Effects of rosiglitazone on gene expression in subcutaneous adipose tissue in highly active antiretroviral therapy-associated lipodystrophy

Fatty liver in lipodystrophy: A review with a focus on therapeutic perspectives of adiponectin and/or leptin replacement

Lipodystrophy is a group of clinically heterogeneous, inherited or acquired, disorders characterized by complete or partial absence of subcutaneous adipose tissue that may occur simultaneously with the pathological, ectopic, accumulation of fat in other regions of the body, including the liver. Fatty liver adds significantly to hepatic and extra-hepatic morbidity in patients with lipodystrophy. Lipodystrophy is strongly associated with severe insulin resistance and related comorbidities, such as hyperglycemia, hyperlipidemia and nonalcoholic fatty liver disease (NAFLD), but other hepatic diseases may co-exist in some types of lipodystrophy, including autoimmune hepatitis in acquired lipodystrophies, or viral hepatitis in human immunodeficiency virus (HIV)-associated lipodystrophy. The aim of this review is to summarize evidence linking lipodystrophy with hepatic disease and to provide a special focus on potential therapeutic perspectives of leptin replacement therapy and adiponectin upregulation in lipodystrophy.

High Molecular Weight (HMW): total adiponectin ratio is low in hiv-infected women receiving protease inhibitors

Background

At the time of the study, the HIV-treatment policy in South Africa included highly active antiretroviral therapy (HAART) regimens 1 (nucleotide reverse transcriptase inhibitors (NRTIs) only), and 2 (protease inhibitors (PI) and NRTIs). HAART is associated with the lipodystrophy syndrome, insulin resistance and reduced total adiponectin (TA) levels. The high molecular weight (HMW):TA ratio is a superior marker of insulin resistance. The aim of this study was to establish whether HMW:TA ratios are low in patients on PIs and whether they correlate with insulin resistance.

Methods

This was a cross-sectional study undertaken in an antiretroviral clinic at a tertiary hospital. The participants were 66 HIV-infected females: 22 were on regimen 2 (PI group), 22 on regimen 1 (non-PI) and 22 treatment naïve (TN), matched for BMI and age. Patients with a history of diabetes or impaired glucose tolerance were excluded. Serum adiponectin multimers were analysed using the AlpcoTM Adiponectin (Multimeric) enzyme immunoassay. Waist hip ratios (WHR), glucose and insulin levels were assessed, and HOMA-IR and QUICKI calculated. Data were analysed non-parametrically and multivariate analysis was performed.

Results

TA and HMW levels were lower in the treatment groups than in the TN group. HMW:TA was lower in the PI than in the non-PI and TN groups, and in the non-PI than in the TN groups. HMW:TA correlated negatively with waist, insulin and HOMA-IR, independently of BMI and duration of therapy. HOMA-IR and QUICKI did not differ among the groups.

Conclusion

HMW:TA is significantly decreased with HAART (particularly with PIs, but also with non-PIs) and may be a more sensitive marker of insulin resistance in these patients than conventional markers or HMW and total adiponectin individually.

Intravenous fish oil lipid emulsion promotes a shift toward anti-inflammatory proresolving lipid mediators

Parenteral nutrition (PN)-associated liver disease (PNALD) is a life-threatening complication of the administration of PN. The development of PNALD may be partly due to the composition of the lipid emulsion administered with PN: soybean oil-based lipid emulsions (SOLE) are associated with liver disease, while fish oil-based lipid emulsions (FOLE) are associated with prevention and improvement of liver disease. The objective of this study was to determine how the choice of lipid emulsion modified the production of bioactive lipid mediators (LMs). We utilized a mouse model of steatosis to study the differential effect of FOLE and SOLE. We subsequently validated these results in serum samples from a small cohort of human infants transitioning from SOLE to FOLE. In mice, FOLE was associated with production of anti-inflammatory, proresolving LMs; SOLE was associated with increased production of inflammatory LMs. In human infants, the transition from SOLE to FOLE was associated with a shift toward a proresolving lipidome. Together, these results demonstrate that the composition of the lipid emulsion directly modifies inflammatory homeostasis.

Pathophysiology of the HIV-Associated Lipodystrophy Syndrome

The widespread use of highly active antiretroviral therapy (HAART) has radically transformed the prognosis of HIV-infected patients in the developed countries. Unfortunately, a serious metabolic syndrome combining peripheral lipoatrohy, central adiposity, insulin resistance, and dyslipidemia has arisen in these individuals. The etiology of this heterogeneous syndrome named lipodystrophy syndrome (LDS) is multifactorial, but adipose tissue is very likely a key factor that contributes to several clinical or metabolic aspects of the syndrome. In peripheral adipose tissue, HAART may act on both preadipocytes and adipocytes to induce fat loss. Several components of the HAART regimen can inhibit preadipocyte differentiation, in particular through alterations in the expression and/or function of the transcription factor sterol responsive element binding protein-1c. In superficial mature adipocytes, HAART promotes insulin resistance and apoptosis. Insulin resistance of peripheral fat cells could be the consequence of increased lipolysis and adipocytokine dysregulation. In turn, the increased free fatty acid disposal and the disturbances in adipocytokine production may induce skeletal muscle and liver insulin resistance, dyslipidemia, and a fat redistribution toward deep depots, causing visceral lipohypertrophy. The metabolic profile observed in LDS is reminiscent of that observed in metabolic syndrome, raising potential implications for cardiovascular risk in these patients. The pathophysiological mechanisms at the basis of this syndrome represent a rational basis for the treatment or prevention of the metabolic complications.

Adiponectin and PPARγ: cooperative and interdependent actions of two key regulators of metabolism

The recent advances in the understanding of adiponectin and other adipokines have highlighted the role of adipose tissue as an active endocrine organ. One of the central regulators of adipocyte biology is peroxisome proliferator-activated receptor gamma (PPARγ), a transcription factor that induces the adipogenic gene expression program during development, promotes adipose remodeling, and regulates the functions of adipocytes in lipid storage, adipokine secretion, and energy homeostasis. Activation of PPARγ results in increased insulin sensitivity in skeletal muscle and liver and improves the secretory profile of adipose tissue, favoring release of insulin-sensitizing adipokines, such as adiponectin, and reducing inflammatory cytokines. Increased adiponectin production is likely a significant mediator of the systemic effects of PPARγ activation. This chapter will review the interplay between PPARγ and adiponectin in regulating metabolism, presenting evidence that PPARγ regulates adiponectin gene expression, processing, and secretion and that the two proteins have overlapping effects on downstream metabolic pathways.

