Possible neuroprotective properties of flunarizine infused after asphyxia in fetal lambs are not explained by effects on cerebral blood flow or systemic blood pressure

Ameliorative effect of flunarizine in cisplatin-induced acute renal failure via mitochondrial permeability transition pore inactivation in rats

This study was aimed to evaluate the protective effect of flunarizine on cisplatin-induced acute renal failure. Administration of cisplatin (6 mg/kg, i.p. on day 6) significantly increased serum blood urea nitrogen and creatinine, urinary N-acetyl β-D-glucosaminidase, tissue thiobarbituric acid reactive substances and total calcium whereas, decreased body weight, fractional excretion of sodium, creatinine clearance tissue-reduced glutathione, mitochondrial cytochrome c oxidase, and ATP levels were observed in acute renal failure rats. Moreover, cisplatin produced histopathological changes in the renal tissue. Furthermore, flunarizine (100, 200, and 300 μM/kg, p.o., for six consecutive days) was administered to evaluate its therapeutic potential in acute renal failure, and the results were compared with cyclosporin A (50 μM/kg, p.o., for six consecutive days) as a reference drug. Flunarizine resulted in the attenuation of cisplatin-induced renal dysfunction, oxidative stress marker, mitochondrial damage, and histopathological changes in rats. Medium and higher doses of flunarizine produced significant renal protective effect which was comparable to cyclosporin A. The results of this study clearly revealed that flunarizine protected the kidney against the nephrotoxic effect of cisplatin via mitochondrial permeability transition pore inactivation potential.

Calcium channel blockers in cerebral ischaemia

Ischaemic stroke usually results from the obstruction of a major cerebral vessel which leads to a decrease in cerebral blood flow, and a subsequent reduction in ATP. This energy loss leads to impaired cellular function due to reduced ATP-dependent processes and a disruption in ionic gradients across membranes. Under these conditions, there is a significant efflux of K+ from cells producing cellular depolarisation and the movement of extracellular calcium into cells through calcium channels. It is this increase in intracellular calcium that leads to the 'calcium toxicity' that has been associated with cerebral ischaemia. Increased intracellular calcium triggers the break-down of phospholipids, proteins and nucleic acids. This is activated by calcium-dependent phospholipases, proteases and endonucleases, and contributes to structural and functional damage of the cell membrane, which compromises cell function and facilitates cell death. Calcium channel blockers are used routinely to treat cardiovascular disease and hypertension. Although some experimental studies over the last decade suggest efficacy/benefit in the treatment of experimental ischaemic stroke, clinical data do not bear this out. This article discusses the role of voltage-operated calcium channel blockers in stroke, and reviews much of the available experimental and clinical data.

Dose-related inversion of cinnarizine and flunarizine effects on mitochondrial permeability transition

We investigated the effects of cinnarizine and flunarizine on mitochondrial permeability transition, ATP synthesis, membrane potential and NAD(P)H oxidation. Both drugs were effective in inhibiting the mitochondrial permeability transition induced either by Ca2+ alone or in the presence of tert-butylhydroperoxide. This protective effect occurred at low concentrations (< 50 microM) of these drugs and was accompanied by the inhibition of NAD(P)H oxidation and the restoration of the mitochondrial membrane potential decreased by a high concentration of Ca2+ (25 microM). However, at higher concentrations (> 50 microM) of cinnarizine and flunarizine and in the absence of both tert-butylhydroperoxide and Ca2+, their effects on the mitochondria were reversed as follows: mitochondrial permeability transition was generated, mitochondrial NAD(P)H was oxidized and membrane potential collapsed. These deleterious effects were not antagonized by cyclosporine A, the most potent inhibitor of the mitochondrial permeability transition, but by 2,6-di-tert-butyl-4-methylphenol, a known antioxidant agent. This mitochondrial effect was neither accompanied by an increase in malondialdehyde production nor by an increase in H2O2 generation, which attested that the effect of both drugs was not due to an increase in reactive oxygen species production. The dual effects of both cinnarizine and flunarizine on mitochondrial functions is discussed with regard to both the protective effect afforded by these drugs against ischemia-reperfusion injury and their side effect observed in some therapeutic situations where an overdosage seems likely.

