Synergistic antiadipogenic effects of HIV type 1 protease inhibitors with tumor necrosis factor alpha: suppression of extracellular insulin action mediated by extracellular matrix-degrading proteases

Sp1 transcription factor interaction with accumulated prelamin a impairs adipose lineage differentiation in human mesenchymal stem cells: essential role of sp1 in the integrity of lipid vesicles

Lamin A (LMNA)-linked lipodystrophies may be either genetic (associated with LMNA mutations) or acquired (associated with the use of human immunodeficiency virus protease inhibitors [PIs]), and in both cases they share clinical features such as anomalous distribution of body fat or generalized loss of adipose tissue, metabolic alterations, and early cardiovascular complications. Both LMNA-linked lipodystrophies are characterized by the accumulation of the lamin A precursor prelamin A. The pathological mechanism by which prelamin A accumulation induces the lipodystrophy associated phenotypes remains unclear. Since the affected tissues in these disorders are of mesenchymal origin, we have generated an LMNA-linked experimental model using human mesenchymal stem cells treated with a PI, which recapitulates the phenotypes observed in patient biopsies. This model has been demonstrated to be a useful tool to unravel the pathological mechanism of the LMNA-linked lipodystrophies, providing an ideal system to identify potential targets to generate new therapies for drug discovery screening. We report for the first time that impaired adipogenesis is a consequence of the interaction between accumulated prelamin A and Sp1 transcription factor, sequestration of which results in altered extracellular matrix gene expression. In fact, our study shows a novel, essential, and finely tuned role for Sp1 in adipose lineage differentiation in human mesenchymal stem cells. These findings define a new physiological experimental model to elucidate the pathological mechanisms LMNA-linked lipodystrophies, creating new opportunities for research and treatment not only of LMNA-linked lipodystrophies but also of other adipogenesis-associated metabolic diseases.

Adipocyte extracellular matrix composition, dynamics and role in obesity

The central role of the adipose tissue in lipid metabolism places specific demands on the cell structure of adipocytes. The protein composition and dynamics of the extracellular matrix (ECM) is of crucial importance for the functioning of those cells. Adipogenesis is a bi-phasic process in which the ECM develops from a fibrillar to a laminar structure as cells move from the commitment phase to the growth phase characterized by storage of vast amounts of triglycerides. Mature adipocytes appear to spend a lot of energy on the maintenance of the ECM. ECM remodeling is mediated by a balanced complement of constructive and destructive enzymes together with their enhancers and inhibitors. ECM remodeling is an energy costing process regulated by insulin, by the energy metabolism, and by mechanical forces. In the obese, overgrowth of adipocytes may lead to instability of the ECM, possibly mediated by hypoxia.

Antiretroviral-related adipocyte dysfunction and lipodystrophy in HIV-infected patients: Alteration of the PPARγ-dependent pathways

Lipodystrophy and metabolic alterations are major complications of antiretroviral therapy in HIV-infected patients. In vitro studies using cultured murine and human adipocytes revealed that some protease inhibitors (PIs) and nucleoside reverse transcriptase inhibitors (NRTIs) were implicated to a different extent in adipose cell dysfunction and that a chronic incubation with some PIs decreased mRNA and protein expression of PPARγ. Defective lamin A maturation linked to PI inhibitory activity could impede the nuclear translocation of SREBP1c, therefore, reducing PPARγ expression. Adipose cell function was partially restored by the PPARγ agonists, thiazolidinediones. Adverse effects of PIs and NRTIs have also been reported in macrophages, a cell type that coexists with, and modulates, adipocyte function in fat tissue. In HIV-infected patients under ART, a decreased expression of PPARγ and of PPARγ-related genes was observed in adipose tissue, these anomalies being more severe in patients with ART-induced lipoatrophy. Altered PPARγ expression was reversed in patients stopping PIs. Treatment of patients with agonists of PPARγ could improve, at least partially, the subcutaneous lipoatrophy. These data indicate that decreased PPARγ expression and PPARγ-related function, resulting from ART-induced adipose tissue toxicity, play a central role in HIV-related lipoatrophy and metabolic consequences.

