Retrorsine (60-240 μM; 24 hours) enhances the production of pyrrole-protein adducts and greatly lowers GSH levels and HSEC-CYP3A4 cell viability [3].

In the PBL model, retrorsine (30 mg/kg; i.p.; twice) inhibits liver regeneration via S or G2/M phase arrest as well as a block that occurs just prior to the cell cycle's G1/S transition [4].

Cell viability assay [3]
Cell Types: HSEC-CYP3A4 Cell
Tested Concentrations: 60 μM, 120 μM, 240 μM
Incubation Duration: 24 hrs (hours)
Experimental Results: Cell viability was Dramatically diminished.

Animal/Disease Models: Male Wistar rat (180±20 g), portal branch ligation (PBL) model [4]
Doses: 30 mg/kg
Route of Administration: intraperitoneal (ip) injection, twice, 2 weeks apart
Experimental Results: Severe damage to liver weight increase Protein and DNA synthesis and induction of cell cycle-related proteins in regenerated leaves after PBL.

Absorption, Distribution and Excretion
In animal studies highest concentrations were found in the liver, lungs, kidneys and spleen. /pyrrolizidine alkaloids/
When pyrrolizidine alkaloids, retrorsine 60 mg/kg, retrorsine n-oxide 60 mg/kg were administered ip to rats, 0.2-12.4% of the doses were excreted in the urine within 24 hr as metabolic pyrroles. There was a rough correlation between the hepatotoxicity of alkaloids and the amount of pyrroles to which they gave rise to in vivo. When rats were dosed orally or ip with retrorsine 50 mg/kg and sacrificed after various times, metabolic pyrroles were found bound strongly to the liver, and to /lesser/ extent the lung and other organs, for 48 hr or more after being formed.

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Metabolism / Metabolites
Studies with retrorsine have confirmed the formation of the n-oxide and pyrrolic metabolites /retrorsine pyrrole/ by the mixed-function oxidase system of the microsomal fraction of rat liver.
In animals, the major metabolic routes of pyrrolizidine alkaloids are: (a) hydrolysis of the ester groups; (b) N-oxidation; and (c) dehydrogenation of the pyrrolizidine nucleus to pyrrolic derivatives. Routes (a) and (b) are believed to be detoxification mechanisms. Route (c) leads to toxic metabolites. Route (a) occurs in liver and blood; routes (b) and (c) are brought about in the liver by the microsomal mixed function oxidase system. /pyrrolizidine alkaloids/
The in vivo metabolism and excretion of the urinary metabolites from the pyrrolizidine alkaloids (PAs), retrorsine (RET) and retrorsine-N-oxide (RET-NO) have been studied in rats. Isatinecic acid (INA), pyrrolic metabolites, N-oxides and retronecine accounted for 31.0, 10.3, 10.8 and 0.39% of the administered RET. Predosing rats with triorthocresyl phosphate (TOCP), had no effect on the excretion of pyrrolic metabolites and INA. Phenobarbital (PB) increased the excretion of both pyrrolic metabolites and INA with a corresponding decrease in the excretion of RET and N-oxides; the retronecin levels remained unaltered. When RET-NO was administered i.p., the urinary levels of pyrrolic metabolites, INA and RET were decreased relative to those treated with RET. The p.o. administration of RET-NO produced significantly higher levels of pyrrolic metabolites, INA and RET. These results suggest that esterase hydrolysis plays a minor role in the formation of INA and that a common metabolic pathway may exist between pyrrolic metabolites and INA formation.
...Retrorsine was administered to a cohort of young adult male rats and examined induction or enhanced expression of mRNA and protein for widely studied hepatic CYP isoforms spanning four families together with the essential enzyme CYP reductase. The protein levels of normally expressed CYPs 1A2, 2B1/2, and 2E1 increase significantly in rat liver microsomes from retrorsine-treated rats compared to untreated control rats (P< 0.05), but protein levels of CYP 4A3, CYP 3A1, and CYP reductase were unchanged after retrorsine treatment. In addition, CYP 1A1 mRNA and protein, which are not detectable in the livers of control rats, were induced after retrorsine exposure. The results of the present study demonstrate enhanced or induced expression of hepatic CYPs 1A1, 1A2, 2E1, and 2B1/2 in response to retrorsine exposure in rats, suggesting that one or more of these enzymes may be involved in retrorsine metabolism.
For more Metabolism/Metabolites (Complete) data for RETRORSINE (6 total), please visit the HSDB record page.

