IGF-1 LR3 (Long Arginine 3 Insulin-like Growth Factor-1) is a synthetic analogue of the endogenous hormone IGF-1. The modification to this peptide not only increases its stability but also enhances its activity.

IGF-1 LR3 binds to the IGF-1 receptor, just as natural IGF-1 would, so it promotes the same kinds of activities, including enhancing cell growth, tissue repair, and altering metabolism.

This article will cover the function of IGF-1, compare the similarities and differences between IGF-1 and IGF-1 LR3, look at the therapeutic uses of this peptide that researchers have investigated, and touch upon the consequences of elevating IGF-1 levels excessively.

The Normal Function of IGF-1 in the Body

Production and Regulation

When growth hormone is released from the pituitary gland, it stimulates tissues, mainly in the liver, to produce IGF-1. This IGF-1 is then released into the bloodstream, where it exerts its growth-promoting effects on various other tissues.

IGF binding proteins bind to IGF-1, regulating its availability and activity at IGF-1 receptors.

The levels of IGF-1 in the body are determined by several factors, including:

• Liver function: Since it is made in the liver, any problems with the liver could mean that less is produced¹.
• Age: IGF-1 levels tend to naturally decline with age.
• Genetic conditions: Problems with the IGF-1 gene itself or genes involved in the processing of the prohormone or receptor can lead to deficiency². IGF1R haploinsufficiency leads to elevated IGF-1 levels but a decreased response to it³.
• Disease: Chronic liver diseases can lower IGF-1 levels⁴. Low levels or reduced responses to the hormone are linked to diseases, such as Alzheimer’s⁵, other neurodegenerative diseases⁶ and cardiovascular disease⁷. Endocrine disorders such as insulin resistance can lead to either elevated or lowered IGF-1 levels, depending on context^8–11.
• Medications: Sodium-glucose cotransporter-2 inhibitors¹², DHEA¹³, dopamine agonists¹⁴ and verapamil¹⁵ can increase IGF-1 levels, while clomiphene citrate¹⁶, atorvastatin¹⁷ and long-term somatostatin analogues can reduce IGF-1¹⁸.

It may already be evident that exceptionally low or high levels should be avoided since there is evidence indicating this increases the risk of disease. This is a complicated, context-dependent topic that we will examine in more detail later in this article. Now that we understand what factors can influence IGF-1 levels, we should learn what IGF-1 actually does in the body.

Role in Growth and Development

It plays a vital role in growth and development, as it promotes:

• Cell proliferation¹⁹
• Organ growth²⁰
• Tissue differentiation¹⁹
• Bone growth and remodelling²¹
• Brain development²²
• Neuroplasticity²²

It is particularly important during childhood and adolescence, when growth and development occur most rapidly. Because of the potentially beneficial activities of IGF-1, researchers have developed IGF-1 LR3.

IGF-1 vs. IGF-1 LR3: What’s the Difference?

In a research setting, IGF-1 LR3 is often used in preference to IGF-1. We will take a look at what makes these two peptides different and how the modifications present in IGF-1 LR3 make it a favourable choice for researchers.

Structure

The main differences between the structures of IGF-1 and IGF-1 LR3 are that the latter has glutamic acid instead of arginine at position 3 and has an extended chain of amino acids at the terminal end. IGF-1 has a half-life of only a few minutes^23,24, while the modifications to IGF-1 LR3 confer greater stability, giving it a half-life of approximately 20-30 hours²⁵. This means that IGF-1 LR3 remains active in the body for much longer than its endogenous version.

Function

The activity of IGF-1 can be controlled by the IGF binding proteins, which bind to IGF-1, preventing it from binding to receptors and blocking its activity.  IGF-1 LR3 cannot be regulated in the same way. Because of the modifications to IGF-1 LR3, IGF binding proteins are less able to bind to it, making it more potent and longer lasting. This is advantageous for research and therapeutic uses.

Applications

Because of its superior stability and potent activity, IGF-1 LR3 is used in research to study pathways activated by IGF-1 signalling. IGF-1 LR3 exerts significant therapeutic benefits and is being tested in preclinical settings for potential applications.

