The Effect of Helicobacter pylori Eradication on Lipid Levels: A Meta-Analysis

Abstract Introduction:Helicobacter pylori (H. pylori) infection is positively associated with cardiovascular diseases, but the involvement of lipids in this association remains unclear. The present study reviewed the changes in circulating lipid levels following H. pylori eradication. Methods: A PubMed database was searched until December 2020 to identify randomized control trials (RCTs) and non-RCTs investigating the effect of H. pylori eradication on the lipid levels in inverse variance-weighted, random-effects meta-analyses. Results: A total of 24 studies (four RCTs and 20 non-RCTs) with 5270 participants were identified. The post-eradication levels were increased for high-density lipoprotein cholesterol (HDL-C; mean difference (MD) 2.28 mg/dL, 95% confidence interval (CI) 1.90 to 2.66) and triglyceride (TG; MD 3.22 mg/dL, 95% CI 1.13 to 5.31) compared with the pre-eradication levels. H. pylori eradication resulted in little to no difference in the low-density lipoprotein-cholesterol levels (MD −2.33 mg/dL, 95% CI −4.92 to 0.26). In the analyses of RCTs only, the findings for elevated HDL-C levels, but not TG, were robust. Conclusions: H. pylori eradication increases the HDL-C levels. Further studies are needed to elucidate the effects of lipid changes following H. pylori eradication on cardiovascular diseases.


Introduction
Helicobacter pylori (H. pylori) is a bacterium that causes chronic gastric inflammation [1,2]. A positive association of H. pylori infection with cardiovascular disease (CVD, e.g., myocardial infarction and stroke) has been recognized [2,3]. As the background theory, H. pylori infection is involved in the pathogenesis of atherosclerosis via activation of a local or systemic inflammatory host reaction and a subsequent induction of plaque progression and instability [2]. As abnormal lipid metabolisms contribute to the development of CVD [4][5][6][7][8][9][10], circulating lipids may be also involved in the relationship between H. pylori and CVD [11].
The existence of H. pylori infection was shown to be associated with a low level of high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein (LDL-C), and total cholesterol (TC) or a high level of triglycerides (TG) in a recent meta-analysis of cross-sectional studies [11]. Nonetheless, the effect of H. pylori eradication on the lipid levels remains unclear. An earlier meta-analysis reported that H. pylori eradication did not alter the lipid levels [12]; however, that analysis included only three studies. Those three studies simply compared the lipid levels in the H. pylori-eradicated group with those in the H. pylori-negative group and did not compare the values before and after H. pylori eradication.
We investigated the changes in the levels of lipids after H. pylori eradication by reviewing meta-analyses of available published studies. Figure 1 shows the process for selecting articles that examined the effect of H. pylori eradication on lipid changes. A total of 250 records were initially screened. After screening, eight studies were identified that had been included during the electronic hand search, 3 of 14 and two were excluded because one did not have the full text available [18] and the other involved the same cohort as another study already included in the review [19]. Ultimately, 24 studies that evaluated the effect of H. pylori eradication on lipid changes were included in our meta-analysis . Figure 1 shows the process for selecting articles that examined the effect of H. pylori eradication on lipid changes. A total of 250 records were initially screened. After screening, eight studies were identified that had been included during the electronic hand search, and two were excluded because one did not have the full text available [18] and the other involved the same cohort as another study already included in the review [19]. Ultimately, 24 studies that evaluated the effect of H. pylori eradication on lipid changes were included in our meta-analysis .  Table 1 summarizes the effect of H. pylori eradication on the lipid levels in 4 RCTs, 4 cohort studies, three case-control studies, and 13 before-after studies    Table 1 summarizes the effect of H. pylori eradication on the lipid levels in 4 RCTs, 4 cohort studies, three case-control studies, and 13 before-after studies . The median values for HDL-C, TG, LDL-C, and TC before H. pylori eradication were 52 The quality of the reviewed randomized and non-randomized studies was scored (Supplementary Materials Figures S1-S2). The overall risks of bias in the four RCTs were classified as low risk in one and some concern in three due to an unclear randomization process, missing outcome data, and no protocol. The quality assessment of the 20 non-RCTs included moderate scores ranging from 4 to 7. The main reason for the downgrade was an unclear medication status for dyslipidemia in 16 of the non-RCTs.

