Catecholamine measurements in phaeochromocytoma: a review

Affinity of Electrochemically Deposited Sol⁻Gel Silica Films towards Catecholamine Neurotransmitters

Dopamine, norepinephrine, and epinephrine neurotransmitters can be detected by electrochemical oxidation in conventional electrodes. However, their similar chemical structure and electrochemical behavior makes a difficult selective analysis. In the present work, glassy carbon electrodes have been modified with silica layers, which were prepared by electroassisted deposition of sol⁻gel precursors. These layers were morphologically and compositionally characterized using different techniques, such as field emission scanning electron microscopy (FESEM), TEM, FTIR, or thermogravimetric analysis⁻mass spectrometry (TG-MS). The affinity of silica for neurotransmitters was evaluated, exclusively, by means of electrochemical methods. It was demonstrated that silica adsorbs dopamine, norepinephrine, and epinephrine, showing different interaction with silica pores. The adsorption process is dominated by a hydrogen bond between silanol groups located at the silica surface and the amine groups of neurotransmitters. Because of the different interaction with neurotransmitters, electrodes modified with silica films could be used in electrochemical sensors for the selective detection of such molecules.

Is there still a place for adrenal venous sampling in the diagnostic localization of pheochromocytoma?

Our objective is to outline the utility of adrenal venous sampling (AVS) with measurements of metanephrine to normetanephrine ratios for diagnostic localization of phaeochromocytoma in a patient with normal plasma levels of catecholamines. A 53-year-old-woman was referred for evaluation of recurrent pheochromocytoma following a right adrenalectomy 14 years earlier. Diagnosis of recurrent disease was established from elevations in plasma metanephrines with normal levels of catecholamines. Magnetic resonance imaging indicated two 1-2 cm masses in the right surgical bed and another 1-1.5 cm mass in the left adrenal. These masses were negative on (123)I-metaiodobenzylguanidine scintigraphy. There was no evidence of a hereditary syndrome. We, therefore, carried out two investigational approaches to identify the tumor masses. Hybrid positron emission tomography/computed tomography with (68)Ga-DOTATOC ((68)Ga-DOTATOC-PET/CT) confirmed the presence of recurrent disease in the right surgical bed and also suggested additional left adrenal involvement. Normal plasma catecholamines precluded the use of adrenal venous sampling (AVS) with catecholamine measurements. Hence, we performed AVS with measurements of plasma metanephrines, which were 4- to 7-fold higher in the left adrenal vein than in central venous plasma. We observed a reversal of the normally high metanephrine to normetanephrine ratio (mean value ± SD 5.28 ± 1.86; range 3.36-8.84, n = 13) to 0.73, establishing the presence of a left adrenal pheochromocytoma. Surgical pathology confirmed bilateral disease. This case highlights a scenario where a combination of (68)Ga-DOTATOC-PET/CT and AVS with measurement of the metanephrine to normetanephrine ratio was crucial for the preoperative assessment of a patient with bilateral pheochromocytoma.

Comparison of diagnostic accuracy of urinary free metanephrines, vanillyl mandelic Acid, and catecholamines and plasma catecholamines for diagnosis of pheochromocytoma

CONTEXT

Recent evidence suggests that plasma-free metanephrines provide a highly sensitive test in patients requiring exclusion of pheochromocytoma. The diagnostic efficacy of urinary free metanephrines, however, has not been evaluated. OBJECTIVE, DESIGN, SETTING, PATIENTS, AND OUTCOME MEASURES: We compared retrospectively the diagnostic efficacy of 24-h urinary free metanephrines with our currently available measurements of 24-h urinary vanillyl mandelic acid (VMA), urinary catecholamines, and plasma catecholamines in 159 outpatients tested in a tertiary referral center for pheochromocytoma over a 4-yr period.

