Interplay Between Systemic Inflammation and Markers of Insulin Resistance in Cardiovascular Prognosis After Heart Transplantation

Rapid intestinal and systemic metabolic reprogramming in an immunosuppressed environment

Intrinsic metabolism shapes the immune environment associated with immune suppression and tolerance in settings such as organ transplantation and cancer. However, little is known about the metabolic activities in an immunosuppressive environment. In this study, we employed metagenomic, metabolomic, and immunological approaches to profile the early effects of the immunosuppressant drug tacrolimus, antibiotics, or both in gut lumen and circulation using a murine model. Tacrolimus induced rapid and profound alterations in metabolic activities within two days of treatment, prior to alterations in gut microbiota composition and structure. The metabolic profile and gut microbiome after seven days of treatment was distinct from that after two days of treatment, indicating continuous drug effects on both gut microbial ecosystem and host metabolism. The most affected taxonomic groups are Clostriales and Verrucomicrobiae (i.e., Akkermansia muciniphila), and the most affected metabolic pathways included a group of interconnected amino acids, bile acid conjugation, glucose homeostasis, and energy production. Highly correlated metabolic changes were observed between lumen and serum metabolism, supporting their significant interactions. Despite a small sample size, this study explored the largely uncharacterized microbial and metabolic events in an immunosuppressed environment and demonstrated that early changes in metabolic activities can have significant implications that may serve as antecedent biomarkers of immune activation or quiescence. To understand the intricate relationships among gut microbiome, metabolic activities, and immune cells in an immune suppressed environment is a prerequisite for developing strategies to monitor and optimize alloimmune responses that determine transplant outcomes.

Rapid intestinal and systemic metabolic reprogramming in an immunosuppressed environment

Intrinsic metabolism shapes the immune environment associated with immune suppression and tolerance in settings such as organ transplantation and cancer. However, little is known about the metabolic activities in an immunosuppressive environment. In this study, we employed metagenomic, metabolomic, and immunological approaches to profile the early effects of the immunosuppressant drug tacrolimus, antibiotics, or both in gut lumen and circulation using a murine model. Tacrolimus induced rapid and profound alterations in metabolic activities within two days of treatment, prior to alterations in gut microbiota composition and structure. The metabolic profile and gut microbiome after seven days of treatment was distinct from that after two days of treatment, indicating continuous drug effects on both gut microbial ecosystem and host metabolism. The most affected taxonomic groups are Clostriales and Verrucomicrobiae (i.e., Akkermansia muciniphila), and the most affected metabolic pathways included a group of interconnected amino acids, bile acid conjugation, glucose homeostasis, and energy production. Highly correlated metabolic changes were observed between lumen and serum metabolism, supporting their significant interactions. Despite a small sample size, this study explored the largely uncharacterized microbial and metabolic events in an immunosuppressed environment and demonstrated that early changes in metabolic activities can have significant implications that may serve as antecedent biomarkers of immune activation or quiescence. To understand the intricate relationships among gut microbiome, metabolic activities, and immune cells in an immune suppressed environment is a prerequisite for developing strategies to monitor and optimize alloimmune responses that determine transplant outcomes.

Fibrotic plaques in heart transplanted patients and their association with insulin resistance syndrome and Lp(a)

BACKGROUND

Angiographic evidence of cardiac allograft vasculopathy (CAV_angio) is a major limiting factor to survival after heart transplantation (HTx). Prevention of CAV_angio is therefore most relevant. Whether modifiable risk factors could be targeted for the prevention of fibrotic plaques, that are common and related to CAV_angio, is not clear.

METHODS AND RESULTS

In a cohort of 74 consecutive HTx patients (median post-transplant interval 9.2 [4.1-15.5] years), we used the high resolution of optical coherence tomography (OCT) to quantify angulation parameters (maximal and mean arc) and plaque load (mean arc*relative plaque length) of fibrotic plaques. Mean arc was defined as the mean value of all angulation measurements per patient. We assessed the association between cardiovascular risk factors and OCT findings. Linear regression analysis showed a significant association of TG/HDL-c with mean fibrotic arc (12.7 [3.9-21.5], p = 0.006) and fibrotic plaque load (2298 [617-3979], p = 0.009) after adjustment for recipient age and sex. We used the median value of fibrotic plaque load to define high fibrotic plaque load. In binary logistic regression analysis, TG/HDL-c (odds ratio [OR] 1.81 with 95% CI [1.09-3.03], p = 0.02) and Lp(a) (OR 1.02 [1.00-1.05], p = 0.02) were associated with high fibrotic plaque load. Multivariable logistic regression analysis confirmed Lp(a) as significant predictor of high fibrotic plaque load (OR 1.03 [1.01-1.05], p = 0.02).

