Disparities in Access to Liver Transplant Referral and Evaluation among Patients with Hepatocellular Carcinoma in Georgia

Liver transplantation offers the best survival for patients with early-stage hepatocellular carcinoma (HCC). Prior studies have demonstrated disparities in transplant access; none have examined the early steps of the transplant process. We identified determinants of access to transplant referral and evaluation among patients with HCC with a single tumor either within Milan or meeting downstaging criteria in Georgia.Population-based cancer registry data from 2010 to 2019 were linked to liver transplant centers in Georgia. Primary cohort: adult patients with HCC with a single tumor ≤8 cm in diameter, no extrahepatic involvement, and no vascular involvement. Secondary cohort: primary cohort plus patients with multiple tumors confined to one lobe. We estimated time to transplant referral, evaluation initiation, and evaluation completion, accounting for the competing risk of death. In sensitivity analyses, we also accounted for non-transplant cancer treatment.Among 1,379 patients with early-stage HCC in Georgia, 26% were referred to liver transplant. Private insurance and younger age were associated with increased likelihood of referral, while requiring downstaging was associated with lower likelihood of referral. Patients living in census tracts with ≥20% of residents in poverty were less likely to initiate evaluation among those referred [cause-specific hazard ratio (csHR): 0.62, 95% confidence interval (CI): 0.42-0.94]. Medicaid patients were less likely to complete the evaluation once initiated (csHR: 0.53, 95% CI: 0.32-0.89).Different sociodemographic factors were associated with each stage of the transplant process among patients with early-stage HCC in Georgia, emphasizing unique barriers to access and the need for targeted interventions at each step.

SIGNIFICANCE

Among patients with early-stage HCC in Georgia, age and insurance type were associated with referral to liver transplant, race, and poverty with evaluation initiation, and insurance type with evaluation completion. Opportunities to improve transplant access include informing referring providers about insurance requirements, addressing barriers to evaluation initiation, and streamlining the evaluation process.

INFUSE: Rationale and design of a multi-center, open label, collaborative study to treat HRS-AKI with continuous terlipressin infusion

Background

Hepatorenal syndrome-acute kidney injury (HRS-AKI) carries significant morbidity and mortality among those with end-stage liver disease. Bolus terlipressin for treatment of HRS-AKI received FDA approval in September 2022. US implementation of terlipressin, however, is hindered by the paucity of local data on the optimal patient population and administration mode, as well as the effect on transplant priority. The INFUSE study is designed to evaluate the use of continuous terlipressin infusion among transplant candidates with advanced liver disease and HRS-AKI.

Methods

Fifty prospective patients with HRS-AKI will receive a single bolus of terlipressin 0.5 mg followed by continuous infusions of terlipressin from 2 to 8 mg/day for up to 14 days. The cohort will be enriched with those listed, in evaluation, or eligible for liver transplantation, while those with ACLF grade 3, MELD ≥35, and serum creatinine >5.0 mg/dL will be excluded. Fifty patients who received midodrine plus octreotide or norepinephrine for HRS-AKI will serve as a retrospective comparator cohort.

Conclusion

The INFUSE study aims to assess the safety and efficacy of continuous terlipressin infusion among largely transplant-eligible patients with HRS-AKI, and to provide US-based data on transplant outcomes. This novel study design simultaneously mitigates terlipressin adverse events while providing renal benefits to patients, thus addressing the unmet medical need of those with HRS-AKI who have limited treatment options and are awaiting liver transplantation in the US.

Prospective Multicenter Study of Early Antiviral Therapy in Liver and Kidney Transplant Recipients of HCV-Viremic Donors

BACKGROUND AND AIMS

Organs from hepatitis C virus (HCV)-viremic donors have been used in HCV-uninfected recipients (D+/R-), but the optimal treatment approach has not been defined. We evaluated the kinetics of HCV infection following transplant in D+/R- kidney-transplant (KT) and liver-transplant (LT) recipients when a preemptive antiviral strategy was used.

APPROACH AND RESULTS

Six US transplant programs prospectively treated D+/R- primary LT and KT recipients with sofosbuvir-velpastasvir for 12 weeks starting once viremia was confirmed following transplant and the patients were judged to be clinically stable, including estimated glomerular filtration rate >30 mL/min. Primary endpoints were sustained virologic response at 12 weeks following transplant and safety (assessed by proportion of treatment-related adverse and serious adverse events). Of the 24 patients transplanted (13 liver, of whom 2 had prior-treated HCV infection; 11 kidney), 23 became viremic after transplant. The median (interquartile range) time from transplant to start of antiviral therapy was 7.0 (6.0, 12.0) versus 16.5 (9.8, 24.5) days, and the median (interquartile range) HCV-RNA level 3 days after transplant was 6.5 (3.9, 7.1) versus 3.6 (2.9, 4.0) log₁₀  IU/mL in LT versus KT recipients, respectively. By week 4 of treatment, 10 of 13 (77%) LT, but only 2 of 10 (20%) KT, had undetectable HCV RNA (P = 0.01). At the end of treatment, all LT recipients were HCV RNA-undetectable, whereas 3 (30%) of the kidney recipients still had detectable, but not quantifiable, viremia. All achieved sustained virologic response at 12 weeks following transplant (lower 95% confidence interval bound: 85%). Serious adverse events considered possibly related to treatment were antibody-mediated rejection, biliary sclerosis, cardiomyopathy, and graft-versus-host disease, with the latter associated with multiorgan failure, premature treatment discontinuation, and death.

CONCLUSIONS

Despite differing kinetics of early HCV infection in liver versus non-liver recipients, a preemptive antiviral strategy is effective. Vigilance for adverse immunologic events is warranted.

Terlipressin plus Albumin for the Treatment of Type 1 Hepatorenal Syndrome

BACKGROUND

The vasoconstrictor terlipressin is used for type 1 hepatorenal syndrome (HRS-1) in many parts of the world and is part of the clinical practice guidelines in Europe.

METHODS

We conducted a phase 3 trial to confirm the efficacy and safety of terlipressin plus albumin in adults with HRS-1. The patients were randomly assigned in a 2:1 ratio to receive terlipressin or placebo for up to 14 days; in both groups, concomitant use of albumin was strongly recommended. The primary end point was verified reversal of HRS, defined as two consecutive serum creatinine measurements of 1.5 mg per deciliter or less at least 2 hours apart and survival without renal-replacement therapy for at least 10 days after the completion of treatment. Four prespecified secondary end points were analyzed with the Hochberg procedure to account for multiple comparisons.

