The increased frequency of organ transplant operations over the decades has given rise to some startling statistics; five-year survival of transplanted tissue is only 50% for lung transplants, 67% for liver transplants and not much better for other organs (HRSA, 2008). These bleak statistics are attributable to the destruction of transplanted tissue by the host’s (tissue recipient’s) immune system, which ultimately leads to the rejection of the transplanted organ.
Despite the widespread use of immunosuppressive drugs and advancements in medical technology, the immune system remains a formidable factor in successful organ transplantation (Malhotra, 2010).
Certain aspects of the immune system are responsible for suppressing inflammation and inhibiting transplant rejection. Important inhibitory components of the immune system are Treg, (or T regulatory cells). The inflammatory cytokines IL-1β, IL-2, IL-6, IL-15, IL-21 and TNFα, by inhibiting the function of Treg cells and promoting the activation of cytotoxic T-cells, are responsible for the intensity of the attack against the transplanted tissue by the host’s immune system (Hanidziar, 2010).
New findings demonstrate that calcineurin inhibitors (CNIs), immunosuppressive drugs widely-prescribed to transplant patients, fail to address an important underlying cause of transplant rejection – insufficient levels of protective Treg cells.
Several nutrients have been shown in peer-reviewed studies to target the specific inflammatory cytokines that are dually responsible for the stimulation of aggressive T-cells and the suppression of protective Treg cells.
Immunological Response to Foreign Tissue
Transplanted tissue contains molecular components of the donor’s immune system, known as the major histocompatibility complex (MHC), coupled with antigen presenting cells (APCs), which interact with the host’s immune system. Donor APCs, with the help of MHCs, present peptides (sections of proteins) derived from the transplanted tissue to specialized receptors, called CB8 receptors, on certain T-cells (white blood cells involved in cellular immunity) of the host. The host’s T-cells recognize that the peptide is foreign and begin traveling through the body in search of cells that contain this peptide.
The host’s T-cells are now “activated” and programmed to destroy the cells of the transplanted tissue. As the activated T-cells travel, they secrete inflammatory cytokines that serve to recruit and activate additional T-cells to help destroy the foreign cells. Importantly, these cytokines stimulate a particularly aggressive class of T-cells, called Th17 cells, as well. This process culminates in the initiation of an inflammatory storm that triggers the host’s immune system to mount a full-fledged assault against the transplanted tissue.
Inflammatory Cytokines and Treg Cells: Pivotal Roles in Tissue Tolerance
The immune system is more than a “seek-and-destroy” mechanism. Certain aspects of the immune system are responsible for suppressing inflammation and inhibiting the tissue destruction caused by activated T-cells. These inhibitory components of the immune system are known as T regulatory, or Treg cells. Treg cells are the counterbalance to aggressive, activated T-cells. Without Treg cells, our immune system would constantly attack our own tissue. In fact, the role of Treg cells in suppressing autoimmune diseases (e.g. diseases in which the immune system attacks the body’s own tissue, like rheumatoid arthritis, lupus, Crohn’s disease, psoriasis, etc.) has been well documented (Walker, 2008).
Treg cells are critical to the tolerance of an allograft (genetically non-identical transplant [All human transplants are allografts, unless the organ is taken from an identical twin]). The more Treg cells present in circulation, the weaker the attack against the transplanted tissue (Demirkiran, 2006). Ironically, the same inflammatory cytokines that stimulate aggressive T-cells also suppress Treg cells, promoting the attack against the transplanted tissue from two angles.
Treg cells and T-cells originate in the thymus, a specialized organ located just behind the sternum, between the lungs. Here, non-functional progenitor cells develop (differentiate) into either the immunomodulatory Treg cells, or the aggressive cytotoxic T-cells, depending on cytokine exposure.
Exposure to high levels of the inflammatory cytokines Il-1β, IL-6, or IL-21 causes progenitor cells to develop into aggressive T-cells, while exposure to sufficient levels of a highly specialized anti-inflammatory cytokine, called transforming growth factor-β (TGFβ), induces differentiation into Treg cells. Significantly, it has been shown that high levels of IL-6 inhibit the ability of TGFβ to effectively induce differentiation of progenitor cells to Treg cells, leading to an increase in the number of allograft-destroying cytotoxic T-cells. (Kimura, 2010; Hanidziar, 2010).
The roles of the inflammatory cytokines IL-1β, IL-2, IL-6, IL-15, IL-21 and TNFα in transplant rejection have been well-studied. By inhibiting the function of Treg cells and promoting the activation of T-cells, these cytokines are responsible for the intensity of the attack against the transplanted tissue by the host’s immune system (Hanidziar, 2010).
One of the most effective strategies for modulating an over-aggressive immune response against transplanted tissue is to target the specific inflammatory cytokines that are dually responsible for the stimulation of aggressive T-cells and the suppression of protective Treg cells.
