Metformin as a protective agent against natural or chemical toxicities: a comprehensive review on drug repositioning.

BACKGROUND: Metformin is the first prescribed drug for hyperglycemia in type 2 diabetes mellitus. Mainly by activating AMPK pathway, this drug exerts various functions that among them protective effects are of the interest. PURPOSE: Herein, we aimed to gather data about the protective impacts of metformin against various natural or chemical toxicities. RESULTS: An extensive search among PubMed, Scopus, and Google Scholar was conducted by keywords related to protection, toxicity, natural and chemical toxins and, metformin. Our literature review showed metformin alongside its anti-hyperglycemic effect has a wide range of anti-toxic effects against anti-tumour and routine drugs, natural and chemical toxins, herbicides and, heavy metals. CONCLUSION: It is evident that metformin is a potent drug against the toxicity of a broad spectrum of natural, chemical toxic agents which is proved by a vast number of studies. Metformin mainly through AMPK axis can protect different organs against toxicities. Moreover, metformin preserves DNA integrity and can be an option for adjuvant therapy to ameliorate side effect of other therapeutics.

Endochondral bone formation is involved in media calcification in rats and in men.

Arterial media calcification is often considered a cell-regulated process resembling intramembranous bone formation, implying a conversion of vascular tissue into a bone-like structure without a cartilage intermediate. In this study, we examined the association of chondrocyte-specific marker expression with media calcification in arterial samples derived from rats with chronic renal failure (CRF) and from human transplant donors. CRF was induced in rats with a diet supplemented with adenine. Vascular calcification was evaluated histomorphometrically on Von Kossa-stained sections and the expression of the chondrocyte markers sox9 and collagen II with the osteogenic marker core-binding factor alpha1 (cbfa1) was determined immunohistochemically. Media calcification was detected in more than half of the rats with CRF. In over half of the rats with severe media calcification, a typical cartilage matrix was found by morphology. All of the animals with severe calcification showed the presence of chondrocyte-like cells expressing the markers sox9, collagen II, and cbfa1. Human aorta specimens showing mild to moderate media calcification also showed sox9, collagen II, and cbfa1 expression. The presence of chondrocytes in association with calcification of the media in aortas of rats with CRF mimics endochondral bone formation. The relevance of this association is further demonstrated by the chondrogenic conversion of medial smooth muscle cells in the human aorta.

Uremia-related vascular calcification: more than apatite deposition.

In the present study, we characterized and compared the mineral phase deposited in the aortic wall of two different frequently used chronic renal failure rat models of vascular calcification. Vascular calcification was induced in rats by either a 4-week adenine treatment followed by a 10-week high-phosphate diet or 5/6 nephrectomy followed by 6 weeks of 0.25 microg/kg/day calcitriol treatment and a high-phosphate diet. Multi-element mapping for calcium and phosphate together with mineral identification was performed on several regions of aortic sections by means of synchrotron X-ray-mu-fluorescence and diffraction. Bulk calcium and magnesium content of the aorta was assessed using flame atomic absorption spectrometry. Based on the diffraction data the Von Kossa-positive precipitate in the aortic regions (N=38) could be classified into three groups: (1) amorphous precipitate (absence of any diffraction peak pattern, N=12); (2) apatite (N=16); (3) a combination of apatite and magnesium-containing whitlockite (N=10). The occurrence of these precipitates differed significantly between the two models. Furthermore, the combination of apatite and whitlockite was exclusively found in the calcitriol-treated animals. These data indicate that in adenine/phosphate-induced uremia-related vascular calcification, apatite is the main component of the mineral phase. The presence of magnesium-containing whitlockite found in addition to apatite in the vitamin D-treated rats, has to be seen in view of the well-known vitamin D-stimulated gastrointestinal absorption of magnesium.

Demonstration of lanthanum in liver cells by energy-dispersive X-ray spectroscopy, electron energy loss spectroscopy and high-resolution transmission electron microscopy.

The appearance of lanthanum in liver cells as a result of the injection of lanthanum chloride into rats is investigated by advanced transmission electron microscopy techniques, including electron energy loss spectroscopy and high-resolution transmission electron microscopy. It is demonstrated that the lysosomes contain large amounts of lanthanum appearing in a granular form with particle dimensions between 5 and 25 nm, whereas no lanthanum could be detected in other surrounding cellular components.

