University of Groningen Lifestyle, Inflammation, and Vascular Calcification in Kidney Transplant Recipients Sotomayor, Camilo G.

University of Groningen

Lifestyle, Inflammation, and Vascular Calcification in Kidney Transplant Recipients

Sotomayor, Camilo G.

DOI:

10.33612/diss.135859726

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2020

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Sotomayor, C. G. (2020). Lifestyle, Inflammation, and Vascular Calcification in Kidney Transplant

Recipients: Perspectives on Long-Term Outcomes. University of Groningen.

https://doi.org/10.33612/diss.135859726

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Chapter 1

Introduction and Aims of This Thesis

Lifestyle, Infl ammation, and Vascular Calcifi cation

in Kidney Transplant Recipients:

Perspectives on Long-Term Outcomes

Camilo G. Sotomayor, Charlotte A. te Velde-Keyzer, Martin H. de Borst,

Gerjan J. Navis, Stephan J.L. Bakker

1

INTRODUCTION AND AIMS OF THIS THESIS

C

hronic kidney disease (CKD) is a major public health problem, with a

current worldwide prevalence of approximately 843 million individuals.

Global mean prevalence was recently reported at 13.4% for all CKD stages

together (CKD stages 1–5), and at 10.6% if only the more severe CKD

stages (CKD stages 3–5) are considered.

_{The burden of CKD stages 3–5}

varies substantially across the world, with e.g. a mean prevalence of 8.1%

in Australia, a mean prevalence of 14.4% in the United States and Canada

combined, and a mean prevalence of 11.9 and 12.1% in Europe and South

America, respectively.

The prevalence of CKD, its detection, treatment and impact on health has

been mainly studied in economically developed countries.

_{Yet, even in these}

circumstances it usually remains a silent, smouldering health threat, with e.g.

rates of awareness of being affl icted with kidney disease of approximately

10% among patients with CKD in an economically developed country like the

United States,

_{wherein, in 2016, approximately 35% of patients diagnosed}

with incident end-stage renal disease (ESRD) received little or no nephrology

care prior to actually being diagnosed with ESRD.

_{Regrettably, prevalence}

of ESRD, and prevalence of renal replacement therapy continues to increase

(

Figures 1 and 2).

End-stage renal disease patients experience a signifi cant decrease in quality

of life and life expectancy.

_{Indeed, ESRD ranks with one of the highest}

burdens of disease at a global level.

_{Regarding economic burden particularly,}

it is relevant to mention that provision of kidney disease care is closely related

with public policies and fi nancial status of countries.

_{While in many}

high-income countries ESRD-associated medical costs for treatment by dialysis

are usually taken care of by the government, in low-income and lower-middle

income countries, ESRD may be not publicly fi nanced.

In The Netherlands, as of January 1

_{2015, 16.277 patients were under}

renal replacement therapy, with an annual incidence of approximately 2.000

patients contributing to the rise in prevalence of patients dependent on

renal replacement therapy. Of note, while annual healthcare costs for Dutch

renal replacement therapy other than transplantation range from €77.000 to

€105.000, kidney transplant expenses steadily decline in the years

post-kidney transplant, with approximate costs of €20.000 already in the second

year post-transplant (

Table 1).

Figure 1. Prevalence of ESRD in the United States population, 1980−2016.

This figure shows a steady increase in ESRD prevalence over recent ~35 years

in the US. Standardized for age, sex, and race. Adapted from United States

Renal Data System. 2018 USRDS Annual Data Report: Epidemiology of

kidney disease in the United States. National Institutes of Health, National

Institute of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, 2018.

Pr evalence of patients in TRR (ppm) 800 700 600 500 400 300 200 100 0 Year 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013

Figure 2. Prevalence of renal replacement therapy in Latin America,

1991−2013. This figure shows a steady increase in prevalence of renal

replacement therapy over recent ~25 years in Latin America. Adapted

from “Latin American Dialysis and Transplant Registry: Experience and

contributions to end-stage renal disease epidemiology” by Cusumano AM et

al., World J Nephrol 2016, 5, 389−397.

