Epigenetic scores of blood-based proteins as biomarkers of general cognitive function and brain health

BACKGROUND

Epigenetic Scores (EpiScores) for blood protein levels have been associated with disease outcomes and measures of brain health, highlighting their potential usefulness as clinical biomarkers. They are typically derived via penalised regression, whereby a linear weighted sum of DNA methylation (DNAm) levels at CpG sites are predictive of protein levels. Here, we examine 84 previously published protein EpiScores as possible biomarkers of cross-sectional and longitudinal measures of general cognitive function and brain health, and incident dementia across three independent cohorts.

RESULTS

Using 84 protein EpiScores as candidate biomarkers, associations with general cognitive function (both cross-sectionally and longitudinally) were tested in three independent cohorts: Generation Scotland (GS), and the Lothian Birth Cohorts of 1921 and 1936 (LBC1921 and LBC1936, respectively). A meta-analysis of general cognitive functioning results in all three cohorts identified 18 EpiScore associations (absolute meta-analytic standardised estimates ranged from 0.03 to 0.14, median of 0.04, PFDR < 0.05). Several associations were also observed between EpiScores and global brain volumetric measures in the LBC1936. An EpiScore for the S100A9 protein (a known Alzheimer disease biomarker) was associated with general cognitive functioning (meta-analytic standardised beta: - 0.06, P = 1.3 × 10-9), and with time-to-dementia in GS (Hazard ratio 1.24, 95% confidence interval 1.08-1.44, P = 0.003), but not in LBC1936 (Hazard ratio 1.11, P = 0.32).

CONCLUSIONS

EpiScores might make a contribution to the risk profile of poor general cognitive function and global brain health, and risk of dementia, however these scores require replication in further studies.

General and specific patterns of cortical gene expression as spatial correlates of complex cognitive functioning

Gene expression varies across the brain. This spatial patterning denotes specialised support for particular brain functions. However, the way that a given gene's expression fluctuates across the brain may be governed by general rules. Quantifying patterns of spatial covariation across genes would offer insights into the molecular characteristics of brain areas supporting, for example, complex cognitive functions. Here, we use principal component analysis to separate general and unique gene regulatory associations with cortical substrates of cognition. We find that the region-to-region variation in cortical expression profiles of 8235 genes covaries across two major principal components: gene ontology analysis suggests these dimensions are characterised by downregulation and upregulation of cell-signalling/modification and transcription factors. We validate these patterns out-of-sample and across different data processing choices. Brain regions more strongly implicated in general cognitive functioning (g; 3 cohorts, total meta-analytic N = 39,519) tend to be more balanced between downregulation and upregulation of both major components (indicated by regional component scores). We then identify a further 29 genes as candidate cortical spatial correlates of g, beyond the patterning of the two major components (|β| range = 0.18 to 0.53). Many of these genes have been previously associated with clinical neurodegenerative and psychiatric disorders, or with other health-related phenotypes. The results provide insights into the cortical organisation of gene expression and its association with individual differences in cognitive functioning.

General and specific patterns of cortical gene expression as spatial correlates of complex cognitive functioning

Gene expression varies across the brain. This spatial patterning denotes specialised support for particular brain functions. However, the way that a given gene's expression fluctuates across the brain may be governed by general rules. Quantifying patterns of spatial covariation across genes would offer insights into the molecular characteristics of brain areas supporting, for example, complex cognitive functions. Here, we use principal component analysis to separate general and unique gene regulatory associations with cortical substrates of cognition. We find that the region-to-region variation in cortical expression profiles of 8235 genes covaries across two major principal components : gene ontology analysis suggests these dimensions are characterised by downregulation and upregulation of cell-signalling/modification and transcription factors. We validate these patterns out-of-sample and across different data processing choices. Brain regions more strongly implicated in general cognitive functioning (g; 3 cohorts, total meta-analytic N = 39,519) tend to be more balanced between downregulation and upregulation of both major components (indicated by regional component scores). We then identify a further 41 genes as candidate cortical spatial correlates of g, beyond the patterning of the two major components (|β| range = 0.15 to 0.53). Many of these genes have been previously associated with clinical neurodegenerative and psychiatric disorders, or with other health-related phenotypes. The results provide insights into the cortical organisation of gene expression and its association with individual differences in cognitive functioning.

