ODP478 Effects of peripheral iodothyronine deiodinases on thyroid hormone economy: Insights from the overexpressing mice

Background

In peripheral tissues, triiodothyronine (T3) production and consequent thyroid hormone actions are mainly regulated by iodothyronine deiodinases (DIOs) classified into 3 types: D1, D2, and D3. Although thyroid hormone economy in the DIO-deficient mice and patients carrying genetic variants of DIOs was well clarified, a condition of DIOs upregulation was not enough elucidated. We aimed to investigate effects of peripheral DIOs on thyroid hormone economy and consequent thyroid hormone action using novel DIO-overexpressing mice that were not yet generated.

Methods

We cloned coding sequences of human DIOs with FLAG-tag and HiBiT-tag sequences into a pcDNA3.1 vector. To obtain full-length proteins, we modified these vectors by cloning selenocysteine insertion sequence of each DIO (SECIS vectors). Western blot analyses and HiBiT lytic assay using HEK293T cells revealed that SECIS vectors expressed full-length proteins with substantial activity. Subsequently, in vivo transfections of pLIVE-based SECIS vectors into male C57BL/6J mice were performed by hydrodynamic gene delivery to generate mice overexpressing DIOs (D1, D2, and D3 mice).

Results

First, we verified that DIOs were successfully overexpressed in the livers using HiBiT lytic assay as well as RT-PCR. Analyses of multiple organs of D3 mice assured that full-length protein was not significantly expressed in the heart, the kidney, and the skeletal muscle. RT-PCR analyses also suggested that the pituitary glands and the thyroid glands were not transfected. We evaluated thyroid hormone economy of DIO-overexpressing mice compared to Empty mice transfected with pLIVE-Empty vector. D1 mice did not have changes in serum thyroid hormone levels, whereas D2 mice had higher serum fT3 levels. Clearer changes were found in D3 mice. They had hypothyroidism with higher serum rT3 levels. Correspondingly, in their livers, rT3 concentration was higher and T3-responsive genes were downregulated. We elucidated by adding the cohort with levothyroxine (LT4) administration because DIO-overexpressing mice had liver T4 insufficiency probably due to consumption by DIOs. Comparisons between the DIO-overexpressing mice with and without LT4 administration revealed that D2 mice presented upregulation of T3-responsive genes by LT4 administration distinct from Empty mice.

Conclusions

We generated DIO-overexpressing mice that expressed human DIOs predominantly in the liver. They provided physiological evidence to integrate the phenotypes of the knockout mice and specific clinical situations. D2 mice seemed to recruit T3 into the circulation as well as in the liver. D3 mice had an overt phenotype characterized by consumptive hypothyroidism. In addition, D3 mice are expected to be a novel hypothyroidism model that does not involve disruption of thyroidal hormone secretion. DIO-overexpressing mice can be generated by single injections of plasmid vectors of interest and can contribute to progress in the field of thyroid hormone economy and action.

Presentation: No date and time listed

High-throughput Screening in Combination With a Cohort Study for Iodothyronine Deiodinases

Regulatory mechanisms of iodothyronine deiodinases (DIOs) require further elucidation, and conventional methods for evaluating DIOs are unsuitable for high-throughput screening (HTS). Here we explored factors of transcriptional regulation of 3 types of DIOs (DIO1, DIO2, and DIO3) from a chemical library using our designed HTS. We constructed HTS based on a promoter assay and performed a screen of 2480 bioactive compounds. For compounds that were clinically approved, we validated hit compounds through a retrospective cohort study in our department that evaluated changes in thyroid function in patients using the compounds as drug therapy. Furthermore, we verified the involvement of DIOs using mice treated with the compounds. Of the hit compounds, 6 and 7 compounds transcriptionally up- and downregulated DIO1, respectively; 34 transcriptionally upregulated DIO2; and 5 and 2 compounds transcriptionally up- and downregulated DIO3, respectively. The cohort study clarified the clinical effects of some hit compounds: ritodrine increased free triiodothyronine (fT3)/free thyroxine (fT4) ratio and decreased serum thyroid-stimulating hormone (TSH) levels, tadalafil increased serum fT3 levels, and tyrosine kinase inhibitors (TKIs) decreased serum fT3 and fT4 levels and increased serum TSH levels. Following in vivo experiments using treated mice, consistent results were observed in ritodrine, which upregulated DIO2 in the thyroid gland. In conclusion, we completed HTS for DIOs and obtained attractive hit compounds. Our cohort study revealed the clinical significance of ritodrine, sildenafil, and TKIs. We hope our unique method will contribute to analyzing various targets and lists of hit compounds will promote understanding of DIOs.

Bezafibrate induces hypothyroidism in a patient with resistance to thyroid hormone β due to a G347R variant

OBJECTIVE

A unique clinical course was observed in a patient with resistance to thyroid hormone β (RTHβ) caused by a variant of the THRB gene leading to the replacement of glycine with arginine in codon 347 (p.G347R). He presented with the syndrome of inappropriate secretion of thyrotropin (TSH) (free T4 [fT4]: 32.43 pmol/L, TSH: 4.67 mIU/L), but slowly developed progressive hypothyroidism (fT4: 8.37 pmol/L, TSH: 100.90 mIU/L) that resolved after suspending bezafibrate (BZ) treatment (fT4: 32.18 pmol/L, TSH: 7.14 mIU/L). This study clinically and experimentally evaluated this interesting phenomenon.