80 82 84 86 88 90 92 94 96 98 00 02 04 06 08 10 12 14 16 2200 2000 1800 1600 1400 1200 1000 800 600 400 200 0

Prevalence (per million)

Standardized prevalence Crude prevalence

1

Table 1. Average annual healthcare costs per modality of renal replacement

therapy in The Netherlands

Dialysis

Phases of Tx

CHD

HHD

CAPD

APD

_{of Tx}

Year

_post-Tx

1

year

2

_post-Tx

year

Total

average

(SD)

annual

costs

€92 616

(21 500)

(12 648)

€87 051

(27 237)

€77 566

(18 890)

€89 932

(39 679)

€85 127

(34 099)

€29 612

(26 571)

€20 156

Total average [mean (standard deviation)] annual costs were calculated including

renal replacement costs and hospital, primary care, mental health care, medication,

medical devices, health care abroad, transportation and others. APD, automated

peritoneal dialysis; CAPD, continuous ambulatory peritoneal dialysis; CHD, centre

haemodialysis; HHD, home haemodialysis; Tx, transplantation.

Compared to chronic dialysis treatment, kidney transplantation is considered

the renal replacement therapy of choice and the gold-standard treatment for

most ESRD patients, because it off ers superior cost-eff ectiveness, quality of

life, and life expectancy.

However, the latter has largely been due to signifi cant improvements

of short-term outcomes.

_{Advances in immunosuppression, tissue typing,}

treatment of infections, and surgical techniques led rates of 1-year graft

survival at a pinnacle, whereas improvement of long-term outcomes

post-transplant remains a major challenge in the kidney post-transplantation fi eld.

On the one hand, the life-saving benefi t of a kidney transplant remains largely

hampered by cumulative injury of a multitude of hazards through immune and

non-immune mechanisms of kidney damage. Over time, these mechanisms

lead to chronic interstitial fi brosis and tubular atrophy as histopathological

consequence and end-stage kidney allograft failure as functional repercussion,

eventually requiring restart of dialysis or re-transplantation as fi nal adverse

clinical event (i.e., graft failure).

On the other hand, kidney transplant recipients (KTR) are at particularly

high risk of premature death, depicting overall mortality rates considerably

higher than that of age-matched controls in the general population (

Figure

3).

_{Indeed, approximately half of all kidney allograft losses are due to}

premature death with a functioning graft, a long-standing pattern that has

remained largely unchanged over recent years.

General population cohort (n = 3432) Renal transplant recipients (n = 606) P < 0.001 0 1 2 3 4 5 Follow-up (years) 90 100 95 85 80 0 Sur vival (%)

Figure 3. Kaplan-Meier curve of mortality in a Dutch cohort of KTR and a

sample of the general population in The Netherlands. This figure illustrates

a considerably higher mortality risk of KTR compared to age- and

sex-matched controls in the general population. Reprinted from “N-terminal

pro-b-type natriuretic peptide and mortality in renal transplant recipients versus

the general population” by Oterdoom LH et al., Transplantation 2009, 87,

1562−1570.

Next, under the general understanding that cardiovascular disease is the

leading cause of premature death post-kidney transplant (

Figure 4), and

thereby importantly challenging the improvement of longevity of KTR,

great efforts have focused on the improvement of long-term cardiovascular

outcomes.

In the clinical setting of KTR after the first-year post-transplant, beyond

hazards of immunological nature, there is a pressing need to systematically

study and characterise the clinical impact of potentially modifiable risk

factors, such as lifestyle, diet and exposure to toxic contaminants, which are

underexplored areas in the kidney transplantation field.

