ß-Cell and renal transplantation options for diabetes.

Despite major advances in structured education, insulin delivery and glucose monitoring, diabetes self-management remains an unremitting challenge. Insulin therapy is inextricably linked to risk of dangerous hypoglycaemia and sustained hyperglycaemia remains a leading cause of renal failure. This review sets out to demystify transplantation for diabetes multidisciplinary teams, facilitating consideration and incorporation within holistic overall person-centred management. Deceased and living donor kidney, whole pancreas and isolated islet transplant procedures, indications and potential benefits are described, in addition to outcomes within the integrated UK transplant programme.

Loss of end-differentiated ß-cell phenotype following pancreatic islet transplantation.

Replacement of pancreatic ß-cells through deceased donor islet transplantation is a proven therapy for preventing recurrent life-threatening hypoglycemia in type 1 diabetes. Although near-normal glucose levels and insulin independence can be maintained for many years following successful islet transplantation, restoration of normal functional ß-cell mass has remained elusive. It has recently been proposed that dedifferentiation/plasticity towards other endocrine phenotypes may play an important role in stress-induced ß-cell dysfunction in type 2 diabetes. Here we report loss of end-differentiated ß-cell phenotype in 2 intraportal islet allotransplant recipients. Despite excellent graft function and sustained insulin independence, all examined insulin-positive cells had lost expression of the end-differentiation marker, urocortin-3, or appeared to co-express the α-cell marker, glucagon. In contrast, no insulin+ /urocortin-3- cells were seen in nondiabetic deceased donor control pancreatic islets. Loss of end-differentiated phenotype may facilitate ß-cell survival during the stresses associated with islet isolation and culture, in addition to sustained hypoxia following engraftment. As further refinements in islet isolation and culture are made in parallel with exploration of alternative ß-cell sources, graft sites, and ultimately fully vascularized bioengineered insulin-secreting microtissues, differentiation status immunostaining provides a novel tool to assess whether fully mature ß-cell phenotype has been maintained.

Characterizing problematic hypoglycaemia: iterative design and preliminary psychometric validation of the Hypoglycaemia Awareness Questionnaire (HypoA-Q).

AIMS: To design and conduct preliminary validation of a measure of hypoglycaemia awareness and problematic hypoglycaemia, the Hypoglycaemia Awareness Questionnaire. METHODS: Exploratory and cognitive debriefing interviews were conducted with 17 adults (nine of whom were women) with Type 1 diabetes (mean ± sd age 48 ± 10 years). Questionnaire items were modified in consultation with diabetologists/psychologists. Psychometric validation was undertaken using data from 120 adults (53 women) with Type 1 diabetes (mean ± sd age 44 ± 16 years; 50% with clinically diagnosed impaired awareness of hypoglycaemia), who completed the following questionnaires: the Hypoglycaemia Awareness Questionnaire, the Gold score, the Clarke questionnaire and the Problem Areas in Diabetes questionnaire. RESULTS: Iterative design resulted in 33 items eliciting responses about awareness of hypoglycaemia when awake/asleep and hypoglycaemia frequency, severity and impact (healthcare utilization). Psychometric analysis identified three subscales reflecting 'impaired awareness', 'symptom level' and 'symptom frequency'. Convergent validity was indicated by strong correlations between the 'impaired awareness' subscale and existing measures of awareness: (Gold: rs =0.75, P < 0.01; Clarke: rs =0.76, P < 0.01). Divergent validity was indicated by weaker correlations with diabetes-related distress (Problem Areas in Diabetes: rs =0.25, P < 0.01) and HbA1c (rs =-0.05, non-significant). The 'impaired awareness' subscale and other items discriminated between those with impaired and intact awareness (Gold score). The 'impaired awareness' subscale and other items contributed significantly to models explaining the occurrence of severe hypoglycaemia and hypoglycaemia when asleep. CONCLUSIONS: This preliminary validation shows the Hypoglycaemia Awareness Questionnaire has robust face and content validity; satisfactory structure; internal reliability; convergent, divergent and known groups validity. The impaired awareness subscale and other items contribute significantly to models explaining recall of severe and nocturnal hypoglycaemia. Prospective validation, including determination of a threshold to identify impaired awareness, is now warranted.

