Mice with a targeted null mutation of the serotonin 5-HT(2C) receptor gene exhibit hyperphagia that leads to a late-onset obesity. Here we show that oxygen consumption was decreased in fed and fasted obese mutants. No phenotypic differences were observed in uncoupling protein-1 (UCP-1) mRNA levels in brown adipose tissues and UCP-3 mRNA in skeletal muscle. UCP-2 mRNA levels were significantly increased in white adipose tissue (4-fold) and skeletal muscle (47%) in older obese mutant mice, whereas UCP-2 mRNA in liver are significantly increased in both young lean (54% increase) and older obese (52% increase) mutant mice. In contrast, 5-HT(2C) receptor mutants displayed age-dependent decreases in beta 3-adrenergic receptor (beta 3-AR) mRNA levels in white adipose tissue, however, no such changes were observed in brown adipose tissue. These results indicate that a mutation of 5-HT(2C) receptor gene leads to a secondary decrease in beta 3-AR gene expression that is related to enhanced adiposity.

The acute phase response is associated with changes in the hepatic expression of genes involved in lipid metabolism. Nuclear hormone receptors that heterodimerize with retinoid X receptor (RXR), such as thyroid receptors, peroxisome proliferator-activated receptors, and liver X receptors, modulate lipid metabolism. We recently demonstrated that these nuclear hormone receptors are repressed during the acute phase response induced by lipopolysaccharide (LPS), consistent with the known decreases in genes that they regulate. In the present study, we show that LPS significantly decreases farnesoid X receptor (FXR) mRNA in mouse liver as early as 8 h after LPS administration, and this decrease was dose-dependent with the half-maximal effect observed at 0.5 microg/100 g of body weight. Gel-shift experiments demonstrated that DNA binding activity to an FXR response element (IR1) is significantly reduced by LPS treatment. Supershift experiments demonstrated that the shifted protein-DNA complex contains FXR and RXR. Furthermore, the expression of FXR target genes, SHP and apoCII, were significantly reduced by LPS (70 and 60%, respectively). Also, LPS decreases hepatic LRH expression in mouse, which may explain the reduced expression of CYP7A1 in the face of SHP repression. In Hep3B human hepatoma cells, both tumor necrosis factor (TNF) and interleukin-1 (IL-1) significantly decreased FXR mRNA, whereas IL-6 did not have any effect. TNF and IL-1 also decreased the DNA binding activity to an IR1 response element and the expression of SHP and apoCII. Importantly, TNF and IL-1 almost completely blocked the expression of luciferase activity linked to a FXR response element promoter construct transfected into Hep3B cells. Together with our earlier studies on the repression of RXRs, peroxisome proliferator-activated receptors, LXRs, thyroid receptors, constitutive androstane receptor, and pregnane X receptor, these results suggest that decreases in nuclear hormone receptors are major contributors to the decreased gene expression that occurs in the negative acute phase response.

Several of the ATP binding cassette (ABC) transporters have recently been shown to play important roles in reverse cholesterol transport (RCT) and prevention of atherosclerosis. In the liver, ABCG5 and ABCG8 have been proposed to efflux sterols into the bile for excretion. ABCG5 and ABCG8 also limit absorption of dietary cholesterol and plant sterols in the intestine. In macrophages, ABCA1 and ABCG1 mediate cholesterol removal from these cells to HDL. Many of these ABC transporters are regulated by the liver X receptor (LXR). We have previously shown that endotoxin (lipopolysaccharide) down-regulates LXR in rodent liver. In the present study, we examined the in vivo and in vitro regulation of these ABC transporters by endotoxin. We found that endotoxin significantly decreased mRNA levels of ABCG5 and ABCG8 in the liver, but not in the small intestine. When endotoxin or cytokines (tumor necrosis factor and interleukin-1) were incubated with J774 murine macrophages, the mRNA levels of ABCA1 were decreased. This effect was rapid and sustained, and was associated with a reduction in ABCA1 protein levels. Endotoxin and cytokines also decreased ABCG1 mRNA levels in J774 cells. Although LXR is a positive regulator of ABCA1 and ABCG1, we did not observe a reduction in protein levels of LXR or in binding of nuclear proteins to an LXR response element in J774 cells. The decrease in ABCG5 and ABCG8 levels in the liver as well as a reduction in ABCA1 and ABCG1 in macrophages during the host response to infection and inflammation coupled with other previously described changes in the RCT pathway may aggravate atherosclerosis.