RESULTS

A total of 300 patients underwent randomization - 199 were assigned to the terlipressin group and 101 to the placebo group. Verified reversal of HRS was reported in 63 patients (32%) in the terlipressin group and 17 patients (17%) in the placebo group (P = 0.006). With respect to the prespecified secondary end points, HRS reversal, defined as any serum creatinine level of 1.5 mg per deciliter or less during the first 14 days, was reported in 78 patients (39%) in the terlipressin group and 18 (18%) in the placebo group (P<0.001); HRS reversal without renal-replacement therapy by day 30, in 68 (34%) and 17 (17%), respectively (P = 0.001); HRS reversal among patients with systemic inflammatory response syndrome (84 patients in the terlipressin group and 48 patients in the placebo group), in 31 (37%) and 3 (6%), respectively (P<0.001); and verified reversal of HRS without recurrence by day 30, in 52 (26%) and 17 (17%), respectively (P = 0.08). At day 90, liver transplantations had been performed in 46 patients (23%) in the terlipressin group and 29 patients (29%) in the placebo group, and death occurred in 101 (51%) and 45 (45%), respectively. More adverse events, including abdominal pain, nausea, diarrhea, and respiratory failure, occurred with terlipressin than with placebo. Death within 90 days due to respiratory disorders occurred in 22 patients (11%) in the terlipressin group and 2 patients (2%) in the placebo group.

CONCLUSIONS

In this trial involving adults with cirrhosis and HRS-1, terlipressin was more effective than placebo in improving renal function but was associated with serious adverse events, including respiratory failure. (Funded by Mallinckrodt Pharmaceuticals; CONFIRM ClinicalTrials.gov number, NCT02770716.).

Emricasan Improves Liver Function in Patients With Cirrhosis and High Model for End-Stage Liver Disease Scores Compared With Placebo

BACKGROUND & AIMS

Caspase-mediated apoptosis and inflammation contribute to progression of liver disease. Emricasan is a pan-caspase inhibitor that reduced serum markers of apoptosis and liver inflammation in patients with hepatitis C and non-alcoholic steatohepatitis (NASH).

METHODS

We performed a multicenter study of 86 patients with cirrhosis (Child-Pugh class A or B; mean score, 6.9; 38% with alcohol-associated cirrhosis, 29% with HCV-associated cirrhosis, and 23% with NASH) and model for end-stage liver disease (MELD) scores of 11-18 (mean, 12.8). Patients were randomly assigned to groups given placebo (N = 42) or Emricasan (25 mg, N = 44), twice daily for 3 months; subjects then received open-label Emricasan (25 mg) twice-daily for 3 months. The primary endpoint was the change from baseline in serum levels of cleaved keratin 18 (CK-18) at month 3.

RESULTS

Seventy-four patients completed the 3-month study period (40 given Emricasan and 34 given placebo); 69 patients received open-label Emricasan for 3 months afterward. At the 3-month timepoint, Emricasan significantly reduced mean MELD (P = .003) and Child-Pugh (P = .003) scores in subjects with high MELD scores (15 or more), compared with placebo, with significant reductions in INR (95% CI, -0.2882 to -0.0866) and total bilirubin (95% CI, -1.5069 to -0.0823) vs placebo. There were no significant differences between Emricasan and placebo groups in mean MELD (P = .466) or Child-Pugh (P = .124) scores overall at 3 months compared to placebo. Of patients with high MELD scores, 6/9 given Emricasan (67%) had a reduction of 2 points or more at month 3, compared with 2/10 given placebo (20%). Serum levels of full-length CK-18 (P = .02) and caspase 3/7 (P < .001), but not cleaved CK-18 (P = .092), decreased significantly at 3 months in the Emricasan vs placebo group. Emricasan was well tolerated, and adverse events were balanced between groups. Emricasan's effects were generally maintained or increased after 6 months of treatment.

CONCLUSIONS

In a randomized trial of patients with cirrhosis, we found 3 months treatment with Emricasan to improve liver function, compared with placebo, reducing MELD and Child-Pugh scores, INR, and total bilirubin in patients with MELD scores ≥15. ClinicalTrials.gov no: NCT02230670.

End-hole Versus Microvalve Infusion Catheters in Patients Undergoing Drug-Eluting Microspheres-TACE for Solitary Hepatocellular Carcinoma Tumors: A Retrospective Analysis

INTRODUCTION

Pre-transplant locoregional therapy for hepatocellular carcinoma (HCC) during bridge-to-transplant impacts recurrence and survival rates following liver transplantation. Optimizing the effectiveness of transarterial chemoembolization (TACE) in this population is imperative, and microvalve infusion catheters offer a means of such improvement.

METHODS

All treatment-naive patients with solitary HCC tumors < 6.5 cm who underwent drug-eluting microspheres (DEM) TACE between 04/2015 and 08/2017 were retrospectively reviewed. Eighty-eight included patients underwent DEM-TACE with either standard end-hole catheters (EH) or microvalve infusion catheters (MVI). The EH (n = 70) and MVI (n = 18) cohorts had similar baseline tumor size, laboratory values, and tumor etiologies.

RESULTS

Initial objective response rates were significantly higher in MVI vs. EH (100% vs. 76.5%, p = 0.019). There was no difference in adverse events between groups (p = 0.265). MVI patients exhibited lower AST (p = 0.003) and ALT (p = 0.044) at 6 months. Blinded pathological analysis of explanted livers showed greater concentrations of microspheres within the tumor relative to the surrounding tissue in MVI explants (88.7 ± 10.6%) versus the EH explants (55.3 ± 32.7%) (p = 0.002). There was significantly higher percentage tumor necrosis in the MVI group (89.0 ± 2.2%) compared with the EH group (56.1 ± 44.5%) (p = 0.006).

CONCLUSION

In this retrospective study of a single-center cohort, DEM-TACE procedures with MVI were associated with improved tumor response, increased deposition of microspheres within tumor tissue, and higher percentage tumor necrosis at explant relative to those performed using EH catheters.

