Lysine alpha-ketoisocaproate

Other Names

2-Keto-4-methylvaleric acid2-Ketoisocaproate2-Ketoisocaproic acid2-Ketoisocapronic acid2-Oxo-4-methylpentanoic acid2-Oxo-4-methylvaleric acid lysine salt2-Oxoisocaproic acid2-Oxoleucine4-Methyl-2-oxopentanoate4-Methyl-2-oxopentanoic acid4-Methyl-2-oxovalerate4-Methyl-2-oxovaleric acid4-Methyl-2-oxovaleric acid lysine saltalpha-Keto-isocaproic acid L-lysine saltalpha-Ketoisocaproatealpha-Ketoisocaproic acidalpha-Ketoisocaproic acid lysine saltalpha-KICketo-analogue of leucineKetoisocaproate lysineKetoleucineKICKIC lysine saltL-Lysine alpha-ketoisocaproateL-Lysine KICleucine keto acidLysine KIC

Synopsis

Lysine Alpha-Ketoisocaproate

1. Identity

Chemical Names and Synonyms

Lysine alpha-ketoisocaproate (abbreviated Lys-KIC or L-KIC) is an ionic salt formed by the combination of the essential amino acid L-lysine (acting as the basic cation) and alpha-ketoisocaproic acid (also known as α-ketoisocaproate, α-KIC, or 4-methyl-2-oxovaleric acid), which serves as the anionic counterpart. The CAS registry number for the lysine salt form is 78000-32-5. The parent acid, alpha-ketoisocaproic acid, carries the systematic IUPAC name 4-methyl-2-oxopentanoic acid and is also called ketoleucine in older literature. α-Ketoisocaproic acid (α-KIC), also known as 4-methyl-2-oxovaleric acid, and its conjugate base and carboxylate, α-ketoisocaproate, are metabolic intermediates in the metabolic pathway for L-leucine.

In its salt form, lysine alpha-ketoisocaproate dissociates completely in aqueous solution. The ornithine and arginine salts of alpha keto acid analogs of the branched chain essential amino acids do not exist in water because they dissociate completely, presumably into the amino acid cation and the keto acid anion. The same behavior is documented for the lysine salt form.

Structural Classification

Alpha-ketoisocaproate belongs to the class of alpha-keto acid analogues of essential amino acids — specifically, it is the keto analogue of the branched-chain amino acid (BCAA) leucine. The keto analog of L-leucine (a dietarily essential amino acid) is alpha-keto-isocaproic acid, which is usually referred to as ketoisocaproate (KIC), or sometimes also as ketoleucine. The key structural feature distinguishing KIC from leucine is the absence of the alpha-amino group, replaced by a ketone (carbonyl) group. Because KAs lack the amino group bound to the α carbon of an amino acid, they can be converted to their respective amino acids without providing additional nitrogen.

Natural Origin and Endogenous Production

Alpha-ketoisocaproate is not obtained from any single botanical or food source as an isolated compound; rather, it is an endogenous metabolite produced in humans and most animals as part of normal leucine catabolism. α-KIC is produced in one of the first steps of the pathway by branched-chain amino acid aminotransferase by transferring the amine on L-leucine onto alpha-ketoglutarate, and replacing that amine with a ketone. The degradation of L-leucine in the muscle to this compound allows for the production of the amino acids alanine and glutamate as well. Any dietary source of leucine — including meat, dairy products, eggs, and legumes — therefore provides a substrate for the endogenous production of α-KIC.

The keto analog of leucine, alpha-ketoisocaproate (KIC), is formed intracellularly from leucine and is released, in part, into the systemic circulation. Because it circulates in plasma, it can be used physiologically as a proxy for intracellular leucine metabolism.

