Differing haemodynamic and catecholamine responses to exercise in three groups with peripheralautonomic dysfunction: insulin-dependent diabetes mellitus, familial amyloid polyneuropathy and pure autonomic failure

The haemodynamic and catecholamine responses to supine exercise, and the effect on standing blood pressure (BP), were studied in three groups with peripheral autonomic dysfunction; insulin-dependent diabetes mellitus (IDDM), familial amyloid polyneuropathy (FAP) and pure autonomic failure (PAF). Healthy normal subjects were studied as controls. With exercise, BP increased in controls, was unchanged in IDDM and FAP, and fell in PAF. Heart rate (HR) increased more in controls than IDDM, FAP or PAF. Cardiac index (CI) increased less in IDDM than controls, FAP or PAF. Systemic vascular resistance (SVR) fell similarly in controls and IDDM, with a greater fall in FAP and PAF. Plasma noradrenaline increased in controls and IDDM only; plasma adrenaline did not change and plasma dopamine was undetectable in all groups. On standing, BP was unchanged in controls; BP fell pre- and post-exercise in IDDM, FAP and PAF, with a significantly greater fall post-exercise in FAP and PAF. In conclusion, the haemodynamic responses to supine exercise and to standing after exercise differed in the three groups with peripheral autonomic dysfunction. These differences, and also the similarities, between different forms of peripheral autonomic dysfunction, may be of relevance to the clinical assessment and therapy of these patients.

Chronic cough in the Holmes-Adie syndrome: association in five cases with autonomic dysfunction

The Holmes-Adie syndrome consists of unilateral or bilateral tonic pupils with near light dissociation and tendon areflexia. It is associated with autonomic disturbances affecting sudomotor and vasomotor function. Five such patients are reported on who also had a troublesome chronic dry cough, which was of unknown aetiology and was resistant to a range of treatments. The cough may be related to involvement of afferent or efferent pathways in the vagus. Chronic cough may be an accompaniment in the Holmes-Adie syndrome, like other forms of autonomic dysfunction.

Indium-111-DTPA-folate as a potential folate-receptor-targeted radiopharmaceutical

Indium-111-labeled diethylenetriamine pentaacetic acid (DTPA)-folate was evaluated as a radiopharmaceutical for targeting tumor-associated folate receptors.

METHODS

Athymic mice were subcutaneously inoculated with approximately 1.8 x 10(6) folate receptor-positive KB (human nasopharyngeal carcinoma) cells, yielding 0.2- to 0.6-g tumors in 15 days, at which time (111)In-DTPA-folate, (111)In-DTPA or (111)In-citrate was administered by intravenous injection.

RESULTS

The (111)In-DTPA-folate conjugate afforded marked tumor-specific (111)In deposition in vivo using this mouse model. The involvement of the folate receptor in mediating tumor uptake of (111)In-DTPA-folate was demonstrated by the blocking of tumor uptake by coadministration of free folic acid (intravenous). The (111)In-DTPA-folate also shows folate receptor-mediated uptake and retention in the kidneys, presumably reflecting radiotracer binding to folate receptors of the proximal tubules. In control experiments, the (111)In-citrate radiopharmaceutical precursor was also shown to afford significant tumor uptake of (111)In, but with much poorer tumor-to-background tissue contrast than that obtained with (111)In-DTPA-folate. Unconjugated (111)In-DTPA showed no tumor affinity.

CONCLUSION

Indium-111-DTPA-folate appears suitable as a radiopharmaceutical for targeting tumor-associated folate receptors.

A kit formulation for preparation of [(111)In]In-DTPA-folate, a folate-receptor-targeted radiopharmaceutical

A kit formulation has been developed for convenient, routine compounding of (111)In-labeled In(III)-DTPA-Folate, an investigational radiopharmaceutical for targeting tumor-associated folate receptors. The kit consists of the DTPA-Folate conjugate in sodium citrate solution, from which [(111)In]In-DTPA-Folate can be rapidly and reliably compounded by the addition of aqueous [(111)In]In(III)-chloride.