Effects of rosiglitazone on abnormal lipid kinetics in HIV-associated dyslipidemic lipodystrophy: a stable isotope study

HIV-associated dyslipemic lipodystrophy (HADL) is a heterogeneous syndrome of fat redistribution, hypertriglyceridemia, and insulin resistance, associated with markedly accelerated rates of lipolysis, intraadipocyte and intrahepatic reesterification, and very low-density lipoprotein-triglyceride synthesis and release. The objective of the study was to determine if rosiglitazone can ameliorate these lipid kinetic defects in patients with HADL. Infusions of [(13)C(1)]palmitate and [(2)H(5)]glycerol were used to measure total and net lipolysis, adipocyte and hepatic reesterification, and plasma free fatty acid (FFA) oxidation in 9 men with HADL, before and after 3 months of treatment with rosiglitazone (8 mg/d). Rosiglitazone treatment significantly increased both total lipolysis (R(a) FFA(total) from 3.37 ± 0.40 to 4.57 ± 0.68 mmol FFA per kilogram fat per hour, P < .05) and adipocyte reesterification (1.25 ± 0.35 to 2.43 ± 0.65 mmol FFA per kilogram fat per hour, P < .05). However, there was no change in net lipolysis (R(a) FFA(net) 2.47 ± 0.43 to 2.42 ± 0.37 mmol FFA per kilogram fat per hour), plasma FFA oxidation (0.30 ± 0.046 to 0.32 ± 0.04 mmol FFA per kilogram lean body mass per hour), or FFA flux available for hepatic reesterification (0.59 ± 0.07 to 0.56 ± 0.10 mmol FFA per kilogram fat per hour). There were significant decreases in fasting plasma insulin concentrations and insulin resistance, but not in fasting plasma lipid or glucose concentrations. There was a significant decrease in waist to hip ratio (0.98 ± 0.02 to 0.95 ± 0.02, P < .05) consistent with a significant increase in hip circumference (0.93 ± 0.02 to 0.95 ± 0.02 m, P < .05), without change in waist circumference. Rosiglitazone significantly increased adipocyte reesterification and improved insulin sensitivity, but the potential benefit of these changes was compromised by increase in total lipolysis. Combining rosiglitazone with agents designed to blunt lipolysis could expand depleted peripheral adipose depots in patients with HIV lipodystrophy.

Rosiglitazone-Mediated Effects on Skeletal Muscle Gene Expression Correlate with Improvements in Insulin Sensitivity in Individuals with HIV-Insulin Resistance

Rosiglitazone, an agonist of peroxisome proliferator activated receptor (PPARγ), improves insulin sensitivity by increasing insulin-stimulated glucose uptake into muscle tissue. This study was undertaken to assess changes in expression of PPAR-regulated genes in muscle tissue following treatment of HIV-associated insulin resistance with rosiglitazone. Muscle gene expression was assessed in twenty-two seronegative HIV subjects (control), 21 HIV-infected individuals with normal insulin sensitivity (HIV-IS) and 19 HIV-infected individuals with insulin resistance (HIV-IR). A subset of the HIV-IR group (N=10) were re-evaluated 12 weeks after treatment with 8 mg/d of rosiglitazone. The HIV-IR group's rosiglitazone-mediated improvement in insulin sensitivity was highly correlated with increased expression of PPARγ and carnitine palmitoyl transferase-1 (CPT-1), (r=0.87, P<.001) and (r=0.95, P<.001), respectively. The changes in PPARγ expression were also correlated with the changes in CPT1 expression (r=0.75, P=.009). The results suggest that rosiglitazone; may have a direct effect on muscle tissue to improve insulin sensitivity.

Exercise training augments the peripheral insulin-sensitizing effects of pioglitazone in HIV-infected adults with insulin resistance and central adiposity

The prevalence and incidence of insulin resistance and type 2 diabetes mellitus (DM) are higher in people treated for human immunodeficiency virus-1 (HIV) infection than in the general population. Identifying safe and effective interventions is a high priority. We evaluated whether the peroxisome proliferator-activated receptor-γ agonist pioglitazone with exercise training improves central and peripheral insulin sensitivity more than pioglitazone alone in HIV-infected adults with insulin resistance and central adiposity. Forty-four HIV-infected adults with baseline insulin resistance and central adiposity were randomly assigned to 4 mo of pioglitazone (30 mg/day) with or without supervised, progressive aerobic, and resistance exercise training (1.5-2 h/day, 3 days/wk). The hyperinsulinemic euglycemic clamp was used to evaluate alterations in central and peripheral insulin sensitivity. Thirty-nine participants completed the study. Hepatic insulin sensitivity improved similarly in both groups. Exercise training augmented the beneficial effects of pioglitazone on peripheral insulin sensitivity. Greater improvements in peripheral insulin sensitivity were associated with reductions in total body and limb adipose content rather than increases in limb adiposity or pioglitazone-induced increases in adiponectin concentration. We conclude that supplementing pioglitazone with increased physical activity improved insulin sensitivity more effectively than pioglitazone alone in HIV-infected adults with insulin resistance and central adiposity. Pioglitazone alone did not significantly increase limb adipose content. Potential cardiovascular benefits of these interventions in HIV need investigation.

Adipokine expression and secretion by canine adipocytes: stimulation of inflammatory adipokine production by LPS and TNFalpha

Adiposity and obesity are increasing in dogs. We have examined here the endocrine function of canine adipose tissue and the regulation of production of inflammation-related adipokines by dog adipocytes. Adiponectin, leptin, IL-6, MCP-1 and TNFalpha genes were expressed in the main adipose depots of dogs, but there were no major depot differences in mRNA levels. Each adipokine was expressed in canine adipocytes differentiated in culture and secreted into the medium (leptin undetected). IL-6, MCP-1 and TNFalpha were also expressed and secreted by preadipocytes; adiponectin and leptin were only expressed after adipocyte differentiation. The inflammatory mediators LPS and TNFalpha had major stimulatory effects on the expression and secretion of IL-6, MCP-1 and TNFalpha; there was a >5,000-fold increase in IL-6 mRNA level with LPS. IL-6 release into the medium was increased >50-fold over 24 h with LPS and TNFalpha, while MCP-1 release was increased 23- and 40-fold by TNFalpha and LPS, respectively. However, there was no effect, or small reductions, in adiponectin and leptin mRNA levels with the inflammatory mediators. Dexamethasone-stimulated leptin gene expression, had no effect on adiponectin expression, but decreased the expression and secretion of IL-6 and MCP-1. The PPARgamma agonist rosiglitazone stimulated both adiponectin and leptin expression and inhibited the expression of IL-6, MCP-1 and TNFalpha; MCP-1 secretion was reduced. These results demonstrate that canine adipocytes express and secrete key adipokines and show that adipocytes of this species are highly responsive to inflammatory mediators with the induction of major increases in the production of inflammation-related adipokines.

Selective effects of PPARgamma agonists and antagonists on human pre-adipocyte differentiation

AIM

The insulin sensitizer rosiglitazone (RTZ) acts by activating peroxisome proliferator and activated receptor gamma (PPAR gamma), an effect accompanied in vivo in humans by an increase in fat storage. We hypothesized that this effect concerns PPARgamma(1) and PPARgamma(2) differently and is dependant on the origin of the adipose cells (subcutaneous or visceral). To this aim, the effect of RTZ, the PPARgamma antagonist GW9662 and lentiviral vectors expressing interfering RNA were evaluated on human pre-adipocyte models.

METHODS

Two models were investigated: the human pre-adipose cell line Chub-S7 and primary pre-adipocytes derived from subcutaneous and visceral biopsies of adipose tissue (AT) obtained from obese patients. Cells were used to perform oil-red O staining, gene expression measurements and lentiviral infections.

