3.1 Cell source and culture conditions of HMC-1 cell line
The HMC-1 cell line is often sourced from cell banks (20 of 50), with the most provided by Dr. Joseph H. Butterfield from Mayo Clinic (6 of 50) followed by American Type Culture Collection (ATCC) (5 of 50), Sigma-Aldrich (2 of 50), and Korean Cell Line Bank (KCLB) (2 of 50). Other cell banks include the Cellcook Biotechnology (CB), National Platform of experimental cell resources (NPECC), National Centre for Cell Science (NCCS), Wu-Han University Cell Collection Center (WUCCC), and Chinese Academy of Sciences (CAS). In addition, HMC-1 cell line from 11 out of 50 publications were gifted by other institutions, with the most from Eiichi Morri Osaka University (4 of 50). Following that, Prof. Jae-Young Um from KyungHee University and Prof. Jong-Sik Jin from Jeonbuk University contributed 2 out of 50 publications each. Other institutes include Hoseo Univeristy (Prof. Hyun-Ja Jeong), Second Military Medical University (ZhiLiang Yu), and Sangji University. However, the authors did not report the original source of their gifted HMC-1 cell line. Finally, 19 of the shortlisted publications did not specify the cell origin. The sources of HMC-1 are summarized in Figure 2.
The composition of the growth medium used for HMC-1 cell line propagation varies among publications. Sigma-Aldrich and MERCK recommend HMC-1 cell line to be maintained in IMDM supplemented with 10% Fetal Bovine Serum (FBS), 1.2mM α-thioglycerol, and 1× penicillin/streptomycin in a 37°C humidified environment with 5% CO2. In actual protocols employed in the publications, most of the articles maintain HMC-1 cell line in IMDM (43 of 50), followed by RPMI-1640 (5 of 50), DMEM (1 of 50) and IMEM (1 of 50). In addition, the media was supplemented with 10% FBS (45 of 50), penicillin/streptomycin (44 of 50), 2mM L-glutamine (4 of 50), monothioglycerol (3 of 50), α-thioglycerol (2 of 50), 10% fetal calf serum (FCS) (2 of 50), 2-mercaptoethanol (1 of 50), amphotericin B (1 of 50), and sodium bicarbonate (1 of 50). Table 1 summarizes the culture medium and conditions to grow HMC-1 cells.
The choice of medium and composition are crucial to provide an optimal environment for cell growth and survival. IMDM, a highly enriched synthetic medium, is often recommended for rapidly proliferating and high-density cell lines. While no studies have reported the correlation between medium composition and the growth of HMC-1 cells, evidence shows that DMEM and RPMI-1640 media can affect the growth and differentiation of several cell lines 25,26. The medium’s excess or lack of calcium ion (Ca2+) and inorganic phosphate (Pi) may attenuate the differentiation of several cell lines. The concentration of 1.8 mM and 0.09 mM of Ca2+ and Pi, respectively, are optimum for cell proliferation 27. L-glutamine is supplemented to the medium to serve as an energy source for rapidly dividing cell lines28. The degradation of L-glutamine to ammonia may be toxic to the cells, where 2 to 3 mM is sufficient to reduce cell growth. Yet, such occurrence is dependent on the cell line 29. In addition, there are contradictory reports on supplementing media with L-glutamine on cytokine release. Coëffier et al. (2001) demonstrated the reduction in pro-inflammatory cytokines (IL-6 and IL-8) from human intestinal mucosa by glutamine via a post-transcriptional pathway30. Glutamine has also decreased the expression of leukotriene C4, monocyte chemoattractant protein (MCP), macrophage inflammatory protein (MIP)-1β, tumor necrosis factor alpha (TNF-α), interleukin (IL)-15, and IL-18 in human intestinal mast cells, and lobectomy patients 31,32. In contrast, several publications observed an increase in Th1 cytokines (IL-2 and IFN-γ) in PMACI-treated intestinal intraepithelial lymphocytes by glutamine33. Similarly, IL-1 and IL-10 were upregulated in glutamine-treated lobectomy patients 32. Other supplements, such as sodium pyruvate in IMDM, have been shown to impair cytokine production by inhibiting inflammatory signalling pathways34.