Resistin is secreted from macrophages in atheromas and promotes atherosclerosis

Resistin up-regulates fractalkine expression in human endothelial cells: lack of additive effect with TNF-alpha

Resistin is a cytokine and fractalkine (Fk) a cell adhesion molecule and chemokine that contribute to human vascular inflammation by mechanisms not clearly defined. We questioned whether resistin induces Fk expression in human endothelial cells (HEC), compared the effect with that of the pro-inflammatory cytokine, TNF-alpha, and evaluated the consequences of co-stimulating HEC with both activators on Fk induction and on the signalling molecules involved. We found that resistin up-regulated Fk expression at comparable level to that of TNF-alpha by a mechanism involving P38 and JNK MAPK and NF-kappaB. Co-stimulation of cells with resistin and TNF-alpha did not increase Fk expression induced by every single inducer. Moreover resistin reduced the expression induced by TNF-alpha in HEC. The new data uncover Fk as a novel molecular link between resistin and inflammation and show that resistin and TNF-alpha have no additive effect in Fk up-regulation or on the signalling molecules implicated.

Age-related differences in the pathogenesis of calcific aortic stenosis: the potential role of resistin

BACKGROUND

Aortic stenosis (AS) is considered as an atherosclerotic related process. However, there are uncertainties whether AS in the elderly is associated with the same pathophysiological processes as in younger patients. We hypothesized that the metabolic determinants of the valvular inflammatory and calcifying processes occurring in elderly patients are different from those observed earlier in life.

METHODS

Among 114 patients operated for a severe AS, a complete plasma lipid blood profile and plasma levels of adipokines (resistin, leptin) were determined. The calcium content of the aortic valve was measured and valvular inflammation was quantified.

RESULTS

Elderly patients (>or=70 years) had significantly lower LDL-C (p=0.02), lower LDL-C associated with small size particles (LDL-C <255 A) (p=0.003), and higher HDL peak particle size than younger patients (p=0.03). In addition, elderly patients had increased plasma leptin (p=0.04) and resistin (p=0.0004) levels compared to the middle-aged group (<70 years). In the elderly patients, higher plasma resistin blood levels were associated with increased valve calcium content and inflammation.

CONCLUSION

The lipid profile of elderly patients was found less atherogenic than that of middle-aged patients. On the other hand, older patients with AS had higher plasma level of resistin which was associated with the degree of valvular calcification and inflammation. These results suggest that, beyond lipid model of atherosclerosis, age-related processes affecting resistin blood levels may also be involved in the late development of AS.

Peripheral mononuclear cell resistin mRNA expression is increased in type 2 diabetic women

Resistin has been shown to cause insulin resistance and to impair glucose tolerance in rodents, but in humans its physiological role still remains elusive. The aim of this study was to examine whether resistin mRNA expression in human peripheral mononuclear cells (PBMCs) and its corresponding plasma levels are altered in type 2 diabetes. Resistin mRNA levels were easily detectable in human PBMC, and found to be higher in DM2 compared to healthy women (P = .05). Similarly, mononuclear mRNA levels of the proinflammatory cytokines IL-1β, TNF-α, and IL-6 were all significantly higher in DM2 compared to control women (P < .001). The corresponding plasma resistin levels were slightly, but not significantly, increased in DM2 women (P = .051), and overall, they correlated significantly with BMI (r = 0.406, P = .010) and waist circumference (r = 0.516, P = .003), but not with fasting insulin levels or HOMA-IR. Resistin mRNA expression is increased in PBMC from DM2 women, together with increased expression of the inflammatory cytokines IL-1β, TNF-α, and IL-6, independent of obesity. These results suggest that resistin and cytokines might contribute to the low-grade inflammation and the increased atherogenic risk observed in these patients.

Resistin increases lipid accumulation by affecting class A scavenger receptor, CD36 and ATP-binding cassette transporter-A1 in macrophages

AIMS

Resistin promotes macrophage-foam cell formation, but the mechanisms are unclear. In macrophages, lipid uptake is regulated by scavenger receptors (SR-A and CD36), while the cholesterol efflux is regulated by SR-BI, ATP-binding cassette transporter-A1 (ABCA1) and ABCG1. We investigated the mechanisms underlying the dysregulation by resistin of these regulators leading to promotion of lipid accumulation in bone marrow-derived macrophages.

MAIN METHODS

Western blotting, real-time PCR and oil red O staining were performed.

KEY FINDINGS

Resistin exacerbated lipid accumulation in oxLDL-treated macrophages. Resistin treatment of oxLDL-untreated macrophages showed increased SR-A and CD36 mRNA and protein levels, and decreased ABCA1 protein level, while having no effect on SR-BI or ABCG1 expression. Up-regulation of SR-A and CD36 by resistin resulted from activation of AP-1 and PPARgamma, respectively, and this was confirmed by the lack of activation of either after AP-1 inhibition using curcumin or SP600125, or PPARgamma inhibition using GW9662, respectively. The down-regulation of ABCA1 by resistin was not accompanied by a reduced mRNA level or an activation of LXRalpha/RXR, but resulted from enhanced protein degradation as revealed by the abolition of the down-regulation after inhibition of the proteasome pathway using ALLN or MG-132. A combined inhibition by SP600125, GW9662 and ALLN prevented resistin-induced exacerbation of lipid accumulation in oxLDL-treated macrophages.

SIGNIFICANCE

Resistin promotes foam cell formation via dysregulation of SR-A, CD36 and ABCA1. SR-A and CD36 are transcriptionally up-regulated by resistin through AP-1 and PPARgamma, respectively, whereas ABCA1 is down-regulated by resistin through proteasome-mediated enhancement of protein degradation.

Plasma resistin levels and risk of myocardial infarction and ischemic stroke

CONTEXT

Resistin is a hormone that has been linked to insulin resistance, inflammatory processes, and coronary heart disease in case-control studies; however, prospective data on the association between plasma resistin levels and future risk of cardiovascular disease are lacking.

OBJECTIVE

The objective of the study was to investigate the association between plasma resistin levels and risk of future myocardial infarction (MI) and ischemic stroke (IS) in a large prospective cohort.