RESULTS

In both models, RTZ was found to stimulate the differentiation of pre-adipocytes into mature cells. This was accompanied by significant increases in both the PPARgamma(1) and PPARgamma(2) gene expression, with a relatively stronger stimulation of PPARgamma(2). In contrast, RTZ failed to stimulate differentiation processes when cells were incubated in the presence of GW9662. This effect was similar to the effect observed using interfering RNA against PPARgamma(2). It was accompanied by an abrogation of the RTZ-induced PPARgamma(2) gene expression, whereas the level of PPARgamma(1) was not affected.

CONCLUSIONS

Both the GW9662 treatment and interfering RNA against PPARgamma(2) are able to abrogate RTZ-induced differentiation without a significant change of PPARgamma(1) gene expression. These results are consistent with previous results obtained in animal models and suggest that in humans PPARgamma(2) may also be the key isoform involved in fat storage.

Adipocyte dysfunction in response to antiretroviral therapy: clinical, tissue and in-vitro studies

PURPOSE OF REVIEW

Lipodystrophy, a major complication of antiretroviral therapy, is an adipose tissue disease involving severe alterations of fat tissue distribution and metabolic functions. Protease inhibitors and nucleoside reverse transcriptase inhibitors (NRTIs) are implicated to different extents. We review recent findings on the toxicity of HIV antiretroviral drugs at the fat cell and tissue levels and point out the underlying pathophysiological mechanisms.

RECENT FINDINGS

Peripheral fat loss and central accumulation are distinct phenomena. Lipoatrophy is the dominant feature after prolonged treatment. Protease inhibitors and NRTIs promote fat tissue disease by separate mechanisms that converge and worsen adipocyte dysfunctions. The pathogenesis involves the mitochondrial toxicity of NRTIs and the adverse effects of protease inhibitors and NRTIs on adipocyte differentiation status, insulin sensitivity, survival and adipokine secretion. Oxidative stress and local inflammation induced by these drugs may participate in the setup of lipodystrophy. Partial and slow reversion can be obtained by switch strategies or drug therapy.

SUMMARY

Patients using antiviral therapy develop severe fat tissue damage. The toxicity of protease inhibitors and NRTIs remains an important issue for patients and clinicians. Since fat tissue regeneration is difficult, it is important to understand the mechanisms by which these drugs alter fat tissue depots.

Thiazolidinediones and the liver in humans

PURPOSE OF REVIEW

To review recent advances in the understanding of the mechanism of action of thiazolidinediones (TZDs) in humans.

RECENT FINDINGS

The liver is characterized by excess fat accumulation due to nonalcoholic causes (non-alcoholic fatty liver disease) in most patients with the metabolic syndrome and type 2 diabetes. Simple steatosis can progress to nonalcoholic steatohepatitis (NASH) and cirrhosis. Both of the commercially available antihyperglycemic TZD agonists, pioglitazone and rosiglitazone, are markedly effective in reducing liver fat content by 30-50% and sensitizing the liver to insulin. This reduces the amount of endogenous and exogenous insulin needed to inhibit hepatic glucose production. Decreases in liver fat are closely correlated with increases in serum adiponectin, which is an insulin-sensitizing adipokine produced exclusively by adipose tissue. Both TZDs are equally effective in reducing liver fat. Regarding lipid metabolism, enhanced hepatic insulin sensitivity would be predicted to lower VLDL and serum triglycerides and increase HDL-cholesterol. Pioglitazone and rosiglitazone have different effects on serum lipids, which cannot be attributed to simple insulin sensitization. Very recently, TZDs have been shown to reduce not only steatosis but possibly also hepatocellular damage in NASH.

SUMMARY

Given the uncertainties in benefits of TZDs in reducing cardiovascular disease in type 2 diabetes, as well as other side-effects (heart failure, fractures), TZDs may in the future be increasingly used in patients with nonalcoholic steatohepatitis.

A rosiglitazone-induced increase in adiponectin does not improve glucose metabolism in HIV-infected patients with overt lipoatrophy

HIV-infected patients on antiretroviral therapy frequently develop changes in body fat distribution and disturbances in glucose metabolism, associated with reduced adiponectin levels. Because adiponectin, principally the high-molecular-weight (HMW) form, has insulin-sensitizing properties, we investigated the effects of an increase in adiponectin on glucose metabolism in HIV-lipodystrophy. In this randomized, double-blind, placebo-controlled trial, we included HIV-1-infected patients with severe lipoatrophy, with an undetectable viral load and who had received neither protease inhibitors nor stavudine for ≥6 mo. Patients were randomized to rosiglitazone [8 mg daily (n = 8)] to increase adiponectin levels or placebo (n = 5) for 16 wk. Peripheral glucose disposal, glucose production, and lipolysis were measured after an overnight fast and during a hyperinsulinemic-euglycemic clamp using stable isotopes. Body composition was assessed by computed tomography and dual-energy X-ray absorptiometry. Although body fat distribution was unaffected, rosiglitazone increased total plasma adiponectin levels by 107% (P < 0.02) and the ratio of HMW to total adiponectin by 73% (P < 0.001). In the placebo group, neither total adiponectin levels (P = 0.62) nor the ratio of HMW to total adiponectin changed (P = 0.94). The marked increase in adiponectin induced by rosiglitazone was not associated with significant changes in basal endogenous glucose production (P = 0.90), basal lipolysis (P = 0.90), insulin-mediated suppression of glucose production (P = 0.17) and lipolysis (P = 0.54) nor with changes in peripheral glucose disposal (P = 0.13). Acknowledging the limited statistical power of our small study, these findings, if confirmed by larger studies, could question the importance of adiponectin in regulating glucose metabolism in HIV-lipodystrophy.

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.

The effects of Thiazolidinediones on metabolic complications and Lipodystrophy in HIV-infected patients

Highly active antiretroviral therapy (HAART)-associated metabolic complications include lipoatrophy (loss of subcutaneous adipose tissue (SAT)) and insulin resistance. Thiazolidinediones are insulin-sensitizing antidiabetic agents which-as an untoward side effect in obese diabetic patients-increase SAT. Furthermore, troglitazone has improved lipoatrophy and glycemic control in non-HIV patients with various forms of lipodystrophy. These data have led to 14 clinical trials to examine whether thiazolidinediones could be useful in the treatment of HAART-associated metabolic complications. The results of these studies indicate very modest, if any, effect on lipoatrophic SAT, probably due to ongoing HAART negating the beneficial effect. The benefit might be more prominent in patients not taking thymidine analoges. Despite the poor effect on lipoatrophy, thiazolidin-ediones improved insulin sensitivity. However, especially rosiglitazone induced harmful effects on blood lipids. Current data do not provide evidence for the use of thiazolidinediones in the treatment of HAART-associated lipoatrophy, but treatment of lipoatrophy-associated diabetes may be warranted. The role of thiazolidinediones for novel indications, such as hepatosteatosis, should be studied in these patients.

Treatment of altered body composition in HIV-associated lipodystrophy: comparison of rosiglitazone, pravastatin, and recombinant human growth hormone

PURPOSE

Treatment options for HIV-associated lipodystrophy syndrome (HALS) remain limited. The objective of this randomized open-label study was to compare three emerging therapies, rosiglitazone, pravastatin, and growth hormone alone and together, in men and women with HALS.