Liver transplantation for fulminant genotype 2a/c hepatitis C virus marked by a rapid recurrence followed by cure

Although chronic hepatitis C is still the leading indication for liver transplantation (LT) in the United States and Europe, acute liver failure caused by hepatitis C is distinctly uncommon and transplantation for fulminant hepatitis C virus (HCV) has not been documented in the United States. We present a case report of fulminant hepatic failure caused by genotype 2a/c HCV not only treated with LT but also complicated by severe, rapid recurrence of HCV within 6 days of transplantation. The risk factor for the initial infection was likely sexual, and there were no explanations for acute hepatitis post-transplant other than recurrent hepatitis C. Treatment with all-oral direct antiviral agents was swiftly initiated during the index hospitalization, leading to resolution of the acute hepatitis and resulting in sustained virologic response. It can only be speculated whether this was an infection with the JFH-1 strain or another similarly virulent genotype 2a/c HCV infection.

Twice-Daily Telaprevir for Posttransplant Genotype 1 Hepatitis C Virus: A Prospective Safety, Efficacy, and Pharmacokinetics Study

OBJECTIVES

Our objective was to determine the safety, efficacy, and pharmacokinetics of telaprevir plus pegylated interferon alfa 2a and ribavirin for chronic, posttransplant genotype 1 hepatitis C virus infection.

MATERIALS AND METHODS

A prospective, single-arm, multicenter, open-label, phase 2b study was conducted at 22 North American sites to assess the safety, efficacy, and pharmacokinetics of pegylated interferon alfa 2a, ribavirin, and twice daily telaprevir in liver transplant recipients with recurrent, chronic hepatitis C without cirrhosis. Baseline liver biopsies were read by a central pathologist. There were planned safety reviews after a sentinel cohort reached treatment weeks 4 and 16. Serial pharmacokinetic sampling was performed for calcineurin inhibitors, telaprevir, and ribavirin.

RESULTS

Sixty-one patients were enrolled and received ≥ 1 dose of study medication; 37 (61%) achieved sustained virologic response. Thirteen of 18 treatment-naive patients (72%), 10 of 11 patients with no or minimal fibrosis (91%), 13 of 15 patients (87%) with interleukin 28B genotype CC, and 36 of 45 patients (80%) with either undetectable or unquantifiable hepatitis C virus RNA at treatment week 4 achieved sustained virologic response. Nine patients (15%) had ≥ 1 drug-related serious adverse event and 7 (11%) discontinued all study drugs due to an adverse event. There were no deaths or acute cellular rejection episodes. During telaprevir treatment, median doses of tacrolimus and cyclosporine were 0.5 mg weekly and 25 mg daily. Target exposures were achieved for telaprevir with twice daily dosing and for ribavirin with reduced initial dosing.

CONCLUSIONS

Telaprevir combination therapy for posttransplant hepatitis C virus infection yielded superior efficacy than historical controls. Adverse events were similar to, but exceeded, those in immunocompetent patients. Calcineurin inhibitor dosing levels were substantially reduced with telaprevir.

Combination therapy with telaprevir for chronic hepatitis C virus genotype 1 infection in patients with HIV: a randomized trial

BACKGROUND

Telaprevir (TVR) plus peginterferon-α2a (PEG-IFN-α2a) and ribavirin substantially increases treatment efficacy for genotype 1 chronic hepatitis C virus (HCV) infection versus PEG-IFN-α2a-ribavirin alone. Its safety and efficacy in patients with HCV and HIV-1 are unknown.

OBJECTIVE

To assess the safety and efficacy of TVR plus PEG-IFN-α2a-ribavirin in patients with genotype 1 HCV and HIV-1 and to evaluate pharmacokinetics of TVR and antiretrovirals during coadministration.

DESIGN

Phase 2a, randomized, double-blind, placebo-controlled study. (ClinicalTrials.gov: NCT00983853).

SETTING

16 international multicenter sites.

PATIENTS

62 patients with HCV genotype 1 and HIV-1 who were HCV treatment-naive and receiving 0 or 1 of 2 antiretroviral regimens were randomly assigned to TVR plus PEG-IFN-α2a-ribavirin or placebo plus PEG-IFN-α2a-ribavirin for 12 weeks, plus 36 weeks of PEG-IFN-α2a-ribavirin.

MEASUREMENTS

HCV RNA concentrations.

RESULTS

Pruritus, headache, nausea, rash, and dizziness were higher with TVR plus PEG-IFN-α2a-ribavirin during the first 12 weeks. During this period, serious adverse events occurred in 5% (2 in 38) of those receiving TVR plus PEG-IFN-α2a-ribavirin and 0% (0 in 22) of those receiving placebo plus PEG-IFN-α2a-ribavirin; the same number in both groups discontinued treatment due to adverse events. Sustained virologic response occurred in 74% (28 in 38) of patients receiving TVR plus PEG-IFN-α2a-ribavirin and 45% (10 in 22) of patients receiving placebo plus PEG-IFN-α2a-ribavirin. Rapid HCV suppression was seen with TVR plus PEG-IFN-α2a-ribavirin (68% [26 in 38 patients] vs. 0% [0 in 22 patients] undetectable HCV RNA levels by week 4). Two patients had on-treatment HCV breakthrough with TVR-resistant variants. Patients treated with antiretroviral drugs had no HIV breakthroughs; antiretroviral exposure was not substantially modified by TVR.

LIMITATION

Small sample size and appreciable dropout rate.

CONCLUSION

In patients with HCV and HIV-1, more adverse events occurred with TVR versus placebo plus PEG-IFN-α2a-ribavirin; these were similar in nature and severity to those in patients with HCV treated with TVR. With or without concomitant antiretrovirals, sustained virologic response rates were higher in patients treated with TVR versus placebo plus PEG-IFN-α2a-ribavirin.

Noncirrhotic portal hypertension in patients with human immunodeficiency virus-1 infection

BACKGROUND & AIMS

Noncirrhotic portal hypertension (NCPH) is unusual in North American patients. This study characterized patients with NCPH and human immunodeficiency virus-1 (HIV-1) infection to identify potential risk factors for this association.

METHODS

Eleven consecutive patients from our urban hepatology clinic with HIV-1 infection and NCPH were the subject of this series. Case histories, including medication lists and laboratory data, were analyzed.

RESULTS

Age at diagnosis was 51 +/- 7 years. CD4 count was 303 +/- 185 cells/mL, and HIV viral load was <75 copies/mL in 9 patients. Didanosine was the only medication taken by all patients; 10 each had taken lamivudine and zidovudine. In the 10 patients tested, 8 had at least 1 thrombophilic abnormality; 6 were deficient in protein S, and 2 had multiple abnormalities. Nodular regenerative hyperplasia was observed in all 11 and portal venulopathy in 5 patients. All patients had esophageal varices; 3 developed variceal bleeding. Six patients had ascites; 2 required transjugular intrahepatic portal systemic shunt.

