Ingredients4-Hydroxyisoleucine (abbreviated 4-HIL or 4-OHIle) is a non-proteinogenic, branched-chain α-amino acid of plant origin. Its systematic IUPAC name is (2S,3R,4S)-2-amino-4-hydroxy-3-methylpentanoic acid, and it carries the CAS number 55399-93-4. It is classed as a non-proteinogenic α-amino acid. The compound is also commonly designated by the synonyms 4-Hydroxy-L-isoleucine and HIL. 4-Hydroxyisoleucine is a peculiar amino acid extracted from fenugreek seeds and never found in mammalian tissues.
Stereochemistry. 4-HIL is a molecule with three chiral centers and is present in fenugreek seeds in the form of two diastereoisomers: the major one with the (2S,3R,4S) configuration, representing about 90% of the total 4-HIL content in the seeds, and a minor diastereoisomer. The predominant biologically active 4-hydroxyisoleucine is the 2S,3R,4S stereoisomer. The absolute configuration was restudied and corrected as being (2S,3R,4S) by Alcock et al. in 1989.
Natural source. 4-Hydroxyisoleucine is an atypical branched-chain amino acid derived from fenugreek (Trigonella foenum-graecum). Trigonella foenum-graecum, commonly known as fenugreek, is an annual herbaceous plant. Fenugreek is widespread in regions of Asia, Africa, and Europe. 4-Hydroxyisoleucine is a unique amino acid which is not found in many plants. 4-HIL accounts for about 80% of the total free amino acid content in fenugreek seeds.
Concentration in seeds. 4-HIL is particularly abundant in fenugreek seeds, with reported concentrations of 0.015%â0.4%. However, levels vary significantly by genotype and growing conditions. In a study across 31 diverse genotypes, 4-hydroxyisoleucine concentrations ranged from 0.41% to 1.90% of seed dry weight. During germination of fenugreek seeds, the concentration of 4-hydroxyisoleucine rose by 33.3%.
Biosynthesis. 4-Hydroxyisoleucine can be detected when isoleucine is incubated with a cell-free extract from etiolated fenugreek seedlings in the presence of various cofactors. Because the reaction was dependent on the presence of FeÂČâș, 2-oxoglutarate, ascorbate, and oxygen, a 2-oxoacidâdependent dioxygenase biosynthetic pathway was suggested. It is synthesised from isoleucine.
Commercial forms and preparations. 4-Hydroxyisoleucine is widely available in the nutraceutical market as fenugreek seed extract formulations. The synthesis of 4-HIL on a large scale is possible using fermentation methods involving the isolation of the L-isoleucine dioxygenase gene from Bacillus thuringiensis, which can yield a greater quantity of 4-HIL than conventional methods (82% attained with fermentation vs. 0.6â39% with conventional methods). Supplement products typically consist of standardized fenugreek seed extracts with a defined 4-HIL content, delivered as capsules or tablets. The extracted natural active compound is highly hygroscopic.
Fenugreek (known as "Methi") is one of the oldest medicinal plants in history; a description of this plant was found on the Ebers Papyrus of 1550 BC in Egypt, one of the two oldest maintained medical documents. Fenugreek seeds were discovered in the tomb of Tutankhamun, reflecting their importance in ancient Egyptian culture.
In traditional Indian systems of medicine such as Ayurveda, Unani, and Siddha, fenugreek occupies a prominent position due to its diverse therapeutic applications. In Ayurveda, fenugreek is well described in the name "Methika" with its therapeutic potentials as medicine, used as a single herb and also as part of many poly-herbal combinations. Fenugreek holds a significant place in the Ayurvedic Pharmacopeia, particularly for managing conditions related to obesity and diabetes (Prameha) and as an enhancer of metabolism. In Ayurveda, fenugreek is used to stimulate digestion, balance blood sugar, and enhance reproductive health; its warming nature is said to ignite "Agni," or digestive fire, making it an effective remedy for sluggish metabolism and gas.
Fenugreek has, through the ages, been used for a variety of health conditions such as diabetes, fever, anorexia, cough, bronchitis, swellings, burns, abscesses, ulcers, and other digestive issues, as well as to treat menopausal symptoms, induce childbirth, and stimulate milk production in breastfeeding women.
Ancient Greek medical practitioner Hippocrates recognized fenugreek's medicinal properties and utilized it as an anti-inflammatory spice. Romans turned to fenugreek to treat various ailments, including fever, respiratory issues, and wounds. In India, known as "Chandrika" or "methika," fenugreek found its place in Ayurvedic medicines, while Chinese practitioners utilized it in Traditional Chinese Medicine, particularly for kidney yang deficiency.
