POS0912 THE EFFECT OF A 24-WEEK TRAINING ON METABOLIC PARAMETERS OF SKELETAL MUSCLE CELLS DERIVED FROM PATIENTS WITH ESTABLISHED IDIOPATHIC INFLAMMATORY MYOPATHIES

Background

Persistent muscle weakness after reduction of inflammation and resistance to immunosuppressive therapy in some patients with idiopathic inflammatory myopathies (IIM) suggest that not only immune but also non-immune mechanisms, such as mitochondrial abnormalities and metabolic disturbance, contribute to the pathogenesis of myositis. Exercise improves muscle function in IIM patients.

Objectives

To evaluate the effect of activities-of-daily-living, resistance and stability training on metabolic parameters of primary tissue culture myotubes established from muscle biopsies obtained from patients with established IIM.

Methods

Seven patients with established IIM underwent a 24-week supervised training focused on activities of daily living, muscle-strengthening and stability. Muscle biopsy was performed before and after the 24-week program in patients, and in healthy controls (n=9). Isolated skeletal muscle cells were grown and differentiated into myotubes for 6 days. After differentiation, the myotubes were cultured for another 24 hours in fresh medium, and then the conditioned media were collected, and the cells were harvested in TRIzol. A relative number of mitochondria was quantified by the ratio between mitochondrial gene (NADH dehydrogenase subunit 1) and reference nuclear gene (lipoprotein lipase) and determined by qPCR. Glucose, pyruvate, lactate, citrate, and fumarate were assessed in a conditioned medium using the comprehensive two-dimensional gas chromatography coupled to time of flight mass spectrometer.

Results

Patients significantly improved their muscle strength and endurance during the 24-week training [1]. There was no difference in the relative number of mitochondria in muscle tissue and myotubes between IIM patients and controls. A significant increase in the number of muscle tissue mitochondria was found in IIM patients after 24 weeks of training (p = 0.004), on average twofold. A similar effect was observed in cultured myotubes, with at least 4 of 7 IIM patients showing a twofold increase in mitochondria number.

Compared with myotubes from HC, myotubes derived from IIM patients consumed non-significantly more glucose and pyruvate from the culture medium; however, their glucose and pyruvate utilization were significantly reduced as a result of the 24-week training (p = 0.016 and p = 0.030, respectively). Skeletal muscle cells from IIM patients before training intervention did not differ from HC cells in the amount of released lactate; however, the lactate concentration in the conditioned medium from myotubes obtained from patients after the 24-week training was significantly lower (p = 0.016). When measuring citrate cycle products released into the culture medium, no difference in citrate and fumarate secretion was observed between myotubes of myositis patients and myotubes of healthy controls. In contrast, their release was significantly (p < 0.05) lower in myotubes from IIM patients after 24 weeks of training compared to muscle cells isolated prior to intervention.

Conclusion

In conclusion, 24 weeks of rehabilitation training in patients with IIM significantly increases the number of mitochondria in muscle tissue. Lower release of lactate and citrate cycle intermediates (citrate and fumarate) by myotubes obtained from patients after training intervention indicates an increase in mitochondrial functional capacity and confirms a positive response to exercise in muscles previously affected by the inflammatory process in IIM.

References

[1]Špiritović M, et al. Arthritis Res Ther. 2021;23(1):173.

Acknowledgements

This work was supported by the Ministry of Health of the Czech Republic grants nr. NU21-05-00322.

Disclosure of Interests

None declared

POS0480 VITAMIN D AND ITS RECEPTOR (VDR) GENE EXPRESSION IN SKELETAL MUSCLE ASSOCIATE WITH DISEASE AND MUSCLE FUNCTION PARAMETERS IN IDIOPATHIC INFLAMMATORY MYOPATHIES

Background

Idiopathic inflammatory myopathies (IIM) are chronic inflammatory disorders characterised, apart from extramuscular manifestations, by symmetrical progressive muscle weakness that may persist even after pharmacological suppression of inflammation, suggesting a significant involvement of nonimmune mechanisms. Low levels of vitamin D have been associated with several autoimmune diseases. Vitamin D is essential for the maintenance of skeletal muscle, and mounting evidence supports its relation to muscle damage, regeneration, and energy metabolism.

Objectives

The aim was to analyse vitamin D and the mediators of its function in muscle tissue of IIM patients, and to associate it with muscle health parameters.

