Removal of asymmetric dimethylarginine during artificial liver support using fractionated plasma separation and adsorption

OBJECTIVE

Asymmetric dimethylarginine (ADMA) is the most potent endogenous nitric oxide synthase inhibitor. Elevated ADMA levels have been linked to increased mortality in different patient populations. Key regulation of ADMA levels mainly takes place in the liver. Hence, ADMA is elevated in liver disease. There is no specific pharmacological treatment to lower the elevated ADMA levels. Hemodialysis is of limited efficiency in removing ADMA as it is highly protein bound. Prometheus is an extracorporeal liver support system which allows the removal of protein-bound toxins. We assessed the efficiency of the Prometheus system in reducing high ADMA levels in patients with liver failure.

MATERIAL AND METHODS

We studied nine patients with acute-on-chronic liver failure and concomitant renal failure already necessitating hemodialysis. Seven patients needed intensive care treatment. Two consecutive sessions of Prometheus therapy of each 4 h were performed in all patients. ADMA and its structural isomer symmetrical dimethylarginine (SDMA) were determined using liquid chromatography-mass spectrometry.

RESULTS

ADMA levels correlated to model for end stage liver disease (MELD) score (r(s) = 0.62; p < 0.0001). Before Prometheus was started, levels of ADMA and SDMA were elevated (1.36 +/- 0.5 micromol/l and 1.90 +/- 0.4 micromol/l, respectively). During Prometheus treatments, plasma levels of ADMA dropped by a mean 25% (p < 0.0001) and SDMA levels by 22% (p < 0.0001). However, there was a significant rebound of ADMA levels between the two therapy sessions (p < 0.01).

CONCLUSIONS

This study shows for the first time that plasma levels of ADMA can be effectively lowered by an artificial liver support system (Prometheus). Effective elimination of ADMA might explain some of the beneficial clinical effects of these systems in patients with liver failure.

Pharmaceutically important pre- and posttranslational modifications on human serum albumin

Recombinant technology allows engineering and production of proteins with desirable properties. Human serum albumin has been developed with recombinant technology, and thus plays an increasing role as a drug carrier in the clinical setting. Genetic variations usually occur on the surface of the protein, and do not impose significant effects on the conformation of albumin. However, binding of fatty acids by genetic variants is affected according to the location of the mutation. Albumin undergoes three major posttranslational modifications, namely, oxidation, glycation, and S-nitrosylation. This review gives an account of the different posttranslational modifications that should be taken into consideration when designing albumin mutant analogues with desirable pharmaceutical properties.

Blood products, volume control, and renal support in the coagulopathy of liver disease

Plasma-based products are commonly used in patients who have chronic liver disease to treat perceived coagulopathy despite unproven efficacy and potentially severe risks, such as transfusion-related acute lung injury, which carries a high mortality rate. Moreover, volume expansion may acutely worsen portal hypertension and increase bleeding from the collateral portal vascular bed. Although factor replacement therapy may be warranted in selected situations, its use should be restricted because of the limitations of target tests, such as international normalized ratio, which poorly reflects presence of bleeding diatheses in patients who have cirrhosis. Renal replacement therapies are frequent adjuncts in patients who have cirrhosis and are acutely decompensated, and may correct uremia-related bleeding diathesis and assist in controlling vascular volume, although they are generally limited to use as a bridge to liver transplantation. Novel extracorporeal therapies are emerging and may also have significant interaction with the hemostatic system. Volume contraction and blood conservation therapies are relatively new and promising approaches to reduce use of blood products in liver transplantation.