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Received: August 23, 2018 | Accepted: December 25, 2018 | Published: January 03, 2019
OBM Hepatology and Gastroenterology 2019, Volume 3, Issue 1, doi:10.21926/obm.hg.1901013
Recommended citation: Tomaszewski M, Wong P. Stem Cell Therapy in the Elderly with Liver Disease. OBM Hepatol Gastroenterol 2019;3(1):16; doi:10.21926/obm.hg.1901013.
© 2019 by the authors. This is an open access article distributed under the conditions of the Creative Commons by Attribution License, which permits unrestricted use, distribution, and reproduction in any medium or format, provided the original work is correctly cited.
The geriatric population with liver diseases is growing which impacts both their survival and quality of life. Liver transplantation is a high stakes and invasive therapy for end stage liver disease, often denied to patients who are at advanced age, with co-morbidities often times being cited as the principal reasons. The most widely accepted definition of geriatric patient is age greater than 65 years . Although the outcomes of geriatric patients undergoing liver transplantation are generally poorer, with stringent patient selection, outcomes have improved [2,3]. Given the morbidity of chronic liver diseases and the complications of liver transplantation specific to the geriatric population, there is an impetus to find novel therapies specifically for the geriatric population. Stem cell therapy is an interesting targeted therapy for such patients given the lack of immune suppression and other perioperative and long-term complications associated with liver transplantation. Stem cell transplantation is less invasive compared to other investigational therapies such as bioartificial liver support systems [4,5,6]. The following review will assess liver disease in the elderly, advances in stem cell therapy and whether there is a role for stem cell therapy in geriatric patients with liver disease.
A number of changes in hepatic anatomy, physiology and natural history of disease have been described in geriatric individuals. They have decreased liver volume and mass of functional liver cells [7,8,9,10]. In elderly humans, a decrease in phase 1 metabolism exists. This potentially results from a documented decrease in blood flow with aging and decrease in cytochrome P450 activity . There is evidence, in animal models, that age negatively impacts the liver’s ability to regenerate . Older rats post hepatectomy displayed slower rates of regeneration when compared to younger rats . This has been corroborated in human trials whereby elderly patients’ livers regenerate to a lesser extent post-partial hepatectomy . Animal models have shown that younger animals are more likely to return to normal liver function following liver injury with carbon tetrachloride when compared to older animals [8,14].
There are many differences in liver diseases when comparing the elderly to the general population. The worse prognosis of elderly patients with certain liver diseases is potentially partially explained by cellular senescence and impaired regeneration [8,12,13,14].
Elderly patients with hepatitis A experience increased jaundice and coagulopathy in addition to prolonged cholestasis, pancreatitis and ascites . The hospitalization and mortality rates are higher amongst these patients [11,16].
Although the opportunities for infection with hepatitis B in the elderly are lower, reports of hepatitis B transmission has been reported in nursing homes. The rate of progression to chronic hepatitis B is higher in the elderly . In adults, the risk of developing chronic infection is less than five percent . In contrast, 59% of elderly patients developed chronic infection in an outbreak of hepatitis B in a nursing home .
Older age at the time of infection with hepatitis C, irrespective of duration of infection, has been associated with increased progression of fibrosis and risk of hepatocellular carcinoma [19,20]. Patients over age 65 with hepatitis C have more advanced fibrosis independent of ALT levels . As a result, elderly patients with hepatitis C can benefit from highly effective direct acting antiviral therapy.
Elderly patients with autoimmune hepatitis actually have lower failure rates, lower mortality rates and decreased need for liver transplantation . They respond well to corticosteroids however are at risk for complications of their use. . Elderly patients diagnosed with primary biliary cholangitis (PBC) at a younger age have a poorer prognosis, although patients diagnosed at an older age show a better prognosis [11,22].
Drug induced liver injury seems to have a larger impact upon elderly patients [11,23]. This may be in part as a result of polypharmacy that affects the geriatric population at a much greater rate . However, the degree of injury is more severe than in younger counterparts when controlled for number of medications .