Effects of strontium on the physicochemical characteristics of hydroxyapatite.

In a previous experimental study using a chronic renal failure rat model, a dose-related multiphasic effect of strontium (Sr) on bone formation was found that could be reproduced in an in vitro set-up using primary rat osteoblasts. The results from the latter study allowed us to distinguish between a reduced nodule formation in the presence of an intact mineralization at low Sr-doses (1 microg/ml) and an interference of the element with the hydroxyapatite (HA) formation at high doses (20-100 microg/ml). To further investigate the latter effect of Sr on physicochemical bone mineral properties, an in vitro study was set up in which the UMR-106 rat osteosarcoma cell line was exposed to Sr, added to the cell culture medium in a concentration range varying between 0-100 microg/ml. Temporal growth and functionality of the culture was investigated by measurement of the alkaline phosphatase activity and calcium (Ca) concentration in the culture medium (used as an index of Ca-incorporation, i.e., HA formation) at various time points. At the end of the culture period (14 days post-confluence), samples of the mineralized cultures were taken for further analysis using X-ray diffraction (XRD) and Fourier Transform Infra-Red Spectroscopy (FTIR). Synthetic HA doped with various Sr concentrations (based on the cell culture and previous experimental studies and yielding Sr/(Sr + Ca) ratios ranging from 0-60%), was prepared and examined for crystal growth and solubility. Crystal size was assessed using scanning electron microscopy (SEM). Ca incorporation indicated a reduced mineralization in the 20 and 100 microg/ml Sr groups vs. controls. Sr-doped synthetic HA showed a significant dose-dependent reduction in crystal growth, as assessed by SEM, and an increase in solubility, apparent from 12.7% Sr/(Sr + Ca) on. Moreover, in both mineralized cultures and synthetic HA, XRD and FTIR analysis showed a reduced crystallinity and altered crystal lattice at similar concentrations. These new data support our previous in vivo and in vitro findings and point to a potential physicochemical interference of Sr with HA formation and crystal properties in vivo.

Re-evaluation and modification of the Stuivenberg Hospital Acute Renal Failure (SHARF) scoring system for the prognosis of acute renal failure: an independent multicentre, prospective study.

BACKGROUND: A prognostic scoring system for hospital mortality in acute renal failure (Stuivenberg Hospital Acute Renal Failure, SHARF score) was developed in a single-centre study. The scoring system consists of two scores, for the time of diagnosis of acute renal failure (ARF) and for 48 h later, each originally based on four parameters (age, serum albumin, prothrombin time and heart failure). The scoring system was now tested and adapted in a prospective study. METHODS: The study involved eight intensive care units. We studied 293 consecutive patients with ARF in 6 months. Their mortality was 50.5%. The causes of ARF were medical in 184 (63%) patients and surgical in 108 (37%). In the latter group, 74 (69%) patients underwent cardiac and 19 (18%) vascular surgery. RESULTS: As the performance of the original SHARF scores was much lower in the multicentre study than in the original single-centre study, we re-analysed the multicentre data to customize the original model for the population studied. The independent variables were the score developed in the original study plus all additonal parameters that were significant on univariate analysis. The new multivariate analysis revealed an additional subset of three parameters for inclusion in the model (serum bilirubin, sepsis and hypotension). For the modified SHARF II score, r(2) was 0.27 at 0 and 0.33 at 48 h, respectively, the receiver operating characteristic (ROC) values were 0.82 and 0.83, and the Hosmer-Lemeshow goodness-of-fit P values were 0.19 and 0.05. CONCLUSION: After customizing and by using two scoring moments, this prediction model for hospital mortality in ARF is useful in different settings for comparing groups of patients and centres, quality assessment and clinical trials. We do not recommend its use for individual patient prognosis.

Renovascular hypertension: diagnostic and therapeutic challenges.

