Direct oral anticoagulants compared to vitamin K antagonists for the treatment of left ventricular thrombi

Background

Left ventricular thrombus (LVT) complicates around one in six cases of acute and chronic left ventricular systolic dysfunction and is associated with an increased risk of stroke, major systemic embolism and death, believed to be ameliorated by anticoagulation. Off-label use of direct oral anticoagulants (DOACs) for LVT has steadily increased, largely based on favourable outcomes in atrial fibrillation and venous thromboembolism, but the safety and efficacy of DOACs versus vitamin K antagonists (VKA) for LVT remains uncertain.

Purpose

The main aim of our study was to compare treatment of LVT with VKA to DOAC, focusing on all-cause mortality, stroke, major systemic emboli and major bleeding.

Methods

We conducted a retrospective observational longitudinal study of patients presenting to two large quaternary centres between 2011 and 2021 with a diagnosis of LVT. Patients were eligible if they had a documented LVT and received anticoagulation with either VKA or DOAC. Baseline data, thrombus characteristics, treatment type and duration, follow up imaging and clinical events were recorded using electronic health care records. Outcome measures included thrombus resolution, stroke and systemic embolism (SSE), major bleeding and mortality.

Results

A total of 955 patients were identified, of whom 901 received treatment with either a VKA (567 pts, 62.9%) or a DOAC (334 pts, 37.1%) and were included in the analysis. Underlying aetiologies included acute myocardial infarction (AMI) (38.3%), chronic ischaemic cardiomyopathy (38.0%) and non-ischaemic cardiomyopathy (23.7%). Rivaroxaban (43.4%) was the most frequently prescribed DOAC followed by apixaban (35.9%), and the remaining on edoxaban (20.7%). AMI related LVT was more commonly treated with DOAC (53.0%) and chronic ischaemic cardiomyopathy with VKA (72.9%).

There was a lower baseline LVEF in the VKA cohort (29.5±13.2 vs 33.1±14.2, p<0.0001). Other demographic features were comparable. Median follow up was 2.5 years (IQR: 1–3.5). There were no differences in follow up duration between the two treatments (p=0.17). Greater rates of thrombus resolution were seen in the DOAC group compared to VKA (1 year: 78.4% vs 51.4%, p<0.0001), with higher rates of persistent thrombus over the follow-up period seen in the VKA group (25.1% vs 12.9%, p<0.0001). Rates of stroke and systemic embolization were similar between the groups (VKA 9.3% vs 9.6% DOAC, p=0.93). Higher rates of bleeding (BARC >3, 8.1% VKA, 3.6% DOAC, p=0.031) (Figure 1A) and mortality (VKA 18.5%, DOAC 10.2%, p=0.001) (Figure 1B) were seen in the VKA group over the follow-up period.

Conclusions

In a large multi-centre registry of LVT of mixed aetiology, anticoagulation with DOAC was associated with earlier and greater rates of thrombus resolution and consequential reduced adverse events (major bleeding and mortality) during follow up. A funding application to support a multi-centre randomised control trial is underway.

Funding Acknowledgement

Type of funding sources: Other. Main funding source(s): This work was supported by the British Heart Foundation (Fellowship FS/CRTF/21/24190 to HM) and the National Institute for Health Research (Biomedical Research Centre Award to Guy's and St Thomas' NHS FT and King's College London).

Subtotal colectomy and ileorectal anastomosis for slow transit constipation: clinical follow-up at median of 15 years

BACKGROUND

Slow transit constipation is characterised by prolonged colonic transit and reliance on laxatives. The pathophysiology is poorly understood and in its most severe form, total colectomy with ileorectal anastomosis is the final treatment option. We present a follow-up study of the long-term function in patients who had surgery for laxative-resistant slow transit constipation.

METHODS

A postal survey was sent to assess bowel frequency, abdominal pain, St Mark's continence score, satisfaction with procedure, likelihood to choose the procedure again, and long-term rates of small bowel obstruction and ileostomy. Longitudinal data from a subgroup studied 23 years previously are reported.

RESULTS

Forty-two patients (male = 2) were available for follow-up out of an initial cohort of 102. Mean time since surgery was 15.9 years (range 1.7-29.7) years. Fifty percent had < 4 bowel motions per day, most commonly Bristol stool 6, mean St Mark's score 7.45. Twenty-one percent had severe incontinence. Satisfaction and likelihood to choose surgery were high (median 10/10). There was a high rate of small bowel obstruction, suggesting pan-intestinal dysmotility in some cases. Conversion to ileostomy occurred in 8 patients. In the longitudinal follow-up in 15 subjects, continence deteriorated (p < 0.01), stool consistency softened (p < 0.01), and stool frequency fell (p < 0.01).

CONCLUSIONS

Satisfactory stool frequency was achieved in the long term, and although 21% had incontinence scores > 12, patient satisfaction was high. This is the longest reported follow-up of colectomy for slow transit constipation, with longitudinal outcomes reported. There was considerable attrition of patients, so larger, longitudinal studies are required to better ascertain the functional outcomes of these patients.

Two-dimensional receptor patterns in the plasma membrane of cells. A critical evaluation of their identification, origin and information content

A concise review is presented on the nature, possible origin and functional significance of cell surface receptor patterns in the plasma membrane of lymphoid cells. A special emphasize has been laid on the available methodological approaches, their individual virtues and sources of errors. Fluorescence energy transfer is one of the oldest available means for studying non-randomized co-distribution patterns of cell surface receptors. A detailed and critical description is given on the generation of two-dimensional cell surface receptor patterns based on pair-wise energy transfer measurements. A second hierarchical-level of receptor clusters have been described by electron and scanning force microscopies after immuno-gold-labeling of distinct receptor kinds. The origin of these receptor islands at a nanometer scale and island groups at a higher hierarchical (mum) level, has been explained mostly by detergent insoluble glycolipid-enriched complexes known as rafts, or detergent insoluble glycolipids (DIGs). These rafts are the most-likely organizational forces behind at least some kind of receptor clustering [K. Simons et al., Nature 387 (1997) 569]. These models, which have great significance in trans-membrane signaling and intra-membrane and intracellular trafficking, are accentuating the necessity to revisit the Singer-Nicolson fluid mosaic membrane model and substitute the free protein diffusion with a restricted diffusion concept [S.J. Singer et al., Science 175 (1972) 720].

The modulation of intracellular glutathione level modulates the mitochondrial response in proliferating rat splenocytes

We have investigated the effect of intracellular reduced glutathione (GSH) levels on the mitochondrial parameters of proliferating rat splenocytes. The intracellular GSH content of the cells was altered by continuous culture with buthionine-S, R-sulfoximine (BSO), a specific inhibitor of GSH synthesis. BSO decreased the GSH levels, inhibited DNA synthesis and caused depolarization of mitochondria in 52% of cells stimulated to proliferate for 72 h. These data support the proposition that GSH influences the lymphocyte proliferation at more than one site, one of which is the energy producing machinery.

Melatonin is an efficient antioxidant

We have compared the peroxyl radical scavenger ability of melatonin with that of vitamin E, ascorbic acid (As.A.), reduced glutathione (GSH) and mannitol. All the antioxidants, except mannitol, prevented the lysis of human erythrocytes exposed to an azo-initiator of peroxyl radicals (2,2'-azo-bis(2-amidinopropane)dihydrochloride) at 37 degrees C. The percentage of this inhibition of erythrocyte lysis varied with the concentration of antioxidants, but the efficiency was melatonin > vitamin E > As.A. > GSH. Based on the assumption that each molecule of vitamin E scavenges two peroxyl radicals, the scavenging capacity of melatonin was four peroxyl radicals/molecule.

