In this study, we learned that the abnormalities of insulin-related indicators played the main role to distinguish GDM and NGT. Combined with the bile acids metabolism profile, we clarified the correlation between specific bile acids and insulin related indicators. Overall, GDM patients exert higher levels of BMI and HbAc1 during the OGTT screening period, in addition, fasting insulin and insulin at 1 and 2 hours post 75-g glucose intake increased significantly in GDM. In terms of bile acid metabolism profile, TDCA and GDCA were the most significantly changed individuals in GDM. Moreover, GDCA was negatively correlated with the insulin resistance index (HOMA-IR) and positively correlated with the β-cell compensation index (DIo). In clinical outcomes assay, there was no significant difference between GDM and NGT, but GDM patients in HOMA-IR Q4 group possessed elevated ration of cesarean section delivery, and patients in DIo Q1 group gained earlier delivery gestational ages. Therefore, our findings suggest that fasting GDCA levels during OGTT may be a useful indicator to evaluate insulin resistance and β-cell compensation, furtherly to predict adverse clinical outcomes of GDM.
GDM shares the similar pathogenesis with T2DM, β-cell function was insufficient to compensate for the need for glycemic homeostasis in pregnancy combined with reduced insulin sensitivity, finally result to increased serum glucose[1]. In addition to glucose and insulin metabolic disorders, lipids metabolism also changed in GDM, total triglycerides, total cholesterol, low-density lipoprotein cholesterol increase gradually throughout pregnancy in GDM[26]. Our results were consistent with previous report in clinical characteristic of GDM, including advanced age, higher BMI, TG and HbA1c.
Bile acids metabolism variation has been partially proved in T2DM, elevation of TBA increased the T2DM incidence, TBA almost doubled in T2DM patients compared with healthy subject[19, 27]. Intrahepatic cholestasis of pregnancy (ICP) was characterized by an increased TBA, ICP women with higher TBA concentration are much more vulnerable to suffering GDM[28]. These studies suggest that TBA probably related to the occurrence of T2DM and GDM. Indeed, in Chinese prospective cohort studies, the incidence of GDM in the group with highest TBA (≥ 4.0 µM) in early pregnancy had a 6.72-fold increased risk of GDM compared with the lowest level. Even after adjusting potential confounders, TBA ≥ 2.0 µM still presented an increased risk for developing GDM[29, 30]. In our research, TBA changed slightly in GDM compared with normal glucose tolerance, this may be partially caused by the difference between the TBA detected by enzymatic cycling assay and the TBA consist of 15 bile acids individuals detected mass spectrometry. This provokes us that more attentiveness should payed to the bile acids components related to glucose metabolism.
Research conducted on a large cohort of Chinese pregnant women in early pregnancy found that fasting serum levels of GUDCA ≤ 0.07 nmol/mL and DCA ≤ 0.28 nmol/mL were independently associated with an increased risk for development of GDM [31].Untargeted metabolomics administrated in pregnant women’s fasting serum during OGTT screening period spot that CA, ios-DCA and dehydio-LCA decreased in GDM[32]. In this research, GDCA and TDCA declined obviously in GDM. The difference between our research and the previous studies may be caused by the difference between targeted and non-targeted detection platforms and the samples collected in different trimesters, as our previous research has illustrated that bile acids metabolism profiles changed periodically with gestational age[20].
GDCA has no correlation with HOMA-IR and fasting insulin in normal glucose tolerance. In GDM, declined GDCA combined with the increased fasting insulin and fasting glucose result in the significant negative correlation between GDCA and HOMA-IR. Studies in vivo and in vitro demonstrated that GDCA is indeed related to insulin secretion and insulin resistance, more importantly, insulin resistance can be alleviated by GDCA administration. For example, fasting for 40 hours induce insulin resistance, while this insulin resistance model has no affect in bile acids metabolism profile. However, postprandial GDCA and insulin concentration changed in a significant positive correlation pattern. Increased GDCA triggered the secretion of insulin in a GLP-1 dependent manner[33]. To some extent, this is helpful to explain why even if GDCA elevated the post glucose intake in GMD patients, but declined baseline of GDCA still make it insufficient to promote insulin secretion via GLP-1, finally failed in the glycemia regulation. Polycystic ovary syndrome (PCOS) is usually accompanied by features of insulin resistance, HOMA-IR of PCOS patients is significantly negatively correlated with GDCA. Mechanistically, the significant increased Bacteroides vulgatus in the gut microbiota of PCOS individuals reduced the GDCA. GDCA combined with GATA-3 in the intestinal group 3 innate lymphoid cell to facilitate the interleukin-22 secretion, which in turn improves the PCOS phenotype including insulin resistance and ovarian function recovery[34]. However, whether variations occurred in GDM gut microbiome declined the GDCA and result in insulin resistance, the confirmation need further research.
Hyperglycemia burdened severely clinical outcome to both maternal and fetus outcome with GDM, but the clinical outcome of the whole GDM was not differed significantly from that of NGT in this study, which may be due to the early lifestyle intervention and even pharmacological therapy. Of note, GDM patients with serious deficiency of insulin compensation and high HOMA-IR subgroups gained worse clinical outcome.
Strengths and limitations
Despite being a single center and small sample size research, this study produced important data about the relationship between Bas metabolism and GDM. Abnormal in specific Bas individual may predict the adverse clinical outcome for GDM. We recognize our study design has the following limitations. The greatest limitation is that the study was cross-sectional, which conversely provoke us to reveal the Bas metabolic profile in early gestational age, so as to spot valuable biomarker for the earlier GDM screening. In addition, the GLP-1 baseline was not measured in the fasting serum, as variations in GLP-1 baseline may influence fasting insulin levels. GLP-1 and Bas changes in 1-h and 2-h post glucose intake were also not detected, which limited the elucidation of the dynamic mechanism of Bas metabolism regulating insulin secretion through GLP-1, moreover, we also realized that our sample size is fairly small which failed us to establish a cut-off point of GDCA. Nevertheless