Repurposing Zidovudine in combination with Tigecycline for treating carbapenem-resistant Enterobacteriaceae infections.

The global emergence of carbapenem-resistant Enterobacteriaceae (CRE) presents a significant clinical concern, prompting the WHO to prioritize CRE as a top priority pathogen in their 2017 global antibiotic-resistant bacteria priority list. Due to the fast-depleting antibiotic arsenal, clinicians are now resorting to using once-abandoned, highly toxic antibiotics such as the polymyxins and aminoglycosides, creating an urgent need for new antibiotics. Drug repurposing, the application of an approved drug for a new therapeutic indication, is deemed a plausible solution to this problem. A total of 1,163 FDA-approved drugs were screened for activity against a clinical carbapenem- and multidrug-resistant E. coli isolate using a single-point 10 µM assay. Hit compounds were then assessed for their suitability for repurposing. The lead candidate was then tested against a panel of clinical CREs, a bactericidal/static determination assay, a time-kill assay and a checkerboard assay to evaluate its suitability for use in combination with Tigecycline against CRE infections. Three drugs were identified. The lead candidate was determined to be Zidovudine (azidothymidine/AZT), an oral anti-viral drug used for HIV treatment. Zidovudine was shown to be the most promising candidate for use in combination with Tigecycline to treat systemic CRE infections. Further experiments should involve the use of animal infection models.

Mapping the high-affinity binding domain of 5-substituted benzimidazoles to the proximal N-terminus of the GluN2B subunit of the NMDA receptor.

BACKGROUND AND PURPOSE: N-methyl-D-aspartate (NMDA) receptors represent an attractive drug target for the treatment of neurological and neurodegenerative disorders associated with glutamate-induced excitotoxicity. The aim of this study was to map the binding domain of high affinity 5-substituted benzimidazole derivatives [N-{2-[(4-benzylpiperidin-1-yl)methyl]benzimidazol-5-yl}methanesulphonamide (XK1) and N-[2-(4-phenoxybenzyl)benzimidazol-5-yl]methanesulphonamide (XK2)] on the GluN2B subunit of the NMDA receptor. EXPERIMENTAL APPROACH: The pharmacological antagonistic profiles of XK1 and XK2 were assessed using in vitro rat primary cerebrocortical neurones and two-electrode voltage clamp on Xenopus oocytes expressing heterologous GluN1/GluN2B receptors. Direct ligand binding was determined using the recombinant amino-terminal domain (ATD) of GluN2B. KEY RESULTS: XK1 and XK2 effectively protected against NMDA-induced excitotoxicity in rat primary cortical neurones. Low concentrations of XK1 (10 nM) and XK2 (1 nM) significantly reversed neuronal death. Both compounds failed to inhibit currents measured from oocytes heterologously expressing GluN1-1a subunit co-assembled with the ATD-deleted GluN2B subunit. XK1 and XK2 showed specific binding to recombinant protein of GluN2B ATD with low nanomolar affinities. Several residues in the recombinant ATD of GluN2B were identified to be critical for conferring XK1 and XK2 sensitivity. The inhibitory effects of XK1 and XK2 were pH-sensitive, being increased at acidic pH. CONCLUSIONS AND IMPLICATIONS: These results demonstrate that XK1 and XK2 are effective neuroprotective agents in vitro and indicate that 5-substituted benzimidazole derivatives inhibit GluN1/GluN2B receptors via direct binding to the ATD of the GluN2B subunit. These compounds represent valuable alternatives to the classical antagonist ifenprodil as pharmacological tools for studying GluN2B-containing NMDA receptors.

GHTD-amide: a naturally occurring beta cell-derived peptide with hypoglycemic activity.

