Microvascular inflammation and acute tubular necrosis are major histologic features of hantavirus nephropathy

The role of peritubular capillaritis in severity of lupus nephritis

Background & ObjectivePresence of lupus nephritis is associated with a shorter time to death in systemic lupus erythematosus. The aim of this study was to determine the frequency of peritubular capillaritis (ptc) and its relationship with both active and chronic lesions in lupus nephritis.Material-MethodsSpecimens from 57 patients were re-evaluated. The degree of inflammation within the peritubular capillaries in each biopsy was assessed according to the Banff classification, and ptc scoring was performed. Additionally, patients were grouped based on high/low activity and chronicity index scores.ResultsForty-five (78.9%) of the patients were female, with a mean age of 27.43 years. Ptc was identified in 45 (78.9%) patients, with ptc scores of 1, 2, and 3 observed in 20 (35.08%), 20 (35.08%), and 5 (8.7%) patients, respectively. Severe ptc (scores 2 or 3) was more commonly detected in patients with elevated serum creatinine (>1.20 mg/dL) compared to those with normal creatinine levels (92.3% vs 29.5%, p < 0.001). The severity of ptc was higher in Class 4 patients than in Class 3 patients (68.2% vs 21.7%, p = 0.005). The rate of high ptc scores was greater in patients with an activity index of 6 or above compared to those with an activity index below 6 (62.5% vs 30.3%, p = 0.032). No significant correlation was found between the chronicity index and ptc.ConclusionsThe findings of this study suggest that ptc is a frequently observed pathological feature in patients with lupus nephritis. Furthermore, the severity of ptc appears to be positively associated with elevated serum creatinine levels, and higher ptc scores are more commonly detected in cases with a high activity index.

A specific molecular signature in SARS-CoV-2-infected kidney biopsies

Acute kidney injury is one of the most important complications in patients with COVID-19 and is considered a negative prognostic factor with respect to patient survival. The occurrence of direct infection of the kidney by SARS-CoV-2, and its contribution to the renal deterioration process, remain controversial issues. By studying 32 renal biopsies from patients with COVID-19, we verified that the major pathological feature of COVID-19 is acute tubular injury (ATI). Using single-molecule fluorescence in situ hybridization, we showed that SARS-CoV-2 infected living renal cells and that infection, which paralleled renal angiotensin-converting enzyme 2 expression levels, was associated with increased death. Mechanistically, a transcriptomic analysis uncovered specific molecular signatures in SARS-CoV-2-infected kidneys as compared with healthy kidneys and non-COVID-19 ATI kidneys. On the other hand, we demonstrated that SARS-CoV-2 and hantavirus, 2 RNA viruses, activated different genetic networks despite triggering the same pathological lesions. Finally, we identified X-linked inhibitor of apoptosis-associated factor 1 as a critical target of SARS-CoV-2 infection. In conclusion, this study demonstrated that SARS-CoV-2 can directly infect living renal cells and identified specific druggable molecular targets that can potentially aid in the design of novel therapeutic strategies to preserve renal function in patients with COVID-19.

Peritubular Capillaritis in Native Kidney Biopsies

OBJECTIVES

To determine the frequency and predictors of peritubular capillaritis (PTCitis) among native kidney biopsies.

METHODS

Consecutive native kidney biopsies of 169 patients were reexamined for capturing possible PTCitis according to the Banff Classification. The relation of PTCitis with demographic and clinicopathological findings was evaluated. Logistic regression analysis was performed to determine predictors of PTCitis.

RESULTS

Peritubular capillaritis was captured in 90 (53.3%) patients, with scores of 1, 2, and 3 in 57 (33.7%), 31 (18.3%), and 2 (1.2%) patients, respectively. The highest frequency of PTCitis was observed in pauci-immune glomerulonephritis. In univariate analysis, male sex, the presence of interstitial inflammation, pauci-immune glomerulonephritis, and a higher serum creatinine level were associated with a higher risk of PTCitis, while severe interstitial fibrosis/tubular atrophy was associated with a lower risk. The presence of interstitial inflammation (odds ratio [OR], 5.94 [95% confidence interval (CI), 1.41-25.03]; P = .015), pauci-immune glomerulonephritis (OR, 3.08 [95% CI, 1.01-9.36]; P = .048), and a higher serum creatinine level (per 1 mg/dL) (OR, 1.56 [95% CI, 1.14-2.11]; P = .005) were independent predictors of PTCitis development in a multivariate regression model.

