Spinal ceramide and neuronal apoptosis in morphine antinociceptive tolerance.

Opiates, like morphine, are the most effective analgesics for treating acute and chronic severe pain, but their use is limited by the development of analgesic tolerance and hypersensitivity to innocuous and noxious stimuli. Because opioids are a mainstay of pain management, restoring their efficacy has great clinical importance. We have recently demonstrated that spinal ceramide, a sphingolipid signaling molecule plays a central role in the development of morphine antinociceptive tolerance. We now report that ceramide upregulation in dorsal horn tissues in response to chronic morphine administration is associated with significant neuronal apoptosis. Inhibition of ceramide biosynthesis attenuated both the increase in neuronal apoptosis and the development of antinociceptive tolerance. These findings indicate that spinal ceramide upregulation is a key pro-apoptotic event that occurs upstream of the development of morphine antinociceptive tolerance and support the rationale for development of inhibitors of ceramide biosynthesis as adjuncts to opiates for the management of chronic pain.

Spinal ceramide modulates the development of morphine antinociceptive tolerance via peroxynitrite-mediated nitroxidative stress and neuroimmune activation.

The effective treatment of pain is typically limited by a decrease in the pain-relieving action of morphine that follows its chronic administration (tolerance). Therefore, restoring opioid efficacy is of great clinical importance. In a murine model of opioid antinociceptive tolerance, repeated administration of morphine significantly stimulated the enzymatic activities of spinal cord serine palmitoyltransferase, ceramide synthase, and acid sphingomyelinase (enzymes involved in the de novo and sphingomyelinase pathways of ceramide biosynthesis, respectively) and led to peroxynitrite-derive nitroxidative stress and neuroimmune activation [activation of spinal glial cells and increase formation of tumor necrosis factor-alpha, interleukin (IL)-1beta, and IL-6]. Inhibition of ceramide biosynthesis with various pharmacological inhibitors significantly attenuated the increase in spinal ceramide production, nitroxidative stress, and neuroimmune activation. These events culminated in a significant inhibition of the development of morphine antinociceptive tolerance at doses devoid of behavioral side effects. Our findings implicate ceramide as a key upstream signaling molecule in the development of morphine antinociceptive tolerance and provide the rationale for development of inhibitors of ceramide biosynthesis as adjuncts to opiates for the management of chronic pain.

Cell cycle regulatory factors in juxta-tumoral renal parenchyma.

The aim of this study was to evaluate regulatory cell cycle factors in juxta-tumoral renal parenchyma in order to obtain information regarding early primary changes occurred in normal renal cells. Specimens of juxta-tumoral renal parenchyma were harvested from the tumoral kidney in 10 patients with no history of treatment before surgery. The expression of p53, Bcl-2, Rb and PCNA was studied by immunohistochemical methods in paraffin-embedded tissues. The apoptotic status was evaluated by flow-cytometry analysis following propidium iodide incorporation. The p53 protein expression was recognized in most of the cases (80%) with different intensities. High intensity apoptotic process detected in juxta-tumoral parenchyma seemed to be p53 dependent and well correlated with the low Bcl-2 expression. 70% of cases were Rb positive. In this type of tissue Rb has only an anti-proliferative and anti-tumoral role. PCNA was present in half of the cases being low expressed due to the tissue regenerating mechanism. Our data suggest that the high intensity of programmed cell death in this type of tissue is supported by the status of cell regulatory factors that control this process. Previous studies have demonstrated that healthy renal tissue has neither apoptosis nor mitotic activity. Juxta-tumoral renal tissue is also displaying normal morphology and DNA content (diploidy) but the microenvironmental status induced by the tumor presence prompts cells to choose death rather than malignant transformation. Further studies are necessary to emphasize if these results have a clinical relevance for the outcome of therapeutical approaches in renal carcinomas.