internal standard

Metformin-d6 hydrochloride (Metformin-d6 hydrochloride) is a deuterated form of Metformin that can be used to study Metformin metabolism in vivo, and is often used as an internal standard for Metformin.ccc_R08 can be used to study HBV infection.ccc_R08 can be used to study HBV infection.

Ochratoxin A-13C20is intended for use as an internal standard for the quantification of ochratoxin A by GC- or LC-MS. Ochratoxin A is a mycotoxin that has been found inAspergillusandPenicillium.1It increases lipid peroxide levels and the number of apoptotic cells, as well as reduces superoxide dismutase activity in rat kidney when administered at a dose of 120 μg/kg.2Topical application of ochratoxin A (80 μg/mouse) induces DNA damage, cell cycle arrest at the G0/G1phase, and apoptosis in mouse skin cells.1It also initiates tumor formation in a two-stage mouse skin tumorigenesis model. Ochratoxin A has been found as a contaminant in a variety of foods.3

Ribavirin-13C5is intended for use as an internal standard for the quantification of ribavirin by GC- or LC-MS. Ribavirin is an antiviral guanosine nucleoside analog.1,2Upon entry into cells, ribavirin is metabolized to an active triphosphate form that induces viral RNA chain termination and inhibits viral polymerases. It reduces replication in a panel of seven RNA and four DNA viruses in Vero cells (EC50s = 2-95 μg/ml).3Ribavirin also reduces replication of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) in Vero cells (EC50= 109.5 μM).4Aerosol administration of ribavirin (30 mg/kg) reduces mortality in a mouse model of influenza A infection.5Formulations containing ribavirin have been used in the treatment of respiratory syncytial virus (RSV), hepatitis C virus (HCV), and viral hemorrhagic fevers. 1.Gilbert, B.E., and Knight, V.Biochemistry and clinical applications of ribavirinAntimicrob. Agents Chemother.30(2)201-205(1986) 2.Gordon, C.J., Tchesnokov, E.P., Woolner, E., et al.Remdesivir is a direct-acting antiviral that inhibits RNA-dependent RNA polymerase from severe acute respiratory syndrome coronavirus 2 with high potencyJ. Biol. Chem.295(20)6785-6797(2020) 3.Kirsi, J.J., North, J.A., McKernan, P.A., et al.Broad-spectrum antiviral activity of 2-β-D-ribofuranosylselenazole-4-carboxamide, a new antiviral agentAntimicrob. Agents Chemother.24(3)353-361(1983) 4.Wang, M., Cao, R., Zhang, L., et al.Remdesivir and chloroquine effectively inhibit the recently emerged novel coronavirus (2019-nCoV) in vitroCell Res.30(3)269-271(2020) 5.Wilson, S.Z., Knight, V., Wyde, P.R., et al.Amantadine and ribavirin aerosol treatment of influenza A and B infection in miceAntimicrob. Agents Chemother.17(4)642-648(1980)

L-Thyroxine-13C9,15N is intended for use as an internal standard for the quantification of L-thyroxine by GC- or LC-MS. L-Thyroxine is a synthetic form of the thyroid hormone thyroxine. In vivo, L-thyroxine (0.9 and 2.7 μg) inhibits synthesis and release of thyrotropin induced by thyrotropin-releasing hormone from the anterior pituitary in mice. It also reverses decreases in levels of circulating thymic serum factor (FTS) and the number of T rosette-forming cells in an old age-induced mouse model of hypothyroidism. Formulations containing L-thyroxine have been used in the treatment of hypothyroidism.

Palmitic acid-13C (C1, C2, C3, and C4 labeled) is intended for use as an internal standard for the quantification of palmitic acid by GC- or LC-MS. Palmitic acid is a common 16-carbon saturated fat that represents 10-20% of human dietary fat intake and comprises approximately 25 and 65% of human total plasma lipids and saturated fatty acids, respectively.1,2Acylation of palmitic acid to proteins facilitates anchoring of membrane-bound proteins to the lipid bilayer and trafficking of intracellular proteins, promotes protein-vesicle interactions, and regulates various G protein-coupled receptor functions.1Red blood cell palmitic acid levels are increased in patients with metabolic syndrome compared to patients without metabolic syndrome and are also increased in the plasma of patients with type 2 diabetes compared to individuals without diabetes.3,4 1.Fatima, S., Hu, X., Gong, R.-H., et al.Palmitic acid is an intracellular signaling molecule involved in disease developmentCell. Mol. Life Sci.76(13)2547-2557(2019) 2.Santos, M.J., López-Jurado, M., Llopis, J., et al.Influence of dietary supplementation with fish oil on plasma fatty acid composition in coronary heart disease patientsAnn. Nutr. Metab.39(1)52-62(1995) 3.Yi, L.-Z., He, J., Liang, Y.-Z., et al.Plasma fatty acid metabolic profiling and biomarkers of type 2 diabetes mellitus based on GC/MS and PLS-LDAFEBS Lett.580(30)6837-6845(2006) 4.Kabagambe, E.K., Tsai, M.Y., Hopkins, P.N., et al.Erythrocyte fatty acid composition and the metabolic syndrome: A National Heart, Lung, and Blood Institute GOLDN studyClin. Chem.54(1)154-162(2008)

