Computer-aided drug screening by molecular docking, molecular dynamics (MD) and structural-activity relationship (SAR) can offer an efficient approach to identify promising drug repurposing candidates for COVID-19 treatment. In this study, computational screening is performed by molecular docking of 1615 Food and Drug Administration (FDA) approved drugs against the main protease (Mpro) of SARS-CoV-2. Several promising approved drugs, including Simeprevir, Ergotamine, Bromocriptine and Tadalafil, stand out as the best candidates based on their binding energy, fitting score and noncovalent interactions at the binding sites of the receptor. All selected drugs interact with the key active site residues, including His41 and Cys145. Various noncovalent interactions including hydrogen bonding, hydrophobic interactions, pi-sulfur and pi-pi interactions appear to be dominant in drug-Mpro complexes. MD simulations are applied for the most promising drugs. Structural stability and compactness are observed for the drug-Mpro complexes. The protein shows low flexibility in both apo and holo form during MD simulations. The MM/PBSA binding free energies are also measured for the selected drugs. For pattern recognition, structural similarity and binding energy prediction, multiple linear regression (MLR) models are used for the quantitative structural-activity relationship. The binding energy predicted by MLR model shows an 82% accuracy with the binding energy determined by molecular docking. Our details results can facilitate rational drug design targeting the SARS-CoV-2 main protease.Communicated by Ramaswamy H. Sarma.

Both low solubility and high hepatic metabolism cause low oral bioavailability of bromocriptine mesylate (BM) leading to very low drug amount in brain. Self-microemulsion (SME) tablets were developed to improve solubility, stimulate lipoprotein synthesis to promote lymphatic transport, avoid hepatic metabolism and target drug to brain. SME liquid containing castor oil, Tween(®) 80 and Cremophor(®) EL was prepared and then adsorbed onto solid carries, Aerosil(®)200, Aeroperl(®)300 or NeusilinUS2(®), yielding SME powders. The optimal ratios of SME liquid to carriers determined from flowability and scanning electron photomicrographs before tableting were 1.5:1, 2:1 and 2.5:1 for Aerosil(®)200, Aeroperl(®)300 and NeusilinUS2(®), respectively. Only Aeroperl(®)300 SME tablet had comparable dissolution to BM commercial tablet. From in vitro study in Caco-2 cells, fluorescein loaded SME tablet showed higher uptake than fluorescein loaded in either oil or surfactant. Although significantly lower amount of drug was permeated from SME tablet than from commercial tablet, higher drug uptake was obviously observed (P<0.05). In addition, higher lipoprotein synthesis expressing as content of apolipoprotein B (apo-B) found in secreted chylomicron resulted in higher drug uptake in co-culture of brain endothelial cells (bEnd.3) and astrocytes (CTX TNA2) from drug loaded SME tablet when compared to commercial tablet (P<0.05) due to binding of apo-B to LDL receptors expressed on the surface of endothelial cells. Therefore, tablet of SME adsorbed onto porous carrier potentially delivered BM to brain via lymphatic transport by increasing the lipoprotein synthesis.

The contribution of conformational heterogeneity to cooperativity in cytochrome P450 3A4 was investigated using the mutant L211F/D214E/F304W. Initial spectral studies revealed a loss of cooperativity of the 1-pyrenebutanol (1-PB) induced spin shift (S(50)=5.4 microM, n=1.0) but retained cooperativity of alpha-naphthoflavone binding. Continuous variation (Job's titration) experiments showed the existence of two pools of enzyme with different 1-PB binding characteristics. Monitoring of 1-PB binding by fluorescence resonance energy transfer from the substrate to the heme confirmed that the high-affinity site (K(D)=0.3 microM) is retained in at least some fraction of the enzyme, although cooperativity is masked. Removal of apoprotein on a second column increased the high-spin content and restored cooperativity of 1-PB binding and of progesterone and testosterone 6beta-hydroxylation. The loss of cooperativity in the mutant is, therefore, mediated by the interaction of holo- and apo-P450 in mixed oligomers.