Non-alcoholic fatty liver disease (NAFLD) is more prevalent amongst the geriatric population. The elderly have more risk factors for NAFLD including hypertension, diabetes and dyslipidemia . Geriatric patients with NAFLD tend to have evidence of more advanced disease. A study demonstrated they are more likely to have lower albumin, alanine aminotransferase (ALT), ALT/aspartate aminotransferase ratio and platelets, higher mean cell volume and more advanced fibrosis on biopsy .
Alcoholic liver disease is becoming increasingly present amongst the geriatric population . Predictably, older patients presenting with alcoholic liver disease have more advanced disease . Outcomes of alcoholic cirrhosis are poor in the elderly – half die within one year of diagnosis .
As the global population continues to age, the number of geriatric patients with liver failure continues to rise. The repercussions of chronic liver disease have a significant negative impact on quality of life amongst the elderly. Geriatric patients with cirrhosis have been shown to have worse self-reported health scores, increased health care resource utilization and more comorbidities . Additionally, they have increased functional disability both with regards to activities of daily living (ADLs) and instrumental activities of daily living (iADLs) requiring almost twice the amount of caregiver hours per week . Furthermore, in patients over age 60 who undergo liver transplantation, quality of life is worse in many domains when compared to age and sex matched controls. These domains included physical functioning, vitality, social functioning, general health, physical role functioning and emotional role functioning . To our knowledge, there has been no study comparing quality of life pre- and post-liver transplantation in the elderly population although this would be of interest. It is clear that liver disease causes significant functional impairment and decreased quality of life in the elderly. As such, it is important to find effective treatments for these patients.
Liver transplantation often represents the only life-saving therapy in end stage liver disease. Although advanced age was initially a contraindication for liver transplantation, recent experience has revealed the intricacy of transplant candidate selection. Initial experience with liver transplantation, in patients more than 60 years old, showed less favourable survival at 1 and 5 years . However, more recent experience with more careful selection of transplantation candidates has yielded similar survival rates . A scoring system developed from poor prognostic factors (ventilator status, diabetes mellitus, hepatitis C virus, creatinine ≥141 micromol/L, combined recipient and donor age ≥120 years) helps determine patients over age 60 who are at higher risk for poor outcomes . Of note, hepatitis C infection will no longer likely be a negative prognostic predictor with the success of direct-acting antivirals.
Transplantation has its shortcomings. Donor organ shortage remains a barrier to transplantation for many patients. In the post-transplant period, the requirement of life-long immune suppression, infectious and neoplastic complications and polypharmacy are limitations. Despite the improved success in transplantation of the elderly, it is clear that a large proportion of patients will not be candidates for liver transplantation on the basis of stringent patient selection and a focus on novel therapies for treatment of liver disease remains essential.
Traditionally thought of as a geriatric syndrome, frailty, independent of age, influences physical, psychological, functional and survival outcomes in chronic liver disease. Sarcopenia, characterized by a loss of skeletal muscle mass and function, is an independent risk factor for transplant wait list mortality [31,32,33]. Despite this, the development of a Model for End-Stage Liver Disease-sarcopenia score performed less well than the traditional Model for End-Stage Liver Disease (MELD) score with regards to prediction of three-month mortality . In this study, sarcopenia was assessed via computed tomography-based imaging that was used to determine the cross-sectional skeletal muscle area. Frailty was a predictor of hospitalization incidence and duration of hospitalization according to a prospective observational study performed in cirrhotic patients on the transplantation waitlist . Although quality of life is already impaired in cirrhotic patients, it is especially low in frail cirrhotic patients. A single centre prospective study negatively correlated frailty with both physical and mental quality of life, independent of severity of cirrhosis by MELD score . Frailty is also a strong predictor of depression in patients with end stage liver disease independent of the severity of cirrhosis . Additionally, worse functional status has been associated with increased post-transplant mortality independent of pre-transplant MELD score . This shows that patients with chronic liver disease and a geriatric profile of frailty and functional dependence suffer worse outcomes in many spheres. Patients undergoing liver transplantation have less frailty at 6- and 12-months post transplantation. However, less frailty prior to transplantation has been associated with an improvement in frailty scores post-transplantation . As a result, attempts have been made targeting frailty in an attempt to alter outcomes. There is some evidence to suggest that TIPS may lead to an improvement in frailty, and that patients who gain muscle mass post-TIPS have favourable mortality rates when compared to patients without improvement of sarcopenia . Attempts have been made to identify performance based physical therapy targets in order to minimize frailty in patients prior to transplantation . Ideally, novel therapies would obviate the need for liver transplantation in frail patients with end stage liver disease and hopefully improve outcomes.
