Data-driven categorization of postoperative delirium symptoms using unsupervised machine learning.

Background: Phenotyping analysis that includes time course is useful for understanding the mechanisms and clinical management of postoperative delirium. However, postoperative delirium has not been fully phenotyped. Hypothesis-free categorization of heterogeneous symptoms may be useful for understanding the mechanisms underlying delirium, although evidence is currently lacking. Therefore, we aimed to explore the phenotypes of postoperative delirium following invasive cancer surgery using a data-driven approach with minimal prior knowledge. Methods: We recruited patients who underwent elective invasive cancer resection. After surgery, participants completed 5 consecutive days of delirium assessments using the Delirium Rating Scale-Revised-98 (DRS-R-98) severity scale. We categorized 65 (13 questionnaire items/day × 5 days) dimensional DRS-R-98 scores using unsupervised machine learning (K-means clustering) to derive a small set of grouped features representing distinct symptoms across all participants. We then reapplied K-means clustering to this set of grouped features to delineate multiple clusters of delirium symptoms. Results: Participants were 286 patients, of whom 91 developed delirium defined according to Diagnostic and Statistical Manual of Mental Disorders, Fifth Edition, criteria. Following the first K-means clustering, we derived four grouped symptom features: (1) mixed motor, (2) cognitive and higher-order thinking domain with perceptual disturbance and thought content abnormalities, (3) acute and temporal response, and (4) sleep-wake cycle disturbance. Subsequent K-means clustering permitted classification of participants into seven subgroups: (i) cognitive and higher-order thinking domain dominant delirium, (ii) prolonged delirium, (iii) acute and brief delirium, (iv) subsyndromal delirium-enriched, (v) subsyndromal delirium-enriched with insomnia, (vi) insomnia, and (vii) fit. Conclusion: We found that patients who have undergone invasive cancer resection can be delineated using unsupervised machine learning into three delirium clusters, two subsyndromal delirium clusters, and an insomnia cluster. Validation of clusters and research into the pathophysiology underlying each cluster will help to elucidate the mechanisms of postoperative delirium after invasive cancer surgery.

Species-Dependent Enhancement of Ovarian Cancer G Protein-Coupled Receptor 1 Activation by Ogerin.

Ogerin is a positive allosteric modulator of human and mouse ovarian cancer G protein-coupled receptors (OGR1s). In the present study, we found that ogerin differentially enhances the activation of OGR1 in various animal species. Amino acid residues of OGR1 that are associated with ogerin are conserved among the species. This suggests that other amino acid residues may be involved in the action of ogerin. Chimeric receptors between human and zebrafish OGR1s showed that the amino acid residues that determine the species specificity of ogerin-induced enhancement reside in the transmembrane and/or intracellular regions of OGR1. This result highlights the importance of first verifying the effectiveness of ogerin to the OGR1 of the species of interest at the cellular level prior to analyzing the physiological and pathophysiological roles of OGR1 in the species.

Involvement of GPR4 in increased growth hormone and prolactin expressions by extracellular acidification in MtT/S cells.

Hormone-secreting pituitary adenomas show unregulated hormonal hypersecretion and cause hyperpituitarism. However, the mechanism of the unregulated hormone production and secretion has not yet been fully elucidated. Solid tumors show reduced extracellular pH, partly due to lactate secretion from anaerobic glycolysis. It is known that extracellular acidification affects hormone secretion. However, whether and how the extracellular acidification influences the unregulated hormone production and secretion remain unknown. In the present study, we found that GPR4, a proton-sensing G protein-coupled receptor, was highly expressed in MtT/S cells, a growth hormone-producing and prolactin-producing pituitary tumor cell line. When we reduced the extracellular pH, growth hormone and prolactin mRNA expressions increased in the cells. Both increased expressions were partially suppressed by a GPR4 antagonist. We also found that extracellular acidification enhanced growth hormone-releasing factor-induced growth hormone secretion from MtT/S cells. These results suggest that GPR4 may play a role in hypersecretion of the hormone from hormone-producing pituitary tumors. A GPR4 antagonist will be a useful tool for preventing the hypersecretion.

Characterization of molecular mechanisms of extracellular acidification-induced intracellular Ca2+ increase in LßT2 cells.

Extracellular acidification regulates endocrine cell functions. Ovarian cancer G protein-coupled receptor 1 (OGR1), also known as GPR68, is a proton-sensing G protein-coupled receptor and is activated by extracellular acidification, resulting in the activation of multiple intracellular signaling pathways. In the present study, we found that OGR1 was expressed in some gonadotropic cells in rat anterior pituitary and in LßΤ2 cells, which are used as a model of gonadotropic cells. When we reduced extracellular pH, a transient intracellular Ca2+ increase was detected in LßT2 cells. The Ca2+ increase was inhibited by a Gq/11 inhibitor and Cu2+, which is known as an OGR1 antagonist. We also found that extracellular acidification enhanced GnRH-induced Gaussia luciferase secretion from LßT2 cells. These results suggest that OGR1 may play a role in the regulation of gonadotropic cell function such as its hormone secretion.

Protons Differentially Activate TDAG8 Homologs from Various Species.

Mammalian T cell death-associated gene 8 (TDAG8)s are activated by extracellular protons. In the present study, we examined whether the TDAG8 homologs of other species are activated by protons as they are in mammals. We found that Xenopus TDAG8 also stimulated cAMP response element (CRE)-driven promoter activities reflecting the activation of Gs/cAMP signaling pathways when they are stimulated by protons. On the other hand, the activities of chicken and zebrafish TDAG8s are hardly affected by protons. Results using chimeric receptors of human and zebrafish TDAG8s indicate that the specificity of the proton-induced activation lies in the extracellular region. These results suggest that protons are not an evolutionarily conserved agonist of TDAG8.

Increased luminescence of the GloSensor cAMP assay in LßT2 cells does not correlate with cAMP accumulation under low pH conditions.

Cyclic adenosine monophosphate (cAMP) plays a pivotal role in gonadotrope responses in the pituitary. Gonadotropin-releasing hormone (GnRH) mediated synthesis and secretion of follicle-stimulating hormone (FSH) and luteinizing hormone (LH) are regulated by both the Gs/cAMP and Gq/Ca2+ signaling pathways. Pituitary adenylate cyclase-activating polypeptide (PACAP) also regulates GnRH responsiveness in gonadotropes through the PACAP receptor, which activates the Gs/cAMP signaling pathway. Therefore, measuring intracellular cAMP levels is important for elucidating the molecular mechanisms of FSH and LH synthesis and secretion in gonadotropes. The GloSensor cAMP assay is useful for detecting cAMP levels in intact, living cells. In this study, we found that increased GloSensor luminescence intensity did not correlate with cAMP accumulation in LßT2 cells under low pH conditions. This result indicates that cell type and condition must be considered when using GloSensor cAMP.

Metals Differentially Activate Ovarian Cancer G Protein-Coupled Receptor 1 in Various Species.

Human, mouse, and zebrafish ovarian cancer G protein-coupled receptors (OGR1s) are activated by both metals and extracellular protons. In the present study, we examined whether pig, rat, chicken, and Xenopus OGR1 homologs could sense and be activated by protons and metals. We found that all homologs stimulated serum response element (SRE)-driven promoter activities when they are stimulated by protons. On the other hand, metals differentially activated the homologs. The results using chimeric receptors of human and zebrafish OGR1s indicate that the specificity of the metal-induced activation lies in the extracellular region. These results suggest that protons are an evolutionally conserved agonist of OGR1. However, the types of metals that activated the receptor differed among the homologs.