AT1 Receptor

Losartan competes with angiotensin II's ability to bind to AT1 receptors in vitro; the concentration that prevents 50% of this binding (IC50) is 20 nmol/L[1]. In VSMCs, losartan increases AMPK phosphorylation in a dose- and time-dependent manner. It also raises the phosphorylation of LKB1, an AMPK upstream kinase, and ACC, a significant downstream target protein in the AMPK signaling cascade. While p27 expression levels remain unchanged, losartan causes a time-dependent increase in p53 and p21 expression. Losartan inhibits the expression of cyclin D and cyclin E, which are necessary for the progression of the cell cycle, as well as Ang II-induced Rb phosphorylation. Therefore, G0/G1 cell cycle arrest—which is reversible by AMPK inhibition, such as compound C or AMPK siRNA, but not by apoptosis—is the mechanism by which losartan suppresses growth[2].

Losartan has a major active metabolite, EXP 3174. EXP3174 is 10–20 times more potent and acts for a longer period of time when administered intravenously than losartan. EXP 3174 has a very low oral bioavailability, though. When dosed at 50–100 mg/d, losartan has a bioavailability of roughly 33%, a half-life of 2 hours (6–9 hours), and a rate of protein binding of 98.7%[1]. In hypertensive rats, treatment with losartan reduces the loss of endothelial progenitor cells (EPCs) in terms of both quantity and function[3].

Antagonists of the type 1 (AT1) angiotensin II (Ang II) receptor increase renin secretion and plasma Ang II levels, and the increased Ang II levels may counteract the effects of the antagonist. Moreover, other investigators have suggested that the reactive increase in Ang II levels may increase bradykinin (BK) levels through stimulation of the type 2 Ang II receptor (AT2). We investigated the acute effects of the AT1 receptor antagonist losartan (intraarterial injection of 10 mg/kg every 12 h) in male Sprague Dawley rats by measuring circulating angiotensin and BK peptides at 6, 12, and 24 h. Whereas acute losartan administration increased blood angiotensin levels four- to sixfold, blood BK levels were unchanged. We also investigated the effects of losartan administered for 8 days (10 mg/kg every 12 hours, by intraperitoneal injection) on circulating and tissue levels of angiotensin and BK peptides, and angiotensin-converting enzyme (ACE). Losartan increased plasma renin levels 100-fold; plasma angiotensinogen levels decreased to 24% of control; and plasma aldosterone levels were unchanged. Ang II levels in plasma, adrenal, lung, heart, and aorta were increased 25-, 8-, 3.5-, 2.4-, and 14-fold, respectively, by losartan administration. By contrast, kidney Ang II levels decreased to 71% of control, accompanied by a decrease in kidney levels of BK-(1-7) and BK-(1-9). No other tissue showed a change in BK peptide levels, except for a reduction in blood levels of BK-(1-8) to 43% of control. Plasma ACE increased by 13-50%, but tissue ACE levels were unchanged. These data demonstrate that losartan has tissue-specific effects on endogenous levels of angiotensin and BK peptides and indicate that increased BK levels do not contribute to the actions of losartan. The absence of a reactive increase in endogenous kidney levels of Ang II indicates that this tissue is likely to be the most sensitive to AT1 receptor antagonism[5].

The MTT assay is used to quantify the viability and proliferation of cells. In a 96-well plate, 5000 cells are seeded with 200 μL media per well for the assay. After allowing the cells to attach over night, the medium is suctioned out. After adding MTT to serum-free medium at a concentration of 1 mg/mL, the mixture is incubated for 4 hours at 37°C. To dissolve the formazan crystals, 100 μL of DMSO is added after the MTT solution is removed. Then, using a microplate reader, absorbance is measured at 570 nm and 600 nm as references. Thus, the variation in absorbance is related to the degree of cell survival.

