Rafael Alis

Inconsistency in circulating irisin levels: what is really happening?

The discovery of irisin as a novel and promising peptidic hormone for the treatment of obesity and diabetes has recently been reported. As a result, great hopes have been raised based on this finding, hypothesizing that irisin might provide additional benefits, not only for obesity and diabetes, but also for a wide range of pathological conditions requiring therapeutical and clinical attention. However, controversial results and conclusions on circulating irisin concentrations and correlations with other variables, including its role in metabolism, have recently been reported. Although laboratory assessment of irisin by ELISA is easily available and may provide interesting information for therapeutics and clinical practice, the heterogeneous and often discrepant results published so far, raise serious concerns about its measurement, indicating that it may still not be ready for use or whether irisin really exists. We highlight here some aspects on these discrepancies and contradictions, and put forward their implications.

Circulating irisin levels are not correlated with BMI, age, and other biological parameters in obese and diabetic patients.

IntroductionIncreasing evidence demonstrates that skeletal muscleproduces and releases substances such as cytokines capableof modulating different metabolic processes [1]. Accord-ingly, these cytokines are classified as ‘‘myokines’’ [2]. Anovel peptidic myokine named ‘irisin’ has been recentlyidentified [3]. Irisin may prove beneficial not only inmonitoring and/or the treatment of obesity and diabetes,but also for a wide range of pathological conditions that arecharacterized by a variable imbalance of energy demandand expenditure [4, 5]. Consequently, great expectationshave been rapidly made based on these findings. In thisregard, a new concept, ‘‘irisinemia,’’ has been recentlysuggested to monitor metabolic disorders such as type 2diabetes (T2D) or obesity, and therefore metabolic syn-drome (MetS) [2]. However, several studies assessed cir-culating irisin concentrations in obese and/or T2D patients,throwing controversial results and conclusions [6]. There-fore, the aim of this study was to evaluate the circulatingirisin levels in obese and T2D patients as well as todetermine whether irisin levels correlate with other com-monly used biochemical parameters in clinical medicine.Materials and methodsOne-hundred and fifty-three subjects divided in 20 controlsand 133 patients were included in this study. Patients wereeither morbid obese [body mass index (BMI)[40](n = 69) or T2D patients (n = 64) [7]. Control subjectswith sedentary lifestyles (performing less than 20 min ofphysical activity per day) were recruited. Morbid obesepatients did not present diabetes and were divided in twogroups. The morbid obese patients with atherogenic dysli-pidemia (MOAD) (n = 34) presented atherogenic dyslipi-demia [triglycerides (TG)[150 mg/dL and high-densitylipoproteins cholesterol (HDL-chol)\40 mg/dL in menor\50 mg/dL in women], while the morbid obese patientswithout atherogenic dyslipidemia (MO) (n = 35) did not

Homocysteine levels in morbidly obese patients. Its association with waist circumference and insulin resistance

The association between morbid obesity and hyperhomocysteinemia (HH) remains controversial and the nature of this relationship needs to be clarified as several metabolic, lipidic, inflammatory and anthropometric alterations that accompany morbid obesity may be involved. In 66 morbidly obese patients, 47 women and 19 men aged 41 ± 12 years and 66 normo-weight subjects, 43 women and 23 men, aged 45 ± 11 years, we determined homocysteine (Hcy) levels along with lipidic, anthropometric, inflammatory and insulin resistance markers. In addition, we investigated the effect of Metabolic Syndrome (MS) and its components on Hcy levels. Obese patients had statistically higher Hcy levels than controls: 12.76 ± 5.30 μM vs. 10.67 ± 2.50 μM; p = 0.006. Moreover, morbidly obese subjects showed higher waist circumference, glucose, insulin, HOMA, leptin, triglycerides, fibrinogen, C reactive protein (CRP) (p < 0.001, respectively), and lower vitamin B12 (p = 0.002), folic acid and HDL-cholesterol (p < 0.001, respectively). In the multivariate regression analysis, waist circumference, glucose, leptin and folic acid levels were independent predictors for Hcy values (p < 0.050). When obese patients were classified as having MS or not, no differences in Hcy levels were found between the two groups (p = 0.752). Yet when we analysed separately each MS component, only abdominal obesity was associated with Hcy levels (p = 0.031). Moreover when considering glucose >110 mg/dL (NCEP-ATPIII criteria) instead of glucose intolerance >100 mg/dl (updated ATPIII criteria), it also was associated with HH (p = 0.042). These results were confirmed in the logistic regression analysis where abdominal obesity and glucose >115 mg/dL constitute independent predictors for HH (OR = 3.2; CI: 1.23-13.2; p = 0.032, OR: 4.6; CI: 1.7-22.2; p = 0.016, respectively). The results of our study indicate that increased Hcy levels are related mostly with abdominal obesity and with insulin resistance. Thus, HH may raise atherothrombotic and thromboembolic risk in these patients.