In the early 1970s, a peptide fraction with insulin potentiating activity was purified from human urine but the identity and origins of the active constituent remained unknown. Here we identify the active component and characterize its origins. The active peptide was identified as an alpha amidated tetrapeptide with the sequence GHTD-amide. The peptide was synthesized and tested for stimulation of glycogen synthesis and insulin potentiation by insulin tolerance testing in insulin-deficient rats, which confirmed GHTD-amide as the active peptide. Tissue localization using a peptide-specific anti-serum and epifluorescent and confocal microscopy showed decoration of pancreatic islets but not other tissues. Confocal microscopy revealed co-localization with insulin and immunogold and electron microscopy showed localization to dense core secretory granules. Consistent with these observations GHTD-amide was found in media conditioned by MIN6 islet beta cells. Sequence database searching found no annotated protein in the human proteome encoding a potential precursor for GHTD-amide. We conclude that the insulin potentiating activity originally described in human urine is attributable to the tetrapeptide GHTD-amide. GHTD-amide is a novel peptide produced by pancreatic beta cells and no precursor protein is present in the annotated human proteome. Stimulation of glycogen synthesis and co-localization with insulin in beta cells suggest that GHTD-amide may play a role in glucose homeostasis by enhancing insulin action and glucose storage in tissues.

Theoretical basis for long-term measurements of equilibrium factors using LR 115 detectors.

In this paper, we propose a method to determine the equilibrium factor using a bare LR 115 detector. The partial sensitivities rhoi of the LR 115 detector to 222Rn and its alpha-emitting short-lived progeny, 218Po and 214Po, were investigated. We first determined the distributions of lengths of major and minor axes of the perforated alpha tracks in the LR 115 detector produced by 222Rn, 218Po and 214Po through Monte Carlo simulations. The track parameters were calculated using a track development model with a published V function, by assuming a removed active layer of 6.54 microm. The distributions determined for different alpha emitters were found to completely overlap with one another. This implied equality of partial sensitivities for radon and its progeny, which was also confirmed through analytical considerations. Equality of partial sensitivities makes possible convenient measurements of the proxy equilibrium factor Fp, which is defined in the present work as (F1+F3) and is equal to the ratio between the sum of concentrations of the two alpha emitting radon progeny (218Po+214Po) to the concentration of radon gas (222Rn). In particular, we have found Fp = (rho/rhoitC0)-1, where rho (track/m2) is the total track density on the detector, rhoi = 0.288 x 10(-2) m, t is the exposure time and C0 (Bq/m3) is the concentration of 222Rn. If C0 is known (e.g. from a separate measurement), we can obtain Fp. The proxy equilibrium factor Fp is also found to be well correlated with the equilibrium factor between radon gas and its progeny through the Jacobi room model. This leads to a novel method for long-term determination of the equilibrium factor.

Measurement of parameters of tracks in CR-39 detector from replicas.

In determining the etched track rate in solid-state nuclear track detectors, track lengths should be determined accurately. A method based on surface profilometry is proposed to determine the track lengths in CR-39 detectors through measurements of their replicas. Tracks from alpha particles with an incident energy of 4 MeV have been chosen to demonstrate the method. After irradiation and chemical etching, resin replicas were made from the tracks, of which the heights were measured by the Form Talysurf PGI Profilometer. The results showed that the surface of the replicas were smooth and the heights of the replicas were uniform, so the replicating fluid should have filled the tracks completely and the replicas truly reflected the dimensions of the tracks. The heights of the replicas were conveniently determined from the lateral view of the replicas generated by the Form Talysurf PGI Profilometer.

The effects of human GH and its lipolytic fragment (AOD9604) on lipid metabolism following chronic treatment in obese mice and beta(3)-AR knock-out mice.

