Structural vulnerabilities and PrEP awareness among Boston heterosexuals and people who inject drugs at risk for HIV: findings from 2018 to 2019 cycles from the Boston, MA site of the NHBS.

Little is known about biopsychosocial factors relating to pre-exposure prophylaxis (PrEP) awareness among people with either heterosexual or injection drug use HIV risk behaviors. Participants engaged in vaginal/anal sex with a person of the opposite sex (N = 515) or were people who injected drugs (PWID; N = 451) in the past 12 months from 2018-2019 in Boston, MA. We examined associations between PrEP awareness and: homelessness; perceived HIV-related stigma; country of birth; bacterial STDs, chlamydia, and/or gonorrhea in the past 12 months, lifetime hepatitis C virus (HCV) infection, sexual orientation, and poverty. More PWID (36.8%) were aware of PrEP than people with heterosexual HIV risk (28%; p = .001). Among people with heterosexual risk, homelessness (aOR = 1.99, p = .003), and among PWID: homelessness (aOR = 2.11, p = .032); bacterial STD (aOR = 2.96, p = .012); chlamydia (aOR = 6.14, p = .008); and HCV (aOR = 2.40, p < .001) were associated with increased likelihood of PrEP awareness. In the combined sample: homelessness (aOR = 2.25, p < .001); HCV (aOR = 2.18, p < .001); identifying as homosexual (aOR = 3.71, p = .036); and bisexual (aOR = 1.55, p = .016) were each associated with PrEP awareness. Although having an STD, HCV, identifying as homosexual or bisexual, and experiencing homelessness were associated with increased PrEP awareness, most participants were unaware of PrEP. Efforts to increase PrEP awareness could engage PWID and heterosexual HIV risk behavior.

Acute kidney injury following endovascular intervention for peripheral artery disease.

BACKGROUND: The incidence of, and risk factors for, acute kidney injury (AKI) after endovascular intervention for peripheral artery disease (PAD) remain unknown. The aim of this study was to assess the proportion of patients who develop AKI and explore the risk factors. METHODS: Prospectively collected data on patients undergoing femoropopliteal endovascular intervention for symptomatic PAD across three vascular centres were analysed. The proportion of patients developing AKI (according to the Kidney Disease Improving Global Outcomes definition) within 48 h, and the proportion developing the composite Major Adverse Kidney Events (MAKE) endpoints (death, dialysis, drop in estimated glomerular filtration rate at least 25 per cent) at 30 days (MAKE30) and remains 90 days (MAKE90) were calculated. Multivariable regression analysis was used to assess predictors of AKI, and the association between AKI and death. RESULTS: Some 2041 patients were included in the analysis. AKI developed in 239 patients (11.7 per cent), with 47 (2.3 per cent) requiring dialysis within 30 days, and 18 (0.9 per cent) requiring ongoing dialysis. The MAKE30 and MAKE90 composite endpoints were reached in 358 (17.5 per cent) and 449 (22.0 per cent) patients respectively. Risk factors for AKI were age, sex, congestive heart failure, chronic limb-threatening ischaemia, emergency procedure, and pre-existing chronic kidney disease. AKI, dementia, congestive heart failure, and major amputation were risk factors for medium-term mortality. CONCLUSION: AKI is a common complication after intervention for PAD and is associated with medium-term mortality.

Perceived benefits of the hepatitis C peer educators: a qualitative investigation.

BACKGROUND: Although opioid-dependent patients are disproportionately impacted by hepatitis C (HCV), many do not receive treatment. In addition to HCV treatment-access barriers, substance-using patients may be reluctant to pursue treatment because of wariness of the medical system, lack of knowledge, or stigma related to HCV treatment. Implementation of a formal peer education program is one model of reducing provider- and patient-level barriers to HCV treatment, by enhancing mutual trust and reducing stigma. METHODS: We used thematic qualitative analysis to explore how 30 HCV patients and peer educators perceived a HCV peer program within an established methadone maintenance program in the USA. RESULTS: Participants unanimously described the program as beneficial. Participants described the peer educators' normalization and dispelling of myths and fears around HCV treatment, and their exemplification of HCV treatment success, and reductions in perceived stigma. Peer educators described personal benefits. CONCLUSIONS: These findings indicate that HCV peer educators can enhance HCV treatment initiation and engagement within opioid substitution programs.

Restenosis after Carotid Interventions and Its Relationship with Recurrent Ipsilateral Stroke: A Systematic Review and Meta-analysis.