Effects of ritonavir on adipocyte gene expression: evidence for a stress-related response

To understand the molecular mechanisms underlying the development of dyslipidemia and lipodystrophy that occurs after administration of aspartic acid protease inhibitors, we examined transcriptional profiles using cDNA microarrays in 3T3-L1 adipocytes exposed to 10 micromol/l ritonavir for 2-21 days. The expression levels of approximately 12,000 transcripts were assessed using the MgU74Av2 mouse microarray chip. Ritonavir altered gene expression of inflammatory cytokines, stress response genes localized to endoplasmic reticulum, oxidative stress genes, apoptosis-related genes, and expression of genes involved in cell adhesion and extracellular matrix remodeling. Microarray analysis also identified a novel gene downregulated by ritonavir, Cidea, whose expression levels may affect free-fatty acid metabolism. These changes suggest a unique, stress-related pattern in adipocytes induced by chronic exposure to the protease inhibitor, ritonavir.

Lipodystrophy in HIV 1-infected patients: lessons for obesity research

Lipodystrophy is a common alteration in HIV 1-infected patients under anti-retroviral treatment. This syndrome is usually associated with peripheral lipoatrophy, central adiposity and, in some cases, lipomatosis, as well as systemic insulin resistance and hyperlipidemia. Research on the ethiopathogenesis of the disease revealed novel aspects of adipose tissue biology highly relevant to obesity research: the pivotal role of mitochondria in white adipose tissue function, the role that interference with master transcription factors of adipogenesis may have in human adipose tissue, the capacity of human white adipose tissue to acquire brown fat-like features, as well as the importance of apoptosis and the potential impact of viral infections in adipose tissue. The dramatic difference between subcutaneous adipose depots, prone to lipoatrophy, and the visceral adipose depots, prone to enlargement, has been further evidenced in the study of the lipodystrophy syndrome. The recognition of a local pro-inflammatory environment in lipoatrophic adipose tissue from affected patients, including macrophage infiltration and enhanced expression of chemokines and cytokines, points to events paradoxically similar to those in the hypertrophied adipose tissue in obesity. However, this also potentially provides an explanation for the existence of systemic alterations common to lipodystrophy and obese patients and reminiscent of the metabolic syndrome.

Impact of genetic polymorphisms on the risk of lipid disorders in patients on anti-HIV therapy

Active anti-HIV therapy can induce hypertriglyceridemia, low high-density lipoprotein (HDL) and insulin resistance, eventually accompanied by clinical lipodystrophy, associated loss of subcutaneous adipose tissue and an increase in abdominal adiposity. The frequency of these metabolic disorders is approximately 50% and host genetic factors might confer particular susceptibility. Variants of apolipoproteins (apo) A5 and C3, interacting with

Clin Chem Lab Med 2007;45:815–21.

HIV-1 Infection Alters Gene Expression in Adipose Tissue, Which Contributes to HIV-1/Haart-Associated Lipodystrophy

Background

The aetiopathogenic bases of HIV-1-/highly active antiretroviral treatment (HAART)-associated lipodystrophy (HALS) are poorly known, but this syndrome indicates that adipose tissue is highly sensitive to either HIV-1 infection, antiretroviral drugs or their combination.

Methods

To assess the relative contribution of infection and drugs, we compared the expression of marker genes corresponding to mitochondrial function, adipocyte differentiation and metabolism, and adipokines in subcutaneous adipose tissue from healthy controls, untreated HIV-1-infected patients, and HIV-1-infected patients treated with HAART with or without HALS.

Results

Subcutaneous adipose tissue from HIV-1-infected patients contained lower concentrations of the mRNA of the mitochondrial DNA-encoded cytochrome c oxidase subunit II than that of controls. These concentrations decreased further in association with HAART. The expression of nuclear genes coding for mitochondrial proteins, peroxisome proliferator-activated receptor-γ, and adipocyte-specific markers was reduced in HIV-1-infected patients, treated or not, with respect to the controls. In contrast, the mRNA concentrations of uncoupling protein-3 and preadipocyte factor-1 increased in lipodystrophic HAART-treated patients. The genes coding for adipokines were strongly affected: tumour necrosis factor-α was upregulated, whereas adiponectin and leptin were downregulated in HIV-1-infected patients, treated or not. Thus, substantial alterations of gene expression were already present when naive patients were compared with controls. Further changes were associated with HAART and with the diagnosis of HALS.

Conclusions

Disturbances in adipose tissue gene expression are already present in untreated HIV-1-infected patients, thus indicating a role of HIV-1 infection itself in eliciting adipose tissue alterations that are worsened by HAART, which ultimately leads to HALS.

