Targeted transgenic overexpression of mitochondrial thymidine kinase (TK2) alters mitochondrial DNA (mtDNA) and mitochondrial polypeptide abundance: transgenic TK2, mtDNA, and antiretrovirals

Mitochondrial toxicity limits nucleoside reverse transcriptase inhibitors (NRTIs) for acquired immune deficiency syndrome. NRTI triphosphates, the active moieties, inhibit human immunodeficiency virus reverse transcriptase and eukaryotic mitochondrial DNA polymerase pol-gamma. NRTI phosphorylation seems to correlate with mitochondrial toxicity, but experimental evidence is lacking. Transgenic mice (TGs) with cardiac overexpression of thymidine kinase isoforms (mitochondrial TK2 and cytoplasmic TK1) were used to study NRTI mitochondrial toxicity. Echocardiography and nuclear magnetic resonance imaging defined cardiac performance and structure. TK gene copy and enzyme activity, mitochondrial (mt) DNA and polypeptide abundance, succinate dehydrogenase and cytochrome oxidase histochemistry, and electron microscopy correlated with transgenesis, mitochondrial structure, and biogenesis. Antiretroviral combinations simulated therapy. Untreated hTK1 or TK2 TGs exhibited normal left ventricle mass. In TK2 TGs, cardiac TK2 gene copy doubled, activity increased 300-fold, and mtDNA abundance doubled. Abundance of the 17-kd subunit of complex I, succinate dehydrogenase histochemical activity, and cristae density increased. NRTIs increased left ventricle mass 20% in TK2 TGs. TK activity increased 3 logs in hTK1 TGs, but no cardiac phenotype resulted. NRTIs abrogated functional effects of transgenically increased TK2 activity but had no effect on TK2 mtDNA abundance. Thus, NRTI mitochondrial phosphorylation by TK2 is integral to clinical NRTI mitochondrial toxicity.

Disassociation of bone resorption and formation by GLP-2: a 14-day study in healthy postmenopausal women

We have previously shown that a single subcutaneous injection of glucagon-like peptide-2 (GLP-2) at 10 p.m. in postmenopausal women results in a dose-dependent decrease in the nocturnal serum and urine concentrations of fragments derived from the degradation of the C-terminal telopeptide region of collagen type I (s-CTX and u-CTX) and u-DPD, markers of bone resorption. In contrast, bone formation, as assessed by serum osteocalcin and procollagen type I N-terminal propeptide (PINP), appeared to be unaffected by treatment with exogenous GLP-2. These effects were further investigated in a 14-day study. The aim was to demonstrate that a parenteral formulation of GLP-2 is safe and well tolerated after repeated dosing in healthy postmenopausal women for 14 days. It was further investigated whether the effects on bone turnover markers were sustained throughout the study period. The study was a double-blind placebo-controlled trial with 60 postmenopausal women and 2 different doses of GLP-2 (1.6 mg and 3.2 mg GLP-2) against a saline control. The data for bone resorption revealed a similar reduction on Day 1 and Day 14, both based on time course and AUC. There were no signs of tachyphylaxis and no serious adverse reaction. Both GLP-2 doses resulted in similar and significant (p<0.001) reduction in bone resorption indicating that the maximum efficacious dose has been approached. Osteocalcin and PINP levels were unaffected at Day 1 and Day 14, suggesting a disassociation between bone resorption and bone formation during GLP-2 treatment.

Effect of chemotherapy on skeletal health in male survivors from testicular cancer and lymphoma

PURPOSE

There are concerns over the late effects of cancer therapy, including accelerated bone loss leading to increased risk of osteoporosis. Treatment-related bone loss is well recognized in breast and prostate cancer, due to overt hypogonadism, but there has been little evaluation of the skeletal effects of chemotherapy alone in adults. This study assesses the extent of bone loss due to previous chemotherapy in men.

EXPERIMENTAL DESIGN

The bone mineral density (BMD) of men who had received previously chemotherapy with curative intent for lymphoma or testicular cancers was compared with that of an age-matched population of men from a cancer control population that had not received chemotherapy. BMD was measured by dual-energy X-ray scanning. Additionally, measurement of sex hormones and the bone turnover markers N-telopeptide fragment of type I collagen and bone-specific alkaline phosphatase were done. All statistical tests were two sided.

RESULTS

One hundred fifteen chemotherapy-treated patients and 102 cancer controls were recruited. There was no statistical difference in BMD between the chemotherapy and control groups at either spine or hip and the mean BMD values in both groups were no lower than that of a reference population. There were no significant differences in estradiol, luteinizing hormone, and testosterone, but follicle-stimulating hormone values were significantly higher in the chemotherapy group (P=0.011). The mean values of NH2-terminal telopeptide fragment of type I collagen and bone-specific alkaline phosphatase were within the reference ranges.

