IL-6 is a multifunctional cytokine that acts as an immune, inflammatory and metabolic mediator. Given these properties, IL-6 is thought to be involved in several HIV-1-related events although data are inconsistent [1–11]. We undertook a cross-sectional study in a cohort of Caucasian Spanish HIV-1-infected patients treated with combination antiretroviral therapy (cART) with and without fat redistribution syndromes (FRS) and in an uninfected control group. Our objectives were to assess the influence of the IL-6 −174G>C single nucleotide polymorphism (SNP) on the risk of HIV-1 infection and on the risk of the development of FRS, and whether perturbations in subcutaneous adipose tissue (SAT) IL-6 messenger RNA expression and in IL-6 plasma levels exist in HIV-1-infected patients with and without FRS.
This was a multicentre case–control study. The study cohort consisted of 414 uninfected controls and 299 adult HIV-1-infected patients. These latter were recruited within a cohort of 1700 HIV-1-infected individuals who had been receiving stable cART for at least one year. We recruited all patients with moderate or severe FRS, which was assessed clinically [7,12,13] (n = 143), and a randomly selected group of patients without FRS (n = 156). Both groups were comparable by age, sex, and length of exposure to cART. Patients with HIV-1-associated cachexia, active opportunistic infections, current inflammatory diseases or conditions, the use of drugs with known metabolic effects or plasma C reactive protein greater than 1 mg/dl were excluded. All participants were native white Spaniards and provided informed consent. The project was approved by local ethical commitees. The IL-6 −174G>C genotype was assessed by restriction fragment-length polymorphism as previously described by our group . IL-6 mRNA quantification in adipose tissue was analysed in 21 uninfected controls, 25 HIV-1-infected patients with FRS and 13 HIV-infected patients without FRS by real-time polymerase chain reaction and expressed relative to cyclophylin A and β-actin as previously described . Plasma IL-6 levels were measured using the commercial kit Human IL6 Quantikine HS High Sensitivity (R&D Systems, Lille, France). The Student's t-test and one-way analysis of variance with the posthoc Bonferroni test were used to compare continuous variables. The Mann–Whitney U test was used to compare non-parametric variables. Qualitative variables were analysed using the χ2 test. Hardy–Weinberg equilibrium was assessed by the χ2 goodness-of-fit test. Two-way analysis of variance, Pearson correlation analyses, Spearman's rank correlation test, and forward stepwise logistic regression analysis with the model adequately fitted by Hosmer and Lemeshow's goodness of fit test were used when needed. A P value of less than 0.05 was considered significant.
HIV-1-infected patients and uninfected controls were comparable by age (42 ± 8.8 versus 41 ± 14.6; P = 0.97) and sex (64.9% versus 60.1% male; P = 0.21). Compared with patients without FRS, the group with FRS had significant perturbations in their anthropometric and metabolic parameters (full data not shown, available on request). Table 1 shows that the IL-6 −174 C/C genotype and the C allele were overrepresented in HIV-1-infected subjects with respect to uninfected controls (P = 0.05 and P = 0.007, respectively). No significant differences were observed in the genotype and allele distribution when patients with and without FRS were compared. Also, the IL-6 genotype did not modulate the rapidity of the onset of FRS (P = NS). IL-6 mRNA expression in SAT was non-significantly different in HIV-1-infected patients with and without FRS, whereas both subsets had significantly greater IL-6 mRNA than uninfected controls (P < 0.001). HIV-1-infected patients had significantly greater plasma IL-6 levels than uninfected controls (2.6 ± 3 versus 1.4 ± 1.4 pg/ml, P < 0.001) but among infected patients plasma IL-6 levels did not differ between patients with and without FRS (P = 1). Plasma IL-6 levels in patients who had or had not received thymidine analogues were non-significantly different, irrespective of the presence or absence of FRS (P = 0.8). We performed several comparisons to assess the relationship between each individual protease inhibitor (PI) that our patients received (indinavir, n = 84; nelfinavir, n = 46; saquinavir, n = 42, ritonavir, n = 41, lopinavir/ritonavir, n = 8), several metabolic outcomes for each PI (FRS, hyperglycaemia, insulin-resistance, hypertriglyceridemia, high low-density lipoprotein cholesterol or low high-density lipoprotein cholesterol, all yes or no (see Domingo et al. , Carr et al. , Christeff et al.  and Ford et al.  for categorization criteria) and plasma IL-6 levels. All comparisons gave non-significant differences (P = NS).