METHOD

Sixty-four subjects received daily rosiglitazone (4 mg, n = 14), pravastatin (40 mg, n = 11), or rosiglitazone plus pravastatin (n = 13) for 48 weeks or recombinant human growth hormone (rhGH; Serostim 2 mg, 12 weeks, n = 13) alone or combined with rosiglitazone (n = 13). Primary endpoint was body composition change by dual X-ray absorptiometry (DXA) and computed tomography (CT).

RESULTS

Rosiglitazone resulted in slow accrual of limb fat detected by DXA (+444 +/- 186 g; p < .05) but not CT. Pravastatin had no consistent significant effects on body composition, although it reduced total and LDL cholesterol. Negative interactions were observed between pravastatin and rosiglitazone. rhGH reduced abdominal fat by CT (-31 +/- 15 cm2, 26%; p < .05) and DXA (-1597 +/- 383 g, 27%; p < .05) and increased trunk and limb lean mass (+10% and +12%, respectively). However, effects largely disappeared within 12 weeks post treatment. rhGH alone impaired insulin sensitivity but not when combined with rosiglitazone.

CONCLUSION

Prolonged rosiglitazone treatment slowly improves lipoatrophy. rhGH rapidly and selectively reduces visceral fat, although effects are short-lived; co-administered rosiglitazone abrogates rhGH-related insulin resistance.

Adipose tissue inflammation and liver fat in patients with highly active antiretroviral therapy-associated lipodystrophy

In this cross-sectional study, we sought to determine whether gene expression of macrophage markers and inflammatory chemokines in lipoatrophic subcutaneous abdominal adipose tissue and liver fat content are increased and interrelated in human immunodeficiency virus (HIV)-1-positive, highly active antiretroviral therapy (HAART)-treated patients with lipodystrophy (HAART+LD+; n = 27) compared with those without (HAART+LD-; n = 13). The study groups were comparable with respect to age, gender, and body mass index. The HAART+LD+ group had twofold more intra-abdominal (P = 0.01) and 1.5-fold less subcutaneous (P = 0.091) fat than the HAART+LD- group. As we have reported previously, liver fat was 10-fold higher in the HAART+LD+ compared with the HAART+LD- group (P = 0.00003). Inflammatory gene expression was increased in HAART-lipodystrophy: CD68 4.5-fold (P = 0.000013), tumor necrosis factor (TNF)-alpha 2-fold (P = 0.0094), chemokine (C-C motif) ligand (CCL) 2 2.5-fold (P = 0.0024), CCL3 7-fold (P = 0.0000017), integrin alphaM (ITGAM) 3-fold (P = 0.00067), epidermal growth factor-like module containing, mucin-like, hormone receptor-like (EMR)1 2.5-fold (P = 0.0038), and a disintegrin and metalloproteinase domain (ADAM)8 3.5-fold (P = 0.00057) higher in the HAART+LD+ compared with the HAART+LD- group. mRNA concentration of CD68 (r = 0.37, P = 0.019), ITGAM (r = 0.35, P = 0.025), CCL2 (r = 0.39, P = 0.012), and CCL3 (r = 0.54, P = 0.0003) correlated with liver fat content. In conclusion, gene expression of markers of macrophage infiltration and adipose tissue inflammation is increased in lipoatrophic subcutaneous abdominal adipose tissue of patients with HAART-associated lipodystrophy compared with those without. CD68, ITGAM, CCL2, and CCL3 expression is significantly associated with accumulation of liver fat.

Insulin regulation of MCP-1 in human adipose tissue of obese and lean women

CCL2 (MCP-1, monocyte chemoattractant protein 1) and CCL3 (MIP-1alpha, macrophage inflammatory protein 1alpha) are required for macrophage infiltration in adipose tissue. Insulin increases CCL2 expression in adipose tissue and in serum more in insulin-resistant obese than in insulin-sensitive lean mice, but whether this is true in humans is unknown. We compared basal expression and insulin regulation of CCL2 and CCL3 in adipose tissue and MCP-1 and MIP-1alpha in serum between insulin-resistant and insulin-sensitive human subjects. Subcutaneous adipose tissue biopsies and blood samples were obtained before and at the end of 6 h of in vivo euglycemic hyperinsulinemia (maintained by the insulin clamp technique) in 11 lean insulin-sensitive and 10 obese insulin-resistant women, and before and after a 6-h saline infusion in 8 women. Adipose tissue mRNA concentrations of monocyte/macrophage markers CD68, EMR1, ITGAM, ADAM8, chemokines CCL2 and CCL3, and housekeeping gene ribosomal protein large P0 (RPLP0) were measured by means of real-time PCR at baseline. In addition, mRNA concentrations of CCL2, CCL3, and RPLP0 were measured after insulin infusion. Levels of MCP-1 and MIP-1alpha were determined in serum, and protein concentration of MCP-1 was determined in adipose tissue at baseline and after insulin infusion. Basally, expression of the macrophage markers CD68 and EMR1 were increased in adipose tissue of insulin-resistant subjects. Insulin increased MCP-1 gene and protein expression significantly more in the insulin-resistant than in the insulin-sensitive subjects. Basally expression of CCL2 and CCL3 and expression of macrophage markers CD68 and ITGAM were significantly correlated. In serum, MCP-1 decreased significantly in insulin-sensitive but not insulin-resistant subjects. MIP-1alpha was undetectable in serum. Insulin regulation of CCL2 differs between insulin-sensitive and -resistant subjects in a direction that could exacerbate adipose tissue inflammation.

The IL-6 system in HIV-1-infection and in HAART-related fat redistribution syndromes

We determined the IL-6 -174 G>C single nucleotide polymorphism, IL-6 mRNA expression in subcutaneous adipose tissue (SAT) and IL-6 plasma levels in HIV-1-infected patients with and without lipodystrophy and uninfected controls. HIV-1-infected patients had a greater prevalence of the IL-6 -174 C/C genotype and the C allele, higher SAT IL-6 mRNA expression and plasma IL-6 levels than controls. The IL-6 -174 G>C genotype distribution and allele frequencies, SAT IL-6 mRNA expression and IL-6 plasma levels were non-significantly different between HIV-1-infected patients with and without lipodystrophy.

HIV lipodystrophy and its metabolic consequences: implications for clinical practice

BACKGROUND

The introduction of highly active antiretroviral therapy (HAART) around 1996 markedly reduced mortality and morbidity from human immunodeficiency virus (HIV) infection. As life expectancy has improved, the chronic complications of HIV and HAART have become increasingly relevant.

SCOPE

This article provides an overview of the HIV-associated lipodystrophy, its pathogenesis and its clinical consequences (based on a search strategy in PubMed including literature published to November 2007).

FINDINGS

Lipodystrophy syndrome is characterized by abnormal fat distribution syndrome associated with metabolic disturbances and includes insulin resistance, deranged glucose and lipid metabolism. It is associated with increased risks of progression to type 2 diabetes and cardiovascular disease. Robust diagnostic criteria are required for lipodystrophy, and subsequent prospective cohort studies and randomized controlled trials are then required to determine the etiology and prognosis of lipodystrophy, and to evaluate therapeutic interventions for this consequence of HAART. Therapies to improve insulin resistance have been tried but they are frequently ineffective, and are limited by potential toxicity in this population. Hence, current management options for HIV associated lipodystrophy are limited and are mostly based on avoidance of risk factors and switching of antiretroviral drugs.