CONCLUSIONS

Peritubular capillaritis is common in native biopsies and more likely to be observed in the presence of interstitial inflammation, pauci-immune glomerulonephritis, and a higher serum creatinine level.

OUP accepted manuscript

Hantavirus-induced diseases are emerging zoonoses with endemic appearances and frequent outbreaks in different parts of the world. In humans, hantaviral pathology is characterized by the disruption of the endothelial cell barrier followed by increased capillary permeability, thrombocytopenia due to platelet activation/depletion and an overactive immune response. Genetic vulnerability due to certain human leukocyte antigen haplotypes is associated with disease severity. Typically, two different hantavirus-caused clinical syndromes have been reported: hemorrhagic fever with renal syndrome (HFRS) and hantavirus cardiopulmonary syndrome (HCPS). The primarily affected vascular beds differ in these two entities: renal medullary capillaries in HFRS caused by Old World hantaviruses and pulmonary capillaries in HCPS caused by New World hantaviruses. Disease severity in HFRS ranges from mild, e.g. Puumala virus-associated nephropathia epidemica, to moderate, e.g. Hantaan or Dobrava virus infections. HCPS leads to a severe acute respiratory distress syndrome with high mortality rates. Due to novel insights into organ tropism, hantavirus-associated pathophysiology and overlapping clinical features, HFRS and HCPS are believed to be interconnected syndromes frequently involving the kidneys. As there are no specific antiviral treatments or vaccines approved in Europe or the USA, only preventive measures and public awareness may minimize the risk of hantavirus infection. Treatment remains primarily supportive and, depending on disease severity, more invasive measures (e.g., renal replacement therapy, mechanical ventilation and extracorporeal membrane oxygenation) are needed.

Flash-Like Albuminuria in Acute Kidney Injury Caused by Puumala Hantavirus Infection

Transient proteinuria and acute kidney injury (AKI) are characteristics of Puumala virus (PUUV) infection. Albuminuria peaks around the fifth day and associates with AKI severity. To evaluate albuminuria disappearance rate, we quantified albumin excretion at different time points after the fever onset. The study included 141 consecutive patients hospitalized due to acute PUUV infection in Tampere University Hospital, Finland. Timed overnight albumin excretion (cU-Alb) was measured during the acute phase in 133 patients, once or twice during the convalescent phase within three months in 94 patients, and at six months in 36 patients. During hospitalization, 30% of the patients had moderately increased albuminuria (cU-Alb 20-200 μg/min), while 57% presented with severely increased albuminuria (cU-Alb >200 μg/min). Median cU-Alb was 311 μg/min (range 2.2-6460) ≤7 days after fever onset, 235 μg/min (range 6.8-5479) at 8-13 days and 2.8 μg/min (range 0.5-18.2) at 14-20 days. After that, only one of the measurements showed albuminuria (35.4 μg/min at day 44). At six months, the median cU-Alb was 2.0 μg/min (range 0.6-14.5). Albuminuria makes a flash-like appearance in PUUV infection and returns rapidly to normal levels within 2-3 weeks after fever onset. In the case of AKI, this is a unique phenomenon.

Hantavirus Infection and the Renal Syndrome

Fever with renal syndrome is currently endemic in Eurasia, where the main etiological agents are the Hantaan and Seoul viruses in Asia (China, South Korea, and the Far East of Russia), in addition to the Seoul, Puumala, and Dobrava viruses in Europe (central, northern, Alpine Massif, Balkans, and western Russia). Lethality rates are higher with Hantaan and Dobrava virus infections (5–10%) when compared to the Puumala and Seoul viruses (1%). With the expansion and geographical migration of the urban rodent (Rattus norvegicus) from the “Old World,” the Seoul virus was introduced into the Americas and is now considered a virus with a cosmopolitan distribution. On the American continent, the presence of the Seoul virus has been confirmed in Brazil, Argentina, and the United States. The hantavirus transmission to humans occurs by inhalation of aerosol-dispersed viral particles present in rodent droppings and saliva. This disease should be clinically differentiated from leptospirosis and other viral hemorrhagic fevers that occur in the same areas of occurrence of hantavirus infections. There is no treatment with antiviral drugs specific for hantavirus. Faced to a suspected hantavirus case, it should be communicated to the local health authorities and provide an eventually intensive care unit support.