Our study provides some relevant insights into the role of IL-6 in HIV-1 infection and in cART-related FRS. With respect to the pathogenesis of HIV-1 infection, we found that the IL-6 −174G>C polymorphism may modulate the risk of infection. Our findings contrast with those of Price et al., who found no differences in the IL-6 −174G>C distribution between uninfected blood donors and different categories of HIV-1-infected patients, although the number of HIV-1-infected patients assessed was low. IL-6 plays a pivotal role in the initial response to infection because it influences both innate and acquired immunity . As both types of immune responses are involved in the first steps of HIV-1 infection, it is biologically plausible to investigate the modulator effect of IL-6 genetic variants on the vulnerability to HIV-1 infection. Our data suggest that the IL-6 −174 G>C SNP could modulate the risk of HIV-1 infection. The fact that our control group comprised individuals with no known risk factors for HIV-1 infection dictates caution when interpreting our findings, the best control group would have been made up of exposed uninfected individuals. We have also shown that there is an overproduction of IL-6 in infected patients under cART compared with uninfected controls. This finding has been recognized for many years  and may be related to the inflammatory phenomenon that accompanies HIV-1 infection and is thought to be responsible for the polyclonal hypergammaglobulinemia observed in these patients .
An additional aim of our study was to extend our present knowledge regarding the pathogenic mechanisms involved in FRS. Although the pathogenesis of FRS is not fully understood , reports elsewhere have elegantly shown an association between nucleoside reverse transcriptase inhibitor thymidine analogues, mitochondrial toxicity and lipoatrophy [21,22]. Note that in our cohort the only independent predictor of the development of FRS was the length of time of stavudine exposure [1–24 months, odds ratio (OR) 8, 95% confidence interval (CI) 1.1–56, P = 0.036; 25–48 months, OR 10, 95% CI 1.6–64, P = 0.01; > 48 months, OR 33, 95% CI 4.3–251, P = 0.001]. A relationship between lipoatrophy, mitochondrial damage and IL-6 has been investigated . Data from our genetic analysis, however, suggest that the IL-6 −174G>C SNP is not related to the development of FRS and its associated metabolic derangements in HIV-1-infected patients on cART. Also, the systemic activation of the IL-6 system, measured as plasma IL-6 levels, which we have detected in our HIV-1-infected cohort is unrelated to the presence or absence of FRS or several metabolic outcomes and to the individual PI drugs to which our patients were exposed.
We recognize some limitations in our study. The cross-sectional nature of our design provides associations, not causality. Moreover, the clinical definition of FRS does not allow us to discount the possibility that some FRS-negative patients could have minor subclinical changes not detectable on a clinical basis, thus some patients in the FRS-negative subset could in fact be false negatives. We believe, however, that this is unlikely in our study because our cohort was made up of extreme FRS phenotypes and comprised only overt FRS versus non-FRS patients, with slight/mild FRS (potential false negatives) being ommited.
In summary, when taken together, our data suggest that the IL-6 system may be involved in HIV-1 pathogenesis but its role in cART-related FRS seems to be low if any.
John Bates kindly improved the English text.
The members of the HIV-1 Lipodystrophy Study Group and co-authors of this paper are: Maria Saumoy, Miguel López-Dupla, Montserrat Broch, Sergi Veloso, Matilde R. Chacón, Merce Miranda, Carmen Aguilar, Eva González, Carles Olona, Joan-Josep Sirvent, Montserrat Olona, Amadeu Saurí, Joan Vendrell, Cristóbal Richart, Consuelo Viladés, Joaquim Peraire, Francesc Vidal (Hospital Universitari de Tarragona Joan XXIII and Universitat Rovira i Virgili); Carlos Alonso-Villaverde, Blai Coll, Sandra Parra, Jordi Joven, Lluis Masana (Hospital Universitari de Sant Joan de Reus and Universitat Rovira i Virgili); Pere Domingo, Maria Antònia Sambeat, Àngels Fontanet, Mar Gutiérrez, Gràcia Mateo (Hospital de la Santa Creu i Sant Pau and Universitat Autònoma de Barcelona).
Sponsorship: This work has been partly financed by grants from the Fondo de Investigacion Sanitaria (FIS 02/1282, 04/1752, 04/0377, 05/1591, 05/1944 and 07/0976); Fundació La Marató de TV3 (02/1830 and 02/1910), Fundación para la Investigación y Prevención del Sida en España (FIPSE 06/36572 and 06/30610); SAF2005-0413; Red de Investigación en Sida (RD06/006/0022) and REDIMET (RD06/0015/0011), Instituto de Salud Carlos III, Ministerio de Sanidad y Consumo. M.S. and B.C. are the recipients of a research career award from the Instituto de Salud Carlos III, Spain. M.R.C. is supported by a fellowship from the Fondo de Investigación Sanitaria CP06/00119.
Conflicts of interest: None.
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