**Acknowlegments**

and making it possible to predict side effects of L-arginine supplementation including cogni‐ tive deficits, epilepsy and a progressive spastic diplegia [86]. Therefore, drugs augmenting AS activity, the step-limiting enzyme of urea cycle, may be a promising strategy for CTLN2 therapy, since AS is the step-limiting enzyme of the urea cycle. A consequence of increased AS activity, a final common pathway is triggered resulting in the excretion of waste nitrogen

As previously mentioned, CTLN2 is not associated with genetic mutation of the AS gene; however, Saheki et al. identified the SLC25A13 gene as being defective in CTLN2 patients. This gene encodes for a Ca2+-dependent mitochondrial solute carrier, designated citrin [88]. According to Saheki et al., it is difficult to predict disease-causing effects of citrin deficiency in CTLN2, since children carrying citrin gene mutations may suffer from CTLN2 after more than 10 years or several decades of being asymptomatic [70]. In view of that, an option to prevent CLTN2 in infants with mutation of the citrin gen is being sought, having in mind that the nutritional management with appropriate intake of proteins only avoids accumula‐

Based on information discussed here, the strategy to increase AS activity in the liver could be an effective treatment for CTLN2 as well to prevent that children diagnosed as carrying SLC25A13 mutations from developing CTLN2 in the future [89]. We believed that direct pharmacological and clinical studies with *Bj*-PROs for these proposals, could turn them into a powerful therapeutic tool. The efficiency of *Bj*-PRO action can yet be improved by the ra‐ tional design of a compound which in the liver accelerates the urea cycle for eliminating am‐

AS as molecular target for drug development will be important for the treatment of a wide variety of diseases associated with deficiency of NO production, and also could transform *Bj*-PROs or their synthetic analogous into blockbuster medicine, as happened in the 80s with Captopril [90, 91]. The properties of *Bj*-PROs enhancing AS activity [14, 17], provides a pre‐ cise pharmacological tool for controlling pathophysiological mechanisms with advantages of uncontrolled application of exogenous L-arginine or NO donors [92]. For instance, the ef‐ fect of exogenous NO donors is not subject to physiological control, thus being more suscep‐ tible of generating undesired ROS [93, 94]. For all these reasons, keeping NO production in a safe level, so that a deleterious threshold would not be reached, is of particular interest. In this way, *Bj*-PROs should serve as structural models for the development of therapeutic agents for the treatment of various diseases related to NO deficiency, as cause or effect, as

Chemical properties of *Bj*-PROs make these peptides even more attractive potential lead compounds for drug development. For instance, *Bj*-PRO-10c is able to penetrate cells, where it remains as an intact molecule for hours [14]. Moreover, *Bj*-PROs contain a notable high proline content [13], which gives them some resistance to hydrolysis by aminopeptidases,

as urea [87].

466 Drug Discovery

tion of nitrogen [70].

**6. Conclusion**

well AS deficiency.

monia or even preventing its accumulation.

H.U. acknowledges grant support from Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) and (Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Brazil. C.L. is grateful for a postdoctoral fellowship awarded by FAPESP.