Potential Benefits of IGF-1 LR3 in the Body

Now that we understand the function of IGF-1 as well as the differences and similarities between it and IGF-1 LR3, we will look at how this hormone could be used to benefit health.

Muscle Growth and Repair

IGF-1 is involved in the growth and repair of muscles, as it stimulates the proliferation of muscle satellite cells, which are essential for muscle regeneration and hypertrophy. It activates signalling pathways which lead to an increase in protein synthesis and muscle fibre growth and inhibits the breakdown and atrophy of muscles²⁶.

During muscle injury, IGF-1 is naturally produced locally, predominantly by immune cells such as macrophages, which helps to reduce inflammation and promote repair²⁷. It promotes mitochondrial biogenesis and turnover in muscle cells to support the energy demands associated with growth and repair²⁸.

These properties make IGF-1 a promising lead for therapies that aim to reduce muscle wastage and degeneration.

Bone Density and Healing

IGF-1 has a significant positive effect on bone healing, which it exerts by stimulating the proliferation and differentiation of osteoblasts, supporting the regeneration of bone tissue after injury²⁹. One study found that it was even more effective than BMP-7 (Bone Morphogenetic Protein -7) in promoting bone repair³⁰.

Cognitive and Neurological Support

IGF-1 has been found to support neurogenesis, synaptic plasticity and neuronal survival, which are important for learning and memory. It is also involved in regulating oxidative stress and mitochondrial function. The dysregulation of these components is associated with increased neurodegeneration and cognitive decline³¹.

Low levels of IGF-1 are associated with reduced cognitive function³², with the age-related decline in IGF-1 possibly contributing to cognitive decline and increased risk of dementia^33,34. Animal studies have found that increases in IGF-1 can improve memory and learning³⁵, while reductions impair cognition³⁶.

In studies looking at Alzheimer’s disease, IGF-1 demonstrated an ability to promote neurogenesis, reduce neuroinflammation and support neuronal survival in animal models³⁷. It may also help to reduce certain symptoms associated with neurodegenerative diseases, such as anxiety and depression^38,39.

Despite these promising results, not all studies have found IGF-1 to demonstrate positive effects on cognitive health. Exceptionally low or high IGF-1 levels are associated with an increased risk of dementia and stroke, and high levels are linked to an increased risk of Parkinson’s disease⁴⁰.

Some of the results gained from studies have left us with what may appear to be inconclusive results as to the role of IGF-1 in cognition and neurodegeneration, but they help to demonstrate how complex this topic is. IGF-1’s positive effect on cognition appears to be dependent on maintaining balanced levels, with excessively high or low levels to be avoided.

Metabolic Effects

IGF-1 regulates protein, carbohydrate, and lipid metabolism. It generally decreases circulating insulin and glucose levels and can promote protein synthesis by activating anabolic signalling. This anabolic signalling inhibits protein degradation, promoting muscle hypertrophy and maintenance²⁶.

It influences both the breakdown of fat (lipolysis) and fat cell formation (adipogenesis). Which one of these it promotes is dependent on factors such as insulin signalling and metabolic state^41,42.

Lipolysis is promoted by IGF-1 under conditions of energy deprivation or metabolic stress, where it can enhance both carbohydrate and lipid metabolism, as well as increase glucose uptake and utilisation. It improves mitochondrial function and increases energy production, which makes sense given that this is a response to a state of low nutritional and caloric intake. At optimal levels, it can promote the burning of energy, helping to alleviate metabolic syndrome⁴³. In adolescents, lower (but in the normal range) IGF-1 levels are associated with higher insulin sensitivity, particularly if they engage in long-term exercise⁴⁴. This may suggest that only low-normal levels are required to exert metabolic benefits.

Conversely, adipogenesis is promoted by IGF-1 when there is an overabundance of energy⁴⁵. When it functions in this manner, it is closely linked to the development of metabolic syndrome, with lower levels being associated with impaired lipid profiles, insulin resistance, higher blood glucose levels and an increased risk of obesity and cardiovascular disease.

The effects of IGF-1 can vary depending on factors such as sex, physiological context and underlying health conditions, demonstrating the complexity of the system that it plays a role in. It would appear that there is an optimal level of IGF-1 that lends itself to peak metabolic health, with a deviation towards deficiency or excess leading more towards metabolic dysregulation.