Mean Changes in Lipid Profiles after H. pylori Eradication
H. pylori eradication was associated with increased levels of HDL-C (MD 2.28 mg/dL; 95% CI 1.90 to 2.66; I 2 = 97%; Figure 2) and TG (MD 3.22 mg/dL; 95% CI 1.13 to 5.31; I 2 = 98%; Figure 3). There were no significant changes in the levels of LDL-C (MD

Figure 5.
Forest plot of the mean changes in total cholesterol levels before and after Helicobacter pylori eradication. Figure 5. Forest plot of the mean changes in total cholesterol levels before and after Helicobacter pylori eradication.

Sub-Group Analyses
In RCTs, H. pylori eradication increased the HDL-C levels (MD 2.90 mg/dL; 95% CI 0.  Figure S7). The sub-group analyses of TG, LDL-C, and TC showed no significant differences (Supplementary Materials Figures S8-S10). In sub-group analyses by country (study location), H. pylori eradication increased the levels of HDL-C regardless of country: Western countries (MD 2.81 mg/dL; 95% CI 1.73 to 3.90; I 2 = 83%) and Asian countries (MD 2.00 mg/dL; 95% CI 1.90 to 2.66; I 2 = 93%) (Supplementary Figure S11). There were no significant effects of H. pylori eradication on the TG, LDL-C, or TC levels in Western or Asian countries (Supplementary Materials Figures S12-S14).

Sensitivity Analyses
The sensitivity analyses with the exclusion of studies that did not describe the levels of HDL-C, TG, LDL-C, or TC before H. pylori eradication were consistent with the primary findings that H. pylori eradication increased the HDL-C levels (Supplementary Materials Figures S15-S18).

