Friday, November 25, 2011

The Brinicle

The normal saline we use in the hospital contains 9 grams of sodium chloride per liter of water. If you look on the bag you will see 0.9% which is the mass concentration expressed as g/dl (0.9 grams per deciliter of water - as there are 10 deciliters in a liter there are 9 grams of sodium chloride in the one liter bag).

The molecular weight of sodium chloride is 58.4 mg/mmol (23.0 mg/mmol from sodium and 35.4 mg/mmol from chloride) hence there are 154 mmol of sodium chloride in the one liter bag of normal saline.

9000mg/58.4mg/mmol = 154 mmol

As there is one molecule of sodium and one molecule of chloride in each molecule of sodium chloride (commonly referred to as salt) there are 154 mmol of sodium in the one liter bag or 3542 mg (well above the daily recommended 2300mg).

Now some craziness: average sea water is 3.5% sodium chloride (there are multiple other ions at much lower concentrations) meaning 35 grams of salt per liter of water!

This leads to some interesting phenomena. Check out this recent BBC time lapse video of something called a "brinicle."

In arctic waters the formation of surface ice forces solutes out of the newly formed solid and into "brine channels" which contain super concentrated sea water. As the concentration of solutes rises the freezing point of the solution drops and the density increases.

This cold dense super concentrated sea water descends towards the sea floor. The distribution of the brine channels can be such that the super concentrated sea water comes out in columns. As it does less concentrated water with a high freezing point around it freezes. When the column reaches the ocean floor the water flows with gravity to the lowest point, freezing everything in its path including animals.

So what sort of salt concentration is this "super concentrated sea water" at? The lowest recorded temperature of sea water I could find was negative 2.6 degrees C. Calculating backward from the freezing point depression equation and assuming all solute in sea water is sodium chloride...

Change in freezing point of solution = KF · m · i

KF = the cryoscopic constant, which is dependent on the properties of the solvent = 1.853 kg/mol for water

m = mol of solute per kg of solvent

i = the van 't Hoff factor (number of solute particles per mol) = 2 for NaCl


2.6 = 1.853 * m * 2

2.6 = 3.706 * m

0.702 = m

0.702 mol/L or 702mmol/L of sodium chloride

58.4 mg/mmol * 702mmol/L = 40,997mg/L or 41g/L or 4.1% sodium chloride

That super concentrated sea water makes our 3% "hypertonic saline" look like weak tea!

Wednesday, November 23, 2011

Obese mice?

Recently there was a very interesting series in three parts in the online magazine concerning the use of mice and rats as surrogates for humans in animal studies. Anyone who has worked with mice in the lab is aware of the conditions that they are generally kept in – they live in small cages with limited opportunity for exercise and have an unlimited food supply. The inevitable consequence of this is that the majority of lab mice and rats are overweight – if not obese. What does this mean for their ability to serve as appropriate controls?

As detailed in an article in PNAS last year, laboratory rodents “metabolically morbid”. They are overweight, insulin-resistant, have premature cardiovascular disease, are prone to infection and cancer and appear to be more likely to develop degenerative neurological disorders. Overall, when you think about it, they aren’t very representative of healthy humans at all. This has major implications for medical research. Laboratory mice as currently bred are cheap, reproduce rapidly and are easily manipulated genetically. Any changes to feeding regimens and exercise availability are going to significantly increase costs associated with their use so there is a trade off between practicality and the unquantified effect that using these obese animals may be having on the results of our experiments. It must be pointed out, however, that most research on mice uses animals that are young and have not had time to become particularly overweight such that this would not apply to all mouse models.

It’s a fascinating topic and the sheer number of citations that the PNAS article has accrued already indicates that others recognize that this is a potentially serious issue. Comments are welcome,

Saturday, November 19, 2011

The Plot Thickens: Role of Plasmin in Edema Formation in Nephrotic Syndrome

I was at the ASN Kidney Week in Philadelphia last week and I had the chance to check out some abstracts and discuss with the authors. Three abstracts called my attention right away. I uploaded a post a few months ago related to the mechanisms of edema in nephrotic syndrome (NS) : in patients with NS, plasminogen is filtered from plasma and activated in distal nephron by enzyme urokinase forming plasmin. Plasmin can then proteolytically activate ENaC by cleavage of the γ-subunit, leading to sodium retention and edema. These are the abstracts:

1. Abstract: [FR-PO1777] Urinary Content of Plasmin(ogen) and Activation of ENaC Current by Urine Resides during Remission of idiopathic Nephrotic Syndrome. Buhl et al.