In addition to the limitations to transplantation that apply to all patients, independent of age - a global shortage of donors, the sequelae of long-term immunosuppression and high medical costs, many elderly patients are not candidates for transplantation given frailty, comorbidities, and data showing worse outcomes in the elderly. As a result, novel therapies, such as stem cell transplantation, are interesting possibilities for elderly patients. Stem cell transplantation is an attractive theoretical target for a frail geriatric population given it is less invasive than other experimental therapies such as bioartificial liver support systems [4,5,6].
Stem cell therapies can be classified into ex vivo such as with bioartificial liver (BAL) or into in vivo where the stem cells are directly infused into the human with a regenerative target. The eventual goal of ex vivo therapies is generally short-term support of liver failure. The research goals of in vivo therapies are short-term support and long-term improvement in hepatic synthetic function.
There are many potential sources for stem cell harvesting in liver disease. In human clinical trials, the bone marrow is the source of the two most common sources of stem cell therapy: mesenchymal stem cells (MSC) and hematopoietic stem cells (HSC) [41,42].
MSCs adhere to plastics, express CD105, CD73 and CD90 which helps to identify them . MSCs may contribute to adult liver regeneration during via the process of mesenchymal-epithelial or epithelial-mesenchymal transition (MET/EMT) . This theory proposes that during hepatic injury some epithelial cells undergo EMT, acquiring myofibroblastic features and contributing to fibrogenesis. However, certain mesenchymal cells undergo MET, revert to epithelial cells that may differentiate into hepatocytes or cholangiocytes. This theory, although controversial, states that it is the balance of EMT and MET that determines the outcomes of liver injury [5,43]. Mesenchymal cells in the liver may originate from hepatic progenitor cells and the bone marrow, migrating to the liver in the context of injury . Additionally, MSCs play a role in modulating liver fibrosis by secreting antiapoptotic factors and trophic factors .
MSCs in most studies to date have been isolated from the bone marrow (BM-MSCs) however other potential sources include the liver, adipose tissue, umbilical cord blood, umbilical cord and amniotic fluid [45,46,47]. Concerns with regards to MSC therapy lie in a theoretical risk for tumorgenicity [48,49,50]. This tumorigenic effect has not been observed in human clinical trials .
HSCs express cell surface markers CD34 and CD133. In a carbon tetrachloride model of liver fibrosis in mice, fibrosis was reduced, and survival increased with infusion of HSCs . The mechanisms underlying this pre-clinical result remain unclear.
Hepatic progenitor cells (HPCs) are hepatic stem cells located in the Canals of Hering. They are rare in normal adult livers however may be activated by liver injury such as oxidative stress caused by alcoholic liver disease and non-alcoholic fatty liver disease [45,52,53]. HPCs can differentiate into hepatocytes, promoting liver regeneration post hepatectomy . An interaction between HPCs and MSCs is important for remodeling after liver injury . Use of liver derived stem cells is limited by low numbers within the liver making their isolation and expansion challenging [41,55]. Additionally a potential for carcinogenesis and fibrogenesis has been observed in vitro .
Multipotent stem/progenitor cells have been identified from the fetal biliary tree. Transplantation of these cells into immunodeficient mice has resulted in differentiation into mature hepatocytes and cholangiocytes . Ethical and legal aspects of fetal stem cell use remain barriers to its implementation [57,58].
Induced pluripotent stem cells (iPSC) bypass the ethical controversy surrounding embryonic stem cells (ESC) as they are produced in vitro from somatic cells. IPSCs have similar attractive properties of ESCs: pluripotency and self-renewal. IPSC use for the moment remains limited to in vitro and animal studies [41,59].
