DISCUSSION
In this long-term follow-up study, we found that H. pylori eradication was related to the decreasing of A1C levels in patients with T2DM or preDM, especially in male and subjects under 65 years of age. To the best of our knowledge, this is the first suggestion of a positive association between H. pylori eradication and improvement in the A1C level in patients with T2DM or preDM over a long period.
This finding is consistent with the results of other studies on the effectiveness of
H. pylori eradication over a short period [
8,
9,
21]. As mentioned previously, Dogan et al. [
10] reported significant changes of FPG and A1C level between baseline and 6 months after
H. pylori eradication in subjects with normal glucose levels. In addition, in 319 patients with T2DM, Cheng et al. [
11] demonstrated that the eradicated group had significant within-group and between-group improvements in A1C, compared with the non-eradicated group. Although the exact mechanism remains unknown, researchers have hypothesized potential mechanisms linking
H. pylori infection to metabolic parameters. Regarding the pathogenesis proposed to associate
H. pylori infection with atherogenic dyslipidemia, experimental investigations have demonstrated that chronic bacterial infections, such as an
H. pylori infection, induces the production of proinflammatory cytokines. These cytokines, such as interleukin 1 (IL-1) and IL-6, interferon-α, and tumor necrosis factor-α, can alter lipid metabolism in variety of ways. It also reduces the activation of adipose tissue lipoprotein lipase, triggers hepatic fatty acid synthesis, influences lipolysis, and stimulates 3-hydroxy-3-methylglutaryl-coenzyme A reductase activity in the liver [
22]. An
H. pylori infection possibly be associated with impaired hepatic IR through the c-Jun/microRNA-203/suppressor of the cytokines that signal three pathway [
23]. In addition, inflammatory cytokines induce the phosphorylation of serine/threonine residues in the insulin receptor, preventing its activation and reducing insulin sensitivity [
24]. Ghrelin is involved in ingestion, appetite, and nutrition, especially lipid absorption and lipogenesis [
25]. It can also regulate insulin sensitivity and stimulate insulin-induced glucose uptake [
26], and an
H. pylori infection can impair its synthesis [
27]. Ghrelin was significantly lower in
H. pylori positive than in
H. pylori-negative individuals [
28]. Low plasma ghrelin levels are associated with elevated FPG levels and IR [
29]. Previously, we found that
H. pylori eradication upregulates preproghrelin mRNA expression and increases plasma acyl ghrelin levels, contributing to the abatement of postprandial distress symptoms in functional dyspepsia [
30]. Another possible explanation involves glucagon-like peptide-1 (GLP-1) and the gut microbiota. GLP-1 regulates glucose homeostasis [
31], has trophic effects on pancreatic beta cells [
32], reduces acid secretion in the stomach, and delays gastric emptying. It also regulates appetite by inducing a feeling of satiety. Specific bacteria, including
Bifidobacterium spp.,
Lactobacillus spp., and
Akkermansia muciniphila spp., contribute to the regulation of incretin hormones such as GLP-1 [
33]. A conventional eradication treatment could improve carbohydrate metabolism by increasing GLP-1 secretion, and this change is closely related to alterations in the gut microbiota [
8,
34], even after a long-term follow-up [
35]. These underlying mechanisms support our observation of the effect of
H. pylori eradication on the decrease of in A1C levels over a long-term follow-up.
An interesting result of this study is that the positive association between the eradication of
H. pylori and A1C levels appeared in patients < 65 years of age. This positive association in younger age is consistent with the results of earlier research on the relationship between
H. pylori infection and MS. Chen et al. [
36] observed that subjects with MS < 50 years of age had a higher prevalence of
H. pylori infection. Similarly, our team demonstrated that the association between
H. pylori seropositivity and MS was present in subjects < 65 years of age but disappeared in the older ones [
12]. Park et al. [
37] reported that the effect of
H. pylori eradication on the risk of dyslipidemia was more evident in subjects < 50 years of age. Altogether MS prevalence was not significantly different regardless of the
H. pylori serological status in older subject, they tend to have other chronic diseases, such as hypertension, hyperlipidemia, or diabetes, contributing to the development of MS. Regardless of geographic location, the
H. pylori infection in most individuals is acquired during early childhood [
38]. This chronic
H. pylori infection plays an important role in the development of development in the adulthood but this systemic inflammation caused by
