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Andrew Mitchell

Publications and source records attributed to Andrew Mitchell.

15 recordsLinked to original sources
PubMed2026

Establishment of Stable Immortalized Human Choroidal Melanocytes for Ocular Research.

PURPOSE: The short lifespan of primary normal choroidal melanocytes (NCMs) in vitro represents a major barrier to mechanistic, functional, and translational studies of choroid biology and uveal melanoma (UM). This study aimed to establish and characterize immortalized human NCM lines that retain melanocytic function, maintain a non-cancerous profile, and are amenable to gene editing. METHODS: NCMs from four donors were immortalized by lentiviral transduction of cyclin-dependent kinase 4 (CDK4R24C), cyclin D1, and human telomerase reverse transcriptase (hTERT), establishing NCM-K4DT lines. Their morphology, melanocytic marker expression, proliferation, and functional properties (melanin synthesis and tyrosinase activity) were evaluated. Genomic stability was assessed by targeted mutation profiling, karyotyping, and copy number variation (CNV) analysis. The tumorigenicity was tested in immunodeficient mice. Plasmid-based CRISPR/Cas9 editing was performed to determine their suitability for gene editing. RESULTS: NCM-K4DT lines retained dendritic-shaped morphology, pigmentation, and expression of PMEL, TYRP1, Melan-A, and SOX10. Cells exhibited enhanced proliferative capacity with preserved cell cycle regulation. Melanin production and tyrosinase activity were comparable to primary NCMs. Genomic profiling confirmed the absence of UM-associated driver mutations and chromosomal abnormalities. In vivo growth assays demonstrated that NCM-K4DT lines did not form tumors within the 3-month observation period. Notably, NCM-K4DT cells were efficiently edited by CRISPR/Cas9. CONCLUSIONS: NCM-K4DT lines represent stable, non-cancerous, and genetically tractable models for studying choroidal melanocyte biology, modeling UM-associated mechanisms, and advancing therapeutic development in ocular research.

Humans↗
PubMed2006

Down-regulation of intestinal drug transporters in chronic renal failure in rats.

Chronic renal failure (CRF) is associated with an increased bioavailability of drugs by a poorly understood mechanism. One hypothesis is a reduction in the elimination of drugs by the intestine, i.e., drug elimination mediated by protein membrane transporters such as P-glycoprotein (Pgp) and multidrug-resistance-related protein (MRP) 2. The present study aimed to investigate the repercussions of CRF on intestinal transporters involved in drug absorption [organic anion-transportingpolypeptide (Oatp)] and those implicated in drug extrusion (Pgp and MRP2). Pgp, MRP2, MRP3, Oatp2, and Oatp3 protein expression and Pgp, MRP2, and Oatp3 mRNA expression were assessed in the intestine of CRF (induced by five-sixth nephrectomy) and control rats. Pgp and MRP2 activities were measured using the everted gut technique. Rat enterocytes and Caco-2 cells were incubated with sera from control and CRF rats to characterize the mechanism of transporters' down-regulation. Protein expression of Pgp, MRP2, and MRP3 were reduced by more than 40% (p < 0.01) in CRF rats, whereas Oatp2 and Oatp3 expression remained unchanged. There was no difference in the mRNA levels assessed by real-time polymerase chain reaction. Pgp and MRP2 activities were decreased by 30 and 25%, respectively, in CRF rats compared with control (p < 0.05). Uremic sera induced a reduction in protein expression and in activity of drug transporters compared with control sera. Our results demonstrate that CRF in rats is associated with a decrease in intestinal Pgp and MRP2 protein expression and function secondarily to serum uremic factors. This reduction could explain the increased bioavailability of drugs in CRF.

ATP Binding Cassette Transporter, Subfamily B↗
PubMed2006

Perforin mediated apoptosis of cerebral microvascular endothelial cells during experimental cerebral malaria.

Cerebral malaria is a serious complication of Plasmodium falciparum infection. We have investigated the role of perforin in the pathogenesis of cerebral malaria in a murine model (Plasmodium berghei ANKA (PbA) infection). C57BL/6 mice demonstrated the typical neuropathological symptoms of experimental cerebral malaria infection from day 5p.i. and became moribund on day 6p.i. This pathology was not seen in PbA-infected, perforin-deficient (pfp-/-) mice. From days 5-6p.i. onwards there was a significant increase in mRNA for granzyme B and CD8, but not CD4, in brain tissue from PbA-infected C57BL/6 and pfp-/- mouse brains. Perforin mRNA was strongly increased in the brains of PbA-infected C57BL/6 mice on day 6p.i. Immunohistochemistry revealed increased perforin staining and elevated numbers of CD8(+) cells within the cerebral microvessels in PbA-infected C57BL/6 at days 5 and 6p.i. compared with uninfected animals. At day 6p.i., there were TUNEL-positive cells and activated caspase-3 positive cells of endothelial morphology in the CNS of PbA-infected C57BL/6 mice. The TUNEL-positive cells were greatly reduced in pfp-/- mice. These results suggest that CD8(+)T lymphocytes induce apoptosis of endothelial cells via a perforin-dependent process, contributing to the fatal pathogenic process in murine cerebral malaria.

