Reactive nitrogen species inhibit branched chain alpha-ketoacid dehydrogenase complex and impact muscle cell metabolism

Branched chain α-ketoacid dehydrogenase complex (BCKDC) is the rate-limiting enzyme in branched chain amino acid (BCAA) catabolism, a metabolic pathway with great importance for human health. BCKDC belongs to the mitochondrial α-ketoacid dehydrogenase complex family, which also includes pyruvate dehydrogenase complex and oxoglutarate dehydrogenase complex. Here, we revealed that BCKDC can be substantially inhibited by reactive nitrogen species (RNS) via a mechanism similar to what we recently discovered with pyruvate dehydrogenase complex and oxoglutarate dehydrogenase complex-RNS can cause inactivating covalent modifications of the lipoic arm on its E2 subunit. In addition, we showed that such reaction between RNS and the lipoic arm of the E2 subunit can further promote inhibition of the E3 subunits of α-ketoacid dehydrogenase complexes. We examined the impacts of this RNS-mediated BCKDC inhibition in muscle cells, an important site of BCAA metabolism, and demonstrated that the nitric oxide production induced by cytokine stimulation leads to a strong inhibition of BCKDC activity and BCAA oxidation in myotubes and myoblasts. More broadly, nitric oxide production reduced the level of functional lipoic arms across the multiple α-ketoacid dehydrogenases and led to intracellular accumulation of their substrates (α-ketoacids), decrease of their products (acyl-CoAs), and a lower cellular energy charge. In sum, this work revealed a new mechanism for BCKDC regulation, demonstrated that RNS can generally inhibit all α-ketoacid dehydrogenases, which has broad physiological implications across multiple cell types, and elucidated the mechanistic connection between RNS-driven inhibitory modifications on the E2 and E3 subunits of α-ketoacid dehydrogenases.

Reactive nitrogen species inhibit branched chain alpha-ketoacid dehydrogenase complex and impact muscle cell metabolism

Branched chain α-ketoacid dehydrogenase complex (BCKDC) is the rate limiting enzyme in branched chain amino acid (BCAA) catabolism, a metabolic pathway with great importance for human health. BCKDC belongs to the mitochondrial α-ketoacid dehydrogenase complex family, which also includes pyruvate dehydrogenase complex (PDHC) and oxoglutarate dehydrogenase complex (OGDC). Here we revealed that BCKDC can be substantially inhibited by reactive nitrogen species (RNS) via a mechanism similar to what we recently discovered with PDHC and OGDC - modifying the lipoic arm on its E2 subunit. In addition, we showed that such reaction between RNS and the lipoic arm of the E2 subunit can further promote inhibition of the E3 subunits of α-ketoacid dehydrogenase complexes. We examined the impacts of this RNS-mediated BCKDC inhibition in muscle cells, an important site of BCAA metabolism, and demonstrated that the nitric oxide production induced by cytokine stimulation leads to a strong inhibition of BCKDC activity and BCAA oxidation in myotubes and myoblasts. More broadly, nitric oxide production reduced the level of functional lipoic arms across the multiple α-ketoacid dehydrogenases and led to intracellular accumulation of their substrates (α-ketoacids), reduction of their products (acyl-CoAs), and a lower cellular energy charge. This work revealed a new mechanism for BCKDC regulation, demonstrated its biological significance, and elucidated the mechanistic connection between RNS-driven inhibitory modifications on the E2 and E3 subunits of α-ketoacid dehydrogenases. Together with previous work, we revealed a general mechanism for RNS to inhibit all α-ketoacid dehydrogenases, which has numerous physiological implications across multiple cell types.

Going, going, gone? Plant species extinction in the 21st century

Prospects for halting it or even slowing its rate are bleak, but perhaps not hopeless.

Cows for fear: is BSE a threat to human health? Bovine spongiform encephalopathy

In 1996, a new variant of Creutzfeldt-Jakob disease (vCJD)-a disease that causes lack of coordination, muscle twitching or jerking, dementia, and, eventually, death-suddenly appeared in Great Britain. It is believed that the victims contracted the disease from eating the beef of cattle stricken with bovine spongiform encephalopathy (BSE), or mad cow disease. As of December 1997, at least 25 people in the United Kingdom and France have contracted vCJD.

Diagnosis-related groups, costs, and outcome for patients in the intensive care unit

Our purpose was to analyze hospital cost, resource utilization, and outcome by age for a large group of patients who required intensive care unit (ICU) services. Patients in the ICU (N = 6331) were stratified by age groups. Mean hospital cost per patient generally increased with age. Older patients (65 years of age and older) who were treated in the ICU had longer hospital lengths of stay, higher mortality rates, and a greater percentage of outlier patients, as compared with younger patients (under 65 years of age). Patients in the ICU would have produced a substantial loss for our medical center under a diagnosis-related group (DRG) all payer prospective payment scheme. Although higher mean costs were associated with older patients, every age group of patients in the ICU that we examined demonstrated a loss under DRGs. As a whole for the 3-year period, patients in the ICU would have generated more than +30 million in losses for our medical center. These losses were a result of a variety of factors, including a greater severity of illness and greater hospital resource utilization. The current DRG hospital payment system appears to be inequitable for the patient who receives treatment in the ICU during the hospital stay. As hospital operating margins continue to decline because of federal and state DRG hospital payment systems, additional pressures may be applied for physicians, nurses, and health care professionals to cut expenses for these patients. In this effort to watch the bottom line, physicians and nurses must not sacrifice the quality of or the access to care for patients who require ICU services.

Pediatric patients, DRG hospital payment, and comorbidities

To determine whether the diagnosis related group (DRG) hospital payment system is causing financial pressure on pediatric hospitals similar to that shown in our previous work in other settings, we analyzed resource consumption for pediatric patients in any of the 251 DRGs not stratified by comorbidities. The new DRG prospective "all payor system" is in effect at our hospital. Analysis of 12,771 pediatric patients by payer (Medicaid and commercial insurance such as Blue Cross) in these DRGs for a 3-year period demonstrated that, as a group, pediatric patients with more comorbidities generated higher total hospital costs, a longer hospital length of stay, a greater percentage of procedures per patient, financial risk under DRG payment, more outliers (expensive patients), and a higher mortality rate than pediatric patients in the same DRGs with fewer comorbidities. This study confirms major inequities in DRG prospective hospital payment for many pediatric patients.

Primary Pseudomonas maltophilia infection of the lung

To our knowledge, this is the first reported case of primary Pseudomonas maltophilia pneumonia. Presenting symptoms were fever and chills of two days' duration and a density in the right upper lobe. Sputum culture showed normal flora, and multiple blood cultures were negative. Antibiotic therapy initially with penicillin and then with carbenicillin was unsuccessful. Selective bronchial aspiration yielded pure cultures of P maltophilia. When an appropriate antibiotic, chloramphenicol, was given, a prompt therapeutic response followed.