Methods

A total of 46 IIM patients (40 females, 6 males; mean age 56.7±12.4; disease duration 6.5±6.0 years; dermatomyositis (21), polymyositis (18), necrotizing myopathy (7)) and 67 healthy controls (HC) (56 females, 11 males; mean age 50.9±14.7) were recruited. In total, 27 IIM patients participated in a 24-week intervention combining activities-of-daily-life, resistance and stability training [1]. Muscle biopsies from m. vastus lateralis (by Bergström needle) were obtained from 7 IIM patients before/after the 24-week training program, and from 13 control IIM patients, and 21 HC. Primary muscle cell cultures were established from these samples. Disease-associated parameters were evaluated by MYOACT/MITAX, MDI, VAS, HAQ, MMT8, FI-2 and CK, myoglobin, LD, ALT, AST, and CRP levels. Myostatin, as a myokine involved in muscle atrophy, was determined from serum samples by ELISA. Circulating concentrations of 25(OH) vitamin D (calcidiol) and active 1,25(OH) vitamin D (calcitriol) were measured by routine biochemistry techniques. Gene expression of vitamin D receptor (VDR) and 25-hydroxyvitamin D 1-alpha-hydroxylase (CYP27B1), an enzyme catalysing calcidiol conversion to hormonally active calcitriol, was determined by real-time PCR in muscle tissue and primary muscle cell cultures. Data are presented as mean ± standard deviation.

Results

Decreased levels of active 1,25(OH)D were observed in IIM patients compared to HC (125.0±45.4 vs. 164.7±49.2 pmol/l; p<0.0001). No difference was found for 25(OH)D. The 24-week training program did not have an effect on 25(OH)D or 1,25(OH)D serum levels. 25(OH)D was significantly associated with CRP (r=-0.322, p=0.040), MITAX (r=-0.380, p=0.021) and HAQ (r=-0.370, p=0.017) in IIM patients, even after correction for BMI, gluccocorticoid (GC) and vitamin D daily supplementation dose. After 24 weeks of exercise, active 1,25(OH)D was positively associated with MMT8 (r=0.866, p<0.0001), FI2 (r=0.608, p=0.013) and HAQ (r=-0.537, p=0.032) (corrected for BMI, GC and vit.D supplementation). Numerically higher gene expression of VDR and CYP27B1 was found in muscle tissue and primary muscle cells in IIM compared to HC. After the 24-week training, gene expression of both VDR and CYP27B1 in primary muscle cells decreased (p=0.031 and p=0.078, respectively). Associations of VDR gene expression with myoglobin (IIM: r=0.510, p=0.026; HC: r=0.473, p=0.035), MMT8 (IIM: r=-0.559, p=0.013), myostatin (IIM: r=-0.519, p=0.023; HC: r=0.586, p=0.005), and CK (HC: r=0.484, p=0.031) were observed in muscle tissue. CYP27B1 gene expression in the muscle was also associated with myoglobin (HC: r=0.501, p=0.024), MMT8 (IIM: r=-0.555, p=0.011) and VDR (IIM: r=0.561, p=0.012; HC: r=0.632, p=0.002).

Conclusion

Decrease of the biologically active form of vitamin D in circulation suggests an impairment of its metabolism in IIM. Vitamin D serum levels and gene expression of its receptor and activating enzyme in muscle tissue associate with disease activity and muscle function parameters indicating an important role of vitamin D in physical fitness and disease manifestations in IIM patients.

References

[1]Špiritović M, et al. Arthritis Res Ther. 2021;23(1):173.

Acknowledgements

This work was supported by the Ministry of Health of the Czech Republic grant nr. NU21-05-00322.

Disclosure of Interests

None declared.

Altered dynamics of lipid metabolism in muscle cells from patients with idiopathic inflammatory myopathy is ameliorated by 6 months of training

KEY POINTS

Regular exercise improves muscle functional capacity and clinical state of patients with idiopathic inflammatory myopathy (IIM). In our study, we used an in vitro model of human primary muscle cell cultures, derived from IIM patients before and after a 6-month intensive supervised training intervention to assess the impact of disease and exercise on lipid metabolism dynamics. We provide evidence that muscle cells from IIM patients display altered dynamics of lipid metabolism and impaired adaptive response to saturated fatty acid load compared to healthy controls. A 6-month intensive supervised exercise training intervention in patients with IIM mitigated disease effects in their cultured muscle cells, improving or normalizing their capacity to handle lipids. These findings highlight the putative role of intrinsic metabolic defects of skeletal muscle in the pathogenesis of IIM and the positive impact of exercise, maintained in vitro by yet unknown epigenetic mechanisms.

