Luigi X. Cubeddu

Changes in serotonin metabolism in cancer patients : its relationship to nausea and vomiting induced by chemotherapeutic drugs

The metabolism of serotonin was studied in cancer patients of their first day of their first course of chemotherapeutic drugs either with strongly or moderately emetogenic regimens. It was observed that strongly emetogenic treatments induce greater increases in serotonin release than moderately emetogenic regimens. High-dose cisplatinum (75 +/- 5 or 83.8 +/- 5 mg m-2) produced a marked increase in the plasma levels and in the urinary excretion of 5-hydroxyindole acetic acid (5-HIAA). Neither platelet nor plasma (platelet-free plasma) serotonin were significantly modified by high-dose cisplatinum. Dacarbazine (283 +/- 22 mg m-2), another strongly emetogenic agent, induced acute nausea and emesis paralleled by marked increases in the urinary excretion of 5-HIAA. Both for high-dose cisplatinum and dacarbazine, the increases in serotonin metabolism occurred with a similar time-course than those of vomiting, and lasted for a period of 4 to 8 h. Low-dose cisplatinum (30.8 +/- 3 mg m-2) as well as cyclophosphamide-based chemotherapies (520 +/- 30 mg m-2) produced very small increases in the urinary excretion of 5-HIAA. Platelet and plasma serotonin levels failed to increase in cyclophosphamide-treated patients. Octreotide, a long-acting somatostatin analog, did not inhibit the increase in urinary 5-HIAA and the nausea and vomiting produced by high-dose cisplatinum. These results suggest that for treatments that induce marked increases in serotonin release such as high-dose cisplatinum or dacarbazine: (a) the amount and time course of serotonin release induced by chemotherapeutic drugs determines the severity, time of onset and pattern of emesis observed; (b) platelet serotonin play no role in chemotherapy-induced emesis; (c) strongly emetogenic regimens release serotonin from enterochromaffin cells; and (d) intestinal release of serotonin is the consequence of the damage induced by the chemotherapeutic drugs on the gut mucosa.

Salt Sensitivity Is Associated With Insulin Resistance in Essential Hypertension

The relationship between salt sensitivity and insulin resistance was investigated in nondiabetic, nonobese (body mass index < or = 28) untreated patients with uncomplicated, mild-to-moderate essential hypertension. Alterations in insulin-mediated glucose disposal were assessed by means of the insulin suppression test. Subjects were classified as salt sensitive and salt resistant according to their blood pressure response to low and high salt intake. Fasting serum glucose levels were within normal limits and did not differ between salt sensitive and salt resistant hypertensives, irrespectively of the level of salt intake. Fasting serum insulin levels increased in salt sensitive patients when on a high intake of salt. The insulin suppression test revealed the existence of marked differences in insulin-mediated glucose uptake between salt sensitive and salt resistant hypertensives. Much higher steady-state glucose values (nanomoles of glucose/ liter) were obtained during the insulin suppression test in salt sensitive than in salt-resistant hypertensives (7.4+/-1.6 v 3.5+/-0.1 under low salt; and 12.5+/-1.1 v 4.3+/-0.1 under high salt intake). The product of glucose times insulin obtained at steady state during low and high salt intakes were 2.5 and 5 times greater, respectively, in salt sensitive than in salt resistant hypertensives. Therefore, the impairment in insulin-mediated glucose disposal observed in salt sensitive hypertensives was present both under low salt (60 to 70 mEq/day) and high salt intake (300 mEq/day). However, it was exacerbated under high salt intake. These results suggest that untreated salt sensitive hypertensives have a considerable impairment in insulin-mediated glucose disposal because of a state of insulin resistance. High salt intake increased BP, induced hyperinsulinemia, and worsened insulin-mediated glucose disposal only in salt sensitive patients. We propose that salt sensitivity contributes, separately from hypertension, to insulin resistance and thus be considered per se as an additional risk factor in the development of cardiovascular disease. Salt sensitivity and insulin resistance may be genetically associated conditions.

Endothelial nitric oxide synthase polymorphism, nitric oxide production, salt sensitivity and cardiovascular risk factors in Hispanics

