GlycA, a novel marker of inflammation, is elevated in systemic lupus erythematosus.

BACKGROUND: GlycA is a novel marker of systemic inflammation detected by nuclear magnetic resonance (NMR) spectroscopy. In the general population, GlycA is correlated with inflammatory markers such as C-reactive protein (CRP) and associated with coronary heart disease and diabetes. The utility of GlycA in patients with systemic lupus erythematosus (SLE) has not been defined. Therefore, we tested the hypothesis that GlycA concentrations are elevated in patients with SLE and associated with other markers of inflammation and coronary atherosclerosis. METHODS: We compared concentrations of GlycA, detected by NMR, in 116 patients with SLE and 84 control subjects frequency-matched for age, sex, and race. SLE disease activity index (SLEDAI) and the SLE Collaborating Clinics damage index (SLICC) were calculated. Acute phase reactants, a panel of cytokines, and a lipid panel were measured. Electron beam computer tomography (EBCT) was used to quantify coronary artery calcification, a measure of coronary artery atherosclerosis. RESULTS: Patients with SLE had higher concentrations of GlycA (398 (350-445)) than control subjects (339 (299-391)) µmol/L, p < 0.001. In patients with SLE, concentrations of GlycA were significantly associated with sedimentation rate (rho = 0.43), C-reactive protein (rho = 0.59), e-selectin (rho = 0.28), intracellular adhesion molecule-1 (rho = 0.30), triglycerides (rho = 0.45), all p < 0.0023 to account for multiple comparisons, but not with creatinine, SLEDAI, SLICC, or coronary calcium scores. CONCLUSIONS: Concentrations of GlycA are higher in patients with SLE than control subjects and associated with markers of inflammation but not with SLE disease activity or chronicity scores or coronary artery calcification.

Genetic variation and coronary atherosclerosis in patients with systemic lupus erythematosus.

Coronary artery disease is the major cause of mortality in patients with systemic lupus erythematosus (SLE). Increased cardiovascular risk in SLE is not explained by traditional risk factors. We examined the hypothesis that genetic variation contributes to the presence of coronary atherosclerosis in patients with SLE. The genotypes of single-nucleotide polymorphisms (SNP) in 152 candidate genes linked with autoimmune or cardiovascular risk were determined in 125 patients with SLE. Coronary artery calcium (CAC), a measure of coronary atherosclerosis, was detected in 32 patients (26%) by electron-beam computed tomography. Polymorphism in 20 of the candidate genes (ADAM33, ADIPOQ, CCL5, CCR7, CDKN2B, CSF1, IL4, IL12A, IL23R, INS, IRF5, MIF, MS4A1, PTGS1, PTPN22, RETN, SELE, TNFSF4, TNFRSF11B, and VCAM1) were nominally associated with the presence of CAC (p-values = 0.001-0.047 after adjustment for age, sex and race). Some of these are known susceptibility genes for SLE and others have been implicated in cardiovascular disease in other populations. No association withstood false discovery rate adjustment. Replication studies in additional cohorts of patients with SLE may be informative.

Free fatty acids are associated with metabolic syndrome and insulin resistance but not inflammation in systemic lupus erythematosus.

Free fatty acids (FFAs) are implicated in the pathogenesis of insulin resistance and atherosclerosis. Inflammatory cytokines promote lipolysis and increase FFAs, a cause of endothelial dysfunction and increased atherosclerosis risk. We hypothesized that increased inflammation is associated with increased FFAs, resulting in insulin resistance and atherosclerosis in patients with systemic lupus erythematosus (SLE). We measured clinical variables, serum FFAs, homeostasis model assessment for insulin resistance (HOMA), inflammatory cytokines, markers of endothelial activation, cholesterol concentrations and coronary artery calcium in 156 patients with SLE and 90 controls. We compared FFAs in patients with SLE and controls using Wilcoxon rank sum tests and further tested for the independent association between FFAs and disease status with adjustment for age, race and sex using multivariable regression models. We assessed the relationship between FFAs and continuous variables of interest using Spearman correlation and multivariable regression analysis. Levels of FFAs were higher in patients with SLE than controls (0.55 mmol/l (0.37-0.71) vs 0.44 mmol/l (0.32-0.60), P = 0.02). Levels of FFAs remained significantly higher among patients with SLE after adjustment for age, race and sex (P = 0.03) but not after further adjustment for body mass index (P = 0.13). FFA levels did not differ according to the usage of current immunosuppressive medications in univariate and adjusted analysis (all P > 0.05). Among patients with SLE, concentrations of FFAs were higher among those with metabolic syndrome compared to those without (0.66 mmol/l (0.46-0.81) vs 0.52 mmol/l (0.35-0.66), P < 0.001). FFAs were positively correlated with insulin resistance (HOMA) (rho = 0.23, P = 0.004, P adjusted = 0.006) and triglyceride levels (rho = 0.22, P = 0.01, P adjusted = 0.004). FFAs were not associated with inflammatory cytokines (IL-6, TNF-α) (all P > 0.05) but were positively associated with levels of E-selectin (rho = 0.33, P = < 0.001, P adjusted = 0.001) and ICAM-1 (rho = 0.35, P < 0.001, P adjusted = 0.001). FFAs were correlated with coronary artery calcium score (rho = 0.20, P = 0.01) but this was attenuated after adjustment for age, race and sex (P = 0.33). From our study we concluded that FFAs are elevated in patients with SLE, particularly those with metabolic syndrome. FFAs in patients with SLE are not associated with markers of generalized inflammation but are associated with insulin resistance and markers of endothelial activation.

