Parabiosis: the Dilution Solution?

In heterochronic parabiosis, joining the circulatory systems of young and old mice causes the older animal to recover some features of youth. The effect has been widely assumed to be driven by pro-youth factors in younger blood, but an alternative hypothesis is possible: that the procedure is instead diluting pro-aging factors in the older partner.

Summary: Scientists have long marveled at the rejuvenating effects of heterochronic parabiosis. When you mix the blood of a young mouse and an old mouse by joining their circulatory systems, the older animal recovers some features of youth, while the young animal becomes functionally older. While many have assumed that these effects were driven by the infusion of pro-youth factors from the young parabiont into the older one, an alternative “Dilution Solution” hypothesis is possible: that the young blood is instead diluting pro-aging factors from the old animal’s blood, as well as allowing the young animal’s livers and kidneys to filter out metabolic toxins through the young animals’ livers and kidneys.

In 2016, a SENS Research Foundation study in the lab of Drs. Irina and Mike Conboy at UC Berkeley gave significant support to the Dilution Solution, and they have now published a pair of new studies showing that literally diluting the aging plasma with injections of saline plus replacement of the relatively inert transport protein albumin promotes even more dramatic rejuvenation effects on body and brain. The studies also suggest a durable re-set of the aging signaling system after breaking pro-aging signaling feedback loops. In the future, repair of the underlying cellular and molecular damage will abrogate those loops at their root, maintaining the youthful signaling system indefinitely.

When researchers surgically conjoin the circulatory systems of a young and an old animal, something remarkable happens: the older animal recovers some features of youth, while the young animal becomes functionally older. This phenomenon of heterochronic parabiosis was first discovered by Clive McCay of Cornell (best known for his work on caloric restriction) in the 1950s, but after a couple of decades of work, the thread lay dormant for the rest of the century. A dramatic revival of heterochronic parabiosis research was triggered by a seminal study published in 2005 by Irina and Mike Conboy at Berkeley, which demonstrated that exposure to the young animal’s circulation dramatically improved the older parabiont’s regenerative response to injury.

The encouraging results of parabiosis — combined with modern tools of which Clive McCay could only dream — have driven a quest to determine the underlying mechanisms of the phenomenon, and how we might capture some of those mechanisms to develop or improve rejuvenation therapies. Broadly, there are two alternative (but not quite mutually exclusive) possible explanations.

One hypothesis (which we will term the “Infusion Solution”) is that one or more factors circulating in young blood is critical to keeping us young, such that the loss of these factors with age progressively robs us of our youthful health, making us biologically older over time.  This is in some ways the more tantalizing explanation, and for a long time it was the most popular, as it suggests an intrinsic fountain of youth. If we could identify the key youth-promoting components of young blood, we could use standard biological techniques to produce more of them (or analogs with advantageous properties, or drugs that stimulate their production) and deliver them up as anti-aging biologics.

The alternative hypothesis (the “Dilution Solution”) posits that instead of there being “youth-promoting” factors in young blood that decline progressively with age, older blood instead becomes progressively saturated with pro-aging factors.

Logically, either hypothesis could explain the most high-level phenomena of parabiosis. So which one was true?

Round One: Seek and Ye Shall Find (or Not)

One way to resolve this question is to look for actual pro-youth or pro-aging factors that:

  • exist at opposite levels in young and old animals’ blood;
  • can mimic some of the effects of parabiosis when injected into an animal with naturally low levels of the substance; and
  • induce those same pro-aging or rejuvenating effects when depleted from an animal with naturally high levels.

Harvard and Stanford researchers published a paper in 2013 announcing that they had identified growth and differentiation factor 11, or GDF-11, as a key youth-promoting factor. The researchers asserted that GDF-11 restored muscle regeneration after injury, increased muscular strength, reduced steady-state levels of genetic damage, reversed dysfunctional age-related growth of the heart, and boosted production of new neurons (neurogenesis), among other benefits, in the aging mouse.