Common Forms and Preparations

In supplemental and research contexts, alpha-ketoisocaproate is presented in several salt forms to improve stability and palatability:

Lysine alpha-ketoisocaproate (Lys-KIC) — the compound that is the subject of this article, formed by combining L-lysine with the free keto acid.
Ornithine alpha-ketoisocaproate (OKIC) — an alternative basic amino acid salt also studied in clinical settings.
Calcium alpha-ketoisocaproate — the historically common industrial form (e.g., supplied by REXIM of Paris), from which free keto acid can be liberated by hydrolysis.
Arginine alpha-ketoisocaproate (AKIC) — a further variant examined mainly in animal studies.

The organic salt portion of such compositions is produced by combining a basic L-amino acid selected from the group consisting of ornithine, lysine and histidine with a branched-chain alpha-keto-acid analog selected from the group consisting of alpha-ketoisovalerate, alpha-ketoisocaproate and alpha-keto-beta-methylvalerate; the salts so derived are combined with calcium, sodium or potassium salts of alpha-hydroxy-gamma-methylthiobutyrate, and the amino acids L-tryptophan, L-tyrosine, and L-threonine.

The free acid form may be prepared from the calcium or sodium salts by addition of excess hydrochloric acid and subsequent extraction with ether and evaporation; the L-ornithine, L-lysine and L-histidine salts of branched-chain keto-acids are prepared by combining equimolar proportions of the amino acid as free bases with the free keto-acids, and precipitating the salts with ethanol.

In finished product form, Lys-KIC appears as a crystalline white powder. It is found in multi-component keto acid/amino acid tablets (such as the commercially available formulation Ketosteril® and its generic equivalents) where it is combined with other keto analogues and essential amino acids. These compositions, which are useful for the nutritional treatment of chronic renal failure, comprise mixtures of salts of a basic L-amino acid and a branched-chain alpha-keto acid, including L-lysine alpha-ketoisocaproate. It is also sold as a standalone supplement powder.

2. Traditional and Historical Use

Lysine alpha-ketoisocaproate as a defined chemical entity has no pre-modern ethnobotanical or traditional medicine history, as it was not isolated or characterized until the mid-twentieth century. Its development is firmly rooted in the scientific and clinical medicine tradition of the latter half of the twentieth century.

The beneficial effect of essential amino acid alpha-keto acid analogs along with a low-protein diet in treating chronic kidney disease was first described in the 1970s and the treatment is still used. Pioneering clinical research in the 1960s and 1970s by investigators including Mackenzie Walser at Johns Hopkins University demonstrated that providing keto analogues of essential amino acids could support nitrogen balance in patients with severe renal insufficiency while dramatically reducing the nitrogen load they had to excrete. The study of keto-analogues combined with protein restriction started since 1967; Richards et al. suggested that a supply of keto-analogues averted the harmful effect produced by the metabolisms of sulphur and phosphorus contained in natural foods.

Three mixtures containing varying proportions of threonine, tyrosine, and the ornithine, lysine, and histidine salts of branched-chain keto acids have been tested as dietary supplements to a 20- to 25-g mixed-quality protein diet in patients with severe chronic uremia; two of the three supplements improved the abnormalities of plasma amino acid concentrations, and slowed or arrested progression of renal insufficiency.

Parallel to the renal application, clinical researchers in the early 1980s investigated whether KIC salts could serve as nitrogen-sparing nutritional agents for critically ill and postoperative patients. The ability of tissues to re-aminate leucine from supplemental alpha-ketoisocaproate has been clinically exploited as a means to treat muscle wasting in acutely traumatized and critically ill patients, while reducing their nitrogen load. This clinical use — supplementing critically ill or post-surgical patients — represents the first deliberate, documented therapeutic application of the compound in human medicine.

Later, the use of Lys-KIC and related keto acid salts as components of multi-ingredient renal nutritional formulas became codified in clinical dietetics practice. These dietary supplements are preferably administered in conjunction with relatively low protein (20 to 30 grams per day) diets additionally supplemented with B vitamins, ascorbic acid, and calcium, such as calcium carbonate or another calcium salt.