CONCLUSION

As the '3 by 5 strategy' of providing HIV drugs to the developing world is implemented worldwide, the numbers of patients adhering to antiretroviral medicines is dramatically increasing. One must be aware that in reducing the burden of acute retroviral disease, the treatments proposed might lead to significant rates of metabolic complications and further exacerbation of the epidemic of diabetes and cardiovascular disease.

Genes involved in fatty acid partitioning and binding, lipolysis, monocyte/macrophage recruitment, and inflammation are overexpressed in the human fatty liver of insulin-resistant subjects

OBJECTIVE

The objective of this study is to quantitate expression of genes possibly contributing to insulin resistance and fat deposition in the human liver.

RESEARCH DESIGN AND METHODS

A total of 24 subjects who had varying amounts of histologically determined fat in the liver ranging from normal (n = 8) to steatosis due to a nonalcoholic fatty liver (NAFL) (n = 16) were studied. The mRNA concentrations of 21 candidate genes associated with fatty acid metabolism, inflammation, and insulin sensitivity were quantitated in liver biopsies using real-time PCR. In addition, the subjects were characterized with respect to body composition and circulating markers of insulin sensitivity.

RESULTS

The following genes were significantly upregulated in NAFL: peroxisome proliferator-activated receptor (PPAR) gamma 2 (2.8-fold), the monocyte-attracting chemokine CCL2 (monocyte chemoattractant protein [MCP]-1, 1.8-fold), and four genes associated with fatty acid metabolism (acyl-CoA synthetase long-chain family member 4 [ACSL4] [2.8-fold], fatty acid binding protein [FABP]4 [3.9-fold], FABP5 [2.5-fold], and lipoprotein lipase [LPL] [3.6-fold]). PPARgamma coactivator 1 (PGC1) was significantly lower in subjects with NAFL than in those without. Genes significantly associated with obesity included nine genes: plasminogen activator inhibitor 1, PPARgamma, PPARdelta, MCP-1, CCL3 (macrophage inflammatory protein [MIP]-1 alpha), PPAR gamma 2, carnitine palmitoyltransferase (CPT1A), FABP4, and FABP5. The following parameters were associated with liver fat independent of obesity: serum adiponectin, insulin, C-peptide, and HDL cholesterol concentrations and the mRNA concentrations of MCP-1, MIP-1 alpha, ACSL4, FABP4, FABP5, and LPL.

CONCLUSIONS

Genes involved in fatty acid partitioning and binding, lipolysis, and monocyte/macrophage recruitment and inflammation are overexpressed in the human fatty liver.

Adiponectin in health and disease

Adipose tissue is an active metabolic tissue that secretes multiple metabolically important proteins, known as adipokines. Adiponectin is an important adipokine because of its beneficial effects on glucose and lipid metabolism. Low levels of adiponectin are associated with disease states such as diabetes and cardiovascular disease. Direct administration of adiponectin has been shown to be beneficial in animal models of diabetes, obesity and atherosclerosis. Adiponectin levels in humans can be increased through indirect methods such as weight loss or treatment with thiazolidinediones. This article will review the epidemiology and therapeutic options with adiponectin.

Increased expression of the macrophage markers and of 11beta-HSD-1 in subcutaneous adipose tissue, but not in cultured monocyte-derived macrophages, is associated with liver fat in human obesity

OBJECTIVE

To determine whether increased expression of macrophage markers and of inflammatory markers in subcutaneous adipose tissue is associated with liver fat in human obesity. We also determined whether expression of TNF (gene encoding TNF-alpha), HSD11B1 (gene encoding 11beta-HSD-1) and RETN (gene encoding resistin) in cultured monocyte-derived macrophages differs between obese/overweight and non-obese subjects.

DESIGN

Cross-sectional comparison of obese/overweight and non-obese subjects with respect to adipose tissue gene expression, gene expression in monocyte-derived macrophages, liver fat content and in vivo insulin sensitivity.

SUBJECTS

Adipose tissue gene expression, gene expression in monocyte-derived macrophages, liver fat content and in vivo insulin sensitivity: 10 healthy non-obese (24.2+/-1.0 kg/m(2)) and 10 healthy obese/overweight (33.1+/-1.7 kg/m(2)) women. Gene expression in monocyte-derived macrophages: seven healthy non-obese (22.1+/-0.7 kg/m(2)) and seven healthy obese/overweight (36.9+/-2.2 kg/m(2)) women.

MEASUREMENTS

Adipose tissue biopsies and blood samples for isolation of peripheral mononuclear cells were taken after an overnight fast. Liver fat content was measured using magnetic resonance proton spectroscopy. Whole body insulin sensitivity was measured using the hyperinsulinemic euglycemic clamp technique. Expression levels of TNF, HSD11B1, RETN and the macrophage markers CD68 and ITGAM were determined by real-time PCR.

RESULTS

In adipose tissue, expression of HSD11B1, ITGAM and CD68 was significantly increased in the obese/overweight as compared to the non-obese group. Expression of all these genes was closely positively correlated with liver fat content and inversely correlated with whole body insulin sensitivity. The associations between expression of CD68, ITGAM and HSD11B1 and liver fat were independent of obesity. There were no differences in TNF, HSD11B1, RETN or CD68 gene expression basally or after stimulation with lipopolysaccharide in monocyte-derived macrophages between obese/overweight and non-obese subjects.

CONCLUSION

Accumulation of fat in the liver is associated with increased adipose tissue inflammation independent of obesity.

Increased resting energy expenditure, fat oxidation, and food intake in patients with highly active antiretroviral therapy-associated lipodystrophy

Highly active antiretroviral therapy (HAART) is associated with metabolic adverse events such as lipodystrophy in human immunodeficiency virus (HIV)-infected patients. The objective of the present study was to evaluate the effects of HAART-associated lipodystrophy on resting energy expenditure and caloric intake. In this cross-sectional study we compared resting energy expenditure (REE) and energy intake in 30 HAART-treated patients with lipodystrophy (HAART+LD+) with 13 HAART-treated patients without lipodystrophy (HAART+LD-). REE was measured using indirect calorimetry, and energy intake was recorded as a 3-day diary of food intake. REE (5,180+/-160 vs. 4,260+/-150 J/min, P<0.01) and also REE expressed per fat-free mass (86+/-1 vs. 78+/-2 J.kg fat-free mass-1.min-1, P<0.01) were significantly higher in the HAART+LD+ than the HAART+LD- group. Rate of lipid oxidation was significantly higher in the HAART+LD+ than the HAART+LD- group. Total energy and fat intakes were significantly increased in the HAART+LD+ compared with the HAART+LD- group. These results imply that HAART-associated lipodystrophy is associated with increased REE and lipid oxidation and with increased caloric and fat intake.

Acquired obesity increases CD68 and tumor necrosis factor-alpha and decreases adiponectin gene expression in adipose tissue: a study in monozygotic twins

CONTEXT

Both acquired and genetic factors regulate adipose tissue function.

OBJECTIVE

We determined whether adipose tissue mRNA expression is regulated by obesity, independently of genetic effects, by studying monozygotic (MZ) twins.