However, a series of subsequent investigations by other researchers showed to most scientists’ satisfaction that the Harvard and Stanford researchers were misidentifying the factor: the substance they were detecting was probably not even GDF-11, and in any case could not plausibly exhibit the effects that they had ascribed to it.

In fact, no signaling molecules have yet met robust criteria for pro-youth factors, with at most weak or incomplete evidence for things like testosterone. By contrast, a series of studies have identified specific pro-aging factors in old blood that cause the young animal to become functionally older, supporting the Dilution Solution hypothesis.

For instance, levels of eotaxin/CCL11 rise with age in the blood of old mice and in the plasma and cerebrospinal fluid (CSF) of otherwise-healthy aging humans. Eotaxin is an inflammatory factor known previously for its role in the allergic response, not brain aging — but Stanford researchers showed that when delivered to young mice (whether as part of parabiosis or through direct injection), it inhibits the formation of new memories and the adaptation of neuronal circuits.

Similarly, the blood of aging humans and mice contains elevated levels of beta-2-microglobulin (B2M), as does the aging mouse hippocampus (a critical region of the brain for new memory formation). B2M is transferred over to young partners during parabiosis, and has a detrimental effect on cognitive functioning and neurogenesis when injected into either the younger animal’s circulation or directly into the hippocampus. There is furthermore a similar, if more complicated, story to be told about transforming growth factor beta (TGF-β) in parabiosis and impaired memory and muscle repair in aging.

Adding to the growing pool of relevant work, Belgian and US researchers recently discovered that cancer cells adopt a more aggressive character when cultured in aged human serum than in serum from young people. The researchers traced this phenomenon back to rising levels of methylmalonic acid (MMA), a byproduct of metabolism of fatty acids produced by gut bacteria that is usually used as a marker of vitamin B12 deficiency.

It’s not clear what’s driving this rise in MMA with age: it didn’t appear to be due to subjects’ B12 levels, for instance, despite the fact that B12 deficiency becomes more common with age. It’s also not clear whether or how it might relate to the classical effects of heterochronic parabiosis, which mostly affect regenerative capacity and have not previously been linked to cancer. But intriguingly, the researchers found that the effects of MMA on cancer cells appear to involve activation of a vicious cycle of TGF-β signaling, which as noted above lurks in the background of many of the classical parabiosis phenomena. Since aging is the main driver of cancer risk, this finding presses the question of whether MMA might be part of the reason — and whether these preliminary effects might be our first glimpse of much wider pro-aging effects of factors in old plasma.

Overall, when we look for evidence of specific molecular culprits for or medicines against the aging process carried through the circulation that might explain the effects of parabiosis, round one goes to the Dilution Solution.

Round Two: Taking the Waste Treatment Plant Offline

Another possible player in the pro-aging/rejuvenating effects of parabiosis that has been largely ignored until recently is the potential role of metabolic toxins and wastes. In addition to the cellular and molecular damage of aging that accumulates in our bodies over time, the body’s normal metabolic processes also produce an enormous amount of more transient metabolic waste every day. In youth, much of what could go to waste is instead reprocessed and reused, and the rest is detoxified and excreted.

As we age, however, the organs responsible for detoxifying and eliminating these wastes — the kidneys, the liver, and to a lesser extent the lungs — age along with the rest of us, and their ability to remove these wastes progressively degrades. As a result, waste levels in blood circulation rise with age. These metabolic toxins are definitely bad for us — just ask a patient waiting for a liver transplant or on haemodialysis. Consistent with this, a biomarker called cystatin C – the most reliable marker of loss of kidney function — is also a powerful predictor of broader age-related decline, including death from cardiovascular disease or any cause, multimorbidity (suffering multiple diseases of aging at once), and declining physical and cognitive function.