CONCLUSIONS

The absence of accelerated bone loss following chemotherapy is reassuring and suggests that standard dose cytotoxic chemotherapy has no lasting clinically important direct effects on bone metabolism.

Influence of the sample matrix on the stability of beta-CTX at room temperature for 24 and 48 hours

The measurement of beta-C-telopeptides of type I collagen (beta-CTX) reflects the rate of bone resorption in a variety of metabolic bone disorders and it is increasingly used to assist diagnosis and follow-up of these pathologies. Since preanalytical biases in the results of this marker can decrease its clinical usefulness, specific stability studies should be developed to prevent that inconsistent results of laboratory testing might affect patient health and waste economical resources. Three blood samples were simultaneously collected without venous stasis into evacuated tubes containing no additives, K2 EDTA or lithium heparin, from 23 out-patients referred to our phlebotomy service for routine laboratory testing. After centrifugation and separation of the specimens, a first aliquot was immediately analyzed, whereas a second and third aliquot was processed after a 24- and 48-hour storage at room temperature (21 degrees C). Beta-CTX was assayed on the automated electrochemiluminescence analyzer E170. A modest and clinically irrelevant underestimation was observed in lithium heparin plasma when compared with either K2 EDTA (-7.1%; 95% C.I. -2.0 to -12.3%; p < 0.001) or serum (-7.8%; 95% C.I. -3.2 to -12.4%; p < 0.001), but not between serum and K2 EDTA (+0.8%, 95% C.I. -5.3 to +6.9%; p = 0.260). Storage at room temperature in K2 EDTA plasma introduced a modest and clinically negligible decay in immunoreactivity (-4.4% and -5.7% at 24 and 48 hours, respectively), whereas storage at room temperature in both serum (-17.6% and -28.6% at 24 and 48 hours, respectively) and lithium heparin plasma (-29.1% and -44.0% at 24 and 48 hours, respectively) was associated with a substantial decay and a larger inter-individual variability in the measurable concentration of the analyte. In conclusion, the results of our investigation demonstrate that EDTA plasma is the most suitable sample matrix for the storage of beta-CTX at room temperature after centrifugation.

Effects of lipopolysaccharide on gene expression of antimicrobial peptides (penaeidins and crustin), serine proteinase and prophenoloxidase in haemocytes of the Pacific white shrimp, Litopenaeus vannamei

For shrimp immune defences, prophenoloxidase (proPO) activating system and antimicrobial peptides in circulating haemocytes play important roles. In the present study, the effects of lipopolysaccharide (LPS) injection on gene expression of penaeidins, crustin, serine proteinase and proPO in haemocytes were determined using real-time reverse transcription-polymerase chain reaction (PCR) in the Pacific white shrimp Litopenaeus vannamei. After injection of LPS, mRNA levels of antimicrobial peptides, penaeidin 2 (PEN2), penaeidin 3 (PEN3), penaeidin 4 (PEN4) and crustin decreased in a dose-dependent manner, while mRNA levels of serine proteinase and proPO did not change significantly. In a time-course experiment, injection of LPS caused significant depression in mRNA levels of PEN2, PEN3, PEN4 and crustin at 4h post-injection, and the depressed mRNA levels returned to initial levels by 72h post-injection. On the other hand, mRNA levels of serine proteinase and proPO did not show a significant change after injection. These results suggest that the antimicrobial peptide system responds to LPS injection at a gene expression level while the proPO system does not respond at a gene expression level.

Heparin modulation of human plasma kallikrein on different substrates and inhibitors

