Adapting neural network models to predict 10-year CVD development based on regional data calibration

Background

The used tools for prediction the individual risk of developing cardiovascular diseases and their complications using machine learning methods have proven better prognostic value in comparison with commonly used scales (e.g., Framingham, SCORE). To create such methods, the long-term accumulation of large amount of qualitative data are required. Moreover, to improve the accuracy of models, it is necessary to take into account regional characteristics that affect health: ethnic, nutritional characteristics, climatic conditions, living standards and medical care. These regional characteristics could significantly affect the development and outcomes of CVDs. However, the amount of regional data is not enough to build a qualitative model. Therefore, it is proposed to create models based on publicly available data and validate them on regional medical data sufficient for validation and calibration.

Methods

Two models were trained using data from the Framingham study. Model 1 was trained on 2 588 patient data and predicts a 10-year CVD probability according to the following risk factors: age, gender, cholesterol, HDL, smoking, SBP, and BP medications. Model 2 was trained on 4,363 patient data and predicts a 10-year death probability from CVD according to the following criteria: age, gender, cholesterol, smoking, SBP, BMI, heart rate. To retrain the obtained models, we used dataset created from data from patients in the northwestern part of Russia. The dataset consists of 438 patients, including the signs used in the trained models. This dataset includes CVD and death from it during a 10-year follow-up

Evaluation

We used randomized data splitting: divided the dataset into a training and a test set with an 80/20 proportion. The models was implement with keras convolution neural network (CNN) using 3 hidden layers. For data validation was used a 10 K-fold method.

Results

We compared the initial model metrics and those obtained after local data retraining. The accuracy of model 1 before retraining is 78%, after – 81.3%, the area under the ROC curve (AUC) before retraining: 0.77 (at 95% CI: 0.72–0.82C), after – 0.803. The accuracy of model 2 before retraining is 79%, after – 85.6%, the area under the ROC-curve (AUC) before retraining: 0.78 (at 95% CI: 0.72–0.82), after – 0.828.

Conclusion

Using this method of retraining predictive models, we can take into account local characteristics of the population and significantly increase the accuracy of predicting events. Expand the population to use the model according to local characteristics.

Funding Acknowledgement

Type of funding source: Private company. Main funding source(s): OOO K-SkAI

Gene expression of catecholamine biosynthetic enzymes following exercise: modulation by age

Both age and exercise training are associated with tissue specific alterations in the catecholaminergic system. We examined the effect of short-term exercise training on tyrosine hydroxylase and dopamine beta-hydroxylase gene expression in adrenals and specific brain regions with aging. In addition, we examined activator protein-1 and cyclic AMP response element transcription factor binding activity in the adrenal medulla. Male, six- and 24-month-old F-344 rats were exercised by treadmill running for five consecutive days. One group was killed immediately and a second group was killed 2h after the last training session. Exercise significantly elevated tyrosine hydroxylase messenger RNA equally in adrenals of both young and old rats. Training had no effect on dopamine beta-hydroxylase messenger RNA in adrenals of young, but levels were elevated in old rats. Binding activities of both activator protein-1 and cyclic AMP response element binding protein were diminished with age in the adrenal medulla. Exercise training had no significant effect on the binding activity of cyclic AMP response element binding protein in either young or old animals, whereas activator protein-1 binding activity increased equally in young and old animals. Exercise training revealed divergent changes in tyrosine hydroxylase messenger RNA in brain catecholaminergic neurons. In the locus coeruleus and the ventral tegmental areas, training elevated tyrosine hydroxylase messenger RNA levels only in young rats. In the substantia nigra, there was no change in young, but a 45% increase in tyrosine hydroxylase messenger RNA in old rats. In the ventral tegmental area, training increased tyrosine hydroxylase gene expression 80% in young but not in old rats. These results indicate that short-term exercise training increases tyrosine hydroxylase messenger RNA levels in young animals in the adrenals, the locus coeruleus and the ventral tegmental area. The responses for exercise training of aged animals differed from the young in brain noradrenergic and dopaminergic nuclei, especially in the substantia nigra, and to some extent in the locus coeruleus and the ventral tegmental area.