Natural Compounds That Target Pro-inflammatory Cytokines Involved in Transplant Immunology
Studies of curcumin, a principle component of the Indian spice turmeric, have identified it as a potent anti-inflammatory agent (Sikora, 2010). In particular, numerous studies have revealed the ability of curcumin to target several cytokines involved in transplant rejection, including IL-1, IL-2, IL-6, IL-21 and TNFα (Jurrmann, 2005; Kim, 2009; Zhang, 2010; Xie, 2009).
An experimental study found that curcumin, in combination with cyclosporine, significantly improved survival time in animals that received a cardiac transplant from donors with incompatible genotypes. Animals treated with curcumin and cyclosporine survived for an average of 28.5 – 35.6 days after receiving a transplant, compared to untreated animals, which survived an average of only 9.1 days. The effect of the combination of curcumin and cyclosporine was greater than the effect of either one alone. The authors concluded that curcumin is efficacious as a novel adjuvant for immune system modulation both in vivo and in vitro (Chueh, 2003).
To more closely examine the immunomodulatory effects of the spice, researchers analyzed the effects of curcumin on lymphocytes of renal transplant patients who were experiencing transplant rejection. They found that the use of curcumin dose-dependently decreased interferon-alpha (an inflammatory cytokine) induction in cultures from patients experiencing acute rejection (38.3%-18.3%) and those experiencing chronic rejection (40.6%-12.9%), when compared with corresponding untreated cultures. Furthermore, the team also noted that curcumin was able to inhibit activation of nuclear factor kappa β (NF-kappa β), an inflammatory transcription factor, and inhibit proliferation of T-cells, having a synergistic effect when combined with cyclosporine. The researchers concluded that curcumin was a pharmacologically safe adjuvant to be used with cyclosporine, and can effectively suppress inflammatory cytokine induction after renal transplant (Bharti, 2010).
Curcumin has also been shown to combat acute renal failure and related oxidative stress caused by chronic administration of cyclosporine in an animal model. Researchers administered a dose of curcumin, equivalent to roughly 145 mg for a 60 kg human, to animals, along with cyclosporine for 21 days. It was shown that curcumin markedly reduced elevated levels of thiobarbituric acid reactive substances (markers of oxidative stress), significantly attenuated renal dysfunction, increased the levels of the antioxidant enzymes superoxide dismutase and catalase and normalized altered renal morphology in cyclosporine treated animals (Tirkey, 2005).
Omega-3 fatty acids, also known for their potent anti-inflammatory properties, are capable of suppressing the inflammatory cytokines IL-1, IL-2, IL-6, IL-15 and TNFα (Cooper, 1993; Manzoni, 2009; Wang, 2008; Muurling, 2003).
Researchers examined the endothelial function, as measured by endothelium-dependent vasodilation, of seven cardiac transplant patients who consumed 5,000 mg of EPA plus DHA daily for three weeks and compared the results to those of seven cardiac transplant control patients who did not receive fish oil. The researchers found that endothelium-dependent vasodilation was significantly improved in the fish oil group (+14% to +15%), while it worsened in the control group over the study period (-1% to -9%) (Fleischhauer, 1993).
In another study, researchers examined the effect of six grams of fish oil taken daily for one month in 40 cyclosporine treated patients who had received a transplanted kidney. It was found that fish oil-treated patients showed a significantly better recovery of renal function after a histologically confirmed rejection episode compared to control. The researchers went on to conclude that “dietary supplements with fish oil favorably influence renal function in the recovery phase following a rejection episode in cyclosporine-treated renal transplant recipients” (Homan van der Hide, 1992).
To evaluate the perioperative safety of fish oil in a transplant population, researchers evaluated hemodynamic, biochemistry and hematological parameters in kidney recipients who received intravenous fish oil for five days postoperatively. The researchers concluded that “administration of [omega-3 fatty acids] is safe in organ donors and in kidney recipients” (Singer, 2004).
In 2008, researchers found that dietary fish oil significantly reduce the severity of rejection to transplanted small bowel tissue in an animal model. They also found that fish oil favorably altered the expression of several genes involved in allograft rejection, and reduced the rate of apoptosis of graft cells. They went on to conclude that “omega-3 polyunsaturated fatty acids can suppress the rejection to mucosal cells of allograft at the time of chronic rejection in small intestinal transplantation, which may be significant in increasing the surviving rate of allograft, delaying the chronic dysfunction, and prolonging the lifetime of both allograft and acceptor.” (Kun, 2008).
Additionally, fish oil was shown to stimulate production of the very important anti-inflammatory cytokine transforming growth factor-β (TGFβ) and decrease the level of circulating cytotoxic T-cells in pregnant women receiving 500 mg DHA and 150 mg EPA daily. Fish oil supplementation was associated with reduced production of multiple inflammatory cytokines. (Krauss-Etschmann, 2008).
