Pharmacokinetics and Bioavailability of the GnRH Analogs in the Form of Solution and Zn2+-Suspension After Single Subcutaneous Injection in Female Rats

BACKGROUND AND OBJECTIVES

Although many synthetic gonadoliberin analogs have been developed, only a few of them, including buserelin, were introduced into clinical practice. Dalarelin, which differs from buserelin by just one aminoacid in the position 6 (D-Ala), is not widely used so far. Gonadotropin-releasing hormone (GnRH) analogs are used to treat many different illnesses and are available in different forms like solution for injection, nasal spray, microspheres, etc. Unfortunately, none of the above drug formulations can release the hormones for 24 h. We assumed that classical suspension could solve this problem.

METHODS

Two sets of experiments were performed. In the first one, buserelin and dalarelin were injected into mature female rats in two forms: suspension, in which the analogs are bounded by Zn²⁺ ions and solution. The pharmacokinetic parameters and bioavailability of the analogs were calculated, based on their concentration in the plasma measured by high-performance liquid chromatography method (HPLC). In the second experiment, the hormones in two different forms were injected into superovulated immature female rats and then the concentration of Luteinizing hormone (LH), Follicle-stimulating hormone (FSH) and 17β-estradiol in the serum was measured by radioimmunological method.

RESULTS

The Extent of Biological Availability (EBA), calculated on the base of AUC_0-∞, showed that in the form of solution buserelin and dalarelin display, respectively, only 13 and 8 % of biological availability of their suspension counterparts. Comparing both analogs, the EBA of dalarelin was half (53 %) that of buserelin delivered in the form of solution and 83 % when they were delivered in the form of suspension. The injection of buserelin or dalarelin, in the form of solution or suspension, into superovulated female rats increased LH, FSH and estradiol concentration in the serum. However, after injection of the analogs in the form of suspension, the high concentration of LH and FSH in the serum persisted longer.

CONCLUSION

Performed studies indicate that GnRH analogs in the form of suspension have higher bioavailability than their solution counterparts. It influences the effects of their action, especially in relation to LH and FSH.

The Norwood procedure - does the type of shunt determine outcome?

BACKGROUND

Stage I palliation of hypoplastic left heart syndrome (HLHS) and its variants is usually performed by a Norwood operation. The management of pulmonary blood flow during this procedure remains controversial. The RV-to-PA conduit (RVPAC) has been proposed as the better alternative compared to a systemic-to-pulmonary shunt (SPS).

METHODS

A retrospective single center chart review of consecutive patients who underwent a Norwood I procedure between 01/1997 and 09/2006 was performed. All patients were operated in deep hypothermia, with or without circulatory arrest, using different shunt modifications according to surgeon's preference. Patients were divided into two groups depending on surgical management for pulmonary blood flow (modified BT shunt [BT] and non-valved RVPAC [Sano]).

RESULTS

Fifty-four patients were included in the study (BT: 31 patients vs. Sano: 23 patients). Diastolic blood pressure during the first 24 hours postoperatively was significantly lower in the BT group (BT: 38.6 +/- 6.9 mmHg vs. Sano: 42.4 +/- 7.2 mmHg; P < 0.01) with a trend towards a higher systolic blood pressure (BT: 74.1 +/- 13.5 mmHg vs. Sano: 69.8 +/- 12.1 mmHg; P = 0.08). Mean circulatory arrest time in the BT group was significantly longer compared to the Sano patients (BT: 41 +/- 21 min vs. Sano: 25 +/- 23 min; P < 0.01). The mean hospital stay was 18.5 days for BT patients and 20 days for Sano patients ( P = 0.45). Early mortality for the total cohort was 14.8 % (n = 8) (BT 19.4 % [n = 6] vs. Sano 8.7 % [n = 2]; P = 0.12). There was no significant difference in inter-stage mortality between the two groups (BT: 18.2 % vs. Sano: 21.1 %; P = 0.47).

CONCLUSION

The results for both established surgical methods (BT and Sano) for the palliation of HLHS and its variants have improved over time and are reaching acceptable early mortality rates. There was a trend towards a favorable early outcome for Sano patients, which did not reach statistical significance in this study due to the low patient numbers.

