Monoamine oxidase activity and triiodothyronine biosynthesis in human cultured thyroid cells.

1. The proposal that monoamine oxidase (MAO) is a source of peroxide in thyroid hormone biosynthesis has been examined by use of isolated cultured human thyroid cells which retain the ability to secrete triiodothyronine (T3) in response to thyroid stimulating hormone (TSH). 2. The results demonstrated the presence of MAO A and B in human thyroid cells which oxidized 5-hydroxytryptamine and 2-phenylethylamine, respectively, and were selectively inhibited by the MAO inhibitors clorgyline and (-)-deprenyl. 3. Addition of propylthiouracil to the culture system induced a 61% reduction in TSH-stimulated T3 secretion, indicating that the bulk of such secretion apparently derives from de novo iodothyronine synthesis. 4. The MAO A and B substrate, tyramine, was ineffective in stimulating T3 secretion. 5. The selective MAO inhibitors, clorgyline and (-)-deprenyl, alone and in combination, and in the presence and absence of tyramine, failed to inhibit basal as well as TSH-stimulated T3 secretion in cultured human thyrocytes. 6. It is therefore apparent that even though thyroid MAO A and B enzyme reactions result in the generation of H2O2, this H2O2 does not seem to play a significant role in T3 biosynthesis.     

Antidepressant potentiation of 5-hydroxytryptophan by L-deprenil in affective illness

In an open trial study, L-Deprenil, an irreversible selective MAO-B inhibitor without 'chesse effect' was given to 14 patients with unipolar and bipolar depression receiving L-5-Hydroxytryptophan (L-5-HTP) and benzerazide. Ten out of 14 patients showed a good response to the combination of drugs and a correlation was found between the degree of platelet MAO inhibition and clinical response. In a double-blind controlled study, 18 affectively ill patients were randomly allocated to L-Deprenil plus L-5-HTP and benzerazide, 21 patients were treated with L-5-HTP and benzerazide and 19 patients with placebo only. Patients treated with the combination of L-Deprenil and L-5-HTP showed a significantly greater clinical improvement than placebo patients but this was not the case for patients treated with 5-HTP alone. A positive relationship was demonstrated between mood improvement and degree of platelet MAO inhibition in patients treated with L-Deprenil.     

Impaired iron homeostasis in Parkinson's disease

Despite physiological systems designed to achieve iron homeostasis, increased concentrations of brain iron have been demonstrated in a range of neurodegenerative diseases. These including the parkinsonian syndromes, the trinucleotide repeat disorders and the dementia syndromes. The increased brain iron is confined to those brain regions most affected by the degeneration characteristic of the particular disorder and is suggested to stimulate cell damage via oxidative mechanisms. Changes in central iron homeostasis have been most closely investigated in PD, as this disorder is well characterised both clinically and pathologically. PD is associated with a significant increase in iron in the degenerating substantia nigra (SN) and is measureable in living PD patients and in post-mortem brain. This increase, however, occurs only in the advanced stages of the disease, suggesting that this phenonoma may be a secondary, rather than a primary initiating event, a hypothesis also supported by evidence from animal experiments. The source of the increased iron is unknown but a variety of changes in iron homeostasis have been identified in PD, both in the brain and in the periphery. The possibility that an increased amount of iron may be transported into the SN is supported by data demonstrating that one form of the iron-binding glycoprotein transferrin family, lactotransferrin, is increased in surviving neurons in the SN in the PD brain and that this change is associated with increased numbers of lactotransferrin receptors on neurons and microvessels in the parkinsonian SN. These changes could represent one mechanism by which iron might concentrate within the PD SN. Alternatively, the measured increased in iron might result from a redistribution of ferritin iron stores. Ferritin is located in glial cells while the degenerating neurons do not stain positive for ferritin. As free radicals are highly reactive, it is unlikely that glial-derived free radicals diffuse across the intracellular space in sufficent quantities to damage neuronal constituents. If intracellular iron release contributes to neuronal damage it seems more probable that an intraneuronal iron source is responsible for oxidant-mediated damage. Such a iron source is neuromelanin (NM), a dark-coloured pigment found in the dopaminergic neurons of the human SN. In the normal brain, NM has the ability to bind a variety of metals, including iron, and increased NM-bound iron is reported in the parkinsonian SN. The consequences of these phenomena for the cell have not yet been clarified. In the absence of significant quantities of iron NM can act as an antioxidant, in that it can interact with and inactivate free radicals. On the other hand, in the presence of iron NM appears to act as a proxidant, increasing the rate of free radical production and thus the oxidative load within the vulnerable neurons. Given that increased iron is only apparent in the advanced stages of the disease it is unlikely that NM is of importance for the primary aetiology of PD. A localised increase in tissue iron and its interaction with NM may be, however, important as a secondary mechanism by increasing the oxidative load on the cell, thereby driving neurodegeneration.     