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Biological Half-Life
Within a few hours, only a relatively small proportion of the administered dose remains in the body. Much of this is in the form of metabolites bound to tissue contents. A pyrrolizidine N-oxide disappeared from the serum after IV administration in animals, with initial half-lives of 3 -20 minutes. /pyrrolizidine alkaloids/

Interactions
...Weanling Porton Wistar rats were given single doses of 30 mg/kg body weight retrorsine by stomach tube...with whole-body irradiation of 400 rads 100 days after dosing, in 31 rats... In 25 survivors, there were 5 hepatomas, 5 mammary tumors, 2 renal carcinomas and 1 case each of carcinoma of the liver with pulmonary metastases, carcinoma of the lung, carcinoma of the colon, hemangioendothelioma of the spleen, osteosarcoma of the humerus, leukemia and spindle-cell tumor of the neck... /no controls presented/
Although most of the toxic effects of retrorsine appear to be mediated via the very reactive metabolite dehydroretrorsine (retrorsine pyrrole), which is produced in the liver by the mixed-function oxidases, the toxicity of this alkaloid does not always relate directly to the activity of the enzymes. Pre-treatment with phenobarbital (pb) which increases the rate of in vitro microsomal production of pyrroles from retrorsine three-fold and that of n-oxides two-fold, protected male rats against retrorsine poisoning (ip Ld50's, 34 mg/kg body weight alone, 67 mg/kg body weight with pb) but increased its toxicity in female rats (ip LD50's, 153 mg/kg body weight alone, 87 mg/kg body weight with pb). However, there were delayed toxic effects, including congestion and edema of the lungs, which are rarely seen after retrorsine /poisoning/.
In male rats, protection against acute deaths was given when mixed-function oxidases were inhibited by skf-525a (ip LD50's, 53 mg/kg body weight) and by a 4-day sucrose diet (ip LD50's, 120 mg/kg body weight), but chronic hepatic and pulmonary lesions developed subsequently.

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Non-Human Toxicity Values
LD50 Mouse iv 59 mg/kg
LD50 Rat ip 34 mg/kg
LD50 Rat iv 38 mg/kg

[1]. Hepatic proliferation in Gunn rats transplanted with hepatocytes: effect of retrorsine and tri-iodothyronine. Cell Prolif. 2005 Jun;38(3):137-46.

[2]. Liver regeneration in response to partial hepatectomy in rats treated with retrorsine: a kinetic study. J Hepatol. 1999 Dec;31(6):1069-74.

[3]. Establishment of a novel CYP3A4-transduced human hepatic sinusoidal endothelial cell model and its application in screening hepatotoxicity of pyrrolizidine alkaloids. J Environ Sci Health C Toxicol Carcinog. 2020;38(2):169-185.

[4]. Retrorsine: a kinetic study of its influence on rat liver regeneration in the portal branch ligation model. J Hepatol. 2003 Jul;39(1):99-105.

Retrorsine is a macrolide.
Retrorsine has been reported in Senecio vernalis, Osyris alba, and other organisms with data available.