Mice of the wild type mate with female Fbn1^C1039G/+ mice at predetermined times. Ocular losartan (0.6 g/L in drinking water; n = 10), propranolol (0.5 g/L; n = 6), or placebo (n = 12) is administered to pregnant female Fbn1^C1039G/+ mice at 14.5 days post-coitum. Up until the age of ten months, therapy is administered during lactation and following weaning. These methods are applied to the sacrifice and examination of mice. In MFS, the current, albeit contentious, standard of care for modulating abnormal growth of the aortic root is β-adrenergic receptor blockade; propranolol and losartan are the comparison drugs. At 7 weeks of age, oral losartan (0.6 g/L in drinking water; n = 5), propranolol (0.5 g/L; n = 7), or a placebo (n = 10) is administered to wild-type and Fbn1^C1039G/+ mice. Following six months of oral treatment, mice are sacrificed.

Absorption, Distribution and Excretion
The oral bioavailability of losartan is approximately 33%. The time to peak concentration (Tmax) of losartan is 1 hour, while that of its active metabolite is 3-4 hours. Taking losartan with food reduces the peak plasma concentration (Cmax), but only decreases the area under the curve (AUC) of losartan and its active metabolite by 10%. After oral administration of 50-80 mg of losartan, the peak plasma concentration (Cmax) is 200-250 ng/mL. After a single oral dose of losartan, 4% of the original drug and 6% of the active metabolite are recovered in the urine. After oral administration of radiolabeled losartan, 35% of the losartan is recovered in the urine and 60% in the feces. After intravenous administration of radiolabeled losartan, 45% is recovered in the urine and 50% in the feces. The volume of distribution (VOD) of losartan is 34.4 ± 17.9 L, and that of its active metabolite (E-3174) is 10.3 ± 1.1 L. The total plasma clearance of losartan is 600 mL/min, and the renal clearance is 75 mL/min. The total plasma clearance of the active metabolite E-3174 is 50 mL/min, and the renal clearance is 25 mL/min. It is unclear whether losartan is excreted into human milk, but significant levels of losartan and its active metabolite have been confirmed in rat milk. After oral administration, losartan is well absorbed (based on the absorption of radiolabeled losartan) and undergoes significant first-pass metabolism; the systemic bioavailability of losartan is approximately 33%. Approximately 14% of losartan is converted to the active metabolite after oral administration. The mean peak concentrations of losartan and its active metabolite are reached at 1 hour and 3–4 hours, respectively. Although the peak plasma concentrations of losartan and its active metabolite are roughly equal, the AUC of the metabolite is approximately four times that of losartan. Food intake slows the absorption of losartan and lowers its Cmax, but has little effect on the AUC of losartan or its metabolites (approximately a 10% reduction). Rat studies have shown that losartan barely crosses the blood-brain barrier. Both losartan and its active metabolites are highly bound to plasma proteins (primarily albumin), with plasma free fractions of 1.3% and 0.2%, respectively. Plasma protein binding remains constant within the concentration range achieved at recommended doses. For more complete data on the absorption, distribution, and excretion of losartan (8 items), please visit the HSDB record page.

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Metabolism/Metabolites
Losartan is metabolized to the aldehyde intermediate E-3179, which is further metabolized by cytochrome P450 (such as CYP2C9) to the carboxylic acid E-3174. Losartan can also be hydroxylated to the inactive metabolite P1. Approximately 14% of losartan is metabolized to E-3174. Losartan is metabolized by CYP3A4, CYP2C9, and CYP2C10. It can also be glucuronidated by UGT1A1, UGT1A3, UGT1A10, UGT2B7, and UGT2B17. Losartan is an orally active drug that undergoes extensive first-pass metabolism via cytochrome P450 enzymes. It is partially converted into an active carboxylic acid metabolite, which is the source of most of the angiotensin II receptor antagonism following losartan treatment. Losartan metabolites have been detected in human plasma and urine. In addition to the active carboxylic acid metabolite, several inactive metabolites are also generated. Following oral and intravenous administration of 14C-labeled losartan potassium, the radioactivity in circulating plasma is primarily attributed to losartan and its active metabolites. In vitro studies have shown that cytochrome P450 2C9 and 3A4 are involved in the biotransformation of losartan into its metabolites. In approximately 1% of study subjects, extremely low conversion of losartan to its active metabolite was observed (less than 1% of the dose, compared to 14% of the dose in normal subjects). Known human metabolites of losartan include losartan carboxylic acid and 2-[5-[2-[4-[[2-butyl-5-chloro-4-(hydroxymethyl)-1H-imidazol-3-onthiol]methyl]phenyl]phenyl]-1,5-dihydrotetrazol-2-yl]-6-(dihydroxymethyl)oxacyclohexane-3,4,5-triol. The terminal elimination half-life of losartan is 1.5–2.5 hours, while the half-life of its active metabolite is 6–9 hours. The terminal half-life of losartan is approximately 2 hours, while the terminal half-life of its metabolites is approximately 6–9 hours.

