Renal clearance of endogenous leptin in hypertensive humans with or without renal artery stenosis

Reduced renal plasma clearance does not explain increased plasma asymmetric dimethylarginine in hypertensive subjects with mild to moderate renal insufficiency

Plasma concentrations of the nitric oxide synthase inhibitor asymmetric dimethylarginine (ADMA) and symmetric dimethylarginine (SDMA) increase already in the early stages of renal insufficiency. There is no agreement as to whether reduced renal plasma clearance (RPCL) contributes to this increase. Therefore, we investigated the relationship between estimated glomerular filtration rate (eGFR), RPCL, and plasma ADMA and SDMA in essential hypertensive patients with mild to moderate renal insufficiency. In 171 patients who underwent renal angiography, we drew blood samples from the aorta and both renal veins and measured mean renal blood flow (MRBF) using the (133)Xe washout technique. RPCL was calculated using arteriovenous concentration differences and MRBF. After correction for potential confounders, reduced eGFR was associated with higher plasma ADMA and SDMA [standardized regression coefficient (β) = -0.22 (95% confidence intervals: -0.41, -0.04) and β = -0.66 (95% confidence intervals: -0.83, -0.49), respectively]. However, eGFR was not independently associated with RPCL of ADMA. Moreover, reduced RPCL of ADMA was not associated with higher plasma ADMA. Contrary to ADMA, reduced eGFR was indeed associated with lower RPCL of SDMA [β = 0.21 (95% confidence intervals: 0.02, 0.40)]. In conclusion, our findings indicate that RPCL of ADMA is independent of renal function in hypertensive patients with mild to moderate renal insufficiency. Unlike the case for SDMA, reduced RPCL of ADMA is of minor importance for the increase in plasma ADMA in these patients, which indicates that increased plasma ADMA in this population is not a direct consequence of the kidneys failing as a plasma ADMA-regulating organ.

Endothelial leptin receptor mutation provides partial resistance to diet-induced obesity

Leptin, a polypeptide hormone produced mainly by adipocytes, has diverse effects in both the brain and peripheral organs, including suppression of feeding. Other than mediating leptin transport across the blood-brain barrier, the role of the endothelial leptin receptor remains unclear. We recently generated a mutant mouse strain lacking endothelial leptin receptor signaling, and showed that there is an increased uptake of leptin by brain parenchyma after its delivery by in situ brain perfusion. Here, we tested the hypothesis that endothelial leptin receptor mutation confers partial resistance to diet-induced obesity. These ELKO mice had similar body weight and percent fat as their wild-type littermates when fed with rodent chow, but blood concentrations of leptin were significantly elevated. In response to a high-fat diet, wild-type mice had a greater gain of body weight and fat than ELKO mice. As shown by metabolic chamber measurement, the ELKO mice had higher oxygen consumption, carbon dioxide production, and heat dissipation, although food intake was similar to that of the wild-type mice and locomotor activity was even reduced. This indicates that the partial resistance to diet-induced obesity was mediated by higher metabolic activity in the ELKO mice. Since neuronal leptin receptor knockout mice show obesity and diabetes, the results suggest that endothelial leptin signaling shows opposite effects from that of neuronal leptin signaling, with a facilitatory role in diet-induced obesity.

Renal handling of matrix Gla-protein in humans with moderate to severe hypertension

Vascular calcifications are common among patients with hypertension. The vitamin K-dependent protein matrix Gla-protein plays an important role in preventing arterial calcification. Since a decrease in renal clearance is a prevalent clinical problem in patients with hypertension, we aimed to study the renal clearance of matrix Gla-protein from the circulation in these patients having a wide range of creatinine clearances. Ninety moderate to severe hypertensive patients who were scheduled for renal angiography were enrolled in the study. In these patients, renal arterial and renal venous blood was sampled prior to the administration of contrast material in order to determine the total renal and single kidney clearance of matrix Gla-protein. The average renal fractional extraction of matrix Gla-protein was 12.8%. There was no significant correlation between creatinine clearance (range 26-154) and renal fractional extraction of matrix Gla-protein in this population. The extraction of matrix Gla-protein was not influenced by the presence of a renal artery stenosis. In conclusion, we demonstrate that the kidney is able to extract matrix Gla-protein from the plasma at a constant level of 12.8%, independent of renal function in hypertensive subjects.

Leptine et grossesse: dogmes, questions et perspectives

Leptin has been primarily considered as a protein secreted by the adipocyte and a regulator of satiety and energy homeostasis. A role for leptin in pregnancy was later suggested as circulating levels of leptin are high in the pregnant woman and leptin is synthetized within the placenta. Placental leptin production is increased in various obstetrical conditions associated with alterations of fetal growth (diabetes, preeclampsia). Furthermore, umbilical leptin can be viewed as a biomarker of fetal adiposity. Our aim is to review the putative roles of leptin in pregnancy.

The known and unknown of leptin in pregnancy

Leptin, which was identified originally as an adipocyte-derived protein, was regarded for years as an exclusive regulator of satiety and energy homeostasis. A role for leptin in pregnancy was later suggested by the findings that plasma levels during gestation are greater than in nongravid individuals and that leptin is synthesized within the fetoplacental unit. Observational studies have established that leptin production is dysregulated in several pathologic stages of pregnancy in association with alterations of fetal growth. For example, an overproduction of leptin by the placenta in pregnancy with diabetes mellitus or hypertension is associated with maternal hyperleptinemia. Evidence is also accumulating that umbilical leptin levels can be viewed as a biomarker of fetal adiposity. Ten years after its discovery as a hormone, we review the known and unknowns of leptin in pregnancy with particular emphasis on its functions in health and disease. We aim to demonstrate that studies of leptin in pregnancy largely have contributed to insight into the mechanisms of leptin action, both as a hormone and as a cytokine.

Interactions between leptin and the human sympathetic nervous system

Results from animal experimentation suggest a 2-way interaction between leptin and the sympathetic nervous system, with leptin causing sympathetic activation and conversely, with the sympathetic system exercising regulatory feedback inhibition over leptin release. We have now tested this hypothesis in humans. In the absence of results from leptin infusions, to test for sympathetic stimulation of leptin release, we sought a quantitative naturalistic linkage of sympathetic activity with leptin plasma concentration across a broad range of leptin values in men of widely differing adiposity. Renal norepinephrine spillover was correlated with plasma leptin (r=0.628, P<0.01), but other measures of sympathoadrenal function did not. To test for sympathetic and adrenomedullary inhibition of leptin release, we studied clinical models of high sympathetic tone, heart failure, and essential hypertension, in which lowered plasma leptin levels might have been expected but were not found; a model of low sympathetic activity, pure autonomic failure, in which plasma leptin level was normal (6.1+/-1.2 vs 12.8+/-3.1 ng/mL in healthy subjects); and a clinical model of reduced epinephrine secretion, healthy aging, in which plasma leptin level again was normal (5.7+/-1.1 ng/mL vs 4.0+/-0.9 ng/mL in men >60 years and <35 years, respectively). Paradoxically, leptin concentration was elevated in heart failure, caused entirely by reduced renal clearance of leptin release, 142.0+/-30.5 mL/min, compared with 56.9+/-18.9 mL/min (P<0.05). These results provide some support for the view that leptin stimulates the sympathetic nervous system, at least for renal sympathetic outflow, but do not confirm the concept of regulatory feedback inhibition of leptin release by the sympathetic nervous system.