Non-alcoholic fatty liver disease (NAFLD) encompasses various pathological manifestations, including lipid deposition, steatosis, and progressive abnormalities in blood sugar/lipids. As the disease advances, hepatocyte ballooning, inflammatory cell infiltration, and fibrosis occur. While animal models should ideally mirror clinical pathology for effective clinical trials, fully reflecting the complex pathogenesis and manifestations of non-alcoholic steatohepatitis (NASH) remains a challenge. Hence, selecting appropriate pathological models aligning with clinical considerations like targeted populations and indications is central to evaluating drug effects across different stages of NASH pathology.
1. Dietary Models
Animal models induced by diets should ideally resemble human dietary patterns. However, inherent differences in natural diets yield varying pathological models compared to humans. Thus, different dietary models, such as high-fat diet (HFD), Western diet (WD), and methionine and choline deficient high-fat diet (MCD), are designed to mimic typical NASH pathology. These models offer distinct pathological mechanisms and manifestations; for instance, MCD models rapidly induce hepatic lipid accumulation and progress to inflammation and fibrosis due to key nutrient deficiencies. Choosing appropriate models for pharmacological evaluation based on drug mechanisms is essential.
Diet composition decides which part of the phenotype appears first: fat and fructose push weight gain and insulin resistance, while choline and methionine restriction drives injury and fibrosis with less metabolic burden.
2. Chemical Induction of Liver Injury or Fibrosis
Chemical agents like carbon tetrachloride (CCl4) and thioacetamide induce liver injury through varied mechanisms, showcasing changes in tissue pathology similar to NASH progression. However, models based on liver cell damage mechanisms unrelated to NAFLD progression cannot serve as primary pharmacological indicators for treating NASH.
CCl4 is activated by hepatocyte enzymes into a reactive metabolite, so the injury it produces is toxicologically informative but not metabolically driven, which is why such models usually sit on a dietary background.
3. Multi-factor Models
Single-factor models may not fully simulate clinical manifestations and entail long modeling cycles, complicating the timing of drug intervention. Combining multiple factors like high-fat diet, chemical liver injury, and pancreatic islet damage offers a combined approach, presenting typical NASH manifestations and assessing drug effects on different pathways. However, simply adding risk factors may not reflect the intrinsic relationship between NASH metabolism and fibrosis interaction, leading to evaluation discrepancies.
Treatment Targets
NASH results from various risk factors, including insulin resistance, oxidative stress, and inflammation, leading to collagen fiber deposition during repair. Intervention strategies focus on regulating glucose and lipid metabolism, anti-inflammatory actions, cell protection, and anti-fibrosis measures.
Current Research Focus and Prospect
Despite numerous candidate drugs under clinical development for NASH, the expanding patient population and substantial clinical need underscore the long road ahead. Advancements in understanding NASH pathogenesis and metabolic pathways have prompted exploration of combination therapies and optimized drug development strategies. However, uncertainties persist in clinical trial phases, necessitating in-depth research into pathogenesis mechanisms, optimization of combination therapies, development of biomarkers for efficacy evaluation, and enhancement of clinical trial designs to expedite the development of effective NASH treatments.
Conclusion
Non-clinical pharmacology studies play a central part in evaluating the efficacy, safety, and mechanism of action of NASH therapeutic drugs. Model selection, observation indicators, and analysis of trial results are what turn a study into evidence a clinical protocol can use. With new technologies such as multi-omics and artificial intelligence, non-clinical studies will further optimize drug development strategies and promote the development of precision medicine for NASH.
Work of this kind sits within NHP Pharmacology, where model choice, dosing route, and endpoints are fixed together, and efficacy readouts feed Pharmacodynamics (PD) interpretation.
Model options for the metabolic and fibrotic phenotypes are listed under NHP(monkey) Disease Models, and study design questions can go through Contact-Us.
