There is increasing awareness that psoriasis is more than 'skin deep'. Several recent reviews focussed on biomarkers indicating the systemic dimension of psoriasis and the aspect of comorbidity psoriasis shares with other chronic inflammatory diseases, such as Crohn's disease and rheumatoid arthritis. Of emerging significance is the relationship to cardiovascular disease, as this contributes substantially to the patients' increased mortality. In this viewpoint, we examine currently available evidence favouring the concept of a causal link between psoriasis and cardiovascular disease: systemic inflammation may cause insulin resistance, which in turn triggers endothelial cell dysfunction, leading to atherosclerosis and finally myocardial infarction or stroke. While this 'psoriatic march' is not yet formally proven, it raises clinically and academically relevant questions, and gains support by recent observations of numerous investigators.

Taken together, several measurements indicative of insulin resistance were found to be significantly correlated with the PASI score. The concept of insulin resistance as a consequence of chronic inflammation and possible pathogenetic cause for comorbidities known to be associated with psoriasis is supported by these data. Our findings validate further studies on larger cohorts as well as interventional studies.

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We document an amelioration of biomarkers of cardiovascular risk in patients with severe plaque-type psoriasis responding to continuous systemic therapy. The impact on the patients'metabolic state was found to be better if the psoriatic inflammation was controlled for longer. Future studies need to compare the cardioprotective effects of different treatment modalities, based on hard clinical endpoints.

Response pathways of the metabolic and the immune system have been evolutionary conserved, resulting in a high degree of integrated regulation. Insulin is a central player in the metabolic system and potentially also in the homeostasis of the skin. Psoriasis is a frequent and often severe autoimmune skin disease, clinically characterized by altered epidermal homeostasis, of which the molecular pathomechanisms are only little understood. In this study, we have examined a potential role for insulin signaling in the pathogenesis of this disease. We show that IL-1β is present in high quantities in tissue fluid collected via microdialysis from patients with psoriasis; these levels are reduced under successful anti-psoriatic therapy. Our results suggest that IL-1β contributes to the disease by dual effects. First, it induces insulin resistance through p38MAPK (mitogen-activated protein kinase), which blocks insulin-dependent differentiation of keratinocytes, and at the same time IL-1β drives proliferation of keratinocytes, both being hallmarks of psoriasis. Taken together, our findings point toward insulin resistance as a contributing mechanism to the development of psoriasis; this not only drives cardiovascular comorbidities, but also its cutaneous phenotype. Key cytokines inducing insulin resistance in keratinocytes and kinases mediating their effects may represent attractive targets for novel anti-psoriatic therapies.

The gamma amino butyric acid B (GABA(B)) receptor is a G protein-coupled receptor (GPCR) involved in synaptic transmission. Recent data indicate it to be also expressed on immune cells, along with chemokine receptors, which are also GPCRs. As GPCRs can undergo heterologous desensitization, we have examined the ability of baclofen, a GABA(B) receptor selective agonist, to interfere with the function of pro-inflammatory chemokine receptors known to be upregulated in cutaneous inflammation. In vitro, baclofen reduces chemotaxis of human peripheral blood mononuclear cells towards CCL2, CCL5, CXCL10, CXCL2 and CX3CL1 in a dose-dependant manner. Protein kinase C inhibitors calphostin C and G0 6976 could reverse this effect, pointing towards the involvement of both calcium-dependent and -independent protein kinase C in baclofen-induced inhibition of chemokine receptors. In an in vivo model of contact hypersensitivity in C57BL/6 mice, intraperitoneal injection of baclofen markedly alleviated signs of inflammation as well as recruitment of neutrophils, monocytes and lymphocytes into the skin. This study demonstrates a new role for the GABA(B) receptor in inflammation, making it a potential new therapeutic target to treat inflammatory skin diseases.

Severe psoriasis is associated with significant cardiovascular mortality. We therefore investigated the effects of systemic therapy on the cardiovascular risk of psoriasis patients. Thirteen consecutive patients receiving fumaric acid esters were included and followed for 24 weeks both clinically and by means of laboratory monitoring, 10 completed the study. Eight of ten patients showed a PASI-50 response. Two of three patients with clinical insulin resistance (Homeostasis Model Assessment of insulin resistance >2.5) showed normal insulin responsiveness at the end of the study. Clinical improvement was paralleled by a reduction of high-sensitive CRP serum levels (median -25%). There was a trend toward reduced serum levels for the vascular endothelial growth factor (median -10%) and resistin (median -4%), while the potentially cardio-protective adiponectin showed a trend toward increased serum levels under therapy (median +19%). Systemic endothelial function assessed by venous occlusion plethysmography revealed an improvement of endothelial vasodilator function after 24 weeks of treatment (p < 0.02). This is the first prospective study documenting an amelioration of endothelial cell function in patients with moderate-to-severe plaque-type psoriasis under effective continuous systemic therapy. Future studies need to compare the cardioprotective effects of different treatment modalities, based on hard end points such as the rate of myocardial infarction.

Psoriasis and psoriatic arthritis are associated with an increased cardiovascular mortality. Although the underlying pathogenesis is not yet fully understood, it is clear that these seemingly organ-specific disorders cause a systemic inflammatory burden as mirrored by elevated biomarkers in the patients' blood. Emerging evidence points toward insulin resistance and endothelial dysfunction as direct consequences; these in turn drive the process of atherosclerosis. As psoriasis and psoriatic arthritis therefore represent cardiovascular risk factors, they must be taken into account by primary care physicians when defining treatment goals for the comorbidities of the respective patients (e.g., arterial hypertension or dyslipidemia). Secondary and tertiary care physicians need to consider a more comprehensive treatment approach, including aspects of lifestyle intervention. Finally, effective long-term anti-inflammatory, disease-modifying therapy may contribute to reducing patients' cardiovascular risk.