The benefit of stem cell therapy has been questioned through the results of many recent human studies (Table 1). A systematic review from 2014 of 33 stem cell therapy trials highlighted this. Most of the trials were small cohort studies. Of 6 RCTs, only 1 by Spahr et al. was deemed to be high quality, mainly because of trial design [42,60]. The systematic review concluded that peripheral administration of HSCs was likely safer than portal vein or hepatic artery injection related to the risks of variceal bleeding and hepatic artery dissection respectively [61,62]. Only 9 of the 33 studies reported positive clinical outcomes with regards to reduction in Child-Pugh and MELD scores – however all studies were of poor or moderate quality. In the randomized control trial by Spahr et al. from 2013, deemed of high quality by the systematic review, of 58 patients with alcoholic hepatitis compared hepatic artery infusion of autologous bone marrow mononuclear cells to standard medical therapy. Geriatric patients were included in the study. Liver function improvement and improvement of liver histology was the same in both arms . Of note, the underlying pathology of alcoholic hepatitis, characterized by inflammation, differs greatly from cirrhosis, characterized by fibrosis but minimal inflammation. A main limitation of this trial was the duration of only 12 weeks.
A subsequent RCT from 2013 by Mohamadnejad et al. assessed peripheral infusion of autologous BM-MSC in 27 patients. This study included elderly patients but was underpowered and did not find a significant difference in Child-Pugh scores, MELD scores, serum albumin, INR, serum transaminases and liver volumes at 12 months . There was a decrease in MELD scores in both the treatment and placebo groups which had previously been observed in non-controlled trials. The improvement of MELD score could have been as a result of improved supportive therapies provided to both the intervention and control groups. This highlights an important limitation of previously published non-controlled trials that reported improvement of MELD scores .
A meta-analysis by Pan et al. from 2014 found a positive clinical benefit of BM-MSC transplantation. However, it had many limitations. Of 5 studies, it included only 2 controlled studies, neither of which was randomized nor blinded. The protocols for stem cell harvesting and infusion differed drastically between included studies. Publication bias was not assessed given there were less than 5 studies in each subgroup. Additionally, the underlying chronic liver diseases of participants were variable. They reported small but significant decrease in MELD score compared to controls (-2.01 [95%CI: -3.35-(-0.68)]) up to 24 weeks and increased albumin (mean 4.39 g/L) at 48 weeks. The lack of randomization and blinding may have led to measurement and performance bias. Taking in to account the limitations in methodology and the very modest improvements of hepatic synthetic function, few conclusions can be drawn from this trial .
Table 1 Human clinical trials in stem cell therapy for liver disease.
Qi et al published a meta-analysis in 2015 that has put into question the benefit of hematopoietic stem cell therapy. With 31 studies included, there was heterogeneity in their results. The MELD score was reduced at 3, 4 and 6 months, however not significantly reduced at 1-2 months and 12 months. This hints that if there is any clinically significant benefit, that this benefit may not be a durable one. Child-Pugh scores were not improved at any time point assessed and there was no significant effect upon mortality. Additionally, there was no significant difference between the incidence of hepatocellular carcinoma between the groups .
Subsequently, a meta-analysis by Liu et al. evaluated the effect of both BM-MSC and HSC transplantation in patients with cirrhosis (of many etiologies) showed a reduction in bilirubin, PT and MELD score compared to baseline . The trials included generally had mean patient ages in the forties or fifties although there were some participants with ages over sixty. This meta-analysis was limited by many different protocols of stem cell injection, stem cell preparation and underlying cause of cirrhosis. As a result, there was a large degree of heterogeneity in the trial. A major limitation of the meta-analysis lies in the fact that none of the trials included were randomized or controlled. The outcome of decrease in MELD score, PT and bilirubin relative to baseline in the absence of comparison to a control group may simply be a result of supportive care and not be related to stem cell therapy.