De Novo Donor-Specific HLA Antibodies Are Associated With Rapid Loss of Graft Function Following Islet Transplantation in Type 1 Diabetes.

Outcomes after islet transplantation continue to improve but etiology of graft failure remains unclear. De novo donor-specific human leukocyte antigen (HLA) antibodies (DSA) posttransplant are increasingly recognized as a negative prognostic marker. Specific temporal associations between DSA and graft function remain undefined particularly in programs undertaking multiple sequential transplants. Impact of de novo DSA on graft function over 12 months following first islet transplant was determined prospectively in consecutive recipients taking tacrolimus/mycophenolate immunosuppression at a single center. Mixed-meal tolerance test was undertaken in parallel with HLA antibody assessment pretransplant and 1-3 months posttransplant. Sixteen participants received a total of 26 islet transplants. Five (19%) grafts were associated with de novo DSA. Five (31%) recipients were affected: three post-first transplant; two post-second transplant. DSA developed within 4 weeks of all sensitizing grafts and were associated with decreased stimulated C-peptide (median [interquartile range]) at 3 months posttransplant (DSA negative: 613(300-1090); DSA positive 106(34-235) pmol/L [p = 0.004]). De novo DSA directed against most recent islet transplant were absolutely associated with loss of graft function despite maintained immunosuppression at 12 months in the absence of a rescue nonsensitizing transplant. Alemtuzumab induction immunosuppression was associated with reduced incidence of de novo DSA formation (p = 0.03).

The UK Pancreas Allocation Scheme for Whole Organ and Islet Transplantation.

In order to develop a national allocation scheme for donor pancreases, factors affecting waiting time and transplant outcomes in the United States (US) and United Kingdom (UK) were analyzed and compared. Blood group, sensitization, dialysis requirement, and whether the patient was waiting for a kidney and pancreas or pancreas alone affected waiting time in both countries; ethnicity and body mass index (BMI) also affected waiting time in the US. Ninety-day pancreas survival was similar in the UK and US, and was poorer for patients receiving a pancreas alone, with older donors, higher BMI and longer duration of ischemia in both countries. Factors affecting outcome, together with published data on factors affecting islet transplantation, informed the development of a points based allocation scheme for deceased donor pancreases in the UK providing equitable access for both whole organ and islet recipients through a single waiting list. Analysis of the allocation scheme 3 years after its introduction in December 2010 showed that the results were broadly as simulated, with a significant reduction in the number of long waiting patients and an increase in the number of islet transplants. There remains a surplus of highly sensitized patients in the waiting list, which the scheme should address in time.

Severe hypoglycaemia in type 1 diabetes mellitus: underlying drivers and potential strategies for successful prevention.

Hypoglycaemia remains an over-riding factor limiting optimal glycaemic control in type 1 diabetes. Severe hypoglycaemia is prevalent in almost half of those with long-duration diabetes and is one of the most feared diabetes-related complications. In this review, we present an overview of the increasing body of literature seeking to elucidate the underlying pathophysiology of severe hypoglycaemia and the limited evidence behind the strategies employed to prevent episodes. Drivers of severe hypoglycaemia including impaired counter-regulation, hypoglycaemia-associated autonomic failure, psychosocial and behavioural factors and neuroimaging correlates are discussed. Treatment strategies encompassing structured education, insulin analogue regimens, continuous subcutaneous insulin infusion pumps, continuous glucose sensing and beta-cell replacement therapies have been employed, yet there is little randomized controlled trial evidence demonstrating effectiveness of new technologies in reducing severe hypoglycaemia. Optimally designed interventional trials evaluating these existing technologies and using modern methods of teaching patients flexible insulin use within structured education programmes with the specific goal of preventing severe hypoglycaemia are required. Individuals at high risk need to be monitored with meticulous collection of data on awareness, as well as frequency and severity of all hypoglycaemic episodes.

Attainment of metabolic goals in the integrated UK islet transplant program with locally isolated and transported preparations.