Leptin and Adiponectin in the HIV Associated Metabolic Syndrome: Physiologic and Therapeutic Implications

Leptin and adiponectin represent two newly discovered adipose tissue derived hormones with important roles in energy homeostasis and insulin resistance. Their interrelations with the manifestations of the HIV associated metabolic syndrome and specific somatomorphic changes i.e. fat redistribution is reviewed. A synopsis of published studies is presented and the potential role of leptin and adiponectin is discussed. We have described an association of the HIV metabolic syndrome with a state of reduced insulin sensitivity due to adiponectin deficiency. The metabolic syndrome is also accompanied by leptin deficiency in lipoatrophic subjects and possibly by a leptin resistance state in lipohypertrophic patients. Adiponectin and / or leptin therapy in a manner similar to other leptin deficiency states may assist in the future management of such patients.

Tumour necrosis factor alpha in fat redistribution syndromes associated with combination antiretroviral therapy in HIV-1-infected patients: potential role in subcutaneous adipocyte apoptosis

BACKGROUND

The pathogenesis of fat redistribution syndromes (FRS) observed in the setting of highly active antiretroviral therapy (HAART) for the treatment of HIV-1-infection remains elusive. A dysregulation of the tumour necrosis factor alpha (TNF-alpha) system occurs in HIV-infected patients with FRS.

MATERIALS AND METHODS

The study looked at both the in vivo and in vitro relationship between TNF-alpha and the degree of subcutaneous adipocyte apoptosis in 60 HIV-1-infected patients on HAART with FRS, another 60 HIV-1-infected patients on HAART without FRS and 60 uninfected control patients. Apoptosis was assessed by the terminal deoxynucleotidyl transferase dUTP (deoxyuridine 5'-triphosphate)-digoxigenin Nick End Labelling (TUNEL) method. Soluble receptors of TNF-alpha were determined by the sandwich enzyme immunoassay technique. The in vitro viability was assessed by staining with 3-(4,5-dimethylthiazol-2-yl)-2,5 diphenyltetrazolium bromide (MTT) and apoptosis by TUNEL.

RESULTS

HIV-1-infected patients with FRS had significantly higher degrees of subcutaneous adipocyte apoptosis than those without FRS (P = 0.0001) and uninfected controls (P < 0.0001). There was a statistically significant association between serum levels of soluble TNF-alpha receptors #1 and #2 and the degree of subcutaneous adipocyte apoptosis in patients with and without FRS (P < 0.0001 for both receptors). In vitro, the addition of TNF-alpha (10 ng mL(-1)) to an adipocyte culture embedded with indinavir, either alone or in clinically relevant combinations with stavudine (d4T) and lamivudine (3TC), significantly decreased adipocyte viability (P = 0.0001) and increased adipocyte apoptosis (P < 0.0001) with respect to that observed with the addition of antiretrovirals alone.

CONCLUSIONS

TNF-alpha plays a significant role in subcutaneous adipocyte apoptosis, which occurs in the setting of FRS in HIV-1-infected patients on highly active antiretroviral therapy.

Plasminogen activator inhibitor type 1 (PAI-1) in plasma and adipose tissue in HIV-associated lipodystrophy syndrome. Implications of adipokines

BACKGROUND

PAI-1, an important inhibitor of fibrinolysis, is increased in obese subjects and has been shown to be an independent risk factor for cardiovascular disease. In the present study, we investigated the association between circulating levels of PAI-1 and locally produced PAI-1 in adipose tissue and body fat distribution and adipokines (TNF-alpha, TNF receptors, IL-6, IL-8) in patients with and without HIV-associated lipodystrophy syndrome (HALS).

MATERIALS AND METHODS

Eighteen men with HALS and 18 men with HIV but without HALS were investigated. DEXA and computed tomography scan were performed to determine total body fat and visceral adipose tissue mass. Insulin sensitivity was determined by the euglycaemic clamp technique. Plasma levels of PAI-1 and cytokines were determined. In addition, PAI-1, TNF-alpha, IL-6 and IL-8 mRNA levels in subcutaneous adipose tissue were measured by real-time reverse transcriptase polymerase chain reaction.