HT-2 toxin-13C22is intended for use as an internal standard for the quantification of HT-2 toxin by GC- or LC-MS. HT-2 toxin is a type A trichothecene mycotoxin and an active, deacetylated metabolite of the trichothecene mycotoxin T-2 toxin .1,2Like T-2 toxin, HT-2 toxin inhibits protein synthesis and cell proliferation in plants.2HT-2 toxin also reduces viability of HepG2, A549, HEp-2, Caco-2, A-204, U937, Jurkat, and RPMI-8226 cancer cells with IC50values ranging from 3.1 to 23 ng/ml and human umbilical vein endothelial cells with an IC50value of 56.4 ng/ml.1It induces oxidative stress, DNA damage, and autophagy in, as well as halts the development of, cultured mouse embryos when used at a concentration of 10 nM.3HT-2 toxin has been found in cereal grains and food products.4,5 1.Nielsen, C., Casteel, M., Didier, A., et al.Trichothecene-induced cytotoxicity on human cell linesMycotoxin Res.25(2)77-84(2009) 2.Nathanail, A.V., Varga, E., Meng-Reiterer, J., et al.Metabolism of the fusarium mycotoxins T-2 toxin and HT-2 toxin in wheatJ. Agric. Food Chem.63(35)7862-7872(2015) 3.Zhang, L., Li, L., Xu, J., et al.HT-2 toxin exposure induces mitochondria dysfunction and DNA damage during mouse early embryo developmentReprod. Toxicol.85104-109(2019) 4.Langseth, W., and Rundberget, T.The occurrence of HT-2 toxin and other trichothecenes in Norwegian cerealsMycopathologia147(3)157-165(1999) 5.Al-Taher, F., Cappozzo, J., Zweigenbaum, J., et al.Detection and quantitation of mycotoxins in infant cereals in the U.S. market by LC-MS/MS using a stable isotope dilution assayFood Control72(Part A)27-35(2017)

1,2-Dipalmitoyl-13C-sn-glycero-3-PC is intended for use as an internal standard for the quantification of 1,2-dipalmitoyl-sn-glycero-3-PC by GC- or LC-MS. 1,2-Dipalmitoyl-sn-glycero-3-PC (DPPC) is a zwitterionic glycerophospholipid commonly used in the formation of lipid monolayers, bilayers, and liposomes for use in a variety of applications.1,2,3,4 It has been used in the formation of proteoliposomes for implantation of γ-glutamyl transpeptidase into human erythrocyte membranes.3 Incorporation of glycosphingolipid antigens into DPPC-containing liposomes increases the immunogenicity of the antigens in mice.4 |1. Ege, C., and Lee, K.Y.C. Insertion of Alzheimer's Aβ40 peptide into lipid monolayers. Biophys. J. 87(3), 1732-1740 (2004).|2. Leekumjorn, S., and Sum, A.K. Molecular simulation study of structural and dynamic properties of mixed DPPC/DPPE bilayers. Biophys. J. 90(11), 3951-3965 (2006).|3. Kalra, V.K., Sikka, S.C., and Sethi, G.S. Transport of amino acids in γ-glutamyl transpeptidase-implanted human erythrocytes. J. Biol. Chem. 256(11), 5567-5571 (1981).|4. Uemura, A., Watarai, S., Iwasaki, T., et al. Induction of immune responses against glycosphingolipid antigens: Comparison of antibody responses in mice immunized with antigen associated with liposomes prepared from various phospholipids. J. Vet. Med. Sci. 67(12), 1197-1201 (2005).

Lauric acid-13C is intended for use as an internal standard for the quantification of lauric acid by GC- or LC-MS. Lauric acid is a medium-chain saturated fatty acid. It has been found at high levels in coconut oil.1Lauric acid induces the activation of NF-κB and the expression of COX-2, inducible nitric oxide synthase (iNOS), and IL-1α in RAW 264.7 cells when used at a concentration of 25 μM.2

Flumequine-13C3is intended for use as an internal standard for the quantification of flumequine by GC- or LC-MS. Flumequine is a fluoroquinolone antibiotic.1It is active againstS. aureus, S. pyogenes, B. subtilis, E. coli, P. aeruginosa, S. faecalis, andK. pneumoniae(MICs = 1-100 μg/ml). Flumequine is also active against field isolates of B. hyodysenteriae (MICs = 6.25-200 μg/ml).2It inhibits DNA gyrase, disrupting supercoiling of bacterial DNA to block transcription and replication.3In vivo, flumequine (50 mg/kg) increases survival in rat models ofP. vulgaris-induced urinary tract infection andP. mirabilis-induced prostatitis.1Formulations containing flumequine have been used in the treatment of urinary tract infections in veterinary medicine. 1.Rohlfing, S.R., Gerster, J.R., and Kvam, D.C.Bioevaluation of the antibacterial flumequine for urinary tract useAntimicrob. Agents Chemother.10(1)20-24(1976) 2.Aller-Morán, L.M., Martínez-Lobo, F.J., Rubio, P., et al.Evaluation of the in vitro activity of flumequine against field isolates of Brachyspira hyodysenteriaeRes. Vet. Sci.10351-53(2015) 3.Smith, J.T.The mode of action of 4-quinolones and possible mechanisms of resistanceJ. Antimicrob. Chemother.18 (Suppl. D)21-29(1986)

13C15-Nivalenol is intended for use as an internal standard for the quantification of nivalenol by GC- or LC-MS. Nivalenol is a trichothecene mycotoxin that has been found inFusarium.1It is lethal to mice (LD50= 6.9 mg/kg).2Nivalenol (5, 10, and 15 mg/kg) also induces thymic, splenic, and Peyer's patch cell apoptosis in mice.3 1.Yang, Z., Concannon, J., Ng, K.S., et al.Tetrandrine identified in a small molecule screen to activate mesenchymal stem cells for enhanced immunomodulationSci. Rep.630263(2016) 2.Yoshizawa, T., and Morooka, N.Studies on the toxic substances in the infected cereals (part 3): Acute toxicities of new trichothecene mycotoxins: Deoxynivalenol and its monoacetateJ. Food Hyg.15(4)261-269(1974) 3.Poapolathep, A., Ohtsuka, R., Kiatipattanasakul, W., et al.Nivalenol-induced apoptosis in thymus, spleen and Peyer's patches of miceExp. Toxicol. Pathol.53(6)441-446(2002)

