Microalbuminuria is an important risk factor for cardiovascular disease and progressive renal impairment. This holds true
in the general population and particularly in those with diabetes, in whom it is common and marks out those likely to develop
macrovascular disease and progressive renal impairment. Understanding the pathophysiological mechanisms through which microalbuminuria
occurs holds the key to designing therapies to arrest its development and prevent these later manifestations.
Microalbuminuria arises from the increased passage of albumin through the glomerular filtration barrier. This requires ultrastructural
changes rather than alterations in glomerular pressure or filtration rate alone. Compromise of selective glomerular permeability
can be confirmed in early diabetic nephropathy but does not correlate well with reported glomerular structural changes. The
loss of systemic endothelial glycocalyx—a protein-rich surface layer on the endothelium—in diabetes suggests that damage to
this layer represents this missing link. The epidemiology of microalbuminuria reveals a close association with systemic endothelial
dysfunction and with vascular disease, also implicating glomerular endothelial dysfunction in microalbuminuria.
Our understanding of the metabolic and hormonal sequelae of hyperglycaemia is increasing, and we consider these in the context
of damage to the glomerular filtration barrier. Reactive oxygen species, inflammatory cytokines and growth factors are key
players in this respect. Taken together with the above observations and the presence of generalised endothelial dysfunction,
these considerations lead to the conclusion that glomerular endothelial dysfunction, and in particular damage to its glycocalyx,
represents the most likely initiating step in diabetic microalbuminuria.
Keywords Diabetes - Glomerular endothelial cell - Glomerular filtration barrier - Glycocalyx - Microalbuminuria - Podocyte