METHODS

We investigated the association between plasma resistin levels and risk of MI and IS in a case-cohort design among 26,490 middle-aged subjects from the European Investigation into Cancer and Nutrition-Potsdam Study without history of MI or stroke at time of blood draw. Plasma resistin levels were measured in baseline blood samples of 139 individuals who developed MI, 97 who developed IS, and 817 individuals who remained free of cardiovascular events during a mean follow-up of 6 yr.

RESULTS

After multivariable adjustment for established cardiovascular risk factors including C-reactive protein, individuals in the highest compared with the lowest quartile of plasma resistin levels had a significantly increased risk of MI (relative risk 2.09; 95% confidence interval 1.01-4.31; P for trend = 0.01). In contrast, plasma resistin levels were not significantly associated with risk of IS (relative risk 0.94; 95% confidence interval 0.51-1.73; P for trend = 0.88).

CONCLUSION

Our data suggest that high plasma resistin levels are associated with an increased risk of MI but not with risk of IS. Further studies are needed to evaluate the predictive value of plasma resistin levels for cardiovascular disease.

Octylphenol stimulates resistin gene expression in 3T3-L1 adipocytes via the estrogen receptor and extracellular signal-regulated kinase pathways

Resistin is known as an adipocyte-specific secretory hormone that can cause insulin resistance and decrease adipocyte differentiation. It can be regulated by sexual hormones. Whether environmental estrogens regulate the production of resistin is still not clear. Using 3T3-L1 adipocytes, we found that octylphenol upregulated resistin mRNA expression in dose- and time-dependent manners. The concentration of octylphenol that increased resistin mRNA levels by 50% was ∼100 nM within 6 h of treatment. The basal half-life of resistin mRNA induced by actinomycin D was lengthened by octylphenol treatment, suggesting that octylphenol decreases the rate of resistin mRNA degradation. In addition, octylphenol stimulated resistin protein expression and release. The basal half-life of resistin protein induced by cycloheximide was lengthened by octylphenol treatment, suggesting that octylphenol decreases the rate of resistin protein degradation. While octylphenol was shown to increase activities of the estrogen receptor (ER) and MEK1, signaling was demonstrated to be blocked by pretreatment with either ICI-182780 (an ERα antagonist) or U-0126 (a MEK1 inhibitor), in which both inhibitors prevented octylphenol-stimulated phosphorylation of ERK. These results imply that ERα and ERK are necessary for the octylphenol stimulation of resistin mRNA expression. Moreover, U-0126 antagonized the octylphenol-increased resistin protein expression and release. These data suggest that the way octylphenol signaling increases resistin protein levels is similar to that by which it increases resistin mRNA levels; it is likely mediated through an ERK-dependent pathway. In vivo, octylphenol increased adipose resistin mRNA expression and serum resistin and glucose levels, supporting its in vitro effect.

Pitavastatin improves serum resistin levels in patients with hypercholesterolemia

AIM

Resistin in serum is associated with high risk in patients with atherosclerosis. This clinical study aimed to investigate whether pitavastatin can regulate the serum level of resistin, together with levels of other inflammatory cytokines and adipocytokines.

METHODS

Forty two outpatients (mean age 65.2 +/- 12.6 yr, M/F: 21/21) with hypercholesterolemia were administered 2 mg of pitavastatin and serum levels of resistin, together with serum levels of adiponectin, leptin, TNF-alpha and hsCRP, were measured before, and 12 weeks after enrollment.

RESULTS

There was no significant gender-related difference in initial serum resistin levels. Pitavastatin significantly decreased LDL-cholesterol after 12 weeks. Initial levels of resistin showed a significant correlation with those of hsCRP (r=0.38, p=0.013), but not TNF-alpha or HOMA-R. Serum resistin, but not adiponectin and leptin, levels were significantly decreased, dropping from 17.1 +/- 9.9 ng/ dL to 15.2+/-10.0 (p=0.001) after 12 weeks of administration. The patient group with a baseline hsCRP > or = 0.1 at enrollment (n=17) had decreased levels of both resistin and hsCRP (p=0.011 and p=0.022, respectively).

CONCLUSION

This study showed the pleiotropic effect of pitavastatin on the serum resistin concentration, suggesting that it may assist in the prevention of atherosclerosis.

Effect of resistin on vascular endothelium secretion dysfunction in rats

Resistin, a novel adipokine, was recently suggested to be involved in the development of endothelial dysfunction. However, the mechanisms of how resistin works are still unknown. This study was performed to investigate the relationship between resistin and phosphatidylinositol 3-kinase (PI3K), with the aim of gaining insight to the mechanisms by which resistin induces changes of secretion function of vascular endothelium. This study was conducted on 60 male 4-week-old Sprague-Dawley rats, which were randomly divided into four groups: resistin group (RS; n = 8), normal saline group (NS; n = 8), high-fat diet group (HF; n = 36), and control group (CO; n = 8). The resistin group was administered two injections of rat recombinant resistin. The diet-induced hyperresistinemia rats were selected from the HF group after the HF group was administered a high-fat diet for 8 weeks. The diet-induced hyperresistinemia rats were randomized into the antibody group (AB; n = 8) and hyperresistinemia group (HR; n = 8). The antibody group was given injections of resistin antibody twice per day and for 3 days. Immunohistochemistry was employed to examine the expression of PI3K p85alpha subunit and endothelial nitric oxide synthase (eNOS) in thoracic artery endothelium. In the resistin group, the levels of endothelin (ET), plasminogen activator inhibitor (PAI), and von Willebrand factor (vWF) were higher and NO was lower than those in the normal saline group. The NO level increased and ET, PAI, and vWF levels decreased in the antibody group when compared with the hyperresistinemia group. After administration of resistin antibody, the expression of PI3Kp85alpha and eNOS proteins in the antibody group was significantly increased but still differed significantly from those in the control group. PI3K grey value was correlated with resistin, PAI-1, vWF, NO, and the expression of eNOS (p < .05), after controlling for the effect of insulin. Resistin can affect the protein expression of PI3Kp85alpha, stimulate release of PAI-1, vWF, and ET, and down-regulate eNOS. The effect of resistin on PI3K signaling pathway might contribute to the development of endothelial secretion dysfunction in young rats.

