Preterm birth: associated neuroendocrine, medical, and behavioral risk factors

Increased CRH secretion by the placenta of pregnant women has been associated with preterm birth. Certain indices of risk, both medical and psychosocial in nature, have been linked to preterm delivery. Levels of total, bound, and free CRH, CRH-binding protein (CRH-BP), and cortisol were measured prospectively in a large sample of pregnant Danish women who delivered preterm and term infants. Measures of maternal serum hormones were taken at 7--23 and 27--37 weeks gestation and, for those who delivered at term, at 37--43 weeks gestation. At 7--23 weeks gestation, maternal levels of total CRH (P = 0.01), bound CRH (P = 0.03), and CRH-BP (P = 0.01) were higher in the preterm than in the term group. At 27--37 weeks gestation, levels of total CRH (P < 0.0001), bound CRH (P < 0.0001), free CRH (P < 0.0001), and cortisol (P < 0.0001) were all higher in the preterm than the term group, whereas levels of CRH-BP (P < 0.0001) were lower in the preterm than in the term group. The best medical and behavioral factors associated with preterm delivery were, respectively, previous preterm delivery (P < 0.0001) and engagement in certain risk-taking behaviors (P = 0.008). The positive relations between preterm delivery and various adverse medical and socioeconomic variables with increases in placental secretion of CRH suggest that the latter may participate in the pathophysiology of preterm delivery.

Corticotropin-releasing factor (CRF), CRF-binding protein (CRF-BP), and CRF/CRF-BP complex in Alzheimer's disease and control postmortem human brain

In Alzheimer's disease (AD) there are dramatic reductions in human corticotropin-releasing factor (hCRF) concentration and reciprocal increases in CRF receptor density in the cortex. hCRF-binding protein (hCRF-BP), hCRF/hCRF-BP complex, and "free" hCRF were measured in 10 brain regions from control and AD postmortem human tissue. In the control brains hCRF-BP was heterogenously distributed and levels were at least 10-fold higher on a molar basis than total hCRF levels, suggesting that one major role of the binding protein is to limit the actions of hCRF at the hCRF receptors. Concordant with this hypothesis, the percentage of total hCRF that was in the bound inactive form ranged from 65 to 90% in most areas examined, with the exception of the caudate and globus pallidus where only 15 and 40% were complexed, respectively. hCRF-BP concentrations were similar in the control and AD groups except for Brodmann area (BA) 39 where there was a small but significant decrease in the AD group. Complexed hCRF levels were significantly decreased in BA 8/BA 9, BA 22, BA 39, nucleus basalis, and globus pallidus in the Alzheimer's group and free hCRF levels were significantly decreased only in three brain areas, BA 4, BA 39, and caudate; substantial (40%) but nonsignificant decreases were also noted in BA 8/BA 9 and BA 22. These data demonstrate that (1) a large proportion of the total hCRF in human brain is complexed to hCRF-BP and thus unavailable for hCRF receptor activation, (2) reductions in total hCRF alone do not necessarily predict reductions in bioactive free hCRF, and (3) total hCRF levels and hCRF-BP levels appear to be the main factors determining the quantity of bound and free hCRF in human brain.

Measurement of corticotropin-releasing factor (CRF), CRF-binding protein (CRF-BP), and CRF/CRF-BP complex in human plasma by two-site enzyme-linked immunoabsorbant assay

The actions of human corticotropin-releasing factor (hCRF) in brain, pituitary, and plasma are modulated by a 37-kDa protein [CRF-binding protein (CRF-BP)] that binds to hCRF and neutralizes the peptide's biological activity, suggesting that only the free unbound peptide is biologically active. To accurately predict the biological consequences resulting from changes in total hCRF levels, we have developed two-site enzyme-linked immunosorbent assays (ELISAs) for hCRF-BP, free hCRF, and the hCRF-BP/hCRF complex. The assays were validated by measuring each factor in 1) maternal plasma at times when CRF and hCRF-BP levels are altered, and 2) plasma from normal elderly human subjects who have undergone a hCRF stimulation test. The hCRF-BP ELISA has a sensitivity of 2.7 fmol and a range of detection from 2.7-8000 fmol. Both the hCRF and hCRF-BP/ hCRF assays have a sensitivity of 0.4 fmol, with a useful range of detection from 0.4-40 fmol. Maternal plasma hCRF-BP levels remained unaltered between the 16-21 and 34-39 month gestational age groups. However, levels rose from 0.88 +/- 0.069 nmol/L in the 16-21 month gestational age group to 1.01 +/- 0.09 nmol/L in the 28-33 month gestational age group. Bound hCRF levels dramatically rose from undetectable at 16-21 months of gestation to 200 +/- 69 and 442 +/- 106 pmol/L in the 28-33 and 34-39 month gestational age groups, respectively. In comparison, free hCRF levels remained low throughout gestation, but dramatically rose to 318 +/- 120 pmol/L from 34-39 months of gestation. Binding site occupancy on the hCRF-BP decreased when bound and free hCRF levels were elevated. After treating the third trimester plasma sample with the high affinity hCRF-BP ligand, alpha-helical CRF-(9-41), all of the bound hCRF was displaced from the binding protein, and free hCRF levels rose from 87 to 284 pmol/L. The plasma hCRF-BP level was 0.9 +/- 0.08 nmol/L in normal human volunteers (10 men and 9 women; mean +/- SD age, 74.2 +/- 7.7 yr), decreased to 60% of basal levels 15 min after a bolus injection of 1 microgram/kg synthetic hCRF, and gradually returned to preinjection levels after 120 min. Conversely, bound and free hCRF levels increased from undetectable levels before hCRF injection to 0.58 +/- 0.03 nmol/L at 15 min and then rapidly decreased to undetectable levels at 120 min. These data validate the ELISAs in combination with high affinity hCRF-BP ligands for measuring bound and free hCRF in human plasma and suggest the utility of these assays for further determining alterations in peripheral CRF in conditions such as pregnancy.

Urocortin interaction with corticotropin-releasing factor (CRF) binding protein (CRF-BP): a novel mechanism for elevating "free' CRF levels in human brain

Here we demonstrate that urocortin, a new mammalian member of the corticotropin-releasing factor (CRF) neuropeptide family has high affinity for both the recombinant human CRF binding protein (CRF-BP) and for a membrane-associated form of the protein solubilized from postmortem human cerebrocortical brain tissue. The rank order of binding potency for both the human recombinant CRF-BP and for the solubilized human brain CRF-BP is: urotensin > hCRF > urocortin > sauvagine. The bound hCRF/hCRF-BP complex was detected in the postmortem human brain tissue using an ELISA assay specific for the hCRF/hCRF-BP complex. A large proportion (65%) of the endogenous hCRF was found to be complexed to the CRF-BP and thus unavailable for CRF receptor activation. Incubation of human brain postmortem tissue extracts with urocortin and urotensin resulted in a dramatic decrease in hCRF/hCRF-BP levels and a concomitant increase in "free' hCRF levels. Thus, urocortin and other putative CRF-related peptides may elevate endogenous levels of "free' hCRF in brain by displacing hCRF from the binding protein. These data define an indirect endogenous mechanism for activation of CRF receptors by new mammalian members of the CRF family of neuropeptides.