Toxicity Summary
Identification and Uses: Losartan is a pale yellow solid, formulated as oral tablets. Losartan is an angiotensin II type 1 (AT1) receptor antagonist. It can be used alone or in combination with other classes of antihypertensive drugs to treat hypertension. It is also used to reduce the risk of stroke in patients with hypertension and left ventricular hypertrophy, and to treat diabetic nephropathy in patients with type 2 diabetes and a history of hypertension. Human Exposure and Toxicity: The most likely manifestations of losartan overdose include hypotension and tachycardia; bradycardia may occur if parasympathetic (vagus nerve) excitation occurs. Losartan is contraindicated during pregnancy. While use of losartan in early pregnancy does not indicate a risk of serious malformations, use in mid-to-late pregnancy may lead to teratogenicity and serious fetal and neonatal toxicity. Fetal toxicity may include anuria, oligohydramnios, fetal craniofacial dysplasia, intrauterine growth restriction, preterm birth, and patent ductus arteriosus. Anuria-associated oligohydramnios may lead to fetal limb contractures, craniofacial malformations, and pulmonary dysplasia. Neonates exposed to losartan in utero may develop severe anuria and hypotension, unresponsive to vasopressors and volume expansion therapy. Animal studies: Losartan potassium did not show carcinogenicity at the maximum tolerated dose in rats and mice. Female rats administered losartan had a slightly higher incidence of pancreatic acinar tumors. Furthermore, in studies of oral administration of losartan to male rats, fertility and reproductive function were not affected. In female animals, toxic doses were associated with significantly reduced corpus luteum/female, implantation/female, and live fetus/female numbers at cesarean section. Since these dose levels did not affect implantation/pregnancy females, post-implantation embryo loss rate, or the number of live fetuses per litter at parturition, the relationship between these results and drug treatment remains unclear. Losartan has been shown to cause adverse reactions in rat fetuses and neonates, including weight loss, physical and behavioral developmental delays, death, and nephrotoxicity. Except for increased neonatal weight, doses associated with these adverse reactions exceeded 25 mg/kg. These results are attributed to drug exposure during late pregnancy and lactation. Losartan was negative in microbial mutagenesis assays, V-79 mammalian cell mutagenesis assays, in vitro alkaline elution assays, and in vitro and in vivo chromosomal aberration assays. Furthermore, the active metabolite did not show genotoxicity in microbial mutagenesis assays, in vitro alkaline elution assays, and in vitro chromosomal aberration assays.

