Acute renal failure (ARF) is more commonly referred to as acute kidney injury (AKI) in modern research and clinical terminology. AKI refers to a rapid decline in renal function within a short period, resulting in impaired excretion of nitrogenous metabolic waste, abnormal regulation of body fluid volume, electrolyte disturbances, and acid-base imbalance.

Keywords: acute kidney injury; acute renal failure; ischemia-reperfusion injury; cisplatin nephrotoxicity; rhabdomyolysis; sepsis-associated AKI; KIM-1; NGAL

1 Research Positioning of AKI Animal Models

1.1 Terminological Relationship Between ARF and AKI

ARF emphasizes sudden renal failure and is more commonly used in earlier literature and traditional descriptions. AKI emphasizes the continuous pathological process of the kidney from mild injury to obvious functional failure, making it more suitable for describing tubular injury, inflammatory responses, microcirculatory disturbance, and molecular biomarker changes. Therefore, in animal experimental design, AKI is recommended as the preferred model name, while ARF may be retained as a traditional term or background explanation.

1.2 Modeling Objectives

The establishment of AKI models usually serves the following research objectives:

(1) Simulating clinical etiologies

These include ischemia-reperfusion, drug nephrotoxicity, rhabdomyolysis, sepsis, obstructive injury, and multifactorial combined injury.

(2) Elucidating injury mechanisms

Key processes include oxidative stress, inflammatory responses, mitochondrial dysfunction, apoptosis, necroptosis, pyroptosis, ferroptosis, and endothelial injury.

(3) Screening intervention drugs

AKI models can be used to evaluate potential renoprotective strategies such as antioxidants, anti-inflammatory agents, mitochondrial protectants, ferroptosis inhibitors, NLRP3 inhibitors, and Nrf2 pathway activators.

(4) Validating biomarkers

Commonly measured indicators include serum creatinine, blood urea nitrogen, cystatin C, NGAL, KIM-1, IL-18, urinary protein, urinary sediment, and histopathological injury scores.

(5) Studying AKI-to-CKD transition

Some models can be used to observe tubulointerstitial fibrosis, capillary rarefaction, chronic inflammation, and incomplete renal functional recovery.

1.3 Principles for Model Selection

The selection of an AKI model should directly correspond to the research question, rather than simply pursuing modeling speed or the magnitude of serum creatinine elevation.

Table 1 Key Points for Selecting Common AKI Animal Models

2 Ischemia-Reperfusion Injury Model

2.1 Modeling Principle

The ischemia-reperfusion injury (IRI) model induces ischemia by temporarily blocking renal blood flow and then restores blood flow to produce reperfusion injury. This model is commonly used to simulate ischemic AKI after renal transplantation, shock, aortic surgery, cardiac surgery, or severe hypotension.

2.2 Modeling Methods

(1) Animal selection

Mice, rats, and rabbits are commonly used. Mice are suitable for genetically modified studies, whereas rats are suitable for physiological indicators, pharmacodynamic evaluation, and pathological assessment.

(2) Surgical methods

Common methods include bilateral renal pedicle clamping, unilateral renal ischemia combined with contralateral nephrectomy, and unilateral renal ischemia with preservation of the contralateral kidney. Bilateral clamping more readily produces obvious renal functional changes, while unilateral models are more suitable for observing local injury and repair processes.

(3) Ischemia duration

The commonly used ischemia duration is approximately 20–45 min in mice and approximately 30–60 min in rats. If the ischemia duration is too short, injury may be insufficient; if it is too long, mortality can increase significantly. The specific duration should be optimized through preliminary experiments according to animal species, age, body weight, anesthesia method, clamping site, and experimental endpoint.

(4) Key procedures

Body temperature should be maintained during modeling to avoid hypothermia reducing the degree of injury. After clamping, the kidney should become darker in color, and after clamp release, blood flow restoration and color recovery should be observed. Body temperature, anesthesia depth, fluid supplementation, surgical duration, and postoperative care all affect model stability.

2.3 Mechanistic Pathways

The core pathological process of the IRI model includes energy depletion during ischemia and inflammatory oxidative injury during reperfusion.

(1) Mitochondrial injury and oxidative stress

Ischemia reduces ATP production, impairs Na⁺/K⁺-ATPase function, and causes cellular edema and disruption of ion homeostasis. After reperfusion, oxygen supply is restored, and mitochondria and NADPH oxidase generate large amounts of ROS, inducing oxidative damage to lipids, proteins, and DNA.

