The lipoprotein composition of plasma and ascitic fluid in liver cirrhosis

Cholesterol Regulation in Age-Related Macular Degeneration: A Framework for Mathematical Modelling of Drusen Biogenesis

In age-related macular degeneration (AMD), there is, in common with many other age-related diseases, the need to distinguish between changes in the ageing eye that lead to disease and those changes that are considered part of a healthy, ageing eye. Various studies investigating the multitude of mechanisms involved in the aetiology of AMD exist within the field of ophthalmology and related medical fields, yet many aspects of it remain poorly understood and only a limited number of therapies are available. A recent study relates drusen's topographically cellular characteristics to the neural retina's metabolic needs and associated cholesterol involvement within the retina. In particular, there is a need to fully understand the maintenance of cholesterol homeostasis in the retina to prevent normal ageing processes from being perturbed towards maculopathy. Here, we present an extensive review of the clinical and physiological features of the ageing retina, as well as mechanisms implicated in pathology, synthesised from a vast body of the published literature. We use this novel synthesis to construct a comprehensive process schematic, encompassing all key species and physiological processes such as nutrients, waste and lipoprotein management. We are therefore able to express these processes in a mathematical language via a comprehensive modelling framework, comprising a set of twenty-three equations spanning three distinct biological compartments. This very general modelling framework may now be adapted to more focused studies on individual mechanisms, processes or components underlying of the many facets of AMD. As an example of such a focused application, we conclude this article with a one-compartment, four-species model of the retinal pigment epithelium, which considers the parametric conditions under which either cholesterol homeostasis or unregulated accumulation of cholesterol may obtain in the ageing eye.

Innate immune dysfunction in acute and chronic liver disease

Liver cirrhosis is a common disease causing great public-health concern because of the frequent complications requiring hospital care. Acute liver failure is also prone to several complications but is rare. One of the main complications for both acute and chronic liver diseases is infection, which regularly causes decompensation of cirrhosis, possibly leading to organ failure and death. This review focuses on innate immune function in cirrhosis, acute-on-chronic liver failure and acute liver failure. The known defects of Kupffer cells, neutrophils and monocytes are discussed, together with the pathophysiological importance of gut permeability, portal hypertension and intrinsic cellular defects, and the role of endotoxin, albumin, lipoproteins and toll-like receptors. Based on these different pathomechanisms, the available information on therapeutic strategies is presented. Antibiotic and probiotic treatment, nutritional support, artificial liver support, and experimental strategies such as inhibition of toll-like receptors and use of albumin and colony-stimulating factors are highlighted.

Ex vivo effects of high-density lipoprotein exposure on the lipopolysaccharide-induced inflammatory response in patients with severe cirrhosis

High-density lipoproteins (HDL) are known to neutralize lipopolysaccharide (LPS). Because patients with cirrhosis have lower HDL levels, this may contribute to LPS-induced ex vivo monocyte overproduction of proinflammatory cytokines. However, the effects of HDL on cytokine production by monocytes from patients with cirrhosis have never been studied. The aim of this study was to determine the effects of HDL on LPS-induced proinflammatory cytokine production in whole blood and isolated monocytes from patients with severe cirrhosis and controls. Plasma levels of HDL and cytokines were determined. The effects of reconstituted HDL (rHDL) on LPS-induced cytokine production in whole blood were assessed by cytokine array and on tumor necrosis factor alpha (TNF-alpha) and interleukin-10 (IL-10) production in isolated monocytes. Plasma HDL levels were significantly lower in patients with cirrhosis than in controls. Plasma levels of TNF-alpha and IL-6 were significantly higher in patients with cirrhosis than in controls. Incubation of rHDL with whole blood prevented LPS-induced TNF-alpha and IL-6 overproduction in patients with cirrhosis. LPS-induced TNF-alpha production and CD14 expression were significantly more marked in cirrhotic monocytes than in control monocytes, and both decreased significantly after rHDL incubation. LPS-induced down-regulation of scavenger receptor, class B, type I (SR-BI) expression was abolished in cirrhotic monocytes.