The objective was to determine whether metabolic goals have been achieved with locally isolated and transported preparations over the first 3 years of the UK's nationally funded integrated islet transplant program. Twenty islet recipients with C-peptide negative type 1 diabetes and recurrent severe hypoglycemia consented to the study, including standardized meal tolerance tests. Participants received a total of 35 infusions (seven recipients: single graft; 11 recipients: two grafts: two recipients: three grafts). Graft function was maintained in 80% at [median (interquartile range)] 24 (13.5-36) months postfirst transplant. Severe hypoglycemia was reduced from 20 (7-50) episodes/patient-year pretransplant to 0.3 (0-1.6) episodes/patient-year posttransplant (p < 0.001). Resolution of impaired hypoglycemia awareness was confirmed [pretransplant: Gold score 6 (5-7); 24 (13.5-36) months: 3 (1.5-4.5); p < 0.03]. Target HbA1c of <7.0% was attained/maintained in 70% of recipients [pretransplant: 8.0 (7.0-9.6)%; 24 (13.5-36) months: 6.2 (5.7-8.4)%; p < 0.001], with 60% reduction in insulin dose [pretransplant: 0.51 (0.41-0.62) units/kg; 24 (13.5-36) months: 0.20 (0-0.37) units/kg; p < 0.001]. Metabolic outcomes were comparable 12 months posttransplant in those receiving transported versus only locally isolated islets [12 month stimulated C-peptide: transported 788 (114-1764) pmol/L (n = 9); locally isolated 407 (126-830) pmol/L (n = 11); p = 0.32]. Metabolic goals have been attained within the equitably available, fully integrated UK islet transplant program with both transported and locally isolated preparations.

Evaluation of a quality-of-life tool for dogs with diabetes mellitus.

BACKGROUND: Diabetes mellitus (DM) management primarily focuses on improvement in blood glucose concentrations and clinical signs. A tool to assess the psychological and social impact of DM and its treatment on quality of life (QoL) previously has only been validated for feline DM. HYPOTHESIS/OBJECTIVES: To validate a diabetic pet and owner-centered individualized measure of impact of DM (DIAQoL-pet) for diabetic dogs and their owners. ANIMALS/SUBJECTS: A total of 101 owners of insulin-treated diabetic dogs were recruited to complete the DIAQoL-pet. METHODS: Discussions and pilot surveys with clinicians and owners of diabetic pets led to the design of 29 specific DM-associated QoL questions. Each item was scored according to impact frequency and perceived importance. An Item-Weighted-Impact-Score (IWIS) for each item was calculated, as was an Average-Weighted-Impact-Score (AWIS) by averaging all IWISs. Principal component analysis and Cronbach's α calculation assessed the measure's reliability. RESULTS: The DIAQoL-pet showed high reliability (Communalities ≥0.5; Cronbach's α 0.85). The AWIS was -2.74 ± 1.7 (mean ± SD). Areas reported as most negatively impacting QoL included: "worry" (IWIS ± SD: -5.92 ± 4.3), "difficulties leaving dog with friends or family" (-5.68 ± 5.1), "worry vision" (-5.58 ± 4.6), "boarding difficulties" (-5.18 ± 5.2), "worry hypoglycemia" (-4.95 ± 4.3), "social life" (-4.82 ± 4.4), "costs" (-4.11 ± 4.7), and "future care"(-4.07 ± 4.6). Eighty-four percent of owners reported negative impact of DM on QoL. CONCLUSIONS AND CLINICAL IMPORTANCE: The DIAQoL-pet proved robust when used by owners of insulin-treated diabetic dogs and identified specific areas most negatively impacting dogs' and their owners' QoL. This tool could be used as an additional assessment parameter in clinical and research settings.

Novel diabetes mellitus treatment: mature canine insulin production by canine striated muscle through gene therapy.

