Intracranial pancreatic islet transplantation increases islet hormone expression in the rat brain and attenuates behavioral dysfunctions induced by MK-801 (dizocilpine)

Intrapleural transplantation of allogeneic pancreatic islets achieves glycemic control in a diabetic non-human primate

Clinical islet transplantation has relied almost exclusively on intraportal administration of pancreatic islets, as it has been the only consistent approach to achieve robust graft function in human recipients. However, this approach suffers from significant loss of islet mass from a potent immediate blood-mediated inflammatory response (IBMIR) and a hypoxic environment. To avoid these negative aspects of the portal site, we explored an alternative approach in which allogeneic islets were transplanted into the intrapleural space of a non-human primate (NHP), treated with an immunosuppression regimen previously reported to secure routine survival and tolerance to allogeneic islets in NHP. Robust glycemic control and graft survival were achieved for the planned study period of >90 days. Our observations suggest the intrapleural space provides an attractive locale for islet transplantation due to its higher oxygen tension, ability to accommodate large transplant tissue volumes, and a lack of IBMIR-mediated islet damage. Our preliminary results reveal the promise of the intrapleural space as an alternative site for clinical islet transplantation in the treatment of type 1 diabetes.

Natural biomaterials in brain repair: A focus on collagen

Biomaterials derived from natural resources have increasingly been used for versatile applications in the central nervous system (CNS). Thanks to their biocompatibility and biodegradability, natural biomaterials offer vast possibilities for future clinical repair strategies for the CNS. These materials can be used for diverse applications such as hydrogels to fill the tissue cavities, microparticles to deliver drugs across the blood-brain barrier, and scaffolds to transplant stem cells. In this review, various uses of prominent protein and polysaccharide biomaterials, with a special focus on collagen, in repair and regenerative applications for the brain are summarized together with their individual advantages and disadvantages.

Long-term effects of intracranial islet grafting on cognitive functioning in a rat metabolic model of sporadic Alzheimer's disease-like dementia

Accumulating evidence suggests that Alzheimer’s disease is associated with brain insulin resistance, as are some other types of dementia. Intranasal insulin administration has been suggested as a potential approach to overcoming brain insulin resistance and improving cognitive functions. Islet transplantation into the cranial subarachnoid cavity was used as an alternative route for insulin delivery into the brain. Recently, the authors showed the short-term beneficial cognitive effect of a small number of intracranially grafted islets in rats with cognitive dysfunction induced by intracerebroventricular administration of streptozotocin (icv-STZ). This was associated with continuous and safe insulin delivery to the rat brain. The current study investigated the long-term effect of intracranial grafting of islets on cognitive functioning in icv-STZ rats. Severe dementia, associated with obesity and cerebral amyloid-β angiopathy, was induced in Lewis inbred rats by icv-STZ. Two months after icv-STZ, one hundred syngeneic islets were transplanted into the cranial subarachnoid space. Two and six months later, cognitive alterations were assessed by Morris water-maze tests. Islet graft survival was evaluated by immunohistochemical and biochemical assays. Improvement was found in spatial learning and memory of grafted rats as opposed to the sham-operated icv-STZ rats. The grafted islets showed intact morphology, intensive expression of insulin, glucagon and glucose transporter 2. Normoglycemic obesity and cerebral amyloid-β angiopathy were found in both grafted and sham-operated icv-STZ rats. In conclusion, islet grafting into cranial subarachnoid space provides an efficient and safe approach for insulin delivery to the brain, leading to a long-term attenuation of icv-STZ-induced cognitive dysfunction.

Intracranial Transplantation of Pancreatic Islets Attenuates Cognitive and Peripheral Metabolic Dysfunctions in a Rat Model of Sporadic Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD) is often associated with brain insulin resistance and peripheral metabolic dysfunctions. Recently, we developed a model of sporadic AD associated with obesity-related peripheral metabolic abnormalities in Lewis rats using intracerebroventricular administration of streptozotocin (icv-STZ).

OBJECTIVE

We aimed to assess the effect of intracranially grafted pancreatic islets on cognitive and peripheral metabolic dysfunctions in the icv-STZ Lewis rats.

METHODS

AD-like dementia associated with obesity was induced in inbred Lewis rats using a single icv-STZ. Two months after icv-STZ, syngeneic islets (100 islets per recipient) were implanted in the cranial subarachnoid cavity of icv-STZ rats. Morris water maze and marble burying tests were used for studying cognitive and behavioral functions. Central and peripheral metabolic alterations were assessed by histological and biochemical assays.