Clinical usefulness of magnetic resonance imaging in multiple system atrophy

OBJECTIVES

To determine the sensitivity, specificity, and positive predictive values of a selection of abnormal findings in the putamen and infratentorial structures on routine magnetic resonance imaging for distinguishing between multiple system atrophy, idiopathic Parkinson's disease, and age matched controls.

PATIENTS AND METHODS

Two neuroradiologists blindly and independently rated axial T2 weighted and proton density MRI of 44 patients with multiple system atrophy, 47 patients with idiopathic Parkinson's disease, and 45 controls. High field (1.5 T) scans were available in 16 patients with multiple system atrophy, 15 patients with idiopathic Parkinson's disease, and 16 controls. All other patients had 0.5 T scans.

RESULTS

On both 0.5 and 1.5 T scans the following items had high specificity but low sensitivity: putaminal atrophy, a hyperintense putaminal rim, and infratentorial signal change. Finding any infratentorial abnormality gave higher sensitivity but lower specificity. Putaminal isointensity or hypointensity relative to globus pallidus, absolute putaminal hypointensity, and altered size of the olives were not useful discriminators. The overall sensitivity was 73% on 0.5 T and 88% on 1.5 T scans. The specificities of these findings for multiple system atrophy in comparison to idiopathic Parkinson's disease and controls on 0.5 T were 95% and 100% respectively, and on 1.5 T were 93% and 91% respectively. Finding any of the described abnormalities on MRI gave a positive predictive value of 93% on the 0.5 T machine, and 85% on the 1.5 T scanner.

Neck and other muscle pains in autonomic failure: their association with orthostatic hypotension

Neck pain in the suboccipital and paracervical region ('coathanger' configuration) is often reported by patients with autonomic failure and orthostatic hypotension. The frequency of this pain, along with pains in the buttock and calf regions, was determined by questionnaire in two major groups with primary chronic autonomic failure--pure autonomic failure (PAF) and multiple system atrophy (MSA). Comparisons were made with Parkinson's disease, cerebellar degeneration and other disorders in which neurological symptoms overlap but in which there was neither autonomic failure nor orthostatic hypotension. Neck pain was present in 93% of patients with PAF, 51% of patients with MSA and 38-47% of the non-autonomic groups. Buttock pain was present in smaller but similar proportions (8-19%) of each group, like calf pain (23-37%). Neck pain in PAF and MSA differed from that in the other groups in being relieved by sitting or lying flat and in being associated with factors that lower blood pressure in these patients. Buttock pain was posturally related in PAF and MSA; for calf pain there was no difference between groups. Neck pain was related to the degree of orthostatic hypotension; in PAF patients, whose postural blood-pressure fall was greater than that in MSA, there was a greater frequency of neck pain.

The sympathetic skin response in peripheral autonomic failure--evaluation in pure failure, pure cholinergic dysautonomia and dopamine-beta-hydroxylase deficiency

The sympathetic skin response (SSR) detects changes in the electrical potential in the skin in response to physiological and electrical stimuli and, therefore, may indicate the integrity of sympathetic cholinergic neural pathways to sweat glands. This has been evaluated in 21 patients with three forms of peripheral autonomic failure. Of these, 15 had pure autonomic failure (PAF) without additional neurological features; investigations indicated both sympathetic and parasympathetic failure. Four patients had pure cholinergic dysautonomia (PCD), with clinical and laboratory features indicating only cholinergic failure. Two siblings had dopamine-beta-hydroxylase (DBH) deficiency with only sympathetic adrenergic failure. None was on drugs affecting cholinergic function. Ten normal individuals were aged-matched with PAF patients and studied as controls. The SSR was recorded from the palmar hand and plantar foot surfaces, using previously described techniques, in response to physiological (auditory, cough and inspiratory gasp) and electrical stimuli. Nerve conduction studies excluded an associated motor or sensory neuropathy. The SSR was present in all normal individuals, and in both patients with DBH deficiency who had preserved cholinergic and sudomotor function, It was absent in all 15 PAF and all four PCD patients with impaired cholinergic function. Therefore, we conclude that the SSR reflected sympathetic cholinergic function in these three different groups with peripheral autonomic failure.

