Bioartificial interventions for organ senescence: Understanding and preventing senescence induced by liver toxins (SILT) in hepatocytes.
Lead Research Organisation:
University of Brighton
Department Name: Sch of Applied Sciences (SAS)
Abstract
The liver is a key organ affected by ageing. It performs many functions including plasma protein synthesis and the conversion of ammonia to urea. Liver dysfunction rates increase markedly with age and can occur both through multiple liver diseases and secondary causes such as metabolic syndrome. For example, non-alcoholic fatty liver disease increases in both frequency and severity in the over 65 age- groups and similar patterns are observed for both alcoholic and autoimmune liver diseases.
Substantial socioeconomic and sex inequalities also exist within liver dysfunction with incidence rates increasing gradually with age to produce the largest inequalities in the oldest age-groups.
The accumulation of endogenous toxins such as bilirubin and ammonia in patient plasma is a general feature of liver failure. These in turn produce life-threatening effects in other organs (e.g. hepatic encephalopathy) contributing to the high mortality associated with liver failure. Transplantation is the preferred treatment for liver failure but there is a serious shortage of organ donors and increasing age independently predicts poor transplant outcomes for both donor and patient. Thus, unless new interventions can be found, this problem will escalate markedly as the global population ages.
One attractive alternative approach is to engineer bioartificial liver systems (BALS). These artificial organs are intended either to act as emergency extracorporeal bridges for patients until a suitable donor organ is available, or to support endogenous organ function until the patient's own liver regenerates. For this a BAL relies on 400-800g of hepatocytes to provide the necessary biotransformation and synthetic functions. However, all such devices tested to date have failed because contact with hepatotoxins present in the serum of animals with liver failure destroys the capacity of the hepatocytes to clear ammonia and synthesise albumin although the cells themselves remain viable.
Recently, we discovered that endogenous plasma hepatotoxins induce cellular senescence in human hepatocytes within hours and it is this key ageing pathway which is responsible for their loss of liver specific functions. However, we have also shown that it is possible to protect cells from this Senescence Induced by Liver Toxins (SILT) using novel small molecules our group has synthesised (resveralogues). Resveratrol itself activates a variety of pathways including the enzyme SIRT1 (which enhances liver regeneration in rodents in vivo) but we have found equivalent protection from SILT using novel analogues with no capacity to activate this enzyme - indicating a novel mechanism.
These discoveries render BALS a potential new clinical intervention for many different disorders and hold out the long-term prospect that older individuals may recover liver function, whether compromised through ageing or acute disease, perhaps avoid transplantation altogether and be considered for this intervention when before they would have been excluded from treatment because of their age. Obstacles to this approach remain, including enhancing our mechanistic understanding of the full protective capacities of our resveralogues, and the engineering challenges of building a prototype device. However, we have also developed novel porous biomaterials which hold great potential as replacements for the current generation of BAL bioreactors. An initial 8-month period will be spent in expanding our prior work in SILT in human hepatocytes to cover rodent and porcine systems (heavily used as in vivo models), next we will use genomics and in silco studies to identify the major pathways by which resveralogues protect against SILT and finally we will optimise a prototype device comprising novel matrices, and cells and evaluate its performance in a close mimic of the in vivo situation when challenged with plasma loaded with liver toxins.
Substantial socioeconomic and sex inequalities also exist within liver dysfunction with incidence rates increasing gradually with age to produce the largest inequalities in the oldest age-groups.
The accumulation of endogenous toxins such as bilirubin and ammonia in patient plasma is a general feature of liver failure. These in turn produce life-threatening effects in other organs (e.g. hepatic encephalopathy) contributing to the high mortality associated with liver failure. Transplantation is the preferred treatment for liver failure but there is a serious shortage of organ donors and increasing age independently predicts poor transplant outcomes for both donor and patient. Thus, unless new interventions can be found, this problem will escalate markedly as the global population ages.
One attractive alternative approach is to engineer bioartificial liver systems (BALS). These artificial organs are intended either to act as emergency extracorporeal bridges for patients until a suitable donor organ is available, or to support endogenous organ function until the patient's own liver regenerates. For this a BAL relies on 400-800g of hepatocytes to provide the necessary biotransformation and synthetic functions. However, all such devices tested to date have failed because contact with hepatotoxins present in the serum of animals with liver failure destroys the capacity of the hepatocytes to clear ammonia and synthesise albumin although the cells themselves remain viable.
Recently, we discovered that endogenous plasma hepatotoxins induce cellular senescence in human hepatocytes within hours and it is this key ageing pathway which is responsible for their loss of liver specific functions. However, we have also shown that it is possible to protect cells from this Senescence Induced by Liver Toxins (SILT) using novel small molecules our group has synthesised (resveralogues). Resveratrol itself activates a variety of pathways including the enzyme SIRT1 (which enhances liver regeneration in rodents in vivo) but we have found equivalent protection from SILT using novel analogues with no capacity to activate this enzyme - indicating a novel mechanism.
These discoveries render BALS a potential new clinical intervention for many different disorders and hold out the long-term prospect that older individuals may recover liver function, whether compromised through ageing or acute disease, perhaps avoid transplantation altogether and be considered for this intervention when before they would have been excluded from treatment because of their age. Obstacles to this approach remain, including enhancing our mechanistic understanding of the full protective capacities of our resveralogues, and the engineering challenges of building a prototype device. However, we have also developed novel porous biomaterials which hold great potential as replacements for the current generation of BAL bioreactors. An initial 8-month period will be spent in expanding our prior work in SILT in human hepatocytes to cover rodent and porcine systems (heavily used as in vivo models), next we will use genomics and in silco studies to identify the major pathways by which resveralogues protect against SILT and finally we will optimise a prototype device comprising novel matrices, and cells and evaluate its performance in a close mimic of the in vivo situation when challenged with plasma loaded with liver toxins.
Technical Summary
We hypothesise that components of the hepatotoxic mixture of metabolites and cytokines that accumulate in plasma during liver failure induce cellular senescence and that this altered phenotype drives the failure to detoxify patient plasma in Bio Artificial Liver Systems (BALS) leading to device and clinical endpoint failure. Our preliminary data support this and we have identified novel polyphenolic compounds that are same in humans and which block this effect.
On the basis of our initial findings we believe that novel SIRT1 independent mechanisms primarily mediate the protective effects of our compounds against SILT. Accordingly, we will identify and target the major pathways controlling SILT using genomic approaches and then optimise novel three-dimensional p(HEMA)-alginate cryogel matrices which we have developed for sustained in vivo use in a novel device which enhances key hepatocyte phenotypes. Such s device incorporating such a cell-polymer system combined with anti-SILT compounds would be an excellent prospect for a successful animal trial after the end of this ADA but we are potentially able to proceed to human clinical trials directly depending on the system and compounds selected.
On the basis of our initial findings we believe that novel SIRT1 independent mechanisms primarily mediate the protective effects of our compounds against SILT. Accordingly, we will identify and target the major pathways controlling SILT using genomic approaches and then optimise novel three-dimensional p(HEMA)-alginate cryogel matrices which we have developed for sustained in vivo use in a novel device which enhances key hepatocyte phenotypes. Such s device incorporating such a cell-polymer system combined with anti-SILT compounds would be an excellent prospect for a successful animal trial after the end of this ADA but we are potentially able to proceed to human clinical trials directly depending on the system and compounds selected.