R-Apomorphine (APO) the catechol-derived dopamine D1-D2 receptor agonist has been shown to be highly potent iron chelator and radical scavenger and inhibitor of membrane lipid peroxidation in vitro, in vivo and in cell culture employing PC12 cells. Its potency has been compared to the prototype iron chelator desferrioxamine (desferal), dopamine, nifedipine and dopamine D2 receptor agonists, bromocriptine, lisuride, pergolide and pramipexole. APO also inhibits brain and mitochondrial protein oxidation. In vivo APO protects against MPTP (N-methyl-4-phenyl-1,2,3,6-tetrahydropyridine)- induced striatal dopaminergic neurodegeneration in C57 black mice with as low as 5 mg/kg. APO is a reversible competitive inhibitor of monoamine oxidase (MAO) A and B with IC50 values of 93 and 214 uM, respectively. The iron chelating and radical scavenging actions of desferal and APO explains their ability to inhibit iron and 6-hydroxydopamine (6-OHDA)-induced neurodegeneration and activation of redox-sensitive transcription factor NF-kappa B and the subsequent transactivation of promoters of genes involved in inflammatory cytokines. Iron is thought to play a pivotal role in neurodegeneration, and APO may be an ideal drug to investigate neuroprotection in Parkinson's disease where iron and oxidative stress have been implicated in the pathogenesis of nigrostriatal dopamine neuron degeneration.

The present study is an attempt to find sites of dopaminergic inhibition along the transduction cascades culminating in gonadotropin (GtH) release in a teleost fish, tilapia. Experiments were carried out on perifused pituitary fragments and in primary culture of trypsinized pituitary cells. Salmon GnRH, chicken GnRH I and II stimulated GtH release in culture with estimated ED50 values of 15.56 pM, 2.55 nM and 8.65 pM, respectively. Apomorphine (APO; 1 microM) totally abolished this stimulation. Dopamine (DA; 1 microM) reduced both basal and GnRHa-stimulated GtH release from perifused pituitary fragments but did not alter the formation of cAMP. In a similar perifusion experiment DA abolished GtH release in response to forskolin (10 microM) with no reduction in cAMP formation. This indicates that one site of the dopaminergic inhibition is distal to cAMP formation, an indication not compatible with the classic characteristic of DA D2 type mode of action. The inhibition of GtH release in culture, caused by 1 microM APO, the specific DA D2 agonists LY 171555 (LY) or bromocryptine (BRCR) could not be reversed by activating protein kinase C (PKC) by DiC8 or the phorbol ester TPA. This would indicate a site for DA action distal to PKC. However, the stimulatory effect of arachidonic acid (AA; 50 microM) in perifusion was not reduced by DA (1 microM) or by APO, LY or BRCR in culture, which suggests a site for DA action proximal to AA formation. APO, LY and BRCR reduced GtH release in response to the Ca2+ ionophore A23187, however, their inhibitory effect was reversed by 10 microM ionomycin.(ABSTRACT TRUNCATED AT 250 WORDS)

Three behavioral models were used to characterize the pharmacological action of BCH 325 on central dopaminergic transmission. The effect of acute SC treatment with BCH 325 upon dopaminergic mechanisms affecting motor activity was studied on the climbing behavior of mice. It was shown that the beta-casomorphin analogue evoked a dose-dependent increase in apomorphine (APO)-induced hypoactivity that was reversed by sulpiride (SULP). In in vitro studies on slices of nucleus accumbens of mice it could be demonstrated that 10(-6) M APO caused a reduction of K(+)-stimulated [14C]dopamine (DA) release that was potentiated following simultaneous incubation with 10(-6) M BCH 325. To prove a postsynaptic influence in D1 receptor-mediated behavior pattern, the action of BCH 325 was studied on bromocriptine (BROMO)-evoked yawning behavior of rats after pretreatment with reserpine (RES) or saline. The peptide could not influence the BROMO yawning after saline administration, but it was able to normalize the number of yawns, which were reduced after RES. To investigate the effect of BCH 325 on postsynaptic D2 receptors, jerking behavior on RES-pretreated rats after a high dose of BROMO was used. Following RES pretreatment only, the number of BROMO-induced jerks was decreased by treatment of rats with 0.5 mumol/kg BCH 325. In contrast, the jerking behavior was enhanced by 0.5 mumol/kg BCH 325 in rats that were additionally treated with alpha-methyl-p-tyrosine (MPT). In biochemical studies on slices of the nucleus accumbens of mice, the in vivo pretreatment with RES caused a reduction of K(+)-stimulated [14C]DA release that was blocked by the SC administration of 0.5 mumol/kg BCH 325.(ABSTRACT TRUNCATED AT 250 WORDS)