Synthesis and evaluation of a monocationic copper(II) radiopharmaceutical derived from N-(2-pyridylmethyl)-N'-(salicylaldimino)-1,3-propanediamine

The monocationic 67Cu complex of N-(2-pyridylmethyl)-N'-(salicylaldimino)-1,3-propanediamine was obtained in high radiochemical purity by reaction of 67Cu2+ with the ligand in ethanol solution. Although this compound exhibited low heart uptake, the desired myocardial retention was observed over the 30 min time period studied in a rat model. Since the octanol/water partition coefficient of [67Cu]Cu(II)-N-(2-pyridylmethyl)-N'-(salicylaldiminato)-1,3- propanediamine] is lower than a value believed to be the optimal myocardial uptake, it is likely that derivatives of this compound with a higher lipophilicity merit further investigation for use in myocardial imaging with copper radioisotopes.

Hypotensive and regional haemodynamic effects of exercise, fasted and after food, in human sympathetic denervation

1. In human sympathetic denervation due to primary autonomic failure, food and exercise in combination may produce a cumulative blood pressure lowering effect due to simultaneous splanchnic and skeletal muscle dilatation unopposed by corrective cardiovascular reflexes. We studied 12 patients with autonomic failure during and after 9 min of supine exercise, when fasted and after a liquid meal. Standing blood pressure was also measured before and after exercise. 2. When fasted, blood pressure fell during exercise from 162 +/- 7/92 +/- 4 to 129 +/- 9/70 +/- 5 mmHg (mean arterial pressure by 22 +/- 5%), P < 0.0005. After the meal, blood pressure fell from 159 +/- 8/88 +/- 6 to 129 +/- 6/70 +/- 4 mmHg (mean arterial pressure by 22 +/- 3%), P < 0.0001, and further during exercise to 123 +/- 6/61 +/- 3 mmHg (mean arterial pressure by 9 +/- 3%), P < 0.01. The stroke distance-heart rate product, an index of cardiac output, did not change after the meal. During exercise, changes in the stroke distance-heart rate product were greater when fasted. 3. Resting forearm and calf vascular resistance were higher when fasted. Calf vascular resistance fell further after exercise when fasted. Resting superior mesenteric artery vascular resistance was lower when fed; 0.19 +/- 0.02 compared with 0.32 +/- 0.06, P < 0.05. After exercise, superior mesenteric artery vascular resistance had risen by 82%, to 0.53 +/- 0.12, P < 0.05 (fasted) and by 47%, to 0.29 +/- 0.05, P < 0.05 (fed). 4. On standing, absolute levels of blood pressure were higher when fasted [83 +/- 7/52 +/- 7 compared with 71 +/- 2/41 +/- 3 (fed), each P < 0.05]. Subjects were more symptomatic on standing post-exercise when fed. 5. In human sympathetic denervation, exercise in the fed state lowered blood pressure further than when fasted and worsened symptoms of postural hypotension.

Abnormal regional blood flow responses during and after exercise in human sympathetic denervation

1. Blood pressure, superior mesenteric artery (SMA) and skeletal muscle blood flow, cardiac index (CI) and systemic vascular resistance responses to supine leg exercise were measured in six age-matched normal subjects (controls) and in eleven subjects with sympathetic denervation due to primary autonomic failure (AF). 2. During exercise, blood pressure rose in controls but fell markedly in AF. After exercise, blood pressure rapidly returned to baseline in controls but remained low in AF. During exercise, systemic vascular resistance fell in controls and AF but tended to fall further in AF and remained low post exercise. CI increased similarly in controls and AF. 3. During exercise, SMA blood flow fell similarly in controls and AF, but the fall initially was slower in AF; recovery was more rapid post exercise in controls. SMA vascular resistance tended to rise less and more slowly in AF and remained elevated post exercise. 4. Forearm muscle (FM) blood flow and FM vascular resistance did not change from resting values in controls or AF post exercise. After exercise, leg muscle (LM) blood flow rose and LM vascular resistance fell equally in both groups although LM blood flow remained elevated, 10 min post exercise in AF. 5. In sympathetically denervated humans, increased blood flow (due to excessive vasodilatation, lack of sympathetic restraint, or both) in leg muscle during and after exercise in combination with impaired splanchnic vasoconstriction in the early stages of exercise may have contributed to exercise-induced hypotension.