ABSTRACT

Exercise improves skeletal muscle function, clinical state and quality of life in patients with idiopathic inflammatory myopathy (IIM). Our aim was to identify disease-related metabolic perturbations and the impact of exercise in skeletal muscle cells of IIM patients. Patients underwent a 6-month intensive supervised training intervention. Muscle function, anthropometric and metabolic parameters were examined and muscle cell cultures were established (m. vastus lateralis; Bergström needle biopsy) before and after training from patients and sedentary age/sex/body mass index-matched controls. [¹⁴ C]Palmitate was used to determine fat oxidation and lipid synthesis (thin layer chromatography). Cells were exposed to a chronic (3 days) and acute (3 h) metabolic challenge (the saturated fatty acid palmitate, 100 μm). Reduced oxidative (intermediate metabolites, -49%, P = 0.034) and non-oxidative (diglycerides, -38%, P = 0.013) lipid metabolism was identified in palmitate-treated muscle cells from IIM patients compared to controls. Three days of palmitate exposure elicited distinct regulation of oxidative phosphorylation (OxPHOS) complex IV and complex V/ATP synthase (P = 0.012/0.005) and adipose triglyceride lipase in patients compared to controls (P = 0.045) (immunoblotting). Importantly, 6 months of training in IIM patients improved lipid metabolism (CO₂ , P = 0.010; intermediate metabolites, P = 0.041) and activation of AMP kinase (P = 0.007), and nearly normalized palmitate-induced changes in OxPHOS proteins in myotubes from IIM patients, in parallel with improvements of patients' clinical state. Myotubes from IIM patients displayed altered dynamics of lipid metabolism and impaired response to metabolic challenge with saturated fatty acid. Our observations suggest that metabolic defects intrinsic to skeletal muscle could represent non-immune pathomechanisms, which can contribute to muscle weakness in IIM. A 6-month training intervention mitigated disease effects in muscle cells in vitro, indicating the existence of epigenetic regulatory mechanisms.

OP0138 CLUSTERIN ASSOCIATES WITH DISEASE MECHANISMS AND INFLAMMATION IN MYOSITIS PATIENTS

Background:

Idiopathic inflammatory myopathies (IIM, myositis) are a heterogeneous group of autoimmune muscle disorders characterized by skeletal muscle weakness and damage, inflammation and extramuscular manifestations. Recent findings suggest that immunological as well as nonimmunological processes, such as endoplasmic reticulum stress, hypoxia, mitochondrial and metabolic dysfunction are involved in the pathogenesis of IIMs [1]. Clusterin (CLU) has been reported to play a protective function in the development of tissue injury, inflammation and autoimmunity, and is involved in the maintenance of immune homeostasis [2].

Objectives:

This study aimed to explore a potential involvement of the circulating levels and skeletal muscle expression of CLU in pathogenic mechanisms of IIM.

Methods:

A total of 85 IIM patients and 86 healthy controls (HC) were recruited. In addition, 20 IIM patients and 21 HC underwent a muscle biopsy. Circulating concentrations of CLU were measured by ELISA. Serum cytokine profile of patients and HC was assessed by Cytokine 27-plex Assay. Immunohistochemical localisation of CLU was assessed in 10 IIM and 4 control muscle tissue specimens. The expression of CLU and myositis related cytokines in muscle tissue was determined by real-time PCR.

Results:

We observed a significant increase of circulating CLU in all IIM patients compared to HC (86.2 (71.6-99.0) vs. 59.6 (52.6-68.4) μg/mL, p < 0.0001). Moreover, CLU serum levels were positively correlated with myositis disease activity assessment (MYOACT) (r = 0.337, p = 0.008), myositis intention-to-treat activity index (MITAX) (r = 0.357, p = 0.004) and global disease assessment evaluated by physician (r = 0.309, p = 0.015). In addition to that, a multivariate redundancy analysis revealed a combined effect of serum CLU and cytokine profile (represented by cytokines and chemokines known to be involved in IIM) on disease activity measures. In muscle tissue, CLU mRNA was significantly increased in IIM patients compared to controls (p = 0.032) and correlated with IL-1β (r = 0.489, p = 0.034), IL-6 (r = 0.581, p = 0.009), TNF (r = 0.485, p = 0.035) and PGC-1α (r = 0.709, p = 0.001) mRNA. Immunohistochemistry revealed CLU accumulation in the cytoplasm of regenerating myofibers.

Conclusion:

Our results show an up-regulation of clusterin in circulation and skeletal muscle of IIM patients that associates with disease activity and inflammation, and its specific expression in regenerating myofibres. Based on our data and the known cytoprotective function of CLU we suggest an attempt of the organism to limit further muscle damage induced by myositis disease mechanisms.

References:

[1]Ernste FC, Reed AM. Idiopathic inflammatory myopathies: current trends in pathogenesis, clinical features, and up-to-date treatment recommendations. Mayo Clin Proc. 2013;88:83-105.

[2]Savkovic V, Gantzer H, Reiser U, Selig L, Gaiser S, Sack U, et al. Clusterin is protective in pancreatitis through anti-apoptotic and anti-inflammatory properties. Biochem Biophys Res Commun. 2007;356:431-7.

Acknowledgments:

This work was supported by GAUK 534217 and the Ministry of Health of the Czech Republic grants nr. 16-33746A and 16-33574A.

