Evaluation of alternative calculation methods for determining LDL cholesterol

BACKGROUND

Due to limitations of the Friedewald formula, alternative methods for calculating low-density lipoprotein cholesterol (LDL-C) were suggested. We evaluated utility of these methods.

METHODS

Ninety three subjects free of coronary heart disease were considered. LDL-C was measured by the homogeneous method, and calculated by the Friedewald formula LDL-C = TC-HDL-(TG/2.2) (LDL1) and alternative formulas LDL-C = 0.41 TC - 0.32 TG + 1.70 apoB - 0.27 (LDL2) and LDL-C = 0.94 TC - 0.94 HDL - 0.435 TG (LDL3).

RESULTS

All three formulas underestimated the measured LDL-C, both in the whole group and in subgroups according to TG levels (TG < 1.7 and in a range of 1.7-4.5 mmol/l, p < 0.001 for all). We found significantly higher bias for all three formulas in subjects with 1.7 < or = TG < 4.5 mmol/l levels. The Friedewald formula showed the lowest assay bias in all the groups investigated. The mean absolute bias for LDL1 was 7.6%, 18.3% for LDL2 and 13.6% for LDL3, respectively. Linear regression analysis showed correlation of calculated LDL-C values with the direct method in the range of r = 0.82 - 0.90 (p < 0.0001 for all, except of LDL2 in 1.7 < or = TG < 4.5 mmol/l group where p = 0.0011).

CONCLUSIONS

The Friedewald formula seems to be a better estimator of LDL-C in our study than the other two alternative formulas; however, it underestimated the LDL-C levels.

Products of DNA, protein and lipid oxidative damage in relation to vitamin C plasma concentration

Oxidative stress plays an important role in the pathogenesis of numerous chronic age-related free radical-induced diseases. Improved antioxidant status minimizes oxidative damage to DNA, proteins, lipids and other biomolecules. Diet-derived antioxidants such as vitamin C, vitamin E, carotenoids and related plant pigments are important in antioxidative defense and maintaining health. The results of long-term epidemiological and clinical studies suggest that protective vitamin C plasma concentration for minimum risk of free radical disease is higher than 50 micromol/l. Products of oxidative damage to DNA (DNA strand breaks with oxidized purines and pyrimidines), proteins (carbonyls) and lipids (conjugated dienes of fatty acids, malondialdehyde) were estimated in a group of apparently healthy adult non-smoking population in dependence on different vitamin C plasma concentrations. Under conditions of protective plasma vitamin C concentrations (>50 micromol/l) significantly lower values of DNA, protein and lipid oxidative damage were found in comparison with the vitamin C-deficient group (<50 micromol/l). The inhibitory effect of higher fruit and vegetable consumption (leading to higher vitamin C intake and higher vitamin C plasma concentrations) on oxidation of DNA, proteins and lipids is also expressed by an inverse significant correlation between plasma vitamin C and products of oxidative damage. The results suggest an important role of higher and frequent consumption of protective food (fruit, vegetables, vegetable oils, nuts, seeds and cereal grains) in prevention of free radical disease.

Homocysteine and its nutritional determinants in two ethnic groups of Slovakia

Determinants of total homocysteine involve demographic (age, sex, ethnic origin), genetic (enzymatic defects of metabolic homocysteine pathways) and acquired factors (deficiency of B-group vitamins, state of health, lifestyle). Plasma levels of total homocysteine and serum levels of vitamin B12, folic acid, vitamin B6 were measured in adult apparently healthy Romany minority subjects (n=119) and compared with those levels in apparently healthy subjects of majority Slovak population (n=146). Mean homocysteine level was similar in both groups (9.92 micromol/l in the Romany vs. 9.61 micromol/l in majority group). Hyperhomocysteinemia was only observed in 3% of both ethnic probands. Vitamin B12 level was equal (301 micromol/l in the Romany and 311 micromol/ in majority group). Deficient levels were found in 4% of the Romany subjects and 9% of the majority subjects. Folic acid level was significantly lower in Romany group (11.3 nmol/l vs. 14.8 nmol/l) with deficiency in 42% of the Romany subjects vs. 28% in the majority subjects. This finding is a consequence of lower consumption of fruit, vegetables, pulses and whole grain products in the Romany group. Vitamin B6 deficiency was found in 68% of the Romany subjects and 40% of majority subjects. This vitamin is homocysteine determinant under excessive methionine intake (overnutrition with predominance of animal protein intake). As was demonstrated in a dietetic questionnaires, the Romany subjects are more frequent consumers of meat and eggs. This nutrition regime should indicate an increased homocysteine level under vitamin B6 deficiency. The results of normal homocysteine levels in the Romany population under condition of higher folic acid and vitamin B6 deficiencies, smoking and higher alcohol consumption may suggest a more effective homocysteine metabolism in relation to different ethnic origin.

