Bioresponsive drug delivery systems for the treatment of inflammatory diseases

Inflammation is intimately related to the pathogenesis of numerous acute and chronic diseases like cardiovascular disease, inflammatory bowel disease, rheumatoid arthritis, and neurodegenerative diseases. Therefore anti-inflammatory therapy is a very promising strategy for the prevention and treatment of these inflammatory diseases. To overcome the shortcomings of existing anti-inflammatory agents and their traditional formulations, such as nonspecific tissue distribution and uncontrolled drug release, bioresponsive drug delivery systems have received much attention in recent years. In this review, we first provide a brief introduction of the pathogenesis of inflammation, with an emphasis on representative inflammatory cells and mediators in inflammatory microenvironments that serve as pathological fundamentals for rational design of bioresponsive carriers. Then we discuss different materials and delivery systems responsive to inflammation-associated biochemical signals, such as pH, reactive oxygen species, and specific enzymes. Also, applications of various bioresponsive drug delivery systems in the treatment of typical acute and chronic inflammatory diseases are described. Finally, crucial challenges in the future development and clinical translation of bioresponsive anti-inflammatory drug delivery systems are highlighted.

Convergence of biological nitration and nitrosation via symmetrical nitrous anhydride

Current perspective holds that the generation of secondary signaling mediators from nitrite (NO₂⁻) requires acidification to nitrous acid (HNO₂) or metal catalysis. Herein, the use of stable isotope-labeled NO₂⁻ and LC-MS/MS analysis of products revealed that NO₂⁻ also participates in fatty acid nitration and thiol S-nitrosation at neutral pH. These reactions occur in the absence of metal centers and are stimulated by nitric oxide (^•NO) autoxidation via symmetrical dinitrogen trioxide (nitrous anhydride, symN₂O₃) formation. While theoretical models have predicted physiological symN₂O₃ formation, its generation is now demonstrated in aqueous reaction systems, cell models and in viv, with the concerted reactions of ^•NO and NO₂⁻ shown to be critical for symN₂O₃ formation. These results reveal new mechanisms underlying the NO₂⁻ propagation of ^•NO signaling and the regulation of both biomolecule function and signaling network activity via NO₂⁻-dependent nitrosation and nitration reactions.

Acid-base profile in patients on PD

Acid-base profile in patients on PD. Secular trends in dialysis dose in peritoneal dialysis (PD) and modes of dialysis delivery [automated PD (APD) versus continuous ambulatory PD (CAPD)] require a reexamination of acid-base status in patients treated with these renal replacement modalities. We explored steady-state acid-base profile and its determinants in 175 patients on CAPD and 77 patients on APD. The majority (62% to 70%) of patients had serum bicarbonate levels in the normal range, and a minority (17% to 27%) had values just above 28 mEq/L. Only a small percentage (10% to 12%) of patients in either the CAPD or the APD groups had a serum HCO3 less than 22 mEq/L, an indication of the successful correction of acidosis in most patients. The anion gap was elevated (> 16 mEq/L) in the majority of patients on CAPD and APD and bore an inverse relationship to serum HCO3 and a direct relationship to serum albumin and serum phosphate. In CAPD patients, but not APD patients, a significant inverse relationship was observed between the anion gap and peritoneal permeability as assessed by four-hour D/P(creatinine). The correction of acidosis in PD appears to be predominantly achieved by the continuous supplementation of alkali via dialysis, with residual renal function not differentiating the degree of correction. Steady-state serum bicarbonate in patients on CAPD appeared to be responsive to the underlying peritoneal membrane permeability characteristics of the patient that govern alkali loss and gain, but the higher dialysate volumes in APD appear to override this effect. Higher albumin, blood urea nitrogen (BUN), and phosphate in patients with lower HCO3 suggest a discrepancy between daily acid load and dialysis dose.

Peritoneal dialysis. Prevention and control of infection

In spite of the reduction in peritonitis and catheter-related infection rates in patients undergoing peritoneal dialysis, these infections remain major sources of morbidity and transfer to haemodialysis. Touch contamination at the time of doing the exchanges is still a major cause of peritonitis and leads to Gram-positive organisms (coagulation-negative staphylococcus) being the most common pathogens. Newer exchange techniques have reduced this incidence but the more serious pathogens (Staphylococcal aureus, pseudomonas and fungi) remain a major problem. Treatment has to be immediate, and hence empirical, giving adequate cover for both Gram-positive and Gram-negative organisms. The use of vancomycin as an initial antibacterial has been discontinued because of the problem of vancomycin-resistant enterococcus. Recent guidelines advocate the use of a first generation cephalosporin combined with ceftazidime (if the urine output is >100 ml/day) or an aminoglycoside in anuric patients. Subsequent therapy changes are made upon bacterial isolation and sensitivities. Vancomycin is reserved for methicillin-resistant staphylococcus. Peritoneal catheter-related infections (exit site and tunnel) are predominantly caused by S. aureus and pseudomonal organisms and can be difficult to eradicate. Tunnel infections invariably involve the catheter dacron cuffs and therefore are more likely to lead to peritonitis; in this situation catheter removal is the treatment of choice. Treatment of exit-site infections is with oral antibacterials (penicillinase-resistant penicillins, cefalexin). Vancomycin is avoided if possible. The identification that nasal carriage of S. aureus predisposes to exit-site and tunnel infections has led to prophylactic regimens to combat this problem. Mupirocin applied at the exit site leads to a reduction in catheter-related infections and peritonitis.