Fluctuating asymmetry in brain structure and general intelligence in 73-year-olds

Fluctuating body asymmetry is theorized to indicate developmental instability, and to have small positive associations with low socioeconomic status (SES). Previous studies have reported small negative associations between fluctuating body asymmetry and cognitive functioning, but relationships between fluctuating brain asymmetry and cognitive functioning remain unclear. The present study investigated the association between general intelligence (a latent factor derived from a factor analysis on 13 cognitive tests) and the fluctuating asymmetry of four structural measures of brain hemispheric asymmetry: cortical surface area, cortical volume, cortical thickness, and white matter fractional anisotropy. The sample comprised members of the Lothian Birth Cohort 1936 (LBC1936, N = 636, mean age = 72.9 years). Two methods were used to calculate structural hemispheric asymmetry: in the first method, regions contributed equally to the overall asymmetry score; in the second method, regions contributed proportionally to their size. When regions contributed equally, cortical thickness asymmetry was negatively associated with general intelligence (β = −0.18,p < .001). There was no association between cortical thickness asymmetry and childhood SES, suggesting that other mechanisms are involved in the thickness asymmetry-intelligence association. Across all cortical metrics, asymmetry of regions identified by the parieto-frontal integration theory (P-FIT) was not more strongly associated with general intelligence than non-P-FIT asymmetry. When regions contributed proportionally, there were no associations between general intelligence and any of the asymmetry measures. The implications of these findings, and of different methods of calculating structural hemispheric asymmetry, are discussed.

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Previous work has shown links between cortical asymmetry and intelligence.

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In the current study, two methods of calculating global cortical hemispheric asymmetry were compared.

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Equal region contribution: the association between cortical thickness asymmetry and general intelligence was β = −0.18.

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Proportional region contribution: no associations between three measures of cortical asymmetry and general intelligence.

Evaluation of intravenous ketorolac administered by bolus or infusion for treatment of postoperative pain. A double-blind, placebo-controlled, multicenter study

BACKGROUND

Ketorolac is a nonsteroidal analgesic that may provide postoperative analgesia without opioid-related side effects. This double-blind, randomized, multicenter study evaluated the analgesic efficacy and safety of intravenous ketorolac in 207 patients during the first 24 h after major surgery.

METHODS

Subjects were assigned to receive one of three analgesic regimens: a ketorolac infusion, ketorolac boluses, or placebo. All subjects had access to intravenous morphine via patient-controlled analgesia (PCA). Evaluations included PCA morphine used, pain assessment (categorical pain intensity scores and visual analogue pain scores), pain relief (categorical pain relief scores), sedation, presence of adverse events, and overall rating of regimens by study observers and patients.

RESULTS

Patients in the ketorolac infusion group (but not the ketorolac bolus group) used less morphine (average 33 mg) than did the placebo group (44 mg) (P = 0.009). Significant differences favoring both ketorolac groups were seen in the pain intensity and the categorical pain relief scores at various time points during the study. At the termination of the study, compared with the placebo group, categorical pain intensity scores were lower in the ketorolac bolus group; visual analogue pain scores were lower in both ketorolac groups; and pain relief scores were higher in the ketorolac bolus group. The incidence of vomiting was significantly greater in the placebo group (27%) than in the ketorolac infusion group (12%) or bolus group (9%) (P = 0.032 and P = 0.005, respectively). The incidence of postoperative fever was 10% in the ketorolac bolus group and 25% in the placebo group (P = 0.013). Study observers noted less nursing difficulty while caring for patients in the ketorolac infusion group (P = 0.015). Study observers and patients in both ketorolac groups reported statistically significant overall drug superiority compared with placebo.

CONCLUSIONS

It is concluded that intravenous boluses or infusions of ketorolac in conjunction with PCA morphine provide effective, safe analgesia after major surgery and improve on the response to PCA morphine alone.

Ergometrine, oxytocin and extradural analgesia

Blood loss and the incidence of emetic sequelae were assessed in 148 patients undergoing midcavity forceps delivery under continuous lumbar extradural analgesia. Five units of oxytocin i.v. was found to be as effective as ergometrine 0.5 mg i.v. in reducing blood loss at delivery. Nausea, retching or vomiting occurred in 35 (46%) of the mothers who received ergometrine and in none of those who received i.v. oxytocin. The cardiovascular side-effects of ergometrine and oxytocin are reviewed and compared with special reference to patients with hypertension and heart disease. It is suggested that 5 units of oxytocin i.v. should be preferred in these high-risk patients. Because of the absence of an emetic action, i.v. oxytocin is preferable to i.v. ergometrine for patients receiving extradural analgesia.