It seems almost inescapable that the improved health of the old parabiont must be a function of more than simply the younger animal’s pro-youth factors, or of having proactively-generated pro-aging factors diluted away. These mere byproducts of normal metabolic processes, rather than intentionally-created pro-aging factors, could also potentially induce an aged animal’s blood to blight its parabiotic partner.

At the urging of SENS Research Foundation CSO Aubrey de Grey, and with SRF funding, pioneering parabiotic researchers Michael and Irina Conboy conducted a study to tease out the role of access to a young animal’s organs in the parabiosis effect in 2015. Working in the Berkeley lab, SRF alumnus Justin Rebo and Keith Causey built a machine capable of exchanging volumes of blood at will, replacing them with equal volumes of blood (or plasma, or other substitute fluid) from an opposite-aged animal without passing the blood through the opposite-aged parabiont. This isolates the effects of true bioactive signaling factors intentionally produced and circulating in young and old animals from the effects of metabolic wastes produced in the old animal that are (or are not) filtered out by an aging liver and kidneys.

Sure enough, the benefits of directly trading old blood for young were dramatically less impressive than the effects of full-on parabiosis complete with the filtering and detoxification services provided by young liver and kidney function. Notably, while exposure to old blood alone was sufficient to profoundly inhibit neurogenesis in young animals (implying the presence of one or more strong new-neuron-repressive factors in aging blood), there was little or no effect of transferring young blood alone to an aging animal on its brain’s neurogenesis (implying the absence of any active pro-neurogenic factors in young blood). Similarly, the mere transfer of old blood into young animals weakened the animals’ abilities to hang from the ceiling of their cage, and such animals failed to show improvements in hanging after practice — whereas old animals did not get any stronger when given blood from a young animal but not organ access.

On the other hand, receipt of young blood did enhance the repair of old animals’ muscles after injury, although the effects were less impressive than what’s seen in parabiosis — and in this case, there was no inhibitory effect on the muscles of young animals exposed to old blood. Similarly, the ability of an old animal’s injured liver to regenerate was enhanced by young blood, and existing age-related fibrosis improved. These experiments show that these health effects are not mediated primarily by removal of metabolic wastes, though certainly they could still be mediated by dilution effects rather than true active-factor transfers.

Round two, then, was a mixed decision, but advantage: Dilution Solution.

Round Three: Clearing the Waters

By this point, a direct test of the dilution hypothesis would seem to be in order — and recently the Conboys ran one. With the blood-replacement machine up and running, they replaced half the blood of old mice — not with young blood, but with saline solution, plus an amount of the albumin protein family equivalent to that in blood, to avoid losing albumin’s important non-signaling functions in transporting different substances around the body.

Like young blood itself, this “neutral blood exchange” (NBE) substitute (as they called it) would lack all of the pro-aging factors that an old mouse’s blood would contain (as well as the metabolic sludge its aging organs would have failed to remove) — but, importantly, would not contain any of the pro-youth molecules that the Infusion Solution hypothesis supposes are responsible for the effects of heterochronic parabiosis.

Remarkably, a single NBE treatment rejuvenated muscle repair capacity of old mice to equivalent levels of quite young control animals, including major improvements in the number of muscle stem cells engaged to regenerate the damaged muscle (the “regenerative index”), the area of muscle where such cells were active, and in the level of fibrosis left behind (Figure 1). NBE also significantly improved liver health in old animals, partially reversing their fibrosis and reducing the pathological fat deposits in the organ.

Figure 1.

After “Dilution” with saline and albumin, aged mouse serum’s effect on muscle repair is rejuvenated. Redrawn from (1).

Looking at the animals’ brains, the Conboys saw something even more intriguing. A single exchange of half the old animals’ blood for saline solution not only matched the effects of young blood on neurogenesis (the birth of new neurons): it boosted neurogenesis by approximately eightfold — substantially more than had been observed in previous heterochronic parabiosis experiments in their own and other researchers’ labs.