RESULTS

The sensitivity of urinary free metanephrines was 100% [25 of 25 patients; 95% confidence interval (CI) 86-100%)] compared with the sensitivity of 84% (21 of 25; 95% CI 64-95%) for urinary catecholamines; 72% (18 of 25; 95% CI 51-88%) for urinary VMA; and 76% (16 of 21; 95% CI 53-92%) for plasma catecholamines. The specificity of urinary free metanephrines was 94% (116 of 123; 95% CI 89-98%), compared with the specificity of 99% (127 of 129; 95% CI 96-100%) for urinary catecholamines; 96% (130 of 134; 95% CI 91-98%) for urinary VMA; and 88% (66 of 75; 95% CI 78-94%) for plasma catecholamines. Receiver operating characteristic curves for all test groups were generated. Pairwise comparisons of the area under the receiver operating characteristic curve for urinary free metanephrines with that of each of the other three test groups individually were: 0.993 (95% CI 0.962-0.999) vs. 0.919 (95% CI 0.862-0.957, P = 0.032) for urine catecholamines; 0.993 (95% CI 0.962-0.999) vs. 0.846 (95% CI 0.778-0.900, P = 0.002) for urine VMA; and 0.992 (95% CI 0.945-0.998) vs. 0.852 (95% CI 0.762-0.918, P = 0.009) for plasma catecholamines. Testing with urinary free metanephrines failed to misidentify a single case of pheochromocytoma, compared with four missed cases for urinary catecholamines, seven missed cases for urinary VMA, and five missed cases for plasma catecholamines.

CONCLUSION

Urinary free metanephrines were superior to urinary VMA, urinary catecholamines, and plasma catecholamines and can provide a valuable test for diagnosis of pheochromocytoma in adults.

Systematic study of long-term stability of 3,4-dihydroxyphenylglycol in plasma for subsequent determination with liquid chromatography

The effect of three storage temperature levels (i.e. +4, -20 and -80 degrees C) and time intervals from sampling (3, 6 and 9 months) on the degradation of 3,4-dihydroxyphenylglycol (DHPG) and norepinephrine (NE) was investigated in a systematic study. Extracted human plasma samples and acidified standard solutions were stored for long periods (up to 9 months) without the addition of any stabilizing agent. DHPG and NE values, determined using a ion-pair reversed-phase high-performance liquid chromatography method with electrochemical detection of coulometric type (IP-RP-HPLC-CD), remained constant over time in those plasma samples and standard solutions that had been stored at the lowest storing temperature (i.e. -80 degrees C). The expected degradation was observed at higher temperature levels. Plasma and standard DHPG degradation can, therefore, be prevented by storing samples at a lower temperature than previously suggested with no need to add any stabilizing agent.

Phaeochromocytoma with normal urinary catecholamines: the potential value of urinary free metadrenalines

BACKGROUND

Normal urine catecholamine values in patients with phaeochromocytoma is an occasional finding and may lead to a missed diagnosis. Additional urinary free metadrenaline analysis may be of value in this situation.

METHODS

In addition to vanillylmandelic acid, homovanillic acid and the catecholamines, urinary free normetadrenaline (fNMA) and free metadrenaline (fMA) were measured. This report describes six confirmed cases of phaeochromocytoma showing normal urinary catecholamine output and compares fMA results and tumour size with other confirmed cases where the urine catecholamines were increased.

RESULTS

Urine catecholamines in these patients with, on average, smaller tumours, were all normal. Urinary fNMA and fMA were available on five patients, and were increased in three. The data suggest that, unlike the catecholamines, urinary fNMA and fMA could be a useful predictor of tumour size.

CONCLUSION

The inclusion of fNMA and fMA in the test profile is likely to be of additional benefit in tumour detection, particularly when catecholamines or other metabolites are normal.

Determination of epinephrine, norepinephrine, dopamine and L-dopa in pharmaceuticals by a photokinetic method

A study of the photochemical reaction of the Rose Bengal (RB)-ethylenediaminetetraacetic acid system in the presence of epinephrine, norepinephrine, dopamine and L-dopa is presented. The rate of photoreduction of RB is dramatically retarded by small amounts of these catecholamines, which have an inhibitory effect on the excited state of RB, which is the activator of the process. Optimum conditions for the determination of catecholamines in the range of concentration between 5 x 10(-6) and 1 x 10(-4) mol dm-3 are described. The proposed method has been applied with excellent results to the determination of catecholamines in pharmaceuticals.