Nicotine infusion modulates immobilization stress-triggered induction of gene expression of rat catecholamine biosynthetic enzymes

The relationship between nicotine and stress is complex and paradoxical. Although people claim they smoke because it relaxes them, nicotine can trigger some of the effects observed with stress, including the release and synthesis of the catecholamines and their biosynthetic enzymes. This study examined one aspect of this confusing relationship between nicotine and stress. Multiple injections of nicotine bitartrate (5 mg/kg) elevated mRNA levels for the catecholamine biosynthetic enzymes, tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), and phenylethanolamine N-methyltransferase, and of preproneuropeptide Y in rat adrenal medulla more than did 1 mg/kg of nicotine bitartrate. In the locus ceruleus, substantia nigra, and ventral tegmental area both doses equally induced TH mRNA levels. Nicotine infusion (15 mg/kg/day) did not affect adrenal mRNA levels for any of the genes of interest and did not increase plasma corticosterone levels. However, in rats pre-exposed to nicotinic infusions, the response to a single immobilization (IMO) stress was markedly attenuated with respect to changes in adrenomedullary TH, DBH, and phenylethanolamine N-methyltransferase mRNA levels and in c-Fos protein levels. In the central nervous system, the chronic infusion of nicotine prevented the induction of TH mRNA by repeated IMO stress in the ventral tegmental area (but not in substantia nigra) and of DBH mRNA by single IMO in the locus ceruleus. These findings may explain some of the complex interactions between stress and exposure to nicotine.

Tryptophan hydroxylase mRNA levels are elevated by repeated immobilization stress in rat raphe nuclei but not in pineal gland

Repeated stress triggers a wide range of adaptive changes in the central nervous system including the elevation of serotonin (5-HT) metabolism and an increased susceptibility to affective disorders. To begin to examine whether these changes are mediated by alterations in gene expression for tryptophan hydroxylase (TPH), the rate-limiting enzyme in 5-HT biosynthesis, we quantitated its mRNA levels by competitive reverse transcription-polymerase chain reaction (RT-PCR). Repeated immobilization stress (2 h, 7 days) elicited a six- or ten-fold rise in TPH mRNA in median raphe nucleus (MRN) and dorsal raphe nucleus (DRN), respectively, without significantly altering TPH mRNA levels in the pineal gland. In contrast, there was little change in mRNA levels for GTP cyclohydrolase I (GTPCH), the rate limiting enzyme in synthesis of the tetrahydrobiopterin (BH4), the obligate cofactor for TPH. This is the first study to reveal stress-elicited activation of TPH gene expression.

Altered gene expression for catecholamine biosynthetic enzymes and stress response in rat genetic model of depression

Although stress is a major contributory factor in the development of depression, the relationship between stress and depression is still unclear. In this study, we evaluated basal mRNA levels of several genes involved in neurotransmitter biosynthesis and the effect of stress in Flinder's Sensitive Line (FSL), a genetic rat model of depression. In adrenals, basal levels of tyrosine hydroxylase (TH), dopamine beta-hydroxylase (DBH), phenylethanolamine N-methyltransferase (PNMT) and GTP cyclohydrolase I (GTPCH) mRNAs were markedly elevated in FSL rats compared to the control strain. As opposed to control strain, immobilization stress (IMO) to FSL rats, did not further raise DBH, PNMT or GTPCH mRNAs and had relatively mild effect on TH. In contrast to enzymes involved in catecholamine biosynthesis, basal NPY and its response to IMO were unchanged in FSL rats. In the brain, the two major dopaminergic nuclei displayed differences. In substantia nigra, TH mRNA levels were similar in both strains, and elevated by IMO only in FSL rats. In ventral tegmental area in FSL rats, TH mRNA was 2-fold higher than in the control strain and not further elevated by IMO. These high basal mRNA levels and abnormal response to stress in several catecholaminergic cell types in FSL rats may be related to the manifestations of depression.