3. Key Constituents, Active Compounds, and Mechanisms of Action

Dual-Component Nature of the Salt

When ingested or dissolved, lysine alpha-ketoisocaproate dissociates into two biologically active components that exert independent physiological effects: L-lysine (an essential amino acid critical for protein synthesis, collagen formation, and carnitine biosynthesis) and alpha-ketoisocaproate (a leucine keto-analogue with pleiotropic metabolic effects). The sections below address the known mechanisms of α-KIC in particular.

Transamination to Leucine

In the accepted description of leucine metabolism, leucine is first transaminated to its ketoacid, alpha-ketoisocaproate (KIC); KIC then enters the mitochondria and is decarboxylated to isovaleryl-CoA by the branched-chain ketoacid dehydrogenase. Importantly, this process is reversible. Tissues can re-aminate α-KIC back to leucine, utilizing nitrogen that would otherwise be excreted as urea. The enzyme catalyzing this reversible step is branched-chain aminotransferase (BCAT2) in skeletal muscle. α-Ketoisocaproic acid (KIC, the ketoacid of leucine) suppresses insulin-stimulated glucose transport in L6 myotubes; this effect is attenuated when branched-chain aminotransferase 2 (BCAT2), the enzyme that catalyzes the reversible conversion of leucine into KIC, is depleted.

Stimulation of Skeletal Muscle Protein Synthesis via mTORC1 and eIF4E

Alpha-KIC shares with leucine the ability to act as a nutrient signal that activates translational initiation pathways in skeletal muscle. Administration of leucine and KIC resulted in greater (P < 0.006) phosphorylation of eukaryotic initiation factor (eIF) 4E binding protein-1 (4E-BP1); protein synthesis in skeletal muscle was greater (P < 0.02) in leucine- and KIC-infused pigs than in those in the control group. These results suggest that the ability of leucine to act as a nutrient signal to stimulate skeletal muscle protein synthesis is specific for leucine and/or its metabolite, KIC.

Additionally, α-ketoisocaproic acid (KIC), an obligatory metabolite of leucine, stimulated mTORC1 signaling but suppressed insulin-stimulated glucose transport (−34%, P < 0.05) in an mTORC1-dependent manner. This finding highlights a dual and context-dependent action of KIC on cellular metabolism.

Conversion to Beta-Hydroxy-Beta-Methylbutyrate (HMB)

An alternative minor metabolic pathway for α-KIC exists in the cytosol. This alternate oxidative pathway occurs in the cytosol and involves oxidation of KIC to beta-hydroxy-beta-methylbutyrate (HMB) by the enzyme KIC-oxygenase. HMB is itself a well-studied compound known to promote muscle protein synthesis and reduce protein breakdown. This pathway means that exogenous α-KIC can serve as a precursor to HMB, linking the two agents biochemically.

Anti-Catabolic and Nitrogen-Sparing Effects

Enhancing muscle recovery following trauma occurs not simply by administering oral or intravenous leucine alone, but instead it responds to increasing the steady-state concentration of alpha-ketoisocaproic acid; this anabolic ketoacid is a major factor in reducing protein catabolism, stimulating muscle synthesis, and sparing glucose oxidation, while stimulating insulin release. The nitrogen-sparing effect is explained principally by the capacity of α-KIC to accept an amino group during re-amination to leucine, thereby recycling nitrogen that would otherwise be lost to urea synthesis.

Attenuation of Muscle Atrophy via Akt-FoxO3a-Myostatin Axis

More recently, mechanistic research has illuminated pathways through which α-KIC combats pathological muscle wasting. KIC attenuates cancer cachexia-induced muscle atrophy by inducing FoxO3a nuclear export, and this phenomenon is regulated in an Akt-dependent manner; the results reveal an Akt-FoxO3a-myostatin axis underlying muscle atrophy in cancer cachexia, suggesting that KIC, through the Akt-FoxO3a pathway, is a potential therapeutic agent for mitigating muscle atrophy.

