title: Bioactive properties of proline-rich peptides derived from dairy milk and colostrum

authors: Tock, Adriënne

abstract: Dipeptidyl peptidase 4 (DPP4) is a serine exopeptidase that cleaves dipeptides from the N-terminus, preferably when proline occupies the penultimate position. This enzyme plays a key role in maintaining glucose homeostasis by degrading insulin secreting incretins, such as gastric inhibitory peptide and glucagon-like peptide 1, thereby reducing insulin secretion. Consequently, inhibiting DPP4 activity has become a major strategy for mitigating the effects of Type 2 diabetes mellitus. A functional food approach involves inhibiting this enzyme with DPP4-inhibiting peptides that are generated from dairy products. Milk and colostrum are associated with various health benefits, largely due to the presence of many bioactive peptides. A significant portion of these are proline-rich peptides (PRPs), some of which exhibit DPP4 inhibitory properties. While many DPP4-inhibitory dairy peptides have been identified or predicted through ‘in silico’ analysis, the variations across different species and between milk and colostrum have yet to be explored.   

This research identified new PRPs in cow, goat, sheep, and deer milk and colostrum and demonstrated that some of these peptides have DPP4-inhibitory activity. Peptide identification and characterisation were performed using liquid chromatography tandem mass spectrometry, a new resin-based DPP4-binding procedure, and in vitro DPP4 inhibition assays. PRPs represented 20-30% of the identified peptides within each sample, with sheep colostrum reaching 35%. Peptides from deer had the lowest alignment with the Cervidae proteome, likely due to database incompleteness. Exact peptide sequence overlap among all samples was minimal. Peptides were chosen for DPP4 inhibition assays based on the resin pull-down assay results, presence of proline in the penultimate position, abundance, length, and origin. Out of the 21 selected peptides, 14 showed over 50% inhibition at 250 µM. Interestingly, these peptides revealed that greater proline content did not reliably predict DPP4 inhibition, which is contradictory to reports in the literature. The top six DPP4-inhibiting peptides were selected for IC50 determination, with values ranging from 46.7 to 103.2 µM. Even though these peptides were all less potent than the reference peptide inhibitor Diprotin A (IC50 of 2.69 ± 1.09 µM, n = 6), they all showed high abundance of at least 105. Additionally, most peptides represented novel sequences that were not previously reported in the literature as DPP4-inhibiting peptides. Pooled peptide fractions from each sample did not show inhibition at the tested concentration, although permeate from a dairy plant showed 34.41% ± 8.27 (n = 3) DPP4 inhibition at only 1.5% w/w of the permeate concentration. AlphaFold 3 predictions revealed that these peptides and Diprotin A docked at similar positions within the DPP4 active site. These findings provide the basis for future studies on interspecies differences, application of novel binding assays to find DPP4 inhibitors, and further exploration of dairy peptides as potential DPP4 inhibitors.

text: Bioactive properties of proline-rich peptides derived from dairy milk and colostrum Dipeptidyl peptidase 4 (DPP4) is a serine exopeptidase that cleaves dipeptides from the N-terminus, preferably when proline occupies the penultimate position. This enzyme plays a key role in maintaining glucose homeostasis by degrading insulin secreting incretins, such as gastric inhibitory peptide and glucagon-like peptide 1, thereby reducing insulin secretion. Consequently, inhibiting DPP4 activity has become a major strategy for mitigating the effects of Type 2 diabetes mellitus. A functional food approach involves inhibiting this enzyme with DPP4-inhibiting peptides that are generated from dairy products. Milk and colostrum are associated with various health benefits, largely due to the presence of many bioactive peptides. A significant portion of these are proline-rich peptides (PRPs), some of which exhibit DPP4 inhibitory properties. While many DPP4-inhibitory dairy peptides have been identified or predicted through ‘in silico’ analysis, the variations across different species and between milk and colostrum have yet to be explored.   