The mitochondrial-derived peptide MOTS-c: a player in exceptional longevity?

Mitochondrial‐derived peptides (MDP) are encoded by functional short open reading frames in the mitochondrial DNA (mtDNA). These include humanin, and the recently discovered mitochondrial open reading frame of the 12S rRNA‐c (MOTS‐c). Although more research is needed, we suggest that the m.1382A>C polymorphism located in the MOTS‐c encoding mtDNA, which is specific for the Northeast Asian population, may be among the putative biological mechanisms explaining the high longevity of Japanese people.

Association between irisin and homocysteine in euglycemic and diabetic subjects

OBJECTIVES The aim of study was to explore whether a relationship exists between homocysteine and irisin in type 2 diabetes (T2D) patients-a population with a high risk of developing cardiovascular disease-and euglycemic controls. DESIGN AND METHODS 69 T2D patients and 75 control subjects (adjusted by body mass index (BMI)) were included in the study. Irisin and homocysteine concentrations and anthropometric and biochemical variables were determined. RESULTS Levels of homocysteine were significantly higher (11.0±3.0 vs 12.4±4.2 μmol/l) and levels of irisin were lower (279±58 vs 263±38 ng/ml) in T2D patients. When both T2D and controls were considered, irisin was found to correlate only with homocysteine (r=-0.215; p=0.011). Moreover, a decreasing trend in irisin levels was observed according to homocysteine tertile (p=0.034). CONCLUSIONS Our results provide evidence of an association between irisin and homocysteine, which may be due to nicotinamide metabolism. The clinical significance of this relationship is unclear, but our findings may prompt further mechanistic research to investigate the role played by irisin in vascular disorders.

Methodological considerations to determine the effect of exercise on brain-derived neurotrophic factor levels

OBJECTIVES Physical exercise up-regulates brain-derived neurotrophic factor (BDNF) in the brain and blood. However, there is yet no consensus about the adequate blood processing conditions to standardize its assessment. We aimed to find a reliable blood sample processing method to determine changes in BDNF due to exercise. DESIGN AND METHODS Twelve healthy university students performed an incremental cycling test to exhaustion. At baseline, immediately after exercise, and 30 and 60 min of recovery, venous blood was drawn and processed under different conditions, i.e. whole blood, serum coagulated for 10 min and 24 h, total plasma, and platelet-free plasma. BDNF concentration was measured by ELISA. RESULTS Exercise increased BDNF in whole blood and in serum coagulated for 24 h when corrected by hemoconcentration. We did not find effects of exercise on BDNF in serum coagulated for 10 min or in plasma samples. Plasma shows heterogeneous BDNF values in response to exercise that are not prevented when platelets are eliminated while homogeneous BDNF levels were found in whole blood or serum coagulated for 24 hour samples. CONCLUSIONS In exercise studies, BDNF levels should be adjusted by hemoconcentration. Our data highlight the importance of blood sample selection since the differences between each one affect significantly the BDNF factor changes due to exercise.

Circulating irisin detection: Does it really work?

The recent discovery of irisin has generated considerable interest in the scientific community. However, many studies on the biochemistry and biology of this intriguing hormone yielded controversial results in humans, which were mostly attributable to a number of drawbacks in the methods used for its detection and measurement.