The interplay of different proteases and glycosaminoglycans is able to modulate the activity of the enzymes and to affect their structures. Human plasma kallikrein (huPK) is a proteolytic enzyme involved in intrinsic blood clotting, the kallikrein-kinin system and fibrinolysis. We investigated the effect of heparin on the action, inhibition and secondary structure of huPK. The catalytic efficiency for the hydrolysis of substrates by huPK was determined by Michaelis-Menten kinetic plots: 5.12x10(4) M-1 s-1 for acetyl-Phe-Arg-p-nitroanilide, 1.40x10(5) M-1 s-1 for H-D-Pro-Phe-Arg-p-nitroanilide, 2.25x10(4) M-1 s-1 for Abz-Gly-Phe-Ser-Pro-Phe-Arg-Ser-Ser-Arg-Gln-EDDnp, 4.24x10(2)M-1 s-1 for factor XII and 5.58x10(2) M-1 s-1 for plasminogen. Heparin reduced the hydrolysis of synthetic substrates (by 2.0-fold), but enhanced factor XII and plasminogen hydrolysis (7.7- and 1.4-fold, respectively). The second-order rate constants for inhibition of huPK by antithrombin and C1-inhibitor were 2.40x10(2) M-1 s-1 and 1.70x10(4) M-1 s-1, respectively. Heparin improved the inhibition of huPK by these inhibitors (3.4- and 1.4-fold). Despite the fact that huPK was able to bind to a heparin-Sepharose matrix, its secondary structure was not modified by heparin, as monitored by circular dichroism. These actions may have a function in the control or maintenance of some pathophysiological processes in which huPK participates.

Anticancer α-Helical Peptides and Structure / Function Relationships Underpinning Their Interactions with Tumour Cell Membranes

Cancer is a major cause of premature death and there is an urgent need for new anticancer agents with novel mechanisms of action. Here we review recent studies on a group of peptides that show much promise in this regard, exemplified by arthropod cecropins and amphibian magainins and aureins. These molecules are alpha-helical defence peptides, which show potent anticancer activity (alpha-ACPs) in addition to their established roles as antimicrobial factors and modulators of innate immune systems. Generally, alpha-ACPs exhibit selectivity for cancer and microbial cells primarily due to their elevated levels of negative membrane surface charge as compared to non-cancerous eukaryotic cells. The anticancer activity of alpha-ACPs normally occurs at micromolar levels but is not accompanied by significant levels of haemolysis or toxicity to other mammalian cells. Structure/function studies have established that architectural features of alpha-ACPs such as amphiphilicty levels and hydrophobic arc size are of major importance to the ability of these peptides to invade cancer cell membranes. In the vast majority of cases the mechanisms underlying such killing involves disruption of mitochondrial membrane integrity and/or that of the plasma membrane of the target tumour cells. Moreover, these mechanisms do not appear to proceed via receptor-mediated routes but are thought to be effected in most cases by the carpet/toroidal pore model and variants. Usually, these membrane interactions lead to loss of membrane integrity and cell death utilising apoptic and necrotic pathways. It is concluded that that alpha-ACPs are major contenders in the search for new anticancer drugs, underlined by the fact that a number of these peptides have been patented in this capacity.

The diabetogenic antibiotic streptozotocin modifies the tryptic digest pattern for peptides of the enzyme O-GlcNAc-selective N-acetyl-β-d-glucosaminidase that contain amino acid residues essential for enzymatic activity

Streptozotocin (STZ) inhibits O-GlcNAc-selective N-acetyl-beta-d-glucosaminidase (O-GlcNAcase), the enzyme that removes O-GlcNAc from proteins. The active site of the enzyme was recently proposed to include aspartates 174, 175, and 177, with STZ inhibition via a transition state analog. We explored the effect of STZ on the tryptic peptide digest pattern of O-GlcNAcase. LC/MS/MS analysis demonstrated that STZ modified two areas of the enzyme. One peptide, LGCFEIAK (894-901), in a C-terminal region previously proposed to possess O-GlcNAcase activity, was methylated by STZ. Another peptide, EYEIEFIYIASPGLDITFSNPK (128-149), was detected only after treatment with STZ and was in an N-terminal region, overlapping a glutamate-rich area containing an adjacent phenylalanine residue. No covalent modification of this peptide could be demonstrated. Detection of this peptide after treatment with STZ was accompanied by the simultaneous inability to detect the nearby peptide KLDQVSQFGCR (157-167), which contains a cysteine residue recently shown to be essential for enzymatic activity. To determine which of the first two peptides might also be important for O-GlcNAcase activity, site-specific mutagenesis was performed. Mutation of the N-terminal phenylalanine and serine residues resulted in almost complete inhibition of activity. In contrast, mutation of conserved C-terminal glycine and cysteine residues caused little inhibition of enzymatic activity. Together, these data extend the region of the active site N-terminally and give independent evidence to support the idea that STZ inhibits O-GlcNAcase through formation of a transition state analog that resides in the active site of the enzyme and in doing so alters its conformation and ensuing tryptic digest pattern.

