The Effects of Sodium-Glucose Co-Transporter-2 Inhibitors (SGLT-2-i) on Fatty Liver, Steato-Hepatitis, Liver Fibrosis, and Hepatocellular Carcinoma-A Review

The drug category of Sodium-Glucose co-transporters 2 inhibitors (SGLT 2 inhibitors) is a newer class of pharmaceutical agents for the management of type-2 diabetes mellitus, with a proved promising cardio-protective effects. In addition to above beneficial effects, Sodium-Glucose co-transporters 2 inhibitors showed their effectiveness to reduce abdominal fat content, amount of fat in liver tissues and progression of inflammation and fibrosis in experimental as well as clinical studies. Non-Alcoholic Fatty Liver Diseases (NAFLD) are common among patients with type 2 diabetes patients and includes fatty liver, Non-Alcoholic Steato-Hepatitis (NASH) and cirrhosis and when present together these disorders exacerbates each other deleterious consequences. This review article is carried out with an objective to find out the effects of Sodium-Glucose co-transporters 2 inhibitors on non-alcoholic fatty liver diseases, steato-hepatitis, fibrosis liver and hepatocellular carcinoma. The authors identified 21 relevant articles including twelve experimental and nine clinical studies with inclusion of 15152 patients, in study period ranges from 20-104 weeks. The analysis of these studies showed beneficial effects SGLT 2 inhibitors on fatty liver, liver function and NASH development, hepatic fibrosis and prevention and regression of hepatocellular carcinoma and concluded that SGLT-2 inhibitors may protect or reduce the incidence of non-alcoholic fatty liver diseases, steato-hepatitis and hepatic fibrosis in type 2 diabetes patients.


INTRODUCTION
The US FDA recently approved Sodium-glucose cotransporter-2 inhibitors (SGLT-2-I) -canagliflozin, dapagliflozin and empagliflozinfor the treatment of patients with type 2 diabetes, who are not reaching the glycaemic control targets [1]. SGLT-2-I suppress renal glucose reabsorption by inhibiting the transporter protein (SGLT-2 protein) present in the S1 segment of proximal renal tubule, which is responsible for the majority of glucose reabsorption from renal tubule and thereby SGLT-2-I enhances the urinary glucose excretion [2,3] and controls the hyperglycaemia.
SGLT-2 inhibition offers several putative advantages. Acting independently of insulin, these agents should not confer a risk of hypoglycaemia and could be employed as monotherapy or in combination with other agents. Given their mechanism of action, these agents should be effective in patients with any degree of insulin resistance or β-cell dysfunction. Due to loss of glucose (calories) in urine and glucose-induced osmotic diuresis [3], the use SGLT-2-I are associated with loss of body weight in type 2 diabetes patients and their mild osmotic diuretic effect could potentially contribute to the reduction of systemic blood pressure [3]. Taken together, all these effects may have a beneficial impact on cardiovascular outcomes [4].
In addition, SGLT-2 Is has been shown their effect to increase glucagon/insulin ratio and shifting the metabolism from glucose to lipid oxidation and furthermore these classes of pharmaceutical agents causes a significant weight loss due to reduction in visceral fat content and body fat mass. Thus it seem to be reasonable that SGLT-2 inhibitors could be more beneficial for patients with concomitant type 2 diabetes and non-alcoholic fatty liver disease [5,6]. SGLT-2 inhibitors were also found effective to reduce the fat content in the liver, improve inflammation, and prevent progression of fibrosis in NAFLD model mice [7].
It is estimated that up to 70% of patients with type 2 diabetes mellitus are affected with non-alcoholic fatty liver disease [7]. The patients suffering from NAFLD may progress to the complications such as Steato-hepatitis, liver cirrhosis and hepatocellular carcinoma. Thus it seem to be reasonable that SGLT-2 inhibitors could be more beneficial for patients with concomitant type 2 diabetes and non-alcoholic fatty liver disease [5,6]. Considering the above information, this article, reviews the relevant studies with objective to determine the effect of SGLT-2 inhibitors in nonalcoholic fatty liver disease and hepatocellular carcinoma.

MATERIALS AND METHODS
An electronic literature search was carried out in the following databases PubMed, MEDLINE and Embase. The key words used were SGLT-2 inhibitors-canagliflozin, dabagliflozin, empagliflozin, steato hepatitis, non-alcoholic fatty liver disease and hepatocellular carcinoma. The search was limited to articles published in English language and conducted in both humans and other animals, with time limit of 5 years from 2013.
To be included for review, the following criteria were considered: patient or animal model of type 2 diabetes and with altered hepatic functional parameters or hepatic injury administered with SGLT-2 inhibitors. Titles and abstracts were screened independently by two authors and full article retrieved for the manuscripts found relevant for the topic. Additional articles were searched and identified through hand searching of the bibliography. The retrieved full text articles were assessed for eligibility for inclusion and data were extracted by the authors using proforma. Any disagreement in selection of articles and data was discussed and solved between the researchers.

RESULTS
The initial total number of 263 articles is identified. After removing duplications and irrelevant results, 34 articles are selected for further reading of abstract and after revision of the contents and application search criteria, a total of 21 evidences are retrieved and selected for final analysis and review ( Figure 1). Out of 21 retrieved articles, twelve studies were experimental studies and nine were clinical studies, which included 15152 patients with type 2 diabetes mellitus and non-alcoholic liver diseases on SGLT-2 is with duration of treatment ranges form 20-104 weeks.