From mild cognitive impairment to Alzheimer's disease - influence of homocysteine, vitamin B12 and folate on cognition over time: results from one-year follow-up

BACKGROUND AND PURPOSE

People with mild cognitive impairment (MCI) have higher risk of developing dementia than the general population. Currently known risk factors for dementia include older age, low education level, gait disorders, hippocampal atrophy, and apolipoprotein E allele. Vascular risk factors may modify the neurodegenerative process. The aim of this study was therefore to assess the influence of vascular (genetic and environmental) risk factors on progression to dementia in an MCI group during a one-year period.

MATERIAL AND METHODS

Fifty-five MCI patients (30 men and 25 women) and 44 controls (25 men and 19 women) matched for age, gender and education were studied. Mild cognitive impairment was diagnosed according to Petersen criteria (Mayo Clinic Group). Neuropsychological evaluation was made. Assessed vascular risk factors included hypertension, cardiovascular disease, diabetes, cigarette smoking, hyperlipidaemia, hyperhomocysteinaemia with vitamin B12 and folate deficiency. Genetic risk factors (APOE polymorphism, C677T and A1298C MTHFR polymorphisms) were also assessed.

RESULTS

Vascular risk factors were found significantly more often in the MCI group (p = 0.041), including APOE4 allele (p = 0.018), hyperhomocysteinaemia (p = 0.012) and folate deficiency (p = 0.023). Discriminant function analysis showed that only age and hypertension are potential factors which may have an influence on progression to dementia in the MCI group within one year of prospective observation.

CONCLUSION

Vascular risk factors are associated with cognitive impairment but do not have a significant influence on progression to dementia in the MCI group.

Selenium levels in blood of upper Silesian population: evidence of suboptimal selenium status in a significant percentage of the population

The selenium status and the relationship of whole-blood selenium and plasma homocysteine are reported for healthy human subjects living in Upper Silesia. A total of 1063 individuals (627 male and 436 female) examined for whole-blood selenium were subdivided into six groups according to age; the youngest included adolescents (n=143) aged 10-15 yr, and the oldest were centenarians (n=132). The mean Se content was relatively low (62.5+/-18.4 microg/L), and it tended to be higher in men (65.9+/-17.2 microg/L) than in women (57.5+/-18.9 microg/L). Selenium levels appeared to be age dependent, as the highest values were observed in young and middle-age adults (21-40 yr), whereas they were significantly lower in adolescents and in the elderly. In more than 40% of apparently healthy adults (aged 21-69 yr), the Se concentration was within the range 60-80 microg/L (i.e., below the lower limit of the nutritional adequacy range [80 microg/L]). A significant inverse correlation between whole-blood selenium and plasma total homocysteine was detected in a smaller population sample of middle-aged and elderly persons (n=204).

Pharmacokinetics of selenium following oral administration selenium preparation in rabbits

The aim of study was to investigate the bioavailability of selenium after oral administration of selenium yeast. As a reference preparation was used sodium selenite. The preparations were investigated in rabbits, according to a randomized two way crossover design in the fasted state. Each animal was given selenium preparation in the form of the single oral dose 0.5 mg Se/kg body weight. A washout period of one week separated both treatment periods. The selenium concentration was determined in serum spectrofluorometry. The divalent equation of one-compartment model was the simplest formula describing the course of selenium changes in serum of rabbits and giving the pharmacokinetic parameters. Pharmacokinetic variables (mean maximum plasma concentration, mean time to reach maximum plasma concentration, and the mean area under the plasma concentration-time curve) were not statistically different for the two preparations. It can be concluded that the two selenium preparations are likely to be bioequivalent.

Antioxidant status in newborns and infants suffering from congenital heart defects

There is a common view that free radicals may play an important role in tissue damage resulting from circulatory insufficiency, cardiosurgery etc. There are very few data concerning the involvement of free radical reactions in the newborns and infants suffering from congenital heart defects (CHD). Antioxidant status was evaluated in 41 newborns and infants under 1 year of age, among them 23 suffering from CHD (14 with left-to-right shunt and 9 with cyanotic heart defect) and 18 healthy controls. The study based on the assessment of activities of antioxidant enzymes in blood (superoxide dismutase, catalase and glutathione peroxidase), levels of low molecular weight antioxidants (vitamin E, uric acid and selenium) and the concentration of malondialdehyde (MDA) as a marker of lipid peroxidation. All subjects had low blood selenium concentration as compared to the level considered as being adequate. Infants suffering from CHD had lower, as compared to healthy controls, plasma vitamin E concentration. The difference was significant in the case of acyanotic ones. The activities of superoxide dismutase and catalase in infants with CHD were not significantly different from the respective values recorded in healthy controls. The activity of glutathione peroxidase in whole blood was the lowest in infants with cyanotic heart defect in whom lipid peroxidation, as evaluated by MDA level, was the most enhanced. Significantly higher plasma concentration of uric acid which may be interpreted as a positive mechanism enabling better protection of red blood cells from peroxidative damage was found in this group of infants. It is concluded that enhanced oxidative stress due to imbalance between prooxidant and antioxidant reactions appears to be associated with congenital heart defect pathology in infants.

