Extracellular fluid volume: A suitable indexation variable to assess impact of bariatric surgery on glomerular filtration rate in patients with chronic kidney disease.

BACKGROUND: Bariatric surgery (BS) might be a nephroprotective treatment in obese patients with chronic kidney disease (CKD), and the non-linear relation between body surface area (BSA) and extracellular fluid volume (ECFV) in obese people raises the question of the most relevant way to scale glomerular filtration rate (GFR) for assessing renal function changes after BS. METHODS: We screened 1774 BS candidates and analysed 10 consecutive participants with CKD stage 3. True GFR (mGFR), measured by the renal clearance of 51Cr-ethylenediaminetetraacetic acid (EDTA), was scaled either to BSA (mGFRBSA) or to ECFV measured by 51Cr-EDTA distribution volume (mGFRECFV) before and one year after BS. RESULTS: The 10 candidates for BS had a mean body mass index of 43.3 ± 3.6 kg/m2 and a mean GFR of 48 ± 8 mL/min/1.73 m2. Six participants had a sleeve gastrectomy and four had a Roux-en-Y gastric bypass. One year after BS, ECFV decreased (23.2 ± 6.2 to 17.9 ± 4.3 L, p = 0.001), absolute mGFR was not significantly modified (74 ± 23 versus 68 ±19 mL/min), mGFRBSA did not change significantly (53 ± 18 versus 56 ± 17 mL/min/1.73 m2) whereas mGFRECFV significantly increased (42 ± 13 versus 50 ± 14 mL/min/12.9 L, p = 0.037). The relation between mGFRECFV and mGFRBSA was different from the identity line before (p = 0.014) but not after BS (p = 0.09). CONCLUSION: There is a difference between mGFRBSA and mGFRECFV following BS and the latter might better reflect the adequacy between renal function and corpulence.

Modulation of glucose metabolism by the renin-angiotensin-aldosterone system.

The renin-angiotensin-aldosterone system (RAAS) is an enzymatic cascade functioning in a paracrine and autocrine fashion. In animals and humans, RAAS intrinsic to tissues modulates food intake, metabolic rate, adiposity, insulin sensitivity, and insulin secretion. A large array of observations shows that dysregulation of RAAS in the metabolic syndrome favors type 2 diabetes. Remarkably, angiotensin-converting enzyme inhibitors, suppressing the synthesis of angiotensin II (ANG II), and angiotensin receptor blockers, targeting the ANG II type 1 receptor, prevent diabetes in patients with hypertensive or ischemic cardiopathy. These drugs interrupt the negative feedback loop of ANG II on the RAAS cascade, which results in increased production of angiotensins. In addition, they change the tissue expression of RAAS components. Therefore, the concept of a dual axis of RAAS regarding glucose homeostasis has emerged. The RAAS deleterious axis increases the production of inflammatory cytokines and raises oxidative stress, exacerbating the insulin resistance and decreasing insulin secretion. The beneficial axis promotes adipogenesis, blocks the production of inflammatory cytokines, and lowers oxidative stress, thereby improving insulin sensitivity and secretion. Currently, drugs targeting RAAS are not given for the purpose of preventing diabetes in humans. However, we anticipate that in the near future the discovery of novel means to modulate the RAAS beneficial axis will result in a decisive therapeutic breakthrough.

Constitutive activation of the renin-angiotensin system reduces visceral fat and improves glucose tolerance in mice.

INTRODUCTION: The renin-angiotensin system (RAS), and particularly angiotensin II, is involved in the control of energy balance, glucose homeostasis and kidney functions. The integrated impact of the RAS on glucose homeostasis is still a matter of debate. MATERIALS AND METHODS: We used a model of constitutive RAS activation in double transgenic mice (dTGM) carrying both human angiotensinogen and human renin genes. We evaluated energy balance, measured renal functions, performed glucose and insulin tolerance tests, and used ramipril to inhibit the angiotensin-converting enzyme. RESULTS: dTGM had a lower physical activity and an increased food intake without change in body weight. Renal impairment was characterized by low-grade albuminuria. High urinary output secondary to polydipsia was associated with proximal tubule dysfunction. Compared to controls, dTGM had a lower hyperglycemia induced by an intraperitoneal glucose administration. This decrease was not due to changes in insulin sensitivity and/or secretion. dTGM had an increased creatinine production and a lower epididymal fat mass. Acute inhibition of angiotensin-converting enzyme with ramipril did not suppress this improved glucose tolerance profile. CONCLUSION: Chronic RAS activation is not sufficient to cause insulin resistance in mice. Moreover, adaptation to constitutive RAS activation in mice results in a better glucose tolerance.