Fenugreek and products thereof are traditionally used as a demulcent, laxative, and lactation stimulant. Fenugreek and its products have been proposed for treatment of conditions as diverse as alopecia, arthritis, cancer, diabetes, gastro-intestinal disorders, high cholesterol, inducing childbirth, infections, inflammation, and wound healing.
It is important to note that there is little traditional use specifically attributed to 4-hydroxyisoleucine itself, as traditional uses of fenugreek involve the whole seed. The isolation, identification, and pharmacological characterization of 4-HIL as a discrete compound are products of modern phytochemistry.
Fenugreek seeds are a chemically complex matrix. In addition to 4-HIL, they contain the alkaloid trigonelline, steroidal saponins (notably diosgenin), and galactomannans (soluble dietary fiber). Fuller and Stephens (2015) summarised the evidence on the physiological effects of three bioactive compounds of fenugreek: diosgenin, 4-hydroxyisoleucine (4-OHIle), and the soluble dietary fibre fraction, with emphasis on the biological mechanisms of action underlying metabolic syndrome. Trigonelline, the alkaloid present in fenugreek seeds, has demonstrated anti-diabetic and analgesic activity. The water-soluble fiber rich in galactomannans has anti-diabetic and lipid-lowering activities.
4-HIL itself stands out for its insulinotropic profile. 4-OHIle is a branched-chain amino acid only present in plants. The peculiar nonprotein branched amino acid 4-hydroxyisoleucine has been described as an efficient compound in the regulation of insulin secretion.
The most thoroughly characterized mechanism of 4-HIL is its ability to potentiate insulin secretion in a strictly glucose-dependent manner. In the landmark 1998 paper by Sauvaire and colleagues published in Diabetes, 4-hydroxyisoleucine was characterized as a new insulinotropic compound. This amino acid had been extracted and purified from fenugreek seeds. 4-Hydroxyisoleucine increases glucose-induced insulin release, in the concentration range of 100 ”mol/l to 1 mmol/l, through a direct effect on isolated islets of Langerhans from both rats and humans.
The stimulating effect of 4-hydroxyisoleucine was strictly glucose dependent: ineffective at low (3 mmol/l) or basal (5 mmol/l) glucose concentrations, the amino acid potentiated the insulin secretion induced by supranormal concentrations of glucose. In the isolated perfused rat pancreas: (1) the pattern of insulin secretion induced by 4-hydroxyisoleucine was biphasic; (2) this effect occurred in the absence of any change in pancreatic α- and Ύ-cell activity; and (3) the more glucose concentration was increased, the more the insulin response was amplified.
Moreover, 4-hydroxyisoleucine did not interact with other agonists of insulin secretion (leucine, arginine, tolbutamide, glyceraldehyde). This amino acid appears to act only on pancreatic beta cells, because the levels of somatostatin and glucagon were not altered.
The glucose-dependence of the insulin response is considered pharmacologically advantageous. The insulinotropic properties of 4-OHIle suggest its potential as an antidiabetic pharmacological compound. This could potentially overcome a common drawback of sulfonylureas, which carry the risk of inducing hypoglycaemia.
Beyond pancreatic effects, 4-HIL also acts peripherally on insulin signaling pathways in muscle, adipose, and hepatic tissue. In addition to stimulating insulin secretion, 4-hydroxyisoleucine reduced insulin resistance in muscle and/or liver by activating insulin receptor substrate-associated phosphoinositide 3 (PI3) kinase activity.
4-Hydroxyisoleucine has been shown to activate the phosphatidylinositol 3-kinase (PI3K)/protein kinase B (Akt) pathway, a central cascade in insulin signaling. Activation of this pathway leads to the translocation of glucose transporter 4 (GLUT4) to the plasma membrane in muscle and adipose cells, thereby increasing glucose uptake from the bloodstream.
In skeletal muscle L6 myocytes, an increase in glucose uptake, phosphorylation of Akt (pAkt) and PI3K, and increased GLUT4 expression have been reported; while in insulin-resistant 3T3-L1 adipocytes and L6 myocytes, the increased glucose uptake and suppression of inflammatory (TNF-α) markers were coupled with increased levels of pIRS-1, PI3K, pAkt, and reduced levels of nuclear factor-ÎșB (NF-ÎșB), JNK1/2, and p38 MAPK.