Food restriction in female Wistar rats. VI. Effect of reduced glutathione on the proliferative response of splenic lymphocytes from ad libitum fed and food restricted animals

The effect of reduced glutathione (GSH) on the proliferative response of splenic lymphocytes from young, adult and old ad libitum (AL) fed as well as from old food-restricted rats was investigated. Food restriction was applied on an every-other-day schedule (EOD) starting from the age of 3.5 months. As was expected, the cells from EOD fed animals responded to concanavalin A (Con A) much better than those from age-matched ad libitum fed rats. The presence of the antioxidant GSH in the culture medium increased the response of lymphocytes in all the models taken into account; furthermore, it decreased the differences due to aging and application of food restriction. According to present knowledge, mitogenic stimulation induces free radical production, and GSH has, among others, a strong antioxidant activity. Thus, present data suggest that splenocytes from EOD animals tolerated the peroxidative stress resulting from mitogenic stimulation better than those from AL fed ones.

The c-myc gene regulates the polyamine pathway in DMSO-induced apoptosis

It is accepted that apoptosis is a gene-controlled process of cellular self-destruction. It occurs during physiological regulation and in pathological situations in the life of a cell. In the immune system, several different intracellular and extracellular factors have been associated with the induction of apoptosis, and the final responses depend on the cell system and the acquired signals. In lymphoid cells, dexamethasone-induced apoptosis is associated with c-myc downregulation in cells that remain in G0-G1 until the point of death. Ornithine decarboxylase (ODC), a key enzyme involved in polyamine biosynthesis, is regulated by c-myc, which is a transcriptional activator implicated not only in the control of cell proliferation and differentiation but also in programmed cell death. As dimethylsulphoxide (DMSO) induces apoptosis in the RPMI-8402 human pre-T cell line, the present study analysed the involvement of the c-myc proto-oncogene and polyamine pathway as mediators of apoptosis. Cell growth, programmed cell death, c-myc expression, ODC activity and intracellular polyamine content were detected after DMSO and difluoromethylornithine (DFMO) treatment. DMSO-treated cells exhibit a decrease in ODC activity and polyamine levels associated with cell growth arrest and programmed cell death induction. The expression of c-myc proto-oncogene, as its mRNA or protein, is specifically down-regulated. DFMO, a well defined polyamine biosynthesis inhibitor, completely blocks ODC activity, resulting in growth inhibition but not apoptosis. Moreover, in these samples no evidence of changes of c-myc expression were found. The results obtained suggest that, in RPMI-8402 cells, DMSO provokes a c-myc-dependent decrease of ODC activity followed by a depletion of intracellular polyamine levels, associated with programmed cell death and cell growth arrest.

A gender--dependent genetic predisposition to produce high levels of IL-6 is detrimental for longevity

Current literature indicates that elevated IL-6 serum levels are associated with diseases, disability and mortality in the elderly. In this paper, we studied the IL-6 promoter genetic variability at -174 C/G locus and its effect on IL-6 serum levels in a total of 700 people from 60 to 110 years of age, including 323 centenarians. We found that the proportion of homozygotes for the G allele at -174 locus decreases in centenarian males, but not in centenarian females. Moreover, we found that, only among males, homozygotes for the G allele at -174 locus have higher IL-6 serum levels in comparison with carriers of the C allele. On the whole, our data suggest that those individuals who are genetically predisposed to produce high levels of IL-6 during aging, i.e. -174 locus GG homozygous men, are disadvantaged for longevity.

Relationship between lipoprotein(a) levels, oxidative stress, and blood pressure levels in patients with essential hypertension

High plasma levels of lipoprotein(a) [Lp(a)] are considered a risk factor for the development of coronary artery disease. In vitro experiments have shown that oxidized Lp(a) is able to impair the arterial endothelium-dependent dilation, thus suggesting a possible role of Lp(a) in the genesis of essential hypertension. The aim of our work was to investigate the correlation of blood pressure levels with plasma Lp(a) concentration, apo(a) isoform size, and peroxidative stress in patients with essential hypertension. The study was performed in 54 untreated hypertensive patients whose blood pressure was monitored for 24 h by ambulatory blood pressure monitoring. Lp(a) concentration was measured by a double monoclonal antibody-based enzyme immunoassay demonstrated to be insensitive to apo(a) size heterogeneity. Apo(a) isoforms were determined by a high-resolution SDS-agarose gel electrophoresis followed by immunoblotting. A significant correlation was found between Lp(a) levels and the night-time systolic and diastolic pressures (r=0.32, P<0.05 and r=0.30, P<0.05, respectively), as well as with the mean night-time fall in systolic and diastolic blood pressures (r=-0.28, P<0.05 and r=-0.29, P<0.05, respectively). These relationships were further potentiated when peroxidative stress data were taken into consideration (r=0.37 and r=0.40, P<0.01 for the night-time systolic and diastolic pressures, respectively and r=-0.34 and r=-0.38, P<0.01 for the night-time fall in systolic and diastolic blood pressures, respectively). Apo(a) isoform size did not affect these relationships. Our data suggest that Lp(a) and peroxidative stress may be involved as cofactors in essential hypertension, with a mechanism that remains to be elucidated.

A gender--dependent genetic predisposition to produce high levels of IL-6 is detrimental for longevity

Current literature indicates that elevated IL-6 serum levels are associated with diseases, disability and mortality in the elderly. In this paper, we studied the IL-6 promoter genetic variability at -174 C/G locus and its effect on IL-6 serum levels in a total of 700 people from 60 to 110 years of age, including 323 centenarians. We found that the proportion of homozygotes for the G allele at -174 locus decreases in centenarian males, but not in centenarian females. Moreover, we found that, only among males, homozygotes for the G allele at -174 locus have higher IL-6 serum levels in comparison with carriers of the C allele. On the whole, our data suggest that those individuals who are genetically predisposed to produce high levels of IL-6 during aging, i.e. -174 locus GG homozygous men, are disadvantaged for longevity.

Increase of homozygosity in centenarians revealed by a new inter-Alu PCR technique

In the present study a novel inter-Alu PCR technique that allows one to detect inter-individual differences in the genomic regions flanked by Alu repetitive sequences was developed. Two primers complementary to sequences present in different Alu repeats and marked with two different fluorochromes were used in the same PCR reaction, and the PCR products were separated and analyzed by capillary electrophoresis using an automatic sequencer. The method is highly reliable, and three patterns of peaks (QM376-400, QM780-790 and QM480) appeared to be representative for germ-line polymorphisms, as suggested by the results obtained in nine couples of monozygotic twins and four three-generation families. The frequency of these polymorphic peaks was studied in two different age groups (100 young subjects and 69 centenarians). In two out of the three regions (QM376-400 and QM480) a significant increase in homozygote genotypes frequency was observed in centenarians. These counterintuitive results suggest that increased homozygosity contributes to human longevity. This novel inter-Alu PCR approach could represent a valuable tool to identify longevity-associated DNA sequences interspersed throughout human genome, without making any a priori assumption about their nature and function.