OBJECTIVE: Do asymptomatic restenoses > 70% after carotid endarterectomy (CEA) and carotid stenting (CAS) increase the risk of late ipsilateral stroke? METHODS: Systematic review identified 11 randomised controlled trials (RCTs) reporting rates of restenosis > 70% (and/or occlusion) in patients who had undergone CEA/CAS for the treatment of primary atherosclerotic disease, and nine RCTs reported late ipsilateral stroke rates. Proportional meta-analyses and odds ratios (OR) at end of follow-up were performed. RESULTS: The weighted incidence of restenosis > 70% was 5.8% after "any" CEA, median 47 months (11 RCTs; 4249 patients); 4.1% after patched CEA, median 32 months (5 RCTs; 1078 patients), and 10% after CAS, median 62 months (5 RCTs; 2716 patients). In four RCTs (1964 patients), one of 125 (0.8%) with restenosis > 70% (or occlusion) after CAS suffered late ipsilateral stroke over a median 50 months, compared with 37 of 1839 (2.0%) in CAS patients with no significant restenosis (OR 0.87; 95% CI 0.24-3.21; p = .8339). In seven RCTs (2810 patients), 13 out of 141 (9.2%) with restenosis > 70% (or occlusion) after CEA suffered late ipsilateral stroke over a median 37 months, compared with 33 out of 2669 (1.2%) in patients with no significant restenoses (OR 9.02; 95% CI 4.70-17.28; p < .0001). Following data correction to exclude patients whose surveillance scan showed no evidence of restenosis > 70% before stroke onset, the prevalence of stroke ipsilateral to an untreated asymptomatic > 70% restenosis was seven out of 135 (5.2%) versus 40 out of 2704 (1.5%) in CEA patients with no significant restenosis (OR 4.77; 95% CI 2.29-9.92). CONCLUSIONS: CAS patients with untreated asymptomatic > 70% restenosis had an extremely low rate of late ipsilateral stroke (0.8% over 50 months). CEA patients with untreated, asymptomatic > 70% restenosis had a significantly higher risk of late ipsilateral stroke (compared with patients with no restenosis), but this was only 5% at 37 months. Overall, 97% of all late ipsilateral strokes after CAS and 85% after CEA occurred in patients without evidence of significant restenosis or occlusion.

Late Survival in Nonoperated Patients with Infrarenal Abdominal Aortic Aneurysm.

OBJECTIVE/BACKGROUND: Historical studies report high rupture rates in patients with nonoperated abdominal aortic aneurysms (AAAs) of > 5.5 cm diameter, although a recent audit has questioned this. METHODS: This was a retrospective review of 138/764 (18%) patients with AAAs evaluated in a preassessment anaesthetic clinic (PAC) between 2006 and 2012, who either did not undergo elective AAA repair or who underwent deferred repair. The remaining 626 underwent repair. Patients with severe comorbidities (dementia, advanced malignancy, life-expectancy < 1 year) and not referred to PAC were excluded. RESULTS: At a median of 27 months, 71 (52%) died, 36 (51%) following rupture. Cumulative survival, free from rupture or surgery for acute symptoms, was 96% at 1 year, 84% at 3 years, and 64% at 5 years, where baseline AAA diameters were 5.5-6.9 cm. For diameters ≥ 7 cm, survival, free from rupture, was 65% at 1 year, 29% at 3 years, and 0% at 5 years. Median interval to rupture was 47 months (AAA diameter 5.5-6.9 cm) and 21 months where baseline diameters were ≥ 7 cm. Rupture accounted for 32% of late deaths in patients with AAAs of 5.5-5.9 cm diameter, 46% in those with AAAs measuring 6.0-6.9 cm in diameter, and 71% in patients with AAA measuring ≥ 7 cm in diameter. CONCLUSION: Approximately half of all late deaths in this nonoperated cohort were not AAA related, suggesting that even had repair been undertaken, it would not have prolonged patient survival. The incidence of rupture in "high-risk" patients with an AAA < 7 cm diameter was < 5% at 1 year, thereby giving ample time to optimise risk factors and improve pre-existing medical conditions prior to undertaking a deferred intervention. Even if these patients did not undergo surgical repair, the risk of late rupture was relatively low. By contrast, nonoperated patients with AAAs ≥ 7 cm in diameter face a very high risk of rupture and will probably benefit from elective surgery, with the caveat that a higher procedural risk might have to be incurred.

Fate of Distal False Aneurysms Complicating Internal Carotid Artery Dissection: A Systematic Review.