Long-term GH treatment is not associated with disadvantageous changes of inflammatory markers and adipocytokines in children born small for gestational age

CONTEXT

Low birth weight is associated with increased risks for adult cardiovascular disease (CVD) and diabetes mellitus type 2 (DM2). Adiponectin and resistin are hormones, considered, respectively, protective and disadvantageous regarding these risks. No data exist on the effect of long-term GH treatment on these hormones and inflammatory markers in children born small for gestational age (SGA).

OBJECTIVE

To describe longitudinal changes in inflammatory markers and adipocytokines during and after a long-term dose-response GH study.

DESIGN

Longitudinal dose-response study [group A: 1 mg/m(2) body surface area (BSA) (approximately 0.033 mg/kg/day) vs. group B: 2 mg/m(2) BSA (approximately 0.067 mg/kg/day)] and comparison with age-related controls.

PATIENTS

One hundred and three SGA children.

MEASUREMENTS

We measured adiponectin, resistin, interleukin-6 (IL-6) and C-reactive protein (CRP) levels at baseline, after 1 and 7 years of GH treatment and 6 months after discontinuation of GH.

RESULTS

Adiponectin levels decreased over time, but remained comparable with controls. Resistin levels increased and remained lower or comparable with controls. There were no significant differences between the GH dosage groups. After the GH treatment was stopped, adiponectin was decreased in group B and resistin increased in group A. GH therapy did not affect IL-6 and CRP levels at any time point. An increase in body mass index (BMI) standard deviation score (SDS) over time was associated with a decrease in adiponectin levels. None of the markers were associated with insulin sensitivity.

CONCLUSIONS

Long-term GH treatment is not associated with disadvantageous changes in adiponectin, resistin, IL-6 and CRP levels, neither during nor after GH treatment.

Hyperresistinemia is associated with coexistence of hypertension and type 2 diabetes

Numerous studies have demonstrated that high blood pressure substantially increases the risk of microvascular and macrovascular complications in patients with type 2 diabetes mellitus (T2DM). Currently, we found that serum resistin, an adipocyte- and monocyte-derived cytokine, was positively correlated with several components of the metabolic syndrome, including hypertension in T2DM. To investigate the association of resistin with an etiologic difference among subjects with hypertension with T2DM, hypertension without T2DM, and normotensive T2DM, we analyzed 210 subjects, including 91 with hypertension with T2DM, 55 with hypertension without T2DM, and 64 with normotensive T2DM. Serum resistin level was higher in subjects with hypertension with T2DM, followed by subjects with normotensive T2DM and hypertension without T2DM, irrespective of antihypertensive treatment status (20.9+/-17.6 and 14.0+/-8.9 versus 11.2+/-7.6 ng/mL, respectively; P<0.01). Simple regression analysis revealed that resistin positively correlated with blood pressure (systolic blood pressure: r=0.29, P<0.01; diastolic blood pressure: r=0.21, P<0.05) and intima-media thickness (r=0.27; P<0.05) in patients with T2DM but not in subjects with hypertension without T2DM. Multiple regression analysis, adjusted for age, gender, body mass index, fasting glucose, high-density lipoprotein cholesterol, white blood cell counts, and glomerular filtration rate, further revealed that resistin was an independent factor for high blood pressure in patients with T2DM (P<0.05). In vitro gene expression analysis in human coronary endothelial cells revealed that resistin induced fatty acid binding protein, a key molecule of insulin resistance, diabetes, and atherosclerosis. These results suggest that hyperresistinemia would contribute to the pathogenesis of hypertension in patients with T2DM, significantly linked to vascular complications and cardiovascular events.

Association of adiponectin and resistin with cardiovascular events in Korean patients with type 2 diabetes: The Korean atherosclerosis study (KAS)

Adiponectin and resistin are proteins that affect insulin resistance and atherosclerosis significantly. We investigated adiponectin and resistin concentrations as predictors of cardiovascular events in Korean patients with type 2 diabetes. The study in 2001 comprised 343 unrelated patients with type 2 diabetes (65+/-9.2 years old). They were followed up for 42 months. The baseline duration of diabetes, smoking status and history of cardiovascular diseases (CVD) were recorded. BMI, blood pressures, HbA1c, lipid profiles, ECG, creatinine and urine microalbumin were measured. Adiponectin and resistin were measured using enzyme-linked immunosorbent assays. The primary endpoint was defined as one of cardiovascular death, myocardial infarct, CABG, stroke, unstable angina or overt nephropathy. Thirty-eight patients (11.1%) experienced primary endpoint during the follow-up. After adjustment for age, sex, BMI, blood pressure and lipid status, participants in the lowest quartile of adiponectin levels compared with the highest had significantly increased risk of primary endpoint (relative risk=3.03; 95% CI 1.09-8.41; p=0.034). In contrast, resistin level had no influence on the risk of primary endpoint. A low level of adiponectin, not resistin, was a significant risk factor for the development of cardiovascular events in these Korean patients with type 2 diabetes.

