How do corticosteroids (CS) affect protein metabolism?

Corticosteroids Cause Increased Protein Catabolism

Corticosteroids significantly increase protein breakdown and loss, causing a net negative protein balance that leads to muscle wasting and altered body composition. 1, 2

Mechanism of Corticosteroid-Induced Protein Catabolism

Corticosteroids affect protein metabolism through several mechanisms:

1. Increased Protein Breakdown:

   • Corticosteroids stimulate ubiquitin-proteasome-dependent proteolysis in skeletal muscle 3
   • They increase the rates of appearance of amino acids (phenylalanine and leucine), reflecting accelerated protein degradation 4, 2
   • In children with Crohn's disease, corticosteroid therapy increased protein breakdown by 26-32% 2

2. Increased Protein Loss:

   • Corticosteroids significantly increase urea production (up to 273% in some studies), indicating greater protein loss 2
   • They cause increased efflux of multiple amino acids from muscle tissue, including phenylalanine, asparagine, arginine, alanine, methionine, and isoleucine 4

3. Potential Impact on Protein Synthesis:

   • Corticosteroids can reduce polyribosomes by approximately 6%, suggesting a decreased capacity for protein synthesis 4
   • However, the effect on actual protein synthesis rates is less consistent across studies 5, 4

Clinical Implications

In Inflammatory Bowel Disease (IBD)

• Corticosteroids increase net protein loss in both children 2 and adults 6 with Crohn's disease
• This contributes to the relative reduction in lean mass and increase in adiposity observed in IBD patients over time 6
• Protein requirements are increased during active IBD (1.2-1.5 g/kg/day recommended) to compensate for this catabolic effect 6

In Other Clinical Contexts

• Corticosteroid-induced protein catabolism affects predominantly type 2 muscle fibers (fast-twitch), leading to selective wasting of certain muscle groups 7
• This can lead to steroid myopathy, characterized by proximal muscle weakness
• Prolonged corticosteroid use contributes to osteoporosis and vertebral compression fractures due to protein loss from bone matrix 6

Management Strategies

1. Increased Protein Intake:

   • During corticosteroid therapy, protein intake should be increased to 1.2-1.5 g/kg/day 6
   • This helps compensate for the increased protein breakdown and loss

2. Nutritional Support:

   • In patients receiving steroids, enteral tube feeding may provide beneficial effects on protein turnover 6
   • Monitoring of anthropometry helps identify patients who develop deficits in lean mass 6

3. Avoid Unnecessary Diet Restrictions:

   • In patients on systemic corticosteroid therapy, salt, sugar, fat, or calorie reduction should not be recommended as the benefit-risk ratio is unfavorable toward a higher risk for malnutrition 6
   • A standard diet should be proposed to cover increased energy expenditure and protein catabolism 6

Special Considerations

• The catabolic effects of corticosteroids may be more pronounced in certain populations, such as children with chronic diseases 6
• The interaction between corticosteroids and inflammatory cytokines can further exacerbate protein breakdown in conditions like sepsis 3
• Short-term, moderate-dose prednisone may not significantly affect protein metabolism in healthy individuals, but longer-term or higher-dose therapy typically does 5

By understanding these mechanisms and implementing appropriate nutritional strategies, the negative impact of corticosteroid-induced protein catabolism can be minimized, helping to preserve muscle mass and function during necessary corticosteroid therapy.