Cystatin C is associated with inflammation but not atherosclerosis in systemic lupus erythematosus.

BACKGROUND: Even mild renal impairment is associated with increased atherosclerosis and cardiovascular mortality. Cystatin C, a novel measure of renal function, is more sensitive than conventional creatinine-based measures for the detection of subtle renal impairment. Increased cystatin concentrations are also associated with cardiovascular risk, independently of conventional measures of renal function. This study examined the hypothesis that cystatin C is elevated in systemic lupus erythematosus (SLE) and is associated with coronary atherosclerosis. METHODS: Serum cystatin C, creatinine, tumor necrosis factor (TNF)-α, interleukin (IL)-6, coronary artery calcium score (CACS), Framingham risk score (FRS), Modified Diet in Renal Disease estimated glomerular filtration rate (MDRD-eGFR), and other clinical parameters were measured in 118 patients with SLE and 83 control subjects. The independent association between concentrations of cystatin C and SLE was evaluated using multivariable linear regression models, and the relationship between renal measures and coronary calcium was assessed with multivariable proportional odds logistic regression models. RESULTS: Cystatin C, but not other measures of renal function, was significantly higher in patients with SLE than in controls (1.09 [interquartile range, IQR: 0.85-1.28] mg/l vs. 0.89 [IQR: 0.76-0.99] mg/l; p < 0.001 after adjustment for age, race, sex and MDRD-eGFR). Cystatin C was significantly associated with SLICC (p = 0.04), erythrocyte sedimentation rate (ESR) (p = 0.02), TNF-α (p = 0.008) and IL-6 (p = 0.01) after adjustment for age, race, and sex. Cystatin C was not significantly correlated with coronary calcium score in SLE (rho=0.096, p = 0.31) and the association remained non-significant after adjustment for age, race, sex, and Framingham risk score (p = 0.99). CONCLUSIONS: Cystatin C was higher in patients with SLE than in control subjects even after adjustment for conventional measures of renal function. Cystatin C was significantly correlated with several markers of inflammation in SLE but was not associated with coronary atherosclerosis. Subtle renal dysfunction does not appear to be directly associated with accelerated atherosclerosis in SLE.

Novel cardiovascular risk prediction models in patients with systemic lupus erythematosus.

Women with systemic lupus erythematosus (SLE) have increased risk for coronary heart disease (CHD) which is underestimated by the Framingham risk score (FRS). We hypothesized that new risk scores that include inflammation or vascular age in the risk calculation would better identify women with SLE at risk for CHD, particularly in those with subclinical coronary atherosclerosis. We calculated the FRS and Reynolds risk score (RRS) in 121 women with SLE and 65 age-matched female controls; coronary age-modified risk scores (camFRS, camRRS) were calculated using coronary age derived from the coronary artery calcium (CAC) score. Risk scores were compared in SLE and controls, and in SLE patients with and without CAC. Although CAC was present in 21 SLE patients (17%) and four controls (6%) (p = 0.033); the FRS, camFRS, RRS, and camRRS, did not differ significantly among SLE and controls (p > 0.05), but were all significantly higher in SLE patients with CAC compared with those without (p < 0.001 for all). The camFRS (8%, p = 0.016) but not camRRS (5%, p = 0.221) assigned significantly more SLE patients to a category of ≥ 10% risk than conventional FRS (1%) and RRS (2%). The RRS was of limited use but coronary age may improve CHD risk prediction in SLE.

Adipocytokines in systemic lupus erythematosus: relationship to inflammation, insulin resistance and coronary atherosclerosis.