The same group from University of Southern Denmark who published the original plasmin study came back again and presented more evidence for their hypothesis. They took spot urine samples from 20 children with active idiopathic NS and compared them to urine samples obtained after remission in the same patients. Urine samples were analyzed for plasmin and plasminogen concentrations and urinary protease activity. Urine plasmin and plasminogen concentrations (normalized to urine creatinine concentration) and urine protease activity were found to be significantly higher in the active phase of NS in comparison to the remission phase. Not only that, the urine samples obtained in the active phase were able to evoked stronger ENaC currents than the urine samples obtained in remission phase.

2. Abstract: [FR-PO1776] Preeclampsia Is Associated with Significant Urinary Excretion of Plasmin(ogen) and the Ability of Urine To Activate ENaC In Vitro. Buhl et al.

The same group above also did another study where urine samples from 16 preeclamptic patients and 17 normotensive, non-proteinuric pregnant women (control) matched on age and gestational age were compared. Urine was analyzed for plasminogen and proteolytic activity. ENaC currents after exposure to urine was monitored in M1 cells by whole cell patch clamp. Urine plasminogen concentration (normalized to urine creatinine concentration) and proteolytic activity were increased in the urine of preeclamptic patients but not in controls. What is more, a significant positive correlation was found in the preeclamptic group between urinary plasmin(ogen) and diastolic blood pressure. The ability of the urine samples from preeclamptic patients to evoke ENaC current was abolished by amiloride to a lower level than the controls, suggesting that there might be small amounts of plasmin (ogen) present in the urine under normal conditions. The authors speculated that this might have a natural anticoagulant effect in the urine.

3. Abstract: [FR-PO1779] Nephron Expression and Distribution of the Plasminogen Receptor, PLG-RKT, and Colocalization with ENaC and uPAR, in Murine Kidney. Nangia et al.

Dr. Parmer’s group at UCSD has identified the presence of a novel Plasminogen Receptor (PLG-RKT). This PLG-RKT, apparently colocalizes with urokinase, and ENaC on the apical surface of the distal nephron, and all of these are present in an orientation to promote Plasminogen activation and ENaC processing. They actually found that urokinase was also present in the proximal tubule but in a less prominent way than in the distal nephron. The significance of the latter is unknown. Therefore, the machinery for sodium retention is present even under normal conditions.

I believe these studies give more support to the Plasmin hypothesis.

Thursday, November 17, 2011

Sickle cell disease and the kidney

Since moving to Baltimore, a city with a large African-American population, earlier this year, I have had the opportunity to see several interesting patients with sickle cell SS disease and renal complications. Here is a mention of some of the kidney abnormalities that occur with SS disease, as well as some of the clinical manifestations.

The underlying pathology of renal sickle cell disease seems to be from microvascular hypoxemia: when red blood cells acquire a sickle shape and obstruct capillary flow, microinfarcts, chronic ischemic injury and medullary hypoxia can occur. Hemosiderin deposits can also be seen on biopsy. Sequelae can include:

1) hyperfiltration. Hypoxia can lead to increased prostaglandin release, which increases GFR. NO synthase may also be upregulated.

2) increased proximal tubular function. The exact causes are unknown, but the proximal tubular upregulates secretion of creatinine, as well as resorption of phosphorus. Thus, creatinine-based estimations of GFR may overestimate renal clearance in sickle cell patients.

3) microalbuminuria. Unclear if this is secondary to ischemia, or if hyperfiltration plays a role. Can progress to overt proteinuria over time. It is interesting to note that parvovirus B19 has been implicated as a cause of nephrotic syndrome in SS disease patients.

4) hyposthenuria. Otherwise known as inability to concentrate or dilute urine; possibly due to impaired water ADH response, although another possibility is that enhanced clearance of interstitial solute washes out the medullary concentration gradient.

5) impaired distal tubular function. Cause unclear. Can lead to decreased distal H+ and/or K+ secretion, and lead to an imcomplete distal RTA.

6) hematuria. Probably from capillary microinfarcts.

7) renal papillary necrosis. From medullary ischemia.

A collapsing form of FSGS as well as MPGN have been reported in conjunction with SS disease.

Amazing (and awful), that a single genetic mutation can cause so much renal havoc!

NKF Spring Meeting

The National Kidney Foundation is accepting abstracts for poster presentations and publication at the upcoming spring clinical meeting in May. Accepted abstracts will be published in the May 2012 issue of the AJKD. Posters accepted and presented will be eligible for a sweet cash prize.