Discussion
The present study meta-analyzed the changes in the lipid levels following H. pylori eradication. The post-eradication HDL-C levels were increased compared with preeradication. However, the post-eradication change in TG levels were unclear, as the results of sub-analyses were not consistent across study designs. The post-eradication LDL-C levels showed little to no change. Since H. pylori infection is positively associated with CVD [2,3], finding a relationship of HDL-C (as a protective factor of CVD) with H. pylori eradication, among the evaluated lipids, is of interest. Understanding the overall changes in lipids following H. pylori eradication may also help us ponder over the connection between bacteria and lipid metabolism.
The increase of 2.28 mg/dL of HDL-C by H. pylori eradication might be slight. Furthermore, recent evidence indicates that an increase of HDL-C with drug therapies may not always be beneficial of the prevention of CVD events [44], and in this line, not only HDL-C levels but also HDL functionals (e.g., anti-inflammatory/oxidant capacity, cholesterol efflux) may be crucial [44]. The clinical relevance of change of HDL-C by H. pylori eradication would be thus discussed. For instance, a 1 mg/dL increase of HDL-C is reported to result in a 3-5% reduction in CVD risk [45]. The linear inverse association between HDL-C and CVD events is also reported at least up to 90 mg/dL in HDL-C [46]. In lifestyle modifications against CVD, exercise and diet increased approximately 1 mg/dL in HDL-C [47] and smoking secession increased approximately 4 mg/dL [48]. Therefore, the changes in HDL-C levels by H. pylori eradication, as observed in the present review, is thought to have clinical relevance on CVD, while there have been no studies on CVD outcomes or HDL functions by HDL-C levels after H. pylori eradication.
H. pylori infection leads to systemic inflammation [49] and oxidative stress [50]. Inflammation and oxidative stress cause a reduction in HDL-C levels [51,52]. Cytokines induce the inflammatory molecule, serum amyloid A, which replaces a major HDL component (apolipoprotein A-I), thereby reducing the HDL-C levels [53]. In addition, inflammation and oxidative stress alter HDL-C-related enzymes; for example, lecithin-cholesterol acyltransferase, cholesterol ester transfer protein, and hepatic lipase levels are reduced while endothelial lipase levels are increased, which can reduce the HDL-C levels [54,55]. Abnormal cholesterol transport is another reason for the reduction in HDL-C levels, a phenomenon seen in H. pylori infection [39,40]. As another etiological mechanism, the microbiome may be involved [56]. H. pylori infection alters the gut microbiota [57], and eradication with antibiotic treatments has been shown to alter the microbiota and reduce H. pylori-induced inflammation [58]. Microbial diversity in the gut microbiota (a favorable phenomenon) can increase the HDL-C levels as it improves the suppression of lipid metabolism (with inflammation and oxidative stress) via bacteria-derived bile acids and short-chain fatty acids [59]. As above-mentioned, in recent evidence [44], not only HDL-C levels but also HDL functions affect the development of CVD. As the functions can be associated with inflammation, oxidative stress and gut microbiota [60,61], future work on HDL, in relation to biomolecules of inflammation/oxidative stress and gut environment, under H. pylori eradication is expected to explain comprehensively the results of the present review.
The existence of H. pylori infection was cross-sectionally associated with a high level of TG [11], and the present review found a slight but additional increase in TG levels following H. pylori eradication. H. pylori eradication increases the appetite [49,62] and improves nutrition [24,63,64], which can often promote obesity. Reductions in hepatic lipase and cholesterol ester transfer protein by the suppression of inflammation following H. pylori eradication or the reduction in the activity of lipoprotein lipase by obesity (insulin resistance) can lead to an increase of TG following H. pylori eradication [48,65,66]. However, according to the results of a sub-analysis of RCTs only, the TG levels were not increased following H. pylori eradication. This may be partly explained by the notion that physiological changes in TG levels are unstably affected by fluctuating factors, such as the diet and individual responses to the diet [67].
The levels of LDL-C and TC did not change markedly following H. pylori eradication, the reasons for which were unclear. First, interestingly, the degree of gastric mucosal atrophy is indicated to be associated with the LDL-C levels [37,39,68]. As advanced atrophy does not clearly change even after H. pylori eradication, this may partially explain the finding of no marked post-eradication changes in the levels of LDL-C or TC. Second, the type of antibiotics in the H. pylori eradication regimen might be considered because antibiotics, especially metronidazole, can reduce serum cholesterol, especially LDL-C levels [69]. In the present review, two studies using metronidazole reduced LDL-C [21,26].
Further studies focusing on the types of antibiotics in the H. pylori eradication regimen, especially metronidazole, are needed to see the changes in the LDL-C and TC levels after eradication.
In the present review, the heterogeneity of the analysis of the effects of H. pylori eradication on HDL-C appeared to be high. The results of a sub-analysis of RCTs showed high heterogeneity relative to non-RCTs. This heterogeneity might depend not only on the study design but also the follow-up period, as a sub-analysis based on the follow-up periods (short-and long-term after eradication) alleviated the heterogeneity. Antibacterial agents for H. pylori eradication are effective at eliminating inflammation in the short term, while improvements in gastric mucosal atrophy and microbial diversification are gradually seen in the long term [58,70,71].
Several limitations associated with the present study warrant mention. First, most studies were not controlled for covariates, such as underlying diseases related to lipid levels (e.g., liver cirrhosis, nephrotic syndrome) [72,73]; however, patients with such diseases might have been inadvertently excluded from the view of no indication of drugs for eradication. Second, the methods for detecting H. pylori infection (e.g., a urea breath test with a comparatively high accuracy among diagnostic methods [74] or a combination of tests) differed among studies. Third, the CVD outcomes following changes in lipid values after H. pylori eradication was not observed in all studies. Forth, we could not perform the subgroup analyses (i.e., participants' sex, successful/unsuccessful eradication of H. pylori), which seemed to give more information, since the individual data were not obtained from the original studies or only limited data on such items were available in the reviewed studies. In the present review including 24 studies, there were only four non-RCTs with the data regarding successful/unsuccessful eradication therapy.
In conclusion, H. pylori eradication increased the HDL-C levels. The findings suggested that H. pylori eradication alters lipid profiles favorably for CVD. The results of more RCTs are required to derive more definitive conclusions.