Effect of human growth hormone (GH)-binding protein in human serum on GH binding to rabbit liver membranes.

The sequence identity of growth hormone-binding protein (GH-BP) with the extracellular domain of GH receptors raised the possibility that circulating GH-BP might affect the binding of human GH (hGH) to its receptors, and thus, its biological effects. To test this hypothesis, we tested the effects of sera with low GH-BP levels (obtained from prepubertal children, girls with anorexia nervosa [AN], and patients with hepatic cirrhosis), normal control sera, and sera with high GH-BP levels (obtained from obese patients) on hGH binding to its receptors. GH-BP activity in patients' sera was measured by incubation with [125I]hGH and the separation of bound hGH from free hGH with dextran-coated charcoal. The effect of GH-BP was studied by preincubation of patients' sera with increasing concentrations of hGH, followed by incubation with [125I]hGH and a rabbit liver membrane preparation known to be rich in GH receptors, and finally by measuring hGH bound to the receptors. In this study, we report on the ability of GH-BP to reduce the inhibitory capacity (IC50) of hGH on [125I]hGH binding to GH receptors. The concentration of GH-BP in serum is positively correlated with the IC50 of hGH incubated with different sera on [125I]hGH binding to its receptors (n = 21; r = .886, P less than .001). In the presence of high serum GH-BP levels, such as those observed in obesity (20.13% +/- 0.71%/0.05 mL serum), the IC50 values were significantly higher than those obtained with sera containing GH-BP levels lower than those measured in human control subjects, such as from prepubertal children, AN patients, and cirrhotic patients.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of prolactin and prostaglandins on the stimulation of prolactin binding sites in the male rat liver

Induction of prolactin hepatic receptors in the male rat by exogenous prolactin and the possible involvement of prostaglandins in this process were studied. When ovine prolactin 500 microgram/kg was administered sc in saline containing 10% PVP (polyvinylpyrrolidone), twice daily for 6.5 days and the rats killed 48 h after the last injection, the specific binding of 125I-labelled ovine prolactin to prolactin hepatic receptors was raised 26-fold, while administration of prolactin in saline only caused a 7-fold increase. A well correlated log dose-response relationship was demonstrated between 12.5 and 500 microgram of prolactin in saline-PVP, with lowest dose causing an 18-fold increase in binding. A shorter 4.5 day treatment of prolactin in saline-PVP caused only a small 3-fold increase in prolactin binding. Scatchard analysis showed that these increases resulted from increases in receptor concentration. The effect of prolactin on the induction of the hepatic receptors could not be mimicked by PGE1, PGE2 or PGF2 alpha, nor could PGF2 alpha synergize with a short treatment with prolactin. Further, indomethacin caused no significant effect on this action of prolactin. It seems that prolactin does not induce its own receptors in the rat liver by stimulation of prostaglandins in this tissue.     

Iron dysregulation in Alzheimer's disease: multimodal brain permeable iron chelating drugs, possessing neuroprotective-neurorescue and amyloid precursor protein-processing regulatory activities as therapeutic agents

Considering the multi-etiological character of Alzheimer's disease (AD), the current pharmacological approaches using drugs oriented towards a single molecular target possess limited ability to modify the course of the disease and thus, offer a partial benefit to the patient. In line with this concept, novel strategies include the use of a cocktail of several drugs and/or the development of a single molecule, possessing two or more active neuroprotective-neurorescue moieties that simultaneously manipulate multiple targets involved in AD pathology. A consistent observation in AD is a dysregulation of metal ions (Fe²⁺, Cu²⁺ and Zn²⁺) homeostasis and consequential induction of oxidative stress, associated with beta-amyloid aggregation and neurite plaque formation. In particular, iron has been demonstrated to modulate the Alzheimer's amyloid precursor holo-protein expression by a pathway similar to that of ferritin L-and H-mRNA translation through iron-responsive elements in their 5′UTRs. This review will discuss two separate scenarios concerning multiple therapy targets in AD, sharing in common the implementation of iron chelation activity: (i) novel multimodal brain-permeable iron chelating drugs, possessing neuroprotective-neurorescue and amyloid precursor protein-processing regulatory activities; (ii) natural plant polyphenols (flavonoids), such as green tea epigallocatechin gallate (EGCG) and curcumin, reported to have access to the brain and to possess multifunctional activities, such as metal chelation-radical scavenging, anti-inflammation and neuroprotection.     

In vitro metabolism of alectinib,a novel potent ALK inhibitor,in human: contribution of CYP3A enzymes

1.?The in vitro metabolism of alectinib, a potent and highly selective oral anaplastic lymphoma kinase inhibitor, was investigated.