Animals↗
PubMed2006

Extranodal marginal zone lymphoma of mucosa-associated lymphoid tissue with initial presentation in the pleura.

Extranodal marginal zone B-cell lymphoma of mucosa-associated lymphoid tissue (EMZL/MALT-type) occurs in a wide variety of body sites; it is well recognized as a form of primary lung lymphoma. However, until recently, pleural presentation of this form of low-grade lymphoma has not been documented. A small series of case reports has brought to attention the potential for primary occurrence or initial presentation in the pleura of EMZL/MALT-type. In this report, we describe an additional patient with EMZL/MALT-type with initial pleural presentation and review the literature. Clinicians and pathologists dealing with lymphoproliferative disorders involving the pleura should be aware of this rare entity.

Humans↗
PubMed2004

Is severe intestinal chronic graft-versus-host disease an indication for surgery? A report of two cases.

Chronic graft-versus-host disease (cGVHD) frequently complicates allogeneic hematopoietic stem cell transplantation (HSCT), but small bowel involvement with obstruction is rarely observed. We report two patients who underwent allogeneic sibling HSCT and developed severe cGVHD involving the small bowel, causing unremitting obstructive symptoms and malnutrition despite maximal immunosuppression. Both patients underwent ileal resection and stricturoplasties. The first patient promptly improved, and remains asymptomatic 32 months after transplant. Three weeks after the resection of 90 cm of small bowel, the second patient developed leaking stricturoplasty and peritonitis, with a relapse of chronic myelogenous leukemia in accelerated phase. Later, an enterocutaneous fistula required additional small bowel resection and ileostomy. The patient subsequently died from pulmonary infection a few weeks after the last surgical procedure. Similar to inflammatory bowel disease, these two cases highlight that surgery may be a valuable option in patients who present with obstructive severe cGVHD refractory to aggressive immunosuppression.

Adult↗
PubMed2004

Clinical and haemodynamic effects of sildenafil in pulmonary hypertension: acute and mid-term effects.

AIM: The treatment of patients with pulmonary arterial hypertension remains a challenge. We set out to investigate the use of sildenafil, a selective inhibitor of phosphodiesterase type 5, in patients with this disease. METHODS AND RESULTS: Ten patients (8 females, mean age 34.5+/-3.3 years) with pulmonary hypertension underwent right heart catheterisation with vasodilator testing using incremental doses of intravenous sildenafil without adverse events. All patients were subsequently commenced on oral sildenafil 50 mg t.d.s. Nine patients had repeat right heart catheterisation 3 months after the commencement of oral therapy. There was a significant reduction in mean pulmonary artery pressure (from 55.8+/-5.9 to 50.4+/-6.1 mmHg, p=0.038 ) and pulmonary vascular resistance (from 10.1+/-1.7 to 8.6+/-1.5 Wood units, p=0.009 ), and an increase in cardiac output (from 4.7+/-0.3 to 5.0+/-0.4 l/min, p=0.15 ). Furthermore, there was a significant increase in the 6-minute walk test, a mean of 112 m. In response to a quality-of-life questionnaire, patients indicated marked clinical improvement on sildenafil. Sildenafil was discontinued in 1 patient due to a transient visual disturbance. The only patient previously awaiting transplantation was removed from the active transplantation list. CONCLUSIONS: Sildenafil is well tolerated in its intravenous and oral forms and appears to improve both pulmonary haemodynamics and the clinical status of patients with pulmonary hypertension after 3 months of oral therapy.

Administration, Oral↗
PubMed2004

Menadione kills trophozoites and cysts of Giardia intestinalis.

Production of reactive oxygen species by redox cycling in the presence of low levels of oxygen has been studied as a possible approach to anti-protozoal chemotherapeutic strategy. Incubation of the diplomonad flagellate Giardia intestinalis with 2-methy-1,4-naphthoquinone (menadione), under anaerobic conditions, gave UV absorption changes characteristic of reduction to menadiol; partial reversal was observed on admitting O(2). Under microaerobic conditions, similar to those on the surface of the jejunal mucosa, trophozoites consumed O(2) rapidly in the presence of menadione; reaction products included singlet O(2) (monitored by single photon counting of O(2)-dependent low-level chemiluminescence) and H(2)O(2) (measured by the formation of Complex I of microperoxidase). Trophozoites became swollen and incapable of regulatory volume control; these irreversible responses led to loss of motility, cessation of flagellar activity and cell death. Comparison of the sensitivities of trophozoites to metronidazole and menadione gave LC(50) values ( microg x ml(-1)) of 1.2 and 0.7, respectively; corresponding values for cysts (measured by in vitro excystation capacities) were >50 and 1.3. Menadione (LD(50) in mice, 0.5 g kg(-1)) is therefore a potentially more useful and general anti-giardial agent than metronidazole, as it is active against cysts as well as trophozoites.

