Protease inhibitor treatments reveal specific involvement of matrix metalloproteinase-9 in human adipocyte differentiation.

We previously showed that human and murine 3T3-F442A preadipocytes produced and released matrix metalloproteinases (MMPs) 2 and 9 and that a treatment by MMP inhibitors resulted in the blockade of murine fat cell adipose conversion. In parallel, investigators reported that other protease inhibitors, the human immunodeficiency virus (HIV) protease inhibitors (PIs) involved in lipodystrophy in humans, also reduced the adipocyte differentiation process of several murine cell lines. The present work was performed to define the effects of MMP inhibitors and HIV-PIs on the human adipocyte differentiation process, to clarify the involvement of MMPs in the control of human adipogenesis, and to determine whether HIV-PIs interact with MMPs in the control of this process. The effect of two MMP inhibitor and four HIV-PI treatments on the differentiation of primary culture human preadipocytes, as well as the putative relationships between HIV-PIs and MMP-2 and -9 expression, release, or activity were investigated. We showed that MMP inhibitors and HIV-PIs reduced the human adipocyte differentiation process as assessed by the decrease of cell protein and/or triglyceride contents and expression of fatty acid binding protein and hormone-sensitive lipase, two adipocyte markers. Unlike MMP inhibitors, HIV-PIs were devoid of any effect per se on recombinant MMP-2 and 9 activities but reduced the expression and release of MMP-9 by human preadipocytes. Thus, the present study indicates that the modulation of the extracellular matrix components through the production and/or activity of MMPs, and, more precisely, MMP-9 might be a key factor in the regulation of human adipose tissue development.

Alteration of amine oxidase activity in the adipose tissue of obese subjects.

OBJECTIVE: To explore the activity of monoamine oxidases (MAOs) and semicarbazide-sensitive amine oxidases (SSAOs) in adipose tissue and blood of lean and moderately obese subjects and to study whether there is a link between these hydrogen peroxide-generating enzymes and blood markers of oxidative stress. RESEARCH METHODS AND PROCEDURES: Nine obese male subjects (BMI 32.6 +/- 0.4 kg/m(2)) and nine controls (BMI 23.4 +/- 0.5) of 24- to 40-year-old subjects were included in the study. MAO and SSAO activities were measured on microbiopsies of abdominal subcutaneous adipose tissue by quantifying (14)C-tyramine and (14)C-benzylamine oxidation. Levels of soluble SSAO, lipid peroxidation products, and antioxidant agents were measured in plasma, whereas cytoprotective enzymes were determined in blood lysates. RESULTS: The high MAO activity found in adipose tissue was diminished by one-half in obese subjects (maximum initial velocity of 1.2 vs. 2.3 nmol tyramine oxidized/mg protein/min). There was no change in SSAO activity, either under its adipose tissue-bound or plasma-soluble form. Plasma levels of lipid peroxidation products and antioxidant vitamins remained unmodified, as well as erythrocyte antioxidant enzymes, whereas circulating triglycerides, insulin, and leptin were increased. DISCUSSION: Although they already exhibited several signs of endocrino-metabolic disorders, the obese men did not exhibit the increase in blood markers of oxidative stress or the decrease in antioxidant defenses reported to occur in very obese or diabetic subjects. The reduced MAO and the unchanged SSAO activities found in obesity suggest that these hydrogen peroxide-generating enzymes expressed in adipocytes are probably not involved in the onset of the oxidative stress found in severe obesity and/or in its complications.