Severe sepsis results in the decreased uptake and oxidation of fatty acids in the heart and cardiac failure. Some of the key proteins required for fatty acid uptake and oxidation in the heart have been shown to be downregulated after endotoxin (LPS) administration. The nuclear hormone receptors, peroxisome proliferator-activated receptor (PPAR) and thyroid receptor (TR), which heterodimerize with the retinoid X receptor (RXR), are important regulators of fatty acid metabolism and decrease in the liver after LPS administration. In the present study, we demonstrate that LPS treatment produces a rapid and marked decrease in the mRNA levels of all three RXR isoforms, PPARalpha and PPARdelta, and TRalpha and TRbeta in the heart. Moreover, LPS administration also decreased the expression of the coactivators CREB-binding protein (CBP)/p300, steroid receptor coactivator (SRC)-1, SRC-3, TR-associated protein (TRAP)220, and PPARgamma coactivator (PGC)-1, all of which are required for the transcriptional activity of RXR-PPAR and RXR-TR. In addition, the mRNA levels of the target genes malic enzyme, Spot 14, sarcoplasmic reticulum Ca2+-ATPase, or SERCA2, the VLDL receptor, fatty acyl-CoA synthetase, fatty acid transporter/CD36, carnitine palmitoyltransferase Ibeta, and lipoprotein lipase decrease in the heart after LPS treatment. The decrease in expression of RXRalpha, -beta, and -gamma, PPARalpha and -delta, and TRalpha and -beta, and of the coactivators CBP/p300, SRC-1, SRC-3, TRAP220, and PGC-1 and the genes they regulate, induced by LPS in the heart, could account for the decreased expression of key proteins required for fatty acid oxidation and thereby play an important role in cardiac contractility. These alterations could contribute to the myocardial dysfunction that occurs during sepsis.

BACKGROUND

Some HIV-infected patients develop fat maldistribution with visceral adipose tissue (VAT) accumulation and metabolic abnormalities. No medical treatment is approved by the US Food and Drug Administration to reduce VAT.

METHODS

In this double-blind trial, 245 HIV-infected patients with excess VAT were randomized to receive placebo (PL), recombinant human growth hormone (r-hGH) at a dose of 4 mg daily (DD) or 4 mg on alternate days (AD) for 12 weeks. For weeks 12 to 24, DD patients were rerandomized to PL (DD-PL) or AD (DD-AD), AD patients continued on AD (AD-AD), and PL patients were switched to DD (PL-DD).

RESULTS

From baseline to week 12, VAT decreased significantly compared with PL in DD (-8.6%, P < 0.001) but not in AD (-4.2%, P = 0.052). Trunk-to-limb fat ratio decreased significantly in both (P < 0.001) compared with PL, as did total cholesterol and non-high-density lipoprotein (HDL) cholesterol (-4.5% and -7.5% in DD, -4.3% and -6.2% in AD). At week 24, all groups displayed significant (P < 0.05) reductions in VAT (-5.3% to -9.5%) and trunk fat (-7.8% to -22.8%). DD-AD and AD-AD also displayed significant (P < 0.05) reductions in non-HDL cholesterol.

CONCLUSIONS

These results suggest that r-hGH dosed at 4 mg daily for 12 weeks decreases VAT and cholesterol concentrations in HIV-infected patients with excess VAT. The optimal regimen to sustain these effects awaits determination.

BACKGROUND

Therapy with HIV protease inhibitors (PI) has been shown to worsen glucose and lipid metabolism, but whether these changes are caused by direct drug effects, changes in disease status, or body composition is unclear. Therefore, we tested the effects of the PI combination lopinavir and ritonavir on glucose and lipid metabolism in HIV-negative subjects.

METHODS

A dose of 400 mg lopinavir/100 mg ritonavir was given twice a day to 10 HIV-negative men. Fasting glucose and insulin, lipid and lipoprotein profiles, oral glucose tolerance, insulin sensitivity by euglycemic hyperinsulinemic clamp, and body composition were determined before and after lopinavir/ritonavir treatment for 4 weeks.

RESULTS

On lopinavir/ritonavir, there was an increase in fasting triglyceride (0.89 +/- 0.15 versus 1.63 +/- 0.36 mmol/l; P = 0.007), free fatty acid (FFA; 0.33 +/- 0.04 versus 0.43 +/- 0.06 mmol/l; P = 0.001), and VLDL cholesterol (15.1 +/- 2.6 versus 20 +/- 3.3 mg/dl; P = 0.05) levels. There were no changes in fasting LDL, HDL, IDL, lipoprotein (a), or total cholesterol levels. Fasting glucose, insulin, and insulin-mediated glucose disposal were unchanged, but on a 2 h oral glucose tolerance test glucose and insulin increased. There were no changes in weight, body fat, or abdominal adipose tissue by computed tomography.