This research identified new PRPs in cow, goat, sheep, and deer milk and colostrum and demonstrated that some of these peptides have DPP4-inhibitory activity. Peptide identification and characterisation were performed using liquid chromatography tandem mass spectrometry, a new resin-based DPP4-binding procedure, and in vitro DPP4 inhibition assays. PRPs represented 20-30% of the identified peptides within each sample, with sheep colostrum reaching 35%. Peptides from deer had the lowest alignment with the Cervidae proteome, likely due to database incompleteness. Exact peptide sequence overlap among all samples was minimal. Peptides were chosen for DPP4 inhibition assays based on the resin pull-down assay results, presence of proline in the penultimate position, abundance, length, and origin. Out of the 21 selected peptides, 14 showed over 50% inhibition at 250 µM. Interestingly, these peptides revealed that greater proline content did not reliably predict DPP4 inhibition, which is contradictory to reports in the literature. The top six DPP4-inhibiting peptides were selected for IC50 determination, with values ranging from 46.7 to 103.2 µM. Even though these peptides were all less potent than the reference peptide inhibitor Diprotin A (IC50 of 2.69 ± 1.09 µM, n = 6), they all showed high abundance of at least 105. Additionally, most peptides represented novel sequences that were not previously reported in the literature as DPP4-inhibiting peptides. Pooled peptide fractions from each sample did not show inhibition at the tested concentration, although permeate from a dairy plant showed 34.41% ± 8.27 (n = 3) DPP4 inhibition at only 1.5% w/w of the permeate concentration. AlphaFold 3 predictions revealed that these peptides and Diprotin A docked at similar positions within the DPP4 active site. These findings provide the basis for future studies on interspecies differences, application of novel binding assays to find DPP4 inhibitors, and further exploration of dairy peptides as potential DPP4 inhibitors.

year: 2025

title: Do high-quality auditors improve non-GAAP reporting?

authors: Feng, Zhuoan

abstract: Prior research finds that clients of high-quality auditors report higher quality GAAP earnings. We extend this research to investigate whether auditor quality is associated with the quality of voluntarily disclosed non-GAAP earnings measures. Using a sample of Australian firms disclosing annual non-GAAP metrics, we find that clients of high-quality auditors are more likely to voluntarily disclose non-GAAP earnings numbers. However, clients of high-quality auditors make adjustments in calculating non-GAAP earnings (non-GAAP exclusions) that are less predictive of future earnings and less value relevant than those of other firms. These results indicate that their adjustments are of higher quality. We also find similar results for US firms using a sample of quarterly non-GAAP earnings disclosures. Overall, our evidence indicates that commonly used indicators of audit quality for GAAP reporting are positively associated with the quality of voluntarily disclosed non-GAAP earnings measures.

text: Do high-quality auditors improve non-GAAP reporting? Prior research finds that clients of high-quality auditors report higher quality GAAP earnings. We extend this research to investigate whether auditor quality is associated with the quality of voluntarily disclosed non-GAAP earnings measures. Using a sample of Australian firms disclosing annual non-GAAP metrics, we find that clients of high-quality auditors are more likely to voluntarily disclose non-GAAP earnings numbers. However, clients of high-quality auditors make adjustments in calculating non-GAAP earnings (non-GAAP exclusions) that are less predictive of future earnings and less value relevant than those of other firms. These results indicate that their adjustments are of higher quality. We also find similar results for US firms using a sample of quarterly non-GAAP earnings disclosures. Overall, our evidence indicates that commonly used indicators of audit quality for GAAP reporting are positively associated with the quality of voluntarily disclosed non-GAAP earnings measures.

