Vitamin E and Pioglitazone: A Comprehensive Systematic Review of Their Efficacy in Non-alcoholic Fatty Liver Disease

Non-alcoholic fatty liver disease (NAFLD) is becoming increasingly prevalent worldwide, especially in people with obesity, dyslipidemia, type 2 diabetes mellitus (T2DM), and metabolic syndrome. Weight loss and dietary modifications are established first-line treatments for NAFLD. Currently, there is no approved drug for NAFLD; however, pioglitazone and vitamin E have shown some beneficial effects. This systematic review covers the comparative efficacies of vitamin E, pioglitazone, and vitamin E plus pioglitazone. As of December 2022, the sources for prior literature review included PubMed, PubMed Central, and Medline. We included studies assessing the efficacy of pioglitazone, vitamin E, and vitamin E plus pioglitazone in improving liver histology, liver markers, and lipid profile when compared to other interventions in patients with NAFLD/non-alcoholic steatohepatitis (NASH). Review materials include randomized control trials (RCTs), traditional reviews, systematic reviews, meta-analyses, and observational studies on human participants published within the last five years in the English language. Studies on animals, pediatric populations, and with insufficient data were excluded from the review. Two authors scanned and filtered articles independently and later performed quality checks. A third reviewer resolved any conflicts. The risk of bias was assessed using the Preferred Reporting Items for Systematic Reviews and Meta-Analyses 2020 guidelines for systematic reviews, the Cochrane Risk of Bias Tool for RCTs, and the Scale for the Assessment of Narrative Review Articles for Traditional Reviews. A total of 21 articles were shortlisted. The results showed that pioglitazone and vitamin E are effective in reducing steatosis, inflammation, and ballooning, reducing liver markers, but there seem to be conflicting data on fibrosis resolution. Pioglitazone decreases triglycerides and increases high-density lipoproteins. One study has suggested that pioglitazone has superior efficacy to vitamin E in fibrosis reduction and vitamin E plus pioglitazone has superior efficacy than pioglitazone alone for NASH resolution. However, these conclusions require further validation through extensive analysis and additional research. In conclusion, diabetic patients with NAFLD can be given pioglitazone, and non-diabetic patients with NAFLD can be given vitamin E.


Introduction And Background
Western countries have seen a sharp increase in the prevalence of non-alcoholic fatty liver disease (NAFLD), which now affects 25% of the world's population.Chronic liver disease is becoming more prevalent in Western industrialized nations, especially in people with central obesity, type 2 diabetes mellitus (T2DM), dyslipidemia, and metabolic syndrome [1,2].The current criteria for diagnosing NAFLD are (1) imaging or histological evidence of hepatic steatosis in more than 5% of the hepatocytes; (2) no significant alcohol consumption; (3) no competing causes of hepatic steatosis; and (4) no coexisting chronic liver disease [1,3].Non-alcoholic steatohepatitis (NASH), which is at the more severe end of the spectrum, is a condition that falls under the umbrella of NAFLD.NAFLD may develop into cirrhosis and fibrosis.In contrast to NASH, where hepatic steatosis is linked to lobular inflammation and apoptosis that can result in fibrosis and cirrhosis, hepatic steatosis has no signs of inflammation [2,3].
Recently, experts in fatty liver disease concluded that the term NAFLD does not accurately describe the state of knowledge regarding the metabolic dysfunction caused by the disease.Metabolic-associated fatty liver disease (MAFLD) has been proposed as a more appropriate term.Like NAFLD, MAFLD is a multisystem disorder with a diverse hepatic manifestation in its underlying causes, presentation, course, and outcomes [3].
The most important factor connected to liver-related events and overall mortality is fibrosis, not steatohepatitis as a diagnosis.Even in the early stages of fibrosis, this effect can be seen, showing a stepwise rise in unfavorable outcomes as the condition progresses [4].
Fibrosis is followed by portal hypertension and hepatocyte dysfunction which are associated with other comorbidities including cardiovascular events, ischemic stroke, and other metabolic complications.NAFLD is also associated with an increased incidence of diabetic retinopathy, nephropathy, and neuropathy [5].
NAFLD affects more than 55% of people with T2DM, and these people are also more likely to develop the more severe forms of NAFLD (e.g., NASH, cirrhosis, or hepatocellular carcinoma) [6].Through complex pathophysiological mechanisms such as insulin resistance, chronic hyperglycemia, lipotoxicity, low-grade inflammation, and increased oxidative stress, T2DM and NAFLD are two pathological conditions that interact to increase the risk of unfavorable clinical outcomes [6,7].According to the European Association for the Study of the Liver (EASL), the European Association for the Study of Diabetes (EASD), and the European Association for the Study of Obesity (EASO) (EASL-EASD-EASO), clinical practice guidelines for the management of fatty liver disease patients with features of metabolic syndrome are recommended to be screened for NAFLD by serum markers or ultrasound [8].The established first-line treatment for NAFLD management is weight loss and dietary modification [6].As there are no specific pharmacological recommendations with a well-established efficacy, NAFLD management is a challenging process.To manage the patient's glycemia, liver function, and lipid profile, treatment is concentrated on associated/co-existing diseases (diabetes, obesity, lipid disorders).Pharmacological therapy is advised for people who do not lose the weight they are expected to and for those who have NASH with a biopsy-proven fibrosis stage of 2 (F2) [9].In recent years pioglitazone, vitamin E, and a combination of both have shown some efficacy in improving NAFLD.This article compares the efficacy of these three pharmacological treatments.

