Regulação integrada do metabolismo da glucose no estado pós-prandial : fisiologia e reversão de processos patológicos

Resumo: Os mecanismos que regulam a homeostase da glucose no pós-prandial são distintos dos mecanismos desencadeados em situações de jejum. Desta forma o fígado parece desempenhar um papel fundamental na acção periférica da insulina após a refeição através de um mecanismo que envolve os nervos parassimpáticos hepáticos e o óxido nítrico (NO). Esta dissertação procura evidenciar a importância de ambos na fi siologia de manutenção da glicémia pós-prandial e na fi siopatologia da resistência à insulina. Dos resultados obtidos observou-se que após a administração de uma refeição mista o perfi l glicémico foi distinto em animais com ou sem ablação dos nervos parassimpáticos hepáticos. A desnervação parassimpática hepática aumentou as excursões de glucose imediatamente após a refeição. Estas diferenças nas excursões de glucose dependentes do parassimpático ocorreram devido a uma diminuição da clearance de glucose, sem que fosse afectada a taxa de aparecimento de glucose no sangue, a produção endógena de glucose e secreção de insulina ou péptido-C. Este aumento das excursões de glucose revelou-se ser devida à diminuição da clearance de glucose pós-prandial exclusivamente no músculo-esquelético, coração e o rim. Concluiu-se que o fígado teria uma função endócrina nestes três órgãos. Surgiu assim a hipótese dos S-nitrosotiois (RSNOs) poderem mimetizar essa resposta endócrina. Testou-se o seu efeito in vivo na sensibilidade à insulina. Para níveis baixos de sensibilidade à insulina, como jejum, desnervação no estado pós-prandial e resistência à insulina os RSNOs potenciaram a sensibilidade à insulina para valores semelhantes ao pós-prandial indicando-os como potenciais fármacos no tratamento da resistência à insulina. O NO e seus derivados ganharam assim uma evidência cada vez maior na acção periférica da insulina e portanto fez-se uma caracterização dos seus níveis desde a fi siologia à fi siopatologia. Os resultados obtidos nesta dissertação permitiram correlacionar a sintetase de óxido nítrico (NOS), enzima responsável pela síntese de NO como um possível marcador da resistência à insulina. Os resultados obtidos contribuíram substancialmente para compreender os mecanismos fi siológicos e fi siopatológicos de manutenção da glicémia após a refeição, colocando o fígado como órgão primordial na regulação periférica (extra-hepática) da captação de glucose.-------- ABSTRACT: The mechanisms responsible for the postprandial response are different from the ones in the fasted state. Therefore the liver seems to play a fundamental role in postprandial insulin action through a mechanism that evolves the hepatic parasympathetic nerves (HPN) and nitric oxide (NO). This work focused on the importance of both, HPN and NO, on postprandial glycemic control and on the pathophysiology of insulin resistance. We observed that after administration of a mixed meal the glycemic profi les with or without the parasympathetic nerves were distinct, increasing glucose excursions after ablation of HPN.This increase in glucose excursions was due to a decrease on the rate of glucose disappearance in extra-hepatic tissues. Glucose appearance rate, endogenous glucose production and insulin secretion were not related to this mechanism. The increase on glucose excursions after the ablation of hepatic parasympathetic system was due to a decrease on glucose clearance on extra-hepatic tissues, namely skeletal-muscle, heart and kidney. We concluded that the liver has an endocrine function on those tissues increasing their glucose uptake.This mechanism led to propose the hypothesis that S-nitrosothiols (RSNOs) could mimic this mechanism. Therefore RSNOs effects on insulin sensitivity were tested. For low insulin sensitivity levels, i.e. fasted state, ablation of the HPN or insulin resistance state induced by a high sucrose diet RSNOs increased insulin sensitivity to levels normally observed in the postprandial state. These results indicated these drugs as potential pharmacological tools in the treatment of insulin resistance. NO and their derivates emerged as fundamental parts of insulin action. A characterization of nitric oxide and nitric oxide synthase (NOS), the enzyme responsible for NO synthesis was part of the work performed. We concluded that NO could be used as a biomarker for insulin resistance states. This work contributed for understanding the mechanism underlying postprandial glycemic control indicating the liver as a key organ in the regulation of peripheral (extra-hepatic) insulin action.