CONCLUSION

TG/HDL-c ratio, a surrogate of insulin resistance syndrome, and Lp(a) were significantly associated with fibrotic plaque in HTx patients. Insulin resistance syndrome and Lp(a) might therefore represent additional targets for CAV prevention.

Medication management of cardiac allograft vasculopathy after heart transplantation

Cardiac allograft vasculopathy (CAV) is a common complication following heart transplantation (HT), resulting in diminished graft survival. The preferred strategy for preventing CAV is optimal medical management; however, for patients who develop CAV, delaying disease progression through effective medication management is equally important. A review of the literature regarding medication management of CAV was conducted via a search of the MEDLINE database. Studies were included if they were published in English, conducted in humans ≥ 18 years of age or older, and used noninvestigational medications. Immunosuppressive medications such as the antiproliferative mycophenolate, the calcineurin inhibitor tacrolimus, and the proliferation signal inhibitors sirolimus and everolimus have been shown to prevent the development of CAV. Certain cardiovascular medications, such as HMG-CoA reductase inhibitors (statins), gemfibrozil, calcium channel blockers, and angiotensin-converting enzyme inhibitors, have also demonstrated efficacy in preventing this disease process. Prevention of CAV has also been observed with prophylaxis against cytomegalovirus infection and antioxidant medications. Despite being commonly used in HT patients, neither antiplatelet agents nor glycemic control have proved effective at preventing CAV. Only sirolimus has been shown to arrest the progress of existing CAV.

Cardiac allograft vasculopathy: diagnosis, therapy, and prognosis

Development of cardiac allograft vasculopathy represents the major determinant of long-term survival in patients after heart transplantation. Due to graft denervation, these patients seldom present with classic symptoms of angina pectoris, and the first clinical presentations are progressive heart failure or sudden cardiac death. Although coronary angiography remains the routine technique for coronary artery disease detection, it is not sensitive enough for screening purposes. This is especially the case in the first year after transplantation when diffuse and concentric vascular changes can be easily detected only by intravascular ultrasound. The treatment of the established vasculopathy is disappointing, so the primary effort should be directed toward early prevention and diagnosis. Due to diffuse vascular changes, revascularization procedures are restricted only to a relatively small proportion of patients with favorable coronary anatomy. Percutaneous coronary intervention is preferred over surgical revascularization since it leads to better acute results and patient survival. Although there is no proven long-term advantage of drug-eluting stents for the treatment of in-stent restenosis, they are preferred over bare-metal stents. Severe vasculopathy has a poor prognosis and the only definitive treatment is retransplantation. This article reviews the present knowledge on the pathogenesis, diagnosis, treatment, and prognosis of cardiac allograft vasculopathy.

Interplay of coronary angiography and intravascular ultrasound in predicting long-term outcomes after heart transplantation

BACKGROUND

Cardiac allograft vasculopathy (CAV) remains the major cause of late graft-related death after heart transplantation (HT). Identification of patients at risk of cardiovascular events has relevant implications in appropriately guiding resources and intensity of follow-up. In this context, the prognostic relevance of serial coronary imaging long-term after HT is unexplored.

METHODS

Recipients with intravascular ultrasound (IVUS) and coronary angiography performed 1 and 5 years after HT were monitored for subsequent 1 to 10 years to analyze the association of serial coronary imaging with cardiovascular death and major cardiovascular events (MACEs).

RESULTS

Included were 131 patients. The MACE incidence was 31.8 per 1,000 patient-years, and cardiovascular mortality was 17.4 per 1,000 patient-years. Progression of coronary lesions detected by angiography and changes in IVUS-defined parameters, including an increase in maximal intimal thickness (MIT) ≥0.35 mm and vascular remodeling, predicted MACE occurrence. However, only MIT change ≥0.35 mm also predicted cardiovascular mortality. Among patients with normal or stable angiography, an MIT change ≥0.35 mm identified those with a significantly higher MACE rate (80 vs 13 events/1,000 patient-years). Worsening metabolic parameters appeared associated with the increasing severity of CAV development.