Seoul Virus Tropism and Pathology in Naturally Infected Feeder Rats

Seoul virus (SEOV) is a zoonotic orthohantavirus carried by black and brown rats, and can cause hemorrhagic fever with renal syndrome in humans. Human cases of SEOV virus infection have most recently been reported in the USA, United Kingdom, France and the Netherlands and were primarily associated with contact with pet rats and feeder rats. Infection of rats results in an asymptomatic but persistent infection. Little is known about the cell tropism of SEOV in its reservoir and most available data is based on experimental infection studies in which rats were inoculated via a route which does not recapitulate virus transmission in nature. Here we report the histopathological analysis of SEOV cell tropism in key target organs following natural infection of a cohort of feeder rats, comprising 19 adults and 11 juveniles. All adult rats in this study were positive for SEOV specific antibodies and viral RNA in their tissues. One juvenile rat was seropositive, but negative in the rRT-PCR. Of the 19 adult rats of which subsequently additional organs were tested, SEOV RNA was detected in all lungs, followed by kidney (79%) and liver (74%). Histopathologic changes associated with SEOV infection were primarily found in the liver, consistent with a pathological diagnosis of a mild hepatitis. In conclusion, natural SEOV infection results in mild inflammation of the liver in the absence of clinical disease.

Proteinuria and the Clinical Course of Dobrava-Belgrade Hantavirus Infection

Purpose

Human infection with Dobrava-Belgrade virus (DOBV) in Northern Germany causes a mild form of hantavirus disease predominantly characterized by acute kidney injury due to interstitial nephritis. We evaluated the largest number of DOBV-infected patients so far regarding clinical course, proteinuria, and prognostic markers.

Patients and Methods

Patients with DOBV-associated hantavirus disease admitted to the Renal Division of the University of Lübeck (Germany) between 1997 and 2012 were included in this study. Symptoms, clinical course, laboratory parameters, and urinary protein analysis were investigated at admission (baseline, t₀), 3–5 days (t_3–5), 10–17 days (t_10–17), and after 1 year of follow-up (t₃₆₅).

Results

Of the 34 patients (male/female ratio: 23/11; age: 41 ± 14 years) included in the study, 4 underwent hemodialysis (HD). Glomerular filtration rate was 17 ± 14 mL/min at t₀ and increased to 27 ± 26 mL/min (t_3–5), 57 ± 20 mL/min (t_10–17), and 84 ± 16 mL/min (t₃₆₅). Albuminuria and tubular proteinuria (α₁- and β₂-microglobulin) decreased during follow-up; the urinary α₁-microglobulin concentration in patients who required HD was significantly higher than that in patients not requiring HD (t₀: 186 ± 51 vs. 45 ± 26 mg/g creatinine; t_3–5: 87 ± 14 vs. 32 ± 16 mg/g creatinine; t_10–17: 63 ± 18 vs. 28 ± 12 mg/g creatinine; p < 0.001).

Conclusions

DOBV infection of inpatients in Northern Germany is associated with severe kidney injury that recovers within a few weeks and normalizes within 1 year. Tubular proteinuria is associated with the severity of kidney injury and the necessity of renal replacement therapy in these DOBV-infected patients.

Haematuria is a marker for the severity of acute kidney injury but does not associate with thrombocytopenia in acute Puumala hantavirus infection

BACKGROUND

Puumala hantavirus (PUUV) causes haemorrhagic fever with renal syndrome characterized by thrombocytopenia, capillary leakage and acute kidney injury (AKI) with proteinuria and haematuria. Although the typical histologic lesion is acute tubulointerstitial nephritis, the amount of glomerular proteinuria predicts the severity of upcoming AKI. Here, we studied the associations of haematuria and proteinuria with the severity of emerging AKI, thrombocytopenia and markers of coagulation and fibrinolysis in PUUV infection.

METHODS

We examined 205 consecutive patients treated for serologically confirmed acute PUUV infection at Tampere University Hospital during 1997-2014. The patients were divided into three groups according to the combined positive result in urine haemoglobin and albumin dipstick tests: 0-2 + (n = 58), 3-4 + (n = 100) and 5-6 + (n = 47).

RESULTS

The medians of maximum creatinine concentrations in the three groups were: 0-2 + 100 μmol/L (range 52-1499), 3-4 + 204 μmol/L (range 65-1071) and 5-6 + 361 μmol/l (range 51-1285) (p < .001). The number of blood platelets (p = .069), and the levels of fibrinogen, prothrombin fragments F1 + 2 and d-dimer (p = .602, p = .113, p = .289, respectively) were not significantly different between the groups. When the amount of haematuria in the dipstick test was examined separately, no association with thrombocytopenia was detected (p = .307 between groups 0, 1+ and 2-3+).