Disclosure of Interests:

None declared

OP0136 THE INFLUENCE OF LONG-TERM EXERCISE AND IN VITRO EXERCISE-MIMICKING STIMULATION ON THE PRODUCTION OF MYOKINES AND CYTOKINES IN MYOTUBES OF PATIENTS WITH CHRONIC IDIOPATHIC INFLAMMATORY MYOPATHIES

Background:

It has been demonstrated several times that endurance exercise has beneficial effects on the condition of patients with idiopathic inflammatory myopathies (IIM). Muscle contraction during exercise is a major stimulus for the release of myokines that are supposed to take part in the beneficial adaption to exercise.

Objectives:

The aim of this study was to find out how a six-month physiotherapy andin vitroexercise-mimicking treatment affect myokine and cytokine production in myotubes of IIM patients.

Methods:

Seven patients with chronic IIM took part in a six-month physiotherapy (stretching and strengthening), which significantly improved their muscle strength and endurance. IIM patients (n=7) before and after the six months exercise and their respective healthy counterparts (HC, n=9) underwent amusculus vastus lateralisbiopsy. Isolated skeletal muscle cells were grown, differentiated into myotubes, which were treated with a pharmacological cocktail: palmitate, forskolin and ionomycin (PFI) to mimic exercise-stimulated contractions in vitro. Myokine and cytokine concentrations produced by myotubes to the culture medium were analyzed with ELISA and the multiplex immunoassay, respectively. RT-PCR was used for the evaluation of myokine gene expression in the cultured myotubes.

Results:

Compared to myotubes of healthy controls, myotubes of IIM patient released more myostatin and activin A into the medium. The myostatin gene was expressed significantly more in muscle cells of patients than in healthy controls’ cells (p<0.05). After a six-month rehabilitation program, activin A secretion was four-fold reduced in myotubes of patients with IIM, while myostatin release and gene expression remained unchanged. In myotubes of IIM patients, less follistatin and more follistatin like 3 were detected in the culture medium compared to HC myotubes. Myotubes derived from IIM patients after six months of rehabilitation secreted twice as much follistatin and half the amount of follistatin like 3 into the medium than myotubes derived from IIM patients prior to rehabilitation (p<0.05). There was no difference in secretion of interleukin (IL) 6, IL-17, tumor necrosis factor (TNF) and vascular endothelial growth factor (VEGF) between myotubes of IIM patients and myotubes of HC. However, six-month exercise significantly (p<0.05) reduced release of IL-6, TNF and VEGF in myotubes of IIM patients. Contrary to our expectation, stimulation of PFI had no effect on the release of myostatin, activin A, follistatin and follistatin like 3, or the expression of their genes. PFI treatment significantly (p<0.05) increased IL-6 secretion in myotubes from HC and IIM patients prior to six months of rehabilitation. On the other hand, it was observed that myotubes of HC and IIM patients exposed to the PFI cocktail secreted significantly less inflammatory cytokines IL-17, TNF and VEGF into the medium compared to unstimulated myotubes (p<0.05).

Conclusion:

In conclusion, long-term exercise influenced the production of myokines and decreased release of inflammatory cytokines in myotubes of IIM patients.In vitroexercise-mimicking treatment increased the secretion of IL-6 and decreased the release of inflammatory cytokines as IL-17, TNF-α and VEGF in myotubes of patients with IIM and healthy individuals.

Acknowledgments:

This work was supported by the Ministry of Health of the Czech Republic grants nr. 16-33746A and donation 140.0000008.

Disclosure of Interests:

None declared

Red palm oil supplementation does not increase blood glucose or serum lipids levels in Wistar rats with different thyroid status

Red palm oil (RPO) is a rich natural source of antioxidant vitamins, namely carotenes, tocopherols and tocotrienols. However, it contains approximately 50 % saturated fatty acids the regular consumption of which could negatively modify lipid profile. The aim of our study was to test whether 7 weeks of RPO supplementation (1 g/kg body weight/day) would affect blood glucose and lipid metabolism in adult male Wistar rats with altered thyroid status. We induced hypothyroidism and hyperthyroidism in rats by oral administration of either methimazole or mixture of thyroid hormones. Different thyroid status (EU - euthyroid, HY - hypothyroid and HT - hyperthyroid) was characterized by different serum thyroid hormones levels (total and free thyroxine and triiodothyronine), changes in the activity of a marker enzyme of thyroid status - liver mitochondrial glycerol-3-phosphate dehydrogenase, and altered absolute and relative heart weights. Fasting blood glucose levels were higher in HT rats in comparison with EU and HY rats, but the changes caused by RPO supplementation were not significant. The achievement of the HY status significantly increased serum levels of total cholesterol, as well as with high-density lipoprotein-cholesterol and low-density lipoprotein-cholesterol: 2.43+/-0.15, 1.48+/-0.09, 0.89+/-0.08 mmol/l, compared to EU: 1.14+/-0.06, 0.77+/-0.06, 0.34+/-0.05 mmol/l and HT: 1.01+/-0.06, 0.69+/-0.04, 0.20+/-0.03 mmol/l, respectively. RPO supplementation did not increase significantly levels of blood lipids but tended to increase glutathione levels in the liver. In conclusion, RPO supplementation did not induce the presumed deterioration of glucose and lipid metabolism in rats with three well-characterized alterations in thyroid status.