CONCLUSIONS

Combined imaging analysis of progression of angiographic lesions and IVUS-detected MIT between 1 and 5 years post-HT allows discriminating patients at high, intermediate, and low risk for adverse long-term cardiovascular outcomes. The metabolic syndrome milieu is confirmed as a key risk factor for long-term CAV progression and adverse prognosis.

Serum adipokine and inflammatory markers before and after liver transplantation in recipients with major cardiovascular events

In the nontransplant setting, aberrant serum adipokine levels are associated with cardiovascular (CV) disease. The effects of liver transplantation (LT) on serum adipokine levels and their association with post-LT CV disease have not been studied. A nested case-control study of 77 patients with major CV events more than 4 months after LT analyzed serum adiponectin, resistin, leptin, C-reactive protein, and apolipoprotein levels measured before transplantation and 4, 12, and 24 months after LT. Adiponectin and resistin levels decreased dramatically after LT in all patients. Recipients with CV disease had lower levels of adiponectin and higher levels of resistin, leptin, C-reactive protein, and apolipoprotein B100 than controls. The pre-LT adiponectin level was associated with a 16% increased risk for CV events for every 1 μg/mL decrease in adiponectin [hazard ratio (HR) = 0.84, P = 0.046]. Pre-LT C-reactive protein levels (HR = 1.03, P = 0.047) and 12-month C-reactive protein levels (HR = 1.03, P = 0.03) were associated with CV events after LT. Pre-LT Diabetes (HR = 2.14, P = 0.09), and post-LT resistin (HR = 1.07, P = 0.07), and apolipoprotein B (HR = 1.08, P = 0.08) were associated with a nonsignificantly increased risk of CV events in this small sample size. In conclusion, pre- and post-LT changes in serum adipokine and inflammatory markers may be signals of an increased risk of CV events after LT, but further study is needed.

Impaired cholesterol efflux capacity and vasculoprotective function of high-density lipoprotein in heart transplant recipients

BACKGROUND

High-density lipoprotein (HDL) metabolism is significantly altered in heart transplant recipients. We hypothesized that HDL function may be impaired in these patients.

METHODS

Fifty-two patients undergoing coronary angiography between 5 and 15 years after heart transplantation were recruited in this cross-sectional study. Cholesterol efflux capacity of apolipoprotein B-depleted plasma was analyzed using a validated assay. The vasculoprotective function of HDL was studied by means of an endothelial progenitor cell migration assay.

RESULTS

HDL cholesterol levels were similar in heart transplant patients compared with healthy controls. However, normalized cholesterol efflux and vasculoprotective function were reduced by 24.1% (p < 0.001) and 27.0% (p < 0.01), respectively, in heart transplant recipients compared with healthy controls. HDL function was similar in patients with and without cardiac allograft vasculopathy (CAV) and was not related to C-reactive protein (CRP) levels. An interaction effect (p = 0.0584) was observed between etiology of heart failure before transplantation and steroid use as factors of HDL cholesterol levels. Lower HDL cholesterol levels occurred in patients with prior ischemic cardiomyopathy who were not taking steroids. However, HDL function was independent of the etiology of heart failure before transplantation and steroid use. The percentage of patients with a CRP level ≥6 mg/liter was 3.92-fold (p < 0.01) higher in patients with CAV than in patients without CAV.

CONCLUSIONS

HDL function is impaired in heart transplant recipients, but it is unrelated to CAV status. The proportion of patients with a CRP level ≥6 mg/liter is prominently higher in CAV-positive patients.

Evolving concepts and treatment strategies for cardiac allograft vasculopathy

OPINION STATEMENT

The central event in the development of allograft vasculopathy is the inflammatory response to immune-mediated and nonimmune-mediated endothelial damage. This response is characterized by the release of inflammatory cytokines, upregulation of cell-surface adhesion molecules, and subsequent binding of leukocytes. Growth factors stimulate smooth muscle cell proliferation and circulating progenitor cells are recruited to sites of arterial injury leading to neointima formation. Because of its diffuse nature, intravascular ultrasound is more sensitive than angiography for early diagnosis. Proliferation signal inhibitors (PSIs) have the capacity to slow vasculopathy progression by inhibiting smooth muscle cell proliferation, but its side effects profile makes its use as a first line agent difficult. Retransplantation is still the only definitive therapy but is available only in selected cases. The current hope is that immunomodulation at the time of transplant could induce long-term tolerance and graft accommodation, leading to less vasculopathy.

