Renal clearances of inulin, polyfructosan-S and a polyethylene glycol (PEG 1,000) in the rat

Advances in targeted therapy for malignant lymphoma

The incidence of lymphoma has gradually increased over previous decades, and it ranks among the ten most prevalent cancers worldwide. With the development of targeted therapeutic strategies, though a subset of lymphoma patients has become curable, the treatment of refractory and relapsed diseases remains challenging. Many efforts have been made to explore new targets and to develop corresponding therapies. In addition to novel antibodies targeting surface antigens and small molecular inhibitors targeting oncogenic signaling pathways and tumor suppressors, immune checkpoint inhibitors and chimeric antigen receptor T-cells have been rapidly developed to target the tumor microenvironment. Although these targeted agents have shown great success in treating lymphoma patients, adverse events should be noted. The selection of the most suitable candidates, optimal dosage, and effective combinations warrant further investigation. In this review, we systematically outlined the advances in targeted therapy for malignant lymphoma, providing a clinical rationale for mechanism-based lymphoma treatment in the era of precision medicine.

History of hepatic bile formation: old problems, new approaches

Studies of hepatic bile formation reported in 1958 established that it was an osmotically generated water flow. Intravenous infusion of sodium taurocholate established a high correlation between hepatic bile flow and bile acid excretion. Secretin, a hormone that stimulates bicarbonate secretion, was also found to increase hepatic bile flow. The sources of the water entering the biliary system with these two stimuli were differentiated by the use of mannitol. An increase in its excretion parallels the increase in bile flow in response to bile acids but not secretin, which led to a quantitative distinction between canalicular and ductular water flow. The finding of aquaglyceroporin-9 in the basolateral surface of the hepatocyte accounted for the rapid entry of mannitol into hepatocytes and its exclusion from water movement in the ductules where aquaporin-1 is present. Electron microscopy demonstrated that bile acids generate the formation of vesicles that contain lecithin and cholesterol after their receptor-mediated canalicular transport. Biophysical studies established that the osmotic effect of bile acids varies with their concentration and also with the proportion of mono-, di-, and trihydroxy bile acids and provides a basis for understanding their physiological effects. Because of the varying osmotic effect of bile acids, it is difficult to quantify bile acid independent flow generated by other solutes, such as glutathione, which enters the biliary system. Monohydroxy bile acids, by markedly increasing aggregation number, severely reduce water flow. Developing biomarkers for the noninvasive assessment of normal hepatic bile flow remains an elusive goal that merits further study.

Assessment of renal function; clearance, the renal microcirculation, renal blood flow, and metabolic balance

Historically, tools to assess renal function have been developed to investigate the physiology of the kidney in an experimental setting, and certain of these techniques have utility in evaluating renal function in the clinical setting. The following work will survey a spectrum of these tools, their applications and limitations in four general sections. The first is clearance, including evaluation of exogenous and endogenous markers for determining glomerular filtration rate, the adaptation of estimated glomerular filtration rate in the clinical arena, and additional clearance techniques to assess various other parameters of renal function. The second section deals with in vivo and in vitro approaches to the study of the renal microvasculature. This section surveys a number of experimental techniques including corticotomy, the hydronephrotic kidney, vascular casting, intravital charge coupled device videomicroscopy, multiphoton fluorescent microscopy, synchrotron-based angiography, laser speckle contrast imaging, isolated renal microvessels, and the perfused juxtamedullary nephron microvasculature. The third section addresses in vivo and in vitro approaches to the study of renal blood flow. These include ultrasonic flowmetry, laser-Doppler flowmetry, magnetic resonance imaging (MRI), phase contrast MRI, cine phase contrast MRI, dynamic contrast-enhanced MRI, blood oxygen level dependent MRI, arterial spin labeling MRI, x-ray computed tomography, and positron emission tomography. The final section addresses the methodologies of metabolic balance studies. These are described for humans, large experimental animals as well as for rodents. Overall, the various in vitro and in vivo topics and applications to evaluate renal function should provide a guide for the investigator or physician to understand and to implement the techniques in the laboratory or clinic setting.

