As a racemic mixture of the natural L‑cystine and its D‑enantiomer, DL‑cystine does not have a specific biological target that differs from L‑cystine. L‑Cystine is a key component of the amino acid pool and serves as a precursor for glutathione, an important antioxidant. It is also involved in protein folding and stability through disulfide bond formation. The D‑enantiomer is not utilized by mammalian enzymes, so the mixture is primarily used as a reference or for studying stereoselectivity. In cell culture, cystine is an essential nutrient that must be supplied. The compound is not a pharmacological agent, so its “target” is the disulfide exchange and redox biology pathways in research contexts.

Commercial ergot supplements have been made from amino acids and their derivatives. They affect the release of anabolic hormones, the availability of fuel for activity, the ability to think clearly under pressure, and the prevention of muscular damage brought on by exertion. They are regarded as advantageous synergistic food ingredients [1].

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In vitro activity of DL‑cystine is evaluated primarily as a nutrient or redox modulator in cell culture. It is a component of many defined media, and its concentration affects cell growth and viability. In biochemical assays, cystine can be reduced to cysteine, which then participates in various redox reactions. It is used as a substrate for enzymes such as cystine reductase and as a standard in amino acid quantification. The compound shows no direct pharmacological activity, but its redox properties make it useful in studies of oxidative stress. It is often used at millimolar concentrations in media. The racemic mixture may be used to assess the stereospecificity of transporters or enzymes.

In vivo, L‑cystine is a non‑essential amino acid that is synthesized from methionine and serine, but it can also be obtained from the diet. It plays a role in protein synthesis, glutathione production, and redox balance. DL‑Cystine, as a racemate, is not typically administered therapeutically, but L‑cystine is used in some nutritional supplements. Animal studies may use labeled cystine to trace metabolism. The D‑form is poorly metabolized, so the mixture is mainly used for research on absorption and stereoselectivity. No specific in vivo efficacy models are associated with the racemic mixture.

Non‑cell experimental workflows for DL‑cystine typically involve analytical chemistry, such as HPLC or amino acid analysis. The compound is used as a reference standard; a typical workflow includes preparing standard solutions in dilute HCl, injecting onto a cation‑exchange column, and detecting with post‑column ninhydrin or fluorescence. For redox studies, cystine can be quantified by Ellman’s reagent after reduction. Calibration curves are established over a concentration range (e.g., 0.1‑10 mM). Method validation includes linearity, precision, and recovery. The compound is also used in enzymatic assays for cystine reductase, where the decrease in NADPH is monitored spectrophotometrically.

In vitro cell‑based workflows involve adding DL‑cystine to cell culture media (e.g., DMEM) at concentrations typically 0.1‑0.4 mM. Cells are cultured under standard conditions, and the effects on proliferation, glutathione levels, or oxidative stress are measured. For example, cells may be treated with cystine‑free media to study cysteine depletion, or with excess cystine to induce oxidative stress. Assays include MTT for viability, GSH/GSSG ratio determination, and ROS measurement using fluorescent probes. The racemic mixture may be used to test the specificity of cystine transporters such as xCT.

In vivo animal workflows are not commonly performed with DL‑cystine, but L‑cystine is studied in models of cystinuria or as a dietary supplement. Animals may be fed a cystine‑deficient diet and supplemented with the racemate to assess growth or tissue levels. Blood and urine samples are collected for amino acid analysis. However, for DL‑cystine, such studies are rare because the D‑form is not utilized. The compound is generally considered safe and is used in some nutritional research.

Pharmacokinetic properties of L‑cystine are well known: it is absorbed in the small intestine via amino acid transporters, distributed to tissues, and metabolized to cysteine, which is then used for protein synthesis or glutathione production. The D‑enantiomer is not efficiently absorbed or metabolized. For DL‑cystine, the overall PK would reflect the L‑component only. The compound is stable under acidic conditions but can be reduced in vivo. No formal ADME studies exist for the racemate.

DL‑Cystine is generally considered safe and is classified as a non‑toxic amino acid. High doses may cause gastrointestinal discomfort. In research, standard laboratory precautions apply. No carcinogenicity or reproductive toxicity data are available for the racemate. It is not a hazardous substance.

[1]. Luckose F, et al. Effects of amino acid derivatives on physical, mental, and physiological activities. Crit Rev Food Sci Nutr. 2015;55(13):1793-807.

Cystine is a sulfur-containing amino acid formed by the oxidation of two cysteine molecules linked by a disulfide bond. It is a metabolite in both humans and mice. Cystine is an organic disulfide, a sulfur-containing amino acid, and a tautomer of cystine zwitterions. It is a covalently linked dimer, non-essential amino acid formed by the oxidation of cysteine. Two cysteine molecules are linked by a disulfide bond to form cystine. There are reports of cystine's presence in fruit flies, along with relevant data. Cystine is not among the 20 essential amino acids; it is a sulfur-containing derivative formed by the oxidation of the thiol side chain of cysteine amino acids. Cystine has antioxidant properties, protecting tissues from radiation and pollution damage, slowing the aging process, and aiding in protein synthesis. Cystine is abundant in many proteins in bone tissue and skin, and is also found in insulin and digestive enzymes such as chromaffin trypsinogen A, papain, and trypsinogen. (NCI04)
Cysteine is a covalently linked dimer, non-essential amino acid formed by the oxidation of cysteine. Two cysteine molecules are linked by a disulfide bond to form cysteine.
See also: Cysteine (note moved to); Cysteine (note moved to).