Mutations in the endothelial nitric oxide synthase (eNOS) gene may be associated with abnormal nitric oxide (NO) production and cardiovascular diseases. In this study, we investigated the prevalence of two eNOS polymorphisms, the Glu298Asp variant on exon 7, and the 4a/b variable number of tandem repeats (VNTR) on intron 4, and their association with blood pressure (BP), NO production, salt sensitivity and cardiovascular risk factors in healthy Venezuelans. The prevalence of both polymorphisms in Venezuelans was comparable to that described for Caucasians, but significantly different from that known for African-Americans and Japanese. The 4a/b genotype was associated with reduced levels of NO metabolites (25% decrease), larger BP lowering in response to salt restriction (9.0 vs 4.8 mmHg, P<0.05), greater prevalence of salt sensitivity (39% in 4a/b and 27% in 4b/b; P<0.05) and with higher LDL-cholesterol levels. The Glu298T polymorphism did not affect NO production, nor it was associated with salt sensitivity. Glu298Asp polymorphism was positively associated with higher weight, triglycerides and LDL-cholesterol. Neither polymorphism was associated with changes in fasting or postload serum glucose, BP, obesity and albuminuria. In conclusion, the prevalence of eNOS polymorphisms is strongly determined by ethnic factors. The 4a/b gene polymorphism could be a genetic susceptibility factor for the BP response to salt intake and for the genetic control of NO production. The reduced NO production in subjects with the 4a/b genotype may be responsible for the increased sensitivity of their BP to salt.

Nitric oxide and salt sensitivity.

Studies in laboratory animals suggest that altered nitric oxide (NO) production may be associated with salt sensitivity. In this investigation we determined whether the endogenous NO production was altered in salt-sensitive human subjects when salt intake was changed. Salt sensitivity was assessed from the magnitude of the blood pressure (BP) lowering obtained when the salt intake was reduced from high to a low intake. The combined urinary excretion of nitrites and nitrates, the major metabolites of NO, was employed as an index of endogenous NO production. Salt-sensitive subjects (n = 23) were older, heavier, and had greater waist-to-hip ratios and higher baseline BP than salt-resistant individuals (n = 25). In salt-sensitive subjects, mean blood pressure (MBP) decreased 11.8+/-0.7 mm Hg, and NO metabolite excretion increased from 823+/-102 to 1530+/-148 mmol/24 h, when salt intake was reduced from 316 to 28 micromol/day. NO metabolite excretion was 45% lower during high salt (0.66+/-0.1 micromol/mg creatinine) than during low salt intake (1.12+/-0.1 micromol/mg creatinine) (P < .001). In contrast, when salt intake was reduced, salt-resistant subjects exhibited no significant mean changes in BP or NO metabolite excretion. During low salt intake, NO metabolite excretion (micromol/ day) was significantly higher in salt-sensitive individuals. The magnitude of decrease of systolic blood pressure, diastolic blood pressure, or MBP induced by reducing salt intake was not related to the increase in urinary excretion of NO metabolite levels (r2 = 0.009; P = .66). In summary, to the extent that urinary NO metabolite levels reflect the activity of the endogenous NO system, our results support the view that salt sensitivity may in part be determined by an inability to increase or to sustain NO production in response to high salt. Insufficient NO production during high salt may in turn lead to altered pressure-natriuresis relationships and to an increase in BP. The possibility that the increase in BP induced by high salt intake in salt-sensitive individuals could be the key factor in reducing NO metabolite levels can not be ruled out.

Participation of Serotonin on Early and Delayed Emesis Induced by Initial and Subsequent Cycles of Cisplatinum‐Based Chemotherapy: Effects of Antiemetics

The role of serotonin as the possible trigger mechanism of vomiting associated with chemotherapeutic drugs was further investigated in cancer patients (n=86). Increases in 5‐hydroxyindoleacetic acid (5‐HIAA) excretion rates (2.5–2.9 times baseline values) were observed 4 to 8 hours after high‐dose cisplatinum (≥50 mg/m2). The daily excretion of 5‐HIAA from 24–48, 48–72, and 72–96 hours after cisplatinum was not different from pre‐cisplatinum levels. These results, together with the efficacy data for 5‐HT3 antagonists, suggests that serotonin may trigger the early, intense period of emesis, but not the period of delayed emesis, following high‐dose cisplatinum. Compared with the first cycle of chemotherapy, higher peak levels and more sustained elevations of 5‐HIAA excretion were found after subsequent cycles, with high‐dose cisplatinum. Further, no evidence of serotonin depletion was found after a single or after repeated cycles of treatment with high‐dose cisplatinum. These data suggest that the more intense emetic response associated to repeated cycles of treatment may be triggered by greater changes in serotonin release. No significant differences in the rate and amount of 5‐HIAA excreted induced by low‐dose (30±2 mg/m2) and high‐dose (84±3 mg/m2) cisplatinum were found between those patients who received dexamethasone (D) (20 mg IV) and those who received metoclopramide (M) (2 mg/kg, IV), irrespectively of the cycle of treatment. Interestingly, for M but not for D, best antiemetic protection was observed when lower amounts of serotonin were released (i.e., low‐dose cisplatinum and initial cycles of treatment). This suggests, that contrary to D, the effects of M, a purported antagonist of 5‐HT3 receptors, are highly dependent on the quantity of serotonin release induced by a chemotherapeutic drug. Finally, our data suggest that D does not interfere with cisplatinum‐induced serotonin release.