BACKGROUND: False aneurysm formation occurs in 13-49% of internal carotid artery dissections (ICADs). In light of the uncertainty regarding the clinical course, expansion rates and optimal treatment of post-ICAD false aneurysms, a systematic review of the literature was undertaken to establish the fate of the nonoperated distal ICA false aneurysm after ICAD. METHODS: PubMed/MEDLINE, Embase, and Cochrane databases were systematically searched up to 13 August 2015 for studies reporting clinical outcomes and imaging surveillance in patients who were found to have developed a false aneurysm associated with ICAD, with specific emphasis on the fate of the nonoperated false aneurysm. RESULTS: Eight studies reported on the course/clinical outcome of ICAD-associated false aneurysms in 166 patients. Of these, five of 166 false aneurysms (3%) increased in size; 86 of 166 (52%) remained unchanged in diameter; 35 of 166 (21%) diminished in size; 32 of 166 (19%) resolved completely; three of 166 (2%) thrombosed; and five 166 (3%) were repaired surgically. Another four of 166 (2%) underwent late surgery (0.5-5.0 years later). During the course of surveillance, none of the nonoperated false aneurysms associated with spontaneous ICAD gave rise to any new neurological or compressive symptoms. CONCLUSIONS: In this systematic review, >95% of nonoperated false aneurysms affecting the distal internal carotid artery that developed after an ICAD did not increase in size and were not associated with any delayed neurological symptoms suggesting that conservative management and serial surveillance is the optimal mode of treatment. As nearly all studies suffered from serious bias, reporting standards for diagnosis and follow-up are needed in order to better define their natural history.

A Social Ecological Model of Syndemic Risk affecting Women with and At-Risk for HIV in Impoverished Urban Communities.

Syndemic risk is an ecological construct, defined by co-occurring interdependent socio-environmental, interpersonal and intrapersonal determinants. We posited syndemic risk to be a function of violence, substance use, perceived financial hardship, emotional distress and self-worth among women with and at-risk for HIV in an impoverished urban community. In order to better understand these interrelationships, we developed and validated a system dynamics (SD) model based upon peer-reviewed literature; secondary data analyses of a cohort dataset including women living with and at-risk of HIV in Bronx, NY (N = 620); and input from a Bronx-based community advisory board. Simulated model output revealed divergent levels and patterns of syndemic risk over time across different sample profiles. Outputs generated new insights about how to effectively explore multicomponent multi-level programs in order to strategically develop more effective services for this population. Specifically, the model indicated that effective multi-level interventions might bolster women's resilience by increasing self-worth, which may result in decreased perceived financial hardship and risk of violence. Overall, our stakeholder-informed model depicts how self-worth may be a major driver of vulnerability and a meaningful addition to syndemic theory affecting this population.

Dual Antiplatelet Therapy Prior to Expedited Carotid Surgery Reduces Recurrent Events Prior to Surgery without Significantly Increasing Peri-operative Bleeding Complications.

OBJECTIVE: A daily Rapid-Access TIA Clinic was introduced in 2008, where symptomatic patients were started on 75 mg aspirin + 40 mg simvastatin by the referring doctor, before attending the clinic. Following clinic assessment, patients with 50-99% stenoses were transferred to the vascular unit for carotid endarterectomy (CEA). In two audits (n = 212 patients), the median delay from transfer to the vascular unit to undergoing CEA was 3 days, during which time 28 patients (13%) suffered recurrent neurological events. It was hypothesized that early introduction of dual antiplatelet therapy (by adding clopidogrel 75 mg once parenchymal haemorrhage was excluded in the TIA clinic) might significantly reduce recurrent events between transfer to the surgical unit and undergoing CEA. METHODS: Prospective audit in 100 consecutive, recently symptomatic patients receiving dual antiplatelet therapy. Endpoints were: prevalence of recurrent events between transfer from the TIA clinic and undergoing CEA; rates of spontaneous embolization prior to undergoing CEA; and prevalence of haemorrhagic complications RESULTS: The median delay from symptom to CEA was 8 days (IQR 5-15). The median delay between transfer from the TIA clinic to CEA was 3 days (IQR 2-5), during which time three patients (3%) suffered recurrent TIAs. This represents a fivefold reduction compared with previous audit data (OR 4.9, 95% CI 1.5-16.6, p = .01) and was matched by a fourfold reduction in the prevalence of spontaneous embolization from 39/189 (21%) previously to 5/83 (5%) in the current audit (OR 4.1, 95% CI 1.5-10.7, p = .0047). The 30-day death/stroke rate was 1%. There were three haemorrhagic complications: stroke caused by haemorrhagic transformation of an infarct; exploration for neck haematoma; and debridement and skin grafting for spontaneous shin haematoma. CONCLUSION: Early introduction of dual antiplatelet therapy was associated with a significant reduction in recurrent neurological events and spontaneous embolization prior to CEA, without incurring a significant increase in major peri-operative bleeding complications.

