Ectopic production and processing of atrial natriuretic peptide in a small cell lung carcinoma cell line and tumor from a patient with hyponatremia

Paraneoplastic endocrine syndromes

The majority of neoplasms are responsible for symptoms caused by mass effects to surrounding tissues and/or through the development of metastases. However, occasionally neoplasms, with or without endocrine differentiation, acquire the ability to secrete a variety of bioactive substances or induce immune cross-reactivity with the normal tissues that can lead to the development of characteristic clinical syndromes. These syndromes are named endocrine paraneoplastic syndromes when the specific secretory components (hormones, peptides or cytokines) are unrelated to the anticipated tissue or organ of origin. Endocrine paraneoplastic syndromes can complicate the patient's clinical course, response to treatment, impact prognosis and even be confused as metastatic spread. These syndromes can precede, occur concomitantly or present at a later stage of tumour development, and along with the secreted substances constitute the biological 'fingerprint' of the tumour. Their detection can facilitate early diagnosis of the underlying neoplasia, monitor response to treatment and/or detect early recurrences following successful initial management. Although when associated with tumours of low malignant potential they usually do not affect long-term outcome, in cases of highly malignant tumours, endocrine paraneoplastic syndromes are usually associated with poorer survival outcomes. Recent medical advances have not only improved our understanding of paraneoplastic syndrome pathogenesis in general but also enhanced their diagnosis and treatment. Yet, given the rarity of endocrine paraneoplastic syndromes, there is a paucity of prospective clinical trials to guide management. The development of well-designed prospective multicentre trials remains a priority in the field in order to fully characterise these syndromes and provide evidence-based diagnostic and therapeutic protocols.

Serum level of arginine-vasopressin influences the prognosis of extensive-disease small-cell lung cancer

PURPOSE

The purpose of this study is to elucidate the influence of serum arginine-vasopressin (AVP) level on prognosis of extensive-disease small-cell lung cancer (ED-SCLC).

METHODS

We retrospectively investigated the clinical records of 163 patients with ED-SCLC, who were admitted to Okayama University Hospital or National Shikoku Cancer Center Hospital. The influence of 14 pretreatment variables on survival was analyzed.

RESULTS

In a multivariate analysis of 163 patients, elevation of serum LDH level (P = 0.028) and poor performance status (PS > or = 2, P = 0.002) were independent poor prognostic factors. In 34 patients whose serum AVP levels were available, high serum AVP level was related to the poor prognosis (P < 0.001). The serum-sodium level did not affect the survival. Median serum level of osmotic pressure in 34 patients was normal (284.9 mOsm/kg), although, serum osmotic pressure was low in four of six patients with high serum AVP level. In all patients with high serum AVP level, serum LDH level was elevated.

CONCLUSIONS

The data from the current study suggested that serum LDH level and PS were the poor prognostic factors for ED-SCLC. But we additionally identified the prognostic significance of serum AVP level, which may be a more useful factor than serum-sodium level.

A metabolic study of patients with lung cancer and hyponatremia of malignancy

PURPOSE

One-third of patients with lung cancer and hyponatremia have no evidence of ectopic arginine vasopressin (AVP) production and the cause of their hyponatremia is not conclusively established. We sought to distinguish patients with hyponatremia caused by elevated AVP versus those with ectopic atrial natriuretic peptide (ANP) via this detailed metabolic study.

EXPERIMENTAL DESIGN

We enrolled 24 patients recently diagnosed with lung cancer in a metabolic study in which patients were placed on sodium and fluid restriction for 4 days. Serum electrolytes, osmolality, urine electrolytes and osmolality, plasma AVP, ANP, aldosterone, urinary cyclic AMP and cyclic guanosine 3',5'-monophosphate were measured daily and tumor tissue was obtained to measure ectopic hormone production. We attempted to characterize the pathophysiology of hyponatremia caused by ectopic ANP production in patients with small cell lung cancer (SCLC) and to determine its effect on the aldosterone axis.

RESULTS

Seven of the nine patients with SCLC presented with hyponatremia and three had elevated ANP levels at presentation without elevation of AVP. All three patients who presented with hyponatremia and elevated ANP showed a decline in serum sodium following fluid restriction, whereas two patients with SCLC and elevated AVP had normalized serum sodium levels. The combination of hyponatremia and elevated ANP was associated with a persistent natriuresis and inappropriately low aldosterone levels despite sodium restriction, suggesting ANP suppression of the aldosterone axis.

CONCLUSIONS

Management of patients with hyponatremia and SCLC should be guided by the knowledge that some patients with SCLC have ectopic production of ANP as the cause of their hyponatremia.

Cardiac endocrine function is an essential component of the homeostatic regulation network: physiological and clinical implications

The discovery of cardiac natriuretic hormones required a profound revision of the concept of heart function. The heart should no longer be considered only as a pump but rather as a multifunctional and interactive organ that is part of a complex network and active component of the integrated systems of the body. In this review, we first consider the cross-talk between endocrine and contractile function of the heart. Then, based on the existing literature, we propose the hypothesis that cardiac endocrine function is an essential component of the integrated systems of the body and thus plays a pivotal role in fluid, electrolyte, and hemodynamic homeostasis. We highlight those studies indicating how alterations in cardiac endocrine function can better explain the pathophysiology of cardiovascular diseases and, in particular of heart failure, in which several target organs develop a resistance to the biological action of cardiac natriuretic peptides. Finally, we emphasize the concept that a complete knowledge of the cardiac endocrine function and of its relation with other neurohormonal regulatory systems of the body is crucial to correctly interpret changes in circulating natriuretic hormones, especially the brain natriuretic peptide.

