Inflammatory adipocyte-derived extracellular vesicles promote leukocyte attachment to vascular endothelial cells

BACKGROUND AND AIMS

Obesity is associated with an increased risk of cardiovascular disease, but the mechanisms involved are not completely understood. In obesity, the adipocyte microenvironment is characterised by both hypoxia and inflammation. Therefore, we sought to determine whether extracellular vesicles (EVs) derived from adipocytes in this setting might be involved in mediating cardiovascular disease, specifically by promoting leukocyte attachment to vascular endothelial cells.

METHODS

Mature 3T3-L1 adipocytes were incubated for 24 h under control, TNF-α (30 ng/mL), hypoxia (1% O₂), or TNF-α+hypoxia (30 ng/mL, 1% O₂) conditions. EVs were isolated by differential ultracentrifugation and analysed by nanoparticle tracking analysis. Primary human umbilical vein endothelial cells (HUVECs) were treated with EVs for 6 h before being lysed for Western blotting to investigate changes in adhesion molecule production, or for use in leukocyte attachment assays.

RESULTS

EVs from adipocytes treated with TNF-α and TNF-α+hypoxia increased vascular cell adhesion molecule (VCAM-1) production in HUVECs compared to basal level (4.2 ± 0.6 and 3.8 ± 0.3-fold increase, respectively (p < 0.05)), an effect that was inhibited by an anti-TNF-α neutralising antibody. Production of other adhesion molecules (E-selectin, P-selectin, platelet endothelial cell adhesion molecule and VE-Cadherin) was unchanged. Pre-incubating HUVECs with TNF-α+hypoxia EVs significantly increased leukocyte attachment compared to basal level (3.0 ± 0.4-fold increase (p < 0.05)).

CONCLUSIONS

Inflammatory adipocyte EVs induce VCAM-1 production in vascular endothelial cells, accompanied by enhanced leukocyte attachment. Preventing adipocyte derived EV-induced VCAM-1 upregulation may offer a novel therapeutic target in the prevention of obesity-driven cardiovascular disease.

Evidence for Adipocyte-Derived Extracellular Vesicles in the Human Circulation

Adipocyte-derived extracellular vesicles (EVs) may serve as novel endocrine mediators of adipose tissue and impact upon vascular health. However, it is unclear whether adipocyte-derived EVs are present in the human circulation. Therefore, the purpose of this study was to seek evidence for the presence of adipocyte-derived EVs in circulating plasma. Size-exclusion chromatography of platelet-free plasma identified fractions 5 to 10 as containing EVs by a peak in particle concentration, which corresponded with the presence of EV and adipocyte proteins. Pooling fractions 5 to 10 and subjecting to ultracentrifugation yielded a plasma EV sample, as verified by transmission electron microscopy (TEM) showing EV structures and Western blotting for EV (e.g., CD9 and Alix) and adipocyte markers. Magnetic beads and a solid-phase assay were used to deplete the EV sample of the four major families of circulating EVs: platelet-derived, leukocyte-derived, endothelial-derived, and erythrocyte-derived EVs. Postdepletion samples from both techniques contained EV structures as visualized by TEM, as well as CD9, Alix, and classic adipocyte proteins. Postdepletion samples also contained a range of other adipocyte proteins from an adipokine array. Adipocyte proteins and adipokines are expressed in optimally processed plasma EV samples, suggesting that adipocyte-derived EVs are secreted into the human circulation.

Tissue expression and correlation of a panel of urinary biomarkers following cisplatin-induced kidney injury

In recent years, there has been considerable activity to identify urinary biomarkers of nephrotoxicity as noninvasive measurements with greater sensitivity and specificity than traditional biomarkers, such as serum creatinine and blood urea nitrogen. Our study aimed to use cisplatin-treated rats to evaluate the use of immunohistochemistry directed at multiple urinary biomarkers in kidney tissue. Tissue levels were compared to urinary levels of these biomarkers to demonstrate tissue specificity and sensitivity. These techniques could also be used in studies where urine samples are not available, such as retrospective studies in drug safety testing, to demonstrate the potential utility of using these biomarkers in future preclinical or clinical studies. All of the biomarkers investigated showed either an increase (kidney injury molecule [KIM-1], osteopontin [OPN], and, clusterin) or a decrease (alpha-glutathione S-transferase and trefoil factor 3) except beta 2 microglobulin (β2MG) that showed no significant changes 5 days after 1.0 mg/kg or 2.5 mg/kg cisplatin treatment. All of the biomarkers except β2MG showed utility as tissue biomarkers, but KIM-1 and OPN expression correlated closely with urinary biomarker measurements and reflect tissue damage. Future studies are needed to determine the wider application of these two markers for detecting renal toxicity following administration of other nephrotoxicants.