Retrorsine is a DNA-binding pyrrolizidine alkaloid. [1]

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].

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In hyperbilirubinemic Gunn rats, pre-treatment with Retrorsine (RS) inhibited the proliferative capacity of host hepatocytes. This inhibition, combined with the stimulatory effect of triiodothyronine (T3), created a selective environment that enhanced the proliferation and engraftment of transplanted hepatocytes (both adult and foetal) in the host liver. Animals pre-treated with RS and then transplanted with hepatocytes showed a reduction in total serum bilirubin (TSB), indicating functional correction of the metabolic deficiency. The combination of RS pre-conditioning and T3 stimulation resulted in a more rapid and sustained improvement in TSB levels compared to RS pre-conditioning alone. The proliferative activity of hepatocytes in the livers of RS-pre-treated rats, as assessed by PCNA labelling index, was significantly lower in non-transplanted controls but was restored and enhanced upon hepatocyte transplantation, especially when combined with T3 administration. [1]

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.

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To inhibit host hepatocyte proliferation and create a selective advantage for transplanted cells, Gunn rats were pre-conditioned with Retrorsine (RS). RS was administered via intraperitoneal injection at a dose of 30 mg/kg body weight. Two injections were given, spaced two weeks apart. Hepatocyte transplantation (either adult or foetal syngeneic cells) was performed four weeks after the second RS injection. Approximately 40 x 10^6 hepatocytes were transplanted via direct injection into the splenic pulp. In some experimental groups, triiodothyronine (T3) was administered subcutaneously at a dose of 400 µg per 100 g body weight, starting on the day of transplantation and repeated every 10 days thereafter. Animals were sacrificed at 1, 7, 30, and 90 days post-transplantation for analysis. [1]

Absorption, Distribution and Excretion
Animal studies have shown that the highest concentrations are found in the liver, lungs, kidneys, and spleen. /Pyrrolizidine Alkaloids/ When rats were intraperitoneally injected with pyrrolizidine alkaloids, retrolidine (60 mg/kg), or retrolidine N-oxide (60 mg/kg), 0.2–12.4% of the dose was excreted in the urine as metabolized pyrroles within 24 hours. There is a general correlation between the hepatotoxicity of the alkaloids and the amount of pyrroles produced in vivo. When rats were sacrificed at different time points after oral or intraperitoneal injection of retrolidine (50 mg/kg), the metabolized pyrrole compounds were found to bind tightly to the liver for 48 hours or longer after generation, with lower binding to the lungs and other organs.

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Metabolism/Metabolites Studies on retrolidine have confirmed that the mixed-function oxidase system of rat liver microsomal components can generate N-oxides and pyrrole metabolites (retrolidine pyrrole). In animals, the main metabolic pathways of pyrrolizidine alkaloids include: (a) ester hydrolysis; (b) N-oxidation; and (c) nuclear dehydrogenation of pyrrolizidine to generate pyrrole derivatives. Pathways (a) and (b) are considered detoxification mechanisms. Pathway (c) generates toxic metabolites. Pathway (a) occurs in the liver and blood; pathways (b) and (c) are mediated by the hepatic microsomal mixed-function oxidase system. /Pyrrolizidine Alkaloids/
This study investigated the in vivo metabolism and urinary excretion of pyrrolizidine alkaloids (PAs), retrolidine (RET), and retrolidine-N-oxide (RET-NO) in rats. Isoidinic acid (INA), pyrrole metabolites, N-oxide, and retrolidine accounted for 31.0%, 10.3%, 10.8%, and 0.39% of the administered RET, respectively. Pre-administration of tri-o-cresol phosphate (TOCP) to rats had no effect on the excretion of pyrrole metabolites and INA. Phenobarbital (PB) increased the excretion of pyrrole metabolites and INA, while correspondingly decreasing the excretion of RET and N-oxides; reterosine levels remained unchanged. Intraperitoneal injection of RET-NO reduced urinary levels of pyrrole metabolites, INA, and RET compared to the RET-treated group. Oral administration of RET-NO significantly increased the levels of pyrrole metabolites, INA, and RET. These results suggest that esterase hydrolysis plays a minor role in INA formation, and that pyrrole metabolites and INA may share a common metabolic pathway. ...A group of young adult male rats were administered reterosine, and the induction or enhancement of mRNA and protein expression of extensively studied hepatic CYP isoenzymes (covering four families) and the essential enzyme CYP reductase were examined. Compared with untreated control rats, the levels of normally expressed CYP1A2, 2B1/2, and 2E1 proteins in the liver microsomes of reteralosin-treated rats were significantly increased (P<0.05), but the protein levels of CYP4A3, CYP3A1, and CYP reductases remained unchanged after reteralosin treatment. Furthermore, CYP1A1 mRNA and protein, which were undetectable in the livers of control rats, were induced to express after reteralosin treatment. These results indicate that exposure to reteralosin in rats enhances or induces the expression of CYP1A1, 1A2, 2E1, and 2B1/2 in the liver, suggesting that one or more of these enzymes may be involved in the metabolism of reteralosin. For more complete metabolite/metabolite data on reteralosin (6 metabolites), please visit the HSDB record page.
Biological Half-Life
Within hours after administration, only a relatively small proportion of the drug remains in the body. Most of it exists as metabolites bound to tissue components. Following intravenous injection in animals, pyrrolizidine N-oxide disappears from the serum, with an initial half-life of 3-20 minutes. /Pyrrolizidine alkaloids/