CONCLUSIONS

Exposure to didanosine and/or a hypercoagulable tendency might predispose patients infected with HIV-1 to vascular changes resulting in NCPH.

Terbinafine-induced hepatic failure requiring liver transplantation

Drug-induced liver disease accounts for about 50% of acute or subacute liver failure in the United States. United Network of Organ Sharing (UNOS) data suggest 8%-20% of liver transplantation in this country per year is for fulminant liver failure due to drugs. Even though the most common medication implicated in acute liver injury is acetaminophen (75%), there are numerous other drugs that are responsible for acute and chronic liver injury. A variety of antifungal medications are known to cause a wide range of liver injury from a mild hepatocellular-cholestatic injury pattern to acute/subacute liver failure. Terbinafine is one of the antifungals that have been associated with such liver injuries. We report a case of terbinafine-induced severe liver failure requiring liver transplantation.

Vanadate stimulates tyrosine phosphorylation of two proteins in Raji human lymphoblastoid cell membranes

A membrane fraction from Raji human lymphoblastoid cells exhibited tyrosine-specific kinase activity. Vanadate increased tyrosine phosphorylation up to 5-fold; serine and threonine phosphorylation were unchanged. The stimulation was detectable within 15 s at 0 degrees C and at concentrations of vanadate (0.3 and 1.0 microM) present in normal tissues and blood. The tyrosine phosphorylation of two substrates, M1 61 000 and 55 000, was dependent upon vanadate and incorporation into these substrates represented the majority of the vanadate-sensitive tyrosine phosphorylation.

Characterization and quantitation of NF-kappaB nuclear translocation induced by interleukin-1 and tumor necrosis factor-alpha. Development and use of a high capacity fluorescence cytometric system

A new quantitative cytometric technique, termed the ArrayScanTM, is described and used to measure NF-kappaB nuclear translocation induced by interleukin (IL)-1 and tumor necrosis factor-alpha (TNFalpha). The amount of p65 staining is measured in both the nuclei defined by Hoechst 33342 labeling and in the surrounding cytoplasmic area within a preselected number of cells/well in 96-well plates. Using this technique in synchronously activated human chondrocytes or HeLa cells, NF-kappaB was found to move to the nucleus with a half-time of 7-8 min for HeLa and 12-13 min for chondrocytes, a rate in each case about 4-5 min slower than that of Ikappa Balpha degradation. IL-1 receptor antagonist and anti-TypeI IL-1 receptor antiserum on the one hand and anti-TNFalpha and monoclonal anti-TNF receptor 1 antibodies on the other hand could be shown to respectively inhibit IL-1 and TNFalpha stimulation in both cell types. In contrast, a polyclonal anti-TNF receptor 1 antiserum exhibited both a 50% agonism and a 50% antagonism to a TNFalpha stimulation in a dose-dependent fashion, indicating that subtle functional responses to complex agonist and antagonist stimuli could be measured. The effects of different proteasome inhibitors to prevent Ikappa Balpha degradation and subsequent NF-kappaB translocation could also be discriminated; Leu-Leu-Leu aldehyde was only a partial inhibitor with an IC50 of 2 microM, while clastolactacystin beta-lactone was a complete inhibitor with an IC50 of 10 microM. The nonselective kinase inhibitor K252a completely inhibited both IL-1 and TNFalpha stimulation in both cell types with an IC50 of 0.4 microM. This concentration, determined after a 20-min stimulation, was shown to be comparable with that obtained for inhibition of IL-6 production induced by a 100-fold lower IL-1 and TNFalpha concentration measured after 17 h of stimulation. These results suggest that the ArrayScanTM technology provides a rapid, sensitive, quantitative technique for measuring early events in the signal transduction of NF-kappaB.

Evaluation of the solid hepatic mass

With the expanding use of abdominal imaging studies, evaluation of solid hepatic masses has become a common clinical challenge. In this review, the clinicopathologic characteristics of the most common causes of solid hepatic masses have been discussed. As the case scenarios demonstrate, the appropriate selection of imaging techniques and proper management of an individual patient depend on the clinical context. Often, complementary radiologic studies are necessary to narrow the differential diagnosis. Percutaneous biopsy or surgery is frequently required to confirm the diagnosis and to exclude malignancy definitively. The evaluation and management of solid hepatic masses is a cooperative venture that requires a multidisciplinary approach.

Post-transfusion acquired malaria complicating orthotopic liver transplantation

Early infectious complications within the first 3 months of orthotopic liver transplantation are common and are associated with significant morbidity and mortality. Here we report the first case of transfusion-acquired malaria in an orthotopic liver transplantation recipient. The patient was found to have Plasmodium ovale malaria during evaluation of a severe febrile illness. The infection was traced to a platelet transfusion and responded to treatment with chloroquine. Risk factors associated with the development of malaria infection are identifiable and should be reviewed from the recipient and donor when possible. Routes of infection in the liver transplant patient would include blood products, the organ itself, and resurgence of latent infection. Theoretically, immunosuppression may have an impact on the disease process. Clinicians caring for these patients need to have a high index of suspicion in order to diagnose and treat malaria effectively in the post-transplant setting. Although rare, malaria should be added to the list of pathogens that can infect organ transplant recipients.

Nuclear imaging of solid hepatic masses

This review has focused on the unique role of radionuclide scintigraphy in characterization of hepatic mass lesions. Radionuclide scintigraphy, unlike most other imaging modalities, is based on specific physiological and biochemical properties of each pathological entity that affects the liver. Hepatic scintigraphy, with its widespread availability, noninvasive nature, and relatively low cost is a powerful adjunct to other imaging techniques in the investigation of hepatic mass lesions. We have reviewed clinical presentation and characteristic findings of most hepatic lesions and have described reported findings with all available imaging modalities with particular emphasis on hepatic scintigraphy (Table 1) as well as a suggested algorithm for workup of solid hepatic masses (Fig 6). Additionally, the role of newer, more specialized techniques including PET scanning, 123I-labeled VIP, and 111In-labeled DTPA-D-Phe-octreotide scanning are reviewed. Hepatic nuclear scintigraphy continues to play an important role in the management of patients with solid hepatic masses.