3-Acetyldeoxy nivalenol-13C17is intended for use as an internal standard for the quantification of 3-acetyldeoxy nivalenol by GC- or LC-MS. 3-Acetyldeoxy nivalenol is a mycotoxin that has been found inF. graminearum.1In vivo, 3-acetyldeoxy nivalenol (40 mg/kg) induces duodenal and splenic cell necrosis, as well as lethality (LD50= 70 mg/kg) in mice.2 1.Jiao, F., Kawakami, A., and Nakajima, T.Effects of different carbon sources on trichothecene production and Tri gene expression by Fusarium graminearum in liquid cultureFEMS Microbiol.Lett.285(2)212-219(2008) 2.Schiefer, H.B., Nicholson, S., Kasali, O.B., et al.Pathology of acute 3-acetyldeoxynivalenol toxicity in miceCan. J. Comp. Med.49(3)315-318(1985)

Rhein-13C4 is intended for use as an internal standard for the quantification of rhein by GC- or LC-MS. Rhein is an anti-inflammatory anthraquinone found in rhubarb and is the bioactive derivative of its prodrug diacerein . At 10 μM, rhein inhibits IL-1β signaling, suppressing signaling through NF-κB, and reduces the expression of the matrix metalloproteases MMP-1 and MMP-13.1 It inhibits IKKβ (IC50 = 11.8 μM), decreasing iNOS and IL-6 expression in LPS-stimulated macrophages but paradoxically increasing TNF-α, IL-1β, and HMBG1 expression.2 Rhein shows efficacy against pancreatic fibrosis, chronic pancreatitis, and hyperglycemia-induced pancreatic β-cell apoptosis.3,4 It also inhibits angiogenesis of breast cancer cells under normoxic and hypoxic conditions.5

Guanfacine-13C,15N3is intended for us as an internal standard for the quantification of guanfacine by GC- or LC-MS. Guanfacine is an α2-adrenergic receptor (α2-AR) agonist with Kivalues of 93, 1,380, and 3,890 nM for α2A-, α2B-, and α2C-ARs, respectively, in a radioligand binding assay.1It has EC50values of 52, 288, and 602 nM for α2A-, α2B-, and α2C-ARs, respectively, for stimulated [35S]GTPγS binding. It also binds to imidazoline receptor 1 (Ki= 19 nM in a radioligand binding assay).2Guanfacine (0.3-5 mg/kg) binds to adrenergic receptors in the central nervous system and lowers blood pressure in hypertensive rats in a dose-dependent manner.3It also improves spatial working memory deficits induced by hypobaric hypoxia in rats.4Formulations containing guanfacine are used in the treatment of high blood pressure and attention deficit hyperactivity disorder (ADHD). 1.Jasper, J.R., Lesnick, J.D., Chang, L.K., et al.Ligand efficacy and potency at recombinant α2 adrenergic receptors: Agonist-mediated [35S]GTPγS bindingBiochem. Pharmacol.55(7)1035-1043(1998) 2.Nikolic, K., Filipic, S., and Agbaba, D.QSAR study of imidazoline antihypertensive drugsBioorg. Med. Chem.16(15)7134-7140(2008) 3.Scholtysik, G.Pharmacology of guanfacineBr. J. Clin. Pharmacol.10(Suppl 1)21S-24S(1980) 4.Kauser, H., Sahu, S., Kumar, S., et al.Guanfacine is an effective countermeasure for hypobaric hypoxia-induced cognitive declineNeuroscience254110-119(2013)

Aflatoxin G1-13C17is intended for use as an internal standard for the quantification of aflatoxin G1by GC- or LC-MS. Aflatoxin G1is a mycotoxin that has been found inA. terricola.1In vivo, aflatoxin G1is lethal to ducklings (LD50= 1.18 mg/kg).2It induces hepatocellular carcinoma tumor formation and lethality in rats when administered at doses of 1.4 and 3 mg/animal, respectively. Aflatoxin G1also inhibits liver and kidney succinate dehydrogenase and fumarase, as well as kidney cytochrome oxidase, NADH oxidase, α-glycerophosphate dehydrogenase, isocitrate dehydrogenase, and malate dehydrogenase in rats.3 1.Moubasher, A.H., el-Kady, I.A., and Shoriet, A.Toxigenic Aspergilli isolated from different sources in EgyptAnn. Nutr. Aliment.31(4-6)607-615(1977) 2.Wogan, G.N., Edwards, G.S., and Newberne, P.M.Structure-activity relationships in toxicity and carcinogenicity of aflatoxins and analogsCancer Res.31(12)1936-1942(1971) 3.Bai, N.J., Pai, M.R., and Venkitasubramanian, T.A.Mitochondrial function in aflatoxin toxicityIndian J. Biochem. Biophys.14(4)347-349(1977)

Zearalenone-13C18is intended for use as an internal standard for the quantification of zearalenone by GC- or LC-MS. Zearalenone is a mycotoxin that has been found inFusariumand has estrogenic activities.1It binds to human estrogen receptor α (ERα) and ERβ (IC50s = 9 and 5.8 nM, respectively).2Zearalenone induces precocious development of mammary tissues in young female pigs and prepucial enlargement in young male pigs.3Zearalenone (1.5-5 mg/kg of diet) induces hyperestrogenism in pigs. It also induces degeneration of meiotic chromatin in oocytes and reduces fertility in pigs when administered at a dose of 200 μg/kg.4Zearalenone has been found as a contaminant in wheat, maize, and barley and livestock feeds.3,4

Dichlorphenamide-13C6is intended for use as an internal standard for the quantification of dichlorphenamide by GC- or LC-MS. Dichlorphenamide is a sulfonamide and an orally bioavailable carbonic anhydrase (CA) inhibitor (Kis = 1.20, 38, 50, and 50 nM for the human CA isoforms CAI, CAII, CAIX, and CAXII, respectively).1It lowers intraocular pressure in rabbits when 50 μl of a 10% solution is applied topically to the eye.2Dichlorphenamide rescues the potassium deficiency and prevents insulin-induced paralysis in a rat model of familial hypokalemic periodic paralysis when administered at a dose of 5.6 mg/kg per day for ten days.3Formulations containing dichlorphenamide have been used in the treatment of glaucoma and primary periodic paralysis.

