MO382: Validation of a Handheld Point-Of-Care Creatinine/EGFR Meter for Evaluating Renal Function

BACKGROUND AND AIMS

Measurement of glomerular filtration rate (GFR) is a cumbersome, time consuming, and expensive process, thus estimated GFR (eGFR) has become a commonly accepted surrogate or screening tool for individuals suspected to have kidney disease. Until recently this required testing through phlebotomy and a large laboratory analyzer. Nova Biomedical (Waltham, MA, USA) has developed a point-of-care (POC) handheld device, the NovaMax Cr/eGFR System that is able to measure creatinine (Cr) and calculate an eGFR using a fingerstick (1.2 µL) of whole blood.

METHOD

A group of 517 subjects (48% male) were recruited for study at three different Clinical Research Organizations (CRO's). The patient population was from both healthy cohorts and those known to have CKD. Creatinine and eGFR was tested on all subjects using a finger stick sample with the NovaMax System and compared with venous blood on a Siemens RXL (Siemens Medical Solutions, Malvern, PA, USA). The CKD-EPI formula was used to calculate eGFR.

RESULTS

The average age was 61.1 years (range 18–91). The range of Cr in the groups were as follows: NovaMax 0.57—>7 mg/dL (7 is the maximum reading), and for the Siemens 0.36–16.79 mg/dL. The range of eGFR was <7–127 mL/min/1.73 m2 on the NovaMax, and 4.3–137 mL/min/1.73 m2 on the Siemens.

See Table 1 for sensitivity and specificity results.

CONCLUSION

The NovaMax Cr/eGFR System is an acceptable alternative for eGFR measurement in patients with a wide range of renal function. Its ability to measure renal function in a variety of settings make it a very useful device for several patient populations: screening patients at risk for CKD or AKI, telenephrology, population screening in low- and middle-income countries, following patients post kidney transplant, and evaluating patients prior to and after contrast imaging studies, among other indications.

Bi-directional modulation of fast inhibitory synaptic transmission by leptin

The hormone leptin has widespread actions in the CNS. Indeed, leptin markedly influences hippocampal excitatory synaptic transmission and synaptic plasticity. However, the effects of leptin on fast inhibitory synaptic transmission in the hippocampus have not been evaluated. Here, we show that leptin modulates GABA(A) receptor-mediated synaptic transmission onto hippocampal CA1 pyramidal cells. Leptin promotes a rapid and reversible increase in the amplitude of evoked GABA(A) receptor-mediated inhibitory synaptic currents (IPSCs); an effect that was paralleled by increases in the frequency and amplitude of miniature IPSCs, but with no change in paired pulse ratio or coefficient of variation, suggesting a post-synaptic expression mechanism. Following washout of leptin, a persistent depression (inhibitory long-lasting depression) of evoked IPSCs was observed. Whole-cell dialysis or bath application of inhibitors of phosphoinositide 3 (PI 3)-kinase or Akt prevented leptin-induced enhancement of IPSCs indicating involvement of a post-synaptic PI 3-kinase/Akt-dependent pathway. In contrast, blockade of PI 3-kinase or Akt activity failed to alter the ability of leptin to induce inhibitory long-lasting depression, suggesting that this process is independent of PI 3-kinase/Akt. In conclusion these data indicate that the hormone leptin bi-directionally modulates GABA(A) receptor-mediated synaptic transmission in the hippocampus. These findings have important implications for the role of this hormone in regulating hippocampal pyramidal neuron excitability.

Leptin reverses long-term potentiation at hippocampal CA1 synapses

The hormone leptin crosses the blood brain barrier and regulates numerous neuronal functions, including hippocampal synaptic plasticity. Here we show that application of leptin resulted in the reversal of long-term potentiation (LTP) at hippocampal CA1 synapses. The ability of leptin to depotentiate CA1 synapses was concentration-dependent and it displayed a distinct temporal profile. Leptin-induced depotentiation was not associated with any change in the paired pulse facilitation ratio or the coefficient of variance, indicating a post-synaptic locus of expression. Moreover, the synaptic activation of NMDA receptors was required for leptin-induced depotentiation as the effects of leptin were blocked by the competitive NMDA receptor antagonist, D-aminophosphovaleric acid (D-AP5). The signaling mechanisms underlying leptin-induced depotentiation involved activation of the calcium/calmodulin-dependent protein phosphatase, calcineurin, but were independent of c-jun NH(2) terminal kinase. Furthermore, leptin-induced depotentiation was accompanied by a reduction in alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) receptor rectification indicating that loss of glutamate receptor 2 (GluR2)-lacking AMPA receptors underlies this process. These data indicate that leptin reverses hippocampal LTP via a process involving calcineurin-dependent internalization of GluR2-lacking AMPA receptors which further highlights the key role for this hormone in regulating hippocampal synaptic plasticity and neuronal development.