Plasma catecholamine responses during a personalized physical stress as a dynamic characterization of essential hypertension

High performance liquid chromatography (HPLC) with electrochemical detection proves to be a reliable method for determination of plasma catecholamines (CA) to assess the possible role of the sympathetic nervous system (SNS) in essential hypertension (EH). The present investigation in a group of 15 normotensive (N) and 13 stable EH patients, homogeneous for age and duration of hypertension, was carried out without treatment in the supine position, up-right position and during a personalized bicycle exercise. Mean blood pressure, mean heart rate, plasma renin activity and plasma aldosterone were also evaluated at the various exertion phases. Norepinephrine (NE) and epinephrine (E) showed a progressive increase in N and in EH patients, reaching the highest values at maximum effort. However, EH patients showed higher E plasma levels than N before maximum effort. Dopamine (DA) reached the highest values in N at maximum effort and in EH patients at recovery time. These findings allow us to foresee the possibility of a better characterization of the SNS role in EH.

Biochemical tests for pheochromocytoma: strategies in hypertensive patients

OBJECTIVE

To determine the optimal clinical strategy utilizing either 1) serum catecholamines, 2) urinary metanephrines, or 3) urinary vanillylmandelic acid measurements in the evaluation of hypertensive patients with suspected pheochromocytoma.

DESIGN

Prospective clinical determination of test-operating characteristics.

SETTING

Tertiary care university medical center.

PATIENTS/PARTICIPANTS

415 patients referred for evaluation of suspected pheochromocytoma.

INTERVENTIONS

All subjects had measurements of the three above-mentioned biochemical tests with the diagnosis of pheochromocytoma established by tissue confirmation.

RESULTS

All three biochemical tests were similar in sensitivity (0.70-0.75), specificity (0.90-0.95), and receiver operating characteristics. With an estimated disease prevalence of 5.9% in symptomatic hypertensive patients, the predictive value of any single negative test would be 98% in ruling out disease.

CONCLUSIONS

All three biochemical tests have similar performance characteristics and only a single test need be performed to exclude pheochromocytoma in most symptomatic hypertensive patients in a primary care population.

Direct concurrent measurement of urinary vanillylmandelic acid, 5-hydroxyindoleacetic acid and homovanillic acid by HPLC. Three methodologies compared

Three different direct HPLC methods for the determination of 3-methoxy-4-hydroxymandelic acid (VMA, vanillylmandelic acid), 5-hydroxyindoleacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylacetic acid (HVA, homovanillic acid) in urine were compared: two spectrofluorometric methods, applying discontinuous gradients, and one serial coulometric linear gradient method. The imprecision study (n = 6) revealed comparable coefficients of variation (CV), intra-assay ranging 1.4-11.1%, and inter-assay ranging 5.9-11.8% for physiological and moderately elevated levels of VMA, 5-HIAA and HVA. All methods showed good linearities up to 100 mumol/L for each of the three compounds studied. Analytical recoveries were 97-114% for VMA, 87-103% for 5-HIAA, and 80-95% for HVA. Recoveries were not dependent on urinary relative densities in the range 1.010-1.030 kg/L or on protein content (prior to acidification) in the range 0.1-3 g/L, or on the pH of conservation in the range 2-5 or on storage temperature in the range -20 - +22 degrees C for three weeks. The distributed-sample comparison revealed acceptable correlations and clinically unimportant accuracy differences between the methods. It is concluded that direct fluorometric and electrochemical HPLC methods can be used in the determination of major catecholamine and serotonin metabolites in human urine for clinical diagnosis and follow-up of neural crest and carcinoid tumours.

