METHODS: ACE inhibitory proteins were isolated from P. cystidiosus based on the bioassay guided purification steps, i.e. ammonium sulphate precipitation, reverse phase high performance liquid chromatography and size exclusion chromatography. Active fraction was then analysed by LC-MS/MS and potential ACE inhibitory peptides identified were chemically synthesized. Effect of in vitro gastrointestinal digestions on the ACE inhibitory activity of the peptides and their inhibition patterns were evaluated.
RESULTS: Two potential ACE inhibitory peptides, AHEPVK and GPSMR were identified from P. cystidiosus with molecular masses of 679.53 and 546.36 Da, respectively. Both peptides exhibited potentially high ACE inhibitory activity with IC50 values of 62.8 and 277.5 μM, respectively. SEC chromatograms and BIOPEP analysis of these peptides revealed that the peptide sequence of the hexapeptide, AHEPVK, was stable throughout gastrointestinal digestion. The pentapeptide, GPSMR, was hydrolysed after digestion and it was predicted to release a dipeptide ACE inhibitor, GP, from its precursor. The Lineweaver-Burk plot of AHEPVK showed that this potent and stable ACE inhibitor has a competitive inhibitory effect against ACE.
CONCLUSION: The present study indicated that the peptides from P. cystidiosus could be potential ACE inhibitors. Although these peptides had lower ACE inhibitory activity compared to commercial antihypertensive drugs, they are derived from mushroom which could be easily obtained and should have no side effects. Further in vivo studies can be carried out to reveal the clear mechanism of ACE inhibition by these peptides.
METHOD: Literature search was performed within the PubMed, ScienceDirect.com and Google Scholar.
RESULTS: The presence of proline at the C-terminal tripeptide of ACE inhibitor can competitively inhibit the ACE activity. The effects of other amino acids are less studied leading to difficulties in predicting potent peptide sequences. The broad specificity of the enzyme may be due to the dual active sites observed on the somatic ACE. The inhibitors may not necessarily competitively inhibit the enzyme which explains why some reported inhibitors do not have the common ACE inhibitor characteristics. Finally, the in vivo assay has to be carried out before the peptides as the antihypertensive agents can be claimed. The peptides must be absorbed into circulation without being degraded, which will affect their bioavailability and potency. Thus, peptides with strong in vitro IC50 values do not necessarily have the same effect in vivo and vice versa.
CONCLUSION: The relationship between peptide amino acid sequence and inhibitory activity, in vivo studies of the active peptides and bioavailability must be studied before the peptides as antihypertensive agents can be claimed.
METHODS: We systematically reviewed the published studies to assess the association of RAS inhibitors with mortality as well as disease severity in COVID-19 patients. A systematic literature search was performed to retrieve relevant original studies investigating mortality and severity (severe/critical disease) in COVID-19 patients with and without exposure to RAS inhibitors.
RESULTS: A total of 59 original studies were included for qualitative synthesis. Twenty-four studies that reported adjusted effect sizes (24 studies reported mortality outcomes and 16 studies reported disease severity outcomes), conducted in RAS inhibitor-exposed and unexposed groups, were pooled in random-effects models to estimate overall risk. Quality assessment of studies revealed that most of the studies included were of fair quality. The use of an ACEI/ARB in COVID-19 patients was significantly associated with lower odds (odds ratio [OR] = 0.73, 95% confidence interval [CI] 0.56-0.95; n = 18,749) or hazard (hazard ratio [HR] = 0.75, 95% CI 0.60-0.95; n = 26,598) of mortality compared with non-use of ACEI/ARB. However, the use of an ACEI/ARB was non-significantly associated with lower odds (OR = 0.91, 95% CI 0.75-1.10; n = 7446) or hazard (HR = 0.73, 95% CI 0.33-1.66; n = 6325) of developing severe/critical disease compared with non-use of an ACEI/ARB.
DISCUSSION: Since there was no increased risk of harm, the use of RAS inhibitors for hypertension and other established clinical indications can be maintained in COVID-19 patients.