Effect of C677T methylenetetrahydrofolate reductase gene polymorphism on plasma homocysteine levels in ethnic groups

The objective of this study was to examine plasma homocysteine levels and C677T methylenetetrahydrofolate reductase (MTHFR) gene polymorphism in two ethnic groups from Slovakia. The samples consisted of general Slovak-Romany population (68 men and 81 women) from Southwestern Slovakia and the Slovak-Caucasians (174 men and 177 women) who participated in the CINDI project. The homocysteine levels were examined by HPLC, the analysis of MTHFR genotypes was done by PCR. The Slovak-Romany men (12.0+/-5.6 (S.D.) micromol/l) and women (9.2+/-2.6 microol/l) have significantly lower plasma homocysteine levels (p<0.024 and p<0.00001) when compared to Caucasians (13.3+/-5.1 micromol/l in men and 11.3+/-4.3 micromol/l in women). The genetic equilibrium is assumed for the gene frequencies of the MTHFR polymorphism in both samples. The distribution of MTHFR genotypes did not differ between the two populations (TT 13 vs. 10.6 %; CT 46.6 vs. 41.7 %; CC 40.4 vs. 47.7 %, chí(2)2 = 2.315, df=2, ns). The effect of MTHFR genotypes on homocysteine levels was not confirmed in the Slovak-Romanies and TT homozygosity significantly increased plasma homocysteine levels only in Slovak-Caucasians (11.5+/-4.4 micromol/l, ns; vs. 14.8+/-4.8 micromol/l, p 0.002, respectively). To our knowledge, this is the first epidemiological study in the Romany population examining distribution of the MTHFR genotypes and their effect on homocysteine levels. Further studies are needed to establish the variety of cardiovascular risk factors among Romanies in order to evaluate the significance of particular factors.

Serum ex vivo lipoprotein oxidizability in patients with ischemic heart disease supplemented with vitamin E

The decreased oxidizability of plasma lipoproteins is related to the increased vitamin E intake and its association with a relatively lower incidence of coronary heart disease has been proposed. We investigated the effect of the in vivo vitamin E supplementation on the oxidizability of serum lipids in patients with ischemic heart disease and a moderate hypercholesterolemia. Thirty-two patients (16 males and 16 postmenopausal women) participated in this placebo-controlled, randomized trial. They were treated with 400 mg vitamin E/day for 6 weeks. The copper-induced serum lipid oxidizability ex vivo was assessed by measuring conjugated diene formation at 245 nm. We also measured vitamin E, malondialdehyde (MDA) and uric acid concentrations in the plasma. Because of observed significant differences in parameters of serum lipid oxidizability (lag time and maximal rate of oxidation), plasma alpha-tocopherol and MDA levels between male patients and postmenopausal women supplemented with vitamin E, the results were compared between both genders. Six weeks of vitamin E supplementation significantly increased plasma vitamin E levels (by 87 %) in male patients but in postmenopausal women only by 34 %. Concomitantly with increased plasma levels of vitamin E the decrease in plasma MDA levels was observed in male patients (decrease by 20 %; p=0.008), but in postmenopausal women the decrease did not attain statistical significance. Plasma uric acid levels were not apparently changed in placebo or vitamin E supplemented groups of patients. The changes in ex vivo serum lipid oxidizability after vitamin E, supplementation have shown a significantly prolonged lag time (by 11 %; p=0.048) and lowered rate of lipid oxidation (by 21 %; p=0.004) in male patients in comparison with postmenopausal women. Linear regression analysis revealed a significant correlation between plasma vitamin E levels and the lag time (r=0.77; p=0.03) and the maximal rate of serum lipid oxidation (r=-0.70; p=0.05) in male patients. However, in postmenopausal women the correlations were not significant. We conclude that 400 mg vitamin E/day supplementation in patients with ischemic heart disease and a moderate hypercholesterolemia influenced favorably ex vivo serum lipid oxidation of male patients when compared with postmenopausal women. The observed differences between both genders could be useful in the selection of the effective vitamin E doses in the prevention of coronary heart disease.

