Role of albumin for transport and distribution of protein bound substances between compartments

Background/Aim: The importance of albumin is undisputed for intravascular transport and distribution of protein bound substances, especially of the toxins accumulating in liver failure.

New encouraging results of intracorporeal albumin using (iv-administration of albumin with HRS [Uriz, Arroyo et al.], cirrhosis and SBP [Sort, Arroyo et al.] and cirrhosis and ascites [Gentilini et al.]) as well as extracorporeal albumin using (MARS® therapy - liver support therapy) give rise to the question about the role of albumin for transport and distribution of protein bound toxins/substances between compartments again.

We just want to introduce a new theory of transport mechanism possibly caused the improvements described in the studies named above.

The principle of MARS® was described at different times before: The patients blood is dialysed against an albumin solution, which is able to take over the protein bound toxins of the blood across the MARS® membrane.

Materials and Methods: We conducted two series of six in-vitro experiments each, with two different MARS® membranes. We used a light version of MARS®, just the blood circuit (containing BSP toxified plasma) and the albumin one, as a closed two loop system without albumin cleaning. We varied several parameters like flow direction, concentration of albumin of plasma and dialysate and also modulated the flow in the different experiments and dialysated the BSP contaminated plasma against an albumin solution.

Results: The parameters of each single experiment were really different. However, there is one result every time: The ratio of BSP concentration vs albumin concentration was the same in plasma and dialysate after 120 mins of experiment.

Discussion: After equalization of the ratio c_BSP/c_alb of plasma and dialysate there was no sign of BSP transport in any direction. That means the gradient of the quotient „c_BSP/c_alb” of plasma and of dialysate seems to be the driving force of transmembranal transport of albumin bound substances.

We also could show that an alteration of the FICK’s principle equation is a sufficient way to describe this transport of albumin bound substances between these two in vitro compartments.

We assume that the mechanism we found in vitro also works in vivo, but we have to show it next. It could be logical that there is a similar easy way for distributing protein bound substances as there is one for water soluble ones. This could explain why MARS® therapy works and why iv-administration of albumin improves the patients‘ condition in the studies named above. May be the best way is to combine both kinds of therapy.

Conclusion: The gradient of the ratio c_subst/c_alb between two compartments is the driving force for transport of protein bound substances between them (in vitro). This can be described by a new alteration of the FICK’s principle equation. The correctness of this theory has to be shown for in vivo conditions.