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Mechanism of Action
The dehydropyrrolizine metabolites...react with water, DNA, and other cell components in vitro, and are cytotoxic. The bioactivation is mediated by a c-oxygenation, a reaction which proceeds very slowly in microsomes from neonates but which increases rapidly in microsomes obtained up to 5 days after birth.
Intragastric admin of 7 mg/kg retrorsine inhibited incorporation of labeled amino acids into rat liver and plasma proteins in vivo. The toxin affected the liver ribosomal aggregates, causing increases in proportion of monomers plus dimers. Incorporation of orotate into liver nuclear RNA was inhibited 1 hr after admin.
Two procedures were used to study the role of liver glutathione in acute toxicity of retrorsine in rats. Glutathione levels in rats were increased to about double that of controls by cysteine and to about 25% that of control by 2-chloroethanol. Acute LD50 of retrorsine (42 mg/kg) to rats is increased by pretreatment with cysteine to 83 mg/kg and decreased by pretreatment with 2-chloroethanol to 23 mg/kg. Two hr after admin of retrorsine (60 mg/kg) the levels of pyrrolic metabolites in the livers of animals pretreated with cysteine or c-chloroethanol are, respectively, about 60% and 200% those of rats given no pretreatment. By 24 hr, the glutathione concentration in livers of retrorsine-dosed rats is higher than those of corresponding controls. Treatment of rats with retrorsine (60 mg/kg) causes a fall in liver concentration of cytochrome p-450, 24 hr after dosing. This loss of cytochrome p-450 is increased in rats pretreated with chloroethanol.
The activation of the alkaloids by mixed-function oxidases leads to pyrrolic dehydro-alkaloids which are reactive alkylating agents. The liver necrosis results from binding of the metabolites with the liver cell. Some metabolites are released into the circulation and are believed to pass beyond the liver to the lung causing vascular lesions. The pyrrolic metabolites are cytotoxic and act on the hepatocytes and on the endothelium of blood vessels of the liver and lung. /pyrrolizidine alkaloids/

C18H25NO6

351.3942

351.168

480-54-6

36168-23-7 (hydrochloride)

5281743

White to off-white solid powder

1.3±0.1 g/cm3

583.2±50.0 °C at 760 mmHg

208-211ºC(lit.)

306.5±30.1 °C

0.0±3.7 mmHg at 25°C

1.590

-0.14

2

7

1

25

627

4

C/C=C\1/C[C@H]([C@@](C(=O)OCC2=CCN3[C@H]2[C@@H](CC3)OC1=O)(CO)O)C

BCJMNZRQJAVDLD-CQRYIUNCSA-N

InChI=1S/C18H25NO6/c1-3-12-8-11(2)18(23,10-20)17(22)24-9-13-4-6-19-7-5-14(15(13)19)25-16(12)21/h3-4,11,14-15,20,23H,5-10H2,1-2H3/b12-3-/t11-,14-,15-,18-/m1/s1

(1R,4Z,6R,7S,17R)-4-ethylidene-7-hydroxy-7-(hydroxymethyl)-6-methyl-2,9-dioxa-14-azatricyclo[9.5.1.014,17]heptadec-11-ene-3,8-dione

2934.99.9001

Powder      -20°C    3 years

                     4°C     2 years

In solvent   -80°C    6 months

                  -20°C    1 month

Note: This product requires protection from light (avoid light exposure) during transportation and storage.

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

DMSO : ~100 mg/mL (~284.58 mM)

Solubility in Formulation 1: ≥ 2.5 mg/mL (7.11 mM) (saturation unknown) in 10% DMSO + 40% PEG300 + 5% Tween80 + 45% Saline (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 400 μL PEG300 and mix evenly; then add 50 μL Tween-80 to the above solution and mix evenly; then add 450 μL normal saline to adjust the volume to 1 mL.
Preparation of saline: Dissolve 0.9 g of sodium chloride in 100 mL ddH₂ O to obtain a clear solution.

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Solubility in Formulation 2: ≥ 2.5 mg/mL (7.11 mM) (saturation unknown) in 10% DMSO + 90% (20% SBE-β-CD in Saline) (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of 20% SBE-β-CD physiological saline solution and mix evenly.
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.

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Solubility in Formulation 3: ≥ 2.5 mg/mL (7.11 mM) (saturation unknown) in 10% DMSO + 90% Corn Oil (add these co-solvents sequentially from left to right, and one by one), clear solution.
For example, if 1 mL of working solution is to be prepared, you can add 100 μL of 25.0 mg/mL clear DMSO stock solution to 900 μL of corn oil and mix evenly.

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