METHODS

A retrospective cohort analysis of non-RTHβ patients was performed at Kyoto University Hospital. Data before BZ treatment were compared to the first data after treatment. Using reporter assays of iodothyronine deiodinases (DIO1, DIO2, DIO3) in HEK293T cells, we performed functional analyses of mutant thyroid hormone receptor β with p.G347R (G347R TRβ). Mice with G347R TRβ were generated by hydrodynamic gene delivery.

RESULTS

In non-RTHβ patients (n = 7), BZ treatment did not change serum free T3 and TSH but significantly increased fT4 (p = .008). BZ administration increased DIO3 reporter activity in the context of G347R TRβ, whereas did not change DIO1 and DIO2 reporter activity. In the livers of mice with G347R TRβ, BZ administration increased reverse T3 content, which corresponded to an increase in Dio3 messenger RNA.

CONCLUSIONS

While hypothyroidism associated with BZ treatment did not occur in non-RTHβ patients, it was observed in a patient with RTHβ due to the p.G347R variant. Liver DIO3 upregulation might involve this hypothyroidism.

Thyroid hormone economy in mice overexpressing iodothyronine deiodinases

In peripheral tissues, triiodothyronine (T3) production and consequent thyroid hormone actions are mainly regulated by iodothyronine deiodinases (DIOs) classified into 3 types: D1, D2, and D3. We aimed to investigate the effects of peripheral DIOs on thyroid hormone economy independent of the hypothalamus-pituitary-thyroid axis. We cloned coding sequences of human DIOs with FLAG-tag and HiBiT-tag sequences into a pcDNA3.1 vector. To obtain full-length proteins, we modified these vectors by cloning the selenocysteine insertion sequence of each DIO (SECIS vectors). Western blot analyses and HiBiT lytic assay using HEK293T cells revealed that SECIS vectors expressed full-length proteins with substantial activity. Subsequently, in vivo transfections of pLIVE-based SECIS vectors into male C57BL/6J mice were performed by hydrodynamic gene delivery to generate mice overexpressing DIOs predominantly in the liver (D1, D2, and D3 mice). After 7 days from transfections, mice were analyzed to clarify phenotypes. To summarize, serum thyroid hormone levels did not change in D1 mice but D2 mice had higher serum free T3 levels. D3 mice developed hypothyroidism with higher serum reverse T3 (rT3) levels. Transfections with levothyroxine administration suggested that thyroid hormone action was upregulated in D2 mice. Our DIO-overexpressing mice provided insights on the physiological properties of upregulated DIOs: D2 augments local thyroid hormone action and recruits T3 into the circulation: D3 decreases circulating T3 and T4 levels with elevated rT3, leading to consumptive hypothyroidism. As D3 mice are expected to be a novel hypothyroidism model, they can contribute to progress in the field of thyroid hormone economy and action.

Exogenous C-type natriuretic peptide therapy for impaired skeletal growth in a murine model of glucocorticoid treatment

Growth retardation is an important side effect of glucocorticoid (GC)-based drugs, which are widely used in various preparations to treat many pediatric diseases. We investigated the therapeutic effect of exogenous CNP-53, a stable molecular form of intrinsic CNP, on a mouse model of GC-induced growth retardation. We found that CNP-53 successfully restored GC-induced growth retardation when both dexamethasone (DEX) and CNP-53 were injected from 4 to 8 weeks old. Notably, CNP-53 was not effective during the first week. From 4 to 5 weeks old, neither CNP-53 in advance of DEX, nor high-dose CNP-53 improved the effect of CNP. Conversely, when CNP-53 was started at 5 weeks old, final body length at 8 weeks old was comparable to that when CNP-53 was started at 4 weeks old. As for the mechanism of resistance to the CNP effect, DEX did not impair the production of cGMP induced by CNP. CNP reduced Erk phosphorylation even under treatment with DEX, while CNP did not changed that of p38 or GSK3β. Collectively, the effect of CNP-53 on GC-induced growth retardation is dependent on age in a mouse model, suggesting adequate and deliberate use of CNP would be effective for GC-induced growth retardation in clinical settings.

Rats deficient C-type natriuretic peptide suffer from impaired skeletal growth without early death

We have previously investigated the physiological role of C-type natriuretic peptide (CNP) on endochondral bone growth, mainly with mutant mouse models deficient in CNP, and reported that CNP is indispensable for physiological endochondral bone growth in mice. However, the survival rate of CNP knockout (KO) mice fell to as low as about 70% until 10 weeks after birth, and we could not sufficiently analyze the phenotype at the adult stage. Herein, we generated CNP KO rats by using zinc-finger nuclease-mediated genome editing technology. We established two lines of mutant rats completely deficient in CNP (CNP KO rats) that exhibited a phenotype identical to that observed in mice deficient in CNP, namely, a short stature with severely impaired endochondral bone growth. Histological analysis revealed that the width of the growth plate, especially that of the hypertrophic chondrocyte layer, was markedly lower and the proliferation of growth plate chondrocytes tended to be reduced in CNP KO rats. Notably, CNP KO rats did not have malocclusions and survived for over one year after birth. At 33 weeks of age, CNP KO rats persisted significantly shorter than wild-type rats, with closed growth plates of the femur in all samples, which were not observed in wild-type rats. Histologically, CNP deficiency affected only bones among all body tissues studied. Thus, CNP KO rats survive over one year, and exhibit a deficit in endochondral bone growth and growth retardation throughout life.

