Science in medicine
2868 The Journal of Clinical Investigation http://www.jci.org Volume 119 Number 10 October 2009
Sepsis and sepsis-induced acute kidney injury:
a life-threatening condition
Sepsis is a characteristic set of systemic reactions to overwhelming
infection. Sepsis, severe sepsis, and septic shock are defined accord-
ing to established criteria (Table 1) (1). Discovery of antibiotics has
dramatically improved the morbidity and mortality of the infectious
diseases for the last decades; indeed, antibiotics and volume resus-
citation are the first line of sepsis treatment strategy (2). However,
overwhelming inflammatory response accompanied by depression
in immunological function causes multiple organ injury and deter-
mines clinical outcomes. In addition to inflammation and immu-
nological dysregulation, a number of different mechanisms contrib-
ute to sepsis at different phases (Figure 1). For instance, systemic
hemodynamics evolves from an early hyperdynamic (“warm shock”)
state to a late hypodynamic (“cold shock”) state.
Sepsis is the leading cause of death in critically ill patients, and the
incidence of sepsis is increasing (3, 4). The mortality rate of severe
sepsis is very high (up to 70%), and the calculated costs exceed $15
billion per year in the United States (3). The rate of severe sepsis dur-
ing hospitalization almost doubled during the last decade and is
considerably greater than previously predicted (5). Sepsis causes mul-
tiorgan failure, including acute kidney injury (AKI) (6), and patients
with both sepsis and AKI have an especially high mortality rate (7).
AKI is diagnosed by a sudden decrease in glomerular filtration rate
(GFR), the primary measure of kidney function, which is currently
detected clinically as a rise in serum creatinine. A multinational pro-
spective observational study including 29,269 critically ill patients
revealed that the occurrence of AKI in the intensive care unit (ICU)
was approximately 6%, the most frequent contributing factor to AKI
being sepsis (50%) (8). Other reports showed that between 45% and
70% of all AKI is associated with sepsis (9–11). Several different patho-
physiological mechanisms have been proposed for sepsis-induced
AKI: vasodilation-induced glomerular hypoperfusion, dysregulated
circulation within the peritubular capillary network, inflammatory
reactions by systemic cytokine storm or local cytokine production
(12), and tubular dysfunction induced by oxidative stress (13).
Continuing concern over the efficacy and safety of the only FDA-
approved therapy for severe sepsis (activated protein C) highlights
the critical need to improve our understanding of the pathophysi-
ology of sepsis and sepsis-induced AKI and to develop novel treat-
ment strategies for critically ill patients (14). A multitude of poten-
tial drug targets have been identified in animal models of sepsis;
however, translation from animals to humans has been exceed-
ingly difficult. Several reviews have pointed out that the failure
to translate results from animals to humans has been attributed
to disease characteristics of sepsis (complexity and heterogeneity),
inappropriate clinical trials (study of ineffective drugs, inadequate
clinical trial designs), and animal models that do not fully mimic
human sepsis (14–17).
Requirements for animal models of sepsis
Human sepsis is currently hypothesized to involve at least two stages:
an initial proinflammatory burst responsible for hypotension and
organ dysfunction, followed by a compensatory antiinflamma-
tory immune response that leads to an immunosuppressed state
often called immune depression or immune dysfunction; however,
these stages can overlap temporally (Figure 1). The latter consists
of altered monocyte antigen presentation, decreased lymphocyte
proliferation and responsiveness, and lymphocyte apoptosis and
anergy (18, 19), which accounts for nosocomial infections and late
deaths in sepsis. Animal models of sepsis need to reproduce the
complexity of human sepsis and its treatment in the ICU. Ideally,
animal models should mimic the pace and severity of human sep-
sis; reproduce key hemodynamic (warm shock followed by cold
shock) and immunologic (proinflammatory stimulation, antiin-
flammatory counterregulation, i.e., immune depression) stages;
mimic histology findings in key organs (lung, liver, spleen, kidney,
etc.) that are frequently modest; and —perhaps counterintuitively
for animal modelers — exhibit variability among animals.