Vitamin E intake reduces plasminogen activator inhibitor type 1 in T2DM patients

Previous studies hypothesised that vitamin E could protect against coronary heart disease and vascular complications in diabetes, but no studies have been performed regarding its eventual effects on fibrinolysis. Nevertheless, in Type 2 diabetes mellitus (T2DM) a profound reduction in the fibrinolytic activity has been demonstrated to be involved in vascular complications, probably due to plasminogen activator inhibitor type 1 (PAI-1) overproduction. On this basis we aimed to verify whether an antioxidant treatment with vitamin E is able to lower PAI-1 plasma levels in T2DM. Thirteen T2DM patients (9 males and 4 females; mean age+/-SD, 64.4+/-3.3 yr) were selected through strict admission criteria. These patients were treated with vitamin E (500 IU/die) for 10 weeks. Glyco-lipometabolic, oxidative and haemocoagulative parameters were evaluated at baseline and after 5, 10, 30 and 60 weeks. Vitamin E levels at different times were [median (interquartile range)] 6.1 (5.3-7.7), 8.5 (7.3-9.9), 9.7 (8.9-12.9), 5.6 (4.4-6.8), 5.7 (4.5-7.1) microg/ml, respectively. Significant differences were found for PAI-1 antigen (p=0.006), PAI-1 activity (p=0.028), apolipoprotein B (p=0.015) and antioxidant defence, evaluated as ferric reducing ability of plasma (FRAP) values (p=0.005). Particularly, decrements were detected for PAI-1 antigen between baseline and the 10th week (p<0.05), followed by an increase back to basal at the 30th week. Similar behaviour was found for PAI-1 activity. Regarding the antioxidant defence, FRAP values increased until the 30th week (p<0.05) with a decrease at the 60th week. These results demonstrate that vitamin E is able to lower PAI-1 levels in diabetic patients but this effect does not seem related to improvements of glycometabolic data or to the increase in FRAP values, suggesting that PAI-1 overproduction can be decreased by other effects of vitamin E on endothelial cells.

Serum paraoxonase is reduced in type 1 diabetic patients compared to non-diabetic, first degree relatives; influence on the ability of HDL to protect LDL from oxidation

Paraoxonase is a serum enzyme with an anti-oxidant function, protecting low density lipoproteins (LDL) from oxidative modifications. Diabetic patients are suggested to be at greater risk of oxidative stress, which may contribute to the significantly higher incidence of vascular disease in this population. Less efficient protection mechanisms may be one feature of the greater susceptibility to oxidation in diabetes. In this context, the present study examined the hypothesis that serum paraoxonase is reduced in type 1 (insulin-dependent) diabetic patients and that the reduction can affect the anti-oxidant capacity of HDL. Serum paraoxonase concentrations and activities were compared in type 1 patients and first degree, non-diabetic relatives with particular attention paid to the confounding effects of paraoxonase gene polymorphisms. In addition, the ability of HDL-paraoxonase to protect low density lipoproteins from oxidation was analysed in an in vitro system. Serum concentrations and enzyme activities of paraoxonase were significantly lower in type 1 patients compared to non-diabetic, first degree relatives. The differences were independent of promoter and coding region polymorphisms, which influence serum concentrations and activities of the enzyme. Overall, paraoxonase concentrations were a mean 13.3+/-4.5% lower (P<0.02) in type 1 patients. Specific activities did not differ between diabetic and non-diabetic groups. The concentration ratios of LDL cholesterol:paraoxonase (1.37+/-0.51 vs. 1.18+/-0.37, P=0.003) and apolipoprotein B:paraoxonase (0.84+/-0.33 vs. 0.71+/-0.40; P=0.012) were significantly higher in diabetic patients, consistent with a reduced capacity to protect LDL from oxidation. In vitro oxidation studies showed that a significantly higher level of lipid hydroperoxides was generated in LDL in the presence of HDL, containing paraoxonase levels equivalent to those of type 1 patients, compared to HDL containing paraoxonase levels equivalent to those of control subjects (mean difference 8.1%, P<0.05). The study demonstrates that serum concentrations of the antioxidant enzyme paraoxonase are significantly lower in type 1 (insulin-dependent) diabetic patients compared to non-diabetic, first-degree relatives, independently of known gene polymorphisms. Concentrations are reduced to an extent that can affect its anti-oxidant capacity. The results are consistent with the contention that modifications to serum paraoxonase in type 1 patients can increase risk of lipoprotein oxidation and, consequently, risk of vascular disease.

Multiple binding sites for melatonin on Kv1.3

Melatonin is a small amino acid derivative hormone of the pineal gland. Melatonin quickly and reversibly blocked Kv1.3 channels, the predominant voltage-gated potassium channel in human T-lymphocytes, acting from the extracellular side. The block did not show state or voltage dependence and was associated with an increased inactivation rate of the current. A half-blocking concentration of 1.5 mM was obtained from the reduction of the peak current. We explored several models to describe the stoichiometry of melatonin-Kv1.3 interaction considering one or four independent binding sites per channel. The model in which the occupancy of one of four binding sites by melatonin is sufficient to block the channels gives the best fit to the dose-response relationship, although all four binding sites can be occupied by the drug. The dissociation constant for the individual binding sites is 8.11 mM. Parallel application of charybdotoxin and melatonin showed that both compounds can simultaneously bind to the channels, thereby localizing the melatonin binding site out of the pore region. However, binding of tetraethylammonium to its receptor decreases the melatonin affinity, and vice versa. Thus, the occupancy of the two separate receptor sites allosterically modulates each other.

Age-dependent changes of serum oxygen radical scavenger capacity and haemoglobin glycosylation in non-insulin-dependent diabetic patients

BACKGROUND

Contradictory results have been reported in the literature concerning the correlation between glycosylated haemoglobin (HbA1c) and peroxidation level in serum of diabetic patients.

OBJECTIVE

To evaluate this correlation in type 2 diabetic patients by comparing the level of HbA1c with the oxygen radical absorbance capacity (ORAC(OH)) of serum.

METHODS

One hundred and five type 2 diabetic patients were enrolled for the study. After having obtained informed consent, venous blood samples were drawn after overnight fast at the time of routine diabetic check-ups. The blood was collected in plain and EDTA (1 mg/ml) tubes. Glycosylated haemoglobin (HbA1c) was determined by cation-exchange chromatography (HPLC), and spectrophotometric detection (Diamat Analyzer, BioRad). Serum was used for biochemical determinations performed by standard laboratory procedures and for ORAC(OH) analysis. This last parameter was determined measuring the loss of beta-phycoerytrin fluorescence due to oxidation by hydroxyl radicals generated by Cu(2+) and H(2)O(2), in the presence and absence of serum. Seventy-eight control age-matched subjects were obtained from the personnel staff of our Research Department and old healthy subjects, selected on the basis of Senieur Protocol, were relatives of the above mentioned personnel.

RESULTS

When the population of diabetic patients was taken as a whole, a decrease of ORAC(OH) has been observed compared to the controls. Moreover, negative correlations were found comparing ORAC(OH) either with HbA1c (r = -0.213; p = 0.029) and with the age of patients (r = -0.27; p = 0.005). To better understand the effect of age, the data were re-examined dividing the diabetics into two populations, i.e. under and over 65 years of age. An age-dependent decrease of ORAC(OH) and an increase in HbA1c levels has been observed comparing these two populations; however, the correlation between the two parameters remained statistically significant only in the oldest group (r = -0.31; p = 0.026).

CONCLUSIONS

Present data point to an involvement of oxidative stress in the glycation of haemoglobin especially in old diabetic patients, and provide support for the potential use of an antioxidant therapy in these patients, irrespective of their glycaemic control.

Nuclear matrix provides linkage sites for translocated NF-kappa B: morphological evidence

In response to the binding of extracellular ligands to cell surface receptors, multiple transcription factors are activated in the cytoplasm and translocated into the nucleus where they exert positive or negative control over cellular genes. The human transcription factor NF-kappa B family regulates the expression of a large number of genes involved in the host defence mechanism. They are typically present in the cytoplasm bound to the inhibitory I kappa B proteins. The activation of NF-kappa B involves the signal-induced degradation of these proteins, allowing NF-kappa B to translocate to the nucleus. In this study, by multiparametric analysis, we recognise in RPMI-8402 DMSO-activated cells the intracellular movement of transcription factor NF-kappa B providing its definite intranuclear collocation. Intact cells, purified nuclei and nuclear matrix preparations after 4 h of treatment were processed for morphological and biochemical analyses. Light and electron microscope observations show, in untreated cells, the presence of NF-kappa B protein homogeneously retained in the cytoplasm. Treated cells display a massive presence of NF-kappa B at the nuclear level bound to the interchromatin region. Immunoblotting of the same specimens confirms the strong association of NF-kappa B with the nuclear scaffold. Taken together, the data presented in this manuscript support a model where DMSO treatment provokes the cleavage and translocation of NF-kappa B from the cytoplasm to the nucleus and, in particular, in the proteinaceous network of the nuclear matrix sustaining the active role of this subcellular structure on regulation of eukaryotic gene expression.

