HIV protease inhibitor induces fatty acid and sterol biosynthesis in liver and adipose tissues due to the accumulation of activated sterol regulatory element-binding proteins in the nucleus

The mechanism by which human immunodeficiency virus (HIV) protease inhibitor therapy adversely induces lipodystrophy and hyperlipidemia has not been defined. This study explored the mechanism associated with the adverse effects of the prototype protease inhibitor ritonavir in mice. Ritonavir treatment increased plasma triglyceride and cholesterol levels through increased fatty acid and cholesterol biosynthesis in adipose and liver. Ritonavir treatment also resulted in hepatic steatosis and hepatomegaly. These abnormalities, which were especially pronounced after feeding a Western type high fat diet, were due to ritonavir-induced accumulation of the activated forms of sterol regulatory binding protein (SREBP)-1 and -2 in the nucleus of liver and adipose, resulting in elevated expression of lipid metabolism genes. Interestingly, protease inhibitor treatment did not alter SREBP mRNA levels in these tissues. Thus, the adverse lipid abnormalities associated with protease inhibitor therapy are caused by the constitutive induction of lipid biosynthesis in liver and adipose tissues due to the accumulation of activated SREBP in the nucleus.

Apolipoprotein E inhibits neointimal hyperplasia after arterial injury in mice

The potential cytostatic function of apolipoprotein (apo) E in vivo was explored by measuring neointimal hyperplasia in response to vascular injury in apoE-deficient and apoE-overexpressing transgenic mice. Results showed a significant increase in medial thickness, medial area, and neointimal formation after vascular injury in both apoE knockout and wild-type C57BL/6 mice. Immunochemical analysis with smooth muscle alpha-actin-specific antibodies revealed that the neointima contained proliferating smooth muscle cells. Neointimal area was 3.4-fold greater, and the intima/medial ratio as well as stenotic luminal area was more pronounced in apoE(-/-) mice than those observed in control mice (P < 0.05). The human apoE3 transgenic mice in FVB/N genetic background were then used to verify a direct effect of apoE in protection against neointimal hyperplasia in response to mechanically induced vascular injury. Results showed that neointimal area was reduced threefold to fourfold in mice overexpressing the human apoE3 transgene (P < 0.05). Importantly, suppression of neointimal formation in the apoE transgenic mice also abolished the luminal stenosis observed in their nontransgenic FVB/N counterparts. These results documented a direct role of apoE in modulating vascular response to injury, suggesting that increasing apoE level may be beneficial in protection against restenosis after vascular surgery.

Adenovirus-mediated human pancreatic lipase gene transfer to rat bile: gene therapy of fat malabsorption

This study explored the potential of using the gene therapy approach, based on adenovirus-mediated expression of pancreatic lipase in the hepatobiliary tract, to increase lipid digestion in the intestinal lumen and promote lipid absorption through the gastrointestinal tract. Recombinant adenovirus containing the human pancreatic lipase cDNA (AdPL) was shown to transduce and mediate pancreatic lipase biosynthesis in rat IEC-6 epithelial cells in vitro. Retrograde infusion of recombinant adenovirus (3 x 10(8) plaque-forming units) containing the bacterial LacZ gene (AdLacZ) into the bile duct of rats resulted in positive X-gal reaction products in the periportal liver cells 7 days after AdLacZ infusion. A high level of human pancreatic lipase was detected in bile after retrograde bile duct infusion of rats with AdPL but not in the bile of animals infused with AdLacZ. Triglyceride hydrolytic activity in the bile of AdPL-infused rats was equivalent to that present in pancreatic juice. In contrast, serum obtained from these animals did not contain any detectable pancreatic lipase activity. These results suggest that ectopic expression of pancreatic enzymes in the hepatobiliary tract may be an alternative therapeutic strategy for treating fat malabsorption due to pancreatic insufficiency.