RESULTS

The icv-STZ induced increases in food intake, body weight, and blood levels of insulin and leptin without alteration of glucose homeostasis. Grafted islets reduced body weight gain, food consumption, peripheral insulin resistance, and hyperleptinemia. Biochemical and histological analysis of the brain revealed viable grafted islets expressing insulin and glucagon. The grafted islets did not affect expression of brain insulin receptors and peripheral glucose homeostasis. Two months after islet transplantation, cognitive and behavioral functioning in transplanted rats were significantly better than the sham-operated icv-STZ rats. No significant differences in the locomotor activity between transplanted and non-transplanted icv-STZ rats were found.

CONCLUSIONS

Intracranial islet transplantation attenuates cognitive decline and peripheral metabolic dysfunctions providing a novel therapeutic approach for sporadic AD associated with peripheral metabolic dysfunctions.

Routes for the delivery of insulin to the central nervous system: A comparative review

Central nervous system (CNS) insulin resistance is a condition in which the cells within the CNS do not respond to insulin appropriately and is often linked to aberrant CNS insulin levels. CNS insulin is primarily derived from the periphery. Aberrant CNS insulin levels can arise due to various factors including i) decreased endogenous insulin transport into the brain, across the blood-brain barrier (BBB), ii) reduced CNS sequestration of insulin, and iii) increased CNS degradation. While the sole route of endogenous insulin transport into the brain is via the BBB, there are multiple therapeutic routes of administration that have been investigated to deliver exogenous insulin to the CNS. These alternative administrative routes can be utilized to increase the amount of CNS insulin and aid in overcoming CNS insulin resistance. This review focuses on the intravenous, intracerebroventricular, intranasal, ocular, and intrathecal routes of administration and compares the impact of insulin delivery.

Selection of Implantation Sites for Transplantation of Encapsulated Pancreatic Islets

Pancreatic islet transplantation has been validated as a valuable therapy for type 1 diabetes mellitus patients with exhausted insulin treatment. However, this therapy remains limited by the shortage of donor and the requirement of lifelong immunosuppression. Islet encapsulation, as an available bioartificial pancreas (BAP), represents a promising approach to enable protecting islet grafts without or with minimal immunosuppression and possibly expanding the donor pool. To develop a clinically implantable BAP, some key aspects need to be taken into account: encapsulation material, capsule design, and implant site. Among them, the implant site exerts an important influence on the engraftment, stability, and biocompatibility of implanted BAP. Currently, an optimal site for encapsulated islet transplantation may include sufficient capacity to host large graft volumes, portal drainage, ease of access using safe and reproducible procedure, adequate blood/oxygen supply, minimal immune/inflammatory reaction, pliable for noninvasive imaging and biopsy, and potential of local microenvironment manipulation or bioengineering. Varying degrees of success have been confirmed with the utilization of liver or extrahepatic sites in an experimental or preclinical setting. However, the ideal implant site remains to be further engineered or selected for the widespread application of encapsulated islet transplantation.

Inhibition of NF-κB activity by aminoguanidine alleviates neuroinflammation induced by hyperglycemia

Neuroinflammation is a key feature of cerebral complication which is associated with diabetes mellitus (DM). Inducible nitric oxide synthase (iNOS) is implicated in the pathogenesis of neuroinflammation. However, how iNOS facilitates the development of inflammation in brain is still unidentified. The aim of the present study was to investigate the association of iNOS and neuroinflammation in diabetic mice, and elucidate the potential mechanisms underlying aminoguanidine (AG), the selective inhibitor of iNOS, protected neurons against inflammation in diabetic mice. In present experiment, diabetic mice model were established by a single intraperitoneal injection of streptozotocin (STZ). AG was administered to diabetic mice for ten weeks after this disease induction. Then we measured iNOS activity in the serum and brain, detected the glial fibrillary acidic protein (GFAP) and ionised calcium binding adaptor molecule-1 (Iba-1) expressions in the brain. Moreover, nuclear factor-kappa B (NF-κB) in cytoplasm and nucleus were tested by IP and WB. Results revealed that high expression of iNOS in serum and brain could be reversed by AG treatment. Furthermore, AG could also inhibit GFAP and Iba-1 expressions, and NF-κB nuclear translocation by inhibiting it from binding to iNOS in cytoplasm. Our findings indicated that iNOS can combine with NF-κB in cytoplasm and promote its nuclear transfer in diabetic mice. Furthermore, AG decreased neuroinflammation through inhibiting iNOS activity and reducing NF-κB nuclear translocation by promoting its dissociation with iNOS in cytoplasm.