_{This evidence is}

needed to guide decision making by clinicians and policy-makers in

post-transplantation care. Furthermore, because kidney post-transplantation aims to

restore kidney function but it incompletely mitigates collateral mechanisms

of disease, such as chronic low-grade inflammation with persistent redox

imbalance, and deregulated mineral and bone metabolism, further research

investigating specific clinical and laboratory readouts with a proposed

involvement in such pathological pathways, may point towards non-traditional

risk factors and reveal novel targets for clinical intervention.

1

Figure 4. Mortality by causes of death with graft function. This fi gures shows

that cardiovascular disease was the leading cause of mortality among american

KTR in 2015. Cardiovascular disease included acute myocardial infarction,

atherosclerotic heart disease, congestive heart failure, cerebrovascular

accident, and arrhythmia/cardiac arrest. Adapted from United States Renal

Data System. 2018 USRDS Annual Data Report: Epidemiology of kidney

disease in the United States. National Institutes of Health, National Institute

of Diabetes and Digestive and Kidney Diseases, Bethesda, MD, 2018.

In the kidney transplantation fi eld, future advances are expected from

amelioration of adverse long-term outcomes by increasing recognition and

developing novel, early and cost-eff ective risk-management strategies focused

on the non-immune aspects of post-kidney transplant care, and thus optimize

long-term health and downturn current rates of premature death in outpatient

KTR.

Part I — Lifestyle; Healthy Diet & Toxic Contaminants

Systematic investigation of traditional and potentially modifi able risks

factors in the post-kidney transplant setting may point towards otherwise

overlooked early risk-management opportunities, and thus provide the basis

for the development of cost-eff ective interventional approaches to increase

the lifespan of KTR. Healthy diet is a cornerstone element of cardio-metabolic

health in the general population.

_{In general, a healthy diet is recommended}

as a cornerstone of cardiovascular disease prevention in all individuals.

Surprisingly, however, little is known about the potential impact of a healthy

Cardiovascular disease

Infection

Malignancy

All other causes

33%

33%

diet on cardiovascular health and survival benefit in kidney patients across the

continuum of CKD stages, in patients undergoing renal replacement therapy,

and remarkably limited evidence is available in the post-kidney transplant

clinical setting.

_{Moreover, native CKD and pre-transplant ESRD patients}

are generally advised to follow seemingly conflicting and challenging dietary

recommendations with the aim of restricting individual nutrients such as

potassium, sodium salt, phosphorus, and protein.

_{Beyond the important}

consideration that this approach may result in an intense burden for CKD

patients, it should be realized that there is scant evidence to support such

restrictive dietary recommendations.

_{Finally, there is a notorious lack of}

studies aimed to aid on the development of evidence-based recommendations

to appropriately apply any pre-transplant dietary advice to the post-kidney

transplant setting.

Fruit and vegetable consumption post-kidney transplantation

With the aim of limiting potassium intake, for example, pre-transplant ESRD

patients have largely been discouraged from a high consumption of fruits and

vegetables, which are, however, well-known essential components of a healthy

diet.

_{Beyond being rich in potassium, fruits and vegetables are rich}

in fibres, polyunsaturated and monounsaturated fatty acids, magnesium,

iron, and generate less acid and contain smaller amounts of saturated fatty

acids, protein, and absorbable phosphorus in comparison to meat.

_{At least}

four servings of fruit and vegetables per day are widely recommended for

the prevention of major chronic diseases in the general population.

_Indeed,

increased consumption of fruits and vegetables has consistently shown to

confer superior cardiovascular prognosis in the general population.

At present, however, post-kidney transplant there is no clear incentive by

transplant healthcare providers to prescribe restoration of the consumption of

these basic items of a healthy diet. This attitude may respond to the fact that it

remains unexplored whether an increase of fruits and vegetables consumption

post-transplantation positively impacts outcomes of KTR, which would be

hypothetically expected by decreasing the excess cardiovascular burden and

premature. Epidemiological studies aimed at estimating a theoretical benefit

of a relative increase of these specific food items are warranted as first step

to, thereafter, investigate potential interventional strategies promoting novel,

cost-effective and patient-centred approaches to the nutritional management

of KTR, adequately informing clinical practice and policy.