Effects of growth hormone on thyroid function are mediated by type 2 iodothyronine deiodinase in humans

PURPOSE

Growth hormone (GH) therapy in adults alters thyroid function, and acromegaly often involves thyroid disease. The present study aimed to elucidate roles and mechanisms of GH in regulating thyroid function.

METHODS

We performed two retrospective observational studies, which focused on consecutive patients with severe adult GH deficiency who received recombinant human GH (rhGH) therapy (n = 20) and consecutive patients with acromegaly who underwent transsphenoidal surgery (TSS) (n = 25). In both studies, serum free triiodothyronine (fT3), free thyroxine (fT4), and fT3/fT4 ratio were examined before and after the interventions. We subsequently administered GH to four human cell lines (HepG2, TSA201, MCF7, and HTC/C3) in vitro, and examined changes in mRNA levels of iodothyronine deiodinases (D1, D2, and D3).

RESULTS

Median serum fT3 level significantly increased after rhGH therapy from 2.38 to 2.78 pg/mL (p < 0.001), and fT4 decreased from 1.115 to 1.065 ng/dL (p = 0.081). TSS significantly decreased median serum fT3 from 3.03 to 2.53 pg/mL (p < 0.001), and increased fT4 from 1.230 to 1.370 ng/dL (p < 0.001). In vitro, GH significantly increased D2 expression at the mRNA level in HTC/C3 cells (p < 0.01), as well as D2 protein and its activity.

CONCLUSIONS

GH increased serum fT3 level and decreased serum fT4 level in humans. Our results suggest that its mechanism involves D2 upregulation. Considering this GH effect on thyroid hormone metabolism, data on thyroid function could be useful in the management of GH deficiency and acromegaly.

Circulating osteocrin stimulates bone growth by limiting C-type natriuretic peptide clearance

Although peptides are safe and useful as therapeutics, they are often easily degraded or metabolized. Dampening the clearance system for peptide ligands is a promising strategy for increasing the efficacy of peptide therapies. Natriuretic peptide receptor B (NPR-B) and its naturally occurring ligand, C-type natriuretic peptide (CNP), are potent stimulators of endochondral bone growth, and activating the CNP/NPR-B system is expected to be a powerful strategy for treating impaired skeletal growth. CNP is cleared by natriuretic peptide clearance receptor (NPR-C); therefore, we investigated the effect of reducing the rate of CNP clearance on skeletal growth by limiting the interaction between CNP and NPR-C. Specifically, we generated transgenic mice with increased circulating levels of osteocrin (OSTN) protein, a natural NPR-C ligand without natriuretic activity, and observed a dose-dependent skeletal overgrowth phenotype in these animals. Skeletal overgrowth in OSTN-transgenic mice was diminished in either CNP- or NPR-C-depleted backgrounds, confirming that CNP and NPR-C are indispensable for the bone growth-stimulating effect of OSTN. Interestingly, double-transgenic mice of CNP and OSTN had even higher levels of circulating CNP and additional increases in bone length, as compared with mice with elevated CNP alone. Together, these results support OSTN administration as an adjuvant agent for CNP therapy and provide a potential therapeutic approach for diseases with impaired skeletal growth.

Clinical Features of Nivolumab-Induced Thyroiditis: A Case Series Study

BACKGROUND

The programmed cell death-1 (PD-1) pathway is a novel therapeutic target in immune checkpoint therapy for cancer. It consists of the PD-1 receptor and its two ligands, programmed death-ligand 1 (PD-L1) and programmed death-ligand 2 (PD-L2). Nivolumab is an anti-PD-1 monoclonal antibody approved for malignant melanoma, advanced non-small cell lung cancer, and advanced renal cell carcinoma in Japan. Thyrotoxicosis and hypothyroidism have both been reported in international Phase 3 studies and national post-marketing surveillance of nivolumab in Japan.

METHODS

This study analyzed five consecutive cases with thyroid dysfunction associated with nivolumab therapy. Second, it examined the mRNA and protein expressions of PD-L1 and PD-L2 by reverse transcription polymerase chain reaction and Western blotting.

RESULTS

All patients were diagnosed with painless thyroiditis. Thyrotoxicosis developed within four weeks from the first administration of nivolumab and normalized within four weeks of onset in three of the five patients. Hypothyroidism after transient thyrotoxicosis developed in two patients, and preexisting hypothyroidism persisted in one patient. The other two patients were treated with glucocorticoids and discontinued nivolumab therapy for comorbid adverse events. One did not develop hypothyroidism, and the other developed mild, transient hypothyroidism. In addition, it was verified that normal thyroid tissue expresses PD-L1 and PD-L2 mRNA and those proteins.