Effects of ramipril in nondiabetic nephropathy: improved parameters of oxidatives stress and potential modulation of advanced glycation end products

Enhanced oxidative stress is involved in the progression of renal disease. Since angiotensin converting enzyme inhibitors (ACEI) have been shown to improve the antioxidative defence, we investigated, in patients with nondiabetic nephropathy, the short-term effect of the ACEI ramipril on parameters of oxidative stress, such as advanced glycation end products (AGEs), advanced oxidation protein products (AOPPs), homocysteine (Hcy), and lipid peroxidation products. Ramipril (2.5-5.0 mg/day) was administered to 12 newly diagnosed patients for 2 months and data compared with a patient group under conventional therapy (diuretic/beta-blockers) and with age- and sex-matched healthy subjects (CTRL). Patients had mild to moderate renal insufficiency and showed, in the plasma, higher fluorescent AGE and carboxymethyllysine (CML) levels, as well as elevated concentrations of AOPPs, lipofuscin and Hcy when compared with CTRL. Basal data of the patients on conventional therapy did not differ significantly from the ramipril group, except for higher Hcy levels in the latter. Administration of ramipril resulted in a drop in blood pressure and proteinuria, while creatinine clearance remained the same. The fluorescent AGEs exhibited a mild but significant decline, yet CML concentration was unchanged. The AOPP and malondialdehyde concentrations decreased, while a small rise in neopterin levels was evident after treatment. The mentioned parameters were not affected significantly in the conventionally treated patients. Evidence that ramipril administration results in a mild decline of fluorescent AGEs is herein presented for the first time. The underlying mechanism may be decreased oxidative stress, as indicated by a decline in AOPPs and malondialdehyde.

[Therapy of hyperhomocysteinemia with vitamin B12]

Prevalence of mild hyperhomocysteinemia in vegetarians and vegans is a consequence of vitamin B12 deficiency. Clinical study of homocysteine reduction by vitamin B12 consisted of subjective healthy adults on alternative nutrition (n = 9) with vitamin B12 deficiency and with mild hyperhomocysteinemia. Vitamin B12 treatment was implemented by 5 intramuscular cyanocobalamin injections of a total content of 2200 micrograms during two weeks. Homocysteine level was significantly reduced (from 22 mumol/l to 11.7 mumol/l; individual reduction 29-55%). Vitamin B12 concentration in blood was significantly increased (from 152 pmol/l to 277 pmol/l; individual % of increase 63-150). The results show a high effect of vitamin B12 treatment in homocysteine value reduction of subjects on alternative nutrition.

[Nutritional determinants of homocysteinemia]

BACKGROUND

Vitamin B12, folate and vitamin B6 are the main determinants of homocysteinemia. These B-group vitamins influence two metabolic pathways of homocysteine reduction, which prevail in dependence to methionine intake. Transsulfuration (vitamin B6) dominates under condition of overnutrition with prevalence of animal food sources, remethylation (vitamin B12 and folic acid) is decisive under conditions of malnutrition, alternative nutrition or optimal traditional diet.

METHODS AND RESULTS

Plasma homocysteine and folic acid, vitamins B12 and B6 in serum were measured in alternative nutrition groups of adults (vegans, vegetarians (lacto + lactoovo), semivegetarians, n = 39) and compared with those values in group consuming traditional diet--control group, general population (n = 35). In alternative nutrition groups, the average homocysteine level is significantly higher (vegans 17.2 mumol/l, vegetarians 12.9 mumol/l, semivegetarians 10.1 mumol/l, control group 9.9 mumol/l); the frequency of hyperhomocysteinemia (over 15 mumol/l) is 50%, 32%, 14% vs. 6% in control group. Vegetarians and vegans have a significantly higher levels of vitamin B6 and folic acid; the frequency of vitamin B6 deficit is 60% and 57% in control group and semivegetarian group vs. 16% and 0% in vegetarian and vegan group. Folate deficit was found in 16% of traditional group vs. 0% in alternative groups. Serum levels of vitamin B12 are significantly reduced in subjects consuming alternative nutrition with deficiency observed in 67% of vegans, 32% of vegetarians, 14% of semivegetarians vs. 0% in control group.

CONCLUSIONS

Vitamin levels in relation to nutritional regime and metabolic pathways of homocysteine show that the mild hyperhomocysteinemia in alternative nutrition is a consequence of vitamin B12 deficiency. In traditionally fed population, higher plasma homocysteine values is caused by folate deficiency. These conclusions are supported by a significantly negative linear correlation of homocysteine--folic acid levels (traditional nutrition) and homocysteine--vitamin B12 levels (alternative nutrition). In case of vitamin B6, a similar correlation was not found.

