Once fertilization occurs with the formation of a zygote, cellular growth occurs continuously until death. Cellular growth is not a process limited to growing children or malignant tumors, it is in fact a highly intricate process involving cell division, proliferation, metabolism, and cell death. If any of the steps involving cellular growth is disrupted, it can result in pathological morbidity and early mortality. The growth of cells is regulated by growth hormone which in turn exerts much of its effects via Insulin-like Growth factor-1. The secretion of Growth Hormone occurs via the somatotropic cells present within the pituitary gland. GH then stimulates the synthesis of IGF-1 via the activation of a transcription signaling pathway in the liver. IGF-1 is responsible for many of the indirect effects of growth hormones on chondrocytes to stimulate bone growth, lean muscle growth, and organomegaly.
L-arginine is a semi-essential amino acid that plays an important role in the promotion of growth hormone secretion during childhood and infancy. It does this by inhibiting somatostatin, which is a potent inhibitor of growth hormone-releasing hormone. In addition to this, L-Arginine activates the mTORC1 signaling pathway to stimulate the synthesis of protein by PI3K pathway secondary activation. L-Arginine also promotes cell growth and proliferation via alternative methods that are not well understood.
Study on the effect of L-Arginine on Growth Hormone and IGF-1
A study on the effect of Growth Hormone and IGF-1 secretion by L-arginine on pituitary cells and hepatocytes was conducted by researchers.
Researchers obtained GH3 and HepG2 cells from the Korean Cell Line Bank which were then cultured in 10% heat-inactivated fetal bovine serum with a combination of antibiotics (1% penicillin/streptomycin). The GH3 and HepG2 cells were kept in a humid environment with 5 % carbon dioxide at a temperature of 37°C.
Quantitative PCR Analysis
Using an old method of extracting RNA, GH3, and HepG2 cell RNA was obtained via RNAiso Plus. The next step was the measurement of gene expression levels of cDNA which was synthesized from the extracted total RNA.
GH and IGF-1 secretion Quantification
GH and IGF-1 concentrations were measured by employing ELISA. Cells were cultured in growth plates containing L-Arginine and estradiol for a total duration of 24 hrs. From the culture plate containing GH3 and HepG2 cells, GH and IGF-1 were measured quantitatively using a microplate reader.
MAPK signaling analysis
With a multi-target Enzyme-Linked Immunosorbent Assay, the overall effect of the amino acid L-Arginine on the signaling pathway MAPK was assessed.
The HepG2 cells cultured overnight were treated with L-arginine for 24 hrs with the conjugation of inhibitors of MEK, MAPK, and JNK. After 24 hrs, using quantitative PCR the total RNA was extracted from the culture.
Results of the Study
Quantitative analysis of the GH3 cells discovered the increased expression of GH mRNA when GH3 cells were grown with L-Arginine. Similar findings were seen in HepG2 cells with increased expression of IGF-1 in cells grown with L-arginine. This finding confirms the effect of L-arginine on the expression of GH and IGF-1 genes.