RDW in patients with systemic lupus erythematosus. Influence of anaemia and inflammatory markers

Red blood cell distribution width (RDW) is a routine parameter that reflects size variations in erythrocytes. High RDW has been associated with cardiovascular events and inflammatory diseases. However, no studies evaluating the association of RDW with systemic lupus erythematosus (SLE) have been published. We aimed to explore the association of RDW with inflammatory markers in SLE. As SLE is often associated with anaemia, we considered this factor in order to know whether RDW is related with inflammation, anaemia or both in SLE. The study included 105 SLE patients (7 men, 98 women; aged 15-73 years) and 105 controls (9 men, 96 women; aged 18-71 years). Patients were divided according to anaemia status (26 with, 79 without). Biochemical, hematological and inflammatory parameters (C-reactive protein (CRP), fibrinogen and erythrocyte aggregation (EA1)) were analyzed. SLE patients showed increased RDW, CRP and EA1 (p < 0.001), and decreased hemoglobin levels (p < 0.001) when compared with controls. RDW was higher in SLE patients with anaemia (a-SLE) as compared with those without anaemia (na-SLE) (p < 0.01) or controls (p < 0.001). CRP in a-SLE was higher than in controls (p < 0.01) but lower than in na-SLE (p < 0.05). In na-SLE RDW correlated directly with fibrinogen and CRP (p < 0.001), but not in a-SLE. Our results indicate that SLE patients show higher RDW irrespectively of anaemia status, and that RDW is influenced by both anaemia and inflammation, but the influence of anaemia is stronger.

Influence of inflammatory and lipidic parameters on red blood cell distribution width in a healthy population

Red blood cell distribution width (RDW) is a routine red blood cell count parameter which has been shown to be associated with inflammatory parameters. Recently, some authors proposed that RDW seems to be a marker of an adverse lipidic profile. In order to clarify whether RDW is related to inflammation, plasma lipids, or both, we determined anthropometric, hematimetric, inflammatory and lipidic parameters in 1111 healthy subjects. RDW correlated directly with age, body mass index (BMI), inflammatory parameters (plasma viscosity, erythrocyte sedimentation rate (ESR), fibrinogen, leukocyte and neutrophil count), and inversely with iron and hematimetric parameters (P <  0.05). When subjects were divided according to gender, RDW correlated inversely with triglycerides only in women (P <  0.05). When subjects were classified into RDW-quartiles, increased RDW values were accompanied by decreased serum iron levels and hematimetric indices (P <  0.01), whereas age and inflammatory markers increased according to RDW-quartiles (P <  0.001 and P <  0.05, respectively). However, plasma lipids did not change with increasing RDW-quartiles (P >  0.05). In the linear regression analysis, age, hemoglobin, MCV (beta coefficient: 0.202, -0.234, -0.316, P <  0.001) and fibrinogen (beta coefficient: 0.059, P = 0.048) were the only independent predictors of RDW. The present study indicates that RDW is associated with inflammatory markers and hematimetric indices, but not with plasma lipid levels in a healthy population.

Hemoconcentration induced by exercise: Revisiting the Dill and Costill equation.

The Dill and Costill equation is used to estimate the exercise‐induced hemoconcentration. However, this calculation requires drawing an extra whole‐blood sample, which cannot be frozen and has to be analyzed with dedicate instrumentation in a relative short time. The aim of the present study was to explore the usefulness of some serum biochemical parameters to estimate hemoconcentration induced by exhaustive exercise. Fourteen healthy male subjects (19–34 years) performed a15‐min running test at 110% of anaerobic threshold speed. Hemoglobin, hematocrit, brain natriuretic peptide (BNP), creatinine, gamma‐glutamyltransferase (GGT), total‐proteins, albumin, total calcium (Ca), K+, Na+, and Cl− were determined in blood samples taken before, after exercise, and after a 30‐min recovery period. Plasma volume loss (ΔPV) was calculated by Dill and Costill equation. At post‐exercise and after recovery, the percentage increments of total‐proteins, albumin, GGT and Ca correlated significantly with ΔPV. Bland–Altman analyses showed that correcting BNP, creatinine, and K+ concentration by Ca percentage increments yield biases and limits of agreement that are acceptable when compared with Dill and Costill equation correction. Ca concentration may be used as a hemoconcentration biomarker in high‐intensity exercise, which would allow scientists and physicians avoid extra costs, facilitate in‐field research, and delayed estimation of hemoconcentration using stored serum samples.