Anaerobiosis↗
PubMed2004

Does sinus rhythm beget sinus rhythm? Long-term follow-up of the patient activated atrial defibrillator.

The aim of this study was to determine the effect of early patient activated cardioversion of atrial fibrillation (AF) using the atrial defibrillator on recurrence of AF. Fifteen patients, mean age 63 +/- 14 years, 80% men, with drug-resistant persistent AF were implanted with the Jewel AF atrial defibrillator. All patients performed self-administered cardioversion for AF recurrences. Over a 2 year follow-up, 238 patient-activated cardioversions were performed in 14 patients. Sinus rhythm was restored on every occasion with 96% of episodes terminating with a single shock. The median time from AF onset to patient awareness of symptoms was 2.5 hours. The median time from onset of symptoms to cardioversion was 3.5 hours. Comparison of the first and second six month period following implant showed a nonsignificant increase in mean total AF duration (75.7 +/- 107.8 hours vs 146.6 +/- 194.1 hours, P = 0.28). Two patients (13%) had a decreasing frequency of AF recurrences. The majority continued to have regular recurrences of AF. The atrial defibrillator is an extremely effective method of restoring sinus rhythm in patients with persistent AF. Regular early use of the atrial defibrillator, increased the duration of sinus rhythm in a minority of patients during long-term follow-up. Most patients had regular recurrences of AF requiring patient-activated cardioversion.

Adult↗
PubMed2004

Improving the acceptability of the atrial defibrillator: patient-activated cardioversion versus automatic night cardioversion with and without sedation (ADSAS 2).

Acceptability of the atrial defibrillator is partly limited by concerns about shock related anxiety and discomfort. Sedation and/or automatic cardioversion therapy during sleep may ease shock discomfort and improve patient acceptability. Three atrial cardioversion techniques were compared: patient-activated cardioversion with sedation, automatic night cardioversion with sedation, and automatic night cardioversion without sedation. Sedation was oral midazolam (15 mg). Fifteen patients aged 60 +/- 13 years were assigned each strategy randomly for three consecutive episodes of persistent atrial fibrillation requiring cardioversion. Patients completed questionnaires for multiple parameters immediately and again at 24 hours postcardioversion. Atrial cardioversion strategies with oral sedation (patient-activated and automatic) significantly reduced shock recall by 77% (P < 0.005), therapy dissatisfaction by 57%-71% (P < 0.03), shock discomfort by 61%-73% (P < 0.01), shock pain by 79%-83% (P < 0.001), and shock intensity by 73%-77% (P < 0.03), compared to automatic night cardioversion without sedation (P < 0.02). Atrial shock pain was short-lived and caused little disruption to the patients' daily routines. Automatic night cardioversion without sedation, resulted in sleep disturbances not seen with the other strategies (42% vs 0%, P < 0.001) as well as concerns about future pain or discomfort. Twelve patients (80%) chose patient-activated cardioversion with sedation as their preferred treatment, and three (20%) remainder chose automatic night cardioversion with sedation. Ninety percent of patients chose automatic night cardioversion without sedation as the least acceptable therapy. Sedation significantly increases atrial shock acceptability regardless of cardioversion method. Shocks without sedation are significantly less acceptable to patients using the atrial defibrillators.

Anxiety↗
PubMed2002

Improved technique of portal vein reconstruction in pediatric liver transplant recipients with portal vein hypoplasia.

BACKGROUND: Children with small or hypoplastic portal veins represent a challenge for liver transplantation. Graft loss of up to 70% has been reported in these patients in the past. A variety of techniques has been used in both cadaveric and living related transplants in an effort to overcome this problem. Variability arises as to whether to use a vascular graft and where on the portal system to attach the graft. METHOD: We present our usage of a simple and straightforward interposition iliac vein allograft fashioned in a manner to achieve large anastomotic cross-sectional area on the confluence of the superior mesenteric/splenic veins. The procedure also overcomes problems of graft vein/portal vein size mismatch in the cases where liver and vein grafts are procured from much larger donors. RESULTS: A total of 14 children presented with hypoplastic portal vein (diameter<5 mm), of a total of 30 consecutive patients requiring cadaveric liver transplants, and benefited from this technique. Median recipient age was 10.5 months. Revascularization times ranged from 22 to 43 min with a mean of 33 min. All patients are alive and well at a mean follow-up of 329 days (10 months). All liver grafts are well and functioning. No portal vein problem was detected. CONCLUSION: Results from this technique are clearly encouraging. Because portal vein hypoplasia is a common problem in pediatric transplant candidates, we believe this alternative technique is of interest and should be added to the transplant surgeon's armamentarium.

