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Neuropeptide Inactivation By Peptidases
Published in Gerard O’Cuinn, Metabolism of Brain Peptides, 2020
Gerard O’Cuinn, Brendan O’Connor, Laura Gilmartin, Maria Smyth
One of the more striking differences between the results obtained with whole animal experiment and those obtained with either membrane enriched particulate fractions or with cultured spinal cord cells concerns the nature of the enzyme converting angiotensin II to angiotensin III. The whole animal experiments indicate the involvement of amastatin (and bestatin) sensitive aminopeptidase A whereas experiments with subcellular fractions indicate the involvement of either amastatin or bestatin insensitive enzymes. One must also consider results from an immunohistochemical approach which has indicated that aminopeptidase A is located in the microvasculature and that no immunohistochemical staining was associated with either glial or neuronal cells161. A similar approach has also placed aminopeptidase M largely in the microvasculature126. While a number of possible routes exist for the degradation of angiotensin II, angiotensin III alone of the metabolites produced retains part of the dipsogenic activity222 and binds to angiotensin II binding sites with significant affinity223,224. The removal of the C-terminal Phe residue to yield angiotensin 1–7 represents an effective inactivation mechanism as this peptide has neglible affinity for angiotensin II receptors223 and possessed no dipsogenic activity222.
Intranasal drug delivery devices and interventions associated with post-operative endoscopic sinus surgery
Published in Pharmaceutical Development and Technology, 2018
Lari K. Dkhar, Jim Bartley, David White, Ali Seyfoddin
Prodrugs have been used to overcome drugs’ poor solubility, insufficient stability, and inadequate absorption across barriers (Higuchi et al. 2016). Lipophilic drugs can pass through bio membranes, but are poorly soluble in water and when administered with a prodrug with a higher hydrophilic character they produce an aqueous nasal formulation with a suitable concentration (Chavan et al. 2014; Mujawar et al. 2014). L-Dopa is poorly soluble in water and developing an intranasal aqueous formulation with an effective dose has been reported challenging (Mujawar et al. 2014; Scaturro et al. 2016). When different prodrugs of L-Dopa were produced, it was observed that their solubility enhanced leading to the development of a rapid and completely absorbed nasal formulations (Scaturro et al. 2016). Additionally, very hydrophilic polar drugs cannot cross bio membranes and substitution with lipophilic prodrugs increases the penetration through the membrane (Mundlia and Kumar 2015; Kaur et al. 2016). Prodrug approach has also been used for improving enzymatic stability of drugs as well (Mujawar et al. 2014). Prodrugs can protect peptide drugs from nasal enzymatic degradation and increase their bioavailability when administered intranasally (Oliveira et al. 2016). Nasal mucus layer and nasal mucosa have a wide variety of enzymes that acts as enzymatic barriers during nasal drug delivery (Kaur et al. 2016). Proteases and peptidases inhibitors have been used to avoid enzymatic degradation. For example, bacitracin, amastatin, boroleucin, and puromycin have been used to prevent enzymatic degradation of drugs such as leucine enkephalin and human growth hormone (Casettari and Illum 2014; Kaur et al. 2016). In the nasal epithelium, small and large hydrophilic drugs may be poorly permeable with insufficient bioavailability (Mujawar et al. 2014; Verma et al. 2016).
ERAP1: a potential therapeutic target for a myriad of diseases
Published in Expert Opinion on Therapeutic Targets, 2020
Emma Reeves, Yasmin Islam, Edward James
Targeting the M1 aminopeptidase family for therapeutic benefit showed initial promise of clinical effect when inhibited with the broad spectrum inhibitors, tosedostat and bestatin, proving efficacious in phase II clinical trials for treatment of AML and lung cancer [47,76,77]. Early aminopeptidase inhibitors, bestatin and amastatin, had poor potency for ERAP1 [41]. By contrast, LeuSH has a higher potency for ERAP1, but like bestatin and amastatin, it is a broad spectrum aminopeptidase inhibitor and therefore not a good candidate for pharmacological modulation of ERAP1 [47]. The subsequent association of ERAP1 with disease, the knowledge that SNPs altered ERAP1 function and greater understanding of the mechanism of action of ERAP1, led to the development of a new generation of inhibitors that were either rationally designed, or identified through small molecule screening, confirmed a greater specificity for ERAP1 inhibition [46,48,78,79]. Using solved crystal structures of ERAP1 as a guide, the rational design approach of potent peptide-based M1 aminopeptidase inhibitors using a phosphinic group as a substrate transition analog yielded the compound DG013A [46]. This compound was identified to be a potent inhibitor of ERAP1 as well as ERAP2, in the sub-nM range, and several studies have confirmed the effect of the compound on ERAP1 inhibition [46,80,81]. DG013A has been shown to enhance antigen presentation in HeLa cells stably transfected with HLA-B*27, as well as increasing the CTL response again murine colon carcinoma CT26 [46]. In addition, this inhibitor affects innate immune responses such as the suppression of ERAP1 dependent TH17 responses in vitro and the down-regulation of macrophage phagocytosis [80,81]. Since its generation, different design approaches have produced inhibitors that have higher selectivity, but are not as potent as DG013A. Thiomersal is proposed to be an ERAP1-specific inhibitor which binds to the Zn atom in the active site, and was shown to reduce ERAP1-dependent antigen presentation in dendritic cells [79]. However, the use of this compound for pharmacological modulation may be confounded by high levels of toxicity. Exploration of the efficacy of nine weakly coordinating zinc binding groups revealed that the potency of inhibitors for ERAP1 may primarily be driven by the occupation of the active site specificity pockets [82]. In 2019, Giastas and colleagues obtained a high-resolution crystal structure (1.60A) of ERAP1 in the closed conformation, with the potent (nM) phosphinic pseudopeptide inhibitor DG046 bound [78,83]. The structures revealed DG046 to bind in the active site with a geometry that mimics a transition state analogue, and allowed detailed mapping of the internal cavity of ERAP1 in the closed conformation [83]. This was the first crystal structure solved at such high-resolution with an ERAP1 inhibitor, a major breakthrough in the barrier of structural studies and inhibitor design.