Prazosin and propranolol in preoperative management of pheochromocytoma

Combined use of prazosin and propranolol was effective in preoperative management of three patients with norepinephrine(NE)‐secreting pheochromocytoma (PHEO). On admission, all were symptomatic and had moderate to severe hypertension despite treatment with diuretics, propranolol, and sympatholytics. Optimal symptomatic and blood pressure (BP) control was achieved with 6 to 10 mg/day prazosin and 120 to 480 mg/day propranolol every 6 hr in equally divided doses. With this therapy, BP and hematocrit were reduced to levels similar to those found in the postoperative period. The daily urinary excretion of catecholamines and their metabolites was not modified during therapy with prazosin and propranolol. There was a drop in supine systolic (40 to 64 mm Hg) and diastolic (32 to 52 mm Hg) BP in all patients 1 to 2 hr after the first dose of prazosin (1‐mg tablet); in two subjects this was accompanied by a larger orthostatic fall (74 and 92 mm Hg systolic; 65 and 78 mm Hg diastolic BP). The high incidence of first‐dose effect suggests that a single oral dose of 1 mg of prazosin could aid in the diagnosis of PHEO. The effectiveness of prazosin in controlling the hypertension induced by NE‐secreting PHEO suggests that, in man, pressure responses to augmented levels of NE are mediated solely through α1‐receptors.

Urinary albumin excretion in lean, overweight and obese glucose tolerant individuals: its relationship with dyslipidaemia, hyperinsulinaemia and blood pressure.

The presence of microalbuminuria has become an important tool for therapeutic intervention. In this study we investigated whether the dysmetabolic syndrome of obesity was associated with or could occur in the absence of microalbuminuria. The study was conducted in 71 clinically healthy, glucose tolerant Hispanics (age: 43u2009±u20091.4 years, body mass index (BMI): 28.7u2009±u20090.6u2009kg/m2, systolic blood pressure (SBP): 117u2009±u20092 mmu2009Hg, diastolic blood pressure (DBP): 77u2009±u20091.3 mmu2009Hg, urinary albumin excretion: 10.2u2009±u20090.6u2009mg/24u2009h). Subjects were classified as lean (BMI <25), overweight (BMI >25 <30) and obsese (BMI >30u2009kg/m2). Greater BMI was associated with higher body weight, waist-to-hip ratio (WHR), BP, fasting insulin, triglyceride, post glucose load insulin and glucose, and lower high-density lipoprotein (HDL) cholesterol levels. However, no significant differences in the urinary albumin excretion (mg/24u2009h) were found between lean (9.0u2009±u20090.9; median: 9.1), overweight (11.3u2009±u20091.2; median: 10.5) and obese (11.1u2009±u20091.2; median: 9.7) subjects. In addition, microalbuminuria (urinary albumin excretion >30u2009mg/24u2009h) was not found in any of the study subjects. For all subjects combined, as well as for each of the groups separately, the urinary albumin excretion was unrelated to the BMI, WHR, body weight, triglyceride, cholesterol (total, LDL or HDL), fasting or post-load glucose and insulin plasma concentrations. Neither in females nor in males, abdominal fat accumulation was associated with an increase in the urinary albumin excretion. However, in the obese groups, urinary albumin excretion was strongly related to the level of SBP (r2: 0.67; Pu2009<u20090.0001) and DBP (r2: 0.55; Pu2009<u20090.0001). In summary, obesity, hyperinsulinaemia and dyslipidaemia per se are not determinants of increased albumin excretion. However, in the obese subjects, the BP, particularly the SBP, was a strong determinant of the level of albumin in the urine. Microalbuminuria may occur later in the course of the dysmetabolic syndrome, due to worsening of hypertension and development of hyperglycaemia.

Effects of metformin on intestinal 5-hydroxytryptamine (5-HT) release and on 5-HT3 receptors

