Distribution of blood in the functional kidney

A targeted metabolomics approach for clinical diagnosis of inborn errors of metabolism

Metabolome, the ultimate functional product of the genome, can be studied through identification and quantification of small molecules. The global metabolome influences the individual phenotype through clinical and environmental interventions. Metabolomics has become an integral part of clinical research and allowed for another dimension of better understanding of disease pathophysiology and mechanism. More than 95% of the clinical biochemistry laboratory routine workload is based on small molecular identification, which can potentially be analyzed through metabolomics. However, multiple challenges in clinical metabolomics impact the entire workflow and data quality, thus the biological interpretation needs to be standardized for a reproducible outcome. Herein, we introduce the establishment of a comprehensive targeted metabolomics method for a panel of 220 clinically relevant metabolites using Liquid chromatography-tandem mass spectrometry (LC-MS/MS) standardized for clinical research. The sensitivity, reproducibility and molecular stability of each targeted metabolite (amino acids, organic acids, acylcarnitines, sugars, bile acids, neurotransmitters, polyamines, and hormones) were assessed under multiple experimental conditions. The metabolic tissue distribution was determined in various rat organs. Furthermore, the method was validated in dry blood spot (DBS) samples collected from patients known to have various inborn errors of metabolism (IEMs). Using this approach, our panel appears to be sensitive and robust as it demonstrated differential and unique metabolic profiles in various rat tissues. Also, as a prospective screening method, this panel of diverse metabolites has the ability to identify patients with a wide range of IEMs who otherwise may need multiple, time-consuming and expensive biochemical assays causing a delay in clinical management.

Two fluid compartments in the renal inner medulla: a view through the keyhole of the concentrating process

Approximately four decades ago, the countercurrent theory became influential in studies on the concentrating process in the mammalian kidney. The theory successfully represented the concentrating process in the outer medulla, but the problem of the concentrating mechanism in the inner medulla, as defined by Homer Smith has remained essentially intractable. In a recent comprehensive review by Knepper and coworkers of various theories and models, attention was refocused on the possible role of hyaluronate (HA) in the inner medullary concentrating process. The authors proposed a hypothesis that HA can convert hydrostatic pressure to concentrating work.Here, we briefly survey the earlier ideas on the role imputed to HA and present a new hypothesis which is different from that of Knepper and coworkers. We estimate that the hydrostatic pressures available in the inner medulla can account only for a very small fraction of the concentrating work. We hypothesize that the role of HA is tied up with extravasated plasma albumin and suggest that owing to the property of HA solutions to exclude other macromolecules, extravasated plasma albumin and HA constitute two fluid compartments in the interstitium in the inner medulla. In this proposed two-compartment model, the Gibbs-Donnan distribution influences the movement of ions and water between the HA and the extravasated albumin compartment. To relate the hypothetical role of HA to the concentrating process, we briefly describe new results obtained by other investigators on the accumulation of urea in the inner medulla. This subject has been critically reviewed recently by Yang & Bankir.Many processes have been identified as contributing to the concentrating process in the mammalian inner medulla. We speculate that among these many processes, the primary responsibility for the final concentration of the excreted urine may be portioned out differently in different mammalian species.

Formulating Paclitaxel in Nanoparticles Alters Its Disposition

PURPOSE

Paclitaxel is active and widely used to treat multiple types of solid tumors. The commercially available paclitaxel formulation uses Cremophor/ethanol (C/E) as the solubilizers. Other formulations including nanoparticles have been introduced. This study evaluated the effects of nanoparticle formulation of paclitaxel on its tissue distribution.

METHODS

We compared the plasma and tissue pharmacokinetics of paclitaxel-loaded gelatin nanoparticles and the C/E formulation. Mice were given paclitaxel-equivalent doses of 10 mg/kg by intravenous injection.

RESULTS

The nanoparticle and C/E formulations showed significant differences in paclitaxel disposition; the nanoparticles yielded 40% smaller area under the blood concentration-time curve and faster blood clearance of total paclitaxel concentrations (sum of free, protein-bound, and nanoparticle-entrapped drug). The two formulations also showed different tissue specificity. The rank order of tissue-to-blood concentration ratios was liver > small intestine > kidney >> large intestine > spleen = stomach > lung > heart for the nanoparticles, and liver > small intestine > large intestine > stomach > lung > or = kidney > spleen > heart for the C/E formulation. The nanoparticles also showed longer retention and higher accumulation in organs and tissues (average of 3.2 +/- 2.3-fold), especially in the liver, small intestine, and kidney. The most striking difference was an 8-fold greater drug accumulation and sustained retention in the kidney.