Allogeneic BM-MSC therapy has been shown to have benefit in hepatitis B acute on chronic liver failure (ACLF). A randomized, open label, non-blinded controlled trial from 2017 by Lin et al. revealed a survival benefit at 24 weeks in the treatment arm (55.6% survival versus 73.2 % (p=0.03)). MELD score and total bilirubin were improved at 24 weeks, although no significant differences in ALT, albumin or INR were observed . Limited by its single center, open label design, the authors also acknowledged the high mortality rates in both groups as a potential source of bias – potentially over-estimating the effect of improvement of biochemical and synthetic outcomes as deceased patients were not assessed at time points following their death. Nonetheless, this trial presents some of the most compelling evidence in support of stem cell therapy specifically in the context of hepatitis B ACLF. The speculated mechanism was that immunomodulation and anti-inflammatory functions of BM-MSCs alleviated hepatic inflammation thus improving hepatic function and decreasing fatal complications. The authors speculated that the allogeneic BM-MSCs have potential advantages compared to autologous BM-MSCs in the treatment of ACLF. Timely intervention is important in ACLF given its rapid onset and progression. Allogeneic BM-MSCs could be prepared as a frozen stock, ready for use. Also, BM-MSCs derived from hepatitis B patients proliferated slowly and underwent senescence . Patients above of the age of 60 were excluded from the trial and therefore this data may not be generalizable to the geriatric population.
A well-designed randomized control trial (REALISTIC trial) from 2018 of 81 patients published in the Lancet revealed no benefit of granulocyte colony stimulating factor (G-CSF) or G-CSF and repeated autologous CD-133 positive HSC infusion over standard of care in patients with compensated cirrhosis . The rationale for using G-CSF arises from pre-clinical studies showing that G-CSF led to faster hepatic regeneration after partial hepatectomy compared to controls . There was no difference in change of MELD score at 90 days nor was there a difference in the trend of MELD score between groups . If anything, serious adverse events were more common in the stem cell and G-CSF group as compared to the G-CSF or standard of care groups. These adverse events were mainly related to decompensation of cirrhosis – ascites, hepatic encephalopathy and sepsis. This study challenged much of the previous literature in a well-designed randomized, controlled trial that was adequately powered, with a modified intention to treat analysis. The HSCs were purified which has previously been shown to decrease liver fibrosis when compared to mixed HSCs . This trial included patients up to an age of 75 and at least a quarter of participants were above age 60.
Many stem cells trials have included elderly patients. The published literature is comprised mainly of small, unblinded trials, assessing heterogeneous patient populations with largely variable protocols for stem cell infusion. Some of these trials were able to achieve statistical significance however this does not imply clinically meaningful outcomes [64,66] and larger well-designed trials have shown negative outcomes [60,63,65,68]. It is clear that for the time being there is no known clinically significant benefit of stem cell therapy in the elderly with liver disease.
With regards to further directions, peripheral route of administration is also likely to be safer when compared to portal vein or hepatic artery administration . Given that older livers are less likely to regenerate and thus display cellular senescence, a potential target would be to assess the benefit of allogeneic MSCs [8,13,14]. Allogeneic BM-MSCs from younger donors could be compared to allogeneic BM-MSC from older donors and autologous BM-MSC from older donors to test this hypothesis. Umbilical cord MSC could also be compared to autologous MSC and has the potential to overcome the barrier of cellular senescence that occurs with aging . If stem cell therapy is to have a role in chronic liver disease amongst geriatric patients, further large, well-designed, randomized controlled trials are needed in order to confirm the possible benefit.
Older livers display impaired regeneration and cellular senescence. Additionally, elderly patients with certain liver diseases have a less favourable course and experience a significant negative impact upon quality of life and functional independence. Frailty and sarcopenia, commonly encountered in geriatric patients, remain significant negative predictors of physical, psychological, functional and survival outcomes in chronic liver disease. Despite advances in patient selection for liver transplantation that are more inclusive of elderly patients, many remain ineligible for liver transplantation. As a result, novel therapies are urgently required to treat this patient population.
Currently, there is no strong evidence to support the use of stem cell therapy modifying clinical meaningful outcomes in patients with chronic liver disease. Large rigorous trials have brought into question the potential benefits hypothesized by other non-randomized and mostly uncontrolled trials. Many trials included the elderly [60,63,65,66,68]. In cirrhosis, especially when using autologous stem cells, cellular senescence may lead to an unfavourable environment for stem cell proliferation [60,73]. Within the elderly, future targets could include the use of umbilical cord or allogeneic MSCs from younger donors which would not suffer from aging differentiation and deficiency in vitality .
MT and PW contributed to the literature review, drafting and editing of the manuscript.
No funding was provided for this review.
The authors have declared that no competing interests exist.