Effects of a low carbohydrate diet and graded exercise during the follicular and luteal phases on the blood antioxidant status in healthy women

The aim of this study was to examine the effect of a low-carbohydrate (L-CHO) diet and graded cycling exercise on the enzymatic and non-enzymatic blood antioxidant defence system in young eumenorrhoeic women. Seven healthy physical education students exercised incrementally until they were fatigued under four different phase-diet conditions of the menstrual cycle, i.e. twice either during the mid-follicular or the mid-luteal phase, in each case either after 3 days of eating a normal mixed diet (59% carbohydrate, 27% fat, 14% protein) or 3 days of eating an isoenergy L-CHO diet (5% carbohydrate, 52% fat, 43% protein). In venous blood samples obtained at rest, immediately post test and during recovery, the activity of antioxidant enzymes and concentrations of reduced glutathione and selenium were determined. Plasma samples were analysed for concentrations of malondialdehyde, vitamin E (alpha-tocopherol), uric acid and activity of creatine kinase. The 3 days of the L-CHO diet, which had been preceded by glycogen-depleting exercise, resulted in a stimulation of the blood antioxidant defence system in young eumenorrhoeic women both at rest and during the graded cycling exercise to maximal oxygen uptake. It seems justified to presume that higher daily doses of haem iron, selenium and alpha-tocopherol provided by the L-CHO diet contributed to the enhancement of catalase activity, the rise in plasma concentrations of alpha-tocopherol and selenium, which resulted in better protection of the cell membranes against damage from peroxides, as reflected by a limited release of creatine kinase into plasma. With the exception of the case of glutathione reductase, the phases of the menstrual cycle had only minor effects on the indices of the blood antioxidant defence system.

Antioxidant defense in centenarians (a preliminary study)

The study was designed to assess the antioxidant defense mechanisms, either enzymatic or non-enzymatic, in a group of sixteen centenarians (one male and fifteen female subjects aged 101 to 105 years) living in the Upper Silesia district (Poland) in order to evaluate the potential role of antioxidant defenses in human longevity. The results of our preliminary study showed that in comparison with young healthy female adults the centenarians had significantly higher red blood cell glutathione reductase and catalase activities and higher, although insignificantly, serum vitamin E level.

Antioxidant defense in centenarians (a preliminary study)

The study was designed to assess the antioxidant defense mechanisms, either enzymatic or non-enzymatic, in a group of sixteen centenarians (one male and fifteen female subjects aged 101 to 105 years) living in the Upper Silesia district (Poland) in order to evaluate the potential role of antioxidant defenses in human longevity. The results of our preliminary study showed that in comparison with young healthy female adults the centenarians had significantly higher red blood cell glutathione reductase and catalase activities and higher, although insignificantly, serum vitamin E level.

Plasma selenium concentration in patients with stomach and colon cancer in the Upper Silesia

Plasma selenium concentration was assessed in 44 patients with cancer of the gastrointestinal tract (19 subjects with stomach cancer and 25 with colon cancer) and 25 age-matched healthy control subjects. Selenium concentration was determined by the fluorometric method. The observed plasma selenium concentrations in gastrointestinal cancer patients (37.0 +/- 11.05 ng Se/ml or 38.4 +/- 12.6 ng Se/ml in stomach or colon cancer patients, respectively) were significantly lower as compared to the healthy age-matched control group (51.4 +/- 14.4 ng Se/ml). The diagnosed low selenium status may be considered as a high risk for cancer development.

[A study of erythrocyte oxidative enzyme activity in patients with laryngeal cancer before and after treatment with a selenium preparation CEROSEL]

The preliminary results of activity changes of antioxidant enzymes (glutathione peroxidase, catalase and superoxide dismutase) in erythrocyte in 19 patients with laryngeal cancer were presented. Enzymes activity in patients was signified three times: before surgery, before and after radiotherapy. During Co-60-therapy patients received leaven preparation of selenium CE-ROSEL in dose 100 micrograms Se/day. Obtained results showed increase of enzymes activity after CE-ROSEL supplementation. This changes are probably the result of selenium influence on protected mechanism before the free radicals.

