P. Princi

`In vitro' evaluation of the antioxidant activity and biomembrane interaction of the plant phenols oleuropein and hydroxytyrosol

Abstract Oleuropein and hydroxytyrosol, two phenolic compounds contained in olives and olive oil, are known to possess several biological properties, many of which may be related, partially at least, to their antioxidant and free radical-scavenger ability. Hence, together with their scavenging activity against the stable 1,1-diphenyl-2-picrylhydrazyl radical (DPPH test), we have investigated the antioxidative effect of oleuropein and hydroxytyrosol in a model system consisting of dipalmitoylphosphatidylcholine/linoleic acid unilamellar vesicles (DPPC/LA LUVs) and a water-soluble azo compound as a free radical generator (LP–LUV test). The results obtained were also interpreted in the light of biophenol interactions, studied by differential scanning calorimetry (DSC), with dimyristoylphosphatidylcholine (DMPC) vesicles as a biological membrane model. Our results obtained in the DPPH and LP–LUV tests confirm the good scavenger activity and antioxidant effect of oleuropein and hydroxytyrosol. However, while both compounds exhibit comparable effectiveness in the DPPH test (hydroxytyrosol being slightly more active than oleuropein), oleuropein seems, in the LP–LUV test, a better antioxidant than hydroxytyrosol. Besides oleuropein shows a better antioxidant activity in the membranous system than in homogenous solution. Furthermore, oleuropein, but not hydroxytyrosol, interacts with DMPC vesicles, causing shifts, toward lower values, of the calorimetric peak temperature ( T m ), associated to the gel to liquid-crystal phase transition, typical for DMPC multilayers. The hypothesis will be discussed that hydroxytyrosol can serve as scavenger of aqueous peroxyl radicals near the membrane surface, while oleuropein acts also as a scavenger of chain-propagating lipid peroxyl radicals within the membranes.

Systemic cytokine administration can affect blood-brain barrier permeability in the rat

The aim of the present study was to clarify the effect of intracarotid injection of interleukin-1 beta (IL-1 beta), interleukin-2 (IL-2), interleukin-6 (IL-6) and tumor necrosis factor-alpha (TNF-alpha) on the permeability of the blood-brain barrier (BBB) in the rat. A regional blood-to-brain transfer constant (Ki) for [14C] alpha-aminoisobutyric acid ([14C]AIB) and the cerebral residual blood volume were calculated 10 min following administration of cytokines (CKs; 1000 U/rat). The injection of IL-2 and IL-6 (but not of IL-1 beta) induced a significant enhancement of Ki values for [14C]AIB within several brain areas; conversely, when the rats were given TNF-alpha, a striking decrease in BBB permeability was observed. The cerebral regional blood volumes appeared significantly lower in the rats injected with IL-6 than in the control animals, but markedly increased following TNF-alpha administration. Our findings confirm the ability of some CKs to affect the permeability of the BBB and/or to act, probably indirectly, as vasomodulator agents of the cerebral microvessel endothelium.

Changes in the permeability of the blood-brain barrier following sodium dodecyl sulphate administration in the rat.

Abstract The blood-brain barrier (BBB) arises from epithelial-like tight junctions that virtually cement adjoining capillary endothelium together in the brain microvascolature. Several experimental manipulations have been shown able to increase the permeability of brain capillaries, by altering endothelial cell membrane integrity or activating specific biochemical pathways involved in regulation of BBB functionality. Because of its amphiphilic nature, sodium dodecyl sulphate (an anionic surfactant widely used as solubilizer or stabilizer in several pharmaceutical preparations; SDS) may enter into interactions with the major membrane components, which are lipids and proteins. The aim of the present study was to determine the effect of an intracarotid infusion of SDS (25, 50 and 100 µg/kg; infusion rate: 3 ml/min for 30 s) on the functionality of the BBB in the rat. An extensive, dose-dependent Evans blue extravasation was observed, in the ipsilateral brain hemisphere, 15 min following SDS infusion. These results were confirmed by the significant increase in [14C]α-aminoisobutyric acid ([14C]AIB) transport (evaluated by calculating a unidirectional transfer constant, Ki, for the tracer from blood to brain) measured in several ipsilateral brain regions 2 min after SDS infusion; this SDS-elicited BBB opening to [14C]AIB proved to be reversible. Since the BBB is created by the plasma membrane and tight junctions of the endothelial cells, the change in BBB permeability caused by SDS might be explained as a nonspecific surfactant-membrane interaction. Furthermore, SDS might affect the functional characteristics of brain vascular endothelial cells by an interaction with specific BBB proteins and/or biochemical pathways. In conclusion, one can suggest that intracarotid infusion of SDS might provide a useful clinical approach for the intentional introduction of different substances into the brain. On the other hand, these findings should call attention to possible dangerous consequences of using SDS as solubilizer in drug excipients.