DESIGN

Seventeen healthy pairs of MZ twins aged 24-27 yr (body mass index 20.0-33.9 kg/m(2), intrapair differences in body weight 0.1-24.7 kg), were identified from the population-based FinnTwin16 cohort. Body fat percent was determined by dual-energy x-ray absorptiometry, sc and intraabdominal fat by magnetic resonance imaging, liver fat by proton spectroscopy, and insulin sensitivity by using the euglycemic insulin clamp technique. Adipocyte cell size and expression of 10 genes (real-time PCR) were determined in sc adipose tissue biopsies. Serum levels of some of the genes were measured using ELISA.

RESULTS

Within MZ twin pairs, acquired obesity was significantly related to increased adipocyte size and increased adipose tissue mRNA expressions of leptin, TNFalpha and the macrophage marker CD68, and decreased mRNA expressions of adiponectin and peroxisome proliferator-activated receptor-gamma. Intrapair differences in liver fat correlated directly with those in leptin and CD68 expression. CD68 expression and serum TNFalpha concentrations were correlated with insulin resistance.

CONCLUSIONS

Acquired obesity independent of genetic influences is able to increase expression of macrophage and inflammatory markers and decrease adiponectin expression in adipose tissue.

Nuclear receptors in lipid metabolism: targeting the heart of dyslipidemia

Dyslipidemia is the sine qua non of atherosclerosis, but it is also strongly associated with the metabolic syndrome, obesity, diabetes, and fatty liver disease. The molecular basis for future therapies requires understanding the pivotal role of nuclear hormone receptors in lipid and inflammatory homeostasis. This review summarizes evidence that the liver X receptor (LXR) and peroxisome proliferator-activated receptor (PPAR) are key transcriptional regulators in lipid metabolism. Additionally, their effects on glucose homeostasis and inflammation make LXR and PPAR signaling networks attractive molecular targets for managing lipid-related diseases.

Effect of pravastatin on body composition and markers of cardiovascular disease in HIV-infected men--a randomized, placebo-controlled study

OBJECTIVES

To determine the effect of the 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitor, pravastatin, on markers of cardiovascular risk and lipodystrophy in HIV-infected, protease inhibitor (PI)-treated men with hypercholesterolaemia.

METHODS

A randomized, placebo-controlled, 16-week study was carried out on 33 HIV-infected, hypercholesterolaemic men (fasting total cholesterol > 6.5 mmol/L) on PI-containing therapy. Patients commenced dietary assessment and advice at week 0 and were randomized to 12 weeks pravastatin (40 mg each night) or placebo from week 4. The primary endpoint was the time-weighted change (TWAUC) in total cholesterol from week 0. Secondary endpoints included TWAUC cholesterol from week 4 (start of pravastatin), total and regional body fat, fasting lipids, glucose, insulin, and markers of cardiovascular risk.

RESULTS

Of 33 men randomized (pravastatin n = 16, mean age 48 years), 31 completed the study. Groups were matched for baseline cholesterol and body composition. Although there was no significant between-group difference in TWAUC cholesterol from week 0 (pravastatin -0.6 +/- 1.0 versus placebo -0.4 +/- 1.0 mmol/L/week; P = 0.8), TWAUC cholesterol from week 4 decreased more in the pravastatin group (-0.8 +/- 1.0 versus -0.3 +/- 0.9 mmol/L/week; P = 0.04). Neither triglycerides nor dietary intake changed. Subcutaneous fat increased significantly with pravastatin (+0.72 +/- 1.55 versus +0.19 +/- 0.48 kg change in limb fat, P < 0.04; +5.2 +/- 8.7 versus -1.3 +/- 13.7 cm change in abdominal subcutaneous fat, P = 0.02). Apart from homocystine, which decreased in the pravastatin group, there were no significant differences in other cardiovascular, lipid or glucose parameters.

CONCLUSIONS

Despite limited effects on cholesterol, 12 weeks use of pravastatin 40 mg each night in HIV-infected men with hypercholesterolaemia resulted in significant increases in subcutaneous fat.

Meta-analysis of the effect of thiazolidinediones on serum C-reactive protein levels

We conducted a meta-analysis of randomized clinical trials to evaluate the effect of thiazolidinediones on serum C-reactive protein levels. Compared with placebo, treatment with thiazolidinediones significantly decreased the serum C-reactive protein levels (mean -0.82 mg/L, 95% confidence interval -1.15 to -0.49 mg/L, p <0.0001). In a subgroup analysis, the effect of thiazolidinediones on the serum C-reactive protein levels was more pronounced in diabetic patients (mean -1.24 mg/L, 95% confidence interval -2.15 to -0.32 mg/L, p = 0.008) compared with nondiabetic patients (mean -0.27 mg/L, 95% confidence interval -0.41 to -0.14 mg/L, p <0.0001).

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.

Acute in vivo effects of insulin on gene expression in adipose tissue in insulin-resistant and insulin-sensitive subjects

AIMS/HYPOTHESIS

We determined the response of selected genes to in vivo insulin in adipose tissue in 21 non-diabetic women.

MATERIALS AND METHODS

The women were divided into insulin-sensitive and -resistant groups based on their median whole-body insulin sensitivity (8.7+/-0.4 vs 4.2+/-0.3 mg kg(-1) min(-1) for insulin-sensitive vs -resistant group). Subcutaneous adipose tissue biopsies were obtained before and after 3 and 6 h of i.v. maintained euglycaemic hyperinsulinaemia. Adipose tissue mRNA concentrations of facilitated glucose transporter, member 1 (SLC2A1, previously known as GLUT1), facilitated glucose transporter, member 4 (SLC2A4, previously known as GLUT4), peroxisome proliferator-activated receptor gamma ( PPARG), peroxisome proliferator-activated receptor gamma co-activator 1alpha (PPARGC1A), 11beta-hydroxysteroid dehydrogenase-1 (HSD11B1), TNF, adiponectin (ADIPOQ), IL6 and the macrophage marker CD68 were measured using real-time PCR.

RESULTS

Basal expression of 'insulin-sensitivity genes' SLC2A4 and ADIPOQ was lower while that of 'insulin-resistance genes', HSD11B1 and IL6 was significantly higher in the insulin-resistant than in the insulin-sensitive group. Insulin significantly increased expression of 'insulin-sensitivity genes' SLC2A4, PPARG, PPARGC1A and ADIPOQ in the insulin-sensitive group, while only expression of PPARG and PPARGC1A was increased in the insulin-resistant group. The expression of 'insulin-resistance genes' HSD11B1 and IL6 was increased by insulin in the insulin-resistant group, but insulin failed to increase HSD11B1 expression in the insulin-sensitive group. At 6 h, expression of HSD11B1, TNF and IL6 was significantly higher in the insulin-resistant than in the insulin-sensitive group. IL6 expression increased significantly more in response to insulin in the insulin-resistant than in the insulin-sensitive group. CD68 was overexpressed in the insulin-resistant as compared with the insulin-sensitive group at both 0 and 6 h.

CONCLUSIONS/INTERPRETATION

These data suggest that genes adversely affecting insulin sensitivity hyperrespond to insulin, while genes enhancing insulin sensitivity hyporespond to insulin in insulin-resistant human adipose tissue in vivo.