Data Sources and Search Strategy
A literature search was conducted in the following databases: PubMed, PubMed Central, and Medline.The search was done from the inception to December 28, 2022.The search strategy included the following keywords and MeSh terms: Vitamin E OR "Vitamin E/therapeutic use"[Majr] AND Pioglitazone OR thiazolidinediones OR "Pioglitazone/therapeutic use"[Majr] AND Non-alcoholic fatty liver disease OR "Nonalcoholic Fatty Liver Disease/drug therapy"[Majr], and was limited to English language.This systematic review follows the reporting guidelines of the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) 2020 statement [10].This review has not been previously registered.

Eligibility Criteria
Inclusion criteria: Studies assessing the effects of vitamin E, pioglitazone, and vitamin E plus pioglitazone on liver histology, liver markers, and lipid profile in patients with NAFLD/NASH were included in this study.Placebo or any other intervention was the comparison group.Randomized control trials (RCTs), observational studies, systematic reviews, meta-analyses, traditional/narrative reviews, and articles published in the last five years were included in this study.
Exclusion criteria: Studies on animals, pediatric populations, and with insufficient or inadequate data were excluded from this review.

Study Selection and Data Extraction
Two reviewers scanned through the available data and were able to independently shortlist articles.A third neutral reviewer resolved any conflict regarding article selection.All available data were transferred to an Excel sheet, and on EndNote, duplicates were removed and followed by scanning of the titles and abstracts according to the inclusion/exclusion criteria.For every study included, we sought data for trial design, country of origin, number of patients, all interventions, the population study focused on, and study findings.The outcomes assessed were liver histology including steatosis, inflammation, and fibrosis; liver markers, including alanine aminotransferase (AST) and aspartate aminotransferase (ALT); and lipid profile, including high-density lipoproteins (HDLs), low-density lipoproteins (LDLs), and triglycerides.

Quality Assessment
Quality assessment was done by two authors independently.Any conflict was resolved through discussion.We used the PRISMA 2020 guidelines to appraise systematic reviews and meta-analyses [10], the Cochrane Risk Assessment Tool for RCTs [11], and the Scale for the Assessment of Narrative Review Articles (SANRA) for traditional review articles [12].

Study Selection
We retrieved 2,868 citations during the initial search.Further applying inclusion and exclusion criteria, 280 articles were found.In total, 30 articles were shortlisted based on relevance according to the title and abstract.After studying the shortlisted articles, nine were excluded based on non-relevance and inadequate data, resulting in 21 studies that fulfilled our inclusion and exclusion criteria .A PRISMA flow diagram presenting the entire process of identifying, filtering, and including all relevant articles is shown in Figure 1.

Quality Appraisal
The quality check for the included systematic reviews and meta-analyses are presented in Table 1, which shows the page number for every reported PRISMA topic in each study.The quality checks for the traditional reviews are presented in Table 2 and for the RCTS in Figure 2 and Figure 3.  S1 Table A1 Page 5, Table 1 Page 882, Table S1 Pages 2-3 18 Page 4, Figure 2 Page 3, Figures 2, 3 Table A3, Figure A2 Page 5, Table 2 Page 882, Table S3 Pages         One RCT compared the effect of vitamin E vs. ursodeoxycholic acid vs. pentoxifylline [13].Two RCTs compared the effect of pioglitazone and tofogliflozin monotherapy and their combination [15,16].One RCT compared three antidiabetic agents, namely, pioglitazone, glimepiride, and dapagliflozin [18], and another measured the effect of pioglitazone on either gender [17].The rest of the studies included other interventions ranging from anti-diabetic drugs to bariatric surgery.

