Nitric Oxide-mediated Vascular Tone in the Fetal Placental Circulation of Patients with Type 1 Diabetes Mellitus

Nitration of p38 MAPK in the placenta: association of nitration with reduced catalytic activity of p38 MAPK in pre-eclampsia

Peroxynitrite, a potent pro-oxidant formed from the interaction of superoxide and nitric oxide, has been widely reported to be nitrating tyrosine residues in proteins resulting in the formation of nitrotyrosine. Biological nitration of tyrosine, a footprint of oxidative injury, has been found to occur in various pathological states including pre-eclampsia, a leading cause of maternal mortality and increased perinatal mortality. Oxidative stress is a major contributor to endothelial dysfunction in pre-eclampsia. Previously, we have demonstrated increased nitrotyrosine immunostaining in placental villous vascular endothelium, surrounding vascular smooth muscle and villous stroma from pre-eclamptic or diabetic pregnancies. Immunoprecipitation (IP) with antinitrotyrosine antibodies followed by immunoblot analysis identified increased nitration of phospho-p38 mitogen-activated protein kinase (MAPK) in the pre-eclamptic placenta. The catalytic activity of p38 MAPK and concentration of phospho-p38 MAPK was also found to be reduced in placentae from pre-eclamptic pregnancies. Comparison of peptide masses of a 42-kDa protein obtained by mass spectrometry with masses of a theoretical tryptic digest of p38 MAPK that was modified by phosphorylation and nitration identified the protein to be p38 MAPK.

Increased plasma pro-B-type natriuretic peptide in infants of women with type 1 diabetes

BACKGROUND

Up to 40% of newborn infants of women with type 1 diabetes have echocardiographic signs of cardiomyopathy. Increased plasma concentrations of B-type natriuretic peptide (BNP) and its precursor (proBNP) are markers of cardiac failure and hypoxia in adults. In this study, we investigated whether plasma concentrations of proBNP and/or BNP are increased in infants of women with type 1 diabetes.

METHODS

Plasma BNP and proBNP were measured with RIAs. The proBNP assay measures both intact proBNP and NH(2)-terminal fragments derived from this precursor, whereas the BNP assay measures only BNP-32 and not proBNP.

RESULTS

Infants of women with diabetes and hemoglobin A(1c) (Hb A(1c)) > or =6.2% before delivery had a higher median plasma proBNP concentration (31 pmol/L; interquartile range, 21-47 pmol/L; n = 16) than infants of healthy women [16 (9-32) pmol/L; n = 21; P = 0.01]. Infants of women with diabetes and Hb A(1c) <6.2% (n = 15) had intermediate values. The plasma BNP and proBNP concentrations were closely associated (r(2) = 0.80; P < 0.0001); within the group of infants of women with diabetes and Hb A(1c) > or =6.2%, both correlated with the degree of fetal stress during labor.

CONCLUSIONS

Maternal diabetes and suboptimal metabolic control may affect the fetal heart and predominantly stimulate proBNP secretion in conjunction with perinatal stress.

Dysfunction of the cyclo-oxygenase pathway in the foetoplacental circulation in Type 1 diabetes mellitus

AIM

In diabetes, perinatal morbidity is significantly increased. This may partly be related to functional changes in the foetoplacental vascular bed. In diabetes models, a defect in the cyclo-oxygenase pathway is a common observation. Therefore, we hypothesized that the human foetoplacental circulation of diabetic patients is characterized by dysfunction of the cyclo-oxygenase pathway, as well.

METHODS

We performed ex-vivo perfusions of isolated placental cotyledons from healthy women (n = 14) and from patients with Type 1 diabetes (n = 9). The contribution of cyclo-oxygenase products to foetoplacental vascular tone was quantified by measuring the response to the cyclo-oxygenase inhibitor indomethacin.

RESULTS

Baseline foetoplacental arterial pressure was comparable between controls and diabetic women (mean +/- sem, 21.7 +/- 1.2 vs. 24.4 +/- 2.0 mmHg). Maximum foetoplacental arterial pressure at highest dose of indomethacin was 32.8 +/- 3.0 mmHg in controls vs. 27.3 +/- 2.3 mmHg in diabetic women. The indomethacin-induced increase in pressure was reduced in diabetes (2.9 +/- 0.7 vs. 11.2 +/- 2.4 mmHg in controls, P = 0.01).

CONCLUSIONS

Under baseline conditions, the net effect of all cyclo-oxygenase products in the foetoplacental vascular bed is vasodilation. In diabetes, this vasodilator effect seems significantly impaired.

Impaired KATP channel function in the fetoplacental circulation of patients with type 1 diabetes mellitus

OBJECTIVE

The increased perinatal morbidity in diabetes may be partly related to vascular dysfunction. Because potassium channels play an important role in the regulation of vascular tone, this study explores the impact of diabetes on potassium channel function in the fetoplacental vascular bed.

STUDY DESIGN

Vascular potassium channel function was investigated by ex vivo dual perfusion of isolated placental cotyledons (n = 47). Appropriate control experiments were carried out to exclude nonspecific effects.

RESULTS

Glibenclamide (KATP channel blocker) increased perfusion pressure to a maximum fetoplacental arterial pressure of 37 +/- 6 mm Hg in controls versus 15 +/- 6 mm Hg in diabetes (P < .05). 4-Aminopyridine (KV channel blocker) equally increased fetoplacental arterial pressure in controls, and in diabetes (21 +/- 4 mm Hg vs 22 +/- 2 mm Hg). Apamin and charybdotoxin (KCa channel blockers) caused a negligible rise in fetoplacental arterial pressure.

CONCLUSION

In the fetoplacental circulation, KATP channels and KV channels significantly contribute to baseline vascular tone. In diabetes, vascular KATP channel function is impaired.

Placental folate transport and binding are not impaired in pregnancies complicated by fetal growth restriction

Maternal folate deficiency is associated with fetal growth restriction, however, transfer of folate across placentae of pregnancies complicated by fetal growth restriction has never been investigated. We studied whether maternal to fetal 5-methyltetrahydrofolate (5MTF) transport in the ex vivo dually perfused isolated cotyledon, binding of [(3)H] folate (PteGlu) to the syncytial microvillous membrane, and protein expression of folate receptor alpha (FR-alpha) and reduced folate carrier (RFC) in these placentae are disturbed. Placental clearance of 5MTF from the maternal perfusate appeared to be non-saturable over a range of 50 to 500 nm, independent of albumin and flow-independent. No statistically significant differences between placentae complicated with fetal growth restriction and uncomplicated pregnancies were observed. Binding characteristics of [(3)H-]PteGlu to microvillous membranes of fetal growth restriction versus control placentae were similar: B(max)of 3.9+/-2.0 (mean+/-s.d.) versus 4.0+/-1.6 pmol/mg protein and a K(d)of 0.037+/-0.010 versus 0.040+/-0.018 nm. Expression of FR-alpha and RFC were not different in placentae of both groups studied. In conclusion, fetal growth restriction appears not to be associated with impaired maternal to fetal placental folate transport, placental receptor binding, or expression of FR-alpha and RFC.