S100A1 utilizes different mechanisms for interacting with calcium-dependent and calcium-independent target proteins

While previous studies have identified target proteins that interact with S100A1 in a calcium-dependent manner as well as target proteins that interact in a calcium-independent manner, the molecular mechanisms of S100A1-target protein interaction have not been elucidated. In this study, point and deletion mutants of S100A1 were used to investigate the contribution of carboxyl terminal amino acids to S100A1 interaction with calcium-dependent and calcium-independent target proteins. First, a recombinant rat S100A1 protein (recS100A1) expressed in bacteria exhibited physical and chemical properties indistinguishable from native S100A1. Next, proteins lacking the carboxyl-terminal nine residues of recS100A1 (Delta85-93), or containing alanine substitutions at Phe 88 (F88A), Phe 89 (F89A), or Trp 90 (W90A), both Phe 88 and Phe 89 (F88/89A), or all three aromatic residues (F88/89A-W90A) were recombinantly expressed. Like recS100A1, F88A, F89A, and W90A proteins interacted with phenyl-Sepharose in a calcium-dependent manner. However, the Delta85-93 protein did not interact with phenyl-Sepharose, indicating that a phenyl-Sepharose-binding region (PSBR) of recS100A1 had been disrupted. The F88/89A and F88/89A-W90A proteins exhibited reduced calcium-dependent interaction with phenyl-Sepharose when compared with recS100A1, demonstrating that the carboxyl-terminal aromatic residues Phe 88, Phe 89, and Trp 90 comprise the PSBR of S100A1. Fluorescence studies showed that the Delta85-93 protein exhibited reduced calcium-dependent interaction with the dodecyl CapZ peptide, TRTK, while W90A bound TRTK with a Kd of 5.55 microM. These results demonstrate that the calcium-dependent target protein-binding site and the PSBR are indistinguishable. In contrast to the calcium-dependent target TRTK, activation of the calcium-independent target protein aldolase A by the point and deletion mutant S100A1s was indistinguishable from native S100A1. These results demonstrate that carboxyl-terminal residues are not required for S100A1 modulation of calcium-independent target protein aldolase A. Alltogether, these results indicate that S100A1 utilizes distinct mechanisms for interaction with calcium-independent and calcium-dependent target proteins.     

Similarity in gallstone formation from 900 kcal/day diets containing 16 g vs 30 g of daily fat: evidence that fat restriction is not the main culprit of cholelithiasis during rapid weight reduction

Diets containing essentially no fat, 1-2 g fat per day, have resulted in cholesterol gallstones. Greater fat may result in less gallbladder stasis. Do gallstones form with greater fat content? We studied 272 moderately obese subjects who had normal gallbladder ultrasonograms. The 900 kcal/day liquid diets contained either 16 g fat (N = 94) or 30 g fat (N = 178) each day for 13 weeks. A second gallbladder ultrasound was performed. Sixteen of 94 (17.0%) of the 16-g fat group developed stones with a weight loss of 18 (+/- 7) kg and a body mass index (BMI) decrease of 6 (+/- 2) kg/m2. Twenty of 178 (11.2%) of the 30-g fat group developed stones (P = 0.18, no difference in stone formation) with similar weight loss of 20 (+/- 7) kg (P = 0.08) and BMI decrease of 7 (+/- 2) kg/m2 (P = 0.04). Substantial fat for rapid weight-reducing diets resulted in gallstone formation. Since experiments have shown that our higher fat diet, containing 10 g fat per meal, results in maximal gallbladder emptying, cholelithiasis from rapid weight loss may not be solely attributable to gallbladder stasis.     

Structure-activity relationship studies of novel carbocyclic influenza neuraminidase inhibitors

A series of influenza neuraminidase inhibitors with the cyclohexene scaffold containing lipophilic side chains have been synthesized and evaluated for influenza A and B neuraminidase inhibitory activity. The size and geometry of side chains have been modified systematically in order to investigate structure-activity relationships of this class of compounds. The X-ray crystal structures of several analogues complexed with neuraminidase revealed that the lipophilic side chains bound to the hydrophobic pocket consisted of Glu276, Ala246, Arg224, and Ile222 of the enzyme active site. The structure-activity relationship studies of this series have also demonstrated remarkably different inhibitory potency between influenza A and B neuraminidase. This indicated that the lipophilic side chains had quite different hydrophobic interactions with influenza A and B neuraminidase despite their complete homology in the active site. Influenza B neuraminidase appeared to be much more sensitive toward the increased steric bulkiness of inhibitors compared to influenza A neuraminidase. From the extensive structure-activity relationship investigation reported in this article, GS 4071 emerged as one of the most potent influenza neuraminidase inhibitors against both influenza A and B strains.     