Standard animal models of sepsis
Sepsis animal models can be divided into three categories: (a)
injection of an exogenous toxin (e.g., LPS); (b) alteration of the
animal’s endogenous protective barrier, such as intestinal leak-
age (e.g., cecal ligation and puncture [CLP] or colon ascendens
Animal models of sepsis and sepsis-induced
kidney injury
Kent Doi,
1
Asada Leelahavanichkul,
2,3
Peter S.T. Yuen,
2
and Robert A. Star
2
1
Department of Nephrology and Endocrinology, University of Tokyo, Tokyo, Japan.
2
NIDDK, NIH, Bethesda, Maryland, USA.
3
Division of Nephrology,
Department of Medicine, Chulalongkorn University, Bangkok, Thailand.
Sepsis is characterized by a severe inflammatory response to infection, and its complications,
including acute kidney injury, can be fatal. Animal models that correctly mimic human disease
are extremely valuable because they hasten the development of clinically useful therapeutics. Too
often, however, animal models do not properly mimic human disease. In this Review, we outline a
bedside-to-bench-to-bedside approach that has resulted in improved animal models for the study
of sepsis — a complex disease for which preventive and therapeutic strategies are unfortunately
lacking. We also highlight a few of the promising avenues for therapeutic advances and biomarkers
for sepsis and sepsis-induced acute kidney injury. Finally, we review how the study of drug targets and biomarkers
are affected by and in turn have influenced these evolving animal models.
Conflict of interest: The authors have declared that no conflict of interest exists.
Citation for this article: J. Clin. Invest. 119:2868–2878 (2009). doi:10.1172/JCI39421.

science in medicine
The Journal of Clinical Investigation http://www.jci.org Volume 119 Number 10 October 2009 2869
stent peritonitis [CASP]); and (c) infusion or instillation of exog-
enous bacteria (Table 2).
LPS-induced inflammation models. Endotoxin, a component of
the outer membrane of Gram-negative bacteria, is involved in the
pathogenesis of sepsis, and an LPS infusion/injection model has
been widely used for sepsis research. LPS administration induces
systemic inflammation that mimics many of the initial clinical fea-
tures of sepsis, including increases in proinflammatory cytokines
such as TNF- _ and IL-1, but without bacteremia (20–22). Treat-
ment of LPS-injected animals with neutralizing antibody against
TNF- _ or IL-1 resulted in improved outcomes for this model (23,
24). A case report describes a patient who self-administered a large
dose of LPS, and the full clinical manifestations of septic shock
developed (25). LPS infusion also causes renal injury, includ-
ing decreased GFR, increased blood urea nitrogen (BUN), and
increased renal neutrophil infiltration (26–28).
Several clinical trials of anti–TNF- _ and anti–IL-1 therapy were
performed based on the promising results in LPS animal studies;
however, these trials failed to improve survival of septic patients
(29, 30). LPS causes much earlier and higher peak levels of cytokine
expression compared with levels observed in human sepsis, with
the notable exception of meningococcal sepsis, a rare, patho-
gen- and site-specific form of sepsis wherein cytokine levels are
comparable to those observed in LPS animal models (21, 31, 32).
Also, some features of LPS infusion such as renal hypoperfusion
and increased BUN are alleviated by volume replacement, which
is routinely performed in clinical management of sepsis (33, 34).
Nevertheless, LPS infusion remains a useful tool for interrogating
a simpler subset of the complex trajectory of sepsis. The LPS dose
can be titrated to mimic early sepsis without hemodynamic com-
promise, which has been useful for studying systemic and renal
responses during the initial phases of sepsis; doses of LPS typi-
cally used induce systemic hypotension and decrease glomerular
perfusion, whereas lower doses of LPS do not cause any systemic
hypotension but still decrease glomerular perfusion (35, 36).