Split Renal Function Outcome after Renal Angioplasty in Patients with Unilateral Renal Artery Stenosis

Abstract. The general use of bilateral rather than separate renal function evaluation has led to the publication of conflicting results concerning the effect of percutaneous transluminal renal angioplasty (PTRA) on renal function, especially in patients with atherosclerotic renal artery stenosis. The aim of this study was to evaluate prospectively, in standardized conditions, split renal function (SRF) and GFR outcome after successful PTRA, by measuring single kidney GFR with synchronous inulin or 51Cr-ethylenediaminetetraacetic acid clearance and 99mTc-diethylenetriamine pentaacetic acid scintigraphy, in a well-defined population of patients with unilateral renal artery stenosis. Thirty-two consecutive hypertensive patients (18 with atherosclerotic and 14 with dysplastic disease) with significant unilateral stenosis of the main native renal artery (≥60%) and normal renal function were included in the study. Renal and angiographic follow-up evaluations were performed 6 mo after PTRA. PTRA alone or combined with stenting (n = 2) was technically successful in all patients. Repeat PTRA was necessary in two patients, evaluated 6 mo after the second PTRA. Six mo after PTRA, total GFR had increased slightly but significantly in the 29 patients with positive lateralization indices. SRF and single-kidney GFR of the stenotic kidney increased significantly, whereas concurrently the GFR and SRF of the nonstenotic kidney decreased significantly. Six mo after successful PTRA reducing renal ischemia, a reversal of both the hypoperfusion of the stenotic side and the hyperperfusion of the nonstenotic side was observed, which was accompanied by a slight increase in total GFR.

Determination of low levels of poly(ethylene glycol) 400 in plasma and urine by capillary gas chromatography-selected ion-monitoring mass spectrometry after solid-phase extraction

A convenient and sensitive method for the quantitative determination of poly(ethylene glycol) 400 in plasma and urine with capillary gas chromatography-mass spectrometry has been developed. The sample preparation involves solid-phase extraction with subsequent derivatization with heptafluorobutyric anhydride, which proved to give the most stable derivative. The derivatization procedure was optimized using experimental design, and different solid-phase extraction columns were evaluated. The limit of quantitation was 1 micromol/l (0.4 microg/ml) for both plasma and urine.

[51Cr]EDTA for measuring total and single nephron glomerular filtration rate in the rat

Clearance and micropuncture experiments were performed in halothane anaesthetized rats. The aim was a comparison of paired estimates of glomerular filtration rate (GFR) from the renal clearance of [51Cr]EDTA (C[51Cr]EDTA) with simultaneous estimates of polyfructosan ((Inutest) CIn), 3H,-and 14C-labelled inulin clearance (C[3H]In and C[14C]In, respectively) and proximal tubular fluid/plasma concentration ratios (TF/P) of [51Cr]EDTA and TF/P ratios of 14C-labelled inulin measured in the same samples. C[51Cr]EDTA correlated well with, but underestimated CIn by approximately 10%. The correlation coefficient (r) was 0.92. C[51Cr]EDTA also correlated with, and underestimated C[14C]In by 6%, r = 0.88, whereas it overestimated C[3H]In by 5%, still with a close correlation (r = 0.92). Paired data on proximal (TF/P) ratios of [51Cr]EDTA and [14C]inulin were collected from early, mid and late proximal convolutions. The data were scattered around the line of identity, r = 0.91. It is concluded that [51Cr]EDTA is a valid alternative for estimates of total renal and single nephron GFR in rats and has the advantage of being less expensive than [14C]inulin.

The glomerular filterability of polyfructosan-S in immature infants

Gel chromatography was performed on 21 plasma, 5 urine and 3 spinal fluid samples from pre-term infants who had received intravenous polyfructosan-S (PF-S), in order to investigate whether all sizes of PF-S molecule are filtered at the glomerulus and penetrate deep extra-cellular fluid compartments. Plasma obtained after 24 h continuous infusion of PF-S had identical chromatograms to the aqueous solution, suggesting no glomerular hold-up of the largest molecules. PF-S had a broader chromatogram than inulin, suggesting that it has larger molecules. Urine and plasma samples obtained early after a single injection had an excess of high molecular weight polyfructoside, suggesting that small molecules penetrate deep extracellular fluid compartments more easily. Spinal fluid samples had an excess of low molecular weight polyfructoside, suggesting slow penetration of the largest molecules.

Impaired intestinal barrier function measured by differently sized polyethylene glycols in patients with chronic renal failure

The intestinal mucosa plays a fundamental role as the site for absorption of nutrients, and as an important barrier from potentially harmful agents in the intestinal lumen. Little is known of the permeability properties of the intestinal mucosa in uraemic patients. The intestinal permeability to differently sized polyethylene glycols (PEGs; range 326-1254 daltons) was studied in nine patients with chronic renal failure (24 hour endogeneous creatinine clearance 5-24 ml/minute). The maximum 24 hour urinary recovery of PEGs was decreased in the uraemic patients but relatively more of the larger than the smaller PEGs were found in these patients. The results suggest a reduced urinary recovery of PEGs caused by renal dysfunction but also a relatively increased intestinal permeability to larger PEGs in the uraemic patients.