Aging and sex influence the permeability of the blood-brain barrier in the rat

The aim of the present study was to investigate the existence of aging- and sex-related alterations in the permeability of the blood-brain barrier (BBB) in the rat, by calculating a unidirectional blood-to-brain transfer constant (Ki) for the circulating tracer [14C]-alpha-aminoisobutyric acid. We observed that: a) the permeability of the BBB significantly increased within the frontal and temporo-parietal cortex, hypothalamus and cerebellum in 28-30 week old rats, in comparison with younger animals; b) in several brain areas of female intact rats higher Ki values (even though not significantly different) were calculated at oestrus than at proestrus; c) in 1-week ovariectomized rats there was a marked increase of Ki values at the level of the frontal, temporo-parietal and occipital cortex, cerebellum and brain-stem. One can speculate that aging- and sex-related alterations in the permeability of the BBB reflect respectively changes in brain neurochemical system activity and in plasma steroid hormone levels.

Evaluation of local cerebral glucose utilization and the permeability of the blood-brain barrier in the genetically epilepsy-prone rat

SummaryThe genetically epileptic-prone rat (GEPR) is a valuable model for the study of gene-linked abnormalities involved in epilepsy. In comparison with normal Sprague-Dawley controls, we found, in GEPRs, a marked depression in local cerebral glucose utilization, widespread throughout the brain. This depression was accompanied by a significant increase of blood-brain barrier permeability and a reduction in regional blood volume. Finally GEPRs showed lower plasma levels of total triiodothyronine than normal controls. One can speculate that alterations in cerebral metabolism and microvascular regulation and thyroid hormone imbalance may be gene-linked factors involved in seizure susceptibility.

Ageing influences haloperidol-induced changes in the permeability of the blood-brain barrier in the rat

Abstract— The effect of the dopaminergic antagonist haloperidol on the permeability of the blood‐brain barier (BBB) to [14C]α‐aminoisobutyric acid was studied in 10–12‐ and 28–30‐week old rats. Following the intraperitoneal injection of haloperidol (1 mg kg−1), an increase in the permeability of the BBB, with respect to younger animals, was observed within the occipital cortex, striatum, hippocampus and hypothalamus in the older rats. No correlation was found between haloperidol‐induced changes and age‐related differences in the permeability of the BBB. Such age‐associated increase in the vulnerability of the BBB when challenged with haloperidol might be related to a deterioration of the dopaminergic control of cerebrovascular permeability.

Multivariate analysis of cardiovascular reflexes applied to the diagnosis of autonomic neuropathy

SummaryA battery of cardiovascular reflex tests is usually performed for the diagnosis of autonomic neuropathy. The tests discriminate well between normal and definitely abnormal autonomic function. However, in some patients the results are borderline and their autonomic status cannot be better defined. We performed multivariate statistical analysis of six cardiovascular autonomic tests with the aim of increasing their diagnostic efficiency. Eighty-five healthy subjects and 95 patients at risk for autonomic neuropathy were studied. Principal component analysis and two pattern recognition methods, the Bayesian technique and the SIMCA method, were applied. It was found that: (1) normal models obtained by Bayesian analysis showed very high specificity and sensitivity; (2) a battery of two tests for parasympathetic function (R-R interval variation test, deep breathing) and two tests for sympathetic function (blood pressure responses to standing and to sustained handgrip) provide an appropriate diagnostic approach, if multivariate analysis is used; (3) multivariate analysis allows a more precisely defined assessment of autonomic nervous system function in so-called borderline patients.

The effect of the calcium antagonist nimodipine upon local cerebral glucose utilization in the rat brain

The new calcium antagonist Nimodipine has been shown to have more powerful dilator action on cerebral than peripheral vessels. The effect of the drug on cerebral metabolism was studied in conscious rats using the /14C/-2-deoxyglucose quantitative autoradiographic technique. Intravenous injection of Nimodipine, 2 mcg/Kg, determined significant increases in local cerebral glucose utilization that appeared to be homogeneous in magnitude and anatomic distribution throughout the brain. This study raises the question whether Nimodipine affects brain functions by other mechanisms than an increase in cerebral blood flow.

Arecoline, but not haloperidol, induces changes in the permeability of the blood-brain barrier in the rat

Abstract— The aim of the present study was to investigate the existence of alterations of the blood‐brain barrier (BBB) permeability in rats injected with centrally acting drugs, by calculating a unidirectional blood‐to‐brain transfer constant (Ki) for the circulating tracer [14C]‐α‐aminoisobutyric acid. The intraperitoneal (i.p.) injection of the dopaminergic antagonist haloperidol (1 mg kg−1) did not modify the regional BBB permeability. When the cholinomimetic agent arecoline hydrobromide (6.25 mg kg−1) was injected i.p. into methylatropine‐pretreated rats, it induced a significant decrease of Kj values within the frontal cortex, parietal cortex, striatum and brain‐stem. Our findings emphasize two concepts: (1) centrally acting drugs, such as arecoline, can induce changes in the BBB permeability, through several mechanisms; (2) there is no predictable correlation of drug stimulation of specific brain neuronal pathways and changes in the permeability of the BBB.

High intensity light exposure increases blood-brain barrier transport in rats

A quantitative technique utilizing 14C-alpha-aminoisobutyric acid as a tracer was used to study the blood-brain barrier permeability modifications induced by environmental stimuli, as the high intensity light exposure. The blood-to-brain transfer constant was significantly increased only in the occipital cortex following the treatment. The possibility that the blood-brain barrier is able to modify its local characteristics in response to cerebral activity changes was discussed.