Treatment of glucocorticoid-induced growth suppression with growth hormone. National Cooperative Growth Study

Growth failure is common during long term treatment with glucocorticoids (GC) due to blunting of GH release, insulin-like growth factor I (IGF-I) bioactivity, and collagen synthesis. These effects could theoretically be reversed with GH therapy. The National Cooperative Growth Study database (n = 22,005) was searched for children meeting the following criteria: 1) pharmacological treatment with GC and GH for more than 12 months, 2) known type and dose of GC, and 3) height measurements for more than 12 months. A total of 83 patients were identified. Monitoring of glucose, insulin, IGF-I, IGF-binding protein-3, type 1 procollagen, osteocalcin, and glycosylated hemoglobin levels was performed in a subset of patients. Stimulated endogenous GH levels were less than 10 microg/L in 51% of patients and less than 7 microg/L in 37% of patients. The mean GC dose, expressed as prednisone equivalents, was 0.5 +/- 0.6 mg/kg day. Baseline evaluation revealed extreme short stature (mean height SD score = -3.7 +/- 1.2), delayed skeletal maturation (mean delay, 3.1 yr), and slowed growth rates (mean, 3.0 +/- 2.5 cm/yr). After 12 months of GH therapy (mean dose, 0.29 mg/kg x weeks), mean growth rate increased to 6.3 +/- 2.6 cm/yr, and height SD score improved by 0.21 +/- 0.4 (P < 0.01). During the second year of GH therapy (n = 44), the mean growth rate was 6.3 +/- 2.0 cm/yr. Prednisone equivalent dose and growth response to GH therapy were negatively correlated (r = -0.264; P < 0.05). Plasma concentrations of IGF-I, IGF-binding protein-3, procollagen, osteocalcin, and glycosylated hemoglobin increased with GH therapy, whereas glucose and insulin levels did not change. The following conclusions were reached. The growth-suppressing effects of GC are counterbalanced by GH therapy; the mean response is a doubling of baseline growth rate. Responsiveness to GH is negatively correlated with GC dose. Glycosylated hemoglobin levels increased slightly, but glucose and insulin levels were not altered by GH therapy.     

Modulating the immune response to genetic immunization

Genetic immunization, also known as DNA or polynucleotide immunization, is a novel strategy for vaccine development in which plasmid DNA encoding either individual or a collection of antigens is directly administered to a host. Such immunization leads to host expression of the delivered foreign gene, resulting in the induction of a specific immune response against the in vivo produced antigen. DNA immunization has been shown to induce protective immune responses in several infectious disease and cancer experimental model systems. Furthermore, DNA vaccines have recently entered the clinic for analysis as both prophylactic and therapeutic agents. Although the mechanisms of immunity to DNA have not yet been fully elucidated, it has become apparent that the immune response achieved by DNA vaccination is quite malleable, and can be manipulated by altering the conditions under which the vaccine is administered. Either through changing the method or location of immunization, altering the number of immunostimulatory sequences in the plasmid, altering the immunization regimen, or coadministering genes for cytokines or costimulatory molecules, one can modulate both the magnitude and orientation of the subsequent immune response. Through maximization of this feature of DNA immunization, we will likely be able to design vaccines and immunotherapeutic agents that are tailored to the correlates of protection for a particular disease, resulting in a new generation of more focused and effective immune stimulating agents.     

Association of elevated alpha 1-antichymotrypsin with cognitive impairment in a prospective study of the very old

OBJECTIVE: The authors investigated the relationships between concentrations of two acute-phase proteins, alpha 1-antichymotrypsin (ACT) and alpha 2-macroglobulin (MAC), and cognitive impairment in the very old. METHOD: Concentrations of ACT and MAC were determined in a prospective study using sera from medically stable elderly nursing home residents. Cognitive impairment was assessed with the Mini-Mental State. RESULTS: Concentrations of ACT were associated with greater cognitive impairment, as reflected by lower Mini-Mental State scores. This relationship did not exist for MAC. CONCLUSIONS: These data extend previous reports that patients with Alzheimer's disease have greater concentrations of ACT in their blood by demonstrating in a diagnostically diverse nursing home population a relationship between serum ACT and mental status. Elevated serum ACT in patients with compromised mental status may reflect a cerebral acute-phase response.     

5-Hydroxytryptamine-induced contraction of the marmoset aorta is mediated by a 5-HT1-like receptor

