Direct measurement of cGMP in blood plasma and urine by radioimmunoassay

A new small molecule inhibitor of soluble guanylate cyclase

Soluble guanylate cyclase (sGC) is a haem containing enzyme that regulates cardiovascular homeostasis and multiple mechanisms in the central and peripheral nervous system. Commonly used inhibitors of sGC activity act through oxidation of the haem moiety, however they also bind haemoglobin and this limits their bioavailability for in vivo studies. We have discovered a new class of small molecule inhibitors of sGC and have characterised a compound designated D12 (compound 10) which binds to the catalytic domain of the enzyme with a K_D of 11 μM in a SPR assay.

Surface plasmon resonance using the catalytic domain of soluble guanylate cyclase allows the detection of enzyme activators

Soluble Guanylate Cyclase (sGC) is the receptor for the signalling agent nitric oxide (NO) and catalyses the production of the second messenger cyclic guanosine monophosphate (cGMP) from guanosine triphosphate (GTP). The enzyme is an attractive drug target for small molecules that act in the cardiovascular and pulmonary systems, and has also shown to be a potential target in neurological disorders. We have discovered that 5-(indazol-3-yl)-1,2,4-oxadiazoles activate the enzyme in the absence of added NO and shown they bind to the catalytic domain of the enzyme after development of a surface plasmon resonance assay that allows the biophysical detection of intrinsic binding of ligands to the full length sGC and to a construct of the catalytic domain.

The lung, whole-body metabolism and disease

It is well recognized that the lung has its own hormonally responsive endogenous metabolism. Less well recognized is the potential of the lung to influence and, in turn, be influenced by the homeostatic mechanisms of the body. It is suggested that the lung could modulate concentrations of circulating hormones and thereby play an indirect exogenous metabolic role in whole-body metabolism. Investigations of patients undergoing cardiopulmonary bypass as well as studies with the perfused rat lung suggest that the lung could make an important direct contribution to whole-body lactate and perhaps alanine production. The control of the endogenous and exogenous metabolism of the lung may be exerted through circulating hormones, substrates, blood gases and lung movement. Disorders of the lung or the whole body may disturb these relationships. In patients with chronic lung disease circulating blood metabolites are affected and conversely in diabetes there are effects on lung metabolism. The unified concept of lung/whole-body metabolism is discussed in relation to therapeutic approaches for the prevention and investigation of neonatal and adult respiratory distress syndromes.

Nitric oxide-evoked transient kinetics of cyclic GMP in vascular smooth muscle cells

Cyclic-3',5'-guanosine monophosphate (cGMP) mediates the intracellular signaling cascade responsible for the nitric oxide (NO) initiated relaxation of vascular smooth muscle (VSM). However, the temporal dynamics, including the regulation of cGMP turnover, are largely unknown. Here we report new mechanistic insights into the kinetics of cGMP synthesis and hydrolysis in primary VSM cells by utilizing FRET-based cGMP-indicators [A. Honda, S.R. Adams, C.L. Sawyer, V. Lev-Ram, R.Y. Tsien, W.R. Dostmann, Proc. Natl. Acad. Sci. U S A 98 (5) (2001) 2437.]. First, 2-(N,N-Diethylamino)-diazenolate 2-oxide (DEA/NO) and 2,2'-(Hydroxynitrosohydrazono)-bis-ethanimine (DETA/NO) induced NO-concentration dependent, transient cGMP responses ("peaks") irrespective of their rates of NO release. The kinetic characteristics of these cGMP peaks were governed by the concerted action of the NO-sensitive guanylyl cyclase (GC) and phosphodiesterase type V (PDE5) as shown by their respective inhibition using 1H-[1,2,4]oxadiazolo[4,3-a]quinoxalin-1-one (ODQ) and Sildenafil. These responses occurred in the presence of moderately elevated cGMP (5-15% FRET ratio), and thus activated PKG and phosphorylated PDE5, suggesting a prominent role for GC in the maintenance and termination of cGMP peaks. Furthermore, cGMP transients could be elicited repeatedly without apparent desensitization of GC or by suppression of cGMP via long-term PDE5 activity. These results demonstrate a continuous sensitivity of the NO/cGMP signaling system, inherent to the phasic nature of smooth muscle physiology.

High plasma cardiac natriuretic peptides associated with enhanced cyclic guanosine monophosphate production in preascitic cirrhosis

BACKGROUND/AIMS

The initial abnormalities of renal sodium handling in cirrhosis remain unclear. The aim of this study was to characterize sodium metabolism in preascitic cirrhosis.