"Hepatitis C treatment turned me around:" Psychological and behavioral transformation related to hepatitis C treatment.

BACKGROUND: Hepatitis C (HCV) is a significant public health problem that primarily affects current and former substance users. However, individuals with a history of substance use are less likely to have access to or engage in HCV care. Psychological and behavioral barriers prevent many HCV-infected individuals from initiating or engaging in HCV treatment. This study aimed to investigate the psychological and behavioral experiences of current and former substance users receiving HCV treatment within a combined methadone and primary care clinic in the United States. METHODS: We conducted 31 semi-structured qualitative interviews with opioid-dependent adults enrolled in an integrated HCV treatment program within a methadone maintenance clinic in the Bronx, NY. We used thematic analysis, informed by grounded theory, and inquired about perceptions of HCV before and after initiating HCV treatment, reasons for initiating HCV treatment, and the decision to participate in individual versus group HCV treatment. RESULTS: Participants described psychological and behavioral transformation over the course of HCV treatment. These included reductions in internalized stigma and shame related to HCV and addiction, increases in HCV disclosure and self-care, reductions in substance use, and new desire to help others who are living with HCV. CONCLUSIONS: Integrating HCV treatment with methadone maintenance has the potential to create psychological and behavioral transformations among substance using adults, including reductions in HCV- and addiction-related shame and improvements in overall self-care.

"Damaging what wasn't damaged already": psychological tension and antiretroviral adherence among HIV-infected methadone-maintained drug users.

Active drug use among HIV-infected persons is associated with poor adherence to highly active antiretroviral therapy (HAART) and suboptimal treatment outcomes. To understand adherence experiences among HIV-infected drug users, we conducted semistructured interviews with 15 participants in a randomized controlled trial evaluating the efficacy of directly observed HAART delivered in methadone maintenance clinics. Interviews were recorded, transcribed, and thematically analyzed. We identified negative and positive psychological themes associated with both drug use and adherence. Participants described tension between negative feelings (denial, shame, and perceived isolation) and positive feelings (acceptance, motivation, empowerment, and perceived connectedness), and they associated this tension with their own drug using and adherence behaviors. Sustained antiretroviral therapy adherence may require increased emphasis on understanding the psychological experience of HIV-infected drug users.

Simulation as a tool to improve the safety of pre-hospital anaesthesia--a pilot study.

We conducted a pilot study of the effects of simulation as a tool for teaching doctor-paramedic teams to deliver pre-hospital anaesthesia safely. Participants undertook a course including 43 full immersion, high-fidelity simulations. Twenty videos taken from day 4 and days 9/10 of the course were reviewed by a panel of experienced pre-hospital practitioners. Participants' performance at the beginning and the end of the course was compared. The total time from arrival to inflation of the tracheal tube cuff was longer on days 9/10 than on day 4 (mean (SD) 14 min 52 s (2 min 6 s) vs 11 min 28 s (1 min 54 s), respectively; p = 0.005), while the number of safety critical events per simulation were fewer (median (IQR [range]) 1.0 (0-1.8 [0-2]) vs 3.5 (1.5-4.8 [0-8], respectively; p = 0.011). Crew resource management behaviours also improved in later simulations. On a personal training needs analysis, participants reported increased confidence after the course.

Personalized dosing of cyclophosphamide in the total body irradiation-cyclophosphamide conditioning regimen: a phase II trial in patients with hematologic malignancy.

This study investigates the efficacy and safety of personalized cyclophosphamide (CY) dosing in 50 patients receiving CY along with total body irradiation (TBI). Participants received CY 45 mg/kg with subsequent therapeutic drug monitoring using Bayesian parameter estimation to personalize the second CY dose to a target area under the curve (AUC) for carboxyethylphosphoramide mustard (CEPM) (a reporter molecule for CY-derived toxins) and for hydroxycyclophosphamide (to ensure engraftment). The mean second CY dose was 66 mg/kg; the total dose ranged from 45 to 145 mg/kg. After completion of this phase II study, we compared participants' clinical outcomes with those of concurrent controls (n = 100) who received TBI along with standard CY doses of 120 mg/kg. Patients receiving personalized CY dosing had significantly lower postconditioning peak total serum bilirubin (P = 0.03); a 38% reduction in the hazard of acute kidney injury (AKI) (P = 0.03); and nonrelapse and overall survival rates similar to those in the controls (P = 0.70 and 0.63, respectively) despite the lower doses of CY administered to most of the patients in the personalized dosage group.