Effect of hyperhomocysteinemia on cardiovascular risk factors and initiation of atherosclerosis in Wistar rats

Hyperhomocysteinemia is considered an independent risk factor for atherosclerosis. The present study was designed to assess the effect of high level of serum homocysteine on other cardiovascular risk factors and markers in rats and to study its mode of action in initiating atherosclerosis. To address this issue, four different doses of methionine (0.1 g/kg, 0.25 g/kg, 0.5 g/kg, 1 g/kg) were orally administered to four groups (Group II, III, IV, V respectively) of rats (6 rats in each group) for a period of 8 weeks to get different level of homocysteine in serum. Group I was administered with saline and served as control. Our results revealed that the level of Total cholesterol, Triglyceride, and Oxidized low-density lipoproteins increased significantly with the increase in the level of serum homocysteine. The levels of Resistin, C-reactive protein and cysteinyl-leukotrienes were found to be significantly high in Group IV (P<0.001 vs Group I) and Group V (P<0.001 vs Group I) at 8 weeks. Total antioxidant capacity and nitrite/nitrate level in serum showed negative correlation with the increased dose of methionine. The mRNA expression and the enzyme activity of 3-hydroxy-3-methylglutaryl coenzyme A (HMG-CoA) reductase significantly increased only in livers of rats of Group V. Furthermore, high mRNA expression of P2 receptors and caveolin were found in aorta of rats administered with high dose of methionine (Group IV and V at 8 weeks). Data obtained from in-vitro effect of homocysteine on isolated aortic arch also showed induction in P2 receptors and caveolin with the increase in the concentration of homocysteine. These findings collectively suggest that hyperhomocysteinemia initiates atherosclerosis by modulating the cholesterol biosynthesis and by significantly inducing the level of other cardiovascular risk factors and markers, which play important role in initiating atherosclerosis.

Obesity, adipokines, and abdominal aortic aneurysm: Health in Men study

BACKGROUND

Obesity is associated with occlusive artery disease but is not considered a risk factor for abdominal aortic aneurysm (AAA). We investigated the association between anthropometric measures of obesity, serum adipokines, and AAA.

METHODS AND RESULTS

As part of a population study, we screened 12,203 men 65 to 83 years of age for AAA using ultrasound; 875 had an AAA (> or = 30 mm). Cardiovascular risk factors and waist and hip circumference were recorded. Serum adipokines were measured in 952 men, 318 of whom had an AAA. Waist circumference (odds ratio [OR], 1.14; 95% confidence interval [CI], 1.06 to 1.22) and waist-to-hip ratio (OR, 1.22; 95% CI, 1.09 to 1.37) were independently associated with AAA after adjustment for other known risk factors. The association was stronger for AAA > or = 40 mm (waist-to-hip ratio: OR, 1.53; 95% CI, 1.26 to 1.85). Serum resistin concentration was strongly independently associated with AAA (OR, 1.53; 95% CI, 1.32 to 1.76) and aortic diameter (beta=0.19, P<0.0001). Serum adiponectin was associated with AAA > or = 30 mm (OR, 1.26; 95% CI, 1.07 to 1.50) but not AAA > or = 40 mm (OR, 1.03; 95% CI, 0.77 to 1.39). Serum leptin was not associated with AAA.

CONCLUSIONS

Measures of obesity are independently associated with AAA. Serum resistin concentrations were more strongly associated with aortic diameter than adipokines that are more intimately associated with adiposity. Further studies are required to investigate the mechanisms linking resistin and AAA.

Resistin induces lipolysis and re-esterification of triacylglycerol stores, and increases cholesteryl ester deposition, in human macrophages

Human resistin, found within atheroma, exerts inflammatory, angiogenic and proliferative effects in vascular cells and may predict coronary events. Here, we investigate mechanisms by which resistin contributes to macrophage 'foam cell' formation. Increases in macrophage (THP-1) cholesteryl ester mass, in the presence or absence of oxidized LDL, were not explained by altered cholesterol efflux. Instead, resistin enhanced fractional turnover of the endogenous triacylglycerol pool, increased uptake and decreased oxidation of exogenous fatty acids, and decreased phosphorylation of acetyl CoA carboxylase, all factors increasing the availability of fatty acyl CoA substrate for acyl CoA: cholesterol acyltransferase-1, thereby enhancing macrophage cholesteryl ester deposition.

Association of plasma resistin with glomerular filtration rate and albuminuria in hypertensive adults

Resistin, a recently discovered proinflammatory cytokine, has been variably associated with insulin resistance, inflammation, and renal dysfunction. We investigated the association of plasma resistin with estimated glomerular filtration rate and albuminuria in 1575 hypertensive adults without known coronary heart disease or stroke (857 blacks and 718 non-Hispanic whites). Resistin was measured by a solid phase sandwich immunoassay, estimated glomerular filtration rate was estimated from serum creatinine, and albuminuria was expressed as urine albumin:creatinine ratio. After adjustment for coronary heart disease risk factors (age, sex, body mass index, smoking history, systolic blood pressure, diabetes, and total and high-density lipoprotein cholesterol) and use of renin-angiotensin blockers and statins, higher plasma resistin levels were associated with lower estimated glomerular filtration rate in both ethnic groups (each P<0.0001); the association remained significant after further adjustment for a marker of insulin resistance (homeostasis model assessment for insulin resistance) and a marker of inflammation (plasma C-reactive protein) and was seen in subjects with and without diabetes (each P<0.0001) in both ethnic groups. Higher plasma resistin levels were associated with a higher urine albumin:creatinine ratio in black subjects with diabetes (P<0.0001) and non-Hispanic white subjects with diabetes (P=0.032), independent of coronary heart disease risk factors, hypertension medication use, and statin use; the association remained significant after additional adjustment for homeostasis model assessment for insulin resistance and C-reactive protein. In adults with hypertension, higher circulating resistin levels were associated with a lower estimated glomerular filtration rate and with increased urine albumin:creatinine ratio in the presence of concomitant diabetes. This association was independent of coronary heart disease risk factors and markers of insulin resistance and inflammation.