METHODS

Ten patients with preascitic cirrhosis and ten controls were studied. All subjects ate a diet providing 120 mmol sodium during an equilibration period lasting 5 days and the study day. On the study day, after remaining in bed, plasma levels of atrial natriuretic peptide, brain natriuretic peptide, renin activity, aldosterone, noradrenaline, and cyclic guanosine monophosphate were measured at 7 am. Thereafter, they were instructed to maintain an upright posture until dinner and the measurements were repeated at 9 am and 6 pm. After having dinner, all subjects were asked to remain in bed and the measurements were repeated at 11 pm. To measure renal sodium and cyclic guanosine monophosphate excretion, 24-h urine collections were performed, starting from 7 pm on the day before the experimental day.

RESULTS

Plasma levels of atrial natriuretic peptide, brain natriuretic peptide and cyclic guanosine monophosphate in patients with preascitic cirrhosis were significantly elevated compared with those in controls at every sampling time (p=0.03 or less, p= 0.04 or less, and p=0.01 or less). In contrast, plasma renin activities at every sampling time were significantly lower in patients than in controls (p= 0.04 or less). Plasma aldosterone and noradrenaline levels were not significantly different at every sampling time in the two groups. No significant differences in daily renal sodium excretion were found. However, urinary cyclic guanosine monophosphate excretion was significantly higher in patients than in controls (p<0.01).

CONCLUSIONS

The initial abnormalities of sodium metabolism in cirrhosis might be characterized by blunted renal responsiveness to natriuretic peptides. The results of the study also provide indirect evidence that the impairment is mainly located at postreceptor levels of signal transduction pathway to the peptides, if the activation of antinatriuretic factors other than renin-angiotensin or sympathoadrenergic systems does not play a role.

Changes in guinea pig plasma cyclic nucleotide levels during the development of a transplantable leukemia

Plasma levels of cyclic AMP and cyclic GMP were determined in 35 guinea pigs for up to 9 days following subcutaneous passage of L2C leukemia cells. Twenty guinea pigs into which normal syngeneic guinea pig thymocytes were passaged served as controls. Cyclic AMP levels in plasma showed little change and were only elevated significantly in test animals on day 9 after passage. In contrast cyclic GMP levels reached a maximum on day 5 after passage of leukemia cells with two to threefold rises over day 1 levels. Increases in leukocyte counts were not observed until day 7 in test animals. Of the other tumour growth indices which were examined, the axillary (draining) node index gave the earliest indication of cell proliferation, with significant elevations on day 3 after passage. The authors conclude that plasma cyclic GMP increases precede increases in white cell counts by at least 2 days, and may reflect an early increase in axillary node growth.

Urinary excretion patterns of cyclic AMP and cyclic GMP following thermal injury

Measurement of 24-h urinary cyclic AMP and cyclic GMP levels in 19 patients for up to nine days after thermal injury has revealed differences in cyclic nucleotide excretion patterns between "severe" and "mild to moderate" groups of burned patients, classified according to a predictive index of burn mortality. Cyclic AMP excretion fell significantly from a high initial level in the "severe" group, but showed no significant change in the "mild to moderate" group. Differences in cyclic AMP excretion between the two groups of patients were only significant on the second day following burn injury. There was no correlation between cyclic AMP output averaged for each patient over the first nine days and percentage body surface area of the burn or the predictive index. In contrast to the results for cyclic AMP excretion, cyclic GMP output rose significantly over the 9-day period in severely burned patients, while levels reached a plateau on days four to six for the moderate to mild group. When cyclic GMP excretion was averaged over the first nine days for each patient, a significant correlation with both percent body surface area of burn and the predictive index of burn mortality was found. The tissue source or sources which are responsible for increased cyclic GMP excretion are as yet unknown.

Selection of antibodies for the immunofluorescent localisation of cyclic GMP in the central nervous system

Radioimmunoassay techniques have been used to determine why only a small number of antibodies against cyclic GMP are able to show immunofluorescent staining in the central nervous system. However, neither the titre, avidity nor specificity as determined in liquid-phase radioimmunoassay employing [3H]cyclic GMP, have been able to predict whether a given antibody will show specific staining, or account for the different sites of immunofluorescent localisation observed with these antibodies. These observations are discussed in terms of the populations of antibody molecules employed in the radioimmunoassay and immunofluorescent procedures.