H. pylori infection may influence MS development somewhat at an early stage, but not in an advanced stage or old age [
39]. Thus early eradication of
H. pylori is more beneficial in terms of prevention of MS.
Our study also suggested a correlation between sex and A1C levels, specifically in male subjects. These results are compatible with previous studies that showed male subjects are more affected by
H. pylori infection than female subjects, such as higher gastric inflammation and activity scores in the antrum with
H. pylori infection [
40]. According to a large dataset including worldwide mortality and prevalence of cancers, the incidence of gastric cancer in male subjects was about twice as high as in female individuals [
41]. Interestingly, in a mouse-model study, severe dysplasia and gastric carcinogenesis predominated in male subjects infected with
H. pylori [
42]. Furthermore, MS was higher in male subjects, except in the age-group of > 70 years, and the MS in female subjects after definite menopause was higher than in male subjects [
12]. Similarly, the
H. pylori infection increased the risk of MS in female subjects aged ≥ 50 years [
43]. Furthermore,
H. pylori infection was a statistically significant predictor of DM incidence in male subjects [
6]. The underlying mechanism is related to estrogen. Ovarian-dependent female hormones, such as estradiol (E2), prevent gastric carcinogenesis and inflammation of the gastric tissue in insulin–gastrin mice infected with
H. pylori. In addition, exogenous E2 supplementation have shown protective effects against the development of
H. pylori-induced gastritis and premalignant lesions through several mechanisms [
44]. In the relationship between MS and E2, recent researches showed that TC, LDL-C, and TG were higher in postmenopausal female subjects than in premenopausal females [
45]. In addition, hormone therapy with estrogen alone has been associated with decreased TC and LDL-C levels and elevated HDL-C levels [
46]. Considering these, we speculate that the difference in the association of
H. pylori infection with DM in our study might be related to sex hormone-induced inflammation.
As our study was a retrospective study from a cohort that selected prospectively for 12 years, the number of subjects became small due to exclusion of missing data among metabolic parameters. Small number of subjects that can weaken the conclusion is one of the limitations of this study. However, the patient selection was not biased, and we collected the data on levels of A1C, TC, TG, LDL-C, HDL-C, FPG, BP and the duration and changes of diabetes medication in each subject from the CDW of SNUBH as well as a medical cohort, which were well maintained. We excluded serologic positivity in the H. pylori-negative group, and thus, chronic inflammation can be reliably excluded in that group. Most previous studies compared only before and after treatment in the H. pylori-infected group without a control group with short-term follow-up period. In our study, subjects were divided into H. pylori-negative, H. pylori-positive with non-eradication, and H. pylori-positive with eradication groups, which allowed us to reliably determine the independent effect of H. pylori eradication compared to the other groups. Due to the nature of DM, it is difficult to observe without drug changes during long-term follow-up. In this study, insulin-based patients were excluded to compensate for this limitation, and patients who changed medication during the observation period showed no significant difference with 17.5% in the negative group, 14.7% in the non-eradicated group and 26% in the eradicated group. And additional analyses were conducted after excluding patients who changed oral medications to confirm that the same results were maintained.
IR can be evaluated using homeostasis model assessment of insulin resistance (HOMA-IR), which uses the fasting insulin level with the fasting glucose level. In our study, the fasting insulin level was not measured in all subjects, so HOMA-IR was unable to be calculated. Future study about the effect of H. pylori eradication in IR using HOMA-IR would be needed.
Despite the statistical significance of H. pylori eradication in A1C and some improvement tendency in FPG, BMI, SBP, and DBP, we have failed to show a correlation between the three groups in other metabolic parameters such as TC, TG, LDL-C, HDL-C. It might be explained that, because we selected a study group in patients with T2DM or prediabetes, results may differ from studies in the dyslipidemia group or the normal lipid group. Also studies have been conducted with a relatively small number of subjects, it may not be possible to determine the effectiveness of eradication therapy in dyslipidemia. Therefore, a large-scale study is needed to determine the effect of H. pylori treatment in patients with dyslipidemia in the future.
In conclusion, H. pylori eradication was related to the decreasing of A1C levels over a long-term follow-up period, especially in male subjects and those < 65 years of age. Our study provides new insights into the role of H. pylori eradication and supports the rationale for recommendation of H. pylori eradication therapy in male or young subjects with T2DM or preDM.