1

Box 1. Characteristics of a healthy diet

•

•

•

•

•

•

•

•

•

≥200 grams of fruit per day (2–3 servings)

≥200 grams of vegetables per day (2–3 servings)

Fish 1–2 times per week, one of which to be oily fi sh

Saturated fatty acids to account for <10% of total energy intake,

through replacement by polyunsaturated fatty acids

Trans unsaturated fatty acids: as little as possible, preferably no intake

from processed food, and <1% of total energy intake from natural

origin

30 grams unsalted nuts per day

<5 grams of sodium salt per day

Consumption of alcoholic beverages should be limited to 2 glasses

per day (20 g/d of alcohol) for men and 1 glass per day (10 g/d of

alcohol) for women

Sugar-sweetened soft drinks and alcoholic beverages consumption

must be discouraged

Fish intake post-kidney transplantation and mercury exposure

Fish are rich in the omega-3 polyunsaturated fatty acids (n-3 PUFA) EPA

(eicosapentaenoic acid) and DHA (docosahexaenoic acid), which are suggested

to yield several benefi cial eff ects for cardiovascular health.

_Circulating

levels of EPA and DHA have been associated with reduced cardiovascular risk

in both healthy populations and in patients with pre-existing cardiovascular

disease.

_{Proposed benefi cial health eff ects of marine-derived n-3 PUFA are}

wide-ranging, favourably impacting infl ammation, fi brosis, lipid metabolism

modulation, plaque stabilization, blood pressure, artery calcifi cation processes,

and endothelial function.

_{These properties render EPA and DHA as of}

encompassing therapeutic potential in the management of cardiovascular risk

of KTR. Indeed, in this particular setting, a recent observational study showed

that plasma levels of marine-derived n-3 PUFA are inversely associated with

cardiovascular mortality risk.

It should be realized, however, that the results of randomized control trials

using supplementation of these individual nutrients are not yet suffi ciently

powered to draw defi nitive conclusions and recommendations for KTR.

Moreover, no study has been devoted to evaluating the potential benefi cial

eff ect of a relatively high dietary fi sh intake, as mostly shown in the general

population.

_{Fish is the main dietary source of n-3 PUFA, and its inclusion}

potentially adverse effects of accompanying intake of high saturated fat as

present in fatty meat products. Not exempt of drawbacks, however, fish is

also the major source of human exposure to organic mercury (with the

exception of industrial accidents or particular occupational exposures).

Therefore, alongside the study of the potential health benefits of

marine-derived n-3 PUFA, weighted investigation of a relatively higher fish intake

not only would be a more cost-effective and patient-centred approach to the

nutritional management of KTR, but also an overall necessary step towards

developing cautious evidence-based dietary guidelines for clinical uptake. Up

to date, it remains unknown whether otherwise beneficial effects of a higher

dietary intake of n-3 PUFA by increasing fish consumption post-kidney

transplantation may be mitigated by postulated increased cardiovascular risk

due to concomitant exposure to mercury.

Cadmium exposure and nephrotoxicity in the post-kidney transplant setting

Ensuingly, cadmium is another heavy metal of environmental and

lifestyle-related concern, with tobacco and diet being its primary sources of exposure.

Previous studies have demonstrated that cadmium may induce hypertension,

which, in turn is associated with accelerated kidney function decline and,

particularly demonstrated in KTR, shortened allograft survival.

_Most

importantly, a strong body of evidence shows that the kidney is the most

sensitive target organ of cadmium-induced body burden, through postulated

direct mechanisms of cadmium-induced injury in this organ, wherein it

accumulates with a half-life of up to 45 years.

_{It is important to note}

that, particularly in settings of long-term oxidative stress such as that of KTR,

cadmium-induced nephrotoxicity may associate with impaired kidney function

at concentrations that are otherwise considered non-toxic.