Interactions
…Porton Wistar rats were given a single dose of 30 mg/kg body weight of reterosine via gastric tube after weaning… 100 days after administration, 31 rats were subjected to 400 rads of whole-body irradiation… Of the 25 surviving rats, 5 had hepatocellular carcinoma, 5 had mammary tumors, 2 had renal cancer, and 1 each had hepatocellular carcinoma with lung metastasis, lung cancer, colon cancer, splenic angioendothelioma, osteosarcoma of the humerus, leukemia, and spindle cell tumor of the neck… /No control group was set/
Although most of the toxic effects of reterosine appear to be mediated by its highly active metabolite dehydroreterosine (reterosine pyrrole), produced in the liver by a mixed-function oxidase, the toxicity of this alkaloid is not always directly related to enzyme activity. Phenobarbital (PB) pretreatment tripled the rate of pyrrole formation from reteralosine in vitro and tripled the rate of N-oxide formation, thus protecting male rats from reteralosine poisoning (LD50 of 34 mg/kg body weight with intraperitoneal injection alone, and 67 mg/kg body weight with PB), but increased toxicity in female rats (LD50 of 153 mg/kg body weight with intraperitoneal injection alone, and 87 mg/kg body weight with PB). However, some delayed toxicities were observed, including pulmonary congestion and edema, which were rare after reteralosine poisoning. In male rats, inhibition of mixed-function oxidase (MMEO) with SKF-525a (LD50 of 53 mg/kg body weight with intraperitoneal injection) or by a 4-day sucrose diet (LD50 of 120 mg/kg body weight with intraperitoneal injection) prevented acute death, but chronic liver and lung damage subsequently occurred.

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Non-human toxicity values>
Mice intravenous injection LD50: 59 mg/kg
Rat intraperitoneal injection LD50: 34 mg/kg
Rat intravenous injection LD50: 38 mg/kg

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This study indicates that the use of such toxins in humans is dangerous due to the carcinogenicity of reterosine and similar toxins. (Carcinogenic potential). This indicates a significant toxicity problem related to its carcinogenicity. [1]

[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.

Raterosin is a macrolide antibiotic. It has been reported in Senecio vernalis, Osyris alba, and several other organisms with relevant data. Mechanism of Action: The dehydropyrrolizine metabolite…reacts with water, DNA, and other cellular components in vitro and exhibits cytotoxicity. Its bioactivation is mediated by C-oxidation, a reaction that proceeds very slowly in neonatal microsomes but rapidly increases in microsomes acquired within 5 days of birth. In vivo gavage administration of 7 mg/kg aterosin to rats inhibited the incorporation of labeled amino acids into rat liver and plasma proteins. The toxin affected hepatic ribosome aggregates, leading to an increased ratio of monomers to dimers. One hour after administration, the incorporation of orotic acid into hepatic nuclear RNA was inhibited. The role of hepatic glutathione in the acute toxicity of aterosin in rats was investigated using two methods. Cysteine increased glutathione levels in rats to approximately twice that of the control group, while 2-chloroethanol increased them to approximately 25% of the control group. The acute LD50 of reteralosine (42 mg/kg) in rats increased to 83 mg/kg after cysteine pretreatment and decreased to 23 mg/kg after 2-chloroethanol pretreatment. Two hours after administration of reteralosine (60 mg/kg), the levels of pyrrole metabolites in the livers of rats pretreated with cysteine or 2-chloroethanol were approximately 60% and 200% of those in untreated rats, respectively. Twenty-four hours later, the glutathione concentration in the livers of reteralosine-treated rats was higher than that in the corresponding control groups. Twenty-four hours after treatment with reteralosine (60 mg/kg), the concentration of hepatic cytochrome P-450 decreased. Rats pretreated with chloroethanol showed increased loss of cytochrome P-450. Mixed-function oxidases activate alkaloids to generate pyrrole dehydroalkaloids, which are active alkylating agents. Metabolites bind to hepatocytes, leading to liver necrosis. Some metabolites are released into the bloodstream and are believed to reach the lungs via the liver, causing vascular damage. Pyrrole metabolites are cytotoxic, acting on hepatocytes as well as the vascular endothelium of the liver and lungs. /pyrrolizidine alkaloids/

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Rectoline can be used as a pharmacological tool to block the proliferative capacity of intrinsic hepatocytes in the recipient liver. It induces extensive polyploidization of hepatocytes, meaning that cells can continue DNA synthesis but cannot divide, ultimately leading to cell death. This creates a "space" and selection pressure that favors the proliferation of subsequently transplanted healthy hepatocytes. In this study, we developed an RS/T3 model (combining RS pretreatment and T3 stimulation) designed to enhance the liver regeneration capacity of transplanted hepatocytes in a metabolic liver disease model (Gunn rats, a model of type I Crigler-Najjar syndrome). This strategy aims to improve the therapeutic efficacy of hepatocyte transplantation as an alternative to whole liver transplantation. [1]

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.)