The influence of erythrocyte maturity on ion transport and membrane lipid composition in the rat

Significant relationships between ion transport and membrane lipid composition (cholesterol, total phospholipids and sphingomyelins) were found in erythrocytes of salt hypertensive Dahl rats. In these animals mean cellular hemoglobin content correlated negatively with Na(+)-K(+) pump activity and Na(+) leak but positively with Na(+)-K(+) cotransport activity. Immature erythrocytes exhibit lower mean cellular hemoglobin content (MCHC) than mature ones. The aim of the present study was to find a relationship between erythrocyte maturity, membrane lipid composition and ion transport activity in Wistar rats aged three months which were subjected to repeated hemorrhage (blood loss 2 ml/day for 6 days) to enrich circulating erythrocytes with immature forms. Immature and mature erythrocyte fractions in control and hemorrhaged rats were separated by repeated centrifugation. Hemorrhaged rats had increased number of reticulocytes but reduced hematocrit and MCHC compared to control rats. Immature erythrocytes of hemorrhaged rats differed from mature ones of control animals by elevated Na(+)-K(+) pump activity, reduced Na(+)-K(+) cotransport activity and increased Rb(+) leak. These ion transport changes in immature erythrocytes were accompanied by higher concentration of total phospholipids in their cell membranes. Membrane phospholipid content correlated positively with Na(+)-K(+) pump activity and cation leaks but negatively with Na(+)-K(+) cotransport activity. Moreover, they were also negatively related with MCHC which correlated negatively with Na(+)-K(+) pump activity and Rb(+) leak but positively with Na(+)-K(+) cotransport activity. Thus certain abnormalities of erythrocyte ion transport and membrane lipid composition detected in hypertensive animals might be caused by higher incidence of immature cells.

ROS production is increased in the kidney but not in the brain of Dahl rats with salt hypertension elicited in adulthood

Enhanced production of superoxide radicals by nicotinamide-adenine dinucleotide phosphate (NADPH) oxidase in the brain and/or kidney of salt hypertensive Dahl rats has been proposed to participate in the pathogenesis of this form of experimental hypertension. Most information was obtained in young Dahl salt-sensitive (DS) rats subjected to high salt intake prior to sexual maturation. Therefore, the aim of our study was to investigate whether salt hypertension induced in adult DS rats is also accompanied with a more pronounced oxidative stress in the brain or kidney as compared to Dahl salt-resistant (DR) controls. NADPH oxidase activity as well as the content of thiobarbituric acid-reactive substances (TBARS) and conjugated dienes (oxidative index), which indicate a degree of lipid peroxidation, were evaluated in two brain regions (containing either hypothalamic paraventricular nucleus or rostral ventrolateral medulla) as well as in renal medulla and cortex. High salt intake induced hypertension in DS rats but did not modify blood pressure in DR rats. DS and DR rats did not differ in NADPH oxidase-dependent production of ROS, TBARS content or oxidative index in either part of the brain. In addition, high-salt diet did not change significantly any of these brain parameters. In contrast, the enhanced NADPH oxidase-mediated ROS production (without significant signs of increased lipid peroxidation) was detected in the renal medulla of salt hypertensive DS rats. Our findings suggest that there are no signs of enhanced oxidative stress in the brain of adult Dahl rats with salt hypertension induced in adulthood.

Chronic antioxidant therapy lowers blood pressure in adult but not in young Dahl salt hypertensive rats: the role of sympathetic nervous system

AIM

It is well-known that salt hypertension is associated with increased oxidative stress. Since the development of salt hypertension is age-dependent, we were interested whether young and adult salt hypertensive Dahl rats differ in oxidative stress level and/or in the effects of chronic antioxidant therapy on blood pressure (BP) level and on the participation of particular vasoconstrictor/vasodilator systems in BP maintenance.

METHODS

Young (5-week-old) and adult (12-week-old) salt-sensitive (Dahl-S) male rats were fed high-salt diet (5% NaCl) and drank tempol solution (2 mm) for 5 weeks. BP was monitored with radiotelemetry and vasoconstrictor/vasodilator balance was evaluated at the end of experiment. Moreover, NO synthase activity, superoxide production and lipoperoxidation were determined in heart, kidney and aorta in separate subgroups of Dahl rats.