Both human GH (hGH) and a lipolytic fragment (AOD9604) synthesized from its C-terminus are capable of inducing weight loss and increasing lipolytic sensitivity following long-term treatment in mice. One mechanism by which this may occur is through an interaction with the beta-adrenergic pathway, particularly with the beta(3)-adrenergic receptors (beta(3)-AR). Here we describe how hGH and AOD9604 can reduce body weight and body fat in obese mice following 14 d of chronic ip administration. These results correlate with increases in the level of expression of beta(3)-AR RNA, the major lipolytic receptor found in fat cells. Importantly, both hGH and AOD9604 are capable of increasing the repressed levels of beta(3)-AR RNA in obese mice to levels comparable with those in lean mice. The importance of beta(3)-AR was verified when long-term treatment with hGH and AOD9604 in beta(3)-AR knock-out mice failed to produce the change in body weight and increase in lipolysis that was observed in wild-type control mice. However, in an acute experiment, AOD9604 was capable of increasing energy expenditure and fat oxidation in the beta(3)-AR knock-out mice. In conclusion, this study demonstrates that the lipolytic actions of both hGH and AOD9604 are not mediated directly through the beta(3)-AR although both compounds increase beta(3)-AR expression, which may subsequently contribute to enhanced lipolytic sensitivity.

Increase of fat oxidation and weight loss in obese mice caused by chronic treatment with human growth hormone or a modified C-terminal fragment.

OBJECTIVE: To observe the chronic effects of human growth hormone (hGH) and AOD9604 (a C-terminal fragment of hGH) on body weight, energy balance, and substrate oxidation rates in obese (ob/ob) and lean C57BL/6Jmice. In vitro assays were used to confirm whether the effects of AOD9604 are mediated through the hGH receptor, and if this peptide is capable of cell proliferation via the hGH receptor. METHOD: Obese and lean mice were treated with hGH, AOD or saline for 14 days using mini-osmotic pumps. Body weight, caloric intake, resting energy expenditure, fat oxidation, glucose oxidation, and plasma glucose, insulin and glycerol were measured before and after treatment. BaF-BO3 cells transfected with the hGH receptor were used to measure in vitro 125I-hGH receptor binding and cell proliferation. RESULTS: Both hGH and AOD significantly reduced body weight gain in obese mice. This was associated with increased in vivo fat oxidation and increased plasma glycerol levels (an index of lipolysis). Unlike hGH, however, AOD9604 did not induce hyperglycaemia or reduce insulin secretion. AOD9604 does not compete for the hGH receptor and nor does it induce cell proliferation, unlike hGH. CONCLUSIONS: Both hGH and its C-terminal fragment reduce body weight gain, increase fat oxidation, and stimulate lipolysis in obese mice, yet AOD9604 does not interact with the hGH receptor. Thus, the concept of hGH behaving as a pro-hormone is further confirmed. This data shows that fragments of hGH can act in a manner novel to traditional hGH-stimulated pathways.

Molecular and cellular actions of a structural domain of human growth hormone (AOD9401) on lipid metabolism in Zucker fatty rats.

A lipolytic domain (AOD9401) of human growth hormone (hGH) which resides in the carboxyl terminus of the molecule and contains the amino acid residues 177-191, has been synthesized using solid-phase peptide synthesis techniques. AOD9401 stimulated hormone-sensitive lipase and inhibited acetyl coenzyme A carboxylase (acetyl CoA carboxylase) in isolated rat adipose tissues, in a similar manner to the actions of the intact hGH molecule. The synthetic lipolytic domain mimicked the effect of the intact growth hormone on diacylglycerol release in adipocytes. Chronic treatment of obese Zucker rats with AOD9401 for 20 days reduced the body weight gain of the animals, and the average cell size of the adipocytes of the treated animals decreased from 110 to 80 microm in diameter. Unlike hGH, synthetic AOD9401 did not induce insulin resistance or glucose intolerance in the laboratory animals after chronic treatment. The results suggest that AOD9401 has the potential to be developed into a therapeutic agent for the control of obesity.

Effects of oral administration of a synthetic fragment of human growth hormone on lipid metabolism.

