Dipeptides in parenteral nutrition: from basic science to clinical applications

Elucidating uptake and metabolic fate of dipeptides in CHO cell cultures using 13C labeling experiments and kinetic modeling

The rapidly growing market of biologics including monoclonal antibodies has stimulated the need to improve biomanufacturing processes including mammalian host systems such as Chinese Hamster Ovary (CHO) cells. Cell culture media formulations continue to be enhanced to enable intensified cell culture processes and optimize cell culture performance. Amino acids, major components of cell culture media, are consumed in large amounts by CHO cells. Due to their low solubility and poor stability, certain amino acids including tyrosine, leucine, and phenylalanine can pose major challenges leading to suboptimal bioprocess performance. Dipeptides have the potential to replace amino acids in culture media. However, very little is known about the cleavage, uptake, and utilization kinetics of dipeptides in CHO cell cultures. In this study, replacing amino acids, including leucine and tyrosine by their respective dipeptides including but not limited to Ala-Leu and Gly-Tyr, supported similar cell growth, antibody production, and lactate profiles. Using 13C labeling techniques and spent media studies, dipeptides were shown to undergo both intracellular and extracellular cleavage in cultures. Extracellular cleavage increased with the culture duration, indicating cleavage by host cell proteins that are likely secreted and accumulate in cell culture over time. A kinetic model was built and for the first time, integrated with 13C labeling experiments to estimate dipeptide utilization rates, in CHO cell cultures. Dipeptides with alanine at the N-terminus had a higher utilization rate than dipeptides with alanine at the C-terminus and dipeptides with glycine instead of alanine at N-terminus. Simultaneous supplementation of more than one dipeptide in culture led to reduction in individual dipeptide utilization rates indicating that dipeptides compete for the same cleavage enzymes, transporters, or both. Dipeptide utilization rates in culture and cleavage rates in cell-free experiments appeared to follow Michaelis-Menten kinetics, reaching a maximum at higher dipeptide concentrations. Dipeptide utilization behavior was found to be similar in cell-free and cell culture environments, paving the way for future testing approaches for dipeptides in cell-free environments prior to use in large-scale bioreactors. Thus, this study provides a deeper understanding of the fate of dipeptides in CHO cell cultures through an integration of cell culture, 13C labeling, and kinetic modeling approaches providing insights in how to best use dipeptides in media formulations for robust and optimal mammalian cell culture performance.

The effects of glycine-glutamine dipeptide replaced l-glutamine on bovine parthenogenetic and IVF embryo development

Relative to alanine and serine amino acid levels, glutamine is highly abundant in follicular fluid, and is an important source of energy required for oocyte maturation and embryo development. Thus, glutamine is an essential component of in vitro embryo culture media. However, glutamine has poor stability and degrades spontaneously in solution to form ammonia and pyrrolidonecarboxylic acid. In the present study, we aimed to explore the effect of substituting l-glutamine with glycine-glutamine, a more stable glutamine, on development of early parthenogenetic embryos and in vitro fertilization (IVF) embryos in bovine. Results revealed that glycine-glutamine can significantly increase cleavage rate (parthenogenetic embryos:87.24% vs. 72.61%, IVF embryos:89.33% vs. 83.79%, P < 0.01), blastocyst number (parthenogenetic embryos:24.98% vs. 18.07%, IVF embryos:33.53% vs. 27.29%, P < 0.01), and blastocyst number (parthenogenetic embryos:96 vs. 76, IVF embryos:114 vs. 109, P < 0.01), reduce blastocyst apoptosis (parthenogenetic embryos:3.72% vs. 6.65%, IVF embryos:2.53% vs.6.23%, P < 0.01), alleviate embryo ammonia toxicity, and reduce the content of reactive oxygen species (ROS) compared with the l-glutamine. In addition, glycine-glutamine can alter epigenetic reprogramming by increasing the expression of HDAC1 (Histone Deacetylase 1) and decreasing the relative expression levels of H3K9 acetylation in early parthenogenetic embryos and IVF embryos. From our present study, we concluded that glycine-glutamine is an effective substitute of glutamine in modified synthetic oviduct fluid with amino acids (mSOFaa).