Arterial Stiffness in HIV-Infected Patients Receiving Highly Active Antiretroviral Therapy

HIV-infected patients receiving highly active antiretroviral therapy (HAART) are at increased risk of cardiovascular events. Reported non-invasive techniques for assessment of blood pressure in this population have been limited to sphygmomanometry. The present cross-sectional study investigated the impact of antiretroviral therapy and the HAART-associated lipodystrophy on aortic blood pressure conditions and arterial stiffness in HAART-treated lipodystrophic ( n=42) and non-lipodys-trophic ( n=17) patients. Pulse wave analysis, novel to this population, was used to evaluate measures of arterial stiffness, including the heart rate corrected augmentation index, AgIHR. Results indicated no significant difference between the study groups in peripheral or aortic blood pressure and AgIHR. Significant correlates of AgIHR included age ( P=0.003), duration of antiretroviral therapy ( P=0.020), lamivudine therapy ( P=0.015) and ritonavir therapy ( P=0.016) as well as cumulative exposure to protease inhibitors ( P=0.030). Time since HIV diagnosis, severity of immunodeficiency or presence of HAART-associated lipodystrophy bore no relationship to AgIHR. In multivariate analysis, duration of antiretroviral therapy ( P=0.046), cumulative exposure to nucleoside reverse transcriptase inhibitors ( P=0.032) and to protease inhibitors ( P=0.011) were identified as independent factors predicting AgIHR. Prolonged antiretroviral treatment, thus, delineates as a risk factor for systemic arterial stiffness and the associated cardiovascular mortality.

HIV antiretroviral treatment alters adipokine expression and insulin sensitivity of adipose tissue in vitro and in vivo

HIV-1-infected patients on antiretroviral therapy frequently develop a lipodystrophy syndrome, characterized by peripheral lipoatrophy and visceral fat redistribution associated with metabolic alterations including dyslipidemia and insulin resistance. Its pathophysiology remains unclear but the antiretroviral treatment, associating protease inhibitors (PIs) and nucleoside analogue inhibitors of the viral reverse transcriptase (NRTIs), plays a major role. Some antiretroviral molecules inhibit differentiation and induce insulin resistance and apoptosis in adipose cells both in vitro and in vivo. In vitro, PIs and NRTIs increase the expression and secretion of pro-inflammatory cytokines such as TNF alpha, IL-6 and L-1beta, which are involved in altered adipocyte functions and decrease that of adiponectin, a positive modulator of insulin sensitivity. Similar alterations are observed in fat and serum from HIV-1-infected lipodystrophic patients under antiviral treatment associating PIs and NRTIs. Altered adipokine secretion could result from patients' exposure to PIs and NRTIs and lead to altered adipocyte differentiation, insulin resistance and apoptosis, ultimately resulting in lipoatrophy. These disorders probably result in a decreased secretion of adiponectin and an increased release of free fatty acids by insulin-resistant adipose tissue. Therefore, they could be involved in whole body insulin resistance and metabolic alterations in lipodystrophic HIV-1-infected patients.

Rosiglitazone up-regulates lipoprotein lipase, hormone-sensitive lipase and uncoupling protein-1, and down-regulates insulin-induced fatty acid synthase gene expression in brown adipocytes of Wistar rats

AIMS/HYPOTHESIS

Although thiazolidinediones are now widely used to treat type 2 diabetes, their mechanism of action remains largely unknown. They are agonists for the transcription factor PPARgamma, and in addition to their insulin-sensitising effects, they can promote adipogenesis and control gene expression in adipose tissues. We have explored the effect of rosiglitazone on insulin-mediated induction of pivotal genes involved in lipid metabolism and thermogenesis in brown fat. The genes studied were: (1) lipoprotein lipase (lpl), which is involved in lipid uptake; (2) hormone-sensitive lipase (hsl), which mobilises fatty acids from stored triglycerides; (3) fatty acid synthase (fas), which regulates de novo lipogenesis; and (4) the uncoupling proteins (ucp) 1 and 3, which control thermogenesis.

METHODS

We used fetal rat primary brown adipocytes cultured with insulin, rosiglitazone or both combined. Then, we studied gene expression by northern and western blotting, as well as 'run-on' and gel-shift assays to identify binding of potential transcription factors to the fas promoter.

RESULTS

Exposure to rosiglitazone for 24 h induced ucp-1, lpl and hsl gene expression and when rosiglitazone was combined with insulin a synergistic effect on lpl and ucp-3 mRNA expression was produced. These effects were consistent with increased LPL and HSL activities as well as respiration rates, mainly in response to exogenous palmitate. In contrast, treatment with rosiglitazone did not alter FAS mRNA basal levels but prevented the induction elicited by insulin in a time- and dose-dependent manner. Correspondingly diminished FAS protein levels and activity, as well as cellular lipid content, were observed, indicating an antilipogenic action of rosiglitazone in brown adipocytes. Furthermore, rosiglitazone impaired insulin increase in the FAS transcription rate by antagonising insulin-induced binding of upstream stimulatory factors to the E-box consensus sequence in the FAS promoter and insulin-induced binding of activating protein-1.

CONCLUSIONS/INTERPRETATION

Rosiglitazone prevents insulin-induced up-regulation of the main lipogenic enzyme but increases the expression of those enzymes involved in lipid uptake and mobilisation, favouring fatty acid utilisation through uncoupled respiration.

Alterations in thigh subcutaneous adipose tissue gene expression in protease inhibitor-based highly active antiretroviral therapy

Use of protease inhibitor (PI)-based highly active antiretroviral therapy (HAART) has been associated with altered regional fat distribution, insulin resistance, and dyslipidemias. To assess how PI-based HAART affects adipocyte gene expression in male HIV-1-infected patients, reverse transcription-polymerase chain reaction was used to quantify messenger RNA expression of adipocyte transcription factors and adipocytokines in thigh and abdominal subcutaneous adipose tissue from male (1) HIV-1 seronegative subjects (control, n = 9), (2) asymptomatic treatment-naive HIV-1-infected patients (naive, n = 6), (3) HIV-1-infected patients who were receiving antiretroviral agents but never received PIs (PI naive, n = 5), (4) HIV-1-infected patients who were receiving PI-based HAART (PI, n = 7), and (5) HIV-1-infected patients who discontinued the PI component of their antiviral therapy more than 6 months before enrollment (past PI, n =7). In the PI group, the messenger RNA expression levels of the CCAAT/enhancer-binding protein alpha , leptin, and adiponectin (18%, P < .01; 23%, P < .05; and 13%, P < .05, respectively) were significantly lower than the levels measured in the PI-naive group. These results are consistent with previous studies on the effects of PIs on cultured adipocytes. Prospective longitudinal studies of thigh fat adipose tissue gene expression could provide further insights on the pathogenesis of metabolic complications associated with PI-based HAART.

Fatty acid transport proteins and insulin resistance

PURPOSE OF REVIEW

Disturbed fatty acid metabolism and homeostasis is associated with insulin resistance. The aim of this review, therefore, is to summarize recent developments relating to the relevance and importance of the fatty acid transport proteins (FATPs) in the aetiology of insulin resistance. In particular, the potential differences between the six members of the FATP family will be considered.

RECENT FINDINGS

FATP1 knockout mice failed to develop insulin resistance associated with lipid infusion or a high-fat diet, as wild-type mice did. FATP1-mediated fatty acid uptake may cause intramuscular lipid accumulation leading to insulin resistance in muscle if the fatty acids are not oxidized. While mouse models demonstrated an absolute requirement for FATP4 for survival, they provided no direct evidence for a role of FATP4 in insulin resistance. However, expression of FATP4 in human adipose tissue was increased in obesity (independent of genetic factors). While other members of the FATP family have important roles in fatty acid metabolism, they have not been clearly linked to insulin resistance. FATP-mediated fatty acid uptake may be driven by intrinsic acyl-CoA synthase activity.