Additional direct evidence against the Infusion Solution hypothesis can be found by drilling a bit further into the details of study. First, if there really were strong youth-promoting factors circulating in young blood, then administering saline-albumin to young animals would have diluted them away and impaired such animals’ regenerative powers. Instead, NBE had no effect on muscle repair or liver health in young animals, demonstrating that such factors either do not exist, or play so little a role in maintaining these processes that you can cut their level in half without consequence.

In fact, NBE actually seemed to enhance neurogenesis even in young mice, although to a lesser degree than it did in the old. Anyone trying to explain the effects of heterochronic parabiosis in the old as the effect of such pro-youth factors will have to explain why halving the concentration of such factors not only lacks harmful effects — but actually seems to benefit the brain.

Spurred on by these striking but limited results, the Conboys looked more broadly at the effects of dilution on the aging brain and cognitive function in a followup paper, showing that a single round of NBE was able to reduce the level of overactive immune cell activity and inflammation in the aging brain, and completely wipe out the difference between young and old animals’ ability to discriminate novel objects by appearance or by texture. On that test, dilution made old brains think like young ones.

Might these effects be due to elimination of senescent cells in the brain? It seemed plausible: senescent cells certainly cause inflammation in their environment, and several previous studies had reported that conventional parabiosis lowered the burden of senescent cells in aging animals. In this followup study, the Conboys confirmed that dilution had the same effect on the aging brain, to a degree similar to the effect of the well-established senolytic (senescent cell-killing) drug navitoclax. Despite this, navitoclax had much less effect on brain inflammation and aggravated immune cells than NBE — and it failed entirely to improve age-related neurogenesis impairment in the aging animals’ brains.

An important but intriguing caveat to these results is that navitoclax is not expected to cross the blood-brain barrier (BBB) — the protective system of tight junctions that shields the brain from toxic substances. The drug’s effects on senescent cells in the brain and resulting inflammation and neurogenesis may therefore have been largely limited to indirect effects of eliminating senescent cells elsewhere in the body (which would prevent inflammatory factors from those cells from reaching the brain), plus a small amount of leak-in of navitoclax because of the age-related breakdown of the BBB. Senolytic drugs or immune therapies that can more effectively reach the aging brain might produce much more profound effects.

Round three again goes to the Dilution Solution, marking strike three for youth-promoting factors.

Hints in Humans

Based on the dilution study, and supported by the earlier study involving direct blood exchange between young and old animals (taking the filtering and detoxification machinery of the liver and kidneys out of the picture), it seems clear that most or all of the effect of young blood on older animals is due to alleviation of the suppressive effects of factors in aged blood on the animal’s tissues.

Would these same effects occur in humans? That study has not been performed (yet! See below), but one part of the animal study did hint that NBE might have similar effects on the liquid information superhighway of aging humans. In a tiny pilot study, the Conboys partnered with Dobri Kiprov, who specializes in apheresis (medical removal of patient blood constituents), to test the effects of the equivalent procedure in humans: an established medical procedure known as therapeutic plasma exchange (TPE), which is used to treat a variety of disorders, mostly of the immune system — as well as, just recently, experimental use to treat advanced COVID-19 cases.

Four volunteers aged 65 to 70 had their blood exchanged with physiologic saline and albumin. Blood samples were taken before and after the procedure and tested for their effects on mouse cells. Compared to blood sampled before TPE, aged human serum taken after a round of dilution increased the proliferation of mouse muscle stem cells, irrespective of added albumin, consistent with what was seen in the mice (Figure 2). Here, as in most of their studies, albumin was apparently not a factor in the results.

Figure 2.

After “Dilution” with saline and albumin, aged human serum’s effect on muscle repair is rejuvenated. Redrawn from (1).

AMBAR, Albumin, Ambiguity

Another trial, completed several years ago, is highly suggestive for dilution effects in aging humans, even though that wasn’t what the trial was designed to test.