Resistin, an adipocytokine, offers protection against acute myocardial infarction

Resistin, an adipocyte-derived hormone, is thought to represent a link between obesity and insulin-resistant diabetes. The potential role of resistin as a cardioprotective agent has not been explored. Our hypothesis is that resistin has a cardioprotective effect that is mediated by the resistin receptor-coupled activation of PI3K/Akt/PKC/K(ATP) dependent pathways. Our studies demonstrated that pretreatment of mouse hearts with 10 nM resistin for 5 min protected the heart against I/R injury in a mouse heart perfusion model. When mouse hearts were subjected to 60 min of LAD ligation followed by 4 h of reperfusion, resistin pretreatment (33 microg/kg) for 30 min or 24 h before ligation was able to significantly reduce the infarct size/risk area. The protective effect of resistin was abolished by wortmannin, as well as by an Akt inhibitor, triciribine. Resistin's protective effect was absent in Akt kinase-deficient mutant mice. The protective effect was also blocked by chelerythrine, a PKC inhibitor, and epsilonV1-2, a PKCepsilon inhibitor. Finally, the protective effect was blocked by 5-hydroxydecanoate, which blocks the opening of mitoK(ATP) channels. Resistin-induced Akt phosphorylation in HL-1 cells was inhibited by wortmannin and triciribine. Resistin also induced PKCepsilon phosphorylation, which was blocked by triciribine. These studies demonstrate that resistin's cardioprotective effect is mediated by PI3K/Akt/PKC dependent pathways. In addition to cardiomyocytes, resistin also induced Akt phosphorylation in endothelial cells and smooth muscle cells, suggesting that resistin receptors are present in these cells. The effect of resistin on apoptosis was assessed in hearts subjected to 30 min of ischemia and 3 h of reperfusion. There were significantly fewer in situ oligo ligation-positive myocyte nuclei in mice treated with resistin. Our results show that resistin can dramatically reduce apoptosis and infarct size, thus protecting the heart against I/R injury.

Efficacy of antioxidant treatment in reducing resistin serum levels: a randomized study

Objectives:

Few in vitro studies have examined the participation of resistin, a recently discovered adipokine, in oxidative processes. We investigated whether in vivo treatment with the antioxidant vitamin C might affect resistin serum levels.

Design:

Randomized prospective open trial.

Setting:

San Giovanni Battista Hospital, Turin, Italy.

Participants:

Eighty healthy individuals.

Intervention:

Administration of 2 g of ascorbic acid orally for 2 wk (n = 40; experimental group) or no supplementation (n = 40; control group).

Outcome measures:

The primary end point was the between-group difference in the before–after change in resistin serum level after vitamin C supplementation. Secondary endpoints were the within- and between-group changes in glucose, insulin, lipid parameters, C-reactive protein fasting values, and markers of oxidative stress.

Results:

In the experimental group, vitamin C supplementation was significantly associated with both resistin concentration reduction (from 4.3 ± 1.5 to 2.9 ± 0.8 ng/ml; 95% confidence interval [CI] −1.87, −1.03) and ascorbic acid level increase (from 9.4 ± 2.9 to 19.0 ± 5.2 mg/l; 95% CI 7.9, 11.2). In the control group, resistin levels did not change significantly (from 4.2 ± 1.0 to 4.3 ± 0.9 ng/ml; 95% CI −0.07, 0.37). The between-group differences were highly significant (p < 0.001). Vitamin C supplementation was also associated with a statistically significant reduction in nitrotyrosine level and incremental increase in reduced glutathione. In a linear regression model, within-individual changes in vitamin C concentrations were inversely correlated with changes in resistin levels in both groups (each unit increase of vitamin C corresponded to a decrease of about 0.10 units of resistin levels (95% CI 0.13, 0.08; p < 0.001).

Conclusion:

This is to our knowledge the first randomized trial in humans that has demonstrated that short-term vitamin C supplementation could significantly reduce resistin levels, independent of changes in inflammatory or metabolic variables. Future investigations of resistin participation in oxidative processes are warranted.

Background: Resistin is a hormone that is produced by fat cells. Much of the work on resistin has been done in mice, and as a result of this research the hormone was thought to explain the link between obesity and development of diabetes. In obese mice, higher levels of resistin are seen, and this hormone seems to interfere with the normal role of insulin in reducing blood sugar levels. However, the exact biochemical pathways in mice and humans seem to be very different, and it is not obvious whether resistin plays the same role in the development of diabetes in humans as it does in mice. At the same time, some researchers have suggested links between resistin and oxidative stress, which is thought to be involved in the development of certain diseases, particularly cardiovascular disease. The researchers here wanted to more fully explore these links by finding out whether an antioxidant, vitamin C, affected levels of resistin in blood. The researchers carried out a trial in healthy human participants, who were randomized to receive 2 g of vitamin C daily for two weeks, or no treatment. The primary outcome of the trial was the change in resistin levels in blood, and the researchers also looked at the levels of other biochemical variables in blood, such as fasting glucose, insulin, cholesterol, fatty acids, and nitrotyrosine.

What the trial shows: The researchers recruited 80 participants into the trial, and 40 were randomized to receive 2 g of vitamin C supplementation for two weeks. Forty individuals acted as “controls” and received no intervention over the two weeks of the trial. Outcomes were assessed for all but two individuals in the control group. Overall, levels of resistin in blood fell substantially over the course of the trial among the individuals in the vitamin C supplementation group, but not in the control arm of the trial, and this difference between groups was statistically significant. The levels of many other biochemical markers in blood, such as glucose, cholesterol, fatty acids, and insulin, did not show statistically significant changes between the randomized groups. However, levels of two markers of oxidative stress did change: levels of nitrotyrosine, which is associated with cell damage and inflammation, seemed to drop in the vitamin C group relative to the control group, and levels of reduced glutathione (an antioxidant) seemed to increase in the vitamin C group relative to the control group.

Strengths and limitations: In this trial, all individuals were randomized at once to the two study groups. While this is unconventional (normally, participants are randomized one by one, as they are screened and deemed eligible for a study), the process would be likely to prevent bias in allocation of individuals to the study groups. Although participants were not blinded to which study group they were assigned to, the laboratory staff measuring biochemical marker levels in blood were blinded to the study groups. A key limitation of this study is that the participants in the control arm did not receive placebo tablets, but rather received no treatment. A placebo control group would have enabled the researchers to blind participants as to whether they received vitamin C or no active intervention. Participants' knowledge of their group assignment (e.g., to receive vitamin C or no intervention) may have affected their response in the trial. Finally, the trial was conducted on a small group of healthy individuals, and no clinical outcomes were examined. Therefore, although the findings are intriguing, their clinical meaning is not clear.

Contribution to the evidence: There are few other studies that have been carried out in humans examining the possibility of a link between resistin levels and oxidative stress. This study suggests that vitamin C administration reduces blood levels of resistin in humans. This finding does not yet clearly point to a specific role for resistin in disease processes or human disease, but raises questions for further study.

