Abstract 430: PCPE2 a Novel Determinant in HDL Biogenesis and Metabolism

Recent attempts to reduce cardiovascular events by pharmacologically raising plasma HDL concentration have not proven efficacious. This has lead to investigations on how to increase functional versus dysfunctional plasma HDL. Our work shows that a functional subfraction from ABCA1 mediated biogenesis of nascent HDL (nHDL) consists of 3 apoA-I, 105 phosphotidylcholine, 27 sphingomyelin and 108 free cholesterol molecules, compositionally reminiscent of lipid rafts. Our studies are now focused on procollagen C-proteinase enhancer 2 (PCPE2), first described by Francone, OL, et al. (2011), to play a significant role in the ABCA1 mediated efflux of cholesterol to apoA-I. Based on previous studies, we hypothesize that PCPE2 binds lipid-free apoA-I thereby aligning specific helices among 3 molecules of apoA-I for lipidation. To test this, we created loss-of-function apoA-I mutant proteins to identify specific helical repeats that participated in nHDL formation. The various mutations span the central helices as well as the N- and C- termini of apoA-I. Opposing cysteines were placed within 3-5 å using a composite 3-D model of lipid-free apoA-I conformation. The mutant apoA-I disulfide “locked” (oxidized) and “unlocked” (reduced) status was monitored using mass spectrometric sequencing. Using both locked and unlocked versions of each of the mutant proteins, secondary structure as well as the extent of lipidation was investigated. In addition, studies, utilizing LDL receptor, PCPE2 double knockout mice (LDLr -/- , PCPE2 -/- ) fed an atherogenic diet have been carried out. Despite having a higher HDL concentration LDLr -/- , PCPE2 -/- mice had significantly more aortic lipid deposition compared to LDLr -/- mice. The absence of PCPE2 substantially reduced the ability to efflux cholesterol suggesting that the HDL was dysfunctional. These data strongly suggest that PCPE2 participates in lipidation by helping apoA-I to either open or target a site on ABCA1 that promotes apoA-I opening.

Reduced hepatic growth hormone (GH) receptor gene expression and increased plasma GH binding protein in experimental uremia

In uremia, reduced longitudinal growth and decreased hepatic insulin-like growth factor-I (IGF-I) secretion despite elevated GH serum levels point to an insensitivity to the action of GH. The molecular basis that accounts for this insensitivity could comprise decreased GH receptor expression in the target organs for GH or binding of GH in the circulation to substances that compete with the receptor. To address this hypothesis, the abundance of hepatic GH receptor mRNA was measured by solution hybridization RNase protection assay in uremic female Sprague-Dawley rats, following two-stage 5/6 nephrectomy, and in pair-fed and in ad libitum-fed sham-operated controls; rat GH binding protein (GHBP) plasma concentration was measured by a sensitive direct RIA. Uremia was associated with a 50% decrease of hepatic GH receptor expression compared to pair-fed controls, which themselves showed a 25% reduction of hepatic GH receptor mRNA abundance when compared to ad libitum-fed controls. Plasma GHBP levels in uremia were markedly higher than in both control groups. Treatment with recombinant human GH (rhGH) (10 IU/kg body wt per day s.c. for 10 days) led to a comparable induction of IGF-I plasma levels and weight gain in uremia and pair-fed controls, indicating that the insensitivity to GH in uremia can be overcome by large rhGH doses. Subcutaneous rhGH injections did not significantly alter the hepatic GH receptor transcript abundance or plasma GHBP levels in any of the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Nonsquamous cancer of the vagina

This report retrospectively analyzes 48 cases of primary vaginal cancer treated at Walter Reed Army Medical Center and the Naval Hospital, Bethesda, from 1962 through 1983. There was an unusually high number of uncommon histologic types. Nine patients had an adenocarcinoma, 5 had a sarcoma, 3 had a melanoma, 2 had an adenosquamous carcinoma, 1 had a lymphoma, and 1 had a carcinoid tumor. The remaining 27 patients had a squamous cell carcinoma. This represents a 43% prevalence of nonsquamous lesions. Nonsquamous cancer of the vagina occurred in patients at an earlier age than squamous cell carcinoma. Presenting symptoms, the location of the tumor within the vagina, and survival rates were similar for both groups. The clinical characteristics and treatment of the patients with nonsquamous tumors are discussed.

The treatment of retroperitoneal fibromatosis with medroxyprogesterone acetate

Wide excision is the recommended primary therapy for retroperitoneal fibromatosis. Radiation therapy and a variety of medications have been used to treat patients with recurrent tumors, but the response to these agents has not been uniform. The patient presented was successfully treated with medroxyprogesterone acetate for recurrent retroperitoneal fibromatosis that was refractory to multiple operative resections and radiation therapy.

Cardiotoxic effects of the venom of the burrowing asp, Atractaspis engaddensis (Atractaspididae, Ophidia)

The venom from the snake Atractaspis engaddensis has a very high lethal potency, with an i.v. LD50 of 0.06-0.075 micrograms per g body weight in mice. The action of the venom is rapid and death results from seemingly neurotoxic effects. However, even at high concentrations, the venom does not block contractions of skeletal muscles that are directly or indirectly stimulated. The most prominent action of the venom is seen in the function of the heart in anesthetized mice, with or without artificial respiration. The changes observed in the ECG are similar to those recorded in human victims and are the result of an A-V block that is caused by an apparent direct action of the venom on the heart.

Nonuniform biosynthesis of multiple hemoglobins in the adult rat and guinea pig

Separation of adult rat bone marrow cells by the method of thin layer countercurrent distribution permits the analyses of 59Fe-tagged erythroid cells for the various multiple hemoglobins and the assignment of such hemoglobins to erythroid cells at different stages of their development. Of the six adult red cell hemoglobins, hemoglobin 5 is synthesized most actively in the earliest erythroid cell whereas hemoglobin 4 (the major hemoglobin of the red cell) is synthesized most actively in the latest erythroid cells, e.g. the reticulocyte. Experimental evidence also indicates that maturation of the erythroid cell is accompanied by a decreased rate of synthesis of hemoglobin 5. The earliest erythroid cells of the marrow contain two hemoglobins, 7 and 8, which are absent in the adult red cell. Similar studies with the guinea pig confirm the nonuniform biosynthesis of its two hemoglobins and suggest that the phenomenon may be a general one among mammalian multiple hemoglobins.