Early in the last decade, Grifols — a global plasma products company — launched the AMBAR (Alzheimer’s Management by Albumin Replacement) trial to test albumin as a treatment for Alzheimer’s dementia of aging (AD). This was based on the facts that albumin is both a major extracellular antioxidant, and the carrier of about 90% of the beta-amyloid (Abeta) in the circulation — Abeta being one of the two key damaged proteins responsible for driving AD.

Previous research had shown that the pool of soluble Abeta in the brain exists in a kind of dynamic balance with the pool of Abeta in the blood. Therefore, lowering the level of circulating Abeta creates an osmotic force that draws soluble Abeta out of the brain, potentially offering protection against harmful effects. This “peripheral sink” approach had previously been demonstrated in animals using antibodies that trap Abeta in the blood, and was thought to be the mechanism for some of the passive antibodies targeting Abeta in human clinical trials.

In AMBAR, Grifols scientists hypothesized that AD patients’ albumin might be so saturated with Abeta that it would have lost its ability to draw out any more. Replacing that old, saturated albumin with fresh new protein would thus restore the youthful capacity to pull Abeta out of the brain and eliminate it via the liver.

The Grifols researchers also thought that patients would benefit from the fresh albumin’s antioxidant capacity. Albumin is a major antioxidant in blood plasma, but becomes more oxidized with age, and even more so in several diseases of aging — including AD, where albumin is more oxidized not only in plasma, but even more so in the cerebrospinal fluid.

Additionally, some patients in the trial were given Grifols’ intravenous immunoglobulin (IVIG) — a mixture of the antibodies in normal, non-infected people’s plasma, hypothesized to possibly contain natural antibodies targeting Abeta and thus further enhance the effect. IVIG had shown promise in several smaller clinical trials, but was largely abandoned after failing in a large one. Grifols scientists mostly included it to replace the antibodies that would be depleted by TPE, but also hoped that it might have some therapeutic effect of its own if combined with the effects of TPE and albumin itself.  

The researchers also entertained the possibility that TPE itself would remove other toxic substances from AD patients’ plasma — but as a kind of haemodialysis, without imagining the sweeping effects seen in the Dilution Solution experiments (or in heterochronic parabiosis). Their real focus was on the albumin.

There were four groups in the trial. One group got a placebo treatment through every step of the trial, on the same schedule as the other groups: a yellowish fluid was circulated around the equipment, but was never actually connected to the patient’s circulation, giving the appearance of TPE without in any way changing a patient’s blood. All three of the remaining groups underwent six weekly sessions of conventional TPE — considered an intensive regime — and then, after a short break, received one session once a month of TPE ‘fortified’ with extra low- or high-dose albumin, with or without IVIG, for the next year.

The results were finally published this summer — and they look very promising. Overall, Therapeutic Plasma Exchange slowed AD patients’ decline in self-care ability by a remarkable 52% (see Figure (A)), and strongly appeared to slow cognitive decline — by an even larger two-thirds (Figure (G)) — but the pooled cognitive effects did not quite pass the standard test of statistical significance.

When you drill down one layer, both the cognitive effects and the activities of daily living were statistically significant when the moderate AD patients were considered separately (see Figures (B,H)). By contrast, there was no effect on either parameter in mild AD patients considered separately, seemingly for no other reason than the lack of any detectable decline in any of the mild AD groups over the course of the trial (Figures (C, I)).

Supposing that the effects in the moderate AD were real: what caused them? Was it the basic TPE that all treatment groups received, or was it the extra albumin added for all groups throughout the last twelve months of the trial? Did the IVIG have any effect at all? If TPE alone was the real driver, are we indeed seeing true dilution effects? There’s unfortunately no way to know for sure: all the treatment groups tend to bunch fairly closely together or to change relative positions throughout the trial ( Figures (D, E, J, and K)).

Overall, AMBAR offers some tantalizing clues about the benefits of the Dilution Solution in Alzheimer’s dementia of aging — but is far from proving or disproving the case.

Plumbing the Depths...