Comparison of the effects of 2,2,2-trifluoroethanol on peptide and protein structure and function

The co-solvent 2,2,2-trifluoroethanol (TFE) has been often used to aid formation of secondary structure in solution peptides or alternately as a denaturant within protein folding studies. Hen egg white lysozyme (HEWL) and a synthetic model peptide defining HEWL helix-4 were used as comparative model systems to systematically investigate the effect of increasing TFE concentrations on the structure of proteins and peptides. HEWL was analyzed using NMR, far-UV CD and fluorescence spectroscopy; with correlation of these results towards changes in enzymatic activity and the helix-4 peptide was analysed using NMR. Data illustrates two conflicting modes of interaction: Low TFE concentrations stabilize tertiary structure, observed from an increase in the number of NMR NOE contacts. Higher TFE concentrations denatured HEWL with the loss of lysozyme tertiary structure. The effects of TFE upon secondary structural elements within HEWL are distinct from those observed for the helix-4 peptide. This illustrates a dissimilar interaction of TFE towards both protein and peptide at equivalent TFE concentrations. The concentration that TFE promotes stabilization over denaturation is likely to be protein dependent although the structural action can be extrapolated to other protein systems with implications for the use of TFE in structural stability studies.

Influence of hormone replacement therapy on proteomic pattern in serum of postmenopausal women

OBJECTIVES

Proteomics approaches to cardiovascular biology and disease hold the promise of identifying specific proteins and peptides or modification thereof to assist in the identification of novel biomarkers.

METHOD

By using surface-enhanced laser desorption and ionization time of flight mass spectroscopy (SELDI-TOF-MS) serum peptide and protein patterns were detected enabling to discriminate between postmenopausal women with and without hormone replacement therapy (HRT).

RESULTS

Serum of 13 HRT and 27 control subjects was analyzed and 42 peptides and proteins could be tentatively identified based on their molecular weight and binding characteristics on the chip surface. By using decision tree-based Biomarker Patternstrade mark Software classification and regression analysis a discriminatory function was developed allowing to distinguish between HRT women and controls correctly and, thus, yielding a sensitivity of 100% and a specificity of 100%. The results show that peptide and protein patterns have the potential to deliver novel biomarkers as well as pinpointing targets for improved treatment. The biomarkers obtained represent a promising tool to discriminate between HRT users and non-users.

CONCLUSION

According to a tentative identification of the markers by their molecular weight and binding characteristics, most of them appear to be part of the inflammation induced acute-phase response.

Identification of 17-alpha-ethynylestradiol-modified active site peptides and glutathione conjugates formed during metabolism and inactivation of P450s 2B1 and 2B6

The oral contraceptive 17-alpha-ethynylestradiol (17EE) is a mechanism-based inactivator of cytochrome P450s (P450s) 2B1 and 2B6. Inactivation of P450s 2B1 and 2B6 in the reconstituted system by [3H]17EE resulted in labeling of the P450 apoprotein. Mass spectral analysis of 17EE-inactivated P450 2B1 showed an increase in the mass of the apoprotein by 313 Da, consistent with the mass of 17EE plus one oxygen atom. P450s 2B1 and 2B6 were inactivated with [3H]17EE and digested with CNBr. Separation of these peptides resulted in the identification of one major labeled peptide for each enzyme. N-Terminal sequencing of these peptides yielded the amino acid sequences PYTDAVIHEI (for P450 2B1) and PYTEAV (for P450 2B6) that corresponded to amino acids P347-M376 and P347-M365 in P450s 2B1 and 2B6, respectively. Electrospray ionization (ESI)-liquid chromatography-mass spectrometry (LC-MS) and matrix-assisted laser desorption ionization (MALDI)-MS analysis of the P450 2B1-derived peptide resulted in a mass of 3654 Da consistent with the mass of the P347-M376 peptide (3385 Da) plus a 268 Da 17EE adduct. Chemically reactive intermediates of 17EE that were generated during the metabolism of 17EE by P450s 2B1 and 2B6 were trapped with gluthathione (GSH). ESI-LC-MS/MS analysis of 17EE-GSH conjugates from the incubation mixtures indicated that P450s 2B1 and 2B6 generated different reactive 17EE intermediates that were responsible for the inactivation and protein modification or the formation of GSH conjugates by these two enzymes.

A randomized, placebo-controlled, 6-month study of once-weekly alendronate oral solution for postmenopausal osteoporosis

OBJECTIVE

This study evaluated the overall safety and tolerability of once-weekly (OW) alendronate 70 mg oral solution (OS) versus OW placebo OS.

METHODS

Postmenopausal, osteoporotic women were enrolled at 51 centers in the United States in a 6-month double-blind, randomized trial. Patients were randomized (1:1) to OW alendronate 70 mg OS or placebo OS. The primary end point was the proportion of patients reporting any upper gastrointestinal (UGI) adverse event (AE) at 6 months. Secondary end points included mean percentage change in urinary N-telopeptide of type I human collagen (NTx) and serum bone-specific alkaline phosphatase (BSAP) at 6 months.