Everolimus therapy is associated with reduced lipoprotein-associated phospholipase A2 (Lp-Pla2) activity and oxidative stress in heart transplant recipients

BACKGROUND

Several studies demonstrated decreased severity and incidence of cardiac allograft vasculopathy (CAV) in heart transplant recipients receiving immunosuppressive therapy with everolimus. However, data regarding the influence of everolimus on risk factors predisposing to CAV are hitherto limited. We here systematically evaluated cardiovascular risk factors in heart transplanted patients, who underwent conversion to everolimus or were maintained on conventional therapy with calcineurin inhibitors (CNI).

METHODS

50 Patients receiving everolimus and 91 patients receiving CNI in addition to mycophenolate mofetil and low-dosed steroids were included in the study. CAV risk factors were determined in plasma or urine using standard enzymatic or immunochemical methods.

RESULTS

No significant differences were observed between both groups with regard to lipid (total, LDL- and HDL-cholesterol), metabolic (glucose, insulin), inflammatory (C-reactive protein, IL-6, myeloperoxidase) and cardiac (troponin I, NT-proBNP) risk factors. However, significantly lower activity of lipoprotein-associated phospholipase A2 (Lp-PLA2) and a negative correlation between the Lp-PLA2 activity and the everolimus concentration were observed in plasmas from everolimus-treated patients. Conversion to everolimus significantly lowered Lp-PLA2 activity in heart transplant recipients. Studies in vitro revealed reduced Lp-PLA2 expression in hepatocytes and macrophages pre-exposed to everolimus. In addition, reduced plasma markers of oxidative stress including oxidized LDL, 8-iso-prostaglandin F2α and protein carbonyls were noted in heart transplant recipients receiving everolimus therapy.

CONCLUSION

Our results suggest that everolimus specifically lowers plasma activity and cellular production of Lp-PLA2 and thereby dampens oxidative stress. These effects may additionally contribute to the reduced CAV incidence observed in heart transplant recipients receiving everolimus therapy.

Low serum IGF-1 is a risk factor for cardiac allograft vasculopathy in cardiac transplant recipients

BACKGROUND

Cardiac allograft vasculopathy (CAV) has an incidence of 43% at 8 years after heart transplantation with extremely limited treatment options and unclear pathogenesis. CAV constitutes a significant complication that limits the long-term survival of heart recipients. Insulin-like growth factor-1 (IGF-1) is associated with different cardiovascular diseases; however, its role in CAV pathogenesis remains unknown.

METHODS

Serum samples of 10 matched recipients with CAV and 10 with no-CAV were initially screened with a protein array. Subsequently, IGF-1- and IGF-binding protein-3 (IGFBP-3) were analyzed using enzyme-linked immunosorbent assay in 44 randomly selected CAV and 50 no-CAV patients at two time points.

RESULTS

The initial screening showed that IGF-1 and IGFBP-3 are differentially expressed in CAV compared with no-CAV patients (P=0.037 and P<0.0001, respectively). Subsequent enzyme-linked immunosorbent assay analyses indicated that serum IGF-1 protein concentrations were significantly lower in CAV patients (159.7±114 ng/mL) as compared with no-CAV patients (234.1±136 ng/mL; P=0.02). Serum IGFBP-3 protein concentrations were significantly lower in CAV (0.46±0.37 mg/L) as compared with no-CAV patients (1.03±0.73 mg/L; P=0.04). Multivariate logistic regression analyses showed that IGF-1 (odds ratio, 0.89; P=0.04) and IGFBP-3 (odds ratio, 0.09; P=0.03) are independent risk factors for CAV.

CONCLUSION

Low IGF-1 and IGFPB-3 serum concentrations are associated with CAV. The assessment of serum IGF-1 and IGFPB-3 might be beneficial in identifying cardiac allograft recipients who are prone to develop CAV. Moreover, IGF-1 might be a useful therapy that could protect cardiac allografts against CAV.

