Biomedical subjects

M M Sousa

Publications and source records attributed to M M Sousa.

9 recordsLinked to original sources

PubMed2001

Internalization of transthyretin. Evidence of a novel yet unidentified receptor-associated protein (RAP)-sensitive receptor.

Transthyretin (TTR) is a plasma carrier of thyroxine and retinol-binding protein (RBP). Though the liver is the major site of TTR degradation, its cellular uptake is poorly understood. We explored TTR uptake using hepatomas and primary hepatocytes and showed internalization by a specific receptor. RBP complexed with TTR led to a 70% decrease of TTR internalization, whereas TTR bound to thyroxine led to a 20% increase. Different TTR mutants showed differences in uptake, suggesting receptor recognition dependent on the structure of TTR. Cross-linking studies using hepatomas and (125)I-TTR revealed a approximately 90-kDa complex corresponding to (125)I-TTR bound to its receptor. Given previous evidence that a fraction of TTR is associated with high-density lipoproteins (HDL) and that in the kidney, megalin, a member of the low-density lipoprotein receptor family (LDLr) internalizes TTR, we hypothesized that TTR and lipoproteins could share related degradation pathways. Using lipid-deficient serum in uptake assays, no significant changes were observed showing that TTR uptake is not lipoprotein-dependent or due to TTR-lipoprotein complexes. However, competition studies showed that lipoproteins inhibit TTR internalization. The scavenger receptor SR-BI, a HDL receptor, and known LDLr family hepatic receptors did not mediate TTR uptake as assessed using different cellular systems. Interestingly, the receptor-associated protein (RAP), a ligand for all members of the LDLr, was able to inhibit TTR internalization. Moreover, the approximately 90-kDa TTR-receptor complex obtained by cross-linking was sensitive to the presence of RAP. To confirm that RAP sensitivity observed in hepatomas did not represent a mechanism absent in normal cells, primary hepatocytes were tested, and similar results were obtained. The RAP-sensitive TTR internalization together with displacement of TTR uptake by lipoproteins, further suggests that a common pathway might exist between TTR and lipoprotein metabolism and that an as yet unidentified RAP-sensitive receptor mediates TTR uptake.

Animals↗

PubMed2000

Evidence for the role of megalin in renal uptake of transthyretin.

The kidney is a major organ for uptake of the thyroid hormone thyroxine (T(4)) and its conversion to the active form, triiodothyronine. In the plasma, one of the T(4) carriers is transthyretin (TTR). In the present study we observed that TTR, the transporter of both T(4) and retinol-binding protein, binds to megalin, the multiligand receptor expressed on the luminal surface of various epithelia including the renal proximal tubules. In the kidney, megalin plays an important role in tubular uptake of macromolecules filtered through the glomerulus. To evaluate the importance of megalin for renal uptake of TTR, we performed binding/uptake assays using immortalized rat yolk sac cells with high expression levels of megalin. Radiolabeled TTR, free as well as in complex with thyroxine or retinol-binding protein, was rapidly taken up by the cells, and the uptake was strongly inhibited by a polyclonal megalin antibody and by the receptor-associated protein, a chaperone-like protein inhibiting ligand binding to megalin. In cell culture, different TTR mutations presented different levels of cell association and degradation, suggesting that the structure of TTR is important for megalin recognition. Both the apo form and the T(4)-bound form were taken up by the cells. Analysis of urine from patients with Dent's disease, a renal tubular disorder that alters receptor-mediated endocytic reabsorption of proteins, identified TTR as an abundant excreted protein. Furthermore, analysis of kidney sections of megalin-deficient mice revealed no immunohistochemical TTR labeling in intracellular vesicles in the proximal tubule cells when compared with wild type control littermates. Taken together, the present data indicate that TTR represents a novel megalin ligand of importance in the thyroid hormone homeostasis.

Animals↗

PubMed2000

Interaction of the receptor for advanced glycation end products (RAGE) with transthyretin triggers nuclear transcription factor kB (NF-kB) activation.

Mutated transthyretin (TTR) fibrils are associated with the pathology of familial amyloidotic polyneuropathy (FAP), in which extracellular amyloid deposits lead to degeneration of cells and tissues, in particular neurons of the peripheral nerve. Here we present evidence that the receptor for advanced glycation end products (RAGE), previously associated with Alzheimer's disease, acts as a selective cell surface acceptor site for both soluble and fibrillar TTR. Immunohistochemical studies demonstrating increased expression of RAGE in FAP tissues suggested the relevance of this receptor to TTR-induced fibrillar pathology. In vitro studies using soluble RAGE showed saturable specific interaction with soluble and fibrillar TTR with a K(d) of approximately 120 nM. However, no binding was observed when soluble TTR was combined with retinol-binding protein, which represents the form in which TTR normally circulates in plasma. Specific binding of TTR to RAGE-transfected Chinese hamster ovary cells (which was completely blocked by anti-RAGE) was observed, confirming that RAGE could mediate TTR binding to cellular surfaces. RAGE-dependent activation of nuclear transcription factor kB (NF-kB) by TTR fibrils was shown in PC-12 cells stably transfected to overexpress the receptor. Furthermore, FAP nerves showed up-regulation of p50, one of the NF-kB subunits, when compared with age-matched controls. From these observations we predict that, in vivo, the presence of TTR fibrils associated with cellular surfaces of FAP patients, by contributing to NF-kB activation, leads to the pathogenesis of neurodegeneration. Further insights into the consequences of the interaction of fibrillar TTR with RAGE may therefore provide a better understanding of neurodegeneration associated with FAP.

Animals↗

PubMed2000

Transthyretin in high density lipoproteins: association with apolipoprotein A-I.