RESULTS

Initially, 454 women were enrolled; 392 (86.3%) completed the study. The mean (SD) age was 65.2 (10) years, and the mean (SD) time since menopause was 19.1 (12) years. The proportion of patients experiencing any UGI AE was significantly higher with alendronate OS (23.7%) compared with placebo solution (15.3%), with a treatment difference of 8.3% (95% CI, 0.8%-15.8%; P = 0.024). The proportion of patients experiencing any esophageal AE was 4.0% with alendronate and 3.0% with placebo (treatment difference, 1.0% [95% CI, -2.7% to 4.8%]). In addition, 4.5% of alendronate and 8.7% of placebo patients discontinued the study due to any clinical AE, and 3.3% of alendronate and 1.8% of placebo patients discontinued due to a UGI AE (difference, 1.5% [95% CI, -1.5% to 4.4%]). Alendronate OS produced significantly greater reductions in both NTx and BSAP than placebo (differences, -47.5% and -38.7%, respectively [both, P < 0.001]).

CONCLUSIONS

In this 6-month study, patients receiving OW alendronate 70 mg OS had a higher rate of UGI AEs than placebo patients. However, rates of serious UGI AEs, discontinuations due to UGI AEs, and esophageal AEs were similar between groups. UGI AEs in the study were generally mild to moderate in severity and did not result in treatment discontinuation. In addition, OW alendronate 70 mg OS significantly reduced biochemical markers of bone turnover.

Effect of Norplant contraceptive on the bones of Nigerian women as assessed by quantitative ultrasound and serum markers of bone turnover

Levonorgestrel is a commonly used progestin-only contraceptive that is available as subdermal (Norplant) and intrauterine implants. Other progestin-only contraceptives such as injectable medroxyprogeterone acetate have been shown to decrease bone mineral density in long-term users. We used calcaneal ultrasound to compare the bone quality of Nigerian women between 25 and 50 years of age who had Norplant implants for 1-4 years to that of women who were not using any form of hormonal contraceptive. The mean stiffness index of women who had Norplant implants for as long as 4 years was not significantly different from that of controls. However, serum markers of bone turnover were significantly decreased in women with Norplant implants compared to age-matched controls. Serum bone-specific alkaline phosphatase was significantly decreased in subjects with Norplant implants for 1 year (13.7+/-6.0 vs. 23.0 U/L for controls, p = .001) and serum NTx was significantly decreased in subjects with implants for 3 years (10.6+/-4.9 vs. 17.6+/-7.7 bone collagen equivalents per liter for controls, p < .001). We conclude that although levonorgestrel contraceptive decreased overall bone turnover, it had no deleterious effect on the bone quality of women using Norplant implants for up to 4 years.

Characterization of adrenomedullin in birds

Adrenomedullin (AM) is a multifunctional evolutionarily highly conserved peptide. Although its genomic and amino acid (aa) sequences are known in several mammalian species and in fish, the structure of the AM gene remains unknown in intermediate phyla, including birds. Here, we report the structure and aa sequence of the chicken (c) AM ortholog. The cAM gene is located at the short arm of chromosome 5, which shows high synteny with the short arm of human (h) chromosome 11, where hAM is located. Key sequences in the third intron have been conserved which allow for an alternative splicing mechanism, similar to the one found in mammals. The preprohormone contains two peptides with high homology to human proadrenomedullin N-terminal 20 peptide (PAMP) and hAM. We found through real-time PCR and immunocytochemistry cAM mRNA and peptide expression in a variety of chicken tissues, which parallel patterns observed for mammals, with the exception that cAM levels are almost non-detectable in brain. Similarly to mammals, cAM expression is upregulated under hypoxic conditions and following dexamethasone treatment. These data demonstrate a high degree of homology between the cAM gene and its mammalian ortholog and evolutionary conservation of the regulatory mechanisms controlling its expression.

Adrenomedullin: a new target for the design of small molecule modulators with promising pharmacological activities

Adrenomedullin (AM) is a 52-amino acid peptide with a pluripotential activity. AM is expressed in many tissues throughout the body, and plays a critical role in several diseases such as cancer, diabetes, cardiovascular and renal disorders, among others. While AM is a protective agent against cardiovascular disorders, it behaves as a stimulating factor in other pathologies such as cancer and diabetes. Therefore, AM is a new and promising target for the development of molecules which, through their ability to regulate AM levels, could be used in the treatment of these pathologies.