Atherosclerotic renal artery stenosis (ARAS) is associated with two common clinical syndromes: renovascular hypertension and ischemic nephropathy, which often coexist. The ensuing renovascular disease constitutes the fastest-growing etiology of end-stage renal disease. Diagnostic work-up for hemodynamical significant renal artery stenosis should be restricted to patients suspected to be at moderate or high risk for renovascular disease. Patients at moderate risk should first undergo a screening test, like Doppler ultrasonography or captopril-enhanced scintigraphy. In case of a positive screening test, renal artery imaging with either spiral computed tomography angiography or magnetic resonance angiography with Gadolinium is indicated. Patients at high risk for renovascular disease may be directly referred for intra-arterial renal artery angiography, the golden standard diagnostic procedure. A renal artery stenosis with narrowing of > 50-60% of the lumen, is considered hemodynamically significant, and may be suitable for treatment with angioplasty or angioplasty plus stent placement (in case of osteal renal artery stenosis). The therapeutic approach of the hypertensive patient with a hemodynamically significant renal artery stenosis is currently a matter of great debate. In any case optimal medical therapy with antihypertensive, lipid-lowering, and platelet-inhibiting drugs should be instituted, since such approach may not only prevent the progression to end-stage renal disease, but may also prevent the progression of extra-renal vascular disease, which affects the majority of these patients. Current evidence suggests that angioplasty (with additional stent placement in case of osteal renal artery stenosis) may benefit a subset of patients with significant RAS, i.e. patients with a resistance index < 80% at the level of the segmental renal arteries, and patients with bilateral RAS or patients with unilateral RAS with a unique functioning kidney. Prospective, randomized and controlled studies with clearly defined clinical endpoints are needed to better define the absolute and relative indications of angioplasty (plus stenting) in the setting of renal artery stenosis.

Renal impairment in patients with inflammatory bowel disease: association with aminosalicylate therapy?

BACKGROUND: In recent years, several case reports have been published suggesting an association between the use of 5-aminosalicylic acid (5-ASA) in patients with inflammatory bowel disease (IBD) and the development of chronic tubulo-interstitial nephritis. Apart from lesions associated to 5-ASA treatment, however, it is clear that IBD itself may also induce renal impairment, albeit the frequency is unknown. METHODS: During 1 year, all IBD patients seen at the outpatient clinic of 27 European centres of gastro-enterology were registered and screened for renal impairment controlling for a possible association with 5-ASA therapy. Patients were questioned about their medical and drug history and their IBD disease activity. Renal screening (calculated creatinine clearance) was performed at baseline, after 6 and 12 months. RESULTS: Included patients (n = 1,529) had a mean age of 39 (range 14-98), 56% had Crohn's disease, 42% ulcerative colitis and 2% indeterminate colitis. Half of the patients used 5-ASA during the study period. Decreased creatinine clearance was observed in 34 patients, among them 13 with chronic renal impairment. Comparing patients with and without renal impairment, no difference could be observed in 5-ASA consumption. In contrast, patients with renal impairment were significantly older, had a lower body mass index and showed a higher frequency of male sex, bowel resection and stoma. CONCLUSION: Although the association between 5-ASA therapy and chronic tubulo-interstitial nephritis is clearly described in several case reports, this prospective study came to the reassuring conclusion that renal impairment in IBD patients is not frequently observed and is rarely associated with 5-ASA therapy.

[Misconduct in clinical scientific investigations]. / Wangedrag in klinisch-wetenschappelijk onderzoek.

The most important ways of misconduct in clinical scientific research are falsifying results, plagiarize and over-interpretation. Motives are prestige, money, pressure of time and conflict of interests. The "publish or perish" phenomenon and the sometimes difficult attainable deadline play an important role. Furthermore, there is a "gray-zone" in which clinical scientific researchers are influenced by the pharmaceutical industry, leading to the writing of tendentious publications. Few data are available concerning the frequency of misconduct. In general, one may say that the phenomenon is underestimated. The number of professional organizations for the detection of misconduct and to start a balanced investigation procedure of this phenomenon is limited. An exception is "Office of Research Integrity" in the US that does pioneering work in the field. Some of the better journals in the profession are making serious efforts to detect misconduct (e.g. New England Journal of Medicine, British Medical Journal). To prevent misconduct the following measures can be considered: education concerning the topic in the faculties of medicine, biomedical sciences and pharmaceutics sciences; extension of the competences of the ethical committees; realistic financing of research and the establishing of a "clinical scientific fund", without any relation with the pharmaceutical industry, for the support of self-generated clinical project after 'peer review'. Finally, the questions can be raised if the Royal Academy of Medicine (Belgium) could not play a role in this important matter.