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Interactions
…This study aimed to evaluate how long-term administration of deoxycorticosterone acetate (DOCA) affected the effects of losartan on blood pressure, kidney injury, and other parameters in N(G)-nitro-L-arginine methyl ester (L-NAME)-induced hypertensive rats. The experiment included the following groups: control group, DOCA group, L-NAME group, L-NAME + losartan group, L-NAME + DOCA group, and L-NAME + DOCA + losartan group. Tail systolic blood pressure was measured twice weekly. After 4 weeks, mean arterial pressure, as well as metabolic, morphological, and renal parameters, were measured. The final mean arterial pressure values were: control group 116 ± 6 mmHg, DOCA group 107 ± 2 mmHg, L-NAME group 151 ± 5 mmHg, L-NAME + losartan group 123 ± 2 mmHg, L-NAME + DOCA group 170 ± 3 mmHg, and L-NAME + DOCA + losartan group 171 ± 5.5 mmHg. Losartan can prevent microalbuminuria, hyaline artery disease, and glomerulosclerosis caused by L-NAME hypertension, but it is ineffective in the L-NAME + DOCA treatment group. …Plasma renin activity was inhibited in the DOCA group (0.55 ± 0.2) and the L-NAME + DOCA group (0.60 ± 10.2), while plasma renin activity was not inhibited in the L-NAME + DOCA + losartan group (5.8 ± 1). The conclusion is that DOCA blocked the preventive effect of losartan on the increase in blood pressure and kidney damage caused by L-NAME hypertension… These data also suggest that losartan prevents L-NAME hypertension by blocking the activity of systemic angiotensin II. /Unspecified salt/
It is known that nonsteroidal anti-inflammatory drugs (NSAIDs) can weaken the effects of some antihypertensive drugs… A multicenter study evaluating the effect of indomethacin on the antihypertensive effects of losartan and captopril has been conducted. After a 4-week placebo washout period, hypertensive patients received 6 weeks of active antihypertensive therapy with 50 mg losartan once daily (n=111)… Subsequently, patients received 1 week of indomethacin combination therapy (75 mg daily). The primary endpoint was the change in mean 24-hour ambulatory diastolic blood pressure after the addition of indomethacin. After 6 weeks of losartan treatment, ambulatory diastolic blood pressure was significantly reduced (5.3 mmHg reduction in the losartan group, P<0.001). Indomethacin significantly reduced 24-hour ambulatory diastolic blood pressure (2.2 mmHg reduction in the losartan group, P<0.05). The daytime diastolic blood pressure variation (7:00 AM to 11:00 PM) was similar to the 24-hour diastolic blood pressure variation in both groups. Nighttime diastolic blood pressure (11:01 PM to 6:59 AM the following morning) was unaffected (0.4 mmHg reduction in the losartan group). Therefore, concomitant treatment with indomethacin and losartan may also weaken the 24-hour antihypertensive response of losartan…/unspecified salt/
There may be potential drug interactions (weakened antihypertensive effect) when angiotensin II receptor antagonists are used in combination with nonsteroidal anti-inflammatory drugs (NSAIDs) (including selective cyclooxygenase-2 (COX-2) inhibitors). Elderly patients, patients with low blood volume (including those receiving concurrent diuretic therapy), or patients with impaired renal function may experience worsening of renal function; patients receiving losartan in combination with nonsteroidal anti-inflammatory drugs (NSAIDs, including selective COX-2 inhibitors) should have their renal function monitored regularly. When losartan potassium is used in combination with rifampin, a decrease in plasma concentrations of losartan and its active metabolites can be observed. For more complete data on drug interactions with losartan (20 items in total), please visit the HSDB record page.

[1]. Angiotensin II type 1 receptor blockers. Circulation, 2001. 103(6): p. 904-12.

[2]. Evidence for expression and function of angiotensin II receptor type 1 in pulmonary epithelial cells. Respir Physiol Neurobiol, 2014.

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[3]. Angiotensin II type I receptor and miR-155 in endometrial cancers: synergistic antiproliferative effects of anti-miR-155 and losartan on endometrial cancer cells. Gynecol Oncol, 2012. 126(1): p. 124-31.

[4]. Losartan, an AT1 antagonist, prevents aortic aneurysm in a mouse model of Marfan syndrome. Science, 2006. 312(5770): p. 117-21.

[5]. Effects of losartan on angiotensin and bradykinin peptides and angiotensin-converting enzyme. J Cardiovasc Pharmacol, 1995. 26(2): p. 233-40.

Therapeutic Uses
Angiotensin II type 1 receptor blocker; antiarrhythmic; antihypertensive. Cozarr is indicated for the treatment of hypertension. It can be used alone or in combination with other antihypertensive drugs, including diuretics. /US product label includes/ Cozarr is indicated for the reduction of stroke risk in patients with hypertension and left ventricular hypertrophy, but there is evidence that this benefit is not present in Black patients. /US product label includes/ Cozarr is indicated for the treatment of diabetic nephropathy in patients with type 2 diabetes and a history of hypertension who have elevated serum creatinine and proteinuria (urine albumin/creatinine ratio = 300 mg/g). In this population, Cozarr reduces the rate of kidney disease progression, measured by the doubling of serum creatinine or the incidence of end-stage renal disease (requiring dialysis or kidney transplantation). /US product label includes/ For more complete data on the therapeutic uses of losartan (6 types), please visit the HSDB record page.