Zanamivir-13C,15N2is intended for use as an internal standard for the quantification of zanamivir by GC- or LC-MS. Zanamivir is a sialic acid analog that inhibits neuraminidase release of newly replicated influenza virus particles.1It has been shown to selectively inhibit the growth of influenza A and B viruses in plaque reduction assays with IC50values ranging from 5 to 14 nM and to directly inhibit influenza A and B virus neuraminidases with IC50values ranging from 0.6 to 7.9 nMin vitro. Intranasal zanamivir administration at 0.4 mg/kg twice daily reduces mortality and viral titers in lung homogenates of mice infected with influenza. 1.Elliott, M.Zanamivir: From drug design to the clinicPhilos. Trans. R. Soc. Lond. B Biol Sci.356(1416)1885-1893(2001)

Zonisamide-13C2,15N is intended for use as an internal standard for the quantification of zonisamide by GC- or LC-MS. Zonisamide is an antiepileptic agent.1 It selectively inhibits the repeated firing of sodium channels (IC50 = 2 μg/ml) in mouse embryo spinal cord neurons and inhibits spontaneous channel firing when used at concentrations greater than 10 μg/ml.2 In rat cerebral cortex neurons, zonisamide (1-1,000 μM) inhibits T-type calcium channels with a maximum reduction of 60% of the calcium current.3 Zonisamide inhibits H. pylori recombinant carbonic anhydrase (CA) and the human CA isoforms I, II, and V with Ki values of 218, 56, 35, and 21 nM, respectively.4,5 In mice, it has anticonvulsant activity against maximal electroshock seizure (MES) and pentylenetetrazole-induced maximal, but not minimal, seizures (ED50s = 19.6, 9.3, and >500 mg/kg, respectively). Zonisamide (40 mg/kg, p.o.) prevents MPTP-induced decreases in the levels of dopamine , but not homovanillic acid or dihydroxyphenyl acetic acid , and increases MPTP-induced decreases in the dopamine turnover rate in mouse striatum in a model of Parkinson's disease.6 Formulations containing zonisamide have been used in the treatment of partial seizures in adults with epilepsy. |1. Masuda, Y., Ishizaki, M., and Shimizu, M. Zonisamide: Pharmacology and clinical efficacy in epilepsy. CNS Drug Rev. 4(4), 341-360 (1998).|2. Rock, D.M., Macdonald, R.L., and Taylor, C.P. Blockade of sustained repetitive action potentials in cultured spinal cord neurons by zonisamide (AD 810, CI 912), a novel anticonvulsant. Epilepsy Res. 3(2), 138-143 (1989).|3. Suzuki, S., Kawakami, K., Nishimura, S., et al. Zonisamide blocks T-type calcium channel in cultured neurons of rat cerebral cortex. Epilepsy Res. 12(1), 21-27 (1992).|4. Nishimori, I., Vullo, D., Minakuchi, T., et al. Carbonic anhydrase inhibitors: Cloning and sulfonamide inhibition studies of a carboxyterminal truncated α-carbonic anhydrase from Helicobacter pylori. Bioorg. Med. Chem. Lett. 16(8), 2182-2188 (2006).|5. De Simone, G., Di Fiore, A., Menchise, V., et al. Carbonic anhydrase inhibitors. Zonisamide is an effective inhibitor of the cytosolic isozyme II and mitochondrial isozyme V: Solution and X-ray crystallographic studies. Bioorg. Med. Chem. Lett. 15(9), 2315-2320 (2005).|6. Yabe, H., Choudhury, M.E., Kubo, M., et al. Zonisamide increases dopamine turnover in the striatum of mice and common marmosets treated with MPTP. J. Pharmacol. Sci. 110(1), 64-68 (2009).

Caffeic acid-13C3 is an isotopically enriched form of caffeic acid that is intended for use as an internal standard for the quantification of caffeic acid by GC- or LC-MS. Caffeic acid is an inhibitor of 5-LO , with IC50 values of 3.7-72 μM, and 12-LO, with IC50 values of 5.1-30 μM.

Aflatoxin B2-13C17(AFB2-13C17) is intended for use as an internal standard for the quantification of AFB2by GC- or LC-MS. AFB2is a mycotoxin that has been found inA. terricola.1It induces hepatic autophagy and apoptosis in broiler chickens when administered at doses of 0.2, 0.4, and 0.8 mg/kg.2AFB2(0.5 and 1 mg/animal) also induces parenchymal cell hyperplasia in rats.3 1.Moubasher, A.H., el-Kady, I.A., and Shoriet, A.Toxigenic Aspergilli isolated from different sources in EgyptAnn. Nutr. Aliment.31(4-6)607-615(1977) 2.Chen, B., Li, D., Li, M., et al.Induction of mitochondria-mediated apoptosis and PI3K/Akt/mTOR-mediated autophagy by aflatoxin B2 in hepatocytes of broilersOncotarget7(51)84989-84998(2016) 3.Wogan, G.N., Edwards, G.S., and Newberne, P.M.Structure-activity relationships in toxicity and carcinogenicity of aflatoxins and analogsCancer Res.31(12)1936-1942(1971)