At the molecular level, KIC suppressed mRNA expression of myostatin, a key regulator of muscle atrophy, more effectively than L-leucine (−26.37 ± 4.11%, p < 0.01); KIC enhanced protein turnover in C2C12 myotubes and maintained 50% cell viability at high concentrations; following conditioned media treatment, KIC suppressed MuRF1 and MAFbx expression in a myostatin-dependent manner, thereby reducing their polyubiquitination.

Insulinotropic Effects

Alpha-KIC has documented effects on pancreatic beta-cell metabolism. KIC by itself is not a mitochondrial substrate for ATP production; KIC must transaminate with glutamate or glutamine to yield alpha-ketoglutarate and leucine; since leucine allosterically activates glutamate dehydrogenase, which also produces alpha-ketoglutarate, the insulinogenic effect of KIC may in part be due to the intramitochondrial generation of alpha-ketoglutarate.

Role in BCAA Catabolism

The first step of BCAA catabolism is mediated by branched chain aminotransferase, Bcat1 or Bcat2, which transfers the amino group from valine, isoleucine, or leucine to alpha-ketoglutarate, producing the corresponding α-ketoacids, including α-ketoisocaproate from leucine; BCKDC then oxidizes these α-ketoacids to their corresponding acyl-CoA products. BCAA oxidation flux is particularly high in skeletal muscle, where it plays a key role in human health; dysregulated BCAA metabolism is associated with many diseases, including cardiovascular disease and metabolic disorders such as diabetes mellitus and obesity.

4. Scientific Evidence by Area of Use

4.1 Chronic Kidney Disease (CKD) and Uremia

This is the most extensively researched clinical application for keto acid supplements including Lys-KIC. The rationale is that ketoacid analogues of essential amino acids provide several potential advantages for people with advanced chronic kidney disease; because KAs lack the amino group bound to the alpha carbon of an amino acid, they can be converted to their respective amino acids without providing additional nitrogen.

It has been well established that a diet with 0.3 to 0.4 g of protein per kilogram per day that is supplemented with KAs and EAAs reduces the generation of potentially toxic metabolic products, as well as the burden of potassium, phosphorus, and possibly sodium, while still providing calcium.

A recent meta-analysis reported that essential amino acid alpha-keto acid analogs can delay the progression of chronic kidney disease by limiting hyperphosphatemia, preventing hyperparathyroidism, and improving the control of arterial blood pressure and malnutrition; essential amino acid alpha-keto acid analogs are recommended in the treatment of stages 3 to 5 chronic kidney disease.

A supply of keto-analogues averted the harmful effect produced by the metabolisms of sulphur and phosphorus contained in natural foods; more researchers confirmed that the combined use of keto-analogues with protein restriction reduced the metabolic wastes or toxicities in CKD patients.

Lys-KIC does not appear in isolation in most CKD clinical trials; instead, it is a component of multi-ingredient keto acid/essential amino acid (KA/EAA) supplements. In the widely cited foundational clinical research, three mixtures containing varying proportions of threonine, tyrosine, and the ornithine, lysine, and histidine salts of branched-chain keto acids were tested as dietary supplements to a 20- to 25-g mixed-quality protein diet in patients with severe chronic uremia; two of the three supplements improved the abnormalities of plasma amino acid concentrations and slowed or arrested progression of renal insufficiency; the second supplement, which contained less threonine and lysine, led to subnormal plasma concentrations of these two amino acids and aggravated hypophosphatemia; the third supplement, which also contained a small amount of the hydroxy analogue of methionine, was the most effective in slowing progression; the results emphasize the importance of optimizing the composition of such supplements.

Evidence strength: Moderate to strong for multi-ingredient keto acid mixtures including Lys-KIC in CKD stages 3–5. Well-supported by multiple controlled clinical trials and a meta-analysis. Evidence specifically attributable to the lysine-salt form as distinct from the free acid or other salt forms is limited, as trials uniformly test multi-component blends.

