Non-alcoholic fatty liver disease (NAFLD) encompasses a
spectrum of progressive liver abnormalities from simple hepatic
steatosis to non-alcoholic steatohepatitis (NASH) to advanced
fibrosis, cirrhosis, and/or hepatocellular carcinoma [1]. Parallel to
the rising burden of obesity and metabolic syndrome, NAFLD has
emerged as the leading cause of chronic liver disease at an estimated
global prevalence of 24% [2]. Besides its known clinical burden for
liver-related morbidity and mortality, NAFLD is potentially linked
with other extra-hepatic chronic diseases and may be considered
a multisystem condition. Particularly, NAFLD increases the risk of
type 2 diabetes, cardiovascular diseases, chronic kidney disease,
and all-cause mortality [1]. Potential pathophysiologic mechanisms
underlying the detrimental effects of NAFLD include hyperglycemia,
systemic inflammation, and increased oxidative stress [3]. Sodiumglucose
cotransporter 2 (SGLT2) inhibitors are a new class of
antidiabetic agents that inhibit the reabsorption of sodium and
glucose in the proximal tubules of the kidney [4]. Commonly
used SGLT2 inhibitors include canagliflozin, dapagliflozin, and
empagliflozin. Large-scale randomized placebo-controlled trials
have demonstrated the benefits of SGLT2 inhibitors in reducing
adverse cardiovascular/renal events in patients with cardiometabolic
conditions, including diabetes, obesity, and chronic
kidney disease [5]. In regard to liver function, numerous studies
have revealed that SGLT2 inhibition reduced the levels of partate
aminotransferase (AST) as well as alanine aminotransferase (ALT)
in patients with type 2 diabetes and established cardiovascular
disease [6], highlighting the potential role of SGLT2 inhibitors in
patients with NAFLD.
The use of SGLT2 inhibitors is associated with reductions in
liver fat content in NAFLD. In a meta-analysis of patients with type
2 diabetes and NAFLD, SGLT2 inhibitors improved hepatic steatosis
and reduced levels of ALT [7]. In the E-LIFT trial which included 52
patients with type 2 diabetes and NAFLD, empagliflozin treatment
reduced liver fat, as measured by MRI-derived proton density fat
fraction [8]. While these results seem to support the role of SLGT2
inhibitors in NAFLD, it is important to note that prior investigations
are carried out in patients with diabetes. Although the reductions
in ALT and AST were independent of levels of glycated hemoglobin
in the EMPA-REG OUTCOME trial [6], the effects of SGLT2 inhibitors
on NAFLD and hard cardiovascular endpoints in the absence
of diabetes remain unknown. Further to this is the uncertain
mechanisms underlying the improvement of NAFLD with SGLT2
inhibitors. While the glucose-lowering effects of SGLT2 inhibitors
have been postulated as a major mechanism through which SGLT2
inhibitors alleviate hepatic dysfunction, the absence of protection
against hepatic dysfunction with other potent hypoglycemic
agents, including DPP4 inhibitors and metformin, speak against
this hypothesis and highlight that there might be other potential
mechanisms responsible for the observed benefits of SGLT2
inhibitors. As our understanding of SGLT2 inhibitors progresses,
their pleiotropic effects are becoming increasingly apparent.
Recent studies have shown that treatment with SGLT2 inhibitors
significantly reduced the levels of pro-inflammatory cytokines
that are associated with NAFLD, including interleukin-6 (IL-6)
and C-reactive protein (CRP) [9,10]. SGLT2 inhibitors also exhibit
antioxidant properties, protecting tissue damage/fibrosis due to
oxidative stress, and might also ameliorate atherosclerotic changes
which are well-known to be associated with NAFLD [11]. Taken
together, SGLT2 inhibitors are a promising therapeutic strategy
for NAFLD. Further clinical trials are warranted to establish the
benefits of SGLT2 inhibitors in patients with NAFLD regardless of
the presence of diabetes to halt the rapidly growing pandemic of
NAFLD and its assorted comorbidities/complications.