4-deoxy Nivalenol-13C15is intended for use as an internal standard for the quantification of 4-deoxy nivalenol by GC- or LC-MS. 4-deoxy Nivalenol is a trichothecene mycotoxin that has been found inFusarium.1It binds to eukaryotic ribosomes and inhibits protein synthesis in mice when administered at doses ranging from 5 to 25 mg/kg. 4-deoxy Nivalenol (0.1 and 0.2 mg/kg) induces emesis in pigs and decreases feed consumption in pigs when administered at a dose of 40 ppb in the diet.2It induces lethality in mice (LD50= 46-78 mg/kg).34-deoxy Nivalenol has been found inF. graminearum-infected cereal grains such as wheat, barley, and corn. 1.Pestka, J.J., and Smolinski, A.T.Deoxynivalenol: Toxicology and potential effects on humansJ.Toxicol.Environ.Health B.Crit.Rev.8(1)39-69(2005) 2.Forsyth, D.M., Yoshizawa, T., Morooka, N., et al.Emetic and refusal activity of deoxynivalenol to swineAppl. Environ. Microbiol.34(5)547-552(1977) 3.Pestka, J.J.Deoxynivalenol: Mechanisms of action, human exposure, and toxicological relevanceArch. Toxicol.84(9)663-679(2010)

5-Fluorouracil-13C,15N2 is intended for use as an internal standard for the quantification of 5-flurouracil by GC- or LC-MS. 5-Fluorouracil is a pyrimidine analog that irreversibly inhibits thymidylate synthase, blocking the synthesis of thymidine which is required for DNA synthesis. Intracellular metabolites of 5-fluorouracil exert cytotoxic effects by either inhibiting thymidylate synthetase, or through incorporation into RNA and DNA, ultimately initiating apoptosis.

Aflatoxin G2-13C17is intended for use as an internal standard for the quantification of aflatoxin G2by GC- or LC-MS. Aflatoxin G2is a mycotoxin that has been found inAspergillus.1It is lethal to ducklings (LD50= 2.83 mg/kg) but is non-toxic to rats when administered at a dose of 200 mg/kg.2 1.Bennett, J.W., and Klich, M.MycotoxinsClin. Microbiol. Rev.16(3)497-516(2003) 2.Wogan, G.N., Edwards, G.S., and Newberne, P.M.Structure-activity relationships in toxicity and carcinogenicity of aflatoxins and analogsCancer Res.31(12)1936-1942(1971)

Nitisinone-13C6is intended for use as an internal standard for the quantification of nitisinone by GC- or LC-MS. Nitisinone is an inhibitor of 4-hydroxyphenylpyruvate dioxygenase (HPPD), which converts 4-hydroxyphenylpyruvate (HPPA) to homogentisate in the tyrosine catabolic pathway.1Nitisinone increases urinary levels of HPPA and 4-hydroxyphenyllactate (HPLA) in rats when administered at a dose of 10 mg/kg. Nitisinone (3 mg/kg) prevents the neonatal lethality of fumarylacetoacetate hydrolase (FAH) deficiency in mice when administered to pregnant dams.2It exhibits hepatoprotective effects inFAH-/-mice, such as prevention of increases in plasma levels of aspartate serine aminotransferase (AST) and conjugated bilirubin, when administration is continued following birth at a dose of 1 mg/kg. Nitisinone (100 μg) decreases urinary excretion of homogentisate and increases urinary excretion of HPPA, HPLA, and 4-hydroxyphenylacetate in a mouse model of alkaptonuria induced by ethylnitrosourea.3Formulations containing nitisinone have been used in the treatment of hereditary tyrosinemia type 1 (HT-1). 1.Ellis, M.K., Whitfield, A.C., Gowans, L.A., et al.Inhibition of 4-hydroxyphenylpyruvate dioxygenase by 2-(2-nitro-4-trifluoromethylbenzoyl)-cyclohexane-1,3-dione and 2-(2-chloro-4-methanesulfonylbenzoyl)-cyclohexane-1,3-dioneToxicol. Appl. Pharmacol.133(1)12-19(1995) 2.Grompe, M., Lindstedt, S., al-Dhalimy, M., et al.Pharmacological correction of neonatal lethal hepatic dysfunction in a murine model of hereditary tyrosinaemia type INat. Genet.10(4)453-460(1995) 3.Suzuki, Y., Oda, K., Yoshikawa, Y., et al.A novel therapeutic trial of homogentisic aciduria in a murine model of alkaptonuriaJ. Hum. Genet.44(2)79-84(1999)

1,2,3-Trioctanoyl-rac-glycerol-13C3 is intended for use as an internal standard for the quantification of 1,2,3-trioctanoyl-rac-glycerol by GC- or LC-MS. 1,2,3-Trioctanoyl-rac-glycerol is a triacylglycerol that contains octanoic acid at the sn-1, sn-2, and sn-3 positions. Dietary administration of 1,2,3-trioctanoyl-rac-glycerol increases hippocampal levels of the glycolytic metabolites glucose 6-phosphate, fructose 6-phosphate, and β-hydroxybutyrate and the seizure threshold in the 6 Hz psychomotor seizure test in mice.1 Formulations containing 1,2,3-trioctanoyl-rac-glycerol have been used in cosmetic products as thickening and skin-conditioning agents.