Evaluation and management of hypo-osmolality in hospitalized patients

Hyponatremia is the most common electrolyte disorder encountered in the clinical setting. Abnormalities of the mechanisms that maintain normal water and sodium metabolism are often present in hospitalized patients, including defects in renal water excretion. All of the current therapeutic approaches in patients with the syndrome of inappropriate antidiuretic hormone secretion and other forms of vasopressin-induced hyponatremia have significant limitations. Studies in animal models and humans have demonstrated that antagonists of the AVP V2 receptor in the kidney are effective in correcting hyponatremia. These new agents have been termed "aquaretics" because of their ability to induce a free water diuresis without the natriuresis or kaliuresis characteristic of diuretic drugs. When approved for clinical use, selective V2, and possibly also combined V1 + V2 receptor antagonists will be helpful in therapy.

Management of small cell lung cancer

Small cell lung carcinoma typically presents as a central endobronchial lesion in chronic cigarette smokers with hilar enlargement and disseminated disease. The diagnostic pathology should be reviewed by a pathologist accomplished in reading pulmonary pathology, and, if any doubt exists in the diagnosis, additional special stains or diagnostic material should be obtained. Patients with extensive stage disease should be managed by combination chemotherapy, whereas patients with limited stage disease should be treated with etoposide/cisplatin plus concurrent chest irradiation. The chemotherapy should be administered for 4 to 6 months and then should be discontinued. Prophylactic cranial irradiation should be given to patients who achieve a complete remission. Patients should be retreated with chemotherapy if they develop a relapse of their small cell lung cancer. The patients who are followed in complete remission should be observed carefully for second cancers, and appropriate therapy should be administered if the cancer reappears.

BNP and congestive heart failure

Brain natriuretic peptide (BNP), a peptide hormone secreted chiefly by ventricular myocytes, plays a key role in volume homeostasis. The plasma concentration of BNP is raised in various pathological states, especially heart failure. Many studies suggest that measurement of plasma BNP has clinical utility for excluding a diagnosis of heart failure in patients with dyspnea or fluid retention and for providing prognostic information in those with heart failure or other cardiac disease. It may also be of value in identifying patients after myocardial infarction in whom further assessment of cardiac function is likely to be worthwhile. Preliminary evidence suggests that measuring the plasma concentration of BNP may be useful in fine tuning therapy for heart failure. Artificially raising the circulating levels of BNP shows considerable promise as a treatment for heart failure. With simpler assay methods now available, it is likely that many physicians will measure plasma BNP to aid them in the diagnosis, risk stratification, and monitoring of their patients with heart failure or other cardiac dysfunction.

Ectopic expression of active processed form of atrial natriuretic peptide in skeletal myoblasts

Atrial natriuretic peptide (ANP) is a cardiac hormone that elicits a profound diuresis, natriuresis, and hypotension. As a preliminary study toward ANP gene therapy of cardiovascular disorders, we have cloned a cDNA for mouse preproANP and carried out expression studies in muscle cells. The expression cassette, which was flanked by ITRs from AAV-2, consisted of HCMV IE enhancer/promoter, preproANP gene, and polyadenylation signal from bovine growth hormone. We transfected this expression vector into primary skeletal myoblasts and examined the following points: (1) secretion of immunoreactive ANP, (2) biological activity, and (3) nature of secreted ANP(s). The conditioned media from cells transfected with ANP vector had significantly higher levels of irANP in comparison to mock control. The secreted irANP had biological activity as confirmed by the elevated level of intracellular cGMP in human umbilical vein endothelial cells. Reverse-phase HPLC analysis showed that the processed form of ANP was the predominant form. These results demonstrate that preproANP gene could be ectopically expressed and correctly processed in skeletal myoblasts, which has implications for development of muscle-based ANP gene therapy.

A prospective study of patients with lung cancer and hyponatremia of malignancy

This study was undertaken to define the impact of arginine vasopressin (AVP) and atrial natriuretic peptide (ANP) on sodium homeostasis in patients with lung cancer. Patients had their serum and urine electrolytes and osmolality determined before and after a saline infusion of 500 ml. The plasma hormones, AVP, ANP, plasma renin activity (PRA), angiotensin II, and aldosterone were determined by radioimmunoassay every 15 min before, during and after the saline infusion. Fifty patients, 31 with small cell lung cancer and 19 with non-small cell lung cancer participated in this trial. All 11 patients (10 patients with small cell lung cancer and one patient with non-small cell lung cancer) who presented with hyponatremia had inappropriately elevated levels of AVP. Elevated plasma AVP levels were highly correlated with the presence of hyponatremia (p < 0.00001). Initial plasma ANP levels were not associated with hyponatremia (p = 0.73). Urinary sodium concentration increased during the saline infusion proportional to the initial plasma level of ANP (p = 0.0045). AVP appears to be elevated in nearly all patients with hyponatremia of malignancy. ANP plasma levels in patients with lung cancer are associated with the ability to excrete a sodium load but do not appear to downregulate renin, angiotensin II, and aldosterone production.