Long-term effects of renal mitochondrial vitality in severe infections and sepsis

Sepsis accounts for 2% of all hospital admissions, can lead to multiple organ
dysfunction syndrome (MODS) and is the leading cause of death among patients
admitted to the intensive care unit (ICU) with a mortality rate of 20-30% (1).
In addition, survivors of sepsis are at major risk for (fatal) cardiovascular
events, with a 3-year mortality rate as high as 47% after hospital discharge
(2). Despite the high mortality during and after sepsis, the pathogenesis
remains poorly understood and therapy is limited to fighting the causative
agents by administrating antibiotics and supply supportive care in the ICU (1,
3). Acute kidney injury (AKI) is in most cases caused by sepsis and is the
strongest predictor of both short- and long-term survival after sepsis (1,
4-8). The occurrence of AKI during sepsis is not only associated with failure
of other organs and an increased mortality risk during sepsis, but is also
strongly associated with the risk for chronic kidney disease (CKD) and
long-term mortality after sepsis (5-9). The pathophysiology of
sepsis-associated AKI is complex and not fully elucidated. The kidneys contain
a large number of mitochondria to support the relatively high ATP-demand
(10-12). Mitochondrial dysfunction, leading to impaired ATP-production, while
free radical formation is increased, is emerging as a key process in the
pathophysiology of sepsis-associated AKI (6, 13). The importance of
mitochondria in sepsis is supported by the observation that ATP levels are
profoundly reduced in sepsis and that biomarkers for mitochondrial dysfunction
and reduced anti-oxidant defense are associated with poor survival (14, 15).
Furthermore, clinical signs of organ failure do not correlate with histological
signs of tissue injury or inflammation in patients with sepsis, although
intracellular levels of ATP are profoundly reduced in organ failure (Aslan and
van Meurs, unpublished data) (13, 16, 17). Interestingly, administration of
mitochondria targeted antioxidants limits renal mitochondrial dysfunction,
attenuates sepsis-induced AKI and improves survival in a murine model of sepsis
(18). Remarkably, not only does renal mitochondrial dysfunction seem to be
involved in the pathogenesis of local injury in the kidney, it may also play a
role in the induction of organ injury during sepsis, through the generation of
free radicals and the release of damage associated molecular patterns (DAMPs)
from damaged mitochondria and injured cells, as well as the production of
pro-inflammatory cytokines (1, 3, 6, 19). Moreover, free radicals can damage
renal mtDNA (20) and thereby permanently affect mitochondrial function,
analogue to the process of aging (21-23). Indeed, mitochondrial function is not
restored after survival from sepsis and leads to impaired long-term muscle
function in mice (24). However, it is not known whether renal mtDNA damage
induced by sepsis may explain the relatively high incidence of CKD and
mortality among sepsis survivors. Analogue to the process of aging, sepsis is
associated with oxidative damage to mtDNA, which may lead to respiratory chain
dysfunction (20-23). In aged individuals, damage to mtDNA is associated with
CKD and important co-morbidities such as diabetes mellitus type 2, and
cardiovascular diseases (21-23). Furthermore, biomarkers for a reduced
mitochondrial function, including inactivation of complex IV in peripheral
blood mononuclear cells, increased free radical formation and reduced levels of
mtDNA in blood are associated with the development of CKD (12, 29). Whether a
similar correlation between mitochondrial function and CKD exists among sepsis
survivors remain to be unraveled. Potentially, oxidative stress during sepsis
induces a comparable aged mitochondrial phenotype and thereby increases the
risk of CKD, cardiovascular events, aging-related diseases and mortality after
survival from sepsis. Thus, mitochondrial dysfunction plays a central role in
the pathophysiology of AKI during sepsis, which is in turn associated with
increased in-hospital and long-term mortality, as well as an increased risk of
CKD among survivors. In this project, we will analyze whether the induction of
damage to (renal) mitochondria during sepsis increases the risk of CKD and
long-term mortality among sepsis survivors.

Primary Objective
The primary objective of the current project is to study the association
between biomarkers for renal mitochondrial damage in sepsis with the change in
renal function and mortality after sepsis.

Secondary Objective(s)
The secondary objectives of the current project are:
- to study the association between biomarkers for renal mitochondrial damage in
sepsis with the occurrence of cardiovascular events, co-morbidity, quality of
life and functional status after sepsis.
- to study the association between sepsis severity and the induction of renal
and systemic mitochondrial damage.
- to study the association between sepsis severity and the induction of renal
and systemic DNA damage.
- to study the association between systemic mitochondrial damage in sepsis with
(change in) renal function, cardiovascular/renal risk factors, cardiovascular
events, co-morbidity, quality of life, health/functional status and mortality
after sepsis.
- to study the association between sepsis severity and the (change in) renal
function, cardiovascular/renal risk factors, cardiovascular events,
co-morbidity, quality of life, functional status and mortality after sepsis.
In addition, the following objectives will be studied in aged individuals (i.e.
> 65 years old):
- to study whether delirious patients demonstrate an aberrant functional status
and number of circulating immune cells compared to patients that do not develop
delirium following sepsis.
- to study the association between peripheral cytokine levels and delirium
following sepsis
- to study the association between the occurrence of delirium during sepsis
with the occurrence of cardiovascular events, co-morbidity, quality of life,
functional status and mortality after sepsis.

This study is designed as a prospective cohort study with a follow-up of 2 year
on the emergency department. The aim of the project is to study whether sepsis
leads to mitochondrial damage, which may in turn explain the increased
cardiovascular morbidity and mortality among sepsis survivors. Therefore,
patients who will be hospitalized with an infection, will be included in our
study. A control group consist of healthy subjects from the PREVEND study,
matched according to age, sex and renal function consisting of patients who
presented with an infection to the ED will be included as controls (Figure 2).
The study is performed as a pilot study, since there is insufficient data
available about the surrogate markers for mitochondrial (DNA) damage biomarkers
that will be measured to perform a power analysis. This pilot study will gather
the data required to make a power analysis for a larger subsequent study. Next
to the values of the surrogate markers for mitochondrial (DNA) damage, this
study will also record various other parameters for the purpose of statistical
analysis. These parameters will be used to detect correlations or confounding
factors. The parameters are described in the following sections and will (where
possible) be extracted from the subject*s medical record.

Study groups
1. hospitalized with infection (n = 100)
2. matched control subjects (n = 100)

Note: the control subjects will be matched according to age, sex and renal
function (KDIGO CKD class) from PREVEND.
*

Study participants will be asked to donate blood through a (minimally invasive)
venapuncture and to donate urine at two different times during their stay in
the hospital, as well as at three different times during the outpatient visits
after hospital discharge. The collection of blood samples will be combined as
much as possible with the collection of blood for normal routine clinical
samples, in order to limit discomfort as as much as possible. To collect blood
/ urine during follow-up, and potentially also for the second time point
(depending on the time of discharge from the hospital), the study participant
have to travel to our center. Study participants may benefit from
participation in the trial by the additional clinical follow-up and treatment
of potential risk factors for (fatal) cardiovascular and renal diseases.