Moexipril-d5 intended for use as an internal standard for the quantification of moexipril by GC- or LC-MS. Moexipril is a prodrug form of the angiotensin converting enzyme (ACE) inhibitor moexiprilat. It is converted to moexiprilat in vivo by side chain ester hydrolysis. Moexipril inhibits ACE in a cell-free assay (IC50 = 2.7 µM for the rabbit enzyme). It also inhibits phosphodiesterase 4 (IC50s = 38, 160, and 230 µM for PDE4B2, PDE4A5 and PDE4D5, respectively). Moexipril (0.1-30 mg/kg per day) reduces blood pressure in spontaneously hypertensive rats.1 It also reduces infarct volume in a rat model of focal cerebral ischemia when used at a concentration of 0.01 mg/kg.

Tiagabine-d6 is intended for use as an internal standard for the quantification of tiagabine by GC- or LC-MS. Tiagabine is an inhibitor of GABA transporter 1. It inhibits seizures induced by DMCM in mice. Tiagabine reduces allodynia in a rodent model of neuropathic pain when used at a dose of 72.8 µmol/kg, and it acts synergistically with gabapentin to delay pain responses in mice in the hot plate test. Formulations containing tiagabine have been used as adjunctive therapies in the treatment of partial seizures.

Gemfibrozil-d6 is intended for use as an internal standard for the quantification of gemfibrozil by GC- or LC-MS. Gemfibrozil is a peroxisome proliferator-activated reporter α and PPARγ agonist. In vivo, gemfibrozil reduces serum total cholesterol, triglyceride, and LDL levels in a rat model of high-cholesterol diet-induced hyperlipidemia. Gemfibrozil reduces atherosclerotic plaque area, superoxide production, and expression of the genes encoding the NF-κB subunit p65 and chemokine (C-C) motif ligand 2 (CCL2) in ApoE-/- mice. Formulations containing gemfibrozil have been used in the treatment of high cholesterol.

Nitrofurantoin-13C3is intended for use as an internal standard for the quantification of nitrofurantoin by GC- or LC-MS. Nitrofurantoin is a nitrofuran antibiotic.1In vivo, nitrofurantoin (25-100 mg/kg) reducesE. colireplication and abscess formation in the renal medulla of infected rats in a dose-dependent manner. It prevents kidney and bladder infection in rats following bladder inoculation with clinical isolates ofP. mirabilis. Nitrofurantoin also prevents alkalization of urine, as well as calculi and abscess formation, in a rat model ofP. vulgarisurinary tract infection.2Formulations containing nitrofurantoin have been used to treat urinary tract infections. 1.Rocha, H., Da Silva Teles, E., and Barros, M.Site of action of nitrofurantoin in experimental urinary tract infectionAppl. Microbiol.18(4)547-549(1969) 2.Hossack, D.J.N.Proteus vulgaris urinary tract infections in rats; treatment with nitrofuran derivativesBr. J. Pharmacol. Chemother.19(2)306-312(1962)

Gliclazide-d4 is intended for use as an internal standard for the quantification of gliclazide by GC- or LC-MS. Gliclazide is a sulfonylurea and an inhibitor of pancreatic β-cell ATP-sensitive potassium (KATP) channels. It is selective for pancreatic β-cell over cardiac and arterial smooth muscle cell KATP channels. Gliclazide (5 μM) increases insulin-induced glucose uptake and glucose transporter 4 (GLUT4) translocation to the plasma membrane in a differentiated 3T3L1 adipocyte model of insulin resistance induced by hydrogen peroxide. Gliclazide (5 and 10 μg/ml) reduces LDL oxidation by human aortic smooth muscle cells (HASMCs), decreasing TBARS content and 8-isoprostane levels. It also decreases oxidized LDL-induced HASMC proliferation and monocyte adhesion when used at concentrations ranging from 1 to 10 μg/ml. Gliclazide (5 mg/kg) reduces serum glucose levels and increases glucose uptake by isolated rat hindquarters in a model of diabetes induced by streptozotocin (STZ).

Fosinopril-d7 is intended for use as an internal standard for the quantification of fosinopril by GC- or LC-MS. Fosinopril is a prodrug form of the angiotensin-converting enzyme inhibitor fosinoprilat. Oral administration of fosinopril inhibits angiotensin I-induced pressor responses in normotensive rats, dogs, and monkeys when administered at doses of 15, 15, and 10 µmol/kg, respectively. Fosinopril reduces fractional shortening and decreases left ventricular size in a porcine model of congestive heart failure. Formulations containing fosinopril have been used in the treatment of hypertension and congestive heart failure.

Oxaliplatin-d10 is intended for use as an internal standard for the quantification of oxaliplatin by GC- or LC-MS. Oxaliplatin is a platinum-containing DNA-crosslinking agent. It induces the formation of DNA inter- and intrastrand crosslinks and DNA-protein adducts, inhibits DNA and RNA synthesis, and induces apoptosis in cancer cells. Oxaliplatin is cytotoxic to cisplatin-sensitive A2780(1A9) and KB-3-1 cells and cisplatin-resistant A2780-E(80) and KB-CP20 cells (IC50s = 0.12, 0.39, 4.7, and 2.7 µM, respectively). It reduces tumor growth in an HCCLM3 mouse xenograft model when administered at doses of 5 or 10 mg/kg once per week. Formulations containing oxaliplatin have been used in the treatment of advanced colorectal cancer and as adjuvants in stage III colon cancer.

Rizatriptan-d6 is intended for use as an internal standard for the quantification of rizatriptan by GC- or LC-MS. Rizatriptan is an agonist of the serotonin receptor subtypes 5-HT1B and 5-HT1D. It is selective for 5-HT1B and 5-HT1D receptors over 5-HT1A receptors. Rizatriptan induces vasoconstriction in isolated human middle meningeal arteries. In vivo, rizatriptan reduces head grooming, the number of oculotemporal strokes, eye blinking, and one-eye closures in a Cacna1a mutant transgenic mouse model of migraine. Formulations containing rizatriptan have been used in the treatment of migraine.