CONCLUSIONS

In the present cases, nivolumab-induced thyrotoxicosis seemed to be associated with painless thyroiditis, while no patient with Graves' disease was observed. A transient and rapid course with subsequent hypothyroidism was observed in nivolumab-induced thyroiditis. In addition, it was verified that PD-L1 and PD-L2 are expressed in normal thyroid tissue. This suggests that nivolumab therapy reduces immune tolerance, even in normal thyroid tissue, and leads to the development of thyroiditis. Treating thyrotoxicosis with only supportive care and considering levothyroxine replacement therapy once subsequent hypothyroidism occurs is proposed. Further investigations are required to confirm whether glucocorticoid therapy and discontinuation of nivolumab therapy prevent subsequent hypothyroidism.

C-type natriuretic peptide restores impaired skeletal growth in a murine model of glucocorticoid-induced growth retardation

Glucocorticoids are widely used for treating autoimmune conditions or inflammatory disorders. Long-term use of glucocorticoids causes impaired skeletal growth, a serious side effect when they are used in children. We have previously demonstrated that C-type natriuretic peptide (CNP) is a potent stimulator of endochondral bone growth. In this study, we investigated the effect of CNP on impaired bone growth caused by glucocorticoids by using a transgenic mouse model with an increased circulating CNP level. Daily administration of a high dose of dexamethasone (DEX) to 4-week-old male wild-type mice for 4weeks significantly shortened their naso-anal length, which was restored completely in DEX-treated CNP transgenic mice. Impaired growth of the long bones and vertebrae by DEX was restored to a large extent in the CNP transgenic background, with recovery in the narrowed growth plate by increased cell volume, whereas the decreased proliferation and increased apoptosis of the growth plate chondrocytes were unaffected. Trabecular bone volume was not changed by DEX treatment, but decreased significantly in a CNP transgenic background. In young male rats, the administration of high doses of DEX greatly decreased N-terminal proCNP concentrations, a marker of CNP production. In organ culture experiments using fetal wild-type murine tibias, longitudinal growth of tibial explants was inhibited by DEX but reversed by CNP. These findings now warrant further study of the therapeutic potency of CNP in glucocorticoid-induced bone growth impairment.

Increased thrombopoietin levels in idiopathic thrombocytopenic purpura patients with a poor response to steroid therapy

The serum thrombopoietin (TPO) levels in 61 idiopathic thrombocytopenic purpura (ITP) patients were found to be slightly increased compared with those of 29 normal subjects. The TPO levels of the 15 ITP patients who had a poor response to steroid therapy (i.e. an unchanged platelet count) were higher than those of the 22 ITP patients who had a good response to steroid therapy (i.e. an increased platelet count) and the normal subjects. The TPO levels in the 15 ITP patients whose platelet count was higher than 10 x 10(4)/microl after the discontinuation of steroid therapy significantly higher than those of the normal subjects. The platelet-associated immunoglobulin G (PAIgG) levels in the ITP patients who had a poor response to steroid therapy were slightly increased compared with the normal subjects and the ITP patients who had a good response to the steroid therapy and the nine ITP patients who did not undergo the steroid therapy. The serum TPO level was negatively correlated only with the megakaryocyte count in the ITP patients, and the megakaryocyte count in the ITP patients who had good responses to the steroid therapy was higher than that in those who had poor responses. These data suggest that serum TPO levels might be important for the prediction of the outcome of ITP patients who receive steroid therapy.

[An elderly case whose residual malignant lymphoma was completely remitted by oral etoposide treatment using unusual dosing schedule]

In a 72-year-old man with malignant lymphoma (Hodgkin's disease, nodular sclerosis type, Stage III S), complete remission was induced by intravenous drip of adriamycin and oral administration of etoposide. After that, a maintenance dose of etoposide (25 mg) was administered every 3 days without observable side effects. From these results, we considered that the dose level and interval of administration are both important for chemotherapy in elderly patients.

New alpha-thiol dipeptide dual inhibitors of angiotensin-I converting enzyme and neutral endopeptidase EC 3.4.24.11

Dual inhibitors of the two zinc metallopeptidases, neutral endopeptidase (NEP, EC 3.4.24.11) and angiotensin-I converting enzyme, have been the focus of much clinical interest for the treatment of hypertension and congestive heart failure. A novel series of alpha-thio dipeptides containing central cyclic non-natural amino acids were prepared and were evaluated for their ability to inhibit these two metallopeptidases in vitro and in vivo. Most of these compounds were found to be excellent dual inhibitors of ACE and NEP in vitro and several were also found to inhibit angiotensin-I (AI) pressor response in conscious rats when given by intravenous administration. Compound 6n, one of our most potent dual inhibitors in vitro, was found to be more efficacious than captopril in the AI pressor experiment when administered orally to conscious rats. This compound was also found to inhibit plasma NEP activity following oral administration to conscious rats and was more efficacious than acetorphan. The structure-activity relationships and biological activity of these dual inhibitors will be discussed.