Fatal Vibrio parahemolyticus septicemia in a patient with cirrhosis. A case report and review of the literature

Vibrio parahemolyticus has been well documented to cause outbreaks of infectious diarrhea, usually related to poor food handling; only rarely has it been reported to cause fetal septicemia. In contrast, Vibrio vulnificus is a well-known cause of septicemia, especially in patients with cirrhosis. A 31-year-old woman with cirrhosis who developed fatal V. parahemolyticus sepsis after ingesting raw seafood is described. We review the clinical syndromes associated with sepsis caused by these two organisms. Leg pain and bullous skin lesions may be a clue to the diagnosis. Febrile patients with cirrhosis should be questioned regarding recent seafood ingestion, and appropriate antibiotics chosen if this history is obtained. Physicians should inform patients at risk to avoid raw seafood in an attempt to prevent this potentially lethal syndrome.

Fast three-dimensional time-of-flight MR angiography of the intra-cranial vasculature

Magnetic resonance angiography is most commonly performed with the three-dimensional (3D) time-of-flight (TOF) technique. As currently practiced, this requires long image acquisition times (5-10 minutes). The authors show that the acquisition time of 3D TOF images can be reduced to less than 1 minute by using a very short TR (< 10 msec). Under normal flow conditions, the major vessels of the circle of Willis were consistently well demonstrated on these fast 3D TOF images. Signal saturation was observed in studies of patients with abnormal blood flow. In those cases, it was demonstrated that serial acquisition of fast 3D TOF data during and after contrast agent administration could be used to overcome the saturation effects. Time-resolved fast 3D TOF imaging during and after contrast agent administration can also provide qualitative assessment of flow and may depict other features that cannot be observed in TOF studies with long imaging times.

Transjugular intrahepatic portosystemic shunting: decreased survival for patients with high APACHE II scores

OBJECTIVES

To determine which clinical characteristics are associated with decreased survival after transjugular intrahepatic portosystemic shunting (TIPS).

METHODS

Forty-nine consecutive patients were treated with TIPS; 46 of them had refractory variceal bleeding. Univariate statistics and logistic regression analyses were used to determine the relationship between clinical, biochemical, and hemodynamic variables and 30-day) survival.

RESULTS

Shunt insertion was successful in 48 (98.0%) of 49 cases. Median portal-systemic gradient was reduced from 22.5 (range 9-36) [median (5th-95th percentile)] to 12 (range 4-20) mm Hg. Thirty (61.2%) of 49 patients survived more than 30 days; four patients died more than 30 days after TIPS in mean follow-up of 8.4 months. Significant differences (p < 0.05) were found between those who survived more than 30 days and those who did not, with respect to preprocedural prothrombin time, bilirubin, albumin, alanine aminotransferase, and treatment with vasopressin and nitrates, balloon tamponade, or mechanical ventilation. Whereas there were no significant differences between the pre- and post-TIPS portal vein pressures and portal-systemic gradients in survivors and non-survivors, the pre- and post-TIPS hepatic vein pressures were significantly lower in survivors. Survival was inversely proportional to Child-Pugh class (p < 0.01) and to APACHE II score (p < 0.01). The single determinant most closely associated with decreased survival in the month after TIPS was the APACHE II score, a score of 18 stratifying patients into those at low and high risk of mortality [odds ratio 21.7 (CI 3.6-131.7)]. Only 1 (7.7%) of 13 patients with Child-Pugh C cirrhosis and an APACHE II score exceeding 18 survived more than 30 days.

CONCLUSIONS

Patients with advanced cirrhosis, especially those with high pre-TIPS APACHE II scores, are at high risk for reduced survival after TIPS, despite adequate portal decompression.

Ursodiol for hepatobiliary disorders

PURPOSE

To explain the rationale supporting the use of ursodiol (ursodeoxycholic acid) for the treatment of patients with cholesterol gallstones and chronic liver diseases and to describe the results obtained in clinical trials.

DATA SOURCES

Personal databases of the authors and MEDLINE were used to identify relevant English-language articles.

STUDY SELECTION

Randomized controlled trials evaluating ursodiol for the treatment of patients with cholesterol gallstones and chronic liver diseases were emphasized.

DATA SYNTHESIS

Ursodiol is at least as effective as chenodiol (chenodeoxycholic acid) for the dissolution of cholesterol gallstones and is associated with fewer adverse effects. Ursodiol desaturates bile, solubilizing cholesterol from the stone surface. The diameter of the largest stone is the most important determinant of successful dissolution. Dissolution with ursodiol is effective for approximately 30% to 50% of stones smaller than 20 mm in diameter, with the best results for small, buoyant stones. A meta-analysis of randomized trials with ursodiol found that the dissolution rate was 37% for patients treated with ursodiol at doses of more than 7 mg/kg per day or of more than 500 mg/d for at least 6 months. Maintenance therapy is effective for prevention of gallstone recurrence. Ursodiol also improves biochemical markers of cholestasis and inflammation when used to treat cholestatic liver diseases. By displacing potentially hepatotoxic bile salts, it appears to interrupt the cycle of cholestatic injury. It may also exert hepatoprotective membrane-stabilizing or immunomodulatory effects (or both). Improvements in laboratory variables are limited to the treatment period, with relapses after withdrawal of therapy. Pruritus may be markedly relieved in individual patients treated with ursodiol.

CONCLUSIONS

Ursodiol is a safe and effective therapy for the treatment of patients with cholesterol gallstones. Although treatment with ursodiol leads to improvement in biochemical markers for cholestatic liver diseases, whether it alters the natural history of these disorders is the subject of ongoing trials.

Intestinal varices: treatment with the transjugular intrahepatic portosystemic shunt

PURPOSE

To perform a retrospective evaluation of transjugular intrahepatic portosystemic shunt (TIPS) placement for treatment of intestinal varices.

MATERIALS AND METHODS

TIPS were placed in nine patients (six women and three men, aged 36-85 years [mean, 64 years]) with small- (n = 6) and large- (n = 3) intestinal varices. Six patients were actively bleeding at the time of shunt placement. One patient with colon cancer underwent prophylactic TIPS placement for variceal decompression before colectomy.

RESULTS

The mean preprocedure portosystemic gradient of 26.8 mm Hg +/- 5.1 was reduced to 8.8 mm Hg +/- 2.9. Bleeding was controlled in all but one case, in which supplemental variceal embolization was required. Two patients died within 5 days of TIPS placement of preexisting multisystem failure. Three patients died of unrelated causes at 2, 6, and 7 months. The remaining patients were alive an average of 15 months after TIPS placement. There was no recurrent bleeding in any case.