Submission Deadline: Extended to December 9th, 2011

Submit abstracts online here.

Wednesday, November 16, 2011

New Cases Site from the UK RA

The UK Renal Association (RA); the professional body for UK nephrologists and renal scientists, has recently started a website to foster discussion of interesting cases (There is also a link in the sidebar). The site remains embryonic whilst a development strategy is debated, but the RA would be very gratfeul for feedback and some comments/discussion of the cases.

Monday, November 7, 2011

Kidney Week App

For those headed to Philly check out the Kidney Week App on the ASN website. Nice way to organize your itinerary, follow the Twitter feed and keep maps handy.

New to the Blogosphere: eAJKD

Former RFN editor Matt Sparks, along with quite a cast of others have helped to launch eAJKD, a companion blog to AJKD. Check it out.

Thursday, November 3, 2011

Renal Fellow Network at ASN

I expect many of you are heading to Kidney Week this year, so we're planning a Renal Fellow Network social night from about 8pm on Friday November 11th in McGillin's Olde Ale House, 1310 Drury Street, Philadelphia, PA 19107.

All are more than welcome to attend, so whether you're an interested reader, a past, present or budding blogger, or just want to forget about how badly your poster went, drop in and say hi. If more than 100 people show up, Gearoid has promised to perform his famous "string dance", although that may not be an incentive for everyone.

RFN are planning to maintain an active presence during the meeting, follow our twitter feed for updates. So come along, get involved, and look forward to meeting up in Philly.

Tuesday, November 1, 2011

From the RFN Archives: Fabry's disease and the kidney

I read a nice review of Fabry’s disease recently, and was surprised to read that its prevalence in ESRD may be as high as 1-2%. That figure is likely an underestimate, given the frequent failure to screen for the disease in patients with nephropathy and other common symptoms. Since a recombinant enzyme to replace missing the endogenous protein is available, it is worth reviewing the clinical presentation of the disease—increased awareness will hopefully result in increased diagnosis and treatment.

Fabry’s is an X-linked lysosomal storage disorder caused by a deficiency in the enzyme alpha-galactosidase A. As a result, a buildup of glycosphyngolipids in cellular lysosomes occurs, a process thought to lead to cellular dysfunction. The effects are particularly seen in the nervous system, causing painful acroparesthesias; cardiac myocytes, leading to hypertrophic cardiomyopathy; and the kidneys, where endothelial storage of glycosphingolipids leads to vascular insufficiency and glomerular damage. A typical affected male will manifest frequent episodes of burning limb pain starting in childhood, which unfortunately respond poorly to analgesics. Other early signs of Fabry’s include gastrointestinal pain and hypohydrosis, due to involvement of nerves innervating the gut and skin. Angiokeratomas, small reddish-purple lesions characteristic of the disease, are often present, especially in the groin area (and are often missed on physical examination).

Cardiac and renal involvement usually manifest after the first or second decades of life. Fabry’s nephropathy initially presents as proteinuria or isosthenuria, later progressing to renal insufficiency. By age 35 years, half of male Fabry’s patients have proteinuria, and by age 50, about half have developed ESRD. While some female heterozygotes develop renal insufficiency, they do so less frequently, and rarely progress to end-stage disease.

Biopsy findings in Fabry disease show lysosomal inclusion bodies containing glycolipid material in visceral epithelial cells, most prominently podocytes. “Zebra bodies”, inclusions of ceramide material in lysosomes, are often seen in the podocytes. Vascular sclerosis along with other chronic changes such as interstitial fibrosis and tubular atrophy are also commonly seen. Fabry’s can be diagnosed definitively by various serum tests measuring the alpha-galactosidase A activity. Sequencing of the GLA gene, mutations of which are known to cause Fabry’s disease, can be helpful in assessing female family members for presence of a carrier state.

Currently, two formulations of recombinant purified alpha-galactosidase A exist, although only one (Fabrazyme, alpha-galactosidase A alpha) is on the market in the U.S. While trials have not been effective in reversing renal damage in ESRD patients, they have shown a significant slowing in the rate of EGFR decrease in patients with mild renal dysfunction (EGFR > 55 mL/min). Despite the inability to rescue kidney function in our dialysis patients, however, screening plays a vital function in establishing family inheritance patterns—and identifying the next generation of Fabry’s patients in the early stages of disease. So, in younger male patients with ESRD of unclear etiology: ask about Fabry’s symptoms, screen them, and help to increase Fabry’s awareness and diagnosis!

Originally posted by Lisa Cohen