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
Losartan is approximately 33% orally bioavailable. Losartan has a Tmax of 1 hour and the active metabolite has a Tmax of 3-4 hours. Taking losartan with food decreases the Cmax but does only results in a 10% decrease in the AUC of losartan and its active metabolite. A 50-80mg oral dose of losartan leads to a Cmax of 200-250ng/mL.
A single oral dose of losartan leads to 4% recovery in the urine as unchanged losartan, 6% in the urine as the active metabolite. Oral radiolabelled losartan is 35% recovered in urine and 60% in feces. Intravenous radiolabelled losartan is 45% recovered in urine and 50% in feces.
The volume of distribution of losartan is 34.4±17.9L and 10.3±1.1L for the active metabolite (E-3174).
Losartan has a total plasma clearance of 600mL/min and a renal clearance of 75mL/min. E-3174, the active metabolite, has a total plasma clearance of 50mL/min and a renal clearance of 25mL/min.
It is not known whether losartan is excreted in human milk, but significant levels of losartan and its active metabolite were shown to be present in rat milk.
Following oral administration, losartan is well absorbed (based on absorption of radiolabeled losartan) and undergoes substantial first-pass metabolism; the systemic bioavailability of losartan is approximately 33%. About 14% of an orally-administered dose of losartan is converted to the active metabolite. Mean peak concentrations of losartan and its active metabolite are reached in 1 hour and in 3-4 hours, respectively. While maximum plasma concentrations of losartan and its active metabolite are approximately equal, the AUC of the metabolite is about 4 times as great as that of losartan. A meal slows absorption of losartan and decreases its Cmax but has only minor effects on losartan AUC or on the AUC of the metabolite (about 10% decreased).
Studies in rats indicate that losartan crosses the blood-brain barrier poorly, if at all.
Both losartan and its active metabolite are highly bound to plasma proteins, primarily albumin, with plasma free fractions of 1.3% and 0.2%, respectively. Plasma protein binding is constant over the concentration range achieved with recommended doses.
For more Absorption, Distribution and Excretion (Complete) data for Losartan (8 total), please visit the HSDB record page.

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Metabolism / Metabolites
Losartan is metabolized to an aldehyde intermediate, E-3179, which is further metabolized to a carboxylic acid, E-3174, by cytochrome P450s like CYP2C9. Losartan can also be hydroxylated to an inactive metabolite, P1. Approximately 14% of losartan is metabolized to E-3174. Losartan can be metabolized by CYP3A4, CYP2C9, and CYP2C10. Losartan can also be glucuronidated by UGT1A1, UGT1A3, UGT1A10, UGT2B7, and UGT 2B17.
Losartan is an orally active agent that undergoes substantial first-pass metabolism by cytochrome P450 enzymes. It is converted, in part, to an active carboxylic acid metabolite that is responsible for most of the angiotensin II receptor antagonism that follows losartan treatment. Losartan metabolites have been identified in human plasma and urine. In addition to the active carboxylic acid metabolite, several inactive metabolites are formed. Following oral and intravenous administration of (14)C-labeled losartan potassium, circulating plasma radioactivity is primarily attributed to losartan and its active metabolite. In vitro studies indicate that cytochrome P450 2C9 and 3A4 are involved in the biotransformation of losartan to its metabolites. Minimal conversion of losartan to the active metabolite (less than 1% of the dose compared to 14% of the dose in normal subjects) was seen in about one percent of individuals studied.
Losartan has known human metabolites that include Losartan carboxylic acid and 2-[5-[2-[4-[[2-butyl-5-chloro-4-(hydroxymethyl)-1H-imidazol-3-ium-3-yl]methyl]phenyl]phenyl]-1,5-dihydrotetrazol-2-yl]-6-(dihydroxymethyl)oxane-3,4,5-triol.

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Biological Half-Life
The terminal elimination half life of losartan is 1.5-2.5 hours while the active metabolite has a half life of 6-9 hours.
The terminal half-life of losartan is about 2 hours and of the metabolite is about 6-9 hours.