Theobromine-d6 is intended for use as an internal standard for the quantification of theobromine by GC- or LC-MS. Theobromine is a methylxanthine alkaloid and derivative of caffeine that has been found in cocoa beans and has diverse biological activities. It is an adenosine A1 receptor antagonist. Theobromine increases AMPK phosphorylation and inhibits adipocyte differentiation, ERK and JNK phosphorylation, and IL-6 and TNF-α production in 3T3-L1 preadipocytes cultured in differentiation medium. It inhibits decreases in renal cortex SIRT1 activity and increases in NADPH oxidase-dependent reactive oxygen species (ROS) production, as well as reduces kidney hypertrophy and albuminuria in a spontaneously hypertensive rat model of streptozotocin-induced diabetes when administered at a dose of 5 mg/kg per day.3 Theobromine is toxic to dogs with an LD50 value of 250 to 500 mg/kg.

Norfluoxetine-d5 is intended for use as an internal standard for the quantification of norfluoxetine by GC- or LC-MS. Norfluoxetine is an active metabolite of the antidepressant fluoxetine. It is formed from fluoxetine by the cytochrome P450 (CYP) isoforms CYP2C9, CYP2C19, and CYP3A. Norfluoxetine inhibits serotonin (5-HT) uptake in rat brain synaptosomal membrane preparations (Ki = 44.7 nM) and isolated human platelets (IC50 = ~15 nM). It has been found in the tissues of fish exposed to wastewater effluent.

Fexofenadine-d6 (MDL-16455-d6) is the deuterium substituent of Fexofenadine and can be used as an internal standard for the determination of non-sofenadine concentrations in human plasma.

Nicorandil-d4 is intended for use as an internal standard for the quantification of nicorandil by GC- or LC-MS. Nicorandil is an activator of sulfonylurea receptor 2B (SUR2B) linked to ATP-sensitive potassium channel Kir6.2 (EC50 = ~10 µM) and a nitric oxide (NO) donor. It is selective for SUR2B/Kir6.2 over the SUR2A/Kir6.2 channel (EC50 = >500 µM). Nicorandil activates soluble guanylate cyclase in a cell-free assay and relaxes partially depolarized isolated bovine coronary artery strips (EC50 = 4.4 µM). It decreases mean blood pressure, coronary resistance, and heart rate, as well as increases coronary sinus outflow, in dogs when administered intravenously at a dose of 1 mg/kg. Nicorandil increases survival and decreases infarct size in a rabbit model of myocardial ischemia-reperfusion injury induced by left coronary artery occlusion. Formulations containing nicorandil have been used in the treatment of angina pectoris.

Pirlindole-d4 is intended for use as an internal standard for the quantification of pirlindole by GC- or LC-MS. Pirlindole is a selective and reversible monoamine oxidase A (MAO-A) inhibitor. It is selective for MAO-A over MAO-B. In rats, it reverses the depressive-like effects induced by chronic mild stress (CMS), increases proliferation of hippocampal neural progenitor cells, and reverses dendritic atrophy in granule neurons. Pirlindole is also an inhibitor of enterovirus-D68 and coxsackievirus B3 (CV-B3), inhibiting the genome replication phase of CV-B3 infection with an EC50 value of 7.7 µM independent of MAO-A activity.

Tasimelteon-d5 is intended for use as an internal standard for the quantification of tasimelteon by GC- or LC-MS. Tasimelteon is a melatonin (MT) receptor agonist. It selectively binds MT1 and MT2 receptors over a panel of 160 additional receptors and enzymes at 10 µM. Tasimelteon inhibits forskolin-induced cAMP accumulation with EC50 values of 0.79 and 1 nM in NIH3T3 cells expressing the MT1 or MT2 receptor, respectively. Formulations containing tasimelteon have been used in the treatment of non-24-hour sleep-wake disorder.

PhIP-D3 is a deuterated internal standard for PhIP.

Clobetasol propionate-d5 is intended for use as an internal standard for the quantification of clobetasol propionate by GC- or LC-MS. Clobetasol propionate is a corticosteroid. It binds to glucocorticoid receptors in a cell-free assay and inhibits proliferation of primary human skin fibroblasts when used at a concentration of 5 µg/ml. Topical administration of clobetasol propionate reduces croton oil-induced ear edema in mice. Formulations containing clobetasol propionate have been used in the treatment of inflammatory skin conditions.

Nifuroxazide-d4 is intended for use as an internal standard for the quantification of nifuroxazide by GC- or LC-MS. Nifuroxazide is a nitrofuran antibiotic. It is active against strains of the enteropathogenic bacteria C. jejuni, Salmonella, Y. enterocolitica, Shigella, and E. coli. It inhibits quorum sensing and virulence factor production in P. aeruginosa. Nifuroxazide inhibits STAT3 activity in a reporter assay and decreases viability of U266 and INA-6 myeloma cells, which have constitutive STAT3 phosphorylation, with EC50 values of approximately 4.5 µM for both. It also decreases viability, migration, and invasion of, and induces apoptosis in, MCF-7, 4T1, and MDA-MB-231 breast cancer cells. Nifuroxazide reduces tumor growth and prevents pulmonary metastasis in a 4T1 murine mammary carcinoma model. It also reduces diarrhea, weight loss, and colon inflammation in a rat model of acetic acid-induced ulcerative colitis.

Pentoxifylline-d6 is intended for use as an internal standard for the quantification of pentoxifylline by GC- or LC-MS. Pentoxifylline is a hemorrheologic agent. It increases the deformability of washed isolated human erythrocytes when used at a concentration of 100 µM. Pentoxifylline (1, 2, and 3 mM) inhibits ADP-induced platelet aggregation in isolated human whole blood. It inhibits thrombus formation induced by ADP in a hamster cheek pouch model when administered at doses of 5, 10, and 20 mg/kg. Formulations containing pentoxifylline have been used in the treatment of intermittent claudication.