ACUTE KIDNEY INJURY CAUSED BY Crotalus AND Bothrops SNAKE VENOM: A REVIEW OF EPIDEMIOLOGY, CLINICAL MANIFESTATIONS AND TREATMENT

SUMMARY Ophidic accidents are an important public health problem due to their incidence, morbidity and mortality. An increasing number of cases have been registered in Brazil in the last few years. Several studies point to the importance of knowing the clinical complications and adequate approach in these accidents. However, knowledge about the risk factors is not enough and there are an increasing number of deaths due to these accidents in Brazil. In this context, acute kidney injury (AKI) appears as one of the main causes of death and consequences for these victims, which are mainly young males working in rural areas. Snakes of the Bothrops and Crotalus genera are the main responsible for renal involvement in ophidic accidents in South America. The present study is a literature review of AKI caused by Bothrops and Crotalus snake venom regarding diverse characteristics, emphasizing the most appropriate therapeutic approach for these cases. Recent studies have been carried out searching for complementary therapies for the treatment of ophidic accidents, including the use of lipoic acid, simvastatin and allopurinol. Some plants, such as Apocynaceae, Lamiaceae and Rubiaceae seem to have a beneficial role in the treatment of this type of envenomation. Future studies will certainly find new therapeutic measures for ophidic accidents.

Mineral and Bone Disease (MBD) on a Kidney Transplant Patient

A 50-year-old post-menopausal recipient of a kidney allograft with bone pain, osteoporosis, persistent hypercalcaemia and elevated parathormone (PTH) levels, despite a satisfactory graft function, was treated with bisphosphonates and cinacalcet starting, respectively, 5 and 6 months after renal transplantation (RT). Sixteen months after treatment, there was improvement of bone mineral density (BMD) measured by dualenergy X-ray absorptiometry (DEXA). A bone biopsy was taken, unveiling a surprising and worrisome result. Post-RT bone disease is different from classic CKD-MBD and should be managed distinctly, including, in some difficult cases, an invasive evaluation through the performance of a bone biopsy, as suggested in the KDIGO guidelines.

OCULAR SYPHILIS IN A KIDNEY TRANSPLANT RECIPIENT

We present a case of ocular syphilis after a renal transplantation involving progressive vision loss without clinically identifiable ocular disease. Electroretinography showed signs of ischemia, especially in the internal retina. A serological test was positive for syphilis. Lumbar puncture revealed lymphocytic meningitis and a positive serologic test for syphilis in the cerebrospinal fluid. The patient was treated with penicillin, and had a quick vision improvement. In the case of transplant recipients, clinicians should always consider the diagnosis of ocular syphilis in cases with unexplained visual acuity decrement, as this condition may cause serious complications if not treated.

Renal Disease in Madeira Islands: Twenty-Seven Years' Experience of Native Kidney Biopsies

Introduction: Renal biopsy plays an essential role either in the diagnosis or in the prognosis of patients with renal disease. In order to assess its epidemiology and evolution in Madeira Islands, we analysed twenty-seven years of native kidney biopsies. Methods: We performed a retrospective analysis of clinical records, including histological revision from 1986 to 2012, totalling 315 native kidney biopsies. They were assessed regarding the temporal evolution both for the quality/indications for renal biopsy and for the patterns of kidney disease. Results: A total of 315 native kidney biopsies were analysed. The patients’ mean age was of 40.8 ± 18.4 years and 50.5%(n = 159) were males. The most common indications for renal biopsy were nephrotic syndrome (36.2%, n = 114) and acute kidney injury (20.0%, n = 63). Among primary glomerular diseases (41.5%, n = 115) the most common were IgA nephropathy (26.1%, n = 30) and focal-segmental glomerulosclerosis (17.4%, n = 20) and among secondary glomerular diseases (31.4%, n = 87), lupus nephritis (51.7%, n = 45) and amyloidosis (20.7%, n = 18). Statistical analysis revealed significant correlation between gender and major pathological diagnosis (Fisher’s exact test, p <.01) and between indications for renal biopsy and major pathological diagnosis (χ2, p <.01). Regarding the temporal evolution, no statistically significant differences were found in the number of renal biopsies (χ2, p =.193), number of glomeruli per sample (Fisher’s exact test, p =.669), age (Kruskal-Wallis, p =.216), indications for renal biopsy (χ2, p =.106) or major pathological diagnosis groups (χ2,p =.649). However, considering the specific clinico-pathological diagnoses and their temporal variation, a statistically significant difference (Fisher’s exact test, p <.05) was found for lupus nephritis and membranous nephropathy with an increasing incidence and for amyloidosis with an opposite tendency. Discussion: The review of the native kidney biopsies from a population with particular characteristics, geographically isolated, such as those from Madeira Islands, showed parallel between epidemiological numbers referring to other European subpopulations, allowing simultaneously a comprehensive approach to our renal biopsy policies.

