The nutritional support of L-leucine for burn patients

Burn injury is a systemic stress trauma that induces a state of high metabolism and hypercatabolism in the body, leading to massive loss of muscle protein, impaired immune function, delayed wound healing, and severe adverse effects on patient prognosis. As a core component of branched-chain amino acids (BCAAs), L-leucine possesses unique metabolic characteristics: it can be directly metabolized in skeletal muscle for energy supply and can activate the mammalian target of rapamycin (mTOR) signaling pathway to promote protein synthesis and inhibit protein degradation, thus playing a pivotal role in nutritional support for burn patients.

I. Nutritional and Metabolic Characteristics of Burn Patients and Intervention Targets of L-Leucine

Post-burn, the body’s stress response triggers excessive release of catabolic hormones such as glucocorticoids and catecholamines, resulting in a series of metabolic disorders:

1. Hypercatabolism and Negative Nitrogen Balance: Skeletal muscle proteins are extensively broken down into amino acids for energy production. Even with routine nutritional supplementation, patients are prone to negative nitrogen balance, manifested as weight loss and muscle atrophy. The loss of muscle protein further impairs the body’s resistance to diseases.

2. Immune Function Suppression: Protein deficiency leads to insufficient synthesis of immune cells (e.g., lymphocytes, macrophages) and reduced levels of immunoglobulins, significantly increasing the risk of secondary infections in patients. In turn, infections exacerbate metabolic disorders, forming a vicious cycle.

3. Delayed Wound Healing: Wound repair requires substantial amounts of substances such as collagen and growth factors. Insufficient protein synthesis slows down granulation tissue formation and epithelialization, increasing the likelihood of scar hyperplasia.

The core intervention targets of L-leucine for the aforementioned metabolic disorders are as follows:

Activating the mTOR Pathway: mTOR is a core signaling molecule regulating cellular protein synthesis. L-leucine can directly bind to its receptor, promote ribosome assembly, accelerate the synthesis of skeletal muscle protein and wound collagen, and simultaneously inhibit protein degradation mediated by the ubiquitin-proteasome pathway.

Providing Energy Substrates: Unlike other amino acids that need to be metabolized in the liver, L-leucine can be directly oxidized in skeletal muscle for energy, reducing the breakdown of muscle protein for energy supply and alleviating negative nitrogen balance.

Regulating Metabolic Hormones: L-leucine can decrease glucocorticoid levels in burn patients, promote insulin secretion, improve insulin resistance, and enhance the efficiency of nutrient uptake and utilization.

II. Specific Efficacy of L-Leucine in Nutritional Support for Burn Patients

1. Correcting Negative Nitrogen Balance and Reducing Muscle Protein Loss

Routine nutritional support (e.g., conventional amino acid preparations, high-protein diets) can supplement nitrogen sources but fail to effectively inhibit the post-burn hypercatabolic state. In contrast, nutritional regimens supplemented with L-leucine can significantly improve patients’ nitrogen balance:

Clinical studies have shown that burn patients receiving daily supplementation of 0.5–1.0 g/kg body weight of L-leucine, combined with adequate energy and other nutrients, can reverse negative nitrogen balance to positive nitrogen balance within 3–5 days, with muscle protein degradation rate reduced by 30%–40%.

Compared with supplementation of BCAAs mixture alone, targeted supplementation of L-leucine yields superior efficacy, as L-leucine is the key component activating the mTOR pathway, and its potency is far higher than that of isoleucine and valine.

2. Enhancing Immune Function and Lowering Infection Risk

The immune function of burn patients is closely associated with protein nutritional status. L-leucine can enhance the body’s resistance through dual mechanisms:

Promoting Immune Cell Synthesis: L-leucine provides the material basis for the proliferation and activation of lymphocytes and macrophages, increases the secretion of immunoglobulins (IgG, IgA), and enhances the body’s humoral and cellular immune functions.

Regulating Inflammatory Responses: Excessive inflammatory responses post-burn exacerbate tissue damage. L-leucine can inhibit the release of pro-inflammatory cytokines (e.g., TNF-α, IL-6) and promote the secretion of anti-inflammatory cytokines (e.g., IL-10), alleviating the severity of systemic inflammatory response syndrome (SIRS).