2.?The main metabolite (M4) in primary human hepatocytes was identified, which is produced by deethylation at the morpholine ring. Three minor metabolites (M6, M1a, and M1b) were also identified, and a minor peak of hydroxylated alectinib (M5) was detected as a possible precursor of M4, M1a, and M1b.

3.?M4, an important active major metabolite, was produced and further metabolized to M6 by CYP3A, indicating that CYP3A enzymes were the principal contributors to this route. M5 is possibly produced by CYP3A and other isoforms as the primary step in metabolism, followed by oxidation to M4 mainly by CYP3A. Alternatively, M5 could be oxidized to M1a and M1b via an NAD-dependent process. None of the non-CYP3A-mediated metabolism appeared to be major.

4.?In conclusion, this study suggests that involvement of multiple enzymes in the metabolism of alectinib reduces its potential for drug–drug interactions.     

Limited potentiation of blood pressure response to oral tyramine by brain-selective monoamine oxidase A-B inhibitor,TV-3326 in conscious rabbits

TV-3326 is a novel cholinesterase inhibitor that produces irreversible brain-selective inhibition of monoamine oxidase (MAO)-A and B and has antidepressant-like activity in rats after chronic oral administration. This study determined whether TV-3326 would cause less potentiation than other irreversible MAO-inhibitors of the blood pressure (BP) response to oral tyramine in conscious rabbits. Dose-response curves were established for the increase in BP induced by tyramine (5-200 mg/kg) administered orally via a naso-pharyngeal tube. From these, the dose that increased BP by 30 mmHg (ED(30)) was computed for each rabbit before and after oral administration of clorgyline, 1 mg/kg for one week, tranylcypromine 10 mg/kg, once, moclobemide, 20 mg/kg 3 times and TV-3326, 26 mg/kg for 2 weeks. Clorgyline, tranylcypromine and TV-3326 inhibited brain MAO-A by 90%; the former two inhibited intestinal MAO-A by 85-97% but TV-3326 had no effect. Tranylcypromine and clorgyline produced 6 and 20-fold increases in the pressor response to tyramine while TV-3326, like moclobemide, only potentiated it 2-fold. If TV-3326 is found to produce as little potentiation of the tyramine response in human subjects, it may be a potentially useful therapeutic agent for the treatment of Alzheimer's disease with depression.     

Novel dual inhibitors of AChE and MAO derived from hydroxy aminoindan and phenethylamine as potential treatment for Alzheimer's disease

Carbamate derivatives of N-propargylaminoindans (Series I) and N-propargylphenethylamines (Series II) were synthesized via multistep procedures from the corresponding hydroxy precursors. The respective rasagiline- and selegiline-related series were designed to combine inhibitory activities of both acetylcholine esterase (AChE) and monoamine oxidase (MAO) by virtue of their carbamoyl and propargylamine pharmacophores. Each compound was tested for these activities in vitro in order to find molecules with similar potencies against each enzyme. Compounds with such dual AChE and MAO inhibitory activities are expected to have potential for the treatment of Alzheimer's disease. The observed SAR also offers insight into the requirements of the active sites on these enzymes. A carbamate moiety was found to be essential for AChE inhibition, which was absent in the corresponding hydroxy precursors. The propargyl group caused 2-70-fold decrease in AChE inhibitory activity (depending on the position of the carbamoyl group) of Series I, but had little or no effect in Series II. Thus, the 6- and 7-carbamyloxyphenyls in Series I were either equipotent to, or slightly (2- to 5-fold) less active as AChE inhibitors than, the corresponding compounds in Series II, while the 4-carbamyloxyphenyls were more potent. The presence of the carbamate moiety in 6- and 7-carbamyloxyphenyls of Series I, considerably decreased MAO-A and -B inhibitory activity, compared to that of the parent hydroxy analogues, while the opposite was true for Series II. Thus, the 6- and 7-carbamyloxyphenyls in Series I were 2-3 orders of magnitude weaker MAO inhibitors while the 4- carbamyloxyphenyls were equipotent with the corresponding compounds in Series II. In both series, N-methylation of the propargylamine enhanced the MAO (A and B equally) inhibitory activities and decreased the AChE inhibitory activity. Two candidates belonging to the indan and tetralin ring systems (24c, 27b) and one phenethylamine (53d) were identified as possible leads for further development based on the following criteria: (a) comparable AChE and MAO-B inhibitory activities, (b) good to moderate AChE inhibitory activity, and (c) lack of strong MAO-A selectivity. However, it is likely that these compounds will be metabolized to the corresponding phenols, with inhibitory activities against AChE and/or MAO-A or -B, different from those of the parent carbamates. Thus, the apparent enzyme inhibition will be a result of the combined inhibition of all of these individual metabolites. The results of our ongoing in vivo screening programs will be published elsewhere.