Disruption of Urate Transport in Familial Renal Glucosuria and Report on SGLT2 Expression in Normal and Pathological Kidney

Familial renal glucosuria (FRG) is a rare co -dominantly inherited benign phenotype characterized by the presence of glucose in the urine. It is caused by mutations in the SLC5A2 gene that encodes SGLT2, a Na+ -glucose co -transporter. The purpose of our current work was twofold: to characterize the molecular and phenotype findings of an FRG cohort and, in addition, to detail the SGLT2 expression in the adult human kidney. The phenotype of FRG pedigrees was evaluated using direct sequencing for the identification of sequence variations in the SLC5A2 gene. The expression of SGLT2 in the adult human kidney was studied by immunofluorescence on kidney biopsy specimens. In the absence of renal biopsies from FRG individuals, and in order to evaluate the potential disruption of SGLT2 expression in a glucosuric nephropathy, we have selected cases of nucleoside analogues induced proximal tubular toxicity. We identified six novel SLC5A2 mutations in six FRG pedigrees and described the occurrence of hyperuricosuria associated with hypouricaemia in the two probands with the most severe phenotypes. Histopathological studies proved that SGLT2 is localized to the brush -border of the proximal tubular epithelia cell and that this normal pattern was found to be disrupted in cases of nucleoside analogues induced tubulopathy. We present six novel SLC5A2 mutations, further contributing to the allelic heterogeneity in FRG, and identified hyperuricosuria and hypouricaemia as part of the FRG phenotype. SGLT2 is localized to the brush -border of the proximal tubule in the adult human normal kidney, and aberrant expression of the co -transporter may underlie the glucosuria seen with the use of nucleoside analogues.

Triple Regimen with Rituximab, Plasmapheresis and Intravenous Immunoglobulin in the Treatment of Dialysis Dependent Acute Humoral-Mediated Rejection in Kidney Grafts

Introduction: The clinical importance of humoral-mediated acute rejection has been progressively recognised. Early recognition and treatment with plasmapheresis and intravenous immunoglobulin have recently improved short term prognosis. Case report: In this report we describe the clinical features of three 2nd transplant patients developing severe acute humoral rejection during the first week post-transplant while on anti-thymocyte globulin therapy. Treatment with plasmapheresis/ intravenous immunoglobulin/rituximab resulted in rapid reversal of oliguria,and recovery of renal function within the 1st week of treatment in 2/3 patients. Diagnosis was confirmed by graft biopsies revealing peritubular neutrophiles and C4d deposits. Sequential graft biopsies in all three patients revealed complete histological recovery within two weeks. One patient never recovered renal function, and one patient lost his graft at three months following hemorrhagic shock. After 2 years follow up, the remaining patient maintains a serum creatinine of 1.1mg/dl. Conclusion: The regimen using plasmapheresis plus intravenous immunoglobulin and rituximab was effective in rapidly reversing severe acute humoral rejection.