A small synthetic peptide sequence of human growth hormone (hGH), AOD-9401, has lipolytic and antilipogenic activity similar to that of the intact hormone. Here we report its effect on lipid metabolism in rodent models of obesity and in human adipose tissue to assess its potential as a pharmacological agent for the treatment of human obesity. C57BL/6J (ob/ob) mice were orally treated with either saline (n = 8) or AOD-9401 (n = 10) for 30 days. From day 16 onward, body weight gain in AOD-9401-treated animals was significantly lower than that of saline-treated controls. Food consumption did not differ between the two groups. Analyses of adipose tissue ex vivo revealed that AOD-9401 significantly reduced lipogenic activity and increased lipolytic activity in this tissue. Increased catabolism was also reflected in an acute increase in energy expenditure and glucose and fat oxidation in ob/ob mice treated with AOD-9401. In addition, AOD-9401 increased in vitro lipolytic activity and decreased lipogenic activity in isolated adipose tissue from obese rodents and humans. Together, these findings indicate that oral administration of AOD-9401 alters lipid metabolism in adipose tissue, resulting in a reduction of weight gain in obese animals. The marked lipolytic and antilipogenic actions of AOD-9401 in human adipose tissues suggest that this small synthetic hGH peptide has potential in the treatment of human obesity.

Metabolic studies of a synthetic lipolytic domain (AOD9604) of human growth hormone.

A synthetic analogue (AOD9604) of the lipolytic domain of human growth hormone (hGH) has been studied for its metabolic actions in obese Zucker rats. Daily treatment with an oral dose of AOD9604 of 500 microg/kg body weight for 19 days reduced over 50% (15.8 +/- 0.6 vs. 35.6 +/- 0.8 g) body weight gain of the animals in comparison with the control. The adipose tissues of the AOD9604--treated animals were found to have an increase in lipolytic activity. In contrast to chronic treatment with intact hGH, chronic treatment with AOD9604 showed no adverse effect on insulin sensitivity of the animals, as demonstrated with euglycemic clamp techniques. The results in the present study suggest that the analogue of the hGH lipolytic domain may have the potential to be developed into an orally usable and safe therapeutic agent for obesity.

Structure and in vivo activity of hypoglycaemic analogues of human growth hormone (6-13).

A range of peptide analogues related to Asu11-human growth hormone (6-13) have been synthesized and tested for hypoglycaemic activity using in vivo insulin tolerance tests. Utilising an alanine scan procedure and a selective amino acid residue approach these structure-activity studies suggest that residues Phe10, Arg8 and the C-terminal beta-turn structure are important for the expression of biological activity.

Reduction of cumulative body weight gain and adipose tissue mass in obese mice: response to chronic treatment with synthetic hGH 177-191 peptide.

The effects of long-term treatment of C57BL/6J (ob/ob) mice with a synthetic carboxylterminal sequence of human growth hormone, hGH 177-191, were investigated. Results indicate that the hGH 177-191 reduced the cumulative body weight gain, and decreased the adipose tissue mass. The lipogenesis in adipose tissues was significantly inhibited by the treatment with hGH 177-191. These findings support the suggestion that hGH 177-191 is the functional domain of hGH for the antilipogenic actions of the intact hormone both in vivo and in vitro. The hGH 177-191 peptide has the potential to be an effective compound for the treatment of human obesity and for the improvement of meat qualities in farm animals.

Effect of an antilipogenic fragment of human growth hormone on glucose transport in rat adipocytes.

The effect of a synthetic C-terminal peptide sequence of human growth hormone, Leu-Arg-Ile-Val-Gln-Cys-Arg-Val-Ser-Glu-Gly-Ser-Cys-Gly-Phe (hGH 177-191) on glucose transport in adipocytes isolated from genetically-obese Zucker rats was investigated. The results showed that the synthetic peptide induced a reduction of basal and insulin-stimulated D[1-14C]-2-deoxyglucose uptake in isolated adipocytes. In comparison with the intact molecule of human growth hormone (hGH), the synthetic peptide at equimolar concentrations was found to be more potent. These findings are consistent with the suggestion that the functional domain responsible for the antilipogenic activity of hGH resides in the C-terminal region of the hGH molecule and the effect on glucose transport may contribute, at least in part, to the antilipogenic property of the peptide hGH 177-191 as well as of the intact hormone.