Discussion
Various comorbidities play a role in the development of NAFLD, including insulin resistance, metabolic syndrome, and oxidative stress [6,7].Lifestyle modification and exercise are the best and the only approved treatment for NAFLD [6].Low-calorie diets and periodic exercise have been proven to improve hepatic function.Diets rich in fruits and vegetables have shown antioxidant and anti-inflammatory benefits, whereas diets with low fiber, vitamins, and minerals accelerate NAFLD progression.Weight loss of 7-10% can regress NASH and liver fibrosis [24].Among the various drugs, vitamin E and pioglitazone have demonstrated beneficial effects on NAFLD patients .

Vitamin E
Vitamin E has antioxidative, anti-fibrotic, anti-inflammatory, and anti-apoptotic effects.It also regulates gene expression and enzymes involved in cellular signaling in the mitogen-activated protein kinase (MAPK) signal transduction pathway [14,31].Vitamin E lowers chemokines, cytokines, and liver markers.Supplementation with at least 200 IU daily of alpha tocopherols reduces oxidative stress and biomarkers such as 4-hydroxynonenal (4-HNE), resulting from lipid peroxidation, and the highest reduction of 4-HNE is seen with a dose of 400 IU daily [7,13].
Studies have shown that vitamin E has beneficial effects on steatosis, inflammation, and ballooning grade but no effect on fibrosis resolution based on the evidence provided by the PIVENS trial [14,[27][28][29]31,32].Sanyal et al. (2010) conducted a three-arm trial of vitamin E vs. pioglitazone vs. placebo.Vitamin E therapy induced a clinical improvement in NASH (43% vs. 19%, p = 0.001), but pioglitazone did not (34% vs. 19%, p = 0.04) [34].Vitamin E and pioglitazone reduced the severity of steatosis, lobular inflammation, and hepatocellular ballooning but not fibrosis.Lee et al. (2022) reviewed many studies and concluded that vitamin E might be an effective treatment in biopsy-proven NASH by improving inflammation; however, the results on fibrosis improvement are conflicting [33].Only one RCT reported the effect of vitamin E on liver aminotransferases and lipid profiles [13].Fouda et al. (2021) compared ursodeoxycholic acid vs. pentoxifylline vs. vitamin E. Vitamin E was found to significantly lower ALT and AST by 50% and 43%, respectively, and to have a stronger tendency to normalize ALT.Most NASH patients who took vitamin E experienced improvement in their clinical symptoms.There was no significant change in lipid profile.

Pioglitazone
Pioglitazone is a peroxisome proliferator-activated receptor gamma agonist that has the potential to improve NAFLD by reducing the size of hypertrophic adipocytes, enhancing insulin sensitivity, promoting adiponectin expression, as well as improving blood lipid profiles.Four RCTs showed the resolution of steatosis with pioglitazone with doses varying between 7.5 and 45 mg [15][16][17][18].Yoneda et al. ( 2021) conducted the TOPiND study in which pioglitazone 15-30 mg (n = 19) and tofogliflozin 20 mg (n = 21) given once daily for 24 weeks reduced the hepatic steatosis measured by magnetic resonance imaging-proton density fat fraction (MRI-PDFF) by −5.56 ± 3.92% (p = 0.0005) from baseline, which was further decreased to −5.98 ± 4.70% (p < 0.0001) in the extension study assessing the combination of tofogliflozin and pioglitazone [15,16].Liver stiffness assessed by magnetic resonance elastography-liver stiffness measurement (MRE-LSM) was decreased after pioglitazone monotherapy but no decrease in type IV collagen 7s was seen.Triglycerides were decreased and HDL was increased in monotherapy and combination therapy.Significant reduction in AST and ALT was seen in both studies.
An RCT reported that liver fatty content (LFC) decreased by 12.1% in the pioglitazone plus lifestyle intervention group (LSI) [17].When compared to the LSI, the LFC of group pioglitazone + LSI decreased in female patients relative to their male counterparts.The effectiveness of pioglitazone was found to be significantly correlated with gender (p = 0.003), which may be related to the fact that androgen levels differ between the sexes.Another RCT, a three-arm trial of pioglitazone vs. glimepiride vs. dapagliflozin, confirmed the findings by showing a significant increase in the liver/spleen ratio by 0.22 ± 0.04, indicating a reduction in liver steatosis and insignificant change in type IV collagen 7s, indicating a slight effect on fibrosis resolution [18].Significant decreases in AST and ALT levels and a significant increase in HDL were observed.However, as this RCT had a high risk of bias, its findings might not be reliable.
Lian and Fu (2021) performed a meta-analysis of four RCTS comparing the efficacy of pioglitazone vs. placebo [19].The study concluded that pioglitazone could significantly improve glucose metabolism and liver function and alter liver histology, such as steatosis grade, inflammation grade, and ballooning grade, although there was no significant difference in fibrosis between pioglitazone and placebo.However, the included studies had a duration of less than 18 months.Furthermore, pioglitazone was efficacious in patients with T2DM combined with NAFLD which significantly reduced AST and ALT and increased HDL levels but no difference in triglycerides or LDL.They also conducted another network meta-analysis with 26 articles comparing different oral hypoglycemic agents and deduced that pioglitazone has a greater effect in reducing AST and ALT compared to other drugs.It ranked as one of the most effective in reducing ALT, significantly improved HDL, and had little effect in reducing LDL [20].
Pioglitazone has the highest likelihood of being ranked the most effective NAFLD activity score and was the best therapy for steatosis, lobular inflammation, and GGT reduction, according to another network metaanalysis of 48 trials involving 2,356 patients [21].It also had a total effective rate of 78% higher than that of the control group (placebo or conventional treatment) [22].The effectiveness of other thiazolidinediones is still unresolved [30].Several studies have emphasized that pioglitazone is effective in improving liver histology, liver markers, and lipid profile [23][24][25][26][27][28][29]31], but data on fibrosis improvement remain contradictory [20,22,24,26,29,31].
The side effects associated with pioglitazone use are weight gain, bladder cancer, bone loss in postmenopausal women, and can cause fluid retention which can lead to congestive heart failure in patients with cardiomyopathy [23,25,28].