4.2 Muscle Protein Synthesis and Sarcopenia

A landmark double-blind, randomized controlled trial (Fuchs et al., 2019) directly tested branched-chain ketoacid ingestion, including α-KIC as a key component, on muscle protein synthesis rates in vivo in older adults. The aim was to compare the impact of ingesting 6 g BCAA, 6 g BCKA, and 30 g milk protein (MILK) on the postprandial rise in circulating amino acid concentrations and subsequent myofibrillar protein synthesis rates in older males; 45 older males (age: 71 ± 1 y; BMI: 25.4 ± 0.8 kg/m²) were randomly assigned to ingest a drink containing 6 g BCAA, 6 g BCKA, or 30 g MILK.

Ingestion of 6 g BCAA, 6 g BCKA, and 30 g MILK increases myofibrillar protein synthesis rates during the early postprandial phase (0–2 h) in vivo in healthy older males; the postprandial increase following the ingestion of 6 g BCAA and BCKA is short-lived, with higher myofibrillar protein synthesis rates only being maintained following the ingestion of an equivalent amount of intact milk protein.

In mechanistic neonatal animal work, protein synthesis in skeletal muscle was greater (P < 0.02) in leucine- and KIC-infused pigs than in those in the control group; norleucine infusion did not affect muscle protein synthesis or translation initiation factor activation; in liver, neither protein synthesis nor activation of translation initiation factors was affected by treatment.

Evidence strength: Preliminary to moderate. The 2019 Fuchs et al. RCT provides direct human evidence that BCKAs including α-KIC acutely stimulate myofibrillar protein synthesis, but the effect was transient compared with intact protein. Longer-term clinical trials specifically testing Lys-KIC for sarcopenia outcomes are lacking.

4.3 Cancer Cachexia-Associated Muscle Atrophy

A 2025 preclinical study investigated whether KIC could attenuate cancer cachexia-associated muscle wasting using mouse and cell culture models. KIC restored Akt-FoxO3a phosphorylation, leading to improved myotube diameter (+63.8 ± 25.71%, p < 0.05) and fusion index (+51.9 ± 22.6%, p < 0.05); immunofluorescence and nuclear fractionation revealed that KIC reduced FoxO3a nuclear accumulation; conditioned media reduced p-Akt–FoxO3a interaction, which was rescued by KIC. In animal models, KIC administration increased body weight (11.11 ± 8.53%), grip strength (24.76 ± 10.58%), and skeletal muscle mass (p < 0.001) in C26 tumour-bearing mice; protein expression of myostatin in the tibialis anterior muscle (−23.57 ± 12.22%, p < 0.05) and serum (−52.11 ± 3.56%, p < 0.001) was lower in KIC-treated mice; KIC increased the mean fibre cross-sectional area in TA (24.51 ± 14.14%, p < 0.01).

Evidence strength: Preliminary — animal and in vitro only. No human clinical trials on cancer cachexia specifically testing Lys-KIC have been published as of the evidence base underlying this article.

4.4 Critical Illness, Postoperative Nitrogen Sparing, and Muscle Wasting

Early human studies tested alpha-ketoisocaproate (free acid or salt form, often orally or intravenously) for nitrogen sparing in fasting or postoperative subjects. In one foundational 1981 study published in the Journal of Clinical Investigation, Mitch, Walser, and Sapir compared nitrogen sparing by leucine versus alpha-ketoisocaproate in fasting obese humans and found that α-KIC induced comparable or superior nitrogen-sparing effects. Traumatized, critically ill hospital patients with eroding muscle mass and nitrogen wasting have been aided with adjuvant dietary intervention using analogs of branched-chain ketoacids and dibasic acids; enhancing muscle recovery following trauma occurs not simply by administering oral or intravenous leucine alone, but instead it responds to increasing the steady-state concentration of alpha-ketoisocaproic acid; this anabolic ketoacid is a major factor in reducing protein catabolism, stimulating muscle synthesis, and sparing glucose oxidation, while stimulating insulin release.