Toxicity Summary
IDENTIFICATION AND USE: Losartan is a light yellow solid that is formulated into oral tablets. Losartan is an angiotensin II type 1 (AT1) receptor antagonist. It is used alone or in combination with other classes of antihypertensive agents in the management of hypertension. It is also used to reduce the risk of stroke in patients with hypertension and left ventricular hypertrophy and for the treatment of 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 could be encountered if parasympathetic (vagal) stimulation occurs. The use of lorsartan during pregnancy is contraindicated. While use during the first trimester does not suggest a risk of major anomalies, use during the second and third trimester may cause teratogenicity and severe fetal and neonatal toxicity. Fetal toxic effects may include anuria, oligohydramnios, fetal hypocalvaria, intrauterine growth restriction, premature birth, and patent ductus arteriosus. Anuria-associated oligohydramnios may produce fetal limb contractures, craniofacial deformation, and pulmonary hypoplasia. Severe anuria and hypotension that is resistant to both pressor agents and volume expansion may occur in the newborn following in utero exposure to losartan. ANIMAL STUDIES: Losartan potassium was not carcinogenic when administered at maximally tolerated dosages to rats and mice. Female rats given losartan had a slightly higher incidence of pancreatic acinar adenoma. Also, fertility and reproductive performance were not affected in studies with male rats given oral doses of losartan. The administration of toxic dosage levels in females was associated with a significant decrease in the number of corpora lutea/female, implants/female, and live fetuses/female at C-section. The relationship of these findings to drug-treatment is uncertain since there was no effect at these dosage levels on implants/pregnant female, percent post-implantation loss, or live animals/litter at parturition. Losartan has been shown to produce adverse effects in rat fetuses and neonates, including decreased body weight, delayed physical and behavioral development, mortality and renal toxicity. With the exception of neonatal weight gain doses associated with these effects exceeded 25 mg/kg. These findings are attributed to drug exposure in late gestation and during lactation. Losartan was negative in the microbial mutagenesis and V-79 mammalian cell mutagenesis assays and in the in vitro alkaline elution assay and in vitro and in vivo chromosomal aberration assays. In addition, the active metabolite showed no evidence of genotoxicity in the microbial mutagenesis, in vitro alkaline elution assay, and in vitro chromosomal aberration assays.

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Interactions
... This study was undertaken to evaluate how the chronic administration of deoxycortisone acetate (DOCA) modifies the effects of losartan on BP, renal injury, and other variables in /N(G)-nitro-L-arginine methyl ester (L-NAME)/ hypertensive rats. The following groups were used: Control, DOCA, L-NAME, L-NAME + losartan, L-NAME + DOCA, and L-NAME + DOCA + losartan. Tail systolic BP was measured twice a week. After 4-wk evolution, mean arterial pressure and metabolic, morphologic, and renal variables were measured. The final mean arterial pressure values were 116 +/- 6 mm Hg for control, 107 +/- 2 mmHg for DOCA, 151 +/- 5 mmHg for L-NAME, 123 +/- 2 mmHg for L-NAME + losartan, 170 +/- 3 mm Hg for L-NAME + DOCA, and 171 +/- 5.5 mmHg for L-NAME + DOCA + losartan. Losartan prevented microalbuminuria, hyaline arteriopathy, and glomerulosclerosis of L-NAME hypertension but was ineffective in L-NAME + DOCA-treated rats. ... Plasma renin activity was suppressed in the DOCA (0.55 +/- 0.2) and L-NAME + DOCA (0.60 +/- 10.2) groups but unsuppressed in the L-NAME + DOCA + losartan group (5.8 +/- 1). The conclusion is that DOCA blocks the preventive effect of losartan on the increased BP and renal injury of L-NAME hypertension ... These data also suggest that losartan prevents L-NAME hypertension by blocking the activity of systemic Ang II. /Salt not specified/
NSAIDs are known to attenuate the effects of some antihypertensive medications ... A multicenter study assessing the effect of indomethacin on the antihypertensive effects of losartan and captopril /was conducted/. After 4 weeks of placebo washout, hypertensive patients received 6 weeks of active antihypertensive therapy with ... 50 mg losartan once daily (n=111) ... This was followed by 1 week of concomitant therapy with indomethacin (75 mg daily). The primary outcome measure was the change in mean 24-hour ambulatory diastolic blood pressure after the addition of indomethacin. ... Losartan significantly lowered ambulatory diastolic blood pressure (losartan -5.3 mm Hg, P:<0.001 ...) after 6 weeks of therapy. Indomethacin significantly attenuated the 24-hour ambulatory diastolic blood pressure for ... losartan (2.2 mm Hg, P:<0.05) ... Changes in daytime diastolic blood pressure (7:00 AM to 11:00 PM) were similar to the 24-hour response in both groups. Nighttime diastolic blood pressure (11:01 PM to 6:59 AM) ... with losartan was unaffected (0.4 mm Hg). Thus, concurrent treatment with indomethacin similarly attenuates the 24-hour antihypertensive response to losartan ... /Salt not specified/
Potential pharmacologic interaction (attenuated hypotensive effects) when angiotensin II receptor antagonists are used concomitantly with nonsteroidal anti-inflammatory agents (NSAIAs), including selective cyclooxygenase-2 (COX-2) inhibitors. Possible deterioration of renal function in geriatric, volume-depleted (including those receiving concomitant diuretic therapy), or renally impaired patients; renal function should be monitored periodically in patients receiving concomitant therapy with losartan and an NSAIA, including selective COX-2 inhibitors.
Decreased plasma concentrations of losartan and its active metabolite observed when losartan potassium is used concomitantly with rifampin.
For more Interactions (Complete) data for Losartan (20 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 Blockers; Anti-Arrhythmia Agents; Antihypertensive Agents
Cozarr is indicated for the treatment of hypertension. It may be used alone or in combination with other antihypertensive agents, including diuretics. /Included in US product label/
Cozarr is indicated to reduce the risk of stroke in patients with hypertension and left ventricular hypertrophy, but there is evidence that this benefit does not apply to Black patients. /Included in US product label/
Cozaar is indicated for the treatment of diabetic nephropathy with an elevated serum creatinine and proteinuria (urinary albumin to creatinine ratio =300 mg/g) in patients with type 2 diabetes and a history of hypertension. In this population, Cozaar reduces the rate of progression of nephropathy as measured by the occurrence of doubling of serum creatinine or end stage renal disease (need for dialysis or renal transplantation). /Included in US product label/
For more Therapeutic Uses (Complete) data for Losartan (6 total), please visit the HSDB record page.

