Human Growth Hormone (HGH), or somatotropin, is a single-chain peptide hormone naturally produced and secreted by the pituitary gland, located at the base of the brain. HGH regulates growth, cell reproduction, and regeneration throughout the body from childhood into adulthood. When the body fails to produce enough of this natural hormone, recombinant human growth hormone (rHGH) is used therapeutically. Recombinant HGH, often referred to as somatropin, is a synthetic version manufactured using advanced biotechnology to ensure an identical structure and consistent supply for medical use.
Engineering Recombinant Human Growth Hormone
The creation of recombinant human growth hormone utilizes recombinant DNA technology. This process involves isolating the specific gene sequence that codes for the human growth hormone protein. The gene is then inserted into a small, circular piece of DNA called a plasmid, which transfers the genetic material.
The engineered plasmid is introduced into a host organism, typically the bacterium Escherichia coli (E. coli). The bacteria are grown in large fermentation tanks, where they use their cellular machinery to read the human gene sequence and mass-produce the HGH protein.
The final step involves a purification process to separate the synthesized hormone from the bacterial cells and other byproducts. This technology yields a pure and safe supply of a hormone that is structurally identical to the 191-amino acid form produced by the human pituitary gland. This method replaced the older practice of extracting HGH from human cadavers, which carried the risk of disease transmission.
How Growth Hormone Affects the Body
Growth hormone exerts its biological influence through both direct and indirect mechanisms across multiple organ systems. The indirect effect is mediated primarily by stimulating the liver to produce Insulin-like Growth Factor 1 (IGF-1). IGF-1 travels through the bloodstream to target tissues, where it promotes growth and cell division.
In children, IGF-1 is largely responsible for stimulating the proliferation of chondrocytes, the cartilage cells at the epiphyseal growth plates of long bones. This stimulation leads to the linear growth that defines increased height before the growth plates fuse at the end of puberty. HGH also directly binds to receptors on various cells, including those in adipose tissue, initiating metabolic changes.
The metabolic actions of HGH are central to its function, particularly its role in regulating body composition and energy use. It promotes lipolysis, the breakdown of fat stores, which provides free fatty acids for energy use. This action helps to spare glucose for use by other tissues, such as the brain, and can lead to a reduction in total body fat.
HGH also impacts protein metabolism by increasing protein synthesis, which contributes to increased lean muscle mass. The hormone has a regulatory effect on glucose, promoting gluconeogenesis (the creation of new glucose) in the liver. Because it can reduce the uptake of glucose by the liver and other tissues, HGH is recognized as having a diabetogenic effect that requires careful monitoring during therapy.
Conditions Treated with Recombinant HGH
Recombinant HGH is a prescription medication approved for treating a specific range of conditions characterized by growth failure or HGH deficiency. The most common indication is Growth Hormone Deficiency (GHD), which can occur in children, resulting in short stature, or in adults, often due to pituitary damage from tumors or radiation. Replacement therapy in adults with GHD can improve bone density, increase muscle mass, and reduce adipose tissue.
Beyond GHD, rHGH is used to treat several distinct genetic and chronic disorders that result in short stature. This includes Turner syndrome, a chromosomal condition affecting development in females, and Prader-Willi syndrome, a complex genetic disorder that causes poor muscle tone and a constant feeling of hunger. For Prader-Willi patients, HGH not only helps with height but also improves body composition by reducing fat mass.
Other approved indications include growth failure in children with chronic kidney disease, where the illness interferes with normal growth. It is also used for children born small for gestational age (SGA) who fail to catch up in growth by the age of two to four years. In adults, rHGH is approved to treat severe muscle wasting, known as cachexia, associated with HIV/AIDS. Treatment is typically a long-term commitment that requires ongoing medical supervision to ensure proper dosing.
Understanding Adverse Effects and Monitoring
While therapeutic use of recombinant HGH is generally considered safe under medical supervision, patients may experience adverse effects. Common side effects are often related to fluid retention, leading to symptoms like peripheral edema (swelling in the arms and legs) and joint or muscle pain. Some patients also report carpal tunnel syndrome, which is another manifestation of fluid retention.
Adverse effects include the potential for increased intracranial pressure, known as benign intracranial hypertension. In children, HGH therapy may also be associated with the progression of scoliosis or an increased risk of slipped capital femoral epiphysis, a hip disorder. The proliferative nature of HGH also raises theoretical concerns about increasing the risk of tumor recurrence in patients who have had prior cancer, though evidence remains inconclusive.
A metabolic concern is the possibility of glucose intolerance or insulin resistance, which can increase the risk of developing Type 2 diabetes. Due to these potential risks, physician supervision and regular monitoring are required components of therapy. Monitoring involves periodic blood tests to check IGF-1 levels, which measure HGH activity in the body. Adjusting the dosage based on IGF-1 levels helps ensure the treatment is effective while mitigating the risks of over-dosing, such as excessive bone growth.