We tested the hypothesis that concentrations of adipocytokines are altered in SLE and associated with coronary atherosclerosis, insulin resistance and inflammation. Concentrations of resistin, leptin, adiponectin and visfatin were measured in 109 patients with SLE and 78 control subjects. Coronary calcification was measured using electron beam-computed tomography, and insulin resistance was defined by the homeostasis model assessment index. Concentrations of adiponectin (28.7 +/- 17.9 vs 22.0 +/- 15.3 microg/mL, P = 0.003), leptin (41.1 +/- 49.9 vs 19.8 +/- 24.6 ng/mL, P < 0.001) and visfatin (7.5 +/- 10.5 vs 4.5 +/- 2.8 ng/mL, P < 0.001) were higher in patients with SLE than in controls. These differences remained significant after adjustment for age, race, sex and body mass index (BMI; all P values < 0.02). Concentrations of resistin (10.7 +/- 7.6 vs 9.1 +/- 5.1 ng/mL, P = 0.41) did not differ in patients and controls. In patients with SLE, leptin was positively associated with BMI (rho = 0.80, P < 0.001), insulin resistance (rho = 0.46, P < 0.001) and C-reactive protein (CRP) (rho = 0.30, P = 0.002), whereas adiponectin was negatively associated with the same factors (rho = -0.40, P < 0.001; rho = -0.38, P < 0.001; rho = -0.22, P = 0.02, respectively). None of the adipocytokines were associated with coronary atherosclerosis in SLE. In conclusion, patients with SLE have increased concentrations of adiponectin, leptin and visfatin. Lower concentrations of adiponectin and higher concentrations of leptin are associated with insulin resistance, BMI and CRP in patients with SLE.

Retention of mitochondrial DNA species in somatic cell hybrids using antibiotic selection.

Interspecific cell hybrids were constructed by fusion of an antimycin-resistant, thymidine kinase- (TK-) Chinese hamster cell line with a chloramphenicol-resistant, hypoxanthine-guanine phosphoribosyl transferase- (HPRT-) mouse cell line. Hybrids were selected in HAT medium alone, or HAT supplemented with chloramphenicol, antimycin, or both antibiotics. Analysis of the mitochondrial DNA (mtDNA) of these hybrids indicates that antibiotic selection directed at the mitochondrial populations results in retention of the resistant parental genome and loss of the sensitive parental genome.

Retention of both parental mitochondrial DNA species in mouse-Chinese hamster somatic cell hybrids.

Interspecific somatic cell hybrids were isolated following the fusion of an oligomycin-resistant derivative of LM (TK-) mouse cells to a chloramphenicol-resistant derivative of AK412 Chinese hamsters cells. Hybrids were selected in either HAT medium, HAT plus chloramphenicol (CAP), HAT plus oligomycin (OLI), or HAT plus chloramphenicol and oligomycin. Cytogenetic analysis of the hybrids indicated that their karyotype reflected the sum of the parents. Hybrids selected in HAT medium alone or HAT plus OLI retained primarily mouse mitochondrial DNA while those selected in HAT plus CAP, or HAT plus CAP plus OLI retained both species of mitochondrial DNA. There was no evidence for mitochondrial DNA recombination, despite the continued growth of these hybrids in CAP plus OLI. Hybrids that were removed from dual antibiotic selection for over three months retained both species of mitochondrial DNA in approximately equal amounts with no detectable loss or rearrangement.

Medium reiteration frequency repetitive sequences in the human genome.

Fourteen novel medium reiteration frequency (MER) families were found, in the human genome, by using two different methods. Repetition frequencies per haploid human genome were estimated for each of these families as well as for six previously described MER DNA families. By these measurements, the families were found to contain variable numbers of elements, ranging from 200 to 10,000 copies per haploid human genome.

Mitochondrial protein synthesis in interspecific somatic cell hybrids.

The fusion of an oligomycin (OLI)-resistant mutant of mouse LM(TK-) cells to a chloramphenicol (CAP)-resistant mutant of AK412 Chinese hamster cells resulted in a series of interspecific somatic cell hybrids. Hybrids selected in HAT medium retained only mouse mitochondrial genomes while hybrids selected in HAT plus CAP and OLI retained both hamster and mouse mitochondrial genomes in approximately equal amounts. Nuclear-coded mitochondrial proteins from both parental species were incorporated into mitochondria in all of the hybrids. However, the mitochondrially coded proteins of three individually isolated hybrid cell lines were predominantly mouse-specific, with only trace amounts of hamster protein detected.

Identification and characterization of new human medium reiteration frequency repeats.

We report nine new families of human medium reiteration frequency interspersed repetitive elements (MER elements). They were identified by computer-assisted analyses. Six of them were independently confirmed as repetitive families by DNA-DNA hybridization, and the number of elements for each of these families was estimated by plaque hybridization assay. The involvement of some of the reported MER elements in genetic rearrangements is demonstrated.