Transient enhancement of oxidant stress and collagen turnover in patients with acute worsening of congestive heart failure

Advances in bone turnover markers

Bone fragility fractures remain an important worldwide health and economic problem due to increased morbidity and mortality. The current methods for predicting fractures are largely based on the measurement of bone mineral density and the utilization of mathematical risk calculators based on clinical risk factors for bone fragility. Despite these approaches, many bone fractures remain undiagnosed. Therefore, current research is focused on the identification of new factors such as bone turnover markers (BTM) for risk calculation. BTM are a group of proteins and peptides released during bone remodeling that can be found in serum or urine. They derive from bone resorptive and formative processes mediated by osteoclasts and osteoblasts, respectively. Potential use of BTM in monitoring these phenomenon and therefore bone fracture risk is limited by physiologic and pathophysiologic factors that influence BTM. These limitations in predicting fractures explain why their inclusion in clinical guidelines remains limited despite the large number of studies examining BTM.

Bone Turnover Markers in the Diagnosis and Monitoring of Metabolic Bone Disease

BACKGROUND

Disorders of bone metabolism, most notably osteoporosis, are highly prevalent and predispose to fractures, causing high patient morbidity and mortality. Diagnosis and monitoring of bone metabolic defects can present a major challenge as these disorders are largely asymptomatic and radiographic measures of bone mass respond slowly to changes in bone physiology.

CONTENT

Bone turnover markers (BTMs) are a series of protein or protein derivative biomarkers released during bone remodeling by osteoblasts or osteoclasts. BTMs can offer prognostic information on fracture risk that supplements radiographic measures of bone mass, but testing using BTMs has to take into account the large number of preanalytic factors and comorbid clinical conditions influencing BTM levels. BTMs respond rapidly to changes in bone physiology, therefore, they have utility in determining patient response to and compliance with therapies for osteoporosis.

SUMMARY

BTMs are a useful adjunct for the diagnosis and therapeutic monitoring of bone metabolic disorders, but their use has to be tempered by the known limitations in their clinical utility and preanalytic variables complicating interpretation.

Target organ damage in acute heart failure

Acute heart failure is a prognostic factor due to its high mortality during the acute phase and the increased frequency of medium to long-term adverse events. The pathophysiological mechanisms triggered during these exacerbations can persist after reaching clinical stability, remaining even after the acute episode has ended. A certain degree of neurohormonal activation, oxidative stress, apoptosis and inflammation (among other conditions) can therefore persist, resulting in organ damage, not just of the myocardium but likely the entire cardiovascular apparatus. This new insight into the persistence of harmful mechanisms that last beyond the exacerbations could be the start of a change in perspective for developing new therapeutic strategies that seek an overall control of hemodynamic and congestive changes that occur during acute decompensated heart failure and changes that remain after achieving clinical stability.

Ca(2+) signaling in the myocardium by (redox) regulation of PKA/CaMKII

Homeostatic cardiac function is maintained by a complex network of interdependent signaling pathways which become compromised during disease progression. Excitation-contraction-coupling, the translation of an electrical signal to a contractile response is critically dependent on a tightly controlled sequence of events culminating in a rise in intracellular Ca(2+) and subsequent contraction of the myocardium. Dysregulation of this Ca(2+) handling system as well as increases in the production of reactive oxygen species (ROS) are two major contributing factors to myocardial disease progression. ROS, generated by cellular oxidases and by-products of cellular metabolism, are highly reactive oxygen derivatives that function as key secondary messengers within the heart and contribute to normal homeostatic function. However, excessive production of ROS, as in disease, can directly interact with kinases critical for Ca(2+) regulation. This post-translational oxidative modification therefore links changes in the redox status of the myocardium to phospho-regulated pathways essential for its function. This review aims to describe the oxidative regulation of the Ca(2+)/calmodulin-dependent kinase II (CaMKII) and cAMP-dependent protein kinase A (PKA), and the subsequent impact this has on Ca(2+) handling within the myocardium. Elucidating the impact of alterations in intracellular ROS production on Ca(2+) dynamics through oxidative modification of key ROS sensing kinases, may provide novel therapeutic targets for preventing myocardial disease progression.

Stromal cell biology--a way to understand the evolution of cardiovascular diseases

Stromal cells, composed of fibroblasts, microvascular endothelial cells, immune cells and inflammatory cells, are critical determinants of the mechanical properties and function of the heart and vasculature, and the mechanisms whereby these types of cells are activated are important to understand the progression of cardiovascular diseases. Emerging studies have suggested that the activation of autocrine and paracrine signaling pathways by stromal cell-derived growth factors, cytokines and bioactive molecules contributes to disease progression. Disruption of the stromal network will result in alterations in the geometry and function in these organs. Interventions targeting the stromal cells (eg, myofibroblasts, microvascular endothelial cells, inflammatory cells) by pharmacological agents or direct gene delivery/small interfering RNA would be potential novel therapeutic strategies to prevent/attenuate the progression of cardiovascular disorders.

Increased isoprostane content in coronary plaques obtained from vulnerable patients

8-Iso-prostaglandin F(2)(alpha) (8-iso-PGF(2)(alpha)), a representative isoprostane, is a reliable biomarker for enhanced oxidant stress in vivo. Its urinary excretion has been proposed as a risk marker in patients with coronary heart disease. Isoprostane content has not yet been well elucidated so far in human coronary plaques. The aim of this study was to evaluate content of immunoreactive 8-iso-PGF(2)(alpha) in directional coronary atherectomy (DCA) specimens from patients with coronary heart diseases. Twenty-seven patients with stable angina pectoris (SAP) and 8 vulnerable patients (5 patients with unstable angina pectoris and 3 with recent myocardial infarction) were subjected to DCA. The specimens from SAP consisted of 14 de novo and 13 restenotic lesions, whereas those from the vulnerable patients were all de novo lesions. Total 8-iso-PGF(2)(alpha) content in the DCA specimens from the vulnerable patients was significantly greater than that from patients with SAP (5.48 (2.70-10.43) versus 2.38 (1.19-4.32)ng/g tissue, median (interquartile range), P<0.05). There was no significant difference in total 8-iso-PGF(2)(alpha) content between de novo and restenotic lesions from patients with SAP (3.25 (1.48-5.05) versus 1.57 (0.62-2.47)ng/g tissue, respectively, P=0.895). Total 8-iso-PGF(2)(alpha) content in apparently normal peripheral artery specimens was only 0.34 (0.26-0.46)ng/g tissue. In conclusion, 8-iso-PGF(2)(alpha) was enriched in the DCA specimens from vulnerable patients, suggesting a crucial role of free radicals in formation of vulnerable plaques and a putative benefit of anti-oxidant therapy on these patients.

The amino- and carboxyterminal cross-linked telopeptides of collagen type I, NTX-I and CTX-I: a comparative review

Bone diseases such as osteoporosis or bone metastases are a continuously growing problem in the ageing populations across the world. In recent years, great efforts have been made to develop specific and sensitive biochemical markers of bone turnover that could help in the assessment and monitoring of bone turnover. The amino- and carboxyterminal cross-linked telopeptides of type I collagen (NTX-I and CTX-I, respectively) are two widely used bone resorption markers that attracted great attention due to their relatively high sensitivity and specificity for the degradation of type I collagen, and their rapid adaptation to automated analyzers. However, the clinical performance of both markers differs significantly depending on the clinical situation. These differences have caused considerable confusion and uncertainty. If used correctly, both markers have great potential to improve the management of many bone diseases. We here review the biochemistry, analytical background and clinical performance of NTX-I and CTX-I, as documented in the accessible literature until March 2008.