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Drug Warnings
/BOXED WARNING/ WARNING: FETAL TOXICITY. When pregnancy is detected, discontinue Cozaar as soon as possible. Drugs that act directly on the renin-angiotensin system can cause injury and death to the developing fetus.
Use of drugs that act on the renin-angiotensin system during the second and third trimesters of pregnancy reduces renal function and increases fetal and neonatal morbidity and death. Resulting oligohydramnios can be associated with fetal lung hypoplasia and skeletal deformations. Potential neonatal adverse effects include skull hypoplasia, anuria, hypotension, renal failure, and death. When pregnancy is detected, discontinue Cozaar as soon as possible. These adverse outcomes are usually associated with the use of these drugs in the second and third trimester of pregnancy. Most epidemiologic studies examining fetal abnormalities after exposure to antihypertensive use in the first trimester have not distinguished drugs affecting the renin-angiotensin system from other antihypertensive agents. Appropriate management of maternal hypertension during pregnancy is important to optimize outcomes for both mother and fetus. In the unusual case that there is no appropriate alternative to therapy with drugs affecting the renin-angiotensin system for a particular patient, apprise the mother of the potential risk to the fetus. Perform serial ultrasound examinations to assess the intra-amniotic environment. If oligohydramnios is observed, discontinue Cozaar, unless it is considered life-saving for the mother. Fetal testing may be appropriate, based on the week of pregnancy. Patients and physicians should be aware, however, that oligohydramnios may not appear until after the fetus has sustained irreversible injury.
Neonates with a history of in utero exposure to Cozaar If oliguria or hypotension occurs, direct attention toward support of blood pressure and renal perfusion. Exchange transfusions or dialysis may be required as a means of reversing hypotension and/or substituting for disordered renal function.
FDA Pregnancy Risk Category: D /POSITIVE EVIDENCE OF RISK. Studies in humans, or investigational or post-marketing data, have demonstrated fetal risk. Nevertheless, potential benefits from the use of the drug may outweigh the potential risk. For example, the drug may be acceptable if needed in a life-threatening situation or serious disease for which safer drugs cannot be used or are ineffective./
For more Drug Warnings (Complete) data for Losartan (21 total), please visit the HSDB record 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 has a long duration of action as it is given once daily. Patients taking losartan should be regularly monitored for hypotension, renal function, and 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.)