Ethanol (ETOH) administered acutely to castrate male rats caused a decline in pituitary luteinizing hormone (LH) and prolactin (PRL) secretion. This was associated with an elevation in hypothalamic and median eminence stores of dopamine (DA) that was related to the dose of alcohol given. Pituitary stalk transection (PST) resulted in a significant rise in plasma PRL levels compared to sham control animals, which suggests that DA in the hypophysial portal blood exerted an inhibitory influence on pituitary PRL secretion. The DA agonist bromocriptine failed to alter mean plasma LH levels in stalk-transected rats. The ETOH-treated castrated rats showed a significant rise in circulating PRL after injection of the DA receptor antagonist haloperidol metabolite II (HAL), but the administration of the DA receptor agonist R(-)-apomorphine HCL (APO) caused plasma PRL to decline to near undetectable levels. Plasma LH levels remained unchanged in the HAL- and APO-treated rats and were similar to those of sham controls. These results suggest that lactotroph DA receptors were still functional. Thus our previous finding of ETOH-induced reduction on LH secretion may be attributable to an inhibitory effect by DA on the luteinizing hormone-releasing hormone (LHRH) peptidergic neurons rather than a direct inhibition by DA on the pituitary gonadotroph.

1. The effects of dopamine agonists on the immobility time in mice were examined. 2. Apomorphine (APO), bupropion (BUP), bromocriptine (BRC) and quinpirole but not SKF 38393 elicited anti-immobility effect. The effect of the agonists was decreased by the D-2 antagonist sulpiride but not by the D-1 antagonist SCH 23390. 3. In animals pretreated with reserpine, the anti-immobility effects of APO and quinpirole were potentiated, while the response of BPU was decreased and that of BRC was not changed. 4. It is concluded that D-2 dopamine receptors are involved in the anti-immobility effects of dopaminergic agents, D-2 dopamine receptors may become hypersensitive by reserpine and BUP exerts its response through indirect dopaminergic if mechanism.

Apomorphine (Apo), a D1/D2 Dopamine (DA) agonist, at high doses (500 micrograms/kg) induces a short-lasting insomnia, antagonized by a secondary injection of corticotropin-like intermediate lobe peptide (CLIP, 10 ng); these effects are also observed with hypophysectomized (hypoX) rats. The administration of the serotonin (5-HT) agonist 8-hydroxy-2-di-n-propylamino-tetralin (8-OHDPAT, 0.3 mg/kg) induces also an insomnia which, unlike Apo, is followed by a significant PS rebound. CLIP, again, antagonizes the 8-OHDPAT-induced insomnia. Finally, Bromocriptine (5 mg/kg), an agonist for both DA and 5-HT, induces first an insomnia (antagonized by CLIP), followed by a PS rebound; these effects persist in hypoX rats.

The ability of bromocriptine (BRC), a dopamine D-2 receptor agonist, to induce climbing behaviour was studied in mice. BRC (2-32 mg/kg IP) evoked climbing behaviour. The maximum effect was obtained with 8 mg/kg, while higher doses of BRC (16 and 32 mg/kg) were less effective. Climbing began about 2 h after injection and was most marked 5 h after bromocriptine administration. Pretreatment of animals with the dopamine antagonist pimozide (0.5 mg/kg IP) decreased BRC-induced climbing. Sulpiride (0.25-1.25 mg/kg IP), a potent D-2 antagonist and/or SCH 23390 (0.025 and 0.05 mg/kg SC), a D-1 receptor antagonist, also decreased the response. Furthermore, the climbing behaviour induced by BRC was abolished by pretreatment with reserpine plus alpha-methyl-p-tyrosine (AMPT). Concomitant administration of apomorphine (APO) and BRC potentiated the effect of APO on climbing. Concomitant injection of BRC and SKF 38393 (SKF, D-1 agonist) reduced the effect of SKF on climbing, while administration of BRC 4 h before SKF potentiated the effect of both drugs. It is suggested that BRC induces climbing through D-1 and/or D-2 dopamine receptors.

