseases, including atherosclerosis and thrombosis. These links are less clear in humans, where the role of adipokines as prognostic marker and/or player in cardiovascular diseases is not as clear as that observed in experimental models. Moreover, plasma adipokine levels might reflect a condition of adipokine-resistance in which adipokine redundancy occurs. The investigation of the cardio-metabolic phenotype of carriers of single nucleotide polymorphisms affecting the levels or function of a specific adipokine might help determine their relevance in humans. Thus, the aim of the present review is to critically discuss the available data, identify the current gaps and provide key concepts that will help clinicians translate the biology of adipokines in the context of atherosclerosis and cardio-metabolic diseases.

Differentiation and quantification of endogenous and recombinant-methionyl human leptin in clinical plasma samples by immunocapture/mass spectrometry

Therapeutic recombinant-methionyl human leptin (r-metHu-Leptin, Mr 16155) shares an identical amino acid sequence with endogenous leptin (endo-leptin, Mr 16024), with the addition of an N-terminal methionyl incorporated during recombinant expression in Escherichia coli. Current immunochemistry-based assays do not allow discrimination between the drug and endo-leptin because of cross reactivity. Using the immunoassay, the total plasma concentration measured in some clinical study subjects receiving r-metHu-Leptin can reach supra-physiological levels. To determine which leptin species contributes to the elevated concentrations detected in some subjects, a mass spectrometry-based method allowing discrimination and quantification of both leptin species was developed. Endo-leptin and r-metHu-Leptin were enriched from plasma matrix proteins by immuno capture, and subsequently injected onto a reversed phase analytical column coupled to an API 4000 Q-TRAP LC-MS/MS system. Multiple charge state ions and specific MRMs were monitored to provide unambiguous differentiation between endo-leptin and r-metHu-Leptin. A "top down" assay distinguishing the two forms of leptin was successfully developed and had a linear range from 15.63 to 1000 ng/ml, low limit of quantification of 15.63 ng/ml. The method was applied to selected clinical samples and revealed that the elevated leptin concentrations observed in some subjects reflected accumulation of r-metHu-Leptin. An LC-MS/MS method was developed for unambiguous differentiation of r-metHu-Leptin from endogenous leptin in human plasma. Using this method, specific quantitative information was obtained for pharmacokinetic studies in a clinical trial. The method should prove useful in quantifying this investigational drug against endo-leptin background in future clinical studies.

Relationship between body mass index and thyrotropin in euthyroid women: differences by smoking, race and menopausal status

OBJECTIVE

To evaluate potential effect modifications on the association between BMI and thyrotropin (TSH) by smoking, race, and menopausal status among euthyroid women.

METHODS

A cross-sectional population-based study was carried out in the city of Rio de Janeiro, Brazil, in 2004-2005. Households (1,500) were selected using three-stage probability sampling. A sample of 1,084 women aged 35 years or older and with TSH values within the reference range (0.3-4.0 mIU/l) was investigated. Weight and height were measured at household and blood collected for serum TSH and anti-thyroperoxidase (anti-TPO) antibody analysis.

RESULTS

Overall, BMI was positively and significantly associated with serum TSH (β = 0.87; p = 0.001). This association was modified by smoking, race, and menopausal status (p < 0.05). Adjusted regression coefficients were 1.78 versus 0.58 comparing smokers with non-smokers, 1.39 for Blacks compared to 0.79 for Non-Blacks, and 0.70 for women in menopause compared to 1.04 for premenopausal women. The percentage of high anti-TPO (greater than 35 UI/ml) was 8.8%, and the association between TSH and BMI was no longer significant in this group.

CONCLUSION

BMI was positively associated with serum TSH specifically in its normal range, but only for those women who tested negative for anti-TPO. Smoking and race are negatively associated with anti-TPO, possibly explaining the effect modification observed.

Free thyroxine is an independent predictor of subcutaneous fat in euthyroid individuals

OBJECTIVE

Thyroid function parameters have been associated with obesity, but associations with the type of adiposity have not been examined. We used ultrasound (US) to assess regional adiposity and investigated associations of thyroid function with parameters of central obesity.

DESIGN

Cross-sectional study.

METHODS

A total of 303 apparently healthy individuals (age 42.9+/-8.8, body mass index (BMI) 19.0-43.3, median 26.2 kg/m(2), 181 women) were examined for indices of the metabolic syndrome. BMI, waist and hip circumference, abdominal subcutaneous fat (SF), and preperitoneal fat (PF) layer was estimated. TSH, free thyroxine (fT(4)), triiodothyronine (T(3)), thyroid autoantibodies, insulin, glucose, and lipid levels were measured. Subjects receiving T(4) (9.2%) were excluded.

RESULTS

SF and SF/PF ratio were inversely correlated with fT(4) levels (r=-0.169, P=0.023, r=-0.193, P=0.009 respectively). In multivariate analysis, fT(4) was a predictor of SF and SF/PF, independently of age, sex, and smoking. SF correlated with TSH levels (r=0.149, P=0.037). PF and SF were positively associated with T(3) levels (r=0.245, P=0.004 and r=0.189, P=0.019 respectively). T(3) levels were positively associated with BMI (r=0.257, P=0.0004), waist perimeter (r=0.324, P<0.0001), and waist-to-hip ratio (WHR; r=0.363, P<0.0001). The T(3)/fT(4) ratio was positively correlated with SF (r=0.182, P=0.028), WHR (r=0.267, P=0.0003), and BMI (r=0.146, P=0.043).

CONCLUSIONS

Increasing SF accumulation as assessed by US is associated with lower fT(4) and higher TSH levels among euthyroid slightly overweight individuals. These associations indicate that subtle variation in thyroid function may participate in regional adiposity.