CONCLUSION

Treatment with 4 weeks of lopinavir/ritonavir in HIV-negative men causes an increase in triglyceride levels, VLDL cholesterol, and FFA levels. Lopinavir/ritonavir leads to a deterioration in glucose tolerance at 2 h, but there is no significant change in insulin-mediated glucose disposal rate by euglycemic hyperinsulinemic clamp.

Infection and inflammation induce the acute-phase response (APR), leading to multiple alterations in lipid and lipoprotein metabolism. Plasma triglyceride levels increase from increased VLDL secretion as a result of adipose tissue lipolysis, increased de novo hepatic fatty acid synthesis, and suppression of fatty acid oxidation. With more severe infection, VLDL clearance decreases secondary to decreased lipoprotein lipase and apolipoprotein E in VLDL. In rodents, hypercholesterolemia occurs attributable to increased hepatic cholesterol synthesis and decreased LDL clearance, conversion of cholesterol to bile acids, and secretion of cholesterol into the bile. Marked alterations in proteins important in HDL metabolism lead to decreased reverse cholesterol transport and increased cholesterol delivery to immune cells. Oxidation of LDL and VLDL increases, whereas HDL becomes a proinflammatory molecule. Lipoproteins become enriched in ceramide, glucosylceramide, and sphingomyelin, enhancing uptake by macrophages. Thus, many of the changes in lipoproteins are proatherogenic. The molecular mechanisms underlying the decrease in many of the proteins during the APR involve coordinated decreases in several nuclear hormone receptors, including peroxisome proliferator-activated receptor, liver X receptor, farnesoid X receptor, and retinoid X receptor. APR-induced alterations initially protect the host from the harmful effects of bacteria, viruses, and parasites. However, if prolonged, these changes in the structure and function of lipoproteins will contribute to atherogenesis.

The acute-phase response (APR) induces alterations in lipid metabolism, and our data suggest that this is associated with suppression of type II nuclear hormone receptors that are key regulators of fatty acid, cholesterol, and bile acid metabolism. Recently, the farnesoid X receptor (FXR), constitutive androstane receptor (CAR), and pregnane X receptor (PXR) were found to regulate DHEA sulfotransferase (Sult2A1), which plays an important role in DHEA sulfation and detoxification of bile acids. Because FXR, PXR, and CAR are suppressed during the APR, we hypothesized that Sult2A1 is downregulated during the APR. To induce the APR, mice were treated with LPS, which will then trigger the release of various cytokines, and the mRNA levels of Sult2A1 and the sulfate donor 3'-phosphoadenosine 5'-phosphosulfate synthase 2 (PAPSS2), as well as the enzyme activity of Sult2A1, were determined in the liver. We found that mRNA levels of Sult2A1 decrease in a time- and dose-dependent manner during the LPS-induced APR. Similar changes were observed in the mRNA levels of PAPSS2, the major synthase of PAPS in the liver. Moreover, hepatic Sult2A1 activity and serum levels of DHEA-sulfate (DHEA-S) were significantly decreased in LPS-treated animals. These results suggest that decreased levels or activities of FXR, PXR, and CAR during the APR could contribute to decreases in Sult2A1, resulting in decreased sulfation of DHEA and lower circulating level of DHEA-S. Finally, we found that both TNF and IL-1 caused a significant decrease in the mRNA level of Sult2A1 in Hep3B human hepatoma cells, suggesting that the proinflammatory cytokines TNF and IL-1 mediate the inhibitory effect of LPS on Sult2A1 mRNA level. Our study provides a possible mechanism by which infection and inflammation are associated with altered steroid metabolism and cholestasis.

Pharmacologic doses of growth hormone (GH) reduce HIV-associated fat accumulation but may worsen glucose metabolism. We investigated the effects of a low dose of GH (1 mg per day) in HIV-infected men with fat accumulation and found that such treatment reduced total fat and increased lean body mass without significant changes in glucose tolerance or insulin sensitivity. Visceral adipose tissue (VAT) levels did not change significantly for the group as a whole, although a reduction in the VAT level was seen in patients with a greater VAT level at baseline.