Increasing membrane unsaturation with aging and longevity

It has now been documented that there is an age-associated increase in membrane PI and lipoxidation-derived molecular damage (see Table ​Table1).1). In general, PI increases during aging in an organ-dependent way.  -http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3865700/

As seen on the above quote it seems that membranes peroxidation index tends to become less favorable with the passage of time, at least in some organisms.   Given that differences in membrane peroxidation index have been associated with differences in lifespan between species and within species this suggest it may be causal.

In the following we see further evidence:

The results showed significantly lower PI and lipoxidation-derived protein damage in brain and spleen from exceptionally old animals when compared to old specimens, and in a range analogous to adult animals. Therefore, low susceptibility to lipid peroxidation and maintenance of adult-like molecular lipoxidative damage could be key factors for longevity achievement.-http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3865700/

 The animals that exhibited most vigorous long term survival seemed to have lower PI similar to younger adults.   While the authors suggest it may be a key to longevity, I would say it may also be a key to indefinite longevity.   It may or may not be the case that if PI is lowered enough the existing biological maintenance and repair mechanisms may be enough to grant negligible senescence.   I would predict that organisms showing negligible senescence would show such peroxidation resistance, that is they would have a lower PI and it may even be significantly lower(depending on threshold or break even point for indefinite homeostatic balance/maintenance), and a quick wikipedia search shows just that in at least one organism

 Abstract:
Summary: The deleterious reactive carbonyls released upon oxidation of polyunsaturated fatty acids in biological membranes are believed to foster cellular aging. Comparative studies in mammals and birds have shown that the susceptibility to peroxidation of membrane lipids peroxidation index (PI) is negatively correlated with longevity. Long-living marine molluscs are increasingly studied as longevity models, and the presence of different types of lipids in the membranes of these organisms raises questions on the existence of a PI-longevity relationship. We address this question by comparing the longest living metazoan species, the mud clam Arctica islandica (maximum reported longevity = 507 year) to four other sympatric bivalve molluscs greatly differing in longevity (28, 37, 92, and 106 year). We contrasted the acyl and alkenyl chain composition of phospholipids from the mitochondrial membranes of these species. The analysis was reproduced in parallel for a mix of other cell membranes to investigate whether a different PI-longevity relationship would be found. The mitochondrial membrane PI was found to have an exponential decrease with increasing longevity among species and is significantly lower for A. islandica. The PI of other cell membranes showed a linear decrease with increasing longevity among species and was also significantly lower for A. islandica. These results clearly demonstrate that the PI also decreases with increasing longevity in marine bivalves and that it decreases faster in the mitochondrial membrane than in other membranes in general. Furthermore, the particularly low PI values for A. islandica can partly explain this species' extreme longevity.

^ Munro, D., and Blier P.U. (2012). The extreme longevity of Arctica islandica is associated with increased peroxidation resistance in mitochondrial membranes. Ageing Cell 11(5): 845-55. doi: 10.1111/j.1474-9726.2012.00847.x. Epub 2012 Jul 25.-wikipedia