Body Weight↗
PubMed2002

Disease recurrence after liver transplantation in Western Australia.

BACKGROUND AND AIM: Orthotopic liver transplantation (OLT) is now the accepted therapy for end-stage chronic liver disease. Long-term survival is now expected in the majority of patients and, consequently, disease recurrence has emerged as a major concern. Our aim was to document the rate of disease recurrence after liver transplantation for conditions other than hepatitis C, in patients followed up by the Western Australian Liver Transplant Service (WALTS). METHODS: The case notes of all post-OLT patients followed up by WALTS were reviewed. Patients were excluded if survival was less than 3 months post-OLT; OLT was performed for hepatitis C alone or follow up was unavailable. Detection and definition of disease recurrence depended on pretransplant diagnosis, and were based on patient interview, biochemical, immunological and serological tests. Radiological and histological confirmation were obtained where clinically indicated. RESULTS: Eighty-seven patients were identified (89 OLTs performed). The overall rate of recurrence was 10%. Recurrence rates by disease were: primary sclerosing cholangitis (17%), primary biliary cirrhosis (12%), autoimmune hepatitis (17%), hepatitis B (40%) and alcoholic liver disease (4%). Alcohol use relapse after transplantation occurred in 25%. The overall survival post-OLT was 87%, with a mean follow up of 53 months. Survival in patients with recurrent disease was 89%. CONCLUSIONS: Disease recurrence after OLT does occur, but overall, it is relatively uncommon. Recurrence rates vary significantly and depend, in part, on indication for OLT. With medium-term follow up, recurrent disease does not have an effect on mortality.

Adolescent↗
PubMed2002

Transvalvular velocities after full aortic root replacement: results from a prospective randomized trial between the homograft and the Medtronic Freestyle bioprosthesis.

BACKGROUND AND AIM OF THE STUDY: Unstented bioprostheses offer better hemodynamics after aortic valve replacement. It has been reported recently that subcoronary implantation of the Freestyle valve may result in increased transvalvular velocities. In a prospective randomized trial, transvalvular velocities were investigated after implantation of a homograft or a Medtronic Freestyle bioprosthesis as a full root. METHODS: A total of 137 patients was randomized to receive either a homograft (group H, n = 64) or a Freestyle (group F, n = 73) root replacement. Echocardiographic investigations were performed at six weeks, six months, and then yearly after surgery. Transvalvular and subvalvular velocities were recorded from each echocardiogram. RESULTS: At follow up, none of the patients showed high transvalvular or subvalvular velocities (>2 m/s). At six weeks after surgery the transvalvular velocity was 1.5+/-0.3 m/s in group H (n = 51) and 1.7+/-0.3 m/s in group F (n = 56) (p = NS), while subvalvular velocities were 0.9+/-0.3 and 1.0+/-0.3 m/s, respectively (p = NS). These findings remained constant up to the three-year follow up, when transvalvular velocity was 1.6+/-0.4 m/s in group H (n = 10) and 1.6+/-0.2 m/s in group F (n = 15) (p = NS). Subvalvular velocities were 0.9+/-0.1 and 0.9+/-0.1 m/s, respectively (p = NS). CONCLUSION: Full aortic root replacement and reimplantation of the coronary arteries either with the Medtronic Freestyle or the homograft valve produces near-normal transvalvular velocities less than were reported for the Freestyle in the subcoronary implantation.

Adult↗
PubMedDate not supplied

Intestinal ischemia after laparoscopic cholecystectomy.

OBJECTIVES: Intestinal ischemia is a rarely reported complication following laparoscopic cholecystectomy. We describe a case of massive small intestinal necrosis 3 days following this procedure. An autopsy determined the cause to be splanchnic hypoperfusion, likely due to the physiologic changes induced by the pneumoperitoneum necessary to conduct the surgery. We sought to determine whether all reported cases of intestinal ischemia following laparoscopic cholecystectomy (LC) shared the same etiology, and if faulty operative technique could be invoked. METHODS: A review of all known published cases of intestinal ischemia following LC was conducted to determine the underlying etiology of ischemia, and whether adequate operative technique had been observed. RESULTS: Multiple causes of intestinal ischemia following LC have been described: splanchnic hypoperfusion, thrombosis of the superior mesenteric artery, and thrombosis of the inferior mesenteric vein. All occurred despite correct operative technique. CONCLUSIONS: Intestinal ischemia following LC has diverse causes. Patient factors rather than faulty operative technique would appear to underlie the development of this rare complication.

Cholecystectomy, Laparoscopic↗