A strong inverse relationship between PAI-1 and Lp(a) in hypertensive Type 2 diabetic patients

Thrombophilia with a contemporary reduction of fibrinolytic activity has been observed both in diabetes mellitus and hypertension. Previously, we found a relationship between plasminogen activator inhibitor Type 1 (PAI-1) and lipoprotein(a) [Lp(a)] in Type 2 diabetes mellitus patients without complications. We hypothesised that this relationship could be due to a compensatory mechanism able to lower the risk of hypofibrinolysis as found in Type 2 diabetes mellitus. The present work was aimed at investigating the influence of concurrent hypertension and diabetes mellitus on the plasma levels of these two fibrinolytic inhibitors. In addition, other risk factors, known to influence the fibrinolytic parameters, were taken into account. Forty-nine Type 2 nonhypertensive diabetic patients without complications, 47 Type 2 hypertensive diabetic patients without complications, 54 non-diabetic hypertensive subjects without complications as well as 87 control subjects were studied. Plasma concentrations of Lp(a), PAI-1 antigen and activity, and the main parameters of oxidative, lipo- and glycometabolic balance were determined. Significant statistical differences between diabetic and non-diabetic subjects were found concerning triglycerides and antioxidant defence (p<0.01). Analysis of variance showed the F test statistically significant in evaluating the Log PAI-1/Lp(a) (p = 0.02). Correlation analysis between Log PAI-1 antigen and Lp(a) was significant in non-hypertensive diabetic patients, as expected (r = -0.38, p<0.01), and even stronger in hypertensive diabetic patients (r = -O.72,p<0.01). These results allow to hypothesise that the relationship between PAI-1/Lp(a) could be determinant in avoiding vascular complications due to diabetes mellitus and hypertension.

Meal-induced oxidative stress and low-density lipoprotein oxidation in diabetes: the possible role of hyperglycemia

Oxidative stress and its contribution to low-density lipoprotein (LDL) oxidation have been implicated in the pathogenesis of vascular diabetic complications. However, the relationship between hyperglycemia, hyperinsulinemia, hyperlipidemia, and oxidative stress is still debated. If plasma glucose and/or insulin and/or lipid are some of the most important determinants of oxidative stress in diabetes, then their typical postprandial elevations in diabetes would be expected to favor oxidative stress and LDL oxidation. To test this hypothesis, in type 2 diabetic patients, we evaluated the effects of two different standard meals designed to produce different levels of postprandial hyperglycemia on the plasma oxidative status and LDL oxidation. The meals were administered in randomized order to each of 10 type 2 diabetic patients. Blood samples were collected at baseline and 60 and 120 minutes after the meals. In every sample, plasma levels of glucose, insulin, cholesterol, triglycerides, nonesterified fatty acids (NEFAs), malondialdehyde (MDA), and the total radical-trapping antioxidant parameter (TRAP) were measured. LDL susceptibility to oxidation was evaluated at baseline and after 120 minutes. Plasma glucose, insulin, triglycerides, and MDA increased and NEFAs and TRAP significantly decreased after either meal. The variations in plasma glucose, MDA, and TRAP were significantly greater and LDL was more susceptible to oxidation after the meal that produced a significantly higher degree of hyperglycemia. These results suggest that postprandial hyperglycemia may contribute to oxidative stress in diabetic patients, providing a mechanistic link between hyperglycemia and diabetic vascular disease.

Melatonin increases the intensity of respiratory burst and prevents L-selectin shedding in human neutrophils in vitro

Effects of melatonin priming of neutrophils and subsequent increase of phorbol 12-miristate 13-acetate stimulated respiratory burst were investigated on the modulation of L-selectin shedding and MAC-1 upregulation. Respiratory burst related H2O2 production and adhesion molecule expression were quantified by flow cytometry. Phorbol 12-miristate 13-acetate dose dependence of intracellular oxidation and adhesion molecule expression showed no relationship between respiratory burst intensity and MAC-1 expression or L-selectin shedding. Treatment of cells with 12.5 nM phorbol 12-miristate 13-acetate resulted in less than 20% of the respiratory burst response, however it induced 91.7% of total MAC-1 expression and 62.8% of L-selectin shedding. Melatonin priming experiments showed also no connection between the extent of respiratory burst and MAC-1 expression, however melatonin priming almost completely prevented L-selectin down-regulation elicited by phorbol 12-miristate 13-acetate, without affecting MAC-1 expression. It is suggested that melatonin may inhibit metalloproteases responsible for L-selectin cleavage.

A significant relationship between plasminogen activator inhibitor type-1 and lipoprotein(a) in non-insulin-dependent diabetes mellitus without complications

We previously found a relationship between plasminogen activator inhibitor type-1 and lipoprotein(a) in non-insulin-dependent diabetes mellitus and hypothesized that this could be due to a compensatory mechanism able to lower the risk of hypofibrinolysis found in type II diabetes mellitus. The aims of the present study were: (1) to confirm the association between plasminogen activator inhibitor type-1 and lipoprotein(a) in a different group of non-insulin-dependent diabetes mellitus patients and (2) to investigate whether the association could be related to diabetic complications. Other vascular risk factors able to influence fibrinolytic parameters such as glycemia, obesity, hypertension, dyslipidemia, and oxidative stress were also considered. Sixty-six non-insulin-dependent diabetes mellitus patients without diabetic complications (48 men, 18 women), 45 non-insulin-dependent diabetes mellitus patients with complications (21 men, 24 women), and 31 control subjects (17 men, 14 women) were studied. Plasma concentrations of lipoprotein(a), plasminogen activator inhibitor type-1 antigen and activity, and the main parameters of lipo- and glycometabolic balance were determined. Antioxidant defense was assayed as oxygen radical absorbance capacity of serum. Statistically significant differences among controls and the two diabetic groups were found for fasting glucose, cholesterol, triglycerides, and oxygen radical absorbance capacity of serum, while no statistically significant differences were evident for plasminogen activator inhibitor type-1 antigen and activity and lipoprotein(a). Regression analysis of log plasminogen activator inhibitor type-1/lipoprotein(a) showed a significant correlation only in diabetic patients without complications (r = -0.57, P < 0.001). These results show that a relationship between plasminogen activator inhibitor type-1 and lipoprotein(a) is characteristic of a diabetic population without complications, supporting the suggestion that this relationship could be a compensatory mechanism of the fibrinolytic system to limit the risks of hypofibrinolysis. A lack or a loss of capacity to balance lipoprotein(a) and plasminogen activator inhibitor type-1 could contribute to the pathogenesis of the diabetic complications.

Phorbol ester synergizes the dimethyl sulfoxide-dependent programmed cell death through diacylglycerol increment

The regulation of cell proliferation or cell death by extracellular factors are the most intensely studied subjects in cell biology. Many conceptual problems remain to be clarified concerning the mechanisms that regulate the programmed cell death. In this work, we focus our attention on the possible role of protein kinase C activation during dimethyl sulfoxide (DMSO)-induced cell death. The present results suggest that the frequency of DMSO-dependent apoptosis of RPMI 8402 thymic lymphoma cells is increased by phorbol ester acetate supplementation. Enhancement of apoptosis can be abolished by cotreatment with the bisindolylmaleimide, a specific PKC inhibitor. The association between PMA and DMSO treatment provokes an early activation of an intracellular signaling mechanism that results, via sustained diacylglycerol elevation, in a possible long-term PKC activation.