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Drug Indications
L-cysteine is said to have anti-inflammatory properties, can combat a variety of toxins, and may help treat osteoarthritis and rheumatoid arthritis. More research is needed before L-cysteine can be used to treat these diseases. Research to date has primarily focused on animal models.

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Mechanism of Action
In some cases, such as acetaminophen overdose, glutathione in the liver is depleted, causing oxidative stress in tissues and leading to loss of cellular integrity. L-cysteine is a major precursor in the synthesis of glutathione.

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DL‑Cystine is primarily used as a research chemical and analytical standard. It is not a drug and has no clinical approval. L‑Cystine is used in some medical conditions (e.g., cystinuria) and as a dietary supplement, but the racemic form is purely for research. The compound is available from chemical suppliers and is stored at room temperature.

C6H12N2O4S2

240.29

240.023

923-32-0

DL-Cystine-d6;352431-53-9;DL-Cystine-d4;108641-83-4

595

White to off-white solid powder

1.6±0.1 g/cm3

468.2±45.0 °C at 760 mmHg

227 °C (dec.)(lit.)

237.0±28.7 °C

0.0±2.5 mmHg at 25°C

1.653

1.23

4

8

7

14

192

0

C(C(C(=O)O)N)SSCC(C(=O)O)N

LEVWYRKDKASIDU-UHFFFAOYSA-N

InChI=1S/C6H12N2O4S2/c7-3(5(9)10)1-13-14-2-4(8)6(11)12/h3-4H,1-2,7-8H2,(H,9,10)(H,11,12)

2-amino-3-[(2-amino-2-carboxyethyl)disulfanyl]propanoic acid

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Room temperature (This product is stable at ambient temperature for a few days during ordinary shipping and time spent in Customs)

H2O: 10 mg/mL (41.62 mM)

Note: Listed below are some common formulations that may be used to formulate products with low water solubility (e.g. < 1 mg/mL), you may test these formulations using a minute amount of products to avoid loss of samples.

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Injection Formulation 1: DMSO : Tween 80： Saline = 10 : 5 : 85 (i.e. 100 μL DMSO stock solution → 50 μL Tween 80 → 850 μL Saline)
*Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH ₂ O to obtain a clear solution.
Injection Formulation 2: DMSO : PEG300 ：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL DMSO → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)
Injection Formulation 3: DMSO : Corn oil = 10 : 90 (i.e. 100 μL DMSO → 900 μL Corn oil)
Example: Take the Injection Formulation 3 (DMSO : Corn oil = 10 : 90) as an example, if 1 mL of 2.5 mg/mL working solution is to be prepared, you can take 100 μL 25 mg/mL DMSO stock solution and add to 900 μL corn oil, mix well to obtain a clear or suspension solution (2.5 mg/mL, ready for use in animals).

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Injection Formulation 4: DMSO : 20% SBE-β-CD in saline = 10 : 90 [i.e. 100 μL DMSO → 900 μL (20% SBE-β-CD in saline)]
*Preparation of 20% SBE-β-CD in Saline (4°C，1 week): Dissolve 2 g SBE-β-CD in 10 mL saline to obtain a clear solution.
Injection Formulation 5: 2-Hydroxypropyl-β-cyclodextrin : Saline = 50 : 50 (i.e. 500 μL 2-Hydroxypropyl-β-cyclodextrin → 500 μL Saline)
Injection Formulation 6: DMSO : PEG300 : castor oil : Saline = 5 : 10 : 20 : 65 (i.e. 50 μL DMSO → 100 μLPEG300 → 200 μL castor oil → 650 μL Saline)
Injection Formulation 7: Ethanol : Cremophor : Saline = 10： 10 : 80 (i.e. 100 μL Ethanol → 100 μL Cremophor → 800 μL Saline)
Injection Formulation 8: Dissolve in Cremophor/Ethanol (50 : 50), then diluted by Saline
Injection Formulation 9: EtOH : Corn oil = 10 : 90 (i.e. 100 μL EtOH → 900 μL Corn oil)
Injection Formulation 10: EtOH : PEG300：Tween 80 : Saline = 10 : 40 : 5 : 45 (i.e. 100 μL EtOH → 400 μLPEG300 → 50 μL Tween 80 → 450 μL Saline)

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Oral Formulation 1: Suspend in 0.5% CMC Na (carboxymethylcellulose sodium)
Oral Formulation 2: Suspend in 0.5% Carboxymethyl cellulose
Example: Take the Oral Formulation 1 (Suspend in 0.5% CMC Na) as an example, if 100 mL of 2.5 mg/mL working solution is to be prepared, you can first prepare 0.5% CMC Na solution by measuring 0.5 g CMC Na and dissolve it in 100 mL ddH2O to obtain a clear solution; then add 250 mg of the product to 100 mL 0.5% CMC Na solution, to make the suspension solution (2.5 mg/mL, ready for use in animals).

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Oral Formulation 3: Dissolved in PEG400
Oral Formulation 4: Suspend in 0.2% Carboxymethyl cellulose
Oral Formulation 5: Dissolve in 0.25% Tween 80 and 0.5% Carboxymethyl cellulose
Oral Formulation 6: Mixing with food powders

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Note: Please be aware that the above formulations are for reference only. InvivoChem strongly recommends customers to read literature methods/protocols carefully before determining which formulation you should use for in vivo studies, as different compounds have different solubility properties and have to be formulated differently.

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 (Please use freshly prepared in vivo formulations for optimal results.)