SUMMARY

Any role in the development of insulin resistance is likely to be different for each member of the FATP family. So far, both FATP1 and FATP4 have been associated with parameters related to insulin resistance. Whether increased FATP-mediated fatty acid uptake is beneficial or detrimental may be dependent on the tissue in question and on the subsequent fate of the fatty acids. These issues remain to be resolved.

Methodological Considerations in Human Studies of Gene Expression in HIV-Associated Lipodystrophy

In the majority of cases, HIV-associated lipodystrophy, lipoatrophy in particular, becomes clinically apparent only after months or years of continuous exposure to antiretroviral medications and, once developed, is difficult to reverse. Many lipid-related side effects of antiretroviral medications result from drug-induced changes in gene expression. As our understanding of the pathogenic mechanisms underlying HIV-associated lipodystrophy improves, it is important to be able to explore changes at a molecular level in order to fully elucidate the mechanisms whereby antiretroviral drugs exert their toxicities. Monitoring changes in gene expression in vivo may enable physicians to identify, predict or prevent drug toxicities early, before irreversible changes in body composition occur. However, monitoring changes in gene expression at a population level presents many methodological challenges that need to be addressed, over and above the considerable intra- and inter-individual variability inherent in the cellular expression of any gene. Careful collection and processing of adequate biological samples, robust laboratory processes and assays, and appropriate study design can help overcome many of these difficulties.

Adiponectin--journey from an adipocyte secretory protein to biomarker of the metabolic syndrome

Adiponectin is an adipocyte-derived hormone that was discovered in 1995. Unlike leptin, which was identified around the same time, the clinical relevance of adiponectin remained obscure for a number of years. However, starting in 2001, several studies were published from different laboratories that highlighted the potential antidiabetic, antiatherosclerotic and anti-inflammatory properties of this protein complex. Methods to measure the protein with high throughput assays in clinical samples were developed shortly thereafter, and as a result hundreds of clinical studies have been published over the past 3 years describing the role of adiponectin in endocrine and metabolic dysfunction. Furthermore, adiponectin research has expanded to include a role for adiponectin in cancer and other disease areas. Although it is an impossible task to summarize the findings from all these studies in a single review, we aim to demonstrate the utility of circulating adiponectin as a biomarker of the metabolic syndrome. Evidence for this relationship will include how decreased levels of plasma adiponectin ('hypoadiponectinaemia') are associated with increased body mass index (BMI), decreased insulin sensitivity, less favourable plasma lipid profiles, increased levels of inflammatory markers and increased risk for the development of cardiovascular disease. Therefore, adiponectin levels hold great promise for use in clinical application serving as a potent indicator of underlying metabolic complications.

Fat in the liver and insulin resistance

Insulin resistance in humans is not always accompanied by obesity, since severe insulin resistance also characterizes patients lacking subcutaneous fat such as those with HAART- (highly-active antiretroviral therapy)-associated lipodystrophy. Both obese and lipodystrophic patients, however, have an increase in the amount of fat hidden in the liver. Liver fat content can be accurately quantified non-invasively by proton magnetic resonance spectroscopy. It is closely correlated with fasting insulin concentrations and direct measures of hepatic insulin sensitivity while the amount of subcutaneous adipose tissue is not. An increase in liver fat content has been shown to predict type 2 diabetes, independently of other cardiovascular risk factors. This is easily explained by the fact that the liver, once fatty, overproduces most of the known cardiovascular risk factors such as very low density lipoprotein (VLDL), glucose, C-reactive protein (CRP), plasminogen activator inhibitor-1 (PAI-1), fibrinogen and coagulation factors. The causes of inter-individual variation in liver fat content, independent of obesity, are largely unknown but could involve differences in signals from adipose tissue such as in the amount of adiponectin produced and differences in fat intake. Adiponectin deficiency characterizes both lipodystrophic and obese insulin-resistant individuals, and serum levels correlate with liver fat content. Liver fat content can be decreased by weight loss and by a low as compared to a high fat diet. In addition, treatment of both lipodystrophic and type 2 diabetic patients with peroxisome proliferators activator receptor-gamma (PPARgamma) agonists, but not metformin, decreases liver fat and markedly increases adiponectin levels. The fatty liver may help to explain why some but not all obese individuals are insulin resistant and why even lean individuals may be insulin resistant, and thereby at risk of developing type 2 diabetes and cardiovascular disease.

Antiretroviral Drugs with Adverse Effects on Adipocyte Lipid Metabolism and Survival Alter the Expression and Secretion of Proinflammatory Cytokines and Adiponectin In Vitro

Objective

The lipodystrophy syndrome is a major adverse effect of highly active antiretroviral therapy (HAART), associated with altered circulating levels and adipose tissue mRNA expression of proinflammatory cytokines interleukin-6 (IL-6) and tumour necrosis factor (TNF)α, and adiponectin. Proinflammatory cytokines and adiponectin, which are secreted by adipose tissue, regulate fat metabolism, insulin sensitivity and adipose cell apoptosis. We examined the direct effects of individual antiretrovirals on lipid metabolism and cytokine and adiponectin production by cultured adipocytes.

Methods

Differentiating 3T3-F442A cells and differentiated 3T3-L1 adipocytes were treated for 12 or 4 days, respectively, with protease inhibitors (PIs) indinavir, nelfinavir, amprenavir, lopinavir and ritonavir, or nucleoside reverse transcriptase inhibitors (NRTIs) stavudine and zidovudine, at near-Cmax concentrations. Lipid metabolism was estimated by Oil Red O staining of intracellular lipids, mRNA expression of fatty acid synthase and adipocyte lipid binding protein 2, and insulin activation of lipogenesis. Apoptosis was estimated by flow cytometry. The expression and secretion of proinflammatory cytokines (IL-6, TNFα and IL-1β) and adiponectin were evaluated by real-time reverse transcription PCR and ELISA.

Results

Chronic treatment of 3T3-F442A differentiating adipocytes and differentiated 3T3-L1 adipocytes with PIs and NRTIs reduced lipid accumulation, mRNA expression of lipid markers and insulin-induced lipogenesis. IL-6, TNFα, IL-1β and adiponectin expression and secretion were markedly altered in differentiating 3T3-F442A adipocytes. PIs had either no effect on differentiated 3T3-L1 adipocytes (TNFα expression and secretion) or their effect was less marked than in 3T3-F442A cells. Indinavir and amprenavir did not alter cytokine secretion and expression by mature adipocytes. The effects of stavudine and zidovudine on differentiating and mature adipocytes were similar, despite the difference in treatment procedure. The drugs with the strongest effect on TNFα expression also increased adipocyte apoptosis, in contrast to the drugs that only moderately increased TNFα expression.

Conclusions

These results suggest that increased cytokine and decreased adiponectin secretion and expression induced by some PIs and NRTIs may contribute to the adipose tissue loss (via apoptosis and lipid leakage) and insulin resistance associated with the lipodystrophy syndrome.