Studies on the life prolonging effect of food restriction: glutathione levels and glyoxalase enzymes in rat liver

Cytosolic and mitochondrial levels of glutathione (GSH) as well as the activities of glyoxalase I (GI) and glyoxalase II (GII), GSH-dependent enzymes involved in the detoxification of 2-ketoaldehydes, were investigated in the liver of ad libitum (AL) fed and food restricted (FR) rat during aging. Both cytosolic and mitochondrial GSH level was lower in old than in adult AL fed rats. Food restriction did not prevent this decrease, but its extent was attenuated considering the cytosolic GSH. As regards the mitochondrial GSH, its content was higher in adult FR animals than in the age-matched AL fed ones. Thus, the subsequent age-dependent decrease of GSH, occurring also in FR animals, resulted in a thiol concentration not different from that observed in young and adult AL fed animals. Considering the enzymatic activities, cytosolic GI decreased in old rats irrespective of diet, whereas GII activity remained constant in all the experimental groups. The higher glutathione content found in both cellular compartments of old FR rats as compared to the old AL fed ones, could help to explain the life prolonging effect of FR treatment. Moreover, the observation that the activity of glyoxalases was not influenced by food restriction does not necessarily mean that the cells of diet-conditioned animals are scarcely protected against the toxic effect of methylglyoxal. Indeed, the production of this compound should be lower in FR animals as compared to AL fed ones, due to the lower level serum glucose concentration during the life span of the former with respect to the latter group.

Pandinus imperator scorpion venom blocks voltage-gated K+ channels in human lymphocytes

Using the patch-clamp technique, we determined that Pandinus imperator scorpion venom blocked whole-cell n-type K+ currents in human peripheral blood lymphocytes in a dose-dependent manner with Kd = 0.02 microgram/ml. K+ channel block was instantaneous and removable by washing with venom-free extracellular solution. The venom-induced block was independent of membrane potential. The venom did not influence activation and inactivation kinetics of the K+ channels, however, accelerated recovery from inactivation. Purified peptides Pi1, Pi2, and Pi3 from the P. imperator venom powerfully blocked Kv1.3 channels in human lymphocytes with Kd values of 9.7 nM, 50 pM, and 0.5 nM, respectively. Flow cytometric membrane potential measurements with the oxonol dye showed that Pi2, the most effective peptide toxin of the P. imperator venom, depolarizes human lymphocytes in accordance with its K+ channel blocking effect.

Melatonin regulates the respiratory burst of human neutrophils and their depolarization

The effect of different doses of melatonin on the respiratory burst as well as on the membrane potential changes of human neutrophils stimulated with phorbol 12-myristate 13-acetate (PMA) was investigated. The intracellular production of reactive oxygen species (ROS) in stimulated neutrophils was quantified in individual cells by flow cytometry, measuring the oxidation of nonfluorescent dihydrorhodamine 123 to the green fluorescent rhodamine 123. The transmembrane potential change was measured using the fluorescent probe oxonol. Preincubating the cells with micromolar concentrations of the indole resulted in an increase of the response to PMA. In two of six subjects investigated, the respiratory burst was also increased by a 10 nM concentration of the indole, but when the melatonin concentration was increased to 2 mM the respiratory burst was inhibited. The change in the transmembrane potential of neutrophils paralleled the respiratory burst. Indeed, the treatment of the cells with doses of melatonin up to 0.5 mM increased the depolarization occurring subsequent to PMA stimulation, whereas 2 mM melatonin concentration decreased the extent of depolarization. To investigate whether melatonin could directly affect the transmembrane potential changes of neutrophils, the extent of depolarization, induced by increasing the extracellular potassium concentration, was measured in cells preincubated with 2 mM melatonin. This treatment resulted in a decrease of the extent of depolarization, which suggests that melatonin can directly alter membrane ion conductance in human neutrophils.

HLA class I and II antigens are partially co-clustered in the plasma membrane of human lymphoblastoid cells

Major histocompatibility complex (MHC) class II molecules displayed clustered patterns at the surfaces of T (HUT-102B2) and B (JY) lymphoma cells characterized by interreceptor distances in the micrometer range as detected by scanning force microscopy of immunogold-labeled antigens. Electron microscopy revealed that a fraction of the MHC class II molecules was also heteroclustered with MHC class I antigens at the same hierarchical level as described by the scanning force microscopy data, after specifically and sequentially labeling the antigens with 30- and 15-nm immunogold beads. On JY cells the estimated fraction of co-clustered HLA II was 0.61, whereas that of the HLA I was 0.24. Clusterization of the antigens was detected by the deviation of their spatial distribution from the Poissonian distribution representing the random case. Fluorescence resonance energy transfer measurements also confirmed partial co-clustering of the HLA class I and II molecules at another hierarchical level characterized by the 2- to 10-nm Förster distance range and providing fine details of the molecular organization of receptors. The larger-scale topological organization of the MHC class I and II antigens may reflect underlying membrane lipid domains and may fulfill significant functions in cell-to-cell contacts and signal transduction.

Membrane properties and lipid peroxidation in food restricted animals

Food restriction (FR) is a well-recognized method of extending mean and maximum longevity of rodents, but the mode of its action remains to be uncovered. This article reviews the effect of FR on the physical-chemical properties and lipid peroxidizability of cellular membranes. FR prevents the age-dependent increase in microviscosity and peroxidizability of cellular membranes. It has been suggested that a decrease in the body temperature occurring in undernourished animals may play a fundamental role in the process. Indeed, the lowering of average body temperature occurring in FR animals may induce a modification in membrane lipid composition, stimulating the cells to counteract the rigidifying effect of lower temperature. Thus, membranes are maintained in a proper functional state by a mechanism similar to that found in poikilotherm animals.

Dynamic receptor superstructures at the plasma membrane

1. INTRODUCTION 68

1.1 Receptor patterns in the plasma membrane 68

1.2 Different types of receptor patterns 71

2. METHODS TO INVESTIGATE NON-RANDOM RECEPTOR CLUSTERING 73

2.1 Fluorescence resonance energy transfer 73

2.2 Flow cytometric energy transfer measurement 78

2.3 Fluorescence anisotropy and energy transfer 79

2.4 Photobleaching energy transfer on single cells 81

2.5 Two-dimensional mapping of receptor superstructures 82

2.6 Detecting single receptor molecules 85

2.7 Chemical identification of receptor clusters 86

2.8 Electron microscopy 87

2.9 Scanning force microscopy 88

3. CONFORMATIONAL STATES OF RECEPTORS 90

3.1 Multi-subunit receptor structures 90

3.2 Physical parameters influencing conformational states 91

3.3 Chemical interactions and receptor conformations 92

4. ON THE ORIGIN OF NATURALLY OCCURRING RECEPTOR CLUSTERS 93

4.1 Synthesis of receptors and their localization in the plasma membrane 93

4.2 Lipid domain structure of the plasma membrane 94

4.3 The validity of the Singer–Nicolson model 94

5. CONCLUSIONS 96

6. ACKNOWLEDGEMENTS 96

7. REFERENCES 97

Dietary restriction affects antioxidant levels in rat liver mitochondria during ageing

Six experimental groups of young (7-month-old) and aged (24-32-month-old) rats, underwent different dietary manipulations (i.e. dietary restriction and/or a vitamin E-depleted diet), and their liver mitochondria were assayed for several antioxidants and peroxidation markers. Glutathione levels were affected both by age and dietary treatment. Coenzyme Q9 and C0Q10 showed the highest levels in the oldest rats where ageing, as well as other oxidative stresses, could induce ubiquinone biosynthesis.