_{Taking also}

into account that the most effective way to reduce cardiovascular disease

in KTR may indeed be preservation of graft function, the aforementioned

constellation of factors turn the investigation of cadmium-associated risk of

encompassing relevance within the study of long-term outcomes of kidney

allograft function.

_{Furthermore, bodily cadmium is susceptible to}

therapeutic interventions.

_{Thus, cadmium-targeted interventional strategies}

may offer novel opportunities to decrease the long-standing high burden

of late kidney graft failure. However, whether the nephrotoxic exposure to

cadmium represents an overlooked hazard for preserved graft functioning

remains unknown.

1

Box 2. Oxidative stress

Oxidative stress is defi ned as an imbalance between the generation and

removal of oxidant species. The most representative biological oxidant

agents are reactive oxygen species (ROS) and reactive nitrogen species

(RNS). The former group includes hydrogen peroxide, superoxide anion

and hydroxyl radical, whereas within the latter group relevant species are

peroxynitrite anion, nitric oxide and nitrogen dioxide radicals. Oxidative

stress occurs when ROS and/or RNS production overwhelms the

endogenous antioxidant defence system, either by excess production and/

or inadequate removal. The antioxidant defence system is constituted by

enzymatic antioxidant agents, including catalase, glutathione peroxidase

and superoxide dismutase. Non-enzymatic antioxidant components

include a diversity of biological molecules, such as ascorbic acid (vitamin

C), α-tocopherol (vitamin E), reduced glutathione, uric acid, carotenoids,

fl avonoids, polyphenols and several other exogenous antioxidants.

Part II — Infl ammation and Oxidative Stress & Vascular Calcifi cation

Traditional risk factors such as diabetes mellitus, smoking, and hypertension,

among others, do not suffi ce to account for the excess burden of premature

cardiovascular death of, otherwise, stable outpatient KTR.

_Indeed,

cardiovascular disease has an atypical nature in KTR when compared with

the general population.

_{Unexplained cardiovascular risk subsidizes}

current eff orts to provide cutting-edge evidence on the potential independent

hazard of novel (non-traditional) cardiovascular risk factors post-kidney

transplantation.

It should be taken into account that while kidney transplantation aims to

restore kidney function, it incompletely abrogates mechanisms of disease.

Moreover, an aggregate of factors specifi c to the transplant milieu such as a

chronic low-grade immunologic response to the kidney allograft, long-term

toxicity of maintenance immunosuppressive, as well as various degrees of

progressive uraemia, contribute to perpetuate chronic infl ammation, redox

imbalance, and deregulated mineral and bone metabolism, which has been

proposed as major independent and evolving pathophysiological mechanisms,

which mitigation may counterbalance ─at least to a considerable extent─

the excess risk of cardiovascular disease and graft failure post-kidney

transplantation.

Inflammation and oxidative stress post-kidney transplantation

Indeed, while the vicious circle between inflammation and oxidative stress

as final common pathway of a multitude of insults plays an established

pathological role in native chronic kidney disease (CKD), its characterization

post-kidney transplant has been less than satisfactory.

_{This is relevant}

because, at a physiological level, the cornerstone role of the complex

interplay between inflammation and oxidative stress provides a theoretical

and conceptual framework upon which upcoming research may deepen the

understanding of the pathophysiological status of KTR once they reach a

seemingly stable clinical stage.

Vitamin C as anti-inflammatory and anti-oxidant agent, and its depletion

post-kidney transplant

Inflammation, specifically the established inflammatory biomarker

high-sensitivity C-reactive protein (hs-CRP) ─which is also an indirect marker of

increased oxidant production─ has been previously shown to be independently

associated with increased mortality risk in KTR.

_{Supported by data}

consistently showing an inverse correlation with hs-CRP in different settings,

vitamin C is well-known by its anti-inflammatory effects.