Previous studies have revealed the presence of transthyretin (TTR) on lipoproteins. To further address this issue, we fractionated plasma lipoproteins from 9 normal individuals, 10 familial amyloidotic polyneuropathy (FAP) patients, and 19 hyperlipidemic subjects using gel filtration. In the majority of the subjects, as well as in 9 of the 10 FAP patients and 14 of the 19 patients with hyperlipidemia, TTR was detected by ELISA in the high density lipoprotein (HDL) fraction. The presence of TTR in HDL was confirmed by direct sequencing and by immunoblotting; using non-reducing conditions, TTR was found by immunoblotting in a high molecular weight complex, which reacted also for apolipoprotein A-I (apoA-I). The amount of TTR present in HDL (HDL-TTR), as quantified by ELISA corresponded to 1;-2% of total plasma TTR. However, no detectable TTR levels were found in HDL fraction from 6 of the hyperlipidemic subjects. No correlation was found between the lack of TTR in HDL and plasma levels of total, LDL-, or HDL-associated cholesterol as well as levels of apoA-I and total plasma TTR. Ligand binding experiments showed that radiolabeled TTR binds to the HDL fraction of individuals with HDL-TTR but not to the corresponding fractions of individuals devoid of HDL-TTR, suggesting that HDL composition may interfere with TTR binding. The component(s) to which TTR binds in the HDL fraction were investigated. Polyclonal antibody against apoA-I was able to block the interaction of TTR with HDL, suggesting that the interaction of TTR with the HDL particle occurs via apoA-I. This hypothesis was further demonstrated by showing the formation of a complex of TTR with HDL and apoA-I by crosslinking experiments. Furthermore, anti-apoA-I immunoblot under native conditions suggested the existence of differences in HDL particle properties and/or stability between individuals with and without HDL-TTR.

Amyloid Neuropathies↗

PubMed1978

Studies of antithyroid antibodies in Down's syndrome.

The presence of antithyroid antibodies (antithyroglobulin and antimicrosomal) in serum of patients with Down's syndrome and their respective mothers were studied based on data from the literature, showing a possible correlation between the presence of these antibodies in the serum of mothers and the birth of mongoloid children. Antithyroid antibodies were studied in 40 patients with Down's syndrome, with ages ranging from 5 months to 21 years old, 24 males and 16 females and in the respective mothers whose ages varied from 22 to 66 years. In none of the analyzed sera of the mongoloids as well of their mothers, the authors were able to detect the antithyroid antibodies studied.

Adolescent↗

PubMedDate not supplied

Non-traumatic acute abdomen: videolaparoscopic approach.

BACKGROUND AND OBJECTIVE: Although videolaparoscopy has been considered a safe method for many elective procedures, its use in traumatic and non-traumatic acute abdomen needs to be evaluated. The aim of this article is to evaluate the role of videolaparoscopy in non-traumatic acute abdomen as a method of diagnosis and treatment. METHODS: Between January 1992 and December 1996, 462 patients' charts were reviewed, retrospectively. Patients were admitted to the emergency room of São Rafael Hospital with symptoms of non-traumatic acute abdomen. Routine investigation of abdominal pain was performed in all patients, followed by videolaparoscopy. The laparoscopic procedures were done with four main purposes: diagnosis (ie, enteritis); diagnosis and treatment (ie, appendicitis); treatment only, when the diagnosis was known (ie, acute cholecystitis); and in cases where the conversion to conventional laparotomy was necessary, indicating the best incision. RESULTS: The vast majority of patients had inflammatory causes of acute abdomen (82.03%); others causes were hemoperitoneum (11.03%), bowel obstruction (3.25%), perforation of a hollow viscera (1.74%), vascular occlusion (1.3%), and negative laparoscopy (0.65%). CONCLUSIONS: This study shows that laparotomy was necessary in only 7.14% of the patients. The videolaparoscopic approach was used for diagnosis (99.35%) and treatment (92.86%) of patients with acute abdomen.

Abdomen, Acute↗

PubMedDate not supplied

Laparoscopic versus open appendicectomy: a comparative study.

There are many questions regarding the advantages and disadvantages a videolaparoscopic approach in the treatment of acute appendicitis. The authors present the results of a non-randomized, prospective study with 496 patients admitted between January 1992 and March 1998 by the General Surgery Service of São Rafael Hospital Salvador-BA-Brazil. The patients were submitted for appendicectomy by video laparoscopy or by the traditional open method, and variables such as surgery duration, morbidity, mortality, costs, and length of stay (LOS) were compared. The results demonstrate that laparoscopic appendicectomy is a safe alternative for treatment of acute appendicitis; however, there are several disadvantages that gradually must be overcome.

Adolescent↗

PubMedDate not supplied

Videolaparoscopic approach of the splenic cyst: a case report.

The authors report a case of an asymptomatic 30-year-old female patient with an extensive cystic lesion continuous with the splenic parenchyma. A review of the literature and use of a videolaparoscopic approach to the treatment of these lesions is presented.

Adult↗

PubMedDate not supplied

Videolaparocholecystectomy: casuistry of 1000 cases.

Despite the ongoing evolution in the medical treatment of biliary pathology, the standard of treatment for gallstones remains cholecystectomy. There are no alternative treatments that have shown the same efficacy as surgery. Current alternative treatments have shown high recurrence and failure rates. Cholecystectomy remains the gold standard for management of gallstones. The surgical access of laparoscopic cholecystectomy accomplished by Mouret in 1987 allows for a reduction in operative trauma, hospital stay, postoperative pain and convalescence. These factors permit a faster return to normal activities. Today, laparoscopic cholecystectomy is performed in almost all medical centers around the world; however, the procedure is not free of complications. The objective of this study was to analyze our first 1000 cases of laparoscopic cholecystectomy, giving emphasis to the morbidity and mortality of the procedure.

Adolescent↗