Effect of acetylcholine on the electrophysiology and proliferative response of human lymphocytes

Using the patch-clamp technique, we determined that 1-15 mM extracellular acetylcholine reduced whole-cell n-type K+ currents in human peripheral blood lymphocytes and accelerated their inactivation. The percentage increase in K+ channel inactivation rate and the degree of drug induced block were independent of membrane potential. In flow cytometric membrane potential measurements with the oxonol dye similar doses of acetylcholine depolarized the lymphocyte population. Both acetylcholine induced K+ channel block and depolarization fully developed within 2 minutes. The depolarizing and K+ channel blocking effects of acetylcholine are in concert. [3H]thymidine incorporation experiments proved that the proliferative response of PHA stimulated peripheral blood lymphocytes was decreased by increasing concentrations of acetylcholine in the 1-50 mM range.

Food restriction increases the protection of erythrocytes against the hemolysis induced by peroxyl radicals

We have investigated the susceptibility to peroxidation of erythrocytes from young, adult and old ad libitum (AL) fed, as well as from adult and old food restricted rats, measuring the rate of hemolysis under controlled peroxidative condition. Food restriction has been applied on an every-other-day (EOD) schedule starting from the age of 3.5 months. The oxidation of red blood cells by molecular oxygen was performed in an aqueous suspension using the azo-compound 2-2'-azo-bis-(2-amidinopropane)hydrochloride (AAPH) as the free radical initiator. Several parameters were calculated from the time-dependent curve of AAPH induced hemolysis. The time required to achieve 50% hemolysis decreased with aging and this decrease was prevented by food restriction. The lag time, which reflects the capacity of the cell to buffer free radicals, was longer in young than in old AL fed animals also this impairment was almost completely prevented in EOD fed animals. The same beneficial effect of food restriction was observed considering the maximal amount of hemolysis attained with the dose of AAPH applied and the time necessary to reach this level. The general picture emerging from the present study is that erythrocyte membranes from EOD fed rats are better protected, than those from AL fed ones, against damages caused by peroxidation. This effect may be due to a difference in the chemical composition of the erythrocyte membranes as it was found in other organs.

Melatonin protects LDL from oxidation but does not prevent the apolipoprotein derivatization

Protective effect of melatonin against Cu++ induced peroxidative modification of low density lipoprotein (LDL) was studied in vitro. Melatonin was used for this purpose because of its known scavenging capacity against hydroxyl and peroxyl radicals. It was demonstrated by the diene formation kinetic analysis that melatonin protected polyunsaturated fatty acids of LDL lipids against peroxidation. Lag time duration was prolonged, peak time was delayed, whereas rate of diene formation was decreased in melatonin treated LDL; however, parameters related to apolipoprotein (apo-B) showed that the protein was derivatized. Fluorescence, relative electrophoretic mobility, lysine residues analysis data, as well as the uptake by macrophages all showed properties similar to those of oxidised LDL. Present data suggest that by-products of melatonin oxidation might react with lysine residues of apo-B, transforming LDL in its atherogenic form.

Glycosylated hemoglobin and fructosamines: does their determination really reflect the glycemic control in diabetic patients?

The present experiment was designed to determine whether scavenging capacity of serum, in addition to glucose level, influences hemoglobin and serum protein glycosylation in non-insulin dependent diabetic patients. For this purpose forty-seven patients homogeneous for age, disease duration, therapy and glyco-metabolic control were selected. Fasting and post-prandial glycemia and insulinemia as well as glycosuria were weekly analysed during the sixty days preceding glycosylated hemoglobin (HbA1c), fructosamines and serum scavenging capacity determination. This last parameter has been evaluated by a method based on the property of beta-phycoerythrin (beta-PE) to loss its fluorescence when damaged by oxygen radicals, that were produced by Cu++ and H2O2. The oxygen radical absorbance capacity (ORACOH) of serum was assayed as the ability of serum to delay the loss of beta-PE fluorescence. As expected, a statistically significant positive correlation was found comparing both fructosamines and HbA1c levels with mean fasting glycemia measured over twenty and sixty days, respectively. The key result of this study is represented by the finding that both HbAlc and fructosamines levels show a statistically significant negative correlation with ORACOH values. This correlation can explain a large percent of the data dispersion occurring when ORACOH is not taken into account. In order to better describe the role of ORACOH, patients were separated into two sub-groups with an ORACOH lower (L-ORACOH) and greater (H-ORACOH) than 100 U/ml. Examining the correlation between mean fasting glycemia and the two glycosylated proteins considered in these two sub-groups, curves with different slopes were obtained, supporting that the rate of glycosylation of both proteins was higher in L-ORACOH patients as compared to those with H-ORACOH. Present data suggest that for a proper interpretation of the HbA1c and fructosamines data in diabetic patients, the scavenging capacity level of serum should be taken into account.

The effect of juglone on the membrane potential and whole-cell K+ currents of human lymphocytes

Using flow cytometric membrane potential measurements with the oxonol dye, we determined that 5.7-57 microM juglone depolarizes human lymphocytes in a dose dependent manner. The depolarizing effect of juglone was verified by patch-clamp. Juglone decreased whole-cell n-type K+ currents in human peripheral blood lymphocytes and accelerated inactivation; however, it did not influence the kinetics of activation of the K+ conductance. The percentage increase in K+ channel inactivation rate and the degree of drug induced block was independent of membrane potential, K+ channel block by juglone fully developed within 4 minutes and was not removable by washing with drug free extracellular solution. Blocking of n-type K+ channels by juglone is in concert with its depolarizing effect on human lymphocytes.

The impairment of mitochondrial membrane potential and mass in proliferating lymphocytes from vitamin E deficient animals is recovered by glutathione

The time-dependent changes of mitochondrial membrane potential and mass have been investigated on splenocytes from control and vit. E deficient rats, stimulated to proliferate with Concanavalin A, in the presence and absence of reduced glutathione (GSH, 5 mM). Rhodamine-123 (Rh-123) and nonyl acridine orange (NAO) were used as specific probes to monitor the membrane potential and mass of mitochondria, respectively, by means of flow cytometry. Rh-123 uptake was high in an increasing number of cells from normally fed animals during the three-day culture period. On the contrary, splenocytes from vitamin E deficient rats showed a biphasic pattern. The number of cells showing a high uptake of Rh-123 increased after 24 hrs. from mitogenic stimulation, then it decreased at the other two time points considered. In parallel, a continuous increase of the number of cells with depolarized organelles (up to 60% by 72 hrs.) has been observed in vit. E deficiency. This impairment was fully prevented by GSH supplementation to the culture medium. In the presence of the thiol, about 80-85% of cells showed activated mitochondria, whereas the number of splenocytes with depolarized organelles did not exceed 17%, irrespective of the diet applied to the animals. The same pattern was observed considering the changes of mitochondrial mass, measured using NAO as a probe. Present results support that GSH may substitute vitamin E in protecting mitochondria from peroxidative damage.

Effect of reduced glutathione on mitochondrial parameters of proliferating splenocytes from young and old rats

The time-dependent changes of mitochondrial membrane potential and mass have been investigated on splenocytes from young, adult and old rats stimulated with Con A in the presence and absence of reduced glutathione (GSH). In addition, the basal level as well as the level of GSH during a 3-day culture period has been determined. No age-dependent changes of cellular GSH content were observed in freshly prepared splenocytes; however, in proliferating cells from old animals the expected increase in GSH levels was delayed. As regards the mitochondrial parameters, their membrane potential and mass were measured by means of the fluorescent probes rhodamine-123 (Rh-123) and nonyl acridine orange (NAO), respectively, and flow cytometry. During aging and with time of culture, an increased number of cells showed depolarization and loss of mitochondrial mass. This age-dependent impairment was completely prevented by addition of GSH to the culture medium, which resulted in a sharp increase in intracellular GSH. The present findings support the view that an impairment of the antioxidant defense system may be responsible for the damage observed in the mitochondria of proliferating splenocytes from old animals.