[Changes in serum levels of lipid peroxidation products during labor and in the puerperium]

OBJECTIVE

To determine the activity of reactive oxygen species (ROS) during labour by characterizing changes in maternal serum levels of lipid peroxidation end-products--MDA and lipofuscin during labour and the early post-partum period. We also tried to evaluate the relationship between levels of lipid peroxides and some clinical characteristics of labour.

DESIGN

Prospective study.

SETTING

Department of Obstetrics and Gynaecology LFUK, Bratislava; Department of clinical laboratories, Ministry of defense SR, Bratislava.

METHODS

Blood samples were obtained from 66 pregnant women with uncomplicated pregnancy at the end of labour and during the early post-partum period. The control group consisted of 19 pregnant women delivering by primary Cesarean section. Blood samples were examined for MDA and lipofuscin by HPLC method. We used paired and unpaired Student's t-test to statistically evaluate our results.

RESULTS

MDA and lipofuscin levels in pregnant women delivering spontaneously compared to those delivering by C-section were significantly elevated (P < 0.05). MDA and lipofuscin levels in pregnant women during spontaneous labour or during by C-section compared to the levels in early post-partum period were not significantly increased. We have not found any correlation between the length of the labour and lipoperoxides concentration.

Plasma levels of advanced glycation end products in children with renal disease

In adults, advanced glycation end products (AGEs) rise slowly in tissues and circulation during aging, and accumulate at an accelerated rate both in diabetes and chronic renal insufficiency (CRI). We aimed to investigate the pattern of AGE accumulation in children/adolescents with CRI and on renal replacement therapy by dialysis and transplantation. Concentrations of fluorescent AGEs, carboxymethyllysine (CML) and lipofuscin-like substance (LFLS, a marker of lipid peroxidation) were followed. Data were obtained from 11 CRI patients on conservative treatment (age 12.6+/-1.7 years, serum creatinine: 205.7+/-17.5 micromol/l), ten patients on renal replacement therapy with dialysis (13.6+/-1.7 years, 698.2+/-48.9 micromol/l) and nine patients after kidney transplantation (15.9+/-1.1 years, 115.9+/-12.0 micromol/l) and comparison made with the data from 28 healthy controls (11.8+/-8.2 years, 44.1+/-8.2 micromol/l). In controls, an age-dependent rise of fluorescent AGE and CML levels was observed. In the CRI group, fluorescent AGEs [0.38+/-0.03x105 arbitrary units (AU)] and CML (369+/-26 ng/ml) concentrations were doubled compared with controls (0.16+/-0.03x105 AU and 189+/-42 ng/ml, respectively) and even higher levels were revealed in dialyzed patients (0.80+/-0.05x105 AU; 650+/-94 ng/ml). Successful kidney transplantation significantly reduced but did not normalize fluorescent AGE levels (0.39+/-0.03 x105 AU), while the decline in CML levels (550+/-47 ng/ml) was insignificant. Plasma LFLS was elevated in CRI (19.6+/- 1.7 AU) and was even higher in dialyzed children (32.0+/-5.3 AU) compared with healthy controls (7.1+/- 1.4 AU). Kidney transplantation did not normalize LFLS levels (20.3+/-5.3 AU), pointing to persistently enhanced lipid peroxidation. Our study provides the first data on enhanced fluorescent AGEs and CML levels in children/adolescents with CRI and on dialysis. Successful renal transplantation decreased but did not normalize AGE levels, probably because of still-impaired renal function with enhanced oxidative stress, as well as the influence of immunosuppressive therapy.

Glutathione S-transferase polymorphisms influence the level of oxidative DNA damage and antioxidant protection in humans

Glutathione S-transferase genotypes GSTT1, GSTM1, GSTP1 were characterised in 155 middle-aged men and compared with parameters of oxidative stress at the level of DNA and lipids, with antioxidant enzymes, and with plasma antioxidants in smokers and non-smokers. Smokers had on average significantly lower levels of Vitamin C, beta-carotene and beta-cryptoxanthin and higher amounts of oxidised purines and pyrimidines in lymphocyte DNA. The GSTM1 null genotype was associated with elevated glutathione as well as with higher Vitamin C concentration in plasma. Vitamin C was higher in GSTT1+ compared with GSTT1 null--as was glucose-6-phosphate dehydrogenase activity. The homozygous GSTP1 a/a genotype was associated with significantly higher levels of GST activity measured in lymphocytes, in comparison with the b/b genotype. Using multifactorial statistical analysis we found significant associations between smoking, GSTP1 genotype, plasma Vitamin C, and purine base damage in lymphocyte DNA. The difference in Vitamin C plasma levels between smokers and non-smokers was seen only with the GSTP1 b/b genotype. This group accounted also for most of the increase in purine oxidation in smokers. In contrast, the link between smoking and oxidised pyrimidines in DNA was seen only in the GSTT1 null group. It seems that polymorphisms in the phase II metabolising enzyme glutathione S-transferase may be important determinants of commonly measured biomarkers.