Four cases of red blood cell aplasia in association with the use of mycophenolate mofetil in renal transplant patients.

Mycophenolate mofetil (MMF) is one of the new immunosuppressive drugs used in renal transplantation. MMF inhibits the de novo purine synthesis. Since this purine synthesis in lymphocytes entirely depends on the de novo pathway, MMF is considered to cause a selective inhibition of T- and B lymphocytes. Recently, 4 transplant patients out of 30 developed a severe anemia in the early post-transplantation period. Their immediate post-transplantation immunosuppression consisted of corticosteroids, cyclosporine and MMF. They all received anti-T-lymphocyte globulin (ATG) as induction treatment or because of rejection. In all 4 patients, iron supplementation and a treatment with erythropoietin were started. Blood loss, deficiencies, hemolysis, drug interactions or viral infections were excluded as causes of the anemia. Bone marrow biopsies were carried out, showing pure red cell aplasia that was ascribed to the use of MMF. Cessation or reduction of MMF was followed by a hematological improvement after 5-9 days. We hypothesized that MMF has a broader antiproliferative effect than its proposed lymphocyte-specific effect.

Anti-B7-1 blocks mononuclear cell adherence in vasa recta after ischemia.

BACKGROUND: Blocking the costimulatory pathway by CTLA-4 Ig, reactive with both B7-1 and B7-2 costimulatory molecules, protects the kidney during acute ischemia/reperfusion injury. This study investigated whether and how B7-1 and/or B7-2 proteins are involved in renal ischemia/reperfusion injury (IRI). METHODS: Uninephrectomized rats were submitted to warm renal ischemia (30 min) and received control monoclonal antibody (mAb; 17E3), anti-B7-1 (3H5), anti-B7-2 (24F), a combination of anti-B7-1/B7-2, or CTLA-4 Ig. Renal function, morphology, and the kinetics of inflammatory cells were studied for a ten-day period. Binding sites of the injected antibodies were detected by secondary staining with anti-mouse Ab. RESULTS: Compared with controls, acute renal failure (ARF) in the anti-B7-1 group was attenuated both functionally and morphologically. Anti-B7-1/B7-2 and CTLA-4 Ig also were protective in IRI. ARF was not altered by anti-B7-2 treatment. Two hours after reperfusion, B7-1 was expressed along the endothelial cells of the ascending vasa recta. Expression of B7-1 increased over time during the first 24 hours and decreased thereafter. Two hours after reperfusion, adherence/accumulation of T cells and monocytes/macrophages was found in the vasa recta of the ischemic kidney. Anti-B7-1-treated animals had fewer T cells and monocytes/macrophages in the vasa recta compared with controls. Leukocyte accumulation in these vessels after anti-B7-2 treatment was not different from IRI controls. CONCLUSION: These observations strongly support the key role of the B7-1 protein in the protection of renal IRI through inhibition of T cell and monocyte adherence at the level of the ascending vasa recta.

What can nephrologists learn from epidemiology?

During the last decade, epidemiology has played an increasing role in the study of renal diseases. In the fields of drug-nephrotoxicity and occupational renal failure, epidemiological research has made an important contribution. In recent years, the specific role of epidemiology in outcome research has gained recognition. Epidemiology is based on observations under real-life conditions using a representative sample of renal patients. Methods range from simple clinical observations and cross-sectional studies to case-control and prospective cohort studies. Contributions and limitations of the different epidemiological approaches are illustrated using the example of the nephrotoxicity of 5-aminosalicylic acid in patients with inflammatory bowel disease.

Oxidative modification of low-density lipoproteins and the outcome of renal allografts at 1 1/2 years.

