Low volumetric bone density is a risk factor for early complications after spine fusion surgery

This study aims to investigate lumbar spine (LS) volumetric bone density (vBMD) as a risk factor for complications (pseudoarthrosis, instrumentation failure, adjacent fractures), re-operation, and time to complication after fusion.

INTRODUCTION

Lumbar spine (LS) fusion surgery is increasingly performed worldwide. Complications after fusion result in significant morbidity and healthcare costs. Multiple factors, including osteoporosis, have been suggested to contribute to risk of complications and re-operation. However, most studies have used DXA, which is subject to artifact in patients with spine pathology, and none have investigated the relationship between BMD and timing of post-operative complications. This study aims to investigate LS volumetric bone density (vBMD) as a risk factor for complications (pseudoarthrosis, instrumentation failure, adjacent fractures), re-operation, and time to complication after fusion.

METHODS

We evaluated a cohort of 359 patients who had initial LS fusion surgery at our institution, had pre-operative LS CTs and post-operative imaging available for review. Demographic factors, smoking status, vBMD, and details of surgical procedure were related to likelihood and timing of post-operative complications.

RESULTS

Mean age was 60 ± 14 years, vBMD 122 ± 37 g/cm³. Median follow-up was 11 months. Skeletal complications occurred in 47 patients (13%); 34 patients (10%) required re-operation. Low vBMD (directly measured and estimated using HU) and smoking were associated with increased risk of skeletal complications. Each increase in baseline vBMD of 10 g/cm³ decreased the complication hazard and increased the complication-free duration in time-to-event analysis (hazard ratio 0.91, 95% CI 0.83-0.98, p < 0.02).

CONCLUSIONS

Low vBMD was a significant risk factor for early post-operative complications in patients undergoing LS fusion. Prospective studies are needed to confirm these findings and to elucidate the optimal timing for follow-up and strategies for prevention of post-operative complications in this population.

Anabolic agents: what is beyond osteoporosis?

Osteoporosis is a common skeletal disorder characterized by low bone mass, which leads to reduced bone strength and an increased risk of fractures. Anabolic agents have been shown to improve bone mass and decrease fracture risk in osteoporosis patients by directly stimulating osteoblasts to produce new bone. Currently, two anabolic agents are available in the USA: recombinantly produced teriparatide (TPTD), which is the fully active (1-34) amino active sequence of human parathyroid hormone (PTH), and abaloparatide (APTD), a synthetic analog of parathyroid hormone-related peptide (PTHrP). At present, both agents are approved only for treatment of patients with osteoporosis at high risk of fracture. Nonetheless, their anabolic properties have led to off-label application in additional settings which include spine fusion, osteonecrosis of the jaw, arthroplasty, and fracture healing. In this article, we summarize available scientific literature regarding the efficacy, effectiveness, and safety of TPTD in these off-label settings.

[Common genital infections]

Vulvo-vaginal infections are frequently encountered by gynecologists and general practitioners. The diagnosis and the recurrence of these affections must lead to a discussion about sexually transmitted disease, notably when trichomonas vaginalis and herpetic infections are found. Even if they do not correspond to classical sexually transmitted diseases, their prevalence is increased by sexual intercourses reports and the number of partners which should also be treated. It is necessary to document the responsible germs, even in case of recurrence as more and more resistance to usual treatments are found together with the appearance of new germs like Candida glabrata.

Determinants of seasonal variation in activity patterns of mouflon

Balancing energetic requirements is a complex process governed by the current condition of the animal, its physiological state, and by the local environment. In response to these factors, animals are expected to adapt their activity patterns. Based on continuous monitoring of 14 GPS-collared animals in southern France, we studied how environmental conditions and reproductive life-cycle periods shape the monthly activity patterns of free-ranging female mouflon ( Ovis gmelini musimon  × Ovis sp. (Blyth, 1841)). More specifically, we analyzed total daily activity, diurnal activity, length of activity bouts, and number of activity bouts. We performed multivariate analyses to account for the relationship between several intercorrelated explanatory variables and monthly activity variables. Mouflon decreased their daily activity, diurnal activity, and length of activity bouts during the hot summer months. Such changes might allow animals to reduce thermoregulation costs. The resulting higher activity in winter compared with summer indicates that summer is the most limiting period for large herbivores in Mediterranean area. Both the number of active bouts and the daily activity increased during spring, when females have access to increased food quality, which ensures a faster digestion, and when they may face high energetic requirements owing to reproduction.