RESULTS

Tempol treatment had quite opposite BP effects in young and adult Dahl-S rats. While it tended to increase BP in young salt hypertensive Dahl-S rats, it significantly lowered BP in the adult ones due to reduced sympathetic vasoconstriction. Importantly, high salt intake substantially reduced NO synthase activity in heart and kidney, and markedly increased superoxide production in kidneys and aorta of adult Dahl-S rats in which BP correlated positively with superoxide production in thoracic aorta and lipoperoxidation in kidneys.

CONCLUSION

Chronic antioxidant therapy lowered BP only in adult salt hypertensive Dahl-S rats in which superoxide levels were increased in both kidneys and aorta. Blood pressure reduction induced by chronic tempol treatment is related to attenuated sympathetic vasoconstriction rather than to augmented NO-dependent vasodilatation.

Hypoxia-induced lipid peroxidation in the brain during postnatal ontogenesis

Reactive oxygen species (ROS) are common products of the physiological metabolic reactions, which are associated with cell signaling and with the pathogenesis of various nervous disorders. The brain tissue has the high rate of oxidative metabolic activity, high concentration of polyunsaturated fatty acids in membrane lipids, presence of iron ions and low capacity of antioxidant enzymes, which makes the brain very susceptible to ROS action and lipid peroxidation formation. Membranes of brain cortex show a higher production of thiobarbituric acid-reactive substances (TBARS) in prooxidant system (ADP.Fe(3+)/NADPH) than membranes from the heart or kidney. Lipid peroxidation influences numerous cellular functions through membrane-bound receptors or enzymes. The rate of brain cortex Na(+),K(+)-ATPase inhibition correlates well with the increase of TBARS or conjugated dienes and with changes of membrane fluidity. The experimental model of short-term hypoxia (simulating an altitude of 9000 m for 30 min) shows remarkable increase in TBARS in four different parts of the rat brain (cortex, subcortical structures, cerebellum and medulla oblongata) during the postnatal development of Wistar rat of both sexes. Young rats and males are more sensitive to oxygen changes than adult rats and females, respectively. Under normoxia or hypobaric hypoxia both ontogenetic aspects and sex differences play a major role in establishing the activity of erythrocyte catalase, which is an important part of the antioxidant defense of the organism. Rats pretreated with L-carnitine (and its derivatives) have lower TBARS levels after the exposure to hypobaric hypoxia. The protective effect of L-carnitine is comparable with the effect of tocopherol, well-known reactive species scavenger. Moreover, the plasma lactate increases after a short-term hypobaric hypoxia and decreases in L-carnitine pretreated rats. Acute hypobaric hypoxia and/or L-carnitine-pretreatment modify serum but not brain lactate dehydrogenase activity. The obtained data seem to be important because the variations in oxygen tension represent specific signals of regulating the activity of many specific systems in the organism.

N-3 polyunsaturated fatty acids supplementation does not affect changes of lipid metabolism induced in rats by altered thyroid status

Epidemiological studies have demonstrated that n-3 polyunsaturated fatty acid (PUFA) consumption is associated with a reduced risk of atherosclerosis and hyperlipidemia. It is well known that lipid metabolism is also influenced by thyroid hormones. The aim of our study was to test whether n-3 PUFA supplementation (200 mg/kg of body weight/day for 6 weeks given intragastrically) would affect lipid metabolism in Lewis male rats with altered thyroid status. Euthyroid, hypothyroid, and hyperthyroid status of experimental groups was well defined by plasma levels of triiodothyronine, the activity of liver mitochondrial glycerol-3-phosphate dehydrogenase, and by relative heart weight. Fasting blood glucose levels were significantly higher in the hyperthyroid compared to the euthyroid and hypothyroid rats (5.0±0.2 vs. 3.7±0.4 and 4.4±0.2 mmol/l, respectively). In hyperthyroid animals, the concentration of plasma postprandial triglycerides was also increased compared to euthyroid and hypothyroid rats (0.9±0.1 vs. 0.5±0.1 and 0.4±0.1 mmol/l, respectively). On the other hand, hypothyroidism compared to euthyroid and hyperthyroid status was associated with elevated plasma levels of total cholesterol (2.6±0.2 vs. 1.5±0.1 and 1.6±0.1 mmol/l, respectively), LDL cholesterol (0.9±0.1 vs. 0.4±0.1 and 0.2±0.1 mmol/l, respectively) as well as HDL cholesterol (1.6±0.1 vs. 1.0±0.1 and 1.3±0.1 mmol/l, respectively). Supplementation of n-3 PUFA in the present study did not significantly modify either relative heart weight or glucose and lipid levels in any thyroid status.