(2) Inflammatory response

After damage-associated molecular patterns are released, they can activate the TLR4/NF-κB pathway, NLRP3 inflammasome, and complement system, promoting the expression of inflammatory factors such as TNF-α, IL-1β, IL-6, and IL-18.

(3) Cell death

Renal tubular epithelial cells can undergo apoptosis, necrosis, necroptosis, pyroptosis, and ferroptosis. Bax/Bcl-2 imbalance, Caspase-3 activation, activation of the RIPK1/RIPK3/MLKL pathway, Caspase-1/Gasdermin D-mediated pyroptosis, and decreased GPX4 may all participate in the injury process.

(4) Repair and fibrosis

After injury, renal tubular epithelial cells can undergo dedifferentiation, proliferation, and redifferentiation. If repair is incomplete, persistent inflammation, capillary rarefaction, TGF-β/Smad signaling activation, and renal interstitial fibrosis may occur.

2.4 Key Detection Indicators

The following indicators are commonly detected in the IRI model:

(1) Renal function indicators

Serum creatinine, blood urea nitrogen, cystatin C, urine volume, urine osmolality, and electrolytes.

(2) Renal injury biomarkers

NGAL, KIM-1, clusterin, IL-18, urinary protein, and urinary sediment.

(3) Inflammation-related indicators

NLRP3, Caspase-1, IL-1β, IL-18, TNF-α, IL-6, NF-κB p65, and HMGB1.

(4) Oxidative stress indicators

ROS, MDA, 4-HNE, SOD, GSH/GSSG, Nrf2, and HO-1.

(5) Histological evaluation

HE, PAS, TUNEL, tubular necrosis score, cast formation, brush border loss, and inflammatory cell infiltration.

3 Nephrotoxic Drug-Induced AKI Models

3.1 Cisplatin-Induced AKI Model

Cisplatin is a classic inducer for chemotherapy drug nephrotoxicity models and mainly damages the proximal renal tubules. This model is suitable for studying drug-induced AKI, mitochondrial injury, DNA damage responses, apoptosis, inflammation, and screening of renoprotective drugs.

(1) Modeling method

In rats, cisplatin is commonly administered as a single intraperitoneal injection, with doses mostly in the range of 5–10 mg/kg. In mice, the dose should be adjusted according to strain and body weight. Obvious renal dysfunction and tubular injury usually appear 3–5 days after administration.

(2) Injury mechanism

Cisplatin can enter renal tubular cells through organic cation transporter 2 (OCT2) and copper transporter-related proteins, triggering DNA damage, mitochondrial respiratory chain dysfunction, ROS accumulation, and cytochrome C release. Apoptotic signaling molecules such as p53, Bax, and Caspase-3 are activated, often accompanied by inflammatory responses, endoplasmic reticulum stress, and ferroptosis-related changes.

(3) Key indicators

Commonly detected indicators include serum creatinine, blood urea nitrogen, KIM-1, NGAL, OCT2, CTR1, p53, Bax, Bcl-2, cleaved Caspase-3, Nrf2, HO-1, GPX4, ACSL4, and 4-HNE.

3.2 Gentamicin-Induced AKI Model

Gentamicin is an aminoglycoside antibiotic that can accumulate in renal proximal tubular cells and cause lysosomal dysfunction, mitochondrial injury, and oxidative stress. This model is suitable for studies of antibiotic-related nephrotoxicity, proximal tubular injury, and antioxidant intervention.

(1) Modeling method

Gentamicin is commonly administered by repeated subcutaneous or intraperitoneal injection for 5–10 days. The dose should be set according to animal species and research objective. A reference range may be 100–200 mg/kg/day, but preliminary experiments are required to balance injury severity and mortality risk.

(2) Injury mechanism

Gentamicin can accumulate in proximal tubular epithelial cells through endocytosis, causing lysosomal phospholipid accumulation, mitochondrial dysfunction, increased ROS, and tubular epithelial cell necrosis or apoptosis.

(3) Key indicators

Common indicators include renal function, KIM-1, NGAL, NAG, MDA, SOD, Caspase-3, Bax/Bcl-2, tubular necrosis score, and brush border injury.

3.3 Application Notes

Nephrotoxic drug-induced models are highly sensitive to animal strain, age, sex, hydration status, administration route, and dose. Excessive cisplatin can easily cause severe systemic toxicity and rapid body weight loss. Excessively prolonged gentamicin administration can lead to obvious mortality or chronic injury. Therefore, the experimental endpoint should be clearly defined before the experiment, whether it is acute injury, recovery process, or chronic outcome.