Antilipogenic action of synthetic C-terminal sequence 177-191 of human growth hormone.

The synthetic C-terminal peptide fragment of human growth hormone, Leu-Arg-Ile-Val Gln-Cys-Arg-Val-Ser-Glu-Gly-Ser-Cys-Gly-Phe (hGH 177-191), was shown to have antilipogenic activity identical with that of the intact molecule of human growth hormone (hGH). No significant lipolytic effect of hGH 177-191 was found as determined by the rate of glycerol release from epididymal fat pads of the peptide-treated rats. The results support the suggestion that the functional domain responsible for the antilipogenic activity of hGH resides in the C-terminal region of the molecule and that the main physiological effect of hGH in lipid metabolism is at the level of lipogenesis.

Hypoglycemic action of a novel constrained analog of human growth hormone-(6-13).

The amino-terminal region of human GH (hGH), in particular the amino acid sequence Leu-Ser-Arg-Leu-Phe-Asp-Asn-Ala[hGH-(6-13)], has been implicated as a functional region for the regulation of energy metabolism by exerting an insulin-potentiating action on insulin-sensitive tissues. Recent structural studies have revealed that the cyclization of the aspartate (Asp11) residue to form the alpha-aminosuccinimide (Asu11) ring is essential for the biological action of peptides related to this hGH fragment. The pharmacological application of these hGH-(6-13) peptides has been hindered by the vulnerability of the alpha-aminosuccinimide to hydrolytic modification leading to the loss of biological action. We have succeeded in stabilizing the structure of the Asu11-hGH-(6-13) peptide by replacing the alpha-aminosuccinimide ring with compatible and less rapidly metabolized gamma-lactam structures. In the present paper we report the bioactivity profile of an analog of hGH-(6-13) containing a gamma-lactam at residue position 11 that mimics the stereoelectronic and conformational characteristics of the alpha-aminosuccinimide ring. In vitro, the gamma-lactam11-hGH-(6-13) peptide analog increased [14C]glucose incorporation into glycogen in muscles and conversion to lipid in adipose tissues. In vivo, the gamma-lactam11-hGH-(6-13) peptide enhanced hypoglycemia during iv insulin tolerance tests. The results demonstrate that the gamma-lactam11-hGH-(6-13) peptide analog has similar biological properties to the Asu11-hGH-(6-13) peptide fragment, but with improved molecular stability and bioavailability.

Synthesis and evaluation of constrained peptide analogues related to the N-terminal region of human growth hormone.

The synthesis and incorporation of two different isomeric gamma-lactam structures into peptide analogues related to hGH [6-13] are described. These peptide analogues and the corresponding aspartimide analogue have been tested for hypoglycemic activity with the intravenous insulin tolerance test. One lactam structure is of the type developed by Freidinger and co-workers, while the isomeric gamma-lactam structure represents a new constrained synthon for use in peptide synthesis. We have found that the hGH [6-13] peptide analogue incorporating the Freidinger lactam was more potent and longer lasting than the aspartimide peptide analogue. The hGH [6-13] peptide analogue incorporating the new gamma-lactam has diminished hypoglycemic activity. The relative biological activities of the three peptide analogues and the possible conformational implications at the physiological site of action are discussed.

Effects of exogenous growth hormone on insulin action and glucose metabolism in the dwarf 'little' mouse.

The in vivo actions of growth hormone (GH) on insulin activity and glucose homeostasis were examined in the GH-deficient Little mouse. The insulin-like action of GH was revealed during glucose tolerance tests on the animals after acute treatment with the hormone and the insulin-antagonistic action was demonstrated in both glucose tolerance tests and insulin tolerance tests on the mice after chronic GH infusion. The primary mechanism of the GH actions is to influence the responses of the target tissues to circulating insulin in vivo. The pancreatic function seems to be of little importance in the alteration of glucose metabolism after acute exposure to GH as no significant change of the levels of plasma insulin was detected. It is concluded that the GH-deficient Little mouse is an ideal laboratory model for the elucidation of the molecular mechanism of the interaction between insulin and GH in the regulation of carbohydrate metabolism.