Separation of peripheral and central cardiovascular actions of angiotensin II

The pressor and vasoconstrictor action of angiotensin II (ANG II) is considered to be caused by a combination of its direct and indirect vascular effects, the latter mediated by the sympathetic nervous system. The purpose of this study was to determine the extent to which the direct and indirect actions of ANG II contribute to its pressor and vascular effects. Blood pressure, cutaneous vascular, and plasma norepinephrine responses to intravenous ANG II were measured in conscious rabbits before and after inhibition of central sympathetic outflow with intravenous and intracisternal clonidine and after ganglionic blockade with intravenous pentolinium. Intravenous ANG II caused a similar dose-related rise in blood pressure before and after sympathetic blockade with intravenous clonidine, intracisternal clonidine, and intravenous pentolinium. In contrast, the dose-related fall in cutaneous ear blood flow and cutaneous ear temperature and rise in cutaneous ear vascular resistance induced by intravenous ANG II were abolished after intravenous clonidine, intracisternal clonidine, and intravenous pentolinium. Heart rate was unchanged after ANG II. There were no changes in back skin or rectal temperature. There was a nonsignificant fall in plasma norepinephrine and no change in epinephrine after ANG II. These results demonstrate that the acute pressor response to intravenous ANG II is mediated by its direct vascular effects and is not dependent on central or ganglionic stimulation of the sympathetic nervous system, in contrast to the effect of ANG II on cutaneous ear vasoconstriction, which is predominantly caused by a centrally mediated increase in sympathetic nervous activity. Our results separate, in conscious rabbits, the direct vascular effects of ANG II from its indirect vascular actions, which are mediated by central sympathetic stimulation in the brain.

Simultaneous arterial and urinary bladder pressure recordings in multiple system atrophy and in spinal disorders with detrusor hyperreflexia

Simultaneous arterial and urinary bladder pressure measurements were recorded during bladder filling in 21 patients with urinary bladder symptoms; seven patients had autonomic failure due to multiple system atrophy (MSA), seven had spinal cord disease of different aetiology with detrusor hyperreflexia (DH) and seven had no neurological abnormalities. A significant increase in average systolic blood pressure (BP) was recorded on bladder filling in the neurologically intact patients (from 110 to 137 mmHg) and in the patients with spinal cord disease and DH (from 109 to 129 mmHg). In those with MSA, the BP rose in four and fell in three patients. The vesicopressor response during cold receptor-mediated DH was not significantly higher when compared with room-temperature saline and when compared with the BP response during bladder filling in the neurologically intact patients. Finally, intravesical lignocaine retained in the bladder for 15 min did not influence the BP response to cold receptor stimulation in patients with spinal cord disease and DH. These findings and their pathophysiological and clinical implications are discussed.

Postprandial hypotension and parkinsonian state in Parkinson's disease

Abnormal postprandial cardiovascular responses such as postprandial hypotension (PPH) occur in primary autonomic failure and contribute significantly to morbidity. The extent and frequency of PPH and its relationship to the parkinsonian state in idiopathic Parkinson's disease (IPD) is unknown. By studying 20 patients with IPD (without autonomic failure) and 16 age-matched controls after both groups ingested a standard isocaloric balanced liquid meal, we have shown that supine PPH complicates IPD and is related to marked worsening of the parkinsonian state as measured by a cumulative score of tremor, rigidity, bradykinesia, posture, and gait. Furthermore, significant postural hypotension is unmasked that results in postural intolerance due to presyncopal symptoms. Our study indicates that, in patients with IPD, ingestion of a meal may lead to abnormal postprandial cardiovascular responses and aggravation of the parkinsonian stage. The underlying mechanisms are unclear, although vasodilatory gut peptides released in response to food ingestion may be contributory.