To further investigate the molecular details of what was driving the effects of the Dilution Solution in their study, the Conboys looked to see what circulating proteins had changed in mouse and human serum one month after NBE or TPE (respectively). Proteins that were prominently changed included mediators and regulators of immunity, formation of new blood vessels, and growth factors (including growth factors active in neuronal tissue).

In the brain-centered followup study we discussed above, the researchers took a more specific look at the effects of NBE or TPE on proteins known to play roles in the health of the aging brain. Fifteen such proteins underwent major shifts from the pre-TPE aging human plasma to their levels one month post-dilution, as did eleven such proteins (although a different set) in the rodents after NBE.

Overall, more proteins in both studies actually had their concentrations increase than decrease one month after TPE/NBE, even though the whole basis of the intervention is to dilute the aging blood of such factors. But this isn’t so surprising: just as “dilution” was shown to interrupt the inhibitory influence of old plasma on tissue regeneration, it also released the inhibitory influences on the aging mouse or person’s production of some endogenous proteins, breaking a kind of pathological signaling gridlock enforced by long-set feedback driven by underlying aging changes. The Conboys even presented a theoretical model of how the effect on feedback loops in the system could either have long tails, or shift up and down in waves over time, leading to an extended period of complex changes in blood constituents.

And we should know more before too long. The Conboys have made clear their intent to explore the effects of NBE further, assessing its impact on the fate of newborn neurons, on cognition in treated mice, on metabolic health, and on tissues other than the classical three (liver, brain, and above all muscle) that have been the primary focus of modern heterochronic parabiosis research.

And one step more: Dobri Kiprov, the Conboys’ partner from California Pacific Medical Center in San Francisco, has planned for both near-term individual experiments with TPE and an eventual move to larger and more rigorous studies to test the potential of TPE as a short-term therapy to restore a more youthful signaling environment.

... and Parting the Waters

Remarkable as the heterochronic parabiosis phenomena are — and provocative as the dilution study is — it’s important to ask the next question, which is why the aging blood is so suppressive. The answer, of course, is that as a mouse or a human ages, the cells and tissues that produce, filter, detoxify, respond to, and metabolize signaling factors that circulate in the blood accumulate cellular and molecular damage. Damage, in turn, causes organs to become dysfunctional, which impairs the production, filtration, and metabolism of factors, just as a damaged television satellite can scramble and distort the signal it receives, transmits, and beams down to receivers on the ground. Additionally, damaged tissues proactively send out signals to recruit immune cells and other factors to assist in their repair — but as the burden of unrepaired (and unrepairable) damage accumulates, the net level of these same factors becomes dysfunctional.

A good example of this is, of course, senescent cells. One of the main evolutionary reasons why senescent cells produce the SASP (the “senescence-associated secretory phenotype” cocktail of inflammatory, growth, and other factors) is because the senescence response originally evolved as part of the response to injury and was later adapted as a bulwark against cancer. When senescent cells have served their purpose, they secrete inflammatory factors that attract immune cells to clear them out. But removal is never complete (something we’re working to enhance or rejuvenate at SENS Research Foundation), and as we age, senescent cells accumulate — and with them, exposure to SASP signaling factors increase. Studies have revealed a surprising disconnect between the level of senescent cells in an organism and the level of “classical” SASP factors in the blood, but recently scientists in several different labs have identified rising levels of novel and established SASP products in the aging blood and linked them to age-related frailty and disease.

Time Magazine, February 23, 2004. Copyright 2004 TIME USA, LLC

Another source of aberrant signaling in the aging blood is atherosclerosis, as first became widely known after a 2004 Time magazine cover story. Blood vessels infiltrated by oxidized LDL particles attract macrophages to engulf these particles, and macrophages themselves secrete additional inflammatory factors to recruit other immune cells into the lesion to back them up. Additionally, atherosclerotic lesions are riddled with senescent cells, which of course are a source of SASP. This is why C-reactive protein (CRP) — a general marker of inflammation — is useful as a marker of cardiovascular risk, even though CRP is not itself causally involved in the disease.

