Effects of cholesterol loading on autoimmune MRL-lpr/lpr mice: susceptibility to hypercholesterolemia and aortic cholesterol deposition

The LC-MS/MS-Based Measurement of Isopimaric Acid in Rat Plasma and Application of Pharmacokinetics

Isopimaric acid (IPA) exhibits a diverse array of pharmacological activities, having been shown to function as an antihypertensive, antitumor, antibacterial, and hypocholesterolemic agent. However, few studies of the pharmacokinetics of IPA have been performed to date, and such analyses are essential to explore the in vivo mechanisms governing the biological activity of this compound. As such, we herein designed a selective LC-MS approach capable of quantifying serum IPA levels in model rats using an Agilent HC-C18 column (250 mm × 4.6 mm, 5 μm) via isocratic elution with a mobile phase composed of methanol 0.5% formic acid (91 : 9, v/v) at a 1 mL/min flow rate. Ion monitoring at m/z 301.2 [M-H]⁻ was used to quantify IPA levels in plasma samples from these rats, while internal standard (IS) levels were assessed at m/z 455.3 [M-H]⁻. After validation, this approach was employed to conduct a pharmacokinetic analysis of rats administered IPA via the oral (p.o. 50, 100, or 200 mg/kg) and intravenous (i.v. 5 mg/kg) routes. Analyses of noncompartmental pharmacokinetic parameters revealed that IPA underwent secondary absorption following oral administration to these animals, with the two tested oral doses (50 and 100 mg/kg) being associated with respective absolute bioavailability values of 11.9% and 17.5%. In summary, this study may provide a foundation for future efforts to explore the mechanistic basis for the pharmacological activity of IPA, offering insights to guide its subsequent clinical utilization.

Aortic VCAM-1: an early marker of vascular inflammation in collagen-induced arthritis

Cardiovascular disease (CVD) is a major cause of morbidity and mortality in rheumatoid arthritis (RA). There are limited experimental data on vascular involvement in arthritis models. To study the link between CVD and inflammation in RA, we developed a model of vascular dysfunction and articular inflammation by collagen‐induced arthritis (CIA) in C57Bl/6 (B6) mice. We studied the expression of vascular inflammatory markers in CIA with and without concomitant hyperlipidic diet (HD). Collagen‐induced arthritis was induced with intradermal injection of chicken type‐II collagen followed by a boost 21 days later. Mice with and without CIA were fed a standard diet or an HD for 12 weeks starting from the day of the boost. Arthritis severity was evaluated with a validated clinical score. Aortic mRNA levels of vascular cell adhesion molecule‐1 (VCAM‐1), inducible nitric oxide synthase (iNOS) and interleukin‐17 were analysed by quantitative RT‐PCR. Vascular cell adhesion molecule‐1 localization in the aortic sinus was determined by immunohistochemistry. Atherosclerotic plaque presence was assessed in aortas. Collagen‐induced arthritis was associated with increased expression of VCAM‐1, independent of diet. VCAM‐1 overexpression was detectable as early as 4 weeks after collagen immunization and persisted after 15 weeks. The HD induced atheroma plaque formation and aortic iNOS expression regardless of CIA. Concomitant CIA and HD had no additive effect on atheroma or VCAM‐1 or iNOS expression. CIA and an HD diet induced a distinct and independent expression of large‐vessel inflammation markers in B6 mice. This model may be relevant for the study of CVD in RA.

Accelerated atherosclerosis in ApoE deficient lupus mouse models

The accelerated development of atherosclerosis with increased risk of cardiovascular disease in systemic lupus erythematosus (SLE) patients is not well understood. An appropriate mouse model would greatly help to understand the mechanisms of this association. We have therefore combined the ApoE(-/-) model of atherosclerosis with three different murine models of SLE. We found that induction of cGVH in B6.ApoE(-/-) mice, breeding a Fas null gene onto the B6.ApoE(-/-) mice, and breeding the ApoE(-/-) defect onto MRL/lpr mice all caused a modest increase of atherosclerosis at 24 weeks of age compared to B6.ApoE(-/-) controls. B cells in B6.ApoE(-/-) mice had certain phenotypic differences compared to congenic C57BL/6 mice, as indicated by high expression of MHC II, Fas, CD86, and by increased number of cells bearing marginal zone phenotype. Furthermore, B6ApoE(-/-) mice had significant titers of anti-oxLDL and anti-cardiolipin autoantibodies compared to their B6 counterparts. Our studies also indicate that, following induction of cGVH, marginal zone B cells in B6.ApoE(-/-) are depleted, and there is considerable increase in anti-oxLDL and anti-cardiolipin abs along with secretion of lupus-specific autoantibodies, such as anti-dsDNA and anti-chromatin abs. Histological sections showed that cGVH and/or Fas deficiency could exacerbate atherosclerosis. The production of anti-oxLDL and anti-cardiolipin in ApoE(-/-) mice was also increased. These observations define a connection between induction of lupus-like symptoms and development of severe atherosclerosis in ApoE deficient lupus mouse models.

Quantitative trait locus analysis of plasma lipoprotein levels in an autoimmune mouse model : interactions between lipoprotein metabolism, autoimmune disease, and atherogenesis

The autoimmune MRL/lpr mouse strain, a model for systemic lupus erythematosus, exhibited an unusual plasma lipoprotein profile, suggesting a possible interaction of autoimmune disease and lipoprotein metabolism. In an effort to examine the genetic basis of such interactions, and to study their relationship to atherogenesis, we performed a quantitative trait locus analysis using a total of 272 (MRL/lprxBALB/cJ) second generation (F2) intercross mice. These mice were examined for levels of total plasma cholesterol, HDL cholesterol, VLDL and LDL cholesterol, unesterified cholesterol, autoantibodies, and aortic fatty streak lesions. Using a genome scan approach, we identified 4 quantitative trait loci controlling plasma lipoprotein levels on chromosomes (Chrs) 5, 8, 15, and 19. The locus on Chr 15 exhibited lod scores of 11.1 for total cholesterol and 6.7 for VLDL and LDL cholesterol in mice fed an atherogenic diet, and it contains a candidate gene, the sterol regulatory element binding protein-2. The locus on Chr 5 exhibited lod scores of 3.8 for total cholesterol and 4.1 for unesterified cholesterol in mice fed an atherogenic diet, and this locus has been observed in 2 previous studies. The locus on Chr 8 exhibited a lod score of 3.1 for unesterified cholesterol in mice fed a chow diet. This locus contains the lecithin-cholesterol acyltransferase gene, and decreased activity of the enzyme in the MRL strain suggests that this gene underlies the quantitative-trait locus. The locus on Chr 19 exhibited a lod score of 8.4 for HDL cholesterol and includes the Fas gene, which is mutated in MRL/lpr mice and is primarily responsible for the autoimmune phenotype in this cross. That the Fas gene is responsible for the HDL quantitative-trait loci is supported by the finding that autoantibody levels were strongly correlated with HDL cholesterol levels (rho=-0.37, P<0.0001) among the F2 mice. HDL cholesterol levels were in turn significantly associated with aortic fatty streak lesions among the F2 mice (rho=-0.17, P=0.006). Further, there was a threshold effect of autoantibody levels on the development of fatty streak lesions (rho=0.45, P=0.004 for 42 F2 mice with anti-dsDNA Ab over 0.5 OD). Our results support the concept that the high prevalence of coronary artery disease in systemic lupus erythematosus is due in part to a reduction of HDL cholesterol levels resulting from the autoimmune disease.