CONCLUSION

TIPS placement is an effective method of decompressing intestinal varices.

Chronic hepatitis C. Advances in diagnostic testing and therapy

The methods for diagnosing hepatitis C virus infection have been evolving since the first-generation enzyme-linked immunosorbent assay antibody test was devised in 1989. In addition to assaying for serum antibodies against viral proteins, serum and liver tissue can be tested for viral RNA, evidence of ongoing viral replication. The improving ability to diagnose hepatitis C has furthered the understanding of the natural history of this infection. Acute hepatitis C results in chronic elevations of serum transaminase levels following nearly one half of cases. Cirrhosis complicates approximately 20% of chronic infections. Long-standing chronic hepatitis C may play a role in the pathogenesis of hepatocellular carcinoma. Sustained normalization of serum transaminase levels, often accompanied by a decrease in or disappearance of viral RNA, occurs in approximately 25% of patients with chronic hepatitis C who are treated with a 6-month course of recombinant interferon alfa. This treatment can occasionally be complicated by hematologic, endocrinologic, and psychiatric adverse effects but is usually fairly well tolerated. Whether interferon therapy will diminish the risk of cirrhosis or carcinoma is not yet known. This article reviews the diagnosis of chronic hepatitis C infection as well as the mechanisms of action, efficacy, and adverse effects associated with interferon alfa therapy.

Hepatic arterial injury after transjugular intrahepatic portosystemic shunt placement: report of two cases

Transjugular intrahepatic portosystemic shunts (TIPS) were placed in two patients for treatment of variceal hemorrhage and refractory ascites. In both patients, branches of the right hepatic artery were inadvertently punctured during portal vein localization. In one case, right hepatic artery occlusion resulted in irreversible liver failure. In the other case, intraperitoneal bleeding resulted from the arterial injury. Embolization could not be performed due to celiac axis occlusion. Four days after surgical repair, the patient died of multiorgan failure. Hepatic arterial injuries are a serious complication of TIPS creation. Aggressive efforts to recanalize occlusions and superselective embolization of extravasation are recommended.

Recurrent bleeding from anorectal varices: successful treatment with a transjugular intrahepatic portosystemic shunt

Anorectal varices are portal-systemic collaterals commonly found in patients with portal hypertension. Although these varices rarely bleed, when bleeding does occur it may be massive and life threatening. Anorectal varices may be mistaken for hemorrhoids and there is no agreed upon method for their definitive diagnosis. Additionally, there is no standard therapy for bleeding anorectal varices, and when techniques designed for the control of hemorrhoidal bleeding are employed the results can be disastrous. We report here the first use of a transjugular intrahepatic portosystemic shunt (TIPS) for the permanent control of bleeding anorectal varices. Magnetic resonance imaging/magnetic resonance venography (MRI/V) was used as a non-invasive method for the identification of anorectal varices and to confirm the successful decompression of these varices with TIPS placement. MRI/V and TIPS may provide significant advances in the diagnosis and treatment of rectal variceal bleeding.

Scintigraphic evaluation of liver masses: cavernous hepatic hemangioma

Hepatic cavernous hemangioma must be included in the differential diagnosis of any hepatic solid mass. It is the second most common neoplasm of the liver, following intrahepatic metastases. With the exception of giant or symptomatic HCH, it does not require specific intervention. The ability to diagnose HCH radiologically (Table 2) has significant clinical importance. When confronted with clinical data and a preliminary radiologic study suggestive of HCH, serial planar blood-pool scintigraphy (with SPECT if the lesion is < 3-4 cm) should probably be the initial diagnostic examination. In comparison to MRI, it is safer, less expensive and easier for some patients to tolerate. For small, deep seated lesions or those adjacent to the heart or large vessels, MRI is the preferred test. Dynamic CT is probably most useful in patients with normal renal function in whom optimal imaging of the extrahepatic abdomen is desired. If the etiology of an incidental hepatic mass suspected to be an HCH is still not evident after these studies, angiography or biopsy are the remaining options. As described, angiography is sensitive and relatively specific for HCH. Although percutaneous biopsy may be associated with increased risk of bleeding, fine-needle biopsy has been shown to be safe for hemangiomas. However, fine-needle biopsy is more useful for confirming a suspected malignancy than for actually diagnosing hemangioma.

Primary aortoduodenal fistula: a unique presentation of a pseudoaneurysm associated with cystic medial necrosis

A 42-yr-old man who exsanguinated from an acute upper gastrointestinal bleed was found to have a primary aortoduodenal fistula on postmortem examination. The fistula arose in an aortic pseudoaneurysm associated with cystic medial necrosis. Although there was no suggestion of Marfan's syndrome on physical examination, there was cystic medial necrosis of not only the involved aorta, but also other systemic arteries. Primary aortoduodenal fistula is a rare cause of acute upper gastrointestinal bleeding and is usually associated with atherosclerotic disease of the aorta. This is the first report of a pseudoaneurysm associated with cystic medial necrosis presenting as an aortoduodenal fistula.

Acute esophageal obstruction: a unique presentation of a giant intramural esophageal leiomyoma

We report the case of a 33-yr-old man who presented with an acute incomplete esophageal obstruction, mimicking food impaction, who was found to have a giant intramural esophageal leiomyoma. The leiomyoma was successfully removed through a longitudinal esophagotomy. This is the first report of a nonpedunculated intramural esophageal leiomyoma presenting as an acute esophageal obstruction.

Effect of glycemic control on the overnight dexamethasone suppression test in patients with diabetes mellitus

Because many of the clinical features associated with Cushing's syndrome are frequently found in patients with diabetes mellitus, diabetic patients are often evaluated for Cushing's syndrome. The initial test for Cushing's syndrome is the 1 mg overnight dexamethasone suppression test (DST), but its value as a screening test in diabetic subjects, especially those with poor glycemic control, has been questioned. To address this issue, an overnight DST was administered to 100 subjects with diabetes. Only 7 patients failed to suppress their plasma cortisol to less than 140 nmol/L (5.0 micrograms/dL), achieving a specificity of 93%. There was no relation between acute glycemic control (as measured by the mean of 4 serum glucose values obtained before receiving dexamethasone) or chronic glycemic control (as measured by glycohemoglobin) and false positive responses to the 1 mg overnight DST. The mean of the measures of acute glycemic control of the 7 subjects who had false positive results, 14.4 +/- 2.8 mmol/L, was not significantly different than that of the 93 subjects with normal responses, 13.2 +/- 3.3 mmol/L. Similarly, the mean glycohemoglobin of the subjects with false positive results, 12.8 +/- 2.4%, was not significantly different than that of the subjects with normal responses, 12.9 +/- 2.5%. There was no correlation between plasma cortisol after dexamethasone and glycohemoglobin (r = 0.05), and only a weak correlation with the mean serum glucose (r = 0.21). We conclude that the 1 mg overnight DST is a valid screening test for Cushing's syndrome in patients with diabetes, regardless of glycemic control.