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Drug Warning
/Black Box Warning/ Warning: Fetal Toxicity. Cozaar should be discontinued as soon as pregnancy is confirmed. Drugs that act directly on the renin-angiotensin system can cause damage or even death to the developing fetus.
Use of drugs that act on the renin-angiotensin system in the second and third trimesters can reduce kidney function and increase morbidity and mortality in the fetus and newborn. Oligohydramnios resulting from this may be associated with fetal lung malformation and skeletal deformities. Potential neonatal adverse reactions include craniosynostosis, anuria, hypotension, kidney failure, and death. Losartan should be discontinued as soon as pregnancy is confirmed. These adverse reactions are often associated with use of such drugs in the second and third trimesters. Most epidemiological studies investigating fetal malformations following the use of antihypertensive drugs in early pregnancy have not differentiated between drugs affecting the renin-angiotensin system and other antihypertensive drugs. Appropriate management of maternal hypertension during pregnancy is crucial for optimizing maternal and infant outcomes. In rare cases where no suitable alternative therapy is available for a particular patient, the pregnant woman should be informed of the potential risks of the drug to the fetus. Perform a series of ultrasound examinations to assess the amniotic environment. If oligohydramnios is observed, losartan should be discontinued unless discontinuation is deemed essential to the pregnant woman's life. Fetal monitoring may be required depending on gestational age. However, patients and physicians should note that oligohydramnios may only occur after irreversible damage to the fetus. Newborns with a history of intrauterine exposure to losartan: If oliguria or hypotension occurs, focus should be placed on maintaining blood pressure and renal perfusion. Exchange transfusion or dialysis may be necessary to reverse hypotension and/or replace impaired kidney function. FDA Pregnancy Risk Classification: D/Clear evidence of risk. Fetal risk has been confirmed by human studies, trial data, or post-marketing data. Nevertheless, the potential benefits of using this drug may outweigh the potential risks. For example, this drug may be appropriate in life-threatening situations or when the patient has a serious illness for which other safer medications are unavailable or ineffective. / For more complete data on drug warnings for losartan (21 total), please visit the HSDB records page.

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Pharmacodynamics
Losartan is an angiotensin II receptor blocker used to treat hypertension, diabetic nephropathy, and to reduce the risk of stroke. Losartan is administered once daily, thus having a relatively long duration of action. Patients taking losartan should be monitored regularly for low blood pressure, renal function, and serum potassium levels.

C22H23CLN6O

422.91

422.162

C, 62.48; H, 5.48; Cl, 8.38; N, 19.87; O, 3.78

114798-26-4

Losartan Carboxylic Acid; 124750-92-1; Losartan-d4 (carboxylic acid); 1246820-62-1; Losartan potassium; 124750-99-8; Losartan-d4; 1030937-27-9; Losartan-d3 Carboxylic Acid; 1189729-40-5; Losartan-d2; 1030936-22-1; Losartan-d9; 1030937-18-8

3961

White to light yellow solid powder

1.4±0.1 g/cm3

682.0±65.0 °C at 760 mmHg

183-184ºC

366.3±34.3 °C

0.0±2.2 mmHg at 25°C

1.681

3.57

2

5

8

30

520

0

ClC1=C(C([H])([H])O[H])N(C([H])([H])C2C([H])=C([H])C(C3=C([H])C([H])=C([H])C([H])=C3C3N=NN([H])N=3)=C([H])C=2[H])C(C([H])([H])C([H])([H])C([H])([H])C([H])([H])[H])=N1

PSIFNNKUMBGKDQ-UHFFFAOYSA-N

InChI=1S/C22H23ClN6O/c1-2-3-8-20-24-21(23)19(14-30)29(20)13-15-9-11-16(12-10-15)17-6-4-5-7-18(17)22-25-27-28-26-22/h4-7,9-12,30H,2-3,8,13-14H2,1H3,(H,25,26,27,28)

[2-butyl-5-chloro-3-[[4-[2-(2H-tetrazol-5-yl)phenyl]phenyl]methyl]imidazol-4-yl]methanol

DUP 89; DUP-89; DUP89

2934.99.03.00

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)

DMSO: ≥ 100 mg/mL (~236.5 mM)

Solubility in Formulation 1: ≥ 2.08 mg/mL (4.92 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 20.8 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: ≥ 2.08 mg/mL (4.92 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 20.8 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.)