Muscle-targeted gene therapy using insulin genes has the potential to provide an inexpensive, low maintenance alternative or adjunctive treatment method for canine diabetes mellitus. A canine skeletal muscle cell line was established through primary culture, as well as through transdifferentiation of canine fibroblasts after infection with a myo-differentiation gene containing adenovirus vector. A novel mutant furin-cleavable canine preproinsulin gene insert (cppI4) was designed and created through de novo gene synthesis. Various cell lines, including the generated canine muscle cell line, were transfected with nonviral plasmids containing cppI4. Insulin and desmin immunostaining were used to prove insulin production by muscle cells and specific canine insulin ELISA to prove mature insulin secretion into the medium. The canine myoblast cultures proved positive on desmin immunostaining. All cells tolerated transfection with cppI4-containing plasmid, and double immunostaining for insulin and desmin proved present in the canine cells. Canine insulin ELISA assessment of medium of cppI4-transfected murine myoblasts and canine myoblast and fibroblast mixture proved presence of mature fully processed canine insulin, 24 and 48 h after transfection. The present study provides proof of principle that canine muscle cells can be induced to produce and secrete canine insulin on transfection with nonviral plasmid DNA containing a novel mutant canine preproinsulin gene that produces furin-cleavable canine preproinsulin. This technology could be developed to provide an alternative canine diabetes mellitus treatment option or to provide a constant source for background insulin, as well as C-peptide, alongside current treatment options.

Rapamycin toxicity in MIN6 cells and rat and human islets is mediated by the inhibition of mTOR complex 2 (mTORC2).

AIMS/HYPOTHESIS: Rapamycin (sirolimus) is one of the primary immunosuppressants for islet transplantation. Yet there is evidence that the long-term treatment of islet-transplant patients with rapamycin may be responsible for subsequent loss of islet graft function and viability. Therefore, the primary objective of this study was to elucidate the molecular mechanism of rapamycin toxicity in beta cells. METHODS: Experiments were performed on isolated rat and human islets of Langerhans and MIN6 cells. The effects of rapamycin and the roles of mammalian target of rapamycin complex 2 (mTORC2)/protein kinase B (PKB) on beta cell signalling, function and viability were investigated using cell viability assays, insulin ELISA assays, kinase assays, western blotting, pharmacological inhibitors, small interfering (si)RNA and through the overproduction of a constitutively active mutant of PKB. RESULTS: Rapamycin treatment of MIN6 cells and islets of Langerhans resulted in a loss of cell function and viability. Although rapamycin acutely inhibited mTOR complex 1 (mTORC1), the toxic effects of rapamycin were more closely correlated to the dissociation and inactivation of mTORC2 and the inhibition of PKB. Indeed, the overproduction of constitutively active PKB protected islets from rapamycin toxicity whereas the inhibition of PKB led to a loss of cell viability. Moreover, the selective inactivation of mTORC2 using siRNA directed towards rapamycin-insensitive companion of target of rapamycin (RICTOR), mimicked the toxic effects of chronic rapamycin treatment. CONCLUSIONS/INTERPRETATION: This report provides evidence that rapamycin toxicity is mediated by the inactivation of mTORC2 and the inhibition of PKB and thus reveals the molecular basis of rapamycin toxicity and the essential role of mTORC2 in maintaining beta cell function and survival.

Evaluation of a quality-of-life tool for cats with diabetes mellitus.

BACKGROUND: Success in management of diabetes mellitus (DM) is defined as improvement of blood glucose concentrations and clinical signs. However, the psychological and social impact of DM and its daily treatment regimen on quality of life (QoL) of both animal and owner is uncertain. HYPOTHESIS/OBJECTIVES: To design, validate, and apply a diabetic pet and owner-centered, individualized measure of impact of DM (DIAQoL-pet). ANIMALS/SUBJECTS: Two hundred and twenty-one owners of insulin-treated diabetic cats were recruited to complete the DIAQoL-pet. METHODS: Discussions and pilot surveys with clinicians and owners of diabetic cats led to the design of 29 specific DM-associated QoL questions. Owners of diabetic cats completed the finalized survey. Each item was scored according to impact frequency and perceived importance. An item-weighted impact score (IWIS) for each item was calculated, as was an average-weighted impact score (AWIS) by averaging all IWISs. Principal component analysis and Cronbach's α calculation assessed the measure's reliability. Two overview questions measured overall QoL and diabetes-dependent QoL. RESULTS: The DIAQoL-pet showed high reliability (Cronbach α 0.83). The AWIS was -1.76 ± 2.4 (mean ± SD). Areas reported as most negatively impacting QoL included: "boarding difficulties" (IWIS ± SD: -4.67 ± 5.3), "owner wanting more control" (-4.34 ± 4.7), "difficulties leaving cat with friends or family" (-4.21 ± 4.7), "worry" (-4.10 ± 3.9), "worry hypo" (-3.67 ± 3.5), "social life" (-3.48 ± 3.9), "costs" (-3.04 ± 3.8), and "work life" (-3.03 ± 3.7). Forty-one percent of owners believed their cat's life would be "a little better" without DM. CONCLUSIONS AND CLINICAL IMPORTANCE: The DIAQoL-pet proved robust and identified specific areas most negatively impacting on diabetic cats and their owners' QoL. This tool warrants further investigation for use in clinical or research settings.