Diagnostic role of gadolinium-DTPA in pediatric neuroradiology. A retrospective review of 655 cases

We retrospectively reviewed the findings in 655 consecutive young patients who underwent contrast-enhanced MR examinations (1.5T) of the head or spine. Their ages ranged from 4 months to 20 years (mean 10 years). There was a 1.7% incidence of minor adverse reactions to gadolinium (Gd)-DTPA, none of which required treatment; no serious adverse reactions were encountered. Based on the radiologic diagnosis the patients were divided into three groups: (1) normal, (2) CNS neoplasm, (3) abnormal but not neoplasm. There were 178 patients thought to have CNS neoplasms and of these 156 (88%) enhanced. Of 124 histologically confirmed neoplasms 115 (93%) showed enhancement after Gd-DTPA. Eight children had histologically confirmed spinal neoplasms; 5 of 6 neurofibromas and 2 ependymomas enhanced. In the 216 patients with abnormalities thought not to be neoplastic, the enhancement rate was 11%; most of the enhancing lesions were vascular malformations. There were very few examples of inflammatory disease, acute trauma or stroke among our patients.

Tet protein domains interact productively to mediate tetracycline resistance when present on separate polypeptides

Both domains, alpha and beta, of the cytoplasmic membrane-localized Tet proteins encoded by the tet gene family (classes A through E) are required for resistance to tetracycline (Tcr) in gram-negative bacteria. Two inactive proteins, each containing a mutation in the opposite domain, are capable of complementation to produce Tcr. Similarly, inactive hybrid proteins expressed by interdomain gene hybrids constructed between tet(B) and tet(C) [tet(B) alpha/(C) beta and tet(C) alpha/(B) beta] together produce significant Tcr via trans complementation (R.A. Rubin and S. B. Levy, J. Bacteriol. 172:2303-2312, 1990). A derivative of tet(B) was constructed to express the two domains of Tet(B) as separate polypeptides, neither containing intact the central, hydrophilic interdomain region. Cells harboring this tet(B) mutant expressed Tcr at about 20% the level conferred by intact tet(B). As expected, no detectable amount of a full-length Tet protein was expressed. A polypeptide corresponding to the alpha domain was observed. Interdomain hybrids between tet(B) and tet(C) containing a frameshift at the fusion junction, designed to result in expression of each of the four domains on separate polypeptides, showed trans complementation without production of detectable full-length proteins. Levels of Tcr were greater than or equal to those previously observed in complementations using full-length hybrid proteins. These results strongly suggest that polypeptides harboring individual alpha and beta domains, lacking an intact interdomain region, can interact productively in the cell to confer Tcr.

Susceptibility to subacute thyroiditis is genetically influenced: familial occurrence in identical twins

Subacute thyroiditis is thought to be virally induced in genetically predisposed individuals because a strong association has been suggested recently between HLA-B35 and patients in whom subacute thyroiditis has developed. Two identical twin brothers were seen at our clinic with the same symptoms and date of onset of hyperthyroidism and enlargement and tenderness of the thyroid, which gave us a unique opportunity to study the genetic predisposition and treatment of this thyroid disease. Diagnostic criteria for subacute thyroiditis were met in both twins, including hyperthyroxinemia, suppression of thyroidal 123I uptake, increased erythrocyte sedimentation rate, transient painful goiter, and absence of antimicrosomal antibodies. Twin B was treated with corticosteroids, and a nonsteroidal anti-inflammatory agent was prescribed for Twin A. The mode of treatment used did not make a difference in affecting the course of the disease. The erythrocyte sedimentation rate was normal after 2 months from onset of symptoms. Results of viral studies were inconclusive. The same HLA typing was found in each twin: A3, B18, B35, Cw4, DR2, DRw10, DQw1. Thus, each was heterozygous for HLA-B35. We reviewed the literature and found a strong association between HLA-B35 and subacute thyroiditis in various ethnic groups tested. Our experience with these identical twins provides additional evidence to suggest that HLA-35 and perhaps Cw4 confer genetic susceptibility in acquiring subacute painful thyroiditis in a possible dominant mode of inheritance.

Decreased activity of Reiter's syndrome after urethrectomy

Reiter's syndrome is a chronic rheumatic disease that develops after infective urethritis or gastroenteritis and has a strong association with the HLA-B27 antigen. How these factors interact remains unclear. We present a patient with Reiter's syndrome who exhibited 2 novel features: unusually severe urethritis that produced strictures requiring surgery, and dramatic regression of his rheumatic manifestations following a urethrectomy.

Interdomain hybrid Tet proteins confer tetracycline resistance only when they are derived from closely related members of the tet gene family

Inner membrane Tet proteins encoded by tet genes in gram-negative bacteria mediate resistance to tetracycline (Tcr) by directing its export. Total sequences for class A, B, and C tet genes demonstrate that their products have a common ancestor, with Tet(A) and Tet(C) being more closely related (78% identical) than either is to Tet(B) (45% identical). The N- and C-terminal halves of Tet(B) and Tet(C) appear to comprise separate domains, and trans-complementation observed between tetracycline sensitive mutants in either domain of Tet(B) suggests separate but interactive functions for these domains. In this present study, interdomain hybrid genes were constructed to express hybrid tet products whose N- and C-terminal halves were derived from different family members [Tet(A/C), Tet(B/C), and Tet(C/B)]. Tet(A/C) specified a level of Tcr comparable to wild-type Tet(C) and 60% that of Tet(A), indicating that domains from these closely related tet products can function in cis. Although neither Tet(B/C) nor Tet(C/B) hybrids conferred significant Tcr, cells producing both of these types of hybrid proteins expressed substantial Tcr, indicating that productive interactions can occur in trans between Tet(B/C) and Tet(C/B). Taken together, these results suggest that highly specific interactions between the N- and C-terminal domains are necessary for Tcr and do not occur in individual hybrids derived from the more distant relatives, Tet(B) and Tet(C). This requirement for specific interactions suggests that N- and C-terminal domains have coevolved in each member of the Tet family.