Pioglitazone Plus Vitamin E
Only one study evaluated the effect of combined vitamin E and pioglitazone.Majzoub et al. ( 2021) conducted a meta-analysis assessing 23 interventions, including vitamin E, pioglitazone, and vitamin E plus pioglitazone [26].The primary outcome measured was ≥1 stage improvement in fibrosis and vitamin E plus pioglitazone yielded no significant results.However, pioglitazone and vitamin E alone were significantly better in achieving ≥1 fibrosis stage resolution vs. placebo with the surface under the cumulative ranking (SUCRA) curve value of 0.65 and 0.61, respectively.For the resolution of NASH, the combination was one of the most effective compared to other drugs, with a SUCRA value of 0.83, followed by pioglitazone, with a SUCRA value of 0.79.However, this study had some limitations, including a small number of head-to-head comparative studies and heterogeneity in the meta-analysis.

Limitations
Our study encountered some limitations.First, vitamin E and pioglitazone together have not been thoroughly studied.Only one study evaluated the impact of the combination [26].Furthermore, every study included reported conflicting results regarding the effects of pioglitazone and vitamin E on fibrosis [27][28][29][30][31][32][33].
Moreover, there were a limited number of participants in the RCTs of the shortlisted meta-analyses, and the majority of studies evaluating pioglitazone were conducted for a brief duration [15,16].Moreover, the majority of the studies were traditional reviews, which are considered to be of lower quality than other types of scientific evidence, which was a limitation of the review process used.Lastly, only three databases were included in the search.Stronger evidence would have been found by searching additional databases.
To clearly explain the effects of vitamin E and pioglitazone together, we imply that an RCT with a large number of participants is performed for a longer duration.We also encourage researchers to look more into the combination of vitamin E and pioglitazone together as research in this particular combination has been lacking, although the efficacy of vitamin E and pioglitazone separately has been established.

Conclusions
NAFLD is a spectrum of diseases, ranging from a milder form of steatosis to a severe form of NASH and resulting hepatocellular carcinoma.Various comorbidities are in play in causing or progression of the disease, including obesity, metabolic syndrome, and T2DM.Dietary modification and lifestyle intervention are the best treatment options.Of the novel drugs being tested for NAFLD, vitamin E and pioglitazone have revealed beneficial effects on the disease histology and serum profile.This study concludes that vitamin E and pioglitazone are both effective in ameliorating steatosis, inflammation, and liver markers.Pioglitazone causes an increase in HDL and a reduction in triglycerides but does not affect LDL.However, pioglitazone has proven to cause weight gain and needs to be cautiously used in patients with cardiomyopathy and postmenopausal women.The combination of vitamin E and pioglitazone, although not studied enough, shows promising results with NASH resolution.All available data are inconclusive regarding fibrosis resolution with all the discussed interventions so further extensive research is required to explore these treatment options.

FIGURE 2 :
FIGURE 2: ROB 2 traffic-light plot displaying quality checks for RCTs.ROB 2: Risk of Bias Assessment Tool 2; RCTs: randomized controlled trials

FIGURE 3 :
FIGURE 3: ROB 2 bar plot displaying quality check for RCTs.ROB 2: Risk of Bias Assessment Tool 2; RCTs: randomized controlled trials

TABLE 2 : Quality check using the SANRA score for traditional reviews.
SANRA: Scale for the Assessment of Narrative Review Articles