Association between serum resistin and carotid intima media thickness in hypertension patients

BACKGROUND

Resistin is an adipocytokine belonging to the family of cysteine rich secretory proteins. We sought to determine if a correlation between resistin levels and carotid atherosclerosis exists in hypertensive patients.

METHODS

This study consisted of 307 treated hypertensive patients. Subjects were grouped into tertiles according to their resistin level.

RESULTS

Carotid intima media thickness (IMT) was significantly highest in the third tertile. The first tertile had a mean carotid IMT and a mean of maximum carotid IMT of 0.63+/-0.08 and 0.81+/-0.10 mm, respectively. The 2nd tertile had measurements of 0.63+/-0.08 and 0.81+/-0.12 mm, and the 3rd tertile 0.67+/-0.12 and 0.86+/-0.11 for the same parameters. (p=0.002). Resistin levels were independently associated with the carotid IMT (mean carotid IMT: R(2)=0.159, p<0.001 and mean of maximum carotid IMT: R(2)=0.162, p<0.001) after controlling for age, gender, HDL cholesterol, triglyceride, LDL cholesterol, smoking and DM. The tertile level of resistin was significantly associated with (odds ratio=3.097, p=0.004) risk of coronary artery disease after controlling for age, gender, HDL cholesterol, triglyceride, LDL cholesterol, smoking, DM and carotid IMT.

CONCLUSION

Serum resistin is independently associated with increasing carotid IMT in treated hypertensive patients.

Implications of resistin plasma levels in subjects undergoing coronary angiography

BACKGROUND

The adipokine resistin, which is thought to serve as a link between obesity and insulin resistance, was recently shown to exert proatherosclerotic features.

OBJECTIVE

Our study aimed to explore the involvement of resistin in cardiovascular disease by investigating the associations of resistin with angiographic coronary artery disease (CAD), cardiovascular risk factors and mortality.

DESIGN

The Ludwigshafen Risk and Cardiovascular Health (LURIC) study is a prospective study of white subjects who had undergone coronary angiography.

PATIENTS AND MEASUREMENTS

Resistin levels were determined in 1162 subjects with (n = 911) and without (n = 251) angiographic CAD. During a mean follow-up period of 5.47 years, 198 deaths occurred among our probands.

RESULTS

Resistin was positively correlated with C-reactive protein (CRP; r = 0.245, P < 0.001), vascular adhesion molecule-1 (VCAM-1; r = 0.327, P < 0.001) and intercellular adhesion molecule-1 (ICAM-1; r = 0.197, P < 0.001) and was negatively correlated with glomerular filtration rate (GFR; r = -0.438, P < 0.001) and high density lipoprotein (HDL; r = -0.196, P < 0.001). Multiple regression analysis revealed that GFR was the strongest predictive variable for resistin. Angiographic CAD, type 2 diabetes, smoking, hypertension and body mass index (BMI) were not associated with resistin. Compared to the first quartile, we observed an increased risk for cardiovascular and noncardiovascular mortality at the fourth quartile of resistin, but only the association between resistin and noncardiovascular mortality remained significant after multivariable adjustments [hazard ratio (HR) 4.92, 95% confidence interval (CI) 1.66-14.6, P = 0.004].

CONCLUSIONS

Resistin plasma concentrations are related to inflammatory processes and renal function but our study does not support the hypothesis of resistin as an independent cardiovascular risk factor. The unexpected association of resistin with noncardiovascular mortality still warrants further study.

Adipose tissue and atherosclerosis: exploring the connection

The prevalence of obesity, especially among the young, is dramatically increasing in the United States. Obesity is associated with accelerated atherosclerosis and increased rates of cardiovascular death. There are many plausible mechanisms by which an increase in adipose tissue could adversely affect the vessel wall. These include the changes in blood pressure, glucose level, lipid/lipoprotein metabolism, and systemic inflammation. In addition, factors secreted by adipose tissue may directly influence vessel wall homeostasis by influencing the function of endothelial cells, arterial smooth muscle cells, and macrophages in the vessel wall. There is general agreement that central, as opposed to peripheral, adipose tissue confers the most cardio-metabolic risk. Although the basis of this differential risk has not been not established, the pattern of gene expression and secretory products in visceral fat would be predicted to be more atherogenic compared with that in subcutaneous peripheral fat. Numerous studies have shown the beneficial effects of weight loss on markers of cardiovascular risk but fewer have demonstrated improvement in direct measures of large vessel disease. The unfolding role of adipose tissue as an important metabolic and secretory organ provides new opportunities for developing more effective approaches for preventing obesity and its atherosclerotic complications.

Changes in fat mass correlate with changes in soluble sCD163, a marker of mature macrophages, in patients with CKD

BACKGROUND

Recently, adipose tissue was shown to contain macrophages capable of contributing to systemic inflammation and cardiovascular disease (CVD). Here, we investigate this putative relationship in patients with chronic kidney disease (CKD) by using the novel macrophage marker soluble (s)CD163.

METHODS

One hundred twenty patients with CKD stage 5 (mean glomerular filtration rate [GFR], 7 +/- 1 mL/min [0.12 +/- 0.02 mL/s; mean age, 53 +/- 1 years; 65% men), 38 patients with CKD stages 3 to 4 (mean GFR, 33 +/- 3 mL/min [0.55 +/- 0.05 mL/s]; mean age, 67 +/- 2 years; 68% men), and 28 healthy controls (mean GFR, 89 +/- 3 mL/min [1.48 +/- 0.05 mL/s]; mean age, 63 +/-2 years; 69% men) were characterized post hoc with a follow-up of up to 5 years (mean, 47 +/- 1 months). sCD163 levels, body composition (dual-energy x-ray absorptiometry), clinical parameters, and levels of circulating inflammatory markers (enzyme-linked immunosorbent assay) were assessed at baseline and, in a subset population, after 1 year of dialysis therapy (hemodialysis, n = 19; peritoneal dialysis, n = 30).