Evidence strength: Moderate for nitrogen-sparing effects demonstrated in controlled human studies in the early 1980s. These trials were small, often used intravenous administration, and employed free-acid or non-lysine-salt forms of α-KIC. Evidence specifically for oral Lys-KIC in modern clinical settings is extrapolated from this older work.

4.5 Hemodialysis: Reducing Amino Acid Losses

A 2023 randomized controlled crossover trial investigated whether branched-chain ketoacid co-ingestion with protein could lower amino acid oxidation during hemodialysis. This study referenced the use of BCKAs including α-KIC as a validated strategy to improve nitrogen economy in dialysis patients. Branched-chain amino acid and branched-chain ketoacid ingestion increases muscle protein synthesis rates in vivo in older adults (double-blind, randomized trial, Am J Clin Nutr, 2019, 110(4): 862–872).

Evidence strength: Emerging. The dialysis-specific application of BCKAs is supported by the broader clinical literature on KA/EAA supplementation in end-stage renal disease, but specific trials testing Lys-KIC in hemodialysis patients as the primary intervention remain limited.

4.6 Glucose Metabolism and Insulin Sensitivity

Mechanistic cell culture studies demonstrate a complex bidirectional effect of α-KIC on glucose metabolism. α-Ketoisocaproic acid (KIC) stimulated mTORC1 signaling but suppressed insulin-stimulated glucose transport (−34%, P < 0.05) in an mTORC1-dependent manner; the effect of KIC on insulin-stimulated glucose transport was abrogated in cells depleted of BCAT2, the enzyme that catalyzes the reversible transamination of KIC to leucine; the conclusion is that although KIC can modulate muscle glucose metabolism, this effect is likely a result of its transamination back to leucine; therefore, limiting the availability of leucine, rather than those of its metabolites, to skeletal muscle may be more critical in the management of insulin resistance.

The insulinotropic properties of α-KIC are mediated partly through beta-cell metabolism: KIC must transaminate with glutamate or glutamine to yield alpha-ketoglutarate and leucine; since leucine allosterically activates glutamate dehydrogenase, which also produces alpha-ketoglutarate, the insulinogenic effect of KIC may in part be due to the intramitochondrial generation of alpha-ketoglutarate.

Evidence strength: Preliminary — primarily in vitro cell culture and animal data. No controlled human clinical trials specifically examining Lys-KIC for glycemic outcomes have been identified in the available literature.

4.7 Hepatic Disease

Alpha-ketoisocaproate has been studied in the context of liver disease, both as a potential nutritional intervention and as a metabolic probe. Organic salts of basic L-amino acids and alpha-keto-analogs of branched chain essential amino acids are known to be useful in the treatment of hepatic disorders and for treatment of renal failure. In hepatic cirrhosis, the metabolism of KIC is profoundly altered: results indicate a dramatic modification of KIC metabolism in the cirrhotic liver; its uptake by the liver is decreased and its incorporation into proteins is increased via an enhancement of transamination to leucine, probably as a consequence of an inhibition of branched-chain keto acid dehydrogenase.

Evidence strength: Preliminary — based on isolated-organ perfusion studies, not controlled human trials specifically testing Lys-KIC in hepatic disease populations.