Age-dependent salt hypertension in Dahl rats: fifty years of research

Fifty years ago, Lewis K. Dahl has presented a new model of salt hypertension - salt-sensitive and salt-resistant Dahl rats. Twenty years later, John P. Rapp has published the first and so far the only comprehensive review on this rat model covering numerous aspects of pathophysiology and genetics of salt hypertension. When we summarized 25 years of our own research on Dahl/Rapp rats, we have realized the need to outline principal abnormalities of this model, to show their interactions at different levels of the organism and to highlight the ontogenetic aspects of salt hypertension development. Our attention was focused on some cellular aspects (cell membrane function, ion transport, cell calcium handling), intra- and extrarenal factors affecting renal function and/or renal injury, local and systemic effects of renin-angiotensin-aldosterone system, endothelial and smooth muscle changes responsible for abnormal vascular contraction or relaxation, altered balance between various vasoconstrictor and vasodilator systems in blood pressure maintenance as well as on the central nervous and peripheral mechanisms involved in the regulation of circulatory homeostasis. We also searched for the age-dependent impact of environmental and pharmacological interventions, which modify the development of high blood pressure and/or organ damage, if they influence the salt-sensitive organism in particular critical periods of development (developmental windows). Thus, severe self-sustaining salt hypertension in young Dahl rats is characterized by pronounced dysbalance between augmented sympathetic hyperactivity and relative nitric oxide deficiency, attenuated baroreflex as well as by a major increase of residual blood pressure indicating profound remodeling of resistance vessels. Salt hypertension development in young but not in adult Dahl rats can be attenuated by preventive increase of potassium or calcium intake. On the contrary, moderate salt hypertension in adult Dahl rats is attenuated by superoxide scavenging or endothelin-A receptor blockade which do not affect salt hypertension development in young animals.

Idebenone-induced recovery of glycerol-3-phosphate and succinate oxidation inhibited by digitonin

Digitonin solubilizes mitochondrial membrane, breaks the integrity of the respiratory chain and releases two mobile redox-active components: coenzyme Q (CoQ) and cytochrome c (cyt c). In the present study we report the inhibition of glycerol-3-phosphate- and succinate-dependent oxygen consumption rates by digitonin treatment. Our results show that the inhibition of oxygen consumption rates is recovered by the addition of exogenous synthetic analog of CoQ idebenone (hydroxydecyl-ubiquinone; IDB) and cyt c. Glycerol-3-phosphate oxidation rate is recovered to 148 % of control values, whereas succinate-dependent oxidation rate only to 68 %. We find a similar effect on the activities of glycerol-3-phosphate and succinate cytochrome c oxidoreductase. Our results also indicate that succinate-dependent oxidation is less sensitive to digitonin treatment and less activated by IDB in comparison with glycerol-3-phosphate-dependent oxidation. These findings might indicate the different mechanism of the electron transfer from two flavoprotein-dependent dehydrogenases (glycerol-3-phosphate dehydrogenase and succinate dehydrogenase) localized on the outer and inner face of the inner mitochondrial membrane, respectively.

Glycerol-3-phosphate dehydrogenase expression and oxygen consumption in liver mitochondria of female and male rats with chronic alteration of thyroid status

In our chronic experiments (over several months), the activity and protein amount of glycerol-3-phosphate dehydrogenase (GPDH) in mitochondria isolated from the liver of adult male and female inbred Lewis strain euthyroid (EU), hyperthyroid (TH), and hypothyroid (HY) rats were analyzed by biochemical and Western blot methods. The TH status was induced by intraperitoneal injections of 3,3',5-triiodo- L-thyronine and the HY status with 0.05% solution of methimazole in drinking water. The TH status led to a significant increase and the HY status to a significant decrease of enzyme activity and protein amount in both male and female animals. These changes were, however, more pronounced in females. The EU and TH female rats also showed a significantly higher activity and the TH female rats showed also a significantly higher enzyme amount in comparison with males, while the HY rats showed low levels in both sexes. The glycerol-3-phosphate-dependent oxygen consumption of freshly isolated rat liver mitochondria from the TH animals was higher in comparison with the EU animals and it was activated by idebenone, a synthetic analogue of coenzyme Q, in both the EU and TH rats. Measurements of serum thyroid hormone levels and analysis of anatomical parameters (relative heart and thyroid gland weights) confirmed that our procedures inducing the TH and HY states are efficient and reliable and that determination of GPDH can serve as an additional criterion for the evaluation of the thyroid hormone status.

Erythrocyte ion transport in rats subjected to acute and chronic hypobaric hypoxia

Our study addresses selected parameters of rat erythrocyte ion transport (Na(+)-K(+) pump, Na(+)-K(+)-2Cl- cotransport, and passive cation fluxes) after acute or chronic hypoxia exposure. We did not find any significant change of ion transport after acute hypoxia. However, chronic hypoxia could modify ion transport because the affinity of Na(+)-K(+) pump for intracellular Na(+) seems to be decreased.