4 Glycerol-Induced Rhabdomyolysis-Associated AKI Model

4.1 Modeling Principle

The glycerol-induced rhabdomyolysis model is used to simulate myoglobinuric AKI caused by crush injury, severe muscle injury, strenuous exercise, ischemic muscle necrosis, or drug-related rhabdomyolysis. After large amounts of myoglobin are released and filtered through the glomerulus, myoglobin forms casts in acidic urine, causing tubular obstruction and direct toxic injury.

4.2 Modeling Method

A common method is intramuscular injection of 50% glycerol into the hindlimb muscles of rats or mice. The commonly used dose range in rats is approximately 8–10 mL/kg, while the mouse dose should be adjusted according to body weight and strain. Water deprivation before modeling can enhance model stability, but it can also increase animal stress and mortality risk; therefore, it should be set cautiously according to ethical requirements and experimental objectives.

4.3 Mechanistic Pathways

(1) Cast obstruction

Myoglobin deposits in acidic urine and can form casts with Tamm-Horsfall protein and other components, leading to tubular lumen obstruction and increased intratubular pressure.

(2) Oxidative injury

Heme iron released from myoglobin can catalyze Fenton reactions, promote ROS generation, and induce lipid peroxidation and mitochondrial injury.

(3) Ferroptosis

Increased free iron, lipid peroxidation accumulation, and reduced GPX4 function can jointly promote ferroptosis. ACSL4 upregulation, increased MDA and 4-HNE, and GSH depletion all indicate the involvement of ferroptosis.

4.4 Key Detection Indicators

(1) Muscle injury indicators

Myoglobin, creatine kinase, and LDH.

(2) Renal function indicators

Serum creatinine, blood urea nitrogen, urine volume, urine color, and urinary myoglobin.

(3) Iron metabolism and ferroptosis indicators

Ferritin, hepcidin, transferrin receptor, GPX4, ACSL4, SLC7A11, MDA, and 4-HNE.

(4) Histological indicators

Cast formation, tubular necrosis, brush border loss, outer medullary injury, and inflammatory cell infiltration.

5 Sepsis-Associated AKI Models

5.1 LPS-Induced Model

The lipopolysaccharide (LPS)-induced model is used to simulate endotoxemia-associated inflammatory responses. This model is relatively easy to perform, induces rapid inflammation, and is suitable for studying the TLR4/MyD88/NF-κB pathway, cytokine release, endothelial injury, and renal tubular inflammatory responses.

(1) Modeling method

In mice, LPS is commonly administered by intraperitoneal or intravenous injection, with a reference dose of approximately 5–10 mg/kg. Dose, administration route, and observation time significantly affect mortality and the degree of renal injury. Low doses are more suitable for inflammatory mechanism studies, while high doses more readily produce a systemic shock-like state.

(2) Mechanistic pathways

LPS activates NF-κB through the TLR4/MyD88 pathway and induces the release of inflammatory factors such as TNF-α, IL-6, and IL-1β. It can also cause endothelial injury, microcirculatory disturbance, abnormal NO regulation, decreased mitochondrial function, and renal tubular stress responses.

(3) Key indicators

TLR4, MyD88, NF-κB p65, TNF-α, IL-6, IL-1β, ICAM-1, VCAM-1, Caspase-1, Gasdermin D, NGAL, and KIM-1.

5.2 CLP Model

Cecal ligation and puncture (CLP) simulates complex sepsis by inducing polymicrobial intra-abdominal infection. Compared with the LPS model, CLP more closely resembles the infection process, immune response, and multi-organ injury characteristics of clinical sepsis.

(1) Modeling method

CLP is performed by ligating part of the cecum and puncturing it to allow intestinal contents to enter the abdominal cavity and induce polymicrobial infection. Model severity is affected by ligation length, needle size, number of punctures, amount of feces extruded, fluid resuscitation, antibiotic use, and postoperative care.

(2) Mechanistic pathways

CLP can induce systemic inflammatory responses, immunosuppression, endothelial barrier disruption, abnormal renal microcirculatory perfusion, and renal tubular metabolic reprogramming. Pyroptosis, apoptosis, mitochondrial injury, and abnormal autophagy may all participate in sepsis-associated AKI.

(3) Key indicators

In addition to renal function and histological indicators, body temperature, activity status, bacterial load, serum inflammatory factors, lactate level, endothelial injury markers, and multi-organ injury indicators should also be monitored.