Design and synthesis of [111In]DTPA-folate for use as a tumor-targeted radiopharmaceutical

Folate-conjugated metal chelates have been proposed as potential imaging agents for cancers that overexpress folate receptors. In a previous study, folic acid was linked through its gamma-carboxyl group to deferoxamine (DF), and the 67Ga-labeled complex ([67Ga]DF-folate) was examined for in vivo tumor targeting efficiency in athymic mice with a human tumor cell implant. Although superb tumor-to-background contrast was obtained, slow hepatobiliary clearance would compromise imaging of abdominal tumors such as ovarian cancer. In the present study, folic acid was conjugated to an alternative chelator, diethylenetriaminepentaacetic acid (DTPA), via an ethylenediamine spacer. The desired DTPA-folate (gamma) regioisomer was synthesized by two different approaches, purified by reversed phase column chromatography, and characterized mainly by analytical HPLC, mass spectroscopy, and NMR. In cultured tumor cells, uptake of [111In]DTPA-folate (gamma) was found to be specific for folate receptor-bearing cells, and the kinetics of uptake were similar to those of free folate and other folate-conjugated molecules. In the normal rat, intravenously administered [111In]DTPA-folate (gamma) was found to be rapidly excreted into the urine, giving intestinal levels of radiotracer 10-fold lower than those observed with [67Ga]DF-folate (gamma) at 4 h. In a preliminary mouse imaging study, a folate receptor-positive KB cell tumor was readily visualized by gamma scintigraphy 1 h following intravenous administration of [111In]DTPA-folate (gamma).

Autonomic effects of selegiline: possible cardiovascular toxicity in Parkinson's disease

OBJECTIVES

The United Kingdom Parkinson's Disease Research Group (UKPDRG) trial found an increased mortality in patients with Parkinson's disease randomised to receive selegiline (10 mg/day) and levodopa compared with those taking levodopa alone. Unwanted effects of selegiline on cardiovascular regulation have been investigated as a potential cause for the unexpected mortality finding of the UKPDRG trial.

METHODS

The cardiovascular responses to a range of physiological stimuli, including standing and head up tilt, were studied in patients with Parkinson's disease receiving levodopa alone and a matched group on levodopa and selegiline.

RESULTS

Head up tilt caused selective and often severe orthostatic hypotension in nine of 16 patients taking selegiline and levodopa, but was without effect on nine patients receiving levodopa alone. Two patients taking selegiline lost consciousness with unrecordable blood pressures and a further four had severe symptomatic hypotension. The normal protective rises in heart rate and plasma noradrenaline were impaired. The abnormal response to head up tilt was reversed by discontinuation of selegiline. Drug withdrawal caused a pronounced deterioration in motor function in 13 of the 16 patients taking selegiline.

CONCLUSION

Therapy with selegiline and levodopa in combination may be associated with severe orthostatic hypotension not attributable to levodopa alone. Selegiline also has pronounced symptomatic motor effects in advanced Parkinson's disease. The possibilities that these cardiovascular and motor findings might be due either to non-selective inhibition of monoamine oxidase or to amphetamine and met-amphetamine are discussed.

Distinction of idiopathic Parkinson's disease from multiple-system atrophy by stimulation of growth-hormone release with clonidine

BACKGROUND

Idiopathic Parkinson's disease is a common neurodegenerative disease that is difficult to distinguish from other parkinsonian syndromes such as multiple-system atrophy (MSA). In MSA, autonomic dysfunction is common and is associated with either parkinsonian or cerebellar features, or both. Differentiation of idiopathic Parkinson's disease from MSA is important because prognosis, complications, and response to therapy vary according to disorder. Our aim was to find out whether clonidine/growth hormone (GH) testing distinguishes idiopathic Parkinson's disease from MSA.