year: 2023-01-01

title: “On and On It Goes”: Representations of the New Zealand Wars in novels, film, and theatre

authors: Sheridan, Brendan Daniel

subjects: History

abstract: This thesis considers fictional representations of the New Zealand Wars. Through the media of novels, feature films, and drama with links to Shakespeare, it explores common features between representations. It examines how these representations change in tone or style over time and how different representations negotiate the complex issues of race, gender, and colonialism.
	I examine key representations ranging from 1861 to 2017 in terms of genre. I begin with the nineteenth-century novel as many of the key tropes used in representations of the New Zealand Wars emerge in this period. I then look at the twentieth-century novel, before concentrating specifically on Maurice Shadbolt and Witi Ihimaera. My discussion then turns to the genres of film and theatre. In all of these diverse representations there are recurring tropes and motifs. Many of the fictions feature stock characters such as the European traveller, the imperial official, and the Māori maiden and bear the imprint of historical romance conventions, popularised by Sir Walter Scott’s Waverly and James Fenimore Cooper’s The Last of the Mohicans. The vast majority of stories take place in the North Island between 1860 and 1870. Variations in the depiction of historical events are shaped by the historical scholarship and dominant ideologies of the time, such as the post-colonial tonal shift that emerges following the publication of work by James Belich and Ranginui Walker. I contextualise representations with their point in history, and how they treat the New Zealand Wars in terms of events, characters, and historical figures. 
	Through this approach, my thesis argues that representations of the New Zealand Wars do not form themselves in isolation and do not occur in isolated clusters. This thesis seeks to demonstrate that representations of the New Zealand Wars occur on a steady continuum. Representations of the conflict exist in parallel to one another (intentional or not) and are affected by the social climate, dominant ideologies, and published histories available to the author at the time of writing. The variety of representations—novel, feature film, stage play—share many core tropes. Even so, chronologically this continuum also features shifts in tone, ideologies, and sympathies. A novel of the 1980s has a very different perspective regarding settlers compared to a novel from the 1860s. In the same manner, a play staged in the 2000s shows a different attitude towards the conflict compared to a film from the 1940s. This thesis demonstrates that while representations of the New Zealand Wars share a common subject, how they approach the material is constantly evolving.

text: “On and On It Goes”: Representations of the New Zealand Wars in novels, film, and theatre This thesis considers fictional representations of the New Zealand Wars. Through the media of novels, feature films, and drama with links to Shakespeare, it explores common features between representations. It examines how these representations change in tone or style over time and how different representations negotiate the complex issues of race, gender, and colonialism.
	I examine key representations ranging from 1861 to 2017 in terms of genre. I begin with the nineteenth-century novel as many of the key tropes used in representations of the New Zealand Wars emerge in this period. I then look at the twentieth-century novel, before concentrating specifically on Maurice Shadbolt and Witi Ihimaera. My discussion then turns to the genres of film and theatre. In all of these diverse representations there are recurring tropes and motifs. Many of the fictions feature stock characters such as the European traveller, the imperial official, and the Māori maiden and bear the imprint of historical romance conventions, popularised by Sir Walter Scott’s Waverly and James Fenimore Cooper’s The Last of the Mohicans. The vast majority of stories take place in the North Island between 1860 and 1870. Variations in the depiction of historical events are shaped by the historical scholarship and dominant ideologies of the time, such as the post-colonial tonal shift that emerges following the publication of work by James Belich and Ranginui Walker. I contextualise representations with their point in history, and how they treat the New Zealand Wars in terms of events, characters, and historical figures. 
	Through this approach, my thesis argues that representations of the New Zealand Wars do not form themselves in isolation and do not occur in isolated clusters. This thesis seeks to demonstrate that representations of the New Zealand Wars occur on a steady continuum. Representations of the conflict exist in parallel to one another (intentional or not) and are affected by the social climate, dominant ideologies, and published histories available to the author at the time of writing. The variety of representations—novel, feature film, stage play—share many core tropes. Even so, chronologically this continuum also features shifts in tone, ideologies, and sympathies. A novel of the 1980s has a very different perspective regarding settlers compared to a novel from the 1860s. In the same manner, a play staged in the 2000s shows a different attitude towards the conflict compared to a film from the 1940s. This thesis demonstrates that while representations of the New Zealand Wars share a common subject, how they approach the material is constantly evolving.

year: 2019