Enhanced gene transfer activity of peptide-targeted gene-delivery vectors

We have evaluated the capacity of the cell-binding heptapeptide SIGYPLP to enhance transgene expression using non-viral and viral gene delivery vectors. Targeted polyplex based vectors showed good levels of DNA uptake in freshly isolated human umbilical vein endothelial cells (HUVECs) compared to untargeted controls, whilst displaying only modest increases in reporter gene activity. The targeted polyplexes showed reduced levels of DNA uptake in cells of a none endothelial origin although they mediated higher levels of transgene expression. The enhanced efficiency of transgene expression may relate to the more rapid rate of cell division. However, since in vivo application of polyplexes is compromised by instability to serum proteins, serum-resistant polyplexes (surface modified with multivalent reactive hydrophilic polymers based on poly[N-(2-hydroxypropyl)methacrylamide] (pHPMA)) were also evaluated for their ability to mediate transgene expression. Surface modification of polyplexes with pHPMA ablates non-specific cell entry, reducing levels of transgene expression, whilst the incorporation of the SIGYPLP peptide into the hydrophilic polymer resulted in restored transgene expression in all formulations tested. The technology of surface modification using pHPMA can also be applied in the context of viruses, masking receptor-binding epitopes and enabling the linkage of novel cell targeting ligands, enabling construction of a virus with receptor-specific infectivity. Retargeting of adenovirus based vectors using the same polymer-peptide construct enhanced levels of transgene expression in HUVECs to greater than 15 times that observed using parental (unmodified) virus, whilst restoring levels of transgene expression in non-endothelial cell lines tested. The use of constructs based on conjugates between hydrophilic polymers and small receptor-binding oligopeptides as agents for retargeting viral or non-viral vectors to cellular receptors represents a simple alternative to the use of antibodies as targeting ligands for cell specific gene delivery.

Statin treatment and a disease-specific pattern of β-amyloid peptides in Alzheimer’s disease

According to the amyloid cascade hypothesis, sporadic Alzheimer's disease (AD) is caused by the production and aggregation of beta-amyloid (Abeta), and the production of Abeta has recently been linked to the metabolism of cholesterol. We have previously published clinical studies where the effect of statin treatment on Abeta production has been investigated. No effect on Abeta was found, which is in disagreement with cell and animal studies. In the present study we investigated the effect of statin treatment on a disease-specific pattern consisting of a C-terminally-truncated quintet of Abeta peptides. Nineteen patients with AD were treated with simvastatin for 12 months and the quintet of Abeta peptides were analysed in cerebrospinal fluid before and after treatment. Also included was a group of 15 untreated patients with AD. We found that the Abeta peptide pattern at baseline was in agreement with earlier findings; however, we did not find any change in the Abeta peptide pattern after statin treatment. We suggest that clinical studies with extended treatment periods are performed where higher dosages of statins are used. We also believe that the pleiotropic effects of statins should be investigated further in order to elucidate the connection between Alzheimer's disease and statin treatment.

Impact of azaproline on Peptide conformation

The amino acid analog azaproline (azPro) contains a nitrogen atom in place of the C(alpha) of proline. Peptides containing azPro were shown to stabilize the cis-amide conformer for the acyl-azPro bond and prefer type VI beta-turns both in crystals and in organic solvents by NMR. The increased stability for cis-amide conformers was relatively minor with respect to the trans-conformers. Further, their conformational preferences were depended on solvent. To elucidate the impact of azPro substitution on amide cis-trans isomerism and peptide conformation, this paper reports ab initio studies on azPro derivatives and a comparison with their cognate Pro derivatives: 1-acetyl-2-methyl pyrrolidine (1), 1-acetyl-2-methyl pyrazolidine (2), Ac-Pro-NHMe (3), Ac-azPro-NHMe (4), Ac-azPro-NMe(2) (5), Ac-azAzc-NHMe (6), and Ac-azPip-NHMe (7). Conformational preferences were explored at the MP2/6-31+G** level of theory in vacuo. Solvation effects for 1 and 2 were studied implicitly using the polarizable continuum model and explicitly represented by interactions with a single water molecule. An increase in the conformational preference for the cis-amide conformer of azPro was clearly seen. An intramolecular hydrogen bond occurred solely in the trans-amide conformer that reduced the preference for the cis-conformer by 2.2 kcal/mol. The larger ring homolog aza-pipecolic acid (azPip), in which this internal hydrogen bond was diminished, significantly augmented stabilization of the cis-amide conformer. In aqueous solution, the preference for the cis-amide conformers was greatly reduced, mainly as a result of interaction between water and the lone pair of the alpha-nitrogen in the trans-amide conformer that was 3.8 kcal/mol greater than that in the cis-conformer. In the azPro analog, the energy barrier for cis-trans amide isomerization was 6 kcal/mol less than that in the cognate Pro derivative. Because the azPro derivatives can stabilize the cis-amide bond and mimic a type VI beta-turn without incorporation of additional steric bulk, such a simple chemical modification of the peptide backbone provides a useful conformational constraint when incorporated into the structure of selected bioactive peptides. Such modifications can scan receptors for biological recognition of reverse turns containing cis-amide bonds by the incorporation of type VI beta-turn scaffolds with oriented appended side chains.

