Elwood H. Labrosse

Metabolism of of catecholamines—Identification and quantification of 3-methoxy-4-hydroxyphenylglycol glucuronide in human urine☆

Abstract The glucuronic acid conjugate of 3-methoxy-4-hydroxyphenylglycol(MHPG) has been isolated from human urine and its identification is described. This compound has been found to be a metabolite of dl -MHPG- 3 h and of DL-norepinephrine- 14 C. The quantities of MHPG, MHPG sulfate and MHPG glucuronide which are present in normal human urine, and in the urine of patients with neuroblastoma, ganglioneuroma and pheochromocytoma, indicate that the glucuronic acid conjugate is a major metabolite of MHPG. In addition, MHPG and its conjugates are markedly increased in the urine of most patients with tumours of neural crest origin. This finding provides further evidence that MHPG is the major metabolite formed within these tumours, and the assay of urinary MHPG, especially after enzymatic hydrolysis of the glucuronide and sulfate conjugates, should be of value in the diagnosis of tumors of neural crest origin.

Tyrosine hydroxylase in neuroblastoma.

Abstract Tyrosine hydroxylase activity was assayed in two neuroblastoma tissues. It was found that the neuroblastoma tyrosine hydroxylase required DMPH4 as a cofactor and was stimulated by Fe2+. These properties are quite similar to those reported for bovine and pheochromocytoma enzymes. Catechol compounds and other inhibitors, at concentrations of 2.5 × 10−5-5 × 10−4 m , inhibited the neuroblastoma enzyme to the same extent as bovine adrenal tyrosine hydroxylase. This finding suggests that neuroblastoma tyrosine hydroxylase is normally susceptible to feedback inhibition, in contrast to the pheochromocytoma enzyme which has been reported to be less sensitive to inhibition by catechols. Both neuroblastoma and pheochromocytoma are associated with increased synthesis of catecholamines; in the case of pheochromocytoma there are large stores of norepinephrine in the tumor, but catecholamine synthesis still continues at an elevated rate, apparently because of a decreased sensitivity to feedback inhibition of the tyrosine hydroxylase in this tumor. On the other hand, in neuroblastoma the catecholamines appear to exert a “normal” feedback inhibition on tyrosine hydroxylase, and, therefore, we must look elsewhere to explain the high rate of catecholamine synthesis, such as lowering of the intracellular catecholamine levels by rapid metabolism. Further investigation will be necessary to establish the alteration of control mechanisms in neuroblastoma.

Glucosylgalactosylhydroxylysine in urine of neuro-blastoma patients

Abstract A glycopeptide, which consists of glucose, galactose and hydroxylysine with a 1 : 1 : 1 molar ratio, has been isolated from urine of a neuroblastoma patient. The hydroxyl group of the hydroxylysine and C 1 of the galactose were shown to be involved in the sugar-amino acid linkage of the glycopeptide. Among eleven neuroblastoma patients whose urinary amino acids were investigated, three patients were found to excrete the glycopeptide.

A biochemical study of neuroblastoma in vivo and in vitro

Abstract Previous investigations on the metabolism in tissue culture of dl - 3 H-norepinephrine by tumors from patients with neuroblastoma have revealed that the tumor tissue itself is capable of converting the dl - 3 H-norepinephrine to 3 H-3-methoxy-4-hydroxyphenylglycol ( 3 H-MHPG). This report concerns studies on a patient with neuroblastoma whose tumor tissue showed the ability to carry out the above transformation. It was found that the levels of MHPG in the tumor and in the blood were higher that the levels of 3-methoxy-4-hydroxymandelic acid (VMA). In addition, the metabolism and excretion of dl -7- 3 H-MHPG in this patient have revealed that 34% of the administered compound was converted to 3 HVMA, 7.3% was excreted as the sulfate conjugate of MHPG, 39.7% was excreted as an unidentified compound, 15% of the tritium appears to be converted to tritium-labeled water, and only 3.6% was excreted as unchanged 3 HMHPG. These findings are consistent with the hypothesis that in those patients who have secreting neuroblastomas there appears to be synthesis of norepinephrine and metabolism of it to a significant extent to 3-methoxy-4-hydroxyphenylglycol which is then released into the blood and further metabolized to 3-methoxy-4-hydroxymandelic acid which is excreted in the urine.

TURNOVER AND EXCRETION OF VMA BY NORMAL VOLUNTEERS AND PATIENTS WITH NEURAL CREST TUMORS

The turnover and excretion of 3-methoxy-4-hydroxymandelic acid (VMA) has been studied in 3 normal volunteers and in 6 patients with neural crest tumors by giving an i.v. injection of 7- 3 H-VMA and assaying the tritium ( 3 H) and 3 H-VMA in serial urine specimens. The urinary excretion of 3 H-VMA was rapid with a a T 1/2 = about 0.5 hr. Up to 13% of the 3 H-label was excreted as 3 H 2 0, but the remainder of the 3 H-VMA was excreted unchanged. These results indicate that the urinary excretion of VMA can be used as a dynamic indicator of synthesis and metabolism of its catecholamine precursors.