CONCLUSIONS

These data indicate that formulation of paclitaxel affects its clearance and distribution into tissues, with preferential accumulation of nanoparticles in the liver, spleen, small intestine, and kidney.

Tissue pharmacokinetics of 2',3'-dideoxyinosine in rats

The present study examined in rats the concentration-time profiles of 2',3'-dideoxyinosine (ddI) in pharmacologically relevant tissues, including organs where drug effects are desired (brain, lymph nodes, spleen), organs with known drug toxicity (pancreas), and major eliminating organs (liver, kidney). ddI was analyzed by high performance liquid chromatography and radioimmunoassay. In the liver, pancreas, spleen, brain and lymph nodes, the highest concentrations were reached between 4 and 7 min after drug administration. The concentrations subsequently declined in parallel with those in plasma, indicating that plasma and these tissues were in rapid equilibrium. The concentrations in these tissues were less or equal to that of plasma. In the kidney, the maximal concentration occurred at a later time of 14 min, after which concentrations also declined in parallel to those in plasma. The kidney concentrations were about 10-fold greater than plasma concentrations. The ratios of tissue-to-plasma concentrations and of areas under the tissue and plasma concentration-time profiles showed a 230- to 300-fold range with the rank order of kidney >> liver approximately pancreas > lymph nodes > spleen >> brain, with respective values of 10.4, 1.09, 0.90, 0.75, 0.42, and 0.04. These data indicate no accumulation of ddI in brain, lymph nodes, spleen, pancreas and liver, and a significant accumulation in the kidney. The low tissue-to-plasma ratios in brain and spleen and a moderate ratio in lymph nodes indicate that further enhancement of the therapeutic effect of ddI requires improved drug delivery and entrapment in these tissues.

Measurement of extravascular renal water by the thermal dye indicator dilution technique

Simple mechanical swelling of the renal parenchyma against an unyielding renal capsule may be responsible in part for the development of oliguria and acute tubular necrosis. However, until now, renal swelling was difficult to measure, except by postmortem gravimetric techniques. A new in vivo technique, the thermal dye double indicator dilution technique, was used to assess renal swelling by measuring extravascular renal water. Ice cold indocyanine green dye solution was injected rapidly into the renal artery of 5 mongrel dogs, and the thermal dilution and dye dilution curves were recorded simultaneously by means of a thermistor catheter in the renal vein. The curves were corrected for the response time of the measuring systems, then the extravascular renal water was compared (renal blood flow multiplied by the difference in mean transit times of the thermal dilution and dye dilution curves). The results were compared to the gravimetrically determined extravascular renal water. A high correlation was found to exist between the thermal dye dilution method and the gravimetric method (r = 0.92, X = 0.65 Y + 19.8, p less than 0.05). These preliminary results are encouraging and warrant further trials, inasmuch as this technique would allow the sequential in vivo measurement of renal edema. It is therefore feasible to quantitate the effect of clinical insults, such as hypovolemic shock or sepsis, on the kidney, and to assess the value of different therapeutic interventions. A small body of evidence attempts to relate the role of simple mechanical swelling of the kidney to the pathogenesis of acute renal failure.

Distribution of chylomicrons and albumin in dog kidney

1. Under specified experimental conditions the distribution space of labelled chylomicrons in the kidney was 13.8 +/- 0.9 ml./100 g. tissue. The assumption is supported that this provides a measure for the quantity of intravascular plasma constituents.2. Values for red blood cells and albumin distribution spaces were 5.2 +/- 0.6 and 20.2 +/- 1.0 ml./100 g tissue, respectively, in the whole kidney. The ratio of tissue haematocrit over simultaneous arterial haematocrit averaged 0.56. The extravascular albumin fraction amounted to about 31.0% of the total albumin in the whole kidney.3. A statistically significant correlation was demonstrated between osmotic urine/plasma (U/P) ratios (within the approximate limits of 0.6-1.8) and quantities of extravascular albumin in the medulla.