METHODS

Clonidine is a centrally active alpha 2-adrenoceptor agonist that raises concentrations of GH in serum in healthy people and those with pure autonomic failure (with peripheral lesions), but not in those with MSA (with a central autonomic deficit). We investigated the effects of clonidine on 14 people with idiopathic Parkinson's disease (without autonomic deficits). 31 people with MSA of the three different clinical forms (parkinsonian, cerebellar, and mixed), 19 people with pure autonomic failure, and 27 healthy participants. In nine people with parkinsonian MSA (MSA-P), the GH response to levodopa was also assessed.

FINDINGS

Clonidine raised serum GH concentrations in patients with idiopathic Parkinson's disease (median increase 8.98 [IQR 6.6-16.6] mU/L), normal participants (13.2 [7.0-18.6] mU/L), and patients with pure autonomic failure (12.5 [5.6-18.2] mU/L). In those with MSA who had central autonomic failure, GH concentrations were unchanged (MSA-P; 0.41 [-0.30 to 2.09] mU/L and cerebellar MSA [MSA-C] 1.67 [0-4.49] mU/L). The GH response to clonidine in idiopathic Parkinson's disease was significantly different from that in MSA-P (p < 0.0002). In MSA-P, the dopamine precursor levodopa raised GH concentrations (from mean 2.7 [SE 1.0] mU/L to mean 18.2 [6.0] mU/L, p < 0.05) and GH-releasing hormone (GHRH) concentrations (from mean 20.6 [3.25] ng/L to mean 68.0 [10.6] ng/L, p < 0.05), excluding dysfunction of pituitary somatotrophs or GHRH neurons as a cause for the absent GH response to clonidine in MSA.

INTERPRETATION

The GH responses to clonidine clearly differentiated idiopathic Parkinson's disease from MSA-C and MSA-P. Together with the levodopa studies they indicated a specific alpha 2-adrenoceptor-hypothalamic deficit in MSA. The clonidine-GH test may provide further insight into central neurotransmitter and alpha 2-adrenoceptor-hypothalamic abnormalities in MSA.

Cardiovascular and hormonal responses to food ingestion in humans with spinal cord transection

In sympathetic denervation due to primary autonomic failure, ingestion of food causes a fall in blood pressure (BP) and exacerbates postural hypotension. It is not known whether these responses occur in tetraplegics with physiologically complete cervical spinal cord transection, who also have sympathetic dysfunction because of disruption of descending spinal sympathetic pathways. We, therefore, studied the effect of a liquid meal on BP, heart rate (HR) and neurohormonal levels in tetraplegics. Paraplegics with low lesions and without sympathetic dysfunction served as controls. After food ingestion, there was no fall in BP in tetraplegics or in controls. HR did not change in either group. After fund, plasma noradrenaline was unchanged in tetraplegics, but rose in controls, while plasma renin activity (PRA) rose in tetraplegics but not in controls. The fall in BP and rise in HR on head-up tilt after the meal in tetraplegics was similar to that before the meal. There was no change in PRA following pre-prandial tilt in either group; post-prandial tilt raised levels in the tetraplegics, unlike in controls. Thus there is considerable variance in the responses to food between tetraplegics and paraplegic controls, and even greater differences when compared with published data in other autonomic disorders with sympathetic dysfunction; this may relate to the site and the nature of the sympathetic lesion and the ability to activate compensatory mechanisms.