Patient-reported outcomes following islet cell or pancreas transplantation (alone or after kidney) in Type 1 diabetes: a systematic review.

AIMS: For selected individuals with complex Type 1 diabetes, pancreatic islet transplantation (IT) offers the potential of excellent glycaemic control without significant hypoglycaemia, balanced by the need for ongoing systemic immunosuppression. Increasingly, patient-reported outcomes (PROs) are considered alongside biomedical outcomes as a measure of transplant success. PROs in IT have not previously been compared directly with the closest alternate treatment option, pancreas transplant alone (PTA) or pancreas after kidney (PAK). METHODS: We used a Population, Intervention, Comparisons, Outcomes (PICO) strategy to search Scopus and screened 314 references for inclusion. RESULTS: Twelve studies [including PRO assessment of PAK, PTA, islet-after kidney (IAK) and islet transplant alone (ITA); n = 7-205] used a total of nine specified and two unspecified PRO measures. Results were mixed but identified some benefits which remained apparent up to 36 months post-transplant, including improvements in fear of hypoglycaemia, as well as some aspects of diabetes-specific quality of life (QoL) and general health status. Negative outcomes included short-term pain associated with the procedure, immunosuppressant side effects and depressed mood associated with loss of graft function. CONCLUSIONS: The mixed results may be attributable to limited sample sizes. Also, some PRO measures may lack sensitivity to detect actual changes, as they exclude issues and domains of life likely to be important for QoL post-transplantation and when patients may no longer perceive themselves to have diabetes. Thus, the full impact of islet/pancreas transplantation (alone or after kidney) on QoL is unknown. Furthermore, no studies have assessed patient satisfaction, which may highlight further advantages and disadvantages of transplantation.

Inability to process and store proinsulin in transdifferentiated pancreatic acinar cells lacking the regulated secretory pathway.

Generation of new beta-cells from the adult pancreas or the embryonic stem cells is being pursued by research groups worldwide. Success will be dependent on confirmation of true beta-cell phenotype evidenced by capacity to process and store proinsulin. The aim of these studies was to robustly determine endocrine characteristics of the AR42J rat pancreatic acinar cell line before and after in vitro transdifferentiation. beta-cell phenotypic marker expression was characterised by RT-PCR, immunostaining, western blotting, ELISA and in human preproinsulin transgene over-expression studies in wild-type AR42J cells and after culture on Matrigel basement membrane matrix with and without growth/differentiation factor supplementation. Pancreatic duodenal homeobox 1 (PDX1), forkhead box transcription factor a2 (Foxa2), glucokinase, pancreatic polypeptide and low-level insulin gene transcription in wild-type AR42J cells were confirmed by RT-PCR. Culture on Matrigel-coated plates and supplementation of medium with glucagon-like peptide 1 induced expression of the beta-cell Glut 2 with maintained expression of insulin and PDX1. Increased biosynthesis and secretion of proinsulin were confirmed by immunocytochemical staining and sensitive ELISA. Absence of the regulated secretory pathway was demonstrated by undetectable prohormone convertase expression. In addition, inability to process and store endogenous proinsulin or human proinsulin translated from a constitutively over-expressed preproinsulin transgene was confirmed. The importance of robust phenotypic characterisation at the protein level in attempted beta-cell transdifferentiation studies has been confirmed. Rodent and human sensitive/specific differential proinsulin/insulin ELISA in combination with human preproinsulin over-expression enables detailed elucidatation of core endocrine functions of proinsulin processing and storage in putative new beta-cells.