RESULTS

HALS patients were characterized by a 3-fold increased visceral adipose tissue (P < 0.001) and reduced limb fat (P < 0.01) as compared with non-HALS patients but with no difference in total fat mass between the groups. Plasma PAI-1 was increased in HALS patients (16.7 ng mL(-1) vs. 8.2 ng mL(-1), P < 0.05). Plasma PAI-1 was positively correlated with BMI (r = 0.74, P < 0.01), plasma TNF-alpha level (r = 0.64, P < 0.01), sTNFR-I (r = 0.38, P < 0.05), and visceral fat (r = 0.67, P < 0.01). Moreover, plasma PAI-1 was negatively associated with insulin sensitivity (r = -0.57, P < 0.01) and the percentage of limb fat (r = -0.57, P < 0.01). A positive correlation was found between plasma PAI-1 and TNF-alpha mRNA level. No association was, however, found between plasma PAI-1 and PAI-1 mRNA level in adipose tissue.

CONCLUSION

Plasma PAI-1 is increased in HALS patients and it is suggested that dysregulation of the TNF-system (high TNFalpha and high sTNFR1) may play a role in up-regulating PAI-1 in HALS.

Endothelial cell dysfunction and the vascular complications associated with type 2 diabetes: assessing the health of the endothelium

Diabetes-associated vascular complications are collectively the major clinical problems facing patients with diabetes and lead to the considerably higher mortality rate than that of the general population. People with diabetes have a much higher incidence of coronary artery disease as well as peripheral vascular diseases in part because of accelerated atherogenesis. Despite the introduction of new therapies, it has not been possible to effectively reduce the high cardiovascular morbidity and mortality associated with diabetes. Of additional concern is the recognition by the World Health Organization that we are facing a global epidemic of type 2 diabetes. Endothelial dysfunction is an early indicator of cardiovascular disease, including that seen in type 2 diabetes. A healthy endothelium, as defined in terms of the vasodilator/blood flow response to an endothelium-dependent vasodilator, is an important indicator of cardiovascular health and, therefore, a goal for corrective interventions. In this review we explore the cellular basis for endothelial dysfunction in an attempt to identify appropriate new targets and strategies for the treatment of diabetes. In addition, we consider the question of biomarkers for vascular disease and evaluate their usefulness for the early detection of and their role as contributors to vascular dysfunction.

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.

Increased systemic and adipose tissue cytokines in patients with HIV-associated lipodystrophy

The lipodystrophy syndrome (adipose tissue redistribution and metabolic abnormalities) observed with highly active antiretroviral therapy (HAART) during human immunodeficiency virus (HIV) infection may be related to increased proinflammatory cytokine activity. We measured acute cytokine (TNF-alpha, IL-6, leptin), glycerol, and lactate secretion from abdominal subcutaneous adipose tissue (SAT), and systemic cytokine levels, in HIV-infected subjects with and without lipodystrophy (HIVL+ and HIVL-, respectively) and healthy non-HIV controls. Lipodystrophy was confirmed and characterized as adipose tissue redistribution in HIVL+ compared with HIVL- and controls, by dual-energy X-ray absorptiometry and by whole body MRI. TNF-alpha secretion from abdominal SAT and circulating levels of IL-6, soluble TNF receptors I and II, and insulin were elevated in HIVL+ relative to HIVL- and/or controls, particularly in HIVL+ undergoing HAART. In the HIV-infected group as a whole, IL-6 secretion from abdominal SAT and serum IL-6 were positively associated with visceral fat and were negatively associated with the relative amount of lower limb adipose tissue (P < 0.01). Decreased leptin and increased lactate secretion from abdominal SAT were specifically associated with HAART. In conclusion, increased cytokine secretion from adipose tissue and increased systemic proinflammatory cytokine activity may play a significant role in the adipose tissue remodeling and/or the metabolic abnormalities associated with the HIV-lipodystrophy syndrome in patients undergoing HAART.

Serum adipocytokines are related to lipodystrophy and metabolic disorders in HIV-infected men under antiretroviral therapy

OBJECTIVES

Adipocytokines, secreted by adipose tissue, may regulate fat metabolism, lipid and glucose homeostasis and insulin sensitivity. We analysed the relations between circulating concentrations of adiponectin, leptin, interleukin-6, tumor necrosis factor alpha and its soluble receptors sTNFR1 and R2, lipodystrophic phenotypes and metabolic alterations in patients under highly active antiretroviral therapy (HAART).

METHODS

We studied 131 consecutive HIV-infected males under protease inhibitor (PI)-based HAART, with body mass index < 27 kg/m2 and C-reactive protein (CRP) < 10 mg/l. Patients were classified in four groups according to clinical examination: no lipodystrophy (NL), lipohypertrophy (LH), lipoatrophy (LA) and mixed lipodystrophy (ML). In addition to adipocytokines, we measured plasma fasting levels of triglycerides, cholesterol, cardiovascular risk markers (high-sensitivity CRP and apolipoproteins B/A1 ratio), fasted and 2 h post-glucose loading glycemia and insulinemia and calculated the quantitative insulin sensitivity check index.