An additional source of aberrant signaling specific to the brain is the breakdown of the blood-brain barrier (BBB) — the protective network of tight-wound blood vessels and associated cells that protect the brain from infiltration by both toxins and otherwise-benign circulating factors (including albumin!) that can damage brain neurons if allowed unrestricted access to this critical organ. BBB breakdown has long been linked to brain inflammation and cognitive impairment in aging mice and models of neurological aging diseases, and has more recently been documented in humans using new technology. A recent study modeling BBB breakdown in young, healthy mice showed that the entry of extraneous proteins into the brain leads to brain inflammation and cognitive impairment; notably, the factor that sets this cascade off is none other than TGF-β.

Other sources of pro-aging factors in the aging circulation include the accumulation of cells bearing large deletions in their mitochondrial DNA (which transfer oxidative stress to their neighbors and into the circulation), the accumulation of extracellular aggregates, damage to the heart from decades of hypertension and subclinical heart attacks, and (as discussed previously) accumulating damage to the filtering and detoxification structures of the kidneys and lungs.

From Dilution to the Repair Revolution

Provocative as these results are, the Dilution Solution is at best a stop-gap, comparable to keeping a badly worn-out engine running by means of frequent oil changes and top-ups.

No truly long-term studies have been done on either NBE or parabiosis, though the fact that weekly injections of young plasma starting at middle age and continuing throughout the lifespan failed to extend life in mice, suggesting a possible downside counteracting the benefits seen in short-term studies. One can well imagine that cancer and stem cell depletion might be among these downsides (by promoting the unchecked proliferation of stem cells).

Ultimately, the way to permanently restore the youthful systemic environment and reap the benefits of parabiosis is to repair the underlying damage that deranges it in the first place. This is just common sense: we all know the right way to deal with burning oil is to repair the engine, not constantly change the oil and put buckets under the car.

By ablating senescent cells (via senolytic drugs or immune rejuvenation or enhancement) — including in the brain, where the senolytic drugs used in the Conboys’ brain study couldn’t directly reach; by removing extracellular aggregates; by applying cell therapy and tissue engineering to the damaged kidneys, liver, heart, and other tissues; by repairing the blood-brain barrier and leaky gut; by making mitochondrial mutations harmless via backup copies; and through other damage-repair solutions, rejuvenation biotechnology can return our bodies to the same structural integrity — and therefore, the same signaling environment — that gave us health and vigor in youth.


  1. Mehdipour M, Skinner C, Wong N, Lieb M, Liu C, Etienne J, Kato C, Kiprov D, Conboy MJ, Conboy IM. Rejuvenation of three germ layers tissues by exchanging old blood plasma with saline-albumin. Aging (Albany NY). 2020 May 30;12(10):8790-8819. doi: 10.18632/aging.103418. Epub 2020 May 30. PMID: 32474458; PMCID: PMC7288913.
  2. Boada M, López OL, Olazarán J, Núñez L, Pfeffer M, Paricio M, Lorites J, Piñol-Ripoll G, Gámez JE, Anaya F, Kiprov D, Lima J, Grifols C, Torres M, Costa M, Bozzo J, Szczepiorkowski ZM, Hendrix S, Páez A. A randomized, controlled clinical trial of plasma exchange with albumin replacement for Alzheimer’s disease: Primary results of the AMBAR Study. Alzheimers Dement. 2020 Jul 27. doi: 10.1002/alz.12137. Epub ahead of print. PMID: 32715623.
  3. Mehdipour M, Mehdipour T, Skinner CM, Wong N, Liu C, Chen CC, Jeon OH, Zuo Y, Conboy MJ, Conboy IM. Plasma dilution improves cognition and attenuates neuroinflammation in old mice. Geroscience. 2020 Nov 15. doi: 10.1007/s11357-020-00297-8. Epub ahead of print. PMID: 33191466.

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