Dicarboxylic acid dipeptide neutral endopeptidase inhibitors

The synthesis of three series of dicarboxylic acid dipeptide neutral endopeptidase 24.11 (NEP) inhibitors is described. In particular, the amino butyramide 21a exhibited potent NEP inhibitory activity (IC50 = 5.0 nM) in vitro and in vivo. Blood levels of 21a were determined using an ex vivo method by measuring plasma inhibitory activity in conscious rats, mongrel dogs, and cynomolgus monkeys. Free drug concentrations were 10-1500 times greater than the inhibitory constant for NEP over the course of a 6 h experiment. A good correlation of free drug concentrations was obtained when comparing values determined by the ex vivo analysis to those calculated from direct HPLC measurements. Plasma atrial natriuretic factor (exogenous) levels were elevated in rats and dogs after oral administration of 19a. Urinary volume and urinary sodium excretion were also potentiated in anesthetized dogs treated with 21a.

A rapid indirect method to determine the plasma concentrations of neutral endopeptidase inhibitors

The selection of therapeutic agents for clinical development is principally based upon pharmacodynamic and pharmacokinetic criteria. Although many compounds are routinely tested in pharmacologic assays, direct pharmacokinetic assessment is difficult and not applicable to a large number of agents. Therefore, we have developed a rapid indirect method based on enzyme inhibition for determining the unbound concentration of NEP 24.11 inhibitors in rat plasma. In the present study, drug levels of compounds from three different classes of NEP 24.11 inhibitors: mercaptoalkyl, carboxyalkyl and aminophosphonates were compared. Studies were carried out in conscious, unrestrained rats. Arterial blood samples were obtained 10, 30, 60, 120, and 240 min after drug administration at 10 mg/kg i.v. or 30 mg/kg p.o. The blood was collected in EDTA and plasma prepared immediately. Protein bound NEP inhibitor was separated from plasma by centrifugation through an ultrafiltration membrane. Following acidification and serial dilution, the concentration of unbound inhibitor was determined in the plasma ultrafiltrate using the in vitro assay for NEP 24.11 inhibition. The results of this study indicated that the mercaptoalkyl inhibitor thiorphan was cleared rapidly from plasma, whereas, the plasma concentrations of the carboxyalkyl inhibitor CGS 23880A (UK-69,578), and the plasma concentrations of the aminophosphonate, CGS 24128, were maintained at high levels for at least 4 hours. Furthermore, the ratio of the NEP inhibitor concentration/IC50 value correlated well with the pharmacologic activity of these compounds.

N-Phosphonomethyl dipeptides and their phosphonate prodrugs, a new generation of neutral endopeptidase (NEP, EC 3.4.24.11) inhibitors

Inhibitors of the zinc protease neutral endopeptidase (NEP, EC 3.4.24.11) offer significant therapeutic interest as antihypertensives due to their ability to potentiate the biological action of the circulating natriuretic hormone ANF (atrial natriuretic factor). N-Phosphonomethyl dipeptides bearing a central (4-phenyl)phenylalanine residue have been designed to exert potent and selective NEP inhibition. In particular, (S)-3-[N-[2- [(phosphonomethyl)amino]-3-(4-biphenylyl)propionyl]amino]propionic acid (10a) (CGS 24592) displayed high inhibitory potency in vitro (IC50 = 1.9 +/- 0.1 nM) and a long plasma half-life in rats but lacked oral bioavailability. This drawback was overcome by using esterase-sensitive (acyloxy)alkyl phosphonates. More remarkable, several diaryl phosphonate derivatives of 10a also performed as effective prodrugs. Specifically, the structurally simple diphenyl phosphonate 18 (CGS 25462) induced potent inhibition of NEP ex vivo for at least 8 h after oral administration to rats (30 mg/kg). Its antihypertensive effect was demonstrated in DOCA-salt rats. At 30 mg/kg orally, 18 caused a significant reduction in mean arterial pressure measuring -35 +/- 7 mmHg at 5-h postdosing. The alpha-aminomethyl phosphonate 18 represents a new generation of selective NEP inhibitors that combine high potency, long duration of action, and oral bioavailability. Therefore, it holds promise as a novel therapeutic agent for the treatment of human hypertension and congestive heart failure.

Design and synthesis of an orally active macrocyclic neutral endopeptidase 24.11 inhibitor

A potent macrocyclic inhibitor of neutral endopeptidase (NEP) 24.11 was designed using a computer model of the active site of thermolysin. This 10-membered ring lactam represents a general mimic for any hydrophobic dipeptide in which the two amino acid side chains bind to an enzyme in a contiguous orientation. The parent 10-membered ring lactam was synthesized and exhibited excellent potency as an NEP 24.11 inhibitor (IC50 = 3 nM). In order to improve oral bioavailability, various functionality was attached to the macrocycle. These modifications lead to CGS 25155, an orally active NEP 24.11 inhibitor that slows down the degradation of the cardiac hormone atrial natriuretic factor, producing a lowering of blood pressure in the DOCA-salt rat model of hypertension.