RESULTS

The patients were HIV-infected and PI-treated for a mean of 8.2 and 1.6 years respectively; 74% presented lipodystrophy, 38% altered glucose tolerance and 42% hypertriglyceridemia. Insulin sensitivity correlated positively with adiponectin and negatively with leptin and interleukin-6. Adiponectin, but not leptin, negatively correlated with all metabolic parameters. Insulin resistance, metabolic defects and cardiovascular risk markers were strongly negatively correlated with the adiponectin/leptin ratio (A/L), and positively with sTNFR1. LA patients had a longer duration of infection but ML patients presented the most severe metabolic alterations, insulin resistance and A/L decrease.

CONCLUSIONS

These results suggest that adiponectin and the TNFalpha system are related to lipodystrophy, insulin resistance and metabolic alterations in patients under PI-based HAART. A/L and sTNFR1 could predict insulin sensitivity and potential cardiovascular risk in these patients.

Agent and cell-type specificity in the induction of insulin resistance by HIV protease inhibitors

OBJECTIVE

To test agent and cell-type specificity in insulin resistance induced by prolonged exposure to HIV protease inhibitors (HPI), and to assess its relation to the direct, short-term inhibition of insulin-stimulated glucose uptake.

METHODS

Following prolonged (18 h) and short (5-10 min) exposure to HPI, insulin-stimulated glucose transport, protein kinase B (PKB) phosphorylation, and GLUT4 translocation were evaluated in 3T3-L1 adipocytes, fibroblasts, L6 myotubes, and L6 cells overexpressing a myc tag on the first exofacial loop of GLUT4 or GLUT1.

RESULTS

Prolonged exposure of 3T3-L1 adipocytes to nelfinavir, but not to indinavir or saquinavir, resulted in increased basal lipolysis but decreased insulin-stimulated glucose transport and PKB phosphorylation. In addition, impaired insulin-stimulated glucose uptake and PKB phosphorylation were also observed in the skeletal muscle cell line L6, and in 3T3-L1 fibroblasts. Interestingly, this coincided with increased basal glucose uptake as well as with elevated total-membrane glucose transporter GLUT1 protein content. In contrast to these unique effects of nelfinavir, the mere presence of any of the agents in the 5 min transport assay inhibited insulin-stimulated glucose-uptake activity. This appeared to be caused by direct and specific interaction of the drugs with GLUT4 fully assembled at the plasma membrane, since insulin-stimulated cell-surface exposure of an exofacial myc epitope on GLUT4 was normal.

CONCLUSIONS

Independent mechanisms for HPI-induced insulin resistance exist: prolonged exposure to nelfinavir interferes with insulin signaling and alters cellular metabolism of adipocytes and muscle cells, whereas a direct inhibitory effect on insulin-stimulated glucose uptake may occurs through specific interaction of HPI with GLUT4.

The effects of protease inhibitors on basal and insulin-stimulated lipid metabolism, insulin binding, and signaling

The objective of our research was to investigate the effects of the protease inhibitors ritonavir, saquinavir, and indinavir on triglyceride synthesis, lipolysis, insulin binding, and signaling in differentiating 3T3 L1 pre-adipocytes. Saquinavir, ritonavir, and indinavir all stimulated triglyceride (TG) synthesis. Additionally, all concentrations of protease inhibitors employed (i.e., 0.1 micro M to 10 micro M) significantly decreased insulin-stimulated TG synthesis. No effects of any of the protease inhibitors were observed either on basal lipolysis or after stimulation of lipolysis with 100 nM noradrenaline. Specific (125)I-insulin binding was observed to be decreased by exposure to all the protease inhibitors throughout the period of adipocyte phenotype development. This was mediated by indinavir through a receptor decrease and had no effect on receptor affinity. During differentiation with ritonavir (i.e., 1-11 days post addition of differentiating cocktail), insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation was ascertained (day 11) and found to be decreased in the ritonavir exposed cells when compared with control cells. The results reported herein demonstrate protease inhibitor effects on basal TG synthesis while exhibiting decreased insulin-stimulated TG synthesis at physiological concentrations of protease inhibitors. These effects may be subsequent to decreased insulin binding and/or IRS-1 tyrosine phosphorylation.