Altered expression of anti-apoptotic proteins in non-involved tissue from cancer-containing breasts.

In a previous investigation reduced apoptosis was identified in normal breast tissue from cancer-containing breasts away from the cancer in comparison to age-matched normal breast from women without cancer. The hypothesis for this study was that defects in expression of apoptotic regulatory and DNA repair proteins would facilitate persistence of genetic alterations and predispose to breast cancer development. Using immunohistochemistry normal breast from 120 age-matched women (58 with breast cancer, 62 without) was analysed for proliferation, apoptosis, bcl2, BAX, caspase 3, Hsp27, Hsp70, BRCA1, ATM and BARD1. All assessments were performed without knowledge as to whether it was a cancer case or control. A significant difference was found for apoptotic index which was higher in controls (P < 0.02). There was no change in apoptotic and proliferation index with age for cancer cases unlike controls. Higher expression of bcl2 (P = 0.001) and Hsp27 (P = 0.001) was found in normal breast from cancer-containing breast in comparison to controls. There were no differences in the other proteins. Apoptosis has been found to be reduced in normal breast in a separate cohort of women with breast cancer, along with increased expression of the anti-apoptotic proteins bcl2 and Hsp27. These alterations in apoptotic regulation would enhance tumour development. Further studies are needed to examine the value of these proteins as risk markers.

Pharmacogenomic associations in ABCB1 and CYP3A5 with acute kidney injury and chronic kidney disease after myeloablative hematopoietic cell transplantation.

Renal disease is a major complication in patients following myeloablative allogeneic hematopoietic cell transplantation (HCT). Post-HCT patients receive immunosuppressive regimens containing calcineurin inhibitor (CNIs), cyclosporine or tacrolimus, for graft-versus-host disease prophylaxis. In this retrospective trial, we investigated pharmacogenomic associations in the multidrug resistance (ABCB1) and cytochrome P450 3A5 (CYP3A5) genes and acute kidney injury (AKI) and chronic kidney disease (CKD) in a cohort of 121 patients. ABCB1 and CYP3A5 are responsible for the renal disposition of CNIs, which are known to be nephrotoxic. AKI was defined as doubling of baseline serum creatinine during the first 100 days post-HCT, and CKD as at least one glomerular filtration rate <60 ml/min/m2 between 6 and 18 months post-HCT. Patients were genotyped for CYP3A5*1>*3 and ABCB1 single nucleotide polymorphisms (SNPs) (1199G>A, 1236C>T, 2677G>T/A and 3435C>T). Odds ratios were calculated using logistic regression. Haplotype estimation and univariate association analyses were performed because of strong ABCB1 linkage disequilibrium (LD). AKI occurred in 48 of 121 patients (39.7%) and CKD in 16 of 66 patients (24.2%). No pharmacogenomic associations were found between ABCB1 and CYP3A5 SNPs and the incidences of AKI or CKD. The degree of LD(r2) between ABCB1 SNPs was estimated as follows: 2677G>T/3435C>T (0.44), 1236C>T/3435C>T (0.42) and 1236C>T/2677G>T (0.72). ABCB1 1199G>A showed no LD to other SNPs (<0.05). No associations were found between the most common ABCB1 haplotypes and AKI or CKD. Since no significant pharmacogenomic associations were observed, tailoring CNIs dosing based on these genotypes is unlikely to lower significantly the risk of renal injury following myeloablative HCT.

Prolonged anorexia and elevated plasma cytokine levels following myeloablative allogeneic hematopoietic cell transplant.

Myeloablative conditioning regimens commonly lead to prolonged anorexia and poor oral intake. In a prospective study of 147 patients receiving CY, total body irradiation and allogeneic hematopoietic cells, we determined the extent of decline in oral intake and assessed plasma cytokine levels and development of acute GVHD as explanations for protracted anorexia. For each patient, daily oral caloric intake was expressed as a percent of estimated basal requirements, calculated as basal energy expenditure, through day 20. Oral caloric intake was significantly reduced in 92% of patients and remained low. The nadir in oral intake occurred at days 10-12, when median oral caloric intake was 3% of basal energy requirements. Plasma cytokines known to affect appetite (IL2, IL6, tumor necrosis factor-alpha) were significantly elevated above normal following conditioning therapy (P<0.001 for each cytokine). Acute GVHD did not appear to affect oral intake to transplant day 20 in this cohort of patients; however, plasma levels of IL6 rose steeply before the clinical onset of GVHD. Persistent fever occurred with the greatest frequency in patients with most profound reduction in oral intake. We conclude that prolonged alterations in oral intake following this myeloablative regimen may be related to circulating cytokines known to alter eating behavior.