1. 5-Hydroxytryptamine (5-HT) exerts both contractile and relaxant effects in the marmoset isolated aorta, actions that are unaffected by the 5-HT2 antagonist ketanserin. The aim of the present study was to define the receptors mediating the contractile activity of 5-HT in the marmoset aorta. 2. Contractile responses were elicited in aortic rings that were either: (i) precontracted submaximally with the thromboxane A2 agonist U44069 in order to amplify the responses; or (ii) exposed to N(omega)-nitro-L-arginine (100 micromol/L) plus LY 53857 (0.1 micromol/L; a 5-HT2 receptor antagonist shown previously to inhibit relaxation). The effect of 5-HT on adenosine 3',5'-cyclic monophosphate (cAMP) formation was also investigated. 3. The effects of agonists and antagonists comprised: (i) agonist potencies in the order 5-carboxamidotryptamine > 5-HT > sumatriptan > 8-hydroxy-2-(di-n-propylamino)tetralin; (ii) inhibition of contractile action of 5-HT by the 5-HT1D antagonist GR 127935; (iii) a contractile response to methysergide; (iv) a lack of effect of tropisetron, an antagonist of 5-HT3 and 5-HT4 receptors; and (v) inhibition of forskolin-stimulated cAMP formation by 5-HT (in the presence of LY 53857), indicative of negative coupling to adenylate cyclase. 4. The above effects fulfill the criteria for a 5-HT1-like receptor. In view of the previous finding that this contractile response is insensitive to ketanserin, it is concluded that the contractile effects of 5-HT in the marmoset aorta are mediated exclusively by a 5-HT1-like receptor.     

Effects of low-dose recombinant human insulin-like growth factor-I on insulin sensitivity, growth hormone and glucagon levels in young adults with insulin-dependent diabetes mellitus

Despite recent interest in the therapeutic potential of recombinant human insulin-like growth factor-I (rhIGF-I) in the treatment of diabetes mellitus, its mechanism of action is still not defined. We have studied the effects of low-dose bolus subcutaneous rhIGF-I (40 microg/kg and 20 microg/kg) on insulin sensitivity, growth hormone (GH) and glucagon levels in seven young adults with insulin-dependent diabetes mellitus (IDDM) using a randomized double-blind placebo-controlled crossover study design. Each was subjected to a euglycemic clamp (5 mmol/L) protocol consisting of a variable-rate insulin infusion clamp (6:00 PM to 8:00 AM) followed by a two-dose hyperinsulinemic clamp (insulin infusion of 0.75 mU x kg(-1) x min(-1) from 8 to 10 AM and 1.5 mU x kg(-1) x min(-1) from 10 AM to 12 noon) incorporating [6,6 2H2]glucose tracer for determination of glucose production/utilization rates. Following rhIGF-I administration, the serum IGF-I level (mean +/- SEM) increased (40 microg/kg, 655 +/- 90 ng/mL, P < .001; 20 microg/kg, 472 +/- 67 ng/mL, P < .001; placebo, 258 +/- 51 ng/mL). Dose-related reductions in insulin were observed during the period of steady-state euglycemia (1 AM to 8 AM) (40 microg/kg, 48 +/- 5 pmol/L, P = .01; 20 microg/kg, 58 +/- 8 pmol/L, P = .03; placebo, 72 +/- 8 pmol/L). The mean overnight GH level (40 microg/kg, 9.1 +/- 1.4 mU/L, P = .04; 20 microg/kg, 9.6 +/- 2.0 mU/L, P = .12; placebo, 11.3 +/- 1.7 mU/L) and GH pulse amplitude (40 microg/kg, 18.8 +/- 2.9 mU/L, P = .04; 20 microg/kg, 17.0 +/- 3.4 mU/L, P > .05; placebo, 23.0 +/- 3.7 mU/L) were also reduced. No differences in glucagon, IGF binding protein-1 (IGFBP-1), acetoacetate, or beta-hydroxybutyrate levels were found. During the hyperinsulinemic clamp conditions, no differences in glucose utilization were noted, whereas hepatic glucose production was reduced by rhIGF-I 40 microg/kg (P = .05). Our data demonstrate that in subjects with IDDM, low-dose subcutaneous rhIGF-I leads to a dose-dependent reduction in the insulin level for euglycemia overnight that parallels the decrease in overnight GH levels, but glucagon and IGFBP-1 levels remain unchanged. The decreases in hepatic glucose production during the hyperinsulinemic clamp study observed the following day are likely related to GH suppression, although a direct effect by rhIGF-I cannot be entirely discounted.     

Relationship between blood pressure and subcortical lesions in healthy elderly people

The germinal center (GC) is an anatomic compartment found in peripheral lymphoid organs, wherein B cells undergo clonal expansion, somatic mutation, switch recombination, and reactivate immunoglobulin gene V(D)J recombination. As a result of somatic mutation, some GC B cells develop higher affinity antibodies, whereas others suffer mutations that decrease affinity, and still others may become self-reactive. It has been proposed that secondary V(D)J rearrangements in GCs might rescue B cells whose receptors are damaged by somatic mutations. Here we present evidence that mature human tonsil B cells coexpress conventional light chains and recombination associated genes, and that they extinguish recombination activating gene and terminal deoxynucleotidyl transferase expression when their receptors are cross-linked. Thus, the response of the recombinase to receptor engagement in peripheral B cells is the opposite of the response in developing B cells to the same stimulus. These observations suggest that receptor revision is a mechanism for receptor diversification that is turned off when antigen receptors are cross-linked by the cognate antigen.