Gene duplication in the evolution of the two complementing domains of gram-negative bacterial tetracycline efflux proteins

The resistance of Gram- bacteria to the broad-spectrum antibiotic tetracycline (Tc) results from energy-dependent drug efflux mediated by the tet gene product, the cytoplasmic membrane Tet protein. Amino acid (aa) sequences deduced from total tet nucleotide sequences of three different resistance determinants (classes A, B and C) indicate that the protein products [Tet(A), Tet(B), and Tet(C)] share a common ancestor. Hydropathic analysis of Tet sequences predicts twelve transmembrane segments in each protein, with six occurring in each half of the molecule. More importantly, the linear distributions of these segments in the N- and C-terminal halves are nearly identical, suggesting that the two halves of each Tet protein are related by a process of tandem gene duplication and divergence. Indeed, a variable but significant conservation of sequence was detected among the N- and C-terminal halves for all possible comparisons of the three proteins. Such conservation was not observed within other prokaryotic integral membrane proteins or when other prokaryotic proteins were compared to Tet halves. Similarity, both in sequence and in predicted transmembrane structural organization, strongly suggests that a common ancestor of Tet(A), Tet(B), and Tet(C) arose by duplication of a gene reading frame specifying a transmembrane protein of approximately 200 aa residues. The two halves of Tet proteins correspond to the two domains, alpha and beta, which have distinct, complementary roles in Tc efflux. Nevertheless, selective constraints to function in the cytoplasmic membrane have apparently led to maintenance of similar patterns of secondary structural organization in these complementary domains.

Genetic analysis of the gentamicin resistance region of pPH1JI and incorporation into a wide host range cloning vehicle

A region of the IncP plasmid pPH1JI encoding resistance to gentamicin, spectinomycin, and streptomycin was characterized by subcloning, deletion, and insertion mutagenesis. Approximate locations of these resistance determinants were established. A 1.6-kb HindIII-SphI segment of this region expresses gentamicin resistance (Gmr) in Escherichia coli when inserted into various plasmid vectors; this DNA segment encodes a polypeptide of 17.5 kDa. Incorporation of this fragment into an IncP cloning vehicle produced a Gmr wide host range vector, pRAR209, which confers levels of Gmr comparable to those expressed by pPH1JI in E. coli, Agrobacterium tumefaciens, and Rhizobium meliloti.

Epidermal growth factor (EGF) stimulates EGF receptor synthesis

Epidermal growth factor (EGF) binds to the extracellular domain of a specific 170,000-dalton transmembrane glycoprotein; this results in rapid removal of both ligand and receptor from the cell surface. In WB cells, a rat hepatic epithelial cell line, ligand-directed receptor internalization leads to receptor degradation. We tested whether the EGF receptor was replenished at a constitutive or enhanced rate following EGF binding by immunoprecipitating biosynthetically labeled EGF receptor from cells cultured with [35S]methionine. EGF stimulated receptor synthesis within 2 h in a dose-dependent manner; this was particularly evident when examining the nascent form of the receptor. To determine the site of EGF action, total WB cell RNA was transferred to nitrocellulose paper after electrophoresis and was hybridized to cDNA probes from both the external and cytoplasmic coding regions of the human EGF receptor. EGF increased receptor mRNA by 3-5-fold. Therefore, at least in some cells, the surface action of EGF that leads to EGF receptor degradation is counterbalanced by a positive effect on receptor synthesis.

Phosphorylation of the hepatic EGF receptor with cAMP-dependent protein kinase

The 170 000 dalton hepatic epidermal growth factor (EGF) receptor is phosphorylated on serine and tyrosine residues. The evidence indicates that distinct protein kinases are involved. Since EGF and agents that elevate cAMP are believed to participate in the regulation of liver regeneration, we tested whether or not the catalytic subunit of cAMP-dependent protein kinase (catalytic subunit), a known serine kinase, would utilize the EGF receptor as a substrate. The catalytic subunit increased phosphorylation of the EGF receptor in purified rat liver plasma membranes. The serine specificity of the catalytic subunit was established by phosphoamino acid analysis of electrophoretically purified EGF receptor. The result was confirmed by catalytic subunit phosphorylation of affinity purified preparations of the EGF receptor. The rates of dephosphorylation of the membrane-associated EGF receptor phosphorylated on different residues were compared. Dephosphorylation of serine residues (after catalytic subunit phosphorylation) was considerably slower (t1/2 greater than 120 sec) than the removal of phosphotyrosine after stimulation with EGF (t1/2 less than 30 sec).

Thermodynamic parameters governing interaction of EcoRI endonuclease with specific and nonspecific DNA sequences

Equilibrium binding of EcoRI endonuclease to DNA has been analyzed by nitrocellulose filter and preferential DNA cleavage methods. Association constants for pBR322 and a 34-base pair molecule containing the EcoRI site of this plasmid in a central position were determined to be 1.9 X 10(11) M-1 and 1.0 X 10(11) M-1 at 37 degrees C, respectively, with the stoichiometry of binding being 0.8 +/- 0.1 mol of endonuclease dimer per mol of DNA. In contrast, the affinity of the enzyme for a pBR322 derivative from which the EcoRI site has been deleted is 3.2 X 10(9) M-1 as judged by competitive binding experiments. If it is assumed that each base pair can define the beginning of a nonspecific binding site, this value corresponds to an affinity for nonspecific sites of 7.4 X 10(5) M-1. Furthermore, the affinity of the endonuclease for the EcoRI-methylated sequence is at least three orders of magnitude less than that for the unmodified recognition site. The dependence on temperature and ionic strength of the equilibrium constant governing specific interactions has also been examined. The temperature dependence of the reaction indicates that entropy increase accounts for 70% of the free energy of specific binding at 37 degrees C. Affinity of the endonuclease for the EcoRI site is highly dependent on NaCl concentration. Analysis of this dependence according to the theory of Record and colleagues (Record, T. M., Jr., Lohman, T. M., and deHaseth, P. (1976) J. Mol. Biol. 107, 145-158) has implicated 8 ion pairs in the stability of specific complexes, a value identical with the number of phosphate contacts determined by ethylation interference analysis (Lu, A. L., Jack, W. E., and Modrich, P. (1981) J. Biol. Chem. 256, 13200-13206). Extrapolation to 1 M NaCl suggests that nonelectrostatic interactions account for 40% of the free energy change associated with specific complex formation.