Glucocorticoids elevate GTP cyclohydrolase I mRNA levels in vivo and in PC12 cells

GTP cyclohydrolase I (GTPCH) is the rate-limiting enzyme in the formation of tetrahydrobiopterin, the cofactor for catecholamine, indolamine and nitric oxide biosynthesis. The effect of glucocorticoids on GTPCH gene expression was examined by direct infusion of cortisol to rats and by incubation of PC12 cells with glucocorticoids. Northern blot analysis revealed that infusion of cortisol for 1 or 7 days elevated levels of the 3.6 kb GTPCH mRNA species in rat adrenal medulla, while the 1.2 kb mRNA species were only increased by 1 day cortisol. Cortisol administration to hypophysectomized animals elicited a 4-5-fold elevation in both forms of GTPCH mRNA. These results indicate that glucocorticoids may be directly involved in the regulation of adrenomedullary GTPCH mRNA levels by physiological stress. Incubation of PC12 cells with plasma from immobilized, but not control, animals increased the level of the 3.6 kb mRNA. Treatment of PC12 cells with dexamethasone for 12-48 h elicited a 4-6-fold elevation in both GTPCH mRNAs. Using the nuclear run-on assay, increased transcription of the GTPCH gene was observed in the rat adrenal medulla with immobilization stress, or in PC12 cells treated with dexamethasone. This is the first report that glucocorticoids can alter GTPCH expression.

Effects of space flight on endocrine system function in experimental animals

The effects exposing rats to space flights of various lengths in a series of COSMOS satellites are reported based on an evaluation of plasma hormone levels and several enzyme activities in the tissues. The results after space flights are compared with those obtained from rats exposed to acute or repeated stress. Space flight induced selective morphological responses in the corticotrophs and gonadotrophs of the pituitary. Plasma levels of ACTH did not change, but plasma growth hormone and TSH levels decreased after longer space flights (>14 days), while prolactin in the plasma increased after short flights (5-7 days). Plasma corticosterone was higher after all flights. Catecholamine levels in plasma increased only after long space flights. These changes in plasma hormone levels affected the activities of enzymes involved in the amino acid metabolism of the liver and lipolysis in the adipose tissues. Norepinephrine level and catecholamine synthesizing enzyme activity in the hypothalamus did not change in flight rats. The norepinephrine content, however, decreased in several nuclei selected from the hypothalamus of flight rats. Increases in plasma insulin and glucose were noted in rats after space flight. Glucagone values in plasma remained unchanged. Comparing these results from flight rats against rats exposed to acute or repeated stress indicate that long stays in microgravity do not represent intensive stressogenic stimulus of the adrenocortical and sympathetic adrenomedullar systems, and hormone alterations observed after space flight may be due primarily to acute stressor activity resulting from a return to Earth's gravity (gravitational stress).

Effects of space flight on Xenopus laevis larval development

Fifty-three fertilized Xenopus laevis embryos at early tail bud stage were launched into orbit aboard a Biocosmos satellite and remained in microgravity for 11.5 days. During this period, the embryos hatched and continued to develop as free-living larvae. Forty-eight individuals survived the mission. Upon recovery these tadpoles had smaller heads/bodies and proportionately longer tails than ground controls. Almost all the flight animals had caudal lordosis and consequently swam in backward somersaults. Compared to ground-based controls, their notochords were significantly larger in cross-sectional area and were deformed. Caudal muscle fibers were less dense and involuted in a fashion indicative of degeneration. In contrast, cranial muscles associated with buccal pumping did not differ between the flight and control animals. Upon landing, the flight larvae were found to be negatively buoyant and lay on the bottom when they were not swimming. They had significantly smaller lungs than controls, suggesting that they had failed to inflate their lungs in microgravity. Additionally, the branchial baskets, gill filters and thymuses all showed signs of retarded development or degeneration. The caudal deformity that we observed in the flight X. laevis has been independently observed in three other space flight experiments where embryos were launched then hatched in space. In contrast, Xenopus larvae from another orbital experiment that were raised from fertilization through hatching in space did not exhibit any caudal abnormalities. These divergent results suggest that either features of the launch itself (i.e., high acceleration and vibration) or an abrupt decrease in gravity during the tail bud stage detrimentally affects musculoskeletal development in anurans.