Influence of age on activities of antioxidant enzymes and lipid peroxidation products in erythrocytes and neutrophils of Down syndrome patients

Thirty-seven individuals with Down syndrome (DS) were divided into four age categories: (i) 1 to < 6 years, (ii) 6 to < 13 years, (iii) 13 to < 20 years, and (iv) over 20 years. Activities of antioxidant enzymes found in individual age categories were different, but the differences between age groups were not statistically significant. We confirmed significantly higher activities of Cu/Zn superoxide dismutase (SOD) and glutathione peroxidase (GPx) in blood cells of people with DS as compared to 35 controls, which consisted, for the first time, of siblings of children with DS. No significant differences were found in activities of catalase and glutathione reductase in DS vs. controls. A significant difference was observed in serum concentration of malondialdehyde (MDA) in DS vs. controls (8.39 +/- 0.34 micromol/l vs. 7.34 +/- 0.27 micromol/l; p = .021) and concentration of MDA in erythrocytes of individuals with DS between the third and fourth age group (p = .05). In DS persons, an elevated ratio of SOD to catalase plus GPx with respect to the controls in all age categories was found, suggesting oxidative imbalance, potentially contributing to accelerated aging observed in these persons.

Effect of diet and 677 C-->T 5, 10-methylenetetrahydrofolate reductase genotypes on plasma homocyst(e)ine concentrations in slovak adolescent population

The objective of this study was to evaluate the effect of diet and 677 C-->T mutation of the methylenetetrahydrofolate reductase (MTHFR) gene on plasma homocyst(e)ine concentrations in an adolescent population (113 males, age: 14.2+/-2.4 years; 202 females, age: 14.9+/-2.1 years) from a region characterized by high cardiovascular mortality. Homocyst(e)ine levels did not differ between males and females (9.4+/-3.5 and 8.9+/-3.1 micromol/l, respectively). The homozygosity for the 677 C-->T MTHFR mutation was found in 4.6 % of subjects. No differences in homocyst(e)ine levels were found between MTHFR genotypes. Analysis of the diet composition which was performed on a 24-hour daily recall basis and a food frequency questionnaire showed a low daily intake of vitamin B6 (males: 1.13 mg/66% RDA; females: 0.92 mg/61% RDA). Daily folic acid intake was 0.21 g/105% RDA in males and 0.23 g/115% RDA in females. The results of our study show that the high homocyst(e)ine levels in the adolescent population were not affected by the 677 C-->T MTHFR mutation. We conclude that an insufficient dietary intake of vitamin B6 and folic acid is responsible for this finding. This is in accord with the recommendation that the dietary allowances for folate should be reset to the originally prescribed levels of 0.4 g/day which should be sufficient to control the homocysteine levels.

[Increased levels of circulating advanced glycation end products in a model of acute renal insufficiency in rats]

BACKGROUND

Advanced glycation end products (AGEs) are formed from proteins and peptides by non-enzymatic glycation or glycooxidation. AGEs are formed slowly during aging, and they accumulate in circulation and tissues in diabetes and chronic renal failure. Kidney plays a key role in the disposal of AGEs. Aim of this study was to verify the hypothesis that, acute loss of renal function with enhanced oxidative and carbonyl stress should result in a rise of circulating AGEs levels.

METHOD AND RESULTS

Acute renal failure (ARI) was induced in rats by bilateral nephrectomy (24-72 hours). The data on AGEs levels, oxidative status and antioxidative defense was compared to those of sham operated animals. 48 hours after the induction of ARI concentrations of AGEs, determined fluorimetrically or as carboxymethyllysine, rose 2-fold, and they correlated with concentrations of creatinine (r = 0.938, p < 0.001 and r = 0.815, p < 0.001, respectively). Malondialdehyde (MDA) and lipofuscine (LF) concentrations rose in a time dependent manner, suggesting an enhanced oxidative and carbonyl stress. Enhanced lipid peroxidation did not result from the suppressed antioxidant defense: activity of superoxide dismutase rose by 50%, while that of glutathione peroxidase was not compromised. Total antioxidant status increased, probably due to the accumulation of uremic toxins with scavenging capacity, such as hyppurate.