Effects of bretylium tosylate on voltage-gated potassium channels in human T lymphocytes

Using the patch-clamp technique, we determined that bretylium tosylate, a quaternary ammonium compound possessing immunomodulating activity, decreased the whole-cell K+ current in human T lymphocytes, in a dose-dependent manner, in the 0.05-5 mM extracellular concentration range. Bretylium tosylate prolonged the recovery from inactivation and accelerated the inactivation and deactivation of the K+ current but did not influence the kinetics of activation or the voltage dependence of activation and steady state inactivation of the K+ conductance. The percentage of drug-induced block was independent of membrane potential. K+ channel block by bretylium tosylate was partially and slowly removable by washing with drug-free extracellular solution. Bovine serum albumin (10 mg/ml) in the bath lifted the drug-induced block almost instantaneously, although not completely. In control experiments bovine serum albumin increased the inactivation time constant of the K+ channels but left the peak K+ current amplitude unaffected. On the basis of the experimental evidence, a gating-dependent allosteric interaction is suggested for the mechanism of drug action. The effective dose range, time of exposure, and reversibility of bretylium tosylate-induced K+ channel block correlated well with the same parameters of the drug-induced inhibition of T lymphocyte activation. The reported effects of bretylium tosylate on T cell mitogenesis can be regarded partly as a consequence of its blocking effects on voltage-gated K+ channels.

Food restriction in female Wistar rats. VII. Mitochondrial parameters in resting and proliferating splenic lymphocytes

The effect of food restriction on the mitochondria of resting and proliferating rat splenocytes was examined, measuring the membrane potential and mass of these organelles, by means of the specific fluorescent probes Rhodamine-123 and Nonyl Acridine Orange, respectively. Food restriction was applied on an every-other-day schedule (EOD) starting at the age of 3.5 months. The ad libitum fed (AL) animals were killed when they were 4, 11 and 24 months old, whereas the EOD rats were killed at 11 and 26 months. Resting lymphocytes from AL rats showed an age-dependent increase of both membrane potential and mass of their mitochondria. However, the mitochondrial mass increased to a larger extent when compared with the membrane potential resulting in a decrease of the respiratory quotient (RQ), i.e. of the respiratory activity per unit of mitochondrial mass. In EOD animals, the mitochondrial membrane potential was lower and the mitochondrial mass was higher in the corresponding age-matched controls, resulting in a further decrease of RQ. Following mitogenic stimulation, most of the cells from young and adult AL rat showed an increase of membrane potential and mass of their mitochondria. In contrast about 50% of cells from old AL rats had depolarized organelles after 72 h from the stimulation. Food restriction was able to prevent these alterations allowing the majority of cells, including those from old animals, to maintain the hyperpolarization of their mitochondria during the 3-day culture. In light of the well known sensitivity of mitochondrial membrane potential to peroxidative stress, present data suggest that the increase of respiration occurring during mitogenesis may increase free radical production, which is better tolerated by cells from EOD animals than by those from AL animals.

Melatonin: a peroxyl radical scavenger more effective than vitamin E

We have compared the peroxyl radical scavenger ability to melatonin with that of vitamin E, vitamin C and reduced glutathione (GSH). In the assay system, beta-phycoerythrin (beta-PE) was used as fluorescent indicator protein, 2-2'-azo-bis(2-amidinopropane)dihydrochloride as a peroxyl radical generator and the water soluble vitamin E analogue. Trolox, as reference standard. Results are expressed as oxygen radical absorbing capacity (ORAC(perox)) units, where 1 ORAC unit equals the net protection produced by 1 microM Trolox. A linear correlation of ORAC values with concentration (0.5-4 microM) of all the substances tested has been observed. However, on molar basis, the relative ORAC(perox) of Trolox, vitamin C, GSH and melatonin was 1:1.12:0:68:2.04, respectively. Thus, melatonin, which is a lipid-soluble compound, was twice more active than vitamin E, believed to be the most effective lipophilic antioxidant.

Vitamin E deficiency impairs the modifications of mitochondrial membrane potential and mass in rat splenocytes stimulated to proliferate

This study was designed to evaluate the time-dependent changes of mitochondrial membrane potential and mass during Con-A-induced proliferation of splenic lymphocytes from rat fed a normal or a vitamin E deficient diet. Rhodamine 123 and Nonyl Acridine Orange were used as specific probes to monitor the membrane potential and mass of mitochondria, respectively, by means of flow cytometry. The results demonstrate that the increase of Rh-123 and NAO uptake observed in cells from normally fed rats was prevented by vitamin E deficiency, at any time considered. After 72 h from Con A stimulation, 62% of cells from controls, as against 16% of cells from vitamin E deficient rats, showed hyperpolarized mitochondria. At the same time, in this last group, 60% of cells had depolarized organelles. The same pattern was observed considering the changes of mitochondrial mass, measured using NAO as a probe. These data support that mitogenic stimulation induced an increase of the respiratory activity of mitochondria with subsequent production of superoxide radicals. This resulted in depolarization and loss of mass of the organelles if the intracellular level of vitamin E is not adequate.

Reduced glutathione recovers the impairment of the proliferative response of splenic lymphocytes from vitamin E-deficient rats

The effect of reduced glutathione (GSH) on the Con A induce proliferative response of splenic lymphocytes from rats fed a normal or vitamin E-deficient diet has been investigated. The animals were killed when they were 12 months old and after 11 months of dietary treatment. As was expected, a decreased response, measured in terms of blast transformation or [(3)H]thymidine incorporation, was observed in vitamin E-deficient animals when compared with the control group. This pattern can be accounted for by the large number of dead cells found in deficient animals. GSH addition into the culture medium resulted in a strong increase of the response in both groups and it eliminated the difference caused by the different dietary regimens. Taking into account that, during proliferation, an increase of respiration occurs which increases the risk of free radical production, present data suggest that GSH may substitute vitamin E in protecting the cells.

Age-dependent modifications of mitochondrial trans-membrane potential and mass in rat splenic lymphocytes during proliferation

The specific fluorescent probes, Rhodamine 123 (Rh-123) and Nonyl-Acridine Orange (NAO) were, respectively, used to monitor the changes in membrane potential and mass of lymphocyte mitochondria during aging and proliferation. An age-dependent increase of the uptake of both fluorochromes was observed in resting cells; however, NAO fluorescence increased to a greater extent when compared with the Rh-123 probe. This resulted in a lower respiratory activity per unit of mitochondrial mass in old cells than in the young ones. Following mitogenic stimulation, most of the lymphocytes from young rats showed an increase in their membrane potential and mass. On the contrary about 50% of cells from old rats had depolarized mitochondria after 72 h from the stimulation. Present data support that mitochondria of lymphocytes from old rats are extremely sensitive to the stressing conditions resulting from mitogenic stimulation.

Bretylium differentiates between distinct signal transducing pathways in human lymphocytes

The selection of signal transducing pathways of T cells depends on the type of triggers. Antigens, antibodies or lectins induce the T cell receptor-CD3 operated pathway, and IL-2 transmits its activation signal via the IL-2 receptor. It has been demonstrated that bretylium, a quaternary ammonium ion, can significantly inhibit the first pathway at the same dose range that stimulates cell activation through the IL-2 receptor system. In the light of the different complexity of the two pathways at the plasma membrane level, and the non-toxic and reversible behavior of the drug, it is suggested that the bretylium induced sustained membrane hyperpolarization is responsible for the observation. This finding may open new possibilities in studying the mechanism of different signal transducing pathways.