Adenosine inhibits IL-12 and TNF-[alpha] production via adenosine A2a receptor-dependent and independent mechanisms

Interleukin 12 (IL-12) is a crucial cytokine in the regulation of T helper 1 vs. T helper 2 immune responses. In the present study, we investigated the effect of the endogenous purine nucleoside adenosine on the production of IL-12. In mouse macrophages, adenosine suppressed IL-12 production. Although the order of potency of adenosine receptor agonists suggested the involvement of A2a receptors, data obtained with A2a receptor-deficient mice showed that the adenosine suppression of IL-12 and even TNF-alpha production is only partly mediated by A2a receptor ligation. Studies with adenosine receptor antagonists or the adenosine uptake blocker dipyridamole showed that adenosine released endogenously also decreases IL-12. Although adenosine increases IL-10 production, the inhibition of IL-12 production is independent of the increased IL-10. The mechanism of action of adenosine was not associated with alterations of the activation of the p38 and p42/p44 mitogen-activated protein kinases or the phosphorylation of the c-Jun terminal kinase. Adenosine failed to affect steady-state levels of either IL-12 p35 or p40 mRNA, but augmented IL-10 mRNA levels. In summary, adenosine inhibits IL-12 production via various adenosine receptors. These results support the notion that adenosine-based therapies might be useful in certain autoimmune and/or inflammatory diseases.

Spermine differentially regulates the production of interleukin-12 p40 and interleukin-10 and suppresses the release of the T helper 1 cytokine interferon-gamma

Polyamines are endogenous immunomodulatory molecules. Recent studies revealed that polyamines suppress the production of proinflammatory cytokines and nitric oxide. In the present study, we investigated the effect of the polyamines spermine, spermidine, and putrescine on the production of interleukin (IL)-12 p40, IL-10, and interferon (IFN-gamma) in mouse peritoneal macrophages and spleen cell suspensions. Spermine, but not spermidine or putrescine, suppressed, in a concentration-dependent manner, the production of IL-12 p40 by lipopolysaccharide (LPS)-stimulated macrophages. The effect of spermine was post-transcriptional, because steady-state levels of messenger ribonucleic acid (mRNAs) for IL-12 (p35 and p40) were not affected. In contrast to its inhibitory effect on IL-12 p40, spermine (0.3-3 microM) augmented IL-10 production. The down-regulation of IL-12 p40 by spermine was independent of enhancement of IL-10 by this agent, for spermine retained its ability to suppress IL-12 production in peritoneal macrophages obtained from IL-10-deficient mice. The alterations in cytokine production by spermine did not involve an effect on early intracellular pathways of LPS signal transduction, including the p38 or p42/44 mitogen-activated protein kinases, or the c-jun terminal kinase. In spleen cell suspensions, spermine suppressed the release of IFN-gamma induced either by LPS or anti-CD3 antibody. In summary, spermine exerts anti-inflammatory effects by suppressing IL-12 and IFN-gamma and by augmenting the production of IL-10.

ATP suppression of interleukin-12 and tumour necrosis factor-alpha release from macrophages

Immune cell activation releases ATP into the extracellular space. ATP-sensitive P2 purinergic receptors are expressed on immune cells and activation of these receptors alters immune cell function. Furthermore, ATP is metabolized by ectonucleotidases to adenosine, which has also been shown to alter cytokine production. In the present study, we investigated how extracellular ATP affects interleukin (IL)-12 and tumour necrosis factor (TNF)-alpha production in bacterial lipopolysaccharide (LPS)-treated murine peritoneal macrophages and we also examined whether extracellular ATP alters the production of the T helper 1 cytokine interferon (IFN)-gamma. Pretreatment of the peritoneal macrophages with ATP or various ATP analogues decreased both IL-12 and TNF-alpha production induced by LPS (10 microgram ml(-1)). The effect of ATP was partially reversed by cotreatment with adenosine deaminase (0.1 - 1 u ml(-1)), suggesting that the suppressive effect of ATP on cytokine production is, in part, due to its degradation products. Immunoneutralization with an anti-IL-10 antibody demonstrated that although ATP increases IL-10 production, the inhibition of IL-12 and TNF-alpha production is independent of the increased IL-10. The effect of ATP was pretranslational, as it suppressed steady state levels of mRNAs for IL-12 (both p35 and p40). In spleen cells stimulated with either LPS (10 microgram ml(-1)) or anti-CD3 (2 microgram ml(-1)) antibody, ATP suppressed, in a concentration-dependent manner, the production of IFN-gamma. These results suggest that extracellular ATP has multiple anti-inflammatory effects and that release of ATP into the extracellular space may play a role in blunting the overactive immune response in autoimmune diseases.