Utilization of tyrosine- and histidine-containing dipeptides to enhance productivity and culture viability

Adequate supply of nutrients, especially providing a sufficient level of specific amino acids, is essential for cell survival and production. Complex raw materials such as soy hydrolysates or yeast extracts are the source for both free amino acids and peptides. However, typical chemically defined (CD) media provide amino acids only in free form. While most amino acids are highly soluble in media and can be provided at fairly high concentrations, certain amino acids such as tyrosine have poor solubility and thus, only a limited amount can be added as a media component. The limited solubility of amino acids in media can raise the risk of media precipitation and instability, and could contribute to suboptimal culture performance due to insufficient nutrient levels to meet cellular demands. In this study, we examine the use of chemically synthesized dipeptides as an alternative method for delivering amino acids to various monoclonal antibody producing cell lines. In particular, we focus on tyrosine-containing dipeptides. Due to their substantially higher solubility (up to 250-fold as compared with free tyrosine), tyrosine-containing dipeptides can efficiently provide large amounts of tyrosine to cultured cells. When tested in fed-batch processes, these supplemental dipeptides exerted positive effects, including enhanced culture viability and titer. Moreover, dipeptide-supplemented cultures displayed improved metabolic profiles including lower lactate and NH 4(+) production, and better pH maintenance. In bioreactor studies using two-sided pH control, a lactate spike occurring on Day 10 and the concomitant high levels of base addition could be prevented with dipeptide supplementation. These beneficial effects could be obtained by one-time addition of dipeptides during inoculation, and did not require further feeds during the entire 11-15-day process. Non-tyrosine-containing dipeptides, such as His-Gly, also showed improved productivity and viability over control cultures.

Developmental expression of PEPT1 and PEPT2 in rat small intestine, colon, and kidney

Mammalian peptide transporters (PEPT1 and PEPT2) play a pivotal role in the absorption of small peptides from the intestine and kidney, respectively, and in the disposition and targeting of peptide or mimetic drugs. However, there are few reports on the molecular basis of their regulation, especially in the young. The aim of this study was to determine the developmental expression of intestinal and renal oligopeptide transporters in rats from embryonic to adult ages. Intestinal segments were collected (i.e. duodenum, jejunum, ileum, and colon) along with whole kidney, and their mRNA and protein levels were measured. Expression levels of PEPT1 were maximal 3-5 d after birth in the duodenum, jejunum, and ileum, and then declined rapidly. Expression was increased transiently at d 24, most notably in the ileum. Adult protein levels were approximately 70% of that observed on d 3-5. Significant PEPT1 expression was observed in colon during the first week of life, but levels were undetectable shortly thereafter through adulthood. PEPT1 and PEPT2 expression is less regulated in rat kidney and more pronounced in older animals. Peptide transporters were also present as early as d 20 of fetal life for all tissues tested. These results are unique in providing the developmental expression of peptide transporter mRNA and protein in distinct regions of the small intestine, colon, and kidney in rat. Our findings suggest that intestinal expression of PEPT1 is induced postpartum, possibly by suckling, and again at the time of weaning, and that the colon may participate in peptide transport early in life.

Supplementation of an elemental enteral diet with alanyl-glutamine decreases bacterial translocation in burned mice

Although there are many reports of the importance of early enteral feeding in maintaining gastrointestinal integrity and preventing bacterial translocation (BT) following burn injury, no diet has been shown clinically to protect the GI tract postburn. Several studies suggest that glutamine (GLN) may benefit gut integrity following injury, shock and other stress. Unfortunately, the free amino acid GLN is unstable in solution. Alanyl-glutamine (ALA-GLN), a soluble form of GLN, maintains long-term stability in solution and could be supplemented to conventional liquid enteral diets. We studied the effects of ALA-GLN supplementation of the elemental diet Vivonex TEN on effecting BT in mice following 32 per cent TBSA full skin thickness burns. Groups A-D were burned. Group A (30 mice) was fed standard rodent chow, which contains extremely high (clinically non-useable) levels of protein. Group B (51 mice) was fasted 24 h, then fed chow 24 h. Group C (64 mice) was fed Vivonex TEN, and Group D (65 mice) received Vivonex TEN plus ALA-GLN (GLN equivalent, 14 g/l). A control group (Group E) consisted of 22 normal mice (no burn injury, chow diet). Mice were assessed for BT by sterile harvesting and plating of mesenteric lymph node tissue, 48 h postburn. Plates were considered positive if any bacterial growth was noted. Non-burned mice exhibited no BT, while burn-fasted mice showed a 64.3 per cent incidence of BT (P = NS).(ABSTRACT TRUNCATED AT 250 WORDS)