RESULTS

sCD163 level increased in patients with both severe (median, 4.3 mg/L; range, 1.3 to 23.4 mg/L) and moderate (median, 3.6 mg/L; range, 1.6 to 9.8 mg/L) CKD compared with controls (median, 2.6 mg/L; range, 0.8 to 7.6 mg/L; P < 0.001). Furthermore, sCD163 levels correlated with both truncal (rho = 0.17; P < 0.05) and total (rho = 0.17; P < 0.05) fat mass, as well as with all measured markers of inflammation and endothelial adhesion molecules. After 1 year, patients who increased body fat mass (average, 11% +/- 5% versus -5% +/- 5%; P < 0.05) also showed a significant increase in sCD163 levels (median, 2.2 versus -0.97 mg/L; P < 0.01). Finally, patients with sCD163 levels greater than 4.0 mg/L had a statistically significantly worse outcome than patients with sCD163 levels less than this value, even after adjustment for age, sex, and diabetes mellitus (chi-square = 19.98; P < 0.001). However, this effect was lost after adjustment for either inflammation or CVD.

CONCLUSION

We show that increasing fat mass is associated with increasing levels of sCD163, a circulating marker of macrophages also associated with inflammatory biomarkers. We thus hypothesize that adipose tissue macrophages may have a role in the proinflammatory state observed in patients with renal disease. Finally, we propose the term "uremic-metabolic syndrome" to describe this state of increased adipose tissue signaling in patients with uremia, a phenomenon that may share some characteristics with the metabolic syndrome of obesity.

Adipokine gene expression in brain and pituitary gland

The brain has been recognized as a prominent site of peptide biosynthesis for more than 30 years, and many neuropeptides are now known to be common to gut and brain. With these precedents in mind it is remarkable that adipose-derived peptides like leptin have attracted minimal attention as brain-derived putative neuromodulators of energy balance. This review outlines the evidence that several adipose-specific genes are also expressed in the central nervous system and pituitary gland. We, and others, confirmed that the genes for leptin, resistin, adiponectin, FIAF (fasting-induced adipose factor) and adiponutrin are expressed and regulated in these tissues. For example, leptin mRNA was readily detectable in human, rat, sheep and pig brain, but not in the mouse. Leptin expression in rat brain and pituitary was regulated through development, by food restriction, and following traumatic brain injury. In contrast, hypothalamic resistin mRNA was unaffected by age or by fasting, but was significantly depleted by food restriction in mouse pituitary gland. Similar results were seen in the ob/ob mouse, and we noted a marked reduction in resistin-positive hypothalamic nerve fibres. Resistin and fiaf mRNA were also upregulated in hypoxic/ischaemic mouse brain. Our studies on the regulation of neuronal adipokines were greatly aided by the availability of clonal hypothalamic neuronal cell lines. One of these, N-1, expresses both rstn and fiaf together with several other neuropeptides and receptors involved in energy homeostasis. Selective silencing of rstn revealed an autocrine/paracrine regulatory system, mediated through socs-3 expression that may influence the feedback effects of insulin and leptin in vivo. A similar convergence of signals in the pituitary gland could also influence anterior pituitary hormone secretion. In conclusion, the evidence is suggestive that brain and pituitary-derived adipokines represent a local regulatory circuit that may fine tune the feedback effects of adipose hormones in the control of energy balance.

Human resistin is a systemic immune-derived proinflammatory cytokine targeting both leukocytes and adipocytes

The characteristics of human resistin (RETN) are unclear and controversial despite intensive adipose-focused research. Its transcriptional and functional similarity with the murine myeloid-specific and CCAAT/enhancer binding protein epsilon (Cebpe)-dependent gene, resistin-like gamma (Retnlg), is unexplored. We examined the human CEBPE-regulatory pathway by unbiased reference and custom gene expression assays. Real-time RT-PCR analysis demonstrated lack of both the transcriptional factor CEBPE and RETN expression in adipose and muscle cells. In contrast, primary myelocytic samples revealed a concerted CEBPE-RETN transcription that was significantly elevated in inflammatory synoviocytes relative to intact peripheral blood mononuclear cells (PBMC). Mouse Cebpe and Retnlg were predictably expressed in macrophages, whereas Retn was abundant in adipocytes. Quite the opposite, a low and inconsistent RETN transcription was seen in some human white adipose tissue (WAT) biopsies without any relationship to body mass index, insulin sensitivity, or fat depot. However, in these cases, RETN was co-detected with CEBPE and the leukocyte-specific marker, EMR1, indicating the presence of inflammatory cells and their possible resistin-mediated effect on adipocytes. Indeed, addition of human resistin to WAT in culture induced, like in PBMC, the inflammatory cytokines IL6, IL8 and TNF. Importantly, the expression of the adipose-specific markers CEBPA, FABP4 and SLC2A4 was unchanged, while the expected inhibitory effect was seen with TNF. Both cytokines increased the mRNA level of CCL2 and MMP3, which may further promote inflammation in WAT. Thus, the myeloid-restricted nature of CEBPE precludes the expression of RETN in human adipocytes which, however, are targeted by this innate immune-derived proinflammatory cytokine.

Prognostic significance of plasma resistin levels in patients with atherothrombotic ischemic stroke

BACKGROUND

Resistin (RSN) is an adipocytokine involved in insulin resistance, obesity and atherosclerosis. This study aimed to investigate the association between plasma RSN and outcome after ischemic stroke.

METHODS

RSN measured within 24 h after the event was related to functional outcome and 5-year survival in 211 subjects with first-ever atherothrombotic ischemic stroke. Prognosis was assessed by the Kaplan Meier and the Cox techniques.

RESULTS

The probabilities of death were 80.4%, 46.2% and 15.7% (p<0.001) for patients stratified according to tertiles of RSN (>30 ng/mL, 20-30 ng/mL and<20 ng/mL, respectively). The proportion of dependency (modified Rankin Scale score>or=3) was greater in 5-year survivors with RSN in the upper tertile (6/11 [54.5%]) compared to the middle (20/56 [35.7%]) and the lowest tertile (8/43 [18.6%]; p<0.01). C-reactive protein levels (hazard ratio [HR] 3.96 [95% CI 2.06, 8.91]; p<0.001), coronary heart disease (2.69 [1.62, 6.23]; p<0.001), RSN levels (2.12 [1.31, 5.08] p<0.001), National Institute of Health Stroke Scale score (2.02 [1.23, 4.49]; p<0.01) and age (1.84 [1.19, 3.93]; p<0.01) were independent predictors of death.