DISCUSSION
Non-alcoholic steato-hepatitis is a common complication among the patients with type 2 diabetes mellitus with a prevalence of 70% and they usually co-exist as manifestation of the metabolic syndrome, which is marked with high level of insulin resistance among these patients [7,8]. To add to this complication of diabetes mellitus, a meta-analysis report concluded that the patients with diabetes mellitus may be associated with elevated risk of hepatocellular carcinoma incidence and mortality, furthermore, patients with diabetes have poor prognosis compared to their counterparts [9,10]. Sodium glucose co-transporter 2 (SGLT-2) inhibitors lower blood glucose levels by inhibiting the reabsorption of glucose in the kidney and promoting the urinary glucose excretion and used to treat type 2 diabetes mellitus [11].
In addition to anti-hyperglycemic effect, SGLT-2 inhibitors have also been reported to have an effect to reduce abdominal fat (Table  1) [12]. SGLT2 inhibitors were also found effective to reduce the fat content in the liver, improve inflammation and prevent progression of fibrosis in NAFLD model mice [13].
Tahara et al. in 2013, studied the effect of ipragliflozin in type 2 diabetic model mice with hepatic steatosis and they observed improvement in hepatic function in animals and evidenced with diminished oxidative stress and inflammatory markers (Table 2) [14]. They examined the effect of ipragliflozin in streptozotocinnicotinamide-induced type 2 diabetic mice with high-fat diet which exhibit impaired insulin secretion, insulin resistance, hyperlipidemia, hepatic-steatosis and obesity.
Four-week repeated administration of ipragliflozin improved hepatic steatosis and obesity along with improvement in diabetic parameters.
In this experimental study, ipragliflozin also shows its effectiveness to reduce plasma and liver levels of oxidative stress biomarkers (thiobarbituric acid reactive substances and protein carbonyl) and inflammatory markers (interleukin 6, tumor necrosis factor α, monocyte chemotactic protein-1 and c-reactive protein) and improved liver injury as assessed by plasma levels of aminotransferases.
This positive effect of SGLT-2 inhibitor is proved by Qiang et al. in their study on rodent model with liseogliflozin [15] and it prevents accumulation of triglycerides and fibrosis in choline deficient L-amino acid defined diet rats [16].
Qiang et al. used mice treated with both nicotinamide and streptozotocin to induce diabetes and then fed a high fat diet containing trans fatty acids (HFDT) for 8 weeks and divide in to 2 groups. One group is treated with luseogliflozin and other one untreated, during this period. Luseogliflozin treated group showed improvement in fatty liver and reversal of elevated liver enzymes in addition to glycaemic control. Above those, luseogliflozin controlled, fibrotic change and increases in collagen deposition with upregulations of collagen1 and smooth muscle actin and inflammatory cytokine expressions observed in the HFDT-fed mouse livers.  (DPP-4) inhibitors. Out of 24 patients, 13 patients were administered a combination of SGLT-2 inhibitors with DPP-4 inhibitors, and 11 patients with combination of SGLT-2 inhibitors with GLP-1 analogues for a median dosing period of 320 days. At the end of the follow-up, body weight (p<0.01) and glycosylated hemoglobin levels (p<0.01) reduced markedly. Serum ALT levels also decreased significantly (p<0.01) and normalized in 14 patients (58.3%) [19]. In controversy to above findings, Levine et al. reported a case in 2016 with the drug dapagliflozin raised the liver enzymes in a type 2 diabetes patient with liver cirrhosis secondary to steatohepatitis and biopsy showed the features of drug induced liver injury [20].
Recently, in another animal study, Tang et al. demonstrated the protective effect of dapagliflozin against renal and liver fibrosis in type 2 diabetes model mice (Table 2) [21]. They conducted an experimental search the dapagliflozin in 18 weeks old db/db mice with objective to determine the hepato-protective effective of SGLT-2 inhibitors and concluded that dapagliflozin improves the liver fibrosis by suppressing hyperglycaemia induced inflammation and oxidative stress.   [22]. This protective role of dapagliflozin is also found in two separate clinical studies in patients with NASH and Type 2 DM by reducing the elevated serum liver enzymes in these patients [23,24]. In a recent randomized controlled clinical trial in patients with NAFLD and diabetes, Kuchay et al. observed a significant reduction in liver fat content in the arm of trial drug empagliflozin [25]. In this randomized controlled trial they compared the treatment group (standard treatment for type 2 diabetes plus empagliflozin 10 mg daily) with control group (standard treatment for type 2 diabetes without empagliflozin) for 20 weeks and observed significant reduction in fatty liver in empagliflozin group (p<0.0001) when compared to control group. This finding supports the observations of a randomized controlled trial with inclusion of the EMPA REG outcome trial showed the hepatic enzyme reducing effect of empagliflozin [26].
The authors searched for the effect of empagliflozin on aminotransferases, which correlates with fatty liver in type 2 diabetes mellitus patients and that empagliflozin significantly reduces aminotransferases in patients with type 2 diabetes patients, in a pattern (reductions in ALT>AST) that is potentially consistent with a reduction in liver fat, especially when ALT levels are high.

CONCLUSION
Above findings point to the evidence of SGLT-2 inhibitors for their effectiveness in the prevention and treatment of hepatocellular damage which is assessed with improvement of liver functional parameters and inflammatory markers. So we can conclude that SGLT-2 inhibitors have a protective role against hepatocellular damage in type 2 diabetes patients by providing glycemic control and suppressing the pro-inflammatory cytokines and oxidative stress. However, it needs a well-designed clinical trial with enrolment of large number of patients with type 2 diabetes and NAFLDs to make authoritative comment on its efficacy in this condition. The animal studies have given some promising evidence for the positive effect of SGLT-2 inhibitors for the treatment of hepatocellular carcinoma. But it requires a well conducted clinical study to prove this finding.

DECLARATIONS Funding
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