CLP of polymicrobial sepsis. CLP is currently the most widely used
animal model of sepsis (15, 37, 38). CLP surgery is straightforward:
ligation distal to the ileocecal valve and needle puncture of ligated
cecum cause leakage of fecal contents into the peritoneum, with
subsequent polymicrobial bacteremia and sepsis (39). This surgical
manipulation, while not well standardized, allows the severity to be
adjusted by the length of ligated cecum and the size and/or number
of the puncture. Supportive treatment with fluids and antibiotics
is quite variable across laboratories and almost always inadequate,
since typically only a single fluid and/or antibiotic dose is given
(40). Multiple species of bacteria are found in the bloodstream (41,
42), and progressive systemic inflammatory response syndrome fol-
lowed by septic shock and multiorgan injury ensues (34, 43, 44).
Mice subjected to CLP generally became severely hypotensive with-
out an apparent hyperdynamic phase (45), although more vigor-
ous fluid resuscitation can result in an early hyperdynamic phase
detected by echocardiography (46). CLP-induced sepsis models
show a cytokine profile similar to that in human sepsis (21, 31, 34),
and anti–TNF- _ treatment fails to alleviate sepsis in CLP models as
in human sepsis (31, 47, 48). Notably, treatment with recombinant
human TNF- _ reduced mortality in CLP-induced sepsis (41). As
described above, human sepsis is considered to have two immuno-
logically different stages: a proinflammatory phase and a compen-
satory antiinflammatory phase. CLP-induced sepsis increased lym-
phocyte apoptosis, which mimics immunosuppression at the later
phase of human sepsis (18, 49, 50). In this respect, CLP-induced
sepsis is completely different from LPS-induced sepsis and more
closely mimics human sepsis.
However, the standard CLP model does not develop reproducible
acute kidney or lung injury. AKI has been detected by changes in
BUN or creatinine in some (51–55) but not other studies (56, 57).
Thus, the standard CLP model encompasses more clinical features
and drug responses of human sepsis than the LPS model but is
still missing some key features, especially kidney and lung injury.
Bacterial infusion or instillation models. Whereas models such as
CLP and CASP are helpful in understanding polymicrobial sepsis,
human sepsis may also be caused by a single pathogen. Bacterial
infusion models can approximate introduction of a single patho-
gen in a controlled manner, allowing reproducible infection. These
Table 1
Sepsis definitions
Condition Description
SIRS Two or more of the following conditions: temperature >38.5°C or <35.0°C; heart rate of >90 beats/min; respiratory rate
of >20 breaths/min or PaCO
2
of <32 mmHg; and wbc count of >12,000 cells/ml, <4,000 cells/ml, or >10% immature
(band) forms
Sepsis SIRS in response to documented infection (culture or Gram stain of blood, sputum, urine, or normally sterile body fluid
positive for pathogenic microorganism; or focus of infection identified by visual inspection)
Severe sepsis Sepsis and at least one of the following signs of organ hypoperfusion or organ dysfunction: areas of mottled skin;
capillary refilling of >3 s; urinary output of <0.5 ml/kg for at least 1 h or renal replacement therapy; lactate of >2 mmol/l;
abrupt change in mental status or abnormal EEG; platelet count of <100,000 cells/ml or disseminated intravascular
coagulation; acute lung injury/ARDS; and cardiac dysfunction (echocardiography)
Septic shock Severe sepsis and one of the following conditions: systemic mean BP of <60 mmHg (<80 mmHg if previous
hypertension) after 20–30 ml/kg starch or 40–60 ml/kg serum saline solution or PCWP between 12 and 20 mmHg; and
need for dopamine of >5 +g/kg/min, or norepinephrine or epinephrine of <0.25 +g/kg/min to maintain mean BP at
>60 mmHg (80 mmHg if previous hypertension)
Refractory septic shock Need for dopamine at >15 +g/kg/min or for norepinephrine or epinephrine at >0.25 +g/kg/min to maintain mean BP
of >60 mmHg (80 mmHg if previous hypertension)
SIRS, systemic inflammatory response syndrome; ARDS, acute respiratory distress syndrome; PCWP, pulmonary capillary wedge pressure.