CONCLUSIONS

High plasma RSN appears to be associated with increased risk of 5-year mortality or disability after atherothrombotic ischemic stroke, independently of other adverse predictors.

Resistin in rheumatoid arthritis synovial tissue, synovial fluid and serum

BACKGROUND

Resistin is a newly identified adipocytokine which has demonstrated links between obesity and insulin resistance in rodents. In humans, proinflammatory properties of resistin are superior to its insulin resistance-inducing effects.

OBJECTIVES

To assess resistin expression in synovial tissues, serum and synovial fluid from patients with rheumatoid arthritis, osteoarthritis and spondylarthropathies (SpA), and to study its relationship with inflammatory status and rheumatoid arthritis disease activity.

METHODS

Resistin expression and localisation in synovial tissue was determined by immunohistochemistry and confocal microscopy. Serum and synovial fluid resistin, leptin, interleukin (IL)1beta, IL6, IL8, tumour necrosis factor alpha, and monocyte chemoattractant protein-1 levels were measured. The clinical activity of patients with rheumatoid arthritis was assessed according to the 28 joint count Disease Activity Score (DAS28).

RESULTS

Resistin was detected in the synovium in both rheumatoid arthritis and osteoarthritis. Staining in the sublining layer was more intensive in patients with rheumatoid arthritis compared with those with osteoarthritis. In rheumatoid arthritis, macrophages (CD68), B lymphocytes (CD20) and plasma cells (CD138) but not T lymphocytes (CD3) showed colocalisation with resistin. Synovial fluid resistin was higher in patients with rheumatoid arthritis than in those with SpA or osteoarthritis (both p<0.001). In patients with rheumatoid arthritis and SpA, serum resistin levels were higher than those with osteoarthritis (p<0.01). Increased serum resistin in patients with rheumatoid arthritis correlated with both CRP (r=0.53, p<0.02), and DAS28 (r=0.44, p<0.05), but not with selected (adipo) cytokines.

CONCLUSION

The upregulated resistin at local sites of inflammation and the link between serum resistin, inflammation and disease activity suggest a role for resistin in the pathogenesis of rheumatoid arthritis.

Resistin worsens cardiac ischaemia-reperfusion injury

We provide the first report of direct effects of resistin upon haemodynamic and neurohumoral parameters in isolated perfused rat heart preparations. Pre-conditioning with 1 nmol L-1 recombinant human resistin prior to ischaemia significantly impaired contractile recovery during reperfusion, compared with vehicle-infused hearts (P<0.05, n=12). This was accompanied by a significant increase in both A-type and B-type natriuretic peptides (P<0.05, n=12 both ANP and BNP vs vehicle), creatine kinase, and tumour necrosis factor-alpha (TNF-alpha) release in resistin-infused hearts. Resistin had no significant effect on myocardial glucose uptake. Co-infusion of resistin with Bay 11 7082 (an NF-kappaB inhibitor) improved contractile recovery following ischaemia and reduced both natriuretic peptide and creatine kinase release. This is the first evidence indicating resistin impairs cardiac recovery following ischaemia, stimulates cardiac TNF-alpha secretion, and modulates reperfusion release of natriuretic peptides and biochemical markers of myocardial damage. A TNF-alpha signalling related mechanism is suggested as one component underlying these effects.

Adipocytokines: mediators linking adipose tissue, inflammation and immunity

There has been much effort recently to define the role of adipocytokines, which are soluble mediators derived mainly from adipocytes (fat cells), in the interaction between adipose tissue, inflammation and immunity. The adipocytokines adiponectin and leptin have emerged as the most abundant adipocyte products, thereby redefining adipose tissue as a key component not only of the endocrine system, but also of the immune system. Indeed, as we discuss here, several adipocytokines have a central role in the regulation of insulin resistance, as well as many aspects of inflammation and immunity. Other adipocytokines, such as visfatin, have only recently been identified. Understanding this rapidly growing family of mainly adipocyte-derived mediators might be of importance in the development of new therapies for obesity-associated diseases.

Increase in serum resistin during weight loss in overweight subjects is related to lipid metabolism

OBJECTIVE

Human resistin has been stated to influence preadipocyte cell numbers and to stimulate adipocyte triglyceride lipolysis in vivo and in vitro. However, its role in human obesity remains unclear.

DESIGN

Cross-sectional study for comparisons of lean and obese subjects, and subsequent longitudinal 4-month weight loss intervention study in obese subjects.

SUBJECTS

Healthy subjects, lean (n=20, BMI<25) and overweight (n=43, BMI>or=25).

MEASUREMENTS

Serum resistin, body weight, body fat, waist-to-hip ratio, as well as markers of insulin resistance and lipid metabolism at baseline and after 4 months of intervention.

RESULTS

Serum resistin was positively correlated to HOMA-IR (partial r=0.288; P=0.055), serum fructosamines (partial r=0.280; P=0.062), serum NEFA (partial r=0.276; P=0.066) and negatively to age (partial r=-0.349; P=0.019) and serum apolipoprotein A-1 (partial r=-0.363; P=0.014). During the intervention, serum resistin increased significantly (P<0.001). The increase was inversely related to changes in waist-to-hip ratio (P=0.025) and positively to serum apolipoprotein B (P=0.011). In males only, the increase in resistin during weight loss was predicted by total serum cholesterol at baseline (r=0.703, P=0.007). No relation was observed between changes in resistin and changes in HOMA-IR.

CONCLUSION

The present study indicates an association between serum resistin and markers of abdominal fat distribution as well as the regulation of lipid metabolism. However, human resistin is unlikely to play an independent role in the regulation of glucose metabolism.