Introduction
Non-alcoholic steatohepatitis (NASH) is a more severe form of non-alcoholic fatty liver disease, characterized by hepatic steatosis (fat accumulation), inflammation, and hepatocyte (liver cell) injury, with or without fibrosis. It has become the most important cause of cirrhosis (scarring of the liver) and hepatocellular carcinoma (liver cancer) and is growing astronomically in most parts of the world. Despite such a great clinical burden, there are no FDA (Food and Drug Administration) approved therapies for NASH; thus, establishing effective treatments is of utmost importance. In this article, recent and emerging therapeutic approaches to NASH are put into perspective in light of the complex nature of the disease.
What Is the Pathogenesis of NASH?
The pathogenesis of NASH is complex and multifactorial, involving metabolic, inflammatory, and fibrotic pathways. Cell death, inflammation, oxidative stress, and ER stress are all key variables in this process. Moreover, the interrelationship between NASH and metabolic syndrome contributes to a further complication of the disease process since insulin resistance and obesity are closely related to disease progression. These pathways must be understood for the development of targeted therapies.
What Are the Emerging Therapies for NASH?
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FXR Agonists
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The farnesoid X receptor (FXR) is a nuclear receptor primarily expressed in the liver, kidneys, intestines, and adrenal glands. Bile acids activate this receptor. FXR plays a critical role in metabolic homeostasis about glucose metabolism and prevents fat accumulation in the liver. FXR also takes part in the immune system. This receptor is expressed in liver immune cells such as Kupffer cells and natural killer cells, which contribute to regulating immune responses. In addition, FXR activation contributes to the regulation of nitric oxide production, which plays a key role in the progression of non-alcoholic steatohepatitis, the most serious form of fatty liver disease. Withaferin A is an agonist of FXR and LXR-α (liver X receptor alpha), which can decrease NAFLD-related liver inflammation and fibrosis.
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Clinical investigations have demonstrated that obeticholic acid (OCA), a strong FXR agonist produced from bile acid, improves liver histology in individuals with nonalcoholic steatohepatitis. However, because of its adverse effects, which include itching, elevated cholesterol, and liver failure, the FDA has not authorized it. Tropifexor is another FXR agonist whose safety and efficacy in treating NASH are currently being studied. For this reason, a number of other FXR agonists are also in development.
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Peroxisome Proliferator-Activated Receptor Agonists PPAR: It targets the family of nuclear receptors named PPARs that regulate genes implicated in glucose and lipid metabolism. Many PPAR agonists include Elafibranor, a PPAR-alpha/ delta dual agonist, and Lanifibranor, a pan-PPAR agonist; all these have shown improvement in liver histology, reduced inflammation, and fibrosis in patients with NASH. These agents are relatively clean regarding safety, although longer-term data from ongoing trials will be required to confirm their benefit.
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THR-Beta Agonists: The goal of thyroid hormone receptor-beta (THR-beta) agonists is to boost lipid metabolism by focusing on the liver without causing the systemic effects that come with thyroid hormone therapy. Clinical trials have proven the potential of Resmetirom (MGL-3196), a selective THR-beta agonist, to reduce liver fat and improve NASH histopathology. This strategy limits the possibility of adverse effects on heart rate and bone health while maximizing the metabolic effects of thyroid hormone in the liver.
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Glucagon-Like Peptide (GLP- 1): GLP-1 controls the amount of blood sugar and minimizes appetite, thus facilitating weight loss. The GLP-1-based emerging therapies using drugs such as Tirzepatide and Semaglutide are effective treatments for a liver condition known as NASH since these improve NASH-related biomarkers and liver health. So far, drugs that either "mimic" GLP-1 or are GLP-1 enhancers have been promising treatments for NASH. Tirzepatide acts on GLP-1 and another hormone called GIP (gastric inhibitory peptide). In clinical trials, it has demonstrated an improvement in NASH and biomarkers associated with this disease. Adverse effects were common and were typically mild to moderate: nausea, vomiting, reduced appetite, bloatedness, and diarrhea. Semaglutide also had strong results for the improvement of NASH without the worsening of liver fibrosis. GLP-1 therapies are established in treating diabetes today and seem very promising for the future treatment of NASH.
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Anti-Fibrotic Agents: Fibrosis is one of the main causes of NASH's progression to more serious liver illnesses. To lessen fibrosis, anti-fibrotic medications such as Cenicriviroc, a dual chemokine receptor (CCR2 or CCR5) antagonist, block inflammatory pathways. According to early-phase trials, Cenicriviroc can improve fibrosis without making NASH worse; nevertheless, more research is required to fully demonstrate its safety and efficacy.
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Combination Therapies: The multifaceted character of NASH has led to an increasing interest in combination treatments that target many pathways at once. Agents with complimentary modes of action can be combined to maximize therapeutic efficacy and minimize adverse effects. For example, a GLP-1 receptor agonist can be paired with an FXR or PPAR agonist. Clinical trials evaluating different combinations are now being conducted to give a more comprehensive approach to NASH therapy.
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Gut Microbiota: The gut microbiota is a target for therapeutic modification in managing NASH. One strategy for restoring a healthy gut microbiome is transplanting fecal microbiota from healthy donors into patients through fecal microbiota transplantation. Preliminary studies indicate that this treatment can even reduce metabolic profiles and inflammation in the liver. In addition, probiotics, living bacteria, and prebiotics, food-like substances that favor the growth of these bacteria, have also been researched for their potential benefits in decreasing liver inflammation and improving metabolic health in patients with NASH.
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Other Novel Approaches: The innovative therapies of microRNA-based and stem cell approaches are NASH's two novel therapeutic options. The former acts at the level of gene expression regulation with mechanistic targets, while the latter is proposed to act primarily by promoting liver regeneration. Although these newer therapeutic options are still in the early phases of development, they appear promising for clinical applications soon. Furthermore, an exosome-based drug delivery system is under exploration to help in the targeted delivery of therapeutic agents to improve drug efficacy and minimize toxicities by directly delivering the drugs to the liver cells affected by NASH.
Conclusion
NASH is a multifaceted, intricate illness with serious consequences for one's health. Although lifestyle adjustments continue to be the mainstay of care, there are prospects for better therapies because of newly developed medicines that target distinct pathways involved in the pathophysiology of NASH. Among the most promising areas of investigation are gut microbiome modulators, anti-inflammatory medicines, PPAR agonists, THR-beta agonists, and anti-fibrotic drugs. As our knowledge of NASH grows, the discovery of innovative treatments and combination methods will be critical in tackling this expanding global health concern. To find safe and effective therapeutics for NASH and improve patient outcomes, further research and clinical trials are necessary.
