Assessment of in situ adipose tissue inflammation by microdialysis

Histological and Molecular Adipose Tissue Changes Are Related to Metabolic Syndrome Rather Than Lipodystrophy in Human Immunodeficiency Virus-Infected Patients: A Cross-Sectional Study

Background

In human immunodeficiency virus (HIV)-infected patients on combination antiretroviral therapy (cART), lipodystrophy shares many similarities with metabolic syndrome, but only metabolic syndrome has objective classification criteria. We examined adipose tissue changes related to lipodystrophy and metabolic syndrome to clarify whether it may be acceptable to focus diagnosis on metabolic syndrome rather than lipodystrophy.

Methods

This is a cross-sectional study of 60 HIV-infected men on cART and 15 healthy men. We evaluated lipodystrophy (clinical assessment) and metabolic syndrome (JIS-2009). We compared adipocyte size, leukocyte infiltration, and gene expression in abdominal subcutaneous adipose tissue biopsies of patients with and without lipodystrophy and with and without metabolic syndrome.

Results

Lipodystrophy was only associated with increased macrophage infiltration (P = .04) and adiponectin messenger ribonucleic acid ([mRNA] P = .008), whereas metabolic syndrome was associated with larger adipocytes (P < .0001), decreased expression of genes related to adipogenesis and adipocyte function (P values between <.0001 and .08), increased leptin mRNA (P = .04), and a trend towards increased expression of inflammatory genes (P values between .08 and .6).

Conclusions

Metabolic syndrome rather than lipodystrophy was associated with major unfavorable abdominal subcutaneous adipose tissue changes. In a clinical setting, it may be more relevant to focus on metabolic syndrome diagnosis in HIV-infected patients on cART with regards to adipose tissue dysfunction and risk of cardiometabolic complications.

Cytokine and Chemokine Recovery Is Increased by Colloid Perfusates during Dermal Microdialysis

Cytokines and chemokines play important roles in cell signalling, and microdialysis is a promising tool for monitoring these inflammation markers ex vivo. Therefore, the collecting of these mediators at the highest concentrations possible is crucial. Depending on the size of the mediator of interest, the collection of these high molecular mass molecules has thus far been difficult due to their low recovery, even when using high cut-off (100 kDa) microdialysis membranes. This study aimed to optimize the recovery of various cytokines and chemokines by validating the use of different perfusates in cutaneous microdialysis, and comparing intravenous (i.v.) colloids, crystalloids, and a lipid emulsion formulations that are approved for i.v. applications. Methods: In vitro and in vivo recovery experiments using six recombinant cytokines varying in molecular size (interleukin-2 (15 kDa), interleukin-6 (20.5 kDa), interleukin-8 (8 kDa), interleukin-12p70 (70 kDa), TNF-α (17.5 kDa), and vascular endothelial growth factor (VEGF) (38 kDa)) were performed in the presence of different perfusates for i.v. applications: Ringer’s lactate, dextran 60 kDa, hydroxyethyl starch 70 kDa, and hydroxyethyl starch 200 kDa solutions as well as a lipid emulsion formulation. Recovery was determined through (i) microdialysis of cytokines and chemokines in Ringer’s lactate solution or human serum in vitro, and (ii) retrodialysis of excised porcine and human skin cadavers in vitro and porcine skin in vivo. Furthermore, we used skin trauma (catheter insertion) and Ultraviolet B irradiation of 3 × 3 cm² skin areas to sample cytokines and chemokines in vivo and compared the amounts that were obtained using crystalloid and colloid perfusates. All the cytokines and chemokines within the dialysates were quantified through a flow cytometry-based bead array assay. Results: Overall, recovery was strongly increased by the colloids, particularly hydroxyethyl starch 70 kDa, in vitro, ex vivo, and in vivo. When compared with the recovery achieved using Ringer’s lactate, this increase was most effective for proteins ranging from 8 to 20.5 kDa. Hydroxyethyl starch 70 kDa significantly increased the recovery of interleukin (IL)-8 in human serum in vitro when compared with Ringer’s lactate. More cytokines and chemokines were recovered using colloids compared with crystalloids. However, the increase in recovery values was lower for IL-12p70 and VEGF. Conclusions: Regarding the dialysate volumes and final dialysate concentrations, colloid perfusates are overall superior to crystalloid perfusates, such as Ringer’s lactate, when sampling cytokines and chemokines, resulting in higher recoveries. However, the sampling of high-molecular-mass cytokines during microdialysis remains challenging, and experimental in vitro data are not completely comparable with data obtained ex vivo or in vivo.

A Review on Microdialysis Calibration Methods: the Theory and Current Related Efforts

Microdialysis is a sampling technique first introduced in the late 1950s. Although this technique was originally designed to study endogenous compounds in animal brain, it is later modified to be used in other organs. Additionally, microdialysis is not only able to collect unbound concentration of compounds from tissue sites; this technique can also be used to deliver exogenous compounds to a designated area. Due to its versatility, microdialysis technique is widely employed in a number of areas, including biomedical research. However, for most in vivo studies, the concentration of substance obtained directly from the microdialysis technique does not accurately describe the concentration of the substance on-site. In order to relate the results collected from microdialysis to the actual in vivo condition, a calibration method is required. To date, various microdialysis calibration methods have been reported, with each method being capable to provide valuable insights of the technique itself and its applications. This paper aims to provide a critical review on various calibration methods used in microdialysis applications, inclusive of a detailed description of the microdialysis technique itself to start with. It is expected that this article shall review in detail, the various calibration methods employed, present examples of work related to each calibration method including clinical efforts, plus the advantages and disadvantages of each of the methods.