Long-Term Survival (>25 Years) of Deceased Donor Kidney Transplant Recipients: a Single-Center Experience

INTRODUCTION: The aim of this preliminary work is to analyze the clinical features of 52 patients with a functional transplanted kidney for >25 years (all first transplant and all deceased donor recipients) and to compare with a similar though more complete study from Hôpital Necker-Paris 2012. METHODS: The mean graft survival at 25 years is 12.7% and at 30 years is 10%. The actual mean serum creatinine concentration is 1.3 mg/L. We analyzed recipient age (mean, 35.9 years) and gender (29 men and 23 women). Donor age was 26.7 ± 10.3 years. Seven patients (13.4%) were transplanted with 1 HLA mismatch, 42.3% with 2 mismatches, and 44.2% with 3 mismatches. Mean cold ischemia time was 15.45 ± 7.7 hours. Of the recipients, 76% had immediate graft function; 38% experienced 1 acute rejection episode and 4 patients had 2 rejection crises. The initial immunosuppressive regimen was azathioprine (AZA) + prednisolone (Pred) in 14 patients, cyclosporin (CSA) + Pred in 13 patients, and CSA + AZA + Pred in 25 patients. Of these patients, 19% maintained their initial regimen, and 54% (28 patients) were very stable on a mixed CSA regimen for >25 years. RESULTS: We present the major complications (diabetes, neoplasia, and hepatitis C virus positivity). CONCLUSION: Our results in deceased donor kidney recipients for >25 years are similar to the mixed population (deceased donors and living donors) presented by the Necker group, although 54% of our patients remain on CSA immunosuppression, contradicting the idea that its use is not compatible with good long-term kidney function in transplant recipients.

Acute Kidney Injury after Pediatric Cardiac Surgery: Risk Factors and Outcomes. Proposal for a Predictive Model

Objectives: To characterize the epidemiology and risk factors for acute kidney injury (AKI) after pediatric cardiac surgery in our center, to determine its association with poor short-term outcomes, and to develop a logistic regression model that will predict the risk of AKI for the study population. Methods: This single-center, retrospective study included consecutive pediatric patients with congenital heart disease who underwent cardiac surgery between January 2010 and December 2012. Exclusion criteria were a history of renal disease, dialysis or renal transplantation. Results: Of the 325 patients included, median age three years (1 day---18 years), AKI occurred in 40 (12.3%) on the first postoperative day. Overall mortality was 13 (4%), nine of whom were in the AKI group. AKI was significantly associated with length of intensive care unit stay, length of mechanical ventilation and in-hospital death (p<0.01). Patients’ age and postoperative serum creatinine, blood urea nitrogen and lactate levels were included in the logistic regression model as predictor variables. The model accurately predicted AKI in this population, with a maximum combined sensitivity of 82.1% and specificity of 75.4%. Conclusions: AKI is common and is associated with poor short-term outcomes in this setting. Younger age and higher postoperative serum creatinine, blood urea nitrogen and lactate levels were powerful predictors of renal injury in this population. The proposed model could be a useful tool for risk stratification of these patients.

Benefits of Selective Vitamin D Receptor Activators in Kidney Transplanted Patients

Severe chronic kidney disease may lead to disturbances, such as hyperphosphatemia, increased secretion of fibroblast growth factor -23 (FGF -23) and vitamin D deficiency. These may increase plasmatic levels of parathyroid hormone, and decrease plasmatic levels of calcium. Altogether, these may contribute to the development of secondary hyperparathyroidism, and to abnormalities in mineral metabolism. Kidney transplantation is the best option to improve longevity and quality of life in end -stage chronic kidney disease patients. Vitamin D deficiency has been associated with cardiovascular disease, which is the leading cause of death in chronic kidney disease. Therefore, diagnosing this deficiency may be pivotal for minimizing mortality in chronic kidney disease, because pharmacological treatments for this deficiency may be prescribed. Calcitriol is indicated for the treatment of vitamin D deficiency, both in chronic kidney disease and in kidney transplanted patients. However, calcitriol may increase the plasmatic levels of calcium and phosphorous, which can lead to vascular calcifications, that have been associated with cardiovascular mortality. Selective vitamin D receptor activators are indicated for the treatment of vitamin D deficiency in chronic kidney disease. These have the advantage of being associated with lower increases of plasmatic levels of calcium and phosphorous. These drugs also seem to have additional effects that may minimise patient morbidity and mortality, especially due to potentially reducing cardiovascular events. Unfortunately, there are few studies about the use of these drugs in kidney transplanted patients. Here we present a review about the physiology of vitamin D, the consequences of its deficiency in chronic kidney disease and in kidney transplanted patients, and about the diagnosis and treatment of this deficiency. Finally, we discuss the new line of research about the efficacy and safety of selective vitamin D receptor activators in kidney transplanted patients.