Inosine inhibits inflammatory cytokine production by a posttranscriptional mechanism and protects against endotoxin-induced shock

Extracellular purines, including adenosine and ATP, are potent endogenous immunomodulatory molecules. Inosine, a degradation product of these purines, can reach high concentrations in the extracellular space under conditions associated with cellular metabolic stress such as inflammation or ischemia. In the present study, we investigated whether extracellular inosine can affect inflammatory/immune processes. In immunostimulated macrophages and spleen cells, inosine potently inhibited the production of the proinflammatory cytokines TNF-alpha, IL-1, IL-12, macrophage-inflammatory protein-1alpha, and IFN-gamma, but failed to alter the production of the anti-inflammatory cytokine IL-10. The effect of inosine did not require cellular uptake by nucleoside transporters and was partially reversed by blockade of adenosine A1 and A2 receptors. Inosine inhibited cytokine production by a posttranscriptional mechanism. The activity of inosine was independent of activation of the p38 and p42/p44 mitogen-activated protein kinases, the phosphorylation of the c-Jun terminal kinase, the degradation of inhibitory factor kappaB, and elevation of intracellular cAMP. Inosine suppressed proinflammatory cytokine production and mortality in a mouse endotoxemic model. Taken together, inosine has multiple anti-inflammatory effects. These findings, coupled with the fact that inosine has very low toxicity, suggest that this agent may be useful in the treatment of inflammatory/ischemic diseases.

Alpha 2A-adrenergic receptor stimulated calcium release is transduced by Gi-associated G(beta gamma)-mediated activation of phospholipase C

Proposed mechanisms by which alpha 2-adrenergic receptors (alpha 2AR) regulate intracellular calcium ([Ca2+]i) include stimulation and inhibition of cell surface calcium channels, stimulation of calcium release via receptor coupling to Gq with subsequent activation of phospholipase C and release of IP3, or stimulation of calcium release via coupling to Gi in an IP3-independent manner. These potential mechanisms were explored in cells that expressed alpha(2A)AR endogenously (HEL cells), permanently transfected CHO cells, and transiently transfected COS-7 cells. Each cell type displayed agonist (UK14304)-dependent increases in [Ca2+]i that were blocked by yohimbine, ablated by pertussis toxin, and largely unaffected by chelation of extracellular calcium. Furthermore, calcium release was associated with IP3 accumulation and was blocked by an inhibitor of phospholipase C (PLC). When expressed in CHO cells, a mutated alpha(2A)AR which has the amino and carboxyl termini of the third intracellular loop substituted with beta 2AR sequence poorly coupled to Gi in adenylyl cyclase assays, and likewise displayed virtually no coupling to increased [Ca2+]i. These results all point toward a Gi- versus a Gq-mediated coupling pathway triggering release of intracellular calcium stores. The possibility that G(beta gamma) subunits released from alpha(2A)AR-Gi coupling is the mechanism of PLC activation was explored in COS-7 cells by coexpressing alpha(2A)AR with the G(beta gamma) inhibitors transducin or a carboxy-terminal portion of the beta AR kinase. Both beta gamma inhibitors markedly inhibited alpha(2A)AR modulation of [Ca2+]i while not affecting thromboxane A2 receptor mediated stimulation of [Ca2+]i via Gq coupling. Thus, alpha(2A)AR couple to calcium release via Gi-associated G(beta gamma) subunits. This coupling is present in multiple cell types and should be considered a major signal transduction pathway of this receptor.