CONCLUSIONS

According to our knowledge our data was first to show a rapid increase in circulating AGEs concentrations in the model of acute renal failure in rats. If AGEs accumulate in acute renal failure in humans, their contribution to acute toxicity, and/or to the development of later complications, might be of a great importance.

Insulin, catecholamines, glucose and antioxidant enzymes in oxidative damage during different loads in healthy humans

Exercise, insulin-induced hypoglycemia and oral glucose loads (50 g and 100 g) were used to compare the production of malondialdehyde and the activity of antioxidant enzymes in healthy subjects. Twenty male volunteers participated in the study. Exercise consisted of three consecutive work loads on a bicycle ergometer of graded intensity (1.5, 2.0, and 2.5 W/kg, 6 min each). Hypoglycemia was induced by insulin (Actrapid MC Novo, 0.1 IU/kg, i.v.). Oral administration of 50 g and 100 g of glucose was given to elevate plasma glucose. The activity of superoxide dismutase (SOD) was determined in red blood cells, whereas glutathione peroxidase (GSH-Px) activity was measured in whole blood. The concentration of malondialdehyde (MDA) was determined by HPLC, catecholamines were assessed radioenzymatically and glucose was measured by the glucose-oxidase method. Exercise increased MDA concentrations, GSH-Px and SOD activities as well as plasma noradrenaline and adrenaline levels. Insulin hypoglycemia increased plasma adrenaline levels, but the concentrations of MDA and the activities of GSH-Px and SOD were decreased. Hyperglycemia increased plasma MDA concentrations, but the activities of GSH-Px and SOD were significantly higher after a larger dose of glucose only. Plasma catecholamines were unchanged. These results indicate that the transient increase of plasma catecholamine and insulin concentrations did not induce oxidative damage, while glucose already in the low dose was an important triggering factor for oxidative stress.

Homocysteine levels in vegetarians versus omnivores

Vitamin B(12), folate, and vitamin B(6) are the main determinants of homocysteinemia. The vegan diet provides no vitamin B(12), but also less strict forms of alternative nutrition may suffer from a deficit of this vitamin. The plasma homocysteine level was measured in alternative nutrition groups of adults (lacto- and lactoovovegetarians, n = 62; vegans, n = 32) and compared with the levels in a group consuming traditional diet (n = 59), omnivores). In the group of vegetarians the average homocysteine level is 13.18 vs. 10.19 micromol/l in omnivores; the frequency of hyperhomocysteinemia is 29 vs. 5% in omnivores. In the group of vegans the average homocysteine value is 15.79 micromol/l (53% of the individual values exceeded 15 micromol/l). Omnivores consume the recommended amount of methionine; however, in individuals consuming an alternative diet, the intake of methionine is deficient (assessed by food frequency questionnaire; lower content of methionine in plant proteins). Under conditions of lower methionine availability the remethylation pathway prevails; therefore, vitamin B(12) and folate were evaluated in relation to the homocysteine level. The serum vitamin B(12) levels are significantly lower in the alternative nutrition groups (214.8 pmol/l in vegetarians, 140.1 pmol/l in vegans vs. 344.7 pmol/l in omnivores); a deficit (<179.0 pmol/l) was found in 26% of the vegetarians and in 78% of the vegans vs. 0% in omnivores. The serum folate levels were within the range of reference values in all groups; however, they were significantly lower in omnivores. The results show that the mild hyperhomocysteinemia in alternative nutrition is a consequence of vitamin B(12) deficiency.

DNA damage of lymphocytes in experimental chronic renal failure: beneficial effects of losartan

BACKGROUND

Kidney diseases are associated with the accumulation of various uremic toxins increasing the oxygen free radical (OFR) activity with a number of serious consequences. One of them could be the impairment of DNA stability with the increased formation of DNA breaks.

METHODS

The study was performed in 4/6 kidney ablation rat nephropathy lasting for three months. The results of sham-operated (Sham), remnant kidney (Nx), and Nx treated by losartan (NxL) were compared.

RESULTS

Nx significantly increased blood pressure, plasma creatinine, urea, hippurate, malondialdehyde (MDA), lipofuscin (LF), and the number of DNA breaks of lymphocytes. Losartan decreased the rise of blood pressure and inhibited the rise of creatinine plasma concentration but not of other variables, while it markedly inhibited the number of DNA breaks (Sham 15.9 +/- 1.1, Nx 54.5 +/- 1.7, P < 0.001; Nx/Sham, NxL 23.3 +/- 2.6 P < 0.001, NxL/Sham and P < 0.001 NxL/Nx).