Changes of insulin in plasma and receptor for insulin in various tissues after the exposure of rats to space flights and hypokinesia

The explanation of the mechanism of the response to gravity changes is of great importance for the determination of the capacity of human subjects to adapt to the load of gravitational stress. Therefore several studies were performed to investigate the activity of endocrine system, since the hormones are involved in the regulation of physiological functions and metabolic processes. However the studies of endocrine system activity during altered gravity conditions, especially during the weightlessness are influenced by the several interventions in biomedical observations due to operational program of astronauts, wide variability in individual response and tolerance, use of extensive countermeasures, differences in the type of space missions and in the studies after landing also a hypergravity effect at landing and variability in postflight readaptation process. The significant changes of plasma insulin and glucose levels were observed in astronauts during space flights and in the first days of recovery period. In the first inflight period plasma insulin levels were increased, unchanged or decreased however after 4-5 weeks of exposure to weightlessness a decrease of insulin plasma levels were noted. After space flights an increase of plasma insulin levels were demonstrated in experimental animals and in human subjects. Since plasma insulin level is considered as most important factor involved in the regulation for insulin receptors in target tissues, an investigation of insulin receptors in various tissues was performed in rats exposed to space flight or to hypokinesia (model used for simulation of some effects of microgravity).

Comparative study of spermatogonial survival after x-ray exposure, high LET (HZE) irradiation or spaceflight

Spermatogonial cell loss has been observed in rats flown on Space Lab 3, Cosmos 1887, Cosmos 2044 and in mice following irradiation with X-ray or with high energy (HZE) particle beams. Spermatogonial loss is determined by cell counting in maturation stage 6 seminiferous [correction of seminferous] tubules. With the exception of Iron, laboratory irradiation experiments (with mice) revealed a similar pattern of spermatogonial loss proportional to the radiation dose at levels less than 0.1 Gy. Helium and Argon irradiation resulted in a 5% loss of spermatogonia after only 0.01 Gy exposure. However, significant spermatogonial loss (45%) occured at this radiation level with Iron particle beams. The loss of spermatogonia during each space flight was less than 10% when compared to control (non-flight) animals. This loss, although small, was significant. Although radiation may be a contributing factor in the loss of spermatogonia during space flight, exposure levels, as determined by dosimetry, were not significant to account for the total cell loss observed.

The effect of space flight on the board of the satellite Cosmos 2044 on plasma hormone levels and liver enzyme activities of rats

The aim of present experiment was to study the changes of corticosterone, insulin and glucose levels in plasma, of the activity of enzymes involved in aminoacid metabolism in liver and the binding of insulin to specific receptors of cell membrane from liver and also of adipose tissue of rats exposed to space flight for 14 days on biosatellite Cosmos 2044. Adult male Wistar rats (body mass 300-370 g) were divided into five groups: intact control rats (AC), rats exposed to space flight (F), animals in synchronous model experiment (S), rats in antiorthostatic hypokinesia (A) and so called operated control group (C). Half of all groups (5 animals) except the intact control were operated 3 days before the experiment (fibulas on both hind legs were broken). The flight animals were sacrificed 5-6 hours after landing. It was observed that plasma insulin levels are increased in rat exposed to 14-day space flight and in synchron experiments. A significant increase of plasma glucose levels was found in flight rats in spite of high insulin concentrations suggesting that in rats exposed to 14-day space a deterioration of tissue sensitivity to insulin could by present. No significant differences of specific insulin binding to liver plasma membrane fraction in flight and intact control animals were observed. A decrease of insulin binding capacity in liver was found in rats in antiorthostatic hypokinesia (A). However in the membrane of adipocytes an important increase of insulin receptors was noted in rats subjected to space flight. These results suggest, that the liver and adipocyte insulin receptors of flight rats did not respond to the increased plasma insulin levels by "down regulation". The determination of plasma corticosterone levels showed that in flight rats and animals exposed to antiorthostatic hypokinesia the plasma hormone levels are significantly elevated. A significant increase of tyrosine aminotransferase and tryptophan pyrrolase activities in liver of flight rats and those exposed to hypokinesia was observed. Also the elevation of alanine amino-transferase in liver was observed in flight rats, while, the activity of aspartate aminotransferase in liver was similar in control and flight animals. These results showed that the changes in liver enzyme activities in rats after 14-day space flight are in agreement with the results observed in previous experiments after a shorter space flight (7 days).