5. Body Systems and Health Areas Associated with Lysine Alpha-Ketoisocaproate

Skeletal Muscle: Stimulation of protein synthesis via mTORC1/eIF4E; anti-catabolic effects through suppression of the MuRF1/MAFbx ubiquitin-proteasome pathway and myostatin downregulation; nitrogen recycling to leucine.
Renal System: Nitrogen sparing enabling very low-protein diets in CKD; reduction of urea generation, phosphorus load, and uremic toxins; potential to slow CKD progression when combined with protein restriction.
Metabolic/Endocrine: Insulin secretion modulation via beta-cell glutamate dehydrogenase activation; complex interactions with insulin-stimulated glucose transport.
Hepatic System: Altered KIC metabolism in cirrhosis; hepatic role in ketogenesis and transamination of the keto acid.
Neurological System: α-KIC is a notable biomarker in maple syrup urine disease; at pathologically elevated levels (as in MSUD) it contributes to neurological toxicity (see Safety section).
Nutritional Protein Metabolism: Serves as a nitrogen-free precursor to leucine, enabling amino acid provision without nitrogen load in nitrogen-restricted patients.

6. Dosage Forms and Dosages Reported in Studies

Forms

Lysine alpha-ketoisocaproate has been studied as:

A component of multi-ingredient oral tablet formulations (e.g., KA/EAA blends used in CKD) administered with each meal.
An intravenous infusion (as the free acid or calcium salt) in critical care and metabolic tracer studies.
An oral powder or tablet in sports nutrition and body composition research.

Dosages Reported in the Scientific Literature

Animal (neonatal pig) infusion study (Escobar et al., 2010): KIC infusion dose of 0 or 400 μmol·kg⁻¹·h⁻¹ for 60 min was evaluated for effects on protein synthesis and activation of translation initiation factors in piglets.
Human RCT on muscle protein synthesis in older adults (Fuchs et al., 2019): The study compared the impact of ingesting 6 g BCAA, 6 g BCKA, or 30 g milk protein on myofibrillar protein synthesis rates in 45 older males (age 71 ± 1 y).
CKD multi-ingredient supplement studies: Dietary supplements containing mixed keto acid salts are preferably administered in conjunction with relatively low protein (20 to 30 grams per day) diets. Specific per-tablet dosing of Lys-KIC varies by formulation; in the widely studied multi-component tablet, the full daily dose of the tablet mixture is typically administered as tablets taken with each meal.
Chronic uremia clinical studies (Walser et al.): Supplements containing ornithine, lysine, and histidine salts of branched-chain keto acids were given as supplements to a 20- to 25-g mixed-quality protein diet in patients with severe chronic uremia.
Cancer cachexia mouse model (2025): KIC administration increased body weight, grip strength, and skeletal muscle mass (p < 0.001) in C26 tumour-bearing mice. (Exact mg/kg dose available in the source paper; not extrapolated here for human use.)

No universally agreed-upon human dosage for standalone Lys-KIC supplementation has been established by a regulatory body or pharmacopeial monograph.

7. Safety Considerations and Interactions

General Safety Profile at Physiological Doses

At nutritional and clinically used supplemental doses, alpha-ketoisocaproate and its lysine salt have a generally acceptable tolerability record in human clinical research, particularly within the decades of use in CKD and postoperative nutrition. Branched chain keto-acids and alpha-ketoisocaproate in particular are known to exhibit a protein sparing effect in patients with chronic renal failure; that is, branched chain keto-acids reduce urinary nitrogen loss; these keto-acids have been used to improve the nitrogen balance in patients suffering from a number of different nitrogen wasting conditions.

Neurotoxicity at Pathologically Elevated Concentrations

A critical safety consideration arises from the pathology of maple syrup urine disease (MSUD), in which the branched-chain alpha-keto acid dehydrogenase complex (BCKDH) is deficient, causing extreme accumulation of BCAAs and their keto acids including α-KIC. The metabolic blockage results in tissue accumulation and high urinary excretion of the branched-chain amino acids leucine, isoleucine and valine, as well as alloisoleucine, and their respective BCKA including α-ketoisocaproic acid; affected patients usually manifest acute episodes of encephalopathy associated with seizures, coma and life-threatening cerebral edema in the first weeks of life, which is followed by progressive neurological deterioration with motor delay, ataxia, intellectual disability and psychiatric symptoms.