Characterization of size-dependent exchange of PEG molecules between the blood and extravascular space in the pig

Different sized polyethylene glycols (PEGs) have been used as probe molecules in studies of size-dependent permeation through the intestinal wall and the glomerular membranes. We have curve-fitted a three-compartment model to the urinary recovery data following intravenous injection of different sized PEG molecules in the pig. The rate constants to and from the extravascular space demonstrate a strong size-dependent selectivity for PEG molecules less than 502 Da, but the rate constants to the urine are almost the same for all PEG molecules. This is discussed in relation to the selectivity in the glomerular filtration, distribution volume, and the use of PEG molecules as tracers in the permeability studies.

Extracellular volume, renal clearance and whole body permeability-surface area product in man, measured after single injection of polyfructosan

In 22 patients non-compartmental analysis was applied to plasma disappearance curves obtained after a single injection of polyfructosan to measure volume of distribution (Vd), renal clearance (Cl) and the whole body permeability-surface area product (PdS) of the indicator. It was found that introduction of the theoretical plasma concentration at time zero, calculated as the injected amount divided by the plasma water volume independently determined, to the curves was necessary to determine the initial slope of the curve and subsequently calculate the PdS. This 'initial phase' approximation had negligible effect on the calculations of Vd and Cl. The approximation, however, allowed extension of the non-compartmental analysis to include calculation of the whole body PdS. The whole body PdS for polyfructosan was found to be 0.68 ml/100g X min or 429 ml/min. Assuming a capillary surface area of the whole human body of 50 cm2g-1, the average whole body diffusional permeability coefficient, Pd, for polyfructosan was found to be: 0.23 X 10(-5) cm X sec-1.

Inulin single injection clearance. Microsample technique useful in children for determination of glomerular filtration rate

The agreement between single injection inulin (polyfructosan) clearance and two reference methods for glomerular filtration rate (GFR) determination, namely standard inulin constant infusion clearance and 51-Cr-EDTA single injection clearance, was investigated. Studies were also made to see whether different results were obtained when capillary and venous blood samples were used in the single injection clearance method. The investigation was made in children from one year of age, adult patients and volunteers. For the single injection technique with inulin or 51-Cr-EDTA, five to seven blood samples were taken in a period of up to 180 min after injection. A bi-exponential plasma disappearance curve was used for calculations of single injection clearances. Good agreement was obtained between venous inulin single injection clearance on the one hand, and standard inulin clearance (correlation coefficient r = 0.86) and 51-Cr-EDTA single injection clearance on the other (r = 0.85). With use of capillary blood samples in inulin single injection clearance, similar good agreement was obtained both with venous 51-Cr-EDTA and with venous inulin single injection clearance (r = 0.85 and r = 0.89 respectively). From these results we conclude that inulin single injection clearance is a reliable method for GFR determinations. This method is recommended, especially in children, as capillary blood samples can be used.

Renal clearances of 14C-inulin and polyfructosan in the rat. Effect of increased ureteral pressure

Polyfructosan has been used as a substitute for inulin in GFR determinations. However, the validity of this substitution in conditions where renal tubular permeability to other substances, such as mannitol, sucrose and other substances, such as mannitol, sucrose and iothalamate, is increased has not been tested. Experiments were performed on 8 rats to compare the clearances of polyfructosan (CPF) and 14C-inulin (CIN) during hydropenia, 3% BW saline expansion, elevation of one ureteral catheter by 30 cm, and following return of increased ureteral pressure to the control level. No significant difference between CPF and CIN could be detected except in the kidney subjected to increased ureteral pressure. However, the magnitude of this difference--which may relate to the different molecular weights of the two compounds--was so small that we conclude that the use of CPF, as an index of GFR, is no less reliable than CIN under the conditions tested.

Passage of inulin and p-aminohippuric acid through artificial membranes: implications for measurement of renal function

Diffusion of inulin and p-aminohippuric acid (PAH) in combined aqueous solution through artificial membranes was measured at room temperature and atmospheric pressure. The membranes had pore diameters of 26, 50, 100, 200, 250, 350, 510 or 990 A. The diffusion of PAH was only restricted with a pore size of 26 A, but inulin diffusion was restricted at 100 A. When diffusion of both solutes was unrestricted (pore diameter greater than or equal to 200 A), PAH diffused four times faster than inulin, and in restricted situations this ratio was even greater. The results of these diffusion studies allow the major and minor molecular dimensions of the solutes to be estimated. Filtration of the two solutes was studied in slowly flowing situations and also with increased temperature and pressure. Pore sizes required for unrestricted filtration were the same as for unrestricted diffusion but the passage ratio was reduced from 4 to 2. These results suggest strongly that two conditions are necessary if the glomerular filtration rate (GFR) of inulin is to equal the true GFR: membrane pore size must be at least 200 A and passage through the membranes must be by bulk transport.