Phaeochromocytoma

Phaeochromocytomas are uncommon among patients with hypertension, and sometimes occur in persons without known hypertension, but are important to detect because they are often lethal but commonly curable, and because they are a clue to the presence of associated conditions. Paroxysmal symptoms (especially headache, palpitations, diaphoresis and anxiety), hypertension that is intermittent, unusually labile or resistant to conventional therapy, and conditions known to be associated raise the clinical suspicion of phaeochromocytoma. Biochemical confirmation is commonly achieved by measurement of urinary catecholamines, metanephrines or VMA. Plasma noradrenaline and adrenaline measurements may be superior to measurements of urinary catecholamine metabolites, but strict attention to the details of sample collection, handling and storage, the many sources of possible biological variation and the effects of drugs is critical if diagnostic error is to be avoided. Patients should be evaluated in the drug-free state if at all possible. Anatomical localization, in the abdomen in the vast majority of cases and usually in the adrenal medullae, can generally be accomplished with computed tomographic scans. Bilateral adrenomedullary tumours are the rule in familial phaeochromocytoma. Most phaeochromocytomas are benign and can be excised totally after medical preparation with an alpha-adrenergic antagonist.

Plasma catecholamines: experience with a single-isotope radioenzymatic assay

The performance of a rapid and sensitive single-isotope radioenzymatic assay for plasma catecholamines, in a routine clinical chemistry laboratory, is reported and discussed. The value of plasma adrenaline and noradrenaline as tumour markers in the diagnosis, tumour localisation, and post-operative follow-up of four patients with phaeochromocytoma is emphasised.

New approach to the localisation of phaeochromocytoma: imaging with iodine-131-meta-iodobenzylguanidine

Thirty eight patients with known or suspected phaeochromocytoma were studied by radioisotope imaging after intravenous administration of iodine-131-meta- iodobenzylguanidine (131I- mIBG ), a radiopharmaceutical which has affinity for chromaffin tumours. Seventeen positive results (including one false positive) and 21 negative results (including two false negatives) were obtained. Clinical accuracy was 92%. Urinary noradrenaline concentrations were raised in all patients with confirmed phaeochromocytoma. These findings show that 131I- mIBG is of value in localising and assessing the extent of chromaffin tumours.

Simultaneous assay of noradrenaline and its deaminated metabolite, dihydroxyphenylglycol, in plasma: a simplified approach to the exclusion of phaeochromocytoma in patients with borderline elevation of plasma noradrenaline concentration

The fate of noradrenaline released from sympathetic endings differs from that of noradrenaline secreted directly into the bloodstream. This has been used to establish a single sample test for the exclusion of phaeochromocytoma in patients with borderline elevation of plasma noradrenaline concentration. This test is based on the measurement of the ratio in plasma of noradrenaline to its deaminated metabolite, dihydroxyphenylglycol (DHPG). The latter was shown to reflect mainly nervous release of noradrenaline and its plasma concentration was not increased during intravenous noradrenaline infusion. In seventeen phaeochromocytoma patients the ratio in plasma of noradrenaline to DHPG was greater than 2 (range 2.05-3.57); in nineteen non-phaeochromocytoma patients the reverse was found, the ratio of DHPG to noradrenaline being greater than 2 (range 2.08-2.74). Since DHPG can be measured simultaneously with noradrenaline, measurement of the plasma ratio of these two catechols may prove a simple method of differentiating phaeochromocytoma from nonphaeochromocytoma patients.

Neuropeptide Y in phaeochromocytomas and ganglioneuroblastomas

Tumour tissue from nineteen patients with phaeochromocytomas and nine with ganglioneuroblastomas contained large numbers of neuropeptide Y (NPY) producing cells and extracts of these tumours had very high concentrations of immunoreactive NPY. Plasma NPY concentrations were also raised, averaging 460 pmol/l in patients with tumours of the sympathetic chain and 55 pmol/l in healthy controls. Since plasma NPY is straightforward to measure and relatively stable, its estimation may prove helpful as a screening tests for phaeochromocytoma.