Mechanistically, there is evidence that α-ketoisocaproic acid, an intermediate in the metabolism of leucine, is a major neurotoxin contributing to the encephalopathic syndrome seen in MSUD. An influx of alpha-ketoisocaproic acid transported by a monocarboxylate transporter (MCT) across the blood-brain barrier may deplete glutamate and glutamine in astrocytes through transamination; glutamate levels are maintained in the brain by BCAA metabolism functions and if not properly maintained can lead to neurological problems that are seen in MSUD individuals. These toxicity observations are relevant to the genetic disorder context of extreme accumulation — not to oral supplementation in individuals with normal BCKDH function.

Notably, in animal experiments designed to dissect MSUD pathophysiology, rats received unilateral intrastriatal injections of α-ketoisocaproic acid (KIC, 8 μmol), α-ketoisovaleric acid (KIV, 8 μmol), α-keto-β-methylvaleric acid (KMV, 6 μmol), or NaCl; KIV elicited clonic convulsions in a dose-response manner, whereas KIC and KMV did not induce seizure-like behavior. This finding suggests that of the MSUD metabolites, α-KIC is less acutely convulsant than α-KIV under these specific experimental conditions, though chronic high accumulation remains neurotoxic.

Relative Bioavailability and Salt Comparison

Comparative animal nutrition research has examined how the identity of the basic amino acid carrier (lysine vs. ornithine vs. histidine) affects the bioavailability of the keto acid moiety. The analog of valine tested was alpha-ketoisovalerate as the ornithine (KIV-Orn), lysine (KIC-Lys) and histidine (KIC-His) salts with resulting efficacies of 50%, 38%, and 49%, respectively; slope-ratio efficacies of KIC-Orn and KIC-His were statistically similar and efficacy of KIC-Lys was inferior to both KIC-Orn and KIC-His. This suggests that, at least for certain keto acid analogues, the lysine salt form may deliver the keto acid component with somewhat lower bioavailability than the ornithine salt, though this comparison was made for a specific analogue (KIV) and direct comparison studies for Lys-KIC specifically are limited.

Potential Interaction with Glucose Metabolism and Insulin Sensitivity

As described under mechanisms, α-KIC suppresses insulin-stimulated glucose transport in skeletal muscle cells in vitro. Because liver and muscle activity of branched-chain keto acid dehydrogenase (BCKDH), the enzyme that irreversibly catabolizes KIC, is diminished in obesity and T2DM, mechanisms that prevent KIC accumulation may have therapeutic potential for the management of insulin resistance. This raises a theoretical concern that supplemental α-KIC might exacerbate insulin resistance in individuals with obesity or type 2 diabetes, though this has not been directly tested in human clinical trials.

CKD Formulation Optimization Considerations

The composition of the multi-ingredient supplement containing Lys-KIC materially affects clinical outcomes. The second supplement tested (in severe chronic uremia), which contained less threonine and lysine, led to subnormal plasma concentrations of these two amino acids and aggravated hypophosphatemia; the results emphasize the importance of optimizing the composition of such supplements. This underscores that the salt form delivers not only the keto acid moiety but also L-lysine, and inadequate amounts of either component can produce metabolic imbalances in clinically ill patients.

Relationship to Maple Syrup Urine Disease

Individuals with MSUD or partial BCKDH deficiency cannot safely metabolize α-KIC through the normal decarboxylation pathway. Maple syrup urine disease (MSUD) is an inherited error in the metabolism of branched-chain amino acids caused by a severe deficiency of the branched-chain alpha-ketoacid dehydrogenase (BCKDH) complex, which ultimately leads to neurological disorders. In such individuals, supplemental α-KIC would be expected to accumulate to neurotoxic levels, representing a frank contraindication.

References

Health Conditions

Health conditions that Lysine alpha-ketoisocaproate may help support.

No conditions available.

Body Systems

Body systems that Lysine alpha-ketoisocaproate may help support.

No body systems available.