Heterocyclic lactam derivatives as dual angiotensin converting enzyme and neutral endopeptidase 24.11 inhibitors

A series of 13- and 14-membered ring lactam derivatives 9a,b, 10, 11, and 12a-c was prepared from L-cysteine. Compounds 9a,b and 12a,b were tested in vitro for inhibition of neutral endopeptidase 24.11 (NEP) and angiotensin converting enzyme (ACE) inhibition. The structure-activity profile of the series is discussed. Compound 9b, a 13-membered ring macrocyclic lactam, had an NEP IC50 of 18 nM and an ACEIC50 of 12 nM in vitro and showed dual plasma inhibition after intravenous or oral administration.

Disposition of thiorphan in DOCA-salt and spontaneously hypertensive rats

Thiorphan was administered intravenously (i.v.) at 10 mg/kg to conscious rats in two different models of hypertension to allow a comparison of pharmacokinetics. The two models were: 1) Deoxycorticosterone acetate (DOCA)-salt uninephrectomized rats; 2) Spontaneously hypertensive rats (SHR), and their respective normotensive controls; 3) Sprague-Dawley (SD) rats; and 4) Wistar-Kyoto rats (WKY). Pharmacokinetic parameters were calculated for total and unbound thiorphan in plasma. In normotensive SD and WKY rats, the volume of distribution, clearance and plasma protein binding of thiorphan were not significantly different. Furthermore, the apparent elimination half-life was not significantly different for total or unbound thiorphan amongst all models. The volume of distribution and plasma clearance for both unbound and total thiorphan, however, were lower in DOCA-salt rats when compared to normotensive control rats by 61-66% and 46-51%, respectively. In contrast, pharmacokinetic parameters for both unbound and total thiorphan were not significantly different between SHR and WKY rats. These results indicate that reduced clearance of thiorphan in DOCA-salt rats may be due to the co-administration of DOCA-salt or altered renal function of the hypertrophic remaining kidney and not solely due to hypertension.

Characterisation of neutral endopeptidase 3.4.24.11 (NEP) in the kidney: comparison between normotensive, genetically hypertensive and experimentally hypertensive rats

Neutral endopeptidase 3.4.24.11 (NEP) has been identified as the major atrial natriuretic factor (ANF) degrading enzyme in rat kidney, therefore, suggesting a possible role for this enzyme in blood volume and pressure regulation. Various experimentally induced and genetically hypertensive rat models have been used to test NEP inhibitors. The presence of different isoforms of NEP in the various hypertensive rat models would have relevance when searching for novel NEP inhibitors. Therefore, we compared the properties of NEP in kidney cortex homogenates in order to test for possible differences in the following hypertensive rat models and their appropriate controls: spontaneously hypertensive rats (SHR), Wistar Kyoto strain (WKY), DOCA-salt hypertensive rats, and Sprague Dawley control rats (SD). No relevant differences were found when comparing the following parameters: (1) specific activity (mean: 204 U/mg protein), (2) Michaelis constant (mean: 280 microM), (3) IC50 of thiorphan (mean: 6.5 nM) and phosphoramidon (mean: 54 nM), (4) pH profiles (optimum at pH 8.0), (5) heat inactivation profiles (half-life 20 min at 65 degrees C), (6) immunotitration of kidney cortex homogenates, (7) molecular weight as determined by gel filtration (92,000 Dalton) and (8) affinity chromatography with concanavalin A. Without evidence for the presence of different NEP isoforms, it is unlikely that divergent findings in DOCA-salt rats and SHR using a given NEP inhibitor are due to isoforms of NEP.

The biological activity of atrial natriuretic factor cleaved by endoprotease 3.4.24.11

Ring cleavage of atrial natriuretic peptide (ANF) between Cys7 and Phe8 by endoprotease 3.4.24.11 yields X-ANF. Since endoprotease 3.4.24.11 may contribute to ANF metabolism in vivo, the present study determined if X-ANF exhibits reduced biological activity in comparison to the parent molecule.

Carnitine metabolism and morphometric change of liver mitochondria in valproate-treated rats

The effect of the administration for 7 or 28 days of 50 mg/kg/day valproate (VPA) on carnitine metabolism and morphological changes of liver mitochondria in immature rats was evaluated. The dose of VPA was almost the same as that we clinically used. Carnitine concentrations in serum, red blood cells (RBC), muscle, liver and urine were measured. The rats treated with VPA for 7 days showed no significant change in carnitine concentration in each tissue examined or by morphology. In the serum, RBC and muscle of rats treated with VPA for 28 days, free carnitine levels decreased, while acylcarnitine levels and the ratio of acylcarnitine to free carnitine (acyl/free ratio) increased. Mitochondrial enlargement was also induced and urinary acyl/free ratio of VPA treated rats was higher than that of control rats after the 14th day of the treatment. These results suggest that carnitine deficiency and morphometric changes in mitochondria occur time dependent even if the dose of VPA is clinically appropriate.

Enkephalinase inhibitors. 1. 2,4-Dibenzylglutaric acid derivatives

The synthesis of two new series of dicarboxylic acid dipeptides and two sulfhydryl-containing inhibitors are described. The in vitro enkephalinase inhibition data and some in vivo analgesic data are presented for these compounds. For the dibenzylglutaric acid series structure-activity relationships and in vivo analgesic activity are discussed. The reverse amides, i.e., 4-amino-2,4-dibenzylbutyric acid derivatives, are also discussed. Two sulfhydryl-containing inhibitors showed good in vivo potency in the mouse jump-latency hot-plate test after peripheral administration at moderate low doses.

