Resveralogues protect HepG2 cells against cellular senescence induced by hepatotoxic metabolites.

Progressive liver disease and dysfunction cause toxic metabolites including ammonia and unconjugated bilirubin to accumulate in plasma. As the population ages alternatives to liver transplantation become increasingly important. One approach for use as a bridge to transplant or recovery is the use of bioartificial liver systems (BALS) containing primary or immortalised hepatocytes as ex-vivo replacements or supports for endogenous liver function. However, exposure to the hepatotoxic metabolites present in plasma causes the rapid failure of these cells to carry out their primary metabolic functions despite remaining viable. Hypothesizing that this loss of core hepatocyte phenotypes was caused by cell senescence we exposed HepG2 cell populations, grown in both standard two-dimensional tissue culture systems and in three dimensional cultures on novel alginate modified HEMA-MBA cryogels, to physiologically reflective concentrations of hepatotoxic metabolites and cytokines. HepG2 cells are forced into senescence by the toxic metabolites in under six hours (as measured by loss of thymidine analog incorporation or detectable Ki67 staining) which is associated with a ten to twenty-fold reduction in the capacity of the cultures to synthesise albumin or urea. This state of senescence induced by liver toxins (SILT) can be prevented by preincubation with either 2-5 µM resveratrol, its major in vivo metabolite dihydroresveratrol or a series of novel resveralogues with differential capacities to scavenge radicals and activate SIRT1 (including V29 which does not interact with the protein). SILT appears to be a previously unrecognised barrier to the development of BALS which can now be overcome using small molecules that are safe for human use at concentrations readily achievable in vivo.

Correction: Population type influences the rate of ageing.

This article was originally published under standard License to Publish, but has now been made available under a CC BY 4.0 license. The PDF and HTML versions of the paper have been modified accordingly.

Population type influences the rate of ageing.

Mutation accumulation is one of the major genetic theories of ageing and predicts that the frequencies of deleterious alleles that are neutral to selection until post-reproductive years are influenced by random genetic drift. The effective population size (Ne) determines the rate of drift and in age-structured populations is a function of generation time, the number of newborn individuals and reproductive value. We hypothesise that over the last 50,000 years, the human population survivorship curve has experienced a shift from one of constant mortality and no senescence (known as a Type-II population) to one of delayed, but strong senescence (known as a Type-I population). We simulate drift in age-structured populations to explore the sensitivity of different population 'types' to generation time and contrast our results with predictions based purely on estimates of Ne. We conclude that estimates of Ne do not always accurately predict the rates of drift between populations with different survivorship curves and that survivorship curves are useful predictors of the sensitivity of a population to generation time. We find that a shift from an ancestral Type-II to a modern Type-I population coincides with an increase in the rate of drift unless accompanied by an increase in generation time. Both population type and generation time are therefore relevant to the contribution mutation accumulation makes to the genetic underpinnings of senescence.

Senescence in the aging process.

The accumulation of 'senescent' cells has long been proposed to act as an ageing mechanism. These cells display a radically altered transcriptome and degenerative phenotype compared with their growing counterparts. Tremendous progress has been made in recent years both in understanding the molecular mechanisms controlling entry into the senescent state and in the direct demonstration that senescent cells act as causal agents of mammalian ageing. The challenges now are to gain a better understanding of how the senescent cell phenotype varies between different individuals and tissues, discover how senescence predisposes to organismal frailty, and develop mechanisms by which the deleterious effects of senescent cells can be ameliorated.