(P-010) Effect of lactate, pH and microbiomes in regulating human endometrial receptivity and pregnancy outcomes

Abstract Authors: Kumar Manish¹, Lai Hoi-Lam¹, Luhan Jiang¹, Pang Herbert², Keith CL Lee^1,3, Ernest HY Ng^1,3, William SB Yeung^1,3 , Kai-Fai Lee<sup>1,3

1</sup> Department of Obstetrics and Gynaecology, School of Clinical Medicine, LKS Faculty of Medicine, University of Hong Kong, Hong Kong, China

² School of Public Health, LKS Faculty of Medicine, University of Hong Kong, Hong Kong, China

³ Shenzhen Key Laboratory of Fertility Regulation, Reproductive Medicine Center, University of Hong Kong - Shenzhen Hospital, China

Abstract Text: Study Question: What is the role of Lactates and pH and Lactobacillus on human endometrial receptivity and pregnancy outcome?

Summary answer: D- and L-lactates at 10 mM, and both acidic (pH 6.4) and alkaline (pH 8.1) pH did not significantly affect trophoblastic spheroid attachment onto endometrial cells. High concentrations of D- and L-lactates suppress spheroid attachment, invasion of trophoblast cells, angiogenesis of HUVEC cells and cytokines production of endometrial cells.

What is known already: Lactobacillus is the most abundant in the vagina and a Lactobacillus dominant uterine microenvironment is associated with better pregnancy outcomes.

Study design, size, duration: In vitro laboratory study and in vivo pregnancy outcome association from 98 patients.

Participants/materials, setting, methods: In-vitro cell culture and analysis, and patient uterine and vaginal fluid collection.

Main results and the role of chance: High D- and L-lactate concentrations ( >10 mM) inhibited the cell viability and proliferation of the human endometrial epithelial Ishikawa and trophoblastic BeWo cells. Culture media at pH 6.1 (acidic), 7.2 (neutral), and 8.1 (alkaline) did not affect the BeWo spheroid attachment on the treated Ishikawa cells. Moreover, high lactate concentrations ( >10 mM) inhibited the invasion of trophoblastic BeWo by the treated Ishikawa cells, as well as tube formation (angiogenesis) in the treated human endothelial HUVEC cells. D- and L-lactate (≥10 mM) induce the production of cytokines in Ishikawa cells including TIMPs, MMPs, IL6, IL6R, and certain Th1/Th2 cytokines. Lastly, Lactobacillus and Bifidobacterium are the most abundant bacteria inside the uterine and vaginal fluid, but their abundance did not correlate pregnancy outcome in IVF patients.



Limitations, reasons for caution: This is in vitro study using cancer cell lines. The sample size of uterine and vaginal fluid is small and limited to our IVF patients.

Wider implications of the findings: Our findings suggested lactate and pH levels did not affect spheroid attachment. The effect of lactate-derived cytokines on trophoblast development, and the whether Lactobacillus, and Bifidobacterium could be promising indicators for pregnancy outcomes prediction warrant further investigation.

Study funding/competing interest(s): This project is partly funded by an HMRF grant (06173976) to KFL.