Studies conducted on resveratrol provide strong evidence that suggests it can help quell the cytokine storm and prolong the survival of transplanted tissue. Resveratrol has been shown to attenuate the action of the cytokines IL-1β, IL-2, IL-6 and TNFα (Shakibaei, 2007; Yu 2005; Wung, 2005; Leiro, 2010).
Resveratrol, at a dose equivalent to 967 mg for a 60 kg human, was shown to significantly increase survival time of animals that received a genetically incompatible liver transplant. Furthermore, resveratrol also reduced levels of cytotoxic T-cells (Wu, 2006).
In a skin graft model, used to study transplant rejection, rats supplemented with relatively small doses of resveratrol, equivalent to approximately 5 mg for a 60 kg human, had notable prolongation of the time period before their skin grafts were rejected. Only ~20% of the allografts in the control group survived greater than nine days post-operation, compared to 100% of the grafts in the group receiving resveratrol. The researchers noted that resveratrol significantly reduced infiltration of T-cells and necrosis in graft tissue (Hsieh, 2007).
Green and Black Tea Polyphenols
Compounds in green and black tea have been identified as particularly powerful anti-inflammatory agents (de Mejia EG, 2009). Studies have shown that components of tea are potent inhibitors of IL-1β, Il-2, IL-6 and TNFα (Wheeler, 2004; Wu, 2009; Hosokawa, 2010; Yuan, 2006).
Cardiovascular health is a major concern for transplant recipients, especially because cyclosporine, an immunosuppressive drug widely used after organ transplantation, is known to impair endothelial function (Morris, 2000).
Black tea consumption was shown to dramatically improve endothelial function, as measured by flow-mediated vasodilation and brachial artery diameter, in a study of renal transplant patients aged 25 – 50 years. The researchers went on to conclude that “based on our study, short-term consumption of black tea may improve endothelial function and endothelium-dependent arterial vasodilation in renal transplant recipients” (Ardalan, 2007).
The flavonoid quercetin is found in significant quantities in apples, onions, grapes and citrus fruits. Quercetin is known to modulate the action of several inflammatory cytokines that are of particular concern to transplant recipients, including IL-1β, IL-2, IL-6, IL-15 and TNFα (Ying, 2009; Yu, 2008; Liu, 2005; Karlsen, 2010; Ruiz, 2007).
Quercetin, in combination with vitamin E, has also been shown in vitro to combat the hepatotoxic effects of cyclosporine. Researchers found that the combination attenuated cyclosporine induced oxidative stress by restoring the activity of the antioxidative enzymes glutathione peroxidase and catalase. They concluded that “our data demonstrates that vitamin E and quercetin play a protective role against the imbalance elicited by cyclosporine between the production of free radicals and antioxidant defence systems, and suggests that a combination of these two antioxidants may find clinical application where cellular damage is a consequence of reactive oxygen species” (Mostafavi-Pour, 2008).
Considering the cytokine suppressive effects of quercetin, a team of researchers evaluated the impact of quercetin on the proliferation of T-cells. The team found that quercetin significantly inhibited T-cell proliferation, suggesting that it may be effective in reducing transplant rejection. They concluded “these results suggest the potential use of these select phytochemicals for treating autoimmune and transplant patients...” (Hushmendy, 2009).
Published studies in recent years have revealed an astonishing number of benefits attributable to vitamin D. Among these benefits, modulating the activity of multiple inflammatory cytokines is especially important in the context of organ transplantation.
Researchers recently discovered that vitamin D was able to prevent a cyclosporine mediated increase in the inflammatory cytokines IL-1β, IL-6 and TNFα in an animal model (Spolidorio, 2010).Vitamin D, in combination with cyclosporine, significantly reduced production of IL-2 and the proliferation of T-cells, and vastly prolonged allograft survival in an animal model of liver transplantation. The authors of this study went on to conclude that vitamin D is effective as an adjunct to immunosuppressive therapy for the prevention and treatment of liver graft rejection (Zhang, 2006).
A very important 2009 study shed light on just how critical vitamin D supplementation is for transplant recipients. Researchers examined the relationship between blood levels of the active form of vitamin D (1,25-dihydroxy vitamin D) and one-year mortality rates of heart transplant patients.
They found that “one-year mortality was 3.7 per 100 person-years in the tertile with the highest [1,25-dihydroxy vitamin D] concentrations, 13.2 per 100 person-years in the intermediate tertile and 32.1 per 100 person-years in the tertile with the lowest [1,25-dihydroxy vitamin D] concentrations.”
This means that the mortality rate was over eight times higher at one year post-transplant in the group with the lowest one-third blood levels of active vitamin D compared to the group with the highest one-third levels of active vitamin D. The researchers also found that higher blood levels of vitamin D were associated with lower levels of the inflammatory marker C-reactive protein, as well as the cytokine TNFα (Zittermann, 2009).