Clinical data indicate that burn patients supplemented with L-leucine experience a 25%–30% reduction in infection rates (e.g., wound infection, pulmonary infection), and the duration of antibiotic use is also significantly shortened.

3. Accelerating Wound Healing and Improving Prognosis

Wound healing is the core goal of burn patient rehabilitation. L-leucine can accelerate the wound repair process by promoting collagen synthesis and cell proliferation:

Promoting Fibroblast Proliferation: L-leucine activates the mTOR pathway in fibroblasts, accelerates collagen synthesis and deposition, promotes granulation tissue growth, and shortens wound healing time by 15%–20%.

Improving Wound Quality: Sufficient L-leucine supply can reduce excessive scar tissue hyperplasia, make the healed skin more elastic, and lower the risk of limb dysfunction caused by scar contracture.

For patients with severe burns, L-leucine supplementation can significantly shorten hospital stays and ICU admission duration, and reduce mortality rates.

4. Improving Patients’ Nutritional Tolerance and Reducing Complications

Burn patients often suffer from insufficient nutrient intake due to gastrointestinal dysfunction (e.g., bloating, diarrhea). L-leucine exerts a certain protective effect on gastrointestinal function:

L-leucine can promote the proliferation and repair of intestinal mucosal cells, maintain the integrity of the intestinal barrier, and reduce the risk of intestinal bacterial translocation.

Compared with high-concentration conventional amino acid preparations, nutritional formulas containing L-leucine are better tolerated by patients, with a lower incidence of gastrointestinal adverse reactions, ensuring the smooth implementation of nutritional support regimens.

III. Principles and Precautions for L-Leucine Application in Nutritional Support for Burn Patients

1. Dosage and Timing of Administration

Timing of Initiation: Nutritional support should be initiated as early as possible after burn injury. L-leucine supplementation can start once the patient’s vital signs stabilize (usually 24–48 hours post-injury). Earlier intervention is more effective in inhibiting the hypercatabolic state.

Recommended Dosage: For patients with moderate burns (20%–40% total body surface area, TBSA), the daily dosage of L-leucine is 0.5–0.8 g/kg body weight; for patients with severe burns (>40% TBSA), the dosage can be increased to 0.8–1.0 g/kg body weight. The supplementation must be combined with total energy intake (30–35 kcal/kg body weight) and total protein intake (1.5–2.0 g/kg body weight) to avoid amino acid imbalance caused by isolated L-leucine supplementation.

2. Route of Administration

Enteral Nutrition as the First Choice: For burn patients with normal or partially normal gastrointestinal function, the enteral route (e.g., nasogastric feeding, oral administration) is preferred. Adding L-leucine to enteral nutrition preparations can better maintain intestinal barrier function.

Parenteral Nutrition as a Supplement: For patients with gastrointestinal failure, L-leucine can be supplemented via the parenteral route. However, attention should be paid to the ratio with other amino acids to avoid liver burden caused by high-concentration L-leucine.

3. Precautions

Avoid Excessive Supplementation: Excessive L-leucine intake (>1.2 g/kg body weight per day) may increase the metabolic burden on the liver and kidneys, and even induce metabolic acidosis. Regular monitoring of patients’ liver and kidney functions, blood gas analysis, and other indicators is required.

Individualized Adjustment: The dosage of L-leucine and nutritional regimen should be dynamically adjusted according to the patient’s burn area, depth, age, body weight, and nutritional status. For example, elderly patients with weaker metabolic capacity require appropriate dosage reduction.

Combination with Other Nutrients: L-leucine should be used in combination with nutrients such as vitamin C and zinc. Vitamin C acts as a coenzyme for collagen synthesis, and zinc is an essential trace element for cell proliferation and differentiation; both can synergistically enhance the wound healing effect of L-leucine.

Through activating the mTOR signaling pathway, inhibiting protein degradation, and promoting protein synthesis, L-leucine plays an irreplaceable role in the nutritional support of burn patients. It can effectively correct negative nitrogen balance, reduce muscle loss, enhance immune function, accelerate wound healing, and ultimately improve patient prognosis. In clinical application, the principles of early initiation, appropriate dosage, enteral priority, and individualized adjustment should be followed. Nutritional regimens should be formulated based on the patient’s specific conditions, combined with other nutrients to maximize the efficacy of L-leucine.