Characterization and localization of leptin receptors in the rat kidney

Characterization and localization of leptin binding sites were investigated in rat kidneys using [125I]leptin as a ligand. [125I]Leptin specific binding was found in high amounts in rat renomedullary membranes. This binding was specific, saturable, time-dependent (K(obs) = 0.055 +/- 0.008 min(-1)) and the dissociation of receptor-bound ligand was slowly reversible (K(-1) = 0.048 +/- 0.013 min(-1)). From saturation experiments, a single class of high-affinity binding sites for leptin was identified with an apparent K(d) of 0.57 +/- 0.14 nM and a B(max) of 45 +/- 10 fmol/mg protein. [125I]Leptin binding was inhibited in a dose-dependent manner by cold leptin and was highly selective since not displaceable by a number of other hormones or peptides. Autoradiographic experiments performed on adult rat kidney sections showed the intense presence of [125I]leptin receptors only in specific areas of the renal inner medulla and also consistent labeling associated with vascular structures in the corticomedullary region. The study of the postnatal developmental expression of leptin receptors in the kidney showed very low expression during the early postnatal period (8-21 days). Full expression of leptin sites was achieved at about 30 days and remained stable throughout adulthood (60 days and upwards). Moreover, in vivo administration of leptin (0.5 mg/kg i.p.) induced a significant and rapid diuretic effect in normally hydrated conscious rats. Thus, these data constitute the first characterization and mapping of [125I]leptin specific binding sites in the rat kidney and raise the possibility of a renal control by leptin.

Characterization of SR 121463A, a highly potent and selective, orally active vasopressin V2 receptor antagonist

SR 121463A, a potent and selective, orally active, nonpeptide vasopressin V2 receptor antagonist, has been characterized in several in vitro and in vivo models. This compound displayed highly competitive and selective affinity for V2 receptors in rat, bovine and human kidney (0.6 < or = Ki [nM] < or = 4.1). In this latter preparation, SR 121463A potently antagonized arginine vasopressin (AVP)-stimulated adenylyl cyclase activity (Ki = 0.26+/-0.04 nM) without any intrinsic agonistic effect. In autoradiographic experiments performed in rat kidney sections, SR 121463A displaced [3H]AVP labeling especially in the medullo-papillary region and confirmed that it is a suitable tool for mapping V2 receptors. In comparison, the nonpeptide V2 antagonist, OPC-31260, showed much lower affinity for animal and human renal V2 receptors and lower efficacy to inhibit vasopressin-stimulated adenylyl cyclase (Ki in the 10 nanomolar range). Moreover, OPC-31260 exhibited a poor V2 selectivity profile and can be considered as a V2/V1a ligand. In normally hydrated conscious rats, SR 121463A induced powerful aquaresis after intravenous (0.003-0.3 mg/kg) or oral (0.03-10 mg/kg) administration. The effect was dose-dependent and lasted about 6 hours at the dose of 3 mg/kg p.o. OPC-31260 had a similar aquaretic profile but with markedly lower oral efficacy. The action of SR 121463A was purely aquaretic with no changes in urine Na+ and K+ excretions unlike that of known diuretic agents such as furosemide or hydrochlorothiazide. In addition, no antidiuretic properties have been detected with SR 121463A in vasopressin-deficient Brattleboro rats. Thus, SR 121463A is the most potent and selective, orally active V2 antagonist yet described and could be a powerful tool for exploring V2 receptors and the therapeutical usefulness of V2 blocker aquaretic agents in water-retaining diseases.