Effect of space flights on plasma hormone levels in man and in experimental animal

An important increase of plasma hormone levels like insulin, TSH and aldosterone was observed in human subjects after space flights, however in the changes of plasma content of ACTH, cortisol, adrenaline and noradrenaline the individual variations were observed in relation to number and duration of space flight. For evaluation of the effects of these changes in plasma hormone levels on metabolic processes also the experiments with small animals subjected to space flights on a board of biosatellite of Cosmos series were running. An elevation of plasma levels of corticosterone, adrenaline, noradrenaline and insulin was found in rats after the space flights of duration from 7 to 20 days. It was demonstrated, that the increase of corticosterone in plasma is followed by the activation of enzymes involved in the amino acid metabolism in rat liver (tyrosine aminotransferase, tryptophanpyrolase, alanine aminotransferase and aspartate aminotransferase). After a short recovery period (2 to 6 days) the plasma corticosterone concentration and also the activity of liver enzymes returned to control levels. The exposition of animals to stress stimuli during this revcovery period showed higher response of corticosterone levels in flight rats as compared to intact controls. The increase of plasma catecholamine levels was not followed by elevation of lipolysis in adipose tissue. This is due to lower response of adipose tissue to catecholamine because a decrease of the stimulation of lipolysis by noradrenaline was observed in animals after space flight. The increase of insulin was not followed by adequate decrease of glucose concentration suggesting a disturbances in glucose utilization similarly as in cosmonauts after a long-term space flight. These results showed that changes in plasma hormone levels, observed after space flight, affected the regulation of metabolic processes in tissues.

Metabolic changes in the animals subjected to space flight

The activity of the enzymes involved in aminoacid metabolism (tyrosine aminotransferase, TAT, tryptophan pyrrolase TP, serine dehydratase, SD) with rapid response to glucocorticoids and enzymes requiring for activity increase repeated administration of corticosterone (alanine aminotransferase, ALT, aspartate aminotransferase, AST) in liver, the changes of lipolysis in adipose tissue and the plasma corticosterone levels were studied in rats subjected to space flight (F), in animals from synchron model experiments (SM, simulated conditions of space flight in laboratory) and in intact controls (C). The increase of plasma corticosterone concentration and of the activity of rapidly (TAT, TP, SD) and slowly activating enzymes (ALT, AST) was found in F group 6-10 hr after space flight (18.5 days on biosatellite COSMOS 1129). This suggested the presence of acute-stress (associated primarily with the landing) and chronic stress induced hypercorticosteronemia during the flight. After the short 6-day period of recovery the plasma corticosterone concentrations and the activities of liver enzymes returned to control levels. The exposition of animals to repeated immobilization stress showed higher response of corticosterone levels in flight rats as compared to intact controls. No changes in basal lipolysis were observed in flight rats in comparison to intact controls, however the stimulation of lipolysis by norepinephrine was lower in animals from F and SM groups. This lower response of lipolytic processes to norepinephrine was found in flight animals also after six days period of recovery. These results showed that there are important changes in the regulation of lipolytic processes in adipose tissue of rats after space flight and in the conditions of model experiments.

Effect of weightlessness on sympathetic-adrenomedullary activity of rats

Three cosmic experiments were performed in which rats spent 18-20 days in space on board the biosatellites "COSMOS 782", "COSMOS 936" and "COSMOS 1129". The following indicators of the sympathetic-adrenomedullary system (SAS) activity were measured: tissue and plasma catecholamines (CA), CA-synthesizing enzymes--tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), phenylethanolamine-N-methyltransferase (PNMT)--as well as CA-degrading enzymes-monoamine oxidase (MAO) and catechol-O-methyltransferase (COMT). Adrenal epinephrine (EPI) and norepinephrine (NE) as well as CA-synthesizing and degrading enzymes were not significantly changed in the animals after flight on COSMOS 782. On the other hand, a significant increase was found in heart CA, the indicator which is usually decreased after stress. 26 days after landing all values were at control levels. The results obtained, compared to our previous stress experiments on Earth, suggest that prolonged weightlessness does not appear to be a pronounced stressful stimulus for the SAS. Heart and plasma CA, mainly NE, were increased both in the group living in the state of weightlessness and the group living in a centrifuge and exposed to artificial gravitation 1 g (COSMOS 936), suggesting again that prolonged weightlessness is not an intensive stressful stimulus for the SAS. The animals exposed after space flight on COSMOS 1129 to repeated immobilization stress on Earth showed a significant decrease of adrenal EPI and an expressive increase of adrenal TH activity compared to stressed animals which were not in space. Thus, the results corroborate that prolonged state of weightlessness during space flight though not representing by itself an intensive stressful stimulus for the sympathetic-adrenomedullary system, was found to potentiate the response of "cosmic rats" to stress exposure after return to Earth.