Changes in exercise capacity induced by heart transplantation: prognostic and therapeutic implications

Survival and exercise performance are key targets of heart transplantation (HT). We designed this study to help in identifying (1) patients with chronic heart failure (CHF) at risk of poor exercise capacity after HT and (2) HT recipients presenting risk factors modifiable with exercise showing a potential impact on outcome. We enrolled 49 HT recipients (age 52 ± 12 years, 84% males) who underwent a cardiopulmonary exercise test before (9 ± 6 months) and after (20 ± 14 months) HT. In the CHF phase, lower peak oxygen consumption (VO(2) ) (odds ratio 0.69, P=0.017) independently predicted peak VO(2) improvement after HT. In the post-HT phase, body mass index (BMI) [adjusted hazard ratio (HR) 1.16, P=0.034] and VE (ventilation)/VCO(2) (carbon dioxide production) slope (adjusted HR 1.07, P=0.031) independently predicted mortality. In conclusion, CHF patients with only a moderate impairment of peak VO(2) are at a risk of failing to achieve a significant improvement of exercise performance after HT. In the post-HT phase, a BMI≥28 and/or a VE/VCO(2) slope ≥47 represent risk factors for death, which are potentially modifiable with exercise. Prospective randomized studies are needed to analyze the effects of training on functional capacity and outcome in the different subsets of HT recipients.

Prophylaxis versus preemptive anti-cytomegalovirus approach for prevention of allograft vasculopathy in heart transplant recipients

BACKGROUND

Cytomegalovirus (CMV) infection may influence the development of cardiac allograft vasculopathy (CAV). Prophylactic or preemptive administration of anti-CMV agents effectively prevents acute CMV manifestations. However, studies comparing allograft-related outcomes between these anti-CMV approaches are lacking. Herein we report a longitudinal observational study comparing CAV development between prophylactic and preemptive approaches.

METHODS

The 1-year change in maximal intimal thickening (MIT) assessed by intravascular ultrasound at 1 and 12 months after heart transplantation (the major surrogate for late survival) was compared in groups of patients routinely assigned to a preemptive strategy (from November 2004 to October 2005; n = 21) or receiving valganciclovir prophylaxis (from November 2005 to October 2006; n = 19). CMV infection was monitored with pp65 antigenemia.

RESULTS

The 1-year increase in MIT was significantly lower in patients receiving prophylaxis compared with those managed preemptively (0.15 +/- 0.17 vs 0.31 +/- 0.20 mm; p = 0.01). Prophylaxed recipients presented less frequently with MIT change > or =0.3 mm (p = 0.03) and > or =0.5 mm (p = 0.10) than those managed preemptively. Prophylaxis was also associated with later onset of CMV infection (p = 0.01), lower peak CMV detection (p < 0.01) and reduced incidence of CMV disease/syndrome (p = 0.04). After adjusting for metabolic risk factors and other possible confounders, prophylaxis remained independently associated with lower risk for MIT change > or =0.3 mm (odds ratio = 0.09, 95% confidence interval 0.01 to 0.93; p = 0.04).

CONCLUSIONS

Universal prophylaxis was associated with delayed onset of CMV infection, lower viral burden, reduced CMV disease/syndrome and less intimal thickening, as compared with a preemptive anti-CMV approach. Randomized studies are required to confirm the potential benefits of prophylaxis vs a preemptive approach in heart transplant recipients.

Cardiac allograft vasculopathy and insulin resistance--hope for new therapeutic targets

Cardiac allograft vasculopathy (CAV) is a major cause of death in patients surviving more than 1 year after heart transplantation. An important cluster of CAV risk factors occurs as a consequence of insulin resistance and manifests as part of the metabolic syndrome. This article summarizes the pathologic features of CAV and reviews the contribution of the major components of insulin resistance in CAV development and progression. It focuses on the few studies that have analyzed the impact of the individual metabolic abnormalities and inflammation and on therapeutic strategies to minimize the clinical manifestation of insulin resistance after heart transplantation.

Cardiac allograft vasculopathy and insulin resistance--hope for new therapeutic targets

Cardiac allograft vasculopathy (CAV) is a major cause of death in patients surviving more than 1 year after heart transplantation. An important cluster of CAV risk factors occurs as a consequence of insulin resistance and manifests as part of the metabolic syndrome. This article summarizes the pathologic features of CAV and reviews the contribution of the major components of insulin resistance in CAV development and progression. It focuses on the few studies that have analyzed the impact of the individual metabolic abnormalities and inflammation and on therapeutic strategies to minimize the clinical manifestation of insulin resistance after heart transplantation.