Negative Health Effects and Risks of Elevated IGF-1

Increased Cancer Risk

IGF-1 promotes cell survival, migration, proliferation, and resistance to stress (including chemotherapy), and does not distinguish between normal or cancerous cells when exerting this activity. These properties are all seen in cancer cells, and several studies have linked IGF-1 to an increased risk of developing cancers⁴⁶.

In people with obesity, IGF levels are raised, which may partly explain the increased risk of developing endocrine cancers, as well as further implicate IGF-1 in cancer development⁴⁷.

Accelerated Aging

The desirable level of IGF-1 is not a value set in stone. Generally, younger people benefit from a higher level as it supports growth and health, but as we age, higher levels are associated with an increased risk of age-related disease and mortality.

Some studies suggest that reducing levels later in life may help to reduce the risk of cancer⁴⁸, while other studies emphasise the importance of raising levels in the brain in order to prevent cognitive decline⁴⁹. Reduced IGF-1 signalling is linked to increased longevity in some animals, but in mammals, where IGF-1 and insulin pathways interact, the effect of IGF-1 levels on healthy aging is less clear⁵⁰.

Excessive IGF-1 signalling increases the activity of the insulin/IGF-1 pathway, which may accelerate some aspects of aging by leading to immunosuppression, cellular senescence, and chronic low-grade inflammation⁵¹.

So, while IGF-1 is important for maintaining health as we age, both insufficiency and excess can lead to negative consequences. The optimal balance for health may depend on a number of individual factors.

Metabolic Imbalance

Although low-normal levels of IGF-1 are associated with insulin sensitivity, excessively high or low levels of IGF-1 are associated with insulin resistance, which can lead to chronic hyperglycaemia, oxidative stress, inflammation and endothelial dysfunction⁵².

 

Maintaining Healthy IGF-1 Levels Naturally

As we have learned, the body naturally regulates IGF-1 in response to our lifestyle, metabolic state and health, so altering factors such as diet, activity levels and other habits can have effects on IGF-1 expression by the body.

Lifestyle and Nutrition

Diet: Diets that are high in protein and consist of a high intake of energy are associated with higher IGF-1 levels⁵³, while fasting, low-calorie, and ketogenic diets are associated with lower IGF-1 levels⁵⁴. Supplements such as a combination of selenium and coenzyme Q10⁵⁵, and DHEA¹³ have been found to increase IGF-1 levels.

Physical exercise: Resistance training is associated with increased IGF-1 levels. One study found a significant increase after 16 weeks of training⁵⁶. The recovery phase of exercise sees an increase in IGF-1 levels, with the greatest increase observed when recovery is active as opposed to passive⁵⁷.

Sleep: Sufficient and good quality sleep helps to improve IGF-1 levels, while disturbances in sleep and inadequate sleep have been shown to reduce IGF-1 and negatively affect cognitive function⁵⁸.

Conclusion

IGF-1 plays an essential role in growth and health by mediating the effects of growth hormone, promoting cell proliferation, differentiation and anabolic processes. It balances bone growth and resorption, stimulates protein synthesis, muscle regeneration and hypertrophy and influences brain development, neuroplasticity, and repair mechanisms.

IGF-1 levels must be carefully balanced, as both excess and deficiency can lead to negative health outcomes. Low IGF-1 is associated with increased mortality, frailty, and medical complications due to the impaired tissue repair and metabolic dysfunction that comes with this deficiency. Excessively high IGF-1 could accelerate aging and lead to metabolic dysfunction. Striking the correct balance is important to maintain good health.

IGF-1 LR3 is more potent than IGF-1 as it has a lower affinity for IGF-1 binding proteins, which can prevent it from binding to receptors. It can also remain active for far longer than endogenous IGF-1 since the body cannot regulate its levels as effectively. This makes it an excellent substitute for IGF-1 during research applications as it strongly and persistently activates IGF-1 receptors.

Since research on IGF-1 LR3 has not progressed beyond preclinical studies, we do not know how it will behave in the human body, and it is not approved for human use outside of research settings. Studies so far would indicate that it does have value as a therapeutic agent if used appropriately.

Buy IGF-1 LR3 here.

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