Lornoxicam-d4 is intended for use as an internal standard for the quantification of lornoxicam by GC- or LC-MS. Lornoxicam is a COX inhibitor and non-steroidal anti-inflammatory drug (NSAID) with anti-inflammatory and analgesic properties. It inhibits production of thromboxane B2 from arachidonic acid in HEL human erythroleukemic cells, which endogenously express COX-1, as well as inhibits LPS-induced formation of prostaglandin F1α from arachidonic acid in Mono-Mac-6 cells, which endogenously express COX-2. Lornoxicam reduces LPS-induced production of nitric oxide and IL-6 in cell-based assays with IC50 values of 65 and 54 µM, respectively. It reduces carrageenan-induced paw edema in rats when administered intravenously at doses ranging from 0.1 to 9 mg/kg. Formulations containing lornoxicam have been used in the management of postoperative pain.

Rasagiline-13C3is intended for use as an internal standard for the quantification of rasagiline by GC- or LC-MS. Rasagiline is an inhibitor of monoamine oxidase B (MAO-B; IC50= 4.43 nM for the rat brain enzyme).1It is selective for MAO-B over MAO-A (IC50= 412 nM for the rat brain enzyme). It inhibits serum and NGF withdrawal-induced apoptosis of PC12 cells when used at concentrations ranging from 0.01 to 100 μM.2Rasagiline inhibits rat brain MAO-Bin vivo(ED50= 0.1 mg/kg).1It reduces cerebral edema in a mouse model of traumatic brain injury.2Rasagiline (0.1 mg/kg) reduces cortical and hippocampal levels of full-length and soluble amyloid precursor protein (APP) in rats and mice. It also reduces α-synuclein-induced substantia nigral neuron loss and improves motor dysfunction in a mouse model of Parkinson's disease.3Formulations containing rasagiline have been used in the treatment of Parkinson's disease. 1.Youdim, M.B.H., Gross, A., and Finberg, J.P.Rasagiline [N-propargyl-1R(+)-aminoindan], a selective and potent inhibitor of mitochondrial monoamine oxidase BBrit. J. Pharmacol.132(2)500-506(2001) 2.Youdim, M.B.H., and Weinstock, M.Molecular basis of neuroprotective activities of rasagiline and the anti-Alzheimer drug TV3326 [(N-propargyl-(3R) aminoindan-5-YL)-ethyl methyl carbamate]Cell. Mol. Neurobiol.21(6)555-573(2001) 3.Kang, S.S., Ahn, E.H., Zhang, Z., et al.α-Synuclein stimulation of monoamine oxidase-B and legumain protease mediates the pathology of Parkinson's diseaseEMBO J.37(12)e98878(2018)

Racecadotril-d5 is intended for use as an internal standard for the quantification of racecadotril by GC- or LC-MS. Racecadotril is a prodrug form of the neprilysin (NEP) inhibitor thiorphan. In vivo, racecadotril reduces or prevents castor oil-induced diarrhea without delaying intestinal transit in rats when administered at doses of 80 or 100 mg/kg, respectively. It also decreases the duration of diarrhea and increases body weight gain in a neonatal gnotobiotic pig model of human rotavirus-induced diarrhea. Formulations containing racecadotril have been used in the treatment of acute diarrhea.

D-Fructose-13C6 can be used as an internal standard for the quantification of D-fructose by GC- or LC-MS.

Indoxyl sulfate-d5 is intended for use as an internal standard for the quantification of indoxyl sulfate by GC- or LC-MS. Indoxyl sulfate is a uremic toxin and a metabolite of tryptophan. It is formed via sulfation of indole, an intermediate generated from tryptophan by intestinal bacteria, by the sulfotransferase (SULT) isoform 1A1 variant 2 (SULT1A1*2) in the liver. Indoxyl sulfate activates the aryl hydrocarbon receptor (AhR) in HepG2 40/6 hepatoma cells (EC50 = 12.1 nM in a reporter assay). It also inhibits the organic anion transporter (OAT) isoforms OAT1 and OAT3 (Kis = 34.2 and 74.4 µM, respectively for the rat transporters) in S2 proximal tubule cells. Indoxyl sulfate (0.2 and 1 mM) increases superoxide anion and nitric oxide levels in isolated human mononuclear blood cells. It increases serum creatinine and blood urea nitrogen (BUN) levels in the 5/6 nephrectomized rat model of chronic renal failure when administered at a dose of 50 mg/kg.

13C6 Glucosylsphingosine (d18:1) is an isotopically enriched form of 1-β-D-glucosylsphingosine (d18:1) that is intended for use as an internal standard for the quantification of 1-β-D-glucosylsphingosine by GC- or LC-MS. 1-β-D-Glucosylsphingosine is a lysolipid derivative of glucosylcerebroside that decreases activity of glucocerebrosidase in LA-N-2 cells in a dose-dependent manner.

Phenytoin-d10 is intended for use as an internal standard for the quantification of phenytoin by GC- or LC-MS. Phenytoin is an anticonvulsant agent and active metabolite of fosphenytoin. Phenytoin is formed from fosphenytoin by tissue phosphatases. It inhibits neuronal voltage-gated sodium channels in a voltage-dependent manner. Phenytoin reduces the neuronal firing frequency and decreases the amplitude of excitatory post-synaptic potentials (EPSPs) in electrically stimulated rat corticostriatal slices. It protects against seizures induced by maximal electroshock (MES) in mice. Formulations containing phenytoin have been used in the treatment of tonic-clonic seizures and status epilepticus.