Identification of protease 3.4.24.11 as the major atrial natriuretic factor degrading enzyme in the rat kidney

We have identified a metalloendoprotease from rat kidney cortex that cleaves the cysteine-phenylalanine bond (Cys7-Phe8) within the 17 amino acid ring structure of atrial natriuretic factor (ANF). Cleavage at this site represents the major ANF degradative activity in rat kidney, and is inhibited by the known metalloendoprotease inhibitors, thiorphan, phosphoramidon and zincov with IC50 values in the nanomolar range. Since these are specific inhibitors of protease 3.4.24.11, both protease 3.4.24.11 and ANF degrading activities were monitored during purification. Both activities copurified at each chromatographic step. Furthermore, purified protease 3.4.24.11 cleaved ANF specifically at the Cys7-Phe8 bond. It is concluded from this work that the major ANF degrading enzyme in rat kidney is protease 3.4.24.11.

Carnitine metabolism in valproate-treated rats: the effect of L-carnitine supplementation

The effect of the administration for 7 days of valproate (500 mg/kg/day) or valproate (500 mg/kg/day) plus L-carnitine (200 mg/kg/day) on carnitine concentrations in serum, red blood cells, muscle, liver, and urine was evaluated. In the serum and muscle of the valproic acid (VPA) group, free carnitine levels decreased, while acyl-carnitine levels and acyl/free ratio increased, when compared to those of the control. When L-carnitine was given to the VPA group, the free carnitine levels increased in the serum, muscle, and liver, and the acyl/free ratio decreased in all tissues when compared to those of the VPA group. The mean of free carnitine level in urine of the VPA group was not different but acylcarnitine increased when compared to values of controls, and after the supplementation with L-carnitine the acylcarnitine (from day 4 to 7) levels were decreased compared to the VPA group. The serum beta-OH-butyrate level in the VPA group was decreased when compared to those of controls and VPA plus L-carnitine groups. These results indicate that L-carnitine supplementation protects against the alteration in carnitine metabolism induced by the administration of VPA.

Degradation of atrial natriuretic factor by kidney cortex membranes. Isolation and characterization of the primary proteolytic product

Synthetic rat atrial natriuretic factor (r-ANF, 1-28) was incubated with rat kidney cortex membranes, and a predominant degradation product was identified by reverse-phase high performance liquid chromatography. The degradation product was subjected to amino acid analyses and found to have a composition identical to r-ANF. Amino-terminal sequence analyses identified two distinct amino-terminal residues and suggested that cleavage had occurred between the cysteine-phenylalanine bond (residues 7 and 8) of r-ANF. This degradative process could be inhibited by 1,10-phenanthroline and EDTA, suggesting that the enzyme responsible for proteolysis is a metalloendoprotease. The enzyme exhibits a Michaelis-Menten constant of approximately 10 microM for the metabolism of r-ANF and has a broad pH optimum between 8.5 and 9.5. These findings suggest that ANF may be initially degraded in the kidney at a single cleavage site within the 17-residue ring structure.

Hepatotoxicity in rat following administration of valproic acid: effect of L-carnitine supplementation

The effect of prolonged administration (7 days) of valproate (VPA, 500 mg/kg/day), or VPA (500 mg/kg/day) with L-carnitine (200 mg/kg/day) on blood carnitine levels and the appearance of liver mitochondria were assessed in the rat. VPA-treated rats showed hypocarnitinemia and enlarged mitochondria when compared with saline-injected control rats. In rats treated with both VPA and L-carnitine, serum and liver carnitine levels were increased by the L-carnitine supplement and the liver mitochondria were not enlarged. L-Carnitine supplement in VPA-medicated patients seems to prevent hepatotoxicity, especially mitochondrial dysfunction.

Hepatotoxicity in rat following administration of valproic acid

Chronic injections of valproic acid (VPA), VPA with phenobarbital (PB), and PB were studied for their effects on liver mitochondrial morphology and carnitine metabolism in rats. Mitochondrial enlargement was induced by the administration of VPA (500 mg/kg/day) for a period of 7 consecutive days. The administration of VPA (500 mg/kg/day)-plus-PB (20 mg/kg/day) for 7 days, however, did not induce megamitochondrial formation, but in these livers an unusual increase was observed in the number of liver mitochondria, microvesicular steatoses, and myeloid bodies. VPA-treated rats had significantly lower levels of serum-free and total carnitine and higher levels of acylcarnitine and acyl to free ratio than those of the controls. The free carnitine concentrations in serum and liver of the rats treated with VPA-plus-PB were much lower as compared with those treated with either VPA or PB. These morphological and biochemical results, especially of carnitine metabolism, suggest that inhibition of beta-oxidation in liver mitochondria occurred in rats treated with VPA and PB and that, in particular, polytherapy with VPA-plus-PB could be clinically hazardous in causing hepatic injury.