Modulation of procainamide toxicity by selenium-enriched yeast in rats

Free radical processes are proposed to play a crucial role in the development of procainamide adverse effects. Therefore, selenium, as a potent antioxidant, may modified procainamide toxicity. To test this hypothesis plasma and liver thiobarbituric acid-reacting substances (TBARS), plasma antioxidant activity (AOA), erythrocyte and liver superoxide dismutase (SOD), catalase, as well as selenium-dependent glutathione peroxidase (Se-GPX) were determined in the following four groups of rats: selenium-treated (Se), procainamide-treated (P), procainamide and selenium-treated (P + Se), and control (C). Morphological studies of leukocytes [tested for lupus erythematosus (LE) cells] and liver were also made. Atypical, i.e. enlarged and swollen, leukocytes resulting from procainamide and selenium treatment were observed. These changes were found in four out of five rats in the Se group, eight out of ten in the P group, and in seven out of ten in the P + Se group. LE-like cells were observed in two rats in the P + Se group. A statistically significant decrease in plasma and liver TBARS by 20% and 36%, respectively, increased activity of SOD by 20%, catalase by 48% and Se-GPX by 15% in erythrocytes, and decreased activity of liver SOD by 17% and catalase by 22% were found in the P + Se group as compared to the P group. These results indicated that selenium exerted antioxidant effects on the procainamide-treated rats. However, selenium did not prevent the development of disturbances in leukocyte morphology, on the contrary, it possibly promoted the conversion of leukocytes to LE cells.

The action of excessive, inorganic silicon (Si) on the mineral metabolism of calcium (Ca) and magnesium (Mg)

The influence of silicon treatment on the levels of calcium and magnesium in blood serum and tissues was studied in rats. The concentrations of both elements were estimated in samples of sera and tissues of rats receiving per os a soluble, inorganic silicon compound--sodium metasilicate nonahydrate (Na2SiO3.9H2O (REACHIM, USSR)), dissolved in the animals' drinking water. A decrease of magnesium concentration in serum was observed with accompanying elevation of registered calcemia. Moreover, a reduction of tissue calcium levels was found with a simultaneous increase of magnesium tissue pool. The results provide evidence for silicon involvement in mineral metabolism. It could result in a modification of pathological processes concerning bone tissue.

Increase in antioxidant activity in procainamide-treated rats

Recent studies suggest that in vivo procainamide oxidation underlies induction of autoimmunity by this drug. Since drug metabolism may be accompanied by generation of reactive oxygen species, plasma and liver thiobarbituric acid reacting substances (TBARS), activity of erythrocyte and liver superoxide dismutase, catalase, selenium-dependent glutathione peroxidase (Se-GPX), and plasma antioxidant activity in procainamide treated rats were evaluated. Procainamide administration increased liver lipid peroxide levels, intensified the activity of liver catalase and erythrocyte superoxide dismutase, as well as plasma antioxidant activity. The remaining biochemical parameters in the treated rats were within control values, except for the decreased erythrocyte catalase activity. We conclude, that the increased activity of free radicals observed in the treated rats could contribute to the development of procainamide induced side effects.

Silicon metabolism. The interrelations of inorganic silicon (Si) with systemic iron (Fe), Zinc (Zn), and copper (Cu) pools in the rat

The influence of silicon treatment on the levels of trace elements zinc (Zn), copper (Cu), and iron (Fe) in serum and tissues was studied in rats. The concentrations of silicon, iron, and zinc were estimated in samples of sera and tissues of rats receiving per os a soluble, inorganic silicon compound--sodium metasilicate nonahydrate (Na2SiO3.9H2O), dissolved in the drinking water. An increase of copper concentrations in liver and aortic walls in the experimental group was observed, with simultaneous reduction of zinc amounts in serum and all the tissue samples in the course of the experiment. The iron concentrations in the analyzed samples did not show any significant changes between both groups. The silicon levels in serum and in all the examined tissues were significantly higher in the tested group. The results provide evidence for the silicon interaction with copper and zinc, which could result in a number of metabolic process modifications, antiatheromatous activity among them.