Systemic and regional (including superior mesenteric) haemodynamic responses during supine exercise while fasted and fed in normal man

The systemic and regional (including superior mesenteric artery, SMA) responses to exercise in the fasting and fed state were studied in ten normal subjects before, during and after 9 min of graded supine bicycle exercise on two separate occasions, when fasted and after a liquid meal. During exercise, blood pressure (BP) and cardiac index rose similarly in both states. Resting SMA blood flow was higher when fed (519 (282-619) versus 240 (133-255) ml/min, p < 0.01). SMA blood flow fell during exercise in both states, to 98 (63-154) ml/min, p < 0.01 when fasted and to 55 (42-149) ml/min, p < 0.01 when fed. SMA vascular resistance rose during exercise in both states, but rose less when fasted by 36 (6-57)% versus 143 (36-240)% (NS). Resting forearm and leg blood flow (FBF and LBF) and vascular resistance (FVR and LVR) were similar fasted and fed. FBF and FVR did not change after exercise in either state. LBF rose and LVR fell similarly in both states. We conclude that in normal subjects, although splanchnic oxygen demand is likely to be greater after food, during light to moderate exercise splanchnic vasoconstriction contributes to maintenance of BP.

Haemodynamic and hormonal effects of two different oral glucose loads in normal human subjects

Systemic and regional haemodynamics and hormonal responses to two isovolaemic, iso-osmotic solutions of 0.5 and 1.0 g/kg of glucose were compared in ten normal young subjects (mean age 24 +/- 3 years). Measurements were made while subjects were supine before glucose and every 15 min for 60 min after ingestion of each solution. Superior mesenteric artery (SMA) blood flow rose similarly after each dose. There were corresponding reductions in SMA vascular resistance after each dose but no difference between doses. Pulsatility index of the SMA was lower after 1.0 g/kg. There was no change in blood pressure, heart rate, cardiac index or forearm muscle blood flow after either dose. Plasma glucose levels rose after each dose and were higher after 1.0 g/kg. There was no difference in the plasma insulin rise between doses. Plasma levels of noradrenaline and adrenaline did not change after either dose. These results suggest that with glucose loads within the ranges we used, changes in SMA blood flow are not dose-related and larger increases in SMA blood flow or in plasma insulin than we observed are needed to reflexly activate cardiac output and raise plasma noradrenaline levels in young normal subjects.

Mixed bis(thiosemicarbazone) ligands for the preparation of copper radiopharmaceuticals: synthesis and evaluation of tetradentate ligands containing two dissimilar thiosemicarbazone functions

A series of four "mixed" bis(thiosemicarbazone) keto aldehyde derivatives containing dissimilar thiosemicarbazone functions were synthesized and evaluated as ligands for preparation of radiocopper-labeled radiopharmaceuticals. The pyruvaldehyde-based mixed bis(thiosemicarbazone) ligands CH3C[=NNHC(S)NH2]CH[=NNHC(S)NHMe] (4a), CH3C[=NNHC(S)NHMe]-CH[=NNHC(S)NH2] (4b), CH3C[=NNHC(S)NH2]CH[=NNHC(S)NMe2] (4c), and CH3C[=NNHC-(S)NHMe]CH[=NNHC(S)NMe2] (4d) were obtained by reaction of thiosemicarbazide, N4-methylthiosemicarbazide, or N4,N4-dimethylthiosemicarbazide with pyruvaldehyde 2-thiosemicarbazones that had been generated by oxidative cleavage of the appropriate pyruvic aldehyde dimethyl acetal 2-thiosemicarbazone. The 67Cu-labeled complexes of ligands 4a-d were prepared and screened in a rat model to assess the potential of each chelate as a 62Cu radiopharmaceutical for imaging with positron emission tomography. In the rat model the 67Cu complexes of ligands 4a-d exhibit significant uptake into the brain and heart after intravenous injection, following trends similar to those previously reported for the related bis(thiosemicarbazone) complexes, Cu-PTS, Cu-PTSM, and Cu-PTSM2 (derived from pyruvaldehyde bis(thiosemicarbazone), pyruvaldehyde bis(N4-methylthiosemicarbazone), and pyruvaldehyde bis(N4,N4-dimethylthiosemicarbazone), respectively). Ultrafiltration studies using solutions of dog and human serum albumin reveal that the 67Cu complexes of ligands 4a-d, like the Cu(II) complex of pyruvaldehyde bis(N4-methylthiosemicarbazone), interact more strongly with human albumin than dog albumin.