4-HIL exerts a multifaceted mechanism of action: (1) it improves glucose uptake by GLUT4 translocation towards the plasma membrane in muscle cells; (2) it inhibits free radical production; and (3) it promotes negative regulation of TNF-α.
4-HIL also activates AMP-activated protein kinase (AMPK), a key cellular energy sensor. AMPK activation enhances glucose uptake and fatty acid oxidation, contributing to improved insulin sensitivity and overall metabolic health.
The beneficial effects of 4-OHIle are related to the regulation of blood glucose, the reduction of lipotoxicity by decreasing plasma triglycerides, FFAs, and total cholesterol, and the improvement of liver function. The mechanism of action is related to a reduced activation of JNK and NF-ÎșB activity.
4-HIL has been shown to improve the secretion of glucose-dependent insulin from pancreatic cells, which is mediated by increasing Akt phosphorylation and suppressing activation of JNK, MAPK, and NF-ÎșB, leading to reduced levels of plasma glucose, triglyceride, free fatty acid, and cholesterol.
In a high-fat diet mouse model, 4-HIL intervention reduced weight gain, liver steatosis, and dyslipidemia; moreover, it increased systemic insulin sensitivity and improved insulin resistance. After administration, the accumulation of M1-like CD11câș macrophages and inflammation in the liver and adipose tissue were reduced. 4-HIL also reduced the proportion of CD11câș macrophages among bone marrow-derived macrophages induced in vitro. These observations demonstrate a role of 4-HIL in insulin resistance in hepatocytes and adipocytes. 4-HIL inhibits obesity-related insulin resistance by reducing inflammation and regulating the state of M1/M2 macrophages.
Previous studies have demonstrated that 4-HI dose-dependently promotes GLP-1-dependent cAMP production and GLP-1R endocytosis. Furthermore, 4-Hydroxyisoleucine enhances insulin receptor-ÎČ and insulin receptor substrate-1 tyrosine phosphorylation.
The greatest body of experimental evidence for 4-HIL concerns its effects on blood glucose and insulin dynamics. The foundational mechanistic work was conducted in vitro and in animal models, with a more limited number of human pharmacokinetic and clinical investigations.
In vitro evidence. 4-Hydroxyisoleucine increases glucose-induced insulin release, in the concentration range of 100 ”mol/l to 1 mmol/l, through a direct effect on isolated islets of Langerhans from both rats and humans. The compound could increase the glucose-induced insulin release from isolated islets of Langerhans in the concentration range of 100 ”M to 1 mM. Its insulin-releasing effect was dependent on glucose concentration: ineffective at low (3 mmol/L) or basal (5 mmol/L) glucose levels and exhibiting a potentiation effect when induced by supranormal (6.6â16.7 mmol/L) concentrations of glucose.
In vivo animal evidence. A study published in the American Journal of PhysiologyâEndocrinology and Metabolism was designed to investigate whether 4-OH-Ile could exert in vivo insulinotropic and antidiabetic properties. Intravenous or oral glucose tolerance tests (IVGTTs and OGTTs) were performed in normal animals and in a type II diabetes rat model. During IVGTT in normal rats or OGTT in normal dogs, 4-OH-Ile at 18 mg/kg improved glucose tolerance. A 50 mg/kg dose of 4-HI increased insulin secretion and had anti-diabetic effects in a rat model of non-insulin-dependent diabetes.
In a model of type 2 diabetes in rats, (2S,3R,4S)-4-OH-Ile was shown to be active and partly corrected hyperglycemia and glucose intolerance.
Human pharmacokinetic data. A study aimed to elucidate the oral pharmacokinetics (PK) of 4-HIL in healthy human volunteers to standardize its dose and dosing regimen. Twelve healthy volunteers received a single oral administration of 150 mg of 4-HIL as fenugreek seed extract tablets, with blood samples collected at various time points within 24 h and plasma levels quantified using liquid chromatography-tandem mass spectrometry. The derived mean EC50 of 4-HIL, needed to reduce blood glucose, was 1.50 ± 0.31 ”g/mL. The PK simulation study indicated that daily intake of 450 mg 4-HIL in all three tested dosing regimens maintained EC50 levels for more than 18 h for glucose-lowering effects.
Clinical evidence (fenugreek extracts standardized for 4-HIL). Small clinical trials and pilot studies in humans with type 2 diabetes and impaired glucose tolerance have reported improvements in fasting blood glucose and insulin levels after supplementation with fenugreek seed extracts standardized for 4-hydroxyisoleucine content. In studies of rats and humans, T. foenum-graecum improved laboratory parameters associated with renal dysfunction and dyslipidemia, increased levels of antioxidants and hormones altered in patients with type 2 diabetes mellitus, and decreased fasting blood glucose, 2-h postprandial plasma glucose, and glycated hemoglobin.