Autoradiographic localization of vasopressin V1a receptors in the rat kidney using [3H]-SR 49059

Localization and characterization of binding sites of the selective non-peptide vasopressin receptor V1a ligand, [3H]-SR 49059, were investigated in the adult rat kidney by quantitative autoradiography using a fast-detecting radioluminographic phosphor-imaging plate system. [3H]-SR 49059, like the other V1a ligands used, showed a total absence of binding in the papilla, discrete and sparse labeling in the cortex and maximal binding in the outer part of the inner medulla. This labeling seemed to be mainly associated with medullary interstitial cells and vascular elements of the vasa recta. Conversely, [3H]-AVP intensely labeled the V2-enriched medulla-papillary portion of the kidney and, to a lesser extent, the cortical structures. [3H]-SR 49059 binding, quantified in the outer part of the inner medulla in rat kidney sections, was time-dependent, reversible, saturable and a single class of high affinity binding sites (Kd = 1.48 +/- 0.16 nM) was identified. The relative potencies of the reference peptide and non-peptide compounds to inhibit [3H]-SR 49059 binding confirm the V1a nature of the site and the stereospecificity of this binding. Thus, [3H]-SR 49059 allows the mapping and characterization of the V1a receptor population present in the rat kidney. The stability and the highly selective affinity of this non-peptide ligand for rat and human V1a receptors make it a suitable probe for the localization of V1a receptors in organs expressing heterogeneous populations of receptors.

SR 120819A, an orally-active and selective neuropeptide Y Y1 receptor antagonist

An orally-active antagonist of neuropeptide Y (NPY) Y1 receptors, SR 120819A, has been characterized. This compound displays highly selective and competitive affinity for rat, guinea-pig and human (Ki = 15 nM) NPY Y1 receptors. In vitro, SR 120819A blocks the inhibitory effect of NPY on adenylyl cyclase activity in human SK-N-MC cells and that of the selective Y1 agonist, [Leu31,Pro34]NPY, on rabbit vas deferens contraction (pA2 = 7.20 +/- 0.07). In vivo, by intravenous route, this compound acts as an antagonist in anesthetized guinea-pigs and, notably, after oral administration, SR 120819A counteracts the pressor response of [Leu31,Pro34]NPY (5 micrograms/kg i.v.) with a long duration of action (> 4 h at 5 mg/kg p.o.). Thus, SR 120819A is the first orally-effective NPY Y1 receptor antagonist yet described. It could be a useful tool for exploring the role of NPY and the therapeutic relevance of an antagonist at NPY Y1 receptors.

Effect of SR-49059, a vasopressin V1a antagonist, on human vascular smooth muscle cells

The effects of SR-49059, a new nonpeptide and selective arginine vasopressin (AVP) V1a antagonist, were investigated in binding and functional studies on cultured human aortic vascular smooth muscle cells (VSMC). Characterization of human vascular V1a receptors, using a specific V1a radioiodinated ligand, showed that [125I]-linear AVP antagonist binding to human VSMC membranes was time dependent, reversible, and saturable. A single population of high-affinity binding sites (apparent equilibrium dissociation constant = 15 +/- 6 pM; maximum binding density = 36 +/- 5 fmol/mg protein, i.e., approximately 3,000 sites/cell) with the expected V1a profile was identified. Exposure of these cells to AVP dose-dependently produced cytosolic free [Ca2+] increase [AVP concentration required to obtain a half-maximal response (EC50) = 23 +/- 9 nM] and proliferation (EC50 = 3.2 +/- 0.5 nM). SR-49059 strongly and stereospecifically inhibited [125I]-linear AVP antagonist binding to VSMC V1a receptors [inhibition constant (Ki) = 1.4 +/- 0.3 nM], AVP-evoked Ca2+ increase [concentration of inhibitor required to obtain 50% inhibition of specific binding (IC50) = 0.41 +/- 0.06 nM], and the mitogenic effects induced by 100 nM AVP (IC50 = 0.83 +/- 0.04 nM). OPC-21268, another nonpeptide V1a antagonist, was more than two orders of magnitude less potent than SR-49059 in these models. However, the consistent affinity (Ki = 138 +/- 21 nM) and activity found with OPC-21268 on human VSMC in comparison with the inactivity already observed for other human V1a receptors (liver, platelets, adrenals, and uterus) strongly suggested the existence of human AVP V1a-receptor subtypes.(ABSTRACT TRUNCATED AT 250 WORDS)

Binding of [3H] SR 49059, a potent nonpeptide vasopressin V1a antagonist, to rat and human liver membranes