CONCLUSIONS

Combined positive result of haematuria and proteinuria in the dipstick test at hospital admission predicted the severity of upcoming AKI in acute PUUV infection. As haematuria was not associated with the severity of thrombocytopenia, it did not indicate increased bleeding tendency, but was rather a marker of acute kidney injury.

Kidney disease in Puumala hantavirus infection

Acute kidney injury (AKI) remains a predominant clinical expression of nephropathia epidemica (NE). Its pathogenesis is not yet fully understood. Here, we describe the tissue injury comprehensively and present new data aimed to characterize the injury and explain its pathophysiology. When compared to tubulointerstitial nephritis of a wide variety of other aetiologies, a high degree of proteinuria is a distinguished trait of NE, a finding that is also helpful in the clinical suspicion of the disease. Recently, novel biomarkers for the prediction of severe AKI, including neutrophil gelatinase-associated lipocalin (NGAL), have been identified and ultrastructural tissue changes have been more accurately described. A role for soluble urokinase-type plasminogen activator (suPAR) in the pathogenesis of NE has been suggested, and data on gene polymorphisms, in relation to the severity of AKI have been presented. Smoking is a risk factor for NE and smoking is also associated with aggravated AKI in NE. Although no specific treatment is in sight, recent case reports concerning therapy directed against vascular permeability and vasodilation are of interest. In fact, future work trying to explain the pathophysiology of AKI might need concentrated efforts towards the mechanisms of increased vascular permeability and vasodilatation, which irrespective of organ manifestation, are two major determinants of NE.

Acute Kidney Injury in Asia

BACKGROUND

Acute kidney injury (AKI) is a common disorder and is associated with a high morbidity and mortality worldwide. The diversity of the climate and of the socioeconomic and developmental status in Asia has a great influence on the etiology and presentation of AKI in different regions. In view of the International Society of Nephrology's 0by25 initiative, more and more attention has been paid to AKI in Asian countries.

SUMMARY

In this review, we summarize the recent achievements with regard to the prevalence and clinical patterns of AKI in Asian countries. Epidemiological studies have revealed the huge medical and economic burden of AKI in Eastern Asian countries, whereas the true epidemiological picture of AKI in the tropical areas is still not well understood. In high-income Asian regions, the presentation of AKI resembles that in other developed countries in Europe and North America. In low-income regions and tropical areas, infections, environmental toxins, and obstetric complications remain the major culprits in most cases of AKI. Preventive opportunities are missed because of failure to recognize the risk factors and early signs of AKI. Patients often present late for treatment or are recognized late by physicians, which leads to more severe kidney injury, multiorgan involvement, and increased mortality. There is significant undertreatment of AKI in many regions, and medical resources for renal replacement therapy are not universally available.

KEY MESSAGES

More efforts should be made to increase public awareness, establish preventive approaches in communities, educate health-care practitioner entities to achieve better recognition, and form specialist renal teams to improve the treatment of AKI. The choice of renal replacement therapy should fit patients' needs, and peritoneal dialysis can be practiced more frequently in the treatment of AKI patients.

FACTS FROM EAST AND WEST

(1) More than 90% of the patients recruited in AKI studies using KDIGO-equivalent criteria originate from North America, Europe, or Oceania, although these regions represent less than a fifth of the global population. However, the pooled incidence of AKI in hospitalized patients reaches 20% globally with moderate variance between regions. (2) The lower incidence rates observed in Asian countries (except Japan) may be due to a poorer recognition rate, for instance because of less systematically performed serum creatinine tests. (3) AKI patients in South and Southeastern Asia are younger than in East Asia and Western countries and present with fewer comorbidities. (4) Asian countries (and to a certain extent Latin America) face specific challenges that lead to AKI: nephrotoxicity of traditional herbal and less strictly regulated nonprescription medicines, environmental toxins (snake, bee, and wasp venoms), and tropical infectious diseases (malaria and leptospirosis). A higher incidence and less efficient management of natural disasters (particularly earthquakes) are also causes of AKI that Western countries are less likely to encounter. (5) The incidence of obstetric AKI decreased globally together with an improvement in socioeconomic levels particularly in China and India in the last decades. However, antenatal care and abortion management must be improved to reduce AKI in women, particularly in rural areas. (6) Earlier nephrology referral and better access to peritoneal dialysis should improve the outcome of AKI patients.