Urea Promotes Polyproline II Helix Formation: Implications for Protein Denatured States

It is commonly assumed that urea denatures proteins by promoting backbone disorder, resulting in random-coil behavior. Indeed, it has been demonstrated that highly denatured proteins obey random-coil statistics. However, the random-coil model is specified by the global geometric properties of a polymeric chain and does not preclude locally ordered backbone structure. While urea clearly disfavors a compact native structure, it is not clear that the resulting backbone conformations are disordered. Using circular dichroism (CD) spectroscopy, we demonstrate that urea promotes formation of left-handed polyproline II (P(II)) helical structures in both short peptides and denatured proteins. The observed increase in P(II) content is sequence-dependent. These data indicate that denatured states possess significant amounts of locally ordered backbone structure. It is time for the formulation of new denatured-state models that take into account the presence of significant local backbone structure. Criteria for such models are outlined.

Interaction of an artificial surfactant in human pulmonary epithelial cells

Surfaxin (lucinactant), a peptide-based surfactant consisting of dipalmitoylphosphatidylcholine (DPPC) plus KL(4) (sinapultide) (a synthetic peptide modeled after human surfactant protein-B), is effective in treating respiratory distress syndrome in preterm infants. Our goal was to determine the uptake and effects of Surfaxin on human pulmonary type II cells isolated from fetal tissue and other lung cell types. Based on previous published reports, we hypothesized that this exogenous synthetic surfactant would have little effect on type II cell surfactant-related physiological features. Human type II cells and A549 and NCI-H441 adenocarcinoma cells incorporated (3)H-KL(4) and (14)C-DPPC components in Surfaxin, but with different kinetics. Fractionation of NCI-H441 and A549 cellular components indicated that the highest specific activity of (3)H-KL(4) was present in the 18,000g cellular fraction (which contains vesicles and lysosomes). The number of lamellar bodies (LBs) appears to increase in human type II cells incubated in the presence of Surfaxin when visualized by light microscopy, while LB structure (determined by electron microscopy) was not altered. Expression of endogenous surfactant protein (SP-A, SP-B, and SP-C) mRNA levels in human type II cells was not altered by the presence of Surfaxin. We conclude that while human type II cells and other lung cell types can incorporate the components of Surfaxin, the surfactant-related physiological functions of these cells are not altered.

FGF-10 induces SP-C and Bmp4 and regulates proximal-distal patterning in embryonic tracheal epithelium

The induction, growth, and differentiation of epithelial lung buds are regulated by the interaction of signals between the lung epithelium and its surrounding mesenchyme. Fibroblast growth factor-10 (FGF-10), which is expressed in the mesenchyme near the distal tips, and bone morphogenetic protein 4 (BMP4), which is expressed in the most distal regions of the epithelium, are important molecules in lung morphogenesis. In the present study, we used two in vitro systems to examine the induction, growth, and differentiation of lung epithelium. Transfilter cultures were used to determine the effect of diffusible factors from the distal lung mesenchyme (LgM) on epithelial branching, and FGF-10 bead cultures were used to ascertain the effect of a high local concentration of a single diffusible molecule on the epithelium. Embryonic tracheal epithelium (TrE) was induced to grow in both culture systems and to express the distal epithelial marker surfactant protein C at the tips nearest the diffusible protein source. TrE cultured on the opposite side of a filter to LgM branched in a pattern resembling intact lungs, whereas TrE cultured in apposition to an FGF-10 bead resembled a single elongating epithelial bud. Examination of the role of BMP4 on lung bud morphogenesis revealed that BMP4 signaling suppressed expression of the proximal epithelial genes Ccsp and Foxj1 in both types of culture and upregulated the expression of Sprouty 2 in TrE cultured with an FGF-10 bead. Antagonizing BMP signaling with Noggin, however, increased expression of both Ccsp and Foxj1.

