Modern laboratory evaluation of peptide and amines: a continuing role for radioimmunoassay?

Modern medicine, and specifically clinical diagnosis, relies, among other diagnostic procedures, on the measurements of the biogenic analytes for elucidation and correlation of specific neuroendocrine markers. Tremendous advances have been made in imaging and radioactive uptake procedures to elucidate tumor presence and characterization. However, such advances only partially provide the fundamental degree of tumor activity and clinical confirmational validity. The author points out in some detail the problems that may arise when the methodological differences presented by each investigational study and investigators are not standardized. This variation causes a concern with the specific objectives of the investigator and the specific aims of the research project at hand, and ultimately for the validity of the published results.

Validation of serum versus plasma measurements of chromogranin a levels in patients with carcinoid tumors: lack of correlation between absolute chromogranin a levels and symptom frequency

OBJECTIVE

Chromogranin A (CGA) levels are used to confirm the diagnosis and monitor the course of patients with neuroendocrine tumors. Chromogranin A levels are significantly reduced when patients are acutely treated with octreotide; however, limited data are available that correlates octreotide long-acting repeatable (LAR) dose or steady state octreotide blood levels to the absolute value of serum or plasma CGA.

METHODS

Plasma, serum, and clinical information on carcinoid syndrome symptoms were collected anonymously from 40 patients treated with long-term octreotide LAR therapy for carcinoid syndrome.

RESULTS

We found a strong positive linear relationship exists between serum and plasma CGA levels (r = 0.9858, P < 0.0001). No correlation existed between plasma octreotide levels or LAR dose and the static, absolute plasma/serum CGA levels. Although, higher mean CGA values were seen in the group whose diarrhea was "not under optimal control" than for the group "under optimal control," these results did not reach statistical significance (P = 0.24). Contrary to our hypotheses, a statistically significant inverse relationship was found between the frequency of flushing and the CGA levels (P = 0.0372). Higher mean CGA values were observed in the "under optimal control" group with flushing symptoms.

CONCLUSIONS

Either serum or plasma can be used to measure CGA levels. Absolute (static) CGA levels do not positively correlate with symptom intensity during LAR therapy. Dynamic (serial) measurements of CGA are necessary to monitor the effectiveness of medical or surgical therapy.

Effect of octreotide LAR dose and weight on octreotide blood levels in patients with neuroendocrine tumors

OBJECTIVES

Octreotide long acting repeatable (LAR) is widely used for the control of symptoms of functional neuroendocrine tumors. At doses of 30 mg/mo, up to 40% of patients require subcutaneous octreotide "rescue" and up to 40% of patients are given more than 30 mg of LAR/mo. Octreotide acetate binds to the sst2 receptor with an affinity (Kd) of approximately 1 x 10(-9) mol/L (approximately equal to 1000 pg/mL), but higher (approximately equal to 10,000 pg/mL) concentrations of octreotide are required to completely saturate this receptor. Octreotide blood level measurement may be useful to guide LAR therapy in symptomatic patients or in patients who have tumor growth on traditional LAR doses. We hypothesize that LAR doses of 60 mg/mo will produce blood levels of 10,000 pg/mL or greater. At identical monthly LAR doses, patients with higher weights will require more medication to achieve similar plasma octreotide levels than individuals with lower body weights.

METHODS

Trough plasma, serum, urine, and saliva octreotide levels were obtained from 52 patients with carcinoid syndrome receiving 20 (n = 8), 30 (n = 19), or 60 mg LAR/mo (n = 10). Octreotide levels were determined by radioimmunoassay.

RESULTS

The mean +/- SD plasma octreotide levels for patients receiving 20, 30, or 60 mg LAR/mo were 2518 +/- 1020, 5241 +/- 3004, and 10,925 +/- 5330 pg/mL, respectively. Patient weight (kilograms) was inversely related to plasma octreotide levels. There was a significant correlation between plasma octreotide levels and octreotide levels measured in urine, saliva, and serum.

CONCLUSIONS

Frequent measurement of octreotide levels may be useful to guide octreotide therapy in patients with poorly controlled symptoms or those patients experiencing tumor growth.

Organic constituents of carbonaceous chondrites

From a brief discussion of forms of meteorite carbon it is concluded that almost all the carbon in the carbonaceous chondrites is present as organic matter. Attempts to extract and identify this organic matter are then reviewed. It is shown that only 25 per cent has been extracted and only about 5 per cent chemically characterized. Of this 5 per cent, most is a complex mixture of hydroxylated aromatic acids together with various hydrocarbons of the paraffin, naphthene and aromatic series. Small amounts of amino acids, sugars and fatty acids also are present. The possible chemical nature of the major fraction is discussed. It is suggested to be a mixture of high-molecular weight aromatic and hydrocarbon polymers. Possible sources of contamination of the meteorites are described and evidence indicating a general lack of organic contaminants is presented. It is concluded, that most of the organic constituents are indigenous to the meteorites and are extra terrestrial in origin. Synthetic processes for the compounds are mentioned and it is concluded that the organic material is probably of abiogenic origin. A brief review on studies of "organized elements" contained within the meteorites is presented. Difficulties of identification are discussed and photographs of some microstructures of several carbonaceous chondrites are presented. No final conclusion about the nature of these objects is possible, but some appear to be various indigenous organic and mineral structures, while others are terrestrial contaminants.

Structural analysis of the molecular evolution of some gastro-entero-pancreatic hormones

By means of a statistical analysis of the occurrence of amino-acid residues in the polypeptide chains of several gastro-entero-pancreatic (GEP) hormones an investigation was undertaken to determine whether any of these hormones might be related to each other--possibly from an evolutionary point of view. Particular interest was paid to the occurrence of small charged segments, i.e. those with acidic or basic amino acid residues, since such segments can be presumed to play a role in hormonal receptor binding mechanisms. By this method hormonal relationships were suggested by the observation that these small charged amino-acid sequences, contained in the hormonal structures, match as a result of non-randomness. It was found that hagfish and human insulin were related on a molecular level not only to the newly discovered (avian, bovine, human) pancreatic polypeptide (PP) but also to some other GEP hormones (VIP, GIP, glucagon) as well as to calcitonin and to the alpha-subunit of the glycoprotein hormones. Interpretation of the statistical data suggests that all these peptide hormones are related by a common hexapeptide sequence which contributed, at an evolutionary point, to their molecular architecture. A hexapeptide segment of APP is statistically related to a sequence of equal size in the carboxy terminal region of the A-chain of both hagfish and human insulin, providing the first instance of their structural similarity. Correlations between PP, insulin, glucagon, VIP, and calcitonin provide a tentative basis for predicting the production of one or more of these peptide hormones by immature or de-differentiated cells of neoplasms and non-neoplastic pathologic lesions of the GEP endocrine system.