_Moreover,

vitamin C is a physiological antioxidant agent, with radical-scavenging and

reducing activities, of paramount importance for protection against diseases

and degenerative processes caused by oxidant stress.

_{This particular}

composite of biochemical properties renders vitamin C as compelling research

candidate to broaden the understanding of the interaction of inflammation

and oxidative stress in the mechanisms leading to excess risk of premature

death post-kidney transplantation. It should be realized, moreover, that

pre-transplant ESRD patients often have an imbalance of several critical trace

elements and vitamins.

_{Vitamin C, particularly, has been shown to be}

removed by conventional haemodialysis membranes, leading to drastic

vitamin C depletion and oxidative stress.

_{Through an inverse mediating}

effect on inflammatory signalling biomarkers, sub-physiological levels of

vitamin C (depletion) may be hypothesized to be implicated in mechanisms

that associate with increased risk of adverse long-term outcomes.

_To

date, however, little is known regarding the prevalence of abnormal vitamin C

status post-kidney transplantation, and whether it contributes to excess risk for

premature death post-kidney transplantation remains unexplored.

1

Advanced glycation endproducts as amplifi ers of oxidative stress and

infl ammatory responses

Infl ammation is referred to as a redox-sensitive mechanism on the basis that

reactive oxygen species may activate transcription factors such as nuclear

factor kappa B (NF-κB), which regulates infl ammatory mediator genes

expression.

_{In this regard, advanced glycation endproducts (AGE)}

are particularly interesting oxidative stress biomarkers because it has been

demonstrated that, upon binding to AGE-specifi c receptors, AGE activate

intracellular pathways that amplify infl ammatory and oxidative stress

responses and regulate the transcription of adhesion molecules through NF-κB

activation.

_{In agreement, data derived from clinical studies in pre-transplant}

ESRD patients support the implication of AGE in the complex feedback loop

between oxidative stress and infl ammation leading to endothelial dysfunction

and adverse cardiovascular eff ects.

Several studies have observed accumulation of AGE in native and transplant

CKD patients, and a strong body of evidence on the general theory of AGE

pathophysiology supports its pivotal role in the initiation and progression of

mechanisms underlying cardiovascular disease. However, few attempts have

been made to investigate the association of AGE with cardiovascular risk

post-kidney transplantation.

_{Through a mediating eff ect on up-regulation}

of infl ammatory, oxidative stress and endothelial dysfunction biomarkers, a

relative increase of AGE may be hypothesized to actively contribute to the

intracellular signalling pathways that ultimately yield excess risk of premature

cardiovascular death in KTR. It remains unknown whether a hypothetical

association with risk of cardiovascular mortality is independent of estimates

of renal function and traditional cardiovascular risk factors such as body mass

index, diabetes, blood pressure and smoking status.

Infl ammation, galectin-3 and fi brosis

Infl ammation is also referred to as a unifying mechanism of injury because

─through a cornerstone signalling link with interstitial fi brosis and tubular

atrophy─ it may hold observations that connect hazards of several natures

with structural damage and detrimental function of the kidney.

Noteworthy, the concept that chronic rejection is responsible for all progressive

long-term kidney graft failure has long ago been reformulated to a hypothesis

of cumulative damage.

_{Thus, repeated insults of both immune and}

atrophy, which represents a final common pathway of injury with adverse

functional consequences.

_{Galectin-3 is a β-galactoside-binding lectin, with a}

postulated key mediating role on kidney tissue fibrosis.

_{In different models}

it has been shown that whether a variety of insults incur on irreversible kidney

fibrosis or not, depends on the expression and secretion of galectin-3.

_In

the general population, moreover, an increasing body of prospective evidence

has related plasma galectin-3 with incident CKD.

_{Because galectin-3}

is both a biomarker of systemic inflammation and kidney fibrosis, it may

broaden our understanding and provide data to further support a unifying link

between repeated inflammatory and pro-oxidant insults and increased risk

of graft failure beyond the first-year post-kidney transplantation. Finally, it

should be realized that the dependent role of galectin-3 on kidney fibrosis, has

been specifically shown in the particular post-kidney transplant setting, in a

murine model.