1. The erectile response to the short-acting dopamine (DA) receptor agonist, apomorphine (Apo) HCl (0.25, 0.5, 0.75 and 1.0 mg sc), and placebo was evaluated in 28 impotent patients and penile circumference monitored using a mercury strain gauge and strip chart recording. 2. A full erection (increment in penile circumference greater than 2 cm and lasting at least one minute) occurred in 17 patients with Apo; no erection developed after placebo. An erection occurred in 6/8 patients with impaired glucose tolerance, 2/6 patients with diabetes mellitus and in both patients on lithium. 3. Nine patients who responded to Apo were treated in an open trial with bromocriptine; 6 reported improvement in potency. 4. Impairment in DA function may play a role in idiopathic impotence and in impotence associated with impaired glucose tolerance and diabetes mellitus. 5. An erectile response to Apo may predict therapeutic response to bromocriptine or other long acting dopaminergic agents. 6. Lithium, which inhibits DA-sensitive adenylate cyclase, does not prevent Apo-induced erections. This provides further support indicating that Apo induces erections by an effect on D2 receptors. 7. The yawning response to placebo and four doses of Apo HC1 (3.5, 5.0, 7.0, and 10.5 ug/kg sc) was evaluated in five normal men using a polygraphic technique. The yawning response was also assessed in normal young (less than 30 yrs; N = 16) and elderly (greater than 60 yrs; N = 12) volunteers. 8. Under experimental conditions of study, placebo induced spontaneous yawning. This was antagonized by 3.5 and 5.0 ug/kg Apo HC1 but increased by 7.0 ug/kg Apo HC1. These observations are compatible with the view that Apo HC1 in doses of 3.5-5.0 ug/kg stimulates presynaptic DA receptors whereas 7.0 ug/kg stimulates postsynaptic DA receptors. 9. Spontaneous and Apo-induced yawning were significantly decreased in the elderly which suggests that D2 receptor function declines with normal aging.

All the dopamine agonists (apomorphine, dipropylamino-5,6-dihydroxytetrahydronaphtalene, piribedil, bromocriptine, CBM 36-733) tested in the 'behavioral despair' test performed in mice had a dose-dependent anti-immobility effect, with the exception of the D-1 dopamine agonist, SKF 38393. This effect occurred at doses that reduced locomotor activity and decreased colonic temperature. A profound hypothermia of the same amplitude resulted from the immersion in water of the control and apomorphine (Apo)-treated mice. The anti-immobility effect of dopamine agonists depends on the stimulation of central dopamine receptors; this effect was antagonized more easily by haloperidol than by domperidone, and dipropylamino-5,6-dihydroxytetrahydronaphtalene was more effective than amino-5,6-dihydroxytetrahydronaphtalene. Their high sensitivity to sulpiride make it likely that the receptors involved correspond to the D-4 subtype. Blockade of dopamine receptors by haloperidol for about 5 days induced a slight hypersensitivity to the Apo effects. In contrast, tolerance to Apo occurred after administration of Apo, 5 mg/kg s.c., 24 and 16 h before testing. These data might reflect the potential antidepressant activity of direct dopamine agonists.

Different effects of chronic treatment with bromocriptine (BRO) on D-1 and D-2 receptors in the rat were studied through behavioral observation and DA receptor binding assays. Chronic BRO led to enhancement of stereotypy to apomorphine (APO), at the same time it increased the density of D-1 receptor binding by 43% and decreased that of D-2 receptor binding by 21%. Our data suggest that BRO has different effects on D-1 and D-2 receptors and the behavioral hypersensitivity caused by BRO may be relevant to the proliferation of D-1 receptor.

Apomorphine (Apo), a short acting dopamine (DA) receptor agonist induces penile erections in normal subjects. The erectile response to one or more doses of Apo HCl (0.25, 0.5, 0.75, 1.0 mg sc) or placebo was investigated in eight impotent subjects and penile tumescence monitored using a mercury strain gauge and strip chart recording. Four patients showed a full erection with Apo and one a partial response. Distressing side effects (nausea, sweating) were associated with non-response or partial response. Three responders to Apo were treated with low doses of the long acting DA receptor agonist, bromocriptine (2.5-3.75 mg/d po); all three showed complete recovery of erectile function within two weeks. A subgroup of impotent patients may have impaired central DA function. Testing with Apo may provide a diagnostic and predictive test to identify such patients who may respond to treatment with low doses of bromocriptine or other DA receptor agonist.