A backbone-cyclic, receptor 5-selective somatostatin analogue: synthesis, bioactivity, and nuclear magnetic resonance conformational analysis.

Cyclo(PheN2-Tyr-D-Trp-Lys-Val-PheC3)-Thr-NH2 (PTR 3046), a backbone-cyclic somatostatin analogue, was synthesized by solid-phase methodology. The binding characteristics of PTR 3046 to the different somatostatin receptors, expressed in CHO cells, indicate high selectivity to the SSTR5 receptor. PTR 3046 is highly stable against enzymatic degradation as determined in vitro by incubation with rat renal homogenate and human serum. The biological activity of PTR 3046 in vivo was determined in rats. PTR 3046 inhibits bombesin- and caerulein-induced amylase and lipase release from the pancreas without inhibiting growth hormone or glucagon release. The major conformation of PTR 3046 in CD3OH, as determined by NMR, is defined by a type II' beta-turn at D-Trp-Lys and a cis amide bond at Val-PheC3.

Correlation between serum levels of soluble tumor necrosis factor receptor and disease activity in systemic lupus erythematosus.

OBJECTIVE: To determine the value of measurement of serum soluble tumor necrosis factor receptor (sTNFR), compared with established parameters such as anti-double-stranded DNA, in monitoring systemic lupus erythematosus (SLE) disease activity, and to determine whether serum sTNFR are bioactive and can effectively inhibit TNF bioactivity. METHODS: Fifty-three consecutive ambulatory or hospitalized SLE patients and 140 consecutive healthy subjects were enrolled in a prospective cohort study. Serum levels of sTNFR were measured by a unique 2-sided capture enzyme-linked immunosorbent assay using mouse monoclonal antibodies and rabbit antisera against the sTNFR. RESULTS: The mean +/- SD concentrations of both the p55 (type I) and p75 (type II) soluble receptors were significantly higher in a group of 46 SLE patients than in controls: 1.89 +/- 0.89 ng/ml versus 0.77 +/- 0.19 ng/ml and 7.25 +/- 3.89 ng/ml versus 3.02 +/- 0.57 ng/ml, respectively (P < 0.0001 for both). The incidence and the extent of the increase among the healthy subjects and these patients (as well as in 7 additional patients on whom sequential studies were performed) correlated with disease activity more than did the occurrence of serum anti-DNA antibodies (correlation coefficients with disease activity 0.81 and 0.85 for p55 and p75 sTNFR, respectively, and 0.51 for anti-DNA antibodies). The increase in sTNFR levels seems to reflect, largely, enhanced formation, and only to a minor extent, reduced clearance due to impairment of renal function. Sera of the SLE patients had a marked inhibitory effect on the in vitro cytocidal activity of TNF, and this was shown to result entirely from their higher sTNFR receptor concentration. CONCLUSION: An increase in serum levels of sTNFR may become a useful marker for SLE activity since it shows a stronger correlation than do any other laboratory or clinical parameters employed presently in the daily clinical setting. At the concentrations attained in the serum of SLE patients, sTNFR effectively inhibit the bioactivity of TNF and may thus be a significant determinant of the intensity of the manifestations of SLE.

Variation in serum levels of the soluble TNF receptors among healthy individuals.

Soluble forms of the two receptors for tumor necrosis factor (TNF) are present in human sera at concentrations that increase greatly in various disease states as well as varying among healthy individuals. Measurements of the soluble TNF receptor (sTNF-R) concentrations in healthy individuals at time lapses of 3 months (17 individuals) or 1 year (51 individuals) showed a significant correlation between the first and the second measurements from each individual, implying that individual differences are stable. Since the sTNF-Rs are believed to function as physiological attenuators of TNF activity, these steady individual differences may contribute to differences in the severity of the harmful effects of TNF in disease states.

Increased serum levels of soluble receptors for tumor necrosis factor in cancer patients.

Soluble forms of the two molecular species of the cell surface receptors for tumor necrosis factor (TNF) have been detected in normal urine. Using enzyme-linked immunosorbent assays for these soluble receptors, we determined their levels in the sera of 40 healthy subjects and 59 patients with solid tumors. The mean +/- SD concentrations of both the soluble type I (p55) and type II (p75) receptors were significantly higher in the cancer patients than in the healthy controls: 1.96 +/- 1.19 versus 0.79 +/- 0.19 ng/ml (P less than 0.001) and 6.43 +/- 4.8 versus 3.2 +/- 0.6 ng/ml (P less than 0.001), respectively. The incidence and the extent of the increase correlated with the staging of disease. Sera of the cancer patients had a marked inhibitory effect on the in vitro cytocidal activity of TNF. This inhibition was proportional to the content of soluble TNF receptors and could be fully abolished by the addition to the sera of specific antibodies against the receptors. Among the cancer patients, the incidence of increase in the concentrations of soluble TNF receptors (about 70%) greatly exceeded that of the serum carcinoembryonic antigen (about 26%), a commonly used cancer marker. The origin of the serum soluble TNF receptors in cancer patients and the physiological implications of their effect on TNF function remain to be elucidated.

Soluble and cell surface receptors for tumor necrosis factor.

Tumor necrosis factor (TNF) initiates its multiple effects on cell function by binding at a high affinity to specific cell surface receptors. Two different molecular species of these receptors, which are expressed differentially in different cells, have been identified. The cDNAs of both receptors have recently been cloned. Antibodies to one of these receptor species (the p55, type I receptor) can trigger a variety of TNF like effects by cross-linking of the receptor molecules. Thus, it is not TNF itself but its receptors that provide the signal for the response to this cytokine. The intracellular domains of the two receptors differ in structure, suggesting that they mediate different activities. Their extracellular domains, however, are structurally related. Both contain cysteine-rich repeats which are homologous to repeated structures found in the extracellular domains of the nerve growth factor receptor and the CDw40 protein. Truncated soluble forms of the two receptors, corresponding to these cysteine-rich repeated structures, have been detected in human urine and were later found to be present also in the serum. The serum levels of those soluble TNF receptors increase dramatically in certain pathological situations. Release of the soluble receptors from the cells seems to occur by proteolytic cleavage of the cell surface forms and appears to be a way of down-regulating the cell response to TNF. Because of their ability to bind TNF, the soluble receptors exert an inhibitory effect on TNF function, and may thus act as physiological attenuators of its activity.