_{Within the clinical kidney transplantation field, however, a}

number of crucial questions remain unanswered. Especially with galectin-3–

targeted pharmacological therapies increasingly becoming available, evidence

of a hypothetical association between galectin-3 levels and risk of long-term

graft survival may point towards novel interventional avenues to potentially

decrease the long-standing burden of late graft failure.

Bone disease and vascular calcification

Chronic kidney disease-mineral and bone disorders (CKD-MBD) is the

clinical entity or syndrome that KDIGO (Kidney Disease: Improving Global

Outcomes) more than a decade ago has coined to embody the disruption of the

complex systems biology enclosed by the kidney, skeleton and cardiovascular

system.

_{In line with previous evidence, the results of a recent elegant study}

by Yilmaz et al. support the hypothesis that decline in cardiovascular risk

post-kidney transplantation depends on partial resolution of inflammation, but

also on resolution of the CKD-MBD.

_{The findings of the aforementioned}

research group support the notion that beyond restoration of organ function

post-kidney transplant, amelioration of inflammation and correction of

CKD-MBD may attenuate excess cardiovascular disease through ─to some extent─

separate biological pathways. In agreement, Cozzolino et al. recently depicted

inflammation and oxidative stress on one hand, and CKD-MBD on the other

hand as major mechanisms underlying a feedback loop that exacerbates

cardiovascular disease in CKD patients (

Figure 5).

1

Chronic Kidney Disease Endothelial dysfunction Atherosclerosis Myocardial fibrosis Inflammation Oxidative stress Uremic toxins

Chronic kidney disease- mineral and bone

disorders Cardiovascular Disease

Figure 5. Cardiovascular disease in chronic kidney disease. This fi gure shows

infl ammation, oxidative stress and uremic toxins on one side, and chronic

kidney disease-mineral and bone disorders on the other side, of independent

mechanisms linking chronic kidney and cardiovascular disease. Adapted

from: “Cardiovascular disease in dialysis patients” by Cozzolino M et al.,

Nephrol Dial Transplant 2019, 33, iii28–iii34.

Within the context of CKD-MBD, vascular calcifi cation ─a currently

established cardiovascular risk factor in KTR, as shown by previous studies

of our group and others─

_{is linked with bone disease through}

inter-related pathophysiological mechanisms that comprise the bone-vascular axis

hypothesis, which contributes to the exceedingly high cardiovascular risk in

native CKD.

_{Post-kidney transplant bone disease is certainly a topic of}

epidemiological relevance due to its high prevalence and its association with

fragility fractures and reduced mobility.

_{Existing research, however, has}

failed to explore a hypothetical contributing role of post-kidney transplant bone

disease to increased risk of vascular calcifi cation in KTR.

_{Evidence for}

this association would further support the existence of a bone-vascular axis,

it would provide data to evaluate its epidemiological relevance post-kidney

transplant, and it may point towards an otherwise overlooked therapeutic

opportunity to at least partially decrease the markedly high cardiovascular

burden post-kidney transplantation.

AIMS OF THIS THESIS

The aim of this thesis was two-fold. First, we aimed to assess whether modifiable

dietary components and potentially toxic environmental contaminants may

at least partially explain increased risk of cardiovascular mortality and late

graft failure in KTR. Secondly, we aimed to investigate specific clinical and

laboratory readouts with a proposed role within persisting mechanisms of

disease post-kidney transplantation (i.e., inflammation and redox imbalance,

and vascular calcification), as potential non-traditional risk factors for adverse

long-term outcomes in KTR.