CONCLUSIONS

The 4/6 kidney ablation nephropathy increases the susceptibility of lymphocyte DNA to breaks, and losartan inhibits the number of breaks by a mechanism independent on glomerular filtration, accumulation of MDA or LF (markers of oxidative stress), and hippurate (marker of the accumulation of middle molecular substances). An independent mechanism, probably the interference with proliferation, is suggested.

Circulating advanced glycation end product levels in rats rapidly increase with acute renal failure

BACKGROUND

Advanced glycation end products (AGEs) are formed on proteins and peptides slowly during aging, and they accumulate in circulation and tissues in diabetes and chronic renal failure. Except for nonenzymatic glycation, enhanced oxidative/carbonyl stress is supposed to participate in their formation. The kidney plays a key role in disposal of AGEs, particularly AGE-peptides. We assumed that even a short time combination of enhanced oxidative/carbonyl stress and a lack of renal function should result in elevation of circulating AGE levels.

METHOD

To verify this hypothesis, two models of acute renal failure in rats, bilateral nephrectomy and bilateral ureteral ligation, were employed, and the data were compared with those of sham-operated animals.

RESULTS

AGE levels determined fluorimetrically or as carboxymethyllysine concentration rose by a factor of three within 48 hours. Enhanced levels of malondialdehyde and lipofuscin pointed to an enhanced oxidative/carbonyl stress. Activity of antioxidant enzymes such as superoxide dismutase and glutathione peroxidase were not compromised, or were even elevated, respectively. Total antioxidant status increased, probably as a consequence of an accumulation of indols and benzoic acid derivatives, uremic toxins with scavenging capacities, as shown for hippurate.

CONCLUSIONS

Evidence was given that circulating AGEs in the model of acute renal failure in rats undergo a substantial rise within a short time period. A source of increased AGEs is not clear, since except for the lack of the kidney function, accelerated synthesis of AGEs under enhanced oxidative/carbonyl stress as well as liberation of AGEs from tissues due to protein catabolism might be anticipated. If AGEs accumulate in acute renal failure in humans, their contribution to acute toxicity, or of the development of the complications later, might be of importance.

Traditional and alternative nutrition--levels of homocysteine and lipid parameters in adults

Values of homocysteine and lipid parameters were measured in groups of adults consuming alternative nutrition (vegetarians/lactoovo/, vegans) and compared with a group consuming traditional diet (omnivores, general population). Frequency of hyperhomocysteinemia was 53% in the vegans group, 28% in vegetarians vs. 5% in omnivores. In conditions of lower methionine intake (reduced content in plant proteins), the remethylation pathway of homocysteine metabolism prevails and it is vitamin B12 and folate-dependent. The intake of vitamin B12 is equal to zero in vegans; vegetarians consume 124% of the RDA vs. 383% in omnivores. Serum vitamin levels are significantly lower in subjects consuming alternative nutrition with deficiency observed in 24% of vegetarians, 78% of vegans vs. 0% in omnivores. Serum folate levels are within the reference range in all groups. Mild hyperhomocysteinemia in the groups consuming alternative diet is a consequence of vitamin B12 deficiency. Vegetarians and vegans meet the RDA for energy and fat, and have a favourable proportion of saturated, mono- and polyunsaturated fatty acids on total energy intake; the ratio of linoleic/alpha-linolenic acid in their diet corresponds with the recommendations. They have low cholesterol consumption and higher vitamin E and C intake. Optimal fat intake of correct composition is reflected in lower values of atherosclerosis risk factors (cholesterol, LDL-cholesterol, atherogenic index, saturated fatty acids, triacylglycerols), and significantly higher levels of protective substances (linoleic acid, alpha-linolenic acid, HDL-cholesterol, vitamin E, vitamin E/cholesterol, vitamin C). Low lipid risk factors but higher findings of mild hyperhomocysteinemia in vegetarians mean a diminished protective effect of alternative nutrition in cardiovascular disease prevention.

Influence of food restriction on dopamine receptor densities, catecholamine concentrations and dopamine turnover in chicken brain

To investigate further a putative role of dopamine in control of food restriction-induced behavioural stereotypies, chickens were fed during rearing on either a daily restricted ration recommended by a breeding company, twice the recommended restricted ration, or ad libitum food. They were killed at 60 days of age and their excised brains were dissected into six regions and homogenized. Densities of dopamine D1 and D2 receptors were assessed, after first estimating binding parameters for [3H]SCH 23390 (D1) and [3H]spiperone (D2) in chicken brain homogenates. Specific binding of both ligands was highest in basal telencephalon. Concentrations of dopamine and its metabolites 3,4-dihydroxyphenylacetic acid and homovanillic acid were also highest in basal telencephalon, whereas noradrenaline and adrenaline levels were highest in diencephalon. Dopamine concentration in basal telencephalon and noradrenaline concentration in diencephalon were increased significantly in response to food restriction, but no effect of feeding treatment was found in dopamine turnover, adrenaline levels, or D1 and D2 receptor densities in any brain region studied. The observed changes in brain catecholamine levels are consistent with roles for dopaminergic and adrenergic mechanisms in the control of food restriction-induced behavioural stereotypies in chickens.