A randomized pilot study in Type 1 diabetes complicated by severe hypoglycaemia, comparing rigorous hypoglycaemia avoidance with insulin analogue therapy, CSII or education alone.

AIM: To determine potential for amelioration of recurrent severe hypoglycaemia without worsening in overall control in individuals with long-standing Type 1 diabetes (T1DM). METHODS: Twenty-one people with T1DM characterized by altered hypoglycaemia awareness and debilitating severe hypoglycaemia were randomized in a pilot 24-week prospective study to optimized analogue therapy (ANALOGUE; lispro/glargine); continuous subcutaneous insulin infusion therapy (CSII; lispro); or re-education with relaxation of blood glucose targets on existing conventional insulin regimen (EDUCATION). Glycaemic profiles and duration of biochemical hypoglycaemia were measured by continuous subcutaneous glucose monitoring and self-monitored blood glucose. RESULTS: Further severe hypoglycaemia was prevented in five participants (71%) in each group (P = 0.06). Incidence of severe hypoglycaemia was: 0.6 (ANALOGUE), 0.9 (CSII), and 3.7 (EDUCATION) episodes per patient year. Restoration of hypoglycaemia awareness was confirmed by validated questionnaire in three (43%) ANALOGUE, four (57%) CSII and five (71%) EDUCATION patients. Glycated haemoglobin (HbA1c) was significantly improved in the ANALOGUE group between weeks 0 and 24 (8.6 +/- 1.1 vs. 7.6 +/- 0.8%; P = 0.04 for change). Non-significant improvement was seen in the CSII group (8.5 +/- 1.9 vs. 7.4 +/- 1.0%; P = 0.06). No change in HbA1c was seen in the EDUCATION group (8.5 +/- 1.1 vs. 8.3 +/- 1.0%; P = 0.54). There were no episodes of diabetic ketoacidosis or any other adverse events in any group. CONCLUSIONS: In this pilot randomized trial comparing optimized ANALOGUE, CSII or EDUCATION alone in unselected individuals with recurrent severe hypoglycaemia, we show potential for restoring hypoglycaemia awareness and preventing further severe hypoglycaemia with concomitant improvement in glycaemic control in ANALOGUE and CSII groups.

Audit of diabetes in a renal transplant population.

AIMS: To determine the prevalence of diabetes and its glycemic control in the renal transplant population of northeast England (Newcastle, Sunderland, Middlesborough, and Carlisle). METHODS: All renal transplant notes in northeast England were reviewed. Data on patient details, type of diabetes, time of onset of diabetes, diabetes medications, time of insulin commencement, date of renal transplant, immunosuppressive medications, and HbA(1C) were recorded. RESULTS: Living renal transplant patients (n = 1073) transplanted between March 1982 and November 5, 2003 were identified. One hundred and nine (10.2%) patients had diabetes, of whom 39 were type 1 and 70 were type 2. Median HBA(1C) in patients with type 1 diabetes on tacrolimus was 10.1% +/- 1.94% (SD) versus 7.8% +/- 1.98% (SD) for patients not on tacrolimus. Among patients with type 2 diabetes, 25 had diabetes prior to transplant and 45 (4.5%) developed posttransplant diabetes (PTDM). Those who developed PTDM and were taking tacrolimus were more likely to require insulin for blood glucose control (0.39 U/kg/24 hours vs 0 U/kg/24 hours; P = .05) compared to those not on tacrolimus. Both type 1 and type 2 diabetics on tacrolimus showed better preservation of renal function as measured by mean serum creatinine (type 1: 145 +/- 53 vs 196 +/- 74, P = .02; type 2 pretransplant: 159 +/- 73 vs 172 +/- 59, P = .35; type 2 posttransplant: 123 +/- 35 vs 167 +/- 63, P = .01). CONCLUSIONS: Tacrolimus use in renal transplant patients with diabetes appeared to be associated with more problematic blood glucose control; however, it seemed to be better at preserving renal function. Intensive blood glucose monitoring is recommended for this group.

Tetracycline-regulated secretion of human insulin in a transfected non-endocrine cell line.