5.3 Application Notes

The LPS model is more suitable for rapid and controllable studies of endotoxin inflammatory pathways. The CLP model is more suitable for evaluating complex infection, immune imbalance, and clinically translatable interventions. Sepsis-associated AKI does not necessarily present as obvious tubular necrosis; in some cases, renal dysfunction is closely related to microcirculatory disturbance, inflammatory mediators, decreased mitochondrial function, and changes in cellular metabolism.

6 Genetically Modified AKI Models

6.1 Model Positioning

Genetically modified models usually do not independently simulate a specific clinical etiology of AKI. Instead, they are used to answer mechanistic questions such as whether a certain gene or pathway participates in AKI occurrence, repair, or chronic progression. Common strategies include global knockout, conditional knockout, transgenic overexpression, reporter mice, and cell-specific gene editing.

6.2 Common Research Directions

(1) Oxidative stress regulation

Pathways such as Nrf2, Keap1, and HO-1 are used to study the effects of antioxidant defense on AKI.

(2) Hypoxic response

HIF-1α, HIF-2α, and their downstream VEGF- and EPO-related pathways are used to study hypoxic adaptation and vascular repair.

(3) Autophagy regulation

Models related to Atg5, Atg7, Beclin-1, and LC3 are used to evaluate the role of renal tubular epithelial autophagy in injury and repair.

(4) Inflammation and pyroptosis

NLRP3, Caspase-1, Gasdermin D, TLR4, and MyD88 models are used to analyze inflammasome and innate immune pathways.

(5) Fibrotic transition

Models related to TGF-β, Smad3, α-SMA, and Collagen I are used to study post-AKI renal interstitial fibrosis and AKI-to-CKD transition.

6.3 Application Points

Genetically modified models usually need to be combined with IRI, cisplatin, LPS, CLP, or glycerol models to determine the role of genes under specific etiological backgrounds. If renal tubular-specific, podocyte-specific, or endothelial cell-specific knockout models are used, the promoter expression site, knockout efficiency, baseline renal phenotype, and time-window changes after injury should be clearly defined.

Table 2 Products Related to AKI Animal Model Evaluation and Mechanistic Research

7 Model Selection According to Different Research Objectives

7.1 Ischemic AKI Research

The IRI model should be prioritized. If reperfusion oxidative stress, microcirculatory injury, and renal transplantation-related mechanisms are the focus, bilateral renal ischemia or unilateral ischemia combined with contralateral nephrectomy can be used. If long-term repair and fibrosis are the focus, relatively mild injury can be induced and the observation period extended.

7.2 Drug Nephrotoxicity Research

The cisplatin model is suitable for studying chemotherapy drug nephrotoxicity, DNA damage, mitochondrial injury, and apoptosis. The gentamicin model is suitable for studies of antibiotic nephrotoxicity, proximal tubular accumulation, and oxidative stress. If transporter mechanisms are being studied, OCT2, CTR1, MATE, and related drug transporters should be emphasized.

7.3 Ferroptosis and Myoglobinuria Research

The glycerol-induced rhabdomyolysis model is more suitable for studying myoglobin-related cast obstruction, free iron-mediated oxidative injury, and ferroptosis. If ferroptosis inhibitors, iron chelators, or lipid peroxidation inhibitors are being studied, this model has strong mechanistic relevance.

7.4 Inflammation and Sepsis-Associated AKI Research

The LPS model is suitable for rapid studies of TLR4/NF-κB, inflammatory factors, and pyroptosis pathways. The CLP model is more suitable for simulating complex infection and clinical sepsis processes. If clinical translation is the focus, the CLP model should be prioritized, with standardized conditions for fluid resuscitation, antibiotics, and postoperative care.

7.5 AKI-to-CKD Transition Research

Extending the observation period after a single acute injury, or using models such as moderate IRI, repeated low-dose toxic stimulation, or unilateral renal ischemia, can be used to study chronic inflammation, maladaptive tubular repair, and renal interstitial fibrosis. Such studies should include indicators such as Masson staining, Sirius Red staining, α-SMA, Collagen I, Fibronectin, and TGF-β/Smad3.

The value of acute kidney injury animal models lies in establishing controllable pathological scenarios for mechanistic analysis and screening of intervention strategies. IRI, cisplatin/gentamicin, glycerol, LPS/CLP, and genetically modified models correspond to different clinical etiologies and molecular pathways. Only by designing model selection, modeling parameters, evaluation indicators, and research endpoints in an integrated manner can the reproducibility and clinical interpretability of AKI experimental results be improved.

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