Pre-eclampsia--a mitochondrial disease?

HELLP syndrome: mechanisms and management

Effective management of HELLP syndrome depends on swift recognition of a condition which often masquerades as other pathology. This article reviews clinical aspects of HELLP syndrome and outlines recent advances in our comprehension of what may be the underlying pathophysiology.

Placental mitochondria as a source of oxidative stress in pre-eclampsia

Pre-eclampsia is a hypertensive disorder of human pregnancy that is a leading cause of premature delivery and fetal growth retardation. It is characterized by hypertension, reduced uteroplacental blood flow, proteinuria and oedema. Pre-eclampsia is associated with increased lipid peroxidation in the maternal circulation and in the placenta. Mitochondria are sources of oxygen radicals and are enriched with polyunsaturated fatty acids that are susceptible to peroxidation. Therefore, the mitochondria could be an important source of oxidative stress and lipid peroxidation. To study this, the level of lipid peroxidation in the mitochondrial fraction of placentae obtained from normally pregnant women (n=8) and women with pre-eclampsia (n=8) was examined. Placental tissues were homogenized and the mitochondrial fraction was isolated by ultracentrifugation. Mitochondrial lipid peroxides were estimated by malondialdehyde (MDA). NADPH and Fe++ were used to stimulate lipid peroxidation. Superoxide dismutase (SOD) was used to inhibit superoxide radicals and mannitol to inhibit hydroxyl radicals. The following results were found: (1) MDA levels were significantly greater in the mitochondrial fraction isolated from pre-eclamptic placentae than from normal placentae (27.4+/-3.0 versus 17.0+/-1.8 nmol/g tissue, mean+/-s.e., P<0.05); (2) the oxidative potential of the pre-eclamptic mitochondrial fraction was also higher than normal as evidenced by the significantly greater stimulation of lipid peroxidation by NADPH and Fe+ + (248+/-25 versus 164+/-35 nmol/g, P<0.05); (3) superoxide dismutase, but not mannitol, attenuated the lipid peroxidation induced by NADPH and Fe+ + demonstrating that superoxide is the radical responsible for mitochondrial lipid peroxidation in this system; and (4) the amount of mitochondrial protein was 47 per cent greater and the activity of the mitochondrial enzyme, citrate synthase, was 56 per cent greater in the pre-eclamptic placentae indicating an increase in the amount of mitochondria in the pre-eclamptic placentae. It is concluded that: (1) mitochondrial lipid peroxidation is increased in pre-eclampsia; (2) the amount of placental mitochondria is increased in pre-eclampsia; (3) placental mitochondria contribute to the abnormal increase in lipid peroxidation that occurs in pre-eclamptic placentae by both an increase in their amount and an increase in their susceptibility to oxidation; and (4) mitochondrial generation of superoxide could be an important source of oxidative stress in pre-eclampsia.

Etiology and pathogenesis of preeclampsia: current concepts

The etiology of preeclampsia is unknown. At present, 4 hypotheses are the subject of extensive investigation, as follows: (1) Placental ischemia-Increased trophoblast deportation, as a consequence of ischemia, may inflict endothelial cell dysfunction. (2) Very low-density lipoprotein versus toxicity-preventing activity-In compensation for increased energy demand during pregnancy, nonesterified fatty acids are mobilized. In women with low albumin concentrations, transporting extra nonesterified fatty acids from adipose tissues to the liver is likely to reduce albumin's antitoxic activity to a point at which very-low density lipoprotein toxicity is expressed. (3) Immune maladaptation-Interaction between decidual leukocytes and invading cytotrophoblast cells is essential for normal trophoblast invasion and development. Immune maladaptation may cause shallow invasion of spiral arteries by endovascular cytotrophoblast cells and endothelial cell dysfunction mediated by an increased decidual release of cytokines, proteolytic enzymes, and free radical species. (4) Genetic imprinting-Development of preeclampsia-eclampsia may be based on a single recessive gene or a dominant gene with incomplete penetrance. Penetrance may be dependent on fetal genotype. The possibility of genetic imprinting should be considered in future genetic investigations of preeclampsia.

Pre-eclampsia: a disorder of placental mitochondria?

Pre-eclampsia is a common, pregnancy-induced, multisystem disease leading to severe complications in the mother and foetus. The aetiology of pre-eclampsia remains a mystery, but a growing body of evidence suggests that a mitochondrial defect might cause the impairement of differentiation and invasion of the trophoblast that leads to this disorder. This hypothesis is the topic of ongoing studies that, if confirmed, would be highly relevant to preventative strategies for this disease.

Antioxidants in the treatment of severe pre-eclampsia: an explanatory randomised controlled trial

OBJECTIVE

To determine whether antioxidant therapy alters the disease process in severe early onset pre-eclampsia, in support of the hypothesis that increased lipid peroxides and reactive oxygen species production-play an important role in the pathogenesis of the disease.

DESIGN

Randomised, double-blind, placebo controlled trial.

SETTING

Two tertiary care, referral hospitals in Johannesburg, South Africa.

PARTICIPANTS

Women with severe pre-eclampsia diagnosed between 24 and 32 weeks of gestation.

INTERVENTION

Combined antioxidant treatment with vitamin E (800 IU/day), vitamin C (1000 mg/day), and allopurinol (200 mg/day).

MAIN OUTCOME MEASURES

PRIMARY OUTCOMES

1. prolongation of pregnancy and 2, biochemical assessment of lipid peroxides and antioxidants.

