Tight junction protein expression and barrier properties of immortalized mouse brain microvessel endothelial cells

The Concept of a Blood-Brain Barrier, Michael Bradbury (Ed.). John Wiley Sons, Interscience Publication (1979), 465, £22.00

Decreased blood-brain barrier permeability to fluorescein in streptozotocin-treated rats

Increased permeability to albumin is a well-known feature of diabetic microvasculature and a negative prognostic factor of vascular complications. The mechanisms responsible for loss of the physiological albumin barrier in diabetic organs remain only partially understood. We have recently demonstrated that the protease μ-calpain is activated in hyperglycemia, which causes endothelial dysfunction and vascular inflammation. In the present study, we investigated whether μ-calpain is involved in the hyperpermeability of the diabetic vasculature. We also investigated the mechanistic roles of hyperglycemia and leukocyte adhesion in this process. Albumin permeability in the intact microcirculation of the Zucker diabetic fatty (ZDF) rat was quantified by intravital microscopy. Extravasation of albumin in the microcirculation of ZDF rats was significantly increased when compared with nondiabetic Zucker lean (ZL) rats. Microvascular albumin leakage was prevented by either antisense depletion of μ-calpain or pharmacological inhibition of calpain in vivo. Calpain inhibition also attenuated urinary albumin excretion in ZDF rats. Glucose concentrations in the range of those found in the blood of ZDF rats increased albumin permeability in nondiabetic ZL rats. Thus, this demonstrates a mechanistic role for hyperglycemia in the hypermeability of diabetes. Depletion of polymorphonuclear leukocytes in vivo failed to prevent glucose-induced hypermeability, which suggests that hyperglycemia can disrupt the physiological endothelial cell barrier of the microcirculation, even in the absence of increased overt leukocyte-endothelium interactions.

https://diabetes.diabetesjournals.org/content/diabetes/56/7/1842.full.pdf

Hyperglycemia Is a Major Determinant of Albumin Permeability in Diabetic Microcirculation: The Role of μ-Calpain

Perfect control of blood glucose levels in diabetic patients might ultimately be achieved with islet or pancreas transplants or with an artificial pancreas. However, to achieve such a goal on a large scale, it will be necessary to overcome the formidable safety or efficacy issues attendant with these approaches (see, e.g., [1, 2]). Meanwhile, in a substantial fraction of the estimated sixty million diabetic patients worldwide, current hypoglycemic therapy provides control of blood sugar levels that, in the long term, is inadequate. That is, current hypoglycemic therapy is still associated with substantial morbidity and mortality from the late microvascular complications of diabetes, principally diabetic neuropathy, retinopathy, and nephropathy. Attempts to achieve better long-term control of blood glucose through aggressive use of insulin and oral hypoglycemic agents, while yielding encouraging results, unfortunately have led to increased incidences of dangerous episodes of severe hypoglycemia.

Aldose reductase inhibitors: Recent developments

Diabetes was induced with streptozotocin in rats weighing about 160 g. These were maintained with age-matched controls for up to 14 months, blood glucose being periodically monitored. Half the diabetic and control rats received the aldose reductase inhibitor, Ponalrestat, in their diet. At 3 weeks, 6-7 months and 13-14 months, the vascular permeability in regions of brain, and in optic and sciatic nerves, were measured by maintaining radiotracers in the bloodstream--125I-albumin (100 min), [14C]sucrose (60 min) and 131I-albumin (5 min)--followed by tissue sampling and counting at termination. 131I-albumin estimated residual intravascular plasma. Diabetes of up to 13-14 weeks caused no measurable increase in the sucrose permeability of microvessels in eight different brain regions, in optic or in sciatic nerve. At 3 weeks of diabetes, sucrose permeability in all brain regions and in optic nerve was reduced relative to that in controls. Extravascular albumin entry into different regions of brain and optic nerve was insignificant and insensitive to diabetes, except in the hypothalamus and optic nerves where it was raised with increasing duration of diabetes. In sciatic nerve, extravascular albumin distribution was markedly increased by diabetes, but sucrose permeability was not demonstrably affected. At the level used in the diet, Ponalrestat reduced the sorbitol content of diabetic sciatic nerve but did not protect again the increased permeability to albumin.

Permeability of blood-brain and blood-nerve barriers in experimental diabetes mellitus in the anaesthetized rat.

Diabetes was induced with streptozotocin in rats weighing about 160 g. These were maintained with age-matched controls for up to 14 months, blood glucose being periodically monitored. Half the diabetic and control rats received the aldose reductase inhibitor, Ponalrestat, in their diet. Distribution of volumes of 131I-albumin (5 min) and 125I-albumin (100 min) were estimated in various tissues at 3 weeks, 6-7 months and 13-14 months of diabetes. The former space was assumed to represent the intravascular plasma space, while the latter was taken to include both the extravascular and intravascular albumin volumes in the kidney. In heart and skeletal muscle, equilibration between the specific activities of extravascular albumin and of plasma albumin was not assumed to be complete at 100 min. In the cortex and medulla of kidney, the extravascular albumin pool increased significantly at 13-14 months of diabetes (for both, P less than 0.01). Significantly increased entry of albumin into the interstitium occurred at 6 months (P less than 0.05) and at 13-14 months (P less than 0.01) in skeletal muscle, and at 13-14 months (P less than 0.05) in heart. The intravascular plasma volumes were not influenced by diabetes and the aldose reductase inhibitor had no effect at any time in either diabetic or control rats. These findings indicate increased movement of plasma albumin into the interstitium in the late phase of diabetes in the heart, skeletal muscle and in the kidney. Enlargement of the interstitial albumin pool is likely to affect the fluid balance between capillary and interstitium and may contribute to the effect of diabetes on the function of these organs.

https://physoc.onlinelibrary.wiley.com/doi/pdf/10.1113/expphysiol.1991.sp003552

GG Pinter

Papers

Permeability of blood-brain and blood-nerve barriers in experimental diabetes mellitus in the anaesthetized rat.

Albumin escape from microvessels in kidney, heart and skeletal muscle in experimental diabetes mellitus in the anaesthetized rat.