BACKGROUND: Previous studies reported a significant association between hyperlipidemia of the recipient and chronic allograft nephropathy (CAN). However, the nature and the pathogenic mechanism of circulating lipid abnormalities in CAN remain unclear. METHODS: In a prospective study of 50 consecutive adult recipients of a cadaveric renal allograft, we investigated the impact of lipid abnormalities on the outcome of the graft at 1 1/2 years. Besides morphometric analysis of implantation and protocol biopsies, clinical and biochemical variables were studied at three-month intervals. Plasma concentrations of oxidized low-density lipoprotein (OxLDL) were determined by means of enzyme-linked immunosorbent assay. Immunohistochemical staining for OxLDL and macrophages was performed on paired renal biopsies. Study end points were the fractional interstitial volume and the 24-hour creatinine clearance at 11/2 years. RESULTS: High-density lipoprotein (HDL) cholesterol of the recipient < or =47 mg/dL was a risk factor for the functional (RR = 1.56; 95% CI, 0.978 to 2.497) and the morphological (RR = 2.75; 95% CI, 1.075 to 7.037) outcome of the graft, mainly in patients without acute rejection (RR = 2.03; 95% CI, 1.13 to 3.65, and RR = 4.67; 95% CI, 1.172 to 18.582, respectively). Interstitial accumulation of OxLDL was inversely associated with HDL cholesterol (R = -0.476, P = 0.019), and was associated with a higher density of tubulointerstitial macrophages (R = 0.656, P = 0.001) and a higher fractional interstitial volume at 11/2 years (P = 0.049). CONCLUSION: Decreased HDL cholesterol levels of the recipient adversely affect the outcome of renal allografts through the accumulation of OxLDL in the renal interstitium of the graft. Interstitial accumulation of OxLDL was associated with the presence of macrophages and the development of interstitial fibrosis.

Bismuth overdosing-induced reversible nephropathy in rats.

Overdosing of colloidal bismuth subcitrate (CBS), used to treat peptic ulcers and Helicobacter pylori infections, has been reported to result in serious, though reversible, nephrotoxicity in humans. However, little is known about the nature of the renal damage induced by bismuth (Bi), and no well-described experimental model exists. Single large oral CBS doses (0.75, 1.5, and 3.0 mmol Bi/kg) were administered to three groups of 20 female Wistar rats. A control group (n = 20) received only the vehicle. Standard kidney function parameters, urinary excretion of N-acetyl-beta-D-glucosaminidase (NAG) and the Bi content were monitored in blood, urine, liver, and kidneys for 14 days. A dose of 3.0 mmol Bi/kg, 100 times the daily therapeutic dose, caused kidney damage within 6 h as detected by proteinuria, glucosuria, and elevated plasma urea and plasma creatinine levels. The kidneys of all animals, except two that died, recovered functionally within 10 days. At a dose of 1.5 mmol Bi/kg, clinical parameters changed less and normalized within 48 h, whereas a dose of 0.75 mmol Bi/kg induced no changes. Histological evaluation revealed that the S3 tubular segment necrotized first with additional necrotization of the S1/S2 segment when more Bi was absorbed. The lesions were accompanied by interstitial infiltrates of CD45+ leukocytes. In summary, we developed a rat model for Bi-induced reversible nephropathy. A large single oral overdose of CBS administered to Wistar rats led to damage to the proximal tubule, especially in the last segment.

Renal osteopontin protein and mRNA upregulation during acute nephrotoxicity in the rat.

BACKGROUND: The effect of segment-specific proximal tubular injury on spatio-temporal osteopontin (OPN) distribution was determined in two different nephrotoxic rat models to evaluate its conceivability with a possible role for OPN in acute renal failure (ARF). OPN gene expression was further determined in proximal and distal tubular cells to investigate the origin of increased renal OPN. METHODS: Renal OPN protein and mRNA expression were compared in the rat during mercuric-chloride- vs gentamicin-induced ARF using immunohistochemistry and in situ hybridization. RESULTS: Mercuric chloride primarily induced tubular injury and subsequent cell proliferation in proximal straight tubules (PST), whereas gentamicin predominantly injured proximal convoluted tubules (PCT). In both models, the distribution of OPN protein was associated with increased OPN mRNA levels in proximal as well as distal tubular cells. However, upregulation was delayed in the proximal tubular segment suffering most from injury, i.e. PCT in gentamicin ARF vs PST in mercuric-chloride ARF. OPN immunostaining at the apical cell membrane from distal tubules was in contrast to perinuclear vesicular staining in proximal tubular cells. CONCLUSIONS: OPN gene and protein expression is induced in both proximal and distal tubular cells during rat toxic ARF. The distinct subcellular localization in proximal vs distal tubular cells indicates differences in OPN processing and/or handling. The spatio-temporal distribution is consistent with a possible role in renal injury and regeneration.