SECONDARY OUTCOMES

data on maternal complications, side effects of treatment, infant outcomes and regular assessment of haematologic and renal parameters.

RESULTS

The proportion of women delivered within 14 days in the antioxidant group was 52% (14/27) compared with 76% (22/29) in the placebo group (relative risk 0.68, 95% confidence interval 0.45-1.04). One woman in each group had eclampsia. Eleven women (42%) in the antioxidant and 16 (59%) in the placebo group required two antihypertensives for blood pressure control. Trial medications were well tolerated with few side effects. Lipid peroxide levels were not significantly altered in the antioxidant and placebo groups. Serum uric acid levels decreased and vitamin E levels increased significantly.

CONCLUSION

The results of this explanatory randomised trial do not encourage the routine use of antioxidants against pre-eclampsia. However, further research with modified strategies such as earlier initiation of therapy or different combinations seem worthwhile.

Decrease in cytochrome c oxidase activity detected cytochemically in the placental trophoblast of patients with pre-eclampsia

This study was designed to explore the possible relationship between cytochemically detectable cytochrome c oxidase (COX) activity in the trophoblast and placental dysfunction in patients with pre-eclampsia. Fifteen placentae (10 from women with an uncomplicated pregnancy and five from patients with pre-eclampsia) were involved in this study. Localization of COX activity in the placental trophoblast was determined by ultrastructural enzyme cytochemistry using DAB as a capturing agent. COX activity was observed in the intracristal spaces and intermembrane spaces of trophoblastic mitochondria. The number of mitochondria positive for COX staining was decreased markedly in the placentae of the women with pre-eclampsia. Trophoblastic mitochondrial dysfunction may be present in placenta of patients with pre-eclampsia.

Mutations in mitochondrial transfer ribonucleic acid genes in preeclampsia

OBJECTIVE

We investigated whether maternally inherited mitochondrial deoxyribonucleic acid mutations could be associated with preeclampsia because mendelian models fail to explain all the aspects of inheritance in preeclampsia.

STUDY DESIGN

In two families with a high occurrence of preeclampsia and eclampsia the 22 mitochondrial transfer ribonucleic acid genes were sequenced in eight and three women, respectively.

RESULTS

An A-to-G mutation in transfer ribonucleic acidleu[UUR] at nucleotide 3243 was found in one family, and in the other there was an A-to-G mutation at nucleotide 12308 in transfer ribonucleic acidleu[CUN]. Mutations of mitochondrial transfer ribonucleic acid genes are generally considered to have systemic consequences, which might explain the multiorgan involvement seen in preeclampsia.

CONCLUSION

We report for the first time mutations in mitochondrial transfer ribonucleic acid genes in two families with a high occurrence of preeclampsia and eclampsia. Mitochondrial dysfunction caused by point mutations of mitochondrial deoxyribonucleic acid is maternally inherited, but in the case of mutations of nuclear genes mitochondrial dysfunction can be inherited as an autosomal recessive or dominant trait.

The calcium-dependent nitric oxide production of human vascular endothelial cells in preeclampsia

OBJECTIVE

Nitric oxide is an important vasodilator, and in this study we studied whether the calcium-dependent nitric oxide production capacity of human umbilical vein endothelial cells was affected by preeclampsia.

STUDY DESIGN

Human umbilical vein endothelial cells were isolated from 11 preeclamptic and 10 normotensive pregnancies. The maximal calcium ionophore A23187-stimulated nitric oxide production capacity was measured as accumulation of nitrate and nitrite into the culture medium, and it was related to the number of viable endothelial cells by measurement of their mitochondrial dehydrogenase activity.

RESULTS

The cell number-related nitric oxide production capacity was similar in preeclamptic and normotensive pregnancies. The total nitric oxide production of cells from preeclamptic pregnancies was significantly lower (p <0.001). This difference, however, was mainly caused by larger amount of viable endothelial cells recovered from normotensive pregnancies.

CONCLUSION

The maximal calcium-dependent nitric oxide production capacity of individual human umbilical vein endothelial cells is not affected by preeclampsia.

Endothelial dysfunction in preeclampsia. Part I: Primary prevention. Therapeutic perspectives

Endothelial dysfunction is the final common pathway in the pathogenesis of preeclampsia. Future therapeutic modalities aimed at preventing or treating preeclampsia should either reduce the extent of (or even prevent) endothelial cell dysfunction (primary prevention) or should reduce the consequences of endothelial cell dysfunction (secondary and tertiary prevention). Relevant potential and promising directions for further research will be discussed. Part I of this review concerns the primary prevention of preeclampsia. The etiology of preeclampsia is still unknown. The 4 hypotheses that are the most popular currently are the placental ischemia hypothesis, the immune maladaptation/spiral artery-decidual ¿toxin' hypothesis, the VLDL (very low density lipoproteins)/TxPA (toxicity preventing activity) hypothesis, and the genetic hypothesis. For the near future only the disturbed VLDL/TxPA balance and the imbalance between free radicals and scavengers appear to be amenable for clinical research purposes.

Epilepsy in a mitochondrial disorder

In a large family with maternally inherited mitochondrial disease, a mild defect in the NADH-ubiquinone oxidoreductase step (complex 1) in the respiratory chain was found. Epilepsy was seen in nine (22%) of the 37 family members. Five of them, belonging to one branch of the family, had myoclonus epilepsy and EEG abnormalities consistent with this. The remaining four patients, belonging to other branches of the family tree, had partial epilepsy. Neurological symptoms also varied in different parts of the family. Possible explanations for the differences in phenotypic expressions are discussed.