Melatonin content in plasma and large intestine of patients with colorectal carcinoma before and after surgery

The distinct melatonin rhythm with higher concentrations during the darktime was found in plasma of both control patients and patients with colorectal carcinoma. Moderate surgery did not induce any changes in plasma melatonin levels, but a pronounced increase in both the day- and nighttime melatonin concentrations was found after surgical treatment for colon cancer. The melatonin content in the tumor tissue did not differ from that in the proximal and the distal parts of the resected gut, which were without signs of malignant changes. Neither concentrations of serotonin nor 5-hydroxyindole acetic acid differed among analyzed parts of the gut. Daytime melatonin concentrations in gut tissue (314.7 +/- 87.8 pg/g of wet tissue) were more than ten times higher than the daytime levels in circulation. It was hypothesized that increased levels of this hormone in the gastrointestinal tract may play an important protective role against the development of colorectal cancer via stimulation of the immune system, protection against free radicals, and interaction with fatty acid uptake and metabolism.

Effects of exogenous melatonin on some endocrine, behavioural and metabolic parameters in Japanese quail Coturnix coturnix japonica

1. Melatonin administration in drinking water (5 micrograms/ml) to Japanese quail resulted in a 20-fold increase of plasma melatonin levels in comparison with the control, day time concentration (0.34 +/- 0.05 vs 6.88 +/- 1.10 nmol/l). 2. Plasma triiodothyronine levels increased (5.8 +/- 0.93 vs 7.97 +/- 0.64 nmol/l), corticosterone decreased (28.04 +/- 3.42 vs 15.96 +/- 2.56 nmol/l) and no significant changes were recorded in thyroxine concentration after the treatment. 3. A higher occurrence of sleeping and lower occurrence of pecking were found in melatonin treated quail. 4. Abdominal fat deposition as well as the content of total lipids in the breast muscle and triacylglycerols in plasma were decreased in treated birds indicating an inhibitory effect of melatonin on lipogenesis. 5. Melatonin increased RNA content in the breast muscle but did not affect plasma glucose concentration and body weight.

Modulation of rat testicular LH/hCG receptors by membrane lipid fluidity

The specific binding of [125I]hCG to rat testicular membrane preparations was investigated as a function of membrane fluidity changed by lipids. Membrane fluidity was measured either by fluorescence depolarization of diphenylhexatriene or ESR spectra of I(1,14), I(12,3) and CAT 16 incorporated into the membrane. Incubation of membrane with cholesteryl-hemisuccinate increased both the rigidity of membrane lipids and the specific binding of [125I]hCG. A similar rigidifying action of saturated fatty acids was, however, not accompanied by increased accessibility of LH/hCG receptors. Treatment of testicular membranes with unsaturated fatty acids enhanced membrane fluidity but specific binding of the gonadotropin disappeared. In spite of the increase of LH/hCG receptors in cell membranes treated with cholesteryl-hemisuccinate, Leydig cells showed decreased sensitivity to cAMP response to LH stimulation. The results indicate that newly exposed LH/hCG receptors are not coupled with the adenylate cyclase system.

Influence of cholesterol and unsaturated fatty acids on [125I]hCG binding to rat testicular membranes

Incubation of testicular membranes with cholesteryl-hemisuccinate resulted in an increase of both the membrane microviscosity and [125I]hCG specific binding. 14C-labelled cholesterol as well as fatty acids were effectively incorporated into membrane preparations. Insertion of unsaturated fatty acids (cis-vaccenic, linoleic, oleic, linolenic and arachidonic) into the membrane decreased its microviscosity under simultaneous disappearance of [125I]hCG specific binding. The latter phenomenon seems to be caused by an increase of nonspecific binding which was not due to the uptake of radio-activity from labelled gonadotropin by fatty acids or double bonds of fatty acids incorporated into testicular membranes or taken up by a resin Amberlite IRA-400. The disappearance of specific binding of [125I]hCG by the fluidizing action of unsaturated fatty acids can be reversed by the subsequent action of cholesterol.