Dazoxiben, UK 38,485 and aspirin: duration of effect for preventing thrombotic sudden death in rabbits

The purpose of this study was to compare the effects of dazoxiben (DAZ), UK 38,485 (UK) and aspirin (ASA) in the prevention of thrombotic sudden death in rabbits. In anesthetized male rabbits, sudden death was produced by intravenous administration of 0.75 mg/kg arachidonic acid (AA). AA increased plasma TxB2 levels from 0.20 +/- 0.10 ng/ml to 8.75 +/- 1.79 ng/ml and produced a 42% reduction in the number of circulating platelets. Death occurred in all animals within 5 minutes. Administration of DAZ (8.6 mumole/kg) 15 min before AA prevented the increase in plasma TxB2, the thrombocytopenia and sudden death while pretreatment with DAZ 2 hr before AA did not. The administration of UK (8.6 mumole/kg) 15 min. 4 hrs or 8 hrs before AA resulted in 100%, 67% and 33% survival, respectively. ASA (110 mumole/kg) administered 2 or 24 hrs before AA inhibited the increase in plasma TxB2 and prevented the fall in platelet counts. All animals pretreated with ASA survived. These data demonstrate that DAZ and UK have only a short to moderate duration of action in preventing AA-induced increases in plasma Tx levels and thrombocytopenia.

Serum and urinary carnitine and organic acids in Reye syndrome and Reye-like syndrome

Free and acyl-carnitine in serum and urine, and urinary organic acids were measured in 6 patients with Reye syndrome and Reye-like syndrome. The free and total carnitine concentrations were significantly reduced in serum during the acute phases of the diseases. Thus, the ratio of acylcarnitine to free carnitine was significantly increased. Urinary excretion of acylcarnitine was greatly increased, and the acylcarnitine to total carnitine ratio was therefore greater than in controls. The urinary organic acids comprised large amounts of lactic acid, dicarboxylic acids and ketone bodies. It is suggested that carnitine deficiency is induced as more carnitine is consumed to buffer the increased amount of toxic acyl-CoA compounds metabolized from free fatty acids and the many organic acids. These results indicate that administration of L-carnitine should generally be considered in patients with Reye syndrome and Reye-like syndrome.

Early diagnosis of herpes simplex virus encephalitis in childhood by the enzyme-linked immunosorbent assay

IgG antibody of cerebro-spinal fluid (CSF) and serum IgM antibody were determined by the enzyme-linked immunosorbent assay (ELISA) in 3 patients with herpes simplex virus encephalitis (HSVE). The ELISA detected the early rise of IgG antibody for herpes simplex virus (HSV) in CSF on the 3rd/4th day from onset of symptoms and IgM antibody in serum similarly on the 3rd/4th day, respectively. CSF albumin, IgG index and daily IgG synthesis during the early phase of HSVE showed significantly high levels. However, there was no significant increase of complement-fixing antibody and neutralizing antibody for HSV of serum and CSF in 2 of 3 patients. The ELISA turned out to be a more sensitive and convenient test for the early diagnosis of HSVE.

Reye-like syndrome associated with valproic acid

A case of a Reye-like syndrome during the course of treatment with VPA was reported. Hyperammonemia and severe liver damage as well as diffuse small droplets in the liver biopsy material were demonstrated. On analysis by gas chromatography/mass spectrometry of the urine immediately after the onset, the metabolites of VPA were detected together with lactate and other substances, and electron microscopic observation of liver biopsy material revealed deformation of mitochondria, disappearance of cristae and electron dense deposits in the matrix.

Properties of hepatic and pancreatic cyclic AMP phosphodiesterase in the cat

Cyclic adenosine-3',5'-monophosphate phosphodiesterase has been characterized in homogenates of feline pancreas and liver. The cyclic AMP phosphodiesterase of feline liver showed a pH optimum at 7.8-7.9. In contrast, cyclic AMP phosphodiesterase activity of feline pancreas increased at up to pH 8.8 without attaining a peak. Hepatic cyclic AMP phosphodiesterase appeared to possess two different enzyme activities, a high and a low affinity form for cyclic AMP. The Michaelis constant for this enzyme was 0.567 and 85.6 microM, respectively. The maximal velocity of this enzyme was 0.135 and 2.84 nmol cyclic AMP hydrolyzed per mg of protein per min. The presence of multiforms of pancreatic cyclic AMP phosphodiesterase was neither demonstrated nor excluded. The kinetics constant for this enzyme for a one-enzyme model without cooperativity was 5.30 microM, and the maximal velocity was 4.97 nmol cyclic AMP hydrolyzed per mg of protein per min.

Clinical effects of anticancer drugs to pancreatic diseases as protein synthesis inhibitors

The anticancer drugs, like 5-Fluorouracil, which are believed to interfere with enzyme protein synthesis in the exocrine cells of pancreas were administered intravenously to fifteen patients with various pancreatic diseases. The improvement of clinical symptoms and the diminution of serum and urinary amylase levels were observed in four cases with acute pancreatitis and two cases with chronic relapsing pancreatitis. The postoperative complications, namely the formation of pancreatic fistula and the rupture of pancreaticojejunostomy, or the aggravation of concomitant pancreatitis were not observed in three cases with benign surgical pancreatic diseases and six cases with pancreatic carcinoma. Furthermore, the diminution of amylase and protein output of pancreatic juice from canulae inserted into pancreatic ducts were observed.