Evidence quality assessment. While the available studies are promising, they are generally small in scale and of short duration, and larger, well-controlled clinical trials are needed to fully establish efficacy and safety in humans. Robust, well-powered, long-term clinical trials specifically evaluating purified 4-hydroxyisoleucine in metabolic syndrome are lacking. While the results are promising and mechanistically plausible, the overall quality and quantity of evidence currently rates as low to moderate. In short, current evidence is strongest at the in vitro and animal levels, with preliminary but not definitive human data.
From the seeds of T. foenum-graecum, 4-hydroxyisoleucine was shown to significantly decrease plasma triglyceride levels by 33% (P<0.002), total cholesterol by 22% (P<0.02), and free fatty acids by 14%, accompanied by an increase in HDL-C/TC ratio by 39% in a dyslipidemic hamster model. This study established 4-hydroxyisoleucine as an antidyslipidemic agent, which had previously been reported only as an antidiabetic agent.
A meta-analysis by Gong et al. (2016) regarding the overall effects of fenugreek on hyperglycaemia and hyperlipidaemia in prediabetes and diabetes found that fenugreek showed hypoglycaemic effects and total cholesterol-lowering efficacy; however, the effects on triglycerides, LDL cholesterol, and high-density lipoprotein cholesterol (HDL-C) were not confirmed, and further studies are needed. Evidence for anti-dyslipidemic effects of purified 4-HIL specifically (as opposed to whole fenugreek preparations) is primarily limited to preclinical models.
4-OHIle has been reported as a glucose-dependent insulinotropic compound through its direct effect on pancreatic islets and its insulin-sensitising effect on muscle, adipose, and liver tissue. 4-Hydroxyisoleucine also reduced body weight in diet-induced obese mice.
Cell culture experiments revealed that 4-HIL increased GLUT4 protein expression markedly in a dose-dependent manner; a 13.6-fold increase was observed in the 4-HIL treatment group compared with the insulin-resistant control group.
In a high-fat diet mouse study, 4-HIL intervention reduced weight gain, liver steatosis, and dyslipidemia; moreover, it increased systemic insulin sensitivity and improved insulin resistance in mice. These are animal-model findings, and their direct translation to human obesity management requires dedicated clinical trials that have not yet been completed.
One research group established an insulin-resistant HepG2 (liver) cell line and determined the molecular mechanisms for 4-OHIle in insulin resistance. Two potential mechanisms were described: a negative regulation of TNF-α production with an improvement in insulin sensitivity, and increased expression of p-IRS-1 and GLUT4 in the insulin-signalling pathway.
Beneficial effects of 4-OHIle are related to the regulation of blood glucose, the reduction of lipotoxicity by decreasing plasma triglycerides, FFAs, and total cholesterol, and the improvement of liver function. Evidence specific to liver outcomes in humans is not yet available from dedicated clinical trials.
More recently, researchers have investigated neurological dimensions of 4-HIL. 4-HI has demonstrated effectiveness as a treatment for post-brain haemorrhage and neurochemical alterations associated with neurological impairment. Researchers have investigated 4-HI's antidepressant-like effects in mice models of depression at doses of 10, 30, or 100 mg/kg. Previous research found that 4-HI enhanced serotonin turnover in the brain. These represent early-stage, preclinical observations with no clinical data in humans.
The following dosages are reported from specific studies only; they are not recommendations and should not be interpreted as such.
Future investigations are needed to validate the optimized 4-HIL dosage of 450 mg per day from fenugreek formulations in clinical contexts, aiming to rationalize its efficacy in patients with diabetes or metabolic syndrome.
Not a single mortality or treatment-related adverse sign was noted during acute (â€2,000 mg/kg) and sub-chronic (90-day repeated doses of 250/500/1,000 mg per kg body weight with a 28-day recovery period) toxicity studies. The oral median lethal dose (LD50) was >2,000 mg/kg in the acute oral toxicity study.
The Ames toxicity score indicated safety of 4-hydroxyisoleucine, with a score of 0.01, where category 1 drugs are classified as Ames positive (toxic) and category 0 represents Ames negative (non-toxic). The risk of oral toxicity is low. The rat oral acute toxicity score is 0.11, which classifies 4-hydroxyisoleucine in category 0 (low-toxicity).
The absence of acute toxicity or genotoxicity suggests that this amino acid has a potential role as a natural product for the treatment of obesity and insulin resistance.
