These include

enhanced insulin resistance (IR), altered lipid metabolism, chronic hypoxia, increased oxidative stress, and enhancement of inflammatory cytokines. Because IR influences histological severity in NAFLD,21, 22 CS may worsen NAFLD through its effect on IR, glucose intolerance, and diabetes development.23, 24 Changes in lipid metabolism induced by CS may also aggravate NAFLD. Experimental studies have shown that CS aggravates the hepatic steatosis elicited by a high-fat diet in mice25, 26 via enhanced fatty acid synthesis through inhibition of adenosine monophosphate–activated protein kinase phosphorylation in liver tissue.25 Chronic hypoxia, Acalabrutinib a hallmark side effect of CS, induces steatosis, liver inflammation, and fibrosis in mice.27-29 CS also causes oxidative stress,30 a recognized mechanism of injury in NAFLD.31

Mice on an ethanol diet develop increased hepatocellular injury when they are exposed to CS, and they have increased levels of cytochrome P450 2E1, which is known to play a role in oxidative injury in NAFLD.28 Finally, CS may worsen NAFLD by enhancing proinflammatory cytokines, such as tumor necrosis factor alpha, that are known to play a key role in NAFLD.32 In this issue of HEPATOLOGY, Azzalini et al.33 provide novel evidence suggesting that CS exacerbates liver injury in NAFLD. In their study, control and obese Zucker rats were divided into smoker and nonsmoker groups according to controlled exposure to CS. Exposure to CS increased alanine aminotransferase ALK inhibitor cancer (ALT) levels and increased hepatocellular ballooning and lobular inflammation in the livers of obese rats, whereas significantly smaller changes were noted in control rats. The authors showed that CS increased oxidative stress and hepatocyte apoptosis in obese rats. In addition, CS exposure induced tissue inhibitor of metalloproteinase 1 and procollagen alpha 2 synthesis at the transcription level. The effects of CS on the ALT level, histological hepatic injury, and expression of fibrogenic genes occurred only with long-term exposure (4 weeks)

to CS and did not occur with a shorter exposure (5 days). This indicates that the aggravating effects of CS on NAFLD are the result ifenprodil of prolonged exposure to CS. The results of Azzalini et al. provide some elucidation of the underlying mechanisms involved in CS-related liver injury not only in NAFLD but potentially also in other types of CLD. The value of the findings of experimental studies such as this study by Azzalini et al. is further underscored by the fact that it would be impossible to conduct a prospective randomized controlled study of the effects of CS in humans with CLD. Even case-control or cohort studies attempting to isolate the effect of CS on CLD prove to be challenging in the clinical setting and are limited by multiple confounders. Nonetheless, the study by Azzalini et al.33 has some limitations.