Around 25% of patients with systemic lupus erythematosus (SLE) could be refractory to conventional therapies. P-glycoprotein expression on cell surface has been implied on drug resistance, however, to date, it is unknown if P-gp serum levels are associated with SLE disease activity. Evaluate the association of serum P-gp levels and SLE with disease activity despite treatment. A cross-sectional study was conducted on 93 female SLE patients, all receiving glucocorticoids at stable doses for the previous 6 months before to baseline. SLE patients were classified into two groups: (a) patients with active disease [SLE disease activity index (SLEDAI) ≥ 3] despite treatment, and (b) patients with inactive disease (SLEDAI < 3) after treatment. Forty-three healthy females comprised the control group. Serum P-gp, anti-DNA, and both anti-nucleosome antibody levels were measured using ELISA. Active-SLE patients despite treatment had higher P-gp levels compared with inactive-SLE after treatment (78.02 ng/mL ± 114.11 vs. 33.75 ng/mL ± 41.11; p = 0.018) or versus reference group subjects (30.56 ng/mL ± 28.92; p = 0.011). P-gp levels correlated with the scores of SLEDAI (r = 0.26; p = 0.01), Mexican-SLEDAI (MEX-SLEDAI) (r = 0.32; p = 0.002), SLICC/ACR damage index (r = 0.47; p < 0.001), and with prednisone doses (r = 0.33; p = 0.001). In the multivariate model, the high P-gp levels were associated with SLICC/ACR score (p = 0.001), and SLEDAI score (p = 0.014). Our findings support a relationship between serum P-gp levels and SLE with disease activity despite treatment, but it requires further validation in longitudinal studies.

Objective. To evaluate the association of -174G/C IL-6 polymorphism with failure in therapeutic response to methotrexate (MTX) or leflunomide (LEF). This prospective, observational cohort included 96 Mexican-Mestizo patients with moderate or severe rheumatoid arthritis (RA), initiating MTX or LEF, genotyped for IL-6 -174G/C polymorphism by PCR-RFLP. Therapeutic response was strictly defined: only if patients achieved remission or low disease activity (DAS-28 < 3.2). Results. Patients with MTX or LEF had significant decrement in DAS-28 (p < 0.001); nevertheless, only 14% and 12.5% achieved DAS-28 < 3.2 at 3 and 6 months. After 6 months with any of these drugs the -174G/G genotype carriers (56%) had higher risk of therapeutic failure compared with GC (RR: 1.19, 95% CI: 1.07–1.56). By analyzing each drug separately, after 6 months with LEF, GG genotype confers higher risk of therapeutic failure than GC (RR = 1.56; 95% CI = 1.05–2.3; p = 0.003), or CC (RR = 1.83; 95% CI = 1.07–3.14; p = 0.001). This risk was also observed in the dominant model (RR = 1.33; 95% CI = 1.03–1.72; p = 0.02). Instead, in patients receiving MTX no genotype was predictor of therapeutic failure. We concluded that IL-6 -174G/G genotype confers higher risk of failure in therapeutic response to LEF in Mexicans and if confirmed in other populations this can be used as promissory genetic marker to differentiate risk of therapeutic failure to LEF.

Osteoporosis (OP) is highly prevalent in rheumatoid arthritis (RA) and is influenced by genetic factors. Single-nucleotide polymorphism (SNP) rs2073618 in the TNFRSF11B osteoprotegerin (OPG) gene has been related to postmenopausal OP although, to date, no information has been described concerning whether this polymorphism is implied in abnormalities of bone mineral density (BMD) in RA. We evaluated, in a case-control study performed in Mexican-Mestizo women with RA, whether SNP rs2073618 in the TNFRSF11B gene is associated with a decrease in BMD. RA patients were classified as follows: (1) low BMD and (2) normal BMD. All patients were genotyped for the rs2073618 polymorphism by PCR-RFLP. The frequency of low BMD was 74.4%. Higher age was observed in RA with low BMD versus normal BMD (62 and 54 years, resp.; p < 0.001). Worse functioning and lower BMI were observed in RA with low BMD (p = 0.003 and p = 0.002, resp.). We found similar genotype frequencies in RA with low BMD versus RA with normal BMD (GG genotype 71% versus 64.4%, GC 26% versus 33%, and CC 3% versus 2.2%, resp.; p = 0.6). We concluded that in Mexican-Mestizo female patients with RA, the rs2073618 polymorphism of the TNRFS11B gene is not associated with low BMD.