CONCLUSIONS

This study shows that rHDL abolishes the LPS-induced overproduction of proinflammatory cytokines in whole blood from patients with severe cirrhosis. These results were confirmed in isolated monocytes from these patients. This suggests that administration of rHDL might be a useful strategy for the treatment of cirrhosis to limit LPS-induced cytokine overproduction.

High-density lipoprotein administration attenuates liver proinflammatory response, restores liver endothelial nitric oxide synthase activity, and lowers portal pressure in cirrhotic rats

In patients with cirrhosis, endotoxic shock is a major complication of portal hypertension, which is related partly to intrahepatic endothelial nitric oxide synthase (eNOS) down-regulation. High-density lipoproteins (HDLs), whose plasma levels are reduced in cirrhosis, have an anti-inflammatory effect by neutralizing circulating lipopolysaccharide (LPS), and they increase eNOS activity in endothelial cells. Therefore, the aim of this study was to assess the effects of reconstituted high-density lipoprotein (rHDL) administration on the LPS-induced proinflammatory response, intrahepatic eNOS regulation, and portal hypertension in cirrhotic rats. Cirrhotic and control rats were pretreated with rHDL or saline and challenged with LPS or saline. The neutralization of LPS in HDL was assessed by the measurement of HDL-bound fluorescent LPS levels. Plasma tumor necrosis factor alpha (TNFalpha) and lipopolysaccharide binding protein (LBP) levels were measured. The expression of hepatic TNFalpha, LBP, inducible nitric oxide synthase (iNOS), and caveolin-1 (a major eNOS inhibitor) and the activity of protein kinase B (Akt; a major eNOS activator) and eNOS were determined. The portal pressure was measured. The plasma HDL levels were significantly lower in cirrhotic rats than in control rats. In cirrhotic rats, the plasma levels of HDL-bound fluorescent LPS were 50% lower than those in controls, and they were restored after rHDL administration. The plasma TNFalpha levels were significantly higher in LPS-challenged cirrhotic rats than in controls and significantly decreased after rHDL administration. rHDL administration decreased hepatic TNFalpha, LBP, iNOS, and caveolin-1 expression, restored hepatic eNOS and Akt activity, and significantly lowered the portal pressure and intrahepatic vascular resistance.

CONCLUSION

In cirrhotic rats, rHDL administration decreases the hepatic proinflammatory signals induced by LPS, restores the hepatic eNOS activity, and lowers the portal pressure. This suggests that the decrease in circulating HDL in cirrhosis plays a role in the excessive proinflammatory response and intrahepatic eNOS down-regulation.

High-density lipoproteins reduce the effect of endotoxin on cytokine production and systemic hemodynamics in cirrhotic rats with ascites

BACKGROUND/AIMS

Hypersensitivity to endotoxin is a recognized feature in cirrhosis. High-density lipoproteins (HDL) have a high capacity to inactivate endotoxin. The aim was to determine if HDL reduces the effect of endotoxin on cytokine production and systemic hemodynamics in experimental cirrhosis.

METHODS

The study was performed in control and rats with carbon-tetrachloride induced cirrhosis with ascites. Hemodynamic parameters were determined before and after several doses of endotoxin. The effects of 25 microg/kg of endotoxin on the serum concentration of TNFalpha and mean arterial pressure (MAP) were determined after treatment with HDL (80 mg/kg) or saline.

RESULTS

Whereas endotoxin decreased MAP only at doses of 100 and 1000 microg/kg in control rats, in cirrhotic rats significant hypotension occurred at doses of 25, 50, 100 and 1000 microg/kg. Following the administration of endotoxin (25 microg/kg) the serum levels of TNFalpha were 140 times higher in cirrhotic than in control rats (89?835+/-21?090 vs. 625+/-137 pg/ml; P<0.001). Serum TNFalpha was 80% lower in cirrhotic rats pretreated with HDL (18?890+/-5012 pg/ml; P<0.001) than in those pretreated with saline. The administration of endotoxin (25 microg/kg) was associated with a significant lower decrease of MAP in cirrhotic rats pretreated with HDL than in those receiving saline (11.9+/-3.5 vs. 24.7+/-4.3%; P<0.05).

CONCLUSIONS

HDL attenuates the increased effect of endotoxin on cytokine production and systemic hemodynamic in cirrhosis.