Animal models for the study of perinatal hypoxic-ischemic encephalopathy: a critical analysis

We critically evaluated various design features from 292 animal studies related to perinatal hypoxic-ischemic encephalopathy (HIE). Rodents were the most frequently used animals in HIE research (26%), followed by piglets (23%) and sheep (22%). Asphyxia with or without ischemia was the most predominant method of producing experimental brain damage, but there were significant variations in specific details, particularly regarding the method and duration of brain insult. In 71% (207/292) of studies the CNS outcomes were tested within 24 h of experimental insult and in 29% (85/292) they were tested 24 h or more after the insult. Acute CNS metabolic end-points were assessed in 82-100% of all studies. In 90% of studies the chronological age of the animal was equivalent to that of human term newborn infant. However, in only 23% (67/292) were clinical neurological, developmental or behavioral outcomes evaluated, and in only 26% (76/292) was neuropathology assessed. While no single animal model was found to be ideal for all HIE research, some models were distinctly superior to others, depending upon the specific research question. The fetal sheep, newborn lamb and piglet models are well suited for the study of acute and subacute metabolic and physiologic endpoints, whereas the rodent and primate models could be used for long-term neurological and behavioral outcome experiments as well. We also feel that standardizing the study design features, including an HI insult method that produces consistent and predictable brain damage is urgently needed. Studies in neuro-ethology should explore how well brains of various animals compare with that of the newborn human infant. There is also a need for developing animal models that mimic clinical entities in which long-term neuro-developmental and behavioral outcomes can be assessed.

Neuronal death after perinatal asphyxia

During perinatal asphyxia several mechanisms aim to limit cerebral damage. However, when the degree of asphyxia passes beyond a certain threshold, brain damage is inevitable. This review focuses on the various factors determining the final cerebral outcome. Metabolic and biochemical events, such as the intracellular level of calcium, the formation of oxygen derived free radicals, the release of excitotoxic neurotransmitters and the interrelationship of these parameters are discussed. Furthermore, steps possibly useful to pharmacologic intervention aiming to reduce cerebral damage are presented.

The T/QRS ratio of the electrocardiogram does not reliably reflect well-being in fetal lambs

OBJECTIVE

Our purpose was to determine the diagnostic power of the T/QRS ratio of the electrocardiogram to predict fetal well-being.

STUDY DESIGN

In 47 fetal lambs (3 to 5 days after surgery, gestational age 123.5 +/- 3.0 days) asphyxia was induced by restriction of uterine perfusion. Fetuses were either pretreated with an adenosine transport inhibitor (n = 16) or a calcium channel blocker (n = 12) or served as controls (n = 19). Arterial oxygen content > or = 1.5 mmol/L or pH > or = 7.15 were chosen as limits for fetal well-being.

RESULTS

Arterial oxygen content was reduced from 3.3 (+/- 1.0) to 1.3 (+/- 0.5) mmol/L, and pH decreased to 7.03 (+/- 0.10). Mortality was 53%. Both drugs did not affect well-being, survival, or the T/QRS ratio. Maximum T/QRS ratios were reached at the peak of asphyxia. Sensitivity and specificity of the T/QRS ratio were 24.0% and 42.6% to predict hypoxemia and 25.1% and 45.3% to predict acidemia. Pearson correlation coefficients for T/QRS ratio versus oxygen content and pH were 0.169 and 0.192, respectively.

CONCLUSIONS

(1) In fetal lambs the T/QRS ratio failed to predict hypoxemia or acidemia. (2) Fetal survival was not correlated with the height of the T/QRS ratio during or after asphyxia.

Effects of asphyxia on the fetal lamb brain

OBJECTIVE

Our purpose was to study the effect of fetal asphyxia on the release of hypoxanthine and xanthine in cerebrospinal fluid and on brain histologic characteristics.

STUDY DESIGN

In seven fetal lambs (3 to 5 days after surgery, gestational age 124.3 +/- 2.6 days) asphyxia was induced by restriction of uterine blood flow.

RESULTS

Fetal pH and base excess were reduced to 6.99 +/- 0.02 and -17.6 +/- 0.9 mmol/L, respectively. Cerebral blood flow increased during asphyxia and returned to normal in the recovery phase. Maximum concentrations of cerebrospinal fluid hypoxanthine and xanthine were reached in the normoxemic recovery phase. This high level of substrates during normoxemia facilitates oxygen free radical formation and may thus aggravate postasphyctic brain damage. Histologic evaluation of the brain 3 days after the insult showed a variable degree of edema. Coagulative neuronal changes, characteristic of irreversible cell death, were only occasionally detected. These changes were most obvious in the Purkinje cells of the cerebellum.

CONCLUSIONS

Fetal asphyxia induced by uterine blood flow restriction is associated with high levels of cerebrospinal fluid hypoxanthine and xanthine in the recovery phase. Microscopically detectable brain damage, although not extensive, is mainly located in the cerebellum.