OUTLINE OF THIS THESIS

Part I — Lifestyle; Healthy Diet & Toxic Contaminants

Post-kidney transplantation there is no clear incentive from the transplant

healthcare providers to withdraw a pre-transplant restricted consumption

of fruits and vegetables, and whether post-kidney transplant function may

interact with a potential benefit of a relatively higher consumption of fruits

and vegetables remains unexplored. In

chapter 2 we investigate whether

relatively higher consumption of fruits and vegetables are prospectively

associated with lower risk of cardiovascular mortality in KTR, and whether

these associations depend on estimated glomerular filtration rate (eGFR) and

proteinuria. Similarly, in

chapter 3 we investigate whether relatively higher

fish intake and marine-derived n-3 PUFA are prospectively associated with

lower risk of overall and cardiovascular death, while taking into account the

theoretical drawback of higher concomitant toxic exposure to organic mercury,

mitigating a hypothetical beneficial effect of marine-derived n-3 PUFA on risk

of death. Further analyses on exposure to potentially toxic contaminants and

risk of adverse outcomes is provided in

chapter 4, wherein we investigate the

nephrotoxic effect of cadmium on risk of late graft failure in KTR. Against the

background that cadmium is particularly hazardous in settings of long-term

redox imbalance, we evaluate the prospective association between plasma

cadmium concentrations and risk of kidney function decline and late graft

failure. Finally, because cadmium metabolism involves proper liver function,

in this chapter we evaluate the interaction of liver enzymes in the association

of plasma cadmium with risk of graft function endpoints.

1

Part II — Infl ammation and Oxidative Stress & Vascular Calcifi cation

In

chapter 5 we approach the study of infl ammation and oxidative stress

on the overall risk of premature death by assessing the impact of

sub-physiological vitamin C status on all-cause mortality risk in KTR with a

functioning graft ≥1-year. We furthermore evaluate whether, and to what

extent, an inverse relation of vitamin C with infl ammatory biomarkers would

mediate the hypothetical benefi t of relatively higher levels of plasma vitamin

C on mortality risk post-kidney transplantation. Next, using the same setting

and study population, in

chapter 6 we focus on the study of infl ammation as

a redox-sensitive mechanism implicated in the underlying mechanisms that

ultimately yield excess cardiovascular risk post-kidney transplantation. For

this purpose, we investigate the prospective association between two specifi c

and directly measured AGE with long-term risk of cardiovascular mortality

in KTR, and we explore whether, and to what extent, such a relationship may

be mediated by a postulated eff ect through amplifi cation of infl ammatory

and oxidative responses, and up-regulation of endothelial dysfunction

biomarkers. In

chapter 7 we report on serum measurements of galectin-3 ─a

novel infl ammatory biomarker with a key mediating role on mechanisms of

kidney tissue fi brosis─ in this population of KTR. Thereafter, we assess its

potential prospective association with overall risk of late kidney graft failure,

while exploring hypothetical interactions with concomitant pro-infl ammatory

conditions and giving, correspondingly, stratifi ed assessment of the association

of galectin-3 on risk of late graft failure.

With previous literature consistently supporting vascular calcifi cation as

independent cardiovascular risk factor explaining, at least to a considerable

extent, excess risk of adverse fatal outcomes in KTR, in

chapter 8 we

explore, for the fi rst time in this clinical setting, the potential existence of

a bone-vascular hypothesis post-kidney transplantation. For this purpose, in

agreement with the KDIGO 2017 clinical practice guidelines, we study the

prevalence of BMD disorders in KTR, non-invasively assessed by a DXA

scan, and evaluate its potential independent association with risk of AAC. The

value and limitations of a DXA scan as imaging method of clinical choice

to provide non-invasive, relatively accurate and cost-eff ective evaluation of

post-transplant bone disease, and further investigate the theoretically broad

contribution of post-transplant bone disease to morbi-morbidity of KTR is

discussed.

Finally,

chapter 9 summarizes the results of the work presented in chapters

2 to 8, providing separate and overall discussion of the main findings, as well

as multi-fold perspectives and implications to inform practice, policy, and

future research.

1

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