4-Hydroxyisoleucine is compliant with important drug-like physicochemical properties and drug-ability rules including Lipinski's, Pfizer, and GlaxoSmithKline (GSK) rules. Pharmacokinetically, it has been predicted to have satisfactory cell permeability. Bloodâbrain barrier permeation may add central nervous system effects, while a very slight probability of being a CYP2C9 substrate exists. None of the well-known toxicities were predicted in silico, being congruent with wet lab results, except for a "very slight risk" for respiratory toxicity predicted.
Because 4-HIL potentiates insulin secretion, a theoretically relevant safety concern is excessive blood glucose lowering. However, the glucose-dependence of its insulinotropic mechanism is considered a safety advantage. The effect of 4-hydroxyisoleucine occurred only when the glucose level was elevated to a supraphysiological range. Nevertheless, combinational use with other insulin-stimulating drugs or insulin itself would require attention to hypoglycemia risk.
4-Hydroxyisoleucine did not interact with other known agonists of insulin secretion (leucine, arginine, tolbutamide, glyceraldehyde) in ex vivo pancreatic preparations. However, because 4-HIL influences the same signaling pathways as insulin sensitizers and secretagogues (PI3K/Akt, AMPK), additive or synergistic pharmacodynamic interactions with antidiabetic medications cannot be excluded and have not been formally studied in human trials. A very slight probability of being a CYP2C9 substrate exists, which may theoretically be relevant for drugs metabolized by CYP2C9, though this has not been studied clinically.
The bulk of safety data originates from animal studies and computational predictions. Long-term human safety data for purified 4-HIL supplementation is not yet available from controlled trials. Larger, well-controlled clinical trials are needed to fully establish efficacy and safety in humans.
All the available evidence suggests that 4-hydroxyisoleucine has tremendous potential to modify the diabetes-induced abnormalities in glycaemic control and lipid metabolism. The compound's most robustly characterized property â glucose-dependent potentiation of insulin secretion â has been replicated across multiple independent laboratories using both rat and human pancreatic islets, lending credibility to its biological plausibility. Its peripheral effects on insulin signaling (PI3K/Akt/GLUT4 axis, AMPK activation, NF-ÎșB/JNK suppression) are supported by cell-culture and animal data across multiple models, including insulin-resistant adipocyte cell lines and high-fat diet rodent models.
Human clinical evidence remains the weakest link. A handful of randomized, controlled human studies have suggested that fenugreek seed extracts enriched in 4-hydroxyisoleucine may modestly improve glycemic control and lipid profiles in individuals with prediabetes or type 2 diabetes. Published clinical trials have reported reductions in fasting blood glucose, HbA1c, and triglycerides, though study sizes are small and methodologies variable. Most human trials have investigated whole fenugreek preparations rather than purified 4-HIL isolates, making it difficult to attribute outcomes specifically to this compound.
(2S,3R,4S)-4-Hydroxyisoleucine is expected to be a promising orally active drug for diabetes and diabetic nephropathy because of its insulinotropic effect, though this expectation remains to be confirmed by large-scale human trials.
Health conditions that 4-hydroxyisoleucine may help support.
4-Hydroxyisoleucine is a unique non-protein amino acid found almost exclusively in fenugreek seeds. It directly stimulates insulin secretion from pancreatic beta cells in a glucose-dependent manner. Multiple in vitro and in vivo studies confirm its insulinotropic and insulin-sensitizing effects.
4-Hydroxyisoleucine is a unique non-protein amino acid from fenugreek seeds characterized as a novel insulinotropic compound (Sauvaire et al., Diabetes, 1998). It stimulates glucose-induced insulin release directly from pancreatic beta cells only at supra-normal glucose concentrations, being inactive at low or basal glucose levels, making it unlikely to cause or worsen hypoglycemia.
4-Hydroxyisoleucine is an unusual amino acid isolated from fenugreek seeds (Trigonella foenum-graecum) that directly increases glucose-dependent insulin secretion from beta cells and improves insulin sensitivity by activating AMPK in skeletal muscle. Studies show it reverses TNF-α-induced insulin resistance and improves blood lipid and glucose profiles in diabetic animal models.
4-Hydroxyisoleucine is the principal bioactive amino acid in fenugreek seeds with documented insulin-secretagogue and insulin-sensitizing activity. It stimulates glucose-dependent insulin secretion from pancreatic beta-cells and has been studied in insulin-resistant states including PCOS.
Body systems that 4-hydroxyisoleucine may help support.
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