The new potent and selective nonpeptide vasopressin V1a antagonist, SR 49059, was tritiated and used for the characterization of rat and human liver AVP V1a receptors. Binding of [3H] SR 49059 was time-dependent, reversible and saturable. A single class of high affinity binding sites was identified with Kd values of 0.63 +/- 0.13 and 2.95 +/- 0.64 nM, in rat and human liver membranes, respectively. The maximal binding capacity (Bmax) was about 7 times higher in rat than in human liver preparations. The relative potencies of several AVP/oxytocin agonists or antagonists to inhibit [3H] SR 49059 binding confirmed that this ligand labeled a homogeneous population of sites with the expected AVP V1a profile. Furthermore, [3H] SR 49059 or unlabeled SR 49059 displayed only slight species differences between rat and human V1a receptors, whereas OPC-21268, another nonpeptide V1a antagonist, exhibited a high species-related potency with more than 500 fold higher affinity for rat than for human liver V1a receptors. Thus, [3H] SR 49059 is the first nonpeptide AVP V1a ligand reported having highly specific activity, stability, specificity and affinity. This makes it a suitable probe for labeling AVP V1a receptors in rat and also in human tissues.

Plasma membrane Na(+)-H+ antiporter and H(+)-ATPase in the medullary thick ascending limb of rat kidney

To characterize H+ transport mechanisms in a fresh suspension of rat medullary thick ascending limb (MTAL) tubules, we have monitored intracellular pH (pHi) with use of the fluorescent probe 2',7'-bis(carboxyethyl)-5,6-carboxyfluorescein. First, a Na(+)-H+ antiporter was identified in bicarbonate-free N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid (HEPES)-buffered media at 25 degrees C. pHi recovery of Na-depleted acidified cells was dependent on extracellular sodium concentration, which was inhibited by amiloride in a manner consistent with simple competitive interaction with one external transport site (amiloride Ki = 1.5-2.1 x 10(-5) M); Na-induced pHi recovery of acidified cells was electroneutral since it was not affected by 5 or 100 mM extracellular potassium in the presence or absence of valinomycin. Second, at 37 degrees C, pHi recovery after acute intracellular acidification caused by 40 mM acetate addition to cell suspension was inhibited 36% by 200-400 nM bafilomycin A1, a macrolide antibiotic that specifically inhibits vacuolar-type H(+)-ATPase at submicromolar concentrations. In addition, amiloride-insensitive pHi recovery was inhibited by bafilomycin A1, 10(-3) M N-ethylmaleimide, and 10(-4) M preactivated omeprazole but not by 10(-5) M vanadate, 10(-4) M SCH 28080, or removal of extracellular potassium. Also, metabolic inhibition by absence of substrate, 10(-4) M KCN, or 5 x 10(-4) M iodoacetic acid inhibited amiloride-insensitive pHi recovery. The inhibitory effects of absence of metabolic substrate and iodoacetic acid were removed by reexposure to glucose and L-leucine and by exogenous ATP, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of H+/HCO3- transport in the medullary thick ascending limb of rat kidney

The rat MTAL secretes protons into the tubular fluid and thus absorbs bicarbonate at substantial rates. Yet the cellular mechanisms of H+/HCO3- transport in the rat MTAL remain largely unsettled. We have performed intracellular pH recovery studies with use of the fluorescent probe BCECF in suspensions of rat MTAL fragments. Luminal H+ secretion occurs by two mechanisms (each responsible for 50% of the normal pHi recovery rate): (1) an electroneutral Na+/H+ antiporter that has an Na-Km of about 11 mM and is inhibited by amiloride (Ki = 2.8 x 10(-5) M); (2) a primary H+ pump that is inhibited by 10(-4) M NEM and 10(-4) M omeprazole, but not by 10(-4) M vanadate or removal of external K. These results suggest the presence of a vacuolar H(+)-ATPase rather than a H(+)-K(+)-ATPase. Basolateral HCO3 exit occurs predominantly by a Cl(-)- and Na(+)-independent electroneutral K+/HCO3- symporter, that has an HCO3-Km of about 17 mM, and is partially inhibited by 10(-4) M DIDS. Basolateral HCO3- efflux was not accompanied by variations of membrane potential monitored with the Em-sensitive fluorescent probe DIS-C3-5, and was not affected by maneuvers that depolarize the cells. It was strongly inhibited by cellular K depletion and dependent on transmembrane K gradient. We conclude that the rat MTAL should secrete protons through both Na+/H+ antiporter and H(+)-ATPase, and that basolateral HCO3- exit should occur through an electroneutral K+/HCO3- symporter.