Long-term constitutive secretion of insulin by implantation of ex vivo transfected cells such as fibroblasts or myoblasts or in situ by intramuscular injection of naked plasmid DNA provides a potential approach to gene therapy for diabetes mellitus. A mechanism for regulating insulin secretion will be necessary to realize the therapeutic potential of this approach. A second obstacle is the inability of non-endocrine host cells to fully process proinsulin. Therefore, alteration of the wild-type cDNA will be necessary to achieve processing of proinsulin by endogenous endoproteases within these cells. The cDNAs for beta-galactosidase (beta), human wild-type proinsulin (hppI1) and a mutated construct (hppI4), in which the dibasic PC2 and PC3 cleavage sites had been altered to form furin cleavage sites, were sub-cloned into four vectors (pCR3, pVR1012, pIRES, pTRE), including a tetracycline responsive plasmid (pTRE) that requires co-transfection with another plasmid encoding a transactivator (pTet-off) for transgene expression. Transient transfection of the COS-7 fibroblast cell line with these constructs was performed using DEAE-dextran and liposomes. Analysis of vector efficiencies revealed that pTRE/pTet-off>pIRES>pCR3>pVR1012. Further analysis demonstrated total pro/insulin secretion of 2.33 ng/10(6) cells/24 h with > or =25% processed to insulin in hppI-1.pTRE/pTet-off-transfected cells compared with 0.39 ng/10(6) cells/24 h and >70% processing in hppI-4.pTRE/pTet-off-transfected cells. In co-transfection studies with pTRE-hppI1/pTet-off and pTRE-hppI4/pTet-off constructs, pro/insulin secretion was inhibited to 65-66% and 36-38% of control (100%) in the presence of 0.01 and 0.1 microg/ml tetracycline respectively over a 24-h incubation period. Furthermore, reversal of tetracycline inhibition was demonstrated for pTRE-hppI1/pTet-off- and pTRE-hppI4/pTet-off-transfected cells. After a 48-h incubation with 1.0 microg/ml tetracycline, total pro/insulin levels were 10 and 14% compared with untreated cells respectively. On tetracycline removal, total proinsulin levels increased and were equivalent to untreated groups 72 h later. In conclusion, regulation of fully processed human insulin secretion has been achieved in a transiently transfected non-endocrine cell line.

Secretion of bioactive human insulin following plasmid-mediated gene transfer to non-neuroendocrine cell lines, primary cultures and rat skeletal muscle in vivo.

The objective of these studies was to evaluate human insulin gene expression following intramuscular plasmid injection in non-diabetic rats as a potential approach to gene therapy for diabetes mellitus avoiding the need for immunosuppression. A wild-type human preproinsulin construct and a mutant construct in which PC2/PC3 sites were engineered to form furin consensus sites were evaluated in in vitro transfections of hepatocyte (HepG2) and myoblast (C2C12/L6) cell lines, primary rat myoblasts, and dermal fibroblasts. In vivo gene transfer by percutaneous plasmid injection of soleus muscle +/- prior notexin-induced myolysis was assessed in rats. In vitro transfection of non-neuroendocrine cell lines and primary cultures with wild-type human preproinsulin resulted in secretion of predominantly unprocessed proinsulin. Employing the mutant construct, there was significant processing to mature insulin (HepG2, 95%; C2C12, 75%; L6, 65%; primary myoblasts, 48%; neonatal fibroblasts, 56%; adult fibroblasts, 87%). In rats aged 5 weeks, circulating human (pro)insulin was detected from 1 to 37 days following plasmid injection and the potential of augmenting transfection efficiency by prior notexin injection was demonstrated (wild-type processing, 87%; mutant, 90%). Relative hypoglycaemia was confirmed by HbA1C (saline, 5.5%; wild type, 5.1%; mutant, 5.1% (P<0.05)). Human (pro)insulin levels and processing (wild-type, 8%; mutant, 53%) were lower in rats aged 9 months but relative hypoglycaemia was confirmed by serum glucose at 10 days (saline, 6.4 mmol/l; wild-type, 6.0 mmol/l; mutant, 5.4 mmol/l). In conclusion, prolonged constitutive systemic secretion of bioactive human (pro)insulin has been attained in non-neuroendocrine cells in vitro and in growing and mature rats following intramuscular plasmid injection.