The response of human lymphocytes to phytohemagglutinin is impaired at different levels during aging

Several parameters generally believed to be necessary for the activation and progression of proliferation of human lymphocytes have been investigated and compared with special reference to aging. The responding capacity of plasma membrane potential to depolarizing and also repolarizing conditions induced by exposure to mitogens like PHA was lower in lymphocytes from old donors as compared to those of young ones. This indicates a significant age-dependent difference in the readiness to respond to channel-activating perturbations. As an early signal of activation, after one hour PHA stimulation the merocyanine 540 uptake by the lipid regions was chosen, based on the property of this fluorescent probe to bind to loosely packed lipids of the plasma membrane. The proteins encoded by the c-myc and c-myb genes were chosen as markers of the G0/G1 and G1/S phased transition, respectively. The mean number of cells that increased the uptake of MC 540 following mitogenic stimulation did not differ in young vs. old individuals. However, 4 samples out of 10 from the old population showed lower MC 540 fluorescence than the lowest signal from the young population. The number of responding cells was decreased during aging when the presence of the c-myc protein was taken as its measure; and this decrease was further accentuated, determining the expression of the c-myb protein. This frequently encountered age-dependent pattern, however, was not followed by the lymphocytes of all old donors. One example is reported in which the MC 540 uptake, the c-myc and c-myb expression in the cells from one old subject fell in the range of the young subjects. However, even in this case, the response of the lymphocytes as measured by 3H-thymidine incorporation was only 64% of that of young subjects. For this sample, we found an impairment of the response at the mitochondrial level. In addition to these parameters, the amount of 3H-thymidine incorporated by the cells expressing the c-myb protein was calculated. The values in old individuals were lower than those in the young, suggesting that not all the cells expressing the c-myb protein were able to synthesize DNA in lymphocyte populations from the elderly. Our data support the view that the age-dependent decline of lymphocyte responsiveness to mitogens can be accounted for by impairments at different levels.(ABSTRACT TRUNCATED AT 400 WORDS)

Glutathione influences the proliferation as well as the extent of mitochondrial activation in rat splenocytes

The time-dependent changes of mitochondrial membrane potential and mass have been investigated on rat splenic lymphocytes stimulated with Con A in the presence and absence of reduced glutathione (GSH). Rhodamine-123 (Rh-123) and nonyl acridine orange (NAO) were used as specific dyes to monitor the membrane potential and mass of mitochondria, respectively. The percentage of cells showing blast transformation and the level of Rh-123 or NAO uptake were analyzed by flow cytometry. Present results demonstrate that a large number of cells showed activated mitochondria already at 24 hr after Con A stimulation and the activation of these organelles was not related to blast transformation. The addition of GSH into the culture medium increased the number of cells responding to mitogenic stimulation. In parallel it augmented the percentage of lymphocytes with activated mitochondria and also prevented their depolarization.

Bretylium-induced voltage-gated sodium current in human lymphocytes

Using the whole-cell variation of the patch-clamp technique it has been determined that 0.25-3 mM bretylium tosylate (BT) exerts a repolarizing effect on partially depolarized human lymphocytes. The repolarizing effect was ouabain (40 microM)-sensitive, and was inhibited by the removal of external Na+ or by the Na(+)-channel-blocker amiloride (10-44 microM), but K(+)-channel-blockers 4-aminopyridine (0.1-5 mM) and quinine (100 microM) had no effect. The drug induced a sodium dependent, amiloride-sensitive transient inward current reaching its maximum value approx. 20-30 s after the administration of BT and lasting for 6-10 min. This current was activated by depolarization within 25 ms at around -42 mV, its inactivation took about 2 s and its reversal potential was +24 +/- 5 mV. An increase in the intracellular sodium concentration (1.8-3.2 mM) has been observed upon the addition of BT by monitoring the SBFI fluorescence of the dye-loaded cells. It has been shown that whole-cell K+ currents are significantly decreased by BT. The existence of voltage and ligand (BT)-gated sodium channels has been postulated in human lymphocytes. These channels are thought to participate in the initiation of membrane repolarization in human lymphocytes, and thereby influence mitogenic or antigen-induced cell-activation processes.

Dynamic physical interactions of plasma membrane molecules generate cell surface patterns and regulate cell activation processes

Molecular interaction and transmembrane signal transducing events generate a very dynamic and ever changing "pattern" in the plasma membranes. Lymphocytes, the key functional elements of the immune system, are eminently suited to be the primary targets to investigate these proximity, mobility, or other physical-chemical changes in their plasma membranes. Recently, a number of experiments suggested that processed peptides from antigens can bind specific components of MHC molecules (Elliott et al., 1991). This is certainly a way to alter their structure. Cell surface patterns of topological nature, assembly and disassembly of oligomeric receptor structure like the IL-2 receptor have been investigated by sophisticated biophysical techniques. The dynamic changes in the two-dimensional cell surface pattern and intramolecular conformational changes within this "larger" macro-pattern may have a strong regulatory role in signal transducing and intercellular recognition processes. Recent data on these problems are presented together with brief and critical discussions.

Lipid peroxidation causes an increase of lipid order and a decrease of 5'-nucleotidase activity in the liver plasma membrane

The effect of peroxidation on 5'-nucleotidase activity as well as on membrane microviscosity has been investigated in liver plasma membranes from Wistar rats. The peroxidation was performed with 100 microM H2O2 and 200 microM FeSO4 and/or with 5 mM t-butylhydroperoxide. Treatment of the membranes with these oxidizing agents resulted in an elevation of the transition temperatures of the polarization of the lipid fluorescent probes 1,6 diphenyl-1,3,5 hexatriene (DPH), 3-p-(6-phenyl) 1,3,5 hexatriene phenylpropionic acid (PA-DPH) as well as of the fluorescent thiol reagent N-(1-pyrene) maleimide (1-PM). The peroxidation resulted in a decrease of the activity of 5'nucleotidase. Our data support that the increase of membrane microviscosity of the lipid domain regulates the activity of 5'-nucleotidase.

Phytohemagglutinin induced changes of membrane lipid packing, c-myc and c-myb encoded protein expression in human lymphocytes during aging

Three parameters which signal different stages of cell activation were analyzed in lymphocytes from young and old subjects. Merocyanine 540 (MC-540) incorporation into the membrane lipid phase was used as a very early marker of activation and was measured after 1 h of phytohemagglutinin (PHA) stimulation. The proteins coded by c-myc and c-myb protooncogenes were determined by appropriate antibodies and were taken as markers of the G0/G1 and G1/S phase transition, respectively. The number of cells which increased the uptake of MC-540 following PHA stimulation did not differ when comparing young and old individuals. Both the number of the responding cells and the size of the response were decreased during aging when the presence of the c-myc protein was taken into account. A consistent decrease of the percentage of lymphocytes able to express the c-myb protein was observed in the cells from old donors as compared to those from the young ones, but the amount of detectable protein per cell remained unchanged. Our data suggest that the deficiency of responsiveness which accompanies aging is due to impairments at different points of the cell cycle. The very low number of cells expressing the c-myb protein is likely the result of step by step elimination of those cells not able to fulfill the requirements to progress along the cell cycle.

Ion channel activity and transmembrane signaling in lymphocytes

Transmembrane signalling refers to the process of transfer of information from the extracellular world into the intracellular space. The information is transduced through several possible pathways. The significance of cell surface dynamics, ion channel activity and drug effects are discussed in the signal transmission, with special reference to Na+ channels and the Ca2+ sensitive potassium channels.