Effects of exogenous growth hormone on lipid metabolism in the isolated epididymal fat pad of the growth hormone-deficient little mouse.

The effects of two preparations of highly purified human GH (hGH) on lipid metabolism were studied in the GH-deficient little mouse (50-60 days old). Marked decreases in incorporation of [14C]glucose into fatty acid and in the activity of acetyl-CoA carboxylase in the epididymal fat pads were observed after i.p. injection of hGH at a dose of 1.0 microgram/g body weight or after continuous infusion of hGH by osmotic minipump. The rate of glucose incorporation into fatty acid decreased from 107.0 +/- 27.6 (S.E.M.) to 38.1 +/- 19.6 mumol/g tissue per h after a single injection of hGH and from 174.1 +/- 28.5 to 56.3 +/- 20.3 mumol/g tissue per h after continuous infusion of hGH for 2 days. Activity of the lipogenic enzyme acetyl-CoA carboxylase was also reduced by more than 50% in the epididymal fat pad from hGH-treated mice in comparison with the corresponding control animals. Incubation of isolated fat pads with hGH (0.1 microgram/ml) revealed similar inhibitory effects of the hormone on fatty acid synthesis and acetyl-CoA carboxylase activity. No lipolytic effect of hGH was found as determined by the rate of glycerol release from epididymal fat pads of little mice following hormone treatment in vivo or in vitro. The results lend strong support to the conclusion that GH inhibits lipogenesis but has no effect on lipolysis in adipose tissues, and indicate that the physiological role of GH in lipid metabolism is concerned mainly with the regulation of anabolic rather than catabolic processes.

Structure and activity of the B-chain of insulin.

Despentapeptide (B26-30)-insulinamide (B25) prepared by a semisynthetic procedure was found to have about 65% of the hypoglycaemic activity of natural insulin. In contrast, the binding of the modified insulin analogue to insulin specific receptors was markedly increased. The discrepancy between the loss of biological potency and the apparent increase in binding affinity for membrane receptors reveals that not all of the biological activity of insulin is regulated by the receptor-binding system. The tetrapeptidamide of the B-chain of insulin (Arg-Gly-Phe-Phe-NH2) was clearly shown to have both insulin-like and insulin-potentiating actions in vivo although it had no effect on insulin receptor function in vitro. Evidence suggests that the small peptide fragment of insulin may be internalized and acts at the post-binding site(s) of the glucose metabolic pathway in target tissues. The present data support the general concept that insulin may exert its complex molecular actions through internalized hormonal fragment as well as the transmembrane mediators generated from receptor binding.

A comparison of cellular actions between gliclazide and a hypoglycaemic peptide fragment of human growth hormone (hGH 6-13).

The mechanisms of hypoglycaemic action of a 'second-generation' sulphonylurea, gliclazide, and a synthetic human growth hormone fragment, hGH 6-13 (Leu-Ser-Arg-Leu-Phe-Asp-Asn-Ala), were compared at the cellular level in rats. Both compounds were shown to be hypoglycaemic in vivo although their molecular structures were totally different. Gliclazide was markedly insulinotropic, as are all hypoglycaemic sulphonylureas, whereas hGH 6-13 had no visible effect on basal levels of plasma insulin. However, in vitro studies with isolated pancreatic islets revealed that hGH 6-13 significantly augmented insulin secretion in the presence of exogenous glucose. One other major difference was that gliclazide had no direct effect on insulin receptor function while the synthetic hGH 6-13 increased the binding of insulin to specific receptors on isolated cells. Results suggested that the human growth hormone fragment hGH 6-13 could be a potential anti-diabetes drug with the ability to potentiate circulating insulin action and to achieve blood glucose normalisation.