Developmental changes of erythrocyte catalase activity in rats exposed to acute hypoxia

The erythrocytes represent an important source of antioxidant capacity of the blood. Catalase (EC 1.11.1.6.) is one of the enzymatic components of their antioxidant defense system. The objective of this study was to follow erythrocyte catalase (CAT) in 7-, 15-, 21-, 35-, 60- and 90-day-old Wistar rats of both sexes in normoxia and after exposure to intensive acute hypobaric hypoxia. During the development CAT activity increases in both sexes, but the rise was usually higher in females. Hypobaric hypoxia increased CAT activity in all studied age groups of both sexes. However, higher CAT activity in females was less affected by hypoxia than the lower activity in males. This was true for nearly all age groups studied. It can be concluded that both ontogenetic aspects and sex differences play a major role in establishing the activity of CAT, which is an important part of the antioxidant defense of the organism.

Developmental changes of erythrocyte catalase activity in rats exposed to acute hypoxia

The erythrocytes represent an important source of antioxidant capacity of the blood. Catalase (EC 1.11.1.6.) is one of the enzymatic components of their antioxidant defense system. The objective of this study was to follow erythrocyte catalase (CAT) in 7-, 15-, 21-, 35-, 60- and 90-day-old Wistar rats of both sexes in normoxia and after exposure to intensive acute hypobaric hypoxia. During the development CAT activity increases in both sexes, but the rise was usually higher in females. Hypobaric hypoxia increased CAT activity in all studied age groups of both sexes. However, higher CAT activity in females was less affected by hypoxia than the lower activity in males. This was true for nearly all age groups studied. It can be concluded that both ontogenetic aspects and sex differences play a major role in establishing the activity of CAT, which is an important part of the antioxidant defense of the organism.

Altered balance of vasoactive systems in experimental hypertension: the role of relative NO deficiency

This review summarizes our findings concerning the altered balance of vasoactive systems (namely sympathetic nervous system and nitric oxide) in various forms of experimental hypertension--genetic hypertension (SHR, HTG rats), salt hypertension (Dahl rats) and NO-deficient hypertension (L-NAME-treated rats). An attempt is made to define relative NO deficiency (compared to the existing level of sympathetic vasoconstriction), to describe its possible causes and to evaluate particular indicators of its extent. A special attention is paid to reactive oxygen species, their interaction with NO metabolism, cell Ca2+ handling and blood pressure regulation. Our current effort is focused on the investigation of abnormal regulation of cytosolic Ca2+ levels in smooth muscle and endothelium of hypertensive animals. Such a research should clarify the mechanisms by which genetic and/or environmental factors could chronically modify blood pressure level.

Altered Na+-K+ pump activity and plasma lipids in salt-hypertensive Dahl rats: relationship to Atp1a1 gene

A genetic variant of the gene for the alpha(1)-isoform of Na(+)-K(+)-ATPase (Atp1a1) was suggested to be involved in the pathogenesis of salt hypertension in Dahl rats through altered Na(+):K(+) coupling ratio. We studied Na(+)-K(+) pump activity in erythrocytes of Dahl salt-sensitive (SS/Jr) rats in relation to plasma lipids and blood pressure (BP) and the linkage of polymorphic microsatellite marker D2Arb18 (located within intron 1 and exon 2 of Atp1a1 gene) with various phenotypes in 130 SS/Jr x SR/Jr F(2) rats. Salt-hypertensive SS/Jr rats had higher erythrocyte Na(+) content, enhanced ouabain-sensitive (OS) Na(+) and Rb(+) transport, and higher Na(+):Rb(+) coupling ratio of the Na(+)-K(+) pump. BP of F(2) hybrids correlated with erythrocyte Na(+) content, OS Na(+) extrusion, and OS Na(+):Rb(+) coupling ratio, but not with OS Rb(+) uptake. In F(2) hybrids there was a significant association indicating suggestive linkage (P < 0.005, LOD score 2.5) of an intragenic marker D2Arb18 with pulse pressure but not with mean arterial pressure or any parameter of Na(+)-K(+) pump activity (including its Na(+):Rb(+) coupling ratio). In contrast, plasma cholesterol, which was elevated in salt-hypertensive Dahl rats and which correlated with BP in F(2) hybrids, was also positively associated with OS Na(+) extrusion. The abnormal Na(+):K(+) stoichiometry of the Na(+)-K(+) pump is a consequence of elevated erythrocyte Na(+) content and suppressed OS Rb(+):K(+) exchange. In conclusion, abnormal cholesterol metabolism but not the Atp1a1 gene locus might represent an important factor for both high BP and altered Na(+)-K(+) pump function in salt-hypertensive Dahl rats.