Solution nuclear magnetic resonance structure of a protein disulfide oxidoreductase from Methanococcus jannaschii.

The solution structure of the protein disulfide oxidoreductase Mj0307 in the reduced form has been solved by nuclear magnetic resonance. The secondary and tertiary structure of this protein from the archaebacterium Methanococcus jannaschii is similar to the structures that have been solved for the glutaredoxin proteins from Escherichia coli, although Mj0307 also shows features that are characteristic of thioredoxin proteins. Some aspects of Mj0307's unique behavior can be explained by comparing structure-based sequence alignments with mesophilic bacterial and eukaryotic glutaredoxin and thioredoxin proteins. It is proposed that Mj0307, and similar archaebacterial proteins, may be most closely related to the mesophilic bacterial NrdH proteins. Together these proteins may form a unique subgroup within the family of protein disulfide oxidoreductases.

Hypercalcemia during the osteogenic phase after rat marrow ablation coincides with increased bone resorption assessed by the NTx marker.

Marrow ablation is a model of bone turnover in which the excavated tibial intramedullary cavity is rapidly and reproducibly filled by osteoblasts with new woven bone (days 6-8), which is then rapidly resorbed by osteoclasts (days 10-15). We showed previously (Magnuson et al., 1997) that marrow ablation induces a dramatic hypercalcemia and hypercalciuria in rats that unexpectedly peaked at the time of maximal osteogenesis and continued throughout the subsequent resorption phase. Based upon the amount of calcium mobilized and a peak of urinary hydroxyproline, we suggested that the hypercalcemia and hypercalciuria were due to increased systemic osteoclastic bone resorption induced by marrow ablation. We now apply a new enzyme-linked immunosorbent assay for rodent alpha(2)(I) N-telopeptide (NTx), a marker of bone resorption, to the marrow ablation model to demonstrate that excretion of NTx parallels that of calcium release in the operated control group. Specifically, maximal NTx/creatinine excretion coincides with the onset of hypercalcemia on days 7-8. A peak of NTx was also observed in methylprednisolone- and deflazacort-treated ablated animals. Analyses for urinary free deoxypyridinoline crosslink failed to detect a significant ablation-induced change in excretion. Interleukin 6 activity was increased in all operated control and glucocorticoid-treated groups after marrow ablation, whereas serum parathyroid hormone remained at presurgical levels in operated controls throughout the 15-day study period. The NTx results confirm that bilateral tibial marrow ablation induces a burst of extratibial bone resorption and hypercalcemia 7-8 days later. We have estimated that the osteogenic phase of the ablation model deposits 40 mg of calcium as hydroxyapatite crystals within the intramedullary cavity on days 6-8; this represents 33%-50% of the total blood calcium content of a young rat. We hypothesize that the size and rapidity of this demand for ionized calcium is met through an extratibial bone resorption pathway of osteoclast formation and activation that anticipates and fulfills this need, and that is initiated at the time of marrow ablation.

Multiple geminate ligand recombinations in human hemoglobin.

The geminate ligand recombination reactions of photolyzed carbonmonoxyhemoglobin were studied in a nanosecond double-excitation-pulse time-resolved absorption experiment. The second laser pulse, delayed by intervals as long as 400 ns after the first, provided a measure of the geminate kinetics by rephotolyzing ligands that have recombined during the delay time. The peak-to-trough magnitude of the Soret band photolysis difference spectrum measured as a function of the delay between excitation pulses showed that the room temperature kinetics of geminate recombination in adult human hemoglobin are best described by two exponential processes, with lifetimes of 36 and 162 ns. The relative amounts of bimolecular recombination to T- and R-state hemoglobins and the temperature dependence of the submicrosecond kinetics between 283 and 323 K are also consistent with biexponential kinetics for geminate recombination. These results are discussed in terms of two models: geminate recombination kinetics modulated by concurrent protein relaxation and heterogeneous kinetics arising from alpha and beta chain differences.