Abstract. Nearly 30% of patients treated with metformin experience gastrointestinal side effects. Since release of 5-hydroxytryptamine (5-HT) from the intestine is associated with nausea, vomiting, and diarrhea, we examined whether metformin induces 5-HT release from the intestinal mucosa. In 40% of tissue biopsy specimens of human duodenal mucosa, metformin (1, 10, and 30xa0µM) caused an increase in 5-HT outflow by 35, 70, and 98%, respectively. Peak increases in 5-HT outflow were observed after 10–15xa0min exposure to metformin, returning to baseline levels after 25xa0min. Tetrodotoxin (1xa0µM) reduced by about 50% the metformin-evoked increase in 5-HT outflow (P<0.05). Metformin-evoked release was not affected by scopolamine + hexamethonium, propranolol, the 5-HT3 receptor antagonist dolasetron, naloxone, or the NK1 receptor antagonist L703606. In the presence of tetrodotoxin (1xa0µM), somatostatin (1xa0µM) further reduced metformin-induced 5-HT release by 15–20%.In view of the 5-HT releasing effects of selective 5-HT3 receptor agonists to which metformin (N-N-dimethylbiguanide) is structurally related, we investigated whether metformin directly interacts with 5-HT3 receptors. Receptor binding (inhibition of [3H]-GR65630 binding) and agonist effects (stimulation of [14C]-guanidinium influx) at 5-HT3 receptors were studied in murine neuroblastoma N1E-115 cells, which express functional 5-HT3 receptors. Metformin up to 0.3xa0mM failed to inhibit [3H]-GR65630 binding and to modify displacement of [3H]-GR65630 binding induced by 5-HT. 5-HT (3xa0µM) stimulated the influx of [14C]-guanidinium in intact N1E-115 cells. Metformin up to 1xa0mM failed to modify basal influx, 5-HT-induced influx, and 5-HT+ substancexa0P-induced influx of [14C]-guanidinium. Our results indicate that metformin induces 5-HT3 receptor-independent release of 5-HT from human duodenal mucosa via neuronal and non-neuronal mechanisms. Part of the gastrointestinal side effects observed during treatment with metformin could, thus, be produced by the release of 5-HT and other neurotransmitter substances within the duodenal mucosa.

Met-enkephalin, leu-enkephalin and other opiate-like peptides in human pheochromocytoma tumors

Abstract Opiate-like peptides, as measured by radioreceptor assay, were present in 20 samples from 9 human pheochromocytoma tumors obtained at surgery. The variation in peptide content of these samples, found in apparently viable tissue, ranged from 6-fold less to 90-fold higher than the mean value in normal human adrenal medulla. Subcellular fractionation of one tumor homogenate indicated that a large fraction of the opiate-like peptides are stored with catecholamines in chromaffin vesicles. Further analysis of pheochromocytoma opioid peptides revealed the presence of cryptic opioid activity, uncovered by trypsin treatment, and of six well-defined opioid peptide peaks, separated by high performance liquid chromatography. Peaks of opioid activity with high performance liquid chromatography retention times identical to met- and leu-enkephalin account for 43% and 27% of the recovered opioid activity, respectively. The massive stores of opioid peptides present and secreted from pheochromocytoma tumors may be responsible for some of the pleiomorphic symptomatology frequently observed in this disease.

Plasma chromogranin A marks emesis and serotonin release associated with dacarbazine and nitrogen mustard but not with cyclophosphamide-based chemotherapies.

Chromogranin A (CgA) is present in high concentrations in enterochromaffin cells, where it is co-localised with serotonin in the storage granules. Plasma CgA has been reported to mark emesis and serotonin release associated with cisplatin treatment. However, it is not known whether plasma CgA could be an indicator of emesis and of serotonin release in patients receiving non-cisplatin chemotherapies. Therefore, in this study we evaluated, in cancer patients, the temporal relationships between the increases in plasma CgA and urinary 5-hydroxyindoleacetic acid (5-HIAA) and the development of vomiting following dacarbazine, nitrogen mustard and cyclophosphamide treatments. Metoclopramide was used as antiemetic. With dacarbazine, nitrogen mustard and cyclophosphamide the median time to the onset of emesis was 2.3, 2.8 and 5.3 h and the duration of intense emesis was 3, 2 and 6 h respectively. Plasma CgA and urinary 5-HIAA increased after dacarbazine- and nitrogen mustard-based chemotherapies, with maximal increases between 4 and 6 h after initiation of drug infusion. The time course for the increases in plasma CgA paralleled that of urinary 5-HIAA and the period of intense emesis. A highly significant (P = 0.0009) positive correlation (r = 0.68) was found between the increases in plasma CgA and in urinary 5-HIAA. Cyclophosphamide treatment was not associated with increases in plasma CgA and in urinary 5-HIAA, despite inducing emesis; this indicates that the increases in CgA and 5-HIAA after dacarbazine and nitrogen mustard are not due to the act of vomiting per se. In summary, plasma CgA is a marker of serotonin release (most likely from enterochromaffin cells) after dacarbazine and nitrogen mustard-based chemotherapies, exocytosis being the most likely mechanism for the release of serotonin. Serotonin released from enterochromaffin cells seems to trigger the emetic response to dacarbazine and nitrogen mustard; however, cyclophosphamide may release serotonin from a different pool (enteric serotonin neurons and/or CNS serotonin?).