Immunosenescence of the CD8(+) T cell compartment is associated with HIV-infection, but only weakly reflects age-related processes of adipose tissue, metabolism, and muscle in antiretroviral therapy-treated HIV-infected patients and controls

Background

Despite effective antiretroviral therapy (ART), HIV-infected patients exhibit systemic inflammation, early onset of age-related diseases, and features of immunosenescence. The role of inflammation in the development of age-related diseases is widely recognized. However, the role of immunosenescence is not well established. Studying immunosenescence in HIV-infection could give insight into its role in ageing processes. In this cross-sectional study, we aimed to investigate whether ART-treated HIV-infected patients exhibit immunosenescence; and whether immunosenescence is associated with age-related processes of inflammation, metabolism, adipose tissue, and muscle. T cell immunosenescence and exhaustion were assessed by flow cytometry analysis of CD8⁺ cells from 43 ART-treated HIV-infected patients (HIV⁺) and ten Controls using markers of differentiation: CD27/CD28; maturation: CD27/CD45RA; senescence: killer cell lectin-like receptor G1 (KLRG1); and exhaustion: programmed death-1 (PD-1). Relationships between CD8⁺ T cell immunosenescence, exhaustion, and age-related processes were assessed using linear regressions.

Results

HIV-infection was strongly associated with more highly differentiated and mature CD8⁺ T cell phenotypes. PD-1 and KLRG1 expression did not differ between HIV⁺ and Controls, but depended on differentiation and maturation stages of the cells. CD8⁺ T cell maturation was associated with age. KLRG1 expression was associated with age, metabolic syndrome, visceral adipose tissue, and high muscle mass. PD-1 expression was not associated with age-related parameters.

Conclusions

HIV-infection strongly affected CD8⁺ T cell differentiation and maturation, whereas age-related processes were only weakly associated with immune parameters. Our findings suggest that, in contrast to inflammation, immunosenescence appears to be highly dependent on HIV-infection and is only to a small extent associated with age-related parameters in well-treated HIV-infection.

Electronic supplementary material

The online version of this article (doi:10.1186/s12865-015-0136-6) contains supplementary material, which is available to authorized users.

Relationship between sarcopenic obesity-related phenotypes and inflammatory markers in postmenopausal women

Ageing is associated with changes in body composition that may result in sarcopenic obesity (SO). Interleukin-6 (IL-6) and C-reactive protein (CRP) are important inflammatory markers related to ageing. SO has been examined as an important public health problem, but its association with inflammatory markers has yet to be investigated. The aim of this study was to investigate the association between SO-related phenotypes and inflammatory markers in postmenopausal women. A total of 130 women (66·7 ± 5·2 years) underwent body composition evaluation using dual-energy X-ray absorptiometry. Volunteers were classified according to a SO definition previously described in the literature. Waist circumference (WC) and handgrip strength (HG) were also measured. Blood samples were collected for CRP, tumour necrosis factor and IL-6 measurements. All the inflammatory markers were higher in SO individuals when compared to non-SO; however, only IL-6 reached statistical significance (median 3·34 versus 1·37 pg ml^-1 ; P<0·05). Also, CRP was significantly correlated (P<0·01) with body mass index (r_s  = 0·34), fat mass (FM; r_s  = 0·25) and WC (r_s  = 0·33). Similarly, IL-6 levels were significantly correlated (P<0·05) to age (r_s  = 0·19), FM (r_s  = 0·19) and WC (r_s  = 0·17). HG was found to be significantly reduced among subjects with higher IL-6 levels (P = 0·02). In summary, the combination of reduced muscle mass and excess body fat (i.e. SO) is associated with elevated inflammatory markers in postmenopausal women. Moreover, CRP and IL-6 are associated with SO-related phenotypes in this population.

Leptin, IL-6, and suPAR reflect distinct inflammatory changes associated with adiposity, lipodystrophy and low muscle mass in HIV-infected patients and controls

Background

HIV-infected patients could exhibit accelerated ageing, since age-associated complications like sarcopenia; increased inflammation; lipodystrophy with loss of subcutaneous adipose tissue and/or gain of visceral adipose tissue (VAT); and cardiovascular disease occur at an earlier age. Inflammation is involved in age-associated complications. However, it is not understood whether it is the same inflammatory changes that are involved in the various ageing-associated complications. Our objective was to study whether leptin, interleukin 6 (IL-6), and soluble urokinase plasminogen activator receptor (suPAR) were associated distinctively with adiposity, lipodystrophy and sarcopenia, in HIV-infected patients and healthy Controls.

Results

Systemic leptin levels were significantly higher in patients with lipodystrophy than without, whereas there was no difference in IL-6 or suPAR levels. Leptin was significantly positively associated with fat mass index (FMI) and abdominal VAT, but not with lean mass index (LMI). IL-6 was significantly associated with both FMI and VAT, and low LMI. High suPAR was associated with low LMI, and weakly with high FMI and VAT.

Conclusions

Leptin reflected adiposity- and lipodystrophy-related inflammation, but not sarcopenia. IL-6 reflected both adiposity-, but also sarcopenia-related inflammation; and suPAR was a marker of sarcopenia-related inflammation. Our results indicate that different inflammatory processes can be active simultaneously contributing to the systemic low grade inflammatory state. Identifying major contributors to circulating leptin, IL-6, and suPAR levels could levels could therefore improve our understanding of which inflammatory processes are involved in the various age-related complications.