A study of signal transduction for the two diuretic peptides of Diploptera punctata

We investigated second messengers involved in the action of the CRF-related peptide Dippu-DH46 and the calcitonin-like peptide Dippu-DH31 in Diploptera punctata. Dippu-DH46 causes a dose-dependent increase in intracellular cAMP levels, its diuretic activity is mimicked by cAMP agonists, but is attenuated by Rp-cAMPS. Dippu-DH46 acts synergistically with kinins and thapsigargin; both mobilize intracellular Ca2+. Dippu-DH46 also acts synergistically with cAMP agonists, and its effect is inhibited by a PKC inhibitor, suggesting it also activates intracellular Ca2+. Dippu-DH31 has no effect on cAMP levels and its activity is not blocked by cAMP agonists. Neither peptide stimulated cGMP levels in a dose-dependent manner, nor does cGMP have any effect on fluid secretion.

Five years of treatment with risedronate and its effects on bone safety in women with postmenopausal osteoporosis

We have recently reported that risedronate preserves normal bone formation and decreases bone remodeling in women with postmenopausal osteoporosis after 3 years of treatment. We report now the results of a 2-year extension study. The primary objective of this study was to determine the effect of 5 years of risedronate treatment (5 mg daily) on bone quality and bone remodeling based on paired transiliac bone biopsies. There were additional measurements that included bone turnover markers and bone mineral density (BMD). Histologic evaluation of biopsy sections (placebo, n = 21; risedronate, n = 27) yielded no pathologic findings after 5 years in either treatment group. Histomorphometric assessment of paired biopsy specimens after 5 years (placebo, n =12; risedronate, n = 13) found no statistically significant differences between treatment groups in structural or resorption parameters. There was a significant reduction in osteoid (-27%) and mineralizing surfaces (-49%) from baseline values in the risedronate group that were also significantly different from placebo at 5 years. Similarly, activation frequency decreased significantly (-77%) in the risedronate group, although it was not significantly different from placebo at 5 years (0.09 vs. 0.21, respectively). Double tetracycline labels were identified in all biopsy specimens indicating continuous bone turnover. After 5 years of risedronate treatment, serum bone-specific alkaline phosphatase (bone ALP) and N-telopeptide (NTX) decreased significantly from baseline by 33.3% and 47.5%, respectively. In the placebo group, bone ALP decreased by 3.9% (P = NS), whereas NTX decreased by 27.0% (P < 0.005). Lumbar spine BMD increased significantly in the risedronate group (9.2%), whereas no significant change was seen in the placebo group (-0.26%). Risedronate was overall well tolerated; during the 2-year study extension nonvertebral fractures occurred in 7 patients in placebo and 2 patients in risedronate groups. The findings from this study are consistent with the antiremodeling effect of risedronate and support long-term bone safety and antifracture efficacy of risedronate treatment.

Peptide metabolism and the control of body fluid homeostasis

In this paper, we review our current understanding of the medicinal chemistry of the major peptide systems, which influence body fluid homeostasis. Electrolytes play pivotal roles in intra- and intercellular communication, acid-base equilibrium and, when bound to several macromolecules, they regulate a myriad of enzymatic proteins, receptors and transcription factors. Cell turgor influences the plasma membrane, which activates mechanically-gated ion channels or mechanoreceptors, and the expression of a number of genes which underlie long-term metabolic responses to hormones, substrates and reactive oxygen intermediates. The altered kinetics and enzymatic cleavage of peptides during water-electrolyte imbalance can contribute to cardiac and renal damage associated with elevated blood pressure. Identification of the enzymes which are responsible for cleavage, together with emerging information about the mechanisms of action and structures of regulatory and effector peptides, has laid a foundation for the discovery of novel drugs, some of which are in use or are now undergoing evaluation in experimental trials. The development of models of hydrosaline challenge with relative efficiency to induce selective water-electrolyte imbalance has permitted the identification of kallikrein-kinin, renin-angiotensin-aldosterone, vasopressin-oxytocin, thyrotropin-releasing hormone and luteinizing hormone-releasing hormone as susceptible substrates. At present, the angiotensin-I converting enzyme inhibitors are well-known efficacious, orally active, blood pressure-lowering agents which have been used in hypertensive patients. In addition to several new analogues of this class of drug, some selective dual inhibitors of angiotensin-I converting enzyme and neutral endopeptidase and inhibitors of aminopeptidases are now also being rationally assayed and their beneficial effects on hypertension and hydromineral balance indicate that this type of drug may have powerful therapeutic effects for disorders of body fluid homeostasis.